MEASUREMENT OF PROPERTIES OF BRITTLE-MATRIX COMPOSITES

Based upon NPL experience of testing carbon fibre-reinforced glass matrix composites in unidirectional and crossply laminated forms, a review is presented covering those aspects of mechanical testing that need to be considered when measuring the mechanical properties of brittle matrix composites. Specimen geometry, gripping techniques and alignment for tension testing are discussed. The limitations of flexure testing in possibly overestimating tensile properties are demonstrated for a material having a low interlaminar shear strength. Interpretation of strain gauge output is discussed in relation to the calculation of Young's modulus, and is compared with extensometer output. The role of matrix cracking and its effect on the ability to make meaningful measurements is discussed. Problems of measurement of fracture toughness, especially in a material with poor interlaminar shear strength, are highlighted through attempts to perform self-similar crack growth tests. (C) 1993 Crown copyright.