PSI - Issue 42

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Darko Pastorcic et al. / Procedia Structural Integrity 42 (2022) 374–381 Darko Pastorcic et al./ Structural Integrity Procedia 00 (2019) 000 – 000

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d)

c)

Fig. 8. equivalent plastic strain to triaxiality for the first failure element: (a) BM in sea: (b) BM at sea slush; (c) BM in the water; (d) HAZ and WM after 36 months

The most damaging environmental condition affecting the test coupons is the sea slush. It is determined that critical equivalent plastic strain decreases as the stress triaxiality increases with the change of the pit size generated by the environment and the exposure. Consequently, this leads to earlier ductile fracture initiation and failure. The result of the simulated FEM tension test is presented together with the stress strain diagram obtained from experimental tensile test, Fig. 9, both with degradation of the yield strength and the ultimate tensile strength. In each test, the failure occurred from the pits that were induced in the base material AH36.

a)

b)

c)

Figure 9. Numerical and experimental tensile test comparison for specimens after 36 months exposure. in : (a) water, (b) sea, (c) sea slush

4. Conclusion This paper presents the numerical analysis of the mechanical characteristics of the butt-welded joints made of AH 36 shipbuilding steel, which were exposed to corrosive environments for 6, 12, 24, 36 months. Measurements were base for development of the numerical model of the corrosion pits and simulated tensile test. The corrosion pits in BM, HAZ and WM were modelled using Poisson process for the distribution of the pits over surface and normal distribution for the pit depth progress. The experimental and numerical results showed failure in BM by all test specimens, because the BM was mostly affected by the corrosive environments, particularly the sea wave exposure. It is shown that with increase of the stress triaxiality, which depends of the pit size and distribution, critical plastic strain decreases, what leads to earlier ductile fracture initiation. The results of this model, based on the real corrosive conditions, can be used for further assessment of the mechanical properties of other types of steel (EH, DH) exposed to sea environment and for the design and analysis of the naval and offshore structures.