Issue 33

D. G. Hattingh et alii, Frattura ed Integrità Strutturale, 33 (2015) 382-389; DOI: 10.3221/IGF-ESIS.33.42 388 The chart of Fig. 6 makes it evident that the use of the MWCM resulted in estimates falling within the wider scatter band between the two characterising the fully-reversed uniaxial and torsional fatigue curve used to calibrate the constants in the MWCM’s governing equations. It is possible to conclude by observing that the obtained level of accuracy is certainly satisfactory, since, from a statistical point of view, we cannot ask a predictive method to be more accurate than the experimental information used to calibrate the method itself. C ONCLUSIONS  The novel FS welding process developed via this project is seen to be capable of producing high quality FS welds in aluminium tubular joints. Such an advance in joining technology is anticipated to have high industrial impact.  The MWCM applied in terms of nominal stresses is a powerful design tool suitable for performing multiaxial fatigue assessment of FS welded connections.  More work needs to be done in order to formalise a comprehensive design approach suitable for designing FS welded joints against multiaxial fatigue loading by directly post-processing the local linear-elastic stress fields acting on the material in the vicinity of the crack initiation locations. A CKNOWLEDGEMENTS he Leverhulme Trust (www.leverhulme.ac.uk) is acknowledged for fully supporting the present research investigation (Project’s Reference Number: IN-2012-107). R EFERENCES [1] Shah, S., Tosunoglu, S., Friction stir welding: current state of the art and future prospects, in: 16 th World Multi- Conference on Systemics, Cybernetics and Informatics, Orlando, Florida, (2012). (available at www.eng.fiu.edu) . [2] Colligan, K. J., Friction stir welding for ship construction, Contract N0014-06-D-0048 for the Office of Naval Research, Concurrent Technologies Corporation, Harrisburg, PA, (2004) (available at www.nmc.ctc.com) . [3] Thomas, W. M. , Nicholas, E. D., Friction stir welding for the transportation industries, Mater. Design, 18(4/6) (1997) 269-273. [4] Burford, D., Widener, C., Tweedy, B., Advances in Friction Stir Welding for Aerospace Applications, in: 6 th AIAA Aviation Technology, Integration and operations Conference, (2006), American Institute for Aviation and Astronautics. doi: 10.2514/6.2006-7730 [5] American National Standards Institute, AWS D17.3/D17.3M:2010, Specification for friction stir welding of aluminum alloys for aerospace hardware, American Welding Society, (2010). [6] MSFC Technical Standard EM 30, MSFC-SPEC-3679, Process specification – welding aerospace hardware, National Space and Aeronautics Administration, (2012). [7] Lomolino, S., Tovo, R., dos Santos, J., On the fatigue behaviour and design curves of friction stir butt-welded Al alloys, Int. J. Fatigue, 27(3) (2005) 305-316. [8] Moreira, P. M. G. P., Santos, T., Tavares, S. M. O., Richter-Trummer, V., Vilaça, P., de Castro, P. M. S. T., Mechanical and metallurgical characterization of friction stir welding joints of AA6061-T6 with AA6082-T6, Mater. Design, 30 (2009) 180-187. [9] Spindel, J. E., Haibach, E., Some considerations in the statistical determination of the shape of S-N cruves, in: R. E. Little and J. C. Ekvall (Eds.), Statistical Analysis of Fatigue Data, ASTM STP 744, (1981) 89–113. [10] Susmel, L., Multiaxial Notch Fatigue: from nominal to local stress-strain quantities, Woodhead & CRC, Cambridge, UK, ISBN: 1 84569 582 8, (2009). [11] Susmel, L., Multiaxial Fatigue Limits and Material Sensitivity to Non-Zero Mean Stresses Normal to the Critical Planes, Fatigue Fract. Eng. Mat. Struct., 31 (2008) 295-309. [12] Susmel, L., Lazzarin, P., A Bi-Parametric Modified Wöhler Curve for High Cycle Multiaxial Fatigue Assessment, Fatigue Fract. Eng. Mat. Struct., 25 (2002) 63-78. T