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A full numerical analysis of elastohydrodynamic lubrication (EHL) of circular point contacts was carried out in the present study under isoviscous conditions with particular reference to metal-on-metal arti®cial hip joints, using a modi®ed Newton±Raphson method. It was found to be possible to incorporate directly the physiological conditions, representative of typical metal-on-metal hip implants under in-vivo walking or in-vitro simulator testing, in the present numerical solutions. The predicted minimum and central ®lm thicknesses were compared favourably with those estimated from various formulae available in the literature. In particular, it was shown that both the minimum and the central ®lm thickness expressions derived by Hamrock and Dowson were reasonably accurate for all the conditions considered in the present study.

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The machinability of an austempered ductile iron with a suitable chemical composition for heavy sections has been assessed. Austempering heat treatment was carried out at three temperatures, 300, 340 and 375uC, after austenitising at 870uC for 100 min. Drilling tests, tool wear and surface roughness measurements were used to evaluate the machinability. Drilling operation failure, severe tool wear and the poorer surface roughness of the specimens austempered at lower temperatures indicated that austempering at higher temperatures clearly resulted in better machinability. The machinability of testpieces austempered at 375uC, which contained higher fractions of retained austenite, was superior to that of testpieces autenitised at lower temperatures, indicating that hardness is an important factor in assessing machinability in addition to high carbon austenite content.