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    摘要激光超声检测技术因为超强的穿透能力和对材料、人体的损害极小以及使用非常方便等特点成为重要的无损检测技术之一。本文讨论了激光激发超声在无损检测中的应用；然后简单阐述了声表面波的形成原理和基本性质，最后通过使用软件仿真获得的相关数据分析不同曲率的牙齿模型对激光超声时频域特性的影响。67449

    首先以脉冲激光激发超声的解析模型为基础，分析了热弹性条件下线光源的激发机理。然后，在仿真软件中建立不同曲率半径的牙齿模型，并使用有限元法数值模拟热弹性机制下激光点源热效应，进而仿真声表面波在牙齿结构表面的传播。

    最后，导出模型表面截点的位移数据，通过对多个截点位移函数的二维傅里叶变换得到表面波的色散曲线分析得出曲率半径较小的模型中声表面波的色散现象较为明显。

    毕业论文关键词  激光超声  声表面波  无损检测   有限元 色散

    毕业设计说明书（论文）外文摘要

    Title    The research of effect that the characteristic of  Teeth construction has to the characteristics of time and frequency domain of the laser-ultrasonic                                            

    Abstract

    Laser ultrasonic detection technology become one of the most important detection technology nowadays because of its characteristics of super ability to penetration, minimal damage to material and human bodies and easy to use. In this paper,the application that the laser ultrasound has in the area of nondestructive detection is discussed. And the principle and the properties of the formation of surface acoustic wave are briefly stated. Finally, the data that got through software simulation is analysed to figure out the effect the the characteristic of teethe construction has to the characteristics of time and frequency domain of the laser ultrasonic.

    Firstly, based on the analytic model of the laser ultrasound, the principle of the line light source arouse in the condition of thermoelasticity is analysed. Then the teeth models which have different radius of curvature

    are built. And using the method of finite element, the heat effect of the laser point source in the condition of thermoelasticity is simulated. Finally, the simulation of spread of the surface acoustic wave in the surface of teeth is given.

    The date of the displacement of the sections in the surface is exported. 

    Through the analysis of dispersion curve got from the 2D-FFT of the data, the trend is got that the teeth models which has the shorter radius have the more obvious dispersion phenomenon.

    Keywords  laser ultrasound;  surface acoustic wave;  nondestructive

              detection;   finite element;   dispersion

    目   次

    1    引言1

    1.1  研究背景及意义1

    1.2  国内外进展2

    1.3  本文的主要工作6

    2    激光激发声表面波的理论基础 7

    2.1  声表面波 7

    2.2  热弹性机制下激发超声的线源模型  10

    3    热性激发声表面波的有限元理论和超声型号的时频分析  13

    3.1  热传导理论13

    3.2  热弹性耦有限元方法14

    3.3  热弹性耦有限元方程15

    4    仿真与计算16

    4.1  牙齿模型有限元法应用背景16

    4.2  计算模型17

    4.3  超声信号时频分析理论21

    4.4  仿真计算数据结果分析22

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