Study On 3D Elasto-plastic Rolling/sliding Contact Problems

Rolling and sliding contact is a common phenomenon in various power and motion transmissions, which widely exists in the processes of gearing, bearing rotation, and rail-wheel contact. During repeated rolling or/and sliding, plastic deformation may occur in the materials of mechanical transmission components, which may affect the surface contact fatigue life and thus influence the security and reliability of the mechanical system.The work reported in this thesis is a portion of the research in the projects from the State Key Laboratory of Mechanical Transmission of Chongqing University, titled “Interfacial Mechanics for Mechanical Transmission Components” and “Typical Transmission Contact Failure and Evidence of Material Variation”, targeting at the contact stress and strain distributions in three-dimensional(3D) elasto-plastic rolling/sliding contact problems. The research starts form fundamental modeling of typical elasto-plastic contact problem, and extends to the interactions of deep-groove ball bearing components under radial load, and to the contact involving heat-treated steels. The research aims to provide analysis tools for exploring the relationship between stresses and strains and rolling contact fatigue lives of typical steels and for supporting the future design of mechanical transmission parts with long service life.Firstly, an elasto-plastic point contact problem of engineering surfaces is studied. The modification of stainless 304 steel surface morphology under the repeated loading is measured, and the results used to verify the contact model. The comparisons show that the model can reasonably well simulate the rough surface contact problems and reproduce the pressure and stress fields under asperities, as well as the corresponding surface/subsurface plastic strains.The contacts between balls and rings of a deep-groove ball bearing can be simplified to elliptical contact problems. The elliptical contact version of the model is implemented to study the maximum elastic approach, stress and strain distributions. The results show that compared with the simplified formula, the model can better handle the static contact problem of bearings under radial loading. Changes in ellipticity can greatly affect the rigid body approach of the rolling elements.Then, the rolling/sliding elliptical contact model is used to investigate the variations of the stress and strain fields caused by interfacial friction. Moreover, rolling contact model is applied to explore the influence of hardness grades caused by heat treatment on the rolling contact fatigue life of heat-treated steels. The results show that friction causes changes in strains and plastic flows opposite to the sliding direction, which accelerates the material to reach the shakedown characteristic. The hardness gradient can make the location of the maximum of residual von Mises stress closer to the surface. Moreover, the rolling contact fatigue life is much longer with higher hardness at the location of the maximum von Mises stress.