Compression properties of composite laminates reinforced with rectangular z-pins

Abstract This paper presents an experimental study investigating the static and fatigue compression properties of unidirectional and quasi-isotropic carbon fiber/epoxy laminates reinforced with rectangular and circular z-pins. The insertion of z-pins did not affect the compression modulus of the specimens, but all z-pinned laminates demonstrated a significantly reduced compression strength compared to unpinned specimens. Rectangular z-pins that were aligned lengthwise to the fiber direction of the laminate ply were observed to cause minor microstructural damages, such as in-plane fiber waviness. Therefore, the use of rectangular z-pins led to a minor reduction of the compression strength in both unidirectional and quasi-isotropic laminates. Especially for a small number of load cycles, the insertion of z-pins resulted in a decrease in the fatigue performance of the tested unidirectional and quasi-isotropic laminates. Since this deterioration was primarily caused by the initial knockdown of the static compression strength of the z-pinned laminates, rectangular z-pins showed superior fatigue performance in both unidirectional and quasi-isotropic laminates.