Explicit Finite Element Analysis Research Articles

Numerical study for the structural analysis of composite laminates subjected to low velocity impact

The paper deals with structural behaviour of laminated composite plates under low velocity impact loading conditions. The aim of the work is to develop numerical finite element models and simulation techniques to be implemented in a numerical procedure, which is aimed to improve designer forecasting capabilities of damaging resistance in composite structures.On the base of advanced material models and of selected failure criteria, the proposed numerical techniques can describe the damage initiation and propagation of impact damages in composite structures.A global/local finite element modeling approach has been proposed, in order to be able to develop explicit finite element analysis of the impact event, including damage initiation and propagation of both interlaminar and intralaminar damages. The same model has been analysed under quasi static compression conditions by taking into account, in a single explicit finite element analysis, both the impact and the after impact damages.For validation purpose, numerical results have been compared with data from two sessions of experimental impact tests, followed by compression after impact tests; the considered impact energy values are 50J and 100J respectively.

Critical-Buckling-Load Assessment of Drillstrings in Different Wellbores by Use of the Explicit Finite-Element Method

Summary Previous theoretical formulations for sinusoidal and helical buckling of drillstrings vary significantly and are mostly proposed for frictionless pipes without tool joints. Finite-element-analysis (FEA) methods have the ability to consider geometric details and nonlinearities. However, traditional FEA methods use shell or solid elements for this problem and are computationally expensive. In this paper, an explicit FEA that is based on beam and connector elements implemented in the Abaqus software (2012) is used to study the problem in different wellbores. The wellbore geometry, formation stiffness, friction load, and friction-induced torque are modeled with connector elements. A typical drillstring in vertical, inclined, horizontal, and curved wellbores is simulated, and the explicit FEA results for sinusoidal- and helical-buckling loads are compared with different theoretical formulations and experimental results in the literature. The effects of length, inclination angle, and string effective weight caused by buoyancy as well as the effect of tool joints in straight and curved wellbores are also studied and compared with present formulations and published experimental results. A full-scale well-buckling test has also been simulated, and load-transfer data are compared with the real-world results. Overall, it is demonstrated that the use of explicit FEA can efficiently study drillstring buckling behavior in straight- and curved-wellbore conditions.

Explicit finite element analysis to predict impact damage response of osteoporosis hip bone

Hip fractures due to sideways falls are a worldwide health problem, especially amongst elderly people. The force experienced by the proximal femur during a fall, and therefore hip fracture, is significantly dependent on density, thickness and stiffness of the body during impact. The process of fracture and healing can only be understood in terms of the structure and composition of the bone and also its mechanical properties. Bone fracture analysis investigates the prediction of various failure mechanisms under different loading conditions. An accurate explicit finite element method will assist scientists and researchers to predict the impact damage response of bone structures. In this paper, the effect of low velocity impact on the osteoporotic hip in ageing people will be studied in LSDYNA. The first part aims to create a three-dimensional (3D) reconstruction and registration of semi-transparent computed tomography scan image data using Simpleware software. In the second part, the effect of cortical thickness and impact velocity on the energy absorption of the hip during a fall will be investigated on a 3D model using the latest techniques. The critical impulse loading of the hip will be the benchmark to improve the design of safety instruments and consequently the well-being of elderly people.

Low intrusive coupling of implicit and explicit time integration schemes for structural dynamics: Application to low energy impacts on composite structures

Simulation of low energy impacts on composite structures is a key feature in aeronautics. Unfortunately it involves very expensive numerical simulations: on the one side, the structures of interest have large dimensions and need fine volumic meshes (at least locally) in order to properly capture damage. On the other side, explicit simulations are commonly used to lead this kind of simulations (Lopes et al., 2009 [1]; Bouvet, 2009 [2]), which results in very small time steps to ensure the CFL condition (Courant et al., 1967 [3]). Implicit algorithms are actually more difficult to use in this situation because of the lack of smoothness of the solution that can lead to prohibitive number of time steps or even to non-convergence of Newton-like iterative processes. It is also observed that non-smooth phenomena are localized in space and time (near the impacted zone). It may therefore be advantageous to adopt a multiscale space/time approach by splitting the structure into several substructures with their own space/time discretization and their own integration scheme. The purpose of this decomposition is to take advantage of the specificities of both algorithms families: explicit scheme focuses on non-smooth areas while smoother parts (actually linear in this work) of the solutions are computed with larger time steps with an implicit scheme. We propose here an implementation of the Gravouil–Combescure method (GC) (Combescure and Gravouil, 2002 [4]) by the mean of low intrusive coupling between the implicit finite element analysis (FEA) code Zset/Zébulon (Z-set official website, 2013 [5]) and the explicit FEA code Europlexus (Europlexus official website, 2013 [6]). Simulations of low energy impacts on composite stiffened panels are presented. It is shown on this application that large time step ratios can be reached, thus saving computation time.

Reliability Analysis of a Composite Plate under Low-Velocity Impact using the Gaussian Response Surface Method

A 3-D explicit dynamic finite element analysis is performed to determine the contact force and displacement between the impactor and the target. The uncertainties associated with the properties of the composite material, loading condition, and assessment of critical stresses affect the failure limit state to a greater extent. The Gaussian response surface method is used to predict the probability of failure. It is found that the system probability of failure is influenced more by delamination than the failure due to matrix cracking. Shear strength (T12) and Young's modulus (E1 and E3) are the most sensitive parameters to influence the composite plate reliability.

Uma simulação eficiente de estruturas sob carregamentos impulsivos e uma apliação expedita

The class of physical problems of metal structures subject to rapid, large amplitude loads, such as occurs when they are submitted to an explosion blast, involves large deformations and inelastic action. Current state of art in explicit dynamic Finite Element Analysis codes require time steps limited by stability requirements rather than by accuracy. For very high rate processes, accuracy would require a very small time step so that the stability limit does not penalize. Acceptable accuracy may not require such small steps if implicit methods are considered. The implicit methods used in quasi‐static analysis, however, require the solution of large systems of equations, and several such systems must be solved at each time step to satisfy the dynamic equilibrium when using Newton iteration. The direct matrix solvers that are used incur in computational costs that grow as n m2, where n is number of degrees‐of‐freedom and m is the band of the front width, thus resulting in prohibitive costs for very large problems. In this work, the use of higher order, implicit time integration and matrix‐free solution of the system of equations is explored. Computational efficiency of explicit codes is combined with the inherent stability of implicit methods. The model developed is applied in the simulation of a complex structure, with elevated computational cost, showing its validity.

PREDICTION OF PROXIMAL FEMORAL FRACTURE IN SIDEWAYS FALLS USING NONLINEAR DYNAMIC FINITE ELEMENT ANALYSIS

Hip fracture incidence caused by sideways falls is increasing year by year. The high morbidity and mortality not only cast a gloom over the life, but also increase the medical cost of the country. From a biomechanical perspective, hip fractures are related to different loading directions. The main purpose of this study is to investigate how different hip fracture types are affected by impact directions. The geometry of a proximal femur was obtained from the CT scan data of a 67-year-old Chinese male. Mimics and Ansys softwares were applied to establish the cortical bone and cancellous bone models. Six different loading cases, i.e., SW1 (α = 120°, β = 0°), SW2 (α = 90°, β = 0°), SW3 (α = 60°, β = 0°), SW4 (α = 20°, β = 0°), SW5 (α = 120°, β = 15°), SW6 (α = 120°, β = 45°) were defined as the angle α with reference to the long axis of the femur in the frontal plane, and β with reference to the femoral neck axis in the horizontal plane. They were established to simulate sideways falls by explicit dynamic nonlinear finite element analyses in ANSYS-LS-DYNA software. The impact speed was 3.17 m/s. Stress and strain analyses with time history of the fracture sites were taken to find the relationships between fracture types and impact directions. SW1–SW4 caused femoral neck fractures, and the maximum principal stresses were 4.5, 6, 5 and 4.8 MPa, respectively. SW5 caused compound fractures including neck fracture and trochanteric fracture, and the maximum principal stresses were 6.8 MPa and 6.5 MPa, respectively. SW6 caused trochanteric fracture, and the maximum principal stress was 4.2 MPa. The maximum principal strains of neck fracture (0.075, 0.135, 0.175, 0.092) and trochanteric fracture (0.045) increased to the maximum values in 10 ms after impact, and were much higher than the ultimate compressive strain of cancellous bone. These results were consistent with the clinical findings. This study showed that falling posture was an important factor leading to different types of fracture. Dynamic simulation was more effective in explaining the fracture mechanism and determining the load direction that caused hip fracture. The study also provided a theoretical basis for more targeted preventive measures for different types of hip fracture in clinics.

Crashworthiness Design of Vehicle Side Door Beam Based on Elliptical Geometry Modification Using Multi-Objective Optimization

Side Door Beam (SDB) is one of the crucial parts of today’s vehicles in order to meet the passenger safety. Through an explicit finite element analysis (FEA), material selection for the SDB under impact is evaluated by using three different sheets of material to achieve the maximum possible specific energy absorption (SEA). To find the lowest peak load, the carefully chosen SDB is investigated based on its orientation angle toward the rigid wall impactor. The elliptical cross section of the selected SDB is taken into account by considering two variables of geometrical parameters; thickness and minor to major diameter ratios. Accordingly, Multi-objective optimization of the SDB is performed using response surface method (RSM) to reach the mentioned objectives and to determine the optimal sectional configuration of the SDB

Experimental and Numerical Study on Response of Sandwich Plate Subjected to Blast Load

This article presents the experimental and numerical study carried out to capture the response of metallic sandwich plate when subjected to air blast loads. A full scale field test is carried out on a sandwich panel with tetrahedral truss core, subjected to the action of pressure waves originating from the detonation of high explosive charges. The time history of acceleration and blast overpressure at the centre of the plate is recorded. An explicit finite element analysis is performed on the sandwich panel with identical geometry. Blast loading is applied usingCONWEPcode. Very good agreement has been observed between the numerical and experimental results. A systematic parametric study is conducted by varying the geometrical and loading parameters of the panel. Performance of panel under blast load is judged on the basis of sandwich panel efficiency. It is observed that geometrical parameters have significant effects on the panel response for varying load. For a fixed core cross section and face sheet thickness, highest panel efficiency is obtained corresponding to a core height of 140 mm.

複合荷重下における船体梁の縦曲げ最終強度に関する研究

FEM analysis using fine-mesh shell models has been increasingly applied to the ultimate longitudinal strength analysis of ship's hull girder. However, the cost and elapsed time necessary for FEM analyses including FE modelling are still large for the design stage. Therefore, it is a common procedure to apply the Smith's method and to evaluate approximately the maximum longitudinal bending strength of a specified cross section. In this case, the effect of shear and warping stresses, which is significant in very large container ships, is not considered. The objective of this study is to propose a method of the analysis of ultimate hull girder strength under combined bending and torsion. The hull girder is modelled by a series of thin-walled beam elements and the average stress-average strain relationship of plate and stiffened panel segments under axial loads considering the effect of shear stress is implemented in the beam elements. The shift of instantaneous neutral axis and shear center can be automatically considered by introducing axial degree of freedom as well as the bending ones in the beam elements, and keeping the zero axial load condition. The proposed simplified method is applied to the test model explained in the 1st report. First, bending and torsional moment is applied to the beam model for a whole model within the elastic range. Then, the ultimate bending strength of cross sections is calculated applying the Smith's method to a beam element considering the warping and shear stresses. On the other hand, nonlinear explicit finite element analyses are adopted for analysis of the test model by using LS-DYNA. The effectiveness of present simplified analysis method of ultimate hull girder strength under combined loads is discussed comparing with the results of experiments and LS-DYNA analyses.

合わせガラスの衝撃破壊挙動に関する陽解法有限要素解析

合わせガラスの衝撃破壊挙動に関する陽解法有限要素解析

Impact of thick PMMA plates by long projectiles at low velocities. Part II: Effect of confinement

A hybrid experimental–numerical investigation of the penetration process in unconfined and confined thick polymethylmethacrylate (PMMA) plates was carried out. The confinement was applied by insertion of the polymeric plate into a conical steel ring. The response of such plates to the impact of long hard steel projectiles having an ogive-head shape in the range of velocities of 165<V0<260 (m/s), was investigated experimentally. The results show that unconfined targets were perforated and broken due to combined effect of penetration and cracking. By contrast, the confined targets were not perforated and could withstand repeated impacts due to suppression of the brittle damage mechanism by the confinement. The tests were modeled using 3D explicit finite element analyses. A good agreement regarding the trajectory of the projectile and the depths of penetration was obtained. The numerical results show that the confinement introduces a negative triaxiality and even some plasticity within the confined plates prior to impact. The increase of plastic failure strain of the PMMA at negative triaxiality reduces the ductile damage during penetration, while the hydrostatic pressure reduces significantly the brittle fracture mechanism. The resisting force to the penetration depends on the failure strain–triaxality relationship, and does not necessarily increase with higher confinement levels.

Impact of thick PMMA plates by long projectiles at low velocities. Part I: Effect of head’s shape

A hybrid experimental–numerical investigation of the penetration process in thick polymethylmethacrylate (PMMA) plates was carried out. The response of such plates to the impact of long hard steel projectiles having either blunt, hemispherical or ogive-head shapes was investigated experimentally in the range of velocities of 100 (m/s)<V0<250 (m/s). The penetration process can be divided into 3 stages: entrance, propagation and backwards bouncing. The last two stages are associated with brittle fracture of the plates. The tests were modeled using 3D explicit finite element analyses. The numerical results provide insight regarding the variations of field variables such as stresses, velocities, resisting forces and energies. A good agreement regarding the trajectory of the projectile and the depths of penetration is obtained. The enhanced backwards bouncing phenomenon is explained, and it is shown that the average deceleration during the penetration process is constant. The resisting force to the penetration is higher for blunt projectiles. It is 10% lower for the hemispherical head and 50% lower for ogive-headed projectiles.

Modelling bearing failure in countersunk composite joints under quasi-static loading using 3D explicit finite element analysis

Three-dimensional explicit finite element modelling is used to predict the quasi-static bearing response of typical countersunk composite fuselage skin joints. In order to accurately simulate bearing failure, a user-defined 3D composite damage model was formulated for Abaqus/Explicit and included Puck failure criteria, a nonlinear shear law and a crack band model to mitigate mesh sensitivity. A novel approach was developed to employ characteristic element lengths which account for the orientation of composite ply cracks in the Abaqus/Explicit solver. Resulting models accurately predicted initial joint sticking behaviour and the elastic loading response of single-bolt and three-bolt joints, but preliminary predictions of bearing failure onset were overly-conservative. Improved failure predictions were obtained by utilising a fracture energy for compressive fibre failure which was considered more relevant for simulating bearing damage. The explicit models were exceptionally robust, showing capability to predict extensive hole crushing. Methods of dramatically improving joint model efficiency were highlighted.

Incrementally objective implicit integration of hypoelastic–viscoplastic constitutive equations based on the mechanical threshold strength model

The present paper focuses on the development of a fully implicit, incrementally objective integration algorithm for a hypoelastic formulation of \(J_{2}\)-viscoplasticity, which employs the mechanical threshold strength model to compute the material’s flow stress, taking into account its dependence on strain rate and temperature. Heat generation due to high-rate viscoplastic deformation is accounted for, assuming adiabatic conditions. The implementation of the algorithm is discussed, and its performance is assessed in the contexts of implicit and explicit dynamic finite element analysis, with the aid of example problems involving a wide range of loading rates. Computational results are compared to experimental data, showing very good agreement.

Explicit Finite Element Analysis of Dynamic Response of Protection Frame System Subjected to Impact Loading

Height limit protection frame of railway bridges apply to the road crossing the railway bridge, its role is to ensure the safety of the railway bridge to prevent road motor vehicles to hit the bridge beam, causing beam damage and even endangering the safety of the railway lines. Therefore, it is necessary to do in-depth discussion of collision mechanism and failure mode of height limit protection frame of railway bridges under the impact of the over-high vehicle, in order to improve the survivability of protection frame to protect the safety of the railway bridge and rail transport. Some rules and characteristics were obtained by establishing collision model of height limit protection frame of railway bridges and the over-high vehicles using the software of ANSYS/LS-DYNA and studying the dynamic response of protection frame impact loading by the vehicle under the different parameters. Thus for the similar protection frame structure design, maintenance and damage assessment provide theoretical support.

Explicit dynamic formulation to demonstrate compliance against quasi-static aircraft seat certification loads (CS25.561) – Part II: Influence of body blocks

Loading an aerospace and automotive seat statically through lap or body blocks is a complex and highly non-linear problem, as the key numerical challenge is to replicate the contact and slipping kinematics between seat, lap block and belt. In addition, severe element distortions and unexpected contact between parts can occur due to the large deformations involved, which result in implicit solvers struggling to find a converged solution. This paper focuses on the use of an explicit Finite Element Analysis (FEA) solver (LS-DYNA3D) for an aircraft seat subject to Certification Specifications CS25.561, although the ideas presented are equally applicable to automotive seat designers. Explicit codes are better able to overcome contact convergence issues and are often used with appropriate damping to achieve a quasi-static solution. This paper reviews the methodology presented in Part I, whereby issues relating to damping, mass and time scaling are outlined in order to overcome the high computational time step costs (Courant-Friedrichs-Lewy (CFL) condition), together with the procedural and error checks required to ensure a quasi-static response. This paper extends the methodology by considering load cases that use lap blocks, such as ‘forward 9g’ and ‘upward 3g’ certification requirements. Alternative modelling approaches to represent the loading mechanism and effect of lap block mass on solution accuracy are discussed. This paper concludes with a verification framework that outlines the quality checks on various model energies and their ratios, where the numerical results are validated against test in terms of displacements and seat kinematics. Thus, ‘Part I’ and ‘Part II’ cover all elements related with the application of an explicit dynamic integration scheme to demonstrate static seat compliance, and together, form a clear framework to assist a Computer Aided Engineering (CAE) analyst involved in applying an explicit integration scheme to solve non-linear quasi-static analyses.

Finite Element Study on Micro Cutting Process of Guide Abrasive Wear

Two-dimensional finite element model is established by ABAQUS Explicit finite element analysis in this paper. It includes abrasive wear micro cutting process between pair of guide. Johnson-cook constitutive model is used to simulate the guide material deformation of wear process. Based on different sizes and different speed of grain, loading, cutting and unloading process are simulated by finite element, guide surface stress distribution and deformation condition are studied in the guide rail pair wear process. The simulation data is obtained by central composite experiments and regression model is gotten by MATLAB. The influence law of the particle radius and speed to guide residual compressive stress and deformation are gotten by the prediction model.

Characterisation of steel components under monotonic loading by means of image-based methods

Ductile damage behaviour of S185 structural steel is determined by coupling numerical and experimental analyses. Monotonic experimental tests are carried out in five different specimen configurations. These mechanical tests are coupled with image-based methods for assessing displacement and strain fields over the gauge section. Three different ductile damage models proposed in the literature for monotonic loading are analysed. Their governing parameters are determined by comparing experimental and numerical mechanical responses. Measurements provided by digital image correlation and feature-tracking methods are used for calibrating and validating non-linear finite element modelling. Numerical analyses built in ANSYS are carried out to compute the necessary parameters (stress–strain and triaxiality histories) to calibrate Johnson–Cook (JC) and Kanvinde–Deierlein (KD) fracture criteria. Also, a calibration of the Gurson–Tvergaard–Needleman (GTN) model is performed based on an explicit finite element analysis in ABAQUS.

Surface flexible rolling for three-dimensional sheet metal parts

To realize highly effective and continuous fabrication of three-dimensional (3D) sheet metal parts, a new forming method, surface flexible rolling forming, has been investigated. This method takes only two integral flexible rolls as the forming tool. In the forming process, a non-uniform elongation in the rolling direction and a bending deformation in the thickness direction occur simultaneously, and finally three-dimensional surface parts are formed. In this work, the basic principle and forming mechanism of surface flexible rolling are studied. A method to calculate the transversal curvature radius of the arc-shaped roll is brought forward, while the feasibility is verified by the explicit dynamic finite element analysis. An experimental device has been developed and the forming experiments have been performed. Typical 3D surface parts including the convex and saddle surface parts have been obtained. Finite element model of surface flexible rolling is established and the effect of forming parameters such as reduction, velocity, bending radius and friction on the surface shape is analyzed. The forming effects including shape errors and thickness changes are studied by the deviation analysis. The results indicate that the formed surface is quite close to the criteria one; the thickness of the parts changes gradually and keeps within a narrow range. The experimental formed parts are measured and the forming accuracy is investigated. The results show that the accuracy is high, and are consistent with the simulation.