An EFG-FE Coupling Method For Macro-Micro Thermal Elasto-Plastic Contact Of Rough Surfaces

Analyzing the contact performance between two surfaces plays a key role in studyingriction, wear, and lubrication in tribological system. The goal of this dissertation is to(?)evelop macro-micro numerical models for understanding contact mechanics characteristicsvith some complicated factors such as surface topography of real rough surfaces,elasto-plastic behaviors, frictional heating, surface effects on micro-scale, etc., with the(?)ssistance of the newly developed numerical methods, called meshfree methods or meshlessnethods, which are regarded to be a potential, flexible and versatile numerical technique in(?)ecent years. It is anticipated that the research results will develop a better understanding andnew methods for macro-micro scale contact mechanics, and advance the state-of-the-art ofmechanical design of engineering systems.Main procedures of meshfree methods are reviewed and discussed. The element-freeGalerkin (EFG) method which is based on the moving least-square approximation is studied.Some numerical examples are carried out by using the EFG method to investigate theimposition of essential boundary conditions by Lagrange multipliers and the influences ofchanging data of weight functions. An element-free Garlerkin-finite element (EFG-FE)coupling method is then presented and implemented.The EFG-FE coupling method, combined with the linear mathematical programmingtechnique, is used to solve two-dimensional elasto-plastic contact problems of rough surfaces.The effects of a few key factors of the meshfree methods, such as the number of Gaussintegration points and parameters that determine the weight function, on the precision ofcontact solutions are investigated. The results indicate that the meshfree methods can moreeasily follow plastic deformations than the finite element method and are more suitable forexpressing plastic flows in the elasto-plastic contact simulations.An adaptive-surface elasto-plaStic asperity contact model is presented in this paper. Sucha model is developed in order to reduce the computing time by removing the surface nodesthat have little influence on the contact behavior of rough surfaces. The effects of differentthresholds on the contact pressure distributions, real contact areas, and the elasto-plastic stress fields in the contacting bodies are investigated and discussed.A thermal elasto-plastic contact model which can consider the effects of temperature-dependent yield strength is developed to investigate the influences of the steady-statefrictional heating on the contact performance of surface asperities and subsurface stress fieldsbetween two contacting bodies. The model is verified through the contact analysis of a rigid,isolated cylinder with a thermal elasto-plastic plane. The results show that the contactpressures of elasto-plastic contact with considering the frictional tractions are no longersymmetric. By comparing the results obtained from the EFG-FE coupling method with thatfrom FEM, it reveals that the contact pressures solved by FEM would be oscillatory if the FEmeshs are produced unsuitably, while this phenomenon will be avoided by using the meshfi'eemethods. Furthermore, the thermal effects on the contact pressure, real area of contact, andaverage gap of real rough surface with different frictional heat inputs under the thermalelasto-plastic contact conditions are studied.A microscale adhesive contact model based on the EFG-FE coupling method is presented.The model is first validated through comparison with theoretical solutions. A numericalsimulation of the adhesive contact between a micro elastic cylinder and a rigid half-space isthen conducted. The adhesive contact characteristics of three metals (Al, Cu and Fe) arestudied at different Tabor parameters. The relationships of the applied load and contact halfwidth of the adhesive contacts are analyzed. Contact pressures, stress contours and deformedprofiles of different cylinder sizes and applied loads are illustrated and discussed. The resultsare compared with published solutions, and good agreements are observed.Finally, some conclusions and observations are given and recent development tendenciesof advanced contact mechanics are discussed and outlined.