Strength of functionally gradient composite hemispherical bearings

Carbon fibre phenolic woven composites are used as journal bearing materials because they have self-lubricating properties and high specific strength at high temperature without the danger of seizure problem with the metallic journals. In order to reduce the frictional coefficient of carbon phenoilc woven composite, in this work, polyetheretherketone (PEEK) powders were mixed near the surface plies to make a functionally gradient material, because the PEEK powder lowers not only the friction coefficient but also the strength of the composite. The effects of PEEK powders and the bottom vent hole in the composite hemispherical bearing (CHB) on the strength were experimentally investigated. Based on the investigation, a new CHB was fabricated by molding rather than machining the hemispherical surface to eliminate crack and delamination and tested in an experimental set-up. The experimental results showed that the new CHB outperformed the existing carbon PEEK CHB both in the endurance life and compressive strength.