Issue 41

J. Toribio et alii, Frattura ed Integrità Strutturale, 41 (2017) 62-65; DOI: 10.3221/IGF-ESIS.41.09 62 Focused on Multiaxial Fatigue Influence of crack micro-roughness on the plasticity-induced fatigue propagation in high strength steel J. Toribio, J.C. Matos, B. González Fracture and Structural Integrity Research Group (FSIRG), University of Salamanca (USAL) E.P.S., Campus Viriato, Avda. Requejo 33, 49022 Zamora, Spain toribio@usal.es, jcmatos@usal.es , bgonzalez@usal.es A BSTRACT . This article deals with the locally multiaxial fatigue behaviour of high strength steel. To this end, the influence of the cracking path deflections (at the micro level) on the plasticity-induced fatigue crack growth is analyzed. With regard to this, a modelling by means of the finite element method was performed for a given stress intensity factor in the Paris regime, considering the existence of micro-roughness in the crack path (local micro-deflections with distinct micro-angles as a function of the microstructure of the material). The numerical results allow one to obtain the fatigue crack propagation rate and compare it with that for the same material in the absence of micro- roughness (with no micro-crack deflections, i.e., uniaxial fatigue behaviour). K EYWORDS . Crack tip; Micro-roughness; Crack deflection; Plasticity-induced fatigue crack propagation; Finite element method. Citation: Toribio, J., Matos, J.C., González, B., Influence of crack micro-roughness on the plasticity-induced fatigue propagation in high strength steel, Frattura ed Integrità Strutturale, 41 (2017) 62-65. 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. I NTRODUCTION atigue cracks exhibit surface micro-roughness caused by material microstructure, e.g., pearlitic steel shows continuous deflections in the fatigue crack path [1]. The non-linear crack configuration should be taken into account in the matter of crack-morphological aspects in fracture mechanics [2], since variations in crack deflection features influence considerably the fatigue crack propagation rates and threshold stress intensity factor range [3]. Elastic- plastic finite element simulations of growing fatigue cracks are used to study the plastic crack advance and the so-called crack closure phenomenon. With regard to plastic crack advance , the Laird-Smith mechanism of propagation by cyclic blunting and re-sharpening, which transfers material from the crack tip towards its flanks, is visualized in [4]. With this sort of modeling procedure, the rate per cycle reproduced common trends of the fatigue cracking dependence on loading range and overload [5]. Paris-like equations obtained from the numerical modeling of plastic crack advance showed good agreement with experimental results [6]. In the matter of plasticity-induced fatigue crack closure , a strong controversy still does exist, with researchers raising doubts about its mere existence [4,5], and others obtaining it as a numerical result [7], although the total length of closed crack at minimum load in plane strain is shown to be a small fraction of the total crack length [8]. F