Effect mechanism and equivalent model of surface roughness on fatigue behavior of nickel-based single crystal superalloy

The global objective of this study was to systematically research the rule and mechanism how surface roughness affects the fatigue property of nickel-based single crystal superalloy. Fatigue tests of specimen with various levels of surface roughness were conducted at 980 degrees C and measured surface topography models were used to perform FE analysis based on crystal plasticity theory and fatigue damage model considering the resolved shear stress and slip rate of slip systems. Eventually, an geometrical equivalent simplification model with surface roughness parameters R-z, R-sm and R-a as modeling parameters for predicting fatigue life more convenient is proposed. Results indicate that micro-defects caused by surface roughness generate stress, plastic strain and damage concentration under fatigue load, which generate fatigue crack initiation, and greater surface roughness produces more severe concentration. The error between simulation prediction life and test result is within 3 times error band.