Crashworthiness assessment of front side members in an auto-body considering the fabrication histories

doi:10.1016/j.ijmecsci.2003.09.022

International Journal of Mechanical Sciences

Volume 45, Issue 10, October 2003, Pages 1645-1660

https://doi.org/10.1016/j.ijmecsci.2003.09.022 Get rights and content

Abstract

This paper is concerned with crash analysis of a front side member in an auto-body considering the effect of fabrication. The front side member is fabricated with sheet metal forming processes that induce forming histories such as plastic work hardening and non-uniform thickness distribution. Numerical simulation is carried out with LS-DYNA3D in order to identify the forming effect on the crashworthiness. The result shows that the crash analysis of the front side member with considering the forming history leads to a different result from that without considering the forming effect. The analysis calculated crash mode, the reaction force and the energy absorption for crashworthiness assessment with the forming effect. The analysis results demonstrate that the design of auto-body members should be carried out considering the forming history for accurate assessment of crashworthiness.

Introduction

The crashworthiness of a car has to be evaluated with the load-carrying capacity and the crash mode at the initial stage of auto-body design. Auto-body members such as a front side member should be designed to efficiently absorb the kinetic energy during the car crash in order to secure occupants from the impact and penetration. The estimation of the energy absorption efficiency of auto-body members requires the accurate crash analysis for the load-carrying capacity and the crash mode. In order to accomplish reliable crash simulation, crashworthiness of auto-body members should be evaluated considering the effect of stamping and forming as well as the dynamic properties of materials. As most load-carrying members of an auto-body are fabricated from the sheet metal forming process, they could possess wrinkling and thinning induced from forming as well as non-uniform distributions of the effective plastic strain and the thickness strain according to the forming condition and their final shapes. Many crash analyses have been, however, carried out neglecting the forming effect induced by stamping and forming processes for estimation of the crashworthiness of an auto-body, providing erroneous results in the crash mode and the amount of crash. Recently, the crash analysis has been performed for auto-body members considering forming effect such as the strain hardening and the non-uniform thickness distribution [1], [2], [3], [4], [5], [6]. These studies insisted that the crash analysis of auto-body structures should be carried out considering forming effects for the purpose of reliable assessment.

Dutton et al. evaluated the crashworthiness of the side-rail considering variations of thickness, plastic strain and residual stress obtained from the hydro-forming analysis [1], [2]. Lee et al. carried out the crash analyses of a sheet formed S-rail and a hydro-formed tube considering the effect of the mesh configuration as well as the thickness, the plastic strain and the residual stress [3]. Kim and Huh considered not only effects of the thickness variation and the effective plastic strain but also the effect of the final formed shape in the collapse analysis of an S-rail structure using the finite element limit analysis [4], [5]. Mikami et al. carried out the frontal crash analysis of a car considering the thickness variation and the plastic strain for the front side member and the under frame [6].

In this paper, the forming histories of a front side member are obtained from simulation of stamping and forming processes so that they can be considered in the estimation of its crashworthiness. Since front side members should play an important role in absorption of the kinetic energy during the front crash, they are fabricated from sheet metals. Forming analysis of each panel of the front side member is carried out with an explicit elasto-plastic finite element analysis code, LS-DYNA3D. Non-uniform distributions of the effective plastic strain and the thickness strain in formed panels are obtained as the forming history from simulation of sheet metal forming. As the first step, draw-bead analysis is performed for calculation of the restraining force of draw-beads with an implicit elasto-plastic finite element analysis code, ABAQUS/Standard. Secondly, the calculated restraining force is applied to forming simulation of each panel as the equivalent restraining force on the flange region. The thickness strain of the inner panel, frame-frt-in, is compared with the thickness strain in a real product for verification of the analysis result.

Crash analysis of the front side member is carried out imposing the forming analysis result on the initial condition. Numerical simulation is performed with LS-DYNA3D in order to evaluate the crashworthiness of the front side member. In order to consider the non-uniform distributions of the effective plastic strain and the thickness as the condition for crash analysis, the forming histories are mapped into the new finite element mesh system. The crash analysis results of the front side member considering the forming histories are compared with that without the forming effect. The forming effect on the crashworthiness is investigated for non-uniform distribution of the thickness and the effective plastic strain separately. The crash analysis results well demonstrate that these forming histories greatly change the crash mode, the load-carrying capacity and the energy absorption efficiency of the front side member. It is noted from the results that design of auto-body members needs to consider the forming effects for a proper and accurate evaluation of the crashworthiness of a car with fabricated members.

Section snippets

Forming analysis of the front side member

A front side member is composed of seven panels as shown in Fig. 1: frame-frt-in; frame-frt-out-A; frame-frt-out-B; reinf-frt-frame-A; reinf-frt-frame-C; reinf-frt-frame-D; and hook-tie-down. The forming histories are calculated with the direct forming analysis for four panels that have great influence on the behavior of the front crash. For the sake of the computational efficiency, the restraining forces of draw-beads in the dies are calculated with an implicit elasto-plastic finite element

Crash analysis of the front side member

A finite element model of the assembled front side member for the crash analysis is shown in Fig. 13. The total mesh system consists of 29842 four-node shell elements and 30788 nodal points. The welding points for assembling seven parts are 93 points that are also modeled in simulation. Finite element models of seven panels that compose the front side member are illustrated in Fig. 1 with the number of nodes and elements specified for each panel. The panels are obtained from the formed ones by

Conclusion

Crash analysis of a front side member has been carried out in order to evaluate the crashworthiness accurately considering the forming history. The analysis investigated the difference of the crash mode, the reaction force and the energy absorption between the results with considering the forming history and without considering the forming effect. Forming analyses of parts of the front side member have been carried out to obtain the distribution of the thickness and the effective plastic strain

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Kellicut A, Cowell B, Kavikondala K, Dutton T, Iregbu S, Sturt R. Application of the results of forming simulation in...
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Comparative crash simulations incorporating the results of sheet forming analyses
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Collapse analysis of auto-body structures considering the effect of fabrication
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Crashworthiness assessment of front side members in an auto-body considering the fabrication histories

Abstract

Introduction

Section snippets

Forming analysis of the front side member

Crash analysis of the front side member

Conclusion

Journal of Materials Processing Technology

Comparative crash simulations incorporating the results of sheet forming analyses

Engineering Computations

Collapse analysis of auto-body structures considering the effect of fabrication

Key Engineering Materials