The Research On The Tensile Damage Of Typical Materials Using Nonlinear Ultrasonic Wave

Early accurate quantification and positioning of structural damage is essential to ensure long-term security service and production safety of equipment.Recent studies show that nonlinear ultrasonic wave is sensitive to micro-nano scale evolution such as dislocation and second-phase precipitation.However,the interaction and mechanism between microstructure evolution and nonlinear ultrasonic signals still needs further research.In this thesis,different degree plastic damage under tensile loading of polycrystalline pure copper,PMMA and 304 austenitic stainless steel were inspected using nonlinear ultrasonic wave.The triadic relationship between evolving microstructures,damage and nonlinear ultrasonic signals was acquired.The main research and conclusions are as follows:(1)Evaluation of tensile plastic damage of polycrystalline pure copper under different heat treatment parameters using ultrasonic nonlinear wave.The results show that the tensile plastic damage of polycrystalline copper is closely related to the change of ultrasonic nonlinear parameters.The influence of dislocation involution on the ultrasonic nonlinear parameters is established by quantitative analysis and their response relationship is developed.(2)The influence of the microstructure evolution of three typical materials of polycrystalline pure copper,PMMA and 304 austenitic stainless steel on the nonlinear ultrasonic signal is systematically analyzed.The results show that the PMMA which has no dislocation involution during tensile damage has little effect on the nonlinear ultrasonic signal;In contrast,polycrystalline copper and 304 stainless steel which have shown significant different forms of dislocation evolution and martensitic transformation have a significant effect on the ultrasonic nonlinear signal.(3)Based on the experimental data of tensile plastic damage and ultrasonic nonlinear parameters of polycrystalline copper,the parameter correction of dislocation string model is established.The results show that the ultrasonic nonlinear parameters caused by the dislocation involution of plastic damage of polycrystalline pure copper are proportional to the dislocation density of 1.2th power,dislocation chord length of 4.45 th power and the internal stress.