Study On The Contact Fatigue Properties Of RV Reducer Crankshaft Considering Residual Stress And Inclusions

As the core component of industrial robot,the poor accuracy retention of RV Reducer has become the key factor restricting the localization and substitution of RV Reducer.Crankshaft is one of the key parts of RV Reducer.The transmission accuracy and service life of the RV Reducer is severely hindered by failure modes such as pitting and spalling on the eccentric cylindrical surface caused by the long-term high cyclic contact stress between the eccentric cylindrical surface of the crankshaft and the roller bearing.The hardness gradients and residual stress distribution in the surface or subsurface region of the crankshaft associated with machining operations exert an enormous function on the rolling contact fatigue（RCF）of the crankshaft.The material defects represented by inclusions will cause local stress concentration,which is easy to become the source of fatigue cracks and accelerate the fatigue failure rate.Therefore,taking the rolling contact fatigue failure of crankshaft as the research object,this paper studies the stress analysis of crankshaft,the numerical modeling of crankshaft contact fatigue and the influence of residual stress distribution on the risk of contact fatigue failure.The technique presented in this study may provide theoretical support for the anti-fatigue design and manufacture of crankshaft.The main research contents of this paper are as follows:（1）The stress analysis of RV Reducer based on static balance and deformation coordination is studied.According to the structural composition and transmission principle of RV Reducer,the stress conditions of key parts crankshaft and needle roller bearing are obtained.The force analysis of needle roller bearing is carried out separately to obtain the contact load on the bearing rolling body,which provides a mechanical basis for the analysis of contact fatigue characteristics of crankshaft.（2）A contact fatigue calculation model considering mechanical property gradient is established.The residual stress and hardness gradient of crankshaft are mathematically characterized,and the cyclic rolling simulation model of crankshaft is established.Combined with Python script for secondary development,the stress-strain response under cyclic load is calculated quickly.Based on the modified Fatemi society multiaxial fatigue criterion,the effects of initial residual stress,hardness gradient and interface friction coefficient on contact fatigue characteristics are investigated.The results show that considering the initial residual stress,the prediction accuracy of the fatigue life model is improved by 32.7%.（3）The correlation law between residual stress distribution parameters and contact fatigue failure risk is studied.Based on the contact fatigue calculation method and Dan Vang multiaxial fatigue criterion,the influence of shot peening residual stress distribution parameters（surface residual stress,peak residual stress,peak residual stress depth,etc.）on fatigue failure risk is analyzed in detail.A contact fatigue model including inclusions is established to analyze the effects of Al₂O₃ non-metallic inclusions on the surrounding stress field,plastic strain,and fatigue failure risk.The results show that inclusions increase the risk of fatigue failure by23.7%.（4）The rolling contact fatigue test bench is used to carry out the equivalent contact fatigue test of crankshaft.The evolution law of residual stress,surface and subsurface fatigue damage is analyzed.The effect of surface shot peening on contact fatigue performance is studied,and the basic verification of contact fatigue calculation model is carried out.The fatigue failure risk of shot peened specimens is 42.5%lower than that of grinding specimens.In this paper,a contact fatigue calculation method of RV Reducer crankshaft considering residual stress and inclusions is established,and the effects of residual stress,hardness gradient and inclusions on fatigue failure risk are quantitatively analyzed.Based on the rolling contact fatigue experiments,the effects of sliding roll ratio,load and surface shot peening on the fatigue failure mode are studied,which provides a theoretical basis for the anti-fatigue design and manufacture of RV Reducer crankshaft.