Study On Ultrasonic Testing Method Of Metal-rubber Multi-interface Bonding Quality

The solid rocket engine,as the power part of various missiles,was subjected to high temperature and high pressure during operation,and the working environment was very bad.In order to meet the requirements,the multi-layer rubber material was usually bonded on the high-strength alloy steel matrix,so that the solid rocket engine could achieve excellent high-strength,heat-insulating and high-temperature-resistant comprehensive performance.However,in the bonding process,there might be such defects as debonding,porosity and strength weakening at the bonding layer between the steel and the rubber-bonded rubber.These defects would seriously affect the service performance of the solid rocket engine.Therefore,it was of great significance to study the ultrasonic testing methods for the multi-interface bonding quality of steel-rubber structures.Firstly,based on the multi-layer bonding structure of steel shell-insulation rubber-liner rubber,the propagation model of ultrasonic wave in multi-layer bonding structure was studied.The mathematical expressions of the ultrasonic echo signals at the interface between the steel shell and the insulation layer rubber and the two interfaces between the insulation layer rubber and the liner rubber were also studied.In addition,a finite element simulation software was used to simulate the propagation of ultrasonic waves on an interface and a two-interface in a multi-layer adhesive structure.Then,the acoustic parameters such as sound velocity,sound attenuation,density and acoustic impedance of steel and silica gel were measured.And prepared a complete debonding sample of a steel shell and a first layer of rubber,an interface weak adhesive sample,a first layer of rubber and a second-layer rubber two-interface complete debonding sample and a steel-water-steel two-interface auxiliary sample.In addition,the sound pressure reflectance and the sound pressure transmittance of an interface and a two-interface in the debonding sample were studied.In the end,three groups of experiments were designed: using the ultrasonic characteristic scanning imaging system to study the debonding characteristic signal of a fully debonding sample at an interface,analyzing the influence of the size of the adhesive defect,the frequency of the ultrasonic transducer and the thickness of the steel shell on the characteristic signal,and using the spectrum analysis technique to verify.This paper studied and analyzed the debonding characteristic signal of an interface weak adhesive sample.Studied the debonding characteristic signal of the two-interface completely debonding sample,and analyzed the influence of the ultrasonic transducer frequency and the thickness of the silica gel on the characteristic signal,and used the smooth pseudo-Wigner-Ville distribution and the wavelet transform to verify.The results showed that for the steel-rubber multilayer bonding structure,the complete debonding defect of interface 6mm could be detected by ultrasonic vertical reflection method,and the weak bonding defect of interface 10 mm could be detected by ultrasonic vertical reflection method.The complete debonding defect of the two interface 18 mm could be detected.The accuracy and reliability of the detection results were verified by spectrum analysis,smooth pseudo-Wigner-Ville distribution and wavelet transform.