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Sample records for dislocation density-based constitutive

  1. A dislocation density based constitutive model for cyclic deformation

    SciTech Connect

    Estrin, Y.; Braasch, H.; Brechet, Y.

    1996-10-01

    A new constitutive model describing material response to cyclic loading is presented. The model includes dislocation densities as internal variables characterizing the microstructural state of the material. In the formulation of the constitutive equations, the dislocation density evolution resulting from interactions between dislocations in channel-like dislocation patterns is considered. The capabilities of the model are demonstrated for INCONEL 738 LC and Alloy 800H.

  2. Application of a Dislocation Density-Based Constitutive Model to Al-Alloyed TWIP Steel

    NASA Astrophysics Data System (ADS)

    Kim, Jinkyung; Estrin, Yuri; De Cooman, Bruno Charles

    2013-09-01

    High Mn steels exhibit an exceptional combination of high strength and large ductility owing to their high strain-hardening rate during deformation. The addition of Al is needed to improve the mechanical performance of TWIP steel by means of the control of the stacking fault energy. In this study, a constitutive modeling approach, which can describe the strain-hardening behavior and the effect of Al on the mechanical properties, was used. In order to understand the deformation behavior of Fe18Mn0.6C and Fe18Mn0.6C1.5Al TWIP steels, a comparative study of the microstructural evolution was conducted by means of transmission electron microscopy and electron backscatter diffraction. The microstructure analysis focused on dislocations, stacking faults, and mechanical twins as these are the defects controlling the strain-hardening behavior of TWIP steels. A comparison of the strain-hardening behavior of Fe18Mn0.6C and Fe18Mn0.6C1.5Al TWIP steels was made in terms of a dislocation density-based constitutive model that goes back to the Kubin-Estrin model. The densities of mobile and forest dislocations are coupled in order to account for the interaction between the two dislocation populations during straining. The model was used to estimate the contribution of dynamic strain aging to the flow stress. As deformation twinning occurred only in a subset of the grains, the grain population was subdivided into twinned grains and twin-free grains. Different constitutive equations were used for the two families of grains. The analysis revealed that (i) the grain size and dynamic recovery effects determine the strain-hardening behavior of the twin-free grains, (ii) the deformation twins, which act as effective barriers to dislocation motion, are the predominant elements of the microstructure that governs the strain hardening of the twinned grains, and (iii) the DSA contribution to strain hardening of TWIP steel is only minor.

  3. Dislocation Density-Based Constitutive Model for the Mechanical Behavior of Irradiated Cu

    SciTech Connect

    Arsenlis, A; Wirth, B D; Rhee, M

    2003-04-10

    Performance degradation of structural steels in nuclear environments results from the development of a high number density of nanometer scale defects. The defects observed in copper-based alloys are composed of vacancy clusters in the form of stacking fault tetrahedra and/or prismatic dislocation loops, which impede dislocation glide and are evidenced in macroscopic uniaxial stress-strain curves as increased yield strengths, decreased total strain to failure, decreased work hardening and the appearance of a distinct upper yield point above a critical defect concentration (neutron dose). In this paper, we describe the development of an internal state variable model for the mechanical behavior of materials subject to these environments. This model has been developed within an information-passing multiscale materials modeling framework, in which molecular dynamics simulations of dislocation--radiation defect interactions, inform the final coarse-grained continuum model. The plasticity model includes mechanisms for dislocation density growth and multiplication and for radiation defect density evolution with dislocation interaction. The general behavior of the constitutive (single material point) model shows that as the defect density increases, the initial yield point increases and the initial strain hardening decreases. The final coarse-grained model is implemented into a finite element framework and used to simulate the behavior of tensile specimens with varying levels of irradiation induced material damage. The simulation results compare favorably with the experimentally observed mechanical properties of irradiated materials in terms of their increased strength, decreased hardening, and decreased ductility with increasing irradiation dose.

  4. Dislocation-density based description of the deformation of a composite material

    NASA Astrophysics Data System (ADS)

    Schulz, K.; Sudmanns, M.; Gumbsch, P.

    2017-09-01

    Composite materials consisting of hard particles in a ductile metallic matrix are of major interest since their strength and deformability can be dramatically changed by varying volume fraction, size and shape of the particles. Understanding dislocation motion in composite materials as the cause of plastic deformation therefore is an important task. Recently, advanced dislocation-based continuum theories of plasticity have been developed for performing meaningful averages over systems of straight and curved dislocation lines in a continuum approach. In this paper, we focus on a single slip heterogeneous microstructure and investigate how the dislocation interactions can be represented in an averaged dislocation density based continuum description. The representation of strong dislocation density gradients is discussed in the context of a formulation, which aims at a coarse-grained resolution. We introduce a set of dislocation density evolution equations which account for the formation and dissolution of dislocation dipoles. By applying the model to a composite structure, we demonstrate that the dislocation density based description can well describe the physical processes in the microstructure and a comparison to discrete dislocation dynamics simulations shows good agreement for the relaxation behavior of the considered composites.

  5. Steel Alloy Hot Roll Simulations and Through-Thickness Variation Using Dislocation Density-Based Modeling

    NASA Astrophysics Data System (ADS)

    Jansen Van Rensburg, G. J.; Kok, S.; Wilke, D. N.

    2017-07-01

    Different roll pass reduction schedules have different effects on the through-thickness properties of hot-rolled metal slabs. In order to assess or improve a reduction schedule using the finite element method, a material model is required that captures the relevant deformation mechanisms and physics. The model should also report relevant field quantities to assess variations in material state through the thickness of a simulated rolled metal slab. In this paper, a dislocation density-based material model with recrystallization is presented and calibrated on the material response of a high-strength low-alloy steel. The model has the ability to replicate and predict material response to a fair degree thanks to the physically motivated mechanisms it is built on. An example study is also presented to illustrate the possible effect different reduction schedules could have on the through-thickness material state and the ability to assess these effects based on finite element simulations.

  6. Steel Alloy Hot Roll Simulations and Through-Thickness Variation Using Dislocation Density-Based Modeling

    NASA Astrophysics Data System (ADS)

    Jansen Van Rensburg, G. J.; Kok, S.; Wilke, D. N.

    2017-10-01

    Different roll pass reduction schedules have different effects on the through-thickness properties of hot-rolled metal slabs. In order to assess or improve a reduction schedule using the finite element method, a material model is required that captures the relevant deformation mechanisms and physics. The model should also report relevant field quantities to assess variations in material state through the thickness of a simulated rolled metal slab. In this paper, a dislocation density-based material model with recrystallization is presented and calibrated on the material response of a high-strength low-alloy steel. The model has the ability to replicate and predict material response to a fair degree thanks to the physically motivated mechanisms it is built on. An example study is also presented to illustrate the possible effect different reduction schedules could have on the through-thickness material state and the ability to assess these effects based on finite element simulations.

  7. A dislocation density-based continuum model of the anisotropic shock response of single crystal α-cyclotrimethylene trinitramine

    NASA Astrophysics Data System (ADS)

    Luscher, D. J.; Addessio, F. L.; Cawkwell, M. J.; Ramos, K. J.

    2017-01-01

    We have developed a model for the finite deformation thermomechanical response of α-cyclotrimethylene trinitramine (RDX). Our model accounts for nonlinear thermoelastic lattice deformation through a free energy-based equation of state developed by Cawkwell et al. (2016) in combination with temperature and pressure dependent elastic constants, as well as dislocation-mediated plastic slip on a set of slip systems motivated by experimental observation. The kinetics of crystal plasticity are modeled using the Orowan equation relating slip rate to dislocation density and the dislocation velocity developed by Austin and McDowell (2011), which naturally accounts for transition from thermally activated to dislocation drag limited regimes. Evolution of dislocation density is specified in terms of local ordinary differential equations reflecting dislocation-dislocation interactions. This paper presents details of the theory and parameterization of the model, followed by discussion of simulations of flyer plate impact experiments. Impact conditions explored within this combined simulation and experimental effort span shock pressures ranging from 1 to 3 GPa for four crystallographic orientations and multiple specimen thicknesses. Simulation results generated using this model are shown to be in strong agreement with velocimetry measurements from the corresponding plate impact experiments. Finally, simulation results are used to motivate conclusions about the nature of dislocation-mediated plasticity in RDX.

  8. A dislocation density-based continuum model of the anisotropic shock response of single crystal α-cyclotrimethylene trinitramine

    SciTech Connect

    Luscher, Darby Jon; Addessio, Francis L.; Cawkwell, Marc Jon; Ramos, Kyle James

    2017-01-01

    Here, we have developed a model for the finite deformation thermomechanical response of α-cyclotrimethylene trinitramine (RDX). Our model accounts for nonlinear thermoelastic lattice deformation through a free energy-based equation of state developed by Cawkwell et al. (2016) in combination with temperature and pressure dependent elastic constants, as well as dislocation-mediated plastic slip on a set of slip systems motivated by experimental observation. The kinetics of crystal plasticity are modeled using the Orowan equation relating slip rate to dislocation density and the dislocation velocity developed by Austin and McDowell (2011), which naturally accounts for transition from thermally activated to dislocation drag limited regimes. Evolution of dislocation density is specified in terms of local ordinary differential equations reflecting dislocation–dislocation interactions. This paper presents details of the theory and parameterization of the model, followed by discussion of simulations of flyer plate impact experiments. Impact conditions explored within this combined simulation and experimental effort span shock pressures ranging from 1 to 3 GPa for four crystallographic orientations and multiple specimen thicknesses. Simulation results generated using this model are shown to be in strong agreement with velocimetry measurements from the corresponding plate impact experiments. Finally, simulation results are used to motivate conclusions about the nature of dislocation-mediated plasticity in RDX.

  9. A dislocation density-based continuum model of the anisotropic shock response of single crystal α-cyclotrimethylene trinitramine

    DOE PAGES

    Luscher, Darby Jon; Addessio, Francis L.; Cawkwell, Marc Jon; ...

    2017-01-01

    Here, we have developed a model for the finite deformation thermomechanical response of α-cyclotrimethylene trinitramine (RDX). Our model accounts for nonlinear thermoelastic lattice deformation through a free energy-based equation of state developed by Cawkwell et al. (2016) in combination with temperature and pressure dependent elastic constants, as well as dislocation-mediated plastic slip on a set of slip systems motivated by experimental observation. The kinetics of crystal plasticity are modeled using the Orowan equation relating slip rate to dislocation density and the dislocation velocity developed by Austin and McDowell (2011), which naturally accounts for transition from thermally activated to dislocation dragmore » limited regimes. Evolution of dislocation density is specified in terms of local ordinary differential equations reflecting dislocation–dislocation interactions. This paper presents details of the theory and parameterization of the model, followed by discussion of simulations of flyer plate impact experiments. Impact conditions explored within this combined simulation and experimental effort span shock pressures ranging from 1 to 3 GPa for four crystallographic orientations and multiple specimen thicknesses. Simulation results generated using this model are shown to be in strong agreement with velocimetry measurements from the corresponding plate impact experiments. Finally, simulation results are used to motivate conclusions about the nature of dislocation-mediated plasticity in RDX.« less

  10. A dislocation density-based continuum model of the anisotropic shock response of single crystal α-cyclotrimethylene trinitramine

    DOE PAGES

    Luscher, Darby Jon; Addessio, Francis L.; Cawkwell, Marc Jon; ...

    2017-01-01

    Here, we have developed a model for the finite deformation thermomechanical response of α-cyclotrimethylene trinitramine (RDX). Our model accounts for nonlinear thermoelastic lattice deformation through a free energy-based equation of state developed by Cawkwell et al. (2016) in combination with temperature and pressure dependent elastic constants, as well as dislocation-mediated plastic slip on a set of slip systems motivated by experimental observation. The kinetics of crystal plasticity are modeled using the Orowan equation relating slip rate to dislocation density and the dislocation velocity developed by Austin and McDowell (2011), which naturally accounts for transition from thermally activated to dislocation dragmore » limited regimes. Evolution of dislocation density is specified in terms of local ordinary differential equations reflecting dislocation–dislocation interactions. This paper presents details of the theory and parameterization of the model, followed by discussion of simulations of flyer plate impact experiments. Impact conditions explored within this combined simulation and experimental effort span shock pressures ranging from 1 to 3 GPa for four crystallographic orientations and multiple specimen thicknesses. Simulation results generated using this model are shown to be in strong agreement with velocimetry measurements from the corresponding plate impact experiments. Finally, simulation results are used to motivate conclusions about the nature of dislocation-mediated plasticity in RDX.« less

  11. A dislocation density-based continuum model of the anisotropic shock response of single crystal α-cyclotrimethylene trinitramine

    SciTech Connect

    Luscher, Darby Jon; Addessio, Francis L.; Cawkwell, Marc Jon; Ramos, Kyle James

    2017-01-01

    Here, we have developed a model for the finite deformation thermomechanical response of α-cyclotrimethylene trinitramine (RDX). Our model accounts for nonlinear thermoelastic lattice deformation through a free energy-based equation of state developed by Cawkwell et al. (2016) in combination with temperature and pressure dependent elastic constants, as well as dislocation-mediated plastic slip on a set of slip systems motivated by experimental observation. The kinetics of crystal plasticity are modeled using the Orowan equation relating slip rate to dislocation density and the dislocation velocity developed by Austin and McDowell (2011), which naturally accounts for transition from thermally activated to dislocation drag limited regimes. Evolution of dislocation density is specified in terms of local ordinary differential equations reflecting dislocation–dislocation interactions. This paper presents details of the theory and parameterization of the model, followed by discussion of simulations of flyer plate impact experiments. Impact conditions explored within this combined simulation and experimental effort span shock pressures ranging from 1 to 3 GPa for four crystallographic orientations and multiple specimen thicknesses. Simulation results generated using this model are shown to be in strong agreement with velocimetry measurements from the corresponding plate impact experiments. Finally, simulation results are used to motivate conclusions about the nature of dislocation-mediated plasticity in RDX.

  12. Dislocation

    MedlinePlus

    Joint dislocation ... It may be hard to tell a dislocated joint from a broken bone . Both are emergencies that ... to repair a ligament that tears when the joint is dislocated is needed. Injuries to nerves and ...

  13. Porosity evolution at high strain rates: atomistic simulations, dislocation analysis, and constitutive modeling

    NASA Astrophysics Data System (ADS)

    Bringa, Eduardo; Ruestes, Carlos; Rodriguez Nieva, Joaquin; Tramontina, Diego; Tang, Yizhe; Meyers, Marc

    2015-06-01

    Mimicking shock compression experiments, our molecular dynamics simulations explore the mechanical response and plasticity effects under uniaxial high strain rate compression (10**7/s to 10**9/s) for Au and Ta single crystals with a collection of spherical nanovoids, with a radius of 3-4 nm, resulting in an initial porosity of %-10%. Dislocation analysis was used to evaluate and quantify the evolution of plasticity. The evolution of dislocations configuration and densities were predicted and successfully compared to an analysis based on Ashby's concept of geometrically-necessary dislocations. The temperature excursion during plastic deformation was used to estimate the mobile dislocation density. The results obtained are compared with a variety of dislocation-based constitutive models. Plastic activity leads to a decrease in porosity until voids disappear completely. Based on the atomistic simulations, a densification regime was observed in all nanoporous samples studied. With these results, a new strain- based porosity model for metals is proposed for simulations at the continuum scale. EB, CR and DT thank support from PICT-0092 and a SeCTyP-UNCuyo grant.

  14. Dislocation

    MedlinePlus

    ... Dislocations can occur in contact sports, such as football and hockey, and in sports in which falls ... downhill skiing, gymnastics and volleyball. Basketball players and football players also commonly dislocate joints in their fingers ...

  15. A defect density-based constitutive crystal plasticity framework for modeling the plastic deformation of Fe-Cr-Al cladding alloys subsequent to irradiation

    SciTech Connect

    Patra, Anirban; Wen, Wei; Martinez Saez, Enrique; Tome, Carlos

    2016-02-05

    It is essential to understand the deformation behavior of these Fe-Cr-Al alloys, in order to be able to develop models for predicting their mechanical response under varied loading conditions. Interaction of dislocations with the radiation-induced defects governs the crystallographic deformation mechanisms. A crystal plasticity framework is employed to model these mechanisms in Fe-Cr-Al alloys. This work builds on a previously developed defect density-based crystal plasticity model for bcc metals and alloys, with necessary modifications made to account for the defect substructure observed in Fe-Cr-Al alloys. The model is implemented in a Visco-Plastic Self Consistent (VPSC) framework, to predict the mechanical behavior under quasi-static loading.

  16. Constitutive model based on dislocation density and ductile fracture of Monel 400 thin sheet under tension

    NASA Astrophysics Data System (ADS)

    Wang, Chuanjie; Xue, Shaoxi; Chen, Gang; Zhang, Peng

    2017-03-01

    In micro-scaled plastic deformation, material strength and ductile fracture behaviors of thin sheet in tension are quite different from those in macro-scale. In this study, uniaxial tensile tests of Monel 400 thin sheets with different microstructures were carried out to investigate the plastic deformation size effect in micro-scale. The experimental results indicate that the flow stress and fracture strain departure from the traditional empirical formula when there are only fewer grains across the thickness. And the number of dimples on the fracture surface is getting smaller with the decreasing ratio of specimen thickness to grain size. Then, a constitutive model based on dislocation density considering the free surface effect in micro-scale is proposed to reveal the mechanism of the flow stress size effect. In addition, a model is proposed considering the surface roughening inducing the thickness nonuniform and the decrease of micro-voids resulting from the reduction of grain boundary density with the decreasing ratio of specimen thickness to grain size. The interactive effects of the surface roughening and the decrease of micro-voids result in the earlier fracture in micro tension of the specimen with fewer grains across the thickness.

  17. Constitutive model based on dislocation density and ductile fracture of monel 400 thin sheet under tension

    NASA Astrophysics Data System (ADS)

    Wang, Chuanjie; Xue, Shaoxi; Chen, Gang; Zhang, Peng

    2017-02-01

    In micro-scaled plastic deformation, material strength and ductile fracture behaviors of thin sheet in tension are quite different from those in macro-scale. In this study, uniaxial tensile tests of Monel 400 thin sheets with different microstructures were carried out to investigate the plastic deformation size effect in micro-scale. The experimental results indicate that the flow stress and fracture strain departure from the traditional empirical formula when there are only fewer grains across the thickness. And the number of dimples on the fracture surface is getting smaller with the decreasing ratio of specimen thickness to grain size. Then, a constitutive model based on dislocation density considering the free surface effect in micro-scale is proposed to reveal the mechanism of the flow stress size effect. In addition, a model is proposed considering the surface roughening inducing the thickness nonuniform and the decrease of micro-voids resulting from the reduction of grain boundary density with the decreasing ratio of specimen thickness to grain size. The interactive effects of the surface roughening and the decrease of micro-voids result in the earlier fracture in micro tension of the specimen with fewer grains across the thickness.

  18. Dislocation-Radiation Obstacle Interactions: Developing Improved Mechanical Property Constitutive Models

    SciTech Connect

    Ian Robertson

    2008-10-10

    The objective of this program was to understand the interaction of dislocations with a wide range of obstacles commonly produced in materials under irradiation (dislocation loops, voids, helium bubbles, stacking fault tetrahedra and radiation-induced precipitates). The approach employed in this program combined multi-scale modeling and dynamic in-situ and static ex-situ transmission electron microscopy experiments.

  19. Constitutive Model Modification of Titanium Alloy Ti-6Al-4V Based on Dislocation Pile-up Theory

    NASA Astrophysics Data System (ADS)

    Zhang, Yi-Chuan; Zhou, Tian-Feng; Che, Jiang-Tao; Liang, Zhi-Qiang; Wang, Xi-Bin

    2016-05-01

    Through the Split Hopkinson Pressure Bar (SHPB) test and the quasi-static tensile test on non-standard specimen of titanium alloy Ti-6Al-4V, the rules of the mechanical property changing with the specimen size under different temperatures are summarized, and the parameters of the classical constitutive Johnson-Cook (JC) model are determined. Based on the dislocation pile-up theory, the classical constitutive JC model is modified by considering the influence of grain size, and the modified JC model is established by adding a functional term Δσ into the classical constitutive model to describe the influence of the grain. The tensile testis analyzed by the finite element method (FEM) simulation. Comparing with the experimental results, the simulation results based on the modified JC model show much better accuracy than that by the classical JC model.

  20. Coupling the Phase Field Method for diffusive transformations with dislocation density-based crystal plasticity: Application to Ni-based superalloys

    NASA Astrophysics Data System (ADS)

    Cottura, M.; Appolaire, B.; Finel, A.; Le Bouar, Y.

    2016-09-01

    A phase field model is coupled to strain gradient crystal plasticity based on dislocation densities. The resulting model includes anisotropic plasticity and the size-dependence of plastic activity, required when plasticity is confined in region below few microns in size. These two features are important for handling microstructure evolutions during diffusive phase transformations that involve plastic deformation occurring in confined areas such as Ni-based superalloys undergoing rafting. The model also uses a storage-recovery law for the evolution of the dislocation density of each glide system and a hardening matrix to account for the short-range interactions between dislocations. First, it is shown that the unstable modes during the morphological destabilization of a growing misfitting circular precipitate are selected by the anisotropy of plasticity. Then, the rafting of γ‧ precipitates in a Ni-based superalloy is investigated during [100] creep loadings. Our model includes most of the important physical phenomena accounted for during the microstructure evolution, such as the presence of different crystallographic γ‧ variants, their misfit with the γ matrix, the elastic inhomogeneity and anisotropy, the hardening, anisotropy and viscosity of plasticity. In agreement with experiments, the model predicts that rafting proceeds perpendicularly to the tensile loading axis and it is shown that plasticity slows down significantly the evolution of the rafts.

  1. Dislocation-Based Si-Nanodevices

    NASA Astrophysics Data System (ADS)

    Reiche, Manfred; Kittler, Martin; Buca, Dan; Hähnel, Angelika; Zhao, Qing-Tai; Mantl, Siegfried; Gösele, Ulrich

    2010-04-01

    The realization of defined dislocation networks by hydrophobic wafer bonding allows the electrical characterization of individual dislocations. The present paper investigates the properties of such dislocations in samples containing high dislocations densities down to only six dislocations. The current induced by a single dislocation is determined by extrapolation of the current measured for various dislocation densities. Based on our present and previously reported analyses the electronic properties of individual dislocations can be inferred. The investigations show that dislocations in the channel of metal-oxide-semiconductor field-effect transistors (MOSFETs) result in increasing drain currents even at low drain and gate voltages. Because a maximum increase of the current is obtained if a single dislocation is present in the channel, arrays of MOSFETs each containing only one dislocation could be realized on the nanometer scale. The distance of the dislocations can be well controlled by wafer bonding techniques.

  2. [Elbow dislocation].

    PubMed

    de Pablo Márquez, B; Castillón Bernal, P; Bernaus Johnson, M C; Ibañez Aparicio, N M

    2017-03-09

    Elbow dislocation is the most frequent dislocation in the upper limb after shoulder dislocation. Closed reduction is feasible in outpatient care when there is no associated fracture. A review is presented of the different reduction procedures.

  3. A physically based constitutive model for FCC single crystals with a single state variable per slip system

    NASA Astrophysics Data System (ADS)

    Demir, Eralp

    2017-01-01

    A new, simple and physically consistent dislocation-density-based continuum model is developed in a large-strain crystal plasticity framework. All the constitutive laws are expressed in a simple and unique way in terms of a single state variable dislocation density. The proposed physically based model predicts experimental single-crystal stress-strain curves along different crystal directions more accurately than a classical model with widely accepted constitutive laws. The polycrystal texture predictions from the dislocation-density-based and classical models having the same single-crystal stress-strain characteristics are in good agreement with the classical model when Taylor-type homogenization is used in conjunction with enough number of grains.

  4. Kneecap dislocation

    MedlinePlus

    Use proper techniques when exercising or playing sports. Keep your knee strong and flexible. Some cases of knee dislocation may not be preventable, especially if physical factors make you more likely to dislocate your knee.

  5. Knee Dislocations

    PubMed Central

    Schenck, Robert C.; Richter, Dustin L.; Wascher, Daniel C.

    2014-01-01

    Background: Traumatic knee dislocation is becoming more prevalent because of improved recognition and increased exposure to high-energy trauma, but long-term results are lacking. Purpose: To present 2 cases with minimum 20-year follow-up and a review of the literature to illustrate some of the fundamental principles in the management of the dislocated knee. Study Design: Review and case reports. Methods: Two patients with knee dislocations who underwent multiligamentous knee reconstruction were reviewed, with a minimum 20-year follow-up. These patients were brought back for a clinical evaluation using both subjective and objective measures. Subjective measures include the following scales: Lysholm, Tegner activity, visual analog scale (VAS), Short Form–36 (SF-36), International Knee Documentation Committee (IKDC), and a psychosocial questionnaire. Objective measures included ligamentous examination, radiographic evaluation (including Telos stress radiographs), and physical therapy assessment of function and stability. Results: The mean follow-up was 22 years. One patient had a vascular injury requiring repair prior to ligament reconstruction. The average assessment scores were as follows: SF-36 physical health, 52; SF-36 mental health, 59; Lysholm, 92; IKDC, 86.5; VAS involved, 10.5 mm; and VAS uninvolved, 2.5 mm. Both patients had excellent stability and were functioning at high levels of activity for their age (eg, hiking, skydiving). Both patients had radiographic signs of arthritis, which lowered 1 subject’s IKDC score to “C.” Conclusion: Knee dislocations have rare long-term excellent results, and most intermediate-term studies show fair to good functional results. By following fundamental principles in the management of a dislocated knee, patients can be given the opportunity to function at high levels. Hopefully, continued advances in the evaluation and treatment of knee dislocations will improve the long-term outcomes for these patients in the

  6. Characterization of Geometrically Necessary Dislocation Content with EBSD-Based Continuum Dislocation Microscopy

    NASA Astrophysics Data System (ADS)

    Ruggles, Timothy J.

    Modeling of plasticity is often hampered by the difficulty in accurately characterizing dislocation density on the microscale for real samples. It is particularly difficult to resolve measured dislocation content onto individual dislocation systems at the length scales most commonly of interest in plasticity studies. Traditionally, dislocation content is analyzed at the continuum level using the Nye tensor and the fundamental relation of continuum dislocation theory to interpret information measured by diffraction techniques, typically EBSD or High Resolution EBSD. In this work the established Nye-Kroner method for resolving measured geometrically necessary dislocation content onto individual slip systems is assessed and extended. Two new methods are also presented to relieve the ambiguity of the Nye-Kroner method. One of these methods uses modified classical dislocation equations to bypass the Nye-Kroner relation, and the other estimates the bulk dislocation density via the entry-wise one-norm of the Nye tensor. These methods are validated via a novel simulation of distortion fields around continuum fields of dislocation density based on classical lattice mechanics and then applied to actual HR-EBSD scans of a micro-indented single crystals of nickel and tantalum. Finally, a detailed analysis of the effect of the spacing between points in an EBSD scan (which is related to the step size of the numerical derivatives used in EBSD dislocation microscopy) on geometrically necessary dislocation measurements is conducted.

  7. Simple Elbow Dislocation.

    PubMed

    Armstrong, April

    2015-11-01

    Simple elbow dislocation refers to those elbow dislocations that do not involve an osseous injury. A complex elbow dislocation refers to an elbow that has dislocated with an osseous injury. Most simple elbow dislocations are treated nonoperatively. Understanding the importance of the soft tissue injury following a simple elbow dislocation is a key to being successful with treatment.

  8. Lateral subtalar dislocation.

    PubMed

    Sharda, Praveen; DuFosse, Julian

    2008-07-01

    Subtalar dislocations are rare in routine orthopedic practice. While many of these dislocations are a result of high-energy injuries such as fall from a height or traffic accidents, it is not uncommon for patients to present after slipping down a few stairs. Two types of dislocation have been described, medial and lateral. The type of dislocation is described according to the position of the foot. In lateral subtalar dislocation the head of talus is found medially and the calcaneus is dislocated laterally. The navicular may lie dorsolateral to the talus. The reverse is true of lateral dislocation. Medial dislocation has been referred to as "basketball foot" due to its preponderance in basketball players.4 The deciding factor is the inverted or everted position of the foot when the force is dissipated through the weak talonavicular and talocalcaneal ligaments. This article presents a case of an adult with lateral subtalar dislocation following a fall.

  9. Dislocation motion and instability

    NASA Astrophysics Data System (ADS)

    Zhu, Yichao; Chapman, Stephen Jonathan; Acharya, Amit

    2013-08-01

    The Peach-Koehler expression for the stress generated by a single (non-planar) curvilinear dislocation is evaluated to calculate the dislocation self stress. This is combined with a law of motion to give the self-induced motion of a general dislocation curve. A stability analysis of a rectilinear, uniformly translating dislocation is then performed. The dislocation is found to be susceptible to a helical instability, with the maximum growth rate occurring when the dislocation is almost, but not exactly, pure screw. The non-linear evolution of the instability is determined numerically, and implications for slip band formation and non-Schmid behavior in yielding are discussed.

  10. Continuity of dislocations

    SciTech Connect

    Bloomer, I.; Charap, J.M.

    1985-09-01

    Dislocation continuity is derived from the Bilby--Kondo theory of dislocations using exterior calculus. Dislocation density is represented by the torsion vector-valued two-form. Burgers vectors are associated with the vector part of the torsion while dislocation lines are associated with the two-form part. The exterior derivative of the torsion is shown to vanish when the crystal curvature vanishes. This implies two simultaneous continuity conditions: Burgers vector conservation and continuity of dislocation lines. On the other hand, dislocation continuity is violated when the curvature does not vanish. Since this can occur on grain boundaries it is inferred that grain boundaries are regions where crystal curvature is concentrated.

  11. Dislocation dynamics in hexagonal close-packed crystals

    DOE PAGES

    Aubry, S.; Rhee, M.; Hommes, G.; ...

    2016-04-14

    Extensions of the dislocation dynamics methodology necessary to enable accurate simulations of crystal plasticity in hexagonal close-packed (HCP) metals are presented. They concern the introduction of dislocation motion in HCP crystals through linear and non-linear mobility laws, as well as the treatment of composite dislocation physics. Formation, stability and dissociation of and other dislocations with large Burgers vectors defined as composite dislocations are examined and a new topological operation is proposed to enable their dissociation. Furthermore, the results of our simulations suggest that composite dislocations are omnipresent and may play important roles both in specific dislocation mechanisms and in bulkmore » crystal plasticity in HCP materials. While fully microscopic, our bulk DD simulations provide wealth of data that can be used to develop and parameterize constitutive models of crystal plasticity at the mesoscale.« less

  12. Dislocation dynamics in hexagonal close-packed crystals

    SciTech Connect

    Aubry, S.; Rhee, M.; Hommes, G.; Bulatov, V. V.; Arsenlis, A.

    2016-04-14

    Extensions of the dislocation dynamics methodology necessary to enable accurate simulations of crystal plasticity in hexagonal close-packed (HCP) metals are presented. They concern the introduction of dislocation motion in HCP crystals through linear and non-linear mobility laws, as well as the treatment of composite dislocation physics. Formation, stability and dissociation of and other dislocations with large Burgers vectors defined as composite dislocations are examined and a new topological operation is proposed to enable their dissociation. Furthermore, the results of our simulations suggest that composite dislocations are omnipresent and may play important roles both in specific dislocation mechanisms and in bulk crystal plasticity in HCP materials. While fully microscopic, our bulk DD simulations provide wealth of data that can be used to develop and parameterize constitutive models of crystal plasticity at the mesoscale.

  13. Sports-related shoulder dislocations: a state-hospital experience.

    PubMed

    Hazmy, C H Wan; Parwathi, A

    2005-07-01

    This retrospective study was conducted in a state hospital set-up and aimed at identifying the incidence of sports-related shoulder dislocations and their characteristics and the sports events involved. All patients with shoulder dislocation related to sporting activities admitted to the hospital from January 1999 to December 2002 were included in the study. There were 18 sports-related shoulder dislocations out of 106 all shoulder dislocations admitted during this 4-year period. The average age of the patients was 25.4 years. All but two were male. All were anterior dislocations. Recurrent dislocation constitutes 78% of the cases with an average of 3 times re-dislocation. Rugby and badminton were the major contributors to the injuries followed by volleyball, soccer and swimming. Conservative treatment was successfully instituted for 88% of the patients and 12% opted for surgical intervention.

  14. Dislocation dynamics in hexagonal close-packed crystals

    SciTech Connect

    Aubry, S.; Rhee, M.; Hommes, G.; Bulatov, V. V.; Arsenlis, A.

    2016-04-14

    Extensions of the dislocation dynamics methodology necessary to enable accurate simulations of crystal plasticity in hexagonal close-packed (HCP) metals are presented. They concern the introduction of dislocation motion in HCP crystals through linear and non-linear mobility laws, as well as the treatment of composite dislocation physics. Formation, stability and dissociation of and other dislocations with large Burgers vectors defined as composite dislocations are examined and a new topological operation is proposed to enable their dissociation. Furthermore, the results of our simulations suggest that composite dislocations are omnipresent and may play important roles both in specific dislocation mechanisms and in bulk crystal plasticity in HCP materials. While fully microscopic, our bulk DD simulations provide wealth of data that can be used to develop and parameterize constitutive models of crystal plasticity at the mesoscale.

  15. Anteromedial subtalar dislocation.

    PubMed

    Stafford, Harry; Boggess, Blake; Toth, Alison; Berkoff, David

    2013-01-25

    Subtalar dislocation is the simultaneous dislocation of the talocalcaneal and talonavicular joints of the foot, typically caused by falls from heights, twisting leg injuries and motor vehicle accidents. The dislocation can occur medially, lateral, anterior or posterior, but most commonly occurs from inversion injury producing a medial dislocation. These dislocations may be accompanied by fractures. Careful physical examination must be performed to assess for neurovascular compromise. Most subtalar dislocations can be treated with closed reduction under sedation. However, if the dislocation is associated with an open fracture it may require reduction in the operating room. Treatment should include postreduction plain x-ray and CT scan to evaluate for proper alignment and for fractures. This article presents a case of medial subtalar dislocation in a 23-year-old football player.

  16. 'Inverse' temporomandibular joint dislocation.

    PubMed

    Alemán Navas, R M; Martínez Mendoza, M G

    2011-08-01

    Temporomandibular joint (TMJ) dislocation can be classified into four groups (anterior, posterior, lateral, and superior) depending on the direction of displacement and the location of the condylar head. All the groups are rare except for anterior dislocation. 'Inverse' TMJ dislocation is a bilateral anterior and superior dislocation with impaction of the mandible over the maxilla; to the authors' knowledge only two cases have previously been reported in the literature. Inverse TMJ dislocation has unique clinical and radiographic findings, which are described for this case. Copyright © 2011 International Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.

  17. Pure Intrathoracic Scapular Dislocation.

    PubMed

    Demirkiran, Nihat Demirhan; Kar, Adem

    2016-01-01

    Scapular dislocation, also known as locked scapula or scapulothoracic dislocation, is a rare entity that can be identified as extrathoracic or intrathoracic dislocation, depending on the penetration of the scapula into the thoracic cavity. The 3 reported cases of intrathoracic scapular dislocations in the literature are associated with a preexisting condition, such as sternoclavicular separation, prior rib fracture, thoracotomy for a lung transplant procedure, or surgical resection of superior ribs during breast or pulmonary tumor excisions. There are also 3 published cases of intrathoracic scapular impaction, involving comminuted scapular fractures with intrathoracic impaction of the inferior fragment through intercostal space. We report an intrathoracic scapular dislocation that was not associated with fracture of the scapula or predisposing factors. To our knowledge, this is the first case of pure intrathoracic dislocation.

  18. Traumatic posterior dislocation of hip in children.

    PubMed

    Kutty, S; Thornes, B; Curtin, W A; Gilmore, M F

    2001-02-01

    Traumatic posterior dislocation of the hip joint in children is an uncommon injury. It constitutes a true orthopedic emergency. It makes up over 80% of pediatric hip dislocations. In children, it can occur as a result of minimal trauma, which is attributed to a soft pliable acetabulum and ligamentous laxity. In skeletally mature adolescents, a greater force is required to dislocate the hip joint. Delay in reduction is associated with long-term complications such as avascular necrosis and degenerative arthritis. Avascular necrosis is related to the duration of dislocation. A poorer prognosis is associated with delay in reduction beyond 6 hours, advanced skeletal maturity, or multiple traumas. Prompt reduction minimizes complications. We report two cases of traumatic posterior dislocation of hip in children aged 3 and 14 years. Both were reduced within 6 hours of dislocation, and review at 6 months revealed normal examination and no evidence of any post-traumatic changes. Post-reduction treatment remains without a consensus. This review highlights the clinical presentation, management, and time-sensitive complications of the injury.

  19. Irreducible posterolateral elbow dislocation.

    PubMed

    Atkinson, Cameron T; Pappas, Nick D; Lee, Donald H

    2014-02-01

    Elbow dislocations are a high-energy traumatic event resulting in loss of congruence of a stable joint. The majority of elbow dislocations can be reduced by closed means and treated conservatively. We present a case of an irreducible elbow dislocation with reduction blocked by the radial head buttonholed through the lateral ligamentous complex. We performed open reduction with release followed by repair of the lateral ligamentous complex. Clinicians need to understand this unique variant of an elbow dislocation to appropriately treat this operative injury.

  20. Dislocated shoulder - aftercare

    MedlinePlus

    ... aftercare; Shoulder subluxation - aftercare; Shoulder reduction - aftercare; Glenohumeral joint dislocation ... that connect bone to bone) of the shoulder joint. All of these tissues help keep your arm ...

  1. Bilateral Anterior Shoulder Dislocation

    PubMed Central

    Siu, Yuk Chuen; Lui, Tun Hing

    2014-01-01

    Introduction: Unilateral anterior shoulder dislocation is one of the most common problems encountered in orthopedic practice. However, simultaneous bilateral anterior dislocation of the shoulders is quite rare. Case Presentation: We report a case of a 75-year-old woman presented with simultaneous bilateral anterior shoulder dislocation following a trauma, complicated with a traction injury to the posterior cord of the brachial plexus. Conclusions: Bilateral anterior shoulder dislocation is very rare. The excessive traction force during closed reduction may lead to nerve palsy. Clear documentation of neurovascular status and adequate imaging before and after a reduction should be performed. PMID:25685749

  2. Discrete dislocations in graphene

    NASA Astrophysics Data System (ADS)

    Ariza, M. P.; Ortiz, M.

    2010-05-01

    In this work, we present an application of the theory of discrete dislocations of Ariza and Ortiz (2005) to the analysis of dislocations in graphene. Specifically, we discuss the specialization of the theory to graphene and its further specialization to the force-constant model of Aizawa et al. (1990). The ability of the discrete-dislocation theory to predict dislocation core structures and energies is critically assessed for periodic arrangements of dislocation dipoles and quadrupoles. We show that, with the aid of the discrete Fourier transform, those problems are amenable to exact solution within the discrete-dislocation theory, which confers the theory a distinct advantage over conventional atomistic models. The discrete dislocations exhibit 5-7 ring core structures that are consistent with observation and result in dislocation energies that fall within the range of prediction of other models. The asymptotic behavior of dilute distributions of dislocations is characterized analytically in terms of a discrete prelogarithmic energy tensor. Explicit expressions for this discrete prelogarithmic energy tensor are provided up to quadratures.

  3. Metallurgy: Starting and stopping dislocations

    NASA Astrophysics Data System (ADS)

    Minor, Andrew M.

    2015-09-01

    A comparison of dislocation dynamics in two hexagonal close-packed metals has revealed that dislocation movement can vary substantially in materials with the same crystal structure, associated with how the dislocations relax when stationary.

  4. Traumatic vertical atlantoaxial dislocation.

    PubMed

    Payer, M; Wetzel, S; Kelekis, A; Jenny, B

    2005-08-01

    We present a case of traumatic vertical atlantoaxial dislocation of 16 millimetres with a fatal outcome. We hypothesize that this extremely rare traumatic vertical atlantoaxial dislocation results from insufficiency of the C1/C2 facet capsules after rupture of the tectorial membrane and the alar ligaments.

  5. Traumatic proximal tibiofibular dislocation.

    PubMed

    Burgos, J; Alvarez-Montero, R; Gonzalez-Herranz, P; Rapariz, J M

    1997-01-01

    Proximal tibiofibular dislocation is an exceptional lesion. Rarer still is its presentation in childhood. We describe the clinical case of a 6-year-old boy, the victim of a road accident. He had a tibiofibular dislocation associated with a metaphyseal fracture of the tibia.

  6. Parallel Dislocation Simulator

    SciTech Connect

    2006-10-30

    ParaDiS is software capable of simulating the motion, evolution, and interaction of dislocation networks in single crystals using massively parallel computer architectures. The software is capable of outputting the stress-strain response of a single crystal whose plastic deformation is controlled by the dislocation processes.

  7. Electronic properties of dislocations

    NASA Astrophysics Data System (ADS)

    Reiche, M.; Kittler, M.; Uebensee, H.; Pippel, E.; Haehnel, A.; Birner, S.

    2016-04-01

    Dislocations exhibit a number of exceptional electronic properties resulting in a significant increase in the drain current of MOSFETs if defined numbers of these defects are placed in the channel. Measurements on individual dislocations in Si refer to a supermetallic conductivity. A model of the electronic structure of dislocations is proposed based on experimental measurements and tight-binding simulations. It is shown that the high strain level on the dislocation core—exceeding 10 % or more—causes locally dramatic changes in the band structure and results in the formation of a quantum well along the dislocation line. This explains experimental findings (two-dimensional electron gas, single-electron transitions). The energy quantization within the quantum well is most important for supermetallic conductivity.

  8. Electromechanical simulations of dislocations

    NASA Astrophysics Data System (ADS)

    Skiba, Oxana; Gracie, Robert; Potapenko, Stanislav

    2013-04-01

    Improving the reliability of micro-electronic devices depends in part on developing a more in-depth understanding of dislocations because dislocations are barriers to charge carriers. To this end, the quasi-static simulation of discrete dislocations dynamics in materials under mechanical and electrical loads is presented. The simulations are based on the extended finite element method, where dislocations are modelled as internal discontinuities. The strong and weak forms of the boundary value problem for the coupled system are presented. The computation of the Peach-Koehler force using the J-integral is discussed. Examples to illustrate the accuracy of the simulations are presented. The motion of the network of the dislocations under different electrical and mechanical loads is simulated. It was shown that even in weak piezoelectric materials the effect of the electric field on plastic behaviour is significant.

  9. Crushed Salt Constitutive Model

    SciTech Connect

    Callahan, G.D.

    1999-02-01

    The constitutive model used to describe the deformation of crushed salt is presented in this report. Two mechanisms -- dislocation creep and grain boundary diffusional pressure solution -- are combined to form the basis for the constitutive model governing the deformation of crushed salt. The constitutive model is generalized to represent three-dimensional states of stress. Upon complete consolidation, the crushed-salt model reproduces the Multimechanism Deformation (M-D) model typically used for the Waste Isolation Pilot Plant (WIPP) host geological formation salt. New shear consolidation tests are combined with an existing database that includes hydrostatic consolidation and shear consolidation tests conducted on WIPP and southeastern New Mexico salt. Nonlinear least-squares model fitting to the database produced two sets of material parameter values for the model -- one for the shear consolidation tests and one for a combination of the shear and hydrostatic consolidation tests. Using the parameter values determined from the fitted database, the constitutive model is validated against constant strain-rate tests. Shaft seal problems are analyzed to demonstrate model-predicted consolidation of the shaft seal crushed-salt component. Based on the fitting statistics, the ability of the model to predict the test data, and the ability of the model to predict load paths and test data outside of the fitted database, the model appears to capture the creep consolidation behavior of crushed salt reasonably well.

  10. Bilateral traumatic hip dislocation associated with sacro-iliac dislocation.

    PubMed

    Galois, L; Meuley, E; Pfeffer, F; Mainard, D; Delagoutte, J P

    We report a rare injury in an 18-year-old woman who sustained posterior bilateral hip dislocation with sacro-iliac dislocation after a high energy motor vehicle accident. She was treated by closed reduction and skeletal traction. Bilateral traumatic hip dislocation is an uncommon occurrence. Rarer still is bilateral traumatic hip dislocation associated with sacro-iliac dislocation because it combines two different mechanisms of trauma. (Hip International 2002; 1: 47-9).

  11. Dislocation mean free paths and strain hardening of crystals.

    PubMed

    Devincre, B; Hoc, T; Kubin, L

    2008-06-27

    Predicting the strain hardening properties of crystals constitutes a long-standing challenge for dislocation theory. The main difficulty resides in the integration of dislocation processes through a wide range of time and length scales, up to macroscopic dimensions. In the present multiscale approach, dislocation dynamics simulations are used to establish a dislocation-based continuum model incorporating discrete and intermittent aspects of plastic flow. This is performed through the modeling of a key quantity, the mean free path of dislocations. The model is then integrated at the scale of bulk crystals, which allows for the detailed reproduction of the complex deformation curves of face-centered cubic crystals. Because of its predictive ability, the proposed framework has a large potential for further applications.

  12. Dislocation core reconstruction induced by carbon segregation in bcc iron

    NASA Astrophysics Data System (ADS)

    Ventelon, Lisa; Lüthi, B.; Clouet, E.; Proville, L.; Legrand, B.; Rodney, D.; Willaime, F.

    2015-06-01

    The relative stability of dislocation core configurations in body-centered-cubic metals is profoundly modified by the presence of solutes. Considering the Fe(C) system, we demonstrate by using density functional theory that carbon atoms destabilize the usual easy core to the benefit of the hard core configuration of the screw dislocation, which is unstable in pure metals. The carbon atom is at the center of a regular prism in a cementitelike local environment. The same dislocation core reconstruction is also found with other solutes (B, N, O) and in W(C). This unexpected low-energy configuration induces a strong solute-dislocation attraction, leading to dislocation core saturation by solute atoms, even for very low bulk solute concentrations. This core reconstruction will constitute an essential factor to account for in solute-segregation related phenomena, such as strain aging.

  13. Galeazzi fracture-dislocations.

    PubMed

    Mikić, Z D

    1975-12-01

    Among 125 patients with the Galeazzi-type fracture-dislocation of the forearm, there were fourteen children and eighty-six adults with the classic Galeazzi lesion, and twenty-five patients with a special type -- fracture of both bones and dislocation of the distal radio-ulnar joint. Conservative management was successful only in children. In adults this method resulted in failure in 80 per cent of cases. The results of operative treatment were much better. The fracture fragments of the radius and the dislocation of the radio-ulnar joint in this complex injury are very unstable, especially in the lesion with fractures of the radius and ulna, and it appears that rigid internal fixation is necessary for the dislocation as well as the fracture. With combined fixation over half of the results were excellent.

  14. A Perspective on Dislocation Dynamics

    NASA Astrophysics Data System (ADS)

    Ghoniem, Nasr M.

    A fundamental description of plastic deformation has been recently pursued in many parts of the world as a result of dissatisfaction with the limitations of continuum plasticity theory. Although continuum models of plastic deformation are extensively used in engineering practice, their range of application is limited by the underlying database. The reliability of continuum plasticity descriptions is dependent on the accuracy and range of available experimental data. Under complex loading situations, however, the database is often hard to establish. Moreover, the lack of a characteristic length scale in continuum plasticity makes it difficult to predict the occurrence of critical localized deformation zones. Although homogenization methods have played a significant role in determining the elastic properties of new materials from their constituents (e.g., composite materials), the same methods have failed to describe plasticity. It is widely appreciated that plastic strain is fundamentally heterogenous, displaying high strains concentrated in small material volumes, with virtually undeformed regions in-between. Experimental observations consistently show that plastic deformation is heterogeneous at all length-scales. Depending on the deformation mode, heterogeneous dislocation structures appear with definitive wavelengths. A satisfactory description of realistic dislocation patterning and strain localization has been rather elusive. Attempts aimed at this question have been based on statistical mechanics, reaction-diffusion dynamics, or the theory of phase transitions. Much of the efforts have aimed at clarifying the fundamental origins of inhomogeneous plastic deformation. On the other hand, engineering descriptions of plasticity have relied on experimentally verified constitutive equations.

  15. Ubiquity of quantum zero-point fluctuations in dislocation glide

    NASA Astrophysics Data System (ADS)

    Landeiro Dos Reis, Marie; Choudhury, Anshuman; Proville, Laurent

    2017-03-01

    Modeling the dislocation glide through atomic scale simulations in Al, Cu, and Ni and in solid solution alloys Al(Mg) and Cu(Ag), we show that in the course of the plastic deformation the variation of the crystal zero-point energy (ZPE) and the dislocation potential energy barriers are of opposite sign. The multiplicity of situations where we have observed the same trend allows us to conclude that quantum fluctuations, giving rise to the crystal ZPE, make easier the dislocation glide in most materials, even those constituted of atoms heavier than H and He.

  16. Dislocations in complex materials.

    PubMed

    Chisholm, Matthew F; Kumar, Sharvan; Hazzledine, Peter

    2005-02-04

    Deformation of metals and alloys by dislocations gliding between well-separated slip planes is a well-understood process, but most crystal structures do not possess such simple geometric arrangements. Examples are the Laves phases, the most common class of intermetallic compounds and exist with ordered cubic, hexagonal, and rhombohedral structures. These compounds are usually brittle at low temperatures, and transformation from one structure to another is slow. On the basis of geometric and energetic considerations, a dislocation-based mechanism consisting of two shears in different directions on adjacent atomic planes has been used to explain both deformation and phase transformations in this class of materials. We report direct observations made by Z-contrast atomic resolution microscopy of stacking faults and dislocation cores in the Laves phase Cr2Hf. These results show that this complex dislocation scheme does indeed operate in this material. Knowledge gained of the dislocation core structure will enable improved understanding of deformation mechanisms and phase transformation kinetics in this and other complex structures.

  17. Constitutional Conservatism

    ERIC Educational Resources Information Center

    Berkowitz, Peter

    2009-01-01

    After their dismal performance in election 2008, conservatives are taking stock. As they examine the causes that have driven them into the political wilderness and as they explore paths out, they should also take heart. After all, election 2008 shows that America's constitutional order is working as designed. Indeed, while sorting out their errors…

  18. Modeling of ultrasonic nonlinearities for dislocation evolution in plastically deformed materials: Simulation and experimental validation.

    PubMed

    Zhu, Wujun; Deng, Mingxi; Xiang, Yanxun; Xuan, Fu-Zhen; Liu, Changjun; Wang, Yi-Ning

    2016-05-01

    A nonlinear constitutive relationship was established to investigate nonlinear behaviors of ultrasonic wave propagation in plastically damaged media based on analyses of mixed dislocation evolution. Finite element simulations of longitudinal wave propagation in plastically deformed martensite stainless steel were performed based on the proposed nonlinear constitutive relationship, in which the contribution of mixed dislocation to acoustic nonlinearity was considered. The simulated results were validated by experimental measurements of plastically deformed 30Cr2Ni4MoV martensite stainless steels. Simulated and experimental results both reveal a monotonically increasing tendency of the normalized acoustic nonlinearity parameter as a function of plastic strain. Microscopic studies revealed that the changes of the acoustic nonlinearity are mainly attributed to dislocation evolutions, such as dislocation density, dislocation length, and the type and fraction of dislocations during plastic loading.

  19. Novel density-based and hierarchical density-based clustering algorithms for uncertain data.

    PubMed

    Zhang, Xianchao; Liu, Han; Zhang, Xiaotong

    2017-09-01

    Uncertain data has posed a great challenge to traditional clustering algorithms. Recently, several algorithms have been proposed for clustering uncertain data, and among them density-based techniques seem promising for handling data uncertainty. However, some issues like losing uncertain information, high time complexity and nonadaptive threshold have not been addressed well in the previous density-based algorithm FDBSCAN and hierarchical density-based algorithm FOPTICS. In this paper, we firstly propose a novel density-based algorithm PDBSCAN, which improves the previous FDBSCAN from the following aspects: (1) it employs a more accurate method to compute the probability that the distance between two uncertain objects is less than or equal to a boundary value, instead of the sampling-based method in FDBSCAN; (2) it introduces new definitions of probability neighborhood, support degree, core object probability, direct reachability probability, thus reducing the complexity and solving the issue of nonadaptive threshold (for core object judgement) in FDBSCAN. Then, we modify the algorithm PDBSCAN to an improved version (PDBSCANi), by using a better cluster assignment strategy to ensure that every object will be assigned to the most appropriate cluster, thus solving the issue of nonadaptive threshold (for direct density reachability judgement) in FDBSCAN. Furthermore, as PDBSCAN and PDBSCANi have difficulties for clustering uncertain data with non-uniform cluster density, we propose a novel hierarchical density-based algorithm POPTICS by extending the definitions of PDBSCAN, adding new definitions of fuzzy core distance and fuzzy reachability distance, and employing a new clustering framework. POPTICS can reveal the cluster structures of the datasets with different local densities in different regions better than PDBSCAN and PDBSCANi, and it addresses the issues in FOPTICS. Experimental results demonstrate the superiority of our proposed algorithms over the existing

  20. Dislocation climb models from atomistic scheme to dislocation dynamics

    NASA Astrophysics Data System (ADS)

    Niu, Xiaohua; Luo, Tao; Lu, Jianfeng; Xiang, Yang

    2017-02-01

    We develop a mesoscopic dislocation dynamics model for vacancy-assisted dislocation climb by upscalings from a stochastic model on the atomistic scale. Our models incorporate microscopic mechanisms of (i) bulk diffusion of vacancies, (ii) vacancy exchange dynamics between bulk and dislocation core, (iii) vacancy pipe diffusion along the dislocation core, and (iv) vacancy attachment-detachment kinetics at jogs leading to the motion of jogs. Our mesoscopic model consists of the vacancy bulk diffusion equation and a dislocation climb velocity formula. The effects of these microscopic mechanisms are incorporated by a Robin boundary condition near the dislocations for the bulk diffusion equation and a new contribution in the dislocation climb velocity due to vacancy pipe diffusion driven by the stress variation along the dislocation. Our climb formulation is able to quantitatively describe the translation of prismatic loops at low temperatures when the bulk diffusion is negligible. Using this new formulation, we derive analytical formulas for the climb velocity of a straight edge dislocation and a prismatic circular loop. Our dislocation climb formulation can be implemented in dislocation dynamics simulations to incorporate all the above four microscopic mechanisms of dislocation climb.

  1. Supersonic Dislocation Bursts in Silicon

    DOE PAGES

    Hahn, E. N.; Zhao, S.; Bringa, E. M.; ...

    2016-06-06

    Dislocations are the primary agents of permanent deformation in crystalline solids. Since the theoretical prediction of supersonic dislocations over half a century ago, there is a dearth of experimental evidence supporting their existence. Here we use non-equilibrium molecular dynamics simulations of shocked silicon to reveal transient supersonic partial dislocation motion at approximately 15 km/s, faster than any previous in-silico observation. Homogeneous dislocation nucleation occurs near the shock front and supersonic dislocation motion lasts just fractions of picoseconds before the dislocations catch the shock front and decelerate back to the elastic wave speed. Applying a modified analytical equation for dislocation evolutionmore » we successfully predict a dislocation density of 1.5 x 10(12) cm(-2) within the shocked volume, in agreement with the present simulations and realistic in regards to prior and on-going recovery experiments in silicon.« less

  2. Supersonic Dislocation Bursts in Silicon

    SciTech Connect

    Hahn, E. N.; Zhao, S.; Bringa, E. M.; Meyers, M. A.

    2016-06-06

    Dislocations are the primary agents of permanent deformation in crystalline solids. Since the theoretical prediction of supersonic dislocations over half a century ago, there is a dearth of experimental evidence supporting their existence. Here we use non-equilibrium molecular dynamics simulations of shocked silicon to reveal transient supersonic partial dislocation motion at approximately 15 km/s, faster than any previous in-silico observation. Homogeneous dislocation nucleation occurs near the shock front and supersonic dislocation motion lasts just fractions of picoseconds before the dislocations catch the shock front and decelerate back to the elastic wave speed. Applying a modified analytical equation for dislocation evolution we successfully predict a dislocation density of 1.5 x 10(12) cm(-2) within the shocked volume, in agreement with the present simulations and realistic in regards to prior and on-going recovery experiments in silicon.

  3. Supersonic Dislocation Bursts in Silicon

    NASA Astrophysics Data System (ADS)

    Hahn, E. N.; Zhao, S.; Bringa, E. M.; Meyers, M. A.

    2016-06-01

    Dislocations are the primary agents of permanent deformation in crystalline solids. Since the theoretical prediction of supersonic dislocations over half a century ago, there is a dearth of experimental evidence supporting their existence. Here we use non-equilibrium molecular dynamics simulations of shocked silicon to reveal transient supersonic partial dislocation motion at approximately 15 km/s, faster than any previous in-silico observation. Homogeneous dislocation nucleation occurs near the shock front and supersonic dislocation motion lasts just fractions of picoseconds before the dislocations catch the shock front and decelerate back to the elastic wave speed. Applying a modified analytical equation for dislocation evolution we successfully predict a dislocation density of 1.5 × 1012 cm-2 within the shocked volume, in agreement with the present simulations and realistic in regards to prior and on-going recovery experiments in silicon.

  4. Quantitative calculation of dislocation mobility

    SciTech Connect

    Swaminarayan, S.; Preston, D.L.

    1999-07-01

    The authors present a new method to calculate the response of dislocations to applied stress. This new method, called the dislocation treadmill, can be used to study the effect of vacancies, interstitials, stresses, strain rate, temperature, etc., on the steady state velocity of the dislocation. The authors demonstrate the use of the method by calculating the response of a dislocation to a constant applied shear stress.

  5. Behavior of dislocations in silicon

    SciTech Connect

    Sumino, Koji

    1995-08-01

    A review is given of dynamic behavior of dislocations in silicon on the basis of works of the author`s group. Topics taken up are generation, motion and multiplication of dislocations as affected by oxygen impurities and immobilization of dislocations due to impurity reaction.

  6. Dislocated Worker Project.

    ERIC Educational Resources Information Center

    1988

    Due to the severe economic decline in the automobile manufacturing industry in southeastern Michigan, a Dislocated Workers Program has been developed through the partnership of the Flint Area Chamber of Commerce, three community colleges, the National Center for Research in Vocational Education, the Michigan State Department of Education, the…

  7. Dislocated Worker Project.

    ERIC Educational Resources Information Center

    1988

    Due to the severe economic decline in the automobile manufacturing industry in southeastern Michigan, a Dislocated Workers Program has been developed through the partnership of the Flint Area Chamber of Commerce, three community colleges, the National Center for Research in Vocational Education, the Michigan State Department of Education, the…

  8. Elbow fractures and dislocations.

    PubMed

    Little, Kevin J

    2014-07-01

    Elbow fractures are common in pediatric patients. Most injuries to the pediatric elbow are stable and require simple immobilization; however, more severe fractures can occur, often requiring operative stabilization and/or close monitoring. This article highlights the common fractures and dislocations about the pediatric elbow and discusses the history, evaluation, and treatment options for specific injuries.

  9. Collective behaviour of dislocations in a finite medium

    NASA Astrophysics Data System (ADS)

    Kooiman, M.; Hütter, M.; Geers, M. G. D.

    2014-04-01

    We derive the grand-canonical partition function of straight and parallel dislocation lines without making a priori assumptions on the temperature regime. Such a systematic derivation for dislocations has, to the best of our knowledge, not been carried out before, and several conflicting assumptions on the free energy of dislocations have been made in the literature. Dislocations have gained interest as they are the carriers of plastic deformation in crystalline materials and solid polymers, and they constitute a prototype system for two-dimensional Coulomb particles. Our microscopic starting level is the description of dislocations as used in the discrete dislocation dynamics (DDD) framework. The macroscopic level of interest is characterized by the temperature, the boundary deformation and the dislocation density profile. By integrating over state space, we obtain a field theoretic partition function, which is a functional integral of the Boltzmann weight over an auxiliary field. The Hamiltonian consists of a term quadratic in the field and an exponential of this field. The partition function is strongly non-local, and reduces in special cases to the sine-Gordon model. Moreover, we determine implicit expressions for the response functions and the dominant scaling regime for metals, namely the low-temperature regime.

  10. Phonon Drag Dislocations at High Pressures

    SciTech Connect

    Wolfer, W.G.

    1999-10-19

    Phonon drag on dislocations is the dominant process which determines the flow stress of metals at elevated temperatures and at very high plastic deformation rates. The dependence of the phonon drag on pressure or density is derived using a Mie-Grueneisen equation of state. The phonon drag is shown to increase nearly linearly with temperature but to decrease with density or pressure. Numerical results are presented for its variation for shock-loaded copper and aluminum. In these cases, density and temperature increase simultaneously, resulting in a more modest net increase in the dislocation drag coefficient. Nevertheless, phonon drag increases by more than an order of magnitude during shock deformations which approach melting. Since the dependencies of elastic moduli and of the phonon drag coefficient on pressure and temperature are fundamentally different, the effect of pressure on the constitutive law for plastic deformation can not simply be accounted for by its effect on the elastic shear modulus.

  11. Single crystal plasticity by modeling dislocation density rate behavior

    SciTech Connect

    Hansen, Benjamin L; Bronkhorst, Curt; Beyerlein, Irene; Cerreta, E. K.; Dennis-Koller, Darcie

    2010-12-23

    The goal of this work is to formulate a constitutive model for the deformation of metals over a wide range of strain rates. Damage and failure of materials frequently occurs at a variety of deformation rates within the same sample. The present state of the art in single crystal constitutive models relies on thermally-activated models which are believed to become less reliable for problems exceeding strain rates of 10{sup 4} s{sup -1}. This talk presents work in which we extend the applicability of the single crystal model to the strain rate region where dislocation drag is believed to dominate. The elastic model includes effects from volumetric change and pressure sensitive moduli. The plastic model transitions from the low-rate thermally-activated regime to the high-rate drag dominated regime. The direct use of dislocation density as a state parameter gives a measurable physical mechanism to strain hardening. Dislocation densities are separated according to type and given a systematic set of interactions rates adaptable by type. The form of the constitutive model is motivated by previously published dislocation dynamics work which articulated important behaviors unique to high-rate response in fcc systems. The proposed material model incorporates thermal coupling. The hardening model tracks the varying dislocation population with respect to each slip plane and computes the slip resistance based on those values. Comparisons can be made between the responses of single crystals and polycrystals at a variety of strain rates. The material model is fit to copper.

  12. Tailoring Superconductivity with Quantum Dislocations.

    PubMed

    Li, Mingda; Song, Qichen; Liu, Te-Huan; Meroueh, Laureen; Mahan, Gerald D; Dresselhaus, Mildred S; Chen, Gang

    2017-08-09

    Despite the established knowledge that crystal dislocations can affect a material's superconducting properties, the exact mechanism of the electron-dislocation interaction in a dislocated superconductor has long been missing. Being a type of defect, dislocations are expected to decrease a material's superconducting transition temperature (Tc) by breaking the coherence. Yet experimentally, even in isotropic type I superconductors, dislocations can either decrease, increase, or have little influence on Tc. These experimental findings have yet to be understood. Although the anisotropic pairing in dirty superconductors has explained impurity-induced Tc reduction, no quantitative agreement has been reached in the case a dislocation given its complexity. In this study, by generalizing the one-dimensional quantized dislocation field to three dimensions, we reveal that there are indeed two distinct types of electron-dislocation interactions. Besides the usual electron-dislocation potential scattering, there is another interaction driving an effective attraction between electrons that is caused by dislons, which are quantized modes of a dislocation. The role of dislocations to superconductivity is thus clarified as the competition between the classical and quantum effects, showing excellent agreement with existing experimental data. In particular, the existence of both classical and quantum effects provides a plausible explanation for the illusive origin of dislocation-induced superconductivity in semiconducting PbS/PbTe superlattice nanostructures. A quantitative criterion has been derived, in which a dislocated superconductor with low elastic moduli and small electron effective mass and in a confined environment is inclined to enhance Tc. This provides a new pathway for engineering a material's superconducting properties by using dislocations as an additional degree of freedom.

  13. Neglected isolated scaphoid dislocation

    PubMed Central

    Baek, Jong-Ryoon; Cho, Seung Hyun; Lee, Yong Seuk; Roh, Young Hak

    2016-01-01

    The authors present a case of isolated scaphoid dislocation in a 40-year-old male that was undiagnosed for 2 months. The patient was treated by open reduction, Kirschner wire fixation, interosseous ligament repair using a suture anchor and Blatt's dorsal capsulodesis. At 6 years followup, his radiographs of wrist showed a normal carpal alignment with a scapholunate gap of 3 mm and no evidence of avascular necrosis (AVN) of the scaphoid. PMID:27904228

  14. Solute atmospheres at dislocations

    DOE PAGES

    Hirth, John P.; Barnett, David M.; Hoagland, Richard G.

    2017-06-01

    In this study, a two-dimensional plane strain elastic solution is determined for the Cottrell solute atmosphere around an edge dislocation in an infinitely long cylinder of finite radius (the matrix), in which rows of solutes are represented by cylindrical rods with in-plane hydrostatic misfit (axial misfit is also considered). The periphery of the matrix is traction-free, thus introducing an image solute field which generates a solute-solute interaction energy that has not been considered previously. The relevant energy for the field of any distribution of solutes coexistent with a single edge dislocation along the (matrix) cylinder axis is determined, and coherencymore » effects are discussed and studied. Monte Carlo simulations accounting for all pertinent interactions over a range of temperatures are found to yield solute distributions different from classical results, namely, (1) Fermi-Dirac condensations at low temperatures at the free surface, (2) the majority of the atmosphere lying within an unexpectedly large non-linear interaction region near the dislocation core, and (3) temperature-dependent asymmetrical solute arrangements that promote bending. The solute distributions at intermediate temperatures show a 1/r dependence in agreement with previous linearized approximations. With a standard state of solute corresponding to a mean concentration, c0, the relevant interaction energy expression presented in this work is valid when extended to large concentrations for which Henry's Law and Vegard's Law do not apply.« less

  15. Dislocation Diffusion in Metallic Materials

    DTIC Science & Technology

    2011-09-08

    DATES COVERED (From - To) April 1,2007-March 31, 2010 4. TITLE AND SUBTITLE Dislocation Diffusion in Metallic Materials 5a. CONTRACT NUMBER...SUPPLEMENTARY NOTES 14. ABSTRACT The goals of this project were: (1) perform a fundamental study of atomic diffusion along dislocation cores in metals and...alloys, (2) develop new methods for the calculation of dislocation diffusion coefficients as functions of temperature and chemical composition and (3

  16. [Congenital knee dislocation: case report].

    PubMed

    Arvinius, C; Luque, R; Díaz-Ceacero, C; Marco, F

    2016-01-01

    Congenital knee dislocation is an infrequent condition with unknown etiology. In some cases it occurs as an isolated condition, while in others it coexists with associated conditions or syndromes. The treatment of congenital knee dislocation is driven by the severity and flexibility of the deformity. The literature includes from serial casting or the Pavlik harness to quadriceps tendon plasty or femoral osteotomies. We report herein the case of a congenital dislocation treated with serial casting with a good outcome.

  17. Design rules for dislocation filters

    SciTech Connect

    Ward, T.; Sánchez, A. M.; Beanland, R.; Tang, M.; Wu, J.; Liu, H.; Dunstan, D. J.

    2014-08-14

    The efficacy of strained layer threading dislocation filter structures in single crystal epitaxial layers is evaluated using numerical modeling for (001) face-centred cubic materials, such as GaAs or Si{sub 1−x}Ge{sub x}, and (0001) hexagonal materials such as GaN. We find that threading dislocation densities decay exponentially as a function of the strain relieved, irrespective of the fraction of threading dislocations that are mobile. Reactions between threading dislocations tend to produce a population that is a balanced mixture of mobile and sessile in (001) cubic materials. In contrast, mobile threading dislocations tend to be lost very rapidly in (0001) GaN, often with little or no reduction in the immobile dislocation density. The capture radius for threading dislocation interactions is estimated to be approximately 40 nm using cross section transmission electron microscopy of dislocation filtering structures in GaAs monolithically grown on Si. We find that the minimum threading dislocation density that can be obtained in any given structure is likely to be limited by kinetic effects to approximately 10{sup 4}–10{sup 5 }cm{sup −2}.

  18. Martensitic phase transition involving dislocations

    NASA Astrophysics Data System (ADS)

    Le, K. C.; Günther, C.

    2015-06-01

    A model of solid-solid phase transition involving dislocations in crystals is proposed within the nonlinear continuum dislocation theory (CDT). The co-existence of phases having piecewise constant plastic slip in laminates is possible for the two-well free energy density. The jumps of the plastic slip across the phase interfaces determine the surface dislocation densities at those incoherent boundaries. The number of phase interfaces should be determined by comparing the energy of dislocation arrays and the relaxed energy minimized among uniform plastic slips.

  19. Misfit dislocations in epitaxy

    NASA Astrophysics Data System (ADS)

    van der Merwe, Jan H.

    2002-08-01

    This article on epitaxy highlights the following: the definition and some historical milestones; the introduction by Frenkel and Kontorowa (FK) of a truncated Fourier series to model the periodic interaction at crystalline interfaces; the invention by Frank and van der Merwe (FvdM)—using the FK model—of (interfacial) misfit dislocations as an important mechanism in accommodating misfit at epilayer-substrate interfaces; the generalization of the FvdM theory to multilayers; the application of the parabolic model by Jesser and van der Merwe to describe, for growing multilayers and superlattices, the impact of Fourier coefficients in the realization of epitaxial orientations and the stability of modes of misfit accommodation; the involvement of intralayer interaction in the latter—all features that impact on the attainment of perfection in crystallinity of thin films, a property that is so vital in the fabrication of useful uniformly thick epilayers (uniformity being another technological requirement), which also depends on misfit accommodation through the interfacial energy that function strongly in the criterion for growth modes, proposed by Bauer; and the ingenious application of the Volterra model by Matthews and others to describe misfit accommodation by dislocations in growing epilayers.

  20. Worker Dislocation and Its Consequences.

    ERIC Educational Resources Information Center

    Rosenbaum, Allan; Zirkin, Barbara G.

    A study examined the socioeconomic characteristcs, family and social supportive services, economic and social difficulties, education and training levels, and ways in which dislocated workers in Maryland found reemployment. Data were collected from in-depth personal interviews with 9 dislocated workers, questionnaires administered to 45 unemployed…

  1. What Is a Constitution?

    ERIC Educational Resources Information Center

    OAH Magazine of History, 1988

    1988-01-01

    Provides a lesson plan designed to help students better understand the concept of a constitution, distinguish constitutional law from statutory law, and recognize examples of constitutional government. (BSR)

  2. Galeazzi fractures and dislocations.

    PubMed

    Giannoulis, Filippos S; Sotereanos, Dean G

    2007-05-01

    In 1934, fractures of the middle and distal third of the radius associated with instability of the distal radial ulnar joint (DRUJ) were described by Galeazzi. This type of lesion is characterized by its unstable nature and the need for open reduction and internal fixation to achieve a satisfactory functional outcome. A high index of suspicion should be maintained by the surgeon, and a thorough examination for instability of the DRUJ must be conducted. The marked instability of this fracture-dislocation complex is further enhanced by the disruption of the triangular fibrocartilage complex, either with or without ulna styloid fracture. Treatment in adults is surgical, and both bone and soft tissue injuries should be addressed.

  3. Dislocation dynamics and core structure

    NASA Astrophysics Data System (ADS)

    Lin, Karin Shu

    2000-10-01

    Understanding the dynamics of dislocations is essential to the accurate prediction of the mechanical properties of materials. In recent years, considerable progress has been made in this area through the development of large computer simulations which seek to model plastic deformation by considering the interactions of many dislocations. However, the many-body nature of the problem, as well as the limitations inherent in the elasticity theory used to describe dislocation interactions, requires that such simulations make certain simplifying assumptions. The work reported here seeks to examine some of the issues relevant to these simulations in two ways. First, the dynamics of a single dislocation are studied through the development and analysis of a mesoscopic, two-dimensional kinetic Monte Carlo simulation of dislocation motion. The stress and temperature dependence of the dislocation velocity is studied, and finite-size effects are discussed. Through a simple analogy to models of crystal growth, it is shown that the simulated dislocations exhibit kinetic roughening with scaling exponents predicted by the Kardar-Parisi-Zhang equation. Second, the structure of dislocation cores is studied at the atomic level in diamond cubic materials. These studies are necessary for understanding dislocation properties at small distances, and can provide accurate parameters for use in larger scale continuum simulations. The first study uses periodic supercells and ab initio techniques to compare two possible reconstructions of the 90° partial dislocation core in diamond. The relative energies are found to depend upon the stress field experienced by a dislocation in the periodic array. By fitting the energies to an isotropic elasticity theory expression for the dislocation core energy, values for the core radius and shear modulus of diamond are extracted and found to agree well with theoretical estimates and experimental observations. A similar analysis using empirical potentials

  4. Buckling of dislocation in graphene

    NASA Astrophysics Data System (ADS)

    Yao, Yin; Wang, Shaofeng; Bai, Jianhui; Wang, Rui

    2016-10-01

    The buckling of dislocation in graphene is discussed through the lattice theory of dislocation and elastic theory. The approximate solution of the buckling is obtained based on the inner stress distribution caused by different structure of dislocations and is proved to be suitable by the simulation. The position of the highest buckling is predicted to be at the vertex of the pentagon far away from the heptagon. The buckling is strongly influenced by the internal stress and the distance between the extrusive area and stretching area, as well as the critical stress σc. The SW defect is proved to be unbuckled due to its strong interaction between extrusion and stretching.

  5. Quenched dislocation enhanced supersolid ordering.

    PubMed

    Toner, John

    2008-01-25

    I show using Landau theory that quenched dislocations can facilitate the supersolid to normal solid transition, making it possible for the transition to occur even if it does not in a dislocation-free crystal. I make detailed predictions for the dependence of the supersolid to normal solid transition temperature T_{c}(L), superfluid density rho_{S}(T,L), and specific heat C(T,L) on temperature T and dislocation spacing L, all of which can be tested against experiments. The results should also be applicable to an enormous variety of other systems, including, e.g., ferromagnets.

  6. Management of acute glenohumeral dislocations.

    PubMed

    Sileo, Michael J; Joseph, Samuel; Nelson, Cory O; Nelson, Corey O; Botts, Jonathan D; Penna, James

    2009-06-01

    The glenohumeral joint is the most commonly dislocated joint in the human body. Glenohumeral joint dislocations account for a large number of orthopedic consultations in inpatient and outpatient settings. A thorough workup is required for accurate diagnosis and appropriate treatment of this injury. Complete history and physical examination and radiographic studies are essential, and reduction should always be attempted. In this article, we review the literature for each phase of the workup for glenohumeral dislocation and describe the anatomy, biomechanics, and basic science of the injury. Featured is a detailed synopsis of the more commonly used reduction maneuvers plus their risks and success rates.

  7. Patellar Dislocations and Reduction Procedure.

    PubMed

    Ramponi, Denise

    2016-01-01

    Acute patellar dislocations are a common injury occurring in adolescents involved in sports and dancing activities. This injury usually occurs when the knee is in full extension and sustains a valgus stress on the knee. The medial patellofemoral ligament is the medial restraint that assists in stabilizing the patella from lateral dislocations. The patella usually dislocates laterally and is usually not difficult to reduce after patient evaluation and prereduction radiographs. After postreduction radiographs confirm proper position of the patella postreduction and the absence of fractures, the patient is usually treated conservatively with initial immobilization, orthopedic referral, and physical therapy.

  8. Statistical analysis of dislocations and dislocation boundaries from EBSD data.

    PubMed

    Moussa, C; Bernacki, M; Besnard, R; Bozzolo, N

    2017-08-01

    Electron BackScatter Diffraction (EBSD) is often used for semi-quantitative analysis of dislocations in metals. In general, disorientation is used to assess Geometrically Necessary Dislocations (GNDs) densities. In the present paper, we demonstrate that the use of disorientation can lead to inaccurate results. For example, using the disorientation leads to different GND density in recrystallized grains which cannot be physically justified. The use of disorientation gradients allows accounting for measurement noise and leads to more accurate results. Misorientation gradient is then used to analyze dislocations boundaries following the same principle applied on TEM data before. In previous papers, dislocations boundaries were defined as Geometrically Necessary Boundaries (GNBs) and Incidental Dislocation Boundaries (IDBs). It has been demonstrated in the past, through transmission electron microscopy data, that the probability density distribution of the disorientation of IDBs and GNBs can be described with a linear combination of two Rayleigh functions. Such function can also describe the probability density of disorientation gradient obtained through EBSD data as reported in this paper. This opens the route for determining IDBs and GNBs probability density distribution functions separately from EBSD data, with an increased statistical relevance as compared to TEM data. The method is applied on deformed Tantalum where grains exhibit dislocation boundaries, as observed using electron channeling contrast imaging. Copyright © 2017 Elsevier B.V. All rights reserved.

  9. Atomic-scale investigation of point defects and hydrogen-solute atmospheres on the edge dislocation mobility in alpha iron

    SciTech Connect

    Bhatia, M. A.; Solanki, K. N.; Groh, S.

    2014-08-14

    resistance to dislocation motion as the dislocation moves though the hydrogen-solute atmospheres. With this systematic, atomistic study of the edge dislocation with various point defects, we show significant increase in obstacle strengths in addition to an increase in the local dislocation velocity during interaction with solute atmospheres. The results have implications for constitutive development and modeling of the hydrogen effect on dislocation mobility and deformation in metals.

  10. Atomic-scale investigation of point defects and hydrogen-solute atmospheres on the edge dislocation mobility in alpha iron

    NASA Astrophysics Data System (ADS)

    Bhatia, M. A.; Groh, S.; Solanki, K. N.

    2014-08-01

    to dislocation motion as the dislocation moves though the hydrogen-solute atmospheres. With this systematic, atomistic study of the edge dislocation with various point defects, we show significant increase in obstacle strengths in addition to an increase in the local dislocation velocity during interaction with solute atmospheres. The results have implications for constitutive development and modeling of the hydrogen effect on dislocation mobility and deformation in metals.

  11. Dislocation dynamics and bacterial growth

    NASA Astrophysics Data System (ADS)

    Amir, Ariel; Nelson, David

    2012-02-01

    Recent experiments have revealed remarkable phenomena in the growth mechanisms of rod-shaped bacteria: proteins associated with the cell wall growth move at constant velocity in circles oriented approximately along the cell circumference (Garner et al., Science 2011, Dom'inguez-Escobar et al., Science 2011, Deng et al., PNAS 2011). We view these dislocations in the partially ordered peptidoglycan structure, and study theoretically the dynamics of these interacting dislocations on the surface of a cylinder. The physics of the nucleation of these dislocations and the resulting dynamics within the model show surprising effects arising from the cylindrical geometry, which are predicted to have important implications on the growth mechanism. We also discuss how long range elastic interactions affect the dynamics of the fraction of active dislocations in the environment.

  12. Pediatric complex divergent elbow dislocation.

    PubMed

    van Wagenberg, Jan-Maarten F; van Huijstee, Pieter J; Verhofstad, Michiel H J

    2011-01-01

    A divergent dislocation of the elbow is a very rare injury, and only a few cases have been described in the literature. It is characterized as a dorsal dislocation of the ulnohumeral joint combined with a lateral dislocation of the proximal radius. All three articulations of the elbow joint are involved. Like in our case, it can be accompanied by an avulsion fracture of the coronoid and a distal radius fracture. For correct understanding of the injury, proper radiographic studies are imperative. In contrast to some earlier reports that advise a conservative approach, we performed a very aggressive operative treatment. To ensure anatomic reconstruction of the elbow, surgical exposure of the various injuries was performed first. After gross reduction of the joint dislocation, definitive osteosynthesis of the distal radius fracture was performed. Subsequently, the coronoid process and lateral collateral ligament could be repaired anatomically, improving the stability of the elbow. An uneventful recovery with excellent elbow motion and stability was achieved.

  13. Dislocation mediated alignment during metal nanoparticle coalescence

    DOE PAGES

    Lange, A. P.; Samanta, A.; Majidi, H.; ...

    2016-09-13

    Dislocation mediated alignment processes during gold nanoparticle coalescence were studied at low and high temperatures using molecular dynamics simulations and transmission electron microscopy. Particles underwent rigid body rotations immediately following attachment in both low temperature (500 K) simulated coalescence events and low temperature (~315 K) transmission electron microscopy beam heating experiments. In many low temperature simulations, some degree of misorientation between particles remained after rigid body rotations, which was accommodated by grain boundary dislocation nodes. These dislocations were either sessile and remained at the interface for the duration of the simulation or dissociated and cross-slipped through the adjacent particles, leadingmore » to improved co-alignment. Minimal rigid body rotations were observed during or immediately following attachment in high temperature (1100 K) simulations, which is attributed to enhanced diffusion at the particles' interface. However, rotation was eventually induced by {111} slip on planes parallel to the neck groove. These deformation modes led to the formation of single and multi-fold twins whose structures depended on the initial orientation of the particles. The driving force for {111} slip is attributed to high surface stresses near the intersection of low energy {111} facets in the neck region. The details of this twinning process were examined in detail using simulated trajectories, and the results reveal possible mechanisms for the nucleation and propagation of Shockley partials on consecutive planes. Deformation twinning was also observed in-situ using transmission electron microscopy, which resulted in the co-alignment of a set of the particles' {111} planes across their grain boundary and an increase in their dihedral angle. As a result, this constitutes the first detailed experimental observation of deformation twinning during nanoparticle coalescence, validating simulation results

  14. Dislocation mediated alignment during metal nanoparticle coalescence

    SciTech Connect

    Lange, A. P.; Samanta, A.; Majidi, H.; Mahajan, S.; Ging, J.; Olson, T. Y.; van Benthem, K.; Elhadj, S.

    2016-09-13

    Dislocation mediated alignment processes during gold nanoparticle coalescence were studied at low and high temperatures using molecular dynamics simulations and transmission electron microscopy. Particles underwent rigid body rotations immediately following attachment in both low temperature (500 K) simulated coalescence events and low temperature (~315 K) transmission electron microscopy beam heating experiments. In many low temperature simulations, some degree of misorientation between particles remained after rigid body rotations, which was accommodated by grain boundary dislocation nodes. These dislocations were either sessile and remained at the interface for the duration of the simulation or dissociated and cross-slipped through the adjacent particles, leading to improved co-alignment. Minimal rigid body rotations were observed during or immediately following attachment in high temperature (1100 K) simulations, which is attributed to enhanced diffusion at the particles' interface. However, rotation was eventually induced by {111} slip on planes parallel to the neck groove. These deformation modes led to the formation of single and multi-fold twins whose structures depended on the initial orientation of the particles. The driving force for {111} slip is attributed to high surface stresses near the intersection of low energy {111} facets in the neck region. The details of this twinning process were examined in detail using simulated trajectories, and the results reveal possible mechanisms for the nucleation and propagation of Shockley partials on consecutive planes. Deformation twinning was also observed in-situ using transmission electron microscopy, which resulted in the co-alignment of a set of the particles' {111} planes across their grain boundary and an increase in their dihedral angle. As a result, this constitutes the first detailed experimental observation of deformation twinning during nanoparticle coalescence, validating simulation results

  15. Dislocation mediated alignment during metal nanoparticle coalescence

    SciTech Connect

    Lange, A. P.; Samanta, A.; Majidi, H.; Mahajan, S.; Ging, J.; Olson, T. Y.; van Benthem, K.; Elhadj, S.

    2016-09-13

    Dislocation mediated alignment processes during gold nanoparticle coalescence were studied at low and high temperatures using molecular dynamics simulations and transmission electron microscopy. Particles underwent rigid body rotations immediately following attachment in both low temperature (500 K) simulated coalescence events and low temperature (~315 K) transmission electron microscopy beam heating experiments. In many low temperature simulations, some degree of misorientation between particles remained after rigid body rotations, which was accommodated by grain boundary dislocation nodes. These dislocations were either sessile and remained at the interface for the duration of the simulation or dissociated and cross-slipped through the adjacent particles, leading to improved co-alignment. Minimal rigid body rotations were observed during or immediately following attachment in high temperature (1100 K) simulations, which is attributed to enhanced diffusion at the particles' interface. However, rotation was eventually induced by {111} slip on planes parallel to the neck groove. These deformation modes led to the formation of single and multi-fold twins whose structures depended on the initial orientation of the particles. The driving force for {111} slip is attributed to high surface stresses near the intersection of low energy {111} facets in the neck region. The details of this twinning process were examined in detail using simulated trajectories, and the results reveal possible mechanisms for the nucleation and propagation of Shockley partials on consecutive planes. Deformation twinning was also observed in-situ using transmission electron microscopy, which resulted in the co-alignment of a set of the particles' {111} planes across their grain boundary and an increase in their dihedral angle. As a result, this constitutes the first detailed experimental observation of deformation twinning during nanoparticle coalescence, validating simulation results

  16. Habitual dislocation of patella: A review

    PubMed Central

    Batra, Sumit; Arora, Sumit

    2014-01-01

    Habitual dislocation of patella is a condition where the patella dislocates whenever the knee is flexed and spontaneously relocates with extension of the knee. It is also termed as obligatory dislocation as the patella dislocates completely with each flexion and extension cycle of the knee and the patient has no control over the patella dislocating as he or she moves the knee1. It usually presents after the child starts to walk, and is often well tolerated in children, if it is not painful. However it may present in childhood with dysfunction and instability. Very little literature is available on habitual dislocation of patella as most of the studies have combined cases of recurrent dislocation with habitual dislocation. Many different surgical techniques have been described in the literature for the treatment of habitual dislocation of patella. No single procedure is fully effective in the surgical treatment of habitual dislocation of patella and a combination of procedures is recommended. PMID:25983506

  17. Dislocation sources in ordered intermetallics

    SciTech Connect

    Yoo, M.H.; Appel, F.; Wagner, R.; Mecking, H.

    1996-09-01

    An overview on the current understanding of dislocation sources and multiplication mechanisms is made for ordered intermetallic alloys of the L1{sub 2}, B2, and D0{sub 19} structures. In L1{sub 2} alloys, a large disparity of edge/screw segments in their relative mobility reduces the efficiency of a Frank-Read Type multiplication mechanism. In Fe-40%Al of the B2 structure, a variety of dislocation sources are available for <111> slip, including ones resulting from condensation of thermal vacancies. In NiAl with the relatively high APB energy, <100> dislocations may result from the dislocation decomposition reactions, the prismatic punching out from inclusion particles, and/or steps and coated layers of the surface. Internal interfaces often provide sites for dislocation multiplication, e.g., grain boundaries, sub-boundaries in Ni{sub 3}Ga, NiAl and Ti{sub 3}Al, and antiphase domain boundaries in Ti{sub 3}Al. As for the crack tip as a dislocation source, extended SISFs trailed by super-Shockley partials emanating form the cracks in Ni{sub 3}Al and Co{sub 3}Ti are discussed in view of a possible toughening mechanism.

  18. On the hierarchy of interfacial dislocation structure

    NASA Astrophysics Data System (ADS)

    Balluffi, R. W.; Olson, G. B.

    1985-04-01

    Many different types of dislocations have been defined in dislocation models for grain boundaries and interphase boundaries. It is emphasized that there is no unique dislocation model for a boundary, and that the formal dislocation content depends upon the choice of the lattice correspondence relating the adjoining lattices. However, it is concluded that no problems of real physical significance arise from this lack of uniqueness. “Best≓, or most useful, descriptions often exist, and these are discussed. A hierarchy consisting of four different types of interfacial dislocations may be distinguished, which is useful in describing the dislocation content of interfaces. These entities are termed: (1) primary interfacial dislocations; (2) secondary interfacial dislocations; (3) coherency interfacial dislocations; and (4) translational interfacial dislocations. While there may be a lack of agreement on terminology in the literature, it is believed that these dislocation types are distinguishable and play unique roles in useful dislocation models for interfaces. Detailed descriptions of these dislocation types are given, and actual examples in real interfaces are presented. It is concluded that dislocation descriptions of interface structures become of purely formal significance in the limit of fully incoherent interfaces since the cores are then delocalized. The utility of various dislocation descriptions therefore depends on the degree to which various types of local coherency exist.

  19. Finite element modeling for dislocation generation in semiconductor crystals grown from the melt

    NASA Astrophysics Data System (ADS)

    Zhu, Xinai

    Dislocations in Gallium Arsenide (GaAs) and Indium Phosphide (InP) single crystals are generated by excessive stresses that are induced during the crystal growth process, and the fabrication and packaging of microelectronic devices/circuits. The presence of dislocations has adverse effects on the performance, lifetime and reliability of the GaAs and InP-based devices/circuits. It is well known that dislocation density can be significantly reduced by doping impurity atoms into the GaAs and InP crystal and/or decreasing the thermal stresses in these crystals during their growth process. In order to reduce the dislocation density generated in the GaAs and InP crystals, the influence of crystal growth parameters and doping impurity atoms on the dislocations reduction in GaAs and InP crystals has to be understood. Therefore, a transient finite element model was developed to simulate the dislocation generation in GaAs and InP crystals grown from the melt. A viscoplastic constitutive equation that couples a microscopic dislocation density with a macroscopic plastic deformation is employed to formulate this transient finite element model, where the dislocation density is considered as an internal state variable and the doping impurity is represented by a drag-stress in this constitutive model. GaAs and InP single crystals grown by the vertical gradient freeze (VGF) process were adopted as examples to study the influences of doping impurity and growth parameters on dislocations generated in these grown crystal. The calculated results show that doping impurity can significantly reduce dislocation generation and produces low-dislocation-density or dislocation free GaAs and InP single crystals. It also shows that the dislocations generated in GaAs and InP crystals increase as the crystal diameter and imposed temperature gradient increase, but do not change or increase slightly as the crystal growth rate increases. Therefore, this finite element model can be effectively used by

  20. Discrete dislocation plasticity analysis of the wedge indentation of films

    NASA Astrophysics Data System (ADS)

    Balint, D. S.; Deshpande, V. S.; Needleman, A.; Van der Giessen, E.

    2006-11-01

    The plane strain indentation of single crystal films on a rigid substrate by a rigid wedge indenter is analyzed using discrete dislocation plasticity. The crystals have three slip systems at ±35.3∘ and 90∘ with respect to the indentation direction. The analyses are carried out for three values of the film thickness, 2, 10 and 50 μm, and with the dislocations all of edge character modeled as line singularities in a linear elastic material. The lattice resistance to dislocation motion, dislocation nucleation, dislocation interaction with obstacles and dislocation annihilation are incorporated through a set of constitutive rules. Over the range of indentation depths considered, the indentation pressure for the 10 and 50 μm thick films decreases with increasing contact size and attains a contact size-independent value for contact lengths A>4 μm. On the other hand, for the 2 μm films, the indentation pressure first decreases with increasing contact size and subsequently increases as the plastic zone reaches the rigid substrate. For the 10 and 50 μm thick films sink-in occurs around the indenter, while pile-up occurs in the 2 μm film when the plastic zone reaches the substrate. Comparisons are made with predictions obtained from other formulations: (i) the contact size-independent indentation pressure is compared with that given by continuum crystal plasticity; (ii) the scaling of the indentation pressure with indentation depth is compared with the relation proposed by Nix and Gao [1998. Indentation size effects in crystalline materials: a law for strain gradient plasticity. J. Mech. Phys. Solids 43, 411-423]; and (iii) the computed contact area is compared with that obtained from the estimation procedure of Oliver and Pharr [1992. An improved technique for determining hardness and elastic-modulus using load and displacement sensing indentation experiments, J. Mater. Res. 7, 1564-1583].

  1. Dislocation Multi-junctions and Strain Hardening

    SciTech Connect

    Bulatov, V; Hsiung, L; Tang, M; Arsenlis, A; Bartelt, M; Cai, W; Florando, J; Hiratani, M; Rhee, M; Hommes, G; Pierce, T; Diaz de la Rubia, T

    2006-06-20

    At the microscopic scale, the strength of a crystal derives from the motion, multiplication and interaction of distinctive line defects--dislocations. First theorized in 1934 to explain low magnitudes of crystal strength observed experimentally, the existence of dislocations was confirmed only two decades later. Much of the research in dislocation physics has since focused on dislocation interactions and their role in strain hardening: a common phenomenon in which continued deformation increases a crystal's strength. The existing theory relates strain hardening to pair-wise dislocation reactions in which two intersecting dislocations form junctions tying dislocations together. Here we report that interactions among three dislocations result in the formation of unusual elements of dislocation network topology, termed hereafter multi-junctions. The existence of multi-junctions is first predicted by Dislocation Dynamics (DD) and atomistic simulations and then confirmed by the transmission electron microscopy (TEM) experiments in single crystal molybdenum. In large-scale Dislocation Dynamics simulations, multi-junctions present very strong, nearly indestructible, obstacles to dislocation motion and furnish new sources for dislocation multiplication thereby playing an essential role in the evolution of dislocation microstructure and strength of deforming crystals. Simulation analyses conclude that multi-junctions are responsible for the strong orientation dependence of strain hardening in BCC crystals.

  2. Dislocation multi-junctions and strain hardening.

    PubMed

    Bulatov, Vasily V; Hsiung, Luke L; Tang, Meijie; Arsenlis, Athanasios; Bartelt, Maria C; Cai, Wei; Florando, Jeff N; Hiratani, Masato; Rhee, Moon; Hommes, Gregg; Pierce, Tim G; de la Rubia, Tomas Diaz

    2006-04-27

    At the microscopic scale, the strength of a crystal derives from the motion, multiplication and interaction of distinctive line defects called dislocations. First proposed theoretically in 1934 (refs 1-3) to explain low magnitudes of crystal strength observed experimentally, the existence of dislocations was confirmed two decades later. Much of the research in dislocation physics has since focused on dislocation interactions and their role in strain hardening, a common phenomenon in which continued deformation increases a crystal's strength. The existing theory relates strain hardening to pair-wise dislocation reactions in which two intersecting dislocations form junctions that tie the dislocations together. Here we report that interactions among three dislocations result in the formation of unusual elements of dislocation network topology, termed 'multi-junctions'. We first predict the existence of multi-junctions using dislocation dynamics and atomistic simulations and then confirm their existence by transmission electron microscopy experiments in single-crystal molybdenum. In large-scale dislocation dynamics simulations, multi-junctions present very strong, nearly indestructible, obstacles to dislocation motion and furnish new sources for dislocation multiplication, thereby playing an essential role in the evolution of dislocation microstructure and strength of deforming crystals. Simulation analyses conclude that multi-junctions are responsible for the strong orientation dependence of strain hardening in body-centred cubic crystals.

  3. Dislocations and other topological oddities

    NASA Astrophysics Data System (ADS)

    Pieranski, Pawel

    2016-03-01

    We will show that the book Dislocations by Jacques Friedel, published half a century ago, can still be recommended, in agreement with the author's intention, as a textbook ;for research students at University and for students at engineering schools as well as for research engineers;. Indeed, today dislocations are known to occur not only in solid crystals but also in many other systems discovered more recently such as colloidal crystals or liquid crystals having periodic structures. Moreover, the concept of dislocations is an excellent starting point for lectures on topological defects occurring in systems equipped with order parameters resulting from broken symmetries: disclinations in nematic or hexatic liquid crystals, dispirations in chiral smectics or disorientations in lyotropic liquid crystals. The discussion of dislocations in Blue Phases will give us an opportunity to call on mind Sir Charles Frank, friend of Jacques Friedel since his Bristol years, who called these ephemeral mesophases ;topological oddities;. Being made of networks of disclinations, Blue Phases are similar to Twist Grain Boundary (TGB) smectic phases, which are made of networks of screw dislocations and whose existence was predicted by de Gennes in 1972 on the basis of the analogy between smectics and superconductors. We will stress that the book by Jacques Friedel contains seeds of this analogy.

  4. A continuum theory of edge dislocations

    NASA Astrophysics Data System (ADS)

    Berdichevsky, V. L.

    2017-09-01

    Continuum theory of dislocation aims to describe the behavior of large ensembles of dislocations. This task is far from completion, and, most likely, does not have a ;universal solution;, which is applicable to any dislocation ensemble. In this regards it is important to have guiding lines set by benchmark cases, where the transition from a discrete set of dislocations to a continuum description is made rigorously. Two such cases have been considered recently: equilibrium of dislocation walls and screw dislocations in beams. In this paper one more case is studied, equilibrium of a large set of 2D edge dislocations placed randomly in a 2D bounded region. The major characteristic of interest is energy of dislocation ensemble, because it determines the structure of continuum equations. The homogenized energy functional is obtained for the periodic dislocation ensembles with a random contents of the periodic cell. Parameters of the periodic structure can change slowly on distances of order of the size of periodic cells. The energy functional is obtained by the variational-asymptotic method. Equilibrium positions are local minima of energy. It is confirmed the earlier assertion that energy density of the system is the sum of elastic energy of averaged elastic strains and microstructure energy, which is elastic energy of the neutralized dislocation system, i.e. the dislocation system placed in a constant dislocation density field making the averaged dislocation density zero. The computation of energy is reduced to solution of a variational cell problem. This problem is solved analytically. The solution is used to investigate stability of simple dislocation arrays, i.e. arrays with one dislocation in the periodic cell. The relations obtained yield two outcomes: First, there is a state parameter of the system, dislocation polarization; averaged stresses affect only dislocation polarization and cannot change other characteristics of the system. Second, the structure of

  5. [Radiocarpal dislocation after a trivial injury].

    PubMed

    Jiménez-Jiménez, I J; Caballero-Martel, J R; Ojeda-Castellano, J

    2015-01-01

    Radiocarpal dislocation is an extremely uncommon injury in Traumatology, and is usually produced by high energy trauma. There are two types of dislocation, type I: pure radiocarpal dislocation and type II: fracture-dislocation. The gold standard treatment according to the literature is surgical treatment fixing the fractures and repairing the injured ligaments. We report a clinical case of radiocarpal dislocation type I in a healthy 19 year-old male after a minor trauma. The dislocation was reduced by traction, and the wrist immobilized in a plaster cast. The functional outcome 12 months after the injury was excellent. Copyright © 2013 SECOT. Published by Elsevier Espana. All rights reserved.

  6. Thermal effects in dislocation theory

    NASA Astrophysics Data System (ADS)

    Langer, J. S.

    2016-12-01

    The mechanical behaviors of polycrystalline solids are determined by the interplay between phenomena governed by two different thermodynamic temperatures: the configurational effective temperature that controls the density of dislocations, and the ordinary kinetic-vibrational temperature that controls activated depinning mechanisms and thus deformation rates. This paper contains a review of the effective-temperature theory and its relation to conventional dislocation theories. It includes a simple illustration of how these two thermal effects can combine to produce a predictive theory of spatial heterogeneities such as shear-banding instabilities. Its main message is a plea that conventional dislocation theories be reformulated in a thermodynamically consistent way so that the vast array of observed behaviors can be understood systematically.

  7. Multiscale Theory of Dislocation Climb.

    PubMed

    Geslin, Pierre-Antoine; Appolaire, Benoît; Finel, Alphonse

    2015-12-31

    Dislocation climb is a ubiquitous mechanism playing a major role in the plastic deformation of crystals at high temperature. We propose a multiscale approach to model quantitatively this mechanism at mesoscopic length and time scales. First, we analyze climb at a nanoscopic scale and derive an analytical expression of the climb rate of a jogged dislocation. Next, we deduce from this expression the activation energy of the process, bringing valuable insights to experimental studies. Finally, we show how to rigorously upscale the climb rate to a mesoscopic phase-field model of dislocation climb. This upscaling procedure opens the way to large scale simulations where climb processes are quantitatively reproduced even though the mesoscopic length scale of the simulation is orders of magnitude larger than the atomic one.

  8. The Constitutional Amendment Process

    ERIC Educational Resources Information Center

    Chism, Kahlil

    2005-01-01

    This article discusses the constitutional amendment process. Although the process is not described in great detail, Article V of the United States Constitution allows for and provides instruction on amending the Constitution. While the amendment process currently consists of six steps, the Constitution is nevertheless quite difficult to change.…

  9. The Constitutional Amendment Process

    ERIC Educational Resources Information Center

    Chism, Kahlil

    2005-01-01

    This article discusses the constitutional amendment process. Although the process is not described in great detail, Article V of the United States Constitution allows for and provides instruction on amending the Constitution. While the amendment process currently consists of six steps, the Constitution is nevertheless quite difficult to change.…

  10. The epidemiology of shoulder dislocations in Malaysia.

    PubMed

    Yeap, J S; Lee, D J K; Fazir, M; Borhan, T A Muhd; Kareem, B A

    2004-12-01

    The case notes of 102 patients (117 shoulder dislocations) were reviewed retrospectively to improve the understanding of the epidemiology of this common injury. Eighty-one dislocations were primary and 36 dislocations were second or recurrent dislocations. The age distribution was characterized by a peak in male patients aged between 21-30 years. The mean age for males was 30.5 years and 47.7 years for females. The male:female ratio in first time dislocations was 5:2, while it was 5:1 in recurrent dislocations. Ninety-eight percent were anterior dislocations and 2% were posterior dislocations. Greater tuberosity fractures were found in 17 patients and almost half of these patients were aged between 41-50 years. The most common cause of first time dislocation was a direct blow or fall onto the shoulder, accounting for 42 patients (55%). The majority of these patients were aged 40 years and above. Next common cause was motor vehicle accident which occurred mostly in the younger age group. Dislocations due to sporting injuries accounted for only 5.3% of all first time dislocations. Nearly 97% were successfully reduced without a general anaesthesia. Seventy-seven percent of the patients had their shoulders immobilized after reduction, mostly with body strapping only. Fifteen patients (14.7%) were referred for physiotherapy for stiffness. Few operations were performed for recurrent dislocations but surgery does not appear to be well accepted as yet by our patients.

  11. Boundary dislocation structure of crystalline composites

    SciTech Connect

    Regel', V.A.; Stepantsov, E.A.; Tovmasyan, A.B.

    1986-01-01

    The authors perform the first studies of the dislocation structure of intergrowth boundaries and the adjoining regions in the example of crystalline composites of lithium flouride single crystals. It has been established that the intergrowth boundary of a crystalline composite consists of two dislocation networks: a network of immobile dislocations and the usual subboundary that may shift from its original position.

  12. Ultrasound Characteristics of Clinically Dislocated But Reducible Hips With DDH.

    PubMed

    Striano, Brendan; Schaeffer, Emily K; Matheney, Travis H; Upasani, Vidayadhar V; Price, Charles T; Mulpuri, Kishore; Sankar, Wudbhav N

    2017-07-21

    Although ultrasound (US) is frequently used in diagnosis and management of infantile developmental dysplasia of the hip, precise ultrasonographic parameters of what constitutes a dislocation, subluxation etc remain poorly defined. The purpose of this study was (1) to describe the ultrasonographic characteristics of a large cohort of clinically dislocated but reducible hips and (2) to begin to develop ultrasonographic definitions for what constitutes a hip dislocation. A retrospective review of prospectively collected data from an international multicenter study group on developmental dysplasia of the hip was conducted on all patients under 6 months of age with hip(s) that were dislocated at rest but reducible based on initial physical examination (ie, Ortolani positive). Femoral head coverage (FHC), alpha angle (α), and beta angle (β) were measured on pretreatment US by the individual treating surgeon, and were recorded directly into the database. Based on 325 Ortolani positive hips, the median FHC on presentation was 10% with an interquartile range of 0% to 23%. A total of 126 of the 327 hips (39%) demonstrated 0% FHC. The 90th percentile was found to be at 33% FHC. Of 264 hips with sufficient α data, the median α was 43 degrees with an interquartile range from 37 to 49 degrees. The 90th percentile for α was at 54 degrees. A total of 164 hips had documented β with a median of 66 degrees and an interquartile range of 57 to 79 degrees; the 90th percentile was at 94 degrees. Analysis of a large cohort of patients with dislocated but reducible hips reveals a median percent FHC of 10%, a median α of 43 degrees, and a median β of 66 degrees on initial US. Using a threshold at the 90th percentile, a sensible ultrasonographic definition of a dislocated hip seems to be FHC≤33%, implying that FHC between 34% and 50% may be reasonably termed a subluxation. Although these findings are consistent with previous, smaller reports, further prospective research is

  13. Solute drag on perfect and extended dislocations

    NASA Astrophysics Data System (ADS)

    Sills, R. B.; Cai, W.

    2016-04-01

    The drag force exerted on a moving dislocation by a field of mobile solutes is studied in the steady state. The drag force is numerically calculated as a function of the dislocation velocity for both perfect and extended dislocations. The sensitivity of the non-dimensionalized force-velocity curve to the various controlling parameters is assessed, and an approximate analytical force-velocity expression is given. A non-dimensional parameter S characterizing the strength of the solute-dislocation interaction, the background solute fraction ?, and the dislocation character angle ?, are found to have the strongest influence on the force-velocity curve. Within the model considered here, a perfect screw dislocation experiences no solute drag, but an extended screw dislocation experiences a non-zero drag force that is about 10 to 30% of the drag on an extended edge dislocation. The solutes can change the spacing between the Shockley partials in both stationary and moving extended dislocations, even when the stacking fault energy remains unaltered. Under certain conditions, the solutes destabilize an extended dislocation by either collapsing it into a perfect dislocation or causing the partials to separate unboundedly. It is proposed that the latter instability may lead to the formation of large faulted areas and deformation twins in low stacking fault energy materials containing solutes, consistent with experimental observations of copper and stainless steel containing hydrogen.

  14. Evolution of geometrically necessary dislocation density from computational dislocation dynamics

    NASA Astrophysics Data System (ADS)

    Guruprasad, P. J.; Benzerga, A. A.

    2009-07-01

    This paper presents a method for calculating GND densities in dislocation dynamics simulations. Evolution of suitably defined averages of GND density as well as maps showing the spatial nonuniform distribution of GNDs are analyzed under uniaxial loading. Focus is laid on the resolution dependence of the very notion of GND density, its dependence upon physical dimensions of plastically deformed specimens and its sensitivity to initial conditions. Acknowledgments Support from the National Science Foundation (CMMI-0748187) is gratefully acknowledged.

  15. Theory of interacting dislocations on cylinders.

    PubMed

    Amir, Ariel; Paulose, Jayson; Nelson, David R

    2013-04-01

    We study the mechanics and statistical physics of dislocations interacting on cylinders, motivated by the elongation of rod-shaped bacterial cell walls and cylindrical assemblies of colloidal particles subject to external stresses. The interaction energy and forces between dislocations are solved analytically, and analyzed asymptotically. The results of continuum elastic theory agree well with numerical simulations on finite lattices even for relatively small systems. Isolated dislocations on a cylinder act like grain boundaries. With colloidal crystals in mind, we show that saddle points are created by a Peach-Koehler force on the dislocations in the circumferential direction, causing dislocation pairs to unbind. The thermal nucleation rate of dislocation unbinding is calculated, for an arbitrary mobility tensor and external stress, including the case of a twist-induced Peach-Koehler force along the cylinder axis. Surprisingly rich phenomena arise for dislocations on cylinders, despite their vanishing Gaussian curvature.

  16. Theory of interacting dislocations on cylinders

    NASA Astrophysics Data System (ADS)

    Amir, Ariel; Paulose, Jayson; Nelson, David R.

    2013-04-01

    We study the mechanics and statistical physics of dislocations interacting on cylinders, motivated by the elongation of rod-shaped bacterial cell walls and cylindrical assemblies of colloidal particles subject to external stresses. The interaction energy and forces between dislocations are solved analytically, and analyzed asymptotically. The results of continuum elastic theory agree well with numerical simulations on finite lattices even for relatively small systems. Isolated dislocations on a cylinder act like grain boundaries. With colloidal crystals in mind, we show that saddle points are created by a Peach-Koehler force on the dislocations in the circumferential direction, causing dislocation pairs to unbind. The thermal nucleation rate of dislocation unbinding is calculated, for an arbitrary mobility tensor and external stress, including the case of a twist-induced Peach-Koehler force along the cylinder axis. Surprisingly rich phenomena arise for dislocations on cylinders, despite their vanishing Gaussian curvature.

  17. Dislocation structures and electrical conduction properties of low angle tilt grain boundaries in LiNbO{sub 3}

    SciTech Connect

    Furushima, Yuho; Nakamura, Atsutomo Toyoura, Kazuaki; Tochigi, Eita; Ikuhara, Yuichi; Matsunaga, Katsuyuki

    2016-10-14

    Dislocations in crystalline materials constitute unique, atomic-scale, one-dimensional structure and have a potential to induce peculiar physical properties that are not found in the bulk. In this study, we fabricated LiNbO{sub 3} bicrystals with low angle tilt grain boundaries and investigated the relationship between the atomic structure of the boundary dislocations and their electrical conduction properties. Observations by using transmission electron microscopy revealed that dislocation structures at the (0001) low angle tilt grain boundaries depend on the tilt angle of the boundaries. Specifically, the characteristic dislocation structures with a large Burgers vector were formed in the boundary with the tilt angle of 2°. It is noteworthy that only the grain boundary of 2° exhibits distinct electrical conductivity after reduction treatment, although LiNbO{sub 3} is originally insulating. This unique electrical conductivity is suggested to be due to the characteristic dislocation structures with a large Burgers vector.

  18. Dislocation structures and electrical conduction properties of low angle tilt grain boundaries in LiNbO3

    NASA Astrophysics Data System (ADS)

    Furushima, Yuho; Nakamura, Atsutomo; Tochigi, Eita; Ikuhara, Yuichi; Toyoura, Kazuaki; Matsunaga, Katsuyuki

    2016-10-01

    Dislocations in crystalline materials constitute unique, atomic-scale, one-dimensional structure and have a potential to induce peculiar physical properties that are not found in the bulk. In this study, we fabricated LiNbO3 bicrystals with low angle tilt grain boundaries and investigated the relationship between the atomic structure of the boundary dislocations and their electrical conduction properties. Observations by using transmission electron microscopy revealed that dislocation structures at the (0001) low angle tilt grain boundaries depend on the tilt angle of the boundaries. Specifically, the characteristic dislocation structures with a large Burgers vector were formed in the boundary with the tilt angle of 2°. It is noteworthy that only the grain boundary of 2° exhibits distinct electrical conductivity after reduction treatment, although LiNbO3 is originally insulating. This unique electrical conductivity is suggested to be due to the characteristic dislocation structures with a large Burgers vector.

  19. Simultaneous shoulder and elbow dislocation.

    PubMed

    Cobanoğlu, Mutlu; Yumrukcal, Feridun; Karataş, Cengiz; Duygun, Fatih

    2014-05-23

    Ipsilateral shoulder and elbow dislocation is very rare and only six articles are present in the literature mentioning this kind of a complex injury. With this presentation we aim to emphasise the importance of assessing the adjacent joints in patients with trauma in order not to miss any accompanying pathologies. We report a case of a 43-year-old female patient with ipsilateral right shoulder and elbow dislocation treated conservatively. The patient reported elbow pain when first admitted to emergency service but she was diagnosed with simultaneous ipsilateral shoulder and elbow injury and treated conservatively. As a more painful pathology may mask the additional ones, one should hasten to help before performing a complete evaluation. Any harm caused to the patient due to this reason would not be a complication but a malpractice.

  20. Simultaneous shoulder and elbow dislocation

    PubMed Central

    Çobanoğlu, Mutlu; Yumrukcal, Feridun; Karataş, Cengiz; Duygun, Fatih

    2014-01-01

    Ipsilateral shoulder and elbow dislocation is very rare and only six articles are present in the literature mentioning this kind of a complex injury. With this presentation we aim to emphasise the importance of assessing the adjacent joints in patients with trauma in order not to miss any accompanying pathologies. We report a case of a 43-year-old female patient with ipsilateral right shoulder and elbow dislocation treated conservatively. The patient reported elbow pain when first admitted to emergency service but she was diagnosed with simultaneous ipsilateral shoulder and elbow injury and treated conservatively. As a more painful pathology may mask the additional ones, one should hasten to help before performing a complete evaluation. Any harm caused to the patient due to this reason would not be a complication but a malpractice. PMID:24859563

  1. [Arthrography in congenital hip dislocation].

    PubMed

    Sipukhin, Ia M; Bazlova, E S; Cheberiak, N V

    1992-01-01

    The paper is concerned with the results of contrast arthrography in 73 children with hip joint dysplasia, among which true dislocations prevailed (70 patients). In addition to bone alterations, arthrography revealed various soft tissue changes like hypertrophy and deformity of limbus, soft tissue interposition, separation of the articular sac with the presence of an isthmus, disintegration of articular cartilages. These findings are used to define indications for surgical intervention as well as for planning the area of operation.

  2. Three-dimensional formulation of dislocation climb

    NASA Astrophysics Data System (ADS)

    Gu, Yejun; Xiang, Yang; Quek, Siu Sin; Srolovitz, David J.

    2015-10-01

    We derive a Green's function formulation for the climb of curved dislocations and multiple dislocations in three-dimensions. In this new dislocation climb formulation, the dislocation climb velocity is determined from the Peach-Koehler force on dislocations through vacancy diffusion in a non-local manner. The long-range contribution to the dislocation climb velocity is associated with vacancy diffusion rather than from the climb component of the well-known, long-range elastic effects captured in the Peach-Koehler force. Both long-range effects are important in determining the climb velocity of dislocations. Analytical and numerical examples show that the widely used local climb formula, based on straight infinite dislocations, is not generally applicable, except for a small set of special cases. We also present a numerical discretization method of this Green's function formulation appropriate for implementation in discrete dislocation dynamics (DDD) simulations. In DDD implementations, the long-range Peach-Koehler force is calculated as is commonly done, then a linear system is solved for the climb velocity using these forces. This is also done within the same order of computational cost as existing discrete dislocation dynamics methods.

  3. Contesting the Constitution: The Constitutional Dialogues.

    ERIC Educational Resources Information Center

    Hilenski, Ferdinand Alexi

    This historical dramatization, prepared for presentation at the 1985 Wyoming Chatauqua, contains three dialogues, set during the administration of President Thomas Jefferson and presenting the issues surrounding the drafting and ratification of the U.S. Constitution. The dialogues are designed to be presented in three segments to permit discussion…

  4. Contesting the Constitution: The Constitutional Dialogues.

    ERIC Educational Resources Information Center

    Hilenski, Ferdinand Alexi

    This historical dramatization, prepared for presentation at the 1985 Wyoming Chatauqua, contains three dialogues, set during the administration of President Thomas Jefferson and presenting the issues surrounding the drafting and ratification of the U.S. Constitution. The dialogues are designed to be presented in three segments to permit discussion…

  5. Scalable Parallel Density-based Clustering and Applications

    NASA Astrophysics Data System (ADS)

    Patwary, Mostofa Ali

    2014-04-01

    Recently, density-based clustering algorithms (DBSCAN and OPTICS) have gotten significant attention of the scientific community due to their unique capability of discovering arbitrary shaped clusters and eliminating noise data. These algorithms have several applications, which require high performance computing, including finding halos and subhalos (clusters) from massive cosmology data in astrophysics, analyzing satellite images, X-ray crystallography, and anomaly detection. However, parallelization of these algorithms are extremely challenging as they exhibit inherent sequential data access order, unbalanced workload resulting in low parallel efficiency. To break the data access sequentiality and to achieve high parallelism, we develop new parallel algorithms, both for DBSCAN and OPTICS, designed using graph algorithmic techniques. For example, our parallel DBSCAN algorithm exploits the similarities between DBSCAN and computing connected components. Using datasets containing up to a billion floating point numbers, we show that our parallel density-based clustering algorithms significantly outperform the existing algorithms, achieving speedups up to 27.5 on 40 cores on shared memory architecture and speedups up to 5,765 using 8,192 cores on distributed memory architecture. In our experiments, we found that while achieving the scalability, our algorithms produce clustering results with comparable quality to the classical algorithms.

  6. Mobility Laws in Dislocation Dynamics Simulations

    SciTech Connect

    Cai, W; Bulatov, V V

    2003-10-21

    Prediction of the plastic deformation behavior of single crystals based on the collective dynamics of dislocations has been a challenge for computational materials science for a number of years. The difficulty lies in the inability of existing dislocation dynamics (DD) codes to handle a sufficiently large number of dislocation lines, to establish a statistically representative model of crystal plasticity. A new massively-parallel DD code is developed that is capable of modeling million-dislocation systems by employing thousands of processors. We discuss an important ingredient of this code--the mobility laws dictating the behavior of individual dislocations. They are materials input for DD simulations and are constructed based on the understanding of dislocation motion at the atomistic level.

  7. Effects of dislocations on electron channeling.

    PubMed

    George, Juby; Pathak, A P

    2009-02-18

    The phenomenon of electron channeling in a crystal affected by dislocations is considered. Earlier we had considered the quantum aspects of the positron channeling in a crystal bent by dislocations where the effects of longitudinal motion of the particle were also considered along with the transverse motion. In this paper, the effective potential for the electron case is found for the two regions of dislocation-affected channel. There is considerable shift in the potential minima due to dislocations. The frequency and the corresponding spectrum of the channeling radiation due to electrons channeling through the perfect channel and the two regions of dislocation-affected channels are calculated. The spectral distribution of radiation intensity changes with the parameters of dislocation. The continuity of wavefunctions and their derivatives is used at the three boundaries and the reflection and transmission coefficients are found using these boundary conditions in the same way as in the positron case.

  8. On the Connection Between the Discrete Dislocation Slip Model and the Orowan Equation

    SciTech Connect

    BRAGINSKY, MICHAEL V.; GLAZOV, MICHAEL V.; RICHMOND, OWEN

    1999-09-08

    Within the framework of thermodynamic theory of plasticity and specific structural-variables (associated with individual dislocations), a transition has been made to an expression containing one internal variable of the averaging type--the density of glissile dislocations, N{sub g}. This expression should be considered a tensorial generalization of the well-known Orowan's equation and relates it directly to the simplest possible case of normal flow in metallic materials. Since most metals display deviations from normality in the flow rule{sup 7} it also clearly indicates that more rigorous assessment of the relation between plastic strain rate and dislocation populations is required especially for materials displaying plastic instabilities in the form of dislocation patterning, strain-softening and strain-rate softening phenomena. The obtained result could be a useful starting point in establishing such rigorous macroscopic relations from microscopic considerations associated with individual dislocations and to find useful applications in dislocation density-related constitutive modeling of plastic deformation.

  9. Binary dislocation junction formation and strength in hexagonal close-packed crystals

    DOE PAGES

    Wu, Chi -Chin; Aubry, Sylvie; Arsenlis, Athanasios; ...

    2015-12-17

    This work examines binary dislocation interactions, junction formation and junction strengths in hexagonal close-packed (hcp ) crystals. Through a line-tension model and dislocation dynamics (DD) simulations, the interaction and dissociation of different sets of binary junctions are investigated involving one dislocation on the (011¯0) prismatic plane and a second dislocation on one of the following planes: (0001) basal, (11¯00) prismatic, (11¯01) primary pyramidal, or (2¯112) secondary pyramidal. Varying pairs of Burgers vectors are chosen from among the common types the basal type < a > 1/3 < 112¯0 >, prismatic type < c > <0001>, and pyramidal type < a+cmore » > 1/3 < 112¯3¯ >. For binary interaction due to dislocation intersection, both the analytical results and DD-simulations indicate a relationship between symmetry of interaction maps and the relative magnitude of the Burgers vectors that constitute the junction. Using analytical formulae, a simple regressive model is also developed to represent the junction yield surface. The equation is treated as a degenerated super elliptical equation to quantify the aspect ratio and tilting angle. Lastly, the results provide analytical insights on binary dislocation interactions that may occur in general hcp metals.« less

  10. Binary dislocation junction formation and strength in hexagonal close-packed crystals

    SciTech Connect

    Wu, Chi -Chin; Aubry, Sylvie; Arsenlis, Athanasios; Chung, Peter C.

    2015-12-17

    This work examines binary dislocation interactions, junction formation and junction strengths in hexagonal close-packed (hcp ) crystals. Through a line-tension model and dislocation dynamics (DD) simulations, the interaction and dissociation of different sets of binary junctions are investigated involving one dislocation on the (011¯0) prismatic plane and a second dislocation on one of the following planes: (0001) basal, (11¯00) prismatic, (11¯01) primary pyramidal, or (2¯112) secondary pyramidal. Varying pairs of Burgers vectors are chosen from among the common types the basal type < a > 1/3 < 112¯0 >, prismatic type < c > <0001>, and pyramidal type < a+c > 1/3 < 112¯3¯ >. For binary interaction due to dislocation intersection, both the analytical results and DD-simulations indicate a relationship between symmetry of interaction maps and the relative magnitude of the Burgers vectors that constitute the junction. Using analytical formulae, a simple regressive model is also developed to represent the junction yield surface. The equation is treated as a degenerated super elliptical equation to quantify the aspect ratio and tilting angle. Lastly, the results provide analytical insights on binary dislocation interactions that may occur in general hcp metals.

  11. Crushed-salt constitutive model update

    SciTech Connect

    Callahan, G.D.; Loken, M.C.; Mellegard, K.D.

    1998-01-01

    Modifications to the constitutive model used to describe the deformation of crushed salt are presented in this report. Two mechanisms--dislocation creep and grain boundary diffusional pressure solutioning--defined previously but used separately are combined to form the basis for the constitutive model governing the deformation of crushed salt. The constitutive model is generalized to represent three-dimensional states of stress. New creep consolidation tests are combined with an existing database that includes hydrostatic consolidation and shear consolidation tests conducted on Waste Isolation Pilot Plant and southeastern New Mexico salt to determine material parameters for the constitutive model. Nonlinear least-squares model fitting to data from the shear consolidation tests and a combination of the shear and hydrostatic consolidation tests produced two sets of material parameter values for the model. The change in material parameter values from test group to test group indicates the empirical nature of the model but demonstrates improvement over earlier work with the previous models. Key improvements are the ability to capture lateral strain reversal and better resolve parameter values. To demonstrate the predictive capability of the model, each parameter value set was used to predict each of the tests in the database. Based on the fitting statistics and the ability of the model to predict the test data, the model appears to capture the creep consolidation behavior of crushed salt quite well.

  12. Factors predisposing to dislocation of the Thompson hemiarthroplasty: 22 dislocations in 338 patients.

    PubMed

    Pajarinen, Jarkko; Savolainen, Vesa; Tulikoura, Ilkka; Lindahl, Jan; Hirvensalo, Eero

    2003-02-01

    In a series of 338 patients, we have retrospectively analyzed technical and anatomical factors, which may predispose to a dislocation of the Thompson hemiprosthesis. 22 patients (7%) had at least 1 dislocation during the 6-month follow-up. The most significant independent factor predisposing to dislocation was the use of a posterior approach (dislocation rate 16%). We examined the radiographs and data on operations in the 22 patients, using 79 random patients without dislocation as controls. Factors correlating with an increase in the incidence of dislocation were the length of the residual femoral neck > 0.5 cm in short patients (< 165 cm), and considerable change in the postoperative offset of the hip. Acetabular measurements showed no correlation to the dislocation. Our findings suggest that the main factors predicting dislocation are technical and not related to anatomical measurements.

  13. Worker Dislocation. Case Studies of Causes and Cures.

    ERIC Educational Resources Information Center

    Cook, Robert F., Ed.

    Case studies were made of the following dislocated worker programs: Cummins Engine Company Dislocated Worker Project; GM-UAW Metropolitan Pontiac Retraining and Employment Program; Minnesota Iron Range Dislocated Worker Project; Missouri Dislocated Worker Program Job Search Assistance, Inc.; Hillsborough, North Carolina, Dislocated Worker Project;…

  14. Elbow dislocation with ipsilateral distal radius fracture

    PubMed Central

    Meena, Sanjay; Trikha, Vivek; Kumar, Rakesh; Saini, Pramod; Sambharia, Abhishek Kumar

    2013-01-01

    Elbow dislocation associated with ipsilateral distal radius fracture is a rare pattern of injury, although it is common for elbow dislocation and forearm fractures to occur separately. We report a rare case of a 20-year-old male who had a posterior elbow dislocation and ipsilateral distal radius fracture. Elbow dislocation was first reduced in extension and distal radius fracture was then reduced in flexion. Both the injuries were conservatively managed. At 6 months follow-up, the patient had no pain in his elbow and minimal pain in his wrist on heavy lifting and had resumed his work as a laborer. PMID:24082758

  15. Elbow dislocation with ipsilateral distal radius fracture.

    PubMed

    Meena, Sanjay; Trikha, Vivek; Kumar, Rakesh; Saini, Pramod; Sambharia, Abhishek Kumar

    2013-07-01

    Elbow dislocation associated with ipsilateral distal radius fracture is a rare pattern of injury, although it is common for elbow dislocation and forearm fractures to occur separately. We report a rare case of a 20-year-old male who had a posterior elbow dislocation and ipsilateral distal radius fracture. Elbow dislocation was first reduced in extension and distal radius fracture was then reduced in flexion. Both the injuries were conservatively managed. At 6 months follow-up, the patient had no pain in his elbow and minimal pain in his wrist on heavy lifting and had resumed his work as a laborer.

  16. Enabling Strain Hardening Simulations with Dislocation Dynamics

    SciTech Connect

    Arsenlis, A; Cai, W

    2006-12-20

    Numerical algorithms for discrete dislocation dynamics simulations are investigated for the purpose of enabling strain hardening simulations of single crystals on massively parallel computers. The algorithms investigated include the /(N) calculation of forces, the equations of motion, time integration, adaptive mesh refinement, the treatment of dislocation core reactions, and the dynamic distribution of work on parallel computers. A simulation integrating all of these algorithmic elements using the Parallel Dislocation Simulator (ParaDiS) code is performed to understand their behavior in concert, and evaluate the overall numerical performance of dislocation dynamics simulations and their ability to accumulate percents of plastic strain.

  17. Congenital dislocation of the patella - clinical case.

    PubMed

    Miguel Sá, Pedro; Raposo, Filipa; Santos Carvalho, Manuel; Alegrete, Nuno; Coutinho, Jorge; Costa, Gilberto

    2016-01-01

    Congenital patellar dislocation is a rare condition in which the patella is permanently dislocated and cannot be reduced manually. The patella develops normally as a sesamoid bone of the femur. This congenital dislocation results from failure of the internal rotation of the myotome that forms the femur, quadriceps muscle and extensor apparatus. It usually manifests immediately after birth, although in some rare cases, the diagnosis may be delayed until adolescence or adulthood. Early diagnosis is important, thereby allowing surgical correction and avoiding late sequelae, including early degenerative changes in the knee. A case of permanent dislocation of the patella is presented here, in a female child aged seven years.

  18. Microdiffraction Analysis of Hierarchical Dislocation Organization

    SciTech Connect

    Barabash, R.I.; Ice, G.E.

    2007-12-19

    This article describes how x-ray microdiffraction is influenced by the number, kind, and organization of dislocations. Particular attention is placed on micro-Laue diffraction, where polychromatic x-rays are diffracted into characteristic Laue patterns that are sensitive to the dislocation content and arrangement. Diffraction is considered for various stages of plastic deformation. For early stages of plastic deformation with random dislocation spacing, the intensity in reciprocal space is redistributed about Laue spots with a length scale proportional to the number of dislocations within the sample volume and with a characteristic shape that depends on the kinds of dislocations and the momentum transfer vector. Unpaired dislocations that contribute to lattice rotations cause the largest redistribution of scattered intensity. In later stages of plastic deformation, strong interactions between individual dislocations cause them to organize into correlated arrangements. Here again, xray diffraction Laue spots are broadened in proportion to the number of excess (unpaired) dislocations inside the wall and to the total number of unpaired walls, but the broadening can be discontinuous. With microdiffraction it is possible to quantitatively test models of dislocation organization.

  19. Massively-Parallel Dislocation Dynamics Simulations

    SciTech Connect

    Cai, W; Bulatov, V V; Pierce, T G; Hiratani, M; Rhee, M; Bartelt, M; Tang, M

    2003-06-18

    Prediction of the plastic strength of single crystals based on the collective dynamics of dislocations has been a challenge for computational materials science for a number of years. The difficulty lies in the inability of the existing dislocation dynamics (DD) codes to handle a sufficiently large number of dislocation lines, in order to be statistically representative and to reproduce experimentally observed microstructures. A new massively-parallel DD code is developed that is capable of modeling million-dislocation systems by employing thousands of processors. We discuss the general aspects of this code that make such large scale simulations possible, as well as a few initial simulation results.

  20. Density-Based Penalty Parameter Optimization on C-SVM

    PubMed Central

    Liu, Yun; Lian, Jie; Bartolacci, Michael R.; Zeng, Qing-An

    2014-01-01

    The support vector machine (SVM) is one of the most widely used approaches for data classification and regression. SVM achieves the largest distance between the positive and negative support vectors, which neglects the remote instances away from the SVM interface. In order to avoid a position change of the SVM interface as the result of an error system outlier, C-SVM was implemented to decrease the influences of the system's outliers. Traditional C-SVM holds a uniform parameter C for both positive and negative instances; however, according to the different number proportions and the data distribution, positive and negative instances should be set with different weights for the penalty parameter of the error terms. Therefore, in this paper, we propose density-based penalty parameter optimization of C-SVM. The experiential results indicated that our proposed algorithm has outstanding performance with respect to both precision and recall. PMID:25114978

  1. Density-based penalty parameter optimization on C-SVM.

    PubMed

    Liu, Yun; Lian, Jie; Bartolacci, Michael R; Zeng, Qing-An

    2014-01-01

    The support vector machine (SVM) is one of the most widely used approaches for data classification and regression. SVM achieves the largest distance between the positive and negative support vectors, which neglects the remote instances away from the SVM interface. In order to avoid a position change of the SVM interface as the result of an error system outlier, C-SVM was implemented to decrease the influences of the system's outliers. Traditional C-SVM holds a uniform parameter C for both positive and negative instances; however, according to the different number proportions and the data distribution, positive and negative instances should be set with different weights for the penalty parameter of the error terms. Therefore, in this paper, we propose density-based penalty parameter optimization of C-SVM. The experiential results indicated that our proposed algorithm has outstanding performance with respect to both precision and recall.

  2. Parallel Density-Based Clustering for Discovery of Ionospheric Phenomena

    NASA Astrophysics Data System (ADS)

    Pankratius, V.; Gowanlock, M.; Blair, D. M.

    2015-12-01

    Ionospheric total electron content maps derived from global networks of dual-frequency GPS receivers can reveal a plethora of ionospheric features in real-time and are key to space weather studies and natural hazard monitoring. However, growing data volumes from expanding sensor networks are making manual exploratory studies challenging. As the community is heading towards Big Data ionospheric science, automation and Computer-Aided Discovery become indispensable tools for scientists. One problem of machine learning methods is that they require domain-specific adaptations in order to be effective and useful for scientists. Addressing this problem, our Computer-Aided Discovery approach allows scientists to express various physical models as well as perturbation ranges for parameters. The search space is explored through an automated system and parallel processing of batched workloads, which finds corresponding matches and similarities in empirical data. We discuss density-based clustering as a particular method we employ in this process. Specifically, we adapt Density-Based Spatial Clustering of Applications with Noise (DBSCAN). This algorithm groups geospatial data points based on density. Clusters of points can be of arbitrary shape, and the number of clusters is not predetermined by the algorithm; only two input parameters need to be specified: (1) a distance threshold, (2) a minimum number of points within that threshold. We discuss an implementation of DBSCAN for batched workloads that is amenable to parallelization on manycore architectures such as Intel's Xeon Phi accelerator with 60+ general-purpose cores. This manycore parallelization can cluster large volumes of ionospheric total electronic content data quickly. Potential applications for cluster detection include the visualization, tracing, and examination of traveling ionospheric disturbances or other propagating phenomena. Acknowledgments. We acknowledge support from NSF ACI-1442997 (PI V. Pankratius).

  3. Interpreting the Constitution.

    ERIC Educational Resources Information Center

    Brennan, William J., Jr.

    1987-01-01

    Discusses constitutional interpretations relating to capital punishment and protection of human dignity. Points out the document's effectiveness in creating a new society by adapting its principles to current problems and needs. Considers two views of the Constitution that lead to controversy over the legitimacy of judicial decisions. (PS)

  4. Constitutional Issues and Iowa.

    ERIC Educational Resources Information Center

    Gore, Deborah, Ed.

    1987-01-01

    Important constitutional issues are presented in a manner appropriate for use in the classroom. Case studies and events from the history of Iowa are used to illuminate the Constitution and Bill of Rights. Freedom of expression and students' rights are discussed in "The Black Armband Case"; free exercise of religion as won by the Iowa's…

  5. The Constitution by Cell

    ERIC Educational Resources Information Center

    Greenhut, Stephanie; Jones, Megan

    2010-01-01

    On their visit to the National Archives Experience in Washington, D.C., students in Jenni Ashley and Gay Brock's U.S. history classes at the Potomac School in McLean, Virginia, participated in a pilot program called "The Constitution by Cell." Armed with their cell phones, a basic understanding of the Constitution, and a willingness to…

  6. Teaching About the Constitution.

    ERIC Educational Resources Information Center

    White, Charles S.

    1988-01-01

    Reviews "The U.S. Constitution Then and Now," a two-unit program using the integrated database and word processing capabilities of AppleWorks. For grades 7-12, the units simulate the constitutional convention and the principles of free speech and privacy. Concludes that with adequate time, the program can provide a potentially powerful…

  7. Interpreting the Constitution.

    ERIC Educational Resources Information Center

    Brennan, William J., Jr.

    1987-01-01

    Discusses constitutional interpretations relating to capital punishment and protection of human dignity. Points out the document's effectiveness in creating a new society by adapting its principles to current problems and needs. Considers two views of the Constitution that lead to controversy over the legitimacy of judicial decisions. (PS)

  8. The Constitution by Cell

    ERIC Educational Resources Information Center

    Greenhut, Stephanie; Jones, Megan

    2010-01-01

    On their visit to the National Archives Experience in Washington, D.C., students in Jenni Ashley and Gay Brock's U.S. history classes at the Potomac School in McLean, Virginia, participated in a pilot program called "The Constitution by Cell." Armed with their cell phones, a basic understanding of the Constitution, and a willingness to…

  9. Multiscale modeling of dislocation-precipitate interactions in Fe: From molecular dynamics to discrete dislocations.

    PubMed

    Lehtinen, Arttu; Granberg, Fredric; Laurson, Lasse; Nordlund, Kai; Alava, Mikko J

    2016-01-01

    The stress-driven motion of dislocations in crystalline solids, and thus the ensuing plastic deformation process, is greatly influenced by the presence or absence of various pointlike defects such as precipitates or solute atoms. These defects act as obstacles for dislocation motion and hence affect the mechanical properties of the material. Here we combine molecular dynamics studies with three-dimensional discrete dislocation dynamics simulations in order to model the interaction between different kinds of precipitates and a 1/2〈111〉{110} edge dislocation in BCC iron. We have implemented immobile spherical precipitates into the ParaDis discrete dislocation dynamics code, with the dislocations interacting with the precipitates via a Gaussian potential, generating a normal force acting on the dislocation segments. The parameters used in the discrete dislocation dynamics simulations for the precipitate potential, the dislocation mobility, shear modulus, and dislocation core energy are obtained from molecular dynamics simulations. We compare the critical stresses needed to unpin the dislocation from the precipitate in molecular dynamics and discrete dislocation dynamics simulations in order to fit the two methods together and discuss the variety of the relevant pinning and depinning mechanisms.

  10. Dislocations

    MedlinePlus

    ... sure kids wear the appropriate safety gear during sports activities. Supervise children when they're playing — a hard fall can happen anywhere, anytime. Avoid tugging hard on a young child's arm or shoulder, which can cause injury or ...

  11. Quantum dislocations in solid Helium-4

    NASA Astrophysics Data System (ADS)

    Aleinikava, Darya

    In this thesis the following problems on properties of solid 4He are considered: (i) the role of long-range interactions in suppression of dislocation roughening at T = 0; (ii) the combined effect of 3He impurities and Peierls potential on shear modulus softening; (iii) the dislocation superclimb and its connection to the phenomenon of "giant isochoric compressibility"; (iv) non-linear dislocation response to the applied stress and stress-induces dislocation roughening as a I-order phase transition in 1D at finite temperature. First we investigate the effect of long-range interactions on the state of edge dislocation at T = 0. Such interactions are induced by elastic forces of the solid. We found that quantum roughening transition of a dislocation at T = 0 is completely suppressed by arbitrarily small long-range interactions between kinks. A heuristic argument is presented and the result has been verified by numerical Monte-Carlo simulations using Worm Algorithm in J-current model. It was shown that the Peierls potential plays a crucial role in explaining the elastic properties of dislocations, namely shear modulus softening phenomenon. The crossover from T = 0 to finite temperatures leads to intrinsic softening of the shear modulus and is solely controlled by kink typical energy. It was demonstrated that the mechanism, involving only the binding of 3He impurities to the dislocations, requires an unrealistically high concentrations of defects (or impurities) in order to explain the shear modulus phenomenon and therefore an inclusion of Peierls potential in consideration is required. Superclimbing dislocations, that is the edge dislocations with the superfluidity along the core, were investigated. The theoretical prediction that superclimb is responsible for the phenomenon of "giant isochoric compressibility" was confirmed by Monte-Carlo simulations. It was demonstrated that the isochoric compressibility is suppressed at low temperatures. The dependence of

  12. Dislocated interests and climate change

    NASA Astrophysics Data System (ADS)

    Davis, Steven J.; Diffenbaugh, Noah

    2016-06-01

    The predicted effects of climate change on surface temperatures are now emergent and quantifiable. The recent letter by Hansen and Sato (2016 Environ. Res. Lett. 11 034009) adds to a growing number of studies showing that warming over the past four decades has shifted the distribution of temperatures higher almost everywhere, with the largest relative effects on summer temperatures in developing regions such as Africa, South America, southeast Asia, and the Middle East (e.g., Diffenbaugh and Scherer 2011 Clim. Change 107 615-24 Anderson 2011 Clim. Change 108 581; Mahlstein et al 2012 Geophys. Res. Lett. 39 L21711). Hansen and Sato emphasize that although these regions are warming disproportionately, their role in causing climate change—measured by cumulative historical CO2 emissions produced—is small compared to the US and Europe, where the relative change in temperatures has been less. This spatial and temporal mismatch of climate change impacts and the burning of fossil fuels is a critical dislocation of interests that, as the authors note, has ‘substantial implications for global energy and climate policies.’ Here, we place Hansen and Sato’s ‘national responsibilities’ into a broader conceptual framework of problematically dislocated interests, and briefly discuss the related challenges for global climate mitigation efforts.

  13. The form of a constitutive equation of plastic deformation compatible with stress relaxation data

    SciTech Connect

    Fortes, M.A.; Rosa, M.E.

    1984-05-01

    Hart's approach to constitutive equations of plasticity and experimental results relevant to his formalism are reanalyzed, with special emphasis on the consequences of the scaling relation observed in the relaxation curves of a large number of materials. Complete constitutive equations containing a single structure variable are proposed which describe the experimentally determined relaxation and tensile test curves. An interpretation of the structure variable is given in terms of the density of obstacles to dislocations. The equations are generalized to include recovery and applied to dislocation creep.

  14. Fast Fourier transform discrete dislocation dynamics

    NASA Astrophysics Data System (ADS)

    Graham, J. T.; Rollett, A. D.; LeSar, R.

    2016-12-01

    Discrete dislocation dynamics simulations have been generally limited to modeling systems described by isotropic elasticity. Effects of anisotropy on dislocation interactions, which can be quite large, have generally been ignored because of the computational expense involved when including anisotropic elasticity. We present a different formalism of dislocation dynamics in which the dislocations are represented by the deformation tensor, which is a direct measure of the slip in the lattice caused by the dislocations and can be considered as an eigenstrain. The stresses arising from the dislocations are calculated with a fast Fourier transform (FFT) method, from which the forces are determined and the equations of motion are solved. Use of the FFTs means that the stress field is only available at the grid points, which requires some adjustments/regularizations to be made to the representation of the dislocations and the calculation of the force on individual segments, as is discussed hereinafter. A notable advantage of this approach is that there is no computational penalty for including anisotropic elasticity. We review the method and apply it in a simple dislocation dynamics calculation.

  15. Dislocation generation during early stage sintering.

    NASA Technical Reports Server (NTRS)

    Sheehan, J. E.; Lenel, F. V.; Ansell, G. S.

    1973-01-01

    Discussion of the effects of capillarity-induced stresses on dislocations during early stage sintering. A special version of Hirth's (1963) theoretical calculation procedures modified to describe dislocation nucleation on planes meeting the sintering body's neck surface obliquely is shown to predict plastic flow at stress levels know to exist between micron size metal particles in the early stages of sintering.

  16. Statistics of dislocation pinning at localized obstacles

    SciTech Connect

    Dutta, A.; Bhattacharya, M. Barat, P.

    2014-10-14

    Pinning of dislocations at nanosized obstacles like precipitates, voids, and bubbles is a crucial mechanism in the context of phenomena like hardening and creep. The interaction between such an obstacle and a dislocation is often studied at fundamental level by means of analytical tools, atomistic simulations, and finite element methods. Nevertheless, the information extracted from such studies cannot be utilized to its maximum extent on account of insufficient information about the underlying statistics of this process comprising a large number of dislocations and obstacles in a system. Here, we propose a new statistical approach, where the statistics of pinning of dislocations by idealized spherical obstacles is explored by taking into account the generalized size-distribution of the obstacles along with the dislocation density within a three-dimensional framework. Starting with a minimal set of material parameters, the framework employs the method of geometrical statistics with a few simple assumptions compatible with the real physical scenario. The application of this approach, in combination with the knowledge of fundamental dislocation-obstacle interactions, has successfully been demonstrated for dislocation pinning at nanovoids in neutron irradiated type 316-stainless steel in regard to the non-conservative motion of dislocations. An interesting phenomenon of transition from rare pinning to multiple pinning regimes with increasing irradiation temperature is revealed.

  17. Palmar dislocation of scaphoid and lunate.

    PubMed

    Idrissi, Khalid Koulali; Galiua, Farid

    2011-09-28

    A palmar dislocation of scaphoid and lunate is uncommon. We have found only 19 reported cases in the literature. We reported a simultaneous, divergent dislocation. The closed reduction followed by percutaneous pinning has given a good result without avascular necrosis of any carpal bone.

  18. Posterior dislocation of the shoulder in athletes.

    PubMed

    Samilson, R L; Prieto, V

    1983-07-01

    Although posterior dislocation of the shoulder is a rare injury in athletes, failure to recognize and properly manage acute dislocation may have serious consequences. The article discusses the incidence, mechanism of injury, classification, pathologic findings, clinical and radiologic diagnosis, and management.

  19. Epidemiology of dislocation after total hip arthroplasty.

    PubMed

    Meek, R M D; Allan, D B; McPhillips, G; Kerr, L; Howie, C R

    2006-06-01

    Instability after total hip arthroplasty is an important complication. It usually occurs in the immediate postoperative period, but the risk also increases with time. There are numerous surgical treatment options, but they have relatively unpredictable outcomes. Numerous factors are associated with dislocation, but research has mainly focused on surgical factors. Epidemiological factors remain the subject of much debate. We aimed to establish the most significant epidemiological factors in Scotland and in particular the dislocation rate in neuromuscular conditions. The Scottish National arthroplasty nonvoluntary registry is based on SMR01 records (Scottish Morbidity Record) data. We analyzed the Scottish National Arthroplasty Project to find patients' dislocation rates up to 1 year postoperatively for surgeon volume, age, gender, previous surgery, diagnosis, and followup duration. There were 14,314 total hip arthroplasties performed from April 1996 to March 2004 with an annual incidence of dislocation of 1.9%. We found an association between rate of dislocation with age, surgical volume, and previous fracture. However, there was no increase in the rate of dislocation associated with gender or with diagnoses of stroke or Parkinson's disease. Our prognostic assessment of dislocation risk allows assessment for methods of reducing dislocation in high risk patients.

  20. Initial dislocation structure and dynamic dislocation multiplication in Mo single crystals

    SciTech Connect

    Hsiung, L M; Lassila, D H

    2000-03-22

    Initial dislocation structure in annealed high-purity Mo single crystals and deformation substructure in a crystal subjected to 1% compression have been examined and studied in order to investigate dislocation multiplication mechanisms in the early stages of plastic deformation. The initial dislocation density is in a range of 10{sup 6} {approx} 10{sup 7} cm{sup -2}, and the dislocation structure is found to contain many grown-in superjogs along dislocation lines. The dislocation density increases to a range of 10{sup 8} {approx} 10{sup 9} cm{sup -2}, and the average jog height is also found to increase after compressing for a total strain of 1%. It is proposed that the preexisting jogged screw dislocations can act as (multiple) dislocation multiplication sources when deformed under quasi-static conditions. Both the jog height and length of link segment (between jogs) can increase by stress-induced jog coalescence, which takes place via the lateral migration (drift) of superjogs driven by unbalanced line-tension partials acting on link segments of unequal lengths. Applied shear stress begins to push each link segment to precede dislocation multiplication when link length and jog height are greater than critical lengths. This dynamic dislocation multiplication source is subsequently verified by direct simulations of dislocation dynamics under stress to be crucial in the early stages of plastic deformation in Mo single crystals.

  1. Glide dislocation nucleation from dislocation nodes at semi-coherent {111} Cu–Ni interfaces

    SciTech Connect

    Shao, Shuai; Wang, Jian; Beyerlein, Irene J.; Misra, Amit

    2015-07-23

    Using atomistic simulations and dislocation theory on a model system of semi-coherent {1 1 1} interfaces, we show that misfit dislocation nodes adopt multiple atomic arrangements corresponding to the creation and redistribution of excess volume at the nodes. We identified four distinctive node structures: volume-smeared nodes with (i) spiral or (ii) straight dislocation patterns, and volume-condensed nodes with (iii) triangular or (iv) hexagonal dislocation patterns. Volume-smeared nodes contain interfacial dislocations lying in the Cu–Ni interface but volume-condensed nodes contain two sets of interfacial dislocations in the two adjacent interfaces and jogs across the atomic layer between the two adjacent interfaces. Finally, under biaxial tension/compression applied parallel to the interface, we show that the nucleation of lattice dislocations is preferred at the nodes and is correlated with the reduction of excess volume at the nodes.

  2. Glide dislocation nucleation from dislocation nodes at semi-coherent {111} Cu–Ni interfaces

    DOE PAGES

    Shao, Shuai; Wang, Jian; Beyerlein, Irene J.; ...

    2015-07-23

    Using atomistic simulations and dislocation theory on a model system of semi-coherent {1 1 1} interfaces, we show that misfit dislocation nodes adopt multiple atomic arrangements corresponding to the creation and redistribution of excess volume at the nodes. We identified four distinctive node structures: volume-smeared nodes with (i) spiral or (ii) straight dislocation patterns, and volume-condensed nodes with (iii) triangular or (iv) hexagonal dislocation patterns. Volume-smeared nodes contain interfacial dislocations lying in the Cu–Ni interface but volume-condensed nodes contain two sets of interfacial dislocations in the two adjacent interfaces and jogs across the atomic layer between the two adjacent interfaces.more » Finally, under biaxial tension/compression applied parallel to the interface, we show that the nucleation of lattice dislocations is preferred at the nodes and is correlated with the reduction of excess volume at the nodes.« less

  3. Constitution, 29 October 1987.

    PubMed

    1987-01-01

    This document contains provisions of chapter 2 (Rights and Duties of Citizens) of the 1987 Constitution of the Republic of Korea relating to equality of the sexes, freedom of movement, free and compulsory education, equal opportunity at work, social protection, housing, and health care. The Constitution states that all citizens are equal before the law with no discrimination in political, economic, social, or cultural life based on sex, religion, or social status. The Constitution also protects freedom of residence and mobility, the right to an equal education, free compulsory education, and working mothers (with specific protection against discrimination). The Constitution directs the state to promote the welfare and rights of women, enhance the welfare of the aged and the young, and protect those incapable of earning a living. Housing development policies will be used to ensure comfortable housing for all citizens. State protection is afforded to mothers and to the health of all citizens.

  4. Acute traumatic posterior elbow dislocation in children.

    PubMed

    Lieber, Justus; Zundel, Sabine M; Luithle, Tobias; Fuchs, Jörg; Kirschner, Hans-Joachim

    2012-09-01

    Traumatic posterior dislocation of the elbow is often associated with significant morbidity and incomplete recovery. The aim of this study was to retrospectively analyse the outcome of 33 children (median age 10.8 years). Patients underwent reduction and assessment of stability under general anaesthesia. Pure dislocations (n=10) were immobilized, whereas unstable fractures (n=23) were stabilized. Refixation of ligaments was performed if stability was not achieved by fracture stabilization alone. Immobilization was continued for 26 (pure dislocations) or 35 days (associated injuries), respectively. Results were excellent (n=9) or good (n=1) after pure dislocation. Results were excellent (n=15), good (n=7) or poor (n=1) in children with associated injuries. Accurate diagnosis, concentric stable reduction of the elbow as well as stable osteosynthesis of displaced fractures are associated with good results in children with acute posterior elbow dislocations.

  5. Bipolar dislocation of the forearm (floating forearm).

    PubMed

    Aşkar, Hüseyin; Ertürk, Cemil; Altay, Mehmet Akif; Akif Altay, Mehmet; Bilge, Ali

    2014-01-01

    Bipolar dislocation of the forearm (floating forearm) is an unusual injury and is therefore often overlooked. We report a 28-year-old male patient who presented at another center with a history of a fall while climbing a tree. The patient's left elbow was treated with closed reduction and immobilization with a long-arm cast brace due to elbow dislocation. However, the patient was admitted with pain and swelling of the wrist to our emergency department the following day. Physical and radiological examination revealed dorsal trans-scaphoid perilunate dislocation. A dorsal incision was performed for open reduction and internal fixation to provide wide surgical exposure. Concomitant occurrence of elbow dislocation and fracture-dislocation of the perilunate is infrequent. Therefore, physicians should be aware of possible additional injuries and current recommended treatment methods.

  6. Dislocation core radii near elastic stability limits

    NASA Astrophysics Data System (ADS)

    Sawyer, C. A.; Morris, J. W., Jr.; Chrzan, D. C.

    2013-04-01

    Recent studies of transition metal alloys with compositions that place them near their limits of elastic stability [e.g., near the body-centered-cubic (BCC) to hexagonal-close-packed (HCP) transition] suggest interesting behavior for the dislocation cores. Specifically, the dislocation core size is predicted to diverge as the stability limit is approached. Here a simple analysis rooted in elasticity theory and the computation of ideal strength is used to analyze this divergence. This analysis indicates that dislocation core radii should diverge as the elastic limits of stability are approached in the BCC, HCP, and face-centered-cubic (FCC) structures. Moreover, external stresses and dislocation-induced stresses also increase the core radii. Density functional theory based total-energy calculations are combined with anisotropic elasticity theory to compute numerical estimates of dislocation core radii.

  7. Internal stresses, dislocation mobility and ductility

    NASA Astrophysics Data System (ADS)

    Saada, G.

    1991-06-01

    The description of plastic deformation must take into account individual mechanisms and heterogeneity of plastic strain. Influence of dislocation interaction with forest dislocations and of cross slip are connected with the organization of dipole walls. The latter are described and their development is explained as a consequence of edge effects. Applications are discussed. La description de la déformation plastique doit prendre en compte les interactions individuelles des dislocations et l'hétérogénéité à grande échelle de la déformation plastique. Les interactions des dislocations mobiles avec la forêt de dislocations, le glissement dévié, ont pour effet la création de parois dipolaires. Celles-ci sont décrites et leur développement est appliqué à partir des effets de bord.

  8. Dislocation substructures and nonproportional hardening. [TEM observations under tension-torsion cyclic loading

    SciTech Connect

    Shiinghwa Doong; Socie, D.F.; Robertson, I.M. )

    1990-10-01

    The dislocation substructures created in 1100 aluminum, OFHC copper, and type 304 and 310 stainless steels by in-phase (proportional) and 90 deg out-of-phase (nonproportional) tension-torsion cyclic loading were examined with a transmission-electron microscope. Multislip structures (cells and subgrains) are observed in aluminum under both in-phase and 90 deg out-of-phase tension-torsion loading. For copper and stainless steel, single-slip structures (planar dislocations, matrix veins, and ladders) are observed after proportional loading, whereas multislip structures (cells and labyrinths) are observed after nonproportional loading. The increased cyclic hardening of copper and stainless steels under nonproportional loading is attributed to the change of dislocation substructures. Based on these observations, formulation of a nonproportionality parameter for constitutive modeling is discussed.

  9. Evolution, Interaction, and Intrinsic Properties of Dislocations in Intermetallics: Anisotropic 3D Dislocation Dynamics Approach

    SciTech Connect

    Chen, Qian

    2008-01-01

    The generation, motion, and interaction of dislocations play key roles during the plastic deformation process of crystalline solids. 3D Dislocation Dynamics has been employed as a mesoscale simulation algorithm to investigate the collective and cooperative behavior of dislocations. Most current research on 3D Dislocation Dynamics is based on the solutions available in the framework of classical isotropic elasticity. However, due to some degree of elastic anisotropy in almost all crystalline solids, it is very necessary to extend 3D Dislocation Dynamics into anisotropic elasticity. In this study, first, the details of efficient and accurate incorporation of the fully anisotropic elasticity into 3D discrete Dislocation Dynamics by numerically evaluating the derivatives of Green's functions are described. Then the intrinsic properties of perfect dislocations, including their stability, their core properties and disassociation characteristics, in newly discovered rare earth-based intermetallics and in conventional intermetallics are investigated, within the framework of fully anisotropic elasticity supplemented with the atomistic information obtained from the ab initio calculations. Moreover, the evolution and interaction of dislocations in these intermetallics as well as the role of solute segregation are presented by utilizing fully anisotropic 3D dislocation dynamics. The results from this work clearly indicate the role and the importance of elastic anisotropy on the evolution of dislocation microstructures, the overall ductility and the hardening behavior in these systems.

  10. Evolution, interaction, and intrinsic properties of dislocations in intermetallics: Anisotropic three-dimensional dislocation dynamics approach

    NASA Astrophysics Data System (ADS)

    Chen, Qian

    The generation, motion, and interaction of dislocations play key roles during the plastic deformation process of crystalline solids. 3D Dislocation Dynamics has been employed as a mesoscale simulation algorithm to investigate the collective and cooperative behavior of dislocations. Most current research on 3D Dislocation Dynamics is based on the solutions available in the framework of classical isotropic elasticity. However, due to some degree of elastic anisotropy in almost all crystalline solids, it is very necessary to extend 3D Dislocation Dynamics into anisotropic elasticity. In this study, first, the details of efficient and accurate incorporation of the fully anisotropic elasticity into 3D discrete Dislocation Dynamics by numerically evaluating the derivatives of Green's functions are described. Then the intrinsic properties of perfect dislocations, including their stability, their core properties and disassociation characteristics, in newly discovered rare earth-based intermetallics and in conventional intermetallics are investigated, within the framework of fully anisotropic elasticity supplemented with the atomistic information obtained from the ab initio calculations. Moreover, the evolution and interaction of dislocations in these intermetallics as well as the role of solute segregation are presented by utilizing fully anisotropic 3D dislocation dynamics. The results from this work clearly indicate the role and the importance of elastic anisotropy on the evolution of dislocation microstructures, the overall ductility and the hardening behavior in these systems.

  11. Constitution, 15 August 1982.

    PubMed

    1987-01-01

    This document reprints major provisions of the 1982 Constitution of Equatorial Guinea. The Constitution calls for protection of the family as the basic building block of society. Foreigners are afforded the same civil rights as citizens and may seek asylum but may not exercise political rights. The Constitution guarantees equality before the law and prohibits discrimination based on ethnic background, race, sex, language, religion, filiation, political or other views, social origin, economic position, or birth. Women are afforded the same rights as men regardless of their marital status. The Constitution also guarantees citizens freedom to travel nationally and internationally and to choose a place of residence. Equatoguineans are also entitled to a standard of living that insures health, nutrition, education, clothing, housing, medical care, and necessary social services. The family policy contained in the Constitution protects all types of legal marriages equally and recognizes nonattachable and inalienable family patrimony. Children are protected from the time of conception, and all inhabitants are guaranteed a basic state education which is compulsory and free. Efforts are also being made to eradicate illiteracy. Women are insured training and promotion for their integration into the active life and development of the country, and farmers are guaranteed traditional ownership of the lands they possess, although the state retains the right of eminent domain.

  12. Increasing preoperative dislocations and total time of dislocation affect surgical management of anterior shoulder instability

    PubMed Central

    Denard, Patrick J.; Dai, Xuesong; Burkhart, Stephen S.

    2015-01-01

    Purpose: Our purpose was to determine the relationship between number of preoperative shoulder dislocations and total dislocation time and the need to perform bone deficiency procedures at the time of primary anterior instability surgery. Our hypothesis was that need for bone deficiency procedures would increase with the total number and hours of dislocation. Materials and Methods: A retrospective review was performed of primary instability surgeries performed by a single surgeon. Patients with <25% glenoid bone loss were treated with an isolated arthroscopic Bankart repair. Those who also had an engaging Hill-Sachs lesion underwent arthroscopic Bankart repair with remplissage. Patients with >25% glenoid bone loss were treated with Latarjet reconstruction. Number of dislocations and total dislocation time were examined for their relationship with the treatment method. Results: Ten arthroscopic Bankart repairs, 13 arthroscopic Bankart plus remplissage procedures, and 9 Latarjet reconstructions were available for review. Total dislocations (P = 0.012) and total hours of dislocation (P = 0.019) increased from the Bankart, to the remplissage, to the Latarjet groups. Patients with a total dislocation time of 5 h or more were more likely to require a Latarjet reconstruction (P = 0.039). Patients with only 1 preoperative dislocation were treated with an isolated Bankart repair in 64% (7 of 11) of cases, whereas those with 2 or more dislocations required a bone loss procedure in 86% (18 of 21) of cases (P = 0.013). Conclusion: Increasing number of dislocations and total dislocation time are associated with the development of glenoid and humeral head bony lesions that alter surgical management of anterior shoulder instability. The necessity for the addition of a remplissage to an arthroscopic Bankart repair or the use of a Latarjet reconstruction increases with only 1 recurrent dislocation. Level of evidence: Level III, retrospective comparative study. PMID:25709237

  13. Ultrasonic Study of Dislocation Dynamics in Lithium -

    NASA Astrophysics Data System (ADS)

    Han, Myeong-Deok

    1987-09-01

    Experimental studies of dislocation dynamics in LiF single crystals, using ultrasonic techniques combined with dynamic loading, were performed to investigate the time evolution of the plastic deformation process under a short stress pulse at room temperature, and the temperature dependence of the dislocation damping mechanism in the temperature range 25 - 300(DEGREES)K. From the former, the time dependence of the ultrasonic attenuation was understood as resulting from dislocation multiplication followed by the evolution of mobile dislocations to immobile ones under large stress. From the latter, the temperature dependence of the ultrasonic attenuation was interpreted as due to the motion of the dislocation loops overcoming the periodic Peierls potential barrier in a manner analogous to the motion of a thermalized sine-Gordon chain under a small stress. The Peierls stress obtained from the experimental results by application of Seeger's relaxation model with exponential dislocation length distribution was 4.26MPa, which is consistent with the lowest stress for the linear relation between the dislocation velocity and stress observed by Flinn and Tinder.

  14. Chronic bilateral dislocation of temporomandibular joint.

    PubMed

    Shakya, S; Ongole, R; Sumanth, K N; Denny, C E

    2010-01-01

    Dislocation of the condyle of the mandible is a common condition that may occur in an acute or chronic form. It is characterised by inability to close the mouth with or without pain. Dislocation has to be differentiated from subluxation which is a self reducible condition. Dislocation can occur in any direction with anterior dislocation being the commonest one. Various predisposing factors have been associated with dislocation like muscle fatigue and spasm, the defect in the bony surface like shallow articular eminence, and laxity of the capsular ligament. People with defect in collagen synthesis like Ehler Danlos syndrome, Marfan syndrome are said to be genetically predisposed to this condition. Various treatment modalities have been used ranging from conservative techniques to surgical methods. Acute dislocations can be reduced manually or with conservative approach and recurrent and chronic cases can be reduced by surgical intervention. Though the dislocation in our case was 4 months a simple manual reduction proved to be successful. We believe that manual reduction can be attempted as first line of treatment prior to surgical intervention.

  15. Modeling the Dynamics of Dislocation Ensembles

    NASA Astrophysics Data System (ADS)

    Ghoniem, Nasr M.

    A fundamental description of plastic deformation is under development by several research groups as a result of dissatisfaction with the limitations of continuum plasticity theory. The reliability of continuum plasticity descriptions is dependent on the accuracy and range of available experimental data. Under complex loading situations, however, the database is often hard to establish. Moreover, the lack of a characteristic length scale in continuum plasticity makes it difficult to predict the occurrence of critical localized deformation zones. It is widely appreciated that plastic strain is fundamentally heterogenous, displaying high strains concentrated in small material volumes, with virtually undeformed regions in-between. Experimental observations consistently show that plastic deformation is internally heterogeneous at a number of length scales [1-3]. Depending on the deformation mode, heterogeneous dislocation structures appear with definitive wavelengths. It is common to observe persistent slip bands (PSBs), shear bands, dislocation pile ups, dislocation cells and sub grains. However, a satisfactory description of realistic dislocation patterning and strain localization has been rather elusive. Since dislocations are the basic carriers of plasticity, the fundamental physics of plastic deformation must be described in terms of the behavior of dislocation ensembles. Moreover, the deformation of thin films and nanolayered materials is controlled by the motion and interactions of dislocations.

  16. Search for Dislocation Free Helium 4 Crystals.

    PubMed

    Souris, F; Fefferman, A D; Haziot, A; Garroum, N; Beamish, J R; Balibar, S

    The giant plasticity of [Formula: see text]He crystals has been explained as a consequence of the large mobility of their dislocations. Thus, the mechanical properties of dislocation free crystals should be quite different from those of usual ones. In 1996-1998, Ruutu et al. published crystal growth studies showing that, in their helium 4 crystals, the density of screw dislocations along the c-axis was less than 100 per cm[Formula: see text], sometimes zero. We have grown helium 4 crystals using similar growth speeds and temperatures, and extracted their dislocation density from their mechanical properties. We found dislocation densities that are in the range of 10[Formula: see text]-10[Formula: see text] per cm[Formula: see text], that is several orders of magnitude larger than Ruutu et al. Our tentative interpretation of this apparent contradiction is that the two types of measurements are somewhat indirect and concern different types of dislocations. As for the dislocation nucleation mechanism, it remains to be understood.

  17. On Dislocation Glide in Planetary Interiors

    NASA Astrophysics Data System (ADS)

    Cordier, P.; Carrez, P.; Gouriet, K.; Kraych, A.; Ritterbex, S.

    2015-12-01

    The dynamics of hot planets depends strongly on how heat is transported to their surfaces through large scale convection flows. This is ultimately controlled by the rheology of high-pressure phases under extreme conditions. Whenever solid rocks are concerned, plastic flow results from the propagation of crystal defects (point defects, dislocations, grain boundaries). In this presentation we focus on the role of pressure on dislocation glide which is usually the most efficient strain-producing mechanism. Dislocation glide is assessed through multiscale numerical modeling. First, dislocations are modeled at the atomic scale based on first-principles calculations to incorporate the influence of pressure. Then the mobility law of dislocation at finite temperature is modeled by describing thermally-activated mechanisms for dislocation glide based on the kink-pair model. Then the flow stress at the grain scale is deduced either from application of the Orowan equation or by dislocation dynamics modeling. This approach is applied to wadsleyite, ringwoodite, bridgmanite and post-perovskite. Mechanical properties are either calculated at laboratory strain-rates to be compared with experiments when available or at mantle strain-rate to assess their efficiency under natural conditions.

  18. Thermodynamic forces in single crystals with dislocations

    NASA Astrophysics Data System (ADS)

    Van Goethem, Nicolas

    2014-06-01

    A simple model for the evolution of macroscopic dislocation regions in a single crystal is presented. This model relies on maximal dissipation principle within Kröner's geometric description of the dislocated crystal. Mathematical methods and tools from shape optimization theory provide equilibrium relations at the dislocation front, similarly to previous work achieved on damage modelling (J Comput Phys 33(16):5010-5044, 2011). The deformation state variable is the incompatible strain as related to the dislocation density tensor by a relation involving the Ricci curvature of the crystal underlying elastic metric. The time evolution of the model variables follows from a novel interpretation of the Einstein-Hilbert flow in terms of dislocation microstructure energy. This flow is interpreted as the dissipation of non-conservative dislocations, due to the climb mechanism, modelled by an average effect of mesoscopic dislocations moving normal to their glide planes by adding or removing points defects. The model equations are a fourth-order tensor parabolic equation involving the operator "incompatibility," here appearing as a tensorial counterpart of the scalar Laplacian. This work encompasses and generalizes results previously announced (C R Acad Sci Paris Ser I 349:923-927, 2011), with in addition a series of physical interpretations to give a meaning to the newly introduced concepts.

  19. Elastic strain relaxation in interfacial dislocation patterns: I. A parametric energy-based framework

    NASA Astrophysics Data System (ADS)

    Vattré, A.

    2017-08-01

    A parametric energy-based framework is developed to describe the elastic strain relaxation of interface dislocations. By means of the Stroh sextic formalism with a Fourier series technique, the proposed approach couples the classical anisotropic elasticity theory with surface/interface stress and elasticity properties in heterogeneous interface-dominated materials. For any semicoherent interface of interest, the strain energy landscape is computed using the persistent elastic fields produced by infinitely periodic hexagonal-shaped dislocation configurations with planar three-fold nodes. A finite element based procedure combined with the conjugate gradient and nudged elastic band methods is applied to determine the minimum-energy paths for which the pre-computed energy landscapes yield to elastically favorable dislocation reactions. Several applications on the Au/Cu heterosystems are given. The simple and limiting case of a single set of infinitely periodic dislocations is introduced to determine exact closed-form expressions for stresses. The second limiting case of the pure (010) Au/Cu heterophase interfaces containing two crossing sets of straight dislocations investigates the effects due to the non-classical boundary conditions on the stress distributions, including separate and appropriate constitutive relations at semicoherent interfaces and free surfaces. Using the quantized Frank-Bilby equation, it is shown that the elastic strain landscape exhibits intrinsic dislocation configurations for which the junction formation is energetically unfavorable. On the other hand, the mismatched (111) Au/Cu system gives rise to the existence of a minimum-energy path where the fully strain-relaxed equilibrium and non-regular intrinsic hexagonal-shaped dislocation rearrangement is accompanied by a significant removal of the short-range elastic energy.

  20. Non-basal dislocations should be accounted for in simulating ice mass flow

    NASA Astrophysics Data System (ADS)

    Chauve, T.; Montagnat, M.; Piazolo, S.; Journaux, B.; Wheeler, J.; Barou, F.; Mainprice, D.; Tommasi, A.

    2017-09-01

    Prediction of ice mass flow and associated dynamics is pivotal at a time of climate change. Ice flow is dominantly accommodated by the motion of crystal defects - the dislocations. In the specific case of ice, their observation is not always accessible by means of the classical tools such as X-ray diffraction or transmission electron microscopy (TEM). Part of the dislocation population, the geometrically necessary dislocations (GNDs) can nevertheless be constrained using crystal orientation measurements via electron backscattering diffraction (EBSD) associated with appropriate analyses based on the Nye (1950) approach. The present study uses the Weighted Burgers Vectors, a reduced formulation of the Nye theory that enables the characterization of GNDs. Applied to ice, this method documents, for the first time, the presence of dislocations with non-basal [ c ] or < c + a > Burgers vectors. These [ c ] or < c + a > dislocations represent up to 35% of the GNDs observed in laboratory-deformed ice samples. Our findings offer a more complex and comprehensive picture of the key plasticity processes responsible for polycrystalline ice creep and provide better constraints on the constitutive mechanical laws implemented in ice sheet flow models used to predict the response of Earth ice masses to climate change.

  1. Numerical implementation of a crystal plasticity model with dislocation transport for high strain rate applications

    NASA Astrophysics Data System (ADS)

    Mayeur, Jason R.; Mourad, Hashem M.; Luscher, Darby J.; Hunter, Abigail; Kenamond, Mark A.

    2016-05-01

    This paper details a numerical implementation of a single crystal plasticity model with dislocation transport for high strain rate applications. Our primary motivation for developing the model is to study the influence of dislocation transport and conservation on the mesoscale response of metallic crystals under extreme thermo-mechanical loading conditions (e.g. shocks). To this end we have developed a single crystal plasticity theory (Luscher et al (2015)) that incorporates finite deformation kinematics, internal stress fields caused by the presence of geometrically necessary dislocation gradients, advection equations to model dislocation density transport and conservation, and constitutive equations appropriate for shock loading (equation of state, drag-limited dislocation velocity, etc). In the following, we outline a coupled finite element-finite volume framework for implementing the model physics, and demonstrate its capabilities in simulating the response of a [1 0 0] copper single crystal during a plate impact test. Additionally, we explore the effect of varying certain model parameters (e.g. mesh density, finite volume update scheme) on the simulation results. Our results demonstrate that the model performs as intended and establishes a baseline of understanding that can be leveraged as we extend the model to incorporate additional and/or refined physics and move toward a multi-dimensional implementation.

  2. Distribution of distances between dislocations in different types of dislocation substructures in deformed Cu-Al alloys

    SciTech Connect

    Trishkina, L. Zboykova, N.; Koneva, N. Kozlov, E.; Cherkasova, T.

    2016-01-15

    The aim of the investigation was the determination of the statistic description of dislocation distribution in each dislocation substructures component forming after different deformation degrees in the Cu-Al alloys. The dislocation structures were investigated by the transmission diffraction electron microscopy method. In the work the statistic description of distance distribution between the dislocations, dislocation barriers and dislocation tangles in the deformed Cu-Al alloys with different concentration of Al and test temperature at the grain size of 100 µm was carried out. It was established that the above parameters influence the dislocation distribution in different types of the dislocation substructures (DSS): dislocation chaos, dislocation networks without disorientation, nondisoriented and disoriented cells, in the walls and inside the cells. The distributions of the distances between dislocations in the investigated alloys for each DSS type formed at certain deformation degrees and various test temperatures were plotted.

  3. [Posterior dislocation of the sternoclavicular joint].

    PubMed

    Mäkinen, Tatu; Madanat, Rami; Heinänen, Mikko; Brinck, Tuomas; Pajarinen, Jarkko

    2013-01-01

    Posterior dislocation of the sternoclavicular joint is a rare injury. It can be associated with life-threatening complications. Computed tomography is the imaging modality of choice with which possible associated injuries can be detected. Acute injuries are managed with closed reduction under general anaesthesia. A fracture-dislocation is inherently more unstable than an isolated dislocation. Surgical treatment is advocated in cases of delayed diagnosis or failed closed reduction. With early diagnosis and treatment, the long-term outcome of this injury is good.

  4. Monteggia fracture-dislocations: A Historical Review

    PubMed Central

    Rehim, Shady A.; Maynard, Mallory A.; Sebastin, Sandeep J.; Chung, Kevin C.

    2014-01-01

    The eponym Monteggia fracture-dislocation originally referred to a fracture of the shaft of the ulna accompanied by anterior dislocation of the radial head that was described by Giovanni Battista Monteggia of Italy in 1814. Subsequently, a further classification system based on the direction of the radial head dislocation and associated fractures of the radius and ulna was proposed by Jose Luis Bado of Uruguay in 1958. This article investigates the evolution of treatment, classification, and outcomes of the Monteggia injury and sheds light on the lives and contributions of Monteggia and Bado. PMID:24792923

  5. [Conservative treatment of congenital patellar dislocation].

    PubMed

    Zajonz, D; Schumann, E; Wojan, M; Moche, M; Heyde, C-E

    2017-02-01

    This article presents the rare case of a boy who was born in our hospital with valgus deformity and external rotation of the right lower leg because of congenital patellar dislocation. In the case presented a stable repositioning of the patella could be achieved by redressment with a plaster cast and leg brace. During a 4-year follow-up there were no tendencies towards dislocation during the clinical examination and no dislocation events were documented. In selected cases an attempt at conservative repositioning and retention treatment appears to be worthwhile before surgical treatment is indicated.

  6. "Conjugate channeling" effect in dislocation core diffusion: carbon transport in dislocated BCC iron.

    PubMed

    Ishii, Akio; Li, Ju; Ogata, Shigenobu

    2013-01-01

    Dislocation pipe diffusion seems to be a well-established phenomenon. Here we demonstrate an unexpected effect, that the migration of interstitials such as carbon in iron may be accelerated not in the dislocation line direction ξ, but in a conjugate diffusion direction. This accelerated random walk arises from a simple crystallographic channeling effect. c is a function of the Burgers vector b, but not ξ, thus a dislocation loop possesses the same everywhere. Using molecular dynamics and accelerated dynamics simulations, we further show that such dislocation-core-coupled carbon diffusion in iron has temperature-dependent activation enthalpy like a fragile glass. The 71° mixed dislocation is the only case in which we see straightforward pipe diffusion that does not depend on dislocation mobility.

  7. “Conjugate Channeling” Effect in Dislocation Core Diffusion: Carbon Transport in Dislocated BCC Iron

    PubMed Central

    Ishii, Akio; Li, Ju; Ogata, Shigenobu

    2013-01-01

    Dislocation pipe diffusion seems to be a well-established phenomenon. Here we demonstrate an unexpected effect, that the migration of interstitials such as carbon in iron may be accelerated not in the dislocation line direction , but in a conjugate diffusion direction. This accelerated random walk arises from a simple crystallographic channeling effect. is a function of the Burgers vector b, but not , thus a dislocation loop possesses the same everywhere. Using molecular dynamics and accelerated dynamics simulations, we further show that such dislocation-core-coupled carbon diffusion in iron has temperature-dependent activation enthalpy like a fragile glass. The 71° mixed dislocation is the only case in which we see straightforward pipe diffusion that does not depend on dislocation mobility. PMID:23593255

  8. Traumatic bilateral knee dislocations, unilateral hip dislocation, and contralateral humeral amputation: a case report.

    PubMed

    Voos, James E; Heyworth, Benton E; Piasecki, Dana P; Henn, R Frank; MacGillivray, John D

    2009-02-01

    Bilateral traumatic knee dislocations are a rarity. We report a case of bilateral traumatic knee dislocations with concomitant right hip dislocation and complete traumatic amputation of the left, nondominant upper extremity at the level of the proximal one-third of the humerus. Angiograms revealed no evidence of popliteal artery injury. Orthopedic treatment consisted of immediate reduction of the dislocations and urgent revision amputation of the upper extremity. Staged, bilateral knee ligamentous reconstructions were performed on hospital days 24 and 29, respectively. Despite this constellation of devastating injuries, the patient had a satisfactory outcome. In patients with high-energy hip or knee dislocations, the bilateral hips and knees should be carefully examined to check for associated fractures and/or dislocations.

  9. Effect of pre-existing immobile dislocations on the evolution of geometrically necessary dislocations during fatigue

    NASA Astrophysics Data System (ADS)

    Irastorza-Landa, Ainara; Grilli, Nicolò; Van Swygenhoven, Helena

    2017-07-01

    The role of pre-existing mobile and immobile dislocation densities on the evolution of geometrical necessary dislocation densities (GNDs) during cyclic fatigue in shear is studied using a continuum dislocation-based model incorporated in a crystal plasticity finite element scheme. Clusters with different immobile dislocation densities are implemented in a homogeneous medium containing a certain mobile dislocation density. It is found that whether GND walls are formed around the initial immobile cluster (or not) strongly depends on the absolute values of initial mobile dislocation density and on the ratio between mobile and immobile densities. The results are discussed in terms of the apparent GND densities experimentally obtained using Laue micro-diffraction.

  10. Fundamentals in generalized elasticity and dislocation theory of quasicrystals: Green tensor, dislocation key-formulas and dislocation loops

    NASA Astrophysics Data System (ADS)

    Lazar, Markus; Agiasofitou, Eleni

    2014-12-01

    The present work provides fundamental quantities in generalized elasticity and dislocation theory of quasicrystals. In a clear and straightforward manner, the three-dimensional Green tensor of generalized elasticity theory and the extended displacement vector for an arbitrary extended force are derived. Next, in the framework of dislocation theory of quasicrystals, the solutions of the field equations for the extended displacement vector and the extended elastic distortion tensor are given; that is, the generalized Burgers equation for arbitrary sources and the generalized Mura-Willis formula, respectively. Moreover, important quantities of the theory of dislocations as the Eshelby stress tensor, Peach-Koehler force, stress function tensor and the interaction energy are derived for general dislocations. The application to dislocation loops gives rise to the generalized Burgers equation, where the displacement vector can be written as a sum of a line integral plus a purely geometric part. Finally, using the Green tensor, all other dislocation key-formulas for loops, known from the theory of anisotropic elasticity, like the Peach-Koehler stress formula, Mura-Willis equation, Volterra equation, stress function tensor and the interaction energy are derived for quasicrystals.

  11. A rebound mechanism for misfit dislocation creation in metallic nanolayers

    SciTech Connect

    Henager, Charles H.; Hoagland, Richard G.

    2004-03-01

    A modified version of the Dregia-Hirth rebound mechanism for misfit dislocation creation is observed in atomistic models of CuNi nanolayered structures. Under applied compression glide dislocations in Cu layers undergo a reaction at the CuNi interface to produce another glide dislocation and a misfit dislocation.

  12. Superolateral dislocation of the condyle: report of a rare case.

    PubMed

    Papadopoulos, H; Edwards, R S

    2010-05-01

    Anterior dislocation of the mandibular condyle is commonly seen in patients with chronic dislocation of their temporomandibular joints. Posterior, superior and lateral dislocation is rare. Superolateral dislocation of an intact condyle, let alone intact mandible is uncommon, usually occurring after a traumatic insult to the mandible. The authors report on such a case, and its management.

  13. Constitutional Law--Elective.

    ERIC Educational Resources Information Center

    Gallagher, Joan; Wood, Robert J.

    The elective unit on Constitutional Law is intended for 11th and 12th grade students. The unit is designed around major course goals which are to develop those concepts whereby students recognize and understand the following three topic areas: 1) Role of the Federal Judicial Branch of Government, 2) Supreme Court Cases Involving the Three Branches…

  14. The Constitutional Heritage.

    ERIC Educational Resources Information Center

    Baxter, Maurice

    Changing political, social, economic, and intellectual conditions over the past two hundred years have demanded innovation and adjustment of legal doctrine, thus giving the United States Constitution a character which the framers of the document could not have predicted. Historically, one must not only understand developments since 1787 but also…

  15. The Constitutional Heritage.

    ERIC Educational Resources Information Center

    Baxter, Maurice

    Changing political, social, economic, and intellectual conditions over the past two hundred years have demanded innovation and adjustment of legal doctrine, thus giving the United States Constitution a character which the framers of the document could not have predicted. Historically, one must not only understand developments since 1787 but also…

  16. Constituting children's bodily integrity.

    PubMed

    Hill, B Jessie

    2015-04-01

    Children have a constitutional right to bodily integrity. Courts do not hesitate to vindicate that right when children are abused by state actors. Moreover, in at least some cases, a child's right to bodily integrity applies within the family, giving the child the right to avoid unwanted physical intrusions regardless of the parents' wishes. Nonetheless, the scope of this right vis-à-vis the parents is unclear; the extent to which it applies beyond the narrow context of abortion and contraception has been almost entirely unexplored and untheorized. This Article is the first in the legal literature to analyze the constitutional right of minors to bodily integrity within the family by spanning traditionally disparate doctrinal categories such as abortion rights; corporal punishment; medical decisionmaking; and nontherapeutic physical interventions such as tattooing, piercing, and circumcision. However, the constitutional right of minors to bodily integrity raises complex philosophical questions concerning the proper relationship between family and state, as well as difficult doctrinal and theoretical issues concerning the ever-murky idea of state action. This Article canvasses those issues with the ultimate goal of delineating a constitutional right of bodily security and autonomy for children.

  17. Sexuality and the Constitution.

    ERIC Educational Resources Information Center

    Copelon, Rhonda

    1987-01-01

    Argues for abortion rights and protection of intimate decisions and relationships. Describes the role and position of women in eighteenth century American society as a means of exposing the fallacy of the anti-abortion movement's insistence on adherence to constitutional text. Discusses the recent attempts to overturn the Roe v. Wade ruling. (PS)

  18. Gender and the Constitution

    ERIC Educational Resources Information Center

    Ginsburg, Ruth Bader

    1975-01-01

    In discussing the constitutional aspects of the sex-role debate in the U.S. the author traces the tradition, compares the present criterion of equal protection to the equal rights argument, and analyzes the equality principle with reference to affirmative action and to childbearing and childrearing, supporting the proposed equal rights amendment.…

  19. The Constitution in Action

    ERIC Educational Resources Information Center

    Potter, Lee Ann

    2007-01-01

    In this article, the author describes the experiences middle school students on a field trip to the new Constitution in Action Learning Lab in the Boeing Learning Center at the National Archives can expect. There, middle school students take on the roles of archivists and researchers collecting and analyzing primary sources from the holdings of…

  20. Sexuality and the Constitution.

    ERIC Educational Resources Information Center

    Copelon, Rhonda

    1987-01-01

    Argues for abortion rights and protection of intimate decisions and relationships. Describes the role and position of women in eighteenth century American society as a means of exposing the fallacy of the anti-abortion movement's insistence on adherence to constitutional text. Discusses the recent attempts to overturn the Roe v. Wade ruling. (PS)

  1. South Africa's Constitutional Change.

    ERIC Educational Resources Information Center

    Getman, Thomas

    1987-01-01

    Describes the striking dichotomy of South Africa's beauty and the squalor resulting from the apartheid policies of the government. Reviews reactions of black South Africans to recent constitutional changes and details efforts to secure more sweeping reform. Includes stories of several individuals who have taken actions which oppose the system of…

  2. Ipsilateral open anterior hip dislocation and open posterior elbow dislocation in an adult.

    PubMed

    Kumar, Sunil; Rathi, Akhilesh; Sehrawat, Sunil; Gupta, Vikas; Talwar, Jatin; Arora, Sumit

    2014-01-01

    Open anterior dislocation of the hip is a very rare injury, especially in adults. It is a hyperabduction, external rotation and extension injury. Its combination with open posterior dislocation of the elbow has not been described in English language-based medical literature. Primary resuscitation, debridement, urgent reduction of dislocation, and adequate antibiotic support resulted in good clinical outcome in our patient. At 18 months follow-up, no signs of avascular necrosis of the femoral head or infection were observed.

  3. Anisotropic Dislocation Line Energy and Crack Tip Dislocation Nucleation in (alpha)RDX

    DTIC Science & Technology

    2013-11-01

    November 2013 Anisotropic Dislocation Line Energy and Crack Tip Dislocation Nucleation in αRDX Lynn B. Munday and Jaroslaw Knap Computational ...public release; distribution is unlimited. 13. SUPPLEMENTARY NOTES 14. ABSTRACT This work reports on the algorithms used to determine the...anisotropic and isotropic elastic properties of dislocations and their nucleation from a crack tip. The appendix contains a numerical implementation of these

  4. Automated identification and indexing of dislocations in crystal interfaces

    DOE PAGES

    Stukowski, Alexander; Bulatov, Vasily V.; Arsenlis, Athanasios

    2012-10-31

    Here, we present a computational method for identifying partial and interfacial dislocations in atomistic models of crystals with defects. Our automated algorithm is based on a discrete Burgers circuit integral over the elastic displacement field and is not limited to specific lattices or dislocation types. Dislocations in grain boundaries and other interfaces are identified by mapping atomic bonds from the dislocated interface to an ideal template configuration of the coherent interface to reveal incompatible displacements induced by dislocations and to determine their Burgers vectors. Additionally, the algorithm generates a continuous line representation of each dislocation segment in the crystal andmore » also identifies dislocation junctions.« less

  5. Automated identification and indexing of dislocations in crystal interfaces

    SciTech Connect

    Stukowski, Alexander; Bulatov, Vasily V.; Arsenlis, Athanasios

    2012-10-31

    Here, we present a computational method for identifying partial and interfacial dislocations in atomistic models of crystals with defects. Our automated algorithm is based on a discrete Burgers circuit integral over the elastic displacement field and is not limited to specific lattices or dislocation types. Dislocations in grain boundaries and other interfaces are identified by mapping atomic bonds from the dislocated interface to an ideal template configuration of the coherent interface to reveal incompatible displacements induced by dislocations and to determine their Burgers vectors. Additionally, the algorithm generates a continuous line representation of each dislocation segment in the crystal and also identifies dislocation junctions.

  6. Hydrogenated vacancies lock dislocations in aluminium

    SciTech Connect

    Xie, Degang; Li, Suzhi; Li, Meng; Wang, Zhangjie; Gumbsch, Peter; Sun, Jun; Ma, Evan; Li, Ju; Shan, Zhiwei

    2016-11-03

    Due to its high diffusivity, hydrogen is often considered a weak inhibitor or even a promoter of dislocation movements in metals and alloys. By quantitative mechanical tests in an environmental transmission electron microscope, here we demonstrate that after exposing aluminium to hydrogen, mobile dislocations can lose mobility, with activating stress more than doubled. On degassing, the locked dislocations can be reactivated under cyclic loading to move in a stick-slip manner. However, relocking the dislocations thereafter requires a surprisingly long waiting time of ~103 s, much longer than that expected from hydrogen interstitial diffusion. Both the observed slow relocking and strong locking strength can be attributed to superabundant hydrogenated vacancies, verified by our atomistic calculations. In conclusion, vacancies therefore could be a key plastic flow localization agent as well as damage agent in hydrogen environment.

  7. Hydrogenated vacancies lock dislocations in aluminium

    DOE PAGES

    Xie, Degang; Li, Suzhi; Li, Meng; ...

    2016-11-03

    Due to its high diffusivity, hydrogen is often considered a weak inhibitor or even a promoter of dislocation movements in metals and alloys. By quantitative mechanical tests in an environmental transmission electron microscope, here we demonstrate that after exposing aluminium to hydrogen, mobile dislocations can lose mobility, with activating stress more than doubled. On degassing, the locked dislocations can be reactivated under cyclic loading to move in a stick-slip manner. However, relocking the dislocations thereafter requires a surprisingly long waiting time of ~103 s, much longer than that expected from hydrogen interstitial diffusion. Both the observed slow relocking and strongmore » locking strength can be attributed to superabundant hydrogenated vacancies, verified by our atomistic calculations. In conclusion, vacancies therefore could be a key plastic flow localization agent as well as damage agent in hydrogen environment.« less

  8. Hydrogenated vacancies lock dislocations in aluminium

    NASA Astrophysics Data System (ADS)

    Xie, Degang; Li, Suzhi; Li, Meng; Wang, Zhangjie; Gumbsch, Peter; Sun, Jun; Ma, Evan; Li, Ju; Shan, Zhiwei

    2016-11-01

    Due to its high diffusivity, hydrogen is often considered a weak inhibitor or even a promoter of dislocation movements in metals and alloys. By quantitative mechanical tests in an environmental transmission electron microscope, here we demonstrate that after exposing aluminium to hydrogen, mobile dislocations can lose mobility, with activating stress more than doubled. On degassing, the locked dislocations can be reactivated under cyclic loading to move in a stick-slip manner. However, relocking the dislocations thereafter requires a surprisingly long waiting time of ~103 s, much longer than that expected from hydrogen interstitial diffusion. Both the observed slow relocking and strong locking strength can be attributed to superabundant hydrogenated vacancies, verified by our atomistic calculations. Vacancies therefore could be a key plastic flow localization agent as well as damage agent in hydrogen environment.

  9. Quenched pinning and collective dislocation dynamics

    PubMed Central

    Ovaska, Markus; Laurson, Lasse; Alava, Mikko J.

    2015-01-01

    Several experiments show that crystalline solids deform in a bursty and intermittent fashion. Power-law distributed strain bursts in compression experiments of micron-sized samples, and acoustic emission energies from larger-scale specimens, are the key signatures of the underlying critical-like collective dislocation dynamics - a phenomenon that has also been seen in discrete dislocation dynamics (DDD) simulations. Here we show, by performing large-scale two-dimensional DDD simulations, that the character of the dislocation avalanche dynamics changes upon addition of sufficiently strong randomly distributed quenched pinning centres, present e.g. in many alloys as immobile solute atoms. For intermediate pinning strength, our results adhere to the scaling picture of depinning transitions, in contrast to pure systems where dislocation jamming dominates the avalanche dynamics. Still stronger disorder quenches the critical behaviour entirely. PMID:26024505

  10. Decoherence in electron backscattering by kinked dislocations.

    PubMed

    Dudarev; Ahmed; Hirsch; Wilkinson

    1999-03-01

    A model is proposed that explains the origin of the bright contrast of dislocation walls consisting of edge dislocation dipoles in electron channelling contrast images (ECCI) of fatigued crystals, when the incident beam is parallel to the edge dislocations. The model is based on the assumption that the contrast arises from the dislocation segments terminating the dipoles. These are modelled as screw-type kinks which scatter electrons. Scattering by randomly distributed kinks leads to the randomization of phase of transmitted and diffracted beams and suppresses the anomalous transmission of electrons. The predicted behaviour of electron-channeling contrast images agrees well with experimental observations.With apologies for using two beams instead of three!

  11. Hydrogenated vacancies lock dislocations in aluminium

    PubMed Central

    Xie, Degang; Li, Suzhi; Li, Meng; Wang, Zhangjie; Gumbsch, Peter; Sun, Jun; Ma, Evan; Li, Ju; Shan, Zhiwei

    2016-01-01

    Due to its high diffusivity, hydrogen is often considered a weak inhibitor or even a promoter of dislocation movements in metals and alloys. By quantitative mechanical tests in an environmental transmission electron microscope, here we demonstrate that after exposing aluminium to hydrogen, mobile dislocations can lose mobility, with activating stress more than doubled. On degassing, the locked dislocations can be reactivated under cyclic loading to move in a stick-slip manner. However, relocking the dislocations thereafter requires a surprisingly long waiting time of ∼103 s, much longer than that expected from hydrogen interstitial diffusion. Both the observed slow relocking and strong locking strength can be attributed to superabundant hydrogenated vacancies, verified by our atomistic calculations. Vacancies therefore could be a key plastic flow localization agent as well as damage agent in hydrogen environment. PMID:27808099

  12. Developmental Dislocation (Dysplasia) of the Hip (DDH)

    MedlinePlus

    ... developmental dysplasia (dislocation) of the hip (DDH), the hip joint has not formed normally. The ball is loose ... be taken to provide detailed pictures of the hip joint. Treatment When DDH is detected at birth, it ...

  13. Dislocation Glasses: Aging during Relaxation and Coarsening

    SciTech Connect

    Bako, B.; Groma, I.; Gyoergyi, G.; Zimanyi, G. T.

    2007-02-16

    The dynamics of dislocations is reported to exhibit a range of glassy properties. We study numerically various versions of 2D edge dislocation systems, in the absence of externally applied stress. Two types of glassy behavior are identified (i) dislocations gliding along randomly placed, but fixed, axes exhibit relaxation to their spatially disordered stable state; (ii) if both climb and annihilation are allowed, irregular cellular structures can form on a growing length scale before all dislocations annihilate. In all cases both the correlation function and the diffusion coefficient are found to exhibit aging. Relaxation in case (i) is a slow power law, furthermore, in the transient process (ii) the dynamical exponent z{approx_equal}6, i.e., the cellular structure coarsens relatively slowly.

  14. Complete dorsal dislocation of the carpal scaphoid with perilunate dorsal dislocation

    PubMed Central

    Kang, Jong Woo; Park, Jong Hoon; Suh, Dong Hun; Park, Jong Woong

    2016-01-01

    Complete dorsal dislocation of the carpal scaphoid combined with dorsal perilunate dislocation is an extremely rare carpal injury. We describe the case of a 23-year-old man who presented with a complete dorsal dislocation of the carpal scaphoid, combined with a perilunate dislocation. Surgical treatment was performed with open reduction and interosseus ligament repair. At 4 years follow up, the patient's wrist pain had completely resolved without limitations of wrist joint motion and without evidence of avascular necrosis of the carpal scaphoid. PMID:27512229

  15. Interactions between glide dislocations and parallel interfacial dislocations in nanoscale strained layers

    SciTech Connect

    Akasheh, F.; Zbib, H. M.; Hirth, J. P.; Hoagland, R. G.; Misra, A.

    2007-08-01

    Plastic deformation in nanoscale multilayered structures is thought to proceed by the successive propagation of single dislocation loops at the interfaces. Based on this view, we simulate the effect of predeposited interfacial dislocation on the stress (channeling stress) needed to propagate a new loop parallel to existing loops. Single interfacial dislocations as well as finite parallel arrays are considered in the computation. When the gliding dislocation and the predeposited interfacial array have collinear Burgers vectors, the channeling stress increases monotonically as the density of dislocations in the array increases. In the case when their Burgers vectors are inclined at 60 deg. , a regime of perfect plasticity is observed which can be traced back to an instability in the flow stress arising from the interaction between the glide dislocation and a single interfacial dislocation dipole. This interaction leads to a tendency for dislocations of alternating Burgers vectors to propagate during deformation leading to nonuniform arrays. Inclusion of these parallel interactions in the analysis improves the strength predictions as compared with the measured strength of a Cu-Ni multilayered system in the regime where isolated glide dislocation motion controls flow, but does not help to explain the observed strength saturation when the individual layer thickness is in the few nanometer range.

  16. Dislocation dynamics simulations of interactions between gliding dislocations and radiation induced prismatic loops in zirconium

    NASA Astrophysics Data System (ADS)

    Drouet, Julie; Dupuy, Laurent; Onimus, Fabien; Mompiou, Frédéric; Perusin, Simon; Ambard, Antoine

    2014-06-01

    The mechanical behavior of Pressurized Water Reactor fuel cladding tubes made of zirconium alloys is strongly affected by neutron irradiation due to the high density of radiation induced dislocation loops. In order to investigate the interaction mechanisms between gliding dislocations and loops in zirconium, a new nodal dislocation dynamics code, adapted to Hexagonal Close Packed metals, has been used. Various configurations have been systematically computed considering different glide planes, basal or prismatic, and different characters, edge or screw, for gliding dislocations with -type Burgers vectors. Simulations show various interaction mechanisms such as (i) absorption of a loop on an edge dislocation leading to the formation of a double super-jog, (ii) creation of a helical turn, on a screw dislocation, that acts as a strong pinning point or (iii) sweeping of a loop by a gliding dislocation. It is shown that the clearing of loops is more favorable when the dislocation glides in the basal plane than in the prismatic plane explaining the easy dislocation channeling in the basal plane observed after neutron irradiation by transmission electron microscopy.

  17. Prolonged unilateral dislocation of the mandible.

    PubMed

    Benny, R A

    1978-08-01

    A 61-year-old white woman dislocated her left condyle. She did not seek care for almost three years. In such a long-standing unilateral dislocation, Gottlieb reported that such extreme adhesions and accumulation of connective tissue develops in the joint cavity that actual reduction is impossible and that violent manipulation may lead to ankylosis. Therefore, in such cases, surgery (condylectomy) is indicated. This was done in our case with good functional results.

  18. Incidence of Posttraumatic Shoulder Dislocation in Poland

    PubMed Central

    Szyluk, Karol J.; Jasiński, Andrzej; Mielnik, Michał; Koczy, Bogdan

    2016-01-01

    Background The incidence of shoulder joint dislocation has been estimated at 11–26 per 100 000 population per year. In our opinion, basic epidemiological data need to be continually updated in studies of large populations. To study the incidence of posttraumatic dislocation of the shoulder joint in the Polish population. Material/Methods We retrospectively investigated the entire Polish population between 1 January 2010 and 1 January 2015. To identify the study group, data collected in the electronic database of the National Health Fund were used. The study group was divided into subgroups to detect possible differences in the incidence of shoulder dislocation with regard to age, sex, and season of the year (month) when the dislocation occurred. Results The cumulative size of the study sample was 192.72 million over the 5 years of the study. We identified 51 409 patients with first posttraumatic shoulder dislocation, at a mean age of 50.83 years (SD 21.12), from 0 to 104 years. The incidence of traumatic shoulder dislocations for the entire study group ranged from 24.75/100 000/year (number of posttraumatic shoulder dislocations per 100 000 persons per year) to 29.09/100 000/year, for a mean of 26.69/100 000/year. Conclusions In this study, the overall incidence of first-time posttraumatic shoulder dislocations in the Polish general population was 26.69 per 100 000 persons per year. These results are higher than estimates presented by other authors. It is necessary to study, regularly update, and monitor this problem in the general population. PMID:27777396

  19. Investigation of the Dynamics of a Screw Dislocation in Copper

    NASA Astrophysics Data System (ADS)

    Kolupaeva, S. N.; Petelina, Yu. P.; Polosukhin, K. A.; Petelin, A. E.

    2015-08-01

    A modification of the mathematical model of forming the crystallographic shear band is proposed in which the strength of elastic interaction between all dislocations of the forming dislocation pileups is taken into account in addition to the Peach-Keller force; lattice, impurity, and dislocation friction; linear tension; viscous braking; and intensity of generation of point defects behind kinks. The model is used to investigate the influence of the dislocation density on the time characteristics of the formation of dislocation loops in copper.

  20. Creep Deformation by Dislocation Movement in Waspaloy.

    PubMed

    Whittaker, Mark; Harrison, Will; Deen, Christopher; Rae, Cathie; Williams, Steve

    2017-01-12

    Creep tests of the polycrystalline nickel alloy Waspaloy have been conducted at Swansea University, for varying stress conditions at 700 °C. Investigation through use of Transmission Electron Microscopy at Cambridge University has examined the dislocation networks formed under these conditions, with particular attention paid to comparing tests performed above and below the yield stress. This paper highlights how the dislocation structures vary throughout creep and proposes a dislocation mechanism theory for creep in Waspaloy. Activation energies are calculated through approaches developed in the use of the recently formulated Wilshire Equations, and are found to differ above and below the yield stress. Low activation energies are found to be related to dislocation interaction with γ' precipitates below the yield stress. However, significantly increased dislocation densities at stresses above yield cause an increase in the activation energy values as forest hardening becomes the primary mechanism controlling dislocation movement. It is proposed that the activation energy change is related to the stress increment provided by work hardening, as can be observed from Ti, Ni and steel results.

  1. Creep Deformation by Dislocation Movement in Waspaloy

    PubMed Central

    Whittaker, Mark; Harrison, Will; Deen, Christopher; Rae, Cathie; Williams, Steve

    2017-01-01

    Creep tests of the polycrystalline nickel alloy Waspaloy have been conducted at Swansea University, for varying stress conditions at 700 °C. Investigation through use of Transmission Electron Microscopy at Cambridge University has examined the dislocation networks formed under these conditions, with particular attention paid to comparing tests performed above and below the yield stress. This paper highlights how the dislocation structures vary throughout creep and proposes a dislocation mechanism theory for creep in Waspaloy. Activation energies are calculated through approaches developed in the use of the recently formulated Wilshire Equations, and are found to differ above and below the yield stress. Low activation energies are found to be related to dislocation interaction with γ′ precipitates below the yield stress. However, significantly increased dislocation densities at stresses above yield cause an increase in the activation energy values as forest hardening becomes the primary mechanism controlling dislocation movement. It is proposed that the activation energy change is related to the stress increment provided by work hardening, as can be observed from Ti, Ni and steel results. PMID:28772421

  2. Nonlocal elasticity tensors in dislocation and disclination cores

    DOE PAGES

    Taupin, V.; Gbemou, K.; Fressengeas, C.; ...

    2017-01-07

    We introduced nonlocal elastic constitutive laws for crystals containing defects such as dislocations and disclinations. Additionally, the pointwise elastic moduli tensors adequately reflect the elastic response of defect-free regions by relating stresses to strains and couple-stresses to curvatures, elastic cross-moduli tensors relating strains to couple-stresses and curvatures to stresses within convolution integrals are derived from a nonlocal analysis of strains and curvatures in the defects cores. Sufficient conditions are derived for positive-definiteness of the resulting free energy, and stability of elastic solutions is ensured. The elastic stress/couple stress fields associated with prescribed dislocation/disclination density distributions and solving the momentum andmore » moment of momentum balance equations in periodic media are determined by using a Fast Fourier Transform spectral method. Here, the convoluted cross-moduli bring the following results: (i) Nonlocal stresses and couple stresses oppose their local counterparts in the defects core regions, playing the role of restoring forces and possibly ensuring spatio-temporal stability of the simulated defects, (ii) The couple stress fields are strongly affected by nonlocality. Such effects favor the stability of the simulated grain boundaries and allow investigating their elastic interactions with extrinsic defects, (iii) Driving forces inducing grain growth or refinement derive from the self-stress and couple stress fields of grain boundaries in nanocrystalline configurations.« less

  3. Nonlocal elasticity tensors in dislocation and disclination cores

    NASA Astrophysics Data System (ADS)

    Taupin, V.; Gbemou, K.; Fressengeas, C.; Capolungo, L.

    2017-03-01

    Nonlocal elastic constitutive laws are introduced for crystals containing defects such as dislocations and disclinations. In addition to pointwise elastic moduli tensors adequately reflecting the elastic response of defect-free regions by relating stresses to strains and couple-stresses to curvatures, elastic cross-moduli tensors relating strains to couple-stresses and curvatures to stresses within convolution integrals are derived from a nonlocal analysis of strains and curvatures in the defects cores. Sufficient conditions are derived for positive-definiteness of the resulting free energy, and stability of elastic solutions is ensured. The elastic stress/couple stress fields associated with prescribed dislocation/disclination density distributions and solving the momentum and moment of momentum balance equations in periodic media are determined by using a Fast Fourier Transform spectral method. The convoluted cross-moduli bring the following results: (i) Nonlocal stresses and couple stresses oppose their local counterparts in the defects core regions, playing the role of restoring forces and possibly ensuring spatio-temporal stability of the simulated defects, (ii) The couple stress fields are strongly affected by nonlocality. Such effects favor the stability of the simulated grain boundaries and allow investigating their elastic interactions with extrinsic defects, (iii) Driving forces inducing grain growth or refinement derive from the self-stress and couple stress fields of grain boundaries in nanocrystalline configurations.

  4. Constitution, 29 March 1987.

    PubMed

    1987-01-01

    This document contains provisions of Haiti's 1987 Constitution relating to the family; the protection of children, aliens, and refugees; and individual rights. The age of majority in Haiti is 18, and political and civil rights are attained at age 21 regardless of sex or marital status. Haitians are equal before the law but native-born Haitians who have never renounced their nationality have special advantages. Human rights are guaranteed in conformity with the Universal Declaration of the Rights of Man. Every citizen has the right to decent housing, education, food, and social security. The state is obligated to provide citizens with appropriate means to protect, maintain, and restore their health. Primary schooling is compulsory and free. Aliens in Haiti enjoy the protection offered citizens, including a limited right to own real property. Political refugees have a right to asylum. The family is considered the foundation of society and enjoys state protection regardless of whether the family is constituted within the bonds of marriage. Legal protection is afforded mothers, children, and the aged. The Constitution also calls for creation of a Family Code to ensure protection and respect for the rights of the family.

  5. Quantum dynamics of a single dislocation

    NASA Astrophysics Data System (ADS)

    de Gennes, Pierre-Gilles

    We discuss the zero temperature motions of an edge dislocation in a quantum solid (e.g., He4). If the dislocation has one kink (equal in length to its Burgers vector b) the kink has a creation energy U and can move along the line with a certain transfer integral t. When t and U are of comparable magnitude, two opposite kinks can form an extended bound state, with a size l. The overall shape of the dislocation in the ground state is then associated with a random walk of persistence length l (along the line) and hop sizes b. We also discuss the motions of kinks under an applied shear stress σ: the glide velocity is proportional to exp(-σ*/σ), where σ* is a characteristic stress, controlled by tunneling processes. Mouvements quantiques d'une dislocation. On analyse le mouvement à température nulle d'une dislocation coin dans un solide quantique (He4). La dislocation peut avoir un cran (d'énergie U) dans son plan de glissement. Le cran peut avancer ou reculer le long de la dislocation par effet tunnel, avec une certaine intégrale de transfert t. Deux crans de signe opposé peuvent former un état lié. En présence d'une contrainte extérieure σ, la ligne doit avancer avec une vitesse ~exp(-σ*/σ) où σ* est une contrainte seuil, contrôlée par l'effet tunnel.

  6. The Constitution in Other Lands.

    ERIC Educational Resources Information Center

    Bill of Rights in Action, 1987

    1987-01-01

    Designed for classroom teaching, this document contains articles on the new constitutions of Japan, South Korea, and the Philippine Islands which were modeled in part on the U.S. Constitution. These countries' experiences with constitutional government are examined, and whether or not the U.S. Constitution can be a suitable model for other…

  7. Thomas Jefferson and the Constitution.

    ERIC Educational Resources Information Center

    Peterson, Merrill D.

    1987-01-01

    Examines Thomas Jefferson's role in the making and interpretation of the United States Constitution. Discusses the dominant features of Jefferson's constitutional theory; the character of Jefferson's presidency; and Jefferson's ongoing concern about constitutional preservation and change. Lists important dates in the history of the constitution.…

  8. The key role of dislocation dissociation in the plastic behaviour of single crystal nickel-based superalloy with low stacking fault energy: Three-dimensional discrete dislocation dynamics modelling

    NASA Astrophysics Data System (ADS)

    Huang, Minsheng; Li, Zhenhuan

    2013-12-01

    To model the deformation of single crystal nickel based superalloys (SCNBS) with low stacking fault energy (SFE), three-dimensional discrete dislocation dynamics (3D-DDD) is extended by incorporating dislocation dissociation mechanism. The present 3D-DDD simulations show that, consistent with the existing TEM observation, the leading partial can enter the matrix channel efficiently while the trailing partial can hardly glide into it when the dislocation dissociation is taken into account. To determine whether the dislocation dissociation can occur or not, a critical percolation stress (CPS) based criterion is suggested. According to this CPS criterion, for SCNBS there exists a critical matrix channel width. When the channel width is lower than this critical value, the dislocation tends to dissociate into an extended configuration and vice versa. To clarify the influence of dislocation dissociation on CPS, the classical Orowan formula is improved by incorporating the SFE. Moreover, the present 3D-DDD simulations also show that the yielding stress of SCNBSs with low SFE may be overestimated up to 30% if the dislocation dissociation is ignored. With dislocation dissociation being considered, the size effect due to the width of γ matrix channel and the length of γ‧ precipitates on the stress-strain responses of SCNBS can be enhanced remarkably. In addition, due to the strong constraint effect by the two-phase microstructure in SCNBS, the configuration of formed junctions is quite different from that in single phase crystals such as Cu. The present results not only provide clear understanding of the two-phase microstructure levelled microplastic mechanisms in SCNBSs with low SFE, but also help to develop new continuum-levelled constitutive laws for SCNBSs.

  9. Continuum Theory of Dislocations: Cell Structure Formation

    NASA Astrophysics Data System (ADS)

    Limkumnerd, Surachate; Sethna, James P.

    2005-03-01

    Line-like topological defects inside metals are called dislocations. These dislocations in late stages of hardening form patterns called cell structures. We are developing a mesoscale theory for the formation of cell structures that systematically derives the order parameter fields and evolution laws from the conserved topological Burgers vector density or the Nye dislocation tensor. (In classical plasticity theories, describing scales large compared to these cells, one normally bypasses the complicated motions of the dislocations by supplying yield surface and plastic hardening function in order to determine the evolution of state variables.) Using Landau approach and a closure approximation, an evolution equation for the dislocation density tensor is obtained by employing simple symmetry arguments and the constraint that the elastic energy must decrease with time at fixed stress. The evolution laws lead to singularity formation at finite times, which we expect will be related to the formation of cell walls. Implementation of finite difference simulations using the upwind scheme and the results in one and higher dimensions will be discussed.

  10. Recurrent elbow dislocation--an uncommon presentation.

    PubMed

    Sunderamoorthy, D; Smith, A; Woods, D A

    2005-09-01

    A 58 year old female attended our A&E department following a fall in the garden with swelling and bruising of the right arm and the elbow. Anteroposterior and lateral radiographs were interpreted as showing a normal elbow joint. A diagnosis of soft tissue injury to the elbow was made and the patient was discharged with advice. She returned 2 days later, did not have an x ray, and again given advice. Three weeks later she was referred back to A&E by the general practitioner with persistent swelling of the elbow. Further radiographs showed a posterolateral dislocation of the elbow. The elbow was reduced under sedation but was subsequently dislocated at follow up, and was treated by external fixator and transolecranon pin. The fixator was removed at 4 weeks and the elbow was then stable. This case highlights that recurrent elbow dislocations due to significant ligament injuries can present in joint and subsequently dislocate. A high index of suspicion is necessary and appropriate referral to the specialist must be made to avoid the morbidity associated with recurrent dislocation. It also emphasises the need to always assess the patient on his or her own merits despite previously normal investigations.

  11. Use of cervical collar in temporomandibular dislocation.

    PubMed

    Jaisani, Mehul R; Pradhan, Leeza; Sagtani, Alok

    2015-06-01

    Dislocation of the temporomandibular joint represents 3 % of all reported dislocated joints. In the last 3 decades many cases of TMJ dislocation have been reported with a wide variety of treatment options ranging from non-surgical conservative approaches to open joint procedures. The question remains whether one method is superior to the others. Conservative treatments are still the option in this part of the continent due to financial constraints and as well as due to availability of skilled manpower. A variety of conservative techniques have been described for reducing dislocations, all of which require 10-14 days of immobilization of the jaw post reduction so as to prevent further episodes of dislocation. Immobilization of the jaw can be done in the form of barrel bandage, barton bandage, head chin cap or maxillomandibular fixation using arch bars. We suggest the use of a cervical collar as a form of post reduction immobilization technique to overcome the inherent disadvantages of conventional forms of immobilization techniques.

  12. A review of nonlinear constitutive models for metals

    NASA Technical Reports Server (NTRS)

    Allen, David H.; Harris, Charles E.

    1990-01-01

    Over the past two decades a number of thermomechanical constitutive theories have been proposed for viscoplastic metals. These models are in most cases similar in that they utilize a set of internal state variables which provide locally averaged representations of microphysical phenomena such as dislocation rearrangement and grain boundary sliding. The state of development of several of these models is now at the point where accurate theoretical solutions can be obtained for a wide variety of structural problems at elevated temperatures. The fundamentals of viscoplasticity are briefly reviewed and a general framework is outlined. Several of the more prominent models are reviewed, and predictions from models are compared to experimental results.

  13. Constitution, 30 September 1987.

    PubMed

    1987-01-01

    This document reprints provisions of Suriname's 1987 Constitution relating to freedom of movement, equality of the sexes, the right to life, the right to physical integrity, equal opportunity in employment, the family, children, maternity benefits, the right to health care, parental responsibilities, free and compulsory education, illiteracy, and housing. All citizens enjoy freedom of movement within the bounds of the law. All people within the territory may claim protection of their person and property, and discrimination is forbidden on the basis of birth, sex, race, language, religion, education, political beliefs, economic position, or other status. Torture or inhuman treatment and punishment is banned, and the right to life is protected by the law. The state guarantees the right to work, and all employees have the right to equal remuneration for equal work, safe working conditions, and sufficient rest and recreation. The family is protected, and husbands and wives are equal before the law. Children have the right to protection, and working women are entitled to paid maternity leave. The state promotes the right to good health by systematic improvements in living and working conditions and dissemination of health education. The right to education is protected by the provision of free general primary education and efforts of the state to enable all citizens to achieve the highest educational levels possible. The Constitution also calls for the institution of a plan to allow the state to create public housing.

  14. Chiral anomaly in Dirac semimetals due to dislocations

    NASA Astrophysics Data System (ADS)

    Chernodub, M. N.; Zubkov, M. A.

    2017-03-01

    The dislocation in Dirac semimetal carries an emergent magnetic flux parallel to the dislocation axis. We show that due to the emergent magnetic field, the dislocation accommodates a single fermion massless mode of the corresponding low-energy one-particle Hamiltonian. The mode is propagating along the dislocation with its spin directed parallel to the dislocation axis. In agreement with the chiral anomaly observed in Dirac semimetals, an external electric field results in the spectral flow of the one-particle Hamiltonian, in pumping of the fermionic quasiparticles out from vacuum, and in creating a nonzero axial (chiral) charge in the vicinity of the dislocation.

  15. High dislocation density of tin induced by electric current

    SciTech Connect

    Liao, Yi-Han; Liang, Chien-Lung; Lin, Kwang-Lung; Wu, Albert T.

    2015-12-15

    A dislocation density of as high as 10{sup 17} /m{sup 2} in a tin strip, as revealed by high resolution transmission electron microscope, was induced by current stressing at 6.5 x 10{sup 3} A/ cm{sup 2}. The dislocations exist in terms of dislocation line, dislocation loop, and dislocation aggregates. Electron Backscattered Diffraction images reflect that the high dislocation density induced the formation of low deflection angle subgrains, high deflection angle Widmanstätten grains, and recrystallization. The recrystallization gave rise to grain refining.

  16. Ethics and constitutional government.

    PubMed

    Albright, James A

    2007-01-01

    The term ethics refers to a set of principles that govern acceptable, proper conduct. Attacks on the Constitution of the United States pose the most serious breach of ethics today. Our country was founded as a republic, not as a democracy. Our Founding Fathers' main concern was to protect citizens from the power of the federal government, so constitutionally, the central government has little or no authority over individual citizens except on federal property. One of the major problems today is the fact that we now have professional politicians. This is due in large part to the lure of financial gain from countless special interest groups. This would change under constitutional law because the federal budget would decrease drastically. Article 1 states that all legislative power is vested in Congress. Congress has only 18 enumerated powers, and almost half of these pertain to defense of the country. Many of our current problems are due to regulatory agencies that have become independent fiefdoms with unconstitutional legislative, as well as executive and judicial, powers. The regulatory agency most relevant to medicine, both clinical care and research, is the FDA. It is now obvious that its basic structure needs to be changed or abolished because its actions are identical to those inherent in authoritarian systems. Constructive change could come from Congress, but it would be most desirable if the Supreme Court would take the lead and reestablish the authority of the Constitution as the Supreme Law of the Land. The FDA's function could be limited to the determination of safety, but preferably its mission would be altered to that of product certification. Defenders of the current system claim that such a drastic change would be too dangerous and their prime example is thalidomide. But it is now known that the market has already solved that problem prior to the government-imposed sanctions. Realistically, market forces and their ramifications, including our legal

  17. Dislocation-Radiation Obstacle Interactions: Developing Improved Mechanical Property Constitutive Models

    SciTech Connect

    B.D. WIrth; Ian M. Robertson

    2007-11-29

    Radiation damage to structural and cladding materials, including austenitic stainless steels, ferritic steels, and zirconium alloys, in nuclear reactor environments results in significant mechanical property degradation, including yield strength increases, severe ductility losses and flow localization, which impacts reliability and performance. Generation IV and advanced fuel cycle concepts under consideration will require the development of advanced structural materials, which will operate in increasingly hostile environments. The development of predictive models is required to assess the performance and response of materials in extreme Gen IV reactor operating conditions (temperature, stress, and pressure), to decrease the time to rapidly assess the properties of new materials and insert them into technological applications (Gen IV and Advanced Fuel Cycle Operations).

  18. On the use of internal state variables in thermoviscoplastic constitutive equations

    NASA Technical Reports Server (NTRS)

    Allen, D. H.; Beek, J. M.

    1985-01-01

    The general theory of internal state variables are reviewed to apply it to inelastic metals in use in high temperature environments. In this process, certain constraints and clarifications will be made regarding internal state variables. It is shown that the Helmholtz free energy can be utilized to construct constitutive equations which are appropriate for metallic superalloys. Internal state variables are shown to represent locally averaged measures of dislocation arrangement, dislocation density, and intergranular fracture. The internal state variable model is demonstrated to be a suitable framework for comparison of several currently proposed models for metals and can therefore be used to exhibit history dependence, nonlinearity, and rate as well as temperature sensitivity.

  19. Crack Tip Dislocation Nucleation in FCC Solids

    NASA Astrophysics Data System (ADS)

    Knap, J.; Sieradzki, K.

    1999-02-01

    We present results of molecular dynamic simulations aimed at examining crack tip dislocation emission in fcc solids. The results are analyzed in terms of recent continuum formulations of this problem. In mode II, Au, Pd, and Pt displayed a new unanticipated mechanism of crack tip dislocation emission involving the creation of a pair of Shockley partials on a slip plane one plane below the crack plane. In mode I, for all the materials examined, Rice's continuum formulation [J. Mech. Phys. Solids 40, 239 (1992)] underestimated the stress intensity for dislocation emission by almost a factor of 2. Surface stress corrections to the emission criterion brought the agreement between continuum predictions and simulations to within 20%.

  20. Chronic Elbow Dislocation: Evaluation and Management.

    PubMed

    Donohue, Kenneth W; Mehlhoff, Thomas L

    2016-07-01

    Chronic elbow dislocation is defined as a dislocation that has remained unreduced for >2 weeks. The soft-tissue and skeletal changes that develop during this time usually prevent successful closed reduction. These changes include the development of extensive intra-articular fibrotic tissue, as well as contracture of the triceps, collateral ligaments, and elbow capsule. Ulnar nerve involvement and associated fractures may also be present. Because treatment of chronic elbow dislocation is challenging, a stepwise approach is used in the evaluation and management of this condition. No large series of data are available to guide treatment. Most patients are treated on the basis of the surgeon's anecdotal experience. Treatment typically involves open reduction, often with the use of hinged external fixators. The role of triceps lengthening or primary collateral ligament reconstruction remains a topic of debate.

  1. Composite Dislocations in Smectic Liquid Crystals

    NASA Astrophysics Data System (ADS)

    Aharoni, Hillel; Machon, Thomas; Kamien, Randall D.

    2017-06-01

    Smectic liquid crystals are characterized by layers that have a preferred uniform spacing and vanishing curvature in their ground state. Dislocations in smectics play an important role in phase nucleation, layer reorientation, and dynamics. Typically modeled as possessing one line singularity, the layer structure of a dislocation leads to a diverging compression strain as one approaches the defect center, suggesting a large, elastically determined melted core. However, it has been observed that for large charge dislocations, the defect breaks up into two disclinations [C. E. Williams, Philos. Mag. 32, 313 (1975), 10.1080/14786437508219956]. Here we investigate the topology of the composite core. Because the smectic cannot twist, transformations between different disclination geometries are highly constrained. We demonstrate the geometric route between them and show that despite enjoying precisely the topological rules of the three-dimensional nematic, the additional structure of line disclinations in three-dimensional smectics localizes transitions to higher-order point singularities.

  2. Evaluation of dislocation energy in thin films

    NASA Astrophysics Data System (ADS)

    Coppeta, R. A.; Holec, D.; Ceric, H.; Grasser, T.

    2015-01-01

    A procedure is proposed to calculate the energy of a misfit dislocation at the interface of a film with a finite thickness and a substrate with semi-infinite thickness when modelled anisotropically and with different elastic properties. The results are compared with the treatments derived by Steeds, Willis, Jain and Bullough, and Freund. The new formula is used to calculate the equilibrium critical thickness for Al?Ga?N/GaN, In?Ga?N/GaN and Si?Ge?/Si heterostructures. A comparison with experimental data from the literature shows good agreement. In contrast to other models, application of the new formula for dislocation energy yields smaller critical thickness for the onset of the misfit dislocations.

  3. Successful Conservative Management of a Dislocated IUD

    PubMed Central

    Inal, Hasan Ali; Ozturk Inal, Zeynep; Alkan, Ender

    2015-01-01

    Background. Intrauterine contraceptive devices (IUDs) are widely utilized all over the world owing to their low cost and high efficacy. Uterine perforation is a rare complication that may occur at IUD insertion resulting in extrauterine location of the IUD. Traditionally, surgical removal of dislocated IUDs has been recommended. Case. A 68-year-old patient who had an IUD (Lippes loop) inserted 32 years ago and whose routine examination incidentally revealed a dislocated IUD in the abdominal cavity. The patient remained asymptomatic during three years of follow-up and the IUD was left in place. Conclusion. Asymptomatic patients, whose vaginal examinations and ultrasonography or X-ray results reveal a dislocated IUD, may benefit from conservative management. PMID:25861494

  4. Dislocation filtering in GaN nanostructures.

    PubMed

    Colby, Robert; Liang, Zhiwen; Wildeson, Isaac H; Ewoldt, David A; Sands, Timothy D; García, R Edwin; Stach, Eric A

    2010-05-12

    Dislocation filtering in GaN by selective area growth through a nanoporous template is examined both by transmission electron microscopy and numerical modeling. These nanorods grow epitaxially from the (0001)-oriented GaN underlayer through the approximately 100 nm thick template and naturally terminate with hexagonal pyramid-shaped caps. It is demonstrated that for a certain window of geometric parameters a threading dislocation growing within a GaN nanorod is likely to be excluded by the strong image forces of the nearby free surfaces. Approximately 3000 nanorods were examined in cross-section, including growth through 50 and 80 nm diameter pores. The very few threading dislocations not filtered by the template turn toward a free surface within the nanorod, exiting less than 50 nm past the base of the template. The potential active region for light-emitting diode devices based on these nanorods would have been entirely free of threading dislocations for all samples examined. A greater than 2 orders of magnitude reduction in threading dislocation density can be surmised from a data set of this size. A finite element-based implementation of the eigenstrain model was employed to corroborate the experimentally observed data and examine a larger range of potential nanorod geometries, providing a simple map of the different regimes of dislocation filtering for this class of GaN nanorods. These results indicate that nanostructured semiconductor materials are effective at eliminating deleterious extended defects, as necessary to enhance the optoelectronic performance and device lifetimes compared to conventional planar heterostructures.

  5. High-temperature discrete dislocation plasticity

    NASA Astrophysics Data System (ADS)

    Keralavarma, S. M.; Benzerga, A. A.

    2015-09-01

    A framework for solving problems of dislocation-mediated plasticity coupled with point-defect diffusion is presented. The dislocations are modeled as line singularities embedded in a linear elastic medium while the point defects are represented by a concentration field as in continuum diffusion theory. Plastic flow arises due to the collective motion of a large number of dislocations. Both conservative (glide) and nonconservative (diffusion-mediated climb) motions are accounted for. Time scale separation is contingent upon the existence of quasi-equilibrium dislocation configurations. A variational principle is used to derive the coupled governing equations for point-defect diffusion and dislocation climb. Superposition is used to obtain the mechanical fields in terms of the infinite-medium discrete dislocation fields and an image field that enforces the boundary conditions while the point-defect concentration is obtained by solving the stress-dependent diffusion equations on the same finite-element grid. Core-level boundary conditions for the concentration field are avoided by invoking an approximate, yet robust kinetic law. Aspects of the formulation are general but its implementation in a simple plane strain model enables the modeling of high-temperature phenomena such as creep, recovery and relaxation in crystalline materials. With emphasis laid on lattice vacancies, the creep response of planar single crystals in simple tension emerges as a natural outcome in the simulations. A large number of boundary-value problem solutions are obtained which depict transitions from diffusional to power-law creep, in keeping with long-standing phenomenological theories of creep. In addition, some unique experimental aspects of creep in small scale specimens are also reproduced in the simulations.

  6. A discrete dislocation analysis of mixed mode fracture at bimaterial interfaces

    NASA Astrophysics Data System (ADS)

    O'Day, Michael; Curtin, William

    2004-03-01

    The influence of mode mixity on crack growth and failure at a metal/ceramic bimaterial interface is examined within the discrete dislocation (DD) plasticity framework. In this method, plasticity occurs via the motion of a large number of dislocations embedded in a linearly elastic medium. No plastic constitutive law is required, however a set of rules governing dislocation nucleation, motion and annihilation is necessary. The numerical procedure uses a superposition technique, developed specifically to allow the efficient solution of DD problems with elastic inhomogeneities. An interface crack exists in the unloaded configuration, and a mode independent cohesive zone law characterizes the interface ahead of the crack tip. The influence of mode mixity on crack growth resistance curve (R-curve) behavior is qualitatively similar to continuum plasticity calculations, where increasing mode mixity leads to increasing toughness. However, deviations can arise due to (i) statistical effects, and (ii) the discrete nature of plasticity. Crack blunting, dislocation patterning and the existence of preferential slip planes all emerge naturally from the boundary value problem solution and give insight into observed R-curve trends.

  7. Constitution, 5 May 1989.

    PubMed

    1989-01-01

    This document contains provisions of Cambodia's Constitution of May 5, 1989. Article 7 gives men and women equal rights in marriage and the family, calls for monogamous marriages, and affords social protection to mothers and children. Article 8 guides parent-child relationships. The 14th article defines state property, and the 15th gives citizens full rights to own, use, and inherit land. The use of agricultural and forested land can only be changed with permission. Article 22 assigns educational responsibilities to the state, including free elementary education and a gradual expansion of higher education. Adult literacy classes are also promoted. Article 26 guarantees free medical consultations, and article 27 gives women a 90-day paid maternity leave. Breast-feeding women are also given special privileges. Article 33 guarantees the right to pay equity and to social security benefits. Article 36 grants the freedom to travel, the inviolability of homes, and privacy in correspondence of all types.

  8. Constitution, 5 October 1988.

    PubMed

    1989-01-01

    This document contains major provisions of the constitution adopted by Brazil on 5 October 1988. This constitution seeks to promote the welfare of all citizens without discrimination. The equality of all citizens is guaranteed, and the equal rights of women are specifically mentioned. Property rights are also guaranteed and defined. Female inmates are granted the right to remain with their children while breast feeding. Workers are guaranteed a minimum wage, a family allowance for dependents, maternity/paternity leave, specific incentives to protect the labor market for women, retirement benefits, free day care for preschool-age children, pay equity, and equal rights between tenured and sporadically employed workers. Agrarian reform provisions are given, including the authority to expropriate land. Social and economic policies to promote health are called for, and public health services are to be decentralized, to be integrated, and to foster community participation. Pension plan and social assistance provisions are outlined as are duties of the state in regard to education. The amount of money to be dedicated to education is set out, and a national educational plan is called for to achieve such goals as the eradication of illiteracy, the universalization of school attendance, the improvement of instruction, and the provision of vocational training. Specific measures are set out to protect and preserve the environment. Family policy deals with issues of marriage, the definition of a family, divorce, the right to family planning services, and the deterrence of domestic violence. Social protection provisions cover mothers and children, handicapped persons, and protection of minors. Finally, the customs and rights of Indians are protected, with special provisions given to protect land tenure and to protect the rights of Indians in water resource development and prospecting and mining activities.

  9. Interaction of dislocations with carbon-decorated dislocation loops in bcc Fe: an atomistic study.

    PubMed

    Terentyev, Dmitry; Anento, Napoleón; Serra, Anna

    2012-11-14

    Properties of ferritic Fe-based alloys are highly sensitive to the carbon content dissolved in the matrix because interstitial carbon is known to strongly interact with lattice point defects and dislocations. As a result, the accumulation of radiation defects and its impact on the change of mechanical properties is also affected by the presence of dissolved interstitial carbon. This work contributes to an understanding of how interstitial carbon atoms influence the properties of small dislocation loops, which form directly in collision cascades upon neutron or ion irradiation and are 'invisible' to (i.e. undetectable by) standard experimental techniques applied to reveal nano-structural damage in metals. We have carried out MD simulations to investigate how the trapping of 1/2 inner product 111 dislocation loops at thermally stable carbon-vacancy complexes, known to form under irradiation, affects the interaction of these dislocation loops with dislocations in bcc Fe. We have considered loops of size 1 and 3.5 nm, which represent experimentally invisible and visible defects, respectively. The obtained results point at the strong suppression of the drag of carbon-decorated loops by dislocations. In the case of direct interaction between dislocation and carbon-decorated loops, invisible loops are found to act as obstacles whose strength is at least twice as high compared to that of undecorated ones. Additional strengthening due to the carbon decoration on the visible loops was also regularly registered. The reasons for the additional strengthening have been rationalized and discussed. It is demonstrated that carbon decoration/segregation at dislocation loops affects not only accumulation of radiation damage under prolonged irradiation but also alters the post-irradiation plastic deformation mechanisms. For the first time, we provide evidence that undetectable dislocation loops decorated by carbon do contribute to the radiation hardening.

  10. Dislocation etching of rough crystal faces

    NASA Astrophysics Data System (ADS)

    Van Enckevort, W. J. P.; Smet, F.

    1988-07-01

    A model for the preferential dissolution near the outcrops of dislocations at rough (K, S or F faces above the roughening temperature) crystal faces has been developed. In contrast to F faces below the roughening transition, no lateral flow of steps from the etched dislocation centre occurs and therefore only small etch pits, either not or only barely visible by optical microscopy are expected to be formed. This was confirmed by etching of K, S and F faces of Bi 4(GeO 4) 3, KH 2PO 4 and potash alum crystals.

  11. Irreducible posterolateral elbow dislocation: a rare injury.

    PubMed

    Fenelon, Christopher; Zafar, Muhammed M; Sheridan, Gerard Anthony; Kearns, Stephen

    2016-12-30

    Posterolateral dislocation of the elbow is an injury commonly treated in the emergency department by closed reduction. Very rarely it can be irreducible and require open reduction. Only four cases of irreducible posterolateral elbow dislocation have been described in the literature over the past 50 years. We report the case of a 20-year-old man who sustained such an injury. Open reduction was performed and revealed the radial head protruding or 'buttonholing' through the lateral collateral ligament complex. This case highlights that continued closed reduction of the elbow should not be attempted, as a mechanical block to reduction can occur making reduction impossible.

  12. Elbow dislocation with complete triceps avulsion.

    PubMed

    Karuppiah, S V; Knox, D

    2014-01-01

    Radio-ulnar Fracture dislocation of the elbow is a high-energy trauma which can be associated with significant ligamentous injury in adults. We report an unusual triad of injury in a patient with avulsion injury of the triceps. This injury can be thought of as a variant of "terrible triad" with dislocation of radio-ulnar joint, radial head fracture, and medial collateral ligament injury with avulsion of the triceps. Elbow has to be stabilized with early repair of the ligaments for a successful outcome.

  13. Elbow Dislocation with Complete Triceps Avulsion

    PubMed Central

    Karuppiah, S. V.; Knox, D.

    2014-01-01

    Radio-ulnar Fracture dislocation of the elbow is a high-energy trauma which can be associated with significant ligamentous injury in adults. We report an unusual triad of injury in a patient with avulsion injury of the triceps. This injury can be thought of as a variant of “terrible triad” with dislocation of radio-ulnar joint, radial head fracture, and medial collateral ligament injury with avulsion of the triceps. Elbow has to be stabilized with early repair of the ligaments for a successful outcome. PMID:24876982

  14. Geometry of dislocated de Broglie waves

    SciTech Connect

    Holland, P.R.

    1987-04-01

    The geometrical structures implicit in the de Broglie waves associated with a relativistic charged scalar quantum mechanical particle in an external field are analyzed by employing the ray concept of the causal interpretation. It is shown how an osculating Finslerian metric tensor, a torsion tensor, and a tetrad field define respectively the strain, the dislocation density, and the Burgers vector in the natural state of the wave, which is a non-Riemannian space of distant parallelism. A quantum torque determined by the quantum potential is introduced and the example of a screw dislocated wave is discussed.

  15. Mesoscale modeling of dislocations in molecular crystals

    NASA Astrophysics Data System (ADS)

    Lei, Lei; Koslowski, Marisol

    2011-02-01

    Understanding the inelastic deformation of molecular crystals is of fundamental importance to the modeling of the processing of drugs in the pharmaceutical industry as well as to the initiation of detonation in high energy density materials. In this work, we present dislocation dynamics simulations of the deformation of two molecular crystals of interest in the pharmaceutical industry, sucrose and paracetamol. The simulations calculate the yield stress of sucrose and paracetamol in good agreement with experimental observation and predict the anisotropy in the mechanical response observed in these materials. Our results show that dislocation dynamics is an effective tool to study plastic deformation in molecular crystals.

  16. Rotator Cuff Tear Consequent to Glenohumeral Dislocation.

    PubMed

    Gilotra, Mohit N; Christian, Matthew W; Lovering, Richard M

    2016-08-01

    The patient was a 21-year-old collegiate running back who was tackled during a football game and sustained a posterior glenohumeral dislocation. He was referred to an orthopaedist and presented 3 weeks after the injury, and, following examination, further imaging was ordered by the orthopaedist due to rotator cuff weakness. Magnetic resonance imaging showed a complete tear of the supraspinatus and infraspinatus, as well as a posterior Bankart lesion, a subscapularis tear, and a dislocation of the biceps long head tendon into the reverse Hill-Sachs lesion. J Orthop Sports Phys Ther 2016;46(8):708. doi:10.2519/jospt.2016.0413.

  17. Changes in the Burgers Vector of Perfect Dislocation Loops without Contact with the External Dislocations

    SciTech Connect

    Arakawa, K.; Hatanaka, M.; Mori, H.; Kuramoto, E.; Ono, K.

    2006-03-31

    We report the observations of a new type of changing process in the Burgers vector of dislocations by in situ transmission electron microscopy. Small interstitial-type perfect dislocation loops in bcc iron with diameters less than approximately 50 nm are transformed from a 1/2<111> loop to another 1/2<111> one or an energetically unfavorable <100> one; furthermore, a <100> loop is transformed to a 1/2<111> one. These transformations occurred on high-energy electron irradiation or simple heating without contact with external dislocations. The origin of these phenomena is discussed.

  18. Dislocation of the lens: a complication after cyclocryotherapy.

    PubMed

    Sony, Parul; Sharma, Namrata; Pangtey, Mayank S

    2002-12-01

    An unusual complication is reported of a case of complete dislocation of the lens after cyclocryotherapy in a patient with neovascular glaucoma. To the best of the authors' knowledge, no case of lens dislocation following cyclocryotherapy has previously been reported.

  19. Effect of dislocations on helium retention in deformed pure iron

    NASA Astrophysics Data System (ADS)

    Gong, Y. H.; Cao, X. Z.; Jin, S. X.; Lu, E. Y.; Hu, Y. C.; Zhu, T.; Kuang, P.; Xu, Q.; Wang, B. Y.

    2016-12-01

    The effects of dislocations created by deformation on helium retention in pure iron, including the helium atoms diffusion along the dislocation line and desorption from dislocation trapping sites, were investigated. The dislocation defect was introduced in specimens by cold-rolling, and then 5 keV helium ions were implanted into the deformed specimens. Slow positron beam technology and thermal desorption spectroscopy were used to investigate the evolution of dislocation defects and the desorption behavior of helium atoms under influence of dislocation. The behaviors of S-E, W-E and S-W plots indicate clearly that lots of helium atoms remain in the deformed specimen and helium atoms combining with dislocation change the distribution of electron density. The helium desorption plot indicates that dislocation accelerates helium desorption at 293 K-600 K and facilitates helium dissociation from HenVm (n/m = 1.8) cluster.

  20. Constitutive models in LAME.

    SciTech Connect

    Hammerand, Daniel Carl; Scherzinger, William Mark

    2007-09-01

    The Library of Advanced Materials for Engineering (LAME) provides a common repository for constitutive models that can be used in computational solid mechanics codes. A number of models including both hypoelastic (rate) and hyperelastic (total strain) constitutive forms have been implemented in LAME. The structure and testing of LAME is described in Scherzinger and Hammerand ([3] and [4]). The purpose of the present report is to describe the material models which have already been implemented into LAME. The descriptions are designed to give useful information to both analysts and code developers. Thus far, 33 non-ITAR/non-CRADA protected material models have been incorporated. These include everything from the simple isotropic linear elastic models to a number of elastic-plastic models for metals to models for honeycomb, foams, potting epoxies and rubber. A complete description of each model is outside the scope of the current report. Rather, the aim here is to delineate the properties, state variables, functions, and methods for each model. However, a brief description of some of the constitutive details is provided for a number of the material models. Where appropriate, the SAND reports available for each model have been cited. Many models have state variable aliases for some or all of their state variables. These alias names can be used for outputting desired quantities. The state variable aliases available for results output have been listed in this report. However, not all models use these aliases. For those models, no state variable names are listed. Nevertheless, the number of state variables employed by each model is always given. Currently, there are four possible functions for a material model. This report lists which of these four methods are employed in each material model. As far as analysts are concerned, this information is included only for the awareness purposes. The analyst can take confidence in the fact that model has been properly implemented

  1. Dislocations in magnetohydrodynamic waves in a stellar atmosphere.

    PubMed

    López Ariste, A; Collados, M; Khomenko, E

    2013-08-23

    We describe the presence of wave front dislocations in magnetohydrodynamic waves in stratified stellar atmospheres. Scalar dislocations such as edges and vortices can appear in Alfvén waves, as well as in general magnetoacoustic waves. We detect those dislocations in observations of magnetohydrodynamic waves in sunspots in the solar chromosphere. Through the measured charge of all the dislocations observed, we can give for the first time estimates of the modal contribution in the waves propagating along magnetic fields in solar sunspots.

  2. This Constitution: A Bicentennial Chronicle.

    ERIC Educational Resources Information Center

    This Constitution, 1986

    1986-01-01

    Providing a link between constitutional scholars and the planners of school and public programs observing the Bicentennial of the United States Constitution, this series of the Bicentennial Chronicles features articles that provide a link between scholars of the Constitution and the people who will be planning programs for the public and for the…

  3. How Democratic Is the Constitution?

    ERIC Educational Resources Information Center

    Goldwin, Robert A., Ed.; Schambra, William A., Ed.

    Designed to help prepare the nation for a thoughtful observance of the Constitutional bicentennial, this publication contains seven essays on the topic of democracy and the Constitution. "Democracy and the Constitution" (Gordon S. Wood) looks at the popular and democratic rhetoric used to justify the federalist system in the late 1700's.…

  4. Dislocation-mediated relaxation in nanograined columnar palladium films revealed by on-chip time-resolved HRTEM testing

    PubMed Central

    Colla, M. -S.; Amin-Ahmadi, B.; Idrissi, H.; Malet, L.; Godet, S.; Raskin, J. -P.; Schryvers, D.; Pardoen, T.

    2015-01-01

    The high-rate sensitivity of nanostructured metallic materials demonstrated in the recent literature is related to the predominance of thermally activated deformation mechanisms favoured by a large density of internal interfaces. Here we report time-resolved high-resolution electron transmission microscopy creep tests on thin nanograined films using on-chip nanomechanical testing. Tests are performed on palladium, which exhibited unexpectedly large creep rates at room temperature. Despite the small 30-nm grain size, relaxation is found to be mediated by dislocation mechanisms. The dislocations interact with the growth nanotwins present in the grains, leading to a loss of coherency of twin boundaries. The density of stored dislocations first increases with applied deformation, and then decreases with time to drive additional deformation while no grain boundary mechanism is observed. This fast relaxation constitutes a key issue in the development of various micro- and nanotechnologies such as palladium membranes for hydrogen applications. PMID:25557273

  5. Hydrogen diffusion in the elastic fields of dislocations in iron

    SciTech Connect

    Sivak, A. B. Sivak, P. A.; Romanov, V. A.; Chernov, V. M.

    2016-12-15

    The effect of dislocation stress fields on the sink efficiency thereof is studied for hydrogen interstitial atoms at temperatures of 293 and 600 K and at a dislocation density of 3 × 10{sup 14} m{sup –2} in bcc iron crystal. Rectilinear full screw and edge dislocations in basic slip systems 〈111〉(110), 〈111〉(112), 〈100〉(100), and 〈100〉(110) are considered. Diffusion of defects is simulated by means of the object kinetic Monte Carlo method. The energy of interaction between defects and dislocations is calculated using the anisotropic theory of elasticity. The elastic fields of dislocations result in a less than 25% change of the sink efficiency as compared to the noninteracting linear sink efficiency at a room temperature. The elastic fields of edge dislocations increase the dislocation sink efficiency, whereas the elastic fields of screw dislocations either decrease this parameter (in the case of dislocations with the Burgers vector being 1/2〈111〉) or do not affect it (in the case of dislocations with the Burgers vector being 〈100〉). At temperatures above 600 K, the dislocations affect the behavior of hydrogen in bcc iron mainly owing to a high binding energy between the hydrogen atom and dislocation cores.

  6. The Use of Ultrasound to Measure Dislocation Density

    NASA Astrophysics Data System (ADS)

    Barra, Felipe; Espinoza-González, Rodrigo; Fernández, Henry; Lund, Fernando; Maurel, Agnès; Pagneux, Vincent

    2015-08-01

    Dislocations are at the heart of the plastic behavior of materials yet they are very difficult to probe experimentally. Lack of a practical nonintrusive measuring tool for, say, dislocation density, seriously hampers modeling efforts, as there is little guidance from data in the form of quantitative measurements, as opposed to visualizations. Dislocation density can be measured using transmission electron microscopy (TEM) and x-ray diffraction (XRD). TEM can directly show the strain field around dislocations, which allows for the counting of the number of dislocations in a micrograph. This procedure is very laborious and local, since samples have to be very small and thin, and is difficult to apply when dislocation densities are high. XRD relies on the broadening of diffraction peaks induced by the loss of crystalline order induced by the dislocations. This broadening can be very small, and finding the dislocation density involves unknown parameters that have to be fitted with the data. Both methods, but especially TEM, are intrusive, in the sense that samples must be especially treated, mechanically and chemically. A nonintrusive method to measure dislocation density would be desirable. This paper reviews recent developments in the theoretical treatment of the interaction of an elastic wave with dislocations that have led to formulae that relate dislocation density to quantities that can be measured with samples of cm size. Experimental results that use resonant ultrasound spectroscopy supporting this assertion are reported, and the outlook for the development of a practical, nonintrusive, method to measure dislocation density is discussed.

  7. Dislocation core fields and forces in FCC metals

    SciTech Connect

    Henager, Charles H.; Hoagland, Richard G.

    2004-04-01

    Atomistic models were used to obtain dislocation core fields for edge, screw, and mixed dislocations in Al and Cu using EAM. Core fields are analyzed using a line force dipole representation, with dilatant and dipole terms. The core field contribution to the force between dislocations is shown to be significant for interactions within 50b.

  8. An Acoustic Profile of Right-Dislocations in French.

    ERIC Educational Resources Information Center

    Ashby, William J.

    1994-01-01

    Provides an acoustic profile of the prosody of right-dislocations in French, using the CECIL computer hardware and software package to analyze 28 right-dislocations occurring in a corpus of natural French discourse. It was found that, although right-dislocations appear to fulfill various functional roles in discourse, no correlation appears…

  9. On onsagers principle, dislocation motion and hydrogen embrittlement

    NASA Technical Reports Server (NTRS)

    Louthan, M. R., Jr.; Mcnitt, R. P.

    1976-01-01

    Onsager's reciprocal relationships from the linear theory of irreversible thermodynamics are applied to hydrogen - dislocation interactions. Existing experimental evidence shows that dislocation motion causes localized hydrogen accumulation; thus, from the Onsager principle, localized hydrogen accumulations will affect dislocation motion and therefore the properties of metals and alloys exposed to hydrogen environments.

  10. The Perceptions of Dislocated Workers under the Workforce Investment Act

    ERIC Educational Resources Information Center

    Wilson, Michael S.; Brown, James M.

    2012-01-01

    This descriptive qualitative case study investigated the perceptions of dislocated workers offered program services through the Workforce Investment Act's (WIA) Dislocated Worker program in Minnesota. This research focused on recently dislocated workers who lost their jobs through no fault of their own and hence were eligible for unemployment…

  11. Hydrogen diffusion in the elastic fields of dislocations in iron

    NASA Astrophysics Data System (ADS)

    Sivak, A. B.; Sivak, P. A.; Romanov, V. A.; Chernov, V. M.

    2016-12-01

    The effect of dislocation stress fields on the sink efficiency thereof is studied for hydrogen interstitial atoms at temperatures of 293 and 600 K and at a dislocation density of 3 × 1014 m-2 in bcc iron crystal. Rectilinear full screw and edge dislocations in basic slip systems <111>{110}, <111>{112}, <100>{100}, and <100>{110} are considered. Diffusion of defects is simulated by means of the object kinetic Monte Carlo method. The energy of interaction between defects and dislocations is calculated using the anisotropic theory of elasticity. The elastic fields of dislocations result in a less than 25% change of the sink efficiency as compared to the noninteracting linear sink efficiency at a room temperature. The elastic fields of edge dislocations increase the dislocation sink efficiency, whereas the elastic fields of screw dislocations either decrease this parameter (in the case of dislocations with the Burgers vector being 1/2<111>) or do not affect it (in the case of dislocations with the Burgers vector being <100>). At temperatures above 600 K, the dislocations affect the behavior of hydrogen in bcc iron mainly owing to a high binding energy between the hydrogen atom and dislocation cores.

  12. Enhanced annealing of the dislocation network under irradiation

    SciTech Connect

    Mordehai, Dan; Martin, Georges

    2011-07-01

    In crystalline metals, the dislocation network is the main source of internal strain, while irradiation steadily injects new sources of internal strain (point defects, defect clusters). As a consequence, the evolution of the dislocation network is driven by irradiation. While the atomistic mechanisms by which the forcing proceeds have long been suggested, namely the partitioning of defect elimination between dislocations and other defect sinks, both in stationary or transient regimes, some of the macroscopic consequences, such as irradiation enhanced dislocation annealing and irradiation driven recrystallization, are left unexplained. In this work we show that dislocation sink strengths for point defects are altered in the presence of neighboring dislocations and their climb motion is coordinated with the dislocation microstructure. A climb model, which takes into account the dislocation network, provides the mechanism for coordinated climb, which is shown to ease dislocation annealing. In particular, we demonstrate that coordinated dislocation climb accelerates the annihilation of dislocation pairs with the opposite sign and the repulsion of dislocations of the same sign, thereby, among other things, promoting the annealing of small-angle tilt boundaries by subgrain rotation.

  13. Constitution, 3 February 1987.

    PubMed

    1987-01-01

    This document contains provisions of the 1987 Constitution of the Philippines. The state policies reprinted from Article 2 note that the state recognizes the sanctity of family life and protects the life of the mother and of the unborn from conception. Women and men are afforded equality before the law. The state prioritizes education, science and technology, arts, culture, and sports and promotes comprehensive rural development and agrarian reform. Provisions reprinted from Article 13 (Social Justice and Human Rights) cover agrarian and natural resources reform, urban land reform and housing, health, and protection of women in the workforce. Sections from Article 14 (Education, Science and Technology, Arts, Culture, and Sports) set forth the state's duty to make quality education accessible to all citizens through a compulsory system of free public education, provision of incentives to deserving students, encouragement of informal education, and provision of adult education. Article 15, on the family, recognizes the family as the foundation of the nation and marriage as the foundation of the family. Spouses have the right to found a family, children have the right to appropriate care, the family has the right to a living wage and income, families or family associations have the right to participate in the planning and implementation of policies and programs that affect them, and the family has the duty to care for its elderly.

  14. Atlantoaxial rotatory dislocation. A case report.

    PubMed

    Niibayashi, H

    1998-07-01

    Report of a child who sustained an acute atlantoaxial rotatory dislocation, associated with fractures of the clavicle and the temporal bone, and rupture of the alar ligament demonstrated by magnetic resonance imaging. To describe the radiographic and pathoanatomic characteristics of the injury process. Only five cases of traumatic atlantoaxial rotatory dislocation associated with fracture of the clavicle have been reported previously. This is the first report of a ruptured alar ligament demonstrated on magnetic resonance imaging in a patient with atlantoaxial rotatory dislocation associated with fractures of the clavicle and the temporal bone. Computed tomography revealed the Type 1 rotatory dislocation described by Fielding and Hawkins, and magnetic resonance imaging delineated the ruptured alar ligament. Traction in a halter, followed by 6 weeks of immobilization with a cervical collar, was successful in the management of the injury. Concomitant fractures of the right temporal bone and the right clavicle may yield excessive left rotation of the atlas on the axis, resulting in the rupture of the right alar ligament. Awareness of this condition allows early diagnosis and effective conservative treatment.

  15. Tailoring noncollinear magnetism by misfit dislocation lines

    NASA Astrophysics Data System (ADS)

    Finco, Aurore; Hsu, Pin-Jui; Kubetzka, André; von Bergmann, Kirsten; Wiesendanger, Roland

    2016-12-01

    The large epitaxial stress induced by the misfit between a triple atomic layer Fe film and an Ir(111) substrate is relieved by the formation of a dense dislocation line network. Spin-polarized scanning tunneling microscopy investigations show that the strain is locally varying within the Fe film and that this variation affects the magnetic state of the system. Two types of dislocation line regions can be distinguished and both exhibit spin spirals with strain-dependent periods (ranging from 3 to 10 nm ). Using a simple micromagnetic model, we attribute the changes of the period of the spin spirals to variations of the effective exchange coupling in the magnetic film. This assumption is supported by the observed dependence of the saturation magnetic field on the period of the zero-field spin spiral. Moreover, magnetic skyrmions appear in an external magnetic field only in one type of dislocation line area, which we impute to the different pinning properties of the dislocation lines.

  16. Ab initio phonon scattering by dislocations

    NASA Astrophysics Data System (ADS)

    Wang, Tao; Carrete, Jesús; van Roekeghem, Ambroise; Mingo, Natalio; Madsen, Georg K. H.

    2017-06-01

    Heat management in thermoelectric and power devices as well as in random access memories poses a grand challenge and can make the difference between a working and an abandoned device design. Despite the prevalence of dislocations in all these technologies, the modeling of their thermal resistance is based on 50-year-old analytical approximations, whose simplicity was driven by practical limitations rather than physical insight. We introduce an efficient ab initio approach based on Green's functions computed by two-dimensional reciprocal space integration. By combining elasticity theory and density functional theory, we calculate the scattering strength of a 90∘ misfit edge dislocation in Si. Because of the breakdown of the Born approximation, earlier literature models fail, even qualitatively. We find that a dislocation density larger than 109cm-2 is necessary to substantially influence thermal conductivity at room temperature and above. We quantify how much of the reduction of thermal conductivity measured in nanograined samples can be explained by realistic dislocation concentrations.

  17. [Habitual dislocation of the temporomandibular joint].

    PubMed

    Hjortdal, O

    1975-02-01

    A case of recurrent dislocation of the left temporamandibular joint is reported. Different methods of treatment are reviewed. The present case was successfully treated with a combination of two methods: 1. Restriction of excessive condylar movement by means of continuous loop wiring and intermaxillary monofilament fishing line. 2. Intra-articular injections of autologous blood.

  18. Dislocation substructure in fatigued duplex stainless steel

    SciTech Connect

    Polak, J. . Lab. de Mecanique de Lille Inst. of Physical Metallurgy, Brno . Academy of Sciences); Degallaix, S. . Lab. de Mecanique de Lille); Kruml, T. . Academy of Sciences)

    1993-12-15

    Cyclic plastic straining of crystalline materials results in the formation of specific dislocation structures. Considerable progress in mapping and understanding internal dislocation structures has been achieved by studying single crystal behavior: however, most structural materials have a polycrystalline structure and investigations of polycrystals in comparison to single crystal behavior of simple metals prove to be very useful in understanding more complex materials. There are some classes of materials, however, with complicated structure which do not have a direct equivalent in single crystalline form. Moreover, the specific dimensions and shapes of individual crystallites play an important role both in the cyclic stress-strain response of these materials and in the formation of their interior structure in cyclic straining. Austenitic-ferritic duplex stainless steel, which is a kind of a natural composite, is a material of this type. The widespread interest in the application of duplex steels is caused by approximately doubled mechanical properties and equal corrosion properties, when compared with classical austenitic stainless steels. Fatigue resistance of these steels as well as the surface damage evolution in cyclic straining have been studied; however, much less is known about the internal substructure development in cyclic straining. In this study the dislocation arrangement in ferritic and austenitic grains of the austenitic-ferritic duplex steel alloyed with nitrogen and cyclically strained with two strain amplitudes, is reported and compared to the dislocation arrangement found in single and polycrystals of austenitic and ferritic materials of a similar composition and with the surface relief produced in cyclic plastic straining.

  19. 14 CFR 314.6 - Qualifying dislocation.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 14 Aeronautics and Space 4 2010-01-01 2010-01-01 false Qualifying dislocation. 314.6 Section 314.6 Aeronautics and Space OFFICE OF THE SECRETARY, DEPARTMENT OF TRANSPORTATION (AVIATION PROCEEDINGS) PROCEDURAL... provided by the Airline Deregulation Act of 1978. ...

  20. Left Dislocation in Near-Native French

    ERIC Educational Resources Information Center

    Donaldson, Bryan

    2011-01-01

    The present study is concerned with the upper limits of SLA--specifically, mastery of the syntax-discourse interface in successful endstate learners of second-language (L2) French (near-native speakers). Left dislocation (LD) is a syntactic means of structuring spoken French discourse by marking topic. Its use requires speakers to coordinate…

  1. Reduction of dislocated hip with transepiphyseal fracture.

    PubMed

    Langan, P; Fontanetta, A P

    1986-09-01

    A case report of a 12-year-old boy who suffered a dislocated hip in a football game. He was unable to walk and was in severe pain when seen in the emergency room. Efforts at closed reduction of the displacement were complicated by the development of a transepiphyseal fracture.

  2. Collapse of defect cascades to dislocation loops

    SciTech Connect

    Kirk, M.A.; Robertson, I.M.; Jenkins, M.L.; English, C.A.; Black, T.J.; Vetrano, J.S.

    1986-04-01

    We review a number of experiments that we have recently performed to investigate the collapse of defect cascades to dislocation loops. This important ion and neutron irradiation phenomenon has been studied with in situ ion bombardment in the Argonne National Laboratory High Voltage Electron Microscope-Ion Accelerator Facility at temperatures of 30 and 300/sup 0/K in Cu/sub 3/Au, Cu, and Fe, and 30, 300 and 600/sup 0/K in Ni. These experiments have demonstrated that individual defect cascades collapse to dislocation loops athermally at 30/sup 0/K in some materials (Ni, Cu and Cu/sub 3/Au), while in another material (Fe) only overlapped cascades produced dislocation loops. A slight sensitivity to the irradiation temperature is demonstrated in Cu/sub 3/Au and Fe, and a strong dependence on the irradiation temperature is seen in Ni. This phenomenon of cascade collapse to dislocation loops in metals at 30/sup 0/K provides an understanding for previous neutron irradiation data. The more detailed dependencies of the collapse probability on material, temperature, bombarding ion dose, ion energy and ion mass contribute much information to a thermal spike model of the collision cascade which we will describe.

  3. Left Dislocation in Near-Native French

    ERIC Educational Resources Information Center

    Donaldson, Bryan

    2011-01-01

    The present study is concerned with the upper limits of SLA--specifically, mastery of the syntax-discourse interface in successful endstate learners of second-language (L2) French (near-native speakers). Left dislocation (LD) is a syntactic means of structuring spoken French discourse by marking topic. Its use requires speakers to coordinate…

  4. Assessment of hardening due to dislocation loops in bcc iron: Overview and analysis of atomistic simulations for edge dislocations

    NASA Astrophysics Data System (ADS)

    Bonny, G.; Terentyev, D.; Elena, J.; Zinovev, A.; Minov, B.; Zhurkin, E. E.

    2016-05-01

    Upon irradiation, iron based steels used for nuclear applications contain dislocation loops of both < 100 > and ½ < 111 > type. Both types of loops are known to contribute to the radiation hardening and embrittlement of steels. In the literature many molecular dynamics works studying the interaction of dislocations with dislocation loops are available. Recently, based on such studies, a thermo-mechanical model to threat the dislocation - dislocation loop (DL) interaction within a discrete dislocation dynamics framework was developed for ½ < 111 > loops. In this work, we make a literature review of the dislocation - DL interaction in bcc iron. We also perform molecular dynamics simulations to derive the stress-energy function for < 100 > loops. As a result we deliver the function of the activation energy versus activation stress for < 100 > loops that can be applied in a discrete dislocation dynamics framework.

  5. Dislocation Processes and Frictional Stability of Faults

    NASA Astrophysics Data System (ADS)

    Toy, V. G.; Mitchell, T. M.; Druiventak, A.

    2011-12-01

    The rate dependence of frictional processes in faults in quartzofeldspathic crust is proposed to change at c. 300°C, because above this temperature asperity deformation can be accommodated by crystal plastic processes. As a consequence, the real fault contact area increases and the fault velocity strengthens. Conversely, faults at lower temperatures are velocity weakening and therefore prone to earthquake slip. We have investigated whether dislocation processes are important around faults in quartzites on seismic timescales, by inducing fault slip on a saw cut surface in novaculite blocks. Deformation was carried out at 450°C and 600°C in a Griggs apparatus. Slip rates of 8.3 x 10-7s-1 allowed total slip, u, of 0.5mm to be achieved in c. 10 minutes. Failure occurred at peak differential stresses of ~1.7 GPa and 1.4 GPa respectively, followed by significant weakening. Structures of the novaculite within and surrounding the fault surface were examined using EBSD, FIB-SEM and TEM to elucidate changes to their dislocation substructure. In the sample deformed at 450°C, a ~50μm thick layer of amorphous / non-crystalline silica was developed on the saw-cut surface during deformation. Rare clasts of the wall rock are preserved within this material. The surrounding sample is mostly composed of equant quartz grains of 5-10μm diameter that lack a preferred orientation, contain very few intercrystalline dislocations, and are divided by organised high angle grain boundaries. After deformation, most quartz grains within the sample retain their starting microstructure. However, within ~10μm of the sliding surface, dislocations are more common, and these are arranged into elongated, tangled zones (subgrain boundaries?). Microfractures are also observed. These microstructures are characteristic of deformation accommodated by low temperature plasticity. Our preliminary observations suggest that dislocation processes may be able to accommodate some deformation around fault

  6. Screw dislocation driven growth of nanomaterials.

    PubMed

    Meng, Fei; Morin, Stephen A; Forticaux, Audrey; Jin, Song

    2013-07-16

    Nanoscience and nanotechnology impact our lives in many ways, from electronic and photonic devices to biosensors. They also hold the promise of tackling the renewable energy challenges facing us. However, one limiting scientific challenge is the effective and efficient bottom-up synthesis of nanomaterials. We can approach this core challenge in nanoscience and nanotechnology from two perspectives: (a) how to controllably grow high-quality nanomaterials with desired dimensions, morphologies, and material compositions and (b) how to produce them in a large quantity at reasonable cost. Because many chemical and physical properties of nanomaterials are size- and shape-dependent, rational syntheses of nanomaterials to achieve desirable dimensionalities and morphologies are essential to exploit their utilities. In this Account, we show that the dislocation-driven growth mechanism, where screw dislocation defects provide self-perpetuating growth steps to enable the anisotropic growth of various nanomaterials at low supersaturation, can be a powerful and versatile synthetic method for a wide variety of nanomaterials. Despite significant progress in the last two decades, nanomaterial synthesis has often remained an "art", and except for a few well-studied model systems, the growth mechanisms of many anisotropic nanostructures remain poorly understood. We strive to go beyond the empirical science ("cook-and-look") and adopt a fundamental and mechanistic perspective to the anisotropic growth of nanomaterials by first understanding the kinetics of the crystal growth process. Since most functional nanomaterials are in single-crystal form, insights from the classical crystal growth theories are crucial. We pay attention to how screw dislocations impact the growth kinetics along different crystallographic directions and how the strain energy of defected crystals influences their equilibrium shapes. Furthermore, such inquiries are supported by detailed structural investigation to

  7. Subacute dislocation of the elbow following Galeazzi fracture-dislocation of the radius: A case report

    PubMed Central

    2011-01-01

    Introduction The Galeazzi fracture-dislocation was originally described by Sir Astley Cooper in 1822 but was named after Italian surgeon Ricardo Galeazzi in 1934. It is an injury classified as a radial shaft fracture with associated dislocation of the distal radioulnar joint and disruption of the forearm axis joint. The associated distal radioulnar joint injury may be purely ligamentous in nature, tearing the triangular fibrocartilaginous complex, or involve bony tissue (that is, ulnar styloid avulsions) or both. We report this case because of the rare association of posterior dislocation of the elbow along with Galeazzi fracture-dislocation. To the best of our knowledge, this has not been previously reported in the English literature. Case presentation A 26-year-old Caucasian man presented to our department after a fall from a motorbike. He sustained a closed, isolated Galeazzi fracture-dislocation of the right forearm and no associated elbow injuries, and this necessitated open reduction and internal fixation of the radius. Post-operative radiographs films were satisfactory. However, clinical and radiological evidence of ipsilateral elbow dislocation was noted at a five-week follow-up, subsequently requiring open reduction of the joint and collateral ligament repair. Our patient was noted to have full elbow and forearm function at three months. Conclusions Although the Galeazzi fracture-dislocation has been classically described as involving only the distal radioulnar joint, traumatic forces can be transmitted to the elbow via the interosseous membrane of the forearm. This can lead to instability of the elbow joint. Therefore, we recommend that, in every case of forearm fracture, both elbow and wrist joints be assessed clinically as well as radiologically for subluxation or dislocation. PMID:22185342

  8. [Modern ideas on the treatment of dislocations and fracture-dislocations in the elbow joint].

    PubMed

    Dul'tsev, I A; Zhabin, G I; Neverov, V A

    2005-01-01

    The authors describe the causes and surgical methods of treatment of fresh and long-standing dislocations and fracture-dislocations in the elbow joint. The indications to using different operative methods and technical-surgical interventions are described in details as well as long-term results of treatment by the literature data. The current methods and the authors' methods of prophylactics and treatment of postoperative complications are analyzed. The methods of rehabilitation of such patients are also described.

  9. Subacute dislocation of the elbow following Galeazzi fracture-dislocation of the radius: A case report.

    PubMed

    Rajeev, Aysha; Senevirathna, Shanaka; Harrison, John

    2011-12-20

    The Galeazzi fracture-dislocation was originally described by Sir Astley Cooper in 1822 but was named after Italian surgeon Ricardo Galeazzi in 1934. It is an injury classified as a radial shaft fracture with associated dislocation of the distal radioulnar joint and disruption of the forearm axis joint. The associated distal radioulnar joint injury may be purely ligamentous in nature, tearing the triangular fibrocartilaginous complex, or involve bony tissue (that is, ulnar styloid avulsions) or both. We report this case because of the rare association of posterior dislocation of the elbow along with Galeazzi fracture-dislocation. To the best of our knowledge, this has not been previously reported in the English literature. A 26-year-old Caucasian man presented to our department after a fall from a motorbike. He sustained a closed, isolated Galeazzi fracture-dislocation of the right forearm and no associated elbow injuries, and this necessitated open reduction and internal fixation of the radius. Post-operative radiographs films were satisfactory. However, clinical and radiological evidence of ipsilateral elbow dislocation was noted at a five-week follow-up, subsequently requiring open reduction of the joint and collateral ligament repair. Our patient was noted to have full elbow and forearm function at three months. Although the Galeazzi fracture-dislocation has been classically described as involving only the distal radioulnar joint, traumatic forces can be transmitted to the elbow via the interosseous membrane of the forearm. This can lead to instability of the elbow joint. Therefore, we recommend that, in every case of forearm fracture, both elbow and wrist joints be assessed clinically as well as radiologically for subluxation or dislocation.

  10. Piezomagnetic fields produced by dislocation sources

    NASA Astrophysics Data System (ADS)

    Sasai, Yoichi

    1994-07-01

    Tectonomagnetic modeling based on the linear piezomagnetic effect is reviewed with special attention to dislocation models. Stacey's scheme was the prototype for such modeling, as proposed in his first seismomagnetic calculations in 1964. The linear piezomagnetic law is presented, in which the stress-induced magnetization is expressed as a linear combination of stress components. The Gauss law for magnetic field and the Cauchy-Navier equation for static elastic equilibrium are combined through linear piezomagnetism and the Hooke law to yield the basic equation for piezomagnetic potential. A representation theorem for its solution is given by surface integrals of the displacement and its normal derivative over the strained body. A Green's function method is developed to compute the piezomagnetic field produced by a dislocation surface in an elastic half-space. Volterra's formula for piezomagnetic potential is derived by modifying Stacey's scheme for tectonomagnetic modeling. The Green's functions for the problem are called elementary piezomagnetic potentials, which are defined as potentials produced by elementary dislocations. Special consideration is required to construct the elementary piezomagnetic potentials, because the stress field around a point dislocation has a singularity of order r -3. The integral representing elementary piezomagnetic potentials is not uniformly convergent. Owing to inappropriate convergency, the Green's functions obtained in an earlier study led to a puzzling outcome. Revised Green's functions give consistent results with those obtained so far by numerical integrations. Generally the piezomagnetic field produced by dislocation sources is weak in the case of a homogeneous earth model. Two enhancement effects for piezomagnetic signals are suggested: one due to inhomogeneous magnetization and the other via bore-hole observations.

  11. Elbow dislocation with irreparable fracture radial head

    PubMed Central

    Tanna, Dilip

    2013-01-01

    Background: Treatment of elbow dislocation with irreparable radial head fracture needs replacement of radial head to achieve stability of elbow. An alternate method in cases of elbow dislocation with radial head fracture can be resection of radial head with repair of medial collateral ligament. We report a retrospective analysis of cases of elbow dislocation with irreparable radial head treated by excision head of radius and repair of MCL. Materials and Methods: Nine patients of elbow dislocation with associated irreparable fractures of the head of the radius were included in this analysis (6 F:3 M, Age: 35-47 years). Radial head excision was done through the lateral approach and MCL was sutured using no 3 Ethibond using medial approach. Above elbow plaster was given for 6 weeks and gradual mobilization was done thereafter. All patients were assessed at final followup using Mayo elbow performance score (MEPS). Results: Mean followup was 19.55 ± 7.12 months (range 14-36 months). There was no extension deficit when compared to opposite side with mean range of flexion of 138.8° ± 6.97° (range 130 -145°). Mean pronation was 87.7° ± 4.4° (range 80-90°) and mean supination was 87.7 ± 4.62° (range 80-90°). The mean MEPS was 98.8 ± 3.33 (range 90-100). No patient had pain, sensory complaints, subluxation or redislocation. All were able to carry out their daily activities without disability. Conclusion: Radial head excision with MCL repair is an acceptable option for treatment of patients with elbow dislocation and irreparable radial head fracture. PMID:23798760

  12. Re-dislocation after corrective osteotomy for chronic dislocation of the radial head in children.

    PubMed

    Suzuki, T; Seki, A; Nakamura, T; Ikegami, H; Takayama, S; Nakamura, M; Matsumoto, M; Sato, K

    2015-11-01

    This retrospective study was designed to evaluate the outcomes of re-dislocation of the radial head after corrective osteotomy for chronic dislocation. A total of 12 children with a mean age of 11 years (5 to 16), with further dislocation of the radial head after corrective osteotomy of the forearm, were followed for a mean of five years (2 to 10). Re-operations were performed for radial head re-dislocation in six children, while the other six did not undergo re-operation ('non-re-operation group'). The active range of movement (ROM) of their elbows was evaluated before and after the first operation, and at the most recent follow-up. In the re-operation group, there were significant decreases in extension, pronation, and supination when comparing the ROM following the corrective osteotomy and following re-operation (p < 0.05). The children who had not undergone re-operation achieved a better ROM than those who had undergone re-operation. There was a significant difference in mean pronation (76° vs 0°) between the non- re-operation and the re-operation group (p = 0.002), and a trend towards increases in mean flexion (133° vs 111°), extension (0° vs 23°), and supination (62° vs 29°). We did not find a clear benefit for re-operation in children with a re-dislocation following corrective osteotomy for chronic dislocation of the radial head.

  13. Constitution, 1989. [Selected provisions].

    PubMed

    1989-01-01

    Chapter XII of the Hungarian Constitution, 1989, details the Fundamental Rights and Duties of Citizens. Everyone lawfully within the territory of Hungary has the right to liberty of movement and the freedom to choose his or her residence, except when restricted by law, including the right to leave his or her residence or county. The Republic of Hungary grants asylum to foreign citizens who were persecuted for racial, religious ethnic, linguistic, or political reasons. Men and women shall equally enjoy all civil, political, economic, social and political rights. Mothers are entitled to special care and protection before and after childbirth; women and juveniles are protected at work by special regulations. Every child has the right to special care an assistance from his or her family, the State, and society, for appropriate physical, spiritual, and moral development. Parents shall decide the kind of education their children receive. Hungary grants equal rights to all person within its territories, without regard to race, color, sex, language, religion, political, or other opinion, national, and social origin, property, birth and other status. Prejudicial discrimination shall be severely punished. Everyone has the right to work, to the free choice of employment and profession and to equal pay for equal work. Citizens have the right to social security, including social services necessary in old age, sickness, disability, widowhood, orphanhood an unemployment through no fault of their own. Hungary guarantees the right to culture for its citizens and realized this right by free and compulsory elementary education, by secondary and higher education which is accessible to all on the basis of capacity, and by the financial support of those receiving an education.

  14. Dislocation kinematics: a molecular dynamics study in Cu

    NASA Astrophysics Data System (ADS)

    Oren, E.; Yahel, E.; Makov, G.

    2017-02-01

    The kinematics and kinetics of edge and screw dislocations in FCC materials were studied by molecular dynamics, with Cu as a case study. It was found that with increasing stress screw dislocations enter into the transonic regime continuously and that they remain stable up to a velocity of about 2.2 km s-1. Edge dislocations are limited by the transverse sound velocity at low stresses and discontinuously cross into the transonic regime at higher stresses. For sufficiently long edge dislocations, the subsonic-transonic transition is initiated by an athermal nucleation process. Finally, an expression for the velocity dependence of the dislocation mobility was derived.

  15. Ulnopalmar dislocation of the fifth carpometacarpal joint. A rare injury.

    PubMed

    Fischer, J W; Waseem, M; Gambhir, A; Creedon, R J

    2002-04-01

    Volar dislocation of the carpometacarpal joint of the little finger is an uncommon injury. It is subdivided in ulnopalmar and radiopalmar dislocations. The injury can easily be missed on standard x-rays. Closed reduction and K-wire fixation has commonly been used in the treatment, although closed reduction and casting has been reported. Only 10 cases of an ulnopalmar dislocation were published previously. We report a case of a simultaneous dislocation of the 4th metacarpophalangeal joint and an ulnopalmar dislocation of the 5th carpometacarpal joint. The combination of these injuries has not been reported yet. We review the available literature and discuss the methods of treatment.

  16. Isolated Carpo-Metacarpal Dislocation of the Thumb

    PubMed Central

    Suresh, SS; Zaki, Hosam; Ahmed, Aamir

    2012-01-01

    Introduction: Isolated dislocations of the trapezio metacarpal joint without associated fracture has been reported very rarely in the literature. There are reports of associated injuries like fracture of the trapezium, dislocation of the metacarpophalangeal joint and fractures of the base of the thumb metacarpal. Case Report: Authors report a case of isolated carpometacarpal dislocation of the right thumb, in an adult, successfully managed conservatively. At 15 months follow up the patient had full function of the hand without any clinical or radiological evidence of instability or posttraumatic arthritis. Conclusion: Isolated dislocations can be successfully managed by closed reduction and immobilization in a back slab, with unstable dislocations requiring surgical intervention. PMID:27298846

  17. Radiation enhanced basal plane dislocation glide in GaN

    NASA Astrophysics Data System (ADS)

    Yakimov, Eugene B.; Vergeles, Pavel S.; Polyakov, Alexander Y.; Lee, In-Hwan; Pearton, Stephen J.

    2016-05-01

    A movement of basal plane segments of dislocations in GaN films grown by epitaxial lateral overgrowth under low energy electron beam irradiation (LEEBI) was studied by the electron beam induced current (EBIC) method. Only a small fraction of the basal plane dislocation segments were susceptible to irradiation and the movement was limited to relatively short distances. The effect is explained by the radiation enhanced dislocation glide (REDG) in the structure with strong pinning. A dislocation velocity under LEEBI with a beam current lower than 1 nA was estimated as about 10 nm/s. The results assuming the REDG for prismatic plane dislocations were presented.

  18. The dynamics of an edge dislocation in a ferromagnetic crystals

    NASA Astrophysics Data System (ADS)

    Dezhin, V. V.; Nechaev, V. N.

    2016-08-01

    The system of equations describing the bending vibrations of the dislocation in the ferromagnetic crystal is written. Elastic and magnetostrictive properties of the ferromagnetic crystals are considered isotropic. The linearization of the resulting system produced a relatively small contribution to the magnetization from the influence of dislocation. In the linear approximation of the dislocation displacement system of equation describing vibrations of a ferromagnetic crystal with an edge dislocation is obtained. The equation of motion of an edge dislocation in a ferromagnetic crystal is found.

  19. Empirical potential simulations of interstitial dislocation loops in uranium dioxide

    NASA Astrophysics Data System (ADS)

    Le Prioux, Arno; Fossati, Paul; Maillard, Serge; Jourdan, Thomas; Maugis, Philippe

    2016-10-01

    Stoichiometric circular shaped interstitial dislocation loop energies are calculated in stoichiometric UO2 by empirical potential simulation. The Burgers vector directions studied are <110> and <111>. The main structural properties of each type of interstitial dislocation loop are determined, including stacking fault energy. Defect energies are compared and a maximum size for stable <111> dislocation loops before transition to <110> dislocation loops is given. A model of dislocation loop energy based on elasticity theory is then fitted on the basis of these simulation results.

  20. Te homogeneous precipitation in Ge dislocation loop vicinity

    SciTech Connect

    Perrin Toinin, J.; Portavoce, A. Texier, M.; Bertoglio, M.; Hoummada, K.

    2016-06-06

    High resolution microscopies were used to study the interactions of Te atoms with Ge dislocation loops, after a standard n-type doping process in Ge. Te atoms neither segregate nor precipitate on dislocation loops, but form Te-Ge clusters at the same depth as dislocation loops, in contradiction with usual dopant behavior and thermodynamic expectations. Atomistic kinetic Monte Carlo simulations show that Te atoms are repulsed from dislocation loops due to elastic interactions, promoting homogeneous Te-Ge nucleation between dislocation loops. This phenomenon is enhanced by coulombic interactions between activated Te{sup 2+} or Te{sup 1+} ions.

  1. Essential Medicines in National Constitutions

    PubMed Central

    Toebes, Brigit; Hogerzeil, Hans

    2016-01-01

    Abstract A constitutional guarantee of access to essential medicines has been identified as an important indicator of government commitment to the progressive realization of the right to the highest attainable standard of health. The objective of this study was to evaluate provisions on access to essential medicines in national constitutions, to identify comprehensive examples of constitutional text on medicines that can be used as a model for other countries, and to evaluate the evolution of constitutional medicines-related rights since 2008. Relevant articles were selected from an inventory of constitutional texts from WHO member states. References to states’ legal obligations under international human rights law were evaluated. Twenty-two constitutions worldwide now oblige governments to protect and/or to fulfill accessibility of, availability of, and/or quality of medicines. Since 2008, state responsibilities to fulfill access to essential medicines have expanded in five constitutions, been maintained in four constitutions, and have regressed in one constitution. Government commitments to essential medicines are an important foundation of health system equity and are included increasingly in state constitutions. PMID:27781006

  2. Dislocation mechanisms in stressed crystals with surface effects

    NASA Astrophysics Data System (ADS)

    Wu, Chi-Chin; Crone, Joshua; Munday, Lynn; Discrete Dislocation Dynamics Team

    2014-03-01

    Understanding dislocation properties in stressed crystals is the key for important processes in materials science, including the strengthening of metals and the stress relaxation during the growth of hetero-epitaxial structures. Despite existing experimental approaches and theories, many dislocation mechanisms with surface effects still remain elusive in experiments. Even though discrete dislocation dynamics (DDD) simulations are commonly employed to study dislocations, few demonstrate sufficient computational capabilities for massive dislocations with the combined effects of surfaces and stresses. Utilizing the Army's newly developed FED3 code, a DDD computation code coupled with finite elements, this work presents several dislocation mechanisms near different types of surfaces in finite domains. Our simulation models include dislocations in a bended metallic cantilever beam, near voids in stressed metals, as well as threading and misfit dislocations in as-grown semiconductor epitaxial layers and their quantitative inter-correlations to stress relaxation and surface instability. Our studies provide not only detailed physics of individual dislocation mechanisms, but also important collective dislocation properties such as dislocation densities and strain-stress profiles and their interactions with surfaces.

  3. Elastic Stiffness of Grain Boundary Scars and Dislocation Dynamics

    NASA Astrophysics Data System (ADS)

    Shin, Homin; Bowick, Mark

    2006-03-01

    We analytically calculate the stiffness of finite-length grain boundaries (scars) on a spherical crystal within the continuum elasticity theory. The scar is composed of an isolated disclination with +1 topological charge together with a finite number of dislocations. We determine the elastic free energy of a single finite-grain boundary scar by considering interacting defects, such as Disclination-Disclination (D-D), Disclination-dislocation (D-d), and dislocation-dislocation (d-d). The harmonic potential binding dislocations to the scar is obtained by determining the free energy of a single dislocation perturbed away from its equilibrium position. The elastic spring constants so obtained are compared to experimental data on dislocation dynamics [1]. We conclude with some comments on interstitial dynamics. [1] Lipowsky, P., Bowick, M. J., Meinke, J. H., Nelson, D. R. and Bausch, A. R. Nature Mater. 4, 407-411 (2005).

  4. Electron energy can oscillate near a crystal dislocation

    NASA Astrophysics Data System (ADS)

    Li, Mingda; Cui, Wenping; Dresselhaus, Mildred S.; Chen, Gang

    2017-01-01

    Crystal dislocations govern the plastic mechanical properties of materials but also affect the electrical and optical properties. However, a fundamental and quantitative quantum field theory of a dislocation has remained undiscovered for decades. Here we present an exactly-solvable one-dimensional quantum field theory of a dislocation, for both edge and screw dislocations in an isotropic medium, by introducing a new quasiparticle which we have called the ‘dislon’. The electron-dislocation relaxation time can then be studied directly from the electron self-energy calculation, which is reducible to classical results. In addition, we predict that the electron energy will experience an oscillation pattern near a dislocation. Compared with the electron density’s Friedel oscillation, such an oscillation is intrinsically different since it exists even with only single electron is present. With our approach, the effect of dislocations on materials’ non-mechanical properties can be studied at a full quantum field theoretical level.

  5. Incidence of elbow dislocations in the United States population.

    PubMed

    Stoneback, Jason W; Owens, Brett D; Sykes, Joshua; Athwal, George S; Pointer, Lauren; Wolf, Jennifer Moriatis

    2012-02-01

    There is minimal published information regarding the epidemiology of simple elbow dislocations. The purpose of this study was to report the estimated incidence of elbow dislocations in the United States, with use of the National Electronic Injury Surveillance System (NEISS) database. The NEISS database includes 102 hospitals representing a random sampling of all patients presenting to U.S. emergency departments. The database was queried for elbow dislocation events. NEISS data for 2002 through 2006 were used for raw data and weighted injury counts. Incidence rates with 95% confidence intervals (95% CI) were calculated by age group and sex, with use of U.S. census data. One thousand and sixty-six elbow dislocations were identified, representing a weighted estimate of 36,751 acute dislocations nationwide. A calculated incidence of 5.21 dislocations per 100,000 person-years (95% CI, 4.74 to 5.68) was noted. The highest incidence of elbow dislocations (43.5%) occurred in those who were ten to nineteen years old (6.87 per 100,000 person-years; 95% CI, 5.97 to 7.76). The incidence rate ratio for the comparison of dislocations in males with those in females was 1.02 (5.26 per 100,000 for males and 5.16 per 100,000 for females). In patients ten years or older, 474 injuries (44.5% of total dislocations) were sustained in sports. Males dislocated elbows in football, wrestling, and basketball. Females sustained elbow dislocations most frequently in gymnastics and skating activities. The estimated incidence of elbow dislocations in the U.S. population is 5.21 per 100,000 person-years, with use of a national database. Adolescent males are at highest risk for dislocation. Nearly half of acute elbow dislocations occurred in sports, with males at highest risk with football, and females at risk with gymnastics and skating activities.

  6. Constitutional Issues--Watergate and the Constitution. Teaching with Documents.

    ERIC Educational Resources Information Center

    National Archives and Records Administration, Washington, DC.

    When U.S. President Richard Nixon resigned in 1974 in the wake of the Watergate scandal, it was only the second time that impeachment of a president had been considered. Although the U.S. Constitution has provisions for a person removed from office to be indicted, there are no guidelines in the Constitution about a President who has resigned. The…

  7. Transtriquetral perihamate fracture-dislocation: case report.

    PubMed

    Moraes, Frederico Barra de; Ferreira, Rodrigo Cunha; Geraldino, Stéphanie Zago; Farias, Renato Silva; Silva, Ricardo Pereira da; Kuwae, Mário Yoshihide

    2016-01-01

    The wrist is a region that is very vulnerable to injuries of the extremities. Among these injuries, fractures of the pyramidal bone (or triquetrum) in association with dislocation of the hamate and carpal instability are uncommon. They are generally correlated with high-energy trauma and may be associated with neurovascular deficits, muscle-tendon disorders, skin lesions or injuries to other carpal bones. Thus, in this report, one of these rare cases of transtriquetral perihamate fracture-dislocation with carpal instability is presented, diagnosed by means of radiography on the right wrist of the patient who presented pain, edema and limitation of flexion-extension of the carpus after trauma to the region. The stages of attending to the case are described, from the initial consultation to the surgical treatment and physiotherapy, which culminated in restoration of the strength and range of motion of the wrist.

  8. Low energy dislocation structures in epitaxy

    NASA Technical Reports Server (NTRS)

    Van Der Merwe, Jan H.; Woltersdorf, J.; Jesser, W. A.

    1986-01-01

    The principle of minimum energy was applied to epitaxial interfaces to show the interrelationship beteen misfit, overgrowth thickness and misfit dislocation spacing. The low energy dislocation configurations were presented for selected interfacial geometries. A review of the interfacial energy calculations was made and a critical assessment of the agreement between theory and experiment was presented. Modes of misfit accommodation were presented with emphasis on the distinction between kinetic effects and equilibrium conditions. Two-dimensional and three-dimensional overgrowths were treated together with interdiffusion-modified interfaces, and several models of interfacial structure were treated including the classical and the current models. The paper is concluded by indicating areas of needed investigation into interfacial structure.

  9. Dislocation-Defect Interactions in Materials

    SciTech Connect

    Robach, J S; Robertson, I M; Ahn, D C; Sofronis, P; Wirth, B D; Arsenlis, T

    2003-02-27

    In order to develop predictive models of the mechanical response of irradiated materials it is necessary to understand the fundamental physical processes controlling the deformation. This is particularly important near yielding where local defect interactions may dominate the behavior. Dislocation-defect interactions in copper containing various densities and distributions of stacking-fault tetrahedra and small dislocation loops were examined dynamically using the in-situ TEM straining technique. Defect annihilation mechanisms as well as the conditions required to produce defect-free channels are proposed. The experimental results are compared to atomistic simulations and continuum mechanics calculations of unit interactions. Based on these observations, an improved continuum model of the mechanical behavior of irradiated materials is presented.

  10. Treatment of Galeazzi fracture-dislocations.

    PubMed

    Maculé Beneyto, F; Arandes Renú, J M; Ferreres Claramunt, A; Ramón Soler, R

    1994-03-01

    Among 33 patients with a Galeazzi-type fracture-dislocation of the forearm, there were two children and 26 adults with a classic Galeazzi injury, and five patients with a Galeazzi-equivalent lesion. The worst results were obtained in type-I lesions. Closed reduction was primarily successful in children. The results of surgical treatment were much better in adults. It is advisable to treat this complex injury by anatomic reduction and internal fixation of the radial shaft fracture. Immobilization in a fully supinated position is recommended to reduce the dislocation of the distal radioulnar joint. Additional temporary radioulnar fixation with Kirschner wires is also necessary in cases of severe derangement of the distal radioulnar joint.

  11. A fast density-based clustering algorithm for real-time Internet of Things stream.

    PubMed

    Amini, Amineh; Saboohi, Hadi; Wah, Teh Ying; Herawan, Tutut

    2014-01-01

    Data streams are continuously generated over time from Internet of Things (IoT) devices. The faster all of this data is analyzed, its hidden trends and patterns discovered, and new strategies created, the faster action can be taken, creating greater value for organizations. Density-based method is a prominent class in clustering data streams. It has the ability to detect arbitrary shape clusters, to handle outlier, and it does not need the number of clusters in advance. Therefore, density-based clustering algorithm is a proper choice for clustering IoT streams. Recently, several density-based algorithms have been proposed for clustering data streams. However, density-based clustering in limited time is still a challenging issue. In this paper, we propose a density-based clustering algorithm for IoT streams. The method has fast processing time to be applicable in real-time application of IoT devices. Experimental results show that the proposed approach obtains high quality results with low computation time on real and synthetic datasets.

  12. A Fast Density-Based Clustering Algorithm for Real-Time Internet of Things Stream

    PubMed Central

    Ying Wah, Teh

    2014-01-01

    Data streams are continuously generated over time from Internet of Things (IoT) devices. The faster all of this data is analyzed, its hidden trends and patterns discovered, and new strategies created, the faster action can be taken, creating greater value for organizations. Density-based method is a prominent class in clustering data streams. It has the ability to detect arbitrary shape clusters, to handle outlier, and it does not need the number of clusters in advance. Therefore, density-based clustering algorithm is a proper choice for clustering IoT streams. Recently, several density-based algorithms have been proposed for clustering data streams. However, density-based clustering in limited time is still a challenging issue. In this paper, we propose a density-based clustering algorithm for IoT streams. The method has fast processing time to be applicable in real-time application of IoT devices. Experimental results show that the proposed approach obtains high quality results with low computation time on real and synthetic datasets. PMID:25110753

  13. Dislocation Concepts in Friction and Wear.

    DTIC Science & Technology

    1980-12-01

    one well-investigated case is explained in this manner, using a work-hardening law that appears to be common in wire drawing . (xi) Dislocation cells...different slip systems. The discussed principles may be illustrated by experimental evidence for the case of wire drawing : In wire drawing the wire axis of...fault energies shift the f cc wire drawing texture so as to favor the > component, as was first pointed out by N. Brown~4 ~ Similarly, therefore, one

  14. Dislocation Etching Solutions for Mercury Cadmium Selenide

    DTIC Science & Technology

    2014-09-01

    Dislocation Etching Solutions for Mercury Cadmium Selenide by Kevin Doyle and Sudhir Trivedi ARL-CR-0744 September 2014...Etching Solutions for Mercury Cadmium Selenide Kevin Doyle and Sudhir Trivedi Sensors and Electron Devices Directorate, ARL prepared by...Solutions for Mercury Cadmium Selenide 5a. CONTRACT NUMBER W811NF-12-2-0019 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) Kevin Doyle and

  15. Dislocations: 75 years of Deformation Mechanisms

    NASA Technical Reports Server (NTRS)

    Schneider, Judy

    2009-01-01

    The selection of papers presented in this section reflect on themes to be explored at the "Dislocations: 75 years of Deformation Mechanisms" Symposium to be held at the Annual 2009 TMS meeting. The symposium was sponsored by the Mechanical Behavior of Materials Committee to give tribute to the evolution of a concept that has formed the basis of our mechanistic understanding of how crystalline solids plastically deform and how they fail.

  16. Management of an Uncomplicated Posterior Elbow Dislocation

    PubMed Central

    Blackard, Douglas; Sampson, Jo-Ann

    1997-01-01

    Objective: To present a case of an uncomplicated posterior elbow dislocation in a US World Cup athlete and discuss her rehabilitation. Background: Traditional protocol for management of this injury has been splint immobilization for several weeks, but research suggests a shortened duration of immobilization and early active motion. Differential Diagnosis: Elbow dislocation with possible fracture. Treatment: The dislocation was reduced and a compression bandage and sling were applied. The sports medicine staff and athlete determined that rehabilitation would involve limited immobilization with a posterior splint. Also, active range-of- motion exercises were to be incorporated early in the range-of- motion program to decrease pain at the articulation. Uniqueness: The athlete was not immobilized and her aggressive five-phase rehabilitation program progressed according to decrease in inflammation and increase in range of motion and strength. Conclusions: Shortened immobilization and return to World Championship competition 6 weeks postinjury had no longterm adverse effects on the athlete. ImagesFig 1.Fig 2.Fig 3.Fig 4.Fig. 5. PMID:16558436

  17. Dislocation Theory of the Fatigue of Metals

    NASA Technical Reports Server (NTRS)

    Machlin, E S

    1949-01-01

    A dislocation theory of fatigue failure for annealed solid solutions is presented. On the basis of this theory, an equation giving the dependence of the number of cycles for failure on the stress, the temperature, the material parameters, and the frequency is derived for uniformly stressed specimens. The equation is in quantitative agreement with the data. Inasmuch as one material parameter is indicated to be temperature-dependent and its temperature dependence is unknown, it is impossible to predict the temperature dependence of the number of cycles for failure. A predicted quantitative correlation between fatigue and creep was found to exist, which suggests the practical possibility of obtaining fatigue data for annealed solid solutions and elements from steady-state creep-rate data for these materials. As a result of this investigation, a modification of the equation for the steady-state creep rate previously developed on the basis of the dislocation theory is suggested. Additional data are required to verify completely the dislocation theory of fatigue.

  18. Congenital subtalar dislocation--a case report.

    PubMed

    Saini, Raghav; Dhillon, M S; Gill, S S

    2009-09-01

    Congenital dislocation of the subtalar joint is one of the rarest forms of presentation of a calcaneo-valgus foot. We report the second case of this type published; an 18-month female child aged was seen with calcaneo-valgus deformity of left foot since birth. She was walking over the medial malleolus and medial border of foot. Radiographs and 3D CT scan of the left foot confirmed the diagnosis of a congenital subtalar dislocation. Surgical correction was achieved through a posterolateral incision, and the reduced joint was fixed with a k-wires for 6 weeks; the foot was immobilized in below knee cast for another 6 weeks, and an ankle foot orthosis was used for another 3 years. At 3 years post-surgical follow up, the child has a plantigrade foot with no functional impairment. Follow up radiographs and 3D CT scan confirmed the maintenance of well aligned talo-calcaneal joint. This type of dislocation should be considered in the differential diagnosis of calcaneo-valgus foot; a clear understanding of the pathology, a precise operative reduction, and long-term use of orthosis results in a favourable outcome.

  19. Dislocation movement and hysteresis in Maraging blades

    NASA Astrophysics Data System (ADS)

    Di Cintio, Arianna; Marchesoni, Fabio; Ascione, Maria; Bhawal, Abhik; De Salvo, Riccardo

    2009-10-01

    All seismic isolation systems developed for gravitational-wave interferometric detectors, such as LIGO, Virgo and TAMA, make use of Maraging steel blades. The dissipation properties of these blades have been studied at low frequencies, by using a geometric anti-spring (GAS) filter, which allowed the exploration of resonant frequencies below 100 mHz. At this frequency an anomalous transfer function was observed in the GAS filter: this is one of several motivations for this work. The many unexpected effects observed and measured are explainable by the collective movement of dislocations inside the material described with the statistic of self-organised criticality. At low frequencies, below 200 mHz, the dissipation mechanism can subtract elasticity from the system even leading to sudden collapse. While Young's modulus is weaker, excess dissipation is observed. At higher frequencies the applied stress is probably too fast to allow the full growth of dislocation avalanches, and less losses are observed, thus explaining the higher Q-factor in this frequency range. The domino effect that leads to the release of entangled dislocations allows the understanding of the random walk of the Virgo and TAMA inverted pendula, the anomalous GAS filter transfer function as well as the loss of predictability of the ring-down decay in the LIGO seismic attenuation system inverted pendula.

  20. [Bilateral Asymmetric Traumatic Dislocation of Hip Joints].

    PubMed

    Paša, L; Veselý, R; Kelbl, M

    2017-01-01

    The authors present a rare case of bilateral asymmetric traumatic dislocation of hip joints, where the left joint was treated conservatively after the reduction, while the right joint, with an acetabular fragment interposition, was treated surgically - by arthroscopically assisted reduction and fixation of an osteochondral fragment of posterior wall of the acetabulum. The female patient healed with no complications, showing an excellent clinical outcome with no signs of instability or limited mobility of hip joints, and also with no signs of para-articular calcification or necrosis of the hip at 1 year after the injury and treatment. Bilateral asymmetric dislocation of hip joint is a rare injury with the total incidence of 150 cases as reported by the literature. Recently, its incidence is higher due to the increased traffic and the associated accident rate. A precise and prompt reduction of the injured hip joint is always necessary, if possible under general anesthesia. Also, it is always necessary to carry out a complete examination of the patient since this type of injury is always caused by a strong force and is often accompanied by injuries of other parts of the body. Key words: bilateral asymmetric dislocation of hip joints, hip arthroscopy, acetabular fracture.

  1. Open Galeazzi fracture with ipsilateral elbow dislocation.

    PubMed

    Adanır, Oktay; Yüksel, Serdar; Beytemur, Ozan; Güleç, M Akif

    2016-08-01

    Combination of the Galeazzi fracture and dislocation of the elbow joint in same extremity is very rare. In this article, we report a 26-year-old male patient with a posterolateral dislocation of the elbow and ipsilateral volar type Galeazzi fracture. We performed closed reduction for the elbow dislocation during admission to the emergency department. Patient was taken to the operating room in the sixth hour of his application to emergency department and open wound on the ulnovolar region of the wrist was closed primarily after irrigation and debridement. We performed open reduction and internal fixation of the radial fracture with a dynamic compression plate. After fixation, we evaluated the stability of the elbow joint and distal radioulnar joint. Distal radioulnar joint was unstable under fluoroscopic examination and fixed with one 1.8 mm Kirschner wire in a pronated position. Then, elbow joint was stable. One year after surgery, patient had no pain or sings of instability. At the last follow-up, range of motion of the elbow was 10°-135° and forearm pronation and supination were 70°.

  2. Atomistic calculations of dislocation core energy in aluminium

    NASA Astrophysics Data System (ADS)

    Zhou, X. W.; Sills, R. B.; Ward, D. K.; Karnesky, R. A.

    2017-02-01

    A robust molecular-dynamics simulation method for calculating dislocation core energies has been developed. This method has unique advantages: It does not require artificial boundary conditions, is applicable for mixed dislocations, and can yield converged results regardless of the atomistic system size. Utilizing a high-fidelity bond order potential, we have applied this method in aluminium to calculate the dislocation core energy as a function of the angle β between the dislocation line and the Burgers vector. These calculations show that, for the face-centered-cubic aluminium explored, the dislocation core energy follows the same functional dependence on β as the dislocation elastic energy: Ec=A sin2β +B cos2β , and this dependence is independent of temperature between 100 and 300 K. By further analyzing the energetics of an extended dislocation core, we elucidate the relationship between the core energy and the core radius of a perfect versus an extended dislocation. With our methodology, the dislocation core energy can accurately be accounted for in models of dislocation-mediated plasticity.

  3. Probing the character of ultra-fast dislocations

    PubMed Central

    Ruestes, C. J.; Bringa, E. M.; Rudd, R. E.; Remington, B. A.; Remington, T. P.; Meyers, M. A.

    2015-01-01

    Plasticity is often controlled by dislocation motion, which was first measured for low pressure, low strain rate conditions decades ago. However, many applications require knowledge of dislocation motion at high stress conditions where the data are sparse, and come from indirect measurements dominated by the effect of dislocation density rather than velocity. Here we make predictions based on atomistic simulations that form the basis for a new approach to measure dislocation velocities directly at extreme conditions using three steps: create prismatic dislocation loops in a near-surface region using nanoindentation, drive the dislocations with a shockwave, and use electron microscopy to determine how far the dislocations moved and thus their velocity at extreme stress and strain rate conditions. We report on atomistic simulations of tantalum that make detailed predictions of dislocation flow, and find that the approach is feasible and can uncover an exciting range of phenomena, such as transonic dislocations and a novel form of loop stretching. The simulated configuration enables a new class of experiments to probe average dislocation velocity at very high applied shear stress. PMID:26592764

  4. Probing the character of ultra-fast dislocations

    SciTech Connect

    Rudd, R. E.; Ruestes, C. J.; Bringa, E. M.; Remington, B. A.; Remington, T. P.; Meyers, M. A.

    2015-11-23

    Plasticity is often controlled by dislocation motion, which was first measured for low pressure, low strain rate conditions decades ago. However, many applications require knowledge of dislocation motion at high stress conditions where the data are sparse, and come from indirect measurements dominated by the effect of dislocation density rather than velocity. Here we make predictions based on atomistic simulations that form the basis for a new approach to measure dislocation velocities directly at extreme conditions using three steps: create prismatic dislocation loops in a near-surface region using nanoindentation, drive the dislocations with a shockwave, and use electron microscopy to determine how far the dislocations moved and thus their velocity at extreme stress and strain rate conditions. We report on atomistic simulations of tantalum that make detailed predictions of dislocation flow, and find that the approach is feasible and can uncover an exciting range of phenomena, such as transonic dislocations and a novel form of loop stretching. Furthermore, the simulated configuration enables a new class of experiments to probe average dislocation velocity at very high applied shear stress.

  5. Modal analysis of dislocation vibration and reaction attempt frequency

    DOE PAGES

    Sobie, Cameron; Capolungo, Laurent; McDowell, David L.; ...

    2017-02-04

    Transition state theory is a fundamental approach for temporal coarse-graining. It estimates the reaction rate for a transition processes by quantifying the activation free energy and attempt frequency for the unit process. To calculate the transition rate of a gliding dislocation, the attempt frequency is often obtained from line tension estimates of dislocation vibrations, a highly simplified model of dislocation behavior. This work revisits the calculation of attempt frequency for a dislocation bypassing an obstacle, in this case a self-interstitial atom (SIA) loop. First, a direct calculation of the vibrational characteristics of a finite pinned dislocation segment is compared tomore » line tension estimates before moving to the more complex case of dislocation-obstacle bypass. The entropic factor associated with the attempt frequency is calculated for a finite dislocation segment and for an infinite glide dislocation interacting with an SIA loop. Lastly, it is found to be dislocation length independent for three cases of dislocation-self interstitial atom (SIA) loop interactions.« less

  6. BBilateral Neglected Anterior Shoulder Dislocation with Greater Tuberosity Fractures

    PubMed Central

    Upasani, Tejas; Bhatnagar, Abhinav; Mehta, Sonu

    2016-01-01

    Introduction: Shoulder dislocations are a very common entity in routine orthopaedic practice. Chronic unreduced anterior dislocations of the shoulder are not very common. Neurological and vascular complications may occur as a result of an acute anterior dislocation of the shoulder or after a while in chronic unreduced shoulder dislocation. Open reduction is indicated for most chronic shoulder dislocations. We report a case of neglected bilateral anterior shoulder dislocation with bilateral displaced greater tuberosity fracture. To the best of our knowledge, only a handful cases have been reported in literature with bilateral anterior shoulder dislocation with bilateral fractures. Delayed diagnosis/reporting is a scenario which makes the list even slimmer and management all the more challenging. Case Report: We report a case of a 35-year-old male who had bilateral anterior shoulder dislocation and bilateral greater tuberosity fracture post seizure and failed to report it for a period of 30 days. One side was managed conservatively with closed reduction and immobilization and the other side with open reduction. No neurovascular complications pre or post reduction of shoulder were seen. Conclusion: Shoulder dislocations should always be suspected post seizures and if found should be treated promptly. Treatment becomes difficult for any shoulder dislocation that goes untreated for considerable period of time PMID:27703939

  7. Probing the character of ultra-fast dislocations

    NASA Astrophysics Data System (ADS)

    Ruestes, C. J.; Bringa, E. M.; Rudd, R. E.; Remington, B. A.; Remington, T. P.; Meyers, M. A.

    2015-11-01

    Plasticity is often controlled by dislocation motion, which was first measured for low pressure, low strain rate conditions decades ago. However, many applications require knowledge of dislocation motion at high stress conditions where the data are sparse, and come from indirect measurements dominated by the effect of dislocation density rather than velocity. Here we make predictions based on atomistic simulations that form the basis for a new approach to measure dislocation velocities directly at extreme conditions using three steps: create prismatic dislocation loops in a near-surface region using nanoindentation, drive the dislocations with a shockwave, and use electron microscopy to determine how far the dislocations moved and thus their velocity at extreme stress and strain rate conditions. We report on atomistic simulations of tantalum that make detailed predictions of dislocation flow, and find that the approach is feasible and can uncover an exciting range of phenomena, such as transonic dislocations and a novel form of loop stretching. The simulated configuration enables a new class of experiments to probe average dislocation velocity at very high applied shear stress.

  8. Analogies between continuum dislocation theory, continuum mechanics and fluid mechanics

    NASA Astrophysics Data System (ADS)

    Silbermann, C. B.; Ihlemann, J.

    2017-03-01

    Continuum Dislocation Theory (CDT) relates gradients of plastic deformation in crystals with the presence of geometrically necessary dislocations. Interestingly, CDT shows striking analogies to other branches of continuum mechanics. The present contribution demonstrates this on two essential kinematical quantities which reflect tensorial dislocation properties: the (resultant) Burgers vector and the dislocation density tensor. First, the limiting process for the (resultant) Burgers vector from an integral to a local quantity is performed analogously to the limiting process from the force vector to the traction vector. By evaluating the balance of forces on a tetrahedral volume element, Cauchy found his famous formula relating traction vector and stress tensor. It is shown how this procedure may be adopted to a continuously dislocated tetrahedron. Here, the conservation of Burger’s vector implicates the introduction of the dislocation density tensor. Second, analogies between the plastic flow of a continuously dislocated solid and the liquid flow of a fluid are highlighted: the resultant Burgers vector of a dislocation ensemble plays a similar role as the (resultant) circulation of a vortex tube. Moreover, both vortices within flowing fluids and dislocations within deforming solids induce discontinuities in the velocity field and the plastic distortion field, respectively. Beyond the analogies, some peculiar properties of the dislocation density tensor are presented as well.

  9. Probing the character of ultra-fast dislocations

    DOE PAGES

    Rudd, R. E.; Ruestes, C. J.; Bringa, E. M.; ...

    2015-11-23

    Plasticity is often controlled by dislocation motion, which was first measured for low pressure, low strain rate conditions decades ago. However, many applications require knowledge of dislocation motion at high stress conditions where the data are sparse, and come from indirect measurements dominated by the effect of dislocation density rather than velocity. Here we make predictions based on atomistic simulations that form the basis for a new approach to measure dislocation velocities directly at extreme conditions using three steps: create prismatic dislocation loops in a near-surface region using nanoindentation, drive the dislocations with a shockwave, and use electron microscopy tomore » determine how far the dislocations moved and thus their velocity at extreme stress and strain rate conditions. We report on atomistic simulations of tantalum that make detailed predictions of dislocation flow, and find that the approach is feasible and can uncover an exciting range of phenomena, such as transonic dislocations and a novel form of loop stretching. Furthermore, the simulated configuration enables a new class of experiments to probe average dislocation velocity at very high applied shear stress.« less

  10. Atomistic calculations of dislocation core energy in aluminium

    DOE PAGES

    Zhou, Xiaowang W.; Sills, Ryan B.; Ward, Donald K.; ...

    2017-02-16

    A robust molecular-dynamics simulation method for calculating dislocation core energies has been developed. This method has unique advantages: It does not require artificial boundary conditions, is applicable for mixed dislocations, and can yield converged results regardless of the atomistic system size. Utilizing a high-fidelity bond order potential, we have applied this method in aluminium to calculate the dislocation core energy as a function of the angle β between the dislocation line and the Burgers vector. These calculations show that, for the face-centered-cubic aluminium explored, the dislocation core energy follows the same functional dependence on β as the dislocation elastic energy:more » Ec = Asin2β + Bcos2β, and this dependence is independent of temperature between 100 and 300 K. By further analyzing the energetics of an extended dislocation core, we elucidate the relationship between the core energy and the core radius of a perfect versus an extended dislocation. As a result, with our methodology, the dislocation core energy can accurately be accounted for in models of dislocation-mediated plasticity.« less

  11. Numerical Simulation of Dislocation Interactions in Strained Layers

    NASA Astrophysics Data System (ADS)

    Schwarz, Klaus W.

    1998-03-01

    Because both the dynamics and the interactions of dislocations are complicated, little is known about the effects that individual dislocations have on each other when they come into close proximity, and, more generally, about the evolution of collections of strongly interacting dislocations. The power of modern supercomputers allows one to address these issues by direct numerical simulation. In our program the stress tensor which moves the dislocations is calculated at every point by evaluating the full Peach-Koehler expression over all of the dislocations present. The self-interaction of the dislocations is regularized by the Brown method of splitting the dislocation in half, moving the two halves outward by some core parameter, and averaging the result. The code can be used to study the interactions between arbitrarily configured dislocations, located on any allowed glide plane, passing from one glide plane to another, and having any allowed Burgers vector, and has been applied to model the behavior of dislocations in semiconducting thin films. The behavior of a threading dislocation as it tries to pass over a misfit dislocation in the layer interface has been investigated, and the blocking effect of the misfit is found to be considerably less than previously estimated. Subsequent studies have calculated the behavior of Frank-Read sources, spiral sources, and corner sources in a strained layer, as well as that of multiple sources operating on various glide planes. For a model in which the layer is assumed to relax through the excitation of a low density of Frank-Read sources, it is found that the interactions between the emitted dislocations result in elaborate dislocation networks. The predicted patterns are strikingly similar to those observed in actual relaxed layers.

  12. Bi-isotropic constitutive relations

    NASA Astrophysics Data System (ADS)

    Sihvola, A. H.; Lindell, I. V.

    1991-03-01

    The constitutive relations of general bi-isotropic media, requiring four material parameters, can be written in different ways to describe their electromagnetic behavior. This communication contains a two-way 'dictionary' between a proposed formulation of the constitutive relations with three other sets of relations, generalized from relations used for chiral materials.

  13. The Constitution and Citizenship Education.

    ERIC Educational Resources Information Center

    Shoemaker, Rebecca S.

    The paper takes the position that the study and understanding of the United States Constitution should be a critical part of citizenship education, especially as its Bicentennial approaches. Several factors suggest that the Constitution has become the most durable document of its kind in history, and that its teaching should be centered in both…

  14. The Constitution and American Radicalism.

    ERIC Educational Resources Information Center

    Lobel, Jules

    1987-01-01

    Discusses the history of the following movements' attitudes towards the Constitution: (1) abolition; (2) feminism; (3) trade unions; (4) socialism and communism; and (5) civil rights and anti-war. Maintains that the tensions in these movements' towards the Constitution represent basic contradictions in the document itself. (PS)

  15. Constitutional Law and Liberal Education.

    ERIC Educational Resources Information Center

    Clor, Harry

    1985-01-01

    By studying constitutional law, students learn about the relationship between democratic theory and practice, one of the main concerns of liberal education. The mind is enlarged when it must apply ethical standards and political ideas to real human problems. How a political science professor teaches constitutional law is discussed. (RM)

  16. Reordering American Constitutional Law Teaching.

    ERIC Educational Resources Information Center

    Gerber, Scott D.

    1994-01-01

    Maintains that constitutional law is the cornerstone of an undergraduate public law curriculum. Asserts that there is a welcome trend toward teaching the subject over a two-semester sequence, instead of only one. Describes course content and teaching strategies used in a college constitutional law course. (CFR)

  17. How Capitalistic Is the Constitution?

    ERIC Educational Resources Information Center

    Goldwin, Robert A., Ed.; Schambra, William A., Ed.

    Second in a three-part series designed to help prepare the nation for a thoughtful observance of the Constitutional bicentennial, this publication contains seven essays on the topic of capitalism and the Constitution. "American Democracy and the Acquisitive Spirit" (Marc F. Plattner) supports the argument that the framers of the…

  18. Constitution And Bylaws: 2004 Edition

    ERIC Educational Resources Information Center

    Distance Education and Training Council, 2004

    2004-01-01

    This document contains the constitution and bylaws of the Distance Education and Training Council. The constitution and bylaws include 13 articles. Sections include: Name; Mission and Goals; Administration of the Council; Membership; Meetings; The Commission; Terms of Office; Officers; Committees; Compensation; Dues and Assessments; Miscellaneous…

  19. The Constitution and Its Critics

    ERIC Educational Resources Information Center

    Main, Thomas J.

    2011-01-01

    In planning a freshman undergraduate curriculum with colleagues recently, the question arose as to what type of understanding educators wanted to impart to their students about the Constitution. The alleged defects of the Constitution that these books point to are wide-ranging and can be classified into various categories. Some problems--such as…

  20. Sternoclavicular dislocation: case report and surgical technique.

    PubMed

    Terra, Bernardo Barcellos; Rodrigues, Leandro Marano; Pádua, David Victoria Hoffmann; Martins, Marcelo Giovanini; Teixeira, João Carlos de Medeiros; De Nadai, Anderson

    2015-01-01

    Sternoclavicular dislocations account for less than 5% of all dislocations of the scapular belt. Most cases of anterior dislocation of the sternoclavicular joint do not present symptoms. However, some patients may develop chronic anterior instability and remain symptomatic, and surgical treatment is indicated in these cases. There is a scarcity of reports in the literature relating to reconstruction using the long palmar tendon in cases of traumatic anterior instability. Although rare, these injuries deserve rapid diagnosis and efficient treatment in order to avoid future complications. The aim of this report was to report on a case of a motocross competitor who developed chronic traumatic anterior instability of the sternoclavicular joint and underwent surgical reconstruction using the autogenous long palmar tendon. The patient was a 33-year-old man with a history of anterior dislocation of the sternoclavicular subsequent to a fall during a maneuver in a motocross competition. Conservative treatment was instituted initially, consisting of use of a functional sling to treat the symptoms for 3 weeks, along with physiotherapeutic rehabilitation for 3 months. We chose to use a modification of the "figure of eight" technique based on the studies by Spencer and Kuhn. A longitudinal incision of approximately 10 cm was made at the level of the sternoclavicular joint. The graft from the ipsilateral long palmar tendon was passed through the orifices in the form of a modified "figure of eight" and its ends were sutured together. The patient was immobilized using an American sling for 4 weeks. After 6 months of follow-up, the patient no longer presented pain or instability when movement of the sternoclavicular joint was required. Minor discomfort and slight prominence of the sternoclavicular joint continued to be present but did not affect the patient's activities. Thus, the patient was able to return to racing 6 months after the operation. Our study presented a case of

  1. Sternoclavicular dislocation: case report and surgical technique☆

    PubMed Central

    Terra, Bernardo Barcellos; Rodrigues, Leandro Marano; Pádua, David Victoria Hoffmann; Martins, Marcelo Giovanini; Teixeira, João Carlos de Medeiros; De Nadai, Anderson

    2015-01-01

    Sternoclavicular dislocations account for less than 5% of all dislocations of the scapular belt. Most cases of anterior dislocation of the sternoclavicular joint do not present symptoms. However, some patients may develop chronic anterior instability and remain symptomatic, and surgical treatment is indicated in these cases. There is a scarcity of reports in the literature relating to reconstruction using the long palmar tendon in cases of traumatic anterior instability. Although rare, these injuries deserve rapid diagnosis and efficient treatment in order to avoid future complications. The aim of this report was to report on a case of a motocross competitor who developed chronic traumatic anterior instability of the sternoclavicular joint and underwent surgical reconstruction using the autogenous long palmar tendon. The patient was a 33-year-old man with a history of anterior dislocation of the sternoclavicular subsequent to a fall during a maneuver in a motocross competition. Conservative treatment was instituted initially, consisting of use of a functional sling to treat the symptoms for 3 weeks, along with physiotherapeutic rehabilitation for 3 months. We chose to use a modification of the “figure of eight” technique based on the studies by Spencer and Kuhn. A longitudinal incision of approximately 10 cm was made at the level of the sternoclavicular joint. The graft from the ipsilateral long palmar tendon was passed through the orifices in the form of a modified “figure of eight” and its ends were sutured together. The patient was immobilized using an American sling for 4 weeks. After 6 months of follow-up, the patient no longer presented pain or instability when movement of the sternoclavicular joint was required. Minor discomfort and slight prominence of the sternoclavicular joint continued to be present but did not affect the patient's activities. Thus, the patient was able to return to racing 6 months after the operation. Our study presented a case

  2. Bertram Hopkinson's pioneering work and the dislocation mechanics of high rate deformations and mechanically induced detonations.

    PubMed

    Armstrong, Ronald W

    2014-05-13

    Bertram Hopkinson was prescient in writing of the importance of better measuring, albeit better understanding, the nature of high rate deformation of materials in general and, in particular, of the importance of heat in initiating detonation of explosives. This report deals with these subjects in terms of post-Hopkinson crystal dislocation mechanics applied to high rate deformations, including impact tests, Hopkinson pressure bar results, Zerilli-Armstrong-type constitutive relations, shock-induced deformations, isentropic compression experiments, mechanical initiation of explosive crystals and shear banding in metals.

  3. Acute patellar dislocation with multiple ligament injuries after knee dislocation and single session reconstruction.

    PubMed

    Gormeli, Gokay; Gormeli, Cemile Ayse; Karakaplan, Mustafa; Gurbuz, Sukru; Ozdemir, Zeynep; Ozer, Mustafa

    2016-06-01

    Knee dislocation is a relatively rare condition of all orthopaedic injuries. Accompanying multiple ligament injuries are common after knee dislocations. A 41-year-old male presented to the emergency department suffering from right knee dislocation in June 2013. The patient had anterior cruciate ligament, medial collateral ligament (MCL), medial patellofemoral ligament (MPFL) rupture, and lateral meniscal tear. A single-bundle anatomic reconstruction, medial collateral ligament reconstruction, medial patellofemoral ligament reconstruction and meniscus repair were performed in single session. At twelve months follow-up; there was 160º flexion and 10° extension knee range of motion. Lysholm knee score was 90. Extensive forces can cause both MCL and MPFL injury due to overload and the anatomical relationship between these two structures. Therefore, patients with valgus instability should be evaluated for both MPFL and MCL tears to facilitate successful treatment.

  4. [Elbow dislocation with ipsilateral proximal radial shaft fracture and radial head dislocation].

    PubMed

    Köhn, N; Mendel, T; Ullrich, B W

    2015-11-01

    Elbow dislocation with ipsilateral proximal radial shaft fracture and dislocated radial head is a rarely described injury. In this article we present the case of a 23-year-old man with this injury. After the initial diagnostics, the radial shaft fracture was osteosynthetically fixed, whereby the anatomical positions of all parts of the elbow joint were correctly aligned and the medial collateral ligament was reconstructed. After 4.5 months the radial shaft fracture was healed with nearly complete functional recovery of the upper extremity. Thus, a good outcome can be expected when all aspects of bony and ligamentous injuries are accurately addressed.

  5. Concurrent palmar lunate dislocation and posterior elbow dislocation: a case report.

    PubMed

    Papanna, Madhavan Chikkapapanna; Al-Hadithy, Nawfal; Sarkar, J S

    2011-12-01

    We report a rare case of concurrent palmar lunate dislocation of the left wrist combined with a posterior dislocation of the left elbow joint in a 40-year-old man. He sustained both injuries after falling onto his outstretched left hand. The elbow was reduced by the closed method. The wrist was treated with open reduction with carpal tunnel decompression and fixation with a Kirschner wire through the volar approach. Both the scapholunate and radioscaphocapitate ligaments were also repaired. At month 3, the patient had no pain in his elbow and minimal pain in his wrist on heavy lifting and had resumed his work as a porter.

  6. Bilateral dorsal trans-scaphoid perilunate fracture–dislocation: A case report

    PubMed Central

    Yildirim, Cengiz; Unuvar, Fatih; Keklikci, Kenan; Demirtas, Mehmet

    2014-01-01

    INTRODUCTION Perilunate dislocations represent one of the most devastating injuries to the carpus. Fortunately, these injuries are relatively rare, constituting approximately 10% of all carpal injuries. One of the problems associated with this injury is the difficulty of its accurate and early recognition. PRESENTATION OF CASE In this study, an uncommon case of bilateral dorsal trans-scaphoid perilunate fracture–dislocation following trauma has been reported. The injury was missed initially and the patient was subsequently operated after two weeks. Anatomic reduction was achieved by closed reduction. After closed reduction, percutaneous pin fixation of the carpus was performed using Kirschner wires. Finally, the scaphoid was stabilized with a headless screw percutaneously. The same procedure was repeated for the other wrist. This was followed by an uneventful post-operative period, with a satisfactory functional outcome at the two-year follow-up, despite non-union of the scaphoid in one side. DISCUSSION The case was examined in detail, and compared to the findings in the literature; observations regarding fracture prognosis were also made. Most authors agree that closed reduction is the initial treatment of choice for trans-scaphoid perilunate fracture–dislocations. In addition, treatment often requires intercarpal fixation within the proximal carpal row. CONCLUSION We believe that closed reduction in these cases should be attempted regarding the potential risks of avascular necrosis and non-union of the affected carpal bones due to open reduction. PMID:24705189

  7. Constitutive model for the dynamic response of a NiTi shape memory alloy

    NASA Astrophysics Data System (ADS)

    Shi, Xiaohong; Zeng, Xiangguo; Chen, Huayan

    2016-07-01

    In this paper, based on irreversible thermodynamic theory, the Helmholtz free energy function, was selected to deduce both the master equations and evolution equations of the constitutive model of a NiTi alloy under high strain. The Helmholtz free energy function contains the parameters of the reflecting phase transition and plastic property. The constitutive model for a NiTi alloy was implemented using a semi-implicit stress integration algorithm. Four successive stages can be differentiated and simulated: parent phase elasticity, martensitic phase transition, martensitic elasticity, and dislocation yield. The simulation results are in good agreement with the experimental results.

  8. Dislocation transport in shock-loaded single crystals

    SciTech Connect

    Johnson, J.N.

    1987-01-05

    It has been previously observed that the impact surface of (100) shock-loaded lithium fluoride is a strong source of dislocations. These dislocations, on one side of the impact surface, are nearly all of the same sign and move in the same direction when the driving (impact) stress is maintained. This produces an excess of like-signed dislocations between the impact surface and the advancing planar shock front. It is shown that inclusion of dislocation transport effects in the equation for dislocation regeneration is required when surface sources are present. A derivation of the general expression of dislocation transport is presented along with some specific results for (100) loaded lithium fluoride. These results have important consequences regarding proper analysis of elastic precursor decay and rate-dependent plastic deformation in shock-loaded solids.

  9. Atomistic simulations of dislocation pileup: Grain boundaries interaction

    DOE PAGES

    Wang, Jian

    2015-05-27

    Here, using molecular dynamics (MD) simulations, we studied the dislocation pileup–grain boundary (GB) interactions. Two Σ11 asymmetrical tilt grain boundaries in Al are studied to explore the influence of orientation relationship and interface structure on dislocation activities at grain boundaries. To mimic the reality of a dislocation pileup in a coarse-grained polycrystalline, we optimized the dislocation population in MD simulations and developed a predict-correct method to create a dislocation pileup in MD simulations. MD simulations explored several kinetic processes of dislocations–GB reactions: grain boundary sliding, grain boundary migration, slip transmission, dislocation reflection, reconstruction of grain boundary, and the correlation ofmore » these kinetic processes with the available slip systems across the GB and atomic structures of the GB.« less

  10. Atomistic simulations of dislocation pileup: Grain boundaries interaction

    SciTech Connect

    Wang, Jian

    2015-05-27

    Here, using molecular dynamics (MD) simulations, we studied the dislocation pileup–grain boundary (GB) interactions. Two Σ11 asymmetrical tilt grain boundaries in Al are studied to explore the influence of orientation relationship and interface structure on dislocation activities at grain boundaries. To mimic the reality of a dislocation pileup in a coarse-grained polycrystalline, we optimized the dislocation population in MD simulations and developed a predict-correct method to create a dislocation pileup in MD simulations. MD simulations explored several kinetic processes of dislocations–GB reactions: grain boundary sliding, grain boundary migration, slip transmission, dislocation reflection, reconstruction of grain boundary, and the correlation of these kinetic processes with the available slip systems across the GB and atomic structures of the GB.

  11. Atomistic modeling of dislocation interactions with twin boundaries in Ti

    NASA Astrophysics Data System (ADS)

    Hooshmand, M. S.; Mills, M. J.; Ghazisaeidi, M.

    2017-06-01

    Dislocation/boundary interactions play a prominent role in mechanical properties and plastic deformation of materials. We study the interaction between prismatic screw < a> , prismatic edge < c> and pyramidal mixed < c+a> dislocations with (\\bar{1}011) and (\\bar{1}013) twin boundaries in titanium using atomistic simulations. Details of the dislocation reactions depend on the slip system, atomic structure of boundary and stress/strain states. All interactions lead to nucleation of twinning dislocations on both twin boundaries, confirming that the interaction with incoming dislocations is a twin growth mechanism. In addition, dissociation of < c> and < c+a> dislocations on the (\\bar{1}013) results in nucleation of a (\\bar{1}012) (tension twin) embryo in the second grain-a new twin nucleation mechanism for (\\bar{1}012) twins as a result of < c> and < c+a> slip.

  12. Dislocation-related plasticity of ceria-stabilized zirconia polycrystals

    SciTech Connect

    Zhe, X.; Hendry, A.; Wang, C.

    1996-06-01

    Much higher plastic strain of 4% in Ce-TZP ceramics was produced by a novel thermal-mechanical process below 450 C. Observation by TEM showed that there were abundant dislocation pile-ups associated with a few martensitic laths in the deformed samples. The density of dislocations increased with thermal-mechanical cycles. These suggested that dislocation multiplication was caused by the high local stress concentration in front of a martensitic lath during the thermal-mechanical deformation. The generation and movement of dislocations introduced extra plasticity beside the transformation plasticity caused by martensite. Meanwhile, movement of dislocations relaxes the interface stress at martensitic laths to prevent reverse martensitic transformation and early cracking of the specimens. The results are discussed in terms of thermal-mechanical action and dislocation multiplication.

  13. Simultaneous Bilateral Fracture Dislocation of the Talus: A Case Report

    PubMed Central

    Taraz-Jamshidi, Mohammad Hosein; Shapari, Omid; Shiravani, Reza; Moalemi, Saeed; Birjandinejad, Ali

    2013-01-01

    Introduction Fracture - dislocations of the talus are typically due to high energy injuries. Displaced fracture - dislocations of the talus have poor outcomes in general and complications are common. Although talar fracture is common and comprises the second most common tarsal fracture, bilateral fracture - dislocations of the talus are rare. Not many reports regarding the subject can be found in the literature. Case Presentation We report a patient with bilateral fracture - dislocations of the talus treated by open reduction and internal fixation. This patient was a 25 year-old man who sustained bilateral fracture - dislocation of the talus due to a motor vehicle accident. Conclusions Bilateral talar fracture - dislocation is rare. The surgical approach discussed together with the pathomechanics of this injury can yield good short term results. PMID:24350160

  14. Constitutional aneuploidy and cancer predisposition†

    PubMed Central

    Ganmore, Ithamar; Smooha, Gil; Izraeli, Shai

    2009-01-01

    Constitutional aneuploidies are rare syndromes associated with multiple developmental abnormalities and the alterations in the risk for specific cancers. Acquired somatic chromosomal aneuploidies are the most common genetic aberrations in sporadic cancers. Thus studies of these rare constitutional aneuploidy syndromes are important not only for patient counseling and clinical management, but also for deciphering the mechanisms by which chromosomal aneuploidy affect cancer initiation and progression. Here we review the major constitutional aneuploidy syndromes and suggest some general mechanisms for the associated cancer predisposition. PMID:19297405

  15. Remarks on turbulent constitutive relations

    NASA Technical Reports Server (NTRS)

    Shih, Tsan-Hsing; Lumley, John L.

    1993-01-01

    The paper demonstrates that the concept of turbulent constitutive relations can be used to construct general models for various turbulent correlations. Some of the Generalized Cayley-Hamilton formulas for relating tensor products of higher extension to tensor products of lower extension are introduced. The combination of dimensional analysis and invariant theory can lead to 'turbulent constitutive relations' (or general turbulence models) for, in principle, any turbulent correlations. As examples, the constitutive relations for Reynolds stresses and scalar fluxes are derived. The results are consistent with ones from Renormalization Group (RNG) theory and two-scale Direct-Interaction Approximation (DIA) method, but with a more general form.

  16. The equivalence between dislocation pile-ups and cracks

    NASA Technical Reports Server (NTRS)

    Liu, H. W.; Gao, Q.

    1990-01-01

    Cracks and dislocation pile-ups are equivalent to each other. In this paper, the physical equivalence between cracks and pile-ups is delineated, and the relationshps between crack-extension force, force on the leading dislocation, stress-intensity factor, and dislocation density are reviewed and summarized. These relations make it possible to extend quantitatively the recent advances in the concepts and practices of fracture mechanics to the studies of microfractures and microplastic deformations.

  17. Isolated volar carpometacarpal dislocation of the fifth digit.

    PubMed

    Lintner, S A; Rettig, A C

    1995-12-01

    McWharter first described volar carpometacarpal dislocations of the fifth digit in 1918. Since then, 14 cases have been reported in the medical literature. Berg and Murphy were first to report a case of ulnopalmar dislocation that was successfully treated with closed reduction and immobilization. Previously reported cases required internal fixation with or without open reduction. We report a fifth carpometacarpal ulnopalmar dislocation, treated with closed reduction and casting.

  18. Dislocations: do you want them moving or in 3D ?

    NASA Astrophysics Data System (ADS)

    Cordier, Patrick; Boioli, Francesca; Bollinger, Caroline; Idrissi, Hosni; Mussi, Alexandre; Clitton Nzogang, Billy; Schryvers, Dominique

    2016-04-01

    Plastic deformation of minerals and rocks can be explained in most cases by the presence of crystal defects. Among those, dislocations represent the most efficient strain-producing actors of deformation. The physics of deformation by dislocations is complex since it is intrinsically multiscale. At the atomic scale, the dislocation core structure controls a fundamental property: their mobility. However, the plastic strain results from the collective behavior of dislocations which can be understood only at the mesoscopic scale. Multiscale numerical modeling has provided a lot of insights on these aspects in the recent years, also in mineral physics. These progress were calling for parallel developments in experiments and characterization. Here we present two studies on dislocations in olivine deformed under lithospheric conditions based in recent developments in transmission electron microscopy. We present plastic deformation experiments performed on olivine in situ, in the transmission electron microscope, at room temperature. The ductile behavior is made possible thanks to the very small size of the specimens (maximum dimension < 5μm) which are prepared by focused ion beam and strained in a special Micro-Electro-Mechanical-System (MEMS) device called push-to-pull (PI 95 TEM PicoIndenter from Hysitron). By performing experiments under constant load, the velocity of [001] screw dislocations has been measured as a function of stress. This mobility law has then been introduced in a Dislocation Dynamics model to determine the stress strain curves. We present also some recent developments on electron tomography of dislocations performed on olivine. The difficulty is here to keep diffraction conditions strictly constant over a wide range of tilt acquisitions. We present some examples obtained by imaging dislocations in weak-beam dark-field using precession electron diffraction. The analysis of dislocation microstructures in 3D is used to characterize dislocations glide

  19. The equivalence between dislocation pile-ups and cracks

    NASA Technical Reports Server (NTRS)

    Liu, H. W.; Gao, Q.

    1990-01-01

    Cracks and dislocation pile-ups are equivalent to each other. In this paper, the physical equivalence between cracks and pile-ups is delineated, and the relationshps between crack-extension force, force on the leading dislocation, stress-intensity factor, and dislocation density are reviewed and summarized. These relations make it possible to extend quantitatively the recent advances in the concepts and practices of fracture mechanics to the studies of microfractures and microplastic deformations.

  20. Jaw Dislocation as an Unusual Complication of Upper Endoscopy

    PubMed Central

    Dellon, Evan S.; Steele, David

    2016-01-01

    This case report presents an unusual complication of upper endoscopy, resulting in jaw dislocation. Temporomandibular joint dislocation is commonly reported in association with anesthesia and intubation, but it is not widely recognized as a complication of gastrointestinal endoscopy. This report also reviews the current literature regarding this complication and discusses the potential causes of dislocation, differential diagnoses for jaw pain following endoscopy, and recommendations for prevention. PMID:27403117

  1. Complete open dislocation of the navicular: a case report.

    PubMed

    Rao, Harish

    2012-01-01

    Complete dislocation of the navicular is rare, and open dislocation even more so. We report a case of a 85-year-old female patient who experienced complete open dislocation of navicular, successfully treated by open reduction and arthrodesis of the naviculocuneiform and calcaneocuboid joints. At 2 years after treatment, the patient was symptom free and had nearly normal foot function. Copyright © 2012 American College of Foot and Ankle Surgeons. Published by Elsevier Inc. All rights reserved.

  2. Peierls Stress of Dislocations in Molecular Crystal Cyclotrimethylene Trinitramine

    DTIC Science & Technology

    2013-06-04

    conditions. The distances between the dislocations in the unit cell and that between these and their images are equal. This ensures that the Peach −Koehler...direction. When the model is distorted and the dislocation cores shift, the interaction with images in the glide plane produces a net Peach −Koehler force on...contribution to the Peach − Koehler force from the stacking fault. When considering partials, the stacking fault is always located between the two dislocations

  3. Dislocation structure of the magnesium nanocrystal in uniaxial loading

    NASA Astrophysics Data System (ADS)

    Vlasova, A. M.; Nikonov, A. Yu.; Zhuravlev, A. K.; Kesarev, A. G.

    2016-11-01

    We report on molecular-dynamics (MD) simulations of compression loading of nanocrystalline magnesium modeled by the embedded-atom method (EAM) potential. It is shown that plastic deformation is by basal slip and (102) twinning. The formation of stable configurations of dislocation grids is observed. Some dislocation reactions are suggested to explain the occurrence of grids. The structure of the dislocation core is shown with the Burgers vector 1 /18 [0 4 ¯43 ] .

  4. Atomistic calculations of dislocation core energy in aluminium

    DOE PAGES

    Zhou, X. W.; Sills, R. B.; Ward, D. K.; ...

    2017-02-16

    A robust molecular dynamics simulation method for calculating dislocation core energies has been developed. This method has unique advantages: it does not require artificial boundary conditions, is applicable for mixed dislocations, and can yield highly converged results regardless of the atomistic system size. Utilizing a high-fidelity bond order potential, we have applied this method in aluminium to calculate the dislocation core energy as a function of the angle β between the dislocation line and Burgers vector. These calculations show that, for the face-centred-cubic aluminium explored, the dislocation core energy follows the same functional dependence on β as the dislocation elasticmore » energy: Ec = A·sin2β + B·cos2β, and this dependence is independent of temperature between 100 and 300 K. By further analysing the energetics of an extended dislocation core, we elucidate the relationship between the core energy and radius of a perfect versus extended dislocation. With our methodology, the dislocation core energy can be accurately accounted for in models of plastic deformation.« less

  5. Mobility of edge dislocations in stressed iron crystals during irradiation

    SciTech Connect

    Korchuganov, A. V. Zolnikov, K. P.; Kryzhevich, D. S.; Chernov, V. M.; Psakhie, S. G.

    2015-10-27

    The behavior of a/2(111)(110) edge dislocations in iron in shear loading and irradiation conditions was studied by means of molecular dynamics simulation. Edge dislocations were exposed to shock waves formed by atomic displacement cascades of different energies. It was shown that starting from a certain threshold amplitude shock waves cause displacement of edge dislocations in the loaded samples. Calculations showed that the larger the shear load and the amplitude of the shock wave, the greater the displacement of dislocations in the crystallite.

  6. Dislocation kinetics and the acoustic-wave approximation for liquids

    SciTech Connect

    Stout, R.B.

    1983-03-01

    A dislocation-dependent model for liquids describes the lattice deformation and the fluidity deformation as additive deformations. The lattice deformation represents distortions of an atom's potential energy structure and is a recoverable deformation response. The fluidity deformation represents discontinuous repositioning of atoms by dislocation kinetics in the lattice structure and is a nonrecoverable deformation response. From this model, one concludes that in liquids the acoustic-wave approximation is a description of a recoverable oscillation deformation that has dissipation because of dislocation kinetics. Other more-complex waves may exist, but such waves would rapidly disappear because of the small thermodynamic potential for dislocation kinetics in liquids.

  7. [Bilateral elbow dislocation related to Essex-Lopresti injury].

    PubMed

    Romero Pérez, B; Marcos García, A; Medina Henríquez, J A; Muratore Moreno, G

    2012-01-01

    Elbow dislocation is second in frequency, after the shoulder, whereas bilateral dislocation is uncommon, even less than dislocations with concurrent associated fractures. One of the least frequent associations is the Essex-Lopresti injury which consists of a fracture of the radial head affecting the distal radioulnar joint with injury to the interosseous membrane. This is a case of bilateral elbow dislocation, one of the elbows associated with the Essex-Lopresti injury. During treatment, the premature closed reduction prevails, previously making sure the elbow is stable, the premise which will determine the orthopedic or surgical treatment of the injury.

  8. Interfacial dislocation motion and interactions in single-crystal superalloys

    SciTech Connect

    Liu, B.; Raabe, D.; Roters, F.; Arsenlis, A.

    2014-10-01

    The early stage of high-temperature low-stress creep in single-crystal superalloys is characterized by the rapid development of interfacial dislocation networks. Although interfacial motion and dynamic recovery of these dislocation networks have long been expected to control the subsequent creep behavior, direct observation and hence in-depth understanding of such processes has not been achieved. Incorporating recent developments of discrete dislocation dynamics models, we simulate interfacial dislocation motion in the channel structures of single-crystal superalloys, and investigate how interfacial dislocation motion and dynamic recovery are affected by interfacial dislocation interactions and lattice misfit. Different types of dislocation interactions are considered: self, collinear, coplanar, Lomer junction, glissile junction, and Hirth junction. The simulation results show that strong dynamic recovery occurs due to the short-range reactions of collinear annihilation and Lomer junction formation. The misfit stress is found to induce and accelerate dynamic recovery of interfacial dislocation networks involving self-interaction and Hirth junction formation, but slow down the steady interfacial motion of coplanar and glissile junction forming dislocation networks. The insights gained from these simulations on high-temperature low-stress creep of single-crystal superalloys are also discussed.

  9. Surface dislocation nucleation controlled deformation of Au nanowires

    SciTech Connect

    Roos, B.; Kapelle, B.; Volkert, C. A.; Richter, G.

    2014-11-17

    We investigate deformation in high quality Au nanowires under both tension and bending using in-situ transmission electron microscopy. Defect evolution is investigated during: (1) tensile deformation of 〈110〉 oriented, initially defect-free, single crystal nanowires with cross-sectional widths between 30 and 300 nm, (2) bending deformation of the same wires, and (3) tensile deformation of wires containing coherent twin boundaries along their lengths. We observe the formation of twins and stacking faults in the single crystal wires under tension, and storage of full dislocations after bending of single crystal wires and after tension of twinned wires. The stress state dependence of the deformation morphology and the formation of stacking faults and twins are not features of bulk Au, where deformation is controlled by dislocation interactions. Instead, we attribute the deformation morphologies to the surface nucleation of either leading or trailing partial dislocations, depending on the Schmid factors, which move through and exit the wires producing stacking faults or full dislocation slip. The presence of obstacles such as neutral planes or twin boundaries hinder the egress of the freshly nucleated dislocations and allow trailing and leading partial dislocations to combine and to be stored as full dislocations in the wires. We infer that the twins and stacking faults often observed in nanoscale Au specimens are not a direct size effect but the result of a size and obstacle dependent transition from dislocation interaction controlled to dislocation nucleation controlled deformation.

  10. Congenital knee dislocation in a 49,XXXXY boy.

    PubMed Central

    Sijmons, R H; van Essen, A J; Visser, J D; Iprenburg, M; Nelck, G F; Vos-Bender, M L; de Jong, B

    1995-01-01

    We report on a 12 year old mentally retarded boy who presented at birth with bilateral knee dislocations, dislocation of the right hip, and general joint laxity. Cytogenetic studies showed a 49,XXXXY karyotype. Hyperlaxity of joints is known to occur in 49,XXXXY patients, but congenital knee dislocation has not been reported. Rarely in 49,XXXXY and 49,XXXXX syndromes Larsen-like features may be seen. Patients with congenital joint dislocation or laxity, combined with other malformations, especially if psychomotor development is delayed, should be karyotyped to exclude chromosomal abnormalities. Images PMID:7643364

  11. Dislocation luminescence in GaN single crystals under nanoindentation

    PubMed Central

    2014-01-01

    This work presents an experimental study on the dislocation luminescence in GaN by nanoindentation, cathodoluminescence, and Raman. The dislocation luminescence peaking at 3.12 eV exhibits a series of special properties in the cathodoluminescence measurements, and it completely disappears after annealing at 500°C. Raman spectroscopy shows evidence for existence of vacancies in the indented region. A comprehensive investigation encompassing cathodoluminescence, Raman, and annealing experiments allow the assignment of dislocation luminescence to conduction-band-acceptor transition involving Ga vacancies. The nanoscale plasticity of GaN can be better understood by considering the dislocation luminescence mechanism. PMID:25593548

  12. Fractal analysis of deformation-induced dislocation patterns

    SciTech Connect

    Zaiser, M. ); Bay, K. . Inst. fuer Theoretische und Angewandte Physik); Haehner, P. . Joint Research Centre TU Braunschweig . Inst. fuer Metallphysik und Nukleare Festkoerperphysik)

    1999-06-22

    The paper reports extensive analyses of the fractal geometry of cellular dislocation structures observed in Cu deformed in multiple-slip orientation. Several methods presented for the determination of fractal dimensions are shown to give consistent results. Criteria are formulated which allow the distinguishing of fractal from non-fractal patterns, and implications of fractal dislocation patterning for quantitative metallography are discussed in detail. For an interpretation of the findings a theoretical model is outlined according to which dislocation cell formation is associated to a noise-induced structural transition far from equilibrium. This allows relating the observed fractal dimensions to the stochastic properties of deformation by collective dislocation glide.

  13. Predicting High Temperature Dislocation Physics in HCP Crystal Structures

    SciTech Connect

    Hunter, Abigail; Carpenter, John S.; Martinez Saez, Enrique

    2016-05-09

    This report applies models and experiments to answer key questions about the way materials deform; specifics regarding phase field dislocations dynamics; as well as high temperature rolling experiments.

  14. Dislocation dynamics. I. A proposed methodology for deformation micromechanics

    SciTech Connect

    Amodeo, R.J.; Ghoniem, N.M. Nuclear Engineering Department, University of California, Los Angeles, Los Angeles, California 90024 )

    1990-04-01

    A new methodology in computational micromechanics, dislocation dynamics (DD), is introduced. Dislocation dynamics is developed for examining the dynamic behavior of dislocation distributions in solid materials. Under conditions of externally applied stress, dislocations exhibit glide with a velocity proportional to a power of the applied stress {sigma}{sup {ital m}} and climb motion with a velocity that is a function of the applied stress and temperature. These motions result from long-range force fields, comprising both externally applied stress and long-range interactions between individual dislocations. Short-range reactions are represented as discrete events. The DD methodology is to be differentiated from particle methods in statistical mechanics (e.g., molecular dynamics and the Monte Carlo method) in two respects. First, DD is developed to study the dynamical behavior of defects'' in the solid. Generally, the density of defects is less than that of the particles that make up the solid. Second, the small number of dislocations allows for a complete dynamical representation of the evolution of dislocations in the material medium without the requirement of statistical averaging. The purpose of the DD methodology is to bridge the gap between experimentally observed phenomena and theoretical descriptions of dislocation aggregates, particularly the evolution of self-organized dislocation structures under temperature, stress, and irradiation conditions.

  15. Lateral subtalar dislocation: Case report and review of the literature

    PubMed Central

    Veltman, Ewout S; Steller, Ernst JA; Wittich, Philippe; Keizer, Jort

    2016-01-01

    A case of complicated lateral subtalar dislocation is presented and the literature concerning this injury is reviewed. Subtalar joint dislocations are rare and often the result of a high-energy trauma. Complications include avascular necrosis of the talus, infection, posttraumatic osteoarthritis requiring arthrodesis and chronic subtalar instability. Negative prognostic factors include lateral and complicated dislocations, total talar extrusions, and associated fractures. A literature search was performed to identify studies describing outcome after lateral subtalar joint dislocation. Eight studies including fifty patients could be included, thirty out of 50 patients suffered a complicated injury. Mean follow-up was fifty-five months. Ankle function was reported as good in all patients with closed lateral subtalar dislocation. Thirteen out of thirty patients with complicated lateral subtalar joint dislocation developed a complication. Avascular necrosis was present in nine patients with complicated injury. Four patients with complicated lateral subtalar dislocation suffered deep infection requiring treatment with antibiotics. In case of uncomplicated lateral subtalar joint dislocation, excellent functional outcome after closed reduction and immobilization can be expected. In case of complicated lateral subtalar joint dislocation immediate reduction, wound debridement and if necessary (external) stabilisation are critical. Up to fifty percent of patients suffering complicated injury are at risk of developing complications such as avascular talar necrosis and infection. PMID:27672576

  16. Dislocation conduction in Bi-Sb topological insulators

    NASA Astrophysics Data System (ADS)

    Hamasaki, Hiromu; Tokumoto, Yuki; Edagawa, Keiichi

    2017-02-01

    Previous theoretical works have predicted that when a specific condition is satisfied, dislocations in three-dimensional topological insulators form one-dimensional gapless states, which are topologically protected against disorder scattering. Here, the predicted dislocation conduction is experimentally investigated in Bi-Sb topological insulators. High-density dislocations with the Burgers vector satisfying the conductivity condition are introduced into Bi-Sb single crystals by plastic deformation. Conductivity measurements for deformed and undeformed samples and those for the deformed samples in different orientations show excess conductivity due to dislocation conduction.

  17. The President and the Constitution.

    ERIC Educational Resources Information Center

    Toler, Frank

    1988-01-01

    Intended for ninth grade students, this ten day unit focuses on the constitutional powers of the President of the United States. Included are worksheets, vocabulary, writing assignments, tests, and quizzes. (JDH)

  18. Are Sanctions on Employers Constitutional?

    ERIC Educational Resources Information Center

    Gollobin, Ira

    1988-01-01

    Questions the constitutional validity of employer sanctions used to deter illegal immigration under the Immigration Reform and Control Act. Points out the anomaly of using criminal penalties to deter a civil, administrative violation. (FMW)

  19. Abnormal human sex chromosome constitutions

    SciTech Connect

    1993-12-31

    Chapter 22, discusses abnormal human sex chromosome constitution. Aneuploidy of X chromosomes with a female phenotype, sex chromosome aneuploidy with a male phenotype, and various abnormalities in X chromosome behavior are described. 31 refs., 2 figs.

  20. Constitutive modeling for isotropic materials

    NASA Technical Reports Server (NTRS)

    Lindholm, U. S.

    1984-01-01

    A state-of-the-art review of applicable constitutive models with selection of two for detailed comparison with a wide range of experimental tests was conducted. The experimental matrix contained uniaxial and biaxial tensile, creep, stress relaxation, and cyclic fatigue tests at temperatures to 1093 C and strain rates from .0000001 to .001/sec. Some nonisothermal cycles will also be run. The constitutive models will be incorporated into the MARC finite element structural analysis program with a demonstration computation made for advanced turbine blade configuration. In the code development work, particular emphasis is being placed on developing efficient integration algorithms for the highly nonlinear and stiff constitutive equations. Another area of emphasis is the appropriate and efficient methodology for determing constitutive constants from a minimum extent of experimental data.

  1. Are Sanctions on Employers Constitutional?

    ERIC Educational Resources Information Center

    Gollobin, Ira

    1988-01-01

    Questions the constitutional validity of employer sanctions used to deter illegal immigration under the Immigration Reform and Control Act. Points out the anomaly of using criminal penalties to deter a civil, administrative violation. (FMW)

  2. The Constitution's Prescription for Freedom.

    ERIC Educational Resources Information Center

    Peach, Lucinda

    1986-01-01

    Examines how the framers of the Constitution came to choose our system of government, how that system was designed to function, and how the separation of powers has served to maintain our democracy despite attempts to violate it. (JDH)

  3. The Constitution's Prescription for Freedom.

    ERIC Educational Resources Information Center

    Peach, Lucinda

    1986-01-01

    Examines how the framers of the Constitution came to choose our system of government, how that system was designed to function, and how the separation of powers has served to maintain our democracy despite attempts to violate it. (JDH)

  4. Surgical outcomes after traumatic open knee dislocation.

    PubMed

    King, Joseph J; Cerynik, Douglas L; Blair, James A; Harding, Susan P; Tom, James A

    2009-09-01

    The purpose of this study is to describe the types of injuries and surgical treatments associated with open knee dislocations and to present the functional outcomes of these patients. Between 2001 and 2005, the medical records of patients that sustained traumatic open knee dislocations at our Level 1 Trauma Center were retrospectively reviewed. Initial surgical intervention was performed in all patients including placement of spanning external fixator, repair of vascular injuries if necessary, and irrigation and debridement of the open wounds. Ligamentous reconstruction was delayed until after limb salvage. The Short Form-12 was the primary outcome measure. Seven patients (five male, two female) had a mean age of 31.9 years (range 22-44) at the time of injury (five right, two left). Motorcycle accident was the most common cause (57%). Follow-up was a mean 27.6 months. The PCL was damaged in all patients. Three patients underwent angiography for absent/diminished pulses on initial exam with two requiring operative intervention. Three patients had associated common peroneal nerve injury (one iatrogenic). Ten (10.7) operative procedures were performed per patient (range 5-18) with an average of 6.6 debridements (range 2-11). Infection rate was 43% with one patient undergoing amputation for infection. Good to excellent results were found in 33% of patients. Most patients (86%) report some residual symptomatic or functional deficit. Due to the injury complexity in open traumatic knee dislocations, the surgical treatment is extensive and challenging. While infection rates are high, aggressive, individualized treatment can lead to satisfactory outcome although full return to activity is difficult to achieve using current treatment methods.

  5. MRI versus radiography of acromioclavicular joint dislocation.

    PubMed

    Nemec, Ursula; Oberleitner, Gerhard; Nemec, Stefan F; Gruber, Michael; Weber, Michael; Czerny, Christian; Krestan, Christian R

    2011-10-01

    Acromioclavicular joint injuries are usually diagnosed by clinical and radiographic assessment with the Rockwood classification, which is crucial for treatment planning. In view of the implementation of MRI for visualization of the acromioclavicular joint, the purpose of this study was to describe the MRI findings of acromioclavicular joint dislocation in comparison with the radiographic findings. Forty-four patients with suspected unilateral acromioclavicular joint dislocation after acute trauma were enrolled in this prospective study. All patients underwent digital radiography and 1-T MRI with a surface phased-array coil. MRI included coronal proton density-weighted turbo spin-echo and coronal 3D T1-weighted fast field-echo water-selective sequences. The Rockwood classification was used to assess acromioclavicular joint injuries at radiography and MRI. An adapted Rockwood classification was used for MRI evaluation of the acromioclavicular joint ligaments. The classifications of acromioclavicular joint dislocations diagnosed with radiography and MRI were compared. Among 44 patients with Rockwood type I-IV injuries on radiographs, classification on radiographs and MR images was concordant in 23 (52.2%) patients. At MRI, the injury was reclassified to a less severe type in 16 (36.4%) patients and to a more severe type in five (11.4%) patients. Compared with the findings according to the original Rockwood system, with the adapted system that included MRI findings, additional ligamentous lesions were found in 11 (25%) patients. In a considerable number of patients, the MRI findings change the Rockwood type determined with radiography. In addition to clinical assessment and radiography, MRI may yield important findings on ligaments that may influence management.

  6. Nonrigid image registration with crystal dislocation energy.

    PubMed

    Luo, Yishan; Chung, Albert C S

    2013-01-01

    The goal of nonrigid image registration is to find a suitable transformation such that the transformed moving image becomes similar to the reference image. The image registration problem can also be treated as an optimization problem, which tries to minimize an objective energy function that measures the differences between two involved images. In this paper, we consider image matching as the process of aligning object boundaries in two different images. The registration energy function can be defined based on the total energy associated with the object boundaries. The optimal transformation is obtained by finding the equilibrium state when the total energy is minimized, which indicates the object boundaries find their correspondences and stop deforming. We make an analogy between the above processes with the dislocation system in physics. The object boundaries are viewed as dislocations (line defects) in crystal. Then the well-developed dislocation energy is used to derive the energy assigned to object boundaries in images. The newly derived registration energy function takes the global gradient information of the entire image into consideration, and produces an orientation-dependent and long-range interaction between two images to drive the registration process. This property of interaction endows the new registration framework with both fast convergence rate and high registration accuracy. Moreover, the new energy function can be adapted to realize symmetric diffeomorphic transformation so as to ensure one-to-one matching between subjects. In this paper, the superiority of the new method is theoretically proven, experimentally tested and compared with the state-of-the-art SyN method. Experimental results with 3-D magnetic resonance brain images demonstrate that the proposed method outperforms the compared methods in terms of both registration accuracy and computation time.

  7. Constitutive modeling for isotropic materials

    NASA Technical Reports Server (NTRS)

    Ramaswamy, V. G.; Vanstone, R. H.; Dame, L. T.; Laflen, J. H.

    1984-01-01

    The unified constitutive theories for application to typical isotropic cast nickel base supperalloys used for air-cooled turbine blades were evaluated. The specific modeling aspects evaluated were: uniaxial, monotonic, cyclic, creep, relaxation, multiaxial, notch, and thermomechanical behavior. Further development of the constitutive theories to model thermal history effects, refinement of the material test procedures, evaluation of coating effects, and verification of the models in an alternate material will be accomplished in a follow-on for this base program.

  8. Kenya Promulgates a New Constitution

    DTIC Science & Technology

    2011-03-10

    issues of governance , rights and individual freedoms. Subsequently a process to write a new constitution started in 2003. It was all inclusive and...all inclusive and participatory in decision-making. The process for reviewing the constitution was reactivated in earnest and delegates drawn from...changes in the separation of powers between the three arms of government , major matters of citizenship , the Bill of Rights, the devolution of government

  9. Palmar divergent dislocation of scaphoid and lunate.

    PubMed

    Kang, Ho-Jung; Shim, Dong-Joon; Hahn, Soo-Bong; Kang, Eung-Shick

    2003-12-30

    A 28-year-old man presented with a palmar divergent dislocation of the scaphoid and lunate. He was treated with an open reduction and an internal fixation with two Kirschner's wires after the 25th day of trauma due to a neurological injury. The results were satisfactory after 18 months follow up without any evidence of avascular necrosis and traumatic arthritis of the scaphoid and lunate. The patient had no limitation in motion or intermittent wrist pain. We reported this case with a brief review of relevant literatures.

  10. Mechanical of Cracks Screened by Dislocations

    DTIC Science & Technology

    1982-01-01

    En principe, on peut obtenir un crittre de rupture totale en prbcisant )a condition locale de clivage sur Ia fissure et la r6sistance du r ~ seau sur...DislocationsRerit G. PERFORMING ORG. REPORT NUMBER ____ ___ ___ ___ _ ___ ___ ___ ____ ___ ___ ___ N/A V. AUT04ORWs CONRAC OR GRANT’ NUMBER(s) R . Ii...Thomson, J. E. Sinclair ARO 36-82 9. PERFORMING ORZANIZATIOha NAME AND ADDRESS r 0. PRPQ;RAM ELEMENT. PROjECT. TASK National Bureau of Standards AE OKUI

  11. Gravitation and the gauge theory of dislocations

    SciTech Connect

    Sardanashvili, G.A.; Gogberashvili, M.Ya.

    1988-09-01

    The gauge theory of gravitation has long been dominated by the model of a gravitational field as a gauge field of the translation group. However, a fiber bundle analysis showed that one cannot identify these two fields. This led to the question concerning the physical meaning of the gauge fields of the translation group. The answer to this question can be given from the point of view of the gauge theory of dislocations. The argument stresses the special character of the gauge field of the translation group, not related to the Einstein gravity, and the incorrectness of the wide-spread attempts to represent gravity as a kind of space-time deformation.

  12. Percutaneous osteosynthesis of Galeazzi fracture-dislocation.

    PubMed

    Gadegone, Wasudeo M; Salphale, Yogesh; Magarkar, Ds

    2010-10-01

    A Galeazzi fracture is defined as a fracture of the radius associated with dislocation of the distal radio-ulnar joint (DRUJ). The conventional surgical technique of nailing does not give enough stability and open reduction, internal fixation with the plate is associated with numerous complications. The stacked nailing for the management of these injuries provides adequate stability, maintains the relationship of the DRUJ and promotes uneventful union by closed technique. The purpose of this study is to evaluate the results of simple, user-friendly, low cost elastic stacked nailing for the management of Galeazzi fracture dislocation. We treated 22 young adults with fresh Galeazzi fracture-dislocation of the forearm, from January 2004 to January 2008, by percutaneous fixation of fracture by stacked elastic nailing at our institute. There were 19 males and three females and the age group ranged from 20-56 years (average 35 years). Surgery was performed within 48 to 72 hours under the guidance of image intensifier. Medullary cavity was filled with two elastic titanium nails having unequal lengths and diameter. One nail acts as a reduction nail and the other acts as a stabilizing nail. The results were evaluated using Mikic criteria based on union, alignment, relationship of the DRUJ, and movements at the inferior radio ulnar joint, elbow and wrist. In six cases, following radiological union, nails in the radius were extracted between six to nine months after operation because of discomfort complained by the patient at site of insertion. After one year follow-up, 18 patients had excellent, four had fair results. Closed reduction and internal fixation of Galeazzi fracture by two elastic rods re-establishes the normal relationship of the fractured fragments and the DRUJ without repair of the ligaments. The stability is achieved by the flexibility and elasticity of the nails, crowding of the medullary canal and anchorage they gain in the radial diaphysis. Elastic nailing

  13. Percutaneous osteosynthesis of Galeazzi fracture-dislocation

    PubMed Central

    Gadegone, Wasudeo M; Salphale, Yogesh; Magarkar, DS

    2010-01-01

    Background: A Galeazzi fracture is defined as a fracture of the radius associated with dislocation of the distal radio-ulnar joint (DRUJ). The conventional surgical technique of nailing does not give enough stability and open reduction, internal fixation with the plate is associated with numerous complications. The stacked nailing for the management of these injuries provides adequate stability, maintains the relationship of the DRUJ and promotes uneventful union by closed technique. The purpose of this study is to evaluate the results of simple, user-friendly, low cost elastic stacked nailing for the management of Galeazzi fracture dislocation. Materials and Methods: We treated 22 young adults with fresh Galeazzi fracture-dislocation of the forearm, from January 2004 to January 2008, by percutaneous fixation of fracture by stacked elastic nailing at our institute. There were 19 males and three females and the age group ranged from 20-56 years (average 35 years). Surgery was performed within 48 to 72 hours under the guidance of image intensifier. Medullary cavity was filled with two elastic titanium nails having unequal lengths and diameter. One nail acts as a reduction nail and the other acts as a stabilizing nail. The results were evaluated using Mikic criteria based on union, alignment, relationship of the DRUJ, and movements at the inferior radio ulnar joint, elbow and wrist. Results: In six cases, following radiological union, nails in the radius were extracted between six to nine months after operation because of discomfort complained by the patient at site of insertion. After one year follow-up, 18 patients had excellent, four had fair results. Conclusion: Closed reduction and internal fixation of Galeazzi fracture by two elastic rods re-establishes the normal relationship of the fractured fragments and the DRUJ without repair of the ligaments. The stability is achieved by the flexibility and elasticity of the nails, crowding of the medullary canal and

  14. The patellofemoral joint: from dysplasia to dislocation.

    PubMed

    Zaffagnini, Stefano; Grassi, Alberto; Zocco, Gianluca; Rosa, Michele Attilo; Signorelli, Cecilia; Muccioli, Giulio Maria Marcheggiani

    2017-05-01

    Patellofemoral dysplasia is a major predisposing factor for instability of the patellofemoral joint. However, there is no consensus as to whether patellofemoral dysplasia is genetic in origin, caused by imbalanced forces producing maltracking and remodelling of the trochlea during infancy and growth, or due to other unknown and unexplored factors.The biomechanical effects of patellofemoral dysplasia on patellar stability and on surgical procedures have not been fully investigated. Also, different anatomical and demographic risk factors have been suggested, in an attempt to identify the recurrent dislocators. Therefore, a comprehensive evaluation of all the radiographic, MRI and CT parameters can help the clinician to assess patients with primary and recurrent patellar dislocation and guide management.Patellofemoral dysplasia still represents an extremely challenging condition to manage. Its controversial aetiology and its complex biomechanical behaviour continue to pose more questions than answers to the research community, which reflects the lack of universally accepted guidelines for the correct treatment. However, due to the complexity of this condition, an extremely personalised approach should be reserved for each patient, in considering and addressing the anatomical abnormalities responsible for the symptoms. Cite this article: EFORT Open Rev 2017;2. DOI: 10.1302/2058-5241.2.160081. Originally published online at www.efortopenreviews.org.

  15. Implicit integration methods for dislocation dynamics

    DOE PAGES

    Gardner, D. J.; Woodward, C. S.; Reynolds, D. R.; ...

    2015-01-20

    In dislocation dynamics simulations, strain hardening simulations require integrating stiff systems of ordinary differential equations in time with expensive force calculations, discontinuous topological events, and rapidly changing problem size. Current solvers in use often result in small time steps and long simulation times. Faster solvers may help dislocation dynamics simulations accumulate plastic strains at strain rates comparable to experimental observations. Here, this paper investigates the viability of high order implicit time integrators and robust nonlinear solvers to reduce simulation run times while maintaining the accuracy of the computed solution. In particular, implicit Runge-Kutta time integrators are explored as a waymore » of providing greater accuracy over a larger time step than is typically done with the standard second-order trapezoidal method. In addition, both accelerated fixed point and Newton's method are investigated to provide fast and effective solves for the nonlinear systems that must be resolved within each time step. Results show that integrators of third order are the most effective, while accelerated fixed point and Newton's method both improve solver performance over the standard fixed point method used for the solution of the nonlinear systems.« less

  16. Implicit integration methods for dislocation dynamics

    SciTech Connect

    Gardner, D. J.; Woodward, C. S.; Reynolds, D. R.; Hommes, G.; Aubry, S.; Arsenlis, A.

    2015-01-20

    In dislocation dynamics simulations, strain hardening simulations require integrating stiff systems of ordinary differential equations in time with expensive force calculations, discontinuous topological events, and rapidly changing problem size. Current solvers in use often result in small time steps and long simulation times. Faster solvers may help dislocation dynamics simulations accumulate plastic strains at strain rates comparable to experimental observations. Here, this paper investigates the viability of high order implicit time integrators and robust nonlinear solvers to reduce simulation run times while maintaining the accuracy of the computed solution. In particular, implicit Runge-Kutta time integrators are explored as a way of providing greater accuracy over a larger time step than is typically done with the standard second-order trapezoidal method. In addition, both accelerated fixed point and Newton's method are investigated to provide fast and effective solves for the nonlinear systems that must be resolved within each time step. Results show that integrators of third order are the most effective, while accelerated fixed point and Newton's method both improve solver performance over the standard fixed point method used for the solution of the nonlinear systems.

  17. Implicit integration methods for dislocation dynamics

    NASA Astrophysics Data System (ADS)

    Gardner, D. J.; Woodward, C. S.; Reynolds, D. R.; Hommes, G.; Aubry, S.; Arsenlis, A.

    2015-03-01

    In dislocation dynamics simulations, strain hardening simulations require integrating stiff systems of ordinary differential equations in time with expensive force calculations, discontinuous topological events and rapidly changing problem size. Current solvers in use often result in small time steps and long simulation times. Faster solvers may help dislocation dynamics simulations accumulate plastic strains at strain rates comparable to experimental observations. This paper investigates the viability of high-order implicit time integrators and robust nonlinear solvers to reduce simulation run times while maintaining the accuracy of the computed solution. In particular, implicit Runge-Kutta time integrators are explored as a way of providing greater accuracy over a larger time step than is typically done with the standard second-order trapezoidal method. In addition, both accelerated fixed point and Newton's method are investigated to provide fast and effective solves for the nonlinear systems that must be resolved within each time step. Results show that integrators of third order are the most effective, while accelerated fixed point and Newton's method both improve solver performance over the standard fixed point method used for the solution of the nonlinear systems.

  18. Displacing lateral meniscus masquerading as patella dislocation.

    PubMed

    Arendt, Elizabeth A; Fontboté, Cristián A; Rohr, Sara R

    2014-10-01

    To alert the treating clinician to an uncommon knee meniscal condition that often masquerades as a more common patella condition. Retrospective chart review of a series of cases was undertaken. A series of 12 knees in 11 patients were referred to an orthopaedic surgeon with a diagnosis of recurrent lateral patella dislocation. Three knees had undergone patella realignment surgery with continuance of symptoms. Eight patients had prior magnetic resonance images read as no meniscal pathology and no acute patella/patella retinacular injury. All patients presented for a consult with a similar history. Under anaesthesia, all knees had a stable patella as judged by physical examination. At the time of surgery, six patients had a frank tear in the lateral meniscus, all of which were readily displaceable. Six knees showed a displaceable lateral meniscus with attenuation but not a visible frank tear. Ten menisci were treated with repair, and two knees underwent partial lateral meniscectomies. Patient follow-up of minimally 18 months revealed no further episodes of "knee-cap dislocation" or symptoms of catching and locking. The clinician treating a patient with a history of a knee locking in flexion should have a high index of suspicion for a lateral meniscus tear or an unstable hypermobile lateral meniscus, despite patient report of perceived patella movement. History of symptoms occurring in knee flexion and attention to patella physical examination should be key factors in this diagnostic conundrum. Retrospective chart review, Level IV.

  19. Concept of healing of recurrent shoulder dislocation.

    PubMed

    D'Angelo, Donato

    2014-01-01

    This paper presents the main surgical techniques applied in the treatment of anterior recurrent shoulder dislocation, aiming the achievement of the normality of articulate movements. This was obtained by combining distinct surgical procedures, which allowed the recovery of a complete functional capacity of the shoulder, without jeopardizing the normality of movement, something that has not been recorded in the case of the tense sutures of the surgical procedures of Putti-Platt, Bankart, Latarjet, Dickson-O'Dell and others. The careful review of the methods applied supports the conclusion that recurrent shoulder dislocation can be cured, since cure has been obtained in 97% of the treated cases. However, some degree of limitation in the shoulder movement has been observed in most of the treated cases. Our main goal was to achieve a complete shoulder functional recovery, by treating simultaneously all of the anatomical-pathological lesions, without considering the so-called essential lesions. The period of post-operatory immobilization only last for the healing of soft parts; this takes place in a position of neutral shoulder rotation, since the use of vascular bone graft eliminates the need for long time immobilization, due to the shoulder stabilization provided by rigid fixation of the coracoid at the glenoid edge, as in the Latarjet's technique. Our procedure, used since 1959, comprises the association of several techniques, which has permitted shoulder healing without movement limitation. That was because of the tension reduction in the sutures of the subescapularis, capsule, and coracobraquialis muscles.

  20. Novel Presentation of Uncommon Wrist Injury: Simultaneous Lunate and Perilunate Fracture Dislocation (scapho-capitate Syndrome) of Both Wrists

    PubMed Central

    Bhat, Anil K.; A, Nishanth; Acharya, Ashwath; Kumar, Yogesh

    2016-01-01

    Introduction: Perilunate and lunate dislocations are uncommon high energy injuries and have extensive soft tissue, cartilaginous and bony damage. The most common pattern is trans-scaphoid perilunate fracture dislocation which constitutes approximately 50% of these injuries. Unusual injury pattern like Scaphocapitate syndrome can occur with fracture through scaphoid waist and capitate that rotates the proximal capitate 180° so that its proximal articular surface points distally. With this case report, we would like to present a novel presentation of an uncommon wrist injury. Case report: We present a case of simultaneous lunate dislocation in one wrist and perilunate fracture dislocation (Scapho- capitate syndrome) in the contralateral wrist which occurred simultaneously in a young male following a two wheeler accident. The injury was missed initially at the primary treating centre. Upon diagnosis, the patient underwent open reduction and internal fixation along with ligament repair. The patient was subsequently followed up for a period of four years and was found to have very good clinical and radiological outcome. Conclusion: These injuries occurring simultaneously in contralateral wrists are exceptionally rare and unusual as the mechanisms of injury are different. These are high velocity injuries and are often missed, especially in presence of other major injuries. These high energy injuries need accurate diagnosis, early and aggressive treatment in order to prevent complications PMID:27703938

  1. Electronic structure study of screw dislocation core energetics in Aluminum and core energetics informed forces in a dislocation aggregate

    NASA Astrophysics Data System (ADS)

    Das, Sambit; Gavini, Vikram

    2017-07-01

    We use a real-space formulation of orbital-free DFT to study the core energetics and core structure of an isolated screw dislocation in Aluminum. Using a direct energetics based approach, we estimate the core size of a perfect screw dislocation to be ≈ 7 |b|, which is considerably larger than previous estimates of 1-3 |b| based on displacement fields. The perfect screw upon structural relaxation dissociates into two Shockley partials with partial separation distances of 8.2 Å and 6.6 Å measured from the screw and edge component differential displacement plots, respectively. Similar to a previous electronic structure study on edge dislocation, we find that the core energy of the relaxed screw dislocation is not a constant, but strongly dependent on macroscopic deformations. Next, we use the edge and screw dislocation core energetics data with physically reasonable assumptions to develop a continuum energetics model for an aggregate of dislocations that accounts for the core energy dependence on macroscopic deformations. Further, we use this energetics model in a discrete dislocation network, and from the variations of the core energy with respect to the nodal positions of the network, we obtain the nodal core force which can directly be incorporated into discrete dislocation dynamics frameworks. We analyze and classify the nodal core force into three different contributions based on their decay behavior. Two of these contributions to the core force, both arising from the core energy dependence on macroscopic deformations, are not accounted for in currently used discrete dislocation dynamics models which assume the core energy to be a constant excepting for its dependence on the dislocation line orientation. Using case studies involving simple dislocation structures, we demonstrate that the contribution to the core force from the core energy dependence on macroscopic deformations can be significant in comparison to the elastic Peach-Koehler force even up to

  2. Dislocation Mechanism of Twinning in Ni-Mn-Ga

    NASA Astrophysics Data System (ADS)

    Zárubová, N.; Ge, Y.; Gemperlová, J.; Gemperle, A.; Hannula, S.-P.

    2012-03-01

    Tensile tests were performed in situ in a transmission electron microscope to investigate the twinning mechanism in non-modulated Ni-Mn-Ga martensite. The reorientation of the twin variants occurs via twinning dislocations. Their generation and movement were followed; the glide plane and Burgers vector were verified. Individual twinning dislocations were visualized.

  3. The strength and dislocation microstructure evolution in superalloy microcrystals

    NASA Astrophysics Data System (ADS)

    Hussein, Ahmed M.; Rao, Satish I.; Uchic, Michael D.; Parthasarathay, Triplicane A.; El-Awady, Jaafar A.

    2017-02-01

    In this work, the evolution of the dislocations microstructure in single crystal two-phase superalloy microcrystals under monotonic loading has been studied using the three-dimensional discrete dislocation dynamics (DDD) method. The DDD framework has been extended to properly handle the collective behavior of dislocations and their interactions with large collections of arbitrary shaped precipitates. Few constraints are imposed on the initial distribution of the dislocations or the precipitates, and the extended DDD framework can support experimentally-obtained precipitate geometries. Full tracking of the creation and destruction of anti-phase boundaries (APB) is accounted for. The effects of the precipitate volume fraction, APB energy, precipitate size, and crystal size on the deformation of superalloy microcrystals have been quantified. Correlations between the precipitate microstructure and the dominant deformation features, such as dislocation looping versus precipitate shearing, are also discussed. It is shown that the mechanical strength is independent of the crystal size, increases linearly with increasing the volume fraction, follows a near square-root relationship with the APB energy and an inverse square-root relationship with the precipitate size. Finally, the flow strength in simulations having initial dislocation pair sources show a flow strength that is about one half of that predicted from simulations starting with single dislocation sources. The method developed can be used, with minimal extensions, to simulate dislocation microstructure evolution in general multiphase materials.

  4. Simultaneous bilateral elbow dislocation in an international gymnast

    PubMed Central

    Syed, A. A.; O'Flanagan, J.

    1999-01-01

    Elbow dislocation is a rare injury in elite athletes. We report an unusual case of simultaneous bilateral elbow dislocations with a unilateral radial head fracture in an international female athlete competing on the asymmetrical bars. These injuries require prompt reduction and immediate mobilisation if an abrupt end to a promising career is to be prevented. 




 PMID:10205699

  5. Thermal activation of dislocations in large scale obstacle bypass

    NASA Astrophysics Data System (ADS)

    Sobie, Cameron; Capolungo, Laurent; McDowell, David L.; Martinez, Enrique

    2017-08-01

    Dislocation dynamics simulations have been used extensively to predict hardening caused by dislocation-obstacle interactions, including irradiation defect hardening in the athermal case. Incorporating the role of thermal energy on these interactions is possible with a framework provided by harmonic transition state theory (HTST) enabling direct access to thermally activated reaction rates using the Arrhenius equation, including rates of dislocation-obstacle bypass processes. Moving beyond unit dislocation-defect reactions to a representative environment containing a large number of defects requires coarse-graining the activation energy barriers of a population of obstacles into an effective energy barrier that accurately represents the large scale collective process. The work presented here investigates the relationship between unit dislocation-defect bypass processes and the distribution of activation energy barriers calculated for ensemble bypass processes. A significant difference between these cases is observed, which is attributed to the inherent cooperative nature of dislocation bypass processes. In addition to the dislocation-defect interaction, the morphology of the dislocation segments pinned to the defects play an important role on the activation energies for bypass. A phenomenological model for activation energy stress dependence is shown to describe well the effect of a distribution of activation energies, and a probabilistic activation energy model incorporating the stress distribution in a material is presented.

  6. Method to reduce dislocation density in silicon using stress

    DOEpatents

    Buonassisi, Anthony; Bertoni, Mariana; Argon, Ali; Castellanos, Sergio; Fecych, Alexandria; Powell, Douglas; Vogl, Michelle

    2013-03-05

    A crystalline material structure with reduced dislocation density and method of producing same is provided. The crystalline material structure is annealed at temperatures above the brittle-to-ductile transition temperature of the crystalline material structure. One or more stress elements are formed on the crystalline material structure so as to annihilate dislocations or to move them into less harmful locations.

  7. Multiscale characterization of dislocation processes in Al 5754

    NASA Astrophysics Data System (ADS)

    Kacher, Josh; Mishra, Raja K.; Minor, Andrew M.

    2015-07-01

    Multiscale characterization was performed on an Al-Mg alloy, Al 5754 O-temper, including in situ mechanical deformation in both the scanning electron microscope and the transmission electron microscope. Scanning electron microscopy characterization showed corresponding inhomogeneity in the dislocation and Mg distribution, with higher levels of Mg correlating with elevated levels of dislocation density. At the nanoscale, in situ transmission electron microscopy straining experiments showed that dislocation propagation through the Al matrix is characterized by frequent interactions with obstacles smaller than the imaging resolution that resulted in the formation of dislocation debris in the form of dislocation loops. Post-mortem chemical characterization and comparison to dislocation loop behaviour in an Al-Cr alloy suggests that these obstacles are small Mg clusters. Previous theoretical work and indirect experimental evidence have suggested that these Mg nanoclusters are important factors contributing to strain instabilities in Al-Mg alloys. This study provides direct experimental characterization of the interaction of glissile dislocations with these nanoclusters and the stress needed for dislocations to overcome them.

  8. The Dislocated Worker: When Training Is Not Enough.

    ERIC Educational Resources Information Center

    Blong, John T.; Shultz, Rose M.

    1990-01-01

    Discusses the socioeconomic effects of plant closings, focusing on the problems faced by dislocated workers who lack the financial resources to complete a retraining program. Describes the Eastern Iowa Community College District's efforts to train and counsel dislocated workers through its Caterpillar Worker Assistance Center. (DMM)

  9. Reprint of: Dynamics of discrete screw dislocations on glide directions

    NASA Astrophysics Data System (ADS)

    Alicandro, R.; De Luca, L.; Garroni, A.; Ponsiglione, M.

    2016-12-01

    We consider a simple discrete model for screw dislocations in crystals. Using a variational discrete scheme we study the motion of a configuration of dislocations toward low energy configurations. We deduce an effective fully overdamped dynamics that follows the maximal dissipation criterion introduced in Cermelli and Gurtin (1999) and predicts motion along the glide directions of the crystal.

  10. Effective mobility of dislocations from systematic coarse-graining

    NASA Astrophysics Data System (ADS)

    Kooiman, M.; Hütter, M.; Geers, MGD

    2015-06-01

    The dynamics of large amounts of dislocations governs the plastic response of crystalline materials. In this contribution we discuss the relation between the mobility of discrete dislocations and the resulting flow rule for coarse-grained dislocation densities. The mobilities used in literature on these levels are quite different, for example in terms of their intrinsic the stress dependence. To establish the relation across the scales, we have derived the macroscopic evolution equations of dislocation densities from the equations of motion of individual dislocations by means of systematic coarse-graining. From this, we can identify a memory kernel relating the driving force and the flux of dislocations. This kernel can be considered as an effective macroscopic mobility with two contributions; a direct contribution related to the overdamped motion of individual dislocations, and an emergent contribution that arises from time correlations of fluctuations in the Peach-Koehler force. Scaling analysis shows that the latter contribution is dominant for dislocations in metals at room temperature. We also discuss several concerns related to the separation of timescales.

  11. A field theory of piezoelectric media containing dislocations

    SciTech Connect

    Taupin, V. Fressengeas, C.; Ventura, P.; Lebyodkin, M.

    2014-04-14

    A field theory is proposed to extend the standard piezoelectric framework for linear elastic solids by accounting for the presence and motion of dislocation fields and assessing their impact on the piezoelectric properties. The proposed theory describes the incompatible lattice distortion and residual piezoelectric polarization fields induced by dislocation ensembles, as well as the dynamic evolution of these fields through dislocation motion driven by coupled electro-mechanical loading. It is suggested that (i) dislocation mobility may be enhanced or inhibited by the electric field, depending on the polarity of the latter, (ii) plasticity mediated by dislocation motion allows capturing long-term time-dependent properties of piezoelectric polarization. Due to the continuity of the proposed electro-mechanical framework, the stress/strain and polarization fields are smooth even in the dislocation core regions. The theory is applied to gallium nitride layers for validation. The piezoelectric polarization fields associated with bulk screw/edge dislocations are retrieved and surface potential modulations are predicted. The results are extended to dislocation loops.

  12. Non-reducible palmar dislocation of the distal radioulnar joint

    PubMed Central

    Zannou, Rupestre S.; Rezzouk, Joel; Ruijs, Aleid C.J.

    2015-01-01

    Abstract A rare case of an isolated traumatic palmar dislocation of the distal radioulnar joint is presented. Clinically, there is a loss of pronation and supination. The dislocation was treated using an open reduction, reinsertion of the capsule-ligamentous complex and temporary stabilization using K-wires. PMID:26158121

  13. Dynamics of discrete screw dislocations on glide directions

    NASA Astrophysics Data System (ADS)

    Alicandro, R.; De Luca, L.; Garroni, A.; Ponsiglione, M.

    2016-07-01

    We consider a simple discrete model for screw dislocations in crystals. Using a variational discrete scheme we study the motion of a configuration of dislocations toward low energy configurations. We deduce an effective fully overdamped dynamics that follows the maximal dissipation criterion introduced in Cermelli and Gurtin (1999) and predicts motion along the glide directions of the crystal.

  14. Computation of the lattice Green function for a dislocation

    NASA Astrophysics Data System (ADS)

    Tan, Anne Marie Z.; Trinkle, Dallas R.

    2016-08-01

    Modeling isolated dislocations is challenging due to their long-ranged strain fields. Flexible boundary condition methods capture the correct long-range strain field of a defect by coupling the defect core to an infinite harmonic bulk through the lattice Green function (LGF). To improve the accuracy and efficiency of flexible boundary condition methods, we develop a numerical method to compute the LGF specifically for a dislocation geometry; in contrast to previous methods, where the LGF was computed for the perfect bulk as an approximation for the dislocation. Our approach directly accounts for the topology of a dislocation, and the errors in the LGF computation converge rapidly for edge dislocations in a simple cubic model system as well as in BCC Fe with an empirical potential. When used within the flexible boundary condition approach, the dislocation LGF relaxes dislocation core geometries in fewer iterations than when the perfect bulk LGF is used as an approximation for the dislocation, making a flexible boundary condition approach more efficient.

  15. Collective Dislocation Dynamics and Avalanches during Fatigue of Aluminum

    NASA Astrophysics Data System (ADS)

    Rhouma, W. Ben; Deschanel, S.; Weiss, J.

    2011-09-01

    We present a study of collective dislocation dynamics and plasticity during fatigue of pure Aluminum from the analysis of continuous and discrete acoustic emission (AE). The three stages of macroscopic fatigue behavior (strain-hardening, shakedown, and strain softening) are clearly differentiated in terms of AE. During the first loading cycles, collective dislocation dynamics consists in dislocation avalanches of various sizes and clustered in time. Once a microstructure of dislocation cells and walls is formed, the spreading of such avalanches is restrained, and the discrete AE strongly decreases. Instead, a symmetrical (tension-compression) continuous AE, maximal at plastic yield, is observed, likely associated to a superposition of numerous, small and uncorrelated motions such as dislocation loops initiation from cell walls. However, some discrete AE activity remains during shakedown, a possible signature of sudden rearrangements of the microstructure occurring at scales larger than its wavelength. Finally, the onset of strain softening is associated to a strong increase of discrete AE, in relation with microcracking. Our results suggest that collective dislocation instabilities and the emergence of a dislocation microstructure are interrelated, and challenge future numerical modeling developments of dislocation assemblies.

  16. The Dislocated Worker: When Training Is Not Enough.

    ERIC Educational Resources Information Center

    Blong, John T.; Shultz, Rose M.

    1990-01-01

    Discusses the socioeconomic effects of plant closings, focusing on the problems faced by dislocated workers who lack the financial resources to complete a retraining program. Describes the Eastern Iowa Community College District's efforts to train and counsel dislocated workers through its Caterpillar Worker Assistance Center. (DMM)

  17. High purity, low dislocation GaAs single crystals

    NASA Technical Reports Server (NTRS)

    Chen, R. T.; Holmes, D. E.; Kirkpatrick, C. G.

    1983-01-01

    Liquid encapsulated Czochralski crystal growth techniques for producing undoped, high resistivity, low dislocation material suitable for device applications is described. Technique development resulted in reduction of dislocation densities in 3 inch GaAs crystals. Control over the melt stoichiometry was determined to be of critical importance for the reduction of twinning and polycrystallinity during growth.

  18. Strength of Dislocation Junctions in FCC-monocrystals with a [\\overline{1}11] Deformation Axis

    NASA Astrophysics Data System (ADS)

    Kurinnaya, R. I.; Zgolich, M. V.; Starenchenko, V. A.

    2017-07-01

    The paper examines all dislocation reactions implemented in FCC-monocrystals with axis deformation oriented in the [\\overline{1}11] direction. It identifies the fracture stresses of dislocation junctions depending on intersection geometry of the reacting dislocation loop segments. Estimates are produced for the full spectrum of reacting forest dislocations. The paper presents the statistical data of the research performed and identifies the share of long strong dislocation junctions capable of limiting the zone of dislocation shift.

  19. The relationship between strain geometry and geometrically necessary dislocations

    NASA Astrophysics Data System (ADS)

    Hansen, Lars; Wallis, David

    2016-04-01

    The kinematics of past deformations are often a primary goal in structural analyses of strained rocks. Details of the strain geometry, in particular, can help distinguish hypotheses about large-scale tectonic phenomena. Microstructural indicators of strain geometry have been heavily utilized to investigate large-scale kinematics. However, many of the existing techniques require structures for which the initial morphology is known, and those structures must undergo the same deformation as imposed macroscopically. Many deformed rocks do not exhibit such convenient features, and therefore the strain geometry is often difficult (if not impossible) to ascertain. Alternatively, crystallographic textures contain information about the strain geometry, but the influence of strain geometry can be difficult to separate from other environmental factors that might affect slip system activity and therefore the textural evolution. Here we explore the ability for geometrically necessary dislocations to record information about the deformation geometry. It is well known that crystallographic slip due to the motion of dislocations yields macroscopic plastic strain, and the mathematics are established to relate dislocation glide on multiple slip systems to the strain tensor of a crystal. This theoretical description generally assumes that dislocations propagate across the entire crystal. However, at any point during the deformation, dislocations are present that have not fully transected the crystal, existing either as free dislocations or as dislocations organized into substructures like subgrain boundaries. These dislocations can remain in the lattice after deformation if the crystal is quenched sufficiently fast, and we hypothesize that this residual dislocation population can be linked to the plastic strain geometry in a quantitative manner. To test this hypothesis, we use high-resolution electron backscatter diffraction to measure lattice curvatures in experimentally deformed

  20. Constitutive modeling for isotropic materials

    NASA Technical Reports Server (NTRS)

    Lindholm, Ulric S.

    1985-01-01

    The objective is to develop a unified constitutive model for finite element structural analysis of turbine engine hot-section components. This effort constitutes a different approach for non-linear finite-element computer codes which have heretofore been based on classical inelastic methods. The unified constitutive theory to be developed will avoid the simplifying assumptions of classical theory and should more accurately represent the behavior of superalloy materials under cyclic loading conditions and high temperature environments. During the first two years of the program, extensive experimental correlations were made with two representative unified models. The experiments were both uniaxial and biaxial at temperatures up to 1093 C (2000 F). In addition, the unified models were adopted to the MARC finite element code and used for stress analysis of notched bar and turbine blade geometries.

  1. Modeling of dislocation dynamics in germanium Czochralski growth

    NASA Astrophysics Data System (ADS)

    Artemyev, V. V.; Smirnov, A. D.; Kalaev, V. V.; Mamedov, V. M.; Sidko, A. P.; Podkopaev, O. I.; Kravtsova, E. D.; Shimansky, A. F.

    2017-06-01

    Obtaining very high-purity germanium crystals with low dislocation density is a practically difficult problem, which requires knowledge and experience in growth processes. Dislocation density is one of the most important parameters defining the quality of germanium crystal. In this paper, we have performed experimental study of dislocation density during 4-in. germanium crystal growth using the Czochralski method and comprehensive unsteady modeling of the same crystal growth processes, taking into account global heat transfer, melt flow and melt/crystal interface shape evolution. Thermal stresses in the crystal and their relaxation with generation of dislocations within the Alexander-Haasen model have been calculated simultaneously with crystallization dynamics. Comparison to experimental data showed reasonable agreement for the temperature, interface shape and dislocation density in the crystal between calculation and experiment.

  2. Conservative Treatment of Carpometacarpal Dislocation of the Three Last Fingers

    PubMed Central

    2016-01-01

    Posterior carpometacarpal (CMC) dislocation is a rare condition. Treatment is usually surgical though no strict consensus can be found upon literature review. If diagnosed early and no associated fractures are found, CMC dislocation could benefit from conservative treatment comprising closed reduction and splint immobilisation. We report the case of a 26-year-old man diagnosed with a posterior dislocation of the third, fourth, and fifth CMC joints after a fall of 1.5 meters, treated by external reduction under procedural sedation and immobilisation with a cast for 6 weeks. Evolution was excellent with no relapse observed during follow-up. Our aim is to increase physician awareness of CMC dislocation so that they seek this injury in the emergency department. Unrecognised CMC dislocation can lead to neurovascular injuries as well as chronic instability and early articular degeneration. PMID:27703817

  3. Trans-Scaphoid Perilunate Fracture Dislocation; A Technical Note

    PubMed Central

    Aslani, Hossein; Bazavar, Mohammad Reza; Sadighi, Ali; Tabrizi, Ali; Elmi, Asghar

    2016-01-01

    Carpal fracture-dislocation is regarded as an unusual orthopedic injury and, thus, orthopedic surgeons are less experienced in dealing with and treating these fractures and dislocations. We report a 20-year-old worker man suffering from an unusual carpal fracture-dislocation. There was trans-scaphoid fracture and lunate dislocation with other carpal proximal bones toward volar of the wrist. Two volar and dorsal approaches were used to treat and stabilize the fracture. It was completely stabilized after open reduction and fixation using several pins. After two days, neural symptoms were completely recovered and the patient was discharged. Postoperative radiographies revealed complete restitution of lesser and greater arcs and normalization of Gilula's line. Scapholunate and lunatocapitate angles reached to less than 60° and 10°, respectively. The combined approach had favorable results for treatment of this unusual type of carpus fracture dislocation. However longer follow up is need to evaluate the arthritis and degenerative changes in wrist. PMID:27331069

  4. Self-force on dislocation segments in anisotropic crystals.

    PubMed

    Fitzgerald, S P; Aubry, S

    2010-07-28

    A dislocation segment in a crystal experiences a 'self-force', by virtue of the orientation dependence of its elastic energy. If the crystal is elastically isotropic, this force is manifested as a couple acting to rotate the segment toward the lower energy of the pure screw orientation (i.e. acting to align the dislocation line with its Burgers vector). If the crystal is anisotropic, there are additional contributions to the couple, arising from the more complex energy landscape of the lattice itself. These effects can strongly influence the dynamic evolution of dislocation networks, and via their governing role in dislocation multiplication phenomena, control plastic flow in metals. In this paper we develop a model for dislocation self-forces in a general anisotropic crystal, and briefly consider the technologically important example of α-iron, which becomes increasingly anisotropic as the temperature approaches that of the α-γ phase transition at 912 °C.

  5. Dislocation structure produced by an ultrashort shock pulse

    SciTech Connect

    Matsuda, Tomoki Hirose, Akio; Sano, Tomokazu; Arakawa, Kazuto

    2014-11-14

    We found an ultrashort shock pulse driven by a femtosecond laser pulse on iron generates a different dislocation structure than the shock process which is on the nanosecond timescale. The ultrashort shock pulse produces a highly dense dislocation structure that varies by depth. According to transmission electron microscopy, dislocations away from the surface produce microbands via a network structure similar to a long shock process, but unlike a long shock process dislocations near the surface have limited intersections. Considering the dislocation motion during the shock process, the structure near the surface is attributed to the ultrashort shock duration. This approach using an ultrashort shock pulse will lead to understanding the whole process off shock deformation by clarifying the early stage.

  6. Linear complexions: Confined chemical and structural states at dislocations.

    PubMed

    Kuzmina, M; Herbig, M; Ponge, D; Sandlöbes, S; Raabe, D

    2015-09-04

    For 5000 years, metals have been mankind's most essential materials owing to their ductility and strength. Linear defects called dislocations carry atomic shear steps, enabling their formability. We report chemical and structural states confined at dislocations. In a body-centered cubic Fe-9 atomic percent Mn alloy, we found Mn segregation at dislocation cores during heating, followed by formation of face-centered cubic regions but no further growth. The regions are in equilibrium with the matrix and remain confined to the dislocation cores with coherent interfaces. The phenomenon resembles interface-stabilized structural states called complexions. A cubic meter of strained alloy contains up to a light year of dislocation length, suggesting that linear complexions could provide opportunities to nanostructure alloys via segregation and confined structural states.

  7. Room-temperature dislocation climb in copper-niobium interfaces

    SciTech Connect

    Wang, Jian; Hoagland, Richard G; Hirth, John P; Misra, Amit

    2008-01-01

    Using atomistic simulations, we show that dislocations climb efficiently in metallic copper-niobium interfaces through absorption and emission of vacancies in the dislocation core, as well as an associated counter diffusion of Cu atoms in the interfacial plane. The high efficiency of dislocation climb in the interface is ascribed to the high vacancy concentration of 0.05 in the interfacial plane, the low formation energy of 0.12 e V with respect to removal or insertion of Cu atoms, as well as the low kinetic barrier of 0.10 eV for vacancy migration in the interfacial Cu plane. Dislocation climb in the interface facilitates reactions of interfacial dislocations, and enables interfaces to be in the equilibrium state with respect to concentrations ofpoint defects.

  8. 3D model retrieval using probability density-based shape descriptors.

    PubMed

    Akgül, Ceyhun Burak; Sankur, Bülent; Yemez, Yücel; Schmitt, Francis

    2009-06-01

    We address content-based retrieval of complete 3D object models by a probabilistic generative description of local shape properties. The proposed shape description framework characterizes a 3D object with sampled multivariate probability density functions of its local surface features. This density-based descriptor can be efficiently computed via kernel density estimation (KDE) coupled with fast Gauss transform. The non-parametric KDE technique allows reliable characterization of a diverse set of shapes and yields descriptors which remain relatively insensitive to small shape perturbations and mesh resolution. Density-based characterization also induces a permutation property which can be used to guarantee invariance at the shape matching stage. As proven by extensive retrieval experiments on several 3D databases, our framework provides state-of-the-art discrimination over a broad and heterogeneous set of shape categories.

  9. High-temperature constitutive modeling

    NASA Technical Reports Server (NTRS)

    Robinson, D. N.; Ellis, J. R.

    1984-01-01

    Thermomechanical service conditions for high-temperature levels, thermal transients, and mechanical loads severe enough to cause measurable inelastic deformation are studied. Structural analysis in support of the design of high-temperature components depends strongly on accurate mathematical representations of the nonlinear, hereditary, inelastic behavior of structural alloys at high temperature, particularly in the relatively small strain range. Progress is discussed in the following areas: multiaxial experimentation to provide a basis for high-temperature multiaxial constitutive relationships; nonisothermal testing and theoretical development toward a complete thermomechanically path dependent formulation of viscoplasticity; and development of viscoplastic constitutive model accounting for initial anisotropy.

  10. Density-based cluster algorithms for the identification of core sets

    NASA Astrophysics Data System (ADS)

    Lemke, Oliver; Keller, Bettina G.

    2016-10-01

    The core-set approach is a discretization method for Markov state models of complex molecular dynamics. Core sets are disjoint metastable regions in the conformational space, which need to be known prior to the construction of the core-set model. We propose to use density-based cluster algorithms to identify the cores. We compare three different density-based cluster algorithms: the CNN, the DBSCAN, and the Jarvis-Patrick algorithm. While the core-set models based on the CNN and DBSCAN clustering are well-converged, constructing core-set models based on the Jarvis-Patrick clustering cannot be recommended. In a well-converged core-set model, the number of core sets is up to an order of magnitude smaller than the number of states in a conventional Markov state model with comparable approximation error. Moreover, using the density-based clustering one can extend the core-set method to systems which are not strongly metastable. This is important for the practical application of the core-set method because most biologically interesting systems are only marginally metastable. The key point is to perform a hierarchical density-based clustering while monitoring the structure of the metric matrix which appears in the core-set method. We test this approach on a molecular-dynamics simulation of a highly flexible 14-residue peptide. The resulting core-set models have a high spatial resolution and can distinguish between conformationally similar yet chemically different structures, such as register-shifted hairpin structures.

  11. Experimentally- and Dislocation-Based Multi-scale Modeling of Metal Plasticity Including Temperature and Rate Effects

    NASA Astrophysics Data System (ADS)

    Nemat-Nasser, Sia

    2005-08-01

    Excluding high-temperature creep, the plastic deformation of metals occurs by the motion of dislocations that produce slip on various slip planes in various slip directions. It is thus natural to seek to develop constitutive relations for metal plasticity, based on the concept of dislocations and their kinematics and kinetics. Such an approach has been successfully used by a number of investigators over the past several decades. More recently, however, the development of the recovery Hopkinson techniques by this writer and his coworkers at UCSD's CEAM, has provided important experimental tools to obtain reliable data on stress-strain response of variety of metals over broad ranges of strain rates and temperatures. A wealth of information has become available to guide and verify constitutive models that are proposed to describe metal plasticity. Using such data, I have been able to create a class of dislocation-based models that involve a few material constants, and seem to accurately characterize the response of a large number of metals over 10-4 to 105/s strain rates, and 77 to 1,300K temperatures.

  12. CHRONICLE: A Two-Stage Density-Based Clustering Algorithm for Dynamic Networks

    NASA Astrophysics Data System (ADS)

    Kim, Min-Soo; Han, Jiawei

    Information networks, such as social networks and that extracted from bibliographic data, are changing dynamically over time. It is crucial to discover time-evolving communities in dynamic networks. In this paper, we study the problem of finding time-evolving communities such that each community freely forms, evolves, and dissolves for any time period. Although the previous t-partite graph based methods are quite effective for discovering such communities from large-scale dynamic networks, they have some weak points such as finding only stable clusters of single path type and not being scalable w.r.t. the time period. We propose CHRONICLE, an efficient clustering algorithm that discovers not only clusters of single path type but also clusters of path group type. In order to find clusters of both types and also control the dynamicity of clusters, CHRONICLE performs the two-stage density-based clustering, which performs the 2nd-stage density-based clustering for the t-partite graph constructed from the 1st-stage density-based clustering result for each timestamp network. For a given data set, CHRONICLE finds all clusters in a fixed time by using a fixed amount of memory, regardless of the number of clusters and the length of clusters. Experimental results using real data sets show that CHRONICLE finds a wider range of clusters in a shorter time with a much smaller amount of memory than the previous method.

  13. Worker Dislocation: A Policy Study and Selected References on Worker Dislocation and the Unemployment Process. An Annotated Bibliography.

    ERIC Educational Resources Information Center

    Clark, Marilyn; And Others

    Dislocated workers are distinguished from chronically unemployed individuals in that the former have a stable work history and are generally unaware of the community's social services programs and how to use them. Dislocated workers frequently lack job search skills and do not see the transferability of their work skills. Often, they have heavy…

  14. A Comparison of Starting Wages and Job Satisfaction for Reemployed Dislocated Workers Participating in the Rock County Dislocated Worker Program.

    ERIC Educational Resources Information Center

    Borremans, Robert T.

    Following the economic recession of the early 1980's and the consequent high levels of unemployment in Rock County, a program was created at the Blackhawk Technical Institute (BTI) to assist dislocated workers reentering the labor force. The Rock County Dislocated Worker Program was intended as a comprehensive program with two principal activities…

  15. Comparison of dislocation density tensor fields derived from discrete dislocation dynamics and crystal plasticity simulations of torsion

    DOE PAGES

    Jones, Reese E.; Zimmerman, Jonathan A.; Po, Giacomo; ...

    2016-02-01

    Accurate simulation of the plastic deformation of ductile metals is important to the design of structures and components to performance and failure criteria. Many techniques exist that address the length scales relevant to deformation processes, including dislocation dynamics (DD), which models the interaction and evolution of discrete dislocation line segments, and crystal plasticity (CP), which incorporates the crystalline nature and restricted motion of dislocations into a higher scale continuous field framework. While these two methods are conceptually related, there have been only nominal efforts focused at the global material response that use DD-generated information to enhance the fidelity of CPmore » models. To ascertain to what degree the predictions of CP are consistent with those of DD, we compare their global and microstructural response in a number of deformation modes. After using nominally homogeneous compression and shear deformation dislocation dynamics simulations to calibrate crystal plasticity ow rule parameters, we compare not only the system-level stress-strain response of prismatic wires in torsion but also the resulting geometrically necessary dislocation density fields. To establish a connection between explicit description of dislocations and the continuum assumed with crystal plasticity simulations we ascertain the minimum length-scale at which meaningful dislocation density fields appear. Furthermore, our results show that, for the case of torsion, that the two material models can produce comparable spatial dislocation density distributions.« less

  16. Dislocation pinning effects induced by nano-precipitates during warm laser shock peening: Dislocation dynamic simulation and experiments

    NASA Astrophysics Data System (ADS)

    Liao, Yiliang; Ye, Chang; Gao, Huang; Kim, Bong-Joong; Suslov, Sergey; Stach, Eric A.; Cheng, Gary J.

    2011-07-01

    Warm laser shock peening (WLSP) is a new high strain rate surface strengthening process that has been demonstrated to significantly improve the fatigue performance of metallic components. This improvement is mainly due to the interaction of dislocations with highly dense nanoscale precipitates, which are generated by dynamic precipitation during the WLSP process. In this paper, the dislocation pinning effects induced by the nanoscale precipitates during WLSP are systematically studied. Aluminum alloy 6061 and AISI 4140 steel are selected as the materials with which to conduct WLSP experiments. Multiscale discrete dislocation dynamics (MDDD) simulation is conducted in order to investigate the interaction of dislocations and precipitates during the shock wave propagation. The evolution of dislocation structures during the shock wave propagation is studied. The dislocation structures after WLSP are characterized via transmission electron microscopy and are compared with the results of the MDDD simulation. The results show that nano-precipitates facilitate the generation of highly dense and uniformly distributed dislocation structures. The dislocation pinning effect is strongly affected by the density, size, and space distribution of nano-precipitates.

  17. Lateral Movement of Screw Dislocations During Homoepitaxial Growth and Devices Yielded Therefrom Free of the Detrimental Effects of Screw Dislocations

    NASA Technical Reports Server (NTRS)

    Neudeck, Philip G. (Inventor); Powell, J. Anthony (Inventor)

    2004-01-01

    The present invention is related to a method that enables and improves wide bandgap homoepitaxial layers to be grown on axis single crystal substrates, particularly SiC. The lateral positions of the screw dislocations in epitaxial layers are predetermined instead of random, which allows devices to be reproducibly patterned to avoid performance degrading crystal defects normally created by screw dislocations.

  18. Comparison of dislocation density tensor fields derived from discrete dislocation dynamics and crystal plasticity simulations of torsion

    SciTech Connect

    Jones, Reese E.; Zimmerman, Jonathan A.; Po, Giacomo; Mandadapu, Kranthi

    2016-02-01

    Accurate simulation of the plastic deformation of ductile metals is important to the design of structures and components to performance and failure criteria. Many techniques exist that address the length scales relevant to deformation processes, including dislocation dynamics (DD), which models the interaction and evolution of discrete dislocation line segments, and crystal plasticity (CP), which incorporates the crystalline nature and restricted motion of dislocations into a higher scale continuous field framework. While these two methods are conceptually related, there have been only nominal efforts focused at the global material response that use DD-generated information to enhance the fidelity of CP models. To ascertain to what degree the predictions of CP are consistent with those of DD, we compare their global and microstructural response in a number of deformation modes. After using nominally homogeneous compression and shear deformation dislocation dynamics simulations to calibrate crystal plasticity ow rule parameters, we compare not only the system-level stress-strain response of prismatic wires in torsion but also the resulting geometrically necessary dislocation density fields. To establish a connection between explicit description of dislocations and the continuum assumed with crystal plasticity simulations we ascertain the minimum length-scale at which meaningful dislocation density fields appear. Furthermore, our results show that, for the case of torsion, that the two material models can produce comparable spatial dislocation density distributions.

  19. Reactions between a <111> screw dislocation and <100> interstitial dislocation loops in alpha-iron modelled at atomic-scale

    SciTech Connect

    Terentyev, Dmitry; Bacon, David J; Osetskiy, Yury N

    2010-03-01

    Interstitial dislocation loops with Burgers vector of <100> type are observed in {alpha}-iron irradiated by neutrons or heavy ions, and their population increases with increasing temperature. Their effect on motion of a 1/2<111> edge dislocation was reported earlier 1. Results are presented of a molecular dynamics study of interactions between a 1/2<111> screw dislocation and <100> loops in iron at temperature in the range 100 to 600 K. A variety of reaction mechanisms and outcomes are observed and classified in terms of the resulting dislocation configuration and the maximum stress required for the dislocation to break away. The highest obstacle resistance arises when the loop is absorbed to form a helical turn on the screw dislocation line, for the dislocation cannot glide away until the turn closes and a loop is released with the same Burgers vector as the line. Other than one situation found, in which no dislocation-loop reaction occurs, the weakest obstacle strength is found when the original <100> loop is restored at the end of the reaction. The important role of the cross-slip and the influence of model boundary conditions are emphasised and demonstrated by examples.

  20. Analysis of flow stress and deformation mechanism under hot working of ZK60 magnesium alloy by a new strain-dependent constitutive equation

    NASA Astrophysics Data System (ADS)

    Ciccarelli, D.; El Mehtedi, M.; Jäger, A.; Spigarelli, S.

    2015-12-01

    The present study investigates the variation of flow stress and microstructural evolution with strain for ZK60 magnesium alloy. A new constitutive equation was used to model the flow stress with excellent results. This constitutive analysis and the microstructural studies carried out on strained samples revealed the existence of two different regimes. At temperatures above 300 °C, moderate grain growth and intragranular dislocation activity. Yet, the calculated value of the activation energy and the marked increase in the equivalent strain to fracture indicated grain boundary sliding as a dominant mechanism in this regime of strain rate and temperature, with dislocation motion playing an ancillary role. At lower temperatures, deformation was exclusively governed by dislocation motion, with the extensive occurrence of dynamic recrystallization, which started at low strains, and absence of grain growth.

  1. Transient vascular compromise of the lunate after fracture-dislocation or dislocation of the carpus.

    PubMed

    White, R E; Omer, G E

    1984-03-01

    Although classic avascular necrosis of the lunate is rare after fracture-dislocation or dislocation of the carpus, these severe carpal injuries can compromise the vascular supply of the lunate. The lunate thus develops a relative increase in radiodensity. Our finding of an incidence of 12.5%--three of 24 cases--suggests a relatively frequent occurrence. The clinical course was transient with resolution of abnormal radiodensity and subjective findings. Moreover, none of the three cases progressed to classic avascular necrosis of the lunate, Kienböck's disease. The clinician should not confuse this transient vascular compromise of the lunate with Kienböck's disease, but should be aware of the entity and its benign, self-limited course and should treat it expectantly.

  2. Stress-free states of continuum dislocation fields: Rotations, grain boundaries, and the Nye dislocation density tensor

    NASA Astrophysics Data System (ADS)

    Limkumnerd, Surachate; Sethna, James P.

    2007-06-01

    We derive general relations between grain boundaries, rotational deformations, and stress-free states for the mesoscale continuum Nye dislocation density tensor. Dislocations generally are associated with long-range stress fields. We provide the general form for dislocation density fields whose stress fields vanish. We explain that a grain boundary (a dislocation wall satisfying Frank’s formula) has vanishing stress in the continuum limit. We show that the general stress-free state can be written explicitly as a (perhaps continuous) superposition of flat Frank walls. We show that the stress-free states are also naturally interpreted as configurations generated by a general spatially dependent rotational deformation. Finally, we propose a least-squares definition for the spatially dependent rotation field of a general (stressful) dislocation density field.

  3. Competing Processes in Reactions between an Edge Dislocation and Dislocation Loops in a Body-Centred Cubic Metal

    SciTech Connect

    Terentyev, Dmitry; Bacon, David J; Osetskiy, Yury N

    2010-01-01

    Molecular dynamics simulation was used to investigate reactions of a 1/2<111>{l_brace}110{r_brace} edge dislocation with interstitial dislocation loops of 1/2<111> and <100> type in a model of iron. Whether loops are strong or weak obstacles depends not only on loop size and type, but also on temperature and dislocation velocity. These parameters determine whether a loop is absorbed on the dislocation or left behind as it glides away. Absorption requires glide of a reaction segment over the loop surface and cross-slip of dipole dislocation arms attached to the ends of the segment: these mechanisms depend on temperature and strain rate, as discussed here.

  4. A Venture in Constitutional Law.

    ERIC Educational Resources Information Center

    Cole, W. Graham; Dillon, Dorothy H.

    1980-01-01

    Senior high girls and boys from two single-sex schools undertook a study of a Supreme Court case that provided insight not only into constitutional law and history but also into how men and women can work together and relate in other ways than dating. (DS)

  5. Take Advantage of Constitution Day

    ERIC Educational Resources Information Center

    McCune, Bonnie F.

    2008-01-01

    The announcement of the mandate for Constitution and Citizenship Day shortly before September, 2005, probably led to groans of dismay. Not another "must-do" for teachers and schools already stressed by federal and state requirements for standardized tests, increasingly rigid curricula, and scrutiny from the public and officials. But the…

  6. The Constitution and Academic Freedom.

    ERIC Educational Resources Information Center

    Gilbertson, Eric R.

    During the past 150 years U.S. courts have demonstrated a special protectiveness toward academics and academic institutions. Academic freedom was not a concern when the U.S. Constitution and the First Amendment were drafted and is not mentioned in the "Federalist Papers." However, decisions by a series of Supreme Court justices led to…

  7. The Geography behind the Constitution.

    ERIC Educational Resources Information Center

    Salter, Christopher L.; Hobbs, Gail L.

    1988-01-01

    Examines some of the geographical elements that influenced the creation of the U.S. Constitution, such as sectionalism, the Piedmont, and the Atlantic Coastal Plain. Focusing on aspects of geography that underlie the thinking, writing, and ratification of the document, the authors explore geography as environment, image-maker, and explicit…

  8. Take Advantage of Constitution Day

    ERIC Educational Resources Information Center

    McCune, Bonnie F.

    2008-01-01

    The announcement of the mandate for Constitution and Citizenship Day shortly before September, 2005, probably led to groans of dismay. Not another "must-do" for teachers and schools already stressed by federal and state requirements for standardized tests, increasingly rigid curricula, and scrutiny from the public and officials. But the…

  9. Painful Spastic Hip Dislocation: Proximal Femoral Resection

    PubMed Central

    Albiñana, Javier; Gonzalez-Moran, Gaspar

    2002-01-01

    The dislocated hip in a non-ambulatory child with spastic paresis tends to be a painful interference to sleep, sitting upright, and perineal care. Proximal femoral resection-interposition arthroplasty is one method of treatment for this condition. We reviewed eight hips, two bilateral cases, with a mean follow-up of 30 months. Clinical improvement was observed in all except one case, with respect to pain relief and sitting tolerance. Some proximal migration was observed in three cases, despite routine post-operative skeletal traction in all cases and careful soft tissue interposition. One case showed significant heterotopic ossification which restricted prolonged sitting. This patient needed some occasional medication for pain. PMID:12180614

  10. Kink pair production and dislocation motion

    NASA Astrophysics Data System (ADS)

    Fitzgerald, S. P.

    2016-12-01

    The motion of extended defects called dislocations controls the mechanical properties of crystalline materials such as strength and ductility. Under moderate applied loads, this motion proceeds via the thermal nucleation of kink pairs. The nucleation rate is known to be a highly nonlinear function of the applied load, and its calculation has long been a theoretical challenge. In this article, a stochastic path integral approach is used to derive a simple, general, and exact formula for the rate. The predictions are in excellent agreement with experimental and computational investigations, and unambiguously explain the origin of the observed extreme nonlinearity. The results can also be applied to other systems modelled by an elastic string interacting with a periodic potential, such as Josephson junctions in superconductors.

  11. Kink pair production and dislocation motion

    PubMed Central

    Fitzgerald, S. P.

    2016-01-01

    The motion of extended defects called dislocations controls the mechanical properties of crystalline materials such as strength and ductility. Under moderate applied loads, this motion proceeds via the thermal nucleation of kink pairs. The nucleation rate is known to be a highly nonlinear function of the applied load, and its calculation has long been a theoretical challenge. In this article, a stochastic path integral approach is used to derive a simple, general, and exact formula for the rate. The predictions are in excellent agreement with experimental and computational investigations, and unambiguously explain the origin of the observed extreme nonlinearity. The results can also be applied to other systems modelled by an elastic string interacting with a periodic potential, such as Josephson junctions in superconductors. PMID:28004834

  12. Disclinations, dislocations, and continuous defects: A reappraisal

    NASA Astrophysics Data System (ADS)

    Kleman, M.; Friedel, J.

    2008-01-01

    Disclinations were first observed in mesomorphic phases. They were later found relevant to a number of ill-ordered condensed-matter media involving continuous symmetries or frustrated order. Disclinations also appear in polycrystals at the edges of grain boundaries; but they are of limited interest in solid single crystals, where they can move only by diffusion climb and, owing to their large elastic stresses, mostly appear in close pairs of opposite signs. The relaxation mechanisms associated with a disclination in its creation, motion, and change of shape involve an interplay with continuous or quantized dislocations and/or continuous disclinations. These are attached to the disclinations or are akin to Nye’s dislocation densities, which are particularly well suited for consideration here. The notion of an extended Volterra process is introduced, which takes these relaxation processes into account and covers different situations where this interplay takes place. These concepts are illustrated by a variety of applications in amorphous solids, mesomorphic phases, and frustrated media in their curved habit space. These often involve disclination networks with specific node conditions. The powerful topological theory of line defects considers only defects stable against any change of boundary conditions or relaxation processes compatible with the structure considered. It can be seen as a simplified case of the approach considered here, particularly suited for media of high plasticity or/and complex structures. It cannot analyze the dynamical properties of defects nor the elastic constants involved in their static properties; topological stability cannot guarantee energetic stability, and sometimes cannot distinguish finer details of the structure of defects.

  13. The length change of a dislocation junction in FCC-single crystals under stress

    NASA Astrophysics Data System (ADS)

    Kurinnaya, Raisa; Zgolich, Marina; Starenchenko, Vladimir; Sadritdinova, Gulnora

    2016-01-01

    The product of dislocation reactions among dislocations of non-coplanar slip systems are dislocation junctions. The paper presents the study on the length change of dislocation junctions under stress. It is revealed that dislocation junctions can be destructed by merging of triple dislocation nodes at certain inclination angles of the glide dislocation and the forest dislocation to the junction line and the corresponding lengths of free segments of intersecting dislocations. Dislocation junctions formed at an arbitrary intersection of segments of the reacting dislocation are investigated. The geometry of the intersection of segments of reacting dislocations, at which dislocation junctions are not completely destructed under stress but cease to be an obstacle for further motion of the glide dislocation, is determined. Such junctions remain in the shear zone, presenting an obstacle to other glide dislocations. Conditions under which the length of the dislocation junction increases with an increase in the stress exceeding the original length are found. The formed extended barrier becomes too strong for the acting stress. Higher stresses are required in order to destruct it. The probability of completely destructible junctions under stress, the probability of non-destructible junctions that remain in the shear zone and replenish the density of dislocation debris, as well as the probability of formation of long strong junctions, which are barriers capable of limiting the shear zone, are determined.

  14. Advancing towards constitutive equations for the metal industry via the LEDS theory

    NASA Astrophysics Data System (ADS)

    Kuhlmann-Wilsdorf, Doris

    2004-02-01

    A prime objective in the development of crystal dislocation theory has been, and at any rate should be, constitutive equations for practical use in the metal forming industry. Protracted controversies regarding workhardening theory have frustrated this goal for the past seven decades. The are fueled by the paradox that plastic deformation is a prime example for the second law of thermodynamics in converting mechanical work into heat with good efficiency, even while in seeming opposition to the second law it typically raises the internal energy of the deformed material. The low-energy dislocation structures (LEDS) theory resolves this difficulty by showing that, as always in inanimate nature, so also plastic deformation proceeds close to minimum free energy. Indeed recent evidence based on deformation band structures proves that plastic deformation typically proceeds very close to minimum energy among the accessible configurations. White plastic strain raises the flow stress, in ductile crystalline materials mostly through generating dislocation structures, but also through twins, kink bands, microcracks and others, Newton’s third law, i.e., force equilibrium, is always stringently obeyed. Therefore, deformation dislocation structures are in thermal equilibrium as long as the stress that generated them remains in place. Based on this concept of free energy minimization, the LEDS theory has long since explained, at least semiquantitatively, all significant aspects of metal strength and deformation, as well as the effects of heat treatments. The LEDS theory is the special case, namely, as pertaining to dislocation structures, of the more general low-energy structures (LEDS) theory that governs all types of deformation independent of the deformation mechanism, and that operates in all types of materials, including plastics.

  15. Advancing towards constitutive equations for the metal industry via the LEDS theory

    NASA Astrophysics Data System (ADS)

    Kuhlmann-Wilsdorf, Doris

    2004-02-01

    A prime objective in the development of crystal dislocation theory has been, and at any rate should be, constitutive equations for practical use in the metal forming industry. Protracted controversies regarding workhardening theory have frustrated this goal for the past seven decades. They are fueled by the paradox that plastic deformation is a prime example for the second law of thermodynamics in converting mechanical work into heat with good efficiency, even while in seeming opposition to the second law it typically raises the internal energy of the deformed material. The low-energy dislocation structures (LEDS) theory resolves this difficulty by showing that, as always in inanimate nature, so also plastic deformation proceeds close to minimum free energy. Indeed recent evidence based on deformation band structures proves that plastic deformation typically proceeds very close to minimum energy among the accessible configurations. While plastic strain raises the flow stress, in ductile crystalline materials mostly through generating dislocation structures, but also through twins, kink bands, microcracks and others, Newton’s third law, i.e., force equilibrium, is always stringently obeyed. Therefore, deformation dislocation structures are in thermal equilibrium as long as the stress that generated them remains in place. Based on this concept of free energy minimization, the LEDS theory has long since explained, at least semiquantitatively, all significant aspects of metal strength and deformation, as well as the effects of heat treatments. The LEDS theory is the special case, namely, as pertaining to dislocation structures, of the more general low-energy structures (LEDS) theory that governs all types of deformation independent of the deformation mechanism, and that operates in all types of materials, including plastics.

  16. Period-doubling reconstructions of semiconductor partial dislocations

    SciTech Connect

    Park, Ji -Sang; Huang, Bing; Wei, Su -Huai; Kang, Joongoo; McMahon, William E.

    2015-09-18

    Atomic-scale understanding and control of dislocation cores is of great technological importance, because they act as recombination centers for charge carriers in optoelectronic devices. Using hybrid density-functional calculations, we present period-doubling reconstructions of a 90 degrees partial dislocation in GaAs, for which the periodicity of like-atom dimers along the dislocation line varies from one to two, to four dimers. The electronic properties of a dislocation change drastically with each period doubling. The dimers in the single-period dislocation are able to interact, to form a dispersive one-dimensional band with deep-gap states. However, the inter-dimer interaction for the double-period dislocation becomes significantly reduced; hence, it is free of mid-gap states. The Ga core undergoes a further period-doubling transition to a quadruple-period reconstruction induced by the formation of small hole polarons. In conclusion, the competition between these dislocation phases suggests a new passivation strategy via population manipulation of the detrimental single-period phase.

  17. Period-doubling reconstructions of semiconductor partial dislocations

    DOE PAGES

    Park, Ji -Sang; Huang, Bing; Wei, Su -Huai; ...

    2015-09-18

    Atomic-scale understanding and control of dislocation cores is of great technological importance, because they act as recombination centers for charge carriers in optoelectronic devices. Using hybrid density-functional calculations, we present period-doubling reconstructions of a 90 degrees partial dislocation in GaAs, for which the periodicity of like-atom dimers along the dislocation line varies from one to two, to four dimers. The electronic properties of a dislocation change drastically with each period doubling. The dimers in the single-period dislocation are able to interact, to form a dispersive one-dimensional band with deep-gap states. However, the inter-dimer interaction for the double-period dislocation becomes significantlymore » reduced; hence, it is free of mid-gap states. The Ga core undergoes a further period-doubling transition to a quadruple-period reconstruction induced by the formation of small hole polarons. In conclusion, the competition between these dislocation phases suggests a new passivation strategy via population manipulation of the detrimental single-period phase.« less

  18. Aspects of Dislocation Behavior in SiC

    SciTech Connect

    Dudley, M.; Chen, Y; Huang, X

    2009-01-01

    A review is presented of the current understanding of the dislocation configurations observed in PVT-grown 4H- and 6H-SiC boules and CVD-grown 4H-SiC homoepitaxial layers. In both PVT-grown boules and CVD-grown epilayers, dislocation configurations are classified according to whether they are growth dislocations, i.e., formed during growth via the replication of dislocations which thread the moving crystal growth front, or result from deformation processes (under either mechanical or electrical stress) immediately following growth, during post growth cooling, i.e., behind the crystal growth front or during device operation. Possible formation mechanisms of growth defects in the PVT grown boules, such as axial screw dislocations and threading edge dislocation walls are proposed. Similarly, possible origins of growth defect configurations in CVD-grown epilayers, such as Frank faults bounded by Frank partials, BPDs and TEDs, are also discussed. In a similar way, the origins of BPD configurations resulting from relaxation of thermal stresses during post-growth cooling of the PVT boules are discussed. Finally, the susceptibility of BPD configurations replicated into CVD grown epilayers from the substrate towards Recombination Enhanced Dislocation Glide (REDG) is discussed.

  19. Transition of dislocation glide to shear transformation in shocked tantalum

    DOE PAGES

    Hsiung, Luke L.; Campbell, Geoffrey H.

    2017-02-28

    A TEM study of pure tantalum and tantalum-tungsten alloys explosively shocked at a peak pressure of 30 GPa (strain rate: ~1 x 104 sec-1) is presented. While no ω (hexagonal) phase was found in shock-recovered pure Ta and Ta-5W that contain mainly a low-energy cellular dislocation structure, shock-induced ω phase was found to form in Ta-10W that contains evenly distributed dislocations with a stored dislocation density higher than 1 x 1012 cm-2. The TEM results clearly reveal that shock-induced α (bcc) → ω (hexagonal) shear transformation occurs when dynamic recovery reactions which lead the formation low-energy cellular dislocation structure becomemore » largely suppressed in Ta-10W shocked under dynamic (i.e., high strain-rate and high-pressure) conditions. A novel dislocation-based mechanism is proposed to rationalize the transition of dislocation glide to twinning and/or shear transformation in shock-deformed tantalum. Lastly, twinning and/or shear transformation take place as an alternative deformation mechanism to accommodate high-strain-rate straining when the shear stress required for dislocation multiplication exceeds the threshold shear stresses for twinning and/or shear transformation.« less

  20. Electron energy can oscillate near a crystal dislocation

    DOE PAGES

    Li, Mingda; Cui, Wenping; Dresselhaus, Mildred S.; ...

    2017-01-25

    Crystal dislocations govern the plastic mechanical properties of materials but also affect the electrical and optical properties. However, a fundamental and quantitative quantum field theory of a dislocation has remained undiscovered for decades. Here in this article we present an exactly-solvable one-dimensional quantum field theory of a dislocation, for both edge and screw dislocations in an isotropic medium, by introducing a new quasiparticle which we have called the ‘dislon’. The electron-dislocation relaxation time can then be studied directly from the electron self-energy calculation, which is reducible to classical results. In addition, we predict that the electron energy will experience anmore » oscillation pattern near a dislocation. Compared with the electron density’s Friedel oscillation, such an oscillation is intrinsically different since it exists even with only single electron is present. With our approach, the effect of dislocations on materials’ non-mechanical properties can be studied at a full quantum field theoretical level.« less

  1. Strength and Dislocation Structure Evolution of Small Metals under Vibrations

    NASA Astrophysics Data System (ADS)

    Ngan, Alfonso

    2015-03-01

    It is well-known that ultrasonic vibration can soften metals, and this phenomenon has been widely exploited in industrial applications concerning metal forming and bonding. In this work, we explore the effects of a superimposed small oscillatory load on metal plasticity, from the nano- to macro-size range, and from audible to ultrasonic frequency ranges. Macroscopic and nano-indentation were performed on aluminum, copper and molybdenum, and the results show that the simultaneous application of oscillatory stresses can lower the hardness of these samples. More interestingly, EBSD and TEM observations show that subgrain formation and reduction in dislocation density generally occurred when stress oscillations were applied. These findings point to an important knowledge gap in metal plasticity - the existing understanding of ultrasound softening in terms of the vibrations either imposing additional stress waves to augment the quasi-static applied load, or heating up the metal, whereas the metal's intrinsic deformation resistance or dislocation interactive processes are assumed unaltered by the ultrasound, is proven wrong by the present results. Furthermore, in the case of nanoindentation, the Continuous Stiffness Measurement technique for contact stiffness measurement assumes that the imposed signal-carrier oscillations do not intrinsically alter the material properties of the specimen, and again, the present results prove that this can be wrong. To understand the enhanced subgrain formation and dislocation annihilation, Discrete Dislocation Dynamics (DDD) simulations were carried out and these show that when an oscillatory stress is superimposed on a quasi-static applied stress, reversals of motion of dislocations may occur, and these allow the dislocations to revisit repeatedly suitable configurations for annihilation. DDD, however, was unable to predict the observed subgrain formation presumably because the number of dislocations that can be handled is not large

  2. Numerical simulation on slabs dislocation of Zipingpu concrete faced rockfill dam during the Wenchuan earthquake based on a generalized plasticity model.

    PubMed

    Xu, Bin; Zhou, Yang; Zou, Degao

    2014-01-01

    After the Wenchuan earthquake in 2008, the Zipingpu concrete faced rockfill dam (CFRD) was found slabs dislocation between different stages slabs and the maximum value reached 17 cm. This is a new damage pattern and did not occur in previous seismic damage investigation. Slabs dislocation will affect the seepage control system of the CFRD gravely and even the safety of the dam. Therefore, investigations of the slabs dislocation's mechanism and development might be meaningful to the engineering design of the CFRD. In this study, based on the previous studies by the authors, the slabs dislocation phenomenon of the Zipingpu CFRD was investigated. The procedure and constitutive model of materials used for finite element analysis are consistent. The water elevation, the angel, and the strength of the construction joints were among major variables of investigation. The results indicated that the finite element procedure based on a modified generalized plasticity model and a perfect elastoplastic interface model can be used to evaluate the dislocation damage of face slabs of concrete faced rockfill dam during earthquake. The effects of the water elevation, the angel, and the strength of the construction joints are issues of major design concern under seismic loading.

  3. Numerical Simulation on Slabs Dislocation of Zipingpu Concrete Faced Rockfill Dam during the Wenchuan Earthquake Based on a Generalized Plasticity Model

    PubMed Central

    Xu, Bin; Zou, Degao

    2014-01-01

    After the Wenchuan earthquake in 2008, the Zipingpu concrete faced rockfill dam (CFRD) was found slabs dislocation between different stages slabs and the maximum value reached 17 cm. This is a new damage pattern and did not occur in previous seismic damage investigation. Slabs dislocation will affect the seepage control system of the CFRD gravely and even the safety of the dam. Therefore, investigations of the slabs dislocation's mechanism and development might be meaningful to the engineering design of the CFRD. In this study, based on the previous studies by the authors, the slabs dislocation phenomenon of the Zipingpu CFRD was investigated. The procedure and constitutive model of materials used for finite element analysis are consistent. The water elevation, the angel, and the strength of the construction joints were among major variables of investigation. The results indicated that the finite element procedure based on a modified generalized plasticity model and a perfect elastoplastic interface model can be used to evaluate the dislocation damage of face slabs of concrete faced rockfill dam during earthquake. The effects of the water elevation, the angel, and the strength of the construction joints are issues of major design concern under seismic loading. PMID:25013857

  4. Complicated Congenital Dislocation of the Knee: A Case Report

    PubMed Central

    Madadi, Firooz; Tahririan, Mohammad A.; Karami, Mohsen; Madadi, Firoozeh

    2016-01-01

    Congenital dislocation of the knee (CDK) is a rare disorder. We report the case of a 7-year-old girl with bilateral knee stiffness, marked anterior bowing of both legs, and inability to walk without aid. Radiologic investigation revealed bilateral knee joint dislocation accompanied by severe anterior bowing of both tibia proximally and posterior bowing of both femur distally, demonstrating a complicated congenital knee dislocation. Two-staged open reduction with proximal tibial osteotomy was performed to align the reduced knee joints. The patient was completely independent in her daily activities after surgical correction. PMID:27847857

  5. Dislocations in extruded Co-49.3 at. pct Al

    NASA Technical Reports Server (NTRS)

    Yaney, D. L.; Nix, W. D.; Pelton, A. R.

    1986-01-01

    Polycrystalline Co-49.3 at. pct Al, which had been extruded at 1505 K, was examined using transmission electron microscopy. Diffraction contrast analysis showed that b = 100 as well as b = 111 line dislocations contribute to elevated temperature deformation in CoAl. Therefore, it was concluded that sufficient slip systems exist in CoAl to allow for general plasticity in the absence of diffusional mechanisms. Line dislocations of the type b = 001 were observed on both 110 and 100 planes while b = 111 line dislocations were observed on 1 -1 0 planes.

  6. Dynamic phases, pinning, and pattern formation for driven dislocation assemblies

    SciTech Connect

    Zhou, Caizhi; Reichhardt, Charles; Olson Reichhardt, Cynthia J.; Beyerlein, Irene J.

    2015-01-23

    We examine driven dislocation assemblies and show that they can exhibit a set of dynamical phases remarkably similar to those of driven systems with quenched disorder such as vortices in superconductors, magnetic domain walls, and charge density wave materials. These phases include pinned-jammed, fluctuating, and dynamically ordered states, and each produces distinct dislocation patterns as well as specific features in the noise fluctuations and transport properties. Lastly, our work suggests that many of the results established for systems with quenched disorder undergoing plastic depinning transitions can be applied to dislocation systems, providing a new approach for understanding pattern formation and dynamics in these systems.

  7. Dynamic phases, pinning, and pattern formation for driven dislocation assemblies

    DOE PAGES

    Zhou, Caizhi; Reichhardt, Charles; Olson Reichhardt, Cynthia J.; ...

    2015-01-23

    We examine driven dislocation assemblies and show that they can exhibit a set of dynamical phases remarkably similar to those of driven systems with quenched disorder such as vortices in superconductors, magnetic domain walls, and charge density wave materials. These phases include pinned-jammed, fluctuating, and dynamically ordered states, and each produces distinct dislocation patterns as well as specific features in the noise fluctuations and transport properties. Lastly, our work suggests that many of the results established for systems with quenched disorder undergoing plastic depinning transitions can be applied to dislocation systems, providing a new approach for understanding pattern formation andmore » dynamics in these systems.« less

  8. Posterior dislocation of the sternoclavicular joint: report of two cases.

    PubMed

    Labronici, Pedro José; Souza, Fabrício Cardoso de; Pires, Robinson Esteves Santos; Santos Filho, Fernando Claudino Dos; Gameiro, Vinicius Schott; Labronici, Gustavo José

    2016-01-01

    The authors report the cases of two young patients who had suffered a sporting accident with posterior traumatic dislocation of sternoclavicular joint. In one of the patients closed reduction was accomplished by keeping the limb in a sling. The second patient, after reduction was done, presented recurrence of the dislocation, thus requiring surgical treatment. It is important to observe the relevance of computed tomography to help diagnosing, as well as monitoring the reduction procedure. The objective of this study was to demonstrate two different types of treatment in a rare injury such as the posterior dislocation of sternoclavicular joint.

  9. Dynamic Phases, Pinning, and Pattern Formation for Driven Dislocation Assemblies

    PubMed Central

    Zhou, Caizhi; Reichhardt, Charles; Olson Reichhardt, Cynthia J.; Beyerlein, Irene J.

    2015-01-01

    We examine driven dislocation assemblies and show that they can exhibit a set of dynamical phases remarkably similar to those of driven systems with quenched disorder such as vortices in superconductors, magnetic domain walls, and charge density wave materials. These phases include pinned-jammed, fluctuating, and dynamically ordered states, and each produces distinct dislocation patterns as well as specific features in the noise fluctuations and transport properties. Our work suggests that many of the results established for systems with quenched disorder undergoing plastic depinning transitions can be applied to dislocation systems, providing a new approach for understanding pattern formation and dynamics in these systems. PMID:25613839

  10. Epidemiology of Elbow Dislocations in High School Athletes.

    PubMed

    Dizdarevic, Ismar; Low, Sara; Currie, Dustin W; Comstock, R Dawn; Hammoud, Sommer; Atanda, Alfred

    2016-01-01

    The elbow is the second most commonly dislocated major joint in the general population. Previous studies that focused on emergency department populations indicate that such injuries occur most frequently among adolescent athletes. To describe the epidemiological rates and patterns of sports-related elbow dislocations in high school athletes. Descriptive epidemiology study. Sports-related injury data for the 2005-2006 through 2013-2014 academic years from a national convenience sample of high schools participating in the National High School Sports-Related Injury Surveillance Study (High School Reporting Information Online [RIO]) were analyzed. Certified athletic trainers participating in High School RIO reported 115 of 1246 (9.2%) elbow injuries as elbow dislocations. A total of 30,415,179 athlete exposures (AEs) were reported during the study period, resulting in a dislocation rate of 0.38 per 100,000 AEs. The majority of the dislocations resulted from boys' wrestling (46.1%) and football (37.4%). Elbow dislocation rates were higher in competition than in practice. Also, 91.3% of dislocations occurred in boys' sports. Among both boys (60.4%) and girls (88.9%), the majority of injuries occurred during varsity sports activities. Contact with another person was the most common injury mechanism (46.9%), followed by contact with the playing surface (46.0%). Dislocations more commonly resulted in removal from play for more than 3 weeks (23.4% vs 6.9%, respectively) or medical disqualification (36.9% vs 7.0%, respectively) compared with other elbow injuries. Dislocations were also more likely to result in surgical treatment than other elbow injuries (13.6% vs 4.7%, respectively). In high school athletes, elbow dislocations result in longer removal from play and are more likely to require surgical treatment than nondislocation-associated elbow injuries. Rates and patterns of elbow dislocations vary by sport. In high-risk sports, focused sport-specific prevention

  11. Spontaneous Late Intraocular Lens and Capsule Tension Ring Dislocation

    PubMed Central

    Koçak Altıntaş, Ayşe Gül; Omay, Aslıhan Esra; Çelik, Selda

    2017-01-01

    In this report, three cases with pseudoexfoliation (PEX) and advanced age with spontaneous intraocular lens (IOL) and capsule tension ring (CTR) dislocation were presented. All of our cases experienced progressive vision loss without an episode of strenuous physical activity, trauma, or any other ocular disease. Spontaneous dislocation was observed 2.5 to 8 years after uneventful phacosurgery. Each patient underwent complete IOL and CTR removal combined with anterior chamber IOL implantation. No complications were noticed during follow-up. As a result, capsule tension ring does not prevent late IOL dislocation after uncomplicated phacosurgery in the presence of PEX. Therefore, close follow-up is essential for patients with PEX. PMID:28405485

  12. Successful salvage of a recurrently dislocating Oxford medial unicompartmental bearing.

    PubMed

    van Tienen, Tony G; Taylor, Susan J; Brink, Rodney B

    2010-04-01

    Dislocation of the bearing of the Oxford medial unicompartmental arthroplasty is a rare but serious complication. We report the case of a 48-year-old woman with a classic anteromedial arthritis who had 2 bearing dislocations within the first 3 months after index surgery. These were attributable to posterior bony impingement of the bearing against a small retained osteophyte. After arthroscopic resection of the osteophyte, she has retained her original components with no further dislocations or signs of impending failure 7 years later. This case report emphasizes the importance of osteophyte removal from the back of the femoral condyle during an Oxford unicompartmental arthroplasty. (c) 2010 Elsevier Inc. All rights reserved.

  13. [How I Treat. An Anterior Temporomandibular Joint Dislocation].

    PubMed

    Gilon, Y; Johnen, J; Nizet, J L

    2015-09-01

    Anterior dislocation of the temporomandibular joint is not uncommon and requires prompt management. A defect of dislocation reduction can lead to severe functional impairment of a complex, and often active joint. The diagnosis is clinical and relatively obvious. It is made by the frontline medical team, general practitioner or emergency doctor. Recurrent cases are a matter for maxillofacial surgeons. This article describes a conventional technique for anterior dislocation reduction, to achieve urgently. The second part of the article deals with the specialized surgical treatment of relapsing forms.

  14. Dislocation core reconstruction in zinc-blende semiconductors

    NASA Astrophysics Data System (ADS)

    Justo, J. F.; Fazzio, A.; Antonelli, A.

    2000-12-01

    Using ab initio total-energy calculations, we computed core reconstruction energies of partial dislocations in zinc-blende semiconductors. The reconstruction energy of 30° partials was found to scale almost linearly with the experimental activation energy of 60° dislocations. The electronic structure of a dislocation shows that in an unreconstructed core, the gap states comprise a half-filled one-dimensional band, which splits up into bonding and antibonding states upon reconstruction. The energy states which lie in the electronic gap come from the core of β-partials, while those related to α-partials remain resonant in the valence band.

  15. Galeazzi fracture with volar dislocation of the distal radioulnar joint.

    PubMed

    Kim, Suezie; Ward, James P; Rettig, Michael E

    2012-11-01

    Galeazzi fracture dislocations are fractures of the distal one-third of the radial diaphysis with traumatic disruption of the distal radioulnar joint (DRUJ). This injury results in subluxation or dislocation of the ulnar head. We present a case of a Galeazzi fracture with a volar dislocation of the DRUJ. Open reduction of the DRUJ with Kirschner wire fixation in pronation was necessary to reduce the joint and maintain anatomic alignment. Repair of the triangular fibrocartilage complex was also necessary to maintain stability of the DRUJ.

  16. Constitutive Law and Flow Mechanism in Diamond Deformation

    DOE PAGES

    Yu, Xiaohui; Raterron, Paul; Zhang, Jianzhong; ...

    2012-11-19

    Constitutive laws and crystal plasticity in diamond deformation have been the subjects of substantial interest since synthetic diamond was made in 1950's. To date, however, little is known quantitatively regarding its brittle-ductile properties and yield strength at high temperatures. In this paper, we report, for the first time, the strain-stress constitutive relations and experimental demonstration of deformation mechanisms under confined high pressure. The deformation at room temperature is essentially brittle, cataclastic, and mostly accommodated by fracturing on {111} plane with no plastic yielding at uniaxial strains up to 15%. At elevated temperatures of 1000°C and 1200°C diamond crystals exhibit significantmore » ductile flow with corresponding yield strength of 7.9 and 6.3 GPa, indicating that diamond starts to weaken when temperature is over 1000°C. Finally, at high temperature the plastic deformation and ductile flow is meditated by the <110>{111} dislocation glide and a very active {111} micro-twinning.« less

  17. Constitutive Law and Flow Mechanism in Diamond Deformation

    SciTech Connect

    Yu, Xiaohui; Raterron, Paul; Zhang, Jianzhong; Lin, Zhijun; Wang, Liping; Zhao, Yusheng

    2012-11-19

    Constitutive laws and crystal plasticity in diamond deformation have been the subjects of substantial interest since synthetic diamond was made in 1950's. To date, however, little is known quantitatively regarding its brittle-ductile properties and yield strength at high temperatures. In this paper, we report, for the first time, the strain-stress constitutive relations and experimental demonstration of deformation mechanisms under confined high pressure. The deformation at room temperature is essentially brittle, cataclastic, and mostly accommodated by fracturing on {111} plane with no plastic yielding at uniaxial strains up to 15%. At elevated temperatures of 1000°C and 1200°C diamond crystals exhibit significant ductile flow with corresponding yield strength of 7.9 and 6.3 GPa, indicating that diamond starts to weaken when temperature is over 1000°C. Finally, at high temperature the plastic deformation and ductile flow is meditated by the <110>{111} dislocation glide and a very active {111} micro-twinning.

  18. Density-based parallel skin lesion border detection with webCL

    PubMed Central

    2015-01-01

    Background Dermoscopy is a highly effective and noninvasive imaging technique used in diagnosis of melanoma and other pigmented skin lesions. Many aspects of the lesion under consideration are defined in relation to the lesion border. This makes border detection one of the most important steps in dermoscopic image analysis. In current practice, dermatologists often delineate borders through a hand drawn representation based upon visual inspection. Due to the subjective nature of this technique, intra- and inter-observer variations are common. Because of this, the automated assessment of lesion borders in dermoscopic images has become an important area of study. Methods Fast density based skin lesion border detection method has been implemented in parallel with a new parallel technology called WebCL. WebCL utilizes client side computing capabilities to use available hardware resources such as multi cores and GPUs. Developed WebCL-parallel density based skin lesion border detection method runs efficiently from internet browsers. Results Previous research indicates that one of the highest accuracy rates can be achieved using density based clustering techniques for skin lesion border detection. While these algorithms do have unfavorable time complexities, this effect could be mitigated when implemented in parallel. In this study, density based clustering technique for skin lesion border detection is parallelized and redesigned to run very efficiently on the heterogeneous platforms (e.g. tablets, SmartPhones, multi-core CPUs, GPUs, and fully-integrated Accelerated Processing Units) by transforming the technique into a series of independent concurrent operations. Heterogeneous computing is adopted to support accessibility, portability and multi-device use in the clinical settings. For this, we used WebCL, an emerging technology that enables a HTML5 Web browser to execute code in parallel for heterogeneous platforms. We depicted WebCL and our parallel algorithm design. In

  19. Density-based parallel skin lesion border detection with webCL.

    PubMed

    Lemon, James; Kockara, Sinan; Halic, Tansel; Mete, Mutlu

    2015-01-01

    Dermoscopy is a highly effective and noninvasive imaging technique used in diagnosis of melanoma and other pigmented skin lesions. Many aspects of the lesion under consideration are defined in relation to the lesion border. This makes border detection one of the most important steps in dermoscopic image analysis. In current practice, dermatologists often delineate borders through a hand drawn representation based upon visual inspection. Due to the subjective nature of this technique, intra- and inter-observer variations are common. Because of this, the automated assessment of lesion borders in dermoscopic images has become an important area of study. Fast density based skin lesion border detection method has been implemented in parallel with a new parallel technology called WebCL. WebCL utilizes client side computing capabilities to use available hardware resources such as multi cores and GPUs. Developed WebCL-parallel density based skin lesion border detection method runs efficiently from internet browsers. Previous research indicates that one of the highest accuracy rates can be achieved using density based clustering techniques for skin lesion border detection. While these algorithms do have unfavorable time complexities, this effect could be mitigated when implemented in parallel. In this study, density based clustering technique for skin lesion border detection is parallelized and redesigned to run very efficiently on the heterogeneous platforms (e.g. tablets, SmartPhones, multi-core CPUs, GPUs, and fully-integrated Accelerated Processing Units) by transforming the technique into a series of independent concurrent operations. Heterogeneous computing is adopted to support accessibility, portability and multi-device use in the clinical settings. For this, we used WebCL, an emerging technology that enables a HTML5 Web browser to execute code in parallel for heterogeneous platforms. We depicted WebCL and our parallel algorithm design. In addition, we tested

  20. [Women, gender, and the Constitution].

    PubMed

    1993-12-01

    Although all the constitutions of Latin America directly or indirectly acknowledge the juridical equality of the sexes, these patriarchal societies continue to maintain institutional power in male hands and to neutralize legal actions favoring women. International instruments such as the Convention on Elimination of All Forms of Discrimination Against Women, approved by the UN in 1979, have given a firmer basis to policies and actions to improve the status of women. Obstacles to full equality of Latin American women are rooted in economic and sociopolitical factors, but lack of true political will also plays a significant role. A number of new laws in the past several years as well as the new Constitution have improved the legal position of Colombian women. The new Constitution recognizes fundamental rights that may be claimed directly before a judge, and social, economic, and collective rights requiring legislative development. Article 43 of the new Constitution states that women will not be subjected to any form of discrimination. Another norm states that women will enjoy special assistance and protection before and after childbirth, in recognition of the social functions of maternity. Article 43 also states that women who are heads of households will receive special assistance, but the corresponding regulations have not yet been promulgated. The mechanism of tutelage has become an important recourse that has been used in several cases in which fundamental rights of women have been violated or threatened because of their sex. The order of tutelage has been used in cases of adolescents expelled from school for pregnancy and of abused wives, as well as to force recognition of the social and economic contributions of housework.

  1. Simulation of the interaction between an edge dislocation and a 1 0 0 interstitial dislocation loop in -iron

    SciTech Connect

    Terentyev, Dmitry; Grammatikopoulos, P.; Bacon, D; Osetsky, Yu N

    2008-01-01

    Atomic-level simulations are used to investigate the interaction of an edge dislocation with h100i interstitial dislocation loops in airon at 300 K. Dislocation reactions are studied systematically for different loop positions and Burgers vector orientations, and results are compared for two different interatomic potentials. Reactions are wide-ranging and complex, but can be described in terms of conventional dislocation reactions in which Burgers vector is conserved. The fraction of interstitials left behind after dislocation breakaway varies from 25 to 100%. The nature of the reactions requiring high applied stress for breakaway is identified. The obstacle strengths of h100i loops, 1/2h111i loops and voids containing the same number (169) of point defects are compared. h100i loops with Burgers vector parallel to the dislocation glide plane are slightly stronger than h100i and 1/2h111i loops with inclined Burgers vector: voids are about 30% weaker than the stronger loops. However, small voids are stronger than small 1/2h111i loops. The complexity of some reactions and the variety of obstacle strengths poses a challenge for the development of continuum models of dislocation behaviour in irradiated iron. 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

  2. Constitutive modeling for isotropic materials

    NASA Technical Reports Server (NTRS)

    Chan, K. S.; Lindholm, U. S.; Bodner, S. R.

    1988-01-01

    The third and fourth years of a 4-year research program, part of the NASA HOST Program, are described. The program goals were: (1) to develop and validate unified constitutive models for isotropic materials, and (2) to demonstrate their usefulness for structural analysis of hot section components of gas turbine engines. The unified models selected for development and evaluation were those of Bodner-Partom and of Walker. The unified approach for elastic-viscoplastic constitutive equations is a viable method for representing and predicting material response characteristics in the range where strain rate and temperature dependent inelastic deformations are experienced. This conclusion is reached by extensive comparison of model calculations against the experimental results of a test program of two high temperature Ni-base alloys, B1900+Hf and Mar-M247, over a wide temperature range for a variety of deformation and thermal histories including uniaxial, multiaxial, and thermomechanical loading paths. The applicability of the Bodner-Partom and the Walker models for structural applications has been demonstrated by implementing these models into the MARC finite element code and by performing a number of analyses including thermomechanical histories on components of hot sections of gas turbine engines and benchmark notch tensile specimens. The results of the 4-year program have been published in four annual reports. The results of the base program are summarized in this report. The tasks covered include: (1) development of material test procedures, (2) thermal history effects, and (3) verification of the constitutive model for an alternative material.

  3. The influence of the dislocation distribution heterogeneity degree on the formation of a non-misoriented dislocation cell substructures in f.c.c. metals

    NASA Astrophysics Data System (ADS)

    Cherepanov, D. N.; Selivanikova, O. V.; Matveev, M. V.

    2016-06-01

    Dislocation loops emitted by Frank-Reed source during crossing dislocations of the non-coplanar slip systems are accumulates jogs on the own dislocation line, resulting in the deceleration of the segments of dislocation loops with high jog density. As a result, bending around of the slowed segments the formation of dynamic dipoles in the shear zone occurs. In the present paper we consider formation mechanism of non-misoriented dislocation cell substructure during plastic deformation of f.c.c. metals and conclude that the increase in the degree heterogeneity of dislocation distribution leads to an increase in the jog density and reduce the mean value of arm dynamic dipoles.

  4. Image reconstruction of muon tomographic data using a density-based clustering method

    NASA Astrophysics Data System (ADS)

    Perry, Kimberly B.

    Muons are subatomic particles capable of reaching the Earth's surface before decaying. When these particles collide with an object that has a high atomic number (Z), their path of travel changes substantially. Tracking muon movement through shielded containers can indicate what types of materials lie inside. This thesis proposes using a density-based clustering algorithm called OPTICS to perform image reconstructions using muon tomographic data. The results show that this method is capable of detecting high-Z materials quickly, and can also produce detailed reconstructions with large amounts of data.

  5. On the implicit density based OpenFOAM solver for turbulent compressible flows

    NASA Astrophysics Data System (ADS)

    Fürst, Jiří

    The contribution deals with the development of coupled implicit density based solver for compressible flows in the framework of open source package OpenFOAM. However the standard distribution of OpenFOAM contains several ready-made segregated solvers for compressible flows, the performance of those solvers is rather week in the case of transonic flows. Therefore we extend the work of Shen [15] and we develop an implicit semi-coupled solver. The main flow field variables are updated using lower-upper symmetric Gauss-Seidel method (LU-SGS) whereas the turbulence model variables are updated using implicit Euler method.

  6. Evolution of dislocation density and character in hot rolled titanium determined by X-ray diffraction

    SciTech Connect

    Dragomir, I.C. . E-mail: iuliana.cernatescu@mse.gatech.edu; Li, D.S.; Castello-Branco, G.A.; Garmestani, H.; Snyder, R.L.; Ribarik, G.; Ungar, T.

    2005-07-15

    X-ray Peak Profile Analysis was employed to determine the evolution dislocation density and dislocations type in hot rolled commercially pure titanium specimens. It was found that dislocation type is dominating the deformation mechanism at all rolling reduction levels studied here. A good agreement was found between the texture evolution and changes in dislocation slip system activity during the deformation process.

  7. The effect of length scale on the determination of geometrically necessary dislocations via EBSD continuum dislocation microscopy.

    PubMed

    Ruggles, T J; Rampton, T M; Khosravani, A; Fullwood, D T

    2016-05-01

    Electron backscatter diffraction (EBSD) dislocation microscopy is an important, emerging field in metals characterization. Currently, calculation of geometrically necessary dislocation (GND) density is problematic because it has been shown to depend on the step size of the EBSD scan used to investigate the sample. This paper models the change in calculated GND density as a function of step size statistically. The model provides selection criteria for EBSD step size as well as an estimate of the total dislocation content. Evaluation of a heterogeneously deformed tantalum specimen is used to asses the method. Copyright © 2016 Elsevier B.V. All rights reserved.

  8. Bulk Dislocation Core Dissociation Probed by Coherent X Rays in Silicon

    SciTech Connect

    Jacques, V. L. R.; Pinsolle, E.; Ravy, S.; Sauvage-Simkin, M.; Le Bolloc'h, D.; Livet, F.

    2011-02-11

    We report on a new approach to probe bulk dislocations by using coherent x-ray diffraction. Coherent x rays are particularly suited for bulk dislocation studies because lattice phase shifts in condensed matter induce typical diffraction patterns which strongly depend on the fine structure of the dislocation cores. The strength of the method is demonstrated by performing coherent diffraction of a single dislocation loop in silicon. A dissociation of a bulk dislocation is measured and proves to be unusually large compared to surface dislocation dissociations. This work opens a route for the study of dislocation cores in the bulk in a static or dynamical regime, and under various external constraints.

  9. Posteromedial dislocation of the ankle without fracture or diastasis.

    PubMed

    Wang, L C; Love, M B

    1993-02-01

    This case report describes a patient with posteromedial dislocation of the ankle without fracture and without disruption of the tibiofibular syndesmosis. The pathogenesis of this uncommon lesion is discussed.

  10. Dislocation Structure and Mobility in hcp ^{4}He.

    PubMed

    Landinez Borda, Edgar Josué; Cai, Wei; de Koning, Maurice

    2016-07-22

    Using path-integral Monte Carlo simulations, we assess the core structure and mobility of the screw and edge basal-plane dislocations in hcp ^{4}He. Our findings provide key insights into recent interpretations of giant plasticity and mass flow junction experiments. First, both dislocations are dissociated into nonsuperfluid Shockley partial dislocations separated by ribbons of stacking fault, suggesting that they are unlikely to act as one-dimensional channels that may display Lüttinger-liquid-like behavior. Second, the centroid positions of the partial cores are found to fluctuate substantially, even in the absence of applied shear stresses. This implies that the lattice resistance to motion of the partial dislocations is negligible, consistent with the recent experimental observations of giant plasticity. Further results indicate that both the structure of the partial cores and the zero-point fluctuations play a role in this extreme mobility.

  11. Open dislocation of the carpal scaphoid: a case report.

    PubMed

    Antuna, S A; Antuna-Zapico, J M

    1997-01-01

    A case of an open volar scaphoid dislocation is presented. The patient was treated surgically, with open reduction of the scaphoid and pinning to the lunate. After 9 years, good clinical and radiographic results were obtained.

  12. Thermal Activation of Dislocations in Large Scale Obstacle Bypass

    SciTech Connect

    Martinez Saez, Enrique; Sobie, Cameron; Wen, Wei; Capolungo, Laurent; Patra, Anirban; McDowell, David L.; Tome, Carlos

    2016-08-18

    Irradiation-created defects diffuse and agglomerate presenting obstacles for the dislocation motion (both glide and climb). This effect leads to hardening and loss of toughness, which might drive the system to failure.

  13. Thermally-Active Screw Dislocations in Si Nanowires and Nanotubes

    NASA Astrophysics Data System (ADS)

    Dumitrica, Traian; Xiong, Shiyun; Ma, Jihong; Volz, Sebastian

    2014-03-01

    New properties appear when nanomaterials contain dislocations. Understanding whether these features, which arise naturally during growth, are beneficial or problematic becomes essential for developing applications. Here we investigate 110 Si nanowire and nanotube structures containing an axial screw dislocation, as described by objective molecular dynamics coupled with the classical Tersoff potential. By means of direct nonequilibrium molecular dynamics simulations, we uncover significant reductions in thermal conductivity when nanostructures contain axial screw dislocations with closed and open cores. Analysis based on the atomistic Green function method reveals that in nanowires, the effect originates largely in the phonon-phonon scattering due to the enhanced anharmonicity introduced by highly distorted core region of the dislocation. In nanotubes, the inner surface compensates effectively for the missing core region. The uncovered effect can act in combination with other already known thermal conductivity limiting mechanisms, and thus can enable the further optimization of the figure of merit for a new family of complex thermoelectric nanomaterials.

  14. Plastic anisotropy and dislocation trajectory in BCC metals

    NASA Astrophysics Data System (ADS)

    Dezerald, Lucile; Rodney, David; Clouet, Emmanuel; Ventelon, Lisa; Willaime, François

    2016-05-01

    Plasticity in body-centred cubic (BCC) metals at low temperatures is atypical, marked in particular by an anisotropic elastic limit in clear violation of the famous Schmid law applicable to most other metals. This effect is known to originate from the behaviour of the screw dislocations; however, the underlying physics has so far remained insufficiently understood to predict plastic anisotropy without adjustable parameters. Here we show that deviations from the Schmid law can be quantified from the deviations of the screw dislocation trajectory away from a straight path between equilibrium configurations, a consequence of the asymmetrical and metal-dependent potential energy landscape of the dislocation. We propose a modified parameter-free Schmid law, based on a projection of the applied stress on the curved trajectory, which compares well with experimental variations and first-principles calculations of the dislocation Peierls stress as a function of crystal orientation.

  15. Open Anterior Dislocation of the Hip in Togo

    PubMed Central

    Anani, Abalo; Yannick, Dellanh; Gamal, Ayouba; Assang, Dossim

    2016-01-01

    Anterior traumatic dislocations of the hip are much less common than posterior dislocations. To date, 14 cases of open anterior dislocation of the hip associated with such injuries, acetabular and femoral head fractures and femoral vascular and nerve damage have been reported. We present a case of a 23-year-old male who sustained open anterior dislocation of the hip with ipsilateral fracture of the greater trochanter after an accident on the public highway. Additional lesions included an iliac wing fracture and a perineal wound. We report this case because of the rarity and seriousness of this injury due to its progressive complications and difficulties related to its management, which are typical to a developing country like ours. PMID:27247749

  16. Dislocation-induced superfluidity in a model supersolid

    NASA Astrophysics Data System (ADS)

    Dasbiswas, Kinjal; Goswami, Debajit; Yoo, Chi-Deuk; Dorsey, Alan

    2010-03-01

    The effect of an edge dislocation in inducing superfluidity is explored by coupling the elastic strain field of the dislocation to the superfluid density, and solving the corresponding Ginzburg-Landau theory. It is shown that superfluid density is induced along a single dislocation below a critical temperature determined by the ground state solution of a 2D Schr"odinger equation with a dipolar potential. This superfluid behavior can be described by a 1D Ginzburg-Landau equation obtained through a weakly nonlinear analysis. We then extend our analysis to a network of dislocation lines considered before by Shevchenko and Toner, which could serve as a model for superflow through solid ^4He. The effect of fluctuations and dynamics are included through a full time dependent Ginzburg-Landau theory.

  17. Ligamentous and capsular restraints to experimental posterior elbow joint dislocation.

    PubMed

    Deutch, Søren R; Olsen, Bo S; Jensen, Steen L; Tyrdal, Stein; Sneppen, Otto

    2003-10-01

    Pathological external forearm rotation (PEFR) relates to posterolateral elbow joint instability, and is considered a possible requisite step in a simple posterior elbow joint dislocation. The aim of this study was to evaluate the capsuloligamentous restraint to PEFR. In all, 18 elbow joint specimens were examined in a joint analysis system developed for experimental elbow dislocation. Sequential cutting of capsule and ligaments followed by stability testing provided specific data relating to each capsuloligamentous structure. The primary stabilizers against PEFR in the extended elbow were the anterior capsule and the lateral collateral ligament complex (LCLC), whereas in the flexed elbow the anterior capsule did not have a stabilizing effect. In flexed joint positions, the LCLC seems to be the only immediate stabilizer against PEFR, and thereby against posterolateral instability and possibly against posterior dislocation. The medial collateral ligament did not have any immediate stabilizing effect, but it prevented the final step of the posterior dislocation.

  18. Plastic anisotropy and dislocation trajectory in BCC metals.

    PubMed

    Dezerald, Lucile; Rodney, David; Clouet, Emmanuel; Ventelon, Lisa; Willaime, François

    2016-05-25

    Plasticity in body-centred cubic (BCC) metals at low temperatures is atypical, marked in particular by an anisotropic elastic limit in clear violation of the famous Schmid law applicable to most other metals. This effect is known to originate from the behaviour of the screw dislocations; however, the underlying physics has so far remained insufficiently understood to predict plastic anisotropy without adjustable parameters. Here we show that deviations from the Schmid law can be quantified from the deviations of the screw dislocation trajectory away from a straight path between equilibrium configurations, a consequence of the asymmetrical and metal-dependent potential energy landscape of the dislocation. We propose a modified parameter-free Schmid law, based on a projection of the applied stress on the curved trajectory, which compares well with experimental variations and first-principles calculations of the dislocation Peierls stress as a function of crystal orientation.

  19. Anterior shoulder dislocation as a complication of surgery for burns.

    PubMed

    Hinton, A E; King, D

    1989-08-01

    An example of anterior dislocation of the shoulder resulting from the positioning of a patient for skin grafting of burns is presented. Complications of positioning patients prone and with their arms abducted and practical measures for their avoidance are discussed.

  20. Dislocation Structure and Mobility in hcp 4He

    NASA Astrophysics Data System (ADS)

    Landinez Borda, Edgar Josué; Cai, Wei; de Koning, Maurice

    2016-07-01

    Using path-integral Monte Carlo simulations, we assess the core structure and mobility of the screw and edge basal-plane dislocations in hcp 4He. Our findings provide key insights into recent interpretations of giant plasticity and mass flow junction experiments. First, both dislocations are dissociated into nonsuperfluid Shockley partial dislocations separated by ribbons of stacking fault, suggesting that they are unlikely to act as one-dimensional channels that may display Lüttinger-liquid-like behavior. Second, the centroid positions of the partial cores are found to fluctuate substantially, even in the absence of applied shear stresses. This implies that the lattice resistance to motion of the partial dislocations is negligible, consistent with the recent experimental observations of giant plasticity. Further results indicate that both the structure of the partial cores and the zero-point fluctuations play a role in this extreme mobility.