激光冲击处理工艺过程数值建模与冲击效应分析-numerical modeling and impact effect analysis of laser shock treatment process.docx

真两种方法研究了冲击作用下材料内部应力波传播特征及其影响因素，提出高功率密度下“残余应力洞”现象的产生是由于冲击区域的边界效应产生稀疏波向冲击中 心传播，引起中心区域材料发生反向塑性变形，从而降低了此处残余压应力。提出了多点搭接冲击处理工艺过程数值仿真的简化方法。对于区域化多点搭接 冲击处理工艺过程的数值仿真，根据单次冲击时横向影响区域有限的特点，基于光 斑几何分布特征，提出了采用对称模块法进行简化计算的方法。通过对所选对称模 块中心点与外围点在同时或分别受到激光冲击时的相互影响的分析，确定对称模块 的尺度范围，最后用对称模块代替整个试件进行仿真计算。通过对搭接冲击残余应 力场的实验测量，验证了该方法的有效性。研究了小能量脉冲激光搭接冲击处理工艺特性。研究发现，搭接冲击可在工件 表面获得均匀的残余压应力场，并且随着搭接率的增加，压应力场增强。但是，小 能量搭接冲击处理不能显著增加最大压应力层深。金相实验分析发现试样表面受到 微弱热影响，产生了有利于提高表面性能的马氏体薄层，但是会降低材料表面残余 压应力。搭接冲击产生残余压应力的同时，不会影响工件表面质量；但是表层显微 硬度得到改善，并且随着搭接率的增加而增大。综上所述，本文以小能量脉冲激光冲击处理技术为研究对象，构建了实现连续 冲击处理功能的实验平台，围绕冲击载荷的作用机理以及材料动态响应过程建立了 激光冲击处理工艺过程数值仿真模型，通过冲击实验对单点和搭接冲击模型进行了 验证，揭示了小能量脉冲激光冲击工艺特性，阐明了不同冲击处理工艺条件下，材 料表层几何和物理性能的变化规律，为小能量脉冲激光冲击处理工艺的工程应用提 供了技术基础。关键词：脉冲激光、冲击处理、数值仿真、动态响应、应力应变Research on the Numerical Simulation and Impact Effects of Laser Shock ProcessingABSTRACTLaser shock processing (LSP) has been proposed as a competitive alternative technology to classical treatments for improving fatigue, corrosion and wearing resistance of metals. More recently, lower power lasers operated at higher frequencies, have been explored for laser shock processing. This thesis presented a systematic research on the numerical simulation and impact effects of laser shock processing with a small energy Nd:YAG laser. Main research and originality innovations are as follows:An experimental technique for successive small energy impacts was developed. Great efforts have been devoted to attain the process of small energy impacts based on the mechanism of laser shock processing. A beam path facility and a sample holder were developed to work with a small energy Nd:YAG laser head. Selections of the transparent overlay and absorbent coating were intensively investigated by experiments. The results showed that flowing water used as transparent overlay, and a black tape used as absorbent coating could ensure an effective shock wave induced by laser shock. The developed experimental setup offered a reliable equipment to perform the investigation on th