PSI - Issue 5

Yoichi Kayamori et al. / Procedia Structural Integrity 5 (2017) 286–293 Yoichi Kayamori et al. / Structural Integrity Procedia 00 (2017) 000 – 000

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1. Introduction

CTOD is an elastic-plastic fracture mechanics parameter, and has been widely used for the fracture toughness evaluation of elastic-plastic materials such as structural steel. Most of the CTOD fracture toughness standards such as WES1108 (2016), BS7448 (1991) and ISO 12135 (2002) have used the plastic hinge model to calculate the plastic component of CTOD. On the other hand, ASTM E1820 (2008) and ISO 15653 Annex-E (2010) avoided using the plastic hinge model, but adopted another calculation method, the conversion of J -integral into CTOD, because the ratio of the initial crack length, a 0 , to the specimen width, W , and strain hardening affect the plastic rotational deformation of the specimen (1993, 2006). These two different CTOD calculations, the conventional plastic hinge model based CTOD and the J -integral based CTOD, do not always result in an identical CTOD toughness value for a certain loading condition (2010), and one method should be reasonably selected to avoid confusion. The authors (2014, 2015) previously investigated the rotational deformation of single edge-notch bend (SE(B)) specimens, and a rotational center was apparently demonstrated in SE(B) specimen models with different strain hardening characteristics, where several Y/T values were assumed. However, it has been unclear whether the plastic hinge model is reliable in other standard fracture toughness specimens such as C(T) even though their strain hardening characteristics are different. In this study, firstly, plastic rotational deformation and some plastic rotational factors for C(T) were reviewed. Secondly, 3-D elastic-plastic FEA was conducted by using a stepped notch 1T C(T) specimen model, and its rotational deformation was investigated. Finally, the plastic rotational factor was determined, and the value was compared with reference data.

Nomenclature a 0

crack length

B E K N r p J

specimen thickness Young’s modulus

J -integral

stress intensity factor

strain hardening exponent for Swift type stress-strain relation

plastic rotational factor yield to tensile ratio

Y/T

V p W

plastic part of the clip gauge opening displacement

specimen width

x

distance from the crack tip

x 0

characteristic distance from the crack tip to the neutral strain point height of the knife edge measurement point from the load line

z

Merkle and Corten coefficient

 

fitting parameter for Swift type stress-strain relation

equivalent plastic strain

p 

crack tip opening displacement, CTOD

   el  pl

elastic component of CTOD plastic component of CTOD 

 FEM CTOD calculated using the deformed crack profile by means of the 45º intercept method  Poisson's ratio  uts  ultimate tensile strength  ys yield stress  equivalent stress