5E-6 Extremum Imitation Study of Thermoelastic Ultrasound Stress Pulse Generation by Laser Pulse

Laser ultrasound has many advantages such as being noncontact, nondestructive, fast, accurate and low cost. Therefore it is usually used detecting and characterizing defects in aerospace materials or aerocraft. For the present, ultrasound generation at the thermoelastic is studied by scholars from home and abroad, the wave form of laser pulse has been simplified to shape wave, triangular wave and quadrilateral wave etc. Although these calculations can be simplified and the results are get easily, it differs greatly from real Gauss laser pulse. In this paper, the sinusoid pulse model which is approximate to real skew-Gaussian pulse laser is adopted. Applying one-dimension heat exchange equation and Navier-Stokes equation, theory model of thermoelastic ultrasound generated by laser pulse is established, and ultrasound stress pulse is studied. Expressions of stress pulse are attained, which sample is feebleness absorbability and its surface is freedom or tightening. Imitation results show that ultrasound stress pulse extremum decreases rapidly along with increasing thickness of sample, and it levels off gradually. Increasing the optical-absorption coefficient, ultrasound stress pulse extremum decreases, but its decreasing amplitude is small. Increasing the sound velocity, ultrasound stress pulse extremum doesn´t change. Increasing the breadth of laser pulse, ultrasound stress pulse extremum increasing rapidly.