Application of Lcr Waves to Evaluate Residual Stresses in the RIM of Railroad Forged Wheels

The process of manufacturing wrought railroad wheels consists of forging heated blocks of steel, which are machined, heated, and quenched to reach the correct level of the mechanical properties to be used in railroads. The process generates compressive hoop stresses in the wheel rim. In field conditions, the original stress pattern can be changed mainly by overheating, which is caused by severe braking. The change from compressive stresses in the rim to traction can facilitate crack propagation. Indeed, even a small crack can propagate suddenly, causing a derailment. This work presents a new approach to evaluate the stresses generated by braking heating. It is based on the acoustoelastic effect, which relates the wave speed of ultrasonic waves to the strain state of the part. The method uses longitudinal critically refracted waves and a simplified system based on ultrasonic commercial products. The results show that the method is a stress sensitive and high resolution way to improve the safety of railroad wheels, making it a suitable alternative to be used at maintenance shops.