Creo Elements Pro 5.0 Mechanica

© TriStar Corporation

MECHANICA

QUICK REFERENCE GUIDE

Sandy_McKinney_2015 creo elements/pro 5.0 mechanica

QUICK REFERENCE GUIDE

Creo Elements/Pro 5.0 Mechanica
Quick Reference Guide

By Thiagu Palaniappan

Published by
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CREO ELEMENTS/PRO 5.0 MECHANICA QUICK REFERENCE GUIDE i



INTRODUCTION creo elements/pro 5.0 mechanica

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Mechanica Technology MANUAL CONVERGENCE IN H-METHOD Deformed Model Graph of Max Stress vs
P-loop pass
Mechanica technology is fundamentally different than con- Convergence is achieved manually in the h-method. In or-
ventional FEA tools. Traditional analysis tools use the “h” der to get accurate results, the user has to refine the mesh
method. Mechanica uses the unique “p” method. H ele- until the solution stops changing, which is considered a con-
ments break the model into small linear elements, while verged solution.
Mechanica’s p elements map the underlying geometry of
the model without any linear simplification. In the h Sandy_McKinney_2015
method, the smaller the elements, the more accurate the
answer is. In the p method, instead of adding more and
more elements, Mechanica adds more math to the existing
elements to get a more accurate answer. Solution quality is
gained not by mesh refinement, but by the automatic raising
of the polynomial order of the elements. Thus, the burden of
getting an accurate answer shifts from the user to the soft-
ware.

Mechanica P-mesh H-method FEA approach on a cantilever beam. P-method approach in Mechanica 1

Traditional P-mesh AUTOMATIC CONVERGENCE IN P-METHOD INTRODUCTION

Mechanica Technology In Mechanica, convergence is achieved automatically by an
adaptive process wherein the polynomial order of the equa-
tions to solve the analysis is increased with each analysis
pass irrespective of the mesh characteristics. This is shown
at right. Mechanica can use up to the ninth order polyno-
mial to achieve a converged solution. This adaptive process
is done during post processing, thereby avoiding any time-
consuming manual pre-processing to get an accurate solu-
tion.

Back to Table of Contents

INTRODUCTION ADVANCED MECHANICA creo elements/pro 5.0 mechanica

Mechanica Modules Advanced Mechanica has all the basic Mechanica functional- QUICK REFERENCE GUIDE
ity plus some additional capabilities.
MECHANICA LITE CAPABILITIES FATIGUE ADVISOR
 Structural: Large deformation, pre-stress static, pre-
Mechanica Lite is included with every seat of Creo Elements/ Fatigue Advisor is required to run a fatigue analysis in
Pro and does not require a Mechanica license. It is a limited- stress modal analyses, contact with friction Mechanica. A fatigue analysis establishes whether the prod-
functionality, trial version of Mechanica that allows static  Vibration: Dynamic time, dynamic frequency, dynamic uct is susceptible to fatigue damage when subjected to cy-
structural analysis on both parts and assemblies that have clic loading.
total surface counts of up to 200. To access Mechanica Lite random, dynamic shock analyses
from within Creo Elements/Pro, click APPLICATIONS >  Thermal: Transient thermal analysis CAPABILITIES
MECHANICA. A guiding interface will walk the user through  Supports 2D model types: Plane strain, plane stress,  Predicts damage and cycles of failure
the model setup since the standard Mechanica toolbars are  Confidence of life prediction
not available in Lite mode. 2D–axisymmetric  Parametric life optimization study
 Materials: Orthotropic and transversely isotropic, non-
MECHANICA (BASIC MECHANICA) Mechanica Operating Modes
linear materials (hyperelastic, elastoplastic)
Mechanica, or basic Mechanica, is a module for Creo Ele-  Idealizations: Advanced masses, advanced shells for INTEGRATED MODE
ments/Pro that allows users to perform structural and ther-
mal simulations on product designs. It is fully integrated laminate layups (composites), advanced springs, ad- In integrated mode, Mechanica is accessed from within Creo
with Creo Elements/Pro with an easy-to-use interface. vanced bolted connections including preload Elements/Pro and is fully integrated into the application.
CAPABILITIES The easiest way to check if the user has an Advanced This mode is typically used by Creo Elements/Pro users.
 Structural: Static, contact, modal, buckling analyses Mechanica license is to try selecting references of one of the
 Thermal: Steady state thermal analysis only 2D model types in the advanced options of Mechanica INDEPENDENT MODE
 Materials: Isotropic analysis only model setup.
 Idealization: Beams, simple shells, simple masses, sim- Independent mode can be used without Creo Elements/Pro.
NOTE: It relies on the independent Mechanica user interface for all
ple and to ground springs There is complete upward model compatibility from simulation modeling, analysis, and design study execution
 Design Study: Standard, sensitivity, optimization Mechanica Lite to full Mechanica (basic or advanced). and results viewing. This is typically used when the CAD
system being used is not Creo Elements/Pro.
Mechanica Modules Back to Table of Contents
FEM MODE

FEM Mode allows the creation of the traditional FEA h-mesh.
Post processing is done using third-party solvers like ANSYS/
NASTRAN.

NATIVE MODE

Native Mode is the default mode of Mechanica and allows
the creation of p-mesh and solving using the p-method.

FEM mode mesh (h) Native mode mesh (p)

INTRODUCTION 2

PROCESS WORKFLOW creo elements/pro 5.0 mechanica

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MODEL GEOMETRY CHECK GEOMETRY Creo Elements/Pro to
CREATION AND DEFEATURE Mechanica

Mechanica can analyze designs done in Creo Elements/Pro Sandy_McKinney_2015Before bringing the model into Mechanica, remove all ge- MATERIAL PROPERTIES
or imported with a neutral file from other CAD systems. It is ometry checks in Creo Elements/Pro by clicking on INFO > IDEALIZATIONS
important to create analysis-friendly parts and assemblies. GEOMETRY CHECKS. Typically, geometry checks will prevent
For example, always create finishing features towards the Mechanica from creating a successful mesh. This could be CONNECTIONS IN ASSEMBLY
end in order to allow for easy defeaturing of the model be- due to a tiny edge, sliver surface, etc. Changing the accuracy CONSTRAINTS
fore taking it into Mechanica. Otherwise, when trying to of the model to remove geometry checks is not recom- LOADS
suppress features not necessary for analysis, required fea- mended because while this might remove the geometry MESH
tures may end up suppressed as well. check, it could cause a regeneration geometry failure which
again contributes to the Mechanica mesh failure. DEFINE ANALYSIS
It is a good practice to follow feature-based modeling in- Always check for interferences and clearances in assembly
stead of including rounds, chamfers, drafts, or holes in the models before activating Mechanica. By default, Mechanica
sketch. Otherwise, it can become a huge task to remove assumes that mated parts are bonded or welded. It is impor-
them during analysis. tant to make sure the interface between parts in Mechanica
are clearly defined based on expected behavior.
If the model geometry has constant thickness, use the Ex-
trude Thicken command or the shell feature in order to auto- Suppress features like chamfers, outer rounds, and drafts as
mate Mechanica shell mesh idealization creation. these will increase the mesh elements but will not change
the analysis results.
The dimensioning scheme should have analysis intent so
that the design can be optimized based on the analysis re-
sults. This will help in selecting appropriate dimensions for
conducting “what if?” scenario design studies such as sensi-
tivity and optimization.

Creo Elements/Pro features such as datum curves and
sketches can be reused in Mechanica to create surface re-
gions (foot prints) and to refine the mesh by adding more
nodes along the curves and sketches. Datum points created
in Creo Elements/Pro can be reused to increase mesh density
as well as assign point loads or constraints.

Relations and parameters can be used while running design
studies within Mechanica. Relations help capture the design
intent while changing the design variable to achieve a cer-
tain analysis objective. Parameters can be used to vary
Mechanica properties such as material properties and loads
while running sensitivity or optimization studies.

Process Workflow Back to Table of Contents 3

PROCESS WORKFLOW creo elements/pro 5.0 mechanica

CONVERGENCE SETUP QUICK REFERENCE GUIDE
RUN ANALYSIS AND
Mechanica Process Overview 2. RUNNING THE ANALYSIS
REVIEW RESULTS
DESIGN VARIABLES AND The following basic four-step process can be used to analyze This step starts with the analysis type definition. Every analy-
most models in Mechanica: sis type has its own requirements. For example, if you want
SHAPE ANIMATE to run a vibration analysis, you will need to define a modal
SENSITIVITY STUDY 1. Building the analysis model (pre-processing) analysis first.
OPTIMIZATION STUDY 2. Running the analysis (post-processing)
REVIEW OPTIMIZATION RESULTS 3. Reviewing the analysis The next step is to set up the memory allocation and post
4. Improving the design process storage location information. The convergence cri-
Process Workflow teria can also be defined at this stage. You can then run the
1. BUILDING THE ANALYSIS MODEL analysis and review the status.

This step starts with Creo Elements/Pro geometry creation, 3. REVIEWING THE ANALYSIS
which is more than just the creation of shapes. Analysis in-
tent can be captured with coordinate systems and unit set- Once the analysis is successfully completed, the results can
ups, dimensions, relations, parent-child relationships and be reviewed in several formats including fringe plots, graphs,
model defeaturing. and vector plots.

The next step is to assign material. New materials can be 4. IMPROVING THE DESIGN
created or reused from the standard Mechanica library or
from a custom library. Based on the material type, additional Based on the analysis results, the design can be improved by
properties like material orientation need to be defined. running design studies like standard design, sensitivity, opti-
mization, or feasibility. But before running any design study,
Mechanica features like loads and constraints must be de- design variables and parameters should be defined, and a
fined in order to run any type of analysis. Mesh creation is regeneration check should be done using shape animate.
optional, since Mechanica creates the mesh automatically
during the analysis run. Optional analysis features like ideali-
zations, regions, and interfaces can also be defined.

Back to Table of Contents PROCESS WORKFLOW 4

GEOMETRY PREPARATION creo elements/pro 5.0 mechanica

Several steps should be taken to ensure that the Creo Ele- Sandy_McKinney_2015CHECK GEOMETRY QUICK REFERENCE GUIDE
ments/Pro geometry is acceptable for meshing in
Mechanica. Most analyses are carried out on existing de- Info > Geometry Checks: Highlights any geometry with Small surfaces created by unaligned surfaces
signs or imported geometry. The design model often con- unclear design intent. A geometry check also refers to a
tains features like rounds, chamfers, small holes, 3D text, or potential regeneration or geometry problem within the A narrow surface created by exterior ribs on a round.
thin geometry that are not important to the analysis model. model. All GeomChecks must be cleaned up for successful The rib on the right with the exterior rounds removed
These features do not alter the stress or deformation results, meshing. If GeomCheck is grayed out, the design intent of will mesh with many fewer elements.
but due to their small sizes, they could generate a large all features is clear.
number of finite elements. Mechanica will compute the
results for each of these elements, and for a large assembly, Analysis > Geometry > Slope: Colors the part according to
this might be computationally expensive. Mechanica could surface slope. This allows easy determination of whether or
run into memory limitation issues during the post process of not edges are sharp and also ensures that geometry changes
the analysis. When using Mechanica, always focus on the are smooth in blends and sweeps.
essentials of the design and not the cosmetics. The follow-
ing methods can better prepare geometry for Mechanica Analysis > Model > Short Edge: Highlights small edges.
analysis.
Analysis > Model > Global Interference: Highlights any
SUPPRESS FEATURES areas of interference for assemblies. Interference should be
avoided in assembly analysis.
Suppress all features that do not have a significant contribu-
tion to the analysis results. It is also important to suppress EXAMPLES OF GEOMETRY THAT ARE DIFFICULT
features which can create small or difficult to mesh surfaces TO MESH
such as rounds, unaligned features, and variable section
blends and sweeps. When Mechanica encounters the following situations during
meshing, it will try to automatically change the mesh set-
REMOVE SURF tings so as to create a successful mesh. However, there is the
potential for a non-converged solution at these locations.
If suppressing features causes regeneration failure, an alter- The geometry preparation phase is critical for mesh genera-
nate method is to remove surf. The Remove feature enables tions as well as final solution accuracy.
you to remove geometry without the need to alter feature
history, reroute, or redefine a number of other features. Small surface created by rounds
When you remove geometry, the neighboring surfaces are
extended or trimmed to converge and close the empty area.

Select a surface, surface set, or single closed-loop chain and
click EDIT > REMOVE.

SIMPLIFIED REPS

In assembly mode, components that will not contribute to
the analysis results can be excluded and a representation
saved for use in Mechanica. This method is better than sup-
pressing the components, as suppressing could cause a re-
generation failure in Creo Elements/Pro.

Geometry Preparation Back to Table of Contents Edges with zero angle 5

GEOMETRY PREPARATION

UNITS creo elements/pro 5.0 mechanica

Mechanica uses the model’s principle system of units to per- QUICK REFERENCE GUIDE
form analyses and store simulation data. This system deter-
mines the default units in which the analysis results are cal- UNIT OPTIONS WITHIN MECHANICA
culated and reported. However, you can override the de-
fault unit system while applying loads and constraints and Heterogeneous units are supported within Mechanica. Units
defining result windows. of all modeling entities can be set on the fly.

The Units Manager in Creo Elements/Pro allows you to Units in results can be changed during the result window
change the principle unit system and to check the units of definition.
the derived quantities. For example, if the principle unit
system is IPS, then the units of stress is psi, but if the princi-
ple unit system is mmNs, the stress is reported in MPA. Click
the Info button in the units manager to access the full list of
derived quantities for each unit system.

The default principle system in Creo Elements/Pro is inch Units of derived quantities 6
lbm second. It is recommended to use IPS instead so that
the force can be applied in pound force (lbf) and the stress Back to Table of Contents
reported in psi. The material property units need not match
the principle units system. For example, Young's modulus
may be assigned in MPA, but the stress can be reported in
psi. The units of all parts in an assembly should match the
principle unit system of the assembly file before taking the
assembly into Mechanica. If the units are inconsistent in the
assembly, Mechanica will prompt you to convert. This auto-
matic conversion of units may not work on family table in-
stances until the generic model is converted manually.

Units

MATERIALS AND MATERIAL PROPERTIES creo elements/pro 5.0 mechanica

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Material assignment is a prerequisite for creating the mesh Sandy_McKinney_2015HYPERELASTIC Material Properties
and running any analysis in Mechanica. Materials can be
assigned to the analysis model in either Creo Elements/Pro A hyperelastic material is a nonlinear material like rubber The following material properties are required to run struc-
or Mechanica. The default material library can be custom- that exhibits instantaneous elastic response to large strains. tural analysis:
ized to include user defined materials. Materials properties Mechanica supports several mathematical models of hypere-
are also available at matweb.com. New materials can be lastic material. The solution accuracy depends on the selec-  Density
saved to either the model or to the library. tion method of the material model.  Young’s modulus
 Poisson’s ratio
In part mode, materials can be assigned to the entire model  Define by tests: Using this option, the experimental  CTE (coefficient of thermal expansion, required if calcu-
or to a volume region. In assembly mode, materials can be data for stress and strain can be specified and the best
assigned to various components, beam and shell idealiza- fitting model for the data can be found. lating stress and deformation due to thermal expan-
tions, and spot weld connections. sion)
 Material model coefficients: Using this option, the
Material Types value of coefficients for a material model can be de- The following material properties are required to run a ther-
fined. The following material models are available: mal analysis:
Based on the stress-strain response of the material, Arruda-Boyce, Mooney-Rivlin, Neo-Hookean, Polyno-
Mechanica can analyze linear, hyperelastic and elastoplastic mial order 2, Reduced Poly. Order 2, and Yeoh.  Specific heat capacity
material types.  Thermal conductivity
ELASTOPLASTIC
LINEAR Material Orientation
When the load is increased beyond the yield strength, mate-
Mechanica can simulate different types of linear materials : rials can undergo plastic deformation. Mechanica defines Material orientations are used to define the principal mate-
Isotropic, Orthotropic, and Transversely Isotropic. elastoplastic materials using isotropic hardening laws, which rial directions for orthotropic or transversely isotropic mate-
are rules that describe the relationship between the flow rials.
 Isotropic: Material with an infinite number of planes of stress and effective plastic strain for a material. The elasto-
material symmetry. Material properties are the same in plastic material definition is done using one of the following The material library file is mmatl.lib, which is located in the
all directions. methods: Creo Elements/Pro load point.

 Orthotropic: Material with symmetry relative to three  Using test data: Stress and strain values from the test
perpendicular planes. Material properties are required data can be specified to find the best-fit curve for a ma-
as three different values. terial model.

 Transversely Isotropic: Material with rotational sym-  Using material constants: Material constants are
metry about an axis. Two values for each material prop- specified based on Perfect Plasticity, Linear Hardening,
erty are required—one for the plane of isotropy and Power Law, or Exponential Law.
one for the remaining principal material direction.

Materials and Material Properties Back to Table of Contents MATERIALS AND MATERIAL PROPERTIES 7

SIMULATION FEATURES creo elements/pro 5.0 mechanica

Simulation features are those created in Mechanica such as Only one boundary at a time can be used to split a surface. QUICK REFERENCE GUIDE
surface and volume regions, datum features and user de- In order to create surface regions using multiple boundaries
fined measures. Since these features are created in as shown, two surface region features have to be created. Mesh density increased due to the volume region.
Mechanica mode, they are not available in the standard
mode of Creo Elements/Pro. In the images below, loads and constrains are applied to
surface regions. More nodes and elements are automatically
Surface Region added to a surface region during mesh generation.

Surface regions are footprints on the analysis model that can
be used for applying loads or constraints and for increasing
the mesh density. They are created by splitting a surface by
either sketching a boundary or by selecting existing curves
chains.

When splitting curved surfaces, there is no need to project Volume Region Results display only for the volume region.
the sketched curve on to the surface. During the creation of
the surface region, the curve is projected automatically as Volume regions can split solids into three-dimensional re- Datum Features
shown below for the surface region on the shaft. gions. Analysis results can be viewed based on volumes
making it easier to check internal stresses and strains. Vol- Any datum feature created within Mechanica mode is
ume regions also help in increasing the mesh density. In grouped under the simulation features and are not available
thermal analysis, heat loads can be added to internal sur- for reuse in the standard mode of Creo Elements/Pro. Typi-
faces of a parent volume. Volume regions are created using cally, datum features created in Mechanica are user-defined
one extrude, re- coordinate systems for applying loads and constraints, da-
volve, sweep, tum points for increasing mesh density, point load and con-
blend, or variable straints, and sketches for creating regions.
section sweep.

Always create surface regions before defining midsurfaces Back to Table of Contents 8
for shell idealizations, as creating surface regions will invali-
date existing shell pairs.

Simulation Features

MEASURES—PREDEFINED, USER-DEFINED, AUTOMATICALLY-DEFINED creo elements/pro 5.0 mechanica

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Measures in Mechanica are evaluated at the end of every User-defined Measures Automatically-defined Measures
successful analysis completion. User-defined measures are
location specific and can be created as probes in the analysis Similar to predefined measures, user-defined measures are Automatically-defined measures are a specific set of meas-
model to track certain outputs like stress, force, velocity, or measures that can evaluate a quantity, but can be custom- ures are automatically defined by Mechanica based on the
acceleration. For example, in a vibration analysis, a user- ized with additional flexibility and functionality. These can type of modeling entities like contacts regions, fastener con-
defined measure to track acceleration at a certain critical be location-specific, time-specific, or frequency-specific nections, or thermal resistance.
location can simulate an accelerometer. Mechanica uses quantities. They can be used to monitor specific aspects of
three types of measures—predefined, user-defined, and the model’s performance like stress or strain at a point in a INTERFACE MEASURES
automatically defined. particular direction. In dynamic analyses, user defined meas-
ures can be used to monitor the model performance like When a contact interface with friction or a thermal resistance
Predefined Measures position, acceleration or velocity at a point. interface is created, the measures shown below are auto-
Sandy_McKinney_2015 matically defined by Mechanica.
Mechanica evaluates a set of predefined quantities based on
the analysis type. These are not location-specific and are
evaluated over the entire analysis model. Among the vari-
ous measures evaluated during a structural analysis typical
measures of interest are von Mises stress, maximum princi-
pal stress, and maximum displacement. For a thermal analy-
sis, the maximum heat flux, and maximum and minimum
temperatures are important predefined measures.

Quantities available to create user defined measures FASTENER CONNECTION MEASURES

For fastener connections, the measures show below are
automatically created.

Predefined structural measures Predefined thermal measures Tracking the deflection of a point location along a direction MEASURES 9

Predefined, User-defined, Automatically-defined Back to Table of Contents

IDEALIZATIONS—SHELLS creo elements/pro 5.0 mechanica

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Idealizations are Mechanica elements that represent the STANDARD SHELLS MIDSURFACE SHELLS
design geometry with elements like beams, shells, springs
and masses. They simplify the fully detailed 3D geometry There are two types of standard shells, simple and advanced. A midsurface shell is created by selecting the pairs of sur-
and are computationally less expensive than a simulation faces, as shown below. Mechanica can automatically detect
without simplification, thereby allowing faster simulation. SIMPLE STANDARD SHELLS opposing surfaces with the selection of one surface.
Simple standard shells are typically applied on surface mod-
Shell Idealization els by associating a thickness and a material, as shown be- In complex models that have large number of surface pairs,
low. it is recommended to use the Auto Detect Shell Pairs option
Thin areas of a model can be represented as shells which is a by specifying the characteristic thickness in the model.
surface with associated thickness. Shells or surface elements Mechanica will search for all shell pairs with a thickness less
are made of quads and triangles which is computationally than the characteristic thickness.
more efficient than the default solid elements like tetra,
wedge and brick. Shell idealizations can be used in struc-
tures with constant thickness that is relatively small com-
pared to the length and width.

There are two types of shells—standard and midsurface.
Standard shells are created by selecting a surface reference
from a model and specifying a material and thickness. Mid-
surface shells are created by selecting surface pairs in the
model. Mechanica will compress the surface pairs into a
single midsurface as shown by the green shell midsurface in
the below example.

ADVANCED STANDARD SHELLS
Advanced standard shells allows homogeneous shells or
shells with laminate properties, as shown below. The layup
below consists of some plies of carbon fabric on either side
of some foam core.

Analysis Model Shell Midsurface

Default Solid Mesh (Tetra) Shell Mesh ( Quad, Tri)

Shells Back to Table of Contents IDEALIZATIONS 10

IDEALIZATIONS—SHELLS creo elements/pro 5.0 mechanica

The midsurface creation on the entire analysis model can be QUICK REFERENCE GUIDE
reviewed by selecting AUTOGEM > REVIEW GEOMETRY…
Shell surfaces are displayed in green by default. If you are using surface regions and shell idealizations, the
surface regions should be created before the shell idealiza-
Sandy_McKinney_2015 tion definition.

Typically, analysis models in Mechanica are composed of
both solid and shell elements. In assemblies and parts, the
thin areas can be defined as shells while the rest of the
analysis model can be solids. The ribs in the model below
are defined as midsurface shells while the rest of the model
is solid.

SHELL PROPERTIES Laminate Stiffness By default, shell idealizations or elements are displayed in
green and solid elements are displayed in blue. The shell to
 Thickness: For standard shells, the thickness needs to A laminate layup is a number of shells, with each shell hav- solid elements connection is automatically taken care of by
be specified after selecting the surface. For midsurface ing its own midsurface. The stress in each ply is calculated link elements, which are displayed in purple.
shells, the thickness is automatically assigned to the during the analysis. The laminate layup consists of a number
shell based on the distance between the surface pairs of plies stacked on each other. The layer repetition pattern
selected. can be specified using one of three symmetry options. For
example, a three layer laminate (a, b, c) would change as
 Material: Material needs to be assigned manually. follows:
 Material orientations: For orthotropic and trans-
 Symmetrical: a b c c b a
versely isotropic materials, the material orientation and  Antisymmetrical: a b c –c –b –a
properties in those directions are required.  No symmetry: a b c
 Shell property (laminate properties): Advanced
shells can be used to simulate composites or laminates For analysis models that contain shell idealizations, do not
by specifying the laminate layup or the laminate stiff- use the surface that will be compressed during midsurface
ness. creation for applying loads and constraints.

Laminate Layup Loads and constraints can be applied on the top or bottom
surfaces and the side edges but not on the side surfaces.
Shells IDEALIZATIONS 11
Back to Table of Contents

IDEALIZATIONS—BEAMS Standard beam sections are defined by selecting the cross creo elements/pro 5.0 mechanica
section shape and specifying required dimensions. The fol-
Beam Idealization lowing standard shapes are available: QUICK REFERENCE GUIDE

Beam idealizations represent structures whose length is The BSCS is used as the reference coordinate system for de-
much greater than the other dimensions. They are one- fining the beam cross section shape. The x-axis is along the
dimensional idealizations and are created by applying a 2D length of the beam. Y and z directions are determined by
cross section to a curve. Rather than analyzing an extruded Mechanica.
section using the solid elements, beam idealization allows
faster simulation by defining the cross section properties. The BCPCS is located at the centroid of the section. The
Typical references used to create beams are curves and BSCS is coincident with the BCPCS for general sections and
points. all standard sections except channel and L sections.
Mechanica automatically determines the BCPCS for channel,
L, and sketched sections. Beam section properties are re-
ported based on BCPCS.

Analysis model Beam idealization

BEAM SECTIONS Beam sections can also be sketched. The area parameters
are calculated based on this sketched geometry.
There are three types of beam sections:
Beam sections can be created on the fly as needed, or stored
 General and retrieved from a library of cross-sections. Beam sections BEAM RELEASE
 Standard can also be saved in a library file called mbmsct.lib, and the
 Sketched beam section directory can be specified as a config.pro op- Mechanica will fix all degrees of freedom at beam ends by
tion (sim_beamsection_path). default. With beam release, certain degrees of freedom can
General beam sections are defined by providing the cross be released at the ends of the beam. The BACS is used for
section properties and do have a specific shape. BEAM ORIENTATION specifying beam releases. The following degrees of freedom
can be released at beam ends:
The following properties are required to define a general Beam orientation affects how the beam relates to the axis
beam section: where Mechanica applies loads and calculates analysis re-  Translational: Dx, Dy, Dz
sults. The following three types of coordinate systems are  Rotational: Rx, Ry, Rz
 Area associated to beams:
 2D moments of Beam releases are
 Beam action coordinate system (BACS) indicated by this
inertia  Beam shape coordinate system (BSCS) graphic icon at the
 Torsional stiff-  Beam centroidal principal coordinate system (BCPCS) end of the beam. An arrow-
head indicates a translational
ness The BACS is used as a reference while applying forces and DOF, and a ring indicates
 Shear parame- moments on beams. It is located on the curve that is used to rotational DOF.
create the beam. The x-axis is always parallel to the axis of
ters the beam or normal to beam section. The y-axis direction is
 Stress grids user-defined.

Beams Back to Table of Contents IDEALIZATIONS 12

IDEALIZATIONS—SPRING, MASS creo elements/pro 5.0 mechanica

QUICK REFERENCE GUIDE

Spring Idealization Sandy_McKinney_2015 MASS TYPES
Spring idealizations must be attached to at least one point in
A spring idealization represents a linear elastic spring con- the analysis model—either a datum point or a vertex.  Simple: This is the default mass type wherein the distri-
nection that can be defined from one point to another or Springs can act as constraints as well. bution can be specified as total mass or the mass per
from point to ground. It adds translational or torsional resis- point to be distributed over all of the points selected.
tance between two points in an analysis model. Mass Idealization The mass must be specified.

Analysis model with spring elements A mass idealization is a one-point element that can be used  Advanced: This mass type allows only the mass per
to represent a concentrated mass at a point without a speci- point distribution. Properties like mass and moments of
SPRING TYPES fied shape or geometry. In an assembly analysis, compo- intertia can be specified relative to a coordinate system.
nents that contribute only mass and not stiffness to the as-
 Simple: The spring is defined by specifying extensional sembly can be simplified as mass idealizations. For inertial  Component at Point: This mass type is available only
and torsional stiffness values. loads, moments of inertia can be specified without including in assembly mode. The mass properties of a selected
the actual geometry. component (part or subassembly) are applied to this
 Advanced: The spring is defined by specifying magni- type of mass idealization.
tude and direction of components for extensional and Back to Table of Contents
torsional stiffness. The component at point mass type is typically useful
when using simplified representations of analysis mod-
 To Ground: The spring is defined by specifying the els. The excluded component's mass properties are
orientation of the components for the extensional and assigned to the point.
torsional stiffness relative to a selected coordinate sys-
tem. It is important to note that the mass idealization will predict
the way a model will behave due to an object at a point in
SPRING PROPERTIES the model and will not predict what happens to the object
itself. If the behavior of the object itself is also one of the
Extensional (Kxx,Kyy,Kzz) and torsional stiffness (Txx,Tyy,Tzz) goals of the analysis, the full geometry of the object has to
can be specified in directions other than those directly in line be included without any kind of idealization.
with the spring’s starting and ending points. These proper-
ties are required for Advanced or To Ground springs. If a component will be simplified in Mechanica using a mass
Spring, Mass element, it is a good practice to analyze the mass properties
in Creo Elements/Pro. The center of gravity can be calcu-
lated which can then be used in Mechanica for the location
of the mass element.

MASS PROPERTIES

The two main mass
properties are mass
and moments of iner-
tia. Moments of inertia
are specified about
each mass element’s
center of gravity rela-
tive to the axes and
principal planes of the
WCS.

IDEALIZATIONS 13

CONNECTIONS—WELDS creo elements/pro 5.0 mechanica

Weld Connections QUICK REFERENCE GUIDE

Weld connections are used to connect midsurface shells in Spot Weld
assembly mode. End and perimeter welds are used for ex-
tending or creating shell elements between midsurface WELD REFERENCES:
components. Spot welds are used to connect components End Welds: Select two surfaces in any order.
using beams. Perimeter Welds: Select the doubler surface first, then
the base surface, and then the edges.
WELD TYPES Spot Weld: Select surfaces in any order and then select a
datum point.
 End weld
 Perimeter weld The query selection can be used to select the appropriate
 Spot weld surfaces when creating weld connections.
 Weld feature
WELD PROPERTIES:
END WELD Perimeter weld: Specify shell thickness
In assembly models that use shell idealizations, when there Spot weld: Specify material and diameter
is a T or L, angled or oblique configuration, end welds can be
used to connect the midsurfaces as shown below. WELD FEATURE
Welds created using the Creo Elements/Pro welding applica-
PERIMETER WELD Perimeter weld tion can be referenced in Mechanica mode using the weld
In assembly models that have a parallel configuration, pe- feature option. The groove and fillet weld features can be
rimeter welds can be used to connect the shell midsurfaces SPOT WELD reused in Mechanica for solids and shell midsurface connec-
along the perimeter of one of the parts. Spot welds are used for modeling structural assembly con- tivity. The weld features created in Creo Elements/Pro
nections like glue tabs, spot welds, rivets, and bolted con- should be surface welds and not lightweight welds.
End and perimeter welds do not simulate actual welds of nections. They accurately transfer load from one part to the
real world. They are just used to connect midsurfaces for other but should not be used to predict localized stresses When using welded connections, the stress in the weld may
shell idealizations. End welds and perimeter welds are not near connection points. They can be created on parts that appear higher than it actually is due to areas of theoretically
required for solid idealizations, for which two parts touching are solids or shells or both. Surfaces connected with spot infinite stress near the weld. The intent for using weld con-
each other are automatically assumed to be welded by de- welds should be within 15 degrees of being parallel to each nections is to predict the failure of components in the analy-
fault. This default interface can be changed. other. sis model and not failure in the weld itself. If the goal of the
analysis is to predict failure in the weld itself, then model the
A spot weld connection is represented by a beam with a welds using solids and rather than using weld connections.
circular cross section. It connects two surfaces in a circular
spot at a point. The datum point used to specify the spot
weld location does not have to be on either of the two sur-
faces being connected. The point is just projected onto the
surface. The beam is connected to the two surfaces by a
special link element, and the surface at the diameter of the
spot weld will be rigid. When using shells, the beam ends
are projected to the midsurface during analysis run.

Welds Back to Table of Contents CONNECTIONS 14

CONNECTIONS—INTERFACE creo elements/pro 5.0 mechanica

QUICK REFERENCE GUIDE

Interface Sandy_McKinney_2015CONTACT INTERFACE  Infinite friction: Con-
tact analysis in
When analyzing assemblies in Mechanica, components with Contact interface enable a contact analysis to determine the Mechanica can analyze
coincident surfaces can be handled using an interface, which non-linear forces generated by two separate components only the normal forces
controls how Mechanica will treat a particular pair of mated coming into contact. It prevents surfaces from being and not the friction
or overlapping surfaces during meshing and analysis. The merged, prevents interpenetration, and calculates contact forces, so instead of
structure mode and thermal mode of Mechanica have differ- pressures and contact area when running a contact analysis. constraining the models
ent types of interfaces. The default interface can be set in Contacts can be defined between a pair of surfaces or be- in contact in the tan-
the Mechanica Model Setup dialog box. tween components. These references can be selected in the gential direction to
Interface Definition dialog box. Contacts can also be created prevent rigid body mo-
Structure Interface types: automatically with auto detect option by setting selection tion, the infinite friction
 Free filtering tolerance like maximum separation distance and option can be checked.
 Contact angle between the surfaces.
 Bonded  Create slippage indi-
CONTACT INTERFACE DEFINITION PROPERTIES cators: The coefficient
Thermal Interface types  References: Specific surface pairs can be selected, or in of static friction can be
 Adiabatic used to determine
 Bonded a complex geometry situation, the component pairs can whether the component would have slipped or not.
 Thermal Resistance be selected. Stresses due to friction are not calculated.
 Split surfaces: Surfaces are split along the boundaries
FREE INTERFACE that help in generating a compatible mesh. PREREQUISITES FOR CONTACT INTERFACE:
 Generate compatible mesh: The position of the nodes  The distance between the surfaces can be no larger
Free interfaces prevent surfaces from being merged and on each of the coincident surfaces will overlap or be
should be defined along surfaces that should not be compatible. than one half the average diagonal lengths of both
merged. Otherwise, the analysis model would have a much surfaces.
larger stiffness than it should.  The surfaces cannot be at an angle greater than 36
degrees with respect to each other.
With a free interface, applied forces do not transfer between  Contact interface is not valid for shell or beam ele-
connected components or surfaces. Mechanica will not pre- ments.
vent interpenetration between components except along
surfaces that have specifically been assigned a contact or BONDED INTERFACE
bonded interface.
If the default interface is Bonded, all components that are
Free interfaces can be created by either selecting surface- mated together or that have coincident surfaces will be
surface or component-component. It can also be set as the merged or assumed to be welded. If a bonded interface is
default interface. If the default interface is set to free, all created between two surfaces, Mechanica automatically
components are free as individual bodies. creates a force measure to calculate the magnitude of resul-
tant force over the bonded surface.

The default interface selection will depend largely on how
much time is spent assigning interfaces. If most compo-
nents are bonded or welded together and only one pair of
components or surfaces have contact between them, then it
is recommended to set the default interface to bonded and
assign contact interface where needed.

Interface Back to Table of Contents CONNECTIONS 15

CONNECTIONS—LINKS, FASTENERS creo elements/pro 5.0 mechanica

Links WEIGHTED LINKS QUICK REFERENCE GUIDE

RIGID LINKS Weighted links are used to distribute masses or loads acting Fastener Connection
at a single source point over a collection of geometric enti-
A rigid link connects geometric entities such as surfaces, ties through which the load is transferred. Fasteners simulate an assembly’s bolts and screws with a
curves, and points so that they remain rigidly connected series of springs. They fasten two components at a specific
during an analysis and will not have any displacement rela- Weighted links transfer load in a balanced manner. This is a location or hole and simulate the load path within the as-
tive to each other. great method to simplify complex assemblies in that it rep- sembly and the amount of load carried by each bolt or
resent them as a point mass and distributes load transfer. screw.
Rigid links are typically used in situations where the entities A weighted link is defined using two types of entities: The stiffness of the fastener can be input manually, or
being selected are not in direct contact with each other and  Dependent Side (point): This is the source point Mechanica can calculate stiffness based on references and
hence would not be bonded by the assembly. Simple rigid materials specified.
links acts in all directions whereas advanced rigid links allow where the mass or force is assigned.
control of the degrees of freedom of the link.  Independent Side (points, edges, surfaces): The ef- FASTENER TYPES

In the example below, the midsurface gaps between the two fect of the dependent side is distributed over the enti-  Bolts: Created on solid or shell element components.
components will prevent analysis using shells. The rigid ties on the independent side.  Screws: Created only for solid element components.
connection between the side surfaces fixes the issue by al- The translational DOF (degrees of freedom) for the in-  Simple fasteners: Created using the material and shaft
lowing no relative displacement between the edges of the dependent side can be specified.
midsurface. Entities on the independent side determine the motion diameter specified.
of a single point on the dependent side. Thus, the  Advanced fasteners: Created based on material and
source point follows the average motion of the target
node group. shaft diameter or spring properties. They have addi-
It is recommended to use weighted links for connecting a tional options like preload, restrict rotations for the fas-
mass element to the model without stiffening the structure. tened parts, and fastener carrying shear.
Although this could be used to distribute forces as well, it is
similar to the TLAP (total load at point) option used in loads.

Links, Fasteners Back to Table of Contents CONNECTIONS 16

CONNECTIONS Sandy_McKinney_2015 PREREQUISITES FOR FASTENERS: creo elements/pro 5.0 mechanica
 Fastener connections can only pass through two
ADVANCED FASTENER DEFINITION QUICK REFERENCE GUIDE
components, and the analysis model must be an
Advanced fasteners have the following properties: assembly. To correct this, the value of the preload needs to be ad-
 The holes used for creating fasteners must be a right justed. Because the static deformation is linear, the preload
 Stiffness: Stiffness is computed using either using di- cylindrical hole, or the hole must be perpendicular should be scaled by the ratio between the applied preload
ameter and material or spring stiffness properties to the component surface and have straight sides. force value and the reported tensile force value.
 The two holes should have approximately the same
 Diameter diameter. The axes of the holes must be approxi- Here is the procedure to apply this correction:
 Material mately parallel to each other.
 Fix Rotations: This option allows Mechanica to auto-  For bolt type fasteners the holes must completely 1. Set up the fastener connections with the desired pre-
penetrate both parts. If one of the hole is a blind or load force value.
matically prevent rotation of fastened components variable depth hole, then a bolt connection cannot
about the bolt or screw. An alternate method of pre- be created. 2. Do not apply any external loads. But for the analysis to
venting rotation is to use constraints on the fastened  For screw type fasteners, one of the holes selected run we would need a dummy load value of zero. So set
components or to add more fasteners. for references must be a blind hole and the other a the value of the external load on the analysis model to
 Carries Shear: If this option is checked, the fastener through hole. be zero.
carries the shear force that passes through the fastener  Fasteners may not work if the two parts are interfer-
connection. If this option is cleared, Mechanica as- ing with each other or if there are intervening com- 3. After applying constraints, run the analysis.
sumes that the shear force passes through the compo- ponents. 4. Check the fastener tensile force reported in the analysis
nents by friction where the components meet.
 Fix Separation: This will ensure that the fastened com- FASTENER PRELOAD report file (Fastener1_tensile_force). This will not be
ponents do not interpenetrate. equal to the preload force applied.
 Preload force: This will simulate the degree to which Preload compresses fastened components together and 5. Change the preload force in the fastener connection to
the bolt or screw will be tightened and the fastener will creates a state where any external force has to relieve this the following calculated correct preload force and apply
compress the components. compression before the fasteners begin to deform. There- external load values as necessary and run the analysis.
 Fastener Head and Nut Diameter fore, when a fastener has preload applied, it will shoulder Correction ratio (CR) = preload force/fastener tensile
 Separation Test Diameter only a small portion of any external load until separation force
occurs. In Mechanica, fasteners are implemented as springs. Correct preload force = original preload force x CR
The stiffness of which is calculated by default from the di-
mensions of the holes selected. Preload is implemented by FASTENER MEASURES
setting the natural length of the spring to be shorter than
the distance between the ends of each hole. Preload is not The following measures are automatically defined measures
non-linear, and it does not take the stiffness of the fastened for fastener connections:
components into consideration.
 Fastener_tensile_force
PRELOAD FORCE VALUE ADJUSTMENT  Fastener_tensile_stress
 Fasteners_shear_force
With zero load on the analysis model, the expectation is that  Fasteners_shear_stress
the fastener tensile force will be equal to the preload force  Fasteners_separation_stress
value. Because the fastener is implemented as a spring, the
preload causes the fastened components to deform under NOTE:
preload. As of the Creo Elements/Pro 5.0 (Pro/ENGINEER Wildfire
5.0) release, an Advanced Mechanica license is required
to apply preload force.

Fasteners Back to Table of Contents CONNECTIONS 17

MESH (AUTOGEM) MESH REFINEMENT creo elements/pro 5.0 mechanica

Mesh Since Mechanica uses the p-method solver, for most analysis QUICK REFERENCE GUIDE
there is no need for mesh refinement. But if a converged
Typically, Mechanica generates mesh during the analysis solution could not be achieved within the ninth order poly- The following options can be used to refine the mesh:
run, but it is a good practice to create and check the mesh nomial, then mesh refinement can be used to get a con-
before running the analysis. Mechanica uses AutoGEM verged solution.  AutoGEM control
(automatic geometric element mesher) to generate and  Change AutoGEM settings
control the mesh. Based on the Mechanica operating mode, Mesh refinement should be done only if the analysis reports  Surface region
the resulting mesh can be either p-mesh or h-mesh. By de- a non-converged solution in a multi-pass analysis. The area  Volume region
fault, p-mesh is generated when using the native mode, but that requires refinement can be identified in the p-level  Datum points
if the FEM mode option is used then the traditional h-mesh fringe plot. The element edges that reached ninth order are
is generated. It is always recommended to use the default the non-converged solution areas that need refinement as AUTOGEM CONTROL
native mode p-mesh to create geometric element mesh. shown below with the red color edges. The AutoGEM Control dialog box has several methods to
The FEM mode should be used only when using a third party control the mesh distribution on the analysis model. These
solver like Ansys or Nastran that requires the traditional h- mesh control options exert additional influence beyond the
mesh. software defaults.

CREATE P-MESH 1. Edge Distribution: This specifies the number of nodes
and their placement intervals along curves or edges.
In order to create the mesh, the material property has to be
assigned first. The element type of the resulting mesh— This method is typically used as shown below to in-
solid, shell, etc.—depends on the type of idealization de- crease the number of nodes on the hole and side edges
fined. that reached the ninth order polynomial and could not
converge with the default number of nodes and ele-
ments.

The mesh can be saved for reuse during analysis run. The Back to Table of Contents MESH 18
mesh file for part is a .mmp file and the mesh file for an as-
sembly is a .mma file. Before starting the analysis post proc-
ess, the settings can be configured to use mesh from exist-
ing file in the Run Settings dialog box.

Mesh (AutoGEM)

MESH (AUTOGEM) 4. Maximum element size: Use this method to control creo elements/pro 5.0 mechanica
the maximum size of the elements created by the mesh
2. Minimum edge length: This method is used to ignore generator. This can be applied to the entire analysis QUICK REFERENCE GUIDE
edges and datum curves with a length smaller than or model as shown below or to specific volumes, surfaces,
equal to a specified length with options to keep or re- edges, or curves. 7. Hard curve: This method is similar to the hard points
tain certain edges except that datum curves can be selected to guide the
for meshing. By mesh creation process as shown below with the circular
default, AutoGEM curve concentric to the hole.
will mesh all
edges of the
analysis model.
Sandy_McKinney_2015
3. Isolate for exclusion: This method is used to isolate 5. Edge length by curvature: This method is used to AUTOGEM SETTINGS
selected points, edges, curves, surfaces, volume, and create smaller elements adjacent to curved surfaces The default AutoGEM settings are optimized to give a supe-
components from the model during analysis. The se- such as areas near curves, fillets, and holes that are rior mesh on typical analysis models. But AutoGEM many
lected geometry is isolated with options to exclude it likely to have high stress concentrations. A dense mesh not be able to mesh all models using these default limit set-
during convergence is achieved by specifying the ratio of the element edge tings. When the mesh creation fails, the default settings can
and measure calcu- length to the radius of curvature as shown below near be changed as follows.
lations. Preselected the hole surface.  Insert points: Add points to create a valid mesh.
singularities like  Move or delete existing points: Relocate or remove
reentrant corners, 6. Hard points: This method is used to select points on
point loads and the analysis model to guide the mesh creation process. existing points for optimal element configuration.
constraints, and AutoGEM will use these hard points as automatic ele-  Modify or delete existing points: Modify or delete
edge loads and con- ment nodes. Points can be created or existing points
straints can also be can be selected. existing elements to optimize or complete element
excluded using this creation.
method. Singulari-  Automatic interrupt: Stop AutoGEM after it creates a
ties are areas of specific percentage of elements.
theoretically infinite  Ignore unpaired surfaces: Unpaired surfaces will be
stress which are excluded from mesh.
undesirable as they  Remove unopposed surfaces: Unopposed surfaces
can skew analysis are excluded from the mesh.
results.
Back to Table of Contents 19
Mesh (AutoGEM)

MESH (AUTOGEM) creo elements/pro 5.0 mechanica

 Create links where needed: Links created to connect MESH DIAGNOSTICS QUICK REFERENCE GUIDE
shell-solid elements or solid quads-solid triangular
faces. The mesh diagnostics will highlight areas on the analysis  Minimum Surface Dimension: This setting ensures
model that Mechanica is having problems meshing due to that all surfaces whose dimensions exceed the mini-
 Create bonding elements: These bonding elements the existing limits as shown below. mum will be retained. AutoGEM merges each of the
are created to link parts in assemblies. surfaces whose dimensions are less than the minimum
In such situations AutoGEM will try to automatically change into an edge whose length represents the original sur-
 Detailed fillet modeling: This will create additional the default settings and create a successful mesh. If it fails face. If the resulting edge is shorter than the value that
elements near fillets for a smooth fringe plot. again, then the settings can be changed manually or the appears in the minimum edge length field, AutoGEM
geometry tolerance setting can be edited. will merge the surface into a vertex.
 Display AutoGEM prompts: During meshing, prompts GEOMETRY TOLERANCE
or message boxes will be displayed that require action If the analysis model fails to mesh, the geometry tolerance  Minimum Cusp Angle: This refers to the minimum
or confirmation to continue meshing. settings can be changed to work around the problem. angle of the cusp formed when two arcs meet or an arc
meets an edge or surface. AutoGEM eliminates any
 Element types: Set element types for solids and shells. angle less than this value by moving the node at the
Tetrahedral elements are the default for solids, and this end of the surfaces or edges to the nearest location that
can be changed to allow other type elements like forms an acceptable angle and hence shortens the sur-
wedge and brick elements. The default setting for faces or edges.
shells is to create quads, but this can be changed to
create triangles only.  Merge Tolerance: This is the distance below which
AutoGEM will merge mated or overlapping surfaces in
AUTOGEM LIMITS assemblies that have shell midsurfaces.
AutoGEM creates and edits the mesh using the following
limits and they can be edited when mesh fails. They can also GEOMETRY TOLERANCE BEST PRACTICES
be used to increase or decrease the number of elements.  If a mesh fails because some of the edges in the

 Allowable angles: Minimum and maximum edge and  Minimum Edge Length: This setting ensures that all model are too small, resolve by increasing the mini-
face angles can be specified. edges whose length exceeds the minimum will be re- mum edge length tolerance value.
tained. AutoGEM and merges the end points of any  If AutoGEM merges away a sliver surface for which
 Max aspect ratio: Ratio between the longest and edge whose length is less than the minimum into a results are important, reduce the minimum surface
shortest length of a facet. single node. This minimum can be an absolute or rela- dimension to force AutoGEM to use that surface.
tive value.  The tolerance values should not vary significantly
 Max edge turn: Maximum angle that the normal to a from the defaults, as a good practice keep these
given edge of a facet can turn from start to end. Back to Table of Contents changes to within 10 percent of the default values.
 Entering extremely large values might prevent
The default limits should be used as much as possible and meshing.
should be changed only when AutoGEM mesh creation fails
due to intricate geometry. Changing these limits might MESH TREATMENT OPTIONS
cause a non-converged solution. It is a good practice to
always check the p-level fringe plot. If the analysis model contain both solid and shell idealiza-
tion, AutoGEM can be directed to use solid only, midsurface
Mesh (AutoGEM) only, or solid and midsurface mesh treatment options.
AutoGEM selects this automatically but it can be changed if
an all-solid mesh should be used instead despite shells hav-
ing been defined in the analysis model.

MESH 20

CONSTRAINTS—DISPLACEMENT, BOLT TYPE creo elements/pro 5.0 mechanica

QUICK REFERENCE GUIDE

Constraints simulate real world boundary conditions on the Sandy_McKinney_2015BOLT TYPE CONSTRAINT Most structural analyses require a constraint on the model to
analysis model. In structure mode, constraints are used to fix run a successful analysis. But for bodies in motion, the inertia
certain portions of the analysis model so that the model To simulate a bolt type constraint a cylindrical coordinate relief option allows the analysis to run without constraints.
cannot move or can move only in a predetermined way. system can be used with the Z axis along the axis of the hole. When inertia relief is used, Mechanica will create a new Car-
A surface region can be created for the bolt head contact tesian coordinate system internally, define a three point
Mechanica has the following types of structural constraints: area and constrained. constraint, and apply body loads to balance the applied
loads.
 Displacement Constraints INSUFFICIENTLY CONSTRAINED MODELS
 Planar, Pin and Ball Constraints Any geometry that is not constrained in the analysis model is
 Symmetry Constraints When a model is insufficiently constrained, the Mechanica assumed to have all the translational and rotational degrees
solver engine will report it, and the analysis will have a fatal of freedom.
Displacement Constraint error. In order to resolve this, run a constrained modal analy-
sis with rigid mode search. The animation of this analysis Solid elements have three translational degrees of freedom
Displacement constraints are used to limit the degrees of result will help in finding the missing constraint in the analy- and no rotational degrees of freedom. Any face of a tetrahe-
freedom of an analysis model and also to prevent rigid body sis model. dral element cannot rotate without translation in one of the
motion. They are applied to portions of the model using a three directions. Mechanica will ignore rotational con-
geometric reference like surface (or surface region), edge or straints on solid.
curve, points. The selected geometry can be constrained in
translations and rotation in each of the coordinate system Constraints can simplify the analysis model. In assemblies,
axes using Free, Fixed, and Prescribed settings. certain components can be excluded from the analysis and
constraints can be used instead.
Every constraint is part of a constraint set. A constraint set is
a collection of constraints that act together at the same time Rotational constraints are valid for shell and beam idealiza-
on the analysis model. tions. When using shell elements, it is a good practice to not
apply constraints on side surfaces that get compressed away
By default, the displacement constraints are based on the during midsurface creation.
WCS (world coordinate system) of the analysis model. A user
-defined coordinate system can also be used as a reference
for special type of constraints, such as bolt type constraints,
using a cylindrical coordinate system.

Prescribed displacement is given when the exact displace-
ment is known but the load or force is not known. The pre-
scribed displacement will act as a load when the analysis is
run. Force required to create the prescribed displacement
can be calculated using a reaction measure at the constraint.

Displacement; Bolt Type; Insufficiently Constrained Models Back to Table of Contents CONSTRAINTS 21

CONSTRAINTS—PLANAR, PIN & BALL; SYMMETRY creo elements/pro 5.0 mechanica

Planar, Pin and Ball Constraints MIRROR SYMMETRY QUICK REFERENCE GUIDE

These constraints allow you to easily create engineering With mirror symmetry, one segment of a model is the mirror CYCLIC SYMMETRY
constraints. image of other segments. The model is cut in half through
the plane, and the constraint is applied through the surface Cyclic symmetry is applied to analysis models that are sym-
 Planar constraints allow full planar movement but for solid idealization, through the edge for shell idealization, metrical about an axis, such as a fan blade or turbine. A seg-
constrains off-plane displacement. This constraint is or through a point for beam idealization that lies on the ment of the geometry is repeated in a cyclic manner but it is
valid only for planar surfaces. plane of symmetry. not a mirror image. This segment is a pie shaped wedge that
can reproduce the entire analysis model by copying it an
 Pin constraints control the translation and rotation To cut the model in half for mirror symmetry, instead of cre- integer number of times about the axis of symmetry.
about the axes of a cylindrical surface in 3D analysis ating an extruded cut, it is a good practice to select a datum
models. This is very useful when a surface needs to plane and use the solidify feature (EDIT > SOLIDIFY) to re- During the creation of cyclic symmetry, Mechanica will calcu-
move in one or more directions while being held in move the other half of the model. late the angle of the pie based on the surfaces selected to
place in the remaining directions. Pin constraints can check if it can be copied an integer number of times to pro-
also specify angular and axial degrees of freedom as duce the entire analysis model. It will generate a warning, as
free or fixed. This constraint is valid only for cylindrical shown below, if it cannot.
surfaces.

 Ball constraints represent a ball joint in which transla-
tion is fixed while rotation is free. This is valid for only
spherical surfaces.

Planar, pin and ball constraints are not valid for large defor-
mation analysis.

Symmetry Constraints When using mirror symmetry, it is important to reduce the Cyclic symmetry constraints should be applied before using
total load value by half. Do not reduce force per unit area AutoGEM to create the mesh. The surfaces selected for sym-
When the loads, constraints, and geometry of an analysis loads (i.e. pressure loads), as will be taken care of automati- metry must map to one another. Do not use cyclic symmetry
model are symmetrical, it is a good practice to subdivide the cally with the total load reduction. for modal and buckling analysis.
model and analyze a symmetric portion instead of the entire
model. This will greatly reduce the number of elements Do not use mirror symmetry when running modal and buck-
thereby saving analysis time and system resources. But ling analyses, as Mechanica will report only the modes that
when working on a symmetric section, an additional con- are symmetrical.
straint is required to prevent the model from deforming
through the plane of symmetry. There are two types of sym-
metry, mirror cyclic.

Planar, Pin and Ball; Symmetry Back to Table of Contents CONSTRAINTS 22

LOADS creo elements/pro 5.0 mechanica

QUICK REFERENCE GUIDE

Loads are applied to the analysis model to simulate what the DISTRIBUTION OPTIONS  Interpolated over entity: Interpolation points with an
model must endure to perform its function. For structural associated scaling factor can be specified to vary the
analysis, a load can be a force, moment, pressure, accelera- Distribution options define how the load magnitude is inter- load over the selected entity.
tion, velocity, or temperature. For thermal analysis, a load is preted mathematically.
a heat condition. Most Mechanica load types are entity Sandy_McKinney_2015 Bearing Load
loads that are applied to specific geometry of the analysis  Total load: This will distribute a load along the length
model like surfaces, edges or points. Some are body loads or area of the selected entity. The integral of the load Bearing loads are applied on holes or pins that are being
like gravity load and centrifugal load. over the selected entity is the total load value specified. pulled or pushed to one side. Axles, bolts, pins, rivets, and
shafts create stresses in the members they connect, along
Force/Moment Load  Force per unit type: This applies a distributed load the bearing surface, or on surface of contact. This special
over the selected entities. The type of unit can be type of load is not uniformly distributed, and is based on
This is the most frequently used load type in Mechanica. It is length, area, or volume. The difference between this Mechanica’s built-in load function.
applied on geometric entities with a specific magnitude and type of load and a pressure load is that the direction of
direction. a pressure load will always be normal to the surface. Bearing loads act in the direction normal to the hole’s axis.
Any load vector parallel to the hole axis will be ignored by
VECTOR DEFINITION OPTIONS  Total load at point (TLAP): Computes and applies the Mechanica. Check the preview to make sure the bearing
equivalent shear, moment, and torsion of a point force load is acting in the correct direction and that the correct
 Components: Three acting at a specified distance from a surface. Moments half of the hole is being loaded.
force components and applied to solid elements must use the TLAP option.
three moment compo- This is because solid elements cannot accept moments Pressure Load
nents can be specified as load input as they cannot be constrained in the rota-
with reference to the tional directions. Pressure is a distributed load created in fluids by the motion
WCS or a user defined of individual molecules. Pressure loads in Mechanica apply a
coordinate system. To apply moments and torque do not select the surface and distributed force per unit area. The main difference between
specify the moment value. Instead, use the TLAP option and the pressure load and the force/moment load is that the
 Direction vector and specify the point at which the total load is applied mathe- direction of the pressure load will always be normal to the
magnitude: A direction matically but distributed on the surface as shown. The point surface while the force/moment load has a director vector.
vector is specified and a is created at the center, and the surface is selected for load
magnitude for the application. It is a good practice to use the surface sets option while se-
force/moment is also lecting multiple surfaces to apply pressure load. This allows
specified. Spatial variation options specify how the load is applied over quick selection of loop surfaces, seed and boundary surfaces,
the selected entity. and solid surfaces.
 Direction points and
magnitude: Direction is defined by  Uniform: Distribution will be uniform over the entity. LOADS 23
selecting two datum points and the  Function of coordinates: An equation or table can be
magnitude is specified.
used to govern how the load varies with respect to the
Loads coordinate system.

Back to Table of Contents

LOADS creo elements/pro 5.0 mechanica

Centrifugal Load Temperature Load QUICK REFERENCE GUIDE

Centrifugal load is created by rotating objects that experi- Temperature load simulates a temperature change over the Before importing, the part for
ence two types of centrifugal loads—force and moment. analysis model. There are three temperature load types. which the loads will be exported
Centrifugal force pushes matter away from the center of should be defined. MDO’s Load
rotation and hence is a function of the angular velocity and  Global Temperature: Specify Export command is located at FILE
the distance from the center. The inertial torque due to ac- a model temperature for the > USE IN STRUCTURE.
celeration is a function of the moments of inertia about the entire analysis model and a
axis of rotation and the angular acceleration. In Mechanica, reference temperature. Loads can be set to be exported
this is a body load and is not specific to geometry or compo- from mechanism dynamic analysis
nents. Density, axis of rotation, and angular velocity/  MEC/T temperature load: The based on the time index or maxi-
acceleration are required for applying centrifugal load. temperature field from a mum loads during the analysis.
Mechanica thermal analysis can
The units for angular velocity is always rad/s. If the model is be brought into the structure Importing the mechanism load
rotating at a speed of 2000 rpm then the value to be input in mode to check the stresses and into Mechanica will not automati-
angular velocity is 2000 x 2π/ 60 rad/s deformation due to thermal cally apply the loads to appropri-
expansion. ate references. This only imports
Gravity Load the load values and the direc-
 External temperature load: tion. The load distribution has
With a gravity load, Mechanica simulates Can import an FNF (finite ele- to be done manually by select-
the effect of gravity by applying accelera- ment neutral file) file that con- ing references like surfaces,
tion due to gravity to the entire model. tains temperature field informa- edges, and points.
Thus, the gravity load is also a body load. tion.
Singularity
In an assembly, applying a gravity load All temperature load types require a
will apply the gravity load automatically reference temperature that is the When applying loads or con-
to all parts in the assembly. zero stress temperature of the analy- straints, singularity or theoreti-
sis model. cally infinite stress might occur
Depending on the unit system the accel- based on the idealization and
eration due to gravity is 9.81m/s², 32.2 ft/ The CTE is a required material property to check stress and the load reference used.
s² or 386.4 in/s² deformation due to thermal expansion. By default, a global
temperature load is applied to all components in an assem- BEST PRACTICES TO AVOID SINGULARITY
bly. If a component should not be affected by temperature,
then assign a CTE value of zero for the material property of  For solid idealization, do not apply loads or constraints
that component. on points and edges as they do not have an area which
will cause the stress to become infinite. Only apply
Mechanism Load loads or constraints to surfaces or surface regions.

MDO in Creo Elements/Pro can calculate acceleration, mo-  For shell idealization, do not apply loads or constraints
mentum and forces acting on each body in an assembly on points. Only apply loads or constraints to edges and
using rigid bodies but does not calculate deformation or surfaces.
stress. These can be imported into Mechanica using the
mechanism load type to calculate deformation and stress.  For beam idealizations, there is no surface to select so
use points or edges to apply loads and constraints.

 Another way to handle singularity is to use the Auto-
GEM control to exclude preselected singularities.

Loads Back to Table of Contents LOADS 24

ANALYSIS—STRUCTURAL creo elements/pro 5.0 mechanica

QUICK REFERENCE GUIDE

Structural Analysis The output tab allows you to select or deselect output quan- MODAL ANALYSIS
tities based on the intent of running the analysis. If the main
A structural analysis is the calculation of a model’s response intent to run a static analysis is to do a deformation analysis A modal analysis is calculates the natural frequencies and
to a loading condition and its boundary conditions. Static, or to check how much the shape of the model changes, then mode shapes of an analysis model to determines the vibra-
modal, and buckling analyses can be done using a basic it is a good practice to deselect the stresses option in the tion characteristics of parts or assemblies. Modal analysis is a
Mechanica license. output tab. This will still calculate the maximum stress in the prerequisite for all dynamic analysis types such as dynamic
model but the fringe or graph output for stress will not be time, dynamic frequency, dynamic shock, and dynamic ran-
STATIC ANALYSIS available. Only the fringe output for displacement and p- dom.
level is available. This will save analysis time as well as disk
A static analysis is used to calculate deformations, stresses space. INPUT
and strains in response to specified loads and constraints. No loads are required for a
This type of analysis is typically performed on parts or assem- PLOTTING GRID RECOMMENDATIONS modal analysis. All loads and
blies in order to find the stress and displacement distribution The density of the plotting grid where Mechanica calculates prescribed displacement con-
over the entire product. The stress and displacement can be results can be set from 2 to 10 with the default setting at 4. straints, if any, are ignored
evaluated in different forms like fringe plots or graphs. However, this default setting may not be enough if stresses during the analysis run. The
vary rapidly over a single element, so it is recommended to model can be analyzed with or
INPUT increase the plotting grid to more accurately capture the without constraints. The mo-
The input for a static analysis is one or more load sets and peak results. The recommended plotting grid for most dal parameters can be evalu-
constraint sets. At least one loadset is required to run any analyses is 7. If the analysis model contains mostly beams it ated based on the number of
static analysis except when the analysis model has a pre- is recommended to set the plotting grid to 10. When this modes or by a specified fre-
scribed displacement constraint. At least one constraint set number is higher, the grid will be finer and Mechanica re- quency range.
is required to run a static analysis, but the Inertia Relief op- ports values of output quantities from more locations on
tion can be used to analyze models without applying any each element. If this value is lower, Mechanica takes less OUTPUT
constraints. time to calculate results and uses less disk space. Increasing The modal frequency values are
or decreasing the plotting grid may not impact the overall reported in the results report
solution, as it is primarily applied to the solution display. file, and mode shapes can be
Sandy_McKinney_2015 displayed using fringe plots.

In a modal analysis, the values of other quantities like dis-
placement are normalized, so the maximum value is always
1. This is because Mechanica will divide all displacements by
the maximum displacement. The modal frequency values
reported are always in cycles per unit of time.

OUTPUT
Typical outputs from a static analysis are stresses, strains and
deformations. Force reactions and user-defined measures at
certain locations on the analysis model can also be evaluated.

A plotting grid applied on a rectangular element

Structural Back to Table of Contents ANALYSIS—BASIC MECHANICA 25

ANALYSIS—STRUCTURAL CONTACT ANALYSIS creo elements/pro 5.0 mechanica

BUCKLING ANALYSIS Contact analysis is a type of static QUICK REFERENCE GUIDE
analysis that is typically used in
Buckling analysis is used to calculate the critical buckling assemblies that have a contact Contact analysis can be configured to display results based
load factor (BLF) for the analysis model with loads applied. interface defined. A contact in- on load intervals. This allows you to check how measures
When an analysis model is subjected to compressive loads terface is applied to a component of interest will vary based on the load variation.
and if the model has a high aspect ratio then it could buckle. or component surface that might
Buckling occurs when a model is subjected to a load less come into contact on application If the main intent of running a contact analysis is to get
than what is required for failure, but that causes the model of load. Otherwise, they could accurate contact pressures using the SPA convergence
to bend under compressive stresses. separate from each other during method, then it is a good practice to use the localized
load application. The load ap- mesh refinement option during the contact analysis defini-
INPUT plied and the resulting deformations and stresses are non- tion. This will improve the accuracy of contact pressure
A static analysis should be defined with loads and con- linear because the contact area varies based on the deforma- calculations.
straints. It is not required to run the static analysis. During tion of the model.
the buckling analysis definition, the static analysis is se- If the value of the slippage indicator becomes positive dur-
lected, which Mechanica uses to calculate stress stiffening in INPUT ing the contact analysis, there is a warning in the analysis
the model due to applied forces. The model’s elastic stiff- Contact analysis re- report that indicates that the models have slid each other.
ness due to geometry and material is calculated during the quires contact interface Contact analysis does not support the following:
buckling analysis. to be defined between  Shells
surfaces or compo-  Large deformation non-linearity
OUTPUT nents.  Prescribed displacements using spherical and cylindri-
The main two outputs from a buckling analysis are BLF and
the mode shape for each buckling mode requested. A static analysis is de- cal coordinate systems
fined, and the nonlinear If there is a fatal error warning about insufficiently con-
If the load applied on the model is L, then the load at which option to include con- strained models, make sure the models in contact are pre-
the model will buckle is L x BLF. It is a good practice to ap- tacts must be selected. vented from tangential motion using either constraints or
ply a unit value for the load so that the BLF will be the critical infinite friction.
load. Buckling analysis should be used only for compressive OUTPUT
loads. The static analysis results should be used for getting Mechanica evaluates the total contact area and the maxi-
stress plots. mum contact pressure over all the contact interfaces in the
analysis model. Contact analysis can check if slippage has
occurred between the components in contact.

Contact analysis is defined within the static analysis defini-
tion, so all the typical measures evaluated for a static analysis
such as stresses, and deformations are also evaluated.

Since contact analysis is a non-linear analysis, Mechanica
uses several iterative steps to run the analysis. The default
maximum number of iterations is 200.

Structural Back to Table of Contents 26

ANALYSIS—THERMAL creo elements/pro 5.0 mechanica

QUICK REFERENCE GUIDE

Steady State Thermal Analysis Sandy_McKinney_2015THERMAL CONVECTIVE BOUNDARY CONDI- PRESCRIBED TEMPERATURE BOUNDARY CONDI-
TIONS TIONS
This analyzes the steady-state thermal response of the analy-
sis model when subjected to heat loads and boundary con- These are typically applied to Similar to displacement constraints in structural analysis, a
ditions. In a thermal study, the energy is transferred due to a external surfaces that are ex- prescribed temperature or reference temperature is required
temperature gradient between surfaces and can occur by posed to air or fluid to simulate to be assigned to geometric references in thermal analysis.
one of three modes: the heat loss due to convection. This simulates a constant temperature to be maintained on
the selected references.
 Conduction: Heat transfer through solids due to This heat transfer is:
change in temperature. For axisymmetric models, a thermal
 Q = hAΔT cyclic symmetry boundary condition
 Convection: Heat transfer between a model surface  h: convection coefficient should be applied.
and the surrounding fluid. This can be free or forced.  A: area
 ΔT: temperature difference A mirror symmetry condition is not
 Radiation: Heat transfer due to electromagnetic radia- applicable for thermal analysis mod-
tion. between the model sur- els. With mirror symmetry, the tem-
face and the surrounding perature on either side of the sym-
The native mode in Mechanica can simulate conduction and air temperature metry plane would be the same and
convection heat transfer. Radiation cannot be modeled thereby no heat transfer would oc-
directly but it can be simulated using convection if the radia- In order for Mechanica to simu- cur
tion is between a black body and another black enclosure late convection heat transfer, it
located at infinity. requires the following: IMPORT THERMAL RESULTS INTO STRUCTURE

HEAT LOADS  Surfaces Typical output quantities from a thermal analysis are tem-
 Convection heat transfer coefficient (h): This is typi- perature, temperature gradient, and heat flux. In order to
Heat loads are typically applied to calculate thermal stresses or mechanical stress due to ther-
geometric references or entire mod- cally derived by simulating the flow using a CFD tool. mal expansion, the results from a Mechanica thermal study
els to simulate a heat source or heat  Bulk temperature: This is the temperature of surround- should be imported into structure mode to run a static
sink. Just like structural loads, the analysis.
heat load distribution and spatial ing air or fluid.
variation can be configured. Heat Analysis models can be switched between thermal and
loads can vary with time if the main The convection coefficient can be imported into Mechanica structure modes using the main menu, EDIT > MECHANICA
intent of the thermal analysis is to get using an external coefficients field file. MODEL SETUP.
a transient response instead of a
steady state response. If an external coefficients filed file is not imported, a positive
value for h can be entered as an empirical data or a standard
A positive heat load value represents value based on thermal databooks or hand calculations.
a heat source, and a negative value
represents a heat sink.

Thermal Back to Table of Contents ANALYSIS—BASIC MECHANICA 27

CONVERGENCE—QUICK CHECK, SPA, MPA creo elements/pro 5.0 mechanica

QUICK REFERENCE GUIDE

The accuracy of Mechanica’s results is dependent on the Single-Pass Adaptive (SPA) Multi-Pass Adaptive (MPA)
convergence method used to solve the analysis. Conver-
gence is a situation wherein the results do not change with This method has a built-in convergence using stress error This convergence method gives the most accurate solution
respect to mesh parameters like polynomial order or the estimates. Mechanica will run the first pass using a polyno- since the convergence tolerance is controlled by the user
number of elements. Since Mechanica uses the p-method, mial order of 3 and calculates local stress errors. Based on and is not dependent on built-in error estimators.
the polynomial order is increased to achieve solution accu- these errors, Mechanica determines a new polynomial orders
racy. One of the following three convergence methods for each element edge and performs a final pass. A final Mechanica runs the first pass with an edge order of 1,
should be selected during the analysis definition stage: stress error is reported at the end of the analysis. This is a thereby using a linear equation to solve. In the second pass,
sampling of the local error estimates that were used to in- all element edge orders are increased to 2, thereby using a
 Quick Check crease the polynomial order. quadratic equation to solve.
 Single-Pass Adaptive (SPA)
 Multi-Pass Adaptive (MPA) With the SPA method, the user does not control the conver- The results from the second pass and first pass are compared
gence tolerance, as it is built into the software. Always check for each element and element edge. If the difference is more
Quick Check the stress error and also the maximum edge order of the than the user-defined convergence tolerance percent, then
second or final pass. If the stress error is low, then there is no the edge order is increased to 3. If the difference is less than
Quick Check can be used to check the feasibility of an analy- need to run the analysis using the MPA method. If the stress the convergence tolerance percent then the same edge or-
sis to make sure that it can run without any major errors. error is high, it is better to run the analysis using the MPA der is retained. This process is repeated for several passes
Mechanica solves the analysis using a uniform polynomial method. until convergence is reached for all elements and element
order of three over the entire analysis model. This method edges.
does not do any kind of convergence. The biggest advantage of the SPA method is the relatively
short run time on complex analysis models as compared to The default minimum and maximum edge order should be
It is a good practice to run complex analysis using the quick the MPA method. used. If the analysis does not converge, then the minimum
check method first before running an MPA analysis. and maximum edge order can be changed. The default con-
The SPA method is available for static, modal, buckling, and vergence of10 percent is applied to all quantities selected for
Before running multiple analyses using batch files, a quick contact analyses. It is not available for pre-stress static analy- convergence. The recommended range for convergence is
check analysis should be run to make sure everything is fine sis. It is not recommended to use the SPA method for con- one to 25 percent.
with the analysis setup. tact analysis as it might result in very long run times.
It is a best practice is to begin with the default 10 percent
The results from a quick check should always be ignored, as and then check the report to see if the analysis converged or
it should only be used to look for any fatal errors during the not. If it is converged, then a lower convergence percent can
analysis run. If the quick check runs successfully without any be used to get more accurate results, although this will in-
errors, then the MPA or SPA method should also run success- crease the run time as Mechanica will need to go through
fully except for reasons such as disk space or memory issues. additional passes. The MPA method typically takes longer
than the SPA method but is more accurate.

Quick Check, SPA, MPA Back to Table of Contents 28

CONVERGENCE—MPA creo elements/pro 5.0 mechanica

MPA CONVERGE ON OPTIONS CONVERGE ON OPTIONS FOR THERMAL ANALYSIS QUICK REFERENCE GUIDE

CONVERGE ON OPTIONS FOR STRUCTURAL ANALYSIS CONVERGENCE GRAPHS
When using the MPA method for structural analyses like
static, pre-stress static, contact, and large deformation, the If the MPA report says that the analysis converged within the
convergence percent is applied to specific measures of inter- convergence percent, then plot the convergence graphs as
est or one of the options as shown below. shown. The x axis of this graph is the p-pass and the y axis is
the measure of interest like von Mises stress, max displace-
ment, temperature, or frequency.

 Local Displacement, Local Strain Energy and Global Sandy_McKinney_2015 Local Temperatures and Local Energy Norms: If thisThe convergence graphs is the best way to check the quality
RMS Stress: This option will also converge on RMS option is selected, the convergence percent is applied of an MPA solution. The graph should have almost zero
stress in addition to displacement and strain energy. to the following: slope near the higher p-levels and a clear trend approaching
 Temperatures along each element edge a value.
 Local Displacement and Local Strain Energy: If this  Energy norms of each element
option is selected, the convergence percent is applied If the MPA reports that the analysis did not converge within
to the following:  Local Temperatures and Local and Global Energy the specified convergence percent, then the following op-
 Displacements along each element edge Norms: This option will converge on global energy tions should be used to get a converged solution:
 Total strain energy of each element norm which is the sum of the energy norms of all ele-
ments in the analysis model.  Check the last pass maximum edge order, if this is nine
 Measures: This is the recommended option wherein then Mechanica has reached the limit.
one or more measures of interest (i.e., maximum stress,  Measures: This option will result in a faster analysis,
maximum displacement) can be selected for conver- with accuracy only for selected measures, such as maxi-  Check the p-level fringe as shown below to identify the
gence. This option will give accurate results only for the mum temperature. location of the edges that reached ninth order polyno-
measure of interest and the analysis run time will be mial.
quicker compared to the other two options. EVALUATING MPA RESULTS

CONVERGE ON OPTIONS FOR MODAL ANALYSIS The first thing to look for after the completion of an analysis
In a modal analysis the frequency is the measure of interest using MPA method is for the message in the report about
and so this option should be selected. the convergence as shown here.

CONVERGE ON OPTIONS FOR BUCKLING ANALYSIS Back to Table of Contents  Apply the mesh controls on these areas that have
Since the BLF is the measure of interest this options should reached the ninth order so that Mechanica can con-
be selected. verge within the specified percent.

MPA, 29

ANALYSIS RUN SETTINGS creo elements/pro 5.0 mechanica

QUICK REFERENCE GUIDE

Once the analysis is defined and ready to run, there are some In such situations it is a best practice to use the following Solver Type
settings to control the output folder locations, solver set- approaches to fix the issue:
tings, and element creation settings. Mechanica can be set to use either the direct or the iterative
 Change the RAM allocation back to default setting of solver to run any analysis. Each solver uses a different
Output Folder Settings 128 MB. method to solve the simultaneous equations during analysis
run.
By default, all the analysis output files are created in the cur-  Try SPA convergence method instead of MPA conver-
rent working directory. This can be changed in the run set- gence. The direct solver is the default solver as it requires less time,
tings or by setting the config option, SIM_RUN_OUT_DIR. disk space, and memory than the iterative solver. When
 Reduce the plotting grid in the output settings. using the direct solver, if the ratio of elapsed time/CPU time
Mechanica creates a temporary folder containing temporary  If you are running modal analysis, reduce the frequency is greater than four, then switch to the iterative solver. If
files during analysis run that is automatically removed as you are using the iterative solver and this ratio is greater
soon as the analysis is completed. The config option to set range or number of modes. than seven, then switch to direct solver. The elapsed time
directory for temporary files is SIM_RUN_TMP_DIR.  Idealizations like shells, beams, mass, and spring should and CPU time is in the report file.

Mesh is typically generated by Mechanica during the analy- be used whenever possible. The default direct solver is recommend for the following:
sis run. If there is an existing mesh file—.mmp (part mesh  De-feature the analysis model.
file) or .mma (assembly mesh file)—then check the run set-  Check for symmetry.  The analysis model contains thin features.
tings to use this mesh file instead of creating elements dur-  Change the model type from 3D to one of the 2D model  The analysis did not converge with the iterative solver.
ing run. If you are running more than one analysis on the  The design study has analyses other than linear static,
model, then the mesh from an existing study can be used. types, if applicable.
 Reduce the number of contact interfaces if running a such as contact analysis, modal or transient thermal.
Mechanica Solver Settings  If the analysis model reports an insufficiently con-
static contact analysis.
The default memory allocation is set to 128 MB. The config strained error and wants to locate constraint problems.
option, SIM_SOLVER_MEMORY_ALLOCATION, can be used NOTE:
to set the memory allocation. The Mechanica solver had a memory limit of 8 GB on 64- The iterative solver can be used in the following situations:
bit operating systems until Pro/ENGINEER Wildfire 2.0.
The memory allocation for Mechanica solver should be set to Beginning with Wildfire 3.0, this 8 GB per process limit  If you run out of disk space when using the direct solver.
half of the physical RAM of the computer. The default alloca- has been removed, and the model size to run Mechanica  If the direct solver takes long time to complete.
tion will be able to run any analysis but changing it to half of analysis is almost unlimited.  When running linear static analysis on solids.
physical RAM will improve the run time.
The iterative solver cannot be used in the following situa-
When the RAM allocation is set to more than half the RAM, tions.
the analysis might slow down or run into a fatal error as
shown at right.  If the design study contains modal analyses.
 If the local sensitivity or optimization design study con-

tains analyses that have temperature loads referencing
thermal analysis.

Analysis Run Settings Back to Table of Contents ANALYSIS RUN SETTINGS 30

RESULTS—FOLDER AND FILES; DISPLAY creo elements/pro 5.0 mechanica

QUICK REFERENCE GUIDE

After a successful analysis run, Mechanica will output solu- Sandy_McKinney_2015 The .rpt file is a text file containing the analysis sum- Results Display
tion files and the results can be displayed in several formats mary.
and options. Mechanica results are dis-
 The .pas file contains a time log of various analysis and played in a separate result
Results Folder and Files file operations. window interface and is ac-
cessed using the rainbow
After an analysis is run, Mechanica will create a results folder  The .err file has error messages that occur during the color icon as shown here.
to store all solution files and associated log files along with a analysis run.
copy of the analysis model. Below is an example results STUDY SELECTION
folder and the various files:  There is a temporary
folder (.tmp) that is cre- The first step in results display is to select a results folder.
Analysis name: tristar_study ated during the analysis Results can be displayed without having the analysis model
Analysis model: tristar_design.prt run which contains the in session because the result folder always contains a back
stiffness matrix. This up copy of the analysis model. It is also not required to have
Contents of the results folder includes several files and a folder is automatically a Mechanica license in order to display results.
another subfolder containing solution files. deleted by Mechanica
upon successful completion of the analysis. DISPLAY TYPE
As soon as the analysis is completed, Mechanica will create a
backup of the analysis model and place it in the analysis ANALYSIS RESULT FILES IN WINDCHILL AND The results display is configured using the Result Window
results folder as shown above. In order to view results, the PRO/INTRALINK Definition dialog box. A successful analysis run is a prerequi-
results folder contents site to display any type of results. The following result dis-
and the subfolder con- The results folder can be compressed and saved to the active play types are available:
tents, shown here, are workspace when using Pro/INTRALINK or Windchill by using  Fringe
required. the Vault Results option as shown here.  Vectors
 Graph
The VAULT RESULTS option is available  Model
only after completion of the analysis
and after the analysis model is checked
in. This will create a compressed .mrs
file in the workspace. This compressed
file contains the entire results folder
and a snapshot of the analysis model.
The compressed results file can be
exported to a local directory.

Windchill creates a derived link from
the results file to the last checked in version of the analysis
model. However, this link does not result in automatic re-
trieval of results file when retrieving the analysis model. The
link only indicates that a particular version of the results
reference a particular version of the model and can be used
when doing a search within Windchill. With the release of
Creo 1.0, PTC plans to allow export of Mechanica results in .ol
(Creo Elements/View) format.

Folder and Files; Display Types Back to Table of Contents RESULTS 31



RESULTS—DISPLAY; GRAPH RESULT WINDOW DEFINITION creo elements/pro 5.0 mechanica

VECTOR GRAPH RESULT WINDOW DEFINITION QUICK REFERENCE GUIDE
During the definition of a graph type result window, the
Vectors display the directional behavior of a quantity as col- display location and display options are grayed out. The x– The graph’s appearance can be controlled using the FOR-
ored arrows that are superimposed over a transparent dis- and y-axis quantities needs to be specified. Based on the MAT > GRAPH option in the Result Window interface. This
play of the model. Each set of arrows represents a different type of the study or analysis, various options are available. will allow control of the x- and y-axis displays, data series
range of values for the quantity. Vector plots use arrow User-defined measures or system-defined measures can also display, and the main graph display properties like back-
length and color to indicate the magnitude of the quantity. be selected for graph results. ground color and label text.

Typical result window definition setups for a sensitivity
study, an optimization study, a static analysis, and an MPA
static analysis are shown below.
Sandy_McKinney_2015
By default, the vectors displayed are 3D. If the system mem- Sensitivity Study Optimization Study The preferred settings for the graph results window can ei-
ory is not sufficient to display 3D vector arrows, use the con- ther be set each time the results are brought into session or
fig option to display the vector plot using 2D arrows set permanently in a file. This is done using a graph prefer-
(SIM_PP_VECTOR_PLOT_ARROW_2D). ences file and a config option. The following procedure sets
up the graph preferences file:
GRAPHS
1. Create an empty text file.
Graph displays are typically used to view the results of sensi- 2. Set the config option, bmgr_pref_file, to point to the
tivity and optimization studies. They can also be used for
any analysis to view the graph of the quantity of interest, like text file.
displacement or stress with reference to geometric refer- 3. Customize the graph display using the FORMAT >
ence. In a vibration analysis, graph plots will output quantity
in reference to time or frequency steps. GRAPH options.
4. Select the SET DEFAULT button in the graph window
The graph results below are for a static analysis. The quan-
tity is in the y-axis of the graph, and the x-axis of the graph options dialog box. This will save all customizations
displays selected edge or curve length from the analysis done to the graph results to the text file created earlier.
model. For sensitivity studies, the y-axis the measure quan- 5. These settings will be used each time a graph is created.
tity and the x-axis is the variable design parameter.
Graph data can be exported as a text file with a .grt exten-
sion or as an Excel file.

Static Analysis MPA Analysis

Display Types Back to Table of Contents RESULTS 33

RESULTS—DISPLAY TYPES; DISPLAY QUANTITY; DISPLAY LOCATION creo elements/pro 5.0 mechanica

MODEL Why do we need stress linearization reports? When looking QUICK REFERENCE GUIDE
at the distribution of stress through the thickness of a thin-
Models can display the analysis model geometry in a de- walled part, this report is useful to compare to the relevant Display Location
formed state or original state, a simple animation of how the ASME codes. The stress linearization utility can help evalu-
model deforms, or an optimized shape of the analysis model. ate a design’s compliance with industry standards, such as Based on the type of design study and idealizations in the
the ASME Boiler and Pressure Vessel code. analysis model, there are several options to specify the re-
The linearized stress of the analysis model can also be dis- sults display location.
played by selecting INFO > LINEARIZED STRESS QUERY. This Display Quantity  All
report is generated by querying two locations on the analy-  Beams
sis model. Mechanica calculates the total local coordinate During the result window definition, the display quantity,  Curves
stress components at each point and then calculates mem- component, and units can be selected.  Surfaces
brane, bending stress, peak stress, and total stress. These  Volumes
values are calculated and reported with respect to a local  Components/layers
coordinate system with the x-axis aligned with the line  Contact surfaces
(stress classification line) connecting the two locations and During the results display of an assembly analysis model, the
with the origin at the midpoint of the line. An additional Components/Layers option is very useful. This can be used
point should be selected to define the xy plane. to show, hide or isolate specific components or layers of an
analysis model as shown below.
Along with typical quantities like
von Mises stress, displacement, If the analysis model is an assembly, the layer tree displays
and temperature, the P-level and the components and any layer containing beam or shell
failure index can also be displayed. definitions. If the analysis model is a part, the layer tree dis-
The failure index is the ratio of the plays only layers containing beam and shell definitions. ,It is
actual stress to the yield strength a good practice to use the isolate option to view the results
of the material and can be used to of selected components or layers and to use the blank op-
determine if the material failed tion to exclude a few components or layers from the display.
under the applied loading condi-
tions. If the failure index is less
than one, the material has not failed.

The failure index option
will be available in the
quantity tab only if the
material tensile yield
stress is specified in the
material property prior to
running the analysis. It is a good practice to include a factor
of safety while entering the yield strength of the material.

When the analysis model is an assembly that consists of sev-
eral materials, the failure index is very useful to determine
which material has failed, as it takes into account the yield
strength of the individual materials of the analysis model.

Display Types; Display Quantity; Display Location Back to Table of Contents RESULTS 34

RESULTS—DISPLAY LOCATION creo elements/pro 5.0 mechanica

QUICK REFERENCE GUIDE

Dynamic query of a fringe plot allows you to check the quan- When viewing fringe plots, a cutting plane or capping sur- The visual characteristics of a displayed result window can
tity values anywhere on the analysis model. These queried face can be used to clip the analysis model to examine the be controlled by selecting FORMAT > RESULT WINDOW. The
values along with their location coordinates can also be dis- interior of the model. This can be created on non-animating appearance and range of values for fringe, contour, and vec-
played on the fringe plot and used in analysis reports. fringe or contour plots. Use INSERT > CUTTING/CAPPING tor plots can be controlled using FORMAT > LEGEND.
SURFS to create these plots.

A cutting surface will slice the analysis model and trim both
sides, whereas a capping surface will slice the model and
trim one of the two sides. More than one cutting surface can
be created, but only one capping surface can be created on
the analysis model, as shown below.
Sandy_McKinney_2015
Annotations of measures created When multiple result windows are displayed, the active win-
after the analysis can be displayed dow has a yellow border. Multiple windows can be selected
automatically. INFO > MEASURES using the SHIFT key to allow all selected windows to be for-
will give the list of measures calcu- matted together. Result windows can also be reordered or
lated, and there is a button to cre- swapped.
ate annotation on the fringe plot
automatically as shown at right. Cutting and capping surfaces are typically used on thick It is not required to have a Mechanica license or the analysis
Annotations can also be created models that may have significant variations of interior stress model in session to create, view, and edit result windows.
manually using INSERT > ANNOTA- or may have unseen deformations. The only requirement is access to the results folder. The
TION where there are options to result interface can be accessed in Creo Elements/Pro at
surround the text with a border, By default, Mechanica displays the outline of the model APPLICATIONS > MECHANICA RESULTS.
add a background color, or define when using cutting or capping surface. This outline can be
a shape with a mouse sketch. hidden using the config option, RESULTS 35
SIM_PP_SHOW_CAP_CUT_OUTLINE.
Display Location
Back to Table of Contents

RESULTS—RESULT WINDOW DEFINITION creo elements/pro 5.0 mechanica

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Result Window Definition These HTML reports capture the vital points of the analysis When comparing the legend values or graph ranges from
with options to include images and animations from the multiple result windows, use the UTILITIES > TIE option.
Result window definitions can be saved as .rwd files that can result window interface.
be retrieved later from the result interface. Common result  The tie option can be applied only to the same types of
window definitions, such as von Mises plots and displace- Fringe plots can also be exported in VRML format. Use the result windows.
ment plots, can also be saved as a result window template config option SIM_PP_VRML_EXPORT_FORMAT to specify
(.rwt file) by selecting FILE > SAVE AS TEMPLATE. This will whether the export format is VRML 1.0 or VRML 2.0.  The quantities displayed must be of the same general
save the definition and some attributes and can be used to category to tie the results. For example, a von Mises
quickly define new result windows based on the template The result windows can also be exported as an image and fringe plot cannot be tied to a displacement fringe plot.
file. saved to commonly used formats such as TIFF, and JPG.
 It is a best practice to use the tie option when compar-
Analysis reports can be generated from within the results During the generation of analysis reports, the result window ing result windows from local sensitivity studies to
interface using FILE > EXPORT > HTML REPORT. interface can be used to capture specific orientations of the check the sensitivity of various design parameters.
analysis model that can reference existing saved views or
can create new views based on precise angles with reference While creating multiple result windows from the same de-
to the screen center or spin center as shown. Select VIEW > sign study or analysis, it is a good practice to use the copy
SPIN/PAN/ZOOM from the Result Window interface to access option to efficiently replicate existing result windows. This
this feature. The model displayed in the Mechanica result avoids the need to browse to the results folder to create a
window can be manipulated in the same way as in standard result window each time.
Creo Elements/Pro mode.
When the analysis has multiple loadsets, the result window
definition can be used to select or deselect specific loadsets
with options to apply a scaling factor to that loadset using
the table shown. Result plots can be viewed based on spe-
cific loadsets. This table can also include frequency, time
steps, modes, and load increments based on the design
study.

During the result window definition, if there is an error after
selecting the results folder, make sure the analysis has com-
pleted and check to see if the analysis was run with a newer
release of Creo Elements/Pro.

Result Window Definition Back to Table of Contents RESULTS 36

DESIGN STUDY—DESIGN VARIABLES, STANDARD DESIGN STUDY creo elements/pro 5.0 mechanica

QUICK REFERENCE GUIDE

Design studies are used to evaluate “what if?” scenarios on Sandy_McKinney_2015Creo Elements/Pro parameters can be used to define design Standard Design Study
the analysis model. They can be used to determine the ef- variables like material properties or even load values by us-
fect of design variables and optimize the model based on ing the following steps: A standard design study can be used to run the analysis at
the analysis objectives. The following types of design stud- specific design variable values. The main advantage of run-
ies can be created in Mechanica: 1. Create Creo Elements/ ning this type of study is that the original analysis model
Pro parameters in stan- dimensions and parameters need not be changed but it
 Standard Design Study dard mode. allows you to run consequential scenarios by changing these
 Sensitivity Design Study dimensions and parameters within the design study.
 Optimization Design Study 2. In Mechanica mode,
right-click on the value Standard design studies allow you to study the behavior of
Design Variables field and select Parame- the analysis model without actual modification. More than
ter. Choose a paramater one analysis can be selected for a design study, or a simple
Design variables are dimensions or parameters that can from the Creo Elements/ regeneration check with the specified new settings can be
change the shape and properties of the analysis model while Pro parameter list. done. Multiple standard design studies should be defined in
running design studies. Design variables can be created for order to run the analysis with different design variable set-
the following: 3. Use this parameter in tings.
design studies by select- The results folder for each design study will have the analysis
 Dimensions ing the parameters icon model with the specified settings of the design study. So the
 Creo Elements/Pro parameters in the design study defi- original model still has original settings but the analysis
 Beam cross section properties nition dialog box. folder contains the model with new settings.
 Material properties
 Laminate layup shell properties When selecting Creo Elements/Pro dimensions as design
variables, it is a good practice to rename the dimension
Once the design variables are defined, Mechanica can be name (i.e, length, radius, thickness) instead of using the de-
instructed to perform the following- fault dimension name (i.e., d23, d10, d4).

 Specify a different setting in a standard design study. Before running a sensitivity or optimization study, it is a
good practice to check for any regeneration failures using
 Specify the range to vary in a sensitivity or optimization the shape animate option in the design study. Mechanica
study. will check if the range for the design variable is feasible from
a regeneration standpoint. The shape animate tool is ac-
cessed from the options button in the study definition dialog
box.

Design Variables, Standard Design Study Back to Table of Contents DESIGN STUDY 37

DESIGN STUDY—SENSITIVITY, OPTIMIZATION creo elements/pro 5.0 mechanica

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Sensitivity Study GLOBAL SENSITIVITY STUDY Optimization Study

There are two types of sensitivity studies in Mechanica: Global sensitivity studies are used to generate a much larger Optimization studies find
 Local sensitivity study picture of how analysis objectives respond to changing one the value of the design
 Global sensitivity study design variable over a specified range. variables needed to
Mechanica will run the analysis at regular intervals within the achieve the best design
LOCAL SENSITIVITY STUDY specified range. The number of intervals or steps are de- within specified limits
fined during the definition of the study. and goals. All design
Local sensitivity studies are used to check the effect of slight variables that passed the
changes in one or more design variables on the analysis The output from a global sensitivity study is a graph plot sensitivity studies are
objectives. with the x-axis being the design variable, and the y-axis be- used as a solution space
A base analysis is selected and all design variables are se- ing any measure or analysis objective like stress, displace- in optimization studies.
lected. The analysis is conducted changing the design vari- ment, temperature, frequency, etc. The global study result
able by +1% and –1% of the current or specified settings. graph can be used to decide on the best value of the design Design limits are typi-
Local sensitivity studies are output to graph plots. This graph variable to be used as a starting point in optimization stud- cally limits on the stress,
will have two points and a line connecting these two points ies. displacement, temperature, or frequency, for example. A
to compare slope. The slopes of each design variable can be goal such as to minimize the stress, mass, or any other meas-
compared to determine the most sensitive design variable. ure should be specified. An optimization study without a
Design variables having zero or a small slope relative to goal will find the nearest possible solution that satisfies the
other design variables can be eliminated from future global design limits, thereby doing a feasibility study.
sensitivity and optimization studies.
Optimization convergence is a toler-
While comparing the graph plots of a local sensitivity study, ance applied to the design limit
it is a good practice to tie (UTILITIES > TIE) the graph quantity values. Repeat p-loop convergence
(y-axis) as shown in the three graphs at right. For example, will instruct Mechanica to do the p-
the y-axis could be the von Mises stress, while the x-axis is level calculations for each shape
the design variable that has been perturbed by one percent. change iteration. Otherwise, it will
simply use the maximum edge or-
der of the initial iteration for all
other iterations.

When the range of the design variables is large, then it is a
good practice to use the remesh after each shape update
option.

Outputs from an optimization study include:

 Graphs of measures against the iterations.
 Standard results for the final optimized model.
 Final design variable values. Use INFO > OPTIMIZE HIS-

TORY from the analysis dialog box to step through
every iteration value on the model.

Sensitivity, Optimization Back to Table of Contents DESIGN STUDY 38

ANALYSIS—PRESTRESS STATIC, PRESTRESS MODAL, LDA creo elements/pro 5.0 mechanica

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An Advanced Mechanica license is required for the following Sandy_McKinney_2015Prestress Modal Analysis INPUT
analysis types: In addition to the stan-
When static loads change the stiffness of the model, the dard static analysis input
 Prestress Static modes and natural frequencies of the model will also change like loads and con-
 Prestress Modal as they are dependent on the stiffness and mass distribution. straints, the load inter-
 Large Deformation The prestress modal analysis should be used in such situa- vals can also be speci-
 Dynamic (Vibration) Analysis tions. Rotating machinery with centrifugal load due to high fied. There some limita-
 Transient Thermal RPM are subject to stress stiffening and spin softening, and tions for using LDA:
pre-stress modal analysis
Prestress Static Analysis can take these into ac-  Beam and shell
count. elements are not
This type of analysis is used when the applied load changes supported.
the stiffness of the model. The effect of prestresses or pres- INPUT
tiffened structures on deformation, stress, and strain can be A previous static analysis  No temperature
analyzed using a pre-stress static analysis, which takes into is required before defin- dependent material
account the loading for stiffness. ing the prestress modal properties.
analysis. As with any
INPUT modal analysis, the  No bearing loads.
A previous static analysis and a new loadset are required as modes within a fre-
an input. As shown here in the Prestress Static Analysis Defi- quency range or the Remember to select the
nition dialog box, the static analysis will run first with just the number of modes can be Nonlinear and Calculate
initial_load, and the specified. Large Deformations
resulting model stiff- options in the Static
ness is calculated OUTPUT Analysis Definition dialog box.
before the application This is the same as any
of the new_load. modal analysis output. OUTPUT
This is the same as the standard static analysis output. If load
It is important to se- Large Deformation Analysis (LDA) intervals were given during the analysis definition, then
lect the loadsets as graph plots can be created between deflection and applied
shown so that the Large Deformation Analysis is used to simulate geometric load confirming the nonlinear response, as shown below. In
new loadset is ap- non-linearity and when rotations and strains are arbitrarily general, if the displacement is more than half of the thick-
plied after the stiff- large such as deformations in elastomers, plastically- ness of the part then the LDA option should be used.
ness calculation due deforming materials, fluids, and biological soft tissue. As of
to existing loadset. Creo Elements/Pro 5.0, Mechanica supports linear elastic and
The scale of the load hyperelastic materials for large deformation analysis.
applied in the previ-
ous static analysis can Why use LDA? The standard static analysis is based on linear
be increased. theory and assumes small deformations only. If the deflec-
tion in a plate is larger than one half of the plate thickness,
OUTPUT the middle surface of the plate is strained appreciably, so the
This is the same as any static analysis output. plate’s geometry is not the same as it was before deforma-
tion. When this condition of large deflection occurs, the
plate is actually stiffer than indicated by ordinary theory, and
the load-deflection relations are nonlinear.

Prestress Static, PreStress Modal, LDA Back to Table of Contents ANALYSIS—ADVANCED MECHANICA 39

ANALYSIS—DYNAMIC creo elements/pro 5.0 mechanica

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Dynamic Analysis Time function: The time history for the load or base excita- OUTPUT
tion is defined using a time function. By default, Mechanica Typical output from a dy-
There are four types of dynamic analysis, which are used to uses the built-in impulse function which uses the Dirac’s namic time analysis are
simulate the response of the analysis model to different Delta function to represent a sudden load. User-defined displacements, velocities,
types of vibration problems: time history can also be used by defining a symbolic func- accelerations, and stresses
tion of time or a table that has time versus magnitude of at different times. Output
 Dynamic Time load, as shown here. intervals can be either auto-
 Dynamic Frequency matically defined by
 Dynamic Random Modes: By default, a dy- Mechanica or user-defined.
 Dynamic Shock namic time analysis will
make use of all modes from Mass Participation Factors can be calcu-
The physical test equivalent of dynamic analysis is the shaker the modal analysis. The lated to get the cumulative mass partici-
table test. number of modes to be pation. If the cumulative mass participa-
used can be limited by using tion is less than 80 percent, then more
DYNAMIC TIME ANALYSIS the Below Specified Fre- modes should be requested in the modal
quency option. All dynamic analysis.
This type of analysis is used to calculate the response of analysis types in Mechanica
analysis models that are subjected to non-periodic or impul- require a modal analysis. Dynamic measures are not automatically
sive time dependent load. predefined in Mechanica, so before run-
Damping Coefficient: This is the percentage of relative ning the dynamic analysis, they have to
INPUT damping, or the ratio between the damping in the system created manually.
Load Definition: The loading can either be load functions and a critically damped system. A single damping coeffi-
or base excitation. Load functions define existing loads on cient can be assigned to all modes, or separate damping Below is a typical dynamic time analysis procedure:
the model with a time history. coefficients can be assigned to individual modes. It can also
be assigned as a function of frequency. 1. Define and run a modal analysis.
Base excitation defines acceleration vector based on time 2. Define the dynamic time analysis with the required
history. With base excitation, Mechanica can provide results The normal range of damping coefficient is zero to 50 per-
based on ground or supports. Stresses will be the same in cent. A damping coefficient of 100 percent means the analy- inputs.
both cases but displacements, velocities, and accelerations sis model is critically damped. In general, welded or bolted 3. Create dynamic measures like stress, acceleration, dis-
will be different based on the frame of reference. steel structures are given a damping coefficient of four per-
cent. placement, etc.
4. Run the dynamic time analysis with output intervals set

to automatic intervals.
5. Examine the analysis report for mass participation fac-

tors using base excitation loading. If cumulative mass
participation has reached 80 percent or more, there is
no need to request additional modes in modal analysis.
Otherwise, rerun the modal analysis by requesting more
modes in order to reach 80 percent cumulative mass
participation.
6. Create a graph plot between the measures, such as
stress versus time, and note the peak times at which the
stress is high.
7. Run the dynamic time analysis with the output intervals
set to user-defined, and specify the peak times from the
last step to calculate full results including fringe plots.

Dynamic Back to Table of Contents ANALYSIS—ADVANCED MECHANICA 40

ANALYSIS—DYNAMIC creo elements/pro 5.0 mechanica

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DYNAMIC FREQUENCY ANALYSIS Sandy_McKinney_2015DYNAMIC RANDOM ANALYSIS In a dynamic random
analysis with base excita-
This type of analysis is used to calculate the response of This analysis is used to calculate the response of analysis tion loading, the value
analysis models that are subjected to a periodic, or cyclical, models that are subjected to non-cyclical vibrations and typed in the base excita-
frequency-dependent load. It is similar to the dynamic time have random vibration problems with the input in the form tion direction vector is
analysis except that the input is defined in the frequency of a power spectral density (PSD) function. squared and scaled by
domain instead of the time domain. Typically, the frequency the defined function. Even though the acceleration is re-
domain is used when the input to a vibration problem is too Generally, there are two approaches for evaluating structural ported in g²/Hz, the base excitation vector should have only
complex to be expressed in the time domain. response to dynamic loading—deterministic and statistical. the value of g in that unit system like 368.4 in/s² or 9.8 m/s².
In Mechanica, the deterministic approach is simulated using
INPUT the dynamic time or frequency analysis wherein the exact OUTPUT
This is the same as with the dy- time history or driving frequency and amplitude are known. The results from a dynamic random analysis are reported in
namic time analysis except that If the loading variation is not completely known but can be terms of response PSD. The values reported at specific out-
the default function used in a defined in a statistical sense like a PSD, then Mechanica can put interval values are spectral density values. For example,
dynamic frequency analysis is a simulate this using the dynamic random analysis. stress would be in psi²/Hz or MPA²/Hz and not in psi or MPA.
uniform function (instead of the Typical output from a dynamic random analysis are power
impulse function used in dy- Random vibration analysis represents the true environment spectral densities and RMS values of displacements, veloci-
namic time) that is a constant value equal to 1 (load is multi- in which airplanes, missiles, robots, and free standing struc- ties, accelerations, and stresses.
plied by 1 over the frequency range), with options to add tures must operate. In a random vibration, all frequencies
user-defined functions or a table to define the frequency might occur simultaneously so the overall response of the The area under the spectral density curve is the root mean
profile of the load. If the analysis model has multiple load- system is calculated statistically from the random vibration square. It can be assumed that naturally occurring vibration
sets, then the phase between the loads need to be defined. environment. follows a normal probability distribution function and so has
a mean of zero. If the mean is zero, then the root mean
OUTPUT INPUT square is equal to the standard deviation (σ or sigma). Re-
Typical output from a dynamic frequency analysis are ampli- In put for a dynamic random analysis is acceleration or force sults from a random vibration can be judged by using three
tude and phase of displacements, velocities, accelerations, over a range of frequencies called a spectrum. These are sigma results. There is a 0.3 percent probability that the
and stresses in the analysis model in response to a load oscil- typically obtained by sampling over a period of time, but are value could be higher than three standard deviations.
lating at different frequencies. The choice to use either a not time-dependent. A better statistical sampling in the
dynamic time or frequency analysis in any given case de- frequency domain will be obtained as the sampling time is The values of stress reported in a dynamic random analysis
pends upon whether the loading is periodic or non-periodic. increased. These measurements are referred to as Spectral are the RMS stresses and not the actual stress in the analysis
If the forcing load is periodic, then it is more convenient to or PSD or more specifically acceleration spectral density model at any point in time. If the maximum stress is found
perform a dynamic frequency analysis, but if the loading is (ASD) or force spectral density (FSD). to be 100 MPA, the three sigma value would be 300 MPA,
non-periodic or impulsive (shock loading), then the dynamic which means there is only 0.3% chance that the stress will be
time analysis should be used. higher than 300 MPA. Therefore, if the requirements specify
that the analysis model should be designed based on 3σ
stresses, create a measure for the root mean square of the
maximum stress and multiply the output by 3. Only vector
quantities of measures can be reported in a dynamic random
analysis. Measures calculating von Mises stress or maximum
displacement magnitude cannot be created or evaluated.

ASD input is typically obtained from empirical data. These
acceleration plots can also be obtained from documents
such as the MIL-STD-810.

Dynamic Back to Table of Contents 41

ANALYSIS—DYNAMIC, TRANSIENT THERMAL, FATIGUE, 2D MODEL TYPE creo elements/pro 5.0 mechanica

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DYNAMIC SHOCK ANALYSIS INPUT INPUT
A time-dependent heat load is applied on the model. The desired number of cycles
This type of analysis is used for seismic analysis and for solv- and the type of cyclic loading
ing vibration problems that are not stationary. It should not OUTPUT is required. A static analysis is
be used to analyze impact or impulsive loading. The thermal response as a function of time is reported. Out- also required to run the fatigue
put intervals with in the time range can be specified. analysis.
INPUT
The load input is a response In transient thermal analysis, the initial temperature has to OUTPUT
spectrum of either displace- be specified. This can either be a uniform temperature over A fatigue analysis can output
ment, velocity, or accelera- the model, or the steady state thermal analysis temperature the following:
tion. The response spectrum distribution can
is used as a weight factor to be applied using  Log Life: The estimated
multiply each individual the MecT option. number of cycles until the
modal shape and then add The initial tem- model breaks.
them together by means of perature should
absolute sum or SRSS match with the  Log Damage: The ratio of accumulated fatigue cycles
method. prescribed tem- and total number of cycles to failure. A value greater
perature values. than 1 indicates failure.
The absolute sum method assumes that the maximum dis-
placements for all the modes happen at the same time, but The accuracy value defined in transient thermal analysis is  Factor of Safety: The permissible factor of safety on
in most cases when one mode achieves maximum response, the acceptable fractional temperature error used to deter- the input load.
other modal responses are less than their individual maxi- mine the time step.
mum. Thus, the absolute sum method over estimates the  Confidence of Life: The ratio of calculated life to the
maximum response. A more realistic way to do this is to use Fatigue Analysis (Fatigue Advisor) target design life. A value below 1 indicates failure.
the SRSS method wherein the modal responses are summed
using the square root of the sum of the squares. SRSS is also When an analysis models is subjected to repeated cycles of Typically, fatigue failure consists of two phases, crack initia-
the recommended method for models where the frequen- loading and unloading, failure can occur due to fatigue even tion and crack growth. Fatigue analysis in Mechanica ana-
cies of major contributing modes are not very close to each if stresses developed are below safe values for static analysis. lyzes the crack initiation phase only, and therefore should
other. Fatigue analysis in Mechanica requires the Fatigue Advisor only be used to determine if a design is likely to suffer from
license. Fatigue-specific material properties such as surface fatigue problems and whether a more detailed analysis or
OUTPUT finish and material types should be specified. A generic set testing is required. Fatigue analysis follows the E-N ap-
Dynamic shock analysis will calculate maximum values of of fatigue properties are built into Mechanica for unalloyed proach or the strain life approach, which is also called low-
displacements, stresses, and mass participation factors in the steels, low alloy steels, titanium alloys, and aluminum alloys. cycle fatigue or local strain approach.
analysis model. Unmodeled features such as welds that cause stress concen-
trations can be accounted for using the fatigue strength 2D Model Type
Transient Thermal Analysis reduction factor. A value of 1 represents no unmodeled
features that cause stress concentrations. An Advanced Mechanica license allows you to simplify the
This type of analysis is used to calcu- analysis models to a 2D model type instead of the default 3D
late the temperature and heat flux in model. This should be set up be-
the analysis model over a specific fore entering Mechanica mode in
time period and to calculate the time the Mechanica model setup dialog
taken by the analysis model to heat box. The 2D surface selected
up or cool down. should contain the xy plane of the
coordinate system.

Dynamic, Transient Thermal, Fatigue, 2D Model Type Back to Table of Contents ANALYSIS—ADVANCED MECHANICA 42

ANALYSIS BEST PRACTICES creo elements/pro 5.0 mechanica

QUICK REFERENCE GUIDE

Batch Files Sandy_McKinney_2015Problem: During fatal errors, Mechanica reports a list of ID Mechanica Process Guide
numbers.
Analyses on large models are computationally expensive Solution: Typically, the Analysis Diagnostics window will The Process Guide will walk you through each step in the
and take a significant amount of time to complete. In such help in such situations by automatic zoom in to the entity on simulation process in Mechanica.
situations, it is a good practice to use batch files for running the model. If the diagnostics window does not show up
the analysis. automatically, select INFO > DIAGNOSTICS. By default, Mechanica has predefined process guides for
If this option does not work, then use the independent static analysis, modal analysis, buckling analysis, and
1. Set up all analyses. mode Mechanica to look at these element IDs. Select FILE > Mechanica Lite. These templates for the process guide are in
2. Run a quick check analysis to make sure the analyses INDEPENDENT MECHANICA to launch the independent XML format. With XML knowledge, expert users can create
mode. Then click UTILITY > MACROS, select Entity_ID, and unique templates that capture a specific series of modeling
are feasible. click the Replay button. and analysis activities and instruct users on how to perform
3. Create batch files for each analysis, or append multiple those activities to a given standard.
Always double-check the material properties, because cer-
analyses in the model to one batch file. tain fatal errors could simply be due to a material property Verification Guide
4. At the end of the workday, just run the batch file value being 0 or no thermal property being assigned when
doing a thermal analysis. The Mechanica help section has a Verifi-
(double click the batch file) to execute analysis. When fatal errors occur in assemblies, it is a good practice to cation Guide that uses a series of prob-
always double check the connections between parts along lems to demonstrate the accuracy and
Creo Elements/Pro or Mechanica need not be launched with clearance and interference. efficiency of Mechanica by comparing
manually to execute the analysis run. Starting the batch Sometimes the engine error can be fixed just by restarting Mechanica’s results to those obtained by
file will automatically run the post process in the back- Creo Elements/Pro or by killing the msengine.exe process traditional analysis codes or theory.
ground, so it only needs access to the license. and restarting the analysis.
Fatal errors might also occur due to insufficient disk space or
How to Fix Fatal Errors During Analy- RAM requirements.
sis Run

There are several reasons for fatal errors that may occur dur-
ing analysis run. Here are some methods to fix such errors.

Problem: A very
common fatal error
is the insufficiently
constrained error
as shown.

Solution: The best
way to fix this is to
run a modal analy-
sis on the same
analysis model
with rigid mode
search. Once the analysis completes, review the animation
of the displacement for the modal analysis, as this will show
the rigid body mode.

Analysis Best Practices Back to Table of Contents ANALYSIS BEST PRACTICES 43







Sandy_McKinney_2015

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