The measuring approach of the nonlinear high-temperature coefficient of thermal expansion during isothermal cooling

Abstract

• The cooling phase after induction heating is used to construct the isothermal process for solid materials. • The isothermal cooling process increases the accuracy of high-temperature strain measurement based on DIC. • The transient curve of temperature and thermal strain during cooling is used to estimate nonlinear CTE. • The method proposed here can be used for estimating nonlinear CTE efficiently and accurately. This paper proposes a novel non-contact approach to characterise the high-temperature nonlinear coefficient of thermal expansion (CTE) based on the digital image correlation (DIC) and the induction heating technique (IHT). Through IHT, the test samples can be heated up to high-temperature rapidly and realise ideal isothermal cooling after heating, which is fully verified by the numerical models and the experiments. Then the digital images at different temperatures are recorded by a CCD camera and subsequently analysed by the DIC method to obtain the strain at various temperature. Based on the strain curve and temperature curve, the nonlinear CTE can be computed. Furthermore, the CTE of Alloy 330 at the temperature range of 500–1100 K is measured through the proposed method. Compared with the literature results, the relative error is no more than 6%, which means the approach has high accuracy. In addition, the method is efficient in nonlinear CTE characterisation, and the entire test time of Alloy 330 in this paper is no more than 5 min.