Research On Damage Location Of Multilayer Composite Plate Based On Lamb Wave

Plate-shaped multilayer composite materials are widely used in industrial and civil fields.In order to avoid property losses caused by safety accidents,it is necessary to detect material damage at the early stage.Because the ultrasonic Lamb wave has the advantages of long propagation distance and low attenuation,it has been widely used in the health monitoring of plate structures.In recent years,it has become a research highlight to locate and image damages in multilayer composite plate by using Lamb waves.However,during the propagation process,the Lamb wave will produce a dispersion effect,and it has multi-modal characteristics,and the phenomenon of modal aliasing will appear.Meanwhile,due to the anisotropic structural characteristics of composite materials,the propagation of Lamb waves in composite materials becomes more complicated,and it is difficult to obtain an accurate location imaging of damage.This paper analyzes the dispersion characteristics of ultrasonic Lamb waves propagating in the carbon fiber multi-layer composite board,and conducts finite element simulation and damage location imaging research.This paper analyzes the basic theory of ultrasonic Lamb wave propagation in multi-layer composite board,and calculates the dispersion curve of Lamb wave in multi-layer carbon fiber composite board in the experiment.Based on the structural characteristics of the composite plate,the Lamb wave governing equation is analyzed and solved.Using the wave governing equation and boundary conditions in the plate,the Lamb wave dispersion governing equation is obtained..The transfer matrix method is used to obtain the relationship between stress and displacement between the upper and lower interfaces of the multilayer composite board,and the dispersion governing equation is solved.Using the solid period theory,the dispersion governing equation is transformed into the characteristic frequency equation,and the finite element calculation is performed to obtain the dispersion curve of the ultrasonic Lamb wave in the carbon fiber multilayer composite board.Based on the Delay-and-Sum(DAS)imaging algorithm,a damage location method by using the average velocity of mixed mode Lamb wave and time difference between sensing paths is proposed.The two-dimensional Fourier transform method is used to obtain the average phase velocity of the mixed mode,and the corresponding group velocity of the mixed mode is calculated.Due to the anisotropic nature of the composite plate,there is a time difference on different paths in the same direction.An improved DAS algorithm by using the time difference and group velocity is presented to estimate the location of the damage.The experimental results on the carbon fiber multilayer composite board show that the improved DAS algorithm can locate and image the damage in the composite board.In order to analyze the propagation characteristics of Lamb waves in the multi-layer carbon fiber composite plate more accurately,the relationship between the dispersion curve and the fiber arrangement direction is explored,and an anisotropic shape factor is introduced to improve the above proposed imaging algorithm.The dispersion curves of different fiber angles of the carbon fiber multilayer composite board are obtained by the finite element characteristic frequency method.A shape factor is calculated from the phase velocity diagrams of dispersion curves in the fiber directions from 0 to 360°,and the propagation time between different paths is further improved.On the basis of the aforementioned imaging algorithm,an anisotropic shape factor is introduced.The imaging experiment was carried out on the carbon fiber multilayer composite board..The experimental results show that this shape factor based method has more accuracy compared with the above-mentioned imaging algorithm.And by studying the relationship between the anisotropic shape factor and the propagation paths,some guidelines are proposed for the optimization of sensor layout for damage location imaging of multilayer composite plate.