PSI - Issue 19

M. Duchet et al. / Procedia Structural Integrity 19 (2019) 585–594 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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bracket can be loaded in bending. The demonstrators were tested in load-controlled mode with a loading ratio R = 0.1.

Fig. 11: clamping line for tension loading (left) and bending loading (right).

3.2. Fatigue results on T-joint demonstrators

Fatigue campaigns were led with different configurations, materials and reinforcement solutions. The objective was to reach roughly 15% of light-weighting. In details were investigated on the T-joint demonstrators the influences of: • the loading mode: tension or bending • the reduction of the thickness from 3.4 mm as reference value • a second pass TIG remelting process • a transverse oscillating welding process • a shot-peening post-treatment of demonstrators According to the objective to reduce the weight of the structure, fatigue results are presented with the reference thickness of 3.4 mm in the as-welded condition. Fig. 12 exposed the fatigue results obtained in tension and bending loading. The reference as-welded configuration -thickness 3.4 mm- is compared with the as-welded reference - thickness 2.7 mm- (in blue). Undoubtedly, the first one offers a better fatigue resistance at 2 million cycles. For instance, under tension loading, the fatigue strength is reduced from 8 kN at 3.4mm down to 5.5 kN at 2.7 mm (a reduction of 30%). Nevertheless, after applying reinforcement solutions, one can notice that each reinforcement solution applied on 2.7 mm thickness exhibits a better fatigue behaviour than the as-welded refence 3.4 mm. One can observe that the improvement solutions have a bigger impact in bending loading than for tension loading. Of course, the reinforcement solutions need to be optimized to obtain their full benefit regarding fatigue. To achieve a good evaluation of the fatigue strength, one of the key points was the determination of an initiation criterion allowing a comparative analysis of fatigue results. Here strain gauges were used, placed at the crack initiation locations. 20% of reduction of the strain gauge amplitude was the defined threshold to stop the tests. Observations of fracture surface do not show fatigue cracks exceeding 10 mm length. A high number of tests have been conducted to