The use of acoustic emission method to evaluate creep-fatigue interaction

Abstract

Acoustic emissions from creep-fatigue crack growth have been examined in 304 stainless steel. Under trapezoidal waveform, acoustic emission signal had different characteristics according to each loading mode. During the tensile creep loading, low counts rate and steady emissions were shown due to the continuous creeping at the crack tip. When the unloading and loading of fatigue cycle, emissions were burst and high counts rate was recoded. This high emission was supporting the fact that the redistribution of stress and strain after stress relaxation of previous creep loading. As the crack grew, total counts were increased due to expansion of plastic zone, however the contribution of each mode to the damage was different according to tensile hold time and maximum load. Experiments with different hold-time and maximum load were shown that the hold time and maximum load were important factors to control the contribution of each mode to the total damage in terms of acoustic emission counts. Overall experimental results indicated that acoustic emission monitoring during creep-fatigue crack growth test was useful to distinguish between the two damage modes and clarify the creep-fatigue interaction in elevated temperature application.