TexPro: Text-Guided PBR Texturing with Procedural Material Modeling

Numerical simulation of U-Drawing test of Fortiform 1050 steel using different material models

<div class="section abstract"><div class="htmlview paragraph">Usage of fiber-filled thermoplastics in automotive structural applications are increasing due to their inherent advantages over metal, which include lighter weight and simplification in assembly. However, accurately predicting the performance of a fiber-filled thermoplastic part can be challenging due to presence of non-linearity and anisotropy in the material behavior. This paper describes material characterization and modeling of fiber-filled thermoplastics for accurate prediction of part performance to enable rapid use of these lighter materials in automotive applications. The grade used for the study is a 30% glass filled PEI, SABIC’s ULTEM<sup>TM</sup> 2300 Resin. Accuracy of the fiber orientation prediction is clearly demonstrated by the plaque level flow simulation validation with the CT-Scan data, followed by structural validations with specimen and part level tests. This study involves a representative cylinder-shaped part that accommodates different thicknesses and multiple manufacturing options. This part is tested for a variety of loading scenarios such as uniaxial tension, uniaxial compression and flexural loading to build confidence in the material data and modeling procedure. Results of simulations performed in widely used commercial software ABAQUS<sup>TM</sup> and Digimat<sup>TM</sup> compared against part tests show high level of accuracy in strength and stiffness predictions for 3mm thickness whereas other thickness specimens show deviations due to skin-core effect. The standard practice of qualifying a material model based on a single thickness specimen is also investigated in this work.</div></div>

Effects of local plastic instabilities in the form of yield point phenomena (YPP) were investigated on local and global deformation and failure behavior of resistance spot-welded tension–shear (TS) samples made from M1700 advanced high-strength steel (AHSS) by means of finite element (FE) simulations. Material models with and without YPP were used in FE simulations, and sensitivity of results to YPP material model characteristics and failure criteria was investigated. Results from FE simulations revealed several stages of load oscillations in predicted global load–displacement curves with different amplitudes depending on material model with YPP. Results also showed the existence of heterogeneous distribution of equivalent stress in heat-affected zone (HAZ) of TS samples with strong sensitivity to the upper and the lower yield stress values in YPP material model. A stress-based failure criterion was added to the damage model to account for this stress heterogeneity, and results from this model showed that the loading and failure behavior of TS sample can significantly change from ductile to premature semi-brittle failure with significant reduction in strength of TS sample. Results from FE simulations were also compared with those from TS experiments and indicated the need for development of proper material and damage models suitable for materials with YPP.

MAT162 is a composite material model, which has been used for simulating ratedependent progressive damage behavior of composite materials under high velocity impact applications such as ballistic penetration and perforation. A limited number of material systems, e.g., (i) unidirectional (UD) S-2 Glass/SC15, (ii) plain weave (PW) S-2 Glass/SC15, (iii) PW S-2 Glass/Phenolic, and (iv) PW E-Glass/Phenolic composites have been characterized for MAT162 material properties and modeling parameters in the literature. This material model needs 37 material properties and parameters to present rate-dependent progressive damage occurred in structure. For this purpose, a series of mechanical characterization tests and model validating experiments and computational simulations need to be performed. In this study, 8HS weave S-2 glass fabric reinforced with SC15 epoxy matrix composites has been characterized for MAT162 applications. Composite laminates of various thickness have been manufactured by hand lay-up method, cured at room temperature (RT) under vacuum and post-cured in an oven under vacuum. In-plane tension, quasistatic punch shear test (QS-PST), quasi-static punch crush test (QS-PCT), three-point bending, short beam shear and model validating low velocity impact (LVI) experiments were performed to determine the material properties and modeling parameters of 8HS S-2 glass/SC15 composites. Experimental damage modes and mechanisms have been quantified and used as input in validating the LS-DYNA computational models.

This paper studies the dynamic and elevated temperature behavior of rolled homogeneous armor steel, which is crucial for applications such as blast, impact, crash, and ballistic resistance. The deformation behavior is analyzed through tensile tests. The tensile tests of RHA steel are conducted at quasi-static 10−4s−1≤εṗ≤10−1s−1 to dynamic 10−1s−1≤εṗ≤36.439s−1 strain-rates and at high temperatures ranging from room temperature (RT,27°C) to 500°C. Phenomenological Johnson-Cook (JC) models and semi-physical Rusinek-Klepaczko (RK) material models are employed in finite element (FE) simulations of tensile tests. The JC failure model, with a small modification, is used along with the material models to simulate the loss of load-bearing capacity of the component. All necessary material parameters are extracted from the test data. The material models and the damage model are integrated into ABAQUS CAE FE software through a user-defined material subroutine (UMAT). The simulated outcomes acquired from diverse material models are validated with relevant experimental findings, and the effectiveness of each material model is evaluated through qualitative and quantitative assessments. Observations reveal limitations in the existing models to accurately replicate material behavior under tension, particularly in the dynamic strain rate, and elevated temperature range. Consequently, a modified version of the JC model (MJC) is explored to better account for the impact of temperature on strain hardening and strain rate hardening. The proposed modification in the material model significantly enhances the predictive accuracy of FE simulations of tensile deformation across the entire spectrum of studied strain rates and temperatures compared to the original JC and RK models.

Recent studies of flapping-wing aerial vehicles have been focused on the aerodynamic performance based on linear materials. Little work has been done on structural analysis based on nonlinear material models. A stress analysis is conducted in this study on membrane flapping-wing aerial vehicles using finite element method based on three material models, namely, linear elastic, Mooney-Rivlin non linear, and composite material models. The purpose of this paper is to understand how different types of materials affect the stresses of a flapping-wing. In the finite element simulation, each flapping cycle is divided into twelve stages and the maximum stress is calculated in each stage. The results show that 1) there are two peak stress values in one flapping cycle; one at the beginning stage of down stroke and the other at the beginning of upstroke, 2) maximum stress at the beginning of down stroke is greater than that at the beginning of upstroke, 3) maximum stress based on each material model is different. The composite and the Mooney-Rivlin nonlinear models produce much less stresses compared to the linear material model; and 4) the ratio of downstroke maximum stress and upstroke maximum stress varies with different material models. This research is helpful in answering why insect wings are so impeccable, thus providing a possibility of improving the design of flapping-wing aerial vehicles.

Driven by the wide range of new material properties offered by multi-material 3D printing, there is emerging need to create predictive material models for these materials. A data driven process for estimating nonlinear material model is presented in this paper. In contrast with classical methods which derive the engineering stress-strain relationship assuming constant cross-section area and fixed length of a specimen, the proposed approach takes full advantage of 3D geometry of the specimen to estimate the material models. Give a hypothetical material model, virtual tensile tests are performed using Finite Element Analysis (FEA) method, and the parameters of the material model are estimated by minimizing the discrepancies of the virtual responses and the experimental results. The detailed material models, numerical algorithms as well as the optimization approaches are presented and finally preliminary results are offered.

Injury due to underbody loading is increasingly relevant to the safety of the modern warfighter. To accurately evaluate injury risk in this loading modality, a biofidelic anthropomorphic test device (e.g., dummy) is required. Finite element model counterparts to the physical dummies are also useful tools in the evaluation of injury risk, but require validated constitutive material models used in the dummy. However, material model fitting can result in models that are over-fit: they match well with the data they were trained on, but do not extrapolate well to new loading scenarios. In this study, we used a hierarchical approach. Material models created from coupon-level tests were evaluated at the component level, and then verified using blinded component and whole body (WB) tests to establish a material model of the anthropomorphic test device (ATD) neck that was not over-fit. Additionally, a combined metric is introduced that incorporates the well-known correlation analysis (CORA) score with peak characteristics to holistically evaluate the material model performance. A Bergstrom Boyce material model fit to one loop of combined compression and tension experimental data performed the best within the training datasets. Its combined metric scores were 2.51 and 2.18 (max score of 3) in a constrained neck and head neck setup, respectively. In the blinded evaluation including flexed, extended, and WB simulations, similar combined scores were observed with 2.44, 2.26, and 2.60, respectively. The agreement between the combined scores in the training and validation dataset indicated that model was not over-fit and can be extrapolated into untested, but similar loading scenarios.

The paper deals with the theory of solution of transverse shock wave propagation in thin plane elastic isotropic plate (Al 99,9). The solution is made for various material and geometric models of the plate. The calculation is performed analytically for Kirchhoff and Rayleigh geometric models and Hook ‘s material model. The plate is fixed around its perimeter. The plate is loaded continuously or by the solitary force acting on the upper facial surface in the perpendicular direction to the midline surface of the unloaded plate. The paper presents the relations and results for transverse displacement, velocity and stress. In the conclusion, the analytical results are compared with the experiment.KeywordsKirchhoffWave propagationThin plates

Accurate material characterization and model calibration are pivotal for simulations used for high-consequence engineering decisions. Current characterization and calibration methods (1) use simplified test specimen geometries and global data, (2) cannot guarantee that sufficient characterization data is collected for a specific model of interest, (3) provide only mean parameter values with no uncertainty quantification, and (4) are sequential, inflexible, and time-consuming. This work developed a new paradigm—coined Interlaced Characterization and Calibration (ICC)—which drives forward the state-of-the-art in model calibration by bringing together recent advancements into one improved workflow. The ICC paradigm (1) employs tools to efficiently use full-field data to calibrate high-fidelity material models, (2) aligns the data needed with the data collected by adopting an optimal experimental design protocol, (3) provides uncertainty metrics on the calibrated model parameters, and (4) incorporates these advances into a quasi real-time feedback loop. The ICC framework was validated synthetically with both low-fidelity and high-fidelity simulations paired with several different elastoplastic material models, and was also demonstrated experimentally with an aluminum 6061 cruciform exemplar specimen. Results showed that the ICC framework—in which Bayesian optimal experimental design actively guided the experiment— resulted in calibrations with similar or better accuracy than predetermined experiments based on subject matter expertise. Moreover, the ICC framework produced a complete model calibration— with quantified uncertainties on model parameters—in 1 week, a 5 - 10× increase in efficiency over traditional approaches. Thus, the ICC paradigm improves both the calibration process and quality, by (1) improving efficiency, which increases agility of solid mechanics modeling and enables utilization of computational simulation (CompSim) at earlier stages of the design cycle and (2) providing quantified, and in some cases reduced, parameter uncertainties, which increases confidence in model predictions and supports credible decision making.

The last few years have seen a decisive move of the movie making industry towards rendering using physically based methods, mostly implemented in terms of path tracing. While path tracing reached most VFX houses and animation studios at a time when a physically based approach to rendering and especially material modelling was already firmly established, the new tools brought with them a whole new balance, and many new workflows have evolved to find a new equilibrium. Letting go of instincts based on hard-learned lessons from a previous time has been challenging for some, and many different takes on a practical deployment of the new technologies have emerged. While the language and toolkit available to the technical directors keep closing the gap between lighting in the real world and the light transport simulations ran in software, an understanding of the limitations of the simulation models and a good intuition of the trade-offs and approximations at play are of fundamental importance to make efficient use of the available resources. In this course, the novel workflows emerged during the transitions at a number of large facilities are presented to a wide audience including technical directors, artists, and researchers.This is the second part of a two part course. While the first part focuses on background and implementation, the second one focuses on material acquisition and modeling, GPU rendering, and pipeline evolution.

This work calibrates an empirical material model for a silicone adhesive by finding the best fit to experimental data over a range of high strain rates. Following the literature precedent of using the empirical nature of the Johnson-Cook model for epoxide modelling, the Modified Johnson-Cook material model is repurposed to enable this for silicone adhesive without the need for a new user-defined material or further development within commercial finite-element method (FEM) software, which significantly reduces the complexity of the implementation. To the authors’ knowledge, such a model is not available anywhere in the open literature. The developed material model is verified against experimental split-Hopkinson pressure bar (SHPB) data of ceramic/steel material couples bonded with a silicone adhesive. This work also tests, by numerical simulation, whether several material models, previously used in the literature for high strain rate modelling of epoxides, can replicate SHPB test data of ceramic/steel material couples bonded with such an adhesive. For silicones, the Modified Johnson-Cook material model, with the calibrated parameters determined in this work, is shown to give good agreement with the results of SHPB testing where the simulation predicted 76.2% transmitted strain, closely matched the experimental value of 70.4%. For epoxides, both the Plastic-Kinematic material model with Cowper-Symonds strain rate scaling, and the Johnson-Cook material model with the Grüneisen equation of state, give good agreement with the results of SHPB testing, with 95.5% and 97.6% transmitted strain respectively, versus the experimental value of 91.2%.

BackgroundDue to the limited number of experimental studies that mechanically characterise human atherosclerotic plaque tissue from the femoral arteries, a recent trend has emerged in current literature whereby one set of material data based on aortic plaque tissue is employed to numerically represent diseased femoral artery tissue. This study aims to generate novel vessel-appropriate material models for femoral plaque tissue and assess the influence of using material models based on experimental data generated from aortic plaque testing to represent diseased femoral arterial tissue.MethodsNovel material models based on experimental data generated from testing of atherosclerotic femoral artery tissue are developed and a computational analysis of the revascularisation of a quarter model idealised diseased femoral artery from a 90% diameter stenosis to a 10% diameter stenosis is performed using these novel material models. The simulation is also performed using material models based on experimental data obtained from aortic plaque testing in order to examine the effect of employing vessel appropriate material models versus those currently employed in literature to represent femoral plaque tissue.ResultsSimulations that employ material models based on atherosclerotic aortic tissue exhibit much higher maximum principal stresses within the plaque than simulations that employ material models based on atherosclerotic femoral tissue. Specifically, employing a material model based on calcified aortic tissue, instead of one based on heavily calcified femoral tissue, to represent diseased femoral arterial vessels results in a 487 fold increase in maximum principal stress within the plaque at a depth of 0.8 mm from the lumen.ConclusionsLarge differences are induced on numerical results as a consequence of employing material models based on aortic plaque, in place of material models based on femoral plaque, to represent a diseased femoral vessel. Due to these large discrepancies, future studies should seek to employ vessel-appropriate material models to simulate the response of diseased femoral tissue in order to obtain the most accurate numerical results.

Coefficients for analytic constitutive and equation of state models (EOS), which are used by many hydro codes at LLNL, are currently stored in a legacy material database (Steinberg, UCRL-MA-106349). Parameters for numerous materials are available through this database, and include Steinberg-Guinan and Steinberg-Lund constitutive models for metals, JWL equations of state for high explosives, and Mie-Gruniesen equations of state for metals. These constitutive models are used in most of the simulations done by ASC codes today at Livermore. Analytic EOSs are also still used, but have been superseded in many cases by tabular representations in LEOS (http://leos.llnl.gov). Numerous advanced constitutive models have been developed and implemented into ASC codes over the past 20 years. These newer models have more physics and better representations of material strength properties than their predecessors, and therefore more model coefficients. However, a material database of these coefficients is not readily available. Therefore incorporating these coefficients with those of the legacy models into a portable database that could be shared amongst codes would be most welcome. The goal of this paper is to describe the MatProp effort at LLNL to create such a database and associated access library that could be used by codes throughout the DOE complex and beyond. We have written an initial version of the MatProp database and access library and our DOE/ASC code ALE3D (Nichols et. al., UCRL-MA-152204) is able to import information from the database. The database, a link to which exists on the Sourceforge server at LLNL, contains coefficients for many materials and models (see Appendix), and includes material parameters in the following categories--flow stress, shear modulus, strength, damage, and equation of state. Future versions of the Matprop database and access library will include the ability to read and write material descriptions that can be exchanged between codes. It will also include an ability to do unit changes, i.e. have the library return parameters in user-specified unit systems. In addition to these, additional material categories can be added (e.g., phase change kinetics, etc.). The Matprop database and access library is part of a larger set of tools used at LLNL for assessing material model behavior. One of these is MSlib, a shared constitutive material model library. Another is the Material Strength Database (MSD), which allows users to compare parameter fits for specific constitutive models to available experimental data. Together with Matprop, these tools create a suite of capabilities that provide state-of-the-art models and parameters for those models to integrated simulation codes. This document is broken into several appendices. Appendix A contains a code example to retrieve several material coefficients. Appendix B contains the API for the Matprop data access library. Appendix C contains a list of the material names and model types currently available in the Matprop database. Appendix D contains a list of the parameter names for the currently recognized model types. Appendix E contains a full xml description of the material Tantalum.

The main goal of this work is the analysis of the procedure for material characterization aimed at elasto-visco-plastic models and their implementation in FEM codes. This will be done in order to perform stress analysis of structural components under repeated cyclical loads and high temperatures The overall development involves theoretical, numerical and experimental methodologies. The study of state of the art of material models, available in FEM codes, has allowed the evaluation of the limits of stress analysis on components subjected to repeated cyclical loads and high temperature. The initial study has also highlighted the necessity to implement complex material models. Traditionally this lack has been faced through the use of factors of safety, which are developed and refined on the basis of the experience and historical backgrounds. For systems where efficient design is of the utmost importance (for example the minimum weight design of an aircraft structure), it is possible that the traditional factors of safety may be overly conservative, so that optimal efficiency cannot be achieved. The implementation of complex material models allows simulating the real material behaviour and taking into account the non-linear interaction between creep and fatigue for structural analysis and life prediction. The results are more dependable and allow reducing the traditional factors of safety, consequently lead to a significant improvement in the designing of structural components. The process of material characterization has been developed through the following phases: designing the necessary experimental data base, choosing the constitutive laws, describing the iterative procedure for determining the coefficients of material model and the procedure of model validation, performed by comparisons between experimental data and simulated ones. It has been described how a poor experimental data base influences the material characterization process and the limits of an automatic procedure. Guidelines have been provided for designing experimental tests able to identify the optimized model parameters. In this way, it will be possible to determine material models with wide range of validity and to allow reducing time and costs of a characterization process. A methodology of structural analysis has been developed through the comparison with procedures of tested validity, in way to allow a correct and safe implementation of elasto-visco-plastic material models. An elasto-visco-plastic analysis on a combustion chamber of aeronautical engine has been performed and component life determined, taking into account the interaction between fatigue and creep.