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Sample records for describe uniaxial stress

  1. Fractional-order viscoelasticity applied to describe uniaxial stress relaxation of human arteries

    NASA Astrophysics Data System (ADS)

    Craiem, Damian; Rojo, Francisco J.; Atienza, José Miguel; Armentano, Ricardo L.; Guinea, Gustavo V.

    2008-09-01

    Viscoelastic models can be used to better understand arterial wall mechanics in physiological and pathological conditions. The arterial wall reveals very slow time-dependent decays in uniaxial stress-relaxation experiments, coherent with weak power-law functions. Quasi-linear viscoelastic (QLV) theory was successfully applied to modeling such responses, but an accurate estimation of the reduced relaxation function parameters can be very difficult. In this work, an alternative relaxation function based on fractional calculus theory is proposed to describe stress relaxation experiments in strips cut from healthy human aortas. Stress relaxation (1 h) was registered at three incremental stress levels. The novel relaxation function with three parameters was integrated into the QLV theory to fit experimental data. It was based in a modified Voigt model, including a fractional element of order α, called spring-pot. The stress-relaxation prediction was accurate and fast. Sensitivity plots for each parameter presented a minimum near their optimal values. Least-squares errors remained below 2%. Values of order α = 0.1-0.3 confirmed a predominant elastic behavior. The other two parameters of the model can be associated to elastic and viscous constants that explain the time course of the observed relaxation function. The fractional-order model integrated into the QLV theory proved to capture the essential features of the arterial wall mechanical response.

  2. Fractional-order viscoelasticity applied to describe uniaxial stress relaxation of human arteries.

    PubMed

    Craiem, Damian; Rojo, Francisco J; Atienza, José Miguel; Armentano, Ricardo L; Guinea, Gustavo V

    2008-09-07

    Viscoelastic models can be used to better understand arterial wall mechanics in physiological and pathological conditions. The arterial wall reveals very slow time-dependent decays in uniaxial stress-relaxation experiments, coherent with weak power-law functions. Quasi-linear viscoelastic (QLV) theory was successfully applied to modeling such responses, but an accurate estimation of the reduced relaxation function parameters can be very difficult. In this work, an alternative relaxation function based on fractional calculus theory is proposed to describe stress relaxation experiments in strips cut from healthy human aortas. Stress relaxation (1 h) was registered at three incremental stress levels. The novel relaxation function with three parameters was integrated into the QLV theory to fit experimental data. It was based in a modified Voigt model, including a fractional element of order alpha, called spring-pot. The stress-relaxation prediction was accurate and fast. Sensitivity plots for each parameter presented a minimum near their optimal values. Least-squares errors remained below 2%. Values of order alpha = 0.1-0.3 confirmed a predominant elastic behavior. The other two parameters of the model can be associated to elastic and viscous constants that explain the time course of the observed relaxation function. The fractional-order model integrated into the QLV theory proved to capture the essential features of the arterial wall mechanical response.

  3. Note: Manganin foil sensor for small uniaxial stress

    NASA Astrophysics Data System (ADS)

    Frampton, M. K.; McLaughlin, N.; Jin, Hu; Zieve, R. J.

    2017-04-01

    We describe a simple manganin foil resistance manometer for uniaxial stress measurements. The manometer functions at low pressures and over a range of temperatures. In this design, no temperature seasoning is necessary although the manometer must be prestressed to the upper end of the desired pressure range. The prestress pressure cannot be increased arbitrarily; irreversibility arising from shear stress limits its range. Attempting larger pressures yields irreproducible resistance measurements.

  4. Note: Manganin foil sensor for small uniaxial stress.

    PubMed

    Frampton, M K; McLaughlin, N; Jin, Hu; Zieve, R J

    2017-04-01

    We describe a simple manganin foil resistance manometer for uniaxial stress measurements. The manometer functions at low pressures and over a range of temperatures. In this design, no temperature seasoning is necessary although the manometer must be prestressed to the upper end of the desired pressure range. The prestress pressure cannot be increased arbitrarily; irreversibility arising from shear stress limits its range. Attempting larger pressures yields irreproducible resistance measurements.

  5. Uniaxial stress control of skyrmion phase

    PubMed Central

    Nii, Y.; Nakajima, T.; Kikkawa, A.; Yamasaki, Y.; Ohishi, K.; Suzuki, J.; Taguchi, Y.; Arima, T.; Tokura, Y.; Iwasa, Y.

    2015-01-01

    Magnetic skyrmions, swirling nanometric spin textures, have been attracting increasing attention by virtue of their potential applications for future memory technology and their emergent electromagnetism. Despite a variety of theoretical proposals oriented towards skyrmion-based electronics (that is, skyrmionics), few experiments have succeeded in creating, deleting and transferring skyrmions, and the manipulation methodologies have thus far remained limited to electric, magnetic and thermal stimuli. Here, we demonstrate a new approach for skyrmion phase control based on a mechanical stress. By continuously scanning uniaxial stress at low temperatures, we can create and annihilate a skyrmion crystal in a prototypical chiral magnet MnSi. The critical stress is merely several tens of MPa, which is easily accessible using the tip of a conventional cantilever. The present results offer a new guideline even for single skyrmion control that requires neither electric nor magnetic biases and consumes extremely little energy. PMID:26460119

  6. Uniaxial stress control of skyrmion phase

    NASA Astrophysics Data System (ADS)

    Nii, Y.; Nakajima, T.; Kikkawa, A.; Yamasaki, Y.; Ohishi, K.; Suzuki, J.; Taguchi, Y.; Arima, T.; Tokura, Y.; Iwasa, Y.

    2015-10-01

    Magnetic skyrmions, swirling nanometric spin textures, have been attracting increasing attention by virtue of their potential applications for future memory technology and their emergent electromagnetism. Despite a variety of theoretical proposals oriented towards skyrmion-based electronics (that is, skyrmionics), few experiments have succeeded in creating, deleting and transferring skyrmions, and the manipulation methodologies have thus far remained limited to electric, magnetic and thermal stimuli. Here, we demonstrate a new approach for skyrmion phase control based on a mechanical stress. By continuously scanning uniaxial stress at low temperatures, we can create and annihilate a skyrmion crystal in a prototypical chiral magnet MnSi. The critical stress is merely several tens of MPa, which is easily accessible using the tip of a conventional cantilever. The present results offer a new guideline even for single skyrmion control that requires neither electric nor magnetic biases and consumes extremely little energy.

  7. Uniaxial-stress-driven transformation in cold compressed glassy carbon

    NASA Astrophysics Data System (ADS)

    Yao, Mingguang; Fan, Xianhong; Zhang, Weiwei; Bao, Yongjun; Liu, Ran; Sundqvist, Bertil; Liu, Bingbing

    2017-09-01

    We show that transformation of glassy carbon (GC) into a translucent superhard carbon phase by cold-compression is obtained in the presence of a uniaxial stress field. This transition accompanies with sp2 to sp3 bonding change in GC, and it is found that the uniaxial stress strongly favors this bonding transition. The transformation of GC causes photoluminescence and significantly increases light transmissivity. Upon decompression, the high pressure phase can be maintained under large uniaxial stress at a chamber pressure even down to ˜10 GPa. We discuss possible mechanisms of these transitions by a distinct bonding process that occurs in noncrystalline carbon.

  8. Electronic processes in uniaxially stressed p-type germanium

    SciTech Connect

    Dubon, Jr., Oscar Danilo

    1996-02-01

    Effect of uniaxial stress on acceptor-related electronic processes in Ge single crystals doped with Ga, Be, and Cu were studied by Hall and photo-Hall effect measurements in conjunction with infrared spectroscopy. Stress dependence of hole lifetime in p-type Ge single crystals is used as a test for competing models of non-radiative capture of holes by acceptors. Photo-Hall effect shows that hole lifetime in Ga- and Be-doped Ge increases by over one order of magnitude with uniaxial stress at liq. He temps. Photo-Hall of Ge:Be shows a stress-induced change in the temperature dependence of hole lifetime. This is consistent with observed increase of responsivity of Ge:Ga detectors with uniaxial stress. Electronic properties of Ge:Cu are shown to change dramatically with uniaxial stress; the results provide a first explanation for the performance of uniaxially stressed, Cu-diffused Ge:Ga detectors which display a high conductivity in absence of photon signal and therefore have poor sensitivity.

  9. Uniaxially stressed Ge:Ga and Ge:Be

    SciTech Connect

    Dubon, O.D. Jr.

    1992-12-01

    The application of a large uniaxial stress to p-type Ge single crystals changes the character of both the valence band and the energy levels associated with the acceptors. Changes include the splitting of the fourfold degeneracy of the valence band top and the reduction of the ionization energy of shallow acceptors. In order to study the effect of uniaxial stress on transport properties of photoexcited holes, a variable temperature photo-Hall effect system was built in which stressed Ge:Ga and Ge:Be could be characterized. Results indicate that stress increases the lifetime and Hall mobility of photoexcited holes. These observations may help further the understanding of fundamental physical processes that affect the performance of stressed Ge photoconductors including the capture of holes by shallow acceptors.

  10. Uniaxially stressed Ge:Ga and Ge:Be

    SciTech Connect

    Dubon, Jr., Oscar Danilo

    1992-12-01

    The application of a large uniaxial stress to p-type Ge single crystals changes the character of both the valence band and the energy levels associated with the acceptors. Changes include the splitting of the fourfold degeneracy of the valence band top and the reduction of the ionization energy of shallow acceptors. In order to study the effect of uniaxial stress on transport properties of photoexcited holes, a variable temperature photo-Hall effect system was built in which stressed Ge:Ga and Ge:Be could be characterized. Results indicate that stress increases the lifetime and Hall mobility of photoexcited holes. These observations may help further the understanding of fundamental physical processes that affect the performance of stressed Ge photoconductors including the capture of holes by shallow acceptors.

  11. Investigation of a Relationship between Uniaxial and Biaxial Chemical Stress Crazing of Cast Acrylic

    DTIC Science & Technology

    1992-01-01

    number) FIELD GROUP SUB-GROUP Craze Initiation Chemical Craze Testing Uniaxial Stress Cast Acrylic Biaxial Stress Isopropyl Alcohol 19. ABSTRACT...cast acrylic with isopropyl alcohol . ASTM Standard Test Methods F484 and F1164 were used as guidelines for the uniaxial craze testing and biaxial...uniaxial and biaxial craze tests was conducted at various stress levels in conjunction with isopropyl alcohol . Isopropyl alcohol was the chosen chemical

  12. Effect of uniaxial stress on coarsening of precipitate clusters

    NASA Astrophysics Data System (ADS)

    Hort, Werner; Johnson, William C.

    1996-06-01

    The influence of moderate applied uniaxial stresses (σapp/ C 44 ≈ 10-3) on the coarsening behavior of misfitting coherent precipitates in binary alloys has been studied. Three-dimensional (3-D) computer simulations of the coarsening have been performed for elastically homogeneous systems with tetragonal misfit strain and elastically heterogeneous systems with dilatational misfit strain. Precipitate shapes are restricted to spheres. Results depend on the sign of the misfit strain, the sign of the applied field, and the character of the elastic heterogeneity: precipitates softer than the matrix phase with positive (negative) misfit strain align along the direction of the applied stress for compressive (tensile) fields and arrange in planes perpendicular to it for tensile (compressive) fields. Precipitates harder than the matrix behave in the opposite way.

  13. Effect of uniaxial stress on gallium, beryllium, and copper-doped germanium hole population inversion lasers

    SciTech Connect

    Chamberlin, Danielle Russell

    1998-05-01

    The effects of stress on germanium lasers doped with single, double, and triple acceptors have been investigated. The results can be explained quantitatively with theoretical calculations and can be attributed to specific changes in the energy levels of acceptors in germanium under stress. In contrast to previous measurements, gallium-doped Ge crystals show a decrease in lasing upon uniaxial stress. The decrease seen here is attributed to the decrease in heavy hole effective mass upon application of uniaxial stress, which results in a decreased population inversion. The discrepancy between this work and previous studies can be explained with the low compensation level of the material used here. Because the amount of ionized impurity scattering in low-compensated germanium lasers is small to begin with, the reduction in scattering with uniaxial stress does not play a significant role in changing the laser operation. Beryllium-doped germanium lasers operate based on a different mechanism of population inversion. In this material it is proposed that holes can transfer between bands by giving their energy to a neutral beryllium atom, raising the hole from the ground to a bound excited state. The free hole will then return to zero energy with some probability of entering the other band. The minimum and maximum E/B ratios for lasing change with uniaxial stress because of the change in effective mass and bound excited state energy. These limits have been calculated for the case of 300 bar [100] stress, and match very well with the observed data. This adds further credence to the proposed mechanism for population inversion in this material. In contrast to Be and Ga-doped lasers, copper-doped lasers under uniaxial stress show an increase in the range of E and B where lasing is seen. To understand this change the theoretical limits for population inversion based on both the optical phonon mechanism and the neutral acceptor mechanism have been calculated. The data are

  14. Trabecular bone microdamage and microstructural stresses under uniaxial compression.

    PubMed

    Nagaraja, Srinidhi; Couse, Tracey L; Guldberg, Robert E

    2005-04-01

    The balance between local remodeling and accumulation of trabecular bone microdamage is believed to play an important role in the maintenance of skeletal integrity. However, the local mechanical parameters associated with microdamage initiation are not well understood. Using histological damage labeling, micro-CT imaging, and image-based finite element analysis, regions of trabecular bone microdamage were detected and registered to estimated microstructural von Mises effective stresses and strains, maximum principal stresses and strains, and strain energy density (SED). Bovine tibial trabecular bone cores underwent a stepwise uniaxial compression routine in which specimens were micro-CT imaged following each compression step. The results indicate that the mode of trabecular failure observed by micro-CT imaging agreed well with the polarity and distribution of stresses within an individual trabecula. Analysis of on-axis subsections within specimens provided significant positive relationships between microdamage and each estimated tissue stress, strain and SED parameter. In a more localized analysis, individual microdamaged and undamaged trabeculae were extracted from specimens loaded within the elastic region and to the apparent yield point. As expected, damaged trabeculae in both groups possessed significantly higher local stresses and strains than undamaged trabeculae. The results also indicated that microdamage initiation occurred prior to apparent yield at local principal stresses in the range of 88-121 MPa for compression and 35-43 MPa for tension and local principal strains of 0.46-0.63% in compression and 0.18-0.24% in tension. These data provide an important step towards understanding factors contributing to microdamage initiation and establishing local failure criteria for normal and diseased trabecular bone.

  15. Effects of stress fiber contractility on uniaxial stretch guiding mitosis orientation and stress fiber alignment.

    PubMed

    Zhao, Lei; Sang, Chen; Yang, Chun; Zhuang, Fengyuan

    2011-09-02

    It has been documented that mitosis orientation (MO) is guided by stress fibers (SFs), which are perpendicular to exogenous cyclic uniaxial stretch. However, the effect of mechanical forces on MO and the mechanism of stretch-induced SFs reorientation are not well elucidated to date. In the present study, we used murine 3T3 fibroblasts as a model, to investigate the effects of uniaxial stretch on SFO and MO utilizing custom-made stretch device. We found that cyclic uniaxial stretch induced both SFs and mitosis directions orienting perpendicularly to the stretch direction. The F-actin and myosin II blockages, which resulted in disoriented SFs and mitosis directions under uniaxial stretch, suggested a high correlation between SFO and MO. Y27632 (10 μM), ML7 (50 μM, or 75 μM), and blebbistatin (50 μM, or 75 μM) treatments resulted in SFO parallel to the principle stretch direction. Upon stimulating and inhibiting the phosphorylation of myosin light chain (p-MLC), we observed a monotonic proportion of SFO to the level of p-MLC. These results suggested that the level of cell contraction is crucial to the response of SFs, either perpendicular or parallel, to the external stretch. Showing the possible role of cell contractility in tuning SFO under external stretch, our experimental data are valuable to understand the predominant factor controlling SFO response to exogenous uniaxial stretch, and thus helpful for improving mechanical models. Copyright © 2011 Elsevier Ltd. All rights reserved.

  16. Uniaxial stress induced symmetry breaking for muon sites in Fe

    NASA Technical Reports Server (NTRS)

    Kossler, W. J.; Namkung, M.; Hitti, B.; Li, Y.; Kempton, J.; Stronach, C. E.; Goode, L. R., Jr.; Lankford, W. F.; Patterson, B. D.; Kuendig, W.

    1984-01-01

    Uniaxial stress was used on Fe single crystals to induce muon precession frequency shifts. The frequency shift for a nominally pure Fe sample at 302K was -0.34 + or - .023 MHz per 100 microstrain along the 100 magnetization axis. This corresponds to a change of magnetic field at the muon of 25.1 + to 1.6G/100 magnetic moment. For an Fe (3wt%Si) single crystal the shifts were -0.348 + or - .008 MHz/100 magnetic moment. The agreement between the shifts for Fe and Fe(3wt%Si) shows the effect to be intrinsic to iron and not strongly impurity sensitive. These shifts and their temperature dependence (1/T) are dominated by the effect of strain inducted population shifts between crystallographically equivalent, but mgnetically inequivalent sites. Their magnitudes are in good agreement ith previous theoretical predictions and by previous extrapolation from calculations on Nb and V especially if both 4T(0) and 1T sites contribute comparably.

  17. The influence of uniaxial compressive stress on the phase transitions and dielectric properties of NaNO2

    NASA Astrophysics Data System (ADS)

    Seyidov, MirHasan Yu.; Mikailzade, Faik A.; Suleymanov, Rauf A.; Bulut, Nebahat; Salehli, Ferid

    2016-06-01

    The effect of uniaxial stress on dielectric properties of sodium nitrite (NaNO2) ferroelectric has been investigated. The real part of the dielectric susceptibility was measured at the frequency of 1 kHz without and on applying compressive uniaxial stress along different crystallographic directions using a uniaxial compress meter. Extraordinary changes in the dielectric constant of NaNO2 under the influence of applied uniaxial stresses were observed for the first time. The shifts of the phase transition points Ti and Tc under the uniaxial stresses σyy and σzz were investigated. The "uniaxial pressure-temperature" phase diagram of NaNO2 was obtained from these results. The observed phenomena were interpreted on the base of the phenomenological Landau theory of phase transitions in NaNO2 by taking into account the uniaxial compressive stress effect. A best agreement between the theoretical predictions and experimental results has been revealed.

  18. A uniaxial stress capacitive dilatometer for high-resolution thermal expansion and magnetostriction under multiextreme conditions

    SciTech Connect

    Küchler, R.; Stingl, C.; Gegenwart, P.

    2016-07-15

    Thermal expansion and magnetostriction are directional dependent thermodynamic quantities. For the characterization of novel quantum phases of matter, it is required to study materials under multi-extreme conditions, in particular, down to very low temperatures, in very high magnetic fields or under high pressure. We developed a miniaturized capacitive dilatometer suitable for temperatures down to 20 mK and usage in high magnetic fields, which exerts a large spring force between 40 to 75 N on the sample. This corresponds to a uniaxial stress up to 3 kbar for a sample with cross section of (0.5 mm){sup 2}. We describe design and performance test of the dilatometer which resolves length changes with high resolution of 0.02 Å at low temperatures. The miniaturized device can be utilized in any standard cryostat, including dilution refrigerators or the commercial physical property measurement system.

  19. A uniaxial stress capacitive dilatometer for high-resolution thermal expansion and magnetostriction under multiextreme conditions.

    PubMed

    Küchler, R; Stingl, C; Gegenwart, P

    2016-07-01

    Thermal expansion and magnetostriction are directional dependent thermodynamic quantities. For the characterization of novel quantum phases of matter, it is required to study materials under multi-extreme conditions, in particular, down to very low temperatures, in very high magnetic fields or under high pressure. We developed a miniaturized capacitive dilatometer suitable for temperatures down to 20 mK and usage in high magnetic fields, which exerts a large spring force between 40 to 75 N on the sample. This corresponds to a uniaxial stress up to 3 kbar for a sample with cross section of (0.5 mm)(2). We describe design and performance test of the dilatometer which resolves length changes with high resolution of 0.02 Å at low temperatures. The miniaturized device can be utilized in any standard cryostat, including dilution refrigerators or the commercial physical property measurement system.

  20. Latent heat in uniaxially stressed KMnF3 ferroelastic crystal

    NASA Astrophysics Data System (ADS)

    Romero, F. J.; Gallardo, M. C.; Jimenez, J.; del Cerro, J.; Salje, E. K. H.

    2000-05-01

    The influence of weak uniaxial stress on both the latent heat and the coexistence interval of the ferroelastic phase transition of KMnF3 has been measured using a sensitive conduction calorimeter. The latent heat of the sample without stress is 0.129 J g-1 and, in the range of \\mbox{0-12} bar, it increases weakly with the stress. The width of the interval where the latent heat appears increases with stress, with an apparently larger coexistence interval. Heating and cooling processes show different kinetic behaviours. On cooling, the maximum of the differential thermal analysis traces splits into two peaks when a uniaxial stress is applied, which is related to the formation of ferroelastic domain patterns.

  1. Surface patterns on single-crystal films under uniaxial stress: Experimental evidence for the Grinfeld instability

    NASA Astrophysics Data System (ADS)

    Berréhar, J.; Caroli, C.; Lapersonne-Meyer, C.; Schott, M.

    1992-11-01

    We study the stress relaxation in single-crystal films of polymerized polydiacetylene, in epitaxy with their monomer substrate. Polymerization induces a uniaxial stress. Two types of surface patterns are observed and studied by atomic force microscopy: films thicker than 175 nm exhibit quasiperiodic cracks perpendicular to the polymer chains; thinner ones exhibit regular wrinkles with the same orientation. The wrinkle surface deformation is stress relaxing and plastic. We show that all experimental results, in particular, the order of magnitude of the pattern spacings, are compatible with the following interpretation: as polymerization proceeds, the uniaxial stress generates a Grinfeld instability (Dok. Akad. Nauk SSSR 290, 1358 (1986) [Sov. Phys. Dokl. 31, 831 (1986)]) fed by surface diffusion. The crack pattern is a secondary instability, initiated at the sites of stress concentration provided by the wrinkles.

  2. The ideal strength of gold under uniaxial stress: an ab initio study.

    PubMed

    Wang, Hao; Li, Mo

    2010-07-28

    We employ an ab initio calculation based on density functional theory to investigate the ideal strength of face-centered cubic crystal Au under uniaxial stress along the [100] direction. We show that the stability of the perfect Au crystal under tensile stress is determined by the tetragonal shear stiffness modulus, with an ideal tensile strength of 4.2 GPa and the corresponding Lagrangian tensile strain of ∼ 0.07. The potential bifurcation from the primary uniaxial loading path is along the tetragonal shear. Under compressive stress, there is a stress-free body-centered cubic phase, which is unstable and ready to transform to a stress-free body-centered tetragonal phase with lower internal energy. The stable region is from - 1.6 to 4.2 GPa in the ideal strength, or from - 0.07 to 0.07 in the Lagrangian strain.

  3. Magnetization changes in 2% Mn pipeline steel induced by uniaxial tensile stress cycles of increasing amplitude

    SciTech Connect

    Guo, X.; Atherton, D.L.

    1995-09-01

    The application of cyclic stress to a ferromagnetic normally gives irreversible magnetization shifts towards the anhysteretic magnetization. Here experimental measurements are presented that show the irreversible magnetization changes induced by cyclic uniaxial isofield stress applied after magnetization at particular points on minor hysteresis loops. Selecting the (M,H) point and magnetization history, then applying stress cycles of increasing amplitude enables irreversible changes, initially away from and later toward the anhysteretic curve, to be obtained. Examples of a second inversion (i.e., irreversible shifts initially toward, then away and subsequently, toward the anhysteretic magnetization) with increasing amplitude cyclic uniaxial stress are also given. Preisach diagrams are used to interpret these results qualitatively in terms of local, more extensive and global anhysteretic states.

  4. Effect of uniaxial stress on substitutional Ni in ZnO

    NASA Astrophysics Data System (ADS)

    Lavrov, E. V.; Herklotz, F.; Kutin, Y. S.

    2013-04-01

    The influence of uniaxial stress on the electronic T13(F)→T23(F) transitions of Ni (d8) in ZnO at 4216, 4240, and 4247 cm-1 is studied. It is shown that the split pattern and polarized properties of IR absorption lines are consistent with a dynamic Jahn-Teller effect in the T23(F) state of the defect.

  5. Enhancing Tc in field-doped fullerenes by applying uniaxial stress

    NASA Astrophysics Data System (ADS)

    Koch, Erik

    2002-08-01

    Capitalizing on the two-dimensional nature of superconductivity in field-effect doped C60, we show that it should be possible to increase the transition temperature Tc by applying uniaxial stress perpendicular to the gate electrode. This method not only holds the promise of substantially enhancing Tc (by about 30 K per GPa), but also provides a sensitive check of the current understanding of superconductivity in the doped fullerenes.

  6. A constitutive equation for the Mullins effect in stress controlled uniaxial extension experiments

    NASA Astrophysics Data System (ADS)

    Johnson, M. A.; Beatty, M. F.

    1993-12-01

    A one-dimensional constitutive equation for the Mullins effect in rubberlike materials, which is motivated by the two phase microstructural material model proposed by Mullins and Tobin [I], is developed in [2]. The constitutive equation is used in [2] to predict the effect of stress softening on the small transverse vibration of a rubber string loaded in uniaxial extension. The two functions which comprise the constitutive equation were assumed to be monotone, but no further analysis of the actual nature of these functions was necessary. In this paper, we examine more closely how the results of a stress controlled uniaxial extension experiment can be used to gain insight into the specific nature of the microstructural strain and the strain amplification functions which comprise the constitutive equation. We examine experimental representations of the two functions which are independent of any special microstructural interpretations. Stress controlled uniaxial extension experiments with buna-n, neoprene, and silicone rubber cords are examined. We demonstrate how the experimental data can be applied to yield representations of the functions of interest to within a multiplicative constant; but no attempt is made to find specific analytical representations of these functions. For buna-n and neoprene samples, we observe behavior consistent with our monotone assumptions, while anomalous behavior is observed with silicone rubber.

  7. Cracking Process and Stress Field Evolution in Specimen Containing Combined Flaw Under Uniaxial Compression

    NASA Astrophysics Data System (ADS)

    Liu, Ting; Lin, Baiquan; Yang, Wei; Zou, Quanle; Kong, Jia; Yan, Fazhi

    2016-08-01

    Hydraulic slotting, an efficient technique for underground enhanced coal bed methane (ECBM) recovery, has been widely used in China. However, its pressure relief mechanism is unclear. Thus far, only limited research has been conducted on the relationships among the mechanical properties, flaw parameters, and crack propagation patterns of coal after hydraulic slotting. In addition, because of the limitations of test methods, an in-depth information is not available for this purpose. In this work, numerical models of specimens containing combined flaws are established based on particle flow code method. Our results provide insights into the effects of flaw inclination angle on the mechanical properties, crack propagation patterns, and temporal and spatial evolution rules of stress field in specimens containing combined flaws during the loading process. Besides, based on the initiation position and underlying mechanism, three types of crack initiation modes are identified from the failure processes of specimens. Finally, the crack propagation pattern is quantitatively described by the fractal dimension, which is found to be inversely proportional to the uniaxial compressive strength and elastic modulus of the specimen. To verify the rationality of the numerical simulation results, laboratory tests were conducted and their results match well with those obtained from the numerical simulation.

  8. Kinetics of interstitial defects in α-Fe: The effect from uniaxial stress

    NASA Astrophysics Data System (ADS)

    Kang, Changwoo; Wang, Qingyu; Shao, Lin

    2017-03-01

    Understanding defect kinetics in a stress field is important for multiscale modeling of materials degradation of nuclear materials. By means of molecular dynamics and molecular statics simulations, we calculate formation and migration energies of self-interstitial atoms (SIA) and SIA clusters (up to size of 5 interstitials) in alpha Fe and identify their stable configurations under uniaxial tensile strains. By applying uniaxial stress along [111], <111> oriented single SIA defects become more stable than <110> oriented SIA, which is opposite to stress-free condition. Diffusion of single SIA defects under [111] tensile stress is facilitated along [111] direction and the diffusion becomes one dimensional (1D). For SIA clusters, their diffusion under zero stress has gradual transition from three dimensional (3D) for small clusters to one dimensional (1D) for large clusters. Under the tensile stress along [111], the 3D to 1D transition is accelerated. For large SIA clusters, the stress effect is quickly saturated with less diffusivity enhancement in comparison with small SIA clusters.

  9. Stress-concentration factors for finite orthotropic laminates with a circular hole and uniaxial loading

    NASA Technical Reports Server (NTRS)

    Hong, C. S.; Crews, J. H., Jr.

    1979-01-01

    Stresses were calculated for finite-width orthotropic laminates with a circular hole and remote uniaxial loading using a two-dimensional finite element analysis with both uniform stress and uniform displacement boundary conditions. Five different laminates were analyzed. Computed results are presented for selected combinations of hole diameter/sheet-width ratio d/w and length-to-width ratio L/w. For small L/w values, the stress-concentration factors K sub tn were significantly different for the uniform stress and uniform displacement boundary conditions. Typically, for the uniform stress condition, the K sub tn values were much larger than for the infinite strip reference condition; however, for the uniform displacement condition, they were only slightly smaller than for this reference. The results for long strips are also presented as width correction factors. For d/w less or = 0.33, these width correction factors are nearly equal for all five laminates.

  10. Chopping skyrmions from magnetic chiral domains with uniaxial stress in magnetic nanowire

    NASA Astrophysics Data System (ADS)

    Liu, Yan; Lei, Na; Zhao, Weisheng; Liu, Wenqing; Ruotolo, Antonio; Braun, Hans-Benjamin; Zhou, Yan

    2017-07-01

    Magnetic skyrmions are envisioned as ideal candidates as information carriers for future spintronic devices, which have attracted a great deal of attention in recent years. Due to their topological protection, the creation and annihilation of magnetic skyrmions have been a challenging task. Here, we numerically demonstrate that a magnetic skyrmion can be created by chopping a chiral stripe domain with a static uniaxial strain/stress pulse. This mechanism not only provides a method to create skyrmions in magnetic nanostructures but also offers promising routes for designing tunable skyrmionic-mechanic devices.

  11. Stress concentration localization in doubly periodic square systems of circular holes in uniaxial compression

    NASA Astrophysics Data System (ADS)

    Mokryakov, V. V.

    2016-07-01

    We consider the stress concentration points in infinite elastic doubly periodic perforated plates (lattices) under the conditions of external uniaxial compression. Special attention is paid to the internal localization of stress concentrations (i.e., to the case of stress concentration origination inside the material rather than on the boundaries of the holes). We consider a parametric domain (depending on the angle of application of the external load and the structure parameter of the lattice) and calculate the domain dimensions (the extreme values of the parameters). We discover a point in the parametric domain at which the following three cases of fracture initiation are possible: two cases on the hole contour and one case inside the material.

  12. Experimental studies the evolution of stress-strain state in structured rock specimens under uniaxial loading

    NASA Astrophysics Data System (ADS)

    Oparin, Viktor; Tsoy, Pavel; Usoltseva, Olga; Semenov, Vladimir

    2014-05-01

    The aim of this study was to analyze distribution and development of stress-stress state in structured rock specimens subject to uniaxial loading to failure. Specific attention was paid to possible oscillating motion of structural elements of the rock specimens under constraints (pre-set stresses at the boundaries of the specimens) and the kinetic energy fractals. The detailed studies into the micro-level stress-strain state distribution and propagation over acting faces of rock specimens subject to uniaxial loading until failure, using automated digital speckle photography analyzer ALMEC-tv, have shown that: • under uniaxial stiff loading of prismatic sandstone, marble and sylvinite specimens on the Instron-8802 servohydraulic testing machine at the mobile grip displacement rate 0.02-0.2 mm/min, at a certain level of stressing, low-frequency micro-deformation processes originate in the specimens due to slow (quasi-static) force; • the amplitude of that deformation-wave processes greatly depends on the micro-loading stage: — at the elastic deformation stage, under the specimen stress lower than half ultimate strength of the specimen, there are no oscillations of microstrains; —at the nonlinearly elastic deformation stage, under stress varied from 0.5 to 1 ultimate strength of the specimens, the amplitudes of microstrains grow, including the descending stage 3; the oscillation frequency f=0.5-4 Hz; —at the residual strength stage, the amplitudes of the microstrains drop abruptly (3-5 times) as against stages 2 and 3; • in the elements of the scanned specimen surface in the region with the incipient crack, the microstrain rate amplitudes are a few times higher than in the undamged surface region of the same specimen. Sometimes, deformation rate greatly grows with increase in the load. The authors have used the energy scanning function of the deformation-wave processes in processing experimental speckle-photography data on the surface of the test specimen

  13. Cryogenic System for Neutron Scattering Experiments with In Situ Pressure Tuning Mechanism: Response of the Antiferromagnetism of URu2Si2 to Uniaxial Stress

    NASA Astrophysics Data System (ADS)

    Kawarazaki, Shuzo; Uwatoko, Yoshiya; Yokoyama, Makoto; Okita, Yuji; Tabata, Yoshikazu; Taniguchi, Toshifumi; Amitsuka, Hiroshi

    2002-10-01

    A handy insertable device to manipulate hydrostatic pressure or uniaxial stress on a sample in a cryostat for neutron scattering experiments is described. The pressure that is generated in a miniature hydraulic oil-cylinder on the top of the inserting stick is transmitted to the sample via a long piston-cylinder unit made of a thick stainless-steel tube and a fiber-reinforced plastics (FRP) rod. One can thus in situ tune the pressure or the stress on the sample without handling the pressure-cell at room temperature outside the cryostat. The device is designed to fit into the ILL-type Orange cryostat so that it can be used in many neutron scattering facilities. A newly designed uniaxial-stress cell and hydrostatic pressure cell to be used with this system are also described. The result of measurement of the hysteresis effect of uniaxial stress on the antiferromagnetism of URu2Si2 at 1.4 K is presented.

  14. Effect of combined external uniaxial stress and dc bias on the dielectric property of BaTiO3-based dielectrics in multilayer ceramic capacitor: thermodynamics and experiments

    NASA Astrophysics Data System (ADS)

    Yang, Gang; Yue, Zhenxing; Sun, Tieyu; Gou, Huanlin; Li, Longtu

    2008-02-01

    The dielectric properties of (Nb, Y)-doped BaTiO3 in a multilayer ceramic capacitor (MLCC) under combined external uniaxial compressive stress and dc bias field were investigated at room temperature by using a modified Ginsburg-Landau-Devonshire thermodynamic theory and the dielectric measurement. It is found that although dc bias decreases the dielectric properties dominantly, the influence of the external uniaixial compressive stress should not be neglected. When applied along a direction perpendicular to the internal electrode layer in the MLCC, the external uniaixal compressive stress will strengthen the negative effect of dc bias. In contrast, the external uniaxial compressive stress along a direction parallel to the internal electrode layer in the MLCC will increase the dielectric permittivity under dc bias field, i.e. improve the ɛ-V response of the MLCC. Furthermore, although there is a difference between the calculated permittivity and the measured permittivity, the effects of the combined external uniaxial compressive stress and dc bias field on the dielectric permittivity described through two approaches are in good agreement.

  15. Band offsets for biaxially and uniaxially stressed silicon-germanium layers with arbitrary substrate and channel orientations

    SciTech Connect

    Eneman, Geert; Roussel, Philippe; Brunco, David Paul; Collaert, Nadine; Mocuta, Anda; Thean, Aaron

    2016-08-07

    The conduction and valence band offsets between a strained silicon-germanium layer and a silicon-germanium substrate are reported for arbitrary substrate and channel crystal orientations. The offsets are calculated both for the case of biaxial stress, corresponding approximately to the stress state of a thin strained channel in a planar field-effect transistor (FET), and for uniaxial stress, which is the approximate stress state for strained channels in a FinFET configuration. Significant orientation dependence is found for the conduction band offset, overall leading to the strongest electron quantum confinement in biaxial-tensile stressed channels on {100}-oriented substrates, and uniaxial-tensile stressed channels in the 〈100〉 and 〈110〉 directions. For biaxially stressed layers on {111} substrates, the conduction band offset is significantly smaller than for {100} or {110} directions. For the valence band offset, the dependence on crystal orientation is found to be small.

  16. Phase transitions in BaTiO3 under uniaxial compressive stress: Experiments and phenomenological analysis

    NASA Astrophysics Data System (ADS)

    Schader, Florian H.; Khakpash, Nasser; Rossetti, George A.; Webber, Kyle G.

    2017-02-01

    The relative permittivity of polycrystalline BaTiO3 was measured from -150 °C to 250 °C at compressive bias stresses up to -500 MPa. Mechanical loading shifted the rhombohedral-orthorhombic, orthorhombic-tetragonal, and tetragonal-cubic phase transition temperatures and produced a pronounced broadening of the dielectric softening in the vicinity of all three transitions. The inter-ferroelectric rhombohedral-orthorhombic and orthorhombic-tetragonal phase transitions were found to be less stress sensitive than the ferroelectric-paraelectric transition occurring between tetragonal and cubic phases at the Curie point. The application of compressive stress resulted in a strong suppression of the relative permittivity, such that at the highest applied stress of -500 MPa, the permittivity in the single phase regions away from the phase transitions was found to display only a weak dependence on temperature between -100 °C and 125 °C. The experimental observations closely followed the predictions of a 2-4-6 Landau polynomial wherein the dielectric stiffness and higher-order dielectric stiffness coefficients are linear functions of uniaxial stress.

  17. Frequency Shift of Polar Whispering Gallery Modes Caused by Uniaxial Stress

    NASA Astrophysics Data System (ADS)

    Wagner, H.-P.; Schmitzer, H.; Lutti, J.; Borri, P.; Langbein, W.

    2010-03-01

    Optical whispering gallery modes in small spheres -so called microcavity optical resonators- have been investigated in the past years because they are promising as single virus or single bacterium detectors and as pressure sensors for microfluidic applications. Due to high Q-factors whispering gallery modes are very sensitive to changes of the shape and the refractive index of the sphere. Both can be caused by mechanical stress. A small exerted compressive force will therefore lead to an energy shift of the resonant modes. The relationship between this energy shift and the exerted force depends on the geometry of the experimental setup. We investigated the energy shift of polar modes in polystyrene beads of 45 micron diameter applying an uniaxial force. With increasing force we find a shift to higher energy for resonator modes with different mode order n and number l. The observed results will be compared with model calculations.

  18. An open-source platform to study uniaxial stress effects on nanoscale devices

    NASA Astrophysics Data System (ADS)

    Signorello, G.; Schraff, M.; Zellekens, P.; Drechsler, U.; Bürge, M.; Steinauer, H. R.; Heller, R.; Tschudy, M.; Riel, H.

    2017-05-01

    We present an automatic measurement platform that enables the characterization of nanodevices by electrical transport and optical spectroscopy as a function of the uniaxial stress. We provide insights into and detailed descriptions of the mechanical device, the substrate design and fabrication, and the instrument control software, which is provided under open-source license. The capability of the platform is demonstrated by characterizing the piezo-resistance of an InAs nanowire device using a combination of electrical transport and Raman spectroscopy. The advantages of this measurement platform are highlighted by comparison with state-of-the-art piezo-resistance measurements in InAs nanowires. We envision that the systematic application of this methodology will provide new insights into the physics of nanoscale devices and novel materials for electronics, and thus contribute to the assessment of the potential of strain as a technology booster for nanoscale electronics.

  19. Studies of deep level transient spectroscopy of DX centers in GaAlAs: Te under uniaxial stress

    SciTech Connect

    Li, Ming-Fu |; Yu, Y.P. |; Weber, E.R.; Haller, E.E. |; Hansen, W.L.; Bauser, E.

    1991-11-01

    DX centers in Al{sub 0.38}Ga{sub 0.62}As doped with Te have been studied by Deep Level Transient Spectroscopy (DLTS) as a function of uniaxial stress. No splitting nor broadening of the DLTS peaks were observed. However, the peak positions and heights depend on the stress and its directions. The results have been analyzed by comparison with existing models and hydrostatic pressure measurements.

  20. Effect of uniaxial stress on the reversible and irreversible permeabilities of 2% Mn pipeline steel

    SciTech Connect

    Makar, J.M.; Atherton, D.L. . Dept. of Physics)

    1994-07-01

    The results of a study of the effects of constant uniaxial stress on the irreversible and reversible differential permeabilities of minor and saturation major hysteresis loops are presented, extending an earlier study which studied those permeability components on the initial magnetization curve. Tension was found to increase both the reversible and irreversible components of the saturation major loop differential permeability in the low magnetization region, and to decrease them in the high magnetization region. The opposite effect was found for compression. This effect was explained as the result of changes in the domain structure of the sample when stressed and a resulting change in the ratio of 90[degree] of 180[degree] domain walls. The differences between the upper and lower branches of the saturation major hysteresis loop reversible relative differential permeability were found to increase in tension and decrease in compression, with more complicated behavior occurring in the irreversible component. Minor loop behavior was also found to vary depending on the magnetization of the sample. In the low magnetization region tension was found to produce higher values and larger variations in both components of the relative differential permeability than the unstressed case, while compression produced lower values and smaller variations. The opposite behavior was found to be true in the high magnetization region, while an intermediate behavior with little or no change in both the relative differential permeability components was found to exist between the two extreme cases.

  1. Effect of uniaxial stress on electroluminescence, valence band modification, optical gain, and polarization modes in tensile strained p-AlGaAs/GaAsP/n-AlGaAs laser diode structures: Numerical calculations and experimental results

    NASA Astrophysics Data System (ADS)

    Bogdanov, E. V.; Minina, N. Ya.; Tomm, J. W.; Kissel, H.

    2012-11-01

    The effects of uniaxial compression in [110] direction on energy-band structures, heavy and light hole mixing, optical matrix elements, and gain in laser diodes with "light hole up" configuration of valence band levels in GaAsP quantum wells with different widths and phosphorus contents are numerically calculated. The development of light and heavy hole mixing caused by symmetry lowering and converging behavior of light and heavy hole levels in such quantum wells under uniaxial compression is displayed. The light or heavy hole nature of each level is established for all considered values of uniaxial stress. The results of optical gain calculations for TM and TE polarization modes show that uniaxial compression leads to a significant increase of the TE mode and a minor decrease of the TM mode. Electroluminescence experiments were performed under uniaxial compression up to 5 kbar at 77 K on a model laser diode structure (p-AlxGa1-xAs/GaAs1-yPy/n-AlxGa1-xAs) with y = 0.16 and a quantum well width of 14 nm. They reveal a maximum blue shift of 27 meV of the electroluminescence spectra that is well described by the calculated change of the optical gap and the increase of the intensity being referred to a TE mode enhancement. Numerical calculations and electroluminescence data indicate that uniaxial compression may be used for a moderate wavelength and TM/TE intensity ratio tuning.

  2. Manipulating Surface States of III-V Nanowires with Uniaxial Stress.

    PubMed

    Signorello, G; Sant, S; Bologna, N; Schraff, M; Drechsler, U; Schmid, H; Wirths, S; Rossell, M D; Schenk, A; Riel, H

    2017-04-10

    III-V compound semiconductors are indispensable materials for today's high-end electronic and optoelectronic devices and are being explored for next-generation transistor logic and quantum technologies. III-V surfaces and interfaces play the leading role in determining device performance, and therefore, methods to control their electronic properties have been developed. Typically, surface passivation studies demonstrated how to limit the density of surface states. Strain has been widely used to improve the electronic transport properties and optoelectronic properties of III-Vs, but the potential of this technology to modify the surface properties still remains to be explored. Here we show that uniaxial stress induces a shift in the energy of the surface states of III-V nanowires, modifying their electronic properties. We demonstrate this phenomenon by modulating the conductivity of InAs nanowires over 4 orders of magnitude with axial strain ranging between -2.5% in compression and 2.1% in tension. The band bending at the surface of the nanostructure is modified from accumulation to depletion reversibly and reproducibly. We provide evidence of this physical effect using a combination of electrical transport measurement, Raman spectroscopy, band-structure modeling, and technology computer aided design (TCAD) simulations. With this methodology, the deformation potentials for the surface states are quantified. These results reveal that strain technology can be used to shift surface states away from energy ranges in which device performance is negatively affected and represent a novel route to engineer the electronic properties of III-V devices.

  3. Numerical Hopkinson Bar Analysis: Uni-Axial Stress and Planar Bar-Specimen Interface Conditions by Design

    DTIC Science & Technology

    2004-09-01

    3- D analysis, uni-axial stress, specimen design, planar bar-specimen interface, transmission tube 16. SECURITY CLASSIFICATION OF: 19a. NAME OF...direction; subscripts i = C, D , and E represent bar-center, specimen-edge, and bar-edge, respectively; superscripts j = 1 and 2; “1” = IB-S interface...S BD / D = 0.60 , S SH / D 1.00= , SD̂ = 0.60. .........13 Figure 11. Axial stress distribution on the surface of ceramic specimen at a different

  4. Modelling and simulation of porcine liver tissue indentation using finite element method and uniaxial stress-strain data.

    PubMed

    Fu, Y B; Chui, C K

    2014-07-18

    We hypothesize that both compression and elongation stress-strain data should be considered for modeling and simulation of soft tissue indentation. Uniaxial stress-strain data were obtained from in vitro loading experiments of porcine liver tissue. An axisymmetric finite element model was used to simulate liver tissue indentation with tissue material represented by hyperelastic models. The material parameters were derived from uniaxial stress-strain data of compressions, elongations, and combined compression and elongation of porcine liver samples. in vitro indentation tests were used to validate the finite element simulation. Stress-strain data from the simulation with material parameters derived from the combined compression and elongation data match the experimental data best. This is due to its better ability in modeling 3D deformation since the behavior of biological soft tissue under indentation is affected by both its compressive and tensile characteristics. The combined logarithmic and polynomial model is somewhat better than the 5-constant Mooney-Rivlin model as the constitutive model for this indentation simulation. Copyright © 2014 Elsevier Ltd. All rights reserved.

  5. Fracture stresses of filament wound tubes under uniaxial and biaxial loads

    NASA Astrophysics Data System (ADS)

    Amaldi, A.; Marchetti, M.

    In this paper are presented the experimental and numerical results obtained by investigating the behavior of angle-ply carbon/epoxy laminated composites when subjected to uniaxial and biaxial loads. Specimens are filament-wound cylindrical tubes with different angles of fiber deposition with respect to the tube's longitudinal axis. About forty specimens are tested. Both uniaxial and biaxial loads are carried out up to specimens' failure using an hydraulic circuit and an axial testing machine to apply internal pressure and tensile or compressive loads in order to investigate the effect of winding angle on the failure strength of the specimens. Three dimensional finite-element and thin-shell analyses are applied to the problem using different failure criteria in order to predict specimens' failure for a comparison with experimental results.

  6. Multiple slip in copper single crystals deformed in compression under uniaxial stress

    SciTech Connect

    Florando, J N; LeBlanc, M M; Lassila, D H

    2006-11-30

    Uniaxial compression experiments on copper single crystals, oriented to maximize the shear for one slip system, show some unexpected results. In addition to the expected activity on the primary slip system, the results show appreciable activity perpendicular to the primary system. The magnitude of the activity orthogonal to the primary varies from being equal to the primary for the as-fabricated samples to 1/5 of the primary in the samples annealed after fabrication.

  7. Performance enhancement in uniaxially tensile stressed GeSn n-channel fin tunneling field-effect transistor: Impact of stress direction

    NASA Astrophysics Data System (ADS)

    Wang, Hongjuan; Han, Genquan; Jiang, Xiangwei; Liu, Yan; Zhang, Chunfu; Zhang, Jincheng; Hao, Yue

    2017-04-01

    In this work, the boosting effect on the performance of GeSn n-channel fin tunneling FET (nFinTFET) enabled by uniaxial tensile stress is investigated theoretically. As the fin rotates within the (001) plane, the uniaxial tensile stress is always along its direction. The electrical characteristics of tensile-stressed GeSn nFinTFETs with point and line tunneling modes are computed utilizing the technology computer aided design (TCAD) simulator in which the dynamic nonlocal band-to-band tunneling (BTBT) algorithm is employed. In comparison with the relaxed devices, tensile-stressed GeSn nFinTFETs achieve a substantial enhancement in band-to-band tunneling generation rate (G BTBT) and on-state current I ON owing to the reduced bandgap E G induced by the tensile stress. Performance improvement of GeSn nFinTFETs induced by tensile stress demonstrates a strong dependence on channel direction and tunneling modes. Under the same magnitude of stress, line-nFinTFETs obtain a more pronounced I ON enhancement over the transistors with point tunneling mode.

  8. Tendon fascicles exhibit a linear correlation between Poisson's ratio and force during uniaxial stress relaxation.

    PubMed

    Reese, Shawn P; Weiss, Jeffrey A

    2013-03-01

    The underlying mechanisms for the viscoelastic behavior of tendon and ligament tissue are poorly understood. It has been suggested that both a flow-dependent and flow-independent mechanism may contribute at different structural levels. We hypothesized that the stress relaxation response of a single tendon fascicle is consistent with the flow-dependent mechanism described by the biphasic theory (Armstrong et al., 1984, "An Analysis of the Unconfined Compression of Articular Cartilage," ASME J. Biomech. Eng., 106, pp. 165-173). To test this hypothesis, force, lateral strain, and Poisson's ratio were measured as a function of time during stress relaxation testing of six rat tail tendon fascicles from a Sprague Dawley rat. As predicted by biphasic theory, the lateral strain and Poisson's ratio were time dependent, a large estimated volume loss was seen at equilibrium and there was a linear correlation between the force and Poisson's ratio during stress relaxation. These results suggest that the fluid dependent mechanism described by biphasic theory may explain some or all of the apparent viscoelastic behavior of single tendon fascicles.

  9. Tuning exciton energy and fine-structure splitting in single InAs quantum dots by applying uniaxial stress

    SciTech Connect

    Su, Dan; Dou, Xiuming; Wu, Xuefei; Liao, Yongping; Zhou, Pengyu; Ding, Kun; Ni, Haiqiao; Niu, Zhichuan; Zhu, Haijun; Jiang, Desheng; Sun, Baoquan

    2016-04-15

    Exciton and biexciton emission energies as well as excitonic fine-structure splitting (FSS) in single InAs/GaAs quantum dots (QDs) have been continuously tuned in situ in an optical cryostat using a developed uniaxial stress device. With increasing tensile stress, the red shift of excitonic emission is up to 5 nm; FSS decreases firstly and then increases monotonically, reaching a minimum value of approximately 10 μeV; biexciton binding energy decreases from 460 to 106 μeV. This technique provides a simple and convenient means to tune QD structural symmetry, exciton energy and biexciton binding energy and can be used for generating entangled and indistinguishable photons.

  10. Terahertz-range spontaneous emission under the optical excitation of donors in uniaxially stressed bulk silicon and SiGe/Si heterostructures

    SciTech Connect

    Zhukavin, R. Kh. Kovalevsky, K. A.; Orlov, M. L.; Tsyplenkov, V. V.; Bekin, N. A.; Yablonskiy, A. N.; Yunin, P. A.; Pavlov, S. G.; Abrosimov, N. V.; Hübers, H.-W.; Radamson, H. H.; Shastin, V. N.

    2015-01-15

    The results of measurements of the total terahertz-range photoluminescence of Group-V donors (phosphorus, antimony, bismuth, arsenic) in bulk silicon and SiGe/Si heterostructures depending on the excitation intensity are presented. The signal of bulk silicon was also measured as a function of uniaxial stress. The results of measurement of the dependence of the spontaneous emission intensity on the uniaxial stress is in rather good agreement with theoretical calculations of the relaxation times of excited states of donors in bulk silicon. Comparative measurements of the spontaneous emission from various strained heterostructures showed that the photoluminescence signal is caused by donor-doped silicon regions.

  11. Experimental observations on uniaxial whole-life transformation ratchetting and low-cycle stress fatigue of super-elastic NiTi shape memory alloy micro-tubes

    NASA Astrophysics Data System (ADS)

    Song, Di; Kang, Guozheng; Kan, Qianhua; Yu, Chao; Zhang, Chuanzeng

    2015-07-01

    In this work, the low-cycle fatigue failure of super-elastic NiTi shape memory alloy micro-tubes with a wall thickness of 150 μm is investigated by uniaxial stress-controlled cyclic tests at human body temperature 310 K. The effects of mean stress, peak stress, and stress amplitude on the uniaxial whole-life transformation ratchetting and fatigue failure of the NiTi alloy are observed. It is concluded that the fatigue life depends significantly on the stress levels, and the extent of martensite transformation and its reverse play an important role in determining the fatigue life. High peak stress or complete martensite transformation shortens the fatigue life.

  12. Inducing a direct-to-pseudodirect bandgap transition in wurtzite GaAs nanowires with uniaxial stress

    NASA Astrophysics Data System (ADS)

    Signorello, G.; Lörtscher, E.; Khomyakov, P. A.; Karg, S.; Dheeraj, D. L.; Gotsmann, B.; Weman, H.; Riel, H.

    2014-04-01

    Many efficient light-emitting devices and photodetectors are based on semiconductors with, respectively, a direct or indirect bandgap configuration. The less known pseudodirect bandgap configuration can be found in wurtzite (WZ) semiconductors: here electron and hole wave-functions overlap strongly but optical transitions between these states are impaired by symmetry. Switching between bandgap configurations would enable novel photonic applications but large anisotropic strain is normally needed to induce such band structure transitions. Here we show that the luminescence of WZ GaAs nanowires can be switched on and off, by inducing a reversible direct-to-pseudodirect band structure transition, under the influence of a small uniaxial stress. For the first time, we clarify the band structure of WZ GaAs, providing a conclusive picture of the energy and symmetry of the electronic states. We envisage a new generation of devices that can simultaneously serve as efficient light emitters and photodetectors by leveraging the strain degree of freedom.

  13. Measurement of the uniaxial mechanical properties of rat skin using different stress-strain definitions.

    PubMed

    Karimi, A; Navidbakhsh, M

    2015-05-01

    The mechanical properties of skin tissue may vary according to the anatomical locations of a body. There are different stress-strain definitions to measure the mechanical properties of skin tissue. However, there is no agreement as to which stress-strain definition should be implemented to measure the mechanical properties of skin at different anatomical locations. Three stress definitions (second Piola-Kichhoff stress, engineering stress, and true stress) and four strain definitions (Almansi-Hamel strain, Green-St. Venant strain, engineering strain, and true strain) are employed to determine the mechanical properties of skin tissue at back and abdomen locations of a rat body. The back and abdomen skins of eight rats are excised and subjected to a series of tensile tests. The elastic modulus, maximum stress, and strain of skin tissues are measured using three stress definitions and four strain definitions. The results show that the effect of varying the stress definition on the maximum stress measurements of the back skin is significant but not when calculating the elastic modulus and maximum strain. No significant effects are observed on the elastic modulus, maximum stress, and strain measurements of abdomen skin by varying the stress definition. In the true stress-strain diagram, the maximum stress (20%), and elastic modulus (35%) of back skin are significantly higher than that of abdomen skin. The true stress-strain definition is favored to measure the mechanical properties of skin tissue since it gives more accurate measurements of the skin's response using the instantaneous values. © 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

  14. Strained Germanium Quantum Well PMOSFETs on SOI with Mobility Enhancement by External Uniaxial Stress

    NASA Astrophysics Data System (ADS)

    Liu, Yan; Niu, Jiebin; Wang, Hongjuan; Han, Genquan; Zhang, Chunfu; Feng, Qian; Zhang, Jincheng; Hao, Yue

    2017-02-01

    Well-behaved Ge quantum well (QW) p-channel metal-oxide-semiconductor field-effect transistors (pMOSFETs) were fabricated on silicon-on-insulator (SOI) substrate. By optimizing the growth conditions, ultrathin fully strained Ge film was directly epitaxially grown on SOI at about 450 °C using ultra-high vacuum chemical vapor deposition. In situ Si2H6 passivation of Ge was utilized to form a high-quality SiO2/Si interfacial layer between the high-κ dielectric and channels. Strained Ge QW pMOSFETs achieve the significantly improved effective hole mobility μ eff as compared with the relaxed Si and Ge control devices. At an inversion charge density of Q inv of 2 × 1012 cm-2, Ge QW pMOSFETs on SOI exhibit a 104% μ eff enhancement over relaxed Ge control transistors. It is also demonstrated that μ eff of Ge pMOSFETs on SOI can be further boosted by applying an external uniaxial compressive strain.

  15. Strained Germanium Quantum Well PMOSFETs on SOI with Mobility Enhancement by External Uniaxial Stress.

    PubMed

    Liu, Yan; Niu, Jiebin; Wang, Hongjuan; Han, Genquan; Zhang, Chunfu; Feng, Qian; Zhang, Jincheng; Hao, Yue

    2017-12-01

    Well-behaved Ge quantum well (QW) p-channel metal-oxide-semiconductor field-effect transistors (pMOSFETs) were fabricated on silicon-on-insulator (SOI) substrate. By optimizing the growth conditions, ultrathin fully strained Ge film was directly epitaxially grown on SOI at about 450 °C using ultra-high vacuum chemical vapor deposition. In situ Si2H6 passivation of Ge was utilized to form a high-quality SiO2/Si interfacial layer between the high-κ dielectric and channels. Strained Ge QW pMOSFETs achieve the significantly improved effective hole mobility μ eff as compared with the relaxed Si and Ge control devices. At an inversion charge density of Q inv of 2 × 10(12) cm(-2), Ge QW pMOSFETs on SOI exhibit a 104% μ eff enhancement over relaxed Ge control transistors. It is also demonstrated that μ eff of Ge pMOSFETs on SOI can be further boosted by applying an external uniaxial compressive strain.

  16. An elastic analysis of stresses in a uniaxially loaded sheet containing an interference-fit bolt

    NASA Technical Reports Server (NTRS)

    Crews, J. H., Jr.

    1972-01-01

    The stresses in a sheet with an interference-fit bolt have been calculated for two sheet-bolt interface conditions: a frictionless interface and a fixed (no-slip) interface. The stress distributions were calculated for various combinations of sheet and bolt moduli. The results show that for repeated loading the local stress range is significantly smaller if an interference bolt is used instead of a loosely fitting one. This reduction in local stress range is more pronounced when the ratio of bolt modulus to sheet modulus is large. The analysis also indicates that currently used standard values of interference cause yielding in the sheet.

  17. Coarse-graining scheme for simulating uniaxial stress-strain response of glassy polymers through molecular dynamics

    NASA Astrophysics Data System (ADS)

    Majumder, Manoj K.; Ramkumar, S.; Mahajan, Dhiraj K.; Basu, Sumit

    2010-01-01

    Simulation of the deformation of polymers below their glass transition through molecular dynamics provides an useful route to correlate their molecular architecture to deformation behavior. However, present computational capabilities severely restrict the time and length scales that can be simulated when detailed models of these macromolecules are used. Coarse-graining techniques for macromolecular structures intend to make bigger and longer simulations possible by grouping atoms into superatoms and devising ways of determining reasonable force fields for the superatoms in a manner that retains essential macromolecular features relevant to the process under study but jettisons unnecessary details. In this work we systematically develop a coarse-graining scheme aimed at simulating uniaxial stress-strain behavior of polymers below their glass transition. The scheme involves a two step process of obtaining the coarse grained force field parameters above glass transition. This seems to be enough to obtain “faithful” stress-strain responses after quenching to below the glass transition temperature. We apply the scheme developed to a commercially important polymer polystyrene, derive its complete force field parameters and thus demonstrate the effectiveness of the technique.

  18. Coarse-graining scheme for simulating uniaxial stress-strain response of glassy polymers through molecular dynamics.

    PubMed

    Majumder, Manoj K; S, Ramkumar; Mahajan, Dhiraj K; Basu, Sumit

    2010-01-01

    Simulation of the deformation of polymers below their glass transition through molecular dynamics provides an useful route to correlate their molecular architecture to deformation behavior. However, present computational capabilities severely restrict the time and length scales that can be simulated when detailed models of these macromolecules are used. Coarse-graining techniques for macromolecular structures intend to make bigger and longer simulations possible by grouping atoms into superatoms and devising ways of determining reasonable force fields for the superatoms in a manner that retains essential macromolecular features relevant to the process under study but jettisons unnecessary details. In this work we systematically develop a coarse-graining scheme aimed at simulating uniaxial stress-strain behavior of polymers below their glass transition. The scheme involves a two step process of obtaining the coarse grained force field parameters above glass transition. This seems to be enough to obtain "faithful" stress-strain responses after quenching to below the glass transition temperature. We apply the scheme developed to a commercially important polymer polystyrene, derive its complete force field parameters and thus demonstrate the effectiveness of the technique.

  19. Stress-intensity factor solutions for cracks at countersunk rivet holes under uniaxial tension

    NASA Astrophysics Data System (ADS)

    Tan, P. W.; Bigelow, C. A.; Odonoghue, P. E.; Atluri, S. N.

    1994-02-01

    To predict crack growth and fracture strengths of riveted joints subjected to widespread fatigue damage, accurate stress and fracture analyses of corner and surface cracks at a rivet hole are needed. The results presented in this report focus on the computation of stress-intensity factor solutions for rivet holes with cracks. The stress-intensity factor solutions for surface and corner cracks at countersunk rivet holes in a plate were obtained using the finite-element-alternating technique. A range of crack shapes, crack sizes, and crack locations under remote tension were considered.

  20. A study on a rigid body boundary layer interface force model for stress calculation and stress strain behaviour of nanoscale uniaxial tension

    NASA Astrophysics Data System (ADS)

    Lin, Zone-Ching; Huang, Jen-Ching

    2004-11-01

    A rigid body boundary layer interface force (RIF) model for stress calculation on the nanoscale is proposed in this paper for calculating stress based on molecular dynamics. The RIF model is used to study the stress-stain behaviour when nanoscale single crystal copper is under uniaxial tension, and is used for 15 tensile simulations each with different strain rate. The stress-strain curve established from simulation was first converted into a true stress-strain curve; a regression analysis was then applied in order to find the flow curve. From simulation results, it is found that the strain rate has large influence on both K and n values of the flow curve. At low strain rate (less than 1 × 1012 s-1), both K and n values decrease with the increase of strain rate. When the strain rate exceeds 1 × 1012 s-1, the strain rate against the K and n values of the flow curve approaches a constant. Flow curve equations considering the influence of strain rate are derived; both complete and simplified forms of flow curve equations are also derived. It is observed that the lower the strain rates, the higher the fluctuations of the stress-strain curve. Furthermore, the increase of strain rate resulting in a smoother stress-strain curve is also found.

  1. Liver tissue characterization from uniaxial stress-strain data using probabilistic and inverse finite element methods.

    PubMed

    Fu, Y B; Chui, C K; Teo, C L

    2013-04-01

    Biological soft tissue is highly inhomogeneous with scattered stress-strain curves. Assuming that the instantaneous strain at a specific stress varies according to a normal distribution, a nondeterministic approach is proposed to model the scattered stress-strain relationship of the tissue samples under compression. Material parameters of the liver tissue modeled using Mooney-Rivlin hyperelastic constitutive equation were represented by a statistical function with normal distribution. Mean and standard deviation of the material parameters were determined using inverse finite element method and inverse mean-value first-order second-moment (IMVFOSM) method respectively. This method was verified using computer simulation based on direct Monte-Carlo (MC) method. The simulated cumulative distribution function (CDF) corresponded well with that of the experimental stress-strain data. The resultant nondeterministic material parameters were able to model the stress-strain curves from other separately conducted liver tissue compression tests. Stress-strain data from these new tests could be predicted using the nondeterministic material parameters. Copyright © 2013 Elsevier Ltd. All rights reserved.

  2. Raman-strain relations in highly strained Ge: Uniaxial ⟨100⟩, ⟨110⟩ and biaxial (001) stress

    NASA Astrophysics Data System (ADS)

    Gassenq, A.; Tardif, S.; Guilloy, K.; Duchemin, I.; Pauc, N.; Hartmann, J. M.; Rouchon, D.; Widiez, J.; Niquet, Y. M.; Milord, L.; Zabel, T.; Sigg, H.; Faist, J.; Chelnokov, A.; Rieutord, F.; Reboud, V.; Calvo, V.

    2017-02-01

    The application of high values of strain to Ge considerably improves its light emission properties and can even turn it into a direct band gap semiconductor. Raman spectroscopy is routinely used for strain measurements. Typical Raman-strain relationships that are used for Ge were defined up to ˜1% strain using phonon deformation potential theory. In this work, we have studied this relationship at higher strain levels by calculating and measuring the Raman spectral shift-strain relations in several different strain configurations. Since differences were shown between the usual phonon deformation potential theory and ab-initio calculations, we highlight the need for experimental calibrations. We have then measured the strain in highly strained Ge micro-bridges and micro-crosses using Raman spectroscopy performed in tandem with synchrotron based micro-diffraction. High values of strain are reported, which enable the calibration of the Raman-strain relations up to 1.8% of in plane strain for the (001) biaxial stress, 4.8% strain along ⟨100⟩, and 3.8% strain along ⟨110⟩. For Ge micro-bridges, oriented along ⟨100⟩, the nonlinearity of the Raman shift-strain relation is confirmed. For the ⟨110⟩ orientation, we have shown that an unexpected non-linearity in the Raman-strain relationship has also to be taken into account for high stress induction. This work demonstrates an unprecedented level of strain measurement for the ⟨110⟩ uniaxial stress and gives a better understanding of the Raman-strain relations in Ge.

  3. Uniaxial-stress tuned large magnetic-shape-memory effect in Ni-Co-Mn-Sb Heusler alloys

    NASA Astrophysics Data System (ADS)

    Salazar Mejía, C.; Küchler, R.; Nayak, A. K.; Felser, C.; Nicklas, M.

    2017-02-01

    Combined strain and magnetization measurements on the Heusler shape-memory alloys Ni45Co5Mn38Sb12 and Ni44Co6Mn38Sb12 give evidence for strong magneto-structural coupling. The sample length changes up to 1% at the martensitic transformation, between a ferromagnetic, austenitic phase at high temperatures and a weakly magnetic, low-symmetry martensitic phase at lower temperatures. Under moderate uniaxial stress, the change in the sample length increases to and saturates at about 3%, pointing to stabilization of a single martensitic variant. A reverse martensitic transformation can also be induced by applying magnetic field: we find that within the temperature range of thermal hysteresis of the martensitic transformation, applying a field can induce a metastable expansion of the sample, while at slightly lower temperatures, the field response is reversible. These findings provide key information for future use of Ni(Co)-Mn-Sb-based Heusler compounds in, e.g., actuators and mechanical switches.

  4. Hypersonic Velocities and Submicrocrack Formation in Ductile Polymers under Uniaxial Tensile Stress

    NASA Astrophysics Data System (ADS)

    Shichijyo, Shiro; Nishimura, Kazuhiro; Shirouzu, Shigenori; Matsushige, Kazumi; Takemura, Tetuo

    1984-07-01

    Longitudinal hypersonic sound velocities in two kinds of ductile polymer, polycarbonate (PC) and polyethylene terephthalate (PET), were examined by Brillouin scattering. These two materials exhibited a decrease in hypersonic sound velocity (the softening phenomenon) when stress was applied, but the amount of softening as well as its angular dependence with respect to the stress direction were much smaller than those for a typical brittle polymer, poly (methyl methacrylate) (PMMA). Furthermore, a correlation between these acoustic properties and the formation of submicrocracks was demonstrated by small-angle X-ray scattering (SAXS) measurements. The difference in the anisotropies in the softening of sound velocity between ductile and brittle polymers is discussed from the viewpoint of the shape and density of the submicrocracks

  5. Recombination luminescence in irradiated silicon-effects of uniaxial stress and temperature variations.

    NASA Technical Reports Server (NTRS)

    Jones, C. E.; Compton, W. D.

    1971-01-01

    Demonstration that luminescence in irradiated silicon consists of a spectral group between 0.80 and 1.0 eV which seems to be independent of impurities, while a lower energy group between 0.60 and 0.80 eV is seen only in pulled crystals. The small halfwidth and temperature dependence of the sharp zero-phonon lines observed in these spectra indicate that the luminescence arises from a bound-to-bound transition. A model is proposed for the transition mechanism. Stress data taken on the 0.79-eV zero-phonon line in pulled crystals can be fit by either a tetragonal 100 (in brackets) defect symmetry or by conduction-band splitting effects. It is suggested that the 0.79-eV zero-phonon line and the 0.60- to 0.80-eV spectral group arise from the EPR G-15 center. Stress data on a zero-phonon line at 0.97 eV associated with the 0.80- to 1.0-eV spectral group can be explained by a trigonal 111 (in brackets) defect. The divacancy is tentatively suggested as responsible for this luminescence spectra.

  6. On the fracture of high temperature alloys by creep cavitation under uniaxial or biaxial stress states

    NASA Astrophysics Data System (ADS)

    Sanders, John W.; Dadfarnia, Mohsen; Stubbins, James F.; Sofronis, Petros

    2017-01-01

    It is well known that creep rupture in high temperature alloys is caused by grain boundary cavitation: the nucleation, growth, and coalescence of voids along grain boundaries. However, it has been observed recently that the multiaxial rupture behavior of a promising class of high temperature alloys (Tung et al., 2014) cannot be captured by a well-known empirical creep rupture model due to Hayhurst. In an effort to gain a better understanding of rupture in these materials, we depart from empirical models and simulate the underlying rupture mechanisms directly, employing two related models of void growth from the literature: one due to Sham and Needleman (1983), and an extension of Sham and Needleman's model due to Van der Giessen et al. (1995). Our results suggest that the experimental observations might be explained in terms of the interplay between bulk creep and gain boundary diffusion processes. Furthermore, we find that Sham and Needleman's original void growth model, combined with our rupture model, is well suited to capture the experimental data considered here. Such a mechanism-based understanding of the influence of multiaxial stress states on the creep rupture behavior of high temperature alloys promises to be of value and to provide a basis for the qualification of these alloys for extended service in a variety of elevated temperature applications.

  7. Phenomenological theory of electric-field-induced phase transition behavior of antiferroelectric ceramic (Pb,Ba,La)(Zr,Sn,Ti)O3 under uniaxial compressive pre-stress

    NASA Astrophysics Data System (ADS)

    Xu, Yonghao; Feng, Yujun; Zhang, Na; Yan, Yangxi; Liao, Liming

    2012-08-01

    The phase transition behavior of antiferroelectric ceramic (Pb,Ba,La)(Zr,Sn,Ti)O3 under uniaxial compressive pre-stress is observed at stress up to 100 MPa using a homebuilt experimental setup in conjunction with a modified Sawyer-Tower circuit. The results reveal that the saturation polarization (Psat) decrease with increasing compressive pre-stress, while the phase transition fields increase as the compressive pre-stress increases. Meanwhile the applied pre-stress virtually does not affect the transition field hysteresis (ΔE). The longitudinal strain (S) increases with increasing compressive pre-stress and reaches to maximum at 20 MPa, and then gradually decreases. A phenomenological thermodynamic theory has been developed to model the first-order phase transition behavior of the material.

  8. Contributions of Domain-Related Phenomena on Dielectric Constant of Lead-Based Ferroelectric Ceramics Under Uniaxial Compressive Pre-Stress

    NASA Astrophysics Data System (ADS)

    Yimnirun, Rattikorn

    The dielectric constant of lead-based ferroelectric ceramics in three different systems, i.e. BT-PZT, PMN-PT and PMN-PZT, was measured under uniaxial compressive pre-stress to investigate the contributions of different domain-phenomena. The dielectric constant was observed at room temperature under the compressive pre-stress up to 15 MPa, 22 MPa and 5 MPa for BT-PZT, PMN-PT and PMN-PZT, respectively, using a homebuilt uniaxial compressometer. Dielectric constant of the BT-PZT ceramics increased significantly with increasing applied stress. Larger changes in the dielectric constant with the applied stress were observed in the PZT-rich compositions. However, for PMN-PT and PMN-PZT ceramic systems, changes in the dielectric constant with the stress were found to depend significantly on the ceramic compositions. The experimental results could be explained by both intrinsic and extrinsic domain-related mechanisms involving domain wall motions, as well as the de-aging phenomenon from the application of the compressive pre-stress. Roles of different types of domains, i.e. micro-domains and nano-domains, were also discussed.

  9. Modifications on A-F hardening rule to assess ratcheting response of materials and its interaction with fatigue damage under uniaxial stress cycles

    NASA Astrophysics Data System (ADS)

    Ahmadzadehrishehri, Gholamreza

    Ratcheting deformation is accumulated progressively over three distinct stages in materials undergoing asymmetrical cyclic stresses. The present thesis evaluates the triphasic ratcheting response of materials from two stand points: (i) Mechanistic approach at which stages of ratcheting progress over stress cycles was related to mechanistic parameters such as stress level, lifespan, mechanical properties and the softening/hardening response of materials. Mechanistic approach formulated in this thesis was employed to assess ratcheting strain over triphasic stages in various steel and copper alloys under uniaxial stress cycles. Good agreements were achieved between the predicted ratcheting strain values based on the proposed formulation and those of experimentally reported. (ii) Kinematic hardening rule approach at which the hardening rule was characterized by the yield surface translation mechanism and the corresponding plastic modulus calculated based on the consistency condition. Various cyclic plasticity models were employed to assess ratcheting response of materials under different loading conditions. The Armstrong-Frederick (A-F) hardening rule was taken as the backbone of ratcheting analysis developed in this thesis mainly due to less complexity and number of coefficients in the hardening rule as compared with other earlier developed hardening rules in the literature. To predict triphasic ratcheting strain over stress cycles, the A-F hardening rule has been further developed by means of new strain rate coefficients gamma 2 and delta. These coefficients improved the hardening rule capability to calibrate and control the rate of ratcheting over its progressive stages. The modified hardening formulation holds the coefficients of the hardening rule to control stress-strain hysteresis loops generated over stress cycles during ratcheting process plus the ratcheting rates over stages I, II, and III. These coefficients were calibrated and defined based on the applied

  10. Uniaxial Compression Experiments on PZT 95/5-2Nb Ceramic: Evidence for an Orientation-Dependent, ''Maximum Compressive Stress'' Criterion for Onset of the F(R1)()A(O) Polymorphic Phase Transformation

    SciTech Connect

    Carlson, L.W.; Grazier, J.M.; Holcomb, D.J.; Montgomery, S.T.; Zeuch, D.H.

    1999-01-01

    Some time ago we presented evidence that, under nonhydrostatic loading, the F{sub R1} {r_arrow} A{sub O} polymorphic phase transformation in unpoled PZT 95/5-2Nb ceramic began when the maximum compressive stress equaled the hydrostatic pressure at which the transformation otherwise took place. More recently, we showed that this simple stress criterion did not apply to nonhydrostatically compressed, poled ceramic. However, unpoled ceramic is isotropic, whereas poled ceramic has a preferred crystallographic orientation and is mechanically anisotropic. If we further assume that the transformation depends not only on the magnitude of the compressive stress, but also its orientation relative to some feature(s) of PZT 95/5-2Nb's crystallography, then these disparate results can be qualitatively resolved. In this report, we first summarize the existing results for unpoled and poled ceramic. Using our orientation-dependent hypothesis and these results, we derive simple arithmetic expressions that accurately describe our previously-observed effects of nonhydrostatic stress on the transformation of unpoled ceramic. We then go on to test new predictions based on the orientation-dependent model. It has long been known that the transformation can be triggered in uniaxial compression: the model specifically requires a steadily increasing axial stress to drive the transformation of a randomly-oriented polycrystal to completion. We show that when the stress is held constant during uniaxial compression experiments, the transformation stops, supporting our hypothesis. We close with a discussion of implications of our model, and ways to test it using poled ceramic.

  11. Cyclic hardening in copper described in terms of combined monotonic and cyclic stress-strain curves

    SciTech Connect

    Chandler, H.D. . School of Mechanical Engineering)

    1995-01-01

    Hardening of polycrystalline copper subjected to tension-compression loading cycles in the plastic region is discussed with reference to changes in flow stress determined from equations describing dislocation glide. It is suggested that hardening is as a result of the accumulation of strain on a monotonic stress-strain curve. On initial loading, the behavior is monotonic. On stress reversal, a characteristic cyclic stress-strain curve is followed until the stress reaches a value in reverse loading corresponding to the maximum attained during the preceding half cycle. Thereafter, the monotonic path is followed until strain reversal occurs at completion of the half cycle. Repetition of the process results in cyclic hardening. Steady state cyclic behavior is reached when a stress associated with the monotonic stress-strain curve is reached which is equal to the stress associated with the cyclic stress-strain curve corresponding to the imposed strain amplitude.

  12. Stress-mediated magnetoelectric memory effect with uni-axial TbCo2/FeCo multilayer on 011-cut PMN-PT ferroelectric relaxor

    NASA Astrophysics Data System (ADS)

    Dusch, Yannick; Tiercelin, Nicolas; Klimov, Alexey; Giordano, Stefano; Preobrazhensky, Vladimir; Pernod, Philippe

    2013-05-01

    We present here the implementation of a magnetoelectric memory with a voltage driven writing method using a ferroelectric relaxor substrate. The memory point consists of a magnetoelastic element in which two orthogonal stable magnetic states are defined by combining uni-axial anisotropy together with a magnetic polarization in the hard axis direction. Using a ferroelectric relaxor substrate, an anisotropic stress is created in the magnetic element when applying a voltage across electrodes. Because of the inverse magnetostrictive effect, the effective anisotropy of the magnetic element is controlled by the applied voltage and used to switch magnetization from one state to the other.

  13. Dependence of the Redshifted and Blueshifted Photoluminescence Spectra of Single InxGa1-xAs/GaAs Quantum Dots on the Applied Uniaxial Stress

    NASA Astrophysics Data System (ADS)

    Jöns, K. D.; Hafenbrak, R.; Singh, R.; Ding, F.; Plumhof, J. D.; Rastelli, A.; Schmidt, O. G.; Bester, G.; Michler, P.

    2011-11-01

    We apply external uniaxial stress to tailor the optical properties of InxGa1-xAs/GaAs quantum dots. Unexpectedly, the emission energy of single quantum dots controllably shifts to both higher and lower energies under tensile strain. Theoretical calculations using a million atom empirical pseudopotential many-body method indicate that the shifting direction and magnitude depend on the lateral extension and more interestingly on the gallium content of the quantum dots. Our experimental results are in good agreement with the underlying theory.

  14. Dielectric responses of modified BaTiO3 ceramics in multilayer ceramic capacitors to the combined uniaxial stress and dc bias field

    NASA Astrophysics Data System (ADS)

    Yang, Gang; Yue, Zhenxing; Gui, Zhilun; Li, Longtu

    2008-10-01

    Dielectric measurements of modified BaTiO3 in a multilayer ceramic capacitor (MLCC) show that the application of external uniaxial stress perpendicular to electric field in a MLCC can lead to a slight increase in the dielectric permittivity. The additional application of a dc bias results in a significantly suppressed dielectric permittivity in the temperature range from 228 to 453 K. These observations can be explained as a result of domain wall movements in grains with a core-shell structure, due to the combined stress and dc bias field. As the dc bias increased up to 5.6 MV/m, the Curie peak, which has diffuse phase transition characteristics in the absence of dc bias, becomes sharper, and two new peaks are induced at about 250 and 315 K. Furthermore, the first order paraelectric-ferroelectric phase transition of the modified BaTiO3 ceramic becomes stronger with increasing dc bias when a uniaxial stress is also applied.

  15. Plane stress yield function described by 3rd-degree spline curve and its application

    NASA Astrophysics Data System (ADS)

    Aamaishi, Toshiro; Tsutamori, Hideo; Iizuka, Eiji; Sato, Kentaro; Ogihara, Yuki; Matsui, Yohei

    2016-08-01

    In this study, a plane stress yield function which is described by 3rd-degree spline curve is proposed. This yield function can predict a material anisotropy with flexibility and consider evolution of anisotropy in terms of both r values and stresses. As an application, hole expanding simulation results are shown to discuss accuracy of the proposed yield function.

  16. Uniaxial Tension Test of Slender Reinforced Early Age Concrete Members

    PubMed Central

    Mimura, Yoichi; Yoshitake, Isamu; Zhang, Wenbo

    2011-01-01

    The present study aims to obtain the tensile properties of early age concrete based on a uniaxial tension test employing RC slender members. First, the paper shows that concrete strain is equal to the strain of rebar at the mid-span of the RC member. The tensile Young’s modulus and the strain capacity of early age concrete are estimated using strain measurements. The experiment indicated that the tensile Young’s modulus at an early age is higher than the compressive modulus. This observation was similar to one found in a previous investigation which used a direct tension test of early age concrete. Moreover, the paper describes how an empirical equation for mature concrete can be applied to the relation between uniaxial tensile strength and splitting tensile strength even in early age concrete. Based on a uniaxial tension test, the paper proposes an empirical equation for the relationship between standard bond stresses and relative slip. PMID:28824146

  17. A comparative study on the uniaxial mechanical properties of the umbilical vein and umbilical artery using different stress-strain definitions.

    PubMed

    Karimi, Alireza; Navidbakhsh, Mahdi

    2014-12-01

    The umbilical cord is part of the fetus and generally includes one umbilical vein (UV) and two umbilical arteries (UAs). As the saphenous vein and UV are the most commonly used veins for the coronary artery disease treatment as a coronary artery bypass graft (CABG), understating the mechanical properties of UV has a key asset in its performance for CABG. However, there is not only a lack of knowledge on the mechanical properties of UV and UA but there is no agreement as to which stress-strain definition should be implemented to measure their mechanical properties. In this study, the UV and UA samples were removed after caesarean from eight individuals and subjected to a series of tensile testing. Three stress definitions (second Piola-Kichhoff stress, engineering stress, and true stress) and four strain definitions (Almansi-Hamel strain, Green-St. Venant strain, engineering strain, and true strain) were employed to determine the linear mechanical properties of UVs and UAs. The nonlinear mechanical behavior of UV/UA was computationally investigated using hyperelastic material models, such as Ogden and Mooney-Rivlin. The results showed that the effect of varying the stress definition on the maximum stress measurements of the UV/UA is significant but not when calculating the elastic modulus. In the true stress-strain diagram, the maximum strain of UV was 92 % higher, while the elastic modulus and maximum stress were 162 and 42 % lower than that of UA. The Mooney-Rivlin material model was designated to represent the nonlinear mechanical behavior of the UV and UA under uniaxial loading.

  18. Educational Leaders Describe a Job Too Big for One: Stress Reduction In the Midst of Leading

    ERIC Educational Resources Information Center

    Wells, Caryn M.

    2013-01-01

    This conceptual paper reviews research findings about the world of stress of principals and superintendents, focusing on the high levels of stress that the educational leaders report. The literature on occupational stress is also explored for its insights on the medical and psychological results of workplace stress and the relationship to stress…

  19. Educational Leaders Describe a Job Too Big for One: Stress Reduction In the Midst of Leading

    ERIC Educational Resources Information Center

    Wells, Caryn M.

    2013-01-01

    This conceptual paper reviews research findings about the world of stress of principals and superintendents, focusing on the high levels of stress that the educational leaders report. The literature on occupational stress is also explored for its insights on the medical and psychological results of workplace stress and the relationship to stress…

  20. The mullins effect in uniaxial extension and its influence on the transverse vibration of a rubber string

    NASA Astrophysics Data System (ADS)

    Johnson, M. A.; Beatty, M. F.

    1993-06-01

    This paper presents a study of the stress softening effect encountered in uniaxial extension and explores its effect on the small amplitude transverse vibration of a stretched rubber cord. An idealization of the uniaxial stressstrain behavior of a stress softening material is presented, the importance of the deformation history is emphasized, and parameters are introduced to track the deformation history. An extended investigation of a model proposed by Mullins and Tobin to quantify stress softening by introduction of a strain amplification factor is then presented. A major result derived from this model is shown to be consistent with results reported by others. The uniaxial stress softening theory is used to describe the transverse vibration behavior of a rubber string subjected to repeated stretching. This appears to be the first application of the softening model of Mullins and Tobin to a dynamical problem. Analytical results are compared with uniaxial stress-strain and transverse vibration experiments performed with buna-n, neoprene, and silicone rubber cords. Both types of experiments provide a simple and novel method to evaluate the predictive success of our uniaxial theory without the need for a specific constitutive model. The pseudoelastic response found in biological tissues is discussed in light of results obtained in the transverse vibration experiments.

  1. Slotted Antenna with Uniaxial Dielectric Covering

    DTIC Science & Technology

    2016-07-08

    1 of 12 SLOTTED ANTENNA WITH UNIAXIAL DIELECTRIC COVERING STATEMENT OF GOVERNMENT INTEREST [0001] The invention described herein may be...therefor. CROSS REFERENCE TO OTHER PATENT APPLICATIONS [0002] None. BACKGROUND OF THE INVENTION (1) Field of the Invention [0003] The present... invention is directed to a slotted antenna having enhanced broadband characteristics. (2) Description of the Prior Art [0004] Slotted cylinder antennas

  2. Suspended monolayer graphene under true uniaxial deformation

    NASA Astrophysics Data System (ADS)

    Polyzos, Ioannis; Bianchi, Massimiliano; Rizzi, Laura; Koukaras, Emmanuel N.; Parthenios, John; Papagelis, Konstantinos; Sordan, Roman; Galiotis, Costas

    2015-07-01

    2D crystals, such as graphene, exhibit the higher strength and stiffness of any other known man-made or natural material. So far, this assertion has been primarily based on modelling predictions and on bending experiments in combination with pertinent modelling. True uniaxial loading of suspended graphene is not easy to accomplish; however such an experiment is of paramount importance in order to assess the intrinsic properties of graphene without the influence of an underlying substrate. In this work we report on uniaxial tension of graphene up to moderate strains of ~0.8%. This has been made possible by sandwiching the graphene flake between two polymethylmethacrylate (PMMA) layers and by suspending its central part by the removal of a section of PMMA with e-beam lithography. True uniaxial deformation is confirmed by the measured large phonon shifts with strain by Raman spectroscopy and the indication of lateral buckling (similar to what is observed for thin macroscopic membranes under tension). Finally, we also report on how the stress is transferred to the suspended specimen through the adhesive grips and determine the value of interfacial shear stress that is required for efficient axial loading in such a system.2D crystals, such as graphene, exhibit the higher strength and stiffness of any other known man-made or natural material. So far, this assertion has been primarily based on modelling predictions and on bending experiments in combination with pertinent modelling. True uniaxial loading of suspended graphene is not easy to accomplish; however such an experiment is of paramount importance in order to assess the intrinsic properties of graphene without the influence of an underlying substrate. In this work we report on uniaxial tension of graphene up to moderate strains of ~0.8%. This has been made possible by sandwiching the graphene flake between two polymethylmethacrylate (PMMA) layers and by suspending its central part by the removal of a section of

  3. A resource allocation model describing consequences of artificial selection under metabolic stress.

    PubMed

    van der Waaij, E H

    2004-04-01

    Long-term selection on production results in increased environmental sensitivity. This often is expressed through decreased fertility and increased health problems. The phenomenon has been described in all common farm animal species. One theory is that potential resource intake is insufficient to express production potential. Additional resources are drawn away from fitness-related traits, such as fertility and health, to further increase observed production. In addition, resources for maintaining fitness depend on the demands by the environment. In a harsh environment, more resources are required for fitness-related traits than in an optimal environment. Literature results show that selection in an optimal environment will increase sensitivity to less optimal environments. The objectives of this paper were to increase understanding of the underlying mechanism behind the development of environmental sensitivity and to gain insight into correlated response(s) when selection is on observed production. A resource allocation model was defined where observed production depended on production potential, resource intake potential, and the allocation of resources to production or fitness, including maintenance, health, and reproduction. Penalties for reproductive performance and probability of survival were included when the proportion of resources assigned to fitness dropped below a certain, environment-related, threshold. Mass selection was practiced on observed production during 40 generations using stochastic simulation. Depending on the heritabilities of the underlying components and on the environment, selection on observed production resulted in a decrease in reproductive rate and in the development of environmental sensitivity when resource intake becomes limiting. Correlations of observed production with underlying components changed across generations, following a nonlinear pattern. The proposed model is simple, but increases the understanding of underlying

  4. Suspended monolayer graphene under true uniaxial deformation.

    PubMed

    Polyzos, Ioannis; Bianchi, Massimiliano; Rizzi, Laura; Koukaras, Emmanuel N; Parthenios, John; Papagelis, Konstantinos; Sordan, Roman; Galiotis, Costas

    2015-08-14

    2D crystals, such as graphene, exhibit the higher strength and stiffness of any other known man-made or natural material. So far, this assertion has been primarily based on modelling predictions and on bending experiments in combination with pertinent modelling. True uniaxial loading of suspended graphene is not easy to accomplish; however such an experiment is of paramount importance in order to assess the intrinsic properties of graphene without the influence of an underlying substrate. In this work we report on uniaxial tension of graphene up to moderate strains of ∼0.8%. This has been made possible by sandwiching the graphene flake between two polymethylmethacrylate (PMMA) layers and by suspending its central part by the removal of a section of PMMA with e-beam lithography. True uniaxial deformation is confirmed by the measured large phonon shifts with strain by Raman spectroscopy and the indication of lateral buckling (similar to what is observed for thin macroscopic membranes under tension). Finally, we also report on how the stress is transferred to the suspended specimen through the adhesive grips and determine the value of interfacial shear stress that is required for efficient axial loading in such a system.

  5. Reliability Analysis of Uniaxially Ground Brittle Materials

    NASA Technical Reports Server (NTRS)

    Salem, Jonathan A.; Nemeth, Noel N.; Powers, Lynn M.; Choi, Sung R.

    1995-01-01

    The fast fracture strength distribution of uniaxially ground, alpha silicon carbide was investigated as a function of grinding angle relative to the principal stress direction in flexure. Both as-ground and ground/annealed surfaces were investigated. The resulting flexural strength distributions were used to verify reliability models and predict the strength distribution of larger plate specimens tested in biaxial flexure. Complete fractography was done on the specimens. Failures occurred from agglomerates, machining cracks, or hybrid flaws that consisted of a machining crack located at a processing agglomerate. Annealing eliminated failures due to machining damage. Reliability analyses were performed using two and three parameter Weibull and Batdorf methodologies. The Weibull size effect was demonstrated for machining flaws. Mixed mode reliability models reasonably predicted the strength distributions of uniaxial flexure and biaxial plate specimens.

  6. Twinning in shear and uniaxial loading in five layered martensite Ni-Mn-Ga single crystals

    NASA Astrophysics Data System (ADS)

    Aaltio, Ilkka; Ge, Yanling; Hannula, Simo-Pekka

    2013-02-01

    Five-layered martensite Ni-Mn-Ga single crystals are known for their exceptionally mobile twin boundaries allowing a shape change under mechanical stress and by magnetic field. The mechanically measured twinning stress has usually been studied in uniaxial mode, however the twinning and detwinning is generally accepted to be resulted by the shear component. We have studied the twinning behavior at uniaxial and shear stress. In addition we have applied the shear stress at different angles in relation to the expected twinning direction [ {10bar 1} ]. The results show that the onset of twinning lays at similar stress levels in both uniaxial and shear modes.

  7. Simple Uniaxial and Uniform Biaxial Deformation of Nearly Isotropic Incompressible Tissues

    PubMed Central

    Hildebrandt, J.; Fukaya, H.; Martin, C. J.

    1969-01-01

    A method is developed for analyzing in a unified manner both uniaxial and uniform biaxial strain data obtained from nearly isotropic tissues. The formulation is a direct application of nonlinear elasticity theory pertaining to large deformations. The general relation between Eulerian stress (σ) and extension ratio (λ) in soft isotropic elastic bodies undergoing uniform deformation takes the simple form: σ = ((λ3 - 1)/λ) f(λ), where f(λ) must be determined for each material. The extension ratio may be either greater than 1.0 (uniaxial elongation), or lie between zero and 1.0 (uniform biaxial extension). Simple analytical functions for f(λ) are most readily found for each tissue by plotting all data as (λ3 - 1)/λσ vs. λ. Of those tissues investigated in this way (dog pericardium and pleura, and cat mesentery and dura), all but pleura could be adequately described by a parabola: 1/f(λ) = 1/k{[(λM - λ)(λ - λm)]/[λM - λm}. In these instances, three material constants per tissue (K, λM, λm) served to predict approximately the stresses attained during both small and large deformations, in strips and sheets alike. It was further found that the uniaxial strain asymptote (λM) was linearly related to the biaxial strain asymptote (ΛM), thus effectively reducing the number of constants by one. PMID:5794107

  8. Scleral Mechanics: Comparing Whole Globe Inflation and Uniaxial Testing

    PubMed Central

    Lari, David R.; Schultz, David S.; Wang, Aaron S.; Lee, On-Tat; Stewart, Jay M.

    2012-01-01

    The purpose of this study was to assess fundamental differences between the mechanics of the posterior sclera in paired eyes using uniaxial and whole globe inflation testing, with an emphasis on the relationship between testing conditions and observed tissue behavior. Twenty porcine eyes, consisting of matched pairs from 10 pigs, were used in this study. Within pairs, one eye was tested with 10 cycles of globe pressurization to 150 mmHg (~10x normal IOP) while biaxial strains were tracked via an optical system at the posterior sclera. An excised posterior strip from the second eye was subjected to traditional uniaxial testing in which mechanical hysteresis was recorded from 10 cycles to a peak stress of 0.13 MPa (roughly equivalent to the circumferential wall stress produced by an IOP of 150 mmHg under the thin-walled pressure vessel assumption). For approximately equivalent loads, peak strains were more than twice as high in uniaxial tests than in inflation tests. Different trends in the load-deformation plots were seen between the tests, including an extended “toe” region in the uniaxial test, a generally steeper curve in the inflation tests, and reduced variability in the inflation tests. The unique opportunity of being able to mechanically load a whole globe under near physiologic conditions alongside a standard uniaxially tested specimen reveals the effects of testing artifacts relevant to most uniaxially tested soft tissues. Whole globe inflation offers testing conditions that significantly alter load-deformation behavior relative to uniaxial testing; consequently, laboratory studies of interventions or conditions that alter scleral mechanics may greatly benefit from these findings. PMID:22155444

  9. Biaxial and uniaxial data for statistical comparisons of a ceramic's strength

    NASA Technical Reports Server (NTRS)

    Giovan, M. N.; Sines, G.

    1979-01-01

    The uniaxial and equibiaxial tensile strengths of a brittle material were measured in bending. Equibiaxial tension was attained by concentric ring loading of disks and uniaxial tension by four-point line loading of plates. The two specimen designs give equal volumes, surface areas, and stress gradients. Ground surfaces and lapped surfaces were tested. The equibiaxial tensile strength of a dense alumina was lower than the uniaxial tensile strengths for both ground and lapped surfaces, 8.5 and 8.1%, respectively. The Batdorf theory of flaw statistics, in which biaxial tensile strengths can be predicted from the statistical distribution of uniaxial tensile strength measurements, agreed with the data.

  10. Experimental Study on Conductivity Anisotropy of Limestone Considering the Bedding Directional Effect in the Whole Process of Uniaxial Compression.

    PubMed

    Xu, Xinji; Liu, Bin; Li, Shucai; Yang, Lei; Song, Jie; Li, Ming; Mei, Jie

    2016-03-04

    Experimental studies were conducted on the changes of the potential differences in different directions during the uniaxial compression on limestone samples parallel and normal to the bedding plane. In the test, electric current was supplied at both ends of the samples, and concurrent measurement was conducted in four measuring lines at a 45-degree angle to each other. First, the change laws of the potential differences in different directions and the similarities and differences of rock samples were summarized. In regards to the uniaxial compression properties and crack growth, the above-mentioned similarities and differences were further analyzed. Then, the anisotropy factor was introduced to further explore the response characteristics. It was found that the anisotropic changes of rock samples went through three stages during the uniaxial compression process, providing a reference for describing the properties in different failure stages of rock samples and obtaining precursory information about the fracture. Besides, the relationship between the peak stress and initial potential difference in a direction normal to the current direction was obtained by means of data fitting, providing a new method of predicting the uniaxial compressive strength of rock samples. According to the preceding analysis, this paper studied rock anisotropy by considering the bedding directional effect in terms of conductivity and provided a reference for subsequent study on rock materials' properties and engineering practices.

  11. Experimental Study on Conductivity Anisotropy of Limestone Considering the Bedding Directional Effect in the Whole Process of Uniaxial Compression

    PubMed Central

    Xu, Xinji; Liu, Bin; Li, Shucai; Yang, Lei; Song, Jie; Li, Ming; Mei, Jie

    2016-01-01

    Experimental studies were conducted on the changes of the potential differences in different directions during the uniaxial compression on limestone samples parallel and normal to the bedding plane. In the test, electric current was supplied at both ends of the samples, and concurrent measurement was conducted in four measuring lines at a 45-degree angle to each other. First, the change laws of the potential differences in different directions and the similarities and differences of rock samples were summarized. In regards to the uniaxial compression properties and crack growth, the above-mentioned similarities and differences were further analyzed. Then, the anisotropy factor was introduced to further explore the response characteristics. It was found that the anisotropic changes of rock samples went through three stages during the uniaxial compression process, providing a reference for describing the properties in different failure stages of rock samples and obtaining precursory information about the fracture. Besides, the relationship between the peak stress and initial potential difference in a direction normal to the current direction was obtained by means of data fitting, providing a new method of predicting the uniaxial compressive strength of rock samples. According to the preceding analysis, this paper studied rock anisotropy by considering the bedding directional effect in terms of conductivity and provided a reference for subsequent study on rock materials’ properties and engineering practices. PMID:28773287

  12. Effect of Water on the Deformation and Failure of Rock in Uniaxial Tension

    NASA Astrophysics Data System (ADS)

    Hashiba, K.; Fukui, K.

    2015-09-01

    To design and construct underground structures, it is essential to understand the mechanical properties of rock in not only compression but also tension. It is well known that water is one of the important factors affecting the deformation and failure of rock. In this study, laboratory tests and numerical simulations were conducted to understand the effect of water on rock properties in uniaxial tension. In the experiments, a testing machine previously used for uniaxial tension tests in dry conditions was modified for tests in wet conditions. Using this machine, complete stress-strain curves from the pre- to postpeak regions of water-saturated specimens in uniaxial tension were obtained. The results for granite, tuff, and two types of andesite showed that the stress-strain curves in wet conditions have a lower initial slope and lower strength than those in dry conditions, and they are strongly nonlinear in the prepeak region. Comparing the changes in the results for uniaxial tension versus compression due to water, it was found that the reduction rate of uniaxial tensile strength was greater than that of uniaxial compressive strength, while the ratio between the reduction rates was almost constant for various rocks. In numerical simulations, the stress-strain curves in the prepeak region under dry and wet conditions could be reproduced by crack extension models under uniaxial tensile stress. Numerical analyses indicated that the nonlinearity of the stress-strain curves is probably due to the longer crack extension in wet compared with dry conditions.

  13. Rosacea Fulminans Precipitated by Acute Stress: A Case Report Describing an Integrative Approach for a Patient Reluctant to Use Isotretinoin

    PubMed Central

    Veerkamp, Patrick; Mousdicas, Nico; Bednarek, Robert

    2016-01-01

    Context Rosacea fulminans is a rare skin disorder with a multifactorial etiology. Stress is one of the common precipitating factors of this condition but is not often targeted in treatment. Isotretinoin is considered part of the first-line therapy for this condition but, in cases where its use is restricted, other therapeutic interventions as part of an integrative approach may be effective. Patient Concerns A 38-y-old female presented with rosacea fulminans brought on by an acutely stressful event. After multiple failed therapies, she experienced resolution of her symptoms with a combination of systemic corticosteroids, antibiotics, diet modification, and stress reduction, with the treatment of stress playing a significant role. Conclusions Stress management and diet modification are key adjunctive therapies in the treatment of rosacea fulminans and need to be addressed more often in treatment. In cases where patients are reluctant or unable to take isotretinoin, an integrative approach may be effective in achieving symptomatic improvement. PMID:28223895

  14. Electrically sign-reversible transverse g -factors of holes in droplet epitaxial GaAs/AlGaAs quantum dots under uniaxial stress

    NASA Astrophysics Data System (ADS)

    Wu, Yu-Nien; Wu, Ming-Fan; Ou, Ya-Wen; Chou, Ying-Lin; Cheng, Shun-Jen

    2017-08-01

    We present a theoretical investigation of anisotropic g -factor tensors of single holes confined in droplet epitaxial GaAs/AlGaAs quantum dots under electrical and mechanical controls using the gauge-invariant discretization method within the framework of four-band Luttinger-Kohn k ⃗.p ⃗ theory. We reveal an intrinsic obstacle to realize the electrical sign reversal of the hole g -factors, being a key condition required for a full spin control in the scheme of g -tensor modulation, for the quantum dots solely with electrical bias control. Constructively, our studies show that, besides electrical gating, slightly stressing an inherently unstrained droplet epitaxial GaAs/AlGaAs quantum dot can offset the transverse hole g -factor to be nearly zero and make the electrical sign reversal of the hole g -factors feasible.

  15. Large deformation of uniaxially loaded slender microbeams on the basis of modified couple stress theory: Analytical solution and Galerkin-based method

    NASA Astrophysics Data System (ADS)

    Kiani, Keivan

    2017-09-01

    Large deformation regime of micro-scale slender beam-like structures subjected to axially pointed loads is of high interest to nanotechnologists and applied mechanics community. Herein, size-dependent nonlinear governing equations are derived by employing modified couple stress theory. Under various boundary conditions, analytical relations between axially applied loads and deformations are presented. Additionally, a novel Galerkin-based assumed mode method (AMM) is established to solve the highly nonlinear equations. In some particular cases, the predicted results by the analytical approach are also checked with those of AMM and a reasonably good agreement is reported. Subsequently, the key role of the material length scale on the load-deformation of microbeams is discussed and the deficiencies of the classical elasticity theory in predicting such a crucial mechanical behavior are explained in some detail. The influences of slenderness ratio and thickness of the microbeam on the obtained results are also examined. The present work could be considered as a pivotal step in better realizing the postbuckling behavior of nano-/micro- electro-mechanical systems consist of microbeams.

  16. Collagen Fibrils in Skin Orient in the Direction of Applied Uniaxial Load in Proportion to Stress while Exhibiting Differential Strains around Hair Follicles

    PubMed Central

    Nesbitt, Sterling; Scott, Wentzell; Macione, James; Kotha, Shiva

    2015-01-01

    We determined inhomogeneity of strains around discontinuities as well as changes in orientation of collagen fibrils under applied load in skin. Second Harmonic Generation (SHG) images of collagen fibrils were obtained at different strain magnitudes. Changes in collagen orientation were analyzed using Fast Fourier Transforms (FFT) while strain inhomogeneity was determined at different distances from hair follicles using Digital Image Correlation (DIC). A parameter, defined as the Collagen Orientation Index (COI), is introduced that accounts for the increasingly ellipsoidal nature of the FFT amplitude images upon loading. We show that the COI demonstrates two distinct mechanical regimes, one at low strains (0%, 2.5%, 5% strain) in which randomly oriented collagen fibrils align in the direction of applied deformation. In the second regime, beginning at 5% strain, collagen fibrils elongate in response to applied deformation. Furthermore, the COI is also found to be linearly correlated with the applied stress indicating that collagen fibrils orient to take the applied load. DIC results indicated that major principal strains were found to increase with increased load at all locations. In contrast, minimum principal strain was dependent on distance from hair follicles. These findings are significant because global and local changes in collagen deformations are expected to be changed by disease, and could affect stem cell populations surrounding hair follicles, including mesenchymal stem cells within the outer root sheath. PMID:28788035

  17. The evaluation of workplaces subjected to heat stress: can ISO 7933 (1989) adequately describe heat strain in industrial workplaces?

    PubMed

    Kampmann, B; Piekarski, C

    2000-02-01

    The International Standard ISO 7933 (1989) Hot environments--Analytical determination and interpretation of thermal stress using calculation of required sweat rate has been proposed for the evaluation of climatic stress within the European system of CEN standards. Comparison of results of studies performed in climatic chambers and those in the field with the predictions of ISO 7933 show that there are considerable problems in using this index in practice. In its present state of development, ISO 7933 seems to be rather a step towards a useable index for evaluating climatic conditions rather than an established climatic index which is applicable in practice. Within the CEN standards, the deficiencies of ISO 7933 are reflected mainly by a restriction of the limits of application within EN 12 515 (1997) which is based on ISO 7933.

  18. Field-Induced Rheology in Uniaxial and Biaxial Fields

    SciTech Connect

    MARTIN, JAMES E.

    1999-10-22

    Steady and oscillatory shear 3-D simulations of electro- and magnetorheology in uniaxial and biaxial fields are presented, and compared to the predictions of the chain model. These large scale simulations are three dimensional, and include the effect of Brownian motion. In the absence of thermal fluctuations, the expected shear thinning viscosity is observed in steady shear, and a striped phase is seen to rapidly form in a uniaxial field, with a shear slip zone in each sheet. However, as the influence of Brownian motion increases, the fluid stress decreases, especially at lower Mason numbers, and the striped phase eventually disappears, even when the fluid stress is still high. In a biaxial field, an opposite trend is seen, where Brownian motion decreases the stress most significantly at higher Mason numbers. to account for the uniaxial steady shear data they propose a microscopic chain model of the role played by thermal fluctuations on the rheology of ER and MR fluids that delineates the regimes where an applied field can impact the fluid viscosity, and gives an analytical prediction for the thermal effect. In oscillatory shear, a striped phase again appears in uniaxial field, at strain amplitudes greater than {approx} 0.15, and the presence of a shear slip zone creates strong stress nonlinearities at low strain amplitudes. In a biaxial field, a shear slip zone is not created, and so the stress nonlinearities develop only at expected strain amplitudes. The nonlinear dynamics of these systems is shown to be in good agreement with the Kinetic Chain Model.

  19. Uniaxial tensile testing approaches for characterisation of atherosclerotic plaques.

    PubMed

    Walsh, M T; Cunnane, E M; Mulvihill, J J; Akyildiz, A C; Gijsen, F J H; Holzapfel, G A

    2014-03-03

    The pathological changes associated with the development of atherosclerotic plaques within arterial vessels result in significant alterations to the mechanical properties of the diseased arterial wall. There are several methods available to characterise the mechanical behaviour of atherosclerotic plaque tissue, and it is the aim of this paper to review the use of uniaxial mechanical testing. In the case of atherosclerotic plaques, there are nine studies that employ uniaxial testing to characterise mechanical behaviour. A primary concern regarding this limited cohort of published studies is the wide range of testing techniques that are employed. These differing techniques have resulted in a large variance in the reported data making comparison of the mechanical behaviour of plaques from different vasculatures, and even the same vasculature, difficult and sometimes impossible. In order to address this issue, this paper proposes a more standardised protocol for uniaxial testing of diseased arterial tissue that allows for better comparisons and firmer conclusions to be drawn between studies. To develop such a protocol, this paper reviews the acquisition and storage of the tissue, the testing approaches, the post-processing techniques and the stress-strain measures employed by each of the nine studies. Future trends are also outlined to establish the role that uniaxial testing can play in the future of arterial plaque mechanical characterisation.

  20. Pairing states of superfluid {sup 3}He in uniaxially anisotropic aerogel

    SciTech Connect

    Aoyama, Kazushi; Ikeda, Ryusuke

    2006-02-01

    Stable pairing states of superfluid {sup 3}He in aerogel are examined in the case with a global uniaxial anisotropy which may be created by applying a uniaxial stress to the aerogel. Due to such a global anisotropy, the stability region of an Anderson-Brinkman-Morel (ABM) pairing state becomes wider. In a uniaxially stretched aerogel, the pure polar pairing state with a horizontal line node is predicted to occur, as a three-dimensional superfluid phase, over a measurable width just below the superfluid transition at T{sub c}(P). A possible relevance of the present results to the case with no global anisotropy is also discussed.

  1. Optimization of a corrugated stiffened composite panel under uniaxial compression

    NASA Technical Reports Server (NTRS)

    Agarwal, B. L.; Sobel, L. H.

    1973-01-01

    An approach of structural optimization has been used to optimize the weight of a simply supported, corrugated hat stiffened composite panel under uniaxial compression. The approach consists of the employment of nonlinear mathematical programming techniques to reach an optimum solution. Some simplifying assumptions are made in the stress analysis to obtain faster convergence to an optimum solution. With these simplifying assumptions the number of unknown design parameters is reduced to twelve.

  2. Uniaxial aerodynamic attitude control of artificial satellites

    NASA Technical Reports Server (NTRS)

    Sazonov, V. V.

    1983-01-01

    Within the context of a simple mechanical model the paper examines the movement of a satellite with respect to the center of masses under conditions of uniaxial aerodynamic attitude control. The equations of motion of the satellite take account of the gravitational and restorative aerodynamic moments. It is presumed that the aerodynamic moment is much larger than the gravitational, and the motion equations contain a large parameter. A two-parameter integrated surface of these equations is constructed in the form of formal series in terms of negative powers of the large parameter, describing the oscillations and rotations of the satellite about its lengthwise axis, approximately oriented along the orbital tangent. It is proposed to treat such movements as nominal undisturbed motions of the satellite under conditions of aerodynamic attitude control. A numerical investigation is made for the above integrated surface.

  3. Reduction of the piezoelectric performance in lead-free (1-x)Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3 piezoceramics under uniaxial compressive stress

    NASA Astrophysics Data System (ADS)

    Ehmke, Matthias C.; Daniels, John; Glaum, Julia; Hoffman, Mark; Blendell, John E.; Bowman, Keith J.

    2012-12-01

    The effect of a uniaxial compressive stress on the properties of BZT-BCT samples across the morphotropic phase boundary (MPB) is investigated using direct piezoelectric coefficient measurements. In contrast to many lead zirconate titanate compositions, the piezoelectric coefficient decreases monotonically with increasing stress and does not show an initial increase or plateau. Electrically softer rhombohedral and MPB compositions are found to be more susceptible to a decrease in piezoelectric coefficient under an increasing pre-stress than tetragonal compositions. Depoling due to ferroelastic domain switching alone, as observed by x-ray diffraction, does not explain this reduction, but instead a decreasing domain wall density is proposed to be responsible for reduced piezoelectric coefficients under increasing compressive stress. The relaxation of the piezoelectric response after complete unloading supports this proposed mechanism.

  4. Exploring the ability of a multiscale coarse-grained potential to describe the stress-strain response of glassy polystyrene.

    PubMed

    Rosch, Thomas W; Brennan, John K; Izvekov, Sergei; Andzelm, Jan W

    2013-04-01

    A new particle-based bottom-up method to develop coarse-grained models of polymers is presented and applied to polystyrene. The multiscale coarse-graining (MS-CG) technique of Izvekov et al. [J. Chem. Phys. 120, 10896 (2004)] is applied to a polymer system to calculate nonbonded interactions. The inverse Boltzmann inversion method was used to parametrize the bonded and bond-angle bending interactions. Molecular dynamics simulations were performed, and the CG model exhibited a significantly lower modulus compared to the atomistic model at low temperature and high strain rate. In an attempt to improve the CG model performance, several other parametrization schemes were used to build other models from this base model. The first of these models included standard frictional forces through use of the constant-temperature dissipative particle dynamics method that improved the modulus, yet was not transferrable to higher temperatures and lower strain rates. Other models were built by increasing the attraction between CG beads through direct manipulation of the nonbonded potential, where an improvement of the stress response was found. For these models, two parametrization protocols that shifted the force to more attractive values were explored. The first protocol involved a uniform shift, while the other protocol shifted the force in a more localized region. The uniformly shifted potential greatly affected the structure of the equilibrium model as compared to the locally shifted potential, yet was more transferrable to different temperatures and strain rates. Further improvements in the coarse-graining protocol to generate models that more satisfactorily capture mechanical properties are suggested.

  5. High temperature inelastic deformation under uniaxial loading - Theory and experiment

    NASA Technical Reports Server (NTRS)

    Chan, K. S.; Lindholm, U. S.; Bodner, S. R.; Walker, K. P.

    1989-01-01

    The elevated-temperature uniaxial inelastic deformation behavior of an Ni-base alloy, B1900 + Hf, is investigated by performing isothermal tensile, creep, cyclic, stress relaxation, and thermomechanical fatigue tests. The range of strain rates examined is from 10 to the -7th to 100 per sec, while the test temperatures range from 25 to 1093 C. This extensive constitutive data base has been used for evaluating the unified constitutive models of Bodner and Partom (1972) and of Walker (1972) which apply for the small-strain regime. Comparison of test results with independent model predictions indicates good agreement over a broad range of loading conditions, demonstrating the applicability of the unified-constitutive-equation approach for describing the strongly nonlinear and temperature-dependent response of meals under a wide range of deformation and thermal histories. Thus the results give confidence that the unified approach is an effective and efficient approach in which complex history-dependent thermoviscoplastic flow can be represented within a single inelastic strain-rate term.

  6. High temperature inelastic deformation under uniaxial loading - Theory and experiment

    NASA Technical Reports Server (NTRS)

    Chan, K. S.; Lindholm, U. S.; Bodner, S. R.; Walker, K. P.

    1989-01-01

    The elevated-temperature uniaxial inelastic deformation behavior of an Ni-base alloy, B1900 + Hf, is investigated by performing isothermal tensile, creep, cyclic, stress relaxation, and thermomechanical fatigue tests. The range of strain rates examined is from 10 to the -7th to 100 per sec, while the test temperatures range from 25 to 1093 C. This extensive constitutive data base has been used for evaluating the unified constitutive models of Bodner and Partom (1972) and of Walker (1972) which apply for the small-strain regime. Comparison of test results with independent model predictions indicates good agreement over a broad range of loading conditions, demonstrating the applicability of the unified-constitutive-equation approach for describing the strongly nonlinear and temperature-dependent response of meals under a wide range of deformation and thermal histories. Thus the results give confidence that the unified approach is an effective and efficient approach in which complex history-dependent thermoviscoplastic flow can be represented within a single inelastic strain-rate term.

  7. Structure and properties of poly (lactic acid)/Sterculia urens uniaxial fabric biocomposites.

    PubMed

    Jayaramudu, J; Reddy, G Siva Mohan; Varaprasad, K; Sadiku, E R; Ray, S Sinha; Rajulu, A Varada

    2013-05-15

    Uniaxial cellulose fabric Sterculia urens reinforced poly (lactic acid) (PLA) matrix biocomposites were prepared by a two-roll mill. In order to assess the suitability of Sterculia fabric as reinforcement for PLA matrix, the PLA/Sterculia fabric biocomposites were prepared. Tensile parameters, such as maximum stress, Young's modulus and elongation-at-break, were determined using the Universal Testing Machine. The effect of alkali treatment and silane-coupling agent on the tensile properties of PLA-based biocomposites was studied. The results of thermogravimetric analysis show that uniaxial treatment of the fabric can improve the degradation temperature of the biocomposites. Moreover, morphological studies by scanning electron microscopy confirmed that better adhesion between the uniaxial fabric and the matrix was achieved. It was established that standard PLA resins are suitable for the manufacture of S. urens uniaxial fabric reinforced biocomposites with excellent engineering properties, useful for food packaging. Copyright © 2013 Elsevier Ltd. All rights reserved.

  8. Uncoupling shear and uniaxial elastic moduli of semiflexible biopolymer networks: compression-softening and stretch-stiffening.

    PubMed

    van Oosten, Anne S G; Vahabi, Mahsa; Licup, Albert J; Sharma, Abhinav; Galie, Peter A; MacKintosh, Fred C; Janmey, Paul A

    2016-01-13

    Gels formed by semiflexible filaments such as most biopolymers exhibit non-linear behavior in their response to shear deformation, e.g., with a pronounced strain stiffening and negative normal stress. These negative normal stresses suggest that networks would collapse axially when subject to shear stress. This coupling of axial and shear deformations can have particularly important consequences for extracellular matrices and collagenous tissues. Although measurements of uniaxial moduli have been made on biopolymer gels, these have not directly been related to the shear response. Here, we report measurements and simulations of axial and shear stresses exerted by a range of hydrogels subjected to simultaneous uniaxial and shear strains. These studies show that, in contrast to volume-conserving linearly elastic hydrogels, the Young's moduli of networks formed by the biopolymers are not proportional to their shear moduli and both shear and uniaxial moduli are strongly affected by even modest degrees of uniaxial strain.

  9. Uncoupling shear and uniaxial elastic moduli of semiflexible biopolymer networks: compression-softening and stretch-stiffening

    PubMed Central

    van Oosten, Anne S. G.; Vahabi, Mahsa; Licup, Albert J.; Sharma, Abhinav; Galie, Peter A.; MacKintosh, Fred C.; Janmey, Paul A.

    2016-01-01

    Gels formed by semiflexible filaments such as most biopolymers exhibit non-linear behavior in their response to shear deformation, e.g., with a pronounced strain stiffening and negative normal stress. These negative normal stresses suggest that networks would collapse axially when subject to shear stress. This coupling of axial and shear deformations can have particularly important consequences for extracellular matrices and collagenous tissues. Although measurements of uniaxial moduli have been made on biopolymer gels, these have not directly been related to the shear response. Here, we report measurements and simulations of axial and shear stresses exerted by a range of hydrogels subjected to simultaneous uniaxial and shear strains. These studies show that, in contrast to volume-conserving linearly elastic hydrogels, the Young’s moduli of networks formed by the biopolymers are not proportional to their shear moduli and both shear and uniaxial moduli are strongly affected by even modest degrees of uniaxial strain. PMID:26758452

  10. Hydrocode and Molecular Dynamics modelling of uniaxial shock wave experiments on Silicon

    NASA Astrophysics Data System (ADS)

    Stubley, Paul; McGonegle, David; Patel, Shamim; Suggit, Matthew; Wark, Justin; Higginbotham, Andrew; Comley, Andrew; Foster, John; Rothman, Steve; Eggert, Jon; Kalantar, Dan; Smith, Ray

    2015-06-01

    Recent experiments have provided further evidence that the response of silicon to shock compression has anomalous properties, not described by the usual two-wave elastic-plastic response. A recent experimental campaign on the Orion laser in particular has indicated a complex multi-wave response. While Molecular Dynamics (MD) simulations can offer a detailed insight into the response of crystals to uniaxial compression, they are extremely computationally expensive. For this reason, we are adapting a simple quasi-2D hydrodynamics code to capture phase change under uniaxial compression, and the intervening mixed phase region, keeping track of the stresses and strains in each of the phases. This strain information is of such importance because a large number of shock experiments use diffraction as a key diagnostic, and these diffraction patterns depend solely on the elastic strains in the sample. We present here a comparison of the new hydrodynamics code with MD simulations, and show that the simulated diffraction taken from the code agrees qualitatively with measured diffraction from our recent Orion campaign.

  11. A combined complex electrical impedance and acoustic emission study in limestone samples under uniaxial loading

    NASA Astrophysics Data System (ADS)

    Saltas, V.; Fitilis, I.; Vallianatos, F.

    2014-12-01

    In the present work, complex electrical impedance measurements in the frequency range of 10 mHz to 1 MHz were carried out in conjunction with acoustic emission monitoring in limestone samples subjected to linear and stepped-like uniaxial loading, up to ultimate failure. Cole-Cole plots of the complex impedance during the stepped loading of limestone have been used to discriminate the contributions of grains interior, grain boundaries and electrode polarization effects to the overall electrical behavior. The latter is well-described with an equivalent-circuit model which comprises components of constant phase elements and resistances in parallel connection. Electrical conductivity increases upon uniaxial loading giving rise to negative values of effective activation volume. This is a strong experimental evidence for the generation of transient electric signals recorded prior to seismic events and may be attributed to charge transfer (proton conduction) due to cracks generation and propagation as a result of the applied stress. The time-series of ac-conductivity at two distinct frequencies (10 kHz, 200 kHz) during linear loading of limestone samples exhibits a strong correlation with the acoustic emission activity obeying the same general self-similar law for critical phenomena that has been reported for the energy release before materials fracture.

  12. High Temperature Slow Crack Growth of Si3N4 Specimens Subjected to Uniaxial and Biaxial Dynamic Fatigue Loading Conditions

    NASA Technical Reports Server (NTRS)

    Choi, Sung R.; Nemeth, Noel N.; Salem, Jonathan A.; Powers, Lynn M.; Gyekenyesi, John P.

    1995-01-01

    The slow crack growth of a hot-pressed silicon nitride was determined at 1300 C in air using dynamic fatigue testing under both uniaxial and biaxial stress states. Good agreement in fatigue parameter exists between the data obtained from uniaxial and biaxial loading conditions. A reasonable prediction of dynamic fatigue from one stress state to another was made using the recently developed CARES/LIFE computer code.

  13. Tubular bioreactor models that include Onsager-Curie scalar cross-phenomena to describe stress-dependent rates of cell proliferation.

    PubMed

    Belfiore, Laurence A; Karim, M Nazmul; Belfiore, Carol J

    2008-06-01

    The theory of heterogeneous catalysis in chemical reactors is employed to simulate laminar flow through tubes at large mass transfer Peclet numbers in which anchorage-dependent cells (i) adhere to a protein coating on the inner surface at r=R(wall), (ii) receive nutrients and oxygen from an aqueous medium via transverse diffusion toward the active wall, and (iii) proliferate in the presence of viscous shear at the cell/aqueous-medium interface. This process is modeled as convective diffusion in cylindrical coordinates with chemical reaction at the boundary, where chemical reaction describes the rate of nutrient consumption. The formalism of irreversible thermodynamics is employed to describe an unusual coupling between viscous shear, or velocity gradients at the cell/aqueous-medium interface, and rates of nutrient consumption. Linear transport laws in chemically reactive systems that obey Curie's theorem predict the existence of cross-phenomena between fluxes (i.e., scalar reaction rates) and driving forces (i.e., 2nd-rank velocity gradient tensor) whose tensorial ranks differ by an even integer-in this case, two. This methodology for stress-dependent chemical reactions yields an additional zeroth-order contribution, via the magnitude of the velocity gradient tensor, to heterogeneous kinetic rate expressions because nutrient consumption and cell proliferation are stress-sensitive. Computer simulations of nutrient consumption suggest that bioreactor designs should consider stress-sensitive reactions when the shear-rate-based Damköhler number (i.e., defined for the first time in this study as the stress-dependent zeroth-order rate of nutrient consumption relative to the rate of nutrient diffusion toward active cells adhered to the tube wall) is greater than 10-20% of the stress-free Damköhler number. Models of bioreactor performance are presented for simple 1st-order, simple 2nd-order, and complex chemical kinetic rate expressions, where the latter considers

  14. Analysis of Sandwich Shells with Metallic Foam Cores based on the Uniaxial Tensile Test

    SciTech Connect

    Mata, H.; Fernandes, A. A.; Parente, M. P. L.; Jorge, R. Natal; Santos, A.; Valente, R. A. F.

    2011-05-04

    On this work, the authors present the development and evaluation of an innovative system able to perform reliable panels of sandwich sheets with metallic foam cores for industrial applications, especially in automotive and aeronautical industries. This work is divided into two parts; in the first part the mathematical model used to describe the behavior of sandwich shells with metal cores form is presented and some numerical examples are presented. In the second part of this work, the numerical results are validated using the experimental results obtained from the mechanical experiments. Using the isotropic hardening crushable foam constitutive model, available on ABAQUS, a set of different mechanical tests were simulated. The isotropic hardening model available uses a yield surface that is an ellipse centered at the origin in the p-q stress plane. Using this constitutive model, the uniaxial tensile test for this material was simulated, and a comparison with the experimental results was made.

  15. Refractometry of Rb2ZnCl4 crystals under uniaxial pressure

    NASA Astrophysics Data System (ADS)

    Stadnik, V. I.; Stakhura, V. B.; Andrievskii, B. V.

    2017-06-01

    The influence of uniaxial pressures applied along the main crystallophysical directions on the dispersion and temperature dependences of the refractive index n i of Rb2ZnCl4 crystals has been investigated. The n i value is found to be rather sensitive to uniaxial pressures, whereas uniaxial stress does not change the character of the dispersion and temperature dependences of n i. The pressure-induced changes in electronic polarizability αi, refraction R, and the parameters of UV oscillators are studied for mechanically deformed Rb2ZnCl4 crystals. The contributions of the UV and IR oscillators to the changes in n i at different temperatures, in different spectral regions, and under different mechanical stresses are estimated. The points of paraelectric-incommensurate-commensurate phase transitions (PTs) are found to undergo a significant pressure-induced shift to different temperature regions, depending on the pressure-application direction.

  16. Gender differences in patient-described pain, stress, and anxiety among patients undergoing treatment for painful conditions in the emergency department.

    PubMed

    Patel, Roma; Biros, Michelle H; Moore, Johanna; Miner, James R

    2014-12-01

    The primary objective of this study was to determine whether patient-described pain correlates with patient-described stress, anxiety, and satisfaction with ongoing treatment and if that correlation differs by gender. This was a prospective observational study at an urban, Level I trauma center conducted between June 1, 2010, and January 1, 2013. Patients reporting pain rated greater than 3 of 10 were eligible. Patients who qualified and consented for participation completed demographic and pain, anxiety, stress, and satisfaction scales at baseline, every 30 minutes, and at discharge. Data were analyzed using analysis of variance, chi-square tests, t-tests, multiple regression, and the Wilcoxon-Mann-Whitney rank test. A total of 7,124 patients were screened for enrollment. Of those, 3,495 (49%) did not qualify at screening for various reasons, including insufficient pain levels (17.5%), elected not to participate (37.7%), did not qualify for other reasons (12.4%), and reason not captured (32.4%). A total of 3,629 (51%) screened patients were eligible and consented. Of those, 620 (16.8%) did not have any data collected past baseline, leaving 3,009 as the final sample size. The patients completing data collection had a median age of 39 years (range = 18 to 90 years), and 50% were male. The mean presenting pain visual analog scale (VAS) score was 71.5 mm. Presenting stress and anxiety VAS scores were significantly higher in females (0.61 and 0.53, respectively) than males (0.56 and 0.50, respectively), whereas presenting pain VAS (0.71 male and 0.72 female) and satisfaction VAS (0.34 male and 0.35 female) did not differ by sex. Ethnicity, education, and income were all statistically different when compared with baseline pain, stress, anxiety, and satisfaction. Male gender was associated with a significant change in pain over time from baseline (coefficient = 0.040, p = 0.037); however, when adjusting for age, ethnicity, education, and income, and for changes in stress

  17. The Uniaxial Tensile Response of Porous and Microcracked Ceramic Materials

    SciTech Connect

    Pandey, Amit; Shyam, Amit; Watkins, Thomas R; Lara-Curzio, Edgar; Lara-Curzio, Edgar; Stafford, Randall; Hemker, Kevin J

    2014-01-01

    The uniaxial tensile stress-strain behavior of three porous ceramic materials was determined at ambient conditions. Test specimens in the form of thin beams were obtained from the walls of diesel particulate filter honeycombs and tested using a microtesting system. A digital image correlation technique was used to obtain full-field 2D in-plane surface displacement maps during tensile loading, and in turn, the 2D strains obtained from displacement fields were used to determine the Secant modulus, Young s modulus and initial Poisson s ratio of the three porous ceramic materials. Successive unloading-reloading experiments were performed at different levels of stress to decouple the linear elastic, anelastic and inelastic response in these materials. It was found that the stress-strain response of these materials was non-linear and that the degree of nonlinearity is related to the initial microcrack density and evolution of damage in the material.

  18. Stress analysis of a secondary-bending specimen

    NASA Astrophysics Data System (ADS)

    Evans, R. L.; Heller, M.

    1993-11-01

    This note describes a two-dimensional finite-element elastic analysis of a uniaxially-loaded bolted secondary-bending specimen which was conducted to provide information relevant to a recent ARL fatigue testing program. Three different approaches were employed to model the bolt/plate interface and the results are compared with thermoelastic stress measurements.

  19. Nano-Plasticity of Single-Wall Carbon Nanotubes Under Uniaxial Compression

    NASA Technical Reports Server (NTRS)

    Srivastava, Deepak; Menon, Madu; Cho, Kyeongjae

    1999-01-01

    Nano-plasticity of thin single-wall carbon nanotubes under uniaxial compression is investigated through generalized tight-binding molecular dynamics (GTBMD) and ab-initio electronic structure methods. A novel mechanism of nano-plasticity of carbon nanotubes under uniaxial compression is observed in which bonding geometry collapses from a graphitic (sp(sup 2)) to a localized diamond like (sp(sup 3)) reconstruction. The computed critical stress (approximately equals 153 G Pa) and the shape of the resulting plastic deformation is in good agreement with recent experimental observation of collapse and fracture of compressed carbon nanotubes in polymer composites.

  20. Polarized actin structural dynamics in response to cyclic uniaxial stretch

    PubMed Central

    Huang, Lawrence; Helmke, Brian P.

    2014-01-01

    Endothelial cell (EC) alignment to directional flow or stretch supports anti-inflammatory functions, but mechanisms controlling polarized structural adaptation in response to physical cues remain unclear. This study aimed to determine whether factors associated with early actin edge ruffling implicated in cell polarization are prerequisite for stress fiber (SF) reorientation in response to cyclic uniaxial stretch. Time-lapse analysis of EGFP-actin in confluent ECs showed that onset of either cyclic uniaxial or equibiaxial stretch caused a non-directional increase in edge ruffling. Edge activity was concentrated in a direction perpendicular to the stretch axis after 60 min, consistent with the direction of SF alignment. Rho-kinase inhibition caused reorientation of both stretch-induced edge ruffling and SF alignment parallel to the stretch axis. Arp2/3 inhibition attenuated stretch-induced cell elongation and disrupted polarized edge dynamics and microtubule organizing center reorientation, but it had no effect on the extent of SF reorientation. Disrupting localization of p21-activated kinase (PAK) did not prevent stretch-induced SF reorientation, suggesting that this Rac effector is not critical in regulating stretch-induced cytoskeletal remodeling. Overall, these results suggest that directional edge ruffling is not a primary mechanism that guides SF reorientation in response to stretch; the two events are coincident but not causal. PMID:25821527

  1. Macroscopic and microscopic investigations on uniaxial ratchetting of two-phase Ti–6Al–4V alloy

    SciTech Connect

    Kang, Guozheng; Dong, Yawei; Liu, Yujie; Jiang, Han

    2014-06-01

    The uniaxial ratchetting of Ti–6Al–4V alloy with two phases (i.e., primary hexagonal close packed (HCP) α and secondary body-centered cubic (BCC) β phases) was investigated by macroscopic and microscopic experiments at room temperature. Firstly, the effects of cyclic softening/hardening feature, applied mean stress and stress amplitude on the uniaxial ratchetting of the alloy were discussed. The macroscopic investigation of Ti–6Al–4V alloy presents obvious strain-amplitude-dependent cyclic softening, as well as a three-staged evolution curve with regard to the ratchetting strain rate. The ratchetting depends greatly on the applied mean stress and stress amplitude while the ratchetting strain increases with the increasing applied mean stress and stress amplitude. Then, the evolution of dislocation patterns and deformation twinning during the uniaxial ratchetting of two-phase Ti–6Al–4V alloy were observed using transmission electron microscopy (TEM). The microscopic observation shows that deformation twinning occurs in the primary α phase and its amount increases gradually during the uniaxial ratchetting. Simultaneously, the planar dislocation evolves from discrete lines to some dislocation nets and parallel lines with the increasing number of cycles. The deformation twinning in the primary α phase is one of main contributions to the uniaxial ratchetting of Ti–6Al–4V alloy, and should be considered in the construction of corresponding constitutive model. - Highlights: • A three-staged ratchetting occurs in the stress-controlled cyclic tests of Ti–6Al–4V alloy. • Dislocation patterns change from discrete lines to nets and parallel lines. • Deformation twinning occurs during the uniaxial ratchetting. • Both dislocation slipping and twinning are the causes of ratchetting.

  2. Effects of uniaxial and biaxial orientation on fiber percolation in conductive polymer composites

    NASA Astrophysics Data System (ADS)

    Chang, Eunse; Ameli, Amir; Mark, Lun Howe; Park, Chul B.

    2015-12-01

    A Monte Carlo simulation was built to estimate the percolation threshold of fibers in a system under different fiber orientations. A 3-D model was built. The orientation effect was modeled by introducing a degree of alignment in the randomly generated fibers via appropriate mathematical relationships and various degrees of uniaxial strain were applied. The critical volume fraction was then analyzed in both normal direction (through-plane) and parallel direction (in-plane) to that of the cross-section plane. The effect of uniaxial orientation was modeled by measuring the through-plane percolation threshold under tensile strain. The effect of biaxial orientation was modeled by measuring the in-plane percolation threshold under compressive strain. The results indicated that the introduction of fiber alignment changed both through-plane and in-plane threshold values, albeit with different trends. With the introduction of slight uniaxial orientation, the through-plane percolation threshold reached a minimum value and further uniaxial orientation gave it a rise, while the in-plane threshold continuously increased with an increase in uniaxial orientation. On the other hand, under compression, an increase in biaxial orientation resulted in a monotonic increase in the through-plane threshold, whereas the in-plane threshold showed a minimal behavior before its rise. The results of this study indicate that the percolation threshold is minimized when fibers are slightly oriented (both uniaxial and biaxial) rather than being completely isotropic, and therefore, generation of conductive paths in a particular direction of interest can be induced via a proper choice of applied orientation with a lower critical concentration, thereby potentially reducing the filler loading. One particular implication of this work is modeling the percolation threshold in cellular polymer composites where local stresses are applied on the fillers around the cell walls during bubble growth.

  3. Uniaxial strain relaxation in He{sup +} ion implanted (110) oriented SiGe layers

    SciTech Connect

    Minamisawa, R. A.; Buca, D.; Trinkaus, H.; Hollaender, B.; Mantl, S.; Destefanis, V.; Hartmann, J. M.

    2009-07-20

    Uniaxially strained (011)Si is attractive for high performance p-channel metal oxide semiconductor field effect transistor devices due to the predicted high hole mobilities. Here, we demonstrate the realization of purely uniaxially relaxed (011) SiGe virtual substrates by He{sup +} ion implantation and thermal annealing. Perfect uniaxial relaxation is evidenced by precise ion channeling angular yield scan measurements and plan view transmission electron microscopy as predicted theoretically on the basis of the layer symmetry dependent dislocation dynamics. Strikingly, misfit dislocations propagate exclusively along the [011] direction in the (011) oriented crystal and, in contrast to (100)Si, no crosshatch is formed. We describe dislocation formation and propagation inducing strain relaxation of (011)SiGe and enlighten the differences to (100) oriented SiGe on Si.

  4. Uniaxial creep as a control on mercury intrusion capillary pressure in consolidating rock salt

    SciTech Connect

    Dewers, Thomas; Heath, Jason E.; Leigh, Christi D.

    2015-09-01

    The nature of geologic disposal of nuclear waste in salt formations requires validated and verified two - phase flow models of transport of brine and gas through intact, damaged, and consolidating crushed salt. Such models exist in oth er realms of subsurface engineering for other lithologic classes (oil and gas, carbon sequestration etc. for clastics and carbonates) but have never been experimentally validated and parameterized for salt repository scenarios or performance assessment. Mo dels for waste release scenarios in salt back - fill require phenomenological expressions for capillary pressure and relative permeability that are expected to change with degree of consolidation, and require experimental measurement to parameterize and vali date. This report describes a preliminary assessment of the influence of consolidation (i.e. volume strain or porosity) on capillary entry pressure in two phase systems using mercury injection capillary pressure (MICP). This is to both determine the potent ial usefulness of the mercury intrusion porosimetry method, but also to enable a better experimental design for these tests. Salt consolidation experiments are performed using novel titanium oedometers, or uniaxial compression cells often used in soil mech anics, using sieved run - of - mine salt from the Waste Isolation Pilot Plant (WIPP) as starting material. Twelve tests are performed with various starting amounts of brine pore saturation, with axial stresses up to 6.2 MPa (%7E900 psi) and temperatures to 90 o C. This corresponds to UFD Work Package 15SN08180211 milestone "FY:15 Transport Properties of Run - of - Mine Salt Backfill - Unconsolidated to Consolidated". Samples exposed to uniaxial compression undergo time - dependent consolidation, or creep, to various deg rees. Creep volume strain - time relations obey simple log - time behavior through the range of porosities (%7E50 to 2% as measured); creep strain rate increases with temperature and applied stress as

  5. Fracture Energy-Based Brittleness Index Development and Brittleness Quantification by Pre-peak Strength Parameters in Rock Uniaxial Compression

    NASA Astrophysics Data System (ADS)

    Munoz, H.; Taheri, A.; Chanda, E. K.

    2016-12-01

    Brittleness is a fundamental mechanical rock property critical to many civil engineering works, mining development projects and mineral exploration operations. However, rock brittleness is a concept yet to be investigated as there is not any unique criterion available, widely accepted by rock engineering community able to describe rock brittleness quantitatively. In this study, new brittleness indices were developed based on fracture strain energy quantities obtained from the complete stress-strain characteristics of rocks. In doing so, different rocks having unconfined compressive strength values ranging from 7 to 215 MPa were examined in a series of quasi-static uniaxial compression tests after properly implementing lateral-strain control in a closed-loop system to apply axial load to rock specimen. This testing method was essential to capture post-peak regime of the rocks since a combination of class I-II or class II behaviour featured post-peak stress-strain behaviour. Further analysis on the post-peak strain localisation, stress-strain characteristics and the fracture pattern causing class I-II and class II behaviour were undertaken by analysing the development of field of strains in the rocks via three-dimensional digital image correlation. Analysis of the results demonstrated that pre-peak stress-strain brittleness indices proposed solely based on pre-peak stress-strain behaviour do not show any correlation with any of pre-peak rock mechanical parameters. On the other hand, the proposed brittleness indices based on pre-peak and post-peak stress-strain relations were found to competently describe an unambiguous brittleness scale against rock deformation and strength parameters such as the elastic modulus, the crack damage stress and the peak stress relevant to represent failure process.

  6. Measuring the complex permittivity tensor of uniaxial biological materials with coplanar waveguide transmission line

    USDA-ARS?s Scientific Manuscript database

    A simple and accurate technique is described for measuring the uniaxial permittivity tensor of biological materials with a coplanar waveguide transmission-line configuration. Permittivity tensor results are presented for several chicken and beef fresh meat samples at 2.45 GHz....

  7. Mechanical response and failure of High Performance Propellant (HPP) subject to uniaxial tension

    NASA Astrophysics Data System (ADS)

    Liu, C.; Thompson, D. G.

    2015-05-01

    As part of a program to characterize and understand the mechanical response and failure behavior of the High Performance Propellant (HPP), uniaxial tensile tests were conducted. The mechanical properties of the HPP solid propellant subject to tension are investigated as a function of both the loading (strain) rate and the temperature. The nominal strain rate varies from 10-6 to 10-2 s-1 and the temperature varies from -50 to 50 °C. Digital image correlation (DIC) technique was used to obtain the full field deformation measurement over the sample surface, from which both the axial strain and the circumferential strain were determined, and as a result, volume changes during the uniaxial tension were studied. Some of the material parameters, e.g., Young's modulus E, the tensile strength σ max, and uniaxial tensile strain at the maximum tensile stress ɛ max, were found to be extremely sensitive to both the strain rate and the temperature. It was also observed that during the linear portion of the uniaxial tension, the HPP is close to incompressible. But when deformation enters the nonlinear regime, volume change of the sample accelerates and such a significant volume increase during the nonlinear portion of the deformation can be attributed to the formation and extension of damage within the gage section, which lead to the macroscopic tearing failure of the material.

  8. The Unloading Modulus of Akdq Steel after Uniaxial and Near Plane-Strain Plastic Deformation

    NASA Astrophysics Data System (ADS)

    Pavlina, E. J.; Levy, B. S.; van Tyne, C. J.; Kwon, S. O.; Moon, Y. H.

    Springback is a problem in the manufacture of a variety of automotive components. To determine springback, it is necessary to know the strength of the material after plastic deformation and the slope of the unloading curve (i.e. the unloading modulus). Prior investigations have shown that the unloading modulus for steels after plastic deformation has a slope that is lower than the normally accepted value for Young's modulus. Previous studies on the slope of the unloading curve were after uniaxial tensile plastic deformation. In the present study, the unloading modulus for an aluminum killed drawing quality (AKDQ) steel was evaluated after both uniaxial and near plane strain deformation. A tube hydroforming system was used for near plane-strain deformation. The average unloading modulus following uniaxial deformation for the AKDQ steel is approximately 168 GPa. The average unloading modulus for the circumferential stress component after near plane-strain deformation is lower than after uniaxial deformation. For a given amount of overall plastic deformation, the axial component of the unloading modulus is greater than the circumferential component, and with increased plastic strain, the unloading modulus for both components decreases. These results demonstrate that the components of the unloading modulus are dependent on the strain path of the prior plastic deformation.

  9. Tearing analysis of a new airship envelope material under uniaxial tensile load

    NASA Astrophysics Data System (ADS)

    Wang, F. X.; Xu, W.; Chen, Y. L.; Fu, G. Y.

    2016-07-01

    This paper experimentally investigated the tearing properties of a new kind of coated woven fabrics, GQ-6, made of ultra-high molecular weight polyethylene fiber. Such material can be used for the envelope materials of a stratospheric airship. First, the uniaxial tearing tests were carried out. Effects of the stretching rate, the initial crack length, and the initial crack orientation on the material's tearing tensile strength were investigated. Experimental results showed that the initial crack length and the initial crack orientation can be represented by the equivalent initial crack length while the stretching rate has a slight influence on tearing behavior of the uniaxial tensile specimens. Then analytical studies using three methods, i.e. Griffith energy theory, the stress intensity factor theory, and Thiele's empirical theory, among which, the stress intensity factor theory gives the best correlation with the test data. Finally, a 48mm threshold of the equivalent initial crack length was recommended to the envelope material in operation.

  10. Uniaxial compression test series on Bullfrog Tuff

    SciTech Connect

    Price, R H; Jones, A K; Nimick, K G

    1982-04-01

    Nineteen uniaxial compressive experiments were performed on samples of the Bullfrog Member of the Crater Flat Tuff, obtained from drillhole USW-G1 at Yucca Mountain on the Nevada Test Site. The water saturated samples were deformed at a nominal strain rate of 10{sup -5} sec{sup -1}, atmospheric pressure and room temperature. Resultant unconfined compressive strengths, axial strains to failure, Young`s moduli and Poisson`s ratios ranged from 4.63 to 153. MPa, .0028 to .0058, 2.03 to 28.9 GPa and .08 to .16, respectively.

  11. Quantitative multiphoton microscopy of murine urinary bladder morphology during in situ uniaxial loading.

    PubMed

    Hornsby, Jack; Daly, Donna M; Grundy, David; Cheng, Fangzhou; Robertson, Anne M; Watton, Paul N; Thompson, Mark S

    2017-09-22

    Urodynamic tests are the gold standard for the diagnosis of bladder dysfunction, and the mechanical compliance of the bladder is an important parameter in these tests. The bladder wall has a layered structure, differentially affected by pathology, so knowledge of the contribution and role of these layers and their constituents to overall bladder compliance will enhance interpretation of these clinical tests. In this study we document the functional morphology of the detrusor and lamina propria of the murine bladder wall using a custom in-situ tensile loading system under multiphoton microscopy (MPM) observation in unloaded state and under incremental uniaxial stretch. Features in the stress-stretch curves of bladder samples were then directly related to corresponding MPM images. Collagen organisation across wall depth was quantified using image analysis techniques. The hypothesis that the lamina propria deformed at low strain by unfolding of the rugae and rearranging collagen fibrils was confirmed. A novel 'pocket' feature in the detrusor was observed along with extensive rearrangement of fibrils in two families at different depths, providing higher stiffness at high stretches in the detrusor. The very different deformations of detrusor and lamina propria were accommodated by the highly coiled structure of collagen in the lamina propria. Imaging and mechanical studies presented here allow gross mechanical response to be attributed to specific components of the bladder wall and further, may be used to investigate the impact of microstructural changes due to pathology or aging, and how they impair tissue functionality. This article reports the first in-situ multiphoton microscopy observations of microstructural deformation under uniaxial tensile loading of ex vivo bladder. We describe collagen rearrangement through the tissue thickness and relate this directly to the stress-stretch behaviour. We confirm for the first time the unfolding of rugae and realignment of

  12. Shear strength of metals under uniaxial deformation and pure shear

    NASA Astrophysics Data System (ADS)

    Latypov, F. T.; Mayer, A. E.

    2015-11-01

    In this paper, we investigate the dynamic shear strength of perfect monocrystalline metals using the molecular dynamics simulation. Three types of deformation (single shear, uniaxial compression and tension) are investigated for five metals of different crystallographic systems (fcc, bcc and hcp). A strong dependence of the calculated shear strength on the deformation type is observed. In the case of bcc (iron) and hcp (titanium) metals, the maximal shear strength is achieved at the uniaxial compression, while the minimal shear strength is observed at the uniaxial tension. In the case of fcc metals (aluminum, copper, nickel) the largest strength is achieved at the pure shear, the lowest strength is obtained at the uniaxial compression.

  13. Superconductivity under uniaxial compression in β-(BDA-TTP) salts

    NASA Astrophysics Data System (ADS)

    Suzuki, T.; Onari, S.; Ito, H.; Tanaka, Y.

    2009-10-01

    In order to clarify the mechanism of organic superconductor β-(BDA-TTP) salts. We study the superconductivity under uniaxial compression with non-dimerized two-band Hubbard model. We have calculated the uniaxial compression dependence of T c by solving the Eliashberg’s equation using the fluctuation exchange (FLEX) approximation. The transfer integral under the uniaxial compression was estimated by the extended Huckel method. We have found that non-monotonic behaviors of T c in experimental results under uniaxial compression are understood taking the spin frustration and spin fluctuation into account.

  14. Nondestructive electromagnetic characterization of uniaxial materials

    NASA Astrophysics Data System (ADS)

    Rogers, Neil G.

    In this dissertation, a method for the simultaneous non-destructive extraction of the permittivity and permeability of a dielectric magnetic uniaxial anisotropic media is developed and several key contributions are demonstrated. The method utilizes a single fixture in which the MUT is clamped between two rectangular waveguides with 6" x 6" PEC flanges. The transmission and reflection coefficients are measured, then compared with theoretically calculated coefficients to find a least squares solution to the minimization problem. One of the key contributions of this work is the development of the total parallel plate spectral-domain Green's function by two independent methods. The Green's function is thereby shown to be correct in form and in physical meaning. A second significant contribution of this work to the scientific community is the evaluation of one of the inverse Fourier transform integrals in the complex plane. This significantly enhances the efficiency of the extraction code. A third significant contribution is the measurement of a number of uniaxial anisotropic materials, many of which were envisioned, designed and constructed in-house using 3D printing technology. The results are shown to be good in the transverse dimension, but mildly unstable in the longitudinal dimension. A secondary contribution of this work that warrants mention is the inclusion of a flexible, complete, working code for the extraction process. Although such codes have been written before, they have not been published in the literature for broader use.

  15. Quantum criticality in a uniaxial organic ferroelectric

    NASA Astrophysics Data System (ADS)

    Rowley, S. E.; Hadjimichael, M.; Ali, M. N.; Durmaz, Y. C.; Lashley, J. C.; Cava, R. J.; Scott, J. F.

    2015-10-01

    Tris-sarcosine calcium chloride (TSCC) is a highly uniaxial ferroelectric with a Curie temperature of approximately 130 K. By suppressing ferroelectricity with bromine substitution on the chlorine sites, pure single crystals were tuned through a ferroelectric quantum phase transition. The resulting quantum critical regime was investigated in detail and was found to persist up to temperatures of at least 30-40 K. The nature of long-range dipole interactions in uniaxial materials, which lead to non-analytical terms in the free-energy expansion in the polarization, predict a dielectric susceptibility varying as 1/T 3close to the quantum critical point. Rather than this, we find that the dielectric susceptibility varies as 1/T 2 as expected and observed in better known multi-axial systems. We explain this result by identifying the ultra-weak nature of the dipole moments in the TSCC family of crystals. Interestingly, we observe a shallow minimum in the inverse dielectric function at low temperatures close to the quantum critical point in paraelectric samples that may be attributed to the coupling of quantum polarization and strain fields. Finally, we present results of the heat capacity and electro-caloric effect and explain how the time dependence of the polarization in ferroelectrics and paraelectrics should be considered when making quantitative estimates of temperature changes induced by applied electric fields.

  16. The contribution of time-dependent stress relaxation in protein gels to the recoverable energy that is used as a tool to describe food texture

    NASA Astrophysics Data System (ADS)

    de Jong, Saskia; van Vliet, Ton; de Jongh, Harmen H. J.

    2015-11-01

    The recoverable energy (RE), defined as the ratio of the work exerted on a test specimen during compression and recovered upon subsequent decompression, has been shown to correlate to sensory profiling of protein-based food products. Understanding the mechanism determining the time-dependency of RE is primordial. This work aims to identify the protein-specific impact on the recoverable energy by stress dissipation via relaxation of (micro)structural rearrangements within protein gels. To this end, caseinate and gelatin gels are studied for their response to time-dependent mechanical deformation as they are known to develop structurally distinct network morphologies. This work shows that in gelatin gels no significant stress relaxation occurs on the seconds timescale, and consequently no time-dependency of the amount of energy stored in this material is observed. In caseinate gels, however, the energy dissipation via relaxation processes does contribute significantly to the time-dependency of reversible stored energy in the network. This can explain the obtained RE as a function of applied deformation at slow deformation rates. At faster deformation, an additional contribution to the dissipated energy is apparent, that increases with the deformation rate, which might point to the role of energy dissipation related to friction of the serum entrapped by the protein-network. This work shows that engineering strategies focused on controlling viscous flow in protein gels could be more effective to dictate the ability to elastically store energy in protein gels than routes that direct protein-specific aggregation and/or network-assembly.

  17. Precessional Switching of Thin Nanomagnets with Uniaxial Anisotropy

    NASA Astrophysics Data System (ADS)

    Devolder, Thibaut; Schumacher, Hans Werner; Chappert, Claude

    This review describes the evolution of the magnetization of uniaxial thin magnets when subjected to fast-rising magnetic-field pulses. We report detailed "all-electrical" experimental investigations of precessional switching on soft uniaxial micrometer-sized thin magnets, and we discuss them using a comprehensive, mostly analytical framework. General criteria are derived for the analytical assessment of the switching ability of any arbitrary set of experimental parameters. For this, we start from the Landau-Lifshitz equation and first consider the precessional switching in a much idealized macrospin, easy-plane loss-free system. We then test the main outputs of this model with time-resolved experiments on advanced Magnetic Random Access Memories (MRAM) cells. Using applied fields above the anisotropy field H k , we prove the quasiperiodic nature of the magnetization trajectory and we demonstrate experimental conditions ensuring a sub-200 ps ballistic magnetization reversal. We then upgrade our model accuracy by taking into account the uniaxial anisotropy and the behavior in hard-axis fields of the order of H k . We derive a simple though reliable estimate of the switching speed; its limiting factors highlight the experimental poor switching reproducibility when close to the minimal hard-axis reversal field H k /2. The latter field does not correspond to the minimal energy cost of the reversal, whose prospective evolution in the future generations of MRAM is predicted. Small departures from the macrospin state are discussed. The effect of damping is modeled using perturbation theory. Finite damping alters the precessional motion periodicity and puts some constraints on the field rise time. A special focus is dedicated to the relaxation-dominated precessional switching: the minimal hard-axis field triggering the switching is shown to be above H k /2 by an extra field cost linked to the damping constant times the square root of M S H k . Finally, the selective

  18. An Elastic Stress-Strain Relationship for Porous Rock Under Anisotropic Stress Conditions

    NASA Astrophysics Data System (ADS)

    Zhao, Yu; Liu, Hui-Hai

    2012-05-01

    A stress-strain relationship within porous rock under anisotropic stress conditions is required for modeling coupled hydromechanical processes associated with a number of practical applications. In this study, a three-dimensional stress-strain relationship is proposed for porous rock under elastic and anisotropic stress conditions. This relationship is a macroscopic-scale approximation that uses a natural-strain-based Hooke's law to describe deformation within a fraction of pores and an engineering-strain-based Hooke's law to describe deformation within the other part. This new relationship is evaluated using data from a number of uniaxial and triaxial tests published in the literature. Based on this new stress-strain relationship, we also develop constitutive relationships among stress, strain, and related stress-dependent hydraulic/mechanical properties (such as compressibility, shear modulus, and porosity). These relationships are demonstrated to be consistent with experimental observations.

  19. Mechanism for amorphization of boron carbide B{sub 4}C under uniaxial compression

    SciTech Connect

    Aryal, Sitaram; Rulis, Paul; Ching, W. Y.

    2011-11-01

    Boron carbide undergoes an amorphization transition under high-velocity impacts, causing it to suffer a catastrophic loss in strength. The failure mechanism is not clear and this limits the ways to improve its resistance to impact. To help uncover the failure mechanism, we used ab initio methods to carry out large-scale uniaxial compression simulations on two polytypes of stoichiometric boron carbide (B{sub 4}C), B{sub 11}C-CBC, and B{sub 12}-CCC, where B{sub 11}C or B{sub 12} is the 12-atom icosahedron and CBC or CCC is the three-atom chain. The simulations were performed on large supercells of 180 atoms. Our results indicate that the B{sub 11}C-CBC (B{sub 12}-CCC) polytype becomes amorphous at a uniaxial strain s = 0.23 (0.22) and with a maximum stress of 168 (151) GPa. In both cases, the amorphous state is the consequence of structural collapse associated with the bending of the three-atom chain. Careful analysis of the structures after amorphization shows that the B{sub 11}C and B{sub 12} icosahedra are highly distorted but still identifiable. Calculations of the elastic coefficients (C{sub ij}) at different uniaxial strains indicate that both polytypes may collapse under a much smaller shear strain (stress) than the uniaxial strain (stress). On the other hand, separate simulations of both models under hydrostatic compression up to a pressure of 180 GPa show no signs of amorphization, in agreement with experimental observation. The amorphized nature of both models is confirmed by detailed analysis of the evolution of the radial pair distribution function, total density of states, and distribution of effective charges on atoms. The electronic structure and bonding of the boron carbide structures before and after amorphization are calculated to further elucidate the mechanism of amorphization and to help form the proper rationalization of experimental observations.

  20. Densest Local Structures of Uniaxial Ellipsoids

    NASA Astrophysics Data System (ADS)

    Schaller, Fabian M.; Weigel, Robert F. B.; Kapfer, Sebastian C.

    2016-10-01

    Connecting the collective behavior of disordered systems with local structure on the particle scale is an important challenge, for example, in granular and glassy systems. Compounding complexity, in many scientific and industrial applications, particles are polydisperse, aspherical, or even of varying shape. Here, we investigate a generalization of the classical kissing problem in order to understand the local building blocks of packings of aspherical grains. We numerically determine the densest local structures of uniaxial ellipsoids by minimizing the Set Voronoi cell volume around a given particle. Depending on the particle aspect ratio, different local structures are observed and classified by symmetry and Voronoi coordination number. In extended disordered packings of frictionless particles, knowledge of the densest structures allows us to rescale the Voronoi volume distributions onto the single-parameter family of k -Gamma distributions. Moreover, we find that approximate icosahedral clusters are found in random packings, while the optimal local structures for more aspherical particles are not formed.

  1. Enhancement of in-plane uniaxial magnetic anisotropy for patterned nanoparticle films fabricated by electric field-assisted deposition

    NASA Astrophysics Data System (ADS)

    Ou, Xiulong; He, Jun; Xia, Zhenjun; An, Jing; Hao, Jiazheng; He, Shuli; Zhao, Dongliang

    2017-08-01

    The patterned FeNi nanoparticle films with strip width 60 μm were prepared by electric field-assisted deposition technique. Application of electric field drove the accelerating deposition of the condensed nanoparticles, promoting the formation of the films with high stacking density. Besides the excellent soft magnetic characteristics, the samples showed an obvious enhancement of in-plane uniaxial magnetic anisotropy when they were annealed in vacuum environment at proper temperatures. The increase of in-plane uniaxial magnetic anisotropy, which is due to the release of stress with increasing temperature, is also confirmed by scanning microwave permeability spectra in GHz range. The experimental results imply that optimization of in-plane uniaxial magnetic anisotropy is particularly attractive for the application of electric field deposited soft magnetic nanoparticle films in the high-temperature processing electromagnetic devices.

  2. Discrete element modeling on the crack evolution behavior of brittle sandstone containing three fissures under uniaxial compression

    NASA Astrophysics Data System (ADS)

    Yang, Sheng-Qi; Huang, Yan-Hua; Ranjith, P. G.; Jiao, Yu-Yong; Ji, Jian

    2015-12-01

    Based on experimental results of brittle, intact sandstone under uniaxial compression, the micro-parameters were firstly confirmed by adopting particle flow code (PFC^{2D}). Then, the validation of the simulated models were cross checked with the experimental results of brittle sandstone containing three parallel fissures under uniaxial compression. The simulated results agreed very well with the experimental results, including the peak strength, peak axial strain, and ultimate failure mode. Using the same micro-parameters, the numerical models containing a new geometry of three fissures are constructed to investigate the fissure angle on the fracture mechanical behavior of brittle sandstone under uniaxial compression. The strength and deformation parameters of brittle sandstone containing new three fissures are dependent to the fissure angle. With the increase of the fissure angle, the elastic modulus, the crack damage threshold, and the peak strength of brittle sandstone containing three fissures firstly increase and secondly decrease. But the peak axial strain is nonlinearly related to the fissure angle. In the entire process of deformation, the crack initiation and propagation behavior of brittle sandstone containing three fissures under uniaxial compression are investigated with respect to the fissure angle. Six different crack coalescence modes are identified for brittle sandstone containing three fissures under uniaxial compression. The influence of the fissure angle on the length of crack propagation and crack coalescence stress is evaluated. These investigated conclusions are very important for ensuring the stability and safety of rock engineering with intermittent structures.

  3. Results of uniaxial and biaxial tests on riveted fuselage lap joint specimens

    NASA Technical Reports Server (NTRS)

    Vlieger, H.

    1994-01-01

    As part of an FAA-NLR collaborative program on structural integrity of aging aircraft, NLR carried out uniaxial and biaxial fatigue tests on riveted lap joint specimens being representative for application in a fuselage. All tests were constant amplitude tests with maximum stresses being representative for fuselage pressurization cycles and R-values of 0.1. The parameters selected in the testing program were the stress level (sigma(sub max) = 14 and 16 ksi) and the rivet spacing (0.75 and 1.0 inch). All specimens contained 3 rows of countersunk rivets, the rivet row spacing was 1 inch and the rivet orientation continuous.

  4. Deformation behavior of lead zirconate titanate ceramics under uniaxial compression measured by the digital image correlation method

    NASA Astrophysics Data System (ADS)

    Chen, Di; Carter, Emma; Kamlah, Marc

    2016-09-01

    The deformation behavior of lead zirconate titanate bulk ceramic specimen under uniaxial compression was monitored by the digital image correlation method and the homogeneity of the deformation was discussed. Combined with using a Sawyer-Tower circuit, the depolarization curve was also obtained. Because of the friction at both the top and bottom surfaces of the lead zirconate titanate ceramic specimen, the distribution of deformation under large uniaxial compressive stresses usually shows a barrel shape. By focusing on correspondingly selected regions of interest and calculating the values of strain components there, the barreling behavior was proved. This barreling behavior is due to elastic strains, in the first place, while the remnant strains are less affected by this phenomenon. All these findings are the experimental justifications for the selection of an aspect ratio of 3:1 for our specimens, where only the central cubic region of a specimen represents the desired purely uniaxial stress state. Only from this region, true uniaxial stress-strain results can be obtained to develop constitutive models.

  5. Edge effects on band gap energy in bilayer 2H-MoS2 under uniaxial strain

    NASA Astrophysics Data System (ADS)

    Dong, Liang; Wang, Jin; Namburu, Raju; O'Regan, Terrance P.; Dubey, Madan; Dongare, Avinash M.

    2015-06-01

    The potential of ultrathin MoS2 nanostructures for applications in electronic and optoelectronic devices requires a fundamental understanding in their electronic structure as a function of strain. Previous experimental and theoretical studies assume that an identical strain and/or stress state is always maintained in the top and bottom layers of a bilayer MoS2 film. In this study, a bilayer MoS2 supercell is constructed differently from the prototypical unit cell in order to investigate the layer-dependent electronic band gap energy in a bilayer MoS2 film under uniaxial mechanical deformations. The supercell contains an MoS2 bottom layer and a relatively narrower top layer (nanoribbon with free edges) as a simplified model to simulate the as-grown bilayer MoS2 flakes with free edges observed experimentally. Our results show that the two layers have different band gap energies under a tensile uniaxial strain, although they remain mutually interacting by van der Waals interactions. The deviation in their band gap energies grows from 0 to 0.42 eV as the uniaxial strain increases from 0% to 6% under both uniaxial strain and stress conditions. The deviation, however, disappears if a compressive uniaxial strain is applied. These results demonstrate that tensile uniaxial strains applied to bilayer MoS2 films can result in distinct band gap energies in the bilayer structures. Such variations need to be accounted for when analyzing strain effects on electronic properties of bilayer or multilayered 2D materials using experimental methods or in continuum models.

  6. Edge effects on band gap energy in bilayer 2H-MoS{sub 2} under uniaxial strain

    SciTech Connect

    Dong, Liang; Wang, Jin; Dongare, Avinash M.; Namburu, Raju; O'Regan, Terrance P.; Dubey, Madan

    2015-06-28

    The potential of ultrathin MoS{sub 2} nanostructures for applications in electronic and optoelectronic devices requires a fundamental understanding in their electronic structure as a function of strain. Previous experimental and theoretical studies assume that an identical strain and/or stress state is always maintained in the top and bottom layers of a bilayer MoS{sub 2} film. In this study, a bilayer MoS{sub 2} supercell is constructed differently from the prototypical unit cell in order to investigate the layer-dependent electronic band gap energy in a bilayer MoS{sub 2} film under uniaxial mechanical deformations. The supercell contains an MoS{sub 2} bottom layer and a relatively narrower top layer (nanoribbon with free edges) as a simplified model to simulate the as-grown bilayer MoS{sub 2} flakes with free edges observed experimentally. Our results show that the two layers have different band gap energies under a tensile uniaxial strain, although they remain mutually interacting by van der Waals interactions. The deviation in their band gap energies grows from 0 to 0.42 eV as the uniaxial strain increases from 0% to 6% under both uniaxial strain and stress conditions. The deviation, however, disappears if a compressive uniaxial strain is applied. These results demonstrate that tensile uniaxial strains applied to bilayer MoS{sub 2} films can result in distinct band gap energies in the bilayer structures. Such variations need to be accounted for when analyzing strain effects on electronic properties of bilayer or multilayered 2D materials using experimental methods or in continuum models.

  7. Controllable strain-induced uniaxial anisotropy of Fe81Ga19 films deposited on flexible bowed-substrates

    NASA Astrophysics Data System (ADS)

    Dai, Guohong; Zhan, Qingfeng; Yang, Huali; Liu, Yiwei; Zhang, Xiaoshan; Zuo, Zhenghu; Chen, Bin; Li, Run-Wei

    2013-11-01

    We propose a convenient method to induce a uniaxial anisotropy in magnetostrictive Fe81Ga19 films grown on flexible polyethylene terephthalate (PET) substrates by bending the substrate prior to deposition. A tensile/compressive stress is induced in the Fe81Ga19 films when PET substrates are shaped from concave/convex to flat after deposition. The stressed Fe81Ga19 films exhibit a significant uniaxial magnetic anisotropy due to the internal stress arising from changes in shape of PET substrates. The easy axis is along the tensile stress direction and the coercive field along easy axis is increased with increasing the internal tensile stress. The remanence of hard axis is decreased with increasing the compressive stress, while the coercive field is almost unchanged. A modified Stoner-Wohlfarth model with considering the distribution of easy axes in polycrystalline films is used to account for the magnetic properties tuned by the strain-controlled magnetoelastic anisotropy in flexible Fe81Ga19 films. Our investigations provide a convenient way to induce uniaxial magnetic anisotropy, which is particularly important for fabricating flexible magnetoelectronic devices.

  8. Deformation micromechanisms of collagen fibrils under uniaxial tension.

    PubMed

    Tang, Yuye; Ballarini, Roberto; Buehler, Markus J; Eppell, Steven J

    2010-05-06

    Collagen, an essential building block of connective tissues, possesses useful mechanical properties due to its hierarchical structure. However, little is known about the mechanical properties of collagen fibril, an intermediate structure between the collagen molecule and connective tissue. Here, we report the results of systematic molecular dynamics simulations to probe the mechanical response of initially unflawed finite size collagen fibrils subjected to uniaxial tension. The observed deformation mechanisms, associated with rupture and sliding of tropocollagen molecules, are strongly influenced by fibril length, width and cross-linking density. Fibrils containing more than approximately 10 molecules along their length and across their width behave as representative volume elements and exhibit brittle fracture. Shorter fibrils experience a more graceful ductile-like failure. An analytical model is constructed and the results of the molecular modelling are used to find curve-fitted expressions for yield stress, yield strain and fracture strain as functions of fibril structural parameters. Our results for the first time elucidate the size dependence of mechanical failure properties of collagen fibrils. The associated molecular deformation mechanisms allow the full power of traditional material and structural engineering theory to be applied to our understanding of the normal and pathological mechanical behaviours of collagenous tissues under load.

  9. Failure Mechanisms of Brittle Rocks under Uniaxial Compression

    NASA Astrophysics Data System (ADS)

    Liu, Taoying; Cao, Ping

    2017-09-01

    The behaviour of a rock mass is determined not only by the properties of the rock matrix, but mostly by the presence and properties of discontinuities or fractures within the mass. The compression test on rock-like specimens with two prefabricated transfixion fissures, made by pulling out the embedded metal inserts in the pre-cured period was carried out on the servo control uniaxial loading tester. The influence of the geometry of pre-existing cracks on the cracking processes was analysed with reference to the experimental observation of crack initiation and propagation from pre-existing flaws. Based on the rock fracture mechanics and the stress-strain curves, the evolution failure mechanism of the fissure body was also analyzed on the basis of exploring the law of the compression-shear crack initiation, wing crack growth and rock bridge connection. Meanwhile, damage fracture mechanical models of a compression-shear rock mass are established when the rock bridge axial transfixion failure, tension-shear combined failure, or wing crack shear connection failure occurs on the specimen under axial compression. This research was of significance in studying the failure mechanism of fractured rock mass.

  10. Resonance of a rectangular microstrip patch on a uniaxial substrate

    NASA Astrophysics Data System (ADS)

    Wong, Kin-Lu; Row, Jeen-Sheen; Kuo, Chih-Wen; Huang, Kuang-Chih

    1993-04-01

    Effects of uniaxial anisotropy in the substrate on the complex resonant frequency of the microstrip patch antenna are investigated in terms of an integral equation formulation. The complex resonant frequency of the microstrip patch antenna is calculated by using Galerkin's method in solving the integral equation. The sinusoidal functions are selected as the basis functions, which show fast numerical convergence. Numerical results also indicate that both the resonant frequency and the half-power bandwidth are increased due to the positive uniaxial anisotropy and, on the other hand, decreased due to the negative uniaxial anisotropy.

  11. Anisotropy of the superconducting transition temperature under uniaxial pressure

    NASA Astrophysics Data System (ADS)

    Chen, X. J.; Lin, H. Q.; Yin, W. G.; Gong, C. D.; Habermeier, H.-U.

    2001-12-01

    The superconducting transition temperature Tc is calculated as a function of uniaxial pressure along the a, b, c directions for optimally doped YBa2Cu3O7-δ on the basis of a hole dispersion of the anisotropic t-J model. There is a good qualitative agreement with experiments. We show that the uniaxial pressure effect on Tc in the ab plane is due to the anisotropies of the hole dispersion and the in-plane pairing interaction, whereas the reduction of Tc under uniaxial compression along the c axis mainly results from the pressure-induced increase of hole concentration of the CuO2 plane.

  12. Pressure prediction in non-uniaxial settings based on field data and geomechanical modeling: a well example

    NASA Astrophysics Data System (ADS)

    Lockhart, L. P.; Flemings, P. B.; Nikolinakou, M. A.; Heidari, M.

    2016-12-01

    We apply a new pressure prediction approach that couples sonic velocity data, geomechanical modeling, and a critical state soil model to estimate pore pressure from wellbore data adjacent to a salt body where the stress field is complex. Specifically, we study pressure and stress in front of the Mad Dog salt body, in the Gulf of Mexico. Because of the loading from the salt, stresses are not uniaxial; the horizontal stress is elevated, leading to higher mean and shear stresses. For the Mad Dog field, we develop a relationship between velocity and equivalent effective stress, in order to account for both the mean and shear stress effect on pore pressure. We obtain this equivalent effective stress using a geomechanical model of the Mad Dog field. We show that the new approach improves pressure prediction in areas near salt where mean and shear stress are different than the control well. Our methodology and results show that pore pressure is driven by a combination of mean stress and shear stress, and highlight the importance of shear-induced pore pressures. Furthermore, the impact of our study extends beyond salt bodies; the methodology and gained insights are applicable to geological environments around the world with a complex geologic history, where the stress state is not uniaxial (fault zones, anticlines, synclines, continental margins, etc.).

  13. Uniaxial Strain Effects on Superconducting Transition in Y0.98Ca0.02Ba2Cu4O8

    NASA Astrophysics Data System (ADS)

    Mito, Masaki; Goto, Hiroki; Matsui, Hideaki; Deguchi, Hiroyuki; Matsumoto, Kaname; Hara, Hiroshi; Ozaki, Toshinori; Takeya, Hiroyuki; Takano, Yoshihiko

    2016-02-01

    The effects of uniaxial strain and hydrostatic pressure on Y0.98Ca0.02Ba2Cu4O8 [called Y0.98(Ca0.02)-124] are investigated via AC magnetic measurements under stress corresponding to a pressure of (at most) 20 GPa. Hydrostatic contraction results in the largest enhancement of the superconducting transition temperature (Tc), whose maximum is 99 K, which is slightly lower than the maximum Tc achieved in YBa2Cu4O8 (called Y-124). The Meissner signal disappears at a hydrostatic pressure of approximately 15 GPa. This pressure region representing the Meissner signal is reduced by the out-of-plane contraction (along the c-axis), whereas it is increased by the in-plane contraction (along the c-plane). In the case of Y-124, both uniaxial contractions result in the disappearance of the Meissner signal at approximately 10 GPa prior to reaching the overdoped region. However, by doping Ca into the Y-site, we could investigate uniaxial strain effects characteristic of the so-called 124 structure without causing the stress-induced structural transition through the underdoped, optimally doped, and overdoped regions. Except for the uniaxial contraction along the b-axis, the other contractions (i.e., hydrostatic contraction, and uniaxial contractions along the a- and the c-axes) exhibit consistent compression effects when Tc is normalized by the highest Tc and the stress is normalized by the stress realizing its highest Tc.

  14. Uniaxially aligned nanofibrous cylinders by electrospinning.

    PubMed

    Jana, Soumen; Cooper, Ashleigh; Ohuchi, Fumio; Zhang, Miqin

    2012-09-26

    Aligned nanofibers have drawn increasing interest for applications in biomedical engineering, electronics, and energy storage systems owing to the unique physicochemical properties provided by their anisotropy and high surface-to-volume ratio. Nevertheless, direct fabrication or assembly of aligned nanofibers into a 3-dimensional standalone construct with practically applicable dimensions presents an enormous challenge. We report a facile method to fabricate aligned nanofibrous cylinders, a widely used geometric form, by electrospinning aligned nanofibers across the gap between a pair of pin electrodes placed apart uniaxially. With this approach, cylindrical nanofibrous constructs of several millimeters in diameter and several centimeters in length can be readily produced. The versatility of the approach was demonstrated with several commonly used polymeric and ceramic materials, including polycaprolactone (PCL), chitosan/PCL, polyvinylidene fluoride, and titania. For a model application in tissue engineering, skeletal muscle cells were cultured on nanofibrous cylinders, which effectively produced highly aligned and densely populated myotubes along the nanofiber orientation, favorable for muscle tissue regeneration. With high structural integrity and stability, these can be directly integrated into devices or implanted in vivo as a standalone construct without the support of a substrate, thus increasing the portability, efficiency, and applicability of aligned nanofibers.

  15. Inducing uniform single-crystal like orientation in natural rubber with constrained uniaxial stretch.

    PubMed

    Zhou, Weiming; Meng, Lingpu; Lu, Jie; Wang, Zhen; Zhang, Wenhua; Huang, Ningdong; Chen, Liang; Li, Liangbin

    2015-07-07

    The effect of flow on crystallization is commonly attributed to entropic reduction, which is caused by stretch and orientation of polymer chains but overlooks the role of flow on final-state free energy. With the aid of in situ synchrotron radiation wide-angle X-ray diffraction (WAXD) and a homemade constrained uniaxial tensile testing machine, polycrystals possessing single-crystal-like orientation rather than uniaxial orientation are found during the constrained stretch of natural rubber, whereas the c-axis and a-axis align in the stretch direction (SD) and constrained direction (CD), respectively. Molecular dynamics simulation shows that aligning the a-axis of crystal nuclei in CD leads to the lowest free energy increase and favors crystal nucleation. This indicates that the nomenclature of strain-induced crystallization may not fully account for the nature of flow-induced crystallization (FIC) as strain mainly emphasizes the entropic reduction of initial melt, whereas stress rather than strain plays the dominant role in crystal deformation. The current work not only contributes to a comprehensive understanding of the mechanism of flow-induced crystallization but also demonstrates the potential application of constrained uniaxial tensile stretch for the creation of functional materials containing polycrystals that possess single-crystal-like orientation.

  16. Analysis of silicon stress/strain relationships

    NASA Technical Reports Server (NTRS)

    Dillon, O.

    1986-01-01

    Results are presented for work on stress-strain relationships in silicon ribbon. Calculations of stress fields, dislocation desities, and buckling were made; uniaxial tensile tests were made on silicon at 1150 C; and dislocation motion studies were performed.

  17. Consistent Parameters for Plastic Anisotropy of Sheet Metal (Part 1-Uniaxial and Biaxial Tests)

    SciTech Connect

    Poehlandt, K.; Schoeck, J.; Lange, K.; Banabic, D.

    2007-04-07

    The anisotropy parameters for sheet metal used hitherto are mainly determined by uniaxial tensile tests. Such tests, however, do not give sufficient information about the yield locus and the forming behaviour in that range where the two principal tensile stresses are of similar magnitude like in stretch forming. The same applies for combined tensile and compressive stress like in deep-drawing. To fill these gaps, new parameters are defined. Their experimental determination is briefly discussed.The 'equibiaxial yield stress' and 'equibiaxial anisotropy' which refer to equibiaxial tensile stress can be determined by cross tensile tests. However, these require a special apparatus. Alternatively experiments for obtaining plane strain can be applied for determining the equibiaxial parameters indirectly. This is possible using conventional tensile testing machines. In this case also anisotropy parameters for plane-strain deformation, the 'semibiaxial anisotropy' in rolling and transverse direction, can be determined.

  18. Anisotropic Thermal Conductivity Measurements on Cross-Linked Polybutadienes in Uniaxial Elongation

    NASA Astrophysics Data System (ADS)

    Venerus, David C.; Kolev, Dimitre

    2008-07-01

    Cross-linked elastomers have numerous applications including automobiles, sporting goods, and biomedical devices. During both their processing and application, these materials experience large mechanical stresses and thermal gradients. In this study, we investigate the mechanical and thermal transport behavior of cross-linked polybutadienes. These materials have been prepared by cross linking well-entangled polybutadienes using an organic peroxide cross-linking agent at low concentration. Samples obtained after nearly complete conversion of the cross-linking agent, which can be characterized as lightly cross-linked (i.e., more than 10 entanglements per cross-link), were subjected to a series of large strain, uniaxial deformations. Measurements of the tensile stress and two components of the thermal conductivity tensor will be reported as a function of elongation. These data are also used to examine the stress-thermal rule in which the stress and thermal conductivity tensors are linearly related.

  19. Impact of uniaxial strain and doping on oxygen diffusion in CeO2

    PubMed Central

    Rushton, M. J. D.; Chroneos, A.

    2014-01-01

    Doped ceria is an important electrolyte for solid oxide fuel cell applications. Molecular dynamics simulations have been used to investigate the impact of uniaxial strain along the <100> directions and rare-earth doping (Yb, Er, Ho, Dy, Gd, Sm, Nd, and La) on oxygen diffusion. We introduce a new potential model that is able to describe the thermal expansion and elastic properties of ceria to give excellent agreement with experimental data. We calculate the activation energy of oxygen migration in the temperature range 900–1900 K for both unstrained and rare-earth doped ceria systems under tensile strain. Uniaxial strain has a considerable effect in lowering the activation energies of oxygen migration. A more pronounced increase in oxygen diffusivities is predicted at the lower end of the temperature range for all the dopants considered. PMID:25317676

  20. Analysis of the Mechanical Behavior, Creep Resistance and Uniaxial Fatigue Strength of Martensitic Steel X46Cr13.

    PubMed

    Brnic, Josip; Krscanski, Sanjin; Lanc, Domagoj; Brcic, Marino; Turkalj, Goran; Canadija, Marko; Niu, Jitai

    2017-04-06

    The article deals with the analysis of the mechanical behavior at different temperatures, uniaxial creep and uniaxial fatigue of martensitic steel X46Cr13 (1.4034, AISI 420). For the purpose of considering the aforementioned mechanical behavior, as well as determining the appropriate resistance to creep and fatigue strength levels, numerous uniaxial tests were carried out. Tests related to mechanical properties performed at different temperatures are presented in the form of engineering stress-strain diagrams. Short-time creep tests performed at different temperatures and different stress levels are presented in the form of creep curves. Fatigue tests carried out at stress ratios R = 0.25 and R = - 1 are shown in the form of S-N (fatigue) diagrams. The finite fatigue regime for each of the mentioned stress ratios is modeled by an inclined log line, while the infinite fatigue regime is modeled by a horizontal line, which represents the fatigue limit of the material and previously was calculated by the modified staircase method. Finally, the fracture toughness has been calculated based on the Charpy V-notch impact energy.

  1. Analysis of the Mechanical Behavior, Creep Resistance and Uniaxial Fatigue Strength of Martensitic Steel X46Cr13

    PubMed Central

    Brnic, Josip; Krscanski, Sanjin; Lanc, Domagoj; Brcic, Marino; Turkalj, Goran; Canadija, Marko; Niu, Jitai

    2017-01-01

    The article deals with the analysis of the mechanical behavior at different temperatures, uniaxial creep and uniaxial fatigue of martensitic steel X46Cr13 (1.4034, AISI 420). For the purpose of considering the aforementioned mechanical behavior, as well as determining the appropriate resistance to creep and fatigue strength levels, numerous uniaxial tests were carried out. Tests related to mechanical properties performed at different temperatures are presented in the form of engineering stress-strain diagrams. Short-time creep tests performed at different temperatures and different stress levels are presented in the form of creep curves. Fatigue tests carried out at stress ratios R=0.25 and R=−1 are shown in the form of S–N (fatigue) diagrams. The finite fatigue regime for each of the mentioned stress ratios is modeled by an inclined log line, while the infinite fatigue regime is modeled by a horizontal line, which represents the fatigue limit of the material and previously was calculated by the modified staircase method. Finally, the fracture toughness has been calculated based on the Charpy V-notch impact energy. PMID:28772749

  2. Scaling laws and deformation mechanisms of nanoporous copper under adiabatic uniaxial strain compression

    SciTech Connect

    Yuan, Fuping Wu, Xiaolei

    2014-12-15

    A series of large-scale molecular dynamics simulations were conducted to investigate the scaling laws and the related atomistic deformation mechanisms of Cu monocrystal samples containing randomly placed nanovoids under adiabatic uniaxial strain compression. At onset of yielding, plastic deformation is accommodated by dislocations emitted from void surfaces as shear loops. The collapse of voids are observed by continuous emissions of dislocations from void surfaces and their interactions with further plastic deformation. The simulation results also suggest that the effect modulus, the yield stress and the energy aborption density of samples under uniaxial strain are linearly proportional to the relative density ρ. Moreover, the yield stress, the average flow stress and the energy aborption density of samples with the same relative density show a strong dependence on the void diameter d, expressed by exponential relations with decay coefficients much higher than -1/2. The corresponding atomistic mechanisms for scaling laws of the relative density and the void diameter were also presented. The present results should provide insights for understanding deformation mechanisms of nanoporous metals under extreme conditions.

  3. The mechanical behaviour of synthetic, poorly consolidated granular rock under uniaxial compression

    NASA Astrophysics Data System (ADS)

    Saidi, F.; Bernabé, Y.; Reuschlé, T.

    2003-07-01

    In order to isolate the effect of grain size and cementation on the mechanical behaviour of poorly consolidated granular rock, we prepared synthetic rock samples in which these two parameters were varied independently. Various proportions of sand, Portland cement and water were mixed and cast in a mold. The mixture was left pressure-free during curing, thus ensuring that the final material was poorly consolidated. We used two natural well-sorted sands with grain sizes of 0.22 and 0.8 mm. The samples were mechanically tested in a uniaxial press. Static Young's modulus was measured during the tests by performing small stress excursions at discrete intervals along the stress-strain curves. All the samples exhibited nonlinear elasticity, i.e., Young's modulus increased with stress. As expected, we found that the uniaxial compressive strength increased with increasing cement content. Furthermore, we observed a transition from grain size sensitivity of strength at cement content less than 20-30% to grain size independence above this value. The measured values of Young's modulus are well explained by models based on rigid inclusions embedded in a soft matrix, at high cement content, and on cemented grain-to-grain contacts, at low cement content. Both models predict grain size independence in well-sorted cemented sands. The observed grain size sensitivity at low cement content is probably due to microstructural differences between fine- and coarse-grained materials caused by small differences in grain sorting quality.

  4. Scaling laws and deformation mechanisms of nanoporous copper under adiabatic uniaxial strain compression

    NASA Astrophysics Data System (ADS)

    Yuan, Fuping; Wu, Xiaolei

    2014-12-01

    A series of large-scale molecular dynamics simulations were conducted to investigate the scaling laws and the related atomistic deformation mechanisms of Cu monocrystal samples containing randomly placed nanovoids under adiabatic uniaxial strain compression. At onset of yielding, plastic deformation is accommodated by dislocations emitted from void surfaces as shear loops. The collapse of voids are observed by continuous emissions of dislocations from void surfaces and their interactions with further plastic deformation. The simulation results also suggest that the effect modulus, the yield stress and the energy aborption density of samples under uniaxial strain are linearly proportional to the relative density ρ. Moreover, the yield stress, the average flow stress and the energy aborption density of samples with the same relative density show a strong dependence on the void diameter d, expressed by exponential relations with decay coefficients much higher than -1/2. The corresponding atomistic mechanisms for scaling laws of the relative density and the void diameter were also presented. The present results should provide insights for understanding deformation mechanisms of nanoporous metals under extreme conditions.

  5. Microstrain fields for cortical bone in uniaxial tension: optical analysis method.

    PubMed

    Kim, D G; Brunski, J B; Nicolella, D P

    2005-01-01

    This study employed an optical strain measurement method, called microdisplacements by machine vision photogrammetry (DISMAP), to measure both the global and local strain fields in microtensile specimens of cortical bone subjected to controlled uniaxial tension. The variation of local maximum principal strains was measured within the gauge region of samples as a function of applied tensile stress during testing. High gradients of local strain appeared around microstructural features in stressed bone even while the global strain for the entire gauge region showed a strong linear correlation with increasing tensile stress (r2 = 0.98, p < 0.0001). The highest local strain around microstructural features in bone was 11.5-79.5 times higher than the global strain.

  6. Bifurcation analysis of the onset of necking in an elastic/plastic cylinder under uniaxial tension

    NASA Technical Reports Server (NTRS)

    Hutchinson, J. W.; Miles, J. P.

    1974-01-01

    The bifurcation problem governing the onset of axisymmetric necking in a circular cylindrical specimen in uniaxial tension is analysed. The specimen is made of an incompressible elastic/plastic material. One end is subject to a prescribed uniform axial displacement relative to the other and both ends are shear free. The true stress at bifurcation is greater than the stress at which the maximum load is attained by an amount which depends on (a) the radius to length ratio of the specimen, (b) the ratio of the elastic shear modulus to the tangent modulus, and (c) the derivative of the tangent modulus with respect to the stress. Bifurcation takes place immediately following attainment of the maximum load when the specimen is sufficiently slender.

  7. Bifurcation analysis of the onset of necking in an elastic/plastic cylinder under uniaxial tension

    NASA Technical Reports Server (NTRS)

    Hutchinson, J. W.; Miles, J. P.

    1974-01-01

    The bifurcation problem governing the onset of axisymmetric necking in a circular cylindrical specimen in uniaxial tension is analysed. The specimen is made of an incompressible elastic/plastic material. One end is subject to a prescribed uniform axial displacement relative to the other and both ends are shear free. The true stress at bifurcation is greater than the stress at which the maximum load is attained by an amount which depends on (a) the radius to length ratio of the specimen, (b) the ratio of the elastic shear modulus to the tangent modulus, and (c) the derivative of the tangent modulus with respect to the stress. Bifurcation takes place immediately following attainment of the maximum load when the specimen is sufficiently slender.

  8. Landau levels in uniaxially strained graphene: A geometrical approach

    SciTech Connect

    Betancur-Ocampo, Y. Cifuentes-Quintal, M.E.; Cordourier-Maruri, G.; Coss, R. de

    2015-08-15

    The effect of strain on the Landau levels (LLs) spectra in graphene is studied, using an effective Dirac-like Hamiltonian which includes the distortion in the Dirac cones, anisotropy and spatial-dependence of the Fermi velocity induced by the lattice change through a renormalized linear momentum. We propose a geometrical approach to obtain the electron’s wave-function and the LLs in graphene from the Sturm–Liouville theory, using the minimal substitution method. The coefficients of the renormalized linear momentum are fitted to the energy bands, which are obtained from a Density Functional Theory (DFT) calculation. In particular, we evaluate the case of Dirac cones with an ellipsoidal transversal section resulting from uniaxially strained graphene along the Arm-Chair (AC) and Zig-Zag (ZZ) directions. We found that uniaxial strain in graphene induces a contraction of the LLs spectra for both strain directions. Also, is evaluated the contribution of the tilting of Dirac cone axis resulting from the uniaxial deformations to the contraction of the LLs spectra. - Highlights: • The LLs in uniaxially strained graphene are found using a geometrical approach. • The energy of the LLs in function of the Dirac cone deformation is presented. • We found that uniaxial strain in graphene induces a contraction of the LLs spectra. • Contraction in LLs spectra depends on the geometrical parameters of the Dirac cone.

  9. Describe Your Favorite Teacher.

    ERIC Educational Resources Information Center

    Dill, Isaac; Dill, Vicky

    1993-01-01

    A third grader describes Ms. Gonzalez, his favorite teacher, who left to accept a more lucrative teaching assignment. Ms. Gonzalez' butterflies unit covered everything from songs about social butterflies to paintings of butterfly wings, anatomy studies, and student haiku poems and biographies. Students studied biology by growing popcorn plants…

  10. Describe Your Favorite Teacher.

    ERIC Educational Resources Information Center

    Dill, Isaac; Dill, Vicky

    1993-01-01

    A third grader describes Ms. Gonzalez, his favorite teacher, who left to accept a more lucrative teaching assignment. Ms. Gonzalez' butterflies unit covered everything from songs about social butterflies to paintings of butterfly wings, anatomy studies, and student haiku poems and biographies. Students studied biology by growing popcorn plants…

  11. Simple Waveforms, Simply Described

    NASA Technical Reports Server (NTRS)

    Baker, John G.

    2008-01-01

    Since the first Lazarus Project calculations, it has been frequently noted that binary black hole merger waveforms are 'simple.' In this talk we examine some of the simple features of coalescence and merger waveforms from a variety of binary configurations. We suggest an interpretation of the waveforms in terms of an implicit rotating source. This allows a coherent description, of both the inspiral waveforms, derivable from post-Newtonian(PN) calculations, and the numerically determined merger-ringdown. We focus particularly on similarities in the features of various Multipolar waveform components Generated by various systems. The late-time phase evolution of most L these waveform components are accurately described with a sinple analytic fit. We also discuss apparent relationships among phase and amplitude evolution. Taken together with PN information, the features we describe can provide an approximate analytic description full coalescence wavefoRms. complementary to other analytic waveforns approaches.

  12. Analysis of Magnetization Curves and Magnetocrystalline Anisotropy of Uniaxial Ferromagnets

    NASA Astrophysics Data System (ADS)

    Lyakhova, M. B.; Zhdanova, O. V.

    2017-01-01

    Theoretical analysis of the processes of magnetization of uniaxial ferromagnetic materials is performed within the Neel theory of magnetic phases. Relations are obtained for the constants of magnetic crystal anisotropy K 1, K 2, the form factor N, and the saturation magnetization I s , at which the magnetization curves exhibit jumps (FOMP). Formulas for computing the saturation fields H s and the jump fields H FOMP are derived for crystals with different types of magnetocrystalline anisotropy MCA. It is shown that the Sucksmith-Thompson method is applicable for computing the first too MCAconstants of uniaxial ferromagnets with any type of MCA. Constants K 1 and K 2 are computed with allowance for the form factor of the specimen. Model magnetization curves are plotted for uniaxial ferromagnets with different types of MCA along and perpendicularly to crystallographic axis c. The analytical results match the model curves well.

  13. Uniaxial phase transition in Si: Ab initio calculations

    NASA Astrophysics Data System (ADS)

    Cheng, C.

    2003-04-01

    Based on a previously proposed thermodynamic analysis, [C. Cheng, W. H. Huang, and H. J. Li, Phys. Rev. B 63, 153202 (2001)] we study the relative stabilities of five Si phases under uniaxial compression using ab initio methods. The five phases are diamond, βSn, simple-hexagonal (sh), simple-cubic, and hexagonal closed-packed structures. The possible phase-transition patterns were investigated by considering the phase transitions between any two chosen phases of the five phases. By analyzing the different contributions to the relative phase stability, we identified the most important factors in reducing the phase-transition pressures at uniaxial compression. We also show that it is possible to have phase transitions occur only when the phases are under uniaxial compression, in spite of no phase transition when under hydrostatic compression. Taking all five phases into consideration, the phase diagram at uniaxial compression was constructed for pressures up to 20 GPa. The stable phases were found to be diamond, βSn, and sh structures, i.e., the same as those when under hydrostatic condition. According to the phase diagram, direct phase transition from the diamond to the sh phase is possible if the applied uniaxial pressures, on increasing, satisfy the condition Px>Pz. Similarly, the sh-to-βSn transition on increasing pressures is also possible if the applied uniaxial pressures are varied from the condition of Px>Pz, on which the phase of sh is stable to the condition Px

  14. Effects of Cyclic Loading on the Uniaxial Behavior of Nitinol

    NASA Astrophysics Data System (ADS)

    Schlun, M.; Zipse, A.; Dreher, G.; Rebelo, N.

    2011-07-01

    The widespread development and use of implants made from NiTi is accompanied by the publication of many NiTi material characterization studies. These publications have increased significantly the knowledge about the mechanical properties of NiTi. However, this knowledge also increased the complexity of the numerical simulation of NiTi implants or devices. This study is focused on the uniaxial behavior of NiTi tubing due to cyclic loading and had the goal to deliver both precise and application-oriented results. Single aspects of this study have already been published (Wagner in Ein Beitrag zur strukturellen und funktionalen Ermüdung von Drähten und Federn aus NiTi-Formgedaechtnislegierungen, Ph.D. Thesis, 2005; Eucken and Duerig in Acta Metall 37:2245-2252, 1989; Yawny et al. in Z Metallkd 96:608-618, 2005); however, there is no publication known that shows all the single effects combined in a "duty cycle case." It was of particular importance to summarize the main effects of pre-strain and subsequent small or large strain amplitudes on the material properties. The phenomena observed were captured in an extended Abaqus® Nitinol material model, presented by Rebelo et al. (A Material Model for the Cyclic Behavior of Nitinol, SMST Extended Abstracts 2010). The cyclic tensile tests were performed using a video extensometer to obtain accurate strain measurement on small electro-polished dog-bone specimen that were incorporated into a stent framework so that standard manufacturing methods could be used for the fabrication. This study indicates that a prestrain beyond 6% strain alters the transformation plateaus and if the cyclic displacement amplitude is large enough, additional permanent deformations are observed, the lower plateau and most notably the upper plateau change. The changes to the upper plateau are very interesting in the sense that an additional stress plateau develops: its "start stress" is lowered thereby creating a new plateau up to the highest level

  15. Uniaxial Properties versus Temperature, Creep and Impact Energy of an Austenitic Steel

    NASA Astrophysics Data System (ADS)

    Brnic, Josip; Turkalj, Goran; Krscanski, Sanjin; Vukelic, Goran; Canadija, Marko

    2017-02-01

    In this paper, uniaxial material properties, creep resistance and impact energy of the austenitic heat-resistant steel (1.4841) are experimentally determined and analysed. Engineering stress-strain diagrams and uniaxial short-time creep curves are examined with computer-controlled testing machine. Impact energy has been determined and fracture toughness assessed. Investigated data are shown in the form of curves related to ultimate tensile strength, yield strength, modulus of elasticity and creep resistance. All of these experimentally obtained results are analysed and may be used in the design process of the structure where considered material is intended to be applied. Based on these results, considered material may be classified as material of high tensile strength (688 MPa/293 K; 326 MPa/923 K) and high yield strength (498 MPa/293 K; 283 MPa/923 K) as well as satisfactory creep resistance (temperature/stress → to strain (%) at 1,200 min: 823 K/167 MPa → to 0.25 %; 923 K/85 MPa → to 0.2 %).

  16. Experimental and numerical study on the unstable crack growth under uniaxial compression

    NASA Astrophysics Data System (ADS)

    Okinaka, T.; Wijerathne, L.

    2017-02-01

    Image analysis with ultra-high-speed camera and two dimensional dynamic numerical analysis are applied to study the rapid unstable growth of wing crack under the uniaxial compression. Growing wing crack terminates and restarts its unstable rapid growth in some cases. Such a termination and restart behavior of the growing crack is studied through the experiment and numerical analysis in this work. First, rectangle transparent specimen, including the initial crack inclined to the compressive axis, is subjected to the uniaxial compression till the wing cracks start unstable rapid growth from both ends of the initial crack. Images of growing cracks and those of stress distribution, visualized as the photo-elastic fringe pattern, are captured by the high speed camera with the frame rate of 500k frames per second. The behavior of growing crack and the change in the stress field due to the crack growth are discussed through the captured images. Next, two dimensional dynamic numerical analysis is carried out. PDS-FEM (Particle Discretization Scheme), which allows the discontinuity of the displacement in the continuous analytical domain, is combined with the central difference time integration scheme to simulate the rapid unstable growth of the wing crack dynamically. The accuracy of the proposed simulation is discussed through the comparison with the images, captured by the experiment.

  17. Pharmacobezoars described and demystified.

    PubMed

    Simpson, Serge-Emile

    2011-02-01

    A bezoar is a concretion of foreign material that forms and persists in the gastrointestinal tract. Bezoars are classified by their material origins. Phytobezoars contain plant material, trichobezoars contain hair, lactobezoars contain milk proteins, and pharmacobezoars contain pharmaceutical products. Tablets, suspensions, and even insoluble drug delivery vehicles can, on rare occasions, and sometimes under specific circumstances, form pharmacobezoars. The goal of this review is to catalog and examine all of the available reports in the English language medical literature that convincingly describe the formation and management of pharmacobezoars. Articles included in this review were identified by performing searches using the terms "bezoar," "pharmacobezoar," and "concretion" in the following databases: OVID MEDLINE, PubMed, and JSTOR. The complete MEDLINE and JSTOR holdings were included in the search without date ranges. The results were limited to English language publications. Articles that described nonmedication bezoars were not included in the review. Articles describing phytobezoars, food bezoars, fecal impactions, illicit drug packet ingestions, enteral feeding material bezoars, and hygroscopic diet aid bezoars were excluded. The bibliographic references within the articles already accumulated were then examined in order to gather additional pharmacobezoar cases. The cases are grouped by pharmaceutical agent that formed the bezoar, and groupings are arranged in alphabetical order. Discussions and conclusions specific to each pharmaceutical agent are included in that agent's subheading. Patterns and themes that emerged in the review of the assembled case reports are reviewed and presented in a more concise format. Pharmacobezoars form under a wide variety of circumstances and in a wide variety of patients. They are difficult to diagnose reliably. Rules for suspecting, diagnosing, and properly managing a pharmacobezoar are highly dependent on the

  18. Mechanical Behaviors and Elastic Parameters of Laminated Fabric URETEK3216LV Subjected to Uniaxial and Biaxial Loading

    NASA Astrophysics Data System (ADS)

    Chen, Jianwen; Chen, Wujun; Wang, Mingyang; Ding, Yong; Zhou, Han; Zhao, Bing; Fan, Jin

    2017-01-01

    A comprehensive experimental study of the laminated fabric URETEK3216LV subjected to mono-uniaxial, uniaxial cyclic and biaxial cyclic loading was performed to expose the detailed mechanical behaviors and determine proper elastic parameters for the laminated fabrics under specific stress states. The elastic modulus-strain curves and elastic parameter response surfaces were used to reveal the mechanical behaviors, and a weighted average method of integrals was proposed to calculate the elastic parameters for different stress states. Results show that typical stress-strain curves consist of three distinct regions during loading: crimp region, nonlinear transition region and yarn extension region, which is consistent with those of the constitutive yarns. The elastic parameters and mechanical behaviors of the laminated fabric are stress-state specific, and they vary noticeably with the experimental protocols, stress ratios and stress levels. The proposed method is feasible to evaluate the elastic parameters no matter what stress states the materials are subjected to, and thus it may offer potential access to obtain accurate design and analysis of the airship structures under different loading conditions.

  19. How Mathematics Describes Life

    NASA Astrophysics Data System (ADS)

    Teklu, Abraham

    2017-01-01

    The circle of life is something we have all heard of from somewhere, but we don't usually try to calculate it. For some time we have been working on analyzing a predator-prey model to better understand how mathematics can describe life, in particular the interaction between two different species. The model we are analyzing is called the Holling-Tanner model, and it cannot be solved analytically. The Holling-Tanner model is a very common model in population dynamics because it is a simple descriptor of how predators and prey interact. The model is a system of two differential equations. The model is not specific to any particular set of species and so it can describe predator-prey species ranging from lions and zebras to white blood cells and infections. One thing all these systems have in common are critical points. A critical point is a value for both populations that keeps both populations constant. It is important because at this point the differential equations are equal to zero. For this model there are two critical points, a predator free critical point and a coexistence critical point. Most of the analysis we did is on the coexistence critical point because the predator free critical point is always unstable and frankly less interesting than the coexistence critical point. What we did is consider two regimes for the differential equations, large B and small B. B, A, and C are parameters in the differential equations that control the system where B measures how responsive the predators are to change in the population, A represents predation of the prey, and C represents the satiation point of the prey population. For the large B case we were able to approximate the system of differential equations by a single scalar equation. For the small B case we were able to predict the limit cycle. The limit cycle is a process of the predator and prey populations growing and shrinking periodically. This model has a limit cycle in the regime of small B, that we solved for

  20. New Described Dermatological Disorders

    PubMed Central

    Cevirgen Cemil, Bengu; Keseroglu, Havva Ozge; Kaya Akis, Havva

    2014-01-01

    Many advances in dermatology have been made in recent years. In the present review article, newly described disorders from the last six years are presented in detail. We divided these reports into different sections, including syndromes, autoinflammatory diseases, tumors, and unclassified disease. Syndromes included are “circumferential skin creases Kunze type” and “unusual type of pachyonychia congenita or a new syndrome”; autoinflammatory diseases include “chronic atypical neutrophilic dermatosis with lipodystrophy and elevated temperature (CANDLE) syndrome,” “pyoderma gangrenosum, acne, and hidradenitis suppurativa (PASH) syndrome,” and “pyogenic arthritis, pyoderma gangrenosum, acne, and hidradenitis suppurativa (PAPASH) syndrome”; tumors include “acquired reactive digital fibroma,” “onychocytic matricoma and onychocytic carcinoma,” “infundibulocystic nail bed squamous cell carcinoma,” and “acral histiocytic nodules”; unclassified disorders include “saurian papulosis,” “symmetrical acrokeratoderma,” “confetti-like macular atrophy,” and “skin spicules,” “erythema papulosa semicircularis recidivans.” PMID:25243162

  1. Physically-Based Reduced Order Modelling of a Uni-Axial Polysilicon MEMS Accelerometer

    PubMed Central

    Ghisi, Aldo; Mariani, Stefano; Corigliano, Alberto; Zerbini, Sarah

    2012-01-01

    In this paper, the mechanical response of a commercial off-the-shelf, uni-axial polysilicon MEMS accelerometer subject to drops is numerically investigated. To speed up the calculations, a simplified physically-based (beams and plate), two degrees of freedom model of the movable parts of the sensor is adopted. The capability and the accuracy of the model are assessed against three-dimensional finite element simulations, and against outcomes of experiments on instrumented samples. It is shown that the reduced order model provides accurate outcomes as for the system dynamics. To also get rather accurate results in terms of stress fields within regions that are prone to fail upon high-g shocks, a correction factor is proposed by accounting for the local stress amplification induced by re-entrant corners. PMID:23202031

  2. Physically-based reduced order modelling of a uni-axial polysilicon MEMS accelerometer.

    PubMed

    Ghisi, Aldo; Mariani, Stefano; Corigliano, Alberto; Zerbini, Sarah

    2012-10-17

    In this paper, the mechanical response of a commercial off-the-shelf, uni-axial polysilicon MEMS accelerometer subject to drops is numerically investigated. To speed up the calculations, a simplified physically-based (beams and plate), two degrees of freedom model of the movable parts of the sensor is adopted. The capability and the accuracy of the model are assessed against three-dimensional finite element simulations, and against outcomes of experiments on instrumented samples. It is shown that the reduced order model provides accurate outcomes as for the system dynamics. To also get rather accurate results in terms of stress fields within regions that are prone to fail upon high-g shocks, a correction factor is proposed by accounting for the local stress amplification induced by re-entrant corners.

  3. Fracture modes under uniaxial compression in hydroxyapatite scaffolds fabricated by robocasting.

    PubMed

    Miranda, Pedro; Pajares, Antonia; Saiz, Eduardo; Tomsia, Antoni P; Guiberteau, Fernando

    2007-12-01

    The fracture modes of hydroxyapatite (HA) scaffolds fabricated by direct-write assembly (robocasting) are analyzed in this work. Concentrated HA inks with suitable viscoelastic properties were developed to enable the fabrication of prototype structures consisting of a 3-D square mesh of interpenetrating rods. The fracture behavior of these model scaffolds under compressive stresses is determined from in situ uniaxial tests performed in two different directions: perpendicular to the rods and along one of the rod directions. The results are analyzed in terms of the stress field calculated by finite element modeling (FEM). This analysis provides valuable insight into the mechanical behavior of scaffolds for bone tissue engineering applications fabricated by robocasting. Copyright 2007 Wiley Periodicals, Inc.

  4. Computer-aided study of the mechanical behavior of the jaw bone fragments under uniaxial compression

    NASA Astrophysics Data System (ADS)

    Kolmakova, Tatyana V.

    2016-08-01

    The article presents the calculated results of the mechanical behavior of simulative bone mesovolumes under uniaxial compression with their architectonics corresponding to the human jaw bone fragments. The results of the calculation show that changes in the structure and mineral content of the bone fragments can lead to the change of their prevailing deformation response. New effective parameters were introduced to reflect the character of the distribution of stresses and strains in the bone mesovolumes. Implants are to be created and selected to correspond to the offered parameters and longitudinal modulus of elasticity of bone mesovolumes in order to maintain the stress and strain state existing in bone macrovolume during the implantation and in order to avoid bone restructuring through its borderline resorption.

  5. Effects of Acoustic Emission and Energy Evolution of Rock Specimens Under the Uniaxial Cyclic Loading and Unloading Compression

    NASA Astrophysics Data System (ADS)

    Meng, Qingbin; Zhang, Mingwei; Han, Lijun; Pu, Hai; Nie, Taoyi

    2016-10-01

    Characteristics of energy accumulation, evolution, and dissipation in uniaxial cyclic loading and unloading compression of 30 sandstone rock specimens under six different loading rates were explored. Stress-strain relations and acoustic emission characteristics of the deformation and failure of rock specimens were analyzed. The densities and rates of stored energy, elastic energy, and dissipated energy under different loading rates were confirmed, and an effective approach for the equivalent energy surface was presented. The energy evolution of rock deformation and failure were revealed. It turns out that the rock deformation behavior under uniaxial cyclic loading and unloading compression remained almost unchanged compared with that of uniaxial compression. The degree of match between reloading stress-strain curves and previous unloading curves was high, thereby demonstrating the memory function of rock masses. The intensity of acoustic emission fluctuated continually during the entire cyclic process. Emissions significantly increased as the stress exceeded the unloading level. The peak of acoustic emission increased with increasing loading stress level. Relationships between energy density and axial load indicate that the rock mass possesses a certain energy storage limitation. The energy evolution of rock masses is closely related to the axial loading stress, rather than to the axial loading rate. With increasing axial loading stress, stored energy varied most rapidly, followed by that of the elastic energy, then dissipated energy. Energy accumulation dominates prior to the axial load reaching peak strength; thereafter, energy dissipation becomes dominant. The input energy causes the irreversible initiation and extension of microcracks in the rock body. Elastic energy release leads to sudden instability of rock bodies and drives rock damage.

  6. Peculiarities of light energy dissipation in uniaxial gyrotropic crystals

    SciTech Connect

    Mityurich, G.S.; Starodubtsev, E.G.

    1994-10-01

    The energy dissipation of electromagnetic waves in uniaxial gyrotropic crystals of types 32, 422, and 622 for arbitrary anisotropic and gyrotropic properties in the presence of multibeam optical interference is theoretically studied. The possibility of measuring the gyrotropic parameters of such crystals by photothermoacoustic techniques is shown, and conditions of the measurement optimization are found. 11 refs., 3 figs.

  7. Negative Refraction in a Uniaxial Absorbent Dielectric Material

    ERIC Educational Resources Information Center

    Jen, Yi-Jun; Lakhtakia, Akhlesh; Yu, Ching-Wei; Lin, Chin-Te

    2009-01-01

    Refraction of light from an isotropic dielectric medium to an anisotropic dielectric material is a complicated phenomenon that can have several different characteristics not usually discussed in electromagnetics textbooks for undergraduate students. With a simple problem wherein the refracting material is uniaxial with its optic axis normal to the…

  8. Multiscale surface roughening of commercial purity titanium during uniaxial tension

    SciTech Connect

    Panin, Alexey; Kazachenok, Marina Kozelskaya, Anna Sinyakova, Elena; Lider, Andrey Sklyarova, Elena

    2015-10-27

    The mechanisms of the surface roughening of the titanium specimens during uniaxial tension were demonstrated. By means of optical profilometry and electron backscattered diffraction it was shown that the formation of surface roughening is a multilevel process. The correlation between the density of slip in some grains, and grain rotation, and their displacement towards the free surface was investigated.

  9. Analysis of Homogel Uniaxial Compression Strength on Bio Grouting Material.

    PubMed

    Park, Kyungho; Kim, Daehyeon

    2016-03-29

    This study analyzed uniaxial compression strength over time by preparing a homogel specimen from a bio grouting material, a cement-like form produced by environment-friendly microbial reactions. Among chemical grouting methods, the most commonly used method is the Labile Waterglass method. In this study, the homogel uniaxial compressive strength of Labile Waterglass (LW) injection material and that of bio grouting material were measured and analyzed. In order to perform the experiment, a total of 10 types of grouting mixing ratios were prepared by a combination of different materials such as Ordinary Portland Cement, Micro Cement, Bio Grouting Material and Sodium Silicate. They were cured in the air, and their homogel uniaxial compression strengths were measured on days 1, 3, 7 and 28 Based on the test results, it was confirmed that the uniaxial strength of the specimen made with Bio Grouting Material, Ordinary Portland Cement and Micro Cement was increased by more than 30% than that of the specimen only used with Ordinary Portland Cement, as a result of hydrogen-released heat reaction between calcium carbonate, the main ingredient of the bio grouting material, and calcium silicate in the cement. This indicates that the use of 30% bio-grouting material instead of cement in the grouting can be a reasonable mixing ratio to save the use of cement, leading to reduction in CO₂ emission.

  10. Negative Refraction in a Uniaxial Absorbent Dielectric Material

    ERIC Educational Resources Information Center

    Jen, Yi-Jun; Lakhtakia, Akhlesh; Yu, Ching-Wei; Lin, Chin-Te

    2009-01-01

    Refraction of light from an isotropic dielectric medium to an anisotropic dielectric material is a complicated phenomenon that can have several different characteristics not usually discussed in electromagnetics textbooks for undergraduate students. With a simple problem wherein the refracting material is uniaxial with its optic axis normal to the…

  11. Magnetic relaxation of nanoparticles with cubic and uniaxial anisotropies

    NASA Astrophysics Data System (ADS)

    Correia, Marcos J.; Schwarzacher, Walther; Ferreira Chagas, Edson; Figueiredo, Wagner

    2016-01-01

    We use Monte Carlo methods to simulate the influence of Brownian rotation on the magnetic properties of a system of single-domain magnetic nanoparticles with cubic and uniaxial magnetic anisotropies. The distinguishing feature of the system is a strongly temperature-dependent viscosity. Such a system has been realized experimentally using magnetic nanoparticles suspended in a freeze-concentrated cryoprotectant solution.

  12. Functional possibilities of nonlinear crystals for frequency conversion: uniaxial crystals

    SciTech Connect

    Andreev, Yu M; Arapov, Yu D; Kasyanov, I V; Grechin, S G; Nikolaev, P P

    2016-01-31

    The method and results of the analysis of phase-matching and nonlinear properties for all point groups of symmetry of uniaxial crystals that determine their functional possibilities for solving various problems of nonlinear frequency conversion of laser radiation are presented. (nonlinear optical phenomena)

  13. The mechanical response of the ovine lumbar anulus fibrosus to uniaxial, biaxial and shear loads.

    PubMed

    Little, J P; Pearcy, M J; Tevelen, G; Evans, J H; Pettet, G; Adam, C J

    2010-02-01

    Analytical and computational models of the intervertebral disc (IVD) are commonly employed to enhance understanding of the biomechanics of the human spine and spinal motion segments. The accuracy of these models in predicting physiological behaviour of the spine is intrinsically reliant on the accuracy of the material constitutive representations employed to represent the spinal tissues. There is a paucity of detailed mechanical data describing the material response of the reinforced-ground matrix in the anulus fibrosus of the IVD. In the present study, the 'reinforced-ground matrix' was defined as the matrix with the collagen fibres embedded but not actively bearing axial load, thus incorporating the contribution of the fibre-fibre and fibre-matrix interactions. To determine mechanical parameters for the anulus ground matrix, mechanical tests were carried out on specimens of ovine anulus, under unconfined uniaxial compression, simple shear and biaxial compression. Test specimens of ovine anulus fibrosus were obtained with an adjacent layer of vertebral bone/cartilage on the superior and inferior specimen surface. Specimen geometry was such that there were no continuous collagen fibres coupling the two endplates. Samples were subdivided according to disc region - anterior, lateral and posterior - to determine the regional inhomogeneity in the anulus mechanical response. Specimens were loaded at a strain rate sufficient to avoid fluid outflow from the tissue and typical stress-strain responses under the initial load application and under repeated loading were determined for each of the three loading types. The response of the anulus tissue to the initial and repeated load cycles was significantly different for all load types, except biaxial compression in the anterior anulus. Since the maximum applied strain exceeded the damage strain for the tissue, experimental results for repeated loading reflected the mechanical ability of the tissue to carry load, subsequent to

  14. Microscopic destruction of ultra-high molecular weight polyethylene (UHMWPE) under uniaxial tension.

    PubMed

    Shibata, Nobuyuki; Tomita, Naohide; Ikeuchi, Ken

    2003-01-01

    To examine the effects of a networked substructure of granular agglomerate on a style of destruction in prosthetic ultra-high molecular weight polyethylene (UHMWPE), uniaxial tensile simulations were carried out using the numerical model based on the discrete element method (DEM). The numerical simulations were performed taking the difference of mechanical characteristics between inter-granular and intra-granular portions of UHMWPE into consideration. A significant increase in stress and strain was observed along grain boundaries where micro cracks were initiated. This finding suggests that the large difference of mechanical properties between intra-granular and inter-granular portions causes significantly increased local stresses and strains in the vicinity of grain boundaries. The tensile simulation resulted in intra-granular destruction, which had good agreement with a result of previous experimental observation. This is presumably because the directions of principal shear stresses do not coincide with those at stress-concentrated grain boundaries. The dependence of the style of material destruction on forms of loading application could be explained by the relationship between directions of principal shear stress and reorientations of stress-concentrated grain boundaries.

  15. Weibull crack density coefficient for polydimensional stress states

    NASA Technical Reports Server (NTRS)

    Gross, Bernard; Gyekenyesi, John P.

    1989-01-01

    A structural ceramic analysis and reliability evaluation code has recently been developed encompassing volume and surface flaw induced fracture, modeled by the two-parameter Weibull probability density function. A segment of the software involves computing the Weibull polydimensional stress state crack density coefficient from uniaxial stress experimental fracture data. The relationship of the polydimensional stress coefficient to the uniaxial stress coefficient is derived for a shear-insensitive material with a random surface flaw population.

  16. Mathematical model relating uniaxial compressive behavior of manufactured sand mortar to MIP-derived pore structure parameters.

    PubMed

    Tian, Zhenghong; Bu, Jingwu

    2014-01-01

    The uniaxial compression response of manufactured sand mortars proportioned using different water-cement ratio and sand-cement ratio is examined. Pore structure parameters such as porosity, threshold diameter, mean diameter, and total amounts of macropores, as well as shape and size of micropores are quantified by using mercury intrusion porosimetry (MIP) technique. Test results indicate that strains at peak stress and compressive strength decreased with the increasing sand-cement ratio due to insufficient binders to wrap up entire sand. A compression stress-strain model of normal concrete extending to predict the stress-strain relationships of manufactured sand mortar is verified and agreed well with experimental data. Furthermore, the stress-strain model constant is found to be influenced by threshold diameter, mean diameter, shape, and size of micropores. A mathematical model relating stress-strain model constants to the relevant pore structure parameters of manufactured sand mortar is developed.

  17. Mathematical Model Relating Uniaxial Compressive Behavior of Manufactured Sand Mortar to MIP-Derived Pore Structure Parameters

    PubMed Central

    Tian, Zhenghong; Bu, Jingwu

    2014-01-01

    The uniaxial compression response of manufactured sand mortars proportioned using different water-cement ratio and sand-cement ratio is examined. Pore structure parameters such as porosity, threshold diameter, mean diameter, and total amounts of macropores, as well as shape and size of micropores are quantified by using mercury intrusion porosimetry (MIP) technique. Test results indicate that strains at peak stress and compressive strength decreased with the increasing sand-cement ratio due to insufficient binders to wrap up entire sand. A compression stress-strain model of normal concrete extending to predict the stress-strain relationships of manufactured sand mortar is verified and agreed well with experimental data. Furthermore, the stress-strain model constant is found to be influenced by threshold diameter, mean diameter, shape, and size of micropores. A mathematical model relating stress-strain model constants to the relevant pore structure parameters of manufactured sand mortar is developed. PMID:25133257

  18. Controllable strain-induced uniaxial anisotropy of Fe{sub 81}Ga{sub 19} films deposited on flexible bowed-substrates

    SciTech Connect

    Dai, Guohong; Zhan, Qingfeng Yang, Huali; Liu, Yiwei; Zhang, Xiaoshan; Zuo, Zhenghu; Chen, Bin; Li, Run-Wei

    2013-11-07

    We propose a convenient method to induce a uniaxial anisotropy in magnetostrictive Fe{sub 81}Ga{sub 19} films grown on flexible polyethylene terephthalate (PET) substrates by bending the substrate prior to deposition. A tensile/compressive stress is induced in the Fe{sub 81}Ga{sub 19} films when PET substrates are shaped from concave/convex to flat after deposition. The stressed Fe{sub 81}Ga{sub 19} films exhibit a significant uniaxial magnetic anisotropy due to the internal stress arising from changes in shape of PET substrates. The easy axis is along the tensile stress direction and the coercive field along easy axis is increased with increasing the internal tensile stress. The remanence of hard axis is decreased with increasing the compressive stress, while the coercive field is almost unchanged. A modified Stoner-Wohlfarth model with considering the distribution of easy axes in polycrystalline films is used to account for the magnetic properties tuned by the strain-controlled magnetoelastic anisotropy in flexible Fe{sub 81}Ga{sub 19} films. Our investigations provide a convenient way to induce uniaxial magnetic anisotropy, which is particularly important for fabricating flexible magnetoelectronic devices.

  19. Failure stress criteria for composite resin.

    PubMed

    De Groot, R; Peters, M C; De Haan, Y M; Dop, G J; Plasschaert, A J

    1987-12-01

    In previous work (Peters and Poort, 1983), the stress distribution in axisymmetric models of restored teeth was analyzed by finite element analysis (FEA). To compare the tri-axial stress state at different sites, they calculated the Von Mises equivalent stress and used it as an indication for weak sites. However, the use of Von Mises' theory for material failure requires that the compressive and tensile strengths be equal, whereas for composite resin the compressive strength values are, on the average, eight times larger than the tensile strength values. The objective of this study was to investigate the applicability of a modified Von Mises and the Drücker-Prager criterion to describe mechanical failure of composite resin. In these criteria, the difference between compressive and tensile strength is accounted for. The stress criteria applied to an uni-axial tensile stress state are compared with those applied to a tri-axial tensile stress state. The uni-axial state is obtained in a Rectangular Bar (RB) specimen and the tri-axial state in a Single-edge Notched Bend (SENB) specimen with a chevron notch at midspan. Both types of specimens, made of light-cured composite, were fractured in a three-point bend test. The size of the specimens was limited to 16 mm x 2 mm x 2 mm (span, 12 mm). Load-deflection curves were recorded and used for linear elastic FEA. The results showed that the Drücker-Prager criterion is a more suitable criterion for describing failure of composite resins due to multi-axial stress states than are the Von Mises criterion and the modified Von Mises criterion.

  20. Second-order moments of an electromagnetic Gaussian Schell-model beam in a uniaxial crystal.

    PubMed

    Shen, Yan; Liu, Lin; Zhao, Chengliang; Yuan, Yangsheng; Cai, Yangjian

    2014-02-01

    We derive the analytical expressions for the second-order moments of an electromagnetic Gaussian Schell-model (EGSM) beam propagating in a uniaxial crystal. With the help of the derived formulas, we study the evolution properties of the propagation factor, the effective radius of curvature and the Rayleigh range of an EGSM beam in a uniaxial crystal. It is found that the evolution properties of an EGSM beam in a uniaxial crystal are much different from its evolution properties in free space and are closely determined by the initial beam parameters and the parameters of the uniaxial crystal. The uniaxial crystal provides one way for modulating the properties of an EGSM beam.

  1. Magnetic order of UPt3 under uniaxial pressure

    NASA Astrophysics Data System (ADS)

    van Dijk, N. H.; Rodière, P.; Yakhou, F.; Fernández-Díaz, M.-T.; Fåk, B.; Huxley, A.; Flouquet, J.

    2001-03-01

    The weak antiferromagnetic order of the heavy fermion superconductor UPt3 has been investigated by elastic neutron-scattering measurements under applied uniaxial pressure up to 6 kbars along the a and c axes of the hexagonal crystal structure. For p\\|\\|c the small antiferromagnetically ordered moment of 0.02 μB/U atom shows a nonlinear decrease for increasing pressures and is still not completely suppressed at the maximum applied pressure of 6 kbars. For p\\|\\|a a significant increase in the magnetic Bragg peak intensity is observed, which suggests an incomplete domain repopulation and confirms the presence of a single-k structure. The Néel temperature of TN=6 K does not substantially change with uniaxial pressure. The results are discussed in relation to the understanding of the unconventional superconducting phase diagram.

  2. Electrical Characteristics of the Uniaxial-Strained nMOSFET with a Fluorinated HfO₂/SiON Gate Stack.

    PubMed

    Chen, Yung-Yu

    2014-03-20

    The channel fluorine implantation (CFI) process was integrated with the Si₃N₄ contact etch stop layer (SiN CESL) uniaxial-strained n-channel metal-oxide-semiconductor field-effect transistor (nMOSFET) with the hafnium oxide/silicon oxynitride (HfO₂/SiON) gate stack. The SiN CESL process clearly improves basic electrical performance, due to induced uniaxial tensile strain within the channel. However, further integrating of the CFI process with the SiN CESL-strained nMOSFET exhibits nearly identical transconductance, subthreshold swing, drain current, gate leakage and breakdown voltage, which indicates that the strain effect is not affected by the fluorine incorporation. Moreover, hydrogen will diffuse toward the interface during the SiN deposition, then passivate dangling bonds to form weak Si-H bonds, which is detrimental for channel hot electron stress (CHES). Before hydrogen diffusion, fluorine can be used to terminate oxygen vacancies and dangling bonds, which can create stronger Hf-F and Si-F bonds to resist consequent stress. Accordingly, the reliability of constant voltage stress (CVS) and CHES for the SiN CESL uniaxial-strained nMOSFET can be further improved by the fluorinated HfO₂/SiON using the CFI process. Nevertheless, the nMOSFET with either the SiN CESL or CFI process exhibits less charge detrapping, which means that a greater part of stress-induced charges would remain in the gate stack after nitrogen (SiN CESL) or fluorine (CFI) incorporation.

  3. Hyperbolic Plasmons and Topological Transitions Over Uniaxial Metasurfaces

    NASA Astrophysics Data System (ADS)

    Gomez-Diaz, J. Sebastian; Tymchenko, Mykhailo; Alù, Andrea

    2015-06-01

    We explore the unusual electromagnetic response of ultrathin anisotropic σ -near-zero uniaxial metasurfaces, demonstrating extreme topological transitions—from closed elliptical to open hyperbolic—for surface plasmon propagation, associated with a dramatic tailoring of the local density of states. The proposed metasurfaces may be implemented using nanostructured graphene monolayers and open unprecedented venues for extreme light confinement and unusual propagation and guidance, combined with large tunability via electric bias.

  4. Hyperbolic Plasmons and Topological Transitions Over Uniaxial Metasurfaces.

    PubMed

    Gomez-Diaz, J Sebastian; Tymchenko, Mykhailo; Alù, Andrea

    2015-06-12

    We explore the unusual electromagnetic response of ultrathin anisotropic σ-near-zero uniaxial metasurfaces, demonstrating extreme topological transitions--from closed elliptical to open hyperbolic--for surface plasmon propagation, associated with a dramatic tailoring of the local density of states. The proposed metasurfaces may be implemented using nanostructured graphene monolayers and open unprecedented venues for extreme light confinement and unusual propagation and guidance, combined with large tunability via electric bias.

  5. Single-molecule spectroscopy of uniaxially oriented terrylene in polyethylene.

    PubMed

    Butter, Jacqueline Y P; Crenshaw, Brent R; Weder, Christoph; Hecht, Bert

    2006-01-16

    Single terrylene molecules doped into linear low-density polyethylene can be oriented by tensile deformation of the matrix. In measurements on ensembles at ambient and on single terrylene molecules at cryogenic temperature, strong orientation along the stretching direction was observed by polarization-resolved confocal microscopy. At cryogenic temperatures narrow and spectrally stable zero-phonon lines were found. The low saturation intensity of 0.07 W cm(-2) is consistent with an uniaxial orientation of terrylene in the sample plane.

  6. Ferromagnetic resonance in a dilute suspension of uniaxial superparamagnetic particles

    NASA Astrophysics Data System (ADS)

    Poperechny, I. S.; Raikher, Yu. L.; Stepanov, V. I.

    2017-02-01

    A consistent theory of ferromagnetic resonance in a dilute suspension of superparamagnetic particles with uniaxial anisotropy of arbitrary strength is presented. The developed approach is used for studying the high-frequency response of a magnetic fluid at different temperatures. It is shown that in a certain temperature interval the absorption line splits into two components. The width of this interval is essentially dependent on the magnitude of the particle anisotropy.

  7. Molecular dynamics simulations of ordering of polydimethylsiloxane under uniaxial extension

    SciTech Connect

    Lacevic, N M; Gee, R H

    2005-03-11

    Molecular dynamics simulations of a bulk melts of polydimethylsiloxane (PDMS) are utilized to study chain conformation and ordering under constant uniaxial tension. We find that large extensions induce chain ordering in the direction of applied tension. We also find that voids are created via a cavitation mechanism. This study represents a validation of the current model for PDMS and benchmark for the future study of mechanical properties of PDMS melts enriched with fillers under tension.

  8. A drop in uniaxial and biaxial nonlinear extensional flows

    NASA Astrophysics Data System (ADS)

    Favelukis, M.

    2017-08-01

    In this theoretical report, we explore small deformations of an initially spherical drop subjected to uniaxial or biaxial nonlinear extensional creeping flows. The problem is governed by the capillary number (Ca), the viscosity ratio (λ), and the nonlinear intensity of the flow (E). When the extensional flow is linear (E = 0), the familiar internal circulations are obtained and the same is true with E > 0, except that the external and internal flow rates increase with increasing E. If E < 0, the external flow consists of some unconnected regions leading to the same number of internal circulations (-3/7 < E < 0) or twice the number of internal circulations (E < -3/7), when compared to the linear case. The shape of the deformed drop is represented in terms of a modified Taylor deformation parameter, and the conditions for the breakup of the drop by a center pinching mechanism are also established. When the flow is linear (E = 0), the literature predicts prolate spheroidal drops for uniaxial flows (Ca > 0) and oblate spheroidal drops for biaxial flows (Ca < 0). For the same |Ca|, if E > 0, the drop is more elongated than the linear case, while E < 0 results in less elongated drops than the linear case. Compared to the linear case, for both uniaxial and biaxial extensional flows, E > 0 tends to facilitate drop breakup, while E < 0 makes drop breakup more difficult.

  9. Evaluation of Anisotropic Yield Functions Characterized by Uniaxial and Biaxial Experiments for Formability of DP590 Sheet Steel

    NASA Astrophysics Data System (ADS)

    Lee, Jin-Woo; Kim, Seok Nyeon; Lee, Myoung-Gyu; Barlat, Frédéric

    2011-05-01

    The Limiting Dome Height (LDH) formability test was evaluated numerically using the finite element analysis and various constitutive models for a DP590 sheet steel sample. Three yield functions, von Mises, Hill's 1948 and Yld2000-2d were used to examine the effect of the yield function on the formability simulation results. The parameters of the two anisotropic yield functions were determined from different experimental tests. For Hill's 1948 model, the anisotropy coefficients were obtained either from the yield stresses or r-values measured in different material directions. The anisotropy coefficients of Yld2000-2d were determined from the conventional uniaxial test-based data and the stresses measured from in-plane biaxial testing. For the hardening behavior, the stress-strain curves were measured using uniaxial tension and balanced biaxial tension tests. The constitutive models were implemented through the user material subroutine in the FE software, ABAQUS. The evaluation was performed by comparing predicted and experimental punch load-displacement curves and sheet thickness variations after the LDH testing. The results for this particular example showed that the non-quadratic yield function and the hardening curve characterized by the biaxial stress state lead to improved predictions of the LDH test.

  10. Compressive Properties of PTFE/Al/Ni Composite Under Uniaxial Loading

    NASA Astrophysics Data System (ADS)

    Wang, Huai-xi; Li, Yu-chun; Feng, Bin; Huang, Jun-yi; Zhang, Sheng; Fang, Xiang

    2017-05-01

    To investigate the mechanical properties of pressed and sintered PTFE/Al/Ni (polytetrafluoroethylene/aluminum/nickel) composite, uniaxial quasi-static and dynamic compression experiments were conducted at strain rates from 10-2 to 3 × 103/s. The prepared samples were tested by an electrohydraulic press with 300 kN loading capacity and a split Hopkinson pressure bar (SHPB) device at room temperature. Experimental results show that PTFE/Al/Ni composite exhibits evident strain hardening and strain rate hardening. Additionally, a bilinear relationship between stress and {{log(}}\\dot{ɛ} ) is observed. The experimental data were fit to Johnson-Cook constitutive model, and the results are in well agreement with measured data.

  11. Isolation of kinetic and spatial properties of uni-axial dynamic tensile loading of OFHC copper

    NASA Astrophysics Data System (ADS)

    Dennis-Koller, D.; Escobedo-Diaz, J. P.; Cerreta, E. K.; Bronkhorst, C. A.; Hansen, B.; Lebensohn, R.; Mourad, H.; Patterson, B.; Tonks, D.

    2012-08-01

    Materials performance is recognized as being central to many emergent technologies. Future technologies will place increasing demands on materials performance with respect to extremes in stress, strain, temperature, and pressure. In this study, the dynamic ductile damage evolution of OFHC Cu is explored as a test bed to understand the role of spatial effects due to loading profile and defect density as well as the role of the kinetics of tensile pulse evolution. Well-characterized OFHC Cu samples of 30 μm, 60 μm, 100 μm, and 200 μm grain sizes were subjected to plate impact uniaxial strain loading in spall geometry to produce early stage (incipient damage. Using 2D metallographic techniques, soft recovered samples were studied to statistically link mesoscale processes to continuum level observations of free surface particle velocity measured with VISAR. Based on these findings, mechanisms for the void nucleation/growth and coalescence are proposed.

  12. Effect of phase symmetry on the NMR spectrum of acetonitrile oriented in a uniaxial-biaxial-uniaxial phase

    NASA Astrophysics Data System (ADS)

    Deepak, H. S. Vinay; Yelamaggad, C. V.; Khetrapal, C. L.; Ramanathan, K. V.

    2016-09-01

    We report here the measurement of the Csbnd H and the Hsbnd H dipolar couplings of the methyl group of acetonitrile oriented in the biaxial liquid crystal potassium laurate/1-decanol/water system. These parameters show large variations when measured as a function of temperature. The variations follow the symmetry of the phase as the liquid crystal goes through the sequence of uniaxial - biaxial - uniaxial phases and show a close correspondence to the phase changes that occur in the liquid crystalline solvent coinciding with the onset of biaxiality. The Hsbnd Csbnd H bond angle calculated after incorporating vibrational corrections to the dipolar couplings is discussed in terms of contributions in the case of the biaxial liquid crystal arising from vibration-rotation interaction effects.

  13. Impact of repeated uniaxial mechanical strain on flexible a-IGZO thin film transistors with symmetric and asymmetric structures

    NASA Astrophysics Data System (ADS)

    Liao, Po-Yung; Chang, Ting-Chang; Su, Wan-Ching; Chen, Bo-Wei; Chen, Li-Hui; Hsieh, Tien-Yu; Yang, Chung-Yi; Chang, Kuan-Chang; Zhang, Sheng-Dong; Huang, Yen-Yu; Chang, Hsi-Ming; Chiang, Shin-Chuan

    2017-06-01

    This letter investigates repeated uniaxial mechanical stress-induced degradation behavior in flexible amorphous In-Ga-Zn-O thin-film transistors (TFTs) of different geometric structures. Two types of via-contact structure TFTs are investigated: symmetrical and UI structure (TFTs with I- and U-shaped asymmetric electrodes). After repeated mechanical stress, I-V curves for the symmetrical structure show a significant negative threshold voltage (VT) shift, due to mechanical stress-induced oxygen vacancy generation. However, degradation in the UI structure TFTs after stress is a negative VT shift along with the parasitic transistor characteristic in the forward-operation mode, with this hump not evident in the reverse-operation mode. This asymmetrical degradation is clarified by the mechanical strain simulation of the UI TFTs.

  14. Phase diagrams and solvation forces of a uniaxial ferromagnet in a slit--the double-parabola approach.

    PubMed

    Wójtowicz, Adam; Napiórkowski, Marek

    2013-12-04

    We obtain the phase diagrams of a uniaxial ferromagnet enclosed in a slit and analyse the properties of the solvation forces acting between the slit walls. Our analysis is based on the mean-field theory applied to the double-parabola Hamiltonian for a uniaxial ferromagnet in a slit, which allows us to derive several results in analytic form. In particular, the Kelvin law and the law describing the influence of the slit width on the position of the delocalization transition as compared to the wetting transition are derived and the corresponding critical exponent is evaluated. The influence of the thermodynamic state of the system on the properties of the solvation forces, in particular their discontinuous behaviour at coexistence lines, is discussed.

  15. Uniaxial strain effects on the superconducting transition in Re-doped Hg-1223 cuprate superconductors

    NASA Astrophysics Data System (ADS)

    Mito, Masaki; Ogata, Kazuma; Goto, Hiroki; Tsuruta, Kazuki; Nakamura, Kazuma; Deguchi, Hiroyuki; Horide, Tomoya; Matsumoto, Kaname; Tajiri, Takayuki; Hara, Hiroshi; Ozaki, Toshinori; Takeya, Hiroyuki; Takano, Yoshihiko

    2017-02-01

    The effects of uniaxial strain and hydrostatic pressure on Hg0.83Re0.18Ba2Ca2.4Cu3.6O14 [Hg0.83 (Re0.18)-1223 ] were investigated by ac magnetic measurements under stress corresponding to a pressure of 20 GPa at maximum. According to a previous thermal study based on the Ehrenfest relation, in-plane contraction should increase the superconducting transition temperature Tc, whereas out-of-plane contraction should decrease Tc. This suggests that the increase in Tc under hydrostatic-pressure contraction must be smaller than that under in-plane contraction. However, the present uniaxial-strain experiments revealed enhancement of Tc under both in-plane and out-of-plane contraction, and the largest enhancement was observed under hydrostatic-pressure contraction. According to a band calculation, all contraction styles induce hole doping from the HgO blocks to the CuO2 blocks, and hydrostatic-pressure contraction yields the largest hole doping among three contractions. This behavior explains well a series of changes in Tc in the stress region of below 8 GPa. More specifically, under hydrostatic-pressure contraction, Tc exhibited an increase, a decrease, and another increase with increasing pressure, and this multistep change is similar to that observed in Bi-2223-type cuprate superconductors, suggesting that it is necessary to distinguish the effect of strain on the middle CuO2 plane in the three-CuO2-plane package from that on the outer planes.

  16. Sensing uniaxial tensile damage in fiber-reinforced polymer composites using electrical resistance tomography

    NASA Astrophysics Data System (ADS)

    Lestari, Wahyu; Pinto, Brian; La Saponara, Valeria; Yasui, Jennifer; Loh, Kenneth J.

    2016-08-01

    This work describes the application of electrical resistance tomography (ERT) in sensing damage in fiber-reinforced polymer composites under uniaxial quasi-static tension. Damage is manifested as numerous matrix cracks which are distributed across the composite volume and which eventually coalesce into intralayer cracks. Hence, tensile damage is distributed throughout the volume, and could be more significant outside the sensor area. In this work, tensile damage of unidirectional glass fiber-reinforced polymer composites (GFRP) and plain weave carbon fiber-reinforced polymer composites (CFRP) is sensed by utilizing a spray-on nanocomposite sensor, which is then instrumented by boundary electrodes. The resistance change distribution within the sensor area is reconstructed from a series of boundary voltage measurements, and ERT is implemented using a maximum a posteriori approach and assumptions on the type of noise in the reconstruction. Results show that this technique has promise in tracking uniaxial damage in composites. The different fiber architectures (unidirectional GFRP, plain weave CFRP) give distinct features in the ERT, which are consistent with the physical behavior of the tested samples.

  17. Alternative methods for ray tracing in uniaxial media. Application to negative refraction

    NASA Astrophysics Data System (ADS)

    Bellver-Cebreros, Consuelo; Rodriguez-Danta, Marcelo

    2007-03-01

    In previous papers [C. Bellver-Cebreros, M. Rodriguez-Danta, Eikonal equation, alternative expression of Fresnel's equation and Mohr's construction in optical anisotropic media, Opt. Commun. 189 (2001) 193; C. Bellver-Cebreros, M. Rodriguez-Danta, Internal conical refraction in biaxial media and graphical plane constructions deduced from Mohr's method, Opt. Commun. 212 (2002) 199; C. Bellver-Cebreros, M. Rodriguez-Danta, Refraccion conica externa en medios biaxicos a partir de la construccion de Mohr, Opt. Pura AppliE 36 (2003) 33], the authors have developed a method based on the local properties of dielectric permittivity tensor and on Mohr's plane graphical construction in order to study the behaviour of locally plane light waves in anisotropic media. In this paper, this alternative methodology is compared with the traditional one, by emphasizing the simplicity of the former when studying ray propagation through uniaxial media (comparison is possible since, in this case, traditional construction becomes also plane). An original and simple graphical method is proposed in order to determine the direction of propagation given by the wave vector from the knowledge of the extraordinary ray direction (given by Poynting vector). Some properties of light rays in these media not described in the literature are obtained. Finally, two applications are considered: a description of optical birefringence under normal incidence and the study of negative refraction in uniaxial media.

  18. Non-destructive quantification of alignment of nanorods embedded in uniaxially stretched polymer films

    NASA Astrophysics Data System (ADS)

    Stoenescu, Stefan; Truong, Vo-Van; Packirisamy, Muthukumaran

    2014-03-01

    Among several methods developed for uniaxial alignment of metallic nanorods for optical applications, alignment by film stretching consists in embedding the rods in a transparent thin film of thermoplastic polymer, followed by simultaneous heating and uniaxial stretching of the composite film. As to the quantification of the resulting alignment, it has been limited to statistical calculations based on microscopic examination, which is incomplete, subject to errors due to geometric distortions of the scanning electron microscope images and destructive, since it involves cutting of samples. In contrast, we present in this paper a non-destructive quantification of the average orientation of the rods, based on a probabilistic approach combined with numerical simulations of absorbance spectra and spectrometric characterization of the composite film. Assuming electromagnetically non-interacting rods, we consider the longitudinal absorbance peak of their ensemble to consist of the superposition of their individual spectra that we obtain by numerical simulation using the size and shape adapted dielectric function of the metal and the finite difference time domain method. The accuracy of the solution depends on the number of discretization intervals, the accuracy of the numerical simulations, and the accurate knowledge of the polydispersity of the rods. For the sake of concreteness, we used nanorods to describe the quantification steps but the method is equally valid for any dichroic particles.

  19. Structural deformations of two-dimensional planar structures under uniaxial strain: the case of graphene.

    PubMed

    Fthenakis, Zacharias G; Lathiotakis, Nektarios N

    2017-03-01

    In the present work, a method for the study of the structural deformations of two dimensional planar structures under uniaxial strain is presented. The method is based on molecular mechanics using the original stick and spiral model and a modified one which includes second nearest neighbor interactions for bond stretching. As we show, the method allows an accurate prediction of the structural deformations of any two dimensional planar structure as a function of strain, along any strain direction in the elastic regime, if structural deformations are known along specific strain directions, which are used to calculate the stick and spiral model parameters. Our method can be generalized including other strain conditions and not only uniaxial strain. We apply this method to graphene and we test its validity, using results obtained from ab initio density functional theory calculations. What we find is that the original stick and spiral model is not appropriate to describe accurately the structural deformations of graphene in the elastic regime. However, the introduction of second nearest neighbor interactions provides a very accurate description.

  20. Non-destructive quantification of alignment of nanorods embedded in uniaxially stretched polymer films

    SciTech Connect

    Stoenescu, Stefan Packirisamy, Muthukumaran; Truong, Vo-Van

    2014-03-21

    Among several methods developed for uniaxial alignment of metallic nanorods for optical applications, alignment by film stretching consists in embedding the rods in a transparent thin film of thermoplastic polymer, followed by simultaneous heating and uniaxial stretching of the composite film. As to the quantification of the resulting alignment, it has been limited to statistical calculations based on microscopic examination, which is incomplete, subject to errors due to geometric distortions of the scanning electron microscope images and destructive, since it involves cutting of samples. In contrast, we present in this paper a non-destructive quantification of the average orientation of the rods, based on a probabilistic approach combined with numerical simulations of absorbance spectra and spectrometric characterization of the composite film. Assuming electromagnetically non-interacting rods, we consider the longitudinal absorbance peak of their ensemble to consist of the superposition of their individual spectra that we obtain by numerical simulation using the size and shape adapted dielectric function of the metal and the finite difference time domain method. The accuracy of the solution depends on the number of discretization intervals, the accuracy of the numerical simulations, and the accurate knowledge of the polydispersity of the rods. For the sake of concreteness, we used nanorods to describe the quantification steps but the method is equally valid for any dichroic particles.

  1. In-situ Synchrotron X-ray Microdiffraction Study of Lattice Rotation in Polycrystalline Materials during Uniaxial Deformations

    SciTech Connect

    Joo, H.D.; Bark, C.W.; Koo, Y.M.; Kim, K.H.; Tamura, N.

    2004-05-12

    Recent experiments have shown that formation of dislocation cell structures and rotation of structural elements at the macroscopic level are fundamental to the development of plastic deformation. However, attention should also be focused on micro-volumes because local stress and strain can significantly differ from their averaged values at the macroscale. In-situ orientation measurements in copper polycrystals during uniaxial deformation were performed using synchrotron x-ray microdiffraction at the Advanced Light Source. We observed heterogeneities in deformation-induced microstructure within individual grains. Different slip systems in particular can be simultaneously activated among neighboring volume elements of individual grains.

  2. Damage tolerance of pressurized graphite/epoxy tape cylinders under uniaxial and biaxial loading. M.S. Thesis

    NASA Technical Reports Server (NTRS)

    Priest, Stacy Marie

    1993-01-01

    The damage tolerance behavior of internally pressurized, axially slit, graphite/epoxy tape cylinders was investigated. Specifically, the effects of axial stress, structural anisotropy, and subcritical damage were considered. In addition, the limitations of a methodology which uses coupon fracture data to predict cylinder failure were explored. This predictive methodology was previously shown to be valid for quasi-isotropic fabric and tape cylinders but invalid for structurally anisotropic (+/-45/90)(sub s) and (+/-45/0)(sub s) cylinders. The effects of axial stress and structural anisotropy were assessed by testing tape cylinders with (90/0/+/-45)(sub s), (+/-45/90)(sub s), and (+/-45/0)(sub s) layups in a uniaxial test apparatus, specially designed and built for this work, and comparing the results to previous tests conducted in biaxial loading. Structural anisotropy effects were also investigated by testing cylinders with the quasi-isotropic (0/+/-45/90)(sub s) layup which is a stacking sequence variation of the previously tested (90/0/+/-45)(sub s) layup with higher D(sub 16) and D(sub 26) terms but comparable D(sub 16) and D(sub 26) to D(sub 11) ratios. All cylinders tested and used for comparison are made from AS4/3501-6 graphite/epoxy tape and have a diameter of 305 mm. Cylinder slit lengths range from 12.7 to 50.8 mm. Failure pressures are lower for the uniaxially loaded cylinders in all cases. The smallest percent failure pressure decreases are observed for the (+/-45/90)(sub s) cylinders, while the greatest such decreases are observed for the (+/-45/0)(sub s) cylinders. The relative effects of the axial stress on the cylinder failure pressures do not correlate with the degree of structural coupling. The predictive methodology is not applicable for uniaxially loaded (+/-45/90)(sub s) and (+/-45/0)(sub s) cylinders, may be applicable for uniaxially loaded (90/0/+/-45)(sub s) cylinders, and is applicable for the biaxially loaded (90/0/+/-45)(sub s) and (0

  3. Residual stress characterization with an ultrasonic/magnetic technique

    NASA Technical Reports Server (NTRS)

    Namkung, M.; Heyman, J. S.

    1984-01-01

    A potentially useful new technique for residual stress characterization in ferromagnetic material is described. The unique feature of this technique is the measurement of small changes in ultrasonic wave velocity by the application of external dc magnetic field in the material under various stress conditions. It was found, in steel, that the fractional change in the natural velocity Delta W/W of waves propagating along the external field direction is affected by the uniaxial stress applied in the same axis. External compression lowers the slope of the Delta W/W curve in the low field region, while external tension generally does the opposite. For most cases, the slope in this region falls below zero under external compression. The result of measurements in specimens with residual stress shows exactly the same tendency.

  4. Power type strain energy function model and prediction of the anisotropic mechanical properties of skin using uniaxial extension data.

    PubMed

    Li, Lin; Qian, Xiuqing; Wang, Hui; Hua, Lin; Zhang, Haixia; Liu, Zhicheng

    2013-10-01

    Many successful models to describe the biomechanical characteristics of planar biological soft tissues are based on strain energy function. However, the parameters in these models are determined by biaxial extension test, which might be difficult to exercise for certain types of soft tissue. This study presents a new constitutive model, the power type strain energy density function model (PTM), and a method to identify its material parameters for rabbit skin using uniaxial extension test of 4-direction strip samples. The abdominal skins from eight rabbits were taken to perform uniaxial tension tests in 7 different directions. The material parameters were identified for each subject based on any 4 out of 7 directions by applying some definite conditions of this issue. For each rabbit, the 35 groups of material parameters were consistent. The 7 material parameters in PTM were identified with root mean square errors <0.061. The results indicate that the material parameters of rabbit skin can be identified from uniaxial extension test data.

  5. A Proposed Uniaxial Compression Test for High Strength Ceramics

    DTIC Science & Technology

    1989-09-01

    is lost and catastrophic collapse ensues. The origin of the microcracks may be microplasticity in the form of twinning, 2 or existing flaws such as...Uniaxial compressive strength tElastic modulus sonic method (strain gage method ) sPoisson’s ratio sonic method MIL-STD-1942(MR) size B, mean flexure...SEA-O5MB, LCDR W. M. Elger Commander, U.S. Armament, Munitions and Chemical 1 SEA-05R 25, C. Zanis Command, Dover, NJ 07801 2 ATTN: Technical Library

  6. Probabilistic simulation of uncertainties in composite uniaxial strengths

    NASA Technical Reports Server (NTRS)

    Chamis, C. C.; Stock, T. A.

    1990-01-01

    Probabilistic composite micromechanics methods are developed that simulate uncertainties in unidirectional fiber composite strengths. These methods are in the form of computational procedures using composite mechanics with Monte Carlo simulation. The variables for which uncertainties are accounted include constituent strengths and their respective scatter. A graphite/epoxy unidirectional composite (ply) is studied to illustrate the procedure and its effectiveness to formally estimate the probable scatter in the composite uniaxial strengths. The results show that ply longitudinal tensile and compressive, transverse compressive and intralaminar shear strengths are not sensitive to single fiber anomalies (breaks, intergacial disbonds, matrix microcracks); however, the ply transverse tensile strength is.

  7. Uniaxially strained silicon by wafer bonding and layer transfer

    NASA Astrophysics Data System (ADS)

    Himcinschi, C.; Radu, I.; Muster, F.; Singh, R.; Reiche, M.; Petzold, M.; Gösele, U.; Christiansen, S. H.

    2007-02-01

    Uniaxial strain on wafer-level was realised by mechanically bending and direct wafer bonding of Si wafers in the bent state followed by thinning one of the Si wafers by the smart-cut process. This approach is flexible and allows to obtain different strain values at wafer-level in both tension and compression. UV micro-Raman spectroscopy was used to determine the strain in the thin transferred Si layers. Numerical modelling by 3D finite elements of the strain provided a good description of the experimental results.

  8. Uniaxial pressure dependence of the antiferromagnetic order in UPt3

    NASA Astrophysics Data System (ADS)

    van Dijk, N. H.; Rodière, P.; Fåk, B.; Huxley, A.; Flouquet, J.; Fernández-Díaz, M. T.; Yakhou, F.

    The weak antiferromagnetic order of the heavy-fermion superconductor UPt3 has been investigated by elastic neutron-scattering measurements under applied uniaxial pressure up to 6 kbar along the a and c axes of the hexagonal crystal structure. For p||c the small antiferromagnetically ordered moment of 0.02μB/U-atom shows a non-linear decrease for increasing pressures and is still not completely suppressed at the maximum applied pressure of 6 kbar. For p||a a significant increase in the magnetic Bragg peak intensity is observed, which suggests an incomplete domain repopulation and confirms the presence of a single-k structure.

  9. Elastic properties of granular materials under uniaxial compaction cycles

    NASA Technical Reports Server (NTRS)

    Warren, N.; Anderson, O. L.

    1973-01-01

    Data on andesitic and basaltic sands are presented showing compressional sound velocity, density, and creep as functions of uniaxial loading through several compaction cycles. Maximum pressures over which acoustic measurements were made were in the range from 600 to 700 bars. The dynamic elastic modulus varies with pressure in a manner analogous to that of a static elastic modulus defined by small pressure perturbations on a typical compaction cycle. After several compaction cycles, two compressional elastic moduli apparently exist at low pressure (thus two modes of compressional wave propagation through the samples are indicated). The elastic moduli observations are briefly discussed in terms of a general expression for compressibility.

  10. Single-crystal copper nanorods under uniaxial tensile load with different period by molecular dynamics

    NASA Astrophysics Data System (ADS)

    Yang, Zailin; Zhang, Yu; Zhang, Guowei; Yang, Yong; Wang, Xizhi

    The single crystal nanorods under uniaxial loading and unloading tensile with different period along crystallographic orientations [1 1 0] and axial directions being applied constant tensile rates are simulated respectively by method of molecular dynamics to elucidate the effect of periodical tensile stress and another mechanical properties of the single crystal copper within the Nano-scope. After stimulation, we compare the different features and phenomenon between the loading style of period and none of period. In the case of periodical loading, nanorods show the various maximum stress at yielding stage, and after yield, the degree of fatigue depends on the period of step heavily. Our results suggest that the mechanical character of single crystal copper nanorods is remarkably influenced by the steps of loading period when we use the maximum yield stress σs at none of periodical loading condition as underlying reference. At the following text description, it has been expressed that the total number of loading and unloading circle may affect the mechanical response of the MD system. When the semi-periodical loading steps or the total steps of whole periodical load near to 5.1 × 103 steps (8.7 × 103 steps for the other model), the model system occurs to the Nano-scale fatigue. And the Nano-scale fatigue will lead to the yield point decreasing in turn on account of various periodical steps.

  11. Hyperelastic Property Measurements of Heat-Cured Silicone Adhesives by Cyclic Uniaxial Tensile Test

    NASA Astrophysics Data System (ADS)

    Li, Jue; Tarvainen, Tapio; Rich, Jaana; Turunen, Markus; Paulasto-Kröckel, Mervi

    2012-09-01

    Most of the commonly used linear elastic properties of silicone adhesives cannot precisely represent their material behavior, knowledge of which is crucial to the reliability study of electronic devices. For this reason, in this paper a widely used silicone adhesive, namely Loctite 5404, is chosen for measuring hyperelastic properties via cyclic uniaxial tensile tests. A special sample preparation procedure is developed to avoid the formation of detrimental air bubbles in the samples. Two maximum strain levels, 20% and 40%, are used in the tests. Each test includes five cyclic loadings to produce a stable stress-strain loop. Three orders of magnitude of strain rate changes are studied, and the stress-strain response of the material is found to be strain rate dependent. The measured stress-strain data are imported into Abaqus finite-element software to calibrate the material coefficients of hyperelastic material models (Mooney-Rivlin, Yeoh, Ogden, and van der Waals models). This is the first time that the hyperelastic properties of the studied silicone adhesive are presented. The determined material coefficients can be used directly in finite-element analyses and thus in reliability studies of electronic devices.

  12. Creep Testing Plastic-Bonded Explosives in Uni-axial Compression

    SciTech Connect

    Gagliardi, F J; Cunningham, B J

    2008-03-13

    High fidelity measurements of time-dependent strain in the plastic-bonded explosives LX-17-1 and PBX 9502 have been performed under constant, uni-axial, compressive load using a custom designed apparatus. The apparatus uses a combination of extensometers and linear variable differential transformers coupled with a data acquisition system, thermal controls, and gravitational loading. The materials being tested consist of a crystalline explosive material mixed with a polymeric binder. The behavior of each material is related to the type of explosive and to the percentage and type of binder. For any given plastic-bonded explosive, the creep behavior is also dependent on the stress level and test temperature. Experiments were conducted using a 3 x 3 stress-temperature matrix with a temperature range of 24 C to 70 C and with stresses ranging from 250-psi to 780-psi. Analysis of the data has shown that logarithmic curve fits provide an accurate means of quantification and facilitate a long-term predictive capability. This paper will discuss the design of the apparatus, experimental results, and analyses.

  13. Stress

    MedlinePlus

    ... sudden negative change, such as losing a job, divorce, or illness Traumatic stress, which happens when you ... stress, so you can avoid more serious health effects. NIH: National Institute of Mental Health

  14. Effect of numerical parameters on characterizing the hardening behavior of ductile uniaxial tension specimens.

    SciTech Connect

    Cordova, Theresa Elena; Dion, Kristin; Laing, John Robert; Corona, Edmundo; Breivik, Nicole L.; Wellman, Gerald William; Shelton, Timothy R.

    2010-11-01

    Many problems of practical importance involve ductile materials that undergo very large strains, in many cases to the point of failure. Examples include structures subjected to impact or blast loads, energy absorbing devices subjected to significant crushing, cold-forming manufacturing processes and others. One of the most fundamental pieces of data that is required in the analysis of this kind of problems is the fit of the uniaxial stress-strain curve of the material. A series of experiments where mild steel plates were punctured with a conical indenter provided a motivation to characterize the true stress-strain curve until the point of failure of this material, which displayed significant ductility. The hardening curve was obtained using a finite element model of the tensile specimens that included a geometric imperfection in the form of a small reduction in the specimen width to initiate necking. An automated procedure iteratively adjusted the true stress-strain curve fit used as input until the predicted engineering stress-strain curve matched experimental measurements. Whereas the fitting is relatively trivial prior to reaching the ultimate engineering stress, the fit of the softening part of the engineering stress-stain curve is highly dependent on the finite element parameters such as element formulation and initial geometry. Results by two hexahedral elements are compared. The first is a standard, under-integrated, uniform-strain element with hourglass control. The second is a modified selectively-reduced-integration element. In addition, the effects of element size, aspect ratio and hourglass control characteristics are investigated. The effect of adaptively refining the mesh based on the aspect ratio of the deformed elements is also considered. The results of the study indicate that for the plate puncture problem, characterizing the material with the same element formulation and size as used in the plate models is beneficial. On the other hand, using

  15. Negative reflection of waves at planar interfaces associated with a uniaxial medium.

    PubMed

    Chen, Hongyi; Xu, Shixiang; Li, Jingzhen

    2009-11-01

    Reflection of waves at planar interfaces associated with a uniaxial medium is theoretically analyzed by examining the boundary condition and the dispersion relation. Simple global expressions of incident and reflected angles of both wave vectors and ray vectors are derived. The relations between them are obtained. It is also shown that negative reflection can be realized in all uniaxial media under certain conditions. Our results offer considerable potential device applications of uniaxial media.

  16. Cyclic uniaxial and biaxial hardening of type 304 stainless steel modeled by the viscoplasticity theory based on overstress

    NASA Technical Reports Server (NTRS)

    Yao, David; Krempl, Erhard

    1988-01-01

    The isotropic theory of viscoplasticity based on overstress does not use a yield surface or a loading and unloading criterion. The inelastic strain rate depends on overstress, the difference between the stress and the equilibrium stress, and is assumed to be rate dependent. Special attention is paid to the modeling of elastic regions. For the modeling of cyclic hardening, such as observed in annealed Type 304 stainless steel, and additional growth law for a scalar quantity which represents the rate independent asymptotic value of the equilibrium stress is added. It is made to increase with inelastic deformation using a new scalar measure which differentiates between nonproportional and proportional loading. The theory is applied to correlate uniaxial data under two step amplitude loading including the effect of further hardening at the high amplitude and proportional and nonproportional cyclic loadings. Results are compared with corresponding experiments.

  17. Uniaxial pressure setup for piezoresistance and magnetoresistance measurements in Heusler materials.

    PubMed

    Bourgault, D; Porcar, L; Bruyère, C; Jacquet, P; Courtois, P

    2013-01-01

    We report on a new uniaxial pressure experimental setup for electrical resistivity measurements working in a 77 K-500 K temperature range and in a magnetic field up to 8 T. Such a continuous uniaxial pressure device enables the study of the piezoresistance and the pressure induced change in electrical properties of bulk samples. Strong influence of uniaxial pressure on transport properties is shown for Ni-Co-Mn-In Heusler single crystal material. A shift of the martensite-austenite first order transformation temperature is measured with an applied uniaxial pressure leading to an electrical resistance changed by up to 120%.

  18. The Microstructural Response of Granular Soil Under Uniaxial Strain

    DTIC Science & Technology

    1993-10-01

    model (1970, Ref. 9) is an example of a model which uses deformation theory. This model is based on the observation that the stress-strain curves of... observed mechanical behavior. This report describes an experimental effort to quantify changes which occur in a cuboid specimen of granular silica material...PREPARATION 56 5.2 TESTING 56 ui PL-TR-92-1064 CONTENTS (Contnued) 6.0 TEST RESULTS AND DISCUSSION 58 6.1 INTRODUCTION 58 6.2 OBSERVATIONS ON THE SPECIMEN

  19. Piezoresistive Properties of Suspended Graphene Membranes under Uniaxial and Biaxial Strain in Nanoelectromechanical Pressure Sensors

    PubMed Central

    2016-01-01

    Graphene membranes act as highly sensitive transducers in nanoelectromechanical devices due to their ultimate thinness. Previously, the piezoresistive effect has been experimentally verified in graphene using uniaxial strain in graphene. Here, we report experimental and theoretical data on the uni- and biaxial piezoresistive properties of suspended graphene membranes applied to piezoresistive pressure sensors. A detailed model that utilizes a linearized Boltzman transport equation describes accurately the charge-carrier density and mobility in strained graphene and, hence, the gauge factor. The gauge factor is found to be practically independent of the doping concentration and crystallographic orientation of the graphene films. These investigations provide deeper insight into the piezoresistive behavior of graphene membranes. PMID:27797484

  20. A CYLINDRICALLY SYMMETRIC UNIAXIAL PML MAXWELL SOLVER FOR TRANSIENT ATMOSPHERIC ELECTRICITY SIMULATIONS

    SciTech Connect

    E. M. SYMBALISTY

    2001-07-01

    The recent interest in high altitude discharges known as red sprites, blue jets, and elves has stimulated the modeling of transient atmospheric electricity. The modeling of these high altitude discharges require an initiating cloud-to-ground or intracloud lightning event in order to pre-condition the electric field between the cloud tops and the ionosphere. In this short paper we describe a finite difference time domain (FDTD) numerical solution of Maxwell's equations based on the Yee (Yee 1966) algorithm coupled with a uniaxial perfectly matched layer (PML, Berenger 1994) boundary treatment. The PML theory has advanced considerably since its original formulation in cartesian coordinates for lossless media, and is computationally efficient to implement. Another boundary treatment possibility for our sources that produce radiative and electrostatic fields, which we do not consider here, is a multipole expansion in the time domain for the electromagnetic fields.

  1. Finite strain response of crimped fibers under uniaxial traction: An analytical approach applied to collagen

    NASA Astrophysics Data System (ADS)

    Marino, Michele; Wriggers, Peter

    2017-01-01

    Composite materials reinforced by crimped fibers intervene in a number of advanced structural applications. Accordingly, constitutive equations describing their anisotropic behavior and explicitly accounting for fiber properties are needed for modeling and design purposes. To this aim, the finite strain response of crimped beams under uniaxial traction is herein addressed by obtaining analytical relationships based on the Principle of Virtual Works. The model is applied to collagen fibers in soft biological tissues, coupling geometric nonlinearities related to fiber crimp with material nonlinearities due to nanoscale mechanisms. Several numerical applications are presented, addressing the influence of geometric and material features. Available experimental data for tendons are reproduced, integrating the proposed approach within an optimization procedure for data fitting. The obtained results highlight the effectiveness of the proposed approach in correlating fibers structure with composite material mechanics.

  2. Estimation of the damage of a porous limestone from continuous (P- and S-) wave velocity measurements under uniaxial loading and different hydrous conditions

    NASA Astrophysics Data System (ADS)

    Eslami, J.; Grgic, D.; Hoxha, D.

    2010-12-01

    The damage of a porous rock (Euville oolitic limestone) was studied through uniaxial stress-cycling tests. An experimental device, allowing the simultaneous and continuous measurement of strains (in two perpendicular directions) and five elastic wave hree P waves and two S waves) velocities in two different directions under fully controlled hydrous conditions, was developed for the work presented in this paper. Hence, the damage was monitored in a really precise and continuous way through the evolution of dynamic and static elastic moduli. The evolutions of wave velocities and elastic moduli, which reproduce very remarkably the shape of the stress-strains curves, showed that the limestone, initially isotropic, became progressively anisotropic during uniaxial loading due to microcrack damage. Indeed, even if the creation of microcracks is probably scattered and isotropic before the coalescence of microcracks, as shown in past studies, pre-existing microcracks and penny-shaped pores which are perpendicular (or almost perpendicular) to the uniaxial stress direction closed, whereas axially-oriented microcracks opened. The anisotropy of the damage is completely reversible but some of the damage is irreversible. VP(90°), which cannot record the opening of these microcracks, started to decrease just before the macroscopic failure of the sample and can detect, therefore, very precisely the macroscopic failure of the material. The influence of water on the strength and deformation of the Euville limestone was analysed by considering both the hydromechanical and physio-chemical (`Rehbinder effect', intergranular pressure solution and subcritical cracking) effects of water.

  3. Mixing of molecular excitation in a uniaxial liquid crystal

    SciTech Connect

    Aver`yanov, E.M.

    1995-07-01

    The influence of the mixing of molecular excitations due to local-field effects on the dielectric and spectral properties of uniaxial liquid crystals is investigated. The general properties of the spectrum of transverse optical excitations of the medium, viz, the sum rules for the oscillator strengths, frequencies, and damping constants of the dielectric function resonances, are established. The restricted applicability of the idea of a back ground polarizability (dielectric function) in the analysis of the mixing of molecular excitations is demonstrated. Mixing is taken into account in deriving new dispersion formulas for the imaginary and real parts of the dielectric tensor, which differ significantly from those used in the literature. A range of applicability has been established for the latter. Qualitative and quantitative interpretations of controversial experimental data for an extensive list of objects are given. The occurrence of mixing of dipole-active molecular vibrations, whose intensity has been found to be strongest for polyphilic objects that form nonchiral ferroelectric phases, has been demonstrated for molecular liquids and uniaxial liquid crystals from various chemical classes for the first time. The mixing of molecular excitations is considered as a possible mechanism for {open_quotes}polarization catastrophe{close_quotes} in liquid crystals having a soft mode in hthespectrum of transverse optical modes of vibration for the high-temperature phase. 53 refs., 1 fig.

  4. Pseudodielectric Functions of Uniaxial Materials in Certain Symmetry Directions

    SciTech Connect

    Jellison Jr, Gerald Earle; Baba, Justin S

    2006-01-01

    The pseudodielectric function is often used to represent ellipsometric data and corresponds to the actual dielectric functions of materials when there is no surface overlayer and the material is isotropic. If a uniaxial material is oriented such that the optic axis is in the plane of incidence or is perpendicular to the plane of incidence, then the cross-polarization terms are zero and appropriate pseudodielectric functions can be determined from the ellipsometry data. We calculate the pseudodielectric functions for uniaxial crystals in three primary symmetry directions: (1) the optic axis is perpendicular to the plane of incidence, (2) the optic axis is in the plane of the sample surface and parallel to the plane of incidence, and (3) the optic axis is in the plane of the sample surface and perpendicular to the plane of incidence. These results are expanded in terms of the difference in the ordinary and extraordinary dielectric functions and compared with the approximation ofAspnes [J. Opt. Soc. Am.70, 1275 (1980)]. Comparisons are made with experimental results on oriented crystals of rutile (TiO2), and a simple procedure is presented to determine the complex dielectric function from standard ellipsometry techniques.

  5. Guiding Spin Spirals by Local Uniaxial Strain Relief

    NASA Astrophysics Data System (ADS)

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

    2016-01-01

    We report on the influence of uniaxial strain relief on the spin spiral state in the Fe double layer grown on Ir(111). Scanning tunneling microscopy (STM) measurements reveal areas with reconstruction lines resulting from uniaxial strain relief due to the lattice mismatch of Fe and Ir atoms, as well as pseudomorphic strained areas. Magnetic field-dependent spin-polarized STM measurements of the reconstructed Fe double layer reveal cycloidal spin spirals with a period on the nm scale. Globally, the spin spiral wave fronts are guided along symmetry-equivalent [11 2 ¯ ] crystallographic directions of the fcc(111) substrate. On an atomic scale the spin spiral propagation direction is linked to the [001] direction of the bcc(110)-like Fe, leading to a zigzag shaped wave front. The isotropically strained pseudomorphic areas also exhibit a preferred magnetic periodicity on the nm scale but no long-range order. We find that already for local strain relief with a single set of reconstruction lines a strict guiding of the spin spiral is realized.

  6. Anomalous thermal response of silicene to uniaxial stretching

    NASA Astrophysics Data System (ADS)

    Hu, Ming; Zhang, Xiaoliang; Poulikakos, Dimos

    2013-05-01

    Silicene—the silicon counterpart of graphene—has a two-dimensional structure that leads to a host of interesting physical and chemical properties of significant utility. We report here an investigation with nonequilibrium molecular dynamics simulations of thermal transport in a single-layer silicene sheet under uniaxial stretching. We discovered that, contrary to its counterpart of graphene and despite the similarity of their honeycomb lattice structure, silicene exhibits an anomalous thermal response to tensile strain: The thermal conductivity of silicene and silicene nanoribbons first increases significantly with applied tensile strain rather than decreasing and then fluctuates at an elevated plateau. By quantifying the relative contribution from different phonon polarizations, we show first that the phonon transport in silicene is dominated by the out-of-plane flexural modes, similar to graphene. We attribute subsequently the unexpected and markedly different behavior of silicene to the interplay between two competing mechanisms governing heat conduction in a stretched silicene sheet, namely, (1) uniaxial stretching modulation in the longitudinal direction significantly depressing the phonon group velocities of longitudinal and transverse modes (phonon softening) and hindering heat conduction, and (2) phonon stiffening in the flexural modes counteracting the phonon softening effect and facilitating thermal transport. The abnormal behavior of the silicene sheet is further correlated to the unique deformation characteristics of its hexagonal lattice. Our study offers perspectives of modulating the thermal properties of low-dimensional structures for applications such as thermoelectric, photovoltaic, and optoelectronic devices.

  7. An Approach to Model Neutron Diffraction Pattern of Uniaxial Deformed Sandstone Using Elastic Properties of Quartz

    NASA Astrophysics Data System (ADS)

    Breuer, S.; Schilling, F. R.; Mueller, B.; Scheffzuek, C.

    2015-12-01

    Mechanical properties of sedimentary rocks such as stress-strain-relations are essential for understanding dynamic processes within the Earth's crust. The measurement of in-situ lattice strain in bulk samples is possible with diffraction methods, e.g. with neutrons. The advantage of neutron diffraction is their high penetration depth, which enables to gather a statistically relevant number of grains by diffraction. The neutron time-of-flight diffraction at the strain diffractometer EPSILON which is located at the pulsed neutron source IBR-2M (JINR Dubna, RUS) enables the detection of the complete diffraction pattern up to λ = 7.1 Å (d = 5.1 Å). Uniaxial cyclic deformation experiments were carried out up to 50 MPa (three steps) on a macroscopically isotropic sandstone from Kuhbach / Lahr (Germany). The aim of the present study is to model diffraction patterns for different applied stress-levels, based on the zero-stress diffraction pattern and known elastic properties of Quartz single crystals. The as received model-predictions are compared to observations, both, in the direction of maximum stress (along the cylindric axis) and perpendicular to it. The results show that the shape of the grains has an influence on the macroscopic elastic behavior of the rock whereas the microscopic strain is affected in a different manner. The model is based on spherical quartz grains. The spheres are divided into slices. By removing some slices, the shape of sand grains is approximated. The reaction of each slice through the applied stress is modelled. Together with the relative volume of each slice and it´s elastic behavior, the diffraction pattern is predicted for different applied loads. Measured and modelled diffraction-patterns at different applied loads are in good agreement.

  8. An Experimental Study of Crack Coalescence Behaviour in Rock-Like Materials Containing Multiple Flaws Under Uniaxial Compression

    NASA Astrophysics Data System (ADS)

    Zhou, X. P.; Cheng, H.; Feng, Y. F.

    2014-11-01

    Experiments on man-made flawed rock-like materials are applied extensively to study the mechanical behaviour of rock masses as well as crack initiation modes and crack coalescence types. A large number of experiments on specimens containing two or three pre-existing flaws were previously conducted. In the present work, experiments on rock-like materials (formed from a mixture of sand, plaster, limestone and water at mass ratio of 126:9:9:16) containing multiple flaws subjected to uniaxial compression were conducted to further research the effects of the layout of pre-existing flaws on mechanical properties, crack initiation modes and crack coalescence types. Compared with previous experiments in which only three types of cracks were found, the present experiments on specimens containing multiple flaws under uniaxial compression revealed five types of cracks, including wing cracks, quasi-coplanar secondary cracks, oblique secondary cracks, out-of-plane tensile cracks and out-of-plane shear cracks. Ten types of crack coalescence occurred through linkage among wing cracks, quasi-coplanar secondary cracks, oblique secondary cracks, out-of-plane shear cracks and out-of-plane tensile cracks. Moreover, the effects of the non-overlapping length and flaw angle on the complete stress-strain curves, the stress of crack initiation, the peak strength, the peak strain and the elastic modulus were also investigated in detail.

  9. Metallographic examinations of Type 304 stainless steel (heat 9T2796) tested in high-temperature uniaxial and multiaxial experiments

    SciTech Connect

    Swindeman, R.W.; Houck, C.W.

    1984-03-01

    The results obtained from a number of metallographic examinations of Type 304 stainless steel specimens were compiled. Samples were obtained from uniaxial and multiaxial tests covering a very broad span of temperatures and times. Special emphasis was on the identification of failure modes, cracking patterns, grain distortion, and grain-boundary microstructures. Uniaxial specimens exhibited the following sequence of failure modes with increasing temperature and time: ductile plastic tearing, ductile plastic shear, wedge cracking, and microvoid cracking. Over most of the temperature range examined (482 to 871/sup 0/C), M/sub 23/C/sub 6/ precipitated on grain boundaries at long times. Sigma phase and possibly ferrite were often present in the stressed areas at temperatures as low as 482/sup 0/C (900/sup 0/F). These metallurgical features promoted a severe loss in creep ductility at long times and low temperatures. Most multiaxial tests were performed under conditions that promoted wedge cracking. Stress gradients also favored surface crack initiation rather than bulk damage. Testing times for multiaxial tests were less than 10,000 h; hence, there was insufficient time for the development of embrittling features such as microvoids, sigma, and ferrite. Long-time multiaxial tests to failure are recommended.

  10. Pre-Peak and Post-Peak Rock Strain Characteristics During Uniaxial Compression by 3D Digital Image Correlation

    NASA Astrophysics Data System (ADS)

    Munoz, H.; Taheri, A.; Chanda, E. K.

    2016-07-01

    A non-contact optical method for strain measurement applying three-dimensional digital image correlation (3D DIC) in uniaxial compression is presented. A series of monotonic uniaxial compression tests under quasi-static loading conditions on Hawkesbury sandstone specimens were conducted. A prescribed constant lateral-strain rate to control the applied axial load in a closed-loop system allowed capturing the complete stress-strain behaviour of the rock, i.e. the pre-peak and post-peak stress-strain regimes. 3D DIC uses two digital cameras to acquire images of the undeformed and deformed shape of an object to perform image analysis and provides deformation and motion measurements. Observations showed that 3D DIC provides strains free from bedding error in contrast to strains from LVDT. Erroneous measurements due to the compliance of the compressive machine are also eliminated. Furthermore, by 3D DIC technique relatively large strains developed in the post-peak regime, in particular within localised zones, difficult to capture by bonded strain gauges, can be measured in a straight forward manner. Field of strains and eventual strain localisation in the rock surface were analysed by 3D DIC method, coupled with the respective stress levels in the rock. Field strain development in the rock samples, both in axial and shear strain domains suggested that strain localisation takes place progressively and develops at a lower rate in pre-peak regime. It is accelerated, otherwise, in post-peak regime associated with the increasing rate of strength degradation. The results show that a major failure plane, due to strain localisation, becomes noticeable only long after the peak stress took place. In addition, post-peak stress-strain behaviour was observed to be either in a form of localised strain in a shearing zone or inelastic unloading outside of the shearing zone.

  11. Numerical Studies on the Failure Process of Heterogeneous Brittle Rocks or Rock-Like Materials under Uniaxial Compression.

    PubMed

    Guo, Songfeng; Qi, Shengwen; Zou, Yu; Zheng, Bowen

    2017-04-01

    In rocks or rock-like materials, the constituents, e.g. quartz, calcite and biotite, as well as the microdefects have considerably different mechanical properties that make such materials heterogeneous at different degrees. The failure of materials subjected to external loads is a cracking process accompanied with stress redistribution due to material heterogeneity. However, the latter cannot be observed from the experiments in laboratory directly. In this study, the cracking and stress features during uniaxial compression process are numerically studied based on a presented approach. A plastic strain dependent strength model is implemented into the continuous numerical tool-Fast Lagrangian Analysis of Continua in three Dimensions (FLAC(3D)), and the Gaussian statistical function is adopted to depict the heterogeneity of mechanical parameters including elastic modulus, friction angle, cohesion and tensile strength. The mean parameter μ and the coefficient of variance (hcv, the ratio of mean parameter to standard deviation) in the function are used to define the mean value and heterogeneity degree of the parameters, respectively. The results show that this numerical approach can perfectly capture the general features of brittle materials including fracturing process, AE events as well as stress-strain curves. Furthermore, the local stress disturbance is analyzed and the crack initiation stress threshold is identified based on the AE events process and stress-strain curves. It is shown that the stress concentration always appears in the undamaged elements near the boundary of damaged sites. The peak stress and crack initiation stress are both heterogeneity dependent, i.e., a linear relation exists between the two stress thresholds and hcv. The range of hcv is suggested as 0.12 to 0.21 for most rocks. The stress concentration degree is represented by a stress concentration factor and found also heterogeneity dominant. Finally, it is found that there exists a

  12. Children describe life after Hurricane Andrew.

    PubMed

    Coffman, S

    1994-01-01

    Hurricane Andrew, which devastated the south Florida coast in August 1992, left over 250,000 people homeless with multiple health and social problems. This nursing study explored the experiences of 17 children, ages 5 through 12, who lived in the geographic area of storm damage. Common experiences described by the children included remembering the storm, dealing with after-effects, and reestablishing a new life. In general, children described a sense of strangeness, articulated as "life is weird" after the hurricane. In addition to stressful responses, many positive reactions were described by children in the study, revealing that the disaster also had a maturing effect.

  13. Molecular dynamics simulation of a solid platinum nanowire under uniaxial tensile strain: Temperature and strain-rate effects

    NASA Astrophysics Data System (ADS)

    Koh, S. J. A.; Lee, H. P.; Lu, C.; Cheng, Q. H.

    2005-08-01

    Nanoscale research has been an area of active research over the past fifteen years. This is due to the overall enhanced properties of nanomaterials due to size effects, surface effects, and interface effects, which typically showed up in materials with characteristic size smaller than 100nm . This study focuses on the molecular dynamics (MD) simulation of an infinitely long, cylindrical platinum nanowire, with an approximate diameter of 1.4nm . The nanowire was subjected to uniaxial tensile strain along the [001] axis. The changes in crystal structure during deformation were analyzed and its mechanical properties were deduced from the simulation. Classical MD simulation was employed in this study, with the empirical Sutton-Chen pair functional used to describe the interatomic potential between the platinum atoms. The Berendsen loose-coupling thermostat was selected for finite-temperature control of the simulated system, with a time constant of 25% of the total relaxation time during each strain increment. The nanowire was subjected to strain rates of 0.04%, 0.4%, and 4.0%ps-1 , at simulation temperatures of 50 and 300K , in order to study the effects of different strain rates and thermal conditions on the deformation characteristics and mechanical properties of the nanowire. It was found that the stress-strain response of the nanowire showed clear periodic, stepwise dislocation-relaxation-recrystallization behavior at low temperature and strain rate, where crystal order and stability were highly preserved. The onset of amorphous crystal deformation occurred at 0.4%ps-1 , and fully amorphous deformation took place at 4.0%ps-1 , with amorphous melting detected at 300K . Due to higher entropy of the nanowire at higher temperature and strain rate, periodic stress-strain behavior became less clearly defined, and superplasticity behavior was observed. This characteristic was significantly enhanced due to the development of a single-walled helical substructure at 300K

  14. Numerical Investigation of the Dynamic Properties of Intermittent Jointed Rock Models Subjected to Cyclic Uniaxial Compression

    NASA Astrophysics Data System (ADS)

    Liu, Yi; Dai, Feng; Zhao, Tao; Xu, Nu-wen

    2017-01-01

    Intermittent jointed rocks, which exist in a myriad of engineering projects, are extraordinarily susceptible to cyclic loadings. Understanding the dynamic fatigue properties of jointed rocks is necessary for evaluating the stability of rock engineering structures. This study numerically investigated the influences of cyclic loading conditions (i.e., frequency, maximum stress and amplitude) and joint geometric configurations (i.e., dip angle, persistency and interspace) on the dynamic fatigue mechanisms of jointed rock models. A reduction model of stiffness and strength was first proposed, and then, sixteen cyclic uniaxial loading tests with distinct loading parameters and joint geometries were simulated. Our results indicate that the reduction model can effectively reproduce the hysteresis loops and the accumulative plastic deformation of jointed rocks in the cyclic process. Both the loading parameters and the joint geometries significantly affect the dynamic properties, including the irreversible strain, damage evolution, dynamic residual strength and fatigue life. Three failure modes of jointed rocks, which are principally controlled by joint geometries, occur in the simulations: splitting failure through the entire rock sample, sliding failure along joint planes and mixed failure, which are principally controlled by joint geometries. Furthermore, the progressive failure processes of the jointed rock samples are numerically observed, and the different loading stages can be distinguished by the relationship between the number of broken bonds and the axial stress.

  15. Nonparaxial propagation of elliptical Gaussian vortex beams in uniaxial crystal orthogonal to the optical axis.

    PubMed

    Wang, Xun; Liu, Zhirong; Zhao, Daomu

    2014-10-01

    Analytical expressions for the three components of nonparaxial propagation of a polarized elliptical Gaussian vortex beam in uniaxial crystal orthogonal to the optical axis are derived. Intensity and phase distributions of the three components of a polarized elliptical Gaussian vortex beam propagating in a uniaxial crystal orthogonal to the optical axis are illustrated by numerical examples. The influences of the initial beam's parameters and the parameters of the uniaxial crystal on the evolution of the beam's intensity and phase distributions in the uniaxial crystal are examined in detail. Results show that the statistical properties of an elliptical Gaussian vortex beam nonparaxially propagating in uniaxial crystal orthogonal to the optical axis are closely determined by the initial beam's parameters and the parameters of the crystal. The beam waist width ω0 not only affects the size of the beam profile in uniaxial crystal but also determines the nonparaxial effect of an elliptical Gaussian vortex beam. The profile of an elliptical Gaussian vortex beam in the uniaxial crystal becomes twisted and tilted, whether the elliptical factor α is greater or smaller than unity. The beam profile is tilted to the left in positive crystal. In contrast, it is inclined to the right in negative crystal. The results indicate that uniaxial crystal provides a convenient method to modulate the intensity and phase distributions of an elliptical Gaussian vortex beam, which is beneficial to optical manipulation of microscopic particles and nonlinear optics involving a specific beam profile and phase.

  16. On the identifiability of the Hill-1948 model with one uniaxial tensile test

    NASA Astrophysics Data System (ADS)

    Bertin, Morgan; Hild, François; Roux, Stéphane

    2017-06-01

    A uniaxial experiment is performed on an ultra-thin specimen made of 17-7 precipitation hardened stainless steel. An anti-wrinkling setup allows for the characterization of the mechanical behavior with Integrated Digital Image Correlation (IDIC). The result shows that a single uniaxial experiment investigated via IDIC possesses enough data (and even more) to characterize a complete anisotropic elastoplastic model.

  17. Nonparaxial propagation of Lorentz-Gauss beams in uniaxial crystal orthogonal to the optical axis.

    PubMed

    Wang, Xun; Liu, Zhirong; Zhao, Daomu

    2014-04-01

    Analytical expressions for the three components of nonparaxial propagation of a polarized Lorentz-Gauss beam in uniaxial crystal orthogonal to the optical axis are derived and used to investigate its propagation properties in uniaxial crystal. The influences of the initial beam parameters and the parameters of the uniaxial crystal on the evolution of the beam-intensity distribution in the uniaxial crystal are examined in detail. Results show that the statistical properties of a nonparaxial Lorentz-Gauss beam in a uniaxial crystal orthogonal to the optical axis are closely determined by the initial beam's parameters and the parameters of the crystal: the beam waist sizes-w(0), w(0x), and w(0y)-not only affect the size and shape of the beam profile in uniaxial crystal but also determine the nonparaxial effect of a Lorentz-Gauss beam; the beam profile of a Lorentz-Gauss beam in uniaxial crystal is elongated in the x or y direction, which is determined by the ratio of the extraordinary refractive index to the ordinary refractive index; with increasing deviation of the ratio from unity, the extension of the beam profile augments. The results indicate that uniaxial crystal provides an effective and convenient method for modulating the Lorentz-Gauss beams. Our results may be valuable in some fields, such as optical trapping and nonlinear optics, where a light beam with a special profile and polarization is required.

  18. Two touching spherical drops in a uniaxial compressional flow: The effect of interfacial slip

    NASA Astrophysics Data System (ADS)

    Goel, Sachin; Ramachandran, Arun

    2016-05-01

    This study presents a semi-analytical solution for the problem of two touching drops with slipping interfaces pushed against each other in a uniaxial compressional flow at low capillary and Reynolds numbers. The jump in the tangential velocity at the liquid-liquid interface is modeled using the Navier slip condition. Analytical solutions of the contact force, the drop-scale stresses, and the drop-scale pressure are provided as functions of the slip coefficient (" separators=" α ) , the viscosity ratio (" separators=" κ ) , and the drop size ratio (" separators=" k ) . Since unequal drop sizes are considered, two problems are solved in the tangent sphere co-ordinate system to determine the steady state position: a pair of touching drops with its contact point at the origin of an axisymmetric straining flow, and two touching drops placed in a uniform flow parallel to the axis of symmetry of the drops. A general observation is that the effect of slip is manifested most strongly for drops whose viscosity is much greater than the suspending fluid (" separators=" κ ≫ 1 ) . For highly viscous drops, the flow and stress fields transition from those corresponding to solid particles for ακ ≪ 1, to those for inviscid drops in the limit ακ ≫ 1. The analytical expressions provided here for the contact force and the stress distributions will serve to provide the restrictions that complete the definition of the lubrication flow problem in the thin film between the two colliding drops. While the contact force that drains fluid out of the thin film is relatively unaffected by slip, the tangential stress and pressure in the near-contact region are mitigated significantly for ακ ≫ 1. The latter is expected to assist coalescence at high capillary numbers.

  19. Co-simulation on vibration characteristics of uniaxial shaker based on AMESim and ADAMS

    NASA Astrophysics Data System (ADS)

    Liu, W.; Zhang, D. B.; Su, M.

    2017-07-01

    In this paper, we propose a selection method of the increased amplitude stability parameter for the unstable motion problem of the uniaxial shaker before its stable operation. On the basis of single-axis shaker dynamics equations, an ADMAS and AMESim combined simulation model is established. According to this model, the vibration characteristics under different parameters are solved by using the control variate method. The simulation results show that the motor speed, the eccentric mass and the inclination of screen surface are the three main factors which affect work starting state of uniaxial shaker. The working efficiency of uniaxial shaker is controlled by the motor speed while the amplitude is affected by the eccentric mass. Moreover, the inclination of screen surface plays a decisive role in the distribution of the vibration track before uniaxial shaker reaching the stable operation state. The relatively stable movement is obtained by optimizing the parameters, which provides a new way to improve the stability of uniaxial shaker.

  20. Calculation of nonlinear magnetic susceptibility tensors for a uniaxial antiferromagnet

    NASA Astrophysics Data System (ADS)

    Lim, Siew-Choo; Osman, Junaidah; Tilley, D. R.

    2000-11-01

    In this paper, we present a derivation of the nonlinear susceptibility tensors for a two-sublattice uniaxial antiferromagnet up to the third-order effects within the standard definition by which the rf magnetization m is defined as a power series expansion in the rf fields h with the susceptibility tensors χ(q) as the coefficients. The starting point is the standard set of torque equations of motion for this problem. A complete set of tensor elements is derived for the case of a single-frequency input wave. Within a circular polarization frame (pnz) expressions are given for the first-order susceptibility, second-harmonic generation, optical rectification, third-harmonic generation and intensity-dependent susceptibility. Some of the coefficients with representative resonance features in the far infrared are illustrated graphically and we conclude with a brief discussion of the implications of the resonance features arising from the calculations and their potential applications.

  1. Fabrication and morphology of uniaxially aligned perylenediimide nanowires

    NASA Astrophysics Data System (ADS)

    Machida, Shinjiro; Tanikatsu, Makoto; Itaya, Akira; Ikeda, Noriaki

    2017-06-01

    Uniaxial alignment of crystalline nanowires consisting of N,N‧-dioctyl-3,4,9,10-perylenedicarboximide (PTCDI-C8) was achieved on poly(tetrafluoroethylene) (PTFE) layers prepared by friction transfer method on a glass substrate. The nanowires were formed by spin-coating a trifluoroacetic acid (TFA) solution of PTCDI-C8 on the PTFE layers and were further grown under TFA vapor atmosphere. The morphology of the PTCDI-C8 nanowires were characterized using atomic force microscope (AFM) and fluorescence optical microscope with changing the dye concentration in the spin coating solution, annealing time in the TFA vapor, and substrate materials. The nanowires prepared on the PTFE layer on a silica-coated silicon or a mica substrate did not grow so well as those on the glass substrate. This result suggests that the surface roughness would affect the PTFE layer and the growth of the PTCDI nanowires.

  2. Programmable Extreme Pseudomagnetic Fields in Graphene by a Uniaxial Stretch

    NASA Astrophysics Data System (ADS)

    Zhu, Shuze; Stroscio, Joseph A.; Li, Teng

    2015-12-01

    Many of the properties of graphene are tied to its lattice structure, allowing for tuning of charge carrier dynamics through mechanical strain. The graphene electromechanical coupling yields very large pseudomagnetic fields for small strain fields, up to hundreds of Tesla, which offer new scientific opportunities unattainable with ordinary laboratory magnets. Significant challenges exist in investigation of pseudomagnetic fields, limited by the nonplanar graphene geometries in existing demonstrations and the lack of a viable approach to controlling the distribution and intensity of the pseudomagnetic field. Here we reveal a facile and effective mechanism to achieve programmable extreme pseudomagnetic fields with uniform distributions in a planar graphene sheet over a large area by a simple uniaxial stretch. We achieve this by patterning the planar graphene geometry and graphene-based heterostructures with a shape function to engineer a desired strain gradient. Our method is geometrical, opening up new fertile opportunities of strain engineering of electronic properties of 2D materials in general.

  3. Classifying human leg motions with uniaxial piezoelectric gyroscopes.

    PubMed

    Tunçel, Orkun; Altun, Kerem; Barshan, Billur

    2009-01-01

    This paper provides a comparative study on the different techniques of classifying human leg motions that are performed using two low-cost uniaxial piezoelectric gyroscopes worn on the leg. A number of feature sets, extracted from the raw inertial sensor data in different ways, are used in the classification process. The classification techniques implemented and compared in this study are: Bayesian decision making (BDM), a rule-based algorithm (RBA) or decision tree, least-squares method (LSM), k-nearest neighbor algorithm (k-NN), dynamic time warping (DTW), support vector machines (SVM), and artificial neural networks (ANN). A performance comparison of these classification techniques is provided in terms of their correct differentiation rates, confusion matrices, computational cost, and training and storage requirements. Three different cross-validation techniques are employed to validate the classifiers. The results indicate that BDM, in general, results in the highest correct classification rate with relatively small computational cost.

  4. Terahertz generation by optical rectification in uniaxial birefringent crystals

    NASA Astrophysics Data System (ADS)

    Rowley, J. D.; Wahlstrand, J. K.; Zawilski, K. T.; Schunemann, P. G.; Giles, N. C.; Bristow, A. D.

    2012-07-01

    The angular dependence of terahertz (THz) emission from birefringent crystals can differ significantly from that of cubic crystals. Here we consider optical rectification in uniaxial birefringent materials, such as chalcopyrite crystals. The analysis is verified in (110)-cut ZnGeP_2 and compared to (zincblende) GaP. Although the crystals share the same nonzero second-order tensor elements, the birefringence in chalcopyrite crystals cause the pump pulse polarization to evolve as it propagates through the crystal, resulting in a drastically different angular dependence in chalcopyrite crystals. The analysis is extended to {012}- and {114}-cut chalcopyrite crystals and predicts more efficient conversion for the {114} crystal cut over the {012}- and {110}-cuts.

  5. Microstructure Evolution of HSLA Pipeline Steels after Hot Uniaxial Compression.

    PubMed

    Liu, Yongchang; Shao, Yi; Liu, Chenxi; Chen, Yan; Zhang, Dantian

    2016-08-24

    The mechanical properties of the high-strength low-alloy pipeline steels were mainly controlled by the subsequent phase transformations after rolling. The influence of hot uniaxial compression on the phase transformation of acicular ferrite was explored by viewing of the deformation degree, the deformation temperature, and the strain rate. The results show that the increase of deformation amounts raises the transformation starting and finishing temperature during the subsequent cooling and also promotes the polygonal ferrite transformation, which leads to the decrease of Vickers hardness accordingly. With the increasing of the deformation temperature, the achieved microstructure becomes coarsened and thus decreases the hardness. As the strain rate increases, the microstructure is refined and thus the hardness increases gradually; increasing the strain rate appropriately is beneficial to the refinement of the microstructure.

  6. Ultimate Capacity of Uniaxially Compressed Steel Plates Strengthened by CFRP

    NASA Astrophysics Data System (ADS)

    Tao, Xin; Cao, S. Y.

    2017-06-01

    This paper presents experimental studies on the ultimate capacity of steel plates strengthened by Carbon Fiber-reinforced polymer (CFRP). Some 40 plates are tested under uniaxial compression along its longitudinal direction. The effect of CFRP pasting, plate slenderness ratio and the boundary conditions are illustrated on the studies. The study shows that the steel plates strengthened by CFRP exhibited higher capacity in comparison to similar plates without CFRP. It also can be seen that multi-layers CFRP pasting were better than the single layer, pasting multi-direction is better than pasting uni-direction, pasting the transverse layer outside is better than pasting the longitudinal layer outside, and the effect of longitudinal layer was better than the transverse layer.

  7. Propagation of Airy Gaussian vortex beams in uniaxial crystals

    NASA Astrophysics Data System (ADS)

    Weihao, Yu; Ruihuang, Zhao; Fu, Deng; Jiayao, Huang; Chidao, Chen; Xiangbo, Yang; Yanping, Zhao; Dongmei, Deng

    2016-04-01

    The propagation dynamics of the Airy Gaussian vortex beams in uniaxial crystals orthogonal to the optical axis has been investigated analytically and numerically. The propagation expression of the beams has been obtained. The propagation features of the Airy Gaussian vortex beams are shown with changes of the distribution factor and the ratio of the extraordinary refractive index to the ordinary refractive index. The correlations between the ratio and the maximum intensity value during the propagation, and its appearing distance have been investigated. Project supported by the National Natural Science Foundation of China (Grant Nos. 11374108, 11374107, 10904041, and 11547212), the Foundation of Cultivating Outstanding Young Scholars of Guangdong Province, China, the CAS Key Laboratory of Geospace Environment, University of Science and Technology of China, the National Training Program of Innovation and Entrepreneurship for Undergraduates (Grant No. 2015093), and the Science and Technology Projects of Guangdong Province, China (Grant No. 2013B031800011).

  8. Classifying Human Leg Motions with Uniaxial Piezoelectric Gyroscopes

    PubMed Central

    Tunçel, Orkun; Altun, Kerem; Barshan, Billur

    2009-01-01

    This paper provides a comparative study on the different techniques of classifying human leg motions that are performed using two low-cost uniaxial piezoelectric gyroscopes worn on the leg. A number of feature sets, extracted from the raw inertial sensor data in different ways, are used in the classification process. The classification techniques implemented and compared in this study are: Bayesian decision making (BDM), a rule-based algorithm (RBA) or decision tree, least-squares method (LSM), k-nearest neighbor algorithm (k-NN), dynamic time warping (DTW), support vector machines (SVM), and artificial neural networks (ANN). A performance comparison of these classification techniques is provided in terms of their correct differentiation rates, confusion matrices, computational cost, and training and storage requirements. Three different cross-validation techniques are employed to validate the classifiers. The results indicate that BDM, in general, results in the highest correct classification rate with relatively small computational cost. PMID:22291521

  9. Homogenization of electromagnetic crystals formed by uniaxial resonant scatterers

    NASA Astrophysics Data System (ADS)

    Belov, Pavel A.; Simovski, Constantin R.

    2005-08-01

    Dispersion properties of electromagnetic crystals formed by small uniaxial resonant scatterers (magnetic or electric) are studied using the local field approach. The goal of the study is to determine the conditions under which the homogenization of such crystals is possible. Therefore the consideration is limited to the frequency region where the wavelength in the host medium is larger than the lattice periods. It is demonstrated that, together with the known restriction for the homogenization related to the large values of the material parameters, there is an additional restriction related to their small absolute values. On the other hand, the homogenization becomes allowed in both cases of large and small material parameters for special directions of propagation. Two unusual effects inherent to the crystals under consideration are revealed: a flat isofrequency contour that allows subwavelength imaging using the canalization regime and birefringence of the extraordinary modes which can be used for beam splitting.

  10. A Robust Uniaxial Force Sensor for Minimally Invasive Surgery

    PubMed Central

    Yip, Michael C.; Yuen, Shelten G.; Howe, Robert D.

    2010-01-01

    This paper presents a novel miniature uniaxial force sensor for use within a beating heart during mitral valve annuloplasty. The sensor measures 5.5 mm in diameter and 12 mm in length and provides a hollow core to pass instrumentation. A soft elastomer flexure design maintains a waterproof seal. Fiber optic transduction eliminates electrical circuitry within the heart, and acetal components minimize ultrasound-imaging artifacts. Calibration uses a nonlinear viscoelastic method, and in vitro tests demonstrate a 0–4-N force range with rms errors of 0.13 N (<3.2%). In vivo tests provide the first endocardial measurements of tissue-minimally invasive surgery instrument interaction forces in a beating heart. PMID:20172798

  11. Inhomogeneous Deformation of AZ31 Magnesium Sheet in Uniaxial Tension

    NASA Astrophysics Data System (ADS)

    Kang, Jidong; Wilkinson, David S.; Mishra, Raja K.

    Inhomogeneous plastic deformation during uniaxial tensile test of AZ31 magnesium sheet has been studied using digital image correlation and electron backscatter diffraction techniques. It is shown that large strain gradients exist on the sheet surface parallel and perpendicular to the loading direction and very little deformation occurs in the thickness direction. The lack of thinning leads to abrupt fracture right after the formation of a premature but profound diffuse neck without transitioning to any localized neck. Such inhomogeneous deformation arises from the strong basal texture of the starting sheet and the resultant need for contraction and double twinning to accommodate strain. The strain distribution on the sheet surface evolves nonlinearly with strain, impacting the measured r-value.

  12. Microstructure Evolution of HSLA Pipeline Steels after Hot Uniaxial Compression

    PubMed Central

    Liu, Yongchang; Shao, Yi; Liu, Chenxi; Chen, Yan; Zhang, Dantian

    2016-01-01

    The mechanical properties of the high-strength low-alloy pipeline steels were mainly controlled by the subsequent phase transformations after rolling. The influence of hot uniaxial compression on the phase transformation of acicular ferrite was explored by viewing of the deformation degree, the deformation temperature, and the strain rate. The results show that the increase of deformation amounts raises the transformation starting and finishing temperature during the subsequent cooling and also promotes the polygonal ferrite transformation, which leads to the decrease of Vickers hardness accordingly. With the increasing of the deformation temperature, the achieved microstructure becomes coarsened and thus decreases the hardness. As the strain rate increases, the microstructure is refined and thus the hardness increases gradually; increasing the strain rate appropriately is beneficial to the refinement of the microstructure. PMID:28773842

  13. Uniaxial and triaxial compression test series on Calico Hills tuff

    NASA Astrophysics Data System (ADS)

    Price, R. H.; Jones, A. K.

    1982-10-01

    Forty-four uniaxial and triaxial compression experiments were performed on samples of the Tuffaceous beds of Calico Hills obtained from drill hole USW-G1 at Yucca Mountain on the Nevada Test Site. Water saturated and room dry test specimens were deformed at nominal strain rates of 0.001,0.00001, 10 to the minus 7th power, s(1), confining pressures of 0.1, 10 and 20 MPa; and room temperature. Resultant unconfined compressive strengths, axial strains to failure, Young's moduli and Poisson's ratios ranged from 14.2 to 42.0 MPa, 0.0037 to 0.0087, 2.52 to 9.72 GPA and 0.17 to 0.37, respectively.

  14. Uniaxial and triaxial compression test series on Calico Hills tuff

    SciTech Connect

    Price, R.H.; Jones, A.K.

    1982-10-01

    Forty-four uniaxial and triaxial compression experiments were performed on samples of the Tuffaceous beds of Calico Hills obtained from drill hole USW-G1 at Yucca Mountain on the Nevada Test Site. Water saturated and room dry test specimens were deformed at nominal strain rates of 10{sup -3}, 10{sup -5} and 10{sup -7} s{sup -1}; confining pressures of 0.1, 10 and 20 MPa; and room temperature. Resultant unconfined compressive strengths, axial strains to failure, Young`s moduli and Poisson`s ratios ranged from 14.2 to 42.0 MPa, 0.0037 to 0.0087, 2.52 to 9.72 GPA and 0.17 to 0.37, respectively.

  15. Rotational spin Hall effect in a uniaxial crystal

    NASA Astrophysics Data System (ADS)

    Fadeyeva, Tatyana A.; Alexeyev, Constantine N.; Rubass, Alexander F.; Ivanov, Maksym O.; Zinov'ev, Alexey O.; Konovalenko, Victor L.; Volyar, Alexander V.

    2012-04-01

    We have considered the propagation process of the phase-matched array of singular beams through a uniaxial crystal. We have revealed that local beams in the array are rotated when propagating. However the right and left rotations are unequal. There are at least two processes responsible for the array rotation: the interference of local beams and the spatial depolarization. The interference takes place in the vortex birth and annihilation events forming the symmetrical part of the rotation. The depolarization process contributes to the asymmetry of the rotation that is called the rotational spin Hall effect. It can be brought to light due to the difference between the envelopes of the dependences of the angular displacement on the inclination angle of the local beams or the crystal length reaching the value some angular degree. The direction of the additional array rotation is exclusively defined by the handedness of the circular polarization in the initial beam array.

  16. Rotational spin Hall effect in a uniaxial crystal.

    PubMed

    Fadeyeva, Tatyana A; Alexeyev, Constantine N; Rubass, Alexander F; Ivanov, Maksym O; Zinov'ev, Alexey O; Konovalenko, Victor L; Volyar, Alexander V

    2012-04-01

    We have considered the propagation process of the phase-matched array of singular beams through a uniaxial crystal. We have revealed that local beams in the array are rotated when propagating. However the right and left rotations are unequal. There are at least two processes responsible for the array rotation: the interference of local beams and the spatial depolarization. The interference takes place in the vortex birth and annihilation events forming the symmetrical part of the rotation. The depolarization process contributes to the asymmetry of the rotation that is called the rotational spin Hall effect. It can be brought to light due to the difference between the envelopes of the dependences of the angular displacement on the inclination angle of the local beams or the crystal length reaching the value of some angular degree. The direction of the additional array rotation is exclusively defined by the handedness of the circular polarization in the initial beam array.

  17. Effective Disappearance of the Meissner Signal in the Cuprate Superconductor YBa2Cu4O8 under Uniaxial Strain

    NASA Astrophysics Data System (ADS)

    Mito, Masaki; Imakyurei, Takumi; Deguchi, Hiroyuki; Matsumoto, Kaname; Hara, Hiroshi; Ozaki, Toshinori; Takeya, Hiroyuki; Takano, Yoshihiko

    2014-02-01

    The effects of uniaxial strain and hydrostatic pressure on YBa2Cu4O8 were investigated through magnetic measurements under stresses of up to 25 GPa. The out-of-plane (along the c-axis), in-plane (along the c-plane), and hydrostatic contractions all initially bring about an increase in the superconducting transition temperature (Tc). In the case of the out-of-plane and in-plane contractions, the Meissner signal disappears at a stress corresponding to about 10 GPa. However, under the hydrostatic contraction, the maximum Tc was about 100 K at 9-12 GPa, and the Meissner effect was observed at pressures of at least 16 GPa.

  18. Stress

    MedlinePlus

    ... Planning Meals Diabetes Meal Plans Create Your Plate Gluten Free Diets Meal Planning for Vegetarian Diets Cook ... stress hormones. Relaxing can help by blunting this sensitivity. There are many ways to help yourself relax: ...

  19. Acoustic emission signals frequency-amplitude characteristics of sandstone after thermal treated under uniaxial compression

    NASA Astrophysics Data System (ADS)

    Kong, Biao; Wang, Enyuan; Li, Zenghua; Wang, Xiaoran; Niu, Yue; Kong, Xiangguo

    2017-01-01

    Thermally treated sandstone deformation and fracture produced abundant acoustic emission (AE) signals. The AE signals waveform contained plentiful precursor information of sandstone deformation and fracture behavior. In this paper, uniaxial compression tests of sandstone after different temperature treatments were conducted, the frequency-amplitude characteristics of AE signals were studied, and the main frequency distribution at different stress level was analyzed. The AE signals frequency-amplitude characteristics had great difference after different high temperature treatment. Significant differences existed of the main frequency distribution of AE signals during thermal treated sandstone deformation and fracture. The main frequency band of the largest waveforms proportion was not unchanged after different high temperature treatments. High temperature caused thermal damage to the sandstone, and sandstone deformation and fracture was obvious than the room temperature. The number of AE signals was larger than the room temperature during the initial loading stage. The low frequency AE signals had bigger proportion when the stress was 0.1, and the maximum value of the low frequency amplitude was larger than high frequency signals. With the increase of stress, the low and high frequency AE signals were gradually increase, which indicated that different scales ruptures were broken in sandstone. After high temperature treatment, the number of high frequency AE signals was significantly bigger than the low frequency AE signals during the latter loading stage, this indicates that the small scale rupture rate of recurrence and frequency were more than large scale rupture. The AE ratio reached the maximum during the sandstone instability failure period, and large scale rupture was dominated in the failure process. AE amplitude increase as the loading increases, the deformation and fracture of sandstone was increased gradually. By comparison, the value of the low frequency

  20. Stretch calculated from grip distance accurately approximates mid-specimen stretch in large elastic arteries in uniaxial tensile tests

    PubMed Central

    Tian, Lian; Henningsen, Joseph; Salick, Max R.; Crone, Wendy C.; Gunderson, McLean; Dailey, Seth H.; Chesler, Naomi C.

    2015-01-01

    The mechanical properties of vascular tissues affect hemodynamics and can alter disease progression. The uniaxial tensile test is a simple and effective method for determining the stress-strain relationship in arterial tissue ex vivo. To enable calculation of strain, stretch can be measured directly with image tracking of markers on the tissue or indirectly from the distance between the grips used to hold the specimen. While the imaging technique is generally considered more accurate, it also requires more analysis, and the grip distance method is more widely used. The purpose of this study is to compare the stretch of the testing specimen calculated from the grip distance method to that obtained from the imaging method for canine descending aortas and large proximal pulmonary arteries. Our results showed a significant difference in stretch between the two methods; however, this difference was consistently less than 2%. Therefore, the grip distance method is an accurate approximation of the stretch in large elastic arteries in the uniaxial tensile test. PMID:25881308

  1. A comparison of the uniaxial deformation of copper and nickel (1 1 19) surfaces: a molecular dynamics study

    PubMed Central

    Pukšič, Nuša; Jenko, Monika; Godec, Matjaž; McGuiness, Paul J.

    2017-01-01

    While a lot is known about the deformation of metallic surfaces from experiments, elasticity theory and simulations, this investigation represents the first molecular-dynamics-based simulation of uniaxial deformation for the vicinal surfaces in a comparison of copper and nickel. These vicinal surfaces are composed of terraces divided by equidistant, mono-atomic steps. The periodicity of vicinals makes them good candidates for the study of the surface steps’ influences on surface dynamics. The simulations of tensile and compressive uniaxial deformations were performed for the (1 1 19) vicinal surfaces. Since the steps on the surfaces serve as stress concentrators, the first defects were expected to nucleate here. In the case of copper, this was found to be the case. In the case of nickel, however, dislocations nucleated beneath the near-surface layer affected by the displacement field generated by the steps. Slip was hindered at the surface step by the vortex in the displacement field. The differences in the deformation mechanisms for the Ni(1 1 19) and Cu(1 1 19) surfaces can be linked to the differences in their displacement fields. This could lead to novel bottom-up approaches to the nanostructuring of surfaces using strain. PMID:28169377

  2. Stretch calculated from grip distance accurately approximates mid-specimen stretch in large elastic arteries in uniaxial tensile tests.

    PubMed

    Tian, Lian; Henningsen, Joseph; Salick, Max R; Crone, Wendy C; Gunderson, McLean; Dailey, Seth H; Chesler, Naomi C

    2015-07-01

    The mechanical properties of vascular tissues affect hemodynamics and can alter disease progression. The uniaxial tensile test is a simple and effective method for determining the stress-strain relationship in arterial tissue ex vivo. To enable calculation of strain, stretch can be measured directly with image tracking of markers on the tissue or indirectly from the distance between the grips used to hold the specimen. While the imaging technique is generally considered more accurate, it also requires more analysis, and the grip distance method is more widely used. The purpose of this study is to compare the stretch of the testing specimen calculated from the grip distance method to that obtained from the imaging method for canine descending aortas and large proximal pulmonary arteries. Our results showed a significant difference in stretch between the two methods; however, this difference was consistently less than 2%. Therefore, the grip distance method is an accurate approximation of the stretch in large elastic arteries in the uniaxial tensile test. Copyright © 2015 Elsevier Ltd. All rights reserved.

  3. A comparison of the uniaxial deformation of copper and nickel (1 1 19) surfaces: a molecular dynamics study.

    PubMed

    Pukšič, Nuša; Jenko, Monika; Godec, Matjaž; McGuiness, Paul J

    2017-02-07

    While a lot is known about the deformation of metallic surfaces from experiments, elasticity theory and simulations, this investigation represents the first molecular-dynamics-based simulation of uniaxial deformation for the vicinal surfaces in a comparison of copper and nickel. These vicinal surfaces are composed of terraces divided by equidistant, mono-atomic steps. The periodicity of vicinals makes them good candidates for the study of the surface steps' influences on surface dynamics. The simulations of tensile and compressive uniaxial deformations were performed for the (1 1 19) vicinal surfaces. Since the steps on the surfaces serve as stress concentrators, the first defects were expected to nucleate here. In the case of copper, this was found to be the case. In the case of nickel, however, dislocations nucleated beneath the near-surface layer affected by the displacement field generated by the steps. Slip was hindered at the surface step by the vortex in the displacement field. The differences in the deformation mechanisms for the Ni(1 1 19) and Cu(1 1 19) surfaces can be linked to the differences in their displacement fields. This could lead to novel bottom-up approaches to the nanostructuring of surfaces using strain.

  4. A comparison of the uniaxial deformation of copper and nickel (1 1 19) surfaces: a molecular dynamics study

    NASA Astrophysics Data System (ADS)

    Pukšič, Nuša; Jenko, Monika; Godec, Matjaž; McGuiness, Paul J.

    2017-02-01

    While a lot is known about the deformation of metallic surfaces from experiments, elasticity theory and simulations, this investigation represents the first molecular-dynamics-based simulation of uniaxial deformation for the vicinal surfaces in a comparison of copper and nickel. These vicinal surfaces are composed of terraces divided by equidistant, mono-atomic steps. The periodicity of vicinals makes them good candidates for the study of the surface steps’ influences on surface dynamics. The simulations of tensile and compressive uniaxial deformations were performed for the (1 1 19) vicinal surfaces. Since the steps on the surfaces serve as stress concentrators, the first defects were expected to nucleate here. In the case of copper, this was found to be the case. In the case of nickel, however, dislocations nucleated beneath the near-surface layer affected by the displacement field generated by the steps. Slip was hindered at the surface step by the vortex in the displacement field. The differences in the deformation mechanisms for the Ni(1 1 19) and Cu(1 1 19) surfaces can be linked to the differences in their displacement fields. This could lead to novel bottom-up approaches to the nanostructuring of surfaces using strain.

  5. An experimental study on fracture mechanical behavior of rock-like materials containing two unparallel fissures under uniaxial compression

    NASA Astrophysics Data System (ADS)

    Huang, Yan-Hua; Yang, Sheng-Qi; Tian, Wen-Ling; Zeng, Wei; Yu, Li-Yuan

    2016-06-01

    Strength and deformability characteristics of rock with pre-existing fissures are governed by cracking behavior. To further research the effects of pre-existing fissures on the mechanical properties and crack coalescence process, a series of uniaxial compression tests were carried out for rock-like material with two unparallel fissures. In the present study, cement, quartz sand, and water were used to fabricate a kind of brittle rock-like material cylindrical model specimen. The mechanical properties of rock-like material specimen used in this research were all in good agreement with the brittle rock materials. Two unparallel fissures (a horizontal fissure and an inclined fissure) were created by inserting steel during molding the model specimen. Then all the pre-fissured rock-like specimens were tested under uniaxial compression by a rock mechanics servo-controlled testing system. The peak strength and Young's modulus of pre-fissured specimen all first decreased and then increased when the fissure angle increased from 0° to 75°. In order to investigate the crack initiation, propagation and coalescence process, photographic monitoring was adopted to capture images during the entire deformation process. Moreover, acoustic emission (AE) monitoring technique was also used to obtain the AE evolution characteristic of pre-fissured specimen. The relationship between axial stress, AE events, and the crack coalescence process was set up: when a new crack was initiated or a crack coalescence occurred, the corresponding axial stress dropped in the axial stress-time curve and a big AE event could be observed simultaneously. Finally, the mechanism of crack propagation under microscopic observation was discussed. These experimental results are expected to increase the understanding of the strength failure behavior and the cracking mechanism of rock containing unparallel fissures.

  6. Failure Investigation for QP Steel Sheets under uniaxial and Equal-Biaxial Tension Conditions

    NASA Astrophysics Data System (ADS)

    Zou, Danqing; Li, Shuhui; He, Ji; Cui, Ronggao

    2016-08-01

    The Quenching and Partitioning (QP) steel sheet is new generation material to induce phase transformation for plasticity in forming vehicle parts. The phase transformation is strongly stress state dependent behavior in experiments, which should affect the failure timing and limit strain in forming processes. In this paper, Nakajima test with QP980 and DP1000 steel sheets under equal-biaxial loading condition is performed for failure behavior. X-ray diffraction (XRD) is adopted to obtain the volume fraction of retained austenite (fA). Digital Image Correlation (DIC) is used to record the surface strain field and its evolution during equal-biaxial tension deformation. The same level Dual Phase (DP) steel is also employed for the purpose of comparison. The results show that phase transformation in QP steel gives small impact on failure strain under equal biaxial tension condition which is contradicted with our understanding. It suggests that failure behavior under uniaxial tension of QP980 is strongly phase transformation dependent. But it shows almost independent under equal biaxial tension condition.

  7. A Quasicontinuum Study of Nanovoid Collapse under Uniaxial Loading in Ta

    SciTech Connect

    Marian, J; Knap, J; Campbell, G

    2007-12-02

    The mechanisms underlying the deformation of nanovoids in Ta single crystals are analyzed when they are subjected to cyclic uniaxial deformation using numerical simulations. Boundary and cell-size effects have been mitigated by means of the Quasicontinuum (QC) method. We have considered {approx} 1 billion-atom systems containing 10.9 nm voids. Two kinds of simulations have been performed, each characterized by a different boundary condition. First, we compress the material along the nominal [0 0 1] direction, resulting in a highly symmetric configuration that results in high stresses. Second, we load the material along the high-index [{bar 4}819] direction to confine plasticity to a single slip system and break the symmetry. We find that the plastic response under these two conditions is strikingly different, the former governed by dislocation loop emission and dipole formation, while the latter is dominated by twinning. We calculate the irreversible plastic work budget derived from a loading-unloading cycle and identify the most relevant yield points. These calculations represent the first fully three-dimensional, fully non-local simulations of any body-centered cubic metal using QC.

  8. Large deformation and amorphization of Ni nanowires under uniaxial strain: A molecular dynamics study

    NASA Astrophysics Data System (ADS)

    Branício, Paulo S.; Rino, José-Pedro

    2000-12-01

    Molecular-dynamics simulations were employed to study deformations on nickel nanowires subjected to uniaxial strain at 300 K using a recently reported embedded-atom (many body) model potential. This embedded-atom model can reproduce exactly the experimental second-order and third-order elastic moduli as well as the phase stability, equation of state and phonon frequency spectra are also in good agreement with experiments. Strong influence was observed in the Young modulus and force constant due to surface effects when considering nanowires with different cross sections. Applying strain rates, from 0.05 to 15% ps-1, we found elastic behavior up to 11.5% strain with corresponding stress of 9.4 GPa. At low strain rates (<0.05% ps-1) the system passes through plastic deformations although keeping the crystalline structure. This ductile process is showed by several snapshots. At this low strain rate regime we observed that the nanowires shows superplasticity. For high strain rates (>=7% ps-1) the system changes continuously from crystalline to amorphous phase. Although this amorphization occurs with no use of liquid quenching or introduction of chemical or physical disorder, so being a different and interesting process, the amorphous resulted is unstable. We studied this instability monitoring the recrystallization process.

  9. Mutual influence of uniaxial tensile strain and point defect pattern on electronic states in graphene

    NASA Astrophysics Data System (ADS)

    Sagalianov, Iyor Yu.; Radchenko, Taras M.; Prylutskyy, Yuriy I.; Tatarenko, Valentyn A.; Szroeder, Pawel

    2017-06-01

    The study deals with electronic properties of uniaxially stressed mono- and multi-layer graphene sheets with various kinds of imperfection: point defects modelled as resonant (neutral) adsorbed atoms or molecules, vacancies, charged impurities, and local distortions. The presence of randomly distributed defects in a strained graphene counteract the band-gap opening and even can suppress the gap occurs when they are absent. However, impurity ordering contributes to the band gap appearance and thereby re-opens the gap being suppressed by random dopants in graphene stretched along zigzag-edge direction. The band gap is found to be non-monotonic with strain in case of mutual action of defect ordering and zigzag deformation. Herewith, the minimal tensile strain required for the band-gap opening (≈12.5%) is smaller than that for defect-free graphene (≈23%), and band gap energy reaches the value predicted for maximal nondestructive strains in the pristine graphene. Effective manipulating the band gap in graphene requires balanced content of ordered dopants: their concentration should be sufficient for a significant sublattice asymmetry effect, but not so much that they may suppress the band gap or transform it into the "quasi- (or pseudo-) gap".

  10. A Surface Damage Investigation on Uniaxial Tensile Test Specimens Prepared by Common Cutting Methods

    DTIC Science & Technology

    1981-02-01

    REPORI’ A SURFACE DAMAGE INVESTIGATION ON UNIAXIAL TENSILE TEST SPECIMENSPREPARED BY COMMON CUTTING METHODS JUN 2 1931 THOMAS J. C. CHEW DALE A...Sýrfa-i-mage Investigation on Uniaxial Tensile Test Specimens Prepared by Common Cutting Method I Spi-.i t’ ,, ., • T7. AUTHORý#) . _" ’ /t’ .• r...Saw 10 2.1.3 Cutting by Milling Machine 11 2.1.4 Cutting by Die Cutter 11 2.2 Uniaxial Tensile Test 12 2.3 Electron Microscope Surface Examination 13 3

  11. Identification of the Hereditary Kernels of Isotropic Linear Viscoelastic Materials in Combined Stress state. 1. Superposition of Shear and Bulk creep

    NASA Astrophysics Data System (ADS)

    Golub, V. P.; Maslov, B. P.; Fernati, P. V.

    2016-03-01

    Relations between the shear and bulk creep kernels of an isotropic linear viscoelastic material in combined stress state and the longitudinal and shear creep kernels constructed from data of creep tests under uniaxial tension and pure torsion are formulated. The constitutive equations of viscoelasticity for the combined stress state are chosen in the form of a superposition of the equation for shear strains and the equation for bulk strains. The hereditary kernels are described by Rabotnov's fractional-exponential functions. The creep strains of thin-walled pipes under a combination of tension and torsion or tension and internal pressure are calculated

  12. The evolution of light spin-orbital momentum within the rotated uniaxial crystal near the perpendicular to its optical axis

    NASA Astrophysics Data System (ADS)

    Sokolenko, Bohdan V.; Rubass, Alex F.; Lapaeva, Svetlana N.; Glymova, Maryna V.; Volyar, Alexander V.

    2013-12-01

    We have experimentally analyzed the behavior of Gaussian beam with elliptical cross-section passed through the uniaxial crystal in direction near perpendicular to the crystal's optical axis. The projection of total angular momentum flux on the axis consists of projection of two components: the spin (SAM) and orbital (OAM) angular momentum. We have revealed that in anisotropic media the SAM describes the polarization state of the beam cross-section and OAM reflects the shape and topological charge of the singularity at ordinary and extraordinary beams. The sum of projections SAM and OAM remains constant. The oscillations of spin-orbital angular momentum projection were described experimentally during the crystal was rotated around z axis with small beam inclination. The low changes in the extraordinary beam cross section and their correlation with polarization state allow us to analyze the form of angular momentum conversion and possibility for generation of polarizing singularities. The feasibility of optical vortex generation in the system of uniaxial crystal with tilted Gaussian beam was theoretically and experimentally investigated.

  13. An open-end burst test method to obtain uniaxial hoop tensile properties of fuel cladding in a hot cell

    NASA Astrophysics Data System (ADS)

    Nakatsuka, Masafumi; Aita, Makoto; Sakamoto, Kan; Higuchi, Toru

    2013-03-01

    The hoop stress-hoop strain relationship of fuel cladding is one of the essential input parameters for safety analysis of fuel rods. The three objectives of this paper were: to propose a burst test method for open-end tube specimens with the uniaxial hoop stress condition; to develop the necessary in-cell high temperature open-end burst (OEB) techniques to implement the method; and to determine the optimum specimen length for the proposed OEB test method. Silicone oil was selected as the pressurization medium, and it was sealed inside the specimens not by welding but by O-rings so that no axial tensile stress was induced in the specimens. The specimens with combined end plugs and O-rings were successfully assembled by manipulators in a hot cell, and a high temperature (⩽350 °C), high pressure (⩽100 MPa) seal was achieved. The optimum specimen length was determined by using ductile and embrittled tubes with various lengths of 30-60 mm and was found to be around 45 mm for typical BWR fuel rods. During the OEB test, internal pressure and diametral expansion were monitored to obtain the basic mechanical performance properties of the fuel cladding such as yield stress, ultimate strength, as well as the true hoop stress-hoop strain curve.

  14. Directional solidification under stress

    NASA Astrophysics Data System (ADS)

    Cantat, Isabelle; Kassner, Klaus; Misbah, Chaouqi; Müller-Krumbhaar, Heiner

    1998-11-01

    Directional solidification under uniaxial stress is analyzed. In the absence of stress, it is well known that the moving planar front undergoes a morphological Mullins-Sekerka (MS) instability. Under uniaxial stress, even an interface at rest develops an instability known by the names of Asaro, Tiller, and Grinfeld (ATG). This paper analyzes the coupling between these two instabilities, a situation on which we have recently given a brief account [Durand et al., Phys. Rev. Lett. 76, 3013 (1996)]. We discover that under favorable circumstances a weak uniaxial stress of the order of 1 bar leads to a dramatic change of the Mullins-Sekerka instability. The threshold, together with the microstructure scale, are shifted by amounts going up to one (or several) decade(s). This effect should open new lines of both experimental and theoretical inquiries. A weakly nonlinear analysis is presented by means of a Landau expansion. It is known that the MS bifurcation is subcritical for a small enough solute partition coefficient, and is supercritical otherwise. The ATG instability is always subcritical. The nonlinear evolution of the ATG instability leads to cusps which grow unstably, leading ultimately to the fracture threshold. It is shown here that due to a subtle coupling between both instabilities, the MS bifurcation in its supercritical regime may cause the MS-ATG coupled bifurcation to be supercritical. Discussions and outlooks are presented. In particular it is appealing to speculate that the creation of giant causeways in igneous rocks can be interpreted within the present context.

  15. Five Describing Factors of Dyslexia

    ERIC Educational Resources Information Center

    Tamboer, Peter; Vorst, Harrie C. M.; Oort, Frans J.

    2016-01-01

    Two subtypes of dyslexia (phonological, visual) have been under debate in various studies. However, the number of symptoms of dyslexia described in the literature exceeds the number of subtypes, and underlying relations remain unclear. We investigated underlying cognitive features of dyslexia with exploratory and confirmatory factor analyses. A…

  16. Five Describing Factors of Dyslexia

    ERIC Educational Resources Information Center

    Tamboer, Peter; Vorst, Harrie C. M.; Oort, Frans J.

    2016-01-01

    Two subtypes of dyslexia (phonological, visual) have been under debate in various studies. However, the number of symptoms of dyslexia described in the literature exceeds the number of subtypes, and underlying relations remain unclear. We investigated underlying cognitive features of dyslexia with exploratory and confirmatory factor analyses. A…

  17. Describing Control in Educational Organizations.

    ERIC Educational Resources Information Center

    Renihan, P. J.; Renihan, F. I.

    This paper describes the construction and application of a framework to investigate control at the policy-making level in education. The minutes of the regular meetings of 21 school boards in British Columbia were analyzed for the period January to December of 1975. Construction of the framework involved (1) definitions of control and…

  18. Viscoelastic properties of vascular endothelial cells exposed to uniaxial stretch

    NASA Astrophysics Data System (ADS)

    Osterday, Kathryn; Chew, Thomas; Loury, Phillip; Haga, Jason; Del Alamo, Juan C.; Chien, Shu

    2011-11-01

    Vascular endothelial cells (VECs) line the interior of blood vessels and regulate a variety of functions in the cardiovascular system. It is widely accepted that VECs will remodel themselves in response to mechanical stimuli, but few studies have analyzed the mechanical properties of these cells under stretch. We hypothesize that uniaxial stretch will cause an anisotropic realignment of actin filaments, and a change in the viscoelastic properties of the cell. To test this hypothesis, VECs were grown on a thin, transparent membrane mounted on a microscope. The membrane was stretched, consequently stretching the cells. Time-lapse sequences of the cells were taken every hour with a time resolution of 10 Hz. The random trajectories of intracellular endogenous particles were tracked using in-house algorithms. These trajectories were analyzed using a novel particle tracking microrheology formulation that takes into account the anisotropy of the cytoplasm of VECs. Supported by NSF CBET-1055697 CAREER Award (JCA) and NIH grants BRP HL064382 (SC), 1R01 HL080518 (SC).

  19. Programmable Extreme Pseudomagnetic Fields in Graphene by a Uniaxial Stretch

    PubMed Central

    Zhu, Shuze; Stroscio, Joseph A.; Li, Teng

    2016-01-01

    Many of the properties of graphene are tied to its lattice structure, allowing for tuning of charge carrier dynamics through mechanical strain. The graphene electro-mechanical coupling yields very large pseudomagnetic fields for small strain fields, up to hundreds of Tesla, which offer new scientific opportunities unattainable with ordinary laboratory magnets. Significant challenges exist in investigation of pseudomagnetic fields, limited by the non-planar graphene geometries in existing demonstrations and the lack of a viable approach to controlling the distribution and intensity of the pseudomagnetic field. Here we reveal a facile and effective mechanism to achieve programmable extreme pseudomagnetic fields with uniform distributions in a planar graphene sheet over a large area by a simple uniaxial stretch. We achieve this by patterning the planar graphene geometry and graphene-based hetero-structures with a shape function to engineer a desired strain gradient. Our method is geometrical, opening up new fertile opportunities of strain engineering of electronic properties of 2D materials in general. PMID:26705640

  20. Van der Waals interaction in uniaxial anisotropic media.

    PubMed

    Kornilovitch, Pavel E

    2013-01-23

    Van der Waals interactions between flat surfaces in uniaxial anisotropic media are investigated in the nonretarded limit. The main focus is the effect of nonzero tilt between the optical axis and the surface normal on the strength of the van der Waals attraction. General expressions for the van der Waals free energy are derived using the surface mode method and the transfer-matrix formalism. To facilitate numerical calculations a temperature-dependent three-band parameterization of the dielectric tensor of the liquid crystal 5CB is developed. A solid slab immersed in a liquid crystal experiences a van der Waals torque that aligns the surface normal relative to the optical axis of the medium. The preferred orientation is different for different materials. Two solid slabs in close proximity experience a van der Waals attraction that is strongest for homeotropic alignment of the intervening liquid crystal for all the materials studied. The results have implications for the stability of plate-like colloids in liquid crystal hosts.

  1. Field dependent elastic anomaly in uniaxial tungsten bronze relaxors

    NASA Astrophysics Data System (ADS)

    Aftabuzzaman, Md; Dec, Jan; Kleemann, Wolfgang; Kojima, Seiji

    2016-10-01

    The electric field effects on the elastic properties of uniaxial Ca x Ba1- x Nb2O6 (x = 0.30, CBN30) single crystals were investigated using broadband Brillouin scattering spectroscopy as functions of temperature and electric field. Remarkable thermal hysteresis was observed between zero field heating and zero field cooling processes. A stretching index β = 2.05 indicates the stretched critical slowing down of polar nanoregions (PNRs). The effect of electric field along [001] direction was clearly observed. Under 1.0 kV/cm field, the alignment of nanodomains and enhancement of the long-range ferroelectric order were observed in the ferroelectric phase. In the field dependent measurement, a mixed state consisting of macrodomains induced by the electric field and nanodomains caused by the random fields was observed at 3.0 kV/cm. The mixed state persists up to 13 kV/cm because of the incomplete switching of the nanodomains to the macrodomains state. A very strong memory effect was also observed.

  2. Propagation of an Airy-Gaussian beam in uniaxial crystals

    NASA Astrophysics Data System (ADS)

    Zhou, Mei-Ling; Chen, Chi-Dao; Chen, Bo; Peng, Xi; Peng, Yu-Lian; Deng, Dong-Mei

    2015-12-01

    Under the paraxial approximation, the analytical propagation expression of an Airy-Gaussian beam (AiGB) in uniaxial crystals orthogonal to the optical axis is investigated. The propagation dynamics of the AiGB is given for different ratios of the extraordinary index to the ordinary refractive index. It has been found that the continuity and the self-bending effect of AiGB become weaker when the ratio increases. From the figure of the maximum intensity of AiGB, one can see that the maximum intensity is not monotone decreasing due to the anisotropic effect of the crystals. The intensity distribution of AiGB in different distribution factors is shown. The AiGB converges toward a Gaussian beam as the distribution factor increases. Project supported by the National Natural Science Foundation of China (Grant Nos. 11374108 and 10904041), the Foundation for the Author of Guangdong Provincial Excellent Doctoral Dissertation, China (Grant No. SYBZZXM201227), the Foundation of Cultivating Outstanding Young Scholars (“Thousand, Hundred, Ten” Program) of Guangdong Province in China, and the Fund from the Key Laboratory of Geospace Environment, University of Science and Technology of China, Chinese Academy of Sciences.

  3. Propagation optical quarks after an uniaxial crystal: the experiment

    NASA Astrophysics Data System (ADS)

    Egorov, Yu. A.; Konovalenko, V. L.; Zinovev, A. O.; Anischenko, P. M.; Glumova, M. V.

    2013-12-01

    There is a lots of different papers reporting about the propagation of the different types of an optical beams in a uniaxial crystals are known by that time. This beams are: Lager-Gaussian and Bessel- Gaussian beams. It is common for all this types of beams, that if propagation axis and crystal axis coincides, and accident beam had a circular polarization, are can get type spiral type degenerated umbilici, which corresponds to the charge 2 optical vortex in the orthogonal polarized beam component, generated by crystal [1] (Fig 1). This generation accurse due to total angular momentum conservation law symmetry axis of the crystal. One to the changing of the spin momentum which is associated with the beam polarization, this leads to the orbital momentum changes that associated with topological charge of formed orthogonal circular component. Double charged optical vortex could be easily perturbed by tilting beam axis with respect to the crystal axis. If the tilt angles are small (<0.1°) central umbilici splits on two lemons and the surrounding ring umbilici splits on two pairs of monster-star. The further increasing of the tilt angle leads to the topological charge of circular components becomes, equal, and additional orbital moment correspond to the beam mass center displacement.

  4. Intergranular stress distributions in polycrystalline aggregates of irradiated stainless steel

    NASA Astrophysics Data System (ADS)

    Hure, J.; El Shawish, S.; Cizelj, L.; Tanguy, B.

    2016-08-01

    In order to predict InterGranular Stress Corrosion Cracking (IGSCC) of post-irradiated austenitic stainless steel in Light Water Reactor (LWR) environment, reliable predictions of intergranular stresses are required. Finite elements simulations have been performed on realistic polycrystalline aggregate with recently proposed physically-based crystal plasticity constitutive equations validated for neutron-irradiated austenitic stainless steel. Intergranular normal stress probability density functions are found with respect to plastic strain and irradiation level, for uniaxial loading conditions. In addition, plastic slip activity jumps at grain boundaries are also presented. Intergranular normal stress distributions describe, from a statistical point of view, the potential increase of intergranular stress with respect to the macroscopic stress due to grain-grain interactions. The distributions are shown to be well described by a master curve once rescaled by the macroscopic stress, in the range of irradiation level and strain considered in this study. The upper tail of this master curve is shown to be insensitive to free surface effect, which is relevant for IGSCC predictions, and also relatively insensitive to small perturbations in crystallographic texture, but sensitive to grain shapes.

  5. Electrical Characteristics of the Uniaxial-Strained nMOSFET with a Fluorinated HfO2/SiON Gate Stack

    PubMed Central

    Chen, Yung-Yu

    2014-01-01

    The channel fluorine implantation (CFI) process was integrated with the Si3N4 contact etch stop layer (SiN CESL) uniaxial-strained n-channel metal-oxide-semiconductor field-effect transistor (nMOSFET) with the hafnium oxide/silicon oxynitride (HfO2/SiON) gate stack. The SiN CESL process clearly improves basic electrical performance, due to induced uniaxial tensile strain within the channel. However, further integrating of the CFI process with the SiN CESL-strained nMOSFET exhibits nearly identical transconductance, subthreshold swing, drain current, gate leakage and breakdown voltage, which indicates that the strain effect is not affected by the fluorine incorporation. Moreover, hydrogen will diffuse toward the interface during the SiN deposition, then passivate dangling bonds to form weak Si-H bonds, which is detrimental for channel hot electron stress (CHES). Before hydrogen diffusion, fluorine can be used to terminate oxygen vacancies and dangling bonds, which can create stronger Hf-F and Si-F bonds to resist consequent stress. Accordingly, the reliability of constant voltage stress (CVS) and CHES for the SiN CESL uniaxial-strained nMOSFET can be further improved by the fluorinated HfO2/SiON using the CFI process. Nevertheless, the nMOSFET with either the SiN CESL or CFI process exhibits less charge detrapping, which means that a greater part of stress-induced charges would remain in the gate stack after nitrogen (SiN CESL) or fluorine (CFI) incorporation. PMID:28788572

  6. How to describe disordered structures

    NASA Astrophysics Data System (ADS)

    Nishio, Kengo; Miyazaki, Takehide

    2016-04-01

    Disordered structures such as liquids and glasses, grains and foams, galaxies, etc. are often represented as polyhedral tilings. Characterizing the associated polyhedral tiling is a promising strategy to understand the disordered structure. However, since a variety of polyhedra are arranged in complex ways, it is challenging to describe what polyhedra are tiled in what way. Here, to solve this problem, we create the theory of how the polyhedra are tiled. We first formulate an algorithm to convert a polyhedron into a codeword that instructs how to construct the polyhedron from its building-block polygons. By generalizing the method to polyhedral tilings, we describe the arrangements of polyhedra. Our theory allows us to characterize polyhedral tilings, and thereby paves the way to study from short- to long-range order of disordered structures in a systematic way.

  7. How to describe disordered structures

    PubMed Central

    Nishio, Kengo; Miyazaki, Takehide

    2016-01-01

    Disordered structures such as liquids and glasses, grains and foams, galaxies, etc. are often represented as polyhedral tilings. Characterizing the associated polyhedral tiling is a promising strategy to understand the disordered structure. However, since a variety of polyhedra are arranged in complex ways, it is challenging to describe what polyhedra are tiled in what way. Here, to solve this problem, we create the theory of how the polyhedra are tiled. We first formulate an algorithm to convert a polyhedron into a codeword that instructs how to construct the polyhedron from its building-block polygons. By generalizing the method to polyhedral tilings, we describe the arrangements of polyhedra. Our theory allows us to characterize polyhedral tilings, and thereby paves the way to study from short- to long-range order of disordered structures in a systematic way. PMID:27064833

  8. Statistical properties of a nonparaxial Gaussian Schell-model beam in a uniaxial crystal.

    PubMed

    Zhang, Lina; Cai, Yangjian

    2011-07-04

    Nonparaxial propagation theory of coherent beams in a uniaxial crystal is extended to the partially coherent case. An analytical formula for the 3×3 cross-spectral density matrix of a nonparaxial Gaussian Schell-model (GSM) beam propagating in a uniaxial crystal orthogonal to the optical axis is derived. Statistical properties, such as the spectral intensity and the degree of polarization, of a nonparaxial GSM beam in a uniaxial crystal are studied numerically. It is found that the statistical properties of a nonparaxial GSM beam are closely determined by its initial beam parameters and the parameters of the crystal. Uniaxial crystal can be used to modulate the spectral density and degree of polarization of a nonparaxial partially coherent beam. Our results may be useful in some applications, such as optical trapping and nonlinear optics, where a light beam with special beam profile and polarization is required.

  9. Electromagnetic Field Representations in Uniaxial Bianisotropic-Semiconductor Material by Cylindrical Vector Wave Functions

    NASA Astrophysics Data System (ADS)

    Cheng, Dajun

    1997-01-01

    Uniaxial bianisotropic-semiconductor material is a generalization of the well-studied semiconductor material and uniaxial medium. It could be realized by arranging chiral objects in a host semiconductor medium, with a preferred direction. This class of material probably opens up the opportunity to realize artificial intelligence in living organisms. In the present study, based on the concept of characteristic waves and the method of angular spectral expansion, electromagnetic field representations in this class of materials are developed. The analysis indicates that solutions of source-free Maxwell equations for uniaxial bianisotropic-semiconductor material can be represented in sum-integral forms of cylindrical vector wave functions. Addition theorem of vector wave functions for uniaxial bianisotropic-semiconductor material can be straightforwardly derived from that of vector wave functions for isotropic medium. An application of the proposed theory in scattering is presented to show how to use these formulations in a practical way.

  10. Isotropic shrinkage of the oxygen octahedron in SrTiO3 under uniaxial pressure

    NASA Astrophysics Data System (ADS)

    Lu, Cong; Temba, Chisato; Nakajima, Nobuo; Kawakami, Shuhei; Ishimatsu, Naoki; Maruyama, Hiroshi

    2017-10-01

    X-ray absorption spectra at the Ti K-edge of a SrTiO3 single crystal under uniaxial pressure were measured to obtain evidence of uniaxial pressure-induced polarization predicted in SrTiO3 from the electronic viewpoint. The pre-edge 3d-e g peak decreases in intensity with increasing uniaxial pressure, together with an energy shift to higher energy side. Contrary to uniaxial deformation, these changes were independent of incident x-ray polarization. This implies the presence of a mechanism that maintains the isotropic coordination environment around a Ti atom, i.e. a tilt and rotation of the TiO6 octahedron accompanied by its isotropic shrinkage, hence the local polarization essential to the ferroelectric order cannot be observed.

  11. Validation of uniaxial and triaxial accelerometers for the assessment of physical activity in preschool children

    USDA-ARS?s Scientific Manuscript database

    Given the unique physical activity patterns of preschoolers, wearable electronic devices for quantitative assessment of physical activity require validation in this population. Study objective was to validate uniaxial and triaxial accelerometers in preschoolers. Room calorimetry was performed over 3...

  12. Computational Study of Uniaxial Deformations in Silica Aerogel Using a Coarse-Grained Model.

    PubMed

    Ferreiro-Rangel, Carlos A; Gelb, Lev D

    2015-07-09

    Simulations of a flexible coarse-grained model are used to study silica aerogels. This model, introduced in a previous study (J. Phys. Chem. C 2007, 111, 15792), consists of spherical particles which interact through weak nonbonded forces and strong interparticle bonds that may form and break during the simulations. Small-deformation simulations are used to determine the elastic moduli of a wide range of material models, and large-deformation simulations are used to probe structural evolution and plastic deformation. Uniaxial deformation at constant transverse pressure is simulated using two methods: a hybrid Monte Carlo approach combining molecular dynamics for the motion of individual particles and stochastic moves for transverse stress equilibration, and isothermal molecular dynamics simulations at fixed Poisson ratio. Reasonable agreement on elastic moduli is obtained except at very low densities. The model aerogels exhibit Poisson ratios between 0.17 and 0.24, with higher-density gels clustered around 0.20, and Young's moduli that vary with aerogel density according to a power-law dependence with an exponent near 3.0. These results are in agreement with reported experimental values. The models are shown to satisfy the expected homogeneous isotropic linear-elastic relationship between bulk and Young's moduli at higher densities, but there are systematic deviations at the lowest densities. Simulations of large compressive and tensile strains indicate that these materials display a ductile-to-brittle transition as the density is increased, and that the tensile strength varies with density according to a power law, with an exponent in reasonable agreement with experiment. Auxetic behavior is observed at large tensile strains in some models. Finally, at maximum tensile stress very few broken bonds are found in the materials, in accord with the theory that only a small fraction of the material structure is actually load-bearing.

  13. Stress state dependence of transient irradiation creep in 20% cold worked 316 stainless steel

    NASA Astrophysics Data System (ADS)

    Foster, John Paul; Bunde, Kermit; Gilbert, E. Robert

    1998-11-01

    Irradiation creep tests were performed in fast reactors using the stress states of uniaxial tension, biaxial tension, bending and torsion. In order to compare the saturated transient strain irradiation creep component, the test data were converted to equivalent strain and equivalent stress. The saturated transient irradiation creep component was observed to depend on the stress state. The highest value was exhibited by the uniaxial tension stress state, and the lowest by the torsion stress state. The biaxial tension and bending stress state transient component values were intermediate. This behavior appears to be related to the dislocation or microscopic substructure resulting from fabrication processing and the applied stress direction.

  14. Evaluation of uniaxial and triaxial shock isolation techniques for a piezoresistive accelerometer

    NASA Astrophysics Data System (ADS)

    Bateman, Vesta I.; Bell, R. Glenn, III; Brown, Fred A.; Davie, Neil T.; Nusser, Michael A.

    Development of both uniaxial and triaxial shock isolation techniques for pyroshock and impact tests has continued this year. The uniaxial shock isolation technique has demonstrated acceptable characteristics for a temperature range of -50 F to +186 F and a frequency bandwidth of DC to 10 kHz. The triaxial shock isolation technique has demonstrated acceptable results for a temperature range of -50 F to 70 F and a frequency bandwidth of DC to 10 kHz.

  15. Propagation properties of elliptical Gaussian beam in uniaxial crystals along the optical axis

    NASA Astrophysics Data System (ADS)

    Liu, Dajun; Wang, He; Wang, Yaochuan; Yin, Hongming

    2015-10-01

    Based on the paraxial vectorial theory of beams propagating in uniaxial anisotropic crystal, we have derived the analytical propagation equations of elliptical Gaussian beam in uniaxial crystal along the optical axis, and given the typical numerical example to illustrate our analytical results. It is found that the x-polarized Gaussian beams split into an ordinary beam and an extraordinary beam, which independently propagate along the optical axis, and the elliptical Gaussian beam loses its initial profile with the propagation distance increasing.

  16. Challenges in describing ribosome dynamics

    NASA Astrophysics Data System (ADS)

    Nguyen, Kien; Whitford, Paul Charles

    2017-04-01

    For decades, protein folding and functional dynamics have been described in terms of diffusive motion across an underlying energy landscape. With continued advances in structural biology and high-performance computing, the field is positioned to extend these approaches to large biomolecular assemblies. Through the application of energy landscape techniques to the ribosome, one may work towards establishing a comprehensive description of the dynamics, which will bridge theoretical concepts and experimental observations. In this perspective, we discuss a few of the challenges that will need to be addressed as we extend the application of landscape principles to the ribosome.

  17. Uniaxial strain-induced mechanical and electronic property modulation of silicene

    PubMed Central

    2014-01-01

    We perform first-principles calculations of mechanical and electronic properties of silicene under uniaxial strains. Poisson's ratio and the rigidity of silicene show strong chirality dependence under large uniaxial strains. The ultimate strains of silicene with uniaxial strain are smaller than those with biaxial strain. We find that uniaxial strains induce Dirac point deviation from the high-symmetry points in the Brillouin zone and semimetal-metal transitions. Therefore, no bandgap opens under the uniaxial strain. Due to its peculiar structure and variable sp3/sp2 ratio of the chemical bond, the deviation directions of Dirac points from the high-symmetry points in the Brillouin zone and variation of Fermi velocities of silicene exhibit significant difference from those of graphene. Fermi velocities show strong anisotropy with respect to the wave vector directions and change slightly before the semimetal-metal transition. We also find that the work function of silicene increases monotonously with the increasing uniaxial strains. PACS numbers 61.46.-w; 62.20.D-; 73.22.Dj PMID:25276108

  18. The anisotropy of magnetic susceptibility of uniaxial superparamagnetic particles: Consequences for its interpretation in magnetite and maghemite bearing rocks

    NASA Astrophysics Data System (ADS)

    Lanci, Luca; Zanella, Elena

    2016-01-01

    A simple model that provides a quantitative description of the magnetic susceptibility of superparamagnetic to stable single-domain uniaxial magnetic particles can be built in the framework of the theory of stochastic resonance. This model expands that of Mullins and Tile (1973) for superparamagnetic grains by considering the dependence of superparamagnetic susceptibility on the particle orientation and thus describes the anisotropy of magnetic susceptibility (AMS) of ensembles of superparamagnetic as well as single-domain particles. The theory predicts that on the contrary of stable single domain, the maximum anisotropy of superparamagnetic particles is parallel to their easy axis and shows that the AMS of ensembles of uniaxial particle is strongly dependent on the distribution of particle grain size, coercivity, measurement temperature, and frequency. It also explains why the inverse AMS pattern expected for stable single-domain particles is rarely observed in natural samples. We use examples of well-characterized obsidian specimens to show that, as predicted by the theory, in the presence of significant superparamagnetic contributions, the maximum susceptibility axis of AMS is directed along the preferential direction of particles easy axis.

  19. Role of Molecular Structure on X-ray Diffraction in Uniaxial and Biaxial Phases of Thermotropic Liquid Crystals

    SciTech Connect

    Acharya, Bharat R.; Kang, Shin-Woong; Prasad, Veena; Kumar, Satyendra

    2009-04-29

    X-ray diffraction is one of the most definitive methods to determine the structure of condensed matter phases, and it has been applied to unequivocally infer the structures of conventional calamitic and lyotropic liquid crystals. With the advent of bent-core and tetrapodic mesogens and the discovery of the biaxial nematic phase in them, the experimental results require more careful interpretation and analysis. Here, we present ab-initio calculations of X-ray diffraction patterns in the isotropic, uniaxial nematic, and biaxial nematic phases of bent-core mesogens. A simple Meier-Saupe-like molecular distribution function is employed to describe both aligned and unaligned mesophases. The distribution function is decomposed into two, polar and azimuthal, distribution functions to calculate the effect of the evolution of uniaxial and biaxial nematic orientational order. The calculations provide satisfactory semiquantitative interpretations of experimental results. The calculations presented here should provide a pathway to more refined and quantitative analysis of X-ray diffraction data from the biaxial nematic phase.

  20. Role of Molecular Structure on X-ray Diffraction in Thermotropic Uniaxial and Biaxial Nematic Liquid Crystal Phases

    SciTech Connect

    Acharya, Bharat R.; Kang, Shin-Woong; Prasad, Veena; Kumar, Satyendra

    2009-08-27

    X-ray diffraction is one of the most definitive methods to determine the structure of condensed matter phases, and it has been applied to unequivocally infer the structures of conventional calamitic and lyotropic liquid crystals. With the advent of bent-core and tetrapodic mesogens and the discovery of the biaxial nematic phase in them, the experimental results require more careful interpretation and analysis. Here, we present ab-initio calculations of X-ray diffraction patterns in the isotropic, uniaxial nematic, and biaxial nematic phases of bent-core mesogens. A simple Meier-Saupe-like molecular distribution function is employed to describe both aligned and unaligned mesophases. The distribution function is decomposed into two, polar and azimuthal, distribution functions to calculate the effect of the evolution of uniaxial and biaxial nematic orientational order. The calculations provide satisfactory semiquantitative interpretations of experimental results. The calculations presented here should provide a pathway to more refined and quantitative analysis of X-ray diffraction data from the biaxial nematic phase.

  1. Ultrasonic properties of random media under uniaxial loading

    NASA Astrophysics Data System (ADS)

    Insana, M. F.; Hall, T. J.; Chaturvedi, P.; Kargel, Ch.

    2001-12-01

    Acoustic properties of two types of soft tissue-like media were measured as a function of compressive strain. Samples were subjected to uniaxial strains up to 40% along the axis of the transducer beam. Measurements were analyzed to test a common assumption made when using pulse-echo waveforms to track motion in soft tissues-that local properties of wave propagation and scattering are invariant under deformation. Violations of this assumption have implications for elasticity imaging procedures and could provide new opportunities for identifying the sources of backscatter in biological media such as breast parenchyma. We measured speeds of sound, attenuation coefficients, and echo spectra in compressed phantoms containing randomly positioned scatterers either stiffer or softer than the surrounding gelatin. Only the echo spectra of gel media with soft scatterers varied significantly during compression. Centroids of the echo spectra were found to be shifted to higher frequencies in proportion to the applied strain up to 10%, and increased monotonically up to 40% at a rate depending on the scatterer size. Centroid measurements were accurately modeled by assuming incoherent scattering from oblate spheroids with an eccentricity that increases with strain. While spectral shifts can be accurately modeled, recovery of lost echo coherence does not seem possible. Consequently, spectral variance during compression may ultimately limit the amount of strain that can be applied between two data fields in heterogeneous media such as lipid-filled tissues. It also appears to partially explain why strain images often produce greater echo decorrelation in tissues than in commonly used graphite-gelatin test phantoms.

  2. On the use of a split Hopkinson pressure bar in structural geology: High strain rate deformation of Seeberger sandstone and Carrara marble under uniaxial compression

    NASA Astrophysics Data System (ADS)

    Zwiessler, Ruprecht; Kenkmann, Thomas; Poelchau, Michael H.; Nau, Siegfried; Hess, Sebastian

    2017-04-01

    There is increasing evidence that seismogenic fractures can propagate faster than the shear wave velocity of the surrounding rocks. Strain rates within the tip region of such super-shear earthquake ruptures can reach deformation conditions similar to impact processes, resulting in rock pulverization. The physical response of brittle rocks at high strain rates changes dramatically with respect to quasi-static conditions. Rocks become stiffer and their strength increases. A measure for the dynamic behavior of a rock and its strain dependency is the dynamic increase factor (DIF) which is the ratio of the dynamic compressive strength to the quasi-static uniaxial compressive strength. To investigate deformation in the high strain rate regime experimentally, we introduce the split Hopkinson pressure bar technology to the structural geology community, a method that is frequently used by rock and impact engineers. We measure the stress-strain response of homogeneous, fine-grained Seeberger sandstone and Carrara marble in uniaxial compression at strain rates ranging from 10+1 to 10+2 s-1 with respect to tangent modulus and dynamic uniaxial compressive strength. We present full stress-strain response curves of Seeberger sandstone and Carrara marble at high strain rates and an evaluation method to determine representative rates of deformation. Results indicate a rate-dependent elastic behavior of Carrara marble where an average increase of ∼18% could be observed at high strain rates of about 100 s-1. DIF reaches a factor of 2.2-2.4. Seeberger sandstone does not have a rate-dependent linear stress-strain response at high strain rates. Its DIF was found to be about 1.6-1.7 at rates of 100 s-1. The onset of dynamic behavior is accompanied with changes in the fracture pattern from single to multiple fractures to pervasive pulverization for increasing rates of deformation. Seismogenic shear zones and their associated fragment-size spectra should be carefully revisited in the

  3. Five Describing Factors of Dyslexia.

    PubMed

    Tamboer, Peter; Vorst, Harrie C M; Oort, Frans J

    2016-09-01

    Two subtypes of dyslexia (phonological, visual) have been under debate in various studies. However, the number of symptoms of dyslexia described in the literature exceeds the number of subtypes, and underlying relations remain unclear. We investigated underlying cognitive features of dyslexia with exploratory and confirmatory factor analyses. A sample of 446 students (63 with dyslexia) completed a large test battery and a large questionnaire. Five factors were found in both the test battery and the questionnaire. These 10 factors loaded on 5 latent factors (spelling, phonology, short-term memory, rhyme/confusion, and whole-word processing/complexity), which explained 60% of total variance. Three analyses supported the validity of these factors. A confirmatory factor analysis fit with a solution of five factors (RMSEA = .03). Those with dyslexia differed from those without dyslexia on all factors. A combination of five factors provided reliable predictions of dyslexia and nondyslexia (accuracy >90%). We also looked for factorial deficits on an individual level to construct subtypes of dyslexia, but found varying profiles. We concluded that a multiple cognitive deficit model of dyslexia is supported, whereas the existence of subtypes remains unclear. We discussed the results in relation to advanced compensation strategies of students, measures of intelligence, and various correlations within groups of those with and without dyslexia. © Hammill Institute on Disabilities 2014.

  4. Thickness-dependent Crack Propagation in Uniaxially Strained Conducting Graphene Oxide Films on Flexible Substrates.

    PubMed

    Sakorikar, Tushar; Kavitha, Maheswari Kavirajan; Vayalamkuzhi, Pramitha; Jaiswal, Manu

    2017-06-01

    We demonstrate that crack propagation in uniaxially strained reduced graphene oxide (rGO) films is substantially dependent on the film thickness, for films in the sub-micron regime. rGO film on flexible polydimethylsiloxane (PDMS) substrate develop quasi-periodic cracks upon application of strain. The crack density and crack width follow contrasting trends as film thickness is increased and the results are described in terms of a sequential cracking model. Further, these cracks also have a tendency to relax when the strain is released. These features are also reflected in the strain-dependent electrical dc and ac conductivity studies. For an optimal thickness (3-coat), the films behave as strain-resistant, while for all other values it becomes strain-responsive, attributed to a favorable combination of crack density and width. This study of the film thickness dependent response and the crack propagation mechanism under strain is a significant step for rationalizing the application of layered graphene-like systems for flexible optoelectronic and strain sensing applications. When the thickness is tuned for enhanced extent of crack propagation, strain-sensors with gauge factor up to ∼470 are realized with the same material. When thickness is chosen to suppress the crack propagation, strain-resistive flexible TiO2- rGO UV photoconductor is realized.

  5. A Numerical Method for Simulating the Microscopic Damage Evolution in Composites Under Uniaxial Transverse Tension

    NASA Astrophysics Data System (ADS)

    Zhi, Jie; Zhao, Libin; Zhang, Jianyu; Liu, Zhanli

    2016-06-01

    In this paper, a new numerical method that combines a surface-based cohesive model and extended finite element method (XFEM) without predefining the crack paths is presented to simulate the microscopic damage evolution in composites under uniaxial transverse tension. The proposed method is verified to accurately capture the crack kinking into the matrix after fiber/matrix debonding. A statistical representative volume element (SRVE) under periodic boundary conditions is used to approximate the microstructure of the composites. The interface parameters of the cohesive models are investigated, in which the initial interface stiffness has a great effect on the predictions of the fiber/matrix debonding. The detailed debonding states of SRVE with strong and weak interfaces are compared based on the surface-based and element-based cohesive models. The mechanism of damage in composites under transverse tension is described as the appearance of the interface cracks and their induced matrix micro-cracking, both of which coalesce into transversal macro-cracks. Good agreement is found between the predictions of the model and the in situ experimental observations, demonstrating the efficiency of the presented model for simulating the microscopic damage evolution in composites.

  6. Uni-axial stretching regulates intracellular localization of Hic-5 expressed in smooth-muscle cells in vivo.

    PubMed

    Kim-Kaneyama, Joo-ri; Suzuki, Wataru; Ichikawa, Kiyoko; Ohki, Takahiro; Kohno, Yoko; Sata, Masataka; Nose, Kiyoshi; Shibanuma, Motoko

    2005-03-01

    Hic-5 is a focal adhesion protein belonging to the paxillin LIM family that shuttles in and out of the nucleus. In the present study, we examined the expression of Hic-5 among mouse tissues by immunohistochemistry and found its expression only in smooth-muscle cells in several tissues. This result is consistent with a previous report on adult human tissues and contradicts the relatively ubiquitous expression of paxillin, the protein most homologous to Hic-5. One factor characterizing smooth-muscle cells in vivo is a continuous exposure to mechanical stretching in the organs. To study the involvement of Hic-5 in cellular responses to mechanical stress, we exposed mouse embryo fibroblasts to a uni-axial cyclic stretching and found that Hic-5 was relocalized from focal adhesions to stress fibers through its C-terminal LIM domains during the stress. In sharp contrast to this, paxillin did not change its focal-adhesion-based localization. Of the factors tested, which included interacting partners of Hic-5, only CRP2 (an only-LIM protein expressed in vascular smooth-muscle cells) and GIT1 were, like Hic-5, localized to stress fibers during the cyclic stretching. Interestingly, Hic-5 showed a suppressive effect on the contractile capability of cells embedded in three-dimensional collagen gels, and the effect was further augmented when CRP2 co-localized with Hic-5 to fiber structures of those cells. These results suggested that Hic-5 was a mediator of tensional force, translocating directly from focal adhesions to actin stress fibers upon mechanical stress and regulating the contractile capability of cells in the stress fibers.

  7. New Magnetically Uniaxial Phases in the Samarium, Iron Binary System.

    NASA Astrophysics Data System (ADS)

    Rani, Raj

    1995-01-01

    For the first time, films magnets of binary rm Sm_5Fe_{17}, and SmFe_{12}, magnetically uniaxial phases have been sputter synthesized without any addition of a phase stabilizing third element. Perpendicular to the film plane, the room temperature saturation magnetization for highly (002) aligned film samples of SmFe_ {12} phase were measured to be 14.3 +/- 0.5 kG and the estimated anisotropy field was 130 +/- 10 kOe. X-ray diffraction studies, hysterisis loop measurements, composition measurements, and projection of moment calculations allowed to identify the SmFe_{12} phase as ThMn_{12} type tetragonal structure with a = 8.438 +/- 0.006 A, and c = 4.805 +/- 0.006 A. Film samples of this phase were synthesized by depositing the material on preheated substrates. For rm Sm_5Fe_{17} phase, the material was first deposited in amorphous form and subsequently crystallized. rm Sm_5Fe_{17 } film samples were synthesized with record high room temperature coercivity of 14.1 kOe for the two element Sm, Fe system. On nitriding rm Sm _2Fe_{17}, profound changes in magnetic properties have occurred, room temperature inplane coercivity rose from 0.75 kOe to 23 kOe. The rm Sm_2Fe_{17}N_ {x} compound retained its parent structure with the cell volume increase of ~7%. The room temperature coercivity as a function of the Sm concentration reached a maximum value of ~23 kOe at a slightly richer than stoichiometric Sm composition. High anisotropy (002) textured film samples of rm Pr(Fe_{12-y-z},Co_{y},Mo _{z})N_{x}, where y = 0-2.5, and z = 0.4-1.0 compounds were synthesized with so far the highest coercivity of 9.4 kOe. X-ray diffraction data showed that the ThMn_{12} type tetragonal structure was retained with a saturation increase in the cell volume over the first 15 minutes of nitriding time at 750 K. The coercivity reached a maximum for nitriding time of 25 minutes of nitriding time. For rm Pr_{1.04}Fe_{10.36 }Co_{1.16}Mo_{0.44}N _{x} sample measured at 293 K, perpendicular to the

  8. Effects of uniaxial strain on electron effective mass and tunneling capability of direct gap Ge1-xSnx alloys

    NASA Astrophysics Data System (ADS)

    Liu, Lei; Liang, Renrong; Wang, Jing; Xu, Jun

    2016-01-01

    Direct gap Ge1-xSnx alloys under [100] and [110] uniaxial strain are comprehensively investigated by theoretical calculations using the nonlocal empirical pseudopotential method (EPM). It is shown that [100] uniaxial tensile strain aids indirect-to-direct gap transition in Ge1-xSnx alloys. The Γ electron effective mass along the optimal direction under [110] uniaxial strain is smaller than those under [100] uniaxial strain and (001) biaxial strain. Additionally, the direct tunneling gap is smallest along the strain-perpendicular direction under [110] uniaxial tensile strain, resulting in a maximum direct band-to-band tunneling generation rate. An optimal [110] uniaxial tensile strain is favorable for high-performance direct gap Ge1-xSnx electronic devices.

  9. Origins of asymmetric stress-strain response in phase transformations

    SciTech Connect

    Sehitoglu, H.; Gall, K.

    1997-12-31

    It has been determined that the transformation stress-strain behavior of CuZnAl and NiTi shape memory alloys is dependent on the applied stress state. The uniaxial compressive stress necessary to macroscopically trigger the transformation is approximately 34% (CuZnAl) and 26% (NiTi) larger than the required uniaxial tensile stress. For three dimensional stress states, the response of either alloy system is dependent on the directions of the dominant principal stresses along with the hydrostatic stress component of the stress state. The stress state effects are dominated by the favored growth and nucleation of more martensite plates in tension versus compression. The effect of different hydrostatic pressure levels between stress states on martensite plates volume change is considered small.

  10. Uniaxial and triaxial compression tests of silicon carbide ceramics under quasi-static loading condition.

    SciTech Connect

    Brannon, Rebecca Moss; Lee, Moo Yul; Bronowski, David R.

    2005-02-01

    To establish mechanical properties and failure criteria of silicon carbide (SiC-N) ceramics, a series of quasi-static compression tests has been completed using a high-pressure vessel and a unique sample alignment jig. This report summarizes the test methods, set-up, relevant observations, and results from the constitutive experimental efforts. Results from the uniaxial and triaxial compression tests established the failure threshold for the SiC-N ceramics in terms of stress invariants (I{sub 1} and J{sub 2}) over the range 1246 < I{sub 1} < 2405. In this range, results are fitted to the following limit function (Fossum and Brannon, 2004) {radical}J{sub 2}(MPa) = a{sub 1} - a{sub 3}e -a{sub 2}(I{sub 1}/3) + a{sub 4} I{sub 1}/3, where a{sub 1} = 10181 MPa, a{sub 2} = 4.2 x 10{sup -4}, a{sub 3} = 11372 MPa, and a{sub 4} = 1.046. Combining these quasistatic triaxial compression strength measurements with existing data at higher pressures naturally results in different values for the least-squares fit to this function, appropriate over a broader pressure range. These triaxial compression tests are significant because they constitute the first successful measurements of SiC-N compressive strength under quasistatic conditions. Having an unconfined compressive strength of {approx}3800 MPa, SiC-N has been heretofore tested only under dynamic conditions to achieve a sufficiently large load to induce failure. Obtaining reliable quasi-static strength measurements has required design of a special alignment jig and load-spreader assembly, as well as redundant gages to ensure alignment. When considered in combination with existing dynamic strength measurements, these data significantly advance the characterization of pressure-dependence of strength, which is important for penetration simulations where failed regions are often at lower pressures than intact regions.

  11. Orientation-specific responses to sustained uniaxial stretching in focal adhesion growth and turnover

    PubMed Central

    Chen, Yun; Pasapera, Ana M.; Koretsky, Alan P.; Waterman, Clare M.

    2013-01-01

    Cells are mechanosensitive to extracellular matrix (ECM) deformation, which can be caused by muscle contraction or changes in hydrostatic pressure. Focal adhesions (FAs) mediate the linkage between the cell and the ECM and initiate mechanically stimulated signaling events. We developed a stretching apparatus in which cells grown on fibronectin-coated elastic substrates can be stretched and imaged live to study how FAs dynamically respond to ECM deformation. Human bone osteosarcoma epithelial cell line U2OS was transfected with GFP-paxillin as an FA marker and subjected to sustained uniaxial stretching. Two responses at different timescales were observed: rapid FA growth within seconds after stretching, and delayed FA disassembly and loss of cell polarity that occurred over tens of minutes. Rapid FA growth occurred in all cells; however, delayed responses to stretch occurred in an orientation-specific manner, specifically in cells with their long axes perpendicular to the stretching direction, but not in cells with their long axes parallel to stretch. Pharmacological treatments demonstrated that FA kinase (FAK) promotes but Src inhibits rapid FA growth, whereas FAK, Src, and calpain 2 all contribute to delayed FA disassembly and loss of polarity in cells perpendicular to stretching. Immunostaining for phospho-FAK after stretching revealed that FAK activation was maximal at 5 s after stretching, specifically in FAs oriented perpendicular to stretch. We hypothesize that orientation-specific activation of strain/stress-sensitive proteins in FAs upstream to FAK and Src promote orientation-specific responses in FA growth and disassembly that mediate polarity rearrangement in response to sustained stretch. PMID:23754369

  12. Ab initio study of Co and Ni under uniaxial and biaxial loading and in epitaxial overlayers

    NASA Astrophysics Data System (ADS)

    Zelený, M.; Legut, D.; Šob, M.

    2008-12-01

    A detailed theoretical study of structural and magnetic behaviors of cubic cobalt and nickel along the bcc-fcc (Bain) transformation paths as well as of hcp cobalt and nickel loaded uniaxially along the [0001] direction at various atomic volumes is presented. The total energies are calculated by spin-polarized full-potential linearized augmented plane-wave method within the generalized gradient approximation and are displayed in contour plots as functions of tetragonal or hcp c/a ratio and atomic volume; the borderlines between the ferromagnetic and nonmagnetic phases are shown. Stability of possible ferromagnetic phases of bcc nickel is analyzed. The calculated contour plots are used to explain and predict the lattice parameters and magnetic states of tetragonal and hcp cobalt and nickel overlayers on various (001) or (111) substrates, respectively. In case of tetragonally deformed structures, the stresses needed to keep the thin films coherent with the substrates are also determined and all Co and Ni overlayers on (001) cubic substrates are predicted to be ferromagnetic. The agreement of available experimental data for Co and Ni overlayers with the results of bulk calculations is remarkable and suggests that the geometrical effect of the substrate, i.e., imposing the lattice dimensions of the substrate in the plane of the film to the film material, is one of the most important factors determining the structure and properties of the film. In this way, the lattice parameters of Co and Ni overlayers may be very well understood in terms of properties of appropriately deformed bulk Co and Ni.

  13. An elastoplastic analysis of a uniaxially loaded sheet with an interference-fit bolt. [using the finite element method

    NASA Technical Reports Server (NTRS)

    Crews, J. H., Jr.

    1974-01-01

    The stresses and strains in a uniaxially loaded sheet with an unloaded interference-fit bolt were calculated by an elastoplastic finite-element analysis. The material properties represented a 7075-T6 aluminum alloy sheet and a steel bolt. The analysis considered the two ideal cases of no slip and no friction at the bolt-sheet interface for a single combination of bolt diameter, interference level, and cyclic loading. When the bolt was inserted, the sheet deformed plastically near the hole; the first tensile load cycle produced additional yielding, but subsequent cycles to the same level caused only elastic cyclic stresses. These stresses together with fatigue data for unnotched specimens were used to estimate crack initiation periods and initiation sites. The cases analyzed with interference-fit bolts were predicted to have crack initiation periods which were about 50 times that for a clearance-fit bolt. Crack initiation was predicted to occur on the transverse axis at a distance of about one radius from the hole.

  14. Field representations in uniaxial bianisotropic-ferrite medium by cylindrical vector wave functions

    NASA Astrophysics Data System (ADS)

    Cheng, Dajun; Lin, Weigan; Zhao, Yushen

    1995-04-01

    The uniaxial bianisotropic-ferrite medium is a generalization of the well-studied magnetically biased ferrite and uniaxial material. It can be manufactured either by immersing randomly oriented short helices and Ω-shaped particles in a magnetically biased ferrite, or by arranging short conductive helices in a magnetized ferrite in a certain manner. It has potential applications in microwave technology, antenna design, and antireflection shielding. In the present consideration, based on the concept of characteristic waves and the method of angular spectral expansion, field representations in uniaxial bianisotropic-ferrite medium are developed. The analysis reveals the solutions of source-free Maxwell's equations for uniaxial bianisotropic-ferrite medium can be represented in sum-integral forms of the circular cylindrical vector wave functions. The addition theorem of vector wave functions for uniaxial bianisotropic-ferrite medium can be straightforwardly derived from that of vector wave functions for isotropic medium. An application of the proposed theory in scattering is presented to show how to use these formulations in a practical way.

  15. Conoscopic polarized interference applied in measuring uniaxial axis direction of electro-optic crystal

    NASA Astrophysics Data System (ADS)

    Liu, Yong; Jiang, Hongzhen; Zhang, Lin; Li, Dong; Liu, Xu; Zheng, Fanglan

    2016-10-01

    The crystal can be used to be electro-optic switch because of its electro-optic modulation. Generally the uniaxial axis of electro-optic crystal is perpendicular to the light injection surface. Due to the manufacturing precision, the uniaxial axis direction has a little angle with the normal of the light injection surface, which affects the electro-optic modulation ability. In conoscopic polarized inference, due to birefraction the ordinary ray and extraordinary ray from crystal interferes after the polarizer. The interference pattern of crystal component is circle fringes with dark cross. The center of interference pattern has relation to the uniaxial axis direction. Using digital camera to capture the pattern and the center position of interferogram can be determinate by image processing program. In repeatability experiments the rms of center position is around 1 pixel. To measure the uniaxial axis direction, the normal direction of the crystal component should also be accurately determinate. Michelson interference method is introduced to determinate the normal direction. If rotate the crystal component around the normal direction in conoscopic polarized interference, the track of interferogram center is a circle theoretically. The circle center is related to the normal direction of crystal component, and the radii is related to the angle uniaxial axis, which can be determinate by least square fitting method. Experiment result shows that the measuring precision can achieves several tens of microradians.

  16. Mechanical and electronic properties of monolayer and bilayer phosphorene under uniaxial and isotropic strains

    NASA Astrophysics Data System (ADS)

    Hu, Ting; Han, Yang; Dong, Jinming

    2014-11-01

    The mechanical and electronic properties of both the monolayer and bilayer phosphorenes under either isotropic or uniaxial strain have been systematically investigated using first-principles calculations. It is interesting to find that: 1) Under a large enough isotropic tensile strain, the monolayer phosphorene would lose its pucker structure and transform into a flat hexagonal plane, while two inner sublayers of the bilayer phosphorene could be bonded due to its interlayer distance contraction. 2) Under the uniaxial tensile strain along a zigzag direction, the pucker distance of each layer in the bilayer phosphorene can exhibit a specific negative Poisson’s ratio. 3) The electronic properties of both the monolayer and bilayer phosphorenes are sensitive to the magnitude and direction of the applied strains. Their band gaps decrease more rapidly under isotropic compressive strain than under uniaxial strain. Also, their direct-indirect band gap transitions happen at the larger isotropic tensile strains compared with that under uniaxial strain. 4) Under the isotropic compressive strain, the bilayer phosphorene exhibits a transition from a direct-gap semiconductor to a metal. In contrast, the monolayer phosphorene initially has the direct-indirect transition and then transitions to a metal. However, under isotropic tensile strain, both the bilayer and monolayer phosphorene show the direct-indirect transition and, finally, the transition to a metal. Our numerical results may open new potential applications of phosphorene in nanoelectronics and nanomechanical devices by external isotropic strain or uniaxial strain along different directions.

  17. Pullout problem and fracture mechanism of quasi-brittle material reinforced with discontinous aligned fibers subjected to uniaxial tension

    NASA Astrophysics Data System (ADS)

    Cheng, Cheng-Jang

    The objective of this research is to characterize the postpeak pseudo strain-hardening behavior of the discontinuous aligned fiber composites subjected to uniaxial tension. In order to fully understand the fiber axial force-debonding relationship, fiber pullout problem was first investigated. Unlike most models this theory assumes a triangularly distributed interface shear stress. Besides, R-curve approach was adopted to evaluate the maximum pullout load. In quasi-brittle materials when the value of energy release rate G increases with the applied load, the value of crack resistance R also increases. As a result, the equality of G and R can only serve as the necessary condition for crack propagation. In order to further distinguish stable and unstable crack propagation, a second condition must be included. Namely, the first derivatives of G and R must also equal to each other for the onset of unstable crack propagation. The applied load corresponding to this status is assumed to be the maximum pullout load the fiber can sustain. The corresponding debond length is referred to critical debond length ldc. It was found that ldc increases with embedment length le. This model reproduced the experimental results pretty well. The same concept of R-curve was adopted to investigate the fracture mechanism of the uniaxial tension problem. While determining strain energy of the fiber reinforced composite, equivalent inclusion method and Mori-Tanaka theory was utilized. Again, whenever the above two conditions are satisfied simultaneously, unstable crack propagation initiates. However, are the fibers being pulled out or is there another unstable crack propagation? The comparison of the force sustained by all the fibers in the entire cross section with its allowable value sets the criterion. Besides, unlike most models, this model takes account of the impact of fiber distribution. Thus a model distinguishing single cracking from multiple cracking fracture mechanism has been

  18. Microstructure of depleted uranium under uniaxial strain conditions

    SciTech Connect

    Zurek, A.K.; Embury, J.D.; Kelly, A.; Thissell, W.R.; Gustavsen, R.L.; Vorthman, J.E.; Hixson, R.H.

    1997-09-01

    Uranium samples of two different purities were used for spall strength measurements. Samples of depleted uranium were taken from very high purity material (38 ppM carbon) and from material containing 280 ppM C. Experimental conditions were chosen to effectively arrest the microstructural damage at two places in the development to full spall separation. Samples were soft recovered and characterized with respect to the microstructure and the form of damage. This allowed determination of the dependence of spall mechanisms on stress level, stress state, and sample purity. This information is used in developing a model to predict the mode of fracture.

  19. CaFe2As2 Under In-Plane Uniaxial Pressure

    NASA Astrophysics Data System (ADS)

    Frampton, Miles; Zieve, Rena; Dioguardi, Adam

    2014-03-01

    Many unconventional superconductors have a planar crystal structure, with a resulting two-dimensional character that favors superconductivity. They tend to have anisotropic behavior and can be very sensitive to uniaxial pressure. Since these materials often grow preferentially as platelets perpendicular to the crystalline c axis, applying in-plane pressure is challenging. We present a new setup for studying thin samples under uniaxial pressure and our results on CaFe2As2. CaFe2As2 undergoes a magnetic transition simultaneously with a tetragonal-to-orthorhombic structural transition. In-plane uniaxial pressure detwins the orthorhombic phase and accentuates the difference between the axes. We find a significant change in Ts as well as anisotropy of the in-plane resistivity that increases with pressure.

  20. Magnetic phase transitions and monopole excitations in spin ice under uniaxial pressure: A Monte Carlo simulation

    SciTech Connect

    Xie, Y. L. Yan, Z. B.; Liu, J.-M.; Lin, L.

    2015-05-07

    In this work, we explore the spin ice model under uniaxial pressure using the Monte Carlo simulation method. For the known spin ices, the interaction correction (δ) introduced by the uniaxial pressure varies in quite a wide range from positive to negative. When δ is positive, the ground state characterized by the ferromagnetic spin chains is quite unstable, and in real materials it serves as intermediate state connecting the ice state and the long range ordered dipolar spin ice ground state. In the case of negative δ, the system relaxes from highly degenerate ice state to ordered ferromagnetic state via a first order phase transition. Furthermore, the domain walls in such ferromagnetic state are the hotbed of the excitations of magnetic monopoles, thus indicating that the uniaxial pressure can greatly increase the monopole density.

  1. Reflection and refraction properties of plane waves on the interface of uniaxially anisotropic chiral media

    NASA Astrophysics Data System (ADS)

    Cheng, Qiang; Cui, Tie Jun

    2006-12-01

    We have investigated the reflection and refraction properties of plane waves incident from free space into a uniaxially anisotropic chiral medium, where the chirality appears only in one direction and the host medium can be either an isotropic dielectric or an anisotropic electric plasma. We show that the reflection and refraction properties are closely related to the dispersion relation of the chiral medium and that negative phase refractions and/or negative group refractions may occur. We further demonstrate that the two eigenwaves within the uniaxially anisotropic chiral medium behave differently with respect to the incident angle, and in some cases only one of them can be supported and transmitted. We have studied the critical angle and Brewster's angle with some special properties. We have also discussed the potential application of the uniaxially anisotropic chiral medium for the polarization beam splitter. Numerical results are given to validate our analysis.

  2. Reflection and refraction properties of plane waves on the interface of uniaxially anisotropic chiral media.

    PubMed

    Cheng, Qiang; Cui, Tie Jun

    2006-12-01

    We have investigated the reflection and refraction properties of plane waves incident from free space into a uniaxially anisotropic chiral medium, where the chirality appears only in one direction and the host medium can be either an isotropic dielectric or an anisotropic electric plasma. We show that the reflection and refraction properties are closely related to the dispersion relation of the chiral medium and that negative phase refractions and/or negative group refractions may occur. We further demonstrate that the two eigenwaves within the uniaxially anisotropic chiral medium behave differently with respect to the incident angle, and in some cases only one of them can be supported and transmitted. We have studied the critical angle and Brewster's angle with some special properties. We have also discussed the potential application of the uniaxially anisotropic chiral medium for the polarization beam splitter. Numerical results are given to validate our analysis.

  3. Electronic properties of Z-shaped graphene nanoribbon under uniaxial strain

    NASA Astrophysics Data System (ADS)

    Ahmadi Fouladi, A.; Ketabi, S. A.

    2015-11-01

    Based on tight-binding approximation and a generalized Green's function method, the effect of uniaxial strain on the electron transport properties of Z-shaped graphene nanoribbon (GNR) composed of an armchair GNR sandwiched between two semi-infinite metallic armchair GNR electrodes is numerically investigated. Our results show that the increase of uniaxial strain enhances the band gap and leads to a metal-to-semiconductor transition for Z-shaped GNR. Furthermore, in the Landauer-Büttiker formalism, the current-voltage characteristics, the noise power resulting from the current fluctuations and Fano factor of strained Z-shaped GNR are explored. It is found the threshold voltage for the current and the noise power increased so that with reinforcement of the uniaxial strain parameter strength, the noise power goes from the Poisson limit to sub-Poisson region at higher bias voltages.

  4. Band gap engineering of Zn based II-VI semiconductors through uniaxial strain

    NASA Astrophysics Data System (ADS)

    Yadav, Satyesh; Ramprasad, Rampi

    2012-02-01

    The electronic structure of bulk wurtzitic ZnX (X=O, S, Se, and Te) under uniaxial strain along the [0001] direction is investigated using hybrid density functional theory calculations and many-body perturbation theory. It is found that uniaxial tensile and large compressive strains decrease the band gap, similar to what has been predicted by semilocal density functional theory (DFT) calculations [Yadav et. al, Phys. Rev. B, 81, 144120 (2010)]. Moreover, the change in the band gap under uniaxial strains predicted by semilocal DFT is in good quantitative agreement with the present results at all strains considered, thereby bringing a measure of redemption to conventional (semi)local DFT descriptions of the electronic structure of at least this class of insulators. The present results have important implications for band gap engineering through strain, especially for complex systems containing a large number of atoms (e.g., nanowires) for which higher-level calculations may be too computationally intensive.

  5. Effect of Uniaxial Strain on Band Structure of Multi-layer WS2

    NASA Astrophysics Data System (ADS)

    Troha, Conrad; Le, Duy; Rahman, Talat

    The ability to tailor band structure of a multi-layer transition metal dichalcogenide is of interest because it opens up utilizations of the material for various applications. Strain is considered a robust way to alter the electronic structure of a material. We performed calculations, using density functional theory, of band structure of multi-layer WS2 under the effects of uniaxial strain. We show that the position of the bottom of conduction band (BCB) at ∑ moves to higher, and at K to lower, energy levels under the effects of uniaxial tensile strain, making multi-layer WS2 closer to a direct band gap material. Our results suggest that uniaxial tensile strain can be used to alter band structure of multi-layer WS2 to achieve higher yield photo luminescence. This work is supported in part by U.S. Department of Energy (DOE DE-FG02-07ER15842).

  6. Influence of the potential well on the breakage rate of colloidal aggregates in simple shear and uniaxial extensional flows.

    PubMed

    Ren, Zhiqiang; Harshe, Yogesh M; Lattuada, Marco

    2015-06-02

    In this work we build on our previous paper (Harshe, Y. M.; Lattuada, M. Langmuir 2012, 28, 283-292) and compute the breakage rate of colloidal aggregates under the effect of shear forces by means of Stokesian dynamics simulations. A library of clusters made of identical spherical particles covering a broad range of masses and fractal dimension values (from 1.8 to 3.0) was generated by means of a combination of several Monte Carlo methods. DLVO theory has been used to describe the interparticle interactions, and contact forces have been introduced by means of the discrete element method. The aggregate breakage process was investigated by exposing them to well-defined shear forces, generated under both simple shear and uniaxial extensional flow conditions, and by recording the time required to reach the first breakage event. It has been found that the breakage rate of clusters was controlled by the potential well between particles as described by DLVO theory. A semiempirical Arrhenius-type exponential equation that relates the potential well to the breakage rate has been used to fit the simulation results. The dependence of the breakage process on the radius of gyration, on the external shear strength, and on the fractal dimension has been obtained, providing a very general relationship for the breakage rate of clusters. It was also found that the fragment mass distribution is insensitive to the presence of electrostatic repulsive interactions. We also clarify the physical reason for the large difference in the breakage rate of clusters between simple shear and the uniaxial extensional flow using a criterion based on the energy dissipation rate. Finally, in order to answer the question of the minimum cluster size that can break under simple shear conditions, a critical rotation number has been introduced, expressing the maximum number of rotations that a cluster exposed to simple shear could sustain before breakage.

  7. Simple uniaxial pressure device for ac-susceptibility measurements suitable for closed cycle refrigerator system.

    PubMed

    Arumugam, S; Manivannan, N; Murugeswari, A

    2007-06-01

    A simple design of the uniaxial pressure device for the measurement of ac-susceptibility at low temperatures using closed cycle refrigerator system is presented for the first time. This device consists of disc micrometer, spring holder attachment, uniaxial pressure cell, and the ac-susceptibility coil wound on stycast bobbin. It can work under pressure till 0.5 GPa and at the temperature range of 30-300 K. The performance of the system at ambient pressure is tested and calibrated with standard paramagnetic salts [Gd(2)O(3), Er(2)O(3), and Fe(NH(4)SO(4))(2)6H(2)O], Fe(3)O(4), Gd metal, Dy metal, superconductor (YBa(2)Cu(3)O(7)), manganite (La(1.85)Ba(0.15)MnO(3)), and spin glass material (Pr(0.8)Sr(0.2)MnO(3)). The performance of the uniaxial pressure device is demonstrated by investigating the uniaxial pressure dependence of La(1.85)Ba(0.15)MnO(3) single crystal with P||c axis. The Curie temperature (T(c)) decreases as a function of pressure with P||c axis (dT(c)dP(||c axis)=-11.65 KGPa) up to 46 MPa. The design is simple, is user friendly, and does not require pressure calibration. Measurement can even be made on thin and small size oriented crystals. The failure of the coil is remote under uniaxial pressure. The present setup can be used as a multipurpose uniaxial pressure device for the measurement of Hall effect and thermoelectric power with a small modification in the pressure cell.

  8. Simple uniaxial pressure device for ac-susceptibility measurements suitable for closed cycle refrigerator system

    NASA Astrophysics Data System (ADS)

    Arumugam, S.; Manivannan, N.; Murugeswari, A.

    2007-06-01

    A simple design of the uniaxial pressure device for the measurement of ac-susceptibility at low temperatures using closed cycle refrigerator system is presented for the first time. This device consists of disc micrometer, spring holder attachment, uniaxial pressure cell, and the ac-susceptibility coil wound on stycast bobbin. It can work under pressure till 0.5GPa and at the temperature range of 30-300K. The performance of the system at ambient pressure is tested and calibrated with standard paramagnetic salts [Gd2O3, Er2O3, and Fe(NH4SO4)26H2O], Fe3O4, Gd metal, Dy metal, superconductor (YBa2Cu3O7), manganite (La1.85Ba0.15MnO3), and spin glass material (Pr0.8Sr0.2MnO3). The performance of the uniaxial pressure device is demonstrated by investigating the uniaxial pressure dependence of La1.85Ba0.15MnO3 single crystal with P ‖c axis. The Curie temperature (Tc) decreases as a function of pressure with P ‖c axis (dTc/dP‖caxis=-11.65K/GPa) up to 46MPa. The design is simple, is user friendly, and does not require pressure calibration. Measurement can even be made on thin and small size oriented crystals. The failure of the coil is remote under uniaxial pressure. The present setup can be used as a multipurpose uniaxial pressure device for the measurement of Hall effect and thermoelectric power with a small modification in the pressure cell.

  9. Structural modeling of carbonaceous mesophase amphotropic mixtures under uniaxial extensional flow

    NASA Astrophysics Data System (ADS)

    Golmohammadi, Mojdeh; Rey, Alejandro D.

    2010-07-01

    The extended Maier-Saupe model for binary mixtures of model carbonaceous mesophases (uniaxial discotic nematogens) under externally imposed flow, formulated in previous studies [M. Golmohammadi and A. D. Rey, Liquid Crystals 36, 75 (2009); M. Golmohammadi and A. D. Rey, Entropy 10, 183 (2008)], is used to characterize the effect of uniaxial extensional flow and concentration on phase behavior and structure of these mesogenic blends. The generic thermorheological phase diagram of the single-phase binary mixture, given in terms of temperature (T) and Deborah (De) number, shows the existence of four T-De transition lines that define regions that correspond to the following quadrupolar tensor order parameter structures: (i) oblate (⊥,∥), (ii) prolate (⊥,∥), (iii) scalene O(⊥,∥), and (iv) scalene P(⊥,∥), where the symbols (⊥,∥) indicate alignment of the tensor order ellipsoid with respect to the extension axis. It is found that with increasing T the dominant component of the mixture exhibits weak deviations from the well-known pure species response to uniaxial extensional flow (uniaxial ⊥nematic→biaxial nematic→uniaxial∥paranematic). In contrast, the slaved component shows a strong deviation from the pure species response. This deviation is dictated by the asymmetric viscoelastic coupling effects emanating from the dominant component. Changes in conformation (oblate⇄prolate) and orientation (⊥⇄∥) are effected through changes in pairs of eigenvalues of the quadrupolar tensor order parameter. The complexity of the structural sensitivity to temperature and extensional flow is a reflection of the dual lyotropic/thermotropic nature (amphotropic nature) of the mixture and their cooperation/competition. The analysis demonstrates that the simple structures (biaxial nematic and uniaxial paranematic) observed in pure discotic mesogens under uniaxial extensional flow are significantly enriched by the interaction of the lyotropic

  10. Combined biaxial and uniaxial mechanical characterization of prosthetic meshes in a rabbit model.

    PubMed

    Röhrnbauer, B; Ozog, Y; Egger, J; Werbrouck, E; Deprest, J; Mazza, E

    2013-06-21

    The present experimental study is aimed at a combined uniaxial and biaxial mechanical characterization of the deformation behavior of two types of prosthetic meshes, SPMM (heavy-weight) and Gynemesh M (light-weight, partly absorbable), after integration in the host tissue. Explants from a full-thickness-abdominal-wall-defect-rabbit-model were tested in the two loading conditions. Corresponding protocols and data analysis procedures for biaxial inflation tests and uniaxial tensile tests were developed. Biaxial responses were observed to be by factor 2-4 stiffer compared to corresponding uniaxial experiments, depending on the material tested. In biaxial loading conditions, SPMM explants were stiffest. Gynemesh M explants and native tissue were similarly compliant at low membrane tensions (<5N/cm) (abdominal wall: 40±23N/cm, Gynemesh M: 59±44N/cm, SPMM: 145±36N/cm). At high membrane tensions (>5N/cm), there were distinct differences in the stiffness of the three groups, SPMM explants being the stiffest, followed by Gynemesh M explants and native tissue being the most compliant. In uniaxial loading conditions, the two explants were similarly stiff and distinctly stiffer than native tissue at low membrane tensions (<5N/cm) (abdominal wall: 9±1N/cm, Gynemesh M: 21±5N/cm, and SPMM: 24±5N/cm). At high membrane tension (>5N/cm), differences between all groups vanished. Biaxial and uniaxial tests yield different results with respect to the mechanical behavior of mesh explants. These findings demonstrate that an evaluation of the mechanical biocompatibility of prosthetic meshes should be based on an experimental configuration (uniaxial or biaxial tension) which reproduces the expected in vivo conditions of mechanical loading and deformation. Copyright © 2013 Elsevier Ltd. All rights reserved.

  11. Design and Validation of a Vacuum Assisted Anchorage for the Uniaxial Tensile Testing of Soft Materials.

    PubMed

    Blose, Kory J; Pichamuthu, Joseph E; Weinbaum, Justin S; Vorp, David A

    2016-01-01

    Current commercial tensile testing systems use spring-loaded or other compression-based grips to clamp materials in place posing a problem for very soft or delicate materials that cannot withstand this mechanical clamping force. In order to perform uniaxial tensile tests on soft tissues or materials, we have created a novel vacuum-assisted anchor (VAA). Fibrin gels were subjected to uniaxial extension, and the testing data was used to determine material mechanical properties. Utilizing the VAA, we achieved successful tensile breaks of soft fibrin gels while finding statistically significant differences between the mechanical properties of gels fabricated at two different fibrinogen concentrations.

  12. Design and Validation of a Vacuum Assisted Anchorage for the Uniaxial Tensile Testing of Soft Materials

    PubMed Central

    Blose, Kory J.; Pichamuthu, Joseph E.; Weinbaum, Justin S.; Vorp, David A.

    2016-01-01

    Current commercial tensile testing systems use spring-loaded or other compression-based grips to clamp materials in place posing a problem for very soft or delicate materials that cannot withstand this mechanical clamping force. In order to perform uniaxial tensile tests on soft tissues or materials, we have created a novel vacuum-assisted anchor (VAA). Fibrin gels were subjected to uniaxial extension, and the testing data was used to determine material mechanical properties. Utilizing the VAA, we achieved successful tensile breaks of soft fibrin gels while finding statistically significant differences between the mechanical properties of gels fabricated at two different fibrinogen concentrations. PMID:27795696

  13. Strong uniaxial magnetic anisotropy in CoFe films on obliquely sputtered Ru underlayer

    SciTech Connect

    Fukuma, Y.; Lu, Z.; Fujiwara, H.; Mankey, G. J.; Butler, W. H.; Matsunuma, S.

    2009-10-01

    Co{sub 90}Fe{sub 10} films with an in-plane uniaxial magnetic anisotropy have been grown on an obliquely sputtered thin Ru underlayer. The anisotropy field can be increased up to 200 Oe. The hysteresis curves show a very high squareness in the easy axis direction and almost no hysteresis in the hard axis direction, suggesting that the induced uniaxial anisotropy is uniform throughout the films. The switching characteristics of the nanoelements fabricated from the films by e-beam lithography are also investigated. There is no degradation of the magnetic anisotropy after the annealing and lithographical process.

  14. Uniaxial crystal growth in thin film by utilizing supercooled state of mesogenic phthalocyanine

    NASA Astrophysics Data System (ADS)

    Fiderana Ramananarivo, Mihary; Higashi, Takuya; Ohmori, Masashi; Sudoh, Koichi; Fujii, Akihiko; Ozaki, Masanori

    2016-06-01

    A method of uniaxial crystal growth in wet-processed thin films of the mesogenic phthalocyanine 1,4,8,11,15,18,22,25-octahexylphthalocyanine (C6PcH2) is proposed. It consists of applying geometrically linear thermal stimulation to a supercooled state of liquid crystalline C6PcH2. The thin film showed highly ordered molecular stacking structure and uniaxial alignment over a macroscopic scale. An explanation of the crystal growth mechanism is suggested by taking into account the temperature range of crystal growth and the hysteresis property of C6PcH2 in the phase transition.

  15. Compressive uniaxially strained silicon on insulator by prestrained wafer bonding and layer transfer

    NASA Astrophysics Data System (ADS)

    Himcinschi, C.; Reiche, M.; Scholz, R.; Christiansen, S. H.; Gösele, U.

    2007-06-01

    Wafer level compressive uniaxially strained silicon on insulator is obtained by direct wafer bonding of silicon wafers in cylindrically curved state, followed by thinning one of the wafers using the smart-cut process. The mapping of the wafer bow demonstrates the uniaxial character of the strain induced by the cylindrical bending. The interfacial properties are investigated by infrared transmission imaging, scanning acoustic microscopy, and transmission electron microscopy. UV-Raman spectroscopy is employed to determine the strain in the thin transferred layer as a function of radius of curvature of the initial bending.

  16. Permanent tuning of the opal stop-band with the application of uniaxial pressure

    NASA Astrophysics Data System (ADS)

    Khokhar, Ali Z.; DeLa Rue, Richard M.; Ren, Kun; Li, Zhi-Yuan; Johnson, Nigel P.

    2007-05-01

    Three-dimensional photonic crystals have been prepared by self-assembly from sub-micrometre polystyrene spheres. Such crystals are known as a synthetic opal and possess a partial stop-band in the \\langle 111\\rangle direction. The stop-band is tuned towards the shorter wavelengths by applying uniaxial pressure along the \\langle 111\\rangle direction of the face-centred cubic opal structure. The tuning is found to be irreversible and it was also observed that the normalized stop-bandwidth increased after applying uniaxial pressure. The experimental results are compared with the simulation results and found to be in very close agreement.

  17. Uniaxial Tensile Strength and Flaw Characterization of SiC-N

    DTIC Science & Technology

    2014-01-01

    October 2010–September 2011 4 . TITLE AND SUBTITLE Uniaxial Tensile Strength and Flaw Characterization of SiC-N 5a. CONTRACT NUMBER W911QX-09-C-0057...242 N Inclusion 7 6008 5.51 252 N Inclusion 4 6150 5.54 255 N Inclusion 1 6560 5.54 272 N Inclusion 10 9201 5.66 365 Y Not Identified 9 10158...Uniaxial Tensile Strength and Flaw Characterization of SiC-N by Jared C. Wright and Jeffrey J. Swab ARL-TR-6794 January 2014

  18. Evaluation of uniaxial and triaxial shock isolation techniques for a piezoresistive accelerometer

    SciTech Connect

    Bateman, V.I.; Bell, R.G. III; Brown, F.A.; Davie, N.T.; Nusser, M.A.

    1990-01-01

    Development of both uniaxial and triaxial shock isolation techniques for pyroshock and impact tests has continued this year. The uniaxial shock isolation technique has demonstrated acceptable characteristics for a temperature range of {minus}50{degrees}F to +186{degrees}F and a frequency bandwidth of DC to 10 kHz. The triaxial shock isolation technique has demonstrated acceptable results for a temperature range of {minus}50{degrees}F to 70{degrees}F and a frequency bandwidth of DC to 10 kHz. 5 refs., 7 figs.

  19. Non-destructive testing of biaxial stress state in ferromagnetic materials

    NASA Astrophysics Data System (ADS)

    Vengrinovich, V. L.; Vintov, D. A.; Dmitrovich, D. V.

    2014-02-01

    The technique for biaxial stress state quantitative non destructive testing using magnetic, namely Barkhausen Noise, measurements is developed and checked experimentally. The main elaboration concerns the application of uni-axial calibration data for bi-axial stress measurement in the material which treatment pre-history is not definitely known. The article is aimed to get over difficulties, accompanying factual nondestructive stress evaluation, implied from its tensor nature. The developed technique of stress calibration and measurement assumes the bi-axial stress components recovery from uni-axial magnetic and Barkhausen noise measurement results. The complete technology, based on new calibration procedure with grid diagrams is considered in the article.

  20. Strength Restoration of Cracked Sandstone and Coal under a Uniaxial Compression Test and Correlated Damage Source Location Based on Acoustic Emissions

    PubMed Central

    Feng, Xiaowei; Zhang, Nong; Zheng, Xigui; Pan, Dongjiang

    2015-01-01

    Underground rock masses have shown a general trend of natural balance over billions of years of ground movement. Nonetheless, man-made underground constructions disturb this balance and cause rock stability failure. Fractured rock masses are frequently encountered in underground constructions, and this study aims to restore the strength of rock masses that have experienced considerable fracturing under uniaxial compression. Coal and sandstone from a deep-buried coal mine were chosen as experimental subjects; they were crushed by uniaxial compression and then carefully restored by a chemical adhesive called MEYCO 364 with an innovative self-made device. Finally, the restored specimens were crushed once again by uniaxial compression. Axial stress, axial strain, circumferential strain, and volumetric strain data for the entire process were fully captured and are discussed here. An acoustic emission (AE) testing system was adopted to cooperate with the uniaxial compression system to provide better definitions for crack closure thresholds, crack initiation thresholds, crack damage thresholds, and three-dimensional damage source locations in intact and restored specimens. Several remarkable findings were obtained. The restoration effects of coal are considerably better than those of sandstone because the strength recovery coefficient of the former is 1.20, whereas that of the latter is 0.33, which indicates that MEYCO 364 is particularly valid for fractured rocks whose initial intact peak stress is less than that of MEYCO 364. Secondary cracked traces of restored sandstone almost follow the cracked traces of the initial intact sandstone, and the final failure is mainly caused by decoupling between the adhesive and the rock mass. However, cracked traces of restored coal only partially follow the traces of intact coal, with the final failure of the restored coal being caused by both bonding interface decoupling and self-breakage in coal. Three-dimensional damage source

  1. Strength Restoration of Cracked Sandstone and Coal under a Uniaxial Compression Test and Correlated Damage Source Location Based on Acoustic Emissions.

    PubMed

    Feng, Xiaowei; Zhang, Nong; Zheng, Xigui; Pan, Dongjiang

    2015-01-01

    Underground rock masses have shown a general trend of natural balance over billions of years of ground movement. Nonetheless, man-made underground constructions disturb this balance and cause rock stability failure. Fractured rock masses are frequently encountered in underground constructions, and this study aims to restore the strength of rock masses that have experienced considerable fracturing under uniaxial compression. Coal and sandstone from a deep-buried coal mine were chosen as experimental subjects; they were crushed by uniaxial compression and then carefully restored by a chemical adhesive called MEYCO 364 with an innovative self-made device. Finally, the restored specimens were crushed once again by uniaxial compression. Axial stress, axial strain, circumferential strain, and volumetric strain data for the entire process were fully captured and are discussed here. An acoustic emission (AE) testing system was adopted to cooperate with the uniaxial compression system to provide better definitions for crack closure thresholds, crack initiation thresholds, crack damage thresholds, and three-dimensional damage source locations in intact and restored specimens. Several remarkable findings were obtained. The restoration effects of coal are considerably better than those of sandstone because the strength recovery coefficient of the former is 1.20, whereas that of the latter is 0.33, which indicates that MEYCO 364 is particularly valid for fractured rocks whose initial intact peak stress is less than that of MEYCO 364. Secondary cracked traces of restored sandstone almost follow the cracked traces of the initial intact sandstone, and the final failure is mainly caused by decoupling between the adhesive and the rock mass. However, cracked traces of restored coal only partially follow the traces of intact coal, with the final failure of the restored coal being caused by both bonding interface decoupling and self-breakage in coal. Three-dimensional damage source

  2. Direct quantification of the mechanical anisotropy and fracture of an individual exoskeleton layer via uniaxial compression of micropillars.

    PubMed

    Han, Lin; Wang, Lifeng; Song, Juha; Boyce, Mary C; Ortiz, Christine

    2011-09-14

    A common feature of the outer layer of protective biological exoskeletons is structural anisotropy. Here, we directly quantify the mechanical anisotropy and fracture of an individual material layer of a hydroxyapatite-based nanocomposite exoskeleton, the outmost ganoine of Polypterus senegalus scale. Uniaxial compression was conducted on cylindrical micropillars of ganoine fabricated via focused ion beam at different orientations relative to the hydroxyapatite rod long axis (θ = 0°, 45°, 90°). Engineering stress versus strain curves revealed significant elastic and plastic anisotropy, off-axial strain hardening, and noncatastrophic crack propagation within ganoine. Off-axial compression (θ = 45°) showed the lowest elastic modulus, E (36.2 ± 1.6 GPa, n ≥ 10, mean ± SEM), and yield stress, σ(Y) (0.81 ± 0.02 GPa), while compression at θ = 0° showed the highest E (51.8 ± 1.7 GPa) and σ(Y) (1.08 ± 0.05 GPa). A 3D elastic-plastic composite nanostructural finite element model revealed this anisotropy was correlated to the alignment of the HAP rods and could facilitate energy dissipation and damage localization, thus preventing catastrophic failure upon penetration attacks.

  3. Variations of electric resistance and H2 and Rn emissions of concrete blocks under increasing uniaxial compression

    USGS Publications Warehouse

    King, C.-Y.; Luo, G.

    1990-01-01

    Electric resistance and emissions of hydrogen and radon isotopes of concrete (which is somewhat similar to fault-zone materials) under increasing uniaxial compression were continuously monitored to check whether they show any pre- and post-failure changes that may correspond to similar changes reported for earthquakes. The results show that all these parameters generally begin to increase when the applied stresses reach 20% to 90% of the corresponding failure stresses, probably due to the occurrence and growth of dilatant microcracks in the specimens. The prefailure changes have different patterns for different specimens, probably because of differences in spatial and temporal distributions of the microcracks. The resistance shows large co-failure increases, and the gas emissions show large post-failure increases. The post-failure increase of radon persists longer and stays at a higher level than that of hydrogen, suggesting a difference in the emission mechanisms for these two kinds of gases. The H2 increase may be mainly due to chemical reaction at the crack surfaces while they are fresh, whereas the Rn increases may be mainly the result of the increased emanation area of such surfaces. The results suggest that monitoring of resistivity and gas emissions may be useful for predicting earthquakes and failures of concrete structures. ?? 1990 Birkha??user Verlag.

  4. Micromagnetic model of noncollective magnetization reversal in ultrathin magnetic dots with in-plane uniaxial anisotropy

    NASA Astrophysics Data System (ADS)

    Fruchart, O.; Kevorkian, B.; Toussaint, J. C.

    2001-05-01

    In most magnetic systems the magnetization reversal is nonuniform, and is initiated in a so-called ``nucleation volume,'' whose dimensions are by far smaller than the total system volume. For simplicity reasons magnetization reversal theories are usually based on the assumption that coherent rotation occurs in this ``nucleation volume.'' In this approach, self-dipolar fields and exchange forces are obviously not well described, because in reality the nucleation volume is coupled with the rest of the system. In the case of ultrathin dots with in-plane uniaxial anisotropy, we could take into account dipolar fields and the exchange stiffness explicitly. The approximations used to derive analytical equations were suggested by experimental results on real dots. The model yields the nonuniform micromagnetic configuration of nucleation volumes. It predicts nucleation and reversal field values, as well as the field dependence of the energy barrier to be overcome to reverse the dot at finite temperature. The (negative) reversal field is found to increase with the dot thickness T and the volume magnetization Ms, and to decrease with the material anisotropy K. In the low-thickness limit, the reversal field Hr approaches the Stoner-Wohlfarth reversal field Ha with a law close to 1-\\|Hr/Ha\\|~M7/2sA- 3/4K-1T3/2, where A is the exchange constant. The relevance of the approximations used is discussed and demonstrated by the good agreement found for all predictions between experiment and/or numerical calculations on the one hand and the model on the other hand.

  5. Simulations of in situ x-ray diffraction from uniaxially compressed highly textured polycrystalline targets

    SciTech Connect

    McGonegle, David Wark, Justin S.; Higginbotham, Andrew; Milathianaki, Despina; Remington, Bruce A.

    2015-08-14

    A growing number of shock compression experiments, especially those involving laser compression, are taking advantage of in situ x-ray diffraction as a tool to interrogate structure and microstructure evolution. Although these experiments are becoming increasingly sophisticated, there has been little work on exploiting the textured nature of polycrystalline targets to gain information on sample response. Here, we describe how to generate simulated x-ray diffraction patterns from materials with an arbitrary texture function subject to a general deformation gradient. We will present simulations of Debye-Scherrer x-ray diffraction from highly textured polycrystalline targets that have been subjected to uniaxial compression, as may occur under planar shock conditions. In particular, we study samples with a fibre texture, and find that the azimuthal dependence of the diffraction patterns contains information that, in principle, affords discrimination between a number of similar shock-deformation mechanisms. For certain cases, we compare our method with results obtained by taking the Fourier transform of the atomic positions calculated by classical molecular dynamics simulations. Illustrative results are presented for the shock-induced α–ϵ phase transition in iron, the α–ω transition in titanium and deformation due to twinning in tantalum that is initially preferentially textured along [001] and [011]. The simulations are relevant to experiments that can now be performed using 4th generation light sources, where single-shot x-ray diffraction patterns from crystals compressed via laser-ablation can be obtained on timescales shorter than a phonon period.

  6. The sensitivity of saturation transfer electron paramagnetic resonance spectra to restricted amplitude uniaxial rotational diffusion.

    PubMed

    Hustedt, E J; Beth, A H

    2001-12-01

    Computational methods have been developed to model the effects of constrained or restricted amplitude uniaxial rotational diffusion (URD) on saturation transfer electron paramagnetic resonance (ST-EPR) signals observed from nitroxide spin labels. These methods, which have been developed to model the global rotational motion of intrinsic membrane proteins that can interact with the cytoskeleton or other peripheral proteins, are an extension of previous work that described computationally efficient algorithms for calculating ST-EPR spectra for unconstrained URD (Hustedt and Beth, 1995, Biophys. J. 69:1409-1423). Calculations are presented that demonstrate the dependence of the ST-EPR signal (V'(2)) on the width (Delta) of a square-well potential as a function of the microwave frequency, the correlation time for URD, and the orientation of the spin-label with respect to the URD axis. At a correlation time of 10 micros, the V'(2) signal is very sensitive to Delta in the range from 0 to 60 degrees, marginally sensitive from 60 degrees to 90 degrees, and insensitive beyond 90 degrees. Sensitivity to Delta depends on the correlation time for URD with higher sensitivity to large values of Delta at the shorter correlation times, on the microwave frequency, and on the orientation of the spin-label relative to the URD axis. The computational algorithm has been incorporated into a global nonlinear least-squares analysis approach, based upon the Marquardt-Levenberg method (Blackman et al., 2001, Biophys. J. 81:3363-3376). This has permitted determination of the correlation time for URD and the width of the square-well potential by automated fitting of experimental ST-EPR data sets obtained from a spin-labeled membrane protein and provided a new automated method for analysis of data obtained from any system that exhibits restricted amplitude URD.

  7. STRESS CONCENTRATION IN AN ELASTOMERIC SHEET SUBJECT TO LARGE DEFORMATIONS

    DTIC Science & Technology

    results were obtained for a sheet with a rigid circular inclusion. It is shown that the stress concentration factor for a Rivlin - Mooney material... Rivlin - Mooney material, however, leads to a decrease in stress concentration with increasing deformations....Biaxial and uniaxial experiments have been conducted on a thin sheet of natural rubber , which can be assumed to be incompressible, isotropic, and

  8. Mechanical characterization of stomach tissue under uniaxial tensile action.

    PubMed

    Jia, Z G; Li, W; Zhou, Z R

    2015-02-26

    In this article, the tensile properties of gastric wall were investigated by using biomechanical test and theoretical analysis. The samples of porcine stomach strips from smaller and greater curvature of the stomach were cut in longitudinal and circumferential direction, respectively. The loading-unloading, stress relaxation, strain creep, tensile fracture tests were performed at mucosa-submucosa, serosa-muscle and intact layer, respectively. Results showed that the biomechanical properties of the porcine stomach depended on the layers, orientations and locations of the gastric wall and presented typical viscoelastic, nonlinear and anisotropic mechanical properties. During loading-unloading test, the stress of serosa-muscle layer in the longitudinal direction was 15-20% more than that in the circumferential direction at 12% stretch ratio, while it could reach about 40% for the intact layer and 50% for the mucosa-submucosa layer. The results of stress relaxation and strain creep showed that the variation degree was obviously faster in the circumferential direction than that in the longitudinal direction, and the ultimate residual values were also different for the different layers, orientations and locations. In the process of fracture test, the serosa-muscle layer fractured firstly followed by the mucosa-submucosa layer when the intact layer was tested, the longitudinal strips firstly began to fracture and the required stress value was about twice as much as that in the circumferential strips. The anisotropy and heterogeneity of mechanical characterization of the porcine stomach were related to its complicated geometry, structure and functions. The results would help us to understand the biomechanics of soft organ tissue. Copyright © 2015 Elsevier Ltd. All rights reserved.

  9. Transverse Uniaxial Composite Thermal Properties Data Base of Thermally Conductive Graphite Fibers with and without Contiguous Grown Graphite Fins

    DTIC Science & Technology

    2013-07-01

    8 8, Thermo -Physical Properties Of ER2 WF YSH50A / Epon 826 – Cure Agent W...9 Uniaxial Composite 9, Thermo -Physical Properties Of ER2 FR1 WOF YSH50A / Epon 826 – Cure...Agent W 11 Uniaxial Composite 10, Thermo -Physical Properties Of ER2 FR2 WOF YSH50A / Epon 826 – Cure Agent W

  10. Stress-Strain Properties of SIFCON in Uniaxial Compression and Tension

    DTIC Science & Technology

    1988-08-01

    since the failure of both materials involves the pullout of fibers from a cementitious matrix. However, the materials will differ in many other respects...properties in either quantitative or qualitative terms. Although technically a fiber concrete , SIFCON differs substantially from ordinary fiber reinforced...be used to ensure infiltration of the tiny spaces between fibers in the molds. Third, the fabrication process of the two materials is very different

  11. Smoothly varying in-plane stiffness heterogeneity evaluated under uniaxial tensile stress

    Treesearch

    Michel Grédiac; Fabrice Pierron; J.M. Considine; F. Pierron; K.T. Turner; P. Lava; X. Tang

    2017-01-01

    Identification of spatially varying stiffness is a challenging, but important, research topic in the mechanics of materials and can provide the necessary information for material suitability, damage, and process control, especially for high‐value applications. One homogeneous and 3 heterogeneous virtual field method (VFM) formulations were used to create a methodology...

  12. Comparing the effects of uniaxial and biaxial strains on the structural stability and electronic structure in wurtzite ZnS

    NASA Astrophysics Data System (ADS)

    Lv, Dong; Duan, Yifeng; Zhao, Botao; Qin, Lixia; Shi, Liwei; Tang, Gang; Shi, Hongliang

    2013-07-01

    Structural stability and electronic structure of wurtzite ZnS under uniaxial and biaxial strains are systematically studied using the HSE hybrid functional. The two types of strain display the markedly different influences on the structural and electronic properties: (I) The newly predicted graphite-like phase is observed at large compressive uniaxial strains, not at large tensile biaxial strains, which is attributed to the different elastic responses to uniaxial and biaxial strains. (II) The direct band structures are obtained in wurtzite ZnS under uniaxial and biaxial strains, whereas the indirect band gaps are only observed in graphite-like ZnS under large uniaxial strain. Our results are different from the widely accepted conclusion but are in good agreement with the available experimental data.

  13. Solid-state (13)C NMR and synchrotron SAXS/WAXS studies of uniaxially-oriented polyethylene.

    PubMed

    Afeworki, Mobae; Brant, Pat; Lustiger, Arnold; Norman, Alexander

    2015-11-01

    We report solid-state (13)C NMR and synchrotron wide-and small-angle X-ray scattering experiments (WAXS, SAXS) on metallocene linear low density polyethylene films (e.g., Exceed™ 1018 mLLDPE; nominally 1MI, 0.918 density ethylene-hexene metallocene copolymer) as a function of uniaxial draw ratio, λ. Combined, these experiments provide an unambiguous, quantitative molecular view of the orientation of both the crystalline and amorphous phases in the samples as a function of draw. Together with previously reported differential scanning calorimetry (DSC), gas transport measurements, transmission electron microscopy (TEM), optical birefringence, small angle X-ray scattering (SAXS) as well as other characterization techniques, this study of the state of orientation in both phases provides insight concerning the development of unusually high barrier properties of the most oriented samples (λ=10). In this work, static (non-spinning) solid-state NMR measurements indicate that in the drawn Exceed(TM) films both the crystalline and amorphous regions are highly oriented. In particular, chemical shift data show the amorphous phase is comprised increasingly of so-called "taut tie chains" (or tie chains under any state of tautness) in the mLLDPE with increasing draw ratio - the resonance lines associated with the amorphous phase shift to where the crystalline peaks are observed. In the sample with highest total draw (λ=10), virtually all of the chains in the non-crystalline region have responded and aligned in the machine (draw) direction. Both monoclinic and orthorhombic crystalline peaks are observed in high-resolution, solid-state magic-angle spinning (MAS) NMR measurements of the oriented PE films. The orientation is comparable to that obtained for ultra-high molecular weight HDPE fibers described as "ultra-oriented" in the literature. Furthermore, the presence of a monoclinic peak in cold-drawn samples suggests that there is an appreciable internal stress associated

  14. Observation of uniaxial anisotropy along the [100] direction in crystalline Fe film.

    PubMed

    Bac, Seul-Ki; Lee, Hakjoon; Lee, Sangyoep; Choi, Seonghoon; Yoo, Taehee; Lee, Sanghoon; Liu, X; Furdyna, J K

    2015-12-04

    We report an observation of uniaxial magnetic anisotropy along the [100] crystallographic direction in crystalline Fe film grown on Ge buffers deposited on a (001) GaAs substrate. As expected, planar Hall resistance (PHR) measurements reveal the presence of four in-plane magnetic easy axes, indicating the dominance of the cubic anisotropy in the film. However, systematic mapping of the PHR hysteresis loops observed during magnetization reversal at different field orientations shows that the easy axes along the and are not equivalent. Such breaking of the cubic symmetry can only be ascribed to the presence of uniaxial anisotropy along the direction of the Fe film. Analysis of the PHR data measured as a function of orientation of the applied magnetic field allowed us to quantify the magnitude of this uniaxial anisotropy field as Oe. Although this value is only 1.5% of cubic anisotropy field, its presence significantly changes the process of magnetization reversal, revealing the important role of the uniaxial anisotropy in Fe films. Breaking of the cubic symmetry in the Fe film deposited on a Ge buffer is surprising, and we discuss possible reason for this unexpected behavior.

  15. Ray-tracing formulas for refraction and internal reflection in uniaxial crystals.

    PubMed

    Beyerle, G; McDermid, I S

    1998-12-01

    Formulas for the calculation of the direction cosines of refracted and internally reflected rays in anisotropic uniaxial crystals are presented. The method is based on a transformation to a nonorthonormal coordinate system in which the normal surface associated with the extraordinary ray is of spherical shape. A numerical example for the case of refraction and internal reflection in calcite is given.

  16. Photorealistic ray tracing of free-space invisibility cloaks made of uniaxial dielectrics.

    PubMed

    Halimeh, Jad C; Wegener, Martin

    2012-12-17

    The design rules of transformation optics generally lead to spatially inhomogeneous and anisotropic impedance-matched magneto-dielectric material distributions for, e.g., free-space invisibility cloaks. Recently, simplified anisotropic non-magnetic free-space cloaks made of a locally uniaxial dielectric material (calcite) have been realized experimentally. In a two-dimensional setting and for in-plane polarized light propagating in this plane, the cloaking performance can still be perfect for light rays. However, for general views in three dimensions, various imperfections are expected. In this paper, we study two different purely dielectric uniaxial cylindrical free-space cloaks. For one, the optic axis is along the radial direction, for the other one it is along the azimuthal direction. The azimuthal uniaxial cloak has not been suggested previously to the best of our knowledge. We visualize the cloaking performance of both by calculating photorealistic images rendered by ray tracing. Following and complementing our previous ray-tracing work, we use an equation of motion directly derived from Fermat's principle. The rendered images generally exhibit significant imperfections. This includes the obvious fact that cloaking does not work at all for horizontal or for ordinary linear polarization of light. Moreover, more subtle effects occur such as viewing-angle-dependent aberrations. However, we still find amazingly good cloaking performance for the purely dielectric azimuthal uniaxial cloak.

  17. Green dyadics in uniaxial bianisotropic-ferrite medium by cylindrical vector wavefunctions

    NASA Astrophysics Data System (ADS)

    Cheng, Dajun; Ren, Wei; Jin, Ya-Qiu

    1997-01-01

    The uniaxial bianisotropic-ferrite medium, which can be fabricated by polymer synthesis techniques, is a generalization of the well-studied chiral medium. It has potential applications in the design of antireflection coating, antenna radomes, and novel microwave components. In the present investigation, based on the concept of spectral eigenwaves, eigenfunction expansion of the Green dyadics in this class of materials is formulated in terms of the cylindrical vector wavefunctions. The formulations are greatly simplified by analytically evaluating the integrals with respect to the spectral longitudinal and radial wavenumbers, respectively. The analysis indicates that the solutions of the source-incorporated Maxwell's equations for a homogeneous uniaxial bianisotropic-ferrite medium are composed of two (or four) eigenwaves travelling with different wavenumbers. Each of these eigenwaves is a superposition of two transverse waves and a longitudinal wave. The Green dyadics of planarly and cylindrically multilayered structures consisting of uniaxial bianisotropic-ferrite media can be straightforwardly obtained by applying the method of scattering superposition and appropriate electromagnetic boundary conditions respectively. The resulting formulations, which can be theoretically verified by comparing their special forms with existing results, provide fundamental basis to analyse the physical phenomena of unbounded and multilayered uniaxial bianisotropic-ferrite media.

  18. Inverted hysteresis loops in magnetically coupled bilayers with uniaxial competing anisotropies: Theory and experiments

    NASA Astrophysics Data System (ADS)

    Valvidares, S. M.; Álvarez-Prado, L. M.; Martín, J. I.; Alameda, J. M.

    2001-10-01

    The magnetization reversal processes in magnetic bilayers with individual uniaxial anisotropies have been studied, both theoretically and experimentally, to analyze the possible existence of inverted hysteresis loops, that is, with negative remanent magnetization (Mr). Kerr effect measurements in amorphous YCo2/YCo2 bilayers and alternating gradient magnetometry in polycrystalline FeNi/FeNi samples reveal that Mr<0 can be observed for certain directions of the applied magnetic field in the sample plane. This property has also been found in CoNbZr films annealed under an applied field. Our theoretical approach shows that the behavior of these magnetic heterogeneous systems with two coupled uniaxial anisotropies can be understood in terms of two competing effective anisotropies, one biaxial (with Kbiax) and one uniaxial (with Kuniax). In particular, a phase diagram has been deduced for the conditions on Kbiax and Kuniax that can produce negative remanence. This description indicates that, under those anisotropy conditions, inverted hysteresis loops can be observed for an applied field close to the hard axis of the effective uniaxial anisotropy, when magnetization reversal is driven by rotations and not by domain nucleation and wall movement. To consider the real situation in a YCo2/YCo2 bilayer sample, the predictions of this phenomenological model have been further improved by micromagnetic calculations, which are in very good agreement with the magneto-optical measurements.

  19. Observation of uniaxial anisotropy along the [100] direction in crystalline Fe film

    NASA Astrophysics Data System (ADS)

    Bac, Seul-Ki; Lee, Hakjoon; Lee, Sangyoep; Choi, Seonghoon; Yoo, Taehee; Lee, Sanghoon; Liu, X.; Furdyna, J. K.

    2015-12-01

    We report an observation of uniaxial magnetic anisotropy along the [100] crystallographic direction in crystalline Fe film grown on Ge buffers deposited on a (001) GaAs substrate. As expected, planar Hall resistance (PHR) measurements reveal the presence of four in-plane magnetic easy axes, indicating the dominance of the cubic anisotropy in the film. However, systematic mapping of the PHR hysteresis loops observed during magnetization reversal at different field orientations shows that the easy axes along the and are not equivalent. Such breaking of the cubic symmetry can only be ascribed to the presence of uniaxial anisotropy along the direction of the Fe film. Analysis of the PHR data measured as a function of orientation of the applied magnetic field allowed us to quantify the magnitude of this uniaxial anisotropy field as Oe. Although this value is only 1.5% of cubic anisotropy field, its presence significantly changes the process of magnetization reversal, revealing the important role of the uniaxial anisotropy in Fe films. Breaking of the cubic symmetry in the Fe film deposited on a Ge buffer is surprising, and we discuss possible reason for this unexpected behavior.

  20. Focal performance analysis of closed-boundary cylindrical microlenses made of uniaxial crystal

    NASA Astrophysics Data System (ADS)

    Lin, Jie; Ye, Jiasheng; Liu, Jianlong; Liu, Shutian

    2007-11-01

    In this paper, we investigate the focal performance of closed-boundary cylindrical microlenses (CBCMs) made of anisotropic uniaxial crystal based on rigorous electromagnetic theory and the boundary element method (BEM). For both TE and TM polarizations, focal performances of the anisotropic CBCMs with different f-numbers are studied in detail. The influence of illumination type on focal performances of CBCMs are also considered. Several focal performance quantities, such as the real focal position, the focal spot size, the diffraction efficiency and the normalized transmitted power, are presented. Numerical results indicate that the focal performance of anisotropic CBCMs made of uniaxial crystal differs greatly in the case of different polarizations. Especially, there exists a large focal shift, which is due to the birefringence effect of a uniaxial crystal. In contrast, for conventional isotropic CBCMs, the focal characteristics for different polarizations are similar. Meanwhile, our analysis indicates that the focal performances of CBCMs with small f-number are sensitive to illumination type. It is expected that the CBCMs made of uniaxial crystal should be used as a micropolarization optical filter in micro-optical systems and also offer useful help in application of CBCMs with small f-number.

  1. Stress impact on elastic anisotropy of triclinic porous and fractured rocks

    NASA Astrophysics Data System (ADS)

    Shapiro, S. A.

    2017-03-01

    Understanding the stress dependence of elastic properties of rocks is important for reservoir characterization and seismic-hazard monitoring. Several known approaches describing this dependence are the following: the nonlinear elasticity theory, effective-medium theories for fractured rocks with stress-dependent crack densities, and the piezosensitivity approach (also called the porosity deformation approach). Here I propose a generalization of the piezosensitivity approach to triclinic rocks. I assume the isotropy of the tensor describing sensitivity of elasticity to small strains of the pore space, and generalize known linear and exponential stress dependencies of compliances. This generalization is capable of describing the effect of loads on elastic properties of anisotropic rocks when the principal stresses are not necessarily aligned with the symmetrical axes of the unstressed anisotropic material. For example, the generalization describes how monoclinic anisotropy changes under isostatic stress or pore pressure, and how tilted transverse isotropy changes to monoclinic anisotropy due to a pseudo-triaxial (or a uniaxial) load. The results are expected to be valid up to several hundred megapascals. This theory is closely related to the two other approaches mentioned above. On the one hand, for unloaded rocks, the theory is consistent with the noninteracting scalar-crack approximation. On the other hand, the theory's predictions of mutual relations between isotropic third-order elastic moduli is in good agreement with literature data on corresponding laboratory measurements. Thus, using the piezosensitivity approach, the physical nonlinearity of rocks can quantitatively be rather well explained by the strain of compliant pores.

  2. Failure behavior after stepwise uniaxial extension of entangled polymer melts

    SciTech Connect

    Sun, Hao; Lin, Panpan; Liu, Gengxin; Ntetsikas, Konstantinos; Misichronis, Konstantinos; Kang, Namgoo; Liu, Jianning; Avgeropoulos, Apostolos; Mays, Jimmy; Wang, Shi-Qing

    2015-04-20

    This paper studies how stepwise extension of various well-entangled polymer melts produce mechanical/structural breakdowns during stress relaxation. Depending on how stepwise extension is imposed on five different styrene-butadiene random copolymers, two different forms of specimen failure are observed. When a step extension is produced with a low Hencky rate or to a low strain below some thresholds, the sample breaks up rather sharply after an appreciable period of induction during which the stress relaxes quiescently. After step extension, the sample draws and undergoes unsustainable necking due to shear yielding, if the step extension is produced with a Hencky rate higher than the Rouse relaxation rate and the magnitude is beyond a Hencky strain of 1.5. Moreover, introduction of long-chain branching suppresses the elastic breakup, postponing it to Hencky strains beyond 2.5. The clearly identifiable characteristics of the elastic yielding may be understood in terms of some speculative interpretations. Finally, more convincing explanations have yet to come from future computer experiments that hopefully the present work is able to motivate.

  3. Material properties of components in human carotid atherosclerotic plaques: A uniaxial extension study

    PubMed Central

    Teng, Zhongzhao; Zhang, Yongxue; Huang, Yuan; Feng, Jiaxuan; Yuan, Jianmin; Lu, Qingsheng; Sutcliffe, Michael P.F.; Brown, Adam J.; Jing, Zaiping; Gillard, Jonathan H.

    2014-01-01

    Computational modelling to calculate the mechanical loading within atherosclerotic plaques has been shown to be complementary to defining anatomical plaque features in determining plaque vulnerability. However, its application has been partially impeded by the lack of comprehensive knowledge about the mechanical properties of various tissues within the plaque. Twenty-one human carotid plaques were collected from endarterectomy. The plaque was cut into rings, and different type of atherosclerotic tissues, including media, fibrous cap (FC), lipid and intraplaque haemorrhage/thrombus (IPH/T) was dissected for uniaxial extension testing. In total, 65 media strips from 17 samples, 59 FC strips from 14 samples, 38 lipid strips from 11 samples, and 21 IPH/T strips from 11 samples were tested successfully. A modified Mooney–Rivlin strain energy density function was used to characterize the stretch–stress relationship. The stiffnesses of media and FC are comparable, as are lipid and IPH/T. However, both media and FC are stiffer than either lipid or IPH/T. The median values of incremental Young’s modulus of media, FC, lipid and IPH/T at λ = 1 are 290.1, 244.5, 104.4, 52.9, respectively; they increase to 1019.5, 817.4, 220.7 and 176.9 at λ = 1.1; and 4302.7, 3335.0, 533.4 and 268.8 at λ = 1.15 (unit, kPa; λ, stretch ratio). The material constants of each tissue type are suggested to be: media, c1 = 0.138 kPa, D1 = 3.833 kPa and D2 = 18.803; FC, c1 = 0.186 kPa, D1 = 5.769 kPa and D2 = 18.219; lipid, c1 = 0.046 kPa, D1 = 4.885 kPa and D2 = 5.426; and IPH/T, c1 = 0.212 kPa, D1 = 4.260 kPa and D2 = 5.312. It is concluded that all soft atherosclerotic tissues are non-linear, and both media and FC are stiffer than either lipid or IPH/T. PMID:25200842

  4. Material properties of components in human carotid atherosclerotic plaques: a uniaxial extension study.

    PubMed

    Teng, Zhongzhao; Zhang, Yongxue; Huang, Yuan; Feng, Jiaxuan; Yuan, Jianmin; Lu, Qingsheng; Sutcliffe, Michael P F; Brown, Adam J; Jing, Zaiping; Gillard, Jonathan H

    2014-12-01

    Computational modelling to calculate the mechanical loading within atherosclerotic plaques has been shown to be complementary to defining anatomical plaque features in determining plaque vulnerability. However, its application has been partially impeded by the lack of comprehensive knowledge about the mechanical properties of various tissues within the plaque. Twenty-one human carotid plaques were collected from endarterectomy. The plaque was cut into rings, and different type of atherosclerotic tissues, including media, fibrous cap (FC), lipid and intraplaque haemorrhage/thrombus (IPH/T) was dissected for uniaxial extension testing. In total, 65 media strips from 17 samples, 59 FC strips from 14 samples, 38 lipid strips from 11 samples, and 21 IPH/T strips from 11 samples were tested successfully. A modified Mooney-Rivlin strain energy density function was used to characterize the stretch-stress relationship. The stiffnesses of media and FC are comparable, as are lipid and IPH/T. However, both media and FC are stiffer than either lipid or IPH/T. The median values of incremental Young's modulus of media, FC, lipid and IPH/T at λ=1 are 290.1, 244.5, 104.4, 52.9, respectively; they increase to 1019.5, 817.4, 220.7 and 176.9 at λ=1.1; and 4302.7, 3335.0, 533.4 and 268.8 at λ=1.15 (unit, kPa; λ, stretch ratio). The material constants of each tissue type are suggested to be: media, c1=0.138kPa, D1=3.833kPa and D2=18.803; FC, c1=0.186kPa, D1=5.769kPa and D2=18.219; lipid, c1=0.046kPa, D1=4.885kPa and D2=5.426; and IPH/T, c1=0.212kPa, D1=4.260kPa and D2=5.312. It is concluded that all soft atherosclerotic tissues are non-linear, and both media and FC are stiffer than either lipid or IPH/T. Copyright © 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

  5. The relationship between indentation and uniaxial creep in amorphous selenium

    SciTech Connect

    Poisl, W.H.; Oliver, W.C.; Fabes, B.D.

    1995-08-01

    Ultralow load indentation techniques can be used to obtain time-dependent mechanical properties, termed indentation creep, of materials. However, the comparison of indentation creep data to that obtained during conventional creep testing is difficult, mainly due to the determination of the strain rate experienced by the material during indentation. Using the power-law creep equation and the equation for Newtonian viscosity as a function of stress and strain rate, a relationship between indentation strain rate,{center_dot}{epsilon}{sub {ital l}}={ital @};Dh/{ital h}, and the effective strain rate occurring during the indentation creep process is obtained. Indentation creep measurements on amorphous selenium in the Newtonian viscous flow regime above the glass transition temperature were obtained. The data was then used to determine that the coefficient relating indentation strain rate to the effective strain rate is equal to 0.09, or{center_dot}{epsilon}=0.0{center_dot}{epsilon}{sub {ital l}}.

  6. Measurement of thermally induced stresses in continuously welded rail through diffuse ultrasonic backscatter

    NASA Astrophysics Data System (ADS)

    Kube, Christopher M.; Fateh, Mahmood; Ghoshal, Goutam; Turner, Joseph A.

    2012-05-01

    The relationship between grain scattering and uniaxial stress has recently been theoretically developed [1]. The scattering results because of reflections at grain boundaries and discontinuities in the microstructure. The acoustoelastic response of individual grains due to temperature and stress gradients has a direct influence on the strength of the scattering. Measurements of mechanically-induced uniaxial compressive stress on a rail section and thermal stresses within continuously welded rail (CWR) were performed. It was found that this technique can produce measurement resolution of at least 10-4/MPa.

  7. Orientation dependence of void growth at triple junction of grain boundaries in nanoscale tricrystal nickel film subjected to uniaxial tensile loading

    NASA Astrophysics Data System (ADS)

    Zhang, Yanqiu; Jiang, Shuyong; Zhu, Xiaoming; Sun, Dong

    2016-11-01

    Molecular dynamics simulation was performed in order to investigate the dependence of void growth on crystallographic orientation at the triple junction of grain boundaries in nanoscale tricrystal nickel film subjected to uniaxial tensile loading. The nucleation, the emission and the transmission of Shockley partial dislocations play a predominant role in the growth of void at the triple junction of grain boundaries. The orientation factors of various slip systems are calculated according to Schmid law. The slip systems activated in a grain of tricrystal nickel film basically conform to Schmid law which is completely suitable for a single crystal. The activated slip systems play an important role in plastic deformation of nanoscale tricrystal nickel film subjected to uniaxial tensile loading. The slip directions exhibit great difference among the activated slip systems such that the void is caused to be subjected to various stress conditions, which further leads to the difference in void growth among the tricrystal nickel films with different orientation distributions. It can be concluded that the grain orientation distribution has a significant influence on void growth at the triple junction of grain boundaries.

  8. In situ ultra-small-angle X-ray scattering study under uniaxial stretching of colloidal crystals prepared by silica nanoparticles bearing hydrogen-bonding polymer grafts.

    PubMed

    Ishige, Ryohei; Williams, Gregory A; Higaki, Yuji; Ohta, Noboru; Sato, Masugu; Takahara, Atsushi; Guan, Zhibin

    2016-05-01

    A molded film of single-component polymer-grafted nanoparticles (SPNP), consisting of a spherical silica core and densely grafted polymer chains bearing hydrogen-bonding side groups capable of physical crosslinking, was investigated by in situ ultra-small-angle X-ray scattering (USAXS) measurement during a uniaxial stretching process. Static USAXS revealed that the molded SPNP formed a highly oriented twinned face-centered cubic (f.c.c.) lattice structure with the [11-1] plane aligned nearly parallel to the film surface in the initial state. Structural analysis of in situ USAXS using a model of uniaxial deformation induced by rearrangement of the nanoparticles revealed that the f.c.c. lattice was distorted in the stretching direction in proportion to the macroscopic strain until the strain reached 35%, and subsequently changed into other f.c.c. lattices with different orientations. The lattice distortion and structural transition behavior corresponded well to the elastic and plastic deformation regimes, respectively, observed in the stress-strain curve. The attractive interaction of the hydrogen bond is considered to form only at the top surface of the shell and then plays an effective role in cross-linking between nanoparticles. The rearrangement mechanism of the nanoparticles is well accounted for by a strong repulsive interaction between the densely grafted polymer shells of neighboring particles.

  9. A model-based method for the characterisation of stress in magnetic materials using eddy current non-destructive evaluation

    NASA Astrophysics Data System (ADS)

    Dahia, Abla; Berthelot, Eric; Le Bihan and, Yann; Daniel, Laurent

    2015-03-01

    A precise knowledge of the distribution of internal stresses in materials is key to the prediction of magnetic and mechanical performance and lifetime of many industrial devices. This is the reason why many efforts have been made to develop and enhance the techniques for the non-destructive evaluation of stress. In the case of magnetic materials, the use of eddy current (EC) techniques is a promising pathway to stress evaluation. The principle is based on the significant changes in magnetic permeability of magnetic materials subjected to mechanical stress. These modifications of magnetic permeability affect in turn the signal obtained from an EC probe inspecting the material. From this principle, a numerical tool is proposed in this paper to predict the EC signal obtained from a material subjected to stress. This numerical tool is a combination of a 3D finite element approach with a magneto-mechanical constitutive law describing the effect of stress on the magnetic permeability. The model provides the variations of impedance of an EC probe as a function of stress. An experimental setup in which a magnetic material subjected to a tension stress is inspected using EC techniques is tailored in order to validate the model. A very good agreement is found between experimental and modelling results. For the Iron-Cobalt alloy tested in this study, it is shown that a uniaxial tensile stress can be detected with an error lower than 3 MPa in the range from 0 to 100 MPa.

  10. Mullins effect in a filled elastomer under uniaxial tension

    DOE PAGES

    Maiti, A.; Small, W.; Gee, R. H.; ...

    2014-01-16

    Modulus softening and permanent set in filled polymeric materials due to cyclic loading and unloading, commonly known as the Mullins effect, can have a significant impact on their use as support cushions. The quantitative analysis of such behavior is essential to ensure the effectiveness of such materials in long-term deployment. In this work we combine existing ideas of filler-induced modulus enhancement, strain amplification, and irreversible deformation within a simple non-Gaussian constitutive model to quantitatively interpret recent measurements on a relevant PDMS-based elastomeric cushion. Also, we find that the experimental stress-strain data is consistent with the picture that during stretching (loading)more » two effects take place simultaneously: (1) the physical constraints (entanglements) initially present in the polymer network get disentangled, thus leading to a gradual decrease in the effective cross-link density, and (2) the effective filler volume fraction gradually decreases with increasing strain due to the irreversible pulling out of an initially occluded volume of the soft polymer domain.« less

  11. Mullins effect in a filled elastomer under uniaxial tension

    SciTech Connect

    Maiti, A.; Small, W.; Gee, R. H.; Weisgraber, T. H.; Chinn, S. C.; Wilson, T. S.; Maxwell, R. S.

    2014-01-16

    Modulus softening and permanent set in filled polymeric materials due to cyclic loading and unloading, commonly known as the Mullins effect, can have a significant impact on their use as support cushions. The quantitative analysis of such behavior is essential to ensure the effectiveness of such materials in long-term deployment. In this work we combine existing ideas of filler-induced modulus enhancement, strain amplification, and irreversible deformation within a simple non-Gaussian constitutive model to quantitatively interpret recent measurements on a relevant PDMS-based elastomeric cushion. Also, we find that the experimental stress-strain data is consistent with the picture that during stretching (loading) two effects take place simultaneously: (1) the physical constraints (entanglements) initially present in the polymer network get disentangled, thus leading to a gradual decrease in the effective cross-link density, and (2) the effective filler volume fraction gradually decreases with increasing strain due to the irreversible pulling out of an initially occluded volume of the soft polymer domain.

  12. The effect of material strain hardening on the buckling strength of a perforated plate under uniaxial loading

    NASA Astrophysics Data System (ADS)

    Patil, Mayuri Suresh

    Plates or members containing plate elements have been used in the offshore, aerospace and construction industry. Cutouts are often located to lighten the weight of the structure, but these cutouts reduce the ultimate strength of the plate. A number of studies have taken place for determining the buckling strength of a perforated plated but few discuss the effect of material strain hardening on the buckling strength of a perforated plate. Buckling strength is often considered as an important criterial to determine the serviceable limit of the perforated plate in the offshore structure. The aim of the present study is to investigate the effect of material strain hardening on the strength characteristic of a perforated plate under uniaxial loading. This load at some point could lead to a possibility of instability. A square plate with perforation is considered here. The plate is considered to be simply supported at all four edges and has been kept straight. The perforation is located at the center of the plate. A number of ANSYS static nonlinear analysis are undertaken with different strain hardening material properties for AL7075. The Ramberg-Osgood method is used to determine the stress-strain curve for different strain hardening values. The plate thickness and the cutout size of the perforation are varied to determine the effect on the strength. The study covers the behavior of the system in the elastic buckling and the elastic-plastic region.

  13. Correction of the post -- necking true stress -- strain data using instrumented nanoindentation

    NASA Astrophysics Data System (ADS)

    Romero Fonseca, Ivan Dario

    strains were 0.028, 0.062 and 0.061 for G101800, C11000 and S30400 respectively. The established corrected curves relating post-necking flow stress to true plastic strain turned out to be well represented by a power-law function. Experimental results dictated that a unique single value for C and for epsilonr is not appropriate to describe materials with different plastic behaviors. Therefore, Tabor's equation, along with the representative plastic strain concept, has been misused in the past. The studied materials exhibited different nanohardness and plastic strain distributions due to their inherently distinct elasto-plastic response. The proposed post-necking correction separates out the effect of triaxiality on the uniaxial true stress-strain curve provided that the nanohardness-flow stress relationship is based on uniaxial values of stress. Some type of size effect, due to the microvoids at the tip of the neck, influenced nanohardness measurements. The instrumented nanoindentation technique proved to be a very suitable method to probe elasto-plastic properties of materials such as nanohardness, elastic modulus, and quasi-static strain rate sensitivity among others. Care should be taken when converting nanohardness to Vickers and vice versa due to their different area definition used. Nanohardness to Vickers ratio oscillated between 1.01 and 1.17.

  14. Mechanical and hydraulic properties of subducted sediments, Nankai Trough accretionary prism: Effect of stress path

    NASA Astrophysics Data System (ADS)

    Kitajima, H.; Chester, F. M.; Biscontin, G.

    2010-12-01

    To understand the evolution of mechanical and hydraulic properties of sediments during burial, underthrusting, underplating, accretion, and exhumation within accertionary subduction zones, triaxial deformation experiments were conducted on consolidated sediment from the Nankai Trough sampled during the Integrated Ocean Drilling Program (IODP) Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) Stage 1 Expeditions. Samples of older, accretionary prism sediments at the forearc basin, underthrust slope sediments beneath the megasplay fault, and overthrust Upper Shikoku Basin sediments along the frontal thrust, were tested using different load paths. Specifically, isotropic loading, uniaxial strain loading, and triaxial compression (at constant confining pressure, Pc), undrained Pc reduction, drained Pc reduction, and triaxial unloading at constant Pc were employed. We find that all samples are overconsolidated and cemented. From the Pc-reduction stress paths, yield surfaces for the sediments are well described by the original Cam-Clay model and Coulomb failure criteria. Combined with results from the other load paths, we determine the yield surfaces for the sediments in situ, constrain the current stress state, and infer the relationship between consolidation state and deformation history including the effect of horizontal stress changes. Porosity evolution is relatively independent of stress path, and the sediment porosity decreases as the yield surface expands. In contrast, permeability evolution depends on the stress path and consolidation state, e.g., permeability reduction by shear-enhanced compaction occurs at a greater rate under triaxial-compression relative to uniaxial-strain and isotropic loading. Improved understanding of the evolution of hydromechanical properties for different load paths is necessary to accurately treat coupling of deformation and fluid flow in accretionary subduction zones.

  15. Geochemical changes and fracture development in Woodford Shale cores following hydrous pyrolysis under uniaxial confinement

    USGS Publications Warehouse

    Birdwell, Justin E.; Lewan, Michael D.; Miller, Michael; Baez, Luis; Beeney, Ken; Sonnenberg, Steve

    2013-01-01

    A uniaxial confinement clamp was used on Woodford Shale cores in hydrous pyrolysis experiments to study fracture development during thermal maturation. The clamp simulates overburden in that it prevents cores from expanding perpendicular to bedding fabric during the volume-increasing reactions associated with petroleum generation. Cores were cut from a slab of immature Woodford Shale and subjected to hydrous pyrolysis under confinement at 300, 330, and 365 °C for 72 hours to induce thermal maturities ranging from early bitumen to maximum expelled-oil generation. Two additional cores were used as experimental controls: (1) a confined core was saturated with water by heating it to 100 °C under hydrous pyrolysis conditions for 72 hours to use for characterization of the original rock, and (2) an unconfined core was heated at 365 °C for 72 hours to evaluate the effects of confinement on petroleum generation and expulsion. X-ray computed tomography (X-CT) imaging and other analyses identified five distinct beds within the cored interval. Using a tentative classification system, beds 1, 2, and 3 are described as dolomitic marlstone (DM) with total organic carbon (TOC) contents of 7.7, 5.8, and 7.7 wt. %, respectively; bed 4 is a cherty quartzose claystone (CQC) with TOC content of 5.5 wt. %; and bed 5 is a quartzose claystone with TOC content of 10.9 wt. %. Bed samples all had similar Rock-Eval hydrogen indices (600 ± 46 mg S2/g-TOC) and Tmax values (433 ± 2 °C), demonstrating organic matter uniformity and low thermal maturity. The X-CT scan of the core heated to 100 °C showed preexisting fractures that were nearly perpendicular to the bedding fabric primarily in the low-TOC DM bed 2 and CQC bed 4. Heating led to enhancement of preexisting fractures in the confined cores with the greatest enhancement occurring in CQC bed 4. The fractures increased in size and intensity with temperature. This is attributed to the internal pressure generated by volume

  16. Quantum spin Hall insulator phase in monolayer WTe2 by uniaxial strain

    NASA Astrophysics Data System (ADS)

    Xiang, Hui; Xu, Bo; Liu, Jinqiu; Xia, Yidong; Lu, Haiming; Yin, Jiang; Liu, Zhiguo

    2016-09-01

    Monolayer WTe2, which is predicted to be large-gap quantum spin Hall (QSH) insulators with distorted 1T (1T') structure, attracts rapidly growing interests. However, the intrinsic semimetallic nature of the monolayer 1T'-WTe2 limits their direct applications based on QSH effect. By first-principles density functional theoretical calculations, we demonstrate a phase transition from semimetal to QSH insulator under the uniaxial strains along a and b axis in monolayer 1T'-WTe2. The electronic phase transition results from the geometric structure deformation upon the uniaxial strains. This suggests monolayer 1T'-WTe2 as a promising material for application in strain-tunable topological quantum electronics.

  17. Deformation analysis of ferrite/pearlite banded structure under uniaxial tension using digital image correlation

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaochuan; Wang, Yong; Yang, Jia; Qiao, Zhixia; Ren, Chunhua; Chen, Cheng

    2016-10-01

    The ferrite/pearlite banded structure causes the anisotropic behavior of steel. In this paper, digital image correlation (DIC) was used to analyze the micro deformation of this microstructure under uniaxial tension. The reliability of DIC for this application was verified by a zero-deformation experiment. The results show that the performance of DIC can satisfy the requirements of the tensile deformation measurement. Then, two uniaxial tensile tests in different directions (longitudinal direction and transverse direction) were carried out and DIC was used to measure the micro deformation of the ferrite/pearlite banded structure. The measured results show that the ferrite bands undergo the main deformation in the transverse tension, which results in the relatively weaker tensile properties in the transverse direction than in the longitudinal direction. This work is useful to guide the modification of the bands morphology and extend the application scope of DIC.

  18. Equilibrium configurations and stability of a damaged body under uniaxial tractions

    NASA Astrophysics Data System (ADS)

    Lanzoni, Luca; Tarantino, Angelo Marcello

    2015-02-01

    This paper deals with the equilibrium problem in nonlinear dissipative inelasticity of damaged bodies subject to uniaxial loading. To model the damage effects, a damage function, affecting the stored energy function, is defined. In the framework of the continuum thermodynamics theory, the constitutive law for damaged hyperelastic materials and an inequality for the energy release rate are derived. By means of an energy-based damage criterion, the irreversible evolution law for the damage function is obtained. After formulating the equilibrium boundary value problem, explicit expressions governing the global development of the equilibrium paths are written. Successively, the stability of the equilibrium solutions are assessed through the energy criterion. For a damaged body under uniaxial loading, seven inequalities are derived. These conditions, if fulfilled, ensure the stability of the solutions under each type of small perturbation. Finally, a number of applications for compressible neo-Hookean and Mooney-Rivlin materials are performed.

  19. Mechanical properties of stanene under uniaxial and biaxial loading: A molecular dynamics study

    SciTech Connect

    Mojumder, Satyajit; Amin, Abdullah Al; Islam, Md Mahbubul

    2015-09-28

    Stanene, a graphene like two dimensional honeycomb structure of tin has attractive features in electronics application. In this study, we performed molecular dynamics simulations using modified embedded atom method potential to investigate mechanical properties of stanene. We studied the effect of temperature and strain rate on mechanical properties of α-stanene for both uniaxial and biaxial loading conditions. Our study suggests that with the increasing temperature, both the fracture strength and strain of the stanene decrease. Uniaxial loading in zigzag direction shows higher fracture strength and strain compared to the armchair direction, while no noticeable variation in the mechanical properties is observed for biaxial loading. We also found at a higher loading rate, material exhibits higher fracture strength and strain. These results will aid further investigation of stanene as a potential nano-electronics substitute.

  20. Switching of the electrical conductivity of plasticized PVC films under uniaxial pressure

    NASA Astrophysics Data System (ADS)

    Vlasov, D. V.; Apresyan, L. A.; Vlasova, T. V.; Kryshtob, V. I.

    2011-11-01

    The jumplike switching of the electrical conductivity in wide-band-gap polymer (antistatic plasticized polyvinylchloride) films under uniaxial pressure is studied. In various plasticized PVC materials, the uniaxial pressure inducing a conductivity jump by four orders of magnitude or higher changes from several to several hundreds of bars, and this effect is retained at a film thickness of several hundred microns, which is two orders of magnitude larger than the critical film thicknesses known for other wide-band-gap polymers. In addition to the earlier interpretation of the conductivity anomalies in plasticized PVC, we proposed a phenomenological electron-molecular dynamic nanotrap model, in which local charge transfer is provided by mobile molecule segments in a plasticized polymer.

  1. Stable evaluation of Green's functions in cylindrically stratified regions with uniaxial anisotropic layers

    SciTech Connect

    Moon, H.; Donderici, B.; Teixeira, F.L.

    2016-11-15

    We present a robust algorithm for the computation of electromagnetic fields radiated by point sources (Hertzian dipoles) in cylindrically stratified media where each layer may exhibit material properties (permittivity, permeability, and conductivity) with uniaxial anisotropy. Analytical expressions are obtained based on the spectral representation of the tensor Green's function based on cylindrical Bessel and Hankel eigenfunctions, and extended for layered uniaxial media. Due to the poor scaling of these eigenfunctions for extreme arguments and/or orders, direct numerical evaluation of such expressions can produce numerical instability, i.e., underflow, overflow, and/or round-off errors under finite precision arithmetic. To circumvent these problems, we develop a numerically stable formulation through suitable rescaling of various expressions involved in the computational chain, to yield a robust algorithm for all parameter ranges. Numerical results are presented to illustrate the robustness of the formulation including cases of practical interest.

  2. The influence of uniaxial prestrain on biaxial r-values in 7075-O aluminium alloy

    SciTech Connect

    Anderson, N.; Brown, D.; McMurray, R. J.; Leacock, A. G.

    2011-05-04

    Biaxial test methods have been used to determine, not only yield behaviour under biaxial conditions, but also the strain response. This paper examines the influence of uniaxial prestrain upon the biaxial r-value by extending the disc compression test procedure proposed by Barlat et al. The extension involved the use of digital image measurements of in-plane strains. The material examined was a 7075-O condition aluminium alloy. The results of the experimental programme indicated that the biaxial r-value is unaffected by uniaxial prestrain. When using the disc compression test, the mode of deformation and therefore the biaxial r-value were found to be very sensitive to the prevailing friction conditions.

  3. Maier-Saupe model for a mixture of uniaxial and biaxial molecules

    NASA Astrophysics Data System (ADS)

    Nascimento, E. S.; Henriques, E. F.; Vieira, A. P.; Salinas, S. R.

    2015-12-01

    We introduce shape variations in a liquid-crystalline system by considering an elementary Maier-Saupe lattice model for a mixture of uniaxial and biaxial molecules. Shape variables are treated in the annealed (thermalized) limit. We analyze the thermodynamic properties of this system in terms of temperature T , concentration c of intrinsically biaxial molecules, and a parameter Δ associated with the degree of biaxiality of the molecules. At the mean-field level, we use standard techniques of statistical mechanics to draw global phase diagrams, which are shown to display a rich structure, including uniaxial and biaxial nematic phases, a reentrant ordered region, and many distinct multicritical points. Also, we use the formalism to write an expansion of the free energy in order to make contact with the Landau-de Gennes theory of nematic phase transitions.

  4. Maier-Saupe model for a mixture of uniaxial and biaxial molecules.

    PubMed

    Nascimento, E S; Henriques, E F; Vieira, A P; Salinas, S R

    2015-12-01

    We introduce shape variations in a liquid-crystalline system by considering an elementary Maier-Saupe lattice model for a mixture of uniaxial and biaxial molecules. Shape variables are treated in the annealed (thermalized) limit. We analyze the thermodynamic properties of this system in terms of temperature T, concentration c of intrinsically biaxial molecules, and a parameter Δ associated with the degree of biaxiality of the molecules. At the mean-field level, we use standard techniques of statistical mechanics to draw global phase diagrams, which are shown to display a rich structure, including uniaxial and biaxial nematic phases, a reentrant ordered region, and many distinct multicritical points. Also, we use the formalism to write an expansion of the free energy in order to make contact with the Landau-de Gennes theory of nematic phase transitions.

  5. The influence of uniaxial prestrain on biaxial r-values in 7075-O aluminium alloy

    NASA Astrophysics Data System (ADS)

    Anderson, N.; Brown, D.; McMurray, R. J.; Leacock, A. G.

    2011-05-01

    Biaxial test methods have been used to determine, not only yield behaviour under biaxial conditions, but also the strain response. This paper examines the influence of uniaxial prestrain upon the biaxial r-value by extending the disc compression test procedure proposed by Barlat et al. [1]. The extension involved the use of digital image measurements of in-plane strains. The material examined was a 7075-O condition aluminium alloy. The results of the experimental programme indicated that the biaxial r-value is unaffected by uniaxial prestrain. When using the disc compression test, the mode of deformation and therefore the biaxial r-value were found to be very sensitive to the prevailing friction conditions.

  6. Double permeability peaks in Ce9Fe91films with in-plane uniaxial anisotropy

    NASA Astrophysics Data System (ADS)

    Zhou, Xueyun; Yao, Dongsheng; Hou, Cuiling; Chen, Rong; Shen, Hong

    2017-09-01

    Ce9Fe91films were fabricated at different temperature by Rf magnetron sputtering. The static and dynamic magnetic properties of these films have been investigated in details. The results reveal that the two films prepared at 293 K and 623 K with the critical film thickness exhibit weak stripe domains and a small perpendicular anisotropy, and their correlated dynamic permeability spectra show one resonance peak, implying the coherent precession of magnetization at such critical thickness. However, the film prepared at 523 K possesses an in-plane uniaxial anisotropy and lower coercive field. And the permeability spectrum displays two peaks, which can be ascribed to the coexistence of the rotatable anisotropy and in-plane uniaxial anisotropy.

  7. Propagation properties of cylindrically polarized vector beam through uniaxial crystals along the optical axis

    NASA Astrophysics Data System (ADS)

    Li, Jia; Chen, Yanru; Cao, Quanjun

    2013-02-01

    Propagation properties of cylindrically polarized vector (CV) beams through uniaxial crystals along the optical axis are studied. Diffracted field components of the propagating beam are derived in analytical expressions. Amplitudes of the field components, intensity distributions as well as degrees of polarization upon the propagation are depicted by numerical plots, respectively. It is shown that the field components along the x and y axis shows in different characteristics which is induced by the anisotropy of uniaxial crystals. Furthermore, effects of the initial polarization angle as well as the ratio of refractive indices on degrees of polarization are separately analyzed. Numerical results indicate that the degrees of polarization of the propagating beam generally show oscillating characteristics which certainly become much more visible during the sustained propagation. These results may provide potential applications to the optical polarization encoding or detection of unknown anisotropic scatterer by the utilization of CV beam as the incident light.

  8. Inverse magnetocaloric effect in the uniaxial paramagnet with non-Kramers ions

    NASA Astrophysics Data System (ADS)

    Kokorina, E. E.; Medvedev, M. V.

    2017-03-01

    It has been shown that, in a uniaxial paramagnet with non-Kramers ions with a spin of S = 1 and single-ion anisotropy of the easy-plane type ( DS Z 2 ), there is a low-field (μ0 H ≤ D) and low-temperature ( k B T < 0.68D) region in which the isothermal magnetization along the hard direction H||O Z increases the magnetic entropy by Δ S M ( T, Δ H = H f - H i > 0) > 0 and the adiabatic magnetization along the same direction reduces the sample temperature by Δ T ad( T, Δ H > 0) < 0 (inverse magnetocaloric effect (MCE)). The main features of the inverse MCE in uniaxial paramagnets with large spins ( S = 2, 3, …) of the non-Kramers ions have been discussed.

  9. Transverse shifts of a light beam reflected from a uniaxially anisotropic chiral slab

    NASA Astrophysics Data System (ADS)

    Xu, Guoding; Li, Jun; Xiao, Yuting; Mao, Hongmin; Sun, Jian; Pan, Tao

    2015-01-01

    We study for the first time the transverse shifts of a Gaussian beam reflected from a uniaxially anisotropic chiral (UAC) slab, where the chirality appears only in one direction and the host medium is a uniaxial crystal or an electric plasma. The results indicate that the transverse shifts are closely related to the propagation behaviors of the eigenwaves in the slab. Specifically, when one or both of the eigenwaves are totally reflected at the second interface of the slab, the spatial transverse shift becomes resonances but is not enhanced; when one eigenwave is totally reflected at the first interface and the other is transmitted at the second interface, the larger and negative transverse shifts can be obtained. The propagation behaviors of the eigenwaves in the UAC slab provide more abundant information about the transverse shifts than in a single interface structure.

  10. Effect of misaligned unidirectional and uniaxial anisotropies on angular dependence of exchange bias

    NASA Astrophysics Data System (ADS)

    Hu, Yong; Wang, Xiaoling; Jia, Ning; Liu, Yan; Du, An

    2015-01-01

    We report a numerical study of the angular dependences of low-temperature exchange bias field (ADEB) and coercivity in the ferromagnetic/antiferromagnetic bilayers with misaligned unidirectional and uniaxial anisotropies. Through choosing a proper antiferromagnet the conventional symmetry in the ADEB may be broken, while the novel behaviors are also dependent on the angle between induced unidirectional and intrinsic uniaxial anisotropies. Finally, we draw conclusions that the two anisotropies with a small misalignment together determine the asymmetric ADEB properties around the easy axis. In contrast, after the magnetically hysteretic measurement rotating through the hard axis, a large misalignment between the anisotropies may change the magnetization reversal mode at the decreasing branch of loop, besides weakening the positive loop shift. Thus the strength of exchange bias field is suppressed while the coercivity is enhanced.

  11. Mechanical properties of stanene under uniaxial and biaxial loading: A molecular dynamics study

    NASA Astrophysics Data System (ADS)

    Mojumder, Satyajit; Amin, Abdullah Al; Islam, Md Mahbubul

    2015-09-01

    Stanene, a graphene like two dimensional honeycomb structure of tin has attractive features in electronics application. In this study, we performed molecular dynamics simulations using modified embedded atom method potential to investigate mechanical properties of stanene. We studied the effect of temperature and strain rate on mechanical properties of α-stanene for both uniaxial and biaxial loading conditions. Our study suggests that with the increasing temperature, both the fracture strength and strain of the stanene decrease. Uniaxial loading in zigzag direction shows higher fracture strength and strain compared to the armchair direction, while no noticeable variation in the mechanical properties is observed for biaxial loading. We also found at a higher loading rate, material exhibits higher fracture strength and strain. These results will aid further investigation of stanene as a potential nano-electronics substitute.

  12. Stable evaluation of Green's functions in cylindrically stratified regions with uniaxial anisotropic layers

    NASA Astrophysics Data System (ADS)

    Moon, H.; Donderici, B.; Teixeira, F. L.

    2016-11-01

    We present a robust algorithm for the computation of electromagnetic fields radiated by point sources (Hertzian dipoles) in cylindrically stratified media where each layer may exhibit material properties (permittivity, permeability, and conductivity) with uniaxial anisotropy. Analytical expressions are obtained based on the spectral representation of the tensor Green's function based on cylindrical Bessel and Hankel eigenfunctions, and extended for layered uniaxial media. Due to the poor scaling of these eigenfunctions for extreme arguments and/or orders, direct numerical evaluation of such expressions can produce numerical instability, i.e., underflow, overflow, and/or round-off errors under finite precision arithmetic. To circumvent these problems, we develop a numerically stable formulation through suitable rescaling of various expressions involved in the computational chain, to yield a robust algorithm for all parameter ranges. Numerical results are presented to illustrate the robustness of the formulation including cases of practical interest.

  13. Reflection and transmission of Gaussian beam from a uniaxial crystal slab

    NASA Astrophysics Data System (ADS)

    Wang, Yan; Yu, Ke; Zha, Xuejun; Xu, Jiwei; Yan, Jinkui

    2006-08-01

    We investigate the characteristics of Gaussian beams reflected and transmitted from a uniaxial crystal slab with an arbitrary orientation of its optical axis. The formulas of the total electric and magnetic fields inside and outside the slab are derived by use of Maxwell's equations and by matching the boundary conditions at the interfaces. Numerical simulations are presented and the field values as well as the power densities are computed. Negative refractions are demonstrated when the beam is transmitted through a uniaxial crystal slab. Beam splitting of the reflected beam is observed and is explained by the resonant transmission for plane waves. Dependences of the lateral shift on the incident angle and beam width are discussed. Negative and positive lateral shifts are observed due to the spatial anisotropic properties.

  14. A uniaxial constitutive model for superelastic NiTi SMA including R-phase and martensite transformations and thermal effects

    NASA Astrophysics Data System (ADS)

    Helbert, Guillaume; Saint-Sulpice, Luc; Arbab Chirani, Shabnam; Dieng, Lamine; Lecompte, Thibaut; Calloch, Sylvain; Pilvin, Philippe

    2017-02-01

    The well-known martensitic transformation is not always the unique solid-solid phase change in NiTi shape memory alloys (SMA). For this material, R-phase can occur from both austenite and martensite. In some applications, macroscopic strain of the material can be limited to 2%. In these cases, R-phase contribution can not be neglected anymore when compared with martensite. Furthermore, different thermomechanical couplings have to be taken into account to carefully predict strain rate effects and to better describe application conditions. In this paper, a new model taking into account various phase transformations with thermomechanical couplings is presented. This model is based on several transformation criteria. In most applications, SMA are used as wires, submitted to tensile-tensile loadings, in the superelasticity working range. Consequently, a uniaxial reduction of the model is presented for its simplicity. A thermodynamic framework is proposed. It enables to describe the internal variables evolution laws. The simple and fast identification process of model parameters is briefly presented. To verify the validity of the proposed model, simulation results are compared with experimental ones. The influences of testing temperature and strain amplitude on the material behavior is discussed. The damping capacity is also studied, using an energy-based criterion.

  15. Cervical Rotatory Manipulation Decreases Uniaxial Tensile Properties of Rabbit Atherosclerotic Internal Carotid Artery

    PubMed Central

    Qi, Ji; Zhang, Lei; Chen, Chao; Mondal, Shubhro; Ping, Kaike; Chen, Yili

    2017-01-01

    Objective. To investigate the effects of one of the Chinese massage therapies, cervical rotatory manipulation (CRM), on uniaxial tensile properties of rabbit atherosclerotic internal carotid artery (ICA). Methods. 40 male purebred New Zealand white rabbits were randomly divided into CRM-Model group, Non-CRM-Model group, CRM-Normal group, and Non-CRM-Normal group. After modeling (atherosclerotic model) and intervention (CRM or Non-CRM), uniaxial tensile tests were performed on the ICAs to assess the differences in tensile mechanical properties between the four groups. Results. Both CRM and modeling were the main effects affecting physiological elastic modulus (PEM) of ICA. PEM in CRM-Model group was 1.81 times as much as Non-CRM-Model group, while the value in CRM-Model group was 1.34 times as much as CRM-Normal group. Maximum elastic modulus in CRM-Model group was 1.80 times as much as CRM-Normal group. Max strains in CRM-Model group and Non-CRM-Model group were 30.98% and 28.71% lower than CRM-Normal group and Non-CRM-Normal group, respectively. However, whether treated with CRM or not, the uniaxial tensile properties of healthy ICAs were not statistically different. Conclusion. CRM may decrease the uniaxial tensile properties of rabbit arteriosclerotic ICA, but with no effect on normal group. The study will aid in the meaningful explanation of the controversy about the harmfulness of CRM and the suitable population of CRM. PMID:28303160

  16. {sup 52}Cr Spinor Condensate: A Biaxial or Uniaxial Spin Nematic

    SciTech Connect

    Diener, Roberto B.; Ho, T.-L.

    2006-05-19

    We show that the newly discovered {sup 52}Cr Bose condensate in zero magnetic field can be a spin nematic of the following kind: a 'maximum' polar state, a 'colinear' polar state, or a biaxial nematic ferromagnetic state. We also present the phase diagram with a magnetic field in the interaction subspace containing the chromium condensate. It contains many uniaxial and biaxial spin nematic phases, which often but not always break time reversal symmetry, and can exist with or without spontaneous magnetization.

  17. Uniaxial magnetic anisotropy of rhombohedral CoCO3 crystals at T = 0 K

    NASA Astrophysics Data System (ADS)

    Men'shikov, V. V.; Rudenko, V. V.; Tugarinov, V. I.; Vorotynov, A. M.; Ovchinnikov, S. G.

    2014-03-01

    A method for calculating the contribution of exchange interaction to uniaxial anisotropy with the use of g' factors has been worked out using CoCO3 crystals as an example. The calculated contribution of dipole-dipole interactions to the anisotropy of CoCO3 is 0.93 cm-1. The sum of the contributions to the anisotropy constant of CoCO3 with the inclusion of the dipole-dipole interactions is 36.1 cm-1.

  18. Microcrack closure in rocks under stress - Direct observation

    NASA Technical Reports Server (NTRS)

    Batzle, M. L.; Simmons, G.; Siegfried, R. W.

    1980-01-01

    Direct observations of the closure of microcracks in rocks under increasing stress are reported. Uniaxial stresses up to 300 bars were applied to untreated and previously heated samples of Westerly granite and Frederick diabase by a small hydraulic press which fit entirely within a scanning electron microscope. Crack closure characteristics are found to depend on crack orientation, with cracks perpendicular to the applied stress closing and those parallel tending to open, as well as crack aspect ratio, crack intersection properties, stress concentrations and surface roughness. Uniaxial and hydrostatic stress measurements are found to be strongly dependent on fracture content as observed by SEM, and the observed hysteresis in strain measurements in the first stress cycles is also related to microscopic processes

  19. Microcrack closure in rocks under stress - Direct observation

    NASA Technical Reports Server (NTRS)

    Batzle, M. L.; Simmons, G.; Siegfried, R. W.

    1980-01-01

    Direct observations of the closure of microcracks in rocks under increasing stress are reported. Uniaxial stresses up to 300 bars were applied to untreated and previously heated samples of Westerly granite and Frederick diabase by a small hydraulic press which fit entirely within a scanning electron microscope. Crack closure characteristics are found to depend on crack orientation, with cracks perpendicular to the applied stress closing and those parallel tending to open, as well as crack aspect ratio, crack intersection properties, stress concentrations and surface roughness. Uniaxial and hydrostatic stress measurements are found to be strongly dependent on fracture content as observed by SEM, and the observed hysteresis in strain measurements in the first stress cycles is also related to microscopic processes

  20. Stress induced long wavelength photoconductivity in doped silicon infrared detectors

    NASA Technical Reports Server (NTRS)

    Houck, J. R.

    1982-01-01

    The long wavelength cutoff of a Si:P detector was extended to 34 microns by the application of a uniaxial stress. An unstressed Si:P photoconductive detector responds to photons of up to 28 microns wavelength. By applying a uniaxial stress to a detector along the /100/ crystal axis, the response was extended to approximately 34 microns. The /100/ axis was chosen as the stress direction because theoretical calculations predicted that such a stress extends the wavelength response more than one along the /110/ axis. These theoretical calculations were based upon fits to experimental data obtained at stresses of up to approximately kbar, and indicated that the extension in wavelength response continues to increase at much larger stresses.

  1. Describing Soils: Calibration Tool for Teaching Soil Rupture Resistance

    ERIC Educational Resources Information Center

    Seybold, C. A.; Harms, D. S.; Grossman, R. B.

    2009-01-01

    Rupture resistance is a measure of the strength of a soil to withstand an applied stress or resist deformation. In soil survey, during routine soil descriptions, rupture resistance is described for each horizon or layer in the soil profile. The lower portion of the rupture resistance classes are assigned based on rupture between thumb and…

  2. Describing Soils: Calibration Tool for Teaching Soil Rupture Resistance

    ERIC Educational Resources Information Center

    Seybold, C. A.; Harms, D. S.; Grossman, R. B.

    2009-01-01

    Rupture resistance is a measure of the strength of a soil to withstand an applied stress or resist deformation. In soil survey, during routine soil descriptions, rupture resistance is described for each horizon or layer in the soil profile. The lower portion of the rupture resistance classes are assigned based on rupture between thumb and…

  3. Investigation of electron mobility and saturation velocity limits in gallium nitride using uniaxial dielectric continuum model

    NASA Astrophysics Data System (ADS)

    Park, K.; Stroscio, M. A.; Bayram, C.

    2017-06-01

    Here we introduce a uniaxial dielectric continuum model with temperature-dependent phonon mode frequencies to study temperature- and orientation-dependent polar-optical-phonon limited electron mobility and saturation velocity in uniaxial semiconductors. The formalism for calculating electron scattering rates, momentum relaxation rates, and rate of energy change as a function of the electron kinetic energy and incident electron angle with respect to the c-axis are presented and evaluated numerically. Electron-longitudinal-optical-phonon interactions are shown to depend weakly on the electron incident angle, whereas the electron-transverse-optical-phonon interactions around the emission threshold energy are observed to depend strongest on the electron incident angle when varied from π/4 to π/2 (with respect to the c-axis). We provide electron mobility and saturation velocity limits in different GaN crystal orientations as a function of temperature and electron concentration. At room temperature and for an electron density of 5 × 1018 cm-3, electron mobility limit of ˜3200 cm2/V s and electron saturation velocity limit of 3.15 × 107 cm/s are calculated. Both GaN electron mobility and saturation velocity are observed to be governed by the longitudinal-optical-phonon interaction, and their directional anisotropy is shown to vary less than 5% as the electron incident angle with respect to the c-axis is varied from 0 to π/2. Overall, we develop a theoretical formalism for calculating anisotropic properties of uniaxial wurtzite semiconductors.

  4. Preparation of uniaxial multichannel silk fibroin scaffolds for guiding primary neurons.

    PubMed

    Zhang, Qiang; Zhao, Yahong; Yan, Shuqin; Yang, Yumin; Zhao, Huijing; Li, Mingzhong; Lu, Shenzhou; Kaplan, David L

    2012-07-01

    Physical guidance cues have been exploited to stimulate neuron adhesion and neurite outgrowth. In the present study, three-dimensional (3-D) silk fibroin scaffolds with uniaxial multichannels (42-142 μm in diameter) were prepared by a directional temperature field freezing technique, followed by lyophilization. By varying the initial silk fibroin concentration, the chemical potential and quantity of free water around cylindrical ice crystals could be controlled to control the cross-section morphology of the scaffold channels. Aligned ridges also formed on the inner surface of the multichannels in parallel to the direction of the channels. In vitro, primary hippocampal neurons were seeded in these 3-D silk fibroin scaffolds with uniaxial multichannels of ∼120 μm in diameter. The morphology of the neurons was multipolar and alignment along the scaffold channels was observed. Cell-cell networks and cell-matrix interactions established by newly formed axons were observed after 7 days in culture. These neurons expressed β-III-tubulin, nerve filament and microtubule-associated protein, while glial fibrillary acidic protein immunofluorescence was barely above background. The ridges on the inner surface of the channels played a critical role in the adhesion and extension of neurons by providing continuous contact guidance. These new 3-D silk scaffolds with uniaxial multichannels provided a favorable microenvironment for the development of hippocampal neurons by guiding axonal elongation and cell migration.

  5. Phase diagram of the uniaxial and biaxial soft-core Gay-Berne model

    NASA Astrophysics Data System (ADS)

    Berardi, Roberto; Lintuvuori, Juho S.; Wilson, Mark R.; Zannoni, Claudio

    2011-10-01

    Classical molecular dynamics simulations have been used to explore the phase diagrams for a family of attractive-repulsive soft-core Gay-Berne models [R. Berardi, C. Zannoni, J. S. Lintuvuori, and M. R. Wilson, J. Chem. Phys. 131, 174107 (2009)] and determine the effect of particle softness, i.e., of a moderately repulsive short-range interaction, on the order parameters and phase behaviour of model systems of uniaxial and biaxial ellipsoidal particles. We have found that isotropic, uniaxial, and biaxial nematic and smectic phases are obtained for the model. Extensive calculations of the nematic region of the phase diagram show that endowing mesogenic particles with such soft repulsive interactions affect the stability range of the nematic phases, and in the case of phase biaxiality it also shifts it to lower temperatures. For colloidal particles, stabilised by surface functionalisation, (e.g., with polymer chains), we suggest that it should be possible to tune liquid crystal behaviour to increase the range of stability of uniaxial and biaxial phases (by varying solvent quality). We calculate second virial coefficients and show that they are a useful means of characterising the change in effective softness for such systems. For thermotropic liquid crystals, the introduction of softness in the interactions between mesogens with overall biaxial shape (e.g., through appropriate conformational flexibility) could provide a pathway for the actual chemical synthesis of stable room-temperature biaxial nematics.

  6. Oriented Morphology and Anisotropic Transport in Uniaxially Stretched Perfluorosulfonate Ionomer Membranes

    SciTech Connect

    J Park; J Li; G Divoux; L Madsen; R Moore

    2011-12-31

    Relations between morphology and transport sensitively govern proton conductivity in perfluorsulfonate ionomers (PFSIs) and thus determine useful properties of these technologically important materials. In order to understand such relations, we have conducted a broad systematic study of H{sup +}-form PFSI membranes over a range of uniaxial extensions and water uptakes. On the basis of small-angle X-ray scattering (SAXS) and {sup 2}H NMR spectroscopy, uniaxial deformation induces a strong alignment of ionic domains along the stretching direction. We correlate ionic domain orientation to transport using pulsed-field-gradient {sup 1}H NMR measurements of water diffusion coefficients along the three orthogonal membrane directions. Intriguingly, we observe that uniaxial deformation enhances water transport in one direction (parallel-to-draw direction) while reducing it in the other two directions (two orthogonal directions relative to the stretching direction). We evaluate another important transport parameter, proton conductivity, along two orthogonal in-plane directions. In agreement with water diffusion experiments, orientation of ionic channels increases proton conduction along the stretching direction while decreasing it in the perpendicular direction. These findings provide valuable fodder for optimal application of PFSI membranes as well as for the design of next generation polymer electrolyte membranes.

  7. Interaction between a disclination and a uniaxial-isotropic phase interface in a nematic liquid crystal.

    PubMed

    Shklyaev, Oleg E; Fried, Eliot

    2008-01-01

    We consider the interaction between a disclination line of strength +/-1/2 and an interface between the uniaxial and isotropic phases of a nematic liquid crystal. We apply a recently developed set of interface conditions including a configurational force balance which generalizes the Gibbs-Thomson equation to account for the curvature elasticity of the uniaxial phase and the orientation dependence of the interfacial free-energy density. We consider a rectangular vessel containing both phases and a disclination. We formulate a relevant free-boundary problem and use numerical methods to determine equilibrium shapes of the interface. When the interfacial free-energy is constant, the shape of the interface is insensitive to whether the strength of the defect is +1/2 or -1/2 and to rotations of the director field consistent with the boundary conditions. Accounting for the dependence of the interfacial free-energy density on the angle between the interfacial unit normal field and the director field eliminates these degeneracies. In particular, when such dependence is taken into account, different solution branches are found, indicating the presence of a bifurcation. We find also that, depending on the magnitude of the anisotropic contribution to the interfacial free-energy density, the interaction between the disclination and the interface may be repulsive or attractive. When the interaction is repulsive, the disclination line positions itself at an energetically optimal distance adjacent to the interface. Otherwise, the uniaxial phase expels the disclination to the interface where a cusp forms.

  8. Dirac points and van Hove singularities of silicene under uniaxial strain

    SciTech Connect

    Lin, Xianqing; Ni, Jun

    2015-04-28

    First-principles calculations have been performed to investigate the low energy electronic properties and van Hove singularities (VHSs) of silicene under uniaxial strain. The Dirac points (DPs) persist when silicene is stretched uniaxially, while they are shifted away from the corners (K points) of the first Brillouin zone (FBZ). The relative positions of DPs with respect to the K points for silicene strained along the armchair (AC) or zigzag (ZZ) direction show opposite tendency compared with strained graphene, which is due to the larger deformation of the unit cell of strained silicene than that of strained graphene. Moreover, for silicene under AC or ZZ strain, the Fermi velocities around DPs along the positive and negative directions of the FBZ show rather significant difference. The nature of the VHS just above the Fermi energy undergoes a transition from the π* band to the σ* band for silicene under increasing AC or ZZ strain. These observations suggest uniaxial strain as an effective route to tune the electronic properties of silicene for potential applications in future electronic devices.

  9. A luminescent nanocrystal stress gauge

    SciTech Connect

    Choi, Charina; Koski, Kristie; Olson, Andrew; Alivisatos, Paul

    2010-10-25

    Microscale mechanical forces can determine important outcomes ranging from the site of material fracture to stem cell fate. However, local stresses in a vast majority of systems cannot be measured due to the limitations of current techniques. In this work, we present the design and implementation of the CdSe/CdS core/shell tetrapod nanocrystal, a local stress sensor with bright luminescence readout. We calibrate the tetrapod luminescence response to stress, and use the luminescence signal to report the spatial distribution of local stresses in single polyester fibers under uniaxial strain. The bright stress-dependent emission of the tetrapod, its nanoscale size, and its colloidal nature provide a unique tool that may be incorporated into a variety of micromechanical systems including materials and biological samples to quantify local stresses with high spatial resolution.

  10. Thermomechanical characterization of Hastelloy-X under uniaxial cyclic loading

    NASA Technical Reports Server (NTRS)

    Ellis, J. R.; Bartolotta, P. A.; Allen, G. P.; Robinson, D. N.

    1986-01-01

    In most high-temperature engineering applications, components are subjected to complex combinations of thermal and mechanical loading during service. A number of viscoplastic constitutive models were proposed which potentially can provide mathematical descriptions of material response under such conditions. Implementation of these models into large finite element codes such as MARC has already resulted in much improved inelastic analysis capability for hot-section aircraft engine components. However, a number of questions remain regarding the validity of methods adopted in characterizing these constitutive models for particular high-temperature materials. One area of concern is that the majority of experimental data available for this purpose are determined under isothermal conditions. This is in contrast to service conditions which, as noted above, almost always involve some form of thermal cycling. The obvious question arises as to whether a constitutive model characterized using an isothermal data base can adequately predict material response under thermomechanical conditions. An experimental program was initiated within the HOST program to address this particular concern. The results of the most recent isothermal and thermomechanical experiments are described.

  11. Utilization of fiber optic Bragg grating sensors in concrete columns confined with glass-fiber-reinforced plastic (GFRP) laminate under uniaxial compression test

    NASA Astrophysics Data System (ADS)

    Chan, Peter K. C.; Lau, Alan K.; Jin, Wei; Zhou, Limin

    1999-01-01

    In this paper we report of experimental studies on strain monitoring by using fiber Bragg grating sensors in concrete structures. The strain variation of the specimen under different loading conditions were monitored by the Fiber- optic Bragg grating (FBG) sensors. The FBG sensors have been pre-installed in the structure by embedding either inside the concrete specimen or at the interface between the concrete and the composites. The strain reading from the fiber grating sensor compares favorably with that obtained from the conventional strain gauge in uni-axial compression testing. The test result generally indicated that the concrete structures can be strengthened significantly by wrapping with glassfiber composites. The sensor embedded at the notch tip provides a very good indication of the health condition of the strengthened structure, especially in high stress concentration area. The strain sensitivity by using FBG sensor is 67 (mu) (epsilon) .

  12. Experimental investigations of electric current under transverse and longitudinal electric field in uniaxially deformed p-Ge

    NASA Astrophysics Data System (ADS)

    Abramov, A. A.; Akimov, V. I.; Dalakyan, A. T.; Tulupenko, Victor N.; Zaitsev, A. M.; Danilov, S. N.; Firsov, D. A.; Shalygin, V. A.

    1999-11-01

    Comparison between cases of longitudinal and transverse directions of uniaxial pressure and strong electric field, affected the bulk hole germanium, to use it for lasting in far IR region has been carried out. Conclusion about preference of crossed directions is made. Threshold pressure, at which stimulated radiation arises, independence of crystallographic direction, along which external influences are applied, is also discussed. The results of experimental investigations of the crossed directions of uniaxial pressure and electric current are given.

  13. Experimental and theoretical analysis on the procedure for estimating geo-stresses by the Kaiser effect

    NASA Astrophysics Data System (ADS)

    Li, Yuan-Hui; Yang, Yu-Jiang; Liu, Jian-Po; Zhao, Xing-Dong

    2010-10-01

    Acoustic emission tests of the core specimens retrieved from boreholes at the depth over 1000 m in Hongtoushan Copper Mine were carried out under uniaxial compressive loading, and the numerical test was also done by using the rock failure process analysis (RFPA2D) code, based on the procedure for estimating geo-stresses by the Kaiser effect under uniaxial compression. According to the statistical damage mechanics theory, the Kaiser effect mechanism was analyzed. Based on these analyses, it is indicted that the traditional method of estimating geo-stresses by the Kaiser effect is not appropriate, and the result is usually smaller than the real one. Furthermore, the greater confining compression in the rock mass may result in a larger difference between the Kaiser effect stresses acquired from uniaxial loading in laboratory and the real in-situ stresses.

  14. Development and evaluation of a device for simultaneous uniaxial compression and optical imaging of cartilage samples in vitro

    SciTech Connect

    Steinert, Marian; Kratz, Marita; Jones, David B.; Jaedicke, Volker; Hofmann, Martin R.

    2014-10-15

    In this paper, we present a system that allows imaging of cartilage tissue via optical coherence tomography (OCT) during controlled uniaxial unconfined compression of cylindrical osteochondral cores in vitro. We describe the system design and conduct a static and dynamic performance analysis. While reference measurements yield a full scale maximum deviation of 0.14% in displacement, force can be measured with a full scale standard deviation of 1.4%. The dynamic performance evaluation indicates a high accuracy in force controlled mode up to 25 Hz, but it also reveals a strong effect of variance of sample mechanical properties on the tracking performance under displacement control. In order to counterbalance these disturbances, an adaptive feed forward approach was applied which finally resulted in an improved displacement tracking accuracy up to 3 Hz. A built-in imaging probe allows on-line monitoring of the sample via OCT while being loaded in the cultivation chamber. We show that cartilage topology and defects in the tissue can be observed and demonstrate the visualization of the compression process during static mechanical loading.

  15. Hydrostatic, uniaxial, and triaxial compression tests on unpoled "Chem-prep" PZT 95/5-2Nb ceramic within temperature range of -55 to 75 degrees C.

    SciTech Connect

    Zeuch, David Henry; Montgomery, Stephen Tedford; Lee, Moo Yul; Hofer, John H.

    2003-10-01

    Sandia is currently developing a lead-zirconate-titanate ceramic 95/5-2Nb (or PNZT) from chemically prepared ('chem-prep') precursor powders. Previous PNZT ceramic was fabricated from the powders prepared using a 'mixed-oxide' process. The specimens of unpoled PNZT ceramic from batch HF803 were tested under hydrostatic, uniaxial, and constant stress difference loading conditions within the temperature range of -55 to 75 C and pressures to 500 MPa. The objective of this experimental study was to obtain mechanical properties and phase relationships so that the grain-scale modeling effort can develop and test its models and codes using realistic parameters. The stress-strain behavior of 'chem-prep' PNZT under different loading paths was found to be similar to that of 'mixed-oxide' PNZT. The phase transformation from ferroelectric to antiferroelectric occurs in unpoled ceramic with abrupt increase in volumetric strain of about 0.7 % when the maximum compressive stress, regardless of loading paths, equals the hydrostatic pressure at which the transformation otherwise takes place. The stress-volumetric strain relationship of the ceramic undergoing a phase transformation was analyzed quantitatively using a linear regression analysis. The pressure (P{sub T1}{sup H}) required for the onset of phase transformation with respect to temperature is represented by the best-fit line, P{sub T1}{sup H} (MPa) = 227 + 0.76 T (C). We also confirmed that increasing shear stress lowers the mean stress and the volumetric strain required to trigger phase transformation. At the lower bound (-55 C) of the tested temperature range, the phase transformation is permanent and irreversible. However, at the upper bound (75 C), the phase transformation is completely reversible as the stress causing phase transformation is removed.

  16. Method of characterizing residual stress in ferromagnetic materials using a pulse histogram of acoustic emission signals

    NASA Technical Reports Server (NTRS)

    Namkung, Min (Inventor); Yost, William T. (Inventor); Kushnick, Peter W. (Inventor); Grainger, John L. (Inventor)

    1992-01-01

    The invention is a method and apparatus for characterizing residual uniaxial stress in a ferromagnetic test member by distinguishing between residual stresses resulting from positive (tension) forces and negative (compression) forces by using the distinct and known magnetoacoustic (MAC) and a magnetoacoustic emission (MAE) measurement circuit means. A switch permits the selective operation of the respective circuit means.

  17. Methods for describing illumination colour uniformities

    NASA Astrophysics Data System (ADS)

    Rotscholl, Ingo; Trampert, Klaus; Herrmann, Franziska; Neumann, Cornelius

    2015-02-01

    Optimizing angular or spatial colour homogeneity has become an important task in many general lighting applications and first requires a valid description of illumination colour homogeneity. We analyse different frequently used methods to describe colour distributions in theory and with measurement data. It is described why information about chromaticity coordinates, correlated colour temperature and global chromaticity coordinate distances are not sufficient for describing colour homogeneity perception of light distributions. We present local chromaticity coordinate distances as expandable and easy implementable method for describing colour homogeneity distributions that is adaptable to the field of view by only one intuitive, physiological meaningful parameter.

  18. How Do Children Describe Spatial Relationships?

    ERIC Educational Resources Information Center

    Cox, M. V.; Richardson, J. Ryder

    1985-01-01

    Describes a study of children's production of locative prepositions in order to test H. Clark's hypotheses regarding the acquisition of spatial terms. Subjects were required to describe the spatial arrangement of two balls arranged in each of three spatial dimensions. (SED)

  19. Effects of uniaxial strain on electron effective mass and tunneling capability of direct gap Ge{sub 1−x}Sn{sub x} alloys

    SciTech Connect

    Liu, Lei; Liang, Renrong Wang, Jing; Xu, Jun

    2016-01-15

    Direct gap Ge{sub 1−x}Sn{sub x} alloys under [100] and [110] uniaxial strain are comprehensively investigated by theoretical calculations using the nonlocal empirical pseudopotential method (EPM). It is shown that [100] uniaxial tensile strain aids indirect-to-direct gap transition in Ge{sub 1−x}Sn{sub x} alloys. The Γ electron effective mass along the optimal direction under [110] uniaxial strain is smaller than those under [100] uniaxial strain and (001) biaxial strain. Additionally, the direct tunneling gap is smallest along the strain-perpendicular direction under [110] uniaxial tensile strain, resulting in a maximum direct band-to-band tunneling generation rate. An optimal [110] uniaxial tensile strain is favorable for high-performance direct gap Ge{sub 1−x}Sn{sub x} electronic devices.

  20. Elastic behavior of porcine coronary artery tissue under uniaxial and equibiaxial tension.

    PubMed

    Lally, C; Reid, A J; Prendergast, P J

    2004-10-01

    The aim of this study was to characterize the nonlinear anisotropic elastic behavior of healthy porcine coronary arteries under uniaxial and equibiaxial tension. Porcine coronary tissue was chosen for its availability and similarity to human arterial tissue. A biaxial test device previously used to test human femoral arterial tissue samples (Prendergast, P. J., C. Lally, S. Daly, A. J. Reid, T. C. Lee, D. Quinn, and F. Dolan. ASME J. Biomech. Eng., Vol. 125, pp. 692-699, 2003) was further developed to test porcine coronary tissue specimens. The device applies an equal force to the four sides of a square specimen and therefore creates a biaxial stretch that demonstrates the anisotropy of arterial tissue. The nonlinear elastic behavior was marked in both uniaxial and biaxial tests. The tissue demonstrated higher stiffness in the circumferential direction in four out of eight cases subjected to biaxial tension. Even though anisotropy is demonstrated it is proposed that an isotropic hyperelastic model may adequately represent the properties of an artery, provided that an axial stretch is applied to the vessel to simulate the in vivo longitudinal tethering on the vessel. Isotropic hyperelastic models based on the Mooney-Rivlin constitutive equation were derived from the test data by averaging the longitudinal and circumferential equibiaxial data. Three different hyperelastic models were established to represent the test specimens that exhibited a high stiffness, an average stiffness, and a low stiffness response; these three models allow the analyst to account for the variability in the arterial tissue mechanical properties. These models, which take account of the nonlinear elastic behavior of coronary tissue, may be implemented in finite element models and used to carry out preclinical tests of intravascular devices. The errors associated with the hyperelastic models when fitting to both the uniaxial and equibiaxial data for the low stiffness, average stiffness, and

  1. Residual stress measurements in carbon steel

    NASA Technical Reports Server (NTRS)

    Heyman, J. S.; Min, N.

    1986-01-01

    External dc magnetic field-induced changes in natural velocity of Rayleigh surface waves were measured in steel specimens under various stress conditions. The low field slopes of curves representing the fractional changes of natural velocity were proved to provide correct stress information in steels with different metallurgical properties. The slopes of curves under uniaxial compression, exceeding about one third of the yield stress, fell below zero in all the specimens when magnetized along the stress axis. The slopes under tension varied among different steels but remained positive in any circumstances. The stress effect was observed for both applied and residual stress. A physical interpretation of these results is given based on the stress-induced domain structure changes and the delta epsilon effect. Most importantly, it is found that the influence of detailed metallurgical properties cause only secondary effects on the obtained stress information.

  2. Experimental studies of random-field effects in uniaxial random antiferromagnets

    SciTech Connect

    Wong, P.Z.; Cable, J.W.; von Molnar, S.; Dimon, P.

    1983-11-01

    We discuss how random fields (RFs) are generated in uniaxial random antiferromagnets (URAFs) by applied fields and review the experiments that have been performed on these systems. They include direct and indirect specific heat measurements, neutron scattering experiments and phase diagram studies. We compare the results of different experiments on different systems, discuss their implications on the theories, and suggest further experiments. A new explanation for the Lorentzian-squared (LSQ) structure factor observed in the neutron scattering experiments is also given. 47 references, 4 figures.

  3. Raman study of uniaxial deformation of single-crystal mats of ultrahigh molecular weight linear polyethylene

    NASA Astrophysics Data System (ADS)

    Zavgorodnev, Yu V.; Chvalun, S. N.; Nikolaeva, G. Yu; Sagitova, E. A.; Pashinin, P. P.; Gordeyev, S. A.; Prokhorov, K. A.

    2015-03-01

    We present for the first time a Raman spectroscopic study of the deformation process of solution-crystallized single-crystal mats of ultrahigh molecular weight linear polyethylene (UHMW PE). We study the deformed regions of the films, drawn only until the formation of the neck, and the films of much higher draw ratios, just before rupture starts. For comparison, we have also carried out Raman investigations of films produced by compression of UHMW PE powder. We have found that the uniaxial molecular orientation in the neck region of the single-crystal mat films develops more slowly as compared to the films, prepared by compression of the UHMW PE powder.

  4. Effect of uniaxial deformation to 50% on the sensitization process in 316 stainless steel

    SciTech Connect

    Ramirez, L.M.; Almanza, E.; Murr, L.E. . E-mail: fekberg@utep.edu

    2004-09-15

    The effect of uniaxial deformation to 50% on the degree of sensitization (DOS) in 316 stainless steel was investigated at 625 and 670 deg. C for 5-100 h using the electrochemical potentiokinetic reactivation (EPR) test. The results showed that the deformation accelerated the sensitization/desensitization process, especially at 670 deg. C. However, the material is still sensitized after up to 100 h of aging time. Transmission electron microscopy was used to corroborate these results. The deformed material showed more carbide precipitates (Cr{sub 23}C{sub 6}) at the grain boundaries and twin intersections than did the nondeformed material.

  5. Evanescent wave amplification and subwavelength imaging by ultrathin uniaxial μ-near-zero material

    SciTech Connect

    Zhao, Yan

    2014-02-15

    We demonstrate strong evanescent wave amplification by a thin slab of uniaxial μ-near-zero (UMNZ) material. It is found that while retaining the same amplification effect, the slab can be made arbitrarily thin when the negative permeability along the axis of anisotropy approaches zero. Numerical results show that using a single layer of split-ring resonators (SRRs) with its thickness equal three thousandth of the incident wavelength (λ/3000), a subwavelength source distribution with λ/4 resolution can be transferred to a distance of λ/3.

  6. Negative reflection in absorbing uniaxial media. Rutile TiO2

    NASA Astrophysics Data System (ADS)

    Diñeiro, J. M.; Alberdi, C.; Hernández, B.; Sáenz, C.

    2017-07-01

    We study the negative reflection of the extraordinary wave inside a slab of an uniaxial anisotropic absorbing material placed between two isotropic materials. The optic axis is contained in the plane of incidence. We particularize for Rutile TiO2 that possesses a high refractive index that makes it suitable for many applications. We show the existence of negative reflection in the ray and study its dependence with the orientation of the optic axis. We also compute the limiting angle for the occurrence of this phenomenon. It is found that negative reflection occurs for almost all values of the angle of incidence.

  7. Structural changes on the surface of tungsten foils under uniaxial tension

    NASA Astrophysics Data System (ADS)

    Korsukov, V. E.; Knyazev, S. A.; Butenko, P. N.; Gilyarov, V. L.; Korsukova, M. M.; Nyapshaev, I. A.; Obidov, B. A.

    2017-02-01

    A change in the surface morphology of recrystallized tungsten foil under the effect of uniaxial tension in ultrahigh vacuum is studied by low-energy electron diffraction and atomic force microscopy. It is found by using low-energy electron diffraction that on the foil surface consisting of separate blocks with dominant face (112), there is a turn in orientation of the structural blocks. The analysis of the topograms of different areas of the side surface of a broken sample, obtained by atomic force microscopy, enabled the association of changes in the atomic structure of the surface layers of foil with a change in its relief by mechanical action.

  8. Research of mechanics of the compact bone microvolume and porous ceramics under uniaxial compression

    SciTech Connect

    Kolmakova, T. V. Buyakova, S. P. Kul’kov, S. N.

    2015-11-17

    The research results of the mechanics are presented and the effective mechanical characteristics under uniaxial compression of the simulative microvolume of the compact bone are defined subject to the direction of the collagen-mineral fibers, porosity and mineral content. The experimental studies of the mechanics are performed and the effective mechanical characteristics of the produced porous zirconium oxide ceramics are defined. The recommendations are developed on the selection of the ceramic samples designed to replace the fragment of the compact bone of a definite structure and mineral content.

  9. Reflection formulae for ray tracing in uniaxial anisotropic media using Huygens's principle.

    PubMed

    Alemán-Castañeda, Luis A; Rosete-Aguilar, Martha

    2016-11-01

    Ray tracing in uniaxial anisotropic materials is important because they are widely used for instrumentation, liquid-crystal displays, laser cavities, and quantum experiments. There are previous works regarding ray tracing refraction and reflection formulae using the common electromagnetic theory approach, but only the refraction formulae have been deduced using Huygens's principle. In this paper we obtain the reflection expressions using this unconventional approach with a specific coordinate system in which both refraction and reflection formulae are simplified as well as their deduction. We compute some numerical examples to compare them with the common expressions obtained using electromagnetic theory.

  10. Plasticity in Cu(111)/Cu46Zr54 glass nanolaminates under uniaxial compression

    NASA Astrophysics Data System (ADS)

    Arman, B.; Brandl, C.; Luo, S. N.; Germann, T. C.; Misra, A.; ćaǧin, T.

    2011-08-01

    We perform large-scale molecular dynamics simulations to investigate plasticity in Cu/Cu46Zr54 glass nanolaminates under uniaxial compression. Partial and full dislocations are observed in the Cu layers, and screw dislocations are seen near the amorphous-crystalline interfaces (ACIs). Nucleation of shear bands in a glass layer is directly induced by the dislocations in the neighboring crystalline Cu layer through ACIs, and they grow from the ACIs into the glass layer and absorb ambient shear transformation zones. Plasticity in the glass layers is realized via pronounced, stable shear banding.

  11. High uniaxial magnetic anisotropy of the Fe1-xSix films synthesized by MBE

    NASA Astrophysics Data System (ADS)

    Yakovlev, Ivan A.; Tarasov, Ivan A.; Lyashchenko, Sergey A.

    2017-10-01

    The structure and the magnetic anisotropy of the films obtained by simultaneous deposition of iron and silicon on n-Si(111) 7×7 at 130 °C are investigated. It is found the uniaxial magnetic anisotropy field for the Fe1-xSix films with x=0.25 (Fe3Si stoichiometric ratio) deposited on Si(111) 7×7 depends on both the surface miscut angle and the oblique sputtering direction and changes from 0.82 Oe up to 117.26 Oe.

  12. High Temperature Environmental Test Facility for Uniaxial Testing under Cyclic Loading

    DTIC Science & Technology

    2007-11-02

    20503. 1. AGENCY USE ONLY ( Leave Blank) 2. REPORT DATE 3. REPORT TYPE AND DATES COVERED March 23, 1998 Final Report (1 Aug 95 to 31 Jul 97) 4 . TITLE...AND SUBTITLE 5. FUNDING NUMBERS High Temperature Environmental Test Facility For Uniaxial F49620-95- 1-04 70 Testing Under Cyclic Loading 6 . AUTHOR(S...extensometer is rated for 1200 ’C. The system is capable of fatigue testing conventional aluminum and titanium materials and high temperature or single crystal

  13. Ultrashort optical waveguide excitations in uniaxial silica fibers: elastic collision scenarios.

    PubMed

    Kuetche, Victor K; Youssoufa, Saliou; Kofane, Timoleon C

    2014-12-01

    In this work, we investigate the dynamics of an uniaxial silica fiber under the viewpoint of propagation of ultimately ultrashort optical waveguide channels. As a result, we unveil the existence of three typical kinds of ultrabroadband excitations whose profiles strongly depend upon their angular momenta. Looking forward to surveying their scattering features, we unearth some underlying head-on scenarios of elastic collisions. Accordingly, we address some useful and straightforward applications in nonlinear optics through secured data transmission systems, as well as laser physics and soliton theory with optical soliton dynamics.

  14. Modeling the electrical resistance of gold film conductors on uniaxially stretched elastomeric substrates

    NASA Astrophysics Data System (ADS)

    Cao, Wenzhe; Görrn, Patrick; Wagner, Sigurd

    2011-05-01

    The electrical resistance of gold film conductors on polydimethyl siloxane substrates at stages of uniaxial stretching is measured and modeled. The surface area of a gold conductor is assumed constant during stretching so that the exposed substrate takes up all strain. Sheet resistances are calculated from frames of scanning electron micrographs by numerically solving for the electrical potentials of all pixels in a frame. These sheet resistances agree sufficiently well with values measured on the same conductors to give credence to the model of a stretchable network of gold links defined by microcracks.

  15. Terahertz lasers based on intracentre transitions of group V donors in uniaxially deformed silicon

    SciTech Connect

    Kovalevsky, K A; Zhukavin, R Kh; Tsyplenkov, V V; Shastin, V N; Abrosimov, N V; Pavlov, S G; Hübers, H W

    2015-02-28

    This paper presents a brief overview of available experimental data on the characteristics of stimulated terahertz emission (4.9 – 6.4 THz) from optically excited neutral group V donors (phosphorus, antimony, arsenic and bismuth) in crystalline silicon subjected to uniaxially compressive strain along the [100] axis. Strain is shown to have a significant effect on the characteristics in question. Optimal strain depends on the dopant and may reduce the threshold pump intensity and improve lasing efficiency. We discuss possible mechanisms behind this effect and estimate the limiting output emission parameters. (terahertz radiation)

  16. Evolution of textures in zirconium alloys deformed uniaxially at elevated temperatures

    NASA Astrophysics Data System (ADS)

    Rodríguez, A. Salinas; Jonas, J. J.

    1992-01-01

    Texture evolution in α-Zr due to uniaxial deformation at 923 to 1123 K was investigated in crystal-bar Zr and Zr-2.5Nb. The temperature range selected corresponds to the two-phase (α + β) field in the Zr-2.5Nb alloy. It was found that uniaxial compression causes a progressive rotation of the (0002) plane normals away from the compression direction and away from the compression plane. In the crystal-bar Zr, the compression texture consists of a [0001] fiber tilted 30 deg from the compression axis. By contrast, in Zr-2.5Nb, a [0001] fiber with an angular spread of 30 deg is obtained. The effect of the β phase present in Zr-2.5Nb at the temperatures investigated was evaluated by testing a Zr-20Nb alloy in compression. The β-phase texture consisted of a weak <111>-<00l> double fiber. Comparison of this texture and the textures observed in Zr-2.5Nb indicates that the β → α transformation takes place by the growth of pre-existing a grains and not according to the Burgers mechanism. This transformation has, therefore, no direct effect on the α-phase texture after cooling to room temperature from the (α + β) field. Uniaxial elongation by swaging of Zr-2.5Nb produces a dualleft< {10bar 10} rightrangle - left[ {0001} right] fiber. Similar results are obtained in hot extruded rods. Modeling of the development of textures in the α phase was performed using linear programming and employing relaxed constraint (RC) models (“curling” for tension and ”pancake” for compression) implemented for hexagonal close-packed (hcp) grains. It is assumed that prismatic, basal, and < c + a> pyramidal slip were the active deformation modes at high temperatures. It is shown that these models reduce the activity of the pyramidal slip systems to realistic values, in contrast to the full constraint (FC) approach, where most of the deformation is accommodated by < c + a> slip. Microstructural evidence is presented regarding the occurrence of ”curling” during uniaxial

  17. Uniaxial pressure dependencies of the phase transitions in GdMnO3

    NASA Astrophysics Data System (ADS)

    Baier, J.; Meier, D.; Berggold, K.; Hemberger, J.; Balbashov, A.; Mydosh, J. A.; Lorenz, T.

    2007-03-01

    GdMnO3 shows an incommensurate antiferromagnetic order below ≃42 K, transforms into a canted A-type antiferromagnet below ≃20 K, and for finite magnetic fields along the b-axis ferroelectric order occurs below ≃12 K. From high-resolution thermal expansion measurements along all three principal axes, we determine the uniaxial pressure dependencies of the various transition temperatures and discuss their correlation to changes of the magnetic exchange couplings in RMnO3(R=La,…,Dy).

  18. An Analytical Approach For Earing In Cylindrical Deep Drawing Based On Uniaxial Tensile Test Results

    NASA Astrophysics Data System (ADS)

    Mulder, J.; Vegter, H.

    2011-05-01

    The prediction of earing and wall thickness distribution in cylindrical deep drawing is a challenging task even for today's FEA programs with advanced yield loci like Yld2004-18p, BBC2003 or Vegter. The current work involves an analytical description of cylindrical deep drawing that is comparable in accuracy to advanced numerical models. The analytical approach shows the importance for these type of simulations of fitting the yield locus description to uniaxial tensile test results in different directions, considering the full hardening curves.

  19. Researches of mechanical behaviour of the bone micro volumes and porous ceramics under uniaxial compression

    NASA Astrophysics Data System (ADS)

    Kolmakova, T. V.; Buyakova, S. P.; Kulkov, S. N.

    2017-02-01

    The research results of the mechanics are presented and the effective mechanical characteristics under uniaxial compression of the simulative micro volume of the compact bone are defined subject to the direction of the collagen-mineral fibers, porosity and mineral content. The experimental and computer studies of the mechanics are performed and the effective mechanical characteristics of the porous zirconium oxide ceramics are defined. The recommendations are developed on the selection of the ceramic samples designed to replace the fragment of the compact bone of a definite structure and mineral content.

  20. Uniaxial strain induced band splitting in semiconducting SrTiO3

    NASA Astrophysics Data System (ADS)

    Chang, Young Jun; Khalsa, Guru; Moreschini, Luca; Walter, Andrew L.; Bostwick, Aaron; Horn, Karsten; MacDonald, A. H.; Rotenberg, Eli

    2013-03-01

    We use angle-resolved photoemission spectroscopy to study the influence of mechanically induced uniaxial strain on the electronic structure of the oxide semiconductor SrTiO3. We observe an orbital splitting between the Ti 3dyz and 3dxy bands, which are degenerate when unperturbed. Using the k·p method, we qualitatively explain the direction and the size of the observed energy splitting. Our comprehensive understanding of band splitting explains the strain induced mobility enhancement of electron-doped SrTiO33 in terms of band degeneracy breaking and reduced interband scattering. Our approach can be extended to differently strained oxide systems.

  1. On the limits of uniaxial magnetic anisotropy tuning by a ripple surface pattern

    SciTech Connect

    Arranz, Miguel A.; Colino, Jose M.; Palomares, Francisco J.

    2014-05-14

    Ion beam patterning of a nanoscale ripple surface has emerged as a versatile method of imprinting uniaxial magnetic anisotropy (UMA) on a desired in-plane direction in magnetic films. In the case of ripple patterned thick films, dipolar interactions around the top and/or bottom interfaces are generally assumed to drive this effect following Schlömann's calculations for demagnetizing fields of an ideally sinusoidal surface [E. Schlömann, J. Appl. Phys. 41, 1617 (1970)]. We have explored the validity of his predictions and the limits of ion beam sputtering to induce UMA in a ferromagnetic system where other relevant sources of magnetic anisotropy are neglected: ripple films not displaying any evidence of volume uniaxial anisotropy and where magnetocrystalline contributions average out in a fine grain polycrystal structure. To this purpose, the surface of 100 nm cobalt films grown on flat substrates has been irradiated at fixed ion energy, fixed ion fluency but different ion densities to make the ripple pattern at the top surface with wavelength Λ and selected, large amplitudes (ω) up to 20 nm so that stray dipolar fields are enhanced, while the residual film thickness t = 35–50 nm is sufficiently large to preserve the continuous morphology in most cases. The film-substrate interface has been studied with X-ray photoemission spectroscopy depth profiles and is found that there is a graded silicon-rich cobalt silicide, presumably formed during the film growth. This graded interface is of uncertain small thickness but the range of compositions clearly makes it a magnetically dead layer. On the other hand, the ripple surface rules both the magnetic coercivity and the uniaxial anisotropy as these are found to correlate with the pattern dimensions. Remarkably, the saturation fields in the hard axis of uniaxial continuous films are measured up to values as high as 0.80 kG and obey a linear dependence on the parameter ω{sup 2}/Λ/t in quantitative agreement

  2. FUNDAMENTAL AREAS OF PHENOMENOLOGY (INCLUDING APPLICATIONS): Application of Equivalent Air Gap Method in Uniaxial Crystal Plate

    NASA Astrophysics Data System (ADS)

    Ren, Wen-Yi; Zhang, Chun-Min; Mu, Ting-Kui

    2009-08-01

    The equivalent air gap method is a simple way to trace the ray propagation in an isotropic medium, but it cannot be applied to an anisotropic medium. We present the exact general expressions of the equivalent air gap thicknesses and the displacements for the plane-parallel uniaxial crystal plates. They are also suitable for the isotropic medium. This method is useful when one determines whether certain size plane-parallel plates can be fitted into the available air of an optical system, and also in the prism system design.

  3. Constitutive modeling of the human Anterior Cruciate Ligament (ACL) under uniaxial loading using viscoelastic prony series and hyperelastic five parameter Mooney-Rivlin model

    NASA Astrophysics Data System (ADS)

    Chakraborty, Souvik; Mondal, Debabrata; Motalab, Mohammad

    2016-07-01

    In this present study, the stress-strain behavior of the Human Anterior Cruciate Ligament (ACL) is studied under uniaxial loads applied with various strain rates. Tensile testing of the human ACL samples requires state of the art test facilities. Furthermore, difficulty in finding human ligament for testing purpose results in very limited archival data. Nominal Stress vs. deformation gradient plots for different strain rates, as found in literature, is used to model the material behavior either as a hyperelastic or as a viscoelastic material. The well-known five parameter Mooney-Rivlin constitutivemodel for hyperelastic material and the Prony Series model for viscoelastic material are used and the objective of the analyses comprises of determining the model constants and their variation-trend with strain rates for the Human Anterior Cruciate Ligament (ACL) material using the non-linear curve fitting tool. The relationship between the model constants and strain rate, using the Hyperelastic Mooney-Rivlin model, has been obtained. The variation of the values of each coefficient with strain rates, obtained using Hyperelastic Mooney-Rivlin model are then plotted and variation of the values with strain rates are obtained for all the model constants. These plots are again fitted using the software package MATLAB and a power law relationship between the model constants and strain rates is obtained for each constant. The obtained material model for Human Anterior Cruciate Ligament (ACL) material can be implemented in any commercial finite element software package for stress analysis.

  4. Stress echocardiography

    MedlinePlus

    Echocardiography stress test; Stress test - echocardiography; CAD - stress echocardiography; Coronary artery disease - stress echocardiography; Chest pain - stress echocardiography; Angina - stress ...

  5. Apoplexia uteri: a rarely described post-mortem finding.

    PubMed

    Beggan, C; Jaber, K; Leader, M

    2013-08-01

    We present a case of apoplexia uteri, a rarely described condition of haemorrhagic necrosis in an atrophic endometrium and myometrium associated with terminal stress. This entity is well recognised in older literature but few recent publications have addressed this condition. It is thought to occur in association with hypoperfusion with passive hyperaemia and reperfusion injury. This case serves to highlight this rarely encountered entity as a possible cause of haemorrhage in an atrophic endometrium in the 'perimortem' period. Incidental findings are occasionally observed in the course of forensic autopsy practice and knowledge of rarely encountered entities, such as that described in this case, is essential to prevent diagnostic uncertainty and misdiagnosis.

  6. Systematically describing gross lesions in corals

    USGS Publications Warehouse

    Work, T.; Aeby, G.

    2006-01-01

    Many coral diseases are characterized based on gross descriptions and, given the lack or difficulty of applying existing laboratory tools to understanding causes of coral diseases, most new diseases will continued to be described based on appearance in the field. Unfortunately, many existing descriptions of coral disease are ambiguous or open to subjective interpretation, making comparisons between oceans problematic. One reason for this is that the process of describing lesions is often confused with that of assigning causality for the lesion. However, causality is usually something not obtained in the field and requires additional laboratory tests. Because a concise and objective morphologic description provides the foundation for a case definition of any disease, there is a need for a consistent and standardized process to describe lesions of corals that focuses on morphology. We provide a framework to systematically describe and name diseases in corals involving 4 steps: (1) naming the disease, (2) describing the lesion, (3) formulating a morphologic diagnosis and (4) formulating an etiologic diagnosis. This process focuses field investigators on describing what they see and separates the process of describing a lesion from that of inferring causality, the latter being more appropriately done using laboratory techniques.

  7. Uniaxial Orientational Order-Disorder Transitions in Diammine Magnesium Halides, Mg

    SciTech Connect

    Leineweber, A.; Jacobs, H.; Fischer, P.; Boettger, G.

    2001-02-01

    Neutron powder diffraction on Mg(ND{sub 3}){sub 2}Cl{sub 2} and Mg(ND{sub 3}){sub 2}Br{sub 2} revealed as a function of temperature uniaxial orientational order-disorder behavior of the ND{sub 3} groups. The crystal structures of both compounds are built up from chains of octahedra {sub {infinity}}{sup 1}[Mg(NH{sub 3}){sub 2}X{sub 4/2}] with X=Cl and Br arranged in different ways relative to each other. At ambient temperatures (X=Cl) and 270 K (X=Br) the ND{sub 3} groups are disordered with respect to a rotation about the bond Mg-N. The D atom density is well described by a fourfold split position, each D ''site'' connecting an N with an X atom: Mg(ND{sub 3}){sub 2}Cl{sub 2}, Cmmm, a=8.1828(6) {angstrom}, b=8.2007(6) {angstrom}, c=3.7543(2) {angstrom}, R(F{sup 2}){sub Bragg}=5.9%; Mg(ND{sub 3}){sub 2}Br{sub 2}, Pbam, a=5.9714(2) {angstrom}, b=11.9175(3) {angstrom}, c=3.98477(8) {angstrom}, R(F{sup 2}){sub Bragg}=7.9%. In both cases the c axis corresponds to the direction of the chains {sub {infinity}}{sup 1}[Mg(NH{sub 3}){sub 2}X{sub 4/2}]. At low temperatures (8 K (X=Cl) and 1.5 K (X=Br)) both compounds are ordered with respect to the ND{sub 3} groups: They are arranged antiferroelectrically on either side of the chains {sub {infinity}}{sup 1}[Mg(NH{sub 3}){sub 2}X{sub 4/2}]. The symmetry is lowered compared to the situation at ambient temperatures and 270 K respectively, which involves in both cases a doubling of the orthorhombic c axis: Mg(ND{sub 3}){sub 2}Cl{sub 2}, Ibmm, a=8.1319(3) {angstrom}, b=8.1338(3) {angstrom}, c=7.4410(2) {angstrom}, R(F{sup 2}){sub Bragg}=5.9%; Mg(ND{sub 3}){sub 2}Br{sub 2}, Pnam, a= 5.92837(8) {angstrom}, b=11.8448(2) {angstrom}, c=7.9117(1) {angstrom}, R(F{sup 2}){sub Bragg}=5.0%. Detailed evaluation of neutron diffraction data of Mg(ND{sub 3}){sub 2}Cl{sub 2} as a function of temperature (50 K < T < 150 K) characterizes the phase transition as continuous with T{sub t}{approx}135 K.

  8. Evolution of elastic properties and acoustic emission, during uniaxial loading of rocks, from the Fogo Volcano in the island of Sao Miguel, Azores; Preliminary results.

    NASA Astrophysics Data System (ADS)

    Moreira, M.; Wallenstein, N.

    2012-04-01

    A Computerized Uniaxial Press working up to 250 kN was installed in the middle 2011 in the Laboratory of Microseismic Monitoring of ISEL. The system is able to record continuous time, pressure and axial strain (1 µm resolution) at 1s sampling rate. The loading platens were designed to integrate acoustic emission (AE) transducers. Signals are acquired and processed through an 8-channel ESG Hyperion Ultrasonic Monitoring System (10 MSPS, 14/16-bit ADC). The first experiments, presented here, were applied to a set of rock samples from the Fogo, an active central volcano in the island of Sao Miguel. Two different volcanic rock types were studied: a fine grained alkali basaltic rock with a porphyritic texture, a porosity of 4.5% and bulk density of 2700 kg m-3 (sample #3); and a benmoreitic rock with a trachytic texture, a porosity of 8.1 %, and bulk density of 2400 kg m-3 (sample #4). Cores from sample #3 were subjected to continuous increasing pressure, until failure. They show a uniaxial compressive strength (UCS) spanning from 60 to 85 MPa and a stress-strain curve with two phases: a first one with relative low Young's Module (YM) followed by a second phase were the YM increases roughly 3 times. The stress transition value occurs broadly in a stress level 50% of the UCS. The AE produced in the process is almost negligible until the YM transition stress level and increases after that. Important pulses of high AE rate occur, (> 100 s-1), associated with the occurrence and propagation of fractures, which are always parallel to the principal stress, showing an evident pattern of tensile fractures. About 20s before the failure, very important deformation rate is observed, the YM strongly decrease, and continuous AE events, with low rate, usually <50 s-1. The failure is accompanied with a sudden rise of AE events with rate > 200 s-1. Cycling stress experiences were also performed showing reversible stress-strain relation for axial pressure below the YM transition level

  9. Uniaxial and Multiaxial Fatigue Life Prediction of the Trabecular Bone Based on Physiological Loading: A Comparative Study.

    PubMed

    Fatihhi, S J; Harun, M N; Abdul Kadir, Mohammed Rafiq; Abdullah, Jaafar; Kamarul, T; Öchsner, Andreas; Syahrom, Ardiyansyah

    2015-10-01

    Fatigue assessment of the trabecular bone has been developed to give a better understanding of bone properties. While most fatigue studies are relying on uniaxial compressive load as the method of assessment, in various cases details are missing, or the uniaxial results are not very realistic. In this paper, the effect of three different load histories from physiological loading applied on the trabecular bone were studied in order to predict the first failure surface and the fatigue lifetime. The fatigue behaviour of the trabecular bone under uniaxial load was compared to that of multiaxial load using a finite element simulation. The plastic strain was found localized at the trabecular structure under multiaxial load. On average, applying multiaxial loads reduced more than five times the fatigue life of the trabecular bone. The results provide evidence that multiaxial loading is dominated in the low cycle fatigue in contrast to the uniaxial one. Both bone volume fraction and structural model index were best predictors of failure (p < 0.05) in fatigue for both types of loading, whilst uniaxial loading has indicated better values in most cases.

  10. Interplay of uniaxial and cubic anisotropy in epitaxial Fe thin films on MgO (001) substrate

    NASA Astrophysics Data System (ADS)

    Mallik, Srijani; Chowdhury, Niru; Bedanta, Subhankar

    2014-09-01

    Epitaxial Fe thin films were grown on annealed MgO(001) substrates at oblique incidence by DC magnetron sputtering. Due to the oblique growth configuration, uniaxial anisotropy was found to be superimposed on the expected four-fold cubic anisotropy. A detailed study of in-plane magnetic hysteresis for Fe on MgO thin films has been performed by Magneto Optic Kerr Effect (MOKE) magnetometer. Both single step and double step loops have been observed depending on the angle between the applied field and easy axis i.e. along ⟨100⟩ direction. Domain images during magnetization reversal were captured by Kerr microscope. Domain images clearly evidence two successive and separate 90° domain wall (DW) nucleation and motion along cubic easy cum uniaxial easy axis and cubic easy cum uniaxial hard axis, respectively. However, along cubic hard axis two 180° domain wall motion dominate the magnetization reversal process. In spite of having four-fold anisotropy it is essential to explain magnetization reversal mechanism in 0°< ϕ < 90° span as uniaxial anisotropy plays a major role in this system. Also it is shown that substrate rotation can suppress the effect of uniaxial anisotropy superimposed on four-fold anisotropy.

  11. Uniaxially strained SiGe(111) and SiGe(100) grown on selectively ion-implanted substrates

    NASA Astrophysics Data System (ADS)

    Sawano, K.; Hoshi, Y.; Kubo, S.; Yamada, S.; Nakagawa, K.; Shiraki, Y.

    2014-09-01

    Selective ion implantation method, which can induce uniaxial strain into Si/Ge heterostructures, is applied to both SiGe/Si(111) and SiGe/Si(100). The effect of ion implantation on the strain relaxation enhancements is confirmed for the SiGe(111). With optimal implantation conditions, the local strain control is realized, and anisotropic strain states are obtained. However, the anisotropy of the strain states in SiGe(111) is much smaller than SiGe(100) due to the dislocation structure. Since the one direction dislocations are unlikely to be generated in SiGe(111), the obtained uniaxial strain is considered to be induced by elastic effect. In contrast, one direction arrays of dislocations are clearly observed for SiGe(100), which indicates that the uniaxial strain induced in SiGe(100) is caused by plastic relaxation. It can be, therefore, concluded that the SiGe(100) is more suitable for obtaining the uniaxial strain than SiGe(111) and that high mobility uniaxially strained channel devices are expected to be realized based on this technique.

  12. Propagation properties of an orthogonal cosine-Gaussian Schell-model beam in uniaxial crystals orthogonal to the optical axis

    NASA Astrophysics Data System (ADS)

    Xu, Hua-Feng; Huang, Lin-Mu; Sheng, Zong-Qiang; Tang, Xu-Dong; Qu, Jun

    2017-08-01

    The analytical expressions for an orthogonal cosine-Gaussian Schell-model (OCGSM) beam propagating in uniaxial crystals orthogonal to the optical axis are derived. Based on the formulas derived, the propagation properties, such as the normalized spectral density, the spectral degree of coherence (SDOC), and the effective beam width of an OCGSM beam in uniaxial crystals are illustrated. Numerical results show that, by changing the beam mode order n and m, the OCGSM beam can split into two- or four-beamlet elliptical beams and keep invariant in uniaxial crystals during propagation, which is different from the conventional Gaussian Schell-model beam. The SDOC of the OCGSM beam will evolve into an elliptical shape and the effective beam width of the OCGSM beam will spread faster along the x direction than the y direction in uniaxial crystals. In addition, the significant influence of the beam mode order, the spatial coherence length and the ratio of the extraordinary refractive index to the ordinary refractive index of the uniaxial crystals on the evolution properties of an OCGSM beam is discussed in detail.

  13. Venus general atmosphere circulation described by Pioneer

    NASA Technical Reports Server (NTRS)

    1981-01-01

    The predominant weather pattern for Venus is described. Wind directions and wind velocities are given. Possible driving forces of the winds are presented and include solar heating, planetary rotation, and the greenhouse effect.

  14. Using ontologies to describe mouse phenotypes

    PubMed Central

    Gkoutos, Georgios V; Green, Eain CJ; Mallon, Ann-Marie; Hancock, John M; Davidson, Duncan

    2005-01-01

    The mouse is an important model of human genetic disease. Describing phenotypes of mutant mice in a standard, structured manner that will facilitate data mining is a major challenge for bioinformatics. Here we describe a novel, compositional approach to this problem which combines core ontologies from a variety of sources. This produces a framework with greater flexibility, power and economy than previous approaches. We discuss some of the issues this approach raises. PMID:15642100

  15. Biaxial Stress Limit for ULDB Film

    NASA Technical Reports Server (NTRS)

    Sterling, W. J.; Rand, J. L.

    2005-01-01

    The current ULDB design applies stress to the shell film biaxially to control creep in the latitudinal direction. The recent change in design paradigm, from a uniaxial to biaxial stress state basis, arose from a new perspective that the biaxial loading can control strain in both principal surface dimensions as discussed below. The current ULDB project path was thus enabled by a more thorough understanding of the nonlinear viscoelastic properties of the shell film material, linear low-density polyethylene (LLDPE). Although a very similar material is also used in NASA zero-pressure (ZPB) and long-duration balloons (LDB), the different stress state requires a new approach to shell material qualification.

  16. Failure of a fiber composite lamina under three-dimensional stresses

    SciTech Connect

    DeTeresa, S J

    1999-08-31

    The efficient use of thick-section fiber composites requires a proven three-dimensional failure model. Numerous failure criteria have been proposed, but the lack of critical experimental results makes it difficult to assess the accuracy of these models. It is shown that the various predictions for failure of a lamina due to the simple state of uniaxial stress plus superposed hydrostatic pressure are disparate. These differences are sufficient to allow evaluation of failure criteria using data that has the normal scatter found for composite materials. A high-pressure test system for fiber composites is described and results for the effects of pressure on the transverse and longitudinal compression strengths of a carbon fiber/epoxy lamina are discussed. Results are compared with a few representative failure models.

  17. PNNL Stress/Strain Correlation for Zircaloy

    SciTech Connect

    Geelhood, Kenneth J.; Beyer, Carl E.; Luscher, Walter G.

    2008-07-18

    Pacific Northwest National Laboratory (PNNL) was tasked with incorporating cladding mechanical property data into the Nuclear Regulatory Commission (NRC) fuel codes, FRAPCON-31 and FRAPTRAN2, by the NRC Office of Nuclear Reactor Research. The objective of that task was to create a mechanical model that can calculate true stress, true strain, and the possible failure of the fuel rod cladding based on uniaxial test data.

  18. Light-induced stress relief to improve flaw tolerance in network polymers

    NASA Astrophysics Data System (ADS)

    Long, Kevin N.; Dunn, Martin L.; Scott, Timothy F.; Turpin, Lucas P.; Qi, H. Jerry

    2010-03-01

    We demonstrate the ability to use photoactivated stress relaxation to improve flaw tolerance in network polymers. Unlike most self-healing polymers, which effectively close flaws by locally introducing healing agents (such as uncured resins), here light is used to relax elevated stresses around a flaw before it reaches a critical state, which reduces the threat that the flaw poses to the structural integrity of the material. In this study, we fabricate specimens with well-defined flaws and uniaxially stretch them to failure. By irradiating the specimens with UV light (365 nm) before failure, the nominal strain at failure is increased by 70% and the corresponding nominal stress is increased by 30% compared with nonirradiated specimens. To better understand the phenomena that occur at the multiaxial stress state at the flaw, we model the photomechanics using a recently developed finite element approach that accurately describes the light propagation, photochemistry, radical-induced network evolution, and the mechanical behavior of the material. Model predictions agree well with the experimental results and elucidate the role that photoinduced stress relaxation has on improving flaw tolerance.

  19. Light-induced stress relief to improve flaw tolerance in network polymers

    SciTech Connect

    Long, Kevin N.; Dunn, Martin L.; Scott, Timothy F.; Turpin, Lucas P.; Qi, H. Jerry

    2010-03-15

    We demonstrate the ability to use photoactivated stress relaxation to improve flaw tolerance in network polymers. Unlike most self-healing polymers, which effectively close flaws by locally introducing healing agents (such as uncured resins), here light is used to relax elevated stresses around a flaw before it reaches a critical state, which reduces the threat that the flaw poses to the structural integrity of the material. In this study, we fabricate specimens with well-defined flaws and uniaxially stretch them to failure. By irradiating the specimens with UV light (365 nm) before failure, the nominal strain at failure is increased by 70% and the corresponding nominal stress is increased by 30% compared with nonirradiated specimens. To better understand the phenomena that occur at the multiaxial stress state at the flaw, we model the photomechanics using a recently developed finite element approach that accurately describes the light propagation, photochemistry, radical-induced network evolution, and the mechanical behavior of the material. Model predictions agree well with the experimental results and elucidate the role that photoinduced stress relaxation has on improving flaw tolerance.

  20. The resonance susceptibility of two-layer exchange-coupled ferromagnetic film with a combined uniaxial and cubic anisotropy in the layers

    NASA Astrophysics Data System (ADS)

    Shul'ga, N. V.; Doroshenko, R. A.

    2016-12-01

    A numerical investigation of the resonance dynamic susceptibility of ferromagnetic exchange-coupled two-layer films with a combined cubic and uniaxial magnetic anisotropy of the layers has been performed. It has been found that the presence of cubic anisotropy leads to the fact that much of the off-diagonal components of the dynamic susceptibility are nonzero. The change of the ferromagnetic resonance frequencies and dynamic susceptibility upon the magnetization along the [100], [010], and [011] directions have been calculated. The evolution of the profile of the dynamic susceptibility occurring during the magnetization has been described. The impact of changes in the distribution of equilibrium and dynamic components of the magnetization on the dependences of the components of the dynamic susceptibility and the ferromagnetic resonance frequency on the external magnetic fields has been discussed.

  1. Multiphonon scattering of light with direct transitions between optical modes in uniaxial single crystals and its application to an all-optical computing

    NASA Astrophysics Data System (ADS)

    Shcherbakov, Alexandre S.; Tepichin Rodriguez, Eduardo; Aguirre Lopez, Arturo

    2004-11-01

    A specific case of a multi-phonon non-collinear light scattering in optically uniaxial media is presented. Compared to our previous studies, an innovation lies in the fact that now we consider passing just the quartet of incident light beams through a single crystal that is perturbed by the triplet of coherent acoustic waves. The exact and closed analytical model for describing this strongly nonlinear phenomenon is developed. In fact, specially designed regime of a four-order light scattering whit direct coupling of all the light modes, when transitions of four input light beams into four output light modes are allowed and electronically controlled, is examined. The feasibility of applying such an effect to an all-optical computing and performing an all-optical adder is analyzed.

  2. Axisymmetric micromechanics of elastic-perfectly plastic fibrous composites under uniaxial tension loading

    NASA Technical Reports Server (NTRS)

    Lee, Jong-Won; Allen, David H.

    1993-01-01

    The uniaxial response of a continuous fiber elastic-perfectly plastic composite is modeled herein as a two-element composite cylinder. An axisymmetric analytical micromechanics solution is obtained for the rate-independent elastic-plastic response of the two-element composite cylinder subjected to tensile loading in the fiber direction for the case wherein the core fiber is assumed to be a transversely isotropic elastic-plastic material obeying the Tsai-Hill yield criterion, with yielding simulating fiber failure. The matrix is assumed to be an isotropic elastic-plastic material obeying the Tresca yield criterion. It is found that there are three different circumstances that depend on the fiber and matrix properties: fiber yield, followed by matrix yielding; complete matrix yield, followed by fiber yielding; and partial matrix yield, followed by fiber yielding, followed by complete matrix yield. The order in which these phenomena occur is shown to have a pronounced effect on the predicted uniaxial effective composite response.

  3. The role of uniaxial deformation on microstructure and dynamics of a bulk-polymerized polyurea

    NASA Astrophysics Data System (ADS)

    Runt, James; Choi, Taeyi; Fragiadakis, Daniel; Roland, C. Michael

    2011-03-01

    Polyureas, formed by the rapid reaction between isocyanates and diamines are attractive for various applications due to their outstanding mechanical properties, which can be tuned by varying component chemistry, molecular weight and stoichiometry. Polyureas synthesized from a modified methylene diphenyl diisocyanate (Isonate 143L) and polytetramethylene oxide-di-p-aminobenzoate (Versalink P1000) are widely utilized and investigated for energy absorbing applications such as impact mitigation and ballistic protection. In order to develop a more complete understanding of their mechanical response, we explore the effect of uniaxial strain on the phase separated microstructure and molecular dynamics. We utilize wide- and small-angle X-ray scattering to investigate amorphous segment and hard domain orientation and broadband dielectric spectroscopy for interrogation of the dynamics Uniaxial deformation was found to significantly perturb the phase separated microstructure and chain orientation, and result in a considerable slowing down and broadening of the polyurea soft phase segmental relaxation. This work is supported by Office of Naval Research.

  4. Volume growth during uniaxial tension of particle-filled elastomers at various temperatures - Experiments and modelling

    NASA Astrophysics Data System (ADS)

    Ilseng, Arne; H. Skallerud, Bjørn; H. Clausen, Arild

    2017-10-01

    A common presumption for elastomeric material behaviour is incompressibility, however, the inclusion of filler particles might give rise to matrix-particle decohesion and subsequent volume growth. In this article, the volumetric deformation accompanying uniaxial tension of particle-filled elastomeric materials at low temperatures is studied. An experimental set-up enabling full-field deformation measurements is outlined and novel data are reported on the significant volume growth accompanying uniaxial tension of two HNBR and one FKM compounds at temperatures of - 18 , 0, and 23 °C. The volumetric deformation was found to increase with reduced temperature for all compounds. To explain the observed dilatation, in situ scanning electron microscopy was used to inspect matrix-particle debonding occurring at the surface of the materials. A new constitutive model, combining the Bergström-Boyce visco-hyperelastic formulation with a Gurson flow potential function is outlined to account for the observed debonding effects in a numerical framework. The proposed model is shown to provide a good correspondence to the experimental data, including the volumetric response, for the tested FKM compound at all temperature levels.

  5. Development of an elastic cell culture substrate for a novel uniaxial tensile strain bioreactor

    PubMed Central

    Moles, Matthew D; Scotchford, Colin A; Ritchie, Alastair Campbell

    2014-01-01

    Bioreactors can be used for mechanical conditioning and to investigate the mechanobiology of cells in vitro. In this study a polyurethane (PU), Chronoflex AL, was evaluated for use as a flexible cell culture substrate in a novel bioreactor capable of imparting cyclic uniaxial tensile strain to cells. PU membranes were plasma etched, across a range of operating parameters, in oxygen. Contact angle analysis and X-ray photoelectron spectroscopy showed increases in wettability and surface oxygen were related to both etching power and duration. Atomic force microscopy demonstrated that surface roughness decreased after etching at 20 W but was increased at higher powers. The etching parameters, 20 W 40 s, produced membranes with high surface oxygen content (21%), a contact angle of 66° ± 7° and reduced topographical features. Etching and protein conditioning membranes facilitated attachment, and growth to confluence within 3 days, of MG-63 osteoblasts. After 2 days with uniaxial strain (1%, 30 cycles/min, 1500 cycles/day), cellular alignment was observed perpendicular to the principal strain axis, and found to increase after 24 h. The results indicate that the membrane supports culture and strain transmission to adhered cells. © 2013 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 102A: 2356–2364, 2014. PMID:23946144

  6. Viewing zone duplication of multi-projection 3D display system using uniaxial crystal.

    PubMed

    Lee, Chang-Kun; Park, Soon-Gi; Moon, Seokil; Lee, Byoungho

    2016-04-18

    We propose a novel multiplexing technique for increasing the viewing zone of a multi-view based multi-projection 3D display system by employing double refraction in uniaxial crystal. When linearly polarized images from projector pass through the uniaxial crystal, two possible optical paths exist according to the polarization states of image. Therefore, the optical paths of the image could be changed, and the viewing zone is shifted in a lateral direction. The polarization modulation of the image from a single projection unit enables us to generate two viewing zones at different positions. For realizing full-color images at each viewing zone, a polarization-based temporal multiplexing technique is adopted with a conventional polarization switching device of liquid crystal (LC) display. Through experiments, a prototype of a ten-view multi-projection 3D display system presenting full-colored view images is implemented by combining five laser scanning projectors, an optically clear calcite (CaCO3) crystal, and an LC polarization rotator. For each time sequence of temporal multiplexing, the luminance distribution of the proposed system is measured and analyzed.

  7. Uniaxial cyclic strain enhances adipose-derived stem cell fusion with skeletal myocytes

    SciTech Connect

    Andersen, Jens Isak; Juhl, Morten; Nielsen, Thøger; Emmersen, Jeppe; Fink, Trine; Zachar, Vladimir; Pennisi, Cristian Pablo

    2014-07-25

    Highlights: • Uniaxial cyclic tensile strain (CTS) applied to ASCs alone or in coculture with myogenic precursors. • CTS promoted the formation of a highly ordered array of parallel ASCs. • Without biochemical supplements, CTS did not support advanced myogenic differentiation of ASCs. • Mechanical stimulation of cocultures boosted fusion of ASCs with skeletal myoblasts. - Abstract: Although adult muscle tissue possesses an exceptional capacity for regeneration, in the case of large defects, the restoration to original state is not possible. A well-known source for the de novo regeneration is the adipose-derived stem cells (ASCs), which can be readily isolated and have been shown to have a broad differentiation and regenerative potential. In this work, we employed uniaxial cyclic tensile strain (CTS), to mechanically stimulate human ASCs to participate in the formation skeletal myotubes in an in vitro model of myogenesis. The application of CTS for 48 h resulted in the formation of a highly ordered array of parallel ASCs, but failed to support skeletal muscle terminal differentiation. When the same stimulation paradigm was applied to cocultures with mouse skeletal muscle myoblasts, the percentage of ASCs contributing to the formation of myotubes significantly exceeded the levels reported in the literature hitherto. In perspective, the mechanical strain may be used to increase the efficiency of incorporation of ASCs in the skeletal muscles, which could be found useful in diverse traumatic or pathologic scenarios.

  8. Magnetic microstructure and magnetic properties of uniaxial itinerant ferromagnet Fe3GeTe2

    DOE PAGES

    León-Brito, Neliza; Bauer, Eric Dietzgen; Ronning, Filip; ...

    2016-08-28

    Here, magnetic force microscopy was used to observe the magnetic microstructure of Fe3GeTe2 at 4 K on the (001) surface. The surface magnetic structure consists of a two-phase domain branching pattern that is characteristic for highly uniaxial magnets in the plane perpendicular to the magnetic easy axis. The average surface magnetic domain width Ds = 1.3 μm determined from this pattern, in combination with intrinsic properties calculated from bulk magnetization data (the saturation magnetization Ms = 376 emu/cm3 and the uniaxial magnetocrystalline anisotropy constant Ku = 1.46 × 107 erg/cm3), was used to determine the following micromagnetic parameters for Fe3GeTe2more » from phenomenological models: the domain wall energy γw = 4.7 erg/cm2, the domain wall thickness δw = 2.5 nm, the exchange stiffness constant Aex = 0.95 × 10–7 erg/cm, the exchange length lex = 2.3 nm, and the critical single domain particle diameter dc = 470 nm.« less

  9. Modification of the classical Heisenberg helimagnet by weak uniaxial anisotropy and magnetic field

    SciTech Connect

    Zaliznyak, I.A.; Zhitomirsky, M.E.

    1995-09-01

    A classical ground state of the isotropic Heisenberg spin Hamiltonian on a primitive Bravais lattice is known to be a single-Q plane helix. Additional uniaxial anisotropy and external magnetic field can greatly distort this structure by generating higher-order (at the wave vectors nQ) Fourier harmonics in the spatial spin configuration. These features are not captured within the usual formalism based on the Luttinger-Tisza theorem, when the classical ground state energy is minimized under the {open_quotes}weak{close_quotes} condition on the lengths of the spins. We discuss why the correct solution is lost in that approach and present another microscopic treatment of the problem. For easy-axis and easy-plane quadratic uniaxial anisotropy it allows one to find the classical ground state for general Q and for any orientation of the magnetic field considering the effect of anisotropy (but not the field) as a perturbation of the exchange structure. As a result, the classical ground state energy, the uniform magnetization, and the magnetic Bragg peak intensities that are measured in the experiments are calculated. 21 refs., 1 fig.

  10. Near-field thermal radiation between homogeneous dual uniaxial electromagnetic metamaterials

    SciTech Connect

    Chang, Jui-Yung; Basu, Soumyadipta; Yang, Yue; Wang, Liping

    2016-06-07

    Recently, near-field thermal radiation has attracted much attention in several fields since it can exceed the Planck blackbody limit through the coupling of evanescent waves. In this work, near-field radiative heat transfer between two semi-infinite dual uniaxial electromagnetic metamaterials with two different material property sets is theoretically analyzed. The near-field radiative heat transfer is calculated using fluctuational electrodynamics incorporated with anisotropic wave optics. The underlying mechanisms, namely, magnetic hyperbolic mode, magnetic surface polariton, electrical hyperbolic mode, and electrical surface polariton, between two homogeneous dual uniaxial electromagnetic metamaterials are investigated by examining the transmission coefficient and the spectral heat flux. The effect of vacuum gap distance is also studied, which shows that the enhancement at smaller vacuum gap is mainly due to hyperbolic mode and surface plasmon polariton modes. In addition, the results show that the contribution of s-polarized waves is significant and should not be excluded due to the strong magnetic response regardless of vacuum gap distances. The fundamental understanding and insights obtained here will facilitate the finding and application of novel materials for near-field thermal radiation.

  11. Analysis of cooperative effects between uniaxial and torsional strains in carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Najafi, Z.; Ahmadkhan Kordbacheh, A.; Afshar, M.

    2016-06-01

    The analyses of the electronic properties of a Single-Wall Carbon Nanotube (SWCN) under both uniaxial and torsional strains are presented with the main intrinsic curvature taken into account. Within tight-binding mechanism, Heyd and Charlier method is extended to cover chiral types of SWCNs using a single π- orbital model for the nanotubes. The variations of the bond lengths and the band gap as functions of chirality and the strain parameters of carbon nanotube are discussed. An improved analytical expression for the deformed geometrical structure of a SWCN with arbitrary chiral indices has been derived, and a numerical band gap analysis of a chiral type is conducted. The existence of an interference or cooperative effect between uniaxial and torsional strains on band gap of a SWCN is found. The results of our calculations show that the cooperative effects depend strongly on the chirality of SWCNs and the strain parameters, so that, in contrast to the other works, there exists some strain parameters for which the cooperative effects are not found in the armchair SWCNs. In addition, it was found that the strain parameters can be chosen to correspond to the cooperative effects in zigzag SWCNs.

  12. Magnetic microstructure and magnetic properties of uniaxial itinerant ferromagnet Fe3GeTe2

    NASA Astrophysics Data System (ADS)

    León-Brito, N.; Bauer, E. D.; Ronning, F.; Thompson, J. D.; Movshovich, R.

    2016-08-01

    Magnetic force microscopy was used to observe the magnetic microstructure of Fe3GeTe2 at 4 K on the (001) surface. The surface magnetic structure consists of a two-phase domain branching pattern that is characteristic for highly uniaxial magnets in the plane perpendicular to the magnetic easy axis. The average surface magnetic domain width Ds = 1.3 μm determined from this pattern, in combination with intrinsic properties calculated from bulk magnetization data (the saturation magnetization Ms = 376 emu/cm3 and the uniaxial magnetocrystalline anisotropy constant Ku = 1.46 × 107 erg/cm3), was used to determine the following micromagnetic parameters for Fe3GeTe2 from phenomenological models: the domain wall energy γw = 4.7 erg/cm2, the domain wall thickness δw = 2.5 nm, the exchange stiffness constant Aex = 0.95 × 10-7 erg/cm, the exchange length lex = 2.3 nm, and the critical single domain particle diameter dc = 470 nm.

  13. Incommensurate phases of a supported nanoparticle film subjected to uniaxial compression

    NASA Astrophysics Data System (ADS)

    You, Siheng; Leahy, Bran; Zhang, Minke; Chua, Yenchao; Lee, Ka Yee C.; Coppersmith, Susan N.; Lin, Binhua

    2014-03-01

    We investigate experimentally and theoretically the sequence of phases that occurs when a self-assembled monolayer of gold nanoparticles supported on a fluid is compressed uniaxially in a Langmuir trough. Uniaxial compression of the monolayer results in the appearance of lines that have been shown to be regions of trilayer. These lines exhibit complex patterns that depend on the extent of compression. We show that these patterns can be understood in terms of an equilibrium statistical mechanical theory, originally developed in the context of commensurate-incommensurate transitions in krypton monolayers adsorbed on graphite, in which there is an energy cost to line deformations and to line intersections. Even though line intersections are energetically costly, they lower the free energy because they cause the entropy of the system to increase when the density of lines is low enough. Our analytic and Monte Carlo analyses of the model demonstrate that the model exhibits two-phase coexistence. Our experimental observations are qualitatively consistent with the predictions of the model. This work is supported by the Wisconsin Alumni Research Foundation, NSF-DMR 0906951, U Chicago MRSEC (NSF-DMR 0820054), and ChemmatCARS (NSF/DOE 0822838).

  14. Study of natural rubber crosslinked in the state of uniaxial deformation

    NASA Astrophysics Data System (ADS)

    Dubrović, I.; Klepac, D.; Valić, S.; Žauhar, G.

    2008-06-01

    A natural rubber (NR) film with the thickness of about 1 mm was prepared by removing the liquid phase from NR latex. Two types of NR films crosslinked by γ-irradiation were investigated: (i) samples irradiated in the relaxed state and (ii) samples irradiated in the state of uniaxial deformation. The total irradiation dose varied from 0 kGy (for nonirradiated NR) to 400 kGy and the degree of deformation, defined as λ=l/ l0 ( l0 and l being the lengths of relaxed and uniaxially deformed sample, respectively), was chosen to be λ=1.0 (relaxed state), λ=1.5 and λ=2.0. The amount of sol and gel phase of NR was determined by extracting the sol component in toluene. A significant decrease in the amount of the sol component (from 14.2% to 33.5%, depending on irradiation dose) was observed by increasing the irradiation dose. It has been shown that the application of deformation during the crosslinking leads to the lower crosslink density. Such an effect can be attributed to the loss of the gel component induced mechanically. The electron spin resonance (ESR) spectra of spin probe diffusing in the NR matrix crosslinked under deformation are influenced by both, the local dynamics of the chain segments and their spacious orientation.

  15. Magnetically controlled rotation and torque of uniaxial microactuators for lab-on-a-chip applications.

    PubMed

    Ranzoni, Andrea; Janssen, Xander J A; Ovsyanko, Mikhail; van IJzendoorn, Leo J; Prins, Menno W J

    2010-01-21

    We demonstrate the controlled rotation and torque generated by uniaxial magnetic microactuators formed by two bound superparamagnetic particles in a fluid. The torque and rotation are precisely controlled by rotating magnetic fields, generated by an external electromagnet or by on-chip current wires. We present the magnetic energy equations and the equations of motion for two-particle microactuators, with contributions from the permanent and induced magnetic moments of the particles. A comparison of theory and experiments allows an estimation of the different moments with accuracy better than 10% across a wide frequency range. At low frequencies and low magnitudes of the applied magnetic field, both the permanent and induced moments of the particles have contributions to the torque. At either high fields or high frequencies, the torque is dominated by the induced moment. The predictability of the torque is highest in the regime of low frequencies and high field, where the torque has a large magnitude and is determined by the magnetic shape anisotropy of the microactuator. A comparison of rotation in bulk fluid and on a chip surface shows an increase of friction by a factor 9 originating from the surface proximity. The detailed understanding of the torque and rotation of two-particle uniaxial magnetic microactuators opens a range of possibilities in lab-on-a-chip applications, such as the actuation of single molecules, fluid mixing in microfluidic chambers, and novel cluster-based assays.

  16. Electrical transport anisotropy of uniaxial polycrystalline samples and the effective medium approximation: An application to HTS

    NASA Astrophysics Data System (ADS)

    Cruz-García, A.; Muné, P.

    2016-08-01

    In this paper we have applied the effective medium approximation (EMA) to a polycrystalline sample made up of uniaxial crystallites with similar behavior to the high critical temperature superconductors (HTS) at the normal state (σab ≫ σc). As a result the dependence of the anisotropy parameter at the level of the sample, μ =σx /σz , on orientation probability of the grains' a-axes along a certain preferential direction, γxa is obtained. The intrinsic and shape anisotropy parameters of the crystallites constitute input data. In addition, the dependence of the orientation factor, f, which has been introduced in current models on the transport properties of HTS, is calculated as a function of γxa. These results offer a tool to interpret electrical transport measurements at normal state in granular uniaxial superconducting materials with certain texture degree, by means of the correlation between microstructure and electrical transport properties. Moreover, the comparison between the model and some experimental data suggests the presence of intragranular planar defects in the polycrystalline superconductors. They may affect the measurement of paracoherent resistivity and consequently the determination of f mainly in Bi based samples.

  17. Uniaxial strain effects on the optoelectronic properties of GaN nanowires

    NASA Astrophysics Data System (ADS)

    Xia, Sihao; Liu, Lei; Kong, Yike; Wang, Meishan

    2016-09-01

    Considering the importance of strain engineering on semiconductors, GaN nanowires under uniaxial compression deformation and stretch deformation are researched using first principle calculations with density functional theory. It is found that the deformation will destroy the stability of the nanowires except a weak stretch. The compression deformation is more difficult than the stretch deformation. Besides, the work function of the nanowires is reduced under increasing compression while that under increasing stretch is reversed. With increasing diameter, the band gaps of the nanowires gradually exhibit a linear decreasing relation as the elongation of uniaxial length of GaN nanowires. With increasing compression, the band gaps change from direct to indirect. The optical calculations exhibit a redshift for the imaginary part of dielectric function. This study demonstrates strain engineering can effectively adjust the optoelectronic characteristics of GaN nanowire. Moderate compression, which induces a lower work function with a direct band gap, can improve the photoemission performance of GaN nanowires.

  18. Magnetization behavior of scandium-substituted barium hexaferrite films having uniaxial axis in the film plane

    NASA Astrophysics Data System (ADS)

    Yoon, S. D.; Vittoria, C.; Oliver, S. A.

    2003-09-01

    Highly oriented films of ( 1 0 1¯ 0 ) BaSc 0.6Fe 11.4O 19 having the magnetic easy axis (crystallographic [0 0 0 1] axis) in the film plane were deposited by pulsed laser deposition onto a-plane ( 1 1 2¯ 0 ) sapphire (Al 2O 3) substrates. Magnetometry and torque magnetometry measurements showed in-plane permanent magnet (magnetic dipole) behavior below a coercive field value of 450 Oe, while high field measurements yielded a uniaxial anisotropy field value of 10 kOe. Measurements at temperatures from 123 to 650 K showed the uniaxial anisotropy field was insensitive to temperature for T<400 K, while the coercive field had a maximum value near 525 K before declining to zero at TC=638 K. This temperature dependence was modeled by an empirical Brown's-type equation for T⩽525 K, where the fitting parameters indicated the presence of surprisingly large effective local demagnetizing fields. The film microstructure is inferred to significantly affect the magnetization behavior, and is also presumed to cause significant ferrimagnetic resonance linewidth broadening compared to BaFe 12O 19 (0 0 0 1) films.

  19. 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.

  20. Quantum formalism to describe binocular rivalry.

    PubMed

    Manousakis, Efstratios

    2009-11-01

    On the basis of the general character and operation of the process of perception, a formalism is sought to mathematically describe the subjective or abstract/mental process of perception. It is shown that the formalism of orthodox quantum theory of measurement, where the observer plays a key role, is a broader mathematical foundation which can be adopted to describe the dynamics of the subjective experience. The mathematical formalism describes the psychophysical dynamics of the subjective or cognitive experience as communicated to us by the subject. Subsequently, the formalism is used to describe simple perception processes and, in particular, to describe the probability distribution of dominance duration obtained from the testimony of subjects experiencing binocular rivalry. Using this theory and parameters based on known values of neuronal oscillation frequencies and firing rates, the calculated probability distribution of dominance duration of rival states in binocular rivalry under various conditions is found to be in good agreement with available experimental data. This theory naturally explains an observed marked increase in dominance duration in binocular rivalry upon periodic interruption of stimulus and yields testable predictions for the distribution of perceptual alteration in time.