Dynamic tribological response of SiC fracture surfaces

Abstract

A new experimental method combining dynamic tribometry based on the torsional Kolsky bar technique and three-dimensional surface profilometry that enables characterization of surface topography and wear has been applied to study the dynamic tribological response of closed silicon carbide (SiC) fracture surface pairs under normal compressive stresses up to 1900 MPa. It is found that global sliding of such a tribo-pair occurs when the interfacial shear stress reaches approximately 39% of the applied normal stress. The engaged interfacial asperity pairs mostly undergo shear-induced disengagement as the sliding initiates. However, surface wear-crushing of asperity-occurs at isolated locations and evolves, though at a decreasing rate, as the sliding progresses, resulting in fine interfacial wear debris particles that act effectively as solid lubricant. The transient behavior of the tribo-pair is affected strongly by the interfacial wear debris, whose response is sensitive to the acceleration rather than the velocity of sliding. Despite the variation of transient response from one experiment to another, the steady-state response is essentially Coulombic (linear) over the sliding velocities examined (0.05–3.4 m/s) with an effective kinetic friction coefficient of 0.36. A dynamic friction model allowing acceleration-dependent overstress and relaxation has been worked out. It is demonstrated that the model can capture the key dynamic features observed in the transient response and recover the Coulombic relation for the steady-state response. The significance of these findings for analyzing shear cracking in SiC deformed under confining stresses is also discussed.