Influence of Multiaxiality of Thermal Field Induced Thermal Stress on Micro Crack Growth Around Cooling Holes

Abstract

A new test equipment was developed so that high cycle non-stationary thermal fatigue loading can be superimposed on stationary low cycle thermo-mechanical fatigue (TMF) loading. By means of the testing equipment, the early growth of small cracks around the cooling holes was investigated under the superimposed condition in a directionally solidified Ni-base superalloy where some cooling holes were artificially introduced for a simulation. The experimental works clearly demonstrated that the crack growth rate under the superimposed condition was significantly accelerated, compared with that under the stationary low cycle TMF loading. This behavior was discussed from the viewpoint multiaxiality of thermal stress induced by nonuniform temperature field around cooling holes.