Laser Ultrasonic Technology In The Honeycomb Sandwich Materials Testing Of The Numerical Simulation Research

Honeycomb sandwich board is widely used in aviation and industry for its unique advantages. However, in the process of producing or in use, it is usually found that poor bonding or even debonding is always exited which made safety exits hazard. Some convenient nondestructive methods should be selected for detecting the flaw. Laser-generated ultrasound detection is a new nondestructive method with a rapid development in recent years. In this paper, acoustic waves propagating in honeycomb sandwich which induced by laser has been studied theoretically. Furthermore, the influence of debonding to the acoustic wave propagation characteristics is also given.Taking into the characters of honeycomb sandwich board, the theoretical model of laser irradiating on the skin of the honeycomb sandwich board which induced the acoustic waves is constructed. Baized on the plane strain function and the theory of thermo-elastically generated ultrasound, the acoustic wave and its propagation which generated by laser irradiating on the honeycomb sandwich whose skin and core is all made up by aluminum is simulated by finite element method (FEM), and so does the debonding situation. When laser irradiated on the honeycomb sandwich board, the transient temperature distribution of the skin is presented according to thermal analysis, and then the time domain waveform is also obtained by thermal-structural coupling. The numerical calculation results indicate that debonding not only affects the acoustic wave in amplitude but also in the velocity of the low frequency component received in the near field. As the debonding affects the time domain of the waveform, the models of laser irradiated on the cell wall and the cell center are present to study the difference between the waveform received on the bottom surface. By the2D-FFT method to do time-frequency analysis, the phase velocity of each ultrasound mode generated in the honeycomb sandwich is presented, and then the impact of the ultrasound propagation velocity due to honeycomb sandwich structure is studied.As the carbon fiber skin is widely used, the model of laser irradiated on this kind of material generating ultrasound is also presented. The influence by the thickness of skin to the acoustic wave propagation characteristic is studied.The main work in this paper is to afford a theoretical basis on laser-generated ultrasound technology for detecting the deboning of the honeycomb sandwich structure.