Investigations on the influence of notched z-pins on the mechanical properties of carbon-fiber reinforced plastics

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Fiber reinforced plastics (FRP) offer excellent mechanical properties regarding the fiber direction due to their microstructural construction of load-bearing fibers and shaping matrix. By contrast, a structure made of FRP loaded perpendicular to the laminate plane exhibits inferior mechanical properties, making it susceptible to delamination, e.g. due to interlaminar shear or impact stresses. The insertion of z-pins through the thickness of polymer matrix composites has been found to be a promising and low-cost method to enhance the interlaminar shear strength and reduce the mentioned vulnerability to delamination. Z-pins are needle-shaped, usually round bars, with diameters of typically 0.1-1.0 mm, and consist of materials with a high stiffness and strength, such as steel, titanium or carbon fiber reinforced plastics (CFRP). In conjunction with pre-impregnated semi-finished products (prepregs), the z-pinning technique is the most commonly used method for through-thickness reinforcement of FRP. Numerous studies have shown that the z-pinning is a very effective method to increase the damage tolerance of FRP. The aim of this project is the further increase of the effectiveness of z-pins by the application of a surface structure via ultra-short laser pulses and thus the creation of a form closure between the pins and laminate. Based on internal preliminary work, the influence of different surface structures on the mechanical properties of carbon fiber reinforced plastics and an optimal surface geometry should be determined.