Failure Analysis of Switch Rails and Crossings Towards Maintenance Improvement: A Case Study of Addis Ababa Light Rail Transit
| dc.contributor.advisor | Daniel Tilahun (Assoc. Prof.) | |
| dc.contributor.author | Ruhama Minwuyelet | |
| dc.date.accessioned | 2025-01-14T13:59:20Z | |
| dc.date.available | 2025-01-14T13:59:20Z | |
| dc.date.issued | 2024 | |
| dc.description.abstract | Railway systems are such a complex transportation systems that consists several components like rails, switches, crossings, check rails, turnout carriers, and some other components. Maintenance of railway “switch and crossing” (S&C) systems is critical for effective and safe train operations. The material degradation and geometry optimization of switches and crossings should be considered for an efficient operation of railway system. The failures of railway tracks are an unavoidable phenomenon that affects the operation intensively. AALRTS rail material is 50 Kg/m U71Mn and the frog is Hadfield steel. Previously different failure assessment and investigation researches have been carried out, however, failure investigation techniques need to be updated frequently and assessed because the problem still exists. Markov chain model was implemented for statistical analysis of critical failures and the output results are “Mean Time To Failure” for both critical and disastrous failures. Based on the results it is possible to recommend that increasing the number o f “Ultrasonic Inspection Cars” test from 3 to 5 or increasing the test interval from 122 days to 73 days per year will minimize “Mean Time To Failure” from 3.1 years to 1.6 years. The mean time to failure results can be an input for a strategic track maintenance planning. “Failure mode, effects, and criticality analysis” (FMECA) were implemented to identify the most critical failure mode with higher risk. The welded rail specimen`s quality, hardness, and microstructural features were evaluated at different cooling rates experimentally. To identify and assess the microstructure feature and hardness of rail welding through different cooling rates three major NDT tests have been employed. Increasing the number of tests of inspection or the inspection interval will minimize the mean time to failure. Generally, all the non-destructive test results demonstrate that there is a noticeable defect on the welded rail cooled at 6°C/s. Comparatively fewer defects were observed on the welded rail cooled at 3°C/s; while acceptable defects were manifested on the one cooled at 2°C/s. The minimum cooling rate can be achieved through both preheating and post-heating process. From the switch panel, “Failure mode, effects, and criticality analysis” (FMECA) results “gauge corner spalling” failure mode was with the highest risk priority number so that its improvement has a great influence on the maintenance efficiency.Additionally, from the detail results of failure mode, effects, and criticality analysis (FMECA) of turnouts; failure modes under high risk category need special attention during maintenance planning and need improvement of rectification techniques. From the results of the analysis six failure modes have been laid under high risk categories whereas two failure modes have been laid under moderate risk categories and four failure modes have been laid under low risk categories. As a conclusion cooling of rail welding`s at 2°C/s cooling rate will give the material good micro-structural feature and better weld quality relatively. This minimum cooling rate 2°C/s achieved by uniform and optimum preheating and post-heating temperatures. Finally, the researcher recommend a controlled cooling rate for welding quality improvement and maintenance efficiency increment. | |
| dc.identifier.uri | https://etd.aau.edu.et/handle/123456789/4108 | |
| dc.language.iso | en_US | |
| dc.subject | Failure assessment | |
| dc.subject | damages on turnouts | |
| dc.subject | failure`s severity | |
| dc.subject | failure modes | |
| dc.subject | sensitivity analysis | |
| dc.subject | Switch rail and crossings. | |
| dc.title | Failure Analysis of Switch Rails and Crossings Towards Maintenance Improvement: A Case Study of Addis Ababa Light Rail Transit | |
| dc.type | Dissertation |