To study cracks, which are affected by bending formation, a hat-shape-forming experiment was conducted and breaking behavior was observed. Then, a prediction method using limited surface strain was investigated. In the case of high-bendability steel, after the occurrence of necking, breakage occurred. It was found that, in this type of breakage, the forming limit could be predicted using a conventional forming limit diagram (FLD), which means that there is limited strain at the middle of the thickness direction. On the other hand, in the case of low-bendability steel, cracks outside the bending surface occurred and grew, followed by breaking without necking. In this case, it was found that the forming limit could be predicted using limit surface strain, which could be obtained by finite element analysis (FEA) and an experiment using V-shape-bending test.
