Improvements to the structural properties of bonded composite joints using z-pins

A novel approach to improving the mechanical properties of carbon fibre reinforced polymer composite joints using through-the-thickness reinforcements, known as z-pins, is described. The effects of z-pin material (i.e. carbon fibre, copper and stainless steel) and the lap joint configurations (i.e. single, double and sextuple) towards the in-plane ultimate strength and failure strain of the composite joints are experimentally investigated. The carbon z-pins were most effective at increasing the strength of the double lap joints. The metal pins were also effective at increasing the double lap joint strength whilst promoting a plasticity-type failure mode, representing pseudo-ductility. This was supplemented by the shear induced bridging of the metal pins and stable debonding of the bondlines. A 20% and 350% improvement in the ultimate load and elongation-to-failure was observed for the single lap joint reinforced with metal z-pins. However, metal z-pins offers no significant improvement towards these mechanical properties for sextuple lap joint. Experimental data shows that the percentage improvement provided by the z-pins was also dependant by the joint type; exhibiting distinct failure modes