NUMERICAL EVALUATION OF HOT STAMPED BLANK B-PILLARS

Abstract

The recent advances in sheet metal forming simulation technology have allowed engineers to predict the sheet metal stamped part performance prior to mass pro-duction by finite element method. However, the accuracy of such simulation meth-od is dependent on many factors such as right material model and its boundary con-ditions. This thesis describes the application of this method in the evaluation of an automotive hot stamped structural part call B-pillar and its variants. The first case study involved the optimization of spot-weld points and locations on a Patchwork blank B-pillar (PWB) made up of two blank materials of different thicknesses. The spot weld was modeled as a rigid link between the parent blank and the additional blank. Throughout the forming simulation, maximum stress and formability of the part were monitored. The same procedure was repeated by increasing the number of spot-weld points and locations. An optimum number of the spot-weld was then de-termined by the onset of wrinkle disappearance. Performance of the optimized spot-weld part was validated by the actual part. The results show the optimum number of spot weld points as predicted by the simulation is between 35-40 whereas the actual part contains 40 spot-weld points. The second case study was to evaluate the crash worthiness performance of different designs of hot formed B-pillars. In this study, in addition to PWB, three other hot formed B-Pillar designs namely Monolithic blank (MB), Tailor welded blank (TWB) and Tailor Rolled Blank (TRW) were evaluated by numerical simulation in accordance with the Insurance Institute for Highway Safety (IIHS) side impact test protocol.. For each design, maximum displacement or intrusion and energy absorption were measured. The results of intrusion tests for all blank models MB, PWB, TWB and TRB recorded displacement of 14.14cm, 14.80cm, 14.87cm and 14.98cm, respectively. These are considered as within the SAFE ZONE as specified by IHSS. However, in terms of energy absorption, the PWB is seemed to be the best performer followed by MB, TRB and TWB. More importantly, the FEM model developed in this research is quite reliable in determining the optimum number of spot weld points.