Determination of in-situ fibre, matrix and interface properties in a composite using tensile tests and an extended shear-lag model

The strength and modulus values of the matrix and of the fibres as incorporated in a ceramic matrix composite (CMC) may differ from those obtained on the matrix and the fibres separately for a number of reasons. The same applies for the interfacial properties obtained from tests on specimens designed for that purpose, and their values in a real CMC. This paper outlines a methodology which allows the determination of the in-situ values of these parameters in the composite. It is based on an evaluation of the results of tensile tests in the light of a newly developed extended shear-lag model. Calibration of the five model parameters leads to the identification of the fibre and matrix moduli, as well as of the interfacial friction coefficient and the radial interface strength. The axial stress profiles obtained from the shear-lag model subsequently allow the determination of the fibre and matrix strength. The methodology is illustrated by application to a 2D woven CMC. In-situ properties at the level of individual tows, and on the level of individual fibres within a longitudinal tow are obtained.