APPLICATION OF THE FINITE-ELEMENT METHOD AND THE FINITE-DIFFERENCE METHOD TO PHOTOTHERMAL INSPECTIONS

Theoretical description of photothermal processes require analytical s olution to the thermal diffusion equation. This solution takes great e fforts, and in many cases an analytical expression is not accessible. In this article, additional solution methods for the thermal diffusion equation, especially for photothermal problems, are presented. These methods are the finite-element method and the finite-difference method ; the latter is described in detail. They enable a closed theory for a ll photothermal processes using a modulated light source and measureme nts in the equilibrium state. The numerics are verified by comparison with some analytically solved problems. The main discussion topic is s urface hardened steel samples. Here, some well-known models for hardne ss profiles and a new approach, calculated by the finite-difference me thod, are discussed. (C) 1996 American Institute of Physics.