PSI - Issue 42

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ScienceDirect

Procedia Structural Integrity 42 (2022) 270–275 Structural Integrity Procedia 00 (2019) 000–000 Structural Integrity Procedia 00 (2019) 000–000

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23 European Conference on Fracture – ECF23 Fatigue life of notches: an e ff ect of manufacturing Kamila Koza´kova´ a,b, ∗ , Stanislava Fintova´ a , Jan Klusa´k a a Institute of Physics of Materials, Czech Academy of Sciences, Zˇ izˇkova 22, 616 00 Brno, Czech Republic b Faculty of Mechanical Engineering, Brno University of Technology, Technicka´ 289 / 2, 616 69 Brno, Czech Republic 23 European Conference on Fracture – ECF23 Fatigue life of notches: an e ff ect of manufacturing Kamila Koza´kova´ a,b, ∗ , Stanislava Fintova´ a , Jan Klusa´k a a Institute of Physics of Materials, Czech Academy of Sciences, Zˇ izˇkova 22, 616 00 Brno, Czech Republic b Faculty of Mechanical Engineering, Brno University of Technology, Technicka´ 289 / 2, 616 69 Brno, Czech Republic

© 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 scientific committee of the 23 European Conference on Fracture – ECF23 © 2020 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 / ) r-review under responsibility of 23 European Conference on Fracture – ECF23 . Keywords: Notches; very high cycle fatigue; aluminum aloy; machining; surface roughness; ultrasonic fatigue tests Abstract In this study, the influence of notches in the area of gigacycle fatigue is investigated. The presented study o ff ers experimental fatigue results of smooth and notched specimens. Specimens were made of AW 7075 - T6511 aluminum alloy and have “v” shape notch with radii of 0.1, 0.2, 0.4, 0.8, 1.5, and 3 mm. The fatigue experiments were performed using an ultrasonic fatigue testing machine at 20 kHz test frequency. Fatigue properties of the material were studied and evaluated up to 10 billion cycles in the area of very high cycle fatigue. All fatigue tests were carried out under uniaxial symmetric tension / compression loading ( R = − 1) at room temperature. As-machined surface and fracture surface of smooth specimens and specimens with 6 di ff erent notch radii were observed under an SEM microscope. Results show that there is a strong influence of the manufacturing process on fatigue lifetime. © 2020 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 23 European Conference on Fracture – ECF23 . Keywords: Notches; very high cycle fatigue; aluminum aloy; machining; surface roughness; ultrasonic fatigue tests Abstract In this study, the influence of notches in the area of gigacycle fatigue is investigated. The presented study o ff ers experimental fatigue results of smooth and notched specimens. Specimens were made of AW 7075 - T6511 aluminum alloy and have “v” shape notch with radii of 0.1, 0.2, 0.4, 0.8, 1.5, and 3 mm. The fatigue experiments were performed using an ultrasonic fatigue testing machine at 20 kHz test frequency. Fatigue properties of the material were studied and evaluated up to 10 billion cycles in the area of very high cycle fatigue. All fatigue tests were carried out under uniaxial symmetric tension / compression loading ( R = − 1) at room temperature. As-machined surface and fracture surface of smooth specimens and specimens with 6 di ff erent notch radii were observed under an SEM microscope. Results show that there is a strong influence of the manufacturing process on fatigue lifetime. When A. Wo¨hler defined the fatigue limit between 10 6 and 10 7 cycles, the main industrial applications were railway car axles and steam engines. Now, the fatigue life of high-speed trains and aircraft turbines is ranging in the gigacycle region, according to a rotation speed of several thousand revolutions per minute. Many components in aircraft are submitted to vibrations, which produce billions of fatigue cycles. Very high cycle fatigue (VHCF) shows that a fatigue limit in the traditional sense does not exist in the gigacyle area Bathias (1999); Mughrabi and Antolovich (2016); Bathias and Paris (2010). Some materials do not exhibit a fatigue limit, but instead display a continuously decreasing S - N curve, even at 10 9 cycles and beyond. These materials include aluminum, nickel, titanium alloys, and high strength steels. For example in structural or stainless steels, the fatigue limit can be observed Klusa´k et al. (2021). In the gigacycle region, cracks in smooth specimens often nucleate at microscopic flaws and defects (pores, inclusions). These cracks lead to “fish-eye” formation around the defects. This fact means that micro-stress-concentrators play important role when material is cyclically loaded with small amplitude reaching high number of cycles. When A. Wo¨hler defined the fatigue limit between 10 6 and 10 7 cycles, the main industrial applications were railway car axles and steam engines. Now, the fatigue life of high-speed trains and aircraft turbines is ranging in the gigacycle region, according to a rotation speed of several thousand revolutions per minute. Many components in aircraft are submitted to vibrations, which produce billions of fatigue cycles. Very high cycle fatigue (VHCF) shows that a fatigue limit in the traditional sense does not exist in the gigacyle area Bathias (1999); Mughrabi and Antolovich (2016); Bathias and Paris (2010). Some materials do not exhibit a fatigue limit, but instead display a continuously decreasing S - N curve, even at 10 9 cycles and beyond. These materials include aluminum, nickel, titanium alloys, and high strength steels. For example in structural or stainless steels, the fatigue limit can be observed Klusa´k et al. (2021). In the gigacycle region, cracks in smooth specimens often nucleate at microscopic flaws and defects (pores, inclusions). These cracks lead to “fish-eye” formation around the defects. This fact means that micro-stress-concentrators play important role when material is cyclically loaded with small amplitude reaching high number of cycles. 1. Introduction 1. Introduction

∗ Corresponding author. Tel.: + 420 532 290 348. E-mail address: kozakova@ipm.cz ∗ Corresponding author. Tel.: + 420 532 290 348. E-mail address: kozakova@ipm.cz

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 scientific committee of the 23 European Conference on Fracture – ECF23 10.1016/j.prostr.2022.12.033 2210-7843 © 2020 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 23 European Conference on Fracture – ECF23 . 2210-7843 © 2020 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 23 European Conference on Fracture – ECF23 .