Nonlinear Ultrasonic Evaluation Of Adhesive Quality Of AZ31 Magnesium Alloy Adhesive Structure

The adhesive structure is widely used in the fields of shipbuilding,machinery,automobile,and national defense due to its uniform stress distribution,high strength,low cost,light weight,etc.However,the existence of kissing debonding defects and bonding strength defects in adhesive structure will lead to the destruction of the integrity of adhesive structure and affect the reliability and safety of the use of adhesive structure.Therefore,ultrasonic testing of the adhesive quality of the adhesive structure is required to ensure product quality and safety.In this paper,AZ31 magnesium-aluminum alloy,epoxy resin adhesive and polyethylene sheet were used to design two types of adhesive samples,one is with the kissing debonding defect area of 0mm×0mm,2mm×2mm,4mm×4mm,6mm×6mm and 8mm×8mm and the other has a curing agent content of 15%,25%,40%,50%,and 75%.The ABAQUS finite element software was used to calculate the nonlinear coefficient of different area kissing debonding defect models and different bond strength models.Besides,samples with different area of kissing debonding defects and samples with different curing agent content were measured by nonlinear ultrasonic testing system.The nonlinear coefficient,sound velocity and attenuation coefficient of the sample were all measured,and tensile tests were performed on all bonded samples to determine their maximum shear force.Finally,the following conclusions are drawn:(1)The results of the tensile test show that the bonding strength gradually decreases when the area of the kissing defect in the sample with different debonding areas increases continuously;and the bonding strength of the samples with different bonding strength increases first and then decreases with the increase of curing agent content.(2)The variation of ultrasonic velocity in different debonding area specimens is not significant with the increase of kissing debonding defect area,the change rate is 5.87%.When measuring the sound velocity of adhesive specimens with different bonding strength,the sound velocity increases with the increase of shear strength of adhesve specimens,and the change rate is 4.1%.(3)The attenuation coefficients of specimens with different debonding areas increase with the increase of kissing defect area,and have a certain correlation with the change rule of bonding strength,with a change rate of 23.96%.When sound wave propagates in specimens with different bonding strength,the attenuation coefficients decrease with the increase of shear strength,with a change rate of 13.02%.(4)When characterizing the kissing debonding defects of different areas,the ABAQUS finite element simulation results and the nonlinear coefficient measurement results show that the nonlinear coefficient increases with the increase of the kissing defect area.The change of bond strength was negatively correlated.The change rates measured by simulation calculation and experiment were 95.15% and 81.21%,respectively.When characterization of adhesive samples with different bonding strengths,ABAQUS finite element simulation and the nonlinear coefficient measurement results show that the nonlinear coefficient decreases with the increase of shear strength.The change rate of the nonlinear coefficient calculated by the simulation is 92.04%,and the rate of change of the nonlinear coefficient measured by the experiment is 88.95%.The results show that,compared with other acoustic parameters,the nonlinear coefficient can better characterize the change of the area of kissing debonding defects and the change of bonding strength.