Stacked laminated composites structures (uni and bi-direcional), unlike homogeneous isotropic materials, exhibit low shear strength (< 60 MPa) and low interlaminar fracture thoughness. As a consequence, premature failure during service can occur and their use are restricted mainly to secondary non-load bearing structures. The use of high toughness matrices in composites is not sufficient to improve the interlaminar fracture toughness. Presently, the use of multi-axis preforms have shown significant improvements in interlaminar fracture toughness of composites and a lot of research has been done using this technology. The present work describes methods to obtain multi-axis preforms for either polymer or thermo-structural composites. Many investigations have shown that addition of a ~1-2% fibre volume fraction normal to main fibre plane is enough to provide an adequate shear and interlaminar fracture resistance for the composite keeping in-plane properties. Multi-axis preforms provide higher isotropy, higher fracture toughness and resistance to thermal stresses during processing and service.
Structural composites; textile preforms; fracture toughness; needling and stitching; interlaminar shear
