On the possibility of Detecting Case/Liner and Liner/Propellant Debonds in a Rocket Motor by means of the ultrasonic multiple reflection pulse echo technique

Abstract

In order to examine whether and to what extent the ultrasonic multiple reflection technique can be used for detecting case/liner and liner/propellant debonds, measurements were performed on samples sawn from a particular case‐bonded rocket motor consisting of a layer of 2.4 mm steel, a layer of 1,3 mm liner material (a polymer) and a thick layer of composite (AP/PU) propellant respectively. It was found that case/liner debonds could be traced reasonably well; liner/propellant debonds, however, could not be evidenced owing to strong quenching of the ultrasound in the liner. Investigations of the texture of the liner material with the aid of a scanning electron microscope proved the strong quenching in the liner to be mainly due to the presence of many voids with diameters of some 50 μm–200 μm which strongly disperse the sound beam.