Modelling of Failure in High Strength Steel Sheets

In this theses the high strength steel Docol 600DP and the ultra high strength steel Docol 1200M are studied. Constitutive laws and failure models are calibrated and verified by the use of experiments and numerical simulations. For the constitutive equations, an eight parameter high exponent yield surface has been adopted, representing the anisotropic behaviour, and a mixed isotropic-kinematic hardening has been used to capture non-linear strain paths. For ductile sheet metals three different failure phenomena have been observed: (i) ductile fracture, (ii) shear fracture, and (iii) instability with localised necking. The models for describing the different failure types have been chosen with an attempt to use just a few tests in addition to these used for the constitutive model. In this work the ductile and shear fracture have been prescribed by models presented by Cockroft-Latham and Bressan-Williams, respectively. The instability phenomenon is described by the constitutive law and the finite element models. The results obtained are in general in good agreement with test results. The thesis is divided into two main parts. The background, theoretical framework, mechanical experiments and finite element models are presented in the first part. In the second part, two papers are appended.