PSI - Issue 72

Nedeljko Vukojević et al. / Procedia Structural Integrity 72 (2025) 157 –163

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Fig. 3. (a) hardness at the welded joint of P460x15mm; (b) hardness at the welded joint of S235x15mm

3.3. Tensile test Tensile tests were conducted on samples extracted from the dish ends at room temperature (+16°C), BAS EN ISO 4136 (2014), BAS EN ISO 6892-1 (2017). The test specimens were modified with a transverse groove in the HAZ, which was the area under investigation. Mechanical properties for Series II samples (after plastic deformation) are higher than in the base material, as presented in Tab.1. Plastic deformation led to material strengthening and an increase in yield stress and tensile strength. Concurrently, a decrease in ductile properties was observed, i.e., reduced elongation and contraction before fracture. Fracture occurred in the HAZ in a controlled manner, indicating "overmatching" of the welded joint, meaning that the mechanical properties in the HAZ were superior to those of the base material. In the HAZ of the welded joint for the S235 steel in Series I, values of contraction and elongation increased relative to Series II, while for the high-strength P460 material these values were reduced. 3.4. Impact energy test Impact testing was carried out on specimens with notches to determine the tendency towards brittle fracture. The impact tests were performed at room temperature (+20°C) using a Charpy pendulum with a 300 J capacity and a 10x10x55 specimen with a 2 mm V-notch, BAS EN ISO 9016(2012), ISO 148-1(2017). The total impact energy consumed in the HAZ of Series II was reduced compared to Series I. The strengthening effect of plastic deformation resulted in lower toughness. Generally, the total impact energy values in the HAZ show a significant tendency toward brittle fracture. 3.5. Fracture mechanics parameters Due to the low values of total impact energy, additional tests of fracture mechanics parameters are performed with the aim of determining the fracture toughness of the samples. Tests are carried out according to standard procedures ASTM E399(2022) and ASTM E1820 (2018), but only on specimens taken after plastic deformation. The samples for the tests are CT specimens of less thickness than the real dish ends. The reduction in thickness was made because the dish ends are spatially curved (spherical part of the dish ends), and therefore do not meet the test conditions prescribed by the fracture mechanics standards. Samples with a thickness of 14 mm are thinned to 11 mm, and samples with a thickness of 6 mm to 3 mm, Fig.4.

Fig. 4. (a) CT specimens, t = 11 mm; (b) CT specimens, t = 3 mm;