Numerical Modeling Of Laser Ultrasound In Unidirectional Fiber-Reinforced Composite Material Using Finite Element Method

In this paper,the theoretical models of transient temperature field generation by the scanning laser source and thermo-elastic generation of laser-ultrasonic in unidirectional fiber-reinforced composite plate have been studied and established by using finite element method.The generation of laser ultrasonic wave,its propagation and waveform characteristics in fiber-reinforced composite material are also studied by theoretical analysis and numerical simulation,the main details are as follows:In accordance with the classic thermal conduction equation,this paper analyzed the changing of material's optical and thermal physical properties under scanning laser irradiation.The transient temperature fields are obtained using finite element method.The numerical results denoted:Temperature profiles in the plate indicate quasi-steady state condition is always been reach,with constant surface temperatures in the proximity of the maximum value.The thermal physical parameters and the moving speed of laser beam strongly affected the temperature distributions in the considered solids.Based on the plane strain and elastodynamics balance equation,the physical process of thermo-elastic coupling of nanosecond laser exciting the ultrasonic in the fiber-reinforced composite material was analyzed by using finite element method;the relationship between the size of grid and time step and the stability of finite element solution was studied;and then the optimized finite element model was established. The numerical results denoted:A fiber-reinforced composite material exhibits isotropic or homogenous behavior for ultrasonic wave propagation perpendicular to the fiber direction,for ultrasonic propagation along the fiber direction,the waveforms show the effects of frequency-dependent dispersion,which results from the heterogeneous character of the material.The finite size of the laser thermo-elastic source which has an optical absorption depth produces strong bipolar longitudinal waves and improves the amplitude and directivity of the longitudinal waves.The magnitude and width of the laser-generated waveform are affected by the width of the line-source and the duration of the pulse,as the dimensions of the pulse are increased in space and time,the displacement waveform becomes broader and its magnitude decreases.Clearly models for ultrasonic generation and propagation in anisotropic materials must include the effect of anisotropy and temperature on the dispersive wave propagation.The results in this paper can provide theoretical support for the research and numerical simulation of moving laser exciting transient temperature field and ultrasonic in unidirectional fiber-reinforced composite plate,as well as for the lossless inspection and evaluation.