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, Macor, 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).

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