Elastoplastic contact models for sphere-flat and conforming rough surface applications

The Hertz solution for elastic contact of a sphere on an elastic half-space and the slip line field solutions for a rigid punch indenting a plastic half-space are used as two asymptotes to obtain the composite elastoplastic hardness model for the three regimes of deformation: elastic, elastoplastic and fully plastic. A solution blending technique is employed. The present elastoplastic hardness model is presented in two different forms: (i) explicit model and (ii) implicit model.;The explicit form of the elastoplastic hardness model, based on contact size, incorporated into the existing constriction resistance model, is used to predict experimental measurements of constriction resistance (sphere-flat, in vacuum). A procedure is proposed to calculate the appropriate value of yield/flow stress for a sphere-flat system undergoing elastoplastic deformation. This model predicts thermal constriction resistance data (tool steel, Ni200 and Carbon steel) with an overall RMS difference of 4.5%.;Thermal contact conductance data obtained from isotropic conforming rough surfaces for five different materials: Ni200, SS304, two zirconium alloys and Al6061 are compared with existing elastic and plastic models. This review revealed that the Cooper, Mikic and Yovanovich (CMY) (1969) model to be the most suitable candidate.;An elastoplastic contact conductance model is then proposed which differs from the CMY model in the deformation aspects, i.e., it is based on the present elastoplastic hardness model. This new model moves smoothly from the elastic asymptote to the plastic asymptote through the elastoplastic regime. The comparison of this model with data involves the determination of an appropriate value of elastoplastic hardness, for a particular interface and applied pressure, which is a strong function of surface parameters and a weak function of the applied pressure. This is accomplished through an iterative technique. The technique uses the model to estimate the appropriate value of the mean contact size and the microhardness.;Vickers microhardness variation with indentation size is examined for tool steel (01). Bulk hardness is varied by heat treatment. Microhardness measurements are made at six different indenter loads. The plots of Vickers microhardness versus indentation size were correlated with a simple power law relation: ;The experimental program included surface roughness characterisation, thermal conductivity and thermal contact conductance measurements of ground-lapped interfaces of untreated and heat treated tool steel (01). The type of deformation associated with contact conductance measurements of untreated tool steel was elastoplastic whereas heat treated tool steel underwent fully elastic deformation. It is found that the interface equivalent elastic modulus for tool steel and some previous data are higher than the equivalent bulk elastic modulus. (Abstract shortened by UMI.)...