Methods for surface roughness elimination from thermal-wave frequency scans in thermally inhomogeneous solids

Abstract

Two approaches for eliminating surface roughness in the thermal-wave frequency response of inhomogeneous solids are developed. The first approach is based on the theoretical formulation of roughness as an effective homogeneous overlayer and is adequate for eliminating low roughness levels from experimental data. The second approach models roughness as random spatial white noise resulting in a linear superposition of logarithmic-Gaussian distributions representing roughness scales in the spatial frequency spectrum and in the modulation frequency domain. Two scales of roughness on the surface of hardened AISI 8620 steel with the same hardness depth profiles are found and the experimental data are reconstructed to retrieve similar inhomogeneous thermal diffusivity depth profiles.