An improved technique for the experimental measurement of specimen surface temperature during Hopkinson-bar tests

The development of an infrared radiometer capable of measuring specimen surface temperatures with a time resolution of about 1 s is described. The radiometer operates either with a single detector, which measures temperatures as low as 25C with an accuracy of C, depending on the surface finish, or with a 12-element detector for which the accuracy is reduced to C at 70C but with which the temperature profile along the specimen in regions of localized deformation, where much higher temperatures are expected, may be determined. A specially designed optical system is used and a dynamic calibration procedure employing an optical chopper is described. Results of a dynamic compression test on a polymer specimen and a high-speed torsion test on a Ti6Al4V alloy are given, illustrating possible applications of the radiometer.