CRACK INITIATION DURING HIGH CYCLE FATIGUE OF AN AUSTENITIC STEEL

We report about plastic strain controlled High Cycle Fatigue (HCF) experiments on an austenitic stainless steel (26% Ni, 15% Cr, 2.3% Ti, 1.3% Mn, 1.2% Mo, 0.3% Al) for both annealed and age hardened conditions. Since twin boundary cracking phenomena were dominant for both conditions, most of the research focused on annealed steel. The local orientation of more than 190 grains was measured by a modified electron channeling technique. In a simplifying model [P. Neumann and A. Tönnessen, Proc. Conf. Fatigue, Charlottsville, U.S.A., Vol. 1, pp. 3-22 (1987); P. Neumann and A. Tönnessen, Proc. Int. Conf. Strength of Metals and Alloys, Tampere, Finland, Vol. 1, p. 743-748 (1987)] these orientation data were used to calculate the local stress concentrations near the twin boundaries. By this method for 89% of the examined twin boundaries we could predict whether a crack would develop or not. A laser interferometric method was used to measure the local plastic strain across different selected twin boundaries. These experiments show that local plasticity is the most important parameter in HCF of f.c.c. polycrystals. © 1990.