Issue 37

L. Susmel et alii, Frattura ed Integrità Strutturale, 37 (2016) 207-214; DOI: 10.3221/IGF-ESIS.37.27 213 It can be concluded from these results that, independently from the adopted stress analysis strategy, the resulting level of accuracy is certainly satisfactory (see Figure 4), since, from a statistical point of view, we cannot expect that a predictive method will be more accurate than the experimental information used to calibrate the method itself. C ONCLUSIONS  For the specific profile of the FS welded fatigue specimens, the fatigue behaviour of the these tubular joints of Al 6082-T6 could successfully be modelled using notch mechanics concepts.  The MWCM was applied not only in terms of nominal and notch stresses, but also in conjunction with the Point Method and was seen to be highly accurate in estimating the fatigue lifetime of the FS welded joints.  For the investigated FS welded connections, the MWCM was seen to be capable of correctly modelling not only the presence of non-zero mean stresses, but also the degree of multiaxiality and non-proportionality of the applied load history. A CKNOWLEDGMENT upport for this work from the Leverhulme Trust through the award of International Network Grant IN-2012-107 is gratefully acknowledged. R EFERENCES [1] Shah, S., Tosunoglu, S. (2012) Friction stir welding: current state of the art and future prospects, in Proceedings of the 16th World Multi-Conference on Systemics, Cybernetics and Informatics, Orlando, Florida, 17-20 July 2012. [2] Colligan, K.J. (2004) Friction stir welding for ship construction, Contract N0014-06-D-0048 for the Office of Naval Research, Concurrent Technologies Corporation, Harrisburg, PA, US (available at www.nmc.ctc.com ). [3] Thomas, W.M., Nicholas, E.D., Friction stir welding for the transportation industries, Mater. Design., 18 (1997) 269- 273. [4] Burford, D., Widener, C., Tweedy, B. (2006) Advances in Friction Stir Welding for Aerospace Applications, in Proceedings of the 6th AIAA Aviation Technology, Integration and operations Conference, AIAA. doi: 10.2514/6.2006-7730. [5] 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. [6] Susmel, L., Multiaxial Notch Fatigue: from nominal to local stress-strain quantities, Woodhead & CRC, Cambridge, UK, (2009) ISBN: 1 84569 582 8. [7] 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. [8] Susmel, L., Tovo, R., Lazzarin, P., The mean stress effect on the high-cycle fatigue strength from a multiaxial fatigue point of view, Int. J. Fatigue, 27 (2005) 928-943. [9] Susmel, L., A simple and efficient numerical algorithm to determine the orientation of the critical plane in multiaxial fatigue problems, Int. J. Fatigue, 32 (2010) 1875–1883. [10] Susmel, L., Tovo, R., Socie, D.F., Estimating the orientation of Stage I crack paths through the direction of maximum variance of the resolved shear stress, Int. J. Fatigue, 58 (2014) 94–101. [11] Susmel, L., Four stress analysis strategies to use the Modified Wöhler Curve Method to perform the fatigue assessment of weldments subjected to constant and variable amplitude multiaxial fatigue loading, Int. J. Fatigue, 64 (2014) 38-54. [12] Spindel, J.E., Haibach, E., Some considerations in the statistical determination of the shape of S-N cruves, in: R. E. Little, J. C. Ekvall (Eds.), Statistical Analysis of Fatigue Data, ASTM STP 744, (1981) 89–113. [13] Susmel, L., Tovo, R., On the use of nominal stresses to predict the fatigue strength of welded joints under biaxial cyclic loadings, Fatigue Fract. Engng. Mater. Struct., 27 (2004) 1005-1024. S