New Ultrasonic Methodology for Determining Temperature Gradient and Its Application to Heated Materials Monitoring

In various fields of science and engineering, temperature measurement has become one of the most fundamental and important issues. For example, in industrial materials processing, it is required to measure the temperature gradient and its transient variation in the material being processed at high temperatures because the temperature state during processing crucially influences the quality of final products. Such temperature measurements are also required for making structural health monitoring at high temperature environments. In this work, a new ultrasonic method for monitoring temperature gradient of a material being heated or cooled is presented. The principle of the method is based on the temperature dependence of the velocity of ultrasonic wave propagating through a material. An effective analysis method coupled with a finite difference calculation is developed to determine one-dimensional temperature distributions in a heated material. To verify the practical feasibility of the method, some experiments have been made. A single side of a steel plate of 30 mm thickness is heated by contacting with a heater and subsequently cooled down by water. Ultrasonic pulse-echo measurements are performed during heating and cooling, and the measured transit time of ultrasound across the steel is used for the analysis to determine the temperature gradient in the steel. Furthermore, rapid heating by contacting with molten aluminium at 700 degree C and rapid cooling by contacting with an ice are evaluated and the transient variations of the temperature gradient in the steel have successfully been monitored.