User-defined Material Model Research Articles

Thermomechanical constitutive behaviour of 3D printed biomimetic polymer material under high strain rates

With the continuous technical breakthroughs of flexible electronics, materials with outstanding application potential are constantly being designed and optimized. Biomimetic polymer materials are particularly appealing due to their versatility and ease of fabrication, but their mechanical reliability, particularly their thermomechanical constitutive behaviour under extreme working loads, remains unclear. In this paper, the impact responses of a 3D printed biomimetic polymer material named “Tangoblack” are investigated under thermomechanical, focusing on the effect of strain rate. By adjusting the pressure of the gas gun in the split Hopkinson pressure bar, different strain rates are achieved, while the high temperature of the tested sample can be controlled using a heating furnace integrated into the experiment system. Materials for pulse shapers are carefully selected to ensure longer durations at nearly constant strain rates. The constitutive behaviour of the biomimetic polymer material is further investigated under a wide strain rate range from 958 s−1 to 2158 s−1 and three different temperatures (20 °C, 70 °C and 120 °C). The results demonstrate a significant dependence of the polymer material on both strain rate and temperature. A rapid increase in forming strain rate enhances the strain hardening process, while simultaneously revealing a substantial temperature softening effect. Then, an improved nonlinear thermoviscoelastic ZWT constitutive model is proposed utilizing the Vogel-Fulcher-Tammann equation and implemented as a user-defined material model in ABAQUS/Explicit. The proposed constitutive model is demonstrated to be distinctly advantageous, which suggests a novel pathway for describing the mechanical reliability of biomimetic polymer materials under extreme working conditions.

FINITE ELEMENT MODELLING AND ANALYSIS OF FREE VIBRATIONS OF AXIALLY FUNCTIONALY GRADED BEAMS WITH NON-UNIFORM CROSS-SECTIONS

The finite element package Abaqus is used for modeling and analysis of free vibrations of axially functional graded beams with non-uniform cross-sections. Considerable attention has been paid to this aspect of the geometry, as it has a significant effect on the behavior of the beam as a structural component. User-defined material model subroutines (UMAT) were developed in a unified way for one- and three-dimensional models of the specified beams to provide numerical implementation of functional material gradients within each finite element. UMAT procedures were programmed in FORTRAN in the MS Visual Studio environment and compiled with the main program package using the Intel Fortran Compiler. In the procedures, material heterogeneity was assigned to each material integration point of appropriate standard one- and three-dimensional finite elements, eliminating the need to design graded finite elements via user-defined element subroutine. Frequencies and mode shapes of free vibrations of one- and three-dimensional axially functional graded beams with non-uniform cross-sections were found using the Lanczos method in Abaqus. An analysis of the accuracy and effectiveness of the proposed modeling approach was carried out, comparing the obtained results with data known in the literature. The presented modeling technique based on user-defined material subroutines provides valuable opportunities for scientists and engineers engaged in the dynamic analysis of structural components made of functionally gradient materials and having variable geometry along the axial direction. Keywords: axially functionally graded beams; non-uniform cross-section beams; free vibrations; graded finite element; Abaqus user defined subroutines

Development of a three-dimensional muscle-driven lower limb model developed using an improved CFD-FE method

Analysis of the musculoskeletal movements (gait analysis) is needed in many scenarios. The in vivo method has some difficulties. For example, recruiting human subjects for the gait analysis is challenging due to many issues. In addition, when plenty of subjects are required, the follow-up experiments take a long period and the dropout of subjects always occurs. An efficient and reliable in silico simulation platform for gait analysis has been desired for a long time. Therefore, a technique using three-dimensional (3D) muscle modeling to drive the 3D musculoskeletal model was developed and the application of the technique in the simulation of lower limb movements was demonstrated. A finite element model of the lower limb with anatomically high fidelity was developed from the MRI data, where the main muscles, the bones, the subcutaneous tissues, and the skin were reconstructed. To simulate the active behavior of 3D muscles, an active, fiber-reinforced hyperelastic muscle model was developed using the user-defined material (VUMAT) model. Two typical movements, that is, hip abduction and knee lifting, were simulated by activating the responsible muscles. The results show that it is reasonable to use the improved CFD-FE method proposed in the present study to simulate the active contraction of the muscle, and it is feasible to simulate the movements by activating the relevant muscles. The results from the present technique closely match the physiological scenario and thus the technique developed has a great potential to be used in the in silico human simulation platform for many purposes.

A novel flexible biocomposite with hemp woven fabric and natural rubber based on lignin green filler: investigation numerical and experimental under high-velocity impact

In this study, the comparison of the behavior of hemp/elastomeric biocomposites based on lignin and carbon black has been investigated experimentally and numerically under the influence of high speed. SEM images confirmed the dispersion and good interaction of lignin in natural rubber with a uniform surface coverage of fibers and the gap of yarns. The results of tensile and dynamic compression tests showed that elastomer with lignin filler improves tensile strength for rubber samples and composites compared to carbon black. The high-velocity impact tests were performed on single-layer and three-layer composites based on lignin and carbon. The penetration resistance and failure mechanism of the composites during impact were validated using a constitutive material model for hemp fabric and a user-defined material model (VUMAT) for the nonlinear behavior of rubber materials with a damage criterion in ABAQUS/Explicit. For one-layer and three-layer flexible composites based on lignin, the ballistic limit is 49 and 96 m s−1, respectively. Compared to carbon-based composites, it has increased by 11.36 and 13% for one-layer and three-layers, respectively. Using the dilute matrix to cover hemp fabric increases the resistance of this type of fabric against high-speed impact. Through tensile failure, the stress is transferred to the surrounding fiber bundles so that more threads can participate in the load-bearing process. As a result, the penetration depth in lignin-based composites is lower, and the protective margin is greater, which increases energy absorption.

Numerical and experimental investigation of impact strength and fracture mechanism of Kevlar and Hemp elastomeric thin biocomposite laminate under high-velocity impact: A comparative study

Thin composite structures reinforced with woven fabrics are widely used in many industrial sectors due to their lightweight, easy access, and high specific performance. Due to safety, the study of fracture mechanisms and energy absorption of thin composite structures is significant. In this study, Kevlar and Hemp elastomeric thin biocomposite laminates with an elastomeric matrix filled with natural lignin filler with a low carbon footprint and with the aim of the sustainability concept of environmental protection have been designed experimentally and numerically for testing under high-velocity impact. The impact resistance of elastomeric composites reinforced with natural fillers is less reported. Good interaction of lignin-filled elastomeric matrix with woven hemp fabric is expected to show impact performance comparable to Kevlar-reinforced composites. For this purpose, Kevlar and hemp thin elastomeric biocomposites are tested under high-velocity impact with almost the same surface density. Also, tensile and dynamic compression tests (Hopkinson test) were performed to check the mechanical properties of the elastomer layer. The proposed laminates' penetration resistance and fracture behavior during an impact according to the Kevlar and hemp fabric constituent material model and the user-defined material model (VUMAT) for the nonlinear behavior of elastomeric materials considering the damage criterion in ABAQUS/Explicit confirmed. The results show, In the thin elastomeric hemp biocomposites, the tensile failure and stress transfer to the surrounding bundles cause more yarns to participate in the load-carrying process. As a result, the low penetration depth and more significant protection margin in fully green hemp composites provide impact performance comparable to Kevlar elastomeric composites.

Multi-scale numerical investigation of deep drawing of 6K21 aluminum alloy by crystal plasticity and a stress-invariant based anisotropic yield function under non-associated flow rule

In this research, the earing characteristics of 6K21 aluminum alloy in circular cup deep drawing are investigated by virtue of experiments and multi-scale simulations including anisotropic Drucker, Hill48, Yld91 yield functions and crystal plastic finite element model (CPFEM). First, the deep drawing experiments of AA 6K21 are carried out to explore the influences of blank holding force (BHF) and blank diameter (BD) on earing profile and mechanical response. The user-defined material model subroutine is written for LS-DYNA explicit code, including constitutive model and ductile fracture criterion under associated or non-associated flow rule (NAFR). The parameters of the crystal plasticity model are calibrated by means of an optimization algorithm. Three yield functions under NAFR and CPFEM are used to predict earing in deep drawing simulation. The effects of five textures on the earing profiles and thickness variables are studied by CPFEM. The results demonstrate that the earing rate decreases slightly as the BHF increases. However, the mechanical response changes insignificantly. Moreover, as the BD increases, both the earing rate and mechanical response increase significantly. Considering computation accuracy and efficiency, the anisotropic Drucker function can accurately character the plastic deformation behavior of deep drawing. For five textures in CPFEM, Cube and Goss textures produce four ears at 0o and 90o from the rolling direction. Brass and S textures form six ears at 0o and 55o. Copper texture fabricates eight ears at 40o and 70o. The influences of five textures on earing rate are Goss > Cube > Copper > Brass > S. Furthermore, there are obvious thickness gradient fluctuations at the corner of the cup in Cube, Goss and Copper textures. It is expected to reduce the earing rate and improve the formability through reasonable allocations of experimental parameters and texture proportions.

A plastic-damage material model for foam concrete under blast loads

Foam concrete is a prospective material in defense engineering to protect structures subjected to intense dynamic loadings such as impact and blast through wave impedance mismatch as well as energy absorption. In the near-field of intense dynamic loadings, the foam concrete is always suffered from a high-pressure stress state associating with complex failures such as pore collapse, shear fracture and tensile fracture. A well-established material model is needed to capture above-mentioned behaviors. In this paper, a plastic-damage material model for foam concrete is proposed focused on its mechanical behavior under high pressures. Firstly, a closed form yield function, a partially-associative flow rule and a new piecewise hardening law are introduced. The yield function is composed of a fracture function describing the mechanical behavior due to microcracks and a continuous cap function describing the mechanical behavior due to pores. The partially-associative flow rule is used to avoid the overestimation of plastic strain induced by the classical associative flow rule. In particular, a new piecewise hardening law is proposed instead of frequently-used exponential ‘‘crush curve’’, which is flexible for fitting test data and can capture the experimentally-observed increase of unloading bulk modulus with increase of pressure. The rate dependency of yield surface is considered to capture the strain-rate effect of foam concrete. And then three independent damage indexes with clear physical background are proposed to describe irreversible degradation caused by microcrack growth and pore collapse. The shear damage caused by shear cracks, tensile damage caused by tensile cracks, and hydrostatic compression damage caused by pore collapse, are separately identified and proposed in the framework of continuum damage mechanics. The proposed model is embedded into the LS-DYNA through the subroutine of user-defined material model. Its performances for predicting complex failures under various stress states at a Gaussian point level are numerically evaluated using a single element, and further used to predict blast response of foam concrete. All the numerical predictions agree with test data well.

Muscle Constitutive Model With a Tangent Modulus Approximation: Ansys Implementation and Verification.

Sophisticated muscle material models are required to perform detailed finite element simulations of soft tissue; however, state-of-the-art muscle models are not among the built-in materials in popular commercial finite element software packages. Implementing user-defined muscle material models is challenging for two reasons: deriving the tangent modulus tensor for a material with a complex strain energy function is tedious and programing the algorithm to compute it is error-prone. These challenges hinder widespread use of such models in software that employs implicit, nonlinear, Newton-type finite element methods. We implement a muscle material model in Ansys using an approximation of the tangent modulus, which simplifies its derivation and implementation. Three test models were constructed by revolving a rectangle (RR), a right trapezoid (RTR), and a generic obtuse trapezoid (RTO) around the muscle's centerline. A displacement was applied to one end of each muscle, holding the other end fixed. The results were validated against analogous simulations in FEBio, which uses the same muscle model but with the exact tangent modulus. Overall, good agreement was found between our Ansys and FEBio simulations, though some noticeable discrepancies were observed. For the elements along the muscle's centerline, the root-mean-square-percentage error in the Von Mises stress was 0.00%, 3.03%, and 6.75% for the RR, RTR, and RTO models, respectively; similar errors in longitudinal strain were observed. We provide our Ansys implementation so that others can reproduce and extend our results.

Multi-criteria decision-making analysis and numerical simulation of the low-velocity impact response of inter-ply S2-glass/aramid woven fabric hybrid laminates

Hybrid composites have gained a lot of attention due to their superior mechanical performance and energy absorption capacity compared to single-fibre counterparts, but studies on the hybridization of aramid and S2-glass fabrics are still scarce. This paper presents a multi-criteria decision-making analysis and numerical simulation applied to the study of the performance of asymmetric inter-ply hybrids of plain-weave aramid and satin-weave S2-glass fabrics/epoxy laminates subjected to low-velocity impact. Different aramid/glass fibre ratios, impact sides and impact energies (19 J, 37 J and 72 J) were investigated. A multi-criteria decision-making analysis was performed to identify the best laminate design based on the technique for order of preference by similarity to the ideal solution which considered areal density, deformation and absorbed energy as design criteria. A novel numerical FE model based on continuum damage mechanics was developed considering non-linear material constitutive behaviour and different interlaminar and intralaminar failure modes. The material model was implemented in Abaqus/Explicit solver using a user-defined material model, and the non-linear material behaviour in the normal direction is considered by defining instantaneous stiffnesses using third-degree polynomials. The results identified single fibre laminates as the worst designs and hybrid laminates with aramid on the impact side as the best design. Besides, for similar fibre ratios, the total delamination area was larger for the impact on aramid layers.

A novel dynamic constitutive model for UHPC under projectile impact

Aimed at numerically predicting the impact resistance and damage pattern of ultra-high performance concrete (UHPC) under projectile impact, this study established a novel dynamic constitutive model for UHPC based on an improved Karagozian & Case concrete (KCC) model newly proposed by authors. Firstly, the established model is introduced, which considers the complex dynamic mechanical properties of UHPC, including the Lode-dependence, strain rate effect, compressive strain hardening and softening, tensile strain softening, volumetric compaction, and shear dilation. Particularly, a four-stage strain softening tensile damage model is adopted for UHPC. Then, the established model is embedded in the commercial hydrocode LS-DYNA as a user defined material model. According to the existing test data of UHPC, the failure surface, strain rate effect, equation of state, and damage model parameters are calibrated for the established model. For comparison, the parameters of the KCC model are also calibrated accordingly. To verify the calibrated material model parameters, single element tests are conducted under tensile and compressive loadings. Finally, the high velocity impact tests performed on both the semi-infinite targets and finite-depth panels with varying striking velocity are simulated, where the established model and the KCC model are respectively adopted for UHPC. It demonstrates that the established model reproduced the impact resistance and damage pattern of UHPC under projectile impact accurately, while the KCC model cannot reflect the dynamic response of UHPC satisfactorily.

Experimental and Numerical Study of the Influence of Pre-Existing Impact Damage on the Low-Velocity Impact Response of CFRP Panels.

This paper presents an experimental and numerical investigation on the influence of pre-existing impact damage on the low-velocity impact response of Carbon Fiber Reinforced Polymer (CFRP). A continuum damage mechanics-based material model was developed by defining a user-defined material model in Abaqus/Explicit. The model employed the action plane strength of Puck for the damage initiation criterion together with a strain-based progressive damage model. Initial finite element simulations at the single-element level demonstrated the validity and capability of the damage model. More complex models were used to simulate tensile specimens, coupon specimens, and skin panels subjected to low-velocity impacts, being validated against experimental data at each stage. The effect of non-central impact location showed higher impact peak forces and bigger damage areas for impacts closer to panel boundaries. The presence of pre-existing damage close to the impact region leading to interfering delamination areas produced severe changes in the mechanical response, lowering the impact resistance on the panel for the second impact, while for non-interfering impacts, the results of the second impact were similar to the impact of a pristine specimen.

An Orthotropic Nonlinear Thermoviscoelastic Model for Polymeric Battery Separators

Structural responses of separators are critical to battery safety. Commonly used separators are dry-processed polymers with anisotropic microstructures. Due to the material anisotropy, rate dependence, and temperature dependence, developing a model for predicting the thermomechanical response of polymeric battery separators has been challenging. This paper presents an orthotropic nonlinear thermoviscoelastic model for predicting the response of polymeric battery separators in thermal ramp scenarios. The model was based on the Schapery nonlinear viscoelastic model and the temperature dependence was introduced through the time-temperature superposition principle (TTSP). The model was implemented in LS-DYNA® finite element (FE) package as a user-defined material model. The model parameters were determined for a polypropylene (PP) separator. The predicted material responses under large deformations in isothermal and non-isothermal temperature conditions for stress relaxation, creep and tensile loadings at different rates agree well with the experimental data.

A Numerical Study on the Influence of Strain Rate in Finite-Discrete Element Simulation of the Perforation Behaviour of Woven Composites.

Predicting the perforation limit of composite laminates is an important design aspect and is a complex task due to the multi-mode failure mechanism and complex material constitutive behaviour required. This requires high-fidelity numerical models for a better understanding of the physics of the perforation event. This work presents a numerical study on the perforation behaviour of a satin-weave S2-glass/epoxy composite subjected to low-velocity impact. A novel strain-rate-dependent finite-discrete element model (FDEM) is presented and validated by comparison with experimental data for impacts at several energies higher and lower than their perforation limit. The strain rate sensitivity was included in the model by developing a novel user-defined material model, which had a rate-dependent bilinear traction separation cohesive behaviour, implemented using a VUSDFLD subroutine in Abaqus/Explicit. The capability of the model in predicting the perforation limit of the composite was investigated by developing rate-sensitive and insensitive models. The results showed that taking the strain rate into account leads to more accurate predictions of the perforation limit and damage morphology of the laminate subjected to impacts at different energies. The experimental penetration threshold of 89 J was estimated as 79 J by the strain-rate-sensitive models, which was more accurate compared to 52 J predicted by the strain-rate-insensitive model. Additionally, the coupling between interlaminar and intralaminar failure modes in the models led to a more accurate prediction of the delamination area when considering the rate sensitivity.

A three-dimensional micromechanical model for simulating ply crack formation in laminates under in-plane tensile loading

Micromechanical models were established to simulate ply cracking in [0/90/0] laminates under tension. A new user-defined material model was developed within a finite element framework to capture inelastic deformation of the matrix and local cavitation-induced and ductile failure. A damage model was used to capture corresponding post-peak behaviour. Representative volume elements (RVEs) of laminates were generated, where the fiber and matrix constituents were explicitly represented in the 90° ply. The experimentally verified simulations revealed local matrix failure onset was governed by brittle cavitation, while subsequent microcracking was influenced by local ductile failure. The model accurately captured the delay in first full ply crack formation for laminates with thinner plies. The role of thermal residual stress, ply constraints, and fiber volume fraction on ply crack formation were investigated. The associated effective energy release rate was predicted and can be used for predicting ply crack multiplication in meso- or macro-scale models.

Predicting the failure mechanism of RC slabs under combined blast and impact loading

The dynamic structural behaviour and failure mechanisms of the reinforced concrete (RC) slabs under the combined blast and impact loading is numerically evaluated using the software LS-DYNA. The developed material model for concrete includes the plasticity behaviour under dynamic loading. The developed model includes the modified equation of state (EOS) which accounts for the loss of cohesive property and increase in compaction strength of the concrete material. The failure surface includes the effect of strain rate along with the lode angle and damage variable. The behaviour of concrete at low and high hydrostatic pressure is predicted with the developed model. The model has been formulated using a user-defined material model (UMAT). The predictions of the developed UMAT and in-built Winfrith concrete model (WCM) is compared with experimental results available in the literature. The developed concrete model can predict the failure mechanisms and the dynamic response of the slab accurately when compared with the results of WCM. Only limited experiments are available on the behaviour of RC slabs under combined blast and impact loading. Hence, the validation for analysis of the impact and blast loading scenario is carried out separately with the experimental results. The performance under the combined loading scenario is analysed by varying the sequence of applying the impact and blast loads. The slab subjected to impact-blast loading showed an increased dynamic response. The slab shows severe spallation, scabbing because of the flexural shear mode of failure caused by impact loading before the initiation of subsequent blast loading. The RC slabs subjected to longer impact duration before the initiation of subsequent blast loading under impact-blast loading scenario exhibited a more dynamic response. The failure of RC slabs under combined blast and impact loads shows increased localized damage and the stress concentration at the support caused by impact mass. The effect of slab thickness and reinforcement percentage is also studied by varying the velocity of the impact mass. The statistical analysis is carried out to study the uncertainty in the stress response of the developed model using the random variation of the input material parameters. The analysis is carried out to find the most influential input material parameter and the parametric study considered to study the combined impact and blast loading response of the slab.

Improvement of the dynamic failure behavior of concrete subjected to projectile impact using user-defined material model

The RHT model, one of the concrete material models, is embedded in commercial tools, and is mainly used for impact and explosive analysis with high strain rates. The original RHT model showed sufficiently similar results for the penetration depth measured by experiments in the low impact velocity. However, as the impact velocity increases, the original model has limitations in expressing the dynamic response of the concrete because yield surfaces and fracture behavior, depending on the strain rate, were underestimated. Although previous studies were conducted to improve the RHT model, the input parameters constituting the RHT model were either adjusted to approximate the experimental data. In this study, we propose a model that can express the improved dynamic tensile failure behavior by reflecting the strain rate-dependent parameters. Unlike the methods used in previous studies, the modified model was established that formulates important parameters to fit well with the experiment using user-defined functions. Based on experimental observations, we introduced a nonlinear crack softening model that reflects strain rate-dependent tensile strength and fracture energy to realistically express fracture strain and impact resistance against dynamic loads. In addition, we embedded a damage model that represents the irreversible volumetric deformation caused by pore collapse as the confinement pressure increases. For the verification of the proposed model, numerical simulations for the two experimental tests (i.e., penetration of thick concrete targets and perforation of thin concrete slabs) were performed. The proposed model shows good agreement with the experimental results, and in particular, it showed that the penetration depth and residual velocity are well estimated. Thus, we confirmed that it is superior in representing the resistance and fracture behaviors of the concrete target.

Behaviour of hybrid glass fibre-reinforced polymer and timber composite laminates under shear loading: Importance of fibre rotation

This paper presents a study aimed at investigating the behaviour of hybrid glass fibre reinforced polymer (GFRP)-timber (HFT) composite laminates under shear loading. A series of V-notched rail shear tests were carried out to determine the properties of HFT laminates, both in perpendicular and parallel to timber grain direction. In addition, shear tests were also conducted for pure timber and GFRP specimens. Except for pure timber specimens loaded parallel to grains, all specimens showed significant non-linear behaviour. During the testing, significant rotation of the glass fibres was observed. To further investigate the behaviour of the shear test specimens, a numerical model was developed. A numerical simulation approach that combines the progressive damage modelling of GFRP and timber with advanced fibre rotation modelling was developed. The simulation approach was implemented in finite element (FE) software program ABAQUS\\Explicit via a vectorized user-defined material model (VUMAT). FE results showed a good agreement with the test results and confirmed the significant influence of fibre rotation on the post peak behaviour of the HFT specimens under shear loading.

Micromechanical assessment of local failure mechanisms and early-stage ply crack formation in cross-ply laminates

Three-dimensional computational micromechanical models are developed to study local failure mechanisms and early-stage ply crack formation in a carbon fiber/epoxy [0/90/0] cross-ply laminate under tensile loading. Pressure-dependent inelastic deformation of the epoxy is captured by a user-defined material model, where brittle cavitation and ductile failure are considered local failure mechanisms. Manufacturing-induced defects, including nonuniform fiber spatial dispersion and resin pockets, are represented in the 90° ply. The effects of ply constraints on the local distortional and dilatational energy densities in the matrix are evaluated. Brittle cavitation is found to be the first and dominating failure mechanism, while local inelastic deformation indirectly influences the number and location of cavitation sites. Inelastic deformation is deemed necessary for predicting the linkage of the microcracks that are induced by brittle cavitation. The study provides important insight into the early-stage formation of ply cracks, which is essential for analyzing the subsequent ply crack formation.

A Progressive Damage Modelling of Glass/Epoxy Cylindrical Structure Subjected to Low-Velocity Impact

Due to the harshness and unpredictability of the tidal site environment, the damage induced by an accidental impact should be considered in the certification of composite cylindrical structures intended to be used in the design of the composite MJM tidal turbine concept. The first part of this paper deals with the effect of different failure criteria based on quadratic stress functions on the low-velocity impact response of thick filament wound glass/epoxy cylindrical structures. A user-defined material model (VUMAT) applied to three-dimensional solid elements was implemented into the finite element software Abaqus-Explicit to explore the effect of failure criteria on the predicted dynamic response with intralaminar damage. The investigated failure criteria include the two-dimensional Hashin criteria presented by Hashin in 1973 and extended to the three-dimensional case by including analytically the out-of-plane stress terms (criteria denoted “Hashin 3D”), the three-dimensional Hashin criteria described by Hashin in 1980 (criteria denoted “Hashin 3D 1980”), the Puck matrix transverse criterion coupled to Hashin criteria (criteria denoted “Hashin-Puck”) and Chang-Chang criteria (criteria denoted “Chang & Chang 1987”). The intralaminar damage model includes damage onset based on quadratic failure criteria, damage evolution, and element deletion from the solid mesh. FEA analyses are carried out with different low-level impact energies. The numerical results show different impact responses as well as the damage characteristics particularly the matrix cracking through the thickness. In the second part the bilinear cohesive zone model (CZM) is employed for modelling the interlaminar damage. The combination of the intralaminar damage model with the interlaminar model is applied using an uncoupled methodology. By comparison with the experimental force–time curves, interface properties used in the cohesive model have been estimated numerically using a reverse methodology and a baseline FEA model. The modelling approach has proven to be capable of reproducing experimental results with good accuracy. The modelling outcomes and predicted damage are therefore intended to be applied in the design loop and development of the MJM tidal turbine prototype where thick filament wound glass/epoxy cylinders are subjected to low-velocity stones impact.

Simulation of softening in high pressure torsion process using continuum damage mechanics model

Severe Plastic Deformations (SPD) processes are used for grain refinement without any loss in ductility. Among various SPD processes, High Pressure Torsion (HPT) is extensively used in industries due to generation of high angle grain boundaries and cost effectiveness. Very little work has been reported on the numerical analysis of softening with recovery that might occur in a work-piece undergoing HPT. The present work is an attempt to study the softening behaviour in HPT processed mild steel and aluminium alloy using the Lemaitre’s continuum damage mechanics (CDM) model. This model is implemented in ABAQUS/Explicit through a user defined material model subroutine (VUMAT). A parametric study is carried out to study the effect on softening of various parameters like the compressive load, the friction at the die-workpiece interface, and the height to diameter ratio. Information about the softening with recovery provides an insight into the hardness and microstructure homogeneity in HPT processed work-piece, which is useful in the design of HPT process.