Numerical Simulation Of Surface Acoustic Wave Generated By Pulsed Laser In Aluminum Pipe

A method based on thermo-optical modulation of ultrasonic waves generated by laser at thesurface of a aluminum cylinder is presented. The propagation rules and the generation of HeadWaves at the cylinder, the choice of the wall thickness for the components in uniform pipes, and theinfluence of the wall thickness on the ultrasound signal at different locations in the non-uniformpipe, are researched.In the process of the analysis of the generation mechanism and the propagation path of the headwave, using the finite element method, a gradually hollowing model is posed, and then, a series offinite element simulation of ultrasonic waves generated by pulsed laser at the surface of a cylinderhave been developed. The numerical results show that: Head Waves generated at the certain range(critical angle) in the body, and then spread along the straight line at a speed slightly larger than theRayleigh waves. In the propagation process, the Head waves move away from the Rayleigh wavesand approximate longitudinal wave. At the interface, the part of the head wave escapes from thebody and spreads along the circumference with a rapid attenuation. The other part of the head wavehas a reflection at the interface with a small attenuation.In order to explore the impact of changes in the wall thickness for the generation and detectionof ultrasound signal, a uniform pipe model and three idealized eccentric pipe models are established.This section analyzes the influence of the propagation of ultrasonic signals at different uniformwall-thickness, emphasizing on the influence of the generation、propagation and receiver ofultrasonic waves at the excitation source, the detection point and the propagation path. Thesimulation results show that: the composition of ultrasonic waves is partly determined by thethickness of the hollow cylinder, and in a certain range, the ultrasonic waves are changing when thethickness of the hollow cylinder is changing; the wall-thickness of the excitation source and itsvicinity within a certain range have a great impact on the components of the ultrasonic signal, tosome extent, and may determine the ultrasound frequency, amplitude and other characteristics;when the wall is thinner, the Rayleigh waves cannot be distinguished; the wall thickness on thepropagation path becomes so small, and the filtering effect will be so obvious that thehigh-frequency component is filtered out, but will resume within a certain extent in other thickness.This work will provide a useful guidance for the use of head waves on the related fields, and thefurther application of laser ultrasonic in cylinder nondestructive testing field.