Mechanics of interface debonding in fibre-reinforced materials

The evaluation of damage in multiphase materials plays a crucial role in their safety assessment under service mechanical actions. In this context, the quantification of the damage associated to fibre-matrix detachment is one of the most important aspects to be carried out for short fibre-reinforced materials. In the present article, the problem of progressive fibre-matrix debonding is examined and a mechanics interpretation of such a phenomenon is developed by relating the shear-lag and the fracture mechanics approach in order to determine the fibre-matrix interface characteristics. A multiscale approach is employed: at macroscopic level, composites with dilute dispersed fibres, arranged in a undirectional or in random orientation, are analysed through a homogenization approach, whereas the problem of axisymmetric debond growth in short fibres is examined at microscopic level. Moreover, a structured' linear elastic interface framework model for crack propagation analysis is applied by defining a microscopic truss structure, enabling to relate each other the classical shear strength approach and the fracture mechanics approach. Finally, a fibre pull-out test and some simple fibre-reinforced structural components are examined. This new proposed point of view on the debonding phenomenon allows a deep understanding of the mechanics of the fibre-matrix interface and enables to characterize such an interface layer that has a relevant role in mechanics design of composites materials.