Ultrasonic Nondestructive Evaluation Of Material Damage Based On Acoustic Nonlinearity

In recent years,metal materials and their bonding structures are widely used in aerospace,automobiles,ships,building materials,machinery manufacturing and other fields.Since the mechanical properties of metal materials and bonding interface are closely related to the safety and reliability of the structures,it is important to detect and evaluate the early degradation of mechanical properties.Nonlinear ultrasonic techniques,which detect damages based on various nonlinear effects of ultrasonic wave propagating in structures,have been proved to be able to identify microscopic material degradation and highly sensitive to micro-damage compared with traditional ultrasonic techniques.Therefore,the nonlinear ultrasonic evaluation of material damage is studied based on the higher harmonic and collinear wave mixing method.First,for the evaluating the damage to bonding interface under cyclic temperature fatigue,specimens made of aluminum alloy 6061 and modified acrylate adhesive are measured experimentally by using the higher harmonic generation.Next,the collinear wave mixing method is numerically studied by using FEM software ABAQUS to verify its effectiveness for damage detection of metal materials and their bonding structures.Finally,an experimental study of collinear wave mixing is carried out on Q235 steels with the localized plastic damage,and the curing process of the modified acrylate adhesive is monitored.In this paper,results are as follows:(1)For the evaluation of bonding interface damage under cyclic temperature fatigue,the acoustic nonlinear parameter(ANP),which serves as an indicator of material properties,remains nearly unchanged in the initial stage of high temperature cyclic fatigue test,and the ANP obviously increases with temperature cyclic time increasing.For low temperature cyclic fatigue test,the ANP increases rapidly with the increase of temperature cyclic time in the initial stage,and its value growth slows down in the later stage.Further discussion shows that the increase of third order elastic constant is the main reason for the change of ANP for high temperature cyclic fatigue,and that the change of the tensile stiffness of the bonding interface is the main source for the change of the ANP for low temperature cyclic fatigue.(2)For the numerical simulation of Q235 steel with the localized plastic damage by collinear wave mixing method,the location of the mixing zone can be controlled by adjusting the trigger time of two primary waves,and the distribution of the resonance amplitude can be obtained for each model.Simulation results show that for the linear elastic material,the resonance amplitude at each position is almost equal.For materials with the localized plastic damage,the resonanc amplitude in the plastic damage zone is significantly increased compared with the undamaged zone at same positon;while in the undamaged regions,the resonance amplitude is almost equal to the linear elastic material at same position.Next,for the specimen of 6061 aluminum alloy/epoxy resin adhesive/6061 aluminum alloy,the collinear wave mixing method for detecting randomly distributed micro-cracks in adhesive layer is investigated by numerical simulation.Results show that the resonance amplitude decreases linearly with the increases of the number of cracks.This phenomenon is the result of interaction between nonlinear parameter and fundamental wave amplitudes in adhesive layer.(3)In the detection of metal materials degradation,the resonance amplitude in the plastic zone of Q235 steels is greater than that in the corresponding position of intact specimen,while in the undamaged zone,the resonance amplitude remains basically unchanged.Besides,quantitative nondestructive evaluation of the plastic damage degree of Q235 steel is studied using collinear wave mixing method.It is found that the resonance amplitude in the plastic zone increases gradually with increasing damage degree.Therefore,collinear wave mixing method can be used to locate the plastic zone and evaluate the damage degree of metal materials.(4)For the evaluation of the curing of adhesive,the resonance amplitude increases rapidly with the curing time during 0～80 minutes.After that,it nearly remains stable during 80～360 minutes.Therefore,collinear wave mixing method can be used to monitor and evaluate the curing process of adhesive.The results of this paper provide a reference for nonlinear ultrasonic evaluation of early damage of metal materials and their bonded structures,and have certain significance for the application and promotion of nonlinear ultrasonic testing technology.