A study of the dynamic tribological response of closed fracture surface pairs by Kolsky-bar compression-shear experiment

The Kolsky torsion bar technique has been utilized successfully to develop a new compression-shear recovery experiment for dynamic tribometry of closed fracture surface pairs. This new experimental design enables combined dynamic compression and shear loading and preserves the residual specimen surface after a single cycle of loading. The experimental design was first verified through a series of dynamic friction experiments on flat 7075-T6 aluminum alloy surface pairs. The technique was then applied to study the dynamic tribological response of closed fracture surface pairs of the same material in conjunction with surface topography examination. It was found that the pre-sliding response depends primarily on normal stress and roughness of as-fractured surface. The response after the initiation of frictional sliding displays an exponential decay with increasing sliding displacement. The long-time steady-state response (if achieved) depends predominantly on normal stress. The results also show that a sufficiently high normal stress may suppress frictional sliding between the fracture surfaces giving rise to a dynamic plastic deformation continuous across the interface. An empirical model describing the key experimental observations is proposed and evaluated against the experimental data. The implication of the findings on shear cracking under high confining stress is discussed. (C) 2004 Elsevier Ltd. All rights reserved.