Improving the delamination fatigue resistance of composites by 3D woven metal and composite Z-filaments

Metallic and composite z-filaments have been reported as effective solutions for improving the interlaminar fatigue resistance of fibre-polymer laminates, which is important to many applications that demand high delamination fatigue endurance. Here, we examine the mechanisms of three different z-filaments made from metallic and fibre composite materials and to quantify their effectiveness in improving the modes I and II interlaminar fatigue resistance. Interlaminar fatigue experiments were conducted under cyclic displacement control conditions using the Double Cantilever Beam (DCB) and End Notch Flexure (ENF) test methods. Results show that, despite the metallic z-filaments having much greater ductility than carbon fibre z-filament, they are less effective in raising the interlaminar fatigue resistance of laminated composites. Of the two metallic filaments, steel z-filaments are more effective at resisting the initiation and growth of fatigue cracks under modes I and II interlaminar cyclic loads than copper filaments. The different extents of improvements of the three filaments are attributed to the differences in their crack bridging efficiency under interlaminar fatigue loading.