Ultrasonic Backscatter Technique for Corrosion Detection in Solid Rocket Motors.

The need within the aerospace industry to requalify hardware that has exceeded its nominal design life is being partially addressed by the development of techniques to periodically inspect hardware for material changes, such as corrosion. Unfortunately, minor corrosion-induced surface changes that can weaken a bondline or prevent the sealing of an O ring do not lead to a significant change in a normally reflected ultrasonic signal. An alternate approach was developed that involves monitoring the backscattered signal from pulses striking the interface at an oblique angle. In this instance, most of the acoustic energy is forward-scattered so as not to compete with the relatively small backscattered signal from small surface changes. Such an approach is very similar to the angle beam techniques commonly used in the inspection of welds. The results from two applications of this technique to the inspection of flight hardware indicate that the presence of detrimental corrosion can be successfully discriminated from the nominal surface finish of the metal.