由于表面粗糙引起的激光声表面波色散的实验和理论研究

摘要

表面粗糙是材料制造过程中必有的副产物,粗糙表面会引起其中传播的声表面波的速度发生变化.在利用激光声表面波对材料性质进行评估时,常用宽带的激光声表面波速度频散特性对材料性质进行反演.为了研究表面粗糙度是否能作为反演的特征参数之一,本文建立了激光在表面粗糙样品中激发声表面波、聚偏氟乙烯换能器宽带接收声表面波的实验装置来研究不同粗糙度表面对声表面波速度的影响;理论上建立了激光在粗糙表面中激发声表面波的计算模型,利用有限元法得到声表面波的时域特征,并进一步得到声表面波的速度色散曲线,理论结果和实验结果能很好地拟合.这为利用激光声表面波对表面粗糙的评估提供理论和实验依据.%In the process of producing materials,the surface roughness always exists.And it can change the velocity of surface acoustic wave（SAW） which propagates in the material.To assess the properties of materials by laser induced SAW,an inverse method based on the wide-band velocity dispersion characteristic of laser-induced SAW is most commonly used.To study whether the surface roughness can be one of the inversion characteristic parameters,an experimental apparatus is constructed in this article.In the apparatus,the SAW is induced in the surface roughness sample by laser,and it is received by a polyvinylidene fluoride transducer with wide frequency band.Using this apparatus,we study the influences of different surface roughnesses on SAW velocity.In the paper a physical model of laser-induced SAW propagating in roughness surface is established theoretically.The time domain characteristic of SAW is obtained by the finite element method,and then the velocity dispersion curve of SAW is achieved.It is concluded that the theoretical result and the experimental result are in good agreement with each other.The studies in this article form theoretical and experimental bases for assessing surface roughness by means of laser-induced SAW technique.