SWEPT FREQUENCY ULTRASONIC INSPECTION METHOD FOR LINER-PROPELLANT SEPARATIONS OF SOLID ROCKET MOTORS

Abstract This paper describes the swept frequency type of ultrasonic inspection method that is usable for inspecting liner-propellant separations of solid rocket motors and successful application of the method to the H-I upper-stage motors. Unfortunately, over the past quarter of a century, the liner-propellant separations have never been inspected practically with usual ultrasonic inspection methods. The special method has been developed at the National Aerospace Laboratory (NAL) since 1968, and the inspection technique is based on the one-dimensional quarter-wavelength resonance principle for the liner thickness under one free and the other fixed end-face boundary condition, which is considered the linear-propellant separation boundary condition of the linear. Since the motor cases have curved (spherical or cylindrical) surfaces, some curved contact surface probes were developed. This method was successfully applied to the apogee and third stage motor of the H-I rocket at the manufacturer and then at the launching site. This inspection has contributed to the successful launchings of the H-I rocket since the first launching in August 1987, and will be able to be applied to the solid rocket booster (SRB) of the H-II rocket in the near future.