Understanding meso interfacial structures between z-pins and laminates in z-pinned laminates

Z-pin pull-out tests from the laminates were conducted to explain the components of the meso interface structure of z-pin/laminate and the debonding position. Three types of z-pins with different molding qualities were investigated. The results revealed that the z-pin/laminate interface was composed of two meso interface components connected in series, including the interface between the outer layer resin of z-pin and the resin of laminate (Interface Ⅰ) and the interface between z-pin's own fiber and its own matrix resin (Interface Ⅱ). Debonding would occur at the weaker one. The z-pin with the best molding quality possessed the highest interfacial bond shear stress, τ_d, and the debonding mainly occurred at Interface Ⅰ. Regarding the z-pin with the worst molding quality, its τ_d was the lower one and the debonding primarily occurred at Interface Ⅱ. While this kind of z-pin exhibited the higher resistance at the final frictional pull-out stage.