Theoretical and Experimental Investigation of a Laser-Induced Photoacoustic Effect near a Hole in Internally Stressed Metal Plates

摘要

This paper is an experimental and theoretical study of changes in a laser-induced photoacoustic signal near a hole in metal plates of D16 aluminum alloy. The process of photoacoustic signal generation from metals is analyzed within the classical thermoelasticity framework, with account for only the thermal effect of laser irradiation on metal lattice deformation. A comparison is made of photoacoustic experimental and theoretical results obtained for a mechanically stressed aluminum alloy plate with a hole. The effect of external mechanical stresses on the behavior of laser photoacoustic signals near the hole is studied experimentally and theoretically. It is found that the classical theory of thermoelasticity is not enough to correctly describe the stress dependence of the photoacoustic signal near a hole in aluminum alloy plates. In order for the obtained experimental and theoretical results to agree, along with the thermal effect of laser irradiation on the lattice, it is necessary to account for the additional effect of the electron gas. A calibration procedure of the laser photoacoustic signal with respect to stress is described. It is shown that internal stresses in metals can be estimated by the photoacoustic method in combination with the hole drilling method.