A new technique for performing tortional split Hopkinson bar experiments at high temperatures

Abstract

Determination of shear mechanical properties of materials under the coupling effect of high strain rates and high temperatures has been an important but challenging issue. On this purpose, an improved high-temperature dynamic torsion experimental method was developed in which an electromagnetic torsional Hopkinson bar equipped with a synchronous assembled system was used. A modified double-flange thin-walled tubular specimen was proposed to achieve offline heating and synchronous assembly while providing a reliable specimen-bar connection. Finite element method (FEM) was employed to analyze the effect of specimen geometry on measurement accuracy. According to the result, recommendations for specimen design as well as a strain measurement correction method were suggested. The optimized double-flange thin-walled tubular specimen was proved to be valid for testing. The cold contact time (CCT), the time during which the hot specimen is in contact with the cold loading bars prior to the arrival of incident stress wave, was measured experimentally by two sets of laser sensor, and a high-speed radiometric infrared camera was employed to determine the temperature drop in specimen during cold contact process. To verify the ability of the proposed dynamic torsion experimental technique at elevated temperatures, experiments on Ti6Al4V alloy and T2 copper were conducted at the strain rate of 500 s−1 and at different temperatures. The maximum experimental temperature for T2 copper is 400 ∘C, and for Ti6Al4V is up to 1000 ∘C.