| Laser peening has the advantages of small surface roughness,obvious plastic deformation,large and deep induced residual compressive stress,which can effectively improve the corrosion resistance and fatigue resistance of metal materials.This paper takes 316 L austenitic stainless steel,the preferred material for hydrogen storage equipment,as the research object.The influence of stress strengthening and structure strengthening effects induced by LP on the vibration fatigue characteristics of hydrogen-charged specimens were analyzed by means of theoretical research,series of experiments and numerical simulation.The strengthening mechanism of hydrogen embrittlement resistance and vibration fatigue resistance of LPed 316 L stainless steel specimens with different power densities followed by hydrogen charging was revealed.The main work is as follows:(1)The mechanism of hydrogen embrittlement and martensitic transformation of stainless steel was studied,and the governing equation and constitutive equation of hydrogen diffusion were discussed.The hydrogen embrittlement resistance mechanism of LPed 316 L stainless steel was revealed from the perspectives of residual compressive stress,grain refinement and dislocation structure.Combined with the structural vibration modal theory,the influence of LP on fatigue limit and stress intensity factor of crack tip of hydrogen-charged specimens was analyzed,and the vibration fatigue life of hydrogen-charged specimens was estimated,which revealed the anti-vibration fatigue life extension mechanism of LPed 316 L stainless steel.(2)LP,electrochemical hydrogen charging,vibration mode and vibration fatigue tests of 316 L stainless steel specimens under different laser power densities were carried out to explore the effects of high amplitude residual compressive stress,grain refinement and dislocation multiplication structure induced by laser peening on hydrogen atom invasion,diffusion motion,hydrogen induced martensitic transformation,natural frequency,damping ratio and vibration fatigue life.Combined with the characteristics of vibration fatigue fracture morphology,the strengthening mechanism of hydrogen embrittlement resistance and vibration fatigue resistance of LPed 316 L stainless steel specimens with different power densities followed by hydrogen charging was revealed.The results show that LP induces the increase of grain refinement and surface dislocation density,which hinders the aggregation and diffusion of hydrogen atoms,reduces the martensite transformation degree of 316 L austenitic stainless steel,and helps to suppress the initiation of microcracks.At the same time,the residual compressive stress induced by LP not only inhibits hydrogen penetration,but also increases the fatigue limit and slows down the crack growth rate.Vibration fatigue test results show that the fatigue life of LPed specimens with different power densities followed by hydrogen charging has been significantly improved,and the maximum amplitude can be up to 79.36%.The fracture morphology analysis further proves that LP can effectively reduce the fatigue crack growth rate of hydrogen-charged specimens,increase the fracture toughness of the material,and then improve the vibration fatigue properties of materials.(3)Based on ABAQUS-MSC.Fatigue software,a coupling calculation model of residual stress field,hydrogen diffusion and vibration Fatigue induced by LP was established.The influence of residual compressive stress distribution induced by LP on hydrogen diffusion behavior of 316 L stainless steel was analyzed.Considering the combined effects of residual compressive stress,hydrogen-induced stress and vibration stress,its influence on the vibration fatigue life of the material was described,and then the strengthening effect of LP on the vibration fatigue property of hydrogen-charged 316 L stainless steel was verified.The experimental and simulation results show that the high amplitude residual compressive stress induced by LP can not only weaken the vibration stress to a certain extent,but also effectively inhibit the infiltration and diffusion of hydrogen atoms to reduce the hydrogen-induced stress,thus delaying the fracture process of the specimen and improving the vibration fatigue life of 316 L stainless steel hydrogen-charged specimen. |
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