Thesis
FATIGUE SIMULATION TECHNOLOGIES OF COLD EXPANSION PROCESSED AEROSPACE ALUMINUM AND RAIL STEEL HOLES USING THE EXTENDED FINITE ELEMENT METHOD
Master of Science (MS), Washington State University
01/2021
Handle:
https://hdl.handle.net/2376/119050
Abstract
In the transportation sector of aviation and the railway, fatigue failures from holes in aircraftstructures and railway tracks can cause severe and catastrophic accidents. To mitigate such engineering failures, fatigue life enhancement for such structural holes is essential. In this present study, the fatigue life enhancement technologies of metallic alloy holes of aerospace-grade material and railway track material are studied numerically. This study aims to investigate the fatigue life of metal holes prepared by multiple hole preparation technologies, including split sleeve cold hole expansion, and edge break. The chosen material for the aerospace structural hole study is 2024-T351 aluminum alloy, which is popular in aircraft structures. The total fatigue life consists of the sum of crack initiation cycles and cracks propagation cycles. Aluminum alloy holes are prepared by two methods, which are as-drilled as the baseline and the split sleeve cold expansion process. Crack initiation cycles are estimated using the strain life method. Within the range of considered yield strength and percentage of cold expansion, the maximum fatigue life improvement with 2024-T351 aluminum alloy is approximately nine times compared with the baseline model. The crack propagation analyses are conducted using the extended finite element method. To reduce the user’s extensive meshing time and the simulation setup complexity, the XFEM’s crack meshing and solving processes are automated with Python and Batch scripting. The developed automation process can conduct the XFEM crack propagation simulations from the initial crack to the final crack until fracture without the user’s crack meshing, and this reduces the user’s time by approximately 96%. The adopted processes are verified with the experimental fatigue results from previous literature, which proved to be in good agreement in terms of crack size and crack cycle estimation. For the rail hole fatigue analysis, railway track holes consist of three different cases such as as-drilled, edge break, and split sleeve cold expansion processed holes. For the study of rail holes, a full-sized rail joint structure model including the two railway tracks, two joint bars, and six-simplified bolt holes is used. It is observed that the presence of compressive residual stresses from the split sleeve cold expansion process notably improves the fatigue cycles. The split sleeve cold expansion processed hole of the railway track shows approximately fourteen times improved fatigue cycles when compared with the baseline model’s failure crack size of 4mm.
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Details
- Title
- FATIGUE SIMULATION TECHNOLOGIES OF COLD EXPANSION PROCESSED AEROSPACE ALUMINUM AND RAIL STEEL HOLES USING THE EXTENDED FINITE ELEMENT METHOD
- Creators
- SUBRATO ROY
- Contributors
- Dave Kim (Advisor)Hua Tan (Committee Member)Sun Kim (Committee Member)
- Awarding Institution
- Washington State University
- Academic Unit
- Engineering and Computer Science (VANC), School of
- Theses and Dissertations
- Master of Science (MS), Washington State University
- Number of pages
- 148
- Identifiers
- 99900591955601842
- Language
- English
- Resource Type
- Thesis