Effect of Sonic and Ultrasonic Radiation on Safety Factors of Rockets and Missiles

In rocket motors, the combustion processes are sources of sonic and ultrasonic waves that penetrate all parts of the vehicle. Consequently, the construction materials are exposed to sonic and ultrasonic radiation of high intensity. It has been known for some time that a relation exists between certain lattice imperfections, applied stresses, and sonic or ultrasonic radiation. Sound energy is absorbed by lattice imperfections, whereas thermal energy is absorbed homogeneously in the material; and, accordingly, an ultrasonic energy input of only 10 ev/unit causes the same large (nearly 40%) reduction in the steady stress of zinc as a thermal energy input of 10 ev/unit. Similar measurements have been made on aluminum, beryllium, tungsten, low-carbon steel, and stainless steel. The results show clearly that the strength of the materials is reduced when exposed to intense sonic or ultrasonic radiation. Consequently, catastrophic effects may occur in those parts of the vehicle where the sonic and ultrasonic energy is concentrated by reflections to produce very high intensities.