Study On Nonlinear Characteristics Of Lamb Waves In Aluminum Plates With Micro Damage

During the use of metallic materials,performance degradation can occur,resulting in dislocation,creep,micro cracks and other microscopic damages.If the damage is further aggravated,it will break,affecting industrial production and there are major safety hazards.Therefore,it is necessary to detect the material nonlinearity damage occurring in the early stage of the material damage.In this paper,the nonlinear characteristics of Lamb wave in aluminum plates with micro damage are studied and the propagation principle of the Lamb wave in metal plates is analyzed and the finite element simulation is performed.The influence of vibration mode on harmonic amplitude and nonlinear coefficient in horizontal and vertical direction is analyzed,and the influence of local strengthening damage on harmonic amplitude and nonlinear coefficient is analyzed,providing reference for engineering application.Finally,the nonlinear characteristics of S₀ mode Lamb wave in aluminum plate are studied.In this paper,the propagation theory equation of Lamb wave in metal plate is first studied to obtain the dispersion equation and draw the dispersion curve;the nonlinear damage theory of metallic materials and the generation of second harmonic,difference frequency and sum frequency of nonlinear Lamb waves are explained,and the cumulative effect of low frequency S₀ mode Lamb wave in the condition of approximate phase velocity matching is analyzed;the nonlinear coefficient of damage evaluation is analyzed theoretically.The vibration mode of Lamb wave is analyzed and the vibration displacement curve of S₀ mode Lamb wave is drawn,and the influence of Lamb wave mode on harmonic and nonlinear coefficients is analyzed.On the basis of theoretical research,a two-dimensional model of Lamb wave propagation in aluminum plates is established by using finite element analysis software ABAQUS,and the ABAQUS user subroutine is used to introduce third-order elastic constants as uniform nonlinear damage for the aluminum plate model.In the aluminum plate model,the three-order elastic constants are changed locally to enhance the damage,the influence of local strengthening damage on the second harmonic and nonlinear coefficient of Lamb wave with the propagation distance of Lamb wave is analyzed,and the local damage of different positions resulting in different deviation of the first maximum point of the curve is analyzed.The interference cancellation effect occurred when two or more local damages are strengthened within a certain distance is analyzed,and different distances between the damages will cause the second harmonic to appear different degrees of weakening.The nonlinear characteristics of S₀ mode Lamb wave in aluminum plate are studied by Finite element simulation,the difference frequency,sum frequency and amplitude-distance curve of the second harmonic are drawn,and the amplitude accumulation distance of the second harmonic and the maximum value of harmonics are compared with the horizontal and vertical difference frequency and sum frequency...