Use of abrupt strain path change for determining subsequent yield surface: experimental study with metal sheets

A basic idea for a method for determining the subsequent yield surface in the vicinity of a current loading point by using an abrupt strain path change has been proposed recently by Kuroda and Tvergaard (Acta mater., 1999, 47, 3879). The proposed method is applied to real experimental studies. In a biaxial tensile testing apparatus, a cruciform specimen is used, with the strains measured by a biaxial-strain gauge. Then, with the hydraulic pressure of two sets of opposing hydraulic cylinders servo-controlled independently, the testing apparatus can be used to prescribe an abrupt change of the strain path. Both a cold-rolled steel sheet and an aluminum alloy sheet are investigated. The differences between the yield surface shapes found by the strain path change procedure and the shapes found by probing the yield points from the elastic region are shown and discussed for different cases.