Fracture Prediction of Mild Steel Sheet and 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. An experimental apparatus that is capable of draw-bending sheet specimens with forming speeds (approximately 100 -1 mm s  ) comparable to those of real press forming machines is designed and built. The test materials are an ultralow-carbon steel sheet and a 590MPa high-strength steel sheet. Specimens undergo bending-unbending under tension when passing over a die profile. The magnitudes of true stress DB  at which the stretch-drawn specimens fractured are precisely determined from the measured data of the drawing force and the crosssectional area of the specimen after fracture. Moreover, multiaxial tube expansion tests are performed to measure the forming limit stresses PT  of the test materials under plane-strain tension. It is found that DB  is larger than PT  by 6-18%. Therefore, it is concluded that the forming limit stress criterion is effective for the fracture prediction in draw-bending.

Effect of Frictional Conditions in Deep Drawing on Formability

“…This may result in rupture. Furthermore, the die shoulder may break because of the relationship between the die shoulder radius and plate thickness [2]- [3].…”