摘要：本文将利用Comsol软件进行有限元数值模拟，用以研究激光作用于金属铝表面时激发声表面波的过程，同时建立用脉冲激光激发声表面波的理论模型。本文所建立的有限元模型，将对金属铝表面的激光超声源的时间-空间特征，以及超声波的产生机理与传播特征之间的定量关系进行研究；并将脉冲激光激发超声的物理过程，在两维平面内基于平面应变理论进行研究分析。为了方便建模，本文引入了等腰三角形形状的表面凹口来表示疲劳裂纹。模拟结果显示在接收点接收的波形成分存在三个不同成分,分别为脉冲激光激发的直达掠面纵波和直达表面波，以及由缺陷反射到达接收点的反射表面波。

本文的研究结果既可以用于激光超声探测原理的数值模拟研究，也可用于激光超声检测技术。

关键词  Comsol软件  有限元  数值模拟  金属铝  表面缺陷  表面波

毕业设计说明书外文摘要

Title   Numerical simulation of surface defect for metal  Materials based on the laser ultrasonic waves     

Abstract：In this paper, the finite element numerical simulation is carried out by using Comsol software to study the process of exciting surface acoustic wave when pulsed laser irradiated on the surface of Aluminum material. At the same time, the theoretical model of excited surface acoustic wave is established. The finite element model established in this paper will study the time-space characteristics of the laser ultrasonic source on the surface of the Aluminum material and the quantitative relationship between the mechanism of the ultrasonic wave and the propagation characteristics. The pulsed laser excitation of the physical process of ultrasonic Two - dimensional plane based on the plane strain theory research and analysis. In order to facilitate modeling, this paper introduces the isosceles triangle shape of the surface of the concave to express fatigue cracks. The result of the operation shows that there are three different main components in the waveform captured at the receiving point; The simulation results show the presence of three different components receiving point waveform components, namely: Direct laser excitation of the surface skimming longitudinal wave pulse and direct surface acoustic wave,And a reflective surface acoustic wave that is reflected by the defect to the receiving point.

The results of this study can be used as a numerical simulation of laser ultrasonic detection principle, but also can be used for laser ultrasonic defect detection technology.

Keywords  Comsol  FEM  Numerical Simulation  Aluminum  Surface defects  Surface acoustic wave

目   次

1  引言 1

1.1  研究背景和研究意义1

1.2  发展过程及研究现状 3

1.3  本文的主要研究工作  4

2  基本理论和数值模型 5

2.1  热弹理论模 5

2.2  数值模型的建立 6

2.3  网格划分方法 7

3  激光超声探测金属铝表面缺陷的有限元模拟 9

3.1  无缺陷金属铝模型 9

3.2  带缺陷的金属铝模型 11

3.3  本章小结 16

结论  17

致谢  18

参考文献19

1  引言

1.1  研究背景和研究意义

现如今科技飞速发展，各行业所使用的材料要求也越来越高，尤其是仪器、车船和航天航空领域。众所周知，金属材料表面若存在表面裂纹等缺陷，会因为应力集中效应，在使用过程中产生金属疲劳，大大地缩短材料的使用寿命，甚至出现安全隐患，因此人们迫切地需要一系列的探测技术来完成对金属材料的缺陷探测。而激光超声无损探测（Nondestructive testing）技术的出现，使得对已成型的金属材料进行无损探测成为现实。