Dynamic compressive failure of a glass ceramic under lateral confinement

An experimental technique has been developed for imposing controlled multi-axial loading on cylindrical ceramic specimens. The multi-axial loading is achieved by superposing passive lateral confinement upon axial compression. Descriptions of the experimental technique, as well as experimental results for a machinable glass ceramic, Macer, are presented. The axial compression was applied using a Kolsky (split Hopkinson) pressure bar modified to apply a single loading pulse. Experiments were also conducted under quasi-static conditions using a servo-hydraulic load frame. The specimens were confined laterally using shrink-fit metal sleeves. The confining pressure ranges from 10 to 230 MPa. Under both quasi-static and dynamic loading conditions, the experimental results showed that the failure mode changes from fragmentation by axial splitting without confinement to localized faulting under moderate lateral confinement (10-120 MPa). The process of fault initiation was characterized in detail for specimens under moderate confinement. Based on the experimental results, a compressive failure mechanism was proposed for brittle materials under moderate lateral confinement. The Mohr-Coulomb failure criterion was found to fit the experimental strength data. The failure criterion is shown to be consistent with the analytical results from a micromechanical model for brittle failure. Transition from brittle to ductile behavior was observed under high confinement (230 MPa). (C) 1997 Elsevier Science Ltd.