Effect of Z-pin on the through-the-thickness strength of woven composite laminates

Delamination failure occurs due to the out-of-plane loading because of the weakness in the thickness directional properties of composite materials. The z-pinned composite has been developed to overcome such a problem. In this study, the mechanical properties of z-pinned composite laminates were examined using the analytical model. The effects of z-pins on the strength in the thickness direction were investigated. Fibers in the laminate are gradually waved by the formation of resin rich zone caused by inserting the z-pins. A constitutive model was developed for the predictions of strengths of woven z-pinned composites. The changes in the strengths in the in-plane and out-of-plane directions of the woven z-pinned composites and the effects of controlling parameters such as the diameter of z-pin and densities of z-pin on the strengths were identified. It was found that the out-of-plane tensile strength increases 14% relative to that of composite without z-pins when the diameter of z-pin is 0.25 mm. However, the in-plane tensile strength and in-plane and out-of-plane shear strengths were reduced to 9%, 7% and 8%, respectively, over the strengths of composite without z-pins. Qualitatively good correlations are obtained between the results of the suggested model and the experiments.