Issue 41

J.M. Vasco-Olmo et alii, Frattura ed Integrità Strutturale, 41 (2017) 157-165; DOI: 10.3221/IGF-ESIS.41.22 157 Focused on Crack Tip Fields Experimental evaluation of CTOD in constant amplitude fatigue crack growth from crack tip displacement fields J.M. Vasco-Olmo, F.A. Díaz University of Jaén, Spain jvasco@ujaen.es fdiaz@ujaen.es F.V. Antunes University of Coimbra, Portugal fernando.ventura@dem.uc.pt M.N. James University of Plymouth, UK M.James@plymouth.ac.uk A BSTRACT . In the current work an experimental study of the crack tip opening displacement (CTOD) is performed to evaluate the ability of this parameter to characterise fatigue crack growth. A methodology is developed to measure and to analyse the CTOD from experimental data. The vertical displacements measured by implementing Digital Image Correlation on growing fatigue cracks are used to measure the CTOD. Fatigue tests at R ratios of 0.1 and 0.6 were conducted on compact-tension specimens manufactured from commercially pure titanium. A sensitivity analysis was performed to explore the effect of the position selected behind the crack tip for the CTOD measurement. The analysis of a full loading cycle allowed identifying the elastic and plastic components of the CTOD. The plastic CTOD was found to be directly related to the plastic deformation at the crack tip. Moreover, a linear relationship between da / dN and the plastic CTOD for both tests was observed. Results show that the CTOD can be used as a viable alternative to ΔK in characterising fatigue crack propagation because the parameter considers fatigue threshold and crack shielding in an intrinsic way. This work is intended to contribute to a better understanding of the different mechanisms driving fatigue crack growth and the address the outstanding controversy associated with plasticity-induced fatigue crack closure. K EYWORDS . Crack tip opening displacement; Fatigue crack growth; Plastic deformation; DIC. Citation: Vasco-Olmo, J.M., Díaz, F.A., Antunes, F.V., James, M.N., Experimental evaluation of CTOD in constant amplitude fatigue crack growth from crack tip displacement fields, Frattura ed Integrità Strutturale, 41 (2017) 157-165. Received: 28.02.2017 Accepted: 15.04.2017 Published: 01.07.2017 Copyright: © 2017 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.