摘要疲劳裂纹通常是由工件几何不规则或材料非均匀性引起的局部应力突变产生的。利用传统的超声检测技术（如脉冲回波法）对早期疲劳裂纹进行检测时，由于此类裂纹尺寸很小以及工件表面其它的散射物（如表面凹槽、腐蚀坑、粗晶粒等）对声波的影响，从而难以有效分辨疲劳裂纹。而裂纹的闭合会对超声波产生强烈的调制作用，表现出明显的参数变化，董利明，李加等提出并搭建了激光辅助加热的微裂纹声表面波检测的实验系统和方法，结果表明，用此实验方法可以有效的检测出样品裂纹。本论文利用该实验方法，对黑玻璃样品进行检测，加热激光照射样品裂纹处时，在相同加热时间不同加热功率及相同加热功率不同加热时间情况下，对裂纹闭合程度对透射声表面波的影响作出比较和分析。9768
关键词 超声检测 激光加热 声表面波 微裂纹
毕业设计说明书（论文）外文摘要
Title Applications of Laser Heating of Ultrasonic Surface Waves for the Detection of Micro-cracks
Abstract
Fatigue crack is usually generated by abrupt change of local stress due to the geometry irregularity of specimen and the inhomogeneous of material. Traditional detecting techniques using ultrasound, such as pulse-echo method, are difficult to distinguish the fatigue crack effectively, because the size of the cracks are so small that they are often hidden from ultrasonic detection by a stronger scattering from the very same structural imperfection, such as surface grooves, corrosion pits, coarse grains, etc. It is well-known that the ultrasonic surface waves are susceptible to crack closure and therefore exhibit strong parametric modulation, a method based on laser heating of ultrasonic surface waves generated by laser for detecting micro-crack of sample is presented by Dong Li-ming and Li Jia. It is found that the micro-cracks can be detected successfully.Thus the method is used for the test of the black glass in this paper.The influence on the acoustic pulses transmission caused by the closure degreen of the micro-crack is analyzed when the laser irradiated on the micro-crack in the condition of different heating power in the same time as well as in the condition of the same heating power in different time.
Keywords ultrasonic detection laser heating ultrasonic surface waves micro-crack
目 次
1 绪论 1
1．1 研究背景 1
1．2 研究意义 2
1．3 国内外研究概况及发展趋势 3
1．4 本文的主要研究内容 4
2 激光超声的激发与检测 6
2．1 激光超声产生机理 6
2．2 热弹机制下激发超声的点线光源模型 6
2.2.1 热弹机制下激发超声的点光源模型 6
2.2.2 热弹机制下激发超声的线光源模型 7
2．3 激光超声表面波的特性 9
2.3.1 激光超声表面波的波形 9
2.3.2 激光超声表面波的方向性 10
2．4 激光超声的检测 11
3 基于激光辅助加热的声表面波微裂纹检测的实验研究 13
3．1 加热激光对裂纹的影响 13
3．2 基于激光辅助加热的声表面波微裂纹检测的实验研究 14 基于激光辅助加热的声表面波微裂纹检测的实验研究:http://www.751com.cn/wuli/lunwen_8585.html