Contents lists available at ScienceDirect Engineering Failure Analysis journal homepage: www.elsevier.com/locate/engfailanal Fatigue fracture analysis of an ADF antenna in a military aircraft Lamine Rebhi a , Branimir Krstic a, ⁎ , Abdelwahid Boutemedjet a , Ljubica Totovski b , Nikola Vucetic c , Miroslav Milutinovic c , Narimane Rezgui a a University of Defence in Belgrade, Military Academy, Generala Pavla Jurisica Sturma 33, 11000 Belgrade, Serbia b Military Technical Institute, Ratka Resanovica 1, 11000 Belgrade, Serbia c University of East Sarajevo, Faculty of Mechanical Engineering, Vuka Karadzica 30, 71123 East Sarajevo, Republic of Srpska, Bosnia and Herzegovina ARTICLE INFO Keywords: Aircraft Antenna Fatigue Corrosion pitting Finite element analysis ABSTRACT The antenna of military aircraft was fractured into two pieces during the flight mission. The fracture occurred in bottom part of antenna. The lower portion of the antenna stayed attached to the fuselage, whereas the upper portion fall off the aircraft. Based on the fractographic ex- amination of the fracture surface, the characteristic beach marks, cleavage-like cracking mode and striation were observed indicating the occurrence of fatigue failure. The fatigue was initiated from very closely grouped corrosion pits located on the external surface of the antenna. Chemical analysis of the corrosion products in these corrosion pits showed the presence of significant amounts of chlorine, sulfur and calcium. Metallographic examination discovered numerous corrosion pits with secondary micro cracks propagating out of them. The nonlinear finite element (FE) analysis show that the antenna is exposed to fully-reversed fatigue loading, inducing cycles of tension and compression on the lateral faces of the antenna. Also, the FE analysis confirmed that the crack was originated in the region with maximum tensile stress in the antenna. 1. Introduction All aircraft that are either civilian or military are equipped with a system of navigational aids allowing the aircraft to navigate to its destination. One of the oldest types of navigational aids by radio wave is the automatic direction finder (ADF), also called radio compass, which is a navigational system that allows an aircraft to locate itself with respect to an emitting antenna. The ADF receiver, often used as a backup navigation aid for visual flight rules (VFR), may be used when there is no longer an optical range for the use of certain navigational systems or when there is no very high frequency omnidirectional radio range (VOR) equipment on the ground or on board. It is used for positioning, receiving communications on low and medium frequency, navigating to a non-directional radio beacon (NDB) station and following an air track. Among the equipment that ADF system includes is the sense aerial, which is the non- directional antenna that receives signals from all directions. In case of sense aerial antenna failure, in the instrumental flight rules (IFR) conditions, the whole ADF system is down, and the pilot can lose its track if there is no VOR system on board. Additionally, if the aircraft is flying inside clouds, or above clouds ceiling with no visual contact with ground, and it is impossible to change back to VFR, it can be in very serious emergency situation, with high possibility of fatal ending. Another possible emergency situation is antenna failure during initial or final approach if there are no other precise approach https://doi.org/10.1016/j.engfailanal.2018.04.013 Received 15 January 2018; Received in revised form 1 April 2018; Accepted 11 April 2018 ⁎ Corresponding author at: University of Defence in Belgrade, Military Academy, Belgrade, Department of Military Mechanical Engineering, Generala Pavla Jurisica Sturma 33, 11000 Belgrade, Republic of Serbia. E-mail address: branimir.krstic@va.mod.gov.rs (B. Krstic). Engineering Failure Analysis 90 (2018) 476–488 Available online 17 April 2018 1350-6307/ © 2018 Elsevier Ltd. All rights reserved. T