Stress Analysis Of The Coating Rolling Bearing

In the process of plasma spraying super-hard coating bearing, thermal deformation will arise because of the different thermal expansion coefficient between the substrate and the coating, if the thermal deformation is restricted, thermal residual stress will come into being,and if the stress exceeds the bounding strength of the coating/substrate, the coating would been desquamated, and then the coating will no longer be working, The behave of the coating will change after being modified, And when it is being pressured, the stress between the coating and the substrate will change a lot. Crack will appear as a result of the contacting stress.In this thesis, on the basis of the rolling bearing, the stress field of the subsurface on hard coating ball bearing is studied. The distribution of static stress, Von Mises stress on subsurface and interface bonding of coating/substrate system was analyzed which can be helpful to the design of coating bearing. provide a theoretical basis for analyzing the characteristics and the failure mechanisms for the substrate/coating system during the preparation and the application. The main contend of the thesis is as follows:1. The binding mode of plasma spraying is elucidated, the goal of coating process ,the present situation and prospects both at home and abroad, the application fields and the work that should be done are introduced.2. Expatiate the basic theory of finite element analysis and the method of solving heat conduction problem and contacting problem and introduce the basic function of ANSYS briefly.3. Elucidate the theory of heat exchange and convection, make the coating plasma spraying as research object, simulate the residual stress from the point of spraying to the time of cooling to room temperature,analyze the distribution of the stress in different condition.the results of thermal stress and the cooling time based on finite element method (FEM) and the solutions of classical thermal are compared to provide the prove the accuracy of FEM mode.To make the physical parameters such as thermal expansion coefficient between the coating and the substrate change smoothly and a undercoating layer and two intermediate layers are added to form a gradient coating. The process of spraying is simulated by the technology of birth and death element and then the process of cooling is analyzed with the transient thermal analysis method.The influence factors of thermal stress is analyzed by different physical parameters,cooling condition and the preheat temperature. The conclusions are:the material of the substrate have great influence to the residual stress. The maximal thermal residual stress appeared between the substrate layer and the intermediate layer,the original stress that formed at the first stage is smaller with the smaller linear expanding coefficient,accordingly,the residual stress is smaller, the thermal residual stress is accordingly smaller,which has advantages to the coasting/substrate system.; It can reduce the discrepancy and relax the stress concentration between the substrate and the coasting by using the multi-layer or gradient coating,and hence the bond situation will be meliorated;The stronger of the convection coefficient, the faster cooling speed of the coasting/substrate system,then a sharper temperature gradient will be formed,which will lead to the greater residual stresses and disadvantageous to the spraying,so rapid cooling is inadvisable; The preheat temperature has great influence to the residual stresses, And there is a relative better preheat temperature extent, in which the residual stress and the range of the saltation are both less than others. The theoretical calculation can provide a reference to choice the preheat temperature in the process of the coating.4.Using the software"ANSYS"as the tool,and using the thrust ball bearing 6408 as object of the research,the distribution of elastic the strain and the stress field of rolling contact with super-hard material has been analyzed based on classic theories of Hertz contacting bearings.Introduced the analytical model of the bearing from Pro/e base on the spatial ax symmetrical structure.In the case of the same restriction and loading.Subject to the result of the contact width and the von mises based on the classical contact calculation and finite element method,The rationality of finite element has been demonstrated.The thickness of the coating is correspondingly thinner compared with the substrate, and there is a problem of disproportion of the thickness. While analyzing the system of the coating and the substrate,a moderate shell element (181) is added to the outer loop of the bearing using the shell technology. Using the contact guide, a surface-surface contacting pair of the outer loop of and the rolling base is constituted by the contact element (174) and target element (170).To the stress field of the super-hard rolling contact bearing, the effect of the elastic modulus and the thickness of the substrate are analyzed. The conclusions are as follows:if the thickness ratio of the substrate and the coating is less than 0.1,the maximum shear stress appeared on the substrate,and the stress decrease with the thickness ratio,however,the maximum shear stress occurred on the surface of the coating and increase with the thickness ratio when the ratio more than 0.1; Since the shear stress high concentrate around the field of the contact point, the position of the maximum shear stress that under the contact point is not changed,but the valve of the stress decrease with along with the elastic modulus, meanwhile,the von mises and shear stress at the interface between substrate and coating have the same trend. The above conclusions show us that it can improve the mechanical characteristics and influence the mechanical behavior of rolling contact by spraying one or more layers of super-hard materials on the substrate.