STAND FOR DETERMINING THE DEPENDENCE OF THE ROD WAVE VELOCITY ON THE TEMPERATURE IN METAL BARS

Abstract

Analysis of changes in the propagation velocity of an acoustic wave is an effective method of structroscopy of various materials. At the same time, technical means are needed to implement its exact calculation. The interfering factor for accurate velocity measurement is the dependence of the acoustic wave velocity on the temperature of the object. The article presents a stand for measuring the rod wave velocity in an extended object with a length of 1 m and a diameter of up to 8 mm with a resolution of 0.14 m/s. The stand contains a heating chamber that allows heating samples in the temperature range of 20…60 ℃ with continuous measurement of the rod wave velocity. The high resolution of the velocity measurement is achieved by sounding the entire body of the sample and calculating the time interval by several reflections. The refinement of the time interval is implemented through frequency oversampling in a multiple greater direction, followed by a correlation comparison of the bottom pulses with each other. When the results are obtained, the sample temperature elongation and the velocity dispersion caused by a change in the recorded signals frequency are taken into account. The results of measuring the rod wave velocity for 60C2, 12X1MF and 12X18N10T steels are presented. Accounting for changes in the recorded signals frequency is based on the calculation of the center of mass in the frequency spectrum of the first and second bottom pulses. The velocity correction is calculated on the basis of dispersion curves in accordance with the steel grade. On the example of steel 60C2, the influence of dispersion of rod wave velocity when heated from 16 to 60 ℃ is taken into account. A change in the center of gravity of the spectrum from 24 to 28 kHz was recorded, which corresponds to a correction of –0.7 m/s.