Size effect in contact compression of nano- and microscale pyramid structures

Micromechanics of friction: effects of nanometre-scale roughness

“…If we consider the hydration effect of the possible potassium ion adsorption, the repulsive pressure required to squeeze out the last monolayer of water does not exceed 20 MPa (Pashley & Israelachvili 1984;Homola et al 1990). In contrast, the local contact pressures of both N-PSA and M-PSA are believed to reach more than 2.5 GPa during the friction test to cause plastic deformation of the asperities (Wang et al 2006). Therefore, the condensed water layer is expected to be squeezed out to form water meniscuses around the contact junction as the gold asperities contact the mica surface.…”

“…It was reported that (Carpick et al 1996b) a platinum tip could only be blunted to form a circular plateau up to 9-10 nm in radius under a high load of 1000 nN, which corresponded to an average pressure of 3.1-3.9 GPa. Wang et al (2006) measured the flattening pressure of a truncated (114) facet gold pyramid asperity experimentally as 2.5 GPa for a contact area of 54 nm equivalent radius. The MD simulation by Ward (2007) also predicted the flattening pressure of a truncated gold pyramid asperity as approximately 3.5 GPa for an equivalent contact radius of 19 nm.…”

“…In most of the theoretical models (Chang et al 1988;Chowdhury & Ghosh 1994), macroscopic plasticity was adopted for the analysis of asperity deformation. However, it has been recognized that the mechanical properties of materials are strongly size-scale dependent (Wang et al 2006;Ward 2007) and the classical continuum plasticity may not be applicable for nano-asperity contacts.…”

Multi-asperity contact: A comparison between discrete dislocation and crystal plasticity predictions

“…The deformed surface deviates from classical plasticity predictions, especially under dry contact loading. The extent to which the deviation from the predictions of conventional continuum plasticity can be attributed to the size dependent response of single asperities, as in [9], or to asperity interactions remains to be determined. On the other hand, the relevance of asperity interactions in forming contact is widely recognized and has been recently emphasized, among others, by Zhao and Chang [11] and Ciavarella [12].…”

“…These predictions are based on classical plasticity theory, and so neglect any additional strengthening due to indentation size effects. Size effects for isolated contacts have been extensively studied both computationally [1][2][3] and experimentally [8,9]. Kim and co-workers have recently undertaken experimental studies on the evolution of multiasperity contact [10].…”