PSI - Issue 42

B.Aydin Baykal et al. / Procedia Structural Integrity 42 (2022) 1350–1360 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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1. Introduction

Nomenclature A Area A*

Critical area (for brittle fracture)

B b 0

Specimen width Ligament length Bend bar specimen

BB CT

Compact tension specimen

d Displacement DBTT Ductile-brittle transition temperature E Young’s modulus FEM Finite element method J J-integral value K Stress intensity factor K Jc Mode I fracture toughness K Jc.limit Maximum allowable calculated fracture toughness K min

Lowest admissible stress intensity factor for fatigue considerations

k ASTM ASTM crack front correction factor k CL Constraint loss correction factor k M Combined correction factor

LWR Light water reactor M, M lim Load limit factor NPP Nuclear power plant r

Miniaturization constant Reactor pressure vessel

RPV

T

Temperature

T 0 V

Reference temperature for ductile-brittle transition

Volume

V*

Critical volume (for brittle fracture)

β ε ν σ

Constraint loss constant Engineering strain

ε pl

Plastic strain Poisson’s ratio Engineering stress

σ* σ YS

Critical stress (for brittle fracture)

Yield strength

Structural integrity of the reactor pressure vessel (RPV) is of critical importance to ensure the safe operation of light water reactors (LWRs). Fracture toughness evaluations based on the Master-Curve method (ASTM-E1921) to determine the reference temperature T 0 of the ductile to brittle transition have recently gained importance for the integrity assessment of irradiated materials. The reference temperature T 0 indexes the median toughness-temperature curve at a toughness value of 100 MPa.m 1/2 obtained with 1T-size specimens (25.4 mm crack front length). Due to the limited number of surveillance specimens, miniaturization of fracture specimens is unavoidable. However, it is well known that fracture toughness is specimen size and geometry dependent and intrinsically scattered due to material inhomogeneity. Typically, specimens with a crack front as small as 4 mm are used to characterize the toughness of irradiated specimens. Miniaturization is a powerful tool for examining the response of large-scale structures under diverse loading