Effect of Fiber Material on Tribological Properties of UHMWPE Water-Lubricated Bearing Composites

Ultra-high molecular weight polyethylene (UHMWPE) has the advantages of excellent self-lubricating properties, low friction coefficient, and high toughness, making it highly promising in the field of water-lubricated bearings. However, low wear resistance and low strength make it difficult for single UHMWPE to meet the wear resistance requirements of water-lubricated bearings, especially under low-speed heavy load operating conditions. Many domestically and internationally studies have shown that adding fiber materials with excellent properties to the base material can improve the tribological properties of the base material. However, the characteristics of fibershighly affect the tribological properties of the manufactured composites. Therefore, it is necessary to study oriented fiber composites made with different fibers to explore the most suitable fibers. In this study, oriented fiber composite materials were prepared by hot pressing Oriented fiber composites of sisal fiber (SF), carbon fiber (CF) and polyester Fiber (PETF) mixed with UHMWPE were prepared by a hot pressing mold. Rtec tribol-tester had been used to carried out the tribological experiments, the friction process between a copper ball and different composite materials was carried out under different loads (5, 10 N) and speeds (20, 40, 60 mm/s). The mechanical properties of the composite materials were tested through Shore hardness and ultimate flexural strength tests. The wettability of the composite materials was tested using a contact angle test, and the wear surface topography was observed using the scanning electron microscope after the test. The results showed that the effect of fiber materials on the tribological properties of composite materials highly depending on their characteristics. The mechanical properties of the fibers, especially hardness and flexural strength, were the key factors affecting the tribological properties of oriented fiber composite materials. The strong supporting role of added fibers in composite materials significantly improved the tribological properties, while the wear resistance and wettability of the fibers were secondary factors affecting the tribological properties of composite materials. Under the experimental conditions, the CF/UHMWPE composite material had the lowest friction coefficient during the friction process with the copper ball. Compared with pure UHMWPE, the CF/UHMWPE composites presented the highest reduction in the friction coefficient, which reached to 36.92% under low speed heavy load operating conditions (10 N, 20 mm/s). This was mainly due to the excellent mechanical properties of carbon fiber, which helped to reduce the friction coefficient of the composite material. In addition, carbon powder, which formed after carbon fiber was worn, could act as a lubricating medium on the surface of the friction pair and further reduced the friction coefficient. The wear volume of the PETF/UHMWPE decreased by 30.56% compared to pure UHMWPE, due to the excellent wear resistance and compressive strength of PETF.