Investigations on Bendability of Lightweight Materials for Various Load Paths

Abstract

This contribution discusses material failure caused by incipient surface cracks on bending edges during predominant bending processes such as those that occur, e.g. when flanging and hemming outer car body parts. In this regard, the determination of bendability for modern lightweight materials is particularly important. Frequently, the deep drawing operation is already superimposed by bending loads; nevertheless the majority of bending stress is applied in the following bending and hemming operation. Forming analysis of deep drawing operations on real car body parts have shown that in hemming regions a variety of pre‐loads occur. These pre‐loads vary in load condition and its intensity. Based on these results this paper describes the experimental investigations on the bending properties for these pre‐load conditions, especially the bending limit after various pre‐load operations. The influence of different pre‐load operations has been investigated by using the established Three‐Point‐Bending‐Test [1]. Bendability of investigated material is evaluated by using optical forming analysis to determine maximal achievable bending strain on the specimen. Furthermore, a modification of the so called Bending Limit Curve (BLC) criterion is introduced for multi‐axial pre‐load conditions to optimize the prediction of material’s bendability.