Issue 33

D. G. Hattingh et alii, Frattura ed Integrità Strutturale, 33 (2015) 382-389; DOI: 10.3221/IGF-ESIS.33.42 382 Focussed on multiaxial fatigue Multiaxial fatigue of aluminium friction stir welded joints: preliminary results D. G. Hattingh Nelson Mandela Metropolitan University, Private Bag X6011, Port Elizabeth 6000, South Africa danie.hattingh@nmmu.ac.za M. N. James University of Plymouth, Drake Circus, Devon PL4 8AA, England, United Kingdom m.james@plymouth.ac.uk L. Susmel The University of Sheffield, Sheffield S1 3JD, United Kingdom l.susmel@sheffield.ac.uk R. Tovo University of Ferrara, via Saragat 1, 44100 Ferrara, Italy roberto.tovo@unife.it A BSTRACT . The aim of the present research is to check the accuracy of the Modified Wöhler Curve Method (MWCM) in estimating the fatigue strength of friction stir (FS) welded tubular joints of Al 6082-T6 subjected to in-phase and out-of-phase multiaxial fatigue loading. The welded samples being investigated were manufactured by equipping an MTS I-STIR process development system with a retracting tool that was specifically designed and optimised for this purpose. These specimens were tested under proportional and non-proportional tension and torsion, the effect of non-zero mean stresses being also investigated. The validation exercise carried out by using the generated experimental results allowed us to prove that the MWCM (applied in terms of nominal stresses) is highly accurate in predicting the fatigue strength of the tested FS welded joints, its usage resulting in estimates falling with the uniaxial and torsional calibration scatter bands. K EYWORDS . Friction stir welding; Multiaxial fatigue; Critical plane. I NTRODUCTION riction stir (FS) welding is a solid-state joining process that results, if applied correctly, in connections characterised by high mechanical performance. The large plastic deformations induced in the weld zone produce dynamically recrystallized fine grains (i.e. in the weld nugget), the low heat input limiting local distortions and the magnitude of residual stresses. These effects are generally beneficial to the dynamic performance of welds. Alongside these advantages, F