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1

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; Bondum, Tommi HØjer

2012-01-01

2

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

3

Creep modeling of textured zircaloy under biaxial stressing  

International Nuclear Information System (INIS)

Anisotropic biaxial creep behavior of textured Zircaloy tubing was modeled using a crystal-plastic uniform strain-rate upper-bound and a uniform stress lower-bound approach. Power-law steady-state creep is considered to occur on each crystallite glide system by fixing the slip rate to be proportional to the resolved shear stress raised to a power. Prismatic, basal, and pyramidal slip modes were considered. The crystallographic texture is characterized using the orientation distribution function determined from a set of three pole-figures. This method is contrasted with a Von-Mises-Hill phenomenological model in comparison with experimental data obtained at 673 deg K. The resulting creep-dissipative loci show the importance of the basal slip mode on creep in heavily cold-worked cladding, whereas prismatic slip is more important for the recrystallized materials. (author)

4

Effects of biaxial loading and residual stresses on constraint  

International Nuclear Information System (INIS)

Finite element analyses have been carried out to determine the elastic stress intensity factors, the plastic limit loads, failure assessment diagrams (FADs) and the T- and Q-stresses for each of three postulated defects. The effect of biaxial loading and residual stresses on the stress intensity factor and T and Q-stress solutions, and the effect of weld-base metal mismatch on the plastic limit load were assessed. Results have also been derived for the reduction in constraint with increasing plasticity up to the limit load. For assessments of a narrow mismatched weld of overmatching strength using standard Option 1 or 2 FADs, up to Lr=1, this parameter should be determined using the lower strength base material yield strength. The decrease in constraint with increasing Lr varies at different positions around the crack front of semi elliptical surface defects. Although constraint is maintained highest just under the free surface towards the ends of the crack, this is generally the region where the stress intensity factor is lowest for tension loading and thus assessments need to take account of both crack tip driving force and constraint

5

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

2011-09-01

6

Temperature dependence of the biaxial modulus, intrinsic stress and composition of plasma deposited silicon oxynitride films  

Science.gov (United States)

Silicon oxynitride films were deposited by plasma-enhanced chemical-vapor deposition. The elemental composition was varied between silicon nitride and silicon dioxide: SiO(0.3)N(1.0), SiO(0.7)N(1.6), SiO(0.7)N(1.1), and SiO(1.7)N(0.%). These films were annealed in air, at temperatures of 40-240 C above the deposition temperature (260 C), to determine the stability and behavior or each composition. the biaxial modulus, biaxial intrinsic stress, and elemental composition were measured at discrete intervals within the annealing cycle. Films deposited from primarily ammonia possessed considerable hydrogen (up to 38 at.%) and lost nitrogen and hydrogen at anneal temperatures (260-300 C) only marginally higher than the deposition temperature. As the initial oxygen content increased a different mechanism controlled the behavior or the film: The temperature threshold for change rose to approximately equal to 350 C and the loss of nitrogen was compensated by an equivalent rise in the oxygen content. The transformation from silicon oxynitride to silica was completed after 50 h at 400 C. The initial biaxial modulus of all compositions was 21-3- GPa and the intrinsic stress was -30 to 85 MPa. Increasing the oxygen content raised the temperature threshold where cracking first occurred; the two film compositions with the highest initial oxygen content did not crack, even at the highest temperature (450 C) investigated. At 450 C the biaxial modulus increased to approximately equal to 100 GPa and the intrinsic stress was approximately equal to 200 MPa. These increases could be correlated with the observed change in the film's composition. When nitrogen was replaced by oxygen, the induced stress remained lower than the biaxial strength of the material, but, when nitrogen and hydrogen were lost, stress-relieving microcracking occurred.

Harding, David R.; Ogbuji, Linus U. T.; Freeman, Mathieu J.

1995-01-01

7

Stress-strain state and stress intensity factor in the vicinity of crack-like defects under biaxial tension of a plate  

Science.gov (United States)

The problem of determining a stress-strain state described by singular and regular terms and a stress intensity factor in the vicinity of the tip of a crack-like defect in a plate under biaxial loading is considered. The Kolosov-Muskhelishvili method is used to obtain expressions for the stress tensor near the vertex of an ellipse, which yield formulas for stresses in the case of blunt cracks. The maximum shear stress, principal stresses, and stress intensity are determined. Formulas for the stress intensity factor under biaxial loading of a plate with a crack-like defect are obtained and can be used in the holographic interferometry method.

Ostsemin, A. A.; Utkin, P. B.

2014-11-01

8

Nonlinear Acoustics Used For Nondestructive Evaluation Of Biaxial Stress Of Solids  

Science.gov (United States)

The acoustoelasticity phenomenon may be the physical foundation of the nondestructive method of the evaluation of stressed states of solids. The reliability of acoustoelastic manner for applied biaxial stress evaluation in linear pipelines of large (820-1420 mm) diameter was proved experimentally. The pipes were closed by special steel bottoms and were exposed step by step to inner pressure of water. The precise measurements of time-of flight of shear and longitudinal waves propagated across the plane of stress acting were made before and during the loading. The values of stresses acting along and across the pipe axes (axial and circumferential stresses, correspondingly) were evaluated in accordance with the experimental and theoretical studying. The difference between stresses evaluated by means of nonlinear acoustics and by theoretical analysis, is not exceed 5% of the steel's yield point.

Nikitina, Nadezhda Ye.

2008-06-01

9

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)

10

Microcracking of High Performance Concrete Subjected to Biaxial Tension - Compression Stresses  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in english The results of an experimental investigation on the microcracking of high-performance concrete subjected to biaxial tension-compression stresses are presented. Short-term static tests and microcracking mapping were performed on 12.5 cm square by 1.25 cm thick plates. Strain controlled tests were exe [...] cuted in a biaxial testing machine constructed at the University of Texas. The primary variables studied were the deformations and the ultimate stress level at each stress ratio as well as the microcracking patterns and total crack lengths. For the microcracking study, the plates, after straining, were impregnated by an epoxy and then examined under a microscope. Microcracks were classified into simple and combined cracks, since this distinction allows for a much better representation of the microcracking process. A simple crack is either a bond or mortar crack where a combined crack contains both of these. For all stress ratios tested, the stress-strain behavior was directly related to the internal microcracking pattern. In all cases, the failure was directly related to the formation and propagation of the combined cracks.

José Marcio F., Calixto.

2002-09-01

11

Microcracking of High Performance Concrete Subjected to Biaxial Tension - Compression Stresses  

Directory of Open Access Journals (Sweden)

Full Text Available The results of an experimental investigation on the microcracking of high-performance concrete subjected to biaxial tension-compression stresses are presented. Short-term static tests and microcracking mapping were performed on 12.5 cm square by 1.25 cm thick plates. Strain controlled tests were executed in a biaxial testing machine constructed at the University of Texas. The primary variables studied were the deformations and the ultimate stress level at each stress ratio as well as the microcracking patterns and total crack lengths. For the microcracking study, the plates, after straining, were impregnated by an epoxy and then examined under a microscope. Microcracks were classified into simple and combined cracks, since this distinction allows for a much better representation of the microcracking process. A simple crack is either a bond or mortar crack where a combined crack contains both of these. For all stress ratios tested, the stress-strain behavior was directly related to the internal microcracking pattern. In all cases, the failure was directly related to the formation and propagation of the combined cracks.

José Marcio F. Calixto

2002-09-01

12

Appraisal of formulas for stresses in bilayered dental ceramics subjected to biaxial moment loading  

Energy Technology Data Exchange (ETDEWEB)

Summary - Objectives: The purpose of this study was to compare three existing sets of formulas predicting stresses in a thin circular plate subjected to biaxial moment loading, such that limitations for each set of formulas could be understood. These formulas include American Society for Testing and Materials (ASTM) formulas for monolayered plates, Roark's formulas for bilayered plates, and Hsueh et al.'s formulas for multilayered plates. Methods: The three sets of formulas were summarized and appraised. Biaxial moment loading is generally achieved using biaxial flexure tests, and the plate is placed on a support ring and loaded in the central region. While both ASTM and Hsueh et al.'s formulas predict stresses through the thickness of the plate, Roark's formulas predict stresses only on the top and the bottom surfaces of the plate. Also, a simply supported plate at its edge is considered in Roark's formulas. We modified Roark's formulas to include the overhang region of the plate to more closely simulate the actual loading configuration. Then, the accuracy of formulas was examined by comparing with finite element results of monolayered and bilayered plates subjected to ring-on-ring loading. Results: Monolayer is a special case of bilayer, and both monolayer and bilayer are special cases of multilayer. For monolayered plates, ASTM and Hsueh et al.'s formulas are identical, and both are in excellent agreement with finite element results. For bilayered plates, Hsueh et al.'s formulas are in excellent agreement with finite element results. For both monolayered and bilayered plates, Roark's formulas deviate from finite element results while the modified Roark's formulas are accurate. Conclusions: Roark's formulas for evaluating the biaxial strength of bilayered dental ceramics will result in errors in predicted stresses which depend on the size of the overhang region of the plate in the actual loading configuration. Also, Roark's formulas are limited to predicting stresses on the top and the bottom surfaces of the plate. On the other hand, Hsueh et al.'s formulas are for multilayered plates and predict stresses through the plate thickness.

Hsueh, Chun-Hway [ORNL; Thompson, G. A. [U.S. Army Dental and Trauma Research Detachment, Greak Lakes

2007-01-01

13

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.

14

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

Energy Technology Data Exchange (ETDEWEB)

Objective of this project is to investigate experimentally and theoretically the effects of neutron embrittlement and biaxial stress on magnetic properties in steels, using various magnetic measurement techniques. If neutron embrittlement and biaxial stress can be measured via changes in magnetic properties, this should ultimately assist in safety monitoring of nuclear power plants and of gas and oil pipelines. This first-year report addresses the issue of using magnetic property changes to detect neutron embrittlement. The magnetic measurements were all done on irradiated specimens previously broken in two in a Charpy test to determine their embrittlement. The magnetic properties of the broken charpy specimens from D.C. Cook did not correlate well with fluence or embrittlement parameters, possible due to metallurgical reasons. correlation was better with Indian Point 2 specimens, with the nonlinear harmonic amplitudes showing the best correlation (R[sup 2][approximately]0.7). However, correlation was not good enough. It is recommended that tests be done on unbroken irradiated Charpy specimens, for which magnetic characterization data prior to irradiation is available, if possible.

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

1993-01-31

15

Neutron diffraction analysis of stresses in an in-plane biaxially-fatigued stainless steel sample of cruciform geometry  

Digital Repository Infrastructure Vision for European Research (DRIVER)

An ex-situ in-plane biaxial low cycle fatigued sample of cruciform geometry made from austenitic stainless steel AISI 321 H was studied with the help of neutron diffraction strain scanning and also in-situ uniaxial loading using a stress rig on the FSD stress-diffractometer at the IBR-2 pulsed nuclear reactor (Dubna). The objectives of the experiment were to measure the macroscopic and microscopic residual stresses, crystallographic phase composition and the mechanical chara...

Taran, Yu V.; Balagurov, A. M.; Schreiber, J.; Korsunsky, A. M.

2008-01-01

16

Shallow Flaws Under Biaxial Loading Conditions, Part II: Application of a Weibull Stress Analysis of the Cruciform Bend Specimen Using a Hydrostatic Stress Criterion  

Energy Technology Data Exchange (ETDEWEB)

Cruciform beam fracture mechanics specimensl have been developed in the Heavy Section Steel Technology (HSST) Program at Oak Ridge National Laboratory (ORNL) to introduce a prototypic, far- field, out-of-plane biaxird bending stress component in the test section that approximates the nonlinear biaxial stresses resulting from pressurized-thernxd-shock or pressure-temperature loading of a nuclear reactor pressure vessel (RPV). 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), shtdlow, surface flaws. 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. Two and three- parameter Weibull models have been calibrated using a new scheme (developed at the University of Illinois) that maps toughness data from test specimens with distinctly different levels of crack-tip constraint to a small scale yielding (SSY) Weibull stress space. These models, using the new hydrostatic stress criterion in place of the more commonly used maximum principal stress in the kernel of the OW integral definition, have been shown to correlate the experimentally observed biaxiaI effect in cruciform specimens, thereby providing a scaling mechanism between uniaxial and biaxial loading states.

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

1999-08-01

17

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.

18

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

19

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

20

Effects of biaxial oscillatory shear stress on endothelial cell proliferation and morphology.  

Science.gov (United States)

Wall shear stress (WSS) on anchored cells affects their responses, including cell proliferation and morphology. In this study, the effects of the directionality of pulsatile WSS on endothelial cell proliferation and morphology were investigated for cells grown in a Petri dish orbiting on a shaker platform. Time and location dependent WSS was determined by computational fluid dynamics (CFD). At low orbital speed (50 rpm), WSS was shown to be uniform (0-1 dyne/cm(2)) across the bottom of the dish, while at higher orbital speed (100 and 150 rpm), WSS remained fairly uniform near the center and fluctuated significantly (0-9 dyne/cm(2)) near the side walls of the dish. Since WSS on the bottom of the dish is two-dimensional, a new directional oscillatory shear index (DOSI) was developed to quantify the directionality of oscillating shear. DOSI approached zero for biaxial oscillatory shear of equal magnitudes near the center and approached one for uniaxial pulsatile shear near the wall, where large tangential WSS dominated a much smaller radial component. Near the center (low DOSI), more, smaller and less elongated cells grew, whereas larger cells with greater elongation were observed in the more uniaxial oscillatory shear (high DOSI) near the periphery of the dish. Further, cells aligned with the direction of the largest component of shear but were randomly oriented in low magnitude biaxial shear. Statistical analyses of the individual and interacting effects of multiple factors (DOSI, shear magnitudes and orbital speeds) showed that DOSI significantly affected all the responses, indicating that directionality is an important determinant of cellular responses. PMID:22012789

Chakraborty, Amlan; Chakraborty, Sutirtha; Jala, Venkatakrishna R; Haribabu, Bodduluri; Sharp, M Keith; Berson, R Eric

2012-03-01

 
 
 
 
21

Effective X-ray elastic constant measurement for in situ stress measurement of biaxially strained AA5754-O  

International Nuclear Information System (INIS)

Accurate measurement of stresses by X-ray diffraction requires accurate X-ray elastic constants. Calibration experiments are one method to determine these for a specific material in a specific condition. In this paper, uniaxial tension experiments are used to investigate the variation of these constants after uniaxial and equal-biaxial plastic deformation for an aluminum alloy (AA5754-O) of interest to the automotive industry. These data are critical for accurate measurement of the biaxial mechanical properties of the material using a recent experimental method combining specialized sheet metal forming equipment with portable X-ray diffraction equipment. The measured effective X-ray elastic constants show some minor variation with increased plastic deformation, and this behavior was found to be consistent for both uniaxially and equal-biaxially strained samples. The use of two average values for effective X-ray elastic constants, one in the rolling direction and one transverse to the rolling direction of the sheet material, is shown to be of sufficient accuracy for the combined tests of interest. Comparison of uniaxial data measured using X-ray diffraction and standard methods show good agreement, and biaxial stress–strain results show good repeatability. Additionally, the calibration data show some non-linear behavior, which is analyzed in regards to crystallographic texture and intergranular stress effects. The non-linear behavior is found to be the result of intehavior is found to be the result of intergranular stresses based on comparison with additional measurements using other X-ray diffraction equipment and neutron diffraction.

22

Quantification and significance of fluid shear stress field in biaxial cell stretching device.  

Digital Repository Infrastructure Vision for European Research (DRIVER)

A widely used commercially available system for the investigation of mechanosensitivity applies a biaxial strain field to cells cultured on a compliant silicone substrate membrane stretched over a central post. As well as intended substrate strain, this device also provides a fluid flow environment for the cultured cells. In order to interpret the relevance of experiments using this device to the in vivo and clinical situation, it is essential to characterise both substrate and fluid environm...

Thompson, Ms; Abercrombie, Sr; Ott, Ce; Bieler, Fh; Duda, Gn; Ventikos, Y.

2011-01-01

23

Effect of grain shape and texture on equi-biaxial creep of stress relieved and recrystallized Zircaloy-4  

International Nuclear Information System (INIS)

Zirconium alloys are extensively used in various types of fission reactors both light and heavy water types for different applications, examples being thin-walled tubing to clad radioactive fuel, grids, channels in boiling water reactors (BWRs) as well as pressure and calandria tubes in pressurized heavy water reactors (PHWRs). Biaxial creep behaviors of stress relieved and recrystallized thin-walled tubing of Zircaloy-4 are considered under equal hoop and axial stresses by internal pressurization superimposed with axial load. Both hoop and axial strains were monitored and the ratio of the strain rates along the hoop to axial directions is considered to represent the degree of anisotropy. The slightly stronger hoop direction of the recrystallized material became weaker compared to the axial direction following cold work and a stress-relief anneal. Crystallographic texture was considered in terms of x-ray pole figures from which the crystallite orientation distribution functions (CODF) were derived. A crystal plasticity model based on slip on representative systems was combined with the CODF to predict the creep anisotropy. It was found that the textural differences between the recrystallized and stress-relieved material is believed to invoke anisotropic grain boundary sliding leading to stress enhancement in the hoop direction. This stress enhancement is shown to account for the observed differences in creep behavior between the present equiaxed and columnar grain strhe present equiaxed and columnar grain structures

24

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

25

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

Energy Technology Data Exchange (ETDEWEB)

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

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

1992-04-01

26

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.

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

2012-12-01

27

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

28

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.

29

Tuning the exciton binding energies in single self-assembled InGaAs/GaAs quantum dots by piezoelectric-induced biaxial stress.  

Science.gov (United States)

We study the effect of an external biaxial stress on the light emission of single InGaAs/GaAs(001) quantum dots placed onto piezoelectric actuators. With increasing compression, the emission blueshifts and the binding energies of the positive trion (X+) and biexciton (XX) relative to the neutral exciton (X) show a monotonic increase. This phenomenon is mainly ascribed to changes in electron and hole localization and it provides a robust method to achieve color coincidence in the emission of X and XX, which is a prerequisite for the possible generation of entangled photon pairs via the recently proposed "time reordering" scheme. PMID:20366855

Ding, F; Singh, R; Plumhof, J D; Zander, T; Krápek, V; Chen, Y H; Benyoucef, M; Zwiller, V; Dörr, K; Bester, G; Rastelli, A; Schmidt, O G

2010-02-12

30

Investigation of in-plane biaxial low cycle fatigued austenitic stainless steel AISI 321. II. Neutron diffraction stress analysis at the IBR-2 pulsed nuclear reactor  

International Nuclear Information System (INIS)

The in-plane biaxial low cycle fatigued sample of the cruciform geometry from austenitic stainless steel AISI 321 was investigated on the time-of-flight neutron Fourier stress-diffractometer. The lattice parameters in the austenite matrix and the martensite inclusions created during the fatigue cycling as well as the martensite volume fraction were measured along two mutually perpendicular planar axes of the sample of the cruciform geometry by using the strain neutron scanner. The phase total residual strain components were calculated using the stress equilibrium relations. The separation of the residual stresses into macro- and microstresses was performed using the mixture rule. The measurements of the applied load-phase elastic strain responses were carried out on a uniaxial load machine. The strong difference between the phase elastic moduli was found out

31

Application of magnetomechanical hysteresis modeling of magnetic techniques for monitoring neutron embrittlement and biaxial stress. First year report, June 1991--June 1992  

Energy Technology Data Exchange (ETDEWEB)

Objective of this project is to investigate experimentally and theoretically the effects of neutron embrittlement and biaxial stress on magnetic properties in steels, using various magnetic measurement techniques. If neutron embrittlement and biaxial stress can be measured via changes in magnetic properties, this should ultimately assist in safety monitoring of nuclear power plants and of gas and oil pipelines. This first-year report addresses the issue of using magnetic property changes to detect neutron embrittlement. The magnetic measurements were all done on irradiated specimens previously broken in two in a Charpy test to determine their embrittlement. The magnetic properties of the broken charpy specimens from D.C. Cook did not correlate well with fluence or embrittlement parameters, possible due to metallurgical reasons. correlation was better with Indian Point 2 specimens, with the nonlinear harmonic amplitudes showing the best correlation (R{sup 2}{approximately}0.7). However, correlation was not good enough. It is recommended that tests be done on unbroken irradiated Charpy specimens, for which magnetic characterization data prior to irradiation is available, if possible.

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

1993-01-31

32

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)

33

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

34

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

35

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

36

Development of biaxial test fixture includes cryogenic application  

Science.gov (United States)

Test fixture has the capability of producing biaxial stress fields in test specimens to the point of failure. It determines biaxial stress by dividing the applied load by the net cross section. With modification it can evaluate materials, design concepts, and production hardware at cryogenic temperatures.

Helf, J. C.; Kelly, R. E.; Kerr, D. A.; Waldron, C. R.

1968-01-01

37

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)

38

Appraisal of biaxial strength testing  

International Nuclear Information System (INIS)

Three biaxial strength tests (ring-on-ring, piston-on-3 ball, and ball-on-ring) were evaluated using finite element analysis. Although in all three tests some uncertainties exist regarding the calculation of fracture stresses from the analytical equation, if fracture occurs within the loading ring, the ring-on-ring loading is thought to give the most accurate measure of strength. In addition, it was found that specimen shape (square vs circular) had no effect on the stress distribution within the supports and that the stress at the edge of the specimen was less than 10% of the maximum stress for an overhang greater than about 40%. Fracture strength measurements on soda-lime glass gave support to these finite element results

39

Fatigue flaw growth behavior in stiffened and unstiffened panels loaded in biaxial tension  

Science.gov (United States)

The effect was investigated of biaxial loading on the flaw growth rate of 2219-T87 aluminum alloy that would be typical of Space Shuttle cryogenic tankage design. The stress distribution and stress concentration factors for several integrally stiffened panels under various loading conditions were obtained. The flaw growth behavior of both stiffened and unstiffened panels under biaxial loading conditions was determined. The effect of a complex stress state was studied by introducing flaws in fillet areas of biaxially loaded stiffened panels.

Beck, E. J.

1973-01-01

40

Biaxial fatigue strength of a fine-grained isotropic graphite for HTTR  

International Nuclear Information System (INIS)

Biaxial fatigue tests on an isotropic graphite IG-11 used in the HTTR were done in the stress regimes of tension-tension and compression-tension at room temperature to evaluate its fatigue strength at the biaxial state. Biaxial fatigue tests at 1,273 K in a vacuum were also done in the latter stress regime. Applied stress levels in the longitudinal direction ranged from 75 to 90% of the mean static strength, and in the transverse direction, from 53 to 74% of the mean strength. It was indicated from the tests that (1) the difference in the fatigue strength between the uniaxial and biaxial was observed when the applied stress levels were smaller than about 90% of the mean strength, (2) the biaxial fatigue strength was found to be larger than that for the uniaxial if the biaxial applied stresses were normalized to the mean biaxial static strength, (3) the biaxial fatigue strength at 1,273 K was equal to or larger than that at room temperature, (4) the evaluation of the integrity of graphite components in the HTTR, from the aspect of the biaxial fatigue, was believed to be conservative on the basis of the uniaxial fatigue strength and the biaxial static strength. (author)

 
 
 
 
41

Biaxial yield surface investigation of polymer-matrix composites.  

Science.gov (United States)

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. PMID:23529150

Ye, Junjie; Qiu, Yuanying; Zhai, Zhi; He, Zhengjia

2013-01-01

42

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

43

Biaxial Creep Specimen Fabrication  

International Nuclear Information System (INIS)

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

44

Analysis and experimental validation of through-thickness cracked large-scale biaxial fracture tests  

International Nuclear Information System (INIS)

Since 1984 TWI has been involved in an extensive series of tests investigating the effects of biaxial loading on the fracture behaviour of A533B steel. Testing conditions have ranged from the lower to upper shelf regions of the transition curve and covered a range of biaxiality ratios. In an attempt to elucidate the trends underlying the experimental results, finite element-based mechanistic models were used to analyse the effects of biaxial loading. For ductile fracture, a modified Gunson model was used and important effects on tearing behaviour were found for through thickness cracked wide plates, as observed in upper shelf tests. For cleavage fracture, both simple T-stress methods and the Anderson-Dodds and Beremin models were used. Whilst the effect of biaxiality on surface cracked plates was small, a marked effect of biaxial loading was found for the through-thickness crack. To further validate the numerical predictions for cleavage fracture, TWI have performed an additional series of lower shelf through thickness cracked biaxial wide plate fracture tests. These tests were performed using various biaxiality loading conditions varying from simple uniaxial loading, through equibiaxial loading, to a biaxiality ratio equivalent to a circumferential crack in a pressure vessel. These tests confirmed the predictions that there is a significant effect of biaxial loading on cleavage fracture of through thickness cracked plate. (orig.)

45

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2010-07-01

46

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

International Nuclear Information System (INIS)

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

47

Fracture assessment of shallow-flaw cruciform beams tested under uniaxial and 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 toughnessf loading-biaxiality on fracture toughness; the conventional maximum principal stress criterion indicated no effect. A three-parameter Weibull model based on the hydrostatic stress criterion is shown to correlate with the experimentally observed biaxial effect on cleavage fracture toughness by providing a scaling mechanism between uniaxial and biaxial loading states. (orig.)

48

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

49

Methodology for dynamic biaxial tension testing of pregnant uterine tissue.  

Science.gov (United States)

Placental abruption accounts for 50% to 70% of fetal losses in motor vehicle crashes. Since automobile crashes are the leading cause of traumatic fetal injury mortality in the United States, research of this injury mechanism is important. Before research can adequately evaluate current and future restraint designs, a detailed model of the pregnant uterine tissues is necessary. The purpose of this study is to develop a methodology for testing the pregnant uterus in biaxial tension at a rate normally seen in a motor vehicle crash. Since the majority of previous biaxial work has established methods for quasi-static testing, this paper combines previous research and new methods to develop a custom designed system to strain the tissue at a dynamic rate. Load cells and optical markers are used for calculating stress strain curves of the perpendicular loading axes. Results for this methodology show images of a tissue specimen loaded and a finite verification of the optical strain measurement. The biaxial test system dynamically pulls the tissue to failure with synchronous motion of four tissue grips that are rigidly coupled to the tissue specimen. The test device models in situ loading conditions of the pregnant uterus and overcomes previous limitations of biaxial testing. A non-contact method of measuring strains combined with data reduction to resolve the stresses in two directions provides the information necessary to develop a three dimensional constitutive model of the material. Moreover, future research can apply this method to other soft tissues with similar in situ loading conditions. PMID:17487086

Manoogian, Sarah; Mcnally, Craig; Calloway, Britt; Duma, Stefan

2007-01-01

50

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

International Nuclear Information System (INIS)

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

51

The Influence of Strain Path on Biaxial Compressive Behavior of AZ31 Magnesium Alloy  

Science.gov (United States)

The strain path dependence of the compressive flow behavior of cast AZ31 magnesium alloy was investigated. Biaxial compression tests with linear strain paths were conducted using a unique biaxial compression device. It was found that the equivalent stress-strain relations varied according to the strain paths. The work contour for linear strain paths was well described by the Logan-Hosford yield criterion. Biaxial compressions with abrupt strain path change were also carried out to investigate the influences of the prestrain amplitude and angular relation of the sequential strain paths on the flow behavior. Rapid increase in the equivalent stress was observed just after the abrupt strain path change. These specific flow behaviors were discussed with regard to the plastic anisotropy, which showed rapid evolution in the early stage of the biaxial compressions.

Shimizu, Ichiro; Tada, Naoya; Nakayama, Kosuke

52

Fatigue of Clip connectors for offshore drilling risers under biaxial tension  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 a...

Gaur Vidit; Mbiakop-Ngassa Armel-Brice; Doquet Véronique; Roguet Eléonore; Persent Emmanuel

2014-01-01

53

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

International Nuclear Information System (INIS)

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

54

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

55

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

56

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.

57

Biaxial wheel/hub test facility. Proceedings  

Energy Technology Data Exchange (ETDEWEB)

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

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

2000-07-01

58

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

59

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

60

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

International Nuclear Information System (INIS)

In this paper, an experimental study into the biaxial strength of plain concrete for containment structures is represented and technical difficulties encountered in the development of a suitable test setup are discussed. Prior to testing for a 1/8 model of cylindrical specimen(?150x300) and four 1/4 models of plate specimens(200x200xT(=30, 50, 60, 70)mm) under uniaxial compression, the strength ratios between both specimens with different geometry shapes were found by nonlinear finite element analyses using ABAQUS. From the results three suitable type of considered plate specimens were selected for failure testing under biaxial stress. As initial approach to develop biaxial strength criteria of plain concrete, the various test data were obtained under uniaxial compression, uniaxial tension and biaxial compression. The test data indicate that the strength of concrete under biaxial compression, f1=f2, is 14.7 percent larger than under uniaxial compression and the Poisson's ratio of concrete is 0.155. Teflon employed to eliminate friction between test specimen and loading platens showed and excellent effect under biaxial compression, f1=f2

 
 
 
 
61

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

62

Biaxial loading effects on fracture toughness of reactor pressure vessel steel  

International Nuclear Information System (INIS)

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

63

Compact biaxial micromachined resonant accelerometer  

Science.gov (United States)

This paper presents a biaxial silicon resonant microaccelerometer characterized by a high sensitivity and a low cross-axis sensitivity. The device has a detection structure with a single inertial mass and two pairs of resonating beams allowing for the simultaneous differential measurement of acceleration acting along two different axes. The design of the accelerometer and in particular the geometrical configuration of the resonating elements is analytically optimized and finalized through finite element simulations. Experimental results on a fabricated device demonstrate a mean differential sensitivity of 250 Hz?g-1 at a polarization voltage of 4 V, around a resonance frequency of 84 kHz.

Caspani, Alessandro; Comi, Claudia; Corigliano, Alberto; Langfelder, Giacomo; Tocchio, Alessandro

2013-10-01

64

Singular values, nematic disclinations, and emergent biaxiality.  

Science.gov (United States)

Both uniaxial and biaxial nematic liquid crystals are defined by orientational ordering of their building blocks. While uniaxial nematics only orient the long molecular axis, biaxial order implies local order along three axes. As the natural degree of biaxiality and the associated frame that can be extracted from the tensorial description of the nematic order vanishes in the uniaxial phase, we extend the nematic director to a full biaxial frame by making use of a singular value decomposition of the gradient of the director field instead. The degrees of freedom are unveiled in the form of quasidefects and the similarities and differences between the uniaxial and biaxial phase are analyzed by applying the algebraic rules of the quaternion group to the uniaxial phase. PMID:23767474

?opar, Simon; Dennis, Mark R; Kamien, Randall D; Žumer, Slobodan

2013-05-01

65

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.)

66

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

Energy Technology Data Exchange (ETDEWEB)

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.

Park, Joong Cheul [Yeungnam Univ., Gyeongsan (Korea, Republic of); Kwon, Jae Do [KAERI, Daejeon (Korea, Republic of)

2005-06-01

67

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

68

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

69

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

Energy Technology Data Exchange (ETDEWEB)

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 {epsilon}-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.

Wada, M. [Department of Mechanical Engineering, Hosei University, Koganei, Tokyo 184-8584 (Japan)], E-mail: mwada_bb@ybb.ne.jp; Naoi, H. [Department of Mechanical Engineering, Hosei University, Koganei, Tokyo 184-8584 (Japan); Yasuda, H. [Department of Mechanical Engineering, Kobe University, Nada, Kobe 657-8501 (Japan); Maruyama, T. [Awaji Materia Co., Ltd. 2-3-13, Kanda-ogawamachi, Chiyoda, Tokyo 101-0052 (Japan)

2008-05-25

70

Biaxial low cycle fatigue behavior and martensite formation of a metastable austenitic cast TRIP steel under proportional Loading  

Energy Technology Data Exchange (ETDEWEB)

In this paper the biaxial low cycle fatigue behavior under proportional loading of a recently developed metastable austenitic stainless cast steel is presented. Total strain controlled tests were carried out on a 250 kN biaxial servohydraulic tension-compression testing machine equipped with a biaxial orthogonal extensometer to measure the principal strains in the gauge area of the used cruciform specimens. The principal stresses were determined based on the compliance after the load reversals. The low cycle fatigue behavior under biaxial synchronous loading is compared to the uniaxial behavior. Therefore, biaxial single step tests and a biaxial multiple step load increase test were carried out. The dependence of the stress state on the cyclic deformation curves, cyclic stress-strain curves and the formation of martensite are described. Finally, the fatigue life relationship according to Basquin and Manson-Coffin was determined and compared to the Smith, Watson and Topper damage parameter, which provides a satisfactory fatigue life prediction. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Kulawinski, D.; Ackermann, S.; Glage, A.; Henkel, S.; Biermann, H. [Institute of Materials Engineering, Technische Universitaet Bergakademie Freiberg (Germany)

2011-09-15

71

Ray-optics analysis of inhomogeneous biaxially anisotropic media :  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Firm evidence of the biaxial nematic phase in liquid crystals, not induced by a magnetic or electric field, has been established only recently. The discovery of these biaxially anisotropic liquid crystals has opened up new areas of both fundamental and applied research. The advances in biaxial liquid crystal-related topics call for a good overview on the propagation of waves through biaxially anisotropic media. Although the literature sporadically discusses biaxial interfaces, the propagation...

Sluijter, M.; Boer, D. K. G.; Urbach, H. P.

2009-01-01

72

Biaxial Loading of Continuously Graded Thermoviscoplastic Materials  

Science.gov (United States)

In this paper we study the problem of biaxial loading of a sheet made of a continuously graded thermoviscoplastic material. The material phases are supposed to exhibit thermal softening, strain-rate sensitivity and strain hardening, continuously varying along all directions. First we formulate the plane stress problem of a non-homogeneous material and study the behavior of temperature, strain and strain-rate related to inhomogeneities of thermomechanical parameters and geometrical defects. Next we present the “effective” instability analysis of Dudzinski and Molinari (Int J Solids Struc 1991), adapted to the non-homogeneous case, to define the critical conditions and select the localization modes by studying the overall strains for which a certain level of instability growth is developed. Finally, we present the numerical simulation of the fully non-linear dynamical problem. Several aspects of the deformation process and the related role of non-homogeneities are analyzed onset of strain and temperature localization, ductility, contours of temperature increase as detectors of instability, interplay with initial defects, multiple necking, decrease of thinning-rate, variation of the multiple necking due to boundary conditions.

Chatzigeorgiou, George; Charalambakis, Nicolas; Kalpakides, Vassilios

2007-03-01

73

Biaxial ratcheting and cyclic plasticity for Bree-type loading. Part 1: Finite element analysis  

Energy Technology Data Exchange (ETDEWEB)

The Bree diagram has been incorporated in the ASME B and PV Code in the elevated temperature Code Case N47 as a design approach for limiting strain accumulation in cylinders subjected to cyclic thermal loadings under sustained primary stress. Since the Bree diagram is based upon uniaxial-stress model, it is pertinent to examine the influence of biaxial stresses on strain growth and cyclic stress-strain hysteresis response. The results of inelastic analyses presented in this paper showed that ratcheting and hysteresis behavior may also occur in the axial direction in addition to the hoop direction. Results of almost 100 load cases were presented to clarify the influence of biaxial membrane and thermal bending stresses on the structural behavior. A design approach for the assessment of this type of problem was suggested which utilizes these results.

Ng, H.W.; Nadarajah, C. [Nanyang Technological Univ., Singapore (Singapore). School of Mechanical and Production Engineering

1996-05-01

74

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

75

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

76

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

77

Studies of biaxial mechanical properties and nonlinear finite element modeling of skin.  

Science.gov (United States)

The objective of this research is to conduct mechanical property studies of skin from two individual but potentially connected aspects. One is to determine the mechanical properties of the skin experimentally by biaxial tests, and the other is to use the finite element method to model the skin properties. Dynamic biaxial tests were performed on 16 pieces of abdominal skin specimen from rats. Typical biaxial stress-strain responses show that skin possesses anisotropy, nonlinearity and hysteresis. To describe the stress-strain relationship in forms of strain energy function, the material constants of each specimen were obtained and the results show a high correlation between theory and experiments. Based on the experimental results, a finite element model of skin was built to model the skin's special properties including anisotropy and nonlinearity. This model was based on Arruda and Boyce's eight-chain model and Bischoff et al.'s finite element model of skin. The simulation results show that the isotropic, nonlinear eight-chain model could predict the skin's anisotropic and nonlinear responses to biaxial loading by the presence of an anisotropic prestress state. PMID:20936741

Shang, Xituan; Yen, Michael R T; Gaber, M Waleed

2010-06-01

78

Biaxial Loading Tests for steel containment vessel  

International Nuclear Information System (INIS)

The Nuclear Power Engineering Corporation (NUPEC) has conducted a 1/10 scale of the steel containment vessel (SCV) test for the understanding of ultimate structural behavior beyond the design pressure condition. Biaxial Loading Tests were supporting tests for the 1/10 scale SCV model to evaluate the method of estimating failure conditions of thin steel plates under biaxial loading conditions. The tentative material models of SGV480 and SPV490 were obtained. And the behavior of SGV480 and SPV490 thin steel plates under biaxial loading conditions could be well simulated by FE-Analyses with the tentative material models and Mises constitutive law. This paper describes the results and the evaluations of these tests. (author)

79

Biaxial tension on polymer in thermoforming range  

Directory of Open Access Journals (Sweden)

Full Text Available This paper presents an experimental characterization of mechanical properties of a polyethylene terephtalate (PET resin classically used in stretch blow moulding process. We have applied on such a material a well established experimental protocol at CEMEF, including new and relevant biaxial tensile tests. The experimental set-up relative to biaxial tension will be presented and described in a first part of the paper. Furthermore, we will focus on the experimental DMTA preliminary tests which are required to estimate the resin sensibility to temperature and strain rate in linear viscoelasticity domain. Finally, we will be interested in the material large strain behaviour: biaxial tensile results are presented and discussed. Finally, such an experimental approach should allow a relevant modelling of polymer physics and mechanics; this point will not be discussed here because of a lack of time.

Billon N.

2010-06-01

80

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

 
 
 
 
81

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

82

Dynamic biaxial tissue properties of the human cadaver aorta.  

Science.gov (United States)

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

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

2006-11-01

83

Electrodeposition of biaxially textured layers on a substrate  

Science.gov (United States)

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

84

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

85

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

86

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

87

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

Science.gov (United States)

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. PMID:24725440

Lyons, Mathew; Winter, Des C; Simms, Ciaran K

2014-06-01

88

Effect of Equal Biaxial Pre-Strain on Forming Limit Diagram of AA5083  

Science.gov (United States)

In this work, the effect of equal biaxial pre-strain on the forming limit curve (FLC) of 5083 aluminum alloy has been investigated. For this purpose, in the first stage, square blanks with dimensions of 200 mm in each length were cut from the original sheet and stretched by a spherical punch to the specified heights. Then, specimens were prepared by cutting the pre-strained blanks with the longitudinal axis parallel and perpendicular to the rolling direction. In the second stage, the specimens were tested by the out-of-plane test method to determine the forming limit diagram (FLD) according to the ISO 12004. Furthermore, forming limit stress diagram (FLSD) was determined by using Hill's quadratic yield function. The results showed that the equal biaxial pre-straining decreased and shifted the FLC to the right hand side of the diagram. However, it had not any effect on the forming limit stress curves.

Zhalehfar, F.; Hosseinipour, S. J.; Nourouzi, S.; Gorji, A. H.

2011-01-01

89

Effect of Equal Biaxial Pre-Strain on Forming Limit Diagram of AA5083  

International Nuclear Information System (INIS)

In this work, the effect of equal biaxial pre-strain on the forming limit curve (FLC) of 5083 aluminum alloy has been investigated. For this purpose, in the first stage, square blanks with dimensions of 200 mm in each length were cut from the original sheet and stretched by a spherical punch to the specified heights. Then, specimens were prepared by cutting the pre-strained blanks with the longitudinal axis parallel and perpendicular to the rolling direction. In the second stage, the specimens were tested by the out-of-plane test method to determine the forming limit diagram (FLD) according to the ISO 12004. Furthermore, forming limit stress diagram (FLSD) was determined by using Hill's quadratic yield function. The results showed that the equal biaxial pre-straining decreased and shifted the FLC to the right hand side of the diagram. However, it had not any effect on the forming limit stress curves.

90

High temperature creep damage under biaxial loading: INCO 718 and 316 (17-12 SPH) steels  

International Nuclear Information System (INIS)

The respective influences of the Von-Mises equivalent stress and of the maximum principal stress on high temperature creep damage of two industrial alloys (Inconel 718 and 17-12 SPH stainless steel) are pointed out in a quantitative way through tensile-torsion biaxial tests. Through inversions of the shear component, the important part taken by the principal direction corresponding to the maximum principal stress is also shown. These results are supported by metallographic observations. Then, an anisotropic form of the damage variable D taking into account the experimental observations is proposed. (orig.)

91

Walk-off correction in biaxial crystals  

Science.gov (United States)

A comprehensive model has been developed to construct phase matching conditions, including Poynting vector directions, parametrically interacting beam wavelengths, relative walk-off angles and polarization states in a biaxial nonlinear single crystal with known refractive index dispersion. The model optimizes phase matching conditions by providing a strategy for walk-off compensation that determines the optimum periodicity of twist-twin Adhesive-Free Bond (AFB(R)) composite pair designs. The model is validated experimentally by measuring the calculated walk-off angles and the crystal orientation of KTP that correlates to the given Poynting vector. The method is useful in reducing uncertainties of OPO designs, in providing walk-off compensation design data, and in confirming the final walk-off corrected design configuration. It is generally applicable to biaxial and uniaxial nonlinear crystals.

Lee, H.-C.; Meissner, H. E.

2007-10-01

92

Valence band structure and density of states effective mass model of biaxial tensile strained silicon based on k · p theory  

International Nuclear Information System (INIS)

After constructing a stress and strain model, the valence bands of in-plane biaxial tensile strained Si is calculated by k · p method. In the paper we calculate the accurate anisotropy valance bands and the splitting energy between light and heavy hole bands. The results show that the valance bands are highly distorted, and the anisotropy is more obvious. To obtain the density of states (DOS) effective mass, which is a very important parameter for device modeling, a DOS effective mass model of biaxial tensile strained Si is constructed based on the valance band calculation. This model can be directly used in the device model of metal—oxide semiconductor field effect transistor (MOSFET). It also a provides valuable reference for biaxial tensile strained silicon MOSFET design. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

93

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.

Angelsky, Oleg V.; Maksimyak, Andrew P.

2010-01-01

94

Biaxial testing for fabrics and foils optimizing devices and procedures  

CERN Document Server

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

Beccarelli, Paolo

2015-01-01

95

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

96

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

International Nuclear Information System (INIS)

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

97

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

98

Biaxial unloading and springback behavior of dual-phase DP590 steel using cruciform specimens  

Science.gov (United States)

The unloading behavior of a dual-phase steel (DP590) from a biaxial state of stress was probed using a newly-designed cruciform specimen. The specimen was designed to develop uniform and relatively large plastic strains (over 15% equivalent logarithmic plastic strain) in the gage section, before failure. Nine radial loading paths in the 1st quadrant of the plane stress space were probed. The experiments involved repeated loading and unloading up to failure. At every unloading, the initial response was found to agree with the linear, orthotropically elastic response of the undeformed material. This first linear response was followed by a second one, at a reduced slope. Beyond that, the recorded response was fully non-linear. The same sequence of events was observed during each reloading. The biaxial non-linear strain recovery components ?xnl and ?ynl were measured to be on average approximately 11% of the elastic strains ?xe and ?ye, respectively. This ratio was found to increase with plastic deformation. Subsequently, these biaxial experiments were used to calibrate the Yld2000-2D yield function.

Korkolis, Yannis P.; Deng, Nengxiu; Kuwabara, Toshihiko

2013-12-01

99

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

Directory of Open Access Journals (Sweden)

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

M. N. Saraf

2013-04-01

100

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

 
 
 
 
101

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

102

In-plane uniaxial and biaxial crushing of a polycarbonate honeycomb  

Science.gov (United States)

The uniaxial and biaxial in-plane crushing of honeycomb is studied through a combination of experiments and analyses. The honeycomb has circular thin-walled polycarbonate cells in a hexagonal arrangement. Under displacement controlled uniaxial compression, the force-displacement response is characterized by three regimes of behavior. In the initial rising part of the response, the deformation is essentially uniform throughout the specimen. Following the load maximum, the deformation localizes in a narrow zone of cells. Collapse then propagates through the specimen while the load remains relatively constant until all the cells have collapsed at which point the load rises sharply. As a result of the rate dependence of the material, the initiation and propagation stresses increase as the rate of crushing of the honeycomb is increased. This crushing process was simulated numerically through the finite element method. The developed models properly address the nonlinearities due to geometry and contact. An elastic-power law viscoplastic constitutive rule is used to model the behavior of the polycarbonate. Results from analyses involving a characteristic cell and from full scale simulations of the experiments are in excellent agreement with the experimental results. Biaxial crushing was performed in a custom biaxial test facility. This facility is capable of crushing specimens in two orthogonal directions simultaneously to volume reductions of nearly 95%. Approximately square specimens were crushed between rigid platens at different biaxiality ratios by varying the two speeds of crushing. The onset of collapse involves localized instabilities as in the uniaxial crushing. However, the extent of the localized deformation varies with the biaxiality ratio. The prevalent mechanisms of collapse as well as the energy absorption capacity of the material also depend on this ratio. The highest energy is required when the specimens are crushed at the same rate in the two directions. Finite element simulations of the biaxial crushing were also performed. The models in these calculations were smaller than the specimens used in the experiments. As a result, the responses differ slightly in the initial stages of crushing, but for larger strains, the predictions agree well with the measurements. The calculated amounts of energy absorbed are in excellent agreement with the experiments. In addition, many of the modes of cell collapse seen in the experiment are reproduced in the simulations.

Papka, Scott Duane

103

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.)

104

A simple biaxial test for exploring failure tensor polynomial criteria of composites  

Science.gov (United States)

Biaxial tests at the anisotropic planes of composite laminae do not provide conclusive evidence for deciding which of the several versions of the failure tensor polynomial (FTP) criterion corresponds to their real behavior. The only way, hitherto, of selecting the appropriate criterion remained the triaxial test. However, difficulties and inaccuracies encountered in running such tests with anisotropic materials and composites have contributed to the almost complete absence of such tests in the literature. In this paper it has been shown that a simple biaxial hydrostatic loading test on a transverse plate corresponding to the isotropic plane of a transversely isotropic material constitutes an accurate technique to decide which version of the criterion is valid. It is proved that the influence of the anisotropy along the strong stress axis normal to the isotropic plane on the failure locus increases considerably the differences in failure between the various criteria and constitutes a safe test for deciding the validity of the appropriate criterion. Tests in biaxial hydrostatic tension or compression with different composite materials have indicated clearly the superiority of the elliptic paraboloid failure surface criterion.

Theocaris, Pericles S.

105

Stretching silicon: A uniaxial and biaxial strain generation process and the resulting mobility enhancement in silicon-on-insulator MOSFETs  

Science.gov (United States)

Strained silicon is of technological interest for its ability to increase charge carrier mobilities in MOSFETs and thereby improve circuit performance without requiring device scaling. At high vertical electric fields, biaxial tensile strain enhances electron mobility while uniaxial compressive strain enhances hole mobility, for example. In the present work, a process is developed to integrate upon a single wafer, for the first time, uniaxially-strained, biaxially-strained and unstrained silicon islands. The ultra-thin ( crystal direction. The strain generation method works by lateral expansion of a silicon/silicon germanium bi-layer island on a viscous borophosphorosilicate glass (BPSG) layer during high temperature (> 700°C) anneal. By manipulating the island geometry from squares to narrow rectangles, biaxial and uniaxial silicon strains are achieved. Numerical simulations of the lateral expansion process for islands of various aspect ratios identify process windows and island geometry requirements for maximum uniaxial strain. The modeled and measured strain results agree well. An undesired buckling process can roughen the film surface during anneals; the buckling and lateral expansion processes compete to determine the final state of the film. The amplitude of buckling can be reduced and its time scale lengthened by thinning the compliant BPSG layer. Differences in 1-D and 2-D buckling on uniaxially- and biaxially-stressed SiGe islands, respectively, are measured, and by comparison to models, attributed to the different magnitudes of 1-D and 2-D stress present in the films. Fully-depleted strained-SOI MOSFETs are fabricated using this strain generation process. By adding a silicon nitride barrier layer below the BPSG, device performance is greatly improved. Biaxial tensile strain of 0.38-0.52% enhances electron and hole mobilities by 30-55%. Comparable uniaxial tension parallel to a or channel improves electron mobilities by up to 72% and hole mobilities by up to 54%.

Peterson, Rebecca Lorenz

106

Fatigue of concrete subjected to biaxial loading in the tension region  

Science.gov (United States)

Rigid airport pavement structures are subjected to repeated high-amplitude loads resulting from passing aircraft. The resulting stress-state in the concrete is a biaxial combination of compression and tension. It is of interest to model the response of plain concrete to such loading conditions and develop accurate fatigue-based material models for implementation in mechanistic pavement design procedures. The objective of this work is to characterize the quasi-static and low-cycle fatigue response of concrete subjected to biaxial stresses in the tensile-compression-tension (t-C-T) region, where the principal tensile stress is larger in magnitude than the principal compressive stress. An experimental investigation of material behavior in the biaxial t-C-T region is conducted. The experimental setup consists of the following test configurations: (a) notched concrete beams tested in three-point bend configuration, and (b) hollow concrete cylinders subjected to torsion with or without superimposed axial tensile force. The damage imparted to the material is examined using mechanical measurements and an independent nondestructive evaluation (NDE) technique based on vibration measurements. The failure of concrete in t-C-T region is shown to be a local phenomenon under quasi-static and fatigue loading, wherein the specimen fails owing to a single crack. The crack propagation is studied using the principles of fracture mechanics. It is shown that the crack propagation resulting from the t-C-T loading can be predicted using mode I fracture parameters. It is observed that crack growth in constant amplitude fatigue loading is a two-phase process: a deceleration phase followed by an acceleration stage. The quasi-static load envelope is shown to predict the crack length at fatigue failure. A fracture-based fatigue failure criterion is proposed, wherein the fatigue failure can be predicted using the critical mode I stress intensity factor. A material model for the damage evolution during fatigue loading of concrete in terms of crack propagation is proposed. The crack growth acceleration stage is shown to follow Paris law. The model parameters obtained from uniaxial fatigue tests are shown to be sufficient for predicting the considered biaxial fatigue response.

Subramaniam, Kolluru V. L.

107

Conductive and robust nitride buffer layers on biaxially textured substrates  

Science.gov (United States)

The present invention relates to epitaxial, electrically conducting and mechanically robust, cubic nitride buffer layers deposited epitaxially on biaxially textured substrates such as metals and alloys. The invention comprises of a biaxially textured substrate with epitaxial layers of nitrides. The invention also discloses a method to form such epitaxial layers using a high rate deposition method as well as without the use of forming gases. The invention further comprises epitaxial layers of oxides on the biaxially textured nitride layer. In some embodiments the article further comprises electromagnetic devices which may have superconducting properties.

Sankar, Sambasivan [Chicago, IL; Goyal, Amit [Knoxville, TN; Barnett, Scott A [Evanston, IL; Kim, Ilwon [Skokie, IL; Kroeger, Donald M [Knoxville, TN

2009-03-31

108

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.

Breiby, Dag W.; Chin, Patrick T.K.

2009-01-01

109

$^{52}$Cr Spinor Condensate$ -- $ A Biaxial or Uniaxial Spin Nematic  

CERN Document Server

We show that the newly discovered $^{52}$Cr Bose condensate in zero magnetic field can be a spin nematic of the following kind: A "maximum" polar state, a "co-linear" polar state, or a biaxial nematic ferromagnetic state. We also present the phase diagram with a magnetic field in the interaction subspace containing the Chromium condensate. It contains many uniaxial and biaxial spin nematic phases, which often but not always break time reversal symmetry, and can exist with or without spontaneous magnetization.

Diener, R B; Diener, Roberto B.; Ho, Tin-Lun

2006-01-01

110

Deformation modes of nanostructured thin film under controlled biaxial deformation  

Digital Repository Infrastructure Vision for European Research (DRIVER)

This paper reports on the mechanical behaviour of nanostructured W/Cu thin films deposited on Kapton® under controlled biaxial loadings thanks to a biaxial testing device developed on DiffAbs beamline at SOLEIL synchrotron (Saint-Aubin, France). In situ tensile tests were carried out combining 2D synchrotron x-ray diffraction (XRD) and digital-image correlation (DIC) techniques. First, the elastic behaviour of the composite metallic film-polymeric substrate was investigated under equi-biaxia...

Djaziri, Soundes; Faurie, Damien; Le Bourhis, Eric; Goudeau, Philippe; Renault, Pierre-olivier; Mocuta, Christian; Thiaudie?re, Dominique; Hild, Franc?ois

2013-01-01

111

Bake hardening of hot rolled multiphase steels under biaxial pre-strained conditions  

Energy Technology Data Exchange (ETDEWEB)

Multiphase steels show a strong bake hardening effect being of importance for shaping of car body structural parts. The raised yield strength is exploited for improved crash resistance. Especially the automotive industry has a growing interest in using this effect. Normally the bake hardening effect is examined in tensile tests whereas under industrial conditions shaping of structural parts shows a wide spread of stress strain behaviour, from uniaxial conditions over plain strain to biaxial ones. So it is obvious that the bake hardening behaviour of a material cannot be described with results of the uniaxial tension test only. To give a first answer to this question, the dependence of the bake hardening effect on different biaxial prestrains was investigated for several hot rolled multiphase steels using various baking temperatures and holding times whereas the bake hardening effect under uniaxial prestrain had already been examined in [5]. Considering the choices to generate biaxial strain, a Marciniak forming tool with a diameter of 250 mm mounted on a 2500 kN hydraulic press was chosen. For control of plastic deformation and adjustment the non-contact measuring system ARGUS, was used. To reduce the quantity of experiments ''design of experiments'' and statistical methods were applied for a martensitic steel, a dual phase steel, a complex phase steel, a ferrite-bainite steel, and a retained austenite steel known as TRIP, all in hot rolled condition. As a result, a formula for yield stress, tensile strength and residual deformability was developed. Furthermore, a method was found to predict easily whether a steel under investigation is qualified for additional experiments in regard to bake hardening or more exactly its response to different baking temperatures and holding times. (orig.)

Palkowski, H.; Anke, T. [Inst. fuer Metallurgie, Werkstoffumformung, Technische Univ. Clausthal, Clausthal-Zellerfeld (Germany)

2006-09-15

112

High temperature creep damage under biaxial loading: INCO 718 and 316 (17-12 SPH) steels  

International Nuclear Information System (INIS)

The respective influence of the Von-Mises equivalent stress and of the maximum principal stress on high temperature creep damage of two industrial alloys (INCO 718 and 17-12 SPH stainless steel) are pointed out in a quantitative way through tensile-torsion biaxial tests. Through inversions of the shear component, the important part taken by the principal direction corresponding to the maximum principal stress is also shown. The results are observed to be opposite according to whether the alloy suffers cyclic hardening as 17-12 SPH does or cyclic softening which is the case of Inco 718. These results are supported by metallographic observations. They demand an anisotropic form for the damage variable D, while besides a time dependence, the kinetic equation must include the part taken by the strain

113

Propagation of short cracks in alloy 800HT and in the steel 22CrMoV12-1 at high temperature under biaxial fatigue  

International Nuclear Information System (INIS)

For the alloy 800HT and the steel 22 CrMoV 12-1 mode I, mode II and biaxial in-phase fatigue tests were performed on thin-walled tube specimens at temperatures from room temperature to 900 C. Under pure torsion the fatigue life for the same equivalent strain range was found to be always longer than for tensile and biaxial loading. The investigation of surface replicas indicated that crack initiation occurred mainly on grain-boundaries. After initiation stage II crack growth was observed for the tensile and biaxial loading. In torsion, the growth rate was significantly lower and the cracks grew mainly in stage I. Above 800 C stage II crack growth was also found under torsion in Alloy 800HT. For low cycle fatigue the ?J integral if formulated in principal stresses and strains was found to be an appropriate parameter to describe crack growth for all loading conditions. (orig.)

114

Propagation of short cracks in alloy 800HT and in the steel 22CrMoV12-1 at high temperature under biaxial fatigue  

Energy Technology Data Exchange (ETDEWEB)

For the alloy 800HT and the steel 22 CrMoV 12-1 mode I, mode II and biaxial in-phase fatigue tests were performed on thin-walled tube specimens at temperatures from room temperature to 900 C. Under pure torsion the fatigue life for the same equivalent strain range was found to be always longer than for tensile and biaxial loading. The investigation of surface replicas indicated that crack initiation occurred mainly on grain-boundaries. After initiation stage II crack growth was observed for the tensile and biaxial loading. In torsion, the growth rate was significantly lower and the cracks grew mainly in stage I. Above 800 C stage II crack growth was also found under torsion in Alloy 800HT. For low cycle fatigue the {Delta}J integral if formulated in principal stresses and strains was found to be an appropriate parameter to describe crack growth for all loading conditions. (orig.) 9 refs.

Mu Zhiping; Vehoff, H. [Max-Planck-Institut fuer Eisenforschung GmbH, Duesseldorf (Germany)

1999-10-01

115

Topology Optimization of Stressed Capacitive RF MEMS Switches  

DEFF Research Database (Denmark)

Geometry design can improve a capacitive radio-frequency microelectromechanical system switch's reliability by reducing the impacts of intrinsic biaxial stresses and stress gradients on the switch's membrane. Intrinsic biaxial stresses cause stress stiffening, whereas stress gradients cause out-of-plane curling. We use topology optimization to systematically generate designs, by minimizing stress stiffening, minimizing curling, or minimizing stress stiffening while constraining the curling behavior. We present the corresponding problem formulations and sensitivity derivations and discuss the role of key elements in the problem formulation.

Philippine, Mandy A.; Sigmund, Ole

2013-01-01

116

Biaxial alignment in sputter deposited thin films  

International Nuclear Information System (INIS)

Biaxially aligned thin films have not only a preferential crystallographic out-of-plane orientation, but also have an alignment along a certain reference direction parallel to the substrate plane. This type of film has been obtained by unbalanced reactive magnetron sputter deposition on both amorphous glass and randomly textured polycrystalline substrates tilted with respect to the incoming material flux. First, we focus on the development of microstructure and crystallographic out-of-plane orientation. The results are summarized in an extended structure zone model. Based on experimental results, a mechanism for the in-plane alignment is proposed which shows that an in-plane alignment can only be obtained when an overgrowth mechanism drives the microstructural evolution of the thin film. The quality of the in-plane alignment can be evaluated from X-ray diffraction pole figures. The influence of several deposition parameters (target-substrate distance, target-substrate angle, deposition pressure, and substrate bias) on the degree of in-plane alignment is discussed. The influence of these parameters can be traced to the influence of two main properties, i.e. the mobility of the adatoms at the growing surface and the angular spread of the incoming material flux. Finally, since impurities are hard to exclude during deposition, their influence on the microstructure, the preferential out-of-plane orientation, and the in-plane alignment is reportedent is reported

117

Biaxial mechanical properties of the native and glutaraldehyde-treated aortic valve cusp: Part II--A structural constitutive model.  

Science.gov (United States)

We have formulated the first constitutive model to describe the complete measured planar biaxial stress-strain relationship of the native and glutaraldehyde-treated aortic valve cusp using a structurally guided approach. When applied to native, zero-pressure fixed, and low-pressure fixed cusps, only three parameters were needed to simulate fully the highly anisotropic, and nonlinear in-plane biaxial mechanical behavior. Differences in the behavior of the native and zero- and low-pressure fixed cusps were found to be primarily due to changes in the effective fiber stress-strain behavior. Further, the model was able to account for the effects of small (misalignments in the cuspal specimens with respect to the biaxial test axes that increased the accuracy of the model material parameters. Although based upon a simplified cuspal structure, the model underscored the role of the angular orientation of the fibers that completely accounted for extreme mechanical anisotropy and pronounced axial coupling. Knowledge of the mechanics of the aortic cusp derived from this model may aid in the understanding of fatigue damage in bioprosthetic heart valves and, potentially, lay the groundwork for the design of tissue-engineered scaffolds for replacement heart valves. PMID:11036555

Billiar, K L; Sacks, M S

2000-08-01

118

Residual stress induced atomic scale buckling of diamond carbon coatings on silicon substrate  

International Nuclear Information System (INIS)

This paper investigates the atomic scale buckling of diamond carbon coatings on silicon substrate caused by residual stresses in two orthogonal directions. It was found that different buckling patterns occurred when the ratio of the residual stresses in the two directions were changed. The size of wrinkles increased on going from uniaxial to biaxial compression of the residual stress fields. A telephone-cord like buckling mode took place when the residual stresses were bi-axially equal

119

Effect of crosslinking density on biaxial relaxation of SBR by using reduced variables. [Styrene-Butadiene Rubber  

Science.gov (United States)

The use of reduced variables to account for the effect of crosslinking density in a styrene-butadiene rubber (SBR) system is demonstrated for general biaxial stress states. Recently published results from stress relaxation tests on five SBR vulcanizates crosslinked to different degrees by tetramethylthiuram disulfide were superposed by using the crosslinking density as a reduction variable. The equilibrium shear modulus calculated from the master relaxation curve at long reduced times was in satisfactory agreement with other results for SBR. The time-axis shifts were related in a linear logarithmic manner to the crosslinking density but had a slope slightly less than values previously reported for elastomer systems.

Arenz, R. J.

1974-01-01

120

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

 
 
 
 
121

Detection of an intermediate biaxial phase in the phase diagram of biaxial liquid crystals: entropic sampling study.  

Science.gov (United States)

We investigate the phase sequence of biaxial liquid crystals, based on a general quadratic model Hamiltonian over the relevant parameter space, with a Monte Carlo simulation which constructs equilibrium ensembles of microstates, overcoming possible (free) energy barriers (combining entropic and frontier sampling techniques). The resulting phase diagram qualitatively differs from the universal phase diagram predicted earlier from mean-field theory (MFT), as well as the Monte Carlo simulations with the Metropolis algorithm. The direct isotropic-to-biaxial transition predicted by the MFT is replaced in certain regions of the space by the onset of an additional intermediate biaxial phase of very low order, leading to the sequence N(B)-N(B1)-I. This is due to inherent barriers to fluctuations of the components comprising the total energy, and may explain the difficulties in the experimental realization of these phases. PMID:25353730

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

2014-05-01

122

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.

2010-03-01

123

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.

1998-12-01

124

Anomalously temperature-independent birefringence in biaxial optical crystals  

International Nuclear Information System (INIS)

Temperature-independent birefringence in a biaxial crystal was predicted theoretically and observed experimentally for the first time. The width of the plot against temperature (the range corresponding to the temperature independence of the birefringence) at a fundamental radiation wavelength of 632.8 nm in a KTP crystal 5.9 mm long was more than 1600C. (letters to the editor)

125

High Tc YBCO superconductor deposited on biaxially textured Ni substrate  

Science.gov (United States)

A superconducting article includes a biaxially-textured Ni substrate, and epitaxial buffer layers of Pd (optional), CeO.sub.2 and YSZ, and a top layer of in-plane aligned, c-axis oriented YBCO having a critical current density (J.sub.c) in the range of at least 100,000 A/cm.sup.2 at 77 K.

Budai, John D. (Oakridge, TN); Christen, David K. (Oakridge, TN); Goyal, Amit (Knoxville, TN); He, Qing (Knoxville, TN); Kroeger, Donald M. (Knoxville, TN); Lee, Dominic F. (Knoxville, TN); List, III, Frederick A. (Andersonville, TN); Norton, David P. (Knoxville, TN); Paranthaman, Mariappan (Knoxville, TN); Sales, Brian C. (Knoxville, TN); Specht, Eliot D. (Knoxville, TN)

1999-01-01

126

Uniaxial and biaxial mechanical properties of porcine linea alba.  

Science.gov (United States)

Incisional hernia is a severe complication post-laparoscopic/laparotomy surgery that is commonly associated with the linea alba. However, the few studies on the mechanical properties of the linea alba in the literature appear contradictory, possible due to challenges with the physical dimensions of samples and variations in protocol. This study focuses on the tensile mechanical characterisation of the porcine linea alba, as determined by uniaxial and equi-load biaxial testing using image-based strain measurement methods. Results show that the linea alba demonstrated a non-linear elastic, anisotropic behaviour which is often observed in biological soft tissues. The transverse direction (parallel to fibres) was found to be approximately eight times stiffer than the longitudinal (cross-fibre) direction under both uniaxial and equi-load biaxial loading. The equi-load biaxial tensile tests revealed that contraction could occur in the transverse direction despite increasing load, probably due to the anisotropy of the tissue. Optical surface marker tracking and digital image correlation methods were found to greatly improve the accuracy of stretch measurement, resulting in a 75% change in the apparent stiffness compared to using strain derived from machine cross-head displacement. Additionally, a finite element model of the experiments using a combination of an Ogden and fibre exponential power law model for the linea alba was implemented to quantify the effect of clamping and tissue dimensions (which are suboptimal for tensile testing) on the results. The preliminary model results were used to apply a correction factor to the uniaxial experimental data prior to inverse optimisation to derive best fit material parameters for the fibre reinforced Ogden model. Application of the model to the equi-load biaxial case showed some differences compared to the experimental data, suggesting a more complex anisotropic model may be necessary to capture biaxial behaviour. These results provide an improved assessment of the mechanical properties of the porcine linea alba for wound closure and other studies. PMID:25460404

Cooney, Gerard M; Moerman, Kevin M; Takaza, Michael; Winter, Des C; Simms, Ciaran K

2014-10-01

127

Anisotropic biaxial creep of textured zircaloy: Application to in-reactor life prediction  

International Nuclear Information System (INIS)

Zirconium alloys are commonly used in light water reactors as thin-walled tubings to prevent coolant-fuel contact and to retain fission gases. These alloys have hexagonal close-packed crystal structure with low c/a ratio at and below the reactor operating temperatures and exhibit preferred orientations or textures. The anisotropic mechanical properties in turn affect their in-service behavior such as in-pile creep-down of the cladding tubes. Creep anisotropy was characterized using biaxial creep tests and the creep-loci constructed at constant energy dissipation deviated from isotropy. The anisotropy parameters derived from the loci agreed with those obtained from the strain-rate ratios at varied stress ratios. Effects of cold work were clearly revealed in that the relatively strong hoop direction for the recrystallized (Rx) material became far weaker

128

Simulation of the effect of texture on limit strain in biaxially stretched steel sheet  

Science.gov (United States)

Limit strains for biaxial stretching are predicted by the Marciniak and Kuczynski (M-K) method, suitably modified to take into account the textures present in sheet steels. The series expansion method is used for this purpose in the framework of the Taylor/Bishop and Hill theory. The effect on the limit strain of yield surface shape is allowed for by the use of an improved P parameter. The experimental limit strains of an AKDQ steel are compared with the forming limit curves (FLCs) predicted on the assumption of two sets of slip systems with different critical resolved shear stresses (CRSSs). The limit strains in equibiaxial stretching with assumed groove orientations are also predicted for some idealized materials containing specific preferred orientations.

Lin, D. W.; Daniel, D.; Jonas, J. J.

1991-09-01

129

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.

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

2013-10-01

130

Biaxial High Cycle Fatigue of a Type 304L Stainless Steel: Cyclic Strains and Crack Initiation Detection by Digital Image Correlation  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Abstract A series of biaxial High Cycle Fatigue tests at room temperature is performed to build up an extensive and well-documented database. The testing specimen is a maltese cross thinned in its centre with non homogeneous strain/stress fields. The experimental protocol uses exclusively full-field strain measurements. The strains (cyclic and residual) as well as the crack initiation detection are obtained by use of Digital Image Correlation (DIC) techniques combined with a multis...

Poncelet, M.; Barbier, G.; Raka, B.; Courtin, S.; Desmorat, R.; Le-roux, J. C.; Vincent, L.

2010-01-01

131

Different stress techniques and their efficiency on triple-gate SOI n-MOSFETs  

Science.gov (United States)

Three techniques to implement mechanical stress in n-channel Multiple Gate MOSFETs (MuGFETs) are investigated through 3D simulations and transconductance measurements. They are: uniaxial stress, biaxial stress and biaxial + uniaxial stress. Four different fin dimensions are evaluated: a narrow and a wide transistor, combined with a short or a long device. It is shown that the stress distribution and the device performance exhibit a dependence on the fin dimensions. For uniaxially strained devices, the dimensions are important as the bending of the silicon required to induce stress in the channel depends on its size. However, for biaxially strained devices the plane of etching in the silicon fin is important, determining the degradation of the stress components. The combination of the two types of stress results in an improvement of some stress components and an overall improvement in the maximum transconductance.

Bühler, R. T.; Agopian, P. G. D.; Collaert, N.; Simoen, E.; Claeys, C.; Martino, J. A.

2015-01-01

132

Rain-snow discrimination with a biaxial lidar ceilometer  

Science.gov (United States)

The Vaisala ceilometer LD-40 Tropopauser is a compact eye-safe biaxial lidar measuring continuously under all possible climatic conditions and scanning the atmosphere up to a height of 13000 m. It uses laser diodes with 855 nm wavelength that are pulsed at an average frequency of 4000 Hz. The distance of the systems range bins is 7.5 m. Its main task is reporting cloud base heights and vertical visibility for aviation safety purposes. The focus of this appear however is directed on the investigation of backscatter data from falling precipitation. The LD-40 ceilometer is able to detect falling precipitation and it can distinguish between rain and snow by examining backscatter data profiles. This ability is caused by the biaxial lidar optics in combination with the different scattering phase functions of rain droplets and snow. A simple rain-snow discrimination algorithm is introduced, routine at the same place, illustrates the backscatter profile differences between the two optical systems.

Muenkel, Christoph

2003-04-01

133

Optical properties of biaxial nanopatterned gold plasmonic nanowired grid polarizer.  

Science.gov (United States)

Gold nanoparticles deposited on self-organized nano-ripple quartz substrates have been studied by spectroscopic Mueller matrix ellipsometry. The surface was found to have biaxial anisotropic optical properties. For electric field components normal to the ripples the periodic and disconnected nature of the in plane nanowires gives rise to an optical response dominated by the localized plasmon resonance. In the direction parallel to the ripples the gold nanoparticles are aligned closely leading to localized plasmon resonances in the infrared. As Au was deposited at an angle oblique to the surface normal, the gold nanoparticles were formed on the side of the ripples facing the incoming evaporation flux. This makes the gold particles slightly inclined, correspondingly the principal coordinate system of the biaxial dielectric tensor results tilted. The anisotropic plasmonic optical response results in a strong polarizing effect, making it suitable as a plasmonic nanowired grid polarizer. PMID:24514665

Aas, Lars Martin Sandvik; Kildemo, Morten; Martella, Christian; Giordano, Maria Caterina; Chiappe, Daniele; Buatier de Mongeot, Francesco

2013-12-16

134

Biaxial Yield Surface Investigation of Polymer-Matrix Composites  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 re...

Zhengjia He; Zhi Zhai; Junjie Ye; Yuanying Qiu

2013-01-01

135

Biaxial Compressive Strain Engineering in Graphene/Boron Nitride Heterostructures  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Strain engineered graphene has been predicted to show many interesting physics and device applications. Here we study biaxial compressive strain in graphene/hexagonal boron nitride heterostructures after thermal cycling to high temperatures likely due to their thermal expansion coefficient mismatch. The appearance of sub-micron self-supporting bubbles indicates that the strain is spatially inhomogeneous. Finite element modeling suggests that the strain is concentrated on the edges with regula...

Wei Pan; Jianliang Xiao; Junwei Zhu; Chenxi Yu; Gang Zhang; Zhenhua Ni; Watanabe, K.; Taniguchi, T.; Yi Shi; Xinran Wang

2012-01-01

136

Double in-plane alignment in biaxially textured thin films  

Science.gov (United States)

The scientific interest and technological relevance of biaxially textured polycrystalline thin films stem from their microstructure that resembles that of single crystals. To explain the origin and predict the type of biaxial texture in off-normally deposited films, Mahieu et al. have developed an analytical model [S. Mahieu et al., Thin Solid Films 515, 1229 (2006)]. For certain materials, this model predicts the occurrence of a double in-plane alignment, however, experimentally only a single in-plane alignment has been observed and the reason for this discrepancy is still unknown. The model calculates the resulting in-plane alignment by considering the growth of faceted grains with an out-of-plane orientation that corresponds to the predominant film out-of-plane texture. This approach overlooks the fact that in vapor condensation experiments where growth kinetics is limited and only surface diffusion is active, out-of-plane orientation selection is random during grain nucleation and happens only upon grain impingement. Here, we compile and implement an experiment that is consistent with the key assumptions set forth by the in-plane orientation selection model by Mahieu et al.; a Cr film is grown off-normally on a fiber textured Ti epilayer to pre-determine the out-of-plane orientation and only allow for competitive growth with respect to the in-plane alignment. Our results show unambiguously a biaxially textured Cr (110) film that possesses a double in-plane alignment, in agreement with predictions of the in-plane selection model. Thus, a long standing discrepancy in the literature is resolved, paving the way towards more accurate theoretical descriptions and hence knowledge-based control of microstructure evolution in biaxially textured thin films.

Elofsson, V.; Saraiva, M.; Boyd, R. D.; Sarakinos, K.

2014-12-01

137

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

138

Importance of transverse dipoles in the stability of biaxial nematic phase: A Monte Carlo study  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Monte Carlo simulation performed on a lattice system of biaxial molecules possessing $D_{2h}$ symmetry and interacting with a second rank anisotropic dispersion potential yields three distinct macroscopic phases depending on the biaxiality of the constituent molecules. The phase diagram of such a system as a function of molecular biaxiality is greatly modified when a transverse dipole is considered to be associated with each molecule so that the symmetry is reduced to $C_{2v...

Ghoshal, Nababrata; Mukhopadhyay, Kisor; Roy, Soumen Kumar

2012-01-01

139

Failure analysis based on microvoid growth for sheet metal during uniaxial and biaxial tensile tests  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The aim of the presented investigations is to perform an analysis of fracture and instability during simple and complex load testing by addressing the influence of ductile damage evolution in necking processes. In this context, an improved experimental methodology was developed and successfully used to evaluate localization of deformation during uniaxial and biaxial tensile tests. The biaxial tensile tests are carried out using cruciform specimen loaded using a biaxial testing machine. In thi...

Abbassi, Fethi; Mistou, Se?bastien; Zghal, Ali

2013-01-01

140

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

International Nuclear Information System (INIS)

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 straative. A CTOD-estimation method for strain -based fracture is suggested for the pipelines when the global strain is 3%. - Highlights: ? 3D FE stress analysis of girth welded pipelines with surface cracks is conducted. ? Both material and geometrical non-linearities are considering in estimating CTOD. ? Existing conservative models result in high rejection rate of welded pipes.

 
 
 
 
141

[Stress].  

Science.gov (United States)

The general adaptation syndrome is discussed on the light of recent discoveries on hypothalamic peptides and of their possible influence in survival and in induction of diseases. The problem of stress in alcoholism is reviewed. The author ends with a short souvenir of Hans Selye. PMID:9341029

Manso, C F

1997-04-01

142

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

143

Initial results of the influence of biaxial loading on fracture toughness  

International Nuclear Information System (INIS)

A testing program to examine the influence of biaxial loads on the fracture toughness of shallow-flaw specimens under conditions prototypic of a reactor pressure vessel was begun. Existing data suggest that shallow-flaw specimens under biaxial loading will exhibit a toughness reduction compared to comparable uniaxial specimens. Quantification of this toughness reduction is the main goal of the biaxial fracture toughness program. A cruciform specimen with a two-dimensional shallow through-thickness flaw under a biaxial load ratio of 0.6:1 was used for biaxial fracture toughness testing. The critical fracture load for each specimen was approximately the same, but the uniaxial specimen withstood substantially more deformation at failure than did the biaxial specimens. Three-dimensional, elastic-plastic, finite-element posttest analyses were necessary to estimate fracture toughness. In all cases, agreement between the measured and computed load vs deformation responses was excellent. Toughness values for the cruciform specimens were compared with data from previously tested, deep- and shallow-crack specimens. Results from these tests indicate that the shallow-crack toughness increase is partially, but not totally, removed by the application of biaxial loading. However, additional data are required to solidify these conclusions. A proposed test matrix for additional uniaxial and biaxial testing is described. This report has been designated HSST Report No. 138signated HSST Report No. 138

144

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

145

Hole doped Dirac states in silicene by biaxial tensile strain  

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

Kaloni, Thaneshwor P.

2013-03-11

146

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)

147

High magnification crack-tip field characterisation under biaxial conditions  

Directory of Open Access Journals (Sweden)

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

B. Moreno

2013-07-01

148

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 mechanical fatigue loadings. (author)

149

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

Science.gov (United States)

Biaxial test methods have been used to determine, not only yield behaviour under biaxial conditions, but also the strain response. This paper examines the influence of uniaxial prestrain upon the biaxial r-value by extending the disc compression test procedure proposed by Barlat et al. [1]. The extension involved the use of digital image measurements of in-plane strains. The material examined was a 7075-O condition aluminium alloy. The results of the experimental programme indicated that the biaxial r-value is unaffected by uniaxial prestrain. When using the disc compression test, the mode of deformation and therefore the biaxial r-value were found to be very sensitive to the prevailing friction conditions.

Anderson, N.; Brown, D.; McMurray, R. J.; Leacock, A. G.

2011-05-01

150

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.

151

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

152

Stress.  

Science.gov (United States)

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

Chambers, David W

2008-01-01

153

Numerical Investigation into the Effect of Uniaxial and Biaxial Pre-Strain on Forming Limit Diagram of 5083 Aluminum Alloy  

Science.gov (United States)

In this paper, numerical simulations are carried out to determine the forming limit diagram (FLD) of 5083 aluminum alloy. The aim is to predict the effect of strain path change on the forming limit curve (FLC) of this alloy. For this purpose, out-of-plane formability test method with hemispherical punch was simulated by using commercial finite element software, ABAQUSE 6.9. In the first stage, square blanks were modeled and then some of them were pre-strained uniaxially by tension test and some others were pre-strained biaxially by stretching over the hemispherical punch. In the second stage, the formability test specimens' models were prepared by trimming the pre-strained blanks with the longitudinal axis parallel and perpendicular to the rolling direction. For trimming, a program was written in MATLAB 7.6 which could determine the new elements and introduce their properties to the FEM model. Ductile fracture criteria were used to predict failure. Furthermore, forming limit stress diagram (FLSD) was determined. The numerical results were compared with the experimental findings. Uniaxial pre-straining increased and shifted the FLC to the left hand side of the diagram for both parallel and perpendicular to the rolling direction. Biaxial pre-straining shifted the FLC to the right hand side of the diagram for both directions, and also decreased the FLC for the specimens parallel to the rolling direction.

Zhalehfar, F.; Hosseinipour, S. J.; Nourouzi, S.; Gorji, A. H.

2011-08-01

154

Tuning biaxiality of nematic phases of board-like colloids by an external magnetic field.  

Science.gov (United States)

We study the influence of a magnetic field on the biaxial nematic phase of board-like goethite colloids both experimentally and theoretically. Using synchrotron small angle X-ray scattering techniques we find that applying a magnetic field along the main director of the biaxial nematic phase leads to a clear decrease in biaxiality with increasing magnetic field strength. Above a certain magnetic field strength the biaxiality is completely suppressed and the biaxial nematic phase transforms into an ordinary prolate uniaxial nematic phase. In order to interpret the physical mechanism behind this phenomenon, we develop a mean-field theory for the liquid crystal phase behaviour of the suspension. Within this theory the magnetic properties of the particles are modelled by taking into account the effect of both the permanent and the induced magnetic dipoles. The resulting phase diagrams support our experimental findings of the field-induced biaxial nematic to prolate uniaxial nematic transition. They additionally predict that for more plate-like particles, which initially would only display oblate nematic ordering of the shortest axis, the rare biaxial phase can be induced by applying a magnetic field with a carefully chosen field strength, a parameter which can be easily tuned. PMID:24652631

Leferink op Reinink, Anke B G M; Belli, Simone; van Roij, René; Dijkstra, Marjolein; Petukhov, Andrei V; Vroege, Gert Jan

2014-01-21

155

Textural Development of AA 5754 Sheet Deformed under In-Plane Biaxial Tension  

Science.gov (United States)

Crystallographic texture evolution was quantified as a function of biaxial strain level and strain path for AA5754-O sheet metal in an effort to provide a physical description of grain rotation resulting from in-plane stretching. Samples were incrementally deformed to near-failure in three strain states (equibiaxial, plane strain, and uniaxial modes) with the rolling direction (RD) and transverse direction (TD) of the sheet parallel to the major stress axis for the latter two cases. The macrotextures were measured using X-ray diffraction techniques. Results showed that for a given strain path similar deformation textures developed in the two material sets (RD- and TD-oriented samples), though the evolution of the deformed texture was not homogeneous over the entire strain range. These variations in orientation intensities were related to the feeder components found in the initial texture and the availability of these components to rotate toward the more stable orientations under the particular mode of deformation. The nonuniform texture development of the sheet along different directions appears to contribute to the anisotropic mechanical response of the sheet during stretching as measured in the evolving multiaxial flow surfaces.

Banovic, S. W.; Iadicola, M. A.; Foecke, T.

2008-09-01

156

Characterizing chaotic dynamics from simulations of large strain behavior of a granular material under biaxial compression.  

Science.gov (United States)

For a given observed time series, it is still a rather difficult problem to provide a useful and compelling description of the underlying dynamics. The approach we take here, and the general philosophy adopted elsewhere, is to reconstruct the (assumed) attractor from the observed time series. From this attractor, we then use a black-box modelling algorithm to estimate the underlying evolution operator. We assume that what cannot be modeled by this algorithm is best treated as a combination of dynamic and observational noise. As a final step, we apply an ensemble of techniques to quantify the dynamics described in each model and show that certain types of dynamics provide a better match to the original data. Using this approach, we not only build a model but also verify the performance of that model. The methodology is applied to simulations of a granular assembly under compression. In particular, we choose a single time series recording of bulk measurements of the stress ratio in a biaxial compression test of a densely packed granular assembly-observed during the large strain or so-called critical state regime in the presence of a fully developed shear band. We show that the observed behavior may best be modeled by structures capable of exhibiting (hyper-) chaotic dynamics. PMID:23556950

Small, Michael; Walker, David M; Tordesillas, Antoinette; Tse, Chi K

2013-03-01

157

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

Science.gov (United States)

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

Agishev, Ravil R; Comeron, Adolfo

2002-12-20

158

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

159

Calculation of band structure in (101)-biaxially strained Si  

Science.gov (United States)

The structure model used for calculation was defined according to Vegard’s rule and Hooke’s law. Calculations were performed on the electronic structures of (101)-biaxially strained Si on relaxed Si1- X Ge X alloy with Ge fraction ranging from X = 0 to 0.4 in steps of 0.1 by CASTEP approach. It was found that [±100] and [00±1] valleys (?4) splitting from the [0±10] valley (?2) constitute the conduction band (CB) edge, that valence band (VB) edge degeneracy is partially lifted and that the electron mass is unaltered under strain while the hole mass decreases in the [100] and [010] directions. In addition, the fitted dependences of CB splitting energy, VB splitting energy and indirect bandgap on X are all linear.

Song, Jianjun; Zhang, Heming; Hu, Huiyong; Fu, Qiang

2009-04-01

160

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

 
 
 
 
161

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

162

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

Science.gov (United States)

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.; Takarada, W.; Kikutani, T.

2014-05-01

163

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

164

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.

165

Superplastic deformation of an Al-Li-Cu-Zr alloy under uniaxial and biaxial tension  

International Nuclear Information System (INIS)

This paper reports that the superplasticity of an Al-Li-Cu-Zr alloy has been studied under uniaxial tension and biaxial bulging conditions using hydrostatic pressure. An optimum tensile elongation of 850% at a strain rate of 3/10-4/sec was obtained at 758 K. The maximum true thickness stain was 1.22 for a biaxially deformed specimen under the same conditions. It was shown that strain rate dependent flow hardening was related to necking refile. It was observed that cavity growth during superplastic deformation depended on the type of loading. Under biaxial bulging conditions, the cavities grew by forming cavity fissure networks along the grain boundaries. It was found that, by the superimposition of hydrostatic pressure, cavitation was retarded and the superplastic ductility was increased in both tensile and biaxial deformation

166

Dynamic monitoring of mobile telecommunication towers exposed to natural loading with a FBG biaxial accelerometer  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In this work the dynamic monitoring of a self supported telecommunications tower is presented. The feasibility of an optical FBG biaxial accelerometer to obtain the structure natural frequencies is demonstrated, recurring only to natural loading.

Antunes, P.; Travanca, R.; Varum, H.; Andre?, P.

2011-01-01

167

Frequency doubling with laser beams transformed by conical refraction in a biaxial crystal  

International Nuclear Information System (INIS)

The second-harmonic generation with laser beams transformed by internal conical refraction in a biaxial crystal was studied in a cascaded two-crystal arrangement, where the biaxial crystal transformed the input Gaussian beam and another nonlinear crystal was used for frequency doubling of the produced conical refraction pattern. Several specific second-harmonic beam profiles obtained for various positions of the nonlinear crystal along the beam propagation direction are considered and discussed

168

Frequency doubling with laser beams transformed by conical refraction in a biaxial crystal  

Science.gov (United States)

The second-harmonic generation with laser beams transformed by internal conical refraction in a biaxial crystal was studied in a cascaded two-crystal arrangement, where the biaxial crystal transformed the input Gaussian beam and another nonlinear crystal was used for frequency doubling of the produced conical refraction pattern. Several specific second-harmonic beam profiles obtained for various positions of the nonlinear crystal along the beam propagation direction are considered and discussed.

Peet, V.; Shchemelyov, S.

2011-05-01

169

Experimental study on the biaxial bending cyclic behaviour of RC columns  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The available experimental studies on the inelastic 3D response of axially loaded members under biaxial bending moment loading histories are limited. Possibly, this is partially due to the uncertainty of combining bending moment’s histories in the two orthogonal directions that adds considerable complication to the problem. Three types of cantilever reinforced concrete columns with constant axial load were subjected to cyclic uniaxial and biaxial tests. It was intended to gain e...

Rodrigues, H.; Are?de, A.; Varum, H.; Costa, A.

2010-01-01

170

Biaxial fatigue tests and crack paths for AISI 304L stainless steel  

Digital Repository Infrastructure Vision for European Research (DRIVER)

AISI 304L stainless steel specimens have been tested in fatigue. The tests were axial, torsional and in-phase biaxial, all of them under load control and R=-1. The S-N curves were built following the ASTM E739 standard and the method of maximum likelihood proposed by Bettinelli. The fatigue limits of the biaxial tests were represented in axes ?-?. The elliptical quadrant, appropriate for ductile materials, and the elliptical arc, appropriate for fragile materials, were included ...

Chaves, V.; Madrigal, C.; Navarro, A.

2014-01-01

171

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)

172

Electronic and optical properties of silicene under uni-axial and bi-axial mechanical strains: A first principle study  

Science.gov (United States)

The uni-axial and bi-axial mechanical strain mediated electronic band structures and dielectric properties of silicene have been investigated. It is found that on applying uni- and bi-axial strains, the band gap opens for smaller strain in silicene. However, on further increase of strain beyond 8% silicene changed into metal. The ultimate tensile strength estimated is 3.4 GPa. Imaginary part of dielectric function shows that the inter-band transitions are red-shifted for uni- and bi-axial tensile strains and are blue shifted for uni- and bi-axial compressive strains. Electron energy loss (EEL) function shows that the ?+? plasmon energies are red-shifted for uni- and bi-axial strains and blue-shifted for compressive strains. The ? plasmons disappears for tensile and asymmetric strains. Bi-axial asymmetric strain is found to have no influence on inter-band transitions and ?+? plasmon energies.

Mohan, Brij; Kumar, Ashok; Ahluwalia, P. K.

2014-07-01

173

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.

174

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

175

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

176

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.)

177

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

178

Fiber kinematics of small intestinal submucosa under biaxial and uniaxial stretch.  

Science.gov (United States)

Improving our understanding of the design requirements of biologically derived collagenous scaffolds is necessary for their effective use in tissue reconstruction. In the present study, the collagen fiber kinematics of small intestinal submucosa (SIS) was quantified using small angle light scattering (SALS) while the specimen was subjected to prescribed uniaxial or biaxial strain paths. A modified biaxial stretching device based on Billiar and Sacks (J. Biomech., 30, pp. 753-7, 1997) was used, with a real-time analysis of the fiber kinematics made possible due to the natural translucency of SIS. Results indicated that the angular distribution of collagen fibers in specimens subjected to 10% equibiaxial strain was not significantly different from the initial unloaded condition, regardless of the loading path (p=0.31). Both 10% strip biaxial stretch and uniaxial stretches of greater than 5% in the preferred fiber direction led to an increase in the collagen fiber alignment along the same direction, while 10% strip biaxial stretch in the cross preferred fiber direction led to a broadening of the distribution. While an affine deformation model accurately predicted the experimental findings for a biaxial strain state, uniaxial stretch paths were not accurately predicted. Nonaffine structural models will be necessary to fully predict the fiber kinematics under large uniaxial strains in SIS. PMID:17154691

Gilbert, Thomas W; Sacks, Michael S; Grashow, Jonathan S; Woo, Savio L-Y; Badylak, Stephen F; Chancellor, Michael B

2006-12-01

179

The influence of the stress state on Ksub(Ic)  

International Nuclear Information System (INIS)

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

180

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.

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

2014-09-01

 
 
 
 
181

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.

182

Temperature dependent biaxial texture evolution in Ge films under oblique angle vapor deposition  

International Nuclear Information System (INIS)

The morphology and texture of Ge films grown under oblique angle vapor deposition on native oxide covered Si(001) substrates at temperatures ranging from 230 deg. C to 400 deg. C were studied using scanning electron microscopy, X-ray diffraction and X-ray pole figure techniques. A transition from polycrystalline to {001} biaxial texture was observed within this temperature range. The Ge films grown at substrate temperatures < 375 deg. C were polycrystalline. At substrate temperatures of 375 deg. C and 400 deg. C, a mixture of polycrystalline and biaxial texture was observed. The 230 deg. C sample consisted of isolated nanorods, while all other films were continuous. The observed biaxial texture is proposed to be a result of the loss of the interface oxide layer, resulting in epitaxial deposition of Ge on the Si and a texture following that of the Si(001) substrates used. The rate of oxide loss was found to increase under oblique angle vapor deposition.

183

Conception and Construction of Biaxial Apparatus for Identification of Axial Orthotropic Material  

International Nuclear Information System (INIS)

Plastbloc is a new process. Its principle is to use compressed and ligatured blocks made of plastic materials. These blocks could be used to build lightweight embankments, to minimize loads on underground pipes and behind retaining walls. Because the compressing during the making of blocks is unidirectional, this material is made up of stake of layers. In this case, it has an axial orthotropy. With the purpose to study the rheological behavior of this material, a large number of simple compression tests were carried out. But the identification of all parameters is possible by realization of biaxial tests. A biaxial apparatus conceived specially for this type of material was built. Preliminary studies showed the good function of this apparatus. Then, biaxial tests were carried out and the characteristic functions were identified. (author)

184

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

185

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

186

Use of sigma1 criterion for evaluating long-term strength of structural steels in a plane stress state  

International Nuclear Information System (INIS)

Conditions are discussed for applicability of the maximum tension ?1 criterion to estimate high-temperature long-term strength of structural materials in a plane stressed state. A non-excessive estimate of long-term strength from ?1 is shown possible only under biaxial tension. It is marked that under biaxial tension tests of thin-walled tubular specimens data on uniaxial strength are obtained as a rule, under axial tension of the pipes in question. In this connection while estimating long-term strength of thin-walled pipes under biaxial tension from the ?1 value it is necessary to take into consideration the level of material cold working in an axial direction. The range of the ?1 criterion applicability to evaluate long-term strength under conditions of biaxial tension is determined for pipes subjected to cold working

187

Polarization features of acoustic spectra in uniaxial and biaxial nematic liquid crystals  

International Nuclear Information System (INIS)

The results of investigation of uniaxial and biaxial nematic liquid crystals dynamics with molecules of the various forms are presented. These condensed matters possess internal spatial anisotropy and for their adequate description introduction of additional dynamic quantities is necessary. They are vectors of spatial anisotropy and conformational degrees of freedom. Investigation of dynamics of the given condensed matters is based on Hamiltonian formalism in which framework the nonlinear dynamic equations for uniaxial and biaxial nematic liquid crystals are derived. Spectra of collective excitations are obtained and their polarization features are investigated.

188

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

Energy Technology Data Exchange (ETDEWEB)

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.

Jau, W.C.; White, R.N.; Gergely, P.

1982-09-01

189

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

190

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

191

Proposed Route to Thin Film Crystal Si Using Biaxially Textured Foreign Template Layers  

Energy Technology Data Exchange (ETDEWEB)

We have developed a new approach to growing photovoltaic-quality crystal silicon (c-Si) films on glass. Other approaches to film c-Si focus on increasing grain size in order to reduce the deleterious effects of grain boundaries. Instead, we have developed an approach to align the silicon grains biaxially (both in and out of plane) so that 1) grain boundaries are "low-angle" and have less effect on the electronic properties of the material and 2) subsequent epitaxial thickening is simplified. They key to our approach is the use of a foreign template layer that can be grown with biaxial texture directly on glass.

Teplin, C. W.; Ginley, D. S.; van Hest, M.F.A.M.; Perkins, J. D.; Young, D. L.; Stradins, P.; Wang, Q.; Al-Jassim, M.; Iwaniczko, E.; Leenheer, A.; Jones, K. M.; Branz, H. M.

2005-11-01

192

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

193

Biaxial High Cycle Fatigue of a type 304L stainless steel: Cyclic strains and crack initiation detection by digital image correlation  

Energy Technology Data Exchange (ETDEWEB)

A series of biaxial High Cycle Fatigue tests at room temperature is performed to build up an extensive and well-documented database. The testing specimen is a maltese cross thinned in its centre with non-homogeneous strain/stress fields. The experimental protocol uses exclusively full-field strain measurements. The strains (cyclic and residual) as well as the crack initiation detection are obtained by use of Digital Image Correlation (DIC) techniques combined with a multi-scale stroboscopic image acquisition in-situ set-up. Nine cruciform specimens made of type 304L austenitic stainless steel are loaded by a multiaxial testing machine. Two kinds of loading paths are presented: equi-biaxial with a load ratio of 0.1, non-proportional with a cyclic load in one direction and a constant load in the other. The experimental results are given (strain amplitude, residual strain, number of cycles to crack initiation) for each loading path. The time history of local strain amplitudes and residual strains are recorded and plotted. Total strain vs. number of cycles fatigue curves show the different trends associated with each loading path. For instance, non-proportional loadings are found very damaging and leading to strong ratchetting effects. The tested material is briefly introduced, followed by an in-depth description of the experimental set-up. The fatigue test campaign results are then presented, with a final discussion. (authors)

Poncelet, M.; Vincent, L. [CEA Saclay, DEN/SRMA, 91 - Gif-sur-Yvette (France); Barbier, G.; Raka, B.; Desmorat, R. [LMT Cachan, ENS Cachan/CNRS/UPMC/PRES Univ. Sud Paris, 94 - Cachan (France); Courtin, S. [AREVA NP SAS, Tour AREVA, 92 - Paris La Defense (France); Barbier, G.; Le-Roux, J.C. [EDF e R and D, Departement Materiaux et Mecanique des Composants, 77 - Moret Sur Loing Cedex, (France)

2010-09-15

194

Numerical Investigations on the Influence of Superimposed Double-Sided Pressure on the Formability of Biaxially Stretched AA6111-T4 Sheet Metal  

Science.gov (United States)

Lightweight materials have been widely used in aerospace, automobile industries to meet the requirement of structural weight reduction. Due to their limited plasticity at room temperature, however, lightweight materials always exhibit distinctly poor forming capability in comparison with conventional deep drawing steels. Based on the phenomenon that the superimposed hydrostatic pressure can improve the plasticity of metal, many kinds of double-sided pressure forming processes have been proposed. In the present study, the Gurson-Tvergaard-Needleman (GTN) damage model combined with finite element method is used to investigate the influence of double-sided pressure on the deformation behavior of biaxially stretched AA6111-T4 sheet metal, including nucleation and growth of microvoids, evaluation of stress triaxiality, and so forth. The Marciniak-Kuczynski (M-K) localized necking model is used to predict the right-hand side of the forming limit diagram (FLD) of sheet metal under superimposed double-sided pressure. It is found that the superimposed double-sided pressure has no obvious effect on the nucleation of microvoids. However, the superimposed double-sided pressure can suppress the growth and coalescence of microvoids. The forming limit curve (FLC) of the biaxially stretched AA6111-T4 sheet metal under the superimposed double-sided pressure is improved and the fracture locus shifts to the left. Furthermore, the formability increase value is sensitive to the strain path.

Liu, Jianguang; Wang, Zhongjin; Meng, Qingyuan

2012-04-01

195

Biaxial High Cycle Fatigue of a type 304L stainless steel: Cyclic strains and crack initiation detection by digital image correlation  

International Nuclear Information System (INIS)

A series of biaxial High Cycle Fatigue tests at room temperature is performed to build up an extensive and well-documented database. The testing specimen is a maltese cross thinned in its centre with non-homogeneous strain/stress fields. The experimental protocol uses exclusively full-field strain measurements. The strains (cyclic and residual) as well as the crack initiation detection are obtained by use of Digital Image Correlation (DIC) techniques combined with a multi-scale stroboscopic image acquisition in-situ set-up. Nine cruciform specimens made of type 304L austenitic stainless steel are loaded by a multiaxial testing machine. Two kinds of loading paths are presented: equi-biaxial with a load ratio of 0.1, non-proportional with a cyclic load in one direction and a constant load in the other. The experimental results are given (strain amplitude, residual strain, number of cycles to crack initiation) for each loading path. The time history of local strain amplitudes and residual strains are recorded and plotted. Total strain vs. number of cycles fatigue curves show the different trends associated with each loading path. For instance, non-proportional loadings are found very damaging and leading to strong ratchetting effects. The tested material is briefly introduced, followed by an in-depth description of the experimental set-up. The fatigue test campaign results are then presented, with a final discussion. (authors)

196

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

197

Texture evolution of vertically aligned biaxial tungsten nanorods using RHEED surface pole figure technique  

International Nuclear Information System (INIS)

Vertically aligned biaxial tungsten nanorods with cubic A15 crystal structure were deposited by DC magnetron sputtering on native oxide covered Si(100) substrates with glancing angle flux incidence (? ? 850) and a two-step substrate rotation mode at room temperature. These vertical nanorods were grown to different thicknesses (10, 25, 50 and 100 nm) and analyzed for biaxial texture evolution using a highly surface sensitive reflection high-energy electron diffraction (RHEED) pole figure technique. The initial polycrystalline film begins to show the inception of biaxial texture with a fiber background between 10 and 25 nm. Biaxial texture development is eventually completed between 50 and 100 nm thicknesses of the film. The out-of-plane crystallographic direction is [002] and the in-plane texture is selected so as to obtain maximum capture area. In a comparison with 100 nm thick inclined tungsten nanorods deposited at 850 without substrate rotation, it is found that the selection of in-plane texture does not maintain maximum in-plane capture area. This anomalous behavior is observed when the [002] texture axis is tilted ? 170 from the substrate normal in the direction towards the glancing incident flux.

198

Thermal stress in GaN epitaxial layers grown on sapphire substrates  

Science.gov (United States)

Thermal stress in GaN epitaxial layers with different thicknesses grown on sapphire substrates by metalorganic vapor phase epitaxy using an AlN buffer layer was investigated. Biaxial compressive stress in the GaN layer, due to the difference in the thermal expansion coefficients between GaN and sapphire, was obtained by measuring the curvature of wafer bending, and the observed stress agreed with the calculated stress. In Raman measurements, the E2 phonon peak of GaN was found to shift and broaden with the stress as a consequence of the change of the elastic constants with strain. The frequency shift ?? (in cm-1) was obtained for the first time, given by the relation: ??=6.2 ?, where the biaxial stress ? is expressed in GPa.

Kozawa, T.; Kachi, T.; Kano, H.; Nagase, H.; Koide, N.; Manabe, K.

1995-05-01

199

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

200

Measuring knife stab penetration into skin simulant using a novel biaxial tension device.  

Science.gov (United States)

This paper describes the development and use of a biaxial measurement device to analyse the mechanics of knife stabbings. In medicolegal situations it is typical to describe the consequences of a stabbing incident in relative terms that are qualitative and descriptive without being numerically quantitative. Here, the mechanical variables involved in the possible range of knife-tissue penetration events are considered so as to determine the necessary parameters that would need to be controlled in a measurement device. These include knife geometry, in-plane mechanical stress state of skin, angle and speed of knife penetration, and underlying fascia such as muscle or cartilage. Four commonly available household knives with different geometries were used: the blade tips in all cases were single-edged, double-sided and without serrations. Appropriate synthetic materials were used to simulate the response of skin, fat and cartilage, namely polyurethane, compliant foam and ballistic soap, respectively. The force and energy applied by the blade of the knife and the out of plane displacement of the skin were all used successfully to identify the occurrence of skin penetration. The skin tension is shown to have a direct effect on both the force and energy for knife penetration and the depth of out of plane displacement of the skin simulant prior to penetration: larger levels of in-plane tension in the skin are associated with lower penetration forces, energies and displacements. Less force and energy are also required to puncture the skin when the plane of the blade is parallel to a direction of greater skin tension than when perpendicular. This is consistent with the observed behaviour when cutting biological skin: less force is required to cut parallel to the Langer lines than perpendicularly and less force is required to cut when the skin is under a greater level of tension. Finally, and perhaps somewhat surprisingly, evidence is shown to suggest that the quality control processes used to manufacture knives fail to produce consistently uniform blade points in knives that are nominally identical. The consequences of this are that the penetration forces associated with nominally identical knives can vary by as much as 100%. PMID:18093771

Gilchrist, M D; Keenan, S; Curtis, M; Cassidy, M; Byrne, G; Destrade, M

2008-05-01

 
 
 
 
201

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)

202

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

Science.gov (United States)

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.

Wang, Guan-Yu; Zhang, He-Ming; Gao, Xiang; Wang, Bin; Zhou, Chun-Yu

2012-05-01

203

Passive biaxial mechanical properties and in vivo axial pre-stretch of the diseased human femoropopliteal and tibial arteries.  

Science.gov (United States)

Surgical and interventional therapies for atherosclerotic lesions of the infrainguinal arteries are notorious for high rates of failure. Frequently, this leads to expensive reinterventions, return of disabling symptoms or limb loss. Interaction between the artery and repair material likely plays an important role in reconstruction failure, but data describing the mechanical properties and functional characteristics of human femoropopliteal and tibial arteries are currently not available. Diseased superficial femoral (SFA, n = 10), popliteal (PA, n = 8) and tibial arteries (TA, n = 3) from 10 patients with critical limb ischemia were tested to determine passive mechanical properties using planar biaxial extension. All specimens exhibited large nonlinear deformations and anisotropy. Under equibiaxial loading, all arteries were stiffer in the circumferential direction than in the longitudinal direction. Anisotropy and longitudinal compliance decreased distally, but circumferential compliance increased, possibly to maintain a homeostatic multiaxial stress state. Constitutive parameters for a four-fiber family invariant-based model were determined for all tissues to calculate in vivo axial pre-stretch that allows the artery to function in the most energy efficient manner while also preventing buckling during extremity flexion. Calculated axial pre-stretch was found to decrease with age, disease severity and more distal arterial location. Histological analysis of the femoropopliteal artery demonstrated a distinct sub-adventitial layer of longitudinal elastin fibers that appeared thicker in healthier arteries. The femoropopliteal artery characteristics and properties determined in this study may assist in devising better diagnostic and treatment modalities for patients with peripheral arterial disease. PMID:24370640

Kamenskiy, Alexey V; Pipinos, Iraklis I; Dzenis, Yuris A; Lomneth, Carol S; Kazmi, Syed A Jaffar; Phillips, Nicholas Y; MacTaggart, Jason N

2014-03-01

204

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

205

Calculations of hole mass in [1 1 0]-uniaxially strained silicon for the stress-engineering of p-MOS transistors  

Science.gov (United States)

The influence of stress on transport properties in p-MOSFETs is rather well known for the case of biaxially strained channels obtained using hetero-epitaxy. However, results concerning biaxial stress do not apply for other stress configurations. For the stress-engineering of sub-45 nm devices, simplified models of the valence-band structure are required, which can predict the variation of their electrical performances for any stress configuration and channel orientation. In this work, we use the analytical formulation of a 6 × 6 k.p strained Hamiltonian to derive transport parameters for holes in the cases of both tensile and compressive (0 0 1)-biaxial and [1 1 0]-uniaxial stress. The model is first validated for the well-known cases of unstrained and (0 0 1)-biaxially strained silicon: our calculations are found to be in strong agreement with previous results obtained using more intensive computations. Then the variations of the different transport parameters for holes (energy splitting, density of states effective mass, and directional mass) as a function of [1 1 0]-uniaxial stress are provided in the energy range 0-55 meV. In particular, we show that the stress-induced changes of the longitudinal hole mass along the channel of p-MOSFETs are consistent with the trends recently observed for the mobility variations in strained devices. These variations of hole mass can be used as a guide for the stress-engineering of the future generations of process-induced strained transistors.

Guillaume, T.; Mouis, M.

2006-04-01

206

Stress variations and relief in patterned GaAs grown on mismatched substrates  

International Nuclear Information System (INIS)

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

207

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

208

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

209

Stresses in sulfuric acid anodized coatings on aluminum  

Science.gov (United States)

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

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

1993-01-01

210

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

211

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

212

A New Direct Process to Prepare YBa2Cu3O7-? films on Biaxially Textured Ag{110}<211>  

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YBCO films were successfully prepared on biaxially textured Ag{110} substrates by using pulsed laser deposition. X-ray diffraction results showed that the degree of preferential orientation of Ag{110} substrates varied with increasing annealing temperature. With a thin template layer deposited at low temperature, YBCO film with c-axis orientation and in-plane biaxial alignment could be obtained at high deposition temperature. Scanning electron microscopy observatio...

Wang, Rongping; Zhou, Yueliang; Pan, Shaohua; He, Meng; Chen, Zhenghao; Yang, Guozhen

1999-01-01

213

"STRESS MANAGEMENT”  

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? ??????? ???????? ?????????? ?? ?? stress management ??? ???’ ???????? ?? ?? ???? ??? ??????????? ?? ?????? ?? ????? ??? ????????? ?????????? ????? (HRM), ?? ????? ???????? ????? ??? ??? ???????????? ??????? ???????????, ???? ???????? ??????????, ????? ??? ????? ?????????? ?????,...

Prof.Univ. Dr. Paul Marinescu

2014-01-01

214

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)

215

The gravity dual of supersymmetric gauge theories on a biaxially squashed three-sphere  

International Nuclear Information System (INIS)

We present the gravity dual to a class of three-dimensional N=2 supersymmetric gauge theories on a biaxially squashed three-sphere, with a non-trivial background gauge field. This is described by a 1/2 BPS Euclidean solution of four-dimensional N=2 gauged supergravity, consisting of a Taub–NUT–AdS metric with a non-trivial instanton for the graviphoton field. The holographic free energy of this solution agrees precisely with the large N limit of the free energy obtained from the localized partition function of a class of Chern–Simons quiver gauge theories. We also discuss a different supersymmetric solution, whose boundary is a biaxially squashed Lens space S3/Z2 with a topologically non-trivial background gauge field. This metric is of Eguchi–Hanson–AdS type, although it is not Einstein, and has a single unit of gauge field flux through the S2 cycle.

216

Genuine effectively biaxial left-handed metamaterials due to extreme coupling.  

Science.gov (United States)

Most left-handed metamaterials cannot be described by local effective permittivity or permeability tensors in the visible or near-infrared due to the mesoscopic size of the respective unit cells and the related strong spatial dispersion. We lift this problem and propose a metamaterial exhibiting artificial magnetism that does not suffer from this restriction. The artificial magnetism arises from the extreme coupling between both metallic films forming the unit cell. We show that its electromagnetic response can be properly described by biaxial local constitutive relations. A genuine biaxial left-handed fishnet metamaterial is suggested, which can be realized by atomic layer deposition to fabricate the nanoscaled spacing layers required for extreme coupling. PMID:22344118

Menzel, Christoph; Alaee, Rasoul; Pshenay-Severin, Ekaterina; Helgert, Christian; Chipouline, Arkadi; Rockstuhl, Carsten; Pertsch, Thomas; Lederer, Falk

2012-02-15

217

Bi-axially crumpled silver thin-film electrodes for dielectric elastomer actuators  

Science.gov (United States)

Metal thin films, which have high conductivity, are much stiffer and may fracture at a much lower strain than dielectric elastomers. In order to fabricate compliant electrodes for use in dielectric elastomer actuators (DEAs), metal thin films have been formed into either zigzag patterns or corrugations, which favour bending and only allow uniaxial DEA deformations. However, biaxially compliant electrodes are desired in order to maximize generated forces of DEA. In this paper, we present crumpled metal thin-film electrodes that are biaxially compliant and have full area coverage over the dielectric elastomer. These crumpled metal thin-film electrodes are more stretchable than flat metal thin films; they remain conductive beyond 110% radial strain. Also, crumpling reduced the stiffening effect of metal thin films on the soft elastomer. As such, DEAs using crumpled metal thin-film electrodes managed to attain relatively high actuated area strains of up to 128% at 1.8 kV (102 V?m?1).

Low, Sze-Hsien; Lau, Gih-Keong

2014-12-01

218

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

219

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

220

Large-Scale Biaxial Friction Experiments with an Assistance of the NIED Shaking Table  

Science.gov (United States)

We constructed a large-scale biaxial friction apparatus using a large shaking table working at NIED (table dimension is 15m x 15m). The actuator of the shaking table becomes the engine of the constant speed loading. We used a 1.5m long rock sample overlaid on a 2m one. Their height and width are both 0.5m. Therefore, the slip area is 1.5m x 0.5m. The 2m long sample moves with the shaking table and the 1.5m sample is fixed to the basement of the shaking table. Thus, the shaking table displacement controls the dislocation between two rock samples. The shaking table can generate 0.4m displacement with a velocity ranging between 0.0125mm/s and 1m/s. We used Indian gabbro for the rock sample of the present experiments. Original flatness of the sliding surface was formed less than 0.024mm undulation using a large-scale plane grinder. Surface roughness evolved as subsequent experiments were done. Wear material was generated during each experiment, whose grain size becomes bigger as the experiments proceed. This might suggest a damage evolution on the sliding surface. In some experiments we did not remove the gouge material before sliding to examine the effect of gouge layer. Normal stress can be applied up to 1.3MPa. The stiffness of this apparatus was measured experimentally and was of the order of 0.1GN/m. We first measured the coefficient of friction at low sliding velocity (0.1~1mm/s) where the steady state was achieved after the slip of ~5mm. The coefficient of friction was about 0.75 under the normal stress between 0.13 and 1.3MPa. This is consistent with those estimated by previous works using smaller rock samples. We observed that the coefficient of friction decreased gradually with increasing slip velocity, but simultaneously the friction curves at the higher velocities are characterized by stick-slip vibration. Our main aim of the experiments is to understand the rupture propagation from slow nucleation to fast unstable rupture during the loading of two contact surfaces. We recorded many unstable slip events that nucleated inside the sliding surface but did not reach the edge of the sliding surface until the termination of slip. These slip events simulate full rupture process during earthquake, including nucleation, propagation and termination of the rupture. We monitored these rupture progress using the strain change propagation measured by 16 semiconductor strain gauges recorded at a sampling rate of 1MHz. In addition, high frequency waves emitted from AE events was continuously observed by 8 piezo-electronic transducers (PZTs) at a sampling rate of 20MHz. These sensors were attached at the edge of the slipping area. The AE event started to occur where the slip was nucleated and the slip area started to expand. Unfortunately, we could not locate all AE events during the unstable rupture, because of the overprints of signals from multiple events in the PZT records. We also monitored the amplitudes of transmitted waves across the sliding surface. The amplitudes decreased just after the stick slip and recovered gradually, suggesting that the transmitted wave amplitudes might reflect the slipped area on the interface.

Fukuyama, E.; Mizoguchi, K.; Yamashita, F.; Togo, T.; Kawakata, H.; Yoshimitsu, N.; Shimamoto, T.; Mikoshiba, T.; Sato, M.; Minowa, C.

2012-12-01

 
 
 
 
221

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)

222

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Shen, Sq; Zhou, B.; Liang, Jq

2004-01-01

223

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

Directory of Open Access Journals (Sweden)

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

Sugita Shukei

2013-01-01

224

Raman spectroscopy of graphene and bilayer under biaxial strain: bubbles and balloons  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In this letter we use graphene bubbles to study the Raman spectrum of graphene under biaxial (e.g. isotropic) strain. Our Gruneisen parameters are in excellent agreement with the theoretical values. Discrepancy in the previously reported values is attributed to the interaction of graphene with the substrate. Bilayer balloons (intentionally pressurized membranes) have been used to avoid the effect of the substrate and to study the dependence of strain on the inter-layer inter...

Zabel, Jakob; Nair, Rahul R.; Ott, Anna; Georgiou, Thanasis; Geim, Andre K.; Novoselov, Kostya S.; Casiraghi, Cinzia

2012-01-01

225

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

226

Biaxial strain effect of spin dependent tunneling in MgO magnetic tunnel junctions  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We study the effect of strain on magnetic tunnel junctions (MTJ) induced by a diamond like carbon (DLC) film. The junction resistance as well as the tunnel magnetoresistance (TMR) reduces with the DLC film. Non-equilibrium Green's function quantum transport calculations show that the application of biaxial strain increases the conductance for both the parallel and anti-parallel configurations. However, the conductance for the minority channel and for the anti-parallel config...

Sahadevan, Ajeesh M.; Tiwari, Ravi K.; Kalon, Gopinadhan; Bhatia, Charanjit S.; Saeys, Mark; Yang, Hyunsoo

2012-01-01

227

New method of biaxial tension test for sheet metal at high temperatures  

International Nuclear Information System (INIS)

A hydrostatic method has been developed to test sheet metal for biaxial tension in a wide range of temperatures and strain rates in order to estimate ductility during pressing. Water is used at the working medium at room temperature and molten salts, sand, flaked graphite -at elevated temperatures. Schemes of testing and test facilities are given. The method has been proved on Kh17N5M3 steel, D16M aluminium alloy and OT4-1 titanium alloy

228

Chaos synchronization in bi-axial magnets modeled by Bloch equation  

International Nuclear Information System (INIS)

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

229

Structure-based constitutive model can accurately predict planar biaxial properties of aortic wall tissue.  

Science.gov (United States)

Structure-based constitutive models might help in exploring mechanisms by which arterial wall histology is linked to wall mechanics. This study aims to validate a recently proposed structure-based constitutive model. Specifically, the model's ability to predict mechanical biaxial response of porcine aortic tissue with predefined collagen structure was tested. Histological slices from porcine thoracic aorta wall (n=9) were automatically processed to quantify the collagen fiber organization, and mechanical testing identified the non-linear properties of the wall samples (n=18) over a wide range of biaxial stretches. Histological and mechanical experimental data were used to identify the model parameters of a recently proposed multi-scale constitutive description for arterial layers. The model predictive capability was tested with respect to interpolation and extrapolation. Collagen in the media was predominantly aligned in circumferential direction (planar von Mises distribution with concentration parameter bM=1.03±0.23), and its coherence decreased gradually from the luminal to the abluminal tissue layers (inner media, b=1.54±0.40; outer media, b=0.72±0.20). In contrast, the collagen in the adventitia was aligned almost isotropically (bA=0.27±0.11), and no features, such as families of coherent fibers, were identified. The applied constitutive model captured the aorta biaxial properties accurately (coefficient of determination R(2)=0.95±0.03) over the entire range of biaxial deformations and with physically meaningful model parameters. Good predictive properties, well outside the parameter identification space, were observed (R(2)=0.92±0.04). Multi-scale constitutive models equipped with realistic micro-histological data can predict macroscopic non-linear aorta wall properties. Collagen largely defines already low strain properties of media, which explains the origin of wall anisotropy seen at this strain level. The structure and mechanical properties of adventitia are well designed to protect the media from axial and circumferential overloads. PMID:25458466

Polzer, S; Gasser, T C; Novak, K; Man, V; Tichy, M; Skacel, P; Bursa, J

2015-03-01

230

Elastic energy and string configurations in the chiral gauge theory of biaxial uniaxial nematic phase transitions  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In nematic liquid crystals (NLCs), topological defects of a chiral origin play a role in phase transitions and lead to phase configurations of nontrivial topology, like those in neutron stars and helium in the A-phase. In the biaxial-uniaxial phase transition, the deformation of the orbit, as the order parameter degeneracy of the NLC, connects together an evolution of topological defects, the surface anchoring energy and elastic Frank modui. In this work we estimate the chir...

Elnikova, L. V.

2014-01-01

231

Measuring knife stab penetration into skin simulant using a novel biaxial tension device  

Digital Repository Infrastructure Vision for European Research (DRIVER)

This paper describes the development and use of a biaxial measurement device to analyse the mechanics of knife stabbings. In medicolegal situations it is typical to describe the consequences of a stabbing incident in relative terms that are qualitative and descriptive without being numerically quantitative. Here, the mechanical variables involved in the possible range of knife-tissue penetration events are considered so as to determine the necessary parameters that would need to be controlled...

Gilchrist, M. D.; Keenan, S.; Curtis, Michael; et al.

2008-01-01

232

Microstructure changes in poly(ethylene terephthalate) in thick specimens under complex biaxial loading  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We present an experimental investigation into the strain-induced crystalline microstructure, under biaxial elongation in Polyethylene terephthalate (PET). The aim of our study is to achieve both mechanical tests representative from the blow-moulding process, and micro- structural measurements. We therefore examine how the microstructure of a polymer subjected to a complex strain field evolves in terms of its crystalline ratio, its molecular orientation and the size of its crystallites. PET in...

Marco, Yann; Chevalier, Luc

2008-01-01

233

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 biax...

Rodrigues, H.; Varum, H.; Are?de, A.; Costa, A.

2013-01-01

234

DIC-aided biaxial fatigue tests of a 304L steel  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Several biaxial fatigue tests are conducted up to 106 cycles at room temperature in the context of a collaboration LMT-Cachan / EDF / AREVA / SNECMA / CEA. Malteses cross specimens of 304L steel, designed to initiate crack in the bulk, are loaded by a triaxial testing machine. A Digital Image Correlation technique is used to measure strain during loading and detect crack initiation early. A special optical assembly and a stroboscopic sampling method are set up in this purpose. Several t...

Le-Roux J.C.; Desmorat R.; Courtin S.; Raka B.; Barbier G.; Vincent L.; Poncelet M.

2010-01-01

235

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

International Nuclear Information System (INIS)

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

236

Biaxial texturing of inorganic photovoltaic thin films using low energy ion beam irradiation during growth  

Energy Technology Data Exchange (ETDEWEB)

We describe our efforts to control the grain boundary alignment in polycrystalline thin films of silicon by using a biaxially textured template layer of CaF{sub 2} for photovoltaic device applications. We have chosen CaF{sub 2} as a candidate material due to its close lattice match with silicon and its suitability as an ion beam assisted deposition (mAD) material. We show that the CaF{sub 2} aligns biaxially at a thickness of {approx}10 nm and, with the addition of an epitaxial CaF{sub 2} layer, has an in-plane texture of {approx}15{sup o}. Deposition of a subsequent layer of Si aligns on the template layer with an in-plane texture of 10.8{sup o}. The additional improvement of in-plane texture is similar to the behavior observed in more fully characterized IBAD materials systems. A germanium buffer layer is used to assist in the epitaxial deposition of Si on CaF{sub 2} template layers and single crystal substrates. These experiments confirm that an mAD template can be used to biaxially orient polycrystalline Si.

Groves, Jaes R [Los Alamos National Laboratory; De Paula, Raymond F [Los Alamos National Laboratory; Hayes, Garrett H [STANFORD UNIV.; Li, Joel B [STANFORD UNIV.; Hammond, Robert H [STANFORD UNIV.; Salleo, Alberto [STANFORD UNIV.; Clemens, Bruce M [STANFORD UNIV.

2010-01-01

237

Biaxial texture development in the ion beam assisted deposition of magnesium oxide  

Energy Technology Data Exchange (ETDEWEB)

Low-energy ion-beam irradiation (<1 keV) during the concurrent deposition of cubic oxide materials results in the growth of crystallographically textured thin films. A model system, magnesium oxide (MgO), has been successfully used as a biaxially textured template film for the heteroepitaxial deposition of many materials with texture dependent properties like high temperature superconductors, tunable microwave materials, and ferroelectrics. Here, we present data on the initial nucleation of biaxial crystallographic texture in this model system using an in situ quartz crystal microbalance (QCM) substrate combined with in situ reflected high-energy electron diffraction (RHEED). Correlation of mass uptake with the RHEED images of the growing surface shows that the development of crystallographic biaxial texture in this material system occurs suddenly as the initially polycrystalline MgO films reaches a critical film thickness of 2 nm. This texture continues to improve during subsequent growth. A simple model shows that the effect is not due simply to coverage effects. We use a combination of in situ RHEED and ex situ transmission electron microscopy to further elucidate the mechanism of this sudden texture formation. We present a physical model to describe this behavior and explain the role of ion-to-atom arrival ratio and underlying nucleation surface on texture development.

Groves, James R., E-mail: jgroves@stanford.edu [Department of Materials Science and Engineering, Stanford University, Stanford, CA 94305 (United States); Superconductivity Technology Center, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Hammond, Robert H. [Geballe Laboratory for Advanced Materials, Stanford University, Stanford, CA 94305 (United States); Matias, Vladimir; DePaula, Raymond F.; Stan, Liliana [Superconductivity Technology Center, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Clemens, Bruce M. [Department of Materials Science and Engineering, Stanford University, Stanford, CA 94305 (United States)

2012-02-01

238

Biaxial texture development in the ion beam assisted deposition of magnesium oxide  

International Nuclear Information System (INIS)

Low-energy ion-beam irradiation (<1 keV) during the concurrent deposition of cubic oxide materials results in the growth of crystallographically textured thin films. A model system, magnesium oxide (MgO), has been successfully used as a biaxially textured template film for the heteroepitaxial deposition of many materials with texture dependent properties like high temperature superconductors, tunable microwave materials, and ferroelectrics. Here, we present data on the initial nucleation of biaxial crystallographic texture in this model system using an in situ quartz crystal microbalance (QCM) substrate combined with in situ reflected high-energy electron diffraction (RHEED). Correlation of mass uptake with the RHEED images of the growing surface shows that the development of crystallographic biaxial texture in this material system occurs suddenly as the initially polycrystalline MgO films reaches a critical film thickness of 2 nm. This texture continues to improve during subsequent growth. A simple model shows that the effect is not due simply to coverage effects. We use a combination of in situ RHEED and ex situ transmission electron microscopy to further elucidate the mechanism of this sudden texture formation. We present a physical model to describe this behavior and explain the role of ion-to-atom arrival ratio and underlying nucleation surface on texture development.

239

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

240

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)

 
 
 
 
241

Influence of a multiaxial stress on the reversible and irreversible magnetic behaviour of a 3%Si-Fe alloy  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The research presented in this paper is motivated by the design of electrical devices submitted to mechanical stress. It aims at studying the magnetic behaviour of ferromagnetic materials submitted to biaxial stress. It deals with the evolution of the magnetic susceptibility, coercive field and magnetic losses with respect to stress, magnetic field level and frequency. These quantities are of primary importance in the design of rotors for high speed rotating machines. The work is focused on t...

Rekik, Mahmoud; Hubert, Olivier; Daniel, Laurent

2014-01-01

242

Large-scale experimental investigation of the effect of biaxial loading on the deformation capacity of pipes with defects  

International Nuclear Information System (INIS)

This paper presents results from large-scale four-point bending tests of 12'' X65 seamless pipes with circumferential defects subjected to different levels of internal pressure. The aim of the tests has been to investigate the effect of biaxial loading on the strain capacity of the pipes. The results from the tests show a significant effect of the biaxial loading. For cases without internal pressure, the pipes fail due to local buckling on the compression side of the pipe. Upon application of internal pressure the failure mode shifts to fracture from the defect on the tension side. The failure bending strain levels for these cases were 1.5-2.25%, whereas the local buckling occurred at strain levels in the range of 3.5-4%. The main reason for this appears to be that the biaxial loading increases the crack driving force for a given applied strain level. No significant effect of the biaxial loading on the ductile tearing resistance was observed. The results are of great importance for fracture assessment of pressurised pipelines loaded into the plastic region, as the biaxial loading effect observed is not accounted for in current fracture assessment procedures

243

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

Energy Technology Data Exchange (ETDEWEB)

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.

HOUSTON,JACK E.; JARAUSCH,K.F.; KIELY,J.D.; RUSSELL,P.E.

1999-10-07

244

Modelling stress-dependent permeability in fractured rock including effects of propagating and bending fractures  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The influence of in-situ stresses on flow processes in fractured rock is investigated using a novel modelling approach. The combined finite-discrete element method (FEMDEM) is used to model the deformation of a fractured rock mass. The fracture wall displacements and aperture changes are modelled in response to uniaxial and biaxial stress states. The resultant changes in flow properties of the rock mass are investigated using the Complex Systems Modelling Platform (CSMP++). CSMP++ is used to ...

Latham, J. P.; Xiang, J.; Belayneh, M.; Nick, H. M.; Tsang, C. F.; Blunt, M. J.

2013-01-01

245

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Mrkic?, Sas?a; Galic?, Kata; Ivankovic?, Marica

2007-01-01

246

Fatigue Assessment of Components Subjected to Non-Proportional Stress Histories  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The fatigue assessment of components subjected to complex loading histories is a challenging topic. Several criteria intended for use under multiaxial stress-states and non-proportional loading have been proposed by many researchers throughout the years. This thesis is intended as a critical review of the fatigue assessment of both proportional and non-proportional stress histories. A database consisting of 268 experimental tests for biaxial fatigue limits were collected from various sources....

Bruun, Oyvind Aleksander

2013-01-01

247

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

248

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 (0minimum surface energy plane vs. fastest growth direction. However, the in-plane orientation selection could still be explained by the largest capture 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

249

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

250

Elasticity and polarization of GaxAl1-xN alloys subjected to uniaxial and biaxial compression  

Science.gov (United States)

Elasticity and polarization of GaxAl1-xN alloys subjected to uniaxial and homogeneous biaxial compression are calculated using first-principles methods. The uniaxial compression along the c-axis reduces Young’s modulus along the c-axis, and enhances bulk modulus and total polarization, whereas the biaxial compression in the plane perpendicular to the c-axis enhances bulk and Young’s moduli. It is also found that when the in-plane biaxial compression is applied by constraining the a-axis lattice constant to that of AlN, the bulk and Young’s moduli dramatically increase with increasing Ga concentration, and the total polarization could be suppressed, even annihilated, and finally enhanced by controlling Ga concentration.

Duan, Y.; Tang, G.; Qin, L.; Shi, L.

2008-11-01

251

Surface morphology and crystallinity of biaxially stretched PET films on the nanoscale  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The surface morphology and crystallinity of biaxially drawn (BD) and amorphous poly(ethylene terephthalate) (PET) films were investigated by means of scanning probe microscopy. The PET surface is best imaged using non- contact mode atomic force microscopy (NC-AFM). Contact mode (C-AFM) under water can also offer a good resolution but the PET surface is not stable for long periods under such conditions. The BD film texture appears to be made up of 'hillocks' of about 20 nm in diameter, while a...

Dinelli, F.; Assender, He; Kirov, K.; Kolosov, Ov

2000-01-01

252

Effects of biaxial strains on the magnetic properties of Co-graphene heterojunctions  

Science.gov (United States)

Using the ab initio calculations, the changes of the magnetic properties of Co atoms on graphene for biaxial strains on graphene were investigated. Our calculation results showed that the compression of graphene changed the magnetic moments of Co adatoms more significantly than the elongation of graphene. From the 3d-electron density of states of Co atoms, the changes of magnetic properties of Co atoms on graphene were found to result from the significant hybridization between Co 3dyz and C 2pz orbitals. It was demonstrated that this 3d-electron hybridization of Co/graphene system originated from the strain-induced change of the local atomic structure.

Lee, Sangho; Choi, Heechae; Chung, Yong-Chae

2012-06-01

253

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

International Nuclear Information System (INIS)

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

254

Dynamic monitoring of a mobile telecommunications tower with a bi-axial optical FBG accelerometer  

Science.gov (United States)

In this work, the structural health monitoring of a self-supported steel tower with 50 meters high used for mobile communications are presented. For this test, a fiber Bragg grating based biaxial horizontal accelerometer was used to obtain the structure frequencies. The frequencies for the first resonant modes were obtained from the acceleration data recorded over time, resulting from the application of mechanical horizontal impulses on the tower. The results shown that the frequencies measured in both directions are within the values expected for this type of structure and can be used to calibrate numerical models that represent their structural behavior.

Antunes, Paulo; Travanca, Rui; Varum, Humberto; André, Paulo

2011-05-01

255

Biaxial thermal creep of two heats of V4Cr4Ti at 700 and 800 oC in a liquid lithium environment  

International Nuclear Information System (INIS)

This paper presents biaxial thermal creep results for the vanadium alloy V4Cr4Ti in liquid lithium using US Heat 832665 and two batches of tubing made from NIFS-Heat-2. The tests were performed at 700 and 800 oC over a stress range of 30-120 MPa using pressurized tube specimens. Lithium environments changed C, N and O concentrations in V4Cr4Ti. Oxygen removal from the alloy to lithium was small when there was a significant pickup of nitrogen during exposures. The creep response of V4Cr4Ti was characterized by an inverted primary creep followed by a secondary creep or an accelerating creep up to creep rupture. A normal primary creep was also observed in US Heat 832665 when tested at 700 oC and 120 MPa. Improved creep rupture properties were observed in the JP-NIFS-Heat-2 specimens compared to the US-NIFS-Heat-2 specimens. Creep response of V4Cr4Ti is apparently dependent on the heat, tubing production, and stress and temperature conditions

256

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

257

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

258

Stress state effect on dynamic strain aging and surface markings during stretching of AlMg7 alloy sheet  

Energy Technology Data Exchange (ETDEWEB)

Stress state effect on dynamic strain aging (DSA) and the related surface appearance was analyzed in uniaxial and biaxial room temperature stretching of AlMg7 alloy sheet. In uniaxial tension the serrated yielding was found pertinent at the entire strain range for the tested material. Stretcher markings, usually noted as A (``flamboyant``) type, formed during yield point elongation, while type B (``parallel bands``) appeared at higher strains, due to the Portevin Le Chatelier effect. Stretching the tested sheet material over an hemispherical punch, and simulating a different degree of biaxiality, the dynamic strain aging (DSA) appeared to be suppressed by increasing the biaxiality, and accordingly the surface morphology was also changed in a complex manner. (orig.) 15 refs.

Romhanji, E.; Glisic, D.; Popovic, M.; Milenkovic, V. [Belgrade Univ. (Yugoslavia). Faculty of Technology and Metallurgy

1998-10-01

259

Growth of YBCO films on MgO-based rolling-assisted biaxially textured substrates templates  

International Nuclear Information System (INIS)

We have developed a simple alternative buffer layer architecture for the rolling-assisted biaxially textured substrates (RABiTS) approach. Buffer layers with both oxygen and metal diffusion barrier properties are of interest. Cube textured magnesium oxide MgO buffers were grown directly on biaxially textured Ni and Ni-W3 at.% substrates using electron beam evaporation. We have also grown epitaxial MgO layers on 2 m long textured Ni-W3 at.% tapes in a reel-to-reel e-beam evaporation. Highly textured LaMnO3 (LMO) buffers were grown on MgO-buffered Ni substrates using rf sputtering. MgO and LMO buffers have been proved to be good oxygen diffusion barriers and Ni diffusion barriers, respectively. YBCO films with a Jc of 1 x 106 A cm-2 at 77 K and self-field were grown on this newly developed architecture of LMO/MgO/Ni using pulsed laser deposition

260

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

Directory of Open Access Journals (Sweden)

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

Belinda Pingguan-Murphy

2012-08-01

 
 
 
 
261

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

262

The gravity dual of supersymmetric gauge theories on a biaxially squashed three-sphere  

Energy Technology Data Exchange (ETDEWEB)

We present the gravity dual to a class of three-dimensional N=2 supersymmetric gauge theories on a biaxially squashed three-sphere, with a non-trivial background gauge field. This is described by a 1/2 BPS Euclidean solution of four-dimensional N=2 gauged supergravity, consisting of a Taub-NUT-AdS metric with a non-trivial instanton for the graviphoton field. The holographic free energy of this solution agrees precisely with the large N limit of the free energy obtained from the localized partition function of a class of Chern-Simons quiver gauge theories. We also discuss a different supersymmetric solution, whose boundary is a biaxially squashed Lens space S{sup 3}/Z{sub 2} with a topologically non-trivial background gauge field. This metric is of Eguchi-Hanson-AdS type, although it is not Einstein, and has a single unit of gauge field flux through the S{sup 2} cycle.

Martelli, Dario, E-mail: dario.martelli@kcl.ac.uk [Department of Mathematics, King' s College, London, The Strand, London WC2R 2LS (United Kingdom); Sparks, James [Mathematical Institute, University of Oxford, 24-29 St Giles' , Oxford OX1 3LB (United Kingdom)

2013-01-01

263

Practical approach in surface modification of biaxially oriented polypropylene films for gravure printability  

Science.gov (United States)

Biaxially oriented polypropylene (BOPP) film is one of the most popularly used materials for the gravure printing process in flexible packaging industry. The skin layers of BOPP film were associated with 3-6 weight % of propylene-ethylene copolymer. These films were completely biaxial-oriented by sequential stretching process after which the film surfaces were subjected to corona treatment integrated in the production line. The FT-IR results exhibited that polar functional groups as carbonyl molecules were established on the corona-treated BOPP film. The contact angles of these BOPP films were measured; the surface free energies (SFE) were then calculated. AFM topographical images also agreed well with the SFE which increased as the contents of propylene-ethylene copolymer increased. An approximated 20% increased SFE was obtained for the BOPP film that was associated with 6% propylene-ethylene copolymer. The printing quality on BOPP films was tested by light microscope which confirmed that the chromatic resolution of the printed images improved down to even more smaller groove sizes, 10 or 5 dot%. This improvement was also examined and found to correspond well with the interfacial tensions and work of adhesion between the inks and the modified BOPP films.

Nuntapichedkul, Boonchai; Tantayanon, Supawan; Laohhasurayotin, Kritapas

2014-09-01

264

On the Elastic Energy Density of Constrained Q-Tensor Models for Biaxial Nematics  

Science.gov (United States)

Within the Landau-de Gennes theory, the order parameter describing a biaxial nematic liquid crystal assigns a symmetric traceless 3 × 3 matrix Q with three distinct eigenvalues to every point of the region ? occupied by the system. In the constrained case of matrices Q with constant eigenvalues, the order parameter space is diffeomorphic to the eightfold quotient {{S}^3/{H}} of the 3-sphere {{S}^3}, where {{H}} is the quaternion group, and a configuration of a biaxial nematic liquid crystal is described by a map from ? to {{S}^3/{H}}. We express the (simplest form of the) Landau-de Gennes elastic free-energy density as a density defined on maps {q: ? to {S}^3}, whose functional dependence is restricted by the requirements that (1) it is well defined on the class of configuration maps from ? to {{S}^3/{H}} (residual symmetry) and (2) it is independent of arbitrary superposed rigid rotations (frame indifference). As an application of this representation, we then discuss some properties of the corresponding energy functional, including coercivity, lower semicontinuity and strong density of smooth maps. Other invariance properties are also considered. In the discussion, we take advantage of the identification of {{S}^3} with the Lie group of unit quaternions {Sp(1) \\cong SU(2)} and of the relations between quaternions and rotations in {{R}^3} and {{R}^4}.

Mucci, Domenico; Nicolodi, Lorenzo

2012-12-01

265

Modeling of CMUTs with Multiple Anisotropic Layers and Residual Stress  

DEFF Research Database (Denmark)

Usually the analytical approach for modeling CMUTs uses the single layer plate equation to obtain the deflection and does not take anisotropy and residual stress into account. A highly accurate model is developed for analytical characterization of CMUTs taking an arbitrary number of layers and residual stress into account. Based on the stress-strain relation of each layer and balancing stress resultants and bending moments, a general multilayered anisotropic plate equation is developed for plates with an arbitrary number of layers. The exact deflection profile is calculated for a circular clamped plate of anisotropic materials with residual bi-axial stress. From the deflection shape the critical stress for buckling is calculated and by using the Rayleigh-Ritz method the natural frequency is estimated.

Engholm, Mathias; Thomsen, Erik Vilain

2014-01-01

266

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 e 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.)

267

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

268

On the sensitivity of directions that support Voigt wave propagation in infiltrated biaxial dielectric materialsrid="fn1"/>  

Science.gov (United States)

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

Mackay, Tom G.

2014-01-01

269

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

270

Growth of biaxially textured template layers using ion beam assisted deposition  

Science.gov (United States)

A two-step IBAD (ion beam assisted deposition) method is investigated, and compared to the conventional IBAD methods. The two step method uses surface energy anisotropy to achieve uniaxial texture and ion beam irradiation for biaxial texture. The biaxial texture was achieved by selective surface etching and enhanced by grain overgrowth. In this method, biaxial texture alignment is performed on a (001) uniaxially textured buffer layer. The material selected for achieving uniaxial texture, YBCO (YBa2Cu3O7-x), has strong surface energy anisotropy. YBCO is chemically susceptible to the reaction with the adjacent layer. Yttria stabilized zirconia (YSZ) was used to prevent the reaction between YBCO and the substrates (polycrystalline Ni alloy [Hastelloy] and amorphous SiNx/Si). A SrTiO3 layer was deposited on the uniaxially textured YBCO layer to retard stoichiometry change with subsequent processing. STO is well lattice matched with YBCO. A top layer of Ni was then deposited. The Ni layer was used for studying the effect of grain overgrowth. The obtained uniaxial Ni films were used for subsequent ion beam processing. Ar ion beam irradiation onto the uniaxially textured Ni film was used to study the effect of selective grain etching in achieving in-plane aligned Ni grains. Additional Ni deposition induces the overgrowth of the in-plane aligned Ni grains and, finally, the overall in-plane alignment. The in-plane alignment is examined with XRD phi scan. The effect of surface polarity of insulating oxide substrates on the epitaxial growth behavior was investigated. The lattice strain energy was the most important factor for determining the orientation of Ni films on a non-polar surface. However, for a polar surface, the surface energy plays an important role in determining the final orientation of the Ni films based on the experimental and theoretical results. Y2O3 growth behavior was also studied. The lattice strain energy is the most important factor for Y2O3 growth on single crystalline substrates. The surface energy anisotropy is the most important factor for the growth on amorphous substrates. The XRD phi scan study shows that Ar ion beam irradiation with favorable angle of incidence enhances the in-plane alignment of Y2O3 films grown on randomly oriented substrates due to the ion channeling.

Park, Seh-Jin

271

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

272

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

273

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

Energy Technology Data Exchange (ETDEWEB)

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

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

1996-12-31

274

Cavitation characteristics of a superplastic 8090 Al alloy during equi-biaxial tensile deformation  

Energy Technology Data Exchange (ETDEWEB)

Cavitation behavior of a superplastic 8090 Al alloy during equi-biaxial tensile deformation has been investigated by deforming the sheet into a right cylindrical die. Cavitation characteristics could be separated into two stages. In stage I, the sheet deformed freely as part of a spherical dome, and the cavity volume increased exponentially with deformation. The evolution of cavity volume was due to both nucleation and growth of cavities. In the second stage, the surface friction would restrict thinning of the sheet, and the cavity volume first increased and then decreased with forming time for all test strain rates. Decrease in cavity volume in the later stage could be related to the cavity shrinkage that resulted from the sintering effect. A higher imposed pressure during forming leaded to a greater average cavity shrinkage rate. The cavitation level could be effectively reduced by a post-sintering procedure. (orig.)

Wu Horngyu [Chung-Hua Univ., Hsinchu (Taiwan). Dept. of Mech. Eng.

2000-10-31

275

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

Science.gov (United States)

Colloidal particles with a dielectric constant mismatch with the surrounding solvent in an external biaxial magnetic or electric field experience an "inverted" dipolar interaction. We determine the phase behavior of such a system using Helmholtz free energy calculations in Monte Carlo simulations for colloidal hard spheres as well as for charged hard spheres interacting with a repulsive Yukawa potential. The phase diagram of colloidal hard spheres with inverted dipolar interactions shows a gas-liquid transition, a hexagonal ABC stacked crystal phase, and a stretched hexagonal-close-packed crystal. The phase diagram for charged spheres is very similar, but displays an additional layered-fluid phase. We compare our results with recent experimental observations. PMID:20515101

Smallenburg, Frank; Dijkstra, Marjolein

2010-05-28

276

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.)

277

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)

278

Electronic structure and optical properties of CuAlO2 under biaxial strain  

International Nuclear Information System (INIS)

An ab initio calculation has been carried out to investigate the biaxial strain ( - 10.71% 2. All the elastic constants (c11, c12, c13, c33) except c44 decrease (increase) during tensile (compressive) strain. The band gap is found to decrease in the presence of tensile as well as compressive strain. The relative decrease of the band gap is asymmetric with respect to the sign of the strain. Significant differences between the parallel and perpendicular components of the dielectric constant and the optical properties have been observed due to anisotropic crystal structure. It is further noticed that these properties are easily tunable by strain. Importantly, the collective oscillation of the valence electrons has been identified for light polarized perpendicular to the c-axis. From calculations, it is clear that the tensile strain can enhance the hole mobility as well as the transparency of CuAlO2. (paper)

279

Mechanical behaviour and microstructural evolution of alloy 800H under biaxial cyclic loading  

International Nuclear Information System (INIS)

The mechanical behaviour of alloy 800H under biaxial cyclic loading was investigated at room temperature and at 800 C. The low-cycle fatigue experiments were carried out using tubular specimens under axial and torsional loading with constant total equivalent strain amplitude following either proportional or nonproportional loading paths. The cyclic hardening observed under nonproportional loading was clearly higher than that under proportional loading. The extra hardening due to the nonproportional loading path was more pronounced at room temperature. The evolution of the dislocation structure was characterized by transmission electron microscopy of specimens after interrupted fatigue tests. The changes in the dislocation structure and the precipitation phenomena are in accordance with the observed mechanical behaviour of the specimens. Twinning was observed in very few grains of some specimens and does not influence the extra hardening under nonproportional loading, martensite was not detected in any specimen. (orig.)

280

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

 
 
 
 
281

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

International Nuclear Information System (INIS)

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

282

Molecular dynamics study on the equal biaxial tension of Cu/Ag bilayer films  

International Nuclear Information System (INIS)

The mechanical behavior, dislocation nucleation and development, and the evolution of interface in Cu/Ag bilayer films during an equal biaxial tension were studied using molecular dynamics simulations. The results show that dislocations are prone to nucleate at the interface of Cu/Ag bilayer film, and then propagate toward the free surface. The deformation defects consist of partial dislocations and intrinsic stacking faults, accompanying with some extrinsic stacking faults and stacking fault tetrahedra which just occur at the interface and propagate in the Cu layer. Compared with Cu and Ag films, Cu/Ag bilayer films have the maximal yield strain. The surface roughness reaches maximum at the yield strain, and then rapidly decreases with the increase of strain. Atoms in stacking faults increase with the strain at the high strain rate, while the rule is reversed at the low strain rate.

283

EFFECTS OF ELECTRIC FIELD ON THE BIAXIAL STRENGTH OF POLED PZT  

Energy Technology Data Exchange (ETDEWEB)

The mechanical integrity of piezoelectric ceramics plays a crucial role in the performance and design of lead zirconate titanate (PZT) piezo stack actuators especially as PZT actuators become physically larger and are sought to operate under harsher conditions. The reliable design of such systems demands additional consideration of a number of issues that include electro-mechanical coupling as well as strength-size scaling. This study addresses some of those issues through the use of ball-on-ring (BoR) equibiaxial flexure strength tests of two PZT piezo ceramics. The BoR biaxial flexure tests were conducted with two PZT materials under different electric fields. Fracture surfaces and failure initiations were analyzed using optical and scanning electronic microscopy. The effects of electric fields on the two-parameter Weibull distribution are discussed. These results will serve as input data for future probabilistic reliability analysis of multilayer PZT piezo actuators.

Wang, Hong [ORNL; Wereszczak, Andrew A [ORNL

2007-01-01

284

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

285

Residual stress and fracture of laminated ceramic membranes  

International Nuclear Information System (INIS)

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

286

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

Directory of Open Access Journals (Sweden)

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

María Blanca Ros

2011-09-01

287

Non-destructive measurement of residual stresses in U-0.8 wt.% Ti by neutron diffraction  

International Nuclear Information System (INIS)

The macroscopic residual stress distribution in ?-quenched and stress levelled U-0.8wt% Ti alloy tubes was studied using neutron diffraction techniques. Residual strains were evaluated from the difference in d-spacings measured in the tubes and in small reference samples machined from each tube. Residual stresses were calculated with the isotropic bulk value of the elastic constraints for polycrystalline ?-U. Quenching from the ? field resulted in a nearly equi-biaxial stress state at every point across the wall thickness of the tube. The magnitude of the radial stress was very small compared with that of the axial and hoop stresses which were compressive at the surfaces and tensile in the interior. Stress levelling relieved almost completely the hoop residual stress without affecting the radial stress. The axial residual stress becomes tensile through the wall thickness and remains constant at about 20% of its magnitude in the as-quenched condition

288

Anisotropic swelling observed during stress-free reirradiation of AISI 304 tubes previously irradiated under stress  

Energy Technology Data Exchange (ETDEWEB)

A 'history effects' experiment was conducted in EBR-II that involved the reirradiation of AISI 304 cladding and capsule tubes. It is shown that when irradiated tubes had not previously experienced stress, subsequent irradiation led to additional swelling strains that were isotropically distributed. However, when tubes previously irradiated under a 2:1 biaxial stress were reirradiated without stress the additional swelling strains were not isotropically distributed. The tubes obviously retained a memory of the previous stress state that appears to be attempting to distribute strains in the directions dictated by the previous stress state. It is clear, however, that the memory of that stress state is fading as the anisotropic dislocation microstructure developed during irradiation under stress is replaced by an isotropic dislocation microstructure during subsequent exposure in the absence of stress. It is also shown that once the transient regime of swelling nears completion, further changes in stress state or irradiation temperature have no influence on the swelling rate thereafter.

Garner, F.A. [Pacific Northwest National Laboratory, Richland, WA (United States)], E-mail: frank.garner@dslextreme.com; Flinn, J.E. [Argonne National Laboratory, EBR-II Project, Idaho Falls, ID (Retired) (United States); Hall, M.M. [Bechtel Bettis Company, West Mifflin, PA (United States)

2009-04-30

289

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

Science.gov (United States)

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

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

2007-04-01

290

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

291

Biaxially-Textured Photovoltaic Film Crystal Silicon on Ion Beam Assisted Deposition CaF2 Seed Layers on Glass  

Energy Technology Data Exchange (ETDEWEB)

We grow biaxially textured heteroepitaxial crystal silicon (c-Si) films on display glass as a low-cost photovoltaic material. We first fabricate textured CaF{sub 2} seed layers using ion-beam assisted deposition, then coat the CaF{sub 2} with a thin, evaporated epitaxial Ge buffer and finally deposit heteroepitaxial silicon on the Ge. The silicon is grown by hot-wire chemical vapor deposition, a high-rate, scalable epitaxy technology. Electron and X-ray diffraction confirm the biaxial texture of the CaF{sub 2} and epitaxial growth of the subsequent layers. Transmission electron microscopy reveals columnar silicon grains about 500 nm across. We fabricate a proof-of-concept epitaxial film c-Si solar cell with an open circuit voltage of 375 mV that is limited by minority carrier lifetime.

Groves, J. R.; Li, J. B.; Clemens, B. M.; LaSalvia, V.; Hasoon, F.; Branz, H. M.; Teplin, C. W.

2012-05-01

292

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

293

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

International Nuclear Information System (INIS)

?-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.

294

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 ...

295

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 ...

296

Cathodoluminescence and Photoconductive Characteristics of Single-Crystal Ternary CdS/CdSe/CdS Biaxial Nanobelts.  

Science.gov (United States)

The cathodoluminescence and optoelectronic properties based on an individual CdS/CdSe/CdS biaxial nanobelt are revealed in the present study. Both typical CdS and CdSe emissions are detected from as-grown CdS/CdSe/CdS nanobelts. The photodetector based on this nanobelt exhibits high sensitivity and excellent cycle stability. This opens a door to rational design of germanium chalcogenide compounds with unique optical properties. PMID:25384889

Hu, Linfeng; Yan, Jian; Kim, Yong; Fei, Guangtao; Watanabe, Kentaro; Sekiguchi, Takashi; Zhang, Lide; Fang, Xiaosheng

2014-11-10

297

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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...

Zidane, Ibrahim; Guines, Dominique; Leotoing, Lionel; Ragneau, Eric

2010-01-01

298

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)

299

Observations of grain-boundary sliding and surface topography in an 8090 Al alloy after uniaxial and biaxial superplastic deformation  

Energy Technology Data Exchange (ETDEWEB)

The surface topography of an 8090 aluminum alloy was studied after uniaxial or biaxial superplastic deformation, with particular reference to grain-boundary sliding (GBS) offsets, grain rotation angles, formation of striated bands (SBs) or fibers, cavity distribution, and cavity formation mechanisms. Additionally, the contribution of GBS or grain separation to the overall strain was evaluated. Striated bands were observed and are thought to be the newly exposed faces of the grains inclined to the specimen`s surface. They were formed by sliding of grains upward and downward relative to the specimen surface. Grooves and crests inside SBs were formed from the relative motion of grain-boundary defects. Fibers were observed and are thought to be the further development of the SBs resulting from the formation of elongated cavities and grain separation. More cavitation was found in equibiaxially strained regions than in other regions subjected to approximately equivalent levels of strain. About 50 pct of the total strain was contributed to GBS in the uniaxial tensile-loaded specimens, as compared to about 30 pct in the biaxial-strained specimens. The effects of grain separation, grain rotation, and secondary GBS may be the reasons for the reduction of the observed strain contribution from GBS in biaxially strained specimens.

Chen, T.R.; Huang, J.C. [National Sun Yat-Sen Univ., Kaohsiung (Taiwan, Province of China). Inst. of Materials Science and Engineering

1999-01-01

300

Biaxially textured YBa 2Cu 3O 7-x films deposited on polycrystalline flexible yttria-stabilized zirconia ceramic substrates  

Science.gov (United States)

Biaxially textured YBa 2Cu 3O 7-x (YBCO) films were grown on polycrystalline flexible yttria-stabilized zirconia (YSZ) ceramic substrates (Ceraflex) buffered with MgO and LaMnO 3 layers. These substrates were initially coated with silica glass to obtain a smooth surface and then biaxially textured MgO buffer layers were deposited by ion beam assisted deposition (IBAD-MgO). Lanthanum manganate (LMO) cap layers and YBCO layers were then deposited by the pulsed laser ablation method. Highly textured YBCO films with a full width half maximum (FWHM) of 6.75° in (1 1 0) phi scans and a FWHM ? 5° in (2 0 0) omega scans were obtained. An initial deposition yielded samples with a Tc > 88 K and a self-field magnetization Jc of 2 × 10 5 A/cm 2 at 77 K. A secondary ion mass spectrometry (SIMS) depth profile of the samples indicated that with the present deposition condition, some La, Mn and Mg diffusion into the YBCO layers is possible and this may reduce the Jc in the self-field. The yield strength (YS) of uncoated Ceraflex substrates was compared with that of metallic substrates and it was found that Ceraflex substrates can have a YS at least 4-5 times higher than the YS of biaxially textured Ni-5 at.%W substrates and ?1.5 times that of Hastelloy TM substrates.

Varanasi, C. V.; Burke, J.; Lu, R.; Wu, J.; Brunke, L.; Chuck, L.; Smith, H. E.; Maartense, I.; Barnes, P. N.

2008-07-01

 
 
 
 
301

A PHYSICS BASED MODEL OF INVERSION CHARGE SHEET (ICS FOR NANOSCALE BIAXIAL STRAINED – SILICON NMOSFET INCLUDING QUANTUM MECHANICAL EFFECT (QME  

Directory of Open Access Journals (Sweden)

Full Text Available In this paper, a physics based model of inversion charge sheet of nanoscale NMOSFETs has been presented. The model is formulated for nanoscale biaxial strained silicon NMOSFET including quantum mechanical effect (QME. The QME is splitting of conduction band due to very thin oxide (tox and very large doping concentration of ultra small geometry of MOSFET. The QME shift the inversion charge sheet into subtracts. To overcome this problem strain technique is used because this shift is very small but this is effect causes increase in the surface potential as well as threshold voltage of nanoscale MOSFET. The modeling approach is to develop the model for inversion charge sheet after combining both QME and strain effect for biaxial strained silicon NMOSFET .The result shows a significant decrease in the inversion charge sheet of increasing the germanium mole fraction (%x in silicon germanium heterostrusture virtual substrate. The presented result has been good agreement with published data. The result shows that QME is minimized by using strain technique in biaxial strained silicon NMOSFET. Presented result is valid for large range of doping concentration as well as mole fraction.

Garima Joshi

2013-01-01

302

Development and evolution of biaxial texture of rolled nickel tapes by ion beam bombardment for high Tc coated conductors  

International Nuclear Information System (INIS)

High quality YBa2Cu3O7-x films on metallic substrates with high critical current densities well over 106 A/cm2 can be prepared by the rolling assisted biaxially textured substrates (RABiTS) method. Nickel or its alloys have been used as biaxially textured substrates formed through a specific rolling and high temperature annealing procedures. In this paper, we report a newly developed process for developing biaxial texture in rolled Ni tape by argon ion beam bombardment. It is named the ion-beam structure modification (ISM) process. In the ISM processed Ni foils, X-ray diffraction ? scans showed the full width-half maximum (FWHM) value of the (2 0 0) peak was 5.7 deg. . And the electron back scattering diffraction (EBSP) analysis based on scanning electron microscopy showed good {1 0 0} cubic orientation and the mean grain size was determined as about 25 ?m. The texture evolution of rolled Ni foils during ISM process is reported also. For ISM process, local temperature elevation and distribution arises from the ion bombardment, coupled with anisotropic incident ion penetration and propagation as a result of channeling effects in the metal lattice, are expected to play the major roles in the development of grain reorientation in the Ni foil. Due to the simplicity and efficiency of the ISM process, the technique shows a great promise for application in the industrial scale production of long-lengths of supescale production of long-lengths of superconductor tapes

303

Development and evolution of biaxial texture of rolled nickel tapes by ion beam bombardment for high Tc coated conductors  

Science.gov (United States)

High quality YBa 2Cu 3O 7 - x films on metallic substrates with high critical current densities well over 10 6 A/cm 2 can be prepared by the rolling assisted biaxially textured substrates (RABiTS) method. Nickel or its alloys have been used as biaxially textured substrates formed through a specific rolling and high temperature annealing procedures. In this paper, we report a newly developed process for developing biaxial texture in rolled Ni tape by argon ion beam bombardment. It is named the ion-beam structure modification (ISM) process. In the ISM processed Ni foils, X-ray diffraction ? scans showed the full width-half maximum (FWHM) value of the (2 0 0) peak was 5.7°. And the electron back scattering diffraction (EBSP) analysis based on scanning electron microscopy showed good {1 0 0} cubic orientation and the mean grain size was determined as about 25 ?m. The texture evolution of rolled Ni foils during ISM process is reported also. For ISM process, local temperature elevation and distribution arises from the ion bombardment, coupled with anisotropic incident ion penetration and propagation as a result of channeling effects in the metal lattice, are expected to play the major roles in the development of grain reorientation in the Ni foil. Due to the simplicity and efficiency of the ISM process, the technique shows a great promise for application in the industrial scale production of long-lengths of superconductor tapes.

Wang, S. S.; Wu, K.; Shi, K.; Liu, Q.; Han, Z.

2004-08-01

304

Reduction of initial stress stiffening by topology optimization  

DEFF Research Database (Denmark)

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

Philippine, M. A.; Sigmund, Ole

2012-01-01

305

Estimation of step-by-step induced stress in a sequential process integration of nano-scale SOS MOSFETs with high-k gate dielectrics  

Science.gov (United States)

The current work proposes a novel technique to incorporate process-induced uni-axial stress for significant mobility boosting in high-performance metal-oxide-semiconductor field-effect-transistors. It has been shown that two existing standard techniques, namely, silicon-on-sapphire and high-k gate dielectrics can be combined to develop such technology. Sapphire has very high elastic constant and thermal expansion coefficient, thereby capable of inducing a significant amount of stress which is observed to be biaxial in nature. However, with the incorporation of different materials during process integration, such biaxial stress is gradually changed to uni-axial nature. The high-k gate dielectric plays the key role in converting the biaxial stress to uni-axial. Several high-k gate dielectrics have been studied and titanium oxide (TiO2) is observed to maximize the induced stress and also effective to convert it to uni-axial. A final average longitudinal channel stress of 0.73 GPa has been obtained.

Chatterjee, Sulagna; Nag Chowdhury, Basudev; Das, Anindita; Chattopadhyay, Sanatan

2013-12-01

306

Amphoteric refraction at the isotropic anisotropic biaxial media interface: an alternative treatment  

Science.gov (United States)

Amphoteric refraction of light (refraction that can be positive or negative depending on the angle of incidence) at the interface between isotropic and anisotropic biaxial media is analysed by means of an alternative method previously developed by the authors. Unlike left-handed materials (LHMs), negative (or abnormal) refraction involving anisotropic media is only due to the intrinsic properties of the media and is only exhibited by non-collinear rays (rays that do not follow an isotropic behaviour). Moreover, the axes of wavevector ellipsoids must be rotated with respect to the normal to the incidence plane. In this paper, only planes of incidence lying normal to a principal axis of the dielectric tensor \\tilde {\\varepsilon } are considered, and consequently comparison between traditional and alternative methods is possible because both geometrical constructions are plane. First, a very simple procedure that allows us to find the direction of wavevector k from the knowledge of non-collinear (n.c.) ray direction is outlined together with the solution of the dual problem: to find the n.c. ray direction from the k one. Then, the abnormal refraction phenomenon is studied and the equivalence between traditional and alternative methods is clearly stated. Finally, two graphical constructions to find the critical angle of incidence and the maximum angle of negative refraction are also proposed.

Bellver-Cebreros, Consuelo; Rodriguez-Danta, Marcelo

2006-12-01

307

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

308

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

International Nuclear Information System (INIS)

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

309

Biaxially textured Mo films with diverse morphologies by substrate-flipping rotation  

International Nuclear Information System (INIS)

A class of nanostructured Mo thin films was grown by DC magnetron sputtering using a robust substrate rotation mode called 'flipping rotation'. 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 perpendicular to the rotational axis, and the incident flux angle changes continuously. Mo nanostructured films, grown under different rotation speeds with three orders of magnitude spread (ranging from 0.008 to 24 rotation min?1), different flipping directions (clockwise and counter-clockwise), and different ending deposition angles, were characterized using scanning electron microscopy (SEM) and reflection high energy electron diffraction (RHEED) surface-pole-figure techniques. Despite their very different morphologies, such as 'C'-shaped, 'S'-shaped, and vertically aligned nanorods, the same (110)[1 1-bar 0] biaxial texture with an average out-of-plane dispersion of ? 15° was observed. In contrast, we showed that only a fiber-textured Mo film was obtained by using the conventional rotation mode where the oblique incident flux angle was fixed with the substrate rotating around the surface normal.

310

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

Science.gov (United States)

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

Johnson, P. B.; Drake, K. R.; Eames, I.; Wojcik, A.

2014-12-01

311

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.)

312

The Design of Cruciform Test Specimens for Planar Biaxial Testing of Fabrics for Inflatable Aerodynamic Decelerators  

Science.gov (United States)

A preliminary analytical study was conducted to investigate the effects of cruciform test specimen geometries on strain distribution uniformity in the central gage section under biaxial loads. Three distinct specimen geometries were considered while varying the applied displacements in the two orthogonal directions. Two sets of woven fabric material properties found in literature were used to quantify the influence of specimen geometries on the resulting strain distributions. The uniformity of the strain distribution is quantified by taking the ratio between the two orthogonal strain components and characterizing its gradient across the central area of the gage section. The analysis results show that increasing the specimen s length relative to its width promotes a more uniform strain distribution in the central section of the cruciform test specimen under equibiaxial enforced tensile displacements. However, for the two sets of material properties used in this study, this trend did not necessary hold, when the enforced tensile displacements in the two orthogonal directions were not equal. Therefore, based on the current study, a tail length that is 1.5 times that of the tail width is recommended to be the baseline/initial specimen design.

Corbin, Cole K.

2012-01-01

313

Caracterización mecánica de aleaciones Ti-Nb mediante ensayos de flexión biaxial  

Directory of Open Access Journals (Sweden)

Full Text Available Nowadays titanium and titanium alloys are increasingly being used in the industry. Particularly ?-Ti alloys that stand out for having great strength properties and low elastic modulus compared to Ti c.p. or Ti-6Al-4V. Among Ti alloys, Ti-Nb alloys with high contents of alloying elements are widely used. In this work Ti-Nb alloys have been obtained using conventional powdermetallurgy. It has been studied the evolution of properties of these alloys as a function of the percentage of niobium. It can be noted the ball on three balls test used in order to characterize the samples.

En la actualidad, cada vez, son más importantes en la industria las aleaciones de titanio. En especial las aleaciones tipo-?, que destacan por tener buenas propiedades resistentes y bajos módulos elásticos, en comparación con el Ti c.p. o el Ti-6Al-4V. Dentro de estas aleaciones cabe destacar las Ti-Nb con altos contenidos en elementos aleantes. En este trabajo se han obtenido, mediante pulvimetalurgia convencional, una serie de aleaciones Ti-Nb, en el rango del 20-40 % de niobio. Se ha obtenido la evolución de las propiedades de dichas aleaciones en función del porcentaje de niobio, mediante la utilización del ensayo de flexión biaxial con tres apoyos (three ball test.

Amigó, V.

2010-12-01

314

Effects of temperature and blank holding force on biaxial forming behavior of aluminum sheet alloys  

Science.gov (United States)

Biaxial forming behavior is investigated for three aluminum sheet alloys (Al 5182 containing 1% Mn (5182+Mn), Al 5754, and 6111-T4) using a heated die and punch in the warm forming temperature range of 200-350 °C. It is found that, while all three alloys exhibit significant improvement in their formability compared with that at room temperature, the non-heat-treatable alloys 5182 + Mn and 5754 give higher part depths than that of heat-treatable 6111-T4. The formability generally increases with decreasing BHP (BHP), but increasing the forming temperature and/or BHP minimizes the wrinkling tendency and improves the forming performance. The stretchability of the sheet alloys increase with increasing temperature and increasing BHP. For the alloys and forming conditions involved in the current study, the formability, measured in terms of part depth, comes mainly from the drawing of metal into the die cavity, although stretching effects do influence the overall forming behavior. The optimum formability is achieved by setting the die temperature 50 °C higher than the punch temperature to enhance the drawing component. Setting the die temperature higher than the punch temperature also improves the strain distribution in a part in such a manner that postpones necking and fracture by altering the location of greatest thinning.

Li, Daoming; Ghosh, Amit K.

2004-06-01

315

Effect of geometrical defects in forming sheet steel by biaxial stretching  

Science.gov (United States)

In-plane, equibiaxial punch stretching tests have been performed to examine the influence of defects on the formability of two grades of ferritic, high-strength, low-alloy steel. The defects are long nar-row grooves installed by local electrolytic dissolution normal to the rolling direction. The results are examined in the context of the Marciniak-Kuczynski (MK) imperfection analysis, and the homo-geneity index, f. The variation of the measured forming limit strain with relative groove depth, ex-pressed by the index f, is compared with calculations employing Hill’s nonquadratic yield function. For the deeply grooved samples, which experience localization and fracture within the groove, the measured dependence corresponds with the one calculated for an exponent M = 1.9. For the most shallow grooves, localization and fracture proceed outside the groove, along the rolling direction, and the forming limit strains are identical to the values ?* = 0.38 and ?* = 0.040, for the un-grooved samples of the two steels. These forming limits correspond to control by inhomogeneities of f ? 0.990 and f ? 0.992, respectively. For the range of defect sizes studied, the severity of de-fects decreases for shorter lengths and narrower widths. It is estimated that, by increasing the homo-geneity index to f = 0.999, an improvement in biaxial forming limit strain to approximately ?* = 0.59 could be obtained.

McCarron, T. J.; Kain, K. E.; Hahn, G. T.; Flanagan, W. F.

1988-08-01

316

Proposed rules for determining allowable compressive stresses for cylinders, cones, spheres, and formed heads  

Energy Technology Data Exchange (ETDEWEB)

The purpose of this report is to propose alternative rules to those given in UG-23(b), UG-28, UG-29, UG-33 and Appendix 1--8 of ASME (1992a) for determining allowable compressive stresses for unstiffened and ring stiffened circular cylinders and cones and unstiffened spherical, ellipsoidal and torispherical heads. The allowable stress equations are based upon theoretical buckling equations which have been reduced by knockdown factors and by plasticity reduction factors which were determined from tests on fabricated shells. This report expands the coverage of load conditions and shell geometries and includes equations for combinations of loads which are not given in ASME (1992a). The proposed rules also apply to shells with higher D/t ratios. Allowable compressive stress equations are presented for cylinders and cones subjected to uniform axial compression, to bending moment applied over the entire cross-section, to external pressure, to loads which produce in-plane shear stresses and to combinations of these loads. Allowable compressive stress equations are presented for formed heads which are subjected to loads which produce unequal biaxial stresses as well as equal biaxial stresses. More accurate equations are given for determining the size of stiffening rings.

Miller, C.D.; Mokhtarian, K.

1995-11-01

317

Stress and stress reduction.  

Science.gov (United States)

Chronic stress contributes to preterm birth (PTB), through direct physiological mechanisms or behavioral pathways. This review identified interventions to prevent PTB through decreased maternal stress. Studies were grouped according to intervention: group prenatal care (11 studies), care coordination (8 studies), health insurance expansion (4 studies), expanded prenatal education/support in the clinic (8 studies), home visitation (9 studies), telephone contact (2 studies), or stress-reduction strategies (5 studies). Group prenatal care had the most evidence for PTB prevention. Comparative studies of PTB prevention through different models of prenatal care and maternal support, education, empowerment, stress-reduction, and coping strategies are needed. PMID:24979355

Straub, Heather; Qadir, Sameen; Miller, Greg; Borders, Ann

2014-09-01

318

Manage Stress  

Science.gov (United States)

... Conditions and Diseases > Heart Health > Manage Stress Manage Stress The Basics Take Action! Ver en español Content ... on: November 25, 2014 The Basics Not all stress is bad. Stress can help protect you in ...

319

Frictional properties of megathrust fault gouges at low sliding velocities: new data on effects of normal stress and temperature  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Friction data used in modelling studies of subduction zone seismogenesis are often poorly representative of in situ conditions. We investigated the influence of in situ effective stresses and temperatures on the frictional properties of (simulated) fault gouges, prepared either from Nankai ODP material or illite shale, at sliding velocities approaching those relevant for earthquake nucleation and SSEs. Biaxial (double direct shear) experiments were performed at room temperature, n...

Hartog, S. A. M. Den; Peach, C. J.; Winter, D. A. M.; Spiers, C. J.; Shimamoto, T.

2011-01-01

320

Glass-reinforced hydroxyapatite composites: secondary phase proportions and densification effects on biaxial bending strength.  

Science.gov (United States)

CaO-P(2)O(5) glasses with additions of MgO and CaF(2) were used as a sintering aid of hydroxyapatite, and glass-reinforced hydroxyapatite composites obtained. Glasses promoted significant changes in the microstructure of the composites, namely with the formation of tricalcium phosphate secondary phases, beta and alpha-TCP. Quantitative phase analysis was performed by the Rietveld method using General Structure Analysis Software. Grain size measurements were carried out on SEM photomicrographs, using a planimetric procedure according to ASTM E 112-88. Flexural bending strength was determined from concentric ring-on-ring testing. Flexural bending strength (FBS) of glass-reinforced hydroxyapatite composites was found to be about twice or three times higher than that of unreinforced hydroxyapatite and tended to depend more on porosity and beta and alpha-TCP secondary phases, rather than on grain size. Traces of alpha-tricalcium phosphate significantly enhanced the strength of the composites. Using the rule of mixtures to estimate the zero porosity bending strength, the Duckworth-Knudsen model applied to the composites gave a porosity correction factor, b, with a value of 4.02. Weibull statistics were also used to analyze biaxial strength data and the level of reinforcement obtained by comparing failure probability for the composites and for the unreinforced hydroxyapatite. Lower activation energies for grain growth were observed for the composites compared to unreinforced hydroxyapatite, which should be attributed to the presence of a liquid glassy phase that promotes atomic diffusion during the sintering process. PMID:10490690

Lopes, M A; Monteiro, F J; Santos, J D

1999-01-01

 
 
 
 
321

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°.

322

Paramagnetic point defects at interfacial layers in biaxial tensile strained (100)Si/SiO2  

Science.gov (United States)

A comparative electron spin resonance study is reported on (100)Si/SiO2 entities, grown by thermal oxidation of biaxial tensile strained (100)Si (sSi) layers, epitaxially grown on a strain relaxed Si0.8Ge0.2 buffer layer, and standard (100)Si. In the as-oxidized state a significant decrease (˜50%) of inherently incorporated interface defects, Pb0 and Pb1, is observed, i.e., the sSi/SiO2 interface is found to be inherently significantly improved in terms of electrically detrimental interface traps (Pb0). After vacuum-ultraviolet irradiation two more SiO2-associated defects appear, namely E?' (generic entity O3?Si.) and EX. Interestingly, a decrease (˜50%) of E?' defect density is observed compared to standard Si/SiO2. This reduction in inherent electrically active interface (Pb0) and near-interface (E?') traps would establish sSi/SiO2 as a superior device structure for all electrical properties where (near)-interfacial traps play a detrimental role. For one, the reduction of detrimental (near)-interface defects may be an additional reason for the commonly reported mobility enhancement in sSi/SiO2 based metal-oxide-semiconductor structures over standard Si/SiO2 ones, and at the same time account for the reported reduction of 1/f noise in the former structures. The data also confirm the generally accepted notion that Pb-type defects are mismatch induced defects.

Somers, P.; Stesmans, A.; Afanas'ev, V. V.; Claeys, C.; Simoen, E.

2008-02-01

323

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

Science.gov (United States)

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

Chamis, C. C.

1976-01-01

324

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

Science.gov (United States)

Biological tissues are subjected to complex loading states in vivo and in order to define constitutive equations that effectively simulate their mechanical behaviour under these loads, it is necessary to obtain data on the tissue's response to multiaxial loading. Single axis and shear testing of biological tissues is often carried out, but biaxial testing is less common. We sought to design and commission a biaxial compression testing device, capable of obtaining repeatable data for biological samples. The apparatus comprised a sealed stainless steel pressure vessel specifically designed such that a state of hydrostatic compression could be created on the test specimen while simultaneously unloading the sample along one axis with an equilibrating tensile pressure. Thus a state of equibiaxial compression was created perpendicular to the long axis of a rectangular sample. For the purpose of calibration and commissioning of the vessel, rectangular samples of closed cell ethylene vinyl acetate (EVA) foam were tested. Each sample was subjected to repeated loading, and nine separate biaxial experiments were carried out to a maximum pressure of 204 kPa (30 psi), with a relaxation time of two hours between them. Calibration testing demonstrated the force applied to the samples had a maximum error of 0.026 N (0.423% of maximum applied force). Under repeated loading, the foam sample demonstrated lower stiffness during the first load cycle. Following this cycle, an increased stiffness, repeatable response was observed with successive loading. While the experimental protocol was developed for EVA foam, preliminary results on this material suggest that this device may be capable of providing test data for biological tissue samples. The load response of the foam was characteristic of closed cell foams, with consolidation during the early loading cycles, then a repeatable load-displacement response upon repeated loading. The repeatability of the test results demonstrated the ability of the test device to provide reproducible test data and the low experimental error in the force demonstrated the reliability of the test data. PMID:19627835

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

2009-07-01

325

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

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

326

Effect of light sources and curing mode techniques on sorption, solubility and biaxial flexural strength of a composite resin  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Adequate polymerization plays an important role on the longevity of the composite resin restorations. OBJECTIVES: The aim of this study was to evaluate the effect of light-curing units, curing mode techniques and storage media on sorption, solubility and biaxial flexural strength (BFS) of a composite resin. MATERIAL AND METHODS: Two hundred and forty specimens were made of one composite resin (Esthet-X) in a stainless steel mold (2 mm x 8 mm Ø), and divided into 24 groups (n=10) established ...

Andreia Assis Carvalho; Francine do Couto Lima Moreira; Rodrigo Borges Fonseca; Carlos José Soares; Eduardo Batista Franco; João Batista de Souza; Lawrence Gonzaga Lopes

2012-01-01

327

Biaxial Flexural Strength of High-Viscosity Glass-Ionomer Cements Heat-Cured with an LED Lamp during Setting  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Adding heat to glass ionomers during setting might improve mechanical properties. The aim was to compare the biaxial flexural strength (BFS) between and within four glass ionomers, by time of exposure to a high-intensity LED light-curing unit. Materials and methods. Samples of Fuji 9 Gold Label, Ketac Molar Easymix, ChemFil Rock, and the EQUIA system were divided into three treatment groups (n = 30): without heating (Group 1), heated with LED lamp of 1400?mW/cm2 for 30?s while setting (Gr...

Frencken, Jo E.; Laura Brain Lascano; Ignacio Mazzola; Ricardo Juan Cabral; Molina, Gustavo Fabi Amp Xe N.

2013-01-01

328

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 lin...

Christov, Ivan C.; Lueptow, Richard M.; Ottino, Julio M.; Sturman, Rob

2014-01-01

329

Optical characterization of wide-gap biaxial CaGa2S4 by spectroscopic ellipsometry and polarized transmission intensities  

International Nuclear Information System (INIS)

Full text : Differently prepared natural 100-oriented cleavage planes of the orthorhombic wide-gap single crystalline CaGa2S4 were examined in two symmetric positions at room temperature over the photon energies 0.8-6.5 eV by spectroscopic ellipsometry. Complimentary polarized transmission intensity technique was applied. The data obtained by both techniques were further treated within standard biaxial approach and the major refraction indices were restored for the practically important range below energy gap. The structure and polarization peculiarities of the obtained pseudodielectric function were related with apparently four critical points of interband electronic transitions in different configurations respectively

330

About the effect of biaxial anisotropy of ferrite-garnet films with magnetization in a film plane direction on the shape of pulsed remagnetization curves  

International Nuclear Information System (INIS)

The curves of pulsed magnetization reversal in iron garnet films with easy-plane anisotropy are studied. Magnetization reversal is initiated by a pulsed magnetic field aligned with the axis of biaxial anisotropy lying in the plane of the film. The curves exhibit kinks at fields close to the effective field of biaxial anisotropy. Magnetization reversal mechanisms in fields above and below the inflection point are discussed. The results of the study obtained for the films of the compositions (LuBi)3(FeGa)5O12 and (YLuBi)3(FeGa)5O12 are provided

331

Managing Stress  

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Full Text Available ... type of situation is called “bad stress” or “chronic stress.” Risks of Stress Never-ending stress can lead to a variety of diseases. It can lead to high blood pressure, which can cause heart problems including heart attacks. Stress can also lead to ...

332

Development of a hysteresis model for R/C columns subjected to bi-axial lateral loading  

International Nuclear Information System (INIS)

Recent investigations on dynamic response of reinforced concrete (R/C) structures have confirmed that the R/C structural members undergo much more inelastic deformation in each of the two mutually perpendicular directions under bi-directional seismic loading, than that observed only under unidirectional ground motion. To predict the seismic response of R/C structure with fair accuracy demands, a faithful model that can incorporate the effect of biaxial bending interaction in column. This model should not have high computational demand but should adequately reflect the stiffness degrading and strength deterioration characteristics of R/C structural members. Present study is an effort to develop such a bi-directional hysteresis model accounting the effect of interaction between lateral loadings in two orthogonal directions. The development of the present model is based on the yield surface approach and it can incorporate both strength and stiffness degradation characteristics, which is unavoidable in R/C structures during cyclic loading. The performance of the proposed model/ is demonstrated through the prediction of available experimental results of a reinforced concrete column, subjected to biaxial loading. (author)

333

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

334

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

International Nuclear Information System (INIS)

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

335

Nucleation and growth of stress relief patterns in sputtered molybdenum films  

International Nuclear Information System (INIS)

Stress relief patterns in sputtered molybdenum films were studied by Nomarski differential interference contrast microscope. As a result of the very large biaxial compressive stress in the film plane, ranging from E/16 to E/130 (where E is Young's modulus), the films were partially buckled and detached from the substrate, exhibiting one of two modes of stress relief pattern, wrinkled spots or wavy ridges. The former mode is a nucleation pattern and the latter a growth pattern. The transition between the two can be interpreted in terms of the stress intensity factor KI at the head of the gap formed due to stress between the film and the substrate. KI can be regarded as measure of the bond strength between the film and the substrate. (author)

336

Computed electronic and optical properties of SnO2 under compressive stress  

Science.gov (United States)

We consider the effects of three different types of applied compressive stress on the structural, electronic and optical properties of rutile SnO2. We use standard density functional theory (DFT) to determine the structural parameters. The effective masses and the electronic band gap, as well as their stress derivatives, are computed within both DFT and many-body perturbation theory (MBPT). The stress derivatives for the SnO2 direct band gap are determined to be 62, 38 and 25 meV/GPa within MBPT for applied hydrostatic, biaxial and uniaxial stress, respectively. Compared to DFT, this is a clear improvement with respect to available experimental data. We also estimate the exciton binding energies and their stress coefficients and compute the absorption spectrum by solving the Bethe-Salpeter equation.

Miglio, A.; Saniz, R.; Waroquiers, D.; Stankovski, M.; Giantomassi, M.; Hautier, G.; Rignanese, G.-M.; Gonze, X.

2014-12-01

337

Managing Stress  

Medline Plus

Full Text Available ... knotted” stomach. This type of situation is called “bad stress” or “chronic stress.” Risks of Stress Never- ... day for at least 30 minutes. Eat and sleep well. A good night’s sleep and nutritious meals ...

338

Managing Stress  

Medline Plus

Full Text Available ... alcohol. Stimulants like these may seem like they reduce stress but the feeling of relief will only ... of people feel overly stressed. Uncertainty of the future can cause stress. Not knowing what is going ...

339

Stress Testing  

Science.gov (United States)

... from the NHLBI on Twitter. What Is Stress Testing? Stress testing provides information about how your heart works during ... is working hard and beating fast. During stress testing, you exercise (walk or run on a treadmill ...

340

Managing Stress  

Medline Plus

Full Text Available ... what causes stress in order to try to control it. Situations that cause stress may not be ... stressors. Many stressful situations can be under your control. You can avoid them completely. For instance, if ...

 
 
 
 
341

Managing Stress  

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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. March of Dimes HR Em 6:19 Choosing ...

342

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. ...

343

Cold Stress  

Science.gov (United States)

... Workplace Safety & Health Topics NIOSH Share Compartir COLD STRESS On this Page Overview Types of Cold Stress ... access to important safety information. Types of Cold Stress Hypothermia | Cold Water Immersion | Frostbite | Trench Foot | Chilblains ...

344

Managing Stress  

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Full Text Available ... stress they may experience: • Headaches. • Tense muscles. • Shaky hands. • Fatigue. • Insomnia. • Heartburn. Stressed people may also feel: • ... Stress can cause muscle knots in the back, hands, and different muscle groups. A massage therapist can ...

345

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

346

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

347

Life Stress  

Science.gov (United States)

... Assessments, and Videos Post-Traumatic Stress Physical Injury Anxiety Health & Wellness Military Sexual Trauma Tobacco Community About Depression Life Stress Alcohol & Drugs Families with Kids Resillience ...

348

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

349

NULIFE - Project CABINET. RPV Assessment under Consideration of Constraint and Warm Pre-Stress Effects  

International Nuclear Information System (INIS)

At the moment, nuclear power plant regulators do not predominantly consider constraint and biaxial effects in their concepts for failure assessment of nuclear components. The warm pre-stressing (WPS) effect is only partly considered in some assessment procedures and codes. There is also a lack of a harmonized treatment of these effects in the safety assessment of European plants. This paper introduces the project CABINET (Constraint and Biaxial Loading Effects and their Interactions Considering Thermal Transients) which is a collaborative project under the EU's Network of Excellence NULIFE. The overall objective of CABINET is to investigate and understand constraint, biaxial loading and WPS effects in terms of a clearly defined application window, especially in the light of long term operation. The focus lies on already available experimental data and methodologies. The intention is to provide recommendations for a harmonized application of those effects in European nuclear safety assessment. The possibility to include different level of analysis depending on input data and acceptance of National Regulatory Body is also being evaluated. Although the CABINET project is not completed yet, it has been found that it is possible to rationalize the different existing codes. (author)

350

Effect of biaxial strain and composition on vacancy mediated diffusion in random binary alloys A first principles study of the SiGe system  

CERN Document Server

We present the results of a systematic study using the density functional theory (within the local density approximation) of the effects of biaxial strain and composition on the self-diffusion of Si and Ge in SiGe alloys diffusing by a vacancy mechanism. The biaxial strain dependence of the vacancy formation energy was reconfirmed with previous calculations. The effect of biaxial strain on the interaction potential energy between a substitutional Ge atom and a vacancy was calculated. These calculations were used to estimate the change in the activation energy (due to biaxial strain) for the self-diffusion of Si and Ge in Si by a vacancy mechanism. The composition dependence of the vacancy formation energy was calculated. A database of ab initio migration energy barriers for vacancy migration in different local environments was systematically developed by considering the effect of the first nearest neighbor sites explicitly and the effect of the other sites by a mean field approximation. A kinetic Monte Carlo ...

Ramanarayanan, P; Clemens, B M; Ramanarayanan, Panchapakesan; Cho, Kyeongjae; Clemens, Bruce M.

2002-01-01

351

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)

352

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.

1996-01-01

353

Job Stress  

Science.gov (United States)

Mind/body health: Job stress Jobs and careers are an important part of our lives. Along with providing a source of income, they help us fulfill our ... of emotional stress. Stress at work Even "dream jobs" have stressful deadlines, performance expectations and other responsibilities. ...

354

Managing Stress  

Medline Plus

Full Text Available ... positive and negative stress and presents tips for managing and preventing stress. What Is Stress? Many scientists see stress as a reaction of our body to sudden changes in the environment. Just like animals, people need extra energy to stay and fight or run ...

355

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)

356

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

357

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

358

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

International Nuclear Information System (INIS)

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

359

Above-bandgap optical properties of biaxially strained GeSn alloys grown by molecular beam epitaxy  

International Nuclear Information System (INIS)

The complex dielectric function of biaxially strained Ge1?xSnx (0???x???0.17) alloys grown on Ge (100) has been determined by spectroscopic ellipsometry from 1.2 to 4.7?eV. The effect of substitutional Sn incorporation and the epitaxial strain on the energy transitions E1, E1?+??1, E0?, and E2 of GeSn alloys is investigated. Our results indicate that the strained GeSn alloys show Ge-like electronic bandstructure with all the transitions shifted downward due to the alloying of Sn. The strain dependence of E1 and E1?+??1 transitions is explained using the deformation potential theory, and values of ?5.4?±?0.4?eV and 3.8?±?0.5?eV are obtained for the hydrostatic and shear deformation potentials, respectively

360

Stress-strain relationship and XRD line broadening in [0001] textured hexagonal polycrystalline materials  

International Nuclear Information System (INIS)

Stress analysis with X-ray diffraction (XRD) for hexagonal polycrystalline materials in the Laue classes 6/mmm and 6/m has been studied on the basis of the crystal symmetry of the constituent crystallites which was proposed by R. Yokoyama and J. Harada ['Re-evaluation of formulae for X-ray stress analysis in polycrystalline specimens with fibre texture', Journal of Applied Crystallography, Vol.42, pp.185-191 (2009)]. The relationship between the stress and strain observable by XRD in a hexagonal polycrystalline material with [0001] fibre texture was formulated in terms of the elastic compliance defined for its single crystal. As a result, it was shown that the average strains obtained in the crystallites for both symmetries of 6/mmm and 6/m are different from each other under the triaxial or biaxial stress field. Then, it turned out that the line width of XRD changes depending on the measurement direction. (author)

 
 
 
 
361

The effect of stress on the dielectric and tunable properties of barium stannate titanate thin films  

Science.gov (United States)

Ba(Sn0.15Ti0.85)O3 thin films were grown on the LaNiO3 buffered LaAlO3, SrTiO3, MgO, and Al2O3 single crystal substrates, respectively. These substrates provide a systematic change in the stress while maintaining the same film microstructure. The stress in the thin film induces an obvious change in the dielectric behavior. The reduction in the ferroelectric transition temperature with increasing biaxial tensile stress is attributed to the suppression of in-plane polarization due to the small lateral grain size in the films. The in-plane tensile stress in this study reduces the unit cell along electric field in the parallel plate capacitor structure and decreases the tunability.

Song, Sannian; Zhai, Jiwei; Gao, Lina; Yao, Xi

2009-02-01

362

Stresses in the Vanuatu subducting slab: A test of two hypotheses  

Science.gov (United States)

Stress inversions of intermediate-depth focal mechanisms in Vanuatu were used to test two hypotheses: that the slab acts as a stress guide and whether intermediate-focus earthquakes occur on preexisting faults. Although the strike of the Vanuatu slab varies by over 70°, the maximum compression ?1 is everywhere slab normal and the least compression ?3 is everywhere within the plane of the slab. This provides strong confirmation of the stress guide hypothesis. In the depth range 61-120 km, the solution space for ?3 forms a girdle pattern in the plane of the slab, indicating bi-axial tension. This gradually changes to down-dip tension at greater depth. We find that preexisting faults may become reactivated by intermediate depth earthquakes but only when the slab stresses favor it: Otherwise new faults are formed. This contradicts the idea that the mechanism of intermediate focus earthquakes requires serpentinite dehydration on preexisting faults.

Christova, Cenka; Scholz, Christopher H.

2003-08-01

363

Performance characterization of a single bi-axial scanning MEMS mirror-based head-worn display  

Science.gov (United States)

The NomadTM Personal Display System is a head-worn display (HWD) with a see-through, high-resolution, high-luminance display capability. It is based on a single bi-axial scanning MEMS mirror. In the Nomad HWD system, a red laser diode emits a beam of light that is scanned bi-axially by a single MEMS mirror. A diffractive beam diffuser and an ocular expand the beam to form a 12mm exit pupil for comfortable viewing. The Nomad display has an SVGA (800x600) resolution, 60Hz frame rate, 23-degree horizontal field of view (FOV) and 3:4 vertical to horizontal aspect ratio, a luminance of 800~900 foot-Lamberts, see-through capability, 30mm eye-relief distance, and 1-foot to infinity focusing adjustment. We have characterized the performance parameters, such as field of view, distortion, contrast ratio (4x4 black and white checker board), modulation depth, exit pupil size, eye relief distance, maximum luminance, dynamic range ratio (full-on-to-full-off ratio), dimming ratio, and luminance uniformity at image plane. The Class-1 eye-safety requirements per IEC 60825-1 Amendment 2 (CDRH Laser Notice No. 50) are analyzed and verified by experiments. The paper describes all of the testing methods and set-ups as well as the representative test results. The test results demonstrate that the Nomad display is an eye-safe display product with good image quality and good user ergonomics.

Liang, Minhua

2002-06-01

364

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

365

STRESS MANAGEMENT  

Directory of Open Access Journals (Sweden)

Full Text Available Today, people are under stress and they talk about the stress them under. The concept of stress is so firmly entrenched in the communal psyche that few people have paused to analyze it, and most people assume that is simply a fact of modern life, beyond anyone's control. Stress management help us how to manage the stress in your life. Stress management is to identify the sources of stress in your life begins with. This is not easy to find it. Your true sources of stress are not always clear, and it's all very easy on your own stress-including thoughts, feeling and behavior naught. Think about how you cope with the stress of life your coping strategies healthy or unhealthy, helpful or unproductive for? Unfortunately, many ways to resolve the problems compound the stress. No one method works for everyone or every situation. There are several models of stress management, each with distinctive explanations of mechanisms for controlling stress.

Shivani

2014-08-01

366

Managing Stress  

Medline Plus

Full Text Available ... Stimulants like these may seem like they reduce stress but the feeling of relief will only last for a very short period of time. In the end, the stress will only get worse as the person becomes ...

367

Managing Stress  

Medline Plus

Full Text Available ... makes a lot of people feel overly stressed. Uncertainty of the future can cause stress. Not knowing ... child is born are all examples of how uncertainty can affect us. It is helpful to classify ...

368

Managing Stress  

Medline Plus

Full Text Available ... Stress has positive effects when it makes us deal constructively with daily problems and meet the challenges. ... stress. If you plan on graduating, taking a new job, getting married, and having a baby all ...

369

Managing Stress  

Medline Plus

Full Text Available ... compulsively tapping fingers. All stressed people do not share these symptoms and feelings. Situations that are stressful ... compliments, and express your feelings and thoughts assertively. Share your thoughts. Share your thoughts with a spouse, ...

370

Managing Stress  

Medline Plus

Full Text Available ... Several studies have associated stress with a weak immune system. The immune system is responsible for fighting diseases and germs that invade the body. With a weakened immune system, a person with chronic stress could become ill ...

371

Managing Stress  

Medline Plus

Full Text Available ... Stress has positive effects when it makes us deal constructively with daily problems and meet the challenges. ... stress may try to relieve it with illicit drugs, smoking, or alcohol. Stimulants like these may seem ...

372

Managing Stress  

Medline Plus

Full Text Available ... studies have associated stress with a weak immune system. The immune system is responsible for fighting diseases and germs that invade the body. With a weakened immune system, a person with chronic stress could become ill ...

373

Managing Stress  

Medline Plus

Full Text Available ... in control, you are setting yourself up for failure and more stress. Reward yourself. Treat yourself as ... stress can lead to serious diseases such as heart disease and depression. It may also lead to ...

374

Managing Stress  

Medline Plus

Full Text Available ... of people feel overly stressed. Uncertainty of the future can cause stress. Not knowing what is going ... think negative thoughts, but try to have a back-up plan in case things go differently than ...

375

Stress echocardiography  

Digital Repository Infrastructure Vision for European Research (DRIVER)

This thesis presents the initial experience on stress echocardiography done at the Department of Cardiology, University Hospital of Rotterdam. The main purposes of this research were: 1) to assess the safety and feasibility of stress echocardiography; 2) to evaluate the sensitivity and specificity of stress echocardiography for the detection of coronary artery disease; 3) to compare the results of stress echocardiography with those obtained at myocardial perfusion scintig...

Salustri, A.

1993-01-01

376

Scale effects on flexural wave propagation in nanoplate embedded in elastic matrix with initial stress  

Science.gov (United States)

In this paper, the small-scale effects on the flexural wave in the nanoplate are studied. Based on the nonlocal continuum theory, the equation of wave motion is derived and the dispersion relation is presented. Numerical simulations are performed to investigate the influences of the scale coefficient, the surrounding elastic matrix and the initial stress on the wave propagation properties. The results show that the nonlocal model provides an appropriate method to investigate the characteristics of the flexural wave in the nanoplate. Furthermore, the direction and amplitude of the biaxial load, the stiffness of the shearing layer and the Winkler foundation can change the wave properties, significantly.

Wang, Yi-Ze; Li, Feng-Ming; Kishimoto, Kikuo

2010-06-01

377

Experimental evaluation of the pure configurational stress assumption in the flow dynamics of entangled polymer melts  

Digital Repository Infrastructure Vision for European Research (DRIVER)

A filament stretching rheometer was used for measuring the startup of uni-axial elongational flow followed by reversed bi-axial flow, both with a constant elongational strain rate. A narrow molecular mass distribution linear polyisoprene with a molecular weight of 483 kg/mole was subjected to the flow in the non-linear flow regime. This has allowed highly elastic measurements within the limit of pure orientational stress, as the time of the flow was considerably smaller than the Rouse time. A...

Rasmussen, Henrik K.; Bejenariu, Anca Gabriela; Hassager, Ole; Auhl, D.

2010-01-01

378

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.)

379

Multiple cracking in uniaxial and biaxial fatigue of 304L stainless steel  

Digital Repository Infrastructure Vision for European Research (DRIVER)

When a mechanical part is subjected to a repeated mechanical stress, it may be damaged after a number of cycles by several crack initiations and the propagation of a main crack. This is the phenomenon of fatigue damage. The thesis specifically deals with possible damage in some components of nuclear plants due to thermal fatigue. Unlike conventional mechanical fatigue damage where a main crack develops in the part, thermal fatigue damage usually results in the appearance of a network of crack...

Rupil, Je?re?mie

2012-01-01

380

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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...

Gilchrist, Michael; Keenan, Stephen; Curtis, Michael; Cassidy, Mary; Byrne, Greg; Destrade, Michel

2008-01-01

 
 
 
 
381

Biaxial Thermal Creep of V-4Cr-4Ti AT 700C and 800C  

Energy Technology Data Exchange (ETDEWEB)

A study of the thermal creep properties of V-4Cr-4Ti was performed using pressurized tube specimens. Creep tubes nominally 4.57 mm OD by 0.25 mm wall thickness were pressurized with high-purity helium gas to mid-wall effective stresses below the uniaxial yield strength. Specimens were heated to 700 and 800C in an ultra-high vacuum furnace and periodically removed to measure the change in OD with a high-precision laser profilometer. The secondary creep rate was found to be power-law dependent on the applied stress with a stress exponent of 3.7 at 700C and 2.7 at 800C. The average activation energy for creep of V-4Cr-4Ti was 299 kJ/mole, which is quite close to the activation energy for self-diffusion in pure vanadium in this temperature regime. The predominant mechanism of creep deformation for the conditions employed in this study is most likely climb assisted dislocation motion.

Kurtz, Richard J.; Hamilton, Margaret L.

2000-09-01

382

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

383

Near tip stress and strain fields for short elastic cracks  

Science.gov (United States)

Recent experimental fatigue crack growth studies have concluded an apparent anomalous behavior of short cracks. To investigate the reasons for this unexpected behavior, the present paper focuses on identifying the crack length circumstances under which the requirements for a single parameter (K(sub I) or delta K(sub I) if cyclic loading is considered) characterization are violated. Furthermore, an additional quantity, the T stress, as introduced by Rice, and the related biaxiality ratio, B, are calculated for several crack lengths and two configurations, the single-edge-cracked and the centrally-cracked specimen. It is postulated that a two-parameter characterization by K and T (or B) is needed for the adequate description of the stress and strain field around a short crack. To further verify the validity of this postulate, the influence of the third term of the Williams series on the stress, strain and displacement fields around the crack tip and in particular on the B parameter is also examined. It is found that the biaxiality ratio would be more negative if the third term effects are included in both geometries. The study is conducted using the finite element method with linearly elastic material and isoparametric elements and axial (mode I) loading. Moreover, it is clearly shown that it is not proper to postulate the crack size limits for 'short crack' behavior as a normalized ratio with the specimen width, a/w; it should instead be stated as an absolute, or normalized with respect to a small characteristic dimension such as the grain size. Finally, implications regarding the prediction of cyclic (fatigue) growth of short cracks are discussed.

Soediono, A. H.; Kardomateas, G. A.; Carlson, R. L.

1994-01-01

384

Stress, Inc.  

Science.gov (United States)

Students explore the physical and psychological effect of stress and tension on human beings. Concepts of stress and stress management are introduced. Students discover how perception serves to fuel a huge industry dedicated to minimizing risk and relieving stress. Students complete a writing activity focused on developing critical thinking skills. Note: The literacy activities for the Mechanics unit are based on physical themes that have broad application to our experience in the world â concepts of rhythm, balance, spin, gravity, levity, inertia, momentum, friction, stress and tension.

Integrated Teaching And Learning Program

385

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

386

Epitaxial growth of CeO2/yttria-stabilized ZrO2 double layer films on biaxially textured Ni tape via electrostatic spray assisted vapour deposition  

International Nuclear Information System (INIS)

Epitaxial growth of CeO2 and yttria-stabilized ZrO2 (YSZ) double layer films has been successfully carried out on biaxially textured nickel substrates at a temperature between 400 and 600 deg. C using electrostatic spray assisted vapour deposition method. The structure of the double layer was characterized by X-ray diffraction and scanning electron microscopy. The results show that highly oriented CeO2/YSZ double buffer films were formed epitaxially onto biaxially textured Ni substrates. The orientation relationships between YSZ layer and Ni substrate are 001YSZ//001Ni and 110YSZ//100Ni, while the orientation relationships between CeO2 and YSZ are 001CeO2//001YSZ and 100CeO2//100YSZ

387

A New Direct Process to Prepare $YBa_{2}Cu_{3}O_{7-\\gamma}$ films on Biaxially Textured Ag{110}<211>  

CERN Document Server

YBCO films were successfully prepared on biaxially textured Ag{110} substrates by using pulsed laser deposition. X-ray diffraction results showed that the degree of preferential orientation of Ag{110} substrates varied with increasing annealing temperature. With a thin template layer deposited at low temperature, YBCO film with c-axis orientation and in-plane biaxial alignment could be obtained at high deposition temperature. Scanning electron microscopy observation revealed that YBCO grains enlarged but Ag grains on the surface of the YBCO films became smaller with increasing deposition temperature. At optimal deposition conditions, Ag atoms diffuse into the YBCO grain boundaries, and then fill in the weak-link regions in the YBCO film, resulting in the conduction easier. Jc value of 5?105A/cm2 was obtained at 77K and zero magnetic field for the best YBCO film in our work.

Wang, R; Pan, S; He, M; Chen, Z; Yang, G; Wang, Rongping; Zhou, Yueliang; Pan, Shaohua; He, Meng; Chen, Zhenghao; Yang, Guozhen

1999-01-01

388

Effect of an external magnetic field on the nematic-isotropic phase transition in mesogenic systems of uniaxial and biaxial molecules  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Influence of an external magnetic field on the nematic-isotropic ($N-I$) phase transition in a dispersion model of nematic liquid crystals, where the molecules are either perfectly uniaxial or biaxial (board-like), has been studied by Monte Carlo simulation. Using multiple histogram reweighting technique and finite size scaling analysis the order of the phase transition, the transition temperature at the thermodynamic limit and the stability limit of the isotropic phase belo...

Ghoshal, Nababrata; Mukhopadhyay, Kisor; Roy, Soumen Kumar

2012-01-01

389

Effect of uniaxial and biaxial crystal-field potential on magnetic properties of a mixed spin-1/2 and spin-1 Ising model on honeycomb lattice  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Magnetic properties of a mixed spin-1/2 and spin-1 Ising model on honeycomb lattice are exactly investigated within the framework of generalized star-triangle mapping transformation. The particular attention is focused on the effect of uniaxial and biaxial crystal-field anisotropies that basically influence the magnetic behaviour of the spin-1 atoms. Our results for the basic thermodynamic quantities, as well as the dynamical time-dependent autocorrelation function indicate ...

Strecka, Jozef; Jascur, Michal

2004-01-01

390

Magnetic properties of a mixed spin-1/2 and spin-3/2 Ising model with an uniaxial and biaxial crystal-field potential  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Magnetic properties of a mixed spin-1/2 and spin-3/2 Ising model on honeycomb lattice are investigated within the framework of an exact star-triangle mapping transformation. The particular attention is focused on the effect of uniaxial and biaxial crystal-field potentials that basically influence the magnetic behaviour of the spin-3/2 atoms. Our results for the basic thermodynamic quantities, as well as the dynamical time-dependent autocorrelation function indicate the spin ...

Jascur, Michal; Strecka, Jozef

2004-01-01

391

Investigations of ultra shallow junction ion implanted biaxial tensile strained silicon by means of X-Ray, Raman and photoacoustic techniques  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The application of strain to the active channel region of the metal-oxide-semiconductor-?eld-e?ect-transistor (MOSFET) has become a necessary practice in integrated circuit (IC) fabrication. The introduction of strain allows increased carrier mobilities, and concomitant device performance enhancements, which are independent of MOSFET scaling. Biaxial tensile strained silicon ("-Si), resulting from epitaxial growth of silicon on a Si1!xGex virtual substrate gives rise to enhanced electron ...

Horan, Ken

2012-01-01

392

Residual stresses  

International Nuclear Information System (INIS)

The principal effect of unloading a material strained into the plastic range is to create a permanent set (plastic deformation), which if restricted somehow, gives rise to a system of self-balancing within the same member or reaction balanced by other members of the structure., known as residual stresses. These stresses stay there as locked-in stresses, in the body or a part of it in the absence of any external loading. Residual stresses are induced during hot-rolling and welding differential cooling, cold-forming and extruding: cold straightening and spot heating, fabrication and forced fitting of components constraining the structure to a particular geometry. The areas which cool more quickly develop residual compressive stresses, while the slower cooling areas develop residual tensile stresses, and a self-balancing or reaction balanced system of residual stresses is formed. The phenomenon of residual stresses is the most challenging in its application in surface modification techniques determining endurance mechanism against fracture and fatigue failures. This paper discusses the mechanism of residual stresses, that how the residual stresses are fanned and what their behavior is under the action of external forces. Such as in the case of a circular bar under limit torque, rectangular beam under limt moment, reclaiming of shafts welds and peening etc. (author)

393

The Effects of Stress State and Cavitation on Deformation Stability During Superplastic Forming  

Science.gov (United States)

The current available models describing superplastic deformation do not account for a number of important characteristics, leading to the current limited predictive capabilities of deformation and failure. In this work, the effects of cavitation and stress state on deformation stability during superplastic forming are investigated using Finite Element simulations. The simulations are performed using constant strain rate forming and using a proposed optimization approach based on a multiscale failure criterion that accounts for stress state, geometrical necking, and microstructural evolution including grain growth and cavitation. The simulations are conducted for the superplastic copper-based alloy Coronze-638 and the superplastic aluminum alloy Al-5083 which are known to develop significant cavitation during deformation. The results clearly show the importance of accounting for microstructural evolution during superplastic forming, especially when the state of stress is biaxial. Furthermore, the results highlight the effectiveness of the proposed optimization technique in reducing the forming time and maintaining the integrity of the formed parts.

Nazzal, Mohammad A.; Khraisheh, Marwan K.

2007-04-01

394

Effect of state of stress on the cavitation behavior of Al 5083 superplastic material  

Energy Technology Data Exchange (ETDEWEB)

In this paper we address the controversial issue of nucleation of cavities in Al 5083 alloys and their subsequent growth to coalescence and failure. We focus on the origin and growth of cavities not only during the primary processing of Al 5083 in sheet forms, but also during the manufacture of these sheets into SPF (superplastic forming) components. Experimental observations of pre-existing cavities in this alloy are made using optical and electron microscopy. The role of sheet rolling direction, and the state of stress during superplastic deformation on the cavity formation and coalescence are also discussed. The effect of the state of stress (uniaxial, plane strain, balanced biaxial, and tri-axial) on the growth characteristics of cavitation is also examined. It is found that the uniaxial model based cavitation cannot directly be extended to predict the behavior of more complex stress states, unless great care is taken to identify the right strain measure for the mapping process. (orig.)

Chandra, Namas; Kalu, Peter [Dept. of Mech. Eng., Florida State Univ., Tallahassee, FL (United States); Khraisheh, Marwan K. [Dept. of MEch. Eng., Univ. of Kentucky, Lexington, KY (United States)

2005-07-01

395

An effective uniaxial tensile stress-strain relationship for prestressed concrete  

International Nuclear Information System (INIS)

This report evaluates the direct tensile strength and an equivalent uniaxial tensile stress-strain relationship for prestressed concrete using data from specimens tested at the University of Alberta which represent segments from the wall of a containment vessel. The stress-strain relationship, when used in conjunction with the BOSOR5 program, enables prediction of the response of prestressed concrete under any biaxial combination of compressive and/or tensile stresses. Comparisons between the experimental and analytical (BOSOR5) load-strain response of the wall segments are also presented. It is concluded that the BOSOR5 program is able to predict satisfactorily the response of the wall segments and multi-layered shell structures. (author)

396

Effects of residual stress, weld toe notch and weld defects on fatigue of welded steel structures  

Science.gov (United States)

In studying the fatigue behavior of fillet welded railroad tank car shell structures, the effects of welding residual stress, weld toe notch, and weld defects on the fatigue of fillet welded A515 steel specimens were evaluated. Both hole-drilling and sectioning measurement techniques were used to obtain residual stress information. Pad-on-plate weld specimens were designed to simulate the tank car structure for welding residual stress measurement. Simple bead-on-plate and fillet weld specimens, which have similar welding residual stresses near the weld end toe to the pad-on-plate specimens, were designed to be as compact as possible for fatigue testing. As-welded and stress-relieved simple weld specimens were tested under pulsed tension and alternating cyclic load conditions to determine stress-life and fatigue crack propagation properties. Weld toe stress concentration effects were determined by strain gage measurement. Fracture surface features and crack initiation sites were studied by visual analysis, scanning electron microscopy, and optical microscopy. Welding residual stresses were found to be biaxial tension-compression near the weld end toe and biaxial tension-tension near the weld center toe. Longitudinal tensile residual stress was significantly relieved when the applied longitudinal tensile cyclic load was greater than 14 Ksi. Test results did not show a consistent effect of tensile residual stress on the fatigue strength under pulsed tension loads. However, tensile residual stress had a significant influence on the fatigue strength under alternating cyclic loads. The weld end toe was associated with a stress concentration factor of approximately 3 and was the most critical factor in initiating fatigue cracks. Weld defects, such as slag inclusions, lack of fusion, and porosity were found to significantly affect the fatigue strength of a welded joint when the load magnitude or mean stress was low. An equivalent crack concept, based on linear elastic fracture mechanics theory, was introduced to quantify the weld toe stress concentration effect. This concept was shown to be effective for fatigue design life prediction of welded structures.

Shen, Wenyu

397

Operator stress  

International Nuclear Information System (INIS)

This paper addresses operator stress in the controlled testing environment of operator licensing accreditation for operation of a nuclear plant facility. From the perspective of stress theory, the authors look at the operator and shift supervisor under accreditation test conditions. They map theory to the real world of nuclear plant operations to reach conclusions concerning the stressfullness of the test situation, and recognize the stress management skills and self control of those operators and shift supervisors who successfully pass the test. (author)

398

Bone Stress  

Science.gov (United States)

In this optics activity, learners examine how polarized light can reveal stress patterns in clear plastic. Learners place a fork between two pieces of polarizing material and induce stress by squeezing the tines together. Learners will observe the colored stress pattern in the image of the plastic that is projected onto a screen using an overhead projector. Learners rotate one of the polarizing filters to explore which orientations give the most dramatic color effects. This activity can be related to bones, as bones develop stress patterns from the loads imposed upon them every day.

Exploratorium, The

2011-12-07

399

"STRESS MANAGEMENT”  

Directory of Open Access Journals (Sweden)

Full Text Available Initially my studied in depth about what is stress and stress management, we visited different colleges and approached different teachers to find out what are the various questions that can be put in our questionnaire. Now our next job was to pen down the questions we could ask teachers which should not be too harsh and direct that makes teachers uncomfortable to cooperate. After making questionnaire the next hurdle that came was what if teachers didn't knew whether they were stressed or what if they refused even though they were stressed.

Amit Kumar

2014-06-01

400

Stress–strain relations for hydrogels under multiaxial deformation  

DEFF Research Database (Denmark)

Constitutive equations are derived for the elastic response of swollen elastomers and hydrogels under an arbitrary deformation with finite strains. An expression is developed for the free energy density of a polymer network based on the Flory concept of flexible chains with constrained junctions and solvent-dependent reference configuration. The importance of introduction of a reference configuration evolving under swelling is confirmed by the analysis of experimental data on nanocomposite hydrogels subjected to swelling and drying. Adjustable parameters in the stress–strain relations are found by fitting observations on swollen elastomers, chemical gels (linked by covalent bonds and sliding cross-links), and physical gels under uniaxial stretching, equi-biaxial tension, and pure shear. Good agreement is demonstrated between the observations and results of numerical simulation. A pronounced difference is revealed between the effect of solvent content on elastic moduli of chemical and physical gels.

Drozdov, Aleksey; Christiansen, Jesper de Claville

2013-01-01

 
 
 
 
401

An isotropic suspension system for a biaxial accelerometer using electroplated thick metal with a HAR SU-8 mold  

International Nuclear Information System (INIS)

In this paper, a novel approach is developed to design an isotropic suspension system using thick metal freestanding micro-structures combining bulk micro-machining with electroplating based on a HAR SU-8 mold. An omega-shape isotropic suspension system composed of circular curved beams that have free switching of imaginary boundary conditions is proposed. This novel isotropic suspension design is not affected by geometric dimensional parameters and always achieves matching stiffness along the principle axes of elasticity. Using the finite element method, the isotropic suspension system was compared with an S-shaped meandering suspension system. In order to realize the suggested isotropic suspension system, a cost-effective fabrication process using electroplating with the SU-8 mold was developed to avoid expensive equipment and materials such as deep reactive-ion etching (DRIE) or a silicon-on-insulator (SOI) wafer. The fabricated isotropic suspension system was verified by electromagnetic actuation experiments. Finally, a biaxial accelerometer with isotropic suspension system was realized and tested using a vibration generator system. The proposed isotropic suspension system and the modified surface micro-machining technique based on electroplating with an SU-8 mold can contribute towards minimizing the system size, simplifying the system configuration, reducing the system price of and facilitating mass production of various types of low-cost sensors and actuators types of low-cost sensors and actuators

402

Imaging with referenceless distortion correction and flexible regions of interest using single-shot biaxial spatiotemporally encoded MRI.  

Science.gov (United States)

Owing to its intrinsic characteristics, spatiotemporally encoded (SPEN) imaging is less sensitive to adverse effects due to field inhomogeneity in comparison with echo planar imaging, a feature highly desired for functional, diffusion, and real-time MRI. However, the quality of images obtained with SPEN MRI is still degraded by geometric distortions when field inhomogeneity exists. In this study, a single-shot biaxial SPEN (bi-SPEN) pulse sequence is implemented, utilizing a 90° and a 180° chirp pulse incorporated with two orthogonal gradients. A referenceless geometric-distortion correction based on the single-shot bi-SPEN sequence is then proposed. The distorted image acquired with the single-shot bi-SPEN sequence is corrected by iterative super-resolved reconstruction involving the field gradients estimated from a field map, which in turn is obtained from its own super-resolved data after a phase-unwrapping procedure without additional scans. In addition, the distortion correction method is applied to improve the quality of the multiple region-of-interest images obtained with single-shot bi-SPEN sequence. PMID:25462700

Li, Jing; Chen, Lin; Cai, Shuhui; Cai, Congbo; Zhong, Jianhui; Chen, Zhong

2015-01-15

403

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 respectivel 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.

404

Tailoring the structural and electronic properties of a graphene-like ZnS monolayer using biaxial strain  

Science.gov (United States)

Our first-principles full-potential density functional theory calculations show that a ZnS monolayer (ML-ZnS), which is predicted to adopt a graphene-like planar honeycomb structure with a direct band gap, undergoes strain-induced modifications in its structure and band gap when subjected to in-plane homogeneous biaxial strain (?). ML-ZnS gets buckled for compressive strain greater than 0.92% ; the buckling parameter ?(= 0.00 Å for planar ML-ZnS) linearly increases with increasing compressive strain (? = 0.435 Å at ? = -5.25%). A tensile strain of 2.91% turns the direct ML-ZnS band gap into indirect. Within our considered strain values of |?| < 6%, the band gap shows linearly decreasing (non-linearly increasing as well as decreasing) variation with tensile (compressive) strain. These predictions (based on our calculations with two atoms per unit cell) may be exploited in future for potential applications in strain sensors and other nano-devices such as nano-electromechanical systems and nano-optomechanical systems.

Behera, Harihar; Mukhopadhyay, Gautam

2014-02-01

405

Vector hysteresis measurements of not oriented grain SiFe steels by a biaxial hall sensors array  

Science.gov (United States)

This work discusses the vector measurement of the effective magnetic field inside a not oriented grain SiFe steel sample, taking into account the effect of the demagnetizing field. We propose an array of biaxial Hall sensors, placed up to the sample surface. The calibration of the system and a suitable extrapolation data strongly reduce the uncertainties of the direct measurement and provide an accurate evaluation of the magnetic field inside the material sample. Although the approach proposed can be also used for industrial frequencies, 50-60 Hz or more, the analysis is limited here to the static case, because we are mainly interested in static magnetic measurements. These measurements are especially useful for the vector characterization of soft magnetic materials and, in particular, for the identification and the experimental validation of vector hysteresis models. The experimental analysis presented in the paper deals with commercial not oriented grain SiFe steels. Experimental data about hysteresis loops and static power losses are given.

Cardelli, E.; Faba, A.

2014-02-01

406

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

407

Wrinkle-to-fold transition in soft layers under equi-biaxial strain: A weakly nonlinear analysis  

Science.gov (United States)

Soft materials can experience a mechanical instability when subjected to a finite compression, developing wrinkles which may eventually evolve into folds or creases. The possibility to control the wrinkling network morphology has recently found several applications in many developing fields, such as scaffolds for biomaterials, stretchable electronics and surface micro-fabrication. Albeit much is known of the pattern initiation at the linear stability order, the nonlinear effects driving the pattern selection in soft materials are still unknown. This work aims at investigating the nature of the elastic bifurcation undertaken by a growing soft layer subjected to a equi-biaxial strain. Considering a skin effect at the free surface, the instability thresholds are found to be controlled by a characteristic length, defined by the ratio between capillary energy and bulk elasticity. For the first time, a weakly nonlinear analysis of the wrinkling instability is performed here using the multiple-scale perturbation method applied to the incremental theory in finite elasticity. The Ginzburg-Landau equations are derived for different superposing linear modes. This study proves that a subcritical pitchfork bifurcation drives the observed wrinkle-to-fold transition in swelling gels experiments, favoring the emergence of hexagonal creased patterns, albeit quasi-hexagonal patterns might later emerge because of an expected symmetry break. Moreover, if the surface energy is somewhat comparable to the bulk elastic energy, it has the same stabilizing effect as for fluid instabilities, driving the formation of stable wrinkles, as observed in elastic bi-layered materials.

Ciarletta, P.

2014-12-01

408

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

409

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

410

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

International Nuclear Information System (INIS)

Results of STXM investigations of a binary mixture (1-TNF =2 :1; SmAb 140 M 180 Iso) known to form a SmAb 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 1-TNF board-like aggregates, in particular the intensity of the low energy peaks associated with aromatic ring * orbitals (284.5 286.5eV), 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 1-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 SmAb phase

411

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

Energy Technology Data Exchange (ETDEWEB)

Results of STXM investigations of a binary mixture (1-TNF =2 :1; SmAb 140 M 180 Iso) known to form a SmAb 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 1-TNF board-like aggregates, in particular the intensity of thelow energy peaks associated with aromatic ring * orbitals (284.5 286.5eV), show that the molecular plane of these aggregates is very sensitiveto the relative orientation of electric field vector E of linearlypolarized light, which is used to determine the molecular orientation inthe LC phase. The observed strong in-plane dichroic signal suggests thepredominant orientation of the 1-TNF aggregates to be along the smecticlayer normal as well as long-range ordering of the in-plane molecularorientation (biaxiality). Orientational maps derived from series ofmeasurements at different sample rotation angles around the specimennormal clearly show a Schlieren-type texture, and permit a detailedexamination of exclusive +-1/2 disclination theoretically predicted forthe SmAb phase.

Kaznacheev, Konstaintin; Hegmann, Torsten

2007-01-25

412

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

413

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.

414

Electronic band structure of wurtzite InN around the fundamental gap in the presence of biaxial strain  

Energy Technology Data Exchange (ETDEWEB)

We present results of a theoretical study of the electronic band structure of wurtzite InN films under biaxial strain in the C-plane (0001) and in planes that correspond to non-polar orientations such as the A-plane (11 anti 20) and the M-plane (1 anti 100). The calculations are performed under the k.p perturbation theory approach using the Bir-Pikus Hamiltonian. The results show that the fundamental bandgap of InN shifts by 30 meV (14 meV) for isotropic tensile (compressive) strain in the C -plane with out-of-plane contraction (dilation) of 0.2%. For films of non-polar orientations, the c-axis lies in the film plane and the strain is expected to be different between directions parallel and perpendicular to c. Such anisotropic strain give rise to valence band mixing which results in dramatic changes in the optical polarization properties as evidenced by the calculated oscillator strengths of the interband transitions. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Bhattacharyya, Jayeeta; Ghosh, Sandip [Department of Condensed Matter Physics and Material Science, Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400005 (India)

2007-02-15

415

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

Science.gov (United States)

In this contribution, we present the application potentiality of biaxial Q-shearing of (27)Al 3QMAS NMR spectra in the analysis of structural defects of aluminium units in aluminosilicates. This study demonstrates that the combination of various shearing transformations of the recorded (27)Al 3QMAS NMR spectra enables an understanding of the broadening processes of the correlation signals of disordered framework aluminosilicates, for which a wide distribution of (27)Al MAS NMR chemical shifts and quadrupolar parameters (i.e., second-order quadrupolar splitting and quadrupole-induced chemical shifts) can be expected. By combining the suitably selected shearing transformation procedures, the mechanisms of the formation of local defects in aluminosilicate frameworks, including Al/Si substitution effects in the next-nearest neighbouring T-sites, variations in bond angles, and/or variations in the physicochemical nature of charge-balancing counter-ions, can be identified. The proposed procedure has been extensively tested on a range of model aluminosilicate materials (kyanite, ?-alumina, metakaolin, analcime, chabazite, natrolite, phillipsite, mordenite, zeolite A, and zeolite Y). PMID:24333044

Kobera, Libor; Brus, Jiri; Klein, Petr; Dedecek, Jiri; Urbanova, Martina

2014-01-01

416

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)

417

Field-induced optically isotropic state in bent core nematic liquid crystals: unambiguous proof of field-induced optical biaxiality  

Science.gov (United States)

The behaviour of bent core (BC) nematic liquid crystals was investigated under dc applied electric field. The optically isotropic state of a sample containing BC nematic was observed under application of low dc electric fields. The quality of the dark state when the sample was inserted between two crossed polarizers was found to be superb and it did not change when rotating the sample between the polarizers. The coupling between the net molecular dipole moment and the applied dc electric field was considered as the origin of the out-of-plane switching of the BC molecules resulting in switching from the field-off bright state to the field-on dark state. The field-induced optically isotropic state is an unambiguous proof of the field-induced biaxiality in the BC nematic liquid crystal. A simple model explaining the appearance of the isotropic optical state in BC nematics and the switching of the sample slow axis between three mutually orthogonal directions under dc applied electric field is proposed.

Elamain, Omaima; Hegde, Gurumurthy; Fodor-Csorba, Katalin; Komitov, Lachezar

2013-11-01

418

Managing Stress  

Medline Plus

Full Text Available ... blood pressure, which can cause heart problems including heart attacks. Stress can also lead to migraine headaches, back pain and ulcers. Several studies have associated stress with a weak immune system. The ... can lead to serious diseases such as heart disease and depression. It may also lead to ...

419

Managing Stress  

Medline Plus

Full Text Available ... with deep breathing. This is a normal body reaction to stress: take a deep breath. By repeatedly inhaling slowly through your nose, holding the breath for a few seconds, then exhaling through your mouth, you can counteract the fast, shallow breathing associated with stress. Relax by clearing ...

420

Managing Stress  

Medline Plus

Full Text Available ... for the body to react to stress. Stretching exercises can be done anywhere and anytime. If possible, exercising is also a great way to stretch the muscles while at the same time taking the mind off the stressor. Relax with massage therapy. Stress can cause muscle knots in the back, ...

 
 
 
 
421

Managing Stress  

Medline Plus

Full Text Available ... It's been added to your dashboard . Managing stress 3:13 Pregnancy is a stressful time for many ... postpartum perio 4:26 Helping Your Baby Th 3:39 Labor and birth: At 4:51 Mild ...

422

Nuclear stress test  

Science.gov (United States)

... Persantine stress test; Thallium stress test; Stress test - nuclear; Adenosine stress test; Regadenoson stress test ... Thallium stress test is a nuclear imaging method that shows how well blood flows into the heart muscle, both at rest and during activity.

423

Magnetostriction measurements of high strength steel under the influence of bi-axial magnetic fields  

Science.gov (United States)

A detailed knowledge of a material's microscopic texture is required in order to produce a realistic model of the magnetization process under applied fields. Previous studies on the magnetostriction in high strength steels have ignored the internal anisotropies due to prior material handling. To this end, a measurement utilizing two perpendicular fields was designed to interrogate the magnetic texture and microstructure of high-strength steel rods. These magnetization and magnetostriction measurements were then fitted to an energy-based domain rotation model which had been altered to address vector fields and uniaxial anisotropies. Given the simplicity of the model it is surprising to see that it captures a number of the general trends in the Data, however the fit is generally poor. Improving upon this data set will allow us to determine general magnetic characteristics of microstructure in the steels. These measurements will be incorporated into a future Vector Preisach model allowing detailed predictions of the magnetic state after stress and field changes in multiple directions.

Burgy, Christopher; Wun-fogle, Marilyn; Restorff, J. B.; Della Torre, Edward; ElBidweihy, Hatem

2014-02-01

424

Mechanically reinforced and biaxially textured Ni alloys composite substrates for coated conductors  

International Nuclear Information System (INIS)

Key requirements for the substrates employed in coated conductors are using magnetic reduced and strengthening materials. In this work, Ni-based alloy composite tapes were designed and prepared in order to meet such needs through a hybrid route. A novel multi-layer of composite tapes was obtained by sintering two pieces of Ni-5at.%W (out layers) connected with Ni-12at.%W mixture powder together using sparking plasma sintering (SPS) technology. The high tungsten contents mixture powder after sintering not only played a role as a joint layer, but also performed high strength and reduced ferromagnetism as an inner layer at the same time. The sharp cube texture was obtained in the composite tapes after the optimized cold rolling and recrystallization. The FWHM values of (1 1 1) Phi-scans and (0 0 2) rocking curves of these tapes were around 9.45oand 5.48o, respectively, measured by X-rays. Extremely, the yield stress of this composite substrate exceeds 320 MPa, the magnetization of the composite substrate being reduced to 10.9 emu/g at 77 K, only 41% in comparison with commercial Ni5W substrate

425

Magnetostriction measurements of high strength steel under the influence of bi-axial magnetic fields  

Energy Technology Data Exchange (ETDEWEB)

A detailed knowledge of a material's microscopic texture is required in order to produce a realistic model of the magnetization process under applied fields. Previous studies on the magnetostriction in high strength steels have ignored the internal anisotropies due to prior material handling. To this end, a measurement utilizing two perpendicular fields was designed to interrogate the magnetic texture and microstructure of high-strength steel rods. These magnetization and magnetos