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Title: Dynamic Strength of Metals in Shock Deformation

Abstract

It is shown that the Hugoniot and the critical shear stress required to deform a metal plastically in shock compression can be obtained directly from molecular dynamics simulations without recourse to surface velocity profiles, or to details of the dislocation evolution. Specific calculations are shown for aluminum shocked along the [100] direction, and containing an initial distribution of microscopic defects. The presence of such defects has a minor effect on the Hugoniot and on the dynamic strength at high pressures. Computed results agree with experimental data.

Authors:
; ;
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
888588
Report Number(s):
UCRL-JRNL-217211
Journal ID: ISSN 0003-6951; APPLAB; TRN: US200618%%428
DOE Contract Number:
W-7405-ENG-48
Resource Type:
Journal Article
Resource Relation:
Journal Name: Applied Physics Letters; Journal Volume: 88; Journal Issue: 23
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ALUMINIUM; COMPRESSION; DEFECTS; DEFORMATION; DISLOCATIONS; DISTRIBUTION; SHEAR; VELOCITY

Citation Formats

Kubota, A, Reisman, D B, and Wolfer, W G. Dynamic Strength of Metals in Shock Deformation. United States: N. p., 2005. Web.
Kubota, A, Reisman, D B, & Wolfer, W G. Dynamic Strength of Metals in Shock Deformation. United States.
Kubota, A, Reisman, D B, and Wolfer, W G. Wed . "Dynamic Strength of Metals in Shock Deformation". United States. doi:. https://www.osti.gov/servlets/purl/888588.
@article{osti_888588,
title = {Dynamic Strength of Metals in Shock Deformation},
author = {Kubota, A and Reisman, D B and Wolfer, W G},
abstractNote = {It is shown that the Hugoniot and the critical shear stress required to deform a metal plastically in shock compression can be obtained directly from molecular dynamics simulations without recourse to surface velocity profiles, or to details of the dislocation evolution. Specific calculations are shown for aluminum shocked along the [100] direction, and containing an initial distribution of microscopic defects. The presence of such defects has a minor effect on the Hugoniot and on the dynamic strength at high pressures. Computed results agree with experimental data.},
doi = {},
journal = {Applied Physics Letters},
number = 23,
volume = 88,
place = {United States},
year = {Wed Nov 09 00:00:00 EST 2005},
month = {Wed Nov 09 00:00:00 EST 2005}
}
  • To gain insight into material strength and inelastic deformation of ceramics under plane shock wave loading, an in-depth study was carried out on polycrystalline silicon carbide (SiC). Two independent methods were used to determine experimentally the material strength in the shocked state: 1) lateral piezoresistance gauge measurements, and 2) compression and shear wave experiments. The two sets of data were in good agreement. The results show that the Poisson's ratio of the SiC increases from 0.162 to 0.194 at the HEL (11.5 GPa). The elastic-inelastic transition is not distinctive. In the shocked state, the material supports a maximum shear stressmore » increasing from 4.5 GPa at the HEL to 7.0 GPa at twice the HEL. This post-HEL strength evolution resembles neither catastrophic failure due to massive cracking nor classical plasticity response. Confining stress, inherent in plane shock wave compression, plays a dominant role in such a behavior. The observed inelastic deformation is interpreted qualitatively using an inhomogeneous mechanism involving both in-grain micro-plasticity and highly confined micro-fissures. Quantitatively, the data are summarized into an empirical pressure-dependent strength model.« less
  • In-material, lateral, manganin foil gauge measurements were obtained in dense polycrystalline silicon carbide (SiC) shocked to peak longitudinal stresses ranging from 10{endash}24 GPa. The lateral gauge data were analyzed to determine the lateral stresses in the shocked SiC and the results were checked for self-consistency through dynamic two-dimensional computations. Over the stress range examined, the shocked SiC has an extremely high strength: the maximum shear stress supported by the material in the shocked state increases from 4.5 GPa at the Hugoniot elastic limit (HEL) of the material (11.5 GPa) to 7.0 GPa at stresses approximately twice the HEL. The lattermore » value is 3.7{percent} of the shear modulus of the material. The elastic{endash}inelastic transition in the shocked SiC is nearly indistinctive. At stresses beyond twice the HEL, the data suggest a gradual softening with increasing shock compression. The post-HEL material strength evolution resembles neither catastrophic failure due to massive cracking nor classical plasticity response. Stress confinement, inherent in plane shock wave compression, contributes significantly to the observed material response. The results obtained are interpreted qualitatively in terms of an inhomogeneous deformation mechanism involving both in-grain microplasticity and highly confined microfissures. {copyright} {ital 1998 American Institute of Physics.}« less
  • A technique is described for estimating the dynamic yield stress in a shocked material. This method employs reloading and unloading data from a shocked state along with a general assumption of yield and hardening behavior to estimate the yield stress in the precompressed state. No other data are necessary for this evaluation, and, therefore, the method has general applicability at high shock pressures and in materials undergoing phase transitions. In some special cases, it is also possible to estimate the complete state of stress in a shocked state. Using this method, the dynamic yield strength of aluminum at 2.06 GPamore » has been estimated to be 0.26 GPa. This value agrees reasonably well with previous estimates.« less
  • Variability in local dynamic plasticity due to material anisotropy in polycrystalline metals is likely to be important on damage nucleation and growth at low pressures. Hydrodynamic instabilities could be used to study these plasticity effects by correlating measured changes in perturbation amplitudes at free surfaces to local plastic behaviour and grain orientation, but amplitude changes are typically too small to be measured reliably at low pressures using conventional diagnostics. Correlations between strength at low shock pressures and grain orientation were studied in copper (grain size ≈ 800 μm) using the Richtmyer–Meshkov instability with a square-wave surface perturbation (wavelength = 150 μm, amplitude = 5 μm), shocked at 2.7 GPa using symmetric plate impacts. A Plexiglas window was pressed against the peaks of the perturbation, keeping valleys as free surfaces. This produced perturbation amplitude changes much larger than those predicted without the window. Amplitude reductions from 64 to 88% were measured in recovered samples and grains oriented close tomore » $$\langle$$0 0 1$$\rangle$$ parallel to the shock had the largest final amplitude, whereas grains with shocks directions close to $$\langle$$1 0 1$$\rangle$$ had the lowest. Finite element simulations were performed with elastic-perfectly plastic models to estimate yield strengths leading lead to those final amplitudes. Anisotropic elasticity and these yield strengths were used to calculate the resolved shear stresses at yielding for the two orientations. In conclusion, results are compared with reports on orientation dependence of dynamic yielding in Cu single crystals and the higher values obtained suggest that strength estimations via hydrodynamic instabilities are sensitive to strain hardening and strain rate effects.« less
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