Study On Cyclic Deformation And Fatigue Failure Mechanism Of G20CrNi2MoA Bearing Alloy Steel

When the bearing is running under high speed and heavy load conditions,sometimes an overload condition occurs.In this case,the asymmetric cyclic stress will lead to the accumulation of local plastic deformation in rolling contact area.Ratcheting effect occurs resulting in premature fatigue failure of bearings.Therefore,it is necessary to consider the failure behavior of the bearing material under overload conditions when analyzing the failure of the bearing.At present,the research on cyclic deformation and fatigue failure behavior of bearing steel materials are insufficient,and the analysis of failure behavior under overload condition is still to be improved.Therefore,it is necessary to take bearing alloy steel G20CrNi2 MoA,the main material of high-speed train bearings as the research object.The ratcheting behavior evolution law of this material under axial,torsional and non-proportional multi-axis loading paths is studied,and a reasonable multi-axis cyclic constitutive model to describe its deformation response is built;The low-cycle fatigue behavior research of this material are carried out and its fatigue under different working conditions is predicted.The research work on bearing alloy steel G20CrNi2 MoA is as follows:(1)The cyclic experiments of uniaxial and non-proportional multiaxial stress loading were carried out.The ratcheting evolution behavior of materials under different working conditions was studied.The effects of average stress,peak stress and non-proportional loading path on peak-valley strain were summarized.At the same time,the difference of ratchet evolution behavior between axial and torsional directions is discussed.(2)A constitutive model for predicting cyclic deformation behavior of G20CrNi2 MoA bearing alloy steel was developed based on the elastoplasticity constitutive theory combining the isotropic hardening law and Ohno-Wang II kinematic hardening law.The threshold stress is proposed to modify the isotropic resistance saturation value so that the ratchet evolution of bearing alloy steel can be more accurately described by the model.At the same time,the model is used to simulate the nonproportional multi-axis path of materials.(3)The low cycle fatigue failure behavior of bearing alloy steel G20CrNi2 MoA was studied.The cyclic softening/hardening properties of materials and the relationship between fatigue life,average stress and peak stress were discussed.Three common models are used to predict the low cycle fatigue life of materials.A modified fatigue strength index is proposed to establish a modified model of G20CrNi2 MoA bearing alloy steel based on Manson-Coffin model.Meanwhile,the average and standard deviation of each fatigue model error are compared to improve the prediction accuracy of the traditional fatigue model of bearing alloy steel for this material.