An alternative ring-test geometry for the evaluation of friction under low normal pressure

Quantitative evaluation of the tribological conditions at the tool–workpiece interface in metal forming is usually accomplished by the ring-compression test. The popularity of the test can be attributed to its practical convenience including the fact that friction can be judged from deformation alone.

Due to the geometrical design of the conventional ring-test, the interface stresses will, however, always be greater than the flow stress of the material, thereby impeding quantification of friction, and evaluation of the behaviour of lubricants, for processes where interface stresses below the flow stress of the material occur.

This paper presents a new complementary ring-test geometry, which allows the characterisation of friction under low pressure conditions. Finite-element analysis in conjunction with metal experiments applying both the conventional and the modified geometry for different lubricants provides the validation for the general feasibility of the proposed test geometry.