Explicit Finite Element Analysis Research Articles

Hierarchical multiscale modeling of Polyvinyl Alcohol/Montmorillonite nanocomposites

Abstract The mechanical responses of low volume fraction Polyvinyl Alcohol (PVA)/Montmorillonite (MMT) nanocomposites were modeled using a hierarchical multiscale modeling method. Nanoscale Molecular Dynamics (MD) and mesoscale Finite Element Analysis (FEA) were used to bridge information regarding deformation mechanics within Polymer/Clay Nanocomposites (PCNs). MD computations of PVA/MMT interfaces were employed to calibrate a Traction-Separation (T-S) relation, which was then upscaled into a cohesive zone model (CZM) to model interfaces between PVA and MMT in a mesomechanical finite element framework. Virtual Composite Structure Generation (VCSG) was used to generate a quasi-realistic Representative Volume Element (RVE), and explicit FEA was performed on the RVE to demonstrate delamination in the PCNs. The FEA featured an elasto-viscoelastic-viscoplastic Internal State Variable (ISV) model for the polymer host (PVA) and a CZM for the interfaces between MMT and PVA. The hierarchical length scale bridging methodology employed here for a polymer based composite has applications for many other material systems.

Ballistic impact analyses of triangular corrugated plates filled with foam core

The usage of sandwich structure is extensively increasing in lightweight protective structures due to its low density and other useful properties. Sandwich panels made of metal sheets with unfilled cellular cores are found to exhibit lower deflections by comparing to an equivalent monolithic plate of same metal and similar mass per unit density. However, the process of localized impact on solid structures involving plastic deformation, high strain rates, temperature effect, material erosion, etc. does not hold effectively as that of monolithic plate. In present work, the applications of the sandwich plate with corrugated core have been extended to develop optimized lightweight armour using foam as medium of its core by explicit finite element analysis (FEA). The mechanisms of hardened steel projectile penetration of aluminum corrugated sandwich panels filled with foams have been numerically investigated by finite element analysis (FEA). A comparative study is done for the triangular corrugated sandwich plate filled with polymeric foam and metallic foam with different densities in order to achieve the optimum penetration resistance to ballistic impact. Corrugated sandwich plates filled with metallic foams are found to be superior when compared to the polymeric one. The optimized results are then compared with that of equivalent solid and unfilled cores structure to observe the effectiveness of foam-filled corrugated sandwich plate which provides an effective resistance to ballistic response. The novel structure can be the alternative to solid aluminum plate in the applications of light weight protection system.

Finite element modeling of structural steel component failure at elevated temperatures

A key issue in evaluating the response of structural systems to fire effects is the representation of material behavior at elevated temperatures. In addition to stress–strain behavior, modeling of fracture is required to capture failure modes such as tear out in connection plates and bolt shear. Fracture can be simulated in explicit finite element analysis using element erosion, in which elements are removed from the analysis when specified failure criteria are satisfied. However, the basis for determining and implementing material failure criteria at elevated temperatures is not well-established in the literature. A finite element material modeling methodology is presented for structural steels and structural bolts at elevated temperatures that incorporates erosion-based modeling of fracture. Temperature-dependent stress–strain relationships for structural steel and structural bolts were combined with a plastic strain-based failure criterion for element erosion to enable modeling of fracture in analysis of structural connections and assemblies. The failure criterion was calibrated against high-temperature experimental data on elongation of tensile coupons at fracture, and its dependence on temperature and mesh size was investigated.

Explicit multiscale modelling of impact damage on laminated composites – Part II: Multiscale analyses

This work describes a multiscale impact damage prediction methodology for laminated composite structures which is based on the HFGMC micromechanical model and the MMCDM damage formulation. The numerical approach is intended for application within explicit finite element analyses and has been employed for modelling of high-velocity impact damage in laminated composite structures. Structural-scale applications and the multiscale framework of the method are presented in this paper whereas introduction and validation of the methodology have been presented in Part I of the paper.By applying the described method, the micromechanical model calculates the local stress/strain fields within the unidirectional composite material, whereas the structural-scale computations have been performed employing Abaqus/Explicit. The Mixed Mode Continuum Damage Mechanics (MMCDM) theory has been utilised as to model the damage and failure modes of the composite material at the micromechanical level. As demonstrated in the Part I paper, the HFGMC and MMCDM model enable modelling of the microdamage nonlinearities at in-plane shear and transverse compressive loading of the composite plies. The micromechanical damage modelling approach has been employed at high-velocity soft-body impact on CFRP and GFRP composite plates in this work. Results of the multiscale damage model have been validated using available experimental data and by comparison with the numerical results obtained using the commonly used ply-level failure criteria and damage models.

Understanding the anomalously long duration time of the transmitted pulse from a soft specimen in a kolsky bar experiment

The reason for the observation of an anomalously long pulse duration time of a signal transmitted from a soft specimen in a Kolsky bar experiment is investigated. A systematic numerical experiment based on explicit finite element analysis has been carried out using elastic specimens with varying elastic moduli. The soft specimen is in a compressive state even after the passage of the pulse because it cannot push the bars, such that a fairly long transmitted pulse is monitored at the gage position of the output bar. The arrival of the second pulse (tensile) from the right-end surface of the output bar releases the first transmitted signal (compressive) coming from the compressed state of the specimen, which puts an end to the fairly long transmitted pulse. Because the observation of a prolonged transmitted pulse is a natural phenomenon, the prolonged transmitted pulse should not annoy researchers in the process of confirming the validity of experiments on soft specimens. Our concern in verifying the validity of experiments can be limited to other aspects such as the process of measurement and the amplification of weak transmitted signals coming from soft specimens.

Dynamic research on single-row slewing bearing with local spalling of inner ring

The working state of equipments such as wind turbines, cranes, and excavators is directly affected by the damage of the slewing bearing. Condition monitoring system is a good method to identify the defects; however, the measuring range and distribution of the sensors have important influence on the monitoring efficacy. Due to the thin-wall and cyclic structure characteristics of a slewing bearing, the defect characteristic response is unusual and unknown. To solve this problem, a finite element model for local defect on the raceway of a slewing bearing was established by ABAQUS, and the operating process of the slewing bearing was simulated based on the explicit dynamic finite element algorithm. The pulse waveforms of vibration responses under different defect sizes are obtained, and the influencing mechanism of the damage sizes on the slewing bearing was studied. The simulation results show that the increase in defect length is the dominant influence on the operation of a slewing bearing and the effect of height is negligible under the same conditions. Furthermore, the explicit dynamic finite element analysis model was reasonable by comparing the simulation results with the test results. Therefore, the localized defect on the raceway surface of a slewing bearing can be reflected by finite element simulation analysis, and the analytical results can help develop the raceway damage monitoring system of a slewing bearing.

Microplane-Triad Model for Elastic and Fracturing Behavior of Woven Composites

A multiscale model based on the framework of microplane theory is developed to predict the elastic and fracturing behavior of woven composites from the mesoscale properties of the constituents and the weave architecture. The effective yarn properties are obtained by means of a simplified mesomechanical model of the yarn, based on a mixed series and parallel coupling of the fibers and of the polymer within the yarns. As a novel concept, each of the several inclined or aligned segments of an undulating fill and warp yarn is represented by a triad of orthogonal microplanes, one of which is normal to the yarn segment while another is normal to the plane of the laminate. The constitutive law is defined in terms of the microplane stress and strain vectors. The elastic and inelastic constitutive behavior is defined using the microplane strain vectors which are the projections of the continuum strain tensor. Analogous to the principle of virtual work used in previous microplane models, a strain energy density equivalence principle is employed here to obtain the continuum level elastic and inelastic stiffness tensors, which in turn yield the continuum level stress tensor. The use of strain vectors rather than tensors makes the modeling conceptually clearer as it allows capturing the orientation of fiber failures, yarn cracking, matrix microcracking, and interface slip. Application of the new microplane-triad model for a twill woven composite shows that it can realistically predict all the orthotropic elastic constants and the strength limits for various layups. In contrast with the previous (nonmicroplane) models, the formulation can capture the size effect of quasi-brittle fracture with a finite fracture process zone (FPZ). Explicit finite-element analysis gives a realistic picture of progressive axial crushing of a composite tubular crush can initiated by a divergent plug. The formulation is applicable to widely different weaves, including plain, twill, and satin weaves, and is easily extensible to more complex architectures such as hybrid weaves as well as two- and three-dimensional braids.

Duality of energy absorption and inertial effects: Optimized structural design for blast loading

This article provides insights into the dynamic response and protection capacity of sacrificial structures mounted on a structural member and subjected to close standoff blast loading. The three main objectives of this study are: (a) exploration of key parameters governing the failure modes of a structural member protected by a sacrificial structure; (b) quantification of blast resistance and protection capacity of the sacrificial structure and underlying structure; and (c) conducting comparative single-degree-of-freedom system analysis and high-resolution explicit finite element analysis aiming at improving current single-degree-of-freedom analysis approaches. Energy absorption and momentum resistance are identified and quantified as the main contributing mechanisms controlling the dynamic response of structural members subjected to high-speed dynamic loading. The displacement of the structural member in the blast direction, the mass per length of the structural member, and the maximum impulse are found to be parameters governing the nonlinear response. The article also presents a response surface approach which might have value for time-efficient optimized structural member design and prediction of nonlinear structural member response to blast loading. This study includes validation of the numerical data through free-air blast test data from the literature.

Microstructure based modeling of ductile fracture initiation in press-hardened sheet metal structures

The manufacturing of sheet metal components with spatially varying microstucture composition and mechanical properties using press-hardening technology is now an established practice in the automotive industry. To estimate the performance envelopes of such components, a multi-scale approach to ductile fracture prediction based on mean-field homogenization is proposed. Two non-interacting fracture criteria are formulated in terms of the local average stress field, referring to inter-phase and intra-phase fracture mechanisms. The overall ductility is governed by the weakest constituent or interface present in the multiphase material. Moreover, instabilities related to the strain localization problem at the macroscale are treated by embedding discontinuities in the element formulation. These are triggered by a localization criterion derived via bifurcation analysis of the homogenized material. Issues concerning numerical implementation include a forward Euler scheme for integrating the mean-field equations, suitable for explicit finite element analysis of heterogeneous materials. Tensile specimens with ten distinctly different microstructure compositions are evaluated, for which useful predictions of the overall force–displacement response and fracture elongations are demonstrated.

An Eulerian approach to soil impact analysis for crashworthiness applications

The primary motivation of this study was the development and implementation of an explicit nonlinear dynamic finite element based methodology for investigating the crashworthiness of small lightweight composite aircraft impacting into soft soil. The technique used to characterise and validate a numerical model for soft soil as an impact terrain is the focus of this paper. The technique used was primarily based on the use of a time explicit Eulerian-based finite element analysis code, and this technique was demonstrated through the finite element analysis of penetrometer drop tests into soft soil. The Eulerian-based finite element approach was considered rather than the more commonly used Lagrangian-based finite element approach in order to reduce numerical instabilities which often occur with the use of Lagrangian solvers when considering problems with large deformations, which is a characteristic of crash analyses. Validation of the numerical model was based on previously published work in which penetrometer drop tests into soft soil/clay were performed at the Utah Test and Training Range. Experimental data were presented in this work, as well as a finite element modelling approach based on Lagrangian methods. Based on the results obtained it was concluded that an Eulerian-based approach to soft soil impact analysis, for crashworthiness applications, is valid. Greater model fidelity may possibly be gained by further investigation of the drop test methodology, viscosity effects, variation of soil mechanical properties through the depth range, and strain rate effects.

Solidity effect on crashworthiness characteristics of thin-walled tubes having various cross-sectional shapes

ABSTRACTIn this paper, effects of solidity and cross-sectional shape on crashworthiness characteristics of thin-walled tubes under dynamic axial impact load are examined. For this purpose, explicit finite element analyses are conducted for tubes having triangular, square, circular, hexagonal, octagonal and multi-cell cross-sectional shapes. The FE model is validated with analytical and experimental results that were reported in literature. It is found that FE solutions agree well with analytical and experimental results presented in the literature. To compare the tubes having different geometric dimensions and shapes on the same ground, the tubes are selected such that they have the same mass and length, and the striker mass and velocity are identical for all tubes as well. By changing solidity of tubes between 0.05 and 0.25, the cross-sectional dimensions of tubes are specified. The crushing force efficiency, crushing strain, total efficiency, structural efficiency and dynamic energy absorbing effectiveness parameters are calculated for various tubes as a function of the solidity parameter. It is concluded that crashworthiness performance of thin-walled tubes is significantly influenced by the solidity and cross-sectional shape. Results about the most effective solidity values and cross-sectional shapes are presented.

Fire behaviour of slender, highly utilized, eccentrically loaded concrete filled tubular columns

This paper investigates the fire performance of highly utilized and eccentrically loaded concrete filled composite columns with slendernesses greater than currently permitted by the simple calculation model in Eurocode 4 Part 1.2. The fire resistance rating was calculated by applying implicit as well as explicit finite element analyses and undertaking sequentially coupled thermal-stress analyses. Initially, published fire tests on concentrically loaded columns as well as columns with a modest load eccentrically (e/h≤0.25) were analysed with normal (NSC) and high strength concrete (HSC). Following the validation of the numerical model against the test data, a parametric study was undertaken on a composite column using a 400mm square hollow section with a fixed-pinned boundary condition and a relative slenderness at room temperature of λ̅=0.6. Load levels ηfi,t of 0.47, 0.35 and 0.24 were considered and, using a constant eccentricity of e/h=0.5, a combination of concentric and eccentric loading was applied to the column, as would occur in practice. The results from the parametric analyses show that the FRR reduces significantly as the bending moment increases on the column. Moreover, although the FRR reduced as the utilization increased, it was found that for highly utilized columns the FRR was less sensitive to changes in the magnitude of the bending moments.

Numerical Implementation of Energy-based Models in Explicit Finite Element Analysis for Sand in Plane Strain Compression

Soil is one of the most complex materials. In finite element analysis, the relevant constitutive model is one of the main key that provides the accurate prediction of strength and deformation characteristic of geotechnical structure. The objective of this study is to implement the elasto-plastic work-hardening-softening constitutive model (Energy-based model) into ABAQUS via VUMAT subroutine. Without updating Jacobian matrix process, the VUMAT subroutine is rather more convenient to implement than UMAT subroutine. Therefore, the high efficiency of strategy to update the new stress and plastic strain energy is crucially important. The VUMAT simulated results on the effect of initial stress and softening behavior were verified by UMAT and the experimental results of Toyoura dense sand under plane strain condition. The VUMAT subroutine could accurately simulate the strength and deformation characteristics of Toyoura sand. However, its results shows the irregularities at transition point.

Damage features and dynamic response of RC beams under blast

Through experimental and numerical study, the anti-blast performance and damage characteristics of reinforced concrete beams with different stirrup ratios were analyzed. Two sets of specimens with two different stirrup ratios were tested under blast loading, with two explosive masses (0.99kg and 1.46kg TNT) considered in each set. Large inelastic deformation and local spallation were observed in all tests. The increase of TNT charge mass is shown to gradually change the damage degree of RC beam. And with an increased stirrup ratio, the deflection, the spall radius and especially the spall depth were observed to decrease. The core concrete of the low stirrup ratio specimens was all damaged to some extent. The experimental results indicate that the stirrup ratio has significant influence on the survivability of RC beams when subjected to blast loading. Numerical studies were implemented using the explicit nonlinear finite element analysis software LS-DYNA. The dynamic response process of RC beams under blast was obtained and the generation mechanism of spallation was analyzed. Four additional numerical models with different stirrup ratios were built and implemented on blast simulations. The results demonstrate that the deflection thickness ratio of RC beam is inversely proportional to the scale distance and the stirrup ratio. Based on the above analysis, an empirical expression on deflection thickness ratio was obtained which considered both the scale distance and the stirrup ratio.

Structural analysis of a cross car beam using finite element models

Purpose – The purpose of this paper is to use PAM-CRASH, a finite element analysis solver, to assess the performance of a mass production vehicle cross car beam (CCB) under an overlap frontal crash scenario (crashworthiness). Simulation results were reviewed according to what is plausible to register regarding some critical points displacements and, moreover, to identify its stress concentrations zones. Furthermore, it was also computed the CCB modal analysis (noise, vibration and harshness (NVH) assessment) in order to examine if its natural modes are within with the original equipment manufacturer (OEM) design targets. Design/methodology/approach – The available data at the beginning of the present study consisted of the structure CAD file and performance requirements stated by the OEM for NVH. No technical information was available concerning crashworthiness. Taking into account these limitations, it was decided to adapt the requirements for other mass production cars of the same category, as regards dynamic loading. A dynamic explicit code finite element analysis was performed throughout the CCB structure simulating the 120e−3 s crash event. For the modal analysis, there were some necessary modifications to the explicit finite element model in order to perform the analysis in implicit code. In addition, the car body in white stiffness was assigned at the boundaries. These stiffness values are withdrawn from the points where the CCB is attached to the car body’s sheet metal components. Findings – Although the unavailability of published results for this particular CCB model prevents a comparison of the present results, the trends and order of magnitude of the crash simulation results are within the expectations for this type of product. Concerning modal analysis, the steering column first natural frequency has a percent deviation from the design lower bound value of 5.09 percent when local body stiffness is considered and of 1.94 percent with fixed boundary conditions. The other requirement of the NVH assessment regarding a 5 Hz minimum interval between first vehicle CCB mode and the first mode of the steering column was indeed achieved with both boundary configurations. Originality/value – This study is a further confirmation of the interest of numerical modeling as a first step before actual experimental testing, saving time and money in an automotive industry that has seen an enormous increase of the demand for new car models in the last decade.

Prediction of annealed glass window response to blast loading

Several software packages that are capable of predicting the response of annealed glass windows to blast loads are evaluated, by comparison to experimental data that has been obtained from full-scale arena blast tests in the field. A total of 34 instrumented, monolithic, glass window panes were subjected to explosive blast waves of varying intensity. A series of small-scale material tests and full-scale pane tests was also performed in the laboratory to obtain mechanical properties for use in the predictive models. The utility of various software tools, based either on single degree of freedom analysis or explicit finite element analysis, is hence assessed, for use in the analysis or design of glazing under blast loading.

Lagrangian Explicit Finite Element Modeling for Spin-Rolling Contact

Spin in frictional rolling contact can cause significant stress, which is the key to understanding and predicting the wear and fatigue behavior of contact components, such as wheels, rails, and rolling bearings. The lateral creep force arising from spin influences the kinematics of a wheelset and thus of vehicles. The solution that is currently employed in the field of elasticity and continuum statics was developed by Kalker and uses a boundary element method (BEM). In this paper, a new approach based on Lagrangian explicit finite element (FE) analysis is employed. This approach is able to consider arbitrary geometric profiles of rails and wheels, complex material behavior and dynamic effects, and some other factors. The new approach is demonstrated using a three-dimensional (3D) model of a wheel with a coned profile rolling along a quarter cylinder and can be easily adapted to apply to wheels and rails of arbitrary profiles. The 3D FE model is configured with elastic material properties and is used to obtain both normal and tangential solutions. The results are compared with those of the Hertz theory and the Kalker's model. The 3D FE model is then configured with elastoplastic material properties to study the spin-rolling contact with plasticity. The continuum dynamics phenomenon is captured by the FE model, which enhances the ability of the model to mimic reality. This improvement considerably extends the applicability of the FE model. The model can be applied to fatigue and wear analyses at gauge corners or rails as well as to deep groove bearings, where a large geometrical spin is present and plastic deformation may be of importance.

Application of uniform design to improve dental implant system.

This paper introduces the application of uniform experimental design to improve dental implant systems subjected to dynamic loads. The dynamic micromotion of the Zimmer dental implant system is calculated and illustrated by explicit dynamic finite element analysis. Endogenous and exogenous factors influence the success rate of dental implant systems. Endogenous factors include: bone density, cortical bone thickness and osseointegration. Exogenous factors include: thread pitch, thread depth, diameter of implant neck and body size. A dental implant system with a crest module was selected to simulate micromotion distribution and stress behavior under dynamic loads using conventional and proposed methods. Finally, the design which caused minimum micromotion was chosen as the optimal design model. The micromotion of the improved model is 36.42 μm, with an improvement is 15.34% as compared to the original model.

Analyzing the potential of GPGPUs for real-time explicit finite element analysis of soft tissue deformation using CUDA

As the presence of finite element implementations on General Purpose Graphics Processing Units (GPGPUs) is the literature increases, detailed and in-breadth testing of the hardware is somewhat lacking. We present an implementation and detailed analysis of an FE algorithm designed for real-time solution, particularly aimed at elasticity problems applied to soft tissue deformation.An efficient parallel implementation of Total Lagrangian Explicit Dynamics implementation is elucidated and the potential for real-time execution is examined. It is shown that in conjunction with modern computing architectures, solution times can be significantly reduced, depending on the solution strategy.The usability of the method is investigated by conducting a broad assay on ranging model sizes and different cards and comparing to an industry-proven FE code Abaqus. In doing so, we study the effect of using single/double precision computation, quantify and present error measurements as a function of the number of time-steps. We also examine the usage of a special texture memory space and its effect on computation for different devices. Adding material complexity in the form of a tissue damage model is presented and its computational impact elucidated. The aggregate results show that, for a particular set of problems, it is possible to compute a simple set of test cases 30–120 times faster than current commercial solutions.According to the speedups achieved, an indication is provided that the GPGPU technology shows promise in the undertaking of real-time FE computation.

Nucleation of squat cracks in rail, calculation of crack initiation angles in three dimensions

A numerical model of wheel-track system is developed for nucleation of squat-type fatigue cracks in rail material. The model is used for estimating the angles of squat cracks in three dimensions. Contact mechanics and multi-axial fatigue analysis are combined to study the crack initiation mechanism in rails. Nonlinear material properties, actual wheel-rail geometries and realistic loading conditions are considered in the modelling process. Using a 3D explicit finite element analysis the transient rolling contact behaviour of wheel on rail is simulated. Employing the critical plane concept, the material points with the largest possibility of crack initiation are determined; based on which, the 3D orientations/angles of the possible squat cracks are estimated. Numerical estimations are compared with sample results of experimental observations on a rail specimen with squat from the site. The findings suggest a proper agreement between results of modelling and experiment. It is observed that squat cracks initiate at an in-plane angle around 13°-22° relative to the rail surface. The initiation angle seen on surface plane is calculated around 29°-48°, while the crack tend to initiate in angles around 25°-31° in the rail cross-section.