PSI - Issue 2_B

W. Rekik et al. / Procedia Structural Integrity 2 (2016) 3491–3500 Author name / Structural Integrity Procedia 00 (2016) 000–000

3500

10

Table 1. Fracture toughness at initiation for both CT and SENT specimens Initial crack configuration

Ji for CT specimens (kJ/m²) Ji for SENT specimens (kJ/m²)

Fusion zone

80 40 17

82 47

Interface FZ/HAZ

HAZ at 11 from the middle of the weld joint

17.5

Base metal

9

10

5. Discussion and conclusions In order to ensure the integrity of welded structures, failure assessment is required and the identification of a detrimental metallurgical zone from a fracture mechanics point of view is of high interest. However, the analysis is highly dependent on the loading mode:  for an imposed displacement loading, the crack first initiates in the base metal (Fig .10) and the heat affected zone close to the base metal. The crack, once initiated in the BM induces probably the collapse of the structure due to the low tearing modulus involved in the crack extension process.  for an imposed loading, fracture initiation occurs first in the HAZ (Fig .10) which can therefore be considered as potential detrimental point of the welded joint. For an analysis based on crack growth more than initiation, the soft heat affected zone (Fig .9) can be considered as the weakest metallurgical zone of the weld joint as it is preferential to crack extension. Acknowledgements The authors express special thanks to G.Perez, CEA research center, for valuable discussions on the mechanical tests conduct. References ASTM E1820 standard:Test Method for Measurement of Fracture Toughness Bardel, D., 2014. Rôle de la microstructure d’un alliage à durcissement structural sur son comportement cycliques aprés un transitoire thermique. Chen, X., Lu, H., Chen, G., Wang, X., 2015. A comparison between fracture toughness at different locations of longitudinal submerged arc welded and spiral submerged arc welded joints of API X80 pipeline steels, Eng. Fract. Mech. 148, 110–121. Cieslak, M.J., Fuerschbach, P.W., 1988. On the weldability, composition, and hardness of pulsed and continuous Nd:YAG laser welds in aluminum alloys 6061,5456, and 5086, Metall. Trans. B. 19, 319–329. Dos Santos, J., Çam, Torster, F., Insfran, A., Riekehr, S., Ventzke, V., et al., 2000. Properties of power beam welded steels, al-and ti-alloys: Significance of strength mismatch, Weld. World. 44, 42–64. Fracture mechanics toughness testing, Parts 1 -4, British Standard Institution Hollomon, J.H., 1945. Tensile deformation. Transaction of the American Institute of Mining, Metallurgical and Petroleum, 162, 268–290. http://www-cast3m.cea.fr/ Laukkanen, A., Nevasma, P., Ehrnstén, U., Rintama, R., 2007. Characteristics relevant to ductile failure of bimetallic welds and evaluation of transferability of fracture properties, Nucl. Eng. Des. 237, 1–15. Liang, Z., 2012. Clustering and Precipitation in Al-Mg-Si Alloys. Nègre, P., Steglich, D., Brocks, W., 2004. Crack extension in aluminium welds: a numerical approach using the Gurson–Tvergaard–Needleman model, Eng. Fract. Mech. 71, 2365–2383. Rekik, W., Ancelet, O., Gardin, C., 2016. Identification of the gradient of mechanical properties in Electron Beam welded joints of thick Al6061-T6 plate, Press. Vessel. Pip.. Roberts, S., Welding Thick Aluminum is Challenging, Can. Ind. Mach.. Ventzke, V., Dos Santos, J.F., Koc, M., Jennequin, G., 1999. Characterisation of electron beam welded aluminium alloys, 4, 317–323. Zhang, Z., Dong, S., Wang, Y., Xu, B., Fang, J., He, P., 2015. Microstructure characteristics of thick aluminum alloy plate joints welded by fiber laser, Mater. Des. 84, 173–177.