50 39 Multiscale damage modelling for variable-angle filament-wound composites Christoff B1 , Almeida Jr H2 , Guedes R3 , Tita V1,3 1 São Carlos School of Engineering, University of São Paulo, 2Queen's University Belfast, 3 Faculty of Engineering of the University of Porto In most engineering applications, composite structures are traditionally manufactured by stacking unidirectional layers in different orientations to obtain a quasi-isotropic behaviour, or by laying straight fibres following conventional angles such 0°,±45°, and 90°. In this kind of design, desired properties are achieved by tailoring the sequence of the laminate. This conventional approach, however, does not fully exploit the anisotropic nature of the laminates. One way to improve the performance of fibre-reinforced composites is by varying the fibre angle piecewise within the ply level, generating the so-called variable stiffness (VS) composites. Such a concept has been systematically used to optimise composite cylinders, mainly based on the manufacturing characteristics of the automated fibre placement (AFP) method. However, AFP does not have a high productivity rate and the minimum fibre steering angle is too high (usually higher than 600 mm), which limits the scope for optimisations. Filament winding (FW) is a wellestablished manufacturing technique to produce composite structures, such as cylinders, tubes, and pressure vessels. Recently, our research group was the first one ever to attempt manufacturing composite cylinders using the VS concept, therein named variable-angle filament-wound (VAFW) composites. The present work aims to give a step further by developing, for the first time, a multiscale damage model accounting for manufacturing-induced imperfections (e.g., resin pockets, fibre gaps and overlaps) intrinsic to VAFW composite cylinders. A micromechanical approach based on the Asymptotic Homogenization Method (AHM) is considered to obtain the effective properties of the VAFW composite, and the patterns of manufacturing defects are obtained via a micro-CT scan. The numerical analyses of the representative volume element (RVE) can then be used to estimate the effect of the manufacturing defects on the effective properties of de VAFW structure. The AHM is considered to obtain the effective properties of the media. The concept of RVE is used to describe a heterogeneous media, i.e., there is a small portion of the domain that repeats itself in a pattern describing the domain. An anisotropic and quasi-periodic elastic body is considered, and the problem is formulated in the bounded subset Ω^ε∈R^3. Two scales are used to depict the media, one at the microscopic level (RVE) and another at the macroscopic level, in which the media is considered a homogeneous and anisotropic body. In Figure 1, different regions within the elastic body are depicted, representing three different regions of the VAFW composite. The first region represents an intact material, the second region represents a region with damaged fibres and the third is a resin-rich region. Microscale analyses using the micro-CT technique in the transversal sections of a VAFW sample taken from a cylinder manufactured via FW are carried out to identify resin pockets, as shows Figure 2. Based on the micro-CT scans, an RVE will be defined. Both deterministic and stochastic analyses are considered to obtain the effective properties of the media.
51 The proposed multiscale approach Resin pockets
52 40 Probabilistic simulation methods in micromechanical modeling of fiberreinforced composites Lubritz J1 1Technical University Of Berlin The design and approval of fiber reinforced composites (FRC) in aircraft construction follow the basic principle of determining permissible characteristic material values which prevent failure within a specified probability. The current approach combines conservative material properties with emprical safety factors and thus leads to a safe design philosophy, which, however, only partialy exploits the lightweight construction potential of FRC. In addition, due to the anisotropic material behavior of FRC multiple material tests have to be performed for complete material characterization. However, the properties determined in this common approach only apply to the manufacturing parameters of the underlying sample series. Production-related deviations of the material properties, for example concerning the fiber volume content and ondulations, cannot be taken into account properly. In order to determine reliable stochastic indicators that can describe these scatters, complex material tests with very large sample sizes are necessary. Therefore, the aim of this work is to develop an approach to calculate stochastic parameters and distributions of FRP with analytical, micro-mechanical material models of FRC using probabilistic simulation methods to reduce the experimental effort. The basic material behavior is described with an existing micromechanical material model, in which macroscopic load conditions are converted into local stresses and strains of the individual components. The macroscopic material behavior is thus described with physically derived parameters that characterize the behavior of the constituents. First, sensitivity analyses were performed to identify the most important input parameters of the model. For these parameters, distribution functions were determined that describe the stochastic scattering. Subsequently, analytical Monte-Carlo-Simulations were performed, taking into account the scatter of the input parameters (micro-level material behavior) to generate scatter of the model output (macroscopic material parameters of the composite). Furthermore, the micromechanical material model was implemented into the finite element software ANSYS using a user-defined material model (USERMAT). Additional numerical Monte-Carlo-Simulations were performed to determine equivalent stochastic distributions of the material parameters. The analytical and numerical results were compared with stochastic characteristic values determined experimentally from material tests. The presented method was performed with a representative laminat manufactured from Out-of-OutoclavePrepreg. It can be shown that the presented method is suitable to predict the relevant material parameters of the investigated laminate. Furthermore, distribution functions for the description of the stochastic scatter could be determined analytically as well as numerically for selected material parameters of the laminate and validated with experimental values. The work contributes to show approaches how the currently deterministic material qualification in the verification of aerospace components can be supported by a simulation-based digital verification. The presented analytical method has the potential to reduce the material tests necessary for the determination of reliable stochastic values on coupon level and thus to lead to considerable cost and time savings.
53 Furthermore, the presented numerical method helps to increase the validity of numerical material simulations of FRC structures by taking into account the manufacturing-related deviations at the micro-level. Stress-strain curve from a single simulation for 0°-tension test Results of Monte-Carlo-Simulation for 0°-tension test (100.000 simulation runs)
54 41 Design Optimization of an Aircraft Canopy against Bird Strike Tezel M1,2, Özkan Ö1 , Acar E1 1Tobb University Of Economics And Technology, 2Rosetsan Missile Industries The collision of aircraft and birds affects flight safety, causes financial losses and loss of lives. Aviation authorities such as the Federal Aviation Administration (FAA) and the European Aviation Safety Agency (EASA) published regulations to reduce the effects of accidents and ensure flight safety. According to crash reports and statistics, windshield, radome, engine, wings and empennage are the areas damaged by birds. FAA has reported a total of 222,753 bird ingestion accidents during the period of 1990–2018 [1]. To ensure that the aircraft structures are resistant to bird strikes, experimental tests are carried out on the aircraft structural parts most affected by the impact. The repetition of experimental testing, the reproduction of leading edge structure and development of designed parts are costly and time-consuming processes. Therefore, numerical simulations (e.g., finite element analyses) are used to analyse bird strike problem. In this paper, design optimization of a design optimization of an aircraft canopy is performed against bird strike square. The canopy consists of five layers of polycarbonate and PVB material. The mass of the bird is 1.8 kg, and it impact the canopy with a velocity of 155 m/s, following EASA CS-25 certification standard. The impact problem is modelled with finite element method using LS-DYNA software. The constructed finite element model is validated by using the experimental data available in literature [2, 3]. In optimization, design variables are selected as the thickness values of each layer of the canopy. A surrogate based optimization is conducted, where response surface and Kriging models are used. Starting from an initial design, the weight of the canopy is minimized such that the panel deformation of the optimized design does not exceed that of the initial design. Our preliminary results showed that the canopy weight can be reduced by 2.5%, without jeopardizing the canopy deformation. This study is supported by the Scientific and Technological Research Council of Türkiye (TÜBİTAK) project no. 20AG027 under program no. 20AG001. References [1] J. Li, Y. Lou, X. Chai, Z. Ma and X. Jin, “Numerical Simulation of Bird Strike on Jet Engine Considering Bird Ingestion Requirements,” Journal of Aircraft, published online, 1-13, 2021, DOI: 10.2514/1.C036076. [2] Q.H. Shah and Y.A. Abakr, “Effect of distance from the support on the penetration mechanism of clamped circular polycarbonate armor plates,” International Journal of Impact Engineering, vol. 35, no. 11, pp. 1244-1250, 2008. [3] M.A. Lavoie, A. Gakwaya, M.N. Ensan, D.G. Zimcik, and D. Nandlall, D. (2009). Bird's substitute tests results and evaluation of available numerical methods. International Journal of Impact Engineering, vol. 36, no. 10-11, pp. 1276-1287, 2009.
55 42 Investigation of conduction welded thermoplastic composite joints in Mode-I and Mode-II loading conditions Fotopoulos K1 , Valilis S2 , Lampeas G1 , Tijs B3 1Athena Research Center, Industrial Systems Institute, 2 Laboratory of Technology and Strength of Materials, Mechanical Engineering and Aeronautics Department, University of Patras, 3 Fokker/GKN Aerospace The use of thermoplastic composites in aeronautical and aerospace structures has been increasing in recent years. The connection of different parts manufactured by thermoplastic materials is usually achieved by the use of mechanical fasteners or adhesives. A novel method of joining thermoplastic composites by using welding is considered as an emerging approach towards reducing the weight and cost of aircraft components. In the present work, an investigation of conduction welded joints subjected to Mode-I and Mode-II loading conditions is presented. An experimental procedure is executed, in order to investigate the behaviour of conduction welded joints under Mode-I and Mode-II loading conditions. Two types of specimens are tested, namely, Double Cantilever Beam (DCB) and End-Notched Flexure (ENF) specimens, subjected to quasi-static and fatigue loading conditions, in order to examine the failure behaviour of conduction welded joints. The investigation extends to the development of appropriate numerical models for the prediction of the mechanical behaviour of components manufactured by thermoplastic composites, joined using conduction welding techniques. Numerical models for DCB and ENF specimens under Mode-I and Mode-II loading conditions are developed using Finite Element (FE) analysis. Several of the principal approaches for numerical prediction of delamination are based on a Fracture Mechanics foundation. Among the different numerical models that have been proposed for delamination prediction, the Cohesive Zone Model (CZM) has been extensively applied due to the accuracy and efficiency it presents. The accurate definition of all parameters that are relevant to delamination initiation and propagation is an intricate task, in order to establish a reliable numerical prediction. In the present work, a finite element numerical analysis approach for simulation of thermoplastic composites is developed, with emphasis on interlaminar damage prediction. The CZM approach is used for the simulation of conduction welded joints and the predictive capabilities of the numerical methodology are validated through comparison with the respective experimental results. The accuracy and computational efficiency of the developed modelling approach is thoroughly investigated and evaluated, with emphasis on the future application of the developed methodology to medium-to-large-scale structures. Acknowledgements: This research work was supported by the Clean Sky 2 programme “Development of a multipurpose test rig and validation of an innovative rotorcraft vertical tail”, with the acronym TAILTEST [TAILTEST no. 865123]; a joint undertaking under the European Union’s Horizon 2020 research.
56 43 Reliable material characterization for crashworthiness simulations of unidirectional composite laminates Falaschetti M1 , Zavatta N1 , Rondina F1 , Troiani E1 , Donati L1 1University Of Bologna Introduction Crashworthiness is the ability of a structure to protect its occupants by absorbing the energy of an impact. This is particularly important for both ground and airborne vehicles. In the last decades, composite materials have been widely used in crashworthy structures due to their favorable Specific Energy Absorption (SEA). Moreover, composite materials allow the tailoring of the component properties, e.g. changing resin and fiber materials, laminate stacking sequence, component geometry, trigger geometry, etc. Numerical simulations have proved to be a valid tool to assess the effects of these parameters, reducing the need for experimental campaigns which are usually costly and time-consuming. Nevertheless, material calibration is a critical step in the implementation of numerical simulations. Many different modeling methods have been implemented depending on the overall size of the model and the finite element discretization length scale. Detailed analyses are used when it is necessary to study the crush failure event, while simplified approaches allow the comparison of several scenarios in a short time. Depending on the adopted strategy, it is possible to implement damage models that can simulate the component behavior under impact conditions: Progressive Failure Models (PFM) adopt traditional failure criteria in combination with an algorithm for element elimination, Continuum Damage Models (CDM) simulate the material softening through internal variables to deteriorate the mechanical properties, Nonlocal Damage Models (NDM) treat cracks and separation of crack planes with cohesive formulation, by smearing their effect across the finite element. ESI Virtual Performance Solution software employs two damage models: a continuum damage model developed by Ladevèze (LV), and a non-local damage model implemented by Waas-Pineda (WP). Methods and Results In this paper, the authors focus on the implementation of LV and WP models. A thorough report of the experimental tests and the required data processing is presented for the unidirectional composite materials. Numerical parameters are obtained by direct comparison of the experimental standard characterization tests, as well as peculiar Compact Tension and Compact Compression tests, with numerical simulation results. Reliable calibration methods are proposed for both LV and WP models: in the first case, an iterative process is needed to obtain a reliable numerical result, while a more straightforward method can be implemented for WP. Finally, the advantages and disadvantages of both models are outlined: in particular, due to the characteristics of the crushing tests, LV shows difficulties maintaining a stable solution while WP, implementing a bilinear softening, results in a more stable dynamic solution. Conclusion The optimization of composite crashworthy components has emphasized the importance of numerical methods to study different scenarios. A reliable calibration procedure was proposed for the Ladevèze and Waas-Pineda models implemented in ESI Virtual Performance Solution software.
57 44 Assessing the prediction uncertainty of Puck failure criterion for unidirectional composite laminates using interval analysis Anagnostopoulou A1 , Sotiropoulos D2 , Tserpes K1 1Department of Mechanical Engineering & Aeronautics, University Of Patras, 2Department of Electrical Engineeering, University of the Peloponnese In this work, an interval-based method developed previously by the authors was employed to assess the uncertainty in the failure analysis of the widely used Puck criteria for composite unidirectional (UD) laminates. Initially, the mechanical properties of the UD lamina were derived using simplified micromechanical equations. For the input properties of the matrix and the fibers, a realistic uncertainty range from 5% to 15% obtained from experimental results was used. The global minimum and maximum values of the mechanical properties were computed using an interval branch-and-bound algorithm. The computed uncertainty for the mechanical properties of the composite lamina ranges from 6.99% to 21.68%. Secondly, interval arithmetic operations were used to evaluate the uncertainty in the Puck-type failure criteria in a closed form. Using the closed-form uncertainties of intervals and sets of stresses obtained by finite element analysis, the uncertainty in the failure predictions was quantified for a graphite/epoxy composite laminate for the loading cases of tension and bending. To evaluate the uncertainty effect on the efficiency of failure criteria, a probability of failure function was used. Α comparison of Puck and Hashin failure criteria that focus in terms of the uncertainty in their performance was also performed for specific failure modes.
58 45 Experimental verification of PEKK stiffened panel under compression Růžek R1 , Karkulín A1 , Šedek J1 1Czech Aerospace Research Centre The paper presents the experimental strain and stress analysis of a thermoplastic composite stiffened panel subjected to compression load. The panel has five stringers with a non-symmetric design, with an artificial crack at the middle stringer interface and is made from a fast-crystallizing polyetherketoneketone (PEKK) carbon composite. The experimental strain and stress analysis is based on digital image correlation, and strain gauges measurements and LVDT sensors. The crack subcritical extension was defined and analyzed. The results show that crack propagation starts early after buckling development at around two thirds of the failure load. The crack growth behaviour is influenced by the buckling shape, which consists of two main modes (with three and four half-waves) in longitudinal direction in each bay. Numerical evaluation is presented and compared with experimental data. Good agreement between experimental and numerical solutions have been achieved. Typical image of the stiffened panel with four half wave buckling shape
59 46 Fatigue behaviour of 10% wt. short glass fibre reinforced recycled Polypropylene with mineral filler in presence of notches Coppola F1 , Ricotta M1 , Garilli M2 , Fabbro L2 , Azzalin I3 , Meneghetti G1 1University of Padova, 2Group Technology Organization, Electrolux Italy S.P.A, 3Consumer Experience, Care Architecture, Electrolux Italy S.P.A Aim This paper presents an experimental investigation of the fatigue behaviour of notched and unnotched specimens made of 10% wt. short glass fibre reinforced recycled Polypropylene with mineral filler. Then, an energy-based approach is proposed for the assessment of fatigue life spent for the crack nucleation. The model is based on the actual damage evolution observed during the fatigue tests: the initiation of a macro crack is caused by damage accumulation in the matrix. Thus, the strain energy density evaluated in the matrix and averaged on a structural volume embracing the notch tip is suggested as fatigue damage index to correlate in a single scatter band the fatigue data of unnotched and notched specimens. To take into account the actual fibre orientation, the structural finite element analyses for the evaluation of the strain energy density in the matrix are coupled with the numerical simulation of the manufacturing process, which is supported by tomographic analyses carried out on the moulded specimens. Methods Net-shape unnotched and V-notched specimens (with notch radius ρ ranging from 0.07 mm to 10 mm) were produced by injection moulding, according to the geometries shown in Figure 1 and they were tested under tension-tension fatigue (load ratio R=0.05). During the fatigue tests, the damage evolution was monitored using a traveling microscope to define the number of cycles spent to nucleate a 0.2-mm-long crack. The fracture surfaces were analysed both at the macroscopic and microscopic level, to investigate the analogies and differences existing between unnotched and notched specimens. Results The fatigue tests were reanalysed in terms of net-section stress amplitude, σa,n, and the stress-life curves for each specimen’s geometry were defined. Some preliminary results relevant to unnotched and severely notched specimens (ρ=0.07 mm) are reported in Figure 2, in terms of number of cycles to the technical crack initiation, Ni. Moreover, the figure shows the results of the statistical analysis assuming a log-normal distribution of the number of cycles to crack initiation and constant scatter for each applied stress amplitude σa,n. Figure 2 reports the fatigue curves for 50%, 10% and 90% survival probabilities with a confidence level of 95%. The figure reports also the inverse slope k of the curves and scatter index Tσ= σa,n,10%/σa,n,90%. Conclusion In this paper the fatigue behaviour of 10% wt. short glass fibre reinforced and recycled Polypropylene specimens filled with mineral filler is investigated, emphasising the material notch sensitivity. In view of this, tension-tension fatigue tests were carried out and the fatigue results were reanalysed in single scatter bands in terms of the strain energy density evaluated in the matrix and averaged on a structural volume embracing the notch tip.
60 Figure 1. Geometry of the tested specimens. Specimen thickness, t=1.80 mm. Figure 2. Fatigue data analysed in terms of net-section stress amplitude.
61 47 Mechanical characterizations on biobased FMLs, being developed for battery boxes, before and after ageing in salt spray chambers Mingazzini C1 , Leoni E1 , Bassi S2 , Delise T1 , Scafe' M1 , De Aloysio G3 , Laghi L3 , Falleti G4,5 1ENEA-SSPT-PROMAS-TEMAF, 2Pisa University. Department of Civil and Industrial Engineering, 3Certimac, 4NANOPROM CHEMICALS srl Societa' Benefit, 5NALUCOAT srl Societa' Benefit Objectives FENICE (upscaling, KAVA9, EIT RawMaterials, www.fenice-composites.eu, 2022-2025) is a EU project, funded with over 2.5 million and aiming at TRL 7, focusing on the topic of fire resistance of battery boxes. FENICE is devoting to current lithium-based modules, trying to cope the potential risks of an increased use in mass production. CERTIMAC is in charge of performing the accelerated ageing tests, to achieve basic data about durability for materials being considered for battery box development. ENEA is developing Fiber Metal Laminates, which seem one of the most effective and sustainable solutions, capable to combine recyclable or biobased resins, with high fire resistance. Anyway, proper aluminium surface finishing is needed, otherwise automotive tests, such as salty spray chamber ageing, cannot be passed. Traditional surface finishing cannot guarantee aluminium proper corrosion and fire protection, without compromising aluminium recyclability, but the project is studying surface vitrification with sol-gel formulations. These advanced treatments were, up to now, not compatible with the adoption in the mass production, but things are changing, following the green transition that is currently bringing a number of small revolutions in the manufacturing sector. Methods Mechanical characterisation of biobased FMLs, in terms of tensile strength, was carried out in accordance with the international standard ASTM D 3039, before and after accelerated ageing test in salt spray chamber. Results The considered surface finishing proved its efficacy in preventing FML degradation in salt spray chamber. Reduced corrosion but also reduced delamination were observed. Conclusions The considered FML can pass basic automotive requirements thank to a thin-film surface finishing, pretty promising for the automotive applications. It’s application on battery boxes will be further enquired in FENICE.
62 48 Thermophysical characterization of innovative and recyclable composites, being developed and considered for battery boxes mass production De Aloysio G1 , Morganti M1 , Laghi L1 , Ghetti L1 , Mingazzini C2 , Bassi S3 , Delise T2 , Leoni E2 1Certimac soc.cons. ar.l., 2ENEA- SSPT- PROMAS - TEMAF, 3University of Pisa,Department of Civil and Industrial Engeneering Objective FENICE (upscaling, KAVA9, EIT RawMaterials, www.fenice-composites.eu, 2022-2025) is a EU project, funded with over 2.5 million and aiming at TRL 7, focusing on fire resistance of battery boxes. FENICE is aimed at improving the materials for current lithium-based modules, trying to cope with the potential risks of an increased use in mass production. The main aim of contribution is to present the preliminary thermophysical characterizations carried out within FENICE. CERTIMAC conducts the thermophysical characterization to collect basic data needed for thermophysical modeling and simulations. The data and simulations are essential both “in use phase” (rapid charge discharge and need to dissipate excessive heat) and “fire accidents” (where thermal insulation opposes fire propagation and possible chain reactions). Firstly, the presentation will allow identifying the international standards and analyze basic characterisation techniques. Secondly, an overview of the solutions considered in Fenice will be provided The basic data are essential to design “safe” multimaterial solutions for both battery boxes and cell spacers. Methods The analyses were conducted through the Light Flash Analysis in the temperature range between room temperature and 500 ° C and allowed determining a complete set of parameters, namely thermal diffusivity, specific heat, thermal conductivity and thermal emissivity. Results Firstly, the thermophysical analysis was performed on basalt based FML polyfurfuryl alcohol (PFA) resin+Al circular samples, with an average thickness of 0.77 mm and a density of about 1.75 g/cm3. The thermal diffusivity showed an almost linear decreasing trend depending on temperature, while the specific heat capacity shows a parabolic one. The thermal conductivity trend is provided by the combination of the previous two parameters and the density. Conclusion The next steps will consist in conducting further analyses also on basalt based FML produced starting from Crosspreg ®, an hybrid epoxy-polyester modified resin, to characterize both types of FML and compare the performances of both the solutions developed within FENICE.
63 49 Chemical recovery of carbon fibers from composites via plasma assisted solvolysis Marinis D1 , Farsari E1 , Amanatides E1 , Mataras D1 1Plasma Technology Laboratory, Department of Chemical Engineering, University of Patras Carbon fiber-reinforced epoxy resin composites (CFRCs) have been widely used in modern industrial applications because of their excellent mechanical properties. The increase in the usage of CFRCs has led to the production of significant amount of waste. This has become a global issue because valuable fibers end up in landfill. Composites that have reached their end of life must be cost-effectively recycled without causing negative environmental impact [1], [2]. Solvolysis, using reactive solvents which can selectively break resin bonds and cross-linked network, has been regarded as one of the most promising recycling methods. The most common oxidation method to recover the fibers is to use oxidants such as nitric acid, oxygen, hydrogen peroxide and peracetic acid. The epoxy resin could be degraded completely, due to the breakage of the C―N bonds [3].The main advantages of this technique are the high fraction of recovered fibers and their excellent mechanical properties. On the other hand, the main disadvantages are (a) the high processing time (many hours) and (b) the produced wastes. In order to overcome these problems, the current work is focused on plasma assisted solvolysis as an alternative method for CFRCs recycling. Plasma generation in contact or inside liquids leads to the formation of highly reactive oxidants, production of UV radiation and strong shock waves that speed up the dissolution of the composites [4].The method was applied for the dissolution of CFRC’s of different masses, sizes and shapes and the effect of plasma parameters and plasma geometry on CF’s recovery rate was investigated. Scanning Electron Microscopy was used to monitor the surface of the recovered fibers and single fiber mechanical testing according to ASTM D3379 was implemented to measure the tensile strength and Young’s modulus of the fibers. The method effectiveness is discussed in terms of the measured recycling rates, the amount of wastes that are produced and fibers quality. References [1] E. Pakdel, S. Kashi, R. Varley, and X. Wang, “Recent progress in recycling carbon fibre reinforced composites and dry carbon fibre wastes,” Resour Conserv Recycl, vol. 166, p. 105340, Mar. 2021, doi: 10.1016/J.RESCONREC.2020.105340. [2] S. Karuppannan Gopalraj and T. Kärki, “A review on the recycling of waste carbon fibre/glass fibrereinforced composites: fibre recovery, properties and life-cycle analysis,” SN Appl Sci, vol. 2, no. 3, pp. 1–21, Mar. 2020, doi: 10.1007/S42452-020-2195-4/TABLES/5. [3] T. Liu, L. Shao, B. Zhao, Y. C. Chang, and J. Zhang, “Progress in Chemical Recycling of Carbon Fiber Reinforced Epoxy Composites,” Macromol Rapid Commun, vol. 43, no. 23, p. 2200538, Dec. 2022, doi: 10.1002/MARC.202200538. [4] P. Vanraes and A. Bogaerts, “Plasma physics of liquids—A focused review,” Appl Phys Rev, vol. 5, no. 3, p. 031103, Sep. 2018, doi: 10.1063/1.5020511.
64 50 DEVELOPMENT OF WATER-BASED INORGANIC MATRICES FOR THE PREIMPREGNATION OF FIRE-RESISTANT LAMINATED COMPOSITES Natali Murri A1 , Papa E1 , Landi E1 , Mingazzini C2 , Medri V1 1CNR-ISSMC, 2ENEA-TEMAF The demand for safe materials to be used in electric vehicles (EVs), and particularly for battery boxes, has been growing fast in the last years especially owing to safety concerns and fire prevention initiatives. At the same time, given the enormous volume of materials involved, the need to limit the economic and environmental costs of the components used in EVs is directing a large part of scientific research towards sustainable solutions, in line with the principles of the circular economy. Therefore, to guarantee an optimal combination between the thermo-mechanical performances that the battery boxes require, and the use of materials and technologies non-invasive for the environment, new composite materials have been developed, based on carbon fiber and water-based inorganic polymeric matrices. These inorganic matrices are formulated starting from aqueous mixtures of aluminosilicate clay powders and amorphous silica, which are chemically activated at room temperature by alkaline solutions of potassium silicates and hydroxides (geopolymerization process). Refractory micro-powders of oxidic ceramics have been added to further functionalize the material and enhance its thermal stability. The result is a slurry with rheological properties in the fresh state perfectly compatible with vacuum impregnation and lamination processes used for the production of traditional composites (FRPs), but at the same time with excellent resistance properties at high temperatures (>750°C) and completely fire resistant. However, a limit in the applicability of this solution on an industrial scale can be given by the limited shelf time of the resin, which can become an important constraint for the rapid mass-production of components. For this purpose, within the "FENICE - Fire rEsistant eNvironmental frIendly CompositEs" project, mixtures specifically designed to be used for the production of pre-impregnated laminates have been studied and tested, and different curing and storage conditions have been investigated. Preliminary results showed that vacuum infiltration methods and vacuum storage at low temperatures can greatly extend the shelf life of the laminates without affecting the resulting mechanical strengths, making them suitable for their adoption in industrial or pre-industrial scale productions. Acknowledgement: EIT RawMaterials GmbH is acknowledged for supporting and funding this research within the project KAVA9 FENICE- Fire rEsistant eNvironmental frIendly CompositEs (Project Agreement n.o. 21099)
65 51 Aging Behavior of Rubber Compounds Prepared with Different ZnO Types Börüban Biṅ göl C 1 , Polat Ş2 , Atapek Ş2 1Brisa Bridgestone Turkey, 2Kocaeli University Zinc oxide is considered as the most widely used activator that influences curing reaction kinetics and promotes short sulphide crosslinks to achieve higher crosslink density in rubber compounds. Besides its effect on curing process, it has beneficial effects on the physical and mechanical properties of rubber as well. However, its level should be minimized in rubber compounds because of its toxicity for human health and environment especially on aquatic wildlife. One of the potential routes for decreasing ZnO level is to use composite ZnO materials where ZnO particles are coated on precipitated CaCO3. In this study, composite ZnO materials having ZnO:CaCO3 ratio as 40:60, 60:40 and 90:10 are used in SBR/BR compounds and their effects on mechanical properties (tensile strength, elongation at break, modulus, and hardness) under aging conditions are investigated and compared with white seal ZnO and active ZnO. The findings have shown that all composite materials including lower ZnO level have no negative effects on mechanical properties under aging conditions, thus they can be used as alternative materials to white seal ZnO and active ZnO.
66 52 Crosspreg® , an innovative reactive hybrid prepreg, mass production dedicate, with a low LCA profile and easy recyclable for Fenice Kic Project Creonti G1 , Mingazzini C, Scafè M 1Crossfire Srl FENICE (upscaling, KAVA9, EIT RawMaterials, www.fenice-composites.eu, 2022-2025) is a EU project, funded with over 2.5 million and aiming at TRL 7, focusing on the topic of fire resistance of battery boxes for the automotive. FENICE is focusing its attention on current lithium-based modules, trying to cope to the potential fire risks of an increased use in mass production. Crossfire is one of the industrialization and commercialization partners of the project, and is enquiring Crosspreg® , their proprietary innovative reactive hybrid prepreg, specifically developed and eco-designed for mass production, using glass fiber and an easyto-be recycled resin with a favorable LCA. This new generation of Reactive Hybrid prepreg will be presented, focusing and discussing its unique peculiarities, fully aligned to the newest market and environmental demands, since it behaves as a thermoset up to its Tg (110°C) then turns into a thermoplastic, behaving like this over its Tg. This high T thermoplastic behavior allow reuse by simple mechanical recycling. The recovered thermoplastic resin was already successfully validated for use in injection molding: the fact that reinforcing fibres are already perfectly wetted and mixed into the resin, makes this secondary raw material available for direct use, without any modification or expensive preparation step. The patented resin formulation is also fast curing and VOC and solvent free, that makes Crosspreg® the ideal semifinished material for the automotive and building applications, making the components in line with the expected performance, at their usual working conditions, while turning into a thermoformable and recyclable thermoplastic beyond Tg, making the components also repairable. Regarding the sustainability issue, the embodied energy content is drastically reduced compared to both conventional thermoset composites and thermoplastic aeronautical ones, with much lower production time and costs, both for the components and their prepregs. This is made possible thanks to the facts that (1) Crosspreg® is solid and stable at RT, so it does not require any frozen transportation and storage; (2) the processing also allows reduced energy demand, since the resin cures in isothermal hot molds within few minutes. In addition the current Crosspreg® formulations already contain important quantities of secondary raw materials (monomers from recycling) but the ongoing further development step is about also introducing bio-sourced raw materials. This improves sustainability, by carbon capture in very durable products, which has to consider both primary and secondary lives of the resin. Finally, regarding the specific fire-requirements for battery box application, fire retardancy can be achieved using additives, which can be easily included into a tailored resin formulation, while reaching a good level of fire resistance (that implies ensuring some residual mechanical strength of the battery box after fire exposure) can also be achieved, by surface modification of components with aluminium, which acts as an oxygen barrier and whose presence is needed anyway, in the case of battery boxes, for EM shielding.
67 53 Fire Resistance characterization and post–fire evaluation of residual mechanical strength Ares P1 , Ballestero J1 , Mingazzini C2 , Leoni E2 , Bassi S2 , Scafe M2 1 Fundacion Gaiker, 2ENEA FENICE (upscaling, KAVA9, EIT RawMaterials, www.fenice-composites.eu) is a EU funded project, focusing on the topic of fire resistance of battery boxes. FENICE is focusing its attention on current lithium-based modules, and, according to the ongoing analysis lead by CRF, both external fire accidents and overheating originating inside the battery boxes can bring to safety issues, if battery boxes materials were not enough resilient to fire. Fire originated by a defective lithium modules, could even create a chain degradation on the adjacent modules, unless a proper fire-resistant and thermal insulating composite layer is interposed as a separator betwen adjacent batteries. The presentation will identify the fire standard tests which seem most appropriate for the tests and the post “fire exposure” mechanical characterisations. This approach is being applied to a number of innovative solutions developed, for example, by ENEA. A sort of compromise is needed since the maximum fire resistance would imply using not recyclable materials, which cannot be accepted in mass produced cars, such as in the mid end automotive, which is being considered in Fenice.
68 54 Mechanical characterizations on bio-based recyclable composites, being developed for fire resistance Benco E1 , Talon C1 , Mingazzini C2 , Scafè M2 1GS4C Srl, 2ENEA FENICE (upscaling, KAVA9, EIT RawMaterials, www.fenice-composites.eu, 2022-2025) is a EU project, funded with over 2.5 million and aiming at TRL 7, focusing on the topic of fire resistance of battery boxes for the automotive. FENICE is focusing its attention on current lithium-based modules, trying to cope to the potential fire risks of an increased use in mass production. As part of the project and ongoing monitoring of the state of the art on the topic, GS4C is enquiring enriched basalt panels with bio-based fire resistant cleavable resin, in both pure composite and FML (Fiber Metal Laminate) configuration, which will be later tested and verified against the other solutions developed within Fenice. Specifically, the presentation will be about the experimental investigations on three different stacks of layers in order to investigate the impact of the different designs on mechanical and fire resistance performances. Aluminium layers will be in this investigation substantially thicker than the one planned in the battery case developed in Fenice to provide background data on the influence of Aluminium thickness on overall performances. Special attention will be paid to impact resistance and fire resistance. Panels will be produced by infusion with a new cleavable bio-based epoxy resin specifically developed for markets requiring high fire resistance in order to improve safety without affecting End of Life recyclability. Fiber layers will be made in weaved 600gsm Filava fabric with a special sizing to increase fire resistance. The proposed Fiber Metal Laminate should give the Fenice team a good representation of what could be obtained with the latest commercially available solutions. A sandwich solution with a core made of infused bamboo mat will also be evaluated as part of the ongoing research for optimising stiffness and lightness, along with increasing impact resistance and pseudoplastic behaviour. Sustainability of the solution is ensured by the fact that adopting a biobased resin and core imply capturing CO2 in durable materials, while Filava is aeronautical grade basalt, with reduced embodied energy thanks to proprietary induction heating furnace. Filava LCA and closed loop recyclability were studied in previous Cradle-to-Cradle Composites (C2CC) EIT RawMaterials upscaling project, KAVA5, EIT, www.c2cc-project.eu, 2019-2022, also devoted to the optimisation of sustainable composites for the automotive, aiming at mass production and recycling of a huge number of identical components.
69 55 Finite element virtual validation on basalt reinforced sustainable composites, based on biobased or innovative cleavable recyclable resins Mingazzini C2 , Leoni E2 , Bassi S3 , Benco E4 , Dalmau J5 , Pullini D1 , Basso M1 1 Stellantis, CRF - South Europe Materials & Sustainable Engineering, 2ENEA, 3Università di Pisa, Dipartimento di Ingegneria Civile ed Industriale, 4GS4C, 5R*CONCEPT FENICE (upscaling, KAVA9, EIT Raw Materials, www.fenice-composites.eu, 2022-2025) is a EU project, funded with over 2.5 million and aiming at TRL 7, focusing on the topic of fire resistance of recyclable battery boxes. The topic of composites sustainability is essential in FENICE, along with design of the component. To develop the approach, basic data measured on promising innovative studied in previous project C2CC (2019-2021, upscaling, KAVA9, EIT Raw Materials, www.c2cc-project.eu) is being discussed, since fire resistance is achievable, in a second moment, by adding proper fire-retardant additives to the resins and surface treatments. In both Eu projects, sustainability is ensured adopting recyclable or biobased resins, and the solutions are in line with latest EU directives regarding end-of-life reuse and c-footprint reduction in the automotive. In the presentation, virtual characterization and finite element modeling and CAE were applied to the front bonnet of FCA 500 Abarth. In the present work, the front bonnet was designed with the usual frame + skin approach, typical of high end automotive, considering the use of the semifinished composite materials (prepregs) produced into the project, followed by hand lay-up lamination and auto clave curing. The approach and the materials are going to be further developed, during Fenice project, for mid end automotive, but the basic mechanical data and the approach would be the same. The main targets are the weight reduction, obtained employing materials with lower footprint, namely a biomass derived epoxy and a cradle-to-cradle recyclable mineral fiber, that is a fiber that (differently from carbon fiber) can be remelted to long fiber with no decrease in mechanical specifications. For recycling both the resin and the fiber, a cleavable hardener was adopted developed by Connora Inc (US), which avoids the need of pyrolysis to recover and recycle the fibers from prepreg scraps and end-of-life components. In particular Basalt Derived Mineral Fibres which are cradle-to cradle (C2C) recyclable, meaning they can be recycled and reused for the original applications, since no performance loss is expected by remelting.
70 56 SiC/SiC composites tolerance to high temperature combustion atmosphere and post ageing mechanical and microstructural characterisation Bassi S1 , Mingazzini C2 , Leoni E2 , Scafè M2 , Fabbri P2 , Vignoles G3 , Rebillat F3 , Antonin O3 , Bertrand P4 1University of Pisa, Department of Civil and Industrial Engineering, 2ENEA SSPT-PROMAS-TEMAF, 3University of Bordeaux, Sciences and Technology, Laboratoire des composites thermostructuraux (LCTS), 4University Bourgogne Franche-Comté, Laboratory ICB, UMR - 6303 CNRS The presentation will discuss WP4 activity, coordinated by ENEA, about experimental study on SiC/SiC composites tolerance to high temperature combustion atmosphere. Water corrosion phenomena are known to affect mechanical properties of SiC-based CMC, due to the formation of a silica, volatile in certain condition. The study will simulate combustion conditions, aiming at using more environmentally friendly alternatives to methane, such as hydrogen, coke oven gas or biomethane, in steel production. It is essential to determine, in each case, if corrosion happens in active (that means continuous degradation) or passive (silica forms a protective "scale" on the component) regime. Since fiber-to-matrix interface can also be degraded, it is important to determine post-ageing mechanical flexural strength (by 4point bending tests). Water corrosion ageing was performed in tubular furnace and direct flame exposure. When the oxidizing species becomes CO2, instead of O2, the formation rate of silica passivating layer is expected to be lower than the volatilization rate, and consequently active oxidation results in continuous weight loss. Ageing tests of SiC/SiC composites were carried out at high temperature in a CO2/H2O/N2 gaseous environment at atmospheric pressure (reference conditions: 1200°C, 10/20/70 v/v). The oxidation kinetics was evaluated from recorded mass variations and measures of surface silicon oxide layer thicknesses from micrographs of polished cross-sections. Bending tests up to failure are carried out at room temperature on these aged samples after different exposure times. Relationships are established between the evolution of mechanical properties, the ageing conditions, and the rates of oxidation reactions. Acknowledgments:The research carried out to write this article was funded under the CEM-WAVE project. This project has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No. 958170. This document only reflects the authors’ view. The European Commission is not responsible for any use that may be made of the information it contains.
71 57 Mechanical characterizations on biobased Sheet Molding Compound (SMC), being developed for battery boxes. Minimi A1 1Microtex Composites Srl FENICE (upscaling, KAVA9, EIT RawMaterials, www.fenice-composites.eu, 2022-2025) is a EU project, funded with over 2.5 million and aiming at TRL 7, focusing on the topic of fire resistance of battery boxes. FENICE is focusing its attention on current lithium-based modules, trying to cope to the potential risks of an increased use in mass production. ENEA has been developing Fiber Metal Laminates, which seem one of the more effective and sustainable solutions, with the capability to combine recyclable or biobased resins, with high fire resistance. Anyway, up to now aluminum layers had been applied on prepregs, by hand lay up, which is not suitable for battery boxes mass production, as it is being requires by the fast transition from internal combustion engines to electrical cars. In FENICE Microtex is developing biobased Sheet Molding Compound (SMC) in an Industrial Pilot Line, with the aim to avoid the need of hand lay up and printing fire-resistant battery boxes (or battery spacers) in one autonomized step. Current results will be presented, and in particular a comparison of the mechanical performances obtained on SMC externally finished with aluminum layer, and FML produced starting from prepregs, with similar specific weight and composition.
72 58 Materials characterization of advanced fillers for composites engineering applications Lapcik L1 , Lapcikova B1 , Murtaja Y1 1Palacky University In Olomouc Four different minerals were investigated, hollow spheres of calcium carbonate, platy mica, needle like wollastonite and glassy perlite and characterized via iGC for surface energy, Freeman powder rheology for flow characterization, cyclic uniaxial die compaction for modulus of elasticity and frequency dependent sound absorption properties. Particle surface energy and particle shape strongly affected the packing density of powder beds. In the case of higher porosity and thus lower bulk density, the powders acoustic absorption was higher in comparison with higher packing density materials. Surface energy profiles and surface energy distributions revealed clear convergence with powder rheology data, where the character of the powder flow at defined consolidation stresses was mirroring either the high cohesion powders properties connected with the high surface energy or powder free flowing characteristics, as reflected in low cohesion of the powder matrix. Figure 1. Stress vs relative displacement of calcium carbonate filler (sample 1) during compression testing (at 80kN compression): A - 10mm/min, B - 1.2mm/min and C. - 0.2mm/min deformation rates.
73 59 Buckling Prediction of Single-Walled Carbon Nanotube-Reinforced Laminated Composite Structures under Hygro-Thermo-Mechanical Conditions Georgantzinos S2 , Antoniou P4 , Stamoulis K1 , Spitas C3 1 Faculty of Technology, Amsterdam University of Applied Sciences, 2 Laboratory for Advanced Materials, Structures and Digitalization, Department of Aerospace Science and Technology, National and Kapodistrian University of Athens, 3Department of Mechanical and Aerospace Engineering, Nazarbayev University, 4General Department, National and Kapodistrian University of Athens Laminated composites are increasingly being used in various applications across industries like automotive, aviation and aerospace due to their superior mechanical properties such as their strength-to-weight and stiffness-to-weight ratio. These characteristics make them a preferred material for lightweight and more efficient structures, all of which translates into reduced costs. Especially in the last decades, the rapid growth of nanotechnology together with the rise of carbon nanostructures (CNs) like graphene and carbon nanotubes (CNTs) have provided new potential for the development of enhanced capabilities and consequently improved structures and applications such as coatings and structural health monitoring. This work presents a comprehensive approach for the buckling analysis of laminated composite structures reinforced with single-walled carbon nanotube (SWCNT) inclusions. A multi-scale framework (Figure 1) is proposed, which integrates various analytical and computational techniques to evaluate the mechanical behavior of SWCNT-reinforced composites under hygro-thermo-mechanical conditions. The Halpin-Tsai equations are employed to estimate the homogenized stiffness characteristics of the nano-reinforced matrix, considering SWCNT agglomeration, orientation, and waviness. The nanoscopic size-dependent characteristics of SWCNTs are also incorporated into the model. The Chamis micromechanical formulae are utilized to evaluate the six independent elastic properties of the nanocomposite lamina, accounting for temperature and moisture effects. To estimate the orthotropic constants of the nano-reinforced composite lamina under hygro-thermo-mechanical factors, the Taguchi design of experiments is utilized, and an integrated relationship is established. The effects of fiber and SWCNT volume fraction, SWCNT aspect ratio, temperature, and moisture content on the critical buckling loading of SWCNT-based laminated composite plates are then investigated using the proposed integrated equation in finite element and continuum models. The results are compared with experimental and theoretical data available in the literature, and the proposed approach is validated. This study represents the first application of a multi-scale-based finite element method to predict the buckling behavior of laminated composites reinforced by CNTs under various hygro-thermo-mechanical factors. The developed approach provides valuable insights into the design and optimization of SWCNT-reinforced composites which can be used in various engineering applications.
74 The multiscale analysis framework for the prediction of the hygro-thermo-mechanical buckling performance of laminated composite structures with CNT inclusions.
75 60 Liquid Hydrogen Storage Tank Virtual Crashworthiness Design Exploration for Civil Aircraft Gallois A1 , Giannopoulos I1 , Theotokoglou E2 1Cranfield University, 2National Technical University of Athens Introduction Liquid Hydrogen (LH2) has been regarded as a promising propellant solution for aviation decarbonization [1,2]. Its properties make it a suitable candidate with adequate energy density but in the need of four times the original fuel storage volumetric space. Airworthiness certification requirements for Hydrogen propellant in aviation are currently maturing. It is of great importance to explore the airframe designs to house the LH2 storage system. Due to various design constraints for the pressurised LH2 cryogenic tanks, there is a strong possibility for the storage locations to be within the fuselage cross section. The focus of the research presented herein, was to study the crashworthiness performance for several proposed airframe designs housing fuel LH2 storage tanks. The design parameters of interest were the structural energy absorption due to downwards airframe crash scenarios and the structural deformation of the structure surrounding the tanks, penetrating the survival space of the occupants. Several structural arrangements were proposed and compared, which were developed based on the Airbus A350 long-haul aircraft fuselage cross section properties [3]. A dominant design proposal arrangement is that of a stretched fuselage that allows the installation of a number of tanks in sequence, within the existing fuselage section cavity. An alternative proposal was based on the conceptually designed Cryoplane project [4], which was modified herein as having the same cross-sectional characteristics to the A350, with additional protrusion on the top to house the LH2 storage. The objectives of this study were to provide insights into the crashworthiness behaviour using virtual crashworthiness testing. Methods The approach was to down select possible design arrangements for the LH2 storage tank within the fuselage cross section. A similar volume of stored Hydrogen was considered for comparison for the proposed designs. Once the configurations were decided, representative fuselage cross sections were numerically modelled. Analysis was performed using nonlinear progressive damage simulations, in FEA Abaqus software [5]. The analysis simulated vertical downward crash scenarios using the current airworthiness certification criteria [6]. Results The results indicated that the energy absorbed by the structure was greatly affected by the proposed alternative designs, as expected. Different design proposals showed different areas of strength and weaknesses with respect to the total energy absorbed by the system and to the penetration of the surrounding collapsing structure. The study highlighted the importance of a required spacing between the tank, and the peripheral airframe and supporting structure. Conclusions Computer simulated, virtually tested crashworthiness scenarios can be used at the preliminary design stage of airframe structures for design space exploration. The study herein provided insights to the
76 crashworthiness performance for a number LH2 storage design proposals as well as it highlighted the proposed design with the best crashworthiness performance characteristics. References [1] https://www.airbus.com/en/newsroom/news/2021-12-how-to-store-liquid-hydrogen-for-zero-emissionflight [2] https://www.ati.org.uk/flyzero/ [3] https://www.janes.com/ [4] https://cordis.europa.eu/project/id/G4RD-CT-2000-00192 [5] https://www.3ds.com/products-services/simulia/products/abaqus/ [6] https://www.easa.europa.eu/en/document-library/certification-specifications Virtual testing of a representative fuselage cross section downward crash case Crash energy absorbed by structural collapse for different storage design arrangements
77 61 Liquid Hydrogen Storage Tank Loading Generation for Civil Aircraft Damage Tolerance Analysis Giannopoulos I1 , Theotokoglou E2 1Cranfield University, 2National Technical University of Athens Introduction Liquid Hydrogen (LH2) has been regarded as a promising propellant solution for aviation decarbonization [1,2]. LH2 storage which takes place at about -253oC, has been solved for the chemical industry, for the land and sea vehicle transportation [3], as well as for the space industry sectors. The storage solutions from these sectors from a structural perspective are either too heavy or with a short life span, both constraints making them unsuitable for aircraft vehicles were mass and longevity is of paramount importance. Lightweight LH2 storage solutions using composite materials have not matured enough to this day, to the point of their structural integrity lasting for more than a few dozens of thermomechanical loading cycles [4,5]. It is anticipated that the first generation of LH2 storage tanks for aviation purposes to utilize metallic lightweight materials that have been proven in service [2]. The LH2 storage solution will aim to operate at a constant absolute internal pressurization environment, to avoid unnecessary boil off the liquid phase. The tank will constantly feed the vehicle’s propulsion system, providing different fuel flow rates based on the propulsion power demand, while heat will constantly ingress from the external environment. These external disturbances to the thermos-fluid dynamic system, will generate thermomechanical pressure fluctuations to the tank structure. The objective of the work presented, is to generate the loading spectrum of the storage tank, subjected to the environmental disturbances and flight mission fuel demand, whilst being supervised by a pressure control system. Methods The method applied to generate the loading spectrum resulted from the modification of an existing dynamic model solution available in the public domain [6], subsequently tailored for civil aircraft flight mission cases. The model is a 1D thermo-fluid dynamic system, connected to the cool props database [7] for retrieving the Hydrogen properties at every stage of the process. Results The results generated by the modelling exercise, are in the form of internal-to-the-tank absolute pressure variations with time, time history that can easily be manipulated to number of loading cycles at specific loading intensity. Subsequent damage tolerance analyses assuming relevant crack sizes at critical locations magnified locally by the stress concentrations, could lead to plausible pre-certification virtual testing results. Conclusions The aircraft industry is in the need of simplistic approaches to modelling the LH2 storage pressure fluctuations, along with fuel properties and behaviour during various flight mission profiles. The simplistic 1D model approach of the LH2 behaviour under storage is capable of capturing the pressure fluctuations for input to respective damage tolerance analyses of metallic LH2 storage tanks. References: [1] https://www.airbus.com/en/newsroom/news/2021-12-how-to-store-liquid-hydrogen-for-zero-emissionflight [2] https://www.ati.org.uk/flyzero/ [3] https://global.kawasaki.com/en/hydrogen/history.html [4] https://cordis.europa.eu/project/id/285117
78 [5] Xu B, Qu L et al. “Progress in research on cryogenic propellant tank for large aerospace vehicles”. Composites Part A, 2021 [6] Daigle, M. Foygel, and V. Smelyanskiy, “Model-based diagnostics for propellant loading systems,” in 2011 Aerospace Conference, 2011, pp. 1–11 [7] http://www.coolprop.org/ Liquid Hydrogen model for deriving the tank structural loading spectrum Parahydrogen Temperature / Density chart from coolprop [7]
79 62 A Novel, Non-Contact NDT Scanner Case Study: Thickness Measurement, Debonding and Crack Detection in Composites Dr. Arno Volker2 , Prof. Konstantinos Stamoulis1 , Mr Donald Tongeren3 , Mr Bart Bekkema4 , Mr Robert Poppe5 1 Faculty of Technology, Amsterdam University of Applied Sciences, 2The Netherlands Organisation for Applied Scientific Research (TNO), 3KLM Royal Dutch Airlines, 4 Science [&] Technology Corporation, 5 JetSupport Several non-destructive techniques (NDT) built upon a wide spectrum of methodologies are used for inspections during the lifecycle of an aircraft. These NDT techniques include the most established, wavebased methods of ultrasonic testing (UT) and acoustic emission or other, emerging methods such as opticalbased laser shearography and computed tomography. Currently, the state-of-the-art NDT that are certified and used in aviation Maintenance, Repair and Overhaul (MRO) are largely labour-intensive and slow processes that are carried out by human operators. These techniques are not only typically time-consuming but also highly dependent on the operator. Furthermore, MRO technicians are trained and certified in various non-destructive techniques and required to periodically repeat this process to be able to perform inspections. Each NDT technique has its own potential but rarely achieves the capabilities for a solution to the problems described as well as for a full-scale diagnosis of possible defects. To match this gap, there’s an increasing need for more efficient, automated and accurate NDT tools that will be able to provide a faster and potentially remote damage assessment. This study presents a novel, non-contact, automated NDT scanning system under development that aims to significantly reduce the inspection times. The proposed technique uses leaky Lamb waves, which radiate in air. A MEMS microphone array on a translation system is used to scan the radiated Lamb wave energy. The stand-off of the microphone array relative to the object under inspection is typically 10 cm or more. An advanced data processing scheme is applied to the measured wave field, making use of the dispersion characteristics of Lamb waves to yield a wall thickness map of the part. The results are automatically processed and presented in a generated maintenance report. An essential step is to map the local sensor coordinates to a reference coordinate system of the entire airplane, allowing for clear communication of the location of any discovered possible defect. Two selected use cases are currently investigated by employing the proposed inspection technique with direct applications on the structural integrity assessment of both airframe and components. First, measurements of thickness in aluminium aircraft structures. This capability is valuable since for example, the measurement of the remaining thickness of blended areas after local corrosion removal is required to determine the compliance with the OEM’s limitations. The novel NDT system can provide a local thickness map of the order of 1mm with comparable resolution and a faster scanning process as compared to conventional NDT techniques. Second, debonding and crack detection in composite structures is explored. A fast and efficient damage assessment in aircraft composite structures is critical in MRO operations since composites are particularly susceptible to impact damage where induced damage can occur within numerous locations and at various levels of scale, making it difficult to efficiently detect and assess. Overall, it is currently concluded that the proposed NDT scanner is a promising tool that can significantly reduce the inspection time, has the potential to automate the damage assessment and overall result in a more efficient process.
80 Results of thickness measurements in aluminium aircraft wing structure. Non Contact NDT System during scanning of wing airframe thicknesses
81 63 An electrostatic glue Geoghegan M1 1Newcastle University In this presentation I shall introduce a new class of water-based glue that is made using commodity materials, inexpensive, scalable, storable, stable in water, and environmentally reversible [1]. I shall present this in the context of a history of our work on pH-controlled adhesion. Weak polyelectrolytes are a class of charged polymer whereby the charge can be controlled. A weak polycation therefore is charged at low pH, with the level of charging increasing with decreasing pH. The reverse is the case for a weak polyanion. It is shown that a grafted polycation (poly[2-(dimethyl amino)ethyl methacrylate] or poly[2-(diethyl amino)ethyl methacrylate]) will adhere to a polyanionic hydrogel in water, poly(methacrylic acid) [2]. It is further shown that these will separate in acidic media. Here, for the first time a quantitative JKR analysis was possible for soft materials in an aqueous environment. By bringing oppositely charged grafted polymers into nanoscopic contact using an atomic force microscopy based experiment, it is possible to show that the adhesion between these weak polyelectrolytes is primarily electrostatic [3]. Methodologies based upon grafted polymers are not convenient for the end-user, who must perform surface chemistry to obtain adhesion. We have developed simple formulations that generate a water-based environmentally reversible adhesive, which can be easily applied as a coating by the customer, and this will be outlined at the end of my presentation. References [1] A. Sierra-Romero, K. Novakovich, and M. Geoghegan " Water-based Adhesive” Adriana Sierra- submitted at the UK patent office October 2022 (application number P340927GB) [2] R. La Spina, M. R. Tomlinson, L. Ruiz-Pérez, A. Chiche, S. Langridge, and M. Geoghegan, Angew. Chem. Int. Ed. 46, 6460 (2007) [3] M. Raftari, Z. J. Zhang, S. R. Carter, G. J. Leggett, and M. Geoghegan "Nanoscale contact mechanics between two grafted polyelectrolyte surfaces" Macromolecules 48 6272 (2015)
82 64 Mechanics of carbon nanomembranes for water separation Dimitropoulos M1 , Trakakis G2 , Pavlou C1 , Kostaras C1 , Meyerbröker N3 , Gehra R3 , Schnieders A3 , Galiotis C1 , Dassios K1 1Dept. of Chemical Engineering, University Of Patras, 2 Institute for Chemical Engineering Sciences, Foundation for Research and Technology Hellas, 3CNM Technologies GmbH Water separation technologies are widely used in many areas of contemporary industries and households, with the goal of removing impurities from water. As a technological substitute for the very effective biological filtration membranes found in nature, ultrathin Carbon Nanomembranes (CNMs) provide a highly selective, fast-flow, energy-efficient water separation technology intended for demanding water treatment applications. The membranes are two-dimensional (2D) materials having sub-nm functional pores and a thickness of about 1 nm; they can have adjustable properties and can be produced in large scale on porous supporting substrates. In order to guarantee the structural stability of the membrane during operation, the goal of this work was to investigate and analyze the mechanical properties of CNMs and their substrates. Unlike macro-materials, measuring the mechanical characteristics of nanometer-thick membranes is a challenging task. Atomic force microscopy was used to measure the membranes' inherent mechanical properties as they were suspended over patterned substrates (AFM) but also supported on atomically-flat substrates. Quantitative nanomechanical, nanoindentation and fatigue tests proved the suitability on the membranes for use in targeted water separation applications.
83 65 Study of mechanical properties of epoxy/graphene and epoxy/halloysite nanocomposites Lapcik L1 , Murtaja Y1 , Lapcikova B1 1Palacky University In Olomouc The paper aimed to compare various mechanical properties of epoxy/graphene and epoxy/halloysite nanocomposites. As fillers graphene nanoplatelets (GnPs) and halloysite nanotubes (HNT) were used at different concentrations. Studied fillers were dispersed in the epoxy resins matrices. The elastic-plastic mechanical behavior modulation was observed utilizing the fillers´ nanoparticles and carboxyl-terminated butadiene–acrylonitrile copolymer rubber (CTBN) modified epoxy resin. The hypothesis of the possible preceding inter-particle gliding of the individual GnPs in the complex resin nanocomposite matrix during mechanical testings was also confirmed. There were observed increased ductility (elongation at break increased from 0.33 mm (neat matrix) to 0.46 mm (1 w.% GnPs) (39 % increase)) and plasticity of the GnPs nanocomposite samples. In contrast, the decreasing mechanical stiffness as reflected in the decreased Young´s modulus of elasticity (from 3.4 GPa to 2.7 GPa (20 % decrease)) was found for the epoxy/HNT nanocomposites. The obtained dynamic stiffness of the investigated nanocomposites confirmed the complexity of the mechanical response of the studied material systems as a combination of the ductile and brittle phenomena. Keywords: graphene, halloysite, nanocomposites, epoxy polymer, CTBN rubber, mechanical testing Acknowledgements Authors LL and YM would like to express their gratitude for financing of this research by the Palacky University in Olomouc internal grants (IGA_PrF_2022_020 and IGA_PrF_2023_024). Financial support to the author YM by Fischer scholarship of the Faculty of Science, Palacky University in Olomouc, in the year 2022/2023, is also gratefully acknowledged. References 1. LAPČÍK, Lubomír, SEPETÇIOĞLU, Harun, MURTAJA, Yousef, LAPČÍKOVÁ, Barbora, VAŠINA, Martin, OVSÍK, Martin, STANĚK, Michal, GAUTAM, Shweta. Study of mechanical properties of epoxy/graphene and epoxy/halloysite nanocomposites. Nanotechnology Reviews. 2023, 12(1) in press. Doi: 10.1515/ntrev-2022- 0520. 2. LAPČÍK, Lubomír, Martin VAŠINA, Barbora LAPČÍKOVÁ, David HUI, Eva OTYEPKOVÁ, Richard W. GREENWOOD, Kristian E. WATERS a Jakub VLČEK. Materials characterization of advanced fillers for composites engineering applications. Nanotechnology Reviews [online]. 2019, 8(1), 503-512. Doi:10.1515/ntrev-2019-0045.
84 Figure 1. Nanofiller concentration dependencies of the unnotched fracture toughness of the studied GnPs and HNT nanocomposites.
85 66 Using the Point Method to estimate failure loads in 3D printed graphenereinforced PLA notched plates. Cicero S1 , Arrieta S1 , Sánchez M1 , Castanon-Jano L2 1 LADICIM (Laboratory of Materials Science and Engineering), University of Cantabria, E.T.S. de Ingenieros de Caminos, Canales y Puertos, Av/ Los Castros 44, Santander, 39005 Cantabria, Spain, 2Department of Transport, Projects and Process Technology, University of Cantabria, 39005 Santander, Spain This work obtains estimations of failure (fracture) loads in 3D printed graphene-reinforced PLA (polylactic acid) plates containing different types of stress risers. With this aim, firstly, several notched plates are tested and conducted to fracture. Then, linear elastic Finite Element (FE) analyses are performed to define the corresponding stress fields and, finally, the Point Method (PM) is applied to establish the failure criterion. The PM asserts that fracture occurs when the stress level reaches the inherent strength (σ0) at a distance from the notch tip equal to L/2, so both parameters (related to each other through the material fracture toughness, Kc) have been defined beforehand. The estimations of fracture loads obtained following this approach are in agreement with the experimental results. Thus, the present work demonstrates the accuracy of the PM to estimate failure loads in this 3D printed material. Geometry of one of the tested specimens. Dimensions in mm.
86 67 Correlation between structure and mechanical properties in α-quartz single crystal by nanoindentation and Confocal Raman microscopy Enríquez Pérez E1 , Del Campo A2 , Jiménez Reinosa J2 , Konstantopoulos G3 , Charitidis C3 , Fernández Lozano J2 1 Instituto De Óptica-csic, 2 Instituto de Cerámica y Vidrio-CSIC, 3 School of Chemical Engineering, National Technical University of Athens Quartz constitutes a very useful material due to its variety of applications, highlighting solid-state physics for material science with applications for devices and sensors, as piezoelectric for microbalances or oscillators for watches, computers, etc. These applications are very sensible to local pressures and stresses, however, there is not much information in the literature about the effect of high local pressures on the structure and their correlation with mechanical properties. In order to provide more information and clarity on this type of stress-structure-mechanical properties correlation, in this work, nanoindentation combined with Raman Confocal microscopy was carried out since it offers a powerful method to obtain information about the structural deformation and mechanical properties produced by high local pressures in α-quartz single crystal. The information obtained by nanoindentation (pile-up, pop-out, hardness and young modulus) has been correlated with the structural data extracted from Raman spectroscopy, concluding that a permanent plastic deformation occurs under the indentation footprint, sharply appearing a new denser phase, which contribution increases with the applied load. a) Raman spectrum of α-quart ((001) direction). b) Raman spectra of different zones of indented footprint. c) Raman image, c) Raman shift image of the footprint, representing different stressed zones.
87 68 Mechanical spectroscopy: Machine learning and high speed nanoindentation for high throughput material evaluation. Dr. Douglas Stauffer1 , Dr Bernard Becker1 , Dr. Eric Hintsala1 , Mr. Benjamin Stadnick1 , Dr Ude Hangen2 1Bruker Nano, 2Bruker Nano GmbH Developing new materials and alloys and assessing their performance under different conditions necessitates the use of high-throughput data acquisition and analysis techniques. Compared to other mechanical tests like tension or compression, standard nanoindentation tests are considered high throughput. These rates can be improved by orders of magnitude, with sub-second indents, making acquisition of datasets up to 1 million measurements possible. This allows for local variations on hardness and modulus spaced at less than 50nm spacing, with maps spanning the mm length scale. Systematic errors such as overlap, local tilt, and influence of neighboring microstructural features need to be avoided. However, this requires accompanying analysis methods to also be high throughput or automated, as datasets of thousands of points are beyond what can be reasonable done by hand. One type of automated analysis of interest is a set of machine learning algorithms known as clustering. This allows rapid grouping of similar data. However, it is also important to understand the error associated with this type of analysis, which can be done via an evaluation framework based on bootstrapping. Several material types are explored: high entropy alloys, multiphase steels, and welds. A 1.1 million datapoint set on a modern Damascene steel. Using closely located arrays fine microstructural features, such as Martensitic lathes, can be observed as variations in local strength.
88 69 NAVMAT: an AI-powered pathway to knowledge sharing on material failures Melanitis N1 , Giannakopoulos G2 , Stamatakis K2 1Hellenic Naval Academy, 2 Institute of Informatics & Telecommunications, NCSR Demokritos Two years ago, the concept and design of a naval materials failure management system, with the acronym NAVMAT, was announced in ICEAF VI. The current paper describes the product development methodology, the system architecture, the modules and features of the operating prototype, as well as future challenges. The fundamental compound of the knowledge management platform is the recording and classification of a failure incident. The business process reflected into and supported by the NAVMAT service is described as follows: An incident is identified, described and associated with a component, which is a part of a system, belonging on a platform such as a ship or a vehicle of even an industrial installation. The component is made out of a specific material, following a suitable fabrication method. The failed component (or system) operates in defined environment, being subjected to a loading regime. It exhibits a mode of failure initially identifiable by the observer, but further assessed and analysed only by an expert. Should such a failure analysis take place, the root cause of failure may also be confirmed. The full documentation of the incident and related content is classified and indexed for future reference. The NAVMAT platform supports different types of users, from the first Reporter to the Analyst and Forensic Engineer through appropriate workflows. In these workflows the provided information can be provided as text, files, images and videos, which can be easily associated to the incident and provide structured information, usable by the NAVMAT system. NAVMAT also supports different security clearance levels to funnel information and access as appropriate, enabling different organizational needs. NAVMAT provides a number of AI-enabled helpers to facilitate the execution of the above process steps. During the incident recording, NAVMAT brings into play reactive real-time search which suggests related incidents and literature to facilitate the editor. It also speeds up the classification of incidents by providing AI-suggested labels, chosen from the (multi-lingual) concepts contained in the carefully engineered, extensible NAVMAT Ontology. On the other hand, the intelligent indexing and search infrastructure of NAVMAT supports easy identification and retrieval of past incidents, reports and publications, by applying Natural Language Processing to create a complete puzzle of previous knowledge related to a specific incident setting. The prototype of the described system has been embedded as a web application validated by potential Users and is being prepared for Operation in a fleet environment. At the same time the applicability and adaptation to other industrial sectors is also considered, since the main components of NAVMAT, from the Ontology to the AI models, can be fine-tuned for various industries applicable (e.g. mechanical, electrical, electronic and other settings).
89 70 A method for the correlation of microstructure with nanomechanical properties in Advanced High Strength Steels for automotive applications Alexandratou A1 , Konstantopoulos G1 , Katsavrias A1 , Bruno F2 , Belforte L2 , Rossi E3 , Rashid S3 , Sebastiani M3 , Charitidis C1 1National Technical University Of Athens (ntua), 2Centro Ricerche FIAT SCPA, 3Università degli studi Roma Tre Objectives This study investigates two important grades of advanced high-strength steels (AHSS) increasingly applied in the automotive industry to reduce vehicle weight cost-effectively, namely transformation-induced plasticity (TRIP) assisted and quenching and partitioning (Q&P) steels. Both grades exhibit an attractive combination of high strength and ductility, attributed to their complex multi-phase microstructure, consisting of ferrite, bainite, or martensite, and retained austenite. Methods The current research is focused on using CSM (Continuous Stiffness Measurement) nanoindentation to characterize the mechanical behavior of individual phases within the steels' microstructure and correlate the micro- and nanostructural features with the mechanical properties. CSM nanoindentation is a dynamic type of nanoindentation that comprises the continuous application of a small oscillating magnitude to the surface of the investigated materials, determining their elastic modulus, hardness, and deformation behavior with high accuracy and, thus, contributing to valuable insights into the microstructure-properties relationship. Electron Backscatter Diffraction (EBSD) was used in order to classify the structural phases. Due to the big data produced, phase analysis was performed utilizing Artificial Intelligence (AI) and Machine Learning, for the phase identification and validation. Results The microstructure of TRIP-assisted steels contains a mixture of ferrite, bainite, and retained austenite, which is the key contributor to their unique combination of properties due to the TRIP effect, offering an increase in strength and ductility during deformation. Q&P steels are also sophisticated alloys with carefully selected chemical compositions subjected to precisely controlled heat treatments, followed by quenching. They mainly consist of a tempered martensite-retained austenite microstructure. Following the partitioning step, the martensitembecomes relatively soft, while the austenite is relatively stable against phase transformation, leading to an excellent balance of high tensile strength and good elongation. Conclusions The results demonstrate a strong correlation between the studied TRIP-assisted and Q&P steel grades' nanomechanical properties, microstructural features, and crystallographic orientation data obtained by Scanning Electron Microscopy (SEM) combined with EBDS. Particular emphasis has been given to identifying the validated through AI, EBSD volume fraction of the phases present in the investigated complex micro- and nanostructures based on nanoindentation mapping, explaining the materials' local hardness and deformation behavior.
90 71 Phase mapping and identification of complex multiphase CuWCrTi material using Nanoindentation testing and Nanodiffraction mapping Katsavrias A1 , Alexandratou A1 , Konstantopoulos G1 , Capria E2 , Schulli T2 , Daniel R3 , Zitek M3 , Charitidis C1 1Research Lab of Advanced, Composite, Nano Materials & Nanotechnology (R-NanoLab), School of Chemical Engineering, National Technical University of Athens, 2European Synchrotron Radiation Facility (ESRF), 3Montanuniversität Leoben, Department Materials Science, Chair of Functional Materials and Materials Systems Objectives In this work, we present a comprehensive characterization of the phases in a complex CuWCrTi sample using Nanoindentation and Nanodiffraction. The alloy was synthesized on a Si wafer by combinatorial physical vapor deposition utilizing four elemental sources including copper, tungsten, chromium, and titanium. The particle flux from each source was controlled by adjusting the source current to ensure a uniform film thickness and a continuous change in the elemental composition on the wafer surface. With that, a controlled formation of multiple phases was possible covering, among others, Cr-rich nanocrystalline Cr-W-Ti phase, Cu- and W-rich Cu-W-Ti and W-Cr-Cu nanocomposite phases, and Ti-rich Ti-Cr-Cu amorphous metallic glasses. Nanoindentation is a widely used method for measuring the mechanical properties of materials at the nanoscale. The objective was to evaluate ten different protocols and validate high-speed mechanical phase mapping on the complex films deposited by PVD (Figure 1), achieving a speed of more than one indent per second, with structural phase mapping performed at ID01 beamline of the European Synchrotron Radiation Facility in Grenoble for validation. Methods High-speed CSM nanoindentation testing is used, to characterize the various phases of the sample in a 4D manner. We employ this technique to determine the elastic modulus and hardness of each phase in the sample at various depths and loads, and Artificial Intelligence (AI) for data post-processing; clustering and classification. Additionally, we use nanodiffraction mapping to identify the crystallographic structure of each phase and correlate the results between the two techniques. By combining these two techniques, we are able to accurately characterize the validated different phases in the sample using AI for handling the Big Data produced by both techniques, including their mechanical and structural properties. Results Our results in Figure 2 provide validation to the developed protocols in order to provide the optimum tuned protocols that enable to gain valuable insights into the behavior complex multi-phase materials to inform the design of improved materials with enhanced mechanical properties.
91 Complex CuCrTiW films deposited on silicon wafer by PVD (left) and high-speed nanoindentation protocols performed (right). Indicative nanoindentation and machine learning classified groups of nanoindentation data in CuW rich region; left: optical image of region of interest, mid: 2D nanoindentation map, right: 3D nanoindentation map.
92 72 Nanomechanical testing of printed nanolayers for application in flexible organic printed electronics devices Kassavetis S1 , Kalampaliki T1 , Laskarakis A1 , Kapnopoulos C1 , Kyriazopoulos V2 , Heben V1 , Paliagkas A1 , Zachariadis A1 , Katsavrias T3 , Konstantopoulos G3 , Mekeridis E2 , Charitidis C3 , Logothetidis S1 1Nanotechnology Lab Ltfn, Aristotle University Of Thessaloniki, 2Organic Electronic Technologies P.C., 3Research Lab of Advanced, Composite, Nano Materials & Nanotechnology (R-NanoLab), School of Chemical Engineering, National Technical University of Athens Flexible organic printed electronics devices (FOPEs) such as Organic Photovoltaics (OPVs) and Organic Light Emitting Diodes are paving the way to new advanced low-cost and large area products for solar energy harvesting and lighting, respectively. FOPE devices are comprised by sequential functional nanolayers with a thickness ranging from 30 nm to 500 nm, which are printed the one on top of the other using different printing and curing conditions. The mechanical properties as well as the adhesion among these nanolayers play a critical role to the FOPEs performance and service life. In this work, we focus on the OPVs and we extensively test the mechanical properties of the OPV nanolayers such as the Transparent Conductive Oxide (TCO), the Electron transport (ETL), and the active nanolayer, using nanoindentation (NI) that provides quantitative results at the nanoscale level. The Continuous Stiffness Measurements NI of two different nanoindetation experimental set-ups was used to study the mechanical behavior of the nanolayers and their interfaces in the OPV stack. The NI testing data from the two nanoindenters are studied comparatively and in relation to the thickness and the surface roughness of the nanolayers, with the aim of accurately extracting the Elastic Modulus (E) and the Hardness (H) of the nanolayers. Two different TCOs were tested, ITO and IMI, grown on top of flexible PET substrate. Both samples showed elastic / plastic deformation. For ITO/PET the E and H values were calculated to 26 GPa and 4.5 GPa, while for the IMI/PET the E=15 GPa and H=3.2 GPa. In both cases, the E and H values were affected by the compliant PET substrate. For the Tin Oxide (SnO) nanolayer, printed as the ETL functional nanolayer (thickness 40-60 nm) on top of TCO, the NI testing showed that the printed SnO nanolayers did not deadhere from the flexible TCO/PET substrate, while their E and H values were 9.2 GPa and 0.58 GPa, respectively. Finally, the NI testing of the active layer (400 nm thick) showed a significant variation of the measured E & H values of the surface compared to these of the bulk. The NI results are correlated with the vertical structure of this nanolayer derived by the characterization of the samples by Atomic Force Microscopy and Vis-UV Spectroscopic Ellipsometry.
93 73 Study of the material engineering properties of high-density poly(ethylene)/perlite nanocomposite materials Murtaja Y1 , Lapcik L1 , Lapcikova B1 1Palacky University In Olomouc This paper was focused on application of the perlite mineral as the filler for polymer nanocomposites in technical applications. A strong effect of the perlite nano-filler on high-density poly(ethylene) (HDPE) composites’ mechanical and thermal properties was found. Also found was an increase of the Young’s modulus of elasticity with the increasing filler concentration. Increased stiffness from the mechanical tensile testing was confirmed by the nondestructive vibrator testing as well. This was based on displacement transmissibility measurements by means of forced oscillation single-degree-of freedom method. Fracture toughness showed a decreasing trend with increasing perlite concentration, suggesting occurrence of the brittle fracture. Furthermore, ductile fracture processes were observed as well at higher filler concentrations by means of SEM analysis. There was also found relatively strong bonding between polymer chains and the filler particles by SEM imagining. Young’s modulus of elasticity (E) vs perlite filler concentration. Inset: applied deformation rates.
94 74 Approach for the fatigue assessment of welds considering nonlinear elastic-plastic material behavior Rudorffer W1 , Wächter M1 , Esderts A1 1 Institute of Plant Engineering and Fatigue Analysis, Clausthal University of Technology In the low-cycle fatigue range plastic deformation cannot be neglected and the assessment of elastic material behavior is no longer performed with sufficient accuracy. The German FKM-guideline “nonlinear” presents a calculation procedure for fatigue assessment based on the notch strain approach. In this contribution the transferability of the algorithms of the FKM-guideline “nonlinear” to welded joints is examined. According to this guideline the calculation of the fatigue life up to crack initiation considering elastic-plastic material behavior under proportional loading is enabled. The assessment is based on linear-elastic stresses, which are determined in finite element calculations and then converted to elastic-plastic stresses. For the structural simulation of the weld joint geometry the same modeling approached as within the notch stress approach are used. The weld seam can be modeled with a substitute radius of 1 mm. The estimation of local stresses and local elastic-plastic strains are determined using notch approximation methods. The required definition of the uniaxial material deformation behavior is carried out via cyclic material properties estimated from the Vickers hardness. Using the Rainflow Hysteresis Counting Method algorithm closed hysteresis loops of the local stresses and local elastic-plastic strains are detected and subsequently the damage parameter are calculated. For the fatigue assessment one of two damage parameters, the PRAM or the PRAJ, can be chosen. The fatigue resistance of the component as damage parameter Wöhler curve, taking into account the strength of the material within the heat affected zone, the support factor and the surface roughness, is defined. The service life calculation may be carried out by taking into account a safety concept. The adjustments of the calculation algorithms of the FKM-guideline “nonlinear” are a proposal for a consistent standardized procedure for applying the notch strain approach to both welds and non-welded components. Taking the Vickers hardness into account when calculating the service life leads to a reliable assessment for welds.
95 75 Investigation of intelligent evaluation method of fretting fatigue life assessment based on hierarchical mechanism-based neural network Yuan H1 , Liu Y1 1Tsinghua University The mechanisms and parameters of fretting fatigue damage are complex and published research papers on this topic are mainly empirical, which cannot be applied to fatigue problems under different mechanisms. A reliable fretting fatigue damage model has not been formed. In the present paper, a hierarchical mechanismbased neural network (HMNN) life prediction method is proposed, which decomposes fretting fatigue into four layers of fatigue problems, and studies them in four progressive neural network layers, decomposing complex fatigue problems into multiple simple sub-problems, such as proportional multi-axial fatigue, nonproportional multi-axial fatigue, notch fatigue, and finally fretting fatigue life models. Each layer of the neural network fatigue model provides an independent fatigue life calculation method for different fatigue problems. HMNN can be used to predict any of the four types of fatigue problems and provides a new complex fatigue evaluation method with reasonable accuracy.
96 76 Study of experimental and theoretical crack directions for specimens with a circular hole under biaxial cyclic loading Chaves V1 , Balbin J1,2, Navarro A1 1University Of Sevilla, 2University of Huelva Introduction Fatigue failure in real components generally occurs from stress concentrations, commonly referred to as notches. There are various models in the literature to predict the fatigue limit in notched components subjected to cyclic multiaxial loading. Three of them are analyzed in this document. Two of these models combine the Critical Plane Approach for unnotched solids under multiaxial loading with Taylor's Theory of Critical Distances (TCD) for notches under axial loading. The third model, the Navarro-Rios model, is a short crack model that analyzes the interaction of the crack with the microstructural barriers of the material in the presence of a notch. In the analysed models, the predictions are made based on the elastic stresses along a line whose length is of the order of the El Haddad small crack parameter, a0. This line used in the models is considered representative of the experimental crack direction in its initial part. In the analyzed models, the direction of the used line varies considerably from one model to another: the Mode I direction, the Mode II direction and a mixed direction between that of Mode I and Mode II, depending on the type of material. Therefore, a great diversity of directions is used even though, evidently, the experimental crack direction is unique for a given geometry, loading and material. Methods In recent years, a study of the experimental fatigue limits and crack directions in its initial part was carried out in hollow cylindrical specimens with a circular hole subjected to cyclic axial, torsional and in-phase biaxial loading. Three materials were tested, a stainless steel, a carbon steel and an aluminum alloy. These materials can be considered as brittle, intermediate ductile-brittle and ductile in fatigue, respectively, which allows this study to analyze the effect of various material fatigue behaviors in the crack direction. The experimental crack directions were measured only for the broken specimens subjected to fatigue at a high number of cycles, with a life above 105 cycles. Results The measured crack directions were on average similar for the three materials and close to Mode I. The analyzed models gave, in general, good predictions of the experimental fatigue limits, although they use directions that are completely different and that they too differ markedly from the experimentally found ones. Besides, the predictions of the models using, in a forced way, the measured experimental directions were good in most cases. Conclusion The experimental crack directions were on average close to the Mode I direction for the studied specimens and for the three studied materials. The analyzed models provide good predictions, even if the experimental crack direction is used to make the predictions.
97 77 VERIFICATION OF A NONLOCAL ANALYTICAL MODEL TO SIMULATE CRACKED NANOBEAMS UNDER MODE I STATIC LOADING Zanichelli A1 , Carpinteri A1 , Ronchei C1 , Scorza D1 , Vantadori S1 1Department of Engineering & Architecture, University of Parma Introduction The recent trend to miniaturise micro- and nano-electronical devices used, for example, in automotive sector, energy industry, biotechnology, medicine and information technology, requires the incorporation of structural components characterised by a micro- or/and a nano-scale length into such devices. In nanostructures characterised by sizes comparable to crystal or molecular distances, size effect is detected. Moreover, although the probability of the defect presence in nanostructures is quite low with respect to that in macrostructures, defects can produce a fatal damage for the whole electronical device. In such a context, classical continuum mechanics cannot be employed to simulate the size-dependent mechanical behaviour, due to its scale-free character. Rather, both atomistic modelling and Generalised Continuum Theories (GCTs) are proposed in several research works to investigate fracture behaviour of nanostructures. In the present paper, the Mode I static bending behaviour of an edge-cracked nanobeam is analysed by applying the Stress-Driven nonlocal Model. Three experimental campaigns performed on (1) a pure FeAl intermetallic single crystalline material, (2) NiAl single crystals, and (3) Si(100), respectively, are analytically simulated. The testing set-up, aimed to experimentally determine the fracture toughness of the above materials, consisted of an edge-cracked cantilever nanobeam, subjected to a transversal point load at the free end. Finally, the experimental data are compared with the obtained analytical results in order to evaluate the accuracy of the proposed model. Method The above edge-cracked cantilever nanobeam is modelled by employing a modification of the classical cracked-beam theory, consisting in dividing the beam into two beam segments connected through a massless elastic rotational spring, located at the cracked section. The problem is examined within the EulerBernoulli beam theory. The bending stiffness of the cracked cross-section is computed by exploiting both the Griffith energy criterion and the conventional Linear Elastic Fracture Mechanics. The nanobeam is analysed by applying the Stress-Driven nonlocal Model. Results Three experimental campaigns, available in the literature and aimed to determine the fracture toughness, are analytically simulated. Such campaigns had been performed on (1) a pure FeAl intermetallic single crystalline material (<010> orientation), (2) NiAl single crystals (<110> and <100> orientation), and (3) silicon (<110> orientation). The edge-cracked cantilever nanobeams had been loaded with a cantilever-based nanoindenter mounted inside a scanning electron microscope, and the force against static deflection curves had been registered. The experimental curves are compared with the analytical ones.
98 Conclusion In the present paper, the Mode I static bending behaviour of an edge-cracked nanobeam is analysed by using the Stress-Driven nonlocal Model. The accuracy of the model is evaluated by taking into account three experimental campaigns available in the literature, aimed to determine the fracture toughness of different materials. The comparison has been performed in terms of force against static deflection curves. In conclusion, it can be stated that the modified classical cracked-beam theory in conjunction with the Stress-Driven nonlocal Model can be a useful tool to analyse the Mode I behaviour of edge-cracked nanobeams under static loading.
99 78 Toughness of Hydrogels Garyfallogiannis K1 , Purohit P1 , Bassani J1 1University Of Pennsylvania INTRODUCTION: Hydrogels are soft, highly deformable materials. Their rupture generally involves large deformations strongly coupled to fluid flow. While the mechanics of the fracture for linear poroelastic behavior has been investigated [1-3], the problem of finite deformations has open issues, in particular the definition of toughness. The rupture of blood clots motivates our research, and we published the first experimental measurement of toughness of a fibrin hydrogel [4]. METHODS: We model a poroelastic material as a compressible (porous) solid infiltrated with fluid. The effect of the fluid is described by a Flory-Rehner model in which the stress depends on an osmotic pressure and chemical potential that drives fluid flow. Motivated by our interest in blood clots, we consider low volume fractions of solid material. A Mode I crack under both plane strain and 3D deformations is considered for both permeable and impermeable fluid boundary conditions. Through detailed finite element analyses, we investigate the crack-tip mechanical and chemical-potential fields. RESULTS: The energy release rate with respect to crack advance is computed in terms of a poroelastic J*- integral [5,6]. For large time-dependent deformations, we find path independence of J* in transient problems resulting from strongly coupled mechanical and chemical-potential effects. Furthermore, the coupling is not limited to the crack- tip region. The effects of loading rate and solid volume fraction are investigated. We consider both tensile dilating [6] and tensile contracting [7] hydrogels. We also consider a critical stretch criterion as a function of solid volume fraction. CONCLUSIONS: We have shown that fluid permeation (flow) directly affects the energy release rate associated with crack propagation. In general, J*=Jmech+Jflow, where the relative contribution of permeation (Jflow) depends strongly on geometry, boundary conditions, and rate of loading. REFERENCES: [1] Hui, C-Y., Long, R. and Ning, J. Stress relaxation near the tip of a stationary mode I crack in a poroelastic solid. J. Appl. Mech., 80(2), 01 (2013). [2] Noselli, G., Lucantonio, A., McMeeking, R. M. and DeSimone, A. Poroelastic toughening in polymer gels: A theoretical and numerical study. J. Mech. Phys. Solids, 94:33{46, (2016). [3] Yu, Y., Bouklas, N., Landis, C. M. and Huang, R. Poroelastic Effects on the Time- and Rate-Dependent Fracture of Polymer Gels. J. Appl. Mech., 87, 031005-1, (2020). [4] Tutwiler, V., Singh, J., Litvinov, R. I., Bassani, J. L. Purohit, P. K. and Weisel, J. W. Rupture of blood clots: Mechanics and pathophysiology. Sci. Adv., 6(35) (2020). [5] Bouklas, N., Landis, C. M. and Huang, R. Effect of solvent diffusion on crack-tip fields and driving force for fracture of hydrogels. J. Appl. Mech., 82(8), 08 (2015). [6] Garyfallogiannis, K., Purohit, P. K. and Bassani, J. L., “Energy release rate for cracks in hydrogels undergoing finite deformations,” J. Mech. Phys. Solids, 167, 105009, (2022). [7] Garyfallogiannis, K., Ramanujam, R. K., Litvinov, R. I., Yu, T. Nagaswami, C., Bassani, J. L., Weisel, J. W., Purohit, P. K., and Tutwiler, V., “Fracture toughness of fibrin gels as a function of protein volume fraction: structural and mechanical origins,” Acta Biomat., (2023).