Mixed mode I/II crack growth investigation for bi-metal FSW aluminum alloy AA7075-T6/pure copper joints

Abstract

Abstract Over the past two decades, a large number of papers have been published for investigating mechanical properties and microstructure of Friction Stir Weld (FSW) joints made of several similar and dissimilar alloys. Crack growth resistance of such joints is an important design parameter for integrity and life assessment of FSW components. In practice, propagation of cracks in structures fabricated by the FSW technique, which initiate in the welding region, can occur under multiaxial and complex tensile-shear loadings. However, review of the literature shows that there are only limited research works regarding mixed mode I/II (i.e. tensile-shear) fracture resistance study of FSW weldments. Thus, to fill this research gap in this paper, mixed mode I/II fracture resistance of dissimilar aluminum alloy AA7075-T6 / pure copper butt joints welded by the FSW is investigated both experimentally and theoretically. First, a novel semi-circular bend shape specimen is proposed for conducting mixed mode I/II fracture tests. Then, due to ductile behavior of the cracked specimens, the experimentally obtained load-carrying capacity (LCC) of the tested specimens is predicted theoretically using the maximum tangential stress (MTS) and mean stress (MS) criteria in conjunction with the Equivalent Material Concept (EMC). It is revealed that both EMC-MTS and EMC-MS combined criteria can predict quite well the experimental results.