Issue 38

N.O. Larrosa et alii, Frattura ed Integrità Strutturale, 38 (2016) 266-272; DOI: 10.3221/IGF-ESIS.38.36 266 Focussed on Multiaxial Fatigue and Fracture Ductile fracture modelling and J-Q fracture mechanics: a constraint based fracture assessment approach N.O. Larrosa, R.A. Ainsworth The University of Manchester, Manchester M13 9PL, UK nicolas.larrosa@manchester.ac.uk A BSTRACT . The reduced state of stress triaxiality observed in shallow cracked components allows an increased capacity to resist crack propagation compared to that observed in deeply cracked specimens. This may be regarded as a higher fracture toughness value which allows a reduction in the inherent conservatism when assessing components in low constraint conditions. This study uses a two-parameter fracture mechanics approach ( J- Q ) to quantify the level of constraint in a component (e.g. a pipe with a surface crack) and in fracture test specimens, i.e. single edge tension [SE(T]) and compact tension [C(T)] specimens, of varying constraint level. The level of constraint of the component is matched to a specific test specimen and therefore the ability of the structure to resist fracture is given by the fracture toughness of the test specimen with a similar J-Q response. Fracture toughness values for different specimens have been obtained from tearing resistance curves ( J -R curves) constructed by means of a virtual testing framework. The proposed engineering approach shows that the combination of a local approach and two-parameter fracture mechanics can be used as a platform to perform more accurate fracture assessments of defects in structures with reduced constraint conditions. K EYWORDS . Crack tip constraint; Ductile fracture modelling; J-Q fracture mechanics. Citation: Larrosa, N.O., Ainsworth, R.A., Ductile fracture modelling and J-Q fracture mechanics: a constraint based fracture assessment approach., Frattura ed Integrità Strutturale, 38 (2016) 266-272. Received: 21.04.2016 Accepted: 01.06.2016 Published: 01.10.2016 Copyright: © 2016 This is an open access article under the terms of the CC-BY 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. I NTRODUCTION n structural integrity assessments, the fracture toughness value used to determine the onset of fracture, Kmat, is commonly derived from deeply cracked specimens with almost square ligaments, using recommended testing standards and validity criteria (e.g. ASTM E1820 [1] and ESIS-P2 [2]). These are designed to ensure high constraint conditions near the crack tip that correspond to lower-bound toughness values independent of specimen size and geometry. There exist cases in which low constraint conditions can be demonstrated. For example, in the Oil and Gas (O&G) industry, during installation, pipeline girth welds are predominantly loaded in tension even if the pipe is globally subjected to bending. The flaw sizes of interest are usually controlled by the weld pass height and are therefore relatively small, I