Abstract
Image analysis with ultra-high-speed camera is applied to the unstable crack growth under quasi-static uniaxial compression. Stress field around the moving crack tip in the transparent specimen is visualized by means of photo-elastic technique and images of growing cracks and the stress field are captured with the frame rate of 250,000 fps. As a result, it is revealed that wing cracks start initiation at each end of the initial defect with time lag, and the time difference in their initiation corresponds to the travelling time of the stress wave, which is released due to the growth of the primary crack, from one end of the initial defect to the other end.
