Fatigue life prediction of rails
Development of an On-Board Measurement System for Railway Vehicle Wheel Flange Wear
Published by (Sensors)
Authors: Pacifique Turabimana, Celestin Nkundineza. Published January 06, 2020
The maintenance of railway systems is critical for their safe operation. However some landscape geographical features force the track line to have sharp curves with small radii. Sharp curves are known to be the main source of wheel flange wear. The reduction of wheel flange thickness to an extreme level increases the probability of train accidents. To avoid the unsafe operation of a rail vehicle, it is important to stay continuously up to date on the status of the wheel flange thickness dimensions by using precise and accurate measurement tools. The wheel wear measurement tools that are based on laser and vision technology are quite expensive to implement in railway lines of developing countries. Alternatively significant measurement errors can result from using imprecise measurement tools such as the hand tools, which are currently utilized by the railway companies such as Addis Ababa Light Rail Transit Service (AALRTS). Thus, the objective of this research is to propose and test a new measurement tool that uses an inductive displacement sensor. The proposed system works in both static and dynamic state of the railway vehicle and it is able to save the historical records of the wheel flange thickness for further analysis. The measurement system is fixed on the bogie frame. The fixture was designed using dimensions of the bogie and wheelset structure of the trains currently used by AALRTS. Laboratory experiments and computer simulations of the electronic system were carried out to assess the feasibility of the data acquisition and analysis method. The noises and unwanted signals due to the dynamics of the system are filtered out from the sensor readings. The results show that the implementation of the proposed measurement system can accurately measure the wheel flange wear. Also, the faulty track section can be identified using the system recorded data and the operational control center data.
The influence of spatial variation of railroad track stiffness on the fatigue life
Published by (Proceedings of the Institution of Mechanical Engineers, Part F: Journal of Rail and Rapid Transit)
Authors: Celestin Nkundineza, Joseph A Turner. Published March 09, 2017
Railroad transportation is very important for the economic growth. The effective maintenance of railroad transportation is a critical factor for its economic sustainability. The high repetitive forces from a moving railcar induce cyclic stresses that lead to bending and potential deterioration of rails due to the initiation and propagation of fatigue cracks. Previous research on the prediction of fatigue life has been done under the assumptions of a uniform track bed and a homogeneous rail. However, the spatial variation of track stiffness is expected to increase the maximum stresses in the rails and, therefore, accelerate the fatigue process. This study is focused on the variations of the track modulus and the impact on fatigue life. The computational procedure is based on several hundreds of finite element models of the rails across a set of crossties chosen from a random ensemble with representative statistical variations. The mean of the track moduli is estimated from the field track deflection dynamic measurement data in comparison with the deflection data from the FE models. A multiaxial fatigue model is used for the estimation of fatigue cycles to crack initiation. The results show that a non-uniform track bed can reduce the fatigue life by up to 100 times in comparison with the behavior expected for a uniform track bed. The results of this study are expected to improve the effective maintenance and scheduling of rail inspection.
Influence of Spatial Variations of Track Stiffness on Fatigue Crack Initiation and Propagation
Published by (ASME/IEEE Joint Rail Conference)
Authors: Celestin Nkundineza , Joseph A. Turner. Published June 10, 2015
The bending of rail due to the repeated loading from railcar wheels is a known source of rail fatigue. If rail stresses are sufficiently high, they can initiate and propagate fatigue cracks after repeated cyclic loading such that they ultimately result in rail failure. Previous analyses of stresses from wheel loads have primarily focused on track beds for which the track stiffness is assumed uniform across a length of many cross-ties. In reality, however, spatial variations of track stiffness are known to exist and are affected by many factors such as the weather. These stiffness variations can lead to stresses that are locally higher than those predicted using models based on uniform average track stiffness alone. The work presented here is focused on the influence of spatial variations of track stiffness along the rail with respect to the maximum stresses generated. A computational model of a rail on a set of cross-ties with a statistically varying stiffness is used to study the maximum stresses generated when the track stiffness is not spatially uniform. The mean and standard deviation of the local track stiffness are varied and the maximum stresses at various positions within the rail are examined. This computational procedure is repeated for an ensemble of local track stiffness profiles to acquire the needed statistics of the corresponding stresses. These stresses are then related to crack initiation and the expected rate of crack propagation relative to the given the statistics of the track stiffness. This work is anticipated to have application for rail maintenance and the scheduling of rail defect inspections.
Stochastic Optimal Control of Linear Multi-Degree-of-Freedom Systems Under Nonstationary Random Excitations
Published by (ASME 2012 International Design Engineering Technical Conferences and Computers and Information in En)
Authors: Celestin Nkundineza , Cho W. S. To. Published September 09, 2013
Stochastic optimal control is an important area of research in engineering systems that undergo disturbances such as earthquake excitations and blast waves. Controlling states such as positions of different parts in these systems is critical in situations in which the system has to operate within limited range of its states. The present investigation is concerned with the application of the stochastic optimal control strategy developed by To (2010) and its implementation as well as providing computed results of linear systems under nonstationary random excitations. In the strategy the feedback matrix is designed based on the achievement of the objectives for individual states in the system through the application of the Lyapunov equation of the system. Every diagonal element in the gain or associated gain matrix is related to the corresponding states. The strategy is applied to two two-degree-of-freedom (dof) systems representing buildings under earthquake excitations. Optimally controlled nonstationary random displacements were obtained by the proposed method and presented in this paper. The computed results include the time-dependent elements of the associated gain matrix. Three-dimensional (3D) graphical representations of the optimally controlled largest peaks of mean squares of displacements and velocities against elements of the feedback gain matrix were included. The latter 3D presentations are important for the design engineer who needs to choose elements of the gain matrix in order to achieve a specific objective in certain states of the system.
Vibration responses of a railcar under rail irregularities: case of Addis Ababa Light Rail Transit Service
Published by (THE 1st EAST AFRICAN COMMUNITY SCIENCE, TECHNOLOGY AND INNOVATION CONFERENCE-2019)
Authors: Gaspard Bizimungu and Celestin Nkundineza. Published October 24, 2019
Track irregularities contribute a large impact on the vibrations of a railcar. However, the track irregularities and track stiffness will alter over time due to the loading and environmental conditions. The measurements of rail irregularities are required to determine their impact on railcar vibrations. Ignoring this can significantly increase future maintenance costs on both vehicle and track. Therefore, this research is about assessing the impact of track irregularities on the rail vehicle vibration for the case of Addis Ababa Light Rail Transit Service. The equations of motion of the half railcar model with twelve degrees of freedom have been derived and solved using MATLAB. The irregularities used as excitation input to the equations of motion were measured along the track segment of Addis Ababa light rail at an interval of 150m each. The Hertzian contact effects were neglected in analytical model for simplicity. On the other hand, Finite Element Method was used to validate the analytical modal equations. The validation was achieved by performing modal analysis of a 3D railcar bogie lumped with the rail car mass via secondary suspension. The natural frequencies provided by 3D FEM are compared with those obtained using lumped parameter model. Then, the effect of primary suspension parameters on the railcar vibration behaviour was investigated. The frequency of the carbody that corresponds to bounce motion provided by lumped parameter model was 14.89Hz while the frequency obtained from modal analysis by FEM was 13.829Hz. The match of frequencies in both models provided confidence in the correctness of the analytical model. These frequencies are in range of human sensitivity to vibrations, which is 0 to 20Hz as specified by ISO 2631. Therefore, rail irregularities with frequency content in this range must be carefully investigated and their effect must be eliminated at the railway lines, by either correcting the track or using proper railcar suspension parameters. In this analysis, the simulation results showed that the developed and validated analytical modal form a basis to determine the parameters of the vertical suspension component that suppress the critical vibrations of the light rail vehicle under track irregularities.
Keywords: Finite Element Method, modal analysis, rail vehicle design, railcar vibrations, track irregularities.
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