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Effect of Strain Rate on Plastic Flow and Failure in Polycrystalline Tungsten

Dümmer, T. and Lasalvia, J. C. and Ravichandran, G. and Meyers, M. A. (1998) Effect of Strain Rate on Plastic Flow and Failure in Polycrystalline Tungsten. Acta Materialia, 46 (17). pp. 6267-6290. ISSN 1359-6454. http://resolver.caltech.edu/CaltechAUTHORS:20150226-153436802

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Abstract

Polycrystalline tungsten (less than 100 p.p.m. impurities) was subjected to different heat treatments to yield different grain morphologies and tested at quasi-static (3×10^(−3)) and dynamic (10^3–4×10^3/s) strain rates. Three mechanisms of deformation were identified and evaluated: slip, twinning, and intergranular cracking. Whereas plastic flow by slip has considerable strain-rate sensitivity in tungsten (which is found to be well represented by the Mechanical Threshold Stress constitutive equation) the cohesive strength of the grain boundaries was found to decrease with heat treatment temperature, but was insensitive to strain-rate changes. Low-strain-rate deformation yielded limited damage at strains as high as 0.25, whereas high-strain-rate deformation led to catastrophic failure at strains between 0.05 and 0.10. Slip and grain-boundary decohesion being competing deformation mechanisms, the material undergoes a ductile-to-brittle transition as the strain rate is increased from 10^(−3) to 10^3/s. Two failure modes are identified: debonding initiated by shear along a grain-boundary facet (similar to the wing-crack mechanism) and debonding initiated at voids. The interactions between microcracks and twins are characterized, and there is both evidence of fracture initiation at twins (intergranular cracks), and twin initiation at cracks (transgranular cracks). Calculations based on existing wing-crack models enable the estimation of the grain-boundary cohesive energies.


Item Type:Article
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http://dx.doi.org/10.1016/S1359-6454(98)00255-9 DOIArticle
http://www.sciencedirect.com/science/article/pii/S1359645498002559PublisherArticle
Additional Information:© 1998 Acta Metallurgica Inc. Received 27 August 1996; accepted 22 June 1998. This research was partially supported by the U.S. Army Research Office under the URI Program on Ultradynamic Performance of Materials (Contract: ARO DAAL 03-92-G-0108) and the U.S. Army Research Laboratory through W. Bruchley. This work is part of an exchange program coordinated at the University of Karlsruhe (TH) by O. Vöhringer. Appreciation is extended to K. S. Vecchio, D. Harach, and A. Rohatgi for performing the quasi-static compression tests, to A. J. Strutt for help in metallography, to J. Hodowany and D. Owen for performing the high- strain-rate compression tests, and to H.-C. B. Chen, Y.-J. Chen, and J. Shih for helpful discussions. The 17508C heat treatments were carried out at Sandia National Laboratories through the kind help of A. Romig Jr and M. Karnowsky. The constructive criticism by the referee is greatly appreciated.
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Funding AgencyGrant Number
Army Research Office (ARO)DAAL 03-92-G-0108
Army Research Laboratory (ARL)UNSPECIFIED
Record Number:CaltechAUTHORS:20150226-153436802
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20150226-153436802
Official Citation:T. Dümmer, J.C. Lasalvia, G. Ravichandran, M.A. Meyers, Effect of strain rate on plastic flow and failure in polycrystalline tungsten, Acta Materialia, Volume 46, Issue 17, November 1998, Pages 6267-6290, ISSN 1359-6454, http://dx.doi.org/10.1016/S1359-6454(98)00255-9. (http://www.sciencedirect.com/science/article/pii/S1359645498002559)
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:55283
Collection:CaltechAUTHORS
Deposited By: Cheryl Gause
Deposited On:03 Mar 2015 00:31
Last Modified:29 Sep 2016 23:17

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