Monitoring of local plasticity using lamb waves

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.