Full-scale Finite Element Model Research Articles

A study on the potential risk of traumatic brain injury due to ground impact in a vehicle-pedestrian collision using full-scale finite element models

In this study, a validated pedestrian finite element model with a detailed brain was utilised to investigate the potential risk of Traumatic Brain Injury (TBI) in relation to ground impact in a vehicle-pedestrian collision. We found that pre-impact transverse pedestrian speed affects post-impact kinematics and subsequent kinetics, which are considerably unpredictable due to the intrinsic complexity of pedestrian crash, and ground impact is likely to cause serious TBIs for struck pedestrians. This finding suggests effective countermeasures for ground impact should be taken into account to reduce TBIs involving vehicle with a higher profile even at the low impact speed levels.

MULTISCALE COMPUTATIONAL EVALUATION OF ELASTO-VISCOPLASTIC DEFORMATION BEHAVIOR OF AMORPHOUS POLYMER CONTAINING MICROSCOPIC HETEROGENEITY DURING UNIAXIAL TENSILE TEST

The two-scale elasto-viscoplastic deformation behavior of amorphous polymer was investigated using the large deformation finite element homogenization method. In order to enable a large time increment for the simulation step in the plastic deformation stage, the tangent modulus method is introduced into the nonaffine molecular chain network theory, which is used to represent the deformation behavior of pure amorphous polymer. Two kinds of heterogeneous microstructures were prepared in this investigation. One was the void model, which contains uniformly or randomly distributed voids, and the other was the heterogeneous strength (HS) model, which contains a distribution of initial shear strength. In the macroscopic scale, initiation and propagation processes of necking during uniaxial tension were considered. The macroscopic nominal stress–strain relation was strongly characterized by the volume fraction and distribution of voids for the void model and by the width of the strength distribution for the HS model. Non-uniform deformation behaviors in microscopic and macroscopic scales are closely related to each other for amorphous polymers because continuous stretching and hardening in the localized zone of the microstructure brings about an increase in macroscopic deformation resistance. Furthermore, computational results obtained from the homogenization model are compared to those obtained from the full-scale finite element model, and the effect of the scale difference between microscopic and macroscopic fields is discussed.

Analysis of the effects of main design parameters variation on the vibration characteristics of a vehicle sub-frame

In the design process of an automobile part, several analysis methods are usually used to evaluate the performance of the part. However, most automobile design engineers do not directly use CAE (computer aided engineering) tools since specific skills are required to obtain practical results. Moreover, CAE requires a huge amount of computation time and cost. To resolve these problems, a new design approach, termed first order analysis (FOA), has been proposed. In this paper, the FOA technique is employed to design a vehicle sub-frame. An equivalent model of the vehicle subframe which only consists of beam elements is proposed and the modal properties obtained with the model are compared to those obtained with a full scale finite element model. The effects of some parameter variations on the modal characteristics of the vehicle sub-frame are investigated by employing the FOA equivalent model.

Thermo-structural model of stacked field-programmable gate arrays with through-silicon vias

A new 3-D full-scale thermo-structural finite element model of two-stack field-programmable gate arrays (FPGAs) with through-silicon vias (TSVs), which is developed from an experimentally validated single-stack FPGA model, is proposed. Typical 3-D distributions and evolutions of temperature and von Mises stress on both the active layers and TSVs are presented.

An iterative procedure for determining effective stress–strain curves of sheet metals

An iterative correction procedure using 3D finite element analysis (FEA) was carried out to determine more accurately the effective true stress–true strain curves of aluminum, copper, steel, and titanium sheet metals with various gage section geometries up to very large strains just prior to the final tearing fracture. Based on the local surface strain mapping measurements within the diffuse and localized necking region of a rectangular cross-section tension coupon in uniaxial tension using digital image correlation (DIC), both average axial true strain and the average axial stress without correction of the triaxiality of the stress state within the neck have been obtained experimentally. The measured stress–strain curve was then used as an initial guess of the effective true stress–strain curve in the finite element analysis. The input effective true stress–strain curve was corrected iteratively after each analysis session until the difference between the experimentally measured and FE-computed average axial true stress–true strain curves inside a neck becomes acceptably small. As each test coupon was analyzed by a full-scale finite element model and no specific analytical model of strain-hardening was assumed, the method used in this study is shown to be rather general and can be applied to sheet metals with various strain hardening behaviors and tension coupon geometries.

NUMERICAL ANALYSIS OF ROLLOVER AND HEAD-ON CRASH RESPONSE OF NON-STEP BUS

As a next-generation metropolitan transportation means, nowadays non-step bus is in the spotlight world widely. However, in the design of non-step bus, the most important consideration should be focused on the securing of the survival space for passengers in unexpected traffic accident. In this context, this paper presents the finite element analysis of the rollover and head-on crash response of a composite non-step bus. A 3-D full-scale finite element model of the non-step bus, together with the simulation conditions which are consistent with the safety test rules established in Europe, is employed for the realistic and reliable numerical analysis.

Reduced-Order Models for the Calculation of Thermal Transients of Heat Conduction/Convection FE Models

On-line calculation of temperature and thermal stresses at critical locations of structural components is currently performed in nuclear and aeronautical applications in order to assess fatigue damage accumulation and residual life. Since it is not possible to use full-scale finite element models because of the large calculation times, ad-hoc simplified algorithms are developed and employed. Thermal stresses commonly arise because of temperature gradients within the component due to heat exchange between the solid and the surrounding fluid. Commonly on-line monitoring methods are based on the assumption that time histories of the temperatures of the fluids around the component are known (e.g., measured) and are used as the inputs for the calculation of temperature and thermal stress at the critical locations of the component. If the temperatures of the surrounding fluid can not be measured, they must be numerically computed integrating an FE model of the fluid in the thermal FE model of the component; as a result, the size of the coupled thermal model is further increased. In the present work, a methodology is developed to reduce the size of thermal models including not only the FE model of the component but also the coupled fluid model. In detail, Guyan reduction and component mode synthesis are applied to a coupled thermal FE model, in order to reduce the size of the problem and to make it suitable for on-line calculations. The appropriate mathematical formulation for the reduction of the fluid FE model has been developed. Two reduction methods are proposed and are applied to the axial symmetric FE model of a turbine disk pointing out their capabilities and limitations for on-line temperature calculation.

Assessment of vehicle roof crush test protocols using FE models: inverted drop tests versus updated FMVSS No. 216

Inverted drop test is a dynamic roof crush test which is simple, realistic, reliable and easily implemented. It can produce repeatable roof impacts that can be used to compare one test run with another and has long been used by the automotive industry and researchers to test roof integrity. However, practical full-scale vehicle roof crush tests are always very costly, especially for finding out the impact orientation for the worst structural behaviour. Computer simulation can provide an effective solution, since it is highly repeatable, and under different environmental conditions permits the variation of parameters to evaluate sensitivity. A full-scale Finite Element model of Ford Fiesta that was originally modelled in parts by Ford Motor Company using Radioss code was translated into LS-DYNA3D and refined through extensive employment of better elements and spotwelds formulation. The inverted drop-test simulation, therefore, was made using a combination of different pitch and roll angles in the search of the worst-case rollover condition. These parametric studies show the critical vehicle orientation at roof impact that causes the highest amount of roof crush to be 10° pitch angle and 12.5° roll angle. This is similar to the test conditions employed in the experimental test using a Renault Clio. The results obtained from simulating these two different vehicles show the existence of some design problems, i.e., a very weak roof that is supported by weak roof rails and weak reinforcing plates. Furthermore, the inverted drop-test simulation results depict clearly the differences between static roof crush tests based on FMVSS No. 216 that is loaded along a fixed orientation and only reflects the roof strength, rather than the pillar's strengths, response in that direction. The dynamic test in that sense is more realistic and closer in nature to a number of recorded real-world accidents.

A modern aerospace modeling approach for evaluation of aircraft fuselage crashworthiness

A 9 [m/s], (30-ft/s) vertical drop test of a fuselage section of a Boeing 737 aircraft was conducted at the FAA William J. Hughes Technical Center in Atlantic City, NJ. Test was performed to evaluate the structural integrity of a conformable auxiliary fuel tank mounted beneath the floor and to determine its effect on the impact response of the airframe structure. The objective of the test was to determine the interaction between a typical transport aircraft fuselage, particularly its floor structure, and a conformable auxiliary fuel tank under severe, but survivable, impact conditions. The fuel tank used in this test is representative of tanks being installed in narrow-body transport aircrafts. The 3 [m], (10-foot) airframe section from a Boeing 737-200 aircraft was dropped from a height of 4.27 [m], (14-feet) generating a vertical impact velocity of 9 [m/s], (30-ft/s). The airframe test section weight of 3,982.5 [kg], (8780-lb) simulated the load density at the maximum takeoff weight condition. The weight included cabin seats, dummy occupants, and simulated fuel in the 1,892.71 liters, (500-gallon) fuel tank. Structural response data were obtained during the impact from instrumentation installed on the fuselage structure, floor structure, and the fuel tank. The fuselage test section sustained severe damage after the test. Portions of the cabin floor were damaged due to the impact with the auxiliary fuel tank located in the cargo compartment. Portions of the fuselage bottom were crushed by approximately 66 [cm], (26-in). The bottom of the fuel tank was punctured in numerous locations causing fuel to leak out. The strength and rigidity of the fuel tank limited the inherent ability of the fuselage structure to absorb energy crushing during the impact. The test data were used to compare with a finite element simulation of the fuselage structure and to gain a better understanding of the impact physics through analytical/experimental correlation. To perform this simulation, a full-scale 3-dimensional finite element model of the fuselage section was developed using the explicit, nonlinear 3-D Finite Element code, LS-DYNA. The emphasis of the simulation was to determine the structural deformation and floor-level acceleration responses obtained from the drop test of the B737 fuselage section with the auxiliary fuel tank.

Crystal plasticity model with enhanced hardening by geometrically necessary dislocation accumulation

A strain gradient dependent crystal plasticity approach is used to model the constitutive behaviour of polycrystal FCC metals under large plastic deformation. Material points are considered as aggregates of grains, subdivided into several fictitious grain fractions: a single crystal volume element stands for the grain interior whereas grain boundaries are represented by bi-crystal volume elements, each having the crystallographic lattice orientations of its adjacent crystals. A relaxed Taylor-like interaction law is used for the transition from the local to the global scale. It is relaxed with respect to the bi-crystals, providing compatibility and stress equilibrium at their internal interface. During loading, the bi-crystal boundaries deform dissimilar to the associated grain interior. Arising from this heterogeneity, a geometrically necessary dislocation (GND) density can be computed, which is required to restore compatibility of the crystallographic lattice. This effect provides a physically based method to account for the additional hardening as introduced by the GNDs, the magnitude of which is related to the grain size. Hence, a scale-dependent response is obtained, for which the numerical simulations predict a mechanical behaviour corresponding to the Hall–Petch effect. Compared to a full-scale finite element model reported in the literature, the present polycrystalline crystal plasticity model is of equal quality yet much more efficient from a computational point of view for simulating uniaxial tension experiments with various grain sizes.