DOI: 10.14489/td.2021.07.pp.056-061

Fedorov A. V., Bychenok V. A., Berkutov I. V., Alifanova I. E.
METHODOLOGY FOR EVALUATION THE UNCERTAINTY OF MEASUREMENT OF MECHANICAL STRESS BY THE ULTRASONIC METHOD WITH THE HELP OF AN OPTICAL-ACOUSTIC SEPARATE-COMBINED TRANSDUCER
(pp. 56-61)

Abstract. The work is devoted to the ultrasonic method for controlling mechanical stresses using ultrasonic head waves. The speed of the head ultrasonic wave is the highest, which allows it to be recorded stably among other types of ultrasonic waves and noises. To determine mechanical stresses, registration of the relative change in the velocity of propagation of the head ultrasonic wave is used, corrected for the change in the measured value caused by the change in the temperature of the test object. Thus, mechanical stresses are not measured directly, but the sources of uncertainty are the results of measurements of the propagation velocity of the head ultrasonic wave, the temperature of the environment and the test object, the coefficients of acoustoelastic and thermoacoustic coupling, and the parameters of the optical-acoustic transducer. The contribution of each of these factors to the results of measurements of mechanical stresses is estimated. On the basis of GOST 34100.3–2017, a method has been developed for asessing the uncertainty of measurements of mechanical stresses by the ultrasonic method using head waves. The dependence of the expanded measurement uncertainty on the value of the measured mechanical stresses was obtained. This dependence shows that measurements of mechanical stresses in the range of less than 100 MPa have an uncertainty of more than 10 % of the measured value. When measuring mechanical stresses over 200 MPa, the measurement uncertainty will not exceed 4 % (at a confidence level of 95 %).The proposed approach to assessing the uncertainty of measurements of mechanical stresses can be useful in the development of requirements for the used measuring instruments, alignment samples and control objects, as well as in the development of methods for monitoring mechanical stresses by the ultrasonic method using an optical-acoustic separate-combined transducer.

Keywords: mechanical stress, ultrasonic method, measurement uncertainty, acoustoelasticity, acoustic tensometry, head wave.