16 Internal Heat Generation in Tension Tests of AISI 316 Using Full-Field Temperature and Strain Measurements 99 Fig. 16.2 Specimen Geometry Fig. 16.3 Exposure time vs. temperature range of the Telops high speed infrared camera This material exhibits high ductility, strong capability of strain hardening, and low thermal conductivity, which all together lead to notable internal heating of the material already at relatively low strain rates. 16.2.2 Full-Field Thermal Imaging and Calibration Thermal image capture is done with Telops FAST-IR 1000 high speed infrared camera, capable of 256 320 pixel resolution at speeds up to 1,000 fps and a reduced pixel resolution at speeds up to 30,000 fps. The exposure time of the IR camera for the specified test was 10 s. With decreasing exposure time the IR camera can register higher surface temperatures, but at the same time the lowest measurable temperature increases so that the usable temperature range at each constant exposure time is ca. 250 K, as seen in Fig. 16.3. To synchronize the Phantom visible camera and the IR camera, they are externally driven by a dual-channel Keysight 33500 series waveform generator, which enables running the cameras at different but phase-synchronized frequencies. In practice, the visual camera typically is run at a frequency which is the same or a multiple of the IR camera frequency. The waveform generator sends TTL level timing pulses to both cameras in an externally triggered burst mode. In tests with the MTS frame, the external trigger to the waveform generator is sent through the digital output port of the controller unit 100 ms
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