Application of nonlocal damage models to sheet forming applications

Damage and fracture are important criteria in the design of products and processes. Traditional assessments of the formability of sheet metal materials are based on the appearance of geometrical instabilities, the necking of the sheet. A commonly used method to predict geometrical instabilities in sheet metal forming processes is the Forming Limit Curve (FLC). However, the use of an FLC has some limitations in case of small radius over thickness ratios, non proportional strain paths and non-traditional forming materials with less formability, such as aluminium and high-strength steels. These materials often fail due to physical instabilities, even before necking starts. For crash simulations the FLC is too conservative as also during necking energy is absorbed. Ductile damage models can be used complementary to the FLC approach to improve the failure predictions.