Wheel Fatigue
Technological advancements in the railway industry have made possible longer wear lives of wheels. Simultaneously, current economical and logistical needs demand increased train speeds and load capacities. These demands result in larger contact forces acting on rails and wheels. Longer wear lives, higher speeds and larger loads have made fatigue the new main cause of railway wheel replacement and re-engineering.
According to the Union Pacific Railroad wheel fracture database, 65% of railroad wheel failures are caused by shattered rims, a form of sub-surface initiated rolling-contact fatigue (RCF). This suggests a need for methods that can effectively predict the occurrence of RCF cracks. Effective predictions require computational tools and mathematical models that can accurately simulate actual material behavior and structural interactions like the contact between railway wheels and rails that takes place as the wheels roll.
The objective of this project is to provide an adequate numerical assessment of the sub-surface crack initiation and propagation in railway wheels. A 3-D FE-model was constructed in ABAQUS® to simulate the stress/strain fields that take place under the rolling-contact of railway wheels on rails. This FE-model constitutes a faithful replica of a railway wheel that is rolled on a rail segment using a “hard-contact” over-closure relationship, and an elastoplastic material model with isotropic and kinematic hardening. This material model considers the wheel’s stabilized structural response (steady-state) in a multi-axial critical-plane fatigue model and accounts for the effect of residual stresses.
The steady-state stress/strain response of the wheel is post-processed using codes written in MatLab® to obtain improved analytical predictions of the sub-surface crack initiation in the railway wheel. Fatigue assessment from this report will be the input to construct a multiscale model with a built in crack to investigate the behavior of sub-surface fatigue crack propagation phase in the railway wheel.
(Sponsor: AAR)
Sprayed Polymer Anti-Corrosion Coatings
Corrosion is an important problem facing all metal components involved in railway transportation, including axles, rails and bridges. Corrosion causes early fatigue and failure of parts, making this both an economic problem and a safety issue. This project proposes the development of a polymer based anti-corrosion coating that can be applied by spraying.
(Sponsor: AAR)
Fatigue Testing of Damaged Rails
Dr. David Allen and Dr. Pete Keating have recently initiated an externally funded project that focuses on experimental observation of fatigue cracking in rails. In this project sections of rail that have previously been in service on heavy haul lines are subjected to both axial and transverse cyclic loading up to 600,000 cycles. During the testing the rails are periodically inspected using phased array ultrasonic transducers as a tool for determining the long term growth of cracks in rails. It is hoped that these tests will provide information critical to the development of rail fatigue models currently under development under other projects.
(Sponsor: AAR)