Explicit Finite Element Analysis Research Articles

틸팅열차의 샌드위치 복합재 차체 구조물에 대한 충돌안전도 평가 및 향상방안 연구

본 논문은 샌드위치 복합재 틸팅열차의 충돌안전도 평가 및 성능 향상방안에 대해 서술하고 있다. 차체 구조물에 적용된 샌드위치 복합재는 알루미늄 하니컴 심재와 유리섬유 및 카본/에폭시 적층 복합재 면재로 이루어져있다. 충돌해석은 외연유한 요소 해석 프로그램인 LS-DYNA3D를 이용하였다. 이때, 유한요소모델링과 충돌해석 계산시간의 절약을 위하여 3차원 유한요소모델과 1차원 등가 모델을 적용하였다. 틸팅열차의 충돌 조건은 철도안전법에 명시하고 있는 4가지 충돌사고 시나리오를 고려하여 해석을 수행하였다. 충돌해석 결과 시나리오-2를 제외한 나머지 충돌 시나리오에서 성능 요구조건을 만족하였다. 충돌 시나리오-2의 충돌안전도 요구조건을 충족하기 위하여 전두부의 적층복합재 커버와 금속프레임의 강성 향상방안을 제안하였으며, 결과적으로 충돌 시나리오-2의 요구조건을 만족하였다. This paper describes the crashworthiness evaluation and performance improvement of tilting train made of sandwich composites. The applied sandwich composite of carbody structure was composed of aluminum honeycomb core and glass/epoxy & carbon/epoxy laminate composite facesheet. Crashworthiness analysis of tilting train was carried out using explicit finite element analysis code LS-DYNA 3D. The 3D finite element model and 1D equivalent model were applied to save the finite element modeling and calculation time for crash analysis. The crash conditions of tilting train were conducted according to four crash scenarios of the Korean railway safety law. It found that the crashworthiness analysis results were satisfied with the performance requirements except the crash scenario-2. In order to meet the crashworthiness requirements for crash scenario-2, the stiffness reinforcement for the laminate composite cover and metal frames of cabmask structure was proposed. Consequentially, it has satisfied the requirement for crash scenario-2.

RC 보의 충격저항성능 향상을 위한 강섬유 및 CFRP Sheet의 보강 효과

본 연구에서는 CFRP sheet 및 강섬유로 보강한 RC보의 충격하중 실험을 유한요소 프로그램으로 모사함으로써 각 보강방법이 충격저항성능 향상에 미치는 영향을 해석적 분석을 통해 알아보았다. RC 보의 동적거동을 효과적으로 분석하기 위해 명시적(Explicit) 유한요소 해석 프로그램인 LS-DYNA를 이용하였으며, RC 보에 가해지는 충격에너지가 단계적으로 증가할 때, RC 보의 에너지 흡수 성능 및 소성변형률 양상을 확인하였다. 해석 결과, CFRP sheet와 강섬유가 보강된 경우, 일반콘크리트 부재에 비해 에너지 흡수율이 급격히 증가했다. 소성변형률 양상을 분석한 결과, CFRP sheet 및 강섬유로 보강된 경우 그렇지 않은 경우에 비해 상대적으로 넓은 부분에 에너지를 분산시킴으로써 국부적으로 에너지가 집중되는 현상을 완화시킬 수 있음을 확인하였다. 또한 소성변형률 양상을 통해 각 부재의 Shear-Plug 균열 형태를 파악하고, 기존의 연구 결과와 비교하였다. In this study, a numerical analysis to investigate the effect of each reinforcing method on the impact resistance was performed by simulating the impact loading test of the RC beams strengthened with CFRP sheets and steel fibers using the finite element analysis program. LS-DYNA, which is the explicit finite element analysis program, was used to analyze the dynamic behavior of RC beams effectively. The energy absorption capacity and plastic strain aspect of RC beams were estimated as the applied impact energy increases step by step. Analysis results indicate that the absorbed energy rates of specimens strengthened with CFRP sheets and steel fibers were higher than those of other specimens. According to the evaluation result of plastic strain aspect, the those concentration was relieved by the dispersion of the impact energy due to the strengthening effects of CFRP sheets and steel fibers. In addition, the tendency of Shear-Plug crack for each specimen was similar to the experimental result of the previous study.

Feasibility and Effectiveness of Heat Pipe Cooling in End Milling Operations: Thermal, Structural Static, and Dynamic Analyses: A New Approach

In this paper, the feasibility and effectiveness of heat pipe cooling in end milling operations are investigated. A new embedded heat pipe technology was utilized to remove the heat generated at the tool-interface in end milling processes. Numerical studies involved four cases, including dry milling, fluid cooling, heat pipe cooling, and heat pipe cooling with cutting fluid supplied. The thermal, structural static, and dynamic characteristics of the end-mill were investigated using a numerical calculation with fast finite element plus solvers based on explicit finite element analysis software. The results demonstrate that the heat pipe end-mill is most feasible and effective in the actual end milling processes.

Numerical Investigation of Flexible Holding Technology for Stretch Forming Process

A new type of discrete clamp stretch forming machine based on flexible holding technology was developed to improve the performance of traditional rigid clamp stretch forming machine used for double-curvature metal sheet forming, and its forming characters were illuminated simply. The FE model of flexible discrete clamp stretch forming was set up, and extensive numerical simulations of spherical parts for both the flexible holding mode and the rigid holding mode were carried out by dynamic explicit finite element analysis. The numerical results show that the distribution of stress, strain and thickness were well-proportioned in the flexible holding mode. The larger the spherical radius is, the smaller the minimum transitional length of sheet metal is. The transitional length of 60mm is suitable for flexible discrete clamp stretch forming in the case of considering the forming quality and material utilization. Then, the stretch forming experiment proves that the flexible holding technology is feasible, and the error contrast illustrates the new type of discrete clamp stretch forming machine is practicable.

Analysis of the High Strain-Rate Behaviour of Polyethylene Based Nanocomposites

Advanced polymeric materials and polymer based nanocomposites are finding an increasing range of industrial and defence applications. These materials have the potential to improve combat survivability, whilst reducing cost and weight. This study deals with nanocomposites manufactured from blends of low density polyethylene (LDPE) with various nanofillers. The high strain rate behaviour of these materials was investigated using the split Hopkinson pressure bar (SHPB) test. The experimental results for non-reinforced materials were used as a reference to analyse the effect of the nanofillers on the properties and performance of the nano­composites. These results, together with those obtained from other mechanical tests, will be used as input into finite-element analyses to simulate the performance of these materials in lightweight armour applications. In the first step, the finite element model was validated by simulating the SHPB test and comparing the predicted results with those from the experiments. Explicit finite element analysis was used for the simulation. The fully developed model was able to demonstrate the behaviour of the test bar and specimen interaction correctly and reasonably good agreement between predicted and experimental results was observed.

Advanced modelling of bird strike on high lift devices using hybrid Eulerian–Lagrangian formulation

The work presented in this paper deals with application of explicit finite element analyses in order to predict bird strike induced impact damage on high lift devices of typical large transport aircraft. The hybrid Eulerian–Lagrangian finite element formulation has been applied as to efficiently model the impact of a highly deformable object on an inboard flap structural model. As structural elements of aeronautical structures are commonly assembled from structural items manufactured from a variety of materials, a damage prediction methodology on aeronautical structures has to be able to model damage in metallic materials as well as in composite and sandwich structures. The presented methodology employs a progressive damage model for composite materials which is based on Hashinʼs failure initiation criterion. Prediction of damage in metallic structural items is based on the equivalent plastic strain, while strain rate effects are included in the hardening behaviour. An important part of the bird strike modelling procedure is the application of a bird replacement material with constitutive response which replicates the forces induced by an impact of a real bird. The bird material is modelled by an equation of state, with properties that match the pressure–density relations of water and air mixtures. The bird replacement material model and Eulerian impactor model have been validated in a comparison with experimental results available in the references. In order to demonstrate the ability of the presented procedure to simulate bird strike induced damage on actual high lift devices, an example of a possible impact scenario is investigated. The input parameters for the simulation have been selected as to simulate a bird strike used to verify the compliance with damage tolerance certification requirements.

On the dynamic response of sandwich panels with different core set-ups subject to global and local blast loads

The recent increase in blast and impact threats has led to an emerging interest in sandwich structures due to their superior performance in such loading environments. The optimised architecture of this class in conjunction with additional benefits of high strength-to-weight and stiffness-to-weight ratios vital to weight-sensitive military applications has led to numerous research works on the topic. In this study, the dynamic response of four circular sandwich panel constructions with different core designs under global and local blast loading conditions has been investigated. Numerical finite element (FE) models have been set up to study the effect of additional core interlayers on blast resistance enhancement of these sandwich panels. The objectives are (1) to assess the existing blast resistance capacity, (2) to increase the dynamic energy absorption, (3) to improve the stress distribution through plastic deformation, and (4) to ensure sacrificial damage to the additional core layers; hence, to avoid the main part of the core being damaged by excessive shear deformation, the dominant failure mode in conventional sandwich panels. A ductile elastomeric layer of polyurea, and a fairly compressible Divinycell-H200 foam layer have been selected as the additional core interlayers, and they have been placed in different arrangements to improve the overall blast resistance of the standard sandwich panel with glass-fibre-reinforced plastic (GFRP) face-sheets, and balsawood core. Dynamic explicit FE analyses were carried out using the commercial package ABAQUS 6.9-1. Comparison of specific kinetic and strain energies shows the effect of additional core layers on the blast energy absorption of a sandwich system. The study shows the improvement in shear failure prevention of the core as a result of the use of additional core layers and a reduction in the level of kinetic and strain energies in the protected core in both absolute and relative terms. The stress contours show a smoother stress distribution in enhanced cases. These conclusions are confirmed and explained by using a qualitative two-degree-of-freedom system with an elastic–viscoplastic spring element representing the integral effects of sacrificial additional core interlayers and a nonlinear spring representing the stiffness of the conventional sandwich system and comparing the results of dynamic analysis with a similar qualitative single-degree-of-freedom model of a conventional sandwich panel.

Numerical simulation of the stress peen forming process and experimental validation

Stress peening forming is widely used in the aeronautics industry to induce curvatures in wing skins. Most of the investigations of stress peen forming are empirical and experimental. In this paper, a three step numerical model that can simulate this process was developed. First, an implicit Finite Element Analysis (FEA) with ANSYS where a prebending moment along the spanwise direction of the component was performed. Then, an explicit FEA with LS-DYNA simulating shot impacts on the pre-stressed component was executed in order to obtain the resulting stresses inside the component. Finally, an implicit FEA with ANSYS was performed for calculating the arc heights and the curvature radii of the component in chordwise and spanwise directions. Numerical analysis of the process shows that the prebending moments have an influence not only on the residual stress profiles but also on the curvatures of the deformed component in chordwise and spanwise directions. This model was used to establish a relationship between the prebending moment and the resulting arc heights and residual stress profiles. The numerical strategies developed in this paper supply a useful tool for studying and optimizing the stress peening process.

Research on Energy Absorption Characteristics of Honeycomb Sandwich Panels

Due to the excellent mechanical properties combined with high strength to weight ratio, honeycomb sandwich panels (HSP) are used increasingly in aerospace, automobile and marine industries. In order to improve the crashworthiness of vehicle body, it is of great significance to study the energy absorption characteristics of the components. For this reason, specific energy absorption (SEA: the energy absorption per unit mass) of HSP was selected to be the objective function in order to find an optimal design of HSP under impact loading. The explicit finite element analysis (FEA) was used to derive response surface (RS) model of SEA, and a single-objective optimization was performed to get the optimal design. Before the optimization design of HSP, the energy-absorptions of HSP and the honeycomb core (HC) were compared with each other. It was found that HSP could absorb much more impact energy than HC due to the stabilizing effect of the face sheets during the process of crushing.

Application of a split-Hopkinson tension bar in a mutual assessment of experimental tests and numerical predictions

This paper shows how experimental test results from a split-Hopkinson tension bar (SHTB) and numerical simulations of the test set-up can be used for mutual verification. Firstly, a SHTB where the tension stress wave is generated by pre-stretching a part of the incident bar is briefly presented. This SHTB is used to carry out tensile tests of four aluminium alloys at high rates of strain, while tests at low to medium strain rates were performed in a servo-hydraulic tensile test machine. Using the test results, the parameters of an anisotropic thermoelastic-thermoviscoplastic constitutive relation and a one-parameter fracture criterion are identified for the materials at hand. Subsequently, the material model is used in explicit finite element analyses of the SHTB tests, including the entire experimental set-up and the stress wave propagation during the test. The numerical predictions were found to represent the observed behaviour in the experimental tests fairly well.

Modelling of Low Velocity Impact of Laminated Composite Substructures

Impact is among the important loading scenario which is required to be addressed for fibre reinforced plastics (FRP) materials in ground or space vehicle applications. The failure behaviour of FRP materials under impact loading is a complex process and a detailed analysis of various mode of failure is necessary. In this paper the failure behaviour of laminated carbon fibre reinforced plastic (CFRP) composite structures under impact loading is investigated by conducting numerical simulations using the explicit finite element analysis ANSYS LS-DYNA software [1]. The impact responses and failure behaviours are being investigated by performing a parametric study and sensitivity analysis in which impact velocity, number of plies, incident angle, friction between contacted surfaces, impactor mass and the geometry are varied in separate cases. The FE model is validated by comparing the numerical results with other published results and good correlations are achieved.

Modelling approach for the prediction of stitch influence during woven fabric draping

The following paper focuses on the development of an accurate and efficient modelling approach for the prediction of fibre angles in woven reinforcements resulting from the influence of localised stitching patterns. The modelling procedure involves a process of calibration valid for both dry and wet woven fabric preform materials and has been carried out using the explicit finite element analysis code LS-DYNA. The details and capabilities of the model are discussed and comparisons are made with real fibre angle measurements taken from dry fabric hemispherical dome and three dimensional test shape forming experiments, under the influence of different stitch patterns. The current model demonstrates a high level of functionality allowing accurate prediction of yarn and stitch pattern movement as well as stresses and strains. Full-scale forming simulations for any desired sheet forming scenario can be performed within reasonable timeframes.

Failure criteria with unilateral conditions for simulation of plate perforation

Abstract Finite element analysis of plate perforation is performed using a thermoelastic–thermoviscoplastic constitutive model and two uncoupled damage criteria with unilateral conditions. The first criterion is based on continuum damage mechanics, while the second is the Cockcroft–Latham criterion. Fracture is assumed to occur at a critical damage, and crack propagation is modelled with element erosion. The identification of the material parameters is based on inverse modelling of a uniaxial tension test. The constitutive model and damage criteria are applied in explicit finite element analysis of the perforation of a 12 mm thick steel plate struck by a blunt projectile in the sub-ordinance velocity regime. The results show the importance of the unilateral conditions in obtaining accurate prediction of the adiabatic shear banding process. The two fracture criteria have comparable dependence on the stress triaxiality and the Lode parameter when the microcrack-closure parameter is set to zero in the criterion based on continuum damage mechanics, and give similar failure mode and ballistic limit in the plate perforation problem.

Performance of cable-stayed bridge pylons subjected to blast loading

Since the terrorist attacks of 2001, concern about potential car bomb attacks on buildings and infrastructure such as bridges and tunnels has increased tremendously. Design for better performance of these structures subjected to blast load is important to prevent progressive collapse of the structure and catastrophic loss of lives. The objective of this research was to study the performance of hollow steel box and concrete-filled composite pylons of a cable-stayed bridge subjected to blast loads. Car bomb detonation on the deck is assumed to be the most likely scenario to occur. A coupled numerical approach with combined Lagrangian and Eulerian models was used to consider the interaction of the deck and pylon with the air that transfers the explosion effect to the bridge. The non-linear explicit finite element analysis program, MD Nastran SOL700 was used to simulate the spatial and time variation of the blast load as well as blast shock wave–bridge interaction response. The blast resistance of two different types of pylons was investigated in a comparative study. The study established damage patterns of the pylon and showed superior performance of the concrete-filled composite pylon over the hollow steel box pylon. For the hollow steel box pylon, the P–Δ effect on the instability of the pylon subjected to blast load was significant.

Static and Fatigue Behaviour of Hexagonal Honeycomb Cores under In-plane Shear Loads

Due to their high specific strength and high specific stiffness properties the use of honeycomb panels is particularly attractive in spacecraft structures. However, the harsh environment produced during the launch of a satellite can subject the honeycomb cores of these sandwich structures to severe quasi-static and dynamic loads, potentially leading to static or early fatigue failures. Knowledge of the static and fatigue behavior of these honeycomb cores is thus a key requirement when considering their use in spacecraft structural applications. This paper presents the findings of an experimental test campaign carried out to investigate the static and fatigue behaviors of aluminum hexagonal honeycomb cores subject to in-plane shear loads. The investigation involved carrying out both static and fatigue tests using the single block shear test method. These results are also discussed in relation to the observed damage and failure modes which have been reported for the statically tested specimens and for the fatigue tested specimens at various stages of fatigue life. As well as conducting tests for the more conventional principal cell orientations (L and W), results are also presented for tests carried out at intermediate orientations to investigate the variation of core shear strength with loading orientation. The results are further investigated using explicit non-linear finite element analysis to model the buckling failure mechanisms of the tested cores.

A Numerical Research on the Penetration into a Semi-Infinite Rolled Homogeneous Armor by a Medium-Caliber Kinetic Energy Projectile

This paper presents numerical analysis on the penetration into a semi-infinite Rolled Homogeneous Armor(RHA) steel target by a medium-caliber projectile at the velocity range from 900m/s to 1000m/s. The projectile was made of a 93% tungsten heavy alloy(WHA) having a diameter of 18mm. LS-DYNA, an explicit non-linear finite element analysis code, was used for the numerical analysis. This kind of penetration problem is generally accompanied by large deformation, high strain rate and thermal softening, accordingly the Johnson-Cook constitutive models combined with Johnson-Cook fracture model and Mie-Gruneisen equation of state were employed to describe the RHA target and the WHA projectile, respectively. Due to the lack of the parameters of the Johnson-Cook failure model of RHA, the corresponding data of 4340 steel were applied for RHA inevitably. Here, two different failure strains for 4340 steel from the literatures were substituted in for RHA and their effects on the numerical analysis results were discussed and compared to the test results in terms of penetration efficiency(P/L) and crater hole shape. A quarter parts of the semi-infinite RHA target and the WHA projectile were only modeled considering the symmetric configuration of the problem for the analysis.

Finite element analysis of impact between cricket ball and cantilever beam

This paper presents an explicit finite element analysis of a cricket ball impacting against a cantilever beam. The model was developed using ABAQUS and was defined in accordance with experimental data. The model is used to determine contact properties associated with impact between cricket balls and sports equipment such as helmets. The developed model was validated through experimental impact tests where the ball was made to impact a cantilever beam at inbound velocities of approximately 17, 23, 38 and 44 m/s. The model's simulation results agreed reasonably well with the experimental results. The friction effects between the cricket ball and the cantilever beam have been considered, and a friction coefficient of 0.2 was adopted for the model. This study is part of a major research project examining the performance of a range of cricket helmets. It is envisaged that the model will be used for design customization and optimization of cricket helmets and other types of protective helmets.

Finite Element Simulation of Thermomechanical Spinning Process

Spinning is frequently used for manufacturing axisymmetric shapes where press tooling might not be justified on grounds of size and production volumes. Spinning also has the possibility of producing parts that could not be deep drawn. The temperature effect is significant on the metal forming processes; for the quality of products and the tools life are extremely affected by it. In this paper, a three-dimensional explicit finite-element analysis (FEA) is employed to simulate the spinning process of an aluminium circular sheet and also we investigate the thermal effects on the conventional spinning process by the explicit finite element method. The energy terms in this study include the plastic strain energy, the frictional sliding energy, and the heat transfer energy. The various mesh types are examined in the simulations. The main benefit of the proposed model will save the tremendous costs in the die designing and the experimental works. The parameters and techniques using in the numerical model are helpful for the design of forming process and the coupling thermal-mechanical analysis.

Linear finite elements with orthogonal discontinuous basis functions for explicit earthquake ground motion modeling

The dynamic explicit finite element method is commonly used in earthquake ground motion modeling. In this method, the element mass matrix is approximately lumped, which may lead to numerical dispersion. On the other hand, the orthogonal finite element method, based on orthogonal polynomial basis functions, naturally derives a lumped diagonal mass matrix and can be applied to dynamic explicit finite element analysis. In this paper, we propose finite elements based on orthogonal discontinuous basis functions, the element mass matrices of which are lumped without approximation. Orthogonal discontinuous basis functions are used to improve the accuracy and reduce the numerical dispersion in earthquake ground motion modeling. We present a detailed formulation of the 4-node tetrahedral and 8-node hexahedral elements. The relationship between the proposed finite elements and conventional finite elements is investigated, and the solutions obtained from the conventional explicit finite element method are compared with analytical solutions to verify the numerical dispersion caused by the lumping approximation. Comparison of solutions obtained with the proposed finite elements to analytical solutions demonstrates the usefulness of the technique. Examples are also presented to illustrate the effectiveness of the proposed method in earthquake ground motion modeling in the actual three-dimensional crust structure. Copyright © 2010 John Wiley & Sons, Ltd.

Transient meshing performance of gears with different modification coefficients and helical angles using explicit dynamic FEA

The gearbox, as the main part of power transmission of many mechanical systems, plays a critical role for the performance of the system. The transient meshing performance of the gears is dependent on their structural parameters like modification coefficient and helical angle among others. In this paper, the effects of modification coefficients and helical angles on the transient meshing performance of the gears are investigated using the method of explicit dynamic finite element analysis (FEA) in an energy point of view. The relationships between the transient meshing performance and modification coefficient or helical angle of gears are obtained by explicit dynamic simulation. The simulation results demonstrate that explicit dynamic FEA can be used for choosing these structural parameters in the design and manufacture of gears to enhance their transient meshing performance.