Analysis of Ultrasonic Elastic Waves in Vibrothermography Using Fem

Vibrothermography is a promising technique that uses elastic ultrasonic wave excitation in solids for quality maintenance, e.g. in aerospace and automotive industry to monitor the integrity of surface or subsurface features. Vibrothermography allows for defect selective imaging using thermal waves that are generated by elastic sound or ultrasound waves. The mechanism involved is local friction or hysteresis that turns a dynamically loaded defect into a heat source, which is identified by a thermography system. Efficient numerical modeling allows a deeper understanding of the physical mechanisms of ultrasonic wave propagation in solids and this paper summarizes some of the recent results in modeling elastic waves to non-destructive evaluation (NDE) of isotropic materials. In this paper, a finite element modeling (FEM) of vibrothermography is presented to investigate the elastic wave propagation around cracks and to predict the time history of elastic waves scattering and diffraction. A fully coupled thermoelastic response is computed by combining stress-strain analysis with the heat equations in order to analyse the influence of the damage for the wave propagation. This work is divided into two parts, the first part describes the theoretical background of elastic waves propagation in isotropic materials. The second part introduces numerical simulations of elastic waves propagating in structures containing cracks.