Ultrasonic measurement of internal temperature distribution

Abstract

Implementation of advanced materials processing strategies are presently hampered by a lack of adequate process-control sensors. For the processing of basic materials, such as steel and aluminium, an internal temperature-distribution sensor is needed. For these metals, the velocity of ultrasound is well known to be a strong function of temperature. We have therefore explored the feasibility of precisely measuring the velocity-temperature relation for a particular steel grade and using this to convert an ultrasonic-velocity distribution (tomogram) for a hot steel body to an internal temperature distribution. To overcome the usual need in conventional tomography for many thousands of path-integral measurements along intersecting ray paths, a priori heat-flow information has been incorporated into the reconstruction algorithms. As a result, for uniformly cooling bodies with the simple geometries usually encountered (e.g. circular, square or rectangular cross sections), the number of measurements can be reduced from many thousands to as few as three to five. Initial experiments on austenitic steel samples of cylindrical and square cross section by using non-contact ultrasonic techniques have shown that this approach yields acceptable temperature profiles at temperatures of up to 750 °C.