Effective and internal stresses in cyclic straining of 316 stainless steel

The hysteresis loop of a 316 austenitic stainless steel was recorded and analysed in order to separate the contributions of the effective and internal stresses. The difficulties of application of the Kuhlmann-Wilsdorf-Laird method are discussed and a new method based on the statistical approach to analysis of the hysteresis loop (SAP method) is proposed. In contrast to the Kuhlmann-Wilsdorf-Laird method, this method allows evaluation of the effective elastic moduli and the effective stresses in tension and in compression without ambiguity. The SAP method was applied to cyclic loading of 316 austenitic stainless steel and the effective elastic moduli and effective and internal stress components of the cyclic stress in cyclic loading and their dependence on the number of cycles and on the applied strain amplitude was studied. The effective elastic moduli decrease appreciably with the strain amplitude. The effective stress represents an important fraction of the total stress (approximately 30%) and for most of the life it is constant. The hardening-softening curves and the cyclic stress-strain curve are determined mostly by the internal stress.