Temperature Control of Pulse Heated Specimens in a Kolsky Bar Apparatus Using Microsecond Time-Resolved Pyrometry

Published

March 1, 2004

Author(s)

D Basak, Richard L. Rhorer, H W. Yoon, Timothy J. Burns, T Matsumoto

Abstract

Analysis of maching processes is important in the understanding and improving of manufacturing methods. The modeling of machining processes relies on high-strain-rate, high-temperature material properties. A split-Hopkinson (or Kolsky) bar has been developed at NIST, for this purpose. By heating the material specimen rapidly with a controlled current pulse prior to the mechanical impact in the bar, structural changes in the specimen are inhibited, thus better simulating conditions during machining. A stress-strain relationship can be determined at various temperatures for a range of materials. For the elevated temperature Kolsky experiments it is essential for the specimen to be maintained at a constant and uniform temperature prior to the dynamic loading. We describe the development and implementation of a near-infrared micro-pyrometer (NIMPY) to the precision control of Kolsky specimen temperature preceding the mechanical impact. The pulse-heating system can be operated either in the transient mode, where the current to the Kolsky specimen is switched off at a preset temperature or time, or in the brief steady-state mode, where the specimen is heated rapidly to achieve the desired temperature (in the range from 400 K to 1300 K) in a short time (about 200 ms) and then held isothermally for a brief period (<2 s). The sensing signal for the feedback is provided by the NIMPY. Based on a feedback control algorithm, a dedicated computer operates a solid-state switch, consisting of field-effect-transistors (FETs), with a fast response time (<5 ms), which controls the current to the Kolsky specimen to achieve isothermal condition. A brief description of a model of the pulse heating process is provided and the predicted specimen temperature history is compared with measured temperature data.

Citation

International Journal of Thermophysics

Volume

25

Pub Type

Journals

Keywords

Kolsky bar apparatus, PID control, pulse heating, pyrometry, temperature control

Citation

Basak, D. , Rhorer, R. , Yoon, H. , Burns, T. and Matsumoto, T. (2004), Temperature Control of Pulse Heated Specimens in a Kolsky Bar Apparatus Using Microsecond Time-Resolved Pyrometry, International Journal of Thermophysics (Accessed April 16, 2024)