Effects of fiber type on the tribological behavior of polyamide composites

An experimental and analytical study of the tribological behavior of polymer composites is presented. Glass, aramid, and carbon fiber-filled polyamide (Nylon 6,6) composites serve as models for understanding friction and wear processes encountered when polymer composites are used in tribological applications. Experimental results not only include measurements of friction and wear, but surface temperatures produced by frictional processes during oscillating contact experiments. Since an optically flat, transparent sapphire disk is used as the oscillating countersurface, surface temperatures can be measured directly at the interface using an infrared microscope.

Experimental results show that the presence of fibers in the polyamide matrix lowers wear, friction, and surface temperature when compared with the unfilled polymer. Rationale for this improved tribological behavior is presented and discussed. Fiber-type is shown to have a direct influence on the tribological behavior of the polymer composite, and the chemical behavior at and near the interface is shown to be significant by examining worn and transferred material through surface analytical techniques. In particular, evidence is presented for the tribochemical degradation of intramolecular bonds in the polyamide macromolecule.

Measurements of surface temperatures are compared with theoretical predictions using models for the real area(s) of contact, and results from “scanning” experiments are also presented in which the infrared microscope is used to measure surface temperatures at possible real areas of contact within the apparent contact region. Instantaneous measurements of surface temperature and friction over a single cycle of motion are also presented which allows for the performance of a frequency domain analysis. This technique not only shows the frequency content of the friction and surface temperature signals, but it also shows correlations between these two parameters. The role of intermolecular attractions in frictional processes is addressed, and evidence for relatively strong intermolecular attractions between the polyamide surface and sapphire disk is discussed.