Tribological Behaviors Of Epoxy Resin And Polyamide 66 Matrix Composites

In recent years, polymers and their nanocomposites are being increasingly used in the field of tribology because of their low frictional coefficient, light weight, high strength, and erosive resistance in comparison with metal. Therefore, more and more researchers spent their emphases on the improvement of the friction and wear properties of polymers and their composites. As an important member of polymer family, epoxy exhibits outstanding mechanical, electrical and adhesive properties and excellent resistance to solvent attack. And it is a kind of thermoset resin used widely. Polyamide is a kind of typical thermoplastic resin and important engineering plastics and has been widely investigated by many researchers. As a result, it possesses not only theoretical significance but important practical value to study the friction and wear properties of epoxy and polyamide matrix composites.For the purposes of improving the tribological properties of epoxy resin and polyamide 66, three kinds of rubber particulates and nano-organoclay were introduced into the resins as modifiers. The following researches were carried out in this dissertation:Firstly, polyoxyalkyleneamine (denoted Jeffamine D2000) and polyurea were introduced to epoxy resin. The tribological behaviors of epoxy composites under dry and water lubricating conditions were investigated. The surface microhardness, morphologies and chemical compositions of epoxy resin and its composites before and after wear were analyzed. The results were as follows:1. Wear mass losses of the pristine epoxy and epoxy/rubber nanocomposites increase with increasing wearing time. The content of Jeffamine D2000 particles has influence on the wear mass losses and friction coefficients of epoxy nanocomposites. The content of 5wt.% nano-rubber is the most effective in reducing the wear mass loss and friction coefficient of the nanocomposites.2. Oxidation occurred on the surfaces of epoxy and epoxy/rubber nanocomposites during dry sliding wear.3. There are marked differences in the response of the wear materials when water lubricator is added in the sliding of polymer composites/steel contact. The friction coefficients of epoxy resin and epoxy/rubber nanocomposites under water lubricating are lower than those during dry friction but the wear mass losses are higher than those during dry friction.4. Wear mass losses of epoxy and epoxy/polyurea composites increase with increasing wearing time at the same load. And the frictional coefficients and wear mass losses of epoxy/polyurea composites are lower than those of pristine epoxy resin. SEM micrographs of worn surfaces of epoxy/polyurea composites indicated that the plastic deformation in part polyurea particulates occurred. This indicated that the toughness of epoxy/polyurea composites was improved with the addition of polyurea, and thus the wear resistance was improved.Secondly, the tribological behavior and wear mechanisms of PA66 and its composites consisting of styrene-ethylene/butylene-styrene triblock rubber particles (SEBS-g-MA) and nano-organoclay under dry and water lubricating conditions were investigated. The glass transition temperature (Tg) and heat stability of PA66 and its composites were also studied. At the same time, the effects of the blending sequence of SEBS-g-MA and nano-organoclay on the tribological behaviors of PA66 and its nanocomposites were studied. The results were as follows:1. The blending sequence affects the wear resistance of the PA66/SEBS-g-MA/organoclay ternary nanocomposites through affecting the microstructure and the final dispersion of the nano-organoclay. The friction coefficients and wear mass losses of PA66+(SEBS-g-MA+organoclay) ternary nanocomposites, in which SEBS-g-MA was first mixed with nano-organoclay and then the SEBS-g-MA/organoclay mixture was blended with PA66, are the smallest under dry and water lubricating conditions.2. The friction coefficients and wear mass losses of PA66+(SEBS-g-MA+organoclay) ternary nanocomposite are the smallest under dry sliding, whereas those of PA66/SEBS-g-MA binary composite are the smallest under water lubricating conditions.3. Pristine PA66, PA66/SEBS-g-MA binary composites and PA66/organoclay nanocomposites could not form a uniform and adherent transfer film on the steel counterface during dry sliding. The transfer films of PA66+(SEBS-g-MA+organoclay) ternary nanocomposites is thin, uniform and coherent compared to that of pristine PA66. This should be responsible for the reduced friction coefficient and wear mass loss.4. The Fe element on the steel counterface surface took part in the tribochemical reaction and was oxidized to the iron oxide Fe2O3 under dry sliding. The transfer film formed by the PA66+(SEBS-g-MA+organoclay) nanocomposites implies that the steel wheel could be more severely oxidized.5. The depression of Tg of PA66/SEBS-g-MA binary composites can be attributed to the presence of the rubber, while Tg of PA66/organoclay can be improved with the addition of organoclay.6. The friction coefficients of PA 66 and its composites under water lubricating sliding are lower than those under dry sliding condition, but the wear mass losses are higher than those under dry sliding.7. The contact temperatures of pristine PA66 in dry sliding systems were simulated by ANSYS/LS-DYNA system, and a comparison between analytical, calculated and experimental results for the flash temperature is presented. The results indicated that the analytical results and calculated results agreed with the experimental results.Finally, the micro-tribology properties of PA66 and its nanocomposites under dry sliding were measured on a Universal Micro-Tribometer, and the wear scars were analyzed. The effects of the normal load and the sliding velocity on the tribological behaviors of PA66 and its nanocomposites were investigated. The results were as follows:1. The volume wear rates of PA66 and its composites decrease with increasing normal load under the same velocity. Under the same conditions, the friction coefficients and wear mass losses of PA66/SEBS-g-MA binary composites are the smallest under dry sliding.2. SEM micrographs of the worn surfaces of PA66 and its nanocomposites indicated that a few fine wear debris attached on the worn surfaces of PA66/SEBS-g-MA composites, whereas flake wear debris were formed by PA66+(SEBS-g-MA+organoclay) nanocomposites. The attachment of wear debris on the worn surfaces resulted in higher surface roughness under dry sliding.