International Journal of Impact Engineering 33 (2006) 735–744 Expanding ring experiments to measure high-temperature adiabatic properties S. Satapathy à , D. Landen Institute for Advanced Technology, The University of Texas at Austin, Austin, TX 78759, USA Available online 20 November 2006 Abstract High-temperature mechanical properties for metals are usually measured under quasi-isothermal conditions, where thermal equilibrium has been achieved by slowly preheating the samples to a predetermined temperature. However, there are several situations of practical interest where the material is heated rapidly, so thermal diffusion is negligible during the time of heat deposition and mechanical deformation. Hypervelocity impact and penetration, shaped charge jet formation, and pulsed heating in electromagnets are some such situations. Experimental evidence from electron beam heating indicates that high-temperature mechanical properties significantly depend on the rapidity of heat deposition. As the time duration of heating is reduced, the amount of local heat transfer decreases due to limited thermal diffusion. Thus, the thermodynamic process deviates from the isothermal process and approaches the adiabatic process for pulsed heating conditions. Therefore, it is imperative that mechanical properties be measured under appropriate thermodynamic conditions. We propose that the electromagnetically driven expanding ring experiment be used to measure the adiabatic mechanical properties of metals. While earlier expanding ring experiments were conducted primarily to obtain high-strain- rate strength and fragmentation data, our primary goal is to obtain high-temperature data under pulsed heating conditions approaching the adiabatic process. Our preliminary data suggest that the adiabatic mechanical properties are quite different from isothermal properties. r 2006 Published by Elsevier Ltd. Keywords: Adiabatic properties; Pulsed heating; Expanding ring 1. Introduction Hypervelocity impacts can generate very high temperatures, on the order of a few thousand degrees [1] as measured from impact flash. Even a relatively lower strain-rate event (10 3 s 1 vs. 10 5 for impact tests) such as the split Hopkinson pressure bar [2] has been shown to generate appreciable temperature rise near the fracture surface in a tensile experiment. Even though direct measurements are not available for very high- strain-rate events such as high-velocity penetration, shaped charge jet formation, high-speed sliding, etc., post- experiment observation and theoretical estimates point to generation of temperatures high enough to lead to melting. Since the thermal diffusion time far exceeds the duration of the event, the processes occur under ARTICLE IN PRESS www.elsevier.com/locate/ijimpeng 0734-743X/$ - see front matter r 2006 Published by Elsevier Ltd. doi:10.1016/j.ijimpeng.2006.09.085 à Corresponding author. Tel.: +1 512 232 4455. E-mail address: sikhanda@iat.utexas.edu (S. Satapathy).