Measurement of Transient Temperature at Super-high-speed Deformation

Except the mechanical behavior, the thermal behavior is also an important issue to evaluate the deformation behavior of materials especially in the situation of high-speed deformation because the thermal softening due to temperature rise gives a strong effect on stress-strain curve. In previous, the thermocouple and infrared detector are widely employed for measuring the temperature rise in 10³ s^-1 of the strain rate range. However, the strain rate range is insufficient when the application to aerospace field is considered. Here, the temperature rise in over 10⁴ s^-1 of the strain rate range is focused on. Both the type-T thermocouple with 80 µm in tip diameter and infrared detector are introduced into a miniaturized testing apparatus based on the split Hopkinson pressure bar (SHPB) technique which is employed to achieve such high strain rate. From the measured results, the responsiveness of thermocouple and infrared detector is discussed based on the stress waves propagating in Hopkinson pressure bars. Then, the applicability of the thermocouple and infrared detector is also discussed by comparing the results obtained from a finite element simulation and theoretical calculation. As a result, both the techniques have a high responsiveness and can be applied to measure the temperature rise in 10⁴ s^-1 of the strain rate range.