PSI - Issue 42

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ScienceDirect

Procedia Structural Integrity 42 (2022) 1113–1120 Structural Integrity Procedia 00 (2019) 000–000 Structural Integrity Procedia 0 ( 0 9) 000–000

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23 European Conference on Fracture – ECF23 Early Crack Growth from Notches under Creep-Fatigue Loading 23 European Conference on Fracture – ECF23 Early Crack Growth from Notches under Creep-Fatigue Loading

Florian Garnadt ∗ , Christian Kontermann, Matthias Oechsner Institut fuer Werksto ff kunde, Grafenstrasse 2, 64283 Darmstadt, Germany Florian Garnadt ∗ , Christian Kontermann, Matthias Oechsner Institut fuer Werksto ff kunde, Grafenstrasse 2, 64283 Darmstadt, Germany

© 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 Abstract Most of the components’ lifetime is consumed in the range of crack initiation and short crack growth. This paper shows the impact of notches in these early stages under creep-fatigue loading at high temperature. With the focus on round bar specimens having a circumferential notch the influence of di ff erent notch shapes, loading levels and conditions is assessed by a crack growth model. The crack tip loading is computed in form of a cyclic e ff ective J -Integral considering the impact of (visco)plasticity induced crack closure based on finite element simulations. Based on this model, notch support factors for same local loading levels and crack depths are computed to quantify the notch support e ff ect. The theoretical results are validated by experiments, where the short crack growth is measured. To give an idea of the applicability potential of the modelling approach, an industry relevant use case is presented. 2020 The Authors. Published by Elsevier B.V. is is an open access article under the CC BY-NC-ND license (http: // cr ativec mmons.org / licenses / by-nc-nd / 4.0 / ) P r-review unde responsibility of 23 European Conference on F acture – ECF23 . Keywords: Notch Support; Creep-Fatigue Loading; Crack Closure Simulation; Cyclic J -Integral; Lifetime Assessment Climate change and respective policy responses have triggered a transformation process of energy markets in many countries recently. It includes substituting the use of fossil by renewable energy sources. To compensate natural fluc tuations of the latter, power plants are required to operate more flexibly. Hence, this paper focuses on applications like gas or steam turbines used in conventional power plants. In this field, turbo machines underlie a higher mechanical and thermal loading through faster ramp-ups and shut-downs. Thus, the lifetime consumption of components increases. Against this background, reconsidering the applied lifetime assessment procedures may be one way to tackle the increased requirements. Therefore, the aim is to reduce the number of assumptions implied in currently used assessment methods reliably. One of those faced in this paper is the influence of notches on short crack growth called fracture mechanical notch support. Fig. 1 (a) shows an example for a component, which has a lot of notches as design features. Usually, the local strain concept by Neuber (1968) is used to determine the local loading at the notch root as the location with the highest stress and probably the spot of crack initiation. Then, fatigue life curves as shown Abstract Most of the components’ lifetime is consumed in the range of crack initiation and short crack growth. This paper shows the impact of notches in these early stages under creep-fatigue loading at high temperature. With the focus on round bar specimens having a circumferential notch the influence of di ff erent notch shapes, loading levels and conditions is assessed by a crack growth model. The crack tip loading is computed in form of a cyclic e ff ective J -Integral considering the impact of (visco)plasticity induced crack closure based on finite element simulations. Based on this model, notch support factors for same local loading levels and crack depths are computed to quantify the notch support e ff ect. The theoretical results are validated by experiments, where the short crack growth is measured. To give an idea of the applicability potential of the modelling approach, an industry relevant use case is presented. © 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: Notch Support; Creep-Fatigue Loading; Crack Closure Simulation; Cyclic J -Integral; Lifetime Assessment 1. Introduction Climate change and respective policy responses have triggered a transformation process of energy markets in many countries recently. It includes substituting the use of fossil by renewable energy sources. To compensate natural fluc tuations of the latter, power plants are required to operate more flexibly. Hence, this paper focuses on applications like gas or steam turbines used in conventional power plants. In this field, turbo machines underlie a higher mechanical and thermal loading through faster ramp-ups and shut-downs. Thus, the lifetime consumption of components increases. Against this background, reconsidering the applied lifetime assessment procedures may be one way to tackle the increased requirements. Therefore, the aim is to reduce the number of assumptions implied in currently used assessment methods reliably. One of those faced in this paper is the influence of notches on short crack growth called fracture mechanical notch support. Fig. 1 (a) shows an example for a component, which has a lot of notches as design features. Usually, the local strain concept by Neuber (1968) is used to determine the local loading at the notch root as the location with the highest stress and probably the spot of crack initiation. Then, fatigue life curves as shown 1. Introduction

∗ Corresponding author. E-mail address: florian.garnadt@tu-darmstadt.de ∗ Corresponding author. E-mail address: florian.garnadt@tu-darmstadt.de

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.2022.12.142 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 u der 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 .