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1 April 2003 Thermal imaging of metals in a Kolsky-bar apparatus
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Abstract
Since the modeling of machining processes relies on high-strain-rate, high-temperature material properties, NIST has built a split-Hopkinson (or Kolsky) bar to determine the stress-strain behavior of rapidly heated materials at high temperatures. Our Kolsky bar has been constructed in the NIST high current pulse-heating facility, which enables electrically heating the samples within ~ 100 milliseconds time duration, immediately before the mechanical impact in the bar. Due to the rapid heating, we avoid possible structural changes in the sample, and a stress-strain relationship can be determined at different temperatures for various test materials. We describe the design and the development of the resistively-heated Kolsky-bar apparatus. The incident and the transmitted bars are constructed of 1.5 m long, 15 mm diameter maraging steel, and a typical sample is a 4 mm-diameter, 2 mm-long cylinder of 1045 steel. The sample is placed between the bars and held by friction. The current is transmitted through the graphite-sleeve bushings of the two bars. The non-contact temperatures are measured using an InGaAs near-infrared micro-pyrometer (NIMPY) and an InSb focal-plane (320 by 256) array (thermal camera). The NIMPY and the thermal camera are both calibrated using a variable-temperature blackbody, and the thermodynamic temperature of the metal is determined using the emissivity determined from the measured infrared spectral reflectance of the metal. Thermal videos of the electrically-heated and the room-temperature impacts will be shown with 1 kHz frame rates, and the changes in the stress-strain curves with the temperature of the samples will be discussed.
© (2003) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Howard W. Yoon, Debasis Basak, Richard L. Rhorer, Eric Whitenton, Timothy J. Burns, Richard Fields, and Lyle Levine "Thermal imaging of metals in a Kolsky-bar apparatus", Proc. SPIE 5073, Thermosense XXV, (1 April 2003); https://doi.org/10.1117/12.488111
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