Environmental durability of z-pinned carbon fibre-epoxy laminate exposed to water

The influence of z-pins on the water absorption properties of a quasi-isotropic carbon fibre-epoxy laminate is assessed. Fibrous composite pins accelerate the moisture absorption rate and increase the total absorbed moisture concentration when the laminate is immersed in water. However, the moisture absorption properties of the laminate are not affected significantly by pins when exposed to hot and humid air. Water diffusion into the z-pinned laminate is aided by interfacial cracks between the pins and laminate. Also, the axial alignment of fibres within the composite pins in the through-thickness direction increases the water absorption rate. Pin pull-out tests reveal that water absorption reduces the mode I crack bridging traction load generated by pins by reducing the shear strength of the pin-laminate interface. This indicates that the mode I delamination toughness induced by pinning is weakened by moisture absorption.