Effects of Deformation Twinning on Energy Dissipation in High Rate Deformed Zirconium
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INTRODUCTION
THE study of energy storage and its complement dissipation during mechanical work is based on the partition of the total work into recoverable and nonrecoverable components. The recoverable component is related to the elastic response of the material. The nonrecoverable, or plastic, component of the total work is consumed by a combination of (1) storage as a permanent change in the material microstructure, (2) dissipation as heat, or (3) depletion by the development of failure. It is the dissipation of plastic work as heat that is usually measured directly to assess how much energy may be stored in a deformed material. Early experiments on several metals including copper, brass, nickel, and aluminum showed that nearly all plastic work is dissipated as heat.[1–3] While these early experiments were performed at time scales over which heat conduction could not be neglected, more recent experiments use infrared thermography during high-strainrate adiabatic loading to reassess heat dissipation in situ. The results of the high-strain-rate studies agree with earlier investigation in that, for most metals, greater than 90 pct of the plastic work is converted to heat.[4–6] Since dislocation slip is the most prevalent mechanism of plastic deformation in fcc and bcc metals, it is likely H.A. PADILLA II, Doctoral Student, and A.J. BEAUDOIN, Professor, are with the Department of Mechanical Science and Engineering, University of Illinois at Urbana–Champaign, Urbana, IL 61801, USA. C.D. SMITH, Doctoral Student, and I.M. ROBERTSON, Department Head, Donald B. Willett Professor of Engineering, are with the Department of Materials Science and Engineering, University of Illinois at Urbana–Champaign, Urbana, IL 61801, USA, and J. LAMBROS, Professor, is with the Department of Aerospace Engineering, University of Illinois at Urbana–Champaign, Urbana, IL 61801, USA. Contact e-mail: [email protected] This article is based on a presentation made in the symposium entitled ‘‘Dynamic Behavior of Materials,’’ which occurred during the TMS Annual Meeting and Exhibition, February 25–March 1, 2007 in Orlando, Florida, under the auspices of The Minerals, Metals and Materials Society, TMS Structural Materials Division, and TMS/ASM Mechanical Behavior of Materials Committee. Article published online November 13, 2007 2916—VOLUME 38A, DECEMBER 2007
that the dissipation of energy as heat is directly linked to that mechanism.[7–11] There is evidence, however, that some metals with an hcp structure do not dissipate all plastic work as heat, implying the storage of significant amounts of energy.[4,12] It has been suggested that deformation twinning might be the mechanism responsible for the energy storage, because many hcp polycrystals deform by this mechanism.[4,13] For example, in the case of hafnium, dissipation of only 20 pct of the plastic work at strains of 15 pct has been reported.[12] Reduced dissipation has not been observed universally among hcp metals, as titanium showed near complete dissipation of plastic work as heat, even th
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