Evaluation of Crack Flaws in Ultrasonic Imaging

Cracks are hazardous flaws. They may be caused by material fatigue, mechanical stresses, or corrosion. Ultrasound can penetrate many materials, hence it is widely used for detection of flaws. However, the use of ultrasound is interfered by several phenomena, such as geometric interface, coarse grain, mode conversion, ringing and measuring techniques. It is practically difficult to perform evaluation directly using the originally received ultrasonic signal as false judgment may be obtained. To effectively analyze ultrasonic images, this work first uses the methods of wavelet transform to reject signal noise. The synthetic aperture focusing technique (SAFT) which is similar to sensor fusion, is then applied to reduce the interference and detect the existence of flaws. We emphasis on crack flaws that are located on the edge of materials. The flaws were manually created in our experiments. Extensive analysis are given with respect to various crack length and depth. The results provide special observation of crack flaws.