In situ investigation of the contact area in elastic–plastic spherical contact during loading–unloading

Abstract

The real contact area between a sphere and a flat during loading, unloading, and cyclic loading-unloading in the elastic-plastic regime of deformations was investigated experimentally. A direct optical technique was used to observe in situ the evolution of the contact area. The experimental results obtained with copper and stainless steel spheres of different diameters that were pressed against a sapphire flat were compared with existing theoretical models, and whenever possible, with previous experimental works. These models are based on the assumption of either perfect slip (i.e., frictionless) or full stick contact condition. Good agreement was found between the experimental and theoretical results for the contact area and mean contact pressure. The existing models for the unloading process fail to accurately predict the residual radius of curvature of fully unloaded spheres, and the irreversibility of multiple loading unloading cycles at least for the several initial cycles. Some recommendations to improve the models are provided.

Experimental Investigation of a Hemisphere Contact with a Hard Flat

“…The results of those tests are not presented in this paper due to technical problems with obtaining constant values of hemispheres radii. Ovcharenko et al [22] obtained similar value of the ratio p/H (0.8) during normal loading of steel spheres with different diameters against the sapphire flat.…”

“…However Tabor used a hard indenter against a deformable plane, contrary to the present experiment and works [19,25], where a deformable sphere was pressed against a hard flat -in this case according to Jamari and Schipper [19] the displaced material of the sphere could expand radially in the contact edge. Kogut and Jackson [22] think that in the contact of a hard sphere with a deformable half-space, different models than JG, KE and SM should be used, for instance model described in paper [23]. It seems that the contact area resulted from truncation of the sphere by the hard flat -similar to AF model [2].…”

“…Steel balls co-acted with steel flat. Diameters of balls were comparatively large (40-100 mm), normal loads were in the range 2000-10000 N. Ovcharenko et al [22] measured contact area in-situ through a microscope. Steel and copper spheres were loaded against the hard sapphire flat.…”

A comparison of stick and slip contact conditions for a coated sphere compressed by a rigid flat

“…The results, presented in Refs. [19,23], were experimentally verified by Overcharenko et al [24]. Goltsberg et al [25] investigated the plastic yield inception of a coated sphere pressed by a rigid flat under the slip contact condition.…”

In-situ Observations of a Multi-Asperity Real Contact Area on a Submicron Scale

“…Several attempts to experimentally analyse a real contact area with an optical method have been reported [32] to [36]. The vast majority of research has involved the contact between an ideally smooth, rigid flat and a ball, which simulates a single asperity peak [29], [35], [37] and [38].…”