See wheel–rail forces through the axle itself
The Hollow Shaft Sensor measures mechanical stress from inside the axle. Explore how wheel–rail loading connects to the changing stress experienced by a rotating axle.
Towards 400 m · Playback changes animation speed only. Vehicle speed remains 40 km/h. Travel reverses automatically at each end.
Drag the blue axle marker, or use Position below, to move along the track.
Why direction changes the forces
In this simulation, the leading axle carries more of the lateral guiding load through a curve. Reverse direction to see how the forces change when the same instrumented axle follows instead of leads.
Distance markers show metres along the track. Rail spacing is exaggerated for clarity. TS / SC / CS / ST mark the boundaries between straights, transitions and circular curves.
What Y/Q tells you
A larger ratio means more sideways force relative to the vertical load supporting the wheel. The graph follows the wheel whose flange guides against the rail. Red highlights when the selected reference threshold of 0.80 is reached or exceeded.
This indicator illustrates loading conditions associated with wheel climb; it does not predict a derailment. The Nadal limit depends on wheel–rail contact conditions; 0.80 is the reference used here.
Sensor location and illustrated stress
The highlighted sensor sits inside the axle bore. Blue arrows show the rails supporting the wheels; grey arrows show lateral forces on the wheels. A red lateral arrow identifies the flanging wheel when its Y/Q reaches the reference threshold.
The marked section is 680 mm from the axle end face. The rotating surface point illustrates bending stress at that section; it is separate from the sensor inside the bore. Contact circles are 1500 mm apart and journals are 2000 mm apart.
Wheel–rail forces
Follow how vertical load is shared between the wheels and how lateral forces change through each curve.
Track loading reference
ΣY is the axle’s combined lateral force, relevant to lateral track stability. The applied locomotive reference is 58.5 kN: 0.85 × the illustrative Prud’homme value of 68.8 kN. These are model references, not a site-specific safety assessment.
Rotating axle stress
As the axle turns under a bending load, a surface point alternates between tension and compression. Follow the stress cycles that matter for fatigue assessment.