The Crack Initiation Mechanism Of Inclusion Matrix Under Rolling Contact Fatigue Is Studied Based On Crystal Plasticity

Rolling contact fatigue is an important damage mechanism in bearing failure,where complex periodical deformation occurs in the contact area.Previous researches on rolling contact fatigue of metallic materials were mainly focused on crack initiation,propagation and microstructure transformation caused by rolling contact fatigue.However,classical metal plasticity theory and phenomenological investigations cannot insight into the intrinsic failure mechanism of rolling contact fatigue.On the other hand,crystal plasticity theory establishes a plastic deformation theory with dislocation slip,and has unique advantages in studying the plastic deformation of metallic materials at the grain level.Therefore,in this thesis,under the framework of classical crystal plasticity theory,the current crystal plasticity finite element method looks insight into the crack initiation of a metallic matrix containing inclusions and the formation mechanism of butterfly under rolling contact fatigue,and predicts the failure life of rolling contact fatigue for matrix material containing inclusions.The main work and innovations of this thesis are as follows:1.Voronoi polygons is used to describe the microstructure characteristics of metallic materials.Voronoi polycrystalline finite element models are established in two approaches,and the orientation of polycrystalline models are arranged randomly.2.Taking into account the structural characteristics of body-centered cubic crystals,a flow criterion that considers the effects of decomposed shear stress,isotropic hardening and kinematic hardening is applied in a single slip system.Methods such as the Taylor expansion,Newton Raphson iteration is applied to derive kinematics formula,incremental formula and Jacobian matrix,which provides a theoretical basis for the realization of the crystal plastic model in the finite element.3.The crystal plasticity constitutive model is written into the ABAQUS finite element analysis software by UMAT user subroutine.The results of the uniaxial tensile test and backscattered electron diffraction experiment of Gcr15 bearing steel at room temperature are combined to construct a multi-crystal representative model,and the material parameters are calibrated.The result of the polycrystalline uniaxial tensile finite element model is analyzed and discussed.4.Two-dimensional rolling contact fatigue Voronoi model is constructed,DLOAD and UTRACLOAD user subroutines are used to establish cyclic Hertz contact fatigue load,the damage mechanism is coupled into the crystal plasticity constitutive model,and the Jump in cycles(JIC)algorithm implemented by USDFLD and UEXTERNALDB user subroutines was used to simulate millions of cycles in rolling contact fatigue.5.The mechanical behavior of Gcr15 bearing steel containing non-metallic inclusions under rolling contact fatigue is studied.The results show that due to the crystal orientation difference between the grains,the rolling contact fatigue damage is unevenly accumulated to form a butterfly-shaped white etched area near the inclusion of bearing steel subsurface.Similarly,the anisotropy and randomness of grain orientation lead to the discretization of fatigue life and the change of crack initiation position,thus the fatigue damage is unevenly distributed.The cycles of simulated fatigue life are compared and agree well with the results in literatures.