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Sample records for plastic strain recovery

  1. Comparative analysis of inelastic strain recovery and plastic deformation in a Ti49.1Ni50.9 (at %) alloy under torsion and bending

    NASA Astrophysics Data System (ADS)

    Grishkov, V. N.; Lotkov, A. I.; Baturin, A. A.; Timkin, V. N.; Zhapova, D. Yu.

    2015-10-01

    The paper reports on an experimental study of inelastic strain recovery, due to superelasticity and shape-memory effects, and plastic deformation under torsion and bending in a binary TiNi alloy containing 50.9 at % of Ni. It is found that the material under torsion and bending displays an anomalously high superelasticity of 16.4% and 13.5% and total recovery strain of 24.6% and 16.4% which exceed the theoretical limit of recoverable strain equal to 10.3% in the alloy involved in a cubic B2 to monoclinic B19' phase transformation. The correlation between the high recovery strains and the intensity and mechanisms of plastic deformation with increasing total strain is discussed.

  2. Computational strain gradient crystal plasticity

    NASA Astrophysics Data System (ADS)

    Niordson, Christian F.; Kysar, Jeffrey W.

    2014-01-01

    A numerical method for viscous strain gradient crystal plasticity theory is presented, which incorporates both energetic and dissipative gradient effects. The underlying minimum principles are discussed as well as convergence properties of the proposed finite element procedure. Three problems of plane crystal plasticity are studied: pure shear of a single crystal between rigid platens as well as plastic deformation around cylindrical voids in hexagonal close packed and face centered cubic crystals. Effective in-plane constitutive slip parameters for plane strain deformation of specifically oriented face centered cubic crystals are developed in terms of the crystallographic slip parameters. The effect on geometrically necessary dislocation structures introduced by plastic deformation is investigated as a function of the ratio of void radius to plasticity length scale.

  3. Anelastic Strain Recovery Analysis Code

    Energy Science and Technology Software Center (ESTSC)

    1995-04-05

    ASR4 is a nonlinear least-squares regression of Anelastic Strain Recovery (ASR) data for the purpose of determining in situ stress orientations and magnitudes. ASR4 fits the viscoelastic model of Warpinski and Teufel to measure ASR data, calculates the stress orientations directly, and stress magnitudes if sufficient input data are available. The code also calculates the stress orientation using strain-rosette equations, and it calculates stress magnitudes using Blanton''s approach, assuming sufficient input data are available.

  4. RESOURCE RECOVERY FROM PLASTIC AND GLASS WASTES

    EPA Science Inventory

    This research program was initiated with the overall objective of assessing and evaluating State-of-the-Art for recovery of glass and plastic from solid waste. Literature was gathered from numerous sources, contacts were made with industrial and recycling organizations, and quest...

  5. Plastic deformation, wrinkling, and recovery in microgel multilayers†

    PubMed Central

    Gaulding, Jeffrey C.; Spears, Mark W.

    2013-01-01

    Microgel multi-layer films assembled from anionic particles and linear polycation were prepared on elastomeric substrates and their self-healing properties studied. Dried films were imaged in situ during mechanical deformation and were determined to undergo plastic deformation in response to linear strain, leading to film buckling upon strain relaxation. Hydration leads to rapid reorganization of the film building blocks, permitting recovery of the film to the undamaged state. Additionally, films were determined to heal in the presence of high relative humidity environments, suggesting that film swelling and hydration is a major factor in the restoration of film integrity, and that full immersion in solvent is not required for healing. Films prepared from microgels with lower levels of acid content and/or polycation length, factors strongly connected to the charge density and presumably the connectivity of the film, also display self-healing characteristics. PMID:24443657

  6. Benchmark cyclic plastic notch strain measurements

    NASA Technical Reports Server (NTRS)

    Sharpe, W. N., Jr.; Ward, M.

    1983-01-01

    Plastic strains at the roots of notched specimens of Inconel 718 subjected to tension-compression cycling at 650 C are reported. These strains were measured with a laser-based technique over a gage length of 0.1 mm and are intended to serve as 'benchmark' data for further development of experimental, analytical, and computational approaches. The specimens were 250 mm by 2.5 mm in the test section with double notches of 4.9 mm radius subjected to axial loading sufficient to cause yielding at the notch root on the tensile portion of the first cycle. The tests were run for 1000 cycles at 10 cpm or until cracks initiated at the notch root. The experimental techniques are described, and then representative data for the various load spectra are presented. All the data for each cycle of every test are available on floppy disks from NASA.

  7. Plasticity and functional recovery in neurology.

    PubMed

    Ramachandran, V S

    2005-01-01

    Experiments on patients with phantom limbs suggest that neural connections in the adult human brain are much more malleable than previously assumed. Three weeks after amputation of an arm, sensations from the ipsilateral face are referred to the phantom; this effect is caused by the sensory input from the face skin 'invading' and activating deafferented hand zones in the cortex and thalamus. Many phantom arms are 'paralysed' in a painful position. If a mirror is propped vertically in the sagittal plane and the patient looks at the reflection of his/her normal hand, this reflection appears superimposed on the 'felt' position of the phantom. Remarkably, if the real arm is moved, the phantom is felt to move as well and this sometimes relieves the painful cramps in the phantom. Mirror visual feedback (MVF) has shown promising results with chronic regional pain syndrome and hemiparesis following stroke. These results suggest two reasons for a paradigm shift in neurorehabilitation. First, there appears to be tremendous latent plasticity even in the adult brain. Second, the brain should be thought of, not as a hierarchy of organised autonomous modules, each of which delivers its output to the next level, but as a set of complex interacting networks that are in a state of dynamic equilibrium with the brain's environment. Both principles can be potentially exploited in a clinical context to facilitate recovery of function. PMID:16138492

  8. Strain gradient effects on cyclic plasticity

    NASA Astrophysics Data System (ADS)

    Niordson, Christian F.; Legarth, Brian Nyvang

    2010-04-01

    Size effects on the cyclic shear response are studied numerically using a recent higher order strain gradient visco-plasticity theory accounting for both dissipative and energetic gradient hardening. Numerical investigations of the response under cyclic pure shear and shear of a finite slab between rigid platens have been carried out, using the finite element method. It is shown for elastic-perfectly plastic solids how dissipative gradient effects lead to increased yield strength, whereas energetic gradient contributions lead to increased hardening as well as a Bauschinger effect. For linearly hardening materials it is quantified how dissipative and energetic gradient effects promote hardening above that of conventional predictions. Usually, increased hardening is attributed to energetic gradient effects, but here it is found that also dissipative gradient effects lead to additional hardening in the presence of conventional material hardening. Furthermore, it is shown that dissipative gradient effects can lead to both an increase and a decrease in the dissipation per load cycle depending on the magnitude of the dissipative length parameter, whereas energetic gradient effects lead to decreasing dissipation for increasing energetic length parameter. For dissipative gradient effects it is found that dissipation has a maximum value for some none zero value of the material length parameter, which depends on the magnitude of the deformation cycles.

  9. The strain path dependence of plastic deformation response of AA5754: Experiment and modeling

    SciTech Connect

    Pham, Minh-Son; Hu, Lin; Iadicola, Mark; Creuziger, Adam; Rollett, Anthony D.

    2013-12-16

    This work presents modeling of experiments on a balanced biaxial (BB) pre-strained AA5754 alloy, subsequently reloaded uniaxially along the rolling direction and transverse direction. The material exhibits a complex plastic deformation response during the change in strain path due to 1) crystallographic texture, 2) aging (interactions between dislocations and Mg atoms) and 3) recovery (annihilation and re-arrangement of dislocations). With a BB prestrain of about 5 %, the aging process is dominant, and the yield strength for uniaxially deformed samples is observed to be higher than the flow stress during BB straining. The strain hardening rate after changing path is, however, lower than that for pre-straining. Higher degrees of pre-straining make the dynamic recovery more active. The dynamic recovery at higher strain levels compensates for the aging effect, and results in: 1) a reduction of the yield strength, and 2) an increase in the hardening rate of re-strained specimens along other directions. The yield strength of deformed samples is further reduced if these samples are left at room temperature to let static recovery occur. The synergistic influences of texture condition, aging and recovery processes on the material response make the modeling of strain path dependence of mechanical behavior of AA5754 challenging. In this study, the influence of crystallographic texture is taken into account by incorporating the latent hardening into a visco-plastic self-consistent model. Different strengths of dislocation glide interaction models in 24 slip systems are used to represent the latent hardening. Moreover, the aging and recovery effects are also included into the latent hardening model by considering strong interactions between dislocations and dissolved atom Mg and the microstructural evolution. These microstructural considerations provide a powerful capability to successfully describe the strain path dependence of plastic deformation behavior of AA5754.

  10. Plasticity and thermal recovery of thin copper wires in torsion

    NASA Astrophysics Data System (ADS)

    Dong, Dong; Dunstan, David J.; Bushby, Andrew J.

    2015-06-01

    Experiments in small-scale plasticity usually focus on small-sized samples. However, studying thin wires with lengths up to metres in torsion has the advantage of giving extremely high strain resolution and reversal of the loading direction. In this way, we explore the early stage of plasticity. Microstrain plastic deformation, dislocation creep and the Bauschinger effects are easily observed. The onset of irreversible deformation was observed and associated with a few dislocations in the largest grains throughout the wire. Easy plastic deformation on reversal of the loading direction was observed following this initial plastic deformation but not before.

  11. Measurement of large strains in ropes using plastic optical fibers

    DOEpatents

    Williams, Jerry Gene; Smith, David Barton; Muhs, Jeffrey David

    2006-02-14

    A method for the direct measurement of large strains in ropes in situ using a plastic optical fiber, for example, perfluorocarbon or polymethyl methacrylate and Optical Time-Domain Reflectometer or other light time-of-flight measurement instrumentation. Protective sheaths and guides are incorporated to protect the plastic optical fiber. In one embodiment, a small rope is braided around the plastic optical fiber to impose lateral compressive forces to restrain the plastic optical fiber from slipping and thus experience the same strain as the rope. Methods are described for making reflective interfaces along the length of the plastic optical fiber and to provide the capability to measure strain within discrete segments of the rope. Interpretation of the data allows one to calculate the accumulated strain at any point in time and to determine if the rope has experienced local damage.

  12. Gradient-type modeling of the effects of plastic recovery and surface passivation in thin films

    NASA Astrophysics Data System (ADS)

    Liu, Jinxing; Kah Soh, Ai

    2016-08-01

    The elasto-plastic responses of thin films subjected to cyclic tension-compression loading and bending are studied, with a focus on Bauschinger and size effects. For this purpose, a model is established by incorporating plastic recovery into the strain gradient plasticity theory we proposed recently. Elastic and plastic parts of strain and strain gradient, which are determined by the elasto-plastic decomposition according to the associative rule, are assumed to have a degree of material-dependent reversibility. Based on the above assumption, a dislocation reversibility-dependent rule is built to describe evolutions of different deformation components under cyclic loadings. Furthermore, a simple strategy is provided to implement the passivated boundary effects by introducing a gradual change to relevant material parameters in the yield function. Based on this theory, both bulge and bending tests under cyclic loading conditions are investigated. By comparing the present predictions with the existing experimental data, it is found that the yield function is able to exhibit the size effect, the Bauschinger effect, the influence of surface passivation and the hysteresis-loop phenomenon. Thus, the proposed model is deemed helpful in studying plastic deformations of micron-scale films.

  13. High strain-rate plastic flow in Fe and Al

    NASA Astrophysics Data System (ADS)

    Smith, Raymond; Eggert, Jon; Rudd, Robert; Bolme, Cynthia; Collins, Gilbert

    2011-06-01

    Understanding the nature and time-dependence of material deformation at high strain rates is an important goal in condensed matter physics. Under dynamic loading, the rate of plastic strain is determined by the flow of dislocations through the crystal lattice and is a complex function of time, distance, sample purity, temperature, internal stresses, microstructure and strain rate. Under shock compression time-dependent plasticity is typically inferred by fitting elastic precursor stresses as a function of propagation distance with a phenomenologically based dislocation kinetics model. We employ a laser-driven ramp wave loading technique to compress 6-70 micron thick samples of bcc-Fe and fcc-Al over a strain rate range of 1e6-1e8 1/s. Our data show that for fixed sample thickness, stresses associated the onset of plasticity are highly dependent on the strain rate of compression and do not readily fit into the elastic stress - distance evolution descriptive of instantaneous shock loading. We find that the elastic stress at the onset of plasticity is well correlated with the strain rate at the onset of plastic flow for both shock- and ramp-wave experiments. Our data, combined with data from other dynamic compression platforms, reveal a sharp increase in the peak elastic stress at high strain rates, consistent with a transition in dislocation flow dominated by phonon drag. smith248@llnl.gov

  14. Maladaptive Plasticity for Motor Recovery after Stroke: Mechanisms and Approaches

    PubMed Central

    Takeuchi, Naoyuki; Izumi, Shin-Ichi

    2012-01-01

    Many studies in human and animal models have shown that neural plasticity compensates for the loss of motor function after stroke. However, neural plasticity concerning compensatory movement, activated ipsilateral motor projections and competitive interaction after stroke contributes to maladaptive plasticity, which negatively affects motor recovery. Compensatory movement on the less-affected side helps to perform self-sustaining activity but also creates an inappropriate movement pattern and ultimately limits the normal motor pattern. The activated ipsilateral motor projections after stroke are unable to sufficiently support the disruption of the corticospinal motor projections and induce the abnormal movement linked to poor motor ability. The competitive interaction between both hemispheres induces abnormal interhemispheric inhibition that weakens motor function in stroke patients. Moreover, widespread disinhibition increases the risk of competitive interaction between the hand and the proximal arm, which results in an incomplete motor recovery. To minimize this maladaptive plasticity, rehabilitation programs should be selected according to the motor impairment of stroke patients. Noninvasive brain stimulation might also be useful for correcting maladaptive plasticity after stroke. Here, we review the underlying mechanisms of maladaptive plasticity after stroke and propose rehabilitation approaches for appropriate cortical reorganization. PMID:22792492

  15. High strain rate loading of polymeric foams and solid plastics

    NASA Astrophysics Data System (ADS)

    Dick, Richard D.; Chang, Peter C.; Fourney, William L.

    2000-04-01

    The split-Hopkinson pressure bar (SHPB) provided a technique to determine the high strain rate response for low density foams and solid ABS and polypropylene plastics. These materials are used in the interior safety panels of automobiles and crash test dummies. Because the foams have a very low impedance, polycarbonate bars were used to acquire the strain rate data in the 100 to 1600 l/s range. An aluminum SPHB setup was used to obtain the solid plastics data which covered strain rates of 1000 to 4000 l/s. The curves for peak strain rate versus peak stress for the foams over the test range studied indicates only a slight strain rate dependence. Peak strain rate versus peak stress curves for polypropylene shows a strain rate dependence up to about 1500 l/s. At that rate the solid poly propylene indicates no strain rate dependence. The ABS plastics are strain rate dependent up to 3500 l/s and then are independent at larger strain rates.

  16. Computational neurorehabilitation: modeling plasticity and learning to predict recovery.

    PubMed

    Reinkensmeyer, David J; Burdet, Etienne; Casadio, Maura; Krakauer, John W; Kwakkel, Gert; Lang, Catherine E; Swinnen, Stephan P; Ward, Nick S; Schweighofer, Nicolas

    2016-01-01

    Despite progress in using computational approaches to inform medicine and neuroscience in the last 30 years, there have been few attempts to model the mechanisms underlying sensorimotor rehabilitation. We argue that a fundamental understanding of neurologic recovery, and as a result accurate predictions at the individual level, will be facilitated by developing computational models of the salient neural processes, including plasticity and learning systems of the brain, and integrating them into a context specific to rehabilitation. Here, we therefore discuss Computational Neurorehabilitation, a newly emerging field aimed at modeling plasticity and motor learning to understand and improve movement recovery of individuals with neurologic impairment. We first explain how the emergence of robotics and wearable sensors for rehabilitation is providing data that make development and testing of such models increasingly feasible. We then review key aspects of plasticity and motor learning that such models will incorporate. We proceed by discussing how computational neurorehabilitation models relate to the current benchmark in rehabilitation modeling - regression-based, prognostic modeling. We then critically discuss the first computational neurorehabilitation models, which have primarily focused on modeling rehabilitation of the upper extremity after stroke, and show how even simple models have produced novel ideas for future investigation. Finally, we conclude with key directions for future research, anticipating that soon we will see the emergence of mechanistic models of motor recovery that are informed by clinical imaging results and driven by the actual movement content of rehabilitation therapy as well as wearable sensor-based records of daily activity. PMID:27130577

  17. Attaching strain gages by ultrasonic plastic welding

    NASA Technical Reports Server (NTRS)

    Sheppard, A. T.; Silbert, L.

    1977-01-01

    Technique employs application of pressure and ultrasound to effect welding of encapsulated strain gates to metallic surfaces. Process requires no heat or adhesives. Technique might also be used to simplify curing of epoxy adhesives and for attachment problems like bonding cryogenic temperature sensors to structural parts.

  18. Strain gradient plasticity theory applied to machining

    SciTech Connect

    Royer, Raphael; Laheurte, Raynald; Darnis, Philippe; Gerard, Alain; Cahuc, Olivier

    2011-05-04

    Machining is the most common manufacturing process. A good behaviour law is necessary in the simulation of machining processes (analytical and finite element modeling). Usually, commonly used behaviour laws such as Jonhson-Cook can bring unsatisfactory results especially for high strain and large deformation processes. Significant differences can appear between experimental and simulation results. The aim of this paper is to present the choices made regarding the behaviour law in this context. This study develops a large deformation strain-gradient theoretical framework with hypothesis linked to metal cutting processes. The theoretical framework has the potential of expressing moments at the tool tip as they were observed in experiments. It will be shown that the theory has the capability of interpreting the complex phenomena found in machining and more particularly in high speed machining.

  19. Strain gradient plasticity theory applied to machining

    NASA Astrophysics Data System (ADS)

    Royer, Raphaël; Laheurte, Raynald; Darnis, Philippe; Gérard, Alain; Cahuc, Olivier

    2011-05-01

    Machining is the most common manufacturing process. A good behaviour law is necessary in the simulation of machining processes (analytical and finite element modeling). Usually, commonly used behaviour laws such as Jonhson-Cook can bring unsatisfactory results especially for high strain and large deformation processes. Significant differences can appear between experimental and simulation results. The aim of this paper is to present the choices made regarding the behaviour law in this context. This study develops a large deformation strain-gradient theoretical framework with hypothesis linked to metal cutting processes. The theoretical framework has the potential of expressing moments at the tool tip as they were observed in experiments. It will be shown that the theory has the capability of interpreting the complex phenomena found in machining and more particularly in high speed machining.

  20. Constitutive modeling and computational implementation for finite strain plasticity

    NASA Technical Reports Server (NTRS)

    Reed, K. W.; Atluri, S. N.

    1985-01-01

    This paper describes a simple alternate approach to the difficult problem of modeling material behavior. Starting from a general representation for a rate-tpe constitutive equation, it is shown by example how sets of test data may be used to derive restrictions on the scalar functions appearing in the representation. It is not possible to determine these functions from experimental data, but the aforementioned restrictions serve as a guide in their eventual definition. The implications are examined for hypo-elastic, isotropically hardening plastic, and kinematically hardening plastic materials. A simple model for the evolution of the 'back-stress,' in a kinematic-hardening plasticity theory, that is entirely analogous to a hypoelastic stress-strain relation is postulated and examined in detail in modeling finitely plastic tension-torsion test. The implementation of rate-type material models in finite element algorithms is also discussed.

  1. Plasticity in bulk metallic glasses investigated via the strain distribution

    SciTech Connect

    Das, Jayanta; Mattern, Norbert; Eckert, Juergen; Bostroem, Magnus; Kvick, Aake; Yavari, Alain Reza; Greer, Alan Lindsay

    2007-09-01

    We measured the atomic-scale elastic strain in order to investigate the yielding of Zr{sub 55}Cu{sub 20}Ni{sub 10}Al{sub 10}Ti{sub 5} and Cu{sub 47.5}Zr{sub 47.5}Al{sub 5} bulk metallic glasses (BMGs) by x-ray synchrotron radiation at room temperature. High resolution strain scanning reveals a deviation from the linear stress-strain relationship at the onset of macroplastic flow. Similar to polycrystalline metals, a saturation of the elastic strain components has been revealed in the case of the ''plastic'' Cu{sub 47.5}Zr{sub 47.5}Al{sub 5} BMG. The results show that the atomic-level elastic strains of the plastic Cu{sub 47.5}Zr{sub 47.5}Al{sub 5} BMG are more homogeneous compared to the 'brittle' Zr{sub 55}Cu{sub 20}Ni{sub 10}Al{sub 10}Ti{sub 5} glass.

  2. Mechanical strength model for plastic bonded granular materials at high strain rates and large strains

    SciTech Connect

    Browning, R.V.; Scammon, R.J.

    1998-07-01

    Modeling impact events on systems containing plastic bonded explosive materials requires accurate models for stress evolution at high strain rates out to large strains. For example, in the Steven test geometry reactions occur after strains of 0.5 or more are reached for PBX-9501. The morphology of this class of materials and properties of the constituents are briefly described. We then review the viscoelastic behavior observed at small strains for this class of material, and evaluate large strain models used for granular materials such as cap models. Dilatation under shearing deformations of the PBX is experimentally observed and is one of the key features modeled in cap style plasticity theories, together with bulk plastic flow at high pressures. We propose a model that combines viscoelastic behavior at small strains but adds intergranular stresses at larger strains. A procedure using numerical simulations and comparisons with results from flyer plate tests and low rate uniaxial stress tests is used to develop a rough set of constants for PBX-9501. Comparisons with the high rate flyer plate tests demonstrate that the observed characteristic behavior is captured by this viscoelastic based model. {copyright} {ital 1998 American Institute of Physics.}

  3. Mechanical strength model for plastic bonded granular materials at high strain rates and large strains

    SciTech Connect

    Browning, R.V.; Scammon, R.J.

    1997-07-01

    Modeling impact events on systems containing plastic bonded explosive materials requires accurate models for stress evolution at high strain rates out to large strains. For example, in the Steven test geometry reactions occur after strains of 0.5 or more are reached for PBX-950l. The morphology of this class of materials and properties of the constituents are briefly described. We then review the viscoelastic behavior observed at small strains for this class of material, and evaluate large strain models used for granular materials such as cap models. Dilatation under shearing deformations of the PBX is experimentally observed and is one of the key features modeled in cap style plasticity theories, together with bulk plastic flow at high pressures. We propose a model that combines viscoelastic behavior at small strains but adds intergranular stresses at larger strains. A procedure using numerical simulations and comparisons with results from flyer plate tests and low rate uniaxial stress tests is used to develop a rough set of constants for PBX-9501. Comparisons with the high rate flyer plate tests demonstrate the viscoelastic based model show that the observed characteristic behavior is captured by this model.

  4. A polycrystal plasticity model of strain localization in irradiated iron

    NASA Astrophysics Data System (ADS)

    Barton, Nathan R.; Arsenlis, Athanasios; Marian, Jaime

    2013-02-01

    At low to intermediate homologous temperatures, the degradation of structural materials performance in nuclear environments is associated with high number densities of nanometric defects produced in irradiation cascades. In polycrystalline ferritic materials, self-interstitial dislocations loops are a principal signature of irradiation damage, leading to a mechanical response characterized by increased yield strengths, decreased total strain to failure, and decreased work hardening as compared to the unirradiated behavior. Above a critical defect concentration, the material deforms by plastic flow localization, giving rise to strain softening in terms of the engineering stress-strain response. Flow localization manifests itself in the form of defect-depleted crystallographic channels, through which all dislocation activity is concentrated. In this paper, we describe the formulation of a crystal plasticity model for pure Fe embedded in a finite element polycrystal simulator and present results of uniaxial tensile deformation tests up to 10% strain. We use a tensorial damage descriptor variable to capture the evolution of the irradiation damage loop subpopulation during deformation. The model is parameterized with detailed dislocation dynamics simulations of tensile tests up to 1.5% deformation of systems containing various initial densities of irradiation defects. The coarse-grained simulations are shown to capture the essential details of the experimental stress response observed in ferritic alloys and steels. Our methodology provides an effective linkage between the defect scale, of the order of one nanometer, and the continuum scale involving multiple grain orientations.

  5. Finite strain discrete dislocation plasticity in a total Lagrangian setting

    NASA Astrophysics Data System (ADS)

    Irani, N.; Remmers, J. J. C.; Deshpande, V. S.

    2015-10-01

    We present two total Lagrangian formulations for finite strain discrete dislocation plasticity wherein the discrete dislocations are presumed to be adequately represented by singular linear elastic fields thereby extending the superposition method of Van der Giessen and Needleman (1995) to finite strains. The finite deformation effects accounted for are (i) finite lattice rotations and (ii) shape changes due to slip. The two formulations presented differ in the fact that in the "smeared-slip" formulation the discontinuous displacement field is smeared using finite element shape functions while in the "discrete-slip" formulation the weak form of the equilibrium statement is written to account for the slip displacement discontinuity. Both these total Lagrangian formulations use a hyper-elastic constitutive model for lattice elasticity. This overcomes the issues of using singular dislocation fields in a hypo-elastic constitutive relation as encountered in the updated Lagrangian formulation of Deshpande et al. (2003). Predictions of these formulations are presented for the relatively simple problems of tension and compression of single crystals oriented for single slip. These results show that unlike in small-strain discrete dislocation plasticity, finite strain effects result in a size dependent tension/compression asymmetry. Moreover, both formulations give nearly identical predictions and thus we expect that the "smeared-slip" formulation is likely to be preferred due to its relative computational efficiency and simplicity.

  6. Linking strain anisotropy and plasticity in copper metallization

    SciTech Connect

    Murray, Conal E. Jordan-Sweet, Jean; Priyadarshini, Deepika; Nguyen, Son

    2015-05-04

    The elastic anisotropy of copper leads to significant variation in the x-ray elastic constants (XEC), which link diffraction-based strain measurements to stress. An accurate depiction of the mechanical response in copper thin films requires a determination of an appropriate grain interaction model that lies between Voigt and Reuss limits. It is shown that the associated XEC weighting fraction, x*, between these limits provides a metric by which strain anisotropy can be quantified. Experimental values of x*, as determined by a linear regression scheme of diffraction data collected from multiple reflections, reveal the degree of strain anisotropy and its dependence on plastic deformation induced during in-situ and ex-situ thermal treatments.

  7. Plastic strain arrangement in copper single crystals in sliding

    SciTech Connect

    Chumaevskii, Andrey V. Lychagin, Dmitry V.; Tarasov, Sergei Yu.

    2014-11-14

    Deformation of tribologically loaded contact zone is one of the wear mechanisms in spite of the fact that no mass loss may occur during this process. Generation of optimal crystallographic orientations of the grains in a polycrystalline materials (texturing) may cause hardening and reducing the deformation wear. To reveal the orientation dependence of an individual gain and simplify the task we use copper single crystals with the orientations of the compression axis along [111] and [110]. The plastic deformation was investigated by means of optical, scanning electron microscopy and EBSD techniques. It was established that at least four different zones were generated in the course of sliding test, such as non-deformed base metal, plastic deformation layer sliding, crystalline lattice reorientation layer and subsurface grain structure layer. The maximum plastic strain penetration depth was observed on [110]-single crystals. The minimum stability of [111]-crystals with respect to rotation deformation mode as well as activation of shear in the sliding contact plane provide for rotation deformation localization below the worn surface. The high-rate accumulation of misorientations and less strain penetration depth was observed on [111]-crystals as compared to those of [110]-oriented ones.

  8. Evolution of plastic anisotropy for high-strain-rate computations

    SciTech Connect

    Schiferl, S.K.; Maudlin, P.J.

    1994-12-01

    A model for anisotropic material strength, and for changes in the anisotropy due to plastic strain, is described. This model has been developed for use in high-rate, explicit, Lagrangian multidimensional continuum-mechanics codes. The model handles anisotropies in single-phase materials, in particular the anisotropies due to crystallographic texture--preferred orientations of the single-crystal grains. Textural anisotropies, and the changes in these anisotropies, depend overwhelmingly no the crystal structure of the material and on the deformation history. The changes, particularly for a complex deformations, are not amenable to simple analytical forms. To handle this problem, the material model described here includes a texture code, or micromechanical calculation, coupled to a continuum code. The texture code updates grain orientations as a function of tensor plastic strain, and calculates the yield strength in different directions. A yield function is fitted to these yield points. For each computational cell in the continuum simulation, the texture code tracks a particular set of grain orientations. The orientations will change due to the tensor strain history, and the yield function will change accordingly. Hence, the continuum code supplies a tensor strain to the texture code, and the texture code supplies an updated yield function to the continuum code. Since significant texture changes require relatively large strains--typically, a few percent or more--the texture code is not called very often, and the increase in computer time is not excessive. The model was implemented, using a finite-element continuum code and a texture code specialized for hexagonal-close-packed crystal structures. The results for several uniaxial stress problems and an explosive-forming problem are shown.

  9. Plasticity and Recovery After Dorsal Column Spinal Cord Injury in Nonhuman Primates.

    PubMed

    Reed, Jamie L; Liao, Chia-Chi; Qi, Hui-Xin; Kaas, Jon H

    2016-01-01

    Here, we review recent work on plasticity and recovery after dorsal column spinal cord injury in nonhuman primates. Plasticity in the adult central nervous system has been established and studied for the past several decades; however, capacities and limits of plasticity are still under investigation. Studies of plasticity include assessing multiple measures before and after injury in animal models. Such studies are particularly important for improving recovery after injury in patients. In summarizing work by our research team and others, we suggest how the findings from plasticity studies in nonhuman primate models may affect therapeutic interventions for conditions involving sensory loss due to spinal cord injury. PMID:27578996

  10. Plasticity and Recovery After Dorsal Column Spinal Cord Injury in Nonhuman Primates

    PubMed Central

    Reed, Jamie L.; Liao, Chia-Chi; Qi, Hui-Xin; Kaas, Jon H.

    2016-01-01

    Here, we review recent work on plasticity and recovery after dorsal column spinal cord injury in nonhuman primates. Plasticity in the adult central nervous system has been established and studied for the past several decades; however, capacities and limits of plasticity are still under investigation. Studies of plasticity include assessing multiple measures before and after injury in animal models. Such studies are particularly important for improving recovery after injury in patients. In summarizing work by our research team and others, we suggest how the findings from plasticity studies in nonhuman primate models may affect therapeutic interventions for conditions involving sensory loss due to spinal cord injury. PMID:27578996

  11. Plasticity of Cu nanoparticles: Dislocation-dendrite-induced strain hardening and a limit for displacive plasticity

    PubMed Central

    Albe, Karsten

    2013-01-01

    Summary The plastic behaviour of individual Cu crystallites under nanoextrusion is studied by molecular dynamics simulations. Single-crystal Cu fcc nanoparticles are embedded in a spherical force field mimicking the effect of a contracting carbon shell, inducing pressure on the system in the range of gigapascals. The material is extruded from a hole of 1.1–1.6 nm radius under athermal conditions. Simultaneous nucleation of partial dislocations at the extrusion orifice leads to the formation of dislocation dendrites in the particle causing strain hardening and high flow stress of the material. As the extrusion orifice radius is reduced below 1.3 Å we observe a transition from displacive plasticity to solid-state amorphisation. PMID:23616936

  12. Plastics disassembly versus bulk recycling: engineering design for end-of-life electronics resource recovery.

    PubMed

    Rios, Pedro; Stuart, Julie Ann; Grant, Ed

    2003-12-01

    Annual plastic flows through the business and consumer electronics manufacturing supply chain include nearly 3 billion lb of high-value engineering plastics derived from petroleum. The recovery of resource value from this stream presents critical challenges in areas of materials identification and recycling process design that demand new green engineering technologies applied together with life cycle assessment and ecological supply chain analysis to create viable plastics-to-plastics supply cycles. The sustainable recovery of potentially high-value engineering plastics streams requires that recyclers either avoid mixing plastic parts or purify later by separating smaller plastic pieces created in volume reduction (shredding) steps. Identification and separation constitute significant barriers in the plastics-to-plastics recycling value proposition. In the present work, we develop a model that accepts randomly arriving electronic products to study scenarios by which a recycler might identify and separate high-value engineering plastics as well as metals. Using discrete eventsimulation,we compare current mixed plastics recovery with spectrochemical plastic resin identification and subsequent sorting. Our results show that limited disassembly with whole-part identification can produce substantial yields in separated streams of recovered engineering thermoplastics. We find that disassembly with identification does not constitute a bottleneck, but rather, with relatively few workers, can be configured to pull the process and thus decrease maximum staging space requirements. PMID:14700333

  13. Dynamically strained ferroelastics: Statistical behavior in elastic and plastic regimes

    NASA Astrophysics Data System (ADS)

    Ding, X.; Lookman, T.; Zhao, Z.; Saxena, A.; Sun, J.; Salje, E. K. H.

    2013-03-01

    The dynamic evolution in ferroelastic crystals under external shear is explored by computer simulation of a two-dimensional model. The characteristic geometrical patterns obtained during shear deformation include dynamic tweed in the elastic regime as well as interpenetrating needle domains in the plastic regime. As a result, the statistics of jerk energy differ in the elastic and plastic regimes. In the elastic regime the distributions of jerk energy are sensitive to temperature and initial configurations. However, in the plastic regime the jerk distributions are rather robust and do not depend much on the details of the configurations, although the geometrical pattern formed after yield is strongly influenced by the elastic constants of the materials and the configurations we used. Specifically, for all geometrical configurations we studied, the energy distribution of jerks shows a power-law noise pattern P(E)˜E-(γ-1)(γ-1=1.3-2) at low temperatures and a Vogel-Fulcher distribution P(E) ˜ exp-(E/E0) at high temperatures. More complex behavior occurs at the crossover between these two regimes where our simulated jerk distributions are very well described by a generalized Poisson distributions P(E)˜E-(γ-1) exp-(E/E0)n with n = 0.4-0.5 and γ-1 ≈ 0 (Kohlrausch law). The geometrical mechanisms for the evolution of the ferroelastic microstructure under strain deformation remain similar in all thermal regimes, whereas their thermodynamic behavior differs dramatically: on heating, from power-law statistics via the Kohlrausch law to a Vogel-Fulcher law. There is hence no simple way to predict the local evolution of the twin microstructure from just the observed statistical behavior of a ferroelastic crystal. It is shown that the Poisson distribution is a convenient way to describe the crossover behavior contained in all the experimental data without recourse to specific scaling functions or temperature-dependent cutoff lengths.

  14. Rehabilitation with Poststroke Motor Recovery: A Review with a Focus on Neural Plasticity

    PubMed Central

    Takeuchi, Naoyuki; Izumi, Shin-Ichi

    2013-01-01

    Motor recovery after stroke is related to neural plasticity, which involves developing new neuronal interconnections, acquiring new functions, and compensating for impairment. However, neural plasticity is impaired in the stroke-affected hemisphere. Therefore, it is important that motor recovery therapies facilitate neural plasticity to compensate for functional loss. Stroke rehabilitation programs should include meaningful, repetitive, intensive, and task-specific movement training in an enriched environment to promote neural plasticity and motor recovery. Various novel stroke rehabilitation techniques for motor recovery have been developed based on basic science and clinical studies of neural plasticity. However, the effectiveness of rehabilitative interventions among patients with stroke varies widely because the mechanisms underlying motor recovery are heterogeneous. Neurophysiological and neuroimaging studies have been developed to evaluate the heterogeneity of mechanisms underlying motor recovery for effective rehabilitation interventions after stroke. Here, we review novel stroke rehabilitation techniques associated with neural plasticity and discuss individualized strategies to identify appropriate therapeutic goals, prevent maladaptive plasticity, and maximize functional gain in patients with stroke. PMID:23738231

  15. Local Plastic-Strain Heterogeneities and Their Impact on the Ductility of Mg

    NASA Astrophysics Data System (ADS)

    Martin, Guilhem; Sinclair, Chad W.; Poole, Warren J.; Azizi-Alizamini, Hamid

    2015-08-01

    Microscale plastic strain heterogeneity can arise in polycrystalline Mg and its alloys in a variety of different ways. In this article, we illustrate how microscale digital image correction based on scanning electron microscope images can reveal this plastic heterogeneity in commercially pure polycrystalline Mg and how such observations provide insight into plasticity, damage, and ductility.

  16. Recovery of strain-hardening rate in Ni-Si alloys.

    PubMed

    Yang, C L; Zhang, Z J; Cai, T; Zhang, P; Zhang, Z F

    2015-01-01

    In this study, the recovery of strain-hardening rate (RSHR) was discovered for the first time in polycrystalline materials (Ni-Si alloys) that have only dislocation activities during tensile test. Detailed microstructure characterizations show that the activation of dislocations in the secondary slip systems during tensile deformation is the major reason for this RSHR. By taking into account other metals that also exhibit RSHR during tension, a more general mechanism for the RSHR was proposed, i.e. the occurrence of a sharp decrease of dislocation mean free path (Λ) during plastic deformation, caused by either planar defects or linear defects. PMID:26487419

  17. Recovery of strain-hardening rate in Ni-Si alloys

    NASA Astrophysics Data System (ADS)

    Yang, C. L.; Zhang, Z. J.; Cai, T.; Zhang, P.; Zhang, Z. F.

    2015-10-01

    In this study, the recovery of strain-hardening rate (RSHR) was discovered for the first time in polycrystalline materials (Ni-Si alloys) that have only dislocation activities during tensile test. Detailed microstructure characterizations show that the activation of dislocations in the secondary slip systems during tensile deformation is the major reason for this RSHR. By taking into account other metals that also exhibit RSHR during tension, a more general mechanism for the RSHR was proposed, i.e. the occurrence of a sharp decrease of dislocation mean free path (Λ) during plastic deformation, caused by either planar defects or linear defects.

  18. Recovery of strain-hardening rate in Ni-Si alloys

    PubMed Central

    Yang, C. L.; Zhang, Z. J.; Cai, T.; Zhang, P.; Zhang, Z. F.

    2015-01-01

    In this study, the recovery of strain-hardening rate (RSHR) was discovered for the first time in polycrystalline materials (Ni-Si alloys) that have only dislocation activities during tensile test. Detailed microstructure characterizations show that the activation of dislocations in the secondary slip systems during tensile deformation is the major reason for this RSHR. By taking into account other metals that also exhibit RSHR during tension, a more general mechanism for the RSHR was proposed, i.e. the occurrence of a sharp decrease of dislocation mean free path (Λ) during plastic deformation, caused by either planar defects or linear defects. PMID:26487419

  19. Contribution of plastic waste recovery to greenhouse gas (GHG) savings in Spain.

    PubMed

    Sevigné-Itoiz, Eva; Gasol, Carles M; Rieradevall, Joan; Gabarrell, Xavier

    2015-12-01

    This paper concentrates on the quantification of greenhouse gas (GHG) emissions of post-consumer plastic waste recovery (material or energy) by considering the influence of the plastic waste quality (high or low), the recycled plastic applications (virgin plastic substitution or non-plastic substitution) and the markets of recovered plastic (regional or global). The aim is to quantify the environmental consequences of different alternatives in order to evaluate opportunities and limitations to select the best and most feasible plastic waste recovery option to decrease the GHG emissions. The methodologies of material flow analysis (MFA) for a time period of thirteen years and consequential life cycle assessment (CLCA) have been integrated. The study focuses on Spain as a representative country for Europe. The results show that to improve resource efficiency and avoid more GHG emissions, the options for plastic waste management are dependent on the quality of the recovered plastic. The results also show that there is an increasing trend of exporting plastic waste for recycling, mainly to China, that reduces the GHG benefits from recycling, suggesting that a new focus should be introduced to take into account the split between local recycling and exporting. PMID:26300422

  20. Experimental determination of the strain and strain rate dependence of the fraction of plastic work converted to heat

    SciTech Connect

    Hodowany, J.; Ravichandran, G.; Rosakis, A.J.

    1995-12-31

    When metals are deformed dynamically, there is insufficient time for heat generated by plastic deformation to be conducted to the surroundings. Thus, the conversion of plastic work into heat at high strain rates can result in significant temperature increases, which contribute to thermal softening, thereby altering a material`s constitutive response. The fraction of plastic work converted to heat represents the strength of the coupling term between temperature and mechanical fields in thermalmechanical problems involving plastic flow. The experimental determination of this constitutive function is important since it is an integral part of the formulation of coupled thermomechanical field equations. This fraction also plays an important role in failure mode characterization for metals deforming at high rates of strain, such as the formation of adiabatic shear bands. This investigation systematically examines the rate of conversion of plastic work to heat in metals under dynamic loading. Temperature was measured in-situ using an array of high speed In-Sb infrared detectors. The plastic work rate and the heat generation rate were determined directly from experimental data. The ratio of heat generation rate to plastic work rate, i.e., the relative rate at which plastic work is converted to heat, was calculated from this data. The functional dependence of this quantity upon strain and strain rate is reported for 1020 steel, 2024 aluminum, Ti-6Al-4V titanium alloy, and C300 maraging steel.

  1. Process for the recovery and separation of plastics

    DOEpatents

    Jody, Bassam J.; Daniels, Edward J.; Pomykala Jr., Joseph A.

    2003-07-29

    A method of separating a portion of acrylonitrile-butadiene-styrene (ABS) from a mixture containing ABS and for separating a portion of ABS and polycarbonate (PC) from a mixture of plastics containing ABS and PC is disclosed. The method includes shredding and/or granulating the mixture of plastics containing ABS and PC to provide a selected particle size; sequentially dispersing the shredded mixture of plastics in a series aqueous solutions having different specific gravities and separating the floating fraction until the desired separation is obtained. Surface tension and pH are also variable to be controlled.

  2. Combinations of stroke neurorehabilitation to facilitate motor recovery: perspectives on Hebbian plasticity and homeostatic metaplasticity

    PubMed Central

    Takeuchi, Naoyuki; Izumi, Shin-Ichi

    2015-01-01

    Motor recovery after stroke involves developing new neural connections, acquiring new functions, and compensating for impairments. These processes are related to neural plasticity. Various novel stroke rehabilitation techniques based on basic science and clinical studies of neural plasticity have been developed to aid motor recovery. Current research aims to determine whether using combinations of these techniques can synergistically improve motor recovery. When different stroke neurorehabilitation therapies are combined, the timing of each therapeutic program must be considered to enable optimal neural plasticity. Synchronizing stroke rehabilitation with voluntary neural and/or muscle activity can lead to motor recovery by targeting Hebbian plasticity. This reinforces the neural connections between paretic muscles and the residual motor area. Homeostatic metaplasticity, which stabilizes the activity of neurons and neural circuits, can either augment or reduce the synergic effect depending on the timing of combination therapy and types of neurorehabilitation that are used. Moreover, the possibility that the threshold and degree of induced plasticity can be altered after stroke should be noted. This review focuses on the mechanisms underlying combinations of neurorehabilitation approaches and their future clinical applications. We suggest therapeutic approaches for cortical reorganization and maximal functional gain in patients with stroke, based on the processes of Hebbian plasticity and homeostatic metaplasticity. Few of the possible combinations of stroke neurorehabilitation have been tested experimentally; therefore, further studies are required to determine the appropriate combination for motor recovery. PMID:26157374

  3. The Impact of Martensite Deformation on Shape Memory Effect Recovery Strain Evolution

    NASA Astrophysics Data System (ADS)

    Lanba, Asheesh; Hamilton, Reginald F.

    2015-08-01

    The one-way shape memory effect of polycrystalline NiTi is investigated after differential levels of martensite deformation. Martensite naturally forms an energy-minimizing configuration, referred to as self-accommodated, of differently oriented martensite variants, which are internally twinned. Stress preferentially orients a select variant that eventually detwins and plastically deforms at the highest stress levels. In this work, the underlying morphology is ascertained based on the evolution of micro-scale deformation measurements using digital image correlation analysis of three characteristic material responses. An initial martensitic structure is deformed at constant temperature. The forward austenite-to-martensite and reverse martensite-to-austenite phase transformations take place during temperature cycling under a constant stress. The austenite-to-martensite transformation is tensile stress induced at a constant temperature and initiates via a localized strain band. For the conversion of self-accommodated martensite to orientated morphology and further deformation, spatially heterogeneous strains accrue over the entire specimen surface. Shape memory recovery during heating, on the other hand, culminates with a centralized strain localization that persists as recovery approaches completion. The recovery temperature differential ( A f - A s) depends on the extent of deformation. This work characterizes the influence of stress on phase transformation and martensite deformation morphology for deformation in the martensitic state compared to the stress-induced phase transformation.

  4. Constitutive response of two plastic-bonded explosive binder materials as a function of temperature and strain-rate

    SciTech Connect

    Cady, C. M.; Blumenthal, W. R.; Gray, G. T. , III; Idar, D. J.

    2004-01-01

    Recently, interest has been shown concerning the mechanical response of plastic-bonded explosives (PBX) and propellants to enable the development of predictive materials models describing the mechanical behavior of these composites. Accordingly, detailed information about the constitutive response is crucial. Compression measurements were conducted on two explosive formulation binders, extruded Estane{trademark} 5703 (hereafter referred to as Estane) and plasticized Estane as a function of temperature from -60 C to +23 C using a specially-designed split Hopkinson pressure bar (strain rate of {approx} 2800 s{sup -1}) and quasi-stattically (strain rates from {approx} 0.001 to 1 s{sup -1}) using a hydraulic load frame. The mechanical response of the Estane was found to exhibit a stronger dependency on strain rate and temperature and higher flow strength for similar test conditions of the materials tested. Plasticized Estane was less sensitively dependent on strain rate and temperature. The visco-elastic recovery of both binders is seen to dominate the mechanical behavior at temperatures above the glass transition temperature (T{sub g}). The binders exhibited increasing elastic loading moduli, E, with increasing strain rate or decreasing temperature, which is similar to other polymeric materials. There is a pronounced shift in the apparent T{sub g} to higher temperatures as the strain rate is increased. At low strain rates the binders exhibit a yield behavior followed by a drop in the flow stress which may or may not recover. At high strain rates the load drop does not occur and the flow stresses level out. A discussion of the Hopkinson bar technique as applied to polymeric or low impedance materials is described in detail.

  5. Biaxial Tensile Test of Cold Rolled IF Steel Sheet for Large Plastic Strain Range

    NASA Astrophysics Data System (ADS)

    Enatsu, Ryotaro; Kuwabara, Toshihiko

    2011-08-01

    Deformation behavior of cold rolled IF steel sheet (SPCE) under biaxial tension has been investigated for large plastic strain range over 15%. The test material was bent and TIG welded to form a tubular specimen with an outer diameter of 46.2 mm and wall thickness of 0.8 mm. The tubular specimens have been subjected to linear stress paths in the first quadrant of stress space with the use of a servo-controlled tension-internal pressure testing machine developed by one of the authors [T. Kuwabara, K. Yoshida, K. Narihara, S. Takahashi, Anisotropic plastic deformation of extruded aluminum alloy tube under axial forces and internal pressure, Int. J. Plasticity 21, 101-117 (2005)]. Moreover, biaxial tensile tests using a cruciform specimen have also been carried out to more precisely measure the deformation behavior for a small strain range following initial yielding. True stress-true plastic strain curves, contours of plastic work in stress space and the directions of plastic strain rates have been measured and compared with those calculated using selected yield functions: the von Mises, Hill's quadratic and Yld2000-2d [Barlat, F., Brem, J.C., Yoon, J.W., Chung, K., Dick, R.E., Lege, D.J., Pourboghrat, F., Choi, S.H., Chu, E., Plane stress yield function for aluminum alloy sheets—Part 1: Theory. Int. J. Plasticity 19, 1297-1319 (2003)]. The plastic deformation behavior up to a work equivalent plastic strain of ɛ0p = 0.19 has been successfully measured. It is found that the test material exhibits differential hardening and that the Yld2000-2d yield function with an exponent of six most closely predicts the contours of plastic work and the directions of plastic strain rates.

  6. Maladaptive spinal plasticity opposes spinal learning and recovery in spinal cord injury

    PubMed Central

    Ferguson, Adam R.; Huie, J. Russell; Crown, Eric D.; Baumbauer, Kyle M.; Hook, Michelle A.; Garraway, Sandra M.; Lee, Kuan H.; Hoy, Kevin C.; Grau, James W.

    2012-01-01

    Synaptic plasticity within the spinal cord has great potential to facilitate recovery of function after spinal cord injury (SCI). Spinal plasticity can be induced in an activity-dependent manner even without input from the brain after complete SCI. A mechanistic basis for these effects is provided by research demonstrating that spinal synapses have many of the same plasticity mechanisms that are known to underlie learning and memory in the brain. In addition, the lumbar spinal cord can sustain several forms of learning and memory, including limb-position training. However, not all spinal plasticity promotes recovery of function. Central sensitization of nociceptive (pain) pathways in the spinal cord may emerge in response to various noxious inputs, demonstrating that plasticity within the spinal cord may contribute to maladaptive pain states. In this review we discuss interactions between adaptive and maladaptive forms of activity-dependent plasticity in the spinal cord below the level of SCI. The literature demonstrates that activity-dependent plasticity within the spinal cord must be carefully tuned to promote adaptive spinal training. Prior work from our group has shown that stimulation that is delivered in a limb position-dependent manner or on a fixed interval can induce adaptive plasticity that promotes future spinal cord learning and reduces nociceptive hyper-reactivity. On the other hand, stimulation that is delivered in an unsynchronized fashion, such as randomized electrical stimulation or peripheral skin injuries, can generate maladaptive spinal plasticity that undermines future spinal cord learning, reduces recovery of locomotor function, and promotes nociceptive hyper-reactivity after SCI. We review these basic phenomena, how these findings relate to the broader spinal plasticity literature, discuss the cellular and molecular mechanisms, and finally discuss implications of these and other findings for improved rehabilitative therapies after SCI. PMID

  7. Recovery and separation of high-value plastics from discarded household appliances

    SciTech Connect

    Karvelas, D.E.; Jody, B.J.; Poykala, J.A. Jr.; Daniels, E.J.; Arman, B. |

    1996-03-01

    Argonne National Laboratory is conducting research to develop a cost- effective and environmentally acceptable process for the separation of high-value plastics from discarded household appliances. The process under development has separated individual high purity (greater than 99.5%) acrylonitrile-butadiene-styrene (ABS) and high- impact polystyrene (HIPS) from commingled plastics generated by appliance-shredding and metal-recovery operations. The process consists of size-reduction steps for the commingled plastics, followed by a series of gravity-separation techniques to separate plastic materials of different densities. Individual plastics of similar densities, such as ABS and HIPS, are further separated by using a chemical solution. By controlling the surface tension, the density, and the temperature of the chemical solution we are able to selectively float/separate plastics that have different surface energies. This separation technique has proven to be highly effective in recovering high-purity plastics materials from discarded household appliances. A conceptual design of a continuous process to recover high-value plastics from discarded appliances is also discussed. In addition to plastics separation research, Argonne National Laboratory is conducting research to develop cost-effective techniques for improving the mechanical properties of plastics recovered from appliances.

  8. RETSCP: A computer program for analysis of rocket engine thermal strains with cyclic plasticity

    NASA Technical Reports Server (NTRS)

    Miller, R. W.

    1974-01-01

    A computer program, designated RETSCP, for the analysis of Rocket Engine Thermal Strain with Cyclic Plasticity is described. RETSCP is a finite element program which employs a three dimensional isoparametric element. The program treats elasto-plastic strain cycling including the effects of thermal and pressure loads and temperature dependent material properties. Theoretical aspects of the finite element method are discussed and the program logic is described. A RETSCP User's Manual is presented including sample case results.

  9. Plastic Straining of Iridium Alloy DOP-26 During Cup Sizing Operations

    SciTech Connect

    Ohriner, Evan Keith; Ulrich, George B; Sabau, Adrian S

    2007-09-01

    DOP-26 iridium alloy cups are used for fuel cladding for radioisotope power systems. The cups are deep drawn and recrystallized prior to final fabrication operations. This study characterizes the plastic deformation of cups during a sizing operation following the recrystallization heat treatment. The purpose of the sizing operation is to achieve the specified roundness, diameter, and radius dimensions of the cup. The operation introduces various levels of plastic strain in the cup. Plastic strain can be a cause of inhomogeneous or abnormal grain growth during subsequent exposure to elevated temperature during the service life of the fueled clad. This is particularly true in the case of cups which have irregularities in the cup walls from the deep drawing operations. Diameter and roundness measurements were made on two cups both before and after sizing. Plastic strain levels were calculated using the ABAQUSTM finite element software. The calculated plastic strain levels in both cups were below 0.025, a value shown to be below the critical strain for abnormal grain growth during a simulated service exposure. The calculated maximum plastic strain was found to increase with increased applied sizing load and was not sensitive to the input value for the clearance between the cup and the sizing die. The calculated geometry of the sized cups was in good agreement with the measurements on the finished cups.

  10. Brain plasticity as a basis for recovery of function in humans.

    PubMed

    Bach-y-Rita, P

    1990-01-01

    One of the factors leading to the virtual neglect of the long-term potential for functional recovery following brain damage was the eclipse of plasticity concepts during the 100 years following Broca's 1861 publication on location of function. However, in the last 30 years evidence has been accumulating that demonstrates the plasticity of the brain and thus recovery potential is a subject of practical as well as theoretical interest. "Unmasking" of relatively inactive pathways, the taking over of functional representation by undamaged brain tissue, and neuronal group selection are among the mechanisms that are being explored. Human models of recovery of function include hemispherectomy patients that have regained bilateral function, facial paralysis patients who recover function (with appropriate rehabilitation) after VII-XII cranial nerve anastomosis, and patients with muscle transpositions to re-establish lost motor functions. The role of early and late rehabilitation, with attention to psychosocial and environmental factors, appears to be critical for recovery. PMID:2395525

  11. In situ identification of elastic-plastic strain distribution in a microalloyed transformation induced plasticity steel using digital image correlation

    NASA Astrophysics Data System (ADS)

    Eskandari, M.; Zarei-Hanzaki, A.; Yadegari, M.; Soltani, N.; Asghari, A.

    2014-03-01

    A non-contact strain measurement technique, based on an in-situ digital image correlation (DIC) method in association with magnetic martensite point measurement (Feritoscopy testing) was applied to study inhomogeneous deformation corresponding to martensitic transformation of a microalloyed low carbon transformation induced plasticity steel during tensile straining. The progress of inhomogeneous deformation is traced by the strain maps. The microstructural observation is used to validate the DIC results. The experimental steel shows continuous yielding with a high true fracture strength of 1410±10 MPa at 25 °C along with the lack of tensile necking. The DIC results show that the yield point is controlled by stress-assisted martensite transformation, which in turn induces the strain inhomogeneity. The latter starts prior to the yield point after straining to 0.016. The microstructural evolution reveals the ɛ-martensite is obtained through stress-assisted martensite formation. After yielding, thanks to the strain-induced martensite transformation, the deformation inhomogeneity in strain maps is increased with strain, corresponding to increasing the volume fraction of martensite. The results suggest that the continuous yielding and initial strain hardening is controlled by stress-assisted martensite formation while the higher total elongation to fracture (80%) and the tensile necking behavior is mainly influenced by the strain-induced martensite transformation.

  12. Prediction of thermal strains in fibre reinforced plastic matrix by discretisation of the temperature exposure history

    NASA Astrophysics Data System (ADS)

    Ngoy, E. K.

    2016-07-01

    Prediction of environmental effects on fibre reinforced plastics habitually is made difficult due to the complex variability of the natural service environment. This paper suggests a method to predict thermal strain distribution over the material lifetime by discretisation of the exposure history. Laboratory results show a high correlation between predicted and experimentally measured strain distribution

  13. Elastic and plastic strain measurement in high temperature environment using laser speckle

    NASA Technical Reports Server (NTRS)

    Chiang, Fu-Pen

    1992-01-01

    Two laser speckle methods are described to measure strain in high temperature environment and thermal strain caused by high temperature. Both are non-contact, non-destructive and remote sensing techniques that can be automated. The methods have different but overlapping ranges of application with one being more suitable for large plastic deformation.

  14. Brain-Controlled Neuromuscular Stimulation to Drive Neural Plasticity and Functional Recovery

    PubMed Central

    Ethier, C.; Gallego, J.A.; Miller, L.E.

    2015-01-01

    There is mounting evidence that appropriately timed neuromuscular stimulation can induce neural plasticity and generate functional recovery from motor disorders. This review addresses the idea that coordinating stimulation with a patient’s voluntary effort might further enhance neurorehabilitation. Studies in cell cultures and behaving animals have delineated the rules underlying neural plasticity when single neurons are used as triggers. However, the rules governing more complex stimuli and larger networks are less well understood. We argue that functional recovery might be optimized if stimulation were modulated by a brain machine interface, to matched the details of the patient’s voluntary intent. The potential of this novel approach highlights the need for a better understanding of the complex rules underlying this form of plasticity. PMID:25827275

  15. Brain-controlled neuromuscular stimulation to drive neural plasticity and functional recovery.

    PubMed

    Ethier, C; Gallego, J A; Miller, L E

    2015-08-01

    There is mounting evidence that appropriately timed neuromuscular stimulation can induce neural plasticity and generate functional recovery from motor disorders. This review addresses the idea that coordinating stimulation with a patient's voluntary effort might further enhance neurorehabilitation. Studies in cell cultures and behaving animals have delineated the rules underlying neural plasticity when single neurons are used as triggers. However, the rules governing more complex stimuli and larger networks are less well understood. We argue that functional recovery might be optimized if stimulation were modulated by a brain machine interface, to match the details of the patient's voluntary intent. The potential of this novel approach highlights the need for a better understanding of the complex rules underlying this form of plasticity. PMID:25827275

  16. The Strength of Plastic Bonded Explosives as a Function of Pressure, Strain Rate and Temperature

    NASA Astrophysics Data System (ADS)

    Wiegand, Donald

    2005-07-01

    Measurements as a function of strain rate and temperature have indicated the importance of the polymer binder in determining the strength of plastic bonded explosives at ambient conditions and low strain rate. Recent measurements of strength as a function of pressure further support this conclusion. As pressure or strain rate are increased or temperature is decreased the strength increases as does the strength of many polymers. In addition, at relatively large values of pressure or strain rate and/or relatively low values of temperature the strength is less sensitive to changes of these quantities. These trends suggest that as the polymer binder becomes stronger with increasing pressure or strain rate or with decreasing temperature, the strength of the explosive component of these composites becomes more important in determining the strength of the composite. Results will be presented for plastic bonded explosives, e.g., LX-14, that demonstrate these trends as a function of pressure, strain rate and temperature.

  17. Brain plasticity and recovery from early cortical injury.

    PubMed

    Kolb, Bryan; Mychasiuk, Richelle; Williams, Preston; Gibb, Robbin

    2011-09-01

    Neocortical development represents more than a simple unfolding of a genetic blueprint: rather, it represents a complex dance of genetic and environmental events that interact to adapt the brain to fit a particular environmental context. Most cortical regions are sensitive to a wide range of experiential factors during development and later in life, but the injured cortex appears to be unusually sensitive to perinatal experiences. This paper reviews the factors that influence how normal and injured brains (both focal and ischemic injuries) develop and adapt into adulthood. Such factors include prenatal experiences in utero as well as postnatal experiences throughout life. Examples include the effects of sensory and motor stimulation, psychoactive drugs (including illicit and prescription drugs), maternal and postnatal stress, neurotrophic factors, and pre- and postnatal diet. All these factors influence cerebral development and influence recovery from brain injury during development. PMID:21950386

  18. Vestibular plasticity following orbital spaceflight: recovery from postflight postural instability

    NASA Technical Reports Server (NTRS)

    Black, F. O.; Paloski, W. H.; Doxey-Gasway, D. D.; Reschke, M. F.

    1995-01-01

    Results of previous studies suggested that the vestibular mediated postural instability observed in astronauts upon return to earth from orbital spaceflight may be exacerbated by an increased weighting of visual inputs for spatial orientation and control of movement. This study was performed to better understand the roles of visual and somatosensory contributions to recovery of normal sensori-motor postural control in returning astronauts. Preflight and postflight, 23 astronaut volunteers were presented randomly with three trials of six sensory organization test (SOT) conditions in the EquiTest system test battery. Sagittal plane center-of-gravity (COG) excursions computed from ground reaction forces were significantly higher on landing day than preflight for those test conditions presenting sway-referenced visual and/or somatosensory orientation cues. The ratio of summed peak-to-peak COG sway amplitudes on the two sway-referenced vision tests (SOTs 3 + 6) compared to the two eyes closed tests (SOTs 2 + 5) was increased on landing day, indicating an increased reliance on visual orientation cues for postural control. The ratio of peak-to-peak COG excursions on sway-referenced surfaces (SOTs 4, 5 & 6) to an earth fixed support surfaces (SOTs 1, 2 & 3) increased even more after landing suggesting primary reliance on somatosensory orientation cues for recovery of postflight postural stability. Readaptation to sway-referenced support surfaces took longer than readaptation to sway-referenced vision. The increased reliance on visual and somatosensory inputs disappeared in all astronauts 4-8 days following return to earth.

  19. Pyrolysis of plastic packaging waste: A comparison of plastic residuals from material recovery facilities with simulated plastic waste

    SciTech Connect

    Adrados, A.

    2012-05-15

    Highlights: Black-Right-Pointing-Pointer Pyrolysis of plastic waste. Black-Right-Pointing-Pointer Comparison of different samples: real waste, simulated and real waste + catalyst. Black-Right-Pointing-Pointer Study of the effects of inorganic components in the pyrolysis products. - Abstract: Pyrolysis may be an alternative for the reclamation of rejected streams of waste from sorting plants where packing and packaging plastic waste is separated and classified. These rejected streams consist of many different materials (e.g., polyethylene (PE), polypropylene (PP), polystyrene (PS), polyvinyl chloride (PVC), polyethylene terephthalate (PET), acrylonitrile butadiene styrene (ABS), aluminum, tetra-brik, and film) for which an attempt at complete separation is not technically possible or economically viable, and they are typically sent to landfills or incinerators. For this study, a simulated plastic mixture and a real waste sample from a sorting plant were pyrolyzed using a non-stirred semi-batch reactor. Red mud, a byproduct of the aluminum industry, was used as a catalyst. Despite the fact that the samples had a similar volume of material, there were noteworthy differences in the pyrolysis yields. The real waste sample resulted, after pyrolysis, in higher gas and solid yields and consequently produced less liquid. There were also significant differences noted in the compositions of the compared pyrolysis products.

  20. Microlattices as architected thin films: Analysis of mechanical properties and high strain elastic recovery

    NASA Astrophysics Data System (ADS)

    Maloney, Kevin J.; Roper, Christopher S.; Jacobsen, Alan J.; Carter, William B.; Valdevit, Lorenzo; Schaedler, Tobias A.

    2013-08-01

    Ordered periodic microlattices with densities from 0.5 mg/cm3 to 500 mg/cm3 are fabricated by depositing various thin film materials (Au, Cu, Ni, SiO2, poly(C8H4F4)) onto sacrificial polymer lattice templates. Young's modulus and strength are measured in compression and the density scaling is determined. At low relative densities, recovery from compressive strains of 50% and higher is observed, independent of lattice material. An analytical model is shown to accurately predict the transition between recoverable "pseudo-superelastic" and irrecoverable plastic deformation for all constituent materials. These materials are of interest for energy storage applications, deployable structures, and for acoustic, shock, and vibration damping.

  1. Measurement of Plastic Stress and Strain for Analytical Method Verification (MSFC Center Director's Discretionary Fund Project No. 93-08)

    NASA Technical Reports Server (NTRS)

    Price, J. M.; Steeve, B. E.; Swanson, G. R.

    1999-01-01

    The analytical prediction of stress, strain, and fatigue life at locations experiencing local plasticity is full of uncertainties. Much of this uncertainty arises from the material models and their use in the numerical techniques used to solve plasticity problems. Experimental measurements of actual plastic strains would allow the validity of these models and solutions to be tested. This memorandum describes how experimental plastic residual strain measurements were used to verify the results of a thermally induced plastic fatigue failure analysis of a space shuttle main engine fuel pump component.

  2. Laboratory experiment of the rock anelastic strain recovery compliances

    NASA Astrophysics Data System (ADS)

    Gao, Lu; Wang, Lianjie

    2012-09-01

    Anelastic strain recovery (ASR) compliances are the important parameters for the ASR in situ stress measurement method to accurately evaluate the magnitude of the stress. The laboratory experiment of the creep and ASR processes for three types of rocks (sandstone, marble and granite) were performed. The tests were carried out at 50% of the uniaxial compressive strength (UCS). And the ASR compliances of the shear mode Jas(t), the volumetric mode Jav(t) and the ratio of Jas(t) and Jav(t) were obtained, respectively. The experimental result show that both the magnitude and increase rate of the ASR compliance greatly depend on the rock type, and the ratios of Jas(t) and Jav(t) trend to different constant values after enough elapsed time for each type of rock specimen.

  3. Delayed treatment with chondroitinase ABC promotes sensorimotor recovery and plasticity after stroke in aged rats.

    PubMed

    Soleman, Sara; Yip, Ping K; Duricki, Denise A; Moon, Lawrence D F

    2012-04-01

    Stroke is the dominant cause of sensorimotor disability that primarily affects the elderly. We now show that neuroplasticity and functional recovery after stroke is constrained by inhibitory chondroitin sulphates. In two blinded, randomized preclinical trials, degradation of chondroitin sulphate using chondroitinase ABC reactivated neuroplasticity and promoted sensorimotor recovery after stroke in elderly rats. Three days after stroke, chondroitinase ABC was microinjected into the cervical spinal cord to induce localized plasticity of forelimb sensorimotor spinal circuitry. Chondroitinase ABC effectively removed chondroitin sulphate from the extracellular matrix and perineuronal nets. Three different tests of sensorimotor function showed that chondroitinase ABC promoted recovery of forelimb function. Anterograde and retrograde tracing showed that chondroitinase ABC also induced sprouting of the contralesional corticospinal tract in the aged treated hemicord. Chondroitinase ABC did not neuroprotect the peri-infarct region. We show for the first time delayed chondroitinase ABC treatment promotes neuroanatomical and functional recovery after focal ischaemic stroke in an elderly nervous system. PMID:22396394

  4. A Practical Data Recovery Technique for Long-Term Strain Monitoring of Mega Columns during Construction

    PubMed Central

    Choi, Se Woon; Kwon, EunMi; Kim, Yousok; Hong, Kappyo; Park, Hyo Seon

    2013-01-01

    A practical data recovery method is proposed for the strain data lost during the safety monitoring of mega columns. The analytical relations among the measured strains are derived to recover the data lost due to unexpected errors in long-term measurement during construction. The proposed technique is applied to recovery of axial strain data of a mega column in an irregular building structure during construction. The axial strain monitoring using the wireless strain sensing system was carried out for one year and five months between 23 July 2010 and 22 February 2012. During the long-term strain sensing, three different types of measurement errors occurred. Using the recovery technique, the strain data that could not be measured at different intervals in the measurement were successfully recovered. It is confirmed that the problems that may occur during long-term wireless strain sensing of mega columns during construction could be resolved through the proposed recovery method. PMID:23966189

  5. Derivation of Relations and Analysis of Tube Bending Processes Using Discontinuous Fields of Plastic Strains

    NASA Astrophysics Data System (ADS)

    Śloderbach, Z.

    2015-05-01

    The generalized strain scheme in bending metal tubes at bending machines with the use of a mandrel presented in Śloderbach (1999; 2002; 20131,2; 2014) satisfies initial and boundary kinematic conditions of bending, conditions of continuity and inseparability of strains. This paper introduces three formal simplifications gradually imposed into forms of principal components of the generalized strain model giving suitable simplifications of the 1st, 2nd and 3rd types. Such mathematical simplifications cause that the obtained strain fields do not satisfy the condition of consistency of displacements and strain continuity. The simplified methods determine safer values of the wall thickness than those from the generalized continuous strain scheme. The condition of plastic incompressibility was used for the derivation of an expression for distribution of wall thickness of the bent elbow in the layers subjected to tension and compression for three examples of discontinuous kinematic strain fields.

  6. Mechanisms of large strain, high strain rate plastic flow in the explosively driven collapse of Ni-Al laminate cylinders

    NASA Astrophysics Data System (ADS)

    Olney, K. L.; Chiu, P. H.; Higgins, A.; Serge, M.; Weihs, T. P.; Fritz, G.; Stover, A.; Benson, D. J.; Nesterenko, V. F.

    2014-05-01

    Ni-Al laminates have shown promise as reactive materials due to their high energy release through intermetallic reaction. In addition to the traditional ignition methods, the reaction may be initiated in hot spots that can be created during mechanical loading. The explosively driven thick walled cylinder (TWC) technique was performed on two Ni-Al laminates composed of thin foil layers with different mesostructues: concentric and corrugated. These experiments were conducted to examine how these materials accommodate large plastic strain under high strain rates. Finite element simulations of these specimens with mesostuctures digitized from the experimental samples were conducted to provide insight into the mesoscale mechanisms of plastic flow. The dependence of dynamic behaviour on mesostructure may be used to tailor the hot spot formation and therefore the reactivity of the material system.

  7. Crystal plasticity based finite element modelling of large strain deformation in AM30 magnesium alloy

    NASA Astrophysics Data System (ADS)

    Izadbakhsh, Adel; Inal, Kaan; Mishra, Raja K.

    2012-04-01

    In this paper, the finite strain plastic deformation of AM30 magnesium alloy has been simulated using the crystal plasticity finite element method. The simulations have been carried out using a rate-dependent elastic-viscoplastic crystal plasticity constitutive model implemented in a user defined material subroutine (UMAT) in the commercial software LS-DYNA. The plastic deformation mechanisms accounted for in the model are the slip systems in the matrix (parent grain), extension twinning systems and the slip systems inside the extension twinned regions. The parameters of the constitutive model have been calibrated using the experimental data. The calibrated model has then been used to predict the deformation of AM30 magnesium alloy in bending and simple shear. For the bending strain path, the effects of texture on the strain accommodated by the deformation mechanisms and bending moment have been investigated. For simple shear, the effects of texture on the relative activity of deformation mechanisms, shear stress and texture evolution have been investigated. Also, the effect of twinning on shear stress and texture evolution has been studied. The numerical analyses predicted a more uniform strain distribution during bending and simple shear for rolled texture compared with extruded texture.

  8. High Strain Rate Characterization of Plastics and Foams Using Polymeric Split Hopkinson Bar

    NASA Astrophysics Data System (ADS)

    Sawas, Omar; Brar, N. S.

    1997-07-01

    High strain rate and high/low temperature response of engineered plastics and foams is relevant and important for the design and development of fighter aircraft canopies, submarine interiors and automobile exterior and interior systems. The mechanical impedance of conventional split Hopkinson bar materials (aluminum or steel) is extremely large compared to those of plastic or foam specimens. To overcome this difficulty of impedance mismatch we have developed the Polymeric Split Hopkinson Bar (PSHB). A viscoelastic model for cast acrylic bar material, which relates stresses and strains as well as particle velocity and strain, is developed to account for the wave dispersion along the bar. The model is verified by comparing the stress strain data on 1100 aluminum and polycarbonate specimens obtained using PSHB and conventional aluminum SHB. Stress-strain data at a strain rate of 103/s on low strength polyurethane foam (density = 0.57 g/cm3) following this technique show that the foam has a recoverable compressive strain of 0.4 at a stress of 2.9 MPa. High strain rate (2x102-2x103/s) data on polycarbonate, generic elastomer, and styrofoam will also be presented.

  9. Temporal plasticity involved in recovery from manual dexterity deficit after motor cortex lesion in macaque monkeys.

    PubMed

    Murata, Yumi; Higo, Noriyuki; Hayashi, Takuya; Nishimura, Yukio; Sugiyama, Yoko; Oishi, Takao; Tsukada, Hideo; Isa, Tadashi; Onoe, Hirotaka

    2015-01-01

    The question of how intensive motor training restores motor function after brain damage or stroke remains unresolved. Here we show that the ipsilesional ventral premotor cortex (PMv) and perilesional primary motor cortex (M1) of rhesus macaque monkeys are involved in the recovery of manual dexterity after a lesion of M1. A focal lesion of the hand digit area in M1 was made by means of ibotenic acid injection. This lesion initially caused flaccid paralysis in the contralateral hand but was followed by functional recovery of hand movements, including precision grip, during the course of daily postlesion motor training. Brain imaging of regional cerebral blood flow by means of H2 (15)O-positron emission tomography revealed enhanced activity of the PMv during the early postrecovery period and increased functional connectivity within M1 during the late postrecovery period. The causal role of these areas in motor recovery was confirmed by means of pharmacological inactivation by muscimol during the different recovery periods. These findings indicate that, in both the remaining primary motor and premotor cortical areas, time-dependent plastic changes in neural activity and connectivity are involved in functional recovery from the motor deficit caused by the M1 lesion. Therefore, it is likely that the PMv, an area distant from the core of the lesion, plays an important role during the early postrecovery period, whereas the perilesional M1 contributes to functional recovery especially during the late postrecovery period. PMID:25568105

  10. Factors contributing to plastic strain amplification in slip dominated deformation of magnesium alloys

    NASA Astrophysics Data System (ADS)

    Sinclair, C. W.; Martin, G.; Lebensohn, R. A.

    2015-12-01

    While plastic strains are never distributed uniformly in polycrystals, it has recently been shown experimentally that the distribution can be extremely heterogeneous in magnesium polycrystals even when the deformation is dominated by slip. Here, we attempt to provide insight into the (macroscopic) factors that contribute to this strain amplification and to explain, from a local perspective, the origins of this strain amplification. To do this, full field VPFFT crystal plasticity simulations have been performed under the simplifying assumption that twinning is inoperative. It is shown that the experimentally observed heterogeneity can be reproduced when a sufficiently high anisotropy in slip system strength is assumed. This can be further accentuated by a weakening of the texture.

  11. Experimental Anelastic Strain Recovery Compliance of Three Typical Rocks

    NASA Astrophysics Data System (ADS)

    Gao, Lu; Lin, Weiren; Sun, Dongsheng; Wang, Hongcai

    2014-11-01

    The experimental determination of anelastic strain recovery (ASR) compliances for three types of rocks (granite, marble, and sandstone) was performed in the laboratory. Preloading of specimens for uniaxial compression creep tests was at 50 % of the uniaxial compressive strength (UCS) for each rock type. We obtained the shear mode Jas( t) and volumetric mode Jav( t) ASR compliances and calculated the ratio of Jas( t) to Jav( t). The Kelvin model for rock rheology was then applied in numerical simulations and the results were in good agreement with the measured data for Jas( t) and Jav( t). These results showed that both the magnitude and rate of increase of the ASR compliances are strongly dependent on the rock type, and the values of the Jas( t)/Jav( t) ratio for a loading of 50 % of the UCS showed a trend leading to different constants for each of the three rock types. Further experimental and numerical analyses showed approximate power-law relationships between the ASR compliances at 50 % of UCS, and both the UCS and the tangential Young's modulus at 50 % of UCS ( E t50). These relationships may be useful for the preliminary estimation of ASR compliances.

  12. Effect of Strain and Strain Path on Texture and Twin Development in Austenitic Steel with Twinning-Induced Plasticity

    NASA Astrophysics Data System (ADS)

    Mishra, Sushil K.; Tiwari, Shashank M.; Kumar, Arun M.; Hector, Louis G.

    2012-05-01

    High-manganese (15 to 30 wt pct) austenitic steels exhibit extreme strain hardening because of twinning with increased strain. Twinning in these low stacking fault materials promotes retention of the austenitic microstructure and impedes dislocation motion. A dearth of information is available concerning the extent to which strain path influences twinning in so-called twinning-induced plasticity (TWIP) steels. The present study focuses on the influence of strain level and strain path on texture and twinning in a high-Mn content TWIP steel (Fe17.2Mn0.6C). Electron back-scatter diffraction was employed to measure the twin fraction, twin deviation, twin boundary length, grain misorientation, and volume fraction of different texture components as a function of both uniaxial and biaxial deformation. This information, which is part of the necessary first step toward linking crystallographic texture and twinning to mechanical properties, was used to quantitatively assess the extent to which these critical metallurgical features depend on the amount of straining and the strain path.

  13. Explicit mixed strain-displacement finite elements for compressible and quasi-incompressible elasticity and plasticity

    NASA Astrophysics Data System (ADS)

    Cervera, M.; Lafontaine, N.; Rossi, R.; Chiumenti, M.

    2016-06-01

    This paper presents an explicit mixed finite element formulation to address compressible and quasi-incompressible problems in elasticity and plasticity. This implies that the numerical solution only involves diagonal systems of equations. The formulation uses independent and equal interpolation of displacements and strains, stabilized by variational subscales. A displacement sub-scale is introduced in order to stabilize the mean-stress field. Compared to the standard irreducible formulation, the proposed mixed formulation yields improved strain and stress fields. The paper investigates the effect of this enhancement on the accuracy in problems involving strain softening and localization leading to failure, using low order finite elements with linear continuous strain and displacement fields (P1P1 triangles in 2D and tetrahedra in 3D) in conjunction with associative frictional Mohr-Coulomb and Drucker-Prager plastic models. The performance of the strain/displacement formulation under compressible and nearly incompressible deformation patterns is assessed and compared to analytical solutions for plane stress and plane strain situations. Benchmark numerical examples show the capacity of the mixed formulation to predict correctly failure mechanisms with localized patterns of strain, virtually free from any dependence of the mesh directional bias. No auxiliary crack tracking technique is necessary.

  14. Explicit mixed strain-displacement finite elements for compressible and quasi-incompressible elasticity and plasticity

    NASA Astrophysics Data System (ADS)

    Cervera, M.; Lafontaine, N.; Rossi, R.; Chiumenti, M.

    2016-09-01

    This paper presents an explicit mixed finite element formulation to address compressible and quasi-incompressible problems in elasticity and plasticity. This implies that the numerical solution only involves diagonal systems of equations. The formulation uses independent and equal interpolation of displacements and strains, stabilized by variational subscales. A displacement sub-scale is introduced in order to stabilize the mean-stress field. Compared to the standard irreducible formulation, the proposed mixed formulation yields improved strain and stress fields. The paper investigates the effect of this enhancement on the accuracy in problems involving strain softening and localization leading to failure, using low order finite elements with linear continuous strain and displacement fields ( P1 P1 triangles in 2D and tetrahedra in 3D) in conjunction with associative frictional Mohr-Coulomb and Drucker-Prager plastic models. The performance of the strain/displacement formulation under compressible and nearly incompressible deformation patterns is assessed and compared to analytical solutions for plane stress and plane strain situations. Benchmark numerical examples show the capacity of the mixed formulation to predict correctly failure mechanisms with localized patterns of strain, virtually free from any dependence of the mesh directional bias. No auxiliary crack tracking technique is necessary.

  15. The exponentiated Hencky-logarithmic strain energy: part III—coupling with idealized multiplicative isotropic finite strain plasticity

    NASA Astrophysics Data System (ADS)

    Neff, Patrizio; Ghiba, Ionel-Dumitrel

    2016-03-01

    We investigate an immediate application in finite strain multiplicative plasticity of the family of isotropic volumetric-isochoric decoupled strain energies F mapsto W_eH(F):= widehat{W}_eH(U) := μ/k e^{k | dev_n log {U}|^2}+κ/2 {widehat{k}} e^{widehat{k} [ tr(log U)]^2}&quad if& det F > 0, + ∞ & quad if & det F ≤ 0, based on the Hencky-logarithmic (true, natural) strain tensor {log U} . Here, {μ > 0} is the infinitesimal shear modulus, {κ=2 μ+3λ/3 > 0} is the infinitesimal bulk modulus with λ the first Lamé constant, {k,widehat{k}} are additional dimensionless material parameters, {F=nabla \\varphi} is the gradient of deformation, {U=√{F^T F}} is the right stretch tensor, and dev n {log {U} =log {U}-1/n tr(log {U})\\cdot{1}} is the deviatoric part of the strain tensor {log U} . Based on the multiplicative decomposition {F=F_e F_p} , we couple these energies with some isotropic elasto-plastic flow rules {F_p {dt}/[F_p^{-1}]in-partial χ(dev_3 Σe)} defined in the plastic distortion F p , where {partial χ} is the subdifferential of the indicator function {χ} of the convex elastic domain {E_e({Σe},1/3{σ}_{y}^2)} in the mixed-variant {Σe} -stress space, {Σe=F_e^T D_{F_e}W_iso(F_e)} , and {W_iso(F_e)} represents the isochoric part of the energy. While {W_eH} may loose ellipticity, we show that loss of ellipticity is effectively prevented by the coupling with plasticity, since the ellipticity domain of {W_eH} on the one hand and the elastic domain in {Σe} -stress space on the other hand are closely related. Thus, the new formulation remains elliptic in elastic unloading at any given plastic predeformation. In addition, in this domain, the true stress-true strain relation remains monotone, as observed in experiments.

  16. Image Correlation Applied to Single Crystal Plasticity Experiments and Comparison to Strain Gage Data

    SciTech Connect

    LeBlanc, M M; Florando, J N; Lassila, D H; Schmidt, T; Tyson II, J

    2005-06-29

    Full-field optical techniques are becoming increasingly popular for measuring the deformation of materials, especially in materials that exhibit non-uniform behavior. While there are many full-field techniques available (e.g. moire interferometry, electronic speckle pattern interferometry (ESPI), holography, and image correlation [1]), for our study of the deformation of single crystals, the image correlation technique was chosen for its insensitivity to vibrations and ability to measure large strains. While the theory and development of the algorithms for image correlation have been presented elsewhere [2,3] a comparative study to a conventional strain measurement device, such as a strain gage rosette, is desired to test the robustness and accuracy of the technique. The 6 Degrees of Freedom (6DOF) experiment, which was specifically designed to validate dislocation dynamics (DD) simulations [4], is ideally suited to compare the two methods. This experiment is different from previous experiments on single crystals in that it allows the crystal to deform essentially unconstrained, in both the elastic and plastic regimes, by allowing the bottom of the sample to move as the sample is being compressed. This unconstrained motion prevents the internal crystal planes from rotating during the deformation as typically seen in the pioneering work of Schmid [5] and Taylor [6]. In the early development of the 6DOF apparatus, stacked strain gage rosettes were used to provide the strain data [7]. While very accurate at small strains, strain gages provide an averaged measurement over a small area and cannot be used to measure the inhomogeneous plastic strains that typically occur during the 6DOF experiment. An image correlation technique can measure the full-field in-plane and out-of-plane deformation that occurs in single crystals, and a comparison to the strain gage data at small strains can test the accuracy of the method.

  17. An Elastic Plastic Contact Model with Strain Hardening for the LAMMPS Granular Package

    SciTech Connect

    Kuhr, Bryan; Brake, Matthew Robert; Lechman, Jeremy B.

    2015-03-01

    The following details the implementation of an analytical elastic plastic contact model with strain hardening for normal im pacts into the LAMMPS granular package. The model assumes that, upon impact, the co llision has a period of elastic loading followed by a period of mixed elastic plas tic loading, with contributions to each mechanism estimated by a hyperbolic seca nt weight function. This function is implemented in the LAMMPS source code as the pair style gran/ep/history. Preliminary tests, simulating the pouring of pure nickel spheres, showed the elastic/plastic model took 1.66x as long as similar runs using gran/hertz/history.

  18. Effect of hydrogen on plastic strain localization and fracture of steels

    NASA Astrophysics Data System (ADS)

    Nadjozhkin, M. V.; Lunev, A. G.; Li, Yu V.; Barannikova, S. A.

    2016-02-01

    The effect of interstitial hydrogen atoms on the mechanical properties and plastic strain localization patterns in tensile tested specimens of low-carbon steels have been studied using a double exposure speckle photography technique. It is found that the mechanical properties of low-carbon steels are affected adversely by hydrogen embrittlement. The deformation diagrams were examined for the deformed samples of low-carbon steels. These are found to show all the plastic flow stages: the linear, parabolic and pre-failure stages would occur for the respective values of the exponent n from the Ludwik-Holomon equation.

  19. Draft Genome Sequences of Sphingobium sp. Strain TCM1 and Sphingomonas sp. Strain TDK1, Haloalkyl Phosphate Flame Retardant- and Plasticizer-Degrading Bacteria

    PubMed Central

    Abe, Katsumasa; Kasai, Daisuke; Fukuda, Masao; Takahashi, Shouji

    2016-01-01

    Sphingobium sp. strain TCM1 and Sphingomonas sp. strain TDK1 are haloalkyl phosphate flame retardant- and plasticizer-degrading bacteria. We report here the draft genome sequences of these strains to provide insights into the molecular mechanism underlying their degradation ability. PMID:27417843

  20. On constitutive relations at finite strain - Hypo-elasticity and elasto-plasticity with isotropic or kinematic hardening

    NASA Technical Reports Server (NTRS)

    Atluri, S. N.

    1984-01-01

    Nagtegaal and de Jong (1982) have studied stresses generated by simple finite shear in the case of elastic-plastic and rigid-plastic materials which exhibit anisotropic hardening. They reported that the shear stress is oscillatory in time. It was found that the occurrence of such an 'anomaly' is not restricted to anisotropic plasticity. Similar behavior in finite shear may result even in the case of hypoelasticity and classical isotropic hardening plasticity theory. The present investigation is concerned with the central problem of 'generalizing' with respect to the finite strain case, taking into account the constitutive relations of infinitesimal strain theories of classical plasticity with isotropic or kinematic hardening. The problem of hypoelasticity is also considered. It is shown that current controversies surrounding the choice of stress rate in the finite-strain generalizations of the constitutive relations and the anomalies surrounding kinematic hardening plasticity theory are easily resolvable.

  1. Strain rate, temperature and representative length scale influence on plasticity and yield stress in copper

    SciTech Connect

    Dupont, Virginie; Germann, Timothy C

    2011-01-18

    Shock compression of materials constitutes a complex process involving high strain rates, elevated temperatures and compression of the lattice. Materials properties are greatly affected by temperature, the representative length scale and the strain rate of the deformation. Experimentally, it is difficult to study the dynamic microscopic mechanisms that affect materials properties following high intensity shock loading, but they can be investigated using molecular dynamics (MD) simulations. Moreover, MD allows a better control over some parameters. We are using MD simulations to study the effect of the strain rate, representative length scale and temperature on the properties of metals during compression. A half-million-atom Cu sample is subjected to strain rates ranging from 10{sup 7} s{sup -1} to 10{sup 12} s{sup -1} at different temperatures ranging from 50K to 1500K. Single crystals as well as polycrystals are investigated. Plasticity mechanisms as well as the evolution of the micro- and macro-yield stress are observed. Our results show that the yield stress increases with increasing strain rate and decreasing temperature. We also show that the strain rate at which the transition between constant and increasing yield stress as a function of the temperature occurs increases with increasing temperature. Calculations at different grain sizes will give an insight into the grain size effect on the plasticity mechanisms and the yield stress.

  2. Analysis of plane-plastic stress problems with axial symmetry in strain-hardening range

    NASA Technical Reports Server (NTRS)

    Wu, M H Lee

    1951-01-01

    A simple method is developed for solving plane-plastic-stress problems with axial symmetry in the strain-hardening range which is based on the deformation theory of plasticity employing the finite-strain concept. The equations defining the problems are first reduced to two simultaneous nonlinear differential equations involving two dependent variables: (a) the octahedral shear strain, and (b) a parameter indicating the ratio of principal stresses. By multiplying the load and dividing the radius by an arbitrary constant, it is possible to solve these problems without iteration for any value of the modified load. The constant is determined by the boundary condition. This method is applied to a circular membrane under pressure, a rotating disk without and with a central hole, and an infinite plate with a circular hole. Two materials, inconel x and 16-25-6, the octahedral shear stress-strain relations of which do not follow the power law, are used. Distributions of octahedral shear strain, as well as of principal stresses and strains, are obtained. These results are compared with the results of the same problems in the elastic range.

  3. Substructure based modeling of nickel single crystals cycled at low plastic strain amplitudes

    NASA Astrophysics Data System (ADS)

    Zhou, Dong

    In this dissertation a meso-scale, substructure-based, composite single crystal model is fully developed from the simple uniaxial model to the 3-D finite element method (FEM) model with explicit substructures and further with substructure evolution parameters, to simulate the completely reversed, strain controlled, low plastic strain amplitude cyclic deformation of nickel single crystals. Rate-dependent viscoplasticity and Armstrong-Frederick type kinematic hardening rules are applied to substructures on slip systems in the model to describe the kinematic hardening behavior of crystals. Three explicit substructure components are assumed in the composite single crystal model, namely "loop patches" and "channels" which are aligned in parallel in a "vein matrix," and persistent slip bands (PSBs) connected in series with the vein matrix. A magnetic domain rotation model is presented to describe the reverse magnetostriction of single crystal nickel. Kinematic hardening parameters are obtained by fitting responses to experimental data in the uniaxial model, and the validity of uniaxial assumption is verified in the 3-D FEM model with explicit substructures. With information gathered from experiments, all control parameters in the model including hardening parameters, volume fraction of loop patches and PSBs, and variation of Young's modulus etc. are correlated to cumulative plastic strain and/or plastic strain amplitude; and the whole cyclic deformation history of single crystal nickel at low plastic strain amplitudes is simulated in the uniaxial model. Then these parameters are implanted in the 3-D FEM model to simulate the formation of PSB bands. A resolved shear stress criterion is set to trigger the formation of PSBs, and stress perturbation in the specimen is obtained by several elements assigned with PSB material properties a priori. Displacement increment, plastic strain amplitude control and overall stress-strain monitor and output are carried out in the user

  4. Evidence of polyethylene biodegradation by bacterial strains from the guts of plastic-eating waxworms.

    PubMed

    Yang, Jun; Yang, Yu; Wu, Wei-Min; Zhao, Jiao; Jiang, Lei

    2014-12-01

    Polyethylene (PE) has been considered nonbiodegradable for decades. Although the biodegradation of PE by bacterial cultures has been occasionally described, valid evidence of PE biodegradation has remained limited in the literature. We found that waxworms, or Indian mealmoths (the larvae of Plodia interpunctella), were capable of chewing and eating PE films. Two bacterial strains capable of degrading PE were isolated from this worm's gut, Enterobacter asburiae YT1 and Bacillus sp. YP1. Over a 28-day incubation period of the two strains on PE films, viable biofilms formed, and the PE films' hydrophobicity decreased. Obvious damage, including pits and cavities (0.3-0.4 μm in depth), was observed on the surfaces of the PE films using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The formation of carbonyl groups was verified using X-ray photoelectron spectroscopy (XPS) and microattenuated total reflectance/Fourier transform infrared (micro-ATR/FTIR) imaging microscope. Suspension cultures of YT1 and YP1 (10(8) cells/mL) were able to degrade approximately 6.1 ± 0.3% and 10.7 ± 0.2% of the PE films (100 mg), respectively, over a 60-day incubation period. The molecular weights of the residual PE films were lower, and the release of 12 water-soluble daughter products was also detected. The results demonstrated the presence of PE-degrading bacteria in the guts of waxworms and provided promising evidence for the biodegradation of PE in the environment. PMID:25384056

  5. Evolution of internal variables in an expanding hollow cylinder at large plastic strains.

    PubMed

    Alexandrov, Sergei; Dinh Kien, Nguyen; Erisov, Yaroslav; Grechnikov, Fedor

    2016-01-01

    An efficient method for calculating the evolution of internal variables in an expanding hollow cylinder of rigid/plastic material is proposed. The conventional constitutive equations for rigid plastic, hardening material are supplemented with quite an arbitrary set of evolution laws for internal variables assuming that the material is incompressible. No restriction is imposed on the hardening law. The problem is solved in Lagrangian coordinates. This significantly facilitates a numerical treatment of the problem. In particular, the initial/boundary value problem is reduced to a system of equations in characteristic coordinates. A finite difference scheme is used for solving these equations. An illustrative example is presented assuming that the internal variables are the equivalent plastic strain and a damage parameter. PMID:27066385

  6. Promoting plasticity in the spinal cord with chondroitinase improves functional recovery after peripheral nerve repair.

    PubMed

    Galtrey, Clare M; Asher, Richard A; Nothias, Fatiha; Fawcett, James W

    2007-04-01

    Functional recovery after peripheral nerve repair in humans is often disappointing. A major reason for this is the inaccuracy of re-innervation of muscles and sensory structures. We hypothesized that promoting plasticity in the spinal cord, through digestion of chondroitin sulphate proteoglycans (CSPGs) with chondroitinase ABC (ChABC), might allow the CNS to compensate for inaccurate peripheral re-innervation and improve functional recovery. The median and ulnar nerves were injured and repaired to produce three grades of inaccuracy of peripheral re-innervation by (i) crush of both nerves; (ii) correct repair of median to median and ulnar to ulnar; and (iii) crossover of the median and ulnar nerves. Mapping of the motor neuron pool of the flexor carpi radialis muscle showed precise re-innervation after nerve crush, inaccurate regeneration after correct repair, more inaccurate after crossover repair. Recovery of forelimb function, assessed by skilled paw reaching, grip strength and sensory testing varied with accuracy of re-innervation. This was not due to differences in the number of regenerated axons. Single injections of ChABC into the spinal cord led to long-term changes in the extracellular matrix, with hyaluronan and neurocan being removed and not fully replaced after 8 weeks. ChABC treatment produce increased sprouting visualized by MAP1BP staining and improved functional recovery in skilled paw reaching after correct repair and in grip strength after crossover repair. There was no hyperalgesia. Enhanced plasticity in the spinal cord, therefore, allows the CNS to compensate for inaccurate motor and sensory re-innervation of the periphery, and may be a useful adjunct therapy to peripheral nerve repair. PMID:17255150

  7. Comparison of experiment and theory for elastic-plastic plane strain crack growth

    SciTech Connect

    Hermann, L; Rice, J R

    1980-02-01

    Recent theoretical results on elastic-plastic plane strain crack growth, and experimental results for crack growth in a 4140 steel in terms of the theoretical concepts are reviewed. The theory is based on a recent asymptotic analysis of crack surface opening and strain distributions at a quasi-statically advancing crack tip in an ideally-plastic solid. The analysis is incomplete in that some of the parameters which appear in it are known only approximately, especially at large scale yielding. Nevertheless, it suffices to derive a relation between the imposed loading and amount of crack growth, prior to general yielding, based on the assumption that a geometrically similar near-tip crack profile is maintained during growth. The resulting predictions for the variation of J with crack growth are found to fit well to the experimental results obtained on deeply cracked compact specimens.

  8. Strong strain rate effect on the plasticity of amorphous silica nanowires

    SciTech Connect

    Yue, Yonghai; Zheng, Kun

    2014-06-09

    With electron-beam (e-beam) off, in-situ tensile experiments on amorphous silica nanowires (NWs) were performed inside a transmission electron microscope (TEM). By controlling the loading rates, the strain rate can be adjusted accurately in a wide range. The result shows a strong strain rate effect on the plasticity of amorphous silica NWs. At lower strain rate, the intrinsic brittle materials exhibit a pronounced elongation higher than 100% to failure with obvious necking near ambient temperature. At the strain rate higher than 5.23 × 10{sup −3}/s, the elongation of the NW decreased dramatically, and a brittle fracture feature behavior was revealed. This ductile feature of the amorphous silica NWs has been further confirmed with the in-situ experiments under optical microscopy while the effect of e-beam irradiation could be eliminated.

  9. Application Of Elastic Perfectly Plastic Cyclic Analysis To Assessment Of Creep Strain

    SciTech Connect

    Carter, Peter; Jetter, Robert I; Sham, Sam

    2012-01-01

    A cyclic elastic-perfectly plastic analysis method is proposed which provides a conservative estimate to cyclic creep strain accumulation within the ratchet boundary. The method is to check for ratcheting based on an elastic-perfectly material with a temperature-dependent pseudo yield stress defined by temperature, time and stress to give 1% creep strain. It does not require stress classification and is also applicable to a full range of temperature above and below the creep regime. This simplified method could be used as a rapid screening calculation, with full time-dependent creep analysis used if necessary.

  10. Elastic-plastic strain acceptance criterion for structures subject to rapidly applied transient dynamic loading

    SciTech Connect

    Solonick, W.

    1996-11-01

    Rapidly applied transient dynamic loads produce stresses and deflections in structures that typically exceed those from static loading conditions. Previous acceptance criteria for structures designed for rapidly applied transient dynamic loading limited stresses to those determined from elastic analysis. Different stress limits were established for different grades of structure depending upon the amount of permanent set considered acceptable. Structure allowed to sustain very limited permanent set is designed to stress limits not significantly greater than yield stress. Greater permanent set in structure under rapidly applied transient dynamic loading conditions is permitted by establishing stress limits that are significantly greater than yield stress but still provide adequate safety margin (with respect to failure). This paper presents a strain-based elastic-plastic (i.e., inelastic) analysis criterion developed as an alternative to the more conservative stress-based elastic analysis stress criterion for structures subjected to rapidly applied transient dynamic loading. The strain limits established are based on a fraction of the strain at ultimate stress obtained from an engineering stress/strain curve of the material. Strains limits are categorized by type as membrane or surface and by region as general, local, or concentrated. The application of the elastic-plastic criterion provides a more accurate, less conservative design/analysis basis for structures than that used in elastic stress-based analysis criteria, while still providing adequate safety margins.

  11. Elastic-Plastic Strain Acceptance Criteria for Structures Subject to Rapidly Applied Transient Dynamic Loading

    SciTech Connect

    W.R. Solonick

    2003-04-01

    Rapidly applied transient dynamic loads produce stresses and deflections in structures that typically exceed those from static loading conditions. Previous acceptance criteria for structures designed for rapidly applied transient dynamic loading limited stresses to those determined from elastic analysis. Different stress limits were established for different grades of structure depending upon the amount of permanent set considered acceptable. Structure allowed to sustain very limited permanent set is designed to stress limits not significantly greater than yield stress. Greater permanent set in structure under rapidly applied transient dynamic loading conditions is permitted by establishing stress limits that are significantly greater than yield stress but still provide adequate safety margin (with respect to failure). This paper presents a strain-based elastic-plastic (i.e., inelastic) analysis criterion developed as an alternative to the more conservative stress-based elastic analysis stress criterion for structures subjected to rapidly applied transient dynamic loading. The strain limits established are based on material ductility considerations only and are set as a fraction of the strain at ultimate stress obtained from an engineering stress/strain curve of the material. Strains limits are categorized by type as membrane or surface and by region as general, local , or concentrated. The application of the elastic-plastic criterion provides a more accurate, less conservative design/analysis basis for structures than that used in elastic stress-based analysis criteria, while still providing adequate safety margins.

  12. Grain-size-independent plastic flow at ultrahigh pressures and strain rates.

    PubMed

    Park, H-S; Rudd, R E; Cavallo, R M; Barton, N R; Arsenlis, A; Belof, J L; Blobaum, K J M; El-dasher, B S; Florando, J N; Huntington, C M; Maddox, B R; May, M J; Plechaty, C; Prisbrey, S T; Remington, B A; Wallace, R J; Wehrenberg, C E; Wilson, M J; Comley, A J; Giraldez, E; Nikroo, A; Farrell, M; Randall, G; Gray, G T

    2015-02-13

    A basic tenet of material science is that the flow stress of a metal increases as its grain size decreases, an effect described by the Hall-Petch relation. This relation is used extensively in material design to optimize the hardness, durability, survivability, and ductility of structural metals. This Letter reports experimental results in a new regime of high pressures and strain rates that challenge this basic tenet of mechanical metallurgy. We report measurements of the plastic flow of the model body-centered-cubic metal tantalum made under conditions of high pressure (>100  GPa) and strain rate (∼10(7)  s(-1)) achieved by using the Omega laser. Under these unique plastic deformation ("flow") conditions, the effect of grain size is found to be negligible for grain sizes >0.25  μm sizes. A multiscale model of the plastic flow suggests that pressure and strain rate hardening dominate over the grain-size effects. Theoretical estimates, based on grain compatibility and geometrically necessary dislocations, corroborate this conclusion. PMID:25723227

  13. Recovery of temperate Desulfovibrio vulgaris bacteriophage on anovel host strain

    SciTech Connect

    Walker, C.B.; Stolyar, S.S.; Pinel, N.; Yen, H.C.; He, Z.; Zhou,J.; Wall, J.D.; Stahl, D.A.

    2007-04-02

    A novel sulfate-reducing bacterium (strain DePue) closelyrelated to Desulfovibrio vulgaris ssp. vulgaris strain Hildenborough wasisolated from the sediment of a heavy-metal impacted lake usingestablished techniques. Although few physiological differences betweenstrains DePue and Hildenborough were observed, pulsed-field gelelectrophoresis (PFGE) revealed a significant genome reduction in strainDePue. Comparative whole-genome microarray and PCR analyses demonstratedthat the absence of genes annotated in the Hildenborough genome as phageor phage-related contributed to the significant genome reduction instrain DePue. Two morphotypically distinct temperate bacteriophage fromstrain Hildenborough were recovered using strain DePue as a host forplaque isolation.

  14. Strain gradient plasticity modeling of the cyclic behavior of laminate microstructures

    NASA Astrophysics Data System (ADS)

    Wulfinghoff, Stephan; Forest, Samuel; Böhlke, Thomas

    2015-06-01

    Two recently proposed Helmholtz free energy potentials including the full dislocation density tensor as an argument within the framework of strain gradient plasticity are used to predict the cyclic elastoplastic response of periodic laminate microstructures. First, a rank-one defect energy is considered, allowing for a size-effect on the overall yield strength of micro-heterogeneous materials. As a second candidate, a logarithmic defect energy is investigated, which is motivated by the work of Groma et al. (2003). The properties of the back-stress arising from both energies are investigated in the case of a laminate microstructure for which analytical as well as numerical solutions are derived. In this context, a new regularization technique for the numerical treatment of the rank-one potential is presented based on an incremental potential involving Lagrange multipliers. The results illustrate the effect of the two energies on the macroscopic size-dependent stress-strain response in monotonic and cyclic shear loading, as well as the arising pile-up distributions. Under cyclic loading, stress-strain hysteresis loops with inflections are predicted by both models. The logarithmic potential is shown to provide a continuum formulation of Asaro's type III kinematic hardening model. Experimental evidence in the literature of such loops with inflections in two-phased FFC alloys is provided, showing that the proposed strain gradient models reflect the occurrence of reversible plasticity phenomena under reverse loading.

  15. Tests and analyses for fully plastic fracture mechanics of plane strain mode I crack growth

    SciTech Connect

    McClintock, F.A.; Parks, D.M.; Kim, Y.J.

    1995-12-31

    Under monotonic loading, structures should ideally be ductile enough to provide continued resistance during crack growth. For fully plastic crack growth in low strength alloys, existing asymptotic solutions for elastic-plastic growing cracks are not applicable because they reach the fracture strain only in regions small compared to the inhomogeneities of the actual fracture process. For the limiting case of non-hardening fully-plastic plane strain crack growth, in a number of geometries and loadings the near-tip fields are characterized in terms of three parameters: an effective angle 2{theta}{sub s} between a pair of slip planes, and the normal stress {sigma}{sub s} and the increment of displacement {delta}u{sub s} across the planes. This three-parameter characterization is in contrast to the one- or two-parameter (K or J and T or Q) characterization in linear or non-linear elastic fracture mechanics. These {theta}{sub s}, {sigma}{sub s}, and {delta}u{sub s} parameters are found form the far-field geometries and loadings through slip line fields or least upper bound analyses based on circular arcs. The resulting crack growth, in terms of the crack tip opening angle (CTOA), is a function of {theta}{sub s}, {sigma}{sub s}, and the material. The geometry of the crack growing between two moving slip planes emanating from its tip reduces this function to the critical fracture shear strain left behind the slip planes, {gamma}f, as a function of {sigma}{sub s}. {gamma}f({sigma}{sub s}) is found theoretically from a hole initiation and growth model. It is also found from preliminary fully plastic crack growth experiments on unequally grooved specimens with fixed-grip extension or 4-point bending of a 1018 CF steel.

  16. A numerical basis for strain-gradient plasticity theory: Rate-independent and rate-dependent formulations

    NASA Astrophysics Data System (ADS)

    Nielsen, K. L.; Niordson, C. F.

    2014-02-01

    A numerical model formulation of the higher order flow theory (rate-independent) by Fleck and Willis [2009. A mathematical basis for strain-gradient plasticity theory - part II: tensorial plastic multiplier. Journal of the Mechanics and Physics of Solids 57, 1045-1057.], that allows for elastic-plastic loading/unloading and the interaction of multiple plastic zones, is proposed. The predicted model response is compared to the corresponding rate-dependent version of visco-plastic origin, and coinciding results are obtained in the limit of small strain-rate sensitivity. First, (i) the evolution of a single plastic zone is analyzed to illustrate the agreement with earlier published results, whereafter examples of (ii) multiple plastic zone interaction, and (iii) elastic-plastic loading/unloading are presented. Here, the simple shear problem of an infinite slab constrained between rigid plates is considered, and the effect of strain gradients, strain hardening and rate sensitivity is brought out. For clarity of results, a 1D model is constructed following a procedure suitable for generalization to 2D and 3D.

  17. Nonlinear rheology and strain recovery of short chain branched polyolefin elastomers and thermoplastic olefin blends

    NASA Astrophysics Data System (ADS)

    Patham, Bhaskar

    Polyolefin elastomers are random copolymers having a polyethylene backbone with the higher olefinic comonomer incorporated as short-chain branches. These random copolymers are widely used as polymer modifiers for thermoplastic materials such as polypropylenes, resulting in thermoplastic olefin (TPO) blends. This thesis addresses the nonlinear rheological behavior of the elastomers and then of the TPO blends. The effects of varying short chain branch density (SCB) on the melt rheology of three ethylene-octene random copolymers have been investigated. In particular, the strain-hardening behavior in extensional flow and strain recovery following nonlinear shear creep has been evaluated. The zero-shear viscosity followed trends in the backbone molecular weight closely. While the three copolymers were indistinguishable in linear viscoelastic creep and recovery, recovery following nonlinear shear creep decreased progressively with increasing SCB density. This reveals that the extent of rapid chain equilibration that occurs over Rouse time scales at higher strains was progressively lower with increasing SCB density. Strain hardening in uniaxial extensional flow was observed for all three copolymers. At strain rates below the primitive chain equilibration rates, strain hardening increases progressively with increasing SCB density. At higher rates, upon onset of primitive chain stretch, the strain hardening behavior for the three melts merges. Two thermoplastic olefin (TPO) blends were characterized in the context of injection molding; the surface morphology of injection molded tensile bars with these materials showed surface defects or flow marks to different extents. The flow marks were traced to different degrees of strain recovery in the dispersed phases of the two blends. This recovery occurred over injection molding timescales of the order of a few seconds. Strain recovery after shear creep was higher in the blend that displayed more severe flow marks in injection

  18. Statistics of plastic events in post-yield strain-controlled amorphous solids

    NASA Astrophysics Data System (ADS)

    Dubey, Awadhesh K.; Hentschel, H. George E.; Procaccia, Itamar; Singh, Murari

    2016-06-01

    Amorphous solids yield in strain-controlled protocols at a critical value of the strain. For larger strains the stress and energy display a generic complex serrated signal with elastic segments punctuated by sharp energy and stress plastic drops having a wide range of magnitudes. Here we provide a theory of the scaling properties of such serrated signals taking into account the system-size dependence. We show that the statistics are not homogeneous: they separate sharply to a regime of "small" and "large" drops, each endowed with its own scaling properties. A scaling theory is first derived solely by data analysis, showing a somewhat complex picture. But after considering the physical interpretation one discovers that the scaling behavior and the scaling exponents are in fact very simple and universal.

  19. Inelastic recovery in nano and ultrafine grained materials

    NASA Astrophysics Data System (ADS)

    Xie, Yuesong; Koslowski, Marisol

    2016-06-01

    Ultrafine and nano grained metals show plastic strain recovery upon unloading and reverse plastic strain during cyclic loading. It has been suggested that these phenomena are related to the residual stress due to grain size inhomogeneity and to grain boundary deformation mechanisms. Transmission electron microscopy (TEM) experiments indicate that dislocation structures also introduce inhomogeneous stress fields that can drive reverse plastic strain. We present dislocation dynamics simulations that show reverse plastic strain during cyclic loading even in microstructures with homogeneous grain size giving support to these TEM experiments. We also perform dislocation dynamics simulations coupled to a kinetic Monte Carlo algorithm to study thermally activated plastic strain recovery upon unloading. Our simulations show that these two plastic recovery processes are related to the formation of dislocation structures during loading, additionally grain size inhomogeneity increases the amount of plastic strain recovered.

  20. In-situ strain localization analysis in low density transformation-twinning induced plasticity steel using digital image correlation

    NASA Astrophysics Data System (ADS)

    Eskandari, M.; Yadegari-Dehnavi, M. R.; Zarei-Hanzaki, A.; Mohtadi-Bonab, M. A.; Basu, R.; Szpunar, J. A.

    2015-04-01

    The effect of deformation temperature on the strain localization has been evaluated by an adapted digital image correlation (DIC) technique during tensile deformation. The progress of strain localization was traced by the corresponding strain maps. The electron backscatter diffraction analysis and tint etching technique were utilized to determine the impact of martensitic transformation and deformation twinning on the strain localization in both elastic and plastic regimes. In elastic regime the narrow strain bands which are aligned perpendicular to the tension direction were observed in temperature range of 25 to 180 °C due to the stress-assisted epsilon martensite. The strain bands were disappeared by increasing the temperature to 300 °C and reappeared at 400 °C due to the stress-assisted deformation twinning. In plastic regime strain localization continued at 25 °C and 180 °C due to the strain-induced alfa-martensite and deformation twinning, respectively. The intensity of plastic strain localization was increased by increasing the strain due to the enhancement of martensite and twin volume fraction. The plastic strain showed more homogeneity at 300 °C due to the lack of both strain-induced martensite and deformation twinning. Effect of deformation mechanism by changing temperature on strain localization is investigated by digital image correlation. EBSD technique is served to validate deformation mechanism as well as microstructural evolution. Strain induced martensite as well as deformation twinning is activated in the present steel affecting strain localization.

  1. Measurements of growth and decay of radiation induced attenuation during the irradiation and recovery of plastic optical fibres

    NASA Astrophysics Data System (ADS)

    Kovačević, M. S.; Savović, S.; Djordjevich, A.; Bajić, J.; Stupar, D.; Kovačević, M.; Simić, S.

    2013-04-01

    In this work, we present the experimental study of the radiation-induced attenuation in step-index polymethyl-methacrylate based plastic optical fibre by exposure to low dose rate ionizing radiation. The low dose exposure has been found to induce significant permanent attenuation in plastic optical fibres. Based on the experimental results, the formula between radiation-induced attenuation and radiation dose is obtained accordingly. The recovery properties of plastic optical fibre also were investigated. The fibre begins to recover immediately after irradiation, but it does not fully recover, i.e. the irradiation leads to permanent damage of polymer.

  2. The potential environmental gains from recycling waste plastics: simulation of transferring recycling and recovery technologies to Shenyang, China.

    PubMed

    Chen, Xudong; Xi, Fengming; Geng, Yong; Fujita, Tsuyoshi

    2011-01-01

    With the increasing attention on developing a low-carbon economy, it is necessary to seek appropriate ways on reducing greenhouse gas (GHG) emissions through innovative municipal solid waste management (MSWM), such as urban symbiosis. However, quantitative assessments on the environmental benefits of urban symbiosis, especially in developing countries, are limited because only a limited number of planned synergistic activities have been successful and it is difficult to acquire detailed inventory data from private companies. This paper modifies and applies a two-step simulation system and used it to assess the potential environmental benefits, including the reduction of GHG emissions and saving of fossil fuels, by employing various Japanese plastics recycling/energy-recovery technologies in Shenyang, China. The results showed that among various recycling/energy-recovery technologies, the mechanical waste plastics recycling technology, which produces concrete formwork boards (NF boards), has the greatest potential in terms of reducing GHG emissions (1.66 kg CO(2)e/kg plastics), whereas the technology for the production of refuse plastic fuel (RPF) has the greatest potential on saving fossil fuel consumption (0.77 kg ce/kg-plastics). Additional benefits can be gained by applying combined technologies that cascade the utilization of waste plastics. Moreover, the development of clean energy in conjunction with the promotion of new waste plastics recycling programs could contribute to additional reductions in GHG emissions and fossil fuel consumption. PMID:20822893

  3. Recovery Kinetics in Commercial Purity Aluminum Deformed to Ultrahigh Strain: Model and Experiment

    NASA Astrophysics Data System (ADS)

    Yu, Tianbo; Hansen, Niels

    2016-06-01

    A new approach to analyze recovery kinetics is developed from a recent model, and microstructural observations are introduced to supplement hardness measurements. The approach involves two steps of data fitting, and the second step of fitting enables an estimation of the apparent activation energy for recovery. This approach is applied to commercial purity aluminum (AA1050) cold rolled to ultrahigh strain (99.6 pct reduction in thickness) and annealed at temperatures from 413 K to 493 K (140 °C to 220 °C). The annealing data fit the recovery model well, and the analysis shows that the apparent activation energy increases during recovery and approaches 190 kJ/mol at the end of recovery, suggesting that solute drag is an important rate-controlling mechanism. The recovery rate for the highly strained Al is found to be higher than that for Al deformed to a lower strain, an effect which is related to an increase in the stored energy (driving force). These findings form the basis for a discussion of recovery mechanisms and the increase in the apparent activation energy during annealing, suggesting an application of the model when optimizing the structure and strength through annealing of nanostructured materials produced by high strain deformation.

  4. Recovery Kinetics in Commercial Purity Aluminum Deformed to Ultrahigh Strain: Model and Experiment

    NASA Astrophysics Data System (ADS)

    Yu, Tianbo; Hansen, Niels

    2016-08-01

    A new approach to analyze recovery kinetics is developed from a recent model, and microstructural observations are introduced to supplement hardness measurements. The approach involves two steps of data fitting, and the second step of fitting enables an estimation of the apparent activation energy for recovery. This approach is applied to commercial purity aluminum (AA1050) cold rolled to ultrahigh strain (99.6 pct reduction in thickness) and annealed at temperatures from 413 K to 493 K (140 °C to 220 °C). The annealing data fit the recovery model well, and the analysis shows that the apparent activation energy increases during recovery and approaches 190 kJ/mol at the end of recovery, suggesting that solute drag is an important rate-controlling mechanism. The recovery rate for the highly strained Al is found to be higher than that for Al deformed to a lower strain, an effect which is related to an increase in the stored energy (driving force). These findings form the basis for a discussion of recovery mechanisms and the increase in the apparent activation energy during annealing, suggesting an application of the model when optimizing the structure and strength through annealing of nanostructured materials produced by high strain deformation.

  5. A new macroscopically anisotropic pressure dependent yield function for metal matrix composite based on strain gradient plasticity for the microstructure

    NASA Astrophysics Data System (ADS)

    Azizi, Reza; Nyvang Legarth, Brian; Niordson, Christian F.

    2013-04-01

    Metal matrix composites with long aligned elastic fibers are studied using an energetic rate independent strain gradient plasticity theory with an isotropic pressure independent yield function at the microscale. The material response is homogenized to obtain a conventional macroscopic model that exhibits anisotropic yield properties with a pressure dependence. At the microscale free energy includes both elastic strains and plastic strain gradients, and the theory demands higher order boundary conditions in terms of plastic strain or work conjugate higher order tractions. The mechanical response is investigated numerically using a unit cell model with periodic boundary conditions containing a single fiber deformed under generalized plane strain conditions. The homogenized response can be modeled by conventional plasticity with an anisotropic yield surface and a free energy depending on plastic strain in addition to the elastic strain. Hill's classical anisotropic yield criterion is extended to cover the composite such that hydrostatic pressure dependency, Bauschinger stress and size-effects are considered. It is found that depending on the fiber volume fraction, the anisotropic yield surface of the composite is inclined compared to a standard pressure independent yield surfaces. The evolution of the macroscopic yield surface is investigated by quantifying both anisotropic hardening (expansion) and kinematic hardening (translation), where the coefficients of anisotropy and the Bauschinger stress are extracted.

  6. Use of endochronic plasticity for multi-dimensional small and large strain problems

    SciTech Connect

    Hsieh, B.J.

    1980-04-01

    The endochronic plasticity theory was proposed in its general form by K.C. Valanis. An intrinsic time measure, which is a property of the material, is used in the theory. the explicit forms of the constitutive equation resemble closely those of the classical theory of linear viscoelasticity. Excellent agreement between the predicted and experimental results is obtained for some metallic and non-metallic materials for one dimensional cases. No reference on the use of endochronic plasticity consistent with the general theory proposed by Valanis is available in the open literature. In this report, the explicit constitutive equations are derived that are consistent with the general theory for one-dimensional (simple tension or compression), two-dimensional plane strain or stress and three-dimensional axisymmetric problems.

  7. Immune Response to Bifidobacterium bifidum Strains Support Treg/Th17 Plasticity

    PubMed Central

    López, Patricia; González-Rodríguez, Irene; Gueimonde, Miguel; Margolles, Abelardo; Suárez, Ana

    2011-01-01

    In this work we analyzed the immune activation properties of different Bifidobacterium strains in order to establish their ability as inductors of specific effector (Th) or regulatory (Treg) responses. First, we determined the cytokine pattern induced by 21 Bifidobacterium strains in peripheral blood mononuclear cells (PBMCs). Results showed that four Bifidobacterium bifidum strains showed the highest production of IL-17 as well as a poor secretion of IFNγ and TNFα, suggesting a Th17 profile whereas other Bifidobacterium strains exhibited a Th1-suggestive profile. Given the key role of Th17 subsets in mucosal defence, strains suggestive of Th17 responses and the putative Th1 Bifidobacterium breve BM12/11 were selected to stimulate dendritic cells (DC) to further determine their capability to induce the differentiation of naïve CD4+ lymphocytes toward different Th or Treg cells. All selected strains were able to induce phenotypic DC maturation, but showed differences in cytokine stimulation, DC treated with the putative Th17 strains displaying high IL-1β/IL-12 and low IL-12/IL-10 index, whereas BM12/11-DC exhibited the highest IL-12/IL-10 ratio. Differentiation of naïve lymphocytes confirmed Th1 polarization by BM12/11. Unexpectedly, any B. bifidum strain showed significant capability for Th17 generation, and they were able to generate functional Treg, thus suggesting differences between in vivo and vitro responses. In fact, activation of memory lymphocytes present in PBMCS with these bacteria, point out the presence in vivo of specific Th17 cells, supporting the plasticity of Treg/Th17 populations and the key role of commensal bacteria in mucosal tolerance and T cell reprogramming when needed. PMID:21966367

  8. High-rate Plastic Deformation of Nanocrystalline Tantalum to Large Strains: Molecular Dynamics Simulation

    SciTech Connect

    Rudd, R E

    2009-02-05

    Recent advances in the ability to generate extremes of pressure and temperature in dynamic experiments and to probe the response of materials has motivated the need for special materials optimized for those conditions as well as a need for a much deeper understanding of the behavior of materials subjected to high pressure and/or temperature. Of particular importance is the understanding of rate effects at the extremely high rates encountered in those experiments, especially with the next generation of laser drives such as at the National Ignition Facility. Here we use large-scale molecular dynamics (MD) simulations of the high-rate deformation of nanocrystalline tantalum to investigate the processes associated with plastic deformation for strains up to 100%. We use initial atomic configurations that were produced through simulations of solidification in the work of Streitz et al [Phys. Rev. Lett. 96, (2006) 225701]. These 3D polycrystalline systems have typical grain sizes of 10-20 nm. We also study a rapidly quenched liquid (amorphous solid) tantalum. We apply a constant volume (isochoric), constant temperature (isothermal) shear deformation over a range of strain rates, and compute the resulting stress-strain curves to large strains for both uniaxial and biaxial compression. We study the rate dependence and identify plastic deformation mechanisms. The identification of the mechanisms is facilitated through a novel technique that computes the local grain orientation, returning it as a quaternion for each atom. This analysis technique is robust and fast, and has been used to compute the orientations on the fly during our parallel MD simulations on supercomputers. We find both dislocation and twinning processes are important, and they interact in the weak strain hardening in these extremely fine-grained microstructures.

  9. Plastic Instability in Complex Strain Paths Predicted by Advanced Constitutive Equations

    NASA Astrophysics Data System (ADS)

    Butuc, Marilena C.; Barlat, Frédéric; Gracio, José J.; Vincze, Gabriela

    2011-08-01

    The present paper aims at predicting plastic instabilities under complex loading histories using an advanced sheet metal forming limit model. The onset of localized necking is computed using the Marciniak-Kuczinsky (MK) analysis [1] with a physically-based hardening model and the phenomenological anisotropic yield criterion Yld2000-2d [2]. The hardening model accounts for anisotropic work-hardening induced by the microstructural evolution at large strains, which was proposed by Teodosiu and Hu [3]. Simulations are carried out for linear and complex strain paths. Experimentally, two deep-drawing quality sheet metals are selected: a bake-hardening steel (BH) and a DC06 steel sheet. The validity of the model is assessed by comparing the predicted and experimental forming limits. The remarkable accuracy of the developed software to predict the forming limits under linear and non-linear strain path is obviously due to the performance of the advanced constitutive equations to describe with great detail the material behavior. The effect of strain-induced anisotropy on formability evolution under strain path changes, as predicted by the microstructural hardening model, is particularly well captured by the model.

  10. Polysialic Acid Glycomimetic Promotes Functional Recovery and Plasticity After Spinal Cord Injury in Mice

    PubMed Central

    Mehanna, Ali; Jakovcevski, Igor; Acar, Ayşe; Xiao, Meifang; Loers, Gabriele; Rougon, Geneviève; Irintchev, Andrey; Schachner, Melitta

    2009-01-01

    Regeneration after injury of the central nervous system is poor due to the abundance of molecules inhibiting axonal growth. Here we pursued to promote regeneration after thoracic spinal cord injury in young adult C57BL/6J mice using peptides which functionally mimic polysialic acid (PSA) and human natural killer cell-1 (HNK-1) glycan, carbohydrate epitopes known to promote neurite outgrowth in vitro. Subdural infusions were performed with an osmotic pump, over 2 weeks. When applied immediately after injury, the PSA mimetic and the combination of PSA and HNK-1 mimetics, but not the HNK-1 mimetic alone, improved functional recovery as assessed by locomotor rating and video-based motion analysis over a 6-week observation period. Better outcome in PSA mimetic-treated mice was associated with higher, as compared with control mice, numbers of cholinergic and glutamatergic terminals and monaminergic axons in the lumbar spinal cord, and better axonal myelination proximal to the injury site. In contrast to immediate post-traumatic application, the PSA mimetic treatment was ineffective when initiated 3 weeks after spinal cord injury. Our data suggest that PSA mimetic peptides can be efficient therapeutic tools improving, by augmenting plasticity, functional recovery when applied during the acute phase of spinal cord injury. PMID:19826404

  11. Mechanisms of microbial oil recovery by Clostridium acetobutylicum and Bacillus strain JF-2

    SciTech Connect

    Marsh, T.L.; Zhang, X.; Knapp, R.M.; McInerney, M.J.; Sharma, P.K.; Jackson, B.E.

    1995-12-31

    Core displacement experiments at elevated pressures were conducted to determine whether microbial processes are effective under conditions that simulate those found in an actual oil reservoir. The in-situ growth of Clostridium acetobutylicum and Bacillus strain JF-2 resulted in the recovery of residual oil. About 21 and 23% of the residual oil was recovered by C. acetobutylicum and Bacillus strain JF-2, respectively. Flooding cores with cell-free culture fluids of C. acetobutylicum with and without the addition of 50 mM acetone and 100 mM butanol did not result in the recovery of residual oil. Mathematical simulations showed that the amount of gas produced by the clostridial fermentation was not showed that the amount of gas produced by the clostridial fermentation was not sufficient to recover residual oil. Oil recovery by Bacillus strain JF-2 was highly correlated to surfactant production. A biosurfactant-deficient mutant of strain JF-2 was not capable of recovering residual oil. These data show that surfactant production is an important mechanism for microbially enhanced oil recovery. The mechanism for oil recovery by C. acetobutylicum is not understood at this time, but the production of acids, solvents, or gases alone cannot explain the observed increases in oil recovery by this organism.

  12. Interaction of heat production, strain rate and stress power in a plastically deforming body under tensile test

    NASA Technical Reports Server (NTRS)

    Paglietti, A.

    1982-01-01

    At high strain rates the heat produced by plastic deformation can give rise to a rate dependent response even if the material has rate independent constitutive equations. This effect has to be evaluated when interpreting a material test, or else it could erroneously be ascribed to viscosity. A general thermodynamic theory of tensile testing of elastic-plastic materials is given in this paper; it is valid for large strain at finite strain rates. It enables discovery of the parameters governing the thermodynamic strain rate effect, provides a method for proper interpretation of the results of the tests of dynamic plasticity, and suggests a way of planning experiments in order to detect the real contribution of viscosity.

  13. Recycling and recovery routes of plastic solid waste (PSW): a review.

    PubMed

    Al-Salem, S M; Lettieri, P; Baeyens, J

    2009-10-01

    Plastic solid waste (PSW) presents challenges and opportunities to societies regardless of their sustainability awareness and technological advances. In this paper, recent progress in the recycling and recovery of PSW is reviewed. A special emphasis is paid on waste generated from polyolefinic sources, which makes up a great percentage of our daily single-life cycle plastic products. The four routes of PSW treatment are detailed and discussed covering primary (re-extrusion), secondary (mechanical), tertiary (chemical) and quaternary (energy recovery) schemes and technologies. Primary recycling, which involves the re-introduction of clean scrap of single polymer to the extrusion cycle in order to produce products of the similar material, is commonly applied in the processing line itself but rarely applied among recyclers, as recycling materials rarely possess the required quality. The various waste products, consisting of either end-of-life or production (scrap) waste, are the feedstock of secondary techniques, thereby generally reduced in size to a more desirable shape and form, such as pellets, flakes or powders, depending on the source, shape and usability. Tertiary treatment schemes have contributed greatly to the recycling status of PSW in recent years. Advanced thermo-chemical treatment methods cover a wide range of technologies and produce either fuels or petrochemical feedstock. Nowadays, non-catalytic thermal cracking (thermolysis) is receiving renewed attention, due to the fact of added value on a crude oil barrel and its very valuable yielded products. But a fact remains that advanced thermo-chemical recycling of PSW (namely polyolefins) still lacks the proper design and kinetic background to target certain desired products and/or chemicals. Energy recovery was found to be an attainable solution to PSW in general and municipal solid waste (MSW) in particular. The amount of energy produced in kilns and reactors applied in this route is sufficiently

  14. Recycling and recovery routes of plastic solid waste (PSW): A review

    SciTech Connect

    Al-Salem, S.M. Lettieri, P.; Baeyens, J.

    2009-10-15

    Plastic solid waste (PSW) presents challenges and opportunities to societies regardless of their sustainability awareness and technological advances. In this paper, recent progress in the recycling and recovery of PSW is reviewed. A special emphasis is paid on waste generated from polyolefinic sources, which makes up a great percentage of our daily single-life cycle plastic products. The four routes of PSW treatment are detailed and discussed covering primary (re-extrusion), secondary (mechanical), tertiary (chemical) and quaternary (energy recovery) schemes and technologies. Primary recycling, which involves the re-introduction of clean scrap of single polymer to the extrusion cycle in order to produce products of the similar material, is commonly applied in the processing line itself but rarely applied among recyclers, as recycling materials rarely possess the required quality. The various waste products, consisting of either end-of-life or production (scrap) waste, are the feedstock of secondary techniques, thereby generally reduced in size to a more desirable shape and form, such as pellets, flakes or powders, depending on the source, shape and usability. Tertiary treatment schemes have contributed greatly to the recycling status of PSW in recent years. Advanced thermo-chemical treatment methods cover a wide range of technologies and produce either fuels or petrochemical feedstock. Nowadays, non-catalytic thermal cracking (thermolysis) is receiving renewed attention, due to the fact of added value on a crude oil barrel and its very valuable yielded products. But a fact remains that advanced thermo-chemical recycling of PSW (namely polyolefins) still lacks the proper design and kinetic background to target certain desired products and/or chemicals. Energy recovery was found to be an attainable solution to PSW in general and municipal solid waste (MSW) in particular. The amount of energy produced in kilns and reactors applied in this route is sufficiently

  15. The potential environmental gains from recycling waste plastics: Simulation of transferring recycling and recovery technologies to Shenyang, China

    SciTech Connect

    Chen Xudong; Xi Fengming; Geng Yong; Fujita, Tsuyoshi

    2011-01-15

    Research highlights: {yields} Urban symbiosis creates compatibility of industrial development and waste management. {yields} Mechanical technology leads to more CO{sub 2} emission reduction. {yields} Energy recovery technology leads to more fossil fuel saving. {yields} Clean energy makes recycling technologies cleaner. {yields} Demand management is crucial for realizing potential environmental gains of recycling. - Abstract: With the increasing attention on developing a low-carbon economy, it is necessary to seek appropriate ways on reducing greenhouse gas (GHG) emissions through innovative municipal solid waste management (MSWM), such as urban symbiosis. However, quantitative assessments on the environmental benefits of urban symbiosis, especially in developing countries, are limited because only a limited number of planned synergistic activities have been successful and it is difficult to acquire detailed inventory data from private companies. This paper modifies and applies a two-step simulation system and used it to assess the potential environmental benefits, including the reduction of GHG emissions and saving of fossil fuels, by employing various Japanese plastics recycling/energy-recovery technologies in Shenyang, China. The results showed that among various recycling/energy-recovery technologies, the mechanical waste plastics recycling technology, which produces concrete formwork boards (NF boards), has the greatest potential in terms of reducing GHG emissions (1.66 kg CO{sub 2}e/kg plastics), whereas the technology for the production of refuse plastic fuel (RPF) has the greatest potential on saving fossil fuel consumption (0.77 kgce/kg-plastics). Additional benefits can be gained by applying combined technologies that cascade the utilization of waste plastics. Moreover, the development of clean energy in conjunction with the promotion of new waste plastics recycling programs could contribute to additional reductions in GHG emissions and fossil fuel

  16. Microstructural and strain rate effects on plastic deformation in aluminum 2219-T87

    NASA Astrophysics Data System (ADS)

    Rincon, Carlos D.

    A fundamental investigation has been conducted on the effects of microstructure and strain rate on the plastic deformation of theta-prime-strengthened 2219 aluminum. The motivation for this work is based upon a previous study which showed inhomogeneous and locally extreme work hardening in the HAZ regions in VPPA 2219-T87 butt welds. This strongly suggests that the HAZ microstructure plays a major role in the deformation and fracture process in precipitation hardened aluminum alloy 2219. Tensile specimens of the weld joint exhibited more rapid work hardening in the heat-affected-zone (HAZ) at higher strain levels. Microhardness contour maps for these welds illustrated that late stage deformation was concentrated in two crossing bands at about 45sp° to the tensile axis. The width of the deformation bands and the ultimate tensile strength seemed to be dictated by the amount of work hardening in the HAZ. In this study, three different heat treatments were used to produce samples with different particle sizes and particle spacings, but all hardened by copper aluminide precipitates of the thetasp' structure. The heat treatments were categorized as being (A) as-received T87 condition, (B) T87 condition aged at approximately 204sp°C for 3 hours and (C) T87 over-aged at 204sp°C for 7 days. Uniaxial tensile tests consisted of two sets of experiments: (1) three heat treatments (A, B, and C) at two strain rates (0.02 minsp{-1} and 0.2 minsp{-1}) and (2) three heat treatments that were interrupted at select stress-strain levels (0.8% and 2% total strain) during the tensile tests at strain rate equal to 0.02 minsp{-1} at room temperature. Furthermore, a detailed transmission electron microscopy (TEM) study demonstrates the microstructural development during tensile deformation. The Voce equation of strain-hardening provides a slightly better fit to the tensile curves than the Ludwik-Hollomon equation. At higher strains, localized areas showed strain fields around thetasp

  17. Dislocation accumulation at large plastic strains -- An approach to the theoretical strength of materials

    SciTech Connect

    Embury, J.D. |; Han, K.

    1999-04-01

    The usual method of introducing engineers to the concept of dislocations and their role in plastic flow is to compare an estimate of the theoretical strength of solid (of order {micro}/30 where {micro} is the shear modulus) and the observed strength of either single crystals ({mu}/10{sup 4}) or practical engineering material such as structural steels where the yield stress in shear is of order {mu}/10{sup 3}. However, if one considers the problem in reverse, one can consider the accumulation of dislocations as an important mechanism by which one can produce engineering materials in which the strength level approaches the theoretical strength. If one assumes that the flow stress can be expressed in terms of te mean free path between stored dislocations or as the square root of the global dislocation density, then one can see the influence of dislocation density in a diagrammatic form. It is clear that the strengthening by dislocation accumulation due to large imposed plastic strains represents an important approach both to the development of new, potentially valuable, engineering materials and an important area of basic understanding in terms of the mechanical response of materials close to their theoretical strength. Thus, this article will survey some of the factors which influence dislocation accumulation at large strains and the consequences of such accumulation processes.

  18. Transformation-rate maxima during lath martensite formation: plastic vs. elastic shape strain accommodation

    NASA Astrophysics Data System (ADS)

    Loewy, Sarah; Rheingans, Bastian; Mittemeijer, Eric J.

    2016-05-01

    Recently, a modulated formation behaviour of lath martensite in Fe-Ni(-based) alloys was observed, exhibiting a series of transformation-rate maxima. This peculiar transformation behaviour was explained on the basis of the hierarchical microstructure of lath martensite, minimising the net shape strain associated with martensite formation, by a block-by-block formation of martensite packages occurring simultaneously in all packages. In the present work, the martensitic transformation upon slow cooling of two Fe-Ni alloys, containing 22 and 25 at.% of Ni, respectively, was investigated by high-resolution dilatometry with the aim of identifying the influence of alloy composition on the modulated transformation behaviour. The differences observed for the two alloys, a more rapid sequence of the transformation-rate maxima and a narrower temperature range in case of Fe-25 at.% Ni, can be explained consistently as a consequence of the lower transformation temperatures in Fe-25 at.% Ni, highlighting the role of temporary accommodation of the shape strain during formation of the lath martensite microstructure: the depression of the transformation toward lower temperatures leads to a higher strength of the austenite, hence resulting in a more elastic (less plastic) temporary accommodation of the shape strain upon block formation and thereby in a more effective mutual compensation of the shape strain by neighbouring blocks. A kinetic model on the basis of energy-change considerations is presented which is able to describe the observed modulated transformation behaviour.

  19. Efficient Recovery of Fluoroquinolone-Susceptible and Fluoroquinolone-Resistant Escherichia coli Strains From Frozen Samples

    PubMed Central

    Lautenbach, Ebbing; Santana, Evelyn; Lee, Abby; Tolomeo, Pam; Black, Nicole; Babson, Andrew; Perencevich, Eli N.; Harris, Anthony D.; Smith, Catherine A.; Maslow, Joel

    2010-01-01

    We assessed the rate of recovery of fluoroquinolone-resistant and fluoroquinolone-susceptible Escherichia coli isolates from culture of frozen perirectal swab samples compared with the results for culture of the same specimen before freezing. Recovery rates for these 2 classes of E. coli were 91% and 83%, respectively. The majority of distinct strains recovered from the initial sample were also recovered from the frozen sample. The strains that were not recovered were typically present only in low numbers in the initial sample. These findings emphasize the utility of frozen surveillance samples. PMID:18279070

  20. Efficient recovery of fluoroquinolone-susceptible and fluoroquinolone-resistant Escherichia coli strains from frozen samples.

    PubMed

    Lautenbach, Ebbing; Santana, Evelyn; Lee, Abby; Tolomeo, Pam; Black, Nicole; Babson, Andrew; Perencevich, Eli N; Harris, Anthony D; Smith, Catherine A; Maslow, Joel

    2008-04-01

    We assessed the rate of recovery of fluoroquinolone-resistant and fluoroquinolone-susceptible Escherichia coli isolates from culture of frozen perirectal swab samples compared with the results for culture of the same specimen before freezing. Recovery rates for these 2 classes of E. coli were 91% and 83%, respectively. The majority of distinct strains recovered from the initial sample were also recovered from the frozen sample. The strains that were not recovered were typically present only in low numbers in the initial sample. These findings emphasize the utility of frozen surveillance samples. PMID:18279070

  1. Mechanism of Ultrafine Grain Formation During Intense Plastic Straining in an Aluminum Alloy at Intermediate Temperatures

    SciTech Connect

    Kaibyshev, R.; Sitdikov, O.; Mazurina, I,; Lesuer, D. R.

    2000-09-21

    The mechanism of grain formation during equal channel angular extrusion (ECAE) in a 2219 Al alloy has been studied at intermediate and high temperatures. It was shown that continuous dynamic recrystallization (CDRX) occurred during intense plastic straining and resulted in the formation of submicrometer grains at temperatures ranging from 250 C to 300 C. Higher temperatures (< 300 C) hindered CDRX. This is caused by the fact that nucleation controls CDRX in the aluminum alloy. Dislocation rearrangements result in the formation of low angle boundary networks at moderate strain. The density of lattice dislocations determines the rate of subgrain formation. In addition, at lower temperatures a low energy dislocation structure (LEDS) forms concurrently with the subgrain structure and stabilizes it. The stability of the subgrain structure is very important for the resulting conversion of low angle boundaries into high angle ones with strain by extensive accumulation of mobile lattice dislocations. Increasing temperature in the range of intermediate temperatures suppresses LEDS formation and decreases the lattice dislocation density. This reduces the rate of the subgrain formation process and CDRX. As a result, at T = 400 C no recrystallized grains were found. At T = 475 C, the new grains form due to geometric dynamic recrystallization (GRX).

  2. Simple structures test for elastic-plastic strain acceptance criterion validation

    SciTech Connect

    Trimble, T.F.; Krech, G.R.

    1997-11-01

    A Simple Structures Test Program was performed where several cantilevered beam and fixed-end beam test specimens (fabricated from HY-80 steel) were subjected to a series of analytically predetermined rapidly applied transient dynamic input loads. The primary objective of the test program was to obtain dynamic nonlinear response for simple structures subjected to these load inputs. Data derived from these tests was subsequently used to correlate to analysis predictions to assess the capability to analytically predict elastic-plastic nonlinear material behavior in structures using typical time-dependent (transient) design methods and the ABAQUS finite element analysis code. The installation of a significant amount of instrumentation on these specimens and post-test measurements enabled the monitoring and recording of strain levels, displacements, accelerations, and permanent set. An assessment of modeling parameters such as the element type and mesh refinement was made using these test results. In addition, currently available material models and the incremental time step procedure used in the transient analyses were evaluated. Comparison of test data to analysis results shows that displacements, accelerations, and peak strain can be predicted with a reasonable level of accuracy using detailed solid models of the tested specimens. Permanent set is overpredicted by a factor of approximately two. However, the accuracy of the prediction of permanent set is being enhanced by updating material modeling in the ABAQUS code to account for effects of strain reversal in oscillatory behavior of dynamically loaded specimens.

  3. Language plasticity in aphasics after recovery: evidence from slow evoked potentials.

    PubMed

    Spironelli, Chiara; Angrilli, Alessandro; Pertile, Marco

    2008-04-01

    With the present experiment we sought to investigate brain plasticity underlying language recovery in a group of seventeen patients with non-fluent aphasia mainly caused by stroke. Patients were screened along three domains of measures: analysis of linguistic components by the Aachener Aphasie Test, combined mapping of their lesion from CT/MRI scans, and functional measure of the reorganized linguistic processes by means of mapping of slow evoked potentials. The spatial dimension and temporal dynamics of word processing were measured in three tasks, Phonological, Semantic and Orthographic. Compared with the matched control group, patients showed relative inhibition (decreased negativity) of left central regions in perisylvian areas, which were damaged in most subjects. In addition, reorganization of linguistic functions occurred within the left hemisphere both at frontal and posterior sites corresponding to spared brain regions. Correlations between linguistic lateralization in the three tasks and AAT subtests point to functional reorganization of phonological processes over left frontal sites and dysfunctional reorganization of semantic processing over left posterior regions. PMID:18252272

  4. Recovery of biological motion perception and network plasticity after cerebellar tumor removal.

    PubMed

    Sokolov, Arseny A; Erb, Michael; Grodd, Wolfgang; Tatagiba, Marcos S; Frackowiak, Richard S J; Pavlova, Marina A

    2014-10-01

    Visual perception of body motion is vital for everyday activities such as social interaction, motor learning or car driving. Tumors to the left lateral cerebellum impair visual perception of body motion. However, compensatory potential after cerebellar damage and underlying neural mechanisms remain unknown. In the present study, visual sensitivity to point-light body motion was psychophysically assessed in patient SL with dysplastic gangliocytoma (Lhermitte-Duclos disease) to the left cerebellum before and after neurosurgery, and in a group of healthy matched controls. Brain activity during processing of body motion was assessed by functional magnetic resonance imaging (MRI). Alterations in underlying cerebro-cerebellar circuitry were studied by psychophysiological interaction (PPI) analysis. Visual sensitivity to body motion in patient SL before neurosurgery was substantially lower than in controls, with significant improvement after neurosurgery. Functional MRI in patient SL revealed a similar pattern of cerebellar activation during biological motion processing as in healthy participants, but located more medially, in the left cerebellar lobules III and IX. As in normalcy, PPI analysis showed cerebellar communication with a region in the superior temporal sulcus, but located more anteriorly. The findings demonstrate a potential for recovery of visual body motion processing after cerebellar damage, likely mediated by topographic shifts within the corresponding cerebro-cerebellar circuitry induced by cerebellar reorganization. The outcome is of importance for further understanding of cerebellar plasticity and neural circuits underpinning visual social cognition. PMID:25017648

  5. Slow plastic strain rate compressive flow in binary CoAl intermetallics

    NASA Technical Reports Server (NTRS)

    Whittenberger, J. D.

    1985-01-01

    Constant-velocity elevated temperature compression tests have been conducted on a series of binary CoAl intermetallics produced by hot extrusion of blended prealloyed powders. The as-extruded materials were polycrystalline, and they retained their nominal 10-micron grain size after being tested between 1100 and 1400 K at strain rates ranging from 2 x 10 to the -4th to 2 x 10 to the -7th per sec. Significant plastic flow was obtained in all cases; while cracking was observed, much of this could be due to failure at matrix-oxide interfaces along extrusion stringers rather than to solely intergranular fracture. A maximum in flow strength occurs at an aluminum-to-cobalt ratio of 0.975, and the stress exponent appears to be constant for aluminum-to-cobalt ratios of 0.85 or more. It is likely that very aluminum-deficient materials deform by a different mechanism than do other compositions.

  6. New regimes of plastic flow at very high pressures and strain rates

    NASA Astrophysics Data System (ADS)

    Remington, Bruce

    2015-06-01

    Recent progress in understanding solid-state plastic flow at very high pressures and strain rates for high energy density (HED) science will be described. These results are relevant to hypervelocity impacts, space hardware durability, planetary formation dynamics, advanced designs for inertial confinement fusion, and basic HED science. We use high power lasers to study the Rayleigh-Taylor and Richtmyer-Meshkov hydrodynamic instability evolution in the solid state plastic flow regime on the Janus, Omega, and NIF lasers, spanning peak pressures from 10 - 500 GPa (0.1 - 5 Mbar). We are pursuing time resolved diffraction experiments to understand the lattice level dynamics resulting from high rate compression of samples. EXAFS experiments probe the atomic level structure and phase, and provide a volume-averaged temperature. We use the very bright, high time resolution x-ray probe at LCLS to examine the detailed lattice response and time evolution right behind the shock front. And finally, shock driven samples are recovered so that the residual microstructure caused by the shock can be examined by SEM, TEM, and other characterization techniques. An overview of these recent results, with comparisons to theory and simulations, will be given. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

  7. 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.

  8. Strain recovery in dual cross-linked polymer grafted nanoparticle networks

    NASA Astrophysics Data System (ADS)

    v S, Balaji; Yashin, Victor; Salib, Isaac; Kowalewski, Tomasz; Matyjaszewski, Krzystof; Balazs, Anna; Anna Balazs Collaboration; Krzystof Matyjaszewski Collaboration

    2013-03-01

    Via computational modeling, we investigate the mechanism of strain-recovery in dual cross-linked polymer grafted nanoparticle networks. The individual nanoparticles are composed of a rigid core and a corona of grafted polymers that encompass reactive end groups. With the overlap of the coronas on adjacent particles, the reactive end groups form permanent or labile bonds, and thus form a ``dual cross-linked'' network. We consider the strain recovery of the material after it is allowed to relax from the application of the tensile force. We apply multiple cycles of tension and relaxation and determine how the stress-strain curves change in the course of these repetitive deformations. Notably, the existing labile bonds can break and new bonds can form in the course of deformation. Hence, a damaged material could be ``rejuvenated'' both in terms of the recovery of strain and the number of bonds, if the relaxation occurs over a sufficiently long time. We show that this rejuvenation depends on the fraction of permanent bonds, strength of labile bonds, and maximal strain.

  9. Direct synchrotron x-ray measurements of local strain fields in elastically and plastically bent metallic glasses

    SciTech Connect

    Wu, Yuan; Stoica, Alexandru Dan; Ren, Yang; Ma, Dong; Gao, Yanfei F.; Bei, Hongbin

    2015-09-03

    In situ high-energy synchrotron X-ray diffraction was conducted on elastically and plastically bent bulk metallic glass (BMG) thin plates, from which distinct local elastic strain fields were mapped spatially. These directly measured residual strain fields can be nicely interpreted by our stress analysis, and also validate a previously proposed indirect residual-stress-measurement method by relating nanoindentation hardness to residual stresses. Local shear strain variations on the cross sections of these thin plates were found in the plastically bent BMG, which however cannot be determined from the indirect indentation method. As a result, this study has important implications in designing and manipulating internal strain fields in BMGs for the purpose of ductility enhancement.

  10. Direct synchrotron x-ray measurements of local strain fields in elastically and plastically bent metallic glasses

    DOE PAGESBeta

    Wu, Yuan; Stoica, Alexandru Dan; Ren, Yang; Ma, Dong; Gao, Yanfei F.; Bei, Hongbin

    2015-09-03

    In situ high-energy synchrotron X-ray diffraction was conducted on elastically and plastically bent bulk metallic glass (BMG) thin plates, from which distinct local elastic strain fields were mapped spatially. These directly measured residual strain fields can be nicely interpreted by our stress analysis, and also validate a previously proposed indirect residual-stress-measurement method by relating nanoindentation hardness to residual stresses. Local shear strain variations on the cross sections of these thin plates were found in the plastically bent BMG, which however cannot be determined from the indirect indentation method. As a result, this study has important implications in designing and manipulatingmore » internal strain fields in BMGs for the purpose of ductility enhancement.« less

  11. Experimental investigation of the quality characteristics of agricultural plastic wastes regarding their recycling and energy recovery potential

    SciTech Connect

    Briassoulis, D.; Hiskakis, M.; Babou, E.; Antiohos, S.K.; Papadi, C.

    2012-06-15

    Highlights: Black-Right-Pointing-Pointer Definition of parameters characterising agricultural plastic waste (APW) quality. Black-Right-Pointing-Pointer Analysis of samples to determine APW quality for recycling or energy recovery. Black-Right-Pointing-Pointer Majority of APW samples from various countries have very good quality for recycling. Black-Right-Pointing-Pointer Upper limit of 50% w/w soil contamination in APW acceptable for energy recovery. Black-Right-Pointing-Pointer Chlorine and heavy metals content in APW below the lowest limit for energy recovery. - Abstract: A holistic environmentally sound waste management scheme that transforms agricultural plastic waste (APW) streams into labelled guaranteed quality commodities freely traded in open market has been developed by the European research project LabelAgriWaste. The APW quality is defined by the APW material requirements, translated to technical specifications, for recycling or energy recovery. The present work investigates the characteristics of the APW quality and the key factors affecting it from the introduction of the virgin product to the market to the APW stream reaching the disposer. Samples of APW from different countries were traced from their application to the field through their storage phase and transportation to the final destination. The test results showed that the majority of APW retained their mechanical properties after their use preserving a 'very good quality' for recycling in terms of degradation. The degree of soil contamination concerning the APW recycling and energy recovery potential fluctuates depending on the agricultural plastic category and application. The chlorine and heavy metal content of the tested APW materials was much lower than the maximum acceptable limits for their potential use in cement industries.

  12. Novel Ti-base superelastic alloys with large recovery strain and excellent biocompatibility.

    PubMed

    Fu, Jie; Yamamoto, Akiko; Kim, Hee Young; Hosoda, Hideki; Miyazaki, Shuichi

    2015-04-01

    In this study, a new Ti-Zr-Nb-Sn alloy system was developed as Ni-free biomedical superelastic alloys with a large recovery strain and excellent biocompatibility. Ti-18Zr-(9-16)Nb-(0-4)Sn alloys were prepared by an Ar arc melting method and the effect of composition on the crystal structure and superelastic properties was investigated. A large superelastic recovery strain of 6.0% was observed in Ti-18Zr-12.5Nb-2Sn, Ti-18Zr-11Nb-3Sn, and Ti-18Zr-9.5Nb-4Sn alloys subjected to cold-rolling and solution treatment. XRD results showed that the large recovery strain of Sn-added alloys is due to a combination effect of a large transformation strain and a strong recrystallization texture. The Ti-18Zr-11Nb-3Sn alloy exhibited excellent cyclic stability with an extremely narrow stress hysteresis about 20MPa. Cytocompatibility was also examined using three types of cell lines, murine fibroblast L929, human osteosarcoma SaOS-2, and human umbilical vein endothelial cell HUVEC and the results showed that the Ti-18Zr-11Nb-3Sn alloy exhibited larger cell covering ratios when compared with those of the Ti-50.5Ni alloy for all kinds of cells. PMID:25676584

  13. Recovery and recycling of plastic wastes. (Latest citations from Oollution Abstracts). Published Search

    SciTech Connect

    Not Available

    1993-02-01

    The bibliography contains citations concerning the recycling of plastics from municipal waste streams, landfills, and scrap from industrial processes. Topics include major advances in industry-led plastics recycling, equipment needed for reprocessing scrap plastic into useful materials, and markets for recycled products. The citations also discuss the types of plastics most economical to recycle and those least likely to be contaminated with toxic or carcinogenic materials which would make reprocessing hazardous. Successful recycling programs developed in Japan and western European countries are detailed. (Contains a minimum of 206 citations and includes a subject term index and title list.)

  14. Recovery and recycling of plastic wastes. (Latest citations from Pollution abstracts). Published Search

    SciTech Connect

    1997-11-01

    The bibliography contains citations concerning the recycling of plastics from municipal waste streams, landfills, and scrap from industrial processes. Topics include major advances in industry-led plastics recycling, equipment needed for reprocessing scrap plastic into useful materials, and markets for recycled products. The citations also discuss the types of plastics most economical to recycle and those least likely to be contaminated with toxic or carcinogenic materials which would make reprocessing hazardous. Successful recycling programs developed in Japan and western European countries are detailed.(Contains 50-250 citations and includes a subject term index and title list.) (Copyright NERAC, Inc. 1995)

  15. Recovery and recycling of plastic wastes. (Latest citations from Pollution abstracts). Published Search

    SciTech Connect

    1996-10-01

    The bibliography contains citations concerning the recycling of plastics from municipal waste streams, landfills, and scrap from industrial processes. Topics include major advances in industry-led plastics recycling, equipment needed for reprocessing scrap plastic into useful materials, and markets for recycled products. The citations also discuss the types of plastics most economical to recycle and those least likely to be contaminated with toxic or carcinogenic materials which would make reprocessing hazardous. Successful recycling programs developed in Japan and western European countries are detailed. (Contains 50-250 citations and includes a subject term index and title list.) (Copyright NERAC, Inc. 1995)

  16. Recovery and recycling of plastic wastes. (Latest citations from Pollution abstracts). NewSearch

    SciTech Connect

    Not Available

    1994-10-01

    The bibliography contains citations concerning the recycling of plastics from municipal waste streams, landfills, and scrap from industrial processes. Topics include major advances in industry-led plastics recycling, equipment needed for reprocessing scrap plastic into useful materials, and markets for recycled products. The citations also discuss the types of plastics most economical to recycle and those least likely to be contaminated with toxic or carcinogenic materials which would make reprocessing hazardous. Successful recycling programs developed in Japan and western European countries are detailed. (Contains a minimum of 220 citations and includes a subject term index and title list.)

  17. Recovery and recycling of plastic wastes. (Latest citations from Pollution abstracts). Published Search

    SciTech Connect

    1995-10-01

    The bibliography contains citations concerning the recycling of plastics from municipal waste streams, landfills, and scrap from industrial processes. Topics include major advances in industry-led plastics recycling, equipment needed for reprocessing scrap plastic into useful materials, and markets for recycled products. The citations also discuss the types of plastics most economical to recycle and those least likely to be contaminated with toxic or carcinogenic materials which would make reprocessing hazardous. Successful recycling programs developed in Japan and western European countries are detailed.(Contains 50-250 citations and includes a subject term index and title list.) (Copyright NERAC, Inc. 1995)

  18. Partial cordierite breakdown during post-seismic recovery: the significance of plastic deformation for cation diffusion and metamorphic equilibrium

    NASA Astrophysics Data System (ADS)

    Büttner, Steffen; Costin, Gelu

    2010-05-01

    Brittle intra-crystal fracturing occurred during a microseismic event in migmatites of the Ordovician Sierras Pampeanas (NW Argentina), forming micro-shear zones and brittle fragments in cordierite. The seismic event occurred at amphibolite facies P-T conditions under high strain rates (≥ 10-7 s-1). During post-seismic recovery and coarsening of crystal fragments, primary cordierite (XMg=0.65) underwent partial breakdown along the deformation zone, forming a secondary mineral assemblage in an alteration zone along grain boundaries of coarsened crystal fragments. The secondary assemblage is restricted to the recovery zone. The breakdown of primary cordierite (CrdP) is accompanied by the formation of secondary sillimanite, magnetite, staurolite (XMg=0.24, ~0.5 wt% ZnO), quartz, and secondary cordierite (CrdS; XMg=0.70-0.80). CrdS, volumetrically the most important secondary phase, forms by diffusion of Mg and Fe, altering CrdP by Fe loss and uptake of Mg. All other secondary phases form by nucleation. Two simultaneous cordierite breakdown reactions have been balanced using CSpace 1.01: 100 CrdP (XMg 0.65) = 21.8 Sil +12.8 Mag + 33.5 Qtz + 5.6 H2O + 89.1 CrdS (XMg 0.75) 100 CrdP (XMg0.65) = 8.1 Mag + 53.6 Qtz + 4.5 H2O + 8.1 St (XMg0.24) + 83.3 CrdS (XMg 0.75) The bulk chemical major element composition of the alteration zone is nearly identical to the composition of primary cordierite, suggesting that elemental exchange between the alteration zone and the cordierite matrix is limited. However, minor fluid influx, supplying Zn, K, Si, and O is indicated by the composition of staurolite, minor formation of biotite and quartz, and by the oxidation of Fe2+ within the alteration zone. The modal composition of the alteration zone has been determined by point counting, which yields similar results like CSpace results (converted into vol%), and MODAN calculations, which calculates modes based on the average alteration zone composition, and the compositions of secondary

  19. Exopolysaccharide production by a genetically engineered Enterobacter cloacae strain for microbial enhanced oil recovery.

    PubMed

    Sun, Shanshan; Zhang, Zhongzhi; Luo, Yijing; Zhong, Weizhang; Xiao, Meng; Yi, Wenjing; Yu, Li; Fu, Pengcheng

    2011-05-01

    Microbial enhanced oil recovery (MEOR) is a petroleum biotechnology for manipulating function and/or structure of microbial environments existing in oil reservoirs for prolonged exploitation of the largest source of energy. In this study, an Enterobacter cloacae which is capable of producing water-insoluble biopolymers at 37°C and a thermophilic Geobacillus strain were used to construct an engineered strain for exopolysaccharide production at higher temperature. The resultant transformants, GW3-3.0, could produce exopolysaccharide up to 8.83 g l(-1) in molasses medium at 54°C. This elevated temperature was within the same temperature range as that for many oil reservoirs. The transformants had stable genetic phenotype which was genetically fingerprinted by RAPD analysis. Core flooding experiments were carried out to ensure effective controlled profile for the simulation of oil recovery. The results have demonstrated that this approach has a promising application potential in MEOR. PMID:21444201

  20. Forced arm use is superior to voluntary training for motor recovery and brain plasticity after cortical ischemia in rats

    PubMed Central

    2014-01-01

    Background and purpose Both the immobilization of the unaffected arm combined with physical therapy (forced arm use, FAU) and voluntary exercise (VE) as model for enriched environment are promising approaches to enhance recovery after stroke. The genomic mechanisms involved in long-term plasticity changes after different means of rehabilitative training post-stroke are largely unexplored. The present investigation explored the effects of these physical therapies on behavioral recovery and molecular markers of regeneration after experimental ischemia. Methods 42 Wistar rats were randomly treated with either forced arm use (FAU, 1-sleeve plaster cast onto unaffected limb at 8/10 days), voluntary exercise (VE, connection of a freely accessible running wheel to cage), or controls with no access to a running wheel for 10 days starting at 48 hours after photothrombotic stroke of the sensorimotor cortex. Functional outcome was measured using sensorimotor test before ischemia, after ischemia, after the training period of 10 days, at 3 and 4 weeks after ischemia. Global gene expression changes were assessed from the ipsi- and contralateral cortex and the hippocampus. Results FAU-treated animals demonstrated significantly improved functional recovery compared to the VE-treated group. Both were superior to cage control. A large number of genes are altered by both training paradigms in the ipsi- and contralateral cortex and the hippocampus. Overall, the extent of changes observed correlated well with the functional recovery obtained. One category of genes overrepresented in the gene set is linked to neuronal plasticity processes, containing marker genes such as the NMDA 2a receptor, PKC ζ, NTRK2, or MAP 1b. Conclusions We show that physical training after photothrombotic stroke significantly and permanently improves functional recovery after stroke, and that forced arm training is clearly superior to voluntary running training. The behavioral outcomes seen correlate with

  1. Metaplasticity and behavior: how training and inflammation affect plastic potential within the spinal cord and recovery after injury

    PubMed Central

    Grau, James W.; Huie, J. Russell; Lee, Kuan H.; Hoy, Kevin C.; Huang, Yung-Jen; Turtle, Joel D.; Strain, Misty M.; Baumbauer, Kyle M.; Miranda, Rajesh M.; Hook, Michelle A.; Ferguson, Adam R.; Garraway, Sandra M.

    2014-01-01

    Research has shown that spinal circuits have the capacity to adapt in response to training, nociceptive stimulation and peripheral inflammation. These changes in neural function are mediated by physiological and neurochemical systems analogous to those that support plasticity within the hippocampus (e.g., long-term potentiation and the NMDA receptor). As observed in the hippocampus, engaging spinal circuits can have a lasting impact on plastic potential, enabling or inhibiting the capacity to learn. These effects are related to the concept of metaplasticity. Behavioral paradigms are described that induce metaplastic effects within the spinal cord. Uncontrollable/unpredictable stimulation, and peripheral inflammation, induce a form of maladaptive plasticity that inhibits spinal learning. Conversely, exposure to controllable or predictable stimulation engages a form of adaptive plasticity that counters these maladaptive effects and enables learning. Adaptive plasticity is tied to an up-regulation of brain derived neurotrophic factor (BDNF). Maladaptive plasticity is linked to processes that involve kappa opioids, the metabotropic glutamate (mGlu) receptor, glia, and the cytokine tumor necrosis factor (TNF). Uncontrollable nociceptive stimulation also impairs recovery after a spinal contusion injury and fosters the development of pain (allodynia). These adverse effects are related to an up-regulation of TNF and a down-regulation of BDNF and its receptor (TrkB). In the absence of injury, brain systems quell the sensitization of spinal circuits through descending serotonergic fibers and the serotonin 1A (5HT 1A) receptor. This protective effect is blocked by surgical anesthesia. Disconnected from the brain, intracellular Cl- concentrations increase (due to a down-regulation of the cotransporter KCC2), which causes GABA to have an excitatory effect. It is suggested that BDNF has a restorative effect because it up-regulates KCC2 and re-establishes GABA-mediated inhibition

  2. Influence of material parameters and crystallography on the size effects describable by means of strain gradient plasticity

    NASA Astrophysics Data System (ADS)

    Bardella, Lorenzo; Giacomini, Alessandro

    In the context of single-crystal strain gradient plasticity, we focus on the simple shear of a constrained strip in order to study the effects of the material parameters possibly involved in the modelling. The model consists of a deformation theory suggested and left undeveloped by Bardella [(2007). Some remarks on the strain gradient crystal plasticity modelling, with particular reference to the material length scales involved. Int. J. Plasticity 23, 296-322] in which, for each glide, three dissipative length scales are considered; they enter the model through the definition of an effective slip which brings into the isotropic hardening function the relevant plastic strain gradients, averaged by means of a p-norm. By means of the defect energy (i.e., a function of Nye's dislocation density tensor added to the free energy; see, e.g., Gurtin [2002. A gradient theory of single-crystal viscoplasticity that accounts for geometrically necessary dislocations. J. Mech. Phys. Solids 50, 5-32]), the model further involves an energetic material length scale. The application suggests that two dissipative length scales may be enough to qualitatively describe the size effect of metals at the microscale, and they are chosen in such a way that the higher-order state variables of the model be the dislocation densities. Moreover, we show that, depending on the crystallography, the size effect governed by the defect energy may be different from what expected (based on the findings of [Bardella, L., 2006. A deformation theory of strain gradient crystal plasticity that accounts for geometrically necessary dislocations. J. Mech. Phys. Solids 54, 128-160] and [Gurtin et al. 2007. Gradient single-crystal plasticity with free energy dependent on dislocation densities. J. Mech. Phys. Solids 55, 1853-1878]), leading mostly to some strengthening. In order to investigate the model capability, we also exploit a Γ-convergence technique to find closed-form solutions in the "isotropic limit

  3. A Modeling Investigation of Thermal and Strain Induced Recovery and Nonlinear Hardening in Potential Based Viscoplasticity

    NASA Technical Reports Server (NTRS)

    Arnold, S. M.; Saleeb, A. F.; Wilt, T. E.

    1993-01-01

    Specific forms for both the Gibb's and the complementary dissipation potentials were chosen such that a complete potential based multiaxial, isothermal, viscoplastic model was obtained. This model in general possesses three internal state variables (two scalars associated with dislocation density and one tensor associated with dislocation motion) both thermal and dynamic recovery mechanisms, and nonlinear kinematic hardening. This general model, although possessing associated flow and evolutionary laws, is shown to emulate three distinct classes of theories found in the literature, by modification of the driving threshold function F. A parametric study was performed on a specialized nondimensional multiaxial form containing only a single tensorial internal state variable (i.e., internal stress). The study was conducted with the idea of examining the impact of including a strain-induced recovery mechanism and the compliance operator, derived from the Gibb's potential, on the uniaxial and multiaxial response. One important finding was that inclusion of strain recovery provided the needed flexibility in modeling stress-strain and creep response of metals at low homologous temperatures, without adversely affecting the high temperature response. Furthermore, for nonproportional loading paths, the inclusion of the compliance operator had a significant influence on the multiaxial response, but had no influence on either uniaxial or proportional load histories.

  4. Developmental and waste reduction plasticity of three black soldier fly strains (Diptera: Stratiomyidae) raised on different livestock manures.

    PubMed

    Zhou, Fen; Tomberlin, Jeffery K; Zheng, Longyu; Yu, Ziniu; Zhang, Jibin

    2013-11-01

    Black soldier flies, Hermetia illucens L., are distributed throughout the temperate and tropic regions of the world and are known an established method for sustainably managing animal wastes. Colonies used to conduct research on the black soldier fly within the past 20 yr have predominately been established from eggs or larvae received from a colony originated from Bacon County, GA. Consequently, little is known about the phenotypic plasticity (i.e., development and waste conversion) across strains from different regions. This study compared the development of three strains of the black soldier fly (Texas; Guangzhou, China; and Wuhan, China) and their ability to reduce dry matter and associated nutrients in swine, dairy, and chicken manure. The Wuhan strain appeared to be more fit. Larvae from Wuhan needed 17.7-29.9% less time to reach the prepupal stage than those from Guangzhou or Texas, respectively. Larvae from Wuhan weighed 14.4-37.0% more than those from Guanghzhou or Texas, respectively. Larvae from the Wuhan strain reduced dry matter 46.0% (swine), 40.1% (dairy), and 48.4% (chicken) more than the Guangzhou strain and 6.9, 7.2, and 7.9% more than the Texas strain. This study demonstrates that phenotypic plasticity (e.g., development and waste conversion) varies across populations of black soldier flies and should be taken into account when selecting and establishing a population as a waste management agent in a given region of the world. PMID:24843926

  5. Parametric analysis of plastic strain and force distribution in single pass metal spinning

    NASA Astrophysics Data System (ADS)

    Choudhary, Shashank; Tejesh, Chiruvolu Mohan; Regalla, Srinivasa Prakash; Suresh, Kurra

    2013-12-01

    Metal spinning also known as spin forming is one of the sheet metal working processes by which an axis-symmetric part can be formed from a flat sheet metal blank. Parts are produced by pressing a blunt edged tool or roller on to the blank which in turn is mounted on a rotating mandrel. This paper discusses about the setting up a 3-D finite element simulation of single pass metal spinning in LS-Dyna. Four parameters were considered namely blank thickness, roller nose radius, feed ratio and mandrel speed and the variation in forces and plastic strain were analysed using the full-factorial design of experiments (DOE) method of simulation experiments. For some of these DOE runs, physical experiments on extra deep drawing (EDD) sheet metal were carried out using En31 tool on a lathe machine. Simulation results are able to predict the zone of unsafe thinning in the sheet and high forming forces that are hint to the necessity for less-expensive and semi-automated machine tools to help the household and small scale spinning workers widely prevalent in India.

  6. Parametric analysis of plastic strain and force distribution in single pass metal spinning

    SciTech Connect

    Choudhary, Shashank E-mail: mohantejesh93@gmail.com E-mail: ksuresh@hyderabad.bits-pilani.ac.in; Tejesh, Chiruvolu Mohan E-mail: mohantejesh93@gmail.com E-mail: ksuresh@hyderabad.bits-pilani.ac.in; Regalla, Srinivasa Prakash E-mail: mohantejesh93@gmail.com E-mail: ksuresh@hyderabad.bits-pilani.ac.in; Suresh, Kurra E-mail: mohantejesh93@gmail.com E-mail: ksuresh@hyderabad.bits-pilani.ac.in

    2013-12-16

    Metal spinning also known as spin forming is one of the sheet metal working processes by which an axis-symmetric part can be formed from a flat sheet metal blank. Parts are produced by pressing a blunt edged tool or roller on to the blank which in turn is mounted on a rotating mandrel. This paper discusses about the setting up a 3-D finite element simulation of single pass metal spinning in LS-Dyna. Four parameters were considered namely blank thickness, roller nose radius, feed ratio and mandrel speed and the variation in forces and plastic strain were analysed using the full-factorial design of experiments (DOE) method of simulation experiments. For some of these DOE runs, physical experiments on extra deep drawing (EDD) sheet metal were carried out using En31 tool on a lathe machine. Simulation results are able to predict the zone of unsafe thinning in the sheet and high forming forces that are hint to the necessity for less-expensive and semi-automated machine tools to help the household and small scale spinning workers widely prevalent in India.

  7. Inhibitory Plasticity Facilitates Recovery of Stimulus Velocity Tuning in the Superior Colliculus after Chronic NMDA Receptor Blockade

    PubMed Central

    Razak, Khaleel A.; Pallas, Sarah L.

    2016-01-01

    The developing nervous system is shaped in important ways by spontaneous and stimulus-driven neural activity. Perturbation of normal activity patterns can profoundly affect the development of some neural response properties, whereas others are preserved through mechanisms that either compensate for or are unaffected by the perturbation. Most studies have examined the role of excitation in activity-dependent plasticity of response properties. Here, we examine the role of inhibition within the context of response selectivity for moving stimuli. The spatial extent of retinal input to the developing hamster superior colliculus (SC) can be experimentally increased by chronic NMDA receptor (NMDAR) blockade. Remarkably, stimulus velocity tuning is intact despite the increase in excitatory inputs. The goal of this study was to investigate whether plasticity in surround inhibition might provide the mechanism underlying this preservation of velocity tuning. Surround inhibition shapes velocity tuning in the majority of superficial layer SC neurons in normal hamsters. We show that despite the NMDAR blockade-induced increase in feedforward excitatory convergence from the retina, stimulus velocity tuning in the SC is maintained via compensatory plasticity in surround inhibition. The inhibitory surround increased in strength and spatial extent, and surround inhibition made a larger contribution to velocity tuning in the SC after chronic NMDAR blockade. These results show that inhibitory plasticity can preserve the balance between excitation and inhibition that is necessary to preserve response properties after developmental manipulations of neural activity. Understanding these compensatory mechanisms may permit their use to facilitate recovery from trauma or sensory deprivation. PMID:17611280

  8. Job strain and vagal recovery during sleep in shift working health care professionals.

    PubMed

    Karhula, Kati; Henelius, Andreas; Härmä, Mikko; Sallinen, Mikael; Lindholm, Harri; Kivimäki, Mika; Vahtera, Jussi; Puttonen, Sampsa

    2014-12-01

    Within sample female nurses/nurse assistants in three shift work, we explored the association of job strain with heart rate variability before and during sleep. The participants (n = 95) were recruited from the Finnish Public Sector Study, from hospital wards that belonged either to the top (high job strain [HJS], n = 42) or bottom quartiles on job strain (low job strain [LJS], n = 53) as rated by Job Content Questionnaire responses. A further inclusion criterion was that participants' own job strain was at least as high (HJS group) or low (LJS group) as their ward's average estimation. Three-week field measurements included sleep diary and actigraphy to study the participants' sleep patterns and sleep-wake rhythm. A subset of three pre-selected, circadian rhythm and recovery controlled measurement days, one morning shift, one night shift and a day off, included 24-h heart rate variability (HRV) measurements. The bootstrapped HRV parameters (HR, HF, LF, LF-to-HF-ratio and RMSSD) 30 min before and during 30 min of sleep with lowest average heart rate showed no statistically significant job strain group differences. No association of exposure to stressful work environment and HRV before and during sleep was found. PMID:25216071

  9. Recovery of PET from packaging plastics mixtures by wet shaking table.

    PubMed

    Carvalho, M T; Agante, E; Durão, F

    2007-01-01

    Recycling requires the separation of materials appearing in a mass of wastes of heterogeneous composition and characteristics, into single, almost pure, component/material flows. The separation of materials (e.g., some types of plastics) with similar physical properties (e.g., specific gravity) is often accomplished by human sorting. This is the case of the separation of packaging plastics in municipal solid wastes (MSW). The low cost of virgin plastics and low value of recycled plastics necessitate the utilization of low cost techniques and processes in the recycling of packaging plastics. An experimental study was conducted to evaluate the feasibility of production of a PET product, cleaned from PVC and PS, using a wet shaking table. The wet shaking table is an environmentally friendly process, widely used to separate minerals, which has low capital and operational costs. Some operational variables of the equipment, as well as different feed characteristics, were considered. The results show that the separation of these plastics is feasible although, similarly to the mineral field, in somewhat complex flow sheets. PMID:17118640

  10. Creep recovery and stress relaxation tests of 6061-0 aluminum

    NASA Technical Reports Server (NTRS)

    Wu, H. C.; Yao, J. C.

    1981-01-01

    The investigation of creep recovery and stress relaxation in aluminum using a closed loop servo-hydraulic test system is described. The practicality of a computer controlled test system for constant plastic strain rate tension tests is demonstrated. The plastic strain rate and the magnitude of the initial strain are shown to have a noticeable effect on subsequent creep behavior of aluminum.

  11. A model for plasticity kinetics and its role in simulating the dynamic behavior of Fe at high strain rates

    SciTech Connect

    Colvin, J D; Minich, R W; Kalantar, D H

    2007-03-29

    The recent diagnostic capability of the Omega laser to study solid-solid phase transitions at pressures greater than 10 GPa and at strain rates exceeding 10{sup 7} s{sup -1} has also provided valuable information on the dynamic elastic-plastic behavior of materials. We have found, for example, that plasticity kinetics modifies the effective loading and thermodynamic paths of the material. In this paper we derive a kinetics equation for the time-dependent plastic response of the material to dynamic loading, and describe the model's implementation in a radiation-hydrodynamics computer code. This model for plasticity kinetics incorporates the Gilman model for dislocation multiplication and saturation. We discuss the application of this model to the simulation of experimental velocity interferometry data for experiments on Omega in which Fe was shock compressed to pressures beyond the {alpha}-to-{var_epsilon} phase transition pressure. The kinetics model is shown to fit the data reasonably well in this high strain rate regime and further allows quantification of the relative contributions of dislocation multiplication and drag. The sensitivity of the observed signatures to the kinetics model parameters is presented.

  12. Prediction of the Elastic-Plastic Stress/Strain Response for Injection-Molded Long-Fiber Thermoplastics

    SciTech Connect

    Nguyen, Ba Nghiep; Bapanapalli, Satish K.; Kunc, Vlastimil; Phelps, Jay; Tucker III, Charles L.

    2009-01-26

    This paper proposes a model to predict the elastic-plastic response of injection-molded long-fiber thermoplastics (LFTs). The model accounts for elastic fibers embedded in a thermoplastic resin that exhibits the elastic-plastic behavior obeying the Ramberg-Osgood relation and J-2 deformation theory of plasticity. It also accounts for fiber length and orientation distributions in the composite formed by the injection-molding process. Fiber orientation was predicted using the anisotropic rotary diffusion model recently developed by Phelps and Tucker for LFTs. An incremental procedure using the Eshelby’s equivalent inclusion method and the Mori-Tanaka model is proposed to compute the overall stress increment resulting from an overall strain increment for an aligned fiber composite that contains the same fiber volume fraction and length distribution as the actual composite. The incremental response of the later is then obtained from the solution for the aligned fiber composite that is averaged over all possible fiber orientations using the orientation averaging method. Failure during incremental loading is predicted using the Van Hattum-Bernado model. The elastic-plastic and strength prediction model for LFTs was validated against the experimental stress-strain results obtained for long glass fiber/polypropylene specimens.

  13. Plasticity of surface structures and β2-adrenergic receptor localization in failing ventricular cardiomyocytes during recovery from heart failure

    PubMed Central

    Lyon, Alexander R.; Nikolaev, Viacheslav O.; Miragoli, Michele; Sikkel, Markus B.; Paur, Helen; Benard, Ludovic; Hulot, Jean-Sebastien; Kohlbrenner, Erik; Hajjar, Roger J.; Peters, Nicholas S.; Korchev, Yuri E.; Macleod, Ken T.; Harding, Sian E.; Gorelik, Julia

    2016-01-01

    Background Cardiomyocyte surface morphology and T-tubular structure are significantly disrupted in chronic heart failure with important functional sequelae, including redistribution of sarcolemmal beta2adrenergic receptors (β2AR) and localized secondary messenger signaling. Plasticity of these changes in the reverse remodeled failing ventricle is unknown. We used AAV9.SERCA2a gene therapy to rescue failing rat hearts, and measured z-groove index, T-tubule density and compartmentalized β2AR-mediated cAMP signals using a combined nanoscale scanning ion conductance microscopy-Förster resonance energy transfer technique. Methods and Results Cardiomyocyte surface morphology, quantified by z-groove index and T-tubule density, was normalized in reverse remodeled hearts following SERCA2a gene therapy. Recovery of sarcolemmal microstructure correlated with functional β2AR redistribution back into the z-groove and T-tubular network, whereas minimal cAMP responses were initiated following local β2AR stimulation of crest membrane, as observed in failing cardiomyocytes. Improvement of β2AR localization was associated with recovery of βAR-stimulated contractile responses in rescued cardiomyocytes. Retubulation was associated with reduced spatial heterogeneity of electrically-stimulated calcium transients, and recovery of myocardial BIN-1 and TCAP protein expression, but not junctophilin-2. Conclusions In summary, abnormalities of sarcolemmal structure in heart failure show plasticity with reappearance of z-grooves and T-tubules in reverse remodeled hearts. Recovery of surface topology is necessary for normalization of β2AR location and signaling responses. PMID:22456061

  14. Extensive neurological recovery from a complete spinal cord injury: a case report and hypothesis on the role of cortical plasticity

    PubMed Central

    Choe, Ann S.; Belegu, Visar; Yoshida, Shoko; Joel, Suresh; Sadowsky, Cristina L.; Smith, Seth A.; van Zijl, Peter C. M.; Pekar, James J.; McDonald, John W.

    2013-01-01

    Neurological recovery in patients with severe spinal cord injury (SCI) is extremely rare. We have identified a patient with chronic cervical traumatic SCI, who suffered a complete loss of motor and sensory function below the injury for 6 weeks after the injury, but experienced a progressive neurological recovery that continued for 17 years. The extent of the patient's recovery from the severe trauma-induced paralysis is rare and remarkable. A detailed study of this patient using diffusion tensor imaging (DTI), magnetization transfer imaging (MTI), and resting state fMRI (rs-fMRI) revealed structural and functional changes in the central nervous system that may be associated with the neurological recovery. Sixty-two percent cervical cord white matter atrophy was observed. DTI-derived quantities, more sensitive to axons, demonstrated focal changes, while MTI-derived quantity, more sensitive to myelin, showed a diffuse change. No significant cortical structural changes were observed, while rs-fMRI revealed increased brain functional connectivity between sensorimotor and visual networks. The study provides comprehensive description of the structural and functional changes in the patient using advanced MR imaging technique. This multimodal MR imaging study also shows the potential of rs-fMRI to measure the extent of cortical plasticity. PMID:23805087

  15. The mechanisms of plastic strain accommodation and post critical behavior of heterogeneous reactive composites subject to dynamic loading

    NASA Astrophysics Data System (ADS)

    Olney, Karl L.

    The dynamic behavior of granular/porous and laminate reactive materials is of interest due to their practical applications; reactive structural components, reactive fragments, etc. The mesostructural properties control meso- and macro-scale dynamic behavior of these heterogeneous composites including the behavior during the post-critical stage of deformation. They heavily influence mechanisms of fragment generation and the in situ development of local hot spots, which act as sites of ignition in these materials. This dissertation concentrates on understanding the mechanisms of plastic strain accommodation in two representative reactive material systems with different heterogeneous mesostructrues: Aluminum-Tungsten granular/porous and Nickel-Aluminum laminate composites. The main focus is on the interpretation of results of the following dynamic experiments conducted at different strain and strain rates: drop weight tests, explosively expanded ring experiments, and explosively collapsed thick walled cylinder experiments. Due to the natural limitations in the evaluation of the mesoscale behavior of these materials experimentally and the large variation in the size scales between the mesostructural level and the sample, it is extremely difficult, if not impossible, to examine the mesoscale behavior in situ. Therefore, numerical simulations of the corresponding experiments are used as the main tool to explore material behavior at the mesoscale. Numerical models were developed to elucidate the mechanisms of plastic strain accommodation and post critical behavior in these heterogeneous composites subjected to dynamic loading. These simulations were able to reproduce the qualitative and quantitative features that were observable in the experiments and provided insight into the evolution of the mechanisms of plastic strain accommodation and post critical behavior in these materials with complex mesotructure. Additionally, these simulations provided a framework to examine

  16. Axonal plasticity underpins the functional recovery following surgical decompression in a rat model of cervical spondylotic myelopathy.

    PubMed

    Dhillon, Rana S; Parker, John; Syed, Yasir A; Edgley, Steve; Young, Adam; Fawcett, James W; Jeffery, Nick D; Franklin, Robin J M; Kotter, Mark R N

    2016-01-01

    Cervical spondylotic myelopathy (CSM) is the most common spinal cord disorder and a major cause of disability in adults. Improvements following surgical decompression are limited and patients often remain severely disabled. Post mortem studies indicate that CSM is associated with profound axonal loss. However, our understanding of the pathophysiology of CSM remains limited.To investigate the hypothesis that axonal plasticity plays a role in the recovery following surgical decompression, we adopted a novel preclinical model of mild to moderate CSM. Spinal cord compression resulted in significant locomotor deterioration, increased expression of the axonal injury marker APP, and loss of serotonergic fibres. Surgical decompression partially reversed the deficits and attenuated APP expression. Decompression was also associated with axonal sprouting, reflected in the restoration of serotonergic fibres and an increase of GAP43 expression. The re-expression of synaptophysin indicated the restoration of functional synapses following decompression. Promoting axonal plasticity may therefore be a therapeutic strategy for promoting neurological recovery in CSM. PMID:27552807

  17. Recovery of a marker strain of Escherichia coli from ozonated water by membrane filtration

    SciTech Connect

    Finch, G.R.; Stiles, M.E.; Smith, D.W.

    1987-12-01

    Selective and nonselective growth media were evaluated at two incubation temperatures, 35 and 44.5 degrees C, for the recovery of a nalidixic acid-resistant marker strain of Escherichia coli ATCC 11775 by membrane filtration from ozonated 0.05 M phosphate buffer (pH 6.9). There were significantly fewer bacteria recovered with the standard m-FC agar when compared with the same growth medium prepared without bile salts and rosolic acid. This effect was particularly noticeable at the elevated incubation temperature of 44.5 degrees C. These findings are contrary to previous work which concluded that the standard American Public Health Association membrane filtration procedure is suitable for recovery of fecal coliform indicator bacteria from ozonated wastewater.

  18. Interlaminar stress recovery near free edge using a layerwise element with enhanced strains

    SciTech Connect

    Moorthy, D.; Mitchell, J.A.; Reddy, J.N.

    1997-07-01

    In the analysis of composite laminates, when the primary concern is the global response, one may choose to model the laminate with layers of different mechanical properties as an effective layer with equivalent mechanical characteristics. A layerwise finite element with enhanced strains is developed for the study of interlaminar stresses near free edge of a laminate in bending. Interlaminar boundary of interest is modeled as an adhesive contact zone between the two halves of the laminate separated at the interface. Interlaminar stresses are then recovered from the contact load that satisfies the equilibrium of the laminate. The stresses recovered thus are compared with other stress recovery procedures.

  19. Translating Principles of Neural Plasticity into Research on Speech Motor Control Recovery and Rehabilitation

    PubMed Central

    Ludlow, Christy L.; Hoit, Jeannette; Kent, Raymond; Ramig, Lorraine O.; Shrivastav, Rahul; Strand, Edythe; Yorkston, Kathryn; Sapienza, Christine

    2008-01-01

    Purpose To review the principles of neural plasticity and make recommendations for research on the neural bases for rehabilitation of neurogenic speech disorders. Method A working group in speech motor control and disorders developed this report, which examines the potential relevance of basic research on the brain mechanisms involved in neural plasticity and discusses possible similarities and differences for application to speech motor control disorders. The possible involvement of neural plasticity in changes in speech production in normalcy, development, aging, and neurological diseases and disorders was considered. This report focuses on the appropriate use of functional and structural neuroimaging and the design of feasibility studies aimed at understanding how brain mechanisms are altered by environmental manipulations such as training and stimulation and how these changes might enhance the future development of rehabilitative methods for persons with speech motor control disorders. Conclusions Increased collaboration with neuroscientists working in clinical research centers addressing human communication disorders might foster research in this area. It is hoped that this paper will encourage future research on speech motor control disorders to address the principles of neural plasticity and their application for rehabilitation. PMID:18230849

  20. Translating Principles of Neural Plasticity into Research on Speech Motor Control Recovery and Rehabilitation

    ERIC Educational Resources Information Center

    Ludlow, Christy L.; Hoit, Jeannette; Kent, Raymond; Ramig, Lorraine O.; Shrivastav, Rahul; Strand, Edythe; Yorkston, Kathryn; Sapienza, Christine M.

    2008-01-01

    Purpose: To review the principles of neural plasticity and make recommendations for research on the neural bases for rehabilitation of neurogenic speech disorders. Method: A working group in speech motor control and disorders developed this report, which examines the potential relevance of basic research on the brain mechanisms involved in neural…

  1. Relaxation of the single-slip condition in strain-gradient plasticity

    PubMed Central

    Anguige, Keith; Dondl, Patrick W.

    2014-01-01

    We consider the variational formulation of both geometrically linear and geometrically nonlinear elasto-plasticity subject to a class of hard single-slip conditions. Such side conditions typically render the associated boundary-value problems non-convex. We show that, for a large class of non-smooth plastic distortions, a given single-slip condition (specification of Burgers vectors) can be relaxed by introducing a microstructure through a two-stage process of mollification and lamination. The relaxed model can be thought of as an aid to simulating macroscopic plastic behaviour without the need to resolve arbitrarily fine spatial scales. PMID:25197243

  2. Cellular basis of morphological variation and temperature-related plasticity in Drosophila melanogaster strains with divergent wing shapes.

    PubMed

    Torquato, Libéria Souza; Mattos, Daniel; Matta, Bruna Palma; Bitner-Mathé, Blanche Christine

    2014-12-01

    Organ shape evolves through cross-generational changes in developmental patterns at cellular and/or tissue levels that ultimately alter tissue dimensions and final adult proportions. Here, we investigated the cellular basis of an artificially selected divergence in the outline shape of Drosophila melanogaster wings, by comparing flies with elongated or rounded wing shapes but with remarkably similar wing sizes. We also tested whether cellular plasticity in response to developmental temperature was altered by such selection. Results show that variation in cellular traits is associated with wing shape differences, and that cell number may play an important role in wing shape response to selection. Regarding the effects of developmental temperature, a size-related plastic response was observed, in that flies reared at 16 °C developed larger wings with larger and more numerous cells across all intervein regions relative to flies reared at 25 °C. Nevertheless, no conclusive indication of altered phenotypic plasticity was found between selection strains for any wing or cellular trait. We also described how cell area is distributed across different intervein regions. It follows that cell area tends to decrease along the anterior wing compartment and increase along the posterior one. Remarkably, such pattern was observed not only in the selected strains but also in the natural baseline population, suggesting that it might be canalized during development and was not altered by the intense program of artificial selection for divergent wing shapes. PMID:25326715

  3. Prediction of the Elastic-Plastic Stress/Strain Response for Injection-Molded Long-Fiber Thermoplastics

    SciTech Connect

    Nguyen, Ba N.; Kunc, Vlastimil; Phelps, Jay H; TuckerIII, Charles L.; Bapanapalli, Satish K

    2009-01-01

    This paper proposes a model to predict the elastic-plastic response of injection-molded long-fiber thermoplastics (LFTs). The model accounts for elastic fibers embedded in a thermoplastic resin that exhibits the elastic-plastic behavior obeying the Ramberg-Osgood relation and J-2 deformation theory of plasticity. It also accounts for fiber length and orientation distributions in the composite formed by the injection-molding process. Fiber orientation was predicted using an anisotropic rotary diffusion model recently developed for LFTs. An incremental procedure using Eshelby's equivalent inclusion method and the Mori-Tanaka assumption is proposed to compute the overall stress increment resulting from an overall strain increment for an aligned-fiber composite that contains the same fiber volume fraction and length distribution as the actual composite. The incremental response of the latter is then obtained from the solution for the aligned-fiber composite by averaging over all fiber orientations. Failure during incremental loading is predicted using the Van Hattum-Bernado model. The model is validated against the experimental stress-strain results obtained for long-glass-fiber/polypropylene specimens.

  4. Effect of chronic stress on short and long-term plasticity in dentate gyrus; study of recovery and adaptation.

    PubMed

    Radahmadi, M; Hosseini, N; Nasimi, A

    2014-11-01

    Stress dramatically affects synaptic plasticity of the hippocampus, disrupts paired-pulse facilitation and impairs long-term potentiation (LTP). This study was performed to find the effects of chronic restraint stress and recovery period on excitability, paired-pulse response, LTP and to find probable adaptation to very long stress in the dentate gyrus. Thirty-eight male Wistar rats were randomly divided into four groups of Control, Rest-Stress (21 days stress), Stress-Rest (recovery) and Stress-Stress (42 days stress: adaptation). Chronic restraint stress was applied 6-h/day. Input-output functions, paired-pulse responses and LTP were recorded from the dentate gyrus while stimulating the perforant pathway. We found that chronic stress attenuated the responsiveness, paired-pulse response and LTP in the dentate gyrus. A 21-day recovery period, after the stress, improved all the three responses toward normal, indicating reversibility of these stress-related hippocampal changes. There was no significant adaptation to very long stress, probably due to severity of stress. PMID:25218805

  5. Study of plastic strain localization mechanisms caused by nonequilibrium transitions in mesodefect ensembles under high-speed loading

    SciTech Connect

    Sokovikov, Mikhail Chudinov, Vasiliy; Bilalov, Dmitry; Oborin, Vladimir; Uvarov, Sergey; Plekhov, Oleg; Naimark, Oleg

    2015-10-27

    The behavior of specimens dynamically loaded during split Hopkinson (Kolsky) bar tests in a regime close to simple shear conditions was studied. The lateral surface of the specimens was investigated in-situ using a high-speed infrared camera CEDIP Silver 450M. The temperature field distribution obtained at different time allowed one to trace the evolution of plastic strain localization. The process of target perforation involving plug formation and ejection was examined using a high-speed infrared camera and a VISAR velocity measurement system. The microstructure of tested specimens was analyzed using an optical interferometer-profiler and a scanning electron microscope. The development of plastic shear instability regions has been simulated numerically.

  6. Flow Curve Determination at Large Plastic Strain Levels to Accurately Constitutive Equations of AHSS in Forming Simulation

    NASA Astrophysics Data System (ADS)

    Lemoine, X.; Sriram, S.; Kergen, R.

    2011-05-01

    ArcelorMittal continuously develops new steel grades (AHSS) with high performance for the automotive industry to improve the weight reduction and the passive safety. The wide market introduction of AHSS raises a new challenge for manufacturers in terms of material models in the prediction of forming—especially formability and springback. The relatively low uniform elongation, the high UTS and the low forming limit curve of these AHSS may cause difficulties in forming simulations. One of these difficulties is the consequence of the relatively low uniform elongation on the parameters identification of isotropic hardening model. Different experimental tests allow to reach large plastic strain levels (hydraulic bulge test, stack compression test, shear test…). After a description on how to determine the flow curve in these experimental tests, a comparison of the different flow curves is made for different steel grades. The ArcelorMittal identification protocol for hardening models is only based on stress-strain curves determined in uniaxial tension. Experimental tests where large plastic strain levels are reached are used to validate our identification protocol and to recommend some hardening models. Finally, the influence of isotropic hardening models and yield loci in forming prediction for AHSS steels will be presented.

  7. Plasticity of subcortical pathways promote recovery of skilled hand function in rats after corticospinal and rubrospinal tract injuries.

    PubMed

    García-Alías, Guillermo; Truong, Kevin; Shah, Prithvi K; Roy, Roland R; Edgerton, V Reggie

    2015-04-01

    The corticospinal and rubrospinal tracts are the predominant tracts for controlling skilled hand function. Injuries to these tracts impair grasping but not gross motor functions such as overground locomotion. The aim of the present study was to determine whether or not, after damage to both the corticospinal and rubrospinal tracts, other spared subcortical motor pathway can mediate the recovery of skilled hand function. Adult rats received a bilateral injury to the corticospinal tract at the level of the medullar pyramids and a bilateral ablation of the rubrospinal axons at C4. One group of rats received, acutely after injury, two injections of chondroitinase-ABC at C7, and starting at 7days post-injury were enrolled in daily reaching and grasping rehabilitation (CHASE group, n=5). A second group of rats received analogous injections of ubiquitous penicillinase, and did not undergo rehabilitation (PEN group, n=5). Compared to rats in the PEN group, CHASE rats gradually recovered the ability to reach and grasp over 42days after injury. Overground locomotion was mildly affected after injury and both groups followed similar recovery. Since the reticulospinal tract plays a predominant role in motor control, we further investigated whether or not plasticity of this pathway could contribute to the animal's recovery. Reticulospinal axons were anterogradely traced in both groups of rats. The density of reticulospinal processes in both the normal and ectopic areas of the grey ventral matter of the caudal segments of the cervical spinal cord was greater in the CHASE than PEN group. The results indicate that after damage to spinal tracts that normally mediate the control of reaching and grasping in rats other complementary spinal tracts can acquire the role of those damaged tracts and promote task-specific recovery. PMID:25666586

  8. Large recovery strain in Fe-Mn-Si-based shape memory steels obtained by engineering annealing twin boundaries

    NASA Astrophysics Data System (ADS)

    Wen, Y. H.; Peng, H. B.; Raabe, D.; Gutierrez-Urrutia, I.; Chen, J.; Du, Y. Y.

    2014-09-01

    Shape memory alloys are a unique class of materials that can recover their original shape upon heating after a large deformation. Ti-Ni alloys with a large recovery strain are expensive, while low-cost conventional processed Fe-Mn-Si-based steels suffer from a low recovery strain (<3%). Here we show that the low recovery strain results from interactions between stress-induced martensite and a high density of annealing twin boundaries. Reducing the density of twin boundaries is thus a critical factor for obtaining a large recovery strain in these steels. By significantly suppressing the formation of twin boundaries, we attain a tensile recovery strain of 7.6% in an annealed cast polycrystalline Fe-20.2Mn-5.6Si-8.9Cr-5.0Ni steel (weight%). Further attractiveness of this material lies in its low-cost alloying components and simple synthesis-processing cycle consisting only of casting plus annealing. This enables these steels to be used at a large scale as structural materials with advanced functional properties.

  9. Plasminogen deficiency causes reduced corticospinal axonal plasticity and functional recovery after stroke in mice.

    PubMed

    Liu, Zhongwu; Li, Yi; Qian, Jianyong; Cui, Yisheng; Chopp, Michael

    2014-01-01

    Tissue plasminogen activator (tPA) has been implicated in neurite outgrowth and neurological recovery post stroke. tPA converts the zymogen plasminogen (Plg) into plasmin. In this study, using plasminogen knockout (Plg-/-) mice and their Plg-native littermates (Plg+/+), we investigated the role of Plg in axonal remodeling and neurological recovery after stroke. Plg+/+ and Plg-/- mice (n = 10/group) were subjected to permanent intraluminal monofilament middle cerebral artery occlusion (MCAo). A foot-fault test and a single pellet reaching test were performed prior to and on day 3 after stroke, and weekly thereafter to monitor functional deficit and recovery. Biotinylated dextran amine (BDA) was injected into the left motor cortex to anterogradely label the corticospinal tract (CST). Animals were euthanized 4 weeks after stroke. Neurite outgrowth was also measured in primary cultured cortical neurons harvested from Plg+/+ and Plg-/- embryos. In Plg+/+ mice, the motor functional deficiency after stroke progressively recovered with time. In contrast, recovery in Plg-/- mice was significantly impaired compared to Plg+/+ mice (p<0.01). BDA-positive axonal density of the CST originating from the contralesional cortex in the denervated side of the cervical gray matter was significantly reduced in Plg-/- mice compared with Plg+/+ mice (p<0.05). The behavioral outcome was highly correlated with the midline-crossing CST axonal density (R2>0.82, p<0.01). Plg-/- neurons exhibited significantly reduced neurite outgrowth. Our data suggest that plasminogen-dependent proteolysis has a beneficial effect during neurological recovery after stroke, at least in part, by promoting axonal remodeling in the denervated spinal cord. PMID:24732409

  10. Plastic flow in shock-loaded silver at strain rates from 104 s-1 to 107 s-1 and temperatures from 296 K to 1233 K

    NASA Astrophysics Data System (ADS)

    Zaretsky, E. B.; Kanel, G. I.

    2011-10-01

    The evolution of elastic-plastic shock waves in 99.9% purity silver samples of 0.127 to 2.0 mm thickness has been studied in a series of VISAR-instrumented planar impact experiments with initial sample temperature varied from 296 to 1233 K. The decay of elastic precursor wave at 933, 1173, and 1233 K temperatures is approximately inversely proportional to the square root of the propagation distance. The latter corresponds to the cubic dependence of initial plastic strain rate, ranged from 104 s-1 to 106 s-1, on the shear stress. At fixed strain rates, the flow stress grows linearly with the temperature but the dependence becomes stronger near the silver melting point, 1234 K. An analysis of the rise times of the plastic shock waves shows that for the same level of shear stress the plastic strain rate at the shock front is significantly higher than that at the top of the elastic precursor wave.

  11. Estimation of Material Parameters in Nonlinear Hardening Plasticity Models and Strain Life Curves for CuAg Alloy

    NASA Astrophysics Data System (ADS)

    Srnec Novak, J.; Benasciutti, D.; De Bona, F.; Stanojević, A.; De Luca, A.; Raffaglio, Y.

    2016-03-01

    This work investigates the cyclic response and low-cycle fatigue behaviour of a CuAg alloy used in crystallizer for continuous casting lines. Therefore isothermal strain-based fatigue tests are first performed on CuAg specimens at different temperature levels (20 °C, 250 °C, 300 °C). The evolution of stress-strain loops recorded during the cyclic tests is used for the parameter identification of several nonlinear hardening models (nonlinear kinematic, nonlinear isotropic). Cyclic stress-strain data from experiments are compared with results from numerical simulations with the identified material parameters, showing a satisfying agreement. Critical examination of numerical results from different models is also performed. Finally, the strain- life fatigue curves estimated from experimental data are compared with approximate strain-life equations (Universal Slopes Equation, 10% Rule) which are obtained from simple tensile tests. The material parameters determined in this work can conveniently be used as inputs in a elasto- plastic finite element simulations of a crystallizer.

  12. Luoyutong Treatment Promotes Functional Recovery and Neuronal Plasticity after Cerebral Ischemia-Reperfusion Injury in Rats

    PubMed Central

    Wang, Ning-qun; Wang, Li-ye; Zhao, Hai-ping; Liu, Ping; Wang, Rong-liang; Song, Jue-xian; Gao, Li; Ji, Xun-ming; Luo, Yu-min

    2015-01-01

    Luoyutong (LYT) capsule has been used to treat cerebrovascular diseases clinically in China and is now patented and approved by the State Food and Drug Administration. In this retrospective validation study we investigated the ability of LYT to protect against cerebral ischemia-reperfusion injury in rats. Cerebral ischemia-reperfusion injury was induced by middle cerebral artery occlusion followed by reperfusion. Capsule containing LYT (high dose and medium dose) as treatment group and Citicoline Sodium as positive control treatment group were administered daily to rats 30 min after reperfusion. Treatment was continued for either 3 days or 14 days. A saline solution was administered to control animals. Behavior tests were performed after 3 and 14 days of treatment. Our findings revealed that LYT treatment improved the neurological outcome, decreased cerebral infarction volume, and reduced apoptosis. Additionally, LYT improved neural plasticity, as the expression of synaptophysin, microtubule associated protein, and myelin basic protein was upregulated by LYT treatment, while neurofilament 200 expression was reduced. Moreover, levels of brain derived neurotrophic factor and basic fibroblast growth factor were increased. Our results suggest that LYT treatment may protect against ischemic injury and improve neural plasticity. PMID:26697095

  13. Luoyutong Treatment Promotes Functional Recovery and Neuronal Plasticity after Cerebral Ischemia-Reperfusion Injury in Rats.

    PubMed

    Wang, Ning-Qun; Wang, Li-Ye; Zhao, Hai-Ping; Liu, Ping; Wang, Rong-Liang; Song, Jue-Xian; Gao, Li; Ji, Xun-Ming; Luo, Yu-Min

    2015-01-01

    Luoyutong (LYT) capsule has been used to treat cerebrovascular diseases clinically in China and is now patented and approved by the State Food and Drug Administration. In this retrospective validation study we investigated the ability of LYT to protect against cerebral ischemia-reperfusion injury in rats. Cerebral ischemia-reperfusion injury was induced by middle cerebral artery occlusion followed by reperfusion. Capsule containing LYT (high dose and medium dose) as treatment group and Citicoline Sodium as positive control treatment group were administered daily to rats 30 min after reperfusion. Treatment was continued for either 3 days or 14 days. A saline solution was administered to control animals. Behavior tests were performed after 3 and 14 days of treatment. Our findings revealed that LYT treatment improved the neurological outcome, decreased cerebral infarction volume, and reduced apoptosis. Additionally, LYT improved neural plasticity, as the expression of synaptophysin, microtubule associated protein, and myelin basic protein was upregulated by LYT treatment, while neurofilament 200 expression was reduced. Moreover, levels of brain derived neurotrophic factor and basic fibroblast growth factor were increased. Our results suggest that LYT treatment may protect against ischemic injury and improve neural plasticity. PMID:26697095

  14. The theory of plasticity in the case of simple loading accompanied by strain-hardening

    NASA Technical Reports Server (NTRS)

    Ilyushin, A A

    1949-01-01

    The author has previously shown that a deformation theory of plasticity is entirely adequate when the loading is simple; that is, when all the applied forces grow in proportion to a single parameter. The author now shows how a general plasticitytheory for any complex loading may be constructed by successively adding quantities of the nature of correction terms to the deformation theory. All of the theories of plasticity so far suggested for the complex loading condition are shown to be special cases of this general theory.

  15. Modeling anisotropic plasticity: Eulerian hydrocode applications of high strain-rate deformation processes

    SciTech Connect

    Clancy, S.P.; Burkett, M.W.; Maudlin, P.J.

    1998-02-01

    Previously developed constitutive models and solution algorithms for anisotropic elastoplastic material strength are implemented in the two dimensional MESA hydrodynamics code. Quadratic yield functions fitted from polycrystal simulations for a metallic hexagonal-close-packed structure are utilized. An associative flow strength formulation incorporating these yield functions is solved using a geometric normal return method. A stretching rod problem is selected to investigate the effects of material anisotropy on a tensile plastic instability (necking). The rod necking rate and topology are compared for MESA simulations performed for both isotropic and anisotropic cases utilizing the elastic-perfectly-plastic and the Mechanical Threshold Stress flow stress models.

  16. Temperature increase of Zircaloy-4 cladding tubes due to plastic heat dissipation during tensile tests at 0.1-10 s-1 strain rates

    NASA Astrophysics Data System (ADS)

    Hellouin de Menibus, Arthur; Auzoux, Quentin; Besson, Jacques; Crépin, Jérôme

    2014-11-01

    This study is focused on the impact of rapid Reactivity Initiated Accident (RIA) representative strain rates (about 1 s-1 NEA, 2010) on the behavior and fracture of unirradiated cold work stress relieved Zircaloy-4 cladding tubes. Uniaxial ring tests (HT) and plane strain ring tensile tests (PST) were performed in the 0.1-10 s-1 strain rate range, at 25 °C. The local temperature increase due to plastic dissipation was measured with a high-speed infrared camera. Limited temperature increases were measured at 0.1 s-1 strain rate. Limited but not strongly localized temperature increases were measured at 1 s-1. Large temperature increase were measured at 5 and 10 s-1 (142 °C at 5 s-1 strain rate in HT tests). The local temperature increase induced heterogeneous temperature fields, which enhanced strain localization and resulted in a reduction of the plastic elongation at fracture.

  17. Fixed allocation patterns, rather than plasticity, benefit recruitment and recovery from drought in seedlings of a desert shrub

    PubMed Central

    Zhang, Yao; Li, Yan; Xie, Jiang-Bo

    2016-01-01

    The response of plants to drought is controlled by the interaction between physiological regulation and morphological adjustment. Although recent studies have highlighted the long-term morphological acclimatization of plants to drought, there is still debate on how plant biomass allocation patterns respond to drought. In this study, we performed a greenhouse experiment with first-year seedlings of a desert shrub in control, drought and re-water treatments, to examine their physiological and morphological traits during drought and subsequent recovery. We found that (i) biomass was preferentially allocated to roots along a fixed allometric trajectory throughout the first year of development, irrespective of the variation in water availability; and (ii) this fixed biomass allocation pattern benefited the post-drought recovery. These results suggest that, in a stressful environment, natural selection has favoured a fixed biomass allocation pattern rather than plastic responses to environmental variation. The fixed ‘preferential allocation to root’ biomass suggests that roots may play a critical role in determining the fate of this desert shrub during prolonged drought. As the major organ for resource acquisition and storage, how the root system functions during drought requires further investigation. PMID:27073036

  18. Fixed allocation patterns, rather than plasticity, benefit recruitment and recovery from drought in seedlings of a desert shrub.

    PubMed

    Zhang, Yao; Li, Yan; Xie, Jiang-Bo

    2016-01-01

    The response of plants to drought is controlled by the interaction between physiological regulation and morphological adjustment. Although recent studies have highlighted the long-term morphological acclimatization of plants to drought, there is still debate on how plant biomass allocation patterns respond to drought. In this study, we performed a greenhouse experiment with first-year seedlings of a desert shrub in control, drought and re-water treatments, to examine their physiological and morphological traits during drought and subsequent recovery. We found that (i) biomass was preferentially allocated to roots along a fixed allometric trajectory throughout the first year of development, irrespective of the variation in water availability; and (ii) this fixed biomass allocation pattern benefited the post-drought recovery. These results suggest that, in a stressful environment, natural selection has favoured a fixed biomass allocation pattern rather than plastic responses to environmental variation. The fixed 'preferential allocation to root' biomass suggests that roots may play a critical role in determining the fate of this desert shrub during prolonged drought. As the major organ for resource acquisition and storage, how the root system functions during drought requires further investigation. PMID:27073036

  19. Bioemulsifier production by a halothermophilic Bacillus strain with potential applications in microbially enhanced oil recovery.

    PubMed

    Dastgheib, S M M; Amoozegar, M A; Elahi, E; Asad, S; Banat, I M

    2008-02-01

    A halothermotolerant Gram-positive spore-forming bacterium was isolated from petroleum reservoirs in Iran and identified as Bacillus licheniformis sp. strain ACO1 by phenotypic characterization and 16S rRNA analysis. It showed a high capacity for bioemulsifier production and grew up to 60 degrees C with NaCl at 180 g l(-1). The optimum NaCl concentration, pH and temperature for bioemulsifier production were 4% (w/v), 8.0, and 45 degrees C, respectively. Although ACO1 did not utilize hydrocarbons, it had a high emulsifying activity (E (24) = 65 +/- 5%) on different hydrophobic substrates. Emulsification was optimal while growing on yeast extract as the sole carbon source and NaNO(3) as the nitrogen source. The efficiency of the residual oil recovery increased by 22% after in situ growth of B. licheniformis ACO1 in a sand-pack model saturated with liquid paraffin. PMID:17876532

  20. Extension of the sorting instructions for household plastic packaging and changes in exposure to bioaerosols at materials recovery facilities.

    PubMed

    Schlosser, O; Déportes, I Z; Facon, B; Fromont, E

    2015-12-01

    The aim of this study was to assess how extending the sorting instructions for plastic packaging would affect the exposure of workers working at materials recovery facility (MRF) to dust, endotoxins, fungi and bacteria, taking into consideration other factors that could have an influence on this exposure. Personal sampling was carried out at four MRFs during six sampling campaigns at each facility, both in sorting rooms and when the workers were involved in "mobile tasks" away from the rooms. The data was analysed by describing the extension of sorting instructions both using a qualitative variable (after vs before) and using data for the pots and trays recycling stream, including or excluding plastic film. Overall, before the extension of the sorting guidelines, the geometric mean of personal exposure levels in sorting rooms was 0.3mg/m(3) for dust, 27.7 EU/m(3) for endotoxins, 13,000 CFU/m(3) for fungi and 1800 CFU/m(3) for bacteria. When workers were involved in mobile tasks away from the rooms, these averages were 0.5mg/m(3), 25.7 EU/m(3), 28,000 CFU/m(3) and 5100 CFU/m(3) respectively.The application by households of instructions to include pots, trays and film with other recyclable plastic packaging led to an increase in exposure to endotoxins, fungi and bacteria at MRFs. For an increase of 0.5 kg per inhabitant per year in the pots, trays and film recycling stream, exposure in sorting rooms rose by a factor of 1.4-2.2, depending on the biological agent. Exposure during mobile tasks increased by a factor of 3.0-3.6. The age of the waste amplified the effect of the extension of sorting instructions on exposure to fungi, bacteria and endotoxins. Factors that had a significant influence on the exposure of workers to dust and/or bioaerosols included the presence of paper, newspapers and magazines in the sorted waste, the order in which incoming waste was treated and the quality of the ventilation system in the sorting rooms. The levels of exposure observed in

  1. An analytical elastic plastic contact model with strain hardening and frictional effects for normal and oblique impacts

    DOE PAGESBeta

    Brake, M. R. W.

    2015-02-17

    Impact between metallic surfaces is a phenomenon that is ubiquitous in the design and analysis of mechanical systems. We found that to model this phenomenon, a new formulation for frictional elastic–plastic contact between two surfaces is developed. The formulation is developed to consider both frictional, oblique contact (of which normal, frictionless contact is a limiting case) and strain hardening effects. The constitutive model for normal contact is developed as two contiguous loading domains: the elastic regime and a transitionary region in which the plastic response of the materials develops and the elastic response abates. For unloading, the constitutive model ismore » based on an elastic process. Moreover, the normal contact model is assumed to only couple one-way with the frictional/tangential contact model, which results in the normal contact model being independent of the frictional effects. Frictional, tangential contact is modeled using a microslip model that is developed to consider the pressure distribution that develops from the elastic–plastic normal contact. This model is validated through comparisons with experimental results reported in the literature, and is demonstrated to be significantly more accurate than 10 other normal contact models and three other tangential contact models found in the literature.« less

  2. An analytical elastic plastic contact model with strain hardening and frictional effects for normal and oblique impacts

    SciTech Connect

    Brake, M. R. W.

    2015-02-17

    Impact between metallic surfaces is a phenomenon that is ubiquitous in the design and analysis of mechanical systems. We found that to model this phenomenon, a new formulation for frictional elastic–plastic contact between two surfaces is developed. The formulation is developed to consider both frictional, oblique contact (of which normal, frictionless contact is a limiting case) and strain hardening effects. The constitutive model for normal contact is developed as two contiguous loading domains: the elastic regime and a transitionary region in which the plastic response of the materials develops and the elastic response abates. For unloading, the constitutive model is based on an elastic process. Moreover, the normal contact model is assumed to only couple one-way with the frictional/tangential contact model, which results in the normal contact model being independent of the frictional effects. Frictional, tangential contact is modeled using a microslip model that is developed to consider the pressure distribution that develops from the elastic–plastic normal contact. This model is validated through comparisons with experimental results reported in the literature, and is demonstrated to be significantly more accurate than 10 other normal contact models and three other tangential contact models found in the literature.

  3. Strain-induced Defects in Carbon Nanotubes: Electronic Tuning and Plastic Limits

    NASA Astrophysics Data System (ADS)

    Zhang, Peihong; Lammert, Paul; Crespi, Vincent

    1998-03-01

    Bond rotation defects can tune the electronic structures of carbon nanotubes (PRL 79, 2093; link). These defects can be created by simple elastic deformations. Continuum elasticity theory augments atomistic calculations of plastic limits and bandgaps as a function of tension.

  4. A leech model for homeostatic plasticity and motor network recovery after loss of descending inputs.

    PubMed

    Lane, Brian J

    2016-04-01

    Motor networks below the site of spinal cord injury (SCI) and their reconfiguration after loss of central inputs are poorly understood but remain of great interest in SCI research. Harley et al. (J Neurophysiol113: 3610-3622, 2015) report a striking locomotor recovery paradigm in the leechHirudo verbanawith features that are functionally analogous to SCI. They propose that this well-established neurophysiological system could potentially be repurposed to provide a complementary model to investigate basic principles of homeostatic compensation relevant to SCI research. PMID:26424582

  5. Some new extensions to multi-mechanism models for plastic and viscoplastic material behavior under small strains

    NASA Astrophysics Data System (ADS)

    Wolff, Michael; Bökenheide, Simone; Böhm, Michael

    2016-05-01

    Multi-mechanism models (MM models) have become an important tool for modeling complex material behavior. In particular, two-mechanism models are used. They are applied to model ratcheting in metal plasticity as well as steel behavior during phase transformations. We consider a small-deformation setting. The characteristic trait of multi-mechanism models is the additive decomposition of the inelastic (e.g., plastic or viscoplastic) strain into several parts. These parts are sometimes called mechanisms. In comparison with rheological models, the mechanisms can interact with each other. This leads to new properties and allows to describe important observable effects. Up to now, each mechanism has one kinematic internal variable. As a new feature, we develop multi-mechanism models (in series) with several kinematic variables for each mechanism as well as with several isotropic variables for each flow criterion. We describe this complex situation by three structural matrices which express the mutual relations between mechanisms, flow criteria, kinematic, and isotropic variables. The well-known Chaboche model with a unique inelastic strain and several kinematic variables represents a special case of these general multi-mechanism models. In this work, we also present a matrix-based approach for these new complex MM models. The presented models can form the basis for developing numerical algorithms for simulation and parameter identification.

  6. Poles Apart: Arctic and Antarctic Octadecabacter strains Share High Genome Plasticity and a New Type of Xanthorhodopsin

    PubMed Central

    Vollmers, John; Voget, Sonja; Dietrich, Sascha; Gollnow, Kathleen; Smits, Maike; Meyer, Katja; Brinkhoff, Thorsten; Simon, Meinhard; Daniel, Rolf

    2013-01-01

    The genus Octadecabacter is a member of the ubiquitous marine Roseobacter clade. The two described species of this genus, Octadecabacter arcticus and Octadecabacter antarcticus, are psychrophilic and display a bipolar distribution. Here we provide the manually annotated and finished genome sequences of the type strains O. arcticus 238 and O. antarcticus 307, isolated from sea ice of the Arctic and Antarctic, respectively. Both genomes exhibit a high genome plasticity caused by an unusually high density and diversity of transposable elements. This could explain the discrepancy between the low genome synteny and high 16S rRNA gene sequence similarity between both strains. Numerous characteristic features were identified in the Octadecabacter genomes, which show indications of horizontal gene transfer and may represent specific adaptations to the habitats of the strains. These include a gene cluster encoding the synthesis and degradation of cyanophycin in O. arcticus 238, which is absent in O. antarcticus 307 and unique among the Roseobacter clade. Furthermore, genes representing a new subgroup of xanthorhodopsins as an adaptation to icy environments are present in both Octadecabacter strains. This new xanthorhodopsin subgroup differs from the previously characterized xanthorhodopsins of Salinibacter ruber and Gloeobacter violaceus in phylogeny, biogeography and the potential to bind 4-keto-carotenoids. Biochemical characterization of the Octadecabacter xanthorhodopsins revealed that they function as light-driven proton pumps. PMID:23671678

  7. Poles apart: Arctic and Antarctic Octadecabacter strains share high genome plasticity and a new type of xanthorhodopsin.

    PubMed

    Vollmers, John; Voget, Sonja; Dietrich, Sascha; Gollnow, Kathleen; Smits, Maike; Meyer, Katja; Brinkhoff, Thorsten; Simon, Meinhard; Daniel, Rolf

    2013-01-01

    The genus Octadecabacter is a member of the ubiquitous marine Roseobacter clade. The two described species of this genus, Octadecabacter arcticus and Octadecabacter antarcticus, are psychrophilic and display a bipolar distribution. Here we provide the manually annotated and finished genome sequences of the type strains O. arcticus 238 and O. antarcticus 307, isolated from sea ice of the Arctic and Antarctic, respectively. Both genomes exhibit a high genome plasticity caused by an unusually high density and diversity of transposable elements. This could explain the discrepancy between the low genome synteny and high 16S rRNA gene sequence similarity between both strains. Numerous characteristic features were identified in the Octadecabacter genomes, which show indications of horizontal gene transfer and may represent specific adaptations to the habitats of the strains. These include a gene cluster encoding the synthesis and degradation of cyanophycin in O. arcticus 238, which is absent in O. antarcticus 307 and unique among the Roseobacter clade. Furthermore, genes representing a new subgroup of xanthorhodopsins as an adaptation to icy environments are present in both Octadecabacter strains. This new xanthorhodopsin subgroup differs from the previously characterized xanthorhodopsins of Salinibacter ruber and Gloeobacter violaceus in phylogeny, biogeography and the potential to bind 4-keto-carotenoids. Biochemical characterization of the Octadecabacter xanthorhodopsins revealed that they function as light-driven proton pumps. PMID:23671678

  8. Uniaxial Pre-strain and Free Recovery (UPFR) as a Flexible Technique for Nitinol Characterization

    NASA Astrophysics Data System (ADS)

    Cadelli, A.; Manjeri, R. M.; Sczerzenie, F.; Coda, A.

    2016-03-01

    The measurement of phase transformation temperatures of superelastic (SE) and shape memory (SM) NiTi alloy products and components was studied in this work. The transformation temperatures of a set of twenty different 300 μm NiTi superelastic wires were measured by two well-established and standardized techniques, namely differential scanning calorimetry (DSC) and bend and free recovery (BFR) and then compared with the results from the Uniaxial Pre-Strain and Free Recovery (UPFR) test. UPFR is a tension-based test, whose aim is to overcome the limitations associated with BFR testing. Within this work, a test procedure has been set up and validated. UPFR is found to be the only method showing a very strong correlation with the mechanical properties measured using the standard uniaxial tensile test method for superelastic NiTi alloy. Further, UPFR has been validated as a robust technique for measuring the R-phase and austenitic transformation temperatures in specimens of various sizes, composition, and of different geometries. This technique overcomes the limitations of BFR and DSC which cannot be used for testing products such as 25 μm SM wire, a 50 μm SE strip, and different springs and microsprings for actuation.

  9. Recovery from retinal lesions: molecular plasticity mechanisms in visual cortex far beyond the deprived zone.

    PubMed

    Hu, Tjing-Tjing; Van den Bergh, Gert; Thorrez, Lieven; Heylen, Kevin; Eysel, Ulf T; Arckens, Lutgarde

    2011-12-01

    In cats with central retinal lesions, deprivation of the lesion projection zone (LPZ) in primary visual cortex (area 17) induces remapping of the cortical topography. Recovery of visually driven cortical activity in the LPZ involves distinct changes in protein expression. Recent observations, about molecular activity changes throughout area 17, challenge the view that its remote nondeprived parts would not be involved in this recovery process. We here investigated the dynamics of the protein expression pattern of remote nondeprived area 17 triggered by central retinal lesions to explore to what extent far peripheral area 17 would contribute to the topographic map reorganization inside the visual cortex. Using functional proteomics, we identified 40 proteins specifically differentially expressed between far peripheral area 17 of control and experimental animals 14 days to 8 months postlesion. Our results demonstrate that far peripheral area 17 is implicated in the functional adaptation to the visual deprivation, involving a meshwork of interacting proteins, operating in diverse pathways. In particular, endocytosis/exocytosis processes appeared to be essential via their intimate correlation with long-term potentiation and neurite outgrowth mechanisms. PMID:21571696

  10. A Critical Assessment of Three Usual Equations for Strain Hardening and Dynamic Recovery

    NASA Astrophysics Data System (ADS)

    Montheillet, Frank; Piot, David; Matougui, Nedjoua; Fares, Mohamed Lamine

    2014-09-01

    The Laasraoui-Jonas (LJ), Kocks-Mecking (KM), and power law (PW) stress-strain equations pertaining to hot working of metals within the range of moderate strains ( i.e., before the occurrence of dynamic recrystallization) are compared. It is shown that it is not possible to select the "best" one to fit a given experimental flow curve, neither in the σ - ɛ nor in the diagram. Noting that each of the three laws depends on two constitutive parameters, transformation formulae are then derived allowing the parameters of one law to be derived from the parameters of any of the two others. The fit of a given LJ equation by a PW law is then discussed. Finally, the transformation formulae are used to estimate the current rate of dynamic recovery when the flow rule is known in the form a PW law. The above theoretical derivations are illustrated by the specific case of a Fe-C alloy in the ferritic phase domain. However, they suggest that the conclusions are widely applicable to hot working of metals and alloys.

  11. Accumulation of plastic strain in Zircaloy-4 at low homologous temperature

    NASA Astrophysics Data System (ADS)

    Matsunaga, Tetsuya; Satoh, Yuhki; Abe, Hiroaki

    2015-10-01

    Time-dependent strain accumulation in Zircaloy-4 was evaluated at 294 K, i.e., homologous temperature (T/Tm, where Tm is the melting temperature) of 0.14, to ascertain the mechanical response in fuel cladding material, even at the time of storage. Although diffusion processes are suppressed, considerable strain accumulation was observed at less than 0.2% offset stress. Transmission electron microscopy and electron backscattered diffraction analyses were used to investigate the dominant microstructural mechanism. Results showed that the heterogeneous dislocation structure generated strain accumulation, where straightly aligned dislocation arrays on the prismatic plane move freely and few deformation twins were formed in the grain interior. Furthermore, few dislocation tangles were observed because the slip systems were limited to one. Therefore, Zircaloy-4 shows weak work-hardening at the low homologous temperature because of the fewer interactions among dislocations, leading to unexpected strain accumulation under constant load conditions.

  12. Correlating the internal length in strain gradient plasticity theory with the microstructure of material

    NASA Astrophysics Data System (ADS)

    Zhao, Jianfeng; Zhang, Xu; Konstantinidis, Avraam A.; Kang, Guozheng

    2015-06-01

    The internal length is the governing parameter in strain gradient theories which among other things have been used successfully to interpret size effects at the microscale. Physically, the internal length is supposed to be related with the microstructure of the material and evolves during the deformation. Based on Taylor hardening law, we propose a power-law relationship to describe the evolution of the variable internal length with strain. Then, the classical Fleck-Hutchinson strain gradient theory is extended with a strain-dependent internal length, and the generalized Fleck-Hutchinson theory is confirmed here, by comparing our model predictions to recent experimental data on tension and torsion of thin wires with varying diameter and grain size. Our work suggests that the internal length is a configuration-dependent parameter, closely related to dislocation characteristics and grain size, as well as sample geometry when this affects either the underlying microstructure or the ductility of the material.

  13. Accumulation of plastic strain in Zircaloy-4 at low homologous temperature

    NASA Astrophysics Data System (ADS)

    Matsunaga, Tetsuya; Satoh, Yuhki; Abe, Hiroaki

    2015-10-01

    Time-dependent strain accumulation in Zircaloy-4 was evaluated at 294 K, i.e., homologous temperature (T/Tm, where Tm is the melting temperature) of 0.14, to ascertain the mechanical response in fuel cladding material, even at the time of storage. Although diffusion processes are suppressed, considerable strain accumulation was observed at less than 0.2% offset stress. Transmission electron microscopy and electron backscattered diffraction analyses were used to investigate the dominant microstructural mechanism. Results showed that the heterogeneous dislocation structure generated strain accumulation, where straightly aligned dislocation arrays on the prismatic plane move freely and few deformation twins were formed in the grain interior. Furthermore, few dislocation tangles were observed because the slip systems were limited to one. Therefore, Zircaloy-4 shows weak work-hardening at the low homologous temperature because of the fewer interactions among dislocations, leading to unexpected strain accumulation under constant load conditions.

  14. Local and Global Stress-Strain Behaviors of Transformation-Induced Plasticity Steel Using the Combined Nanoindentation and Finite Element Analysis Method

    NASA Astrophysics Data System (ADS)

    Jeong, Hyeok Jae; Lim, Nam Suk; Lee, Bong Ho; Park, Chan Gyung; Lee, Sunghak; Kang, Seong-Hoon; Lee, Ho Won; Kim, Hyoung Seop

    2014-12-01

    Transformation-induced plasticity (TRIP) steels have excellent strain hardening exponents and resistibility against tensile necking using the strain-induced martensite formation that occurs as a result of the plastic deformation and strain on the retained austenite phase. Detailed studies on the microstructures and local mechanical properties, as well as global mechanical properties, are necessary in order to thoroughly understand the properties of TRIP steels with multiple phases of ferrite, bainite, retained austenite, and martensite. However, methods for investigating the local properties of the various phases of the TRIP steel are limited due to the very complicated and fine microstructures present in TRIP steel. In this study, the experimental and numerical methods, i.e., the experimental nanoindenting results and the theoretical finite element analyses, were combined in order to extract the local stress-strain curves of each phase. The local stress-strain curves were in good agreement with the values presented in the literature. In particular, the global plastic stress-strain behavior of the TRIP steel was predicted using the multiple phase unit cell finite element analysis, and this demonstrated the validity of the obtained properties of each local phase. The method of extracting the local stress-strain curves from the nanoindenting curves and predicting the global stress-strain behavior assists in clarifying the smart design of multi-phase steels.

  15. Local and Global Stress-Strain Behaviors of Transformation-Induced Plasticity Steel Using the Combined Nanoindentation and Finite Element Analysis Method

    NASA Astrophysics Data System (ADS)

    Jeong, Hyeok Jae; Lim, Nam Suk; Lee, Bong Ho; Park, Chan Gyung; Lee, Sunghak; Kang, Seong-Hoon; Lee, Ho Won; Kim, Hyoung Seop

    2014-09-01

    Transformation-induced plasticity (TRIP) steels have excellent strain hardening exponents and resistibility against tensile necking using the strain-induced martensite formation that occurs as a result of the plastic deformation and strain on the retained austenite phase. Detailed studies on the microstructures and local mechanical properties, as well as global mechanical properties, are necessary in order to thoroughly understand the properties of TRIP steels with multiple phases of ferrite, bainite, retained austenite, and martensite. However, methods for investigating the local properties of the various phases of the TRIP steel are limited due to the very complicated and fine microstructures present in TRIP steel. In this study, the experimental and numerical methods, i.e., the experimental nanoindenting results and the theoretical finite element analyses, were combined in order to extract the local stress-strain curves of each phase. The local stress-strain curves were in good agreement with the values presented in the literature. In particular, the global plastic stress-strain behavior of the TRIP steel was predicted using the multiple phase unit cell finite element analysis, and this demonstrated the validity of the obtained properties of each local phase. The method of extracting the local stress-strain curves from the nanoindenting curves and predicting the global stress-strain behavior assists in clarifying the smart design of multi-phase steels.

  16. Plastic deformation experiments to high strain on mantle transition zone minerals wadsleyite and ringwoodite in the rotational Drickamer apparatus

    NASA Astrophysics Data System (ADS)

    Hustoft, Justin; Amulele, George; Ando, Jun-ichi; Otsuka, Kazuhiko; Du, Zhixue; Jing, Zhicheng; Karato, Shun-ichiro

    2013-01-01

    We report the results of plastic deformation experiments on polycrystalline wadsleyite and ringwoodite performed at 15-23 GPa and 1300-2100 K conducted using the rotational Drickamer apparatus (RDA). Wadsleyite was synthesized from fine-grained (˜2 μm) San Carlos olivine in a Kawai-type multianvil apparatus; the average grain size of the resulting wadsleyite was 1.2 μm. The initial water content of the undeformed wadsleyite was 24,000-26,000 H/106 Si but the final water content is variable and less than the initial water content. Ringwoodite was synthesized from wadsleyite in situ in the RDA. Both strain and stress were measured in situ using a synchrotron x-ray facility. Determinations of strains and strain rates were made from x-ray radiographs of the sample, using a Mo foil strain marker in the sample assembly. The state of stress was determined from the observed d-spacing of multiple lattice planes as a function of azimuth angle. Samples were deformed at various strain rates at around 10-4-10-5 s-1. Deformation mechanisms were inferred from the stress exponent and the microstructures. We determined the stress exponent n for wadsleyite to be 6±3, suggesting dislocation creep was the dominant deformation mechanism in wadsleyite. At grain sizes of ˜1 μm, our samples were still deforming primarily by dislocation creep. However, small dislocation-free grains are also observed suggesting that diffusion creep may operate in some parts of our samples.

  17. The role of dissipation and defect energy in variational formulations of problems in strain-gradient plasticity. Part 2: single-crystal plasticity

    NASA Astrophysics Data System (ADS)

    Reddy, B. D.

    2011-11-01

    Variational formulations are constructed for rate-independent problems in small-deformation single-crystal strain-gradient plasticity. The framework, based on that of Gurtin (J Mech Phys Solids 50: 5-32, 2002), makes use of the flow rule expressed in terms of the dissipation function. Provision is made for energetic and dissipative microstresses. Both recoverable and non-recoverable defect energies are incorporated into the variational framework. The recoverable energies include those that depend smoothly on the slip gradients, the Burgers tensor, or on the dislocation densities (Gurtin et al. J Mech Phys Solids 55:1853-1878, 2007), as well as an energy proposed by Ohno and Okumura (J Mech Phys Solids 55:1879-1898, 2007), which leads to excellent agreement with experimental results, and which is positively homogeneous and therefore not differentiable at zero slip gradient. Furthermore, the variational formulation accommodates a non-recoverable energy due to Ohno et al. (Int J Mod Phys B 22:5937-5942, 2008), which is also positively homogeneous, and a function of the accumulated dislocation density. Conditions for the existence and uniqueness of solutions are established for the various examples of defect energy, with or without the presence of hardening or slip resistance.

  18. The Effect of transient change in strain rate on plastic flow behaviour of Al-Mg-Si alloy at elevated temperatures

    SciTech Connect

    Petrov, P.; Voronkov, V.; Potapenko, K.; Ivanov, V.

    2011-05-04

    In extrusion forging processes, the abrupt changes in strain rate follows the plastic deformation of a material within the deforming zone. To simulate accurately this effect, the specific experimental investigation of the plastic flow during the transient change in strain rate should be performed. The present paper deals with the investigation of this effect on the flow stress of an Al-Mg-Si alloy during its deformation at 350 deg. C. The investigation consists of two steps. Both steps are connected to the monotonic uniaxial compression loading of a cylindrical specimen. During the first step the flow behaviour of the alloy is investigated at the constant strain rate wihin the range of 0.1-50 s{sup -1} at the temperature range of 350-430 deg. C. During the second step the strain rate is abruptly increased or decreased from its current value at a fixed engineering strain of 17-21%. From the beginning of the test up to the strain of 17-21% the value of the strain rate is constant and equal to either 1 s{sup -1} or 10 s{sup -1}. At the strain of 17-21% the value of a strain rate is either increased to 10 s{sup -1} or decreased to 1 s{sup -1}.The results of the experimental investigations were used to determine the isothermal flow stress-strain curves of the Al-Mg-Si alloy as well as the heat effect of plastic deformation of the alloy. On basis of these curves, the strain rate sensitivity index m as a function of true strain and temperature was determined. This parameter allows to optimize a technological process of hot forging of the aluminium alloy as well as it is very important data for the construction of a phenomenological flow stress model.

  19. The Effect of transient change in strain rate on plastic flow behaviour of Al-Mg-Si alloy at elevated temperatures

    NASA Astrophysics Data System (ADS)

    Petrov, P.; Voronkov, V.; Potapenko, K.; Ivanov, V.

    2011-05-01

    In extrusion forging processes, the abrupt changes in strain rate follows the plastic deformation of a material within the deforming zone. To simulate accurately this effect, the specific experimental investigation of the plastic flow during the transient change in strain rate should be performed. The present paper deals with the investigation of this effect on the flow stress of an Al-Mg-Si alloy during its deformation at 350° C. The investigation consists of two steps. Both steps are connected to the monotonic uniaxial compression loading of a cylindrical specimen. During the first step the flow behaviour of the alloy is investigated at the constant strain rate wihin the range of 0.1-50 s-1 at the temperature range of 350-430° C. During the second step the strain rate is abruptly increased or decreased from its current value at a fixed engineering strain of 17-21%. From the beginning of the test up to the strain of 17-21% the value of the strain rate is constant and equal to either 1 s-1 or 10 s-1. At the strain of 17-21% the value of a strain rate is either increased to 10 s-1 or decreased to 1 s-1. The results of the experimental investigations were used to determine the isothermal flow stress-strain curves of the Al-Mg-Si alloy as well as the heat effect of plastic deformation of the alloy. On basis of these curves, the strain rate sensitivity index m as a function of true strain and temperature was determined. This parameter allows to optimize a technological process of hot forging of the aluminium alloy as well as it is very important data for the construction of a phenomenological flow stress model.

  20. The stress-strain relationships in wood and fiber-reinforced plastic laminae of reinforced glued-laminated wood beams

    NASA Astrophysics Data System (ADS)

    Tingley, Daniel Arthur

    The reinforcement of wood and wood composite structural products to improve their mechanical properties has been in practice for many years. Recently, the use of high-strength fiber-reinforced plastic (FRP) as a reinforcement in such applications has been commercialized. The reinforcement is manufactured using a standard pultrusion process or alternatively a sheet-forming process commonly referred to as "pulforming". The high-modulus fibers are predominately unidirectional, although off-axis fibers are often used to enhance off-axis properties. The fibers used are either of a single type or multiple types, which are called "hybrids". Unidirectional, single, and hybrid fiber FRP physical properties and characteristics were compared to wood. Full-scale reinforced glulams were tested. Aramid-reinforced plastics (ARP) used as tensile reinforcements were found to be superior in strength applications to other types of FRP made with fiber, such as carbon and fiberglass. Carbon/aramid-reinforced plastic (CARP) was shown to be superior in both modulus and strength design situations. Fiberglass was shown to be suitable only in hybrid situations with another fiber such as aramid or carbon and only in limited use situations where modulus was a design criteria. The testing and analysis showed that the global response of reinforced glulam beams is controlled by localized strength variations in the wood such as slope of grain, knots, finger joints, etc. in the tensile zone. The elemental tensile strains in the extreme wood tensile laminae, due to global applied loads, were found to be well below the strain at failure in clear wood samples recovered from the failure area. Two areas affecting the relationship between the wood and the FRP were investigated: compatibility of the wood and FRP materials and interface characteristics between the wood and FRP. The optimum strain value at yield point for an FRP was assessed to be slightly higher than the clear wood value in tension for a

  1. Treadmill training induced lumbar motoneuron dendritic plasticity and behavior recovery in adult rats after a thoracic contusive spinal cord injury.

    PubMed

    Wang, Hongxing; Liu, Nai-Kui; Zhang, Yi Ping; Deng, Lingxiao; Lu, Qing-Bo; Shields, Christopher B; Walker, Melissa J; Li, Jianan; Xu, Xiao-Ming

    2015-09-01

    Spinal cord injury (SCI) is devastating, causing sensorimotor impairments and paralysis. Persisting functional limitations on physical activity negatively affect overall health in individuals with SCI. Physical training may improve motor function by affecting cellular and molecular responses of motor pathways in the central nervous system (CNS) after SCI. Although motoneurons form the final common path for motor output from the CNS, little is known concerning the effect of exercise training on spared motoneurons below the level of injury. Here we examined the effect of treadmill training on morphological, trophic, and synaptic changes in the lumbar motoneuron pool and on behavior recovery after a moderate contusive SCI inflicted at the 9th thoracic vertebral level (T9) using an Infinite Horizon (IH, 200 kDyne) impactor. We found that treadmill training significantly improved locomotor function, assessed by Basso-Beattie-Bresnahan (BBB) locomotor rating scale, and reduced foot drops, assessed by grid walking performance, as compared with non-training. Additionally, treadmill training significantly increased the total neurite length per lumbar motoneuron innervating the soleus and tibialis anterior muscles of the hindlimbs as compared to non-training. Moreover, treadmill training significantly increased the expression of a neurotrophin brain-derived neurotrophic factor (BDNF) in the lumbar motoneurons as compared to non-training. Finally, treadmill training significantly increased synaptic density, identified by synaptophysin immunoreactivity, in the lumbar motoneuron pool as compared to non-training. However, the density of serotonergic terminals in the same regions did not show a significant difference between treadmill training and non-training. Thus, our study provides a biological basis for exercise training as an effective medical practice to improve recovery after SCI. Such an effect may be mediated by synaptic plasticity, and neurotrophic modification in the

  2. Dislocation microstructures and strain-gradient plasticity with one active slip plane

    NASA Astrophysics Data System (ADS)

    Conti, Sergio; Garroni, Adriana; Müller, Stefan

    2016-08-01

    We study dislocation networks in the plane using the vectorial phase-field model introduced by Ortiz and coworkers, in the limit of small lattice spacing. We show that, in a scaling regime where the total length of the dislocations is large, the phase field model reduces to a simpler model of the strain-gradient type. The limiting model contains a term describing the three-dimensional elastic energy and a strain-gradient term describing the energy of the geometrically necessary dislocations, characterized by the tangential gradient of the slip. The energy density appearing in the strain-gradient term is determined by the solution of a cell problem, which depends on the line tension energy of dislocations. In the case of cubic crystals with isotropic elasticity our model shows that complex microstructures may form in which dislocations with different Burgers vector and orientation react with each other to reduce the total self-energy.

  3. Quantifying the Rates of Sn Whisker Growth and Plastic Strain Relaxation Using Thermally-Induced Stress

    NASA Astrophysics Data System (ADS)

    Pei, Fei; Bower, Allan F.; Chason, Eric

    2016-01-01

    Whiskers and hillocks that grow out of Sn-based coatings are a critical reliability issue in Pb-free electronics. Although their growth is widely regarded as a stress-relaxation mechanism, quantitative understanding of the relationship between the stress, growth kinetics, and strain relaxation is still lacking. In this work, the well-controlled strain induced by thermal-expansion mismatch was used to study the whiskering behavior of electroplated Sn films. Stress was quantified by monitoring wafer-curvature and the density of whiskers and hillocks was measured simultaneously by use of optical microscopy. Evolution of the volume of individual features was also measured by scanning electron microscopy after different periods of heating. The measurements were used to develop a model for temperature-dependent and stress-dependent growth kinetics of whiskers and hillocks and to determine the amount of strain relaxation which occurs as a result of their formation.

  4. Modeling anisotropic plasticity: Eulerian hydrocode applications of high strain-rate deformation processes

    SciTech Connect

    Clancy, S.P.; Burkett, M.W.; Maudlin, P.J.

    1997-05-01

    Previously developed constitutive models and solution algorithms for anisotropic elastoplastic material strength are implemented in the two-dimensional MESA hydrodynamics code. Quadratic yield functions fitted from polycrystal simulations for a metallic hexagonal-close-packed structure are utilized. An associative flow strength formulation incorporating these yield functions is solved using a geometric normal return method. A stretching rod problem is selected to investigate the effects of material anisotropy on a tensile plastic instability (necking). The rod necking rate and topology are compared for MESA simulations performed for both isotropic and anisotropic cases utilizing the Mechanical Threshold Stress flow stress model.

  5. Bulk Nanolayered Composites: Interfacial Influence on Microstructural Evolution at Large Plastic Strains

    SciTech Connect

    Mara, Nathan A.; Carpenter, John S.; Han, Weizhong; Zheng, Shijian; McCabe, Rodney J.; Wang, Jian; Beyerlein, Irene J.

    2012-07-31

    Conclusions are: (1) As-processed ARB material has similar morphology, chemistry as PVD, but different interfacial structure; (2) Density of interfaces AND interfacial structure play a role in determining hardness, an example is twinning in Cu at the {l_brace}112{r_brace}Cu//{l_brace}112{r_brace}Nb interface and higher strength, no twinning in Cu in the {l_brace}111{r_brace}Cu//{l_brace}110{r_brace}Nb interface; and (3) Need to understand effects of processing history to predict the effects on the interfaces we produce - Amount of strain, Strain Path, Annealing.

  6. Compaction process in sedimentary basins: the role of stiffness increase and hardening induced by large plastic strains

    NASA Astrophysics Data System (ADS)

    Deudé, V.; Dormieux, L.; Maghous, S.; Barthélémy, J. F.; Bernaud, D.

    2004-11-01

    This paper is devoted to the simulation of large strain compaction process in sedimentary basins. Special attention is paid to the effects of large porosity changes on the elastic and plastic mechanical properties of the sediment material. The latter are introduced in the constitutive behaviour in the framework of a micromechanical reasoning. In particular, the proposed approach avoids the problem of negative porosities that are predicted by classical models under high confining pressures.Some closed-form solutions are presented in the simplified case of one-dimensional compaction. While the influence of stiffness increase is shown to be negligible as regards the compaction law, it proves to affect significantly the stress and porosity profiles. Copyright

  7. Full-Field Strain Measurement On Titanium Welds And Local Elasto-Plastic Identification With The Virtual Fields Method

    SciTech Connect

    Tattoli, F.; Casavola, C.; Pierron, F.; Rotinat, R.; Pappalettere, C.

    2011-01-17

    One of the main problems in welding is the microstructural transformation within the area affected by the thermal history. The resulting heterogeneous microstructure within the weld nugget and the heat affected zones is often associated with changes in local material properties. The present work deals with the identification of material parameters governing the elasto--plastic behaviour of the fused and heat affected zones as well as the base material for titanium hybrid welded joints (Ti6Al4V alloy). The material parameters are identified from heterogeneous strain fields with the Virtual Fields Method. This method is based on a relevant use of the principle of virtual work and it has been shown to be useful and much less time consuming than classical finite element model updating approaches applied to similar problems. The paper will present results and discuss the problem of selection of the weld zones for the identification.

  8. Myocardial Strain and Strain Rate in Kawasaki Disease: Range, Recovery, and Relationship to Systemic Inflammation/Coronary Artery Dilation

    PubMed Central

    Frank, Benjamin; Davidson, Jesse; Tong, Suhong; Martin, Blake; Heizer, Heather; Anderson, Marsha S; Glode, Mary P; Dominguez, Samuel R; Jone, Pei-Ni

    2016-01-01

    Background Kawasaki Disease (KD), a systemic vasculitis of medium sized vessels, is the most common cause of acquired heart disease among children in the developed world. Some KD patients demonstrate echocardiographic evidence of depressed myocardial mechanics. However, the incidence, etiology, and reversibility of abnormal mechanics in KD patients remain undefined. Methods and results We retrospectively studied 41 KD patients and measured myocardial strain and strain rate by velocity vector imaging from pre-treatment and convalescent echocardiograms. Pre-treatment procalcitonin, C-reactive protein (CRP), and coronary artery z-scores were obtained in all patients and compared between the groups with preserved versus depressed acute phase mechanics. The change in mechanics between the acute and convalescent phases was also assessed. Patients with initially low longitudinal strain improved by the convalescent period (mean difference - 4.0%; p<0.005) with the greatest improvement occurring in patients with the lowest initial strain (−7.3%; p<0.05). Patients with higher initial strain did not change significantly by the convalescent period. Patients with lower longitudinal and circumferential strain demonstrated higher median procalcitonin levels (1.2 vs. 0.3 ng/mL; p<0.05 and 1.8 vs. 0.4 ng/mL; p<0.05 respectively) and a trend towards higher CRP, but no difference in coronary artery z-scores. Strain rate was not associated with inflammatory markers or coronary artery z-scores. Conclusions The range of strain found in our cohort was large. Improvement in mean strain was driven primarily by patients with lower initial strain. Lower strain was associated with increased markers of systemic inflammation, but not proximal coronary artery changes. PMID:27182455

  9. Effects of gasket on coupled plastic flow and strain-induced phase transformations under high pressure and large torsion in a rotational diamond anvil cell

    NASA Astrophysics Data System (ADS)

    Feng, Biao; Levitas, Valery I.

    2016-01-01

    Combined plastic flow and strain-induced phase transformations (PTs) under high pressure in a sample within a gasket subjected to three dimensional compression and torsion in a rotational diamond anvil cell (RDAC) are studied using a finite element approach. The results are obtained for the weaker, equal-strength, and stronger high-pressure phases in comparison with low-pressure phases. It is found that, due to the strong gasket, the pressure in the sample is relatively homogenous and the geometry of the transformed zones is mostly determined by heterogeneity in plastic flow. For the equal-strength phases, the PT rate is higher than for the weaker and stronger high-pressure phases. For the weaker high-pressure phase, transformation softening induces material instability and leads to strain and PT localization. For the stronger high-pressure phase, the PT is suppressed by strain hardening during PT. The effect of the kinetic parameter k that scales the PT rate in the strain-controlled kinetic equation is also examined. In comparison with a traditional diamond anvil cell without torsion, the PT progress is much faster in RDAC under the same maximum pressure in the sample. Finally, the gasket size and strength effects are discussed. For a shorter and weaker gasket, faster plastic flow in radial and thickness directions leads to faster PT kinetics in comparison with a longer and stronger gasket. The rates of PT and plastic flows are not very sensitive to the modest change in a gasket thickness. Multiple experimental results are reproduced and interpreted. Obtained results allow one to design the desired pressure-plastic strain loading program in the experiments for searching new phases, reducing PT pressure by plastic shear, extracting kinetic properties from experiments with heterogeneous fields, and controlling homogeneity of all fields and kinetics of PTs.

  10. Modeling anisotropy plasticity : 3D Eulerian hydrocode simulations of high strain rate deformation processes.

    SciTech Connect

    Burkett, M. W.; Clancy, S. P.; Maudlin, P. J.; Holian, K. S.

    2001-01-01

    Previously developed constitutive models and solution algorithms for anisotropic elastoplastic material strength have been implemented in the three-dimensional Conejo hydrodynamics code. The anisotropic constitutive modeling is posed in an unrotated material frame of reference using the theorem of polar decomposition to obtain rigid body rotation. Continuous quadratic yield functions fitted from polycrystal simulations for a metallic hexagonal-close-packed structure were utilized. Simple rectangular shear problems, R-value problems, and Taylor cylinder impact data were used to verify and validate the implementation of the anisotropic model. A stretching rod problem (involving large strain and high strain-rate deformation) was selected to investigate the effects of material anisotropy. Conejo simulations of rod topology were compared for two anisotropic cases.

  11. Modeling Anisotropic Plasticity: 3D Eulerian Hydrocode Simulations of High Strain Rate Deformation Processes

    NASA Astrophysics Data System (ADS)

    Burkett, Michael W.; Clancy, Sean P.; Maudlin, Paul J.; Holian, Kathleen S.

    2002-07-01

    Previously developed constitutive models and solution algorithms for anisotropic elastoplastic material strength have been implemented in the three-dimensional Conejo hydrodynamics code. The anisotropic constitutive modeling is posed in an unrotated material frame of reference using the theorem of polar decomposition to obtain rigid body rotation. Continuous quadratic yield functions fitted from polycrystal simulations for a metallic hexagonal-close-packed structure were utilized. Simple rectangular shear problems, R-Value problems, and Taylor cylinder impact data were used to verify and validate the implementation of the anisotropic model. A stretching rod problem (involving large strain and high strain-rate deformation) was selected to investigate the effects of material anisotropy. Conejo simulations of rod topology were compared for two anisotropic cases.

  12. Modeling Anisotropic Plasticity: 3D Eulerian Hydrocode Simulations of High Strain Rate Deformation Processes

    NASA Astrophysics Data System (ADS)

    Burkett, Michael; Clancy, Sean; Maudlin, Paul; Holian, Kathleen

    2001-06-01

    : Previously developed constitutive models and solution algorithms for anisotropic elastoplastic material strength has been implemented in the three-dimensional CONEJO hydrodynamics code. CONEJO is an explicit, Eulerian continuum mechanics code that is utilized to predict formation processes associated with material deformation at elevated strain-rates and is a code development project under the Accelerated Strategic Computing Initiative (ASCI) program. Some special features of CONEJO include a high-order advection algorithm, a material interface tracking scheme, and van Leer monotonic advection-limiting. The anisotropic constitutive modeling is posed in an unrotated material frame using the theorem of polar decomposition to describe rigid body rotation. An Euler-Rodrigues description is used to quantify the rigid body rotations. Continuous quadratic yield functions fitted from polycrystal simulations for a metallic hexagonal-close-packed structure were utilized. Associative flow formulations incorporating these yield functions were solved using a geometric normal return method. Simple rectangular shear problems, "R-value" problems, and Taylor cylinder impact test data were utilized to verify and validate the implementation of the anisotropic model. A "stretching rod" problem (involving large strain and strain-rate deformation) was selected to investigate the effects of material anisotropy for this deformation process. The rod necking rate and topology was compared for CONEJO simulations using several isotropic and anisotropic descriptions that utilized the Mechanical Threshold Stress (MTS) model.

  13. Effect of Pre-straining on the Shape Recovery of Fe-Mn-Si-Cr-Ni Shape Memory Alloys

    NASA Astrophysics Data System (ADS)

    Maji, Bikas C.; Krishnan, Madangopal; Verma, Amit; Basu, R.; Samajdar, I.; Ray, Ranjit K.

    2015-02-01

    The effect of pre-straining on the shape recovery behavior of Fe-14Mn-6Si-9Cr-5Ni (wt pct) shape memory alloy (SMA) has been studied. The shape recovery associated with the reverse ɛ martensitic transformation, i.e., ɛ → γ, was characterized by dilatometry using specimens which were pre-strained to different extent (0 to 14 pct). Dilatometric studies revealed that in Fe-Mn-Si-Cr-Ni SMA, the shape recovery takes place in two stages: (i) in the first stage, the unpinned fraction of stress-induced ɛ martensite reverts back to parent phase γ in the temperature regime of 353 K to 653 K (80 °C to 380 °C) and (ii) in the second stage the remaining "pinned" ɛ martensite is unpinned by the decomposition of deformation-induced α' martensite in the temperature range of 743 K to 893 K (470 °C to 620 °C). The amount of recovery in the first stage decreases with pre-strain, whereas it increases in the second stage. The ɛ → γ transformation finish temperature, A f, increases with increase in pre-strain amount, though the reverse transformation start temperature, A S, remains unaffected. Microstructural characterization revealed that the amount of deformation-induced α' martensite depends on the mode of straining and the crystallographic texture of the starting material. The reversion of α' martensite is seen to occur by the precipitation of Fe5Ni3Si2-type intermetallic π-phase within these plates.

  14. Plasticity in Ultra Fine Grained Materials

    SciTech Connect

    Koslowski, Marisol

    2015-04-15

    Understanding the mechanisms of deformation of nanocrystalline (nc) materials is critical to the design of micro and nano devices and to develop materials with superior fracture strength and wear resistance for applications in new energy technologies. In this project we focused on understanding the following plastic deformation processes described in detail in the following sections: 1. Plastic strain recovery (Section 1). 2. Effect of microstructural variability on the yield stress of nc metals (Section 2). 3. The role of partial and extended full dislocations in plastic deformation of nc metals (Section 3).

  15. Construction and evaluation of an exopolysaccharide-producing engineered bacterial strain by protoplast fusion for microbial enhanced oil recovery.

    PubMed

    Sun, Shanshan; Luo, Yijing; Cao, Siyuan; Li, Wenhong; Zhang, Zhongzhi; Jiang, Lingxi; Dong, Hanping; Yu, Li; Wu, Wei-Min

    2013-09-01

    Enterobacter cloacae strain JD, which produces water-insoluble biopolymers at optimal temperature of 30°C, and a thermophilic Geobacillus strain were used to construct an engineered strain for exopolysaccharide production at high temperatures by protoplast fusion. The obtained fusant strain ZR3 produced exopolysaccharides at up to 45°C with optimal growth temperature at 35°C. The fusant produced exopolysaccharides of approximately 7.5 g/L or more at pH between 7.0 and 9.0. The feasibility of the enhancement of crude oil recovery with the fusant was tested in a sand-packed column at 40°C. The results demonstrated that bioaugmentation of the fusant was promising approach for MEOR. Mass growth of the fusant was confirmed in fermentor tests. PMID:23856587

  16. The role of macroscopic hardening and individual length-scales on crack tip stress elevation from phenomenological strain gradient plasticity

    NASA Astrophysics Data System (ADS)

    Komaragiri, Uday; Agnew, Sean R.; Gangloff, Richard P.; Begley, Matthew R.

    This paper quantifies the effect of strain gradient plasticity (SGP) on crack tip stress elevation for a broad range of applied loading conditions and constitutive model parameters, including both macroscopic hardening parameters and individual material length-scales controlling gradient effects. Finite element simulations incorporating the Fleck-Hutchinson SGP theory are presented for an asymptotically sharp stationary crack. Results identify fundamental scaling relationships describing (i) the physical length-scales over which strain gradients are prominent, and (ii) the degree of stress elevation over conventional Hutchinson-Rice-Rosengren (HRR) fields. Results illustrate that the three length-scale theory predicts much larger SGP effects than the single length-scale theory. Critically, the first length-scale parameter dominates SGP stress elevation: this suggests that SGP effects in fracture can be predicted using the length-scales extracted from nanoindentation, which exhibits similar behavior. Transitional loading/material parameters are identified that establish regimes of SGP relevance: this provides the foundation for the rational application of SGP when developing new micromechanical models of crack tip damage mechanisms and associated subcritical crack propagation behavior in structural alloys.

  17. Enhancement of Biodegradable Plastic-degrading Enzyme Production from Paraphoma-like Fungus, Strain B47-9.

    PubMed

    Sameshima-Yamashita, Yuka; Koitabashi, Motoo; Tsuchiya, Wataru; Suzuki, Ken; Watanabe, Takashi; Shinozaki, Yukiko; Yamamoto-Tamura, Kimiko; Yamazaki, Toshimasa; Kitamoto, Hiroko

    2016-03-01

    To improve the productivity of Paraphoma-like fungal strain B47-9 for biodegradable plastic (BP)-degrading enzyme (PCLE), the optimal concentration of emulsified poly(butylene succinate-co-adipate) (PBSA) in the medium was determined. Emulsified PBSA was consumed as a sole carbon source and an inducer of PCLE production by strain B47-9. Among the various concentrations of emulsified PBSA [0.09-0.9% (w/v)] used in flask cultivation, 0.27% yielded the maximum enzyme activity within a short cultivation period. To evaluate the residual concentration of emulsified PBSA in culture, emulsified PBSA in aliquots of culture supernatant was digested in vitro, and the concentration of released monomerised succinic acid was determined. Regardless of the initial concentration of emulsified PBSA in medium, PCLE activity was detected after residual succinic acid decreased below 0.04 mg/mL in culture broth. Jarfermentation was performed at a 0.27% PBSA concentration. Among the various airflow rates tested, 1 LPM resulted in a PCLE production rate of 1.0 U/mL/day. The enzyme activity in the resulting culture filtrate (4.2 U/2 mL) was shown to degrade commercial BP films (1 × 1 cm, 20 µm thickness) within 8 hours. PMID:26876678

  18. STRAIN RATE AND TEMPERATURE DEPENDENT BEHAVIORS FOR TRANSFORMATION INDUCED PLASTICITY (TRIP) STEELS

    SciTech Connect

    Sun, Xin; Stephens, Elizabeth V.; Khaleel, Mohammad A.

    2008-01-03

    Base material properties for TRIP800 have been characterized under different automotive manufacturing and operating temperatures ranging from -40°C to 93°C, as well as strain rates ranging from 1/sec to 400/sec. Transformation kinetics for material points undergone high rate deformation has been quantified using a modified X-ray diffraction technique. The results clearly indicate the temperature dependency of the TRIP steel dynamic performance. At room temperature, the total elongation is around 33%, similar to those under quasi-static loading conditions. Under higher or lower temperature, however, TRIP800 has reduced ductility under dynamic loading.

  19. Recovery

    NASA Video Gallery

    This video discusses the recovery events that occur in high-power rocketry and the various devices used in safely recovering the rocket. The video includes a discussion of black powder and ejection...

  20. [Recovery].

    PubMed

    Estingoy, Pierrette; Gilliot, Élodie; Parisot, Clément

    2015-01-01

    The historical fatalism of the impossibility of recovering from psychosis eased from the 1970s with the shaping of the idea of a possible recovery. Recovery is today the objective for the patient and caregivers. The key to achieving this lies in the encounter with Others. A collective approach, on the level of the institution, must be established. The aim is to create opportunities for the patient to express their doubts and feelings. PMID:26363659

  1. Dynamic response of Cu4Zr54 metallic glass to high strain rate shock loading: plasticity, spall and atomic-level structures

    SciTech Connect

    Luo, Shengnian; Arman, Bedri; Germann, Timothy C; Cagin, Tahir

    2009-01-01

    We investigate dynamic response of Cu{sub 46}Zr{sub 54} metallic glass under adiabatic planar shock wave loading (one-dimensional strain) wjth molecular dynamics simulations, including Hugoniot (shock) states, shock-induced plasticity and spallation. The Hugoniot states are obtained up to 60 CPa along with the von Mises shear flow strengths, and the dynamic spall strength, at different strain rates and temperatures. The spall strengths likely represent the limiting values achievable in experiments such as laser ablation. For the steady shock states, a clear elastic-plastic transition is identified (e.g., in the shock velocity-particle velocity curve), and the shear strength shows strain-softening. However, the elastic-plastic transition across the shock front displays transient stress overshoot (hardening) above the Hugoniot elastic limit followed by a relatively sluggish relaxation to the steady shock state, and the plastic shock front steepens with increasing shock strength. The local von Mises shear strain analysis is used to characterize local deformation, and the Voronoi tessellation analysis, the corresponding short-range structures at various stages of shock, release, tension and spallation. The plasticity in this glass is manifested as localized shear transformation zones and of local structure rather than thermal origin, and void nucleation occurs preferentially at the highly shear-deformed regions. The Voronoi and shear strain analyses show that the atoms with different local structures are of different shear resistances that lead to shear localization (e.g., the atoms indexed with (0,0,12,0) are most shear-resistant, and those with (0,2,8,1) are highly prone to shear flow). The dynamic changes in local structures are consistent with the observed deformation dynamics.

  2. Improving the High-Cycle Fatigue Lives of Fe-30Mn-0.9C Twinning-Induced Plasticity Steel Through Pre-straining

    NASA Astrophysics Data System (ADS)

    Wang, B.; Zhang, Z. J.; Shao, C. W.; Duan, Q. Q.; Pang, J. C.; Yang, H. J.; Li, X. W.; Zhang, Zhe-Feng

    2015-08-01

    The tensile properties, high-cycle fatigue properties, and microstructure evolutions during fatigue process of as-received and pre-strained Fe-30Mn-0.9C twinning-induced plasticity (TWIP) steel were investigated. It is found that the fatigue lives of the TWIP steel can be effectively improved through pre-straining, since the deformation twins induced by pre-straining could effectively lead to the improved yield strength and the homogenized deformation. This study may provide possible ways for improving the high-cycle fatigue properties of TWIP steels.

  3. Fabric Transitions in Quartz via Visco-Plastic Self-Consistent Modelling: Axial Compression and Simple Shear under Constant Strain

    NASA Astrophysics Data System (ADS)

    Morales, L. F. G.; Lloyd, G. E.; Mainprice, D.

    2014-12-01

    Quartz is a common crustal mineral that deforms plastically in a wide range of temperatures and pressures, leading to the development of different types of crystallographic preferred orientation (CPO) patterns. In this contribution we present the results of an extensive modelling of quartz fabric transitions via visco-plastic self- consistent (VPSC) approach. For that, we have performed systematic simulations using different sets of relative critical resolved shear stress of the main quartz slip systems. We have performed these simulations in axial compression and simple shear regimes under constant Von Mises equivalent strain of 100% (γ=1.73), assuming that the aggregates deformed exclusively by dislocation glide. Some of the predicted CPOs patterns are similar to those observed in naturally and experimentally deformed quartz. Nevertheless, some classical CPO patterns usually interpreted as resulting from dislocation glide (e.g. Y-maxima due to prism slip) are clearly not developed in the simulated conditions. In addition we report potentially new preferred orientation patterns that might develop in high temperature conditions, both in axial compression and simple shear. We have demonstrated that CPOs generated under axial compression are usually stronger that those predicted under simple shear, due to the continuous rotation observed in the later simulations. The fabric strength depends essentially on the dominant active slip system, and normally the stronger CPOs result from dominant basal slip in , followed by rhomb and prism [c] slip, whereas prism slip does not produce strong fabrics. The opening angle of quartz [0001] fabric used as a proxy of temperature seems to be reliable for deformation temperatures of ~400°C, when the main slip systems have similar behaviours.

  4. Measurement of true stress-strain curves and evolution of plastic zone of low carbon steel under uniaxial tension using digital image correlation

    NASA Astrophysics Data System (ADS)

    Zhu, Feipeng; Bai, Pengxiang; Zhang, Jingbin; Lei, Dong; He, Xiaoyuan

    2015-02-01

    Three-dimensional digital image correlation has been utilized widely in many fields due to its advantages of non-contact, full-field measurement and simplicity. Based on 3D-DIC measurement system and electronic universal testing machine, two uniaxial tension tests for low carbon steel specimen were performed to acquire the true stress-strain curves. An assumption was made that specimen's cross section keeps as a circle in tension test whose diameter could be determined by calculation of the curvature of surface shape. Therefore, true stress of specific cross section was acquired and hence the true stress-strain curves were obtained. In addition, the evolution of plastic zone of specimen under uniaxial tension was studied as well. And experimental results indicate that at certain time instant of expanding process of plastic zone, region that has already entered the plastic zone and that has not entered such zone yet is keeping in a constant deformed state, while region that is entering the plastic zone provides axial plastic deformation, which is almost equal to crosshead movement of testing machine.

  5. Plasticity induced by pre-existing defects during high strain-rate loading

    NASA Astrophysics Data System (ADS)

    Bringa, Eduardo

    2014-03-01

    High strain-rate deformation of metals has been typically studied for perfect monocrystals. Computational advances now allow more realistic simulations of materials including defects, which lower the Hugoniot Elastic Limit, and lead to microstructures differing from the ones from perfect monocrystals. As pre-existing defects one can consider vacancy clusters, dislocation loops, grain boundaries, etc. New analysis tools allow analysis of dislocation densities and twin fractions, for both f.c.c. and b.c.c. metals. Recent results for defective single crystal Ta [Tramontina et al.., High Energy Den. Phys. 10, 9 (2014), and Ruestes et al., Scripta Mat. 68, 818 (2013)], and for polycrystalline b.c.c metals [Tang et al., Mat. Sci. Eng. A 580, 414 (2013), and Gunkelmann et al., Phys. Rev. B 86, 144111 (2012)] will be highlighted, alongside new results for nanocrystalline Cu, Ta, Fe, and Zr [Ruestes et al., Scripta Mat. 71, 9 (2014)]. This work has been carried out in collaboration with D. Tramontina, C. Ruestes, E. Millan, J. Rodriguez-Nieva, M.A. Meyers, Y. Tang, H. Urbassek, N. Gunkelmann, A. Stukowski, M. Ruda, G. Bertolino, D. Farkas, A. Caro, J. Hawreliak, B. Remington, R. Rudd, P. Erhart, R. Ravelo, T. Germann, N. Park, M. Suggit, S. Michalik, A. Higginbotham and J. Wark. Funding by PICT2008-1325 and SeCTyP U.N. Cuyo.

  6. Interaction Between Recovery, Recrystallization, and NbC Strain-Induced Precipitation in High-Mn Steels

    NASA Astrophysics Data System (ADS)

    Llanos, Laura; Pereda, Beatriz; López, Beatriz

    2015-11-01

    The interaction between recovery, recrystallization, and strain-induced precipitation in two high-Mn steels, one of them microalloyed with Nb (0.1 pct) was investigated using mechanical testing and advanced microscopy techniques. Double-hit torsion tests were carried out in the 1373 K to 1173 K (1100 °C to 900 °C) temperature range in order to characterize the fractional softening behavior. Quenched specimens were analyzed using electron backscatter diffraction and transmission electron microscopy to determine the recrystallized fraction, the precipitation state, and the austenite microstructure evolution. At the highest temperature, 1373 K (1100 °C), similar softening kinetics were found in both steels. However, at temperatures lower than 1273 K (1000 °C) for the Nb steel, strain-induced precipitation was observed to take place resulting in significant softening retardation. For the base steel at all the temperatures investigated, and for the Nb steel in the absence of strain-induced precipitation, the mechanical softening corresponded well with the recrystallized fraction. However, when strain-induced precipitation took place, a major deviation was observed denoting a significant contribution of recovery to the fractional softening. Within the deformed grains, a substructure consisting of "subgrain bands" or microbands was developed. The precipitates were found mainly on the elongated subgrain boundaries, or at dislocations within the subgrains. This configuration was maintained after the migration of the recrystallization front.

  7. Flow Curve Determination at Large Plastic Strain Levels: Limitations of the Membrane Theory in the Analysis of the Hydraulic Bulge Test

    NASA Astrophysics Data System (ADS)

    Lemoine, X.; Iancu, A.; Ferron, G.

    2011-05-01

    Nowadays, an accurate determination of the true stress-strain curve is a key-element for all finite element (FE) forming predictions. Since the introduction of Advanced High Strength Steels (AHSS) for the automotive market, the standard uniaxial tension test suffers the drawback of relatively low uniform elongations. The extrapolation of the uniaxial stress-strain curve up to large strains is not without consequence in forming predictions—especially formability and springback. One of the means to solve this problem is to use experimental tests where large plastic strain levels can be reached. The hydraulic bulge test is one of these tests. The effective plastic strain levels reached in the bulge test are of about 0.7. From an experimental standpoint, the biaxial flow stress is estimated using measurement of fluid pressure, and calculation of thickness and curvature at the pole, via appropriate measurements and assumptions. The biaxial stress at the pole is determined using the membrane equilibrium equation. The analysis proposed in this paper consists of performing "virtual experiments" where the results obtained by means of FE calculations are used as input data for determining the biaxial stress-strain law in agreement with the experimental procedure. In this way, a critical discussion of the experimental procedure can be made, by comparing the "experimental" stress-strain curve (Membrane theory curve) with the "reference" one introduced in the simulations. In particular, the influences of the "(die diameter)/thickness" ratio and of the plastic anisotropy are studied, and limitations of the hydraulic bulge test analysis are discussed.

  8. Recovery of polypropylene and polyethylene from packaging plastic wastes without contamination of chlorinated plastic films by the combination process of wet gravity separation and ozonation.

    PubMed

    Reddy, Mallampati Srinivasa; Okuda, Tetsuji; Nakai, Satoshi; Nishijima, Wataru; Okada, Mitsumasa

    2011-08-01

    Wet gravity separation technique has been regularly practiced to separate the polypropylene (PP) and polyethylene (PE) (light plastic films) from chlorinated plastic films (CP films) (heavy plastic films). The CP films including poly vinyl chloride (PVC) and poly vinylidene chloride (PVDC) would float in water even though its density is more than 1.0g/cm(3). This is because films are twisted in which air is sometimes entrapped inside the twisted CP films in real existing recycling plant. The present research improves the current process in separating the PP and PE from plastic packaging waste (PPW), by reducing entrapped air and by increasing the hydrophilicity of the CP films surface with ozonation. The present research also measures the hydrophilicity of the CP films. In ozonation process mixing of artificial films up to 10min reduces the contact angle from 78° to 62°, and also increases the hydrophilicity of CP films. The previous studies also performed show that the artificial PVDC films easily settle down by the same. The effect of ozonation after the wet gravity separation on light PPW films obtained from an actual PPW recycling plant was also evaluated. Although actual light PPW films contained 1.3% of CP films however in present case all the CP films were removed from the PPW films as a settled fraction in the combination process of ozonation and wet gravity separation. The combination process of ozonation and wet gravity separation is the more beneficial process in recovering of high purity PP and PE films from the PPW films. PMID:21530222

  9. Biosurfactant-producing and oil-degrading Bacillus subtilis strains enhance oil recovery in laboratory sand-pack columns.

    PubMed

    Gudiña, Eduardo J; Pereira, Jorge F B; Costa, Rita; Coutinho, João A P; Teixeira, José A; Rodrigues, Lígia R

    2013-10-15

    Microbial Enhanced Oil Recovery (MEOR) technology uses microorganisms and their metabolites to retrieve unrecoverable oil from mature reservoirs. In situ stimulation of biosurfactant-producing and oil-degrading microorganisms reduces the capillary forces retaining the oil inside the reservoir and decreases its viscosity, thus promoting oil flow and consequently production. In this work, a sand-pack column model was designed to simulate oil recovery operations and evaluate mobilization of residual oil by the selected microorganisms. Four different hydrocarbon mixtures and three Bacillus subtilis strains isolated from crude oil samples were used. Additional oil recoveries ranged from 6 to 24% depending on the hydrocarbon mixture and microorganism used. Biosurfactant production was observed with all the microorganisms and hydrocarbon mixtures studied. The oils recovered after incubation with B. subtilis isolates showed a reduction in the percentage of long-chain n-alkanes and lower viscosity when compared with the original oils. The results obtained suggest that stimulation of the selected B. subtilis strains in situ can contribute to mobilize entrapped oil in mature reservoirs. PMID:23911831

  10. Effect of constitutive equations on qualitative behavior of solutions in the vicinity of bi-material interfaces at large plastic strains

    NASA Astrophysics Data System (ADS)

    Alexandrov, Sergei; Goldstein, Robert

    2016-04-01

    The main objective of the present paper is to compare, by means of a problem permitting a closed-form solution, qualitative behavior of solutions based on three models of strain hardening plasticity and two models of viscoplasticity. The elastic portion of the strain tensor is neglected. The study focuses on the solution behavior near frictional interfaces. The solution behavior essentially depends on the model chosen. Such features of the solutions as nonexistence and singularity are emphasized. The key constitutive parameter that divides all the models considered into two groups is the saturation stress. In particular, under certain conditions no solution satisfying the regime of sticking exists for the models that involve the saturation stress. Qualitative comparison with numerous experimental observations is made. It is concluded that models with a saturation stress, including the models considered in the present paper, may be capable of describing the generation of a narrow layer of severe plastic deformation in the vicinity of frictional interfaces.

  11. Reducing β-glucosidase supplementation during cellulase recovery using engineered strain for successive lignocellulose bioconversion.

    PubMed

    Guo, Hong; Zou, Shaolan; Liu, Boshi; Su, Rongxin; Huang, Renliang; Qi, Wei; Zhang, Minhua; He, Zhimin

    2015-01-01

    Enzyme recycling by re-adsorption is one of the primary methods for reducing enzyme usage in lignocellulose conversion. This work proposes the combination of an engineered yeast strain that expresses β-glucosidase with enzyme recycling to reduce the amount of supplemented β-glucosidase in enzyme recycling experiments. Using the engineered strain, a slight increase in ethanol concentration was obtained after a 96-h fermentation of pretreated corncobs. Ethanol concentrations increased by 34.7% and 62.7% in the following two recycle rounds using the engineered strain compared with those using its parental strain without β-glucosidase addition. Furthermore, with the addition of β-glucosidase at 30CBU/g cellulose, the ethanol concentration after two recycle rounds exceeded 90% of that observed in the first SSF round with the engineered strain at a high initial cellulase loading of 45FPU/g cellulose. PMID:25863900

  12. Control of nitrogenase recovery from oxygen inactivation by ammonia in the cyanobacterium Anabaena sp. strain CA (ATCC 33047).

    PubMed Central

    Smith, R L; Van Baalen, C; Tabita, F R

    1990-01-01

    The control of nitrogenase recovery from inactivation by oxygen was studied in Anabaena sp. strain CA (ATCC 33047). Nitrogenase activity (acetylene reduction) in cultures grown in 1% CO2 in air was inhibited by exposure to 1% CO2-99% O2 and allowed to recover in the presence of high oxygen tensions. Cultures exposed to hyperbaric levels of oxygen in the presence of 10 mM NH4NO3 were incapable of regaining nitrogenase activity, whereas control cultures returned to 65 to 80% of their original activity within about 3 h after exposure to high oxygen tension. In contrast to the regulation of heterocyst differentiation and nitrogenase synthesis, recovery from oxygen inactivation in this organism was shown to be under the control of NH4+ rather than NO3-. PMID:2110151

  13. The Synechococcus Strain PCC 7942 glnN Product (Glutamine Synthetase III) Helps Recovery from Prolonged Nitrogen Chlorosis

    PubMed Central

    Sauer, Jörg; Dirmeier, Ulrike; Forchhammer, Karl

    2000-01-01

    We report the cloning and sequencing of the glnN gene encoding a class III glutamine synthetase from the cyanobacterium Synechococcus strain PCC 7942. Mapping of the transcriptional start site revealed a DNA sequence in the promoter region that resembles an imperfect NtcA binding motif. Expression of glnN is impaired in NtcA- and PII-deficient mutants. The only parameter which was negatively affected in the glnN mutant compared to the wild type was the recovery rate of prolonged nitrogen-starved cells with low concentrations of combined nitrogen. PMID:10986271

  14. The Synechococcus strain PCC 7942 glnN product (glutamine synthetase III) helps recovery from prolonged nitrogen chlorosis.

    PubMed

    Sauer, J; Dirmeier, U; Forchhammer, K

    2000-10-01

    We report the cloning and sequencing of the glnN gene encoding a class III glutamine synthetase from the cyanobacterium Synechococcus strain PCC 7942. Mapping of the transcriptional start site revealed a DNA sequence in the promoter region that resembles an imperfect NtcA binding motif. Expression of glnN is impaired in NtcA- and P(II)-deficient mutants. The only parameter which was negatively affected in the glnN mutant compared to the wild type was the recovery rate of prolonged nitrogen-starved cells with low concentrations of combined nitrogen. PMID:10986271

  15. A multi-scale model of dislocation plasticity in α-Fe: Incorporating temperature, strain rate and non-Schmid effects

    SciTech Connect

    Lim, H.; Hale, L. M.; Zimmerman, J. A.; Battaile, C. C.; Weinberger, C. R.

    2015-01-05

    In this study, we develop an atomistically informed crystal plasticity finite element (CP-FE) model for body-centered-cubic (BCC) α-Fe that incorporates non-Schmid stress dependent slip with temperature and strain rate effects. Based on recent insights obtained from atomistic simulations, we propose a new constitutive model that combines a generalized non-Schmid yield law with aspects from a line tension (LT) model for describing activation enthalpy required for the motion of dislocation kinks. Atomistic calculations are conducted to quantify the non-Schmid effects while both experimental data and atomistic simulations are used to assess the temperature and strain rate effects. The parameterized constitutive equation is implemented into a BCC CP-FE model to simulate plastic deformation of single and polycrystalline Fe which is compared with experimental data from the literature. This direct comparison demonstrates that the atomistically informed model accurately captures the effects of crystal orientation, temperature and strain rate on the flow behavior of siangle crystal Fe. Furthermore, our proposed CP-FE model exhibits temperature and strain rate dependent flow and yield surfaces in polycrystalline Fe that deviate from conventional CP-FE models based on Schmid's law.

  16. A multi-scale model of dislocation plasticity in α-Fe: Incorporating temperature, strain rate and non-Schmid effects

    DOE PAGESBeta

    Lim, H.; Hale, L. M.; Zimmerman, J. A.; Battaile, C. C.; Weinberger, C. R.

    2015-01-05

    In this study, we develop an atomistically informed crystal plasticity finite element (CP-FE) model for body-centered-cubic (BCC) α-Fe that incorporates non-Schmid stress dependent slip with temperature and strain rate effects. Based on recent insights obtained from atomistic simulations, we propose a new constitutive model that combines a generalized non-Schmid yield law with aspects from a line tension (LT) model for describing activation enthalpy required for the motion of dislocation kinks. Atomistic calculations are conducted to quantify the non-Schmid effects while both experimental data and atomistic simulations are used to assess the temperature and strain rate effects. The parameterized constitutive equationmore » is implemented into a BCC CP-FE model to simulate plastic deformation of single and polycrystalline Fe which is compared with experimental data from the literature. This direct comparison demonstrates that the atomistically informed model accurately captures the effects of crystal orientation, temperature and strain rate on the flow behavior of siangle crystal Fe. Furthermore, our proposed CP-FE model exhibits temperature and strain rate dependent flow and yield surfaces in polycrystalline Fe that deviate from conventional CP-FE models based on Schmid's law.« less

  17. Recovery of plastic wastes from dumpsite as refuse-derived fuel and its utilization in small gasification system.

    PubMed

    Chiemchaisri, Chart; Charnnok, Boonya; Visvanathan, Chettiyappan

    2010-03-01

    An effort to utilize solid wastes at dumpsite as refuse-derived fuel (RDF) was carried out. The produced RDF briquette was then utilized in the gasification system. These wastes were initially examined for their physical composition and chemical characteristics. The wastes contained high plastic content of 24.6-44.8%, majority in polyethylene plastic bag form. The plastic wastes were purified by separating them from other components through manual separation and trommel screen after which their content increased to 82.9-89.7%. Subsequently, they were mixed with binding agent (cassava root) and transformed into RDF briquette. Maximum plastic content in RDF briquette was limit to 55% to maintain physical strength and maximum chlorine content. The RDF briquette was tested in a down-draft gasifier. The produced gas contained average energy content of 1.76 MJ/m(3), yielding cold gas efficiency of 66%. The energy production cost from this RDF process was estimated as USD0.05 perkWh. PMID:19758801

  18. The Effect of Single Crystal Elastic and Plastic Anisotropy on Strain Heterogeneity: Comparison of Olivine to Other Common Minerals

    NASA Astrophysics Data System (ADS)

    Cline, C. J., II; Burnley, P. C.

    2013-12-01

    In order to extrapolate the rheological behavior of polycrystalline earth materials to conditions and timescales that are unachievable in a laboratory setting, some sort of model is required. Numerical models are particularly appealing for this task but for these models to provide a sound platform for extrapolation they must be based on a complete understanding of all deformation mechanics that are operating in the real material. In a simplified description these mechanics can be thought of as having three components 1) the individual grains, 2) the grain boundaries and 3) the macroscopic aggregate response, which can be thought of as the interaction of the other two components within the polycrystal. Traditionally, the aggregate response is thought to represent the summed or average behavior of all individual grains deforming under the influence of the macroscopic stress tensor but; recent work within our lab using finite element models (FEM) has shown that local stress fields within the aggregate are not representative of the macroscopic stress tensor and can vary in both direction and magnitude. These variations in the stress tensor produce a pattern similar to force chains that are observed in deformation experiments on granular materials; and appear to be a direct consequence of stress percolation which is controlled by the anisotropy of the elastic and plastic strengths of the individual grains. To test this hypothesis we will conduct a suite of deformation experiments utilizing multiple monomineralic polycrystals that have a range of single crystal anisotropies. In order to infer the direction of stress acting on each grain and reconstruct the total modulation of stress direction throughout the sample, we have chosen materials that form microstructures that are sensitive to stress direction, such as deformation twins and kink bands. This experimental technique will allow for a direct comparison between the single crystal anisotropy of a material and the

  19. Deformation mechanism study of a hot rolled Zr-2.5Nb alloy by transmission electron microscopy. I. Dislocation microstructures in as-received state and at different plastic strains

    SciTech Connect

    Long, Fei; Daymond, Mark R. Yao, Zhongwen

    2015-03-07

    Thin foil dog bone samples prepared from a hot rolled Zr-2.5Nb alloy have been deformed by tensile deformation to different plastic strains. The development of slip traces during loading was observed in situ through SEM, revealing that deformation starts preferentially in certain sets of grains during the elastic-plastic transition region. TEM characterization showed that sub-grain boundaries formed during hot rolling consisted of screw 〈a〉 dislocations or screw 〈c〉 and 〈a〉 dislocations. Prismatic 〈a〉 dislocations with large screw or edge components have been identified from the sample with 0.5% plastic strain. Basal 〈a〉 and pyramidal 〈c + a〉 dislocations were found in the sample that had been deformed with 1.5% plastic strain, implying that these dislocations require larger stresses to be activated.

  20. Deformation mechanism study of a hot rolled Zr-2.5Nb alloy by transmission electron microscopy. I. Dislocation microstructures in as-received state and at different plastic strains

    NASA Astrophysics Data System (ADS)

    Long, Fei; Daymond, Mark R.; Yao, Zhongwen

    2015-03-01

    Thin foil dog bone samples prepared from a hot rolled Zr-2.5Nb alloy have been deformed by tensile deformation to different plastic strains. The development of slip traces during loading was observed in situ through SEM, revealing that deformation starts preferentially in certain sets of grains during the elastic-plastic transition region. TEM characterization showed that sub-grain boundaries formed during hot rolling consisted of screw ⟨a⟩ dislocations or screw ⟨c⟩ and ⟨a⟩ dislocations. Prismatic ⟨a⟩ dislocations with large screw or edge components have been identified from the sample with 0.5% plastic strain. Basal ⟨a⟩ and pyramidal ⟨c + a⟩ dislocations were found in the sample that had been deformed with 1.5% plastic strain, implying that these dislocations require larger stresses to be activated.

  1. Fermentation and recovery of the EcoRl restriction enzyme with a genetically modified Escherichia coli strain

    SciTech Connect

    Botterman, J.H.; DeBuyser, D.R.; Spriet, J.A.; Vansteenkiste, G.C.; Zabeau, M.

    1985-09-01

    The fermentation and recovery of the EcoRl restriction endonuclease with a genetically modified Escherichia coli strain is investigated. Vast amounts of product could be obtained after cultivation in a 20-L computer-coupled pilot fermentor and purification of the recovered wet cells. It was found that in the end the product is at least inhibitory and probably lethal to the cells (the lethality has been proven with genetic experiments) so that optimum yield requires an optimized choice for the time instant of induction. Growth after induction and product formation require substantial amounts of oxyge, which must be supplied if a high population level is to be achieved. pH control may alleviate the burden of high oxygen supply. Quantitative assessment after the different purification stages indicate that approximately 15% active enzyme can be obtained from the total amount produced.

  2. Axonal plasticity and functional recovery after spinal cord injury in mice deficient in both glial fibrillary acidic protein and vimentin genes

    NASA Astrophysics Data System (ADS)

    Menet, V.; Prieto, M.; Privat, A.; Giménez Y Ribotta, M.

    2003-07-01

    The lack of axonal regeneration in the injured adult mammalian spinal cord leads to permanent functional disabilities. The inability of neurons to regenerate their axon is appreciably due to an inhospitable environment made of an astrocytic scar. We generated mice knock-out for glial fibrillary acidic protein and vimentin, the major proteins of the astrocyte cytoskeleton, which are upregulated in reactive astrocytes. These animals, after a hemisection of the spinal cord, presented reduced astroglial reactivity associated with increased plastic sprouting of supraspinal axons, including the reconstruction of circuits leading to functional restoration. Therefore, improved anatomical and functional recovery in the absence of both proteins highlights the pivotal role of reactive astrocytes in axonal regenerative failure in adult CNS and could lead to new therapies of spinal cord lesions.

  3. Effect of High Tensile Strain Rate on the Evolution of Microstructure in Fe-Mn-C-Al Twinning-Induced Plasticity (TWIP) Steel

    NASA Astrophysics Data System (ADS)

    Das, Tuhin; Saha, Rajib; Bera, Supriya; Dahmen, Kirsten; Ghosh, Mainak; Haldar, Arunansu; Bleck, Wolfgang; Chowdhury, Sandip Ghosh

    2015-01-01

    Fe-17.8Mn-0.52C-0.5Al TWIP steel has been investigated under high-strain rate conditions. Twinning along with stacking faults and high dislocation densities in the austenite matrix has been evaluated by X-ray diffraction line profile analysis and transmission electron microscopy. The samples strained at 100 s-1 show a gradient in the evolution of the dislocation density along the gage length except the fracture end where the density shows a decrease. In case of the samples strained at 1 s-1, the evolution of density shows attainment of a near-saturation stage. Electron backscatter diffraction analysis shows that the decrease in the dislocation density as well as near-saturation stage is due to dynamic recovery as well as dynamic recrystallization at region near the fracture end. The dynamically recrystallized grains are related to the deformed matrix through twin relationship.

  4. Recovery of electric energy from formate by using a recombinant strain of Escherichia coli.

    PubMed

    Ojima, Yoshihiro; Kawata, Teruyoshi; Matsuo, Nahoko; Nishinoue, Yosuke; Taya, Masahito

    2014-10-01

    Recombinant Escherichia coli cells were applied for the recovery of electric energy from formate. Initially, the fdh gene, which encodes formate dehydrogenase (FDH) of Mycobacterium vaccae, was introduced into E. coli cells to allow efficient degradation of formate. The constructed microbial fuel cell (MFC) with E. coli BW25113 cells carrying fdh gene showed appreciable generation of current density in the presence of formate as a substrate. Current density and polarization curves revealed that the performance of MFC under examined conditions was limited by the electron transfer from bulk liquid to the electrode surface; accordingly, agitation resulted in an increase in the current density and achieved a coulombic efficiency of 21.7 % on the basis of formate consumed. Thus, gene recombination enables E. coli cells to utilize formate as a fuel for MFC. PMID:24676530

  5. Distributions of energy storage rate and microstructural evolution in the area of plastic strain localization during uniaxial tension of austenitic steel

    NASA Astrophysics Data System (ADS)

    Oliferuk, W.; Maj, M.

    2015-08-01

    The presented work is devoted to an experimental determination of the energy storage rate in the area of strain localization. The experimental procedure involves two complementary techniques: i.e. infrared thermography (IRT) and visible light imaging. The results of experiments have shown that during the evolution of plastic strain localization the energy storage rate in some areas of the deformed specimen drops to zero. To interpret the decrease of the energy storage rate in terms of micro-mechanisms, microstructural observations using Transmission Electron Microscopy (TEM) and Electron Back Scattered Diffraction (EBSC) were performed. On the basis of microstructural studies it is believed that a 0 value of energy storage rate corresponds to the state in which only two dominant components of the texture appear, creating conditions for crystallographic shear banding.

  6. Critical stresses for Si/sub x/Ge/sub 1-//sub x/ strained-layer plasticity

    SciTech Connect

    Tsao, J.Y.; Dodson, B.W.; Picraux, S.T.; Cornelison, D.M.

    1987-11-23

    We have measured the temperature-dependent onset of strain relief in metastable Si/sub x/Ge/sub 1-//sub x/ strained layers grown on Ge substrates. On the basis of these measurements, and physical arguments, we propose that strained-layer breakdown is most directly determined not by thickness and lattice mismatch, but rather by (1) an ''excess'' stress (the difference between that due to misfit strain and that due to dislocation line tension) and (2) temperature. With use of these parameters, observed regimes of stability and metastability are shown to be described within a simple, unified framework.

  7. Valproic acid modulates brain plasticity through epigenetic chromatin remodeling in the blind rat: implications for human sight recovery.

    PubMed

    Fetter-Pruneda, I; Martínez-Méndez, R; Olivos-Cisneros, L; Diaz, D; Padilla-Cortés, P; Báez-Saldaña, A; Gutiérrez-Ospina, G

    2011-01-01

    Blindness is a pervasive sensory condition that imposes diverse difficulties to carry on with activities of daily living. In blind individuals, the brain is subjected to a large scale reorganization characterized by expanded cortical territories associated with somatosensory and auditory functions and the recruitment of the former visual areas to perform bimodal somatosensory and auditory integration. This poses obstacles to efforts aimed at reassigning visual functions to the recruited visual cortex in the blind, especially after the end of the ontogentic sensitive period. Devising pharmacological measures to modulate the magnitude of brain plasticity could improve our chances of recovering visual functions in the blind. Here, by using the primary somatosensory cortex (S1) in the rat as a working model, we showed that valproic acid administered through the mother's milk prevents cortical reorganization in blinded rats by delaying neuronal histone de-acetylation. These results suggest that in the future, we might be able to devise epigenetic pharmacological measures that could improve our chances of reassigning visual functions to the once deprived former visual cortex in the blind, by modulating the magnitude of brain plasticity during critical times of development. PMID:22423589

  8. Culture and recovery of macrophages and cell lines from tissue culture-treated and -untreated plastic dishes.

    PubMed

    Fleit, S A; Fleit, H B; Zolla-Pazner, S

    1984-03-30

    Macrophages can be separated from other cell types by their ability to readily attach and spread on glass or on plastic surfaces which are treated for optimal growth of cultured cells (tissue culture-treated plastic). To detach macrophages from these surfaces, techniques must be used which require prior preparation of special flasks or vessels, utilize expensive equipment, are time-consuming and almost uniformly require that the macrophages be exposed to various chemicals. We now report that macrophages can be enriched and recovered efficiently after attachment to disposable polystyrene bacteriologic petri dishes simply by gentle scraping with a rubber policeman. In this paper we compare this method to others currently in use in which resident peritoneal cells, peritoneal exudate cells or cells from bone marrow-derived cultures are detached from treated dishes using cold shock, chelating agents and lidocaine. In all studies, advantages were noted when cells were incubated in untreated dishes and detached by gentle scraping. In addition, untreated dishes supported the growth of adherent cell lines IC-21 and L929B and yielded large numbers of cells, with high viability, which were easily harvested. PMID:6423730

  9. Bacillus amyloliquefaciens TSBSO 3.8, a biosurfactant-producing strain with biotechnological potential for microbial enhanced oil recovery.

    PubMed

    Alvarez, Vanessa Marques; Jurelevicius, Diogo; Marques, Joana Montezano; de Souza, Pamella Macedo; de Araújo, Livia Vieira; Barros, Thalita Gonçalves; de Souza, Rodrigo Octavio Mendonça Alves; Freire, Denise Maria Guimarães; Seldin, Lucy

    2015-12-01

    A screening for biosurfactant-producing bacteria was conducted with 217 strains that were isolated from environmental samples contaminated with crude oil and/or petroleum derivatives. Although 19 promising biosurfactant producers were detected, strain TSBSO 3.8, which was identified by molecular methods as Bacillus amyloliquefaciens, drew attention for its production of a high-activity compound that presented an emulsification activity of 63% and considerably decreased surface (28.5 mN/m) and interfacial (11.4 mN/m) tensions in Trypticase Soy Broth culture medium. TSBSO 3.8 growth and biosurfactant production were tested under different physical and chemical conditions to evaluate its biotechnological potential. Biosurfactant production occurred between 0.5% and 7% NaCl, at pH values varying from 6 to 9 and temperatures ranging from 28 to 50 °C. Moreover, biosurfactant properties remained the same after autoclaving at 121 °C for 15 min. The biosurfactant was also successful in a test to simulate microbial enhanced oil recovery (MEOR). Mass spectrometry analysis showed that the surface active compound was a surfactin, known as a powerful biosurfactant that is commonly produced by Bacillus species. The production of a high-efficiency biosurfactant, under some physical and chemical conditions that resemble those experienced in an oil production reservoir, such as high salinities and temperatures, makes TSBSO 3.8 an excellent candidate and creates good expectations for its application in MEOR. PMID:26350801

  10. Quasi-plane-hypothesis of strain coordination for RC beams seismically strengthened with externally-bonded or near-surface mounted fiber reinforced plastic

    NASA Astrophysics Data System (ADS)

    Ren, Zhenhua; Zeng, Xiantao; Liu, Hanlong; Zhou, Fengjun

    2013-03-01

    The application of fiber reinforced plastic (FRP), including carbon FRP and glass FRP, for structural repair and strengthening has grown due to their numerous advantages over conventional materials such as externally bonded reinforcement (EBR) and near-surface mounted (NSM) strengthening techniques. This paper summarizes the results from 21 reinforced concrete beams strengthened with different methods, including externally-bonded and near-surface mounted FRP, to study the strain coordination of the FRP and steel rebar of the RC beam. Since there is relative slipping between the RC beam and the FRP, the strain of the FRP and steel rebar of the RC beam satisfy the quasi-plane-hypothesis; that is, the strain of the longitudinal fiber that parallels the neutral axis of the plated beam within the scope of the effective height ( h 0) of the cross section is in direct proportion to the distance from the fiber to the neutral axis. The strain of the FRP and steel rebar satisfies the equation: ɛ FRP= βɛ steel, and the value of β is equal to 1.1-1.3 according to the test results.