PSI - Issue 2_A

Toshiyuki Meshii et al. / Procedia Structural Integrity 2 (2016) 704–711 Toshiyuki Meshii and Kenichi Ishihara / Structural Integrity Procedia 00 (2016) 000–000

705

2

Keywords: fracture toughness; transition temperature; test specimen thickness effect; modified Ritchie-Knott-Rice failure criterion; elastic-plastic finite element analysys

Nomenclature B

Specimen thickness Young’s modulus

E

J

J -integral

J c , J cFEA

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

J s

J obtained at converged  22d

K c

SIF corresponding to the fracture load P c Maximum stress intensity factor during precracking

K max

2 )} 1/2 : Cleavage fracture toughness

K Jc

= { EJ c /(1-  = ( b 0  YS )/ J c

M

P , P c

Load and fracture load

P max , P min

Maximum and minimum force during precracking Conditional value in ASTM E399 and P corresponding to J s

P Q , P s

T 11

In-plane T -stress

V g , V LL

Crack mouth opening displacement (CMOD) and load line displacement

W

Specimen width Crack length

a

b 0

= ( W - a ): Initial ligament size

1/2 / K 

= T 11 (  a )





Crack-tip opening displacement (CTOD)

 t

Poisson’s ratio 

 

 

Initial blunted notch 

 B ,  B0  YS ,  YS0

True and nominal tensile strength True and nominal yield stress

Crack-opening stress

 22  22c  22d

Critical crack-opening stress

 22 measured at a distance from the crack tip equal to four times the crack-tip opening displacement (CTOD)  t at the specimen mid-plane

Converged value of  22d

 22d0

1. Introduction The test specimen size effect of fracture toughness J c of the material in the ductile-to-brittle transition temperature (DBTT) region is known to not be ignored. One practical approach was to use the 1-inch thickness (1T) compact tension (CT) test specimen in structural integrity assessment of cracked structures (IAEA, 2009). To support this practice, a method to convert J c obtained with other sized CT specimens is provided in ASTM E1921 (ASTM, 2010). On the other hand, a large number of fracture toughness test data have been collected for the single edge notched bend (SE(B)) specimens. In order to practically use the SE(B) test data in engineering application, it is essential for converting J c obtained from different sized SE(B) specimen to the 1T CT specimen J c . Another issue is a large scatter in J c . This issue has been studied extensively (Beremin et al., 1983; James, Ford and Jivkov, 2014; Wallin, Saario and Törrönen, 1984) and an engineering framework named master curve method (ASTM, 2010) seems to be widely accepted. However, master curve does not give a distinct procedure to convert J c s between SE(B) and CT specimens, though master curve reference temperature difference of 10 o C is known (Wallin et al., 2001). 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