正弦脉冲激光热弹激发超声应力脉冲仿真研究

Imitation study of sinusoid pulse laser thermoelastically generated ultrasound stress pulse

应用一维热传导方程和Navier-Stokes方程,采用简化的正弦脉冲波形模型对激光激发产生的超声应力脉冲进行了理论研究,分别得出弱吸收试样表面是钳紧或自由情况下应力脉冲的表达式。仿真结果表明表面钳紧时应力脉冲是单极性的,自由时是双极性的,应力脉冲宽度远大于激光脉冲宽度;试样厚度增加,应力脉冲的极值减小;激光脉冲宽度增大,应力脉冲的极值大大提高,宽度也随之增大;试样的声速和光吸收系数增大,应力脉冲的宽度减小,极值变化不大。

Applying one - dimension heat exchange equation and Navier - Stokes equation, ultrasound stress pulse that is generated by laser is studied by using simplification sinuseid pulse model. Expressions of stress pulse are attained, which sample is feebleness absorbability and its surface is freedom or tightening. Imi- tation results show that stress pulse of tightening surface is monopolar and freedom surface is ambipular, the breadth of stress pulse is much bigger than laser pulse＇. Increasing thickness of sample, extremum of stress pulse decreases. Increasing the breadth of laser pulse, extremum and breadth of stress pulse increase greatly. The breadth of stress pulse decrease with increasing sample＇s sound velocity and optics absorption coefficient, but its extremum changes little.