Identification of voids and cracks by ultrasonic technique

Ultrasonic is one of the most wide use of nondestructive evaluation technique. Voids and cracks are the most common defects in a solid. In this investigation, the ultrasonic technique is used to distinguish the defects between the void and crack. As an incident wave impinges on the crack tip, the diffractive wave can be detected from various angles. The amplitude of the diffraction is dependent on the receiving angle. For a void, the incident wave is scattered, the amplitude of the scattering wave is also dependent on the receiving angle. By comparing the amplitudes between the diffractive wave and the scattering wave, one is able to identify the defect of a void or a crack from the other. In this work, 5MHz of longitudinal and shear transducers are used and placed in a variety of incident and receiving angles to examine the difference between the void and crack. The experimental results are validated by the theoretical calculation. In order to identify the void and crack, it is required to have significant difference between the diffractive and scattering waves. The range of the detecting angle, which possesses a meaningful difference between the diffractive and scattering waves, is proposed through the numerical and experimental study to help the identification of the void and crack.