Issue 31

J. Lopes et alii, Frattura ed Integrità Strutturale, 31 (2015) 67-79; DOI: 10.3221/IGF-ESIS.31.06 67 Inter-laminar shear stress in hybrid CFRP/austenitic steel J. Lopes, M. Freitas ICEMS and Departamento de Engenharia Mecânica. Instituto Superior Técnico. Universidade de Lisboa. Av. Rovisco Pais 1049-001 Lisboa. Portugal D. Stefaniak DLR, Institute of Composite Structures and Adaptive Systems, Ottenbecker Damm 12, 21684 Stade, Germany P.P. Camanho IDMEC. Pólo FEUP. Rua Dr. Roberto Frias. 4200-465 Porto. Portugal A BSTRACT . Bolted joints are the most common solution for joining composite components in aerospace structures. Critical structures such as wing to fuselage joints, or flight control surface fittings use bolted joining techniques. Recent research concluded that higher bearing strengths in composite bolted joints can be achieved by a CFRP/ Titanium hybrid lay-up in the vicinity of the bolted joint. The high costs of titanium motivate a similar research with the more cost competitive austenitic steel. An experimental program was performed in order to compare the apparent inter-laminar shear stress (ILSS) of a CFRP reference beam with the ILSS of hybrid CFRP/Steel beams utilizing different surface treatments in the metallic ply. The apparent ILSS was determined by short beam test, a three-point bending test. Finite element models using cohesive elements in the CFRP/Steel interface were built to simulate the short beam test in the reference beam and in the highest inter- laminar shear stress hybrid beam. The main parameters for a FEM simulation of inter laminar shear are the cohesive elements damage model and appropriate value for the critical energy release rate. The results show that hybrid CFRP/Steel have a maximum ILSS very similar to the ILSS of the reference beam. Hybrid CFRP/Steel is a competitive solution when compared with the reference beam ILSS. FEM models were able to predict the maximum ILSS in each type of beam. K EYWORDS . Fracture; Fatigue; Durability; Case studies; Experimental techniques; Numerical techniques. I NTRODUCTION omposite materials have been used in aerospace applications in the past four decades. Their use has grown in the share of weight of aircrafts (from the very specific use in nose cones and radomes of the Airbus A300 to the full barrel composite fuselage of the Boeing 787) and also in complexity. The development of composite manufacturing has enabled the shift from rather simple shells and sandwich structures to full composite assemblies like elevators, horizontal and vertical tail planes, and the already mentioned full barrel composite fuselage. This shift from modular architecture to integral architecture [1] has had many advantages: It has reduced the number of components of an assembly and therefore the number of fasteners. It has simplified the manufacturing process by reducing the number C