Laser-induced shock compression of monocrystalline copper: characterization and analysis
TL;DR: In this paper, a method for estimating dislocation densities is proposed, based on nucleation of loops at the shock front and their extension due to residual shear stresses behind the front.
About: This article is published in Acta Materialia.The article was published on 2003-03-14. It has received 219 citations till now. The article focuses on the topics: Slip (materials science) & Crystal twinning.
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TL;DR: In this article, it was found that after annealing the hardness of the samples does not fall as low as is known for heavily deformed copper at normal strain rates, e.g., cold rolling.
104 citations
TL;DR: In this article, a dislocation-based model was proposed for void collapse in copper, which gave excellent agreement with the stress threshold found in the nonequilibrium molecular-dynamics simulations for void collapsing as a function of void radius.
Abstract: Nonequilibrium molecular-dynamics (MD) simulations show that shock-induced void collapse in copper occurs by emission of shear loops. These loops carry away the vacancies which comprise the void. The growth of the loops continues even after they collide and form sessile junctions, creating a hardened region around the collapsing void. The scenario seen in our simulations differs from current models that assume that prismatic loop emission is responsible for void collapse. We propose a dislocation-based model that gives excellent agreement with the stress threshold found in the MD simulations for void collapse as a function of void radius.
101 citations
TL;DR: In this paper, a model of plasticity that couples discrete dislocation dynamics and finite element analysis is used to investigate shock-induced dislocation nucleation in copper single crystals, and homogeneous nucleation of dislocations is included based on large scale atomistic shock simulations.
Abstract: A model of plasticity that couples discrete dislocation dynamics and finite element analysis is used to investigate shock-induced dislocation nucleation in copper single crystals. Homogeneous nucleation of dislocations is included based on large-scale atomistic shock simulations. The resulting prodigious rate of dislocation production takes the uniaxialy compressed material to a hydrostatically compressed state after a few tens of picoseconds. The density of dislocations produced in a sample with preexisting dislocation sources decreases slightly as shock rise time increases, implying that relatively lower densities would be expected for isentropic loading using extremely long rise times as suggested experimentally.
93 citations
TL;DR: In this paper, a multiscale approach was developed to study alloy behavior under high-rate loading (at the strain rates >10 5 ǫ s −1 ). But the authors focused on investigation of the mechanisms and kinetics of plastic deformation of alloys.
92 citations
TL;DR: In this article, the deformation and failure of bulk Cu-Nb nanocomposites with a nominal layer thickness of 135nm was investigated under planar shock loading, and it was observed that little substructural evolution was evident after shock compression to a peak stress of 7 GPa, while specimens were fully spalled after loading to 7GPa under free surface conditions.
89 citations
References
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27 Sep 1994
TL;DR: In this paper, the authors present a method to produce dynamic deformation at high strain rates by using Shear Bands (Thermoplastic Shear Instabilities) and dynamic fracture.
Abstract: Dynamic Deformation and Waves. Elastic Waves. Plastic Waves. Shock Waves. Shock Waves: Equations of State. Differential Form of Conservation Equations and Numerical Solutions to More Complex Problems. Shock Wave Attenuation, Interaction, and Reflection. Shock Wave-Induced Phase Transformations and Chemical Changes. Explosive-Material Interactions. Detonation. Experimental Techniques: Diagnostic Tools. Experimental Techniques: Methods to Produce Dynamic Deformation. Plastic Deformation at High Strain Rates. Plastic Deformation in Shock Waves. Shear Bands (Thermoplastic Shear Instabilities). Dynamic Fracture. Applications. Indexes.
2,609 citations
"Laser-induced shock compression of ..." refers background or methods in this paper
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...The dislocation density can be expressed as a function of pressure, P, through one of the equations obtained directly from the Rankine–Hugoniot equations and the equation of state [22]:...
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...In a similar manner, the residual temperature, TR, can be obtained from [22]:...
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TL;DR: An improved description of copper and ironcylinder impact (Taylor) test results has been obtained through the use of dislocation-mechanics-based constitutive relations in the Lagrangian material dynamics computer program EPIC•2.
Abstract: An improved description of copper‐ and iron‐cylinder impact (Taylor) test results has been obtained through the use of dislocation‐mechanics‐based constitutive relations in the Lagrangian material dynamics computer program EPIC‐2. The effects of strain hardening, strain‐rate hardening, and thermal softening based on thermal activation analysis have been incorporated into a reasonably accurate constitutive relation for copper. The relation has a relatively simple expression and should be applicable to a wide range of fcc materials. The effect of grain size is included. A relation for iron is also presented. It also has a simple expression and is applicable to other bcc materials but is presently incomplete, since the important effect of deformation twinning in bcc materials is not included. A possible method of acounting for twinning is discussed and will be reported on more fully in future work. A main point made here is that each material structure type (fcc, bcc, hcp) will have its own constitutive beha...
1,718 citations
TL;DR: In this article, a constitutive expression for the twinning stress in BCC metals is developed using dislocation emission from a source and the formation of pile-ups, as rate-controlling mechanism.
1,366 citations
TL;DR: In this paper, a periodic relation between shear stress and atomic shear displacement is assumed to hold along the most highly stressed slip plane emanating from a crack tip, which allows some small slip displacement to occur near the tip in response to small applied loading and, with increase in loading, the incipient dislocation configuration becomes unstable and leads to a fully formed dislocation which is driven away from the crack.
Abstract: Dislocation nucleation from a stressed crack tip is analyzed based on the Peierls concept. A periodic relation between shear stress and atomic shear displacement is assumed to hold along the most highly stressed slip plane emanating from a crack tip. This allows some small slip displacement to occur near the tip in response to small applied loading and, with increase in loading, the incipient dislocation configuration becomes unstable and leads to a fully formed dislocation which is driven away from the crack. An exact solution for the loading at that nucleation instability is developed via the J -integral for the case when the crack and slip planes coincide, and an approximate solution is given when they do not. Solutions are also given for emission of dissociated dislocations, especially partial dislocation pairs in fcc crystals. The level of applied stress intensity factors required for dislocation nucleation is shown to be proportional to √γ us , where γ us , the unstable stacking energy, is a new solid state parameter identified by the analysis. It is the maximum energy encountered in the block-like sliding along a slip plane, in the Burgers vector direction, of one half of a crystal relative to the other. Approximate estimates of γ us are summarized and the results are used to evaluate brittle vs ductile response in fcc and bcc metals in terms of the competition between dislocation nucleation and Griffith cleavage at a crack tip. The predictions seem compatible with known behavior and also show that in many cases solids which are predicted to first cleave under pure mode I loading should instead first emit dislocations when that loading includes very small amounts of mode II and III shear. The analysis in this paper also reveals a feature of the near-tip slip distribution corresponding to the saddle point energy configuration for cracks that are loaded below the nucleation threshold, as is of interest for thermal activation.
1,320 citations
01 Jan 1940
TL;DR: In this paper, the size of a dislocation and critical shear stress for its motion were calculated for a single dislocation with respect to the size and motion of the dislocation.
Abstract: Calculations are made of the size of a dislocation and of the critical shear stress for its motion.
1,226 citations