Frictional heating of tribological contacts

Wherever friction occurs, mechanical energy is transformed into heat. The tem­ perature rise associated with this heating can have an important influence on the tribological behaviour of the contacting components. Apart from determining per­ formance, thermal phenomena affect reliability and may cause failure of the con­tact. In the first part of this thesis the emphasis will be on the numerical calculation of the contact temperature given a heat source distribution, e.g. by means of a measured coefficient of friction. In order to calculate this contact temperature, a multilevel algorithm has been derived which allows for a non-uniform division of the heat generated in the contact and different bulk temperatures. Simulations for elliptic heat sources with uniform and semi-ellipsoidal distribu­ tions, which are of specific importance for contacts operating under conditions of dry and boundary lubrication, have resulted in accurate function fits for the average and maximum contact temperature. These function fits are based on asymptotic solutions for small and large Peclet numbers and are valid for arbitrary Peclet numbers. The function fits enable simple treatment of tribological contacts as part of a thermal network. The second part of this thesis deals with the EHL-line contact problem. First a model, which allows for Non-Newtonian lubricant behaviour and thermal effects, is described. For this model a multilevel algorithm is developed. The algorithm has been applied to a moderately loaded case, using a simplified energy equation. For this case, results show a significant decrease in minimum film thickness for increasing slip. Finally this thesis is concluded with some recommendations for future research.

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