PSI - Issue 2_A

Toshiyuki Meshii et al. / Procedia Structural Integrity 2 (2016) 697–703 Toshiyuki Meshii , Teruhiro Yamaguchi/ Structural Integrity Procedia 00 (2016) 000–000

698

2

E

Young’s modulus

J

J -integral

J c , J c FEA

Fracture toughness and J obtained at the fracture load P c via FEA

J s

J obtained at σ 22d converged

K c K J c

SIF corresponding to the fracture load P c

An elastic-plastic equivalent SIF derived from the J -integral at the point of J c Median (50% cumulative failure probability) Master Curve fracture toughness K J c(0.02), K J c(0.98) 2 % lower bound and 98% upper bound of Master Curve fracture toughness K max Maximum stress intensity factor during precracking K o Scale parameter specified in ASTM E1921 M K J cmed

= ( b 0 σ YS )/ J c : Parameter which gives information on the initial ligament size to fracture process zone size

N P

Number of specimens tested

Load

P c , P Q

Fracture load and conditional value in ASTM E399 Maximum and Minimum force during precracking

P max , P min

P s V g W

P corresponding to J s

Crack mouth opening displacement (CMOD)

Specimen width

a

Crack length of a test specimen = ( W - a ) : Initial ligament length

b 0

Crack-tip opening displacement (CTOD)

δ t ν

Poisson’s ratio

σ B , σ B0 σ YS , σ YS0

True and nominal tensile strength True and nominal yield stress

Crack-opening stress

σ 22

Critical crack-opening stress

σ 22c σ 22d

σ 22 measured at a distance from the crack tip equal to four times δ t at the specimen mid-plane

Converged value of σ 22d

σ 22 d0

1. Introduction Designing important components, such as reactor pressure vessels (RPVs), to operate at temperatures where the material behaves in a ductile manner is a conservative requirement intended to ensure that any crack, which may be present in the components, would extend in ductile manner. During operation RPV steel may be subject to neutron irradiation which reduces the ductile–to–brittle transition temperature (DBTT). Because continued operation of nuclear power plants thus requires that safety margin of RPV are demonstrated for operating temperature, temperature dependence of the fracture toughness of RPV steel has continuously collected attention of researchers and design engineers. One of the widely accepted methods to predict the cleavage fracture toughness temperature dependence is the master curve approach (Wallin, 1993, 1998, 2002). The approach assumes the statistical weakest link model for cleavage fracture and uses Weibull distribution to express the scatter in fracture toughness K J c . The procedure is based on the concept of a normalized curve of “median” fracture toughness defined in terms of K J c -values for 1-T (25 mm thick) size specimens versus temperature applicable to hold experimentally for a wide range of ferritic pressure vessel and structural steels. Despite the efforts to apply the method, the approach is not without its limitations. For example, some recent studies have reported that the Weibull parameters vary with size and temperature and are different from those stated in the Master Curve, and thus, the K J c temperature dependence (Berejnoi and Perez Ipiña, 2015; James et al., 2014). On the other hand, predicting the “lower bound” fracture toughness for a specific specimen configuration has been another interest. Chen et al. insisted that “it is necessary to distinguish the concepts of the lower bound toughness or the lower boundary of toughness values from that of the scatter band of toughness. The former is a