Issue 48

F. V. Antunes et alii, Frattura ed Integrità Strutturale, 48 (2019) 666-675; DOI: 10.3221/IGF-ESIS.48.63 666 Focused on the “Portuguese contributions for Structural Integrity” Fatigue crack growth in notched specimens: a numerical analysis F.V. Antunes, R. Branco, P. Prates, J.D.M. Costa University of Coimbra, Portugal fernando.ventura@dem.uc.pt, http://orcid.org/0000-0002-0336-4729 ricardo.branco@dem.uc.pt, http://orcid.org/0000-0001-2345-6789 pedro.prates@dem.uc.pt, http://orcid.org/0000-0001-2345-6789 jose.domingos@dem.uc.pt A BSTRACT . Fatigue crack growth (FCG) is linked to irreversible and non- linear processes happening at the crack tip, which explains different problems observed in the use of da/dN-  K curves. The replacement of  K by non- linear crack tip parameters, namely the crack tip opening displacement (CTOD) is an interesting alternative. The objective in here is to study the effect of notches on FCG using the plastic CTOD range,  p . M(T) specimens with lateral notches of different radius (1, 2, 4 and 8 mm were analysed numerically, keeping the total depth constant (8 mm). The increase of crack length increases  p and therefore FCG rate. For plane stress state, the formation of the residual plastic wake with crack propagation, produces crack closure which compensates the effect of crack length and there is a stabilization of  p . The reduction of notch radius increases  p for all crack lengths, particularly for the shortest ones. For plane strain state there is almost no crack closure therefore  p is higher than for plane stress state, and the effect of crack length produces a relatively fast increase of  p . K EYWORDS . Fatigue crack growth; Notches; Plastic CTOD; Crack closure. Citation: Antunes, V. V., Branco, R., Prates, P., Costa J.D.M., Fatigue crack growth in notched specimens: a numerical analysis, Frattura ed Integrità Strutturale, 48 (2019) 666-675. Received: 18.09.2018 Accepted: 11.11.2018 Published: 01.01.2019 Copyright: © 2019 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 he study of fatigue crack propagation is usually based on relations between the crack increment per load cycle, da/dN, and the stress intensity factor range,  K.  1  . The dN-  K relationship is supposed to be invariant relatively to the shape and size of the cracked component.  K is a linear elastic parameter, however it controls the small-scale cyclic plastic deformation occurring at the crack tip  2  . Nevertheless, da/dN-  K relations have several limitations, namely: (i) such curves are completely phenomenological, not derived from physics, and the fitting parameters have units with no physical justification; (ii) such curves are only valid in the small-scale yielding range; (iii) and da/dN depends on other parameters, including the stress ratio and the load history. Different concepts have been proposed to overcome the limitations identified in the use of dN-  K relationships, which are effectively caused by using a linear elastic parameter to quantify the non-linear irreversible processes responsible for T