Study On Ultrasonic Nondestructive Testing Method For Riveting Quality Of Mechanical Interlock Zone Of SPR Joint

The nondestructive testing of structure of mechanical interlock zone of SPR joint is an urgent problem in the field of automobile lightweight body-in-white connection quality testing and evaluation.This project mainly focuses on the analysis of the characteristics of the oblique sound field of immersion ultrasonic,the edge detection of the structure based on the ultrasonic C-scan image analysis,and the research on the ultrasonic detection method and its application of the structure of mechanical interlock zone of SPR joint.The research contents and conclusions are as follows:Based on the basic principles of wave and ray acoustics,the characteristics of the oblique sound field of immersion ultrasonic were studied.Discriminate and analyze the influence of ultrasonic incident angle on focused sound field,amplitude and normalized TOF value of ultrasonic A-scan signal.Conclusions are as follows:When the inclined angle of the inclined plane is less than 2~°,it has little influence on the amplitude of the ultrasonic A-scan signal,and visible incline is horizontal;According to the Huygens-Fresnel principle,the minimum frequency of the ultrasonic probe is15 MHz in order to make the ultrasonic signal not diffracted at the nail tip;When the ultrasonic probe is oblique incident,the ultrasonic signal amplitude decreases gradually with the increase of the inclination angle of the specimen,and the normalized TOF value gradually increases with the increase of the inclination angle of the specimen.Based on ultrasonic C-scan image analysis,the characteristics of sound pressure distribution at the edge of the structure were developed,and the theoretical formula of sound intensity distribution at the edge of the structure was established,which was verified by experiments.The results show that the gray-position curve extracted from ultrasonic C-scan image has a certain change rule at the edge of the structure.It shows the change characteristic of concave first and then convex,and there is an inflection point in the gray-position curve,which can be used as the boundary point of the structure.The experimental verification also shows that the error of the inflection point as the boundary measurement point of the ultrasonic C-scan image corresponding to the structure is the least.A method for ultrasonic inspection of mechanical interlock zone of SPR joint was established.With immersion focused ultrasound scanning microscope,the nondestructive testing of mechanical interlock zone of SPR joint was carried out.The results show that the residual bottom thickness can be measured and the position、size and morphology of riveting defects can be judged by using ultrasonic B-scan image and C-scan image;The inclination angle of the inner diameter surface is inversely proportional to the amplitude of the ultrasonic A-scan signal and the gray value of the C-scan image;The structure of mechanical interlock zone can be characterized by the ultrasonic C-scan image of the inner diameter plane;The expanded diameter of rivet measured by ultrasonic C-scan image processing of inner diameter surface based on Canny operator is larger than the actual value;While the inflection point of the gray-position curve extracted from the ultrasonic C-scan image of the inner diameter surface as the rivet edge measurement error is the smallest;The inflection point can be used as the rivet boundary point,and then the expanded diameter of rivet can be calculated accurately.