Issue 41

A. Cernescu, Frattura ed Integrità Strutturale, 41 (2017) 307-313; DOI: 10.3221/IGF-ESIS.41.41 307 Focused on Crack Tip Fields The influence of crack tip shielding on fatigue crack propagation Anghel Cernescu Politehnica University of Timisoara, Romania anghelcernescu@gmail.com , anghelcernescu@yahoo.com, http://orcid.org/0000-0001-9513-9643 A BSTRACT . The fatigue crack propagation is one of the major problems and of the real concern in the evaluation of the structural integrity of components. This is due to the fact that once a fatigue crack has been detected it is also known its effect on the component; respectively it will cause failure at one time. In this situation, the problem is focused on determining the character of propagation of the crack so that it can be estimated and respectively delayed as possible the failure moment. The fatigue crack propagation character is determined by the stress state at the crack tip and the behavior of the material in which the crack is propagates. One of the phenomena with great influence on the fatigue crack propagation character is the crack tip stress shielding phenomena. In this paper the overloading effect is explained in terms of crack tip shielding mechanisms that guide the fatigue crack growth in plastic zone. The results indicate a change of fatigue crack propagation character once its tip enters into a plastic zone. K EYWORDS . Fatigue crack growth rate; Crack tip shielding; Crack closure; Overloading cycle; Plastic zone. Citation: Cernescu, A., The influence of crack tip shielding on fatigue crack propagation, Frattura ed Integrità Strutturale, 41 (2017) 307-313. Received: 28.02.2017 Accepted: 03.05.2017 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. I NTRODUCTION ne of the current approaches of fatigue damage predictions is based on the damage tolerance concept. This concept starts from the premise that each component has a potential defect and the fatigue life is based on the number of cycles required for an initial crack to grow to the critical value. Using an appropriate fatigue crack growth equation, the initial fatigue crack is propagated through iterative calculations that take into account the loading spectrum, material properties and component geometry. One of the elements that confer the degree of accuracy of fatigue crack growth predictions is represented by the crack closure phenomenon. According to the review made by M. N. James, [1], on the crack closure, the first study that has highlighted such a phenomenon was presented by Christensen in 1963, [2]. Performing fatigue crack growth tests on center-cracked specimens of 2024-T3 aluminum alloy it was observed an increase in fatigue life occurred in the presence of trapped oxide particles between the fracture surfaces. However, of reference are the Elber’s studies from 1970 and 1971, [3-4]. Based on residual stress distribution and resultant forces analysis in center-cracked plate specimen under zero-to-tension loading, Elber showed that the crack is fully open only for a part of the loading cycle. This being attributed to the field of plastic deformations in the wake of O