PSI - Issue 61

Shahriar Afkhami et al. / Procedia Structural Integrity 61 (2024) 53–61 Shahriar Afkhami et al./ Structural Integrity Procedia 00 (2019) 000 – 000

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Fig. 2. Stress-strain curves of the welded specimens and their hardness fluctuations on the cold-formed side following their bending radius.

Fig. 3. Failure location of the samples subjected to quasi-static tensile tests.

According to the DIC results of each test (Fig. 4), the plastic deformation of the welded samples was initiated from the weld metal; however, by test progress, the focus of plastic deformation changes from the weld metal into the base material. The change of location in the localized deformation during the test stems from the different hardening behavior of the weld metal compared to the base. Considering the microstructural differences between the weld and base metals, the weld contained a lower fraction of martensite with more ferritic features than the base materials [4]. This difference can contribute to the weld metal’s lower yielding point and higher hardening capacity than the base metal. The change of localized plastic deformation from the weld metal to the base material can also explain the similar plastic deformation routes of the samples with different DOCs up to a particular strain ( ≈ 3%) in Fig. 2 and then diverging from each other beyond this certain deformation point. In other words, the plastic deformation was governed by the weld metal until a certain deformation stage ( ≈ 3% in Fig. 2), and beyond that limit, the base metal is the governing material. Fracture surface analysis of the tensile specimens indicated predominantly ductile fracture features in all the broken samples, regardless of the DOC in their bent side. As shown in Fig. 5, even in the welded joint with a bent base metal with R = 10 mm ( ≈ 14% DOC), the fracture surface was a mixture of dimples and cleavage features, indicating a mixed ductile failure for the welded specimens. The relatively limited average depth of the dimples points to the limited ductility of the welded joint. According to Fig. 5, microvoid coalescence was the dominant fracture mechanism in the welded joints, regardless of their DOC. Also, a lamination was detected along the center line of the failed specimen in Fig. 5; however, this discontinuity is deemed to have an insignificant role in the failure of the samples since the