Fracture Prediction for High-strength Steel Sheet Subjected to Draw-bending Using Forming Limit Stress Criterion

Abstract

A fracture criterion for sheet metals subjected to draw-bending is investigated using the concept of the forming limit stress criterion. The test material used is a 1.0-mm-thick high- strength steel sheet with a tensile strength of 590MPa. The specimen undergoes bendingunbending under tension when passing over the die profile. The drawing speed was set to 5-100 mm • s-1. The magnitude of true stress σDB when a specimen fractured has been precisely determined. Moreover, multiaxial tube expansion tests of the test material are performed to measure the forming limit stress σPT of the test material under plane-strain tension. It is found that σDB is larger than σPT by 2.8-6.3%. Therefore, it is concluded that the forming limit stress criterion is effective as a fracture criterion in draw-bending.