Friction, lubrication, and wear have a strong influence on the performance and behavior of mechanical systems. This paper deals with different friction models for sliding contacts running under different conditions. The models presented are suited to different situations, depending on the type of contact, running conditions, and the behavior of interest. The models will be discussed from simulation and tribological points of view. The different types of friction models considered are:

center dot friction models for transient sliding under dry, boundary and mixed lubrication conditions,

center dot friction models for micro-displacements of engineering surfaces subjected to transient sliding,

center dot friction models often used in the simulation and control of technical systems,

center dot combined friction models that represent physical behaviors fairly well but are also suitable for use in simulating systems,

center dot friction models that take into account the stochastic nature of interacting surface asperities

This paper investigates how a model for boundary lubricated rolling and sliding contacts can be integrated in a dynamic rigid body model of a mechanical system in order to improve the accuracy of simulations of system behavior. The system modeled is test equipment for the measurement of transient friction in rolling sliding contact between two discs. Two different models of the system were constructed: one neglecting the rolling and sliding contact and the other integrating it in the system model. In the integrated contact model, the pressure distribution was computed using an elastic foundation model. A brush model was used for the friction calculation. Simulations were performed with both models and validated by experiments. The results show that the contact needs to be included in the model in order to capture the behavior of the system. Since the contact model used can handle both microslip and gross slip, it is applicable to a wide range of contact conditions.

Thefriction and wear of rolling and sliding contacts are criticalfactors for the operation of machine elements such as bearings,gears, and cam mechanisms. In precision machines, for example, themain concern is to compensate for frictional losses, so asto improve control accuracy. In other applications it is oftendesirable to minimize friction losses to improve efficiency, though sometimeshigh friction is desired to prevent sliding and wear. Theaim of this study is to simulate the behavior ofa test equipment and show that simulations can be usedto study and optimize mechanical systems that include rolling andsliding contact. Simulations can be used to study the systemas a whole, as well as the contact conditions. Thetest equipment and the measurement procedure used are described. Inthe simulations, a contact model designed to handle transient contactconditions is integrated into a system model. The results showthat the contact strongly influences the system. The simulations showthat the use of a contact model allows the simulationof systems that contain contacts with different amounts of slip,and that such simulations can be used to study thecontact as well as the system. Surface roughness influences thecontact stiffness and is included in the simulations.