250 192 Optimization of the cupro-nickel and graphene co-deposition process based on the fracture toughness characteristics. Baiocco G1 , Salvi D1 , Stamopoulos A2 , Ucciardello N1 1Università Degli Studi Di Roma Tor Vergata, 2University of L'Aquila Copper nickel composite coatings are of great interest in many industrial applications due to their outstanding mechanical, physical and electro-catalytic properties. Also, the incorporation of inert particles within the film has already been demonstrated to increase such features. However, the production of Ni-Cu coating, especially with high Ni content, usually results in films with high defects and roughness. Instead, nanoparticle embedding may entail an increased defect number within the coatings lattice. However, pulsed electrodeposition is known for offering the co-deposition of uniform, smooth and defect-free coating in addition to better control of inert particle inclusion. This work aims to optimize a pulsed process for the codeposition of Cu-Ni-Gr with a low defect and internal stress to enhance the coating performance. Therefore, a fracture mechanics experimental analysis is conducted to evaluate the impact of the presence of manufacturing defects and their mobility within the electroplated metal matrix.
251 193 Investigation of Defects in Composite Structures produced with the Fused Filament Fabrication technique using X-Ray Computed Tomography Stamopoulos A1 , Pace F1 , Glinz J2 , Senck S2 1University Of L'Aquila, 2University of Applied Sciences Upper Austria, Stelzhamerstraße 23 Fused Filament Fabrication (FFF) is an additive manufacturing (AM) method that has reached in the last few years a great employment in the production of composite structures. The combination of neat short fiberthermoplastic filaments with continuous prepreg fibers enabled the possibility to produce components of high geometrical complexity. In addition, these structures are characterized by comparably increased mechanical properties due to the presence of continuous fibers. Nevertheless, a lot of manufacturing defects may be introduced in the final product, such as porosity/voids, fiber misalignment and waviness as well as insufficient impregnation of the fiber bundles. These defects are mainly related to errors attributed to the printing process. In the present work, an experimental campaign is presented, where samples in the form of tensile specimens were considered. These samples were produced combining Onyx (short carbon fiber/PA6) and continuous fiber prepreg filaments. These filaments contained either carbon or glass continuous fibers. The neat Onyx material was considered as reference while continuous fiber samples containing 2, 4, 6, 8, 10 and 12 reinforcing layers were considered, keeping constant, on the other hand, the total layer number at 16. All the produced samples were subjected to micro X-Ray Computed Tomography measurements. State of the art CT data analysis software was implemented, enabling the detection, quantification, and visualization of voids in various zones of the obtained composite structure. The results revealed an increasing overall porosity volume fraction while the number of continuous fiber layers increased. Furthermore, a through-the-thickness porosity analysis was conducted for assessing the distribution of the voids, especially those related to the presence of continuous fibers. In fact, the deposition of reinforcing layers appears to favor the development of large voids. The differences between the continuous carbon and glass fiber reinforced samples are also presented, leading to observations about their applicability and the overall repeatability of the FFF process when short and long carbon fiber filaments are put together. The results are correlated with tensile tests output, revealing the relation between these defects and their effect on the tensile performance of these samples. The present analysis may be considered as a step further on understanding the FFF process output when combining short and long carbon/glass fibers and while increasing the overall continuous fiber layers that aim to reinforce the material.
252 194 Analysis of the effect of pressure cycle on the impregnation level of textile glass fiber reinforced thermoplastic composites for automotive applications Stamopoulos A1 , Di Ilio A1 , Creonti G2 1University Of L'Aquila, 2Crossfire srl Nowadays, thermoplastic composite materials are finding more space in automotive applications due to their unique features they exhibit, contributing to aspects such as the greener direction of materials and their feasibility/sustainability due to lower production costs. An effective method for producing semifinished composite products is the continuous press, a fabrication method used by the majority of the CFRTP manufacturers. According to this method, a textile is placed between 2 thermoplastic films inside a press and, after the application of a combined pressure and temperature cycle, the impregnation is achieved. However, a critical aspect is the level of impregnation with respect to the time spent. Therefore, for achieving a good quality, the cycle may vary from seconds to minutes, altering on the other hand the productiveness of the process. In the present work, an experimental approach is conducted for investigating the effectiveness of this fabrication method. Plates of woven textile GF/Polypropylene were produced in different pressure cycles. The impregnation level is investigated using optical microscopy while the effect of the variation of consolidation is quantified by means of mechanical testing.
253 195 Identification of the Manufacturing Defects in Composite Structures produced with the Filament Winding technique with contact and noncontact inspection methods D'Emilia G1 , Gaspari A2 , Stamopoulos A1 , Natale E1 , Chiominto L1 1University of L'Aquila, 2Polytechnic of Bari The filament winding technique is an essential fabrication method for producing pressure vessels and cylinder-like structures of composite materials. Since this technique is the most adequate to produce components for H2 storage, the accurate identification of the defects derived by the process is fundamental. In fact, these defects may be introduced by different causes in various phases of the production and, in the form of initial structural or aesthetic damage, may alter the pressure vessel’s characteristics. Therefore, accurate defect detection and process optimization are essential for producing safe and high-pressure capacity vessels. In the present work, a root causes analysis is implemented to link some of the process parameters to the outcome in terms of defect detection and their relation with fabrication parameters. On the other hand, this is crucial to identify the most suitable measurement techniques, able to catch the defects of interest. In this context, the potentialities, and limits of both contact and non-contact measurement techniques are explored. These techniques are applied in products fabricated with precise process parameters such as the winding angle. The aim of the work is to assess the effectiveness of the inspection techniques when applied to cylindrical filament wound components, to investigate the applicability in critical aspects such as the thickness variation, the coverage level and the gap between consecutive filaments and, finally to exploit this information for optimizing the process and introducing an effective in-line control solution.
254 196 Mode I fracture toughness for hygrothermally-aged filament wound composites Pollet A1 , Almeida Jr H2 , Stamopoulos A3 , Amico S1 1 Federal University of Rio Grande do Sul, 2Queen's University Belfast, 3University of L’Aquila This work aims at assessing the effect of hygrothermal conditioning on the Mode I fracture toughness behaviour of glass/epoxy and carbon/epoxy composite materials manufactured by filament winding. Cylinders (136 mm in diameter) are manufactured using distinct winding angles (±90°, ±75°, ±60° and ±45), and the specimens are conditioned in water at room temperature and at 70 °C. A PTFE film is inserted during the winding of the cylinders as an artificial crack, as shown in Figure 1. After that, the cylinder is cut at the desired width to meet the recommendations of the ASTM D5528M-21 standard. Ending blocks are designed and produced with a radius of 68 mm, and a fast-curing epoxy structural adhesive is used to glue the sample to the ending blocks. Water absorption was monitored until equilibrium, which varies with the material, the water temperature and the winding angle, reaching a maximum value for the ±45°, being 1.10% for the glass/epoxy and 1.74% for carbon/epoxy for water at room temperature, and 1.30% and 2.95% for water at 70 °C. These results are directly related to the void content, which are 3.20% for glass/epoxy and 3.41% for carbon/epoxy samples. As for fracture toughness, glass/epoxy composites show superior performance compared to carbon/epoxy ones in terms of peak load and strain energy release rate. A reduction in fracture toughness with the winding angle is observed, the highest for ±90° and the lowest for ±45°, and the specimens conditioned at room temperature are less prone to delamination than those at 70 °C. In addition, higher fracture toughness is found for carbon/epoxy compared to glass/epoxy specimens of the same winding angle and conditioning. Fractographic images display fibre bridging and fibre/matrix pull-out at the interlaminar region of all specimens. Conditioned specimens in water at room temperature show higher peak force and strain energy release rates compared to non-conditioned composites, which is attributed to matrix plasticisation. Conditioned samples in hot water have poorer behaviour compared to the non-conditioned or conditioned at room temperature samples. Steps to insert the artificial crack during winding of the cylinders.
255 The mode I fracture toughness test on the curved filament wound sample.
256 197 A “mean object” approach to simulate manufacturing-induced porosity in filament-winded composites Srivastava C1 , Stamopoulos A2 , Grammatikos S1 1ASEMlab - Advanced and Sustainable Engineering Materials Laboratory, Group of Sustainable Composites, Department of Manufacturing and Civil Engineering, Norwegian University of Science and Technology, 2Department of Industrial and Information Engineering and Economy (DIIIE), University of L'Aquila The presence of voids in composite materials can hamper their overall structural integrity, and hence, a better understanding of voids in composite materials has been a field of study for numerous years. Filament-winded composite materials have a complex heterogenous structure composed of numerous scattered resin-rich areas caused due to multiaxial tape layup causing; the structures made from filament winding are prone to voids where the morphology of the voids varies from spherical to long and thin ellipsoids with principal axes along the tape-laying direction. This variation in size, volume, orientation and sphericity impedes the growth of high-fidelity simulation methods used for filament-winded composites. In this work, the manufacturing-induced voids in filament-winded composite structures are detected with the help of micro-CT imaging and their effect is analyzed using FE simulations. These voids are not artificially manufactured and represent the natural distribution in filament-winded structures. The voids are segmented from the rest of the composite material using a grey intensity threshold, and their size and orientation are calculated using an inertia tensor. The voids are then clustered through a K-mean clustering algorithm, where the clustering criteria was the most prominent orientation along the tape laying direction. Clusters are then represented through a "conglomerated approach", where a blob-shaped 3D object represents the equivalent volume fraction in the different coupons taken from a panel of a filament-winded structure. Hence, a knockdown factor is calculated, which can be used to degrade the properties of these structures, and hence a better understanding of the behaviour of filament-winded structures can be achieved. In the future, this approach's results will be verified against experimental observations from literature and testing. "Mean Object" representation of porosity in filament wound composite
257 198 Crack growth simulation of bonded joints under mixed mode loading Münch L1 , Rose P2 , Middendorf P1 , Linke M2 1University Of Stuttgart, 2Hamburg University of Applied Sciences The simulation of crack propagation under fatigue loading in adhesive joints and adjacent parts, in order to design and develop fatigue resistant joints, is still a challenge today. Thus, many approaches are being developed for different applications. Cohesive zone elements are already implemented into commercial software but often extended through user defined subroutines. This study combines different subroutines for intralaminar, interlaminar and adhesive damage to predict the crack path through different layers of a lamina originating from an adhesive pre-crack. To achieve this interlaminar/adhesive subroutine builds upon a user-defined material for crack growth, which describes the cohesive stress and damage in the joint [1]. A second user defined subroutine developed at the HAW Hamburg is used for intralaminar damage. The described composite joint is modelled on a mesoscopic level with one layer of cohesive elements and one layer of solids per lamina ply to enable fiber failure and delamination under fatigue loading. The adhesive bond is modelled as a single cohesive element layer. Both subroutines are implemented in the FEM-software and linked to exchange information between the material models. The aim of the communication is to transfer the good simulation results achieved with the individual user subroutines to a complex damage scenario of more realistic nature. These scenarios require the crack being able to jump through fiber layers or to initiate delaminations due to matrix damage in adjacent composite layers. In this study the possibilities and limitation of the combined subroutines are demonstrated on different Cracked Lap Shear (CLS) specimens, designed to promote or prevent a crack from propagating through multiply layers. The crack is hereby controlled by the positioning of the 0° ply, fiber orientation in load direction, which acts as a barrier. This allows for an evaluation of the communication and the crack path as well as the actual predicted crack propagation rates. The simulation study is further measured against test results and crack propagation simulations performed with only a single user subroutine active. REFERENCES [1] R. Sachse, A. K. Pickett, W. Essig, P. Middendorf, Experimental and numerical investigation of the influence of rivetless nut plate joints on fatigue crack growth in adhesively bonded composite joints. International Journal of Fatigue Vol. 105, pp. 262–275, 2017.
258 199 Introduction to a High Fidelity Simulation Framework for the Development of Damage Tolerant Bonded Joints Sachse R1 , Hoffmann M1 , Körwien T1 1Airbus Defence And Space Gmbh Introduction The application of bonded joints in primary aircraft structures has the potential to disrupt future manned and unmanned air systems. However, the application of bonded high load transfer joints is limited due to missing design and sizing methods. The LuFo research project JoinDT recognizes this issue on an Airbus Group level and aims to develop high-fidelity as well as industrial design and sizing methods for bonded joints. Methods In this paper, an integrated high-fidelity simulation framework is introduced. To virtually design damage tolerant bonded joints, first, the initial damage caused by an impact is modelled, including damage in the adhesive, as well as in the laminate. This initial damage state is then mapped to a fatigue crack growth analysis, modelling damage growth within the adhesive and the laminate. The results are again mapped to a residual strength analysis verifying limit load capability. The individual models rely on stacked-shell or stacked-solid models featuring an intra-laminar damage model for unidirectional carbon fiber reinforced composites made of 8552/IM7 prepreg. Additionally delamination within the laminate as well damage in the adhesive is modelled using cohesive zone elements. The individual model development is performed at the research institutes of University of Stuttgart, DLR FA Braunschweig, Hamburg University of Applied Science and Fraunhofer IFAM. The integration of the different models into a simulation framework is done by Wölfel GmbH. Besides the Simulation framework an extensive test programme is performed, featuring wide single lap shear specimen. Configurations tested include undamaged specimen, specimen with an artificial damage in the adhesive bondline and with impact damage loaded under static and fatigue conditions. Results and Conclusion Test results show a complex damage state and damage progression at any of the mentioned loading scenarios. This undermines the need for a high-fidelity End-to-End Simulation Framework, which the project successfully implemented. It was demonstrated that the initial damage state due to impact loading can be captured and correctly processed through the subsequent fatigue and residual strength simulations. The effect of damage and damage progression on residual strength of the material can therefore be analysed to support virtual testing.
259 Development Process
260 200 Static residual strength analysis of fibre composite bonded joints after impact and fatigue using mesoscale progressive damage analysis Völkerink O1 , Schollerer M1 , Kosmann J1 , Holzhüter D1 , Hühne C1 1Deutsches Zentrum Für Luft- Und Raumfahrt E.v. Adhesive bonding as joining technology for fibre composite aircraft structures has many advantages over mechanical fasteners. Bonded joints resist corrosion, seal, weigh less than fastened joins, ensure a homogeneous load introduction and do not require any hole drilling. ´ Although bonded fibre composite structures have a high resistance to fatigue damage, they are prone to impact damage. For this reason, in addition to the static strength of the pristine, undamaged structure, the residual static strength with impact and fatigue damages is needed during sizing of the aircraft structures. A damaged fail-safe structure must still have the capability to bear 80 to 100 % of limit load, which describes the maximum load authorized during flight. To date, this information is obtained by the airframer through physical testing due to a lack of validated analysis tools. This work investigates whether the residual strength as well as the failure mode of a bonded structure with (artificial) pre-damages can be acquired by virtual testing using numerical analyses. To compile a residual strength analysis tool as part of a impact - fatigue - static strength simulation tool chain, a FEM-based mesoscale progressive damage analysis using Abaqus / Explicit is set up. The main feature of the method is a user-defined material model based on the plasticity model by Sun and Chen in combination with the Failure Mode Concept by Cuntze to model the behaviour of the fibre composite adherends. A solidas well as a continuum shell-based modelling of the adherends is investigated. These two adherend modelling strategies are combined with two different modelling approaches for the film adhesive. The simpler approach uses only cohesive elements to describe the adhesives behaviour. A more sophisticated one combines solid elements using the exponential Drucker-Prager yield model with a cohesive surface in the middle of the adhesive layer to model cohesive failure. The so-compiled four different modelling variants are validated against large, 100 mm wide, single lap joint coupon specimens tested under tensile load. The specimens are made from HexPly 8552-IM7 prepreg material and a Henkel Hysol EA9695 0.05 NW film adhesive. One test series is pristine and two other series contain (artificial) pre-damages. Based on the comparison with the physical experiments, a recommendation for a modelling strategy is made. With this information, a validated tool to predict the static residual strength and failure mode by virtual testing is provided and used in the joint research project ”JoinDT - Joining with predictable Damage Tolerance” funded by the German Federal Ministry for Economics and Climate Action.
261 Numerical model of bonded single lap shear specimen with interlaminar damage
262 201 A numerical simulation method for impact damage in adhesively bonded joints Bastek M1 , Middendorf P 1University Of Stuttgart - Institute Of Aircraft Design Carbon fibre reinforced plastics (CFRP) are widely used in the aerospace industry. However, the joining of structural components is still a research topic as screws and rivets are mainly used today. Adhesive joints offer a new approach where no holes weaken the structure. The lower weight is another benefit due to the absence of rivets leading to lower fuel consumption and consequently lower CO2 emissions. In addition, fewer machining steps are required. To avoid an excessive physical testing programme to prove the damage tolerance of bonded joints, numerical simulations of impact damage are crucial. Virtual testing allows damage tolerance to be analysed early in the development process without the need for costly testing. The final testing effort for certification can be minimised by performing a few selected tests. In addition, real damage can be evaluated numerically. To develop a virtual test environment, a numerical method for low velocity impacts on bonded CFRP joints is developed based on a three-stage impact test programme with gradually increasing complexity. First, non-bonded CFRP impact specimens are tested at different impact energies to characterise the damage of the adherent material. The impact testing of fully bonded specimens to investigate the adhesive's damage behaviour is the second stage. In the third stage, impact tests are carried out on specimen with single lap joints. Accompanying the experimental programme, numerical simulations are set up and a stacked shell simulation method is developed in Abaqus/Explicit. Analogous to the physical experiments, the numerical simulations first predict the damage of non-bonded CFRP specimens. The simulation is then extended to fully bonded specimens and finally the single overlap configuration is implemented in the simulations. Based on numerical investigations like the meshing method, element size and deletion strategies, a simulation method is developed. The final modelling approach with stacked shells for the adherents and cohesive zone elements for the adhesive shows good agreement with the experimental results in terms of load-displacement curves and ultrasonic scans. The findings of this numerical investigation show that the developed simulation method is able to predict low velocity impact damages in adhesively bonded single lap joints.
263 202 A mapping methodology for damage transfer between different numerical modules in a virtual testing chain of bonded CFRP joints Erdmann P1 1Wölfel Engineering GmbH & Co. KG Introduction Material or Component tests require many resources, especially in the case of carbon fiber reinforced plastics. Therefore, a replacement of physical by virtual tests via numerical models is pursued. In this context, a virtual testing chain for the verification of bonded CFRP joints is developed in scope of the JoinDT project. The goal is to analyse the structural behaviour and the damage growth under different loading scenarios. In the virtual testing chain different modules each representing a loading scenario will be executed in a sequence. The modules cover the effects of damage initiation and damage growth due to impact, fatigue and residual strength. Thereby each of the modules requires a different numerical model, challenging the processing of their individual output variables for physical damage quantities. Methods With respect to the virtual testing chain for bonded CFRP joints the damages observed in one module need to be transferred to the following module(s). For example an initial damage e.g. due to impact is the reference for the following fatigue module requiring mapping of the damaged regions. Therefore, a mapping strategy and methodology based on physical quantities for damage and damage coordinates are developed. The method is able to map interlaminar, intralaminar and adhesive damage between the different modules mentioned beforehand. Results and Conclusion A demonstration on different virtual specimens confirms the mapping strategy and the method itself, enabling a virtual testing chain for bonded CFRP joints. Mapping of interlaminar, intralaminar and adhesive damages can be proven successfully between the individual modules of impact, fatigue and residual strength while their specific requirements are met. The virtual testing chain, the requirements of the individual modules, the mapping strategy and the mapping method will be presented.
264 203 Investigation of the influence of design parameters onto the cracked lap shear specimen Rose P1,2 , Linke M1 , Busquets D2 1Hamburg University of Applied Sciences, 2Universitat Politècnica de València Parallel to the continuously increasing percentage of carbon fiber-reinforced plastics in the primary structure of aircraft over the past decades, the attention to adhesive bonding technology as the joining method has increased as well. These joints require a numerical design based on a detailed characterisation of the adhesive to use. The material model for the numerical design often needs fracture characteristics, for the fracture behaviour under Mode I and Mode II loads, standardised tests are available which are based on the same specimen geometry. For combined loads (mixed mode), the mixed mode bending test (MMB) offers the possibility to investigate these loading conditions on the same specimen geometry. However, it is reported that the MMB test fixture affects the test results due to its own weight [1] and stiffness. The Cracked Lap Shear (CLS) specimen allows a mixed-mode loading condition to be generated without a special test fixture using a simple tensile test. The mixed-mode ratio produced is nearly constant over a wide range of crack growth [2] and is representative of the loading conditions found in many structural applications of bonded joints [1]. However, this specimen is not standardised, so very dissimilar specimen designs are used in the literature [1 - 3]. In this study, the primary design parameter considered is the specimen width in terms of its application for adhesive characterisation, with a typical layup having a 0° layer in contact with the bond line. By varying the specimen width between 5 and 40 mm, its influence is shown by the results of quasi-static and also fatigue tests. In addition, CLS specimens with the same layup but without an adhesive layer between the adherents are investigated to study the effects of width scaling with and without a toughened adhesive bond. While the static tests show a linear relationship between specimen width and joint strength, it is different in fatigue tests, where the crack growth rate increases with decreasing specimen width, both for specimens with and without adhesive bond between the joining partners. To sum up, narrower specimens are particularly advantageous for the validation of material models with complex damage, as the calculation time can be reduced without coarsening the mesh, moreover the cost to carry out the testing can be reduced. However, if crack stop features are to be investigated, a wide specimen width is preferable because of the hole in the specimen that is typically required for such features. REFERENCES: [1] I. Floros, K. Tserpes (2019), Fatigue crack growth characterization in adhesive CFRP joints, Composite Structures, Volume 207, Pages 531-536, ISSN 0263-8223, https://doi.org/10.1016/j.compstruct.2018.09.020. [2] R. Sachse, A.K. Pickett, W. Essig, P. Middendorf, (2017), Experimental and numerical investigation of the influence of rivetless nut plate joints on fatigue crack growth in adhesively bonded composite joints, International Journal of Fatigue, Volume 105, 2017, Pages 262-275, ISSN 0142-1123, https://doi.org/10.1016/j.ijfatigue.2017.08.001 [3] J. Jokinen, M. Kanerva, (2017), Analysis of cracked lap shear testing of tungsten-CFRP hybrid laminates, Engineering Fracture Mechanics, Volume 175, 2017, Pages 184-200, ISSN 0013-7944, https://doi.org/10.1016/j.engfracmech.2017.01.029
265 204 Crack tracking on element level for fatigue calculations of adhesively bonded joints Wulf A1 , Nagel C1 , Hesebeck O1 1 Fraunhofer-IFAM The use of cohesive zone models (CZM) together with special cohesive zone elements (CZE) today to calculate the mechanical behaviour of adhesively bonded joints is widely used. Whereas the static behaviour even under high strain rates will be modelled accurately due to a lot of different CZM the modelling of fatigue behaviour of adhesively bonded joints is object of miscellaneous current research activities. There are three different approaches available. First is a cycle by cycle approach [3]. A different approach is a cycle jump strategy [5,6]. This approach uses a combination of damage and fracture mechanics to model the damage evolution during fatigue loading. The third approach utilizes the maximum fatigue load [4]. All these approaches use a traction separation law to model the static behaviour of adhesive joints in combination with an evolution law to model the fatigue degradation and crack propagation process. In order to represent a correct crack growth rate a link between the damage variable of CZM and the crack growth rate is necessary which usually requires assumptions on the cohesive zone length. To avoid knowledge of cohesive zone lengths only integration points at the crack tip are considered which necessitate a crack tracking method. In [1,2] such a method was developed and implemented respectively. These approaches take external databases in order to track the crack front, which on the other hand yields considerable data traffic during fatigue calculations and increases simulation time. To overcome the drawback of external databases a crack tracking method on element level was developed. In order to calculate the physical crack front within the element the damage field is interpolated and scanned from the element edges. Locations within the element with a damage value of one represent crack surface. Locations where the damage value is less than one represent the damaged area of the element (Fig. 1). Due to the use of the element’s interpolation functions and damage values at the integration points (nodes) the crack surface and crack front is continuous over a patch of elements. This approach is implemented as a user element into the FE-code ABAQUS. This work has been financially supported through the Project Joining with predictable Damage Tolerance - JoinDT by the German Ministry of Economics and Energy following a decision of the German Bundestag. The support is gratefully acknowledged. References [1] R. Sachse, A.K. Pickett, W. Essig, P. Middendorf, Int. J. Fatigue, 105, 2017, pp. 262-275 [2] L.F. Kawashita, S.R. Hallet, Int. J. Solids and Structures, 49, 2012, pp. 2898-2913. [3] K.L. Roe, T. Siegmund, Engineering Fracture Mechanics, 2003, 70, pp. 209-232.
266 [4] P. Robinson, U. Galvanetto, D. Tumino, G. Bellucci, D. Violeau, Int. J. Numerical Methods in Engineering, 2005, 63, pp. 1824-1848. [5] A. Turon, P.P. Camanho, J. Costa, C.G. Davila, Mechanics of Materials, 2006, 38, pp. 1072-1089. [6] A. Turon, J. Costa, P.P. Camanho, C.G. Davila, Composites, 2006, A38, pp. 2270-2282. Figure 1: Crackfront in the physical and convective coordinate space
267 205 Degradation of Thermoelectric Materials and their Protection by Chromium-based Coatings Zhang Z1 , Gurtaran M1 , Li X1 , Dong H1 1 Surface Engineering Group, School Of Metallurgy And Materials, the University of Birmingham With the advance of phonon engineering and electron engineering schemes, the performance of thermoelectric material is continuously progressed in the last decades. However, there are still some hurdles to bringing this technology to the market: inadequate mechanical properties, insufficient thermal stability, and unreliable contact. In this work, different thermoelectric materials and their degradation mechanisms especially at elevated temperatures are reviewed. For example, the brittleness nature of PbTe and Bi2Te3 discounts them in commercial applications. In contrast, CoSb3-based skutterudites work well at temperatures below 400 °C, but they are susceptible to oxidation. TE materials containing high vapour pressure elements of Pb, Ge, Te, Sb, Sn, etc, usually have high sublimation rates and ease diffusing at higher working temperatures. To maintain the chemical stability of TE materials, different approaches have been attempted from employing oxidizing resistant materials (i.e adding Si into PbTe) to improving the application environment, and developing surface coatings like Si3N4, Al2O3, Enamel, Nano-SiO2, composite glass, aerogel, heat resistance paint. Following the brief of the techniques and materials used to protect different thermoelectric blocks, we have investigated the thermal stability of the compact and uniform CrSix coatings deposited by a close field unbalanced magnetron sputtering technique. Characterisation of the layers before and after oxidation was evaluated through systematic analyses of surfaces and cross-sections using different techniques, including SEM/EDX, TEM and XRD. The coatings applied on TE blocks made of Magnesium silicide and Hf-free half Heusler alloys were also assessed for practical thermoelectric module applications.
268 206 Improvement of IFSS of CFRP composites by ASP treatments Li X1 , Dashtbozorg B1 , Dong H1 1University of Birmingham, UK Weak fibre/matrix interfacial shear strength (IFSS) will cause the initiation of interface cracks and accelerate their propagation, leading to failure of the composite structures. The current research reported an advanced active screen plasma (ASP) technique, which effectively modified carbon surface, thus improved interface share strength (IFSS) of the carbon fibre reinforced polymer composites (CFRPC). Active screen plasma treatments are advanced surface modification techniques capable of modifying both electrically conductive and non-conductive materials with versatile and customisable processing conditions. Within this work, different ASP treatments conditions were used to modify carbon fibres (Torayca T700SC) with gas mixtures containing both nitrogen and argon. Contact angles were measured by a combined method of direct angle measurements and calculation-based recordings. Raman and XRD analysis were utilised to confirm the modification of the fibres. Single fibre push-out testing was performed on the composites made using the most promising ASP treated fibres and compared with the untreated CFs. The IFSS values were calculated based on the push-out tests results and the outcomes have showed a significant IFSS increase of ASP modified CRPC as compared with the untreated counterpart. Key words: Active screen plasma treatments, Interface share strength, Carbon fibre reinforced polymer composites Funding: This research was funded by the EU H2020 Project Carbon4Power, under Grant no. 953192.
269 207 Oxidation Behaviour of CrSi Coatings for Combating Degradation of 316 Austenitic Stainless Steel at High Temperatures Gurtaran M1 , Zhang Z1 , Li X1 , Dong H1 1The University Of Birmingham Austenitic stainless steels are materials of choice for high temperature applications from nuclear power plants to the automotive industry owing to their excellent mechanical propertied and high corrosion resistance. However, the oxidation resistance of austenitic stainless steels was worsened when the surfaces of the components expose to an aggressive environment. Many researchers deposited protective metal coatings, such as Al, Cr and Si on stainless steel by using different technique. However, pure metal coatings are limited by their poor high-temperature mechanical properties, and it is suggested that a small amount of additional element doping in pure metal elements could improve the oxidation resistance under aggressive environment. In this study, a closed-field unbalanced magnetron sputtering system, which is environmentally friendly and high deposition efficiency, was used to deposit CrSi coatings on 316 austenite stainless steel. Closed-field unbalanced magnetron sputtering system utilised separate Cr and Si targets and the appropriate content of Cr and Si of the coatings was adjusted by changing the currents applied to the targets. A series CrSi coatings with different silicon/Cr ratios were produced and their oxidation behaviour at elevated temperatures were investigated. By analysing the weight gain, surface morphology and microstructure, composition and phase constituents, the optimized coating to protect the stainless steel has been identified. Keywords: CrSi coating, magnetron sputtering, oxidation, degradation Funding: This research was funded by (1) EU H2020 Project FAST-SMART under Grant no. 862289 and (2) Ministry of National Education of the Republic of Turkey.
270 208 Active screen plasma nitriding of laser powder bed fusion processed 316L stainless steel for the application of fuel cell bipolar plates Lin K1 , Qiao J1 , Gu D 1Nanjing University Of Aeronautics And Astronautics 316L stainless steel (316L SS) is widely used to fabricate bipolar plates of proton exchange membrane fuel cells (PEMFC) due to its good corrosion resistance, electrical conductivity and low cost. Laser powder bed fusion (LPBF) is capable to process complex flow field structures on 316L SS bipolar plates, which is promising to improve the performance of PEMFC. However, insufficient corrosion resistance and relatively high interfacial contact resistance (ICR) become the major obstacle to the widespread of LPBF-processed 316L SS bipolar plates. In this work, active screen plasma nitriding (ASPN) was used to modify 316L SSs fabricated by LPBF process and forging, respectively. The results showed that the nitrided layer of LPBFprocessed 316L SS (2000 mm/s, 300 W) exhibited the highest surface nitrogen concentration (52.9 %), thickest nitriding layer (11.1 μm) and highest average hardness (10.682 GPa). The ICR values were decreased significantly after ASPN treatment. Due to the higher nitrogen concentration, the corrosion current of nitrided LPBF-processed 316L SS (2000 mm/s, 300 W) was much lower than that of the nitrided forged 316L SS. In addition, by comparing multiscale microstructures between LPBF-processed 316L SS and forged 316L SS, the ASPN mechanism of LPBF-processed 316L SS was proposed.
271 209 Plain fretting crack initiation - experimental and numerical fracture mechanics analyses Knabner D1 , Suchý L1 , Hasse A1 1Technische Universität Chemnitz The phenomenon of fretting fatigue affects component joints and leads to a significant reduction in strength. Existing strength hypotheses unfortunately often fail to correctly predict fretting fatigue failure as they are developed for failure mechanics of plain fatigue. As is well known from the literature, the local tribological parameters slip amplitude s and contact pressure p have a major influence on the tolerable fretting fatigue strength. It is also known from literature that even plain fretting causes crack initiation. Based on these findings, the aim of this work was to determine the crack depths that occur under plain fretting conditions for different combinations of slip amplitude and contact pressure. This subsequently allows crack evaluation using fracture mechanics approaches. The tests were carried out on cast iron EN GJS-700 and aluminium EN AW-7075 T651 due to their use in applications in engine and aircraft construction with a risk of fretting fatigue. The counter-body material was C45+N in both test cases. The experiments were accomplished on a double actuated fretting pad test bench. A flat-to-flat contact was used as the contact condition, as conform contacts are usually used in real applications. The fretting pads were actuated by piezo-electric actuators to generate the slip while the fretting wear specimen was fixed. For each of the two material pairings 20 plain fretting tests were performed with 5 mio. cycles for each test. The range of parameters tested was p=10 MPa to 40 MPa; s=5 µm to 20 µm for the cast iron and p=5 MPa to 20 MPa; s=5 µm to 20 µm for the aluminum. Each parameter combination was tested twice, resulting in 10 different evaluable parameter combinations per material pairing. The specimen were then cut and polished across the fretting scar and the geometry of the initiated cracks was examined on the microscope. Subsequent fracture mechanics finite element simulations allow the determination of the required external loads for the different combinations of s and p that will lead to crack growth and hence fretting fatigue failure of the material. As shown in Figure 1, it was found that the depth of the initiated cracks is different for the different parameter combinations of p and s, which corresponds to the expectations explained at the beginning. This resulted in different calculated fretting fatigue strengths of the materials.
272 Test principle of the plain fretting tests, exemplary cracks initiated and observed crack lengths for different parameter combinations of s and p
273 Environmental Degradation, NDT, and SHM (Abstracts 210-246)
274 210 Corrosion and wear performance of a biomedical CoCrMo alloy fabricated by Vacuum Arc Melting Emmanouilidou S1 , Papagiannopoulos A1 , Lekatou A1 1University Of Ioannina The present work is focused on investigating the corrosion resistance and sliding wear behavior of a Co-28Cr6Mo alloy fabricated by Vacuum Arc Melting (VAM) for biomedical applications. The motivation for this work is to explore an effective way of fabricating these alloys in terms of cost, ease of manufacture and property boosting by employing a Rapid Solidification Method. In particular, VAM, a simple, cost-effective technique, is herein adopted as an alternative to additive and subtractive manufacturing processes, with the aim to produce Co-Cr-Mo biomedical alloys with high corrosion resistance and mechanical properties as well as minimal porosity. Regarding the experimental methodology, the prepared samples were remelted five times in a VAM furnace to ensure a homogeneous microstructure. The microstructure was evaluated by X-Ray Diffraction, Optical Microscopy and Scanning Electron Microscopy (SEM/EDX). Corrosion resistance testing was conducted by cyclic potentiodynamic polarization in simulated body fluid (SBF) at 37°C and pH=7.4±0.1. The dry sliding wear behavior was studied by the ball-on-disk technique. As regards the main results, the Co-Cr-Mo VAM specimens had a dendritic microstructure with a slight segregation of Mo and minimal porosity (1-2 vol.%). The specimens exhibited very high resistance to uniform resistance (corrosion current densities of the order of 10-4 mA/cm2), true passivity (passive currents << 0.1 mA/cm2) and non-susceptibility to localized corrosion in SBF at 37 oC. Low wear rates were also attained (order of 10-5 mm3/(N m)). The response to the surface degradation properties was found equivalent to that of analogues prepared by subtractive manufacture and additive manufacture techniques. To conclude, the Co-Cr-Mo alloy prepared by Vacuum Arc Melting is considered appropriate for biomedical uses, as far as the response to surface degradation properties is concerned.
275 211 Fly ash as a corrosion inhibitor of AISI 316L and 304L stainless steel concrete reinforcements under the combined effect of acid rain and seawater Tsouli S1 , Goutzos P1 , Kleftakis S1 , Lekatou A1 1University Of Ioannina The utilization of modern materials, such as stainless steel, in the framework of the restoration of monuments has been a common practice in the last decades. Stainless steel reinforcement assures the durability of reinforced concrete structures under aggressive environments. However, stainless steel is susceptible to localized corrosion in chloride containing environments. Reinforced concrete has been the most widely employed construction material worldwide throughout the last two centuries due to its high alkalinity. The partial replacement of Ordinary Portland cement (OPC) with fly ash (FA) is an economical, ecological and reliable solution, especially when dealing with cultural heritage. The beneficial role of FA on the corrosion resistance of reinforced concrete has mainly been attributed to the pozzolanic reaction of SiO2 with Ca(OH)2 leading to the formation of the corrosion resistant calcium-silicate-hydrate (C-S-H). Following authors' previous works on the effect of FA on the inhibition of stainless steel corrosion in acid rain mimicking solutions, the main objective of the present study is to investigate the role of FA, pH value and steel type on the electrochemical performance of 316L and 304L stainless steel concrete reinforcement in acid rain environments further burdened by seawater. In more details, the corrosion performance of 316L and 304L stainless steel is examined in terms of cyclic polarization in a slightly alkaline solution (pH≃8) simulating corroded concrete exposing steel reinforcement to direct acid rain & seawater attack, as well as in a strongly alkaline solution (pH≃12) simulating fresh concrete exposed to a combination of acid rain & seawater. At the same time, the feasibility of replacing 316L with the more economical 304L stainless steel is also examined. Both electrolytes contained saturated Ca(OH)2 (simulating a concrete pore solution), an acid rain mimicking solution, FA (0 wt.% - 25 wt.% of the dry mixture) and 3.5 wt.% NaCl. The beneficial effect of FA (up to 20 wt.%) on the corrosion resistance of 316L and 304L rebars was demonstrated in terms of thermodynamic tendency for corrosion, corrosion kinetics and passive film stability for both electrolytes. However, a deteriorating effect was realized at the 25 wt.% FA addition. Both steels showed very low corrosion current densities and true passivity, but susceptibility to localized corrosion (at high anodic potentials though). At both pH values, 304L manifested worse corrosion behavior than 316L. Nevertheless, the feasibility of replacing 316L with 304L stainless steel in critical applications provided that FA is included in the concrete mixture as a corrosion inhibitor, even at low contents (15 wt.%), has been proven for the combined environments.
276 212 Development of a tool for the prediction of wear in spur gears. Application to wind turbine's pitch system. García M1 , Cubillas D1 , Escalero M1 1 Ikerlan The fact that many wind farms are reaching their expected lifetime represents a major issue faced by the wind energy sector. In particular, the decomissioning is costly and the recycling of some components is difficult or even impossible, what has attracted the attention towards lifetime extension as a possible green solution. The key technological challenge is the development of tools that predict the degradation of the structural components through the extended lifetime stage, with the ultimate objective of preventing failure and its undesired consequences. This work addresses the development of a tool for predicting the wear of the gears that enable the pitch rotation of wind turbine blades. A evolutive methodology is proposed to solve the various problems involved in wear (force equilibrium, contact, kynematics, stresses and wear) and an experimental campaign is conducted to characterize the main material data required by the methodology, namely the friction coefficient and the coefficient of wear. A MATLAB tool for the automatic execution of the methodology is developed and some partial results are contrasted against finite element calculations. Finally, the wear is predicted in the pitch gears, considering the particular the case of a 5MW NREL model and realistic operating conditions.
277 213 The Corrosion Resistance of High-Strength Steels: An Examination of Microstructural Effects Using Localised Electrochemical Methods Dr. Aytac Yilmaz1 , MSc Satyakam Kar1 , MSc Gaojie Li1 , Dr. Konstantina Traka1 , Prof. Jilt Sietsma1 , Prof. Maria J. Santofimia1 , Dr. Yaiza Gonzalez-garcia1 1Delft University Of Technology High-strength steels are essential for various applications, including oil and gas production, transportation and infrastructure, due to their impressive mechanical properties, availability, and cost-effectiveness. However, steel corrosion poses significant economic, environmental, and safety risks. Since corrosion is directly related to the microstructure, it is necessary to develop innovative methods to design microstructures that exhibit improved corrosion resistance. The knowledge of relationships between microstructure and corrosion is limited since microstructural features synergistically affect corrosion behavior, making it challenging to understand the sole effect of a microstructural feature. In our work, the individual effect of several microstructural features on passivity and corrosion behaviour is investigated. The focus is on dislocation density [1], grain size [2,3], crystallographic orientation [2], and phases [4]. Model alloys were designed to limit the synergistic effect of microstructural features on corrosion performance. The effect of microstructure on overall corrosion properties is studied with conventional electrochemical methods – i.e. potentiodynamic measurements, electrochemical impedance spectroscopy (EIS), and Mott-Schottky analysis. To further identify the role of individual features on corrosion, advanced electrochemical techniques such as microcapillary cell, scanning electrochemical microscopy (SECM), and in-situ atomic force microscopy (AFM) are also applied. Our findings provide new insight into the relationship between microstructure and corrosion behavior, which can be instrumental in developing novel methods for designing high-strength steels with better corrosion performance. [1] A. Yilmaz, K. Traka, S. Pletincx, T. Hauffman, J. Sietsma, Y. Gonzalez-Garcia, “Effect of microstructural defects on passive layer properties of interstitial free (IF) ferritic steels in alkaline environment” Corrosion Science 182 (2021) 109271 [2] S. Kar, A. Yilmaz, K. Traka, J. Sietsma, Y. Gonzalez-Garcia, “Role of Grain Size and Recrystallization Texture in the Corrosion Behavior of Pure Iron in Acidic Medium” Metals 13 (2023) 388 [3] A. Yilmaz, X. Li, S. Pletincx, T. Hauffman, J. Sietsma, Y. Gonzalez-Garcia, “Passive Film Properties of Martensitic Steels in Alkaline Environment: Influence of the Prior Austenite Grain Size” Metals 12 (2022) 292 [4] A. Yilmaz, C. Ozkan, J. Sietsma, Y. Gonzalez-Garcia, “Properties of Passive Films Formed on FerriteMartensite and Ferrite-Pearlite Steel Microstructures” Metals 11 (2021) 594
278 214 Effect of Environmentally Friendly Surface Treatments on the Corrosion Behavior of New Al-Li Alloys Dr. Alexandra Karanika1 , Dr. Nikolaos Vourdas1 1 Hellenic Aerospace Industry, Greece Aluminum-lithium (Al-Li) alloys have gained significant attention in aeronautical applications, due to their low density, improved mechanical properties, weldability, corrosion resistance and formability. In this study, the effect of environmentally friendly surface treatments on the corrosion behavior of a new Al-Li alloy, specifically 2198 Al-Li, is investigated. The two environmentally friendly surface treatments examined are Chrome-free Thin Film Sulphuric Acid Anodizing (TFSA) and Sol-Gel in combination with environmentally friendly primer and top coat. The corrosion behavior of the Al-Li alloy treated with TFSA or Sol-Gel is compared against a conventional 2024 aeronautical alloy treated with Chromic Acid Anodizing (CAA). Corrosion resistance is evaluated through accelerated corrosion test, such as exfoliation corrosion, as well as visual inspection techniques. The results indicate that both TFSA and Sol-Gel treatments combined with the coating system perform equal in comparison to the conventional CAA treatment and chromate systems. The environmentally friendly anodizing form protective oxide layers on the Al-Li alloy surface, which effectively inhibit the corrosion process. However, the corrosion resistance of the Al-Li alloy treated with Sol-Gel only, without the primer and top coat cannot outperform to that of the CAA. This research contributes to the development of environmentally friendly surface treatments for Al-Li alloys, which can enhance their corrosion resistance and promote their utilization in aeronautical applications. The work performed within the frame of the European Research Project Clean Sky 2 ecoTECH
279 215 Plasma Enhanced Chemical Vapor Deposition of SiOxCyHz thin films for corrosion protection of metallic surfaces Farsari E1 , Voulgaris C1 , Amanatides E1 , Mataras D1 1Plasma Technology Laboratory, Department of Chemical Engineering, University Of Patras Plasma deposited SiOxCyHz films are widely used coatings in several sectors (microelectronics, food packaging, biomaterial science, corrosion resistive coatings) due to their special chemical, electrical and mechanical properties. Their structure, which may vary from inorganic silicon oxide to silicone – like materials, and therefore their applicability depends on the deposition process. Low pressure plasma enhanced chemical vapor deposition, atmospheric pressure dielectric barrier discharges and atmospheric pressure plasma jets using organosilicon compounds (e.g. TEOS, HMDSO, HMDNS ) as precursors have been proposed. For each process, parameters such as the precursor type, its mass flow and concentration, the presence of reactive gases as O2, the excitation frequency and the input power, affect both the chemical composition and the deposition rate of the coatings. In this work the plasma enhanced chemical vapor deposition of SiOxCyHz materials for the corrosion protection of metallic surfaces is examined. First, we investigate the low pressure deposition of silicon oxide-like coatings. The experiments were performed in a parallel plate capacitively coupled plasma reactor using TEOS /O2 mixtures. The effect of the RF power, the TEOS content and the total pressure on the deposition rate and the physicochemical properties of the coatings was examined. The deposition rate was determined in situ using Laser Reflectance Interferometry while FTIR spectroscopy and FSEM were used for the physicochemical characterization of the deposited coatings. Coatings resistance against corrosion was evaluated by applying Electrochemical Impedance Spectroscopy (EIS). Films deposited through high plasma power conditions, low pressure and high fraction of TEOS in O2, containing low amounts of carbon, present extremely good protection of aluminum surfaces from galvanic corrosion. However, substrates pretreatment is necessary in order to improve the coatings adhesion on the surfaces. Although the materials deposited through low pressure discharges exhibit satisfying properties against corrosion, the deposition rates are rather low (<180 nm/min). In an attempt to increase the deposition rate, an atmospheric pressure plasma jet was used in order to deposit SiOxCyHz. In this case HMDSO/ Ar mixtures were selected as precursors and the effect of process parameters on the deposition rate and the chemical composition of the coatings was examined. Preliminary results show that deposition rates up to 400 nm/min can be achieved while the carbon content of the coatings, as derived using FTIR spectroscopy, can be rather low. The low carbon content of the films makes them possible candidates as anti-corrosive coatings.
280 216 Modelling mechanically induced failure of PEO coated extruded magnesium Gazenbiller E1 , Konchakova N1 , Serdechnova M1 , Blawert C1 , Höche D1 , Zheludkevich M1,2 1 Institute of Surface Science, Helmholtz-zentrum Hereon, 2 Faculty of Engineering, Kiel University Plasma Electrolyte Oxidation (PEO) is an effective low-cost method which is utilized to create ceramic oxide coatings on Mg alloy surface in order to protect the material from corrosion and wear. The coating’s properties like its porosity and thickness can be adjusted by PEO experimental conditions. The presence of the coating has an impact on the mechanical properties of the Mg substrate, e.g. the tensile test response and critical damage strain. In this work, a FEM model of a PEO coated Mg alloy specimen in a slow-strain rate tensile test is established which allows to correlate the coating’s properties including the observed PEO crack spacing to the stress-strain response, damage initiation and critical specimen failure. This industrial relevant example could be used as a demonstration case for the development on the EMMC Translation concept and integration to the digital materials modeling environment like OntoTrans OTE or Open Innovation Platforms. We kindly appreciate the financial support of DFG (HO4478/6-2, OE558/20-2), OntoTrans (Grant Agreement No 862136) and VIPCOAT (Grant Agreement No 952903).
281 217 Interoperability of experimental and simulation data along production chains on the VIPCOAT Open Innovation Platform Konchakova N1 , Klein P2 , Visser P3 , Preisig H4 , Hagelien T5 1Helmholtz-zentrum Hereon, 2 Fraunhofer Institute for Industrial Mathematics, 3AkzoNobel, 4NTNU, 5 SINTEF The destructive effect of environmental exposure and corrosion-induced degradation often determine the service life of engineering structures. Organic coatings loaded with corrosion inhibitors and/or corrosion inhibiting pigments are the most common means to protect metallic structures. Leaching is the primary active protective mechanism of corrosion-inhibiting primers. These primers are loaded with sparingly soluble salts to provide a reservoir of corrosion-inhibiting ions. In case of a defect, the coating will absorb moisture, which triggers the dissolution of the corrosion inhibitor and its release into the defect. Developing new active protective coatings is a challenging and time- and resources-consuming experimental process. Numerical simulations of the diffusion processes can support and accelerate the development of protective coating formulations with optimal corrosion protection properties. This industrial example is one of four demonstration cases of the VIPCOAT Open Innovation Platform (OIP). The materials modelling of the protective coating behaviour at the platform covers multi-scale simulations using different software. The interrelated software and external platforms should be able to read and understand the experimentally and numerically generated data. Proper data documentation facilitates interoperability, management and reusability of materials data collected by different experimentalists, used and processed by modelling specialists, and transferred through digital environments like Open Innovation Platforms. The VIPCOAT project establishes an interoperable innovation framework focused on the modelling-supported development of novel green active protective coatings for Al surfaces used in the aerospace industry and assisting interoperability by using ontology tools. To provide targeted digital services for industrial end-users, an interoperable data & knowledge exchange is organized on the VIPCOAT OIP in a (semi-) automized manner. This contribution demonstrates an approach for engineering data documentation using experimental and modelling data for inhibitors leaching analysis as an example. The designed data catalogue facilitates the interoperable sharing of data resources among (industrial) organizations and researchers. Furthermore, the method handles the metadata description for many data formats used for modelling and decision support services. A best practice approach to data documentation for effective data management is demonstrated. Firstly, comprehensive cataloguing of data sources is performed, followed by metadata extraction. The resulting metadata is then mapped to standard vocabularies and ontological concepts, which form the core of a common language. This approach enhances the interoperability of data, enabling efficient sharing and
282 analysis. Furthermore, this approach ensures that data is well-organized and easily accessible, which is crucial for effective data management. Finally, emphasis is placed on the utilization of engineering data documentation, which benefits the scientific community and industry in damage prevention and failure prediction through-out a distributed production chain. Acknowledgment: VIPCOAT: H2020-NMBP-TO-IND-2020, Grant Agreement 952903.
283 218 How modelling can accelerate the design of active protective coatings? Zheludkevich M1 1Helmholtz Zentrum Hereon The destructive effect of environment and the corrosion induced degradation are the important problems which determine the service life of many metallic components. The application of organic coatings is the most common and cost effective method of improving protection and durability of metallic structures. However, the degradation processes develop faster after disruption of the protective barrier. Therefore, an active protection based on “self-healing” of defects in coatings is necessary to provide long-term effect. Combining relevant simulation methods and creating a digital twin covering the main aspects of design and performance of active protective coatings can be an effective way to accelerate development and acceptance of such coatings by industry. This paper will be based on a few examples how modelling can clarify the mechanistic details and how it can help to select efficient components for active protective coatings. The general approach of combining the complementary simulation tools for acceleration of coating development will be presented.
284 219 Numerical simulation of corrosion-induced damage on Al-Cu-Li 2198 alloy Louka E2 , Papanikos P2 , Margaritis M1 , Charalampidou C1 , Alexopoulos N1 1Research Unit of Advanced Materials, Department of Financial Engineering, University Of The Aegean, 2Department of Product and Systems Design Engineering, University of the Aegean The low density, increase mechanical properties, increased damage tolerance and corrosion resistance of wrought Al-Cu-Li alloys led to the replacement of the conventional aluminium alloys by them. Their complex precipitation hardening system, including δ (Al3Li), θ (Al2Cu), T1 (Al2CuLi) and S (Al2CuMg) phases, leads to improved hardness and strength properties. However, they may accelerate corrosion attack in these alloys due to the different microstructural characteristics of the Al - matrix and therefore increase their corrosion susceptibility. Thus, it is of major importance for the aviation industries to be able to predict the corrosion – induced degradation of these alloys. Corrosion damage was modeled both as surface notches and as pitting distribution of the deteriorated surface of AA2198-T8 of 3.2 mm nominal thickness. A three-dimensional parametric finite element model was developed using ANSYS to take as an input the size and shape (morphology) of the corrosion products. The model also considers the randomness of size and shape of the corroded products and the size of the hydrogen embrittled zone. The evolution of damage during loading is predicted using a progressive damage modelling scheme. The model can assess the residual mechanical properties of corroded structures and provide useful information concerning the mechanics of damage evolution from the deteriorated surface to the hydrogen embrittled zone and to the pristine material. The latter is enhanced with a fully parametric theoretical investigation with respect to the pitting damage and depth of hydrogen embrittlement as related to corrosion exposure time. Acknowledgements. The work has been financed by the Hellenic Foundation for Research and Innovation H.F.R.I.-Project ID 03385 Acronym CorLi-Corrosion susceptibility, degradation and protection of advanced AlLi aluminium alloys.
285 220 Investigation on the effect of artificial ageing kinetics on corrosion susceptibility of Al-Cu-Li 2198 alloy Zheludkevich M2 , Charalampidou C1 , Margaritis M1 , Alexopoulos N1 1Research Unit of Advanced Materials, Department of Financial Engineering, School of Engineering, University of the Aegean, 2 Institute of Surface Science, Hereon Helmholtz Zentrum The increasing demand in the aviation industry for continuous improvement in energy efficiency along with mechanical performance and damage tolerance, led to the development of lighter metallic structures. Third generation Al-Cu-Li alloys were developed to replace the conventional Al-Cu aluminum alloys, since they can offer approximately 5 % weight reduction of the structure as well as improved property balance and corrosion resistance. Their improved mechanical properties are often attributed to their precipitation hardening system, including δ (Al3Li), θ (Al2Cu), T1 (Al2CuLi) and S (Al2CuMg) second-phase precipitates. Nevertheless, these kinds of precipitates may influence the electrochemical behaviour of such alloys, due to the different electrochemical behaviour of the intermetallic phases and the matrix [1 , 2, 3], and consequently increase corrosion susceptibility. The size and population of such intermetallic phases alters significantly during natural ageing of the aluminum structures. For the simulation of the natural ageing of the aluminum structures, usually artificial ageing heat-treatment is performed in order to accelerate the thermos-mechanical transformations that have an immediate impact on the metallurgical structure, on the residual stress state and finally on the mechanical properties. Alloys from the 2xxx aluminum alloy series, e.g., 2024, was found to have higher corrosion resistance when artificially aged at certain tempers, such as T6, than at T3 [4]. Hence, it is of major importance to investigate the effect of artificial ageing on corrosion behaviour on the third generation Al-Cu-Li alloys. The material used was a wrought aluminum alloy 2198-T3 which was received in sheet form of 3.2 mm nominal thickness. Small rectangular specimens [10 mm x 20 mm] were machined from the sheets and then the specimens were exposed to artificial ageing heat-treatment for different ageing times; different ageing tempers were selected that corresponded to under-ageing (UA), peak-ageing (PA) and over-ageing (OA) tempers. Exposure of the specimens to 3.5 wt. % NaCl solution according to ASTM G44 specification was performed for different exposure times to investigate the effect of artificial ageing on the corrosion evolution. Electrochemical impedance spectroscopy as well as potentiodynamic polarization measurements were performed to identify the corrosion kinetics and simulate the corrosion-induced degradation mechanism. The results were correlated with the respective results from light optical microscopy investigations. Artificial ageing was found to affect the corrosion kinetics and corrosion-induced degradation mechanism of the investigated Al alloy, with the peak-aged specimens presented the highest corrosion resistance. [1] V. Guillaumin, G. Mankowski, Corrosion Science 41 (1999) 421-438. [2] A. Boag, A.E. Hughes, A.M. Glenn, T.H. Muster, Corrosion Science 53 (2011) 17–26.
286 [3] C. Blanc, B. Lavelle, G. Mankowski, Corrosion Science 39 (1997) 495-510. [4] L. Korb, D. Olson (Eds.), ASM Handbook: Corrosion, 13, 9th edition, ASM International, Metals Park, OH, USA, 1992.
287 221 The effect of artificial ageing kinetics on mechanical performance of Al-CuLi alloy AA2198 Birbilis N2 , Charalampidou C1 , Alexopoulos N1 1Research Unit of Advanced Materials, Department of Financial Engineering, School of Engineering, University of the Aegean, 2 Faculty of Science, Engineering and the Built Environment, Deakin University To achieve improved fuel efficiency and lower operating costs, the aerospace and aviation industries have adopted the use and development of third generation Al-Cu-Li alloys. Precipitation hardening is the major strengthening mechanism in these alloys, including the formation of δ (Al3Li), θ (Al2Cu), T1 (Al2CuLi) and S (Al2CuMg) type phases. T1 is considered to be the major strengthening phase in Al-Cu-Li alloys with Li content less than 2.0 wt. %. The precipitation of such intermetallic phases, which is significantly accelerated during artificial ageing, leads to an increase in the tensile properties (e.g., yield stress Rp, ultimate tensile strength Rm, and hardness, etc.), along with an attendant decrease in ductility due to the formation of strain fields that restrict dislocation movement [1]. For the simulation of naturally aged aluminum structures, artificial ageing (heat-treatment) is performed to accelerate the thermally induced phase transformations to achieve a balance of specific mechanical properties. However, the precise effect of intermetallic phases on mechanical properties, namely tensile behaviour, depends on several factors that includes the size, shape and population (density), of precipitates - all of which are influenced by the ageing time and temperature. It therefore remains important to investigate the artificial ageing kinetics on the microstructural transformations that occur within next generation Al-Cu-Li alloys. The material studied here was wrought aluminum alloy 2198-T3 which was received in sheet form of 3.2 mm nominal thickness. Small rectangular specimens (10 mm x 20 mm) were machined from the sheets and the specimens were exposed to isothermal artificial heat treatment for different holding times, to simulate different ageing tempers, namely under-ageing (UA), peak-ageing (PA) and over-ageing (OA). Quantitative microstructural analysis through light optical microscopy, SEM, TEM and EDX analysis was performed on the artificially aged specimens for the different tempers. The results show the quantitative characteristics of the precipitates for the above identified tempers of the alloy. Acknowledgements. The work has been financed by the Hellenic Foundation for Research and Innovation H.F.R.I.-Project ID 03385 Acronym CorLi-Corrosion susceptibility, degradation and protection of advanced AlLi aluminium alloys. [1] S. G. Epstein, J. G. Kaufman, P. Pollak, Aluminum and its alloys, Aluminum Association, Inc, Washington, D.C., 1994.
288 222 The effect of pre-stretching induced microstructural transformations on the corrosion behaviour of Al-Cu-Li 2198 alloy Mostert R1 , Pretorius C1 , Salojee M1 , Charalampidou C2 , Alexopoulos N2 , Kourkoulis S3 1Department of Material Sciences and Metallurgical Engineering, University Of Pretoria, 2Research Unit of Advanced Materials, Department of Financial Engineering, School of Engineering, University of the Aegean, 3 Lab of Testing and Materials, Department of Mechanics, National Technical University of Athens During the last decades, Al–Cu–Li alloys have a key role in the aerospace industry due to their lightweight characteristics, improved mechanical properties and damage tolerance characteristics. Nevertheless, they were found to be highly susceptible to intragranular, transgranular and exfoliation corrosion attack. The conventional manufacturing process of aerospace aluminium plates sheet includes stretching after solution heat treatment for homogenization of the residual stresses developed on quenching, during which the material is typically plastically strained between 2 and 5 % [1]. In 3rd generation Al-Cu-Li alloys, this stretching procedure enhances the optimum distribution of T1 precipitates, which is the main strengthening phase of these alloys as well as nucleation of the dislocations. It has been widely shown that a small prestretching level prior to artificial ageing produces a uniform distribution of dislocations within the matrix, which act as heterogeneous nucleation sites for the T1 second-phase precipitates [2,3]. Additionally, this stretching procedure was found to accelerate precipitation within the matrix, avoiding grain boundary precipitation which leads to a detrimental effect on toughness as well as to intergranular corrosion attack [4, 5]. The present work aims to examine the effect of tensile pre-stretching on a typical 3rd generation Al-Cu-Li alloy's ageing kinetics, microstructure evolution and subsequent corrosion susceptibility. The material used was a wrought aluminum alloy 2198-T8 which was received in sheet form of 3.2 mm nominal thickness. Tensile test coupons according to ASTM E8 were subjected to three (3) different prestretching levels and their microstructural characterization was performed with SEM, EDX and TEM analyses. The results showed that the grain size and the precipitates of the pre-stretched samples play a pivotal role on the corrosion susceptibility of the specimens. Acknowledgements. The work has been financed by the Hellenic Foundation for Research and Innovation H.F.R.I.-Project ID 03385 Acronym CorLi-Corrosion susceptibility, degradation and protection of advanced AlLi aluminium alloys. [1] J.W. Martin, Precipitation Hardening (1998), 2nd ed., Butterworth-Heinemann, Oxford. [2] B.M. Gable et al., J. Light Met. 1 (2001), 1-14. [3] W.A. Cassada et al., Metall. Trans. A 22 (1991), 299-306. [4] Y. Ma et al., Corros. Sci. 107 (2015), 41–48. [5] Y. Ma et al., Corros. Eng. Sci. Technol. 50 (2015), 420–424.
289 223 The effect of solution aggressiveness on the corrosion-induced degradation of Al-Cu-Li 2198 alloy Charalampidou M1 , Alexopoulos N1 , Zheludkevich M2 , Blawert C2 1Research Unit of Advanced Materials, Department of Financial Engineering, University Of The Aegean, 2 Institute of Surface Science, Hereon Helmholtz – Zentrum Geesthacht Improvement in energy efficiency and mechanical performance along with maintenance of damage tolerance in aviation industry led to the development of new, lighter metallic structures with improved mechanical properties. Third generation Al-Cu-Li alloys developed to replace the conventional aluminium alloys, since they can offer weight and energy savings as well as enhanced property balance and corrosion resistance. Their improved mechanical properties are attributed to their complex precipitation hardening system including δ (Al3Li), θ (Al2Cu), T1 (Al2CuLi) and S (Al2CuMg) phases. Nevertheless, these precipitates may influence the electrochemical behaviour of the alloys due to the different microstructural characteristics of the matrix and therefore increase their corrosion susceptibility. The material used in this study was a wrought aluminium alloy 2198-T8 which was received in sheet form of 3.2 mm nominal thickness. Exposure of the specimens to three different corrosive environments, e.g. exfoliation corrosion (EXCO), 3.5% wt. NaCl as well as Harrison’s solution were used according to specifications ASTM G34, ASTM G44 and ASTM D5894 respectively, in order to investigate the effect of solution aggressiveness on the corrosion-induced degradation mechanism. The corroded specimens were examined with light optical microscopy as well as with electrochemical techniques (e.g. electrochemical impedance spectroscopy – EIS and potentiodynamic polarization) in order to investigate the corrosion attack mechanism. It was found that the EXCO solution leads to higher degradation of corrosion resistance when compared against the other two solutions studied, especially for short exposure times. However, significant differences were found regarding the surface corrosion attack mechanism.
290 224 A Novel Non-Local Structural Health Monitoring Method for Real-time Crack Growth Analysis Ganjdoust F1 , Kefal A1 , Javili A2 1 Sabanci University, 2Bilkent University Crack monitoring is one of the critical problems encountered in the failure analysis of composite structures. Crack monitoring is studied by identifying the onset of crack opening and predicting the crack progression path. The inverse finite element method (iFEM) is a mesh-based shape-sensing approach and damage detection toolbox based on the minimization of a least-squares functional, which has proven to be an efficient structural health monitoring (SHM) approach. Because the domain must be discretized into elements for the iFEM to reconstruct the displacement field, this approach is susceptible to numerical errors. Specifically, in the case of crack monitoring problems, where the solution field is not smooth or has discontinuities, finding the solution to the differential equations will be challenging. In the present study, the governing differential equations of the iFEM are reformulated to integral equations using the peridynamic differential operator (PDDO) to mitigate this issue. PDDO is a non-local numerical approach developed to calculate various orders of differentiation of a given field. In this approach, every point has a domain of interaction referred to as its family. The value of the solution field and its derivatives at each point in the domain are evaluated through the non-local interactions of the points within their respective families. This article proposes a novel crack monitoring scheme by incorporating the PDDO within the iFEM framework, which captures the crack opening and predicts the crack growth path accurately. To show the capabilities of the present approach, two case studies have been presented herein. It is shown that applying the proposed methodology to these examples yields accurate predictions of the crack behavior. In addition, the numerical simulations are shown to be consistent with the reference solutions.
291 225 Development of novel multi-dimensional data fusion technique for evaluation of adhesive bonded joints using ultrasonic and X-ray radiographic non-destructive testing Bhat G1 , Yilmaz B1,2, Smagulova D1 , Cicėnas V 1 , Žukauskas E1 , Jasiuniene E1,3 1Prof. K. Baršauskas Ultrasound Research Institute, Kaunas University Of Technology, 51423, 2Acoustic and Electromagnetic Methods Division, Bundesanstalt für Materialforschung und -prüfung (BAM), 12205, 3Department of Electronics Engineering, Kaunas University of Technology, 51367 Non-destructive evaluation techniques have been extensively used to detect flaws in materials without damaging the component being investigated. Nevertheless, each NDE technique has distinct advantages and disadvantages that could eventually contribute to inaccurate results. The aim of this study is to develop multi-dimensional data fusion technique by incorporating data from ultrasonic and X-ray radiographic testing in order to increase the accuracy and reliability of defect detection in NDE. Two different specimens of aluminium single lap joint with brass inclusions and delamination were inspected using pulse-echo immersion ultrasonic testing and X-ray radiographic testing. Different features of peak-to-peak amplitude, attenuation, absolute energy, and frequency domain maximum amplitude were extracted from the ultrasonic results. Similarly, from the X-ray radiography results Harris corner detection, amplitude, fast corner detection, and Sobel edge detection were extracted. Then, the accuracy of the defect size estimation was evaluated in both the ultrasonic and X-ray radiography features. The results have demonstrated that the X-ray radiography outperforms the immersion ultrasonic testing in terms of defect sizing in aluminum lap joint having brass inclusions, while the immersion ultrasonic testing results have performed noticeably better than the X-ray radiography in delaminated aluminium single lap joint. Furthermore, the features of both ultrasonic and X-ray radiography were analyzed separately and then fused using weighted average, Hadamard product, Dempster-Shafer and pyramid saliency algorithms to obtain the most effective approach for defect assessment.
292 226 Monitoring of structures integrity in operation Chmelko V1 , Koščo T 1 Slovak University of Technology In general, the assessment of the strength and integrity of a structure requires knowledge of two sets of parameters: the material parameters under service conditions and the loading parameters of the structure. The most challenging task is the knowledge of all significant operational states under conditions that may be different from the design service. Thanks to advances in measurement and computing technology, it is possible to deploy increasingly accurate and complex monitoring systems directly in the operation of major structures. Pressure pipeline integrity monitoring systems will be presented that monitor pressure and fatigue safety of pipelines in service, as well as vibration safety. When corrosion wall loss is detected, the integrity of a pipeline with a weakened wall can also be monitored under certain assumptions. In the operation of cable-stayed bridges, the condition of the cables is a key factor in the serviceability of the bridge. The detection and monitoring of rope prestress during bridge operation will be discussed. Front panel of the monitoring system for the structure of the pipeline yard above the ground installed at the compressor station
293 227 Low-frequency air-coupled transducer based damage detection in composite materials Wandowski T1 , Kudela P1 , Radzienski M1 1 Institute of Fluid-Flow Machinery In this paper results of non-destructive testing (NDT) of composite panel is presented. The NDT method is based on guided wave propagation phenomenon. Non-contact elastic wave generation is based on low frequency air-coupled transducer (ACT). In this purpose resonant transducer with frequency 40 kHz is utilized. Utilisation of low frequency waves allows to reduce the effects of wave attenuation in composite material. Elastic wave sensing is based on scanning laser vibrometry what together with ACT utilization allows to perform full non-contact damage assessment process. Full wavefield measurement are performed. Damage localization is based on wavenumber irregularity mapping (WIM) algorithm. Moreover problem of acoustic to elastic wave conversion is investigated. In this research panel made of fibre reinforced polymer composite is investigated. Authors investigate simulated damage (Teflon inserts) and real damage (delamination).
294 228 Improved Damage Mapping with Hyperbola Approach for Guided Waves Based Structural Health Monitoring Using Fiber Bragg Grating sensors Soman R1 , Peters K2 , Wandowski T1 , Ostachowicz W1 1 Institute Of Fluid Flow Machinery, PAN, 2North Carolina State University Ultrasonic guided waves (GW) are commonly used in aerospace, civil, and mechanical industries for inspecting the health of a structure non-destructively. Traditionally the piezoelectric based actuators and sensors have been used for the actuation and sensing of GW. But due to the superior performance of fiber Bragg grating sensors (FBG) (immunity to electromagnetic noise, small size, low weight and ability to multiplex) their use is on an increase. The shortcomings of the FBG sensors include their directional sensitivity, passive nature and in some cases low sensitivity. The low sensitivity can be overcome by using the FBG sensors in so called remote configuration. There are several techniques that are used for damage mapping. The most commonly used in reflection based assessment domain are the ellipse based and hyperbola based approaches. In the previous work by the authors they have shown that the hyperbola approach for damage mapping has inherent benefits when it comes to using for FBG sensors in remote configurations. Hyperbola approach is based on the time difference of arrival (TDOA). The time in the arrival time for two sensors with a common actuator is used for obtaining the hyperbola. The superposition of these hyperbolas for all possible actuator and sensor pairs may be used for damage localization. The ellipse is a closed shape while a hyperbola is an open shape, so often the damage localization with the hyperbola approach may lead to false localization. But due to the benefits it offers for the sensors in the remote configuration improved implementations of the hyperbola approach are desired. In this paper a new improved hyperbola approach for damage mapping is proposed. In order to limit the number of hyperbolas to only those TDOAs for damage mapping a binary variable is introduced. So only the regions of the structure which match the time of arrival for the sensor actuator pairs and fulfill the locus of a point for the TDOA are mapped. This limits the number of hyperbolas which are identified as possible damage and improves the damage localization. The methodology is employed on a simple aluminum plate. The performance of the new approach is compared with the ellipse based and the original hyperbola based approach. The results indicate that indeed the hyperbola approach improves the localization. Also the computational load is reduced allowing more real time damage mapping.
295 229 RIMA network of Digital Innovation Hubs a tool to for the innovation in Inspection and Maintenance of infrastructures Leroux C1 , Mertz M 1Cea Regular inspections and maintenance of infrastructure and equipment are critical to the safe and efficient operation in many industrial sectors, such as oil & gas or transport infrastructure. Inspection and Maintenance (I&M) Robotics is a field that is experiencing rapid growth and that has a large potential to facilitate faster, safer and cheaper operations. It can be challenging for end users of the robotics solutions to follow along the technological development in order to select the best solutions to pursue, and it can be equally challenging for technology providers to gain trust with their potential customers. The creation of networks of Digital Innovation Hubs (DIHs) is an approach used by the European Union to help European companies to handle digital challenges in a dynamic way and thus to become more competitive. This work summarizes the current status and progress made in the DIH network Robotics for Inspection and Maintenance (RIMA) with respect to establishing and developing market services for the network and DIHs in general, including sharing some best practices and ideas for making the services sustainable.
296 230 Implementation of a Robotic Mobile Manipulator moving a NDT probe inside Steel Cylinder Concrete Pipes for Corrosion Assessment Lucet E1 , Kfoury F1 , Si Larbi L1 1Université Paris-Saclay, CEA List One of ACES European research project (grant agreement n°900012) objectives is to assess the corrosion of steel cylinder concrete pipes (SCCP). Such pipes, used to carry chloride contaminated water from nuclear power plants, are made waterproof with a steel liner incorporated between 2 cylindrical layers of concrete. This steel liner is subject to corrosion damages due to chlorides, and inspection from inside the pipe is essential for detecting corroded zones in early stages, before waterproofing is compromised. Until now, non-destructive techniques (NDT) are applied manually against the pipe concrete inner wall. This is a long and tedious procedure in narrow pipes between 600mm and 1000mm internal diameter, hence the interest to automate it. The specificities of this task, as well as a state of the art of existing robotic solutions, first led us to propose the design of a teleoperated robotic mobile manipulator solution that is fully adapted without being too complex and expensive. This article then focuses on the realization, the deployment and the experimental assessment of such a solution in a realistic environment. We present the CAD and mechanical prototype developed to meet the measurement constraints related to the use of two types of NDT probes, namely potential mapping (PM) and galvanostatic pulse (GP), in SCCP environment. The software architecture is deployed on the embedded controllers of the mobile base and of the manipulator, in order to ensure the supervision of the whole system movements. An open source robotic middleware (ROS) is used for the mobile platform controller, and a software solution developed internally at CEA (Cortex) is used to control the manipulator. A communication architecture is implemented between the two controllers and a third remote computer ensuring the remote operation and the monitoring of on-board sensors (cameras, IMU and Lidar). A navigation strategy dedicated to posture control of the mobile platform is exposed and experimented. Then, measurement process functionalities are implemented and evaluated in a real SCCP. Finally, the performance of the robotic solution is evaluated and future improvement for operating on other pipe configurations are discussed.
297 CAD front view of the robotic mobile manipulator operating inside a 600mm pipe
298 231 Combining Thick and Thin Film Sensor Manufacturing Techniques for Realization of Smart Components via High and Low Pressure Die Casting Lehmhus D1 , Cen M2 , Struss A1 , de Rijk T2 , Pille C1 , Klatt A2 , Lang W2 1 Fraunhofer Institute for Manufacturing Technology and Advanced Materials IFAM, 2 Institute for Microsensors, -actuators and -systems IMSAS, University of Bremen Objectives: Recent developments like autonomous driving have increased the interest of the automotive industry in structural health and condition monitoring of safety-relevant components often manufactured via High or Low Pressure Die Casting (HPDC, LPDC). Specifically the latter process is important in this field as the improved quality of castings produced facilitates T6 heat treatments aimed at optimizing the components‘ mechanical performance. The specific challenge associated with this approach is that it adds a further, potentially critical thermal load which may compromise the characteristics of the integrated sensor: Typical T6 heat treatments include a solution heat treatment step performed only slightly below the solidus temperature of typical AlSiMg casting alloys, while lasting several hours and thus providing ample time for diffusion within the sensor build-up. Methods: The present study compares results obtained in HPDC and LPDC on thick film and hybrid thick/thin film sensor systems prepared by means of screen printing and, in the case of the hybrid variant, PlasmaEnhanced Chemical as well as Physical Vapour Deposition (PECVD, PVD) on Aluminum substrates. The response of the sensor systems to the thermal loads associated with the casting process is evaluated both in model as well as actual casting experiments and matched with process simulation data gained from the MAGMASOFT® casting simulation software package. Results: The focus is on the influence on general properties of the piezoresistive sensors as well as on their response to thermal and mechanical stimuli. The results show that in contrast to HPDC, in the case of LPDC, which is often combined with T6 heat treatments, specifically the extended solution heat treatment (SHT) process is critical, as it induces interdiffusion and grain growth processes between and within individual layers of the build-up (insulation, adhesion-promoting and actual sensor layer) which in the worst case can lead to trenching phenomena in the Pt sensor layer that adversely affect the properties of the sensor, increasing its apparent resistance by several orders of magnitude [2]. The respective trends have been studied via resistance measurements on samples subjected to casting and stepwise SHT temperature profiles, accompanied by SEM imaging and XPS measurements, the latter aimed at quantifying interdiffusion effects. The sensitivity of these sensors, i. e. their response to (a) change of temperature and (b) mechanical strain, have also been investigated. Conclusion: Further scrutiny of the respective processes showed that a thickness increase of the sensor layer from approximately 100 to 350 nm effectively limits these phenomena. An adaptation of solution heat treatment parameters towards shorter times of exposure to the aforementioned temperature levels may even cancel out the degrading effects completely, yielding sensors suitable for integration in both HPDC and LPDC processes.
299 [1] Lehmhus, D.; Rahn, T.; Pille, C.; Busse, M. Integrating Electronic Components, Sensors and Actuators in Cast Metal Components: An Overview of the State of the Art. Springer Lecture Notes in Networks and Systems 546 (2023) 350-361. [2] Schmid, U.; Seidel, H. Effect of high temperature annealing on the electrical performance of titanium/platinum thin films. Thin Solid Films 516 (2008) 898-906. General layout of the of the hybdrid sensor system combining screen printed, thick film technology-based insulating layers and conductive paths with the actual sensor produced via physical vapour deposition (PVD). Surface appearance of the 350 nm Pt sensor layer in as manufactured (pristine) state and after simulated casting and heat treatment (images taken on sample without top insulation).