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.

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The uncertainty of wear volumes measured using surface scanning techniques is often neglected or assumed to be equivalent to the instrument error. A method is proposed that accounts for the number of wear volume scans, the variations in those scans, and the geometry of the experimental system as an improved measure of uncertainty. It demonstrates that the uncertainty in volume is directly correlated to the number of scans taken. A nonuniform wear track was used to validate the method, and the minimal and optimal number of scans was found.

Multifunctional tribological coatings rely on combinations of materials to improve properties, such as lubricity and wear resistance. For example, some polymer composites exhibit favorable tribological performance as solid lubricants. Here, classical molecular dynamics simulations are used to investigate the tribological behaviors of a mixed system of polyethylene (PE) sliding over polytetrafluoroethylene (PTFE) with the results compared with the sliding of the relevant homogeneous systems. In particular, oriented cross-linked PTFE and PE surfaces are slid in several relative sliding directions such that the surface chains are in-registry or out-of-registry and at various applied normal loads. The simulation results quantify the ways in which the mixed PTFE-PE system behaves differently than either of the homogeneous systems due to the lack of interlocking phases at the interface. These findings are compared with experimental production of polyetheretherketone (PEEK)-PTFE composites that have unusually low wear rates of 7.0 9 10 -8 mm 3 /Nm, coupled with a steady, low friction coefficient of l = 0.11 for over two million sliding cycles. The simulation results explain the atomic-scale origins of the frictional properties of this composite.