Evaluation of the fibre/matrix interface strength by the pushing out of fibres of non-symmetrical cross-section

The fibre/matrix interface strength is an important parameter to determine such mechanical properties of fibrous composites as fracture toughness of brittle-fibre/brittle-matrix systems, creep resistance of composites reinforced with brittle fibre and creeping matrix, etc. Therefore, a methodology for measuring that parameter is of a primary importance for composite technology. The well-known technique of pushing out the fibre from a disk of the composite provides sufficiently reliable information on the interface behaviour. In the present paper, this technique is modified to be used for composites with an arbitrary shape of the fibre cross-section. The concept of technical modification of the traditional scheme is based on replacement of a rigid indentor, which normally has a sharp corner, with a metal ball located between the fibre surface and an ‘indentor’ that has a flat surface. This allows us to apply the load to a fibre of an arbitrary cross-section sufficiently uniformly. Interpretation of the results includes obtaining a dependence of the critical load on disk thickness. The applicability and reliability of the method are illustrated by results of testing oxide-fibre/Ni-based-matrix composites.