Criteria of plasticity in contact of the spherical asperities of the rough surface

It is assumed that the influence of the remaining contacting asperities is equal to the action of the uniform loading qc outside the asperity contour. Three parameters are suggested as possible criteria of occurrence of plastic deformation in the subsurface layer of contact of a single asperity: critical value εc in which the equivalent stress is equal to the yield point σy; the relative contact area ηip at which plastic deformations occur; the ratio of the maximum pressure at the contact area to the yield point σy. For single asperities, the stability of the relative contact area at which plastic deformation begins is indicated. The criteria for plasticity characterizing respectively the onset of plastic deformation in the near-surface layer ηp ∗ and on the contact surface η̅p ∗ are proposed. The values of the criteria do not depend on the loading conditions and are determined by the complex parameter fy characterizing the microgeometry of the asperities and the mechanical properties of the material.