Issue 41

Y. Nadot et alii, Frattura ed Integrità Strutturale, 41 (2017) 220-226; DOI: 10.3221/IGF-ESIS.41.30 220 Focused on Multiaxial Fatigue Gradient approach for the evaluation of the fatigue limit of welded structures under complex loading Y. Nadot, D. Halm, F. Dal Cero Coelho Institut PPRIME, ISAE ENSMA, CNRS, Université de Poitiers, Téléport 2, 1 avenue Clément Ader, BP 40109, 86961 FUTUROSCOPE CHASSENEUIL Cedex, France yves.nadot@ensma.fr A BSTRACT . Welded ‘T-junctions’ are tested at different load ratio for constant and variable amplitude loading. Fatigue results are analyzed through the type of fatigue mechanisms depending on the loading type. A gradient approach (WSG: Welded Stress Gradient) is used to evaluate the fatigue limit and the comparison with experimental results shows a relative good agreement. Non- linear cumulative damage theory is used to take into account the variable amplitude loading. K EYWORDS . Weld; Fatigue; Gradient. Citation: Nadot Y., Halm D., Dal Cero Coelho F., Gradient approach for the evaluation of the fatigue limit of welded structures under complex loading, Frattura ed Integrità Strutturale, 41 (2017) 220-226. Received: 28.02.2017 Accepted: 03.05.2017 Published: 01.07.2017 Copyright: © 2017 This is an open access article under the terms of the CC-BY 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. I NTRODUCTION he objective of this paper is to propose a methodology to evaluate the fatigue life of a welded structure submitted to variable amplitude loading. A previous study [1] was dedicated to the understanding of the variable amplitude loading on the material behaviour itself under variable amplitude loading. The fatigue criterion used [2] is able to take into account complex loading such as multiaxial with phase shift. A non-linear cumulative damage theory is used [1] in order to take into account the effect of the variable amplitude loading. This paper describes the test results, the criterion used and details a relative simple proposition to take into account the heterogeneous stress field around the hot spot of the welded structure. We propose a methodology based on the stress gradient measured in correlation with the geometry. EXPERIMENTAL RESULTS he welded sample is presented in Fig. 1b. The material is a high strength steel used in the automotive industry. The grip system used (Fig. 1a) allows tension or bending with good control of the boundary conditions (no pre-stress induced by the system). The cross section of the welded junction is presented in Fig. 1c. Fatigue tests are conducted T T