Characterization of micro-crack evolution using Nonlinear Lamb waves

Abstract

Recent studies show that nonlinear ultrasonic methods are better than conventional linear ultrasonic methods that are sensitive only to severe defects. Micro-cracks grow at a low rate on the early stage. However, once the surface crack length reaches to a critical size, the cracks would propagate to final fracture quickly. For this reason, it is important to identify the fatigue crack initiation and growth mechanisms of the material. Nonlinear ultrasonic Lamb waves technique have been considered as a positive method for accurately evaluating the early stages of material degradation. So research on micro-cracks detection using nonlinear acoustic character, is both of theoretical significance and practical value. However, there was little research concerning micro-cracks whose lengths are limited to 0.5 mm. Nonlinear Lamb waves were used to detect the growth of micro-cracks in this research. The experimental results could be concluded that the nonlinear effects of ultrasonic Lamb waves might offer a potential for accurately evaluating the micro-cracks in solid plates.