PSI - Issue 41

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ScienceDirect

Procedia Structural Integrity 41 (2022) 208–214 Structural Integrity Procedia 00 (2022) 000–000 Structural Integrity Procedia 00 (2022) 000–000

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2nd Mediterranean Conference on Fracture and Structural Integrity Investigation of crack path near cold expanded hole Peter Zobec*, Jernej Klemenc 2nd Mediterranean Conference on Fracture and Structural Integrity Investigation of crack path near cold expanded hole Peter Zobec*, Jernej Klemenc Faculty of mechanical engineering, University of Ljubljana, Asˇkercˇeva 6, 1000 Ljubljana, Slovenia Faculty of mechanical engineering, University of Ljubljana, Asˇkercˇeva 6, 1000 Ljubljana, Slovenia

© 2022 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 MedFract2Guest Editors. © 2022 The Authors. Published by Elsevier B.V. his is an open access article under the CC BY-NC-ND license (http: // creativec mmons.org / licenses / by-nc-nd / 4.0 / ) er-review under responsibility of th MedFract2Guest Editors. Keywords: Cold hole expansion; Fatigue crack growth; Residual stress Abstract In a structure, holes are concentrators of stresses. When the structure is subjected to a cyclic load, the holes should be carefully designed to prevent the occurrence of fatigue cracks. The now well-accepted technique of cold expanding holes itigates the e ff ect of stress concentration by introducing an area of compressive stress near the hole surface. The resulting compressive residual stress is balanced by an area of tensile stress, which is detrimental from a fatigue standpoint. In this study, we do not focus on the formation of fatigue cracks at the surface of the cold expanded hole, but investigate the path of the fatigue crack approaching a region ith such a hole. Using a special algorithm to simulate fatigue crack growth, we show that the cold expanded hole attracts the growing crack. This insight sheds new light on the beneficial e ff ects of cold expanded holes. © 2022 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 MedFract2Guest Editors. Keywords: Cold hole expansion; Fatigue crack growth; Residual stress Abstract In a structure, holes are concentrators of stresses. When the structure is subjected to a cyclic load, the holes should be carefully designed to prevent the occurrence of fatigue cracks. The now well-accepted technique of cold expanding holes mitigates the e ff ect of stress concentration by introducing an area of compressive stress near the hole surface. The resulting compressive residual stress is balanced by an area of tensile stress, which is detrimental from a fatigue standpoint. In this study, we do not focus on the formation of fatigue cracks at the surface of the cold expanded hole, but investigate the path of the fatigue crack approaching a region with such a hole. Using a special algorithm to simulate fatigue crack growth, we show that the cold expanded hole attracts the growing crack. This insight sheds new light on the beneficial e ff ects of cold expanded holes. Cold Hole Expansion (CHE) is a technique for introducing beneficial compressive residual stresses near a hole [1– 4]. The first applications of CHE are credited to aircraft manufacturer Boeing to reinforce holes in aluminium alloy structures[5–8]. Today, this is an accepted practice in both the manufacturing and maintenance phases of aerospace vehicles. Another important area of CHE is the rail system. Rails were initially connected by bolted joints, which were weak points in the design. Nowadays, rails are welded together and bolted joints are mainly used to isolate sections of the rail-track system, for example, at track turns with high maintenance frequency or for signal purposes where the bolted joint serves as an electrical current insulator [9–12]. These are examples of structures subjected to fatigue loading, and uncontrolled fatigue cracking is of paramount importance to safety. A hole in a dynamically loaded structure acts like a stress concentration detail. It reduces the load-bearing area and, depending on the radius of the hole, increases the nominal stress. Higher fatigue stress means shorter fatigue life or fewer load cycles to crack Cold Hole Expansion (CHE) is a technique for introducing beneficial compressive residual stresses near a hole [1– 4]. The first applications of CHE are credited to aircraft manufacturer Boeing to reinforce holes in aluminium alloy structures[5–8]. Today, this is an accepted practice in both the manufacturing and maintenance phases of aerospace vehicles. Another important area of CHE is the rail system. Rails were initially connected by bolted joints, which were weak points in the design. Nowadays, rails are welded together and bolted joints are mainly used to isolate sections of the rail-track system, for example, at track turns with high maintenance frequency or for signal purposes where the bolted joint serves as an electrical current insulator [9–12]. These are examples of structures subjected to fatigue loading, and uncontrolled fatigue cracking is of paramount importance to safety. A hole in a dynamically loaded structure acts like a stress concentration detail. It reduces the load-bearing area and, depending on the radius of the hole, increases the nominal stress. Higher fatigue stress means shorter fatigue life or fewer load cycles to crack 1. Introduction 1. Introduction

∗ Corresponding author. E-mail address: peter.zobec@fs.uni-lj.si ∗ Corresponding author. E-mail address: peter.zobec@fs.uni-lj.si

2452-3216 © 2022 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 MedFract2Guest Editors. 10.1016/j.prostr.2022.05.023 2210-7843 © 2022 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 MedFract2Guest Editors. 2210-7843 © 2022 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 MedFract2Guest Editors.