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° to the loading direction, respectively)were investigated by experiments and simulations. The production process of Ø 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, Ø 0.11 mm Z-pins can effectively reduce the strain level around the notch compared with the unpinned specimen. Ø 0.11 mm Z-pins aligned at 45° to the loading direction resulted in a 9 percent increase in open-hole tensile strength and a 54.1 percent reduction in delamination damage area. Finally, the simulation optimization is used to find that the 30° alignment has a better effect of suppressing delamination.