Use of Circumferentially Cracked Bar sample for CTOD fracture toughness determination in the upper shelf regime

Abstract

ABSTRACT. In this work, the use of circumferentially cracked bar (CCB) sample to determine material fracture toughness in the upper shelf regime for carbon steels has been investigated. Since high fracture toughness materials are known to exhibit extensive crack tip blunting before ductile crack initiation, accurate specimen design is required to provide realistic fracture toughness measurement. Here, a CCB was designed to have similar loss of constraint as for SENT sample. Continuum damage mechanics was used to predict the occurrence of ductile crack initiation and propagation. Finite element analysis was performed to predict specimen response and to compare computed J-integral crack driving force with measured CTOD. Finally, experimental tests were performed on X65 carbon steel and the measured critical CTOD was compared with available fracture data obtained with SENT.

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“…A similar phenomenon of peak J-integral values at the crack front center was observed at a cryogenic temperature of -195 0 C. As expected, the CMOD values are constant along the crack front for all plate orientations. Gentile et al [13] have performed FE analysis to predict specimen response through crack driving parameters viz. computed J-integral with measured CTOD.…”

“…Figs. 13 to 18 present the variation of J-integral, CMOD and CTOD at different plate locations dependent on plate temperature and orientations. The decrease in J-integral and CMOD was noticed at a cryogenic temperature at both location and plate orientations.…”

“…The fracture toughness depends on specimen geometry, load, and type of specimen, which coined the term constraint. Constraint generated at the crack front is measured through well-defined constraint parameters under Linear Elastic Fracture Mechanics (LEFM) and Elastic-Plastic Fracture Mechanics (EPFM) [7,8,9,10,11,12,13,14]. These constraint parameters are defined concerning either the stress field or the displacement field around the crack front.…”