Quantitative Characterization And Automatic Identification Of New Different Index Of Typical Damage Of Composite Materials

Under the action of cyclic load,the composite plates are prone to fatigue damage,causing microscopic changes in dislocations and crack initiation,and reducing structural strength.If it cannot be detected and evaluated in time,the crack damage will accelerate and expand under load,even cause structural breaking and a serious accident.Therefore,research on the detection and evaluation methods of typical damage of composite materials has important theoretical and engineering application value for ensuring the safe operation of equipment.In this paper,three typical damages of composite plates(contact nonlinear delamination,matrix crack and delamination)are studied,and the automatic identification,quantification and localization detection methods of damage are studied.The paper introduces the basic theory of Lamb wave propagation in material plates,including the propagation rules and characteristics of Lamb waves,and the generation process of cumulative second harmonics of nonlinear Lamb waves.On the basis of this theory,the linear and nonlinear damages of composite plates were qualitatively identified and quantified using ?-index,recursive quantitative analysis index and correlation dimension.Firstly,the preliminary identification of three typical damages of composite materials is carried out.The higher harmonic effect of nonlinear Lamb waves generated by contact nonlinear delamination damage is used to identify contact delamination damage from three typical damages,and then the damage features including time domain peak,power spectral density,power spectral density change rate,power spectral density change and energy are extracted from the damage signal of matrix crack and delamination.These two damages of different type are classified by SPSO-TWSVM classifier.In this paper,?-index is used to detect the nonlinear harmonics and quantitatively characterize the contact nonlinear delamination.The Duffing-Holmes oscillator and Lyapunov exponent are used to detect the nonlinear harmonics and locate the contact nonlinear delamination under strong noise background.The Lyapunov exponent corresponding to the nonlinear time series of the Duffing system is used as the quantized measure of the state transition of the vibrator.The ultrasonic guided wave probabilistic imaging method for the nonlinear damage of the composite is proposed by using the Lyapunov exponent as the damage index.The experimental results showed that the Lyapunov damage index(LDI)can image the single delamination or multiple delaminations with higher resolution and better preciseness,compared with the nonlinearity parameter and the conventional damage index,especially under the noise interference.The nonlinear characteristics and their fused characteristic of the RQA index are used to quantify the matrix crack.The fused feature is used as imaging parameter to locate the matrix crack.Through simulation and experiment,the fused feature which has strong sensitivity to the early stage of fatigue damage can well characterize the degree of micro-defects.Quantitative analysis of delamination is carried out by using correlation dimension,and the correlation dimension is used as imaging parameter to locate the delamination damage.