Wheels - Determination of residual stresses and of their distribution in the rims of monobloc wheels against UIC Leaflet 510-5

During work conducted by the ERRI Committee of Experts B 169 to determine the cracking threshold of block-braked monobloc wheels, three features influencing the radial cracking of the wheels were pinpointed: residual stresses in the wheel rim, thermal cracks and the toughness of the material. The work focused on standard ORE wheels and similar wheel types.

Using iso-stress curves, it was possible to determine the distribution of residual stresses in the wheel rim and in particular their development in the direction of propagation of a crack. Ultrasound measurements enabled the maximum value of residual stresses to be determined in a range of 300 - 400 MPa. However, this upper limit only applies to standard ORE wheels and other similar wheel types.

The average residual stresses occurring in the wheel rims of monobloc wheels dimensioned against UIC Leaflet 510-5 are known, though their distribution is not. These wheels’ supposed higher safety levels against thermal stresses (compared to current monobloc wheels) cannot therefore currently be gauged. In order to enable definitive conclusions to be drawn from a safety point of view, it is vital that the distribution of residual stresses for these new wheel types be known.

This study has achieved its initial goal, which was to determine the distribution of residual stresses in the rims of wheels certified against UIC Leaflet 510-5:

• for new “stress-resistant” wheels, the results are similar in the critical areas (running circle and lip),
• for worn wheels, the RAFIL wheel is similar to the ORE wheel. The Valdunes wheel performs better in terms of the lip, but its level of residual stresses on the theoretical running circle remains the highest.