Temperature distributions for typical cases of orthogonal machining with a continuous chip were obtained numerically by solving the steady two-dimensional energy equation using the finite element method. The distribution of heat sources in both the primary and secondary zones was calculated from the strain-rate and flow stress distributions. Strain, strain-rate and velocity distributions were calculated from deformed grid patterns obtained from quick-stop experiments. Flow stress was considered as a function of strain, strain-rate and temperature. The chip, workpiece and tool (actual shape and size) were treated as one system and material properties such as density, specific heat and thermal conductivity were considered as functions of temperature.

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Angle-dispersive x-ray powder diffraction experiments have been performed on yttrium metal up to 183 GPa. We find that the recently discovered oF 16 structure observed in the high-Z trivalent lanthanides is also adopted by yttrium above 106 GPa, pressures where it has a superconducting temperature of ∼20 K. We have also refined both tetragonal and rhombohedral structures against the diffraction data from the preceding "distorted-fcc" phase and we are unable to state categorically which of these is the true structure of this phase. Finally, analysis of yttrium's equation of state reveals a marked change in the compressibility upon adoption of the oF 16 structure, after which the compression is that of a 'regular' metal. Electronic structure calculations of oF 16-Y confirm its stability over oF 8 structure seen in Nd and Sm, and provide insight into the nature of the shift of orbital character from s to d under compression.

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A theory is given for calculating chip geometry, cutting forces, etc., from fundamental work material properties and cutting conditions. The flow stress properties of the work material (0·16 per cent carbon steel) used in the analysis are taken from high-speed compression test results. The theory predicts the main trends observed in machining experiments and a limited comparison with experimental results shows good quantitative agreement. A possible explanation for the occurrence of a built-up edge, involving the dynamic strain ageing (blue-brittleness) of the chip along the tool-chip interface, is considered and found to be consistent with the results.