The Effects of Loading History and Crack Geometry on Time-Dependent Fatigue Crack Growth at Elevated to High Temperatures

摘要

Time-dependent fatigue crack growth was investigated in detail for a high strength nickel alloy, and several significant results were found, which are not displayed in conventional fatigue crack growth tests. Under a variety of loading conditions including dwell and mission loadings at elevated to high temperatures, fatigue crack propagation and creep crack growth tests were conducted for different crack geometries. Test results show that the crack growth rate is geometry dependent, and R-Ratio dependency (a ratio of minimum loading over maximum loading) under dwell loading conditions is reverse to those observed in conventional fatigue crack growth tests. The test results demonstrate that commonly used stress intensity factor (SIF) based fracture mechanics methodologies do not fully characterize time-dependent fatigue crack growth at elevated to high temperatures. Constraint loss of fracture mechanics was tried to correlate to the effects of crack geometry and loading conditions on dwell crack growth rate. A phenomenological model was developed to include constraint effects and model predictions have demonstrated close agreement with test data.