Hold-Time Effects in Elevated Temperature Fatigue Crack Propagation

Abstract

An experimental investigation was conducted to evaluate the effects of hold times on the fatigue crack growth rate of Inconel 718 at 649°C using compact tension specimens. Tests were run under computer-controlled constant K conditions using compliance to determine crack length. Hold times ranging from 5 to 50 s were applied at maximum, minimum, and intermediate load levels. The data show that the hold times at maximum load were the most damaging in terms of crack growth rate. Hold times greater than 5 s led to purely time-dependent crack growth behavior which was predictable from sustained load data using K as a correlating parameter. Hold times at minimum or intermediate load levels had little or no effect on crack growth rate. A linear cumulative damage model based solely on fatigue and sustained load data was found to be adequate for spectrum loading so long as the hold times were at maximum load.