Compression fatigue properties of z-pinned quasi-isotropic carbon/epoxy laminate with barely visible impact damage

This paper presents an experimental study into the use of z-pins to improve the compression fatigue properties of quasi-isotropic carbon fibre–epoxy composite containing barely visible impact damage (BVID). The study investigates the effect of increasing volume content of z-pins (up to 4%) on the barely visible impact damage resistance, post-impact compression fatigue properties, and fatigue damage mechanisms of a quasi-isotropic carbon–epoxy material. The study reveals new insights into the impact damage resistance of z-pinned composites. Z-pins induce different responses in the compression fatigue properties of the quasi-isotropic composite following low or high-energy impact loading. Z-pins proved ineffective at increasing the fatigue properties when the quasi-isotropic composite contained low-energy BVID. However, z-pins were effective at improving the fatigue performance of the composite with high-energy BVID, with the post-impact fatigue life and fatigue endurance limit increasing with the pin content. The improvement in fatigue performance is due solely to the increased resistance against high-energy impact damage imposed by the z-pins. It is also found that z-pins do not affect the fatigue mechanism or fatigue damage growth rate of the composite containing BVID.