Enhancement of Delamination Resistance by Novel Z-pinning for Composite Laminated Structures

Abstract

Z-pin reinforced laminates are usually manufactured by inserting the pins vertically into the laminate. However, in the present work, we consider a method in which pins are inserted at an angle to the vertical to enhance pullout strength via mechanical interlocking. This method of reinforcement not only increases the contact area of the z-pin with the laminate, but also reduces the stresses in the interface layer between the pin and the laminate, thus delaying delamination. Experiments were conducted to verify computational results 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 with increasing pin angles. In addition, a novel variety of pin, namely the threaded pin, was used to reinforce laminate specimens and tested under tensile loading. Results showed that the threaded pin provided superior pullout strengths when compared with laminates with smooth steel and carbon fiber inserts.