Study of aspherical femoral head aiming long-life artificial hip joint

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To improve lubricating condition in artificial joint, it is necessary to know the magnitude of contact stress. In this study, some parametric equations were derived to calculate contact pressure in conformal contacts. The results obtained from the equations were confirmed to agree with that of FEM calculation.Influence of contact pressure distribution on the coefficient of friction was investigated for some polymeric bearings in dry and lubricated conditions. Reciprocal pin on plate sliding test and Soda pendulum type sliding tests were carried out. It was found that the contact pressure distribution has a significant effect on the coefficient of friction in lubricated condition. The coefficient of friction became smaller when the pin was sliding with the lower contact pressure side ahead. The coefficient of friction in dry conditim does not depend on sliding direction regardless of contact pressure distribution.The effect of an orientation of grinding direction of the surface to sliding direction on the coefficient of friction was also studied by using a reciprocal sliding tester. It was found that the coefficient of friction became smallest in the case of sliding direction perpendicular to the grinding direction. Conversely, it became largest in the case of sliding direction parallel to the grinding direction. Furthermore a method of slide track calculation was studied by introducing angular velocity in a fixed coordinate system and a moving coordinate system as well.