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Contact Stress in Rail Joint Region
The growth of fatigue and surface cracks due to impact and frequent contact stress in rail joint regions has been the cause of many rail damages and losses in recent years. In addition, the noise and vibrations on the wagon due to the impact from the wheel in the region of the rail joint led to the discomfort of passengers.
On 25 January 2018, the Pioltello train derailment was due to a broken rail joint region. 3 women have been killed.
Rail Joint Region Design Consideration
There are a few factors to consider regarding fatigue, impact, and contact stress in the rail joint region:
- Fatigue – The rail joint is a point of discontinuity where stresses can concentrate. This can lead to higher stresses and fatigue damage compared to mid-rail locations. Repeated wheel impacts at the joint can cause gradual crack initiation and propagation over time. Rail joint designs aim to minimize stress concentrations and provide adequate clamping force to mitigate fatigue.
- Impact – When wheels pass over the rail joint, there is a slight impact force due to the height difference between the two rail sections. This impact force generates dynamic stresses that contribute to fatigue damage. Specialty rail joint designs use elastic elements to absorb some of the impact energy and reduce forces transmitted to the rail.
- Contact stress – As wheels pass over the joint, there is a momentary increase in contact stress between the wheel and rail. This is due to the change in the rail profile at the joint. High contact stress can accelerate the wear of both the wheel tread and railhead. Certain rail joint designs incorporate elastic packing layers to distribute contact stress over a wider area.
- Rail joint maintenance – The rail joint must be periodically inspected, lubricated, tightened, and adjusted to maintain proper performance. Neglecting maintenance can accelerate deterioration and lead to more severe impacts, higher stresses, and premature failure.
Stress Analysis of UIC60 Rail Wheel under Rolling Contact Fatigue Conditions
FEA in Railway Industry
FEA (finite element analysis) is a powerful tool used in the railway industry for:
Rail and wheel design
FEA can be used to optimize the design of rails and wheels to minimize stress concentrations, deformations, and fatigue damage. Parameters like rail profile, wheel tread profile, metallurgy, etc. can be evaluated using FEA models.
Rail joint design
As mentioned earlier, rail joints experience higher stresses and fatigue damage. FEA can help improve joint designs by evaluating things like clamping forces, elastic pads, profiles, etc.
Bogie and wagon body design
FEA is used to design and optimize railway bogies and wagon bodies. Properties like stiffness, load distribution, deformation, and stresses under operating loads can be analyzed.
Track structure design
The design of track components like sleepers, fastenings, ballast, etc. can be optimized using FEA. Parameters like load distribution, deformations, contact stresses, etc. are important.
Collision and impact analysis
FEA crash simulations can be performed to evaluate the impact response of rails, wheels, bogies, and wagon bodies in case of collisions. This helps improve crashworthiness and safety.
Derailment analysis
FEA derailment simulations can provide insights into derailment causes, mechanisms, and effects. This data can be used to improve track and rolling stock design to prevent derailments.
In summary, FEA offers many benefits for railway applications like optimizing designs for performance, durability, and safety. It provides a virtual testing environment to evaluate designs before physical prototyping and testing. The level of detail and accuracy of FEA models has improved significantly over the years.
FEA Project
In this FEA project, to reduce the growth of fatigue and surface cracks in the joint rail region and passenger comfort, the parameters of axial force, speed, span, and joint angle were examined. These parameters have been done according to the rail profile used in the Iranian industry UIC60 and S1002 and the UIC 864-8 standard fish plate.
Simulation of wheel movement on rails and investigation of impact and surface stresses in the region of rail joints.
One of the types of connecting two rails (especially in the design of an interlocking system) with a certain length is the use of connecting rods. The joint method is such that two rails and two fish plates are connected with 4 or 6 bolts.
Investigation of the effect of rail joint gap angle on the distribution of contact and impact stresses
The results show that the angle of the rail gap has a significant effect on the impact stresses and the ISF parameter.
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