PSI - Issue 57

Available online at www.sciencedirect.com Available online at www.sciencedirect.com ScienceDirect Structural Integrity Procedia 00 (2022) 000 – 000

www.elsevier.com/locate/procedia

ScienceDirect

Procedia Structural Integrity 57 (2024) 365–374

© 2024 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 Fatigue Design 2023 organizers Abstract The frequency effect is a commonly encountered challenge in ultrasonic fatigue testing (UFT) of low-carbon, ferritic steels, wherein factors such as the increased strain rate and reduced test duration change the apparent fatigue resistance of the tested material. The usability of UFT for rapid fatigue testing of these materials is therefore limited as the results cannot be directly compared to conventional fatigue results. In this investigation, fatigue curves were evaluated at frequencies of 20Hz and 20kHz for two comparable grades of ferritic structural steels: Q355B and S355JR, using different conventional frequency specimen geometries. Methods to evaluate the frequency sensitivity of the steels based on the finite life regime were adapted from previously proposed models in literature to produce corrected curves and to allow comparison to similar steels in literature. It was found that previously reported results may be overestimating the frequency sensitivity due to the influence of size effects. It was also found that these models are of limited use for producing corrected SN curves based on UFT data. © 2023 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 Fatigue Design 2023 organizers Keywords: ultrasonic fatigue testing; very high cycle fatigue; structural steels; frequency effect; strain rate effects; size effects 1. Introduction Historically, a fatigue limit value has been considered for most metallic materials around 10 6 load cycles, beyond which it is assumed that plasticity is negligible and correspondingly an infinite fatigue life can be expected. It has become apparent in recent years, however, that this fatigue limit value is a fallacy and that fatigue failure can still occur up to the billions of cycles, into the very high cycle fatigue (VHCF) regime (Bathias 1999). Obtaining test Fatigue Design 2023 (FatDes 2023) Application of finite-life frequency sensitivity evaluation methods to UFT of ferritic structural steels Lewis Milne a *, Yevgen Gorash a , Tugrul Comlekci a , Donald MacKenzie a a Dept. of Mechanical and Aerospace Engineering, University of Strathclyde, 75 Montrose Street, Glasgow, G1 1XJ, UK

* Corresponding author. Tel.: +44 (0)141-574-5082 E-mail address: lewis.milne.2015@uni.strath.ac.uk

2452-3216 © 2023 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 Fatigue Design 2023 organizers

2452-3216 © 2024 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 Fatigue Design 2023 organizers 10.1016/j.prostr.2024.03.039