Vibro-thermography of calibrated defects in hybrid plates focusing on viscoelastic heat generation

ABSTRACT Ultrasound excited vibro-thermography is based on the local heat generation due to the friction between the opposite surfaces of the defect, the plastic deformation around the defect, and/or the viscoelastic loss. This paper presents vibro-thermography applied to hybrid plates containing viscoelastic material when the viscoelastic heat generation mechanism alone is considered. The debonding-like calibrated defects without friction surfaces in the hybrid plate are detected. The dynamic temperature field is obtained by both experiment and numerical simulation. The influence of excitation frequency on the temperature increase over the defects is analysed by modelling the thermo-mechanical coupled field. The results show that the viscoelastic loss of the non-metal material is the leading factor of the local temperature increase over defects; an excitation frequency has its selective heating character to defects; a defect has a so-called defect characteristic frequency which can act as the optimal excitation frequency for this defect to be detected; the defect characteristic frequency is between the two local defect resonance frequencies corresponding to the simply supported boundary and the clamped boundary, respectively.