Study On The Effect Of Thermodynamic Characteristics Of Moving Contact On Friction And Wear

With the rapid development of science and technology, energy consumption, material loss and environmental pollution are still to be faced all over the world. The friction and wear performance of friction pair is not the natural characteristic of the material itself, but a real-time process which is affected by various factors. This paper uses theoretical derivation and numerical simulation to study the variation laws of contact force, temperature and the total heat coduction of friction pair during the sliding process based on thermodynamic characristics of moving contact. The main research contents and conclusions are as follows:The classical eigenfuction method for the solution of contact problems involving wear is formulated in the context of the finitie element method. Static reduction is used to reduce the full stiffness matrix to the reduced contact stiffness matrix by eliminating the internal degrees of freedom. Based on Archard wear law, a general solution to the transient problem can be written as an eigenfuction series, which defines an extremely efficient method for tracking the changes in contact pressure due to wear from running-in stage to normal wear stage in sliding systems.On the base of the statistical characteristics of the rough suface, the transient contact interaction of asperities on the opposing sliding surfaces and heat conduction problem are discussed from the micro thermodynamic point of view. Greenwood and Williamson model is developed to a transient model of sliding thermal contact to predict the average heat flux between two bodies at different temperatures and the mean normal contact pressure as functions of the separation between reference planes in the two surfaces. Meanwhile, it is found that the effective thermal conductance is an approximately linear function of nominal contact pressure, but it also increases with the square root of the sliding speed and decreases with the 3/4 power of the combined RMS roughness. The results can be used to define an effective thermal contact resistance and division of frictional heat in macroscale(e.g., finite element) models of engineering components, requiring as input only the measured roughness and material properties.Theoretical reaserach on the flash temperature shows that the flash temperature resulting from a single asperity contact has a monotonic relationship with the maximum interference. It increses firstly and then decreases with the increasement of the contact time. The maximum value appears at the moment when the contact time is about 82.5% of the total contact time. The average flash temperature increases modestly with increase in nominal pressure, but the dependence is very weak. Finite element results are also presented for the total heat exchange and the flash temperature between two asperities on opposing sliding rough surfaces during a single transient interaction. Dimensional analysis shows that the results can be expressed as functions of a single dimensionless parameter, the asperity Peclet number. At high Peclet number, the dimentionless total heat flux is positively related to1 2Pe?, and the dimentionless flash temperature is proportional to1 2Pe. While at very low Peclet number, the dimentionless total heat flux is inversely proportional to Pe and the dimentionless flash temperature increases proportion to Pe. Eventually, functions of dimentionless total heat flux and the dimentionless flash temperature for the whole range of Peclect numbr are obtained.Finite element models are presented for the influence of the reciprocal motion on the macro heat conduction due to temperature difference. Through secondary development of ABAQUS finite element software, the thermal contact conductance is defined as a function of the sliding speed, the local contact pressure, material propertities and the surface roughness. The effect laws of the three dimentionless parameters which are ?(the ratio of the magnitude of the sliding distance and the length of the upper block), ?(the dimentionless frequency) and ?(comprises of the material properties of the sliding pair, the surface roughness parameters and the local contact pressure) on the dimentionless mean normal heat flux have been researched. The results lay the foundation for the engineering research on the sliding contact heat conduction problem of piston ring-cylinder linear in internal-combustion engine.