Issue 41

Y. Nadot et alii, Frattura ed Integrità Strutturale, 41 (2017) 220-226; DOI: 10.3221/IGF-ESIS.41.30 221 up to a variation of the amplitude of the displacement of 10 % (Fig. 1d). This variation leads to a 2.5 mm depth fatigue crack in the middle of the welded junction as illustrated in Fig. 2. The welded junction is designed such as the crack is not very deep at the end of the welded line. The initiation site is systematically identified after the test and reported in a schematic drawing of the cross section of the welded junction. Fatigue tests are conducted at low frequency, under force controlled and sinusoidal wave. The load ratio is specified for each test. The fatigue results are presented using the amplitude of the force. Figure 1 : (a) Fatigue device with grip system; (b) welded sample; (c) cross section of welded junction; (d) arrest criterion. Figure 2 : (a) Fatigue crack depth from the surface; (b) general view of the welded junction; (c) crack depth profile in depth. Fatigue tests results under tensile constant amplitude loading are presented in Fig. 3 for three different load ratios. The initiation site is the same whatever the load ratio, at the root of the weld. We can conclude from Fig. 3 that the governing parameter is the amplitude of the loading whatever the load ratio, this result is classical for welded structures under high cycle fatigue loading. The slope of the Basquin curve ‘m’ is given for each loading, the results show that this parameter is close to 3, again a standard result for welded structures.