Blunt defect assessment in the framework of the failure assessment diagram

• Published in: The International journal of pressure vessels and piping 2016-10, Vol.146, p.39-54
• Main Authors: Han, Jae-Jun, Larrosa, Nicolas, Kima, Yun-Jae, Ainsworth, Robert A.
• Format: Article
• Language: English
• Subjects: Blunt defects; Defect assessment; Effective fracture toughness; Failure assessment diagram; Finite element analysis; J-integral; Stress-modified fracture strain; Virtual testing
• ISSN: 0308-0161; 1879-3541
• DOI: 10.1016/j.ijpvp.2016.07.006

In order to reduce over-conservatism in fitness-for-service assessment procedures, experimental evidence and recent analytical developments recognise the importance of considering the actual shape of non-sharp flaws and/or the real geometric constraint conditions at the crack tip. This paper addresses the effect of blunt defects on the structural integrity assessment of reactor pressure vessel (RPV) and pipeline steels. Parametric studies for compact tension specimens with various notch root radii are performed using finite element analysis. The notch fracture toughness, the resistance to the onset of ductile cracking and the J-integral, quantifying the notch driving force, are evaluated. A stress-modified fracture strain model is used as a virtual testing method. The results are analyzed in the framework of the failure assessment diagram (FAD), showing that the existing shape of the FAD is also suitable for assessments of blunt defects and how the concepts introduced can be used to reduce the conservatism in defect assessment, define margins on failure and indicate when plastic collapse is the dominant failure mechanism. •Ductile fracture simulations for standard C(T) specimens with a wide range of notch radii.•J-R curves were constructed using both the domain integral method and the FE load-displacement results.•Reserve factors on load could be up to a factor of 3 greater for notched specimens than for specimens with sharp cracks.•The analysis to become geometry independent and can be used, in principle, to assess any defective component or structure.•An alternative framework to one and two parameter fracture mechanics for assessing constraint effect on fracture toughness.