Residual Stress Field Simulation And Vibration Fatigue Life Research Of 2024-T351 Aluminum Alloy Subjected To Cryogenic Laser Peening

Cryogenic laser peening(CLP)is a novel surface modification technology which causes plastic deformation of materials at ultra-low temperature and ultra-high strain rate to strengthen the material.Compared with room temperature-laser peening(RT-LP),it can inhibit the initiation and propagation of fatigue cracks and improve the fatigue life of the material significantly by inducing higher-amplitude compressive residual stress and finer microstructure in the material.In this paper,2024-T351 aluminum alloy was taken as the research object.The effect of CLP on the microstructure and vibration fatigue property was studied by experiment,and the mechanism of life extension was explored.Through numerical simulation and response surface methodology(RSM),the process parameters of CLP were optimized and the influence of process parameters on residual stress field was investigated.The main research contents are as follows:(1)The experiment of CLP was carried out.The hardness and microstructure of2024-T351 aluminum alloy samples before and after CLP were tested by microhardness tester,OM and TEM.The grain size,dislocation structure and density and phase structure induced by RT-LP and CLP were compared and analyzed.The gradient distribution law of microstructure in depth direction was obtained.The distribution law of microhardness induced by RT-LP and CLP was studied.The effect rule of CLP on the microstructure of2024-T351 aluminum alloy and its strengthening mechanism were explored.(2)The constitutive model and shock wave pressure model of the material under the condition of ultra-low temperature and ultra-high strain rate were established,the residual stress field induced by CLP was simulated based on ABAQUS and was verified by experiments.The response surface optimization of process parameters was carried out based on Design Expert.The mathematical model between the process parameters of CLP and the average surface residual stress,the depth of residual compressive stress layer and the maximum surface compressive residual stress was established.The influence of shock wave pressure,peening times and peening temperature on the residual stress field was studied,and the optimal process parameter scheme was achieved.(3)The vibration fatigue test was carried out.The influence of CLP on the vibration fatigue life and fatigue damage of materials was studied.The fracture morphology wasobserved by SEM,the distribution dislocation of S-phase in the fatigue source area of CLPed sample was the deepest,the distance between fatigue bands in the fatigue crack growth area was the smallest,the dimple in the final fracture area was the largest and the deepest,and the large dimple contains the small dimple.The mechanism of life extension and fatigue fracture was explored.The results show that through the plastic deformation under the coupling action of ultra-low temperature and ultra-high strain rate,grain refinement and the sub structure of dislocation were induced in 2024-T351 aluminum alloy,which increased the amplitude and stability of compressive residual stress.The vibration fatigue life of material was effectively increased by microstructure strengthening and stress strengthening.