Bearings are parts to placed between sliding surfaces to reduce wear and friction between them. In applications where it is not possible to use a liquid lubricant, self-lubricating solids are used. Aircraft landing gear is one of the many applications of self-lubricating bearings. Today, materials like aluminum-bronze, phosphor-bronze and PTFE composites are used in the manufacture of bearings for landing gear. In this research, the tribological properties of four samples of aluminum, aluminum-bronze, phosphorus-bronze and PTFE/Kevlar have been compared in the working conditions of a specific aircraft landing gear. A reciprocating pin-on-disc wear tester was used to eva‎luate the tribological properties. In this device, a 1.3505 steel ball with a diameter of 10 mm, and a hardness of about 65 HRC was used as a countersurface. To study the effect of load on wear behavior, tests were performed at loads of 5, 8, 12, 16 and 20 N, sliding speed of 0.1 m/s and a distance of 400 meters. To determine the wear rate, the weight change of the samples was measured using a scale with an accuracy of 0.0001 grams. The surface roughness of the samples was measured by a portable roughness meter, and the metallographic study of the metal samples was done by an optical microscope and an X-ray diffraction device. To determine the wear mechanism, the worn surface of the samples, and the pin used for each sample, were studied by an electron microscope. The friction coefficient of phosphorus-bronze and PTFE/Kevlar samples was high at the beginning, then decreased to reach a stable level, but the friction coefficient of aluminum and aluminum-bronze samples increased at the beginning of the test and then became stable. This shows that the main wear mechanism for aluminum and Aluminum-Bronze is abrasive, and for Phosphor-Bronze and PTFE/Kevlar is adhesive wear. The wear rate decreased with time for all samples, and showed a decreasing trend with increasing load for aluminum, aluminum-bronze and phosphor-bronze, and an increasing trend for the PTFE/Kevlar sample. Microscopic images of the wear track showed that the main wear mechanism for aluminum and aluminum-bronze is abrasive, and for phosphor-bronze and PTFE/Kevlar is adhesive wear. Some extend of pulverization were observed on the surface of the PTFE/Kevlar sample, and delamination was observed on the surface of the aluminum and phosphorus-bronze samples. According to the results obtained from the wear and friction test, PTFE/Kevlar can be a suitable candidate for use in heavy aircraft weighing more than 50 tons, while aluminum-bronze and phosphor-bronze can be used in light aircraft and drones.

محمود منيرواقفي

علي شفيعي , رحمت اله عمادي