Identification of Strain Hardening Phenomena in Sheet Metal at Large Plastic Strains

A new experimental/numerical method to identify post-necking strain hardening phenomena in ductile sheet metal is presented. The identification of the post-necking strain hardening behaviour is based on the minimization of the external and the internal work in the necking zone during a tensile test. The proposed method takes the material state and the shape of the whole deforming tensile specimen into account. The post-necking hardening behaviour of a cold rolled interstitial-free steel sheet is identified. A hardening law which enables disentangling pre –and post-necking strain hardening behaviour is presented. The method is experimentally validated using an independent material test. For that purpose, the uniaxial tube expansion test is conducted to obtain uniaxial strain hardening behaviour beyond the point of maximum uniform strain in a tensile test. Finally, the presented method is compared with a hydraulic bulge test.