Measurement of Ultrasonic Nonlinear Parameter by Using Electromagnetic Acoustic Transducer

摘要

The nonlinear ultrasonic technology is generally known as an effective method for the microcrack detection. However, most of the previous experimental studies were limited by a contact nonlinearity method. since measurement by the contact method is affected by the coupling conditions, additional nonlinear coefficient are lead into the measurement. This research presents a novel technique for nonlinear ultrasonic wave measurements that uses a non-contact, electromagnetic ultrasonic transducer (EMAT); and is much more efficient than piezoelectric-based detection. And for a better understanding and a more in-depth analysis of the macroscopic nonlinear behavior of microcrack, the developed FEM modeling approach is built to simulate microcrack induced nonlinearities manifested in ultrasonic waves and analyzed experimentally. The 2D finite element simulation is implemented in the multi-physics module of COMSOL, and the performance between Rayleigh wave EMAT and microcrack includes transduction process that the electromagnetic field and mechanical field are coupled together by electromagnetic force, wave propagation process, nonlinear acoustic response process as shown in Figure.1.This study has yielded a quantitative characterization strategy for microcrack using EMAT, facilitating deployment of structural health monitoring by noncontact electromagnetic nondestructive testing.