Dynamics of dry sliding contact: Interface forces and surface topography

In engineering, contact between surfaces is the principal method of transforming the movements and stresses generated by motors to the moving parts of mechanisms. Surfaces of machined parts are not perfectly smooth. Their roughness or waviness may induce additional dynamic loading of the interface, along with that from moving machinery components. High dynamic contact forces can affect the entire system behavior, thus requiring a comprehensive characterization of the effects of surface topography on system dynamics.; The first part of this research begins with a review of the previous work related to the modeling of friction in a dynamic system. Then it describes a numerical study of friction between two rough but flat surfaces that steadily or quasi-statically slide over each other. In the contact model used, friction results from forces developed during elastic deformation and shear resistance of adhesive junctions at the contact areas. Contacts occur between asperities and have arbitrary orientations with respect to the surfaces. The proposed method, when applied to the classical problem of a sphere on a half-space as a benchmark, showed good agreement with previous results. Calculations show how friction changes with surface roughness and also demonstrate the method's efficiency.; In the case of contact between two rough and wavy surfaces, the surface waviness leads to a non-uniform spatial distribution of true contacts over the interface. True contacts on wavy surfaces occur only at and near the wave crests. A need to consider both surface waviness and roughness makes it unfeasible to solve contact problems with large number of asperity contacts. The second part of the thesis presents a computational method for the analysis of contact between two rough wavy surfaces for which the nominal contact area may be arbitrarily large. Using a multi-level substructuring technique, the method efficiently handles the complexities associated with modeling both surface waviness and roughness. Numerical simulations using this method yield estimates of the total true contact area and the contact approach values that agree well with the results reported earlier.; In the last part of this research, a computational method is developed to analyze the dynamics of sliding contact between two elastic solids by relating interfacial forces to surface roughness, material properties, and external loads. The analytical model used here takes into consideration both the dynamics of a system and the constitutive properties of the sliding interface. These interface properties are determined by numerically solving for steady sliding contact of surfaces based on the profilometric data about their roughness. The relationships between contact deformation and interfacial forces needed for the simulation of system dynamics are obtained by performing the quasi-static analysis for a range of external loads. As an improvement to conventional models, the predicted random changes of contact parameters during sliding are the primary source of roughness-induced excitation of system dynamics. The numerical results from the model are validated experimentally. They show how surface roughness affects sliding system dynamics suggesting the usefulness of the present method in developing design guidelines to control friction-induced vibration and sounds.