Case-hardening inspection of steel using photothermal phase maxima

Starting from the exact solution for the photothermal signal in semi-infinite materials with an exponential and with a piecewise linear thermal conductivity profile, a set of equations valid for a broad class of profiles is derived for the direct computation of the conductivity profile depth and surface conductivity from the properties of the photothermal phase maximum alone. By virtue of the usual anticorrelation between conductivity gradient and hardening gradient, this can be used for the assessment of case depth and surface hardening of case-hardened steels. The results compare very well with the results of Vickers hardness tests. The methodology only applies to concave conductivity profiles, excluding e.g., sigmoidal shapes.status: publishe