Fracture Resistance Evaluation of Fibre Reinforced Brittle Matrix Composites

Abstract

Determination of the fracture toughness using a specimens with straight and/or chevron notch in the three (four) point bend test for monolithic ceramic materials can be taken as standardized techniques. In case of composite materials, mainly of brittle matrix reinforced by unidirectional fibres the crack growth resistance increases as the crack propagates. In addition, the long fibres stimulate delaminations along fibre – matrix interface perpendicularly to the major crack. Fracture toughness determination (in the loading mode I) in cases when delaminations take place is difficult. The chevron notch technique could be the right way to overcome this difficulty and obtain exact fracture toughness characteristics by its natural ability to “keep” the direction of major crack. Based on fractographic analyses some examples are described to show potential of the chevron notch technique for fracture resistance characterisation of the studied composite including comparison of data from chevron and straight notch technique etc.