Detection of multiple thin surface cracks using vibrothermography with low-power piezoceramic-based ultrasonic actuator-a numerical study with experimental verification

Ultrasonic vibrations in cracked structures generate heat at the location of defects mainly due to frictional rubbing and viscoelastic losses at the defects. Vibrothermography is an effective nondestructive evaluation method which uses infrared imaging (IR) techniques to locate defects such as cracks and delaminations by detecting the heat generated at the defects. In this paper a coupled thermo-electro-mechanical analysis with the use of implicit finite element method was used to simulate a low power (10W) piezoceramic-based ultrasonic actuator and the corresponding heat generation in a metallic plate with multiple surface cracks. Numerical results show that the finite element software Abaqus can be used to simultaneously model the electrical properties of the actuator, the ultrasonic waves propagating within the plate, as well as the thermal properties of the plate. Obtained numerical results demonstrate the ability of these low power transducers in detecting multiple cracks in the simulated aluminum plate. The validity of the numerical simulations was verified through experimental studies on a physical aluminum plate with multiple surface cracks while the same low power piezoceramic stack actuator was used to excite the plate and generate heat at the cracks. An excellent qualitative agreement exists between the experimental results and the numerical simulation's results.