Numerical And Experimental Study Of Lamb Wave Nonlinear Detection Of Damage Propagation Of Composites Under Different Tensile Loads

Because of its high strength,high specific stiffness,strong designability,and good processing and other advantages,composite materials are widely used in aerospace,shipbuilding,lightweight automobile,and engineering and construction fields.However,its complex processing process and harsh and changeable service environment often lead to various defects or damages in its internal structure.These minor damages may degrade the overall stiffness and strength of the material,and even cause serious safety accidents in engineering applications.In order to avoid this situation,it is necessary to develop a nondestructive testing method which can detect the early internal micro-damage of materials quickly and effectively.Nonlinear ultrasonic detection has been widely used in the field of nondestructive testing because of its sensitivity to early micro-damage.In this paper,the nonlinear response of nonlinear Lamb wave under different tensile displacement loads and the influence of different detection distances and the number of fatigue cycles at the initial stage of fatigue loading on the nonlinear coefficient are studied by combining experiment and finite element numerical simulation.Firstly,the propagation characteristics of ultrasonic waves in a single-layer anisotropic plate are introduced,and the propagation characteristics of ultrasonic waves in a multi-layer anisotropic plate are deduced by using the global matrix method.Through its wave equation,numerical analysis software is used to draw the Lamb wave dispersion curve in the composite laminate,and the multi-modal and easy dispersion characteristics of Lamb wave are introduced.According to the principle of dispersion curve and mode selection,the frequency of Lamb used in this study is selected.At the same time,the relative nonlinear coefficient β is defined to characterize the nonlinear response in the material.Secondly,the nonlinear response of composite laminates subjected to tensile damage was studied by experimental method,and the experimental scheme,material selection and specimen preparation were briefly described.A nonlinear ultrasonic Lamb wave detection platform was built to test specimens with different tensile displacements,and the influence of excitation-receiving distance on nonlinear coefficients was studied.Then,the relationship between cyclic loading times,loading frequency and the detected nonlinear coefficient of composite material under cyclic loading is studied experimentally.The results show that at the initial stage of fatigue loading,the nonlinear coefficient is positively related to the loading times but not to the loading frequency.Finally,the nonlinear response of composite laminates subjected to tensile damage is studied by finite element numerical simulation software.A simulation model with three analysis steps including stretching-vibration-ultrasonic detection was established.The simulation results were compared with the experimental data to verify the validity of the simulation model,and then the relationship among nonlinear coefficient,tensile displacement and damage area was studied.Finally,the effect of material layering angle on tensile damage and nonlinear response is studied.