Abstract
Abstract
Compression of rings is now an established technique for hot friction testing. However, there are subtleties that the investigator needs to be aware of in order to interpret results correctly. The significance of oxides and lubricants in terms of insulation levels and surface mechanics is investigated. Deformation profiles of the rings arising from the constrained plastic flow give a direct indication of the sensitivity of parameters describing the interface conditions. Fully coupled finite element modelling is used to simulate the experimental work on a comparative basis and is then extended to explore the influencing parameters on the physics of the process and examination of either continuous or step changes in friction. Both experimental and analytical work show that complex relations exist between heat exchange and surface traction and that these also depend upon parameters such as reduction, scale thickness and initial temperature. The conclusion is that the scale thickness with its mix of oxides is the dominant index in establishing predictive relations between the surface shear, contact pressure, temperature gradients and modes of lubrication.
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