Pullout performance of circumferentially notched z-pins in carbon fiber reinforced laminates

This paper presents an experimental study on the pullout performance of circumferentially notched cfrp z-pins in carbon fiber/epoxy laminates. Unidirectional pullout specimens were reinforced with z-pins at a volume content of 1.0%. Four different notch depths were used to investigate their effect on the bridging forces and the dissipated energy during pullout. Compared to smooth z-pins, notched pins were found to provide much higher bridging forces, with the lowest notch depth of 25 µm being the most effective. The debonding force and maximum friction force could be increased up to 87% and 76%, respectively. Because of the enhanced bridging forces, notched z-pins were able to increase the amount of energy that is dissipated during pin pullout. Notching the pins was found to have no influence on the stiffness of the pins during pin pullout. The calculated decrease in strength was 10-28%, depending on the notch depth of the pins.