Influence of friction and adhesion on the onset of plasticity during normal loading of spherical contacts
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abstract
Increasing contact loading causes early transformation from elastic to elastic-plastic deformations in many conventional systems as well as micro/nano-electro-mechanical systems. The load required for yielding and the location of the onset of plasticity is critical in the robustness of systems with contacts. For frictionless (such as fully-lubricated) contacts, inception of plastic yielding occurs beneath the contact surface. However, frictional slip (contact shear) and adhesion push the inception of plastic yielding toward the contact surface. The influence of elastic mismatch, shear tractions and adhesive normal tractions on the subsurface stress field is studied analytically by superposition of the Hertzian stress field and the stress field created by the shear and additional (due to adhesion) normal tractions. Specifically, three contact conditions have been studied in this work: (i) frictionless, (ii) finite friction, and (iii) infinite friction (full stick). Also, a finite-element model is developed to verify certain assumptions in the analytical solution for the contact with finite friction. The results obtained are applied to two sets of in situ nanoindentation experiments to explain the change in the yielding behavior of submicrometer polycrystalline aluminum grains. 2012 Elsevier Ltd. All rights reserved.
