Effect of grit-blasting on the fracture toughness of hybrid titanium-thermoplastic composite joints

The aim of this study was to determine the effect of the metal surface roughness on the mechanical performance of titanium-unidirectional C/PEKK composite joints. Various surface morphologies were obtained by grit-blasting the titanium surface using different blasting pressures. Subsequently, test coupons were manufactured by co-consolidating titanium-unidirectional C/PEKK in an autoclave. Topographical characterization of the titanium surface and evaluation of interfacial fracture toughness were carried out, in order to correlate joint mechanical performance to titanium's roughness parameters. Furthermore, crack surface analysis was conducted, by means of optical microscopy, to identify and quantify the failure mechanisms driving joint mechanical performance. Results show that rougher surfaces significantly improve the fracture toughness of the hybrid interface. For titanium surfaces with an average roughness exceeding 2.5 μm, the interfacial fracture toughness was found to be comparable to the interlaminar fracture toughness typically measured for thermoplastic composite laminates.