High-Temperature Tensile Testing of Metal Tubes with Small Diameters by Resistance Heating Method

Resistance heating (RH) method has been proposed to be used for assisting the high-temperature tensile testing of metal tubes with small diameters. Digital image correlation (DIC) with laser speckles was adopted to measure the displacement and true strain of the deformed material. Magnesium alloy tubes of ZM21 with an outer diameter of 6 mm and gauge length of 10 mm were used. Tensile tests were conducted at both room and high temperatures under a nominal strain rate of 0.01 s−1. The displacement and nominal strains measured by DIC were compared with that measured by a non-contacting extensometer. True stress-strain curves and full-field strain were obtained. As results, the temperature of the tube increased to 400 ℃ and became stable within 50 s. The maximum temperature difference within the gauge was 24 ℃. The good agreement of the nominal strains calculated by DIC and the extensometer validated the accuracy of the displacement measured by this system. The true stress-strain curves simply calculated from the nominal stress and strain have been confirmed inaccurate to express the flow stress of the material. The measurement of full-field strain has been achieved.