Issue 43

L.C.H. Ricardo, Frattura ed Integrità Strutturale, 43 (2018) 57-78; DOI: 10.3221/IGF-ESIS.43.04 57 Crack Propagation by Finite Element Method Luiz Carlos H. Ricardo Materials Technology Department, IPEN, University of São Paulo, Brazil, Instituto de Pesquisas Energéticas e Nucleares Av. Lineu Prestes 2242 - Cidade Universitária - São Paulo - SP BRASIL- CEP: 05508-000. lricardo@ipen.br, https://orcid.org/0000-0002-1712-1437 A BSTRACT . Crack propagation simulation began with the development of the finite element method; the analyses were conducted to obtain a basic understanding of the crack growth. Today structural and materials engineers develop structures and materials properties using this technique. The aim of this paper is to verify the effect of different crack propagation rates in determination of crack opening and closing stress of an ASTM specimen under a standard suspension spectrum loading from FD&E SAE Keyhole Specimen Test Load Histories by finite element analysis. To understand the crack propagation processes under variable amplitude loading, retardation effects are observed. K EYWORDS . Fatigue; Crack propagation simulation; Finite element method; Retardation. Citation: L.C.H. Ricardo, Crack Propagation by Finite Element Method, Frattura ed Integrità Strutturale, 43 (2018) 57-78. Received: 02.10.2017 Accepted: 01.11.2017 Published: 01.01.2018 Copyright: © 2018 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 most common technique for predicting the fatigue life of automotive, aircraft and wind turbine structures is Miner’s rule [1]. Despite the known deviations, inaccuracies and proven conservatism of Miner’s cumulative damage law, it is even nowadays being used in the design of many advanced structures. Fracture mechanics techniques for fatigue life predictions remain as a back up in design procedures. The most important and difficult problem in using fracture mechanics concepts in design seems to be the use of crack growth data to predict fatigue life. The experimentally obtained data is used to derive a relationship between stress intensity range (  K) and crack growth per cycle (da/dN). In cases of fatigue loaded parts containing a flaw under constant stress amplitude fatigue, the crack growth can be calculated by simple integration of the relation between da/dN and  K . However, for complex spectrum loadings, simple addition of the crack growth occurring in each portion of the loading sequence produces results that, very often, are more erroneous than the results obtained using Miner’s rule with an S-N curve. Retardation tends to cause conservative results using Miner’s rule when the fatigue life is dominated by the crack growth. However, the opposite effect generally occurs when the life is dominated by the initiation and growth of small cracks. In these cases, large cyclic strains, which might occur locally at stress raisers due to overload, may pre-damage the material and lower its resistance to fatigue. The experimentally derived crack growth equations are independent of the loading sequence and depend only on the stress intensity range and the number of cycles for that portion of the loading sequence. The central problem in the successful utilization of fracture mechanic techniques applied to the fatigue spectrum is to obtain a clear understanding T