PSI - Issue 60

Available online at www.sciencedirect.com Structural Integrity Procedia 00 (2023) 000 – 000 Available online at www.sciencedirect.com ScienceDirect

www.elsevier.com/locate/procedia

ScienceDirect

Procedia Structural Integrity 60 (2024) 372–381

© 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 ICONS 2023 Organizers Abstract The paper presents findings of the failure analysis of a control rod that resulted in accident to a helicopter during a routine flight. The helicopter crashed due to several events that led to loss of control. Post-accident wreckage examination showed that failure in the non-rotating control rod connecting the swash plate and bell crank was the primary component that led to the accident. The control rod was manufactured from Ti-6Al-4V alloy. Fractography studies revealed that the control rod failed by fatigue mechanism. The fatigue crack initiated at the rod-to-eye-end transition fillet. Fatigue crack initiation was associated with presence of deep machining marks on the fillet surface. After initiation at the machining marks, the crack propagated through the thickness as well as along the machining mark over a length on either side of the crack origin. Study revealed presence of multiple fatigue cracks on the machining marks on the fillet surface. Analysis showed that the primary cause of the fatigue failure of the non rotating control rod was the stress concentration effect arising from the deep machining marks at vulnerable location, which is the rod – to – eye transition fillet surface. Issues related to the fitment of the bearing in the control rod led to fretting on the inner bearing surface, and this damage contributed to the initiation of the fatigue cracks. © 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) Third International Conference on Structural Integrity 2023 (ICONS 2023) Failure analysis of non-rotating control rod of a helicopter V.Venkatesh * , K. Raghavendra, M.Madan, M.Sujata and S.K. Bhaumik a Materials Science Division, National Aerospace Laboratories, Council of Scientific and Industrial Research (CSIR), Bangalore 560017, INDIA

Peer-review under responsibility of the ICONS 2023 Organizers Keywords: non-rotating control rod; fatigue; fretting; stress concentration

1. Introduction The control systems of the helicopter are critical for ensuring safe and efficient operation. Every component of the control system must be meticulously designed, manufactured and maintained to uphold the highest standards of reliability and safety. Any deviation from the design, and/or flaw in these components can be a potential root cause for mishaps, leading to accidents that lead to loss of life (Bhaumik et al., 2008). The helicopter control system

* Corresponding author. E-mail address: venkateshmt92@gmail.com

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 ICONS 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 ICONS 2023 Organizers 10.1016/j.prostr.2024.05.058