PSI - Issue 18

Available online at www.sciencedirect.com Structural Integrity Procedia 00 (2019) 000–000 Available online at www.sciencedirect.com ScienceDirect Structural Integrity Procedia 00 (2019) 000–000 Available online at www.sciencedirect.com ScienceDirect

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Procedia Structural Integrity 18 (2019) 645–650

25th International Conference on Fracture and Structural Integrity A numerical analysis of fatigue crack closure using CTOD B. Marques a , L.P. Borrego a,b *, J. M. Ferreira a , F. V. Antunes a , R. Branco a a CEMMPRE, Department of Mechanical Enginnering, University of Coimbra, 3004-516 Coimbra, Portugal b Coimbra Polytechnic - ISEC, Rua Pedro Nunes, 3030-199 Coimbra, Portugal Abstract The crack closure level was determined numerically using the finite element method for six materials and different load conditions. The crack opening level was found to be higher than the crack closure level and a value of 0.9 was obtained for the ratio between both parameters. For values of plane stress crack closure up to 30% there is no crack closure for plane strain. However, above 30%, a linear trend is observed, with a slope higher than 45º, which means that the variation of plane strain closure is faster than the variation of plane stress closure. The comparison with literature models showed significant differences, which were attributed to the complexity of the crack closure phenomenon. The analysis of crack tip stress showed that a significant influence of crack closure but also that below crack closure there are things happening at the crack tip. 25th International Conference on Fracture and Structural Integrity A numerical analysis of fatigue crack closure using CTOD B. Marques a , L.P. Borrego a,b *, J. M. Ferreira a , F. V. Antunes a , R. Branco a a CEMMPRE, Department f Mechanical nginnering, Univer ity of Coimbra, 3004-516 Coimbra, Portugal b Coimbra Polytechnic - ISEC, Rua Pedro Nunes, 3030-199 Coimbra, Portugal Abstract The crack closur level was determined numerically using t e finite el ment method for six materials and different load conditions. The crack opening level was found to b higher than the crack closure level and a value of 0.9 was obtain d for the ratio between both parameters. For values of plane stress crack cl sure up to 30% there is no cr ck closure for plane strain. However, above 30%, a linear trend is observed, with a slope higher than 45º, which means that the variation of plane strain closure is faster than the variation of plane stress closure. The comparison with literatur models showed significant differences, which were attributed to the complexity of the crack closure phenomenon. The analysis of crack tip stress showed that a significant influence of crack closure but also that below crack closure there are things happening at the crack tip.

© 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Gruppo Italiano Frattura (IGF) ExCo. © 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Gruppo Italiano Frattura (IGF) ExCo. © 2019 The Autho s. Publ shed by Elsevier B.V. Peer-review under responsibility of the Gruppo Italiano Frattura (IGF) ExCo. Keywords: Crack propagation; Crack closure; CTOD; Finite element analysis. Keywords: Crack propagation; Crack closure; CTOD; Finite element analysis.

1. Introduction The mean stress has a significant effect on crack propagation life and must be included in prediction models. However, there is no consensus in the fatigue community regarding the dominant mechanism explaining the mean stress effect. The concept of crack closure has been widely used. This phenomenon consists in the contact of crack flanks during a portion of the load cycle, which is expected to affect the crack tip fields, reducing fatigue crack growth 1. Introduction The mean stress has a significant effect on crack propagation life and ust be included in prediction mod ls. However, there is no consensus in the fatigue community regarding the dominant mechanism explaining the mean stress effect. The concept of cr ck closure has been widely used. T is phenomenon consists in the contact of crack flanks during a portion of the load cycle, which is expected to affect the crack tip fields, reducing fatigue crack growth

2452-3216 © 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Gruppo Italiano Frattura (IGF) ExCo. 2452-3216 © 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Gruppo Italiano Frattura (IGF) ExCo. * Correspon ing author. Tel.: +351239790200; fax: +351239790331. E-mail address: borrego@isec.pt * Corresponding author. Tel.: +351239790200; fax: +351239790331. E-mail address: borrego@isec.pt

2452-3216  2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Gruppo Italiano Frattura (IGF) ExCo. 10.1016/j.prostr.2019.08.211