PSI - Issue 13

Vitor Scarabeli Barbosa et al. / Procedia Structural Integrity 13 (2018) 367–372 Author name / Structural Integrity Procedia 00 (2018) 000 – 000

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DBT SE(B) RPV PCVN

Ductile-to-brittle transition

single-edge notch specimen under bending

Reactor pressure vessel

Pre-Cracked Charpy V-notch specimen

2. Material and Experimental Procedures

The material employed in this study is a typical high-strength-low alloy structural steel ASTM A572 Grade 50 with 376 MPa yield stress and 555 MPa tensile strength at room temperature ( T ≈ 20 °C) . Mechanical tensile tests also provide the stress-strain data at the test temperature ( T = − 20 °C ) which corresponds to the lower-shelf, ductile to-brittle transition behavior for the tested steel. Figure 1(a) shows the engineering stress-strain curve for the tested material at these temperatures. Figure 1(b) provides the measured toughness-temperature properties for the material in terms of conventional Charpy V-notch impact energy (a set of 30 Charpy-V notch (CVN) impact specimens in the T-L orientation). In this plot, the solid symbols represent the experimentally measured Charpy energy whereas the solid line is the hyperbolic tangent curve fitting defined by API 579 (2016).

a) b) Fig. 1. (a) Engineering stress-strain curve (average stress-strain response using data from three test specimens) for the tested ASTM A572 Grade 50 steel at room temperature and at -20 °C; (b) Charpy-V impact energy (T-L orientation) versus temperature for the tested material. Table 1 summarizes the mechanical properties obtained from the tensile tests conducted on longitudinal tensile specimens. This table also provides an improved estimate for the hardening exponent given by API 579 (2016). Table 1. Tensile properties of tested A572 Grade 50 steel at room temperature and at test temperature corresponding to the transverse plate direction ( σ ys and σ uts denote the yield stress and tensile strength). T (°C) σ ys (MPa) σ uts (MPa) σ ys / σ uts n 20 376 555 1.5 8.0 -20 407 601 1.5 8.0 To investigate the effects of increased span on fracture toughness values measured in the DBT region, a series of toughness tests was carried out on standard and non-standard PCVN specimens in the T-L orientation. The fracture mechanics tests include plane-sided, precracked Charpy (PCVN) specimen with a/W = 0 . 5, B = 10 mm, W = 10 mm and S = 4 W , 6 W and 8 W . Here, a is the crack size, W denotes the specimen width, B represents the specimen thickness and S is the specimen span. To assess the potential influence of side groove on the fracture toughness values, fracture tests were also conducted on side-grooved PCVN specimens with S = 6 W having a net thickness of 80% the overall thickness (10% side-groove on each side). Further, to provide a baseline reference temperature, T 0 , for the tested material, fracture toughness tests were also performed on conventional, plane-sided SE(B) specimens with a/W = 0 . 5, B = 25 mm, W = 50 mm and S = 4 W loaded under 3-point bending.