Issue 35

L. C. H. Ricardo et alii, Frattura ed Integrità Strutturale, 35 (2016) 456-471; DOI: 10.3221/IGF-ESIS.35.52 456 Crack simulation models in variable amplitude loading - a review 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. Carlos Alexandre J. Miranda Nuclear Engineering Department, IPEN, University of Sao Paulo, Brazil, Instituto de Pesquisas Energéticas e Nucleares Av. Lineu Prestes 2242 - Cidade Universitária - São Paulo - SP BRASIL- CEP: 05508-000 A BSTRACT . This work presents a review of crack propagation simulation models considering plane stress and plane strain conditions. It is presented also a chronological different methodologies used to perform the crack advance by finite element method. Some procedures used to edit variable spectrum loading and the effects during crack propagation processes, like retardation, in the fatigue life of the structures are discussed. Based on this work there is no consensus in the scientific community to determine the best way to simulate crack propagation under variable spectrum loading due the combination of metallurgic and mechanical factors regarding, for example, how to select and edit the representative spectrum loading to be used in the crack propagation simulation. K EYWORDS . Fatigue; Crack propagation simulation; Finite element method; Retardation. 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 of T