Development of Fatigue Life Estimation Method of Metal Materials Using Laser Speckle Sensors

本文研究了一种利用光学方法检测金属材料在疲劳加载过程中表面性能变化和疲劳寿命估算的方法。这项研究得出的结果如下。(1)我们开发了一种光学装置，用于观察He-Ne激光照射物体时反射光形成的散斑图案，并开发了一种系统，用于输入散斑图案图像并分析图像。(2)在恒应力幅循环加载下，试件的散斑模式随着加载次数的增加而变化。我们推导了一个参数来评估散斑图案的宽度(3)。我们研究了表面粗糙度和表面轮廓的频率分布随加载周期的增加而变化。澄清了散斑图案宽度、表面粗糙度和表面轮廓频率分布宽度之间的对应关系。(4)推导了不同应力幅值下散斑图参数与加载次数关系的实验方程。(5)利用实验方程推导出了一种估算疲劳寿命的方法，并与实验数据进行了比较，结果表明，在疲劳早期（如疲劳寿命的1 / 4）就可以估算出疲劳寿命。(6)将该方法应用于低周疲劳试验。结果表明，随着疲劳损伤的进行，散斑图逐渐变宽，与高周疲劳相似，该方法可应用于低周疲劳。

In this study, a Method is investigated to detect change in surface properties of metal materials and to estimate fatigue life during fatigue loading using optical method. Results derived from this study are shown below.(1)We developed an optical setup to observe speckle pattern formed by the reflected light when a He-Ne laser illuminates the object and also a system to input an image of the speckle pattern and analyze the image.(2)When a steel specimen is loaded cyclically with a constant stress amplitude, it was clarified that speckle pattern changes with number of loading cycles. We derived a parameter to evaluate width of the speckle pattern(3)We investigated change of surface roughness and frequency distribution of surface profiles depending on increase of loading cycles. It was clarified that there is a correspondence between width of speckle pattern, surface roughness and width of frequency distribution of surface profiles.(4)We derived an experimental equation, which expresses the relation between a parameter of the speckle pattern and number of loading cycles for different stress amplitudes.(5)We derived a method to estimate fatigue life using the experimental equation and comparison with the experimental data showed that estimation of fatigue life is possible at the early stage of fatigue, such as a quarter of fatigue life.(6)We applied this method to low cycle fatigue. The result showed that speckle pattern broadens as fatigue damage proceeds similar to the case of high cycle fatigue and it was found that this method can be applied to low cycle fatigue.