Evaluation of Graphite Fiber Reinforced Plastic Composites for Use in Unlubricated Sliding Bearings

Conforming shoe-type specimens of radial fiber graphite/epoxy, tangential fiber graphite/epoxy, and radial fiber graphite/polyimide were fabricated and evaluated as bearing materials. Their performance was compared against that of specimens cut from commercially available Teflon-lined (TFE-lined) bearings of MS 21240 type. All the test specimens were run against hardened steel sleeves. Test conditions included bearing loads ranging from 9 to 30 ksi (6.2 × 107 to 20.7 × 107 N/m2); oscillatory motion of ±25 deg at 30 or 60 cpm (0.5 or 1.0 Hz); equilibrium sleeve temperatures at the start of test ranging from 80 to 400°F (300 to 477 K); and test durations of 2 h except where earlier specimen failure occurred. Compressive strength and thermal conductivity measurements were also made on the graphite/epoxy materials. At temperatures of 350°F (450 K) and lower, the TFE material exhibited the best friction and wear characteristics of the four materials tested. The graphite/polyimide material exhibited friction and wear performance superior to that of either of the graphite/epoxy materials over the range of conditions used. At combinations of high load and temperatures in excess of 350°F (450 K), the wear rate of graphite/polyimide material was comparable to that of the TFE material, although friction was higher.