Angle beam shear wave nondestructive testing

Angle beam immersion and contact techniques are commonly used ultrasonic nondestructive testing (NDT) techniques. Since the incident angle of the longitudinal wave is not normal, the mode conversion of the waves will occur at the interface. Due to diffraction, wave interference and the complexity of mode conversions, the accuracy of transmitted shear wave NDT is not always better than transmitted longitudinal wave NDT. In this study, we try to determine the optimum wave type of the transmitted wave and optimum incident angle of the longitudinal wave, so that we can use appropriate transducers and wedges, whose characteristics can be obtained from the manufacturer to perform the angle beam ultrasonic NDT efficiently and effectively. The cumulative transmission energies of longitudinal and shear waves were calculated and some angle beam ultrasonic NDT experiments were performed. Our results indicate that the transmitted longitudinal wave is recommended for scanning cracks in a lightweight alloy of aluminum (over 90%), copper, magnesium and manganese, whose oblique angles are less than 34 degrees for the angle beam immersion test. The transmitted shear wave should be used to scan oblique cracks greater than 34 degrees. Moreover, for angle beam contact testing, the transmitted longitudinal wave can be used to scan the oblique cracks in the aluminum alloy whose oblique angles are less than 61 degrees and the transmitted shear wave can be used to scan the oblique cracks greater than 61 degrees. The wavelength of transmitted shear waves is shorter than that of longitudinal waves at the same frequency; hence the transmitted shear wave has better resolution than transmitted longitudinal waves. However, for the same frequency and propagation distance, the transmitted shear wave will be attenuated faster than transmitted longitudinal waves. Hence, it is not suitable to use transmitted shear waves to detect deep discontinuities and to test strongly attenuated material.