Development for Evaluation of Long-Term Corrosion Fatigue Damage by Hybrid Method of Scanning Atomic Force Microscopy and Laser Speckle Pattern Analysis

利用激光散斑和原子力显微镜对拉伸试验和疲劳试验中产生的表面形貌进行了监测。在拉伸实验中，斑纹的峰值强度随塑性应变的增大而减小，峰值强度半值处的斑纹宽度随塑性应变的增大而增大。这种关系不是塑性应变的唯一函数，即加载方向的宽度小于垂直加载方向的宽度。然而，半值宽度被表示为原子力显微镜测量的表面粗糙度的唯一函数。疲劳试验中，斑纹峰值强度随加载循环次数变化不大。半值宽度随着加载循环次数的增加而增大，直至疲劳寿命的一半。在疲劳寿命的后半期，宽度几乎是恒定的。在疲劳试验中，加载方向的宽度小于垂直加载方向的宽度。宽度由原子力显微镜测量的表面粗糙度控制。这种关系与应力幅值无关，但与拉伸试验得到的结果不同。本研究用原子力显微镜阐明了金属材料损伤过程中激光散斑变化的物理基础。通过将该方法应用于在役机器和结构部件，可以估算其剩余寿命。

Surface morphology developed in tension test and fatigue test were monitored by laser speckle pattern and atomic force microscopy. In tension test, the peak intensity of the speckle pattern decreased with plastic strain, and the breadth of the pattern at the half-value of the peak intensity increased with plastic strain. The relations were not unique functions of the plastic strain, i.e., the breadth in the loading direction was smaller than that in the direction perpendicular to the loding. The half-value breadth, however was expressed as a unique function of the surface roughness measured by the atomic force microscopy. In fatigue test, the change of peak intensity of the speckle pattern with number of loading cycles was small. The half-value breadth was increased with number of loading cycles up to the half of the fatigue life. In the last half period of fatigue life, the breadth was almost constant. Also in fatigue test, the breadth in the loading direction was smaller than the direction perpendicular to the loading. The breadth was controlled by the surface roughness measured by the atomic force microscopy. The relation was independent of stress amplitude, but it was not the same as that obtained in tension test.In the present study, the physical basis of the change in laser speckle pattern during the damaging process in metallic materials was clarified by the atomic-force microscopy. By applying this method to the machine and structural components in service, their remaining life can be estimated.