Residual stress in railway wheels: software and algorithm

The client is an Italian company in ultrasonic testing. Its instrument for railway wheels assesses the internal stress state of monolithic wheels. An instrument like this is only as good as its software: acquiring the signal, showing it clearly and producing a record the inspector can trust.

• EMAT probes that need no coupling agent: two identical transducers send shear waves polarised at right angles, one parallel and one perpendicular to the rolling surface.
• Acoustic birefringence: the flight time of each wave to the first echo from the bottom wall gives the speed difference between the two planes.
• A mechanical probe, positioned magnetically, that moves along the radius of the wheel and measures at different points.
• Software, controlled from a PC, that moves the probe, acquires the data and calculates the stress from the speed difference and the material's acoustoelastic coefficient.

The instrument's software was written, and the algorithm that measures the residual stress was co-designed, by Michele Nunno. The detector gives the average circumferential stress across the thickness of the wheel rim, at different points along the radius.

The residual stress of a railway wheel is measured with a contact-free probe and calculated by the algorithm co-designed with the client, in software written for it.