Effect of stress on ultrasonic signals: Assessment of the effect of compressive stress on the ultrasonic signl from tache ovale defects (LR-IMS-019)

A small number of rails had broken in track because of tache ovale defects, which had not been detected by either manual ultrasonic testing or the Ultrasonic Test Unit. One possible cause was that the defect faces were being pressed together by compressive stress, allowing ultrasonic energy to pass through.