publications

2023

1. 

   Experimental Investigation on the Arc Damage and Fatigue Crack Initiation Risk of Copper-Silver Contact Wires

   Ozgun Sunar, and David Fletcher

   IEEE Transactions on Power Delivery, Apr 2023

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   Contact wires are subjected to both mechanical and electrical interactions while electrical energy is transmitted to the trains by overhead lines and train pantographs. Particularly, an increase in the speed of trains can result in greater contact force fluctuations and more intense pantograph arcs, therefore, these mechanical and electrical interactions have potential to drive failure of Overhead Line Equipment (OLE) conductors. In this paper, the effect on fatigue crack initiation risk of material ablation from the contact wire surface due to arc discharge is experimentally investigated under laboratory conditions. Fatigue life, crack propagation directions and crack initiation locations in arc-exposed copper silver contact wire samples are compared with those in comparable arc-free samples. The results show that under the conditions of having arc damage on the contact wire surface could result in 50 per cent shorter fatigue life compared to arc-free contact wires. It is often considered that wear rather than fatigue cracking defines the life of the contact wires, but under some conditions with the combination of arcing, the fatigue life in the contact wire can become the controlling failure risk. Therefore, in determining system life and maintenance requirements the fatigue life of the contact wire should be taken into consideration at locations where the arc discharge is likely.

2. 

   Investigation of Contact Force and Stress Relationship in Overhead Line Contact Wires with Finite Element Method

   Özgün SUNAR

   Demiryolu Mühendisliği, Jul 2023

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   Railway overhead line electrification (OLE) is used for providing continuous power to the trains throughout catenary wires and the current collector device of the pantograph. The interaction of contact force exerted by the pantograph and contact wire is an important topic in regulating OLE dynamics. OLE components are subjected to fluctuating contact forces due to the trains running with high speed, therefore, it is important to estimate service life of contact wires and pantograph carbon collectors by considering contact wire/pantograph interference. This study performs a number of contact force and stress/strain analysis of standard OLE designs used in Europe, Series 1, Sicat S1.0, Sicat H1.0, Re250 and EAC 350, with finite element method. The results establish a link between stress levels and contact force in the contact lines depending on the design parameters of contact wire type, pretension, span-length, and contact wire material. Understanding the bending of the contact wire due to the contact force will help to predict potential failures in mainlines and extend our knowledge of safety and reliability of various OLE design parameters.

2022

1. 

   A new small sample test configuration for fatigue life estimation of overhead contact wires

   Ozgun Sunar, and David Fletcher

   Proceedings of the Institution of Mechanical Engineers, Part F: Journal of Rail and Rapid Transit, Aug 2022

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   Fatigue in railway overhead line electrification (OLE) contact wires can cause sudden catastrophic failures. The contact wire interacting with the pantograph both mechanically and electrically is subjected to tension and repetitive bending due to the pantograph contact force. Recently, fatigue failures of OLE have risen in prominence with increases in train speed. To address this a new fatigue test configuration has been developed. The study focuses on a method for testing the wire as a component enabling fatigue life evaluation of worn wires, or exploring the effect of installation damage, through component level evaluation of crack initiation and propagation. The new test configuration places a 400 mm-length contact wire in a combination of bending and pretension with realistic boundary conditions replicating service conditions for longer spans. The results are presented in a strain-life format to provide data for a wide range of potential service conditions.

2021

1. 

   Arc Damage Identification and Its Effects on Fatigue Life of Contact Wires in Railway Overhead Lines (PhD Thesis)

   Ozgun Sunar

   The University of Sheffield ISNI:0000 0004 9356 9895, Aug 2021

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2. 

   Laboratory Assessment of ARC Damage in Railway Overhead Contact Lines With a Case Study on Copper-Silver and Low Oxygen Content Copper

   Ozgun Sunar, David Fletcher, and Adam Beagles

   IEEE Transactions on Power Delivery, Oct 2021

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   In this study the main goal is to produce a new method which provide to minimize manufacturing and test periods for leaf springs. Before fatigue life determination of leaf springs, parameters which effect on fatigue life prediction and parabolic leaf spring design have investigated. Parabolic leaf spring’s FEM model’sstress and fatigue life analysis have substantiated with Ansys Workbench 14.5 and Ansys nCode Design Life 14.5. The results obtained were verified by comparing the value of physical tests. This finite element fatigue life studies have proved that it is possible to reach fatigue life prediction of the leaf spring used in light and heavy commercial vehicles without longtime experiments tests on track after prototype manufacturing

3. 

   Case study: Mechanical and metallurgical investigation of arc damage in overhead line contact wires

   Ozgun Sunar, and David Fletcher

   The Journal of Permanent Way Institution, Oct 2021

2016

1. 

   Finite Element Modeling of Leaf Springs for the Prediction of Fatigue Life Finite Element Modeling of Leaf Springs for the Prediction of Fatigue Life

   Özgün Sunar, and Mehmet Çevik

   In , Oct 2016

   Issue: August 2015

2015

1. TEK KATLI YAPRAK YAYLARDA SONLU ELEMANLAR YÖNTEMİ İLE YORULMA ANALİZİ - FATIGUE ANALYSIS OF SINGLE LEAF SPRINGS WITH FINITE ELEMENT METHOD

   Özgün Sunar, and Mehmet Çevik

   Celal Bayar Üniversitesi Fen Bilimleri Dergisi, Jun 2015

   Publisher: C.B.U. Journal of Science

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   In this study the main goal is to produce a new method which provide to minimize manufacturing and test periods for leaf springs. Before fatigue life determination of leaf springs, parameters which effect on fatigue life prediction and parabolic leaf spring design have investigated. Parabolic leaf spring’s FEM model’sstress and fatigue life analysis have substantiated with Ansys Workbench 14.5 and Ansys nCode Design Life 14.5. The results obtained were verified by comparing the value of physical tests. This finite element fatigue life studies have proved that it is possible to reach fatigue life prediction of the leaf spring used in light and heavy commercial vehicles without longtime experiments tests on track after prototype manufacturing