PSI - Issue 68

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Procedia Structural Integrity 68 (2025) 486–492 Structural Integrity Procedia 00 (2024) 000–000 Structural Integrity Procedia 00 (2024) 000–000

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European Conference on Fracture 2024 Fatigue limit assessment of interacting small defects by cyclic R-curve analysis Stefan Fladischer a, ∗ , Michael Stoschka a , Florian Gru¨n a a Montanuniversita¨t Leoben, Chair of Mechanical Engineering, Franz Josef-Straße 18, 8700 Leoben, Austria European Conference on Fracture 2024 Fatigue limit assessment of interacting small defects by cyclic R-curve analysis Stefan Fladischer a, ∗ , Michael Stoschka a , Florian Gru¨n a a Montanuniversita¨t Leoben, Chair of Mechanical Engineering, Franz Josef-Straße 18, 8700 Leoben, Austria

Abstract This study focuses on the numerical simulation of short crack growth to investigate geometric interaction e ff ects between small neighboring defects under consideration of crack closure. In an extensive parameter study, circular cracks of various sizes and interaction distances are investigated. The simulation procedure follows a cyclic R-curve analysis in order to determine the fatigue limit of maximum non-propagating crack formation. The interaction e ff ects are quantified in the form of novel geometry factors for interacting cracks as well as the degradation of the fatigue limit due to crack size and proximity. The results are compared to experimental validation tests performed on additively manufactured specimens containing artificial defects. © 2025 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 ECF24 organizers. Keywords: short crack growth; interaction e ff ect; defect interaction; fatigue limit; cyclic R-curve analysis; non-propagating crack Abstract This study focuses on the numerical simulation of short crack growth to investigate geometric interaction e ff ects between small neighboring defects under consideration of crack closure. In an extensive parameter study, circular cracks of various sizes and interaction distances are investigated. The simulation procedure follows a cyclic R-curve analysis in order to determine the fatigue limit of maximum non-propagating crack formation. The interaction e ff ects are quantified in the form of novel geometry factors for interacting cracks as well as the degradation of the fatigue limit due to crack size and proximity. The results are compared to experimental validation tests performed on additively manufactured specimens containing artificial defects. © 2025 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 ECF24 organizers. Keywords: short crack growth; interaction e ff ect; defect interaction; fatigue limit; cyclic R-curve analysis; non-propagating crack © 2025 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 ECF24 organizers

1. Introduction 1. Introduction

The presence of manufacturing process based imperfection in cast or additively manufactured metallic components, even under optimized processing conditions, is inevitable. Small imperfections, or defect networks, acting as stress concentrators and crack nucleation sites can significantly a ff ect the fatigue performance of components. Based on the fracture mechanical assessment of short cracks, the Kitagawa-Takahashi diagram describes the degradation of the fatigue limit due to the presence of defects (Kitagawa and Takahashi, 1976; El Haddad et al., 1979). Depending on their geometric configuration, interaction e ff ects between neighboring stress-concentrators have to be considered for reliable fatigue design (Murakami, 2019). Numerous investigations on the interaction e ff ects between various kinds of defects have been conducted in the past. These can be separated into the analysis of experimental test results and the stress field based analysis of defect interactions. The latter is treated by the analysis of stress concentrations at blunt notches like voids, and the study of stress field singularities at cracks and sharp crack-like notches. In summary, interaction e ff ects need to be considered, The presence of manufacturing process based imperfection in cast or additively manufactured metallic components, even under optimized processing conditions, is inevitable. Small imperfections, or defect networks, acting as stress concentrators and crack nucleation sites can significantly a ff ect the fatigue performance of components. Based on the fracture mechanical assessment of short cracks, the Kitagawa-Takahashi diagram describes the degradation of the fatigue limit due to the presence of defects (Kitagawa and Takahashi, 1976; El Haddad et al., 1979). Depending on their geometric configuration, interaction e ff ects between neighboring stress-concentrators have to be considered for reliable fatigue design (Murakami, 2019). Numerous investigations on the interaction e ff ects between various kinds of defects have been conducted in the past. These can be separated into the analysis of experimental test results and the stress field based analysis of defect interactions. The latter is treated by the analysis of stress concentrations at blunt notches like voids, and the study of stress field singularities at cracks and sharp crack-like notches. In summary, interaction e ff ects need to be considered,

2452-3216 © 2025 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 ECF24 organizers 10.1016/j.prostr.2025.06.086 ∗ Corresponding author. Tel.: + 43-3842-402-1470 ; fax: + 43-3842-402-1402. E-mail address: stefan.fladischer@unileoben.ac.at 2210-7843 © 2025 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 ECF24 organizers. ∗ Corresponding author. Tel.: + 43-3842-402-1470 ; fax: + 43-3842-402-1402. E-mail address: stefan.fladischer@unileoben.ac.at 2210-7843 © 2025 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 ECF24 organizers.