PSI - Issue 77

Jan Kec et al. / Procedia Structural Integrity 77 (2026) 264–271

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Compact Tension (CT) specimens (B = 8 mm, W = 50 mm, side -grooved to B N = 6 mm) were extracted in N-P orientation, with the crack propagating through the weld centerline. FCGR and FT tests followed ASTM E647 and E1820, respectively, using Instron 8501 (Fig. 2a) and 8033 servo-hydraulic machines. The test was performed at a constant force amplitude with a sinusoidal waveform (f = 1 Hz, R = 0.5 ). The FCGR was measured in stress intensity factor range Δ K ≈ 15 MPa.m 0.5 to 30 MPa.m 0.5 , i.e. in the Paris region. Crack opening displacement (COD) was measured via a custom-built extensometer resistant to the aggressive environment (Fig. 2b). Fatigue crack growth was measured using the compliance technique. The equation for determining the crack length using the compliance technique and determining the ΔK is given in ASTM E647. The FT test used the methodology of determining fracture mechanical parameters on a single specimen using the compliance technique. A constant load line displacement (LLD) rate of 0.5 mm/min was chosen for loading and unloading. The starting point of LLD was 0.2 mm and subsequent increments were always in 0.1mm. The equations for the determination of stress intensity factor, J-integral and elastic compliance are given in ASTM E1820. The CT samples were hydrogen-charged electrochemically using a 0.5M NaCl electrolyte and a constant current density of -10 mA·cm -2 , corresponding to a hydrogen uptake of 0.03 wppm measured by thermal desorption analysis. Following the FCGR and FT tests, the samples were cryogenically fractured by immersion in liquid nitrogen and then broken using an Instron 8033 servo-hydraulic testing machine. Fractographic examination was conducted using an Olympus DSX-1000 digital microscope and a Zeiss EVO MA 10 scanning electron microscope (SEM) to characterize the fracture mechanisms.

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Fig. 2. (a) Instron 8501 servo-hydraulic testing machine with environmental chamber; (b) detail of environmental chamber, extensometer, PT electrode and CT specimen during testing.