Laboratory based experiments to assess the “damage tolerance” of any new material system are a pre-requisite to engineering design, especially for aerospace components. In the case of CMCs, macro-scale specimens are preferred containing representative fibre-matrix architectures that support the definition of mechanical properties under service representative stress states.

The combination of complex internal structure and inevitable processing artefacts within CMCs provides numerous sites for damage initiation. Damage then progresses in an inhomogeneous manner prior to ultimate failure at some critical location. Traditional techniques employed for strain measurement (extensometry/strain gauges) prove to be ineffective tools when testing these advanced composites. More complex characterization is essential in order to assess the localised response of the material.

Advanced techniques, specifically digital image correlation and acoustic emission, have been applied to the evaluation of an CVI/MI silicon carbide reinforced/silicon carbide CMC tested at the elevated temperature of 800°C under fatigue loading. The spatial and temporal indications of damage were correlated to the observable forms of damage initiation and progression. Ancillary use of an in-situ SEM loading stage provided insight into the crack opening and closing mechanisms active within this material when under cyclic stress.

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