Enhancement of composite open-hole tensile strength via fine Z-pins arrangements

The damage to structural performance caused by cut-out or holes is inevitable. In this paper, a new method to improve the tensile strength of open-hole laminates by using ultrasound-guided machine to control different fine Z-pin arrangement angles was proposed. The influence of systematically changing size parameters (0.11 mm, 0.28 mm and 0.5 mm diameters) and the direction of arrangement (unenhanced, parallel, vertical and 45 degrees to the loading direction, respectively) were investigated by experiments and simulations. The production process of o 0.11 mm Z-pin with tensile strength up to 3500Mpa is firstly proposed. Z-pins with larger diameters have a certain inhibition effect on the depth of delamination damage, the connected resin-rich area seriously reduces the open-hole tensile strength when increasing the volume contents. In contrast, o 0.11 mm Z-pins can effectively reduce the strain level around the notch compared with the unpinned specimen. o 0.11 mm Z-pins aligned at 45 degrees to the loading direction resulted in a 9% increase in open-hole tensile strength and a 54.1% reduction in delamination damage area. Finally, the simulation optimization is used to find that the 30 degrees alignment has a better effect of suppressing delamination.