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Numerical Simulation of Thermoelastic Stress Field and Laser Ultrasound in Transversely Isotropic Plate

On the basis of an analysis of two important parameters, meshing size and time step, as well as the stability of solution, the generation of laser-generated ultrasound waves in a transversely isotropic plate is investigated using the finite element method (FEM). Taking into account the effects of thermal diffusion and optical penetration, as well as the finite width and duration of the laser source, the transient temperature distributions in a unidirectional fiber-reinforced composite plate are calculated, and the stress fields and the laser-generated acoustic field propagating in the principal planes are obtained. The generation of stress fields excited by the rapid thermal expansion of the laser-irradiated region is analyzed. The numerical results indicate that the unidirectional fiber-reinforced composite plate exhibits isotropic behavior when the wave vector is perpendicular to the fiber direction and that the laser ultrasonic waveforms are affected by the anisotropic nature of the plate when the wave vector is parallel to the principal plane including the fiber direction. The numerical results also indicate that, different from the case of isotropic materials, the features of the laser-generated ultrasound waveform, including velocities, amplitudes, and the propagation angle range of the head wave, have a close relationship with the propagation plane and propagating direction in anisotropic specimens.