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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01 Jan 2015
TL;DR: It is shown here how to identify the different types of phytochemical deposits in the blood of a person infected with E.coli.
Abstract: هلاقم تاعلاطا هدیکچ یشهوژپ هلاقم لماک :تفایرد 01 نمهب 1392 :شریذپ 23 نمهب 1392 :تیاس رد هئارا 16 رهم 1393 ،اهییاجبان يروئت زا هدافتسا و يراتخاسزیر هاگدید ساسا رب و یشرب نایرج شنت رب رثوم ياهرتماراپ ندرک ظاحل اب ،قیقحت نیا رد تازلف يور رب رادیاپ كوش جوم يراذگراب خساپ یسررب يارب يروئت لدم کی FCC هدش هئارا ، يداینب طباور هئارا اب قیقحت نیا .تسا ی هب ،كوش جوم يارب رادومن ،هطبار نیا یلیلحت لح اب.تسا هتفای تسد کیتسلاپ یگدیشک و یشرب شنت لماش ییاهن هطبار ک .تسا هدش مسر ،کیتسلاپ رثوم لکش رییغت بسح رب یشرب شنت يارب اهنت و يدعب کی شنرک ضرف اب ،هدش هئارا يداینب طباور ،قیقحت نیا يروآون نیرتمهم .تسا هدش هئارا كوش جوم يراذگراب يژرنا ياقب نوناق زا هدافتسا یپورتنآ دیلوتخرن نتفرگ رظن رد اب یم هدام رد كوش جوم يراذگراب رثا رد یم اهییاجبان تکرح و ندش لینآ ،داجیا زا یشان یپورتنآ دیلوت.دشاب دشاب جوم تعرس تارثا ا هدش هتفرگ رارق یسررب دروم ،کیتسلاپ یگدیشک بسح رب یلامعا شنت و لک یگدیشک ،كوش راتخاس یسررب هب نینچمه .تس رثکادح كوش جوم داجیا يارب یلامعا يراذگراب ..تسا هدش هتخادرپ فلتخم ياهیراذگراب رثا رد ،كوش جوم GPa 25 تحص.تسا موینیمولآ ژایلآ يور رب رگید عجارم رد دوجوم یبرجت ياهشیامزآ يروئت ياهلدم اب جیاتن هسیاقم قیرط زا ،اهرادومن و طباور یجنس 6061 .دراد دوجو هدش هئارا لدم و یبرجت جیاتن نیب یبوخ قفاوت .تسا هتفریذپ تروص ، :ناگژاو دیلک جوم كوش رییغت لکش کیتسلاپ ینیمولآ مو 6061 یپورتنآ
1 citations
TL;DR: In this paper, the authors describe experiments that study the ring fragmentation of OFHC copper, at strain rates around 10 4 s -1. Diagnostics include high speed photography, laser velocimetry, and soft capture of fragments.
1 citations
TL;DR: The detwinning process in a 9 nm graphene-constrained Cu nanoparticle was investigated at 1009 °C via in situ high-resolution transmission electron microscopy, and two new twins were formed; the four twin zones rotated synergistically before vanishing.
Abstract: In this work, the detwinning process in a 9 nm graphene-constrained Cu nanoparticle was investigated at 1009 °C via in situ high-resolution transmission electron microscopy. Instead of the expected reverse glide of the twinning dislocations, two new twins were formed; the four twin zones rotated synergistically before vanishing. Furthermore, the twin boundary migration energy and the system energy were increased continuously with detwinning. The increased resistance to twin boundary migration in constrained nanoparticles enriches our understanding of the twinning mechanism and may facilitate the design of high-strength and high-ductility nanomaterials.
1 citations
15 Jun 2010
1 citations
TL;DR: In this article , large-scale molecular dynamics simulations of shock-induced lattice rotation in three model crystals whose behavior has previously been characterized in dynamic-compression experiments are presented, and the texture changes predicted by the simulations are consistent with those measured experimentally using in situ x-ray diffraction.
Abstract: When compressed, a metallic specimen will generally experience changes to its crystallographic texture due to plasticity-induced rotation. Ultrafast x-ray diffraction techniques make it possible to measure rotation of this kind in targets dynamically compressed over nanosecond timescales to the kind of pressures ordinarily encountered in planetary interiors. The axis and the extent of the local rotation can provide hints as to the combination of plasticity mechanisms activated by the rapid uniaxial compression, thus providing valuable information about the underlying dislocation kinetics operative during extreme loading conditions. We present large-scale molecular dynamics simulations of shock-induced lattice rotation in three model crystals whose behavior has previously been characterized in dynamic-compression experiments: tantalum shocked along its [101] direction, and copper shocked along either [001] or [111]. We find that, in all three cases, the texture changes predicted by the simulations are consistent with those measured experimentally using in situ x-ray diffraction. We show that while tantalum loaded along [101] and copper loaded along [001] both show pronounced rotation due to asymmetric multiple slip, the orientation of copper shocked along [111] is predicted to be stabilized by opposing rotations arising from competing, symmetrically equivalent slip systems.
1 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