Ultrasound Propagation And Testing Analysis In Coating Structure Under Stress State

The core technology and industrial application of additive manufacturing are of great significance for promoting intelligent manufacturing and improving the national manufacturing innovation capacity.However,how to accurately quantify the residual stress in the coating after the additive manufacturing technology is formed and realize the accurate non-destructive testing of residual stress is the primary problem the development of additive manufacturing technology faced.In order to meet the increasing demand of forming quality evaluation in additive manufacturing technology,on the basis of a large number of static load tensile and compression tests,this dissertation made a research of ultrasonic nondestructive testing method of internal residual stress of solid metal and its coating structures by ultrasonic nondestructive testing which combined with the plasma spray welding and laser cladding material manufacturing technology.It mainly includes the following research contents:(1)The influence of material distribution and forming condition of solid metal and its coating structures to the process of ultrasound propagation was analyzed.Based on the acoustoelasticity theory,the process model of ultrasound propagation was built which taken material distribution and stress of solid metal and its coating structures as considering.The characterization parameters of stress(apparent difference and apparent line strain of ultrasound)and based on the material distribution characteristics of stress-ultrasound elasticity coefficient were put forward.(2)Ultrasound propagation characteristic test in residual stress field was designed.Three types of specimens were prepared by combining plasma spray welding,laser cladding technology and other processing and heat treatment technologies.The residual stress distribution status in the specimen was simulated by static load stretching and compression.The corresponding ultrasonic testing parameters were set for different samples.Ultrasonic signals(amplitude and beam path)were collected at different positions in the samples for calibration and the parameters representing stress(ultrasonic apparent line strain)were extracted.The mapping relationship between stress and ultrasonic apparent line strain was established.(3)Through the contrastive analysis of the theoretical model and the test results,the theoretical model agree well with experimental results and the relative error of stress-ultrasound elasticity coefficient between the test fitting equation and the theoretical model is less than 8%,which verify the validity of the theoretical model.Based on the established stress-ultrasound propagation model,the ultrasonic nondestructive testing method for residual stress in solid metal materials(single metal or composite materials with coated structures)is proposed.Based on the design with defects as the calibration and the requirement of ultrasonic testing accuracy in the test,a method for correcting the effect of internal stress on the nondestructive testing of defects in solid metal materials was proposed.