Thermal shock fracture in cross-ply fibre-reinforced ceramic–matrix composites

Abstract

The onset of matrix cracking due to thermal shock in a range of simple and multi-layer cross-ply laminates comprising a calcium aluminosilicate (CAS) matrix reinforced with Nicalon® fibres is investigated analytically. A comprehensive stress analysis under conditions of thermal shock, ignoring transient effects, is performed and fracture criteria based on either a recently derived model for the thermal shock resistance of unidirectional Nicalon®/glass ceramic–matrix composites or fracture mechanics considerations are formulated. The effect of material thickness on the apparent thermal shock resistance is also modelled. Comparison with experimental results reveals that the accuracy of the predictions is satisfactory and the reasons for some discrepancies are discussed. In addition, a theoretical argument based on thermal shock theory is formulated to explain the observed cracking patterns.

Keywords:

• ceramic–matrix composites
• cracking
• thermal shock

Acknowledgements

CK wishes to acknowledge financial support from the Engineering and Physical Sciences Research Council (EPSRC) of the UK and the ‘Alexander S. Onassis’ Public Benefit Foundation. PAS and JAY would like to acknowledge the encouragement that they received from Professor Kelly in the late 1980s to pursue research on ceramic matrix composites. Twenty years on, they can both recall memorable discussions with Professor Kelly during the course of lengthy car journeys from Guildford to Derby.

Notes

Note

1. Pryce and Smith 11 argue that [0/90]_3s and [0₂/90₄]_s cross-ply Nicalon®/CAS laminates exhibit what is termed ‘unconstrained’ cracking under monotonic tensile loading, i.e. the pre-existing critical flaw is smaller than the thickness of the central 90° plies. They also came to the conclusion that the initial flaw in the eight central plies of the [0₂/90₄]_s laminate can be considered to be longer than the one in the central double transverse ply of the [0/90]_3s.