Crack onset and growth at the fibre–matrix interface under a remote biaxial transverse load. Application of a coupled stress and energy criterion

A theoretical model for prediction of the critical load generating a crack onset at the fibre–matrix interface under a remote biaxial transverse load is presented. In particular, this work is focused on the tension dominated failure. After an abrupt onset the crack grows unstably up to achieving an arrest length. A simple plane strain model of a single circular inclusion surrounded by an unbounded matrix allows obtaining conclusions approximately valid for a dilute fibre packing. Linear isotropic elastic behaviour is assumed for both inclusion and matrix. Two classical elastic solutions for both perfectly bonded and partially debonded circular inclusions are used together with a coupled stress and energy criterion, proposed recently in the framework of finite fracture mechanics, and a phenomenological law for fracture toughness of interface cracks growing in fracture mixed mode. The obtained analytical and semi-analytical expressions make easy studying the influence of all the dimensionless parameters governing the fibre–matrix system behaviour: Dundurs elastic bimaterial constants αα and ββ, the interface brittleness number γγ and the load biaxiality parameter ηη. A size effect of the inclusion radius on the critical load is predicted, smaller inclusions being stronger and less dependent on the secondary load. Finally, an experimental procedure for measurement of the fibre–matrix interface fracture and strength properties is proposed.