Simulations of Surface Waves Generated Using Laser Ultrasonics

Abstract

Computer programs for solving the thermoelastic equations describing wave generation and propagation caused by the interaction of a laser pulse with a metal surface have been developed over the last several years [1–3]. One approach is to manipulate the thermoelastic equations using transform techniques and then use numerical methods to invert the equations and solve for wave displacements. Another approach is to spatially discretize the geometry of the model using finite elements and integrate the equations of motion through time. The finite element formulation may be fully coupled or as a further approximation the thermal problem can be solved separately from the mechanical problem. The work reported here sought to develop a technique to use a commercial finite element code (ABAQUS [4]) to simulate surface waves generated in laser ultrasonics. A general purpose finite element code provides the advantages of large element and material libraries and the ability to consider complex geometries and boundary conditions. Sanderson’s [3] computer code, which solves the coupled thermoelastic problem using numerical transform techniques, was used to validate the finite element model developed. Validation was erformed using simple models and boundary conditions. Subsequent finite element simulations were used to examine the effects of simulated stress gradients (in-plane and through-thickness) on waveforms. Temperature dependent properties and the effect of including an elastic-plastic constitutive material model in the mechanical analysis were also briefly examined.