| Research Abstract |
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.
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