PSI - Issue 42

Toru Yagi et al. / Procedia Structural Integrity 42 (2022) 702–713 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

705

4

length of test specimens [mm]

L S

length of span in three-point bending test [mm] initial notch depth of test specimens [mm] curvature radius of test specimens [mm]

a 0

R

P load in fracture toughness test [kN] g clip gauge opening displacement [mm] ν Poisson’s ration YS yield stress [MPa] E young’s module [MPa] d dynamic stress intensity factor [MPa √m ] universal function of crack speed V crack velocity [m/s] 1 longitudinal wave speed [m/s] 2 shear wave speed [m/s] r Raileigh wave velocity [m/s] closure side ligament closure effect [MPa √m ] LBZ width of local brittle zone [mm] d,c fracture toughness of material [MPa √m ] 2. Experiment 2.1. Material

To observe in detail the behaviour of pop-in, specially manufactured welded joints that can ensure the occurrence of pop-ins are prepared. NRL-S which is a brittle material is welded on the centre of base metal, WELTEN780, and then covered by MGS-80 which is a tough material. The chemical composition of these materials is shown in Table 1. The NRL-S is used to represent the local brittle zone of the welded-joints. The local brittle zone, LBZ, is discrete microstructural regions in a weld heat affected zone that exhibit significantly lower resistance to fracture initiation than surrounding material. The joint geometry of this “brittle bead specimen” is shown in Fig. 1.1. S ection notch specimens which is a reproduction of real weld with local brittle zone, shown in Fig. 2.2 (a), and surface notch specimens which the brittle area is fully distributed along the crack tip for reference, shown in Fig. 2.2 (b), are prepared. The area surrounded by red colour represents the NRL-S. Table 1. Chemical compositions of steel and weld from manufacture’s data sheet (mass %) Size C Si Mn P S Cu Ni Cr Mo B WELTEN780 32 mmt 0.17 0.25 1.56 0.011 0.002 0.01 0.02 0.46 0.01 0.0011 NRL-S 4 mm φ 0.21 1.21 1.55 0.025 0.003 1.51 MG-S80 1.2 mm φ 0.09 0.32 1.05 0.008 0.010 2.71 0.24