Laser ultrasound imaging of mechanical stresses near holes and indented areas: Experimental results and theoretical model

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Experimental results on the behavior of laser ultrasonic signals near holes in stressed ceramics and metals are presented. The data obtained are analyzed within the framework of the standard theory of thermoelasticity. It is shown that this approach is not able to explain the behavior of laser ultrasonic signals in stressed materials. A new model of thermoelasticity taking into account thermal perturbation of non-stationary defect states with relaxation is presented and analyzed. It is demonstrated that strong stress dependence of the laser ultrasonic signals provides an opportunity to estimate mechanical stresses in different materials. An example of mechanical stress effect on the laser ultrasonic image near Rockwell indentation zones in metals is presented.