Fracture prediction of hole expansion forming using forming limit stress criterion

Abstract

The fracture prediction of a hole expansion forming for a cold rolled steel sheet is investigated using the concept of forming limit stress criterion. Multiaxial tube expansion tests (MTET) (T. Kuwabara and F. Sugawara, 2014), in which linear paths in the first quadrant of the stress space are applied to tubular specimens, are performed to measure the contours of plastic work and the directions of the plastic strain rates of the test material. The anisotropic parameters and the exponent of the Yld2000-2d yield function (F. Barlat et al., 2003) are optimized to approximate the material test data. Marciniak-Kuczynski type forming limit analyses (Z. Marciniak and K. Kuczynski, 1967) are performed to determine the forming limit stress surface (FLSS) in a stress space. It is concluded that the FLSS calculated using an appropriate material model calibrated using the MTET is effective in predicting the necking timing in the hole expansion forming of the test material.