AN ALTERNATIVE RING-TEST GEOMETRY FOR THE EVALUATION OF FRICTION UNDER LOW NORMAL-PRESSURE

Quantitative evaluation of the tribological conditions at the tool-wor kpiece 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 f rom deformation alone. Due to the geometrical design of the convention al ring-test, the interface stresses will, however, always be greater than the how stress of the material, thereby impeding quantification o f friction, and evaluation of the behaviour of lubricants, for process es where interface stresses below the flow stress of the material occu r. This paper presents a new complementary ring-test geometry, which a llows 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 lubrica nts provides the validation for the general feasibility of the propose d test geometry. (C) 1998 Elsevier Science S.A. All rights reserved.