Material Parameters Of Model Research Articles

Study on Parameter Identification Method for the Anisotropic Yield Function Yld2000-2D

Material anisotropy and choice of constitutive material model are key factors that govern the accuracy of stamping analysis, but determination of parameters for the constitutive material model is challenging task without biaxial tests which is not widely installed in general testing institutions. In this study, a method without the biaxial tests is proposed for determining the YLD2000-2d yield function parameter from the Lankford value obtained from the 7-direction uniaxial tensile test. Parameters of the YLD2000-2d yield function are obtained solving the proposed equations with an optimization technique, but several candidate parameters sets are retrieved due to complexity of the yield function. Thus, selection from the candidate sets is discussed.

A thermomechanical simulation method for fused deposition modeling

Abstract3D printing is a complex manufacturing method with completely new challenges. One of them is the simulation of the whole process. In this contribution the building process of the 3D printed part is thermomechanically coupled simulated with step by step element activation along a path from a slicer program. Thereby a hyperelastic material model and material parameters from literature are used. Simulation results of an exemplifying building process are in good agreement with corresponding experiments.

Temperature-dependent Charpy impact property of 3D printed 15-5 PH stainless steel

In this study, the impact property of 3D printed 15-5 PH stainless steel was investigated at low (77 K), room (298 K), and high temperatures (723 K) using integrated experimental and modelling studies. The finite element model was based on the Johnson-Cook phenomenological material model and fracture parameters. The experimentally measured impact energies are 0.01, 6.78 ± 4.07, and 50.84 ± 3.39 J cm−2, at the low, room, and high temperatures, respectively. The experimental and modelling predicted impact energies are in good agreement. The microstructures show that the steel exhibits a brittle behaviour at low and room temperatures as indicated by a transgranular fracture, but changes to a more ductile behaviour at high temperatures as illustrated by microvoid coalescence induced facture morphology.

Analysis of the stress and deformation states in the vertical flat-jack test

Performing a realistic assessment of unreinforced masonry structures involves designing and executing appropriate experimental tests on masonry components for determining the material model parameters to be used in structural analysis. Considering recent developments in which inverse analysis was used as calibration framework, a vertical flat-jack test is investigated in this paper. Two simplified models are described for the analysis of the stress state in the masonry due to the pressure transferred by the flat-jack. Furthermore, with the aim of designing the sensor setup for the test, a POD analysis on the deformation state of the structure is carried out, highlighting the basic deformation modes which govern the response. The results show that high stresses and local modes can occur in the proximity of the flat-jack, and thus local use of FRP reinforcement is recommended to avoid undesired brittle crack propagation which may prevent accurate calibration of mortar joint mechanical characteristics.

Experimental and stochastic analysis of lyophilisation

The development of the freeze-drying processes through the use of a combination of targeted experiments and the application of multidimensional computational models is applied increasingly in pharmaceutical practice, especially for scale-up purposes. This study deals with the analysis of uncertainties in the data on material properties and model parameters, and their influence on the results delivered by advanced computational models of lyophilisation. As a means of uncertainty analysis, the Stochastic Collocation Method is applied, allowing the use of existing reliable deterministic models as black boxes in the stochastic computations. As a deterministic model, the lyophilisation model is used, based on the axisymmetric approximation of a vial, and the Boundary Element Method as a solver. Five parameters, covering material properties, process conditions and model constants, are selected for the sensitivity analysis simulation of the lyophilisation of an aqueous mannitol solution. The results show that during the initial stage of the primary drying heat transfer from the shelf is crucial, and that the uncertainties in the contact surface area and material properties of the vial play a more important role than the thermal properties of the drying material. When the temperature of the material reaches its distinct primary drying stage level the mass transfer through the porous cake becomes the most important, with great sensitivity to the Knudsen diffusivity in the porous cake. We observed uncertainties in the results for the primary drying time in the order of ±6%, and uncertainties in the results for temperatures of ±0.6°C in the frozen material and ±3°C in the porous cake. The uncertainty analysis proved to be a great help in determining the critical parameters in the heat and mass transfer during the important primary drying step, which led to a better definition of the numerical model for use in the context of design space determination.

Fracture mechanics based fatigue life prediction for a weld toe crack under constant and variable amplitude random block loading—Modeling and uncertainty estimation

Propagation of weld toe cracks under cyclic loading is often predicted using fracture mechanics. In as welded condition, most of the propagation life is spent as a short crack, which is known to behave differently than a long crack. Several studies have been conducted with the aim of correlating the fatigue crack growth rate and the threshold condition of small cracks to the well known linear elastic crack driving force parameter ΔK, the stress intensity factor range. In many cases, the application of such models requires the quantification of material properties and model parameters that are difficult to obtain from tests, and therefore scarcely available. The present paper bypasses this inconvenience by making use of the square root of area, area, parameter proposed by Murakami. Successively, a linear elastic fracture mechanics based fatigue crack growth model is formulated for physically short and long cracks under constant and variable amplitude random block loading. The uncertainty of the model parameters is quantified in a frequentist statistical framework.

Constitutive model of unplasticized polyvinyl chloride for numerical stress-strain analysis

The mechanical properties of unplasticized polyvinyl chloride (UPVC) are modified during the manufacturing process of a product. Therefore, the data on the mechanical behavior of this material available in the scientific literature varies greatly. This requires that the type of mechanical behavior of the material and the corresponding constitutive model to be determined on a case-by-case basis. In the present work, an investigation of the mechanical behavior of UPVC is presented in order to select a model, best describing the material behavior at highly heterogeneous stress distributions within the structure. Twelve specimens from different parts of PVC window frames and sashes made by Weiss Profil, Bulgaria, have been tested under tension according to Bulgarian standard 12602-81. The mechanical behavior of the material and the corresponding material characteristics have been determined from the stress-strain curve obtained by the test. The research is directed at identifying the material model parameters, incorporated in FEM software used for the stress-strain analysis of load-bearing structures.

A flexible framework for sequential estimation of model parameters in computational hemodynamics

A major challenge in constructing three dimensional patient specific hemodynamic models is the calibration of model parameters to match patient data on flow, pressure, wall motion, etc. acquired in the clinic. Current workflows are manual and time-consuming. This work presents a flexible computational framework for model parameter estimation in cardiovascular flows that relies on the following fundamental contributions. (i) A Reduced-Order Unscented Kalman Filter (ROUKF) model for data assimilation for wall material and simple lumped parameter network (LPN) boundary condition model parameters. (ii) A constrained least squares augmentation (ROUKF-CLS) for more complex LPNs. (iii) A “Netlist” implementation, supporting easy filtering of parameters in such complex LPNs. The ROUKF algorithm is demonstrated using non-invasive patient-specific data on anatomy, flow and pressure from a healthy volunteer. The ROUKF-CLS algorithm is demonstrated using synthetic data on a coronary LPN. The methods described in this paper have been implemented as part of the CRIMSON hemodynamics software package.

Investigating the Effect of Cementite Particle Size and Distribution on Local Stress and Strain Evolution in Spheroidized Medium Carbon Steels using Crystal Plasticity‐Based Numerical Simulations

Herein, micromechanical material deformation behavior of medium carbon steel—with varying cementite particle size and distribution—under monotonic tensile load is modeled. The statistical phase morphology data are collected from the microscopy images of 83% spheroidized C45EC steel. Virtual microstructures for nine different cases are constructed using Dream.3D by varying the concentrations of small, large, and bimodal cementite particles on the ferrite grain boundaries. A crystal plasticity‐based numerical simulation model, i.e., DAMASK, is used to simulate the local material deformation behavior. The material model parameters for elastic–plastic ferrite and elastic cementite phases are adopted from the literature and calibrated by modifying the fitting parameters to match the experimentally observed material flow curve. It is observed that the cementite particle size and distribution in the primary phase affect the local mechanical behavior of the material. An analysis of deformation at 20% of global strain has helped in the qualitative understanding of factors affecting the stress and strain concentration points. The evolution of stresses and strains in the least and the most stressed representative volume elements (RVEs) has provided interesting information regarding the path followed by the dislocation movement during deformation. The study has provided insight into the factors affecting the material's global and local deformation behavior.

Extracting HCP Zerilli-Armstrong material parameters for magnesium alloy AZ31B from orthogonal cutting tests

This work reports on a methodology to extend Oxley’s analysis of the thick shear zone to account for HCP materials. Ultimately, the work extracts Zerilli-Armstrong (ZA) constitutive equation’ material parameters for AZ31B, an HCP crystal structure magnesium-based alloy. The methodology for accomplishing this utilizes three tasks namely: 1) Extension of thick shear zone approach for machining force simulation to account for Zerilli-Armstrong HCP material model, 2) measure cutting and thrust edge forces from orthogonal cutting tests (uncut chip thickness and cutting speed values varying between 0.05 and 0.4 mm/rev and 50–400 m/min, respectively), and 3) numerically determine updated material model parameters for AZ31B by minimizing the difference between the methodology-predicted forces and those experimentally measured. Comparing numerical data with the experiments, the determined AZ31B material model with updated parameters yielded predictability of R 2 of 0.94 and 0.91 for cutting and thrust forces, respectively. Additional validations were conducted by favorably comparing flow stress numerical predictions for AZ31B with literature-published histories at wide operating ranges of temperature, strain, and strain rate values. The presented methodology for finding HCP Zerilli-Armstrong material model parameters based on orthogonal cutting tests may serve as complementary alternative to time-consuming tension-compression flow stress experiments.

Determination of the material model and damage parameters of a carbon fiber reinforced laminated epoxy composite for high strain rate planar compression

The progressive failure of a 0°/90° laminated carbon fiber reinforced epoxy composite was modeled in LS-DYNA using the MAT_162 material model, including the strain rate, damage progression and anisotropy effects. In addition to conventional standard and non-standard tests, double-shear and Brazilian tests were applied to determine the through-thickness shear modulus and the through-thickness tensile strength of the composite, respectively. The modulus reduction and strain softening for shear and delamination parameters were calibrated by low velocity drop-weight impact tests. The rate sensitivities of the modulus and strength of in-plane and through-thickness direction were determined by the compression tests at quasi-static and high strain rates. The fidelity of the determined model parameters was finally verified in the in-plane and through-thickness direction by the 3D numerical models of the Split Hopkinson Pressure Bar compression tests. The numerical bar stresses and damage progressions modes showed acceptable correlations with those of the experiments in both directions. The composite failed both numerically and experimentally by the fiber buckling induced fiber-matrix axial splitting in the in-plane and the matrix shear fracture in the through-thickness direction.

Full-field stress computation from measured deformation fields: A hyperbolic formulation

Recent developments in imaging techniques and correlation algorithms enable measurement of strain fields on a deforming material at high spatial and temporal resolution. In such cases, the computation of the stress field from the known deformation field becomes an interesting possibility. This is known as an inverse problem. Current approaches to this problem, such as the finite element update method, are generally over-determined and must rely on statistical approaches to minimize error. This provides approximate solutions in some cases, however, implementation difficulties, computational requirements, and accuracy are still significant challenges. Here, we show how the inverse problem can be formulated deterministically and solved exactly in two or three dimensions for large classes of materials including isotropic elastic solids, Newtonian fluids, non-Newtonian fluids, granular materials, plastic solids subject to co-directionality, and some other plastic solids subject to associative or non-associative flow rules. This solution is based on a single assumption of the alignment of the principal directions of stress and strain or strain rate. No further assumptions regarding incompressibility, pressure independence, yield surface shape or the hardening law are necessary. This assumption leads to a closed, first order, linear system of hyperbolic partial differential equations with variable coefficients. The solution of this class of problems is well established and hence the equations can be solved to give the solution for any geometry and loading condition, enabling broad applicability to a variety of problems. We provide a numerical proof-of-principle study of the plastic deformation of a two-dimensional bar with spatially varying yield stress and strain hardening coefficient. The results are validated against the solution of the corresponding forward problem – solved with a commercial finite element solver – indicating the solution is exact up to numerical error (the normalized root mean square error of the stress is 1.63×10−4). No model calibration or material parameters are required. The sensitivity of the solution to error in the input data is also analyzed. Interestingly, this solution procedure lends itself to a simple physical interpretation of stress propagation through the material. Finally, we provide some examples showing how this approach may be analytically applied to both solid and fluid mechanics problems.

Simulation of springback in cyclic wipe-bending

This paper proposes a bending method to measure the robustness of advanced material constitutive models, which are developed aiming to precisely express material responses including the Bauschinger effect, permanent softening, etc. Such constitutive models, in general, require multiple sophisticated material tests, e.g. cyclic uniaxial tension-compression, followed by appropriate numerical optimizations to identify corresponding material model parameters. These tests, for example, intrinsically require anti-buckling measures for specimens that can lead to redundant frictional forces and biaxial effects. Besides, the strategy for the optimization of material parameters or the selection of elastic modulus model is also an important point to influence the final performances. In an effort to provide more robust reliability for springback simulation results, a wipe-bending tool enabling cyclic load reversals has been developed as an intermediate validator positioned between the role of the cyclic uniaxial tension-compression and that of the U-drawbending. Predicted springback results employing the Yoshida-Uemori model have shown that this approach can be considered as an effective way to confirm both the reliability of material model parameters and the capability of a selected constitutive model in a part development or tooling stage.

Microscopic Damage Model for Fibrous Composites Considering Randomness in Constituent Materials

For the multiscale damage behaviour simulation of advanced materials with hierarchical and random heterogeneous microstructures such as fibrous composites by finite element method, the mathematical homogenization method has been extended to the stochastic nonlinear multiscale method. A first-order perturbation based stochastic homogenization method was developed to calculate the microscopic strain, as well as the homogenized macroscopic properties considering randomness in the mechanical properties of constituent materials. Based on the calculated stochastic microscopic strain, the damage simulation framework was proposed for fibrous composites. For a demonstrated application, a numerical example of a single short fiber reinforced plastic composite was carried out. The damage propagation in the interphase between fiber and matrix was predicted in a stochastic way considering the physical random parameters for the interphase material model. The influences of the randomness on damage volume fraction and damage propagation of the interphase were discussed.

A detailed finite element investigation of the effects of local lateral high-velocity impacts on the ultimate strength of unstiffened steel plates subjected to uniaxial in-plane compression

In this paper, the ultimate strength of unstiffened steel plates under uniaxial in-plane compression is numerically studied considering the local lateral impact of a rigid-body impactor. The plates are made of mild steel, where its behaviour is modelled by using the Johnson-Cook material model. The material parameters of the Johnson-Cook material model calibrated by the authors were employed for predicting the behaviour of the target in order to numerically reproduce the impact tests. The value of average in-plane stress of the plates is determined accounting for the collision of rigid-body impactor with masses of 50–150 gr and velocities of 400–1200 m/s. Moreover, the effects of stress waves induced as a result of lateral impact of the rigid-body impactor on the ultimate strength of the plates under uniaxial in-plane compression are also assessed. The results indicate that the ultimate strength of the plate decreases due to stress-wave creation and thus, it is required to take that into account. Besides, it is revealed that assuming the final damaged state of the plate after being laterally impacted by the rigid-body impactor as an initial condition, does not yield a correct response when evaluating its ultimate compressive strength under uniaxial in-plane compression.

Investigations on the Application of the Downhill-Simplex-Algorithm to the Inverse Determination of Material Model Parameters for FE-Machining Simulations

Modeling the machining process by means of simulation techniques became more and more popular within the last decades. The increasing use of simulation techniques can be attributed to the enhancing computational performance. To accurately model the machining process, different input models are required. Among them, the material model has a crucial impact on the quality of the simulated results. To determine the underlying material model parameters, an inverse procedure has been established, where the material model parameters are adjusted within a chip formation simulation until a reasonable match between simulations and experiments is achieved. However, the procedure of the inverse determination requires high computational efforts and is not robust. This paper presents a novel approach to determine material model parameters inversely from FE-machining simulations by means of the Downhill-Simplex-Algorithm. An effect study was conducted to investigate the influence of the initial simplex, the boundary conditions, and the underlying parameters of the Downhill-Simplex-Algorithm. Further, the validated procedure has been extended to consider multiple cutting conditions and an adaptive step-size has been implemented into the algorithm. The results of the procedure were validated by re-identification of process observables from the target simulations and it was aimed to re-identify the material model parameters of the target simulations. Based on the algorithm, a robust and systematical method has been developed to determine material model parameters inversely from the machining process.

On the Reliability of Suction Measurements for Skin Characterization.

in vivo skin characterization methods were shown to be useful in the detection of microstructural alterations of the dermis due to skin diseases. Specifically, the diagnostic potential of skin suction has been widely explored, yet measurement uncertainties prevented so far its application in clinical assessment. In this work, we analyze specific factors influencing the reliability of suction measurements. We recently proposed a novel suction device, called Nimble, addressing the limitations of existing instruments, and applied it in clinical trials quantifying mechanical differences between healthy skin and scars. Measurements were performed with the commercial device Cutometer and with the new device. A set of new suction measurements was carried out on scar tissue and healthy skin, and FE-based inverse analysis was applied to determine corresponding parameters of a hyperelastic-viscoelastic material model. FE simulations were used to rationalize differences between suction protocols and to analyze specific factors influencing the measurement procedure. Tissue stiffness obtained from Cutometer measurements was significantly higher compared to the one from Nimble measurements, which was shown to be associated with the higher deformation levels in the Cutometer and the nonlinear mechanical response of skin. The effect of the contact force exerted on skin during suction measurements was quantified, along with an analysis of the effectiveness of a corresponding correction procedure. Parametric studies demonstrated the inherently higher sensitivity of displacement- over load-controlled suction measurements, thus rationalizing the superior ability of the Nimble to distinguish between tissues.

Martian Ice Revealed by Modeling of Simple Terraced Crater Formation

AbstractArcadia Planitia, a region in the northern midlatitudes of Mars, displays an uncommonly high abundance of simple craters with a concentric morphology, which is indicative of layering beneath the surface. Radar measurements suggest that the near surface layers could be made of excess water ice. In this study, we select two of these impact structures of similar size (Dc ~ 500 m), model their formation through iSALE shock physics code, and investigate the dependence of the final crater morphology on the material model parameters (cohesion and friction coefficient). Our parameter study shows that the intact and damaged cohesions of the nonporous ice play a fundamental role to obtain a good fit between our models and the topographic profiles taken from the digital terrain models in terms of crater diameter, crater wall inclination, and depth and size of the upper terrace. The central pit shape is instead controlled by the damaged friction coefficient of the basaltic crust, but it is mainly affected by projectile density and speed. Our results confirm that two layers of relatively pure water ice, each with different rheology and porosity, can explain the unique double‐terraced morphology of impact craters in Arcadia Planitia. The low values of cohesion we find for the ice might point to snowfall as emplacement mechanism in the region. The different thicknesses of the ice layers in the two crater areas seem to suggest variations in ice deposition and/or evolution history across Arcadia Planitia.

Fractional derivative group shear wave speeds for model-based viscoelastic characterization

We present a method for model-based viscoelastic characterization using shear wave elastography. The shear wave displacement signal is differentiated to a series of fractional derivative orders, and the group speed of the signal at each derivative order is calculated. These speeds are compared to a look up table built from simulations for a given viscoelastic material model. The best-fit material parameters are chosen to minimize the mean square difference between the group speeds from the look up table and experimental measurements across all fractional derivative orders. Various two- and three-parameter viscoelastic material models are tested. The technique is validated in simulations with ultrasonic tracking and demonstrated in three viscoelastic phantoms with material properties that match those associated with different degrees of liver fibrosis. Comparatively, phase velocity curves are computed, and parameters determined by fitting analytic expressions for phase velocity for a given material model. The fractional derivative group speed-based technique gives model parameters with lower mean square error than fitting material model parameters directly to phase velocities. Additionally, we conclude these viscoelastic phantoms are sufficiently characterized by a two-parameter material model and are better characterized by the Linear Attenuation model than the more commonly used Voigt model.

Comparison of porcine and human adipose tissue loading responses under dynamic compression and shear: A pilot study

Understanding the mechanical properties of human adipose tissue, and its influence on seat belt-pelvis interaction is beneficial for computational human body models that are developed for injury prediction in the vehicle crashworthiness simulations. While various studies have characterized adipose tissue, most of the studies used porcine adipose tissue as a surrogate, and none of the studies were performed at loading rates relevant for motor vehicle collisions. In this work, the mechanical response of human and porcine adipose tissue was studied. Two dynamic loading modes (compression and simple shear) were tested in adipose tissue extracted from the human abdomen and porcine back. An Ogden hyperelastic model was used to fit the loading response, and specific material parameters were obtained for each specimen. Two-sample t-tests were performed to compare the effective shear moduli and peak stresses from porcine and human samples. The material response of the human adipose tissue was consistent with previous studies. Porcine adipose tissue was found to be significantly stiffer than human adipose tissue under compression and shear loading. Also, when material model parameters were fit to only one loading mode, the predicted response in the other mode showed a poor fit.