Application of numerical modeling for developing the calibration curve of a high-temperature strain gauge

Аuthors

Mironikhin A. N.

Company «Composite», 4, Pioneerskaya str., Korolev, Moscow region, 141070, Russia

e-mail: oismp@kompozit-mv.ru

Abstract

The paper considers the design of a high-temperature strain gauge previously developed by the au-thor. The device is intended to measure longitudinal strain in specimens during thermomechanical tests of uniaxial tension or compression in the temperature range from 20 °C to 2500 °C. The imple-mentation and actual operation of such a device involve solving the problem of determining its cali-bration characteristic over the entire operating temperature range under conditions of high-intensity thermal exposure. The aim of this work is to refine and correct the previously developed mathemati-cal model describing the operation of the strain gauge, followed by determining its high-temperature calibration characteristic using numerical simulation.
The study investigates the temperature distribution and stress-strain state of the extension probe – the most thermally loaded component of the design, which is made of carbon-carbon composite material. Numerical solutions are obtained for the steady-state heat conduction in a nonlinear formulation, as well as for the bending problem of an I-beam, taking into account the temperature dependence of the thermophysical and mechanical properties of the material. Additionally, the bending problem for a non-uniform I-beam has been formulated and solved, where the material exhibits different elastic moduli under tension Et and compression Ec. The calculations were performed for various test tem-peratures and heat exchange parameters of the extension probe with the surrounding medium, while varying the thermophysical and mechanical properties of the material.
The changes in the bending compliance of extension probes at high temperature have been investigat-ed, which, when not taken to account, may generally lead to additional systematic errors in strain measurements. The results of numerical modelling showed that the considered strain gauge design ex-hibits dimensional stability at high temperatures. They also confirmed the low sensitivity of the cali-bration coefficient to the devices operating temperature conditions and the associated peculiarities of the material’s thermomechanical behavior. The calibration curve of the high-temperature strain gauge generated through virtual modelling is applicable to actual physical measurement procedures. The ap-proach proposed in this work has reduced significantly costs as well as simplified and accelerated the experimental validation process for the designed and manufactured strain gauge.

Keywords:

high temperature strain gauge, calibration of a strain gauge, carbon-carbon composite material, bend-ing compliance of a non-uniform beam, different elastic moduli in tension and compression

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