Effects of AHSS Sheared Edge Conditions on Crash Energy Absorption in Component Bend Test

Edge fracture of advanced high strength steels (AHSS) can occur in both the stamping process and the crash event. Fracture due to poor sheared edge conditions in the stamping process was reduced with a recently developed optimal shearing process for AHSS. Currently, the improvement in the energy absorption due to the improved edge condition during crashes performed under different loading conditions had not been closely verified. The purpose of this study is to design and build a miniature component of AHSS and a three-point bending test for investigating the influence of various conditions of the sheared edge on the energy absorption in crashes. AHSS including DP600, TRIP780, DP980 and DP1180 were selected in the study. A small channel component was developed and fabricated using DP980 to simulate key features of the B-pillar. The exposed non-constrained, as-sheared edge was subject to stretch bending forces in three-dimensional space during the three-point bending test. Two bottom rollers equipped in the three-point bending test allowed the test specimen to bend freely without generating extra friction force between the test material and tooling. Previously developed shearing parameters were fine-tuned for generating the test specimen on the flexible shearing machine and then compared to the specimens made by water jet cutting and laser cutting. A life cycle analysis was also conducted by FEA to evaluate the new design of the shear blade. The experiment results indicate the improvement of the sheared edge conditions can also increase the material energy absorption in crashes. The laser cut sample has the best energy absorption capability, while the conventional cutting edge shows the worst. In addition to the three-point bending test, a wedge bend test was conducted on the flat sample and reached a similar energy absorption trend as in the component bend test. The wedge bend test on flat sample is recommended for baseline comparison in material bendability and crash energy absorption capability among different advanced high strength steels.