The Relaxation Of Shot Peening Residual Stress And Its Effect On Fatigue Life Of 7075 Aluminum Alloy With Simulation And Experimental Study

Shot peening as a surface hardening process can effectively increase the fatigue life of the specimen.Under normal circumstances,it is generally believed that shot peening can improve fatigue life of the specimen due to the introduction of residual stress,and based on it to study its impact on the fatigue life,but the residual stress is not static and not stable,it can be relaxed due to changes in external conditions,which will weaken the effect of shot peening on fatigue life.So,when investigating the residual stress on the fatigue life of shot peening specimens,the effect of residual stress relaxation on fatigue life must be taken into account.Therefore,in this paper,the residual stress relaxation of the shot peening 7075 aluminum alloy is investigated and the effect of crack propagation on the residual stress redistribution is studied.Finally,the effect of residual stress relaxation on the fatigue life is studied through experiments and numerical simulations.The main research contents are as follows:(1)In order to predict the changes of residual stress relaxation and redistribution of shot peening,three types of shot peening were performed on 7075 aluminum alloy specimens,and the residual stress along the depth direction of the specimen was measured by X-stress 3000.The three-point bending experiment explores the influence of cycles,external load strength,initial shot peening intensity and stress ratio on the residual stress relaxation,revealing that the real reason of the residual stress relaxation effect is the occurrence of new plasticity within the material due to the effect of external loads.Strain causes relaxation and redistribution of initial peening residual stress.(2)A three-point bending numerical simulation model containing initial residual stress was established by ABAQUS software.Through load analysis step,crack extension analysis step and unloading step,the effect of micro crack propagation on stress redistribution was explored.In addition,the effect of strength,initial shot strength and crack length on residual stress redistribution around the crack was further studied.(3)In order to study the effect of residual stress relaxation on fatigue life,the ABAQUS software was used to establish a numerical simulation model with the same size in the second chapter.The 7075 aluminum alloys were tested with and without three-point bending experiment.The residual stress of the three-point bending experiment is distributed along the depth of the test specimen,and then the residual stress of the specimen subjected to the three-point bending test is measured.After this,the stress has been relaxed.A further three-bending fatigue test was performed to measure the fatigue life.Comparing the same external load strength,cycles and stress ratios,the numerical simulation model and experimental results verify the numerical simulation model.Finally,the effect of residual stress relaxation caused by different factors,namely stress ratio,external load strength,and cycles on fatigue life are explored.