3D reinforcement of stiffener-to-skin T-joints by Z-pinning and tufting

Carbon fibre/epoxy T-stiffener-to-skin joint was reinforced through the thickness, either by insertion of Z-Fiber® before autoclave cure of prepreg or by tufting of dry preform with a glass thread before resin injection and cure. The joints pull-off resistance increased significantly for both types of T-joints under both quasi-static and fatigue loading conditions. In the case of the tufted joints, the delamination between the skin and the stiffener stopped completely and the samples failed in bending. It is shown that a finite element model is successful in reproducing qualitatively the cracking progression in the unreinforced and 3D reinforced T-joint provided that the action of the through-the-thickness reinforcement is modelled by discrete nodal forced placed so as to replicate the physical reality.