Mixed Mode Fracture Toughness of an Adhesive Bonded Joint

Adhesive joints are continuously emerging as candidate to replace traditional fastening systems, such as riveting or welding, in primary structural applications. A wide class of components belonging to electronic, automotive and aerospace industries contains adhesive joints, however, the reliability during service constitutes a major technical problem as these contain flaws. Therefore, their use in critical structural applications necessitates the developments of robust integrity assessment methodologies and testing procedures. In the present paper, the interfacial fracture resistance of Al/Epoxy joints has been studied using a Cracked Lap Shear (CLS) specimen loaded in four point bending. In particular, experimental results are rationalized by means of finite element analyses (FEA) of the test specimen and some interesting features concerning interfacial facture issues are elucidated. Interfacial fracture toughness is pointed out in terms of the critical strain energy release rate and of the phase angle of the complex Stress Intensity Factor (cSIF). In addition, fracture surfaces are analyzed and the locus of failure is discussed.