Research On Damage Detection Of CFRP Composite Plate Based On Nonlinear Ultrasound

Compared with metallic material,composite material has more complex properties.The coupling and development process of material defects are various.Early microcracks are the main damage,and it’s detection is more difficult.Compared with traditional ultrasound,nonlinear ultrasound is more sensitive to early damage.Among them,Lamb wave is more suitable for thin plate component detection.Therefore,high frequency nonlinear Lamb ultrasound to study the early damage detection of composite materials is used in this paper.Firstly,based on the traditional 3D elastic model and the global matrix method,the governing equations of the dispersion curves of Lamb waves in transversely isotropic materials are obtained.The phase velocity and group velocity dispersion curves of Lamb waves are obtained.Based on the above research,the appropriate excitation frequency and cut-off frequency are selected to establish the foundation for the subsequent simulation.Secondly,the relationship between crack parameters and nonlinear coefficients is studied by ABAQUS simulation.In order to avoid the influence of reflection echo,a damping absorber layer was added to the boundary to find optimal parameters so as to effectively absorb the reflection echoes.The relationship between three crack parameters,which are the crack length,width and angle respectively and the nonlinear coefficient was studied.The results show that the nonlinear coefficient is proportional to the crack length when the crack width is constant.When the crack length is constant,the nonlinear coefficient is inversely proportional to the crack width.If the angle exists,the nonlinear coefficient will decrease.Finally,the phase reversal method based on mixing technique is used to determine the direction of crack angle.Due to the dispersion characteristics of high frequency Lamb wave in the plate,high frequency Lamb detection is not suitable for multi-probe detection.Therefore,mixing technology is chosen in this paper.The results show that when the crack angle is changed,the maximum direction of the nonlinear coefficient and the envelope shape connected by the nonlinear coefficients in eight directions will change.The crack angle can be determined effectively by the envelope shape and the direction of the maximum nonlinear coefficient.