Implications of the yield stress/tensile stress ratio to the SINTAP failure assessment diagrams for homogeneous materials

The treatment in structural integrity assessment procedures of materials operating in the plastic regime incorporates an inherent quantification of strain hardening behaviour through the knowledge of yield and ultimate tensile strength and, therefore, the ratio of yield stress to tensile stress, the so-called Y/ T ratio. In this paper, basic principles of the Y/ T ratio, and its treatment in codes, are first summarised. The development of the underlying equations for description of the failure assessment diagrams for the SINTAP homogeneous materials procedure is then described and the rationale behind the expressions used at the various levels of the procedure are explained. These cover estimation methods for determining Y/ T ratio, strain hardening exponent and the treatment of yield plateaus. The results of a test programme carried out to investigate the Y/ T issue on steels of varying grade, process route, thickness, and hence Y/ T ratio, are then presented with emphasis on the use of these data to validate the homogeneous materials’ procedure.