Investigation On Vibration Fatigue Characteristic Of TC6 Alloy Subjected To Cryogenic Laser Peening

Cryogenic laser peening(CLP)is a novel surface modification technology that combining the effect of ultra-high strain rate and cryogenic treatment.Based on the microstructure and stress strengthening effect,CLP could effectively suppress the initiation and expansion rate of fatigue cracks in the surface layer,and realize the fatigue life extension of the structural parts.In this paper,TC6 titanium alloy was taken as the research object.The combination of numerical simulation and experimental research was used to study the influence law of residual stress field and microstructure of the materials subjected to CLP.The mechanism of vibration fatigue life extension after CLP treatment was also explored.The main research contents in the thesis are as follows:(1)Based on elastoplastic mechanics,the dynamic response characteristics and synergistic strengthening mechanism of cryogenic temperature and ultra-high strain rate were analyzed.The material constitutive model for CLP was determined.The shock wave pressure and residual stress field were estimated.Based on the fracture mechanics of materials,the vibration fatigue failure process and the fatigue crack propagation characteristics were investigated.(2)The experiments and numerical simulation of CLP process were carried out.The characteristics of residual stress field induced by CLP were summarized.The strengthening mechanism of compressive residual stress after CLP treatment was explored.The laser power density and cryogenic temperature of CLP were analyzed and optimized.Based on the results of TEM observation,the effects of CLP on the grain size,dislocation configuration and twin structure of the material were studied.The microscopic strengthening mechanism of the materials treated by CLP with the coupling of heat and force was analyzed.(3)The vibration fatigue tests of TC6 titanium alloy specimens were carried out.The vibration fatigue life of different treatment specimens was achieved and compared.The fracture morphologies of fatigue failure specimens were observed by SEM.The vibration fatigue life extension mechanism of CLP was analyzed.Meanwhile,the FEA method of vibration fatigue life and failure risk nodes of CLP treated specimens were established,andthe numerical simulation of vibration fatigue specimens under CLP treatment was also conducted.