|
Citation
|
Abedrabbo N, Mayer R, Thompson A, Salisbury C, Worswick MJ, van Riemsdijk I. Int. J. Impact Eng. 2009; 36(8): 1044-1057. |
|
Abstract
|
There is a strong motivation in the automotive sector to increase vehicle fuel efficiency. One important method of achieving this goal is the use of lightweight structures. At the same time, however, these new lighter structures must maintain or exhibit improved crash energy absorption. Multiple candidates for replacing mild steel in automotive structures have been proposed such as advanced high-strength steels, aluminum or magnesium alloys, and composite materials. Advanced high-strength steels (AHSSs), in particular, are attractive candidate materials, offering higher strength for energy absorption and the opportunity to reduce weight through use of thinner gauges. However, though mild steels are highly formable, the increase in strength achieved using AHSS materials is at the expense of a reduction in formability. Thus, there is a need to address the formability of high-strength steel tubes. In addition, the history of the forming processes performed on these materials influences the behaviour of the final component in the impact test. Therefore, it is important to study the energy absorption characteristics of advanced high-strength steels in the as-formed condition during crash testing.
The performance of non-hydroformed and hydroformed structural steel tubes in component-level crash testing was investigated using both experimental and analytical techniques. In particular, the focus was on high-strength steels that may have potential to enhance crashworthiness of automobiles. Monolithic tubes made from multiple materials and wall thicknesses were considered in this study. The following materials were used: conventional drawing quality (DDQ) steels; high-strength low alloy (HSLA-350) steels; and advanced high-strength steel (AHSS) materials comprising the dual phase alloys DP600 and DP780. The goal of this research was to study the interaction between the forming and crash response of these materials in order to evaluate their potential for use in vehicle design for crashworthiness. The tubes were hydroformed using two methods known as low- and high-pressure processes. Material characterization of all materials was carried out through quasi-static and high strain rate tensile tests in the range of 0.00333-1500 s-1, and rate sensitive constitutive models for all materials were developed. The nonlinear explicit dynamic finite element code LS-DYNA, in conjunction with the validated constitutive models, was used to simulate both the hydroforming processes and the crash tests performed on the tubes. The energy absorption characteristics of the different tubes were calculated and the results from the numerical analyses were compared against the experimental data. This comparison was performed in order to determine whether the interactions between forming and crush could be adequately predicted using finite element analysis. The effects of thickness changes, work hardening, and component geometry, which resulted from hydroforming, on the crash response were also investigated. A study of the significance of strain rate and the importance of performing detailed material characterization on the accuracy of the numerical analysis was performed. Also, a parametric study on the effect of transferring forming history data between simulations on the accuracy of the numerical analysis was performed, and the importance of carrying forward the histories between multiple forming simulations was demonstrated. |