Crack growth characteristic and damage evaluation under creep-fatigue interactive condition for w-added high-cr steel

Crack growth characteristic under the conditions of high temperature creep and fatigue interaction is dominated by both of cyclic dependent mechanism due to fatigue and time dependent mechanism due to the time of load application (creep). For many cases with decrease in load frequency this characteristic changes from the cyclic dependent mechanism to the time dependent mechanism through an unstable transition region induced by creep and fatigue competitive mechanisms. To understand the physical mechanism of the interactive effects of creep and fatigue it is important to clarify the damage mechanisms around the crack. In the present study the experiments of creep-fatigue crack growth tests and the quantitative analysis of damage by measuring Vickers hardness were conducted to understand the interactive effects of creep and fatigue on the crack growth characteristic. Additionally by observing the material microstructure using EBSD damage mechanisms were clarified. As a result it was found that the creep effect contributes the expansion of damage region and the fatigue effect increases the density of damage within a given region. Interaction of these effects resulted in the occurrence of unstable transition region on the characteristic of creep-fatigue life.