Delamination properties of z-pinned composites in hot-wet environment

The effect of hot-wet environment (75 °C and 85% relative humidity) on the delamination fracture properties and interlaminar toughening mechanisms of z-pinned carbon fibre-epoxy composite is investigated. The absorption rate of water from the hot-wet environment into the composite is accelerated slightly by z-pins, although the pins did not change the saturation limit of the material. Absorbed water weakens the pin/composite interface and this lowers the ultimate elastic traction load generated by z-pins under mode I interlaminar loading. However, once the pin/composite interface has failed, the traction load and energy required to pull-out the z-pins is not affected by absorbed water. The mode I interlaminar fracture toughness and low-energy impact damage resistance of z-pinned composites is not degraded significantly by exposure to hot-wet environment, and this is because absorbed water does not affect the pull-out traction properties of z-pins.