Z-pin bridging in composite delamination

Traditional fibre composites are manufactured by stacking together a number of plies, in which the fibres are orientated to provide in-plane reinforcement for the composite. A direct consequence of this process is that no fibres are positioned across the laminate thickness. Interlaminar delamination becomes the most common failure mode in composite laminates. A successful solution to this problem is to provide through-thickness reinforcement to the laminated composites because bridging by reinforcing fibres in the laminate thickness provides direct closure tractions to the delamination crack faces. Many techniques have been developed to enhance the strength of the composite laminates in the thickness direction, or z-direction. Among them, a novel approach, so-called z-pinning, has been developed. In this technique, short pins initially contained in foam are inserted into the composite through a combination of heat and pressure compacting the foam.