Formability Evaluation of Advanced High Strength Hot-rolled Steel Sheets

Abstract

In the industrial sheet metal forming, the process optimization considering forming failure is very important to reduce the cost of products. In order to predict forming failure in the thinning mode of sheet metal forming, Chung et al. [1, 2] have classified forming failure as failure without strain localization and failure with strain localization. As for the case of failure with strain localization, the numerical analysis of sheet metal forming have been performed under plane stress condition using shell element and the strain-based forming limit diagram (FLD) which was developed by Keeler and Backhofen [3] have been used as strain localization criterion as the most common practice. However, as the demand of usage for the advanced high strength hot-rolled steel sheets increases in the automotive industry, the conventional formability prediction method using shell element (under plane stress condition) and the strain-based forming limit diagram (FLD) does not properly work because of hot-rolled sheets thickness. However, failure with strain localization is predictable without referring to the forming limit diagram but directly evaluating strain localization for (critical) material elements strain localization if mechanical behavior is properly described [1, 2]. In this research, mechanical properties of advanced high strength hot-rolled sheets, HB780 and DP780, were properly characterized and their formability evaluation procedure was proposed.