A new plate impact configuration is described for subjecting lubricants to simple shearing motion under uniform hydrostatic pressure. Thin layers (∼50 μm thick) of the lubricant are confined between two hard metallic plates which are subjected to impact by a parallel plate that is inclined relative to the direction of approach in order to induce both pressure and shear loading. Stress waves in the hard plates are monitored by laser interferometry; all measurements are made before unloading waves arrive from the periphery. For approximately one microsecond the compressed lubricant is subjected to a simple shearing motion and a continuous record of the shear stress and shear rate is obtained. Results presented for the lubricant 5P4E at pressures of 1-5 GPa and shear rates of approximately 9 × 105 s−1 show good agreement with available data on the dependence of the limiting shear stress on the confining pressure at lower pressures and lower shearing rates.

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