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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= ̅ 1 ∫ ∙ ̅ ̅

(3)

0 where ̅ is equivalent plastic deformation and T av is average triaxiality. 3.3. Material properties

The specimens comprise three zones: BM, HAZ and WM, each with different mechanical properties, which were taken into consideration. The width of each zone was determined through the hardness testing of the specimens. The mechanical properties of the AH36 steel (BM) obtained from the tensile test in air are: yield stress 320MPa (slightly less than 355MPa, value from ASTM A131), ultimate tensile strength 450MPa, Young’s modulus 2 08 GPa. According to Lee and Wierzbicki (2005), fracture occurs at the equivalent plastic strain 0.43 and 0.4 triaxiality, what gives α = 0.78 . Furthermore, the toughness parameter is in a relationship to the Charpy V notch toughness, through the following expression, Kanvinde and Deierlein (2006):  = 0.016 ∙ CVN − 0.93 (4) where CVN is the upper shelf Charpy V Notch energy. For AH 36, CVN is 105 J at room temperature, the value is obtained from the test Fig. 2(a), what gives α = 0.75 , close to previously calculated α . The hardening model for AH 36 flat specimens (rectangle cross section) is given through combined Swift Voce hardening model, Cerik and Choung (2020): ̅ = ∙ ∙ ( 0 + ̅ ) + (1 − ) ∙ ( 0 + ∙ (1 − (− ∙ ̅ ) )) (5) where σ̅ P is the equivalent plastic stress, ϵ̅ P is equivalent plastic strain, while , , , ϵ 0 , 0, , are the parameters obtained from tension test and data fitting(AH36 specimen) presented in Table 2. Table 2. Swift Voce hardening law parameters BM Steel α A ϵ 0 n σ 0 Q Β AH 36 0.51 876.5MPa 0.01529 0.263 297 MPa 273MPa 14.47 The welding of steels is affected by both the temperature and composition which have huge influence on the microstructure development and consequently on the mechanical properties. The hardness of the HAZ is therefore higher than by the BM, Fig. 2(b) and it is base for estimating the yield stress and tensile strength, Akselsen et al.(1989), Pavlina and Van Tyne (2008), which are 370 MPa and 500 MPa respectively and for the assessment of the hardening power law, Zhu and Leis (2005). = 730 ∙ 0.122 (6) where is the true plastic stress, true plastic strain. The parameter for SMCS criterion is 1.66 and it is assessed from equation (4) for CVN=162 J at room temperature, HAZ Fig. 2(a). Weld metal, wire ER50-6, has 527 MPa yield strength and 647 MPa tensile strength and hardening power law, Ran et al.,( 2019): = 931 ∙ 0.133 (7) The parameter for SMCS criterion α is 2.66 and it is assessed from equation (4) for CVN=200 J at room temperature, WM Fig. 2(a).