Ultrasonics techniques for the evaluation of stress states in railroad wheels and rails

In order to evaluate the stress states in rims of monoblock railroad whees, automated ultrasonic set-ups (UER) have been built. 19 of these set-ups are already under industrail use; several thousands of wheels have been tested. The set-up takes advantage of an eletromagnetic ultrasonic trasducer which generates the ultrasound in the material so that no coupling is needed. This transducer together with a set-up for the automated data acquisition and evaluation enables the determination of the principal stress difference circumferential (tan) - circumferential (rad) along a radial trace with a spatial sampling distance of 1mm. The profile of the difference of the stresses along the circumferential (tan) and circumferential (rad) direction of the wheel along the height of the rim gives strong evidences concerning the stress state. Among the nondestructive techniques the ultrsonic techniques hold high promise to reach the goal. On the one hand, these techniques are not as dependent on the microstructural states as the magnetic and nagneto-elastic techniques and on the other hand, there are already set-ups available for the automated and locus- and time-contnuous data aqisition and evaluation.