PSI - Issue 57

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Procedia Structural Integrity 57 (2024) 271–279 Structural Integrity Procedia 00 (2023) 000–000 Structural Integrity Procedia 00 (2023) 000–000

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Fatigue Design 2023 (FatDes 2023) Plasticity-induced crack closure in the presence of loading irregularities in short cracks initiated at interior defects Fatigue Design 2023 (FatDes 2023) Plasticity-induced crack closure in the presence of loading irregularities in short cracks initiated at interior defects

Kimmo Ka¨rkka¨inen a, ∗ , Joona Vaara b , Tero Frondelius a,b,c a Materials and Mechanical Engineering, Pentti Kaiteran katu 1, 90014 University of Oulu, Finland b R & D and Engineering, Wa¨rtsila¨, P.O.Box 244, 65101, Vaasa, Finland c Faculty of Built Environment, Tampere University, Korkeakoulunkatu 7, 33720, Finland Kimmo Ka¨rkka¨inen a, ∗ , Joona Vaara b , Tero Frondelius a,b,c a Materials and Mechanical Engineering, Pentti Kaiteran katu 1, 90014 University of Oulu, Finland b R & D and Engineering, Wa¨rtsila¨, P.O.Box 244, 65101, Vaasa, Finland c Faculty of Built Environment, Tampere University, Korkeakoulunkatu 7, 33720, Finland

© 2024 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0 ) Peer-review under responsibility of the scientific committee of the Fatigue Design 2023 organizers © 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http: // creativecommons.org / licenses / by-nc-nd / 4.0 / ) Peer-review under responsibility of the scientific committee of the Fatigue Design 2023 organizers. Keywords: Fatigue; Fracture; Plasticity; Overload; Underload Abstract A crack propagation finite-element model of interior defect-initiated short cracks under near-threshold loading conditions is used to investigate the e ff ect of plasticity-induced crack closure in the presence of a single overload and underload. The e ff ect of an overload predicted by the present model is qualitatively very similar to what is commonly reported, but in this case an underload produces a di ff ering result to the literature consensus, yielding a similar but weaker e ff ect as the overload. Extended acceleration of crack propagation due to a single underload might not be attributable to plasticity-induced crack closure under plane strain conditions. A distinct crack profile shape consequent of crack tip blunting is present with both loading irregularities. A new method for examining crack closure for the entire crack surface is presented. © 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http: // creativecommons.org / licenses / by-nc-nd / 4.0 / ) Peer-review under responsibility of the scientific committee of the Fatigue Design 2023 organizers. Keywords: Fatigue; Fracture; Plasticity; Overload; Underload Abstract A crack propagation finite-element model of interior defect-initiated short cracks under near-threshold loading conditions is used to investigate the e ff ect of plasticity-induced crack closure in the presence of a single overload and underload. The e ff ect of an overload predicted by the present model is qualitatively very similar to what is commonly reported, but in this case an underload produces a di ff ering result to the literature consensus, yielding a similar but weaker e ff ect as the overload. Extended acceleration of crack propagation due to a single underload might not be attributable to plasticity-induced crack closure under plane strain conditions. A distinct crack profile shape consequent of crack tip blunting is present with both loading irregularities. A new method for examining crack closure for the entire crack surface is presented. Plasticity-induced crack closure (Elber, 1970) is a well-known, intrinsic mechanism reducing crack driving force. In Mode I tensile loading a plastic zone is formed in front of the crack tip. Once the crack propagates into this plastic zone, a geometric incompatibility arises between the crack flanks, called a plastic wake, increasing the load cycle portion where the crack is in contact. Other important mechanisms of crack closure include oxide and roughness induced closure (Pippan and Hohenwarter, 2017). As interior cracking is considered in present study, oxide-induced closure is absent. Roughness-induced closure is omitted, although it should have a contribution to the total crack closure influence in the physical counterpart. E ff ects of variable amplitude loading in fatigue crack propagation have been extensively covered in literature (Wheeler, 1972; Makabe et al., 2004; Zhao et al., 2008; Fang et al., 2022), and have been directly linked to crack Plasticity-induced crack closure (Elber, 1970) is a well-known, intrinsic mechanism reducing crack driving force. In Mode I tensile loading a plastic zone is formed in front of the crack tip. Once the crack propagates into this plastic zone, a geometric incompatibility arises between the crack flanks, called a plastic wake, increasing the load cycle portion where the crack is in contact. Other important mechanisms of crack closure include oxide and roughness induced closure (Pippan and Hohenwarter, 2017). As interior cracking is considered in present study, oxide-induced closure is absent. Roughness-induced closure is omitted, although it should have a contribution to the total crack closure influence in the physical counterpart. E ff ects of variable amplitude loading in fatigue crack propagation have been extensively covered in literature (Wheeler, 1972; Makabe et al., 2004; Zhao et al., 2008; Fang et al., 2022), and have been directly linked to crack 1. Introduction 1. Introduction

∗ Corresponding author. E-mail address: kimmo.karkkainen@oulu.fi ∗ Corresponding author. E-mail address: kimmo.karkkainen@oulu.fi

2452-3216 © 2024 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of the scientific committee of the Fatigue Design 2023 organizers 10.1016/j.prostr.2024.03.029 2210-7843 © 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http: // creativecommons.org / licenses / by-nc-nd / 4.0 / ) Peer-review under responsibility of the scientific committee of the Fatigue Design 2023 organizers. 2210-7843 © 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http: // creativecommons.org / licenses / by-nc-nd / 4.0 / ) Peer-review under responsibility of the scientific committee of the Fatigue Design 2023 organizers.