Analysis of Non-linearity of The Weld Region in Carbon Steel Using a High Power Ultrasonic Transducer

Quantified parameter of ultrasonic non-linearity or non-linearity parameter, β is defined as the ratio of the second harmonic components to the square of the fundamental frequency components of received signals. The β can be used to evaluate the microscopic degradations, damages and cracking of materials. Because the amplitude of second harmonic signal is relatively small, it requires a method to get a meaningful and reliable signal quality of second harmonics. A high power ultrasonic transducer with a single crystal LiNbO₃ and a high power ultrasonic generator are used to get higher amplitude of second harmonic signals. The technique can be a potential tool to diagnose the early stage of cracking or micro-cracking in the welds. We have made a high power ultrasonic transducer using LiNbO₃ single crystal and compared ultrasonic nonlinear response with conventional PZT transducer. The second harmonic components in the frequency domain were clearly detected with the single crystal LiNbO3 transducers, but not with the conventional PZT transducers. The frequency analysis method using the high power LiNbO3 transducers could be a promising technique to distinguish the weld region from the base materials. The technique can be useful to diagnose the early stage of materials degradation and detection of the micro-crack or the closed cracks in the welds.