On the Use of Concave-Side Rule and Critical-Distance Methods to Predict the Influence of Bending on Sheet-Metal Formability

The stress/strain gradient has a clear stabilizing effect in the initiation of necking and subsequent failure of metal sheets. In situations where bending due to mild or small forming radius are present, the influence of these gradients cannot be neglected by using the mean strain through the specimen thickness as a representative strain. Therefore, classical failure criteria, assuming uniform stress/strain in thickness, should be carefully applied. The present work analyses the capability of the Concave or Convex-Side Rules along with the concept of Critical-Distance to describe the evolution of failure by necking or by fracture in stretch-bending conditions.