Optical In Situ Micro Tribometer for Analysis of Real Contact Area for Contact Mechanics, Adhesion, and Sliding Experiments

Abstract

An instrument has been developed that allows in situ optical analysis and tribological measurements for contacts between solid bodies; an interferometric optical analysis can be used to measure and observe contact size, contact geometry, near contact topography, tribofilm formation, tribofilm motion, tribofilm thickness, wear debris formation, and wear debris morphology. The optical arrangement is in such a way that a 0th order interference fringe highlights the real contact area of contact, while near contact regions are height-mapped with higher order Newton's rings interference fringes. Images synchronized with force and position measurements allow for the potential to test and validate models for contact mechanics, adhesion, and sliding. The contact and friction measurement between a rough rubber sphere and a polished glass counterface were studied over a range of loads from 1 to 50 mN.

Experimental Investigation of a Hemisphere Contact with a Hard 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].…”

“…The normal load was restricted to 200 N. Diameters of steel and hard spheres were 2.38 -4.76 mm, and 5-15 mm, respectively. Similar stand was presented in paper [23]. The normal load was limited to 2 N.…”

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

“…If a threshold was applied to the obtained unprocessed image, fringes surrounding the actual contacts would produce false contacts, which would result in an overestimated contact area. To reduce this error and assess the actual contact area, each image was post-processed with the image-processing technique introduced by Krick et al [29]. In Fig.…”

“…In the literature [22] to [31] several experimental techniques are described for real-contact-area measurements. Probably the most practical in-situ methods for real-contact-area measurements are based on the electrical [24] and thermal [25] contact resistance, as well as ultrasonic [26] and [27] and optical [28] and [29] principles. However, the most common technique for a realcontact-area measurement is the optical method, the only critical limitation of which is the transparency of one of the contacting bodies so the light can pass through into the contact.…”

“…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].…”