Monitoring of Local Plasticity Using Lamb Waves

Abstract

An experimental method was developed to monitor local plasticity in metallic materials using Lamb waves. A double-edge-notched beam specimen under tensile loading was employed to induce the local plasticity in notch area. By exciting Lamb waves using actuators in two different ways, the obtained wave signals at different stress levels of the specimen were analyzed through wavelet analysis by proposing a signal index I. By virtue of the finite element analysis on the tensile behavior of the specimen, it was found that I almost kept constant under elastic deformation and rapidly increased when the local plastic deformation occurred and extended, and then stopped growing when the plastic zone was up to a certain size. Therefore, the change of I, which is attributed to the occurrence and evolution of small and local plastic zone in the notch area, can be used to effectively monitor local plasticity.

An EMAT for improving the purity and amplitude of S0 Lamb waves

“…At the low frequency-thickness product ( f • d), the S 0 wave propagates with less dispersion and is therefore more suitable for measuring the elastic characteristics of thin plates or detecting their possible defects [22,23]. For example, studies have shown that low-frequency S 0 waves can be used to assess the damage of plasticity [24] and cracks [25][26][27]. When detecting defects with S 0 waves, the reflected waves of A 0 waves at the edges of thin plates or at the edges of defects can cause superposition, which will cause great difficulties in data analysis [28][29][30].…”

Simulations on Monitoring and Evaluation of Plasticity-Driven Material Damage Based on Second Harmonic of S0 Mode Lamb Waves in Metallic Plates

“…An effective and reliable inspection technique for continuous monitoring and evaluation of early-stage nonlinearities in materials is necessary for engineering parts. Among all kinds of nondestructive methods studied for efficient damage detection and evaluation, the ultrasonic method is most useful and has been widely exploited for many decades [ 1 , 2 , 3 , 4 ]. Traditional ultrasonic inspection and monitoring methods are usually anchored on linear theory, and the characterization parameters are velocity attenuation, transmission, and reflection coefficients of the ultrasonic wave.…”

“…Traditional ultrasonic inspection and monitoring methods are usually anchored on linear theory, and the characterization parameters are velocity attenuation, transmission, and reflection coefficients of the ultrasonic wave. However, conventional linear ultrasonic evaluation and monitoring methods are not sensitive to early stage micro-damage or micro-plastic deformation [ 4 ], and the smallest crack that current linear ultrasonic based approaches can monitor or evaluate is only approximately 1 mm [ 5 ]. This drawback limits their applications and does not allow early preventive actions [ 5 , 6 , 7 ].…”