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1

Biaxial Stress Limit for ULDB Film  

Science.gov (United States)

The current ULDB design applies stress to the shell film biaxially to control creep in the latitudinal direction. The recent change in design paradigm, from a uniaxial to biaxial stress state basis, arose from a new perspective that the biaxial loading can control strain in both principal surface dimensions as discussed below. The current ULDB project path was thus enabled by a more thorough understanding of the nonlinear viscoelastic properties of the shell film material, linear low-density polyethylene (LLDPE). Although a very similar material is also used in NASA zero-pressure (ZPB) and long-duration balloons (LDB), the different stress state requires a new approach to shell material qualification.

Sterling, W. J.; Rand, J. L.

2005-01-01

2

Analysis of Biaxially Stressed Bridge Deck Plates  

DEFF Research Database (Denmark)

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 presents a detailed investigation of the ultimate capacity of simply supported plates subjected to biaxial loads. The full interaction domain of combinations of compressive and tensile loads has been investigated including a large number of imperfections. It was found that non-standard imperfection modes in parts of the interaction domain lead to more critical and lower ultimate capacity than critical buckling mode imperfections.

Jönsson, Jeppe

2012-01-01

3

Thermal ratcheting under biaxial stress states  

International Nuclear Information System (INIS)

Thermal ratcheting, the phenomenon of net strain accumulation due to plastic straining of pressure vessels under cyclic thermal loading, is an important factor in the design of nuclear reactor pressure vessels. In this paper a cyclic thermal gradient loading idealized by means of a step distribution through the pressure vessel wall and biaxial thermoelastic-plastic stress-strain models presently used in design calculations are adequate for spherical and cylindrical shells under internal pressure; however, for uniaxial loading and for torsional loading, the use of these models may underestimate the accumulated ratchet strain. (Auth.)

4

Biaxial stress relaxation in glassy polymers - Polymethylmethacrylate.  

Science.gov (United States)

Biaxial stress relaxation studies were performed on glassy polymethylmethacrylate in combined torsion-tension strain fields using a specially designed apparatus with exceptionally high stiffness and low cross talk between the torsional and tensile load measuring transducers. It was found that at low strain levels uniaxial tension relaxation is slower than pure torsion relaxation; tensile-component relaxation rates are unaffected by the level of torsional strain; torsional-component relaxation rates decrease as tensile strain is increased; uniaxial tension relaxation rates approach the pure torsion rates at higher strains (about 2%). A phenomenological treatment is presented which shows that relaxation rates can be coupled to the strain fields in which they are observed and yet be consistent with the concepts of linear viscoelasticity and the Boltzmann superposition integral.

Sternstein, S. S.; Ho, T. C.

1972-01-01

5

Effect of Increasing Speed on Stress of Biaxial Bogie Frames  

Directory of Open Access Journals (Sweden)

Full Text Available Increasing the trains’ speed has always been one of the goals of any railway industry and train manufacturers. Also, the influence of the train speed on bogie’s dynamics has an immense importance. Therefore, it is important to analyze the effect of train speed on the stress distribution in different parts of train structure. In this study the result of the increasing speed on the applied stresses of a biaxial bogie frame has been examined. For this purpose, a biaxial bogie frame has been modeled using finite element analysis. Static and dynamic forces applied on the bogie with biaxial frame have been obtained for different speeds and rail roughness. The Von Mises stresses are adopted as equivalent stresses in the strength calculation. The results show that maximum stress always has been induced in the bogie bowl also the increase in bogie’s speed has remarkable effect on the increment of applied stresses in the bogie frame.

Ali Ziaei Asl

2011-03-01

6

Biaxial stress effects on estimating J under combined mechanical and thermal stresses  

International Nuclear Information System (INIS)

In this paper, the applicability to bi-axial stress states of a simple approximation proposed in our previous work for quantifying the elastic-plastic J under combined primary and secondary stresses is investigated.To produce the bi-axial stress states, circumferential cracked pipes under combined pressure, axial tension (or compression) and thermal stresses are considered. The results suggest that the proposed approximation can be applied to bi-axial stress states, and is slightly more conservative for bi-axial mechanical stresses than for uni-axial ones. The degree of conservatism decreases with increasing strain hardening exponent and with increasing relative magnitude of secondary stress. - Highlights: ? A method to estimate J under combined primary and secondary stresses was proposed by the authors. ? This paper extends the proposed method to biaxial primary stress states. ? We find that the proposed approximation can be applied to bi-axial stress states. ? The proposed approximation is slightly more conservative for biaxial stresses than for uniaxial ones. ? The degree of conservatism decreases with increasing hardening exponent and relative magnitude of secondary stress.

7

Mean stress effects in biaxial fatigue of Inconel 718  

International Nuclear Information System (INIS)

Biaxial fatigue tests were conducted on Inconel 718 thin-walled tubular specimens to quantify the effect of mean stress. The specimens were loaded in combined tension and torsion in strain control at room temperature. Fatigue lives ranged from 3000 to 15,000 cycles depending on the mean stress. These data were correlated with a parameter based on the maximum plastic shear strain amplitude, normal strain amplitude and mean normal stress on the plane of maximum shear strain amplitude. This parameter was combined with the Coffin-Manson equation for estimating fatigue lives. Observations of the cracking behavior show that mean stress affects the rate of crack growth and distribution of cracks

8

Cyclic Biaxial Stress Measurement Method Using the Grain Growth Direction in Electrodeposited Copper Foil  

Digital Repository Infrastructure Vision for European Research (DRIVER)

A method that uses grain growth direction in electrodeposited copper foil to measure cyclic biaxial stress is examined in this paper. The grain growth direction is measured by image processing software after a cyclic loading test for various biaxial stress ratios is carried out. Since the grain growth occurs in two directions and its directions correspond closely with the direction of maximum shearing stress when the biaxial stress ratio is negative, the principal stress can be measur...

2010-01-01

9

An apparatus for measuring bi-axial stresses  

International Nuclear Information System (INIS)

The invention relates to an apparatus for measuring biaxial stresses in a metal test-piece submitted to severe environmental conditions. An apparatus according to the invention is characterized by an outer envelope, e.g. of stainless steel, with an inner coating and a high electrical conductivity, a moving piston fixed to the test-piece and a pressurizing conduct for forming a cavity capable of resonating according two frequency-modes, said cavity being coupled to a hyper-frequency source by means of a wave-guide, frequency variations being detected for obtaining a measurement of the test piece biaxial stress. An apparatus according to the invention is suitable in particular for testing materials for nuclear reactors and caustic environments

10

Study on thermal fatigue endurance under biaxial stress state  

International Nuclear Information System (INIS)

The design specifications for pressure vessels permit the yield point to be exceeded considerably in the case of secondary stresses. Pressure vessel components must therefore often be designed for fatigue endurance. Dimensioning in accordance with the ASME Code has hitherto been based on uniaxial mechanical tests with emphasis on high safety factors. The influence of a multi-axial stress on the number of load cycles and the effect of thermal cycles on the course of material fatigue remain largely unclear. The recent investigations described here are aimed at determining in suitable experiments to what extent actual stresses set up by thermal cycles in a biaxial stress field are covered by the simple approach hitherto used in practice. At the same time the limitations of the materials when exposed to these complex stresses are determined. The following experiments were carried out to solve the above questions: thermal biaxial load cycle tests with carbon and austenitic steels, determination of service life as a function of the constrained strains, determination of the stress/strain curve in the form of a Bauschinger loop. Establishing the stress/strain curve is especially important since from it is derived the tangent modulus introduced in the computation of the buckling stress of components subjected to such stresses. Results are given and discussed. (author)

11

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

International Nuclear Information System (INIS)

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

12

Cyclic Biaxial Stress Measurement Method Using the Grain Growth Direction in Electrodeposited Copper Foil  

Directory of Open Access Journals (Sweden)

Full Text Available A method that uses grain growth direction in electrodeposited copper foil to measure cyclic biaxial stress is examined in this paper. The grain growth direction is measured by image processing software after a cyclic loading test for various biaxial stress ratios is carried out. Since the grain growth occurs in two directions and its directions correspond closely with the direction of maximum shearing stress when the biaxial stress ratio is negative, the principal stress can be measured using Mohr's stress circle. On the other hand, when the biaxial stress ratio is positive, above-mentioned feature does not occur. Therefore, the first principal stress can be measured based on the grain growth density. The number of grains necessary to measure the biaxial stress is estimated by a statistical approach.

Daisuke Hino

2010-01-01

13

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

International Nuclear Information System (INIS)

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

14

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

International Nuclear Information System (INIS)

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, ?1, ?2, 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 ?1, ?2 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

15

On stress measurement errors in biaxial tensile testing and the impact on yield surface identification  

Science.gov (United States)

In a biaxial tensile test on the sheet metal the calculation of the local stress tensor is based on the experimentally measured biaxial forces and surface strain at a well-defined position within the biaxial gauge area. The surface strains in this study are measured via our in-house digital image correlation system. A numerical method is proposed to estimate the influence of the experimental strain measurement error with respect to the stress error and the amount of plastic work per unit volume. In addition, the impact of the strain measurement error on the accuracy of yield surface identification is discussed.

Coppieters, Sam; Hakoyama, Tomoyuki; Yanaga, Daisaku; Lava, Pascal; Kuwabara, Toshihiko

2013-12-01

16

Creep, stress relaxation and biaxial ratchetting of type 304 stainless steel after cyclic preloading  

International Nuclear Information System (INIS)

A series of tests for creep, stress relaxation, and biaxial ratchetting of type 304 stainless steel after cyclic preloading were carried out to investigate their interaction. The interesting fact was pointed out that back stress in cyclic plasticity played an important role to describe creep, relaxation, and biaxial ratchetting following cyclic preloading. Then, the test results showed that the material behavior due to creep after cyclic preloading could be represented by the modified Bailey-Norton law with stress levels evaluated from the current center of the yield surface, i.e., back stress which was determined by the hybrid constitutive model for cyclic plasticity proposed by the authors. In addition, biaxial ratchetting of axial strain induced by cyclic shear straining after cyclic preloading was expressed by the shear stress amplitude, the number of cycle and the axial stress level from the current center

17

Phonon deformation potentials of hexagonal GaN studied by biaxial stress modulation  

Directory of Open Access Journals (Sweden)

Full Text Available In this work, a biaxial stress modulation method, combining the microfabrication technique, finite element analysis and a weighted averaging process, was developed to study piezospectroscopic behavior of hexagonal GaN films, epitaxially grown by metalorganic chemical vapor deposition on c-sapphire and Si (111 substrates. Adjusting the size of patterned islands, various biaxial stress states could be obtained at the island centers, leading to abundant stress-Raman shift data. With the proposed stress modulation method, the Raman biaxial stress coefficients of E2H and A1 (LO phonons of GaN were determined to be 3.43 cm-1/GPa and 2.34 cm-1/GPa, respectively.

Jun-Yong Lu

2011-08-01

18

Optimization of magnetic properties of Co /Pd multilayers by applying a large persistent biaxial stress  

Science.gov (United States)

We report about optimization of the effective perpendicular magnetic anisotropy (Keff) of [Pd(0.98nm)/Co(tnm)]30 multilayers by applying an in-plane biaxial tensile stress by loading the Ta substrate with hydrogen. The stress induced anisotropy enhances the Keff, which in turn increases the coercive field and the squareness of the perpendicular magnetization curves. A quantitative analysis of the data using a simple model yields magnetostriction constants for the [Pd(0.98nm)/Co(tnm)]30 multilayers which are in good agreement with the literature values. We conclude that the Keff can be significantly enhanced by applying persistent in-plane biaxial tensile stress.

Mohanan, Senthilnathan; Herr, Ulrich

2007-11-01

19

A Novel Biaxial Specimen for Inducing Residual Stresses in Thermoset Polymers and Fibre Composite Material  

DEFF Research Database (Denmark)

A new type of specimen configuration with the purpose of introducing a well-defined biaxial residual (axisymmetric) stress field in a neat thermoset or a fibre composite material is presented. The ability to experimentally validate residual stress predictions are an increasing need for design engineers when they challenge the material limits in present and future thermoset and composite component. In addition to the new specimen configuration this paper presents an analytical solution for the residual stress state in the specimen. The analytical solution assumes linear elastic and isotropic material behaviour. Experimental strain release measurements and the analytical solution determine the residual stress state present in the material. A demonstration on neat epoxy is conducted and residual stress predictions of high accuracy and repeatability have been achieved. The precise determination of the biaxial stress state in the specimen after cure makes it suitable for calibrating residual stress models.

Jakobsen, Johnny; Andreasen, Jens Henrik

2014-01-01

20

Martensitic transformation in Ni-Al - the effect of biaxial stress  

International Nuclear Information System (INIS)

Full text: Previous work on a Ni0.625Al0.375 crystal has shown that there are significant differences between the thermal expansion behaviour in three different directions. The current work focuses on the effect of an applied biaxial stress in one of these [100] directions. Measurements taken using a capacitance dilatometer show that the applied stress has a dramatic effect on the thermal expansion properties of the crystal. The most obvious effect in a single [100] direction can be seen upon cooling through the martensitic transformation temperature. The unstressed crystal exhibits negative strain at Ms (the martensite start temperature) while the biaxially stressed crystal undergoes a positive strain at Ms. The martensitic transformation has also been observed using optical microscopy. In the absence of the biaxial stress, the strain associated with the martensitic transformation is accommodated by extensive cracking of the crystal. When the biaxial stress is applied, the cracking is much less severe and the martensitic transformation more uniform in appearance

 
 
 
 
21

Photoelastic and numerical investigation of stress distributions around fault models under biaxial compressive loading conditions  

Science.gov (United States)

This paper presents the results of a photoelastic and numerical study of stress distributions (contours and trajectories) around fault models of various geometries, submitted to a biaxial compressive load. It aims to describe typical biaxial stress behaviours and emphasize the existing differences with the well-known uniaxial compressive load case. Stress trajectories are sometimes shown by joint sets acting as markers of a paleostress field, and they can be interpreted by particular shallow tension-compression situations. At depth fractures can be reactivated, or can dilate under conditions of triaxial compression, and behaviour is essentially controlled by a high stress ratio (high ?3/ ?1 ratio). In spite of the potential importance of such stress states on fracture permeability and fluid flow, and although they are frequently found at depth in a reservoir context, such stress conditions are poorly investigated, particularly in terms of stress perturbations. The presented analogue experiments consisted of compression tests done on polymethylmethacrylate (PMMA) plates; this material has mechanical properties comparable to those of brittle rocks in the upper crust, and presents birefringence. The samples contained open defects acting as faults, and the stress trajectories around these faults were investigated using a photoelastic device. Comparable numerical experiments were realised with a finite-element code (Franc 2D), using frictionless fault models. First, the effect of an increasing biaxial compressive load ratio ?3/ ?1 on stress trajectories around an isolated open defect was explored. It was shown that the stress trajectories were drastically modified when ?3/ ?1 increased from 0.2 to 0.4, this result being consistent with previous studies. In particular, when ?3/ ?1 was superior or equal to 0.4, external isotropic points around where trajectories diverged (called repulsive isotropic points) appeared near the tips, but away from the defects. They tended to move away from the defects towards the main load direction when ?3/ ?1 increased. The described isotropic points were points of stress trajectory divergence, i.e. points where stress decreased, implying that zones around them were strongly unfavourable to shear reactivation. Second, stress trajectories around fault models of various geometries (oblique isolated defect, dilational jog, compressive jog, and complex patterns) were studied, the applied biaxial compressive load ratio being 0.7. These biaxial stress trajectories were compared with similar uniaxial stress trajectories in order to explore the existing differences between the two regimes. It enabled new stress trajectory geometries to be described and interpreted. In particular, numerous external repulsive isotropic points were observed, and defect tips were shown to be zones of high convergence of stress trajectories. Furthermore, in contrast to the uniaxial compressive load case, stress trajectories and stress contours were geometrically similar within dilational and compressive jogs under biaxial compressive load. For both jog types, the centre of the overlapping zone, and the areas along the wall of a jog-defining fault and facing the overlapping tip of the other fault, proved to be zones of low mean stress, implying that fluids may migrate towards them from the tips of the faults, in response to mean stress gradients. Furthermore, the centre of the jogs exhibiting a high differential stress was a favourable area in terms of fracture reactivation, which may facilitate fluids transfer and storage. It was also observed that for both the uniaxial and biaxial compressive loads, isotropic zones were localised at the acute angle between branching defects.

de Joussineau, Ghislain; Petit, Jean-Pierre; Gauthier, Bertrand D. M.

2003-02-01

22

Residual stresses in biaxially fatigued austenitic stainless steel sample of cruciform geometry  

Science.gov (United States)

A specifically designed cruciform-shaped austenitic stainless steel AISI 321 sample was subjected to ex-situ biaxial tension-compression cycling to establish ferromagnetic martensitic phase conversion under the action of plastic deformation. The time-of-flight neutron diffraction technique was employed for in-plane residual stress determination in this sample for both the austenitic and martensitic phases. The 2D data enabled determination of macro-, micro-, hydro- and deviatoric contributions to the total phase stresses.

Taran, Yu V.; Balagurov, A. M.; Schreiber, J.; Evans, A.; Venter, A. M.

2012-02-01

23

Stress biaxiality in high-burnup PWR fuel cladding under reactivity-initiated accident conditions  

International Nuclear Information System (INIS)

In order to promote a better understanding of failure mechanisms of high-burnup pressurized water reactor (PWR) fuels under reactivity-initiated accident (RIA) conditions, stress biaxiality in cladding has been estimated for the pellet-cladding (PC) mechanical interaction (PCMI) phase. The estimation was based on an analysis of the transient elongations of a pellet stack and a cladding tube measured in RIA-simulating experiments in the nuclear safety research reactor (NSRR) using the RANNS code. Stress biaxiality in the high-burnup PWR fuel cladding during the PCMI phase has been estimated to be 0.7-0.8, on average, at the mid-wall of the cladding. A comparison with fresh fuel test results and a sensitivity analysis showed that the effects of burnup and pulse width on cladding stress biaxiality are less than 10% for the investigated range. The present analysis also indicated that PC friction is strong, and that the cladding constraint on pellet stack elongation is significant irrespective of burnup. Therefore, it is recommended that strong PC friction be assumed, which is similar to the mechanical bonding condition, and that fuel pellets be treated as deformable materials in models of fuel behavior during the PCMI phase. (author)

24

Numerical analysis of interacting cracks in biaxial stress field  

International Nuclear Information System (INIS)

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)

25

Ductility of Zircaloy canning tubes in relation to stress ratio in biaxial testing  

International Nuclear Information System (INIS)

A biaxial-burst testing machine has been designed in which biaxial plane stress tests can be carried out on tubular material with any stress ratio in the range sigma/sub THETA/:sigma/sub z/ 4:5 to 2:1, where 2:1 implies the closed-end burst test. Unirradiated Zircaloy tubes cold worked 80 percent, recrystallized at 5750C, and characterized by a texture having a basal pole tilt angle of 33 deg were tested at room temperature with various stress ratios, namely, 4:5, 1:1, 5:4, 3:2, and 2:1. In addition, tension and open-end burst tests were carried out in conventional machines. The uniform ductility measured as uniform effective strain displays a minimum at the stress ratio 3:2. It has been found experimentally that the stress ratio for minimum uniform ductility corresponds to deformation under a plane strain loading condition, that is, the stress ratio which gives no change in the tube length

26

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

International Nuclear Information System (INIS)

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

27

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

International Nuclear Information System (INIS)

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)

28

Numerical analysis of branched cracks in bi-axial stress fields  

International Nuclear Information System (INIS)

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)

29

A new analytical method for stress intensity factors based on insitu measurement of crack deformation under biaxial tension  

International Nuclear Information System (INIS)

A new approach for the calculation of stress intensity factors (SIF) for isotropic and orthotropic materials under biaxial tension loading was proposed in this paper. In order to determine SIF from the full-field displacement data, an asymptotic expansion of the crack tip displacement field was performed. The deforming shape and surface residual stress of the crack tip was obtained at the early extended stage of the loading process by using optical microscope and X-ray diffraction measurement. During this stage, a modified Dugdale Model, which takes into account the coupled effect at the crack tip, was proposed for the open displacement of the crack tip. In this paper, the SIFs of two types of silicon steel sheet with isotropic and orthotropic properties were calculated using the modified Dugdale Model based on the biaxial tension experimental data. From the results, it was found that analysis using the modified Dugdale Model is an effective way to evaluate SIF under biaxial stress.

30

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

International Nuclear Information System (INIS)

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.

31

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

Energy Technology Data Exchange (ETDEWEB)

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.

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

32

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

Energy Technology Data Exchange (ETDEWEB)

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.

Sablik, M.J.; Kwun, H.; Rollwitz, W.L.; Cadena, D.

1992-01-01

33

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

International Nuclear Information System (INIS)

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

34

Dynamic uniaxial and biaxial stress-strain relationships for austenitic stainless steels  

International Nuclear Information System (INIS)

Fast breeder containment structures may be subjected to explosive accidents which deform the material at high strain rates, with load release and reloading by reflected waves, multiaxially. As a contribution to the study of such special loading conditions, the effect of the strain rate (from 10-2 to 103s-1) on the uniaxial flow curves of the steels AISI 304L, AISI 316L and AISI 321, virgin, welded and irradiated up to 2.2 dpa, at temperatures up to 9500C, is discussed here. The typical differences in dynamic material properties shown by virgin materials when compared to defective materials should also be investigated in a multiaxial state of stress. In fact two main questions demand an answer: Are the current yield and fracture criteria sufficient in order to transfer the uniaxial results to dynamic biaxial loading conditions. How may the results obtained for the small specimens used for dynamic testing be transferred to large structures. In order to provide an experimental basis for answering these questions and, therefore, for supporting the formulation of constitutive equations, the following biaxial testing devices have been developed: - An electro-mechanical device and a hydropneumatic machine for strain rates up to 102s-1, acting on small cruciform specimens (cross-section up to 20 mm2). A high-load apparatus (5 MN, strain rate up to 102s-1), acting on large steel specimens with a cross section of up to 5000 mm2, where the statistical distribution of defects determines the strength of the real structure. Preliminary results obtained by developing such tests are reported. General remarks on the structure of some models of constitutive equations are presented. (orig.)

35

Model for analysis of biaxial and triaxial stresses by x-ray diffraction assuming orthotropic materials  

International Nuclear Information System (INIS)

In this work we aim to develop expressions for the calculation of biaxial and triaxial stresses in polycrystalline anisotropic materials, and to determine their elastic constants using the theory of elasticity for continuum isochoric deformations; thus, we also derive a model to determine residual stress. The constitutive relation between strain and stress in these models must be assumed to be orthotropic, obeying the generalized Hooke's law. One technique that can be applied with our models is that of X-ray diffraction, because the experimental conditions are similar to the assumptions in the models, that is, it measures small deformations compared with the sample sizes and the magnitude of the tensions involved, and is insufficient to change the volume (isochoric deformation). Therefore, from the equations obtained, it is possible to use the sin2 ? technique for materials with texture or anisotropy by first characterizing the texture through the pole figures to determine possible angles ? that can be used in the equation, and then determining the deformation for each diffraction peak with the angles ? obtained from the pole figures. (author)

36

Analyses of Failure Mechanisms and Residual Stresses in Graphite/Polyimide Composites Subjected to Shear Dominated Biaxial Loads  

Science.gov (United States)

This research contributes to the understanding of macro- and micro-failure mechanisms in woven fabric polyimide matrix composites based on medium and high modulus graphite fibers tested under biaxial, shear dominated stress conditions over a temperature range of -50 C to 315 C. The goal of this research is also to provide a testing methodology for determining residual stress distributions in unidirectional, cross/ply and fabric graphite/polyimide composites using the concept of embedded metallic inclusions and X-ray diffraction (XRD) measurements.

Kumosa, M.; Predecki, P. K.; Armentrout, D.; Benedikt, B.; Rupnowski, P.; Gentz, M.; Kumosa, L.; Sutter, J. K.

2002-01-01

37

Lattice diffusion and surface segregation of B during growth of SiGe heterostructures by molecular beam epitaxy: Effect of Ge concentration and biaxial stress  

International Nuclear Information System (INIS)

Si1-xGex/Si1-yGey/Si(100) heterostructures grown by molecular beam epitaxy were used in order to study B surface segregation during growth and B lattice diffusion. Ge concentration and stress effects were separated. Analysis of B segregation during growth shows that (i) for layers in epitaxy on (100)Si, B segregation decreases with increasing Ge concentration, i.e., with increased compressive stress; (ii) for unstressed layers, B segregation increases with Ge concentration; (iii) at constant Ge concentration, B segregation increases for layers in tension and decreases for layers in compression. The contrasting behaviors observed as a function of Ge concentration in compressively stressed and unstressed layers can be explained by an increase of the equilibrium segregation driving force induced by Ge additions and an increase of near-surface diffusion in compressively stressed layers. Analysis of lattice diffusion shows that (i) in unstressed layers, B lattice diffusion coefficient decreases with increasing Ge concentration; (ii) at constant Ge concentration, the diffusion coefficient of B decreases with compressive biaxial stress and increases with tensile biaxial stress; (iii) the volume of activation of B diffusion [?V=-kT(d ln D/dP)] is positive for biaxial stress while it is negative in the case of hydrostatic pressure. This confirms that under a biaxial stress the activation volume is reduced to the relaxation volumeme is reduced to the relaxation volume

38

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

International Nuclear Information System (INIS)

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

39

Mechanical behavior of irradiated 20% cold-worked Type 316 stainless steel subjected to a biaxial stress state  

International Nuclear Information System (INIS)

The recently developed Controlled Biaxial Rate (CBSR) test system was used to perform constant temperature, constant diametral strain rate tests on fast reactor cladding. The CBSR test is analogous to conventional uniaxial tests; however, the CBSR stress state is more prototypic of in-reactor transient conditions. Results from CBSR testing of irradiated 20% cold worked Type 316 stainless steel cladding of Fast Flux Test Facility (FFTF) geometry are reported for specimens irradiated in the Experimental Breeder Reactor-II (EBR-II) at temperatures from 370 to 6800C and fluences to 1.3 x 1023 n/cm2. Tests were performed at constant diametral strain rates between 10-5/s and 10-3/s at constant test temperature ranging from 400 to 7000C

40

Creep behavior of Portland cement, mortar, and concrete under biaxial stress  

Energy Technology Data Exchange (ETDEWEB)

Equipment developed at the Oak Ridge National Laboratory was used to make uniaxial and biaxial creep tests on mortar, normal weight concrete and lightweight concrete using both sealed and unsealed specimens. Some of the results are questionable because of the poor performance of the strain gages. Nevertheless, useful information was obtained on shrinkage, creep and Poisson's ratio. Generally speaking, the results were consistent with the work of other investigators. Both the shrinkage and creep were highest for the mortar and lowest for the normal weight concrete and intermediate for the lightweight concrete. The shrinkage and creep were highest for the unsealed specimens. A Poisson's ratio effect in creep was noted but the magnitudes were slightly less than those expected for elastic loadings.

Kesler, C.E.

1977-03-01

 
 
 
 
41

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

International Nuclear Information System (INIS)

Biaxial fatigue tests on discs of a ferritic and an austenitic steel. Loading by thermal cycles. Comparison of the results with those from uniaxial strain-controlled tests at constant temperatures. (orig.) 891 IHOE/orig. 892 HIS

42

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.  

Science.gov (United States)

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. PMID:23277999

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

2012-12-01

43

Dynamic uniaxial and biaxial stress-strain relationships for austenitic stainless steels  

International Nuclear Information System (INIS)

Fast breeder containment structures could be subjected to explosive accidents and impact of missiles, which give rise to propagation and successive reflections of tension waves which deform the material at constant or changing strain rate, with load release and reloading eventually in compression, along multiaxial directions. Constitutive equations, required for calculation codes, should be able to describe the behaviour of the material under these different dynamic loading conditions. In order to provide an experimental basis to the formulation of the constitutive equations, we have developed a hydropneumatic machine and a Hopkinson bar with which we determined the stress-strain curves for austenic stainless steels (AISI 304L, AISI 316L) at constant strain rates ranging from 102s-1 to 103s-1, in uniaxial tension. From these tests we observed that the main effects of strain rate on the dynamic flow curves of these steels at room temperature are the substantial increase of the flow stress and the marked reduction of ductility with increasing strain rate. (orig.)

44

Influence of biaxial stress on the magnetic properties of cobalt nanoparticles  

Energy Technology Data Exchange (ETDEWEB)

Co nanoparticles with an average diameter of 25 nm have been produced using an inert gas condensation technique. The particles were deposited on Si substrates and covered in situ with a 20 nm Cu film. When the substrate coverage exceeds 5 %, the remanent magnetization along the in-plane direction was larger than that along the out-of-plane direction which is attributed to the dipolar interaction between the particles. For Co particles on Ta substrates, the effect of stress on the magnetic properties of isolated particles was studied. A thin film of phospholipids (DOPC) on the Ta substrate was used to avoid the agglomeration of the particles during deposition. The lipid layer was removed in an oxygen plasma, afterwards the particles were reduced to metallic Co again using a hydrogen plasma and subsequently covered with 20nm of SiO{sub x}. The effect of stress on the magnetic properties of these particles was studied by loading the Ta substrate with hydrogen. For 0.6% of strain in the Ta substrate, out-of-plane magnetization measurements showed an increase of the saturation field H{sub s} and a reduction of the remanent magnetization. This indicates that 25 nm cobalt nanoparticles have a positive magnetostriction.

Saranu, Srinivasa; Herr, Ulrich [Institut fuer Mikro- und Nanomaterialien, Universitaet Ulm, 89081 Ulm (Germany); Wiedwald, Ulf; Ziemann, Paul [Institut fuer Festkoerperphysik, Universitaet Ulm, 89069 Ulm (Germany)

2008-07-01

45

Effect of biaxial stress on single particle states and binding energies of charged excitons and biexciton in In(Ga)As/GaAs(001) self-assembled quantum dots  

International Nuclear Information System (INIS)

We study the effect of an external biaxial stress on single particle states and binding energies of charged excitons and biexciton relative to that of neutral exciton in In(Ga)As/GaAs(001) quantum dots. We performed million-atom empirical pseudopotential calculations on realistic In(Ga)As/GaAs(001) quantum dots. We find that compressive biaxial stress increases the electron localization and hole delocalization. The binding energies of the positive trion and biexciton increase under compressive stress. Depending upon the value of binding energy of biexciton and available biaxial stress, the binding energy of biexciton can be tuned to zero which allows for the generation of entangled photon pairs across generations in biexciton cascade process in In(Ga)As/GaAs(001) self-assembled quantum dots.

46

Effect of biaxial stress on single particle states and binding energies of charged excitons and biexciton in In(Ga)As/GaAs(001) self-assembled quantum dots  

Energy Technology Data Exchange (ETDEWEB)

We study the effect of an external biaxial stress on single particle states and binding energies of charged excitons and biexciton relative to that of neutral exciton in In(Ga)As/GaAs(001) quantum dots. We performed million-atom empirical pseudopotential calculations on realistic In(Ga)As/GaAs(001) quantum dots. We find that compressive biaxial stress increases the electron localization and hole delocalization. The binding energies of the positive trion and biexciton increase under compressive stress. Depending upon the value of binding energy of biexciton and available biaxial stress, the binding energy of biexciton can be tuned to zero which allows for the generation of entangled photon pairs across generations in biexciton cascade process in In(Ga)As/GaAs(001) self-assembled quantum dots.

Singh, Ranber; Bester, Gabriel [Max-Planck-Institut fuer Festkoerperforschung, Stuttgart (Germany); Ding, Fei; Plumhof, Johannes; Zander, Tim; Rastelli, Armando; Schmidt, Oliver [Institute for Integrative Nanosciences, IFW Dresden, Dresden (Germany)

2010-07-01

47

Biaxial model for bounding creep ratchetting in shells  

International Nuclear Information System (INIS)

The concept of elastic core stress is used to derive bounds for the maximum inelastic strains in shells of revolution subjected to pressure and cyclic thermal loads in the creep regime. Solutions are obtained for primary membrane stresses of arbitrary biaxiality and thermal bending of arbitrary biaxiality. The stress regimes where previously derived uniaxial solutions can be conservatively used are defined. The new biaxial solutions provide more efficient bounds than the uniaxial solutions for the maximum strains in pressurized spheres and cylinders

48

Biaxial model for bounding creep ratchetting in shells  

Energy Technology Data Exchange (ETDEWEB)

The concept of elastic core stress is used to derive bounds for the maximum inelastic strains in shells of revolution subjected to pressure and cyclic thermal loads in the creep regime. Solutions are obtained for primary membrane stresses of arbitrary biaxiality and thermal bending of arbitrary biaxiality. The stress regimes where previously derived uniaxial solutions can be conservatively used are defined. The new biaxial solutions provide more efficient bounds than the uniaxial solutions for the maximum strains in pressurized spheres and cylinders.

O' Donnell, W.J.; Porowski, J.S.

1981-01-01

49

NESC VII European project: demonstration of warm pre-stressing effect in biaxial loading conditions - Bending tests on 18MND5 cruciform specimens  

International Nuclear Information System (INIS)

In the framework of NESC VII European project, a large experimental program has been dedicated to demonstrate the Warm Pre Stressing (WPS) effect in different testing configurations. One of the CEA (France) contributions to this project is the realization of five point bending tests on large cruciform specimens considering different WPS loading cycles. The five cruciform specimens, sponsored by EDF (France) and IRSN (France), are made of 18MND5 steel. Two of them have been tested on a same LCF (Load-Cool-Fracture) loading cycle, including an isothermal pre-loading at T-WPS = -30 degrees C followed by a cooling down to T-FRAC = -150 degrees C at a constant load before an isothermal reloading up to fracture at T-FRAC. The results presented in this paper give a successful demonstration of the Warm Pre Stressing effect in biaxial loading conditions on a LCF cycle. (authors)

50

Engineering piezoresistivity using biaxially strained silicon  

DEFF Research Database (Denmark)

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 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 enhance the performance of ezoresistive stress sensors.

Pedersen, Jesper Goor; Richter, Jacob

2008-01-01

51

Analytical modeling of the effect of crack depth, specimen size, and biaxial stress on the fracture toughness of reactor vessel steels  

International Nuclear Information System (INIS)

Fracture, toughness values for A533-B reactor pressure vessel (RPV) steel obtained from test programs at Oak Ridge National Laboratory (ORNL) and University of Kansas (KU) are interpreted using the J-A2 analytical model. The analytical model is based on the critical stress concept and takes into consideration the constraint effect using the second parameter A2 in addition to the generally accepted first parameter J which represents the loading level. It is demonstrated that with the constraint level included in the model effects of crack depth (shallow vs deep), specimen size (small vs. large), and loading type (uniaxial vs biaxial) on the fracture toughness from the test programs can be interpreted and predicted

52

Analytical modeling of the effect of crack depth, specimen size, and biaxial stress on the fracture toughness of reactor vessel steels  

Science.gov (United States)

Fracture, toughness values for A533-B reactor pressure vessel (RPV) steel obtained from test programs at Oak Ridge National Laboratory (ORNL) and University of Kansas (KU) are interpreted using the J-A(sub 2) analytical model. The analytical model is based on the critical stress concept and takes into consideration the constraint effect using the second parameter A(sub 2) in addition to the generally accepted first parameter J which represents the loading level. It is demonstrated that with the constraint level included in the model effects of crack depth (shallow vs deep), specimen size (small vs. large), and loading type (uniaxial vs biaxial) on the fracture toughness from the test programs can be interpreted and predicted.

Chao, Yuh-Jin; Lam, Poh-Sang

1995-02-01

53

Application of magnetomechanical hysteresis modeling to magnetic techniques for monitoring neutron embrittlement and biaxial stress. Progress report, June 1991--December 1991  

Energy Technology Data Exchange (ETDEWEB)

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.

Sablik, M.J.; Kwun, H.; Rollwitz, W.L.; Cadena, D.

1992-01-01

54

Evaluation of anisotropic effective stress-strain criteria for the biaxial yield and flow of 2024 aluminum tubes  

International Nuclear Information System (INIS)

2024 aluminum tubes, heat treated to a T6 and T8 temper, were tested in combinations of tension-internal pressure and tension-torsion loading. Yield loci and flow behavior were determined for both modes of loading and compared to theoretical predictions. Both tempers of 2024 aluminum exhibited crystallographic textures and anisotropic yield and flow. Hill's quadratic yield criterion and the associated flow rule under-estimate balanced biaxial yield and flow, which is consistent with hydraulic bulge data on other face-centered cubic metals. Hill's nonquadratic criterion, which adds one additional parameter, and Bassani's criterion, which adds two parameters, predict the anisotropic yield behavior much more accurately. Predictions of the complete flow behavior, including strain paths, with these anisotropic criteria could be improved markedly by including provisions for planar anisotropy

55

NESC VII European project: demonstration of warm pre-stressing effect in biaxial loading conditions - Bending tests on 18MND5 cruciform specimens and their interpretation  

International Nuclear Information System (INIS)

In the framework of the NESC VII European project, a large experimental program has been dedicated to characterize the Warm Pre-Stressing (WPS) effect in different testing configurations. One of the CEA (France) contributions to this project is the realization of five point bending tests on large cruciform specimens considering different WPS loading cycles. The five cruciform specimens, sponsored by EDF (France) and IRSN (France), are made of 18MND5 steel. Two of them have been tested on a same LCF (Load-Cool-Fracture) loading cycle and two others on the same LCTF (Load-Cool-Transient-Fracture) loading cycle. The experimental results presented in this paper give a successful demonstration of the WPS effect in biaxial loading conditions either on a LCF or on a LCTF cycle. During the test interpretations, different models have then been tested and compared in order to evaluate their ability to predict the cleavage fracture in the case of different WPS loading cycles. They all provide very conservative predictions whatever loading cycle is concerned. (authors)

56

A Biaxial Fatigue Specimen for Uniaxial Loading  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The aim of this paper is to present a novel un-notched fatigue test specimen in which a biaxial stress state is achieved using a uniaxial loading condition. This allows the problem of multi-axial fatigue to be studied using relatively common one-axis servo-hydraulic testing machines. In addition the specimen presented here is very compact and can be made using a small volume of material (100x40x4.5mm). For this specimen, the degree of biaxiality, defined by the parameter is equal to approxima...

Bellett, Daniel; Morel, Franck; Morel, Anne; Lebrun, Jean-lou

2011-01-01

57

Planar Biaxial Behavior of Fibrin-Based Tissue-Engineered Heart Valve Leaflets  

Digital Repository Infrastructure Vision for European Research (DRIVER)

To design more effective tissue-engineered heart valve replacements, the replacement tissue may need to mimic the biaxial stress–strain behavior of native heart valve tissue. This study characterized the planar biaxial properties of tissue-engineered valve leaflets and native aortic valve leaflets. Fibrin-based valve equivalent (VE) and porcine aortic valve (PAV) leaflets were subjected to incremental biaxial stress relaxation testing, during which fiber alignments were measured, over a ran...

Robinson, Paul S.; Tranquillo, Robert T.

2009-01-01

58

Biaxial Yield Surface Investigation of Polymer-Matrix Composites  

Directory of Open Access Journals (Sweden)

Full Text Available This article presents a numerical technique for computing the biaxial yield surface of polymer-matrix composites with a given microstructure. Generalized Method of Cells in combination with an Improved Bodner-Partom Viscoplastic model is used to compute the inelastic deformation. The validation of presented model is proved by a fiber Bragg gratings (FBGs strain test system through uniaxial testing under two different strain rate conditions. On this basis, the manufacturing process thermal residual stress and strain rate effect on the biaxial yield surface of composites are considered. The results show that the effect of thermal residual stress on the biaxial yield response is closely dependent on loading conditions. Moreover, biaxial yield strength tends to increase with the increasing strain rate.

Zhengjia He

2013-03-01

59

Biaxial Creep Specimen Fabrication  

Energy Technology Data Exchange (ETDEWEB)

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.

JL Bump; RF Luther

2006-02-09

60

Biaxial magnetic grain alignment  

International Nuclear Information System (INIS)

Full text: We describe a dynamic magnetic grain alignment technique which can be used to produce YBCO thick films with a high degree of biaxial texture. The technique is, however, generally applicable to preparing ceramics or composite materials from granular materials with orthorhombic or lower crystal symmetry and is therefore not restricted to superconducting applications. Because magnetic alignment is a bulk effect, textured substrates are not required, unlike epitaxial coated tape processes such as RABiTS. We have used the technique to produce thick films of Y-247 on untextured silver substrates. After processing to Y-123 the films show a clear enhancement of critical current density relative to identically prepared untextured or uniaxially textured samples. We describe procedures for preparing materials using magnetic biaxial grain alignment with the emphasis on alignment in epoxy, which can give extremely high texture. X-ray rocking curves with FWHM of as little as 1-2 degrees have been measured

 
 
 
 
61

Fragmentation in Biaxial Tension  

Energy Technology Data Exchange (ETDEWEB)

We have carried out an experiment that places a ductile stainless steel in a state of biaxial tension at a high rate of strain. The loading of the ductile metal spherical cap is performed by the detonation of a high explosive layer with a conforming geometry to expand the metal radially outwards. Simulations of the loading and expansion of the metal predict strain rates that compare well with experimental observations. A high percentage of the HE loaded material was recovered through a soft capture process and characterization of the recovered fragments provided high quality data, including uniform strain prior to failure and fragment size. These data were used with a modified fragmentation model to determine a fragmentation energy.

Campbell, G H; Archbold, G C; Hurricane, O A; Miller, P L

2006-06-13

62

Biaxial Testing of 2219-T87 Aluminum Alloy Using Cruciform Specimens  

Science.gov (United States)

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.

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

1997-01-01

63

Biaxial failure surfaces of 2020 and PGX graphites  

International Nuclear Information System (INIS)

Graphite shows an increase in strength with an increase in temperature, and this characteristic makes graphite a prime candidate for structural applications in the high temperature gas-cooled reactors (HTGR). The core support structure in the HTGR uses high strength graphite. Its ultimate strength under a combined stress state is important for design use. A test program was therefore initiated to determine the multiaxial behavior of two specific types of graphites, in particular the biaxial failure surface which is to be correlated with various failure theories. The two candidate graphites are a fine-grain 2020 (of Stackpole Carbon Company) and a coarse-grain PGX (of Union Carbide Corp). Tubular specimens are used and are subjected axial loading and internal or external pressure. Various ratios of biaxial stresses are examined but emphasis is placed in the first and fourth stress quadrants. The tensile fracture pattern reveals a cleavage failure mode. Compressive failure occurs when a limiting value (equivalent to cohesion and internal friction) on any given plane is reached. The maximum stresses at the time of failure are calculated using the thick-wall cylinder formula. A modified Coulomb-Mohr theory with tension-cutoffs proposed by B. Paul (1961) fits the biaxial test data very well. The theory is consistent with the observed fracture patterns and mechanism. The theory appears to give a better correlation with the biaxial test data than the maximum normal stress, mest data than the maximum normal stress, maximum shear stress, maximum distortion energy and Tsai and Wu's strength tensor theories. The failure surfaces obtained are for thin tubular specimen configuration in which the stress state is relatively uniform. The volume and grain size effects are nearly the same. In the application of the failure surfaces to the core support component design, these factors, non-uniform stress state, the volume and grain size effects should be included. (orig.)

64

Residual stress fields in surface-treated silicon carbide for space industry--comparison of biaxial and triaxial analysis using different X-ray methods  

International Nuclear Information System (INIS)

Any mechanical surface treatment and machining leaves 'footprints' in the form of residual stress fields in the surface region of technical parts or components, which are detectable by X-ray diffraction. In the present paper, we applied different X-ray methods to investigate the residual stress state in the near-surface zone of sintered silicon carbide after mechanical surface processing. Using the sin2 ?-based 'universal plot' method, we found steep gradients for the in-plane components ?11 and ?22 in the form of high compressive stresses at the surface, which change into tensile stresses within a few microns. To gain information on the triaxial residual stress state, we applied the scattering vector method, which is based on strain depth profiling by sample rotation around the diffraction vector. For the in-plane stresses, we observed gradients similar to those obtained by the 'universal plot' method, but they were shifted on the absolute scale towards tensile stress. We explain this difference by 'pseudo-macroscopic' tensile residual stress fields ?33, which act normal to the surface and therefore pretend higher in-plane compressive stresses ?ii (i = 1, 2), if they are not regarded in the evaluation procedure

65

Post-buckling capacity of bi-axially loaded rectangular steel plates  

DEFF Research Database (Denmark)

Results from a detailed numerical investigation of the post-buckling behaviour of rectangular simply supported steel plates subjected to biaxial in-plane loading are presented. The Steel plates are loaded through forced edge displacements. The effects of initial imperfections, aspect ratio, plate slenderness and edge displacement ratio are included in the investigations presented. Capacity interaction curves are established in the bi-axial stress domain. It turns out that for certain stress ratios the imperfections dominating the ultimate capacity are not affine to the lowest classical buckling mode for biaxial stress. It is of great interest that short wave imperfections of a lower magnitude compared to conventionally used imperfections are seen to lower the capacity of the bi-axially loaded plates. The topic is of major concern in the flange plates of long span bridges with multi box girder configurations.

Jönsson, Jeppe

2012-01-01

66

Lattice diffusion and surface segregation of B during growth of SiGe heterostructures by molecular beam epitaxy: effect of Ge concentration and biaxial stress  

CERN Document Server

Si1-xGex/Si1-yGey/Si(100) heterostructures grown by Molecular Beam Epitaxy (MBE) were used in order to study B surface segregation during growth and B lattice diffusion. Ge concentration and stress effects were separated. Analysis of B segregation during growth shows that: i) for layers in epitaxy on (100)Si), B segregation decreases with increasing Ge concentration, i.e. with increased compressive stress, ii) for unstressed layers, B segregation increases with Ge concentration, iii) at constant Ge concentration, B segregation increases for layers in tension and decreases for layers in compression. The contrasting behaviors observed as a function of Ge concentration in compressively stressed and unstressed layers can be explained by an increase of the equilibrium segregation driving force induced by Ge additions and an increase of near-surface diffusion in compressively stressed layers. Analysis of lattice diffusion shows that: i) in unstressed layers, B lattice diffusion coefficient decreases with increasing...

Portavoce, A; Christensen, J S; Gas, P; Ronda, A; ccsd-00002812, ccsd

2004-01-01

67

Biaxiality of chiral liquid crystals  

International Nuclear Information System (INIS)

Using extended deGennes-Ginzburg-Landau free energy expansion in terms of the anisotropic part of the dielectric tensor field Q??(?) 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

68

Biaxially oriented film on flexible polymeric substrate  

Science.gov (United States)

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.

Finkikoglu, Alp T. (Los Alamos, NM); Matias, Vladimir (Santa Fe, NM)

2009-10-13

69

Biaxial fatigue of fiber-reinforced composites at cryogenic temperatures - 1. Fatigue fracture life and mechanisms  

International Nuclear Information System (INIS)

A study of biaxial fatigue of glass fiber-reinforced composites subjedted to in-phase, cyclic tensile and torsional loading at cryogenic temperatures is presented. Fatigue failure of the composite is investigated in terms of cyclic fracture, stiffness degradation, and energy dissipation. Fatigue fracture lives of the cryogenic composite are obtained for the cases of various combinations of cyclic tensile and torsional stresses. A power-law realtionship is established between the range of cyclic octahedral shear stress and the number of cycles to fracture. Influences of hydrostatic mean stress and stress biaxiality ratio on fatigue fracture of the fiber composite are determined. Fracture mechanisms in the material during the cryogenic biaxial fatigue are examined by using optical and scananing electron microscopes. 21 refs

70

Plastic behaviour and forming limit during biaxial compressions of magnesium alloy AZ31 at room temperature  

Directory of Open Access Journals (Sweden)

Full Text Available The plastic behaviour and compressive fracture of AZ31 magnesium alloy were examined at room temperature. The uniaxial compression tests and biaxial compression tests along linear and nonlinear strain paths were carried out until fracture using a unique biaxial compression testing machine developed by author. The results revealed the evolution of plastic anisotropy in biaxial compressions, that is the strain path dependency of work hardening. The adaptability of several forming limit criteria to the compressive fracture of AZ31 alloy was discussed. It was found that the uniform estimation of compressive forming limits by uniaxial and biaxial compressions was difficult by Freudenthal criterion and Oyane criterion. The result of Tresca energy criterion suggested that the criterion based on shear stress has possibility to predict the compressive forming limits at room temperature of AZ31 alloy.

Shimizu I.

2010-06-01

71

Fatigue of Clip connectors for offshore drilling risers under biaxial tension  

Directory of Open Access Journals (Sweden)

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.

Gaur Vidit

2014-06-01

72

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

Science.gov (United States)

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

Jackson, Wade C.; Ratcliffe, James G.

2013-01-01

73

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

Science.gov (United States)

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

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

1995-01-01

74

In situ characterization of martensite variant formation in nickel-titanium shape memory alloy under biaxial loading  

International Nuclear Information System (INIS)

Martensite morphology in a NiTi alloy under uni- and biaxial loading was studied in situ using high-resolution microscopy, electron backscatter diffraction and local strain analyses. The results obtained clearly indicate that a different martensite morphology, including a higher number of martensite variants, evolved in NiTi under biaxial stress states. However, the phase transformation was still triggered by shear stresses, eventually affecting deformation and fatigue-related phenomena.

75

The biaxial strength and fracture criteria for HTGR graphites  

International Nuclear Information System (INIS)

The strength and fracture criteria at the biaxial stress state were examined for two grades of HTGR graphites, i.e., a fine-grained isotropic IG-11 and a medium-grained semi-isotropic PGX. The biaxial stress state was realized using a servohydraulic testing machine in combination with an apparatus for applying the internal pressure or the torque force to a tubular specimen. Three kinds of specimens were tested at room temperature: (1) the larger specimens with different wall thicknesses (2 to 20 mm) to make clear the effect of wall thickness on the biaxial strength, (2) the smaller ones with wall thickness of 2 mm to obtain data for the statistical analysis, and (3) specimens tested at ORNL to examine if there is any discrepancy in the strength data which may result from the differences in the rig and specimen size. Main results are: (1) As for the failure surface no significant effect of wall thickness was observed though the number of the specimens tested was not large enough to evaluate the data statistically. (2) On the basis of the statistical analysis of the data on the smaller IG-11 specimens, the modified maximum strain energy criterion gave the best fit to the data points both in the first and fourth quadrants of the fracture surface. (3) The data obtained at ORNL fell on the scatter band of the JAERI data, which indicated that no appreciable difference in the biaxial strength of IG-11 graphite was found despite the difference in the test fixture and specimen dimensions. (4) The maximum strain energy criterion was also believed to be most appropriate for PGX graphite for the first quadrant of the failure surface. (author)

76

Biaxially Stretched Polycarbonate Film For Capacitors  

Science.gov (United States)

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.

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

1992-01-01

77

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

International Nuclear Information System (INIS)

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

78

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

Energy Technology Data Exchange (ETDEWEB)

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.

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

1998-06-01

79

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

International Nuclear Information System (INIS)

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

80

Peripheral shear strength of biaxially tensioned reinforced concrete wall elements  

International Nuclear Information System (INIS)

The results of a series of tests on biaxially tensioned, orthogonally reinforced concrete panels subjected to punching shear are presented and discussed. Contrary to existing U.S. code provisions, the punching shear capacity is not reduced significantly as the biaxial tension level is increased to as much as 0,8fsub(y) in the reinforcement. A design equation is proposed that gives 4?f'sub(c) shear stress for zero biaxial tension and a linear decrease to 3.1?f'sub(c) as the tension is increased to 0.9fsub(y). The size of the loading pad under the punching force and the shear span have little effect on the strength but the pattern of the failure crack does change with these geometric variables. The splitting crack tends to connect the edge of the loading pad and the supports. More testing is recommended to evaluate a few additional variables, such as the use of inserts which receive the punching force. (orig.)

 
 
 
 
81

A proposal of parameter to predict biaxial fatigue life for CF8M cast stainless steels  

International Nuclear Information System (INIS)

Biaxial low cycle fatigue test was carried out to predict fatigue life under combined axial-torsional loading condition which is that of in-phase and out-of-phase for CF8M cast stainless steels. Fatemi Socie(FS) parameter which is based on critical plane approach is not only one of methods but also the best method that can predict fatigue life under biaxial loading condition. But the result showed that, biaxial fatigue life prediction by using FS parameter with several different parameters for the CF8M cast stainless steels is not conservative but best results. So in this present research, we proposed new fatigue life prediction parameter considering effective shear stress instead of FS parameter which considers the maximum normal stress acting on maximum shear strain and its effectiveness was verified

82

Shape recovery characteristics of biaxially prestrained Fe-Mn-Si-based shape memory alloy  

International Nuclear Information System (INIS)

Fe-Mn-Si-based shape memory alloy has already been used practically for steel pipe joints. In most of the applications including the steel pipe joints, it is possible to estimate the reduction of diameter from the experimental data of the shape recovery after uniaxial stretching of the alloy materials. However, studies on shape recovery effects after biaxial stretching are important for the extensive applications of the alloy. In this study, we investigated the shape recovery strain after uniaxial and biaxial stretching and the microstructures of the alloy in order to see the effects of uniaxial and biaxial prestrain on the stress-induced martensitic transformation. Amounts of shape recovery strain in the biaxially prestrained specimens are smaller than those in the uniaxially prestrained specimens. Transmission electron microscopy revealed that reverse transformations of stress-induced martensitic ?-phase are prevented by slip bands formed at the same time in the biaxially prestrained specimens, but not in the uniaxially prestrained specimens. The technological data and interpretations presented in this study should be useful in forming design guidelines for promoting the extensive applications of Fe-Mn-Si-based shape memory alloy

83

Biaxial tensile testing and constitutive modeling of human supraspinatus tendon.  

Science.gov (United States)

The heterogeneous composition and mechanical properties of the supraspinatus tendon offer an opportunity for studying the structure-function relationships of fibrous musculoskeletal connective tissues. Previous uniaxial testing has demonstrated a correlation between the collagen fiber angle distribution and tendon mechanics in response to tensile loading both parallel and transverse to the tendon longitudinal axis. However, the planar mechanics of the supraspinatus tendon may be more appropriately characterized through biaxial tensile testing, which avoids the limitation of nonphysiologic traction-free boundary conditions present during uniaxial testing. Combined with a structural constitutive model, biaxial testing can help identify the specific structural mechanisms underlying the tendon's two-dimensional mechanical behavior. Therefore, the objective of this study was to evaluate the contribution of collagen fiber organization to the planar tensile mechanics of the human supraspinatus tendon by fitting biaxial tensile data with a structural constitutive model that incorporates a sample-specific angular distribution of nonlinear fibers. Regional samples were tested under several biaxial boundary conditions while simultaneously measuring the collagen fiber orientations via polarized light imaging. The histograms of fiber angles were fit with a von Mises probability distribution and input into a hyperelastic constitutive model incorporating the contributions of the uncrimped fibers. Samples with a wide fiber angle distribution produced greater transverse stresses than more highly aligned samples. The structural model fit the longitudinal stresses well (median R(2) ? 0.96) and was validated by successfully predicting the stress response to a mechanical protocol not used for parameter estimation. The transverse stresses were fit less well with greater errors observed for less aligned samples. Sensitivity analyses and relatively affine fiber kinematics suggest that these errors are not due to inaccuracies in measuring the collagen fiber organization. More likely, additional strain energy terms representing fiber-fiber interactions are necessary to provide a closer approximation of the transverse stresses. Nevertheless, this approach demonstrated that the longitudinal tensile mechanics of the supraspinatus tendon are primarily dependent on the moduli, crimp, and angular distribution of its collagen fibers. These results add to the existing knowledge of structure-function relationships in fibrous musculoskeletal tissue, which is valuable for understanding the etiology of degenerative disease, developing effective tissue engineering design strategies, and predicting outcomes of tissue repair. PMID:22482671

Szczesny, Spencer E; Peloquin, John M; Cortes, Daniel H; Kadlowec, Jennifer A; Soslowsky, Louis J; Elliott, Dawn M

2012-02-01

84

Design optimization of cruciform specimens for biaxial fatigue loading  

Directory of Open Access Journals (Sweden)

Full Text Available In order to correctly assess the biaxial fatigue material properties one must experimentally test different load conditions and stress levels. With the rise of new in-plane biaxial fatigue testing machines, using smaller and more efficient electrical motors, instead of the conventional hydraulic machines, it is necessary to reduce the specimen size and to ensure that the specimen geometry is appropriated for the load capacity installed. At the present time there are no standard specimen’s geometries and the indications on literature how to design an efficient test specimen are insufficient. The main goal of this paper is to present the methodology on how to obtain an optimal cruciform specimen geometry, with thickness reduction in the gauge area, appropriated for fatigue crack initiation, as a function of the base material sheet thickness used to build the specimen. The geometry is optimized for maximum stress using several parameters, ensuring that in the gauge area the stress is uniform and maximum with two limit phase shift loading conditions. Therefore the fatigue damage will always initiate on the center of the specimen, avoiding failure outside this region. Using the Renard Series of preferred numbers for the base material sheet thickness as a reference, the reaming geometry parameters are optimized using a derivative-free methodology, called direct multi search (DMS method. The final optimal geometry as a function of the base material sheet thickness is proposed, as a guide line for cruciform specimens design, and as a possible contribution for a future standard on in-plane biaxial fatigue tests.

R. Baptista,

2014-10-01

85

Biaxially textured articles formed by powder metallurgy  

Science.gov (United States)

A biaxially textured alloy article comprises 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 ; compacted and heat treated, then rapidly recrystallized 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.

Goyal, Amit (Knoxville, TN); Williams, Robert K. (Knoxville, TN)

2001-01-01

86

Structural failure of two-density-layer cohesionless biaxial ellipsoids  

Science.gov (United States)

This paper quantitatively evaluates structural failure of biaxial cohesionless ellipsoids that have a two-density-layer distribution. The internal density layer is modeled as a sphere, while the external density layer is the rest of the part. The density is supposed to be constant in each layer. The present study derives averaged stresses over the whole volume of these bodies and uses limit analysis to determine their global failure. The upper bound of global failure is considered in terms of the size of the internal layer and the aspect ratio of the shape. The result shows that the two-density-layer causes the body to have different strength against structural failure.

Hirabayashi, Masatoshi

2014-07-01

87

Biaxial Deformation Behavior and Enhanced Formability of Ultrafine-Grained Pure Copper  

Science.gov (United States)

Coarse-grained commercially pure Cu was subjected to equal channel angular pressing at room temperature for 2 passes and 12 passes resulting in grain refinement down to the ultrafine scale. Uniaxial tensile testing revealed that as-ECAP Cu samples have very high strength, but low uniform elongation and elongation to failure, whereas small punch testing showed that strain in biaxial stretching of the as-ECAP Cu specimens was comparable to that in the coarse-grained Cu. Analysis of surface relief demonstrated extensive microlocalization of plastic flow into microshear bands during biaxial stretching of the as-ECAP Cu specimens. The effect of microstructure and stress state on formability of the material and the mechanisms governing its plastic deformation are discussed. It is suggested that although the high strength as-ECAP Cu exhibits poor ductility in uniaxial tension, in other strain paths such as biaxial stretching, it can show high formability which is sufficient for metal-forming processes.

Moreno-Valle, E. C.; Monclus, M. A.; Molina-Aldareguia, J. M.; Enikeev, N.; Sabirov, I.

2013-05-01

88

The biaxial biomechanical behavior of abdominal aortic aneurysm tissue.  

Science.gov (United States)

Rupture of the abdominal aortic aneurysm (AAA) occurs when the local wall stress exceeds the local wall strength. Knowledge of AAA wall mechanics plays a fundamental role in the development and advancement of AAA rupture risk assessment tools. Therefore, the aim of this study is to evaluate the biaxial mechanical properties of AAA tissue. Multiple biaxial test protocols were performed on AAA samples harvested from 28 patients undergoing open surgical repair. Both the Tangential Modulus (TM) and stretch ratio (?) were recorded and compared in both the circumferential (?) and longitudinal (L) directions at physiologically relevant stress levels, the influence of patient specific factors such as sex, age AAA diameter and status were examined. The biomechanical response was also fit to a hyperplastic material model. The AAA tissue was found to be anisotropic with a greater tendency to stiffen in the circumferential direction compared to the longitudinal direction. An anisotropic hyperelastic constitutive model represented the data well and the properties were not influenced by the investigated patient specific factors however, a future study utilizing a larger cohort of patients is warranted to confirm these findings. This work provides further insights on the biomechanical behavior of AAA and may be useful in the development of more reliable rupture risk assessment tools. PMID:25201606

O'Leary, Siobhan A; Healey, Donagh A; Kavanagh, Eamon G; Walsh, Michael T; McGloughlin, Tim M; Doyle, Barry J

2014-12-01

89

Vertically aligned biaxially textured molybdenum thin films  

Energy Technology Data Exchange (ETDEWEB)

Vertically aligned, biaxially textured molybdenum nanorods were deposited using dc magnetron sputtering with glancing flux incidence (alpha = 85 degrees with respect to the substrate normal) and a two-step substrate-rotation mode. These nanorods were identified with a body-centered cubic crystal structure. The formation of a vertically aligned biaxial texture with a [110] out-of-plane orientation was combined with a [-110] in-plane orientation. The kinetics of the growth process was found to be highly sensitive to an optimum rest time of 35 seconds for the two-step substrate rotation mode. At all other rest times, the nanorods possessed two separate biaxial textures each tilted toward one flux direction. While the in-plane texture for the vertical nanorods maintains maximum flux capture area, inclined Mo nanorods deposited at alpha = 85 degrees without substrate rotation display a [-1-1-4] in-plane texture that does not comply with the maximum flux capture area argument. Finally, an in situ capping film was deposited with normal flux incidence over the biaxially textured vertical nanorods resulting in a thin film over the porous nanorods. This capping film possessed the same biaxial texture as the nanorods and could serve as an effective substrate for the epitaxial growth of other functional materials.

Krishnan, Rahul [Department of Materials Science and Engineering, Rensselaer Polytechnic Institute, Troy, New York 12180 (United States); Riley, Michael [Department of Chemical and Biological Engineering, Rensselaer Polytechnic Institute, Troy, New York 12180 (United States); Lee, Sabrina [US Army Armament Research, Development and Engineering Center, Benet Labs, Watervliet, New York 12189 (United States); Lu, Toh-Ming [Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, Troy, New York 12180 (United States)

2011-09-15

90

Vertically aligned biaxially textured molybdenum thin films  

International Nuclear Information System (INIS)

Vertically aligned, biaxially textured molybdenum nanorods were deposited using dc magnetron sputtering with glancing flux incidence (alpha = 85 degrees with respect to the substrate normal) and a two-step substrate-rotation mode. These nanorods were identified with a body-centered cubic crystal structure. The formation of a vertically aligned biaxial texture with a [110] out-of-plane orientation was combined with a [-110] in-plane orientation. The kinetics of the growth process was found to be highly sensitive to an optimum rest time of 35 seconds for the two-step substrate rotation mode. At all other rest times, the nanorods possessed two separate biaxial textures each tilted toward one flux direction. While the in-plane texture for the vertical nanorods maintains maximum flux capture area, inclined Mo nanorods deposited at alpha = 85 degrees without substrate rotation display a [-1-1-4] in-plane texture that does not comply with the maximum flux capture area argument. Finally, an in situ capping film was deposited with normal flux incidence over the biaxially textured vertical nanorods resulting in a thin film over the porous nanorods. This capping film possessed the same biaxial texture as the nanorods and could serve as an effective substrate for the epitaxial growth of other functional materials.

91

Vertically aligned biaxially textured molybdenum thin films  

Science.gov (United States)

Vertically aligned, biaxially textured molybdenum nanorods were deposited using dc magnetron sputtering with glancing flux incidence (alpha = 85° with respect to the substrate normal) and a two-step substrate-rotation mode. These nanorods were identified with a body-centered cubic crystal structure. The formation of a vertically aligned biaxial texture with a [110] out-of-plane orientation was combined with a [-110] in-plane orientation. The kinetics of the growth process was found to be highly sensitive to an optimum rest time of 35 seconds for the two-step substrate rotation mode. At all other rest times, the nanorods possessed two separate biaxial textures each tilted toward one flux direction. While the in-plane texture for the vertical nanorods maintains maximum flux capture area, inclined Mo nanorods deposited at alpha = 85° without substrate rotation display a [-1-1-4] in-plane texture that does not comply with the maximum flux capture area argument. Finally, an in situ capping film was deposited with normal flux incidence over the biaxially textured vertical nanorods resulting in a thin film over the porous nanorods. This capping film possessed the same biaxial texture as the nanorods and could serve as an effective substrate for the epitaxial growth of other functional materials.

Krishnan, Rahul; Riley, Michael; Lee, Sabrina; Lu, Toh-Ming

2011-09-01

92

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

Energy Technology Data Exchange (ETDEWEB)

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)

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

93

Biaxial extension of knitted steel fibre fabrics  

Science.gov (United States)

In this paper knitted steel fibre fabrics will be tested in biaxial extension. An in-house developed biaxial extension machine is used to apply a variety of strain conditions, which allows investigating the coupling between the wale and course direction of the fabrics and the degree of anisotropy in the fabric. Prior to testing a pretension level, to compensate the slack nature of the fabric, is determined by using a laser-measuring device. The strain inside the fabric is measured using a CCD camera technique. The results show the non-linear behaviour of the fabric and the coupling between the wale and the course direction. This will lead to a test protocol that can be used to evaluate the biaxial response of different types of knitted fabrics.

Vanclooster, K.; Eshghyar, A.; Lomov, S. V.

2011-05-01

94

Biaxial Fatigue Testing of Thin Films  

International Nuclear Information System (INIS)

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

95

Anisotropic yield surfaces in bi-axial cyclic plasticity  

International Nuclear Information System (INIS)

Some aspects of the behaviour of yield surfaces and work-hardening surfaces occurring in biaxial cyclic plasticity have been studied experimentally and theoretically. The experimental work consisted of subjecting thin-walled tubular steel specimens to cyclic plastic torsion in the presence of sustained axial loads of various magnitudes. The experimental results show that considerable anisotropy is induced when the cyclic shear strains are dominant. Although the true shapes of yield and work-hardening surfaces can be very complex, a mathematical model is presented which includes both anisotropy and Bauschinger effects. The model is able to qualitatively predict the deformation patterns during a cycle of applied plastic shear strain for a range of sustained axial stresses and also indicate the material response to changes in axial stress. (orig.)

96

Experimental and analytical comparison of constraint effects due to biaxial loading and shallow-flaws  

International Nuclear Information System (INIS)

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. The focus of studies described herein is on the evaluation of a micromechanical scaling model based on critical stressed volumes for quantifying crack-tip constraint through applications to experimental 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. Shallow-crack effects and far-field tensile out-of-plane biaxial loading have been identified as constraint issues that influence both fracture toughness and the extent of the toughness scatter band. Results from applications indicate that 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. Crack-tip constraint analyses of the shallow-crack cruciform specimen based on near-tip stress fields. Crack-tip constraint analyses of the shallow-crack cruciform specimen subjected to uniaxial or biaxial loading conditions are shown to represent a significant challenge for these methodologies. Unresolved issued identified from these analyses require resolution as part of a validation process for biaxial loading applications

97

Neutron diffraction investigation of an in-plane biaxial fatigued stainless steel sample of cruciform geometry  

Energy Technology Data Exchange (ETDEWEB)

Fatigue and fracture under multiaxial stresses are among the most important current research topics aimed at ensuring improved reliability of industrial components. An ex situ in-plane biaxial low cycle fatigued sample of cruciform geometry from austenitic stainless steel AISI 321 H was investigated on the FSD stress-diffractometer at the IBR-2 pulsed nuclear reactor by using the neutron strain scanner and the uniaxial stress rig. The phase composition of fatigued material was determined and the residual macrostresses and phase microstresses were measured. To the best of our knowledge, no neutron diffraction investigations of materials subjected to biaxial loading have been previously carried out. The first results of the neutron diffraction experiment are presented and discussed.

Taran, Yu V; Balagurov, A M; Sheverev, S G [Frank Laboratory of Neutron Physics, Joint Institute for Nuclear Research, Dubna (Russian Federation); Schreiber, J [Fraunhofer Institute for Nondestructive Testing (Dresden branch) (Germany); Korsunsky, A M; Vorster, W J J [Department of Engineering Science, University of Oxford (United Kingdom); Bomas, H; Stoeberl, C [Division of Material Science, Foundation Institute for Materials Science, Bremen (Germany)], E-mail: taran@nf.jinr.ru

2008-03-12

98

Neutron diffraction investigation of an in-plane biaxial fatigued stainless steel sample of cruciform geometry  

Science.gov (United States)

Fatigue and fracture under multiaxial stresses are among the most important current research topics aimed at ensuring improved reliability of industrial components. An ex situ in-plane biaxial low cycle fatigued sample of cruciform geometry from austenitic stainless steel AISI 321 H was investigated on the FSD stress-diffractometer at the IBR-2 pulsed nuclear reactor by using the neutron strain scanner and the uniaxial stress rig. The phase composition of fatigued material was determined and the residual macrostresses and phase microstresses were measured. To the best of our knowledge, no neutron diffraction investigations of materials subjected to biaxial loading have been previously carried out. The first results of the neutron diffraction experiment are presented and discussed.

Taran, Yu V.; Balagurov, A. M.; Sheverev, S. G.; Schreiber, J.; Korsunsky, A. M.; Vorster, W. J. J.; Bomas, H.; Stoeberl, C.

2008-03-01

99

Electrodeposition of biaxially textured layers on a substrate  

Energy Technology Data Exchange (ETDEWEB)

Methods of producing one or more biaxially textured layer on a substrate, and articles produced by the methods, are disclosed. An exemplary method may comprise electrodepositing on the substrate a precursor material selected from the group consisting of rare earths, transition metals, actinide, lanthanides, and oxides thereof. An exemplary article (150) may comprise a biaxially textured base material (130), and at least one biaxially textured layer (110) selected from the group consisting of rare earths, transition metals, actinides, lanthanides, and oxides thereof. The at least one biaxially textured layer (110) is formed by electrodeposition on the biaxially textured base material (130).

Bhattacharya, Raghu N; Phok, Sovannary; Spagnol, Priscila; Chaudhuri, Tapas

2013-11-19

100

Towards the biaxial nematic phase via specific intermolecular interactions  

International Nuclear Information System (INIS)

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

 
 
 
 
101

Biaxially textured metal substrate with palladium layer  

Science.gov (United States)

Described is an article comprising a biaxially textured metal substrate and a layer of palladium deposited on at least one major surface of the metal substrate; wherein the palladium layer has desired in-plane and out-of-plane crystallographic orientations, which allow subsequent layers that are applied on the article to also have the desired orientations.

Robbins, William B [Maplewood, MN

2002-12-31

102

Ferroelectricity in low-symmetry biaxial nematic liquid crystals.  

Science.gov (United States)

Order parameters and phenomenological theory for both high- and low-symmetry biaxial nematic phases are presented and it is predicted that the chiral low-symmetry biaxial phase must be ferroelectric. This conclusion is based on general symmetry arguments and on the results of the Landau-de Gennes theory. The microscopic mechanism of the ferroelectric ordering in this chiral biaxial phase is illustrated using a simple molecular model based on dispersion interactions between biaxial molecules of low symmetry. Similar to the chiral smectic C* phase, the ferroelectricity in the chiral biaxial nematic phase is improper, i.e., polarization is not a primary order parameter and is not determined by dipolar interactions. Ferroelectric ordering in biaxial nematics may be found, in principle, in materials composed of chiral analogues of the tetrapod molecules which are known to exhibit biaxial phases. PMID:21386515

Osipov, Mikhail A; Gorkunov, Maxim V

2010-09-15

103

Ferroelectricity in low-symmetry biaxial nematic liquid crystals  

Energy Technology Data Exchange (ETDEWEB)

Order parameters and phenomenological theory for both high- and low-symmetry biaxial nematic phases are presented and it is predicted that the chiral low-symmetry biaxial phase must be ferroelectric. This conclusion is based on general symmetry arguments and on the results of the Landau-de Gennes theory. The microscopic mechanism of the ferroelectric ordering in this chiral biaxial phase is illustrated using a simple molecular model based on dispersion interactions between biaxial molecules of low symmetry. Similar to the chiral smectic C* phase, the ferroelectricity in the chiral biaxial nematic phase is improper, i.e., polarization is not a primary order parameter and is not determined by dipolar interactions. Ferroelectric ordering in biaxial nematics may be found, in principle, in materials composed of chiral analogues of the tetrapod molecules which are known to exhibit biaxial phases. (fast track communication)

Osipov, Mikhail A [Department of Mathematics and Statistics, University of Strathclyde, Glasgow G1 1XH (United Kingdom); Gorkunov, Maxim V, E-mail: m.osipov@strath.ac.u [A V Shubnikov Institute of Crystallography, Russian Academy of Sciences, 119333 Moscow (Russian Federation)

2010-09-15

104

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

LENUS (Irish Health Repository)

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.

Lyons, Mathew

2014-06-03

105

Structural failure of two-density-layer cohesionless biaxial ellipsoids  

CERN Document Server

This paper quantitatively evaluates structural failure of biaxial cohesionless ellipsoids that have a two-density-layer distribution. The internal density layer is modeled as a sphere, while the external density layer is the rest of the part. The density is supposed to be constant in each layer. The present study derives averaged stresses over the whole volume of these bodies and uses limit analysis to determine their global failure. The upper bound condition of global failure is considered in terms of the size of the internal layer and the aspect ratio of the shape. The result shows that the two-density-layer causes the body to have different strength against structural failure.

Hirabayashi, Masatoshi

2014-01-01

106

Biaxial hot-drawing of poly(ethylene terephthalate): An experimental study spanning the processing range  

Digital Repository Infrastructure Vision for European Research (DRIVER)

An experimental study was made of hot-drawing of PET films under biaxial stress, relevant to industrial orientation processing. The aim was to generate a data set more comprehensive than previously available, to support the development of an improved constitutive model for PET, suitable for process modelling. Isotropic, almost-amorphous films were prepared by extrusion from two grades of PET, with differing molecular weight. The ranges of strain-rate and temperature encompassed were 0.2-16 s-...

Buckley, Cp; Lew, Cy

2011-01-01

107

Biaxial crystal-based optical tweezers  

DEFF Research Database (Denmark)

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 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.

Hanson, Steen Grüner

2010-01-01

108

Biaxial tension of fibrous tissue: using finite element methods to address experimental challenges arising from boundary conditions and anisotropy.  

Science.gov (United States)

Planar biaxial tension remains a critical loading modality for fibrous soft tissue and is widely used to characterize tissue mechanical response, evaluate treatments, develop constitutive formulas, and obtain material properties for use in finite element studies. Although the application of tension on all edges of the test specimen represents the in situ environment, there remains a need to address the interpretation of experimental results. Unlike uniaxial tension, in biaxial tension the applied forces at the loading clamps do not transmit fully to the region of interest (ROI), which may lead to improper material characterization if not accounted for. In this study, we reviewed the tensile biaxial literature over the last ten years, noting experimental and analysis challenges. In response to these challenges, we used finite element simulations to quantify load transmission from the clamps to the ROI in biaxial tension and to formulate a correction factor that can be used to determine ROI stresses. Additionally, the impact of sample geometry, material anisotropy, and tissue orientation on the correction factor were determined. Large stress concentrations were evident in both square and cruciform geometries and for all levels of anisotropy. In general, stress concentrations were greater for the square geometry than the cruciform geometry. For both square and cruciform geometries, materials with fibers aligned parallel to the loading axes reduced stress concentrations compared to the isotropic tissue, resulting in more of the applied load being transferred to the ROI. In contrast, fiber-reinforced specimens oriented such that the fibers aligned at an angle to the loading axes produced very large stress concentrations across the clamps and shielding in the ROI. A correction factor technique was introduced that can be used to calculate the stresses in the ROI from the measured experimental loads at the clamps. Application of a correction factor to experimental biaxial results may lead to more accurate representation of the mechanical response of fibrous soft tissue. PMID:23445049

Jacobs, Nathan T; Cortes, Daniel H; Vresilovic, Edward J; Elliott, Dawn M

2013-02-01

109

Modelizing ratcheting in biaxial tests  

International Nuclear Information System (INIS)

A new constitutive equation has been developed on a purely phenomenological basis in order to interpret ratcheting experiments. The model is based on a generalized Arsmstrong-Frederick equation for the kinematic variable; the coefficients of this equation are functions of both instantaneous and accumulated plastic strain. The experiments described relate to austenitic stainless steel (17-12 SPH) tubular specimens subjected to cyclic torsional loading under constant tensile stress at 600 deg C. Comparisons between experimental and theoretical results show that the model reasonably well predicts not only ratcheting but also hysteresis loops and the cyclic hardening curve

110

Yielding of 6061-T6 aluminium tubings under dynamic biaxial loadings  

International Nuclear Information System (INIS)

A test vehicle for applying biaxial, tension-internal pressure, loading to thin-walled tubular specimens over a range of loading rates has been developed. The test vehicle consists of a housing, a number of pistons and three pressure chambers. Static axial and hoop stresses can be obtained and controlled independently. For additional dynamic loading, the dynamic piston assembly which produces internal pressure to the specimen is driven inward by an impact of a spherical pendulum. The dynamic stress path of the specimen is a part of the natural response of the system partially controllable through adjusting the initial static stress state and impact velocity. (orig.)

111

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

International Nuclear Information System (INIS)

The effect of biaxial loading on the ductile tearing 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 (75 mm by 2 m by 2 m) manufactured from a ferritic steel. The first test specimen was loaded in uniaxial tension and the second test specimen was loaded bi-axially. This paper presents experimental details and results of the two wide plate tests and describes the analysis work being undertaken which is required to interpret the experiments satisfactorily. Preliminary results of this analysis work are presented. The following main conclusions may be drawn from the work contained in this report: 1) The initiation applied stress, evaluated by the ACPD method, for the biaxial specimen, GNSR/1.OB, was approximately 20% higher than that for the uniaxial specimen, GNSR/1.OU indicating an effective benefit of biaxial loading. 2) The maximum applied stresses were similar in the two tests with that for the biaxial test being slightly higher than that for the uniaxial test; 106.7 MPa in GNSR/1.OU for 5.3 mm of tearing .7 MPa in GNSR/1.OU for 5.3 mm of tearing and 108.7 MPa in GNSR/1.OB for 3.2 mm of tearing. 3) All the R6 results conservatively under-predicted the applied load for the amounts of ductile tearing obtained in the tests (i.e. 3.5 mm and 5.3 mm in GNSR/1.OU and 3.2 mm and 1.3 mm in GNSR/1.OB). 4) For the GNSR/1.OU bottom crack tip and both crack tips in GNSR/1.OB, it would seem likely that the conservatism would still apply even if the cracks had been grown up to instability. However, for the GNSR/1.OU top crack tip, it is likely that the R6 results would be non-conservative for crack extensions of a few millimetres more than was obtained at that crack tip in the test. 5) Preliminary elastic-plastic finite element analyses carried out for the test plate designs have shown that the effect of the biaxial loading is to reduce the J-Integral values from the uniaxially loaded case of GNSR/1.OU

112

Biaxial Testing of 2195 Aluminum Lithium Alloy Using Cruciform Specimens  

Science.gov (United States)

A cruciform biaxial test specimen was used to test the effect of biaxial load on the yield of aluminum-lithium alloy 2195. Fifteen cruciform specimens were tested from 2 thicknesses of 2195-T8 plate, 0.45 in. and 1.75 in. These results were compared to the results from uniaxial tensile tests of the same alloy, and cruciform biaxial tests of aluminum alloy 2219-T87.

Johnston, W. M.; Pollock, W. D.; Dawicke, D. S.; Wagner, John A. (Technical Monitor)

2002-01-01

113

Time-dependent biaxial mechanical behavior of the aortic heart valve leaflet.  

Science.gov (United States)

Despite continued progress in the treatment of aortic valve (AV) disease, current treatments continue to be challenged to consistently restore AV function for extended durations. Improved approaches for AV repair and replacement rests upon our ability to more fully comprehend and simulate AV function. While the elastic behavior the AV leaflet (AVL) has been previously investigated, time-dependent behaviors under physiological biaxial loading states have yet to be quantified. In the current study, we performed strain rate, creep, and stress-relaxation experiments using porcine AVL under planar biaxial stretch and loaded to physiological levels (60 N/m equi-biaxial tension), with strain rates ranging from quasi-static to physiologic. The resulting stress-strain responses were found to be independent of strain rate, as was the observed low level of hysteresis ( approximately 17%). Stress relaxation and creep results indicated that while the AVL exhibited significant stress relaxation, it exhibited negligible creep over the 3h test duration. These results are all in accordance with our previous findings for the mitral valve anterior leaflet (MVAL) [Grashow, J.S., Sacks, M.S., Liao, J., Yoganathan, A.P., 2006a. Planar biaxial creep and stress relaxatin of the mitral valve anterior leaflet. Annals of Biomedical Engineering 34 (10), 1509-1518; Grashow, J.S., Yoganathan, A.P., Sacks, M.S., 2006b. Biaxial stress-stretch behavior of the mitral valve anterior leaflet at physiologic strain rates. Annals of Biomedical Engineering 34 (2), 315-325], and support our observations that valvular tissues are functionally anisotropic, quasi-elastic biological materials. These results appear to be unique to valvular tissues, and indicate an ability to withstand loading without time-dependent effects under physiologic loading conditions. Based on a recent study that suggested valvular collagen fibrils are not intrinsically viscoelastic [Liao, J., Yang, L., Grashow, J., Sacks, M.S., 2007. The relation between collagen fibril kinematics and mechanical properties in the mitral valve anterior leaflet. Journal of Biomechanical Engineering 129 (1), 78-87], we speculate that the mechanisms underlying this quasi-elastic behavior may be attributed to inter-fibrillar structures unique to valvular tissues. These mechanisms are an important functional aspect of native valvular tissues, and are likely critical to improve our understanding of valvular disease and help guide the development of valvular tissue engineering and surgical repair. PMID:17570376

Stella, John A; Liao, Jun; Sacks, Michael S

2007-01-01

114

Biaxial direct tensile tests in a large range of strain rates. Results on a ferritic nuclear steel  

Energy Technology Data Exchange (ETDEWEB)

Constitutive equations are usually calibrated only trough the experimental results obtained by means of unixial tests because of the lack of adequate biaxial experimental data especially at high strain rate conditions. These data are however important for the validation of analytical models and also for the predictions of mechanical behaviour of real structures subjected to multiaxial loading by numerical simulations. In this paper some developments are shown concerning biaxial cruciform specimens and different experimental machines allowing biaxial tests in a large range of strain rates. This experimental campaign has also allowed study of the influence of changing the strain paths. Diagrams of equivalent stress versus straining direction and also equivalent plastic fracture strain versus straining direction are shown. (orig.)

Albertini, C.; Labibes, K.; Montagnani, M.; Pizzinato, E.V.; Solomos, G.; Viaccoz, B. [Commission of the European Communities, Ispra (Italy). Joint Research Centre

2000-09-01

115

Damage and failure behavior of metal matrix composites under biaxial loads  

Science.gov (United States)

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.

Kirkpatrick, Steven Wayne

116

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

Science.gov (United States)

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.

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

2014-04-01

117

An instrument to obtain the correct biaxial hyperelastic parameters of silicones for accurate DEA modelling  

Science.gov (United States)

The analytical formulas describing the behaviour of dielectric elastomer actuators (DEAs) are based on hyperelastic strain energy density functions. The analytical modelling of a DEA will only lead to meaningful results if the dielectric elastomer can be accurately represented by the chosen hyperelastic model and if its parameters are carefully matched to the elastomer. In the case of silicone elastomers, we show that the strain energy density of a thin elastomeric membrane depends on the maximum deformation the membrane was previously submitted to (Mullins effect). We also show that using model parameters coming from an uniaxial pull-test to predict the behaviour of the elastomer in an equi-biaxial configuration leads to erroneous results. We have therefore built a measurement setup, which allows testing thin elastomeric membranes under equi-biaxial stress by inflating them with a pressure source. When modelling a DEA under equi-biaxial stretch, the measurement data can be used directly, without the need of an hyperelastic model, leading to voltage-stretch prediction closer the the measured stress-stretch behaviour of the dielectric membrane.

Rosset, Samuel; Maffli, Luc; Houis, Simon; Shea, Herbert R.

2014-03-01

118

Effect of biaxial loading on the fracture behavior of a ferritic steel component  

International Nuclear Information System (INIS)

The effect of biaxial loading on the ductile tearing 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 center through-crack specimens (75 mm by 2 m by 2 m) 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 wide plate tests and describes the analysis work being undertaken which is required to interpret the experiments satisfactorily. Preliminary results of this analysis work are presented. 2 refs., 19 figs

119

Experimental studies of yield phenomena in biaxially loaded metals  

International Nuclear Information System (INIS)

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

120

Experimental studies of yield phenomena in biaxially loaded metals. [Review  

Energy Technology Data Exchange (ETDEWEB)

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.

Hecker, S.S.

1976-01-01

 
 
 
 
121

Biaxial mechanical tests in zircaloy-4  

International Nuclear Information System (INIS)

The texture of the zircaloy-4 tubes used as cladding in nuclear fuel elements determines anisotropy of the mechanical properties. As a consequence, the uniaxial tests to determine the mechanical behaviour of the tubes are incomplete. Furthermore, the cladding in use is subject to creep with a state of biaxial tensions. For this reason it is also important to determine the biaxial mechanical properties. The creep tests were performed by internal pressure for a state of axial to circumferential tensions of 0.5. Among the experimental procedures are described: preparation of the test specimens, pressurizing equipment, and the implementation of a device that permits a permanent register of the deformation. For the non-irradiated Atucha type zircaloy-4 sheaths, experimental curves of circumferential deformation versus time were obtained, in tests at constant pressure and for different values of temperature and pressure. An empirical function was determined to adjust the experimental values for the speed of the circumferential deformation in terms of the initial tension applied, temperature and deformation, and the change of the corresponding parameters in accordance to the range of the tensions. Also the activation energy for creep was determined. (M.E.L.)

122

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

International Nuclear Information System (INIS)

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

123

Reflection of electromagnetic waves at a biaxial-isotropic interface  

Science.gov (United States)

The reflection of electromagnetic waves at a plane boundary between isotropic and biaxial media has been investigated using the kDB approach. The general case has been considered in which the principal dielectric axes of the biaxial medium are oriented at an arbitrary angle to the normal of the plane boundary. In general, two characteristic waves propagate in the biaxial medium, leading to coupling of vertical and horizontal polarizations in the reflected waves. Some special cases are illustrated. The results have applications to problems in remote sensing and integrated optics.

Njoku, E. G.

1983-01-01

124

Study of short cracks under biaxial fatigue  

Directory of Open Access Journals (Sweden)

Full Text Available In this paper a methodology for evaluating crack initiation under biaxial conditions is presented. The methodology consists of evaluating the crack length automatically with digital processing of highmagnification images of the crack. The methodology was applied to study five different strain conditions on a low carbon ferritic-pearlitic steel specimen with tubular shape. A hole of 150 ?m diameter was drilled to enforce the crack to initiate at a particular spot. Different combinations of axial and torsional strains were analysed during the initiation stage of the crack. The setup employed allowed detection of the crack to within 6 ?m from the edge of the hole on average and monitoring of the crack during early stages. Fatigue crack propagation curves clearly showed oscillations due to microstructure. It was also observed that these oscillations decreased as the torsional component of the strain was increased.

P. Lopez-Crespo,

2014-11-01

125

Biaxially Oriented CdSe Nanorod  

DEFF Research Database (Denmark)

The shape, structure, and orientation of rubbing-aligned cadmium selenide (CdSe) nanorods on polymer coated glass substrates have been studied using transmission electron microscopy (TEM) and grazing incidence X-ray scattering combined with computer simulations. The nanorods are found to be of wurtzite structure and highly monodisperse, and have an essentially ellipsoidal shape with short axes of 8 nm and long axis of 22 nm. The nanorods exhibit preferred biaxial orientation with the hexagonal a?c-plane parallel to the sample surface and the c-axis oriented along the rubbing direction of the sample. Some tendency of smectic-A ordering is observed. A quantitative model incorporating atomic structure, rod shape, and preferred orientation was developed for numerically simulating the diffraction peak positions, widths, and intensities, giving good correlation with the experimental observations.

Andreasen, Jens Wenzel

2009-01-01

126

Measurement of thermal expansion coefficient and biaxial modulus of DWDM filters using phase-shift Interferometer  

Science.gov (United States)

Dense-wavelength-division-multiplexing (DWDM) filter is a very sensitive component in wavelength shift. The temperature shift of central wavelength (TSCW) of filter is depended on the mechanical properties of the stress. In this paper, a modified Stoney's equation was applied to analyze the thermal stress of DWDM filters for the reason of the thickness ratio (thin film thickness/substrate thickness) larger than 1%. The phase-shift interferometer and TSCW were applied to measure and achieve the coefficient of thermal expansion (CTE), biaxial modulus, temperature optical coefficient, stress optical coefficient, and Poisson ratio of DWDM filter. Based on this method, we can obtain the CTE of DWDM filter 0.87pm/ °C ,the biaxial modulus 41 GPa, Poisson ratio 0.22, temperature optical coefficient 1.4×10-5 / °C, and stress optical coefficients -1.9×10-12 /Pa. To achieve zero TSCW for a DWDM filter, the CTE of the substrate should be 10.36ppm/ °C.

Kuo, Chien-Cheng; Chen, Sheng-Hui; Lee, Cheng-Chung

2008-09-01

127

Magneto-optical technique for detecting biaxial nematic phase  

Science.gov (United States)

There have been numerous attempts to find a thermotropic liquid crystal that exhibits a biaxial phase. There have been findings of biaxial order in bent-core nematic liquid crystals; however, there are recent reports that call this into question. One reason for this discrepancy is the difficulty in unambiguously identifying the biaxiality. Based on a previously described electro-optical technique, we have developed a technique that uses magnetic field, thus widening its application to any bent-core nematic material. The field orients the uniaxial director along the optical path length, and we search for birefringence perpendicular to this direction. We expect one of two situations to occur: if the material is uniaxial, the induced phase difference will decrease asymptotically to zero as the field increases. However, if the material is biaxial, the induced phase will extrapolate to a non-zero value. Results on one calamitic liquid crystal show that this method yields the expected result, namely the lack of biaxial nematic phase. We also tested several bent-core nematic liquid crystals and found that none of these materials exhibits a biaxial nematic phase.

Ostapenko, Tanya; Gleeson, J. T.; Sprunt, S. N.; Jakli, A.

2011-03-01

128

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

Science.gov (United States)

Deformation behavior of cold rolled IF steel sheet (SPCE) under biaxial tension has been investigated for large plastic strain range over 15%. The test material was bent and TIG welded to form a tubular specimen with an outer diameter of 46.2 mm and wall thickness of 0.8 mm. The tubular specimens have been subjected to linear stress paths in the first quadrant of stress space with the use of a servo-controlled tension-internal pressure testing machine developed by one of the authors [T. Kuwabara, K. Yoshida, K. Narihara, S. Takahashi, Anisotropic plastic deformation of extruded aluminum alloy tube under axial forces and internal pressure, Int. J. Plasticity 21, 101-117 (2005)]. Moreover, biaxial tensile tests using a cruciform specimen have also been carried out to more precisely measure the deformation behavior for a small strain range following initial yielding. True stress-true plastic strain curves, contours of plastic work in stress space and the directions of plastic strain rates have been measured and compared with those calculated using selected yield functions: the von Mises, Hill's quadratic and Yld2000-2d [Barlat, F., Brem, J.C., Yoon, J.W., Chung, K., Dick, R.E., Lege, D.J., Pourboghrat, F., Choi, S.H., Chu, E., Plane stress yield function for aluminum alloy sheets—Part 1: Theory. Int. J. Plasticity 19, 1297-1319 (2003)]. The plastic deformation behavior up to a work equivalent plastic strain of ?0p = 0.19 has been successfully measured. It is found that the test material exhibits differential hardening and that the Yld2000-2d yield function with an exponent of six most closely predicts the contours of plastic work and the directions of plastic strain rates.

Enatsu, Ryotaro; Kuwabara, Toshihiko

2011-08-01

129

Magneto-optical technique for detecting the biaxial nematic phase  

Science.gov (United States)

The existence of the elusive biaxial phase has been the subject of much discussion since it was predicted by Freiser in 1970. More recently, there have been numerous attempts to find a thermotropic liquid crystal that exhibits a biaxial phase and with this, conflicting reports about whether such a phase has been positively identified in bent-core liquid crystals. One reason for the discrepancy is that there is currently no way to rule out surface effects or anchoring transitions, both of which may give a false positive identification of a uniaxial-biaxial nematic transition. We have developed a technique that uses a magnetic field to align the uniaxial director, thus widening its application to any bent-core nematic material.

Ostapenko, T.; Zhang, C.; Sprunt, S. N.; Jákli, A.; Gleeson, J. T.

2011-08-01

130

Depletion-induced biaxial nematic states of boardlike particles  

International Nuclear Information System (INIS)

With the aim of investigating the stability conditions of biaxial nematic liquid crystals, we study the effect of adding a non-adsorbing ideal depletant on the phase behavior of colloidal hard boardlike particles. We take into account the presence of the depletant by introducing an effective depletion attraction between a pair of boardlike particles. At fixed depletant fugacity, the stable liquid-crystal phase is determined through a mean-field theory with restricted orientations. Interestingly, we predict that for slightly elongated boardlike particles a critical depletant density exists, where the system undergoes a direct transition from an isotropic liquid to a biaxial nematic phase. As a consequence, by tuning the depletant density, an easy experimental control parameter, one can stabilize states of high biaxial nematic order even when these states are unstable for pure systems of boardlike particles. (paper)

131

Method of depositing buffer layers on biaxially textured metal substrates  

Science.gov (United States)

A laminate article comprises a substrate and a biaxially textured (RE.sup.1.sub.x RE.sup.2.sub.(1-x)).sub.2 O.sub.3 buffer layer over the substrate, wherein 0YSZ between the CeO.sub.2 layer and the (RE.sup.1.sub.x RE.sup.2.sub.(1-x)).sub.2 O.sub.3 buffer layer. The substrate can be a biaxially textured metal, such as nickel. A method of forming the laminate article is also disclosed.

Beach, David B. (Knoxville, TN); Morrell, Jonathan S. (Knoxville, TN); Paranthaman, Mariappan (Knoxville, TN); Chirayil, Thomas (Knoxville, TN); Specht, Eliot D. (Knoxville, TN); Goyal, Amit (Knoxville, TN)

2002-08-27

132

Method for forming biaxially textured articles by powder metallurgy  

Science.gov (United States)

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.

Goyal, Amit (Knoxville, TN); Williams, Robert K. (Knoxville, TN); Kroeger, Donald M. (Knoxville, TN)

2002-01-01

133

Failure locus of polypropylene nonwoven fabrics under in-plane biaxial deformation  

Science.gov (United States)

The failure locus, the characteristics of the stress-strain curve and the damage localization patterns were analyzed in a polypropylene nonwoven fabric under in-plane biaxial deformation. The analysis was carried out by means of a homogenization model developed within the context of the finite element method. It provides the constitutive response for a mesodomain of the fabric corresponding to the area associated to a finite element and takes into account the main deformation and damage mechanisms experimentally observed. It was found that the failure locus in the stress space was accurately predicted by the Von Mises criterion and failure took place by the localization of damage into a crack perpendicular to the main loading axis.

Ridruejo, Alvaro; González, Carlos; Llorca, Javier

134

Damage tolerance of pressurized graphite/epoxy tape cylinders under uniaxial and biaxial loading  

Science.gov (United States)

The damage tolerance behavior of internally pressurized, axially slit, graphite/epoxy tape cylinders was investigated. Specifically, the effects of axial stress, structural anisotropy, and subcritical damage were considered. In addition, the limitations of a methodology which uses coupon fracture data to predict cylinder failure were explored. This predictive methodology was previously shown to be valid for quasi-isotropic fabric and tape cylinders but invalid for structurally anisotropic (+/-45/90)(sub s) and (+/-45/0)(sub s) cylinders. The effects of axial stress and structural anisotropy were assessed by testing tape cylinders with (90/0/+/-45)(sub s), (+/-45/90)(sub s), and (+/-45/0)(sub s) layups in a uniaxial test apparatus, specially designed and built for this work, and comparing the results to previous tests conducted in biaxial loading. Structural anisotropy effects were also investigated by testing cylinders with the quasi-isotropic (0/+/-45/90)(sub s) layup which is a stacking sequence variation of the previously tested (90/0/+/-45)(sub s) layup with higher D(sub 16) and D(sub 26) terms but comparable D(sub 16) and D(sub 26) to D(sub 11) ratios. All cylinders tested and used for comparison are made from AS4/3501-6 graphite/epoxy tape and have a diameter of 305 mm. Cylinder slit lengths range from 12.7 to 50.8 mm. Failure pressures are lower for the uniaxially loaded cylinders in all cases. The smallest percent failure pressure decreases are observed for the (+/-45/90)(sub s) cylinders, while the greatest such decreases are observed for the (+/-45/0)(sub s) cylinders. The relative effects of the axial stress on the cylinder failure pressures do not correlate with the degree of structural coupling. The predictive methodology is not applicable for uniaxially loaded (+/-45/90)(sub s) and (+/-45/0)(sub s) cylinders, may be applicable for uniaxially loaded (90/0/+/-45)(sub s) cylinders, and is applicable for the biaxially loaded (90/0/+/-45)(sub s) and (0/+/-45/90)(sub s) cylinders. This indicates that the ratios of D(sub 16) and D(sub 26) to D(sub 11), as opposed to the absolute magnitudes of D(sub 16) and D(sub 26), may be important in the failure of these cylinders and in the applicability of the methodology. Discontinuities observed in the slit tip hoop strains for all the cylinders tested indicate that subcritical damage can play an important role in the failure of tape cylinders. This role varies with layup and loading condition and is likely coupled to the effects of structural anisotropy. Biaxial failure pressures may exceed the uniaxial values because the axial stress contributes to the formation of 0 deg ply splitting (accompanied by delamination) or similar stress-mitigating subcritical damage. The failure behavior of similar cylinders can also vary as a result of differences in the role of subcritical damage as observed for the case of a biaxially loaded (90/0/+/-45)(sub s) cylinder with a 12.7 mm slit. For this case, the methodology is valid when the initial coupon and cylinder fracture modes agree. stress modify the slit tip stress states in cylinders from those found in flat plates since similarity of these stress states is a fundamental assumption of the current predictive methodology.

Priest, Stacy Marie

1993-12-01

135

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

Science.gov (United States)

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.

Jeon, Eun-Beom; Park, Jae-Dong; Song, Jung Han; Lee, Hye Jin; Kim, Hak-Sung

2012-10-01

136

Measurement and Analysis of Ultra-Thin Austenitic Stainless Steel Sheet under Biaxial Tensile Loading and In-Plane Reverse Loading  

Science.gov (United States)

Biaxial tensile tests of austenitic stainless steel sheet (SUS304) 0.2mm thick have been carried out using cruciform specimens. The specimens are loaded under linear stress paths in a servo-controlled biaxial tensile testing machine. Plastic orthotropy remained coaxial with the principal stresses throughout every experiment. The successive contours of plastic work in biaxial stress space changed their shapes progressively, exemplifying differential work hardening. The geometry of the entire family of the work contours and the directions of plastic strain rates have been precisely measured and compared with those calculated using conventional yield functions. Yld2000-2d [Barlat, F., Brem, J.C., Yoon, J.W., Chung, K., Dick, R.E., Lege, D.J., Pourboghrat, F., Choi, S.H. and Chu, E., International Journal of Plasticity, Vol. 19, (2003), pp. 1297-1319.] with an exponent of 6 was capable of reproducing the general trends of the work contours and the directions of plastic strain rates with good accuracy. Furthermore, in order to quantitatively evaluate the Bauschinger effect of the test material, in-plane tension/compression tests are conducted. It was found that the non-dimensional (? /?u) - ?? /(?u/ E) curves measured during unloading almost fall on a single curve and are not affected by the amount of pre-strain, where ? is the current stress during unloading, ?u is the stress immediately before unloading, ?? (< 0) is the total strain increment during unloading.

Murakoso, Satoko; Kuwabara, Toshihiko

137

Biaxial testing of canine annulus fibrosus tissue under changing salt concentrations  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in portuguese A mecânica in vivo do anel fibroso do disco intervertebral é baseada em carregamento biaxial ao invés de uniaxial. As propriedades materiais do anel estão intimamente ligadas à osmolaridade no tecido. O artigo apresenta experimentos de relaxação biaxiais do anel fibroso de um tecido canino sob mudan [...] ças abruptas na concentração externa de sal. A assinatura da força devido à mudança brusca de salinidade resulta em uma progressiva e monótona mudança na tensão em direção a um novo valor de equilíbrio. Embora o número de amostras não permita nenhuma conclusão quantitativa, as tendências podem abrir uma luz no entendimento das interações complexas na direção das forças, deformações e orientação das fibras por um lado e a osmolaridade do tecido por outro lado. A resposta dual devido à uma mudança na deformação é compreendida como uma resposta imediata antes do fluido escoar para dentro ou para fora do tecido, seguido de uma progressiva readaptação da quantidade de fluido notempo devido ao gradiente do potencial químico entre o tecido e a solução externa. Abstract in english The in vivo mechanics of the annulus fibrosus of the intervertebral disc is one of biaxial rather than uniaxial loading. The material properties of the annulus are intimately linked to the osmolarity in the tissue. This paper presents biaxial relaxation experiments of canine annulus fibrosus tissue [...] under stepwise changes of external salt concentration. The force tracings show that stresses are strongly dependent on time, salt concentration and orientation. The force tracing signature of are sponse to a change instrain, is one of a jumpin stress that relaxes partly as the new strain is maintained. The force tracing signature of a stepwise change in salt concentration is a progressive monotonous change in stress towards a new equilibrium value. Although the number of samples does not allow any definitive quantitative conclusions, the trends may shed light on the complex interaction among the directionality of forces, strains and fiber orientation on one hand, and on the other hand, the osmolarity of the tissue. The dual response to a change in strain is understood as an immediate response before fluid flows in or out of the tissue, followed by a progressive readjustment of the fluid content in time because of the gradient in fluid chemical potential between the tissue and the surrounding solution.

Jacques M., Huyghe.

138

Biaxial testing of canine annulus fibrosus tissue under changing salt concentrations  

Directory of Open Access Journals (Sweden)

Full Text Available The in vivo mechanics of the annulus fibrosus of the intervertebral disc is one of biaxial rather than uniaxial loading. The material properties of the annulus are intimately linked to the osmolarity in the tissue. This paper presents biaxial relaxation experiments of canine annulus fibrosus tissue under stepwise changes of external salt concentration. The force tracings show that stresses are strongly dependent on time, salt concentration and orientation. The force tracing signature of are sponse to a change instrain, is one of a jumpin stress that relaxes partly as the new strain is maintained. The force tracing signature of a stepwise change in salt concentration is a progressive monotonous change in stress towards a new equilibrium value. Although the number of samples does not allow any definitive quantitative conclusions, the trends may shed light on the complex interaction among the directionality of forces, strains and fiber orientation on one hand, and on the other hand, the osmolarity of the tissue. The dual response to a change in strain is understood as an immediate response before fluid flows in or out of the tissue, followed by a progressive readjustment of the fluid content in time because of the gradient in fluid chemical potential between the tissue and the surrounding solution.A mecânica in vivo do anel fibroso do disco intervertebral é baseada em carregamento biaxial ao invés de uniaxial. As propriedades materiais do anel estão intimamente ligadas à osmolaridade no tecido. O artigo apresenta experimentos de relaxação biaxiais do anel fibroso de um tecido canino sob mudanças abruptas na concentração externa de sal. A assinatura da força devido à mudança brusca de salinidade resulta em uma progressiva e monótona mudança na tensão em direção a um novo valor de equilíbrio. Embora o número de amostras não permita nenhuma conclusão quantitativa, as tendências podem abrir uma luz no entendimento das interações complexas na direção das forças, deformações e orientação das fibras por um lado e a osmolaridade do tecido por outro lado. A resposta dual devido à uma mudança na deformação é compreendida como uma resposta imediata antes do fluido escoar para dentro ou para fora do tecido, seguido de uma progressiva readaptação da quantidade de fluido notempo devido ao gradiente do potencial químico entre o tecido e a solução externa.

Jacques M. Huyghe

2010-03-01

139

Critical role of the sample preparation in experiments using piezoelectric actuators inducing uniaxial or biaxial strains.  

Science.gov (United States)

We report on a systematic study of the stress transferred from an electromechanical piezo-stack into GaAs wafers under a wide variety of experimental conditions. We show that the strains in the semiconductor lattice, which were monitored in situ by means of X-ray diffraction, are strongly dependent on both the wafer thickness and on the selection of the glue which is used to bond the wafer to the piezoelectric actuator. We have identified an optimal set of parameters that reproducibly transfers the largest distortions at room temperature. We have studied strains produced not only by the frequently used uniaxial piezostressors but also by the biaxial ones which replicate the routinely performed experiments using substrate-induced strains but with the advantage of a continuously tunable lattice distortion. The time evolution of the strain response and the sample tilting and/or bending are also analyzed and discussed. PMID:24182124

Butkovi?ová, D; Marti, X; Saidl, V; Schmoranzerová-Rozkotová, E; Wadley, P; Holý, V; N?mec, P

2013-10-01

140

Biaxial fatigue loading of notched composites  

Science.gov (United States)

Thin-walled, 2.54-cm diameter tubular specimens of graphite/epoxy were fatigue cycled in combinations of axial, torsional, and internal pressure loading. Two different four-ply layup configurations were tested: (0-90)s and (+ or- 45)s; each tube contained a 0.48-cm diameter circular hole penetrating one wall midway along the tube length. S-N curves were developed to characterize fatigue behavior under pure axial, torsional, or internal pressure loading, as well as combined loading fatigue. A theory was developed based on a plane stress model which enabled the S-N curve for combined stress states to be predicted from the S-N data for the uniaxial loading modes. Correlation of the theory with the experimental data proved to be remarkably good.

Francis, P. H.; Walrath, D. E.; Sims, D. F.; Weed, D. N.

1977-01-01

 
 
 
 
141

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

CERN Document Server

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...

Fadeyeva, Tatyana; Anischenko, Pavel; Volyar, Alexander

2011-01-01

142

Biaxial casting method and apparatus for isolating radioactive waste  

International Nuclear Information System (INIS)

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

143

Mesogen polarity effects on biaxial nematics. Centrally located dipoles.  

Science.gov (United States)

We investigate the phase organisation of thermotropic biaxial Gay-Berne (GB) mesogens yielding a biaxial nematic (Nb) phase upon endowing them with a central point dipole. We study the effects of changing the strength and orientation of the dipole on the phase behaviour, and in particular we examine, using molecular dynamics (MD) simulations, the possibility of improving the stability of the Nb phase. After mapping the boundaries of the Nb phase, we find that the strength of the embedded dipole is the parameter with the strongest influence on the mesogenic properties, while its orientation plays a minor role. For these central dipole systems, we find that the Nb phase organisation is stable only for mesogens with relatively weak dipole moments, while it disappears if electrostatic interactions become comparable in magnitude with dispersion interactions. PMID:24100468

Querciagrossa, Lara; Ricci, Matteo; Berardi, Roberto; Zannoni, Claudio

2013-11-21

144

Strain Measurement System Developed for Biaxially Loaded Cruciform Specimens  

Science.gov (United States)

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.

Krause, David L.

2000-01-01

145

Identification of material parameters using bi-axial machine  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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...

Flores, Paulo; Montleau, P.; Mathonet, V.; Moureaux, P.; Habraken, Anne

2004-01-01

146

Design of a biaxial mechanical loading bioreactor for tissue engineering.  

Science.gov (United States)

We designed a loading device that is capable of applying uniaxial or biaxial mechanical strain to a tissue engineered biocomposites fabricated for transplantation. While the device primarily functions as a bioreactor that mimics the native mechanical strains, it is also outfitted with a load cell for providing force feedback or mechanical testing of the constructs. The device subjects engineered cartilage constructs to biaxial mechanical loading with great precision of loading dose (amplitude and frequency) and is compact enough to fit inside a standard tissue culture incubator. It loads samples directly in a tissue culture plate, and multiple plate sizes are compatible with the system. The device has been designed using components manufactured for precision-guided laser applications. Bi-axial loading is accomplished by two orthogonal stages. The stages have a 50 mm travel range and are driven independently by stepper motor actuators, controlled by a closed-loop stepper motor driver that features micro-stepping capabilities, enabling step sizes of less than 50 nm. A polysulfone loading platen is coupled to the bi-axial moving platform. Movements of the stages are controlled by Thor-labs Advanced Positioning Technology (APT) software. The stepper motor driver is used with the software to adjust load parameters of frequency and amplitude of both shear and compression independently and simultaneously. Positional feedback is provided by linear optical encoders that have a bidirectional repeatability of 0.1 ?m and a resolution of 20 nm, translating to a positional accuracy of less than 3 ?m over the full 50 mm of travel. These encoders provide the necessary position feedback to the drive electronics to ensure true nanopositioning capabilities. In order to provide the force feedback to detect contact and evaluate loading responses, a precision miniature load cell is positioned between the loading platen and the moving platform. The load cell has high accuracies of 0.15% to 0.25% full scale. PMID:23644779

Bilgen, Bahar; Chu, Danielle; Stefani, Robert; Aaron, Roy K

2013-01-01

147

Modelization of ratcheting in biaxial experiments  

International Nuclear Information System (INIS)

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

148

Xenon NMR of phase biaxiality in liquid crystals.  

Science.gov (United States)

Biaxial thermotropic nematic liquid crystals would be of great importance in liquid crystal display technology. Less than a decade ago, such liquid crystals were suggested. The biaxiality of the phases was confirmed using (2)H NMR spectroscopy of deuterated probe molecules. The spectra were collected from a sample rotating around an axis perpendicular to the external magnetic field, resulting in a two-dimensional powder pattern. We have proposed an alternate technique that is based on the second order quadrupole shift detectable in (131)Xe NMR spectra of dissolved xenon. The method has many advantages, such as the NMR spectra are taken from a static sample and the (131)Xe quadrupole coupling tensor is extremely sensitive to the symmetry of the phase. In the present study, we report results obtained on a 600-MHz NMR spectrometer. Together with the data of our earlier study, they confirm that the asymmetry parameter of the (131)Xe quadrupole coupling tensor in the nematic phase of a ferroelectric liquid crystal is 0.85 and in the smectic A phase ca 0.62, indicating significant phase biaxiality. PMID:24771455

Jokisaari, Jukka; Zhu, Jianfeng

2014-10-01

149

Biaxial response of ovine spinal cord dura mater.  

Science.gov (United States)

The dura mater performs a major functional role in the stability and mechanical response of the spinal cord complex. Computational techniques investigating the etiology of spinal cord injury require an accurate mechanical description of the dura mater. Previous studies investigating the mechanical response of the dura mater have reported conflicting results regarding the anisotropic stiffness of the dura in the longitudinal and circumferential direction. The aim of this study was to investigate the biaxial response of the dura mater in order to establish the tissue level mechanical behavior under physiological loading scenarios. To this end, square sections of the dura were tested in a custom biaxial setup under a comprehensive uniaxial and biaxial loading protocol. The resultant data were fit via a transversely isotropic continuum model and an anisotropic continuum constitutive model. The transversely isotropic formulation failed to accurately predict the dura mater?s uniaxial behavior. The anisotropic formulation accurately predicted the uniaxial response in both longitudinal and circumferential directions. Significantly higher stiffness (pmechanical response in the longitudinal and circumferential directions and future studies should utilize an anisotropic two fiber family continuum model to accurately describe dura mater mechanics. PMID:24583806

Shetye, Snehal S; Deault, Matthew M; Puttlitz, Christian M

2014-06-01

150

The circumferential mechanical properties of bamboo with uniaxial and biaxial compression tests  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The objective of this study was to investigate the effect of uniaxial and biaxial compression loadings on the circumferential-radial mechanical properties of bamboo. A novel biaxial testing device, called the 3D composite material analysis system, was developed to conduct biaxial compression tests. Strain field analysis was characterized with the help of the digital speckle correlation method (DSCM). The effects of four different environmental treatments (I. air-drying, II. constant temperatu...

Zehui Jiang,; Fuming Chen; Ge Wang; Xing’e Liu; Shi, Sheldon Q.; Hai-tao Cheng

2012-01-01

151

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

Science.gov (United States)

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 for either placement method.

D'Alessandro, Kacie Caple

152

STRESS  

Science.gov (United States)

During this activity, students will use the available resources to learn more about stress, the effects of stress and how to handle stress. This activity focuses on the Utah fifth grade health core Standard 1: The students will learn ways to improve mental health and manage stress. During this project, students are given two different scenarios and ...

Hancey, Ms.

2010-04-27

153

Fracture capacity of girth welded pipelines with 3D surface cracks subjected to biaxial loading conditions  

Energy Technology Data Exchange (ETDEWEB)

Offshore pipelines installed by reeling method are subjected to large plastic strains. When the steel pipes are joined by girth welding, both surface and embedded cracks are inevitably initiated in welding zone. The pipe lines should have adequate resistance against both crack extension by tearing and unstable fracture during installation as well as during operation. However, common flaw assessment procedures, e.g. BS 7910:2005 , are not explicitly developed for such situations with large plastic strains. The main objective of the current paper is to find a way to assess fracture capability of a practical pipeline subject to large plastic deformation. In our study, the evolution of crack tip opening displacement (CTOD) of the pipeline with semi-eliptical surface crack in weld girth is investigated under biaxial loading conditions (uniaxial tensile and internal pressure) using three dimensional elastic-plastic finite element analysis. The effects of crack depth, ratio of semi-major axis to semi-minor axis and internal pressure are examined. The results show that at moderate levels of global strain, the variation of CTOD with global strain can be well approximated by a simple linear relationship under tensile loading as well as biaxial loading conditions. Comparing the fracture assessment for the welded pipe made by BS 7910:2005 with that made by our current study, it is found that the assessment from BS7910:2005 is over conservative. A CTOD-estimation method for strain -based fracture is suggested for the pipelines when the global strain is 3%. - Highlights: Black-Right-Pointing-Pointer 3D FE stress analysis of girth welded pipelines with surface cracks is conducted. Black-Right-Pointing-Pointer Both material and geometrical non-linearities are considering in estimating CTOD. Black-Right-Pointing-Pointer Existing conservative models result in high rejection rate of welded pipes.

Dake, Yi [School of Mechanical and Aerospace Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798 (Singapore); Sridhar, Idapalapati, E-mail: msridhar@ntu.edu.sg [School of Mechanical and Aerospace Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798 (Singapore); Xiao Zhongmin [School of Mechanical and Aerospace Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798 (Singapore); Kumar, Shashi Bhushan [Det Norske Veritas Pte Ltd, 10 Science Park Drive, Singapore 118224 (Singapore)

2012-04-15

154

An engineering method for determining nonproportionality parameter under biaxial fatigue loading  

International Nuclear Information System (INIS)

Increased requirements to reliability and cost-effectiveness imposed on structural elements of modern machinery, oil, gas, and nuclear industry give rise to the necessity of the modelling of mechanical behavior of vital parts under loading regimes close to operating conditions. The loads occurring in service are in most cases cyclic, multiaxial and nonproportional. Under such conditions, in zones of increased stress concentrations cyclically unstable materials can deform beyond the elastic limit and undergo considerable cyclic hardening. In the region of low-cycle fatigue these factors influence appreciably the lifetime of the material. Thus from fatigue experiments it is known that a 5--10% change in the thin-wall tubular specimen stress state may lead to a change in its lifetime of an order of magnitude and higher. A new engineering method for defining a nonproportionality parameter is proposed for a wide class of cyclic strain paths with a prescribed maximum range of plastic or total strains. This parameter makes it possible to establish an unambiguous linear dependence between the strain path shape and the stress level in a stabilized state under biaxial cyclic loading. Its efficiency was analyzed for predicting the maximum level of hardening for different cycle paths in the space of total and plastic strains

155

Comparisons of planar and tubular biaxial tensile testing protocols of the same porcine coronary arteries.  

Science.gov (United States)

To identify the orthotropic biomechanical behavior of arteries, researchers typically perform stretch-pressure-inflation tests on tube-form arteries or planar biaxial testing of splayed sections. We examined variations in finite element simulations (FESs) driven from planar or tubular testing of the same coronary arteries to determine what differences exist when picking one testing technique vs. another. Arteries were tested in tube-form first, then tested in planar-form, and fit to a Fung-type strain energy density function. Afterwards, arteries were modeled via finite element analysis looking at stress and displacement behavior in different scenarios (e.g., tube FESs with tube- or planar-driven constitutive models). When performing FESs of tube inflation from a planar-driven constitutive model, pressure-diameter results had an error of 12.3% compared to pressure-inflation data. Circumferential stresses were different between tube- and planar-driven pressure-inflation models by 50.4% with the planar-driven model having higher stresses. This reduced to 3.9% when rolling the sample to a tube first with planar-driven properties, then inflating with tubular-driven properties. Microstructure showed primarily axial orientation in the tubular and opening-angle configurations. There was a shift towards the circumferential direction upon flattening of 8.0°. There was also noticeable collagen uncrimping in the flattened tissue. PMID:23132151

Keyes, Joseph T; Lockwood, Danielle R; Utzinger, Urs; Montilla, Leonardo G; Witte, Russell S; Vande Geest, Jonathan P

2013-07-01

156

Biaxially stretchable, integrated array of high performance microsupercapacitors.  

Science.gov (United States)

We report on the fabrication of a biaxially stretchable array of high performance microsupercapacitors (MSCs) on a deformable substrate. The deformable substrate is designed to suppress local strain applied to active devices by locally implanting pieces of stiff polyethylene terephthalate (PET) films within the soft elastomer of Ecoflex. A strain suppressed region is formed on the top surface of the deformable substrate, below which PET films are implanted. Active devices placed within this region can be isolated from the strain. Analysis of strain distribution by finite element method confirms that the maximum strain applied to MSC in the strain suppressed region is smaller than 0.02%, while that on the Ecoflex film is larger than 250% under both uniaxial strain of 70% and biaxial strain of 50%. The all-solid-state planar MSCs, fabricated with layer-by-layer deposited multiwalled carbon nanotube electrodes and patterned ionogel electrolyte of poly(ethylene glycol) diacrylate and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide having high-potential windows, are dry-transferred onto the deformable substrate and electrically connected in series and parallel via embedded liquid metal interconnection and Ag nanowire contacts. Liquid metal interconnection, formed by injecting liquid metal into the microchannel embedded within the substrate, can endure severe strains and requires no additional encapsulation process. This formed MSC array exhibits high energy and power density of 25 mWh/cm(3) and 32 W/cm(3), and stable electrochemical performance up to 100% uniaxial and 50% biaxial stretching. The high output voltage of the MSC array is used to light micro-light-emitting diode (?-LED) arrays, even under strain conditions. This work demonstrates the potential application of our stretchable MSC arrays to wearable and bioimplantable electronics with a self-powered system. PMID:25347595

Lim, By Yein; Yoon, Jangyeol; Yun, Junyeong; Kim, Daeil; Hong, Soo Yeong; Lee, Seung-Jung; Zi, Goangseup; Ha, Jeong Sook

2014-11-25

157

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 different physical mechanisms are identi...

Fukuda, Atsuo; Vij, Jagdish Kumar

2007-01-01

158

Thermotropic biaxial nematics: [1] highly desirable materials, still elusive?  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in english On the basis and with the inclusion of results described in a previous paper [2], submitted for publication almost two years ago, we add some comments on very recent developments regarding both the design and synthesis of thermotropic nematogens of low-molecular weight, supposed biaxial in character [...] , as well as puzzles, still unsolved, with methods of their unambiguous identification. In general, this update may demonstrate the complexity and problematic nature inherent in this topical subject of research indicated by a struggle over a very relevant, but very difficult matter.

Klaus, Praefcke.

159

Vavilov-Cherenkov radiation in the biaxial triglycine sulphate crystal  

International Nuclear Information System (INIS)

Some properties of the Cherenkov radiation in the biaxial triglycine sulphate crystal were analysed. The radiation properties were studied for cases of protons moving in the direction of the main three dielectric axes. The measurements were performed with a 660 MeV proton beam. A quantitative agreement of experiment with Muzikarms theoretical calculations on the directional properties was observed. In all the cases qualitative agreement was obtained concerning the azimuthal distribution of the radiation intensity of the extraordinary waves of both polarities as well as concerning the polarization properties predicted by Obdrzalek's formulae. (author)

160

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

Energy Technology Data Exchange (ETDEWEB)

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.

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

2014-09-01

 
 
 
 
161

The influence of uniaxial prestrain on biaxial r-values in 7075-O aluminium alloy  

International Nuclear Information System (INIS)

Biaxial test methods have been used to determine, not only yield behaviour under biaxial conditions, but also the strain response. This paper examines the influence of uniaxial prestrain upon the biaxial r-value by extending the disc compression test procedure proposed by Barlat et al. The extension involved the use of digital image measurements of in-plane strains. The material examined was a 7075-O condition aluminium alloy. The results of the experimental programme indicated that the biaxial r-value is unaffected by uniaxial prestrain. When using the disc compression test, the mode of deformation and therefore the biaxial r-value were found to be very sensitive to the prevailing friction conditions.

162

Stress  

Scientific Electronic Library Online (English)

Full Text Available SciELO Portugal | Language: Portuguese Abstract in portuguese O presente artigo faz uma revisão histórica do Stress e define-o. Apresenta o Síndroma de Adaptação Geral (SAG), abordando os diversos aspectos biológicos, psicológicos e sociais, bem como os sintomas e sinais do Stress. Refere os aspectos psicossociais do Stress, as causas deste na pessoa, família [...] e sociedade. Descrevem-se as formas de medida e avaliação do Stress, a importância do Stress como agente não patológico e as suas consequências na saúde, focando os mecanismos de adaptação ao Stress. Abstract in english This article presents a historical view of Stress and its definition. The General Adaptation Syndrome (GAS) is described, focusing on the biological, psychological and social aspects of Stress, with their signs and symptoms. The psychosocial aspects of Stress are described, presenting the causes at [...] the personal, family and society. The ways of assessing Stress are presented, and its importance as a non pathological factor and its consequences in health, and discussing the ways of coping with Stress.

Abel Matos, Santos; João Jácome De, Castro.

163

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

International Nuclear Information System (INIS)

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 m

164

An Experimental and Analytical Evaluation of a Biaxial Test for Determining Shear Properties of Composite Materials  

Science.gov (United States)

The results of an experimental and analytical investigation of a biaxial tension/compression test for determining shear properties of composite materials are reported. Using finite element models of isotropic and orthotropic laminates, a specimen geometry was optimized. A kinematic fixture was designed to introduce an equal and opposite pair of forces into a specimen with a one inch square test section. Aluminum and several composite laminates with the optimized geometry and a configuration with large stress gradients were tested in the fixture. The specimens were instrumented with strain gages in the center of the test section for shear stiffness measurements. Pure shear strain was measured. The results from the experiments correlated well with finite element results. Failure of the specimens occurred through the center of the test section and appeared to have initiated at the high stress points. The results lead to the conclusion that the optimized specimen is suitable for determining shear modulus for composite materials. Further revisions to the specimen geometry are necessary if the method is to give shear strength data.

Kennedy, John M.; Barnett, Terry R.

1988-01-01

165

Biaxial creep strains at notch roots -- Measurement and modeling  

International Nuclear Information System (INIS)

Creep and creep-fatigue interaction effects have become increasingly important at higher operating temperatures of power generating systems. The cooling tubes in pressurized heavy water nuclear reactors are examples of components where these effects may be critical. Here, biaxial strains were measured at the roots of single notches in zirconium alloy specimens under loading and creep conditions (up to 1200 hours) at 250 C. A laser-based interferometric technique was used; details of the measurement procedures are given in another paper. Here, the Bodner model is incorporated into the ABAQUS finite element code and used to predict the biaxial strains at the notch root during loading and for a creep duration of 100 hours. The strains during loading agree quite well with the measured ones while the predicted creep strains are smaller. This discrepancy is attributed to the lack of precision in determining the constants for the Bodner model from smooth-specimen tests. Both the measurement technique and the Bodner model are well-suited for studies of notch response

166

PLASTIC DEFORMATION AND FRACTURE OF STEELS UNDER DYNAMIC BIAXIAL LOADING  

Energy Technology Data Exchange (ETDEWEB)

Dynamic equi-biaxial bulging of thin AerMet 100 alloy plates was studied. The plates were deformed using a gas-gun driven flyer plate test set-up at impact velocities between 1.0 and 2.0 km/sec. The results indicate that in addition to biaxial stretching (and thinning) of the plate, internal cavitation (spallation fracture) results from the complex wave interactions within the plate. No outward evidence of damage was observed at the lower velocities, in the range of 1.0-1.2 km/sec. Fine scale cracking of the plates was observed at impact velocity above approximately 1.4 km/sec. Complete specimen fracture, in the form of multiple petals and pie-shaped fragments, was observed at impact velocity above 1.6 km/sec. Hydrodynamic computer code simulations were performed, prior to and in conjunction with the experiments, to aid in experiment design and interpretation of the experimental data.

Syn, C; Moreno, J; Goto, D M; Belak, J; Grady, D

2004-07-08

167

Biaxial optical anisotropy of self aligned silver nanoparticles and nanowires  

International Nuclear Information System (INIS)

In the present study ion beam sputtering has been used for pre-structuring of a silicon substrate followed deposition of metal by e-beam evaporation. First a low energy ion beam (Ar+, 500 eV) is incident on the substrate surface at an angle of 67 to the surface normal to produce well ordered (20-50 nm) ripple patterns. Then physically vaporized Ag atoms are deposited at grazing angle of 70 to the surface normal and normal to the ripples direction. Varying deposition parameters, i.e. ripple periodicity, substrate temperature and atomic flux, we were able to produce well ordered nanoparticles and nanowires. Self-aligned Ag nanoparticles and nanowires deposited on pre-patterned ripple surfaces exhibit strong optical anisotropy. Generalised ellipsometry measurements show that off diagonal Jones matrix elements (?ps, ?ps, ?sp, ?sp) are non zero and vary with Eulers angle ?. This indicates that such a medium is biaxial in nature. A biaxial layer model approach is used to calculate dielectric functions for such a system. Tauc-Lorentz oscillators are used along x and y direction independently and Drude model along z-direction for nanoparticles. This approach provides a very good fitting with the measured Jones matrix element ?pp, ?pp, ?ps, ?ps, ?sp, ?sp. Different cases for ordered nanoparticles and wires are presented.ted.

168

Energy Storage and Dissipation in Random Copolymers during Biaxial Loading  

Science.gov (United States)

Random copolymers composed of hard and soft segments in a glassy and rubbery state at the ambient conditions exhibit phase-separated morphologies which can be tailored to provide hybrid mechanical behaviors of the constituents. Here, phase-separated copolymers with hard and soft contents which form co-continuous structures are explored through experiments and modeling. The mechanics of the highly dissipative yet resilient behavior of an exemplar polyurea are studied under biaxial loading. The hard phase governs the initially stiff response followed by a highly dissipative viscoplasticity where dissipation arises from viscous relaxation as well as structural breakdown in the network structure that still provides energy storage resulting in the shape recovery. The soft phase provides additional energy storage that drives the resilience in high strain rate events. Biaxial experiments reveal the anisotropy and loading history dependence of energy storage and dissipation, validating the three-dimensional predictive capabilities of the microstructurally-based constitutive model. The combination of a highly dissipative and resilient behavior provides a versatile material for a myriad of applications ranging from self-healing microcapsules to ballistic protective coatings.

Cho, Hansohl; Boyce, Mary

2012-02-01

169

Stress  

Science.gov (United States)

This project collects resources for studying mental health and stress issues with middle schoolers. Teens and stress Science NetLinks: The Laughing Brain 2: A Good Laugh Dealing with anger Stress-o-meter Look at each of the above sites. Choose one and read the content. Write a one-paragraph summary. Play interactive games and take quizzes. Keep a log of what you do. Tell which site you liked best and why. Watch the following video for positive things teens do to reduce the stress ...

Deaton, Mrs.

2011-06-10

170

Biaxial strength of cross-ply carbon fiber-reinforced composite laminates fabricated by lapped molding technique  

Energy Technology Data Exchange (ETDEWEB)

A failure criterion must be considered for each failure mode and parameters of the model determined in each case. In this study, a failure criterion was developed by introducing the notion of equivalent biaxial strength under biaxial loading of tension and torsion. The experimental results showed that the equivalent biaxial strength has a power-type relation to a parameter, cos {psi}. The failure strength under biaxial loading can be predicted as a function of tensile strength, torsional strength and biaxial ratio. Scattering of the experimental data can be predicted using a Weibull distribution function and the concept of equivalent biaxial strength. The model should accurately predict the biaxial strength of general laminated composite materials. (orig.)

Lee, C.S.; Hwang, W. [Pohang Univ. of Sci. and Technol. (Korea). Dept. of Mech. Eng.

1999-11-01

171

Thermotropic Uniaxial and Biaxial Nematic and Smectic Phases in Bent-Core Mesogens  

International Nuclear Information System (INIS)

Two azo substituted achiral bent-core mesogens have been synthesized. Optical polarizing microscopy and synchrotron X-ray scattering studies of both compounds reveal the existence of the thermotropic uniaxial and biaxial nematic and three smectic phases at different temperatures in these single component small molecule systems. The transition from the uniaxial to biaxial nematic phase is confirmed to be second order. The transitions from the biaxial nematic to the underlying smectic phase and between the smectic phases have barely discernible heat capacity signatures and thus are also second order.

172

Thermotropic Uniaxial and Biaxial Nematic and Smectic Phases in Bent-Core Mesogens  

Energy Technology Data Exchange (ETDEWEB)

Two azo substituted achiral bent-core mesogens have been synthesized. Optical polarizing microscopy and synchrotron X-ray scattering studies of both compounds reveal the existence of the thermotropic uniaxial and biaxial nematic and three smectic phases at different temperatures in these single component small molecule systems. The transition from the uniaxial to biaxial nematic phase is confirmed to be second order. The transitions from the biaxial nematic to the underlying smectic phase and between the smectic phases have barely discernible heat capacity signatures and thus are also second order.

Prasad, Venna; Kang, Shin-Woong; Suresh, K.A.; Joshi, Leela; Wang, Qingbing; Kumar, Satyendra (Raman); (Kent); (CLCR)

2010-07-20

173

Conductive layer for biaxially oriented semiconductor film growth  

Science.gov (United States)

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.

Findikoglu, Alp T. (Los Alamos, NM); Matias, Vladimir (Santa Fe, NM)

2007-10-30

174

Magnetic properties of biaxially oriented Ni-V substrates  

Energy Technology Data Exchange (ETDEWEB)

The paper presents the structural and magnetic properties of a new non-magnetic biaxially textured substrate based on Ni{sub 100{minus}x}V{sub x} solid-solution for YBa{sub 2}Cu{sub 3}O{sub 7{minus}y} tape fabrication. The effective atomic magnetic moment monotonously decreases with the vanadium concentration, causing a corresponding decrease of Curie temperature. The Curie temperature reaches the zero value at about 11.5% of vanadium. The texturing studies revealed that (100)[-001] cube texture can be easily developed up to x = 11 at.%, by a cold rolling process followed by a recrystallization thermal treatment. The X-ray {omega} and {phi} scans have demonstrated that the samples have a good out-of-plane and in-plane texture for the whole solubility range, with FWHM of 7{degree} and 11{degree}, respectively. The correlation between the magnetic and structural anisotropy was also studied.

Bettinelli, D.; Petrisor, T.; Gambardella, U.; Boffa, V. [ENEA Centro Ricerche Frascati, Rome (Italy); Ceresara, S. [Centro Innovazione Lecco (Italy); Nistor, L. [Technical Univ. of Cluj-Napoca (Romania); Pop, V. [Babes-Bolyai Univ., Cluj-Napoca (Romania); Scardi, P. [Univ. di Trento (Italy). Dipt. di Ingegneria dei Materiali

1999-04-20

175

Characteristics of Plane Wave Propagation in Biaxially Anisotropic Gyrotropic Media  

International Nuclear Information System (INIS)

Propagation characteristics of electromagnetic waves at the interface between an isotropic regular medium and a biaxially anisotropic gyrotropic medium are investigated. The results indicate that the reflection and refraction properties of electromagnetic waves are closely dependent on the dispersion relation of the gyrotropic media, and that anomalous total reflection and negative refraction may occur. The existence conditions of total transmission are also considered. It is found that total transmission arises when the TE-polarized incident waves are normal to the interface and the physical parameters of the two media are chosen properly, which are quite different from the existence conditions of total transmission at the anisotropic left-handed material interface. Numerical results are given to validate our theoretical analysis

176

A biaxial test for rheological and formability identification  

Directory of Open Access Journals (Sweden)

Full Text Available Accurate constitutive laws and formability limits of materials are essential for a numerical optimization of sheet forming processes. The main objective of this work is to develop a new experimental device able to give for a unique specimen a good prediction of rheological parameters and formability under conditions (low and intermediate strain rates close to the ones met in processes. The proposed device is a servo-hydraulic testing machine provided with four independent dynamic actuators allowing biaxial tensile tests on a dedicated specimen. By localizing necking in the central zone of the specimen, the strain path in this zone is controlled by the speed ratio between the two axes and the whole forming limit curve can be covered. Such a specimen is proposed throngh a numerical and experimental validation procedure. Finally, an experimental forming limit curve for the aluminium alloy AA5086 is determined thanks to a rigorous procedure for detecting the onset of necking in the specimen.

Ragneau E.

2010-06-01

177

Multiscale strain analysis of tissue equivalents using a custom-designed biaxial testing device.  

Science.gov (United States)

Mechanical signals transferred between a cell and its extracellular matrix play an important role in regulating fundamental cell behavior. To further define the complex mechanical interactions between cells and matrix from a multiscale perspective, a biaxial testing device was designed and built. Finite element analysis was used to optimize the cruciform specimen geometry so that stresses within the central region were concentrated and homogenous while minimizing shear and grip effects. This system was used to apply an equibiaxial loading and unloading regimen to fibroblast-seeded tissue equivalents. Digital image correlation and spot tracking were used to calculate three-dimensional strains and associated strain transfer ratios at macro (construct), meso, matrix (collagen fibril), cell (mitochondria), and nuclear levels. At meso and matrix levels, strains in the 1- and 2-direction were statistically similar throughout the loading-unloading cycle. Interestingly, a significant amplification of cellular and nuclear strains was observed in the direction perpendicular to the cell axis. Findings indicate that strain transfer is dependent upon local anisotropies generated by the cell-matrix force balance. Such multiscale approaches to tissue mechanics will assist in advancement of modern biomechanical theories as well as development and optimization of preconditioning regimens for functional engineered tissue constructs. PMID:22455913

Bell, B J; Nauman, E; Voytik-Harbin, S L

2012-03-21

178

Applicability of a particularly simple model to nonlinear elasticity of slide-ring gels with movable cross-links as revealed by unequal biaxial deformation.  

Science.gov (United States)

The strain energy density function (F) of the polyrotaxane-based slide-ring (SR) gels with movable cross-links along the network strands is characterized by unequal biaxial stretching which can achieve various types of deformation. The SR gels as prepared without any post-preparation complication exhibit considerably smaller values of the ratio of the stresses (?y/?x) in the stretched (x) and constrained (y) directions in planar extension than classical chemical gels with heterogeneous and nearly homogeneous network structures do. This feature of the SR gels leads to the peculiar characteristic that the strain energy density function (F) has no explicit cross term of strains in different directions, which is in contrast to F with explicit strain cross terms for most chemical gels and elastomers. The biaxial stress-strain data of the SR gels are successfully described by F of the Gent model with only two parameters (small-strain shear modulus and a parameter representing ultimate elongation), which introduces the finite extensibility effect into the neo-Hookean model with no explicit cross term of strain. The biaxial data of the deswollen SR gels examined in previous study, which underwent a considerable reduction in volume from the preparation state, are also well described by the Gent model, which is in contrast to the case of the classical chemical gels that the stress-strain relations before and after large deswelling are not described by a common type of F due to a significant degree of collapse of the network strands in the deswollen state. These intriguing features of nonlinear elasticity of the SR gels originate from a novel function of the slidable cross-links that can maximize the arrangement entropy of cross-linked and non-cross-linked cyclic molecules in the deformed networks. PMID:25296836

Kondo, Yuuki; Urayama, Kenji; Kidowaki, Masatoshi; Mayumi, Koichi; Takigawa, Toshikazu; Ito, Kohzo

2014-10-01

179

Applicability of a particularly simple model to nonlinear elasticity of slide-ring gels with movable cross-links as revealed by unequal biaxial deformation  

Science.gov (United States)

The strain energy density function (F) of the polyrotaxane-based slide-ring (SR) gels with movable cross-links along the network strands is characterized by unequal biaxial stretching which can achieve various types of deformation. The SR gels as prepared without any post-preparation complication exhibit considerably smaller values of the ratio of the stresses (?y/?x) in the stretched (x) and constrained (y) directions in planar extension than classical chemical gels with heterogeneous and nearly homogeneous network structures do. This feature of the SR gels leads to the peculiar characteristic that the strain energy density function (F) has no explicit cross term of strains in different directions, which is in contrast to F with explicit strain cross terms for most chemical gels and elastomers. The biaxial stress-strain data of the SR gels are successfully described by F of the Gent model with only two parameters (small-strain shear modulus and a parameter representing ultimate elongation), which introduces the finite extensibility effect into the neo-Hookean model with no explicit cross term of strain. The biaxial data of the deswollen SR gels examined in previous study, which underwent a considerable reduction in volume from the preparation state, are also well described by the Gent model, which is in contrast to the case of the classical chemical gels that the stress-strain relations before and after large deswelling are not described by a common type of F due to a significant degree of collapse of the network strands in the deswollen state. These intriguing features of nonlinear elasticity of the SR gels originate from a novel function of the slidable cross-links that can maximize the arrangement entropy of cross-linked and non-cross-linked cyclic molecules in the deformed networks.

Kondo, Yuuki; Urayama, Kenji; Kidowaki, Masatoshi; Mayumi, Koichi; Takigawa, Toshikazu; Ito, Kohzo

2014-10-01

180

Effects of pre-annealing on the uni- and bi-axial stretching behavior of poly(ethylene naphthalate) films  

International Nuclear Information System (INIS)

Effect of pre-annealing on stress and birefringence behavior of poly(ethylene naphthalate) (PEN) films during stretching and relaxation processes was investigated. Amorphous and non-oriented PEN films were pre-annealed under the conditions of different temperatures and periods. The pre-annealed films were stretched uniaxially or equi-biaxially and then relaxed at fixed length. It was found that pre-annealing did not cause any notable change for the initial behavior of refractive indices variation, whereas the behaviors after necking were significantly affected. Through the comparison between in-plane and out-of-plane birefringence and the analysis of wide-angle x-ray diffraction patterns of drawn films of both stretching modes, it was confirmed that the orientation of naphthalene ring in the film plane was enhanced by pre-annealing

 
 
 
 
181

Effects of pre-annealing on the uni- and bi-axial stretching behavior of poly(ethylene naphthalate) films  

Energy Technology Data Exchange (ETDEWEB)

Effect of pre-annealing on stress and birefringence behavior of poly(ethylene naphthalate) (PEN) films during stretching and relaxation processes was investigated. Amorphous and non-oriented PEN films were pre-annealed under the conditions of different temperatures and periods. The pre-annealed films were stretched uniaxially or equi-biaxially and then relaxed at fixed length. It was found that pre-annealing did not cause any notable change for the initial behavior of refractive indices variation, whereas the behaviors after necking were significantly affected. Through the comparison between in-plane and out-of-plane birefringence and the analysis of wide-angle x-ray diffraction patterns of drawn films of both stretching modes, it was confirmed that the orientation of naphthalene ring in the film plane was enhanced by pre-annealing.

Abe, T., E-mail: kikutani.t.aa@m.titech.ac.jp; Takarada, W., E-mail: kikutani.t.aa@m.titech.ac.jp; Kikutani, T., E-mail: kikutani.t.aa@m.titech.ac.jp [Dept. Organic and Polymeric Materials, Tokyo Institute of Technology (Japan)

2014-05-15

182

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

Science.gov (United States)

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.

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

2011-05-01

183

Tuning electronic and magnetic properties of partially hydrogenated graphene by biaxial tensile strain: a computational study  

Science.gov (United States)

Using density functional theory calculations, we have investigated the effects of biaxial tensile strain on the electronic and magnetic properties of partially hydrogenated graphene (PHG) structures. Our study demonstrates that PHG configuration with hexagon vacancies is more energetically favorable than several other types of PHG configurations. In addition, an appropriate biaxial tensile strain can effectively tune the band gap and magnetism of the hydrogenated graphene. The band gap and magnetism of such configurations can be continuously increased when the magnitude of the biaxial tensile strain is increased. This fact that both the band gap and magnetism of partially hydrogenated graphene can be tuned by applying biaxial tensile strain provides a new pathway for the applications of graphene to electronics and photonics.

2014-01-01

184

Tuning electronic and magnetic properties of partially hydrogenated graphene by biaxial tensile strain: a computational study  

Science.gov (United States)

Using density functional theory calculations, we have investigated the effects of biaxial tensile strain on the electronic and magnetic properties of partially hydrogenated graphene (PHG) structures. Our study demonstrates that PHG configuration with hexagon vacancies is more energetically favorable than several other types of PHG configurations. In addition, an appropriate biaxial tensile strain can effectively tune the band gap and magnetism of the hydrogenated graphene. The band gap and magnetism of such configurations can be continuously increased when the magnitude of the biaxial tensile strain is increased. This fact that both the band gap and magnetism of partially hydrogenated graphene can be tuned by applying biaxial tensile strain provides a new pathway for the applications of graphene to electronics and photonics.

Song, Er Hong; Ali, Ghafar; Yoo, Sung Ho; Jiang, Qing; Cho, Sung Oh

2014-09-01

185

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

CERN Document Server

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...

Mackay, Tom G

2013-01-01

186

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

DEFF Research Database (Denmark)

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 particular been concerned with the effect of biaxial strain (compressive and tensile) on the diffusion of pure vacancy-assisted diffusers (Sb and, partly, Ge) and pure interstitial-assisted diffusers (B and P). It is found that compressive biaxial strain retards the diffusion of the interstitial-assisted diffusers, whereas tensile biaxial strain enhances the diffusion of these impurities. The opposite is the case for the vacancy-assisted diffusers.

Fage-Pedersen, Jacob

2005-01-01

187

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

International Nuclear Information System (INIS)

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(?2x + ?2y) - ?/E(?x?y)]dV (1). From equation (1) a mathematical deduction to solve in terms of ? of this case was developed employing Genetic Algorithms, where ? 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.

188

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

Energy Technology Data Exchange (ETDEWEB)

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.

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

189

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

International Nuclear Information System (INIS)

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)

190

The effect of the stress far field on the crack tip behaviour  

Directory of Open Access Journals (Sweden)

Full Text Available The boundary value problem of an infinite purely elastic sheet with
a traction-free crack loaded with a uniform shear and biaxial tension at
infinity is solved. It is shown that the singular terms of stress and displacement functions are inadequate to predict the direction of initial crack extension. The independence of the J vector of the biaxial parameter is also proved.

A. PIVA

1979-06-01

191

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

Science.gov (United States)

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 different physical mechanisms are identified as responsible for the emergence of biaxiality: (i) anisotropic fluctuations of the long molecular axis, (ii) a biased rotation around the long axis, and (iii) the local field effect. By means of a simple theoretical investigation, we conclude that these two types of trends are due mainly to the opposite signs of the biaxial order parameter C , which represents the second mechanism: the biased rotation around the long axis. This means that the central phenyl planes of molecules belonging to materials having biaxiality that increases with temperature are oriented on the average parallel to the tilt plane (the shortest index of refraction axis normal to the tilt plane), and, on the contrary, in those of the others molecules are oriented perpendicular to the tilt plane (the shortest index of refraction axis lying in the tilt plane). Thus, the direction of the phenyl ring plane of the liquid crystal molecules determines the different temperature dependencies of the biaxiality. It is also shown that the phenomenon of sign reversal of the biaxiality is due to the competitive contributions of the first and second physical mechanisms. PMID:17677473

Song, Jang-Kun; Chandani, A D L; Fukuda, Atsuo; Vij, J K; Kobayashi, Ichiro; Emelyanenko, A V

2007-07-01

192

Preparation of biaxially oriented TlCu-1234 thin films  

CERN Document Server

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...

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

1999-01-01

193

Theory and Simulation of Extensional Flow-Induced Biaxiality in Discotic Mesophases  

Science.gov (United States)

Flow-induced biaxiality is simulated for a uniaxial discotic nematic liquid crystal subjected to a constant uniaxial, isothermal, incompressible, irrotational, extensional, three dimensional flow, using a previously presented model [Singh A.P. and Rey A.D., J. Phys. II France 4 (1994) 645]. Numerical and analytical solutions of the director triad (n, m, l), and uniaxial (S) and biaxial (P) alignments are given. The unit sphere description of the director triad is used to discuss and analyze the sensitivity of the director triad trajectories and the coupled alignment (uniaxial and biaxial) relaxations to the initial orientation, nematic potential (U), and to the alignment Deborah number (dimensionless extension rate). The evolution of the director triad is given by the rotation of a moving diad (n, l) around a fixed director (m). When the poles of the orientation unit sphere are along the extension axis, and the equator lies in the compression plane of the flow, it is found that the director diad (n, l) dynamics follow geodesic flow and the trajectories belong to the same meridians (great circles through the poles). The space of stable steady state orientation of the uniaxial director n and the biaxial director m is the whole compression plane (the equator of the unit sphere), while that of the biaxial director l is the extension direction (poles). A high degree extension flow-induced biaxiality is found when the uniaxial director is away from the extension axis and when S is relatively low. The scalar order parameter couplings are captured by analyzing the trajectories in the alignment triangle. Computed scientific visualizations of biaxial molecular orientation distributions are used to correlate the director triad dynamics and the alignment's dynamics. The tensor order parameter is used to calculate the main flow-birefringences, thus providing a direct way to verify the theoretical predictions of this paper.

Singh, Arvinder P.; Rey, Alejandro D.

1995-09-01

194

An analytical model for the ductile failure of biaxially loaded type 316 stainless steel subjected to thermal transients  

International Nuclear Information System (INIS)

Failure properties are calculated for the case of biaxially loaded type 316 stainless steel tubes that are heated from 300 K to near melting at various constant rates. The procedure involves combining a steady state plastic-deformation rate law with a strain hardening equation. Integrating under the condition of plastic instability gives the time and plastic strain at which ductile failure occurs for a given load. The result is presented as an analytical expression for equivalent plastic strain as a function of equivalent stress, temperature, heating rate and material constants. At large initial load, ductile fracture is calculated to occur early, at low temperatures, after very little deformation. At very small loads deformation continues for a long time to high temperatures where creep rupture mechanisms limit ductility. In the case of intermediate loads, the plastic strain accumulated before the occurrence of unstable ductile fracture is calculated. Comparison of calculated results is made with existing experimental data from pressurized tubes heated at 5.6 K/s and 111 K/s. When the effect of grain growth on creep ductility is taken into account from recrystallization data, agreement between measured and calculated uniform ductility is excellent. The general reduction in ductility and failure time that is observed at higher heating rate is explained via the model. The model provides an analytical expression for the ductility and failure time during transients for biaxially loaded type 316 stainless steel as a function of the initial temperature and load, as well as the material creep and strain hardening parameters. (orig.)

195

An analytical model for the ductile failure of biaxially loaded type 316 stainless steel subjected to thermal transients  

Science.gov (United States)

Failure properties are calculated for the case of biaxially loaded type 316 stainless steel tubes that are heated from 300 K to near melting at various constant rates. The procedure involves combining a steady state plastic-deformation rate law with a strain hardening equation. Integrating under the condition of plastic instability gives the time and plastic strain at which ductile failure occurs for a given load. The result is presented as an analytical expression for equivalent plastic strain as a function of equivalent stress, temperature, heating rate and material constants. At large initial load, ductile fracture is calculated to occur early, at low temperature, after very little deformation. At very small loads deformation continues for a long time to high temperatures where creep rupture mechanisms limit ductility. In the case of intermediate loads, the plastic strain accumulated before the occurrence of unstable ductile fracture is calculated. Comparison of calculated results is made with existing experimental data from pressurized tubes heated at 5.6 K/s and 111 K/s. When the effect of grain growth on creep ductility is taken into account from recrystallization data, agreement between measured and calculated uniform ductility is excellent. The general reduction in ductility and failure time that is observed at higher heating rate is explained via the model. The model provides an analytical expression for the ductility and failure time during transients for biaxially loaded type 316 stainless steel as a function of the initial temperature and load, as well as the material creep and strain hardening parameters.

Dimelfi, R. J.

1987-01-01

196

Anisotropically biaxial strain in a-plane AlGaN on GaN grown on ?-plane sapphire  

International Nuclear Information System (INIS)

In this study, the anisotropically biaxial strain in a-plane AlGaN on GaN is investigated by X-ray diffraction (XRD) analysis using an AlGaN/GaN heterostructure grown on r-plane sapphire. In accordance with XRD reciprocal lattice space mapping, when the AlN molar fraction x in the AlGaN layer is 0.18, the AlGaN layer is fully strained under tensile stress and grows coherently on the underlying GaN layer. However, when x is as large as 0.31, partial relaxation is observed only in the c-axis direction. The tensile stress in the AlGaN layer is calculated taking the actual in-plane lattice constants of the underlying GaN layer into account, and it was found that the stress in the a-plane AlGaN layer in the c-axis direction is approximately 1.7 times lager than that in the m-axis direction. (author)

197

A simplified technique for shakedown limit load determination of a large square plate with a small central hole under cyclic biaxial loading  

International Nuclear Information System (INIS)

A simplified technique for determining the shakedown limit load of a structure was previously developed and successfully applied to benchmark shakedown problems involving uniaxial states of stress. In this paper, the simplified technique is further developed to handle cyclic biaxial loading resulting in multi-axial states of stress within the large square plate with a small central hole problem. Two material models are adopted namely: an elastic-linear strain hardening material model obeying Ziegler's linear kinematic hardening (KH) rule and an elastic-perfectly-plastic (EPP) material model. The simplified technique utilizes the finite element (FE) method and employs small displacement formulation to determine the shakedown limit load without performing lengthy time consuming full elastic-plastic cyclic loading FE simulations or conventional iterative elastic techniques. The simplified technique is utilized to generate the shakedown domain for the plate problem subjected to cyclic biaxial tension along its edges. The outcomes of the simplified technique showed very good correlation with the results of analytical solutions as well as full elastic-plastic cyclic loading FE simulations. Material hardening showed no effect on the shakedown domain of the plate in comparison to employing EPP-material.

198

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

Science.gov (United States)

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

Brüggenwirth, Martin; Fricke, Heiko; Knoche, Moritz

2014-01-01

199

Formation of biaxially textured molybdenum thin films under the influence of recrystallization conditions  

Energy Technology Data Exchange (ETDEWEB)

This article highlights the formation of biaxially textured body centered cubic Mo nanorods under recrystallization conditions using glancing angle deposition. The flux incidence angle has been changed ({alpha} = 0 deg., 70 deg. and 85 deg. away from the surface normal) to observe its effect on the formation of biaxial texture under a constant low Ar pressure environment (0.306 Pa). Only at a glancing flux incidence ({alpha} = 85 deg.), the directional diffusion overcomes the effect of recrystallization to yield a highly biaxial texture. In another study, a normal flux incidence ({alpha} = 0 deg.) was kept constant and the Ar pressure was changed (0.67, 1.33 and 2.67 Pa) to see its influence on the film morphology and the resulting texture. The Ar pressure variation was aimed at attempting a zone transformation in accordance with the structure zone model. While the morphology appeared to agree with the expected zone transformation, the texture did not.

Krishnan, Rahul, E-mail: krishr2@rpi.edu [Department of Materials Science and Engineering, Rensselaer Polytechnic Institute, Troy, NY 12180 (United States); Riley, Michael [Department of Chemical and Biological Engineering, Rensselaer Polytechnic Institute, Troy, NY 12180 (United States); Lee, Sabrina [US Army Armament Research, Development and Engineering Center, Benet Labs, Watervliet, NY 12189 (United States); Lu, Toh-Ming [Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, Troy, NY 12180 (United States)

2011-06-01

200

Formation of biaxially textured molybdenum thin films under the influence of recrystallization conditions  

International Nuclear Information System (INIS)

This article highlights the formation of biaxially textured body centered cubic Mo nanorods under recrystallization conditions using glancing angle deposition. The flux incidence angle has been changed (? = 0 deg., 70 deg. and 85 deg. away from the surface normal) to observe its effect on the formation of biaxial texture under a constant low Ar pressure environment (0.306 Pa). Only at a glancing flux incidence (? = 85 deg.), the directional diffusion overcomes the effect of recrystallization to yield a highly biaxial texture. In another study, a normal flux incidence (? = 0 deg.) was kept constant and the Ar pressure was changed (0.67, 1.33 and 2.67 Pa) to see its influence on the film morphology and the resulting texture. The Ar pressure variation was aimed at attempting a zone transformation in accordance with the structure zone model. While the morphology appeared to agree with the expected zone transformation, the texture did not.

 
 
 
 
201

Biaxial CdTe/CaF2 films growth on amorphous surface  

International Nuclear Information System (INIS)

A continuous and highly biaxially textured CdTe film was grown by metal organic chemical vapor deposition on an amorphous substrate using biaxial CaF2 nanorods as a buffer layer. The interface between the CdTe film and CaF2 nanorods and the morphology of the CdTe film were studied by transmission electron microscopy (TEM) and scanning electron microscopy. Both the TEM and X-ray pole figure analysis clearly reveal that the crystalline orientation of the continuous CdTe film followed the {111} biaxial texture of the CaF2 nanorods. A high density of twin faults was observed in the CdTe film. Furthermore, the near surface texture of the CdTe thin film was investigated by reflection high-energy electron diffraction (RHEED) and RHEED surface pole figure analysis. Twinning was also observed from the RHEED surface pole figure analysis.

202

Device and method of optically orienting biaxial crystals for sample preparation.  

Science.gov (United States)

An optical instrument we refer to as the "biaxial orientation device" has been developed for finding the optical plane, acute bisectrix, and obtuse bisectrix in biaxial crystals by means of optically aligning conoscopically formed melatopes and measuring the angular coordinates of the melatopes, where the angular values allow for determination of the optical plane containing the optical axes using a vector algebra approach. After determination of the optical plane, the instrument allows for the sample to be aligned in the acute bisectrix or obtuse bisectrix orientations and to be transferred to a simple mechanical component for subsequent grinding and polishing, while preserving the orientation of the polished faces relative to the optical plane, acute bisectrix, and obtuse bisectrix during the grinding and polishing process. Biaxial crystalline material samples prepared in the manner are suitable for accurate spectroscopic absorption measurements in the acute bisectrix and obtuse bisectrix directions as well as perpendicular to the optical plane. PMID:25273705

Thomas, Timothy; Rossman, George R; Sandstrom, Mark

2014-09-01

203

The Relationship Between Microstructure and Toughness of Biaxially Oriented Semicrytalline Polyester Films  

International Nuclear Information System (INIS)

The relationship between microstructure and toughness of biaxially stretched semicrystalline polyester films was investigated. Optically transparent films were prepared by simultaneous biaxial stretching of melt-cast sheets near the glass transition temperature. Copolyesters of polyethylene terephthalate (PET) with different compositions of two diols: ethylene glycol (EG) and cyclohexane dimethanol (CHDM), and stoichiometrically matched terephthalic acid were used to produce films with different degrees of crystallinity. In addition, the PET films with different crystalline morphologies were produced by constrained high temperature annealing of biaxially oriented films. The toughness, degree of crystallinity and crystalline morphology/molecular ordering were studied using mechanical testing, synchrotron small-angle X-ray scattering (SAXS), wide-angle X-ray diffraction (WAXD) techniques, and differential scanning calorimetry (DSC). The results indicate that the toughness of a semicrystalline polymeric film is determined by the interconnectivity of the crystalline phase within the amorphous phase and is greatly influenced by the degree of crystallinity and the underlying crystalline morphology.

204

Phase transition and band-structure tuning in InN through uniaxial and biaxial strains.  

Science.gov (United States)

The phase transitions and band structure of InN under uniaxial and biaxial strains are systematically investigated using first-principles calculations. The main findings are summarized as follows: (I) although graphite-like phases are observed for both types of strain, the phase transitions are drastically different: second order for uniaxial strain and first order for biaxial strain. Furthermore, the second-order transition is driven by elastic and dynamical instabilities, whereas the first-order transition is driven only by elastic instability. (II) The wurtzite bandgap is always direct and that of the graphite-like phase is always indirect. Furthermore, the wurtzite bandgap is drastically enhanced by compressive uniaxial strain but reduced by tensile uniaxial strain. However, both biaxial strains greatly reduce the bandgap and eventually the semi-metallic phases are achieved. PMID:24305640

Duan, Yifeng; Qin, Lixia; Shi, Liwei; Tang, Gang; Shi, Hongliang

2014-01-15

205

The self-propelled Brownian spinning top: dynamics of a biaxial swimmer at low Reynolds numbers  

CERN Document Server

Recently, the Brownian dynamics of self-propelled (active) rod-like particles was explored to model the motion of colloidal microswimmers, catalytically-driven nanorods, and bacteria. Here, we generalize this description to biaxial particles with arbitrary shape and derive the corresponding Langevin equation for a self-propelled Brownian spinning top. The biaxial swimmer is exposed to a hydrodynamic Stokes friction force at low Reynolds numbers, to fluctuating random forces and torques as well as to an external and an internal (effective) force and torque. The latter quantities control its self-propulsion. Due to biaxiality and hydrodynamic translational-rotational coupling, the Langevin equation can only be solved numerically. In the special case of an orthotropic particle in the absence of external forces and torques, the noise-free (zero-temperature) trajectory is analytically found to be a circular helix. This trajectory is confirmed numerically to be more complex in the general case involving a transient...

Wittkowski, Raphael

2011-01-01

206

ANALYTICAL MODEL OF SURFACE POTENTIAL AND THRESHOLD VOLTAGE OF BIAXIAL STRAINED SILICON NMOSFET INCLUDING QME  

Directory of Open Access Journals (Sweden)

Full Text Available In this paper physics based analytical model for threshold voltage of nanoscale biaxial strained nMOSFET has been presented. The maximum depletion depth and surface potential in biaxial strained–Si nMOSFET is determined, taking into account both the quantum mechanical effects (QME and effects of strain in inversion charge sheet. The results show that a significant decrease in threshold voltage occurs with the increase in the germanium content in the silicon germanium layer. The results have been compared with the published data and the effect of variation of channel doping concentration has been examined.

Garima Joshi

2012-11-01

207

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

International Nuclear Information System (INIS)

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.

208

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

International Nuclear Information System (INIS)

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

209

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

International Nuclear Information System (INIS)

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

210

Mechanisms for ion-irradiation-induced relaxation of stress in mosaic structured Cu thin films  

International Nuclear Information System (INIS)

In this paper, helium (He) ion irradiations with various fluences were performed on sputtered Cu thin films with a mosaic structure to evolve biaxial stress. X-ray diffraction of the ?-2? method was used to determine the residual strains in the thin films by measuring the spacing of the crystallographic planes. The results show the in-plane biaxial tensile stress has been reduced by ion irradiation. A new proposed model is discussed to explain the ion-irradiation-induced stress release in mosaic structured Cu thin films.

211

Investigation of the influence of multiaxial stress states and material anisotropy on the residual stress measurement according to the hole drilling method  

International Nuclear Information System (INIS)

Numerical calculations and experimental results indicate that applying uniaxial formalism to two-dimensional stress states leads to considerable errors. A biaxial formalism is presented which gives in such cases precise values for residual stresses. For extremely anisotropic materials no generally applicable formalism can be derived. However, in the case of small degrees of texture the expected errors are marginal. (orig.)

212

Strain rate-dependent flow stress curves in the large deformation range  

Science.gov (United States)

This paper deals with the construction method of the flow stress curve at various strain rates in the large deformation range. The hydraulic bulge test is carried out for EDDQ and 590DP steel sheets in order to obtain equibiaxial flow stress curves according to the punch speed. By using the measured curves, the stress data at various plastic strains is fitted by Cowper-Symonds model in order to analyze the strain rate sensitivity and determine the stress value at the designated strain rate. Equi-biaxial flow stress curves at various strain rates are constructed by fitting the determined stress value with Swift model with respect to the plastic strain. Finally, equi-biaxial flow stress curves are converted into uniaxial flow stress curves by using Yld2000-2d yield function. A suggested procedure can be utilized to construct the uniaxial flow stress curves at various strain rates in the large deformation range.

Bae, Gihyun

2013-12-01

213

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

International Nuclear Information System (INIS)

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

214

Peripheral (punching) shear strength of biaxially tensioned reinforced concrete wall elements  

International Nuclear Information System (INIS)

Results are presented for the peripheral shear strength of orthogonally reinforced concrete wall elements carrying various levels of biaxial tension in combination with the punching shear force. This loading condition occurs in containments and other nuclear structures at attachments to the walls and at penetrations through the walls. (orig./HP)

215

Consistent stress-strain ductile fracture model as applied to two grades of beryllium  

International Nuclear Information System (INIS)

Published yield and ultimate biaxial stress and strain data for two grades of beryllium are correlated with a more complete method of characterizing macroscopic strain at fracture initiation in ductile materials. Results are compared with those obtained from an exponential, mean stress dependent, model. Simple statistical methods are employed to illustrate the degree of correlation for each method with the experimental data

216

Detection of phase biaxiality in liquid crystals by use of the quadrupole shift in 131Xe NMR spectra.  

Science.gov (United States)

An experimental method to unambiguously distinguish between uniaxial and biaxial liquid crystal phases is introduced. The method is based on the second order quadrupole shift (SOQS) observable in 131Xe NMR spectra of xenon dissolved in liquid crystals. It is shown that besides revealing the biaxiality, the 131Xe SOQS offers a novel method to determine the tilt angle in smectic C phases. As an example, the 131Xe SOQS in a ferroelectric liquid crystal is reported. It yields up a biaxial phase in between isotropic and smectic C phases. PMID:21231771

Jokisaari, Jukka P; Kantola, Anu M; Lounila, Juhani A; Ingman, L Petri

2011-01-01

217

Rapid biaxial texture development during nucleation of MgO thin films during ion beam-assisted deposition  

International Nuclear Information System (INIS)

We propose a mechanism for the nucleation of highly aligned biaxially textured MgO on amorphous Si3N4 during ion beam-assisted deposition. Using transmission electron microscopy, reflection high-energy electron diffraction, energy dispersive x-ray analysis, and ellipsometery, we have observed that highly aligned biaxially textured grains emerge from a 'diffraction-amorphous' film when the film thickens from 3.5 to 4.5 nm. Transmission electron microscopy dark-field images also show the onset of rapid grain growth during this same film thickness interval. These results suggest biaxial texturing through aligned solid phase crystallization

218

Determination of flow stress by the hydraulic bulge test  

Directory of Open Access Journals (Sweden)

Full Text Available In sheet metal forming operations the mechanical properties of the sheet metal (stress-strain curve, flow stress greatly influence metal flow and product quality. Accurate determination of the stress-strain relationship is important in process simulation by finite element method. In this paper the sheet thickness gradation in different points of the hemisphere formed in the bulge test is analysed, both theoretically and experimentally. A precise determination of sheet thickness at the pole is very important in the precise determination of stress-strain relationship. The use of the hydraulic bulge test for estimation of flow stress under biaxial stress-strain state is discussed.

Slota, J.

2008-01-01

219

A k · p analytical model for valence band of biaxial strained Ge on (001) Si1?xGex  

International Nuclear Information System (INIS)

In this paper, the dispersion relationship is derived by using the k · p method with the help of the perturbation theory, and we obtain the analytical expression in connection with the deformation potential. The calculation of the valence band of the biaxial strained Ge/(001)Si1?xGex is then performed. The results show that the first valence band edge moves up as Ge fraction x decreases, while the second valence band edge moves down. The band structures in the strained Ge/ (001)Si0.4Ge0.6 exhibit significant changes with x decreasing in the relaxed Ge along the [0, 0, k] and the [k, 0, 0] directions. Furthermore, we employ a pseudo-potential total energy package (CASTEP) approach to calculate the band structure with the Ge fraction ranging from x = 0.6 to 1. Our analytical results of the splitting energy accord with the CASTEP-extracted results. The quantitative results obtained in this work can provide some theoretical references to the understanding of the strained Ge materials and the conduction channel design related to stress and orientation in the strained Ge pMOSFET. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

220

Biaxial creep behavior of ribbed GCFR cladding at 6500C in nominally pure helium (99.99%)  

International Nuclear Information System (INIS)

Biaxial creep-rupture tests were conducted on 12 prototypic GCFR fuel-cladding specimens at 6500C 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

 
 
 
 
221

A novel indirect tensile test method to measure the biaxial tensile strength of concretes and other quasibrittle materials  

International Nuclear Information System (INIS)

A novel indirect tensile test method, the biaxial flexure test (BFT) method, has been developed to measure the biaxial tensile strength of concretes. The classical modulus of rupture (MOR) test has been generalized to three dimensions. In this method, we use a circular plate as the new test specimen. This plate is supported by an annular ring. We apply an external load to this specimen through a circular edge. The centers of the specimen, the loading device and the support are identical. The biaxial tensile strength measured by this new method is about 19% greater than the uniaxial tensile strength obtained from the classical modulus of rupture test as reported by other researchers. However, at the same time, we also found that the stochastic deviation of the biaxial tensile strength is about 63% greater than the uniaxial strength

222

Rupture propagation speed during earthquake faulting reproduced by large-scale biaxial friction experiments  

Science.gov (United States)

Earthquakes are generated by unstable frictional slip along pre-existing faults. Both laboratory experiments and numerical simulations have shown that the rupture process involves an initial quasi-static phase, a subsequent accelerating phase and a main dynamic rupture phase. During the main phase, the rupture front propagates at either subshear or supershear velocity, which affects the seismic wave radiation pattern. An examination on what controls the speed is crucial for improvement of earthquake hazard mitigation. Thus We conducted stick-slip experiments on meter-scale Indian gabbro rocks to observe the rupture process of the unstable periodic slip events and to measure the rupture speed along the fault. The simulated fault plane is 1.5m in length and 0.1m in width and ground by #200-300. The fault is applied at a constant normal stress of 6.7MPa and sheared parallel to the longitudinal direction of the fault at a slip rate of 0.1mm/s and up to a displacement of 40cm. The long, narrow fault geometry leads to in-plane shear rupture (mode II). in which the rupture front propagates in the direction of slip, which mimics large strike-slip earthquake faulting. Compressional-(Vp) and shear-(Vs) wave velocities of the rock sample are calculated to be 6.92km/s and 3.62km/s, respectively, based on the elastic properties (Young's modulus, 103GPa; Poisson's ratio, 0.331; Shear modulus, 38GPa). 32 biaxial strain gauges for shear strain and 16 single-axis strain gauges for normal strain were attached along the longitudinal direction of the fault at intervals of 5cm and 10cm, respectively. The local strain data were recorded at a sampling rate of 1MHz within 16 bit resolution. Load calls attached outside the fault plane measured the whole normal and shear forces applied on the fault plane, which was recorded by the same recording system. We have confirmed that the rupture process of unstable slip events consistsing of 1) an initial quasi-static phase where the slipped area spread on the fault at velocities of less than 10 m/s, 2) an accelerating phase where the rupture propagation accelerates up to 100 m/s, and 3) a main rupture phase where the rupture propagates dynamically at elastic wave velocities. These rupture nucleation process is consistent with those reported in previous studies. However, between 2) and 3) , we sometimes observed a discontinuity of rupture propagation in space and time, which is inconsistent with [Ohnaka & Shen, 1999]. Next, we estimated the rupture velocity of the main rupture phase from spatial-temporal variation in local shear strain associated with the dynamic stress reduction induced by fault slip. While several slip events showed the subshear rupture propagation similar to regular natural earthquakes, some were faster than Vs. Such supershear rupture propagation has been studied theoretically in 1970's, and reported for large strike-slip faulting earthquakes. Except for Passelègue et al. [2013], however, few laboratory experiments on rocks have confirmed the presence and this study has reproduced supershear rupture events along meter-scale fault during stick-slip experiments. We shall discuss the relationship between the rupture propagation speed and the stress heterogeneity along the fault monitored by based on the a dense array of local strain gauges.

Mizoguchi, K.; Fukuyama, E.; Yamashita, F.; Takizawa, S.; Kawakata, H.

2013-12-01

223

Fatigue biaxiale à grand nombre de cycles : étude expérimentale et modèle d'endommagement à deux échelles probabiliste  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Les structures industrielles sont soumises à des sollicitations complexes dont certaines biaxiales. Afin d'étudier de manière expérimentale l'influence de la biaxialité du chargement sur la durée de vie, des essais de fatigue biaxiale à grand nombre de cycles sont menés sur matériaux acier inoxydable austénitique 304L CLI, et alliage de titane. Une géométrie d'éprouvette en croix, affinée en son centre a été dimensionnée pour cette étude. Une vingtaine d'essais en efforts im...

Barbier, Gre?gory

2009-01-01

224

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

CERN Document Server

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.

Li Peng; Mazumder, J

2003-01-01

225

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

International Nuclear Information System (INIS)

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

226

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  

Energy Technology Data Exchange (ETDEWEB)

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)

Aubin, V

2001-11-15

227

Nucleation of epitaxial yttria-stabilized zirconia on biaxially textured (001) Ni for deposited conductors  

International Nuclear Information System (INIS)

The nucleation of (001)-oriented yttria-stabilized zirconia (YSZ) directly on the (001) Ni surface is realized via nucleation on an oxygen-terminated nickel surface using pulsed-laser deposition. Under conditions where the nickel surface is either oxygen free or substantially covered with NiO, a mixed orientation of YSZ occurs. The epitaxial YSZ layer grown on a biaxially textured Ni(001) surface was used as a single buffer layer for a high temperature superconducting coated conductor architecture, yielding superconducting YBa2Cu3O7 films with high critical current densities, Jc. This architecture eliminates the necessity for a multilayer buffer architecture, since high Jc superconducting films are achieved with no intermediate buffer layer between the (001) YSZ and the biaxially textured metal. (c) 2000 American Institute of Physics

228

Torsional and biaxial (tension-torsion) fatigue damage mechanisms in Waspaloy at room temperature  

Science.gov (United States)

Strain controlled torsional and biaxial (tension-torsion) low cycle fatigue behavior of Waspaloy was studied at room temperature as a function of heat treatment. Biaxial tests were conducted under proportional and nonproportional cyclic conditions. The deformation behavior under these different cyclic conditions was evaluated by slip trace analysis. For this, a Schmidt-type factor was defined for multiaxial loading conditions, and it was shown that when the slip deformation is predominant, nonproportional cycles are more damaging than proportional or pure axial or torsional cycles. This was attributed to the fact that under nonproportional cyclic conditions, deformation was through multiple slip, as opposed to single slip for other loading conditions, which gave rise to increased hardening. The total life for a given test condition was found to be independent of heat treatment. This was interpreted as being due to the differences in the cycles to initiation and propagation of cracks.

Jayaraman, N.; Ditmars, M. M.

1989-01-01

229

Structure and cathodoluminescence of individual ZnS/ZnO biaxial nanobelt heterostructures.  

Science.gov (United States)

We report on a controlled synthesis of two novel semiconducting heterostructures: heterocrystalline-ZnS/single-crystalline-ZnO biaxial nanobelts and side-to-side single-crystalline ZnS/ZnO biaxial nanobelts via a simple one-step thermal evaporation method. In the first heterostructure, a ZnS domain is composed of the heterocrystalline superlattice (3C-ZnS) N /(2H-ZnS) M [111]-[0001] with the atomically smooth interface between wurtzite and zinc blende ZnS fragments. High-spatial resolution cathodoluminescence studies on individual heterostructures for the first time reveal a new ultraviolet emission peak ( approximately 355 nm), which is not observed in separate ZnS or ZnO nanostructures. The present hererostructures are expected to become valuable not only with respect to fundamental research but also for a design of new broad-range ultraviolet nanoscale lasers and sensors. PMID:18687012

Yan, Jian; Fang, Xiaosheng; Zhang, Lide; Bando, Yoshio; Gautam, Ujjal K; Dierre, Benjamin; Sekiguchi, Takashi; Golberg, Dmitri

2008-09-01

230

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

Directory of Open Access Journals (Sweden)

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.

Nishant K. Kumar

2013-04-01

231

Stability of Biaxial Nematic Phase for Systems with Variable Molecular Shape Anisotropy  

CERN Document Server

We study the influence of fluctuations in molecular shape on the stability of the biaxial nematic phase by generalizing the mean field model of Mulder and Ruijgrok [Physica A {\\bf 113}, 145 (1982)]. We limit ourselves to the case when the molecular shape anisotropy, represented by the alignment tensor, is a random variable of an annealed type. A prototype of such behavior can be found in lyotropic systems - a mixture of potassium laurate, 1-decanol, and $D_2O$, where distribution of the micellar shape adjusts to actual equilibrium conditions. Further examples of materials with the biaxial nematic phase, where molecular shape is subject to fluctuations, are thermotropic materials composed of flexible trimeric- or tetrapod-like molecular units. Our calculations show that the Gaussian equilibrium distribution of the variables describing molecular shape (dispersion force) anisotropy gives rise to new classes of the phase diagrams, absent in the original model. Depending on properties of the shape fluctuations, th...

Longa, L; Longa, Lech; Wydro, Thomas

2007-01-01

232

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

International Nuclear Information System (INIS)

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 ?/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. (condensed matter: structure, mechanical and thermal properties)

233

Behaviour of reinforced concrete column under biaxial cyclic loading—state of the art  

Science.gov (United States)

The cyclic behaviour of reinforced concrete columns has been object of many experimental studies in the last years, mostly focused on the unidirectional loading of columns under constant axial load conditions. In this research work, the existing test on reinforced concrete (RC) columns under biaxial load has been reviewed, underlying their main findings. In general, the experimental results show that the RC columns' response is highly dependent on the loading pattern, and the biaxial loading induces a decrease in the maximum strength and anticipates each damage state. Thus, in columns where demands are expected with large moments in both directions, specific detailing should be provided in their critical regions in order to improve the columns' performance and avoid premature failure.

Rodrigues, Hugo; Varum, Humberto; Arêde, Antonio; Costa, Aníbal G.

2013-12-01

234

COLLAGEN FIBER ALIGNMENT AND BIAXIAL MECHANICAL BEHAVIOR OF PORCINE URINARY BLADDER DERIVED EXTRACELLULAR MATRIX  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The collagen fiber alignment and biomechanical behavior of naturally occurring extracellular matrix (ECM) scaffolds are important considerations for the design of medical devices from these materials. Both should be considered in order to produce a device to meet tissue specific mechanical requirements (e.g., tendon vs. urinary bladder), and could ultimately affect the remodeling response in vivo. The present study evaluated the collagen fiber alignment and biaxial mechanical behavior of ECM ...

Gilbert, Thomas W.; Wognum, Silvia; Joyce, Erinn M.; Freytes, Donald O.; Sacks, Michael S.; Badylak, Stephen F.

2008-01-01

235

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

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in english 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 thi [...] s 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

Bandar Mohammed Abdullah, Al-Makramani; Abdul Aziz Abdul, Razak; Mohamed Ibrahim, Abu-Hassan.

2010-12-01

236

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 the linear region was found to be very small. The rheological properties at small deformations hardly depended on the cultivar. A higher water content of the dough resulted in a lower value for the ...

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

2004-01-01

237

Simple method of Brewster angle measurement for the determination of refractive indices in transparent biaxial crystal  

Science.gov (United States)

A new approach is reported for the measurement of Brewster angles in transparent biaxial crystals. The Brewster angles for potassium hydrogen phthalate (KAP) single crystal are also calculated from available refractive index data by our method. The measured values agree well with the calculated values, confirming our theory. The measured values of the Brewster angles of KAP are60 degree(s)03'+/- 5' and 58 degree(s)30'+/- 5'.

Kejalakshmy, N.; Srinivasan, K.

2001-11-01

238

Characterization of Engineered Tissue Development Under Biaxial Stretch Using Nonlinear Optical Microscopy  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Little is known about the precise mechanical stimuli that cells sense and respond to as they maintain or refashion the extracellular matrix in multiaxially loaded native or bioengineered tissues. Such information would benefit many areas of research involving soft tissues, including tissue morphogenesis, wound healing, and tissue engineering. A custom tissue culture device has been constructed that can impart well-defined biaxial stretches on cruciform-shaped, fibroblast-seeded collagen gels ...

Hu, Jin-jia; Humphrey, Jay D.; Yeh, Alvin T.

2009-01-01

239

Maximizing the Energy Density of Dielectric Elastomer Generators Using Equi-Biaxial Loading  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Dielectric elastomer generators (DEGs) for harvesting electrical energy from mechanical work have been demonstrated but the energy densities achieved are still small compared with theoretical predictions. We show that significant improvements in energy density (560 J/kg with a power density of 280 W/kg and an efficiency of 27%) can be achieved using equi-biaxial stretching, a mechanical loading configuration that maximizes the capacitance changes. We demonstrate the capacitance of dielectric ...

Clarke, David R.; Huang, Jiangshui; Shian, Samuel; Suo, Zhigang

2013-01-01

240

Hot cell installation for biaxial creep and burst testing of cladding specimens  

International Nuclear Information System (INIS)

The L.H.M.A. hot laboratory provides a range of facilities for the mechanical testing of cladding material from irradiated fuel pins. This paper gives a brief description of the apparatus for biaxial creep and burst testing that has been developed in the laboratory. This equipment is installed in a relatively small ?-?-? lead-shielded hot cell. Techniques for specimen preparation and conditioning as well as the test procedures are indicated. (author)

 
 
 
 
241

Cruciform-shaped specimens for elevated temperature biaxial testing of lightweight materials  

Science.gov (United States)

A custom biaxial testing fixture was used to evaluate new cruciform geometries. Specimens consisting of AA5083, Mg AZ31B, and TWIP steel were quasi-statically deformed to failure at 300oC. We elucidate geometric differences between specimens that accumulate plastic deformation within their gauge areas and those that prematurely fracture. Strain fields are computed with digital image correlation for selected geometries.

Abu-Farha, F.; Hector, L. G.; Khraisheh, M.

2009-08-01

242

Damage localization and failure locus under biaxial loading in glass-fiber nonwoven felts  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The pattern of damage localization and fracture under uniaxial and biaxial tension was studied in glass–fiber nonwoven felts. The analyses were carried out within the framework of the finite-element simulation of plain and notched specimens in which the microstructure of the felt, made up of fiber bundles connected at the cross point through an organic binder, was explicitly represented. Following previous experimental observations, fracture by interbundle decohesion and energy dissipation ...

Ridruejo Rodri?guez, A?lvaro; Gonza?lez Marti?nez, Carlos Daniel; Llorca Martinez, Francisco Javier

2012-01-01

243

Presentation of the new biaxial wheel test rig at BORBET  

Energy Technology Data Exchange (ETDEWEB)

The test rig offers the following advantages: (a) Simulation of different types of loads in the development phase, such as Eurocycle test cycles, arbitrary test courses, figure eight driving and circular courses. (b) Short testing times: 10 000 km in four days correspond to 300 000 km in normal operations. (c) Realistic deformation of all wheel and hub areas under operational loads. (d) Little material consumption. (e) Performance of stress analyses. (f) Complete replacement of previous test procedures and drive tests. (g) Easy handling and adaptation of the load program. (h) More ecnomic, more reliable, and more environmentally friendly strength test taking into account the safety aspects. (orig./AKF)

Voellmecke, F.J. [BORBET GmbH, Hallenberg-Hesborn (Germany)

2000-07-01

244

Biaxial CdTe/CaF{sub 2} films growth on amorphous surface  

Energy Technology Data Exchange (ETDEWEB)

A continuous and highly biaxially textured CdTe film was grown by metal organic chemical vapor deposition on an amorphous substrate using biaxial CaF{sub 2} nanorods as a buffer layer. The interface between the CdTe film and CaF{sub 2} nanorods and the morphology of the CdTe film were studied by transmission electron microscopy (TEM) and scanning electron microscopy. Both the TEM and X-ray pole figure analysis clearly reveal that the crystalline orientation of the continuous CdTe film followed the {l_brace}111{r_brace}<121> biaxial texture of the CaF{sub 2} nanorods. A high density of twin faults was observed in the CdTe film. Furthermore, the near surface texture of the CdTe thin film was investigated by reflection high-energy electron diffraction (RHEED) and RHEED surface pole figure analysis. Twinning was also observed from the RHEED surface pole figure analysis.

Yuan, W., E-mail: yuanw@rpi.ed [Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, 110, 8th St., Troy, NY 12180 (United States); Tang, F.; Li, H.-F.; Parker, T. [Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, 110, 8th St., Troy, NY 12180 (United States); LiCausi, N. [Department of Electrical, Computer and Systems Engineering, Rensselaer Polytechnic Institute, 110, 8th St., Troy, NY 12180 (United States); Lu, T.-M. [Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, 110, 8th St., Troy, NY 12180 (United States); Bhat, I. [Department of Electrical, Computer and Systems Engineering, Rensselaer Polytechnic Institute, 110, 8th St., Troy, NY 12180 (United States); Wang, G.-C. [Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, 110, 8th St., Troy, NY 12180 (United States); Lee, S. [US Army Armament Research, Development and Engineering Center, Benet Labs, Watervliet, NY 12189 (United States)

2009-10-30

245

Measurement of the biaxial properties of nineteenth century canves primings using electronic speckle pattern interferometry  

Science.gov (United States)

This paper reports on the use of electronic speckle pattern interferometry (ESPI) for the measurement of the biaxial tensile properties of English 19th century canvas primings and their constituent materials. Typically, such primings are comprised of a complex structure of layers, each with different mechanical properties. ESPI has been shown to be an effective technique for investigating complex composite structures and it is especially useful for understanding the behaviour of heterogeneous materials in which non-uniform strains can occur. The flexibility of canvas primings presents a more difficult application for both biaxial tensile testing and ESPI strain measurements. A series of experiments have been carried out to measure the Poisson's ratio of the three main constituents of a 19th Century priming as composites and of an original 19th century primed canvas. The samples have been uniaxially tensioned on a biaxial tensile tester designed specifically to investigate the mechanical properties of paintings on canvas. Measurements of deformation have made using a two-dimensional in-plane ESPI configuration. The results have shown that Poisson's ratio decreases as the constituents of a painting are built up. Preliminary tests on thermally aged and original primings suggest that for a painting without cracks it is the embrittled paint which determines the mechanical response of the painting at an relative humidity of 35-40%.

Young, Christina

1999-07-01

246

YSZ buffer layers and YBCO superconducting tapes with enhanced biaxial alignment and properties  

International Nuclear Information System (INIS)

Commercial applications of YBa2Cu3O7 (YBCO) superconducting cables require viable and scalable manufacturing processes. We have investigated the evolution of the biaxial alignment of yttria-stabilized zirconia (YSZ) buffer layers with increasing film thickness (50-900 nm) and report on a method of fabricating highly aligned YBCO tapes using a thin epitaxial YSZ buffer layer as template. The method employs magnetron and ion beam assisted deposition (IBAD) techniques followed by epitaxial growth to produce the buffer architectures IBAD-YSZ and epi-YSZ/IBAD-YSZ onto optically polished hastelloy metal substrates. Subsequent in situ deposition of YBCO films is used to determine the biaxial alignment at the surface of the buffer architecture, and to show that 100-200 nm thick epi-YSZ layers suffice to yield YBCO tapes that have enhanced biaxial alignment (?phi=9-10 deg. ) and high critical current densities: Jc(77 K)=(1-2)x106 A cm-2 and Jc(5 K,1 T)=8x106 A cm-2. Atomic force microscopy of the surface microstructure of the YSZ buffer layers and YBCO films reveals some grain coarsening in the epi-YSZ layers compared to the IBAD-YSZ layers while the YBCO tapes show significant outgrowths (?200 nm) and large grains (800-1200 nm) that are similar to high-Jc YBCO films grown on single crystal MgO(1 0 0) substrates

247

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

International Nuclear Information System (INIS)

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 ? and ? 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

248

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

Science.gov (United States)

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.

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

2014-03-01

249

Online estimation algorithm for a biaxial ankle kinematic model with configuration dependent joint axes.  

Science.gov (United States)

The kinematics of the human ankle is commonly modeled as a biaxial hinge joint model. However, significant variations in axis orientations have been found between different individuals and also between different foot configurations. For ankle rehabilitation robots, information regarding the ankle kinematic parameters can be used to estimate the ankle and subtalar joint displacements. This can in turn be used as auxiliary variables in adaptive control schemes to allow modification of the robot stiffness and damping parameters to reduce the forces applied at stiffer foot configurations. Due to the large variations observed in the ankle kinematic parameters, an online identification algorithm is required to provide estimates of the model parameters. An online parameter estimation routine based on the recursive least-squares (RLS) algorithm was therefore developed in this research. An extension of the conventional biaxial ankle kinematic model, which allows variation in axis orientations with different foot configurations had also been developed and utilized in the estimation algorithm. Simulation results showed that use of the extended model in the online algorithm is effective in capturing the foot orientation of a biaxial ankle model with variable joint axis orientations. Experimental results had also shown that a modified RLS algorithm that penalizes a deviation of model parameters from their nominal values can be used to obtain more realistic parameter estimates while maintaining a level of estimation accuracy comparable to that of the conventional RLS routine. PMID:21280877

Tsoi, Y H; Xie, S Q

2011-02-01

250

Self-propelled Brownian spinning top: dynamics of a biaxial swimmer at low Reynolds numbers.  

Science.gov (United States)

Recently the Brownian dynamics of self-propelled (active) rodlike particles was explored to model the motion of colloidal microswimmers, catalytically driven nanorods, and bacteria. Here we generalize this description to biaxial particles with arbitrary shape and derive the corresponding Langevin equation for a self-propelled Brownian spinning top. The biaxial swimmer is exposed to a hydrodynamic Stokes friction force at low Reynolds numbers, to fluctuating random forces and torques as well as to an external and an internal (effective) force and torque. The latter quantities control its self-propulsion. Due to biaxiality and hydrodynamic translational-rotational coupling, the Langevin equation can only be solved numerically. In the special case of an orthotropic particle in the absence of external forces and torques, the noise-free (zero-temperature) trajectory is analytically found to be a circular helix. This trajectory is confirmed numerically to be more complex in the general case of an arbitrarily shaped particle under the influence of arbitrary forces and torques involving a transient irregular motion before ending up in a simple periodic motion. By contrast, if the external force vanishes, no transient regime is found, and the particle moves on a superhelical trajectory. For orthotropic particles, the noise-averaged trajectory is a generalized concho-spiral. We furthermore study the reduction of the model to two spatial dimensions and classify the noise-free trajectories completely finding circles, straight lines with and without transients, as well as cycloids and arbitrary periodic trajectories. PMID:22463211

Wittkowski, Raphael; Löwen, Hartmut

2012-02-01

251

Incremental response of a model granular material by stress probing with DEM simulations  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We use DEM simulations on a simple 2D model of a granular material to test for the applicability of elastoplasticity (yield criterion, flow rule) to the response to stress increments of arbitrary directions. We apply stress probles in a three-dimensional stress space to various intermediate states (investigation points) along the biaxial compression path, and pay special attention to the influence of the magnitude of the increments The elastic part of the material response is systematically i...

Froiio, Francesco; Roux, Jean-noe?l

2010-01-01

252

Thermal fatigue loading for a type 304-L stainless steel used for pressure water reactor: investigations on the effect of a nearly perfect biaxial loading, and on the cumulative fatigue life  

International Nuclear Information System (INIS)

Fatigue-life curves are used in order to estimate crack-initiation, and also to prevent water leakage on Pressure Water Reactor pipes. Such curves are built exclusively from push-pull tests performed under constant and uniaxial strain or stress-amplitude. However, thermal fatigue corresponds to a nearly perfect biaxial stress state and severe loading fluctuations are observed in operating conditions. In this frame, these two aspects have been successively investigated in this paper: In order to investigate on potential difference between thermal fatigue and mechanical fatigue, tests have been carried out at CEA using thermal fatigue devices. They show that for an identical level of strain-amplitude, the number of cycles required to achieve crack-initiation is significantly lower under thermal fatigue. This enhanced damage results probably from a perfect biaxial state under thermal fatigue. In this frame, application of the multiaxial Zamrik's criterion seems to be very promising. In order to investigate on cumulative damage effect in fatigue, multi-level strain controlled fatigue tests have been performed. Experimental results show that linear Miner's rule is not verified. A loading sequence effect is clearly evidenced. The double linear damage rule ('DLDR') improves significantly predictions of fatigue-life. (authors)

253

Thermal fatigue loading for a type 304-L stainless steel used for pressure water reactor: investigations on the effect of a nearly perfect biaxial loading, and on the cumulative fatigue life  

Energy Technology Data Exchange (ETDEWEB)

Fatigue-life curves are used in order to estimate crack-initiation, and also to prevent water leakage on Pressure Water Reactor pipes. Such curves are built exclusively from push-pull tests performed under constant and uniaxial strain or stress-amplitude. However, thermal fatigue corresponds to a nearly perfect biaxial stress state and severe loading fluctuations are observed in operating conditions. In this frame, these two aspects have been successively investigated in this paper: In order to investigate on potential difference between thermal fatigue and mechanical fatigue, tests have been carried out at CEA using thermal fatigue devices. They show that for an identical level of strain-amplitude, the number of cycles required to achieve crack-initiation is significantly lower under thermal fatigue. This enhanced damage results probably from a perfect biaxial state under thermal fatigue. In this frame, application of the multiaxial Zamrik's criterion seems to be very promising. In order to investigate on cumulative damage effect in fatigue, multi-level strain controlled fatigue tests have been performed. Experimental results show that linear Miner's rule is not verified. A loading sequence effect is clearly evidenced. The double linear damage rule ('DLDR') improves significantly predictions of fatigue-life. (authors)

Fissolo, A.; Gourdin, C.; Bouin, P.; Perez, G. [CEA Saclay, Direct Etud Nucl DM2S, SEMT, LISN, F-91191 Gif Sur Yvette (France)

2010-07-01

254

Determination of structural steel service life under cyclic creep in plane stress state  

Energy Technology Data Exchange (ETDEWEB)

Results of cyclic creep tests are given for 15Kh2NMFA steel under uniaxial and biaxial tension. A relation is suggested for determining steel life under cyclic creep in the plane stressed state. Theoretical and experimental results are found to be in good agreement.

Giginyak, F.F.; Storcbak, M.V.

1983-10-01

255

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

International Nuclear Information System (INIS)

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)

256

Biaxial Texture Evolution of Nanostructured Films under Dynamic Shadowing Effect and Applications  

Science.gov (United States)

Texture formation and evolution in polycrystalline films are quite complicated, and they still remain as challenging subjects. Oblique angle deposition is an effective way to control the texture due to the shadowing effect introduced by oblique incident flux. A new dynamic oblique angle sputter deposition technique, called flipping rotation, was developed. In this rotation mode, the substrate is arranged to rotate continuously at a fixed speed around an axis lying within and parallel to the substrate. The incident flux is always perpendicular to the rotational axis and the flux incident angle relative to the substrate normal changes continuously. To study the texture formation and evolution of Mo and W films grown by DC magnetron sputter depositions, three film categories were prepared: (1) normal incidence deposition without the shadowing effect, (2) stationary oblique angle deposition at various fixed flux incident angles with static shadowing effect, and (3) convention rotation and flipping rotation deposition with dynamic shadowing effect. Under the normal incidence deposition, ultrathin (2.5 nm) to thin (100 nm) Mo films have been deposited on SO2 membranes on transmission electron microscopy (TEM) grids. These samples can be directly compared with the films grown on glass or native oxide covered Si substrates. The result of a fiber texture with the [110] out-of-plane direction implies that the growth has gone through a recrystallization process that selects the minimum surface energy plane parallel to the substrate. This is in contrast to the conventional understanding of the selection of out-of-plane orientation, which is the fastest growth direction [100] at room temperature based on the low Mo homologous temperature (room temperature/melting temperature) of ~0.1. Under stationary oblique angle deposition, Mo thin films in the range of 175 nm to 1300 nm were observed to undergo a dramatic change in crystal texture orientation from a (110)[11¯¯0] biaxial texture that has the minimum energy plane (110) parallel to the substrate surface at low oblique angle deposition (0capture area model where the in-plane texture favors the orientations along the largest capture area or length facing the flux. Under dynamic shadowing effect using the newly developed dynamic flipping rotation of the substrate, both Mo and W thin films in the range of 550 nm to 650 nm grown on amorphous substrates have (110)[11¯0] biaxial textures with a body center cubic (BCC) structure characterized by a reflection high-energy electron diffraction pole figure technique developed in house. Depending on the rotational speed in the flipping rotation, the biaxial textures can have various morphologies, such as vertical, S-shape, or C-shape nanocolumns, as observed by scanning electron microscopy. The possible growth mechanisms in the formation of various morphologies due to different degrees of shadowing effect were suggested. This is in contrast with the films grown by conventional rotation, which usually have fiber textures with different out-of-plane orientation, [111] for Mo, or even a different phase, A15 for W. The biaxial Mo(110) and W(110) thin films were used as buffer layers to grow semiconductor films of GaN for the LED applications and CdTe for the thin film photovoltaic applications. Detailed X-ray pole figure analyses show the heteroepitaxial growth of GaN/Mo, GaN/W, and CdTe/Mo. A prototype biaxial CdTe film based Schottky junction solar cell on biaxial Mo film has been fabricated and characterized. Although the open circuit voltage is small for the prototype device, th

Chen, Liang

257

Biaxially mechanical tuning of 2-D reversible and irreversible surface topologies through simultaneous and sequential wrinkling.  

Science.gov (United States)

Controlled buckling is a facile means of structuring surfaces. The resulting ordered wrinkling topologies provide surface properties and features desired for multifunctional applications. Here, we study the biaxially dynamic tuning of two-dimensional wrinkled micropatterns under cyclic mechanical stretching/releasing/restretching simultaneously or sequentially. A biaxially prestretched PDMS substrate is coated with a stiff polymer deposited by initiated chemical vapor deposition (iCVD). Applying a mechanical release/restretch cycle in two directions loaded simultaneously or sequentially to the wrinkled system results in a variety of dynamic and tunable wrinkled geometries, the evolution of which is investigated using in situ optical profilometry, numerical simulations, and theoretical modeling. Results show that restretching ordered herringbone micropatterns, created through sequential release of biaxial prestrain, leads to reversible and repeatable surface topography. The initial flat surface and the same wrinkled herringbone pattern are obtained alternatively after cyclic release/restretch processes, owing to the highly ordered structure leaving no avenue for trapping irregular topological regions during cycling as further evidenced by the uniformity of strains distributions and negligible residual strain. Conversely, restretching disordered labyrinth micropatterns created through simultaneous release shows an irreversible surface topology whether after sequential or simultaneous restretching due to creation of irregular surface topologies with regions of highly concentrated strain upon formation of the labyrinth which then lead to residual strains and trapped topologies upon cycling; furthermore, these trapped topologies depend upon the subsequent strain histories as well as the cycle. The disordered labyrinth pattern varies after each cyclic release/restretch process, presenting residual shallow patterns instead of achieving a flat state. The ability to dynamically tune the highly ordered herringbone patterning through mechanical stretching or other actuation makes these wrinkles excellent candidates for tunable multifunctional surfaces properties such as reflectivity, friction, anisotropic liquid flow or boundary layer control. PMID:24490823

Yin, Jie; Yagüe, Jose Luis; Boyce, Mary C; Gleason, Karen K

2014-02-26

258

Theory of biaxial graded-index optical fiber. M.S. Thesis  

Science.gov (United States)

A biaxial graded-index fiber with a homogeneous cladding is studied. Two methods, wave equation and matrix differential equation, of formulating the problem and their respective solutions are discussed. For the wave equation formulation of the problem it is shown that for the case of a diagonal permittivity tensor the longitudinal electric and magnetic fields satisfy a pair of coupled second-order differential equations. Also, a generalized dispersion relation is derived in terms of the solutions for the longitudinal electric and magnetic fields. For the case of a step-index fiber, either isotropic or uniaxial, these differential equations can be solved exactly in terms of Bessel functions. For the cases of an istropic graded-index and a uniaxial graded-index fiber, a solution using the Wentzel, Krammers and Brillouin (WKB) approximation technique is shown. Results for some particular permittivity profiles are presented. Also the WKB solutions is compared with the vector solution found by Kurtz and Streifer. For the matrix formulation it is shown that the tangential components of the electric and magnetic fields satisfy a system of four first-order differential equations which can be conveniently written in matrix form. For the special case of meridional modes, the system of equations splits into two systems of two equations. A general iterative technique, asymptotic partitioning of systems of equations, for solving systems of differential equations is presented. As a simple example, Bessel's differential equation is written in matrix form and is solved using this asymptotic technique. Low order solutions for particular examples of a biaxial and uniaxial graded-index fiber are presented. Finally numerical results obtained using the asymptotic technique are presented for particular examples of isotropic and uniaxial step-index fibers and isotropic, uniaxial and biaxial graded-index fibers.

Kawalko, Stephen F.

1990-01-01

259

Spin Squeezing of Superposition of Biaxial State and Two Qubit Bell State  

Science.gov (United States)

In this study we investigate the spin squeezing in superposition of a Biaxial state (Mallesh et al. in J. Phys. A, Math. Gen. 33:779-789, 2000 and Sirsi in Theoretical studies on spin distributions in external electric and magnetic fields, 1995) and Bell state. Numerical and analytical solutions for the length of mean spin, mean spin direction and spin squeezing are given. It is shown that both the mean spin direction and spin squeezing parameter are determined by the coefficients of superposition and the relative phase.

Ashourisheikhi, Sakineh

2014-04-01

260

Engineering of the space-variant linear polarization of vortex-beams in biaxially induced crystals.  

Science.gov (United States)

We considered the propagation of Bessel beams through the biaxially induced birefringent crystal implemented by the mechanical torsion of the uniaxial crystal around its optical axis. Analyzing the solutions to the wave equation in the form of eigenmodes, we found that the system enables us to convert the beams with a uniform distribution of the linear polarization at the beam cross section into radially, azimuthally, and spirally polarized beams. Moreover, we revealed that the above system permits us to convert the beams with the space-variant linear polarization in accordance with the rule -s?s+1, where s is the topological index of the centered polarization singularity. PMID:22505105

Fadeyeva, Tatyana A; Alexeyev, Constantin N; Anischenko, Pavel M; Volyar, Alexander V

2012-04-01

 
 
 
 
261

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

International Nuclear Information System (INIS)

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

262

Dynamic instabilities of fracture under biaxial strain using a phase field model  

CERN Document Server

We present a phase field model of the propagation of fracture under plane strain. This model, based on simple physical considerations, is able to accurately reproduce the different behavior of cracks (the principle of local symmetry, the Griffith and Irwin criteria, and mode-I branching). In addition, we test our model against recent experimental findings showing the presence of oscillating cracks under bi-axial load. Our model again reproduces well observed supercritical Hopf bifurcation, and is therefore the first simulation which does so.

Henry, H; Henry, Herve; Levine, Herbert

2004-01-01

263

Analytic expressions of optical retardation of biaxial compensation films for liquid crystal displays  

Science.gov (United States)

Analytic expressions of effective optical retardation and direction of the effective optic axis of biaxial plates for obliquely incident light are derived for small birefringence. The expressions are applied to optimize the birefringence of compensation films for liquid crystal displays with vertical surface alignment. Birefringence values of the compensation films are obtained in analytical form for a given retardation of the liquid crystal layer. Numerical calculations with the Berreman method confirm that compensation films with the birefringence calculated by the analytical expressions suppress light leakage at the black state much more than conventional compensation films with normal dispersion in wavelength.

Yang, Young-Cheol; Yang, Denge-Ke

2009-10-01

264

A Nanomembrane-Based Bandgap-Tunable Germanium Microdisk Using Lithographically-Customizable Biaxial Strain for Silicon-Compatible Optoelectronics  

CERN Document Server

Strain engineering has proven to be vital for germanium-based photonics, in particular light emission. However, applying a large permanent biaxial strain to germanium has been a challenge. We present a simple, CMOS-compatible technique to conveniently induce a large, spatially homogenous strain in microdisks patterned within ultrathin germanium nanomembranes. Our technique works by concentrating and amplifying a pre-existing small strain into the microdisk region. Biaxial strains as large as 1.11% are observed by Raman spectroscopy and are further confirmed by photoluminescence measurements, which show enhanced and redshifted light emission from the strained microdisks. Our technique allows the amount of biaxial strain to be customized lithographically, allowing the bandgaps of different microdisks to be independently tuned in a single mask process. Our theoretical calculations show that this platform can deliver substantial performance improvements, including a >200x reduction in the lasing threshold, to bia...

Sukhdeo, David S; Kang, Ju-Hyung; Brongersma, Mark L; Saraswat, Krishna C

2014-01-01

265

The characteristics of high-temperature biaxial fatigue strength in type 304 stainless steel for FBR high-temperature structures  

International Nuclear Information System (INIS)

As a link the chain of ''Study for practical use of Tank Type FBR'', ''Practical use of inelastic analysis method to FBR structural design'' is carried out as a cooperative study for three years from 1984. In a cooperative study, investigation such as high-temperature deformation behavior and high-temperature fatigue life characteristics of structure materials is one of the most important problems. So we conduct tension compresion-tortion tests with Type 304 stainless steel to evaluate biaxial fatigue life characteristics at high temperature. As the first step to investigate fatigue life characteristics of reactor vessel material subjected to cyclic thermalstress, we test under time independent fatigue condition. This report shows evaluation results of these tests. We find that biaxial fatigue lives have good relation to Brown's equivalent shear strain parameter which is biaxial fatigue evaluation parameter included crack propagation characteristics. (author)

266

Biaxially aligned MgO - buffer layers on metallic substrates for the deposition of YBCO - thin films  

International Nuclear Information System (INIS)

The crucial problem of YBCO - thin films on metallic substrates is to reach a sufficient critical current density considerably above a million A/cm2. Simply c - axes oriented growth during deposition is not sufficient, an additional orientation of the crystals in the plane parallel to the substrate is indispensable. Other groups demonstrated the possibility to deposit a biaxially aligned YSZ buffer - layer on polycrystalline Hastelloy substrates by Ion - Beam - Assisted - Deposition (IBAD). The practicability of these buffer layers to deposit biaxially aligned YBCO was established by X - ray pole figures and measurement of the critical current density. Here, a new sputtering procedure to deposit biaxially aligned buffer layers without an ion - beam gun will be presented. First results of the practicability of this deposition procedure and the achieved quality of the buffer layers will be discussed. (orig.)

267

Structural and electronic properties of wurtzite GaX (X = N, P, As, Sb, Bi) under in-plain biaxial strains  

Science.gov (United States)

Using first-principles density functional theory, we have investigated the structural and electronic properties of GaX (X = N, P, As, Sb, Bi) systems under in-plain biaxial strains. All GaX systems transfer from the typical wurtzite to pseudographitic phases when the in-plane tensile strains are large enough. Our findings indicate that the elastic stiffness coefficients have a direct correlation with the strains. The variations of the band gap energy are diverse with respect to the compressive and tensile biaxial strains. For tensile biaxial strains, the band gap decreases substantially as the increasing of the strains. Upon compressive biaxial strains, the band gap initially increases, and then undergoes a decline. In addition, we find that there exists an indirect to direct band gap transition of GaP at certain in-plane biaxial strains. These results give a good understanding of strain-based GaX series heteroepitaxy thin films.

Cao, Huawei; Lu, Pengfei; Zhang, Xianlong; Yu, Zhongyuan; Han, Lihong; Chen, Jun; Wang, Shumin

2014-03-01

268

Biaxiality of Liquid Crystal Formed by Bent-Core Molecules with a Transverse Dipole Moment Deviating from their Angular Bisector  

International Nuclear Information System (INIS)

Monte Carlo simulations are performed to study the phase diagram of liquid crystals formed by bent-core molecules with a strong transverse dipole moment deviating from their angular bisector. The results show that the strong dipolar interaction, after suppressing uniaxial phases, encourages biaxiality, which leads to a Landau point or even to a Landau line in the phase diagram, inducing a more stable biaxial nematic phase. It is also found that a deviation of dipole moment from the angular bisector also suppresses uniaxiality in the small bend-angle regime

269

Dynamic buckling of columns by biaxial moments and uniform end torque  

Science.gov (United States)

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.

Leung, A. Y. T.

2010-05-01

270

Novel properties of wave propagation in biaxially anisotropic left-handed materials  

CERN Document Server

Some physically interesting properties and effects of wave propagation in biaxially anisotropic left-handed materials are investigated in this paper. We show that in the biaxially gyrotropic left-handed material, the left-right coupling of circularly polarized light arises due to the negative indices in permittivity and permeability tensors of gyrotropic media. It is well known that the geometric phases of photons inside a curved fiber in previous experiments often depend on the cone angles of solid angles subtended by a curve traced by the direction of wave vector of light, at the center of photon momentum space. Here, however, for the light propagating inside certain anisotropic left-handed media we will present a different geometric phase that is independent of the cone angles. The extra phases of electromagnetic wave resulting from the instantaneous helicity inversion at the interfaces between left- and right- handed (LRH) media is also studied in detail by using the Lewis-Riesenfeld invariant theory. Som...

Shen, J Q

2003-01-01

271

Band gap engineering of FeS2 under biaxial strain: a first principles study.  

Science.gov (United States)

The promising photovoltaic activity of pyrite (FeS2) is attributed to its excellent optical absorptivity and earth abundance, but its band gap, 0.95 eV, is slightly lower than the optimum value of 1.3 eV. Here we report the first investigation of strained FeS2, whose band gap can be increased by ?0.3 eV. The influence of uniaxial and biaxial strains on the atomic structure as well as the electronic and optical properties of bulk FeS2 is systematically examined by the first principles calculations. We found that the biaxial strain can effectively increase the band gap with respect to uniaxial strain. Our results indicate that the band gap increases with increasing tensile strain to its maximum value at 6% strain, but under the increasing compressive strain, the band gap decreases almost linearly. Moreover, the low intensity states at the bottom of the conduction band disappear and a sharp increase in the intensity appears at the lower energy level under the tensile strain, which causes the red shift of the absorption edge and enhances the overall optical absorption. With the increase of the band gap and enhanced optical absorption, FeS2 will make a better photovoltaic material. PMID:25308322

Xiao, Pin; Fan, Xiao-Li; Liu, Li-Min; Lau, Woon-Ming

2014-10-21

272

Robust control for a biaxial servo with time delay system based on adaptive tuning technique.  

Science.gov (United States)

A robust control method for synchronizing a biaxial servo system motion is proposed in this paper. A new network based cross-coupled control and adaptive tuning techniques are used together to cancel out the skew error. The conventional fixed gain PID cross-coupled controller (CCC) is replaced with the adaptive cross-coupled controller (ACCC) in the proposed control scheme to maintain biaxial servo system synchronization motion. Adaptive-tuning PID (APID) position and velocity controllers provide the necessary control actions to maintain synchronization while following a variable command trajectory. A delay-time compensator (DTC) with an adaptive controller was augmented to set the time delay element, effectively moving it outside the closed loop, enhancing the stability of the robust controlled system. This scheme provides strong robustness with respect to uncertain dynamics and disturbances. The simulation and experimental results reveal that the proposed control structure adapts to a wide range of operating conditions and provides promising results under parameter variations and load changes. PMID:19345940

Chen, Tien-Chi; Yu, Chih-Hsien

2009-07-01

273

Method of depositing a protective layer over a biaxially textured alloy substrate and composition therefrom  

Science.gov (United States)

A laminate article consists of a substrate and a biaxially textured protective layer over the substrate. The substrate can be biaxially textured and also have reduced magnetism over the magnetism of Ni. The substrate can be selected from the group consisting of nickel, copper, iron, aluminum, silver and alloys containing any of the foregoing. The protective layer can be selected from the group consisting of gold, silver, platinum, palladium, and nickel and alloys containing any of the foregoing. The protective layer is also non-oxidizable under conditions employed to deposit a desired, subsequent oxide buffer layer. Layers of YBCO, CeO.sub.2, YSZ, LaAlO.sub.3, SrTiO.sub.3, Y.sub.2 O.sub.3, RE.sub.2 O.sub.3, SrRuO.sub.3, LaNiO.sub.3 and La.sub.2 ZrO.sub.3 can be deposited over the protective layer. A method of forming the laminate article is also disclosed.

Goyal, Amit (Knoxville, TN); Kroeger, Donald M. (Knoxville, TN); Paranthaman, Mariappan (Knoxville, TN); Lee, Dominic F. (Knoxville, TN); Feenstra, Roeland (Knoxville, TN); Norton, David P. (Gainesville, FL)

2002-01-01

274

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

International Nuclear Information System (INIS)

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

275

Biaxial creep deformation of Zircaloy-4 PWR fuel cladding in the alpha,(alpha + beta) and beta phase temperature ranges  

International Nuclear Information System (INIS)

The biaxial creep behaviour of Zircaloy-4 fuel cladding has been determined at temperatures between 973 - 1073 K in the alpha phase range, in the duplex (alpha + beta) region between 1098 - 1223 K and in the beta phase range between 1323 - 1473 K. This paper presents the creep data together with empirical equations which describe the creep deformation response within each phase region. (author)

276

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

Energy Technology Data Exchange (ETDEWEB)

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.

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

2009-08-27

277

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

Energy Technology Data Exchange (ETDEWEB)

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.

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

2009-04-29

278

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

LENUS (Irish Health Repository)

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.

2011-05-01

279

Effect of test temperature on micro crack growth behaviour for SUS316L stainless steel in biaxial low cycle fatigue; SUS316L ko no tajiku tei saikuru hiroka deno bisho kiretsu shinten kyodo ni oyobosu shiken ondo no eikyo  

Energy Technology Data Exchange (ETDEWEB)

In case of high temperature machines like steam turbine or gas turbine, thermal stress is caused by the temperature gradients and sorrounding restriction of the parts during use and this often becomes the cause for machine damage. In general, the thermal stress depends on the thermal expansion and the surrounding restriction, therefore, the stress condition is in multi axial stress condition. Therefore, it is necessary to consider the multiaxiality of stress and strain while evaluating the damage of parts. Further, in case of high temperature material subjected to repeated load, many microcracks are occurred and these are combined, grew and finally cause failure. Accordingly, in order to maintain the reliability of the machines, it is necessary to evaluate the damage by grasping the crack generation and propagation behavior. In this research, biaxial low cycle fatigue tests were conducted on SUS 316L stainless steel at room temperature, 550{degree}C and 650{degree}C, and the effect of stress multiaxiality and test temperature on microcrack growth behavior was studied. 8 refs., 9 figs., 1 tab.

Isobe, N.; Sakurai, S. [Hitachi Ltd., Tokyo (Japan). Mechanical Engineering Research Lab.

1995-12-15

280

Development of serial measurement system for three-dimensional stress determination by over-coring the strains on borehole wall  

International Nuclear Information System (INIS)

In order to determine the three-dimensional stress state in serial order, the authors developed the serial measurement system for three-dimensional stress determination by over-coring the strains on the borehole wall. The serial stress measurements give the value of the stresses with high accuracy and bring the regional stress variations. In this paper, the authors describe the studies through FEM analysis on the effect of over-coring diameter, the influence of strain gauge length and the behavior of strain on the borehole wall, induced by biaxial external loading. We developed the multi-strain gauge mounted packer and examined it by measuring the strains on the borehole wall through biaxial loading test. The Laboratory tests showed its applicability to practical use. (author)

 
 
 
 
281

Low energy ion beam assisted deposition of biaxially aligned yttria stabilized zirconia films on polycrystalline Ni-Cr alloy  

International Nuclear Information System (INIS)

(001)-oriented and in-plane aligned yttria stabilized zirconia (YSZ) thin films have been synthesized on polycrystalline Ni-Cr alloy substrates by low energy ion beam assisted deposition (IBAD). The biaxial alignment of YSZ films on polycrystalline substrates was found to be mainly controlled by the incident angle and energy of the bombarding Ar+ ions. Under incident angle of 55 and ion energy of 250-500 eV, optimal biaxial alignment of the film was obtained. The biaxial alignment of the YSZ needs about 1000 A thickness to develop. Monte Carlo method has been used to simulate the formation of YSZ biaxial alignment with Ar+ bombarding zirconia crystals oriented with left angle 001 right angle parallel to normal of the film. Results of the simulation indicate that when the energy of the bombarding ions is below 50 eV, there is no obvious difference in the sputtering yields and the radiation damage of zirconia between different incident angles. However with the ion energy increasing, the variation increases rapidly. When the ion energy reaches 250 eV, the sputtering yields and the radiation damage of the (001)-oriented zirconia induced by Ar+ bombardment along [111] direction (54.7 from [001]) of the zirconia are minimum as compared with those induced by Ar+ bombardment along other directions. It could be concluded that YSZ grains with [001] orientation normal to the substrate are far less sputtered than other oriented grains under ion beam bombardment at 55 incident angle, which causes (001)-oriented YSZ grains to prevail over initial random oriented grains. So that the biaxial alignment is formed. (orig.)

282

The Correlation of Stress-State and Nano-Mechanical Properties in Au  

International Nuclear Information System (INIS)

A dependence of elastic response on the stress-state of a thin film has been demonstrated using the interfacial force microscope (IFM). Indentation response was measured as a function of the applied biaxial stress-state for 100 nm thick Au films. An increase in measured elastic modulus with applied compressive stress, and a decrease with applied tensile stress was observed. Measurements of elastic modulus before and after applying stress were identical indicating that the observed change in response is not due to a permanent change in film properties

283

Pseudo-dynamic buckling experiments on thin cylindrical shells under biaxial seismic loads  

International Nuclear Information System (INIS)

A buckling design research program has been carried out to establish seismic design guidelines for a fast breeder reactor. In doing so, the buckling strength of the cylindrical part of the reactor vessel of a fast breeder reactor under horizontal and vertical seismic loads has been clarified. The effects of axial loads on the horizontal seismic responses in pre- and post-buckling states of thin cylindrical shells are investigated. Pseudo-dynamic buckling experiments are performed to study the dynamic buckling characteristics of thin cylindrical structures when subjected to seismic loads. The buckling tests use model cylinders made of an aluminum plate and a biaxial loading test apparatus. The axial seismic loads reduce the lateral load-carrying capacity of the shells in the pre- and post-buckling regions so that they amplify the horizontal response displacement. An amplification factor that accounts for the effects of the vertical loads is presented and its validity is verified experimentally. (orig.)

284

Pseudo-dynamic buckling experiment of thin cylindrical shells under biaxial seismic loads  

International Nuclear Information System (INIS)

Pseudo-dynamic budding experiments are performed to study the dynamic buckling characteristics of the main vessel of a fast breeder reactor when subjected to seismic loads. The effects of axial loads on the horizontal seismic responses in pre- and post-buckling states of thin cylindrical shells are investigated. The buckling tests use model cylinders made of aluminum plate and a biaxial loading test apparatus. The axial seismic loads reduce the lateral load carrying capacity of the shells in the pre- and post-buckling region so that they amplify the horizontal response displacement. An amplification factor that accounts for the effects of the vertical loads is presented and its validity is verified experimentally. (author)

285

Fatigue damage rule of LY12CZ aluminium alloy under sequential biaxial loading  

Science.gov (United States)

A series of biaxial two-level variable amplitude loading tests are conducted on smooth tubular specimens of LY12CZ aluminium alloy. The loading paths of 90° out-of-phase, 45° out-of-phase and 45° in-phase are utilized. The fatigue damage cumulative rules under two-level step loading of three loading paths are analyzed. By introducing a parameter ? which is a function of the phase lag angle between the axial and the torsional loading, a new multiaxial nonlinear fatigue damage cumulative model is proposed. The proposed model is evaluated by the experimental data for two-level loading, multi-level loading of LY12CZ aluminium alloy, and multi-level loading of 45 steel. Fatigue lives predicted are within a factor of 2 scatter band.

Wang, YingYu; Zhang, DaChuan; Yao, WeiXing

2014-01-01

286

Mechanism of in-plane alignment in magnetron sputtered biaxially aligned yttria-stabilized zirconia  

Science.gov (United States)

Biaxially aligned yttria-stabilized zirconia (YSZ) thin films were deposited on polycrystalline non-aligned stainless steel and amorphous glass by unbalanced magnetron sputtering. The mechanism responsible for the specific in-plane alignment has been investigated by carrying out specific depositions. The obtained results led to the proposed growth model. Also the influence of several deposition parameters (target-substrate distance, target-substrate angle and pressure) on the degree of in-plane alignment has been investigated. The degree of in-plane alignment depends on these parameters because they influence the angular spread of the incoming material flux during the deposition. This angular spread of the incoming material flux has been calculated by simulating the transport of sputtered particles through the gas phase. According to the proposed growth model there is a correlation between the calculated angular spread of the material flux and the experimentally observed in-plane alignment.

Mahieu, Stijn; Ghekiere, Pieter; Depla, Diederik; De Gryse, Roger; Lebedev, Oleg I.; Van Tendeloo, Gustaf

2006-04-01

287

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

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in english 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 glycosami [...] noglycans 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

Belinda, Pingguan-Murphy; Illida, Nawi.

288

Effect of film thickness and biaxial strain on the curie temperature of EuO  

Science.gov (United States)

The effects of film thickness and epitaxial strain on the magnetic properties of commensurate EuO thin films grown on single crystalline (001) yttria-stabilized zirconia (YSZ) and (110) LuAlO3 substrates are presented. Magnetic measurements show a reduction in the Curie temperature (TC) for EuO/YSZ films thinner than ˜10 nm. Additionally, the EuO/LuAlO3 films exhibit a systematically lower TC than the corresponding EuO/YSZ films. This further reduction in TC is attributed to the effect of biaxial tensile strain arising from lattice mismatch: 0.0% for EuO/YSZ and +1.0% for EuO/LuAlO3.

Melville, A.; Mairoser, T.; Schmehl, A.; Birol, T.; Heeg, T.; Holländer, B.; Schubert, J.; Fennie, C. J.; Schlom, D. G.

2013-02-01

289

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

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in english 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 glycosami [...] noglycans 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

Belinda, Pingguan-Murphy; Illida, Nawi.

2012-08-01

290

Uniaxial and biaxial mechanical characterization of a prosthetic mesh at different length scales.  

Science.gov (United States)

This study is aimed at a comprehensive experimental analysis of the mechanical behavior of a prosthetic mesh considering different length scales. Uniaxial and biaxial protocols are developed to evaluate global mechanical phenomena of the dry mesh. Furthermore, procedures for local deformation analysis and evaluation of corresponding homogenized kinematic measures are described. The global mechanical response of the prosthetic mesh is characterized by anisotropy, a nonlinear force response, hysteresis and preconditioning effects. The local deformation analysis allows to identify mesh specific phenomena related to mechanisms at the unit cell level. The global and the local kinematic responses of the mesh are seen to be directly related to clinical observations and help to understand associated complications, such as wrinkle formation, dislocation or erosion. In that sense, this study contributes to the analysis of mechanical biocompatibility of mesh implants and proposes protocols for comprehensive mesh product descriptions. PMID:24041753

Röhrnbauer, B; Mazza, E

2014-01-01

291

Mechanical Behaviour of Woven Graphite/Polyimide Composites with Medium and High Modulus Graphite Fibers Subjected to Biaxial Shear Dominated Loads  

Science.gov (United States)

A major limitation of woven fiber/polymer matrix composite systems is the inability of these materials to resist intralaminar and interlaminar damage initiation and propagation under shear-dominated biaxial loading conditions. There are numerous shear test methods for woven fabric composites, each with its own advantages and disadvantages. Two techniques, which show much potential, are the Iosipescu shear and +/- 45 deg tensile tests. In this paper, the application of these two tests for the room and high temperature failure analyses of woven graphite/polyimide composites is briefly evaluated. In particular, visco-elastic micro, meso, and macro-stress distributions in a woven eight harness satin (8HS) T650/PMR-15 composite subjected to these two tests are presented and their effect on the failure process of the composite is evaluated. Subsequently, the application of the Iosipescu tests to the failure analysis of woven composites with medium (T650) and high (M40J and M60J) modulus graphite fibers and PMR-15 and PMR-II-50 polyimide resins is discussed. The composites were tested as-supplied and after thermal conditioning. The effect of temperature and thermal conditioning on the initiation of intralaminar damage and the shear strength of the composites was established.

Kumose, M.; Gentz, M.; Rupnowski, P.; Armentrout, D.; Kumosa, L.; Shin, E.; Sutter, J. K.

2003-01-01

292

Growth of biaxially textured BaxPb1-xTiO3 ferroelectric thin films on amorphous Si3N4  

International Nuclear Information System (INIS)

We prepared highly aligned, biaxially textured BaxPb1-xTiO3 (PBT) on amorphous Si3N4 by using an ion-beam-assisted deposited MgO as a template layer. PBT was deposited on a biaxially textured MgO using sol-gel synthesis, metal-organic chemical-vapor deposition, and molecular beam epitaxy. The biaxial texture of the PBT was inherited from the MgO template. The reflection high-energy electron diffraction (RHEED) and cross-section transmission electron microscopy (TEM) experiments suggest that exposure of the MgO template to atmospheric moisture before PBT heteroepitaxy resulted in a significant narrowing of the PBT in-plane orientation distribution. The microstructures of the biaxially textured PBT films were analyzed by x-ray diffraction, RHEED, and TEM. The dynamic contact mode electrostatic force microscopy polarization hysteresis loops confirmed that these films are ferroelectric

293

Enantiotropic nematics from cross-like 1,2,4,5-tetrakis(4'-alkyl-4-ethynylbiphenyl)benzenes and their biaxiality studies.  

Science.gov (United States)

The theoretically predicted optimum length/breadth/width ratio for maximizing shape biaxiality was investigated experimentally by the facile and successful synthesis of cross-shaped compound 3, which showed enantiomeric nematic phase behavior. This cross-like core structure could alternatively be viewed as two fused V-shaped mesogens, which have recently immerged as a new direction in biaxial nematic research, at the bending tips that can act as a new structure for biaxial investigations. Whilst the thermal analysis data of compound 3 did not meet the expected theoretical values for biaxial nematics, surface-induced biaxiality was evidenced by optical studies. Cluster-size analysis within the nematic phase of compound 3 revealed the formation of meta-cybotactic nematics, which approached the cluster sizes of cybotactic nematics. The split small-angle 2D X-ray diffraction patterns of magnetic-field-aligned samples indicated that the nematic phase was composed of small smectic?C-like clusters with the tilting of molecules within the clusters. The wide-temperature-range enantiomeric nematic phase of cross-like compound 3 enabled the molecular skeleton to serve as an alternative skeleton to bent-rod mesogens, which exhibited nematic phases with the potential competition of transitions to higher-order liquid-crystalline phases and crystallization, for future biaxial investigations. PMID:22745006

Chen, Hsiu-Hui; Lin, Hsing-An; Lai, Yin-Hui; Lin, Shu-Yu; Chiang, Chien-Hung; Hsu, Hsiu-Fu; Shih, Tzenge-Lien; Lee, Jey-Jau; Lai, Chien-Chen; Kuo, Ting-Shen

2012-07-27

294

High-cycle and long-life fatigue of 25CrMo4 under multiaxial load conditions by three alternating stresses  

International Nuclear Information System (INIS)

Statistically verified experimental results from high-cycle and long-life fatigue tests (HCF and LLF) with altogether 537 unnotched solid cylindrical and thin-walled hollow specimen are demonstrating the fatigue behaviour (S-N-characteritics, scatterband) of 25CrMo4 under uniaxial loading with superimposed static stresses (consideration of the mean stress effect) and under biaxial loadings in variation of phase differences between the three combined normal and torsional stresses ?x, ?y, ?xy. The fatigue strength is commonly decreasing with life time in the high-cycle regime until reaching the fatigue endurance limit in the transition range to infinite life. The 'ductility level' ?W/?W and the 'mean stress sensibility' p=p (?W, ?zSch, Rm) are relatively independent of the intensity by stress amplitudes and fatigue life to failure. In comparison with the specific case of biaxial combined loading with synchroneous amplitudes, the fatigue resistance characteristics are detrimentally influenced by out-of-phase normal stresses ?x, ?y; a phase difference of 180deg between the normal stress amplitudes is the most critical state of combination, especially in the lower cycle regime caused by a greater slope coefficient (probability of survival Ps=50%). On the contrary is there in the high-cycle regime as well as in the long-life range no significant influence to the fatigue strength by biaxial load conditions of simultaneously normal stresses with out-of-phase torsional stress ?xy. (orig.)

295

Structural and electronic properties of LaO ?-doped SrTiO3 caused by biaxial strain  

Science.gov (United States)

?-doping in SrTiO3 plays a pivotal role for oxide electronics. By first-principles density functional calculations, we reveal that the electronic and structural properties of LaO ?-doped SrTiO3 can be drastically altered by compressive biaxial inplane strains. We predict the existence of a critical inplane strain (?c) above which many interesting phenomena occur, including (i) a profound symmetry breaking to the doping-induced electron states, (ii) a dramatic decline of the electron potential over a short distance of 2.5 Å near the doping layer, (iii) a new structure pattern of cation-anion displacements, and (iv) the emergence of unusual downward dispersions in the conduction bands with negative effective masses for electrons. The microscopic insight for these interesting phenomena is provided. Our study demonstrates that biaxial inplane strain can effectively modify the electronic properties in ?-doped SrTiO3 for the purpose of oxide electronics.

Adhikari, Rajendra; Fu, Huaxiang

2014-09-01

296

Atomistic analysis of strain relaxation in [11xAF0]-oriented biaxially strained ultrathin copper films  

Science.gov (United States)

Results are reported of a systematic atomic-scale computational analysis of strain relaxation mechanisms and the associated defect dynamics in nanometer-scale thin or ultrathin Cu films that are subjected to a broad range of biaxial tensile strains. The films contain pre-existing voids and the film planes are oriented normal to the [11¯0] crystallographic direction. The analysis is based on isothermal-isostrain molecular-dynamics simulations according to an embedded-atom-method parameterization for Cu and employing multimillion-atom slab supercells. In addition to an initial elastic response for an applied biaxial strain level ?Gungor and D. Maroudas, J. Appl. Phys. 97, 113527 (2005); M. R. Gungor and D. Maroudas, Appl. Phys. Lett. 87, 171913 (2005)].

Kolluri, Kedarnath; Gungor, M. Rauf; Maroudas, Dimitrios

2009-11-01

297

Electronic and magnetic properties of vanadium doped AlN nanosheet under in-plane biaxial strains  

Science.gov (United States)

First-principles calculations have been performed to investigate the electronic and magnetic properties of V-doped AlN nanosheet under in-plane biaxial strains. It is found that V atom favors to substitute for Al site with the lowest formation energy. The magnetic coupling of three different configurations are studied and configuration I is demonstrated to possess room temperature ferromagnetism. The stable ferromagnetic coupling is mediated by double exchange mechanism. In addition, the in-plane biaxial strains corresponding to tensile and compressive strains can affect and manipulate the magnetic interaction of V-doped AlN nanosheet in different ways. These results are conductive to design AlN based two dimensional diluted magnetic semiconductors.

Cao, Huawei; Lu, Pengfei; Yu, Zhongyuan; Chen, Jun; Wang, Shumin

2014-09-01

298

Transport anisotropy in biaxially strained La(2/3)Ca(1/3)MnO(3) thin films  

CERN Document Server

Due to the complex interplay of magnetic, structural, electronic, and orbital degrees of freedom, biaxial strain is known to play an essential role in the doped manganites. For coherently strained La(2/3)Ca(1/3)MnO(3) thin films grown on SrTiO(3) substrates, we measured the magnetotransport properties both parallel and perpendicular to the substrate and found an anomaly of the electrical transport properties. Whereas metallic behavior is found within the plane of biaxial strain, for transport perpendicular to this plane an insulating behavior and non-linear current-voltage characteristics (IVCs) are observed. The most natural explanation of this anisotropy is a strain induced transition from an orbitally disordered ferromagnetic state to an orbitally ordered state associated with antiferromagnetic stacking of ferromagnetic manganese oxide planes.

Klein, J; Carbone, G; Vigliante, A; Alff, L; Gross, R

2002-01-01

299

Effect of residual stress on the nanoindentation response of (100) copper single crystal  

International Nuclear Information System (INIS)

Experimental measurements were used to investigate the effect of residual stress on the nanoindentation of (100) copper single crystal. Equi-biaxial tensile and compressive stresses were applied to the copper single crystal using a special designed apparatus. It was found that residual stresses greatly affected peak load, curvature of the loading curve, elastically recovered depth, residual depth, indentation work, pile-up amount and contact area. The Suresh and Giannakopoulos and Lee and Kwon methods were used to calculate the residual stresses from load-depth data and morphology observation of nanoindents using atomic force microscopy. Comparison of the obtained results with stress values from strain gage showed that the residual stresses analyzed from the Suresh and Giannakopoulos model agreed well with the applied stresses. -- Highlights: ? Residual stresses greatly affected various nanoindentation parameters. ? The contact area can be accurately measured from AFM observation. ? The residual stresses analyzed from the S and G model agreed well with applied stresses.

300

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

International Nuclear Information System (INIS)

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)

 
 
 
 
301

Aspects thermodynamiques du comportement en fluage biaxial de l'aluminium (99,5 % en poids) à haute température  

Digital Repository Infrastructure Vision for European Research (DRIVER)

La connaissance antérieure d'un potentiel d'écoulement en fluage biaxial permet de développer un modèle thermodynamique de comportement viscoplastique à un seul type de variables internes. Avec l'introduction d'une variable interne (de vitesse de déformation), duale de la contrainte interne; nous pouvons identifier : — la puissance de dissipation intrinsèque ?, — l'énergie libre ? H, — la fonction de dissipation D. Une application quantitative est donnée dans le cas du compor...

Lexcellent, Ch

1984-01-01

302

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

International Nuclear Information System (INIS)

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.)

303

Incremental stress-strain law for graphite under multiaxial loadings  

International Nuclear Information System (INIS)

An incremental stress-strain law for describing the nonlinear, compressible and asymmetric behavior of graphite under tension and compression as well as complex loadings is derived based on a dry friction model in the theory of plasticity. Stress-strain relations are defined by longitudinal-lateral strain measurements for specimens under uniaxial tension-compression. Agreements with experimentally determined curves from biaxial loading experiments are shown. Agreements in finite element computations using the present model with strain measurements for diametral compression and 4-point bend tests of graphite are also obtained. (orig.)

304

Incremental stress-strain law for graphite under multiaxial loadings  

International Nuclear Information System (INIS)

An incremental stress-strain law for describing the nonlinear, compressible and asymmetric behavior of graphite under tension and compression as well as complex loadings is derived based on a dry friction model in the theory of plasticity. Stress-strain relations are defined by longitudinal-lateral strain measurements for specimens under uniaxial tension-compression. Agreements with experimentally determined curves from biaxial loading experiments are shown. Agreements in finite element computations using the present model with strain measurements for diametral compression and 4-point bend tests of graphite are also obtained

305

Buffer layers on metal surfaces having biaxial texture as superconductor substrates  

Science.gov (United States)

Buffer layer architectures are epitaxially deposited on biaxially-textured rolled substrates of nickel and/or copper and their alloys for high current conductors, and more particularly buffer layer architectures such as Y.sub.2 O.sub.3 /Ni, YSZ/Y.sub.2 O.sub.3 /Ni, RE.sub.2 O.sub.3 /Ni, (RE=Rare Earth), RE.sub.2 O.sub.3 /Y.sub.2 O.sub.3 /Ni, RE.sub.2 O.sub.3 /CeO.sub.2 /Ni, and RE.sub.2 O.sub.3 /YSZ/CeO.sub.2 /Ni, Y.sub.2 O.sub.3 /Cu, YSZ/Y.sub.2 O.sub.3 /Cu, RE.sub.2 O.sub.3 /Cu, RE.sub.2 O.sub.3 /Y.sub.2 O.sub.3 /Cu, RE.sub.2 O.sub.3 /CeO.sub.2 /Cu, and RE.sub.2 O.sub.3 /YSZ/CeO.sub.2 /Cu. Deposition methods include physical vapor deposition techniques which include electron-beam evaporation, rf magnetron sputtering, pulsed laser deposition, thermal evaporation, and solution precursor approaches, which include chemical vapor deposition, combustion CVD, metal-organic decomposition, sol-gel processing, and plasma spray.

Paranthaman, Mariappan (Knoxville, TN); Lee, Dominic F. (Knoxville, TN); Kroeger, Donald M. (Knoxville, TN); Goyal, Amit (Knoxville, TN)

2000-01-01

306

The formation of vertically aligned biaxial tungsten nanorods using a novel shadowing growth technique  

Energy Technology Data Exchange (ETDEWEB)

Biaxially textured tungsten nanorods (A15 crystal structure) have been grown by oblique angle DC magnetron sputtering using a novel rotation mode called 'two-step rotation'. In this mode, the substrate is given a fast rotation through 180{sup 0} at 90 rpm and this is followed by a rest period of 30 s. These nanorods are vertically aligned and have a [100] texture normal to the substrate along with preferential in-plane texture as shown by x-ray pole figure analysis. In contrast, the tungsten nanorods obtained without substrate rotation are slanted at an angle of {approx}45{sup 0} and have a [100] texture tilted 16{sup 0} with respect to the substrate normal. The flux is incident from two diametrically opposite points on the sample at an oblique angle, averaging out the growth into vertical columns that retain the in-plane texture. Scanning electron microscopy shows that the tungsten nanorods have a mixture of {l_brace}211{r_brace} and {l_brace}421{r_brace} crystal habits; these planes are both minimum surface energy planes for a cubic A15 crystal structure.

Krishnan, R [Department of Materials Science and Engineering, Rensselaer Polytechnic Institute, 110 8th Street, Troy, NY 12180 (United States); Parker, T; Lu, T-M [Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, 110 8th Street, Troy, NY 12180 (United States); Lee, S [US Army Armament Research, Development and Engineering Center, Benet Labs, Watervliet, NY 12189 (United States)

2009-11-18

307

Analysis of biaxial strain in InN(0001) epilayers grown by molecular beam epitaxy  

International Nuclear Information System (INIS)

The in-plane lattice parameters of InN, GaN and Al2O3 in a InN/GaN/Al2O3(0001) heterostructure have been measured as a function of temperature in the range of 25-350 C, using high resolution X-ray diffraction. The results reveal that both the GaN and InN crystals follow the in-plane thermal expansion of the Al2O3 substrate's lattice and there is no rearrangement of misfit dislocations at the InN/GaN and GaN/Al2O3 interfaces. It was also found that either compressive or tensile character of residual biaxial strain is possible for the InN films, depending on the two-dimensional (2D) or three-dimensional (3D) growth mode of InN on the GaN(0001) buffer layer. The tensile strain is inherent to the nucleation and coalescence of 3D islands. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

308

Uniaxial and biaxial properties of terminally sterilized porcine urinary bladder matrix scaffolds.  

Science.gov (United States)

Scaffolds composed of extracellular matrix have been successfully used to support the reconstruction of a variety of tissues in preclinical studies and in clinical applications. As an off-the-shelf product, extracellular matrix (ECM) scaffolds must be subjected to terminal sterilization before use. The choice of sterilization method may alter the integrity of the ECM's composition and structure such that the mechanical and material properties are adversely affected. The present study evaluated selected structural properties of an ECM scaffold derived from the urinary bladder termed urinary bladder matrix after being sterilized by three different methods: ethylene oxide (ETO) (750 mg/h for 16 h), gamma irradiation (2.0 Mrads), or electron beam irradiation (e-beam) (2.2 Mrads). The structural properties that were evaluated include maximum force, maximum elongation, maximum tangential stiffness, energy dissipation, and ball-burst strength. All sterilization methods affected at least two of the measured properties. ETO was shown to have the least detrimental effect upon the measured properties. Gamma and e-beam irradiation were shown to decrease the uniaxial and biaxial strength, maximum tangential stiffness, and the energy dissipation of the ECM scaffolds. The present study showed that the choice of terminal sterilization method affects the structural properties of scaffolds composed of extracellular matrix. PMID:17618508

Freytes, Donald O; Stoner, Richard M; Badylak, Stephen F

2008-02-01

309

On constitutive descriptors of the biaxial mechanical behaviour of human abdominal aorta and aneurysms.  

Science.gov (United States)

The abdominal aorta (AA) in older individuals can develop an aneurysm, which is of increasing concern in our ageing population. The structural integrity of the ageing aortic wall, and hence aneurysm, depends primarily on effective elastin and multiple families of oriented collagen fibres. In this paper, we show that a structurally motivated phenomenological 'four-fibre family' constitutive relation captures the biaxial mechanical behaviour of both the human AA, from ages less than 30 to over 60, and abdominal aortic aneurysms. Moreover, combining the statistical technique known as non-parametric bootstrap with a modal clustering method provides improved confidence intervals for estimated best-fit values of the eight associated constitutive parameters. It is suggested that this constitutive relation captures the well-known loss of structural integrity of elastic fibres owing to ageing and the development of abdominal aneurysms, and that it provides important insight needed to construct growth and remodelling models for aneurysms, which in turn promise to improve our ability to predict disease progression. PMID:20659928

Ferruzzi, J; Vorp, D A; Humphrey, J D

2011-03-01

310

Fabrication of biaxially textured Cu-Ni alloy tapes for YBCO coated conductor  

Science.gov (United States)

Nickel is well suited as a substrate material for YBa 2Cu 3O 7- x coated conductors. However, nickel’s ferromagnetism leads to AC losses when it is used in AC applications. In this paper, Cu-Ni non-magnetic tapes were made for YBa 2Cu 3O 7- x film deposition. The biaxially textured Cu-Ni alloy tapes were formed through heavy cold rolling followed by recrystallization heat treatment. Cu-Ni alloy tapes with sharp cube texture, full width at half maximum (FWHM) less than 9° for X-ray (1 1 1) ?-scan, were obtained. The NiO(2 0 0) buffer layer was formed on Cu-Ni alloy tapes by using surface-oxidation epitaxy method. The textures of the substrate and the NiO(2 0 0) buffer layer were characterized by X-ray diffraction ?-2 ?-scan, ?-scan and pole figures. The surface morphology of NiO buffer layer on the Cu-Ni alloy tapes was observed by scanning electron microscope.

Shi, K.; Zhou, Y.; Meng, J.; Yang, J.; Hu, G. Y.; Gu, H. W.; Yuan, G. S.

2003-04-01

311

The formation of vertically aligned biaxial tungsten nanorods using a novel shadowing growth technique  

International Nuclear Information System (INIS)

Biaxially textured tungsten nanorods (A15 crystal structure) have been grown by oblique angle DC magnetron sputtering using a novel rotation mode called 'two-step rotation'. In this mode, the substrate is given a fast rotation through 1800 at 90 rpm and this is followed by a rest period of 30 s. These nanorods are vertically aligned and have a [100] texture normal to the substrate along with preferential in-plane texture as shown by x-ray pole figure analysis. In contrast, the tungsten nanorods obtained without substrate rotation are slanted at an angle of ?450 and have a [100] texture tilted 160 with respect to the substrate normal. The flux is incident from two diametrically opposite points on the sample at an oblique angle, averaging out the growth into vertical columns that retain the in-plane texture. Scanning electron microscopy shows that the tungsten nanorods have a mixture of {211} and {421} crystal habits; these planes are both minimum surface energy planes for a cubic A15 crystal structure.

312

A threshold-based fall-detection algorithm using a bi-axial gyroscope sensor.  

Science.gov (United States)

A threshold-based algorithm, to distinguish between Activities of Daily Living (ADL) and falls is described. A gyroscope based fall-detection sensor array is used. Using simulated-falls performed by young volunteers under supervised conditions onto crash mats and ADL performed by elderly subjects, the ability to discriminate between falls and ADL was achieved using a bi-axial gyroscope sensor mounted on the trunk, measuring pitch and roll angular velocities, and a threshold-based algorithm. Data analysis was performed using Matlab to determine the angular accelerations, angular velocities and changes in trunk angle recorded, during eight different fall and ADL types. Three thresholds were identified so that a fall could be distinguished from an ADL: if the resultant angular velocity is greater than 3.1 rads/s (Fall Threshold 1), the resultant angular acceleration is greater than 0.05 rads/s(2) (Fall Threshold 2), and the resultant change in trunk-angle is greater than 0.59 rad (Fall Threshold 3), a fall is detected. Results show that falls can be distinguished from ADL with 100% accuracy, for a total data set of 480 movements. PMID:17222579

Bourke, A K; Lyons, G M

2008-01-01

313

High Current Density YBCO Coated Conductors On Strengthened Biaxially Textured Ni-W Substrates  

International Nuclear Information System (INIS)

High current density YBa2Cu3O7-? (YBCO) films were fabricated on rolling-assisted biaxially textured substrates (RABiTS) with a layer sequence of CeO2/YSZ/(dip-coated or e-beam seed)/Ni-W (3 at. %). Electron-beam evaporation was used to deposit Y2O3 seed layers. A reel-to-reel continuous dip-coating unit was used to deposit Gd2O3 and La2Zr2O7 (LZO) seed layers. Scanning Auger Microprobe analysis of the textured Ni-W substrates indicated the presence of sulfur segregation at the surface. This possibly facilitated the growth of epitaxial e-beam Y2O3 seed layers directly on Ni-W substrates through sulfur c2x2 superstructure. Highly aligned, continuous and crack-free Y2O3, Gd2O3, LZO seed layers were obtained. Both YSZ and CeO2 cap layers were deposited on all of these seed layers using rf-magnetron sputtering. The YBCO films were then grown on these buffered Ni-W substrates by either pulsed laser deposition (PLD) or ex-situ BaF2 precursor process. A high Jc of 1.9 MA/cm2 at 77 K and self-field was obtained on both Y2O3 and LZO seed layers. The performance of solution seed layers approached that of the vacuum seed layers

314

From numerical calculations to materials testing homologation: a biaxial fatigue reliability prediction methodology for structural components  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in english This article investigates a fatigue approach conducted from the design phase to testing approval. It considerers modern analytical and experimental tools for structural durability assessment over each development phase for two reference components aiming an early approval methodology validation for [...] a new design. A Finite element analysis procedure was used to set critical spots for measurements minimizing the data acquisition efforts. Based on measured data, strain life calculation was done for two reference components in order to set the release goals for a new design submitted to this approach. An innovative fatigue experimental technique is proposed using component extracted specimens and an edited input cycle loads. Considering the random data from a standard test track and signal proportionality evaluation, while assuming the Brown Miller equation for bi-axial fatigue together with Ramberg-Osgood model, equivalent damage load blocks were edited and used as input for durability assessment on specimens representing the component material. The results for the three parts materials were plotted as Weibull diagram for B10 life estimation. Fatigue life results showed good correlation with the reference parts structural performance thus validating the method as well as approving the new design for production without additional on-vehicle durability testing. The methodology and the fatigue testing proposal is therefore recommended for future applications on similar developments.

Daniel Muller, Spinelli; Caio de Carvalho, Scozzafave; Dirceu, Spinelli; Waldek Wladimir, Bose Filho.

1237-12-01

315

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

Energy Technology Data Exchange (ETDEWEB)

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.

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

1999-04-20

316

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

International Nuclear Information System (INIS)

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

317

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

Science.gov (United States)

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 300Hz. The total charge calculated by the charging current indicates that the stored charge in the capacitor under the electric field of 400 V/?m 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.

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

2013-10-01

318

Optical emission of biaxial ZnO-ZnS nanoribbon heterostructures  

Science.gov (United States)

The electronic structure and optical properties of biaxial ZnO-ZnS heterostructure nanoribbons (NRs) have been investigated using x-ray absorption near-edge structures (XANES) and x-ray excited optical luminescence (XEOL). The XANES were recorded in total electron yield and wavelength-selected photoluminescence yield across the K- and L3,2-edges of zinc and sulfur and the K-edge of oxygen. The XEOL from the NRs exhibit a very weak band-gap emission at 392 nm and two intense defect emissions at 491 and 531 nm. The synchrotron x-ray pulse (˜100 ps, 153 ns repetition rate) was used to track the optical decay dynamics from ZnO-ZnS NR, which can be described by two lifetimes (7.6 and 55 ns). Comparison with similar measurements for ZnO and ZnS nanowires reveals that the luminescence from ZnO-ZnS NRs was dominated by the ZnO component of the NR as the ZnS component contributes little. The implication of this observation is discussed.

Murphy, M. W.; Zhou, X. T.; Ko, J. Y. P.; Zhou, J. G.; Heigl, F.; Sham, T. K.

2009-02-01

319

Optical emission of biaxial ZnO?ZnS nanoribbon heterostructures  

Energy Technology Data Exchange (ETDEWEB)

The electronic structure and optical properties of biaxial ZnO-ZnS heterostructure nanoribbons (NRs) have been investigated using x-ray absorption near-edge structures (XANES) and x-ray excited optical luminescence (XEOL). The XANES were recorded in total electron yield and wavelength-selected photoluminescence yield across the K- and L{sub 3,2}-edges of zinc and sulfur and the K-edge of oxygen. The XEOL from the NRs exhibit a very weak band-gap emission at 392 nm and two intense defect emissions at 491 and 531 nm. The synchrotron x-ray pulse (- 100 ps, 153 ns repetition rate) was used to track the optical decay dynamics from ZnO-ZnS NR, which can be described by two lifetimes (7.6 and 55 ns). Comparison with similar measurements for ZnO and ZnS nanowires reveals that the luminescence from ZnO-ZnS NRs was dominated by the ZnO component of the NR as the ZnS component contributes little. The implication of this observation is discussed.

Murphy, M.W.; Zhou, X.T.; Ko, J.Y.P.; Zhou, J.G.; Heigl, F.; Sham, T.K.; (UWO)

2009-03-25

320

Plasma Surface Functionalization of Biaxially Oriented Polypropylene Films with Trimethyl Borate  

Directory of Open Access Journals (Sweden)

Full Text Available The radiofrequency plasma (13.56 MHz was employed to polymerize trimethyl borate (TMB monomer/N2 gas mixture on the surface of biaxially oriented polypropylene (BOPP films. Plasma polymer coated polypropylene films were examined by flame retardancy test (limiting oxygen index, LOI. The highest LOI value calculated for the untreated BOPP sample was 18.4 (v/v O2% and 24.2 (v/v O2% for the 55 W 30 minutes treated sample. The plasma polymers were characterized by FTIR spectroscopy and AFM. According to the FTIR results, the -OH, B-CH3, B-O, and BH2 functional groups were detected. It was found that the highest surface roughness belonged to 40 W 30 min treated BOPP sample which was calculated as 9.78 nm (10 ?m × 10 ?m. Moreover, the wettability of the modified BOPP film surfaces was characterized via contact angle measurements. The water contact angle values have decreased from 109.6? to the lowest value of 68.2? after the plasma treatment. The results showed that TMB/N2 plasma modification could be used as an alternative method for the enhancement of flame retardancy and hydrophilicity of BOPP film.

Nursel Dilsiz

2011-09-01

 
 
 
 
321

The formation of vertically aligned biaxial tungsten nanorods using a novel shadowing growth technique.  

Science.gov (United States)

Biaxially textured tungsten nanorods (A15 crystal structure) have been grown by oblique angle DC magnetron sputtering using a novel rotation mode called 'two-step rotation'. In this mode, the substrate is given a fast rotation through 180 degrees at 90 rpm and this is followed by a rest period of 30 s. These nanorods are vertically aligned and have a [100] texture normal to the substrate along with preferential in-plane texture as shown by x-ray pole figure analysis. In contrast, the tungsten nanorods obtained without substrate rotation are slanted at an angle of approximately 45 degrees and have a [100] texture tilted 16 degrees with respect to the substrate normal. The flux is incident from two diametrically opposite points on the sample at an oblique angle, averaging out the growth into vertical columns that retain the in-plane texture. Scanning electron microscopy shows that the tungsten nanorods have a mixture of {211} and {421} crystal habits; these planes are both minimum surface energy planes for a cubic A15 crystal structure. PMID:19847032

Krishnan, R; Parker, T; Lee, S; Lu, T-M

2009-11-18

322

Radiative recombination and optical gain spectra in biaxially strained n-type germanium  

Science.gov (United States)

We calculate band-to-band radiative transition rate spectra in pure Ge as functions of applied tensile strain, heavy doping, charge injection density, and temperature. Direct and indirect phonon-assisted transitions are considered. Deformation potential theory is adopted to describe the conduction and valence near-gap edges. Biaxial strain has required appropriate treatment of system anisotropy through the evaluation of the mass tensor components for the different bands involved in the studied transitions. Population distribution in the ? and L conduction valleys and in the valence states near ? have been evaluated accordingly considering the degeneracy condition of the sample, induced by high doping and high injection charge density. Also the effect of strain on the dipole matrix elements have been properly taken into account. The energy-resolved near-infrared spontaneous recombination spectra and the TE and TM polarized absorption/gain spectra have been obtained for a broad range of n-type doping, strain values, and excitation densities. We conclude that, despite the free carrier losses, net gain values as high as 6000 cm-1, are achievable for doping density and strain values reported in the literature.

Virgilio, M.; Manganelli, C. L.; Grosso, G.; Pizzi, G.; Capellini, G.

2013-06-01

323

Study of the superconducting phase in silicene under biaxial tensile strain  

Science.gov (United States)

The electron-doped silicene under the influence of the biaxial tensile strain is predicted to be the phonon-mediated superconductor. By using the Eliashberg formalism, we investigate the thermodynamic properties of the superconducting silicene in the case when the tension is 5% and the electron doping equals 3.5×1014 cm-2. Under such conditions, silicene monolayer is expected to exhibit the highest superconducting transition temperature (TC). In particular, based on the electron-phonon spectral function and assuming a wide range of the Coulomb pseudopotential values (???) it is stated that the superconducting transition temperature decreases from 18.7 K to 11.6 K. Similar behavior is observed in the case of the zeroth temperature superconducting energy gap at the Fermi level: 2?(0)? meV. Other thermodynamic parameters differ from the predictions of the Bardeen-Cooper-Schrieffer theory. In particular, the ratio of the energy gap to the critical temperature changes in the range from 4.14 to 3.87. The ratio of the specific heat jump to the specific heat in the normal state takes the values from 2.19 to 2.05, and the ratio of the critical temperature and specific heat in the normal state to the thermodynamic critical field increases from 0.143 to 0.155. It is also determined that the maximum value of the electron effective mass equals 2.11 of the electron band mass.

Durajski, A. P.; Szcz??niak, D.; Szcz??niak, R.

2014-12-01

324

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

International Nuclear Information System (INIS)

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

325

Time-dependent strains and stresses in a pumpkin balloon  

Science.gov (United States)

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:

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

2006-01-01

326

Residual stresses in weld-clad reactor pressure vessel steel  

International Nuclear Information System (INIS)

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 approximatalstress 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

327

Polymerization shrinkage and stress development in amorphous calcium phosphate/urethane dimethacrylate polymeric composites  

Digital Repository Infrastructure Vision for European Research (DRIVER)

This study explores how substituting a new high molecular mass oligomeric poly(ethylene glycol) extended urethane dimethacrylate (PEG-U) for 2-hydroxyethyl methacrylate (HEMA) in photo-activated urethane dimethacrylate (UDMA) resins affects degree of vinyl conversion (DC), polymerization shrinkage (PS), stress development (PSSD) and biaxial flexure strength (BFS) of their amorphous calcium phosphate (ACP) composites. The composites were prepared from four types of resins (UDMA, PEG-U, UDMA/HE...

Antonucci, J. M.; Regnault, W. F.; Skrtic, D.

2010-01-01

328

Biaxial thermomechanical fatigue on a 304L-type austenitic stainless steel  

International Nuclear Information System (INIS)

Various components of nuclear power plants are submitted to very sharp multiaxial thermomechanical loadings, due for instance to the incomplete mixing of flows at different temperatures. As an example, thermal fatigue damage has been detected in auxiliary loops of the primary cooling circuits of Pressurized Water Reactors. In particular, crack networks were observed in in-service pipes submitted to thermomechanical loading resulting from cyclic temperature gradients across the wall-thickness of components in 304 L type austenitic stainless steel. The thermal fatigue behaviour of AISI 304 L type steel has been studied using a specific thermal fatigue test, called Splash, developed in order to reproduce experimentally such thermomechanical biaxial loading in the thickness of parallelepipedic specimens. All tests have been performed at a maximum temperature of 320 C, but with different minimum temperatures. First, the morphological characteristics of the growing networks were analysed, in surface and in depth. Crack initiation is multiple and occurs on sliding lines or at material defects. Crack network stabilization is observed after 400 000 cycles at a temperature of 150 C. The maximum depth is 2.5 mm. Secondly, the stability of the thermal-fatigue crack-networks previously obtained was investigated under additional isothermal mechanical loading (four-point bend tests). Selection mechanisms of a dominating crack are observed, showing a great influence of shielding effehowing a great influence of shielding effects, branching and tortuous path. Comparison of the dominating crack behaviour with one having a single crack initiated at a notch tip reveals a significant delay effect. (orig.)

329

Collagen fiber alignment and biaxial mechanical behavior of porcine urinary bladder derived extracellular matrix.  

Science.gov (United States)

The collagen fiber alignment and biomechanical behavior of naturally occurring extracellular matrix (ECM) scaffolds are important considerations for the design of medical devices from these materials. Both should be considered in order to produce a device to meet tissue specific mechanical requirements (e.g., tendon vs. urinary bladder), and could ultimately affect the remodeling response in vivo. The present study evaluated the collagen fiber alignment and biaxial mechanical behavior of ECM scaffold material harvested from porcine urinary bladder tunica mucosa and basement membrane (together referred to as urinary bladder matrix (UBM)) and ECM harvested from urinary bladder submucosa (UBS). Since the preparation of UBM allows for control of the direction of delamination, the effect of the delamination method on the mechanical behavior of UBM was determined by delaminating the submucosa and other abluminal layers by scraping along the longitudinal axis of the bladder (apex to neck) (UBML) or along the circumferential direction (UBMC). The processing of UBS does not allow for similar directional control. UBML and UBS had similar collagen fiber distributions, with a preferred collagen fiber alignment along the longitudinal direction. UBMC showed a more homogenous collagen fiber orientation. All samples showed a stiffer mechanical behavior in the longitudinal direction. Despite similar collagen fiber distributions, UBML and UBS showed quite different mechanical behavior for the applied loading patterns with UBS showing a much more pronounced toe region. The mechanical behavior for UBMC in both directions was similar to the mechanical behavior of UBML. There are distinct differences in the mechanical behavior of different layers of ECM from the porcine urinary bladder, and the processing methods can substantially alter the mechanical behavior observed. PMID:18801572

Gilbert, Thomas W; Wognum, Silvia; Joyce, Erinn M; Freytes, Donald O; Sacks, Michael S; Badylak, Stephen F

2008-12-01

330

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

International Nuclear Information System (INIS)

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

331

Biaxial texture development in aluminum nitride layers during off-axis sputter deposition  

International Nuclear Information System (INIS)

Polycrystalline aluminum nitride (AlN) layers were deposited by pulsed-dc reactive magnetron sputtering from a variable deposition angle ? = 0°–84° in 5 mTorr pure N2 at room temperature. X-ray diffraction pole figure analyses show that layers deposited from a normal angle (? = 0°) exhibit fiber texture, with a random in-plane grain orientation and the c-axis tilted by 42° ± 2° off the substrate normal, yielding wurtzite AlN grains with the {1012} plane approximately parallel (±2°) to the substrate surface. However, as ? is increased to 45°, two preferred in-plane grain orientations emerge, with populations I and II having the c-axis tilted toward and away from the deposition flux, by 53° ± 2° and 47° ± 1° off the substrate normal, respectively. Increasing ? further to 65° and 84°, results in the development of a single population II with a 43° ± 1° tilt. This developing biaxial texture is attributed to a competitive growth mode under conditions where the adatom mobility is sufficient to cause intergrain mass transport, but insufficient for the thermodynamically favored low energy {0001} planes to align parallel to the layer surface. Consequently, AlN nuclei are initially randomly oriented and form a kinetically determined crystal habit exposing {0001} and {1120} facets. The expected direction of its highest growth rate is 49° ± 5° tilted relative to the c-axis, in good agreement with the 42°–53° measured tilt. The in-plane in-plane preferred orientation for ? > 0° is well explained by the orientation dependence in the cross section of the asymmetric pyramidal nuclei to capture directional deposition flux. The observed tilt is ideal for shear mode electromechanical coupling, which is maximized at 48°.

332

Measurement of biaxial mechanical properties of soft tubes and arteries using piezoelectric elements and sonometry  

International Nuclear Information System (INIS)

Arterial elasticity has gained importance in recent decades because it has been shown to be an independent predictor of cardiovascular diseases. Several in vivo and ex vivo techniques have been developed to characterize the elastic properties of vessels. In vivo techniques tend to ignore the anisotropy of the mechanical properties in the vessel wall, and therefore fail to characterize elasticity in different directions. Ex vivo techniques have been focused on studying the mechanical properties in different axes. In this paper, we present a technique that uses piezoelectric elements to measure the elasticity of soft tubes and excised arteries in two directions while maintaining the natural structure of these vessels. This technique uses sonometry data from piezoelectric elements to measure the strain in the longitudinal and circumferential directions while the tubes/arteries are being pressurized. We conducted experiments on urethane tubes to evaluate the technique and compared the experimental results with mechanical testing done on the materials used for making the tubes. We then performed sonometry experiments on excised pig carotid arteries assuming that they are transversely isotropic materials. To evaluate the sensitivity of this technique to changes in the material properties, we changed the temperature of the saline bath in which the arteries were immersed. The calculated Young's modulus from sonometry experiments for the urethane tubes and the mechanical testihe urethane tubes and the mechanical testing values showed good agreement, deviating no more than 13.1%. The elasticity values from the excised arteries and the behavior with the temperature changed agreed with previous work done in similar arteries. Therefore, we propose this technique for nondestructive testing of the biaxial properties of soft material tubes and excised arteries in their natural physiological shape.

333

Influences of wear material, fault roughness and loading rate on stick-slip behavior revealed by large-scale biaxial friction experiments  

Science.gov (United States)

We investigated the stick-slip events during large-scale biaxial friction experiments. We used a pair of large square-column rock samples, whose contact area was 1.5 m x 0.5 m (for detailed features of the apparatus, please refer to Fukuyama et al., 2012 in this meeting). The experiments were carried out with the loading rates from 0.0125 mm/s to 1 m/s under the constant normal stress between 0.13 and 1.3 MPa. The maximum displacement was 0.4 m. The experiments were repeatedly carried out under various mechanical conditions, and the total amount of displacement attained to 77 m. The sliding surfaces were flattened within 24 ?m undulation before the series of experiments. With the experiments proceeding, the sliding surfaces were evolved and generated wear materials. To investigate the effect of wear material on friction behavior, we sometimes kept and sometimes removed the wear material on the sliding surfaces. We observed a variation of stress drops even under the same mechanical condition, which could be caused by the change in the state of sliding surface, i.e. wear material and roughness on the surface since the machine characteristics remained the same during the experiments. Unfortunately, since we could not make direct measurements of the amount of wear material and fault roughness, we introduced a parameter W related to the amount of wear material and defined as the accumulation of product of normal stress (N) and displacement (D). This is derived from the theoretical examination that the thickness of gouge layer is proportional to N and D (Scholz, 1987, Geology). We defined another parameter R related to fault roughness. Since ND is thought to be the shear damage during each experiment, its total accumulation can be equal to R whereas W is reset to 0 after removing the wear material. We found that the stress drop is negatively proportional to both R and W independent of loading rate, and the amount of stress drop can be expressed as a multivariate function of R and W. This finding is consistent with the previous study by Anthony and Marone (2005, JGR), who reported that stress drops decrease with increasing thickness of gouge layer and surface roughness. In particular, the correlation at loading rate of 100 mm/s is so high (the coefficient of determination by multi-regression attains to 0.87). This indicates that the stick-slip behavior is dominantly controlled by wear material and fault roughness at this loading rate. In contrast, as to the dependence of stress drop on the loading rate, we observed an opposite relation to that by previous studies whose loading range was between 0.1 ?m/s and 3 mm/s (Mair et al., 2002, JGR; Anthony and Marone, 2005, JGR); the stress drop increased with the increase of loading rate from 0.1 mm/s to 100 mm/s in the present experiments. This positive correlation comes from the decreases in residual coefficient of friction with the loading rate because the peak coefficients of friction are almost constant at these loading rates. This discrepancy may come from the differences in the loading rate and the velocity weakening process of rock friction (e.g. Di Toro et al., 2011, Nature), though there remain other possibilities such as the machine stiffness.

Yamashita, F.; Fukuyama, E.; Mizoguchi, K.; Togo, T.

2012-12-01

334

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

Energy Technology Data Exchange (ETDEWEB)

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.

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

335

Reduction of critical current density in a spin valve with a perpendicular polarizer and a planar biaxial free layer  

International Nuclear Information System (INIS)

Ultrafast magnetization switching of a spin valve consisting of a perpendicularly magnetized polarizer and an in-plane magnetized free layer with uniaxial and higher order anisotropy is studied. Here we report the analytical results in which a modified asteroid and current-field state diagram are derived from an effective one-dimensional free energy for higher order anisotropy. Because additional crystalline axes provide an additional nutation channel, the critical current density for the biaxial case is smaller than that commonly observed for quadratic anisotropy. This will be of importance for the design of spin-torque-transfer magnetic random access memories and nano-oscillators.

336

Influence of dipole-dipole correlations on the stability of the biaxial nematic phase in the model bent-core liquid crystal  

International Nuclear Information System (INIS)

A molecular theory of biaxial nematic ordering in the system of bent-core molecules has been developed in the two-particle cluster approximation which enables one to take into account short-range polar correlations determined by both electrostatic dipole-dipole interaction and polar molecular shape. All orientational order parameters and short-range correlation functions are calculated numerically as functions of temperature in the uniaxial and in the biaxial nematic phases, and the results are compared with the ones obtained in the mean-field approximation and in the cluster approximation but without taking into consideration the dipole-dipole interaction. It is shown that short-range polar correlations and, in particular, the dipole-dipole correlations dramatically increase the temperature of the transition into the biaxial nematic phase and enhancing its stability range. The results are also very sensitive to the value of the opening angle of a model bent-core molecule. (fast track communication)

337

Status of the MeLoDIE Experiment, an Advanced Device for Online Biaxial Study of the Irradiation Creep of LWR Cladding  

International Nuclear Information System (INIS)

As a prototype of future instrumented material experiments in the Jules Horowitz Reactor (JHR), the CEA in collaboration with VTT is in the process of starting the MeLoDIE experiment in the OSIRIS reactor in about a year. MeLoDIE is an initiative to go beyond the 'cook and look' concept, often used for past material experiments in MTRs. Its innovative sample holder aims to an online measurement of the biaxial creep of a LWR cladding sample under twice the typical fast neutron flux in LWRs. It is designed to perform an online-controlled biaxial loading of the sample and an online biaxial measurement of its deformation with sensors co-designed with IFE Halden. Technical challenge is to perform reliably accurate measurements under the high nuclear heat load of in-core locations while keeping within their tight space and safety constraints. (author)

338

Electro-optic technique to study biaxiality of liquid crystals with positive dielectric anisotropy: the case of a bent-core material.  

Science.gov (United States)

We propose that, for materials having positive dielectric anisotropy, the biaxiality can be clearly verified or excluded by measuring the transmitted light intensity as a function of electric field. If the material is biaxial and is observed in homeotropically aligned cells, the schlieren texture should not disappear (transmitted intensity is not zero) even at very high fields, since the field does not affect the distribution of the second director normal to the main director. On the other hand, if the material is uniaxial the transmitted intensity should decrease with increasing field and a perfect homeotropic texture can be achieved at high fields. We have studied a bent-core compound in which a uniaxial-biaxial nematic (N_{u}-N_{b}) transition has been reported. This material has a positive dielectric anisotropy at low frequencies, so we could apply the technique described above. Our studies indicate that the material is uniaxial in the entire nematic range. PMID:19391886

Van Le, Khoa; Mathews, Manoj; Chambers, Martin; Harden, John; Li, Quan; Takezoe, Hideo; Jákli, Antal

2009-03-01

339

Análisis de vigas tubulares de acero estructural propensas a la falla por pandeo local sometidas a flexión biaxial / Analysis of steel hollow structural beams prone to local buckling failure subjected to biaxial bending  

Scientific Electronic Library Online (English)

Full Text Available SciELO Venezuela | Language: Spanish Abstract in spanish Este trabajo presenta una formulación general para el análisis de las vigas tipo cajón de acero estructural sometidas a flexión biaxial. El modelo se ha desarrollado en el marco de la teoría del daño concentrado. En este enfoque, los modelos se basan en métodos de la mecánica del daño continuo y del [...] concepto de rótula plástica. El modelo fue implementado en un programa comercial de elementos finitos. Para calibrar el modelo, fue realizado un conjunto de ensayos experimentales en el Laboratorio de Mecánica Estructural de la Universidad Centroccidental Lisandro Alvarado. El modelo fue calibrado mediante simulaciones numéricas de estos ensayos, encontrándose una buena concordancia entre las pruebas experimentales y las simulaciones numéricas. Abstract in english This paper presents a general formulation for the analysis of steel hollow structural beams prone to local buckling subjected to biaxial bending. The model has been developed within the framework of Lumped Damage Mechanics. In this approach, the models are based on methods of Continuum Damage Mechan [...] ics and the concept of plastic hinge. The model was implemented in a commercial finite element program. In order to calibrate the model, a set of experimental tests were carried out in the Structural Mechanics Laboratory at Universidad Centroccidental Lisandro Alvarado. The model was evaluated by the numerical simulation of these tests, obtaining a good agreement between the experimental tests and the numerical simulations.

NÉSTOR L, GUERRERO; MARÍA E, MARANTE; RICARDO, PICÓN; MARGGI, ROJAS; JULIO, FLÓREZ LÓPEZ.

2006-12-01

340

Análisis de vigas tubulares de acero estructural propensas a la falla por pandeo local sometidas a flexión biaxial / Analysis of steel hollow structural beams prone to local buckling failure subjected to biaxial bending  

Scientific Electronic Library Online (English)

Full Text Available SciELO Venezuela | Language: Spanish Abstract in spanish Este trabajo presenta una formulación general para el análisis de las vigas tipo cajón de acero estructural sometidas a flexión biaxial. El modelo se ha desarrollado en el marco de la teoría del daño concentrado. En este enfoque, los modelos se basan en métodos de la mecánica del daño continuo y del [...] concepto de rótula plástica. El modelo fue implementado en un programa comercial de elementos finitos. Para calibrar el modelo, fue realizado un conjunto de ensayos experimentales en el Laboratorio de Mecánica Estructural de la Universidad Centroccidental Lisandro Alvarado. El modelo fue calibrado mediante simulaciones numéricas de estos ensayos, encontrándose una buena concordancia entre las pruebas experimentales y las simulaciones numéricas. Abstract in english This paper presents a general formulation for the analysis of steel hollow structural beams prone to local buckling subjected to biaxial bending. The model has been developed within the framework of Lumped Damage Mechanics. In this approach, the models are based on methods of Continuum Damage Mechan [...] ics and the concept of plastic hinge. The model was implemented in a commercial finite element program. In order to calibrate the model, a set of experimental tests were carried out in the Structural Mechanics Laboratory at Universidad Centroccidental Lisandro Alvarado. The model was evaluated by the numerical simulation of these tests, obtaining a good agreement between the experimental tests and the numerical simulations.

NÉSTOR L, GUERRERO; MARÍA E, MARANTE; RICARDO, PICÓN; MARGGI, ROJAS; JULIO, FLÓREZ LÓPEZ.

 
 
 
 
341

Effect of saliva and blood contamination on the bi-axial flexural strength and setting time of two calcium-silicate based cements: Portland cement and biodentine.  

Science.gov (United States)

This study evaluated the effect of contamination with saliva and blood on the bi-axial flexural strength and setting time of pure gray Portland cement and Biodentine (Septodont, Allington, UK). A one-way ANOVA showed that contamination caused no significant difference between the cements in bi-axial flexural strength (P> 0.05). However there was a significant difference in setting time (PBiodentine, regardless of the contaminant, and contamination with blood increased the setting time of both materials. Biodentine was similar in strength to Portland cement, but had a shorter setting time for both contaminated and non-contaminated samples. PMID:24922995

Alhodiry, W; Lyons, M F; Chadwick, R G

2014-03-01

342

a Prism Coupling Study of Optical Anisotropy in Polyimide Including Moisture, Stress, and Thickness Effects.  

Science.gov (United States)

The study focuses on polymer systems which are currently used in microelectronics, particularly the commercially available polyimides: BTDA-ODA/MPDA (made from benzophenone tetracarboxylic dianhydride and the diamines oxydianiline and meta-phenylene diamine); PMDA-ODA (made from pyromellitic dianhydride and oxydianiline); and BPDA-PDA (made from biphenyl dianhydride and para-phenylene diamine). The non-destructive planar optical waveguiding technique of prism coupling is used to measure the film thickness and the in-plane (nTE) and out-of-plane (nTM) refractive indices at a wavelength of 0.63 mu m (HeNe laser). The film birefringence is calculated as the difference between nTE and nTM. Birefringence values confirm that the polymer chains in the solvent-cast films are preferentially oriented in plane, leading to a transverse isotropic film geometry. Film birefringence is shown to correlate qualitatively with the rigid-rod nature of the polyimide. A suspended membrane load-deflection technique is used to measure the in-plane biaxial stress and the in-plane biaxial modulus of the films. Film properties are measured on adhered films, which are in a state of residual stress, free films, which are in a zero-stress state, and on films which are biaxially stretched to an intermediate stress state. Use of the empirical model allows data taken on adhered films, at several humidities, to be analyzed to extract values of zero-stress birefringence and stress -optic coefficient. The extrapolated zero-stress birefringence is confirmed with free film measurements, and the stress -optic coefficient is confirmed with stretched film measurements. Varying the solution dilution and spin speed, to obtain different thickness films, is found to affect the film properties, including birefringence, in-plane coefficient of thermal expansion, and residual biaxial stress, in a way that is correlated with film thickness. Modelling shows that a substrate-mediated through-thickness gradient in film properties could account for the experimentally observed behavior. Optical and mechanical measurements are also made to study the effect of extended cure, simulating re-work, on the polyimide BTDA-ODA/MPDA. The adhered film birefringence is found to increase with extended cure, due to stress and orientation changes in the films. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253 -1690.) (Abstract shortened by UMI.).

Noe, Susan Cunningham

343

Texture mechanisms and microstructure of biaxial thin films grown by oblique angle deposition  

Energy Technology Data Exchange (ETDEWEB)

In order to understand the texture formation mechanism in thin films grown under oblique angle deposition (OAD), TiAlN films were deposited at room temperature (RT) under various incident angles. We show that both in-plane and out-of-plane crystallographic orientations respond strongly to the deposition angle. For {alpha} = 0 , the pole figures show a (111) and (200) mixed out-of-plane orientation with random in-plane alignment. In contrast, under OAD, inclined textures are observed with the (111) direction moving toward the incident flux direction and the (200) moving away, showing substantial in-plane alignment. This observation suggests that TiAlN crystals prefer to grow with the (200) direction perpendicular to the substrate while maintaining the minimization of the surface free energy by maximizing the (111) surface area toward the incident flux. The in-plane texture, which is randomly oriented at normal incidence, gives rise to two preferred orientations under oblique angles - one along the direction of flux and other away from the deposition source. The biaxial texture results from a competition among texture mechanism related to surface mobilities of adatoms, geometrical and directional effects. The surface and cross-section of the films were observed by scanning electron microscopy (SEM). OAD films develop a kind of smooth tiles of a roof structure, with no faceted crystallites. The columns of these films were tilted toward the direction of incident flux. The dependence of (111) texture tilt angle and column angle {beta} on the incidence flux angle {alpha} is evaluated using four well-known models. Transmission electron microscopy (TEM) study reveals a voided, intercolumnar structure with oblique growth toward the flux direction. The selected area diffraction pattern (SAED) pattern supports the pole figure observations. Measurements of the nanoindentation test were performed in order to discuss the change of mechanical properties as a function of incident flux angle. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Shetty, A.R.; Karimi, A. [Institut de Physique de la Matiere Condensee (IPMC), Ecole Polytechnique Federale de Lausanne (EPFL), Lausanne (Switzerland)

2012-08-15

344

Theory of light-induced deformation of azobenzene elastomers: effects of the liquid-crystalline interactions and biaxiality.  

Science.gov (United States)

We study light-induced deformation of azobenzene elastomers which can display liquid-crystalline (LC) order. It is shown that photomechanical behavior of azobenzene elastomers is determined by the strength of the LC interactions, which is proportional to the density of rodlike azobenzene chromophores. At weak LC interactions, a uniaxial order and uniaxial deformation of azobenzene elastomers along the polarization vector of the light E is observed. At strong LC interactions, the light is able to induce a phase transition from the uniaxial to the biaxial state, with two axes being related to the vector E and to a preferable alignment of the chromophores in the plane perpendicular to E. The phase transition can be of either the first or the second order. Azobenzene elastomers can demonstrate elongation or contraction along the polarization vector E, depending on the orientation distribution of chromophores around the main chains of network strands. The results of the theory are in a qualitative agreement with experiments and computer simulations, which demonstrate biaxial ordering in azo-containing polymers. PMID:25254355

Toshchevikov, Vladimir; Saphiannikova, Marina

2014-10-23

345

The Effects of Biaxial Strain and Chemical Ordering on the Band Gap of InGaN  

Energy Technology Data Exchange (ETDEWEB)

The authors have performed first-principles calculations to examine the effects of biaxial strain and chemical ordering on the band gap of wurtzite In{sub x}Ga{sub 1{minus}x}N in the range 0 {le} x {le} 0.5. The results for unstrained, random alloys are in good agreement with theoretical estimates and measurements on unstrained zinc-blende alloys, but are in poor agreement with recent measurements on strained wurtzite alloys which display significantly lower gaps. Biaxial strain is found to have a non-linear effect on calculated alloy gaps, increasing them for x < 0.25 and decreasing them for x > 0.25. However, the overall agreement with measured wurtzite values remains poor. Chemical ordering along the [0001] direction in strained alloys is found to decrease the band gaps considerably, yielding much improved agreement with measurements. They discuss their results with regard to current theories concerning the optical properties of wurtzite InGaN alloys.

WRIGHT,ALAN F.; VANSCHILFGAARDE,MARK

2000-07-17

346

Fracture mechanisms and lifetime prediction of PM 15 Vol. % SiCp-2011Al composite under different stress states  

International Nuclear Information System (INIS)

Fracture mechanisms of PM 15 vol. % SiCp-2011Al composite, has been studied under different stress states, at a high temperature, 375 degree C. The study has been extended to include the lifetime prediction of the material. Specimens of three different stress states; uniaxial tension, biaxial shear and triaxial tension stress states were employed. The mechanical tests have been conducted on a universal testing machine. Rupture lifetime for the three stress states are estimated and compared together using four different multiaxial stress rupture parameters. Each of these parameters was built on different set of physical basics that control the creep rupture. The validity of these parameters is judged according to how well the rupture time of triaxial and biaxial stress states can be predicted using the rupture data of uniaxial stress state. The results of the present study indicate that the lifetime of the specimens under multiaxial stresses can be estimated from uniaxial tension data using Cane's mechanistic parameter. The SEM observations show that cavity nucleation and growth dominate the early stages of high temperature fracture of the present composite. No indication of any change in the fracture mode has been observed as a result of changing the stress state.

347

Managing Stress  

Medline Plus

Full Text Available Managing Stress Introduction Stress is a physical and emotional reaction that everyone experiences as they encounter changes in life. ... tips for managing and preventing stress. What Is Stress? Many scientists see stress as a reaction of ...

348

Managing Stress  

Medline Plus

Full Text Available ... type of situation is called “bad stress” or “chronic stress.” Risks of Stress Never-ending stress can ... With a weakened immune system, a person with chronic stress could become ill more often. People who ...

349

Managing Stress  

Science.gov (United States)

Managing Stress Introduction Stress is a physical and emotional reaction that everyone experiences as they encounter changes in life. ... tips for managing and preventing stress. What Is Stress? Many scientists see stress as a reaction of ...

350

Stress Management  

Science.gov (United States)

... Friendly Worksites Program Requirements Fit-Friendly Resources 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 ...

351

Biaxial aromatics with face-on/edge-on stacking adaptability: an STM/STS study of 1D nanowires assembled via rotatable ethynyls.  

Science.gov (United States)

Scanning tunnelling microscopy/spectroscopy reveals significant electronic communications between edge-on biphenyl moieties of a benzene core derivatised biaxially with four ethynyl-biphenyls. The key to the successful assembly of conjugated 1D nanowires is the rotatable features of ethynyls, which allow dual adaptability of edge-on and face-on orientations for the aromatic rings. PMID:24901992

Lee, Shern-Long; Wu, Hung-Jen; Hsu, Yu-Ju; Chen, Hsiu-Hui; Hsu, Hsiu-Fu; Chen, Chun-Hsien

2014-10-21

352

Biaxial and antiferroelectric structure of the orthogonal smectic phase of a bent-shaped molecule and helical structure in a chiral mixture system  

Science.gov (United States)

We examined the biaxial and antiferroelectric properties in the Smectic-APA (Sm-APA) phase of bent-shaped DC-S-8. The biaxiality, which results from the existence of a secondary director, was well established from birefringence observations in the homeotropically aligned Sm-APA. By entering into Sm-APA phase, the birefringence (?n, difference between two refractive indices of short axes) continuously increased from 0 to 0.02 with decreasing temperature. The antiferroelectric switching and second harmonic generation (SHG) activity on the field-on state were also observed in the Sm-APA phase, and the evaluated spontaneous polarization (PS) value strongly depended on temperature. The temperature dependence of ?n and PS resembles each other and follows Haller's approximation, showing that the biaxiality is due to polar packing in which the molecules are preferentially packed with their bent direction arranged in the same direction, and that the phase transition of Sm-APA to Sm-A is second order. The biaxiality was further examined in chiral Sm-APA*. Doping with chiral components induced the helical twisting of the secondary director in the Sm-APA* phase, which was confirmed by observing the reflection of the circular dichroism (CD) bands in the homeotropically aligned cell. The helical pitch of Sm-APA* is tunable in the range of 300-700 nm wavelength with a variation in the chiral content of 5 to 10 weight (wt)%.

Kang, Sungmin; Nguyen, Ha; Nakajima, Shunpei; Tokita, Masatoshi; Watanabe, Junji

2013-05-01

353

Biaxial flexural strength and phase transformation of Ce-TZP/Al2O3 and Y-TZP core materials after thermocycling and mechanical loading  

Science.gov (United States)

PURPOSE The purpose of the present study was to evaluate the effect of thermocycling and mechanical loading on the biaxial flexural strength and the phase transformation of one Ce-TZP/Al2O3 and two Y-TZP core materials. MATERIALS AND METHODS Thirty disc-shaped specimens were obtained from each material. The specimens were randomly divided into three groups (control, thermocycled, and mechanically loaded). Thermocycling was subjected in distilled water for 10000 cycles. Mechanical loading was subjected with 200 N loads at a frequency of 2 Hz for 100000 times. The mean biaxial flexural strength and phase transformation of the specimens were tested. The Weibull modulus, characteristic strength, 10%, 5% and 1% probabilities of failure were calculated using the biaxial flexural strength data. RESULTS The characteristic strengths of Ce-TZP/Al2O3 specimens were significantly higher in all groups compared with the other tested materials (P<.001). Statistical results of X-ray diffraction showed that thermocycling and mechanical loading did not affect the monoclinic phase content of the materials. According to Raman spectroscopy results, at the same point and the same material, mechanical loading significantly affected the phase fraction of all materials (P<.05). CONCLUSION It was concluded that thermocycling and mechanical loading did not show negative effect on the mean biaxial strength of the tested materials. PMID:25006387

Bankoglu Gungor, Merve; Ayd?n, Cemal; Karakoca Nemli, Secil; Turhan Bal, Bilge; T?ras, Tulay

2014-01-01

354

Effect of Low Pressure Nitrogen DC Plasma on Optical Properties of Biaxial-Oriented Polypropylene (BOPP), Poly Methyl Methacrylate (PMMA) and Poly Vinyl Chloride (PVC) Films  

Science.gov (United States)

In this paper properties of Biaxial-Oriented Polypropylene, Poly Vinyl Chloride and Poly Methyl Methacrylate samples treated by DC glow discharge of N2 plasma have been investigated by UV-Vis_NIR spectrophotometer. It was found that plasma treatment change chemical structure of polymer surfaces. In addition, absorption coefficient, refractive index and extinction coefficient of all treated samples have been slightly changed.

Mortazavi, S. H.; Ghoranneviss, M.; Faryadras, S.

2012-06-01

355

Determination of biaxial texture of thick film EuBa2Cu3O7-? homo-substrate by x-ray diffraction  

International Nuclear Information System (INIS)

We have initially aligned polycrystalline EuBa2Cu3O7-? (Eu-123) Superconductor using a magnetic force and a mechanical force simultaneously to fabricate biaxially aligned rare earth (RE) substituted Eu-123 thick films as homo-substrates for growth of epitaxial YBa2Cu3O7-? superconductor thin films. The characterization of such Eu-123 thick films by X-ray pole figure study indicated that the polycrystalline Eu-123 grains having substantial biaxial alignment with their grain [001] axes perpendicular to the surfaces of the thick films and [010] axes parallel to the magnetic field direction in the specimen plane. We were the first to determine the biaxial alignment of Eu-123 homo-substrate by quantitative analysis of X-ray diffraction ?-circle and ?-circle scans of (013)/(103) reflections, demonstrating a degree of 33% alignment for both c-axis and a-b axis. The application of the biaxial alignment method to polycrystalline oxides as presented in this paper establishes a new paradigm for the processing of bulk materials. (author)

356

Effects of magnitude and direction of the biaxial compressive strain on the formation and migration of a vacancy in Ge by using density functional theory  

Science.gov (United States)

The effects of the magnitude and direction of biaxial compressive strain on the formation and migration barrier of a neutral vacancy in germanium were studied using density functional theory. Bulk Ge cells with (100) and (111) planes under various in-plane biaxial compressive strains were investigated to model epitaxial Ge on Si1-xGex substrate. Biaxial compressive strain decreases the vacancy formation energy by 68% and 81% for the (100) and (111) supercells, respectively, when Ge is assumed to be epitaxially grown on Si. The biaxial compressive strain hardly affects the migration behavior of a vacancy in the (100) supercell. On the contrary, in the (111) supercell, the migration barrier energy shows anisotropic behavior; the migration along the perpendicular and virtually parallel directions with respect to the strain becomes distinctly more difficult and slightly easier, respectively. The effects of strain on the formation and migration of the vacancy were explained by the atomic relaxation around it and electron redistribution. By comparing the formation energy and migration barrier energy, vacancy formation was suggested to be dominant for vacancy-mediated diffusion in Ge.

Lee, Joohwi; Duk Na, Kwang; Lee, Seung-Cheol; Hwang, Cheol Seong; Choi, Jung-Hae

2011-08-01

357

Apparent dependence of rate- and state-dependent friction parameters on loading velocity and slip displacement inferred from the large-scale biaxial friction experiment data  

Science.gov (United States)

We estimated the constitutive parameters in the rate- and state-dependent friction law by numerical simulations, using the results of large-scale biaxial rock friction experiments. Fukuyama et al. (2012, AGU Fall meeting) constructed the large-scale rock friction experiments using the shaking table at NIED. Sliding surface dimension was 1.5 m long and 0.5 m wide. During the experiments, many stick-slip events occurred, which had the following features. (i) Stress drops and recurrence intervals of the stick-slip events increased with slip displacement within a single experiment that started after the removal of gouges on the surface. (ii) Stress drops and recurrence intervals are more or less stable through an experiment, when several preceding experiments were done without gouge removal. (iii) Steady-state stress drops become large (Yamashita et al., 2012, AGU Fall meeting) and recurrence intervals become short when the loading velocity becomes fast among several experiments. We applied a single-degree-freedom spring-slider model to the friction data. The shear stress of the block obeys the rate- and state-dependent friction law (Slip law; Ruina law). We performed fully dynamic simulations. The stiffness of the spring and the mass of the block were estimated and measured in the large-scale friction experiments, respectively. We performed many numerical simulations with various values of b and L, keeping the a value constant. Then, we estimated the values of b and L which provide stick-slip behavior consistent with the experimental results. We used the experimental data when the normal stress is 1.33 MPa and the loading velocity is either 0.1 mm/s or 1.0mm/s. Our numerical simulation results suggest that (1) to fit the observation (i), we had to increase both b and L as the slip displacement increases, and (2) to fit the observation (iii), we had to increase both b and L as the loading velocity increases. The changes in b and L values are more significantly dependent on the loading velocity than on the slip displacement. Marone & Kilgore (1993, Nature) suggested that L increases with increasing gouge layer thickness. Because gouges were produced during the large-scale friction experiments, our forward modeling result (1) can be explained due to the production of gouges. In contrast, the result of large-scale friction experiments (iii) is inconsistent with previous studies (Mair et al., 2002, JGR; Anthony & Marone, 2005, JGR), as pointed out by Yamashita et al. (2012, AGU Fall meeting). This contradiction may come from the fact that the slip surface is larger and the loading velocity is higher in the present large-scale experiments than in the previous ones. We will discuss the physical interpretations of the apparent variation of b and L as is obtained in our result (2).

Urata, Y.; Yamashita, F.; Fukuyama, E.

2013-12-01

358

Strength and residual stresses of functionally graded Al2O3/ZrO2 discs prepared by electrophoretic deposition  

International Nuclear Information System (INIS)

Biaxial strength testing of functionally graded Al2O3/ZrO2 discs revealed that the strength of such discs, prepared by electrophoretic deposition, was almost doubled from 288 MPa for pure Al2O3 to 513 MPa for the graded discs; this was due to the compressive surface residual thermal stresses in the Al2O3 surface layer caused by the graded compositional profile. The surface compressive stress measured by means of X-ray diffraction was compared with the analytically calculated stress distribution in the graded component

359

Strain versus stress in a model granular material a Devil's staircase  

CERN Document Server

The series of equilibrium states reached by disordered packings of rigid, frictionless discs in two dimensions, under gradually varying stress, are studied by numerical simulations. Statistical properties of trajectories in configuration space are found to be independent of specific assumptions ruling granular dynamics, and determined by geometry only. A monotonic increase in some macroscopic loading parameter causes a discrete sequence of rearrangements. For a biaxial compression, we show that, due to the statistical importance of such events of large magnitudes, the dependence of the resulting strain on stress direction is a Levy flight in the thermodynamic limit.

Combe, G; Combe, Gael; Roux, Jean-Noel

2000-01-01

360

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

International Nuclear Information System (INIS)

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 2?-scan and ?-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

 
 
 
 
361

Bi-axial magnetic orientation in a twinned ErBa2Cu3Oy superconductor by controlling grain size  

International Nuclear Information System (INIS)

Bi-axial magnetic orientation in ErBa2Cu3Oy (Er123) superconductor with a twinned microstructure was demonstrated. A ball-milling process effectively improved the degree of the in-plane and c-axis orientation of Er123 powder samples oriented in a modulated rotating magnetic field of 10 T. From the relationship between the particle size and the degree of orientation, it is concluded that pulverization induced the appearance of the in-plane magnetic anisotropy of Er123 grains through inhomogenization of two different types of domains in their grains. The present study presents a production technique of RE123 bulk magnets and coated conductors without epitaxy technology.

362

Engineering of optical polarization based on electronic band structures of A-plane ZnO layers under biaxial strains  

Science.gov (United States)

In-plane anisotropic strains in A-plane layers on the electronic band structure of ZnO were investigated from the viewpoint of optical polarization anisotropy. Investigations utilizing k.p perturbation theory revealed that energy transitions and associated oscillation strengths were dependent on in-plane strains. The theoretical correlation between optical polarizations and in-plane strains was experimentally demonstrated using A-plane ZnO layers with different in-plane strains. Finally, optical polarization anisotropy and its implications for in-plane optical properties are discussed in relation to the energy shift between two orthogonal directions. Higher polarization rotations were obtained in an A-plane ZnO layer with in-plane biaxially compressive strains as compared to strain-free ZnO. This study provides detailed information concerning the role played by in-plane strains in optically polarized applications based on nonpolar ZnO in the ultra-violet region.

Matsui, Hiroaki; Hasuike, Noriyuki; Harima, Hiroshi; Tabata, Hitoshi

2014-09-01

363

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

DEFF Research Database (Denmark)

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 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 for a speed range of 50 to 2000 rpm. A method for initial rotor position of BEGA is proposed based on injection of a very short voltage pulse in the machine dc excitation, the method being independency of machine parameters. Experimental results for initial rotor position estimation proved accuracy below 10 electrical degrees in less than 2 ms test time.

Coroban-Schramel, Vasile; Boldea, Ion

2009-01-01

364

Bi-axial magnetic orientation in a twinned ErBa2Cu3Oy superconductor by controlling grain size  

Science.gov (United States)

Bi-axial magnetic orientation in ErBa2Cu3Oy (Er123) superconductor with a twinned microstructure was demonstrated. A ball-milling process effectively improved the degree of the in-plane and c-axis orientation of Er123 powder samples oriented in a modulated rotating magnetic field of 10 T. From the relationship between the particle size and the degree of orientation, it is concluded that pulverization induced the appearance of the in-plane magnetic anisotropy of Er123 grains through inhomogenization of two different types of domains in their grains. The present study presents a production technique of RE123 bulk magnets and coated conductors without epitaxy technology.

Horii, S.; Tanoue, T.; Yamaki, M.; Maeda, T.; Shimoyama, J.

2011-05-01

365

Biaxial mechanical properties of the human thoracic and abdominal aorta, common carotid, subclavian, renal and common iliac arteries.  

Science.gov (United States)

The biomechanics of large- and medium-sized arteries influence the pathophysiology of arterial disease and the response to therapeutic interventions. However, a comprehensive comparative analysis of human arterial biaxial mechanical properties has not yet been reported. Planar biaxial extension was used to establish the passive mechanical properties of human thoracic (TA, [Formula: see text]) and abdominal (AA, [Formula: see text]) aorta, common carotid (CCA, [Formula: see text]), subclavian (SA, [Formula: see text]), renal (RA, [Formula: see text]) and common iliac (CIA, [Formula: see text]) arteries from 11 deceased subjects ([Formula: see text] years old). Histological evaluation determined the structure of each specimen. Experimental data were used to determine constitutive parameters for a structurally motivated nonlinear anisotropic constitutive model. All arteries demonstrated appreciable anisotropy and large nonlinear deformations. Most CCA, SA, TA, AA and CIA specimens were stiffer longitudinally, while most RAs were stiffer circumferentially. A switch in anisotropy was occasionally demonstrated for all arteries. The CCA was the most compliant, least anisotropic and least frequently diseased of all arteries, while the CIA and AA were the stiffest and the most diseased. The severity of atherosclerosis correlated with age, but was not affected by laterality. Elastin fibers in the aorta, SA and CCA were uniformly and mostly circumferentially distributed throughout the media, while in the RA and CIA, elastin was primarily axially aligned and concentrated in the external elastic lamina. Constitutive modeling provided good fits to the experimental data for most arteries. Biomechanical and architectural features of major arteries differ depending on location and functional environment. A better understanding of localized arterial mechanical properties may support the development of site-specific treatment modalities for arterial disease. PMID:24710603

Kamenskiy, Alexey V; Dzenis, Yuris A; Kazmi, Syed A Jaffar; Pemberton, Mark A; Pipinos, Iraklis I; Phillips, Nick Y; Herber, Kyle; Woodford, Thomas; Bowen, Robert E; Lomneth, Carol S; MacTaggart, Jason N

2014-11-01

366

Comparative analysis of the biaxial mechanical behavior of carotid wall tissue and biological and synthetic materials used for carotid patch angioplasty.  

Science.gov (United States)

Patch angioplasty is the most common technique used for the performance of carotid endarterectomy. A large number of patching materials are available for use while new materials are being continuously developed. Surprisingly little is known about the mechanical properties of these materials and how these properties compare with those of the carotid artery wall. Mismatch of the mechanical properties can produce mechanical and hemodynamic effects that may compromise the long-term patency of the endarterectomized arterial segment. The aim of this paper was to systematically evaluate and compare the biaxial mechanical behavior of the most commonly used patching materials. We compared PTFE (n? = ?1), Dacron (n ?=? 2), bovine pericardium (n ?= ?10), autogenous greater saphenous vein (n ?= ?10), and autogenous external jugular vein (n ?=? 9) with the wall of the common carotid artery (n ?=? 18). All patching materials were found to be significantly stiffer than the carotid wall in both the longitudinal and circumferential directions. Synthetic patches demonstrated the most mismatch in stiffness values and vein patches the least mismatch in stiffness values compared to those of the native carotid artery. All biological materials, including the carotid artery, demonstrated substantial nonlinearity, anisotropy, and variability; however, the behavior of biological and biologically-derived patches was both qualitatively and quantitatively different from the behavior of the carotid wall. The majority of carotid arteries tested were stiffer in the circumferential direction, while the opposite anisotropy was observed for all types of vein patches and bovine pericardium. The rates of increase in the nonlinear stiffness over the physiological stress range were also different for the carotid and patching materials. Several carotid wall samples exhibited reverse anisotropy compared to the average behavior of the carotid tissue. A similar characteristic was observed for two of 19 vein patches. The obtained results quantify, for the first time, significant mechanical dissimilarity of the currently available patching materials and the carotid artery. The results can be used as guidance for designing more efficient patches with mechanical properties resembling those of the carotid wall. The presented systematic comparative mechanical analysis of the existing patching materials provides valuable information for patch selection in the daily practice of carotid surgery and can be used in future clinical studies comparing the efficacy of different patches in the performance of carotid endarterectomy. PMID:22168740

Kamenskiy, Alexey V; Pipinos, Iraklis I; MacTaggart, Jason N; Kazmi, Syed A Jaffar; Dzenis, Yuris A

2011-11-01

367

Manage Stress  

Science.gov (United States)

... Conditions and Diseases > Heart Health > Manage Stress Manage Stress The Basics Take Action! Ver en español Content ... on: August 19, 2014 The Basics Not all stress is bad. Stress can help protect you in ...

368

Managing Stress  

Medline Plus

Full Text Available ... situation is called “bad stress” or “chronic stress.” Risks of Stress Never-ending stress can lead to ... sure to tell your massage therapist which massaging strokes make you feel good. Ask for help. Ask ...

369

Effect of biaxial loading and geometry on prediction of low-cycle fatigue life  

International Nuclear Information System (INIS)

Data to predict failure by low-cycle fatigue are mainly based on uniaxial constant amplitude tests on solid specimens, although in practically all cases the state of stress of a reactor component is multiaxial. The effect of multiaxiality has been investigated on thin-walled tubular specimens. For the uniaxial loading condition a comparison has been made with tests on solid specimens. The investigated materials were 18Cr-11Ni steel (type AISI 304) at 200C and 5500C and Nb-stabilized 2 1/4Cr1Mo steel at 5000C. The thin-walled tubular specimens have been loaded by combinations of cyclic axial load and cyclic torsion, with which a range of principal stress ratios between -1 2/sigma1 2/?epsilon1 <= -0.5 could be achieved. (orig.)

370

Application of the virtual crack closure technique to calculate stress intensity factors for through cracks with an oblique elliptical crack front:  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Fractographic observations on fatigue tested 2024 T3 clad aluminium riveted lap-splice joints indicate oblique fronts after the initial surface or corner crack at a rivet hole has penetrated through the sheet thichness. No stress intensity factor solutions are available for this geometry subjected to remote biaxial tension, remote bending, rivet loading, and rivet interference, which are typical for a pressurized fuselage of a transport aircraft. However, comparisons are made with solutions f...

Fawaz, S.

1998-01-01

371

Ultimate strength criteria of concrete under bi-axial and tri-axial loading  

International Nuclear Information System (INIS)

The possibility of using numerical method for the analysis of reinforced concrete structures is limited by the incomplete knowledge of the behavior of concrete under multiaxial stress states. While many experimental and theorectical investigations have been and are presently carried out to clarify this problem, an attempt is being made here to use the available experimental data to achieve an ultimate strength criterion apt to be used in an analytical model. (orig.)

372

Effects of concentration-dependent elastic modulus on the diffusion of lithium ions and diffusion induced stress in layered battery electrodes  

Science.gov (United States)

A stress assisted diffusion model considering concentration-dependent elastic modulus of active material has been established for the multi-layered electrodes of lithium batteries. The physical mechanism for the effect of modulus variation on the Li-ion diffusion and corresponding biaxial stress is well elucidated. Moreover, the analytic solutions of maximum stress in both active layer and collector are respectively derived. It has been found that the modulus stiffening gives rise to the additional stress gradient and enhances Li-ion diffusion, therefore to increase the biaxial stress in the plate electrode. In contrast, modulus softening makes the stress assisted diffusion less significant and the corresponding stresses are reduced. These coupled effects are more significant during potentiostatic charging and galvanostatic charging with high charging rates. Moreover, the maximum stress in the active layer is independent of charging process, but depends upon the elastic modulus variation due to Li-ion insertion. Finally, with increasing thickness ratio between collector and active material, the impacts of concentration dependent modulus on the Li-ion diffusion in active layer decreases, whereas this effect on maximum stress in the current collector increases.

He, Y.-L.; Hu, H. J.; Song, Y.-C.; Guo, Z.-S.; Liu, C.; Zhang, J.-Q.

2014-02-01

373

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

International Nuclear Information System (INIS)

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

374

Measuring the interface stress: Silver/nickel interfaces  

International Nuclear Information System (INIS)

Interface stress is a surface thermodynamics quantity associated with the reversible work of elastically straining an internal solid interface. In a multilayered thin film, the combined effect of the interface stress of each interface results in an in-plane biaxial volume stress acting within the layers of the film that is inversely proportional to the bilayer thickness. We calculated the interface stress of an interface between {111} textured Ag and Ni on the basis of direct measurements of the dependence of the in-plane elastic strains on the bilayer thickness. The strains were obtained using transmission x-ray diffraction. Unlike previous studies of this type, we used freestanding films so that there was no need to correct for intrinsic stresses resulting from forces applied by the substrate that can lead to large uncertainties of the calculated interface stress value. Based on the lattice parameters of the bulk, pure elements, an interface stress of -2.02±0.26 N/m was calculated using the x-ray diffraction results from films with bilayer thicknesses greater than 5 nm. This value is somewhat smaller than previous measurements obtained from as-deposited films supported by substrates. For smaller bilayer thicknesses the apparent interface stress becomes smaller in magnitude, possibly due to a loss of layering in the specimens. (c) 1999 Materials Research Society

375

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

Science.gov (United States)

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.

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

2012-03-01

376

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

International Nuclear Information System (INIS)

The process of choosing a site for a nuclear waste repository means that many aspects have to be taken into consideration. One of these is that the repository has to be mechanically stable for a long time. The mechanical stability of the rock is very difficult to determine. One of several factors, which determine the mechanical stability, is the virgin state of stress. The thesis project consists of two parts. In the first part the state of stress at Aespoe Hard Rock Laboratory had to be defined. This was done based on earlier rock stress measurements conducted during the years 1988 to 1997. Two different measurement techniques have been used, hydraulic fracturing and overcoring. During the overcoring two types of cells have been used, CSIRO HI-cell and a cell developed by the Swedish State Power Board (SSPB). In the second part of the project, investigation of the correlation between the stress and geological structures are made using numerical modelling tools such as FLAC, UDEC and 3DEC. The rock stress measurements using the hydraulic fracturing gave orientations of the horizontal stress that coincide with earlier hydraulic fracturing measurements conducted in Scandinavia. The magnitudes of rock stresses are slightly lower than the earlier reported stress magnitudes for the Scandinavian part of the earth crust. The rock stresses obtained from the overcoring resulted in higher stresses than what was predicted by the hydraulic fracturing measurements. However, the orc fracturing measurements. However, the orientation of the maximum horizontal stresses coincides well between the two techniques. The orientation is also more or less constant with respect to increasing depth. The state of stress at Aespoe is defined by using the results from the hydraulic fracturing and the measurements conducted by SSPB-cell. The measurements from the SSPB-cell are used since these have a Poisson's ratio that corresponds well with the uniaxial tests of rock samples and since the measurements have been done at a distance from 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. If slip will occur or not depends, thus, on a comb

377

Microplane model for concrete subject to plane stresses  

International Nuclear Information System (INIS)

The microplane model proves in this paper to be suitable also to the description of the multiaxial behavior of concrete, subjected either to tension or to compression, with or without shear. The microcracking, which is the most relevant caused of nonlinearity, is assumed to be localized in the thin mortar layers (cement paste and fine aggregates) which separate the coarse aggregate particles: these layers, called ''microplanes'' or ''weak planes'', are assumed to be present both at the microscopic and at the macroscopic level. Each microplane is characterized by a uniaxial constitutive relationship between the normal stress and the normal strain. The behavior of the concrete as a whole is adequately described (loading in compression, strain softening excluded; loading in tension, strain softening included; unloaded either from previous tension or from previous compression). Attention is focused on plane stress situations. Comparisons are made with many test data on the biaxial behavior of concrete. (orig./HP)

378

Managing Stress  

Medline Plus

Full Text Available ... heart attacks. Stress can also lead to migraine headaches, back pain and ulcers. Several studies have associated ... When people are under stress they may experience: • Headaches. • Tense muscles. • Shaky hands. • Fatigue. • Insomnia. • Heartburn. Stressed ...

379

Managing Stress  

Medline Plus

Full Text Available ... page It's been added to your dashboard . Managing stress 3:13 Pregnancy is a stressful time for ... Here are practical suggestions to help you manage stress. Risk of C-section: W 2:44 Babies ...

380

Managing Stress  

Medline Plus

Full Text Available ... presents tips for managing and preventing stress. What Is Stress? Many scientists see stress as a reaction ... body’s normal reaction to a somewhat dangerous situation is an increase in heart rate and muscle tension ...

 
 
 
 
381

Managing Stress  

Medline Plus

Full Text Available ... body, feelings, and behavior? Can you list 7 things that make you feel stressed? Feeling overwhelmed, either ... or accumulating debt. Preventing Stress There are several things you can do to prevent stress. The following ...

382

Managing Stress  

Medline Plus

Full Text Available ... succeed. These types of situations are called “challenges,” “good stress,” or “acute stress.” When situations that cause ... to shop together! Plan major lifestyle changes. Many good major changes can cause stress. If you plan ...

383

Managing Stress  

Medline Plus

Full Text Available ... when it becomes continuous. These negative effects can lead to depression and heart disease. This reference summary ... stress.” Risks of Stress Never-ending stress can lead to a variety of diseases. It can lead ...

384

Managing Stress  

Medline Plus

Full Text Available ... make you feel stressed? Feeling overwhelmed, either at work or at home, makes a lot of people feel overly stressed. Uncertainty of the future can cause stress. Not knowing what is going to happen after ...

385

Managing Stress  

Medline Plus

Full Text Available ... page It's been added to your dashboard . Managing stress 3:13 Pregnancy is a stressful time for ... Here are practical suggestions to help you manage stress. Gestational diabetes 3:46 How your baby grows: ...

386

Stress incontinence  

Science.gov (United States)

Incontinence - stress ... over 2 cups of urine in their bladder. Stress incontinence occurs when the muscles that control your ... the pelvic area or the prostate (in men) Stress incontinence is the most common type in women. ...

387

Stress concentration around an atelectatic region: a finite element model.  

Science.gov (United States)

Lung parenchyma surrounding an atelectatic region is thought to be subjected to increased stress compared with the rest of the lung. Using 37 hexagonal cells made of linear springs, Mead et al. (1970) measured a stress concentration greater than 30% in the springs surrounding a stiffer central cell. We re-examine the problem using a 2D finite element model of 500 cells made of thin filaments with a non-linear stress-strain relationship. We study the consequences of increasing the central stiff region from one to nine contiguous cells in regular hexagonal honeycombs and random Voronoi honeycombs. The honeycomb structures were uniformly expanded with strains of 15%, 30%, 45% and 55% above their resting, non-deformed geometry. The curve of biaxial stress vs. fractional area change has a similar shape to that of the pressure-volume curve of the lung, showing an initial regime with relatively flat slope and a final regime with decreasing slope, tending toward an asymptote. Regular honeycombs had little variability in the maximum stress in radially oriented filaments adjacent to the central stiff region. In contrast, some filaments in random Voronoi honeycombs were subjected to stress concentration approximately 16 times the average stress concentration in the radially oriented filaments adjacent to the stiff region. These results may have implications in selecting the appropriate strategy for mechanical ventilation in ARDS and defining a "safe" level of alveolar pressure for ventilating atelectatic lungs. PMID:25048678

Makiyama, A M; Gibson, L J; Harris, R S; Venegas, J G

2014-09-15

388

Biaxial testing of pericardium using electronic speckle-pattern interferometry (ESPI)  

Science.gov (United States)

An apparatus for measuring the mechanical properties of thin living biological membranes such as pericardium (the sac which encloses the heart) is presented. The apparatus, using 16 actuators to apply stresses in the plane of the membrane, measures in-plane displacements and strain by means of electronic speckle pattern interferometry (ESPI). As opposed to conventional speckle interferometers which use light reflected from the surface under test, the apparatus presented here collects the light transmitted through the membrane, as pericardium is translucent and reflects very little light. Furthermore, in order to be preserved in a healthy state, the biological membrane must be kept immersed in a bath of physiological solution during the measurement experiments. Results of mechanical stretch experiments are presented where the infinitesimal strain tensor components were measured over the entire surface of a 10 mm diameter circular specimen of pericardium.

Charette, Paul G.; Hunter, Ian W.; Hunter, Peter J.

1993-02-01

389

Mechanics of Stabbing: Biaxial Measurement of Knife Stab Penetration of Skin Simulant  

CERN Document Server

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...

Gilchrist, Michael D; Curtis, Michael; Cassidy, Mary; Byrne, Greg; Destrade, Michel; 10.1016/j.forsciint.2007.10.010

2008-01-01

390

Wettability and optical properties of O2 and CF4 plasma treated biaxially oriented semicrystalline poly(ethylene terephthalate) films  

Science.gov (United States)

Influence of low pressure O2, CF4, and successive O2 and CF4 RF plasma treatment on optical properties and wettability of biaxially oriented semicrystalline poly(ethylene terephthalate) (PET) was examined. Produced by industrial stretch-blow molding PET films of the 300 ?m thickness were chosen for the experiments. Influence of the aging was also investigated by storing plasma treated samples at room conditions for 60 days. It was revealed that O2 plasma treated samples suffered from the hydrophobic recovery and long term improvement of hydrophilicity was only a moderate. Energetic CF4 plasma treatment was able to form a large number of surface active sites which in turn was capable to attach the oxygen containing groups and to increase the hydrophilicity. However, aged for 10-60 days CF4 plasma treated PET films have showed a large scattering of the contact angle values measured on the same surface. Successive O2 and CF4 plasma treatment, despite induced hydrophobicity of as treated films, after 3 days of aging have resulted in highly homogeneous hydrophilic (? ? 20°) surfaces which have retained their hydrophilicity for the entire period of investigation. Moreover, combined plasma treatment of PET films has not influenced significantly the transmission of visible light. So, such a treatment can be considered as beneficial for the production of highly homogeneous hydrophilic surfaces without significant influence on their optical properties.

Jucius, D.; Grigali?nas, V.; Kopustinskas, V.; Lazauskas, A.; Guobien?, A.

2012-12-01

391

Identification of a self-limiting reaction layer in Ni-3 at.% W rolling-assisted biaxially textured substrates  

Energy Technology Data Exchange (ETDEWEB)

Analytical transmission electron microscopy was used to identify the presence of a self-limiting reaction layer developed within rolling-assisted biaxially textured Ni-3 at.% W substrates during the pulsed laser deposition of thick YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} (YBCO) films. Improvements in YBCO film quality and physical properties were attributed in part to the development of a NiWO{sub 4} layer at the buffer-substrate interface. The formation of NiWO{sub 4} between NiO and the Ni-3 at.% W substrate was observed to restrict the growth of NiO within the coated conductor during YBCO deposition at elevated temperatures. A 5-8 nm thick NiWO{sub 4} layer, identified through both electron diffraction and energy dispersive spectroscopy, was found to limit NiO growth to between 20 and 25 nm in thickness. The NiWO{sub 4} layer was found to have a [100] orientation relationship to the substrate normal, with multiple variants observed.

Leonard, K J; Goyal, A; Kang, S; Yarborough, K A; Kroeger, D M [Oak Ridge National Laboratory, Metals and Ceramics Division, Oak Ridge, TN 37831-6116 (United States)

2004-11-01

392

Fabrication of High Current YBa2Cu3O7-y Coated Conductors Using Rolling-Assisted Biaxially Textured Substrates  

International Nuclear Information System (INIS)

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

393

A Study in Three-Dimensional Chaotic Dynamics: Granular Flow and Transport in a Bi-Axial Spherical Tumbler  

CERN Document Server

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...

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

2014-01-01

394

High JC YBCO films on biaxially textured Ni with oxide buffer layers deposited using evaporation and sputtering techniques  

Science.gov (United States)

Epitaxial buffer layers of CeO 2 and yttria-stabilised ZrO 2 (YSZ) have been deposited on biaxially textured nickel substrates using evaporation and rf sputtering. The buffer layers were characterised by XRD, SEM and optical microscopy. YBa 2Cu 3O 7- ? (YBCO) films were deposited by high pressure dc sputtering on CeO 2/YSZ/CeO 2 buffered substrates and the resulting superconducting properties were measured inductively. On exclusively evaporated buffers critical current densities of up to 0.6 MA/cm 2 (77.3 K, H=0 T) were achieved. The buffer layers showed some cracks after YBCO deposition, which we considered to be responsible for the relatively low JC. In contrast buffer architectures with evaporated CeO 2 followed by rf sputtering of YSZ and CeO 2 remained completely free of cracks after YBCO deposition. Critical current densities between 1.5 and 2.6 MA/cm 2 (77 K, H=0 T) in 400 nm thick YBCO films were obtained reproducibly. The critical temperatures TC ranged between 87 and 92 K and the typical width ? TC of the transition was 1.5 K.

Kreiskott, S.; Getta, M.; Mönter, B.; Piel, H.; Pupeter, N.

2003-01-01

395

High JC YBCO films on biaxially textured Ni with oxide buffer layers deposited using evaporation and sputtering techniques  

International Nuclear Information System (INIS)

Epitaxial buffer layers of CeO2 and yttria-stabilised ZrO2 (YSZ) have been deposited on biaxially textured nickel substrates using evaporation and rf sputtering. The buffer layers were characterised by XRD, SEM and optical microscopy. YBa2Cu3O7-? (YBCO) films were deposited by high pressure dc sputtering on CeO2/YSZ/CeO2 buffered substrates and the resulting superconducting properties were measured inductively. On exclusively evaporated buffers critical current densities of up to 0.6 MA/cm2 (77.3 K, H=0 T) were achieved. The buffer layers showed some cracks after YBCO deposition, which we considered to be responsible for the relatively low JC. In contrast buffer architectures with evaporated CeO2 followed by rf sputtering of YSZ and CeO2 remained completely free of cracks after YBCO deposition. Critical current densities between 1.5 and 2.6 MA/cm2 (77 K, H=0 T) in 400 nm thick YBCO films were obtained reproducibly. The critical temperatures TC ranged between 87 and 92 K and the typical width ?TC of the transition was 1.5 K

396

Development of an in-plane biaxial test for forming limit curve (FLC) characterization of metallic sheets  

International Nuclear Information System (INIS)

The main objective of this work is to propose a new experimental device able to give for a single specimen a good prediction of rheological parameters and formability under static and dynamic conditions (for intermediate strain rates). In this paper, we focus on the characterization of sheet metal forming. The proposed device is a servo-hydraulic testing machine provided with four independent dynamic actuators allowing biaxial tensile tests on cruciform specimens. The formability is evaluated thanks to the classical forming limit diagram (FLD), and one of the difficulties of this study was the design of a dedicated specimen for which the necking phenomenon appears in its central zone. If necking is located in the central zone of the specimen, then the speed ratio between the two axes controls the strain path in this zone and a whole forming limit curve can be covered. Such a specimen is proposed through a numerical and experimental validation procedure. A rigorous procedure for the detection of numerical and experimental forming strains is also presented. Finally, an experimental forming limit curve is determined and validated for an aluminium alloy dedicated to the sheet forming processes (AA5086)

397

Molecular ordering in a biaxial smectic-A phase studied by scanning transmission X-ray microscopy (STXM).  

Science.gov (United States)

Results of STXM investigations of a binary mixture (-TNF = 2 : 1; SmA(b) 140 M 180 Iso) known to form a SmA(b) phase [T. Hegmann, J. Kain, S. Diele, G. Pelzl and C. Tschierske, Angew. Chem. Int. Ed., 2001, 40, 887] are presented. Near edge X-ray absorption fine spectra (NEXAFS) of the -TNF board-like aggregates, in particular the intensity of the low energy peaks associated with aromatic ring pi* orbitals (284.5-286.5 eV), show that the molecular plane of these aggregates is very sensitive to the relative orientation of electric field vector E of linearly polarized light, which is used to determine the molecular orientation in the LC phase. The observed strong in-plane dichroic signal suggests the predominant orientation of the -TNF aggregates to be along the smectic layer normal as well as long-range ordering of the in-plane molecular orientation (biaxiality). Orientational maps derived from series of measurements at different sample rotation angles around the specimen normal clearly show a Schlieren-type texture, and permit a detailed examination of exclusive +/-(1/2) disclination theoretically predicted for the SmA(b) phase. PMID:17396182

Kaznacheev, Konstantin; Hegmann, Torsten

2007-04-14

398

Strain mapping near a triple junction in strained Ni-based alloy using EBSD and biaxial nanogauges  

Energy Technology Data Exchange (ETDEWEB)

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.

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

399

Strain mapping near a triple junction in strained Ni-based alloy using EBSD and biaxial nanogauges  

International Nuclear Information System (INIS)

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.

400

Growth of thin Al2O3 films on biaxially oriented polymer films by atomic layer deposition  

International Nuclear Information System (INIS)

The effects of thin film nucleation and initial growth on roughness, chemistry and thermomechanical properties of polymer film surfaces were studied. Al2O3 was deposited onto commercial biaxially oriented polypropylene and polylactic acid films at 80 °C by using atomic layer deposition technique. Both substrates, especially the more hydrophobic polypropylene, showed initial growth through Al2O3 clusters. There was a faster deposition of Al2O3 on polylactic acid film than on polypropylene at the early stages of the Al2O3 deposition. There were also indications of chemical interactions between polylactic acid and trimethyl aluminum used as a precursor for Al2O3. Changes in the thermo-mechanical properties of the polymer surfaces with Al2O3 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: ? Growth of atomic layer deposited Al2O3 at 80 °C was studied on commercial films. ? Both substrate films showed early Al2O3 growth through clusters. ? Initial growth rate depends on the nature of the substrate film surface. ? There were indications of chemical interactions between substrate and practions between substrate and precursor. ? Film thickness and chemical interactions affect thermo-mechanical properties.