PSI - Issue 23

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

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Procedia Structural Integrity 23 (2019) 481–486

© 2019 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 ICMSMF organizers © 201 9 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 IC MSMF organizers. Resista c to fatigue crack propagation i div ded to the in rinsic (eff ctiv ) component and the ext insic compone t, represented by crack closure, which is very significant in the near-threshold regim . Crack growth rate measurements were done on the compact tension specim ns made of the ferritic-pearli ic teel for automotive at the stress ratio R = 0.1 and R = 0.8. Crack closure was quantified from the experimentally measured data using the effective crack growth rate curve d a /d N - Δ K eff an a new expressi n of the rack closure ratio R cl = K cl / K max depending on plasticity-induced crack closure, r ug nes -induced crack losure, oxide-induced crack cl sure and the exponent of the Paris power law. The presented methodology helps to analyse the crack closure mechanisms and to calibrate parameters used in the crack closure models. © 201 9 The Authors. Published by Elsevier B.V. This is an ope acces article under CC BY-NC-ND lic nse (http://creativecommon org/licenses/by-nc-nd/4.0/) Peer-review under responsibility of the scientific committee of the IC MSMF organizers. 9th International Conference on Materials Structure and Micromechanics of Fracture Crack Closure in the Near-threshold Region in Metallic Materials Tomáš Vojtek a,b * , Pavel Pokorný a , Luboš Náhlík a , Diego Herrero c and Pavel Hutař a a Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Žižkova 22, 616 62 Brno, Czech Republic b Central European Institute of Technology (CEITEC), Brno University of Technology, Purkyňo va 123, 612 00 Brno, Czech Republic c Sidenor I+D, Barrio Ugarte, Basauri, 48970, Spain 9th International Conference on Materials Structure and Micromechanics of Fracture Crack Closure in the Near-threshold Region in Metallic Materials Tomáš Vojtek a,b * , Pavel Pokorný a , Luboš Náhlík a , Diego Herrero c and Pavel Hutař a a Institute of Phys cs of Materials, Academy of Scie ces of the Czech Repub ic, Žižkova 22, 6 6 62 Brno, Czech Republic b Central European Institute of Technology (CEITEC) rno Unive sity of Technology Purkyňo va 123, 612 00 Brno, Czech Republic c Sidenor I+D, Barrio Ugarte, Basauri, 48970, Spain Abstract Abstract Resistance to fatigue crack propagation is divided into the intrinsic (effective) component and the extrinsic component, represented by crack closure, which is very significant in the near-threshold regime. Crack growth rate measurements were done on the compact tension specimens made of the ferritic-pearlitic steel for automotive at the stress ratio R = 0.1 and R = 0.8. Crack closure was quantified from the experimentally measured data using the effective crack growth rate curve d a /d N - Δ K eff and a new expression of the crack closure ratio R cl = K cl / K max depending on plasticity-induced crack closure, roughness-induced crack closure, oxide-induced crack closure and the exponent of the Paris power law. The presented methodology helps to analyse the crack closure mechanisms and to calibrate parameters used in the crack closure models.

Keywords: crack closure, effective crack growth rate curve, plasticity-induced crack closure, steel Keywords: crack closure, effective crack growth rate curve, plasticity-induced crack closure, steel

1. Introduction 1. Introduction

Materials resistance to fatigue crack propagation should be divided into the intrinsic and the extrinsic component (Suresh (1998)). The intrinsic resistance opposes the 'effective crack driving force' which is responsible for the actual mechanical damage of material ahead of the crack tip (cyclic plastic deformation). The extrinsic resistance corresponds to crack tip shielding, mostly realized by crack closure processes in the crack wake. It is important to Materials resistance to fatigue crack propagation should be divided into the intrinsic and the extrinsic component (Suresh (1998)). The intrinsic resist nce opp ses the 'effective rack driving f rce' which is responsibl for th actual mechani al damage of material ahead of the crack tip (cyclic plastic deformation). The extrinsic resistance corresponds to crack tip shielding, mostly realized by crack closure processes in the crack wake. It is important to

* Corresponding author. Tel.: +420-532-290-362. E-mail address: vojtek@ipm.cz * Correspon ing author. Tel.: +420-532-290-362. E-mail address: vojtek@ipm.cz

2452-3216 © 2019 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 IC MSMF organizers. 2452-3216 © 2019 The Authors. Published by Elsevier B.V. This is an ope acces article under CC BY-NC-ND lic nse (http://creativecommon org/licenses/by-nc-nd/4.0/)

Peer-review under responsibility of the scientific committee of the IC MSMF organizers.

2452-3216 © 2019 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 ICMSMF organizers 10.1016/j.prostr.2020.01.132