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Sample records for biaxial stress

  1. Analysis of Biaxially Stressed Bridge Deck Plates

    Jönsson, Jeppe; Bondum, Tommi Højer

    The ultimate state analysis of bridge deck plates at the intersection zone between main girders and transverse beams is complicated by biaxial membrane stresses, which may be in compression or tension in either direction depending on the bridge configuration and the specific location. This paper ...

  2. Reverse loading tests of steel tube under biaxial stress states

    Yanaga, Daisaku; Kuroda, Kouichi; Yaita, Satoshi; Kuwabara, Toshihiko

    2015-01-01

    Biaxial loading and reverse loading tests were performed using seamless carbon steel tubes. Biaxial stress components in the axial and circumferential directions were applied to the tubular specimens using a servo-controlled multiaxial tube expansion testing machine developed by Kuwabara and Sugawara (2013). The tubular specimens were loaded under linear tensile stress paths. Contours of plastic work were measured in the principal stress space, and the differential hardening (DH) behavior was...

  3. Biaxial failure criteria and stress-strain response for concrete of containment structure

    Biaxial failure criteria and stress-strain response for plain concrete of containment structure on nuclear power plants are studied under uniaxial and biaxial stress(compression-compression, compression-tension, and tension-tension combined stress). The concrete specimens of a square plate type are used for uniaxial and biaxial loading. The experimental data indicate that the strength of concrete under biaxial compression, f2/f1=-1/-1, is 17 percent larger than under uniaxial compression and the poisson's ratio of concrete is 0.1745. On the base of the results, a biaxial failure envelope for plain concrete that the uniaxial strength is 5660 psi are provided, and the biaxial failure behaviors for three biaxial loading areas are plotted respectively. And, various analytical equations having the reliability are proposed for representations of the biaxial failure criteria and stress-strain response curves of concrete

  4. Application of magnetomechanical hysteresis modeling of magnetic techniques for monitoring neutron embrittlement and biaxial stress

    Research was done on the biaxial stress problem accomplished in the first half of the second year. All of the work done was preparatory to magnetic measurements. Issues addressed were: construction of a model for extracting changes in the magnetic properties of a specimen from the readings of an indirect sensor; initial development of a model for how biaxial stress alters the intrinsic magnetic properties of thespecimen; use of finite element stress analysis modeling to determine a detailed shape for the cruciform biaxial stress specimen; and construction of the biaxial stress loading apparatus

  5. Acoustic emission under biaxial stresses in unflawed 21-6-9 and 304 stainless steel

    Acoustic emission (AE) testing has been carried out with uniaxial and biaxial (2:1 stress ratio) stressing of smooth samples of 21-6-9 and 304 stainless steel (SS). Uniaxial testing was done with simple tensile and compression samples as well as with the special biaxial specimens. Biaxial tensile stressing was accomplished with a specially designed specimen, which had been used previously to characterize AE in 7075 aluminum under biaxial stressing. Results were obtained for air-melt and for vacuum-melt samples of 21-6-9 SS. The air-melt samples contain considerably more inclusion particles than the vacuum-melt samples. For the 304 SS, as received material was examined. To allow AE correlations with microstructure, extensive characterization of the 21-6-9 microstructure was carried out. Significant differences in AE occur in biaxially stressed specimens as compared to uniaxially stressed samples. 15 figures, 3 tables

  6. Numerical analysis oriented biaxial stress-strain relation and failure criterion of plain concrete

    A biaxial stress-strain relation and failure criterion is proposed, which is applicable to structural analysis methods. The formulation of material behavior of plain concrete in biaxial stress-state was developed. A nonlinear elastic, anisotropic stress-strain relation was derived with two moduli of elasticity, E1, E2 and Poisson's ratios, ν1, ν2, which depend on the prevailing biaxial stress state. The stress-strain relation is valid in the whole biaxial stress field, that means with a smooth transition between the domains of tension/tension, tension/compression and compression/compression. The stress-dependent moduli E1, E2 and the Poisson's ratios ν1, ν2 are approximated by polynomials, trigonometrical and exponential functions. A failure criterion was defined by approximating the test results of the biaxial ultimate concrete strength with a 7th degree polynomial, which is also valid in the whole biaxial stress domain. The definition of the state of failure is given as a function of stresses as well as strains. Initial parameters of the formulation of the biaxial material behavior are the uniaxial cylindrical strength of concrete and the initial values of Young's modulus and Poisson's ratio. A simple expansion of this formulation makes it applicable not only to normal but also to light-weight concrete. Comparison of numerically calculated stress-strain curves up to the ultimate biaxial stresses which indicate the failure criteria with those obtained from tests show a very good agreement. It is shown, that the biaxial stress-strain relation can be extended for use in cases of triaxial tension/tension/compression stress state. Numerical examples of analysis of concrete slabs show the importance of incorporation of a realistic material behavior for better safety estimations

  7. Evaluation of micro fatigue crack growth under equi-biaxial stress by membranous pressure fatigue test

    For preventing nuclear power plant (NPP) accidents, NPPs are required to ensure system safety in long term safe operation under aging degradation. Now, fatigue accumulation is one of major ageing phenomena and are evaluated to ensure safety by design fatigue curve that are based on the results of uniaxial fatigue tests. On the other hand, thermal stress that occurs in piping of actual components is not uniaxial but equi-biaxial. For accurate evaluation, it is required to conform real circumstance. In this study, membranous pressure fatigue test was conducted to simulated equi-biaxial stress. Crack initiation and crack growth were examined by replica investigation. Calculation result of equivalent stress intensity factor shows crack growth under equi-biaxial stress is faster than under uniaxial stress. It is concluded that equi-biaxial fatigue behavior should be considered in the evaluation of fatigue crack initiation and crack growth. (author)

  8. Long-term strength of Kh13M2S2 in biaxial stressed state

    Long-term strength of thin-walled tubular and plane samples of Kh13M2S2 steel at 650 deg C was studied. The tubular samples were loaded with internal gas pressure which resulted in a biaxial stressed state, the plane ones were loaded with uniaxial extension. Statistical processing of the experimental results was carried out, the straight lines of long-term strength with confidence intervals were plotted. Of four studied criteria of the complex stressed state the best coincidence of the experimental results under biaxial and uniaxial load is obtained using the Lebedev criterion

  9. The failure behavior of the cladding with outer surface pre-crack in biaxial stress test

    Biaxial stress tests using the unirradiated Cold Worked Stress Relieved (CWSR) Zircaloy-4 cladding with an outer surface pre-crack were conducted under room temperature condition. To reproduce the biaxial stress states assumed in RIA conditions, Expansion Due to Compression (EDC) test which induces uniaxial stress states was developed using a tensile test machine. Constant tensile loads, 0, 5.0 and 10.0 kN, were applied to specimens through each test, respectively. All specimens failed in the tests, and the failure morphology was similar to that observed in the PIEs conducted for the pulse irradiation experiments using a high burnup fuel. The longitudinal strain (εtz) at failure clearly increased with increasing tensile loads and the circumferential strain (εtθ) at failure decreased significantly in 5.0 and 10.0 kN tests compared to 0 kN tests. These data obtained in this study are considered as the fundamentals to quantify the failure criteria of claddings in a biaxial stress state. (author)

  10. Numerical analysis of interacting cracks in biaxial stress field

    The stress corrosion cracks as seen for example in PWR steam generator tubing made of Inconel 600 usually produce highly irregular kinked and branched crack patterns. Crack initialization and propagation depends on stress state underlying the crack pattern. Numerical analysis (such as finite element method) of interacting kinked and branched cracks can provide accurate solutions. This paper discusses the use of general-purpose finite element code ABAQUS for evaluating stress fields at crack tips of interacting complex cracks. The results obtained showed reasonable agreement with the reference solutions and confirmed use of finite elements in such class of problems.(author)

  11. A new analytical model about the relationship between nominal failure stresses and porosity for foamed metals under biaxial tension

    Foamed metals have been widely used as various engineering materials, and their mechanical properties have also been drawing extensive attention. In the present paper, a new mechanical and analytical model is established for these materials with isotropic three-dimensional reticulated structure under biaxial tension, and the mathematical equation about biaxial nominal stresses is deduced for the biaxial tension at the beginning of failure of the porous body. With the relevant experiment, the relation formula is proved to be very effective. Different from the relevant theoretical system of Gibson and Ashby, the present mathematical relationship can be conveniently achieved from directly using the 'beam theory' on this mechanical and analytical model. In addition, this relationship can be further expressed as the mathematical relationship among the nominal failure 'deviatoric stress', the nominal failure 'average stress' and porosity, but the concepts of both the 'deviatoric stress' and the 'average stress' can appear just from the mathematical treatment

  12. Numerical analysis of branched cracks in bi-axial stress fields

    The stress corrosion cracks as seen for example in PWR steam generator tubing made of Inconel 600 are usually found to be of highly irregular kinked and branched shapes. Numerical analysis of kinked and branched cracks in bi-axial plane stress fields using methods such as finite or boundary element method may provide useful and cost effective solutions. However, accurate analysis of complex shaped cracks requires very fine meshes and, consequently, excessively high computational efforts. This paper discusses some possible strategies of numerical modeling of kinked and branched cracks in general bi-axial stress field using the general-purpose finite element code ABAQUS. The strategies discussed include J-integral and stress intensity factor solutions with different mesh densities. The accuracy of the numerical results obtained is compared with reference solutions from the literature. The main result of the paper is an optimal numerical strategy, which maximizes the accuracy of the result at as low computational efforts as feasible. The selected optimal strategy is expected to be used in the future simulations of large networks of inter-granular stress corrosion cracks at the grain-size scale using incomplete random tessellation.(author)

  13. Estimation of low cycle fatigue life of elbows considering bi-axial stress effect

    Elbow pipes are commonly used in the piping systems of power plants and chemical plants. The stress states at elbow part are complex and quite different from those of the straight pipes. It is well known that the fatigue lives of metals under simple push-pull conditions were successfully predicted by the Manson's universal slope method. However, it have been pointed out by the several researchers that the low cycle fatigue lives of elbows under combined cyclic bending and inner pressure could not be predicted by the Manson's universal slope method. However, the reasons for this are not made clear. In this work, the low cycle fatigue tests and the finite element analysis of elbows under cyclic bending and inner pressures were carried out. It was found that the bi-axial stress ratio, which is a ratio of hoop stress and axial stress, at elbows are quite high. Considering the bi-axial stress ratio, the revised Manson's universal slope method was proposed in this paper. It was shown that the low cycle fatigue lives of elbows under combined cyclic bending and inner pressure were predicted conservatively by the proposed method. (author)

  14. Biaxial stresses, surface roughness and microstructure in evaporated TiO2 films with different deposition geometries

    The residual stresses, surface roughness and microstructure in titanium oxide films prepared by electron-beam evaporation and deposited with different geometries were investigated, with particular focus on the in-plane anisotropy of the biaxial stresses and microstructures. Thin films were deposited with various deposition angles on B270 glass substrates and silicon wafers. Two different types of deposition geometries were studied. The residual stress in the thin films was examined by a phase-shifting Twyman-Green interferometer. The optical constants, biaxial stress and surface roughness were found to be related to the evolution of the anisotropic microstructures in the films. The results revealed that the anisotropic stresses that developed in the evaporated titanium oxide films were dependent upon the deposition geometry and microstructure of the films.

  15. Numerical and experimental analysis of the directional stability on crack propagation under biaxial stresses

    In this paper, the case of Single Edge Notch (SEN) specimens subject to opening/compressive loading was analyzed; The loads are applied in several ratios to evaluate the influence of the specimen geometry, and the Stress Intensity Factor (SIF) K1 values on the directional stability of crack propagation. The main purpose of this work is to evaluate the behaviour of the fracture propagation, when modifying the geometry of the SEN specimen and different relationships of load tension/compression are applied. Additionally, the precision of the numerical and experimental analysis is evaluated to determine its reliability when solving this type of problems. The specimens are subjected to biaxial opening/compression loading; both results (numerical and experimental) are compared in order to evaluate the condition of directional stability on crack propagation. Finally, an apparent transition point related to the length of specimens was identified, in which the behaviour of values of SIF changes for different loading ratios.

  16. Numerical and experimental analysis of the directional stability on crack propagation under biaxial stresses

    RodrIguez-MartInez, R; Urriolagoitia-Calderon, G; Urriolagoitia-Sosa, G; Hernandez-Gomez, L H [Instituto Politecnico Nacional Seccion de Estudios de Posgrado e Investigacion (SEPI), Escuela Superior de IngenierIa Mecanica y Electrica (ESIME), Edificio 5. 2do Piso, Unidad Profesional Adolfo Lopez Mateos ' Zacatenco' Col. Lindavista, C.P. 07738, Mexico, D.F. (Mexico); Merchan-Cruz, E A; RodrIguez-Canizo, R G; Sandoval-Pineda, J M, E-mail: rrodriguezm@ipn.m, E-mail: urrio332@hotmail.co, E-mail: guiurri@hotmail.co, E-mail: luishector56@hotmail.co, E-mail: eamerchan@gmail.co, E-mail: ricname@hotmail.co, E-mail: jsandovalp@ipn.m [Instituto Politecnico Nacional Seccion de Estudios de Posgrado e Investigacion (SEPI), Escuela Superior de IngenierIa Mecanica y Electrica (ESIME). Unidad profesional, AZCAPOTZALCO, Av. de las Granjas No. 682, Col. Sta. Catarina Azcapotzalco, C.P. 02550, Mexico D.F. (Mexico)

    2009-08-01

    In this paper, the case of Single Edge Notch (SEN) specimens subject to opening/compressive loading was analyzed; The loads are applied in several ratios to evaluate the influence of the specimen geometry, and the Stress Intensity Factor (SIF) K{sub 1} values on the directional stability of crack propagation. The main purpose of this work is to evaluate the behaviour of the fracture propagation, when modifying the geometry of the SEN specimen and different relationships of load tension/compression are applied. Additionally, the precision of the numerical and experimental analysis is evaluated to determine its reliability when solving this type of problems. The specimens are subjected to biaxial opening/compression loading; both results (numerical and experimental) are compared in order to evaluate the condition of directional stability on crack propagation. Finally, an apparent transition point related to the length of specimens was identified, in which the behaviour of values of SIF changes for different loading ratios.

  17. Application of magnetomechanical hysteresis modeling to magnetic techniques for monitoring neutron embrittlement and biaxial stress

    The objective is to investigate experimentally and theoretically the effects of neutron embrittlement and biaxial stress on magnetic properties in steels, using various magnetic measurement techniques. Interaction between experiment and modeling should suggest efficient magnetic measurement procedures for determining neutron embrittlement biaxial stress. This should ultimately assist in safety monitoring of nuclear power plants and of gas and oil pipelines. In the first six months of this first year study, magnetic measurements were made on steel surveillance specimens from the Indian Point 2 and D.C. Cook 2 reactors. The specimens previously had been characterized by Charpy tests after specified neutron fluences. Measurements now included: (1) hysteresis loop measurement of coercive force, permeability and remanence, (2) Barkhausen noise amplitude; and (3) higher order nonlinear harmonic analysis of a 1 Hz magnetic excitation. Very good correlation of magnetic parameters with fluence and embrittlement was found for specimens from the Indian Point 2 reactor. The D.C. Cook 2 specimens, however showed poor correlation. Possible contributing factors to this are: (1) metallurgical differences between D.C. Cook 2 and Indian Point 2 specimens; (2) statistical variations in embrittlement parameters for individual samples away from the stated men values; and (3) conversion of the D.C. Cook 2 reactor to a low leakage core configuration in the middle of the period of surveillance. Modeling using a magnetomechanical hysteresis model has begun. The modeling will first focus on why Barkhausen noise and nonlinear harmonic amplitudes appear to be better indicators of embrittlement than the hysteresis loop parameters

  18. Photoluminescence spectra and biaxial stress effects of yellow 1S excitons in Cu2O thin films recrystallized epitaxially between paired MgO plates

    We investigated biaxial stress effects on the yellow 1S ortho excitons in Cu2O thin films recrystallized between paired MgO plates by measuring photoluminescence spectra, X-ray diffraction and polarization microscope images. On the MgO (001) surface, we found two kinds of epitaxial growth modes of the Cu2O thin films. In such thin films, the yellow 1S ortho exciton states split into two or three levels depending on the respective epitaxial growth modes due to the different biaxial stresses owing to the lattice mismatches between Cu2O and MgO. By using effective Hamiltonians including such biaxial stress effects, we estimated the strengths of the biaxial stresses from the energy splittings of the 1S ortho excitons and confirmed the two kinds of epitaxial growth modes in our Cu2O thin films. - Highlights: • Two different oriented Cu2O thin films were epitaxially grown between paired MgO (001) plates. • The thin films were applied biaxial stresses due to lattice mismatch between Cu2O and MgO. • The lattice mismatch stresses can change yellow 1S exciton states in Cu2O thin films. • We report the biaxial stress strengths by analyzing splitting energies of the 1S ortho excitons

  19. Investiagation on the finite fatigue strength of materials subjected to biaxial stress as a result of changing temperatures

    Design specifications for pressure vessels permit the yield point to be exceeded considerably in the case of secondary stress. Pressure components must therefore often be designed for finite fatigue strength. Dimensioning in accordance with the ASME code has hitherto been based on the results of uniaxial mechanical tests at constant temperature, using high safety factors. The author's own tests intend determine to what extent real loads are covered by thermal cycles in a biaxial stress field. At the same time, the limits of use of these materials under complex loads are determined. Therefore, in this research program biaxial cyclic tests were carried out on disks of unalloyed and austenitic materials. Lifetime was determined in dependence of the prevented deformations. The temperature cycles are between a low limiting temperature of 500C and a higher one of 3000C, 4000C or 5000C. (orig./RW) 891 RW/orig.- 892 RKD

  20. Stress Ratio Effects on the fatigue Properties of Biaxially Loaded Tubular FRP-Specimens – Experimental Study

    Marques, Jorge Filipe Simões

    2013-01-01

    In this work tubular fiber reinforced specimens are tested for fatigue life. The specimens are biaxially loaded with tension and shear stresses, with a load angle β of 30° and 60° and a load ratio of R=0,1. There are many factors that affect fatigue life of a fiber reinforced material and the main goal of this work is to study the effects of load ratio R by obtaining S-N curves and compare them to the previous works (1). All the other parameters, such as specimen production, fatigue loading f...

  1. Biaxial stress evaluation in GeSn film epitaxially grown on Ge substrate by oil-immersion Raman spectroscopy

    Takeuchi, Kazuma; Suda, Kohei; Yokogawa, Ryo; Usuda, Koji; Sawamoto, Naomi; Ogura, Atsushi

    2016-09-01

    GeSn is being paid much attention as a next-generation channel material. In this work, we performed the excitation of forbidden transverse optical (TO) phonons from strained GeSn, as well as longitudinal optical (LO) phonons, under the backscattering geometry from the (001) surface by oil-immersion Raman spectroscopy. Using the obtained LO/TO phonons, we derived the phonon deformation potentials (PDPs), which play an important role in the stress evaluation, of the strained Ge1‑ x Sn x for the first time. The results suggest that PDPs are almost constant for the Ge1‑ x Sn x (x < 0.032). Biaxial stress calculated using the derived PDPs reasonably indicated the isotropic states.

  2. Determination of out-of-plane biaxial stress effects on fracture toughness for shallow surface cracks in reactor pressure vessel steels

    Pressurized-thermal-shock loading in a reactor pressure vessel (RPV) produces significant positive out-of-plane stresses along the crack front for both circumferential and axial cracks. Experimental evidence, while very limited, seems to indicate that a reduction in toughness is associated with out-of-plane biaxial loading when compared with toughness values obtained under uniaxial conditions. The motivation and objectives of a testing program to determine the effects of out-of-plane biaxial loading on fracture toughness of RPV steels are presented. A cruciform bend specimen that meets specified criteria for the testing program is analyzed using three-dimensional, elastic-plastic, finite-element techniques. These analysis results provide the basis for proposed test conditions that are judged likely to produce a biaxial loading effect in the cruciform bend specimen

  3. Interference of wedge-shaped protrusions on the faces of a Griffith crack in biaxial stress. Final report

    Boulet, J.A.M. [Tennessee Univ., Knoxville, TN (United States)

    1992-04-01

    An initial investigation of the influence of protrusion interference on the fracture toughness required to prevent unstable propagation of a Griffith crack in a brittle material is described. The interference is caused by relative shear displacement of the crack faces when subjected to remote biaxial stress with neither principal stress parallel to the crack. It is shown that for room temperature cracks smaller than about one centimeter in silicon carbide, or about one millimeter in silicon nitride, the presence of interference changes the fracture stress. A mathematical model based on linear elasticity solutions and including multiple interference sites at arbitrarily specified positions on the crack is presented. Computations of the change in required fracture toughness and its dependence on wedge geometry (size and vertex angle), applied stresses (orientation and magnitude), and location of the interference site are discussed. Results indicate that a single interference site has only a slight effect on required toughness. However, the influence of interference increases monotonically with the number of interference sites. The two-dimensional model described herein is not accurate when the interference sites are closely spaced.

  4. Investigation of the biaxial stress of Al-doped ZnO thin films on a flexible substrate with RF magnetron sputtering

    Huang, Kuo-Ting; Chen, Hsi-Chao; Cheng, Po-Wei; Chang, Jhe-Ming

    2016-01-01

    Transparent conductive Al-doped ZnO (AZO) thin films were deposited onto poly(ethylene terephthalate) (PET) substrate, using the radio frequency (RF) magnetron sputtering method. The residual stress of flexible electronics was investigated by a double beam shadow moiré interferometer with phase shifting interferometry (PSI). Moreover, the biaxial stress of AZO thin films can be graphically represented by using Mohr’s circle of stress. The residual stress of AZO thin films becomes more compressive with the increase in sputtering power. The maximum residual stress is -1115.74 MPa, and the shearing stress is 490.57 MPa at a sputtering power of 200 W. The trends of residual stress were evidenced by the X-ray diffraction (XRD) patterns and optical properties of AZO thin films. According to the evaluation results of the refractive index and the extinction coefficient, the AZO thin films have better quality when the sputtering power less than 100 W.

  5. Acoustic phonon propagation in ultra-thin Si membranes under biaxial stress field

    We report on stress induced changes in the dispersion relations of acoustic phonons propagating in 27 nm thick single crystalline Si membranes. The static tensile stress (up to 0.3 GPa) acting on the Si membranes was achieved using an additional strain compensating silicon nitride frame. Dispersion relations of thermally activated hypersonic phonons were measured by means of Brillouin light scattering spectroscopy. The theory of Lamb wave propagation is developed for anisotropic materials subjected to an external static stress field. The dispersion relations were calculated using the elastic continuum approximation and taking into account the acousto-elastic effect. We find an excellent agreement between the theoretical and the experimental dispersion relations. (paper)

  6. A fast real time measurement system to track in and out of plane optical retardation/ birefringence, true stress, and true strain during biaxial stretching of polymer films

    Cakmak, M.; Hassan, M.; Unsal, E.; Martins, C.

    2012-12-01

    An instrumented and highly integrated biaxial stretching system was designed and constructed to obtain true stress, true strain, and optical behavior of polymeric films during biaxial stretching. With programmable drive motors, any form of temporally varying biaxial deformation profiles, including linear, exponential, logarithmic as well as cyclic, can be applied to a square-shaped films. This machine allows the investigation of mechano-optical behavior of films under profiles captured in industrial processes. To overcome the edge effects, the samples are painted with a dot pattern that is imaged using a high speed video capture system. This system accurately determines the locations of the each dot matrix in subsequent images acquired and calculates the true strains in both directions. The in-plane optical retardation is determined using spectral birefringence method that uses polarized white light and optical spectrometer in the optical train. This is carried out automatically at less than 10 nm in retardation resolution with the light beam passing through the symmetry center of the sample. Out of plane retardation is measured with an identical optical train tilted 45° to the plane of the film with its light beam going through the same spot on the sample as 0° beam. The true stress and birefringences are calculated with the determined instantaneous thickness of the film. With this system, the stress optical behavior of PET's is determined up to very large deformation levels at moderate to high deformation rates. Beyond the initial linear stress optical behavior, these films exhibit sudden positive deviation from linearity and this start of nonlinearity was directly associated with the stress induced crystallization.

  7. Biaxial fatigue of metals the present understanding

    Schijve, Jaap

    2016-01-01

    Problems of fatigue under multiaxial fatigue loads have been addressed in a very large number of research publications. The present publication is primarily a survey of biaxial fatigue under constant amplitude loading on metal specimens. It starts with the physical understanding of the fatigue phenomenon under biaxial fatigue loads. Various types of proportional and non-proportional biaxial fatigue loads and biaxial stress distributions in a material are specified. Attention is paid to the fatigue limit, crack nucleation, initial micro crack growth and subsequent macro-crack in different modes of crack growth. The interference between the upper and lower surfaces of a fatigue crack is discussed. Possibilities for predictions of biaxial fatigue properties are analysed with reference to the similarity concept. The significance of the present understanding for structural design problems is considered. The book is completed with a summary of major observations.

  8. Ultrasonic fatigue testing device under biaxial bending

    C. Brugger

    2016-07-01

    Full Text Available A new fatigue testing device has been developed to test specimens under biaxial loading at 20 kHz. A flat smooth specimen with a disc geometry is placed on a torus frame and cyclically loaded at the center of its upper face. Disc bending generates a biaxial proportional stress state at the center of the lower face. Any positive loading ratio can be applied. A cast aluminum alloy (used to produce cylinder heads has been tested under biaxial bending using this device in order to determine its fatigue strength at 109 cycles under high hydrostatic pressure. Self-heating is moderate but macroscopic fatigue cracks after testing are very long. First results in VHCF regime are consistent with literature results obtained under similar stress state but in HCF regime and at 20 Hz.

  9. Optimal design of biaxial tensile cruciform specimens

    Demmerle, S.; Boehler, J. P.

    1993-01-01

    F OR EXPERIMENTAL investigations concerning the mechanical behaviour under biaxial stress states of rolled sheet metals, mostly cruciform flat specimens are used. By means of empirical methods, different specimen geometries have been proposed in the literature. In order to evaluate the suitability of a specimen design, a mathematically well defined criterion is developed, based on the standard deviations of the values of the stresses in the test section. Applied to the finite element method, the criterion is employed to realize the shape optimization of biaxial cruciform specimens for isotropic elastic materials. Furthermore, the performance of the obtained optimized specimen design is investigated in the case of off-axes tests on anisotropic materials. Therefore, for the first time, an original testing device, consisting of hinged fixtures with knife edges at each arm of the specimen, is applied to the biaxial test. The obtained results indicate the decisive superiority of the optimized specimens for the proper performance on isotropic materials, as well as the paramount importance of the proposed off-axes testing technique for biaxial tests on anisotropic materials.

  10. Comparison of recent rubber-elasticity theories with biaxial stress-strain data: The slip-link theory of Edwards and Vilgis

    Meissner, Bohumil; Matějka, Libor

    2002-01-01

    Roč. 43, č. 13 (2002), s. 3803-3809. ISSN 0032-3861 R&D Projects: GA ČR GA104/00/1311 Institutional research plan: CEZ:AV0Z4050913 Keywords : theory of rubber elasticity * biaxial deformations * experimental testing Subject RIV: CD - Macromolecular Chemistry Impact factor: 1.838, year: 2002

  11. A Langevin-elasticity-theory-based constitutive equation for rubberlike networks and its comparison with biaxial stress-strain data. Part I

    Meissner, Bohumil; Matějka, Libor

    2003-01-01

    Roč. 44, č. 16 (2003), s. 4599-4610. ISSN 0032-3861 R&D Projects: GA ČR GA104/00/1311; GA AV ČR IAA4050008 Institutional research plan: CEZ:AV0Z4050913 Keywords : theory of rubber elasticity * biaxial deformations * experimental testing Subject RIV: CD - Macromolecular Chemistry Impact factor: 2.340, year: 2003

  12. Biaxial Creep Specimen Fabrication

    This report documents the results of the weld development and abbreviated weld qualification efforts performed by Pacific Northwest National Laboratory (PNNL) for refractory metal and superalloy biaxial creep specimens. Biaxial creep specimens were to be assembled, electron beam welded, laser-seal welded, and pressurized at PNNL for both in-pile (JOYO reactor, O-arai, Japan) and out-of-pile creep testing. The objective of this test campaign was to evaluate the creep behavior of primary cladding and structural alloys under consideration for the Prometheus space reactor. PNNL successfully developed electron beam weld parameters for six of these materials prior to the termination of the Naval Reactors program effort to deliver a space reactor for Project Prometheus. These materials were FS-85, ASTAR-811C, T-111, Alloy 617, Haynes 230, and Nirnonic PE16. Early termination of the NR space program precluded the development of laser welding parameters for post-pressurization seal weldments

  13. Biaxial Creep Specimen Fabrication

    JL Bump; RF Luther

    2006-02-09

    This report documents the results of the weld development and abbreviated weld qualification efforts performed by Pacific Northwest National Laboratory (PNNL) for refractory metal and superalloy biaxial creep specimens. Biaxial creep specimens were to be assembled, electron beam welded, laser-seal welded, and pressurized at PNNL for both in-pile (JOYO reactor, O-arai, Japan) and out-of-pile creep testing. The objective of this test campaign was to evaluate the creep behavior of primary cladding and structural alloys under consideration for the Prometheus space reactor. PNNL successfully developed electron beam weld parameters for six of these materials prior to the termination of the Naval Reactors program effort to deliver a space reactor for Project Prometheus. These materials were FS-85, ASTAR-811C, T-111, Alloy 617, Haynes 230, and Nirnonic PE16. Early termination of the NR space program precluded the development of laser welding parameters for post-pressurization seal weldments.

  14. Biaxial dynamic testing of nuclear containment steel

    A test program has been initiated at the laboratories of the European Union Joint Research Centre of Ispra to investigate combined effects of high strain rates and biaxial stresses. The purpose is to assess the material behavior up to rupture in the special conditions which are produced during an explosion inside a nuclear metal containment. In the paper the main features of the campaign are discussed. (author). 19 refs., 4 figs

  15. Low-cycle fatigue behaviour and microstructure of copper and alpha-brass under biaxial load paths

    Henkel, S; Fischer, J; Biermann, H [TU Bergakademie Freiberg, Institute for Materials Engineering, Gustav-Zeuner-Strasse 5, D-09599 Freiberg (Germany); Balogh, L; Ungar, T, E-mail: henkel@ww.tu-freiberg.d [Eoetvoes University, Department of General Physics, PO Box 32, 1518 Budapest (Hungary)

    2010-07-01

    The low-cycle fatigue behaviour of copper and a-brass CuZn30 was investigated in uniaxial and biaxial tests. Planar biaxial fatigue tests were carried out using cruciform samples with proportional stain paths with and without phase shift between the two axes. Microcharacterisation was performed by electron microscopy as well as by high-resolution X-ray line profile analysis. The biaxial cyclic stress-strain curves show good agreement with the uniaxial ones using the von Mises equivalent strain hypothesis. The dislocation densities and microhardness values of the biaxial case, however, show significantly lower values compared to the uniaxial case at equivalent von Mises stresses.

  16. Biaxial Testing of 2219-T87 Aluminum Alloy Using Cruciform Specimens

    Dawicke, D. S.; Pollock, W. D.

    1997-01-01

    A cruciform biaxial test specimen was designed and seven biaxial tensile tests were conducted on 2219-T87 aluminum alloy. An elastic-plastic finite element analysis was used to simulate each tests and predict the yield stresses. The elastic-plastic finite analysis accurately simulated the measured load-strain behavior for each test. The yield stresses predicted by the finite element analyses indicated that the yield behavior of the 2219-T87 aluminum alloy agrees with the von Mises yield criterion.

  17. Singular values, nematic disclinations, and emergent biaxiality

    Dennis, Mark R.; Žumer, Slobodan; Kamien, Randall D.; Čopar, Simon

    2015-01-01

    Both uniaxial and biaxial nematic liquid crystals are defined by orientational ordering of their building blocks. While uniaxial nematics only orient the long molecular axis, biaxial order implies local order along three axes. As the natural degree of biaxiality and the associated frame that can be extracted from the tensorial description of the nematic order vanishes in the uniaxial phase, we extend the nematic director to a full biaxial frame by making use of a singular value decomposition ...

  18. Fracture assessment of shallow-flaw cruciform beams tested under uniaxial and biaxial loading conditions

    A technology to determine shallow-flaw fracture toughness of reactor pressure vessel (RPV) steels is being developed for application to the safety assessment of RPVs containing postulated shallow surface flaws. Matrices of cruciform beam tests were developed to investigate and quantify the effects of temperature, biaxial loading, and specimen size on fracture initiation toughness of two-dimensional (constant depth), shallow, surface flaws. The cruciform beam specimens were developed at Oak Ridge National Laboratory (ORNL) to introduce a far-field, out-of-plane biaxial stress component in the test section that approximates the nonlinear stresses resulting from pressurized-thermal-shock or pressure-temperature loading of an RPV. Tests were conducted under biaxial load ratios ranging from uniaxial to equibiaxial. These tests demonstrated that biaxial loading can have a pronounced effect on shallow-flaw fracture toughness in the lower transition temperature region for an RPV material. The cruciform fracture toughness data were used to evaluate fracture methodologies for predicting the observed effects of biaxial loading on shallow-flaw fracture toughness. Initial emphasis was placed on assessment of stress-based methodologies, namely, the J-Q formulation, the Dodds-Anderson toughness scaling model, and the Weibull approach. Applications of these methodologies based on the hydrostatic stress fracture criterion indicated an effect of loading-biaxiality on fracture toughness; the conventional maximum principal stress criterion indicated no effect. A three-parameter Weibull model based on the hydrostatic stress criterion is shown to correlate with the experimentally observed biaxial effect on cleavage fracture toughness by providing a scaling mechanism between uniaxial and biaxial loading states. (orig.)

  19. Biaxial low-cycle fatigue failure of 316 stainless steel at elevated temperatures

    High-strain, biaxial fatigue tests between the limiting conditions of uniaxial push-pull and fully reversed pure torsional loading were repeated on two batches of AISI 316 stainless steel, one tested at 4000C, the other at 5500C. An equivalent plastic shear strain range was shown to be superior to the octahedral equivalent strain for correlating biaxial fatigue endurance data. The stable cyclic stress-strain behaviour for any biaxial state is best represented in terms of the maximum shear stress and shear strain. At 5500C dynamic strain aging has a significant effect on both plastic flow and endurance for certain strain rates. Both Stage I and Stage II cracks were identified in the biaxial tests. (author)

  20. Flexural rigidity of biaxially loaded reinforced concrete rectangular column sections

    Resheidat, M.; Ghanma, M.; Sutton, C.; Chen, Wai-Fah

    1995-05-01

    An exact analysis is carried out utilizing the parabola-rectangle stress-strain curve for concrete and a typical idealized stress-strain curve for steel to develop the moment-curvature relationship for biaxially loaded reinforced concrete rectangular column sections. Based on that, the flexural rigidity EI of the section is determined at the yield curvature. A computer program is written by FORTRAN 77 to handle the required computations. The influence of material properties, the effect of steel ratios, and the impact of axial loads on the EI estimation were investigated. This study leads to the development of a new equation to estimate the flexural rigidity EI of reinforced concrete biaxially loaded rectangular columns in which these factors were considered. It is shown that the new equation stems from the actual behavior of the column. Therefore, it is recommended for general use in the design of slender columns.

  1. Development of pressurized disc type fatigue testing system for equi-biaxial fatigue

    A testing method for investigating fatigue strength under equi-biaxial stress/strain condition was developed. In this method, the equi-biaxial stress condition was achieved by applying pressure on the surfaces of a disc-type specimen, for which the disc edge was constrained by supporting jigs. Air pressure was used to apply the cyclic loading and the failure of the specimen was determined by detecting the crack penetration of the specimen thickness. This method allows application of the cyclic equi-biaxial stress without a complex testing apparatus or a complex controlling system such as the testing system using the cruciform or tubular specimens, conventionally used for the fatigue test under the equi-biaxial stress condition. After developing the testing system, the configuration of the disc-type specimen was designed by finite element analysis so that a crack would be initiated at the center of the specimen. Then, carbon steel (SS400 in JIS) specimens were subjected to the fatigue test. The developed system was demonstrated to be able to initiate a fatigue crack at the center of the specimen and to detect the specimen failure successfully. The test results showed that the fatigue lifetime under equi-biaxial stress was longer than that under uniaxial stress for the same Von Mises equivalent strain range. (author)

  2. Biaxial creep of zircaloy: Texture and temperature effects

    Zircaloy is commonly used as a cladding material for nuclear fuel elements. The cladding is subject to time-varying multiaxial stresses in service and the ability to accurately predict cladding behavior is necessary to maintain fuel integrity. This work investigates the biaxial creep behavior of recrystallized zircaloy at three temperatures and with four different crystallographic textures. In addition to measuring the creep behavior, the crystallographic texture is used to independently predict the creep behavior. 48 refs

  3. Limit load assessment of centre cracked plates under biaxial loading

    Fitness-for-service of equipment and components containing defects is generally assessed using procedures such as BS 7910, API 579 and R6. There is currently little detailed advice in these procedures on the effects of biaxial and triaxial loading on fracture. This poster shows some theoretical bounding solutions of the plastic limit load for centre cracked plates under a variety of biaxial loading ratios and compares the estimates with those found by numerical methods using finite element (FE) analysis using Abacus CAE modelling software. The limit load of a structure is the maximum load that it can carry before plastic collapse occurs; this is often when the plastic zone has become large enough to spread from the crack tip to a remote boundary. For an elastic-perfectly plastic material, the irreversible deformation will continue at stresses no higher than the yield stress. The model for these limit load solutions is a bi-axially loaded plate of width 2W and height 2H, a centre crack of width 2a, acted on by remotely applied uniform stresses σ2 perpendicular to the crack and Bσ2 parallel to the crack, where B is the biaxial loading ratio, it means the ratio of the parallel to the perpendicular stress. A quarter plate of an elastic-perfectly plastic material has been modelled. The results show that an exact solution has been found for negative and low positive values of B. For B > 1, the lower bound solution is conservative for all values of a/W and B

  4. Biaxiality of chiral liquid crystals

    Using extended deGennes-Ginzburg-Landau free energy expansion in terms of the anisotropic part of the dielectric tensor field Qαβ(χ) a connection between the phase biaxiality and the stability of various chiral liquid crystalline phases is studied. In particular the cholesteric phase, the cubic Blue Phases and the phases characterized by an icosahedral space group symmetry are analysed in detail. Also a general question concerning the applicability of the mean-field approximation in describing the chiral phases is addressed. By an extensive study of the model over a wide range of the parameters a new class of phenomena, not present in the original deGennes-Ginzburg-Landau model, has been found. These include: a) re-entrant phase transitions between the cholesteric and the cubic blue phases and b) the existence of distinct phases of the same symmetry but of different biaxialities. The phase biaxiality serves here as an extra scalar order parameter. Furthermore, it has been shown that due to the presence of the competing bulk terms in the free energy, the stable phases may acquire a large degree of biaxiality, also in liquid crystalline materials composed of effectively uniaxial molecules. A study of icosahedral space group symmetries gives a partial answer to the question as to whether an icosahedral quasicrystalline liquid could be stabilized in liquid crystals. Although, in general, the stability of icosahedral structures could be enhanced by the extra terms in the free energy no absolutely stable icosahedral phase has been found. (author). 16 refs, 3 figs, 1 tab

  5. Biaxially oriented film on flexible polymeric substrate

    Finkikoglu, Alp T.; Matias, Vladimir

    2009-10-13

    A flexible polymer-based template having a biaxially oriented film grown on the surface of a polymeric substrate. The template having the biaxially oriented film can be used for further epitaxial growth of films of interest for applications such as photovoltaic cells, light emitting diodes, and the like. Methods of forming such a flexible template and providing the polymeric substrate with a biaxially oriented film deposited thereon are also described.

  6. Biaxially textured articles formed by plastic deformation

    Goyal, Amit

    2001-01-01

    A method of preparing a biaxially textured article comprises the steps of providing a metal preform, coating or laminating the preform with a metal layer, deforming the layer to a sufficient degree, and rapidly recrystallizing the layer to produce a biaxial texture. A superconducting epitaxial layer may then be deposited on the biaxial texture. In some embodiments the article further comprises buffer layers, electromagnetic devices or electro-optical devices.

  7. Rolling process for producing biaxially textured substrates

    Goyal, Amit

    2004-05-25

    A method of preparing a biaxially textured article includes the steps of: rolling a metal preform while applying shear force thereto to form as-rolled biaxially textured substrate having an a rotated cube texture wherein a (100) cube face thereof is parallel to a surface of said substrate, and wherein a [100] direction thereof is at an angle of at least 30.degree. relative to the rolling direction; and depositing onto the surface of the biaxially textured substrate at least one epitaxial layer of another material to form a biaxially textured article.

  8. Fatigue of Clip connectors for offshore drilling risers under biaxial tension

    Gaur Vidit

    2014-06-01

    Full Text Available Drilling riser connectors designed by IFPEN undergo cyclic in-phase biaxial tension in their critical area. This type of loading was reproduced on steel tubular specimens loaded in cyclic tension and internal pressure. The fatigue lives were substantially reduced when the load biaxiality was increased from 0 to 0.4 and then further to 1, which was not captured by existing fatigue criteria. A deeper investigation is thus in progress. Emphasis is laid on the separate evaluation of mean stress and biaxiality effects, often treated in the same way in existing criteria. The influence of load biaxiality on the resistance of the steel to fatigue-corrosion in seawater will also be investigated.

  9. Investigation of the Leak Response of a Carbon-Fiber Laminate Loaded in Biaxial Tension

    Jackson, Wade C.; Ratcliffe, James G.

    2013-01-01

    Designers of pressurized structures have been reluctant to use composite materials because of concerns over leakage. Biaxial stress states are expected to be the worst-case loading condition for allowing leakage to occur through microcracks. To investigate the leakage behavior under in-plane biaxial loading, a cruciform composite specimen was designed that would have a relatively large test section with a uniform 1:1 biaxial loading ratio. A 7.6-cm-square test section was desired for future investigations of the leakage response as a result of impact damage. Many iterations of the cruciform specimen were evaluated using finite element analysis to reduce stress concentrations and maximize the size of the uniform biaxial strain field. The final design allowed the specimen to go to relatively high biaxial strain levels without incurring damage away from the test section. The specimen was designed and manufactured using carbon/epoxy fabric with a four-ply-thick, quasi-isotropic, central test section. Initial validation and testing were performed on a specimen without impact damage. The specimen was tested to maximum biaxial strains of approximately 4500micro epsilon without apparent damage. A leak measurement system containing a pressurized cavity was clamped to the test section and used to measure the flow rate through the specimen. The leakage behavior of the specimen was investigated for pressure differences up to 172 kPa

  10. Biaxial wheel/hub test facility. Proceedings

    Fischer, G.; Grubisic, V. [eds.

    2000-07-01

    The 4{sup th} meeting aims to exchange the experience and knowledge of engineers during several presentations and discussions about new developments required for a reliable, time and cost reducing validation of the wheel/hub assembly. Tremendous development of the wheel performance, described by the ratio of the rated load (kg) versus the wheel weight (kg) had taken place during the last 5000 years. Starting from the ratio of 3 for wooden 2-piece-disc-wheels in Mesopotamia it needed nearly 1000 years to increase the ratio to approx 5 at light-weight spoke wheels for fighting carriages, found in the grave of king Tutenchamon in Egypt. Modern light alloy wheels of commercial vehicles reach values up to 160 kg/kg. Additionally the comlex design of the modern systems for cars and commercial vehicles comprising wheel, brake, hub, bearing, spindle and hub carrier, including different materials and their treatment, fasteners, press-fits, require an appropriate testing procedure. The variable loading conditions, caused by operational wheel forces, brake and torque moments including heating, may result in changing tolerances and press-fits during operation and consequently in different damage mechanisms. This can be simulated in the Biaxial Wheel Test Machine, whereby corresponding load programs are necessary. An overview about all biaxial test machines in usage at the end of 1999 is shown in the introduction. The total number is 17 for cars, 7 for commercial vehicles and 1 for trains. The six presentations of this meeting were consequently concentrated on: (a) recommendations for a standardization of load programs of the German Wheel Committee, (b) the simulation of brake and torque events and (c) the possibility for a numerical stress analyses and fatigue life assessment. (orig./AKF)

  11. Discrete Element Simulations and Experiments on the Deformation of Cohesive Powders in a bi-axial Box

    Imole, O.I.; Kumar, N; Magnanimo, V.; S. Luding

    2012-01-01

    We compare element test experiments and simulations on the deformation of frictional, cohesive particles in a bi-axial box. We show that computer simulations with the Discrete Element Method qualitatively reproduce a uniaxial compression element test in the true bi-axial tester. We highlight the effects of friction and polydispersity on our simulations and present the second stress response namely the deviatoric stress as a function of the deviatoric strain.

  12. Biaxially Stretched Polycarbonate Film For Capacitors

    Yen, Shaio-Ping S.; Lowry, Lynn E.; Bankston, Clyde P.

    1992-01-01

    Report describes experiments on effects of biaxial stretching on crystal structures, dielectric properties, and sellected thermal and mechanical properties of biaxially stretched polycarbonate films. Highest stretch ratios produce highest degree of crystallinity, with single crystalline phase and distribution of crystallites more nearly isotropic than uniaxially oriented film. Electrical properties at high temperatures improved.

  13. An experimental study on the biaxial strength of the plain concrete for containment structures

    In this paper, an experimental study into the biaxial strength of plain concrete for containment structures is represented and technical difficulties encountered in the development of a suitable test setup are discussed. Prior to testing for a 1/8 model of cylindrical specimen(φ150x300) and four 1/4 models of plate specimens(200x200xT(=30, 50, 60, 70)mm) under uniaxial compression, the strength ratios between both specimens with different geometry shapes were found by nonlinear finite element analyses using ABAQUS. From the results three suitable type of considered plate specimens were selected for failure testing under biaxial stress. As initial approach to develop biaxial strength criteria of plain concrete, the various test data were obtained under uniaxial compression, uniaxial tension and biaxial compression. The test data indicate that the strength of concrete under biaxial compression, f1=f2, is 14.7 percent larger than under uniaxial compression and the Poisson's ratio of concrete is 0.155. Teflon employed to eliminate friction between test specimen and loading platens showed and excellent effect under biaxial compression, f1=f2

  14. Biaxial loading effects on fracture toughness of reactor pressure vessel steel

    The preliminary phases of a program to develop and evaluate fracture methodologies for assessing crack-tip constraint effects on fracture toughness of reactor pressure vessel (RPV) steels have been completed by the Heavy-Section Steel Technology (HSST) Program. Objectives were to investigate effect of biaxial loading on fracture toughness, quantify this effect through existing stress-based, dual-parameter, fracture-toughness correlations, or propose and verify alternate correlations. A cruciform beam specimen with 2-D, shallow, through-thickness flaw and a special loading fixture was designed and fabricated. Tests were performed using biaxial loading ratios of 0:1 (uniaxial), 0.6:1, and 1:1 (equi-biaxial). Critical fracture-toughness values were calculated for each test. Biaxial loading of 0.6:1 resulted in a reduction in the lower bound fracture toughness of ∼12% as compared to that from the uniaxial tests. The biaxial loading of 1:1 yielded two subsets of toughness values; one agreed well with the uniaxial data, while one was reduced by ∼43% when compared to the uniaxial data. Results were evaluated using J-Q theory and Dodds-Anderson (D-A) micromechanical scaling model. The D-A model predicted no biaxial effect, while the J-Q method gave inconclusive results. When applied to the 1:1 biaxial data, these constraint methodologies failed to predict the observed reduction in fracture toughness obtained in one experiment. A strain-based constraint methodology that considers the relationship between applied biaxial load, the plastic zone width in the crack plane, and fracture toughness was formulated and applied successfully to the data. Evaluation of this dual-parameter strain-based model led to the conclusion that it has the capability of representing fracture behavior of RPV steels in the transition region, including the effects of out-of-plane loading on fracture toughness. This report is designated as HSST Report No. 150

  15. Fracture assessment of HSST Plate 14 shallow-flaw cruciform bend specimens tested under biaxial loading conditions

    Bass, B.R.; McAfee, W.J.; Williams, P.T.; Pennell, W.E.

    1998-06-01

    A technology to determine shallow-flaw fracture toughness of reactor pressure vessel (RPV) steels is being developed for application to the safety assessment of RPVs containing postulated shallow surface flaws. Matrices of cruciform beam tests were developed to investigate and quantify the effects of temperature, biaxial loading, and specimen size on fracture initiation toughness of two-dimensional (constant depth), shallow, surface flaws. The cruciform beam specimens were developed at Oak Ridge National Laboratory (ORNL) to introduce a far-field, out-of-plane biaxial stress component in the test section that approximates the nonlinear stresses resulting from pressurized-thermal-shock or pressure-temperature loading of an RPV. Tests were conducted under biaxial load ratios ranging from uniaxial to equibiaxial. These tests demonstrated that biaxial loading can have a pronounced effect on shallow-flaw fracture toughness in the lower transition temperature region for an RPV material. The cruciform fracture toughness data were used to evaluate fracture methodologies for predicting the observed effects of biaxial loading on shallow-flaw fracture toughness. Initial emphasis was placed on assessment of stress-based methodologies, namely, the J-Q formulation, the Dodds-Anderson toughness scaling model, and the Weibull approach. Applications of these methodologies based on the hydrostatic stress fracture criterion indicated an effect of loading-biaxiality on fracture toughness; the conventional maximum principal stress criterion indicated no effect. A three-parameter Weibull model based on the hydrostatic stress criterion is shown to correlate the experimentally observed biaxial effect on cleavage fracture toughness by providing a scaling mechanism between uniaxial and biaxial loading states.

  16. Fracture assessment of HSST Plate 14 shallow-flaw cruciform bend specimens tested under biaxial loading conditions

    A technology to determine shallow-flaw fracture toughness of reactor pressure vessel (RPV) steels is being developed for application to the safety assessment of RPVs containing postulated shallow surface flaws. Matrices of cruciform beam tests were developed to investigate and quantify the effects of temperature, biaxial loading, and specimen size on fracture initiation toughness of two-dimensional (constant depth), shallow, surface flaws. The cruciform beam specimens were developed at Oak Ridge National Laboratory (ORNL) to introduce a far-field, out-of-plane biaxial stress component in the test section that approximates the nonlinear stresses resulting from pressurized-thermal-shock or pressure-temperature loading of an RPV. Tests were conducted under biaxial load ratios ranging from uniaxial to equibiaxial. These tests demonstrated that biaxial loading can have a pronounced effect on shallow-flaw fracture toughness in the lower transition temperature region for an RPV material. The cruciform fracture toughness data were used to evaluate fracture methodologies for predicting the observed effects of biaxial loading on shallow-flaw fracture toughness. Initial emphasis was placed on assessment of stress-based methodologies, namely, the J-Q formulation, the Dodds-Anderson toughness scaling model, and the Weibull approach. Applications of these methodologies based on the hydrostatic stress fracture criterion indicated an effect of loading-biaxiality on fracture toughness; the conventional maximum principal stress criterion indicated no effect. A three-parameter Weibull model based on the hydrostatic stress criterion is shown to correlate the experimentally observed biaxial effect on cleavage fracture toughness by providing a scaling mechanism between uniaxial and biaxial loading states

  17. Evaluation of constraint methodologies applied to a shallow-flaw cruciform bend specimen tested under biaxial loading conditions

    A technology to determine shallow-flaw fracture toughness of reactor pressure vessel (RPV) steels is being developed for application to the safety assessment of RPVs containing postulated shallow surface flaws. Matrices of cruciform beam tests were developed to investigate and quantify the effects of temperature, biaxial loading, and specimen size on fracture initiation toughness of two-dimensional (constant depth), shallow surface flaws. The cruciform beam specimens were developed at Oak Ridge National Laboratory (ORNL) to introduce a prototypic, far-field. out-of-plane biaxial stress component in the test section that approximates the nonlinear stresses resulting from pressurized-thermal-shock or pressure-temperature loading of an RPV. Tests were conducted under biaxial load ratios ranging from uniaxial to equibiaxial. These tests demonstrated that biaxial loading can have a pronounced effect on shallow-flaw fracture toughness in the lower transition temperature region for RPV materials. The cruciform fracture toughness data were used to evaluate fracture methodologies for predicting the observed effects of biaxial loading on shallow-flaw fracture toughness. Initial emphasis was placed on assessment of stress-based methodologies. namely, the J-Q formulation, the Dodds-Anderson toughness scaling model, and the Weibull approach. Applications of these methodologies based on the hydrostatic stress fracture criterion indicated an effect of loading-biaxiality on fracture toughness, the conventional maximum principal stress criterion indicated no effect

  18. Engineering piezoresistivity using biaxially strained silicon

    Pedersen, Jesper Goor; Richter, Jacob; Brandbyge, Mads;

    2008-01-01

    piezocoefficient on temperature and dopant density is altered qualitatively for strained silicon. In particular, we find that a vanishing temperature coefficient may result for silicon with grown-in biaxial tensile strain. These results suggest that strained silicon may be used to engineer the iezoresistivity to......We calculate the shear piezocoefficient of p-type silicon with grown-in biaxial strain using a 66 k·p method. We find a significant increase in the value of the shear piezocoefficient for compressive grown-in biaxial strain, while tensile strain decreases the piezocoefficient. The dependence of the...

  19. Graphene flakes under controlled biaxial deformation

    Androulidakis, Charalampos; Koukaras, Emmanuel N.; Parthenios, John; Kalosakas, George; Papagelis, Konstantinos; Galiotis, Costas

    2015-12-01

    Thin membranes, such as monolayer graphene of monoatomic thickness, are bound to exhibit lateral buckling under uniaxial tensile loading that impairs its mechanical behaviour. In this work, we have developed an experimental device to subject 2D materials to controlled equibiaxial strain on supported beams that can be flexed up or down to subject the material to either compression or tension, respectively. Using strain gauges in tandem with Raman spectroscopy measurements, we monitor the G and 2D phonon properties of graphene under biaxial strain and thus extract important information about the uptake of stress under these conditions. The experimental shift over strain for the G and 2D Raman peaks were found to be in the range of 62.3 ± 5 cm-1/%, and 148.2 ± 6 cm-1/%, respectively, for monolayer but also bilayer graphenes. The corresponding Grüneisen parameters for the G and 2D peaks were found to be between 1.97 ± 0.15 and 2.86 ± 0.12, respectively. These values agree reasonably well with those obtained from small-strain bubble-type experiments. The results presented are also backed up by classical and ab initio molecular dynamics simulations and excellent agreement of Γ-E2g shifts with strains and the Grüneisen parameter was observed.

  20. Crack under biaxial loading: Two-parameter description and prediction of crack growth direction

    Seitl, Stanislav

    2014-01-01

    Roč. 31, APR (2014), s. 44-49. ISSN 0213-3725 R&D Projects: GA MŠk(CZ) 7AMB14AT012 Institutional support: RVO:68081723 Keywords : Concrete * T-stress * cracks growth prediction * numerical calculation * biaxial loading Subject RIV: JL - Materials Fatigue, Friction Mechanics

  1. A confocal rheoscope to study bulk or thin-film material under uniaxial or biaxial shear

    Lin, Neil Y C; Cheng, Xiang; Leahy, Brian; Cohen, Itai

    2016-01-01

    We present a new design of a confocal rheoscope that enables us to precisely impose a uniform uniaxial or biaxial shear. The design consists of two precisely-positioned parallel plates. Our design allows us to adjust the gap between the plates to be as small as 2$\\pm$0.1 $\\mu$m, allowing for the exploration of confinement effects. By using our shear cell in conjunction with a biaxial force measurement device and a high-speed confocal microscope, we are able to measure the real-time biaxial stress while simultaneously imaging the material 3D structure. We illustrate the importance of the instrument capabilities by discussing the applications of this instrument in current and future research topics in colloidal suspensions.

  2. STRAIN-CONTROLLED BIAXIAL TENSION OF NATURAL RUBBER: NEW EXPERIMENTAL DATA

    Pancheri, Francesco Q.

    2014-03-01

    We present a new experimental method and provide data showing the response of 40A natural rubber in uniaxial, pure shear, and biaxial tension. Real-time biaxial strain control allows for independent and automatic variation of the velocity of extension and retraction of each actuator to maintain the preselected deformation rate within the gage area of the specimen. Wealso focus on the Valanis-Landel hypothesis that is used to verify and validate the consistency of the data.Weuse a threeterm Ogden model to derive stress-stretch relations to validate the experimental data. The material model parameters are determined using the primary loading path in uniaxial and equibiaxial tension. Excellent agreement is found when the model is used to predict the response in biaxial tension for different maximum in-plane stretches. The application of the Valanis-Landel hypothesis also results in excellent agreement with the theoretical prediction.

  3. Topology Optimization of Stressed Capacitive RF MEMS Switches

    Philippine, Mandy A.; Sigmund, Ole; Rebeiz, Gabriel M.;

    2013-01-01

    Geometry design can improve a capacitive radio-frequency microelectromechanical system switch's reliability by reducing the impacts of intrinsic biaxial stresses and stress gradients on the switch's membrane. Intrinsic biaxial stresses cause stress stiffening, whereas stress gradients cause out-o...

  4. Biaxial tensile tests of the porcine ascending aorta.

    Deplano, Valérie; Boufi, Mourad; Boiron, Olivier; Guivier-Curien, Carine; Alimi, Yves; Bertrand, Eric

    2016-07-01

    One of the aims of this work is to develop an original custom built biaxial set-up to assess mechanical behavior of soft tissues. Stretch controlled biaxial tensile tests are performed and stereoscopic digital image correlation (SDIC) is implemented to measure the 3D components of the generated displacements. Using this experimental device, the main goal is to investigate the mechanical behavior of porcine ascending aorta in the more general context of human ascending aorta pathologies. The results highlight that (i) SDIC arrangement allows accurate assessment of displacements and so stress strain curves, (ii) porcine ascending aorta has a nearly linear and anisotropic mechanical behavior until 30% of strain, (iii) porcine ascending aorta is stiffer in the circumferential direction than in the longitudinal one, (iv) the material coefficient representing the interaction between the two loading directions is thickness dependent, (v) taking into account the variability of the samples the stress values are independent of the stretch rate in the range of values from 10(-3) to 10(-1)s(-1) and finally, (vi) unlike other segments of the aorta, 4-month-old pigs ascending aorta is definitely not a relevant model to investigate the mechanical behavior of the human ascending aorta. PMID:27211783

  5. Growth of inclined fatigue cracks using the biaxial CJP model

    G. Laboviciute

    2015-07-01

    Full Text Available The CJP model of crack tip stresses is a modified version of the Williams crack tip stress field which takes account of simplified stress distributions that arise from the presence of a zone of plastic deformation associated with the crack flanks and crack tip, and that act on the elastic field responsible for driving crack growth. The elastic stress field responsible for crack growth is therefore controlled by the applied loading and by the induced boundary stresses at the interface with the plastic zone. This meso-scale model of crack tip stresses leads to a modified set of crack tip stress intensity factors that include the resultant influence of plastic wake-induced crack tip shielding, and which therefore have the potential to help resolve some longstanding controversies associated with plasticity-induced closure. A full-field approach has now been developed for stress using photoelasticity and also for displacement using digital image correlation. This paper considers the characterisation of crack growth rate data with the biaxial CJP model, using compact tension specimens that contain inclined cracks at the notch tip with initial angles of 30°, 45° and 60° to the horizontal axis. Significant experimental difficulties are experienced in growing cracks in a biaxial field under uniaxial tensile loading, as the natural tendency of the crack is to turn so that it becomes perpendicular to the maximum principal stress direction. However, crack angle is not an issue in the CJP model which calculates the stress field parallel with, and perpendicular to, the crack plane. These stress components can be rotated into directions comparable with the usual KI and KII directions and used to calculate stress intensity parameters that should be directly comparable with the standard stress intensity formulations. Another difficulty arises, however, in finding published expressions for KI and KII for CT specimens with curved or kinked cracks. The CJP model

  6. Evaluating the time and temperature dependent biaxial strength of Gore-Select {sup registered} series 57 proton exchange membrane using a pressure loaded blister test

    Grohs, Jacob R.; Dillard, David A.; Case, Scott W. [Department of Engineering Science and Mechanics, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061-0219 (United States); Li, Yongqiang; Lai, Yeh-Hung; Gittleman, Craig S. [Electrochemical Energy Research Lab, GM R and D, General Motors Corporation, 10 Carriage Street, Honeoye Falls, NY 14472-0603 (United States); Ellis, Michael W. [Department of Mechanical Engineering, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061-0238 (United States)

    2010-01-15

    Temperature and humidity fluctuations in operating fuel cells impose significant biaxial stresses in the constrained proton exchange membranes (PEMs) of a fuel cell stack. The strength of the PEM, and its ability to withstand cyclic environment-induced stresses, plays an important role in membrane integrity and consequently, fuel cell durability. In this study, a pressure loaded blister test is used to characterize the biaxial strength of Gore-Select {sup registered} series 57 over a range of times and temperatures. Hencky's classical solution for a pressurized circular membrane is used to estimate biaxial strength values from burst pressure measurements. A hereditary integral is employed to construct the linear viscoelastic analog to Hencky's linear elastic exact solution. Biaxial strength master curves are constructed using traditional time-temperature superposition principle techniques and the associated temperature shift factors show good agreement with shift factors obtained from constitutive (stress relaxation) and fracture (knife slit) tests of the material. (author)

  7. Biaxial Fatigue Testing of Thin Films

    A new experimental setup, which allows for testing in an equi-biaxial loading condition, has been developed and applied to investigate the fatigue behaviour of thin films. A load controlled cycling, performed at room temperature on flat specimens, reproduces the strain amplitude and mean strain in the film corresponding to a thermal cycling in a given temperature range. The setup is based on the ring-on-ring test, which has been successfully used in biaxial fracture testing of glass and ceramics, and includes an optical in-situ failure detection system. The method is validated for specimens consisting in a gold film deposited on a polymer substrate

  8. Towards the biaxial nematic phase via specific intermolecular interactions

    Omnes, L

    2001-01-01

    The work described in this thesis has been focussed on the search of an elusive liquid crystal phase, known as the biaxial nematic phase. Indeed, despite nearly thirty years of intense research, no-one has been able to characterise unambiguously a biaxial nematic phase in a low-molar-mass thermotropic system. Our research is based on the concept of molecular biaxiality as distinct from shape biaxiality. Thus, we are seeking to design palladium complexes where specific intermolecular interactions could exist. Therefore, a few original synthetic strategies were developed to tackle the challenge of discovering the biaxial nematic phase

  9. Dynamic biaxial tissue properties of the human cadaver aorta.

    Shah, Chirag S; Hardy, Warren N; Mason, Matthew J; Yang, King H; Van Ee, Chris A; Morgan, Richard; Digges, Kennerly

    2006-11-01

    This study focuses on the biaxial mechanical properties of planar aorta tissue at strain rates likely to be experienced during automotive crashes. It also examines the structural response of the whole aorta to longitudinal tension. Twenty-six tissue-level tests were conducted using twelve thoracic aortas harvested from human cadavers. Cruciate samples were excised from the ascending, peri-isthmic, and descending regions. The samples were subjected to equibiaxial stretch at two nominal speed levels using a new biaxial tissue-testing device. Inertia-compensated loads were measured to facilitate calculation of true stress. High-speed videography and regional correlation analysis were used to track ink dots marked on the center of each sample to obtain strain. In a series of component-level tests, the response of the intact thoracic aorta to longitudinal stretch was obtained using seven aorta specimens. The aorta fails within the peri-isthmic region. The aorta fails in the transverse direction, and the intima fails before the media or adventitia. The aorta tissue exhibits nonlinear behavior. The aorta as complete structure can transect completely from 92 N axial load and 0.221 axial strain. Complete transection can be accompanied by intimal tears. These results have application to finite element modeling and the better understanding of traumatic rupture of the aorta. PMID:17311166

  10. Structural stability and theoretical strength of Cu crystal under equal biaxial loading

    Jian-Min Zhang; Zhong-Liang Lin; Yan Zhang; Vincent Ji

    2010-02-01

    Cu has been used extensively to replace Al as interconnects in ULSI and MEMS devices. However, because of the difference in the thermal expansion coefficients between the Cu film and the Si substrate, large biaxial stresses will be generated in the Cu film. Thus, the Cu film becomes unstable and even changes its morphologies which affects the device manufacturing yield and ultimate reliability. The structural stability and theoretical strength of Cu crystal under equal biaxial loading have been investigated by combining the MAEAM with Milstein-modified Born stability criteria. The results indicate that, under sufficient tension, there exists a stress-free BCC phase which is unstable and slips spontaneously to a stress-free metastable BCT phase by consuming internal energy. The stable region ranges from −15.131 GPa to 2.803 GPa in the theoretical strength or from −5.801% to 4.972% in the strain respectively.

  11. Biaxial load effects on the crack border elastic strain energy and strain energy rate

    Eftis, J.; Subramonian, N.; Liebowitz, H.

    1977-01-01

    The validity of the singular solution (first term of a series representation) is investigated for the crack tip stress and displacement field in an infinite sheet with a flat line crack with biaxial loads applied to the outer boundaries. It is shown that if one retains the second contribution to the series approximations for stress and displacement in the calculation of the local elastic strain energy density and elastic strain energy rate in the crack border region, both these quantities have significant biaxial load dependency. The value of the J-integral does not depend on the presence of the second term of the series expansion for stress and displacement. Thus J(I) is insensitive to the presence of loads applied parallel to the plane of the crack.

  12. Mechanical characterisation of porcine rectus sheath under uniaxial and biaxial tension.

    Lyons, Mathew

    2014-06-03

    Incisional hernia development is a significant complication after laparoscopic abdominal surgery. Intra-abdominal pressure (IAP) is known to initiate the extrusion of intestines through the abdominal wall, but there is limited data on the mechanics of IAP generation and the structural properties of rectus sheath. This paper presents an explanation of the mechanics of IAP development, a study of the uniaxial and biaxial tensile properties of porcine rectus sheath, and a simple computational investigation of the tissue. Analysis using Laplace׳s law showed a circumferential stress in the abdominal wall of approx. 1.1MPa due to an IAP of 11kPa, commonly seen during coughing. Uniaxial and biaxial tensile tests were conducted on samples of porcine rectus sheath to characterise the stress-stretch responses of the tissue. Under uniaxial tension, fibre direction samples failed on average at a stress of 4.5MPa at a stretch of 1.07 while cross-fibre samples failed at a stress of 1.6MPa under a stretch of 1.29. Under equi-biaxial tension, failure occurred at 1.6MPa with the fibre direction stretching to only 1.02 while the cross-fibre direction stretched to 1.13. Uniaxial and biaxial stress-stretch plots are presented allowing detailed modelling of the tissue either in silico or in a surrogate material. An FeBio computational model of the tissue is presented using a combination of an Ogden and an exponential power law model to represent the matrix and fibres respectively. The structural properties of porcine rectus sheath have been characterised and add to the small set of human data in the literature with which it may be possible to develop methods to reduce the incidence of incisional hernia development.

  13. Miniature load cell instrumentation for finite deformation biaxial testing of elastomers

    Arenz, R. J.; Landel, R. F.; Tsuge, K.

    1974-01-01

    Accuracy of biaxial test equipment to examine the nonlinear mechanical behavior of thin sheet specimens of elastomeric materials has been hampered by lack of precise determination of the force distribution along the sides of the specimen. It has been necessary to use an effective width established by approximate means to obtain the stress from the overall force applied along the edges. To avoid this experimental difficulty, individual miniature proof-ring load cells utilizing semiconductor strain gages have been developed and applied to the support hooks for the thin sheet specimens. Typical results are shown for time-dependent stress distributions for all degrees of biaxiality. An accurate evaluation of the effective specimen width is now possible.

  14. Biaxial crystal-based optical tweezers

    Angelsky, Oleg V.; Maksimyak, Andrew P.; Maksimyak, Peter P.;

    2010-01-01

    We suggest an optical tweezer setup based on an optically biaxial crystal. To control movements of opaque particles, we use shifts. The results of experimental studies are reported which are concerned with this laser tweezer setup. We demonstrate a movement of microparticles of toner using a sing...... singular-optical trap, rotation of particles due to orbital angular momentum of the field, and converging or diverging of two different traps when changing transmission plane of polariser at the input of our polarisation interferometer....

  15. Biaxial testing for fabrics and foils optimizing devices and procedures

    Beccarelli, Paolo

    2015-01-01

    This book offers a well-structured, critical review of current design practice for tensioned membrane structures, including a detailed analysis of the experimental data required and critical issues relating to the lack of a set of design codes and testing procedures. The technical requirements for biaxial testing equipment are analyzed in detail, and aspects that need to be considered when developing biaxial testing procedures are emphasized. The analysis is supported by the results of a round-robin exercise comparing biaxial testing machines that involved four of the main research laboratories in the field. The biaxial testing devices and procedures presently used in Europe are extensively discussed, and information is provided on the design and implementation of a biaxial testing rig for architectural fabrics at Politecnico di Milano, which represents a benchmark in the field. The significance of the most recent developments in biaxial testing is also explored.

  16. Method for making biaxially textured articles by plastic deformation

    Goyal, Amit

    2002-01-01

    A method of preparing a biaxially textured article comprises the steps of providing a metal preform, coating or laminating the preform with a metal layer, deforming the layer to a sufficient degree, and rapidly recrystallizing the layer to produce a biaxial texture. A superconducting epitaxial layer may then be deposited on the biaxial texture. In some embodiments the article further comprises buffer layers, electromagnetic devices or electro-optical devices.

  17. Damage and failure behavior of metal matrix composites under biaxial loads

    Kirkpatrick, Steven Wayne

    Metal matrix composites (MMCs) are being considered for increased use in structures that require the ductility and damage tolerance of the metal matrix and the enhanced strength and creep resistance at elevated temperatures of high performance fibers. Particularly promising for advanced aerospace engines and airframes are SiC fiber/titanium matrix composites (TMCs). A large program was undertaken in the Air Force to characterize the deformation and failure behaviors of TMCs and to develop computational models that can be used for component design. The effort reported here focused on a SiC SCS-6/Timetal 21S composite under biaxial loading conditions. Biaxial loading conditions are important because multiaxial stresses have been shown to influence the strength and ductility of engineering materials and, in general, structural components are subjected to multiaxial loads. The TMC material response, including stress-strain curves and failure surfaces, was measured using a combination of off-axis uniaxial tension and compression tests and biaxial cruciform tests. The off-axis tests produce combinations of in-plane tension, compression, and shear stresses, the mix of which are controlled by the relative angle between the fiber and specimen axes. The biaxial cruciform tests allowed independent control over the tensile or compressive loads in the fiber and transverse directions. The results of these characterization tests were used to develop a microstructural constitutive model and failure criteria. The basis of the micromechanical constitutive model is a representative unit volume of the MMC with a periodic array of fibers. The representative unit volume is divided into a fiber and three matrix cells for which the microstructural equilibrium and compatibility equations can be analyzed. The resulting constitutive model and associated failure criteria can be used to predict the material behavior under general loading conditions.

  18. Biaxial thermal creep of Inconel 617 and Haynes 230 at 850 and 950 °C

    The biaxial thermal creep behavior of Inconel 617 and Haynes 230 at 850 and 950 °C was investigated. Biaxial stresses were generated using the pressurized tube technique. The detailed creep deformation and fracture mechanism have been studied. Creep curves for both alloys showed that tertiary creep accounts for a greater portion of the materials’ life, while secondary creep only accounts for a small portion. Fractographic examinations of the two alloys indicated that nucleation, growth, and coalescence of creep voids are the dominant micro-mechanisms for creep fracture. At 850 °C, alloy 230 has better creep resistance than alloy 617. When subjected to the biaxial stress state, the creep rupture life of the two alloys was considerably reduced when compared to the results obtained by uniaxial tensile creep tests. The Monkman–Grant relation proves to be a promising method for estimating the long-term creep life for alloy 617, whereas alloy 230 does not follow the relation. This might be associated with the significant changes in the microstructure of alloy 230 at high temperatures

  19. Biaxial thermal creep of Inconel 617 and Haynes 230 at 850 and 950 °C

    Tung, Hsiao-Ming, E-mail: hmtung2@gmail.com [Institute of Nuclear Energy Research, Longtan, Taoyuan 32546, Taiwan, ROC (China); Mo, Kun; Stubbins, James F. [Department of Nuclear, Plasma, and Radiological Engineering, University of Illinois at Urbana-Champaign, 104 South Wright Street, Urbana, IL 61801 (United States)

    2014-04-01

    The biaxial thermal creep behavior of Inconel 617 and Haynes 230 at 850 and 950 °C was investigated. Biaxial stresses were generated using the pressurized tube technique. The detailed creep deformation and fracture mechanism have been studied. Creep curves for both alloys showed that tertiary creep accounts for a greater portion of the materials’ life, while secondary creep only accounts for a small portion. Fractographic examinations of the two alloys indicated that nucleation, growth, and coalescence of creep voids are the dominant micro-mechanisms for creep fracture. At 850 °C, alloy 230 has better creep resistance than alloy 617. When subjected to the biaxial stress state, the creep rupture life of the two alloys was considerably reduced when compared to the results obtained by uniaxial tensile creep tests. The Monkman–Grant relation proves to be a promising method for estimating the long-term creep life for alloy 617, whereas alloy 230 does not follow the relation. This might be associated with the significant changes in the microstructure of alloy 230 at high temperatures.

  20. Biaxial thermal creep of Inconel 617 and Haynes 230 at 850 and 950 °C

    Tung, Hsiao-Ming; Mo, Kun; Stubbins, James F.

    2014-04-01

    The biaxial thermal creep behavior of Inconel 617 and Haynes 230 at 850 and 950 °C was investigated. Biaxial stresses were generated using the pressurized tube technique. The detailed creep deformation and fracture mechanism have been studied. Creep curves for both alloys showed that tertiary creep accounts for a greater portion of the materials' life, while secondary creep only accounts for a small portion. Fractographic examinations of the two alloys indicated that nucleation, growth, and coalescence of creep voids are the dominant micro-mechanisms for creep fracture. At 850 °C, alloy 230 has better creep resistance than alloy 617. When subjected to the biaxial stress state, the creep rupture life of the two alloys was considerably reduced when compared to the results obtained by uniaxial tensile creep tests. The Monkman-Grant relation proves to be a promising method for estimating the long-term creep life for alloy 617, whereas alloy 230 does not follow the relation. This might be associated with the significant changes in the microstructure of alloy 230 at high temperatures.

  1. Investigation of in-plane biaxial low cycle fatigued austenitic stainless steel AISI 321. I. Mechanical testing on the planar biaxial load machine

    During fatigue loading of structural materials such as stainless steel, changes in the microstructure which affect the mechanical and physical properties occur. Experimental simulation of the loading conditions that induce the changes can be performed by mechanical loading, usually in the form of uniaxial tension-compression cycling. However, real machines and structures are subjected to more complex multiaxial stresses. Fatigue and fracture under multiaxial stresses are one of the most important current topics aimed at ensuring improved reliability of industrial components. The first step towards better understanding of this problem is to subject the materials to biaxial loading. The material examined was low austenitic stainless steel AISI 321 H. A set of the four samples of cruciform geometry was subjected to the biaxial tension-compression fatigue cycling with the frequency of 0.5 Hz at the applied load of 10-17 kN. The samples are intended for the neutron diffraction measurements of the residual stresses and the mechanical characterizations on a dedicated stress-diffractometer

  2. Effect of biaxial loading on the fracture behaviour of a ferritic steel component

    The effect of biaxial loading on the ductile behaviour of a through-wall crack in a ferritic steel structure under contained yield is of particular interest to the structural integrity argument for reactor pressure vessels. This results from the fact that there are many instances in practice (for example a crack in a circumferential weld), where a significant applied stress is present in the direction parallel to the crack as well as in the perpendicular direction. Two large plate ductile tearing tests have been performed on centre through-crack specimens (75mm by 2m by 2m) manufactured from a ferritic steel. The first test specimen was loaded in uniaxial tension and the second test specimen was loaded biaxially. This paper presents experimental details and results of the two plate tests and describes the analysis work undertaken to interpret the experiments satisfactorily. ((orig.))

  3. Biaxially textured articles formed by power metallurgy

    Goyal, Amit; Williams, Robert K.; Kroeger, Donald M.

    2003-08-26

    A biaxially textured alloy article having a magnetism less than pure Ni includes a rolled and annealed compacted and sintered powder-metallurgy preform article, the preform article having been formed from a powder mixture selected from the group of mixtures consisting of: at least 60 at % Ni powder and at least one of Cr powder, W powder, V powder, Mo powder, Cu powder, Al powder, Ce powder, YSZ powder, Y powder, Mg powder, and RE powder; the article having a fine and homogeneous grain structure; and having a dominant cube oriented {100} orientation texture; and further having a Curie temperature less than that of pure Ni.

  4. Biaxially textured articles formed by powder metallurgy

    Goyal, Amit; Williams, Robert K.; Kroeger, Donald M.

    2004-09-14

    A biaxially textured alloy article having a magnetism less than pure Ni includes a rolled and annealed compacted and sintered powder-metallurgy preform article, the preform article having been formed from a powder mixture selected from the group of mixtures consisting of: at least 60 at % Ni powder and at least one of Cr powder, W powder, V powder, Mo powder, Cu powder, Al powder, Ce powder, YSZ powder, Y powder, Mg powder, and RE powder; the article having a fine and homogeneous grain structure; and having a dominant cube oriented {100} orientation texture; and further having a Curie temperature less than that of pure Ni.

  5. Biaxial Flexural Strength and Estimation of Size on the Strength Properties of FRP Composites

    M. N. Saraf

    1990-04-01

    Full Text Available Fibre reinforced plastics (FRP are widely used as structural materials. For designing structural components, a designer is provided with data based on unidirectional testing. But in real structural applications the component is subjected to multiaxial stress throughout the material. Hence a multiaxial test is a better gauge of the behaviour of FRP components in service. In the present paper a ring-on-ring method was adopted which produces biaxial flexural stress on the FRP specimen. Wubull's statistical weakest link theory was applied to standardize the complexity and to assess the reliability of the results.

  6. Magnetic response of FeNbCuBSi RQ ribbons to bi-axial strain

    Nanocrystalline strip samples of the FeNbCuBSi class that are macroscopically heterogeneous due to surface /volume differences have been investigated. This heterogeneity is found to be a general property of the class. It represents a base for mutual force influence between the surface and the majority volume beneath. The bi-axial in-plane stress exerted by the ribbon surfaces on the volume is demonstrated first of all by a magnetoelastic anisotropy. The contribution of the creep-induced anisotropy, which can build up under the surface stress at post-treatment temperature, is also found possible

  7. Experimental studies of yield phenomena in biaxially loaded metals

    Realistic materials properties input represents one of the major limitations in computer stress analysis in the plastic range. Lack of data on the response of many structural materials to multiaxial loading requires modeling plastic behavior. Such models can at best predict the response of a limited class of materials for a limited range of loading. A summary of biaxial plasticity experiments on metals is presented to provide a testing ground for such models and to serve as a reference guide for materials that may be of practical interest. Most of the work has been done on materials assumed to exhibit time-and-pressure-independent plastic flow. Special attention is focused on initial and subsequent yield conditions and stress-strain relations. Some specific examples of material behavior that does not fall within the assumptions of classical plasticity theories are discussed. These include time-dependence as evidenced in creep, cyclic loading and strain-rate effects, pressure dependence, large strain behavior, microstructural changes and failure laws. 15 figures, 277 references

  8. Biaxial loading and shallow-flaw effects on crack-tip constraint and fracture toughness

    A program to develop and evaluate fracture methodologies for the assessment of crack-tip constraint effects on fracture toughness of reactor pressure vessel (RPV) steels has been initiated in the Heavy-Section Steel Technology (HSST) Program. Crack-tip constraint is an issue that significantly impacts fracture mechanics technologies employed in safety assessment procedures for commercially licensed nuclear RPVs. The focus of studies described herein is on the evaluation of two stressed-based methodologies for quantifying crack-tip constraint (i.e., J-Q theory and a micromechanical scaling model based on critical stressed volumes) through applications to experimental and fractographic data. Data were utilized from single-edge notch bend (SENB) specimens and HSST-developed cruciform beam specimens that were tested in HSST shallow-crack and biaxial testing programs. Results from applications indicate that both the J-Q methodology and the micromechanical scaling model can be used successfully to interpret experimental data from the shallow- and deep-crack SENB specimen tests. When applied to the uniaxially and biaxially loaded cruciform specimens, the two methodologies showed some promising features, but also raised several questions concerning the interpretation of constraint conditions in the specimen based on near-tip stress fields. Fractographic data taken from the fracture surfaces of the SENB and cruciform specimens are used to assess the relevance of stress-based fracture characterizations to conditions at cleavage initiation sites. Unresolved issues identified from these analyses require resolution as part of a validation process for biaxial loading applications. This report is designated as HSST Report No. 142

  9. Tensile Property of Bi-axial Warp Knitted Structure

    沈为

    2003-01-01

    The tensile property of bi-axial warp knitted fabrics is tested and compared with that of the plain weave fabric. The results show that there are obvious differences between the tensile property of a bi-axial warp knitted fabric and that of a plain weave fabric.The former can give fuller play to the property of a high modulus yarn than the latter. The tensile strength of a bi-axial warp knitted fabric is linear with the number of yarns in the direction of force.

  10. Characterization Of Biaxial Strain Of Poly(L-Lactide) Tubes

    Løvdal, Alexandra Liv Vest; Andreasen, Jens Wenzel; Mikkelsen, Lars Pilgaard;

    2016-01-01

    ) biaxial strain process, the mechanical properties of biaxial strained tubes can be further improved. This study investigated these properties in relation to their morphology and crystal orientation. Both processes yield the same mechanical strength and modulus, yet exhibit different crystal orientation......Poly(L-lactide) (PLLA) in its L-form has promising mechanical properties. Being a semi-crystalline polymer, it can be subjected to strain-induced crystallization at temperatures above Tg and can thereby become oriented. Following a simultaneous (SIM) biaxial strain process or a sequential (SEQ...

  11. Biaxial Behavior of Ultra-High Performance Concrete and Untreated UHPC Waffle Slab Bridge Deck Design and Testing

    D'Alessandro, Kacie Caple

    2013-01-01

    Ultra-high performance concrete (UHPC) was evaluated as a potential material for future bridge deck designs. Material characterization tests took place to identify potential challenges in mixing, placing, and curing UHPC. Biaxial testing was performed to evaluate behavior of UHPC in combined tension and compression stress states. A UHPC bridge deck was designed to perform similarly to a conventional concrete bridge deck, and a single unit bridge deck section was tested to evaluate the desi...

  12. Three-Dimensional Static and Dynamic Analysis of a Composite Cruciform Structure Subjected to Biaxial Loading: A Discontinuum Approach

    Navarro-Zafra, J.; Curiel-Sosa, J. L.; Serna Moreno, M. C.

    2016-04-01

    A three-dimensional structural integrity analysis using the eXtended Finite Element Method (XFEM) is considered for simulating the crack behaviour of a chopped fibre-glass-reinforced polyester (CGRP) cruciform specimen subjected to a quasi-static tensile biaxial loading. This is the first time this problem is accomplished for computing the stress intensity factors (SIFs) produced in the biaxially loaded area of the cruciform specimen. A static crack analysis for the calculation of the mixed-mode SIFs is carried out. SIFs are calculated for infinite plates under biaxial loading as well as for the CGRP cruciform specimens in order to review the possible edge effects. A ratio relating the side of the central zone of the cruciform and the crack length is proposed. Additionally, the initiation and evolution of a three-dimensional crack are successfully simulated. Specific challenges such as the 3D crack initiation, based on a principal stress criterion, and its front propagation, in perpendicular to the principal stress direction, are conveniently addressed. No initial crack location is pre-defined and an unique crack is developed. Finally, computational outputs are compared with theoretical and experimental results validating the analysis.

  13. Determination of flow curves under equibiaxial stress conditions

    Mulder, J.; Vegter, H.; Ha, J.J.; Boogaard, van den A.H.

    2012-01-01

    Three experimental methods have been used to establish flow curves for a low carbon steel under biaxial stress conditions: the hydraulic bulge test, the stack compression test and the biaxial tensile test. The individual tests are discussed and the results for a DC06 IF steel grade compared. Initial

  14. Measurement and material modeling of biaxial work-hardening behavior for pure titanium sheet

    Sumita, Takeshi; Kuwabara, Toshihiko

    2013-12-01

    Biaxial tensile tests of a commercial pure titanium sheet (JIS ♯1) were performed using a servo-controlled multiaxial tube expansion testing machine developed by one of the authors [Kuwabara, T. and Sugawara, F., Multiaxial tube expansion test method for measurement of sheet metal deformation behavior under biaxial tension for a large strain range, Int. J. Plasticity, 45 (2013), 103-118]. Tubular specimens with an inner diameter of 54 mm were fabricated by roller bending and TIG welding the as-received test material with a thickness of 0.5 mm. Several linear stress paths in the first quadrant of the stress space were applied to the tubular specimens to measure the contours of plastic work and the directions of the plastic strain rates for an equivalent plastic strain range of 0.05 ≤ ɛ0p ≤ 0.30. It was found that the shapes of the work contours significantly changed with an increase in ɛ0p and that the Yld2000-2d yield function could reproduce the differential work hardening behavior of the test material by changing the material parameters and the exponent as functions of ɛ0p.

  15. Nondestructive measurement of esophageal biaxial mechanical properties utilizing sonometry.

    Aho, Johnathon M; Qiang, Bo; Wigle, Dennis A; Tschumperlin, Daniel J; Urban, Matthew W

    2016-07-01

    Malignant esophageal pathology typically requires resection of the esophagus and reconstruction to restore foregut continuity. Reconstruction options are limited and morbid. The esophagus represents a useful target for tissue engineering strategies based on relative simplicity in comparison to other organs. The ideal tissue engineered conduit would have sufficient and ideally matched mechanical tolerances to native esophageal tissue. Current methods for mechanical testing of esophageal tissues both in vivo and ex vivo are typically destructive, alter tissue conformation, ignore anisotropy, or are not able to be performed in fluid media. The aim of this study was to investigate biomechanical properties of swine esophageal tissues through nondestructive testing utilizing sonometry ex vivo. This method allows for biomechanical determination of tissue properties, particularly longitudinal and circumferential moduli and strain energy functions. The relative contribution of mucosal-submucosal layers and muscular layers are compared to composite esophagi. Swine thoracic esophageal tissues (n  =  15) were tested by pressure loading using a continuous pressure pump system to generate stress. Preconditioning of tissue was performed by pressure loading with the pump system and pre-straining the tissue to in vivo length before data was recorded. Sonometry using piezocrystals was utilized to determine longitudinal and circumferential strain on five composite esophagi. Similarly, five mucosa-submucosal and five muscular layers from thoracic esophagi were tested independently. This work on esophageal tissues is consistent with reported uniaxial and biaxial mechanical testing and reported results using strain energy theory and also provides high resolution displacements, preserves native architectural structure and allows assessment of biomechanical properties in fluid media. This method may be of use to characterize mechanical properties of tissue engineered esophageal

  16. Nondestructive measurement of esophageal biaxial mechanical properties utilizing sonometry

    Aho, Johnathon M.; Qiang, Bo; Wigle, Dennis A.; Tschumperlin, Daniel J.; Urban, Matthew W.

    2016-07-01

    Malignant esophageal pathology typically requires resection of the esophagus and reconstruction to restore foregut continuity. Reconstruction options are limited and morbid. The esophagus represents a useful target for tissue engineering strategies based on relative simplicity in comparison to other organs. The ideal tissue engineered conduit would have sufficient and ideally matched mechanical tolerances to native esophageal tissue. Current methods for mechanical testing of esophageal tissues both in vivo and ex vivo are typically destructive, alter tissue conformation, ignore anisotropy, or are not able to be performed in fluid media. The aim of this study was to investigate biomechanical properties of swine esophageal tissues through nondestructive testing utilizing sonometry ex vivo. This method allows for biomechanical determination of tissue properties, particularly longitudinal and circumferential moduli and strain energy functions. The relative contribution of mucosal–submucosal layers and muscular layers are compared to composite esophagi. Swine thoracic esophageal tissues (n  =  15) were tested by pressure loading using a continuous pressure pump system to generate stress. Preconditioning of tissue was performed by pressure loading with the pump system and pre-straining the tissue to in vivo length before data was recorded. Sonometry using piezocrystals was utilized to determine longitudinal and circumferential strain on five composite esophagi. Similarly, five mucosa–submucosal and five muscular layers from thoracic esophagi were tested independently. This work on esophageal tissues is consistent with reported uniaxial and biaxial mechanical testing and reported results using strain energy theory and also provides high resolution displacements, preserves native architectural structure and allows assessment of biomechanical properties in fluid media. This method may be of use to characterize mechanical properties of tissue engineered

  17. Residual stresses of water-jet peened austenitic stainless steel

    The specimen material was austenitic stainless steel, SUS316L. The residual stress was induced by water-jet peening. The residual stress was measured using the 311 diffraction with conventional X-rays. The measured residual stress showed the equi-biaxial stress state. To investigate thermal stability of the residual stress, the specimen was aged thermally at 773K in air to 1000h. The residual stress kept the equi-biaxial stress state against the thermal aging. Lattice plane dependency of the residual stress induced by water-jet peening was evaluated using hard synchrotron X-rays. The residual stress measured by the soft lattice plane showed the equi-biaxial stress state, but the residual stress measured by the hard lattice plane did not. In addition, the distributions of the residual stress in the depth direction were measured using a strain scanning method with hard synchrotron X-rays and neutrons. (author)

  18. Polycrystalline ferroelectric or multiferroic oxide articles on biaxially textured substrates and methods for making same

    Goyal, Amit; Shin, Junsoo

    2015-03-31

    A polycrystalline ferroelectric and/or multiferroic oxide article includes a substrate having a biaxially textured surface; at least one biaxially textured buffer layer supported by the substrate; and a biaxially textured ferroelectric or multiferroic oxide layer supported by the buffer layer. Methods for making polycrystalline ferroelectric and/or multiferroic oxide articles are also disclosed.

  19. The measurement of residual stresses in claddings

    The ring core method, a variation of the hole drilling method for the measurement of biaxial residual stresses, has been extended to measure stresses from depths of about 5 to 25mm. It is now possible to measure the stress profiles of clad material. Examples of measured stress profiles are shown and compared with those obtained with a sectioning technique. (author)

  20. Irreversible magnetic processes under biaxial and uniaxial magnetic anisotropies

    Pokharel, S.; Akioya, O.; Alqhtany, N. H.; Dickens, C.; Morgan, W.; Wuttig, M.; Lisfi, A.

    2016-05-01

    Irreversible magnetic processes have been investigated in magnetic systems with two different anisotropy symmetries (uniaxial and biaxial) through angular measurement of the switching field, the irreversible susceptibility and the magnetic viscosity. These two systems consist of two-dimensional cobalt ferrite hetero-structures epitaxially grown on (100) and (110) MgO substrate. It is found that for uniaxial anisotropy the irreversible characteristics of the magnetization are large and display a strong angular dependence, which exhibits its maximum at the easy axis and drops quickly to vanish at the hard axis. However, for biaxial anisotropy the magnetization irreversible characteristics are considerably reduced and are less sensitive to the field angle.

  1. Method for forming biaxially textured articles by powder metallurgy

    Goyal, Amit; Williams, Robert K.; Kroeger, Donald M.

    2002-01-01

    A method of preparing a biaxially textured alloy article comprises the steps of preparing a mixture comprising Ni powder and at least one powder selected from the group consisting of Cr, W, V, Mo, Cu, Al, Ce, YSZ, Y, Rare Earths, (RE), MgO, CeO.sub.2, and Y.sub.2 O.sub.3 ; compacting the mixture, followed by heat treating and rapidly recrystallizing to produce a biaxial texture on the article. In some embodiments the alloy article further comprises electromagnetic or electro-optical devices and possesses superconducting properties.

  2. Planar biaxial testing of soft biological tissue using rakes: A critical analysis of protocol and fitting process.

    Fehervary, Heleen; Smoljkić, Marija; Vander Sloten, Jos; Famaey, Nele

    2016-08-01

    Mechanical characterization of soft biological tissue is becoming more and more prevalent. Despite the growing use of planar biaxial testing for soft tissue characterization, testing conditions and subsequent data analysis have not been standardized and vary widely. This also influences the quality of the result of the parameter fitting. Moreover, the testing conditions and data analysis are often not or incompletely reported, which impedes the proper comparison of parameters obtained from different studies. With a focus on planar biaxial tests using rakes, this paper investigates varying testing conditions and varying data analysis methods and their effect on the quality of the parameter fitting results. By means of a series of finite element simulations, aspects such as number of rakes, rakes׳ width, loading protocol, constitutive model, material stiffness and anisotropy are evaluated based on the degree of homogeneity of the stress field, and on the correlation between the experimentally obtained stress and the stress derived from the constitutive model. When calculating the aforementioned stresses, different definitions of the section width and deformation gradient are used in literature, each of which are looked into. Apart from this degree of homogeneity and correlation, also the effect on the quality of the parameter fitting result is evaluated. The results show that inhomogeneities can be reduced to a minimum for wise choices of testing conditions and analysis methods, but never completely eliminated. Therefore, a new parameter optimization procedure is proposed that corrects for the inhomogeneities in the stress field and induces significant improvements to the fitting results. Recommendations are made for best practice in rake-based planar biaxial testing of soft biological tissues and subsequent parameter fitting, and guidelines are formulated for reporting thereof in publications. PMID:26854936

  3. Time-evolving collagen-like structural fibers in soft tissues: biaxial loading and spherical inflation

    Topol, Heiko; Demirkoparan, Hasan; Pence, Thomas J.; Wineman, Alan

    2016-05-01

    This work considers a previously developed constitutive theory for the time dependent mechanical response of fibrous soft tissue resulting from the time dependent remodeling of a collagen fiber network that is embedded in a ground substance matrix. The matrix is taken to be an incompressible nonlinear elastic solid. The remodeling process consists of the continual dissolution of existing fibers and the creation of new fibers. Motivated by experimental reports on the enzyme degradation of collagen fibers, the remodeling is governed by first order chemical kinetics such that the dissolution rate is dependent upon the fiber stretch. The resulting time dependent mechanical response is sensitive to the natural configuration of the fibers when they are created, and different assumptions on the nature of the fiber's stress free state are considered here. The response under biaxial loading, a type of loading that has particular significance for the characterization of biological materials, is studied. The inflation of a spherical membrane is then analyzed in terms of the equal biaxial stretch that occurs in the membrane approximation. Different assumptions on the natural configuration of the fibers, combined with their time dependent dissolution and reforming, are shown to emulate alternative forms of creep and relaxation response. This formal similarity to viscoelastic phenomena occurs even though the underlying mechanisms are fundamentally different from the mechanism of macromolecular reconfiguration that one typically associates with viscoelastic response.

  4. Bi-axial fracture strength characteristic of an ultra-thin flash memory chip

    Recently, ultra-thin chips with thicknesses of under 35 µm have emerged as an option for thinner, high performance electronic devices. For reliable electronic devices and high throughput packaging processes, the mechanical properties of ultra-thin chips need to be accurately understood. In this study, the fracture strength of an ultra-thin flash memory chip was measured using a ball-on-ring (BOR) test. To evaluate and validate the bi-axial strength in the BOR test, a finite element analysis was performed. It was compared with the analytical solution based on Hertzian contact theory. Flash memory chip specimens with different thicknesses were prepared and their bi-axial strengths were tested with respect to various wafer thinning process parameters such as grinding speed and polishing time. Raman spectroscopy was used to characterize the residual stress generated during the wafer thinning process. The surface roughness of the silicon wafer was measured using an atomic force microscope under various wafer thinning conditions. From the study, the fracture strength characteristics of the ultra-thin chip could be established as a function of the wafer thinning parameters. (paper)

  5. Fatigue life prediction of magnetorheological elastomers subjected to dynamic equi-biaxial cyclic loading

    Prediction of fatigue life is of great significance in ensuring that dynamically loaded rubber components exhibit safety and reliability in service. In this text, the dynamic equi-biaxial fatigue behaviour of magnetorheological elastomer (MREs) using a bubble inflation method is described. Wöhler (S–N) curves for both isotropic and anisotropic MREs were produced by subjecting the compounds to cycling over a range of stress amplitudes (σa) between 0.75 MPa and 1.4 MPa. Changes in physical properties, including variation in stress–strain relations and complex modulus (E*) during the fatigue process were analysed. It was found that the complex modulus of MRE samples decreased throughout the entire fatigue test and failure took place at a limiting value of approximately 1.228MPa ± 4.38% for isotropic MREs and 1.295 ± 10.33% for anisotropic MREs. It was also determined that a dynamic stored energy criterion can be used as a plausible predictor in determining the fatigue life of MREs. - Highlights: • The first Wöhler curves for MREs subjected to equi-biaxial loading were presented. • Anisotropic MREs exhibited higher fatigue resistance than isotropic MREs. • There is a limiting value of complex modulus (E*) at which fatigue failure will occur. • The dynamic stored energy criterion can be used as a fatigue life predictor

  6. BEGA-a biaxial excitation Generator for automobiles

    Scridon, S.; Boldea, Ion; Tutelea, L.;

    2005-01-01

    This paper presents the design and test results for a biaxial excitation generator/motor for automobiles (BEGA), which has a three-phase stator and a salient-pole excited heteropolar rotor with multiple flux barriers filled with low-cost permanent magnets (PMs). For this new generator, the low-vo...

  7. Computational analysis of fluid flow within a device for applying biaxial strain to cultured cells.

    Lee, Jason; Baker, Aaron B

    2015-05-01

    In vitro systems for applying mechanical strain to cultured cells are commonly used to investigate cellular mechanotransduction pathways in a variety of cell types. These systems often apply mechanical forces to a flexible membrane on which cells are cultured. A consequence of the motion of the membrane in these systems is the generation of flow and the unintended application of shear stress to the cells. We recently described a flexible system for applying mechanical strain to cultured cells, which uses a linear motor to drive a piston array to create biaxial strain within multiwell culture plates. To better understand the fluidic stresses generated by this system and other systems of this type, we created a computational fluid dynamics model to simulate the flow during the mechanical loading cycle. Alterations in the frequency or maximal strain magnitude led to a linear increase in the average fluid velocity within the well and a nonlinear increase in the shear stress at the culture surface over the ranges tested (0.5-2.0 Hz and 1-10% maximal strain). For all cases, the applied shear stresses were relatively low and on the order of millipascal with a dynamic waveform having a primary and secondary peak in the shear stress over a single mechanical strain cycle. These findings should be considered when interpreting experimental results using these devices, particularly in the case when the cell type used is sensitive to low magnitude, oscillatory shear stresses. PMID:25611013

  8. DEM Simulation of Biaxial Compression Experiments of Inherently Anisotropic Granular Materials and the Boundary Effects

    Zhao-Xia Tong

    2013-01-01

    Full Text Available The reliability of discrete element method (DEM numerical simulations is significantly dependent on the particle-scale parameters and boundary conditions. To verify the DEM models, two series of biaxial compression tests on ellipse-shaped steel rods are used. The comparisons on the stress-strain relationship, strength, and deformation pattern of experiments and simulations indicate that the DEM models are able to capture the key macro- and micromechanical behavior of inherently anisotropic granular materials with high fidelity. By using the validated DEM models, the boundary effects on the macrodeformation, strain localization, and nonuniformity of stress distribution inside the specimens are investigated using two rigid boundaries and one flexible boundary. The results demonstrate that the boundary condition plays a significant role on the stress-strain relationship and strength of granular materials with inherent fabric anisotropy if the stresses are calculated by the force applied on the wall. However, the responses of the particle assembly measured inside the specimens are almost the same with little influence from the boundary conditions. The peak friction angle obtained from the compression tests with flexible boundary represents the real friction angle of particle assembly. Due to the weak lateral constraints, the degree of stress nonuniformity under flexible boundary is higher than that under rigid boundary.

  9. Effectiveness of the modified fatigue criteria for biaxial loading of notched specimen in high-cycle region

    Major, Štěpán; Hubálovský, Š.; Kocour, Vladimír; Valach, Jaroslav

    Vol. 732. Zürich: Trans Tech Publications, 2015 - (Polach, P.), s. 63-70 ISBN 978-3-03835-413-0. ISSN 1660-9336. [EAN 2014. Conference on experimental stress analysis. /52./. Mariánské Lázně (CZ), 02.06.2014-05.06.2014] Institutional support: RVO:68378297 Keywords : notched specimen * multiaxial criteria * biaxial loading * fatigue life * bending-torsion loading * high-cycle loading Subject RIV: JM - Building Engineering http://www.scientific.net/AMM.732.63

  10. The fine structure of the vortex-beams in the biaxial and biaxially-induced birefringent media caused by the conical diffraction

    Fadeyeva, Tatyana; Anischenko, Pavel; Volyar, Alexander

    2011-01-01

    We consider the paraxial propagation of nondiffracting singular beams inside natural biaxial and biaxially-induced birefringent media in vicinity of one of the optical axes in terms of eigenmode vortex-beams, whose angular momentum does not change upon propagation. We have predicted a series of new optical effects in the natural biaxial crystals such as the stable propagation of vector singular beams bearing the coupled optical vortices with fractional topological charges, the conversion of the zero-order Bessel beam with a uniformly distributed linear polarization into the radially-, azimuthally- and spirally-polarized beams and the conversion of the space-variant linear polarization in the combined beam with coupled vortices. We have revealed that the field structure of the vortex-beams in the biaxially-induced crystals resembles that in the natural biaxial crystals and form the vector structure inherent in the conical diffraction. However, the mode beams in this case do not change the propagation direction...

  11. Strain Measurement System Developed for Biaxially Loaded Cruciform Specimens

    Krause, David L.

    2000-01-01

    A new extensometer system developed at the NASA Glenn Research Center at Lewis Field measures test area strains along two orthogonal axes in flat cruciform specimens. This system incorporates standard axial contact extensometers to provide a cost-effective high-precision instrument. The device was validated for use by extensive testing of a stainless steel specimen, with specimen temperatures ranging from room temperature to 1100 F. In-plane loading conditions included several static biaxial load ratios, plus cyclic loadings of various waveform shapes, frequencies, magnitudes, and durations. The extensometer system measurements were compared with strain gauge data at room temperature and with calculated strain values for elevated-temperature measurements. All testing was performed in house in Glenn's Benchmark Test Facility in-plane biaxial load frame.

  12. Identification du comportement de composites en fatigue bi-axiale

    Busca, Damien

    2014-01-01

    La connaissance du comportement de composites sous un état de contraintes multi-axial reste un enjeu majeur pour l’optimisation du dimensionnement des structures. La machine de fatigue bi-axiale présente au LGP permet de générer un état de contrainte bi-axial par l’utilisation d’éprouvettes cruciformes. La conception des éprouvettes reste un enjeu majeur pour les chercheurs pour répondre aux problèmes spécifiques liés aux matériaux composites. Un nouveau type d’éprouvette cruciforme en compos...

  13. Irreversible magnetic processes under biaxial and uniaxial magnetic anisotropies

    S. Pokharel

    2016-05-01

    Full Text Available Irreversible magnetic processes have been investigated in magnetic systems with two different anisotropy symmetries (uniaxial and biaxial through angular measurement of the switching field, the irreversible susceptibility and the magnetic viscosity. These two systems consist of two-dimensional cobalt ferrite hetero-structures epitaxially grown on (100 and (110 MgO substrate. It is found that for uniaxial anisotropy the irreversible characteristics of the magnetization are large and display a strong angular dependence, which exhibits its maximum at the easy axis and drops quickly to vanish at the hard axis. However, for biaxial anisotropy the magnetization irreversible characteristics are considerably reduced and are less sensitive to the field angle.

  14. Theory of nine elastic constants of biaxial nematics

    Liu Hong

    2008-01-01

    In this paper, a rotational invariant of interaction energy between two biaxial-shaped molecules is assumed and in the mean field approximation, nine elastic constants for simple distortion patterns in biaxial nematica are derived in terms of the thermal averagewhere D(l)mn is the Wigner rotation matrix.In the lowest order terms, the elastic constants depend on coefficients г,г',λ, order parameters Q0=Q0+Q2vj'j''j(r12) and probability function fk'k'' k (r12), where r12 is the distance between two molecules, andλis proportional to temperature. Q0 and Q2 are parameters related to multiple moments of molecules. Comparing these results with those obtained from Landau-de Gennes theory, we have obtained relationships between coefficients, order parameters used in both theories. In the special case of uniaxial nematics, both results are reduced to a degenerate case where K11=K33.

  15. Biaxial casting method and apparatus for isolating radioactive waste

    Hazardous radioactive waste is compacted and cast into safely handled monolithic castings having a radiation barrier wall completely enclosing the radioactive waste by centrifugal casting processes in which the barrier wall may be either a pre-formed shell transported to the jobsite or it may be formed by biaxial centrifugal casting and curing of the barrier wall in a mold. When a pre-formed shell is used, means are provided for thickening the radiation barrier if necessary by biaxial casting of additional barrier material inside of the shell. Castable radioactive material is cast inside the barrier wall before removal of the casting mold from the finished cast monolith. The cast monolith is supported for rotation as the mold is removed therefrom so that additional impact resisting and radiation barrier material can also easily be applied to the exterior surface monolith if radiation leakage exceeds tolerance levels. (author) figs

  16. Scaling rules for critical current density in anisotropic biaxial superconductors

    Li, Yingxu; Kang, Guozheng; Gao, Yuanwen

    2016-06-01

    Recent researches highlight the additional anisotropic crystallographic axis within the superconducting plane of high temperature superconductors (HTS), demonstrating the superconducting anisotropy of HTS is better understood in the biaxial frame than the previous uniaxial coordinates within the superconducting layer. To quantitatively evaluate the anisotropy of flux pinning and critical current density in HTS, we extend the scaling rule for single-vortex collective pinning in uniaxial superconductors to account for flux-bundle collective pinning in biaxial superconductors. The scaling results show that in a system of random uncorrected point defects, the field dependence of the critical current density is described by a unified function with the scaled magnetic field of the isotropic superconductor. The obtained angular dependence of the critical current density depicts the main features of experimental observations, considering possible corrections due to the strong-pinning interaction.

  17. High magnification crack-tip field characterisation under biaxial conditions

    Moreno, B.(Universidad de Los Andes, Bogota, Colombia); Lopez-Crespo, P; Zapatero, J.

    2013-01-01

    This work presents a novel methodology for characterising fatigue cracks under biaxial conditions. The methodology uses high magnification Digital Image Correlation (DIC) technique for measuring displacement and strain crack-tip fields. By applying micro-speckle pattern on the metal surface it is possible to achieve high magnification for DIC technique. The speckles were created by electro-spray technique. The validity of this novel technique is demonstrated by direct comparison with stan...

  18. Identification of material parameters using bi-axial machine

    Flores, Paulo; de Montleau, P.; Mathonet, V.; Moureaux, P. (collab.); Habraken, Anne

    2004-01-01

    Experimental testing equipment is built in order to identify material parameters of complex phenomenological constitutive laws. This equipment consists in a bi-axial test machine able to perform plane strain and simple shear tests separately or simultaneously and a Miyauchi simple shear test device; an optical extensometer is used to identify the strain field. The article focus on the validation of the results of this new equipment by comparing with results obtained by standard machines and/o...

  19. Aspekte der Modellierung des Tragverhaltens von Textilbeton unter biaxialer Beanspruchung

    Beyer, Frank R.; Zastrau, Bernd W.

    2011-01-01

    Zur Bemessung und Simulation von flächigen Textilbetonstrukturen werden Berechnungsmodelle benötigt, die das Materialverhalten unter biaxialer Beanspruchung abbilden können. Für eindimensionale Strukturen existieren einige Modelle, zu deren Weiterentwicklung eine Erweiterung zur Abbildung des biaxialen Materialverhaltens vorgeschlagen wird. In diesem Beitrag werden die notwendigen Erweiterungen und deren Umsetzbarkeit bei der Modellierung diskutiert und bewertet. For design and simulation...

  20. High temperature low cycle biaxial fatigue of two steels

    Biaxial low cycle fatigue tests at various temperatures and strain rates were performed on 1% Cr-Mo-V steel and AISI 316 stainless steel under combined torsional and axial loads. A correlation for fatigue strength has been derived, and it is also shown that if the Gough ellipse quadrant criterion is rephrased in terms of strain amplitudes, it may be used as a safe design rule for ductile metals in both the low and high cycle fatigue regimes. (author)

  1. Efficient Driving of Piezoelectric Transducers Using a Biaxial Driving Technique.

    Samuel Pichardo

    Full Text Available Efficient driving of piezoelectric materials is desirable when operating transducers for biomedical applications such as high intensity focused ultrasound (HIFU or ultrasound imaging. More efficient operation reduces the electric power required to produce the desired bioeffect or contrast. Our preliminary work [Cole et al. Journal of Physics: Condensed Matter. 2014;26(13:135901.] suggested that driving transducers by applying orthogonal electric fields can significantly reduce the coercivity that opposes ferroelectric switching. We present here the experimental validation of this biaxial driving technique using piezoelectric ceramics typically used in HIFU. A set of narrow-band transducers was fabricated with two sets of electrodes placed in an orthogonal configuration (following the propagation and the lateral mode. The geometry of the ceramic was chosen to have a resonance frequency similar for the propagation and the lateral mode. The average (± s.d. resonance frequency of the samples was 465.1 (± 1.5 kHz. Experiments were conducted in which each pair of electrodes was driven independently and measurements of effective acoustic power were obtained using the radiation force method. The efficiency (acoustic/electric power of the biaxial driving method was compared to the results obtained when driving the ceramic using electrodes placed only in the pole direction. Our results indicate that the biaxial method increases efficiency from 50% to 125% relative to the using a single electric field.

  2. Modelization of ratcheting in biaxial experiments

    A new unified viscoplastic constitutive equation has been developed in order to interpret ratcheting experiments on mechanical structures of fast reactors. The model is based essentially on a generalized Armstrong Frederick equation for the kinematic variable; the coefficients of the dynamic recovery term in this equation is a function of both instantaneous and accumulated inelastic strain which is allowed to vary in an appropriate manner in order to reproduce the experimental ratcheting rate. The validity of the model is verified by comparing predictions with experimental results for austenitic stainless steel (17-12 SPH) tubular specimens subjected to cyclic torsional loading under constant tensile stress at 6000C

  3. Directional Differences in the Biaxial Material Properties of Fascia Lata and the Implications for Fascia Function

    Eng, Carolyn M.; Pancheri, Francesco Q.; Lieberman, Daniel E.; Biewener, Andrew Austin; Dorfmann, Luis

    2014-01-01

    Fascia is a highly organized collagenous tissue that is ubiquitous in the body, but whose function is not well understood. Because fascia has a sheet-like structure attaching to muscles and bones at multiple sites, it is exposed to different states of multi- or biaxial strain. In order to measure how biaxial strain affects fascia material behavior, planar biaxial tests with strain control were performed on longitudinal and transversely oriented samples of goat fascia lata (FL). Cruciform samp...

  4. Biaxial Behavior of Ultra-High Performance Concrete and Untreated UHPC Waffle Slab Bridge Deck Design and Testing

    D'Alessandro, Kacie Caple

    Ultra-high performance concrete (UHPC) was evaluated as a potential material for future bridge deck designs. Material characterization tests took place to identify potential challenges in mixing, placing, and curing UHPC. Biaxial testing was performed to evaluate behavior of UHPC in combined tension and compression stress states. A UHPC bridge deck was designed to perform similarly to a conventional concrete bridge deck, and a single unit bridge deck section was tested to evaluate the design methods used for untreated UHPC. Material tests identified challenges with placing UHPC. A specified compressive strength was determined for structural design using untreated UHPC, which was identified as a cost-effective alternative to steam treated UHPC. UHPC was tested in biaxial tension-compression stress states. A biaxial test method was developed for UHPC to directly apply tension and compression. The influence of both curing method and fiber orientation were evaluated. The failure envelope developed for untreated UHPC with random fiber orientation was suggested as a conservative estimate for future analysis of UHPC. Digital image correlation was also evaluated as a means to estimate surface strains of UHPC, and recommendations are provided to improve consistency in future tests using DIC methods. A preliminary bridge deck design was completed for untreated UHPC and using established material models. Prestressing steel was used as primary reinforcement in the transverse direction. Preliminary testing was used to evaluate three different placement scenarios, and results showed that fiber settling was a potential placement problem resulting in reduced tensile strength. The UHPC bridge deck was redesigned to incorporate preliminary test results, and two single unit bridge deck sections were tested to evaluate the incorporated design methods for both upside down and right-side up placement techniques. Test results showed that the applied design methods would be conservative

  5. Deformation and strain hardening behavior of powder metallurgical TRIP steel under quasi-static biaxial-planar loading

    Kulawinski, D., E-mail: dirk.kulawinski@iwt.tu-freiberg.de [Institute of Materials Engineering, Technische Universität Bergakademie Freiberg, Gustav-Zeuner-Street 5, 09599 Freiberg (Germany); Ackermann, S. [Institute of Materials Engineering, Technische Universität Bergakademie Freiberg, Gustav-Zeuner-Street 5, 09599 Freiberg (Germany); Seupel, A. [Institute of Mechanics and Fluid Dynamics, Technische Universität Bergakademie Freiberg, Lampadiusstraße 4, 09599 Freiberg (Germany); Lippmann, T.; Henkel, S. [Institute of Materials Engineering, Technische Universität Bergakademie Freiberg, Gustav-Zeuner-Street 5, 09599 Freiberg (Germany); Kuna, M. [Institute of Mechanics and Fluid Dynamics, Technische Universität Bergakademie Freiberg, Lampadiusstraße 4, 09599 Freiberg (Germany); Weidner, A.; Biermann, H. [Institute of Materials Engineering, Technische Universität Bergakademie Freiberg, Gustav-Zeuner-Street 5, 09599 Freiberg (Germany)

    2015-08-26

    The present paper investigates a metastable austenitic stainless steel under different biaxial-planar load paths by using a cruciform specimen geometry. The material behavior was described by stress–strain curves and initial yield surface. Furthermore, the hardening behavior was determined by load sequence tests. To investigate the influence of the stress state on the martensite formation a ferrite sensor as well as electron backscatter diffraction measurements were used. Two cruciform specimen geometries were utilized and compared for the considered load cases. The stress state within the cruciform specimens was evaluated by an elastic unloading procedure with subsequent calculation of the stress components. Isotropic initial yielding and non-isotropic hardening were found. A recommendation for the use of the cruciform specimen geometry with respect to the load case is given.

  6. Global limit load solutions for plates with surface cracks under combined biaxial forces and cross-thickness bending

    Lower bound limit load solutions for surface cracks in plates under combined end force, cross-thickness bending moment and tensile/compressive membrane stress parallel to the crack are derived based on the von Mises yield criterion. From these solutions, particular limit loads for plates with extended surface cracks and through-thickness cracks or uncracked plates under the same loading conditions are obtained. The limit load solutions for surface cracks in plates under combined tension and bending due to Lei and Fox can be reproduced from the solutions in this paper by setting the stress parallel to the crack plane to zero. - Highlights: • Lower bound global limit load solution for rectangular surface cracks in plates. • Combined biaxial stress/force and cross-thickness bending moment. • Solutions based on lower bound limit load theorem and von Mises yield criterion. • Solutions valid for proportional/non-proportional loading

  7. Behavior of annealed type 316 stainless steel under monotonic and cyclic biaxial loading at room temperature

    This paper addresses the elastic-plastic behavior of type 316 stainless steel, one of the major structural alloys used in liquid-metal fast breeder reactor components. The study was part of a continuing program to develop a structural design technology applicable to advanced reactor systems. Here, behaviour of solution annealed material was examined through biaxial stress experiments conducted at room temperature under radial loadings (√3tau=sigma) in tension-torsion stress space. The effects of both stress limited monotonic loading and strain limited cyclic loading were determined on the size, shape and position of yield loci corresponding to small offset strain (10 microstrain) definition of yield. In the present work, the aim was to determine the extent to which the constitutive laws previously recommended for type 304 stainless steel are applicable to type 316 stainless steel. It was concluded that for the conditions investigated, the inelastic behavior of the two materials are qualitatively similar. Specifically, the von Mises yield criterion provides a reasonable approximation of initial yield behavior and the subsequent hardening behavior, at least under small offset definitions of yield, is to the first order kinematic in nature. (Auth.)

  8. Fatigue Behavior of Plain Concrete Under Biaxial Compression:Experiments and Theoretical Model

    朱劲松; 宋玉普; 曹伟

    2003-01-01

    The effects of different lateral confinement stress on the fatigue behavior of and cumulative damage to plain concrete are investigated experimentally. Eighty 100 mm×100 mm×100 mm specimens of ordinary strength concrete are tested under constant- or variable-amplitude fatigue loading and lateral confinement pressure in two orthogonal directions. A fatigue equation is developed by modifying the classical Aas-Jakobsen S-N equation for taking into account the effect of the confined stress on fatigue strength of plain concrete. The results of variable-amplitude fatigue tests indicate that the linear damage theory proposed by Palmgren and Miner is unreasonable in the biaxial stress state. A nonlinear cumulative damage model that could model the effects of the magnitude and sequence of variable-amplitude fatigue loading and lateral confinement pressure is proposed on the basis of the evolution laws of the residual strains in the longitudinal direction during fatigue tests. The residual fatigue life predicted by this model is found to be in good agreement with the results of the experimental research.

  9. Temperature-induced sign reversal of biaxiality observed by conoscopy in some ferroelectric Sm- C* liquid crystals

    Fukuda, Atsuo; VIJ, JAGDISH KUMAR

    2007-01-01

    PUBLISHED Article number 011709 We have studied various ferroelectric liquid crystals to find the average molecular direction of the shortest axis in the perfectly unwound state by using tilted conoscopic measurements. We find that there exist two types of temperature dependencies of the biaxiality. Some materials exhibit increasing biaxiality while others show decreasing biaxiality with increasing temperature. The former shows a temperature-induced sign reversal of biaxiality. Three di...

  10. Experimental realization of biaxial liquid crystal phases in colloidal dispersions of boardlike particles

    van den Pol, E; Petukhov, A.V.; Thies-Weesie, D.M.E.; Belov, D.V.; Vroege, G.J.

    2009-01-01

    Biaxial nematic and biaxial smectic phases were found in a colloidal model system of goethite ( -FeOOH) particles with a simple boardlike shape and short-range repulsive interaction. The macroscopic domains were oriented by a magnetic field and their structure was revealed by small angle x-ray scatt

  11. Phase Matching of SHG in Arbitrary Directions of Biaxial Crystals

    YANG Shengli; CHEN Mouzhi

    2002-01-01

    In this paper, propagation and polarization characteristics of optical waves in arbitrary directions in a biaxial crystal are analyzed, and universal relationships of refractive index dependence on their propagation directions and the principal refractive indices for two perpendicular polarization waves propagating in arbitrarily directions are derived from indicatrix equation. By using these relationships, methods of collinear phase matching (PM) of SHG are developed, and general expressions of the collinear PM angle dependent of the principal indices are given for SHG in arbitrarily directions. The expressions may be used to make optimization design of PM by computer for the SHG and to select optimum PM direction and to raise the SHG conversion efficiencies.

  12. High magnification crack-tip field characterisation under biaxial conditions

    B. Moreno

    2013-07-01

    Full Text Available This work presents a novel methodology for characterising fatigue cracks under biaxial conditions. The methodology uses high magnification Digital Image Correlation (DIC technique for measuring displacement and strain crack-tip fields. By applying micro-speckle pattern on the metal surface it is possible to achieve high magnification for DIC technique. The speckles were created by electro-spray technique. The validity of this novel technique is demonstrated by direct comparison with standard extensometer measurements, under tension-compression and torsion conditions. In order to image the correct region, the notch effect on the fatigue life was also evaluated.

  13. Material Identification Using a Bi-Axial Test Machine

    Flores, Paulo; Moureaux, Pierre; Habraken, Anne

    2005-01-01

    This paper shows the identification of material parameters for a DC06 IF steel sheet of 0.8 mm by mechanical tests. The experimental equipment used consists of a tensile test machine, a bi-axial test machine able to perform plane-strain and simple shear tests separately or simultaneously and an optical strain gauge. Tensile, plane-strain and simple shear tests were performed at 0°, 45° and 90° from the sheet rolling direction in order to identify Hill 1948 and Hosford 1979 yield criteria. ...

  14. Hole doped Dirac states in silicene by biaxial tensile strain

    Kaloni, Thaneshwor P.

    2013-03-11

    The effects of biaxial tensile strain on the structure, electronic states, and mechanical properties of silicene are studied by ab-initio calculations. Our results show that up to 5% strain the Dirac cone remains essentially at the Fermi level, while higher strain induces hole doped Dirac states because of weakened Si–Si bonds. We demonstrate that the silicene lattice is stable up to 17% strain. It is noted that the buckling first decreases with the strain (up to 10%) and then increases again, which is accompanied by a band gap variation. We also calculate the Grüneisen parameter and demonstrate a strain dependence similar to that of graphene.

  15. FAILURE MODE AND CONSTITUTIVE MODEL OF PLAIN HIGH-STRENGTH HIGH-PERFORMANCE CONCRETE UNDER BIAXIAL COMPRESSION AFTER EXPOSURE TO HIGH TEMPERATURES

    Zhenjun He; Yupu Song

    2008-01-01

    An orthotropic constitutive relationship with temperature parameters for plain highstrength high-performance concrete (HSHPC) under biaxial compression is developed. It is based on the experiments performed for characterizing the strength and deformation behavior at two strength levels of HSHPC at 7 different stress ratios including α = σ2 : σ3 = 0.00 : -1, -0.20 : -1, -0.30 : -1, -0.40 : -1, -0.50 : -1, -0.75 : -1, -1.00 : -1, after the exposure to normal and high temperatures of 20, 200, 300, 400, 500 and 600℃, and using a large static-dynamic true triaxial machine. The biaxial tests were performed on 100 mm × 100 mm × 100 mm cubic specimens, and friction-reducing pads were used consisting of three layers of plastic membrane with glycerine in-between for the compressive loading plane. Based on the experimental results, failure modes of HSHPC specimens were described. The principal static compressive strengths, strains at the peak stress and stress-strain curves were measured; and the influence of the temperature and stress ratios on them was also analyzed. The experimental results showed that the uniaxial compressive strength of plain HSHPC after exposure to high temperatures does not decrease dramatically with the increase of temperature. The ratio of the biaxial to its uniaxial compressive strength depends on the stress ratios and brittleness-stiffness of HSHPC after exposure to different temperature levels. Comparison of the stress-strain results obtained from the theoretical model and the experimental data indicates good agreement.

  16. Implementation of a Biaxial Resonant Fatigue Test Method on a Large Wind Turbine Blade

    Snowberg, D.; Dana, S.; Hughes, S.; Berling, P.

    2014-09-01

    A biaxial resonant test method was utilized to simultaneously fatigue test a wind turbine blade in the flap and edge (lead-lag) direction. Biaxial resonant blade fatigue testing is an accelerated life test method utilizing oscillating masses on the blade; each mass is independently oscillated at the respective flap and edge blade resonant frequency. The flap and edge resonant frequency were not controlled, nor were they constant for this demonstrated test method. This biaxial resonant test method presented surmountable challenges in test setup simulation, control and data processing. Biaxial resonant testing has the potential to complete test projects faster than single-axis testing. The load modulation during a biaxial resonant test may necessitate periodic load application above targets or higher applied test cycles.

  17. Multi-cracking in uniaxial and biaxial fatigue of 304L stainless steel

    When a mechanical part is subjected to a repeated mechanical stress, it may be damaged after a number of cycles by several cracks initiation and propagation of a main crack. This is the phenomenon of fatigue damage. The thesis deals specifically with possible damage to some components of nuclear plants due to thermal fatigue. Unlike conventional mechanical fatigue damage where a main crack breaks the part, the thermal fatigue damage usually results in the appearance of a surface crack network. Two aspects are discussed in the thesis. The first is the experimental study of fatigue multiple cracking stage also called multi-cracking. Two mechanical test campaigns with multi-cracking detection by digital image correlation were conducted. These campaigns involve uniaxial and equi-biaxial mechanical loads in tension/compression without mean stress. This work allows to monitor and to observe the evolution of different networks of cracks through mechanical solicitations. The second is the numerical simulation of the phenomenon of fatigue damage. Several types of model are used (stochastic, probabilistic, cohesive finite elements). The experimental results have led to identify a multiple crack initiation law in fatigue which is faced with the numerical results. This comparison shows the relevance of the use of an analytical probabilistic model to find statistical results on the density of cracks that can be initiated with thermal and mechanical fatigue loadings. (author)

  18. An experimental study of biaxial yield in modified 9Cr-1Mo steel at room temperature

    Ellis, J. R.

    1985-01-01

    Described are two biaxial experiments which investigated yield, hardening, and flow behavior in modified 9Cr-1Mo steel at room temperature. The aim of these experiments was to determine whether the procedures recommended in NE Standard F9-5T for inelastic design analysis are applicable for this material in normalized and tempered condition. The first experiment investigated small offset yield behavior subsequent to radial preloads (sq rt of 3 sub sigma 12 = sub sigma 11) in tension-torsion stress space. The second experiment investigated yield behavior subsequent to nonradial preloads and also the time-dependent flow occurring during 0.5 hour periods at constant stress. The results of these experiments were qualitatively similar to those obtained earlier for types 304 and 316 stainless steel. Specifically, the von Mises yield criterion was found to provide a reasonable approximation of initial yield behavior. Although the subsequent yield surfaces suffered considerable distortion from their near-circular form after both radial and nonradial preloads, the hardening behavior was to the first order kinematic in nature. The strain-time data obtained during the 0.5 hr hold periods showed characteristics typical of creep curves. As in the case of earlier experiments, the high initial flow rates diminished more rapidly than would be estimated from elevated temperature data.

  19. Simulation of Complex Cracking in Plain Weave C/SiC Composite under Biaxial Loading

    Cheng, Ron-Bin; Hsu, Su-Yuen

    2012-01-01

    Finite element analysis is performed on a mesh, based on computed geometry of a plain weave C/SiC composite with assumed internal stacking, to reveal the pattern of internal damage due to biaxial normal cyclic loading. The simulation encompasses intertow matrix cracking, matrix cracking inside the tows, and separation at the tow-intertow matrix and tow-tow interfaces. All these dissipative behaviors are represented by traction-separation cohesive laws. Not aimed at quantitatively predicting the overall stress-strain relation, the simulation, however, does not take the actual process of fiber debonding into account. The fiber tows are represented by a simple rule-of-mixture model where the reinforcing phase is a hypothetical one-dimensional material. Numerical results indicate that for the plain weave C/SiC composite, 1) matrix-crack initiation sites are primarily determined by large intertow matrix voids and interlayer tow-tow contacts, 2) the pattern of internal damage strongly depends on the loading path and initial stress, 3) compressive loading inflicts virtually no damage evolution. KEY WORDS: ceramic matrix composite, plain weave, cohesive model, brittle failure, smeared crack model, progressive damage, meso-mechanical analysis, finite element.

  20. Powder-in-tube and thick-film methods of fabricating high temperature superconductors having enhanced biaxial texture

    Goyal, Amit; Kroeger, Donald M.

    2003-11-11

    A method for forming an electronically active biaxially textured article includes the steps of providing a substrate having a single crystal metal or metal alloy surface, deforming the substrate to form an elongated substrate surface having biaxial texture and depositing an epitaxial electronically active layer on the biaxially textured surface. The method can include at least one annealing step after the deforming step to produce the biaxially textured substrate surface. The invention can be used to form improved biaxially textured articles, such as superconducting wire and tape articles having improved J.sub.c values.

  1. Practical method for analysis and design of slender reinforced concrete columns subjected to biaxial bending and axial loads

    Bouzid, T.; Demagh, K.

    2011-03-01

    Reinforced and concrete-encased composite columns of arbitrarily shaped cross sections subjected to biaxial bending and axial loads are commonly used in many structures. For this purpose, an iterative numerical procedure for the strength analysis and design of short and slender reinforced concrete columns with a square cross section under biaxial bending and an axial load by using an EC2 stress-strain model is presented in this paper. The computational procedure takes into account the nonlinear behavior of the materials (i.e., concrete and reinforcing bars) and includes the second - order effects due to the additional eccentricity of the applied axial load by the Moment Magnification Method. The ability of the proposed method and its formulation has been tested by comparing its results with the experimental ones reported by some authors. This comparison has shown that a good degree of agreement and accuracy between the experimental and theoretical results have been obtained. An average ratio (proposed to test) of 1.06 with a deviation of 9% is achieved.

  2. Spatial filtering efficiency of monostatic biaxial lidar: analysis and applications.

    Agishev, Ravil R; Comeron, Adolfo

    2002-12-20

    Results of lidar modeling based on spatial-angular filtering efficiency criteria are presented. Their analysis shows that the low spatial-angular filtering efficiency of traditional visible and near-infrared systems is an important cause of low signal/background-radiation ratio (SBR) at the photodetector input The low SBR may be responsible for considerable measurement errors and ensuing the low accuracy of the retrieval of atmospheric optical parameters. As shown, the most effective protection against sky background radiation for groundbased biaxial lidars is the modifying of their angular field according to a spatial-angular filtering efficiency criterion. Some effective approaches to achieve a high filtering efficiency for the receiving system optimization are discussed. PMID:12510915

  3. Conductive layer for biaxially oriented semiconductor film growth

    Findikoglu, Alp T.; Matias, Vladimir

    2007-10-30

    A conductive layer for biaxially oriented semiconductor film growth and a thin film semiconductor structure such as, for example, a photodetector, a photovoltaic cell, or a light emitting diode (LED) that includes a crystallographically oriented semiconducting film disposed on the conductive layer. The thin film semiconductor structure includes: a substrate; a first electrode deposited on the substrate; and a semiconducting layer epitaxially deposited on the first electrode. The first electrode includes a template layer deposited on the substrate and a buffer layer epitaxially deposited on the template layer. The template layer includes a first metal nitride that is electrically conductive and has a rock salt crystal structure, and the buffer layer includes a second metal nitride that is electrically conductive. The semiconducting layer is epitaxially deposited on the buffer layer. A method of making such a thin film semiconductor structure is also described.

  4. Biomechanical properties of the transverse carpal ligament under biaxial strain.

    Holmes, Michael W R; Howarth, Samuel J; Callaghan, Jack P; Keir, Peter J

    2012-05-01

    The transverse carpal ligament (TCL) influences carpal stability and carpal tunnel mechanics, yet little is known about its mechanical properties. We investigated the tissue properties of TCLs extracted from eight cadaver arms and divided into six tissue samples from the distal radial, distal middle, distal ulnar, proximal radial, proximal middle, and proximal ulnar regions. The 5% and 15% strains were applied biaxially to each sample at rates of 0.1, 0.25, 0.5, and 1%/s. Ligament thickness ranged from 1.22 to 2.90 mm. Samples from the middle of the TCL were thicker proximally than distally (p carpal bone attachments. These properties contribute to the understanding of carpal tunnel mechanics that is critical to understanding disorders of the wrist. PMID:22042748

  5. Electromagnetic biaxial microscanner with mechanical amplification at resonance.

    Cho, Ah Ran; Han, Aleum; Ju, Suna; Jeong, Haesoo; Park, Jae-Hyoung; Kim, Inhoi; Bu, Jong-Uk; Ji, Chang-Hyeon

    2015-06-29

    We present the design, fabrication, and measurement results of an electromagnetic biaxial microscanner with mechanical amplification mechanism. A gimbaled scanner with two distinct single-crystal silicon layer thicknesses and integrated copper coils has been fabricated with combination of surface and bulk micromachining processes. A magnet assembly consisting of an array of permanent magnets and a pole piece has been placed under the substrate to provide high strength lateral magnetic field oriented 45° to two perpendicular scanning axes. Micromirror has been supported by additional gimbal to implement a mechanical amplification. A 1.2mm-diameter mirror with aluminum reflective surface has been actuated at 60Hz for vertical scan and at 21kHz for horizontal scan. Maximum scan angle of 36.12° at 21.19kHz and 17.62° at 60Hz have been obtained for horizontal and vertical scans, respectively. PMID:26191691

  6. Electromagnetic biaxial vector scanner using radial magnetic field.

    Han, Aleum; Cho, Ah Ran; Ju, Suna; Ahn, Si-Hong; Bu, Jong-Uk; Ji, Chang-Hyeon

    2016-07-11

    We present an electromagnetic biaxial vector-graphic scanning micromirror. In contrast to conventional electromagnetic actuators using linear magnetic field, proposed device utilizes a radial magnetic field and uniquely designed current paths to enable the 2 degree-of-freedom scanning motion. As the radial field is generated by concentrically assembled magnets placed under the scanner die, large driving torque can be generated without the aid of hermetic packaging and relatively small device volume can be achieved. Mechanical half scan angle of 6.43° and 4.20° have been achieved at DC current of 250mA and 350mA for horizontal and vertical scans, respectively. Forced actuation along both scan axes has been realized by feedback control. PMID:27410851

  7. Surface polaritons in symmetry planes of biaxial crystals

    Furs, A N; Galynsky, V M; Barkovsky, L M [Department of Theoretical Physics, Belarussian State University, Fr. Skarina Ave. 4, Minsk 220050 (Belarus)

    2005-09-16

    The problem of the surface polariton existence in symmetry planes of non-magnetic biaxial crystals is studied theoretically. The plane interface of such a crystal and a semi-infinite isotropic medium is considered. With the use of the integral formalism formulated in our earlier work, the dispersion equation is derived for the polaritons under consideration. The existence conditions for the dispersion equation solutions are obtained in the form of algebraic inequalities for principal values of inverse dielectric permittivity tensors. If these conditions are satisfied, then excitation of surface waves is possible along the allowed propagation directions, which constitute sectors in the interface plane. Exact expressions are obtained that determine location of these sectors with respect to the symmetry axes of the crystal.

  8. [Incisions for biaxial and coaxial microincision cataract surgery].

    Müller, M; Kohnen, T

    2010-02-01

    Microincision cataract surgery (MICS) represents a new level in the development of cataract surgery. Phacoemulsification with intraocular lens (IOL) implantation via incisions of biaxial approach, with separation of the phaco tip and irrigation (B-MICS). Compared with standard small-incision cataract surgery, the advantages of MICS are less corneal astigmatism and fewer corneal surface irregularities, with favorable implications for visual quality and early rehabilitation. In the effort toward smaller incisions, special interest should be given to wound integrity, especially regarding the risk of endophthalmitis. With limited corneal elastic capacity, irreversible expansion of the incision with tissue laceration may occur. Smaller incisions are superior only if they cause less trauma. This requires an optimized relationship between incision size and manipulation during IOL implantation as well as attention to safety issues. MICS offers a platform for new benchmarks in phacoemulsification. PMID:20107810

  9. Collective behaviour and spacing of necks in ductile plates subjected to dynamic biaxial loading

    Zaera, R.; Rodríguez-Martínez, J. A.; Vadillo, G.; Fernández-Sáez, J.; Molinari, A.

    2015-12-01

    Diffuse or localized dynamic necking of a sheet metal is a major issue in high speed forming processes, leading to unacceptable thinning and even failure if fully developed, and in the dynamic behaviour of metallic structural elements of small thickness used for energy absorption purposes. This process is frequently related to the collective development of localization bands resulting in a necking pattern which depends on the sheet properties and on the loading conditions. This work investigates the spacing between necking bands in sheets made of a thermoviscoplastic metal and submitted to dynamic biaxial loading. For that task a linear perturbation technique, derived within a 2D framework which specifically accounts for stress triaxiality effects upon strain localization, has been developed. Using this methodology, a dominant instability mode can be identified, whose wavelength is related to the necking-band spacing. Likewise, fully 3D finite element simulations have been performed in order to verify and complement the outcomes of the aforementioned theoretical approach. The effects of loading conditions (loading path and loading rate), and thermal coupling on the stability of the deformation process and on the distance between necking bands are examined. We have shown that the neck spacing increases with the ratio of strains and decreases with the loading rate and the temperature rise.

  10. DYNAMIC STRAIN MAPPING AND REAL-TIME DAMAGE STATE ESTIMATION UNDER BIAXIAL RANDOM FATIGUE LOADING

    National Aeronautics and Space Administration — DYNAMIC STRAIN MAPPING AND REAL-TIME DAMAGE STATE ESTIMATION UNDER BIAXIAL RANDOM FATIGUE LOADING SUBHASISH MOHANTY*, ADITI CHATTOPADHYAY, JOHN N. RAJADAS, AND...

  11. Maier-Saupe model for a mixture of uniaxial and biaxial molecules

    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.

  12. On the sensitivity of directions which support Voigt wave propagation in infiltrated biaxial dielectric materials

    Mackay, Tom G

    2013-01-01

    Voigt wave propagation (VWP) was considered in a porous biaxial dielectric material which was infiltrated with a material of refractive index $n_a$. The infiltrated material was regarded as a homogenized composite material in the long-wavelength regime and its constitutive parameters were estimated using the extended Bruggeman homogenization formalism. In our numerical studies, the directions which support VWP were found to vary by as much as $300^\\circ$ per RIU as the refractive index $n_a$ was varied. The sensitivities achieved were acutely dependent upon the refractive index $n_a$ and the degrees of anisotropy and dissipation of the porous biaxial material. The orientations, shapes and sizes of the particles which constitute the infiltrating material and the porous biaxial material exerted only a secondary influence on the maximum sensitivities achieved. Also, for the parameter ranges considered, the degree of porosity of the biaxial material had little effect on the maximum sensitivities achieved. These n...

  13. Stress

    Keller, Hanne Dauer

    2015-01-01

    Kapitlet handler om stress som følelse, og det trækker primært på de få kvalitative undersøgelser, der er lavet af stressforløb.......Kapitlet handler om stress som følelse, og det trækker primært på de få kvalitative undersøgelser, der er lavet af stressforløb....

  14. Description of the flow behaviour of a high strength austenitic steel under biaxial loading by a constitutive equation

    Uniaxial and biaxial tension-torsion tests were carried out on a high strength austenitic steel at room temperature in the strain rate range from 10-5 to 102 s-1. This material shows a strong dependence of strength on strain rate. The yield loci of the combined tests are described by ellipses. The size and the shape of these ellipses are functions of strain and strain rate. The quasi-static and dynamic tension and tension-torsion behaviour of the austenitic steel is described by Perzyna's constitutive equation. There is good agreement between measured and calculated results if a yield criterion as a function of strain and strain rate, and a formula which contains the dependence of flow stress on strain rate based on thermal activation, are included. (orig.)

  15. Identification of a Visco-Elastic Model for PET Near Tg Based on Uni and Biaxial Results

    Luo, Yun Mei; Chevalier, Luc; Monteiro, Eric

    2011-05-01

    The mechanical response of Polyethylene Terephthalate (PET) in elongation is strongly dependent on temperature, strain and strain rate. Near the glass transition temperature Tg, the stress-strain curve presents a strain softening effect vs strain rate but a strain hardening effect vs strain under conditions of large deformations. The main goal of this work is to propose a viscoelastic model to predict the PET behaviour when subjected to large deformations and to determine the material properties from the experimental data. The viscoelastic model is written in a Leonov like way and the variational formulation is carried out for the numerical simulation using this model. To represent the non-linear effects, an elastic part depending on the elastic equivalent strain and a non-Newtonian viscous part depending on both viscous equivalent strain rate and cumulated viscous strain are tested. The model parameters can then be accurately obtained through the comparison with the experimental uniaxial and biaxial tests.

  16. Comparative efficiency analysis of different nonlinear modelling strategies to simulate the biaxial response of RC columns

    Hugo Rodrigues; Humberto Varum; Antonio Arede; Anibal Costa

    2012-01-01

    The performance of different nonlinear modelling strategies to simulate the response of RC columns subjected to axial load combined with cyclic biaxial horizontal loading is compared. The models studied are classified into two categories according to the nonlinearity distribution assumed in the elements: lumped-plasticity and distributed inelasticity. For this study, results of tests on 24 columns subjected to cyclic uniaxial and biaxial lateral displacements were numerically reproduced. The ...

  17. Two-Particle Cluster Theory for Biaxial Nematic Phase Based on a Recently Proposed Interaction Potential

    ZHANG Zhi-Dong; ZHANG Yan-Jun; SUN Zong-Li

    2006-01-01

    @@ Two-particle cluster theory is applied to study the biaxial nematic phase formed by biaxial molecules interacting with a simplified model proposed by Sonnet et al. [Phys. Rev. E 67 (2003) 061701]. For the temperature dependences of the internal energy per particle and of the order parameters, the two-particle theory yields an improved result compared with mean field theory. Concerning the phase diagram, the two-particle theory gives the numerical result in qualitative agreement with the mean field theory.

  18. Biaxial-Type Concentrated Solar Tracking System with a Fresnel Lens for Solar-Thermal Applications

    Tsung Chieh Cheng; Chao Kai Yang; Lin, I.

    2016-01-01

    In this paper, an electromechanical, biaxial-type concentrated solar tracking system was designed for solar-thermal applications. In our tracking system, the sunlight was concentrated by the microstructure of Fresnel lens to the heating head of the Stirling engine and two solar cells were installed to provide the power for tracking system operation. In order to obtain the maximum sun power, the tracking system traces the sun with the altitude-azimuth biaxial tracing method and accurately main...

  19. Fatigue Test Design: Scenarios for Biaxial Fatigue Testing of a 60-Meter Wind Turbine Blade

    Post, Nathan [National Renewable Energy Lab. (NREL), Golden, CO (United States)

    2016-07-01

    Current practice in commercial certification of wind turbine blades is to perform separate flap and lead-lag fatigue tests. The National Renewable Energy Laboratory has been researching and evaluating biaxial fatigue testing techniques and demonstrating various options, typically on smaller-scale test articles at the National Wind Technology Center. This report evaluates some of these biaxial fatigue options in the context of application to a multimegawatt blade certification test program at the Wind Technology Testing Center in Charlestown, Massachusetts.

  20. Biaxial nematic phases in fluids of hard board-like particles.

    Martínez-Ratón, Y; Varga, S; Velasco, E

    2011-08-01

    We use density-functional theory, of the fundamental-measure type, to study the relative stability of the biaxial nematic phase, with respect to non-uniform phases such as smectic and columnar, in fluids made of hard board-like particles with sizes σ(1) > σ(2) > σ(3). A restricted-orientation (Zwanzig) approximation is adopted. Varying the ratio κ(1) = σ(1)/σ(2) while keeping κ(2) = σ(2)/σ(3), we predict phase diagrams for various values of κ(2) which include all the uniform phases: isotropic, uniaxial rod- and plate-like nematics, and biaxial nematic. In addition, spinodal instabilities of the uniform phases with respect to fluctuations of the smectic, columnar and plastic-solid types are obtained. In agreement with recent experiments, we find that the biaxial nematic phase begins to be stable for κ(2)≳ 2.5. Also, as predicted by previous theories and simulations on biaxial hard particles, we obtain a region of biaxiality centred at κ(1)≈κ(2) which widens as κ(2) increases. For κ(2)≳ 5 the region κ(2)≈κ(1) of the packing-fraction vs. κ(1) phase diagrams exhibits interesting topologies which change qualitatively with κ(2). We have found that an increasing biaxial shape anisotropy favours the formation of the biaxial nematic phase. Our study is the first to apply FMT theory to biaxial particles and, therefore, it goes beyond the second-order virial approximation. Our prediction that the phase diagram must be asymmetric in the neighbourhood of κ(1)≈κ(2) is a genuine result of the present approach, which is not accounted for by previous studies based on second-order theories. PMID:21701729

  1. Optimal design and examination study of biaxial tensile specimens for solid propellant%固体推进剂双向拉伸试件优化设计及试验

    贾永刚; 张为华; 张炜

    2011-01-01

    基于Kelly提出的十字形试件,设计了一种新型固体推进剂双向拉伸试件。利用ANSYS有限元软件对试件双向加载过程试验区中引起的应力应变的数值模拟,实现了十字形试件的优化设计,经过优化的试件在满足双轴试验要求方面有了明显的改进。通过对丁羟复合固体推进剂试件双向加载力学行为试验研究,获得不同拉伸速率双向拉伸应力—应变破坏曲线,为推进剂材料破坏分析的经验准则提供判据。结果表明,固体推进剂断裂延伸率的双向弱化效应很明显,双向加载比例为等双拉状态时,其双向断裂延伸率比单向断裂延伸率降低37.5%。%A new-style biaxial tensile specimen of solid propellant is designed,based on the cruciform specimens proposed by Kelly.By using the finite element analysis ANSYS,the stress and displacement of specimens in the test section is simulated and the optimization of the cruciform specimens is realized.The stress and displacement fields in the central test section exhibit an excellent homogeneity and the maximum equivalent Von-Mises stress corresponding to the central part of the test section.In particular,the mechanical behavior of the biaxial tensile for HTPB propellant are tested,and the stress-strain wreck curves of biaxial tension are obtained under different tension speed.These data offer criterion for the wreck analysis of propellant material.The results show that the biaxial weakening of solid propellant is remarkable,and the Von-Mises rupture elongation of biaxial tensile decline about 37.5% to uniaxial tensile while the biaxial loads are equivalent.

  2. Phase diagram of the uniaxial and biaxial soft-core Gay-Berne model

    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.

  3. Prediction of crack growth direction by Strain Energy Sih's Theory on specimens SEN under tension-compression biaxial loading employing Genetic Algorithms

    Rodriguez-MartInez R; Lugo-Gonzalez E; Urriolagoitia-Calderon G; Urriolagoitia-Sosa G; Hernandez-Gomez L H; Romero-Angeles B; Torres-San Miguel Ch, E-mail: rrodriguezm@ipn.mx, E-mail: urrio332@hotmail.com, E-mail: guiurri@hotmail.com, E-mail: luishector56@hotmail.com, E-mail: romerobeatriz98@hotmail.com, E-mail: napor@hotmail.com [INSTITUTO POLITECNICO NACIONAL Seccion de Estudios de Posgrado e Investigacion (SEPI), Escuela Superior de Ingenieria Mecanica y Electrica (ESIME), Edificio 5. 2do Piso, Unidad Profesional Adolfo Lopez Mateos ' Zacatenco' Col. Lindavista, C.P. 07738, Mexico, D.F. (Mexico)

    2011-07-19

    Crack growth direction has been studied in many ways. Particularly Sih's strain energy theory predicts that a fracture under a three-dimensional state of stress spreads in direction of the minimum strain energy density. In this work a study for angle of fracture growth was made, considering a biaxial stress state at the crack tip on SEN specimens. The stress state applied on a tension-compression SEN specimen is biaxial one on crack tip, as it can observed in figure 1. A solution method proposed to obtain a mathematical model considering genetic algorithms, which have demonstrated great capacity for the solution of many engineering problems. From the model given by Sih one can deduce the density of strain energy stored for unit of volume at the crack tip as dW = [1/2E({sigma}{sup 2}{sub x} + {sigma}{sup 2}{sub y}) - {nu}/E({sigma}{sub x}{sigma}{sub y})]dV (1). From equation (1) a mathematical deduction to solve in terms of {theta} of this case was developed employing Genetic Algorithms, where {theta} is a crack propagation direction in plane x-y. Steel and aluminium mechanical properties to modelled specimens were employed, because they are two of materials but used in engineering design. Obtained results show stable zones of fracture propagation but only in a range of applied loading.

  4. Cyclic plasticity of an austenitic-ferritic stainless steel under biaxial non proportional loading

    Austenitic-ferritic stainless steels are supplied since about 30 years only, so they are yet not well-known. Their behaviour in cyclic plasticity was studied under uniaxial loading but not under multiaxial loading, whereas only a thorough knowledge of the phenomena influencing the mechanical behaviour of a material enables to simulate and predict accurately its behaviour in a structure. This work aims to study and model the behaviour of a duplex stainless steel under cyclic biaxial loading. A three step method was adopted. A set of tension-torsion tests on tubular specimen was first defined. We studied the equivalence between loading directions, and then the influence of loading path and loading history on the stress response of the material. Results showed that duplex stainless steel shows an extra-hardening under non proportional loading and that its behaviour depends on previous loading. Then, in order to analyse the results obtained during this first experimental stage, the yield surface was measured at different times during cyclic loading of the same kind. A very small plastic strain offset (2*10-5) was used in order not to disturb the yield surface measured. The alteration of isotropic and kinematic hardening variables were deduced from these measures. Finally, three phenomenological constitutive laws were identified with the experimental set. We focused our interest on the simulation of stabilized stress levels and on the simulation of the cyclic hardening/softening behaviour. The comparison between experimental and numerical results enabled the testing of the relevance of these models. (authors)

  5. Electret properties of biaxially stretched polypropylene films containing various additives

    Hillenbrand, J [Institute for Communications Technology, Darmstadt University of Technology, 64283 Darmstadt (Germany); Behrendt, N [Polymer Engineering, University of Bayreuth, 95447 Bayreuth (Germany); Altstaedt, V [Polymer Engineering, University of Bayreuth, 95447 Bayreuth (Germany); Schmidt, H-W [Macromolecular Chemistry I, University of Bayreuth, 95447 Bayreuth (Germany); Sessler, G M [Institute for Communications Technology, Darmstadt University of Technology, 64283 Darmstadt (Germany)

    2006-02-07

    Isotactic polypropylene (i-PP) films containing additives such as the commercial {alpha} -nucleation agent NA11 and the anorganic filler particles CaCO{sub 3} and Al{sub 2}O{sub 3} were biaxially stretched. As a result, the films assume a cellular morphology with oblong cavities extending in the direction of the film elongation. In the present study, stretched films of 50 {mu}m thickness with additive concentrations of 0.05-10 mass per cent were charged with a corona method to potentials of 400 or 500 V. The stability of the charges was tested isothermally at temperatures of 90 and 120 deg. C and by means of thermally stimulated discharge (TSD) experiments. The isothermal measurements show, for the above additives with concentrations higher than about 0.3%, a reduction of the charge decay with increasing additive concentrations. Compared with reference films of pure PP, the potential decay of the films containing additive concentrations of 10% is significantly reduced. Correspondingly, the TSD measurements indicate a shift of the main discharge peak to higher temperatures up to the melting temperature. Generally, the voiding and thus the stability also increases with the stretching ratio. These improvements of the charge stability are attributed to the barrier effect of the cavities. The results are of interest with respect to the various applications of PP electrets, such as ferroelectret devices and air filters.

  6. Electret properties of biaxially stretched polypropylene films containing various additives

    Hillenbrand, J.; Behrendt, N.; Altstädt, V.; Schmidt, H.-W.; Sessler, G. M.

    2006-02-01

    Isotactic polypropylene (i-PP) films containing additives such as the commercial α -nucleation agent NA11 and the anorganic filler particles CaCO3 and Al2O3 were biaxially stretched. As a result, the films assume a cellular morphology with oblong cavities extending in the direction of the film elongation. In the present study, stretched films of 50 µm thickness with additive concentrations of 0.05-10 mass per cent were charged with a corona method to potentials of 400 or 500 V. The stability of the charges was tested isothermally at temperatures of 90 and 120 °C and by means of thermally stimulated discharge (TSD) experiments. The isothermal measurements show, for the above additives with concentrations higher than about 0.3%, a reduction of the charge decay with increasing additive concentrations. Compared with reference films of pure PP, the potential decay of the films containing additive concentrations of 10% is significantly reduced. Correspondingly, the TSD measurements indicate a shift of the main discharge peak to higher temperatures up to the melting temperature. Generally, the voiding and thus the stability also increases with the stretching ratio. These improvements of the charge stability are attributed to the barrier effect of the cavities. The results are of interest with respect to the various applications of PP electrets, such as ferroelectret devices and air filters.

  7. Biaxially textured copper-iron alloys for coated conductors

    Gallistl, Bernhard; Hassel, Achim Walter [Institute for Chemical Technology of Inorganic Materials, Johannes Kepler University, Altenberger Str. 69, 4040 Linz (Austria); Kirchschlager, Raimund [Institute for Semiconductor and Solid State Physics, Johannes Kepler University, Altenberger Str. 69, 4040 Linz (Austria)

    2012-05-15

    Two copper based biaxially textured alloys containing 0.37 and 0.91 wt.%-Fe have been investigated for the use as substrate material for coated conductors. Average full width at half maximum (FWHM) values of 7.3 (CuFe0.37) and 6.8 (CuFe0.91) for in-plane alignment and 7.2 (CuFe0.37, CuFe0.91) for out-of-plane are achieved. Ultimate tensile strength for the two alloys is found to be much higher compared to the values for Cu and CuFe2.35. Hysteresis losses are dramatically reduced compared to other available substrate materials. Magnetisation data for both alloys obtained at 5 K show an anticipated saturation magnetisation (M{sub s}) <0.35 {mu}Wb m kg{sup -1}, which is less than 1% of pure Ni. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  8. Preparation of biaxially oriented TlCu-1234 thin films

    Khan, N A; Tateai, F; Kojima, T; Ishida, K; Terada, N; Ihara, H

    1999-01-01

    The single phase of TlCu-1234 superconductor thin films is prepared for the first time by the amorphous phase epitaxy (APE) method, which is thallium treatment of sputtered amorphous phase at 900 degrees C for 1 h. The amorphous $9 phase is prepared by sputtering from the stoichiometric target composition CuBa/sub 2/Ca/sub 3/Cu/sub 4/O/sub 12-y/. The films on the SrTiO/sub 3/ substrate are aligned biaxially after the thallium treatment. Highly reproducible $9 TlCu-1234 films are prepared by this method. The XRD reflected a predominant single phase with the c-axis lattice constant of 18.74 AA. This lattice constant value is in between that of Cu-1234 (17.99 AA) and Tl-1234 (19.11 AA) . The $9 pole figure measurements of (103) reflection of the films showed a-axis-oriented crystals with Delta phi =0.8 degrees . The composition of the films after energy dispersive X-ray (EDX) measurements is Tl/sub 0.8/Cu/sub 0.2/Ba/sub $9 2/Ca/sub 3/Cu/sub 4/O /sub 12-y/. From the resistivity measurements, the T/sub c/ is 113 K...

  9. An anisotropic hyperelastic constitutive model of brain white matter in biaxial tension and structural-mechanical relationships.

    Labus, Kevin M; Puttlitz, Christian M

    2016-09-01

    Computational models of the brain require accurate and robust constitutive models to characterize the mechanical behavior of brain tissue. The anisotropy of white matter has been previously demonstrated; however, there is a lack of data describing the effects of multi-axial loading, even though brain tissue experiences multi-axial stress states. Therefore, a biaxial tensile experiment was designed to more fully characterize the anisotropic behavior of white matter in a quasi-static loading state, and the mechanical data were modeled with an anisotropic hyperelastic continuum model. A probabilistic analysis was used to quantify the uncertainty in model predictions because the mechanical data of brain tissue can show a high degree of variability, and computational studies can benefit from reporting the probability distribution of model responses. The axonal structure in white matter can be heterogeneous and regionally dependent, which can affect computational model predictions. Therefore, corona radiata and corpus callosum regions were tested, and histology and transmission electron microscopy were performed on tested specimens to relate the distribution of axon orientations and the axon volume fraction to the mechanical behavior. These measured properties were implemented into a structural constitutive model. Results demonstrated a significant, but relatively low anisotropic behavior, yet there were no conclusive mechanical differences between the two regions tested. The inclusion of both biaxial and uniaxial tests in model fits improved the accuracy of model predictions. The mechanical anisotropy of individual specimens positively correlated with the measured axon volume fraction, and, accordingly, the structural model exhibited slightly decreased uncertainty in model predictions compared to the model without structural properties. PMID:27214689

  10. Control of biaxial strain in single-layer molybdenite using local thermal expansion of the substrate

    Plechinger, Gerd; Castellanos-Gomez, Andres; Buscema, Michele; van der Zant, Herre S. J.; Steele, Gary A.; Kuc, Agnieszka; Heine, Thomas; Schüller, Christian; Korn, Tobias

    2015-03-01

    Single-layer MoS2 is a direct-gap semiconductor whose electronic band structure strongly depends on the strain applied to its crystal lattice. While uniaxial strain can be easily applied in a controlled way, e.g., by bending of a flexible substrate with the atomically thin MoS2 layer on top, experimental realization of biaxial strain is more challenging. Here, we exploit the large mismatch between the thermal expansion coefficients of MoS2 and a silicone-based substrate to apply a controllable biaxial tensile strain by heating the substrate with a focused laser. The effect of this biaxial strain is directly observable in optical spectroscopy as a redshift of the MoS2 photoluminescence. We also demonstrate the potential of this method to engineer more complex strain patterns by employing highly absorptive features on the substrate to achieve non-uniform heat profiles. By comparison of the observed redshift to strain-dependent band structure calculations, we estimate the biaxial strain applied by the silicone-based substrate to be up to 0.2%, corresponding to a band gap modulation of 105 meV per percentage of biaxial tensile strain.

  11. Stress.

    Chambers, David W

    2008-01-01

    We all experience stress as a regular, and sometimes damaging and sometimes useful, part of our daily lives. In our normal ups and downs, we have our share of exhaustion, despondency, and outrage--matched with their corresponding positive moods. But burnout and workaholism are different. They are chronic, dysfunctional, self-reinforcing, life-shortening habits. Dentists, nurses, teachers, ministers, social workers, and entertainers are especially susceptible to burnout; not because they are hard-working professionals (they tend to be), but because they are caring perfectionists who share control for the success of what they do with others and perform under the scrutiny of their colleagues (they tend to). Workaholics are also trapped in self-sealing cycles, but the elements are ever-receding visions of control and using constant activity as a barrier against facing reality. This essay explores the symptoms, mechanisms, causes, and successful coping strategies for burnout and workaholism. It also takes a look at the general stress response on the physiological level and at some of the damage American society inflicts on itself. PMID:18846841

  12. The influence of stress state on the reorientation of hydrides in a zirconium alloy

    Cinbiz, Mahmut N.; Koss, Donald A.; Motta, Arthur T.

    2016-08-01

    Hydride reorientation can occur in spent nuclear fuel cladding when subjected to a tensile hoop stress above a threshold value during cooling. Because in these circumstances the cladding is under a multiaxial stress state, the effect of stress biaxiality on the threshold stress for hydride reorientation is investigated using hydrided CWSR Zircaloy-4 sheet specimens containing ∼180 wt ppm of hydrogen and subjected to a two-cycle thermo-mechanical treatment. The study is based on especially designed specimens within which the stress biaxiality ratios range from uniaxial (σ2/σ1 = 0) to "near-equibiaxial" tension (σ2/σ1 = 0.8). The threshold stress is determined by mapping finite element calculations of the principal stresses and of the stress biaxiality ratio onto the hydride microstructure obtained after the thermo-mechanical treatment. The results show that the threshold stress (maximum principal stress) decreases from 155 to 75 MPa as the stress biaxiality increases from uniaxial to "near-equibiaxial" tension.

  13. Biaxial tensile tests identify epidermis and hypodermis as the main structural elements of sweet cherry skin.

    Brüggenwirth, Martin; Fricke, Heiko; Knoche, Moritz

    2014-01-01

    The skin of developing soft and fleshy fruit is subjected to considerable growth stress, and failure of the skin is associated with impaired barrier properties in water transport and pathogen defence. The objectives were to establish a standardized, biaxial tensile test of the skin of soft and fleshy fruit and to use it to characterize and quantify mechanical properties of the sweet cherry (Prunus avium) fruit skin as a model. A segment of the exocarp (ES) comprising cuticle, epidermis, hypodermis and adhering flesh was mounted in the elastometer such that the in vivo strain was maintained. The ES was pressurized from the inner surface and the pressure and extent of associated bulging were recorded. Pressure : strain responses were almost linear up to the point of fracture, indicating that the modulus of elasticity was nearly constant. Abrading the cuticle decreased the fracture strain but had no effect on the fracture pressure. When pressure was held constant, bulging of the ES continued to increase. Strain relaxation upon releasing the pressure was complete and depended on time. Strains in longitudinal and latitudinal directions on the bulging ES did not differ significantly. Exocarp segments that released their in vivo strain before the test had higher fracture strains and lower moduli of elasticity. The results demonstrate that the cherry skin is isotropic in the tangential plane and exhibits elastic and viscoelastic behaviour. The epidermis and hypodermis, but not the cuticle, represent the structural 'backbone' in a cherry skin. This test is useful in quantifying the mechanical properties of soft and fleshy fruit of a range of species under standardized conditions. PMID:24876301

  14. Liquid crystal display modes in a nontilted bent-core biaxial smectic liquid crystal

    Nagaraj, Mamatha; Panarin, Y. P.; Vij, J. K.; Keith, C.; Tschierske, C.

    2010-11-01

    Liquid crystal display (LCD) modes associated with the rotation of the secondary director in nontilted, biaxial smectic phase of an achiral bent-core compound are demonstrated. For LCDs, we find that at least four display modes are possible using SmAPA phase of the studied material, in which the minor directors in adjacent layers are aligned antiferroelectrically. The advantages of these modes include low driving field (1-2 V/μm), high contrast ratio 1000:1, relatively fast switching time of 0.5 ms and continuous gray scale. The molecular short axis or the polar axis in a negative dielectric, biaxial material is oriented by the in-plane electric field by a combination dielectric biaxiality and polarity at low electric fields and polarity at higher fields.

  15. Phase Shift of Polarized Light after Transmission through a Biaxial Anisotropic Thin Film

    Hou, Yong-Qiang; Li, Xu; He, Kai; Qi, Hong-Ji; Yi, Kui; Shao, Jian-Da

    2013-01-01

    Based on the theoretical analysis of biaxial birefringent thin films with characteristic matrix method, we investigate the phase shift on transmission of a tilted columnar biaxial film at normal and oblique incidence over 300-1200 nm for s- and p-polarized waves. Compared with the simplified calculation method, the interference effects of the birefringent thin film are considered to yield more accurate results. The quarter wavelength phase shift calculated with the characteristic matrix method is consistent with that monitored with in situ measurement by two-angle ellipsometry, which validates our complied program for the calculation of the phase shift of the biaxial anisotropic thin film. Furthermore, the characteristic matrix method can be easily used to obtain continuous adjustable phase retardation at oblique incidence, whereas the simplified calculation method is valid for the case of normal incidence. A greater generality and superiority of the characteristic matrix method is presented.

  16. Phase Shift of Polarized Light after Transmission through a Biaxial Anisotropic Thin Film

    Based on the theoretical analysis of biaxial birefringent thin films with characteristic matrix method, we investigate the phase shift on transmission of a tilted columnar biaxial film at normal and oblique incidence over 300–1200 nm for s- and p-polarized waves. Compared with the simplified calculation method, the interference effects of the birefringent thin film are considered to yield more accurate results. The quarter wavelength phase shift calculated with the characteristic matrix method is consistent with that monitored with in situ measurement by two-angle ellipsometry, which validates our complied program for the calculation of the phase shift of the biaxial anisotropic thin film. Furthermore, the characteristic matrix method can be easily used to obtain continuous adjustable phase retardation at oblique incidence, whereas the simplified calculation method is valid for the case of normal incidence. A greater generality and superiority of the characteristic matrix method is presented

  17. The elusive thermotropic biaxial nematic phase in rigid bent-core molecules

    Bharat R Acharya; Andrew Primak; Theo J Dingemans; Edward T Samulski; Satyendra Kumar

    2003-08-01

    The biaxial nematic liquid crystalline phase was predicted several decades ago. Several vigorous attempts to find it in various systems resulted in mis-identifications. The results of X-ray diffraction and optical texture studies of the phases exhibited by rigid bent-core molecules derived from 2,5-bis-(-hydroxyphenyl)-1,3,4-oxadiazole reveal that the biaxial nematic phase is formed by three compounds of this type. X-ray diffraction studies reveal that the nematic phase of these compounds has the achiral symmetry D2h, in which the overall long axes of the molecules are oriented parallel to each other to define the major axis of the biaxial phase. The apex of the bent-cores defines the minor axis of this phase along which the planes containing the bent-cores of neighboring molecules are oriented parallel to each other.

  18. Spin splitting in bulk wurtzite AlN under biaxial strain

    Kao, Hsiu-Fen; Lo, Ikai; Chiang, Jih-Chen; Lee, Meng-En; Wu, C. L.; Wang, W. T.; Chen, Chun-Nan; Hsu, Y. C.

    2012-05-01

    The spin-splitting energies in biaxially strained bulk wurtzite material AlN are calculated using the linear combination of atomic orbital (LCAO) method, and the equi-spin-splitting distributions in k-space near the minimum-spin-splitting (MSS) surfaces are illustrated. These data are compared with those derived analytically by two-band k . p (2KP) model. It is found that the results from these two methods are in good agreement for small k. However, the ellipsoidal MSS surface under biaxial compressive strain does not exist in the 2KP model, because the data points are far from the Γ point. Instead, three basic shapes of the MSS surface occur in the wurtzite Brillouin zone: a hyperboloid of two sheets, a hexagonal cone, and a hyperboloid of one sheet, evaluated from the LCAO method across the range of biaxial strains from compressive to tensile.

  19. Biaxial Stretch Improves Elastic Fiber Maturation, Collagen Arrangement, and Mechanical Properties in Engineered Arteries.

    Huang, Angela H; Balestrini, Jenna L; Udelsman, Brooks V; Zhou, Kevin C; Zhao, Liping; Ferruzzi, Jacopo; Starcher, Barry C; Levene, Michael J; Humphrey, Jay D; Niklason, Laura E

    2016-06-01

    Tissue-engineered blood vessels (TEVs) are typically produced using the pulsatile, uniaxial circumferential stretch to mechanically condition and strengthen the arterial grafts. Despite improvements in the mechanical integrity of TEVs after uniaxial conditioning, these tissues fail to achieve critical properties of native arteries such as matrix content, collagen fiber orientation, and mechanical strength. As a result, uniaxially loaded TEVs can result in mechanical failure, thrombus, or stenosis on implantation. In planar tissue equivalents such as artificial skin, biaxial loading has been shown to improve matrix production and mechanical properties. To date however, multiaxial loading has not been examined as a means to improve mechanical and biochemical properties of TEVs during culture. Therefore, we developed a novel bioreactor that utilizes both circumferential and axial stretch that more closely simulates loading conditions in native arteries, and we examined the suture strength, matrix production, fiber orientation, and cell proliferation. After 3 months of biaxial loading, TEVs developed a formation of mature elastic fibers that consisted of elastin cores and microfibril sheaths. Furthermore, the distinctive features of collagen undulation and crimp in the biaxial TEVs were absent in both uniaxial and static TEVs. Relative to the uniaxially loaded TEVs, tissues that underwent biaxial loading remodeled and realigned collagen fibers toward a more physiologic, native-like organization. The biaxial TEVs also showed increased mechanical strength (suture retention load of 303 ± 14.53 g, with a wall thickness of 0.76 ± 0.028 mm) and increased compliance. The increase in compliance was due to combinatorial effects of mature elastic fibers, undulated collagen fibers, and collagen matrix orientation. In conclusion, biaxial stretching is a potential means to regenerate TEVs with improved matrix production, collagen organization, and mechanical

  20. Preliminary results from biaxial shallow-flaw fracture toughness tests on reactor pressure vessel steel

    Reactor pressure vessel (RPV) operating life can be limited by radiation-induced embrittlement and in this regard a loading condition of particular interest is postulated pressurized-thermal-shock (PTS). The calculated fracture initiation resistance of an RPV is based on the ASME KIc fracture toughness curve, which was developed using specimens with negligible out-of-plane strain (i.e., plane-strain conditions). For the shallow flaws of interest in the PTS analysis and for uniaxial loading, the fracture toughness appears to be considerably greater than KIc. However, PTS loads produce both a significant crack-opening load and a significant positive out-of-plane load along the crack front for both circumferential and axial flaws. Experimental evidence is scarce but seems to indicate that, for conditions prototypic of an RPV, a reduction in fracture toughness takes place associated with out-of-plane biaxial loading when compared with uniaxial loading conditions in shallow-flaw specimens. Additional experimental fracture toughness data under biaxial loading are necessary to evaluate the effect of biaxial loads in an RPV under PTS conditions. The Heavy-Section Steel Technology (HSST) program sponsored by the US Nuclear Regulatory Commission (NRC) is conducting an exploratory, ''proof-of-principle'' series of out-of-plane, biaxial-bending, fracture-toughness tests using specimens with shallow flaws. Cruciform specimens with an approximate cross section of 100 x 100 mm (4 x 4 in.) and with a straight-through, two-dimensional, shallow flaw, are being loaded in bending across two perpendicular planes for biaxial loading. This paper presents the initial test results under uniaxial and biaxial loading and compares the test results with HSST shallow-crack data

  1. Characteristics of residual stresses of water jet peened stainless steel

    The material of the specimen was austenitic stainless steel, SUS316L. The residual stresses in the specimen was introduced by a water jet peening (WJP). The change in the residual stress with thermal aging at 773K was measured by an X-ray stress measurement. The WJP residual stresses were an equi-biaxial stress state, and the compressive residual stress did not decrease against the thermal aging. To investigate dependence of the residual stress on a lattice plane, the WJP residual stresses were measured using hard synchrotron X-rays. (author)

  2. The fabrication and high temperature stability of biaxially textured Ni tape by ion beam structure modification method

    For the conventional rolling assisted biaxially textured metallic substrate (RABiTS) process, a large degree of cold rolling deformation and a subsequent high temperature annealing procedure are required to obtain adequately biaxially textured Ni tape. Recently, we have reported a newly developed process, named as ion beam structure modification (ISM), for fabricating biaxially textured Ni tape by use of low energy argon ion beam bombardment. In this paper, the biaxial texture of ISM processed Ni tape and its thermal stability at high temperatures are investigated. Results show that Ni tape processed under optimum ISM conditions, the (2 0 0) rocking curve FWHM is less than 5.7 deg. , and the (1 1 1) phi-scan FWHM is less than 7.5 deg. . High temperature annealing does not impair the biaxial-texture already developed in ISM processed Ni foils, although ISMs should not be regarded as a complete equilibrium process

  3. Behavior of reinforced concrete slabs subjected to combined punching shear and biaxial tension

    This investigation was a continuing study of peripheral (punching) shear strength of precracked, biaxially tensioned, orthogonally reinforced concrete slabs. This research was motivated by the need to determie the strength of a reinforced concrete containment vessel wall when subjected to combined internal pressure and punching shear loads normal to the wall. The study served to determine the effect of three major variables (shear span, size of loaded area, and reinforcing steel ratio) on punching shear strength of slabs that were precracked in biaxial tension and then held at one of the two tension levels (0 or 0.8f/sub y/) during shear load application

  4. Effective-Field Theory on High Spin Systems with Biaxial Crystal Field

    JIANG Wei; GUO An-Bang; LI Xin; WANG Xi-Kun; BAI Bao-Dong

    2006-01-01

    Based on the effective-field theory with self-spin correlations and the differential operator technique,physical properties of the spin-2 system with biaxial crystal field on the simple cubic, body-centered cubic, as well as faced-centered lattice have been studied. The influences of the external longitudinal magnetic field on the magnetization,internal energy, specific heat, and susceptibility have been discussed in detail. The phenomenon that the magnetization in the ground state shows quantum effects produced by the biaxial transverse crystal field has been found.

  5. Scratch resistance anisotropy in biaxially oriented polypropylene and poly(ethylene terephthalate) films

    Using a diamond-tipped stylus, scratch tests were conducted on biaxially oriented polypropylene and poly(ethylene terephthalate) films in the two draw directions, i.e., the machine-direction (MD) and the transverse-direction (TD) along which the draw ratios are different. Atomic force microscopy study of those scratches revealed a significant anisotropy in the scratch resistance between the MD and TD for both of the polymer films. We confirmed that the scratch resistance of polymer strands is closely related to the draw ratios, which determine the mechanical strength and optical clarity of biaxially oriented polymer films

  6. Electronic and optical properties of kesterite Cu2ZnSnS4 under in-plane biaxial strains: First-principles calculations

    The electronic structures and optical properties of Cu2ZnSnS4 (CZTS) under in-plane biaxial strain were systematically investigated using first-principles calculations based on generalized gradient approximation and hybrid functional method, respectively. It is found that the fundamental bandgap at the Γ point decreases linearly with increasing tensile biaxial strain perpendicular to c-axis. However, a bandgap maximum occurs as the compressive biaxial strain is 1.5%. Further increase of compressive strain decreases the bandgap. In addition, the optical properties of CZTS under biaxial strain are also calculated, and the variation trend of optical bandgap with biaxial strain is consistent with the fundamental bandgap.

  7. Biaxial creep deformation behavior of Fe–14Cr–15Ni–Ti modified austenitic stainless steel fuel cladding tube for sodium cooled fast reactor

    Highlights: • Significant amounts of creep strain is observed in the axial and hoop directions. • Hoop strain is much higher than the axial strain. • Steady state hoop rate is lower than steady state axial rate. • Steady state hoop rate is comparable with creep rate evaluated from uniaxial tests. • Alloy D9 exhibits anisotropy in creep deformation. - Abstract: Twenty percent cold worked Fe–14Cr–15Ni–Ti modified austenitic stainless steel is used as the cladding tube material for the fuel pins of the Prototype Fast Breeder Reactor in India. Biaxial creep properties of the tubes have been studied at 973 K by carrying out creep tests by internally pressurizing the tubes. Hoop and axial components of creep strain were measured and found to be significantly different. For a given gas pressure, steady state hoop rate was higher than the axial rate. Steady state hoop and axial creep rates followed Norton's power law with the same stress exponent n = 7. Steady state hoop rates determined from biaxial creep tests agreed with the steady state creep rates determined from uniaxial creep tests. For a thin walled closed tube under internal pressure, significant axial deformation along with hoop deformation is indicative of anisotropic deformation of the material

  8. Biaxial creep deformation behavior of Fe–14Cr–15Ni–Ti modified austenitic stainless steel fuel cladding tube for sodium cooled fast reactor

    Mathew, M.D., E-mail: mathew@igcar.gov.in [Mechanical Metallurgy Division, Indira Gandhi Centre for Atomic Research, Kalpakkam 603 102, Tamil Nadu (India); Ravi, S.; Vijayanand, V.D.; Latha, S. [Mechanical Metallurgy Division, Indira Gandhi Centre for Atomic Research, Kalpakkam 603 102, Tamil Nadu (India); Dasgupta, Arup [Physical Metallurgy Group, Indira Gandhi Centre for Atomic Research, Kalpakkam 603 102, Tamil Nadu (India); Laha, K. [Mechanical Metallurgy Division, Indira Gandhi Centre for Atomic Research, Kalpakkam 603 102, Tamil Nadu (India)

    2014-08-15

    Highlights: • Significant amounts of creep strain is observed in the axial and hoop directions. • Hoop strain is much higher than the axial strain. • Steady state hoop rate is lower than steady state axial rate. • Steady state hoop rate is comparable with creep rate evaluated from uniaxial tests. • Alloy D9 exhibits anisotropy in creep deformation. - Abstract: Twenty percent cold worked Fe–14Cr–15Ni–Ti modified austenitic stainless steel is used as the cladding tube material for the fuel pins of the Prototype Fast Breeder Reactor in India. Biaxial creep properties of the tubes have been studied at 973 K by carrying out creep tests by internally pressurizing the tubes. Hoop and axial components of creep strain were measured and found to be significantly different. For a given gas pressure, steady state hoop rate was higher than the axial rate. Steady state hoop and axial creep rates followed Norton's power law with the same stress exponent n = 7. Steady state hoop rates determined from biaxial creep tests agreed with the steady state creep rates determined from uniaxial creep tests. For a thin walled closed tube under internal pressure, significant axial deformation along with hoop deformation is indicative of anisotropic deformation of the material.

  9. Large-deformation properties of wheat dough in uni- and biaxial extension. Part I. Flour dough

    Sliwinski, E.L.; Kolster, P.; Vliet, van T.

    2004-01-01

    Rheological and fracture properties of optimally mixed flour doughs from three wheat cultivars which perform differently in cereal products were studied in uniaxial and biaxial extension. Doughs were also tested in small angle sinusoidal oscillation. In accordance with previously published results t

  10. 2D nonlocal versus 3D bifurcation studies for biaxially loaded plates

    Benallal, A.; Tvergaard, Viggo

    1998-01-01

    The main objective of this work is to analyse how a two-dimensional second gradient plasticity model is able to reproduce the three-dimensional bifurcation behaviour for a biaxially loaded flat plate. While it is found that the simple model used here is able to capture them qualitatively for the ...

  11. Phase diagram of colloidal spheres in a biaxial electric or magnetic field

    Smallenburg, F.; Dijkstra, M.

    2010-01-01

    Colloidal particles with a dielectric constant mismatch with the surrounding solvent in an external biaxial magnetic or electric field experience an “inverted” dipolar interaction. We determine the phase behavior of such a system using Helmholtz free energy calculations in Monte Carlo simulations fo

  12. The effect of biaxial strain on impurity diffusion in Si and SiGe

    Larsen, Arne Nylandsted; Zangenberg, Nikolaj; Fage-Pedersen, Jacob

    2005-01-01

    Results from diffusion studies of different impurities in biaxially strained Si and Si"1"-"xGe"x for low x-values will be presented. The structures are all molecular-beam epitaxy (MBE) grown on strain-relaxed Si"1"-"xGe"x layers, and the impurity profiles are introduced during growth. We have in...

  13. Biaxial loading and shallow-flaw effects on crack-tip constraint and fracture-toughness

    Uniaxial tests of single-edged notched bend (SENB) specimens with both deep- and shallow-flaws have shown elevated fracture-toughness for the shallow flaws. The elevation in fracture-toughness for shallow flaws has been shown to be the result of reduced constraint at the crack-tip. Biaxial loading has the potential to increase constraint at the crack-tip and thereby reduce some of the shallow-flaw, fracture-toughness elevation. Biaxial fracture-toughness tests have shown that the shallow-flaw, fracture-toughness elevation is reduced but not eliminated by biaxial loading. Dual-parameter, fracture-toughness correlations have been proposed to reflect the effect of crack-tip constraint on fracture-toughness. Test results from the uniaxial and biaxial tests were analyzed using the dual-parameter technology. Discrepancies between analysis results and cleavage initiation site data from fractographic examinations indicate that the analysis models are in need of further refinement. Addition of a precleavage, ductile-tearing element to the analysis model has the potential to resolve the noted discrepancies

  14. On the sensitivity of directions that support Voigt wave propagation in infiltrated biaxial dielectric materials

    Mackay, Tom G.

    2014-01-01

    Voigt wave propagation (VWP) was considered in a porous biaxial dielectric material that was infiltrated with a material of refractive index n. The infiltrated material was regarded as a homogenized composite material in the long wavelength regime, and its constitutive parameters were estimated using the extended Bruggeman homogenization formalism. In our numerical studies, the directions that support VWP were found to vary by as much as 300 deg per RIU as the refractive index n was varied. The sensitivities achieved were acutely dependent upon the refractive index n and the degrees of anisotropy and dissipation of the porous biaxial material. The orientations, shapes, and sizes of the particles that constitute the infiltrating material and the porous biaxial material exerted only a secondary influence on the maximum sensitivities achieved. Also, for the parameter ranges considered, the degree of porosity of the biaxial material had little effect on the maximum sensitivities achieved. These numerical findings bode well for the possible harnessing of VWP for optical sensing applications.

  15. Biaxial flexural strength of Turkom-Cera core compared to two other all-ceramic systems

    Bandar Mohammed Abdullah Al-Makramani

    2010-12-01

    Full Text Available Advances in all-ceramic systems have established predictable means of providing metal-free aesthetic and biocompatible materials. These materials must have sufficient strength to be a practical treatment alternative for the fabrication of crowns and fixed partial dentures. OBJECTIVES: The aim of this study was to compare the biaxial flexural strength of three core ceramic materials. MATERIAL AND METHODS: Three groups of 10 disc-shaped specimens (16 mm diameter x 1.2 mm thickness - in accordance with ISO-6872, 1995 were made from the following ceramic materials: Turkom-Cera Fused Alumina [(Turkom-Ceramic (M Sdn Bhd, Puchong, Selangor, Malaysia], In-Ceram (Vita Zahnfabrik, Bad Säckingen, Baden-Württemberg, Germany and Vitadur-N (Vita Zahnfabrik, Bad Säckingen, Baden-Württemberg, Germany, which were sintered according to the manufacturer's recommendations. The specimens were subjected to biaxial flexural strength test in an universal testing machine at a crosshead speed of 0.5 mm/min. The definitive fracture load was recorded for each specimen and the biaxial flexural strength was calculated from an equation in accordance with ISO-6872. RESULTS: The mean biaxial flexural strength values were: Turkom-Cera: 506.8±87.01 MPa, In-Ceram: 347.4±28.83 MPa and Vitadur-N: 128.7±12.72 MPa. The results were analyzed by the Levene's test and Dunnett's T3 post-hoc test (SPSS software V11.5.0 for Windows, SPSS, Chicago, IL, USA at a preset significance level of 5% because of unequal group variances (P<0.001. There was statistically significant difference between the three core ceramics (P<0.05. Turkom-Cera showed the highest biaxial flexural strength, followed by In-Ceram and Vitadur-N. CONCLUSIONS: Turkom-Cera core had significantly higher flexural strength than In-Ceram and Vitadur-N ceramic core materials.

  16. Electric field induced biaxiality and the electro-optic effect in a bent-core nematic liquid crystal

    Nagaraj, Mamatha; Panarin, Y. P.; Manna, U.; Vij, J. K.; Keith, C.; Tschierske, C.

    2010-01-01

    We report the observation of a biaxial nematic phase in a bent-core molecular system using polarizing microscopy, electro-optics, and dielectric spectroscopy, where we find that the biaxiality exists on a microscopic scale. An application of electric field induces a macroscopic biaxiality and in consequence gives rise to electro-optic switching. This electro-optic effect shows significant potential in applications for displays due to its fast high-contrast response. The observed electro-optic switching is explained in terms of the interaction of the ferroelectric clusters with the electric field.

  17. The influence of the stress state on Ksub(Ic)

    To get a first impression of the influence of stress states of higher multi-axiality than plane strain on Ksub(c) a specimen has been created, in which a bi-axial nominal stress state arises by uniaxial tension. This is attained by tension superimposed by transverse bending stress. The stress distribution without crack was analysed by photoelasticity as well as by finite element method. The results were identical. The stress distribution in the fracture (crack) plane was somewhat inhomogeneous, of course. But the ratio of the stress parallel to the tension axis to that perpendicular to it was max. 1:0.3 with a mean value 1:0.15. Specimens of this type were machined from a rolled sheet of the steel 22 NiMoCr 37, with specimen thickness of about 50 mm. For comparison single-edge notched specimens of the same cross section were prepared from the same material. Fatigue cracks were made following ASTM Recommendations. The fracture mechanics tests were carried out at a temperature of -1000C. Although valid Ksub(Ic)-values following the rigorous intention of the linear elastic fracture mechanics (ASTM Recommendations) were not obtained, the differences between the results of the two types of specimens and stress states were significant. The Ksub(Q)-values of the bi-axial stressed specimen were about 25% lower than that of the single-edge notched specimen. The deviation of the load-displacement trace from the linear elastic behavior was greater for the single-edge notched specimens than for the bi-axial stressed specimens. The consequences of these results for the assessment of flaws in pressure vessels are evident considering that bi-axial nominal stress states occur in pressure vessels

  18. Biaxial creep behavior of ribbed GCFR cladding at 650/sup 0/C in nominally pure helium (99. 99%)

    Yaggee, F. L.; Purohit, A.; Grajek, W. J.; Peoppel, R. B.

    1977-11-01

    Biaxial creep-rupture tests were conducted on 12 prototypic GCFR fuel-cladding specimens at 650/sup 0/C and a nominal hoop stress of 241.3 MPa. All test specimens were fabricated from 20% cold-worked Type 316 stainless steel tubes that were ribbed on the outer surface by mechanical grinding or electro-chemical etching. Test variables included specimen length and the presence or absence of weld-reinforcing end collars. Test results have indicated that, compared with data on smooth specimens, ribbing has no detrimental effect on creep-rupture lifetime. Specimens fabricated from tubes ribbed by electrochemical etching exhibit a significantly shorter creep-rupture lifetime and a higher secondary (steady-state) creep rate than specimens fabricated from tubes ribbed by mechanical grinding. Specimen length does not strongly affect creep-rupture lifetime, but the presence of an end collar does exhibit a significant influence on both the axial strain profile and the ratio of maximum diametral strain at the failure site to average diametral strain away from the failure site. The ribs do not inhibit the propagation of fissure or rupture failures.

  19. Monte Carlo simulations of biaxial structure in thin hybrid nematic film based upon spatially anisotropic pair potential

    Zhang Zhi-Dong; Chang Chun-Rui; Ma Dong-Lai

    2009-01-01

    Hybrid nematic films have been studied by Monte Carlo simulations using a lattice spin model,in which the pair potential is spatially anisotropic and dependent on elastic constants of liquid crystals.We confirm in the thin hybrid nematic film the existence of a biaxially nonbent structure and the structarc transition from the biaxial to the bent-director structure,which is similar to the result obtained using the Lebwohl-Lasher model.However,the step-like director's profile,characteristic for the biaxial structure,is spatially asymmetric in the film because the pair potential leads to K1≠K3.We estimate the upper cell thickness to be 69 spin layers,in which the biaxial structure can be found.

  20. Strength Behavior of High Strength R/C Columns under Biaxial Bending-Shear and Varying Axial Load

    MIZOGUCHI, Mitsuo; Arakawa, Takashi; ARAI, Yasuyuki

    1991-01-01

    Twelve short square R/C columns using high-strength concrete were tested to examine the effects of biaxial bending-shear force and varying axial load on the shear and flexural strength behavior. The columns were cyclically deflected either along their transverse principal axis to produce uniaxial bending-shear or along their diagonal to produce biaxial bending-shear. For columns failing in flexure, the experimental results were found to be in close agreement with the computed values given by ...

  1. Room temperature growth of biaxially aligned yttria-stabilized zirconia films on glass substrates by pulsed-laser deposition

    Li Peng; Mazumder, J

    2003-01-01

    Room temperature deposition of biaxially textured yttria-stabilized zirconia (YSZ) films on amorphous glass substrates was successfully achieved by conventional pulsed-laser deposition. The influence of the surrounding gases, their pressure and the deposition time on the structure of the films was studied. A columnar growth process was revealed based on the experimental results. The grown biaxial texture appears as a kind of substrate independence, which makes it possible to fabricate in-plane aligned YSZ films on various substrates.

  2. Room temperature growth of biaxially aligned yttria-stabilized zirconia films on glass substrates by pulsed-laser deposition

    Room temperature deposition of biaxially textured yttria-stabilized zirconia (YSZ) films on amorphous glass substrates was successfully achieved by conventional pulsed-laser deposition. The influence of the surrounding gases, their pressure and the deposition time on the structure of the films was studied. A columnar growth process was revealed based on the experimental results. The grown biaxial texture appears as a kind of substrate independence, which makes it possible to fabricate in-plane aligned YSZ films on various substrates

  3. Comparison of recent rubber elasticity theories with biaxial stress-strain data

    Meissner, Bohumil; Matějka, Libor

    Cracow : Rzeszów University of Technology, 2000. s. L-1. ISBN 83-86697-13-X. [Polymer Networks Group Meeting: Polymer Networks 2000, Formation-Structure-Properties /15./. 17.07.2000-21.07.2000, Cracow] R&D Projects: GA ČR GA104/00/1311 Subject RIV: CF - Physical ; Theoretical Chemistry

  4. Preliminary assessment of the effects of biaxial loading on reactor pressure vessel structural-integrity-assessment technology

    Effects of biaxial loading on shallow-flaw fracture toughness were studied to determine potential impact on structural integrity assessment of a reactor pressure vessel (RPV) under pressurized thermal shock (PTS) transient loading and pressure-temperature (PT) loading produced by reactor heatup and cooldown transients. Biaxial shallow-flaw fracture-toughness tests results were also used to determine the parameter controlling fracture in the transition temperature range, and to develop a related dual-parameter fracture-toughness correlation. Shallow-flaw and biaxial loading effects were found to reduce the conditional probability of crack initiation by a factor of nine when the shallow-flaw fracture-toughness KJc data set, with biaxial-loading effects adjustments, was substituted in place of ASME Code KIc data set in PTS analyses. Biaxial loading was found to reduce the shallow-flaw fracture toughness of RPV steel such that the lower-bound curve was located between ASME KIc and KIR curves. This is relevant to future development of P-T curve analysis procedures. Fracture in shallow-flaw biaxial samples tested in the lower transition temperature range was shown to be strain controlled. A strain-based dual-parameter fracture-toughness correlation was developed and shown to be capable of predicting the effect of crack-tip constraint on fracture toughness for strain-controlled fracture

  5. Cyclic plasticity of an austenitic-ferritic stainless steel under biaxial non proportional loading; Plasticite cyclique d'un acier inoxydable austeno-ferritique sous chargement biaxial non-proportionnel

    Aubin, V

    2001-11-15

    Austenitic-ferritic stainless steels are supplied since about 30 years only, so they are yet not well-known. Their behaviour in cyclic plasticity was studied under uniaxial loading but not under multiaxial loading, whereas only a thorough knowledge of the phenomena influencing the mechanical behaviour of a material enables to simulate and predict accurately its behaviour in a structure. This work aims to study and model the behaviour of a duplex stainless steel under cyclic biaxial loading. A three step method was adopted. A set of tension-torsion tests on tubular specimen was first defined. We studied the equivalence between loading directions, and then the influence of loading path and loading history on the stress response of the material. Results showed that duplex stainless steel shows an extra-hardening under non proportional loading and that its behaviour depends on previous loading. Then, in order to analyse the results obtained during this first experimental stage, the yield surface was measured at different times during cyclic loading of the same kind. A very small plastic strain offset (2*10{sup -5}) was used in order not to disturb the yield surface measured. The alteration of isotropic and kinematic hardening variables were deduced from these measures. Finally, three phenomenological constitutive laws were identified with the experimental set. We focused our interest on the simulation of stabilized stress levels and on the simulation of the cyclic hardening/softening behaviour. The comparison between experimental and numerical results enabled the testing of the relevance of these models. (authors)

  6. Non-linear Response of Two-way Asymmetric Multistorey Building Under Biaxial Excitation

    Nishant K. Kumar

    2013-04-01

    Full Text Available Seismic analysis is generally performed by creating a structural model which is excited with forces in two orthogonal directions separately i.e. they are subjected to uniaxial excitation. But an actual earthquake will have its effect in both the directions simultaneously. Limited research has been carried out on effect of such biaxial excitation. This paper deals with the non-linear performance of multi-storey buildings under biaxial excitation using various time-histories. The angle of incidence of earthquake forces will be varying between 0 to 360 degrees. Three building plans, with eccentricity along each of x and z directions in plan and a third with eccentricity in both the orthogonal direction, have been studied.Time history analysis has been carried out using SAP2000 after validating a preliminary model with experimental results available in reference literature.

  7. Mechanical properties of stanene under uniaxial and biaxial loading: A molecular dynamics study

    Mojumder, Satyajit [Department of Mechanical Engineering, Bangladesh University of Engineering and Technology, Dhaka 1000 (Bangladesh); Amin, Abdullah Al [Department of Mechanical and Aerospace Engineering, Case western Reverse University, Cleveland, Ohio 44106 (United States); Islam, Md Mahbubul, E-mail: mmi122@psu.edu [Department of Mechanical and Nuclear Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802 (United States)

    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.

  8. Tunable biaxial in-plane compressive strain in a Si nanomembrane transferred on a polyimide film

    Kim, Munho; Mi, Hongyi; Cho, Minkyu; Seo, Jung-Hun; Ma, Zhenqiang, E-mail: mazq@engr.wisc.edu [Department of Electrical and Computer Engineering, University of Wisconsin–Madison, Madison, Wisconsin 53706 (United States); Zhou, Weidong [Department of Electrical Engineering, University of Texas at Arlington, Arlington, Texas 76019 (United States); Gong, Shaoqin [Department of Biomedical Engineering and Wisconsin Institute for Discovery, University of Wisconsin–Madison, Madison, Wisconsin 53706 (United States)

    2015-05-25

    A method of creating tunable and programmable biaxial compressive strain in silicon nanomembranes (Si NMs) transferred onto a Kapton{sup ®} HN polyimide film has been demonstrated. The programmable biaxial compressive strain (up to 0.54%) was generated utilizing a unique thermal property exhibited by the Kapton HN film, namely, it shrinks from its original size when exposed to elevated temperatures. The correlation between the strain and the annealing temperature was carefully investigated using Raman spectroscopy and high resolution X-ray diffraction. It was found that various amounts of compressive strains can be obtained by controlling the thermal annealing temperatures. In addition, a numerical model was used to evaluate the strain distribution in the Si NM. This technique provides a viable approach to forming in-plane compressive strain in NMs and offers a practical platform for further studies in strain engineering.

  9. Mechanical properties of stanene under uniaxial and biaxial loading: A molecular dynamics study

    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

  10. Biaxially aligned buffer layers of cerium oxide, yttria stabilized zirconia, and their bilayers

    Biaxially aligned cerium oxide (CeO2) and yttria stabilized zirconia (YSZ) films were deposited on Ni-based metal (Hastelloy C276) substrates held at room temperature using ion beam assisted (IBAD) magnetron deposition with the ion beam directed at 55 degree to the normal of the film plane. In addition, we achieved, room-temperature epitaxial growth of CeO2 by bias sputtering to form biaxially aligned CeO2/YSZ bilayers. The crystalline structure and in-plane orientation of films was investigated by x-ray diffraction techniques. Both the IBAD CeO2 and YSZ films, and the CeO2/YSZ bilayers have a (111) pole in the ion beam direction. copyright 1997 American Institute of Physics

  11. Biaxially aligned buffer layers of cerium oxide, yttria stabilized zirconia, and their bilayers

    Gnanarajan, S.; Katsaros, A.; Savvides, N.

    1997-05-01

    Biaxially aligned cerium oxide (CeO2) and yttria stabilized zirconia (YSZ) films were deposited on Ni-based metal (Hastelloy C276) substrates held at room temperature using ion beam assisted (IBAD) magnetron deposition with the ion beam directed at 55° to the normal of the film plane. In addition, we achieved, room-temperature epitaxial growth of CeO2 by bias sputtering to form biaxially aligned CeO2/YSZ bilayers. The crystalline structure and in-plane orientation of films was investigated by x-ray diffraction techniques. Both the IBAD CeO2 and YSZ films, and the CeO2/YSZ bilayers have a (111) pole in the ion beam direction.

  12. Chaos synchronization in bi-axial magnets modeled by Bloch equation

    In this paper, we show that the bi-axial magnetic material modelled by Bloch equation admits chaotic solutions for a certain set of numerical values assigned to the system of parameters and initial conditions. Using the unidirectional linear and nonlinear feedback schemes, we demonstrate that two such systems can be synchronized together. The chaotic synchronization is discussed in the context of complete synchronization which means that the difference of the states of two relevant systems converge to zero. (author)

  13. Non-proportional tension-shear experiments in a biaxial test facility

    Riel, van, A.C.M.J.; Boogaard, van den, F.E.; Huetink, J.

    2006-01-01

    This paper discusses the results obtained from experiments on DC06 mild steel with a biaxial test facility. The two presented tests are non-proportional tests consisting of a two stage strain path. First the samples are deformed in the tensile direction after which simple shear deformation is applied. In the one case elastic unloading is applied after the tensile deformation, while in the other case the tensile deformation is directly followed by the simple shear deformation. For the test wit...

  14. Novel biaxial tensile test for studying aortic failure phenomena at a microscopic level

    Sugita Shukei

    2013-01-01

    Full Text Available Abstract Background An aortic aneurysm is a local dilation of the aorta, which tends to expand and often results in a fatal rupture. Although larger aneurysms have a greater risk of rupture, some small aneurysms also rupture. Since the mechanism of aortic rupture is not well understood, clarification of the microstructure influencing the failure to rupture is important. Since aortic tissues are stretched biaxially in vivo, we developed a technique to microscopically observe the failure of an aortic rupture during biaxial stretch. Methods A thinly sliced porcine thoracic aortic specimen was adhered to a circular frame and pushed onto a cylinder with a smaller diameter to stretch the specimen biaxially. To induce failure to rupture at the center, the specimen was thinned at the center of the hole as follows: the specimen was frozen while being compressed with metal plates having holes, which were 3 mm in diameter at their centers; the specimen was then sliced at 50-μm intervals and thawed. Results The ratio of the thickness at the center to the peripheral area was 99.5% for uncompressed specimens. The ratio decreased with an increase in the compression ratio εc and was 47.3% for specimens with εc = 40%. All specimens could be stretched until failure to rupture. The probability for crack initiation within the cylinder was εc εc >30%, respectively. Among specimens ruptured within the cylinder, 93% of those obtained from the mid-media showed crack initiation at the thin center area. Conclusions Aortic tissues were successfully stretched biaxially until failure, and their crack initiation points were successfully observed under a microscope. This could be a very useful and powerful method for clarifying the mechanism of aortic rupture. We are planning to use this technique for a detailed investigation of events occurring at the point of failure when the crack initiates in the aortic aneurysm wall.

  15. Characterization of biaxial mechanical behavior of porcine aorta under gradual elastin degradation

    Zeinali-Davarani, Shahrokh; Chow, Ming-Jay; Turcotte, Raphaël; Zhang, Yanhang

    2013-01-01

    Arteries are composed of multiple constituents that endow the wall with proper structure and function. Many vascular diseases are associated with prominent mechanical and biological alterations in the wall constituents. In this study, planar biaxial tensile test data of elastase-treated porcine aortic tissue (Chow et al. 2012) is re-examined to characterize the altered mechanical behavior at multiple stages of digestion through constitutive modeling. Exponential-based as well as recruitment-b...

  16. Calculation of tunnel splitting in a biaxial spin particle with an applied magnetic field

    Shen, SQ; Zhou, B.; Liang, JQ

    2004-01-01

    The level splitting formulae of excited states as well as ground state for a biaxial spin particle in the presence of an applied magnetic field are obtained in a simple way from Schrödinger theory. Considering the boundary condition of the wave function, we obtain the tunneling splitting of the energy levels for half-integral spins as well as for the integral spins. The results obtained are compared with those previously derived by complicated pseudoparticle methods and numerical calculation ...

  17. Fracture Propagation Characteristic and Micromechanism of Rock-Like Specimens under Uniaxial and Biaxial Compression

    Xue-wei Liu; Quan-sheng Liu; Shi-bing Huang; Lai Wei; Guang-feng Lei

    2016-01-01

    This paper presents a set of uniaxial and biaxial compression tests on the rock-like material specimens with different fracture geometries through a rock mechanics servo-controlled testing system (RMT-150C). On the basis of experimental results, the characteristics of fracture propagation under different fracture geometries and loading conditions are firstly obtained. The newly formed fractures are observed propagating from or near the preexisting crack tips for different specimens, while the...

  18. Effect of biaxial versus coaxial microincision cataract surgery on optical quality of the cornea

    Tamer Fahmy Eliwa

    2015-01-01

    Full Text Available Context: Visual function is determined by a combination of the cornea, which has a larger effect and internal aberrations generated by the intraocular lens and those induced by the surgery. These corneal refractive changes are related to the location and size of the corneal incision. The smaller the incision, the lower the aberrations and the better the optical quality. Aims: To compare the effect of uneventful coaxial versus biaxial microincision cataract surgery (MICS on the corneal aberrations. Settings and Design: Retrospective interventional nonrandomized comparative case study comprised 40 eyes of 36 patients with primary senile cataract. Subjects and Methods: They were divided into two groups: Group I (20 eyes had operated by biaxial MICS and Group II (20 eyes had operated by coaxial MICS. Each group were assessed by corneal topography and wavefront analysis over 6 mm pupil size preoperatively and 1-month postoperatively. Statistical Analysis Used: Statistical analysis was performed using SPSS for Windows (version 17.0.1, SPSS, Inc.. The paired t-test was used to compare the mean values of corneal aberrations preoperatively and 1-month postoperatively in each group. Results: There was a significant increase in trefoil and quatrefoil in biaxial MICS (P = 0.063, 0.032 respectively while other aberrations insignificantly changed. The coaxial MICS showed a significant increase in root mean square (RMS of total high order aberrations (HOAs (P = 0.02 and coma (0.028, but not the others. In comparison to each other, there was the insignificant difference as regards astigmatism, RMS of individual and total HOAs. Conclusions: Coaxial and biaxial MICS are neutral on corneal astigmatism and aberrations.

  19. Effect of Corneal Incision Enlargement on Surgically Induced Astigmatism in Biaxial Microincision Cataract Surgery

    Mehmet Tetikoğlu

    2016-06-01

    Full Text Available Objectives: To evaluate surgically induced astigmatism (SIA in biaxial microincision cataract surgery with enlargement of one corneal incision during intraocular lens implantation (IOL. Materials and Methods: Data from 683 eyes with cataract that underwent biaxial microincision cataract surgery and IOL were retrospectively analyzed. The operated eyes were divided into 4 groups defined by final corneal incision length after IOL implantation. There were 83 eyes with 1.6 mm corneal incisions (group 1 and 200 eyes in each of the 2, 2.4, and 2.8 mm corneal incision groups (groups 2, 3 and 4, respectively. SIA was assessed using preoperative and postoperative keratometric values at one month. Results: The mean magnitude of SIA was 0.83±0.4 D in group 1, 0.93±0.5 D in group 2, 1.03±0.6 D in group 3 and 1.04±0.7 D in group 4. The SIA showed statistically significant differences between the four groups (p=0.05. Pairwise group comparisons revealed significant differences between groups 1 and 3 and groups 1 and 4 (p=0.005. Conclusion: Biaxial microincision cataract surgery with an incision size of 1.6 mm resulted in the least SIA. Enlargement of the corneal incision beyond 2.0 mm during IOL implantation led to significant increases in SIA. We believe that with the development and dissemination of IOLs which can be inserted through small corneal incisions, biaxial microincision cataract surgery will be the best choice to prevent SIA and increase visual acuity

  20. Electrodeposition of biaxially textured nickel substrates for coated conductor by magnetic texturing

    An innovative method to fabricate biaxially textured nickel substrates applicable to coated conductor is developed. This method used the industrially scalable electrodeposition method combined with external magnetic field. The biaxially textured Ni layer was formed by electrodeposition process under external magnetic field. The electrodeposited Ni substrate has been characterized by means of X-ray diffraction and shows well-developed biaxial texture (Δθ∼7.29 deg., Δphi∼8.14 deg. ). A CeO2 buffer layer was epitaxially grown on the electrodeposited Ni substrates subsequently by thermal evaporation. In addition, a continuous processing of long tape was tried to test the compatibility of electrodeposition with further scale-up. The grown 20 cm-long Ni tape shows good crystallinity but non-uniform texture. Pinhole-free and smooth surface was obtained by additives and electropolishing. The magnetic texturing in the electrodeposition process offers a simple and economical way to quasi-single-crystalline metal substrates suitable for coated conductor

  1. Fabrication and reliable implementation of an ionic polymer-metal composite (IPMC) biaxial bending actuator

    Lee, Gil-Yong; Choi, Jung-Oh; Kim, Myeungseon; Ahn, Sung-Hoon

    2011-10-01

    Ionic polymer-metal composites (IPMCs) are one of the most popular types of electro-active polymer actuator, due to their low electric driving potential, large deformation range, and light weight. IPMCs have been used as actuators or sensors in many areas of biomedical and robotic engineering. In this research, IPMCs were studied as a biaxial bending actuator capable of smart and flexible motion. We designed and fabricated this bending actuator and implemented it to have a reliable actuating motion using a systematic approach. The resulting device was bar shaped with a square cross section and had four insulated electrodes on its surface. By applying different voltages to these four electrodes, a biaxial bending motion can be induced. To construct this actuator, several fabrication processes were considered. We modified the Nafion stacking method, and established a complete sequence of actuator fabrication processes. Using these processes, we were able to fabricate an IPMC biaxial bending actuator with both high actuating force and high flexibility. Several experiments were conducted to investigate and verify the performance of the actuator. The IPMC actuator system was modeled from experimentally measured data, and using this actuator model, a closed-loop proportional integral (PI) controller was designed. Reference position tracking performances of open-loop and closed-loop systems were compared. Finally, circular motion tracking performances of the actuator tip were tested under different rotation frequencies and radii of a reference trajectory circle.

  2. Biaxial Texture Evolution in MgO Films Fabricated Using Ion Beam-Assisted Deposition

    Xue, Yan; Zhang, Ya-Hui; Zhao, Rui-Peng; Zhang, Fei; Lu, Yu-Ming; Cai, Chuan-Bing; Xiong, Jie; Tao, Bo-Wan

    2016-04-01

    The growth of multifunctional thin films on flexible substrates is important technologically, because flexible electronics require such a platform. In this study, we examined the evolution of biaxial texture in MgO films prepared using ion beam-assisted deposition (IBAD) on a Hastelloy substrate. Texture and microstructure developments were characterized through in situ reflection high-energy electron diffraction monitoring, x-ray diffraction, and atomic force microscopy, which demonstrated that biaxial texture was developed during the nucleation stage (~2.2 nm). The best biaxial texture was obtained with a thickness of approximately 12 nm. As MgO continued to grow, the influence of surface energy was reduced, and film growth was driven by the attempt to minimize volume free-energy density. Thus the MgO grains were subsequently rotated at the (002) direction toward the ion beam. In addition, an approach was developed for accelerating in-plane texture evolution by pre-depositing an amorphous MgO layer before IBAD.

  3. Loading system mechanism for dielectric elastomer generators with equi-biaxial state of deformation

    Fontana, M.; Moretti, G.; Lenzo, B.; Vertechy, R.

    2014-03-01

    Dielectric Elastomer Generators (DEGs) are devices that employ a cyclically variable membrane capacitor to produce electricity from oscillating sources of mechanical energy. Capacitance variation is obtained thanks to the use of dielectric and conductive layers that can undergo different states of deformation including: uniform or non-uniform and uni- or multi-axial stretching. Among them, uniform equi-biaxial stretching is reputed as being the most effective state of deformation that maximizes the amount of energy that can be extracted in a cycle by a unit volume of Dielectric Elastomer (DE) material. This paper presents a DEG concept, with linear input motion and tunable impedance, that is based on a mechanical loading system for inducing uniform equi-biaxial states of deformation. The presented system employs two circular DE membrane capacitors that are arranged in an agonist-antagonist configuration. An analytical model of the overall system is developed and used to find the optimal design parameters that make it possible to tune the elastic response of the generator over the range of motion of interest. An apparatus is developed for the equi-biaxial testing of DE membranes and used for the experimental verification of the employed numerical models.

  4. Strain uniformity in biaxial specimens is highly sensitive to attachment details.

    Eilaghi, Armin; Flanagan, John G; Brodland, G Wayne; Ethier, C Ross

    2009-09-01

    Biaxial testing has been used widely to characterize the mechanical properties of soft tissues and other flexible materials, but fundamental issues related to specimen design and attachment have remained. Finite element models and experiments were used to investigate how specimen geometry and attachment details affect uniformity of the strain field inside the attachment points. The computational studies confirm that increasing the number of attachment points increases the size of the area that experiences sensibly uniform strain (defined here as the central sample region where the ratio of principal strains E(11)/E(22)talc-sprinkled rubber specimens loaded using wire "rakes." Points on a grid having 12 x 12 bays were tracked, and a detailed strain map was constructed. A finite element model based on the actual geometry of an experiment having an off-pattern rake tine gave strain patterns that matched to within 4.4%. Finally, simulations using nonequibiaxial strains indicated that the strain field uniformity was more sensitive to sample attachment details for the nonequibiaxial case as compared to the equibiaxial case. Specimen design and attachment were found to significantly affect the uniformity of the strain field produced in biaxial tests. Practical guidelines were offered for design and mounting of biaxial test specimens. The issues addressed here are particularly relevant as specimens become smaller in size. PMID:19725692

  5. Flexural strength of dental composite restoratives: comparison of biaxial and three-point bending test.

    Chung, S M; Yap, A U J; Chandra, S P; Lim, C T

    2004-11-15

    This study compared two test methods used to evaluate the flexural strength of resin-based dental composites. The two test methods evaluated were the three-point bending test4 and the biaxial flexural test. Materials used in this investigation were from the same manufacturer (3M ESPE) and included microfill (A110), minifill (Z100 and Filtek Z250), polyacid modified (F2000), and flowable [Filtek Flowable (FF)] composites. Flexural strength was determined with the use of both test methods after 1 week of conditioning in water at 37 degrees C. Data were analyzed with the use of an ANOVA/Scheffe test and an independent-samples t test at significance level 0.05. Mean flexural strength (n = 7) ranged from 66.61 to 147.21 and 67.27 to 182.81 MPa for three-point bending and ball-on-three-ball biaxial test methods, respectively. In both test methods, Z100 was significantly stronger than all other composites evaluated. In the three-point bending test, flexural strength of Z250 was significantly higher than A110, F2000 and FF, and FF was significantly stronger than A110 and F2000. The biaxial test method arrived at the same conclusions except that there was no significant difference between Z250 and FF. Pearson's correlation revealed a significantly (p bending test. PMID:15386492

  6. 3D shape identification of parallelepiped flaw by means of biaxial MFLT using neural network

    In this paper, we attempt to evaluate the three-dimensional shape of a parallelepiped flaw and identify its location, i.e. the horizontal position and the located surface, by means of biaxial Magnetic Flux Leakage Testing (MFLT), employing a Neural Network (NN). The specimen is a magnetic material (SS400) subjected to a magnetic field, and the magnetic flux in the specimen leaks near the flaw. We measure the biaxial Magnetic Flux Leakage (MFL), i.e, the tangential and the normal components of the MFL, along a line parallel to the specimen's surface. We then approximate the measured biaxial MFL distributions by means of elementary functions with a small number of coefficients. The approximation coefficients are extracted as Characteristic Quantities (CQs) of the MFL distribution. The horizontal position of the flaw along the measurement line is characterized by some of these CQs. NN is used to infer the cross section of the flaw, i.e, the width, depth, and located surface of the CQs. By repeating a similar process along several measurement lines parallel to the specimen's surface, we can identify the three-dimensional shape of the flaw, including its location. The NN, trained with several known flaws, was found to be able to evaluate the three-dimensional shape and location of a parallelepiped flaw with a high level of accuracy. (author)

  7. Fabrication and reliable implementation of an ionic polymer–metal composite (IPMC) biaxial bending actuator

    Ionic polymer–metal composites (IPMCs) are one of the most popular types of electro-active polymer actuator, due to their low electric driving potential, large deformation range, and light weight. IPMCs have been used as actuators or sensors in many areas of biomedical and robotic engineering. In this research, IPMCs were studied as a biaxial bending actuator capable of smart and flexible motion. We designed and fabricated this bending actuator and implemented it to have a reliable actuating motion using a systematic approach. The resulting device was bar shaped with a square cross section and had four insulated electrodes on its surface. By applying different voltages to these four electrodes, a biaxial bending motion can be induced. To construct this actuator, several fabrication processes were considered. We modified the Nafion stacking method, and established a complete sequence of actuator fabrication processes. Using these processes, we were able to fabricate an IPMC biaxial bending actuator with both high actuating force and high flexibility. Several experiments were conducted to investigate and verify the performance of the actuator. The IPMC actuator system was modeled from experimentally measured data, and using this actuator model, a closed-loop proportional integral (PI) controller was designed. Reference position tracking performances of open-loop and closed-loop systems were compared. Finally, circular motion tracking performances of the actuator tip were tested under different rotation frequencies and radii of a reference trajectory circle

  8. Characterization of Three-Dimensional Magnetic Alignment for Magnetically Biaxial Particles

    Yamaguchi, Masuhiro; Ozawa, Shun; Yamamoto, Isao; Kimura, Tsunehisa

    2013-01-01

    The three-dimensional magnetic alignment (3DMA) is analytically investigated for magnetically biaxial particles with the susceptibility χ1>χ2>χ3 in an amplitude-modulated (AM) elliptic field B= i1Bb1cos ωt + i2Bb2sin ωt as a prototype method for 3DMA. The distribution function and the biaxial ordering matrix are numerically calculated by the Boltzmann distribution and the rotational diffusion equation. The 3DMA attains the optimum performance in the rapid rotation regime (RRR) with the infinity rotation frequency ω while the RRR is effectively available at lower rotation frequencies. The intermediate magnetization axis χ2 is inferior to the easy and hard magnetization axes χ1 and χ3 in the time development and the equilibrium state of alignment. In all the methods for 3DMA, the dynamic and equilibrium behavior in the RRR are universally characterized by the reduced energy α= V(Bb1)2(χ3 - χ1)/(2µ0kBT), the biaxial deviation of susceptibility k = (χ2-χ1)/(χ3-χ1), the field modulation factor q = (b2/b1)2, and the reduced time tr = | α| Dt where D is the rotational diffusion constant.

  9. Biaxial Texture Evolution in MgO Films Fabricated Using Ion Beam-Assisted Deposition

    Xue, Yan; Zhang, Ya-Hui; Zhao, Rui-Peng; Zhang, Fei; Lu, Yu-Ming; Cai, Chuan-Bing; Xiong, Jie; Tao, Bo-Wan

    2016-07-01

    The growth of multifunctional thin films on flexible substrates is important technologically, because flexible electronics require such a platform. In this study, we examined the evolution of biaxial texture in MgO films prepared using ion beam-assisted deposition (IBAD) on a Hastelloy substrate. Texture and microstructure developments were characterized through in situ reflection high-energy electron diffraction monitoring, x-ray diffraction, and atomic force microscopy, which demonstrated that biaxial texture was developed during the nucleation stage (~2.2 nm). The best biaxial texture was obtained with a thickness of approximately 12 nm. As MgO continued to grow, the influence of surface energy was reduced, and film growth was driven by the attempt to minimize volume free-energy density. Thus the MgO grains were subsequently rotated at the (002) direction toward the ion beam. In addition, an approach was developed for accelerating in-plane texture evolution by pre-depositing an amorphous MgO layer before IBAD.

  10. Biaxially aligned YSZ and CeO2 buffer layers on hastelloy prepared by magnetron IBAD

    Full text: The development of high-current, flexible superconducting YBCO tapes is based on a metal substrates overcoated with a biaxially aligned oxide buffer layer to serve as a template for the epitaxial growth of c-axis oriented Yba2Cu3O7 thin films. A secondary function of the buffer is to act as a diffusion barrier to metal species to prevent them from poisoning the superconducting film. Widely studied oxide buffer layers include yttria-stabilised zirconia (YSZ) and cerium oxide (CeO2) produced by ion-beam-assisted deposition (IBAD). We have combined IBAD with magnetron sputtering to deposit biaxially aligned YSZ and CeO2 on Hastelloy C276 substrates held at room temperature. The ion beam is directed at 55deg to the normal of the film plane. In addition, we achieved room temperature epitaxial growth of CeO2 films on IBAD YSZ films by bias sputtering to form biaxially aligned CeO2/YSZ bilayers. The crystalline quality and inplane orientation of the films (200 nm thick) were investigated by x-ray diffraction techniques including ω and φ scans and pole figures. The IBAD YSZ and CeO2 films have a (111) pole in the ion beam direction with a full width at half maximum, FWHM = 24 - 30 deg; the CeO2/YSZ bilayer is similarly aligned with FWHM = 32 deg

  11. Biaxially aligned template films fabricated by inclined-substrate deposition for YBCO-coated conductor applications.

    Ma, B.; Li, M.; Koritala, R. E.; Fisher, B. L.; Erck, R. A.; Dorris, S. E.; Miller, D. J.; Balachandran, U.

    2002-08-12

    Inclined substrate deposition (ISD) has the potential for rapid production of high-quality biaxially textured buffer layers, which are important for YBCO-coated conductor applications. We have grown biaxially textured MgO films by ISD at deposition rates of 20-100 {angstrom}/sec. Columnar grains with a roof-tile surface structure were observed in the ISD-MgO films. X-ray pole figure analysis revealed that the (002) planes of the ISD-MgO films are tilted at an angle from the substrate normal. A small {phi}-scan full-width at half maximum (FWHM) of {approx}9{sup o} was observed on MgO films deposited at an inclination angle of 55{sup o}. In-plane texture in the ISD MgO films developed in the first 0.5 {micro}m from the interface, then stabilized with further increases in film thickness. YBCO films deposited by pulsed laser deposition on ISD-MgO buffered Hastelloy C276 substrates were biaxially aligned with the c-axis parallel to the substrate normal. T{sub c} of 91 K with a sharp transition and transport J{sub c} of 5.5 x 10{sup 5} A/cm{sup 2} at 77 K in self-field were measured on a YBCO film that was 0.46-{micro}m thick, 4-mm wide, 10-mm long.

  12. Instability of a Biaxial Nematic Liquid Crystal Formed by Homeotropic Anchoring on Surface Grooves

    ZHANG Zhi-Dong; XUAN Li

    2011-01-01

    A method used to treat the elastic distortion of a uniaxial nematic liquid crystal induced by homogeneous anchoring on the surface grooves is generalized to biaxial nematic liquid crystals under the homeotropic anchoring condition.Employing some approximations for the elastic constants,we obtain an additional term in the elastic energy per unit area which depends on the angle between the minor director at infinity and the direction of the grooves,with a period of π/2.This leads to instability on the surface grooves so that two states with crossed minor directors are energetically indistinguishable.Our theoretical study explains why the homeotropic alignment method developed for uniaxial liquid crystals loses efficacy for biaxial nematics.In most liquid crystal devices,the liquid crystals are sandwiched between two substrates coated with alignment layers.In the absence of externally applied fields,the orientation of the liquid crystal in the cell is determined by the anchoring condition of the alignment layer.[1-3] One usually distinguishes three main types of liquid crystalline director alignment near solid walls:homeotropic,homogeneous (or planar) and tilted orientations.Here we study the first of these and consider the biaxial nematic phase,which was observed in lyotropic systems as early as 1980[4] and has been confirmed by deuterium NMR spectroscopy.%A method used to treat the elastic distortion of a uniaxial nematic liquid crystal induced by homogeneous anchoring on the surface grooves is generalized to biaxial nematic liquid crystals under the homeotropic anchoring condition. Employing some approximations for the elastic constants, we obtain an additional term in the elastic energy per unit area which depends on the angle between the minor director at infinity and the direction of the grooves, with a period of π/2. This leads to instability on the surface grooves so that two states with crossed minor directors are energetically indistinguishable. Our

  13. In situ biaxial texture analysis of MGO films during growth on amorphous substrates by ion beam-assisted deposition

    Brewer, R. T. (Rhett T.); Arendt, P. N. (Paul N.); Atwater, H. A. (Harry A.); Groves, J. R. (James R.)

    2001-01-01

    We used a previously reported kinematical electron scattering model to develop a RHEED based method for performing quantitative analysis of mosaic polycrystalline thin film in-plane and out-of-plain grain orientation distributions. RHEED based biaxial texture measurements are compared to X-Ray and transmission electron microscopy measurements to establish the validity of the RHEED analysis method. In situ RHEED analysis reveals that the out of plane orientation distribution starts out very broad, and then decreases during IBAD MgO growth. Other results included evidence that the in-plane orientation distribution narrows, the grain size increases, and the film roughens as film thickness increases during IBAD MgO growth. Homoepitaxy of MgO improves the biaxial texture of the IBAD layer, making X-ray measurements of IBAD films with an additional homoepitaxial layer not quantitatively representative of the IBAD layer. Systematic offsets between RHEED analysis and X-ray measurements of biaxial texture, coupled with evidence that biaxial texture improves with increasing film thickness, indicate that RHEED is a superior technique for probing surface biaxial texture.

  14. Study of the effect of an equi-biaxial loading on the fatigue lifetime of austenitic stainless steel

    Fatigue lifetime assessment is essential in the design of structures. Under-estimated predictions may result in unnecessary in service inspections. Conversely, over-estimated predictions may have serious consequences on the integrity of structures.In some nuclear power plant components, the fatigue loading may be equi-biaxial because of thermal fatigue. So the potential impact of multiaxial loading on the fatigue life of components is a major concern. Meanwhile, few experimental data are available on austenitic stainless steels. It is essential to improve the fatigue assessment methodologies to take into account the potential equi-biaxial fatigue damage. Hence this requires obtaining experimental data on the considered material with a strain tensor in equi-biaxial tension. The aim of this study is to present the experimental and numerical results obtained with a device 'FABIME2' developed in the LISN in collaboration with EDF and AREVA. The association of the experimental results, obtained on the new experimental fatigue device FABIME2, with the numerical analyses obtained by FEM simulation with Cast3M code, has enabled to define the aggravating effect of the equi-biaxial fatigue loading. However, this effect is covered by the Design fatigue curve defined from the nuclear industry. For the crack propagation, a first simplified approach enables to study the kinetic behavior of crack propagation in equi-biaxial fatigue. (author)

  15. Stress variations and relief in patterned GaAs grown on mismatched substrates

    Cathodoluminescence scanning electron microscopy studies reveal significant variations in stress across etched patterns of GaAs grown on both InP and Si substrates. The stress in the epilayer is relieved at convex corners and in patterned areas with dimensions on the order of 10 μm. The stress is uniaxial near the edge of a patterned region and changes to biaxial away from the edge, producing nonuniformities in the optical properties of patterned regions

  16. Ductile Tearing of Thin Aluminum Plates Under Blast Loading. Predictions with Fully Coupled Models and Biaxial Material Response Characterization

    Corona, Edmundo [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Gullerud, Arne S. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Haulenbeek, Kimberly K. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Reu, Phillip L. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

    2015-06-01

    The work presented in this report concerns the response and failure of thin 2024- T3 aluminum alloy circular plates to a blast load produced by the detonation of a nearby spherical charge. The plates were fully clamped around the circumference and the explosive charge was located centrally with respect to the plate. The principal objective was to conduct a numerical model validation study by comparing the results of predictions to experimental measurements of plate deformation and failure for charges with masses in the vicinity of the threshold between no tearing and tearing of the plates. Stereo digital image correlation data was acquired for all tests to measure the deflection and strains in the plates. The size of the virtual strain gage in the measurements, however, was relatively large, so the strain measurements have to be interpreted accordingly as lower bounds of the actual strains in the plate and of the severity of the strain gradients. A fully coupled interaction model between the blast and the deflection of the structure was considered. The results of the validation exercise indicated that the model predicted the deflection of the plates reasonably accurately as well as the distribution of strain on the plate. The estimation of the threshold charge based on a critical value of equivalent plastic strain measured in a bulge test, however, was not accurate. This in spite of efforts to determine the failure strain of the aluminum sheet under biaxial stress conditions. Further work is needed to be able to predict plate tearing with some degree of confidence. Given the current technology, at least one test under the actual blast conditions where the plate tears is needed to calibrate the value of equivalent plastic strain when failure occurs in the numerical model. Once that has been determined, the question of the explosive mass value at the threshold could be addressed with more confidence.

  17. Life estimation of low-cycle fatigue of pipe elbows. Proposed criteria of low-cycle fatigue life under the multi-axial stress field

    Pipe elbows were important parts frequently used in the pipelines of nuclear power, thermal power and chemical plants, and their integrity needed to be assured under seismic loads and thermal stresses considering local wall thinning or complex stress distribution due to special configuration different from straight pipe. This article investigated in details elastic-plastic stress-strain state of pipe elbow using finite element analysis and clarified there existed high bi-axial stress field at side inner surface of pipe elbow axial cracks initiated. Bi-axial stress factor was around 0.6 for sound elbow and up to 0.95 for local wall thinning at crown. Fracture strain of 1.15 was reduced to around 0.15 for bi-axial stress factor from 0.6 to 0.9. Normalized fatigue life for bi-axial stress field (0.6 - 0.8) was largely reduced to around 15, 19 and 10% of fatigue life of uni-axial state dependent on material strength level. Proposed revised universal slopes taking account of multi-axial stress factor could explain qualitatively effects of strain range, internal pressure and ratchet strain (pre-strain) on low-cycle fatigue life of pipe elbow. (T. Tanaka)

  18. Biaxial creep deformation of Zircaloy-4 in the high alpha phase temperature range

    The ballooning response of Zircaloy-4 fuel tubes during a postulated loss-of-coolant accident may be calculated from a knowledge of the thermal environment of the rods and the creep deformation characteristics of the cladding. In support of such calculations biaxial creep studies have been performed on fuel tubes supplied by Westinghouse, Wolverine and Sandvik of temperatures in the alpha phase range. This paper presents the results of an investigation of their respective creep behaviour which has resulted in the formulation of equations for use in LOCA fuel ballooning codes. (author)

  19. Control of biaxial strain in single-layer Molybdenite using local thermal expansion of the substrate

    Plechinger, G.; Castellanos-Gomez, A.; Buscema, M.; van der Zant, H. S. J.; Steele, G. A.; Kuc, A.; Heine, T.; Schüller, C; Korn, T.

    2015-01-01

    Single-layer MoS2 is a direct-gap semiconductor whose electronic band structure strongly depends on the strain applied to its crystal lattice. While uniaxial strain can be easily applied in a controlled way, e.g., by bending of a flexible substrate with the atomically thin MoS2 layer on top, experimental realization of biaxial strain is more challenging. Here, we exploit the large mismatch between the thermal expansion coefficients of MoS2 and a silicone-based substrate to apply a controllabl...

  20. Biaxially stretchable supercapacitors based on the buckled hybrid fiber electrode array

    Zhang, Nan; Zhou, Weiya; Zhang, Qiang; Luan, Pingshan; Cai, Le; Yang, Feng; Zhang, Xiao; Fan, Qingxia; Zhou, Wenbin; Xiao, Zhuojian; Gu, Xiaogang; Chen, Huiliang; Li, Kewei; Xiao, Shiqi; Wang, Yanchun; Liu, Huaping; Xie, Sishen

    2015-07-01

    In order to meet the growing need for smart bionic devices and epidermal electronic systems, biaxial stretchability is essential for energy storage units. Based on porous single-walled carbon nanotube/poly(3,4-ethylenedioxythiophene) (SWCNT/PEDOT) hybrid fiber, we designed and fabricated a biaxially stretchable supercapacitor, which possesses a unique configuration of the parallel buckled hybrid fiber array. Owing to the reticulate SWCNT film and the improved fabrication technique, the hybrid fiber retained its porous architecture both outwardly and inwardly, manifesting a superior capacity of 215 F g-1. H3PO4-polyvinyl alcohol gel with an optimized component ratio was introduced as both binder and stretchable electrolyte, which contributed to the regularity and stability of the buckled fiber array. The buckled structure and the quasi one-dimensional character of the fibers endow the supercapacitor with 100% stretchability along all directions. In addition, the supercapacitor exhibited good transparency, as well as excellent electrochemical properties and stability after being stretched 5000 times.In order to meet the growing need for smart bionic devices and epidermal electronic systems, biaxial stretchability is essential for energy storage units. Based on porous single-walled carbon nanotube/poly(3,4-ethylenedioxythiophene) (SWCNT/PEDOT) hybrid fiber, we designed and fabricated a biaxially stretchable supercapacitor, which possesses a unique configuration of the parallel buckled hybrid fiber array. Owing to the reticulate SWCNT film and the improved fabrication technique, the hybrid fiber retained its porous architecture both outwardly and inwardly, manifesting a superior capacity of 215 F g-1. H3PO4-polyvinyl alcohol gel with an optimized component ratio was introduced as both binder and stretchable electrolyte, which contributed to the regularity and stability of the buckled fiber array. The buckled structure and the quasi one-dimensional character of the

  1. Biaxial high cycle fatigue: experimental investigation and two-scale damage model

    This research thesis first describes the multi-axial fatigue phenomenon in the cases of mechanical and complex loadings, discusses multi-axial fatigue criteria, and presents the approach of fatigue by incremental damage mechanics. Then, it reports an experimental investigation of fatigue crack initiation under biaxial polycyclic fatigue in 304L austenitic stainless steel and in titanium alloy. The author presents a probabilistic two-scale damage model, and then reports the assessment of multi-axial fatigue life by means of this model

  2. SPICE compatible analytical electron mobility model for biaxial strained-Si-MOSFETs

    This paper describes an analytical model for bulk electron mobility in strained-Si layers as a function of strain. Phonon scattering, columbic scattering and surface roughness scattering are included to analyze the full mobility model. Analytical explicit calculations of all of the parameters to accurately estimate the electron mobility have been made. The results predict an increase in the electron mobility with the application of biaxial strain as also predicted from the basic theory of strain physics of metal oxide semiconductor (MOS) devices. The results have also been compared with numerically reported results and show good agreement. (semiconductor devices)

  3. Failure analyses of filament-wound graphite/epoxy cylinders under biaxial loading

    This paper discusses macroscopic and microscopic failure behavior of filament-wound (90/+/-20)/sub s/ graphite/epoxy thin-wall cylinders subjected to biaxial loading. Experimental results, elastic constants, and strengths are compared with analytical predictions. The Tsai-Wu failure criterion gave reasonable agreement between theoretical and experimental results. Specimens machined from failed cylinders were examined using scanning electron microscopy. Interply and intraply cracking were observed. These microscopic failure mechanisms are not accounted for in any failure criterion available in the literature. 6 references, 8 figures, 2 tables

  4. Biaxial nematic phases in fluids of hard board-like particles

    Martinez-Raton, Yuri; Varga, Szabolcs; Velasco, Enrique

    2011-01-01

    We use density-functional theory, of the fundamental-measure type, to study the relative stability of the biaxial nematic phase, with respect to non-uniform phases such as smectic and columnar, in fluids made of hard board-like particles with sizes $\\sigma_1>\\sigma_2>\\sigma_3$. A restricted-orientation (Zwanzig) approximation is adopted. Varying the ratio $\\kappa_1=\\sigma_1/\\sigma_2$ while keeping $\\kappa_2=\\sigma_2/\\sigma_3$, we predict phase diagrams for various values of $\\kappa_2$ which i...

  5. Application of Bi-axial Warp Knitted Structures in Concrete Constructions

    李炜; 陈南梁

    2001-01-01

    The warp knitted bi-axial directionally oriented structure (D. O. S. ) reinforcement substrates applied to building construction are discussed in comparison to woven fabrics. One of usage barriers of reinforced cement with gloss-grid is its sensitivity to alkali existed in the cement which will lead to the reduction of its service-life. The tests show that the treatment by sol-gel method to protect the composite from alkali corrosion is effective. Then two formulae of sol-gel solution are also recommended here for application.

  6. Collinear Acousto-Optical Transformation of Bessel Light Beams in Biaxial Gyrotropic Crystals

    Belyi, V. N.; Kulak, G. V.; Krokh, G. V.; Shakin, O. V.

    2016-05-01

    The collinear acousto-optical transformation of Bessel light beams in biaxial gyrotropic crystals into two annular, internal conical refraction beams with orthogonal elliptical polarization is studied. It is found that the diffraction efficiency is maximal (~50-60%) for low ultrasound intensities and varies slightly with further increases in acoustic power. At high ultrasound intensities, the intensities of the transmitted and diffracted annular beams differ insignificantly. The possible use of this acousto-optical interaction for creating collinear tuneable narrow-band acousto-optical filters at low ultrasonic frequencies is demonstrated.

  7. Stresses in sulfuric acid anodized coatings on aluminum

    Alwitt, R. S.; Xu, J.; Mcclung, R. C.

    1993-01-01

    Stresses in porous anodic alumina coatings have been measured for specimens stabilized in air at different temperatures and humidities. In ambient atmosphere the stress is tensile after anodic oxidation and is compressive after sealing. Exposure to dry atmosphere causes the stress to change to strongly tensile, up to 110 MPa. The stress increase is proportional to the loss of water from the coating. These changes are reversible with changes in humidity. Similar reversible effects occur upon moderate temperature changes. The biaxial modulus of the coating is about 100 GPa.

  8. Investigation of the Residual Stress State in an Epoxy Based Specimen

    Baran, Ismet; Jakobsen, Johnny; Andreasen, Jens Henrik;

    2015-01-01

    Abstract. Process induced residual stresses may play an important role under service loading conditions for fiber reinforced composite. They may initiate premature cracks and alter the internal stress level. Therefore, the developed numerical models have to be validated with the experimental...... observations. In the present work, the formation of the residual stresses/strains are captured from experimental measurements and numerical models. An epoxy/steel based sample configuration is considered which creates an in-plane biaxial stress state during curing of the resin. A hole drilling process with a...... material models, i.e. cure kinetics, elastic modulus, CTE, chemical shrinkage, etc. together with the drilling process using the finite element method. The measured and predicted in-plane residual strain states are compared for the epoxy/metal biaxial stress specimen....

  9. Electronic and optical properties of kesterite Cu{sub 2}ZnSnS{sub 4} under in-plane biaxial strains: First-principles calculations

    Li, Chun-Ran [State Key Laboratory of Superhard Materials and College of Physics, Jilin University, Changchun 130012 (China); College of Mathematics and Physics, Bohai University, Jinzhou 121013 (China); Li, Yong-Feng, E-mail: liyongfeng@jlu.edu.cn [State Key Laboratory of Superhard Materials and College of Physics, Jilin University, Changchun 130012 (China); Key Laboratory of Physics and Technology for Advanced Batteries (Ministry of Education), College of Physics, Jilin University, Changchun 130012 (China); Yao, Bin, E-mail: binyao@jlu.edu.cn [State Key Laboratory of Superhard Materials and College of Physics, Jilin University, Changchun 130012 (China); Key Laboratory of Physics and Technology for Advanced Batteries (Ministry of Education), College of Physics, Jilin University, Changchun 130012 (China); Yang, Gang [Key Laboratory of Physics and Technology for Advanced Batteries (Ministry of Education), College of Physics, Jilin University, Changchun 130012 (China); Ding, Zhan-Hui [State Key Laboratory of Superhard Materials and College of Physics, Jilin University, Changchun 130012 (China); Deng, Rui [School of Materials Science and Engineering, Changchun University of Science and Technology, Changchun 130022 (China); Liu, Lei [State Key Laboratory of Luminescence and Applications, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, No. 3888 Dongnanhu Road, Changchun 130033 (China)

    2013-11-08

    The electronic structures and optical properties of Cu{sub 2}ZnSnS{sub 4} (CZTS) under in-plane biaxial strain were systematically investigated using first-principles calculations based on generalized gradient approximation and hybrid functional method, respectively. It is found that the fundamental bandgap at the Γ point decreases linearly with increasing tensile biaxial strain perpendicular to c-axis. However, a bandgap maximum occurs as the compressive biaxial strain is 1.5%. Further increase of compressive strain decreases the bandgap. In addition, the optical properties of CZTS under biaxial strain are also calculated, and the variation trend of optical bandgap with biaxial strain is consistent with the fundamental bandgap.

  10. Effects of the biaxial transverse crystal-field on the phase diagrams of a spin-1 nanowire

    Magoussi, H.; Zaim, A.; Boughrara, M.; Kerouad, M.

    2016-09-01

    By using the effective field theory based on a probability distribution method, the phase diagrams and the magnetic properties of an Ising nanowire in the presence of the biaxial transverse crystal-field are investigated. The effects of the biaxial transverse crystal field, the interfacial coupling and the exchange interaction in the surface on the phase diagram, the magnetization and the internal energy are examined. Some characteristic phenomena are found such as the tricritical behavior, the critical end point and the re-entrant phenomenon.

  11. Upregulation of matrix synthesis in chondrocyte-seeded agarose following sustained bi-axial cyclic loading

    Belinda Pingguan-Murphy

    2012-08-01

    Full Text Available OBJECTIVES: The promotion of extracellular matrix synthesis by chondrocytes is a requisite part of an effective cartilage tissue engineering strategy. The aim of this in vitro study was to determine the effect of bi-axial cyclic mechanical loading on cell proliferation and the synthesis of glycosaminoglycans by chondrocytes in threedimensional cultures. METHOD: A strain comprising 10% direct compression and 1% compressive shear was applied to bovine chondrocytes seeded in an agarose gel during two 12-hour conditioning periods separated by a 12-hour resting period. RESULTS: The bi-axial-loaded chondrocytes demonstrated a significant increase in glycosaminoglycan synthesis compared with samples exposed to uni-axial or no loading over the same period (p<0.05. The use of a free-swelling recovery period prior to the loading regime resulted in additional glycosaminoglycan production and a significant increase in DNA content (p<0.05, indicating cell proliferation. CONCLUSIONS: These results demonstrate that the use of a bi-axial loading regime results in increased matrix production compared with uni-axial loading.

  12. Dynamic buckling of columns by biaxial moments and uniform end torque

    Leung, A. Y. T.

    2010-05-01

    A new concept of uniform torque is proposed for the dynamic torsional buckling analysis. A dynamic biaxial moments and torque buckling theory is presented for analysis in structural dynamics. Second-order effects of the axial force, biaxial moments and torque are considered. The consistent natural boundary moments and forces are derived to ensure the symmetry of the dynamic stiffness matrix in fulfilling the requirement of the reciprocal theorem and conservation of energy. The exact dynamic stiffness matrix is obtained using power series expansion. The derivatives of the analytical dynamic stiffness matrix with respect to different loading and geometric parameters are derived explicitly for sensitivity and continuation analyses. Generally distributed axial force can be analyzed without difficulty. It is pointed out that non-uniform sections may not be handled by power series due to the convergent problem. Global pictures for all kinds of linear dynamic buckling are given for the first time. The methodology is based on finite element formulation and therefore it can easily be extended to analyze structural frames.

  13. Electrical Transport in SrTiO3 Under Biaxial Strain

    Kajdos, Adam; Jalan, Bharat; Allen, James; Stemmer, Susanne

    2012-02-01

    Mobility engineering with strain is widely used for conventional semiconductors, but has only recently been proposed for complex oxides such as SrTiO3. The conduction band structure of SrTiO3 is complicated with multiple degenerate bands derived from the Ti 3d orbitals. Strain is thus expected to have a significant effect by lifting this degeneracy and altering the occupancy and curvature of the bands. Indeed, a 300% increase in the electron mobility with values exceeding 128,000 cm^2/Vs at 1.8 K was demonstrated in MBE-grown SrTiO3 films subjected to uniaxial compressive strain [1]. For heterostructure engineering, the effect of biaxial strain is relevant. Here, the electron mobilities in SrTiO3 subjected to biaxial strain are investigated through growth of coherent films on lattice-mismatched substrates. Lightly-doped (high-mobility) strained SrTiO3 films below the critical thickness are insulating because of significant surface depletion, which increases with decreasing temperature due to the high dielectric constant of SrTiO3. We show that highly-doped, low-mobility capping layers address this problem, but require a multilayer model to analyze the Hall data in terms of the mobility in the lightly doped layer. [1] B. Jalan et al., Appl. Phys. Lett. 98, 132102 (2011)

  14. Biaxial-Type Concentrated Solar Tracking System with a Fresnel Lens for Solar-Thermal Applications

    Tsung Chieh Cheng

    2016-04-01

    Full Text Available In this paper, an electromechanical, biaxial-type concentrated solar tracking system was designed for solar-thermal applications. In our tracking system, the sunlight was concentrated by the microstructure of Fresnel lens to the heating head of the Stirling engine and two solar cells were installed to provide the power for tracking system operation. In order to obtain the maximum sun power, the tracking system traces the sun with the altitude-azimuth biaxial tracing method and accurately maintains the sun’s radiation perpendicular to the plane of the heating head. The results indicated that the position of heating head is an important factor for power collection. If the sunlight can be concentrated to completely cover the heating head with small heat loss, we can obtain the maximum temperature of the heating head of the Stirling engine. Therefore, the temperature of heating head can be higher than 1000 °C in our experiment on a sunny day. Moreover, the results also revealed that the temperature decrease of the heating head is less than the power decrease of solar irradiation because of the latent heat of copper and the small heat loss from the heating head.

  15. Can singly charged oxygen vacancies induce ferromagnetism in biaxial strained ZnO?

    Gai, Yanqin; Jiang, Jiaping; Wu, Yuxi; Tang, Gang

    2016-04-01

    The electronic and magnetic properties of the singly charged oxygen vacancy ({{V}{{O}}}+) in undoped ZnO under biaxial strains are investigated by density functional theory calculations. A net magnetic moment (MM) of 0.561 μB is obtained for {{V}{{O}}}+ in ZnO under no strains, but the magnetic interaction between them is antiferromagnetic. The formation energy of V O and {{V}{{O}}}+, the MM induced by {{V}{{O}}}+, as well as the coupling type and strength between {{V}{{O}}}+{{s}} vary with the application of biaxial strains. Compressive strains can enhance the concentrations of V O and {{V}{{O}}}+, enlarge the MM, and strengthen the antiferromagnetic interactions between them at lower V O concentrations. However, at higher V O concentrations, the coupling varies from sizable antiferromagnetic to negligible weak ferromagnetic, and then becomes paramagnetic with the increase of compression. Antiferromagnetic results are further confirmed by the local density approximation with Hubbard U (LDA + U) calculations.

  16. Fracture Propagation Characteristic and Micromechanism of Rock-Like Specimens under Uniaxial and Biaxial Compression

    Xue-wei Liu

    2016-01-01

    Full Text Available This paper presents a set of uniaxial and biaxial compression tests on the rock-like material specimens with different fracture geometries through a rock mechanics servo-controlled testing system (RMT-150C. On the basis of experimental results, the characteristics of fracture propagation under different fracture geometries and loading conditions are firstly obtained. The newly formed fractures are observed propagating from or near the preexisting crack tips for different specimens, while the propagation paths are affected by the loading condition obviously. Then, by adopting acoustic emission (AE location technique, AE event localization characteristics in the process of loading are investigated. The locations of AE events are in good agreement with the macroscopic fracture propagation path. Finally, the micromechanism of macroscopic fracture propagation under uniaxial and biaxial compression conditions is analyzed, and the fracture propagation can be concluded as a result of microdamage accumulation inside the material. The results of this paper are helpful for theory and engineering design of the fractured rock mass.

  17. Inclined-substrate deposition of biaxially aligned template films for YBCO-coated conductors.

    Ma, B.; Li, M.; Fisher, B. L.; Koritala, R. E.; Balachandran, U. (Energy Technology)

    2002-10-15

    Inclined-substrate deposition (ISD) of magnesium oxide (MgO) produces biaxially textured template films at high deposition rates. This process is promising for the fabrication of the second-generation superconducting wires. Biaxially aligned MgO films ({approx}1.5 {mu}m thick) were deposited on polished Hastelloy C276 (HC) substrates by ISD at deposition rates of 20-100 {angstrom}/s. Buffer films were subsequently deposited on these template films, and YBCO films were deposited epitaxially on the substrates by pulsed laser deposition. X-ray pole figure analysis and {psi}- and {omega}-scans were used for texture characterization. Good in- and out-of-plane textures were observed, with MgO(0 0 2) {phi}-scan full-width at half maximum (FWHM) of 9.2{sup o} and {omega}-scan FWHM of 5.4{sup o}, respectively. T{sub c} of 90 K with a sharp transition, and J{sub c} {approx} 2 x 10{sup 5} A/cm{sup 2}, were obtained on a 0.5 {mu}m thick, 0.5 cm wide, and 1 cm long YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} (YBCO) film at 77 K in self-field.

  18. Inclined-substrate deposition of biaxially aligned template films for YBCO-coated conductors

    Ma, B.; Li, M.; Fisher, B. L.; Koritala, R. E.; Balachandran, U.

    2002-10-01

    Inclined-substrate deposition (ISD) of magnesium oxide (MgO) produces biaxially textured template films at high deposition rates. This process is promising for the fabrication of the second-generation superconducting wires. Biaxially aligned MgO films (≈1.5 μm thick) were deposited on polished Hastelloy C276 (HC) substrates by ISD at deposition rates of 20-100 Å/s. Buffer films were subsequently deposited on these template films, and YBCO films were deposited epitaxially on the substrates by pulsed laser deposition. X-ray pole figure analysis and φ- and ω-scans were used for texture characterization. Good in- and out-of-plane textures were observed, with MgO(0 0 2) φ-scan full-width at half maximum (FWHM) of 9.2° and ω-scan FWHM of 5.4°, respectively. Tc of 90 K with a sharp transition, and Jc≈2×10 5 A/cm 2, were obtained on a 0.5 μm thick, 0.5 cm wide, and 1 cm long YBa 2Cu 3O 7- δ (YBCO) film at 77 K in self-field.

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

    Acharya, Bharat R.; Kang, Shin-Woong; Prasad, Veena; Kumar, Satyendra; (Kent); (Platypus)

    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.

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

    Acharya, Bharat R.; Kang, Shin-Woong; Prasad, Veena; Kumar, Satyendra; (Kent); (CLCR); (Platypus)

    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.

  1. Growth of Biaxially Textured Yttria-Stabilized Zirconia Thin Films on Si(111) Substrate by Ion Beam Assisted Deposition

    MU Hai-Chuan; REN Cong-Xin; JIANG Bing-Yao; DING Xing-Zhao; YU Yue-Hui; WANG Xi; LIU Xiang-Huai; ZHOU Gui-En; JIA Yun-Bo

    2000-01-01

    The (001) oriented yttria-stabilized zirconia (YSZ) films with in-plane biaxial texture have been deposited on Si(lll ) substrates by ion beam assisted deposition at ambient temperature. The effects of ion/atom arrival rate ratio (R=(Ar+ +O2+)/ZrO2) and incident angle of bombarding ion beam on the film texture development were investigated. It was found that the in-plane biaxial texture of the films was improved gradually with increasing ion/atom arrival rate ratio R up to a critical value 1.9, but it was degraded with the further increase of R. The optimal in-plane biaxial texture, whose full width at half maximum of the (lll) φ-scan spectrum is 14°, can be obtained at R=1.9 and incident angle of 55°. For a fixed R, the optimal crystallinity and in-plane biaxial alignment of the YSZ films did not appear at the same incident angle and showed an opposite variation with the change of the incident angle from 51° to 55°. C-axis lignment (perpendicular to substrate surface) does not show any substantial variation with the change of incident angle within the range of 47° - 56°.

  2. Mechanical response of cross-ply Si3N4/BN fibrous monoliths under uniaxial and biaxial loading

    Mechanical properties of hot-pressed Si3N4/BN fibrous monoliths (FMs) were evaluated under ambient conditions in four-point and biaxial flexure modes. Effects of cell orientation, 0degree/90degree and ±45degree, on elastic modulus and fracture strength of the FMs were investigated. Fracture surfaces were examined by scanning electron microscopy

  3. Transient and residual stresses in a pressable glass-ceramic before and after resin-cement coating determined using profilometry.

    2011-05-01

    The effect of heat-pressing and subsequent pre-cementation (acid-etching) and resin-cementation operative techniques on the development of transient and residual stresses in different thicknesses of a lithium disilicate glass-ceramic were characterised using profilometry prior to biaxial flexure strength (BFS) determination.

  4. Study on damage characteristics of marble under biaxial compression%双轴压缩状态下大理岩破坏特性的试验研究

    李昂; 邵国建; 雷冬; 朱义欢

    2012-01-01

    Compression tests were conducted to Jinping marble in uniaxial and biaxial conditions. Based on stress-strain curves of different loading stress path, the characteristics of strain have been analyzed under different stress state while studying the process of cracks from being formed to being expanded which led the sample failure on the surface in the end. From uniaxial experiment results of different scales, the trend of size effect has been proved. It is revealed the failure format and regulation of Jinping marble in biaxial condition. Reference will be provided for practice project of underground curve in excavation.%针对锦屏一级水电工程深部大理岩,分别进行了单、双轴加载下的岩样试验.基于不同加载应力路径下岩样的应力-应变关系曲线,分析了大理岩在不同加载状态下的变形特征,研究了岩样表面裂缝形成、扩展直至破坏的全过程.从不同岩样尺寸的实验结果出发,探讨了尺寸效应对岩石强度的影响趋势,揭示了双轴应力条件下大理岩的破坏形式和破坏规律.所得结论可为实际地下洞室工程中的开挖效应分析提供参考依据.

  5. Effect of Temperature and Mechanical Stress on Barrier Properties of Polymeric Films Used for Food Packaging

    Mrkić, Saša; Kata GALIĆ; Marica IVANKOVIĆ

    2007-01-01

    Abstract The permeance of carbon dioxide, oxygen, nitrogen, and air through commercial polymers based on polyethylene (PE), biaxially oriented polypropylene (BOPP), and polyamide (PA) used for food packaging is reported. The influence of temperature (from 10 to 60?C) and crease stress cycles (30, 50, 70, and 110) on gas permeance is also analyzed. Generally, the highest changes in gas permeance changes with increased stress cycles are observed with films having a metallized layer i...

  6. Field-induced transformations in the biaxial order of non-tilted phases in a bent-core smectic liquid crystal

    Panarin, Y. P.; Nagaraj, Mamatha; Vij, J. K.; Keith, C.; Tschierske, C.

    2010-10-01

    The structural and electro-optic investigations of an achiral bent-core molecule in SmAPA phase, in which the polar directors in the neighboring layers are arranged anti-ferroelectrically, show that it undergoes transformation from one biaxial to another biaxial structure via a quasi-stable uniaxial structure on the application of the electric field. The non-continuous change in biaxiality is explained by an intermediate state in which the secondary directors in the neighboring layers are perpendicular to each other.

  7. Biaxial lidar efficiency rising based on improving of spatial selectivity and stability against background radiation

    Agishev, R.R.; Bajazitov, R.A.; Galeyev, M.M. [Kazan State Technical Univ., Tatarstan (Russian Federation). Dept. of Radioelectronic and Quantum Systems

    1996-12-31

    A criterion of spatial-angular efficiency (SAE) of remote electro-optical systems for atmosphere monitoring is formulated. The dependencies of the SAE from normalized range and minimal operating range for different optical receiving schemes of ground-based biaxial lidar are analyzed. It is shown that low SAE of traditional VIS and NIR systems are a main cause of a low signal-to-background-noise ratio at the photodetector input, the considerable measurements errors. and the following low accuracy of atmospheric optical parameters reconstruction. The most effective protection against sky background radiation in such systems consists in forming an angular field according to the introduced SAE criterion. Some approaches to achieve high value of the SAE-parameter for receiving system optimization are discussed.

  8. The Landau-de Gennes theory of nematic liquid crystals: Uniaxiality versus Biaxiality

    Majumdar, Apala

    2011-12-01

    We study small energy solutions within the Landau-de Gennes theory for nematic liquid crystals, subject to Dirichlet boundary conditions. We consider two-dimensional and three-dimensional domains separately. In the two-dimensional case, we establish the equivalence of the Landau-de Gennes and Ginzburg-Landau theory. In the three-dimensional case, we give a new definition of the defect set based on the normalized energy. In the threedimensional uniaxial case, we demonstrate the equivalence between the defect set and the isotropic set and prove the C 1,α-convergence of uniaxial small energy solutions to a limiting harmonic map, away from the defect set, for some 0 < a < 1, in the vanishing core limit. Generalizations for biaxial small energy solutions are also discussed, which include physically relevant estimates for the solution and its scalar order parameters. This work is motivated by the study of defects in liquid crystalline systems and their applications.

  9. Abrasion resistance of biaxially oriented polypropylene films coated with nanocomposite hard coatings

    Wang, Jing; Zhu, Yaofeng; Fu, Yaqin

    2013-11-01

    KMnO4-treated, functionalized, biaxially oriented polypropylene (BOPP) films coated with nano-silica hybrid material were synthesized. The abrasion resistance of the films was examined using a reciprocating fabric abrasion tester. Functional groups were confirmed by Fourier-transform infrared spectroscopy. Contact angle measurements were performed on the BOPP film surface to quantify the effectiveness of the functionalization. Results indicate that the abrasion resistance and roughness of the composite film were significantly affected by the modification of the BOPP film. Water surface contact angle of the modified BOPP films decreased from 90.1° to 71.4°,when KMnO4 concentration increased from 0 M to 0.25 M. Wettability of the BOPP films clearly improved after KMnO4 treatment. Abrasion resistance of the functionalized films coated with hybrid materials improved by 27.4% compared with that of the original film.

  10. Development of a synchrotron biaxial tensile device for in situ characterization of thin films mechanical response

    Geandier, G. [Departement PMM, Institut Pprime, UPR 3346 CNRS, Universite de Poitiers-ENSMA, SP2MI, Teleport 2, Boulevard Marie et Pierre Curie, BP 30179-86962 Futuroscope Chasseneuil Cedex (France); Synchrotron SOLEIL, L' Orme des Merisiers, BP 48, 91192 Gif sur Yvette (France); LPMTM, UPR 9001 CNRS, Universite Paris-Nord, 93430 Villetaneuse (France); Thiaudiere, D.; Bouaffad, A. [Synchrotron SOLEIL, L' Orme des Merisiers, BP 48, 91192 Gif sur Yvette (France); Randriamazaoro, R. N.; Chiron, R.; Castelnau, O.; Faurie, D. [LPMTM, UPR 9001 CNRS, Universite Paris-Nord, 93430 Villetaneuse (France); Djaziri, S.; Lamongie, B.; Diot, Y.; Le Bourhis, E.; Renault, P. O.; Goudeau, P. [Departement PMM, Institut Pprime, UPR 3346 CNRS, Universite de Poitiers-ENSMA, SP2MI, Teleport 2, Boulevard Marie et Pierre Curie, BP 30179-86962 Futuroscope Chasseneuil Cedex (France); Hild, F. [LMT Cachan, 61 Avenue du President Wilson, 94235 Cachan Cedex (France)

    2010-10-15

    We have developed on the DIFFABS-SOLEIL beamline a biaxial tensile machine working in the synchrotron environment for in situ diffraction characterization of thin polycrystalline films mechanical response. The machine has been designed to test compliant substrates coated by the studied films under controlled, applied strain field. Technological challenges comprise the sample design including fixation of the substrate ends, the related generation of a uniform strain field in the studied (central) volume, and the operations from the beamline pilot. Preliminary tests on 150 nm thick W films deposited onto polyimide cruciform substrates are presented. The obtained results for applied strains using x-ray diffraction and digital image correlation methods clearly show the full potentialities of this new setup.

  11. Impacts of virtual substrate doping on high frequency characteristics of biaxially strained Si PMOSFET

    Khatami, Mohammad Mahdi; Shalchian, Majid; Kolahdouz, Mohammadreza

    2015-09-01

    Formation of a parasitic channel in biaxially strained Si channel p-MOSFET, degrades performance of the device. In this paper the effect of SiGe (virtual substrate) doping on formation of parasitic channel and high frequency characteristics of the strained MOSFET has been studied. Simulation results, indicate that increasing virtual substrate's doping from e.g. 4 × 1015 cm-3 to 4 × 1017 cm-3 effectively eliminates parasitic channel by reducing hole concentration from 1 × 1017 cm-3 to 1 × 1011 cm-3 in the parasitic channel. This improves MOSFET's characteristics including parasitic capacitances and channel length modulation. Also it has been demonstrated that the highest unity-gain bandwidth might be achieved at doping level of 4 × 1017 cm-3.

  12. Comparison of calculation methods for the tunnel splitting at excited states of biaxial spin models

    Cui Xiao-Bo; Chen Zhi-De

    2004-01-01

    We present the calculation and comparison of tunnel splitting at excited levels of biaxial spin models by various methods, including the generalized instanton method, the generalized path integral method for coherent spin states,the perturbation method, and the exact method by numerical diagonalization of the Hamiltonian. It is found that,for integer spin with spin number around 10, tunnel splitting predicted by the generalized path integral for coherent spin states is about 10-n times of the exact numerical result for the nth excited level, while the ratio of the results of the perturbation method and the exact numerical method diverges in the large spin limit. We thus conclude that the generalized instanton method is the best approximate way for calculating tunnel splitting in spin models.

  13. Measurement of refractive index of biaxial potassium titanyl phosphate crystal plate using reflection spectroscopic ellipsometry technique

    A K Chaudhary; A Molla; A Asfaw

    2009-10-01

    The paper reports the measurement of refractive indices and anisotropic absorption coefficients of biaxial potassium titanyl phosphate (KTP) crystal in the form of thin plate using reflection ellipsometry technique. This experiment is designed in the Graduate Optics Laboratory of the Addis Ababa University and He–Ne laser ( = 632.8 nm), diode laser ( = 670.0 nm) and temperature-tuned diode laser ( = 804.4 and 808.4 nm), respectively have been employed as source. The experimental data for , are fitted to the Marquardt–Levenberg theoretical model of curve fitting. The obtained experimental data of refractive indices are compared with different existing theoretical and experimental values of KTP crystals and found to be in good agreement with them.

  14. Powder metallurgy for the fabrication of bi-axially textured Ni tapes for YBCO coated conductors

    Bi-axially textured Ni tapes for YBCO coated conductors were fabricated by forming, sintering, cold rolling and heat treatment of Ni powder compacts. The powder metallurgy process consists of filling of fine Ni powders in a rubber mold, cold isostatical pressing in a water chamber and sintering of the powder compacts. The sintered compacts were cold-rolled and made into tapes with a thickness of 100 micron and then heat-treated at 1000 deg. C for various time periods for the development of the (2 0 0) texture. The (2 0 0) texture of Ni tape was successfully formed through the optimization of the recrystallization heat treatment condition for the cold rolled Ni tapes. The full width half maximum of the Ni tapes was 8-10 deg. and the atomic force microscopy surface roughness was 3-5 nm

  15. Voigt wave investigation in the KGd(WO4)2:Nd biaxial laser crystal

    Brenier, Alain

    2015-07-01

    We have investigated the Nd3+-doped KGd(WO4)2 biaxial laser crystal for wave propagation directions in the vicinity of the optical axis at wavelengths tunable around 800 nm. The angular absorption distribution was found to be strongly anisotropic. Increasing absorption, the optical axis splits in two new ones able to propagate unchanged a left or a right circularly polarized light and able to propagate a circularly polarized Voigt wave with a linear spatial dependence. The intensities of the transmitted light in different configurations of polarizations were investigated. The angular displacement of the two optical axes versus the absorbed wavelengths was measured and explained with a single oscillator model. The light energy propagation was found distributed inside a crescent-shaped area.

  16. Development of a synchrotron biaxial tensile device for in situ characterization of thin films mechanical response

    We have developed on the DIFFABS-SOLEIL beamline a biaxial tensile machine working in the synchrotron environment for in situ diffraction characterization of thin polycrystalline films mechanical response. The machine has been designed to test compliant substrates coated by the studied films under controlled, applied strain field. Technological challenges comprise the sample design including fixation of the substrate ends, the related generation of a uniform strain field in the studied (central) volume, and the operations from the beamline pilot. Preliminary tests on 150 nm thick W films deposited onto polyimide cruciform substrates are presented. The obtained results for applied strains using x-ray diffraction and digital image correlation methods clearly show the full potentialities of this new setup.

  17. Biaxially aligned YBa2Cu3O7-x thin film tapes

    We report the formation of biaxially oriented films of yttorium-stabilized ZrO2 (YSZ) on a polycrystalline, Ni-based alloy (Hastelloy c276) by Ion-Beam-Assisted Deposition (IBAD), and the subsequent a-b plane aligned YBa2Cu3O7-x (YBCO) films deposited by laser ablation. Jc of 6.0x104A/cm2 (77K, 0 T) and 1.4x104A/cm2 (77K, 0.6 T) were obtained. A new method to prevent intergranular-weak-links has been developed for application of oxide superconducting thin films, for tape-shaped cables, magnets, magnetic shields, microwave devices, etc. (orig.)

  18. Biaxially aligned YBa 2Cu 3O 7-x thin film tapes

    Iijima, Yasuhiro; Tanabe, Nobuo; Ikeno, Yoshimitsu; Kohno, Osamu

    1991-12-01

    We report the formation of biaxially oriented films of yttorium-stabilized ZrO 2 (YSZ) on a polycrystalline, Ni-based alloy (Hastelloy c276) by Ion-Beam-Assisted Deposition (IBAD), and the subsequent a-b plane aligned YBa 2Cu 3O 7-x (YBCO) films deposited by laser ablation. Jc of 6.0×10 4 A/cm 2 (77 K, O T) and 1.4×10 4 A/cm 2 (77 K, 0.6 T) were obtained. A new method to prevent intergranular-weak-links has been developed for application of oxide superconducting thin films, for tape-shaped cables, magnets, magnetic shields, microwave devices, etc.

  19. UV protective zinc oxide coating for biaxially oriented polypropylene packaging film by atomic layer deposition

    Lahtinen, Kimmo, E-mail: kimmo.lahtinen@lut.fi [ASTRaL, Lappeenranta University of Technology, Sammonkatu 12, FI-50130 Mikkeli (Finland); Kääriäinen, Tommi, E-mail: tommi.kaariainen@colorado.edu [ASTRaL, Lappeenranta University of Technology, Sammonkatu 12, FI-50130 Mikkeli (Finland); Johansson, Petri, E-mail: petri.johansson@tut.fi [Paper Converting and Packaging Technology, Tampere University of Technology, P.O.Box 589, FI-33101 Tampere (Finland); Kotkamo, Sami, E-mail: sami.kotkamo@tut.fi [Paper Converting and Packaging Technology, Tampere University of Technology, P.O.Box 589, FI-33101 Tampere (Finland); Maydannik, Philipp, E-mail: philipp.maydannik@lut.fi [ASTRaL, Lappeenranta University of Technology, Sammonkatu 12, FI-50130 Mikkeli (Finland); Seppänen, Tarja, E-mail: tarja.seppanen@lut.fi [ASTRaL, Lappeenranta University of Technology, Sammonkatu 12, FI-50130 Mikkeli (Finland); Kuusipalo, Jurkka, E-mail: jurkka.kuusipalo@tut.fi [Paper Converting and Packaging Technology, Tampere University of Technology, P.O.Box 589, FI-33101 Tampere (Finland); Cameron, David C., E-mail: david.cameron@miktech.fi [ASTRaL, Lappeenranta University of Technology, Sammonkatu 12, FI-50130 Mikkeli (Finland)

    2014-11-03

    Biaxially oriented polypropylene (BOPP) packaging film was coated with zinc oxide (ZnO) coatings by atomic layer deposition (ALD) in order to protect the film from UV degradation. The coatings were made at a process temperature of 100 °C using diethylzinc and water as zinc and oxygen precursors, respectively. The UV protective properties of the coatings were tested by using UV–VIS and infrared spectrometry, differential scanning calorimetry (DSC) and a mechanical strength tester, which characterised the tensile and elastic properties of the film. The results obtained with 36 and 67 nm ZnO coatings showed that the ZnO UV protective layer is able to provide a significant decrease in photodegradation of the BOPP film under UV exposure. While the uncoated BOPP film suffered a complete degradation after a 4-week UV exposure, the 67 nm ZnO coated BOPP film was able to preserve half of its original tensile strength and 1/3 of its elongation at break after a 6-week exposure period. The infrared analysis and DSC measurements further proved the UV protection of the ZnO coatings. The results show that a nanometre scale ZnO coating deposited by ALD is a promising option when a transparent UV protection layer is sought for polymer substrates. - Highlights: • Atomic layer deposited zinc oxide coatings were used as UV protection layers. • Biaxially oriented polypropylene (BOPP) film was well protected against UV light. • Formation of UV degradation products in BOPP was significantly reduced. • Mechanical properties of the UV exposed BOPP film were significantly improved.

  20. UV protective zinc oxide coating for biaxially oriented polypropylene packaging film by atomic layer deposition

    Biaxially oriented polypropylene (BOPP) packaging film was coated with zinc oxide (ZnO) coatings by atomic layer deposition (ALD) in order to protect the film from UV degradation. The coatings were made at a process temperature of 100 °C using diethylzinc and water as zinc and oxygen precursors, respectively. The UV protective properties of the coatings were tested by using UV–VIS and infrared spectrometry, differential scanning calorimetry (DSC) and a mechanical strength tester, which characterised the tensile and elastic properties of the film. The results obtained with 36 and 67 nm ZnO coatings showed that the ZnO UV protective layer is able to provide a significant decrease in photodegradation of the BOPP film under UV exposure. While the uncoated BOPP film suffered a complete degradation after a 4-week UV exposure, the 67 nm ZnO coated BOPP film was able to preserve half of its original tensile strength and 1/3 of its elongation at break after a 6-week exposure period. The infrared analysis and DSC measurements further proved the UV protection of the ZnO coatings. The results show that a nanometre scale ZnO coating deposited by ALD is a promising option when a transparent UV protection layer is sought for polymer substrates. - Highlights: • Atomic layer deposited zinc oxide coatings were used as UV protection layers. • Biaxially oriented polypropylene (BOPP) film was well protected against UV light. • Formation of UV degradation products in BOPP was significantly reduced. • Mechanical properties of the UV exposed BOPP film were significantly improved

  1. Effect of Molecular Flexibility on the Nematic-to-Isotropic Phase Transition for Highly Biaxial Molecular Non-Symmetric Liquid Crystal Dimers

    María Blanca Ros

    2011-09-01

    Full Text Available In this work, a study of the nematic (N–isotropic (I phase transition has been made in a series of odd non-symmetric liquid crystal dimers, the α-(4-cyanobiphenyl-4’-yloxy-ω-(1-pyrenimine-benzylidene-4’-oxy alkanes, by means of accurate calorimetric and dielectric measurements. These materials are potential candidates to present the elusive biaxial nematic (NB phase, as they exhibit both molecular biaxiality and flexibility. According to the theory, the uniaxial nematic (NU–isotropic (I phase transition is first-order in nature, whereas the NB–I phase transition is second-order. Thus, a fine analysis of the critical behavior of the N–I phase transition would allow us to determine the presence or not of the biaxial nematic phase and understand how the molecular biaxiality and flexibility of these compounds influences the critical behavior of the N–I phase transition.

  2. In-situ Curing Strain Monitoring of a Flat Plate Residual Stress Specimen Using a Chopped Stand Mat Glass/Epoxy Composite as Test Material

    Jakobsen, J.; Skordos, A.; James, S.; Correia, R. G.; Jensen, M.

    2015-12-01

    The curing stresses in a newly proposed bi-axial residual stress testing configuration are studied using a chopped strand mat glass/epoxy specimen. In-situ monitoring of the curing is conducted using dielectric and fibre Bragg grating sensors. It is confirmed that a bi-axial residual stress state can be introduced in the specimens during curing and a quantification of its magnitude is presented. An alternative decomposition method used for converting the dielectric signal into a material state variable is proposed and good agreement with models found in the literature is obtained. From the cure cycles chosen it is suggested that any stress build up in the un-vitrified state is relaxed immediately and only stress build up in the vitrified state contributes to the residual stress state in the specimen.

  3. STRENGTH CRITERION FOR PLAIN CONCRETE UNDER MULTIAXIAL STRESS BASED ON DAMAGE POISSON'S RATIO

    Ding Faxing; Yu Zhiwu

    2006-01-01

    A new unified strength criterion in the principal stress space has been proposed for use with normal strength concrete (NC) and high strength concrete (HSC) in compressioncompression-tension, compression-tension-tension, triaxial tension, and biaxial stress states. The study covers concrete with strengths ranging from 20 to 130 Mpa. The conception of damage Poisson's ratio is defined and the expression for damage Poisson's ratio is determined basically.The failure mechanism of concrete is illustrated, which points out that damage Poisson's ratio is the key to determining the failure of concrete. Furthermore, for the concrete under biaxial stress conditions, the unified strength criterion is simplified and a simplified strength criterion in the form of curves is also proposed. The strength criterion is physically meaningful and easy to calculate, which can be applied to analytic solution and numerical solution of concrete structures.

  4. Effect of Biaxial Stretching at Temperatures and Strain Histories Comparable to Injection Stretch Blow Moulding on Tensile Modulus for Polyethylene Terephthalate (PET)

    Tan, C. W.; Menary, G. H.; Harkin-Jones, E. M. A.; Armstrong, C. G.; Martin, P. J.

    2007-04-01

    This study is particularly relevant to the injection stretch blow moulding (ISBM) process where PET material is typically biaxially stretched to form bottles for the water and carbonated soft drinks industry. The aim of this paper is to investigate the effect of biaxial stretching on the mechanical properties of Polyethylene Terephthalate (PET) using a custom built biaxial testing machine. An initially amorphous PET sample was prepared via injection moulding to form a square sample (76mm × 76mm) suitable for stretching on the machine. This sample was then subjected to a series of biaxial tests (simultaneous and sequential) within a temperature range between 85°C and 110 °C, strain rates in the range of 1s-1 to 32s-1 and stretch ratios in the range of 1.5 to 3. Specimens were subsequently cut from the biaxial stretched sheets and used to measure the tensile modulus. Results showed that there is almost no effect found for strain rate and temperature on modulus development whilst stretch ratio and mode of deformation played the most important role on modulus development on PET under biaxial deformation.

  5. Biaxial Strain in the Hexagonal Plane of MnAs Thin Films: The Key to Stabilize Ferromagnetism to Higher Temperature

    Garcia, V.; Sidis, Y.; Marangolo, M.; Vidal, F.; Eddrief, M.; Bourges, P.; Maccherozzi, F.; Ott, F.; Panaccione, G.; Etgens, V. H.

    2007-09-01

    The α-β magnetostructural phase transition in MnAs/GaAs(111) epilayers is investigated by elastic neutron scattering. The in-plane parameter of MnAs remains almost constant with temperature from 100 to 420 K, following the thermal evolution of the GaAs substrate. This induces a temperature dependent biaxial strain that is responsible for an α-β phase coexistence and, more importantly, for the stabilization of the ferromagnetic α phase at a higher temperature than in the bulk. We explain the premature appearance of the β phase at 275 K and the persistence of the ferromagnetic α phase up to 350 K with thermodynamical arguments based on the MnAs phase diagram. It results that the biaxial strain in the hexagonal plane is the key parameter to extend the ferromagnetic phase well over room temperature.

  6. Statics and field-driven dynamics of transverse domain walls in biaxial nanowires under uniform transverse magnetic fields

    Lu, Jie

    2016-06-01

    In this work, we report analytical results on transverse domain wall (TDW) statics and field-driven dynamics in quasi-one-dimensional biaxial nanowires under arbitrary uniform transverse magnetic fields (TMFs) based on the Landau-Lifshitz-Gilbert equation. Without axial driving fields, the static TDW should be symmetric about its center while twisted in its azimuthal angle distribution. By decoupling polar and azimuthal degrees of freedom, an approximate solution is provided which reproduces these features to a great extent. When an axial driving field is applied, the dynamical behavior of a TDW is viewed as the response of its static profile to external excitations. By means of the asymptotic expansion method, the TDW velocity in the traveling-wave mode is obtained, which provides the extent and boundary of the "velocity-enhancement" effect of TMFs on TDWs in biaxial nanowires. Finally, numerical simulations are performed and strongly support our analytics.

  7. Reexamination of the mean-field phase diagram of biaxial nematic liquid crystals: Insights from Monte Carlo studies

    Kamala Latha, B.; Jose, Regina; Murthy, K. P. N.; Sastry, V. S. S.

    2015-07-01

    Investigations of the phase diagram of biaxial liquid-crystal systems through analyses of general Hamiltonian models within the simplifications of mean-field theory (MFT), as well as by computer simulations based on microscopic models, are directed toward an appreciation of the role of the underlying molecular-level interactions to facilitate its spontaneous condensation into a nematic phase with biaxial symmetry. Continuing experimental challenges in realizing such a system unambiguously, despite encouraging predictions from MFT, for example, are requiring more versatile simulational methodologies capable of providing insights into possible hindering barriers within the system, typically gleaned through its free-energy dependences on relevant observables as the system is driven through the transitions. The recent paper from this group [Kamala Latha et al., Phys. Rev. E 89, 050501(R) (2014), 10.1103/PhysRevE.89.050501], summarizing the outcome of detailed Monte Carlo simulations carried out employing an entropic sampling technique, suggested a qualitative modification of the MFT phase diagram as the Hamiltonian is asymptotically driven toward the so-called partly repulsive regions. It was argued that the degree of (cross) coupling between the uniaxial and biaxial tensor components of neighboring molecules plays a crucial role in facilitating a ready condensation of the biaxial phase, suggesting that this could be a plausible factor in explaining the experimental difficulties. In this paper, we elaborate this point further, providing additional evidence from curious variations of free-energy profiles with respect to the relevant orientational order parameters, at different temperatures bracketing the phase transitions.

  8. Domain Walls and Anchoring Transitions Mimicking Nematic Biaxiality in the Oxadiazole Bent-Core Liquid Crystal C7

    Kim, Young-Ki; Cukrov, Greta; Xiang, Jie; Shin, Sung-Tae; Lavrentovich, Oleg D.

    2015-01-01

    We investigate the origin of secondary disclinations that were recently described as a new evidence of a biaxial nematic phase in an oxadiazole bent-core thermotropic liquid crystal C7. With an assortment of optical techniques such as polarizing optical microscopy, LC PolScope, and fluorescence confocal polarizing microscopy, we demonstrate that the secondary disclinations represent non-singular domain walls formed in an uniaxial nematic during the surface anchoring transition, in which surfa...

  9. Biaxial bending of slender HSC columns and tubes filled with concrete under short- and long-term loads: I) Theory

    Rodríguez-Gutiérrez, Jose A.; Jose Dario Aristizabal-Ochoa

    2014-01-01

    An analytical method that calculates both the short- and long-term response of slender columns made of high-strength concrete (HSC) and tubes filled with concrete with generalized end conditions and subjected to transverse loads along the span and axial load at the ends (causing a single or double curvature under uniaxial or biaxial bending) is presented. The proposed method, which is an extension of a method previously developed by the authors, is capable of predicting not only the complete ...

  10. Electrically conducting oxide buffer layers on biaxially textured nickel alloy tapes by reel-to-reel MOCVD process

    Reel-to-reel MOCVD process for continuous growth of electrically conducting buffer layers on biaxially textured Ni5W tapes has been developed. The new buffer layer architechture is presented: 200 nm (La, Ba)2CuO4/40 nm (La, Ba)MnO3/Ni5W. Constituting layers with high structural quality have been grown on moving tapes (in plane FWHM ≤ 60 and out of plane FWHM ≤ 30)

  11. Development of 1366 K (20000F) strain sensor and biaxial strain transducer for use to 1033 K (14000F)

    The development and evaluation of (a) the Battelle-Columbus Laboratories (BCL) resistance strain gage system for measurement of strains to 1366 K (20000F), and (b) a biaxial strain transducer, utilizing above system, for measurements to 1033 K (14000F) are described. Data are presented which depict pertinent gage and transducer performance characteristics. The paper should be of particular interest to those in need of strain data at temperatures exceeding the limits of commercially available electric resistance strain gages. (orig.)

  12. Effect of Ceramic Surface Treatments After Machine Grinding on the Biaxial Flexural Strength of Different CAD/CAM Dental Ceramics

    Bagheri, Hossein; Hooshmand, Tabassom; Aghajani, Farzaneh

    2015-01-01

    Objectives: This study aimed to evaluate the effect of different ceramic surface treatments after machining grinding on the biaxial flexural strength (BFS) of machinable dental ceramics with different crystalline phases. Materials and Methods: Disk-shape specimens (10mm in diameter and 1.3mm in thickness) of machinable ceramic cores (two silica-based and one zirconia-based ceramics) were prepared. Each type of the ceramic surfaces was then randomly treated (n=15) with different treatments as ...

  13. Biaxial Q-shearing of 27Al 3QMAS NMR spectra: insight into the structural disorder of framework aluminosilicates

    Kobera, Libor; Brus, Jiří; Klein, Petr; Dědeček, Jiří; Urbanová, Martina

    57-58, February–April (2014), s. 29-38. ISSN 0926-2040 R&D Projects: GA ČR(CZ) GA13-24155S; GA AV ČR IAA400400904 Institutional support: RVO:61389013 ; RVO:61388955 Keywords : 27Al 3QMAS NMR * biaxial shearing * zeolite s Subject RIV: JN - Civil Engineering; CF - Physical ; Theoretical Chemistry (UFCH-W) Impact factor: 2.266, year: 2014

  14. First principles prediction of the electronic structure and carrier mobilities of biaxially strained molybdenum trioxide (MoO3)

    Dandogbessi, Bruno S.; Akin-Ojo, Omololu

    2016-08-01

    The electronic band structures of unstrained and biaxially strained MoO3 were determined by first-principles density functional theory calculations. From the band structures, the effects of strain on the charge carrier mobilities were investigated. These mobilities were calculated based on deformation potential theory. First, we found that the electron effective masses of unstrained bulk pristine MoO3 are about three times smaller than the corresponding hole effective masses, and, second, the electron mobility is about ten times the hole mobility, making the compound an electron transport material. Our results also show that, when compressed biaxially, as the strain increases from 0% to 1.5%, the electron (hole) mobility increases by 0% to 53% (0% to 17%). On the other hand, the application of a biaxial tensile strain decreases the electron (hole) mobility by 65% to 0% (90% to 0%), as the tensile strain increases from 0% to 1.5 % . These changes are caused mainly by the fact that the carrier effective masses reduce (increase) upon application of compressive (tensile) strain. Only the acoustic-phonon limited carrier mobilities were computed; hence, the actual mobilities cannot be less than the values obtained in this work.

  15. RF magnetron-sputtered ZNO thin films: on the evolution of microstructure and residual stresses

    Özen, İstem; Ozen, Istem

    2006-01-01

    Thin ZnO films (200-500 nm) were deposited onto glass, mica, and Si(100) substrates, to study the relations between microstructure and residual stresses. The ranges for the substrate temperature, chamber pressure, and RF power were room temperature-200 °C, 0.009-0.4 mbar, and 100-125 W, respectively. The strain measurements by x-ray diffraction and the biaxial stress model showed that the films were under residual compressive stresses from -2 to -8 GPa. 5-11 percent of those stresses were ind...

  16. Bi-Axial Solar Array Drive Mechanism: Design, Build and Environmental Testing

    Scheidegger, Noemy; Ferris, Mark; Phillips, Nigel

    2014-01-01

    The development of the Bi-Axial Solar Array Drive Mechanism (BSADM) presented in this paper is a demonstration of SSTL's unique space manufacturing approach that enables performing rapid development cycles for cost-effective products that meet ever-challenging mission requirements: The BSADM is designed to orient a solar array wing towards the sun, using its first rotation axis to track the sun, and its second rotation axis to compensate for the satellite orbit and attitude changes needed for a successful payload operation. The tight development schedule, with manufacture of 7 Flight Models within 1.5 year after kick-off, is offset by the risk-reduction of using qualified key component-families from other proven SSTL mechanisms. This allowed focusing the BSADM design activities on the mechanism features that are unique to the BSADM, and having an Engineering Qualification Model (EQM) built 8 months after kick-off. The EQM is currently undergoing a full environmental qualification test campaign. This paper presents the BSADM design approach that enabled meeting such a challenging schedule, its design particularities, and the ongoing verification activities.

  17. Modeling of stored charge in metallized biaxially oriented polypropylene film capacitors based on charging current measurement.

    Li, Hua; Wang, Bowen; Li, Zhiwei; Liu, De; Lin, Fuchang; Dai, Ling; Zhang, Qin; Chen, Yaohong

    2013-10-01

    Metallized biaxially oriented polypropylene film (BOPP) capacitors are widely used in pulsed power systems. When the capacitor is used as the energy storage equipment under high electric field, more charges should be provided to maintain the voltage of the capacitor. This should be ascribed to the completion of the slow polarization which may take several hours or even longer. This paper focuses on the stored charge in metallized BOPP film capacitors. The modeling of the stored charge by the equivalent conversion of circuits is conducted to analyse the slow polarization in the BOPP film. The 3-RC network is proposed to represent the time-dependent charge stored in the capacitor. A charging current measurement system is established to investigate the charge storage property of the capacitor. The measurement system can measure the long time charging current with a sampling rate of 300 Hz. The total charge calculated by the charging current indicates that the stored charge in the capacitor under the electric field of 400 V/μm is 13.5% larger than the product of the voltage and the capacitance measured by the AC bridge. The nonlinear effect of the electric field on the slow polarization charge is also demonstrated. And the simulation of charge storage based on the 3-RC network can match well with the trend of the stored charge increasing with the time. PMID:24182144

  18. The effects of surface contamination on the biaxially textured substrate for YBCO thick film deposition

    The epitaxial growth of YBa2Cu3O7-x (YBCO) films on biaxially textured substrates is one of the most promising technique for the fabrication of high current superconducting tapes operating at high temperature. Ni is very attractive as substrate because it easily develops a/ (100)[001] cubic texture. The low oxidation resistance represents the main drawback of the Ni substrate. In order to better assess the role of oxygen on the Ni substrates, a surface physics technique as Auger spectroscopy has been used. It has allowed to evaluate the amount of impurities for different Ni processing and exposure to the air. The results demonstrate that the surface contamination can be efficiently removed by RF sputtering before buffer layer deposition. This procedure allows to obtain CeO2/Pd/Ni architecture by laser ablation with a good epitaxy both of Pd and CeO2 films. On the contrary, when CeO2 is directly deposited on Ni a low epitaxy is obtained. The Auger analysis confirms that the formation of (111) NiO at the Ni-CeO2 interface hampers the epitaxial growth of the ceria film

  19. Biaxial Dielectrophoresis Force Spectroscopy: A Stoichiometric Approach for Examining Intermolecular Weak Binding Interactions.

    Park, In Soo; Kwak, Tae Joon; Lee, Gyudo; Son, Myeonggu; Choi, Jeong Woo; Choi, Seungyeop; Nam, Kihwan; Lee, Sei-Young; Chang, Woo-Jin; Eom, Kilho; Yoon, Dae Sung; Lee, Sangyoup; Bashir, Rashid; Lee, Sang Woo

    2016-04-26

    The direct quantification of weak intermolecular binding interactions is very important for many applications in biology and medicine. Techniques that can be used to investigate such interactions under a controlled environment, while varying different parameters such as loading rate, pulling direction, rupture event measurements, and the use of different functionalized probes, are still lacking. Herein, we demonstrate a biaxial dielectrophoresis force spectroscopy (BDFS) method that can be used to investigate weak unbinding events in a high-throughput manner under controlled environments and by varying the pulling direction (i.e., transverse and/or vertical axes) as well as the loading rate. With the BDFS system, we can quantitatively analyze binding interactions related to hydrogen bonding or ionic attractions between functionalized microbeads and a surface within a microfluidic device. Our BDFS system allowed for the characterization of the number of bonds involved in an interaction, bond affinity, kinetic rates, and energy barrier heights and widths from different regimes of the energy landscape. PMID:27007455

  20. A numerical study of macro-mesoscopic mechanical properties of gangue backfill under biaxial compression

    Huang Zhimin; Ma Zhanguo; Zhang Lei; Gong Peng; Zhang Yankun; Liu Fei

    2016-01-01

    Based on the Particle Flow Code (PFC2D) program, we set up gangue backfill models with different gangue contents and bond strength, and studied the stress–strain behaviours, the pattern of shear band and force chains, motion and fragmentation of particles under biaxial compression. The results show that when the bond strength or contents of gangue are high, the peak strength is high and the phenomena of post-peak softening and fluctuation are obvious. When gangue contents are low, the shape of the shear band is sym-metrical and most strong force chains transfer in soil particles. With an increase in gangue content, the shape of the shear band becomes irregular and the majority of strong force chains turn to transfer in gangue particles gradually, most of which distribute along the axial direction. When the gangue content is higher than 50%, the interconnectivity of strong force chains decreases gradually;at the same time, the strong force chains become tilted and the stability of the system tends to decrease. With an increase in external loading, the coordination numbers of the system increase at first and then decrease and the main pattern of force chains changes into columnar from annular. However, after the forming of the advanta-geous shear band, the force chains external to the shear band maintain their columnar shape while the inner ones bend obviously. As a result, annular force chains form.

  1. Numerical analysis of soil-rock mixture's meso-mechanics based on biaxial test

    ZHANG Hai-yang; XU Wen-jie; YU Yu-zhen

    2016-01-01

    Soil-rock mixture(S-RM)is a widely distributed geotechnical medium composed of "soil" and "rock block" different both in size and strength. Internal rock blocks form special and variable meso-structural characteristics of S-RM. The objective of this work was to study the control mechanism of meso-structural characteristics on mechanical properties of S-RM. For S-RM containing randomly generated polygonal rock blocks, a series of biaxial tests based on DEM were conducted. On the basis of research on the effects of rock blocks' breakability and sample lateral boundary type (rigid, flexible) on macroscopic mechanical behavior of S-RM, an expanded Mohr-Coulomb criterion in power function form was proposed to represent the strength envelop. At the mesoscopic level, the variations of meso-structure such as rotation of rock block, and the formation mechanism and evolution process of the shear band during tests were investigated. The results show that for S-RM with a high content of rock block, translation, rotating and breakage of rock blocks have crucial effects on mechanical behavior of S-RM. The formation and location of the shear band inside S-RM sample are also controlled by breakability and arrangement of rock blocks.

  2. Localized strain measurements of the intervertebral disc annulus during biaxial tensile testing.

    Karakolis, Thomas; Callaghan, Jack P

    2015-01-01

    Both inter-lamellar and intra-lamellar failures of the annulus have been described as potential modes of disc herniation. Attempts to characterize initial lamellar failure of the annulus have involved tensile testing of small tissue samples. The purpose of this study was to evaluate a method of measuring local surface strains through image analysis of a tensile test conducted on an isolated sample of annular tissue in order to enhance future studies of intervertebral disc failure. An annulus tissue sample was biaxial strained to 10%. High-resolution images captured the tissue surface throughout testing. Three test conditions were evaluated: submerged, non-submerged and marker. Surface strains were calculated for the two non-marker conditions based on motion of virtual tracking points. Tracking algorithm parameters (grid resolution and template size) were varied to determine the effect on estimated strains. Accuracy of point tracking was assessed through a comparison of the non-marker conditions to a condition involving markers placed on tissue surface. Grid resolution had a larger effect on local strain than template size. Average local strain error ranged from 3% to 9.25% and 0.1% to 2.0%, for the non-submerged and submerged conditions, respectively. Local strain estimation has a relatively high potential for error. Submerging the tissue provided superior strain estimates. PMID:25145810

  3. Transverse-electric/transverse-magnetic polarization converter using 1D finite biaxial photonic crystal.

    Ouchani, Noama; Bria, Driss; Djafari-Rouhani, Bahram; Nougaoui, Abdelkarim

    2007-09-01

    We show that by using a one-dimensional anisotropic photonic structure, it is possible to realize optical wave polarization conversion by reflection and transmission processes. Thus a single incident S(P) polarized plane wave can produce a single reflected P(S) polarized wave and a single transmitted P(S) polarized wave. This polarization conversion property can be fulfilled with a simple finite superlattice (SL) constituted of anisotropic dielectric materials. We discuss the appropriate choices of the material and geometrical properties to realize such structures. The transmission and reflection coefficients are calculated in the framework of the Green's function method. The amplitude and the polarization characteristics of reflected and transmitted waves are determined as functions of frequency, wave vector k(parallel) (parallel to the interface), and the orientations of the principal axes of the layers constituting the SL. Specific applications of these results are given for a SL consisting of alternating biaxial anisotropic layers NaNO(2)/SbSI sandwiched between two identical semi-infinite isotropic media. PMID:17767240

  4. Remote monitoring of bi-axial loads on a lifting surface moving unsteadily in water

    A system of measuring the bi-axial load on a lifting surface (blade) which is freely moving and operates submerged in water at the laboratory scale is described. A blade with a span of 500 mm, a chord of 60 mm and a thickness of 9 mm (15% of the chord) was employed and the lift/drag forces were measured using a bespoke strain-gauge based load cell located at the mid-span of the blade, measuring bending moments in two independent directions. The requirement to move freely dictated that the load cell was encapsulated within the blade, along with signal conditioning circuitry, power supply and a data logger with wireless transmission. Submerged operation in water resulted in very short transmission distances, meaning that data were recorded and subsequently transferred using an aerial placed close to the blade while it was stationary. Assumptions based on Euler–Bernoulli beam bending theory were used to infer the total load from measurements of the bending moment at the mid-span and example data from a freely moving aerofoil on a Darrieus-type tidal energy extraction device are presented. The novelty of this system lies in its combination of free movement, submerged operation and small scale. (paper)

  5. A Parametric Study of Mixing in a Granular Flow a Bi-Axial Spherical Tumbler

    Christov, Ivan C; Ottino, Julio M; Sturman, Rob

    2015-01-01

    We report on a computational parameter space study of mixing protocols for a half-full bi-axial spherical granular tumbler. The quality of mixing is quantified via the intensity of segregation (concentration variance) and computed as a function of three system parameters: angles of rotation about each tumbler axis and the flowing layer depth. Only the symmetric case is considered in which the flowing layer depth is the same for each rotation. We also consider the dependence on $\\bar{R}$, which parametrizes the concentric spheroids ("shells") that comprise the volume of the tumbler. The intensity of segregation is computed over 100 periods of the mixing protocol for each choice of parameters. Each curve is classified via a time constant, $\\tau$, and an asymptotic mixing value, $bias$. We find that most choices of angles and most shells throughout the tumbler volume mix well, with mixing near the center of the tumbler being consistently faster (small $\\tau$) and more complete (small $bias$). We conclude with ex...

  6. MTOR-independent induction of autophagy in trabecular meshwork cells subjected to biaxial stretch.

    Porter, Kristine M; Jeyabalan, Nallathambi; Liton, Paloma B

    2014-06-01

    The trabecular meshwork (TM) is part of a complex tissue that controls the exit of aqueous humor from the anterior chamber of the eye, and therefore helps maintaining intraocular pressure (IOP). Because of variations in IOP with changing pressure gradients and fluid movement, the TM and its contained cells undergo morphological deformations, resulting in distention and stretching. It is therefore essential for TM cells to continuously detect and respond to these mechanical forces and adapt their physiology to maintain proper cellular function and protect against mechanical injury. Here we demonstrate the activation of autophagy, a pro-survival pathway responsible for the degradation of long-lived proteins and organelles, in TM cells when subjected to biaxial static stretch (20% elongation), as well as in high-pressure perfused eyes (30mmHg). Morphological and biochemical markers for autophagy found in the stretched cells include elevated LC3-II levels, increased autophagic flux, and the presence of autophagic figures in electron micrographs. Furthermore, our results indicate that the stretch-induced autophagy in TM cells occurs in an MTOR- and BAG3-independent manner. We hypothesize that activation of autophagy is part of the physiological response that allows TM cells to cope and adapt to mechanical forces. PMID:24583119

  7. Biaxial Solar Tracking System Based on the MPPT Approach Integrating ICTs for Photovoltaic Applications

    Raúl Gregor

    2015-01-01

    Full Text Available The smart grid and distributed generation based on renewable energy applications often involve the use of information and communication technology (ICT coupled with advanced control and monitoring algorithms to improve the efficiency and reliability of the electrical grid and renewable generation systems. Photovoltaic (PV systems have been recently applied with success in the fields of distributed generation due to their lower environmental impact where the electrical energy generation is related to the amount of solar irradiation and thus the angle of incident ray of the sun on the surface of the modules. This paper introduces an integration of ICTs in order to achieve the maximum power point tracking (MPPT using a biaxial solar tracking system for PV power applications. To generate the references for the digital control of azimuth and elevation angles a Global Positioning System (GPS by satellites is used which enables acquiring the geographic coordinates of the sun in real-time. As a total integration of the system a communication platform based on the 802.15.4 protocol for the wireless sensor networks (WSNs is adopted for supervising and monitoring the PV plant. A 2.4 kW prototype system is implemented to validate the proposed control scheme performance.

  8. Particle flow of ceramic breeder pebble beds in bi-axial compression experiments

    Pebble beds of Tritium breeding ceramic material are investigated within the framework of developing solid breeder blankets for future nuclear fusion power plants. For the thermo-mechanical characterisation of such pebble beds, bed compression experiments are the standard tools. New bi-axial compression experiments on 20 and 30 mm high pebble beds show pebble flow effects much more pronounced than in previous 10 mm beds. Owing to the greater bed height, conditions are reached where the bed fails in cross direction and unhindered flow of the pebbles occurs. The paper presents measurements for the orthosilicate and metatitanate breeder materials that are envisaged to be used in a solid breeder blanket. The data are compared with calculations made with a Drucker-Prager soil model within the finite-element code ABAQUS, calibrated with data from other experiments. It is investigated empirically whether internal bed friction angles can be determined from pebble beds of the considered heights, which would simplify, and broaden the data base for, the calibration of the Drucker-Prager pebble bed models

  9. The effects of surface contamination on the biaxially textured substrate for YBCO thick film deposition

    Apicella, M.L.; Boffa, V.; Celentano, G.; Fabbri, F.; Petrisor, T. [ENEA Centro Ricerche Frascati, Rome (Italy)

    1999-04-20

    The epitaxial growth of YBa{sub 2}Cu{sub 3}O{sub 7{minus}x} (YBCO) films on biaxially textured substrates is one of the most promising technique for the fabrication of high current superconducting tapes operating at high temperature. Ni is very attractive as substrate because it easily develops a/ (100)[001] cubic texture. The low oxidation resistance represents the main drawback of the Ni substrate. In order to better assess the role of oxygen on the Ni substrates, a surface physics technique as Auger spectroscopy has been used. It has allowed to evaluate the amount of impurities for different Ni processing and exposure to the air. The results demonstrate that the surface contamination can be efficiently removed by RF sputtering before buffer layer deposition. This procedure allows to obtain CeO{sub 2}/Pd/Ni architecture by laser ablation with a good epitaxy both of Pd and CeO{sub 2} films. On the contrary, when CeO{sub 2} is directly deposited on Ni a low epitaxy is obtained. The Auger analysis confirms that the formation of (111) NiO at the Ni-CeO{sub 2} interface hampers the epitaxial growth of the ceria film.

  10. A study on the validity of stress measurements in jointed crystalline rock

    In conclusion, USBM gages seem to be a good way to measure stresses in crystalline-rock block tests. Principal stresses measured within the block align very well under uniaxial stress and appear to be related to the fracture orientation under biaxial stress. Better alignment with respect to the applied stress directions would be expected to develop if higher applied stresses were attainable. Flatjack construction precluded application of pressures above 5.6 MPa. Variation of stress magnitudes within the block result in part from the difficulty in separating modulus variation from stress field variation. Determination of anisotropic elastic properties and their application in USBM gage reduction would probably improve measured stress results. Further investigations in this area are currently being pursued at CSM, in conjunction with the University of Colorado

  11. Time-dependent strains and stresses in a pumpkin balloon

    Gerngross, T.; Xu, Y.; Pellegrino, S.

    2006-01-01

    This paper presents a study of pumpkin-shaped superpressure balloons, consisting of gores made from a thin polymeric film attached to high stiffness, meridional tendons. This type of design is being used for the NASA ULDB balloons. The gore film shows considerable time-dependent stress relaxation, whereas the behaviour of the tendons is essentially time-independent. Upon inflation and pressurization, the "instantaneous", i.e. linear-elastic strain and stress distribution in the film show significantly higher values in the meridional direction. However, over time, and due to the biaxial visco-elastic stress relaxation of the the material, the hoop strains increase and the meridional stresses decrease, whereas the remaining strain and stress components remain substantially unchanged. These results are important for a correct assessment of the structural integrity of a pumpkin balloon in a long-duration mission, both in terms of the material performance and the overall stability of the shape of the balloon. An experimental investigation of the time dependence of the biaxial strain distribution in the film of a 4 m diameter, 48 gore pumpkin balloon is presented. The inflated shape of selected gores has been measured using photogrammetry and the time variation in strain components at some particular points of these gores has been measured under constant pressure and temperature. The results show good correlation with a numerical study, using the ABAQUS finite-element package, that includes a widely used model of the visco-elastic response of the gore material:

  12. SIMULATIONS OF MULTIPLE SOURCES IN BIAXIALLY STRESSED BOREHOLES: 2.5 DIMENSIONAL FINITE DIFFERENCE METHOD. (R825225)

    The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Concl...

  13. Effect of sandblasting and residual stress on strength of zirconia for restorative dentistry applications

    Kiran Chintapalli, Ravi; Mestra Rodríguez, Álvaro Miguel; García Marro, Fernando; Anglada Gomila, Marcos Juan

    2014-01-01

    Sandblasting is a commonly used surface treatment technique for dental crowns to improve the adhesion of the mating parts of a restoration. The goal of this work is to study the effect of different sandblasting conditions on the mechanical properties of 3 mol% yttria stabilized tetragonal zirconia (3Y-TZP), such as biaxial strength, surface elastic modulus, contact hardness and residual stresses induced by sandblasting. The specimens were sandblasted considering two different particle sizes (...

  14. Energetical and multiscale approaches for the definition of an equivalent stress for magneto-elastic couplings

    A main limitation of most models describing the effect of stress on the magnetic behavior is that they are restricted to uniaxial - tensile or compressive - stress. Nevertheless, stress is multiaxial in most of industrial applications. An idea to overcome the strong limitation of models is to define a fictive uniaxial stress, the equivalent stress, that would change the magnetic behavior in a similar manner than a multiaxial stress. A first definition of equivalent stress, called the deviatoric equivalent stress, is proposed. It is based on an equivalence in magneto-elastic energy. This formulation is first derived for isotropic materials under specific assumptions. An extension to orthotropic media under disoriented magneto-mechanical loading is made. A new equivalent stress expression, called generalized equivalent stress, is then proposed. It is based on an equivalence in magnetization. Inverse identification of equivalent stress is made possible thanks to a strong simplification of the description of the material seen as an assembly of elementary magnetic domains. It is shown that this second proposal is a generalization of the deviatoric expression. Equivalent stress proposals are compared to former proposals and validated using experimental results carried out on an iron-cobalt sheet submitted to biaxial mechanical loading. These results are compared to the predictions obtained thanks to the equivalent stress formulations. The generalized equivalent stress is shown to be a tool able to foresee the magnetic behavior of a large panel of materials submitted to multiaxial stress. - Research highlights: → Classical magneto-elastic models restricted to uniaxial stress. → Stress demonstrated multiaxial in most of industrial applications. → Proposals of deviatoric and generalized equivalent stresses - multidomain modeling. → Experimental validation using iron-cobalt sheet submitted to biaxial loading. → Generalization of former proposals and modeling of

  15. Residual stress and fracture of laminated ceramic membranes

    Bilayer laminated ceramic membranes were produced comprising a layer of gadolinia-doped ceria (CGO) 180 microm thick and a layer of yttria-stabilized zirconia (YSZ) 5 microm thick. The residual stresses in the laminates at room temperature were estimated from their curvature and the elastic constants of the individual layers. The fracture of the laminates was studied in biaxial flexure at 35 and 800 C. The mean failure stress in the CGO in the laminates was much greater than in unlaminated CGO. This is due partly to an improved microstructure from the lamination process and partly to the restraint of the compressively stressed YSZ. The combined effects of higher failure stress and residual stresses lead to the laminated membranes having higher apparent strength than single layer CGO membranes by factors of between 1.75 and 4.06

  16. Residual stresses in weld-clad reactor pressure vessel steel

    Cladding of low alloy nuclear reactor pressure vessel steel with austenitic stainless steel introduces in heavy section components high residual stresses which may cause microcrack formation in stress relief heat treatment. In this investigation an attempt is made to contribute to the solution of the stress relief cracking problem by determining quantitatively the magnitude and distribution of the residual stresses after cladding and after subsequent stress relief heat treatment. The distribution of residual stresses was determined on the basis of a combined experimental-mathematical procedure. Heavy section plate specimens of low alloy steel as base material were given an austenitic monolayer-cladding using the techniques of strip electrode and plasma hot wire cladding, respectively. A number of plates was stress relief heat treated. Starting from the cladded surface the thickness of the plates was reduced by subsequent removal of layers of material. The elastic strain reaction to the removal of each layer was measured by strain gauges. From the data obtained the biaxial residual stress distribution was computed as a function of thickness using relations which are derived for this particular case. In summary, lower residual stresses are caused by reduced thickness of the components. As the heat input, is decreased at identical base material thickness, the residual stresses are lowered also. The height of the tensile residual stress peak, however, remains approximataly constant. In stress relief annealed condition the residual stresses in the cladding are in tension; in the base material the residual stresses are negligibly small

  17. Dependence of electronic properties of germanium on the in-plane biaxial tensile strains

    The hybrid HSE06 functional with the spin–orbit coupling effects is used to calculate the habituation of the electronic properties of Ge on the (0 0 1), (1 1 1), (1 0 1) in-plane biaxial tensile strains (IPBTSs). Our motivation is to explore the nature of electronic properties of tensile-strained Ge on different substrate orientations. The calculated results demonstrate that one of the most effective and practical approaches for transforming Ge into a direct transition semiconductor is to introduce (0 0 1) IPBTS to Ge. At 2.3% (0 0 1) IPBTS, Ge becomes a direct bandgap semiconductor with 0.53 eV band gap, in good agreement with the previous theoretical and experimental results. We find that the (1 1 1) and (1 0 1) IPBTSs are not efficient since the shear strain and inner displacement of atoms introduced by them quickly decrease the indirect gap of Ge. By investigating the dependence of valence band spin–orbit splitting on strain, we prove that the dependency relationship and the coupled ways between the valence-band states of tensile-strained Ge are closely related to the symmetry of strain tensor, i.e., the symmetry of the substrate orientation. The first- and second-order coefficients describing the dependence of indirect gap, direct gap, the valence band spin–orbit coupling splitting, and heavy-hole–light-hole splitting of Ge on IPBTSs have been obtained by the least squares polynomial fitting. These coefficients are significant to quantitatively modulate the electronic properties of Ge by tensile strain and design tensile-strained Ge devices by semiconductor epitaxial technique

  18. Dependence of electronic properties of germanium on the in-plane biaxial tensile strains

    Yang, C.H. [State Key Laboratory of Information Photonics and Optical Communications, Beijing University of Posts and Telecommunications (BUPT), Beijing 100876 (China); Yu, Z.Y., E-mail: yuzhongyuan30@gmail.com [State Key Laboratory of Information Photonics and Optical Communications, Beijing University of Posts and Telecommunications (BUPT), Beijing 100876 (China); Liu, Y.M.; Lu, P.F. [State Key Laboratory of Information Photonics and Optical Communications, Beijing University of Posts and Telecommunications (BUPT), Beijing 100876 (China); Gao, T. [Institute of Atomic and Molecular Physics, Sichuan University, Chengdu 610065 (China); Li, M.; Manzoor, S. [State Key Laboratory of Information Photonics and Optical Communications, Beijing University of Posts and Telecommunications (BUPT), Beijing 100876 (China)

    2013-10-15

    The hybrid HSE06 functional with the spin–orbit coupling effects is used to calculate the habituation of the electronic properties of Ge on the (0 0 1), (1 1 1), (1 0 1) in-plane biaxial tensile strains (IPBTSs). Our motivation is to explore the nature of electronic properties of tensile-strained Ge on different substrate orientations. The calculated results demonstrate that one of the most effective and practical approaches for transforming Ge into a direct transition semiconductor is to introduce (0 0 1) IPBTS to Ge. At 2.3% (0 0 1) IPBTS, Ge becomes a direct bandgap semiconductor with 0.53 eV band gap, in good agreement with the previous theoretical and experimental results. We find that the (1 1 1) and (1 0 1) IPBTSs are not efficient since the shear strain and inner displacement of atoms introduced by them quickly decrease the indirect gap of Ge. By investigating the dependence of valence band spin–orbit splitting on strain, we prove that the dependency relationship and the coupled ways between the valence-band states of tensile-strained Ge are closely related to the symmetry of strain tensor, i.e., the symmetry of the substrate orientation. The first- and second-order coefficients describing the dependence of indirect gap, direct gap, the valence band spin–orbit coupling splitting, and heavy-hole–light-hole splitting of Ge on IPBTSs have been obtained by the least squares polynomial fitting. These coefficients are significant to quantitatively modulate the electronic properties of Ge by tensile strain and design tensile-strained Ge devices by semiconductor epitaxial technique.

  19. Development of a biaxial compression device for biological samples: preliminary experimental results for a closed cell foam.

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

    2009-07-01

    Biological tissues are subjected to complex loading states in vivo and in order to define constitutive equations that effectively simulate their mechanical behaviour under these loads, it is necessary to obtain data on the tissue's response to multiaxial loading. Single axis and shear testing of biological tissues is often carried out, but biaxial testing is less common. We sought to design and commission a biaxial compression testing device, capable of obtaining repeatable data for biological samples. The apparatus comprised a sealed stainless steel pressure vessel specifically designed such that a state of hydrostatic compression could be created on the test specimen while simultaneously unloading the sample along one axis with an equilibrating tensile pressure. Thus a state of equibiaxial compression was created perpendicular to the long axis of a rectangular sample. For the purpose of calibration and commissioning of the vessel, rectangular samples of closed cell ethylene vinyl acetate (EVA) foam were tested. Each sample was subjected to repeated loading, and nine separate biaxial experiments were carried out to a maximum pressure of 204 kPa (30 psi), with a relaxation time of two hours between them. Calibration testing demonstrated the force applied to the samples had a maximum error of 0.026 N (0.423% of maximum applied force). Under repeated loading, the foam sample demonstrated lower stiffness during the first load cycle. Following this cycle, an increased stiffness, repeatable response was observed with successive loading. While the experimental protocol was developed for EVA foam, preliminary results on this material suggest that this device may be capable of providing test data for biological tissue samples. The load response of the foam was characteristic of closed cell foams, with consolidation during the early loading cycles, then a repeatable load-displacement response upon repeated loading. The repeatability of the test results demonstrated the

  20. Development of a methodology for the assessment of shallow-flaw fracture in nuclear reactor pressure vessels: Generation of biaxial shallow-flaw fracture toughness data

    McAfee, W.J.; Bass, B.R.; Bryson, J.W.

    1998-07-01

    A technology to determine shallow-flaw fracture toughness of reactor pressure vessel (RPV) steels is being developed for application to the safety assessment of RPVs containing postulated shallow-surface flaws. Shallow-flaw fracture toughness of RPV material has been shown to be higher than that for deep flaws, because of the relaxation of crack-tip constraint. This report describes the preliminary test results for a series of cruciform specimens with a uniform depth surface flaw. These specimens are all of the same size with the same depth flaw. Temperature and biaxial load ratio are the independent variables. These tests demonstrated that biaxial loading could have a pronounced effect on shallow-flaw fracture toughness in the lower transition temperature region for RPV materials. Through that temperature range, the effect of full biaxial (1:1) loading on uniaxial, shallow-flaw toughness varied from no effect near the lower shelf to a reduction of approximately 58% at higher temperatures.

  1. Biaxial bending of slender hsc columns and tubes filled with concrete under short- and long-term loads: ii) verification

    Rodríguez-Gutiérrez, Jose A.; ARISTIZABAL-OCHOA, JOSE DARIO

    2014-01-01

    An analytical method that calculates both the short- and long-term response of slender columns made of high-strength concrete (HSC) and of tubes filled with concrete with generalized end conditions that are subjected to transverse loads along the span and to axial loads at the ends (causing single- or double-curvature under uniaxial or biaxial bending) is presented in a companion paper. The columns that can be analyzed with this method include those with solid and hollow rectangular, circular...

  2. Catalytic surface modification of roll-milled poly(ε-caprolactone) biaxially stretched to ultra-thin dimension

    A novel roll-milling polymer processing technique along with biaxial stretching was used to fabricate 10 μm thick poly(ε-caprolactone) films. A less invasive collagen surface modification was used, involving a reaction between corona-preactivated membranes and ferrous-containing acrylic acid solution at the low temperature of 42 oC. Successful modified films were characterized by Toluidine Blue O assay and X-ray photoelectron spectroscopy. Human umbilical vein endothelial cells also showed both higher proliferation rate and differentiated cobblestone morphology on these collagen-immobilized substrates

  3. Catalytic surface modification of roll-milled poly({epsilon}-caprolactone) biaxially stretched to ultra-thin dimension

    Foo, H.L. [Graduate Programme in Bioengineering, National University of Singapore (Singapore); Bionic Materials Technology Group, Biomaterials Center, National Institute for Materials Science (Japan); Taniguchi, A. [Bionic Materials Technology Group, Biomaterials Center, National Institute for Materials Science (Japan); Yu, H. [Graduate Programme in Bioengineering, National University of Singapore (Singapore); Department of Physiology, National University of Singapore (Singapore); Okano, T. [Bionic Materials Technology Group, Biomaterials Center, National Institute for Materials Science (Japan); Institute of Biomedical Engineering, Tokyo Women' s Medical University (Japan); Teoh, S.H. [Graduate Programme in Bioengineering, National University of Singapore (Singapore) and Department of Mechanical Engineering, National University of Singapore (Singapore)]. E-mail: mpetsh@nus.edu.sg

    2007-03-15

    A novel roll-milling polymer processing technique along with biaxial stretching was used to fabricate 10 {mu}m thick poly({epsilon}-caprolactone) films. A less invasive collagen surface modification was used, involving a reaction between corona-preactivated membranes and ferrous-containing acrylic acid solution at the low temperature of 42 {sup o}C. Successful modified films were characterized by Toluidine Blue O assay and X-ray photoelectron spectroscopy. Human umbilical vein endothelial cells also showed both higher proliferation rate and differentiated cobblestone morphology on these collagen-immobilized substrates.

  4. Limit load solution for an edge cracked plate under combined independent bi-axial membrane and bending

    A limit load solution for an edge cracked plate that includes any combination of biaxial bending and membrane loading is developed in the study. This solution will then be compared to the solution within the Miller Compendium and that obtained from Finite Element (FE) analyses. The solutions applicability to a cylinder will also be considered through the use of FE modeling. Through these comparisons it is hoped that the derived limit load solution can be validated and guidance for its applicability to a cylinder provided

  5. Biaxial Strain in the Hexagonal Plane of MnAs Thin Films: The Key to Stabilize Ferromagnetism to Higher Temperature

    Garcia, V.; Sidis, Y.; Marangolo, M.; Vidal, F.; Eddrief, M; Bourges, P.; Maccherozzi, F.; Ott, F.; Panaccione, G.; Etgens, V. H.

    2007-01-01

    The alpha-beta magneto-structural phase transition in MnAs/GaAs(111) epilayers is investigated by elastic neutron scattering. The in-plane parameter of MnAs remains almost constant with temperature from 100 K to 420 K, following the thermal evolution of the GaAs substrate. This induces a temperature dependent biaxial strain that is responsible for an alpha-beta phase coexistence and, more important, for the stabilization of the ferromagnetic alpha-phase at higher temperature than in bulk. We ...

  6. Modification of valence-band symmetry and Auger threshold energy in biaxially compressed InAs1-xSbx

    Strained-layer superlattices (SLS's) with biaxially compressed InAs1-xSbx were characterized using magnetophotoluminescence and compared with unstrained InAs1-xSbx alloys. Holes in the SLS exhibited a decrease in effective mass, approaching that of the electrons. In the two-dimensional limit, a large increase in the Auger threshold energy accompanies this strain-induced change in SLS valence-band symmetry. Correspondingly, the activation energy for nonradiative recombination in the SLS's displayed a marked increase compared with that of the unstrained alloys. Strained-layer superlattices and alloy activation energies are in agreement with estimated Auger threshold energies

  7. Polarization properties of lasing near an optical axis in the KGd(WO4)2:Nd biaxial crystal

    Fluorescence and stimulated emission were obtained for propagation directions in the vicinity of the optical axis from the biaxial Nd-doped KGd(WO4)2 crystal. We visualized the peculiar role of the optical axis by fluorescence conoscopy. A fourth spectroscopic parameter due to the monoclinic symmetry was exhibited. Intra-laser-cavity conoscopy was performed in conjunction with the lasing in order to indicate the role of the elliptical modes. The lasing efficiency was found to be in agreement with the relative intensity of the left and right circular polarized components of the fluorescence near the optical axis. (letter)

  8. Active-flux based motion sensorless vector control of biaxial excitation generator/motor for automobiles (BEGA)

    Coroban-Schramel, Vasile; Boldea, Ion; Andreescu, Gheorghe-Daniel;

    2009-01-01

    the active-flux concept the estimated rotor position is given by the sum of the active flux angle and torque angle. The active flux is calculated by subtracting the term Lq i s from the estimated stator flux vector. The experimental results validate the active flux-principle and show good performance......This paper proposes a novel, active-flux based, motion-sensorless vector control structure for biaxial excitation generator for automobiles (BEGA) for wide speed range operation. BEGA is a hybrid excited synchronous machine having permanent magnets on q-axis and a dc excitation on daxis. Using...

  9. Tuning of the electronic and optical properties of single-layer indium nitride by strain and stress

    Jalilian, Jaafar; Naseri, Mosayeb; Safari, Shima; Zarei, Mina

    2016-09-01

    Using first principles calculations, electronic and optical properties of indium nitride graphene-like structure have been studied under various stress and strain values. The results exhibit that this compound in the range of ±6 applied biaxial strain remains a direct band gap semiconductor. Also, exerting stress and strain reduces the energy band gap of the considered materials. The optical calculations illustrate that applying stress and strain on system results in blue and red shift in optical spectra. All obtained results presented that we can tune the optoelectronic properties of indium nitride by applying stress and strain.

  10. Enhanced carrier mobility and direct tunneling probability of biaxially strained Ge{sub 1−x}Sn{sub x} alloys for field-effect transistors applications

    Liu, Lei; Liang, Renrong, E-mail: liangrr@tsinghua.edu.cn, E-mail: junxu@tsinghua.edu.cn; Wang, Jing; Xu, Jun, E-mail: liangrr@tsinghua.edu.cn, E-mail: junxu@tsinghua.edu.cn [Tsinghua National Laboratory for Information Science and Technology, Institute of Microelectronics, Tsinghua University, Beijing 100084 (China)

    2015-05-14

    The carrier transport and tunneling capabilities of biaxially strained Ge{sub 1−x}Sn{sub x} alloys with (001), (110), and (111) orientations were comprehensively investigated and compared. The electron band structures of biaxially strained Ge{sub 1−x}Sn{sub x} alloys were calculated by the nonlocal empirical pseudopotential method and the modified virtual crystal approximation was adopted in the calculation. The electron and hole effective masses at the band edges were extracted using a parabolic line fit. It is shown that the applied biaxial strain and the high Sn composition are both helpful for the reduction of carrier effective masses, which leads to the enhanced carrier mobility and the boosted direct band-to-band-tunneling probability. Furthermore, the strain induced valance band splitting reduces the hole interband scattering, and the splitting also results in the significantly enhanced direct tunneling rate along the out-of-plane direction compared with that along the in-plane direction. The biaxially strained (111) Ge{sub 1−x}Sn{sub x} alloys exhibit the smallest band gaps compared with (001) and (110) orientations, leading to the highest in-plane and out-of-plane direct tunneling probabilities. The small effective masses on (110) and (111) planes in some strained conditions also contribute to the enhanced carrier mobility and tunneling probability. Therefore, the biaxially strained (110) and (111) Ge{sub 1−x}Sn{sub x} alloys have the potential to outperform the corresponding (001) Ge{sub 1−x}Sn{sub x} devices. It is important to optimize the applied biaxial strain, the Sn composition, and the substrate orientation for the design of high performance Ge{sub 1−x}Sn{sub x} field-effect transistors.

  11. Biaxially oriented CdTe films on glass substrate through nanostructured Ge/CaF2 buffer layers

    Lord, R. J.; Su, P.-Y.; Bhat, I.; Zhang, S. B.; Lu, T.-M.; Wang, G.-C.

    2015-09-01

    Heteroepitaxial CdTe films were grown by metal organic chemical vapor deposition on glass substrates through nanostructured Ge/CaF2 buffer layers which were biaxially oriented. It allows us to explore the structural properties of multilayer biaxial semiconductor films which possess small angle grain boundaries and to test the principle of a solar cell made of such low-cost, low-growth-temperature semiconductor films. Through the x-ray diffraction and x-ray pole figure analysis, the heteroepitaxial relationships of the mutilayered films are determined as [111] in the out-of-plane direction and CdTe//Ge//{ }{{{CaF}}2} in the in-plane direction. The I-V curves measured from an ITO/CdS/CdTe/Ge/CaF2/glass solar cell test structure shows a power conversion efficiency of ˜η = 1.26%, illustrating the initial success of such an approach. The observed non-ideal efficiency is believed to be due to a low shunt resistance and high series resistance as well as some residual large-angle grain boundary effects, leaving room for significant further improvement.

  12. BiTEP (biaxially textured electroplating): A novel route for making improved coated conductors, based on a well established technique

    We present a new technique for the deposition of Ni on cube textured Ni alloy substrates. It is superior to the commonly used PVD and CVD coating methods and easy to scale up from the laboratory to an industrial long length process. The new route, called 'BiTEP' (biaxially textured electroplating), where biaxially textured Ni alloy substrates are electrolytically plated with Ni, is shown to lead to an outstanding transfer of the texture from the substrate to the pure Ni layer. Several platings from 130 nm to 1.5 μm thickness were made on Ni96W4, Ni87Cr6.5W6.5 and Ni90Cr10 substrates, applying different current densities during electroplating, from 0.2 to 2 A dm-2. All investigated samples showed epitaxy between the substrates and the Ni film, independent of the layer thickness, the current density used for electroplating, and the substrate material. In Ni-W substrate tapes a sharp cube recrystallization texture with FWHM (111) of -2 (77 K, self-field) in YBCO. Furthermore, commercially available constantan (Ni 44.4 wt%, Cu 54.19 wt%, the rest: Mn, Fe) from our partner ThyssenKrupp VDM was investigated

  13. Synthesis, structuring and characterization of rare earth oxide thin films: Modeling of the effects of stress and defects on the phase stability

    This work studies the effects of the deposition parameters on the microstructure and the related residual stress in a rare earth oxide thin film. This study is focused on the yttrium sesquioxide (Y2O3) thin films deposited on Si (100) substrates using the ion beam sputtering technique. This technique allows the control of the microstructure and the related residual stress in the thin films by monitoring the energy of the argon beam used in the deposition process. Measurements of the stresses within the oxide layer were performed by the X-ray diffraction-sin2Ψ method. The results show that the classic model of a pure biaxial in-plane model of stress, generally proposed in thin films, is not satisfying. A model that includes a hydrostatic stress due to the crystalline defects generated during the deposition process and a biaxial stress called a fixation stress, gives a good agreement with the experimental results. This modeling of the residual stress, based on nanometer-scale inclusions (point, extended defects) inducing a hydrostatic stress field, leads to a quantitative analysis of the nature and the concentration of the defects. This work shows results that establish a relationship between residual stress, defects and non-equilibrium phase stabilization during growth. - Highlights: • Microstructure of Y2O3 thin films • Measurements of residual stresses in the thin films • Modeling of a triaxial residual stress state • Stress-induced stabilization of non-equilibrium phase

  14. Effect of external stress on phase diagrams and dielectric properties of epitaxial ferroelectric thin films grown on orthorhombic substrates

    L(U) Ye-gang; DENG Shui-feng; GONG Lun-jun; YANG Jian-tao

    2006-01-01

    A Landau-Ginsburg-Devonshire(LD)-type thermodynamic theory was used to describe the effect of external stress on phase diagrams and dielectric properties of epitaxial ferroelectric thin films grown on orthorhombic substrates which induce nonequally biaxial misfit strains in the films plane. The "misfit strain-external stress" and "external stress-temperature" phase diagrams were constructed for single-domain BaTiO3(BT) and PbTiO3(PT) thin films. It is shown that the external stress may lead to the rotation of the spontaneous polarization and a gradual change of its magnitude, which may result in phase transition. Nonequally biaxial misfit strains dependence of the stability of polarization states may be governed by external stress. At room temperature,stress-induced ferroelectric/paraelectric phase transition which occurs in film on cubic substrate does not take place in the ferroelectric thin film grown on orthorhombic substrate. It is also shown that the nonequally misfit strains in the film plane may lead to the appearance of new phases which do not form in films grown on cubic substrates under external stress. The dependence of the dielectric response on the external stress is also studied. It is shown that the dielectric constants of single-domain PT and BT films are very sensitive to the external stress under the given anisotropic misfit strains-temperature conditions. It presents theoretical evidence that the external stress and anisotropic misfit strains can be employed for improving the thin films physical properties.

  15. Reduction of initial stress stiffening by topology optimization

    Philippine, M. A.; Sigmund, Ole; Rebeiz, G. M.;

    2012-01-01

    Topology optimization is a rigorous method of obtaining non-intuitive designs. We use it to obtain a capacitive RF switch that stiffens little in response to an increase of the in-plane biaxial stresses that typically develop during MEMS fabrication. The actuation voltage is closely related to the...... membrane's stiffness, and is more stable for a stress insensitive switch. We employ the Solid Isotropic Material with Penalization (SIMP) method with the Method of Moving Asymptotes (MMA) and a robust formulation to minimize the ratio between the compliance at a low stress level and that at a high stress...... level. We include a volume constraint and a compliance constraint. Topology optimized designs are compared to an intuitively-designed RF switch. The switches contain similar features. The compliance constraint is varied such that the topology optimized switch performance approaches the intuitively...

  16. Analysis of rock stress and rock stress measurements with application to Aespoe HRL

    the opening where no influence from the openings can be expected. Since the magnitudes of the rock stresses differ between overcoring and hydraulic fracturing, some efforts have been made to find possible causes for this. The rock stresses when conducting overcoring gave higher values overall, which could be explained by high Poisson's ratios and a minor influence from the opening as the stress measurements might have been done in the disturbed zone. The high Poisson's ratio may depend on the stress-induced microcracks, which might be initiated during the overcoring of the cell, during the drilling of the pilot borehole, in which the cell is installed, and during biaxial testing. Statistical analysis showed that there is significant differences between the mean values of Poisson's ratio obtained from biaxial tests of cores containing the CSIRO HI-cell and the SSPB-cell. Poisson's ratio is about 0.34 for CSIRO HI-cell while the SSPB-cell gave a Poisson's ratio of 0.23. The analysis also showed that Young's modulus does not differ between the techniques. The modelling in FLAC was made to simulate the overcoring and biaxial testing. The result show that it is possible to obtain extensional strain in the core during overcoring if the major principal stress is perpendicular to the borehole axis. This may lead to microcracking occurring in the core causing high Poisson's ratio, which results in higher stresses. It can also be seen from the simulation of the biaxial testing that extensional strain is achieved even if the hollow core is not damaged during overcoring. The analyses using UDEC was made to study the effect of different properties of a discontinuity, such as the dip angle, Young's modulus, Poisson's ratio, density and the normal and shear stiffness. The analyses showed that an inclined discontinuity affects the stresses especially if sliding occurs. So, the dip angle does not solely, determine the amount of disturbance of the state of stress around a discontinuity

  17. First- and second-order phase transitions between quantum and classical regimes for the escape rate of a biaxial spin system

    Kim, G H

    1999-01-01

    The particle Hamiltonian for a biaxial spin system with a transverse or longitudinal magnetic field is investigated. We apply the Hamiltonian to the quantum-classical escape rate transition in small magnets. It is found that the phase boundary separating the first- and second-order transition is greatly influenced by the transverse anisotropy constant as well as the external magnetic field.

  18. Effects of Interphase Modification and Biaxial Orientation on Dielectric Properties of Poly(ethylene terephthalate)/Poly(vinylidene fluoride-co-hexafluoropropylene) Multilayer Films.

    Yin, Kezhen; Zhou, Zheng; Schuele, Donald E; Wolak, Mason; Zhu, Lei; Baer, Eric

    2016-06-01

    Recently, poly(vinylidene fluoride) (PVDF)-based multilayer films have demonstrated enhanced dielectric properties, combining high energy density and high dielectric breakdown strength from the component polymers. In this work, further enhanced dielectric properties were achieved through interface/interphase modulation and biaxial orientation for the poly(ethylene terephthalate)/poly(methyl methacrylate)/poly(vinylidene fluoride-co-hexafluoropropylene) [PET/PMMA/P(VDF-HFP)] three-component multilayer films. Because PMMA is miscible with P(VDF-HFP) and compatible with PET, the interfacial adhesion between PET and P(VDF-HFP) layers should be improved. Biaxial stretching of the as-extruded multilayer films induced formation of highly oriented fibrillar crystals in both P(VDF-HFP) and PET, resulting in improved dielectric properties with respect to the unstretched films. First, the parallel orientation of PVDF crystals reduced the dielectric loss from the αc relaxation in α crystals. Second, biaxial stretching constrained the amorphous phase in P(VDF-HFP) and thus the migrational loss from impurity ions was reduced. Third, biaxial stretching induced a significant amount of rigid amorphous phase in PET, further enhancing the breakdown strength of multilayer films. Due to the synergistic effects of improved interfacial adhesion and biaxial orientation, the PET/PMMA/P(VDF-HFP) 65-layer films with 8 vol % PMMA exhibited optimal dielectric properties with an energy density of 17.4 J/cm(3) at breakdown and the lowest dielectric loss. These three-component multilayer films are promising for future high-energy-density film capacitor applications. PMID:27163929

  19. Stress Management

    ... Awards Healthy Workplace Food and Beverage Toolkit Stress Management Banner 1 - To Stress or Not to Stress - ... Decide But We Can Help What Is Stress Management? Banner 2 - Stress Continuum Graphic Banner Live life ...

  20. Childhood Stress

    ... 5 Things to Know About Zika & Pregnancy Childhood Stress KidsHealth > For Parents > Childhood Stress Print A A ... and feel stress to some degree. Sources of Stress Stress is a function of the demands placed ...

  1. Influence of reversible epitactical stress on the electronic properties of thin superconducting films

    In this thesis new stress techniques are applied on thin superconducting (La,Sr)2CuO4 and BaFe1.8Co0.2As2 films. At one hand piezoelectric substrates are applied, which make a biaxial stress of the thin film deposed there possible, whereby the lattice parameters of the substrate are altered by an electric field. At the other hand on the base of flexible substrates by means of a bending experiment a uniaxial lattice deformation of thin film is realized.

  2. Ion-beam assisted deposition of MgO with in situ RHEED monitoring to control Bi-axial texture

    Arendt, P. N. (Paul N.); Foltyn, S. R. (Stephen R.); Jia, Quanxi; DePaula, R. F. (Raymond Felix); Dowden, P. C. (Paul C.); Kung, H. (Harriett); Holesinger, T. G. (Terry G.); Stan, L. (Liliana); Emmert, L. A. (Luke A.); Peterson, E. J. (Eric J.); Groves, J. R. (James R.)

    2001-01-01

    We have studied the growth of magnesium oxide using ion-beam assisted deposition (IBAD) to achieve (100) oriented, bi-axially textured films with low mosaic spread, for film thicknesses of 10 nm on silicon substrates. We have refined the process by using reflected high-energy electron diffraction (RHEED) to monitor the growth of IBAD MgO films and found that the diffracted intensity can be used to determine (and ultimately control) final in-plane texture of the film. Here we present results on our work to develop the use of real-time RHEED monitoring to deposit well-oriented IBAD MgO films. The results have been corroborated with extensive grazing-incidence X-ray diffraction (GID). Results of these analyses have allowed us to deposit films on metallic substrates with in-plane mosaic spread less than 7{sup o}.

  3. Self-field ac losses in biaxially aligned Y endash Ba endash Cu endash O tape conductors

    Self-field ac losses were measured by the conventional ac four-probe method in biaxially aligned Y endash Ba endash Cu endash O tapes using polycrystalline Hastelloy tapes with textured yttria-stabilized-zirconia buffer layers. The ac losses increased in proportion to the fourth power of transport current in the high Jc sample, and agreed well with Norris close-quote equation for thin strip conductors. However, the low Jc sample had rather higher losses than Norris close-quote prediction, suggesting excessive magnetic flux penetration caused by percolated current paths. The results confirmed Norris close-quote prediction of the low ac losses for thin strip conductors, and indicated the importance of removing percolated structures of current paths to avoid higher ac losses than the theoretical predictions based on uniform conductors. copyright 1997 American Institute of Physics

  4. Study of the growth of biaxially textured CeO2 films during ion-beam-assisted deposition

    Biaxially textured CeO2 films were deposited on Hastelloy C276 substrates at room temperature using ion-beam-assisted e-beam evaporation with the ion beam directed at 55 deg. to the normal of the film plane. The crystalline structure and in-plane orientation of films were investigated by x-ray diffraction 2θ-scan and φ-scan. The orientation of the films was studied as a function of ion-to-atom ratio and film thickness. The ion-to-atom ratio was varied by independently adjusting the deposition rate and the ion current density. Under optimum condition, (200) textured CeO2 films have been successfully grown on Hastelloy C276

  5. Study of the growth of biaxially textured CeO{sub 2} films during ion-beam-assisted deposition

    Kim, Chang Su [Department of Metallurgical Engineering, Yonsei University, Seodaemoon Ku, Shinchon Dong 134, Seoul 120-749 (Korea, Republic of); Jo, Sung Jin [Department of Metallurgical Engineering, Yonsei University, Seodaemoon Ku, Shinchon Dong 134, Seoul 120-749 (Korea, Republic of); Jeong, Soon Moon [Department of Metallurgical Engineering, Yonsei University, Seodaemoon Ku, Shinchon Dong 134, Seoul 120-749 (Korea, Republic of); Kim, Woo Jin [Department of Metallurgical Engineering, Yonsei University, Seodaemoon Ku, Shinchon Dong 134, Seoul 120-749 (Korea, Republic of); Baik, Hong Koo [Department of Metallurgical Engineering, Yonsei University, Seodaemoon Ku, Shinchon Dong 134, Seoul 120-749 (Korea, Republic of); Lee, Se Jong [Department of Materials Science and Engineering, Kyungsung University, Busan 608-736 (Korea, Republic of); Song, Kie Moon [Department of Applied Physics, Konkuk University, Chungju 380-701 (Korea, Republic of)

    2005-03-01

    Biaxially textured CeO{sub 2} films were deposited on Hastelloy C276 substrates at room temperature using ion-beam-assisted e-beam evaporation with the ion beam directed at 55 deg. to the normal of the film plane. The crystalline structure and in-plane orientation of films were investigated by x-ray diffraction 2{theta}-scan and {phi}-scan. The orientation of the films was studied as a function of ion-to-atom ratio and film thickness. The ion-to-atom ratio was varied by independently adjusting the deposition rate and the ion current density. Under optimum condition, (200) textured CeO{sub 2} films have been successfully grown on Hastelloy C276.

  6. Study of the growth of biaxially textured CeO2 films during ion-beam-assisted deposition

    Kim, Chang Su; Jo, Sung Jin; Jeong, Soon Moon; Kim, Woo Jin; Baik, Hong Koo; Lee, Se Jong; Song, Kie Moon

    2005-03-01

    Biaxially textured CeO2 films were deposited on Hastelloy C276 substrates at room temperature using ion-beam-assisted e-beam evaporation with the ion beam directed at 55° to the normal of the film plane. The crystalline structure and in-plane orientation of films were investigated by x-ray diffraction 2θ-scan and phgr-scan. The orientation of the films was studied as a function of ion-to-atom ratio and film thickness. The ion-to-atom ratio was varied by independently adjusting the deposition rate and the ion current density. Under optimum condition, (200) textured CeO2 films have been successfully grown on Hastelloy C276.

  7. Uniaxial and biaxial ratchetting study of SA333 Gr.6 steel at room temperature

    The phenomenon of ratchetting is defined as constant accumulation of plastic strain or deformation under combined steady state and cyclic loading. It can reduce the fatigue life or can cause failure of piping components or systems subjected to seismic or other cyclic loads. The uniaxial ratchetting characteristics of SA333 Gr.6 steel have been investigated at room temperature in the present paper. The specimens were subjected to cyclic axial stress with a constant mean stress of 200 MPa and a varying amplitude stress of 149, 174, 199 and 224 MPa. Tests were also performed on 203.2 mm, Sch 80, SA333 Gr. 6 carbon steel straight pipe. The pipe was subjected to a constant internal pressure of 18 MPa and a cyclic bending load. The effects of amplitude of load on the rate of ratchetting have also been investigated in the present paper. The uniaxial experiments showed that specimens exhibited shakedown at low stress amplitude after some strain accumulation. However, specimens experienced continuous ratchetting at higher stress amplitudes with no shakedown before failure. Ovalization of the pipe cross-section was observed when the pipe was subjected to constant internal pressure and cyclic point load. Local bulging was observed at higher loading. The pipe did not show any shakedown behaviour for the given cycles of loading and exhibited continuous ratchetting under the varying amplitude loading

  8. Failure mechanics of fiber composite notched charpy specimens. [stress analysis

    Chamis, C. C.

    1976-01-01

    A finite element stress analysis was performed to determine the stress variation in the vicinity of the notch and far field of fiber composites Charpy specimens (ASTM Standard). NASTRAN was used for the finite element analysis assuming linear behavior and equivalent static load. The unidirectional composites investigated ranged from Thornel 75 Epoxy to S-Glass/Epoxy with the fiber direction parallel to the long dimension of the specimen. The results indicate a biaxial stress state exists in (1) the notch vicinity which is dominated by transverse tensile and interlaminar shear and (2) near the load application point which is dominated by transverse compression and interlaminar shear. The results also lead to the postulation of hypotheses for the predominant failure modes, the fracture initiation, and the fracture process. Finally, the results indicate that the notched Charpy test specimen is not suitable for assessing the impact resistance of nonmetallic fiber composites directly.

  9. Ferromagnetic resonance in thin films submitted to multiaxial stress state: application of the uniaxial equivalent stress concept and experimental validation

    Gueye, M.; Zighem, F.; Belmeguenai, M.; Gabor, M.; Tiusan, C.; Faurie, D.

    2016-07-01

    In this paper a unique expression of the anisotropy field induced by any multiaxial stress state in a magnetic thin film and probed by ferromagnetic resonance is derived. This analytical development has been made using the uniaxial equivalent stress concept, for which correspondances between definitions given by different authors in the literature is found. The proposed model for the anisotropy field has been applied to \\text{C}{{\\text{o}}2}\\text{FeAl} thin films (25 nm) stressed both by piezoelectric actuation (non-equi-biaxial) or by bending tests (uniaxial) and measured with a broadband ferromagnetic resonance technique. The overall exprimental data can be easily plotted on a unique graph from which the magnetostriction coefficient has been estimated.

  10. Manage Stress

    ... Manage Stress Print This Topic En español Manage Stress Browse Sections The Basics Overview Signs and Health ... of 9 sections The Basics: Benefits of Lower Stress What are the benefits of managing stress? Over ...

  11. Manage Stress

    ... Manage Stress Print This Topic En español Manage Stress Browse Sections The Basics Overview Signs and Health ... and Health Effects What are the signs of stress? When people are under stress, they may feel: ...

  12. Lattice strain development in Inconel-690 under bi-axial compression and tension

    Toda, Rebecca Midori

    Nuclear reactor steam generator tubes, manufactured from Nickel alloys such as Inconel 690 (INC690), are potentially susceptible to failure by Stress Corrosion Cracking where crack initiation may be exacerbated by internal stress fields. A more comprehensive understanding of this potential failure mechanism was gained via an exploration of a model of INC690.s behaviour under Constrained loading conditions in compression and tension. An Elasto-Plastic Self-Consistent (EPSC) model was used to predict the lattice stresses and strains resulting from Constrained loading in INC690 for four crystallographic planes. The internal strain fields generated under such conditions were shown to be markedly different from those developed under Uniaxial loading. Finite Element Modeling was used to design tensile and compression samples as well as a testing rig that would allow the application of a compressive load along one axis of the specimen with simultaneous constraint along another and free-deformation along the third. Lattice strain measurements were done for both compressive and tensile loading using Time-Of-Flight neutron diffraction. The predicted and experimental values showed reasonable agreement; mainly in terms of crystallographic plane interaction and behaviour. Iterative computer modeling was used to achieve a more realistic depiction of the lattice strains developed. This research allowed for an extension on the Uniaxial findings by examining the material's behaviour under more complex loading that better approximates steam generator tube operating conditions.

  13. Fracture energy of stick-slip events in a large scale biaxial experiment

    The concept of apparent fracture energy for the shear failure process is employed by many authors in modeling earthquake sources as dynamically extending shear cracks. Using records of shear strain and relative displacement from stick-slip events generated along a simulated, prepared fault surface in a large (1.5m x 1.5m x 0.4m) granite block and a slip-weakening model for the fault, direct estimates of the apparent shear fracture energy of the stick-slip events have been obtained. For events generated on a finely ground fault surface, apparent fracture energy ranges from 0.06 J/m2 at a normal stress of 1.1 MPa to 0.8 J/m2 at a normal stress of 4.6 MPa. In contrast to estimates for tensile crack formation, we find that the apparent fracture energy of stick-slip events increases linearly with normal stress. The results for the slip-weakening model for the stick-slip events are generally consistent with constitutive fault models suggested by observations of stable sliding in smaller scale experiments

  14. Polarization Manipulation via Orientation Control in Polycrystalline BiFeO3 Thin Films on Biaxially Textured, Flexible Metallic Tapes

    Shin, Junsoo [ORNL; Goyal, Amit [ORNL; Jesse, Stephen [ORNL; Heatherly Jr, Lee [ORNL

    2011-01-01

    (111)-, (101)-, and (001)-oriented polycrystalline BiFeO3 films were fabricated on rolling-assisted biaxially textured substrates (RABiTS) with appropriate, buffer layer engineering of heteroepitaxially grown buffer multilayers on RABiTS. The crystallographic orientation and polarization direction were confirmed using X-ray diffraction and piezoresponse force microscopy (PFM), respectively. All the films exhibited excellent ferroelectric properties. Switching spectroscopy PFM demonstrated that the switching polarization in (111)-oriented polycrystalline BiFeO3 films is higher than (101) or (001) oriented films. These high-quality, BiFeO3 films on low-cost, flexible, biaxially textured metallic tapes with controllable orientation and polarization are attractive for application in flexible ferroelectric devices.

  15. Biaxial order and a rotation of the minor director in the nematic phase of an organo-siloxane tetrapode by the electric field

    Merkel, K.; Nagaraj, M.; Kocot, A.; Kohlmeier, A.; Mehl, G. H.; Vij, J. K.

    2012-03-01

    Biaxiality in the nematic phase for a liquid crystalline tetrapode made up of organo-siloxanes mesogens is investigated using polarized infrared spectroscopy. An ordering of the minor director for the homeotropically aligned sample is found to depend on the amplitude of the in-plane electric field. On increasing the in-plane electric field, the minor director, lying initially along the rubbing direction, rotates to the direction of the applied field. The scalar order parameters of the second rank tensor are found to depend significantly on the strength of the electric field. A most significant increase is found in the nematic order parameter and in the parameter that characterizes the phase biaxiality.

  16. Effect of biaxial strain and external electric field on electronic properties of MoS2 monolayer: A first-principle study

    Nguyen, Chuong V.; Hieu, Nguyen N.

    2016-04-01

    In this work, making use of density functional theory (DFT) computations, we systematically investigate the effect of biaxial strain engineering and external electric field applied perpendicular to the layers on the band gaps and electronic properties of monolayer MoS2. The direct-to-indirect band gaps and semiconductor-to-metal transition are observed in monolayer MoS2 when strain and electric field are applied in our calculation. We show that when the biaxial strain and external electric field are introduced, the electronic properties including band gaps of monolayer MoS2 can be reduced to zero. Our results provide many useful insights for the wide applications of monolayer MoS2 in electronics and optoelectronics.

  17. Nonorthogonal [Formula: see text] tight-binding parameterization of single-layer phosphorene under biaxial strain and application to FETs.

    Lee, Jaehyun; Seo, Jumbeom; Oh, Jung Hyun; Shin, Mincheol

    2016-06-17

    This paper presents a new set of [Formula: see text] tight-binding (TB) parameters for single-layer phosphorene within the Naval Research Laboratory (NRL) scheme. For this, we develop the numerical algorithm to find the NRL TB parameters fitted to ab initio results. It is shown that the proposed NRL TB parameters successfully reproduce the band structure of a single-layer phosphorene, and even under biaxial or uniaxial strain, they appropriately describe the effects, such as modification of anisotropic effective masses and band gap. Via the top-of-the-barrier model, we also investigate the performance of single-layer phosphorene FETs under biaxial strain with the NRL TB Hamiltonian and find that the results are well in accordance with those of previous studies. PMID:27159924

  18. Spin-to-orbital angular momentum conversion for Bessel beams propagating along the optical axes of homogeneous uniaxial and biaxial crystals

    A study is made of the dynamics of the spin-to-orbital angular momentum conversion for zero-order and high order circularly polarized Bessel beams propagating along the optical axes of homogeneous uniaxial and biaxial crystals. Implementation of Bessel beams and a slab of homogeneous uniaxial crystal allow one to realize a highly efficient (about 100%) optical process in which the direct conversion of the optical angular momentum from the spin form to the orbital form takes place. It is shown that only in a biaxial crystal is there freedom from compensation of spin and orbital angular momentum exchanges with matter and, as a result, the optical torque emerges, which influences the plate. (paper)

  19. Nonorthogonal {{sp}}^{3}{{d}}^{5} tight-binding parameterization of single-layer phosphorene under biaxial strain and application to FETs

    Lee, Jaehyun; Seo, Jumbeom; Oh, Jung Hyun; Shin, Mincheol

    2016-06-01

    This paper presents a new set of {{sp}}3{{d}}5 tight-binding (TB) parameters for single-layer phosphorene within the Naval Research Laboratory (NRL) scheme. For this, we develop the numerical algorithm to find the NRL TB parameters fitted to ab initio results. It is shown that the proposed NRL TB parameters successfully reproduce the band structure of a single-layer phosphorene, and even under biaxial or uniaxial strain, they appropriately describe the effects, such as modification of anisotropic effective masses and band gap. Via the top-of-the-barrier model, we also investigate the performance of single-layer phosphorene FETs under biaxial strain with the NRL TB Hamiltonian and find that the results are well in accordance with those of previous studies.

  20. High-performance poly-Si thin film transistors with highly biaxially oriented poly-Si thin films using double line beam continuous-wave laser lateral crystallization

    Yamano, Masayuki; Kuroki, Shin-Ichiro; Sato, Tadashi; Kotani, Koji

    2014-01-01

    Highly biaxially oriented poly-Si thin films were formed by double-line beam continuous-wave laser lateral crystallization (DLB-CLC). The crystallinities of the DLB-CLC poly-Si thin films were (110), (111), and (211) for the laser scan, transverse, and surface directions, respectively, and an energetically stable Σ3 grain boundary was observed to be dominant. All silicon grains were elongated in the laser scan direction and one-dimensionally very large silicon grains with lengths of more than 100 µm were fabricated. Using these biaxially oriented polycrystalline silicon (poly-Si) films, low-temperature poly-Si TFTs (LTPS-TFTs) were fabricated at low temperatures (≦550 °C) by a metal gate self-aligned process. As a result, a TFT with a high electron field effect mobility of μFE = 450 cm2 V-1 s-1 in a linear region was realized.

  1. High critical current density superconducting tapes by epitaxial deposition of YBa2Cu3Ox thick films on biaxially textured metals

    A method to obtain long lengths of flexible, biaxially oriented substrates with smooth, chemically compatible surfaces for epitaxial growth of high-temperature superconductors is reported. The technique uses well established, industrially scalable, thermomechanical processes to impart a strong biaxial texture to a base metal. This is followed by vapor deposition of epitaxial buffer layers (metal and/or ceramic) to yield chemically compatible surfaces. Epitaxial YBa2Cu3Ox films grown on such substrates have critical current densities exceeding 105 A/cm2 at 77 K in zero field and have field dependencies similar to epitaxial films on single crystal ceramic substrates. Deposited conductors made using this technique offer a potential route for the fabrication of long lengths of high-Jc wire capable of carrying high currents in high magnetic fields and at elevated temperatures. copyright 1996 American Institute of Physics

  2. Nucleation and growth of stress relief patterns in sputtered molybdenum films

    Stress relief patterns in sputtered molybdenum films were studied by Nomarski differential interference contrast microscope. As a result of the very large biaxial compressive stress in the film plane, ranging from E/16 to E/130 (where E is Young's modulus), the films were partially buckled and detached from the substrate, exhibiting one of two modes of stress relief pattern, wrinkled spots or wavy ridges. The former mode is a nucleation pattern and the latter a growth pattern. The transition between the two can be interpreted in terms of the stress intensity factor KI at the head of the gap formed due to stress between the film and the substrate. KI can be regarded as measure of the bond strength between the film and the substrate. (author)

  3. Evaluation of multiaxial stress in textured cubic films by x-ray diffraction

    Zhang Jian-Min; Xu Ke-Wei

    2005-01-01

    X-ray diffraction is used extensively to determine the residual stress in bulk or thin film materials on the assumptions that the material is composed of fine crystals with random orientation and the stress state is biaxial and homogeneous through the x-ray penetrating region. The stress is calculated from the gradient of ε~ sin2 ψ linear relation. But the method cannot be used in textured films due to nonlinear relation. In this paper, a novel method is proposed for measuring the multiaxial stresses in cubic films with any [hkl] fibre texture. As an example, a detailed analysis is given for measuring three-dimensional stresses in FCC films with [111] fibre texture.

  4. Residual stress in AlN films grown on sapphire substrates by molecular beam epitaxy

    Rong, Xin; Wang, Xinqiang; Chen, Guang; Pan, Jianhai; Wang, Ping; Liu, Huapeng; Xu, Fujun; Tan, Pingheng; Shen, Bo

    2016-05-01

    Residual stress in AlN films grown by molecular beam epitaxy (MBE) has been studied by Raman scattering spectroscopy. A strain-free Raman frequency and a biaxial stress coefficient for E2(high) mode are experimentally determined to be 657.8 ± 0.3 cm-1 and 2.4 ± 0.2 cm-1 / GPa, respectively. By using these parameters, the residual stress of a series of AlN layers grown under different buffer layer conditions has been investigated. The residual compressive stress is found to be obviously decreased by increasing the Al/N beam flux ratio of the buffer layer, indicating the generation of tensile stress due to stronger coalescence of AlN grains, as also confirmed by the in-situ reflection high energy electron diffraction (RHEED) monitoring observation. The stronger coalescence does lead to improved quality of AlN films as expected.

  5. Increasing the band gap of FeS{sub 2} by alloying with Zn and applying biaxial strain: A first-principles study

    Xiao, Pin [School of Material Science and Engineering, State Key Laboratory of Solidification Processing, Northwestern Polytechnic University, 127 YouYi Western Road, Xi’an, Shaanxi 710072 (China); Beijing Computational Science Research Center, Beijing 100084 (China); Fan, Xiao-Li, E-mail: xlfan@nwpu.edu.cn [School of Material Science and Engineering, State Key Laboratory of Solidification Processing, Northwestern Polytechnic University, 127 YouYi Western Road, Xi’an, Shaanxi 710072 (China); Beijing Computational Science Research Center, Beijing 100084 (China); Zhang, Han; Fang, Xiaoliang [School of Material Science and Engineering, State Key Laboratory of Solidification Processing, Northwestern Polytechnic University, 127 YouYi Western Road, Xi’an, Shaanxi 710072 (China); Liu, Li-Min, E-mail: limin.liu@csrc.ac.cn [Beijing Computational Science Research Center, Beijing 100084 (China); Chengdu Green Energy and Green Manufacturing Technology R& D Center, Chengdu, Sichuan 610207 (China)

    2015-04-25

    Highlights: • The combined effect of doping and biaxial strain on the physical properties of FeS{sub 2} was studied. • The band gap of FeS{sub 2} is widen by ∼0.29 eV under 5% tensile strain with Zn alloying at 6.25% concentration. • Alloying with Zn and biaxial tensile strain effectively improve the electronic and optical properties of FeS{sub 2}. - Abstract: The combined effect of alloying and biaxial strain on atomic structure, as well as electronic and optical properties of FeS{sub 2} was first examined by the first-principles calculation. By allaying with Zn, our results show that the band gap of Fe{sub 1−x}Zn{sub x}S{sub 2} alloy increases firstly and then decreases with increasing Zn concentration, the maximum enlargement of band gap is ∼0.1 eV. The left shift of the absorption threshold enhances the overall optical absorptivity. By imposing biaxial strain on the Zn-doped FeS{sub 2}, the band gap decreases under compressive strain, but increases from 0.95 eV to 1.14 eV under 5% tensile strain. More specially, strain widens the band gap of Zn-doped FeS{sub 2} by ∼0.19 eV, and the overall optical absorptivity is further enhanced by the combination of strain and Zn-doping. With the increase of the band gap by ∼0.29 eV and the high optical absorptivity, FeS{sub 2} is a more promising material for photovoltaic applications.

  6. Increasing the band gap of FeS2 by alloying with Zn and applying biaxial strain: A first-principles study

    Highlights: • The combined effect of doping and biaxial strain on the physical properties of FeS2 was studied. • The band gap of FeS2 is widen by ∼0.29 eV under 5% tensile strain with Zn alloying at 6.25% concentration. • Alloying with Zn and biaxial tensile strain effectively improve the electronic and optical properties of FeS2. - Abstract: The combined effect of alloying and biaxial strain on atomic structure, as well as electronic and optical properties of FeS2 was first examined by the first-principles calculation. By allaying with Zn, our results show that the band gap of Fe1−xZnxS2 alloy increases firstly and then decreases with increasing Zn concentration, the maximum enlargement of band gap is ∼0.1 eV. The left shift of the absorption threshold enhances the overall optical absorptivity. By imposing biaxial strain on the Zn-doped FeS2, the band gap decreases under compressive strain, but increases from 0.95 eV to 1.14 eV under 5% tensile strain. More specially, strain widens the band gap of Zn-doped FeS2 by ∼0.19 eV, and the overall optical absorptivity is further enhanced by the combination of strain and Zn-doping. With the increase of the band gap by ∼0.29 eV and the high optical absorptivity, FeS2 is a more promising material for photovoltaic applications

  7. The influence of external magnetic fields on phase states and spectra of coupled magnetoelastic waves in a biaxial non-Heisenberg ferromagnetic

    The spectra of coupled magnetoelastic waves of a biaxial non-Heisenberg ferromagnetic in an external magnetic field have been investigated. It is shown that in such systems there are phase transitions taking place through the changing of the magnitude of the magnetization vector. However, these transitions run through a weak quasiphonon mode. The phase diagrams of the system are constructed for different relations between material constants

  8. The biaxial nonlinear crystal BiB3O6 as a polarization entangled photon source using non-collinear type-II parametric down-conversion

    Halevy, A.; Megidish, E.; Dovrat, L.; Eisenberg, H. S.; De Becker, P; Bohatý, L.

    2011-01-01

    We describe the full characterization of the biaxial nonlinear crystal BiB3O6 (BiBO) as a polarization entangled photon source using non-collinear type-II parametric down-conversion. We consider the relevant parameters for crystal design, such as cutting angles, polarization of the photons, effective nonlinearity, spatial and temporal walk-offs, crystal thickness and the effect of the pump laser bandwidth. Experimental results showing entanglement generation with high rates and a comparison t...

  9. The critical state of an inclined layer in a sheet specimen with negative loading biaxiality coefficient

    DILMAN V.L.; DHEYAB A.N.

    2016-01-01

    We study conditions for the loss of stability in a plastic deformation of a layer of weaker material in a sheet specimen. The layer is not collinear with the exterior forces acting in the sheet plane, which are orthogonal to each other and have opposite signs. The parameters of the problem are: the angle between the layer and the direction of exterior forces; the ratio of stresses due to exterior forces; the ratio of strengths of the layer material and the main material of the sheet specimen;...

  10. Stress Management

    GÜÇLÜ, Nezahat

    2001-01-01

    Stress is defined as a neutral physiological phenomenon, in terms of the non-specific response of the human body to any demand. Stress migt be positive or negative, stimulus or threat. This paper is intended to provide answers to the following questions: (1) what is stress? (2) who is stressed? (3) what are the causes of stress in organisation? (4) How prevalent is stress in organisation? (5) What is stress management?

  11. Damage evolution under cyclic multiaxial stress state: A comparative analysis between glass/epoxy laminates and tubes

    Quaresimin, M.; Carraro, P.A.; Mikkelsen, Lars Pilgaard;

    2014-01-01

    In this work an experimental investigation on damage initiation and evolution in laminates under cyclic loading is presented. The stacking sequence [0/θ2/0/-θ2]s has been adopted in order to investigate the influence of the local multiaxial stress state in the off-axis plies and the possible effect...... θ has been chosen in order to obtain local multiaxial stress states in the off-axis plies similar to those in previous studies for biaxially loaded tubes. Results concerning damage initiation and growth for these two specimen configurations are shown to be consistent for similar local multiaxial...

  12. Nuclear stress test

    ... Persantine stress test; Thallium stress test; Stress test - nuclear; Adenosine stress test; Regadenoson stress test; CAD - nuclear stress; Coronary artery disease - nuclear stress; Angina - nuclear ...

  13. Understanding Nonlinear Dielectric Properties in a Biaxially Oriented Poly(vinylidene fluoride) Film at Both Low and High Electric Fields.

    Li, Yue; Ho, Janet; Wang, Jianchuan; Li, Zhong-Ming; Zhong, Gan-Ji; Zhu, Lei

    2016-01-13

    Understanding nonlinear dielectric behavior in polar polymers is crucial to their potential application as next generation high energy density and low loss dielectrics. In this work, we studied nonlinear dielectric properties of a biaxially oriented poly(vinylidene fluoride) (BOPVDF) film under both low and high electric fields. For fundamental nonlinear dielectric constants at low fields (measure up to the third harmonics. It was observed that the low-field dielectric nonlinearity for the BOPVDF disappeared above 10 Hz at room temperature, suggesting that the low-field dielectric nonlinearity originated from ionic migration of impurity ions rather than dipolar relaxation of the amorphous segments. Above the coercive field (EC ≈ 70 MV/m), bipolar electric displacement-electric field (D-E) loop tests were used to extract the nonlinear behavior for pure PVDF crystals, which had a clear origin of ferroelectric switching of polar crystalline dipoles and domains and nonpolar-to-polar (α → δ → β) phase transformations. By using HVBDS, it was observed that the ferroelectric switching of polar crystalline dipoles and domains in BOPVDF above the EC always took place between 20 and 500 Hz regardless of a broad range of temperature from -30 to 100 °C. This behavior was drastically different from that of the amorphous PVDF dipoles, which had a strong dependence on frequency over orders of magnitude. PMID:26698912

  14. Semiconductor-topological insulator transition of two-dimensional SbAs induced by biaxial tensile strain

    Zhang, Shengli; Xie, Meiqiu; Cai, Bo; Zhang, Haijun; Ma, Yandong; Chen, Zhongfang; Zhu, Zhen; Hu, Ziyu; Zeng, Haibo

    2016-06-01

    A stibarsen [derived from Latin stibium (antimony) and arsenic] or allemontite, is a natural form of arsenic antimonide (SbAs) with the same layered structure as arsenic and antimony. Thus, exploring the two-dimensional SbAs nanosheets is of great importance to gain insights into the properties of group V-V compounds at the atomic scale. Here, we propose a class of two-dimensional V-V honeycomb binary compounds, SbAs monolayers, which can be tuned from semiconductor to topological insulator. By ab initio density functional theory, both α-SbAs and γ-SbAs display a significant direct band gap, while others are indirect semiconductors. Interestingly, in an atomically thin β-SbAs polymorph, spin-orbital coupling is significant, which reduces its band gap by 200 meV. Especially under biaxial tensile strain, the gap of β-SbAs can be closed and reopened with concomitant change of band shapes, which is reminiscent of band inversion known in many topological insulators. In addition, we find that the Z2 topological invariant is 1 for β-SbAs under the tensile strain of 12%, and the nontrivial topological feature of β-SbAs is also confirmed by the gapless edge states which cross linearly at the Γ point. These ultrathin group-V-V semiconductors with outstanding properties are highly favorable for applications in alternative optoelectronic and quantum spin Hall devices.

  15. Microstructural Characterisation of Non-Magnetic Ni-BASED Biaxially Textured Substrates for Hts Coated Conductor Applications

    Villa, E.; Tuissi, A.; Tomov, R.; Evetts, J. E.

    For the production of HTS coated conductor devices, NiV and NiCr (Ni-based alloys) are the most important, non-magnetic, high strength and biaxially textured substrates developed from pure Ni. The Ni88V12 and Ni85Cr15 (at. %) alloys have been melted in Plasma Arc Furnace and textured tapes have been prepared, after heavy cold rolling, by recrystallization heat treatment under high vacuum. The suitable working conditions have been found to obtain not only the {100} cube texture but also the correct grain shape and size for the following deposition process. Out of plane orientation of these substrates has been investigated by θ-2θ X-ray diffraction measurements and in plane orientation study has been completed by pole figures. The microstructure has been observed by optical microscopy: it has been carried out on samples obtained after an annealing treatment (Grain Size Adjustment) and on recrystallized samples in different conditions. As preliminary mechanical investigation the microhardness values have been detected for each step of the working procedure. The accuracy of the cubic texture and the grain structure are affected by the processing condition, in particular the temperature of the GSA seems a very important parameter which influences the final characteristics of the tapes.

  16. Strain mapping near a triple junction in strained Ni-based alloy using EBSD and biaxial nanogauges

    Clair, A. [Laboratoire Interdisciplinaire Carnot de Bourgogne, UMR 5209 CNRS, Universite de Bourgogne, 9 Avenue Alain Savary, BP 47870, 21078 Dijon Cedex (France); Foucault, M.; Calonne, O. [Areva ANP, Centre Technique Departement Corrosion-Chimie, 30 Bd de l' industrie, BP 181, 71205 Le Creusot (France); Lacroute, Y.; Markey, L.; Salazar, M.; Vignal, V. [Laboratoire Interdisciplinaire Carnot de Bourgogne, UMR 5209 CNRS, Universite de Bourgogne, 9 Avenue Alain Savary, BP 47870, 21078 Dijon Cedex (France); Finot, E., E-mail: Eric.Finot@u-bourgogne.fr [Laboratoire Interdisciplinaire Carnot de Bourgogne, UMR 5209 CNRS, Universite de Bourgogne, 9 Avenue Alain Savary, BP 47870, 21078 Dijon Cedex (France)

    2011-05-15

    Research highlights: > Surface strains measured using nanogauge were compared to the texture obtained by EBSD. > Statistics of the principal strain discern the grains according to the Schmid factor. > Strain hotspots were localized near a triple junction of alloy 600 under tensile loading. > Asymetrical profile of the GB strains is a criterion for surface cracking initiation. - Abstract: A key element for analyzing the crack initiation in strained polycrystalline alloys is the local quantification of the surface strain distribution according to the grain texture. Using electron backscattered diffraction, the local microstructure was determined to both localize a triple junction and deduce the local Schmid factors. Kernel average misorientation (KAM) was also used to map the areas of defect concentration. The maximum principal strain and the in-plane shear strain were quantified using the biaxial nanogauge. Distortions of the array of nanodots used as spot markers were analyzed near the triple junction. The crystallographic orientation and the surface strain were then investigated both statistically for each grain and locally at the grain boundaries. The superimposition of microstructure and strain maps allows the high strain gradient (reaching 3-fold the applied strain) to be localized at preferential grain boundaries near the triple junction. The Schmid factors and the KAM were compared to the maximum principal strain and the in-plane shear strain respectively. The polycrystalline deformation was attributable first to the rotation of some grains, followed by the elongation of all grains along their preferential activated slip systems.

  17. The diverse electronic properties of C4N3 monolayer under biaxial compressive strain: a theoretical study

    Wu, Haiping; Liu, Yuzhen; Kan, Erjun; Ma, Yanming; Xu, Wenjie; Li, Jie; Yan, Meichen; Lu, Ruifeng; Wei, Jianfeng; Qian, Yan

    2016-07-01

    Because of the observation of half-metallicity in graphitic carbon nitride C4N3 (g-C4N3), extensive research has recently been focused on this compound. Using density-functional calculations, herein diverse electronic properties of g-C4N3 were engineered by applying biaxial compressive strain. The calculated results demonstrate that g-C4N3 preserves ferromagnetic half-metallicity when the strain is lower than  ‑2%, accompanied by a decrease of the half-metallic gap. When the compressive strain ranges from  ‑5 to  ‑3%, the compound turns into nonmagnetic metal. By increasing the strain on the end, it becomes a nonmagnetic semiconductor. Further investigations show that all nonmagnetic semiconductors possess a direct band gap with a value of around 1.6 eV. This fact indicates that g-C4N3 can be applied in spintronic or photovoltaic fields under a strain environment.

  18. Characterisation of the mechanical properties of infarcted myocardium in the rat under biaxial tension and uniaxial compression.

    Sirry, Mazin S; Butler, J Ryan; Patnaik, Sourav S; Brazile, Bryn; Bertucci, Robbin; Claude, Andrew; McLaughlin, Ron; Davies, Neil H; Liao, Jun; Franz, Thomas

    2016-10-01

    Understanding the passive mechanical properties of infarcted tissue at different healing stages is essential to explore the emerging biomaterial injection-based therapy for myocardial infarction (MI). Although rats have been widely used as animal models in such investigations, the data in literature that quantify the passive mechanical properties of rat heart infarcts is very limited. MI was induced in rats and hearts were harvested immediately (0 day), 7, 14 and 28 days after infarction onset. Left ventricle anterioapical samples were cut and underwent equibiaxial and non equibiaxial tension followed by uniaxial compression mechanical tests. Histological analysis was conducted to confirm MI and to quantify the size of the induced infarcts. Infarcts maintained anisotropy and the nonlinear biaxial and compressive mechanical behaviour throughout the healing phases with the circumferential direction being stiffer than the longitudinal direction. Mechanical coupling was observed between the two axes in all infarct groups. The 0, 7, 14 and 28 days infarcts showed 438, 693, 1048 and 1218kPa circumferential tensile moduli. The 28 day infarct group showed a significantly higher compressive modulus compared to the other infarct groups (p=0.0060, 0.0293, and 0.0268 for 0, 7 and 14 days groups). Collagen fibres were found to align in a preferred direction for all infarct groups supporting the observed mechanical anisotropy. The presented data are useful for developing material models for healing infarcts and for setting a baseline for future assessment of emerging mechanical-based MI therapies. PMID:27434651

  19. Fabrication of High Current YBa2Cu3O7-y Coated Conductors Using Rolling-Assisted Biaxially Textured Substrates

    High critical current YBa2Cu3O7-y (referred to as YBCO) coated conductors were fabricated with a layer sequence of YBCO/YSZ/CeO2/Ni. The cube (100) texture in the starting Ni substrates was obtained by cold rolling followed by recrystallization. A thin CeO2 (Cerium Oxide) layer with a thickness of 100-200 was grown epitaxially on the biaxially textured-Ni substrates using an e-beam evaporation technique. This was followed by the growth of a thick (2 film had a dense microstructure. The microstructure of the e-beam YSZ film was porous whereas the sputtered YSZ film was dense. The YBCO films were grown by pulsed laser deposition on both e-beam and sputtered YSZ layers. A transport critical current density of 1 x l06 A/cm2 at 77 K was obtained for 0.8 m thick YBCO Rims on both YSZ surfaces in zero field. To demonstrate the quality and compatibility of the e-beam CeO2 layers; YBCO films were also grown on CeO2-buffered YSZ (100) single crystal substrates using e-beam co-evaporated Y-BaF2-Cu precursors followed by a post-annealing process. A transport critical current density of over 1 x lO6A/cm2 at 77 K was obtained on a 0.3 m thick YBCO film in zero field

  20. Effect of Ceramic Surface Treatments After Machine Grinding on the Biaxial Flexural Strength of Different CAD/CAM Dental Ceramics

    Bagheri, Hossein; Aghajani, Farzaneh

    2015-01-01

    Objectives: This study aimed to evaluate the effect of different ceramic surface treatments after machining grinding on the biaxial flexural strength (BFS) of machinable dental ceramics with different crystalline phases. Materials and Methods: Disk-shape specimens (10mm in diameter and 1.3mm in thickness) of machinable ceramic cores (two silica-based and one zirconia-based ceramics) were prepared. Each type of the ceramic surfaces was then randomly treated (n=15) with different treatments as follows: 1) machined finish as control, 2) machined finish and sandblasting with alumina, and 3) machined finish and hydrofluoric acid etching for the leucite and lithium disilicate-based ceramics, and for the zirconia; 1) machined finish and post-sintered as control, 2) machined finish, post-sintered, and sandblasting, and 3) machined finish, post-sintered, and Nd;YAG laser irradiation. The BFS were measured in a universal testing machine. Data based were analyzed by ANOVA and Tukey’s multiple comparisons post-hoc test (α=0.05). Results: The mean BFS of machined finish only surfaces for leucite ceramic was significantly higher than that of sandblasted (P=0.001) and acid etched surfaces (P=0.005). A significantly lower BFS was found after sandblasting for lithium disilicate compared with that of other groups (Plaser irradiation (Plaser irradiation may lead to substantial strength degradation of zirconia. PMID:27148372

  1. A Study in Three-Dimensional Chaotic Dynamics: Granular Flow and Transport in a Bi-Axial Spherical Tumbler

    Christov, Ivan C; Ottino, Julio M; Sturman, Rob

    2014-01-01

    We study 3D chaotic dynamics through an analysis of transport in a granular flow in a half-full spherical tumbler rotated sequentially about two orthogonal axes (a bi-axial "blinking" tumbler). The flow is essentially quasi-2D in any vertical slice of the sphere during rotation about a single axis, and we provide an explicit exact solution to the model in this case. Hence, the cross-sectional flow can be represented by a twist map, allowing us to express the 3D flow as a linked twist map (LTM). We prove that if the rates of rotation about each axis are equal, then (in the absence of stochasticity) particle trajectories are restricted to 2D surfaces consisting of a portion of a hemispherical shell closed by a "cap"; if the rotation rates are unequal, then particles can leave the surface they start on and traverse a volume of the tumbler. The period-one structures of the governing LTM are examined in detail: analytical expressions are provided for the location of period-one curves, their extent into the bulk of...

  2. Mechanics of Stabbing: Biaxial Measurement of Knife Stab Penetration of Skin Simulant

    Gilchrist, Michael D; Curtis, Michael; Cassidy, Mary; Byrne, Greg; Destrade, Michel; 10.1016/j.forsciint.2007.10.010

    2008-01-01

    In medicolegal situations, the consequences of a stabbing incident are described in terms that are qualitative without being quantitative. Here, the mechanical variables involved in knife-tissue penetration events are used to determine the parameters needed to be controlled in a measurement device. They include knife geometry, in-plane mechanical stress state of skin, angle and speed of knife penetration, and underlying fascia. Four household knives with different geometries were used. Synthetic materials were used to simulate the response of skin, fat and cartilage: polyurethane, foam, and ballistic soap, respectively. The force and energy applied by the blade and the skin displacement were used to identify skin penetration. The skin tension is shown to have a direct effect on the force and energy for knife penetration and on the depth of displacement of the simulant prior to penetration: larger levels of in-plane tension in the skin are associated with lower penetration forces, energies and displacements. L...

  3. A criterion for high-cycle fatigue life and fatigue limit prediction in biaxial loading conditions

    Pejkowski, Łukasz; Skibicki, Dariusz

    2016-08-01

    This paper presents a criterion for high-cycle fatigue life and fatigue strength estimation under periodic proportional and non-proportional cyclic loading. The criterion is based on the mean and maximum values of the second invariant of the stress deviator. Important elements of the criterion are: function of the non-proportionality of fatigue loading and the materials parameter that expresses the materials sensitivity to non-proportional loading. The methods for the materials parameters determination uses three S-N curves: tension-compression, torsion, and any non-proportional loading proposed. The criterion has been verified using experimental data, and the results are included in the paper. These results should be considered as promising. The paper also includes a proposal for multiaxial fatigue models classification due to the approach for the non-proportionality of loading.

  4. Stress-strain relationship and XRD line broadening in [0001] textured hexagonal polycrystalline materials

    Stress analysis with X-ray diffraction (XRD) for hexagonal polycrystalline materials in the Laue classes 6/mmm and 6/m has been studied on the basis of the crystal symmetry of the constituent crystallites which was proposed by R. Yokoyama and J. Harada ['Re-evaluation of formulae for X-ray stress analysis in polycrystalline specimens with fibre texture', Journal of Applied Crystallography, Vol.42, pp.185-191 (2009)]. The relationship between the stress and strain observable by XRD in a hexagonal polycrystalline material with [0001] fibre texture was formulated in terms of the elastic compliance defined for its single crystal. As a result, it was shown that the average strains obtained in the crystallites for both symmetries of 6/mmm and 6/m are different from each other under the triaxial or biaxial stress field. Then, it turned out that the line width of XRD changes depending on the measurement direction. (author)

  5. Stress and structural damage sensing piezospectroscopic coatings validated with digital image correlation

    Gregory Freihofer

    2015-03-01

    Full Text Available The piezospectroscopic effect, relating a material’s stress state and spectral signature, has recently demonstrated tailorable sensitivity when the photo-luminescent alpha alumina is distributed in nanoparticulate form within a matrix. Here, the stress-sensing behavior of an alumina-epoxy nanoparticle coating, applied to a composite substrate in an open hole tension configuration, is validated with the biaxial strain field concurrently determined through digital image correlation. The coating achieved early detection of composite failure initiation at 77% failure load, and subsequently tracked stress distribution in the immediate vicinity of the crack as it progressed, demonstrating non-invasive stress and damage detection with multi-scale spatial resolution.

  6. On the determination of Poisson's ratio of stressed monolayer and bilayer submicron thick films

    Martins, P; Brida, S; Barbier, D

    2008-01-01

    In this paper, the bulge test is used to determine the mechanical properties of very thin dielectric membranes. Commonly, this experimental method permits to determine the residual stress (s0) and biaxial Young's modulus (E/(1-u)). Associating square and rectangular membranes with different length to width ratios, the Poisson's ratio (u) can also be determined. LPCVD Si3N4 monolayer and Si3N4/SiO2 bilayer membranes, with thicknesses down to 100 nm, have been characterized giving results in agreement with literature for Si3N4, E = 212 $\\pm$ 14 GPa, s0 = 420 $\\pm$ 8 and u = 0.29.

  7. Evaluation of biaxial flexural strength and modulus of filled and unfilled adhesive systems = Avaliação da resistência flexural biaxial e módulo de flexão de sistemas adesivos

    Liberti, Michele Santana

    2009-01-01

    Full Text Available Objetivo: O objetivo deste estudo foi avaliar a resistência flexural e o módulo de flexão de dois sistemas adesivos, através de ensaio de resistência flexural biaxial. Metodologia: Os adesivos (Pentron Clinical Technologies estudados foram: Bond 1 (B1 e NanoBond (NB. Treze discos de cada adesivo foram preparados com dimensões aproximadas de 6,1 mm de diâmetro e 0,6 mm de espessura. Os discos de adesivos foram confeccionados utilizando-se moldes de teflon e fotopolimerizados com aparelho XL 3000 (3M ESPE. Após armazenamento por 10 dias, os discos foram testados em máquina universal de ensaio (Instron 5844, com velocidade de 1,27 mm/min. Os dados foram submetidos à análise de variância (1 fator ao nível de significância de 0,05. Resultados: Os valores médios (±DP de resistência flexural para os adesivos foram (em MPa: B1- 89,7±7,6 e NB- 131,1±9,5. Os valores médios de módulo flexural (±DP foram (em MPa: B1- 1999,9±258,4 e NB- 2314,5±271,0. Conclusão: O adesivo contendo partículas de carga (NB mostrou maiores valores de resistência flexural e módulo de flexão que o adesivo B1

  8. Biaxial bending of slender HSC columns and tubes filled with concrete under short- and long-term loads: I Theory

    Jose A. Rodríguez-Gutiérrez

    2014-07-01

    Full Text Available An analytical method that calculates both the short- and long-term response of slender columns made of high-strength concrete (HSC and tubes filled with concrete with generalized end conditions and subjected to transverse loads along the span and axial load at the ends (causing a single or double curvature under uniaxial or biaxial bending is presented. The proposed method, which is an extension of a method previously developed by the authors, is capable of predicting not only the complete load-rotation and load-deflection curves (both the ascending and descending parts but also the maximum load capacity. The columns that can be analyzed include solid and hollow (rectangular, circular, oval, C-, T-, L-, or any arbitrary shape cross sections and columns made of circular and rectangular steel tubes filled with HSC. The fiber method is used to calculate the moment-curvature diagrams at different levels of the applied axial load (i.e., the M-P-φ curves, and the Gauss method of integration (for the sum of the contributions of the fibers parallel to the neutral axis is used to calculate the lateral rotations and deflections along the column span. Long-term effects, such as creep and shrinkage of the concrete, are also included. However, the effects of the shear deformations and torsion along the member are not included. The validity of the proposed method is presented in a companion paper and compared against the experimental results for over seventy column specimens reported in the technical literature by different researchers.

  9. Cation ordering and effect of biaxial strain in double perovskite CsRbCaZnCl6

    Here, we investigate the electronic structure, energetics of cation ordering, and effect of biaxial strain on double perovskite CsRbCaZnCl6 using first-principles calculations based on density functional theory. The two constituents (i.e., CsCaCl3 and RbZnCl3) forming the double perovskite exhibit a stark contrast. While CsCaCl3 is known to exist in a cubic perovskite structure and does not show any epitaxial strain induced phase transitions within an experimentally accessible range of compressive strains, RbZnCl3 is thermodynamically unstable in the perovskite phase and exhibits ultra-sensitive response at small epitaxial strains if constrained in the perovskite phase. We show that combining the two compositions in a double perovskite structure not only improves overall stability but also the strain-polarization coupling of the material. Our calculations predict a ground state with P4/nmm space group for the double perovskite, where A-site cations (i.e., Cs and Rb) are layer-ordered and B-site cations (i.e., Ca and Zn) prefer a rocksalt type ordering. The electronic structure and bandgap in this system are shown to be quite sensitive to the B-site cation ordering and is minimally affected by the ordering of A-site cations. We find that at experimentally accessible compressive strains CsRbCaZnCl6 can be phase transformed from its paraelectric ground state to an antiferroelectric state, where Zn atoms contribute predominantly to the polarization. Furthermore, both energy difference and activation barrier for a transformation between this antiferroelectric state and the corresponding ferroelectric configuration are predicted to be small. The computational approach presented here opens a new pathway towards a rational design of novel double perovskites with improved strain response and functionalities

  10. Film stresses and electrode buckling in organic solar cells

    Brand, Vitali

    2012-08-01

    We investigate the film stresses that develop in the polymer films and metal electrodes of poly(3-hexyl thiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM) bulk heterojunction (BHJ) organic solar cells. A compressive biaxial stress of ∼-36 MPa was measured in PEDOT:PSS while a tensile stress of ∼6 MPa was measured in the BHJ layer. We then analyze the effect of electrode deposition rate on the film stresses in the Al electrode. Compressive stresses of ∼-100 to -145 MPa in the Al electrode lead to a buckling instability resulting in undulating electrode surface topography. The BHJ layer was found to have the lowest cohesion (∼1.5-1.8 J/m 2) among the layers of the solar cell and dependent on the Al electrode deposition rate. The cohesive failure path in the BHJ layer exhibited the same periodicity and orientation of the Al electrode buckling topography. We discuss the implications of the film stresses on damage processes during device fabrication and operation. © 2012 Elsevier B.V. All rights reserved.

  11. Twist viscosities and flow alignment of biaxial nematic liquid crystal phases of a soft ellipsoid-string fluid studied by molecular dynamics simulation.

    Sarman, Sten; Laaksonen, Aatto

    2012-09-14

    We have calculated the twist viscosity and the alignment angle between the director and the stream lines in shear flow of a liquid crystal model system, which forms biaxial nematic liquid crystals, as functions of the density, from the Green-Kubo relations by equilibrium molecular dynamics simulation and by a nonequilibrium molecular dynamics algorithm, where a torque conjugate to the director angular velocity is applied to rotate the director. The model system consists of a soft ellipsoid-string fluid where the ellipsoids interact according a repulsive version of the Gay-Berne potential. Four different length-to-width-to-breadth ratios have been studied. On compression, this system forms discotic or calamitic uniaxial nematic phases depending on the dimensions of the molecules, and on further compression a biaxial nematic phase is formed. In the uniaxial nematic phase there is one twist viscosity and one alignment angle. In the biaxial nematic phase there are three twist viscosities and three alignment angles corresponding to the rotation around the various directors and the different alignments of the directors relative to the stream lines, respectively. It is found that the smallest twist viscosity arises by rotation around the director formed by the long axes, the second smallest one arises by rotation around the director formed by the normals of the broadsides, and the largest one by rotation around the remaining director. The first twist viscosity is rather independent of the density whereas the last two ones increase strongly with density. One finds that there is one stable director alignment relative to the streamlines, namely where the director formed by the long axes is almost parallel to the stream lines and where the director formed by the normals of the broadsides is almost parallel to the shear plane. The relative magnitudes of the components of the twist viscosities span a fairly wide interval so this model should be useful for parameterisation

  12. A comparison of stress in cracked fibrous tissue specimens with varied crack location, loading, and orientation using finite element analysis.

    Peloquin, John M; Elliott, Dawn M

    2016-04-01

    Cracks in fibrous soft tissue, such as intervertebral disc annulus fibrosus and knee meniscus, cause pain and compromise joint mechanics. A crack concentrates stress at its tip, making further failure and crack extension (fracture) more likely. Ex vivo mechanical testing is an important tool for studying the loading conditions required for crack extension, but prior work has shown that it is difficult to reproduce crack extension. Most prior work used edge crack specimens in uniaxial tension, with the crack 90° to the edge of the specimen. This configuration does not necessarily represent the loading conditions that cause in vivo crack extension. To find a potentially better choice for experiments aiming to reproduce crack extension, we used finite element analysis to compare, in factorial combination, (1) center crack vs. edge crack location, (2) biaxial vs. uniaxial loading, and (3) crack-fiber angles ranging from 0° to 90°. The simulated material was annulus fibrosus fibrocartilage with a single fiber family. We hypothesized that one of the simulated test cases would produce a stronger stress concentration than the commonly used uniaxially loaded 90° crack-fiber angle edge crack case. Stress concentrations were compared between cases in terms of fiber-parallel stress (representing risk of fiber rupture), fiber-perpendicular stress (representing risk of matrix rupture), and fiber shear stress (representing risk of fiber sliding). Fiber-perpendicular stress and fiber shear stress concentrations were greatest in edge crack specimens (of any crack-fiber angle) and center crack specimens with a 90° crack-fiber angle. However, unless the crack is parallel to the fiber direction, these stress components alone are insufficient to cause crack opening and extension. Fiber-parallel stress concentrations were greatest in center crack specimens with a 45° crack-fiber angle, either biaxially or uniaxially loaded. We therefore recommend that the 45° center crack case be

  13. Voltage controlled biaxial strain in VO2 films grown on 0.72Pb(Mg1/3Nb2/3)-0.28PbTiO3 crystals and its effect on the transition temperature

    Petraru, A.; Soni, R.; Kohlstedt, H.

    2014-09-01

    Vanadium oxide thin films (VO2) were deposited on 0.72Pb(Mg1/3Nb2/3)-0.28PbTiO3 (PMN-PT) crystalline substrates using pulsed laser deposition method. Due to their huge piezoelectric coefficients in the order of 2500 pm/V, the PMN-PT substrates are used to impose additional amount of biaxial strain to the VO2 films by applying an external bias to the substrates. The influence of the biaxial strain on the transition temperature and on the conductive properties of the VO2 films is investigated in this work. Thus, a change in the biaxial strain of -0.8 × 10-3 applied in the (110) plane of the rutile cell of the VO2 lowered the metal-to-insulator transition temperature by 1.35 °C.

  14. Fourier space method for calculating the propagation of laser radiation in biaxial crystals taking into account the angle between the eigenpolarisations

    We have proposed a technique for calculating the propagation of laser radiation in biaxial optical crystals in arbitrary directions. The technique is based on the use of the Fourier space method and takes into account both diffraction and angle beween the eigenpolarisations of the spatial spectrum components, phase shift differences for them with account for all orders of the spatial dispersion and also the features of the boundary conditions at the input and output facets. Using internal conical refraction as an example, we have compared the results of calculations with experimental data. (nonlinear optical phenomena)

  15. STRESS MANAGEMENT

    Charu Jain

    2015-02-01

    Full Text Available Everyone has the right to live their life very happily. But the question arises,“Do they really live their life happily”. The answer is “No”. Human beings are not living their life happily because of stress, tension and depression in their life. Due to stress, tension and depression, a person cannot focus on their work properly and as a result of this, their focus from the work has been diverted, results in bad performance at home and at work. In this article, my focus is on stress management and how to reduce stress. Stress management encompasses those techniques which helps the human beings to survive their life by reducing stress. Stress can come at any stage of life. Stress can’t be removed totally but it can be reduced and alter. Stress management plays a vital role in human being life.

  16. Stress relief and texture formation in aluminium nitride by plasma immersion ion implantation

    The effect on the intrinsic stress in AlN films of applying pulsed bias during cathodic arc deposition has been studied. We find that the stress depends only on the pulse voltage-pulse frequency product, V f. The form of the dependence is well fitted by an exponential function whose parameters can be interpreted physically. The preferred orientation changes progressively with V f, from hexagonal crystallites having their direction in the plane of the film at low V f, to hexagonal crystallites having their direction normal to the plane of the film at high V f. The in-plane orientation may be consistent with energy minimization in a biaxial stress field whereas the normal orientation is consistent with the alignment of a channelling direction with the ion beam

  17. An effective uniaxial tensile stress-strain relationship for prestressed concrete

    This report evaluates the direct tensile strength and an equivalent uniaxial tensile stress-strain relationship for prestressed concrete using data from specimens tested at the University of Alberta which represent segments from the wall of a containment vessel. The stress-strain relationship, when used in conjunction with the BOSOR5 program, enables prediction of the response of prestressed concrete under any biaxial combination of compressive and/or tensile stresses. Comparisons between the experimental and analytical (BOSOR5) load-strain response of the wall segments are also presented. It is concluded that the BOSOR5 program is able to predict satisfactorily the response of the wall segments and multi-layered shell structures. (author)

  18. Macroscopic biaxiality and electric-field-induced rotation of the minor director in the nematic phase of a bent-core liquid crystal

    Nagaraj, Mamatha; Merkel, K.; Vij, J. K.; Kocot, A.

    2010-09-01

    Biaxiality in the nematic phase has been investigated for the bent-core liquid-crystal para-heptylbenzoate diester, using polarised IR spectroscopy. Anisotropic fluctuations of the nematic director are discussed in terms of the self-assembly of the chiral conformers. The ordering of the minor director for the homeotropicaly aligned sample is found to depend on the rubbing of the substrates of the cell and the amplitude of in-plane electric field. On increasing the in-plane electric field, the rotation of the minor director in the plane of the substrate is observed with an angle of approximately 45°, where initially the minor director is shown to lie along the rubbing direction. It is also shown that on the average the long axis of the molecules is normal to the substrate with surface treatment, with and without rubbing. The electric in-plane field combined with rubbing is shown to induce biaxial order in the nematic phase of a material with negative dielectic anisotropy for the first time.

  19. On the Novel Biaxial Strain Relaxation Mechanism in Epitaxial Composition Graded La1−xSrxMnO3 Thin Film Synthesized by RF Magnetron Sputtering

    Yishu Wang

    2015-11-01

    Full Text Available We report on a novel method to fabricate composition gradient, epitaxial La1−xSrxMnO3 thin films with the objective to alleviate biaxial film strain. In this work, epitaxial, composition gradient La1−xSrxMnO3, and pure LaMnO3 and La0.67Sr0.33MnO3 thin films were deposited by radio frequency (RF magnetron sputtering. The crystalline and epitaxy of all films were first studied by symmetric θ–2θ X-ray diffraction (XRD and low angle XRD experiments. Detailed microstructural characterization across the film thickness was conducted by high-resolution transmission electron microscopy and electron diffraction. Four compositional gradient domains were observed in the La1−xSrxMnO3 film ranging from LaMnO3 rich to La0.67Sr0.33MnO3 at the surface. A continuous reduction in the lattice parameter was observed accompanied by a significant reduction in the out-of-plane strain in the film. Fabrication of the composition gradient La1−xSrxMnO3 thin film was found to be a powerful method to relieve biaxial strain under critical thickness. Besides, the coexistence of domains with a composition variance is opening up various new possibilities of designing new nanoscale structures with unusual cross coupled properties.

  20. Multi-mode technique for the determination of the biaxial Y{sub 2}SiO{sub 5} permittivity tensor from 300 to 6 K

    Carvalho, N. C., E-mail: natalia.docarmocarvalho@research.uwa.edu.au; Le Floch, J-M.; Tobar, M. E. [School of Physics, The University of Western Australia, Crawley 6009 (Australia); ARC Centre of Excellence for Engineered Quantum Systems (EQuS), 35 Stirling Hwy, Crawley 6009 (Australia); Krupka, J. [Instytut Mikroelektroniki i Optoelektroniki PW, Koszykowa 75, 00-662 Warsaw (Poland)

    2015-05-11

    The Y{sub 2}SiO{sub 5} (YSO) crystal is a dielectric material with biaxial anisotropy with known values of refractive index at optical frequencies. It is a well-known rare-earth (RE) host material for optical research and more recently has shown promising performance for quantum-engineered devices. In this paper, we report the first microwave characterization of the real permittivity tensor of a bulk YSO sample, as well as an investigation of the temperature dependence of the tensor components from 296 K down to 6 K. Estimated uncertainties were below 0.26%, limited by the precision of machining the cylindrical dielectric. Also, the electrical Q-factors of a few electromagnetic modes were recorded as a way to provide some information about the crystal losses over the temperature range. To solve the tensor components necessary for a biaxial crystal, we developed the multi-mode technique, which uses simultaneous measurement of low order whispering gallery modes. Knowledge of the permittivity tensor offers important data, essential for the design of technologies involving YSO, such as microwave coupling to electron and hyperfine transitions in RE doped samples at low temperatures.

  1. Distribution and viability of fetal and adult human bone marrow stromal cells in a biaxial rotating vessel bioreactor after seeding on polymeric 3D additive manufactured scaffolds

    Anne eLeferink

    2015-10-01

    Full Text Available One of the conventional approaches in tissue engineering is the use of scaffolds in combination with cells to obtain mechanically stable tissue constructs in vitro prior to implantation. Additive manufacturing by fused deposition modeling is a widely used technique to produce porous scaffolds with defined pore network, geometry, and therewith defined mechanical properties. Bone marrow derived mesenchymal stromal cells (MSCs are promising candidates for tissue engineering based cell therapies due to their multipotent character. One of the hurdles to overcome when combining additive manufactured scaffolds with MSCs is the resulting heterogeneous cell distribution and limited cell proliferation capacity. In this study, we show that the use of a biaxial rotating bioreactor, after static culture of human fetal MSCs (hfMSCs seeded on synthetic polymeric scaffolds, improved the homogeneity of cell and extracellular matrix (ECM distribution and increased the total cell number. Furthermore, we show that the relative mRNA expression levels of indicators for stemness and differentiation are not significantly changed upon this bioreactor culture, whereas static culture shows variations of several indicators for stemness and differentiation. The biaxial rotating bioreactor presented here offers a homogeneous distribution of hfMSCs, enabling studies on MSCs fate in additive manufactured scaffolds without inducing undesired differentiation.

  2. Surface roughness of MgO thin film and its critical thickness for optimal biaxial texturing by ion-beam-assisted deposition

    We investigated the deposition time dependences of the in-plane grain alignment (Δφ) and the surface roughness (w) of biaxially textured MgO thin films fabricated by ion-beam-assisted deposition (IBAD) and found a strong correlation between them. The time evolution of the surface roughness of IBAD-MgO showed an abrupt increase at the same time corresponding to the beginning of the deterioration in Δφ. The roughness versus thickness profiles obtained under different deposition conditions with different assisting ion-beam currents collapsed to a single curve, even though the deposition rates were significantly different in each condition. This implies that the abrupt increase in roughness occurred at the same thickness--of about 4 nm--irrespective of the deposition rate. The result also indicated that the Δφ deterioration began with the same thickness of about 4 nm. This ''critical'' thickness of about 4 nm might be related to the completion of the crystallization of the film. Further, deposition beyond the critical thickness, therefore, became merely a homoepitaxial deposition under the ''IBAD'' condition, which was far from optimal because of the ion bombardment and low temperature (no-heating), and thus Δφ deteriorated. Based on these considerations, we propose an approach to attain a sharp texture in a IBAD-MgO-based biaxial substrate; moreover, we demonstrated this approach using a two-step deposition process.

  3. Heat Stress

    ... Publications and Products Programs Contact NIOSH NIOSH HEAT STRESS Recommend on Facebook Tweet Share Compartir NEW Criteria ... hot environments may be at risk of heat stress. Exposure to extreme heat can result in occupational ...

  4. Cold Stress

    ... Publications and Products Programs Contact NIOSH NIOSH COLD STRESS Recommend on Facebook Tweet Share Compartir Workers who ... cold environments may be at risk of cold stress. Extreme cold weather is a dangerous situation that ...

  5. Caregiver Stress

    ... current/fahc.html/ Search Share Embed Caregiver stress Caregivers care for someone with an illness, injury, ... be rewarding, but it can also be challenging. Stress from caregiving is common. Women especially are at ...

  6. Feeling Stressed

    ... of depression, which needs treatment. Learn more about depression and how to get help. How does my body act when stressed? top Your body has a ... stress doesn't feel very good. When your body is hit by stress, try to calm it down. Taking some deep ... anxiety disorders , alcohol and drug abuse , smoking , and ...

  7. Understanding Stress.

    Bellott, Fred K.

    Stress affects everyone in his/her work and everyday life. Some persons are more effective when they are under a certain level of stress, but there are limits to the amount of stress under which one can perform effectively. Competition within complex organizations today is a risk factor not often recognized by the organizations. All organizations…

  8. Residual stress determination in PECVD TiN coatings by X-ray diffraction: a parametric study

    Thomsen, N.B.; Horsewell, Andy; Mogensen, K.S.; Eskildsen, S.S.; Mathiasen, C.; Bøttiger, J.

    The main objective of this research is to study the residual macroscopic stress in titanium-nitride, TiN, coatings deposited onto a tool steer substrate. The measurements were performed with a theta-theta decoupled X-ray diffractometer. The coatings were manufactured using an industrial pulsed......-DC plasma-enhanced chemical vapour deposition (PECVD) technique. The coatings were characterized in terms of microstructure, mechanical and tribological properties. A parametric study of the deposition parameters was performed. Process pressure, bias voltage, temperature and partial gas flows (argon......, hydrogen, nitrogen and titanium tetra chloride) were varied in an effort to obtain optimal coating properties. Besides the bi-axial stress, the stress-free lattice constant, d(0), are presented as well as an indication of the changes in texture as a function of process parameter. Total macroscopic stress...

  9. Biaxially textured composite substrates

    Groves, James R.; Foltyn, Stephen R.; Arendt, Paul N.

    2005-04-26

    An article including a substrate, a layer of a metal phosphate material such as an aluminum phosphate material upon the surface of the substrate, and a layer of an oriented cubic oxide material having a rock-salt-like structure upon the metal phosphate material layer is provided together with additional layers such as a HTS top-layer of YBCO directly upon a layer of a buffer material such as a SrTi.sub.x Ru.sub.1-x O.sub.3 layer.

  10. Comparison of Some Mechanical and Physical Methods for Measurement of Residual Stresses in Brush-Plated Nickel Hardened Gold and Silver Coatings

    Harri LILLE

    2016-03-01

    Full Text Available Hard gold and silver are applied in coating owing to their high hardness, good wear and corrosion resistance for engineering application (e.g. on generators slip rings, sliding contacts and small machine parts and are typically plated on copper (mostly, brass and bronze. The studied nickel-hardened gold and silver coatings were brush plated on open thin-walled copper ring substrates. Residual stresses in the coatings were calculated from the curvature changes of the substrates. Biaxial intrinsic residual stresses were also determined by nanoindentation testing and by the X-ray technique. The values of the residual stresses represented tensile stresses and when determined by the techniques used they were comparable within a maximum limit of measurement uncertainty. These stresses relax; the dependence of relaxation time was approximated by a linear-fractional function.

  11. On the evolution of residual stress at different substrate temperatures in sputter-deposited polycrystalline Mo thin films by x-ray diffraction

    The evolution of in-plane biaxial residual stress in polycrystalline Mo thin films deposited on Si at different substrate temperature were investigated using x-ray diffraction methods. The analyses were performed using both single and multi hkl reflection peak shifts methods in the asymmetric grazing incidence geometry. High compressive stress builds up in films synthesized at low substrate temperature while tensile stresses which are relatively low in magnitude manifest themselves at high substrate temperature. While such an evolutionary pattern is a direct consequence of competition between the intrinsic and thermal components of stress and varies as a function of temperature, the predominant cause of intrinsic compressive stress in Mo films deposited at low substrate temperature was traced to oxygen impurities incorporated in the film during the growth process. (paper)

  12. Effect of biaxial strain induced by piezoelectric PMN-PT on the upconversion photoluminescence of BaTiO₃:Yb/Er thin films.

    Wu, Zhenping; Zhang, Yang; Bai, Gongxun; Tang, Weihua; Gao, Ju; Hao, Jianhua

    2014-11-17

    Thin films of Yb3+/Er3+ co-doped BaTiO3 (BTO:Yb/Er) have been epitaxially grown on piezoelectric Pb(Mg1/3Nb2/3)0.7Ti0.3O3 (PMN-PT) substrates. Biaxial strain can be effectively controlled by applying electric field on PMN-PT substrate. A reversible, in situ and dynamic modification of upconversion photoluminescence in BTO:Yb/Er film was observed via converse piezoelectric effect. Detailed analysis and in situ X-ray diffraction indicate that such modulations are possibly due to the change in the lattice deformation of the thin films. This result suggests an alternative method to rationally tune the upconversion emissions via strain engineering. PMID:25402140

  13. Application of a linear elastic - brittle interface model to the crack initiation and propagation at fibre-matrix interface under biaxial transverse loads

    Mantič, V; Blázquez, A; Graciani, E; París, F

    2013-01-01

    The crack onset and propagation at the fibre-matrix interface in a composite under tensile/compressive remote biaxial transverse loads is studied by a new linear elastic - (perfectly) brittle interface model. In this model the interface is represented by a continuous distribution of springs which simulates the presence of a thin elastic layer. The constitutive law for the continuous distribution of normal and tangential of initially linear elastic springs takes into account possible frictionless elastic contact between fibre and matrix once a portion of the interface is broken. A brittle failure criterion is employed for the distribution of springs, which enables the study of crack onset and propagation. This interface failure criterion takes into account the variation of the interface fracture toughness with the fracture mode mixity. The main advantages of the present interface model are its simplicity, robustness and its computational efficiency when the so-called sequentially linear analysis is applied. Mo...

  14. The biaxial nonlinear crystal BiB3O6 as a polarization entangled photon source using non-collinear type-II parametric down-conversion

    Halevy, A; Dovrat, L; Eisenberg, H S; Becker, P; Bohatý, L

    2011-01-01

    We describe the full characterization of the biaxial nonlinear crystal BiB3O6 (BiBO) as a polarization entangled photon source using non-collinear type-II parametric down-conversion. We consider the relevant parameters for crystal design, such as cutting angles, polarization of the photons, effective nonlinearity, spatial and temporal walk-offs, crystal thickness and the effect of the pump laser bandwidth. Experimental results showing entanglement generation with high rates and a comparison to the well investigated beta-BaB2O4 (BBO) crystal are presented as well. Changing the down-conversion crystal of a polarization entangled photon source from BBO to BiBO enhances the generation rate as if the pump power was increased by more than three times. Such an improvement is currently required for the generation of multiphoton entangled states.

  15. The biaxial nonlinear crystal BiB₃O₆ as a polarization entangled photon source using non-collinear type-II parametric down-conversion.

    Halevy, A; Megidish, E; Dovrat, L; Eisenberg, H S; Becker, P; Bohatý, L

    2011-10-10

    We describe the full characterization of the biaxial nonlinear crystal BiB₃O₆ (BiBO) as a polarization entangled photon source using non-collinear type-II parametric down-conversion. We consider the relevant parameters for crystal design, such as cutting angles, polarization of the photons, effective nonlinearity, spatial and temporal walk-offs, crystal thickness and the effect of the pump laser bandwidth. Experimental results showing entanglement generation with high rates and a comparison to the well investigated β-BaB₂O₄ (BBO) crystal are presented as well. Changing the down-conversion crystal of a polarization entangled photon source from BBO to BiBO enhances the generation rate as if the pump power was increased by 2.5 times. Such an improvement is currently required for the generation of multiphoton entangled states. PMID:21997051

  16. Epitaxial growth of YBa2Cu3O7-δ on Ni89V11 non-magnetic biaxially textured substrate using NiO as buffer layer

    The superconducting YBa2Cu3O7-δ/CeO2/NiO multilayer structure was grown in situ by pulsed-laser deposition on biaxially textured Ni89V11 non-magnetic alloy. The role of vanadium is to decrease the Curie temperature of Ni and to favour the formation of oriented NiO. The (00l)NiO buffer layer has been formed by the controlled oxidation of the Ni-V substrate under 10 mTorr oxygen pressure and at 700 deg. C. The critical current density of 0.6 MA cm-2, at 77 K and zero magnetic field, was obtained for 0.7 μm thick YBa2Cu3O7-δ films. (author)

  17. 双轴压缩条件下碎石集料静力剪切特性研究%Static Shear Behavior of Crushed Rock Aggregate Subjected to Biaxial Compression

    王鹏程; 刘建坤; 李旭; 房建宏

    2014-01-01

    基于离散单元法,利用PFC2D内置Fish语言编制碎石集料双轴实验条件,结合计算机语言与PFC2D中Clump命令编制将球形单元转化为随机多边形块体单元的程序。通过对比室内大型三轴试验对数值模型进行参数标定与验证,在此基础上分析3种典型粒径碎石集料的应力-应变特性以及抗剪强度特性。结果表明,围压对集料的应力-应变特性影响明显。对于不同粒径的碎石集料而言,随着围压的增加,偏应力峰值增加而应力比减小;在本文选定的围压范围内碎石集料均呈现出先压缩最终剪胀的特性,围压越大,压缩量大,最终的剪胀越不明显;碎石集料的强度包络线为非线性,相同围压条件下的抗剪强度随着粒径的增大而增加;表征摩擦角随围压的增加而减小,相同围压下,粒径越大,表征摩擦角也越大。%With the discrete element method(DEM ) ,biaxial compressions test conditions for crushed rock aggre-gate were established in the Fish language and the Clump logic commands in PFC 2D were incorporated into the computer language to simulate the crushed rock aggregate of irregular shapes .Compared with large-scale labo-ratory triaxial tests ,the parameters of the numerical model were calibrated and validated .The stress-deforma-tion and shearing strength of the crushed stone aggregate of three typical particle sizes were analyzed .The re-search results demonstrate as follws :The confining pressure influences the stress-strain characteristics of aggre-gate significantly ;for aggregate of different particle sizes ,along with adding of the confining pressure ,the peak deviatoric stress increases while the stress ratio decreases ;within the specified range of confining pressure initial compression and subsequent dilation are observed with the aggregate ,the higher the confining pressure ,the lar-ger the compression and the smaller the dilation ;the shear strength

  18. Computer simulations of 3C-SiC under hydrostatic and non-hydrostatic stresses.

    Guedda, H Z; Ouahrani, T; Morales-García, A; Franco, R; Salvadó, M A; Pertierra, P; Recio, J M

    2016-03-01

    The response of 3C-SiC to hydrostatic pressure and to several uni- and bi-axial stress conditions is thoroughly investigated using first principles calculations. A topological interpretation of the chemical bonding reveals that the so-called non-covalent interactions enhance only at high pressure while the nature of the covalent Si-C bonding network keeps essentially with the same pattern. The calculated low compressibility agrees well with experimental values and is in concordance with the high structural stability of this polymorph under hydrostatic pressure. Under uniaxial [001] stress, the c/a ratio shows a noticeable drop inducing a closure of the band gap and the emergence of a metallic state around 40 GPa. This behavior correlates with a plateau of the electron localization function exhibiting a roughly constant and non-negligible value surrounding CSi4 and SiC4 covalent bonded units. PMID:26922870

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

    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.

  20. Debriefing Stress.

    Hill, Jonnie L.; Lance, Cynthia G.

    2002-01-01

    Discussion pf the stress associated with the educational use of games and simulations focuses on a study of graduate students that used the Myers-Briggs Type Indicator to determine that people with certain personality types experience stress at different intensities. Also found that all participants, regardless of personality type, needed…

  1. Oxidative stress

    This book contains 18 chapters. Some of the chapter titles are: Oxidative Stress: Introductory Remarks; Radiolysis of DNA and Model Systems in the Presence of Oxygen; Organic Peroxy Free Radicals as Ultimate Agents in Oxygen Toxicity; Antimalarials; and the Role of Dietary Components in Oxidative Stress in Tissues

  2. Geopotential Stress

    Schiffer, Christian; Nielsen, S.B.

    Density heterogeneity in the Earth’s lithosphere causes lateral pressure variations. Horizontal gradients of the vertically integrated lithostatic pressure, the Geopotential Energy (GPE), are a source of stresses (Geopotential Stress) that contribute to the Earth’s Stress Field. In theory the GPE...... is linearly related to the lithospheric part of the Geoid. The Geopotential Stress can be calculated if either the density structure and as a consequence the GPE or the lithospheric contribution to the Geoid is known. The lithospheric Geoid is usually obtained by short pass filtering of satellite Geoid...... are not entirely suitable for the stress calculations but can be compiled and adjusted. We present an approach in which a global lithospheric density model based on CRUST2.0 is obtained by simultaneously fitting topography and surface heat flow in the presence of isostatic compensation and long-wavelength lateral...

  3. Stress effects

    This chapter reviews the manner in which the influence of stress on a composite Cu/Ti-Nb superconductor brings about a deterioration of its electrical properties and those of the magnet wound from it. Training and electrical fatigue are considered. Static and dynamic stress effects are discussed as are dynamic stress effects -- repeated tension. The authors also examine dynamic stress effects--tension-compression. Several extensive case studies have been undertaken of the effects of both static and dynamic tensile and compressive stresses on the current-carrying properties of composite superconductors. Single-core and multi-filamentary Cu- or Al-stabilized monoliths, as well as cables, have been investigated and several representative studies are reviewed

  4. Intrinsic stress in ZrN thin films: Evaluation of grain boundary contribution from in situ wafer curvature and ex situ x-ray diffraction techniques

    Koutsokeras, L. E. [Departement Physique et Mecanique des Materiaux, Institut Pprime, CNRS-Universite de Poitiers-ENSMA, UPR 3346, SP2MI, Teleport 2, Bd M et P Curie, F 86962 Chasseneuil-Futuroscope (France); Department of Materials Science and Engineering, University of Ioannina, Ioannina 45110 (Greece); Abadias, G. [Departement Physique et Mecanique des Materiaux, Institut Pprime, CNRS-Universite de Poitiers-ENSMA, UPR 3346, SP2MI, Teleport 2, Bd M et P Curie, F 86962 Chasseneuil-Futuroscope (France)

    2012-05-01

    Low-mobility materials, like transition metal nitrides, usually undergo large residual stress when sputter-deposited as thin films. While the origin of stress development has been an active area of research for high-mobility materials, atomistic processes are less understood for low-mobility systems. In the present work, the contribution of grain boundary to intrinsic stress in reactively magnetron-sputtered ZrN films is evaluated by combining in situ wafer curvature measurements, providing information on the overall biaxial stress, and ex situ x-ray diffraction, giving information on elastic strain (and related stress) inside crystallites. The thermal stress contribution was also determined from the in situ stress evolution during cooling down, after deposition was stopped. The stress data are correlated with variations in film microstructure and growth energetics, in the 0.13-0.42 Pa working pressure range investigated, and discussed based on existing stress models. At low pressure (high energetic bombardment conditions), a large compressive stress is observed due to atomic peening, which induces defects inside crystallites but also promotes incorporation of excess atoms in the grain boundary. Above 0.3-0.4 Pa, the adatom surface mobility is reduced, leading to the build-up of tensile stress resulting from attractive forces between under-dense neighbouring column boundary and possible void formation, while crystallites can still remain under compressive stress.

  5. Intrinsic stress in ZrN thin films: Evaluation of grain boundary contribution from in situ wafer curvature and ex situ x-ray diffraction techniques

    Low-mobility materials, like transition metal nitrides, usually undergo large residual stress when sputter-deposited as thin films. While the origin of stress development has been an active area of research for high-mobility materials, atomistic processes are less understood for low-mobility systems. In the present work, the contribution of grain boundary to intrinsic stress in reactively magnetron-sputtered ZrN films is evaluated by combining in situ wafer curvature measurements, providing information on the overall biaxial stress, and ex situ x-ray diffraction, giving information on elastic strain (and related stress) inside crystallites. The thermal stress contribution was also determined from the in situ stress evolution during cooling down, after deposition was stopped. The stress data are correlated with variations in film microstructure and growth energetics, in the 0.13-0.42 Pa working pressure range investigated, and discussed based on existing stress models. At low pressure (high energetic bombardment conditions), a large compressive stress is observed due to atomic peening, which induces defects inside crystallites but also promotes incorporation of excess atoms in the grain boundary. Above 0.3-0.4 Pa, the adatom surface mobility is reduced, leading to the build-up of tensile stress resulting from attractive forces between under-dense neighbouring column boundary and possible void formation, while crystallites can still remain under compressive stress.

  6. Modeling of delayed strains of concrete under biaxial loadings. Application to the reactor containment of nuclear power plants; Modelisation des deformations differees du beton sous sollicitations biaxiales. application aux enceintes de confinement de batiments reacteurs des centrales nucleaires

    Benboudjema, F

    2002-12-15

    The prediction of delayed strains is of crucial importance for durability and long-term serviceability of concrete structures (bridges, containment vessels of nuclear power plants, etc.). Indeed, creep and shrinkage cause cracking, losses of pre-stress and redistribution of stresses, and also, rarely, the ruin of the structure. The objective of this work is to develop numerical tools, able to predict the long-term behavior of concrete structures. Thus, a new hydro mechanical model is developed, including the description of drying, shrinkage, creep and cracking phenomena for concrete as a non-saturated porous medium. The modeling of drying shrinkage is based on an unified approach of creep and shrinkage. Basic and drying creep models are based on relevant chemo-physical mechanisms, which occur at different scales of the cement paste. The basic creep is explicitly related to the micro-diffusion of the adsorbed water between inter-hydrates and intra-hydrates and the capillary pores, and the sliding of the C-S-H gel at the nano-porosity level. The drying creep is induced by the micro-diffusion of the adsorbed water at different scales of the porosity, under the simultaneous effects of drying and mechanical loadings. Drying shrinkage is, therefore, assumed to result from the elastic and delayed response of the solid skeleton, submitted to both capillary and disjoining pressures. Furthermore, the cracking behavior of concrete is described by an orthotropic elastoplastic damage model. The coupling between all these phenomena is performed by using effective stresses which account for both external applied stresses and pore pressures. This model has been incorporated into a finite element code. The analysis of the long-term behavior is also performed on concrete specimens and prestressed concrete structures submitted to simultaneous drying and mechanical loadings. (author)

  7. Hypervelocity Impact of Unstressed and Stressed Titanium in a Whipple Configuration in Support of the Orion Crew Exploration Vehicle Service Module Propellant Tanks

    Nahra, Henry K.; Christiansen, Eric; Piekutowski, Andrew; Lyons, Frankel; Keddy, Christopher; Salem, Jonathan; Miller, Joshua; Bohl, William; Poormon, Kevin; Greene, Nathanel; Rodriquez, Karen

    2010-01-01

    Hypervelocity impacts were performed on six unstressed and six stressed titanium coupons with aluminium shielding in order to assess the effects of the partial penetration damage on the post impact micromechanical properties of titanium and on the residual strength after impact. This work is performed in support of the definition of the penetration criteria of the propellant tanks surfaces for the service module of the crew exploration vehicle where such a criterion is based on testing and analyses rather than on historical precedence. The objective of this work is to assess the effects of applied biaxial stress on the damage dynamics and morphology. The crater statistics revealed minute differences between stressed and unstressed coupon damage. The post impact residual stress analyses showed that the titanium strength properties were generally unchanged for the unstressed coupons when compared with undamaged titanium. However, high localized strains were shown near the craters during the tensile tests.

  8. Stress incontinence

    ... to identify and control your pelvic floor muscles. Kegel exercises : These exercises can help keep the muscle ... stress incontinence and they bother you. Prevention Doing Kegel exercises may help prevent symptoms. Women who are ...

  9. Stressing academia?

    Opstrup, Niels; Pihl-Thingvad, Signe

    Incongruences between the individual and the organizational work context are potential stressors. The present study focuses on the relationship between a complementary need-supply fit and Danish researchers’ self-perceived job stress. Strain is expected to increase as organizational supplies fall...... short of individual need while high degrees of fit will mitigate stress. The analysis is based on a stratified random sample including 2127 researchers at 64 Danish university departments and covering all main areas of research and all academic staff categories. The results show that fit with regard to...... “soft” dimensions as freedom and independence in the job, personal and professional development at work, and receiving peer recognition is highly significant for the researchers’ self-perceived stress-level. The better the fit is the lower stress-levels the researchers’ on average report. On the other...

  10. Stress fractures

    The diagnosis of a stress fracture should be considered in patients presented with pain after a change in activity, especially if the activity is strenuous and the pain is in the lower extremities. Since evidence of the stress fracture may not be apparent for weeks on routine radiographs, proper use of other imaging techniques will allow an earlier diagnosis. Prompt diagnosis is especially important in the femur, where displacement may occur

  11. Modeling of delayed strains of concrete under biaxial loadings. Application to the reactor containment of nuclear power plants

    The prediction of delayed strains is of crucial importance for durability and long-term serviceability of concrete structures (bridges, containment vessels of nuclear power plants, etc.). Indeed, creep and shrinkage cause cracking, losses of pre-stress and redistribution of stresses, and also, rarely, the ruin of the structure. The objective of this work is to develop numerical tools, able to predict the long-term behavior of concrete structures. Thus, a new hydro mechanical model is developed, including the description of drying, shrinkage, creep and cracking phenomena for concrete as a non-saturated porous medium. The modeling of drying shrinkage is based on an unified approach of creep and shrinkage. Basic and drying creep models are based on relevant chemo-physical mechanisms, which occur at different scales of the cement paste. The basic creep is explicitly related to the micro-diffusion of the adsorbed water between inter-hydrates and intra-hydrates and the capillary pores, and the sliding of the C-S-H gel at the nano-porosity level. The drying creep is induced by the micro-diffusion of the adsorbed water at different scales of the porosity, under the simultaneous effects of drying and mechanical loadings. Drying shrinkage is, therefore, assumed to result from the elastic and delayed response of the solid skeleton, submitted to both capillary and disjoining pressures. Furthermore, the cracking behavior of concrete is described by an orthotropic elastoplastic damage model. The coupling between all these phenomena is performed by using effective stresses which account for both external applied stresses and pore pressures. This model has been incorporated into a finite element code. The analysis of the long-term behavior is also performed on concrete specimens and prestressed concrete structures submitted to simultaneous drying and mechanical loadings. (author)

  12. Identification of a Visco-Elastic Model for PET Near Tg Based on Uni and Biaxial Results

    Luo, Yun Mei; CHEVALIER, Luc; Monteiro, E

    2011-01-01

    The mechanical response of Polyethylene Terephthalate (PET) in elongation is strongly dependent on temperature, strain and strain rate. Near the glass transition temperature Tg, the stress-strain curve presents a strain softening effect vs strain rate but a strain hardening effect vs strain under conditions of large deformations. The main goal of this work is to propose a viscoelastic model to predict the PET behaviour when subjected to large deformations and to determine the material propert...

  13. Stress in childhood

    ... Medical treatments produce even greater stress. Recognition of parental stress (such as divorce or financial crisis) is a ... Children may not recognize that they are stressed. Parents may suspect stress if the child has experienced a stressful situation ...

  14. What Is Stress Management?

    ... Workplace Food and Beverage Toolkit What Is Stress Management? Updated:Jul 7,2016 What is Stress Management? ... FAQs About Stress Last reviewed - 6/2014 Stress Management • Home • How Does Stress Affect You? Introduction FAQs ...

  15. Influence of Intermediate Stress on Yielding of Berea Sandstone

    Jourine, S.; Karner, S. L.; Kronenberg, A. K.; Chester, F. M.

    2003-12-01

    The onset of brittle failure of Berea sandstone has been investigated under varying stress states by subjecting solid and hollow cylindrical samples to confining pressure Pc (to 120 MPa) and axial stress σ z (to 260 MPa) in a conventional triaxial deformation apparatus. Inelastic yielding of solid and hollow samples is marked by cascading acoustic emissions and axial displacements that depart from the initial linear elastic response. For hollow samples, uniaxial (σ z > σ Θ = σ r = 0) and biaxial (σ z > σ Θ > σ r = 0 or σ Θ > σ z > σ r = 0) stress states are obtained with deviators that (1) are maximum at the inner wall, (2) decay in a predictable manner with increasing radius prior to yielding, and (3) are insensitive to frictional boundary conditions at piston-sample contacts throughout much of the sample. X-ray CT scans of deformed samples reveal different modes of failure associated with the stress states imposed. Zones of anomalous X-ray density within hollow samples that mark deformed sandstone are localized near the inner wall, nearly midway between sample ends, and inner walls have lost their cylindrical geometry. Axial cavities of hollow samples become elliptical when axial stress is the intermediate principal stress (σ z = σ 2), with geometries resembling wellbore break-outs used to infer in-situ horizontal stresses in scientific drilling studies, while toroidal spalls are developed when the tangential stress is the intermediate stress (σ Θ = σ 2). Our results for solid specimens under conventional triaxial conditions (σ z > σ r = σ Θ > 0) are in agreement with results reported for Berea sandstone. However, the results for hollow specimens require a yield criterion that includes intermediate stress σ 2. Yield criteria that fit our combined data may be expressed in terms of first and second invariants of stress I1 and J2; for example, using the modified Wiebols and Cook (1968) criterion, J21/2 = A + B I1 + C I12, data for Berea

  16. Arbejdslivet - Stress

    Abrahamian, Natalie; Bøgh Johansen, Katrine; Strand Henriksen, Nicoline; Schmidt, Cecilie; Møller, Michael; Atke Jakobsen, Simone; Fulgsig Simonsen, Mia My; Ceran, Gülcan

    2016-01-01

    The following report will evolve around the theme of stress. Our focus will be the work conditions for midwives based on the empirical data compiled by our interviews and an observation at the maternity ward at Nordsjællands Hospital in Hillerød. The academics of this report will be centered around the psychological theory by Richard S. Lazarus combined with other relevant theories regarding psychology, stress and the work conditions of the post-modernity. The purpose of this report is to exa...

  17. Stress Analysis

    Burcharth, Hans F.

    The following types of forces contribute to the stresses in a Dolos in a pack exposed to waves: 1)Gravity forces Compaction forces (mainly due to settlements, gravity and flow forces) 2) Flow forces 3) Impact forces (impacts between moving concrete blocks)......The following types of forces contribute to the stresses in a Dolos in a pack exposed to waves: 1)Gravity forces Compaction forces (mainly due to settlements, gravity and flow forces) 2) Flow forces 3) Impact forces (impacts between moving concrete blocks)...

  18. Stressed podocytes

    Svenningsen, Per

    2015-01-01

    conditions and in response to injury induced by endoplasmatic reticulum (ER) stress (Golubinskaya et al., 2015). Their report shed light on the complex regulation of Best3 in podocytes and will help pave the way for future studies on the pathogenesis of kidneys diseases with podocyte injury. This article is...

  19. STRESS ECHOCARDIOGRAPHY

    Salustri, Alessandro

    1994-01-01

    textabstractIn the studies reported in this thesis, stress echocardiography (either with exercise or with pharmacological agents) and myocardial perfusion scintigraphy have been performed in different groups of patients and in different clinical conditions. Some practical aspects on the protocols of echocardiographic tests are briefly reported

  20. Stress Tests

    Our Nuclear Facilities have recently operated in a special regime. Since March until December they were scrutinised by a team verifying and drilling all possible scenarios in case of emergency situations, earthquake, floods or long-term power supply loss. Stress tests were the hard job but their findings are already now a great contribution. (author)

  1. Modeling of the cold work stress relieved Zircaloy-4 cladding tubes mechanical behavior under PWR operating conditions

    This paper proposes a damaged viscoplastic model to simulate, for different isotherms (320, 350, 380, 400 and 420 degC), the out-of-flux anisotropic mechanical behavior of cold work stress relieved Zircaloy-4 cladding tubes over the fluence range 0-85.1024 nm-2 (E > 1 MeV). The model, identified from uni and biaxial tests conducted at 350 and 400 degC, is validated from tests performed at 320, 380 and 420 degC. This model is able to simulate strain hardening under internal pressure followed by a stress relaxation period (thermal creep), which is representative of a pellet cladding mechanical interaction occurring during a power transient (class 2 incidental condition). Both the integration of a scalar state variable, characterizing the damage caused by a bombardment with neutrons, and the modification of the static recovery law allowed us to simulate the fast neutron flux effect (irradiation creep). (author)

  2. Three-Dimensional Packing Structure and Electronic Properties of Biaxially Oriented Poly(2,5-bis(3-alkylthiophene-2-yl)thieno[3,2- b ]thiophene) Films

    Cho, Eunkyung

    2012-04-11

    We use a systematic approach that combines experimental X-ray diffraction (XRD) and computational modeling based on molecular mechanics and two-dimensional XRD simulations to develop a detailed model of the molecular-scale packing structure of poly(2,5-bis (3-tetradecylthiophene-2-yl) thieno[3,2-b]thiophene) (PBTTT-C 14) films. Both uniaxially and biaxially aligned films are used in this comparison and lead to an improved understanding of the molecular-scale orientation and crystal structure. We then examine how individual polymer components (i.e., conjugated backbone and alkyl side chains) contribute to the complete diffraction pattern, and how modest changes to a particular component orientation (e.g., backbone or side-chain tilt) influence the diffraction pattern. The effects on the polymer crystal structure of varying the alkyl side-chain length from C 12 to C 14 and C 16 are also studied. The accurate determination of the three-dimensional polymer structure allows us to examine the PBTTT electronic band structure and intermolecular electronic couplings (transfer integrals) as a function of alkyl side-chain length. This combination of theoretical and experimental techniques proves to be an important tool to help establish the relationship between the structural and electronic properties of polymer thin films. © 2012 American Chemical Society.

  3. Annealing induced coherent evolutions of biaxial strain and antiferromagnetic-insulator phase in La0.625Ca0.375MnO3 films

    Han, Yunxin; Wu, Wenbin; Jiang, Guoshun; Zhu, Changfei

    2012-09-01

    La0.625Ca0.375MnO3 (LCMO) films with thicknesses between 7 and 54 nm were epitaxially grown on (LaAlO3)0.3(Sr2AlTaO6)0.35 (001) [LSAT (001)] substrates by using pulsed laser deposition. For this epitaxial system, antiferromagnetic-insulator (AFI) state can be controlled by changing the film thickness and annealing time with various epitaxial strain states, although this phenomenon is absent in the relatively thick films or bulk samples. The consistency between magnetization and resistivity data suggests all these interesting transport behaviors are attributed to the fluctuation of AFI volume fractions and their instability. Especially, there are huge low-field magnetoresistance over -54% (32 nm) at 0.1 T and enhanced magnetoresistance over a broad temperature range. Based on these above results, annealing induced coherent evolutions of biaxial strain and AFI phase in LCMO epitaxial films is a consequence of the strain-driven orbital ordered state, and this may make an approach for a possible application of strongly correlated electron devices.

  4. Comparative Study on Tribological Behavior of Biaxial Glass Fiber/Al2O3/SiC Epoxy Journal Bearing Under Various Test Conditions

    T. Narendiranath Babu

    2014-08-01

    Full Text Available Composite journal bearings are becoming more popular now a day because they eliminate the possibility of seizure failure to the bearings. The major drawback of the gun metal bearings is the seizure failure. To overcome this problem, the composite journal bearings are widely used by the industries. In this study, the fiber reinforced plastic composed of glass fiber with epoxy resin composite /Al2O3/SiC journal bearing having the composition of 10-20% are tested under various operating conditions and the results are compared with gun metal journal bearing. This study focuses on the dimensional stability, temperature, friction, surface roughness and surface topography behavior of biaxial glass fiber epoxy composite with and without lubrication at different speeds and loads. It has been observed that the friction and temperature increases with increase in load but it’s very less when compared to gun metal bearing. It is found that there is loss in weight due to increase in temperature and friction but the loss in weight is very less which is approximately 1 g. In the earlier research, most of the bearings are tested under very low speed with more catastrophic failure due to various loading conditions. Therefore in this study the composite journal bearing is tested from low speed to high speed with different loading conditions and their effects has been studied. This composite journal will save the significant cost to the industries by reducing the coefficient of friction, temperature, lubrication etc.

  5. Analysis and optimization of oxide buffer layers related to YBCO films deposited by CSD and MOCVD on biaxially textured NiW substrates

    The studies based on epitaxial buffer layers of CeO2 and Yttria-stabilised ZrO2 (YSZ) having been deposited on biaxially textured nickel substrates using thermal reactive evaporation and rf sputtering in continuous deposition processes in reel-to-reel systems. Starting from the well known architecture of CeO2/YSZ/CeO2 the thickness of the different buffer layers was varied. Misorientation, porosity and roughness was analyzed and optimized for YBCO deposition by MOCVD und CSD. The grain morphology and the behavior of the grain boundary networks in YBCO coated conductors have been shown to depend on both the YBCO deposition method and the buffers layer. The possibility of using only one and two buffers layer and conductive layers of perovskite type was studied. X-ray-diffraction, SEM and TEM have been used to investigate the microstructure of both the buffer layers and the YBCO films. Optimal growth conditions of YBCO for the different buffer layers have been determined. YBCO films were deposited by CSD, MOCVD and for comparison by high pressure dc sputtering, resulting on CeO2/YSZ/CeO2 buffered substrates Jc values higher than 2 MA/cm2. The resulting superconducting properties were measured by inductive characterization and by Hall probe measurements of the magnetic field due to induced magnetization currents. (orig.)

  6. Chemical Solution-Based Epitaxial Oxide Films on Biaxially Textured Ni-W Substrates with Improved Out-of-Plane Texture for YBCO-Coated Conductors

    Bhuiyan, M. S.; Paranthaman, M.; Sathyamurthy, S.

    2007-10-01

    Epitaxial films of rare-earth (RE) niobates (where the rare earth includes La, Ce, and Nd) and lanthanum tantalate with pyrochlore structures were grown directly on biaxially textured nickel-3 at.% tungsten (Ni-W) substrates using a chemical solution deposition (CSD) process. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) analysis revealed the surface morphology of the films to be smooth and homogeneous. Detailed X-ray diffraction analysis showed that the films of pyrochlore RE niobate and La-tantalate are highly textured with cube-on-cube epitaxy. The overall texture quality of the films was investigated by measuring the full-width half-maximum (FWHM) of the (004) and (222) rocking curves. We observed a sharper texture for both lanthanum niobate (La3NbO7) and lanthanum tantalate (La3TaO7) films compared to the underlying Ni-W substrate, though they have a larger lattice misfit with the Ni-W substrates. These results were comparable to the texture improvement observed in vacuum-deposited Y2O3 seed layers. Texture improvement in the seed layer is the key towards obtaining YBCO films with a␣higher critical current density. Hence, solution-deposited La3NbO7 and La3TaO7 films can be used as a seed layer towards developing all metalorganic-deposited (MOD) buffer/YBCO architectures.

  7. Highly reinforced, low magnetic and biaxially textured Ni-7 at.%W/Ni-12 at.%W multi-layer substrates developed for coated conductors

    Mechanically strengthened, highly cube textured Ni-7 at.%W/Ni-12 at.%W multi-layer substrates developed for coated conductors have been prepared by the advanced spark plasma sintering technique. The key innovation for developing this weakly magnetic and reinforced substrate was to use a new powder metallurgy and sintering route to bond multi-layers of Ni7W/Ni12W/Ni7W together in order to get an initial ingot, followed by the optimized cold working and annealing. Particular efforts were made in view of the optimization of the design, pressing as well as the heat treatment processes of the starting ingots to obtain a chemically gradient composite bulk, thus ensuring the subsequent cold deformation. The produced composite substrates have a strong {100} texture on Ni7W outer layers. The percentage of the biaxially orientated grains within a misorientation angle of 10 deg. is as high as 97.5%, while the length percentage of low-angle grain boundaries ranging from 2 deg. to 10 deg. in the composite substrate reaches 87.2%. Moreover, the yield strength σ0.2 of the tape approaches 333 MPa, and the saturation magnetization is substantially reduced by 81.6% at 77 K when compared to that of a commercial used Ni5W substrate

  8. Ion-beam-assisted deposition of biaxially aligned yttria-stabilized zirconia template films on metallic substrates for YBCO-coated conductors

    Ma, B.; Li, M.; Fisher, B. L.; Balachandran, U.

    2002-07-01

    Biaxially textured yttria-stabilized zirconia (YSZ) films were grown on mechanically polished Hastelloy C276 (HC) substrates by ion-beam-assisted deposition and electron-beam evaporation. The surface root-mean-square (RMS) roughness of the polished HC substrates was ≈3 nm, as measured by atomic force microscopy (AFM). A water-cooled sample stage was used to hold the substrate temperature below 100 °C during deposition. RMS roughness of ≈3.3 nm was measured on the deposited YSZ films by AFM. X-ray pole figures were conducted for texture analysis; in-plane texture measured from YSZ (111) φ-scan FWHM was 13.2° and out-of-plane texture from the YSZ (002) ω-scan FWHM was 7.7°. An ≈10 nm thick CeO2 buffer layer was deposited on the YSZ film at 800 °C before YBCO films were ablated by pulsed laser deposition at 780 °C in a 250 mTorr flowing oxygen environment. Good in-plane texture with FWHM ≈ 7° was observed in YBCO films. Tc = 90 K, with sharp transition, and transport Jc of ≈2.2 × 106 A cm-2 were observed in a 0.5 μm thick, 5 mm wide, and 1 cm long sample at 77 K in self-field.

  9. Development of biaxially textured buffer layers on rolled-Ni substrates for high current YBa2Cu3O7-y coated conductors

    This paper describes the development of 3 buffer layer architectures with good biaxial textures on rolled-Ni substrates using vacuum processing techniques. The techniques include pulsed laser ablation, e-beam evaporation, dc and rf magnetron sputtering. The first buffer layer architecture consists of an epitaxial laminate of Ag/Pd(Pt)/Ni. The second buffer layer consists of an epitaxial laminate of CeO2/Pd/Ni. The third alternative buffer layer architecture consists of an epitaxial laminate of YSZ/CeO2/Ni. The cube (100) texture in the Ni was produced by cold rolling followed by recrystallization. Crystallographic orientations of the Pd, Ag, CeO2, and YSZ films grown were all (100). We recently demonstrated a critical- current density of 0.73x106 A/cm2 at 77 K and zero field on 1.4 μm thick YBa2Cu3O7-y (YBCO) film. This film was deposited by pulsed laser ablation on a YBCO/YSZ/CeO2/Ni substrate

  10. Ion-beam-assisted deposition of biaxially aligned yttria-stabilized zirconia template films on metallic substrates for YBCO-coated conductors

    Ma, B. [Energy Technology Division, Argonne National Laboratory, Argonne, IL (United States)]. E-mail: bma@anl.gov; Li, M.; Fisher, B.L.; Balachandran, U. [Energy Technology Division, Argonne National Laboratory, Argonne, IL (United States)

    2002-07-01

    Biaxially textured yttria-stabilized zirconia (YSZ) films were grown on mechanically polished Hastelloy C276 (HC) substrates by ion-beam-assisted deposition and electron-beam evaporation. The surface root-mean-square (RMS) roughness of the polished HC substrates was {approx}3 nm, as measured by atomic force microscopy (AFM). A water-cooled sample stage was used to hold the substrate temperature below 100 deg. C during deposition. RMS roughness of {approx}3.3 nm was measured on the deposited YSZ films by AFM. X-ray pole figures were conducted for texture analysis; in-plane texture measured from YSZ (111) {phi}-scan FWHM was 13.2 deg. and out-of-plane texture from the YSZ (002) {omega}-scan FWHM was 7.7 deg. An {approx}10 nm thick CeO{sub 2} buffer layer was deposited on the YSZ film at 800 deg. C before YBCO films were ablated by pulsed laser deposition at 780 deg. C in a 250 mTorr flowing oxygen environment. Good in-plane texture with FWHM {approx}7 deg. was observed in YBCO films. T{sub c} 90 K, with sharp transition, and transport J{sub c} of {approx}2.2x10{sup 6} A cm{sup -2} were observed in a 0.5 {mu}m thick, 5 mm wide, and 1 cm long sample at 77 K in self-field. (author)

  11. Ion-beam-assisted deposition of biaxially aligned yttria-stabilized zirconia template films on metallic substrates for YBCO-coated conductors

    Biaxially textured yttria-stabilized zirconia (YSZ) films were grown on mechanically polished Hastelloy C276 (HC) substrates by ion-beam-assisted deposition and electron-beam evaporation. The surface root-mean-square (RMS) roughness of the polished HC substrates was ∼3 nm, as measured by atomic force microscopy (AFM). A water-cooled sample stage was used to hold the substrate temperature below 100 deg. C during deposition. RMS roughness of ∼3.3 nm was measured on the deposited YSZ films by AFM. X-ray pole figures were conducted for texture analysis; in-plane texture measured from YSZ (111) φ-scan FWHM was 13.2 deg. and out-of-plane texture from the YSZ (002) ω-scan FWHM was 7.7 deg. An ∼10 nm thick CeO2 buffer layer was deposited on the YSZ film at 800 deg. C before YBCO films were ablated by pulsed laser deposition at 780 deg. C in a 250 mTorr flowing oxygen environment. Good in-plane texture with FWHM ∼7 deg. was observed in YBCO films. Tc 90 K, with sharp transition, and transport Jc of ∼2.2x106 A cm-2 were observed in a 0.5 μm thick, 5 mm wide, and 1 cm long sample at 77 K in self-field. (author)

  12. Approximation of properties of hyperelastic materials with use of energy-based models and biaxial tension data

    Jamróz, Weronika

    2016-06-01

    The paper shows the way enrgy-based models aproximate mechanical properties of hiperelastic materials. Main goal of research was to create a method of finding a set of material constants that are included in a strain energy function that constitutes a heart of an energy-based model. The most optimal set of material constants determines the best adjustment of a theoretical stress-strain relation to the experimental one. This kind of adjustment enables better prediction of behaviour of a chosen material. In order to obtain more precised solution the approximation was made with use of data obtained in a modern experiment widely describen in [1]. To save computation time main algorithm is based on genetic algorithms.

  13. Test plan for suitability assessment of five overcoring stress measurement techniques

    Tests are to be conducted at the Near-Surface Test Facility (NSTF) to assess the suitability of five overcoring techniques for in situ stress determination in a jointed basalt. The overcoring methods to be investigated use the following instrumentation to measure strain relief by overcoring a pilot borehole: USBM borehole deformation gage, CSIRO hollow inclusion stress cell, cast epoxy inclusion, the Lulea triaxial strain cell and the ''doorstopper'' biaxial strain cell. The tests are to provide data regarding the state of stress below the NSTF. This information is to be used in the evaluation of each method of overcoring. During the course of field testing, an attempt is to be made to adapt conventional overcoring techniques and analytical methods to the basalt medium. If overcoring stress determination in basalt is shown suitable, then additional studies will be identified to further adapt a technique for use at depth. In addition to the five overcoring techniques to be tested at the NSTF, stress measurements by Hydrofracturing are to be conducted to provide data for direct comparison with overcoring results. 16 refs., 18 figs

  14. Equi-penetration grazing incidence X-ray diffraction method: Stress depth profiling of ground silicon nitride

    In this work a new modification of the grazing incidence X-ray diffraction method for residual stress determination is presented. This equi-penetration grazing incidence X-ray diffraction method is especially suitable for the precise determination of the residual stress depth profile in materials. It originates from a sin2ψ approach based on the determination of the lattice spacing of various selected diffraction planes. Additionally, for each measurement the condition ∂τ/∂ψ = 0 is here fulfilled and one dataset corresponds strictly to a specific mean penetration depth τ independent of the tilt angle ψ. This can be achieved by the individual adjustment of the incidence angle for each measured diffraction maximum. In the actual work, the influence of different surface finishes on the stress depth profile of commercial silicon nitride ceramic samples is investigated. The ground specimen displays an almost biaxial compressive stress parallel and near to the specimen surface of 3 GPa, which decreases almost up to zero in a depth of 5 μm. After the polishing process, the specimens show a strongly reduced compressive stress maximum at the surface of 1 GPa, which diminishes similarly with increasing depth. The orientation between the stress component and the grinding direction is of minor influence. Furthermore, the influence of a possible residual stress component perpendicular to the sample surface is discussed

  15. Behavior of Three Metallic Alloys under Combined Axial-Shear Stresses at Elevated Temperature

    Colaiuta, J. F.; Lissenden, C. J.; Lerch, B. A.

    2003-01-01

    Type 316 stainless steel, Haynes 188, and Inconel 718 samples were subjected to an axial-shear strain controlled loading history while the specimen temperature was held at 650 C to quantify the evolution of material state under a complex biaxial load path when the material is in the viscoplastic domain. Yield surfaces were constructed in the axial-shear stress plane using a sensitive, 30 x 10(exp -6)m/m, equivalent offset strain definition for the yield strain. Subsequent yield surfaces were constructed at various points along the strain path to define the material evolution. These subsequent yield surface translated, expanded, and distorted relative to the initial yield surface. Each of these very different materials exhibited components of isotropic, kinematic and distortional hardening. Furthermore, subsequent yield surfaces for each material have a very well defined front face and a poorly defined, flattened, back side.

  16. Tensile strength and internal stress determination in salt compacts by diametrical and axial compression tests

    Due to the brittle character of the material an indirect method (diametrical and axial compression testing) was adopted for tensile strength determination. Two lots of compacts were prepared from salt powder, by pressing it in steel dyes by means of a hydraulic press. For uniaxial tests, cylindrical compacts were used. Biaxial tests were done on disk-shaped compacts, each disk having a diametrical V-shaped cut on one of its plane areas. The punches used for compression tests, were designed to obtain a ratio of 1.2 between their curvature radius and sample radius. At the same time with the tensile strength, the stress intensity factor (KIC and KIIC values) has been obtained. The results obtained are in good agreement with the mechanical properties of the salt, previously reported. (Authors)

  17. Stress and your heart

    Coronary heart disease - stress; Coronary artery disease - stress ... Your body responds to stress on many levels. First, it releases stress hormones that make you breathe faster. Your blood pressure goes up. Your muscles ...

  18. Stress and Pregnancy

    ... Home > Pregnancy > Body & lifestyle changes > Stress and pregnancy Stress and pregnancy E-mail to a friend Please ... at increased risk for health problems. What causes stress during pregnancy? The causes of stress are different ...

  19. Repetitive Stress Injuries

    ... Can I Help a Friend Who Cuts? Repetitive Stress Injuries KidsHealth > For Teens > Repetitive Stress Injuries Print ... t had any problems since. What Are Repetitive Stress Injuries? Repetitive stress injuries (RSIs) are injuries that ...

  20. Stress and Mood

    ... Relaxation Emotions & Relationships HealthyYouTXT Tools Home » Stress & Mood Stress & Mood Many people who go back to smoking ... story: Time Out Times 10 >> share What Causes Stress? Read full story: What Causes Stress? >> share The ...

  1. Oxidative stress

    Stevanović Jelka

    2012-01-01

    Full Text Available The unceasing need for oxygen is in contradiction to the fact that it is in fact toxic to mammals. Namely, its monovalent reduction can have as a consequence the production of short-living, chemically very active free radicals and certain non-radical agents (nitrogen-oxide, superoxide-anion-radicals, hydroxyl radicals, peroxyl radicals, singlet oxygen, peroxynitrite, hydrogen peroxide, hypochlorous acid, and others. There is no doubt that they have numerous positive roles, but when their production is stepped up to such an extent that the organism cannot eliminate them with its antioxidants (superoxide-dismutase, glutathione-peroxidase, catalase, transferrin, ceruloplasmin, reduced glutathion, and others, a series of disorders is developed that are jointly called „oxidative stress.“ The reactive oxygen species which characterize oxidative stress are capable of attacking all main classes of biological macromolecules, actually proteins, DNA and RNA molecules, and in particular lipids. The free radicals influence lipid peroxidation in cellular membranes, oxidative damage to DNA and RNA molecules, the development of genetic mutations, fragmentation, and the altered function of various protein molecules. All of this results in the following consequences: disrupted permeability of cellular membranes, disrupted cellular signalization and ion homeostasis, reduced or loss of function of damaged proteins, and similar. That is why the free radicals that are released during oxidative stress are considered pathogenic agents of numerous diseases and ageing. The type of damage that will occur, and when it will take place, depends on the nature of the free radicals, their site of action and their source. [Projekat Ministarstva nauke Republike Srbije, br. 173034, br. 175061 i br. 31085

  2. Growth of thin Al{sub 2}O{sub 3} films on biaxially oriented polymer films by atomic layer deposition

    Vaehae-Nissi, Mika, E-mail: mika.vaha-nissi@vtt.fi [VTT Technical Research Centre of Finland, P.O. Box 1000, FI-02044 VTT (Finland); Kauppi, Emilia, E-mail: emilia.kauppi@vti.fi [VTT Technical Research Centre of Finland, P.O. Box 1000, FI-02044 VTT (Finland); Sahagian, Khoren, E-mail: khoren@anasysinstruments.com [Anasys Instruments, 121 Gray Avenue, Suite 100, Santa Barbara, CA 93101 (United States); Johansson, Leena-Sisko, E-mail: leena-sisko.johansson@aalto.fi [Aalto University, School of Chemical Technology, Department of Forest Products Technology, P.O. Box 16100, FI-00076 AALTO (Finland); Peresin, Maria Soledad; Sievaenen, Jenni; Harlin, Ali [VTT Technical Research Centre of Finland, P.O. Box 1000, FI-02044 VTT (Finland)

    2012-11-01

    The effects of thin film nucleation and initial growth on roughness, chemistry and thermomechanical properties of polymer film surfaces were studied. Al{sub 2}O{sub 3} was deposited onto commercial biaxially oriented polypropylene and polylactic acid films at 80 Degree-Sign C by using atomic layer deposition technique. Both substrates, especially the more hydrophobic polypropylene, showed initial growth through Al{sub 2}O{sub 3} clusters. There was a faster deposition of Al{sub 2}O{sub 3} on polylactic acid film than on polypropylene at the early stages of the Al{sub 2}O{sub 3} deposition. There were also indications of chemical interactions between polylactic acid and trimethyl aluminum used as a precursor for Al{sub 2}O{sub 3}. Changes in the thermo-mechanical properties of the polymer surfaces with Al{sub 2}O{sub 3} also evidenced the differences between the substrate polymer films. The near surface interphase formed in polylactic acid probably contributed to the strong increase and scattering in the softening temperature during the early thin film growth. - Highlights: Black-Right-Pointing-Pointer Growth of atomic layer deposited Al{sub 2}O{sub 3} at 80 Degree-Sign C was studied on commercial films. Black-Right-Pointing-Pointer Both substrate films showed early Al{sub 2}O{sub 3} growth through clusters. Black-Right-Pointing-Pointer Initial growth rate depends on the nature of the substrate film surface. Black-Right-Pointing-Pointer There were indications of chemical interactions between substrate and precursor. Black-Right-Pointing-Pointer Film thickness and chemical interactions affect thermo-mechanical properties.

  3. Caracterización mecánica de aleaciones Ti-Nb mediante ensayos de flexión biaxial

    Amigó, V.

    2010-12-01

    Full Text Available Nowadays titanium and titanium alloys are increasingly being used in the industry. Particularly β-Ti alloys that stand out for having great strength properties and low elastic modulus compared to Ti c.p. or Ti-6Al-4V. Among Ti alloys, Ti-Nb alloys with high contents of alloying elements are widely used. In this work Ti-Nb alloys have been obtained using conventional powdermetallurgy. It has been studied the evolution of properties of these alloys as a function of the percentage of niobium. It can be noted the ball on three balls test used in order to characterize the samples.

    En la actualidad, cada vez, son más importantes en la industria las aleaciones de titanio. En especial las aleaciones tipo-β, que destacan por tener buenas propiedades resistentes y bajos módulos elásticos, en comparación con el Ti c.p. o el Ti-6Al-4V. Dentro de estas aleaciones cabe destacar las Ti-Nb con altos contenidos en elementos aleantes. En este trabajo se han obtenido, mediante pulvimetalurgia convencional, una serie de aleaciones Ti-Nb, en el rango del 20-40 % de niobio. Se ha obtenido la evolución de las propiedades de dichas aleaciones en función del porcentaje de niobio, mediante la utilización del ensayo de flexión biaxial con tres apoyos (three ball test.

  4. Formaldehyde stress

    2010-01-01

    Formaldehyde,one of the most toxic organic compounds,is produced and processed in human cells.The level of human endogenous formaldehyde is maintained at a low concentration(0.01-0.08 mmol L-1 in blood) under physiological conditions,but the concentration increases during ageing(over 65 years old).Clinical trials have shown that urine formaldehyde concentrations are significantly different between elderly Alzheimer’s patients(n=91) and normal elderly volunteers(n=38)(P<0.001).Abnormally high levels of intrinsic formaldehyde lead to dysfunction in cognition such as learning decline and memory loss.Excess extracellular and intracellular formaldehyde could induce metabolic response and abnormal modifications of cellular proteins such as hydroxymethylation and hyperphosphorylation,protein misfolding,nuclear translocation and even cell death.This cellular response called formaldehyde stress is dependent upon the concentration of formaldehyde.Chronic impairments of the brain resulted from formaldehyde stress could be one of the mechanisms involved in the process of senile dementia during ageing.

  5. Studies on explosively driven cracks under confining in-situ stresses

    Simha, K.R.Y.; Fourney, W.L.; Dick, R.D.

    1984-01-01

    Successful explosive gas well stimulation requires a thorough understanding of explosively driven cracks under confining in-situ stresses. In a previous paper (Simha, et al 1983) the problem of explosively driven cracks was experimentally investigated to reveal the features of crack propagation. It was observed that the explosively driven crack propagation is the result of two different but overlapping phases. The first phase involving the initiation and early time crack propagation is entirely governed by the explosively generated stress transients. The rapidly decaying stress transients then lead to the second phase of crack propagation largely controlled by the in-situ stresses. The purpose of this paper is to more fully understand the characteristics of the first phase concerning the initiation and early time propagation of explosively driven cracks. Experiments are conducted with plastic models under biaxial compression and the dynamic event is observed with a high speed multiple spark gap camera of the Cranz-Schardin type. The experimental observations are utilized to propose analytical models of crack initiation under explosive loading to aid in the design of multiple fracturing necessary for successful application of modern well stimulation techniques. 8 references, 4 figures.

  6. Effect of Zirconia Thickness on the Tensile Stress of Zirconia Based All-Ceramic Restorations

    Masood Shiezadeh

    2015-09-01

    Full Text Available Introduction: The purpose of the presented study was to evaluate the effect of zirconia thickness on the tensile stress of zirconia based all-ceramic restorations. Methods: Twenty zirconia disks with 10mm diameter were prepared in two groups using CAD/CAM system. The thickness of zirconia was 0.5mm in first group and 0.3mm in second group. After sintering, 0.4mm glass ceramic porcelain was applied to each disk. Then, sintering and glazing of porcelain carried out. Instron testing machine with 1mm/min crosshead speed used to evaluate the failure load of the samples. Biaxial Flexural strength standard formula employed to calculate tensile stress of specimens. Statistical analysis performed using SPSS software. Results: Although data analysis showed more maximum tensile stress in 1st group, no significant differences were found between two groups. Conclusion: Zirconia with 0.5mm and 0.3mm thicknesses cause similar tensile stress in all-ceramic restorations and thickness of these laminates could be reduced to 0.7mm.

  7. Vibration and Stability of Thick Simply Supported Shallow Shells Subjected to In-Plane Stresses

    MATSUNAGA, H.

    1999-08-01

    The effects of higher order deformations on natural frequencies and buckling stresses of a thick shallow shell with reactangular planform subjected to uniaxial and biaxial in-plane stresses are studied. Based on the power series expansion of displacement components, a set of fundamental dynamic equations of a two-dimensional higher order shallow shell theory is derived through Hamilton's principle. Several sets of truncated approximate theories which can take into account the complete effects of higher order deformations such as shear deformations with thickness changes and rotatory inertia are applied to solve the vibration and stability problems of a thick shallow shell. Three types of simply supported shallow shells with positive, zero and negative Gaussian curvatures are considered. In order to assure the accuracy of the present theory, convergence properties of the lowest two natural frequencies for the first vibration moder=s=1 are examined in detail. The present results are also compared with those of existing theories. In the case of a simply supported shallow shell, buckling stresses can be calculated from the natural frequencies without in-plane stresses.

  8. Stress assessment in piping under synthetic thermal loads emulating turbulent fluid mixing

    Highlights: • Generation of complex space-continuous and time-dependent temperature fields. • 1D and 3D thermo-mechanical analyses of pipes under complex surface thermal loads. • Surface temperatures and stress fluctuations are highly linearly correlated. • 1D and 3D results agree for a wide range of Fourier and Biot numbers. • Global thermo-mechanical loading promotes non-equibiaxial stress state. - Abstract: Thermal fatigue assessment of pipes due to turbulent fluid mixing in T-junctions is a rather difficult task because of the existing uncertainties and variability of induced thermal stresses. In these cases, thermal stresses arise on three-dimensional pipe structures due to complex thermal loads, known as thermal striping, acting at the fluid-wall interface. A recently developed approach for the generation of space-continuous and time-dependent temperature fields has been employed in this paper to reproduce fluid temperature fields of a case study from the literature. The paper aims to deliver a detailed study of the three-dimensional structural response of piping under the complex thermal loads arising in fluid mixing in T-junctions. Results of three-dimensional thermo-mechanical analyses show that fluctuations of surface temperatures and stresses are highly linearly correlated. Also, surface stress fluctuations, in axial and hoop directions, are almost equi-biaxial. These findings, representative on cross sections away from system boundaries, are moreover supported by the sensitivity analysis of Fourier and Biot numbers and by the comparison with standard one-dimensional analyses. Agreement between one- and three-dimensional results is found for a wide range of studied parameters. The study also comprises the effects of global thermo-mechanical loading on the surface stress state. Implemented mechanical boundary conditions develop more realistic overall system deformation and promote non-equibiaxial stresses

  9. Stress assessment in piping under synthetic thermal loads emulating turbulent fluid mixing

    Costa Garrido, Oriol, E-mail: oriol.costa@ijs.si; El Shawish, Samir, E-mail: samir.elshawish@ijs.si; Cizelj, Leon, E-mail: leon.cizelj@ijs.si

    2015-03-15

    Highlights: • Generation of complex space-continuous and time-dependent temperature fields. • 1D and 3D thermo-mechanical analyses of pipes under complex surface thermal loads. • Surface temperatures and stress fluctuations are highly linearly correlated. • 1D and 3D results agree for a wide range of Fourier and Biot numbers. • Global thermo-mechanical loading promotes non-equibiaxial stress state. - Abstract: Thermal fatigue assessment of pipes due to turbulent fluid mixing in T-junctions is a rather difficult task because of the existing uncertainties and variability of induced thermal stresses. In these cases, thermal stresses arise on three-dimensional pipe structures due to complex thermal loads, known as thermal striping, acting at the fluid-wall interface. A recently developed approach for the generation of space-continuous and time-dependent temperature fields has been employed in this paper to reproduce fluid temperature fields of a case study from the literature. The paper aims to deliver a detailed study of the three-dimensional structural response of piping under the complex thermal loads arising in fluid mixing in T-junctions. Results of three-dimensional thermo-mechanical analyses show that fluctuations of surface temperatures and stresses are highly linearly correlated. Also, surface stress fluctuations, in axial and hoop directions, are almost equi-biaxial. These findings, representative on cross sections away from system boundaries, are moreover supported by the sensitivity analysis of Fourier and Biot numbers and by the comparison with standard one-dimensional analyses. Agreement between one- and three-dimensional results is found for a wide range of studied parameters. The study also comprises the effects of global thermo-mechanical loading on the surface stress state. Implemented mechanical boundary conditions develop more realistic overall system deformation and promote non-equibiaxial stresses.

  10. AE characteristics during stress corrosion cracking of sensitized type 304 stainless steel pipes

    The objective of this study was to get a better understanding on acoustic emission (AE) characteristics during stress corrosion cracking (SCC) processes of Type 304 stainless steel, to apply AE techniques to detection and monitoring of SCC of the type experienced with stainless steel boiling water reactor piping. SCC tests were performed on pipe specimens with 20 mm inner diameter. Before testing, all pipe specimens were solution-treated and then sensitized. The SCC tests were conducted in the circulating corrosion test equipment containing the pipe specimen under three kinds of bi-axial stresses, of which Mises equivalent stresses were kept at 172 MNm (17.5 kg/mm2). The test conditions were: the test temperature: 2250C; the concentration of chloride ion: approximately 50 ppm; the concentration of dissolved oxygen: approximately 10 ppm; the flow rate of water: 10 l/hr. Main results were: (1) the failure was caused mainly by intergranular stress corrosion cracking; (2) AE characteristics during the SCC test may be divided into three stages; (3) the most probable AE sources in the 3rd stage may be the phenomena due to the propagation of intergranular stress corrosion cracks; (4) the propagation velocity of intergranular stress corrosion cracks seems to become higher, as the hoop stress applied to the pipe specimens increases, even in the cases of the same value of Mises' equivalent stress; and (5) at the leakage due to SCC, cumulative counts, signal waveforms and peak-amplitude distributions shows a great change and the leakage is readily detectable by standard AE techniques. (author)

  11. The influence of deformation-induced residual stresses on the post-forming tensile stress/strain behavior of dual-phase steels

    Hance, Brandon Michael

    It was hypothesized that, in dual-phase (DP) steels, strain partitioning between ferrite (alpha) and martensite (alpha') during deformation results in a distribution of post-deformation residual stresses that, in turn, affects the subsequent strength, work hardening behavior and formability when the strain path is changed. The post-forming deformation-induced residual stress state was expected to depend upon the microstructure, the amount of strain and the prestrain path. The primary objective of this research program was to understand the influence of deformation-induced residual stresses on the post-forming tensile stress/strain behavior of DP steels. Three commercially produced sheet steels were considered in this analysis: (1) a DP steel with approximately 15 vol. % martensite, (2) a conventional high-strength, low-alloy (HSLA) steel, and (3) a conventional, ultra-low-carbon interstitial-free (IF) steel. Samples of each steel were subjected to various prestrain levels in various plane-stress forming modes, including uniaxial tension, plane strain and balanced biaxial stretching. Neutron diffraction experiments confirmed the presence of large post-forming deformation-induced residual stresses in the ferrite phase of the DP steel. The deformation-alphainduced residual stress state varied systematically with the prestrain mode, where the principal residual stress components are proportional to the principal strain components of the prestrain mode, but opposite in sign. For the first time, and by direct experimental correlation, it was shown that deformation-induced residual stresses greatly affect the post-forming tensile stress/strain behavior of DP steels. As previously reported in the literature, the formability (residual tensile ductility) of the IF steel and the HSLA steel was adversely affected by strain path changes. The DP steel presents a formability advantage over the conventional IF and HSLA steels, and is expected to be particularly well suited for

  12. Managing Leadership Stress

    Bal, Vidula; McDowell-Larsen, Sharon

    2011-01-01

    Everyone experiences stress, and leaders face the additional stress brought about by the unique demands of leadership: having to make decisions with limited information, to manage conflict, to do more with less . . . and faster! The consequences of stress can include health problems and deteriorating relationships. Knowing what signs of stress to look for and having a strategy for increasing your resources will help you manage leadership stress and be more effective over a long career.Table of ContentsThe Stress of Leadership 7Why Is Leadership Stressful? 8Stress Assessment 13When Stress Is Wh

  13. Effect of substrate anisotropy on magnetic state and stress state in magnetostrictive multilayers

    There is a strong interaction of stress and magnetization in magnetostrictive materials which can be traced back to the corresponding elastic energy and magnetoelastic energy terms. In particular, an applied stress or magnetic field can be used to provide a bias which can then ensure large magnetostrictive actuation at minimum coercive field. The use of stress is especially interesting in the case of thin films because it can be conveniently introduced by means of the substrate. In this work, the basic formulations for the elastic, magnetoelastic and potential magnetic energies of an isotropic material, and the assumption that the film is in state of plane stress are combined in a consistent model that is used to study the effect of a stress bias which is created by bending a substrate during deposition of a magnetostrictive multilayer. Using this framework, the biaxial stresses induced in the thin film after the substrate is released and the multilayer total energy are calculated. The effect of energy contributions from strains in the thickness direction is shown to be unimportant, since they provide a constant, orientation-independent contribution which does not affect in-plane magnetization switching. The multilayer total energy, which is shown to vary with magnetic domain orientation, is minimized to find the orientation of the easy axis as well as to estimate the magnetization along various hard axis directions when an external field is applied in those directions. The uniaxial anisotropy energy and the anisotropy field are also calculated and the results are in good agreement with reported data. These calculations are seen to offer significant improvement over the ones obtained with previous models that consider films subjected to uniaxial stresses and to be governed only by variations of the magnetoelastic energy

  14. Quantitative determination of molecular structure in multilayered thin films of biaxial and lower symmetry from photon spectroscopies. I. Reflection infrared vibrational spectroscopy

    Parikh, Atul N.; Allara, David L.

    1992-01-01

    A semitheoretical formalism based on classical electromagnetic wave theory has been developed for application to the quantitative treatment of reflection spectra from multilayered anisotropic films on both metallic and nonmetallic substrates. Both internal and external reflection experiments as well as transmission can be handled. The theory is valid for all wavelengths and is appropriate, therefore, for such experiments as x-ray reflectivity, uv-visible spectroscopic ellipsometry, and infrared reflection spectroscopy. Further, the theory is applicable to multilayered film structures of variable number of layers, each with any degree of anisotropy up to and including full biaxial symmetry. The reflectivities (and transmissivities) are obtained at each frequency by solving the wave propagation equations using a rigorous 4×4 transfer matrix method developed by Yeh in which the optical functions of each medium are described in the form of second rank (3×3) tensors. In order to obtain optical tensors for materials not readily available in single crystal form, a method has been developed to evaluate tensor elements from the complex scalar optical functions (n̂) obtained from the isotropic material with the limitations that the molecular excitations are well characterized and obey photon-dipole selection rules. This method is intended primarily for infrared vibrational spectroscopy and involves quantitative decomposition of the isotropic imaginary optical function (k) spectrum into a sum of contributions from fundamental modes, the assignment of a direction in molecular coordinates to the transition dipole matrix elements for each mode, the appropriate scaling of each k vector component in surface coordinates according to a selected surface orientation of the molecule to give a diagonal im(n̂) tensor, and the calculation of the real(n̂) spectrum tensor elements by the Kramers-Kronig transformation. Tensors for other surface orientations are generated by an

  15. Apparatus for measuring local stress of metallic films, using an array of parallel laser beams during rapid thermal processing

    The novel apparatus described here was developed to investigate the thermo-mechanical behavior of metallic films on a substrate by acquiring the wafer curvature. It comprises an optical module producing and measuring an array of parallel laser beams, a high resolution scanning stage, a rapid thermal processing (RTP) chamber and several accessorial gas control modules. Unlike most traditional systems which only calculate the average wafer curvature, this system has the capability to measure the curvature locally in 30 ms. Consequently, the real-time development of biaxial stress involved in thin films can be fully captured during any thermal treatments such as temperature cycling or annealing processes. In addition, the multiple parallel laser beam technique cancels electrical, vibrational and other random noise sources that would otherwise make an in situ measurement very difficult. Furthermore, other advanced features such as the in situ acid treatment and active cooling extend the experimental conditions to provide new insights into thin film properties and material behavior

  16. Apparatus for measuring local stress of metallic films, using an array of parallel laser beams during rapid thermal processing

    Huang, R.; Taylor, C. A.; Himmelsbach, S.; Ceric, H.; Detzel, T.

    2010-05-01

    The novel apparatus described here was developed to investigate the thermo-mechanical behavior of metallic films on a substrate by acquiring the wafer curvature. It comprises an optical module producing and measuring an array of parallel laser beams, a high resolution scanning stage, a rapid thermal processing (RTP) chamber and several accessorial gas control modules. Unlike most traditional systems which only calculate the average wafer curvature, this system has the capability to measure the curvature locally in 30 ms. Consequently, the real-time development of biaxial stress involved in thin films can be fully captured during any thermal treatments such as temperature cycling or annealing processes. In addition, the multiple parallel laser beam technique cancels electrical, vibrational and other random noise sources that would otherwise make an in situ measurement very difficult. Furthermore, other advanced features such as the in situ acid treatment and active cooling extend the experimental conditions to provide new insights into thin film properties and material behavior.

  17. Stress and Coping with Stress in Adolescence

    Petra Dolenc

    2015-01-01

    Because of the many developmental changes in adolescence, young people are exposed to greater likelihood of experiencing stress. On the other hand, this period is critical for developing effective and constructive coping strategies. In the contribution, we summarize part of what is known about stress, stress responses and coping. Throughout, we focus on common stressful events among adolescents and emphasize the importance of dealing successfully with stressors in their daily lives. Finally, ...

  18. Prenatal Maternal Stress Programs Infant Stress Regulation

    Davis, Elysia Poggi; Glynn, Laura M.; Waffarn, Feizal; Sandman, Curt A.

    2010-01-01

    Prenatal exposure to inappropriate levels of glucocorticoids (GCs) and maternal stress are putative mechanisms for the fetal programming of later health outcomes. The current investigation examined the influence of prenatal maternal cortisol and maternal psychosocial stress on infant physiological and behavioral responses to stress. The study sample comprised 116 women and their full term infants. Maternal plasma cortisol and report of stress, anxiety and depression were assessed at ...

  19. Stress and Migraine

    ... disabling headaches . Home > Stress and Migraine Print Email Stress and Migraine ACHE Newsletter Sign up for our newsletter by entering your e-mail address below. Stress and Migraine Mia Minen, MD MPH Key Points: ...

  20. Stress and Heart Health

    ... Recognition & Awards Healthy Workplace Food and Beverage Toolkit Stress and Heart Health Updated:Jun 13,2014 When ... Health and Heart Health Last reviewed 6/2014 Stress Management • Home • How Does Stress Affect You? Introduction ...

  1. Overcoming job stress

    ... medlineplus.gov/ency/patientinstructions/000884.htm Overcoming job stress To use the sharing features on this page, ... stay healthy and feel better. Causes of Job Stress Although the cause of job stress is different ...

  2. Stress urinary incontinence

    Incontinence - stress ... over 2 cups of urine in their bladder. Stress incontinence occurs when the muscles that control your ... area or the prostate (in men) Unknown causes Stress incontinence is the most common type in women. ...

  3. Stress Management

    Prof.Univ. Dr. Paul Marinescu

    2007-01-01

    Η παρούσα διατριβή ασχολείται με το stress management και κατ’ επέκταση με το ρόλο που αναλαμβάνει να παίξει το τμήμα της Διοίκησης Ανθρωπίνων Πόρων (HRM), το πλέον υπεύθυνο τμήμα για την διεκπεραίωση τέτοιων καταστάσεων, όταν διάφοροι παράγοντες, εντός και εκτός εργασιακού χώρου, προκαλούν stress στους εργαζόμενους μιας επιχείρησης / ενός οργανισμού. Επικεντρώνει την προσοχή στην συμβολή του τμήματος HR σε μια επιχείρηση, ενώ γίνεται μια αναφορά στους διάφορους ρόλους που καλείται να αναλάβ...

  4. Juror stress.

    Hafemeister, T L

    1993-01-01

    That jurors may be harmed as a result of their carrying out their civic duties is receiving increased attention from the courts and the media (Sevilla & Beyers, 1990; Craver, 1993). The pilot tests reported here represent initial efforts to undertake a proactive project for identifying and mitigating the possible adverse effects of stress on jurors and to contribute to the understanding and treatment of secondary trauma for at-risk groups. In many ways juries are the black box of the legal system. Their decision-making process is typically shrouded in mystery. So that they may fully explore the issues and examine their consciences, jurors meet privately when reaching their decision and, beyond entering a verdict, are typically not required to provide the rationale for their verdict. Furthermore, jurors are often reluctant to discuss the bases for their verdicts after the trial is over and an unspoken code of honor may limit their willingness to critique their fellow jurors. Perhaps in part because we know so little about their decision-making process, as well as because of their intrinsic and symbolic importance to the legal system, there may be a tendency to take jurors for granted and to assume that they are relatively unaffected by their jury duties. Although jurors are expected to appear impassive and emotionally detached in court, for some trials it is only the rare individual who will not be emotionally moved by what he or she has seen and heard or by the gravity of the decision that is required. Several recent cases have provided a glimpse of what goes on within this black box and suggest that greater attention may need to be given to the needs of these jurors. PMID:8193058

  5. Prenatal Maternal Stress Programs Infant Stress Regulation

    Davis, Elysia Poggi; Glynn, Laura M.; Waffarn, Feizal; Sandman, Curt A.

    2011-01-01

    Objective: Prenatal exposure to inappropriate levels of glucocorticoids (GCs) and maternal stress are putative mechanisms for the fetal programming of later health outcomes. The current investigation examined the influence of prenatal maternal cortisol and maternal psychosocial stress on infant physiological and behavioral responses to stress.…

  6. Teacher Wellness: Too Stressed for Stress Management?

    Kipps-Vaughan, Debi; Ponsart, Tyler; Gilligan, Tammy

    2012-01-01

    Healthier, happier teachers promote healthier, happier, and more effective learning environments. Yet, many teachers experience considerable stress. Studies have found that between one fifth and one fourth of teachers frequently experience a great deal of stress (Kyriacou, 1998). Stress in teaching appears to be universal across nations and…

  7. Stress Management in Organizations

    Roxana Capotescu

    2008-01-01

    Employee stress has increasingly become a concern for many organizations. Although it is not possible to eliminate stress entirely, people can learn to manage it. Many organizations have adopted occupational stress management programs to try and reduce the stress levels of their workforce. The high cost of work stress related problems highlights the need to spend more time evaluating work stress interventions and publishing the findings so that other organizations can gain insight into progra...

  8. Phase transformations and residual stresses in environmental barrier coatings

    Harder, Bryan J.

    Silicon-based ceramics (SiC, Si3N4) are promising materials for high-temperature structural applications in turbine engines. However, the silica layer that forms on these materials is susceptible to attack from water vapor present in combustion environments. To protect against this degradation, environmental barrier coatings (EBCs) were developed to protect the underlying substrate. In the case of silicon carbide (SiC), multilayer coating systems consist of a Ba1-xSrxAl2Si 2O8 (BSAS) topcoat, a mullite or mullite + SrAl2Si 2O8 (SAS) interlayer, and a silicon bond coat. In this work, biaxial strains were measured on as-sprayed and heat-treated samples to analyze the stress and phase evolution in the coating system as a function of depth and temperature. Models were used to compare the results with an ideal coating system. In the assprayed state, tensile stresses as high as 175 MPa were measured, and cracking was observed. After thermally cycling the samples, stresses were significantly reduced and cracks in the topcoat had closed. The addition of SAS to the interlayer increased the compressive stress in the BSAS topcoat in thermally-cycled samples, which was desirable for EBC applications. The BSAS topcoat transformed from the as-deposited hexacelsian state to the stable celsian above 1200°C. This phase transformation is accompanied by a CTE reduction. The kinetics of the hexacelsian-to-celsian transformation were quantified for freestanding plasma-sprayed BSAS. Activation energies for bulk bars and crushed powder were determined to be ˜340 kJ/mol and ˜500 kJ/mol, respectively. X-ray diffraction and electron backscatter diffraction were used to establish how microstructural constraints reduce the transformation energy. Barrier coating lifetime and stability are also influenced by exposure to reactive, low-melting point calcium-magnesium-aluminosilicate (CMAS) deposits formed from dust and sand. Multilayer doped aluminosilicate coatings and bulk BSAS material were

  9. Stress and Reliability Analysis of a Metal-Ceramic Dental Crown

    Anusavice, Kenneth J; Sokolowski, Todd M.; Hojjatie, Barry; Nemeth, Noel N.

    1996-01-01

    Interaction of mechanical and thermal stresses with the flaws and microcracks within the ceramic region of metal-ceramic dental crowns can result in catastrophic or delayed failure of these restorations. The objective of this study was to determine the combined influence of induced functional stresses and pre-existing flaws and microcracks on the time-dependent probability of failure of a metal-ceramic molar crown. A three-dimensional finite element model of a porcelain fused-to-metal (PFM) molar crown was developed using the ANSYS finite element program. The crown consisted of a body porcelain, opaque porcelain, and a metal substrate. The model had a 300 Newton load applied perpendicular to one cusp, a load of 30ON applied at 30 degrees from the perpendicular load case, directed toward the center, and a 600 Newton vertical load. Ceramic specimens were subjected to a biaxial flexure test and the load-to-failure of each specimen was measured. The results of the finite element stress analysis and the flexure tests were incorporated in the NASA developed CARES/LIFE program to determine the Weibull and fatigue parameters and time-dependent fracture reliability of the PFM crown. CARES/LIFE calculates the time-dependent reliability of monolithic ceramic components subjected to thermomechanical and/Or proof test loading. This program is an extension of the CARES (Ceramics Analysis and Reliability Evaluation of Structures) computer program.

  10. Effect of large mechanical stress on the magnetic properties of embedded Fe nanoparticles.

    Saranu, Srinivasa; Selve, Sören; Kaiser, Ute; Han, Luyang; Wiedwald, Ulf; Ziemann, Paul; Herr, Ulrich

    2011-01-01

    Magnetic nanoparticles are promising candidates for next generation high density magnetic data storage devices. Data storage requires precise control of the magnetic properties of materials, in which the magnetic anisotropy plays a dominant role. Since the total magneto-crystalline anisotropy energy scales with the particle volume, the storage density in media composed of individual nanoparticles is limited by the onset of superparamagnetism. One solution to overcome this limitation is the use of materials with extremely large magneto-crystalline anisotropy. In this article, we follow an alternative approach by using magneto-elastic interactions to tailor the total effective magnetic anisotropy of the nanoparticles. By applying large biaxial stress to nanoparticles embedded in a non-magnetic film, it is demonstrated that a significant modification of the magnetic properties can be achieved. The stress is applied to the nanoparticles through expansion of the substrate during hydrogen loading. Experimental evidence for stress induced magnetic effects is presented based on temperature-dependent magnetization curves of superparamagnetic Fe particles. The results show the potential of the approach for adjusting the magnetic properties of nanoparticles, which is essential for application in future data storage media. PMID:21977439

  11. Effect of large mechanical stress on the magnetic properties of embedded Fe nanoparticles

    Srinivasa Saranu

    2011-06-01

    Full Text Available Magnetic nanoparticles are promising candidates for next generation high density magnetic data storage devices. Data storage requires precise control of the magnetic properties of materials, in which the magnetic anisotropy plays a dominant role. Since the total magneto-crystalline anisotropy energy scales with the particle volume, the storage density in media composed of individual nanoparticles is limited by the onset of superparamagnetism. One solution to overcome this limitation is the use of materials with extremely large magneto-crystalline anisotropy. In this article, we follow an alternative approach by using magneto-elastic interactions to tailor the total effective magnetic anisotropy of the nanoparticles. By applying large biaxial stress to nanoparticles embedded in a non-magnetic film, it is demonstrated that a significant modification of the magnetic properties can be achieved. The stress is applied to the nanoparticles through expansion of the substrate during hydrogen loading. Experimental evidence for stress induced magnetic effects is presented based on temperature-dependent magnetization curves of superparamagnetic Fe particles. The results show the potential of the approach for adjusting the magnetic properties of nanoparticles, which is essential for application in future data storage media.

  12. Research opportunities and facilities at ORNL`s residual stress user center

    Hubbard, C.R.; Watkins, T.R.; Kozaczek, K.; Wang, X.-L.; Spooner, S.

    1994-09-01

    The High Temperature Materials Laboratory (HTML) User Program at ORNL was established to help solve high-temperature materials problems that limit the efficiency and reliability of advanced energy-conversion systems. Both proprietary and nonproprietary research can be conducted within the user program. The facilities are open to researchers in US industry, universities, and federal laboratories. The Residual Stress User Center (RSUC), one of the six HTML user centers, was recently established and consists of two high precision x-ray diffraction systems for measurement of residual strain and texture. Both biaxial and triaxial residual strain data can be collected. Attachments to the diffraction system include a position sensitive detector and a laser specimen positioning system. The RSUC has capabilities for electropolishing and strain measurement with strain gauges. A complementary neutron diffraction facility has recently been developed and demonstrated at the High Flux Isotope Reactor at ORNL. The neutron diffraction facility enables mapping of macro residual stresses throughout the volume of a component, complementing the near surface stress measurements available by x-ray diffraction. The neutron facility has been proposed as an addition to the RSUC.

  13. Stress and Health

    Rod, Naja Hulvej

    2014-01-01

    Background Stress is an important public health issue. One in ten Danish adults experience high levels of stress in their daily lives and stress is one of the main occupational health problems in Europe. The link between stress and health is still debated in the scientific literature...... and the pathways underlying these potential health effects are far from elucidated. The dissertation contributions to the literature on stress and health by empirically testing the relationship between stress and major chronic disorders and by providing new evidence on the underlying physiological, psychological...... and behavioral mechanisms. Stress is a complex concept and in order to better understand the relation between stress and health, the dissertation works with a clear distinction between the health consequences of different types of stress including external stressors, perceived stress, and measures of the stress...

  14. The effect of academic stress and attachment stress on stress-eaters and stress-undereaters.

    Emond, Michael; Ten Eycke, Kayla; Kosmerly, Stacey; Robinson, Adele Lafrance; Stillar, Amanda; Van Blyderveen, Sherry

    2016-05-01

    It is well established that stress is related to changes in eating patterns. Some individuals are more likely to increase their overall food intake under conditions of stress, whereas others are more likely to consume less food when stressed. Attachment style has been linked to disordered eating and eating disorders; however, comparisons of eating behaviors under attachment versus other types of stress have yet to be explored. The present laboratory study examined the eating patterns in self-identified stress-undereaters and stress-eaters under various types of stress. More specifically, the study examined the effects of academic and attachment stress on calorie, carbohydrate and sugar consumption within these two groups. Under the guise of critiquing student films, university students viewed either one of two stress-inducing videos (academic stress or attachment stress, both designed to be emotionally arousing) or a control video (designed to be emotionally neutral), and their food intake was recorded. Results demonstrated that the video manipulations were effective in inducing stress. Differential patterns of eating were noted based on group and stress condition. Specifically, stress-undereaters ate fewer calories, carbohydrates and sugars than stress-eaters in the academic stress condition, but not in the attachment stress or control condition. Findings suggest that specific types of stressors may influence eating behaviors differently. PMID:26850311

  15. Stress og insomni

    Jennum, Poul; Zachariae, Bobby

    2012-01-01

    Insomnia and stress are two conditions, which are strongly associated and appear to be pathophysiologically integrated: the occurrence of stress increases the risk of insomnia, insomnia exacerbates stress, and coexistence of both factors has a negative influence on their prognosis. Stress...

  16. Stress and eating behavior

    Peters, Achim; Langemann, Dirk

    2010-01-01

    How stress, the stress response, and the adaptation of the stress response influence our eating behavior is a central question in brain research and medicine. In this report, we highlight recent advances showing the close links between eating behavior, the stress system, and neurometabolism.

  17. Stress og insomni

    Jennum, Poul; Zachariae, Bobby

    2012-01-01

    Insomnia and stress are two conditions, which are strongly associated and appear to be pathophysiologically integrated: the occurrence of stress increases the risk of insomnia, insomnia exacerbates stress, and coexistence of both factors has a negative influence on their prognosis. Stress and...

  18. Stress in Bangladeshi Bengoli.

    Alam, Samsul

    This report discusses the stress patterns of Bengali as spoken in Bangladesh. One of the findings indicate that every word has stress in the first syllable, with additional stress in the first syllable of the first word of the phrase. The Bengali language does not have penultimate and antepenultimate stress. Because there is no rule for changing…

  19. Fact Sheet on Stress

    ... items) NIMH (7 items) Share Fact Sheet on Stress Download PDF Download ePub Q&A on Stress for Adults: How it affects your health and ... to avoid more serious health effects. What is stress? Stress can be defined as the brain's response ...

  20. STRESS MANAGEMENT PRACTICES & TIPS

    UDAYSINH MANEPATIL

    2013-01-01

    Everyday, in every walk of life, We come across stress. As much as people wishfor stress free life. Such a task would be impossible to achieve. Stress is part and parcel ofour lives. Contemporary stress tends to be even more pervasive, persistence andinsidious.