Fatigue Fracture Mechanism And Life Prediction Of 40Cr Steel Notched Components Treated By Shot Peening

Most engineering components will inevitably have sudden changes in cross-section such as notches and cracks,which will cause serious local stress concentration in practical application,thus easy to fracture and failure under cyclic load.In order to study the practical problems encountered in such projects,small specimens with notches are often used to explore the effect of cyclic load on the safety performance of components.This paper takes medium carbon alloy quenched and tempered 40Cr steel,which is commonly used in gear as the research object,and uses shot peening to improve the surface integrity of the notch.The changes of microhardness,microstructure,surface morphology,residual stress,fatigue limit and fatigue fracture morphology of the materials under different shot peening intensity and coverage parameters were analyzed by comprehensive comparison.The effects of shot peening on surface integrity and fatigue properties of 40Cr steel were systematically studied in this paper.At the same time,on the basis of the existing methods for predicting the local fatigue strength of notched components,the prediction of the local fatigue strength of notched components after shot peening is deeply explored.The local fatigue strength of notched 40Cr steel specimens treated by shot peening was predicted and evaluated by means of the combination of experiment,theory and simulation,taking into account the effects of stress gradient,residual stress,work hardening and surface roughness.The experimental observation and research show that after shot peening treatment,a certain depth of plastic deformation layer and higher residual compressive stress are formed on the surface of quenched and tempered 40Cr steel.With the increase of shot peening intensity,the surface microhardness of the material increases obviously.By observing the three-dimensional morphology of the surface,it is found that the surface roughness increases with the increase of shot peening intensity,and the surface integrity can be improved by increasing the parameters of shot peening coverage.The fatigue test results show that the shot peening treatment can improve the fatigue performance of the 40Cr steel notched components.The fatigue limit of different shot peening parameters was increased by 14.3%~29%compared with the un-peened specimens at 2×10~6 cycles.When the fatigue limit is maximized,the shot peening intensity was 0.2 mmA and the coverage was 400%.Based on the"line elastic finite element method-stress gradient method"to evaluate the fatigue life of notched components,this paper comprehensively consider the effects of shot peening on the surface integrity of materials such as residual stress,work hardening and surface roughness.The local fatigue strength prediction method of shot peening specimens for 40Cr steel notched components was corrected.Finally,the predicted values showed a good correspondence with the experimental data,and the average error was within±5%.This provides a new method for predicting the fatigue life of notched components after shot peening.