This work began through support of the Federal Research Administration and focused on the changes in ultrasonic scattering that occur due to changes in stress in a polycrystalline material, whether from applied loads or residual stress.
The rail stress research utilizes diffuse ultrasonic backscatter to quantify changes in longitudinal rail stress. We have developed the acoustoelastic scattering theory that includes all possible wave types and stress configurations and confirmed several aspects experimentally. Figures: diffuse ultrasonic backscatter measurements during laboratory tests and on a rail while in service.
This work expanded to bridges through support of the Nebraska Department of Roads and to samples with residual stress from water quenching. Figures: ultrasonic device used to monitor stress in a tension bar of a steel through-truss bridge; changes in backscatter before (red) and after (green) annealing of a steel sample that was quenched with water.