Study Of The Ultrasonic Propagation Characteristics Of Bonded Structure Based On The Oblique Incidence Technique

Bonded structure has been widely used in many important sectors such asaviation, aerospace and military industries. However, catastrophic events occursometimes because of debonding or lack of bonding strength of bonding interface.Therefore, the study on the propagation characteristics of the adhesive structure hasimportant academic value and the potential for engineering applications.At present, ultrasonic inspection has become one of the most widely usednon-destructive testing technology of bonding structure, compared to other ultrasonictesting method, ultrasonic oblique incidence method’advantage is to improve thedetection sensitivity without having to increase the frequency of ultrasonic wave.This article studies the propagation characteristics of the bonding structure usingultrasonic oblique incidence method through theoretical and experimental study.Including the study of the reflection characteristics and transmission characteristics,especially research the reflective properties and transmission characteristics of theweak bonding structure, the major research work includes:(1)The mechanical model of the semi-infinite solid bonding structure wasestablished, the reflection and transmission of single interface was used to derivedreflection and transmission coefficients formula of bonding interface under ultrasonicoblique incidence condition theoretically.The numerical simulation was done by usingMatlab software and the influence of the change of incidence angle on the reflectioncharacteristics and transmission characteristics of the bonding structure wasanalyzed.In addition, the propagation characteristics of the weak bonding interfacethrough changing the stiffness ratio was studied.The results show that, the detectionsensitivity can be improved by choosing the incidence angle when ultrasonic obliqueincidence.For the weak bonding structure,its reflection cofficient curve is between thereflection cofficient curves of ideal bonding and debonded condition, and whenincidence angle is smaller than a certain angle, the reflection cofficient curves driftupwards.(2)The mechanical model of single-layer board and the infinite solid bondingstructure in liquid were established, and the reflection and transmission coefficientsformula of the single-layer board and the bonding structure in liquid using impedancemethod were derived theoretically.The influence of adhesive layer thickness and otherparameters on the transmission coefficients and resonant frequency was analyzed.Thepropagation characteristics of the weak bonding structure by changing the interfacestiffness coefficient was studied. The results show that, for bonding structure in waterwhen ultrasonic oblique incidence,the change of parameters(incidence angle,etc) willchange the resonant frequency point and peaks of transmission coefficients;when the interface stiffness coefficient is small, there is multiple peaks phenomenon in thefrequncy response of transmission coefficients of weak bonding structure,while forthe ideal bonding structure, multiple peaks phenomenon will disappear.(3)Based on the foregoing model, a detection system of the transmissioncoefficient was designed to measure the transmission coefficients of immersionsigle-layer board and bonding structure.The devices of this test system are too simpleto estabilish easily in the laboratory.And the system is suitable for specimens withdifferent thickness.First of all, the theory was verified through the spectrum analysisof the transmission signal data.Secondly, the incidence angle,steel thickness and otherparameters were changed to study the influence of test parameters on the transmissioncharacteristics.Finally, the transmission characteristics of weak bonding structure wasstudied. The results show that the test results are in good agreement with thetheoretical results;the influences of incidence angle and other parameters on thechanging of transmission characteristics are the same as the theoretical analysis results;for the weak bonding structure, the decrease of the stiffness coefficient does notchange the resonant frequency,but the peak of the transmission coefficient will bereduced and there will be the "mutiple peaks" phenomenon.