Nonlinear Explicit Finite Element Code Research Articles

Modelling the effect of lateral inertia on the dynamic response of aluminium square tube extrusions

Crashworthiness of automotives require the design of crush tubes installed as a frontal structure to absorb energy by deforming plastically during collision. The crushing behaviour of aluminium extrusions modelled as square tubes is investigated under quasi-static and dynamic loading conditions using the non-linear explicit finite element code LS DYNA. Previous works have attributed the dynamic increase of the peak and mean crushing load of aluminium thin-walled structures under axial compression, to inertia effects. Results of our investigation revealed that there is a considerable thickening of the shell side walls before and during progressive folding. This shell thickening is established as the cause of lateral inertia which consequently results in increased crush strength. In addition, a positive correlation was established between the shell thickening and crushing speeds. 

Numerical investigation of dynamic response of honeycomb sandwich panels filled with circular tubes under low velocity impact in the in-plane direction

Honeycomb sandwich structures, composed of many regularly arranged hexagonal cores and two skins, show excellent impact performance due to strong energy absorption capability under impact loads. In this paper, a numerical study of low velocity impact on honeycomb sandwich panels filled with circular tubes in the in-plane direction was performed. To calibrate the numerical model, simulation results in the out-of-plane direction are compared with the experimental ones. The numerical modelling of the drop weight test was carried out using the nonlinear explicit finite element code Abaqus/Explicit. The impact responses are presented as the contact force between the impactor and the panel versus the time. It was concluded that the filled honeycomb panel absorbs the same amount of impact energy in a shorter time than an empty one. In addition, the deflections of the front and back face-sheets are investigated. The panel degradation and the stress distribution during the crushing are also discussed.

Quasi-static axial crushing of multi-walled (spiral) aluminium tubes fabricated by roll bending: Experimental and numerical investigation

This study investigates the crashworthiness performance of multi-walled (spiral) tubes fabricated by roll bending aluminium alloy sheets. Quasi-static axial crushing tests of specimens were first conducted, and then numerical models were built to simulate the tests using the explicit non-linear finite element code LS─DYNA. After the experimental validation of the numerical simulation, a new series of conventional (closed-section) circular tube models of the same axial length, mean diameter, and cross-sectional area as those of the corresponding spiral models were built for comparison. The deformation patterns of the spiral tubes were found to be virtually the same as those of the closed-section tubes and despite being substantially open-section shells, those with more than two spirals collapsed progressively for crushing lengths that corresponded to 2/3 of their axial length. Moreover, the specific energy absorption, the energy absorption per spiral and the crush force efficiency of the tubes examined improved with respect to the number of spirals reaching peak values for around three to four spirals.

Behaviour of Steel-Concrete Composite (SCC) girder under impact due to rock fall

This paper presents a comprehensive numerical investigation on static and dynamic behaviour of the steel-concrete-composite (SCC) girders. Finite element model of steel concrete composite girder under quasi static loads is generated and the responses are validated with the experimental results conducted by the first author. Subsequently, the FE model is adopted to predict the dynamic behaviour of the SCC girder due to rock fall. In order to understand the significance of the studs in SCC girder and their behaviour under impact loading due to rock fall, in this regard two cases are demonstrated. First case is to understand the behaviour of SCC girders without any shear connection and, second is with full shear connection. All the numerical investigations are carried out using commercially available nonlinear explicit finite element code ABAQUS. During finite element analysis the attention has been paid to appropriately model the symmetry boundary conditions, and material behaviour for both steel and concrete. The well suited concrete damage plasticity model is adopted and input parameters are provided based on the standard laboratory tests. Present numerical model could closely predict the flexural capacities for three SCC girders having various stud spacing's. The progressive movement of plastic zone in the steel beam section has been found with the increased loading. This indicates maximum utilization of steel beam capacity as the neutral axis lies near top flange. Failure mode of the composite girder under rock fall event have also been predicted which may be helpful in the design of a protective strategy.

Prediction of slamming pressure considering fluid-structure interaction. Part I: numerical simulations

ABSTRACT Marine structures are subjected to slamming loads characterised by high hydrodynamic pressure within short time durations. Such loads can cause local and global damages to structures. This paper, which is Part I in a series, reports a numerical investigation of slamming loads acting on flat stiffened plates and their dynamic response. The nonlinear explicit finite element code LS-Dyna with the Multi-Material Arbitrary Lagrangian-Eulerian (MMALE) solver was adopted to simulate the slamming impact on marine structures. The numerical method was validated by the relevant experimental data from the open literature in a comparison of slamming pressure and deflection data, as well as existing formulations. The Eulerian formulation was applied to describe the fluid flow, and a Lagrange formulation was employed to model flat stiffened plates. A penalty coupling algorithm was utilised to realise the fluid-structure interaction (FSI) between the plate and the fluid. Bilinear strain hardening with no strain-rate hardening and effect of the heat-affected zone (HAZ) were considered for the numerical simulation of the aluminum model, while nonlinear strain hardening and strain-rate hardening were adopted to verify the steel models. Effects of key influenced parameters such as water impact velocity, material behaviour, and air cushion on the slamming response were addressed accordingly. Additionally, a simulation of water hitting structure was proposed to investigate the slamming load characteristics acting on the bottom decks of offshore structures. As the next paper in this continuing series, Part II will present empirically derived formulations for prediction of slamming loads based on extensive parametric studies of actual scantlings of offshore structures, using the simulation methodology of water hitting proposed herein in Part I.

Experimental and numerical study on the crashworthiness evaluation of an intercity coach under frontal impact conditions

In this study, the energy absorption capacity of a front body of a bus during a frontal crash was investigated. The strength of the bus structure was examined by considering the ECE-R29 European regulation requirements. The nonlinear explicit finite element code LS-DYNA was used for the crash analyses. First, the baseline bus structures without any improvements were analyzed and the weak parts of the front end structure of the bus body were examined. Experimental tests are conducted to validate the finite element model. In the second stage, the bus structure was redesigned in order to strengthen the frontal body. Finally, the redesigned bus structure was compared with the baseline model to meet the requirements for ECE-R29. In addition to the redesign performed on the body, energy absorption capacity was increased by additional energy absorbers employed in the front of bus structure. This study experimentally and numerically investigated the energy absorption characteristics of a steering wheel armature in contact with a deformable mannequin during a crash. Variations in the location of impact on the armature, armature orientation, and mannequin were investigated to determine the effects of the energy absorption characteristics of the two contacting entities.

High-velocity impact loading in honeycomb sandwich panels reinforced with polymer foam: a numerical approach study

The employment of lightweight structures is one of the most important goals in various industries. The lightweight sandwich panel is an excellent energy absorber and also a perfect way for decreasing the risk of impact. In this paper, a numerical study of high-velocity impact on honeycomb sandwich panels reinforced with polymer foam was performed. The results of numerical simulation are compared with the experimental findings. The numerical modeling of high-velocity penetration process was carried out using nonlinear explicit finite-element code, LS-DYNA. The aluminum honeycomb structure, unfilled honeycomb sandwich panel, and the sandwich panels filled with three types of polyurethane foam (foam 1: 56.94, foam 2: 108.65, and foam 3: 137.13 kg/m3) were investigated to demonstrate damage modes, ballistic limit velocity, absorbed energy, and specific energy absorption (SEA) capacity. The numerical ballistic limit velocity of sandwich panels, filled with three types of foam, was more than that of a bare honeycomb core and unfilled sandwich panel. In addition, the numerical results showed that the sandwich panel filled with the highest density foam could increase the strength of sandwich panel and the numerical specific energy absorption of this structure was 23% more than that of unfilled. Finally, the numerical results were in good agreement with experimental findings.

Multi-objective crashworthiness optimization of thin-walled multi-cell tubes with different wall lengths

Thin-walled tubes are extensively used in the automotive industry because of their high energy absorption capacity and lightweight advantages. These structures are expected to have high energy absorption and low peak force during any collision. In this study, to obtain low peak crushing force, different wall lengths have applied to the thin-walled tubes. Different wall lengths have investigated using doubly-walled walled, inner multi-cell walled and multi-cell walled tubes obtained from square, hexagon, octagon and circle cross-sections. To evaluate crashworthiness performance dynamic impact analyses at a constant velocity are carried out using the non-linear explicit Finite Element (FE) code Radioss. According to the FE results, tubes with different wall lengths give lower peak crushing force (PCF) of up to 36% compared to normal tubes. On the other hand, in tubes with different wall lengths, there is a decrease of up to 6% in specific energy absorption (SEA) compared to normal tubes. Thus, considering the decrease of the PCF, the advantage of tubes with different wall lengths is presented. Optimization studies have carried out for the second type octagonal tube with different wall lengths (O2G) and the third type octagonal tube with different wall lengths (O3G) which give better SEA and PCF values between all tubes.

Prediction of slamming pressure considering fluid-structure interaction. Part II: Derivation of empirical formulations

This is Part II in a series of papers. Part I [1] investigated the slamming responses of flexible flat stiffened steel and aluminum plates using the nonlinear explicit finite element code LS-Dyna with the Multi-Material Arbitrary Lagrangian-Eulerian (MMALE) solver. Subsequently, a simplified finite element FSI model of water hitting structures that is realistically close to the slamming phenomenon occurring on the bottom part of offshore structures was proposed. The proposed FSI methodology presented in Part I was verified by comparison with the relevant test data. It was evident that the use of the proposed numerical method presented in Part I was very effective for a benchmarking investigation of slamming load considering the hydroelastic effect. However, the method required much effort in terms of computation time and power analysis resources. The present study, Part II, aimed, as an alternative to the FSI analysis approach, to develop empirical formulae for prediction of slamming loads acting on deformable flat stiffened plates used in marine applications. This paper begins by describing the limitations of the existing approaches based on theoretical, experimental and even numerical studies conducted in the past for estimation of slamming loads. Next, it presents, based on the simulation methodology developed in Part I, rigorous parametric studies that had been performed on actual scantlings of marine-seagoing structures. The effects of structural geometry and water impact velocity on slamming pressure are then investigated in detail. Subsequently, the parametric results are analyzed and utilized to derive empirical formulations for the prediction of slamming loads acting on flat stiffened plates of marine structures. The accuracy and reliability of the proposed formulations are established by comparison with the results of the test and other existing formulations. The proposed formulations are expected to be used for the purposes of the design without any time-consuming FSI analysis of advanced and optimal structures that are robust to slamming.

Numerical analysis of elastomer buffer embedded in the suspension of automobile for vibration damping improvement

Elastomers, due to their excellent damping and energy absorption characteristics and low cost are used extensively in automobile industry to isolate the structures from vibration and shock loads. In this study, it was aimed to analyze the damping performance of an elastomer buffer embedded in the suspension of an automobile. To reach to this aim, vibration simulation of an automobile suspension model was conducted by using a nonlinear explicit finite element code, Abaqus. In order to simulate the damping behavior of elastomer buffer, the hyperelastic and linear viscoelastic material models were used together. The numerical model was validated with results of exact solution method in terms of transmissibility ratio and phase shift in a wide range of input excitation frequencies. Good agreement was observed between the exact solution and finite element results, which indicate that finite element model is sufficiently accurate. To examine the damping performance of the buffer, the displacement time history curves were extracted for suspension with and without buffer under the sinusoidal base excitation. The vibrating motions of suspension for both conditions were compared. The comparison results proved that the elastomer buffer was effective in improvement of damping performance of suspension. It reduced the amplitude of vibration and oscillation time of sprung mass remarkable in excitation frequencies around and over the natural frequency of the system.

Drop test simulation and surrogate-based optimization of a dishwasher mechanical structure and its packaging module

A drop test simulation of the mechanical structure of a redesigned dishwasher is performed by using a detailed finite element (FE) model. The nonlinear explicit FE code LS-DYNA® is used for the drop impact simulations. The FE model is validated through real tests of two drop scenarios (vertical and inclined to the side). An optimization study is performed in order to determine the optimum design variables for better crash performance. The effects of geometric parameters and material properties on the weights of certain components (ie, dogleg plate and bottom foam) are investigated. A surrogate-based optimization approach is used to find optimum values for the dogleg plate thickness, bottom foam density and increment of the bottom foam height to minimize the weights of both components. Two different surrogate models are used to predict optimization problem constraints that have a crucial role in the crash performance of the dishwasher mechanical structure and packaging module: the polynomial response surface and radial basis functions. The results showed that the dogleg plate mass can be slightly reduced and the bottom foam mass can be significantly reduced in order to obtain the optimum dishwasher configuration and better crashworthiness. The weights of the dogleg plate and bottom foam could be lowered by as much as 5.95 and 24.8 %, respectively. Finally, multi-objective optimization is performed by minimizing a composite objective function that provides a compromise between the weights of both components. The results showed that weight reductions of 2.3 and 21.5 % could be obtained for the dogleg plate and bottom foam, respectively.

Experiment and numerical simulation of a full-scale helicopter composite cockpit structure subject to a bird strike

Bird strike is one of the most critical safety issues in aviation, which usually leads to catastrophic casualties. In this paper, an effective FE–SPH coupling model is developed to investigate the structure crashworthiness performance of a helicopter composite cockpit (HCC) subject to a bird strike by using an explicit nonlinear finite element code ANSYS/LS-DYNA 3D. The mechanical parameters of the bird constitutive model are obtained by a bird strike test on flat plate and the validated bird model is subsequently implemented to simulate a bird striking on HCC according to Federal Aviation Regulation 29.631. A full-scale HCC bird strike experiment is also performed under the same impact condition to certify airworthiness requirement as well as validate the FE model. The high agreement between the experiment and numerical analysis builds confidence in future use of FE method as a predictive tool. Based on numerical results, a structure design modification is also performed to enhance the structure stiffness and improve bird strike resistance.

A study of diamond wire rock cutting process analysis by FEM

In this paper diamond wire cutting method has been proposed to cut the rock in the tunnel face. Diamond wire saw method could cut the rock from tunnel face with very minor vibration and noise. In this study rock cutting process has been simulated with FEM method by using LS-DYNA explicit non-linear finite element code. Normal load act as an prime factor when cutting the rock surface. For observing the effect of normal load on bead, several experiments has been conducted by varying normal loads on the bead. From each experiment, cutting rate has been calculated to compare the cutting rate with different load conditions. By increasing the normal load on bead, cutting rate increases drastically.

A new approach for coupling external dynamics and internal mechanics in ship collisions

This paper proposes a new model, which efficiently couples the external dynamics and internal mechanics in ship collision accidents. This method is especially useful for design purposes since the detailed ship hull profile is not needed.Ship motions in the horizontal plane are considered. The collision forces are calculated using the explicit nonlinear finite element code LS-DYNA. The hydrodynamic forces in surge, sway and yaw are calculated using a traditional ship maneuvering model with a series of nondimensional coefficients determined from experiments. These forces are applied to the center of gravity (COG) of the ship with the user defined load subroutine in LS-DYNA and are solved together with structural response analysis during simulation.The proposed 3DOF coupled method was applied to calculations of an offshore supply vessel colliding with a rigid plate and a submersible platform. The results were compared with those predicted by a decoupled method. Ship motions with the proposed method compared reasonably with SIMO simulations. The advantages and limitations of the method were further discussed in the view of the equivalent added masses.

High strain rate tensile behavior of Al-4.8Cu-1.2Mg alloy

The purpose of the current study is to perform quasi static and high strain rate tensile tests on Al-4.8Cu-1.2Mg alloy under different strain rates ranging from 0.01–3500/s and also at temperatures of 25,100, 200 and 300°C. The combined effect of strain rate, temperature and stress triaxiality on the material behavior is studied by testing both smooth and notched specimens. Johnson–Cook (J–C) constitutive and fracture models are established based on high strain rate tensile data obtained from Split hopkinson tension bar (SHTB) and quasi-static tests. By modifying the strain hardening and strain rate hardening terms in the Johnson–Cook (J–C) constitutive model, a new J–C constitutive model of Al-4.8Cu-1.2Mg alloy was obtained. The improved Johnson–Cook constitutive model matched the experiment results very well. With the Johnson–Cook constitutive and fracture models, numerical simulations of tensile tests at different conditions for Al-4.8Cu-1.2Mg alloy were conducted. Numerical simulations are performed using a non-linear explicit finite element code autodyn. Good agreement is obtained between the numerical simulation results and the experiment results. The fracture surfaces of specimens tested under various strain rates and temperatures were studied under scanning electron microscopy (SEM).

Experimental and Numerical Analyses of Dented Stiffened Panels

Numerical–experimental correlation study for small scale damaged stiffened panels was performed. Six small scale models were fabricated. Two of them were employed for the correlation of intact panels and the remaining four for the correlation of dented panels. Ultimate strength analyses were carried out in order to adjust the numerical model for further use in parametric studies. The damage was imposed by a local indentation of the panels. Measurements of geometric imperfection distributions and damage shapes have been performed before and after the damage using a laser tracker equipment. The numerical models were represented by shell elements assuming finite membrane strains and large rotations, considering both geometric and material nonlinearities. Results obtained showed very good agreement between experimental and numerical analyses for both intact and dented panels. Additionally, numerical simulations of damaged stiffened panels were performed. The aim of the parametric study was to evaluate the behavior up to and beyond buckling, to observe the strength loss due to the presence of the damage on the panel. The explicit nonlinear finite element code from abaqus program was employed to simulate the dent damage. Therefore, distortions and the residual stresses due to the damage were both considered in subsequent numerical compression analyses.

Multi-cornered thin-walled sheet metal members for enhanced crashworthiness and occupant protection

Crash energy management in frontal crumple zone of the automotive body is one of the key elements for the design of automotive structure. Improving energy absorption characteristics reduces the magnitude of forces transferred to the occupant compartments. Here, a new strategy has been proposed to improve energy absorption efficiency of thin-walled columns by introducing extra stable corners in the cross-section. Several profiles of multi-corner thin-walled columns obtained through this strategy were presented and their crashworthiness capacities under axial crush loading were investigated analytically, experimentally, and numerically. First, explicit formulations for predicting the mean crushing force of multi-corner thin-walled columns were derived using the theory of super folding element (SFE). Predicted results of these formulations showed a good agreement with the results of quasi-static experiments and CAE simulations, which were performed by explicit non-linear finite element code through LS-DYNA. Based on this agreement, other significant crashworthiness assessment parameters were then investigated experimentally and numerically. Newly introduced 12-edge section with high energy absorption capacity was developed and its dominance was established through the responses in quasi-static experiments and CAE simulations. Finally, the foundational dominance of the 12-edge section was extended to the dynamic environment through a full vehicle crash test simulation to evaluate overall reduction in crashworthiness parameters which reflected occupant safety. Interestingly, in the case of using 12-edge section as crush absorbers, specific energy absorption (SEA), dash intrusion and maximum occupant’s chest deceleration showed significant improvement, compared to the baseline design which used a rectangular section.

Finite element modeling of wing bird strike

Bird strike events are a potential dangerous problem faced by flight safety nowadays. These events are usually simulated through numerical approaches due mainly to the technical difficulties and high costs associated with experimental tests. The consequences of bird impact can be severe and, therefore, the aircraft components have to be certified for a proven level of bird impact resistance before being put into service. Bird impact poses serious threats to military and civilian aircrafts as they lead to fatal structural damage to critical aircraft components. The exposed aircraft components such as windshields, radomes, leading edges, engine structure, and blades are vulnerable to bird strikes. Among a large number of structural tests an aircraft structure needs a certification requirement for a proven level of impact resistance against bird impacts. Bird strike experiments are very expensive and henceforth explicit numerical modeling techniques have grown importance. Parts of aircraft construction are intensively vulnerable to damage during flight by bird impact. The theoretical approach and results of numerical simulations of dynamic response of the wing loaded by the bird impact are presented. The numerical simulation is carried out using smooth particle hydrodynamics (SPH) method running in the nonlinear explicit finite element code ANSYS AUTODYN. The focus is given to the validation of the stress, strain and deflection of wing on the impact zone. The dependency of given parameters on the variation of ellipsoidal bird aspect ratio, impact velocity and wing design details was discussed. As well, some results of experimental data were given. The behavior of aircraft leading edge against high speed bird impact was successfully simulated and the effect of various parameters on its dynamic response was studied. Numerical model was validated with published experimental results and further employed to investigate the influence of various parameters on dynamic behavior of aircraft leading edge.

Impact Behavior of Square Crash Box Structures Having Holes at Corners

In this paper, an analytical prediction and numerical simulation of the behavior of square crash box structures having hole at corners on dynamic axial crushing are studied. The focus of the present theoretical prediction is to calculate the mean crushing force and maximum crushing force during the folding process subjected to axial impact loading. Then, the effect of hole size to the crushing response of square crash box structures was also evaluated. For validation, an explicit non-linear commercial finite element code LS-DYNA was used to predict the response of the structures subjected to axial crushing. It was found that results of numerical method and theoretical prediction were in good agreement. The results showed that, by inserting holes at corners, the folding can be controlled to be always started from the hole, and peak crush load on the first fold can be reduced significantly. Meanwhile, the decreasing of mean crushing force is insignificant compared to the one without holes. Hence, the characteristic of impact energy absorption in a progressive buckling can be improved, the damage in passenger compartment can be minimized, and the deceleration level can be kept in safe level to prevent injury of the passenger.

Impact and Energy Absorption of TWB Thin-Walled Structures with Polygonal Cross-Sections

Nowadays, thin-walled structures and different materials destined to absorb kinetic energy initiated a great interest among the researchers from the auto, naval, military industries even from the protection equipment production industry. The main role of these structures is to absorb and dissipate the kinetic energy so the maximum level of deceleration to be limited. Thus, the structures collapse through progressive buckling. The aim is to control this progressive buckling as efficient as possible through the collapse mode or the construction technique. This collapsing mode is well described and characterised by the international literature [.The plastic strain history of the components constituting the thin-walled structure is very important because each bending, stretching process or tensioning brings with it self-a series of transformations which compete to influence the dynamic response of this kind of structures [2].In this study, all the above presented aspects were taken into consideration in the analysis of the impact and energy absorption behaviour regarding thin-walled structures by using explicit nonlinear finite element code LS_Dyna V971. The thin-walled structures involved in this research are made from tailor welded blanks (TWB) and were subject of axial impact crashing tests. There were used three types of cross-section shapes: rectangular, pentagonal and hexagonal. In order to have a fare comparison study, all the studied structures had a 250mm cross-section perimeter and a height of 250mm, also. Each structure is constituted from four, five or six sheet metal parts bonded together.