Negative Load Ratio Fatigue Crack Growth Rate Testing on Austenitic Stainless Steel in a Simulated Primary Water Environment

Light water reactor coolant environments are known to significantly enhance the fatigue crack growth rate of austenitic stainless steels. However, most available data in these high temperature pressurized water environments have been derived using specimens tested at positive load ratios, whilst many plant transients involve significant compressive as well as tensile stresses. The extent to which the compressive loading impacts on the environmental enhancement of fatigue crack growth and more importantly on the processes leading to retardation of those enhanced rates is therefore unclear, potentially leading to excessive conservatism in current assessment methodologies. A test methodology using corner cracked tensile specimens has been developed which provides significant advantages over more conventional specimen geometries in terms of autoclave testing at negative load ratios. Finite element analysis of the specimen geometry has been performed to generate effective stress intensity factors, Keff, for specimens loaded in fully reverse loading. Test data generated in both air and water are compared to conventional compact tension specimen data to validate the test methodology.