Issue 36

L. C. H. Ricardo et alii, Frattura ed Integrità Strutturale, 36 (2016) 201-215; DOI: 10.3221/IGF-ESIS.36.20 201 Technical note Influence of the crack propagation rate in the obtaining opening and closing stress intensity factor 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 Carlos Alexandre J. Miranda Nuclear Engineering Department, IPEN, University of Sao Paulo, Brazil Instituto de Pesquisas Energéticas e Nucleares 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 as criterion design. 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. The crack propagation simulation was based on release nodes at the minimum loads to minimize convergence problems. To understand the crack propagation processes under variable amplitude loading, retardation effects are discussed. K EY WORDS : Fatigue; Crack propagation simulation; Finite element method; Retardation. I NTRODUCTION he most common technique for predicting the fatigue life of automotive, aircraft, wind turbine and many other 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, 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 T