Forming Strain Path and Cold Work Embrittlement in Sheet Steels

The post forming performance of automotive components has continued to be an important but challenging issue in materials science and engineering. The modeling community must know the strength of the formed parts to be able to predict behavior such as crash worthiness, high cycle fatigue resistance and dent resistance. Furthermore, the ductility and toughness of the formed parts must be known for safety and warranty reasons. A review of some previous work reveals that there are levels of complexity in understanding these relationships that are often overlooked. Phenomena such as the Bauschinger Effect and compressive work embrittlement complicate the prediction of post formed properties. This is especially true when the forming strain path contains a compressive component. Previous work has shown that when a tensile stress is applied in a direction of compressive forming strain, drastic reductions in strength and toughness may result. The goal of this paper is to discuss these interactions and to suggest how they might complicate our view of the performance of cold formed parts.