Whole-Field Visualization and Evaluation of Fatigue Damage Using Laser Slit Beam

Abstract

In this study, we investigated a method to evaluate fatigue damage of steels in the whole view field without contact using laser. In high cycle fatigue of mild steels, slipbands are firstly produced on material surface and the slipband density increases with progress of fatigue damage. In our previous work, we used a laser spot beam illuminating the fatigue damaged area of a specimen surface and diffusion pattern of the reflected light from the specimen surface changes due to surface change. We are able to evaluate fatigue damage based on diffusion pattern change due to surface property change caused by slipbands at an observing point. But it is important to find first the position where fatigue damage starts. In this study, we tried three types of optical setups to detect fatigue damaged area in the whole view field of the observing area with a CCD camera and evaluate fatigue damage. The diffusion pattern change accompanied by the loading cycles was observed under constant stress amplitude with the three optical setups. The results showed that there is a possibility of detecting fatigue damaged area and also evaluating fatigue damage by the optical setup using slit beam. Observation in the whole view field is possible scanning the slit beam on the specimen surface.