Design of through thickness reinforced composite/metal joints-with the help of finite element analysis and quasistatic testing using digital image correlation

Through thickness reinforced composite/metal joints represent an approach for lightweight hybrid joint design. Small fasteners, called pins, penetrate the composite laminate and create a form fit between metal and composite joint partner. This paper presents quasistatic testing on through thickness reinforced composite/steel and composite/titanium joints, produced in a closed mold resin transfer molding process. Testing results were analyzed with the help of digital image correlation techniques. However, digital image correlation can only capture the surface of the specimen. Mechanical interactions between all joint members, namely pins, steel or titanium tab and composite joint member cannot be fully investigated. Therefore, finite element analysis was used to determine stress states at different load levels. Furthermore, it was found that fiber undulations, caused by stamping the pins in the dry preform, lead to a serious degradation of laminate properties and reduced joint stiffness and strength.