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

The fracture of ceramic-matrix composites is frequently complex, invol ving the evolution of subcritical damage which strongly affects the fi nal 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 sc anning electron microscope. This technique enables detailed characteri zation of the subcritical damage and of the crack interactions which o ccur 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 pre liminary evaluation of the unnotched tensile response of the material, followed by in situ observations on two common delamination geometrie s: four-point bending and double cantilever beam. The tensile behaviou r of edge-notched specimens is described in the companion paper.