Creep Effects in Nanometer-scale Contacts to Viscoelastic Materials: A Status Report

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Abstract
Effects of creep on the behavior of nanometer-scale contacts to viscoelastic materials are described from the viewpoint of the contact mechanics theory developed by Ting. The two most important effects are: (1) The time at which maximum contact area and maximum deformation occur can be delayed substantially from the time of maximum applied load. (2) The deformation at separation is related to the loss tangent. These long-range effects due to creep are distinct from the much shorter-range crack tip effects induced by adhesion at the periphery of the contact and associated with the names Barquins and Maugis. Consideration of relevant time scales reveals that creep effects are expected to dominate in SFM-scale contacts for a wide range of compliant viscoelastic materials. Guidelines for selection of optimal experimental parameters for nanometer-scale studies are presented. The need for a comprehensive theory is emphasized.

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