DIRECT OBSERVATION OF THE FRACTURE OF CAS-GLASS SIC COMPOSITES .1. DELAMINATION

The fracture of ceramic-matrix composites is frequently complex, involving the evolution of subcritical damage which strongly affects the final failure process, and which is very specimen dependent. In this and a companion paper, observations of fracture mechanisms are described for a calcium-alumino-silicate (CAS) glass reinforced with SiC fibres. The tests were principally undertaken dynamically in situ within a scanning electron microscope. This technique enables detailed characterization of the subcritical damage and of the crack interactions which occur prior to final failure. It is shown that meaningful modelling of fracture processes in these materials generally requires this level of detail in identifying the micromechanisms. This paper describes a preliminary evaluation of the unnotched tensile response of the material, followed by in situ observations on two common delamination geometries: four-point bending and double cantilever beam. The tensile behaviour of edge-notched specimens is described in the companion paper.