Study on Improvement of Fatigue Strength Reliability in Machine and Structure by Laser Peening Treatment

赋予机械结构以高的功能特性，提高其疲劳强度的可靠性，有利于实现轻量化、节能化、节材化和高效化。本研究对机械和结构材料进行了激光喷丸处理，目的是提高材料的疲劳强度可靠性，并弄清其提高机理。本研究采用无保护层的低能量YAG激光器在水中进行激光处理，所用材料为核电站结构用奥氏体不锈钢，汽车零部件用铸造铝合金和高强度工具钢。在研究中使用的所有材料中，证实LP处理提高了疲劳强度。研究表明，LP处理的改善效果主要来自于材料表层的残余压应力和应变硬化. LP处理对预裂纹材料疲劳裂纹扩展过程的抑制作用是由LP处理产生的残余压应力和裂纹尖端塑性变形的裂纹闭合效应引起的。3.利用同步辐射装置的微CT成像技术，表面疲劳裂纹被成功地非破坏性地和三维地可视化。

It is useful for the reducing of weight, energy, materials and the high efficiency to improve the fatigue strength reliability of machines and structures by giving high functional property. In the present research, the laser peening (LP) treatment is performed on machines and structural materials, and it is the porpose of the research to improve the fatigue strength reliability in the materials and to make clear the mechanism of the improvement The laser treatment of low energy YAG laser without protective coating is wsasused in water The materials used in the research a were austenitic stainless steels for nuclear plant structures, cast aluminum alloy for automobile parts and high strength tool steels.The main conclusions obtained in the research are as followings1. In all of the materials used in the research, it is confirmed to improve the fatigue strength by the LP treatment. And it is clear that the improvement effects were induced from compressive residual stress and the strain hardening in the surface layer of materials by the LP treatment.2. The restrained effects for fatigue crack propagation process were confirmed for the pre-cracked materials by the LP treatment And, the effects were induced from the compressive residual stress and the crack closure effect by plastic deformation near crack tip by the LP treatment.3.By the micro computed tomographic (μ CT) imaging technology with syncroton radiation equipment, surface fatigue cracks were successfully visualized non-destructively and three-dimensionally.