Development of ultrasonic tomography for residual stress mapping. Final report

The volumetric stress distribution in nuclear reactor piping and pressure vessels is becoming an increasingly important parameter in nondestructive evaluation. This report describes research and development of instrumentation leading toward a means of measuring subsurface stress distributions in metals. Based on the principles of Computerized Tomography (CT), an ultrasonic tomographic instrument system has been developed. The microprocessor-based system uses an ultrasonic linear array to acquire time-of-flight data to an accuracy of 0.5 to 1.0 ns. The data is processed using a modified ART (Algebraic Reconstruction Technique) program. A two-dimensional map of the velocity distribution is displayed on a monitor. The velocity distribution is interpreted or calibrated in terms of stress through the acousto-elastic coefficients