Improving the structural properties and damage tolerance of bonded composite joints using z-pins

Abstract

The effect of z‐pin reinforcement on the structural properties and damage tolerance of composite joints is experimentally studied in this article. The ultimate load, failure strain, and absorbed energy capacity of carbon fiber‐epoxy T‐joints and single lap joints increased rapidly with the volume content of z‐pins. The improvement to these properties was due to the capacity of z‐pins to resist unstable (rapid) delamination growth along the bonded region to the T‐joints (induced by interlaminar mode I stress) and lap joints (induced by interlaminar mode II stress) by forming a crack bridging traction zone. Large increases to the damage tolerance of T‐joints and lap joints containing pre‐existing bond‐line cracks were also achieved by z‐pins. The z‐pins formed a bridging traction zone across the delaminated bond‐line which retained high strength in the joints, even in the presence of very long cracks which severely weakened conventional joints.