Damage characterisation of thermally shocked cross-ply ceramic composite laminates

Abstract

Damage due to thermal shock in cross-ply Nicalon/calcium aluminosilicate ceramic matrix composites has been investigated. Heated specimens of two simple [(0°/90°)_s and (90°/0°)_s] and two multi-layer [(0°/90°)_3s and (90°/0°)_3s] materials were quenched into water at room temperature. Crack morphologies were assessed by reflected light microscopy and scanning electron microscopy. The use of image assembling software allowed the generation of reflected light microscopy images of all of the thermally-shocked surfaces onto which the crack patterns were then superimposed. This allowed clear identification of damage mechanisms and accurate quantification of damage accumulation with increasing severity of thermal shock. Damage was first detected in the central plies of each composite. Composites with 0° central plies exhibited slightly higher resistance to thermal shock than their counterparts with 90° central plies. Although damage extended to the outer plies as the severity of the shock increased, crack density was found to vary with position at every shock: it was highest in the central plies and gradually reduced towards the outer plies. Multiple matrix cracking perpendicular to the fibre direction was the damage mode identified in 0° plies, while 90° plies contained cracks that ran along the ply length. At more severe shocks the morphology of these crack patterns was affected in significantly different ways. In addition, the thinner, simple cross-ply composites exhibited much higher resistance to thermal shock than their multi-layer counterparts.