Study On Effects Of Residual Stress On Contact Properties Of Parts In Pre-Stressed Hardening Grinding

Rolling contact fatigue failure is one of the main forms of fatigue failure.In industrial applications,many parts are failed due to rolling contact fatigue,such as rolling bearings,ball screws,gears,rails,rollers,etc.Surface damage of the parts caused by rolling contact fatigue,such as pitting and peeling of rolling bearings and gears makes the mechanical equipment running unnormal or even producing serious accidents.During the manufacture of mechanical parts,different processing technologies produce different surface integrity indexes such as hardness,residual stress and surface roughness in the surface of the parts.Numerous literatures indicate that the residual stress have a big impact on the contact properties of the parts surface.So in this paper,the effect of residual stress on rolling contact fatigue crack initiation life and rolling contact fatigue crack growth life is studied by applying the multi-axial fatigue damage criterion and the crack tip stress intensity factor,respectively.Pre-stressed hardening grinding or PSHG for short which is a combined machining,can not only produce strengthened layer on the parts surface,but also control the residual stress of the parts surface at the same time.In this paper,the rolling contact fatigue properties of the surface of parts in PSHG new technology are studied in detail,the specific research work is as follows:Firstly,this paper introduces the background and significance of this research,the research status of contact fatigue and the advantages of PSHG machining which provide experimental and theoretical basis for studying the effect of residual stress on the rolling contact fatigue properties of parts surface in PSHG process.Secondly,the rolling contact fatigue experiment plan is designed,then,obtaitning the experiment specimens with different residual stress as the main variable.The rolling contact fatigue experiment is carried out on the rolling contact fatigue testing machine,and then,comparing surface fatigue damage of the experiment specimens by the scanning electron microscopy observation,analyzing the effects of residual stress on rolling contact fatigue properties of PSHG parts surface.Thirdly,based on the rolling contact fatigue crack initiation theories,the finite element model of rolling contact fatigue crack initiation is established and simulated with different residual stress as the control variable,then obtaining the stress and strain data of each specimen during rolling contact.The theoretical results of the rolling contact fatigue crack initiation life are obtained by calculating the stress and strain data,and using the theoritical results to analy the effects of residual stress on the rolling contact fatigue crack initiation life of PSHG parts surface.Fourthly,combining the finite element simulation method and theoretical analysis method,and using this combined method to obtain the crack tips stress intensity factor and to calculate the crack propagation rate and simulate the crack propagation process.In the end,using the simulated results to analy the effects of residual stress on the rolling contact fatigue crack propagation life of PSHG parts surface.Finally,the effect of residual stress on the crack initiation and propagation is analyzed based on the both experimental and theoretical studies for a further study.The results show that PSHG process can effectively control the residual stress of parts surface to improve the surface rolling contact fatigue properties.The residual stress in the specimens,surface is redistributed and finally tends to be stable residual compressive stress after a few cycles of rolling contact stress.The initial residual compressive stress can increase the value of the ultimately stable residual compressive stress compared with the initial residual tensile stress.The initial residual compressive stress reduces the crack initiation life of the specimens compared with the initial residual tensile stress.The greater the residual compressive stress value is after stabilization,the more favorable to weaken the crack propagation rate.