A Statistical Model For Torsional Friction Of Plate-on-plate Contact

The asperity scale friction model was developed by applicating the friction and contact theory of two contact speres to study the contact and friction behavior of two contact asperities. The effect of interaction between nearby asperities has been considered in this asperity scale model. Then the character of the rough surface was characterized through the probability method, and the sliding mechanism was defined by the asperities’ height and tangential displacement, and the asperity scale friction model was extended to the macroscopic scale friction model of rough surfaces contact by statistical method. In order to make the reciprocating moving friction model siutable for torsion contact, the torsional contact area was divided into small circulars, and the torsional friction model was developed by statistical method. With the torsional friction model, the torsional friction behavior of MC nylon-45# steel and the efffect of normal pressure, roughness and nrominal contact area on torsional friction behavior were studied. At last, the prediction veracity of the torsional friction model was verified used the self-made torsional friction test of plate on plate contact. The main conclusions were listed as follows:1 The asperity scale friction model developed with the BKE contact model can adapt to biger normal deformation than CEB and KE model,so has better applicability.2 Reciprocating distances have important influence on the shape of F-δ curves. But it has little influence on initial location where gross slip occured. Roughness has no influence on the shape of F-δ curves and the initial location where gross slip occured. The friction force increase rapidly as the decrease of the roughness(less than Ra1.6), when the roughness increases(larger than Ra1.6), the friction force has an increase tendency. The normal force has no influence on on the shape of F-δ curves and the initial location where gross slip occured. But the maximum friction force linear increases with the increase of normal force.3 The inputting parameters of the torsional friction model were mechanical properties, roughness parameters, angular displacement, and its outputs were T-θ curves. The slip ratio of contact asperities and gross slip radius under different angular displacement can be computed use the judgement formula of asperities sliding state and the probability density function of asperities height.4 When contact radius increased, the maximum torque reflected a linear increase. As the nrominal contact area increased, the gross slip radius and the slip ratio ofo the contact asperities increased. When surface roughness was little than Ra1.6, the maximum torque increased quickly with the decrease of surfece roughness. When the sueface roughness was lager than Ra1.6, the maximum torque reflected an increase trend. When contact pressure increased, the maximum torque also reflected a linear increase.