Influences of ellipse cooling holes on creep crack initiation and surface morphology of nickel based superalloys

A creep damage model is developed with the consideration of cavitation and material microstructure degradation as damage factors. Five models are studied with different ratios between the length of ellipse hole axis parallel (denoted by y) and perpendicular to the loading direction (denoted by x), where y maintains constant. Two loading conditions are taken into account: constant external load and constant net section stress. The creep crack initiation time increases with increasing y/x ratio at both loading conditions. The stress distribution morphologies are quite similar for all the models at the start of creep where there are high stress strips between holes in the adjacent rows and low stress strips between holes in the same rows. During the creep, stress relaxation and redistribution induce some differences in the morphologies for different models at the crack initiation time. The damage distributions provide important information on crack initiation and propagation path.