Tensile fatigue properties of a 3D orthogonal woven composite

The tensile fatigue properties of a specific type of 3D orthogonal woven composite that contained different volume contents of through-thickness reinforcing fibres (called z-binders) was studied in this paper. The 3D woven composite contained z-binder contents of 0.3, 0.5 or 1.1% by volume. The fatigue life (S–N curve) and residual fatigue strength (after one million load cycles) of the 3D woven composites was lower than a 2D woven composite. Furthermore, the fatigue life and strength of the 3D woven composite decreased with increasing z-binder content. The fatigue performance was degraded due to the development of fatigue-induced damage caused by the insertion of the z-binders. Plastic shear yielding and cracking of the polymer matrix surrounding the z-binders was found to initiate fatigue damage in the 3D woven composite. Mode I interlaminar fracture tests were also performed on the 3D woven composites to demonstrate the large improvement to the delamination toughness gained by increasing the z-binder content.