Color-change Method to Detect and Characterize the Fatigue Damage Process of 304 Stainless Steel

Color-change method was used to detect and characterize the surface damage of 304 stainless steel in the process of fatigue. And combined with scanning electron microscopy (SEM) observation, the color-change characteristic during different fatigue damage stages, as well as the effect of surface roughness and stress amplitude on color-change test results was studied. The results show that with the increase of sample deformation, the color-change experienced three stages, i.e., the area of color-change was large and homogeneous, the area of color-change was partial, and the area of color-change was similar to the shape of surface cracks. These three stages were corresponding to the damage of the surface passivation film and initiation of micro cracks on the surface, the main crack initiation, and the long main crack propagation respectively. The higher sample surface roughness and the greater stress amplitude of the fatigue test were, the higher color-change values were.