Ali Esmaeili disputerar 10 januari, 10:00 i VDL, Chalmers Tvärgata 4c.
Avhandlingens titel: Modelling of cyclic and viscous behaviour of thermomechanically loaded pearlitic steels; Application to tread braked railway wheel
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There are about 1 million kilometers of railway rail lines and about 25-50 million wheels in service in the world. Due to increasing demands (such as axle loads, running speeds of trains, etc.) the maintenance costs have increased in the recent years. Accounting for the enormous size of the railway network and the number of wheels, even 1% cost reductions translate to a huge amount of money for infrastructure managers and train operators. Furthermore, the performance of rails and wheels is important for the safety of railway operation. Hence, a grand challenge for the metallurgists, engineers, and railway managers is to minimize the causes of rail and wheel damage and failures.
Due to the geometry of the railway rails and wheels, a typical wheel-rail contact surface is merely the size of a coin. The material in the vicinity of this contact is subjected to very high loads. These loads are generated due to axle loads that can be from 10 tonnes up to 40 tonnes (for heavy duty railways) and also frictional forces in the rail-wheel interface caused by train acceleration, braking, and curving.
Add to that the frictional heat generated between brake block and wheel during braking or between wheel and rail during braking and acceleration which might result in elevated temperatures up to 500℃. In severe cases, such as malfunctioning traction systems, temperatures might even reach 800-1000℃. These complex loading conditions might result in damage and failure of the rail and wheel material causing major maintenance costs in the railway industry.
To be able to understand load limits (e.g. the maximum allowed train axle loads), to plan an efficient maintenance schedule and also to improve the components’ design for obtaining sufficiently long life of the components, we need to have a good understanding of the material behaviour in the components under operational conditions.
Due to high strength, high wear resistance and relatively low cost, pearlitic steels are widely used for railway rails and wheels. In this thesis, an effort has been made to develop material models that are able to numerically simulate the behaviour of the pearlitic steel in railway wheels when subjected to mechanical and thermal loads. These models are used to simulate different scenarios of railway operational conditions and for study of possible damage mechanisms that might result in failure of the wheel material.
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