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Showing papers by "Marc A. Meyers published in 2006"


Journal ArticleDOI
TL;DR: The mechanical properties of nanocrystalline materials are reviewed in this paper, with emphasis on their constitutive response and on the fundamental physical mechanisms, including the deviation from the Hall-Petch slope and possible negative slope, the effect of porosity, the difference between tensile and compressive strength, the limited ductility, the tendency for shear localization, fatigue and creep responses.

3,828 citations


Journal ArticleDOI
TL;DR: In this paper, a comparison of shell properties with respect to the micro-structural architecture and sample orientation was carried out on three types of sea shells: conch, giant clam, and red abalone.

132 citations


Journal ArticleDOI
01 Jul 2006-JOM
TL;DR: In this article, the overall design principles in biological structural composites and illustrates them for five examples; sea spicules, the abalone shell, conch shell, the toucan and hornbill beaks, and the sheep crab exoskeleton.
Abstract: Biological materials are complex composites that are hierarchically structured and multifunctional. Their mechanical properties are often outstanding, considering the weak constituents from which they are assembled. They are for the most part composed of brittle (often, mineral) and ductile (organic) components. These complex structures, which have risen from millions of years of evolution, are inspiring materials scientists in the design of novel materials. This paper discusses the overall design principles in biological structural composites and illustrates them for five examples; sea spicules, the abalone shell, the conch shell, the toucan and hornbill beaks, and the sheep crab exoskeleton.

131 citations


Journal ArticleDOI
TL;DR: In this article, the authors compared 2D continuum simulations with experiments measuring perturbation growth from the Rayleigh-Taylor instability in solid state samples and deduced the microscopic dislocation dynamics that underlies this 1D-3D lattice relaxation.
Abstract: Solid state experiments at extreme pressures (102100 GPa) and strain rates (10 6 –10 8 s 21 )a re being developed on high energy laser facilities, and offer the possibility for exploring new regimes of materials science. These extreme solid state conditions can be accessed with either shock loading or with a quasi-isentropic ramped pressure drive. Velocity interferometer measurements establish the high pressure conditions. Constitutive models for solid state strength under these conditions are tested by comparing 2D continuum simulations with experiments measuring perturbation growth from the Rayleigh–Taylor instability in solid state samples. Lattice compression, phase and temperature are deduced from extended X-ray absorption fine structure (EXAFS) measurements, from which the shock induced a2v phase transition in Ti and the a2e phase transition in Fe, are inferred to occur on subnanosec time scales. Time resolved lattice response and phase can also be measured with dynamic X-ray diffraction measurements, where the elastic– plastic (1D–3D) lattice relaxation in shocked Cu is shown to occur promptly (,1 ns). Subsequent large scale molecular dynamics (MD) simulations elucidate the microscopic dislocation dynamics that underlies this 1D–3D lattice relaxation. Deformation mechanisms are identified by examining the residual microstructure in recovered samples. The slip-twinning threshold in single crystal Cu shocked along the [001] direction is shown to occur at shock strengths of ,20 GPa, whereas the corresponding transition for Cu shocked along the [134] direction occurs at higher shock strengths. This slip twinning threshold also depends on the stacking fault energy (SFE), being lower for low SFE materials. Designs have been developed for achieving much higher pressures, P.1000 GPa, in the solid state on the National Ignition Facility (NIF) laser.

105 citations


Journal ArticleDOI
TL;DR: In this paper, a polycrystalline zirconium alloy (Zircadine 702, containing 0.7% Hf) was subjected to high plastic strains (shear strains of 25−100) at a high strain rate (∼104−s−1) in an experimental setup comprising of a hat-shaped specimen deformed in a split Hopkinson bar.

94 citations


Journal ArticleDOI
01 Apr 2006-JOM
TL;DR: A review of the principal mechanisms responsible for the plastic deformation of nanocrystalline metals can be found in this article, where the authors show that with a decrease in grain size there is a gradual shift in the relative importance of the deformation mechanisms away from the ones operating in the conventional polycrystalline domain.
Abstract: This article presents a review of the principal mechanisms responsible for the plastic deformation of nanocrystalline metals. As the concentration of grain boundaries increases, with a decrease in grain size there is a gradual shift in the relative importance of the deformation mechanisms away from the ones operating in the conventional polycrystalline domain. This is predicted by molecular dynamics simulations that indicate a preponderance of dislocation emission/annihilation at grain boundaries and grain-boundary sliding when grain sizes are in the range 20–50 nm. Experiments show, in general, a saturation in work hardening at low strains, which is indicative of a steady-state dislocation density. This saturation is accompanied by an increased tendency toward shear localization, which is supportive of dislocation generation and annihilation at grain boundaries. Dislocation analyses recently proposed corroborate the computational predictions and provide a rational foundation for understanding the mechanical response.

76 citations


Journal ArticleDOI
TL;DR: In this paper, the deformation mechanism of nanocrystalline Ni at ultrahigh strain rates (>107s−1) was investigated, and it was shown that dislocation activity is a prevalent deformation mechanisms for the grain sizes studied.
Abstract: The deformation mechanism of nanocrystalline Ni (with grain sizes in the range of 30–100 nm) at ultrahigh strain rates (>107s−1) was investigated. A laser-driven compression process was applied to achieve high pressures (20–70 GPa) on nanosecond timescales and thus induce high-strain-rate deformation in the nanocrystalline Ni. Postmortem transmission electron microscopy examinations revealed that the nanocrystalline structures survive the shock deformation, and that dislocation activity is a prevalent deformation mechanism for the grain sizes studied. No deformation twinning was observed even at stresses more than twice the threshold for twin formation in micron-sized polycrystals. These results agree qualitatively with molecular dynamics simulations and suggest that twinning is a difficult event in nanocrystalline Ni under shock-loading conditions.

76 citations


Journal Article
TL;DR: In this article, the formation and microstructural evolution of localized shear bands were characterized by scanning electron microscopy (SEM) and transmission electron microscope (TEM) images.

67 citations


Journal ArticleDOI
TL;DR: In this article, the structure and mechanical response of a Toco toucan (Ramphastos toco) beak were established, and the beak was found to be a sandwich composite with an exterior of keratin scales (50 Am diameter and 1 Am thickness) and a core composed of fibrous network of closed-cells made of collagen.

64 citations


Journal ArticleDOI
TL;DR: In situ diffraction is a technique to probe directly the lattice response of materials during the shock loading process as mentioned in this paper, which is used to record diffraction patterns from multiple lattice planes simultaneously.

12 citations


Journal ArticleDOI
TL;DR: In this article, single crystalline copper was subjected to quasi-isentropic compression via gas-gun and laser loading at pressures between 18GPa and 59GPa.
Abstract: Single crystalline copper was subjected to quasi-isentropic compression via gas-gun and laser loading at pressures between 18GPa and 59GPa. The deformation substructure was analyzed via transmission electron microscopy (TEM). Twins and laths were evident at the highest pressures, and stacking faults and dislocation cells in the intermediate and lowest pressures, respectively. The Preston-Tonks-Wallace (PTW) constitutive description was used to model the slip-twinning process in both cases.

Proceedings ArticleDOI
09 Aug 2006
TL;DR: In situ X-ray diffraction allows the determination of the structure of transient states of matter as discussed by the authors, which can be used to study how single crystals of metals (copper and iron) react to uniaxial shock compression.
Abstract: In situ X‐ray diffraction allows the determination of the structure of transient states of matter We have used laser‐plasma generated X‐rays to study how single crystals of metals (copper and iron) react to uniaxial shock compression We find that copper, as a face‐centred‐cubic material, allows rapid generation and motion of dislocations, allowing close to hydrostatic conditions to be achieved on sub‐nanosecond timescales Detailed molecular dynamics calculations provide novel information about the process, and point towards methods whereby the dislocation density might be measured during the passage of the shock wave itself We also report on recent experiments where we have obtained diffraction images from shock‐compressed single‐crystal iron The single crystal sample transforms to the hcp phase above a critical pressure, below which it appears to be uniaxially compressed bcc, with no evidence of plasticity Above the transition threshold, clear evidence for the hcp phase can be seen in the diffraction images, and via a mechanism that is also consistent with recent multi‐ million atom molecular dynamics simulations that use the Voter‐ Chen potential We believe these data to be of import, in that they constitute the first conclusive in situ evidence of the transformed structure of iron during the passage of a shock wave

Proceedings ArticleDOI
09 Aug 2006
TL;DR: In this paper, a transmission electron microscopy study of quasi-isentropic high-pressure loading (peak pressures between 18 GPa and 52 GPa) of polycrystalline and monocrystalline copper was carried out.
Abstract: A transmission electron microscopy study of quasi‐isentropic high‐pressure loading (peak pressures between 18 GPa and 52 GPa) of polycrystalline and monocrystalline copper was carried out. Deformation mechanisms and defect substructures at different pressures were analyzed. Current evidence suggests a deformation substructure consisting of twinning at the higher pressures and heavily dislocated laths and dislocation cells at the intermediate and lower pressures, respectively. Evidence of stacking faults at the intermediate pressures was also found. Dislocation cell sizes decreased with increasing pressure and increased with distance away from the surface of impact.

Journal ArticleDOI
TL;DR: In this paper, the microstructural evolution of the finite volume of material that comprises the shear band at several levels of deformation was studied in commercial grade HCP-Zr alloy for its relative ease in forming shear bands.
Abstract: The mechanics of shear band formation has been studied in HCP-Zr to examine the microstructural evolution of the finite volume of material that comprises the shear band at several levels of deformation. Commercial grade HCP-Zr alloy is employed in the study for its relative ease in forming shear bands owing to its significant work hardening rate and significant plastic anisotropy. Hat shaped specimens are subjected to large plastic shear strains (of the order of 25-100) at strain rates of ∼10 4 s -1 in a split-Hopkinson bar experimental setup. The extent of deformation is controlled using different hat heights (0.75mm, 1.0mm and 2.0mm) that produce discrete levels of shear strain implicit in the shear band formed. Results suggest that despite the extreme constraint of the hat-shape specimen multiple shear bands occur in the confined region, which coalesce upon large deformations. Electron Microscopy examinations of the narrow shear band regions reveal a microstructure dominated by ultra-fine grains of the order of 200 nm. Such observations of fine grain size are consistent across the range of deformation studied here despite the vast differences in diffraction signature. Thus while the occurrence of a shear band ensures fine-grain size, subsequent reorganizations most likely occur as deformation is incremented. The microstructural evolution exhibits a characteristic path including a radical alteration of the grain orientation spectrum in the shear band. Experimental evidence suggests that this process is sub-divided in two parts i) formation of fine grains, with spatial textural relationships, which upon continuing deformation create ii) completely randomized structures. The criteria and bounds of such reorganizations are evaluated.


Proceedings ArticleDOI
26 May 2006
TL;DR: In this article, the authors used laser-plasma generated X-rays to study how single crystals of metals (copper and iron) react to uniaxial shock compression, and observed rapid plastic flow (in the case of copper), and directly observed the famous alpha-epsilon transition in Iron.
Abstract: The past few years have seen a rapid growth in the development and exploitation of X-ray diffraction on ultrafast time-scales. One area of physics which has benefited particularly from these advances is the the field of shock-waves. Whilst it has been known for many years that crystalline matter, subjected to uniaxial shock compression, can undergo plastic deformation and, for certain materials, polymorphic phase transformations, it has hitherto not been possible to observe the rearrangement of the atoms on the pertinent timescales. We have used laser-plasma generated X-rays to study how single crystals of metals (copper and iron) react to uniaxial shock compression, and observed rapid plastic flow (in the case of copper), and directly observed the famous alpha-epsilon transition in Iron. These studies have been complemented by large-scale multi-million atom molecular dynamics simulations, yielding significant information on the underlying physics.© (2006) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Proceedings ArticleDOI
09 Aug 2006
TL;DR: In this article, the post-shaking cooling for laser and plate-impact samples was shown to be 103 ∼ 104 faster than that of the plate•impact sample at the higher pressure level, due to the presence of micro-shearbands.
Abstract: Monocrystalline copper samples with orientations of [001] and [221] were shocked at pressures ranging from 20 GPa to 60 GPa using two techniques: direct drive lasers and explosively driven flyer plates. The pulse duration for these techniques differed substantially: 40 ns for the laser experiments at 0.5 mm into the sample and 1.1 ∼1.4 μs for the flyer‐plate experiments at 5 mm into the sample. The residual microstructures were dependent on orientation, pressure, and shocking method. For the flyer‐plate experiments, the longer pulse duration allow shock‐generated defects to reorganize into lower energy configurations. Calculations show that the post shock cooling for laser shock is 103 ∼ 104 faster than that of the plate‐impact shock, propitiating recovery and recrystallization conditions for the latter. At the higher pressure level extensive recrystallization was observed in the plate‐impact samples. An effect to contribute significantly to the recrystallization is the existence of micro‐shearbands, which increase the local temperature.

Proceedings ArticleDOI
09 Aug 2006
TL;DR: In this paper, in-situ x-ray diffraction was used to study the response of single crystal iron under shock conditions, and the results showed a uniaxial compression of the initially bcc lattice along the shock direction by up to 6% at 13 GPa and a further collapse of the lattice by 15-18% and a transformation to the hcp structure.
Abstract: In‐situ x‐ray diffraction was used to study the response of single crystal iron under shock conditions. Measurements of the response of [001] iron showed a uniaxial compression of the initially bcc lattice along the shock direction by up to 6% at 13 GPa. Above this pressure, the lattice responded with a further collapse of the lattice by 15–18% and a transformation to the hcp structure. The in‐situ measurements are discussed and results summarized.

Proceedings ArticleDOI
09 Aug 2006
TL;DR: In this paper, reverse Taylor impact tests have been carried out on ultrafine grained copper processed by Equal Channel Angular Pressing (ECAP) and the results showed that the constitutive response of copper of varying grain sizes was obtained through quasistatic and dynamic mechanical tests and incorporation into constitutive models.
Abstract: Reverse Taylor impact tests have been carried out on ultrafine grained copper processed by Equal Channel Angular Pressing (ECAP). Tests were conducted on an as‐received OFHC Cu rod and specimens that had undergone sequential ECAP passes (2 and 8). The average grain size ranged from 30 μm for the initial sample to less than 0.5 μm for the 8‐pass samples. The dynamic deformation states of the samples, captured by high speed digital photography were compared with computer simulations run in AUTODYN‐2D using the Johnson‐Cook constitutive equation with constants obtained from stress‐strain data and by fitting to an experimentally measured free surface velocity trace. The constitutive response of copper of varying grain sizes was obtained through quasistatic and dynamic mechanical tests and incorporation into constitutive models.

Journal ArticleDOI
TL;DR: In this paper, the authors evaluated the effect of the immediate load on the healing process of the bone-implant interfacial tissue without compromising its stability, and found that the tissues formed after 12 weeks were different between loaded and unloaded groups, but both were mechanically stable.
Abstract: Ti-6Al-4V alloy mini-implants were inserted in rabbit’s tibiae and immediately loaded with 1 N. The healing process was analyzed by SEM in the assessment periods of 1, 4, and 12 weeks. Results showed that the tissues formed after 12 weeks were different between loaded and unloaded groups, but both of them were mechanically stable. The compression and traction areas in the loaded group did not present difference between each other. This investigation showed that the immediate load affected the healing process of the bone-implant interfacial tissue, without compromising its stability.