Residual Stress Measurement on Wheels and Axles

Part of the qualification of a new wheel and axle are the residual stress measurements derived from the manufacturing process.

Wheels undergo a differential quenching process in which the wheel rolling surface is cooled down faster generating, together with an increase of hardness, also compressive stresses In the order of -150 MPa that have an excellent ability in stopping the propagation of initial surface cracks or sub-surface defects.
Residual stresses in the wheel rim can be measured by strain gauges, evaluating the strain variation before and after the cutting of a wheel slice, or by a ultra-sound technique (EMAT).