Experimental investigation of the shear strength of lubricants subjected to high pressure and temperature

In order to evaluate the relationship between limiting shear strength and pressure for a lubricant an experimental apparatus has been built. Pressures up to 2.2 GPa and temperatures up to 200°C are attainable simultaneously. Thus the limiting shear strength-pressure relationship has been surveyed in a wide range. Several types of natural and synthetic lubricants have been tested. The results show that all the mineral oils tested behave in quite a similar way. Synthetic lubricants do not show this behaviour, but the relationship between limiting shear strength and pressure depends strongly upon the chemical base of the synthetic lubricants. The behaviour of grease does not differ from that of liquid lubricants. The pressures at which the lubricants change from a liquid to a solid behaviour have also been measured.