Effects of asperity shape and summit height distributions on friction and wear characteristics

Abstract

Assuming that hard asperities are conical or hemispherical, the total cross-sectional areas Sp plowed by them and mean friction coefficient were compared theoretically for the normal distributions of three dimensional summit and two dimensional surface heights on a profile curve. Moreover, when abrasive grains are conical, the ratio α b of volume removed as a debris to volume of grooves plowed by abrasive grains was obtained experimentally for various metals against an abrasive paper. The wear rate of metals was also estimated by using the mean cross-sectional areas of micro-grooves on worn surfaces and the α b values. As a result, the following facts were found, (1) The total cross-sectional areas Sp plowed by hard conical asperities with various slopes are independent of the both distributions of three dimensional summit heights and two dimensional surface heights on a profile curve. (2) The Sp value plowed by hard conical or hemispherical asperities with the transferred wear particles of various lengths are smaller than those plowed by the asperities without transferred particles and the friction coefficient for the hemispherical asperities are smaller than those for the conical ones except for high contact pressure. (3) The longer the lengths of hard hemispherical asperities in the sliding direction, the smaller the Sp value becomes. This trend can be observed during running-in of abrasive wear and so on. (4) The specific wear rate for abrasive wear of various metals can be estimated from the relationship between α b values and tan θ/ p f (tan θ; mean slope of asperities, p f; mean flow pressure of metal) and α b values and that between tan θ/ p f and Sp/ n values on the basis of a hard conical asperity.