Pull-out testing of multiscale structured metallic z-reinforcements for CFRP laminates

A testing method is presented to determine the pull-out behavior of interleaving metallic z-reinforcements for carbon fiber reinforced polymer (CFRP) laminates and joints. Energy absorbing mechanisms are described with respect to the metallic materials and means of surface pretreatment applied. Mechanical, wet-chemical and physical pretreatments result in milli-, micro- and nanoscaled oxide morphologies of titanium and stainless steel surfaces. Both, a high macro roughness of the reinforcement surface and a low difference in thermal expansion with regard to the surrounding CFRP is clearly proven to feature the highest level of energy absorption during pull-out tests. Surface analyses through scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) indicate laser-induced nanostructure's scale and morphology to provide good adhesion properties but not to allow macroscopic friction between metal surface and epoxy resin.