Fatigue crack detection on rough surfaces by optical Fourier analysis

Abstract

This paper deals with diffracted and scattered light spatial frequency signatures of surface piercing fatigue cracks. Emphasis is on determining the effects of roughness and lay pattern characteristics of machined surfaces on crack signatures. Fatigue crack features were observed in the combined crack-surface roughness signature with a He–Ne system over a 10–40-μin. roughness range depending on lay direction. Operation at even higher roughness levels should be achieved with longer wavelength laser sources. Crack model studies that include roughness show analytically the peak broadening effects on the crack signature.