Font Size: 

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.