The ultrasonic NDT technique utilizing the longitudinal or transverse waves induced by Lamb wave in thin plates

This paper presents a new ultrasonic NDT technique for measuring the thickness of a nonmetal material (called the cladding material) with low sound velocity which is cladded on the one side of a thin metal plate (called the base) with high sound velocity such as tubes, thins and other closed containers, testing and inspecting the unglued area between them, detecting the inner defect of the composite from the side of the base in case that the measurement and inspection has to be carried out on the side of the base. The principle of the technique is that a longitudinal or transverse wave induced by the pulse Lamb wave in the base is transmitted in certain direction into the compounded material, then reflected by the upper and lower boundary of the compounded material. The same mode pulse Lamb wave is formed while the longitudinal or transverse wave in the compounded material return the base