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Title: Spall strength dependence on grain size and strain rate in tantalum

In this paper, we examine the effect of grain size on the dynamic failure tantalum during laser-shock compression and release and identify a significant effect of grain size on spall strength, which is opposite to the prediction of the Hall-Petch relationship because spall is primarily intergranular in both poly and nanocrystalline samples; thus, monocrystals have a higher spall strength than polycrystals, which, in turn, are stronger in tension than ultra-fine grain sized specimens. Post-shock characterization reveals ductile failure which evolves by void nucleation, growth, and coalescence. Whereas in the monocrystal the voids grow in the interior, nucleation is both intra and intergranular in the poly and ultra-fine-grained crystals. The fact that spall is primarily intergranular in both poly and nanocrystalline samples is strong evidence for higher growth rates of intergranular voids, which have a distinctly oblate spheroid shape in contrast with intragranular voids, which are more spherical. The length geometrically-necessary dislocations required to form a grain-boundary (intergranular) void is lower than that of grain-interior (intragranular) void with the same maximum diameter; thus, the energy required is lower. Consistent with prior literature and theory we also identify an increase with spall strength with strain rate from 6x10 6 to 5x10 7more » s -1. Molecular dynamics calculations agree with the experimental results and also predict grain-boundary separation in the spalling of polycrystals as well as an increase in spall strength with strain rate. Finally, an analytical model based on the kinetics of nucleation and growth of intra and intergranular voids and extending the Curran-Seaman-Shockey theory is applied which shows the competition between the two processes for polycrystals.« less
Authors:
 [1] ; ORCiD logo [2] ; ORCiD logo [3] ;  [3] ;  [4] ;  [5] ; ORCiD logo [5] ;  [6] ;  [6] ;  [6] ;  [6] ;  [4] ; ORCiD logo [3]
  1. Univ. of California, San Diego, CA (United States); Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  2. Univ. of California, San Diego, CA (United States); Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  3. Univ. of California, San Diego, CA (United States)
  4. Arizona State Univ., Tempe, AZ (United States)
  5. Univ. of Southern California, Los Angeles, CA (United States)
  6. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Publication Date:
Grant/Contract Number:
NA0002930; FG52-09NA29043; AC52-07NA27344; 09-LR-06-118456-MEYM; DMR-1160966
Type:
Accepted Manuscript
Journal Name:
Acta Materialia
Additional Journal Information:
Journal Volume: 158; Journal ID: ISSN 1359-6454
Publisher:
Elsevier
Research Org:
Univ. of California, San Diego, CA (United States); Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Univ. of Southern California, Los Angeles, CA (United States)
Sponsoring Org:
USDOE National Nuclear Security Administration (NNSA); Univ. of California (United States); National Science Foundation (NSF)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; spall strength; strain rate; grain size; texture; void growth
OSTI Identifier:
1462277