Improving the delamination resistance of fibre reinforced polymer composites using 3D woven metal Z-Filaments

This paper presents a new approach for greatly increasing the delamination resistance of fibre reinforced polymer composites via through-the-thickness weaving of high-strength, high-toughness metal z-filaments. Dry carbon fabric preforms were woven in the through-thickness direction with thin and continuous stainless steel or copper filaments, and then infused with epoxy resin to create 3D woven composites. The modes I and II interlaminar fracture toughness properties of the resultant composites are compared with those of a 3D woven composite reinforced with z-filament made of continuous carbon fibre tows. Experimental testing and finite element modelling of delamination crack growth reveals that metal z-filaments can promote much greater improvements to the mode I interlaminar fracture toughness compared to carbon z-filament. The steel z-filament increases the mode I delamination resistance by over 50 times, with the fracture toughness value (similar to 28 kJ/m(2)) being the highest reported value for composite laminates. The metal z-filaments are less effective than the carbon z-filament at increasing the mode II delamination resistance, although the improvements are still large. The magnitude of improvements in modes I and II delamination toughness by metal z-filaments depends on several factors, including the alloy type, mechanical properties (e.g. tensile strength and ductility), volume fractions, and crack bridging toughening mechanisms.