Laser Excitation In The Metal Wedge Ultrasonic Guided Wave Propagation

Dispersion Properties of guided-wave and waveforms of guided-wave excited by pulsed laser in metal wedge are studied theoretically in this paper.Established a theoretical model of guided wave propagation in metal wedge based on Elasticity. Using displacement potential function method for solving Navier-Stokes equations, derived dispersion equation of guided-wave in metal wedge combined with free stress boundary conditions. Using numerical method for solving the dispersion equation, and dispersion curves for different wedge angles are compared and analyzed. Small-angle wedge and wide-angle wedge dispersion properties of guided-wave are quite different. Guided-wave dispersion curves are similar to the case in flat in small-angle wedge with slowly linearly varying thickness. Dispersion characteristics of guided-waves in the wide-angle wedge have quite different than the flat, and waveform varies with the wedge angle. Finally, reasons for the changes of guided wave dispersion characteristics are given to explain.Based on the thermoelastic mechanism of laser ultrasound, and ignore the thermal diffusion and optical penetration effect, consider the pulsed laser as a point force source excitation guided waves in surface of metal wedge. Solving wave equation in elastic media under the point force source boundary conditions using double Fourier transform method. Determine four coefficients of integral transform solution with the boundary condition, and out-of-plane displacement(waveform)is calculated using double IFFT method. Programming to solve guided-wave waveform with several different angles metal wedge, and waveforms on different positions are compared and analyzed. Guided-wave shape varies with the thickness of wedge, the Lamb wave wavform characteristics significantly in the small thickness position, and show the Rayleigh wave characteristics in the location of large thickness. And with the wedge angle increases, this change more obvious trend. Finally, changes of the waveform in aluminium wedge are studied experimentally, and consistent the theoretical calculation result.This study result provide a theoretical basis for laser-ultrasonic nondestructive testing of metal wedge and wedge-shaped metal structure.