Predicting crack initiation site in polycrystalline nickel through surface topography changes

摘要

Fatigue loading generates plastic deformation and strain localization on the surface of polycrystalline metals, which are known to be the precursor for crack initiation. The plastic deformations manifest.themselves in.the form of surface roughening that can be characterized using surface profiling techniques. In this study, surface topology changes on the surface of a nickel specimen under cyclic loading are monitored and analyzed to investigate the correlation between surface topography changes and crack initiation. Defining the surface roughness parameters as the damage index, an algorithm was formulated to predict the crack initiation location well before the formation of a visible crack. In addition, the crack initiation time can also be determined based on the saturation of the surface roughness damage index as well as the rebound of the surface height near the crack initiation location.