Enhancement of Delamination Resistance with Threaded and Anchored Z Pins in Composite Laminated Structures

Abstract

Z-pinning is a technique where composite laminates are typically reinforced with metal or composite fiber pins inserted vertically into the laminate. In the present work, novel approaches to the current z-pinning technology are investigated to increase delamination resistance of the laminate. Using threaded pins for reinforcement increases mechanical interlocking between the pin and the laminate as well as the epoxy-pin contact area thus delaying delamination. When smooth metal pins are used for reinforcement, anchoring their ends on to the surface of the laminate before curing delays delamination through pin gripping. Experiments were conducted to compare pin pullout strengths under tensile loading conditions on reinforced laminates manufactured from IM8-epoxy prepregs. Test results showed increase in pullout strengths and thus the potential for increase in delamination resistance when threaded or anchored pins were used. In addition, fracture toughness and delamination resistance under mode-I loading were investigated by performing experiments on DCB specimens. Results indicate superior delamination resistance properties for both threaded pin and anchored pin inserts.