INDENTATION-INDUCED CONTACT DEFORMATION AND DAMAGE OF GLASSLIKE CARBON

Fracture mechanics are examined for the Vickers-indentation-induced contact deformation and damage of glassy carbons produced by different densification processes. The indentation load versus indentation depth relationship during the loading-unloading cycle reveals that the contact deformation is purely elastic even under such a sharp indentation, which subsequently leads to an indentation-induced ring/cone crack system instead of the median/radial crack system. The processes and mechanisms of such an anomalous surface crack system are related to the very open microstructure of glassy carbons. The ring/cone cracks induced by Vickers indentation are, however, significantly different in nature from the well-known Hertzian cone crack which is induced by pressing a spherical indenter on a brittle surface. Demonstrated is the superiority of glassy carbons to ordinary brittle ceramic materials in resistance to strength degradation by contact with hard particles such as in ballistic situations.