Ultrasonics for locomotive wheel integrity

Presents results of our examination of EMAT systems to determine their ability to be used in an in-situ system on unclean railroad wheels. First, EMAT systems with meander coils were used to create surface acoustic waves (SAW) on a test wheel with a hairline tangential crack. The intensity of the reflection was studied as a function of liftoff distance, and found to create a signal to noise ratio of 40 to 4 as the liftoff changed from zero to 2 mm. The attenuation of the SAW as it travelled on the surface of the wheel was also examined. Next, EMAT transducers that create angled shear waves in the system were examined. The maximum transmission of signal through an undamaged section was compared to the maximum transmission through a damaged section with favorable results, even at significant liftoff. Mathematical predictions were then done with finite element method (CAPA), which fit the experiments well. Finally, C-Scan, coupled transducer, and magnetic particle inspection were used on a section of the wheel to verify the position and size of the defect. In conclusion, preliminary results indicate that EMATs can be used for the first time to create automated systems for examining railroad wheels for both surface inspections and bulk volume inspections