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2. PHD Thesis / Tesis PHD
3. Faculty of Engineering and Built Environment / Fakulti Kejuruteraan dan Alam Bina

Title:	Finite Element Analysis Of Fatigue Crack Initiation And Propagation In Rail Track Under Rolling Contact Loading
Authors:	Norie Allafi Ali Akeel (P44196)
Supervisor:	Zainuddin Bin Sajuri, Assoc. Prof. Dr.
Keywords:	Finite Element Analysis Fatigue Crack Initiation Propagation In Rail Track Under Rolling Contact Loading Materials--Fatigue
Issue Date:	15-Aug-2013
Description:	Recent development in rail based transportation in Malaysia is made for higher frequency and speedy commuter services to fulfil the demand of increasing number of passengers. Heavy traffics and loads lead to reduction in rail track lifetime due to damages and cracks formed on the railhead surface, that caused by repeated rolling contact between wheel and rail. The problem is that engineers find it hard to predict the remaining lifetime of the damaged and cracked rail track based on the hairline cracks observed on the railhead surface. Therefore, this study is aims to identify the damages of railhead surface, and predict fatigue initiation life and crack propagation direction due to rolling contact fatigue (RCF). Identification of damages and cracks was performed by sectioning, slicing and polishing the railhead crown of severely damaged Keretapi Tanah Melayu Berhad (KTMB) rail track before observing under an optical microscope. A 3D wheel/rail contact model was developed to analyse the stress distribution at the contact area and compared it with the hardness distribution on the railhead surface. Finite element method (FEM) code ANSYS 11.0 was used to simulate the stress distribution and fatigue initiation life in the rail track at the straight, transition and curving track area under the rolling contact loading. FORTRAN and Post2D software were then utilized to predict the fatigue crack propagation trajectory as well as the stress intensity factors. The source code program language used is capable in modelling crack propagation in 2D under the mixed mode loading. Crack propagation analysis of the rail track is modified and modelled into a four points bending model following the geometry, materials properties and loading provided by KTMB. The damage identification results showed that the length of cracks observed was about 1 to 4 mm and propagated incline into subsurface at about 30° to the running surface of the railhead. Hardness tests on the railhead cross-section revealed that hardness increased at the area close to the contact between rail and wheel where damages and cracks could be observed. This feature was due to work hardening resultant from the repeated rolling contact of rail and wheel surface. The FE simulation showed that the highest stress distribution regions were matched with the area of severely damage and of highest hardness area. The hardness value obtained from experiment was 41.8 HRC. The maximum value of fatigue crack initiation life was determined at 18958 cycles as compared with the smaller curve radius and higher load as the longer fatigue crack initiation lives of rail track. In order to investigate the stress intensity factors values and crack length direction, the mixed mode loading analysis was carried out. It was found that mode I stress intensity factor KI governing the propagation of crack with slight effect of mode II stress intensity factor KII at the first few millimetres crack propagation. The model developed is capable to simulate the stress distribution and predict fatigue lifetime and crack propagation direction of the rail track. In this study, the stress distribution analysis from the model developed was successfully simulated and the critical and potential area for crack initiation was predicted. A model to predict the behaviour of wheel/rail contact, and to simulate crack initiation and stress distribution at the straight, transition and curving areas were proposed. The finding of this study could be used by engineers to create flexible designs of rail track curve radius, and control the train speed to reduce fatigue damages.,PhD
Pages:	221
Call Number:	TA418.38 .A396 2013 3
Publisher:	UKM, Bangi
Appears in Collections:	Faculty of Engineering and Built Environment / Fakulti Kejuruteraan dan Alam Bina

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