Failure criterion for graphene in biaxial loading—a molecular dynamics study

International Nuclear Information System (INIS)

Yazdani, Hessam; Hatami, Kianoosh

2015-01-01

Molecular dynamics simulations are carried out in order to develop a failure criterion for infinite/bulk graphene in biaxial tension. Stresses along the principal edge configurations of graphene (i.e. armchair and zigzag directions) are normalized to the corresponding uniaxial ultimate strength values. The combinations of normalized stresses resulting in the failure of graphene are used to define failure envelopes (limiting stress ratio surfaces). Results indicate that a bilinear failure envelope can be used to represent the tensile strength of graphene in biaxial loading at different temperatures with reasonable accuracy. A circular failure envelope is also introduced for practical applications. Both failure envelopes define temperature-independent upper limits for the feasible combinations of normalized stresses for a graphene sheet in biaxial loading. Predicted failure modes of graphene under biaxial loading are also shown and discussed. (paper)

Biaxial fatigue of metals the present understanding

CERN Document Server

Schijve, Jaap

2016-01-01

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

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

International Nuclear Information System (INIS)

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

1999-01-01

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

Biaxial stress driven tetragonal symmetry breaking and high-temperature ferromagnetic semiconductor from half-metallic CrO2

Science.gov (United States)

Xiao, Xiang-Bo; Liu, Bang-Gui

2018-03-01

It is highly desirable to combine the full spin polarization of carriers with modern semiconductor technology for spintronic applications. For this purpose, one needs good crystalline ferromagnetic (or ferrimagnetic) semiconductors with high Curie temperatures. Rutile CrO2 is a half-metallic spintronic material with Curie temperature 394 K and can have nearly full spin polarization at room temperature. Here, we find through first-principles investigation that when a biaxial compressive stress is applied on rutile CrO2, the density of states at the Fermi level decreases with the in-plane compressive strain, there is a structural phase transition to an orthorhombic phase at the strain of -5.6 % , and then appears an electronic phase transition to a semiconductor phase at -6.1 % . Further analysis shows that this structural transition, accompanying the tetragonal symmetry breaking, is induced by the stress-driven distortion and rotation of the oxygen octahedron of Cr, and the half-metal-semiconductor transition originates from the enhancement of the crystal field splitting due to the structural change. Importantly, our systematic total-energy comparison indicates the ferromagnetic Curie temperature remains almost independent of the strain, near 400 K. This biaxial stress can be realized by applying biaxial pressure or growing the CrO2 epitaxially on appropriate substrates. These results should be useful for realizing full (100%) spin polarization of controllable carriers as one uses in modern semiconductor technology.

A novel biaxial specimen for inducing residual stresses in thermoset polymers and fibre composite material

DEFF Research Database (Denmark)

Jakobsen, Johnny; Andreasen, Jens Henrik; Jensen, Martin

2015-01-01

engineers when they challenge the material limits in present and future thermoset and composite component. In addition to the new specimen configuration, this paper presents an analytical solution for the residual stress state in the specimen. The analytical solution assumes linear elastic and isotropic......A new type of specimen configuration with the purpose of introducing a well-defined biaxial residual (axisymmetric) stress field in a neat thermoset or a fibre composite material is presented. The ability to experimentally validate residual stress predictions is an increasing need for design...

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

Energy Technology Data Exchange (ETDEWEB)

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

1998-06-01

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

Design of a cruciform bend specimen for determination of out-of- plane biaxial tensile stress effects on fracture toughness for shallow cracks

International Nuclear Information System (INIS)

Bass, B.R.; Bryson, J.W.; Mcafee, W.J.; Pennell, W.E.; Theiss, T.J.

1993-01-01

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

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

International Nuclear Information System (INIS)

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

1998-01-01

A technology to determine shallow-flaw fracture toughness of reactor pressure vessel (RPV) steels is being developed for application to the safety assessment of RPVs containing postulated shallow surface flaws. Matrices of cruciform beam tests were developed to investigate and quantify the effects of temperature, biaxial loading, and specimen size on fracture initiation toughness of two-dimensional (constant depth), shallow surface flaws. The cruciform beam specimens were developed at Oak Ridge National Laboratory (ORNL) to introduce a 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

Limit load assessment of centre cracked plates under biaxial loading

International Nuclear Information System (INIS)

Meek, C.; Ainsworth, R.A.

2015-01-01

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

Field-Induced Rheology in Uniaxial and Biaxial Fields

International Nuclear Information System (INIS)

MARTIN, JAMES E.

1999-01-01

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

Biaxial deformation behaviour of poly-ether-ether-ketone

Science.gov (United States)

Turner, Josh; Menary, Gary; Martin, Peter

2018-05-01

The biaxial tensile properties of thin poly-ether-ether-ketone (PEEK) films are presented. Investigation into the biaxial mechanical behaviour of PEEK films will provide a preliminary insight into the anticipated stress/strain response, and potential suitability, to the possible fabrication of thin walled parts through stretch blow moulding and thermoforming processes - with the multi-axial state of strain imposed onto the heated thermoplastic sheet representative of the expected strain history experienced during these material forming processes. Following identification of the prospective forming temperature window, the biaxial mechanical behaviour of the material is characterized under differing modes of deformation, at a nominal strain rate of 1 s-1. The temperature dependence is outlined within - with an appreciable increase in flow behaviour correlated with specimen temperature exceeding its glass transition temperature (Tg).

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)

Taran, Yu.V.; Balagurov, A.M.; Kuznetsov, A.N.; Schreiber, J.; Bomas, H.; Stoeberl, Ch.; Rathjen, P.; Vorster, W.J.J.; Korsunsky, A.M.

2007-01-01

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

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

International Nuclear Information System (INIS)

Wada, M.; Naoi, H.; Yasuda, H.; Maruyama, T.

2008-01-01

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 ε-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

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

Science.gov (United States)

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

2010-06-01

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.

Corrosion Fatigue Crack Growth Behavior at Notched Hole in 7075 T6 Under Different Biaxial Stress Ratios

Science.gov (United States)

2016-08-18

Subjected to Biaxial Cyclic Loads.” Engineering Fracture Mechanics , 78:1516- 1528, 2011. [37] Sih, G.C.. “A Special Theory of Crack Propagation...of Aeronautics and Astronautics Graduate School of Engineering and Management Air Force Institute of Technology Air University Air Education and...environments from pre- cracked notched circular hole in a 7075-T6 cruciform specimen using a fracture mechanics approach. With stress ratio of R

Single-source mechanical loading system produces biaxial stresses in cylinders

Science.gov (United States)

Flower, J. F.; Stafford, R. L.

1967-01-01

Single-source mechanical loading system proportions axial-to-hoop tension loads applied to cylindrical specimens. The system consists of hydraulic, pneumatic, and lever arrangements which produce biaxial loading ratios.

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

LENUS (Irish Health Repository)

Lyons, Mathew

2014-06-03

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

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

Science.gov (United States)

Jackson, Wade C.; Ratcliffe, James G.

2013-01-01

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

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

International Nuclear Information System (INIS)

Wiesner, C.S.; Goldthorpe, M.R.; Andrews, R.M.; Garwood, S.J.

1999-01-01

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.)

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

International Nuclear Information System (INIS)

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

1992-01-01

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

Biaxial charts for rectangular reinforced columns in accordance with ...

African Journals Online (AJOL)

linearity arising from the non-linear stress-strain relationships and the cracking of the cross-section. · As a result, the systematic production of biaxial design charts necessitates the application of numerical methods that are based on iterations.

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

International Nuclear Information System (INIS)

Theiss, T.J.; Bass, B.R.; Bryson, J.W.

1993-01-01

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

Local behavior of an AISI 304 stainless steel submitted to in situ biaxial loading in SEM

Energy Technology Data Exchange (ETDEWEB)

Caër, C., E-mail: celia.caer@gmail.com; Pesci, R.

2017-04-06

The microstructural response of a coarse grained AISI 304 stainless steel submitted to biaxial tensile loading was investigated using SEM and X-ray diffraction. The specimen geometry was designed to allow for biaxial stress state and incipient crack in the center of the active part under biaxial tensile loading. This complex loading was performed step by step by a micromachine fitting into a SEM chamber. At each loading step FSD pictures and EBSD measurements were carried out to study the microstructural evolution of the alloy, namely grain rotations and misorientations, stress-induced martensite formation and crack propagation. According to their initial orientation, grains are found to behave differently under loading. Approximately 60% of grains are shown to reorient to the [110] Z orientation under biaxial tensile loading, whereas the 40% left undergo high plastic deformation. EBSD and XRD measurements respectively performed under loading and on the post mortem specimen highlighted the formation of about 4% of martensite.

Biaxial loading effects on the growth of cracks

International Nuclear Information System (INIS)

Brown, M.W.; Miller, K.J.; Walker, T.J.

1983-01-01

Fatigue crack growth under different biaxial stress states is considered for both small scale yielding and high bulk stress conditions. Analytical and elastic finite element results are compared favourably alongside experimental results on a AISI 316 stainless steel at both room and elevated temperatures. Differences in crack growth rates are compared against different crack tip cyclic plastic zone sizes for various degrees of mixed mode loading, thereby overcoming the limitations of the Paris Law and LEFM. The usefulness of the approach is indicated for studies in the behaviour of materials subjected to thermal shock. Where steep temperature gradients are introduced due to rapid thermal transients, high strains are produced which propagate fatigue cracks under cyclic conditions. Since stress gradients are generally associated with thermal shock situations, the cracks grow through a plastically deformed region near the surface into an elastic region. A unified approach to fatigue behaviour, encompassing both linear elastic and elastic-plastic fracture mechanics, will enable analysis of thermal shock situations. The approach to crack propagation developed here shows that cyclic growth rates are a function of a severe strain zone size in which local stresses exceed the tensile strength, i.e. monotonic instability. The effects of stress biaxiality and mixed mode loading are included in the analysis, which may be extended to general yielding situations. (orig.)

Biaxial loading effects on fracture toughness of reactor pressure vessel steel

International Nuclear Information System (INIS)

McAfee, W.J.; Bass, B.R.; Bryson, J.W. Jr.; Pennell, W.E.

1995-03-01

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

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

Science.gov (United States)

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

2012-03-01

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. Copyright © 2011 Wiley Periodicals, Inc.

Methodology for dynamic biaxial tension testing of pregnant uterine tissue.

Science.gov (United States)

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

2007-01-01

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.

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

KAUST Repository

Pancheri, Francesco Q.

2014-03-01

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

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

International Nuclear Information System (INIS)

Park, Joong Cheul; Kwon, Jae Do

2005-01-01

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

Meso-Scale Finite Element Analysis of Mechanical Behavior of 3D Braided Composites Subjected to Biaxial Tension Loadings

Science.gov (United States)

Zhang, Chao; Curiel-Sosa, Jose L.; Bui, Tinh Quoc

2018-04-01

In many engineering applications, 3D braided composites are designed for primary loading-bearing structures, and they are frequently subjected to multi-axial loading conditions during service. In this paper, a unit-cell based finite element model is developed for assessment of mechanical behavior of 3D braided composites under different biaxial tension loadings. To predict the damage initiation and evolution of braiding yarns and matrix in the unit-cell, we thus propose an anisotropic damage model based on Murakami damage theory in conjunction with Hashin failure criteria and maximum stress criteria. To attain exact stress ratio, force loading mode of periodic boundary conditions which never been attempted before is first executed to the unit-cell model to apply the biaxial tension loadings. The biaxial mechanical behaviors, such as the stress distribution, tensile modulus and tensile strength are analyzed and discussed. The damage development of 3D braided composites under typical biaxial tension loadings is simulated and the damage mechanisms are revealed in the simulation process. The present study generally provides a new reference to the meso-scale finite element analysis (FEA) of multi-axial mechanical behavior of other textile composites.

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

Energy Technology Data Exchange (ETDEWEB)

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

1992-04-01

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

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

International Nuclear Information System (INIS)

Bass, B.R.; Bryson, J.W.; Theiss, T.J.; Rao, M.C.

1994-01-01

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

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

International Nuclear Information System (INIS)

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

2014-01-01

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

Biaxial fatigue crack propagation behavior of perfluorosulfonic-acid membranes

Science.gov (United States)

Lin, Qiang; Shi, Shouwen; Wang, Lei; Chen, Xu; Chen, Gang

2018-04-01

Perfluorosulfonic-acid membranes have long been used as the typical electrolyte for polymer-electrolyte fuel cells, which not only transport proton and water but also serve as barriers to prevent reactants mixing. However, too often the structural integrity of perfluorosulfonic-acid membranes is impaired by membrane thinning or cracks/pinholes formation induced by mechanical and chemical degradations. Despite the increasing number of studies that report crack formation, such as crack size and shape, the underlying mechanism and driving forces have not been well explored. In this paper, the fatigue crack propagation behaviors of Nafion membranes subjected to biaxial loading conditions have been investigated. In particular, the fatigue crack growth rates of flat cracks in responses to different loading conditions are compared, and the impact of transverse stress on fatigue crack growth rate is clarified. In addition, the crack paths for slant cracks under both uniaxial and biaxial loading conditions are discussed, which are similar in geometry to those found after accelerated stress testing of fuel cells. The directions of initial crack propagation are calculated theoretically and compared with experimental observations, which are in good agreement. The findings reported here lays the foundation for understanding of mechanical failure of membranes.

Topology Optimization of Stressed Capacitive RF MEMS Switches

DEFF Research Database (Denmark)

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

2013-01-01

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

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

International Nuclear Information System (INIS)

Murty, K.L.; Tanikella, B.V.; Earthman, J.C.

1994-01-01

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 structures

Ray-optics analysis of inhomogeneous biaxially anisotropic media

NARCIS (Netherlands)

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

2009-01-01

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

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

Energy Technology Data Exchange (ETDEWEB)

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

2000-09-01

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

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

International Nuclear Information System (INIS)

RodrIguez-MartInez, R; Urriolagoitia-Calderon, G; Urriolagoitia-Sosa, G; Hernandez-Gomez, L H; Merchan-Cruz, E A; RodrIguez-Canizo, R G; Sandoval-Pineda, J M

2009-01-01

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

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

Energy Technology Data Exchange (ETDEWEB)

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

2009-08-01

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

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

Czech Academy of Sciences Publication Activity Database

Seitl, Stanislav

2014-01-01

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

Sequential Indentation Tests to Investigate the Influence of Confining Stress on Rock Breakage by Tunnel Boring Machine Cutter in a Biaxial State

Science.gov (United States)

Liu, Jie; Cao, Ping; Han, Dongya

2016-04-01

The influence of confining stress on rock breakage by a tunnel boring machine cutter was investigated by conducting sequential indentation tests in a biaxial state. Combined with morphology measurements of breaking grooves and an analysis of surface and internal crack propagation between nicks, the effects of maximum confining stress and minimum stress on indentation efficiency, crack propagation and chip formation were investigated. Indentation tests and morphology measurements show that increasing a maximum confining stress will result in increased consumed energy in indentations, enlarged groove volumes and promoted indentation efficiency when the corresponding minimum confining stress is fixed. The energy consumed in indentations will increase with increase in minimum confining stress, however, because of the decreased groove volumes as the minimum confining stress increases, the efficiency will decrease. Observations of surface crack propagation show that more intensive fractures will be induced as the maximum confining stress increases, whereas the opposite occurs for an increase of minimum confining stress. An observation of the middle section, cracks and chips shows that as the maximum confining stress increases, chips tend to form in deeper parts when the minimum confining stress is fixed, whereas they tend to formed in shallower parts as the minimum confining stress increases when the maximum confining stress is fixed.

Numerical development of a new correlation between biaxial fracture strain and material fracture toughness for small punch test

Energy Technology Data Exchange (ETDEWEB)

Kumar, Pradeep [Homi Bhabha National Institute, Anushaktinagar, Mumbai 400094 (India); Dutta, B.K., E-mail: bijon.dutta@gmail.com [Homi Bhabha National Institute, Anushaktinagar, Mumbai 400094 (India); Chattopadhyay, J. [Homi Bhabha National Institute, Anushaktinagar, Mumbai 400094 (India); Reactor Safety Division, Bhabha Atomic Research Centre, Mumbai 400085 (India)

2017-04-01

The miniaturized specimens are used to determine mechanical properties of the materials, such as yield stress, ultimate stress, fracture toughness etc. Use of such specimens is essential whenever limited quantity of material is available for testing, such as aged/irradiated materials. The miniaturized small punch test (SPT) is a technique which is widely used to determine change in mechanical properties of the materials. Various empirical correlations are proposed in the literature to determine the value of fracture toughness (J{sub IC}) using this technique. bi-axial fracture strain is determined using SPT tests. This parameter is then used to determine J{sub IC} using available empirical correlations. The correlations between J{sub IC} and biaxial fracture strain quoted in the literature are based on experimental data acquired for large number of materials. There are number of such correlations available in the literature, which are generally not in agreement with each other. In the present work, an attempt has been made to determine the correlation between biaxial fracture strain (ε{sub qf}) and crack initiation toughness (J{sub i}) numerically. About one hundred materials are digitally generated by varying yield stress, ultimate stress, hardening coefficient and Gurson parameters. Such set of each material is then used to analyze a SPT specimen and a standard TPB specimen. Analysis of SPT specimen generated biaxial fracture strain (ε{sub qf}) and analysis of TPB specimen generated value of J{sub i}. A graph is then plotted between these two parameters for all the digitally generated materials. The best fit straight line determines the correlation. It has been also observed that it is possible to have variation in J{sub i} for the same value of biaxial fracture strain (ε{sub qf}) within a limit. Such variation in the value of J{sub i} has been also ascertained using the graph. Experimental SPT data acquired earlier for three materials were then used to get J

Biaxial testing for nuclear grade graphite by ball on three balls assessment

International Nuclear Information System (INIS)

Mohd Reusmaazran Yusof; Yusof Abdullah

2012-01-01

Nuclear grade (high-purity) graphite for fuel element and moderator material in Advanced Gas Cooling Reactors (AGR) displays large scatter in strength and a non-linear stress-strain response from the damage accumulation. These responses can be characterized as quasi-brittle behaviour. Current assessments of fracture in core graphite components are based on the linear elastic approximation and thus represent a major assumption. The quasi-brittle behaviour gives challenge to assess the real nuclear graphite component. The selected test method would help to bridge the gap between microscale to macro-scale in real reactor component. The small scale tests presented here can contribute some statistical data to manifests the failure in real component. The evaluation and choice of different solution design of biaxial test will be discussed in this paper. The ball on-three ball test method was used for assessment test follows by numerous of analytical method. The results shown that biaxial strength of the EY9 grade graphite depends on the method used for evaluation. Some of the analytical methods use to calculate biaxial strength were found not to be valid and therefore should not be used to assess the mechanical properties of nuclear graphite. (author)

Anisotropic yield surfaces in bi-axial cyclic plasticity

International Nuclear Information System (INIS)

Rider, R.J.; Harvey, S.J.; Breckell, T.H.

1985-01-01

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

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

Science.gov (United States)

Murakoso, Satoko; Kuwabara, Toshihiko

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

Biaxial testing for fabrics and foils optimizing devices and procedures

CERN Document Server

Beccarelli, Paolo

2015-01-01

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

Accessible switching of electronic defect type in SrTi O3 via biaxial strain

Science.gov (United States)

Chi, Yen-Ting; Youssef, Mostafa; Sun, Lixin; Van Vliet, Krystyn J.; Yildiz, Bilge

2018-05-01

Elastic strain is used widely to alter the mobility of free electronic carriers in semiconductors, but a predictive relationship between elastic lattice strain and the extent of charge localization of electronic defects is still underdeveloped. Here we considered SrTi O3 , a prototypical perovskite as a model functional oxide for thin film electronic devices and nonvolatile memories. We assessed the effects of biaxial strain on the stability of electronic defects at finite temperature by combining density functional theory (DFT) and quasiharmonic approximation (QHA) calculations. We constructed a predominance diagram for free electrons and small electron polarons in this material, as a function of biaxial strain and temperature. We found that biaxial tensile strain in SrTi O3 can stabilize the small polaron, leading to a thermally activated and slower electronic transport, consistent with prior experimental observations on SrTi O3 and distinct from our prior theoretical assessment of the response of SrTi O3 to hydrostatic stress. These findings also resolved apparent conflicts between prior atomistic simulations and conductivity experiments for biaxially strained SrTi O3 thin films. Our computational approach can be extended to other functional oxides, and for the case of SrTi O3 our findings provide concrete guidance for conditions under which strain engineering can shift the electronic defect type and concentration to modulate electronic transport in thin films.

Biaxial Loading Tests for steel containment vessel

Energy Technology Data Exchange (ETDEWEB)

Miyagawa, T. [Nuclear Power Engineering Corp., Tokyo (Japan); Wright, D.J.; Arai, S.

1999-07-01

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)

Biaxial Loading Tests for steel containment vessel

International Nuclear Information System (INIS)

Miyagawa, T.; Wright, D.J.; Arai, S.

1999-01-01

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)

In-situ neutron diffraction study of Zircaloy 4 subjected to biaxial tension

Energy Technology Data Exchange (ETDEWEB)

Gharghouri, M.A. [Canadian Neutron Beam Centre, Chalk River Laboratories, Chalk River, ON (Canada); McDonald, D.; Xiao, L. [Atomic Energy of Canada Limited, Chalk River, ON (Canada)

2014-07-01

Zircaloy-4 is widely used as fuel element cladding in nuclear reactors. Pellet-clad interaction (PCI) failure is a concern for many water reactor fuel designs. Extensive work on the mechanism of PCI failure has led to the conclusion that stress corrosion cracking (SCC) induced by iodine vapour in the temperature range relevant to fuel operation is the most probable cause of PCI failure in zirconium alloy fuel element cladding. In-situ neutron diffraction measurements performed on tubular Zircaloy-4 specimens simultaneously pulled in tension and pressurized internally will provide information on the effects of stress biaxiality on the distribution of stresses at the crystal level during loading. (author)

Biaxiality of chiral liquid crystals

International Nuclear Information System (INIS)

Longa, L.; Trebin, H.R.; Fink, W.

1993-10-01

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

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)

Taran, Yu.V.; Balagurov, A.M.; Sheverev, S.G.; ); Schreiber, J.; Bomas, H.; Korsunsky, A.M.

2007-01-01

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

Fatigue behavior of boxing welded joint under biaxial cyclic loads; 2juku kurikaeshi kajuka ni okeru kakumawashi yosetsu keishu no hiro kyodo

Energy Technology Data Exchange (ETDEWEB)

Takahashi, I.; Takada, A.; Akiyama, S.; Ushijima, M.; Maenaka, H. [Ministry of Transportation, Tokyo (Japan)

1998-12-31

Various forces such as gravity, wave induced force, inertial force etc. compositely act on a ship body from various directions. Therefore, while discussing strength or life of structural elements of ship body, it is necessary to understand the effects of the composite force condition. In this study, fatigue tests of boxing welded joint under rectangular biaxial cyclic loads are performed, the following results are obtained. Even under he biaxial cyclic loads, it is the same as the uniaxial test, the cracks occurred at the boxing weld toes propagate almost in the straight y-direction, but no oblique propagation of the cracks caused by the lad in the y-direction occurs. That the crack at initial stage of the crack progress is improved in y-direction can be illustrated by the facts that the residual stress in x-direction near the toes reaches to the yield stress, and the stress concentration in the welded toes is bigger in x-direction than that in y-direction. But as for prediction of the progress route, a further study including amplitude ratio of the biaxial loads, effects of width of test specimen is necessary. 4 refs., 12 figs., 4 tabs.

Experimental Studies on Strength Behaviour of Notched Glass/Epoxy Laminated Composites under Uni-axial and Bi-axial Loading

Science.gov (United States)

Guptha, V. L. Jagannatha; Sharma, Ramesh S.

2017-11-01

The use of FRP composite materials in aerospace, aviation, marine, automotive and civil engineering industry has increased rapidly in recent years due to their high specific strength and stiffness properties. The structural members contrived from such composite materials are generally subjected to complex loading conditions and leads to multi-axial stress conditions at critical surface localities. Presence of notches, much required for joining process of composites, makes it further significant. The current practice of using uni-axial test data alone to validate proposed material models is inadequate leading to evaluation and consideration of bi-axial test data. In order to correlate the bi-axial strengths with the uni-axial strengths of GFRP composite laminates in the presence of a circular notch, bi-axial tests using four servo-hydraulic actuators with four load cells were carried out. To determine the in-plane strength parameters, bi-axial cruciform test specimen model was considered. Three different fibre orientations, namely, 0°, 45°, and 90° are considered with a central circular notch of 10 mm diameter in the present investigation. From the results obtained, it is observed that there is a reduction in strength of 5.36, 2.41 and 13.92% in 0°, 45°, and 90° fibre orientation, respectively, under bi-axial loading condition as compared to that of uni-axial loading in laminated composite.

Material law for concrete under multiaxial stress

International Nuclear Information System (INIS)

Geistefeldt, H.

1977-01-01

In this paper a general triaxial set of finite strain-stress relations is derived, which can include a step-by-step way nearly all known factors and curves of material response. The finite constitutive equations representing the behaviour of concrete are related to the main strain-directions. The elastic part, the functions for uniaxial behaviour, those for biaxial response and finally the relation-parts, nonzero only in triaxial stress-state, can be reset separately by suitable functions which have been adjusted to the material response of actual concrete known from special tests. With a new and very short biaxial failure criterion for concrete, which has been stated and compared with test results, the analytic description of the biaxial behaviour of Kupfer's concrete is completed. With some additional assumptions the proposed failure criteria and the strain-stress equations for concrete are extended to the biaxial response of uncracked orthogonally reinforced concrete response. (Auth.)

Biaxial Testing of 2195 Aluminum Lithium Alloy Using Cruciform Specimens

Science.gov (United States)

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

2002-01-01

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

Regional and depth variability of porcine meniscal mechanical properties through biaxial testing.

Science.gov (United States)

Kahlon, A; Hurtig, M B; Gordon, K D

2015-01-01

The menisci in the knee joint undergo complex loading in-vivo resulting in a multidirectional stress distribution. Extensive mechanical testing has been conducted to investigate the tissue properties of the knee meniscus, but the testing conditions do not replicate this complex loading regime. Biaxial testing involves loading tissue along two different directions simultaneously, which more accurately simulates physiologic loading conditions. The purpose of this study was to report mechanical properties of meniscal tissue resulting from biaxial testing, while simultaneously investigating regional variations in properties. Ten left, fresh porcine joints were obtained, and the medial and lateral menisci were harvested from each joint (twenty menisci total). Each menisci was divided into an anterior, middle and posterior region; and three slices (femoral, deep and tibial layers) were obtained from each region. Biaxial and constrained uniaxial testing was performed on each specimen, and Young's moduli were calculated from the resulting stress strain curves. Results illustrated significant differences in regional mechanical properties, with the medial anterior (Young's modulus (E)=11.14 ± 1.10 MPa), lateral anterior (E=11.54 ± 1.10 MPa) and lateral posterior (E=9.0 ± 1.2 MPa) regions exhibiting the highest properties compared to the medial central (E=5.0 ± 1.22 MPa), medial posterior (E=4.16 ± 1.13 MPa) and lateral central (E=5.6 ± 1.20 MPa) regions. Differences with depth were also significant on the lateral meniscus, with the femoral (E=12.7 ± 1.22 MPa) and tibial (E=8.6 ± 1.22 MPa) layers exhibiting the highest Young's moduli. This data may form the basis for future modeling of meniscal tissue, or may aid in the design of synthetic replacement alternatives. Copyright © 2014 Elsevier Ltd. All rights reserved.

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)

Chao, Yuh-Jin

1995-01-01

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 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 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

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

International Nuclear Information System (INIS)

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

2016-01-01

Hydride reorientation can occur in spent nuclear fuel cladding when subjected to a tensile hoop stress above a threshold value during cooling. Because in these circumstances the cladding is under a multiaxial stress state, the effect of stress biaxiality on the threshold stress for hydride reorientation is investigated using hydrided CWSR Zircaloy-4 sheet specimens containing ∼180 wt ppm of hydrogen and subjected to a two-cycle thermo-mechanical treatment. The study is based on especially designed specimens within which the stress biaxiality ratios range from uniaxial (σ_2/σ_1 = 0) to “near-equibiaxial” tension (σ_2/σ_1 = 0.8). The threshold stress is determined by mapping finite element calculations of the principal stresses and of the stress biaxiality ratio onto the hydride microstructure obtained after the thermo-mechanical treatment. The results show that the threshold stress (maximum principal stress) decreases from 155 to 75 MPa as the stress biaxiality increases from uniaxial to “near-equibiaxial” tension.

Lightweight, Low-CTE Tubes Made From Biaxially Oriented LCPs

Science.gov (United States)

Rubin, Leslie; Federico, Frank; Formato, Richard; Larouco, John; Slager, William

2004-01-01

Tubes made from biaxially oriented liquid-crystal polymers (LCPs) have been developed for use as penetrations on cryogenic tanks. ( Penetrations in this context denotes feed lines, vent lines, and sensor tubes, all of which contribute to the undesired conduction of heat into the tanks.) In comparison with corresponding prior cryogenic-tank penetrations made from stainless steels and nickel alloys, the LCP penetrations offer advantages of less weight and less thermal conduction. An additional major advantage of LCP components is that one can tailor their coefficients of thermal expansion (CTEs). The estimated cost of continuous production of LCP tubes of typical sizes is about $1.27/ft ($4.17/m) [based on 1998 prices]. LCP tubes that are compatible with liquid oxygen and that feature tailored biaxial molecular orientation and quasi-isotropic properties (including quasi-isotropic CTE) have been fabricated by a combination of proprietary and patented techniques that involve the use of counterrotating dies (CRDs). Tailoring of the angle of molecular orientation is what makes it possible to tailor the CTE over a wide range to match the CTEs of adjacent penetrations of other tank components; this, in turn, makes it possible to minimize differential-thermal expansion stresses that arise during thermal cycling. The fabrication of biaxially oriented LCP tubes by use of CRDs is not new in itself. The novelty of the present development lies in tailoring the orientations and thus the CTEs and other mechanical properties of the LCPs for the intended cryogenic applications and in modifications of the CRDs for this purpose. The LCP tubes and the 304-stainless-steel tubes that the LCP tubes were intended to supplant were tested with respect to burst strength, permeability, thermal conductivity, and CTE.

Magnetic response of FeNbCuBSi RQ ribbons to bi-axial strain

Energy Technology Data Exchange (ETDEWEB)

Butvin, P. E-mail: fyzipbut@nic.savba.sk; Butvinova, B.; Frait, Z.; Sitek, J.; Svec, P

2000-06-02

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

Magnetic response of FeNbCuBSi RQ ribbons to bi-axial strain

International Nuclear Information System (INIS)

Butvin, P.; Butvinova, B.; Frait, Z.; Sitek, J.; Svec, P.

2000-01-01

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

High temperature strength of Hastelloy XR under biaxial stress states

International Nuclear Information System (INIS)

Muto, Yasushi; Hada, Kazuhiko; Koikegami, Hajime; Ohno, Nobutada.

1991-01-01

Biaxial(tension/torsion) creep and creep-fatigue tests were conducted on Hastelloy XR at 950degC in air. Hastelloy XR is a nickel base solution-annealed heat resistant alloy. Thin-walled tubular test specimens were employed. As results of the creep tests, the von Mises' flow rule was revealed to be applicable very well. Under the torsion load, sufficient growth of voids was necessary to initiate the fracture and this resulted in longer life time compared with that under the tension load. Only a few number of small voids could be observed and very long life times were attained under the compression load. The creep-fatigue tests revealed that superposition of constant torsion load on a cyclic axial load reduced the cycles to failure significantly and the amount of reduction was consistent with the prediction by the linear life fraction rule. (author)

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)

Kuang Qian-Wei; Liu Hong-Xia; Wang Shu-Long; Qin Shan-Shan; Wang Zhi-Lin

2011-01-01

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)

Biaxial Creep Specimen Fabrication

Energy Technology Data Exchange (ETDEWEB)

JL Bump; RF Luther

2006-02-09

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

Biaxial Creep Specimen Fabrication

International Nuclear Information System (INIS)

JL Bump; RF Luther

2006-01-01

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

Biaxial magnetic grain alignment

International Nuclear Information System (INIS)

Staines, M.; Genoud, J.-Y.; Mawdsley, A.; Manojlovic, V.

2000-01-01

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

Conductive and robust nitride buffer layers on biaxially textured substrates

Science.gov (United States)

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

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.

Depletion-induced biaxial nematic states of boardlike particles

International Nuclear Information System (INIS)

Belli, S; Van Roij, R; Dijkstra, M

2012-01-01

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

Biaxial potential of surface-stabilized ferroelectric liquid crystals

Science.gov (United States)

Kaznacheev, Anatoly; Pozhidaev, Evgeny; Rudyak, Vladimir; Emelyanenko, Alexander V.; Khokhlov, Alexei

2018-04-01

A biaxial surface potential Φs of smectic-C* surface-stabilized ferroelectric liquid crystals (SSFLCs) is introduced in this paper to explain the experimentally observed electric-field dependence of polarization P˜cell(E ) , in particular the shape of the static hysteresis loops. Our potential consists of three independent parts. The first nonpolar part Φn describes the deviation of the prime director n (which is the most probable orientation of the long molecular axes) from the easy alignment axis R , which is located in the boundary surface plane. It is introduced in the same manner as the uniaxial Rapini potential. The second part Φp of the potential is a polar term associated with the presence of the polar axis in a FLC. The third part Φm relates to the inherent FLC biaxiality, which has not been taken into consideration previously. The Φm part takes into account the deviations of the secondary director m (which is the most probable orientation of the short molecular axes) from the normal to the boundary surface. The overall surface potential Φs, which is a sum of Φn,Φp , and Φm, allows one to model the conditions when either one, two, or three minima of the SSFLC cell free energy are realized depending on the biaxiality extent. A monodomain or polydomain structure, as well as the bistability or monostability of SSFLC cells, depends on the number of free-energy minima, as confirmed experimentally. In this paper, we analyze the biaxiality impact on the FLC alignment. We also answer the question of whether the bistable or monostable structure can be formed in an SSFLC cell. Our approach is essentially based on a consideration of the biaxial surface potential, while the uniaxial surface potential cannot adequately describe the experimental observations in the FLC.

Biaxial experimental and analytical characterization of a dielectric elastomer

Science.gov (United States)

Helal, Alexander; Doumit, Marc; Shaheen, Robert

2018-01-01

Electroactive polymers (EAPs) have emerged as a strong contender for use in low-cost efficient actuators in multiple applications especially related to biomimetic and mobile-assistive devices. Dielectric elastomers (DE), a subcategory of these smart materials, have been of particular interest due to their large achievable deformation and favourable mechanical and electro-mechanical properties. Previous work has been completed to understand the behaviour of these materials; however, their properties require further investigation to properly integrate them into real-world applications. In this study, a biaxial tensile experimental evaluation of 3M™ VHB 4905 and VHB 4910 is presented with the purpose of illustrating the elastomers' transversely isotropic mechanical behaviours. These tests were applied to both tapes for equibiaxial stretch rates ranging between 0.025 and 0.300 s-1. Subsequently, a dynamic planar biaxial visco-hyperelastic constitutive relationship was derived from a Kelvin-Voigt rheological model and the general Hooke's law for transversely isotropic materials. The model was then fitted to the experimental data to obtain three general material parameters for either tapes. The model's ability to predict tensile stress response and internal energy dissipation, with respect to experimental data, is evaluated with good agreement. The model's ability to predict variations in mechanical behaviour due to changes in kinematic variables is then illustrated for different conditions.

Biaxial wheel/hub test facility. Proceedings

Energy Technology Data Exchange (ETDEWEB)

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

2000-07-01

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

Fatigue and creep-fatigue strength of 304 steel under biaxial strain conditions

International Nuclear Information System (INIS)

Asayama, Tai; Aoto, Kazumi; Wada, Yusaku

1990-01-01

A series of fatigue and creep-fatigue tests were conducted with 304 stainless steel at 550degC under a variety of biaxial strain conditions. Fatigue life under nonproportional loading conditions showed a significant life reduction compared with that of proportional loading, and this life reduction was reasonably estimated by taking into account the strain paths along which the strain history is imposed. Furthermore, a marked life reduction was shown to occur under nonproportional loading by imposing a strain hold period at a peak tensile strain. This life reduction was evaluated by the linear damage rule. It was shown to be possible to estimate the fatigue damage and the creep damage under nonproportional loading by a linear damage rule by estimating a stress relaxation behavior by Mises-type equivalent stress or Huddleston-type equivalent stress. (author)

Study of lattice strain evolution during biaxial deformation of stainless steel using a finite element and fast Fourier transform based multi-scale approach

International Nuclear Information System (INIS)

Upadhyay, M.V.; Van Petegem, S.; Panzner, T.; Lebensohn, R.A.; Van Swygenhoven, H.

2016-01-01

A multi-scale elastic-plastic finite element and fast Fourier transform based approach is proposed to study lattice strain evolution during uniaxial and biaxial loading of stainless steel cruciform shaped samples. At the macroscale, finite element simulations capture the complex coupling between applied forces in the arms and gauge stresses induced by the cruciform geometry. The predicted gauge stresses are used as macroscopic boundary conditions to drive a mesoscale elasto-viscoplastic fast Fourier transform model, from which lattice strains are calculated for particular grain families. The calculated lattice strain evolution matches well with experimental values from in-situ neutron diffraction measurements and demonstrates that the spread in lattice strain evolution between different grain families decreases with increasing biaxial stress ratio. During equibiaxial loading, the model reveals that the lattice strain evolution in all grain families, and not just the 311 grain family, is representative of the polycrystalline response. A detailed quantitative analysis of the 200 and 220 grain family reveals that the contribution of elastic and plastic anisotropy to the lattice strain evolution significantly depends on the applied stress ratio.

Experimental studies of yield phenomena in biaxially loaded metals

International Nuclear Information System (INIS)

Hecker, S.S.

1976-01-01

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

Implantable biaxial piezoresistive accelerometer for sensorimotor control.

Science.gov (United States)

Zou, Qiang; Tan, Wei; Sok Kim, Eun; Singh, Jasspreet; Loeb, Gerald E

2004-01-01

This paper describes the design, fabrication and test results of a novel biaxial piezoresistive accelerometer and its incorporation into a miniature neuromuscular stimulator called a BION. Because of its highly symmetric twin mass structure, the X and Z axis acceleration can be measured at the same time and the cross axis sensitivity can be minimized by proper piezoresistor design. The X and Z axis sensitivities of the biaxial accelerometer are 0.10 mV/g/V and 1.40 mV/g/V, respectively, which are further increased to 0.65 mV/g/V and 2.40 mV/g/V, respectively, with extra silicon mass added to the proof mass. The cross-axis sensitivity is less than 3.3% among X, Y and Z-axis. An orientation tracking method for human segments by measuring every joint angle is also discussed in this paper. Joint angles can be obtained by processing the outputs of a pair of biaxial accelerometers (placed very close to the joint axis on the adjacent limb links), without having to integrate acceleration or velocity signals, thereby avoiding errors due to offsets and drift.

Sol-gel deposition of buffer layers on biaxially textured metal substances

Science.gov (United States)

Shoup, Shara S.; Paranthamam, Mariappan; Beach, David B.; Kroeger, Donald M.; Goyal, Amit

2000-01-01

A method is disclosed for forming a biaxially textured buffer layer on a biaxially oriented metal substrate by using a sol-gel coating technique followed by pyrolyzing/annealing in a reducing atmosphere. This method is advantageous for providing substrates for depositing electronically active materials thereon.

The influence of the stress state on Ksub(Ic)

International Nuclear Information System (INIS)

Aurich, D.; Helms, R.; Schmidt, P.; Veith, H.; Ziebs, J.

1977-01-01

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 -100 0 C. 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

Failure of composite plates under static biaxial planar loading

Science.gov (United States)

Waas, Anthony M.; Khamseh, Amir R.

1992-01-01

The project involved detailed investigations into the failure mechanisms in composite plates as a function of hole size (holes centrally located in the plates) under static loading. There were two phases to the project, the first dealing with uniaxial loads along the fiber direction, and the second dealing with coplanar biaxial loading. Results for the uniaxial tests have been reported and published previously, thus this report will place emphasis on the second phase of the project, namely the biaxial tests. The composite plates used in the biaxial loading experiments, as well as the uniaxial, were composed of a single ply unidirectional graphite/epoxy prepreg sandwiched between two layers of transparent thermoplastic. This setup enabled us to examine the failure initiation and propagation modes nondestructively, during the test. Currently, similar tests and analysis of results are in progress for graphite/epoxy cruciform shaped flat laminates. The results obtained from these tests will be available at a later time.

Biaxial testing of canine annulus fibrosus tissue under changing salt concentrations

Directory of Open Access Journals (Sweden)

Jacques M. Huyghe

2010-03-01

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

Material law for concrete under multiaxial stress

International Nuclear Information System (INIS)

Geistefeldt, H.

1977-01-01

In this paper a general triaxial set of finite strain-stress relations is derived, which can include in a step-by-step way nearly all known factors and curves of material response. The finite constitutive equations representing the behavior of concrete are related to the main strain-directions. The elastic part, the functions for uniaxial behavior, those for biaxial response and finally the relation-parts, nonzero only in triaxial stress-state, can be reset separately by suitable functions which have been adjusted to the material response of actual concrete known from special tests. In nonlinear incremental analysis a potential is usually assumed in incremental material behavior to keep incremental stiffness matrices symmetric. If the proposed generalized set of constitutive equations is restricted to special types of functions, the resulting tangent stiffness is symmetric. Special functions for the various parts are presented, the tangent stiffness of which can easily be derived explicitly by partial differentiation of the related strain-stress relations. Thus the application of the proposed constitutive equations in incremental nonlinear analysis is very effective. The free coefficients of one general set of equations are adjusted step by step to the results of Kupfer's biaxial tests under shorttime loading. With a new and very short bixial failure criterion for concrete, which has been stated and compared with test results, the analytic description of the biaxial behavior of Kupfer's concrete is completed. With some additional assumptions the proposed failure criteria and the strain-stress equations for concrete are extended to the biaxial response of uncracked othogonally reinforced concrete response

Method for forming biaxially textured articles by powder metallurgy

Science.gov (United States)

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

2002-01-01

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

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

International Nuclear Information System (INIS)

Foster, J.P.; Gilbert, E.R.

1998-01-01

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

Engineering piezoresistivity using biaxially strained silicon

DEFF Research Database (Denmark)

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

2008-01-01

of the piezocoefficient on temperature and dopant density is altered qualitatively for strained silicon. In particular, we find that a vanishing temperature coefficient may result for silicon with grown-in biaxial tensile strain. These results suggest that strained silicon may be used to engineer the iezoresistivity...

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)

Ando, Kotoji; Takahashi, Koji; Matsuo, Kazuya; Urabe, Yoshio

2013-01-01

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)

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

International Nuclear Information System (INIS)

Pennell, W.E.; Bass, B.R.; Bryson, J.W.; McAfee, W.J.; Theiss, T.J.; Rao, M.C.

1993-01-01

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

Investigation of the Residual Stress State in an Epoxy Based Specimen

DEFF Research Database (Denmark)

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

2015-01-01

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

Stress state in perforated plates

International Nuclear Information System (INIS)

Visner, J.

1977-01-01

The method is described of photoelastic measurement of stress concentration factors (s.c.f) in plates perforated by a square, triangular and diagonal grid of circular holes and loaded by uniaxial or biaxial tensile stress. A loading equipment which was developed and its modifications are described. Stress concentration factors found are compared with theoretical and experimental results given in references. (author)

ANALYSIS OF STRESS-STRAIN STATE OF REINFORCED CONCRETE PLATE AROUND SUPPORT ZONES

Directory of Open Access Journals (Sweden)

Oleg V. Kabantsev

2017-03-01

Full Text Available Structural analysis of the formation and evolution processes of structural microdestruction with the tran-sition to macrorestriction occurring during plastic deformation of masonry under biaxial stresses. The dependencies that determine the amount of the plastic phase of the deformation of masonry. Identified processes and their corre-sponding strength criteria, which play a key role in the implementation phase of plastic deformation. It is shown that plastic deformation of masonry under biaxial stresses occurs when the physical line operation of the basic ma-terials of masonry (brick and mortar. Found that the plastic properties of masonry under biaxial stresses are deter-mined by the processes occurring at the nodes of contact interaction of brick and mortar in horizontal and vertical joints. According to the results of numerical studies the values of the coefficients of ductility of masonry at different variants of mechanical characteristics of brick, mortar and adhesive strength of their interaction.

Stick-slip behavior of Indian gabbro as studied using a NIED large-scale biaxial friction apparatus

Science.gov (United States)

Togo, Tetsuhiro; Shimamoto, Toshihiko; Yamashita, Futoshi; Fukuyama, Eiichi; Mizoguchi, Kazuo; Urata, Yumi

2015-04-01

This paper reports stick-slip behaviors of Indian gabbro as studied using a new large-scale biaxial friction apparatus, built in the National Research Institute for Earth Science and Disaster Prevention (NIED), Tsukuba, Japan. The apparatus consists of the existing shaking table as the shear-loading device up to 3,600 kN, the main frame for holding two large rectangular prismatic specimens with a sliding area of 0.75 m2 and for applying normal stresses σ n up to 1.33 MPa, and a reaction force unit holding the stationary specimen to the ground. The shaking table can produce loading rates v up to 1.0 m/s, accelerations up to 9.4 m/s2, and displacements d up to 0.44 m, using four servocontrolled actuators. We report results from eight preliminary experiments conducted with room humidity on the same gabbro specimens at v = 0.1-100 mm/s and σ n = 0.66-1.33 MPa, and with d of about 0.39 m. The peak and steady-state friction coefficients were about 0.8 and 0.6, respectively, consistent with the Byerlee friction. The axial force drop or shear stress drop during an abrupt slip is linearly proportional to the amount of displacement, and the slope of this relationship determines the stiffness of the apparatus as 1.15 × 108 N/m or 153 MPa/m for the specimens we used. This low stiffness makes fault motion very unstable and the overshooting of shear stress to a negative value was recognized in some violent stick-slip events. An abrupt slip occurred in a constant rise time of 16-18 ms despite wide variation of the stress drop, and an average velocity during an abrupt slip is linearly proportional to the stress drop. The use of a large-scale shaking table has a great potential in increasing the slip rate and total displacement in biaxial friction experiments with large specimens.

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

Science.gov (United States)

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

2014-10-07

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

Slow strain rate stress corrosion cracking under multiaxial deformation conditions: technique and application to admiralty brass

International Nuclear Information System (INIS)

Blanchard, W.K.; Heldt, L.A.; Koss, D.

1984-01-01

A set of straightforward experimental techniques are described for the examination of slow strain rate stress corrosion cracking (SCC) of sheet deforming under nearly all multiaxial deformation conditions which result in sheet thinning. Based on local fracture strain as a failure criterion, the results contrast stress corrosion susceptibility in uniaxial tension with those in both plane strain and balanced biaxial tension. These results indicate that the loss of ductility of the brass increases as the stress state changes from uniaxial toward balanced biaxial tension

The measurement of residual stresses in claddings

International Nuclear Information System (INIS)

Hofer, G.; Bender, N.

1978-01-01

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

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)

Rodriguez-MartInez R; Lugo-Gonzalez E; Urriolagoitia-Calderon G; Urriolagoitia-Sosa G; Hernandez-Gomez L H; Romero-Angeles B; Torres-San Miguel Ch

2011-01-01

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

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

Science.gov (United States)

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

2015-03-01

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

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

International Nuclear Information System (INIS)

Wu, K.; Wang, S.S.; Meng, J.; Han, Z.

2004-01-01

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

Bandgap-customizable germanium using lithographically determined biaxial tensile strain for silicon-compatible optoelectronics.

Science.gov (United States)

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

2015-06-29

Strain engineering has proven to be vital for germanium-based photonics, in particular light emission. However, applying a large permanent biaxial tensile strain to germanium has been a challenge. We present a simple, CMOS-compatible technique to conveniently induce a large, spatially homogenous strain in circular structures patterned within germanium nanomembranes. Our technique works by concentrating and amplifying a pre-existing small strain into a circular region. Biaxial tensile 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 germanium. Our technique allows the amount of biaxial strain to be customized lithographically, allowing the bandgaps of different germanium structures to be independently customized in a single mask process.

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

International Nuclear Information System (INIS)

Pennell, W.E.; Bass, B.R.; Bryson, J.W.; Dickson, T.L.; McAfee, W.J.; Merkle, J.G.

1996-01-01

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

Biaxial mechanical tests in zircaloy-4

International Nuclear Information System (INIS)

Mintzer, S.R.; Bordoni, R.A.A.; Falcone, J.M.

1980-01-01

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.) [es

Effects of repeated biaxial loads on the creep properties of cardinal ligaments.

Science.gov (United States)

Baah-Dwomoh, Adwoa; De Vita, Raffaella

2017-10-01

The cardinal ligament (CL) is one of the major pelvic ligaments providing structural support to the vagina/cervix/uterus complex. This ligament has been studied mainly with regards to its important function in the treatment of different diseases such as surgical repair for pelvic organ prolapse and radical hysterectomy for cervical cancer. However, the mechanical properties of the CL have not been fully determined, despite the important in vivo supportive role of this ligament within the pelvic floor. To advance our limited knowledge about the elastic and viscoelastic properties of the CL, we conducted three consecutive planar equi-biaxial tests on CL specimens isolated from swine. Specifically, the CL specimens were divided into three groups: specimens in group 1 (n = 7) were loaded equi-biaxially to 1 N, specimens in group 2 (n = 8) were loaded equi-biaxially to 2N, and specimens in group 3 (n = 7) were loaded equi-biaxially to 3N. In each group, the equi-biaxial loads of 1N, 2N, or 3N were applied and kept constant for 1200s three times. The two axial loading directions were selected to be the main in-vivo loading direction of the CL and the direction that is perpendicular to it. Using the digital image correlation (DIC) method, the in-plane Lagrangian strains in these two loading directions were measured throughout the tests. The results showed that CL was elastically anisotropic, as statistical differences were found between the mean strains along the two axial loading directions for specimens in group 1, 2, or 3 when the equi-biaxial load reached 1N, 2N, or 3N, respectively. For specimens in group 1 and 2, no statistical differences were detected in the mean normalized strains (or, equivalently, the increase in strain over time) between the two axial loading directions for each creep test. For specimens in group 3, some differences were noted but, by the end of the 3rd creep test, there were no statistical differences in the mean normalized strains between

Strain Measurement System Developed for Biaxially Loaded Cruciform Specimens

Science.gov (United States)

Krause, David L.

2000-01-01

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

Effects of various surface treatments on the biaxial flexural properties of yttria-stabilized zirconia ceramics

Directory of Open Access Journals (Sweden)

Teerthesh Jain

2018-01-01

Conclusions: Air particle abrasion with CoJet Sand, LTD, and CTs had no negative impact on biaxial flexural strength indeed it increased the biaxial flexural strength. Hence, these surface treatments can be done in routine clinical practice to improve the performance of ceramic restorations.

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

Science.gov (United States)

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

2016-06-01

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

Biaxial crystal-based optical tweezers

DEFF Research Database (Denmark)

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

2010-01-01

We suggest an optical tweezer setup based on an optically biaxial crystal. To control movements of opaque particles, we use shifts. The results of experimental studies are reported which are concerned with this laser tweezer setup. We demonstrate a movement of microparticles of toner using...... a 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....

Monitoring Poisson's ratio of glass fiber reinforced composites as damage index using biaxial Fiber Bragg Grating sensors

OpenAIRE

Yılmaz, Çağatay; Yilmaz, Cagatay; Akalın, Çağdaş; Akalin, Cagdas; Kocaman, Esat Selim; Suleman, A.; Yıldız, Mehmet; Yildiz, Mehmet

2016-01-01

Damage accumulation in Glass Fiber Reinforced Polymer (GFRP) composites is monitored based on Poisson's ratio measurements for three different fiber stacking sequences subjected to both quasi-static and quasi-static cyclic tensile loadings. The sensor systems utilized include a dual-extensometer, a biaxial strain gage and a novel embedded-biaxial Fiber Bragg Grating (FBG) sensor. These sensors are used concurrently to measure biaxial strain whereby the evolution of Poisson's ratio as a functi...

Biaxial nominal state of stress at the crack front

International Nuclear Information System (INIS)

Dietmann, H.; Kussmaul, K.

1979-01-01

In fracture toughness testing with CT-specimens there is an unaxial nominal stress state caused by the nominal stress psub(y) perpendicular to the crack surface. This paper investigates the question whether the fracture toughness, or generally speaking, the fracture load, is influenced by additional nominal stresses psub(x) and psub(z) in the crack surface, i.e. by a multiaxial stress state. (orig.)

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

Energy Technology Data Exchange (ETDEWEB)

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

2011-07-19

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

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

International Nuclear Information System (INIS)

Abbassi, Fethi; Mistou, Sebastien; Zghal, Ali

2013-01-01

Highlights: ► Cruciform specimen designed and biaxial tensile test carried out. ► Stereo Correlation Image technique is used for 3D full-filed measurements. ► SEM fractography analysis is used to explain the fracture mechanism. ► Constitutive modeling of the necking phenomenon was developed using GTN model. - Abstract: 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 this experimental investigation, Stereo-Image Correlation technique has is used to produce the heterogeneous deformations map within the specimen surface. Scanning electron microscope is used to evaluate the fracture mechanism and the micro-voids growth. A finite element model of uniaxial and biaxial tensile tests are developed, where a ductile damage model Gurson–Tvergaard–Needleman (GTN) is used to describe material deformation involving damage evolution. Comparison between the experimental and the simulation results show the accuracy of the finite element model to predict the instability phenomenon. The advanced measurement techniques contribute to understand better the ductile fracture mechanism

Discrete Element Simulations and Experiments on the Deformation of Cohesive Powders in a Bi-Axial Box

NARCIS (Netherlands)

Imole, Olukayode Isaiah; Kumar, Nishant; Magnanimo, Vanessa; Luding, Stefan

2012-01-01

We compare element test experiments and simulations on the deformation of frictional, cohesive particles in a bi-axial box. We show that computer simulations with the Discrete Element Method qualitatively reproduce a uniaxial compression element test in the true bi-axial tester. We highlight the

Biaxial vent extruder

International Nuclear Information System (INIS)

Idemoto, A.; Maki, Y.; Oda, N.

1981-01-01

A biaxial vent extruder is described for processing of slurry-like waste fluids or radioactive waste fluids which have a hopper cylinger, a solidifying substance port and a solidified substance port. A plurality of vent cylinders each having a vent port are provided with a plunger type scraper. An extruding cylinder having a single opening for a main screw is connected to the assembled vent cylinders. The main screw extends to the upstream end of the extruding cylinder and a sub-screw extends to the extruding cylinder. The screws each having a full flight engaging the other and a set of rings are mounted on the screws near the respective vent port inlets. The screws are rotated in different directions and inwardly with respect to the vent ports. Rotors may be mounted on the screws to break down solid particles

Efficient Driving of Piezoelectric Transducers Using a Biaxial Driving Technique.

Directory of Open Access Journals (Sweden)

Samuel Pichardo

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

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

Directory of Open Access Journals (Sweden)

Zhao-Xia Tong

2013-01-01

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

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

DEFF Research Database (Denmark)

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

2016-01-01

Poly(L-lactide) (PLLA) in its L-form has promising mechanical properties. Being a semi-crystalline polymer, it can be subjected to strain-induced crystallization at temperatures above Tg and can thereby become oriented. Following a simultaneous (SIM) biaxial strain process or a sequential (SEQ...

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

International Nuclear Information System (INIS)

Itamoto, Masaharu; Kuwabara, Kazumichi; Tanno, Takeo; Nakayama, Yoshiki; Mizuta, Yoshiaki

2007-01-01

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

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

Directory of Open Access Journals (Sweden)

Bandar Mohammed Abdullah Al-Makramani

2010-12-01

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

Shear Piezoelectricity in Poly(vinylidenefluoride-co-trifluoroethylene): Full Piezotensor Coefficients by Molecular Modeling, Biaxial Transverse Response, and Use in Suspended Energy-Harvesting Nanostructures.

Science.gov (United States)

Persano, Luana; Catellani, Alessandra; Dagdeviren, Canan; Ma, Yinji; Guo, Xiaogang; Huang, Yonggang; Calzolari, Arrigo; Pisignano, Dario

2016-09-01

The intrinsic flexible character of polymeric materials causes remarkable strain deformations along directions perpendicular to the applied stress. The biaxial response in the shear piezoelectricity of polyvinylidenefluoride copolymers is analyzed and their full piezoelectric tensors are provided. The microscopic shear is exploited in single suspended nanowires bent by localized loading to couple flexural deformation and transverse piezoelectric response. © 2016 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Numerical analysis of interacting cracks in biaxial stress field

International Nuclear Information System (INIS)

Kovac, M.; Cizelj, L.

1999-01-01

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

Research on Design and Simulation of Biaxial Tensile-Bending Complex Mechanical Performance Test Apparatus

Directory of Open Access Journals (Sweden)

Hailian Li

2017-09-01

Full Text Available In order to realize a micro-mechanic performance test of biaxial tensile-bending-combined loading and solve the problem of incompatibility of test apparatus and observation apparatus, novel biaxial-combined tensile-bending micro-mechanical performance test apparatus was designed. The working principle and major functions of key constituent parts of test apparatus, including the servo drive unit, clamping unit and test system, were introduced. Based on the finite element method, biaxial tensile and tension-bending-combined mechanical performances of the test-piece were studied as guidance to learn the distribution of elastic deformation and plastic deformation of all sites of the test-piece and to better plan test regions. Finally, this test apparatus was used to conduct a biaxial tensile test under different pre-bending loading and a tensile test at different rates; the image of the fracture of the test-piece was acquired by a scanning electron microscope and analyzed. It was indicated that as the pre-bending force rises, the elastic deformation phase would gradually shorten and the slope of the elastic deformation phase curve would slightly rise so that a yield limit would appear ahead of time. Bending speed could exert a positive and beneficial influence on tensile strength but weaken fracture elongation. If bending speed is appropriately raised, more ideal anti-tensile strength could be obtained, but fracture elongation would decline.

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

International Nuclear Information System (INIS)

Bradai, Soumaya

2014-01-01

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

Anomalously temperature-independent birefringence in biaxial optical crystals

International Nuclear Information System (INIS)

Grechin, Sergei G; Dmitriev, Valentin G; Dyakov, Vladimir A; Pryalkin, Vladimir I

2000-01-01

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 160 0 C. (letters to the editor)

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

Energy Technology Data Exchange (ETDEWEB)

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

2016-07-01

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

Uniaxial and biaxial tensioning effects on thin membrane materials. [large space structures

Science.gov (United States)

Hinson, W. F.; Goslee, J. W.

1980-01-01

Thin laminated membranes are being considered for various surface applications on future large space structural systems. Some of the thin membranes would be stretched across or between structural members with the requirement that the membrane be maintained within specified limits of smoothness which would be dictated by the particular applications such as antenna reflector requirements. The multiaxial tensile force required to maintain the smoothness in the membrane needs to be determined for use in the structure design. Therefore, several types of thicknesses of thin membrane materials have been subjected to varied levels of uniaxial and biaxial tensile loads. During the biaxial tests, deviations of the material surface smoothness were measured by a noncontacting capacitance probe. Basic materials consisted of composites of vacuum deposited aluminum on Mylar and Kapton ranging in thickness from 0.00025 in (0.000635 cm) to 0.002 in (0.00508 cm). Some of the material was reinforced with Kevlar and Nomex scrim. The uniaxial tests determined the material elongation and tensile forces up to ultimate conditions. Biaxial tests indicated that a relatively smooth material surface could be achieved with tensile force of approximately 1 to 15 Newtons per centimeter, depending upon the material thickness and/or reinforcement.

Experimental Investigation of the Influence of Confining Stress on Hard Rock Fragmentation Using a Conical Pick

Science.gov (United States)

Li, Xibing; Wang, Shaofeng; Wang, Shanyong

2018-01-01

High geostress is a prominent condition in deep excavations and affects the cuttability of deep hard rock. This study aims to determine the influence of confining stress on hard rock fragmentation as applied by a conical pick. Using a true triaxial test apparatus, static and coupled static and dynamic loadings from pick forces were applied to end faces of cubic rock specimens to break them under biaxial, uniaxial and stress-free confining stress conditions. The cuttability indices (peak pick force, insertion depth and disturbance duration), failure patterns and fragment sizes were measured and compared to estimate the effects of confining stress. The results show that the rock cuttabilities decreased in order from rock breakages under stress-free conditions to uniaxial confining stress and then to biaxial confining stress. Under biaxial confining stress, only flake-shaped fragments were stripped from the rock surfaces under the requirements of large pick forces or disturbance durations. As the level of uniaxial confining stress increased, the peak pick force and the insertion depth initially increased and then decreased, and the failure patterns varied from splitting to partial splitting and then to rock bursts with decreasing average fragment sizes. Rock bursts will occur under elastic compression via ultra-high uniaxial confining stresses. There are two critical uniaxial confining stress levels, namely stress values at which peak pick forces begin to decrease and improve rock cuttability, and those at which rock bursts initially occur and cutting safety decreases. In particular, hard rock is easiest to split safely and efficiently under stress-free conditions. Moreover, coupled static preloading and dynamic disturbance can increase the efficiency of rock fragmentation with increasing preloading levels and disturbance amplitudes. The concluding remarks confirm hard rock cuttability using conical pick, which can improve the applicability of mechanical excavation in

Thermodynamics of diffusion under pressure and stress: Relation to point defect mechanisms

International Nuclear Information System (INIS)

Aziz, M.J.

1997-01-01

A thermodynamic formalism is developed for illuminating the predominant point defect mechanism of self- and impurity diffusion in silicon and is used to provide a rigorous basis for point defect-based interpretation of diffusion experiments in biaxially strained epitaxial layers in the Si endash Ge system. A specific combination of the hydrostatic and biaxial stress dependences of the diffusivity is ±1 times the atomic volume, depending upon whether the predominant mechanism involves vacancies or interstitials. Experimental results for Sb diffusion in biaxially strained Si endash Ge films and ab initio calculations of the activation volume for Sb diffusion by a vacancy mechanism are in quantitative agreement with no free parameters. Key parameters are identified that must be measured or calculated for a quantitative test of interstitial-based mechanisms. copyright 1997 American Institute of Physics

Monitoring Local Changes in Granite Rock Under Biaxial Test: A Spatiotemporal Imaging Application With Diffuse Waves

Science.gov (United States)

Xie, Fan; Ren, Yaqiong; Zhou, Yongsheng; Larose, Eric; Baillet, Laurent

2018-03-01

Diffuse acoustic or seismic waves are highly sensitive to detect changes of mechanical properties in heterogeneous geological materials. In particular, thanks to acoustoelasticity, we can quantify stress changes by tracking acoustic or seismic relative velocity changes in the material at test. In this paper, we report on a small-scale laboratory application of an innovative time-lapse tomography technique named Locadiff to image spatiotemporal mechanical changes on a granite sample under biaxial loading, using diffuse waves at ultrasonic frequencies (300 kHz to 900 kHz). We demonstrate the ability of the method to image reversible stress evolution and deformation process, together with the development of reversible and irreversible localized microdamage in the specimen at an early stage. Using full-field infrared thermography, we visualize stress-induced temperature changes and validate stress images obtained from diffuse ultrasound. We demonstrate that the inversion with a good resolution can be achieved with only a limited number of receivers distributed around a single source, all located at the free surface of the specimen. This small-scale experiment is a proof of concept for frictional earthquake-like failure (e.g., stick-slip) research at laboratory scale as well as large-scale seismic applications, potentially including active fault monitoring.

Effects of monoclinic symmetry on the properties of biaxial liquid crystals

Science.gov (United States)

Solodkov, Nikita V.; Nagaraj, Mamatha; Jones, J. Cliff

2018-04-01

Tilted smectic liquid crystal phases such as the smectic-C phase seen in calamitic liquid crystals are usually treated using the assumption of biaxial orthorhombic symmetry. However, the smectic-C phase has monoclinic symmetry, thereby allowing disassociation of the principal optic and dielectric axes based on symmetry and invariance principles. This is demonstrated here by comparing optical and dielectric measurements for two materials with highly first-order direct transitions from nematic to smectic-C phases. The results show a high difference between the orientations of the principal axes sets, which is interpreted as the existence of two distinct cone angles for optical and dielectric frequencies. Both materials exhibit an increasing degree of monoclinic behavior with decreasing temperature. Due to fast switching speeds, ferroelectric smectic-C* materials are important for fast modulators and LCoS devices, where the dielectric biaxiality influences device operation.

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

International Nuclear Information System (INIS)

Ellis, J.R.; Robinson, D.N.; Pugh, C.E.

1978-01-01

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

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

International Nuclear Information System (INIS)

Stout, M.G.; Hecker, S.S.; Bourcier, R.

1983-01-01

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

Film stresses and electrode buckling in organic solar cells

KAUST Repository

Brand, Vitali; Levi, Kemal; McGehee, Michae D.; Dauskardt, Reinhold H.

2012-01-01

We investigate the film stresses that develop in the polymer films and metal electrodes of poly(3-hexyl thiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM) bulk heterojunction (BHJ) organic solar cells. A compressive biaxial

Stresses in sulfuric acid anodized coatings on aluminum

Science.gov (United States)

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

1993-01-01

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

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

Science.gov (United States)

Sebastián, Nerea; López, David Orencio; Diez-Berart, Sergio; de la Fuente, María Rosario; Salud, Josep; Pérez-Jubindo, Miguel Angel; Ros, María Blanca

2011-01-01

In this work, a study of the nematic (N)–isotropic (I) phase transition has been made in a series of odd non-symmetric liquid crystal dimers, the α-(4-cyanobiphenyl-4’-yloxy)-ω-(1-pyrenimine-benzylidene-4’-oxy) alkanes, by means of accurate calorimetric and dielectric measurements. These materials are potential candidates to present the elusive biaxial nematic (NB) phase, as they exhibit both molecular biaxiality and flexibility. According to the theory, the uniaxial nematic (NU)–isotropic (I) phase transition is first-order in nature, whereas the NB–I phase transition is second-order. Thus, a fine analysis of the critical behavior of the N–I phase transition would allow us to determine the presence or not of the biaxial nematic phase and understand how the molecular biaxiality and flexibility of these compounds influences the critical behavior of the N–I phase transition. PMID:28824100

Effect of metal chloride solutions on coloration and biaxial flexural strength of yttria-stabilized zirconia

Science.gov (United States)

Oh, Gye-Jeong; Lee, Kwangmin; Lee, Doh-Jae; Lim, Hyun-Pil; Yun, Kwi-Dug; Ban, Jae-Sam; Lee, Kyung-Ku; Fisher, John G.; Park, Sang-Won

2012-10-01

The effect of three kinds of transition metal dopants on the color and biaxial flexural strength of zirconia ceramics for dental applications was evaluated. Presintered zirconia discs were colored through immersion in aqueous chromium, molybdenum and vanadium chloride solutions and then sintered at 1450 °C. The color of the doped specimens was measured using a digital spectrophotometer. For biaxial flexural strength measurements, specimens infiltrated with 0.3 wt% of each aqueous chloride solution were used. Uncolored discs were used as a control. Zirconia specimens infiltrated with chromium, molybdenum and vanadium chloride solutions were dark brown, light yellow and dark yellow, respectively. CIE L*, a*, and b* values of all the chromium-doped specimens and the specimens infiltrated with 0.1 wt% molybdenum chloride solution were in the range of values for natural teeth. The biaxial flexural strengths of the three kinds of metal chloride groups were similar to the uncolored group. These results suggest that chromium and molybdenum dopants can be used as colorants to fabricate tooth colored zirconia ceramic restorations.

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

International Nuclear Information System (INIS)

Low, Sze-Hsien; Lau, Gih-Keong

2014-01-01

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 Vμm −1 ). (paper)

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)

Fissolo, A.; Gourdin, C.; Bouin, P.; Perez, G.

2010-01-01

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)

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

CERN Document Server

Li Peng; Mazumder, J

2003-01-01

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

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

International Nuclear Information System (INIS)

Rupil, J.

2012-01-01

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) [fr

Biaxially stretchable supercapacitors based on the buckled hybrid fiber electrode array

Science.gov (United States)

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

2015-07-01

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

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

Energy Technology Data Exchange (ETDEWEB)

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

2015-09-28

Stanene, a graphene like two dimensional honeycomb structure of tin has attractive features in electronics application. In this study, we performed molecular dynamics simulations using modified embedded atom method potential to investigate mechanical properties of stanene. We studied the effect of temperature and strain rate on mechanical properties of α-stanene for both uniaxial and biaxial loading conditions. Our study suggests that with the increasing temperature, both the fracture strength and strain of the stanene decrease. Uniaxial loading in zigzag direction shows higher fracture strength and strain compared to the armchair direction, while no noticeable variation in the mechanical properties is observed for biaxial loading. We also found at a higher loading rate, material exhibits higher fracture strength and strain. These results will aid further investigation of stanene as a potential nano-electronics substitute.

A novel constrained H2 optimization algorithm for mechatronics design in flexure-linked biaxial gantry.

Science.gov (United States)

Ma, Jun; Chen, Si-Lu; Kamaldin, Nazir; Teo, Chek Sing; Tay, Arthur; Mamun, Abdullah Al; Tan, Kok Kiong

2017-11-01

The biaxial gantry is widely used in many industrial processes that require high precision Cartesian motion. The conventional rigid-link version suffers from breaking down of joints if any de-synchronization between the two carriages occurs. To prevent above potential risk, a flexure-linked biaxial gantry is designed to allow a small rotation angle of the cross-arm. Nevertheless, the chattering of control signals and inappropriate design of the flexure joint will possibly induce resonant modes of the end-effector. Thus, in this work, the design requirements in terms of tracking accuracy, biaxial synchronization, and resonant mode suppression are achieved by integrated optimization of the stiffness of flexures and PID controller parameters for a class of point-to-point reference trajectories with same dynamics but different steps. From here, an H 2 optimization problem with defined constraints is formulated, and an efficient iterative solver is proposed by hybridizing direct computation of constrained projection gradient and line search of optimal step. Comparative experimental results obtained on the testbed are presented to verify the effectiveness of the proposed method. Copyright © 2017 ISA. Published by Elsevier Ltd. All rights reserved.

Stabilisation problem in biaxial platform

Directory of Open Access Journals (Sweden)

Lindner Tymoteusz

2016-12-01

Full Text Available The article describes investigation of rolling ball stabilization problem on a biaxial platform. The aim of the control system proposed here is to stabilize ball moving on a plane in equilibrium point. The authors proposed a control algorithm based on cascade PID and they compared it with another control method. The article shows the results of the accuracy of ball stabilization and influence of applied filter on the signal waveform. The application used to detect the ball position measured by digital camera has been written using a cross platform .Net wrapper to the OpenCV image processing library - EmguCV. The authors used the bipolar stepper motor with dedicated electronic controller. The data between the computer and the designed controller are sent with use of the RS232 standard. The control stand is based on ATmega series microcontroller.

Stabilisation problem in biaxial platform

Science.gov (United States)

Lindner, Tymoteusz; Rybarczyk, Dominik; Wyrwał, Daniel

2016-12-01

The article describes investigation of rolling ball stabilization problem on a biaxial platform. The aim of the control system proposed here is to stabilize ball moving on a plane in equilibrium point. The authors proposed a control algorithm based on cascade PID and they compared it with another control method. The article shows the results of the accuracy of ball stabilization and influence of applied filter on the signal waveform. The application used to detect the ball position measured by digital camera has been written using a cross platform .Net wrapper to the OpenCV image processing library - EmguCV. The authors used the bipolar stepper motor with dedicated electronic controller. The data between the computer and the designed controller are sent with use of the RS232 standard. The control stand is based on ATmega series microcontroller.

On the field-induced switching of molecular organization in a biaxial nematic cell and its relaxation

Science.gov (United States)

Ricci, Matteo; Berardi, Roberto; Zannoni, Claudio

2015-08-01

We investigate the switching of a biaxial nematic filling a flat cell with planar homogeneous anchoring using a coarse-grained molecular dynamics simulation. We have found that an aligning field applied across the film, and acting on specific molecular axes, can drive the reorientation of the secondary biaxial director up to one order of magnitude faster than that for the principal director. While the π/2 switching of the secondary director does not affect the alignment of the long molecular axes, the field-driven reorientation of the principal director proceeds via a concerted rotation of the long and transversal molecular axes. More importantly, while upon switching off a (relatively) weak or intermediate field, the biaxial nematic liquid crystal is always able to relax to the initial surface aligned director state; this is not the case when using fields above a certain threshold. In that case, while the secondary director always recovers the initial state, the principal one remains, occasionally, trapped in a nonuniform director state due to the formation of domain walls.

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

Data.gov (United States)

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

Effect of surface acid etching on the biaxial flexural strength of two hot-pressed glass ceramics.

Science.gov (United States)

Hooshmand, Tabassom; Parvizi, Shaghayegh; Keshvad, Alireza

2008-07-01

The purpose of this study was to assess the effect of surface acid etching on the biaxial flexural strength of two hot-pressed glass ceramics reinforced by leucite or lithium disilicate crystals. Forty glass ceramic disks (14-mm diameter, 2-mm thick) consisting of 20 leucite-based ceramic disks (IPS Empress) and 20 lithia disilicate-based ceramic (IPS Empress 2) were produced by hot-pressing technique. All specimens were polished and then cleaned ultrasonically in distilled water. Ten specimens of each ceramic group were then etched with 9% hydrofluoric (HF) acid gel for 2 minutes and cleaned ultrasonically again. The biaxial flexural strength was measured by the piston-on-three-ball test in a universal testing machine. Data based on ten specimens in each group were analyzed by two-way ANOVA (alpha= 0.05). Microstructure of ceramic surfaces before and after acid etching was also examined by a scanning electron microscope. The mean biaxial flexural strength values for each group tested were (in MPa): nonetched IPS Empress = 118.6 +/- 25.5; etched IPS Empress = 102.9 +/- 15.4; nonetched IPS Empress 2 = 283.0 +/- 48.5; and etched IPS Empress 2 = 250.6 +/- 34.6. The results showed that the etching process reduced the biaxial flexural strengths significantly for both ceramic types (p= 0.025). No significant interaction between the ceramic type and etching process was found (p= 0.407). From the results, it was concluded that surface HF acid etching could have a weakening effect on hot-pressed leucite or lithia disilicate-based glass ceramic systems.

Experiment to measure the effects of biaxial strain on the critical current of NbTi superconductor

International Nuclear Information System (INIS)

Froelich, K.J.

1975-01-01

Twisted multifilament, copper-clad NbTi superconductors have been axially and biaxially strained at 4.2K with a 7.5T background field. A simply-constructed cryogenic loading frame was built and used to strain the conductor. Results on 1.27 mm x 3.13 mm conductor have shown that degradation of less than .3 percent of critical current occurred when the wire was biaxially strained to +3260 μepsilon in the axial direction and -1875 μepsilon in the transverse direction. Degradation approaches 3 percent of critical current at approximately 6000 μepsilon in the axial direction only

Insertion Testing of Polyethylene Glycol Microneedle Array into Cultured Human Skin with Biaxial Tension

Science.gov (United States)

Takano, Naoki; Tachikawa, Hiroto; Miyano, Takaya; Nishiyabu, Kazuaki

Aiming at the practical use of polyethylene glycol (PEG) microneedles for transdermal drug delivery system (DDS), a testing apparatus for their insertion into cultured human skin has been developed. To simulate the variety of conditions of human skin, biaxial tension can be applied to the cultured human skin. An adopted testing scheme to apply and control the biaxial tension is similar to the deep-draw forming technique. An attention was also paid to the short-time setup of small, thin and wet cultured skin. One dimensional array with four needles was inserted and influence of tension was discussed. It was found that tension, deflection of skin during insertion and original curvature of skin are the important parameters for microneedles array design.

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

International Nuclear Information System (INIS)

Priddy, T.G.; Benzley, S.E.; Ford, L.M.

1980-01-01

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

Biaxially textured articles formed by powder metallurgy

Science.gov (United States)

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

2003-07-29

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

Biaxially textured articles formed by power metallurgy

Science.gov (United States)

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

2003-08-26

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

Biaxially textured articles formed by powder metallurgy

Science.gov (United States)

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

2003-08-05

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

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

Directory of Open Access Journals (Sweden)

V. Chaves

2014-10-01

Full Text Available 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 σ-τ. The elliptical quadrant, appropriate for ductile materials, and the elliptical arc, appropriate for fragile materials, were included in the graph. The experimental values were better fitted with an elliptical quadrant, despite the ratio between the pure torsion and tension fatigue limits, τFL/σFL, is 0.91, close to 1, which is a typical value for fragile materials. The crack direction along the surface has been analyzed by using a microscope, with especial attention to the crack initiation zones. The crack direction during the Stage I has been compared with theoretical models.

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

Science.gov (United States)

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

2016-06-01

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

Experimental evidence for stress enhanced swelling

International Nuclear Information System (INIS)

Bates, J.F.; Gilbert, E.R.

1976-01-01

Experimental evidence is presented which shows that the application of a biaxial stress during irradiation can increase the magnitude of irradiation-induced swelling observed in tubular specimens. It is shown that this increase in swelling is linear below the proportional elastic limit of the material and decreases above this value of stress. In the linear region a relationship is found between total swelling and stress free swelling. The phenomenon of reduced swelling is evaluated on the basis of increased cold work due to pre-irradiation straining. This analysis yields a relationship of dislocation density proportional to stress to the 3.82 power. Additional analyses using dislocation density proportional to sigma 2 (sigma = hoop stress) yield a similar but sharper decrease in swelling after the proportional elastic limit is reached. (Auth.)

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)

Aubin, V

2001-11-15

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

Time-dependent strains and stresses in a pumpkin balloon

Science.gov (United States)

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

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 distributions 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 gore material the em hoop strains increase and the em meridional stresses decrease whereas the em 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

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

DEFF Research Database (Denmark)

Benallal, A.; Tvergaard, Viggo

1998-01-01

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

Most effective way to improve the hydrogen storage abilities of Na-decorated BN sheets: applying external biaxial strain and an electric field.

Science.gov (United States)

Tang, Chunmei; Zhang, Xue; Zhou, Xiaofeng

2017-02-15

Density functional calculations were used to investigate the hydrogen storage abilities of Na-atoms-decorated BN sheets under both external biaxial strain and a vertical electric field. The Na atom generally has the weakest binding strength to a given substrate compared with the other elements in the periodic table [PANS, 2016, 113, 3735]. Consequently, it is understudied in comparison to other elements and there are few reports about the hydrogen storage abilities of Na-decorated nanomaterials. We calculated that the average binding energy (E b ) of Na atoms to the pure BN sheet is 1.08 eV, which is smaller than the cohesive energy of bulk Na (1.11 eV). However, the E b can be increased to 1.15 eV under 15% biaxial strain, and further up to 1.53 eV with the control of both 15% biaxial strain and a 5.14 V nm -1 electric field (E-field). Therefore, the application of biaxial strain and an external upward E-field can prevent clustering of the Na atoms on the surface of a BN sheet, which is crucial for the hydrogen storage. Each Na atom on the surface of a BN sheet can adsorb only one H 2 molecule when no strain or E-field is applied; however, the absorption increases to five H 2 molecules under 15% biaxial strain and six H 2 molecules under both 15% biaxial strain combined with a 5.14 V nm -1 E-field. The average adsorption energies for H 2 of BN-(Na-mH 2 ) (m = 1-6) are within the range of practical applications (0.2-0.6 eV). The hydrogen gravimetric density of the periodic BN-(Na-6H 2 ) 4 structure is 9 wt%, which exceeds the 5.5 wt% value that should be met by 2017 as specified by the US Department of Energy. On the other side, removal of the biaxial strain and E-field can help to desorb the H 2 molecule. These findings suggest a new route to design hydrogen storage materials under near-ambient conditions.

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

International Nuclear Information System (INIS)

Dimelfi, R.J.

1987-01-01

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.)

New classes of bi-axially symmetric solutions to four-dimensional Vasiliev higher spin gravity

Energy Technology Data Exchange (ETDEWEB)

Sundell, Per; Yin, Yihao [Departamento de Ciencias Físicas, Universidad Andres Bello,Republica 220, Santiago de Chile (Chile)

2017-01-11

We present new infinite-dimensional spaces of bi-axially symmetric asymptotically anti-de Sitter solutions to four-dimensional Vasiliev higher spin gravity, obtained by modifications of the Ansatz used in https://arxiv.org/abs/1107.1217, which gave rise to a Type-D solution space. The current Ansatz is based on internal semigroup algebras (without identity) generated by exponentials formed out of the bi-axial symmetry generators. After having switched on the vacuum gauge function, the resulting generalized Weyl tensor is given by a sum of generalized Petrov type-D tensors that are Kerr-like or 2-brane-like in the asymptotic AdS{sub 4} region, and the twistor space connection is smooth in twistor space over finite regions of spacetime. We provide evidence for that the linearized twistor space connection can be brought to Vasiliev gauge.

Non-monotonic probability of thermal reversal in thin-film biaxial nanomagnets with small energy barriers

Directory of Open Access Journals (Sweden)

N. Kani

2017-05-01

Full Text Available The goal of this paper is to investigate the short time-scale, thermally-induced probability of magnetization reversal for an biaxial nanomagnet that is characterized with a biaxial magnetic anisotropy. For the first time, we clearly show that for a given energy barrier of the nanomagnet, the magnetization reversal probability of an biaxial nanomagnet exhibits a non-monotonic dependence on its saturation magnetization. Specifically, there are two reasons for this non-monotonic behavior in rectangular thin-film nanomagnets that have a large perpendicular magnetic anisotropy. First, a large perpendicular anisotropy lowers the precessional period of the magnetization making it more likely to precess across the x^=0 plane if the magnetization energy exceeds the energy barrier. Second, the thermal-field torque at a particular energy increases as the magnitude of the perpendicular anisotropy increases during the magnetization precession. This non-monotonic behavior is most noticeable when analyzing the magnetization reversals on time-scales up to several tens of ns. In light of the several proposals of spintronic devices that require data retention on time-scales up to 10’s of ns, understanding the probability of magnetization reversal on the short time-scales is important. As such, the results presented in this paper will be helpful in quantifying the reliability and noise sensitivity of spintronic devices in which thermal noise is inevitably present.

Mechanical properties of biaxially strained poly(L-lactide) tubes: Strain rate and temperature dependence

DEFF Research Database (Denmark)

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

2017-01-01

Poly(l-lactide) (PLLA) is a bioabsorbable polymer with high stiffness and strength compared to the other commercially available bioabsorbable polymers. The properties of PLLA can be improved by straining, causing deformation-mediated molecular orientation. PLLA tubes were biaxially strained above...

Chaos synchronization in bi-axial magnets modeled by Bloch equation

International Nuclear Information System (INIS)

Moukam Kakmeni, F.M.; Nguenang, J.P.; Kofane, T.C.

2005-10-01

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)

Equi-biaxial loading effect on austenitic stainless steel fatigue life

Directory of Open Access Journals (Sweden)

C. Gourdin

2016-10-01

Full Text Available Fatigue lifetime assessment is essential in the design of structures. Under-estimated predictions may result in unnecessary in service inspections. Conversely, over-estimated predictions may have serious consequences on the integrity of structures. In some nuclear power plant components, the fatigue loading may be equibiaxial because of thermal fatigue. So the potential impact of multiaxial loading on the fatigue life of components is a major concern. Meanwhile, few experimental data are available on austenitic stainless steels. It is essential to improve the fatigue assessment methodologies to take into account the potential equi-biaxial fatigue damage. Hence this requires obtaining experimental data on the considered material with a strain tensor in equibiaxial tension. Two calibration tests (with strain gauges and image correlation were used to obtain the relationship between the imposed deflection and the radial strain on the FABIME2 specimen. A numerical study has confirmed this relationship. Biaxial fatigue tests are carried out on two austenitic stainless steels for different values of the maximum deflection, and with a load ratio equal to -1. The interpretation of the experimental results requires the use of an appropriate definition of strain equivalent. In nuclear industry, two kinds of definition are used: von Mises and TRESCA strain equivalent. These results have permitted to estimate the impact of the equibiaxiality on the fatigue life of components

Modeling of CMUTs with Multiple Anisotropic Layers and Residual Stress

DEFF Research Database (Denmark)

Engholm, Mathias; Thomsen, Erik Vilain

2014-01-01

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....

The impact of hydrofluoric acid etching followed by unfilled resin on the biaxial strength of a glass-ceramic.

Science.gov (United States)

Posritong, Sumana; Borges, Alexandre Luiz Souto; Chu, Tien-Min Gabriel; Eckert, George J; Bottino, Marco A; Bottino, Marco C

2013-11-01

To evaluate the null hypotheses that hydrofluoric (HF) acid etching time would neither decrease the biaxial flexural strength of a glass-based veneering ceramic nor enhance it after silane and unfilled resin (UR) applications. Disc-shaped IPS e.max ZirPress specimens were allocated into 12 groups: G1-control (no-etching), G2-30 s, G3-60 s, G4-90 s, G5-120 s, G6-60 s+60 s. Groups (G7-G12) were treated in the same fashion as G1-G6, but followed by silane and UR applications. Surface morphology and roughness (Ra and Rq) of the ceramics were assessed by means of scanning electron microscopy (SEM) and profilometry, respectively. Flexural strength was determined by biaxial testing. Data were analyzed by two-way ANOVA and the Sidak test (α=0.05). Weibull statistics were estimated and finite element analysis (FEA) was carried out to verify the stress concentration end areas of fracture. The interaction (etching time vs. surface treatment) was significant for Ra (p=0.008) and Rq (0.0075). Resin-treated groups presented significantly lower Ra and Rq than non-treated groups, except for the 60s group (pceramic microstructure and that the UR was able to penetrate into the irregularities. A significant effect of etching time (p=0.029) on flexural strength was seen. G7-G12 presented higher strength than G1-G6 (pceramic flexural strength. Moreover, the flexural strength could be enhanced after UR treatment. Copyright © 2013 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

A study of extracellular matrix remodeling in aortic heart valves using a novel biaxial stretch bioreactor.

Science.gov (United States)

Lei, Ying; Masjedi, Shirin; Ferdous, Zannatul

2017-11-01

In aortic valves, biaxial cyclic stretch is known to modulate cell differentiation, extracellular matrix (ECM) synthesis and organization. We designed a novel bioreactor that can apply independent and precise stretch along radial and circumferential directions in a tissue culture environment. While this bioreactor can be used for either native or engineered tissues, this study determined matrix remodeling and strain distribution of aortic cusps after culturing under biaxial stretch for 14 days. The contents of collagen and glycosaminoglycans were determined using standard biochemical assays and compared with fresh controls. Strain fields in static cusps were more uniform than those in stretched cusps, which indicated degradation of the ECM fibers. The glycosaminoglycan content was significantly elevated in the static control as compared to fresh or stretched cusps, but no difference was observed in collagen content among the groups. The strain profile of freshly isolated fibrosa vs. ventricularis and left, right, and noncoronary cusps were also determined by Digital Image Correlation technique. Distinct strain patterns were observed under stretch on fibrosa and ventricularis sides and among the three cusps. This work highlights the critical role of the anisotropic ECM structure for proper functions of native aortic valves and the beneficial effects of biaxial stretch for maintenance of the native ECM structure. Copyright © 2017 Elsevier Ltd. All rights reserved.

Biaxial mechanics and inter-lamellar shearing of stem-cell seeded electrospun angle-ply laminates for annulus fibrosus tissue engineering.

Science.gov (United States)

Driscoll, Tristan P; Nakasone, Ryan H; Szczesny, Spencer E; Elliott, Dawn M; Mauck, Robert L

2013-06-01

The annulus fibrosus (AF) of the intervertebral disk plays a critical role in vertebral load transmission that is heavily dependent on the microscale structure and composition of the tissue. With degeneration, both structure and composition are compromised, resulting in a loss of AF mechanical function. Numerous tissue engineering strategies have addressed the issue of AF degeneration, but few have focused on recapitulation of AF microstructure and function. One approach that allows for generation of engineered AF with appropriate (+/-)30° lamellar microstructure is the use of aligned electrospun scaffolds seeded with mesenchymal stem cells (MSCs) and assembled into angle-ply laminates (APL). Previous work indicates that opposing lamellar orientation is necessary for development of near native uniaxial tensile properties. However, most native AF tensile loads are applied biaxially, as the disk is subjected to multi-axial loads and is constrained by its attachments to the vertebral bodies. Thus, the objective of this study was to evaluate the biaxial mechanical response of engineered AF bilayers, and to determine the importance of opposing lamellar structure under this loading regime. Opposing bilayers, which replicate native AF structure, showed a significantly higher modulus in both testing directions compared to parallel bilayers, and reached ∼60% of native AF biaxial properties. Associated with this increase in biaxial properties, significantly less shear, and significantly higher stretch in the fiber direction, was observed. These results provide additional insight into native tissue structure-function relationships, as well as new benchmarks for engineering functional AF tissue constructs. Copyright © 2013 Orthopaedic Research Society.

Light propagation in a magneto-optical hyperbolic biaxial crystal

Science.gov (United States)

Kuznetsov, Evgeniy V.; Merzlikin, Alexander M.

2017-12-01

The light propagation through a magneto-optical hyperbolic biaxial crystal is investigated. Magnetization of the structure results in splitting and reconnection of an isofrequency near the self-intersection point and thus it leads to the disappearance of conical refraction in a crystal. In its turn the isofrequency splitting leads to band gap opening and makes it possible to steer the beam. These effects allow to control the light propagation by means of an external magnetostatic field. The Poynting's vector distribution in the crystal is calculated by means of a Fourier transform in order to demonstrate the aforementioned effects.

On the Landau-de Gennes Elastic Energy of a Q-Tensor Model for Soft Biaxial Nematics

Science.gov (United States)

Mucci, Domenico; Nicolodi, Lorenzo

2017-12-01

In the Landau-de Gennes theory of liquid crystals, the propensities for alignments of molecules are represented at each point of the fluid by an element Q of the vector space S_0 of 3× 3 real symmetric traceless matrices, or Q-tensors. According to Longa and Trebin (1989), a biaxial nematic system is called soft biaxial if the tensor order parameter Q satisfies the constraint tr(Q^2) = {const}. After the introduction of a Q-tensor model for soft biaxial nematic systems and the description of its geometric structure, we address the question of coercivity for the most common four-elastic-constant form of the Landau-de Gennes elastic free-energy (Iyer et al. 2015) in this model. For a soft biaxial nematic system, the tensor field Q takes values in a four-dimensional sphere S^4_ρ of radius ρ ≤ √{2/3} in the five-dimensional space S_0 with inner product = tr(QP). The rotation group it{SO}(3) acts orthogonally on S_0 by conjugation and hence induces an action on S^4_ρ \\subset {S}_0. This action has generic orbits of codimension one that are diffeomorphic to an eightfold quotient S^3/H of the unit three-sphere S^3, where H={± 1, ± i, ± j, ± k} is the quaternion group, and has two degenerate orbits of codimension two that are diffeomorphic to the projective plane RP^2. Each generic orbit can be interpreted as the order parameter space of a constrained biaxial nematic system and each singular orbit as the order parameter space of a constrained uniaxial nematic system. It turns out that S^4_ρ is a cohomogeneity one manifold, i.e., a manifold with a group action whose orbit space is one-dimensional. Another important geometric feature of the model is that the set Σ _ρ of diagonal Q-tensors of fixed norm ρ is a (geodesic) great circle in S^4_ρ which meets every orbit of S^4_ρ orthogonally and is then a section for S^4_ρ in the sense of the general theory of canonical forms. We compute necessary and sufficient coercivity conditions for the elastic energy by

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

International Nuclear Information System (INIS)

Lundholm, Beatrice

2000-11-01

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

Dynamic strain aging of zircaloy-4 PWR fuel cladding in biaxial stress state

International Nuclear Information System (INIS)

Park, Ki Seong; Lee, Byong Whi

1989-01-01

The expanding copper mandrel test performed at three strain rates (3.2x10E-5/s,2.0x10E-6/s and 1.2x10E-7/s) over 553-873 K temperature range by varying the heating rates (8-10deg C/s,1-2deg C/s and 0.5deg C/s) in air and in vacuum (5x10E-5 torr). The yield stress peak, the strain rate sensitivity minimum and the activation volume peaks could be explained in terms of the dynamic strain aging. The activation energy for dynamic strain aging obtained from the yield stress peak temperature and strain rate was 196 KJ/mol and this value was in good agreement with the activation energy for oxygen diffusion in α-zirconium and Zircaloy-2 (207-220KJ/mol). Therefore, oxygen atoms are responsible for the dynamic strain aging which appeared between 573K and 673K. The yield stress increase due to the oxidation was obtained by comparing the yield stress in air with that in vacuum and represented by the percentage increase of yield stress (σ y a -σ y v /σ y v ). The slower the strain rate, the greater the percentage increase occurs. In order to estimate the yield stress of PWR fuel cladding material under the service environment, the yield stress in water was obtained by comparing the oxidation rate in air that in water assuming the relationship between the oxygen pick-up amount and the yield stress increase. (Author)

Correlation of 0.67um scatter with local stress in Ge impacted with the modified Cambridge liquid jet device

Science.gov (United States)

Wilson, Michael; Price, D.; Strohecker, Steve

1994-09-01

Germanium witness samples were impacted with the NAWCADWAR modified Cambridge liquid jet device introducing varying levels of damage about the center of each sample. Surface damage statistics were collected, scatter measurements were made at 0.67 micrometers and the samples were failed in tension using a bi-axial flexure test setup. The level and character of the damage was correlated with the reflected scatter measurements as a function of local stress and flaw size distribution. Bi-axial flexure data was analyzed to predict fracture stress and the probability of failure of the germanium samples. The mechanical data were then correlated with the scatter data in order to correlate the BRDF with the material failure. The BRDF measurements were taken in several different orientations in order to study the differences in scatter character for the in-plane and out-of-plane conditions.

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

International Nuclear Information System (INIS)

Hubert, Olivier; Daniel, Laurent

2011-01-01

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

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

International Nuclear Information System (INIS)

Aubin, V.

2001-11-01

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)

Creep-fatigue life property of FBR high-temperature structural materials under tension-torsion loading and life evaluation method

International Nuclear Information System (INIS)

Ogata, Takashi; Nitta, Akito

1994-01-01

Creep-fatigue damage in high temperature structural components in a FBR progress under multiaxial stress condition depending on their operating conditions and configuration. Therefore, multiaxial stress effects on creep-fatigue damage evolution must be clarified to make precise creep-fatigue damage evaluation of these components. In this study, creep-fatigue tests in FBR high temperature materials such as SUS304, 316FR stainless steels and a modified 9Cr steel were conducted under biaxial stress subjecting tension-compression and torsion loading, in order to examine biaxial stress effects on failure mechanism and life property, and to discuss creep-fatigue life evaluation methods under biaxial stress. Main results obtained in this study are summarized as follows: 1. The main cracks under cyclic torsion loading propagated by shear mode in three materials. But intergranular failure was occurred in SUS304 and 316FR, and transgranular failure was observed in Mod.9Cr steel. 2. Nonlinear damage accumulation model proposed based on uniaxial creep-fatigue test results was extended to apply for creep-fatigue damage evaluation under biaxial stress state by considering the biaxial stress effects on fatigue and creep damage evolution. 3. It was confirmed that creep-fatigue life under biaxial stress could be predicted by the extended evaluation method with higher accuracy than existing methods. (author)

Computer program for stresses and buckling of heated composite-stiffened panels and other structures (BUCLASP 3)

Science.gov (United States)

Viswanathan, A. V.; Tamekuni, M.; Tripp, L. L.

1974-01-01

General-purpose program is intended for thermal stress and instability analyses of structures such as axially-stiffened curved panels. Two types of instability analyses can be effected by program: (1) thermal buckling with temperature variation as specified and (2) buckling due to in-plane biaxial loading.

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

Science.gov (United States)

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

2013-05-01

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

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

Science.gov (United States)

Chen, Tien-Chi; Yu, Chih-Hsien

2009-07-01

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

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

LENUS (Irish Health Repository)

2011-05-01

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

Dependence of the optical conductivity on the uniaxial and biaxial strains in black phosphorene

Science.gov (United States)

Yang, C. H.; Zhang, J. Y.; Wang, G. X.; Zhang, C.

2018-06-01

By using the Kubo formula, the optical conductivity of strained black phosphorene was studied. The anisotropic band dispersion gives rise to an orientation dependent optical conductivity. The energy gap can be tuned by the uniaxial and biaxial strains which can be observed from the interband optical conductivity polarized along the armchair (x ) direction. The preferential conducting direction is along the x direction. The dependence of the intraband optical conductivity along the zigzag (y ) direction on the Fermi energy and strain exhibits increasing or decreasing monotonously. However, along the x direction this dependence is complicated which originates from the carriers' inverse-direction movements obtained by two types of the nearest phosphorus atom interactions. The modification of the biaxial strain on the energy structure and optical-absorption property is more effective. The imaginary part of the total optical conductivity (Im σ ) can be negative around the threshold of the interband optical transition by modifying the chemical potential. Away from this frequency region, Im σ exhibits positive value. It can be used in the application of the surface plasmon propagations in multilayer dielectric structures.

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

Directory of Open Access Journals (Sweden)

Belinda Pingguan-Murphy

2012-08-01

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

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

International Nuclear Information System (INIS)

Gaboriaud, R.J.; Paumier, F.; Lacroix, B.

2014-01-01

This work studies the effects of the deposition parameters on the microstructure and the related residual stress in a rare earth oxide thin film. This study is focused on the yttrium sesquioxide (Y 2 O 3 ) thin films deposited on Si (100) substrates using the ion beam sputtering technique. This technique allows the control of the microstructure and the related residual stress in the thin films by monitoring the energy of the argon beam used in the deposition process. Measurements of the stresses within the oxide layer were performed by the X-ray diffraction-sin 2 Ψ method. The results show that the classic model of a pure biaxial in-plane model of stress, generally proposed in thin films, is not satisfying. A model that includes a hydrostatic stress due to the crystalline defects generated during the deposition process and a biaxial stress called a fixation stress, gives a good agreement with the experimental results. This modeling of the residual stress, based on nanometer-scale inclusions (point, extended defects) inducing a hydrostatic stress field, leads to a quantitative analysis of the nature and the concentration of the defects. This work shows results that establish a relationship between residual stress, defects and non-equilibrium phase stabilization during growth. - Highlights: • Microstructure of Y 2 O 3 thin films • Measurements of residual stresses in the thin films • Modeling of a triaxial residual stress state • Stress-induced stabilization of non-equilibrium phase

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

International Nuclear Information System (INIS)

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

1977-11-01

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

Nondestructive measurement of esophageal biaxial mechanical properties utilizing sonometry

Science.gov (United States)

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

2016-07-01

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

The influence of quench sensitivity on residual stresses in the aluminium alloys 7010 and 7075

International Nuclear Information System (INIS)

Robinson, J.S.; Tanner, D.A.; Truman, C.E.; Paradowska, A.M.; Wimpory, R.C.

2012-01-01

The most critical stage in the heat treatment of high strength aluminium alloys is the rapid cooling necessary to form a supersaturated solid solution. A disadvantage of quenching is that the thermal gradients can be sufficient to cause inhomogeneous plastic deformation which in turn leads to the development of large residual stresses. Two 215 mm thick rectilinear forgings have been made from 7000 series alloys with widely different quench sensitivity to determine if solute loss in the form of precipitation during quenching can significantly affect residual stress magnitudes. The forgings were heat treated and immersion quenched using cold water to produce large magnitude residual stresses. The through thickness residual stresses were measured by neutron diffraction and incremental deep hole drilling. The distribution of residual stresses was found to be similar for both alloys varying from highly triaxial and tensile in the interior, to a state of biaxial compression in the surface. The 7010 forging exhibited larger tensile stresses in the interior. The microstructural variation from surface to centre for both forgings was determined using optical and transmission electron microscopy. These observations were used to confirm the origin of the hardness variation measured through the forging thickness. When the microstructural changes were accounted for in the through thickness lattice parameter, the residual stresses in the two forgings were found to be very similar. Solute loss in the 7075 forging appeared to have no significant effect on the residual stress magnitudes when compared to 7010. - Highlights: ► Through thickness residual stress measurements made on large Al alloy forgings. ► Residual stress characterised using neutron diffraction and deep hole drilling. ► Biaxial compressive surface and triaxial subsurface residual stresses. ► Quench sensitivity of 7075 promotes significant microstructural differences to 7010. ► When precipitation is

An effective uniaxial tensile stress-strain relationship for prestressed concrete

International Nuclear Information System (INIS)

Chitnuyanondh, L.; Rizkalla, S.; Murray, D.W.; MacGregor, J.G.

1979-02-01

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)

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

International Nuclear Information System (INIS)

Obermeier, F.; Nicak, Tomas; Keim, Elisabeth; Fekete, Tamas; Scibetta, Marc; Planman, Tapio; Laukkanen, Anssi; Carcia, Carlos Cueto-Felgueroso; Sattari-Far, Iradj

2012-01-01

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)

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

International Nuclear Information System (INIS)

Trommler, Sascha

2014-01-01

In this thesis new stress techniques are applied on thin superconducting (La,Sr) 2 CuO 4 and BaFe 1.8 Co 0.2 As 2 films. At one hand piezoelectric substrates are applied, which make a biaxial stress of the thin film deposed there possible, whereby the lattice parameters of the substrate are altered by an electric field. At the other hand on the base of flexible substrates by means of a bending experiment a uniaxial lattice deformation of thin film is realized.

Elastic stability of biaxially loaded longitudinally stiffened composite structures.

Science.gov (United States)

Viswanathan, A. V.; Tamekuni, M.; Tripp, L. L.

1973-01-01

A linear analysis method is presented for the elastic stability of structures of uniform cross section, that may be idealized as an assemblage of laminated plate-strips, flat and curved, and beams. Each plate-strip and beam covers the entire length of the structure and is simply supported on the edges normal to the longitudinal axis. Arbitrary boundary conditions may be specified on any external longitudinal side of plate-strips. The structure or selected plate-strips may be loaded in any desired combination of inplane biaxial loads. The analysis simultaneously considers all modes of instability and is applicable for the buckling of laminated composite structures. Some numerical results are presented to indicate possible applications.

Laser damage metrology in biaxial nonlinear crystals using different test beams

Science.gov (United States)

Hildenbrand, Anne; Wagner, Frank R.; Akhouayri, Hassan; Natoli, Jean-Yves; Commandre, Mireille

2008-01-01

Laser damage measurements in nonlinear optical crystals, in particular in biaxial crystals, may be influenced by several effects proper to these materials or greatly enhanced in these materials. Before discussion of these effects, we address the topic of error bar determination for probability measurements. Error bars for the damage probabilities are important because nonlinear crystals are often small and expensive, thus only few sites are used for a single damage probability measurement. We present the mathematical basics and a flow diagram for the numerical calculation of error bars for probability measurements that correspond to a chosen confidence level. Effects that possibly modify the maximum intensity in a biaxial nonlinear crystal are: focusing aberration, walk-off and self-focusing. Depending on focusing conditions, propagation direction, polarization of the light and the position of the focus point in the crystal, strong aberrations may change the beam profile and drastically decrease the maximum intensity in the crystal. A correction factor for this effect is proposed, but quantitative corrections are not possible without taking into account the experimental beam profile after the focusing lens. The characteristics of walk-off and self-focusing have quickly been reviewed for the sake of completeness of this article. Finally, parasitic second harmonic generation may influence the laser damage behavior of crystals. The important point for laser damage measurements is that the amount of externally observed SHG after the crystal does not correspond to the maximum amount of second harmonic light inside the crystal.

Biaxial Mechanical Evaluation of Absorbable and Nonabsorbable Synthetic Surgical Meshes Used for Hernia Repair: Physiological Loads Modify Anisotropy Response.

Science.gov (United States)

Cordero, A; Hernández-Gascón, B; Pascual, G; Bellón, J M; Calvo, B; Peña, E

2016-07-01

The aim of this study was to obtain information about the mechanical properties of six meshes commonly used for hernia repair (Surgipro(®), Optilene(®), Infinit(®), DynaMesh(®), Ultrapro™ and TIGR(®)) by planar biaxial tests. Stress-stretch behavior and equibiaxial stiffness were evaluated, and the anisotropy was determined by testing. In particular, equibiaxial test (equal simultaneous loading in both directions) and biaxial test (half of the load in one direction following the Laplace law) were selected as a representation of physiologically relevant loads. The majority of the meshes displayed values in the range of 8 and 18 (N/mm) in each direction for equibiaxial stiffness (tangent modulus under equibiaxial load state in both directions), while a few achieved 28 and 50 (N/mm) (Infinit (®) and TIGR (®)). Only the Surgipro (®) mesh exhibited planar isotropy, with similar mechanical properties regardless of the direction of loading, and an anisotropy ratio of 1.18. Optilene (®), DynaMesh (®), Ultrapro (®) and TIGR (®) exhibited moderate anisotropy with ratios of 1.82, 1.84, 2.17 and 1.47, respectively. The Infinit (®) scaffold exhibited very high anisotropy with a ratio of 3.37. These trends in material anisotropic response changed during the physiological state in the human abdominal wall, i.e. T:0.5T test, which the meshes were loaded in one direction with half the load used in the other direction. The Surgipro (®) mesh increased its anisotropic response (Anis[Formula: see text] = 0.478) and the materials that demonstrated moderate and high anisotropic responses during multiaxial testing presented a quasi-isotropic response, especially the Infinit(®) mesh that decreased its anisotropic response from 3.369 to 1.292.

Residual stress analysis on materials with steep stress gradient by using X-ray incidence at higher angles

International Nuclear Information System (INIS)

Ohya, Shin-ichi; Yoshioka, Yasuo; Maeno, Shigeki

1996-01-01

X-ray stress measurements for isotropic polycrystalline are materials are usually carried out by the sin 2 ψ method under the assumption of no stress gradient in X-ray penetration depth. When a steep stress gradient exists in the vicinity of surface layer, however, non-linear sin 2 ψ relation is observed and the sin 2 ψ method cannot be applied on such cases. Although several X-ray stress analyzers have been developed for materials with steep stress gradient in the surface layer, it is desirable to use diffraction data at higher incident angles of ψ 0 as possible as close on 90 degrees in order to determine the both values of surface stress and stress gradient with high accuracy. In the present study, an X-ray stress analyzer based on Ω geometry was fabricated to enable X-ray incidence at higher angle of ψ 0 . The X-ray detector was positioned on -η side against X-ray incident beam. Both of the residual surface stress and stress gradient were determined by use of the COSψ method on shot-peened steel and silicon nitride specimens. This prototype stress analyzer was found effective to perform a biaxial or triaxial stress analysis. (author)

Modeling of plates with multiple anisotropic layers and residual stress

DEFF Research Database (Denmark)

Engholm, Mathias; Pedersen, Thomas; Thomsen, Erik Vilain

2016-01-01

Usually the analytical approach for modeling of plates uses the single layer plate equation to obtain the deflection and does not take anisotropy 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 an excellent agreement between the two models is seen with a relative difference of less than 2% for all calculations. The model was also used to extract the cell capacitance, the parasitic capacitance and the residual stress of a pressure sensor composed of a multilayered plate of silicon and silicon oxide...

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

DEFF Research Database (Denmark)

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

2009-01-01

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 th...... electrical degrees in less than 2 ms test time....

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

International Nuclear Information System (INIS)

Dutta, Sekhar Chandra; Chowdhury, Rajib; Roy, Raghupati; Reddy, G. Rami

2003-01-01

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)

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

Directory of Open Access Journals (Sweden)

Tsung Chieh Cheng

2016-04-01

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

Hole doped Dirac states in silicene by biaxial tensile strain

KAUST Repository

Kaloni, Thaneshwor P.

2013-03-11

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

Hole doped Dirac states in silicene by biaxial tensile strain

KAUST Repository

Kaloni, Thaneshwor P.; Cheng, Yingchun; Schwingenschlö gl, Udo

2013-01-01

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.

Active control of residual tool marks for freeform optics functionalization by novel biaxial servo assisted fly cutting.

Science.gov (United States)

Zhu, Zhiwei; To, Suet; Zhang, Shaojian

2015-09-01

The inherent residual tool marks (RTM) with particular patterns highly affect optical functions of the generated freeform optics in fast tool servo or slow tool servo (FTS/STS) diamond turning. In the present study, a novel biaxial servo assisted fly cutting (BSFC) method is developed for flexible control of the RTM to be a functional micro/nanotexture in freeform optics generation, which is generally hard to achieve in FTS/STS diamond turning. In the BSFC system, biaxial servo motions along the z-axis and side-feeding directions are mainly adopted for primary surface generation and RTM control, respectively. Active control of the RTM from the two aspects, namely, undesired effect elimination or effective functionalization, are experimentally demonstrated by fabricating a typical F-theta freeform surface with scattering homogenization and two functional microstructures with imposition of secondary phase gratings integrating both reflective and diffractive functions.

Biaxial seismic behaviour of reinforced concrete columns =

Science.gov (United States)

Rodrigues, Hugo Filipe Pinheiro

A analise dos efeitos dos sismos mostra que a investigacao em engenharia sismica deve dar especial atencao a avaliacao da vulnerabilidade das construcoes existentes, frequentemente desprovidas de adequada resistencia sismica tal como acontece em edificios de betao armado (BA) de muitas cidades em paises do sul da Europa, entre os quais Portugal. Sendo os pilares elementos estruturais fundamentais na resistencia sismica dos edificios, deve ser dada especial atencao a sua resposta sob acoes ciclicas. Acresce que o sismo e um tipo de acao cujos efeitos nos edificios exige a consideracao de duas componentes horizontais, o que tem exigencias mais severas nos pilares comparativamente a acao unidirecional. Assim, esta tese centra-se na avaliacao da resposta estrutural de pilares de betao armado sujeitos a acoes ciclicas horizontais biaxiais, em tres linhas principais. Em primeiro lugar desenvolveu-se uma campanha de ensaios para o estudo do comportamento ciclico uniaxial e biaxial de pilares de betao armado com esforco axial constante. Para tal foram construidas quatro series de pilares retangulares de betao armado (24 no total) com diferentes caracteristicas geometricas e quantidades de armadura longitudinal, tendo os pilares sido ensaiados para diferentes historias de carga. Os resultados experimentais obtidos sao analisados e discutidos dando particular atencao a evolucao do dano, a degradacao de rigidez e resistencia com o aumento das exigencias de deformacao, a energia dissipada, ao amortecimento viscoso equivalente; por fim e proposto um indice de dano para pilares solicitados biaxialmente. De seguida foram aplicadas diferentes estrategias de modelacao nao-linear para a representacao do comportamento biaxial dos pilares ensaiados, considerando nao-linearidade distribuida ao longo dos elementos ou concentrada nas extremidades dos mesmos. Os resultados obtidos com as varias estrategias de modelacao demonstraram representar adequadamente a resposta em termos das curvas

ANALYSIS OF STRESS-STRAIN STATE OF REINFORCED CONCRETE PLATE AROUND SUPPORT ZONES

OpenAIRE

Oleg V. Kabantsev; Kirill O. Pesin; Alexey V. Karlin

2017-01-01

Structural analysis of the formation and evolution processes of structural microdestruction with the tran-sition to macrorestriction occurring during plastic deformation of masonry under biaxial stresses. The dependencies that determine the amount of the plastic phase of the deformation of masonry. Identified processes and their corre-sponding strength criteria, which play a key role in the implementation phase of plastic deformation. It is shown that plastic deformation of masonry under biax...

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

Energy Technology Data Exchange (ETDEWEB)

Chaudhry, Amit; Sangwan, S. [UIET, Panjab University, Chandigarh (India); Roy, J. N., E-mail: amit_chaudhry01@yahoo.com [Solar Semiconductro Pvt. Ltd, Hyderabad (India)

2011-05-15

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

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

International Nuclear Information System (INIS)

Chaudhry, Amit; Sangwan, S.; Roy, J. N.

2011-01-01

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

Redesigning axial-axial (biaxial) cruciform specimens for very high cycle fatigue ultrasonic testing machines.

Science.gov (United States)

Montalvão, Diogo; Wren, Andrew

2017-11-01

The necessity to increase performances in terms of lifetime and security in mechanical components or structures is the motivation for intense research in fatigue. Applications range from aeronautics to medical devices. With the development of new materials, there is no longer a fatigue limit in the classical sense, where it was accepted that the fatigue limit is the stress level such that there is no fracture up to 1E7 cycles. The recent development of ultrasonic testing machines where frequencies can go as high as 20 kHz or over enabled tests to be extended to ranges larger than 1E9 in just a few days. This area of studies is now known as Very High Cycle Fatigue (VHCF). On the other hand, most of the existing test equipment in the market for both classical and VHCF are uniaxial test machines. However, critical components used in Engineering applications are usually subjected to complex multi-axial loading conditions. In this paper, it is presented the methodology to redesigning existing cruciform test specimens that can be used to create an in-plane biaxial state of stress when used in 'uniaxial' VHCF ultrasonic testing machines (in this case, the term 'uniaxial' is used not because of the state of stress created at the centre of the specimen, but because of the direction at which the load is applied). The methodology is explained in such a way that it can be expanded to other existing designs, namely cruciform designs, that are not yet used in VHCF. Also, although the approach is presented in simple and logical terms, it may not be that obvious for those who have a more focused approach on fatigue rather than on modal analysis. It is expected that by contributing to bridging the gap between the sciences of modal analysis and fatigue, this research will help and encourage others exploiting new capabilities in VHCF.

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

Science.gov (United States)

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

2014-02-26

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

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

Energy Technology Data Exchange (ETDEWEB)

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

1977-11-01

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

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

Science.gov (United States)

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

2015-09-01

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

Characterization of mechanical properties of pericardium tissue using planar biaxial tension and flexural deformation.

Science.gov (United States)

Murdock, Kyle; Martin, Caitlin; Sun, Wei

2018-01-01

Flexure is an important mode of deformation for native and bioprosthetic heart valves. However, mechanical characterization of bioprosthetic leaflet materials has been done primarily through planar tensile testing. In this study, an integrated experimental and computational cantilever beam bending test was performed to characterize the flexural properties of glutaraldehyde-treated bovine and porcine pericardium of different thicknesses. A strain-invariant based structural constitutive model was used to model the pericardial mechanical behavior quantified through the bending tests of this study and the planar biaxial tests previously performed. The model parameters were optimized through an inverse finite element (FE) procedure in order to describe both sets of experimental data. The optimized material properties were implemented in FE simulations of transcatheter aortic valve (TAV) deformation. It was observed that porcine pericardium TAV leaflets experienced significantly more flexure than bovine when subjected to opening pressurization, and that the flexure may be overestimated using a constitutive model derived from purely planar tensile experimental data. Thus, modeling of a combination of flexural and biaxial tensile testing data may be necessary to more accurately describe the mechanical properties of pericardium, and to computationally investigate bioprosthetic leaflet function and design. Copyright © 2017 Elsevier Ltd. All rights reserved.

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

International Nuclear Information System (INIS)

Zhu, Li-na; Xu, Bin-shi; Wang, Hai-dou; Wang, Cheng-biao

2012-01-01

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

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

International Nuclear Information System (INIS)

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

2004-01-01

High quality YBa 2 Cu 3 O 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 ω 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 μm. 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

Effects of core-to-dentin thickness ratio on the biaxial flexural strength, reliability, and fracture mode of bilayered materials of zirconia core (Y-TZP) and veneer indirect composite resins.

Science.gov (United States)

Su, Naichuan; Liao, Yunmao; Zhang, Hai; Yue, Li; Lu, Xiaowen; Shen, Jiefei; Wang, Hang

2017-01-01

Indirect composite resins (ICR) are promising alternatives as veneering materials for zirconia frameworks. The effects of core-to-dentin thickness ratio (C/Dtr) on the mechanical property of bilayered veneer ICR/yttria-tetragonal zirconia polycrystalline (Y-TZP) core disks have not been previously studied. The purpose of this in vitro study was to assess the effects of C/Dtr on the biaxial flexural strength, reliability, and fracture mode of bilayered veneer ICR/ Y-TZP core disks. A total of 180 bilayered 0.6-mm-thick composite resin disks in core material and C/Dtr of 2:1, 1:1, and 1:2 were tested with either core material placed up or placed down for piston-on-3-ball biaxial flexural strength. The mean biaxial flexural strength, Weibull modulus, and fracture mode were measured to evaluate the variation trend of the biaxial flexural strength, reliability, and fracture mode of the bilayered disks with various C/Dtr. One-way analysis of variance (ANOVA) and chi-square tests were used to evaluate the variation tendency of fracture mode with the C/Dtr or material placed down during testing (α=.05). Light microscopy was used to identify the fracture mode. The mean biaxial flexural strength and reliability improved with the increase in C/Dtr when specimens were tested with the core material either up and down, and depended on the materials that were placed down during testing. The rates of delamination, Hertzian cone cracks, subcritical radial cracks, and number of fracture fragments partially depended on the C/Dtr and the materials that were placed down during testing. The biaxial flexural strength, reliability, and fracture mode in bilayered structures of Y-TZP core and veneer ICR depend on both the C/Dtr and the material that was placed down during testing. Copyright © 2016 Editorial Council for the Journal of Prosthetic Dentistry. Published by Elsevier Inc. All rights reserved.

Effect of biaxial strain and external electric field on electronic properties of MoS{sub 2} monolayer: A first-principle study

Energy Technology Data Exchange (ETDEWEB)

Nguyen, Chuong V., E-mail: chuongnguyen11@gmail.com [Institute of Research and Development, Duy Tan University, Da Nang (Viet Nam); School of Mechanical Engineering, Le Quy Don Technical University, Ha Noi (Viet Nam); Hieu, Nguyen N. [Institute of Research and Development, Duy Tan University, Da Nang (Viet Nam)

2016-04-01

In this work, making use of density functional theory (DFT) computations, we systematically investigate the effect of biaxial strain engineering and external electric field applied perpendicular to the layers on the band gaps and electronic properties of monolayer MoS{sub 2}. The direct-to-indirect band gaps and semiconductor-to-metal transition are observed in monolayer MoS{sub 2} when strain and electric field are applied in our calculation. We show that when the biaxial strain and external electric field are introduced, the electronic properties including band gaps of monolayer MoS{sub 2} can be reduced to zero. Our results provide many useful insights for the wide applications of monolayer MoS{sub 2} in electronics and optoelectronics.

Film stresses and electrode buckling in organic solar cells

KAUST Repository

Brand, Vitali

2012-08-01

We investigate the film stresses that develop in the polymer films and metal electrodes of poly(3-hexyl thiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM) bulk heterojunction (BHJ) organic solar cells. A compressive biaxial stress of ∼-36 MPa was measured in PEDOT:PSS while a tensile stress of ∼6 MPa was measured in the BHJ layer. We then analyze the effect of electrode deposition rate on the film stresses in the Al electrode. Compressive stresses of ∼-100 to -145 MPa in the Al electrode lead to a buckling instability resulting in undulating electrode surface topography. The BHJ layer was found to have the lowest cohesion (∼1.5-1.8 J/m 2) among the layers of the solar cell and dependent on the Al electrode deposition rate. The cohesive failure path in the BHJ layer exhibited the same periodicity and orientation of the Al electrode buckling topography. We discuss the implications of the film stresses on damage processes during device fabrication and operation. © 2012 Elsevier B.V. All rights reserved.

Finite element analysis of the biaxial cyclic tensile loading of the elastoplastic plate with the central hole: asymptotic regimes

Science.gov (United States)

Turkova, Vera; Stepanova, Larisa

2018-03-01

For elastistoplastic structure elements under cyclic loading three types of asymptotic behavior are well known: shakedown, cyclic plasticity or ratcheting. In structure elements operating in real conditions ratcheting must always be excluded since it caused the incremental fracture of structure by means of the accumulation of plastic strains. In the present study results of finite-element (FEM) calculations of the asymptotical behavior of an elastoplastic plate with the central circular and elliptic holes under the biaxial cyclic loading for three different materials are presented. Incremental cyclic loading of the sample with stress concentrator (the central hole) is performed in the multifunctional finite-element package SIMULIA Abaqus. The ranges of loads found for shakedown, cyclic plasticity and ratcheting are presented. The results obtained are generalized and analyzed. Convenient normalization is suggested. The chosen normalization allows us to present all computed results, corresponding to separate materials, within one common curve with minimum scattering of the points. Convenience of the generalized diagram consists in a possibility to find an asymptotical behavior of an inelastic structure for materials for which computer calculations were not made.

Formation of biaxial texture in metal films by selective ion beam etching

Energy Technology Data Exchange (ETDEWEB)

Park, S.J. [Department of Materials Science and Engineering, University of Florida, 106 Rhines Hall, P.O. Box 116400, Gainesville, FL 32611 (United States); Norton, D.P. [Department of Materials Science and Engineering, University of Florida, 106 Rhines Hall, P.O. Box 116400, Gainesville, FL 32611 (United States)]. E-mail: dnort@mse.ufl.edu; Selvamanickam, Venkat [IGC-SuperPower, LLC, 450 Duane Avenue, Schenectady, NY 12304 (United States)

2006-05-15

The formation of in-plane texture via ion bombardment of uniaxially textured metal films was investigated. In particular, selective grain Ar ion beam etching of uniaxially textured (0 0 1) Ni was used to achieve in-plane aligned Ni grains. Unlike conventional ion beam assisted deposition, the ion beam irradiates the uniaxially textured film surface with no impinging deposition flux. The initial uniaxial texture is established via surface energy minimization with no ion irradiation. Within this sequential texturing method, in-plane grain alignment is driven by selective etching and grain overgrowth. Biaxial texture was achieved for ion beam irradiation at elevated temperature.

Formation of biaxial texture in metal films by selective ion beam etching

International Nuclear Information System (INIS)

Park, S.J.; Norton, D.P.; Selvamanickam, Venkat

2006-01-01

The formation of in-plane texture via ion bombardment of uniaxially textured metal films was investigated. In particular, selective grain Ar ion beam etching of uniaxially textured (0 0 1) Ni was used to achieve in-plane aligned Ni grains. Unlike conventional ion beam assisted deposition, the ion beam irradiates the uniaxially textured film surface with no impinging deposition flux. The initial uniaxial texture is established via surface energy minimization with no ion irradiation. Within this sequential texturing method, in-plane grain alignment is driven by selective etching and grain overgrowth. Biaxial texture was achieved for ion beam irradiation at elevated temperature

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

International Nuclear Information System (INIS)

Hermsmeyer, S.; Reimann, J.

2002-01-01

Pebble beds of ceramic material are investigated within the framework of developing solid breeder blankets for future fusion power plants. A thermo-mechanical characterisation of such pebble beds is mandatory for understanding the behaviour of pebble beds, and thus the overall blanket, under fusion environment conditions. The mechanical behaviour of pebble beds is typically explored with uni-axial, bi-axial and tri-axial compression experiments. The latter two types of experiment are particularly revealing since they contain explicitly, beyond a compression behaviour of the bed, information on the conditions for pebble flow, i.e. macroscopic relocation, in the pebble bed. (orig.)

Stress anisotropy and stress gradient in magnetron sputtered films with different deposition geometries

International Nuclear Information System (INIS)

Zhao, Z.B.; Yalisove, S.M.; Bilello, J.C.

2006-01-01

Mo films were deposited via magnetron sputtering with two different deposition geometries: dynamic deposition (moving substrate) and static deposition (fixed substrate). The residual stress and structural morphologies of these films were investigated, with particular focus on in-plane anisotropy of the biaxial stress and stress gradient across the film thickness. The results revealed that the Mo films developed distinct states of residual stress, which depended on both deposition geometry and film thickness. With the dynamic geometry, the Mo films generally exhibited anisotropic stress. Both the degree of anisotropy and the magnitude of stress varied as functions of film thickness. The variation of stress was linked to the evolution of anisotropic microstructures in the films. The Mo films from the static geometry developed isotropic residual stress, which was more compressive and noticeably larger in magnitude than that of the Mo films from the dynamic geometry. Aside from these disparities, the two types of Mo films (i.e., anisotropic and isotropic) exhibited notably similar trends of stress variation with film thickness. Depth profiling indicated the presence of large stress gradients for the Mo films, irrespective of the deposition geometries. This observation seems to be consistent with the premise that Mo films develop a zone T structure, which is inherently inhomogeneous along the film thickness. Moreover, the largest stress gradient for both types of deposition geometries arises at roughly the same film depth (∼240 nm from substrate), where the stresses sharply transits from highly compressive to less compressive or even tensile. This appears to correspond to the boundary region that separates two distinct stages of microstructural evolution, a feature unique to zone T-type structure

Pattern zoology in biaxially pre-stretched elastic bilayers: from wrinkles and creases to fracture-like ridges

Science.gov (United States)

Al-Rashed, Rashed; Lopez JiméNez, Francisco; Reis, Pedro

The wrinkling of elastic bilayers under compression has been explored as a method to produce reversible surface topography, with applications ranging from microfluidics to tunable optics. We introduce a new experimental system to study the effects of pre-stretching on the instability patterns that result from the biaxial compression of thin shells bound to an elastic substrate. A pre-stretched substrate is first prepared by pressurizing an initially flat elastomeric disk and bulging it into a nearly hemispherical thick shell. The substrate is then coated with a thin layer of a polymer suspension, which, upon curing, results in a thin shell of nearly constant thickness. Releasing the pre-stretch in the substrate by deflating the system places the outer film in a state of biaxial compression, resulting in a variety of buckling patterns. We explore the parameter space by systematically varying the pre-stretch, the substrate/film stiffness mismatch, and the thickness of the film. This results in a continuous transition between different buckling patterns, from the dimples and wrinkles that are traditionally associated with the buckling of elastic bilayers, to creases and high aspect ratio `fracture-like' ridges, where the pre-stretch plays an essential role.

Numerical modelling of fracture initiation and propagation in biaxial tests on rock samples

CSIR Research Space (South Africa)

Van de Steen, B

2001-03-01

Full Text Available and Peirce, 1995). Additional edges can be obtained in the Voronoi tessellation, by connecting the geometric centre of the Voronoi polygons with the vertices of the polygons. These last elements are further referred to as the internal fracture paths, while... samples without flaws therefore display a very brittle behaviour (Napier and Peirce, 1995). To obtain a more plastic behaviour, it may be necessary to adjust the flaw density as well (D0 to D0b, Table 2). The brittleness of the simulated biaxial tests...

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

International Nuclear Information System (INIS)

Donaldson, A.T.; Horwood, R.A.; Healey, T.

1983-01-01

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)

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

International Nuclear Information System (INIS)

Singh, D.; Cruse, T. A.; Hermanson, D. J.; Goretta, K. C.; Zok, F. W.; McNulty, J. C.

2000-01-01

Mechanical properties of hot-pressed Si 3 N 4 /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

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

International Nuclear Information System (INIS)

Salinas-Rodriguez, A.; Root, J.H.; Holden, T.M.; Macewen, S.R.; Ludtka, G.M.

1990-01-01

The macroscopic residual stress distribution in γ-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 α-U. Quenching from the γ 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

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

Science.gov (United States)

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

2014-03-01

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

Ab initio study of Co and Ni under uniaxial and biaxial loading and in epitaxial overlayers

Czech Academy of Sciences Publication Activity Database

Zelený, Martin; Legut, Dominik; Šob, Mojmír

2008-01-01

Roč. 78, č. 22 (2008), 224105/1-224105/11 ISSN 1098-0121 R&D Projects: GA ČR GD106/05/H008; GA AV ČR IAA1041302; GA MŠk OC 147 Institutional research plan: CEZ:AV0Z20410507 Keywords : ab initio calculations * epitaxial overlayers * uniaxial and biaxial loading Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.322, year: 2008

Stress measurements in the Naesliden Mine

Energy Technology Data Exchange (ETDEWEB)

Leijon, B. [Univ. of Luleaa, Sweden; Carlsson, H.; Myrvang, A.

1980-05-15

Determinations of virgin stresses were performed at an early stage of the Naesliden Project in order to obtain input data for the finite element models of the mine. The Leeman three-dimensional overcoring technique was used at five locations on levels ranging from 210 m to 460 m below surface. Stress data were obtained at four of these locations. The results show an excess of horizontal stresses whilst the vertical stress is in accordance with the gravitational load from the overburden. The major and intermediate principal stresses are sub-horizontal and directed respectively perpendicular and parallel to the schisotsity of the wall rock and the strike of the tabular ore body. The minor principal stress is directed almost vertically. Stresses were also measured close to a stope on 300 m level in the mine. Biaxial and triaxial overcoring measurements were made at eighteen points between 0.25 m and 7.2 m above the roof of the stope. The stresses were found to have magnitudes of about 70 MPa close to the roof and to decrease rapidly with the distance from the roof. Stress measurements were made in connection with slot blastings in the foot wall, the latter measure being made in an attempt to de-stress the roof of stope 3. Two methods were used for stress monitorings, both showing that expected stress changes did not take place. Long-term stress guages have been installed in the ore body in order to monitor expected re-distributions of stresses due to mining. So far, the recorded stress changes are below 5 MPa.

Intradomain Textures in Block Copolymers: Multizone Alignment and Biaxiality

Science.gov (United States)

Prasad, Ishan; Seo, Youngmi; Hall, Lisa M.; Grason, Gregory M.

2017-06-01

Block copolymer (BCP) melt assembly has been studied for decades, focusing largely on self-organized spatial patterns of periodically ordered segment density. Here, we demonstrate that underlying the well-known composition profiles (i.e., ordered lamella, cylinders, spheres, and networks) are generic and heterogeneous patterns of segment orientation that couple strongly to morphology, even in the absence of specific factors that promote intra or interchain segment alignment. We employ both self-consistent field theory and coarse-grained simulation methods to measure polar and nematic order parameters of segments in a freely jointed chain model of diblock melts. We show that BCP morphologies have a multizone texture, with segments predominantly aligned normal and parallel to interdomain interfaces in the respective brush and interfacial regions of the microdomain. Further, morphologies with anisotropically curved interfaces (i.e., cylinders and networks) exhibit biaxial order that is aligned to the principal curvature axes of the interface.

Computational and experimental investigation of local stress fiber orientation in uniaxially and biaxially constrained microtissues

NARCIS (Netherlands)

Obbink - Huizer, C.; Foolen, J.; Oomens, C.W.J.; Borochin, M.A.; Chen, C.S.; Bouten, C.V.C.; Baaijens, F.P.T.

2014-01-01

The orientation of cells and associated F-actin stress fibers is essential for proper tissue functioning. We have previously developed a computational model that qualitatively describes stress fiber orientation in response to a range of mechanical stimuli. In this paper, the aim is to quantitatively

Reduction of initial stress stiffening by topology optimization

DEFF Research Database (Denmark)

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

2012-01-01

Topology optimization is a rigorous method of obtaining non-intuitive designs. We use it to obtain a capacitive RF switch that stiffens little in response to an increase of the in-plane biaxial stresses that typically develop during MEMS fabrication. The actuation voltage is closely related...... 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....

Experimental study of the flow rules of a 316 stainless steel at high and low stresses

International Nuclear Information System (INIS)

Delobelle, P.; Oytana, C.

1984-01-01

Creep flow rules of 316L stainless steel are studied in tensile and axial-torsion experiments. Through tensile and biaxial proportional loadings it is shown that at low creep values of epsilonkT/DGb a single kinematical variable: the internal stress takes a part in these laws. This is confirmed in non-proportional experiments. The power law with the power of nsup(*)approx.=2 relates applied and internal stresses. At higher creep rates a second scalar internal variable must be introduced and the power law no longer applies. Limiting functions in steady creep are determined for hardening and recovery. (orig.)

Potential drop crack growth monitoring in high temperature biaxial fatigue tests

International Nuclear Information System (INIS)

Fitzgerald, B.P.; Krempl, E.

1993-01-01

The present work describes a procedure for monitoring crack growth in high temperature, biaxial, low cycle fatigue tests. The reversing DC potential drop equipment monitors smooth, tubular type 304 stainless steel specimens during fatigue testing. Electrical interference from an induction heater is filtered out by an analog filter and by using a long integration time. A Fourier smoothing algorithm and two spline interpolations process the large data set. The experimentally determined electrical potential drop is compared with the theoretical electrostatic potential that is found by solving Laplace's equation for an elliptical crack in a semi-infinite conducting medium. Since agreement between theory and experiment is good, the method can be used to measure crack growth to failure from the threshold of detectability

Modelling of tension stiffening for normal and high strength concrete

DEFF Research Database (Denmark)

Christiansen, Morten Bo; Nielsen, Mogens Peter

1998-01-01

form the model is extended to apply to biaxial stress fields as well. To determine the biaxial stress field, the theorem of minimum complementary elastic energy is used. The theory has been compared with tests on rods, disks, and beams of both normal and high strength concrete, and very good results...

X-ray diffraction study of stress relaxation in cubic boron nitride films grown with simultaneous medium-energy ion bombardment

International Nuclear Information System (INIS)

Abendroth, B.; Gago, R.; Eichhorn, F.; Moeller, W.

2004-01-01

Relaxation of the intrinsic stress of cubic boron nitride (cBN) thin films has been studied by x-ray diffraction (XRD) using synchrotron light. The stress relaxation has been attained by simultaneous medium-energy ion bombardment (2-10 keV) during magnetron sputter deposition, and was confirmed macroscopically by substrate curvature measurements. In order to investigate the stress-release mechanisms, XRD measurements were performed in in-plane and out-of-plane geometry. The analysis shows a pronounced biaxial state of compressive stress in the cBN films grown without medium-energy ion bombardment. This stress is partially released during the medium-energy ion bombardment. It is suggested that the main path for stress relaxation is the elimination of strain within the cBN grains due to annealing of interstitials

Experimental study of internal conical refraction in a biaxial crystal with Laguerre–Gauss light beams

International Nuclear Information System (INIS)

Peet, V

2014-01-01

The effect of internal conical refraction (CR) in a biaxial crystal was studied using Laguerre–Gauss light beams LG 0 ℓ with ℓ=1 and 2, while the lowest-order LG 0 0 beam was used as a reference. The transition from ordinary double refraction to CR was examined. It has been shown that double refraction of an LG 0 ℓ beam forms two focal spots containing ℓ dark stripes. These stripes evolve into ℓ+1 dark rings over an annular focal image when CR is established, and it results in a fine-structure of ℓ+2 bright focal rings with different intensities. In a sharp contrast to the lowest-order reference, the multiring focal structure has a distinct asymmetry with respect to the focal image plane. It has been shown that bright off-axis ‘hot spot’ can be formed on the far-field profiles of outgoing light beams when the biaxial crystal is slightly tilted, and a small angle between the propagation axis of the beam and the optic axis of the crystal arises. These off-axis light structures emerge as either a charge-one optical vortex or a zero-charge spot with annihilated vorticity. Polarization selection reveals J 1 or J 0 Bessel-like profiles of the corresponding ‘hot spots’, and a complex pattern of forked fringes in the dark region near the beam core. (paper)

Bi-axial M-. Phi. analyses of RC columns using fiber model and comparison with experimental results. 2 jikumage wo ukeru hashirabuzai no M-. Phi. kankei eno fiber model no tekigosei

Energy Technology Data Exchange (ETDEWEB)

Murayama, Y.; Tokuyama, S.; Furuichi, K. (Kajima Corp., Tokyo (Japan))

1991-10-31

In order to examine the accuracy of a fiber model for analyzing the stability of towers of a cable-stayed bridge subjected to biaxial bending force due to earthquake, experimental results of column test specimens were compared with analytical results. The relation between biaxial bending moment and curvature (M-{Phi}) was measured in biaxial bending model experiment using a reinforcement ratio, axial compressive force and loading pattern as parameters. Since the relation was greatly affected by axial modeling of a reinforcing material, the parameter analysis was conducted by paying particular attention to reinforcement models (bilinear model, cubic one and Ramberg-Osgood one). As a result, the Ramberg-Osgood model was suitable for columns with a large longitudinal reinforcement ratio and large axial tension such as seen in highrise buildings, while the cubic model was more suitable for columns with a small ratio such as seen in cable-stayed bridges. 4 refs., 10 figs., 1 tab.

Mechanical properties of two-way different configurations of prestressed concrete members subjected to axial loading

Energy Technology Data Exchange (ETDEWEB)

Zhang, Chaobi; Chen, Jian Yun; Xu, Qiang; Li, Jing [School of Civil and Hydraulic Engineering, Dalian University of Technology, Dalian (China)

2015-08-15

In order to analyze the mechanical properties of two-way different configurations of prestressed concrete members subjected to axial loading, a finite element model based on the nuclear power plant containments is demonstrated. This model takes into account the influences of different principal stress directions, the uniaxial or biaxial loading, and biaxial loading ratio. The displacement-controlled load is applied to obtain the stress-strain response. The simulated results indicate that the differences of principal stress axes have great effects on the stress-strain response under uniaxial loading. When the specimens are subjected to biaxial loading, the change trend of stress with the increase of loading ratio is obviously different along different layout directions. In addition, correlation experiments and finite element analyses were conducted to verify the validity and reliability of the analysis in this study.

Test plan for suitability assessment of five overcoring stress measurement techniques

International Nuclear Information System (INIS)

Gregory, E.C.; Rundle, T.A.; McCabe, W.M.; Kim, K.

1982-08-01

Tests are to be conducted at the Near-Surface Test Facility (NSTF) to assess the suitability of five overcoring techniques for in situ stress determination in a jointed basalt. The overcoring methods to be investigated use the following instrumentation to measure strain relief by overcoring a pilot borehole: USBM borehole deformation gage, CSIRO hollow inclusion stress cell, cast epoxy inclusion, the Lulea triaxial strain cell and the ''doorstopper'' biaxial strain cell. The tests are to provide data regarding the state of stress below the NSTF. This information is to be used in the evaluation of each method of overcoring. During the course of field testing, an attempt is to be made to adapt conventional overcoring techniques and analytical methods to the basalt medium. If overcoring stress determination in basalt is shown suitable, then additional studies will be identified to further adapt a technique for use at depth. In addition to the five overcoring techniques to be tested at the NSTF, stress measurements by Hydrofracturing are to be conducted to provide data for direct comparison with overcoring results. 16 refs., 18 figs

Ferroelectric properties of Pb(Zr,Ti)O3 films under ion-beam induced strain

Science.gov (United States)

Lee, Jung-Kun; Nastasi, Michael

2012-11-01

The influence of an ion-beam induced biaxial stress on the ferroelectric and dielectric properties of Pb(Zr,Ti)O3 (PZT) films is investigated using the ion beam process as a novel approach to control external stress. Tensile stress is observed to decrease the polarization, permittivity, and ferroelectric fatigue resistance of the PZT films whose structure is monoclinic. However, a compressive stress increases all of them in monoclinic PZT films. The dependence of the permittivity on stress is found not to follow the phenomenological theory relating external forces to intrinsic properties of ferroelectric materials. Changes in the ferroelectric and dielectric properties indicate that the application of a biaxial stress modulates both extrinsic and intrinsic properties of PZT films. Different degrees of dielectric non-linearity suggests the density and mobility of non-180o domain walls, and the domain switching can be controlled by an applied biaxial stress and thereby influence the ferroelectric and dielectric properties.

Tunnel splitting in biaxial spin models investigated with spin-coherent-state path integrals

International Nuclear Information System (INIS)

Chen Zhide; Liang, J.-Q.; Pu, F.-C.

2003-01-01

Tunnel splitting in biaxial spin models is investigated with a full evaluation of the fluctuation functional integrals of the Euclidean kernel in the framework of spin-coherent-state path integrals which leads to a magnitude of tunnel splitting quantitatively comparable with the numerical results in terms of diagonalization of the Hamilton operator. An additional factor resulted from a global time transformation converting the position-dependent mass to a constant one seems to be equivalent to the semiclassical correction of the Lagrangian proposed by Enz and Schilling. A long standing question whether the spin-coherent-state representation of path integrals can result in an accurate tunnel splitting is therefore resolved

An interim report on shallow-flaw fracture technology development

International Nuclear Information System (INIS)

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

1995-01-01

Shallow-flaw fracture technology is being developed for application to the safety assessment of radiation-embrittled nuclear reactor pressure vessels (RPVS) containing flaws. Fracture mechanics tests on RPV steel, coupled with detailed elastic-plastic finite-element analyses of the crack-tip stress fields, have shown that (1) constraint relaxation at the crack tip of shallow surface flaws results in increased data scatter but no increase in the lower-bound fracture toughness, (2) the nil ductility temperature (NDT) performs better than the reference temperature for nil ductility transition (RT NDT ) as a normalizing parameter for shallow-flaw fracture toughness data, (3) biaxial loading can reduce the shallow-flaw fracture toughness, (4) stress-based dual-parameter fracture toughness correlations cannot predict the effect of biaxial loading on shallow-flaw fracture toughness because in-plane stresses at the crack tip are not influenced by biaxial loading, and (5) a strain-based dual-parameter fracture toughness correlation can predict the effect of biaxial loading on shallow-flaw fracture toughness

Effects of hydrostatic pressure and biaxial strains on the elastic and electronic properties of t-C8B2N2

Science.gov (United States)

Zhu, Haiyan; Shi, Liwei; Li, Shuaiqi; Duan, Yifeng; Zhang, Shaobo; Xia, Wangsuo

2018-04-01

The effects of hydrostatic pressure and biaxial strains on the elastic and electronic properties of a superhard material t-C8B2N2 have been studied using first-principles calculations. The structure is proven to be mechanically and dynamically stable under the applied external forces. All the elastic constants (except C66) and elastic modulus increase (decrease) with increasing pressure and compressive (tensile) biaxial strain ɛxx. A microscopic model is used to calculate the Vicker's hardness of every single bond as well as the crystal. The hardness of t-C8B2N2 (64.7 GPa) exceeds that of c-BN (62 GPa) and increases obviously by employing pressure and compressive ɛxx. Furthermore, the Debye temperature and anisotropy of sound velocities for t-C8B2N2 have been discussed. t-C8B2N2 undergoes an indirect to direct bandgap transition when ɛxx > 2%; however, the indirect bandgap character of the material remains under pressure.

Experimental investigation on transformation, reorientation and plasticity of Ni47Ti44Nb9 SMA under biaxial thermal–mechanical loading

International Nuclear Information System (INIS)

Chen, Xiang; Peng, Xianghe; Chen, Bin; Han, Jia; Zeng, Zhongmin; Hu, Ning

2015-01-01

The constitutive behavior of shape memory alloy (SMA) Ni 47 Ti 44 Nb 9 specimens subjected to different thermal–mechanical loading histories was investigated experimentally. This involved the application of strain by different proportional or non-proportional paths in the biaxial ϵ−γ plane at −60 °C (M s + 30 °C), the interaction between stress-induced martensitic transformation, reorientation and plastic deformation, temperature-induced reverse martensitic transformation and strain recovery. The results show that the equivalent stress–strain curves, as well as the pure shear and pure tensile curves, depend strongly on the thermal–mechanical loading history. For specimens deformed previously to the same equivalent strains by different paths, the equivalent recovery strains after unloading are similar, as are the spans between the reverse transformation start and final temperatures. The activated martensite variants depend strongly on loading history. The recovery of the axial strain component and that of the shear strain component due to reverse transformation occur synchronously and develop along the shortest path in the ϵ−γ plane. The results may provide some new and useful information on the effects of transformation, plasticity and loading paths for further studies and applications of such materials. (paper)

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

International Nuclear Information System (INIS)

Stadel, O; Samoilenkov, S V; Muydinov, R Yu; Schmidt, J; Keune, H; Wahl, G; Gorbenko, O Yu; Korsakov, I E; Melnikov, O V; Kaul, A R

2006-01-01

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) 2 CuO 4 /40 nm (La, Ba)MnO 3 /Ni5W. Constituting layers with high structural quality have been grown on moving tapes (in plane FWHM ≤ 6 0 and out of plane FWHM ≤ 3 0 )

The role of mechanical boundary conditions in the soft mode dynamics of PbTiO3.

Science.gov (United States)

McCash, Kevin; Mani, B K; Chang, C-M; Ponomareva, I

2014-10-29

The role of different mechanical boundary conditions in the soft mode dynamics of ferroelectric PbTiO3 is systematically investigated using first-principles-based simulations and analytical model. The change in the soft mode dynamics due to hydrostatic pressure, uniaxial and biaxial stresses and biaxial strains is studied in a wide temperature range. Our computations predict: (i) the existence of Curie-Weiss laws that relate the soft mode frequency to the stress or strain; (ii) a non-trivial temperature evolution of the associated Curie-Weiss constants; (iii) a qualitative difference between the soft mode response to stresses/strains and hydrostatic pressure. The latter finding implies that the Curie-Weiss pressure law commonly used for residual stress estimation may not apply for the cases of uniaxial and biaxial stresses and strains. On the other hand, our systematic study offers a way to eliminate this difficulty through the establishment of Curie-Weiss stress and strain laws. Implications of our predictions for some available experimental data are discussed.

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

International Nuclear Information System (INIS)

Yokoyama, Ryouichi

2011-01-01

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)

Mechanical control of the electro-optical properties of monolayer and bilayer BC3 by applying the in-plane biaxial strain

Science.gov (United States)

Behzad, Somayeh

2017-11-01

Recently, a new two-dimensional (2D) material, the 2D BC3 crystal, has been synthesized. Here, the mechanical control of the electro-optical properties of monolayer and bilayer BC3 by applying the biaxial strain is investigated. The electronic structure calculations showed that the strain-free monolayer and bilayer BC3 are indirect band-gap semiconductors with band gap of 0.62 and 0.29 eV, respectively, where the conduction band minimum (CBM) is at the M point whereas the valence band maximum (VBM) is at the Γ point. The doubly degenerated bands in the monolayer BC3 are splitted in the bilayer BC3 due to the interlayer interactions. Both monolayer and bilayer BC3 remain indirect gap semiconductor under biaxial tensile strain and their band gaps increases with strain. On the other hand, by increasing the magnitude of tensile strain, the optical spectra shift to the lower energies and the static dielectric constant increases. These findings suggest the potential of strain-engineered 2D BC3 in electronic and optoelectronic device applications.

Ratchetting behavior of primary heat transport (PHT) piping material SA-333 carbon steel subjected to cyclic loads at room temperature

International Nuclear Information System (INIS)

Kulkarni, S.; Desai, Y.M.; Kant, T.; Reddy, G.R.; Gupta, C.; Chakravarthy, J.K.

2004-01-01

Ratchetting behavior of SA-333 Gr. 6 carbon steel used as primary heat transport (PHT) piping material has been investigated with three constitutive models proposed by Armstrong-Frederick, Chaboche and Ohno-Wang involving different hardening rules. Performance of the above mentioned models have been evaluated for a broad set of uniaxial and biaxial loading histories. The uniaxial ratchetting simulations have been performed for a range of stress ratios (R) by imposing different stress amplitudes and mean stress conditions. Numerical simulations indicated significant ratchetting and opening of hysteresis loop for negative stress ratio with constant mean stress. Application of cyclic stress without mean stress (R = -1.0) has been observed to produce negligible ratchet-strain accumulation in the material. Simulation under the biaxial stress condition was based on modeling of an internally pressurized thin walled pipe subjected to cyclic bending load. Numerical results have been validated with the experiments as per simulation conditions. All three models have been found to predict the observed accumulation of circumferential strain with increasing number of cycles. However, the Armstrong Frederick (A-F) model was found to be inadequate in simulating the ratchetting response for both uniaxial as well as biaxial loading cases. The A-F model actually over-predicted the ratchetting strain in comparison with the experimental strain values. On the other hand, results obtained with the Chaboche and the Ohno-Wang models for both the uniaxial as well as biaxial loading histories have been observed to closely simulate the experimental results. The Ohno-Wang model resulted in better simulation for the presents sets of experimental results in comparison with the Chaboche model. It can be concluded that the Ohno-Wang model suited well compared to the Chaboche model for above sets of uniaxial and biaxial loading histories. (authors)

BUCLASP 3: A computer program for stresses and buckling of heated composite stiffened panels and other structures, user's manual

Science.gov (United States)

Tripp, L. L.; Tamekuni, M.; Viswanathan, A. V.

1973-01-01

The use of the computer program BUCLASP3 is described. The code is intended for thermal stress and instability analyses of structures such as unidirectionally stiffened panels. There are two types of instability analyses that can be effected by PAINT; (1) thermal buckling, and (2) buckling due to a specified inplane biaxial loading. Any structure that has a constant cross section in one direction, that may be idealized as an assemblage of beam elements and laminated flat and curved plate strip-elements can be analyzed. The two parallel ends of the panel must be simply supported, whereas arbitrary elastic boundary conditions may be imposed along any one or both external longitudinal side. Any variation in the temperature rise (from ambient) through the cross section of a panel is considered in the analyses but it must be assumed that in the longitudinal direction the temperature field is constant. Load distributions for the externally applied inplane biaxial loads are similar in nature to the permissible temperature field.

Reassessment of the role of stress in development of radiation-induced microstructure

International Nuclear Information System (INIS)

Garner, F.A.; Wolfer, W.G.; Brager, H.R.

1978-10-01

Data are now accumulating which clearly demonstrate that the stress state plays a strong role in the development of void and dislocation microstructure in metals during neutron irradiation. In these experiments the application of a tensile biaxial stress state at constant fluence and temperature has been found to lead to a progressively decreasing metal density with increasing stress. The effect of stress on the concurrent development of voids, Frank interstitial loops and dislocation networks has been studied with transmission electron microscopy. The results of these experiments clearly show that the densities of both Frank loops and voids are enhanced by a tensile stress field, with the relevant operating variable being the hydrostatic stress. More importantly it appears that any anisotropy in the stress field is reflected in a corresponding anisotropy that develops in the number of Frank loops that form on the various (111) planes. The loop density that develops on each plane exhibits a clear and direct dependence on the resolved normal stress component at each plane. Although the data from these experiments have been previously interpreted to support the existence of stress-assisted nucleation mechanisms for both loops and voids, further analysis has shown both of these explanations to be deficient in one or more respects, and both models have been replaced

Residual stresses in weld-clad reactor pressure vessel steel

International Nuclear Information System (INIS)

Bertram, W.

1975-01-01

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

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

International Nuclear Information System (INIS)

Donaldson, A.T.; Healey, T.; Horwood, R.A.L.

1985-01-01

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

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

Energy Technology Data Exchange (ETDEWEB)

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

2014-11-03

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

Analysis of Simple Creep Stress Calculation Methods for Creep Life Assessment

Energy Technology Data Exchange (ETDEWEB)

Seo, Jun Min; Lee, Han Sang; Kim, Yun Jae [Korea Univ., Daejeon (Korea, Republic of)

2017-08-15

Creep analysis takes much more time than elastic or elastic-plastic analysis. In this study, we conducted elastic and elastic-plastic analysis and compared the results with creep analysis results. In the elastic analysis, we used primary stress, which can be classified by the Mα-tangent method and stress intensities recommended in the ASME code. In the elastic-plastic analysis, we calculated the parameters recommended in the R5 code. For the FE models, a bending load, uniaxial load, and biaxial load were applied to the cross shaped welded plate, and a bending load and internal pressure were applied to the elbow pipe. To investigate the element size sensitivity, we conducted FE analysis for various element sizes for the cases where bending load was applied to the cross shaped welded plate. There was no significant difference between the creep.

A multi-axis confocal rheoscope for studying shear flow of structured fluids

KAUST Repository

Lin, Neil Y. C.; McCoy, Jonathan H.; Cheng, Xiang; Leahy, Brian; Israelachvili, Jacob N.; Cohen, Itai

2014-01-01

of confinement effects. By using our shear cell in conjunction with a biaxial force measurement device and a high-speed confocal microscope, we are able to measure the real-time biaxial stress while simultaneously imaging the material three-dimensional structure

Preparation of biaxially oriented TlCu-1234 thin films

CERN Document Server

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

1999-01-01

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

Adaptive fuzzy trajectory control for biaxial motion stage system

Directory of Open Access Journals (Sweden)

Wei-Lung Mao

2016-04-01

Full Text Available Motion control is an essential part of industrial machinery and manufacturing systems. In this article, the adaptive fuzzy controller is proposed for precision trajectory tracking control in biaxial X-Y motion stage system. The theoretical analyses of direct fuzzy control which is insensitive to parameter uncertainties and external load disturbances are derived to demonstrate the feasibility to track the reference trajectories. The Lyapunov stability theorem has been used to testify the asymptotic stability of the whole system, and all the signals are bounded in the closed-loop system. The intelligent position controller combines the merits of the adaptive fuzzy control with robust characteristics and learning ability for periodic command tracking of a servo drive mechanism. The simulation and experimental results on square, triangle, star, and circle reference contours are presented to show that the proposed controller indeed accomplishes the better tracking performances with regard to model uncertainties. It is observed that the convergence of parameters and tracking errors can be faster and smaller compared with the conventional adaptive fuzzy control in terms of average tracking error and tracking error standard deviation.

The effect of casting conditions on the biaxial flexural strength of glass-ceramic materials.

Science.gov (United States)

Johnson, A; Shareef, M Y; Walsh, J M; Hatton, P V; van Noort, R; Hill, R G

1998-11-01

To assess the effect of mould and glass casting temperatures on the biaxial flexural strength (BFS) of two different types of castable glass-ceramic, using existing laboratory equipment and techniques. Two castable glass-ceramic materials were evaluated. One glass (LG3) is based on SiO2-Al2O3-P2O5-CaO-CaF2, and is similar in composition to glasses used in the manufacture of glass-ionomer cements. The other glass (SG3) is based on SiO2-K2O-Na2O-CaO-CaF2, and is a canasite-based material. Both materials were used to produce discs of 12 mm diameter and 2 mm thickness using the same lost-wax casting process as used for metal castings. Mould temperatures of between 500 degrees C and 1000 degrees C and glass casting temperatures of between 1100 degrees C and 1450 degrees C were evaluated. The cast discs were cerammed and the biaxial flexural strength determined with a Lloyd 2000 R tester. A significant difference was found for the BFS in the range of mould temperatures evaluated, with the optimum investment mould temperature being 590 degrees C for LG3 and 610 degrees C for SG3 (p = 0.0002 and p = 0.019, respectively). No significant differences were seen between any of the glass casting temperatures evaluated. The mould temperature for castable glass-ceramic materials produced using the lost-wax casting process can have a significant effect on BFS. The optimum mould temperature may differ slightly depending on the type of material being used. The glass casting temperature of these materials does not appear to have a significant effect on BFS.

The effect of core material, veneering porcelain, and fabrication technique on the biaxial flexural strength and weibull analysis of selected dental ceramics.

Science.gov (United States)

Lin, Wei-Shao; Ercoli, Carlo; Feng, Changyong; Morton, Dean

2012-07-01

The objective of this study was to compare the effect of veneering porcelain (monolithic or bilayer specimens) and core fabrication technique (heat-pressed or CAD/CAM) on the biaxial flexural strength and Weibull modulus of leucite-reinforced and lithium-disilicate glass ceramics. In addition, the effect of veneering technique (heat-pressed or powder/liquid layering) for zirconia ceramics on the biaxial flexural strength and Weibull modulus was studied. Five ceramic core materials (IPS Empress Esthetic, IPS Empress CAD, IPS e.max Press, IPS e.max CAD, IPS e.max ZirCAD) and three corresponding veneering porcelains (IPS Empress Esthetic Veneer, IPS e.max Ceram, IPS e.max ZirPress) were selected for this study. Each core material group contained three subgroups based on the core material thickness and the presence of corresponding veneering porcelain as follows: 1.5 mm core material only (subgroup 1.5C), 0.8 mm core material only (subgroup 0.8C), and 1.5 mm core/veneer group: 0.8 mm core with 0.7 mm corresponding veneering porcelain with a powder/liquid layering technique (subgroup 0.8C-0.7VL). The ZirCAD group had one additional 1.5 mm core/veneer subgroup with 0.7 mm heat-pressed veneering porcelain (subgroup 0.8C-0.7VP). The biaxial flexural strengths were compared for each subgroup (n = 10) according to ISO standard 6872:2008 with ANOVA and Tukey's post hoc multiple comparison test (p≤ 0.05). The reliability of strength was analyzed with the Weibull distribution. For all core materials, the 1.5 mm core/veneer subgroups (0.8C-0.7VL, 0.8C-0.7VP) had significantly lower mean biaxial flexural strengths (p Empress and e.max groups, regardless of core thickness and fabrication techniques. Comparing fabrication techniques, Empress Esthetic/CAD, e.max Press/CAD had similar biaxial flexural strength (p= 0.28 for Empress pair; p= 0.87 for e.max pair); however, e.max CAD/Press groups had significantly higher flexural strength (p Empress Esthetic/CAD groups. Monolithic core

Biaxial analysis of synthetic scaffolds for hernia repair demonstrates variability in mechanical anisotropy, non-linearity and hysteresis.

Science.gov (United States)

Deeken, Corey R; Thompson, Dominic M; Castile, Ryan M; Lake, Spencer P

2014-10-01

Over the past 60 years, the soft tissue repair market has grown to include over 50 types of hernia repair materials. Surgeons typically implant these materials in the orientation that provides maximum overlap of the mesh over the defect, with little regard for mechanical properties of the mesh material. If the characteristics of the meshes were better understood, an appropriate material could be identified for each patient, and meshes could be placed to optimize integration with neighboring tissue and avoid the mechanical mis-match that can lead to impaired graft fixation. The purpose of this study was to fully characterize and compare the mechanical properties of thirteen types of hernia repair materials via planar biaxial tensile testing. Equibiaxial (i.e., equal simultaneous loading in both directions) and strip biaxial (i.e., loading in one direction with the other direction held fixed) tests were utilized as physiologically relevant loading regimes. After applying a 0.1N pre-load on each arm, samples were subjected to equibiaxial cyclic loading using a triangular waveform to 2.5mm displacement on each arm at 0.1Hz for 10 cycles. Samples were then subjected to two strip biaxial tests (using the same cyclic loading protocol), where extension was applied along a single axis with the other axis held fixed. The thirteen evaluated mesh types exhibited a wide range of mechanical properties. Some were nearly isotropic (C-QUR™, DUALMESH(®), PHYSIOMESH™, and PROCEED(®)), while others were highly anisotropic (Ventralight™ ST, Bard™ Mesh, and Bard™ Soft Mesh). Some displayed nearly linear behavior (Bard™ Mesh), while others were non-linear with a long toe region followed by a sharp rise in tension (INFINIT(®)). These materials are currently utilized in clinical settings as if they are uniform and interchangeable, and clearly this is not the case. The mechanical properties most advantageous for successful hernia repairs are currently only vaguely described

Shear flow simulations of biaxial nematic liquid crystals

Science.gov (United States)

Sarman, Sten

1997-08-01

We have calculated the viscosities of a biaxial nematic liquid crystal phase of a variant of the Gay-Berne fluid [J. G. Gay and B. J. Berne, J. Chem. Phys. 74, 3316 (1981)] by performing molecular dynamics simulations. The equations of motion have been augmented by a director constraint torque that fixes the orientation of the directors. This makes it possible to fix them at different angles relative to the stream lines in shear flow simulations. In equilibrium simulations the constraints generate a new ensemble. One finds that the Green-Kubo relations for the viscosities become linear combinations of time correlation function integrals in this ensemble whereas they are complicated rational functions in the conventional canonical ensemble. We have evaluated these Green-Kubo relations for all the shear viscosities and all the twist viscosities. We have also calculated the alignment angles, which are functions of the viscosity coefficients. We find that there are three real alignment angles but a linear stability analysis shows that only one of them corresponds to a stable director orientation. The Green-Kubo results have been cross checked by nonequilibrium shear flow simulations. The results from the different methods agree very well. Finally, we have evaluated the Miesowicz viscosities [D. Baalss, Z. Naturforsch. Teil A 45, 7 (1990)]. They vary by more than 2 orders of magnitude. The viscosity is consequently highly orientation dependent.

A critical analysis of the Mises stress criterion used in frequency domain fatigue life prediction

Directory of Open Access Journals (Sweden)

Adam Niesłony

2016-10-01

Full Text Available Multiaxial fatigue failure criteria are formulated in time and frequency domain. The number of frequency domain criteria is rather small and the most popular one is the equivalent von Mises stress criterion. This criterion was elaborated by Preumont and Piefort on the basis of well-known von Mises stress concept, first proposed by Huber in 1907, and well accepted by the scientific community and engineers. It is important to know, that the criterion was developed to determine the yield stress and material effort under static load. Therefore the direct use of equivalent von Mises stress criterion for fatigue life prediction can lead to some incorrectness of theoretical and practical nature. In the present study four aspects were discussed: influence of the value of fatigue strength of tension and torsion, lack of parallelism of the SN curves, abnormal behaviour of the criterion under biaxial tensioncompression and influence of phase shift between particular stress state components. Information contained in this article will help to prevent improper use of this criterion and contributes to its better understanding

Failure criteria for low-temperature irradiated organic composite insulation systems

International Nuclear Information System (INIS)

Schutz, J.B.; Fabian, P.E.

1997-01-01

Composite insulation systems in fusion magnet applications are often subjected to conditions of combined through thickness compression and shear at varying stress ratios. Characterization of insulation system strength under these conditions requires unidirectional shear and compression tests, as well as biaxial shear/compression testing to define the systems failure envelope. An appropriate failure criteria would reduce the number of tests required to define this envelope, and would give designers a better estimate of material strengths at intermediate stress ratios. Biaxial shear/compression testing requires the use of metallic sandwich specimens, which are susceptible to activation during irradiation. A reliable failure criteria which eliminates the need for biaxial characterization would also reduce the difficulty and expense involved in radiation effects characterization while still providing a complete failure envelope. Several generalized failure criteria, taken from classical composites analysis, were reformulated for application in the shear/compression quadrant. The maximum stress and Tsai-Hill criteria were found to be inadequate to represent the biaxial failure envelope. The generalized Tsai-Wu tensor quadratic failure criterion was also examined. Application of this criterion requires through thickness tensile strength data. Through thickness tensile strengths of insulation systems have not been routinely characterized, but limited data are available. Utilizing unidirectional through thickness tension, compression, and interlaminar shear strength data, the Tsai-Wu failure criteria was found to agree well with biaxial shear/compression test data

Comparison of Some Mechanical and Physical Methods for Measurement of Residual Stresses in Brush-Plated Nickel Hardened Gold and Silver Coatings

Directory of Open Access Journals (Sweden)

Harri LILLE

2016-05-01

Full Text Available Hard gold and silver are applied in coating owing to their high hardness, good wear and corrosion resistance for engineering application (e.g. on generators slip rings, sliding contacts and small machine parts and are typically plated on copper (mostly, brass and bronze. The studied nickel-hardened gold and silver coatings were brush plated on open thin-walled copper ring substrates. Residual stresses in the coatings were calculated from the curvature changes of the substrates. Biaxial intrinsic residual stresses were also determined by nanoindentation testing and by the X-ray technique. The values of the residual stresses represented tensile stresses and when determined by the techniques used they were comparable within a maximum limit of measurement uncertainty. These stresses relax; the dependence of relaxation time was approximated by a linear-fractional function.DOI: http://dx.doi.org/10.5755/j01.ms.22.1.7439

Effect of shallow angles on compressive strength of biaxial and triaxial laminates.

Science.gov (United States)

Jia, Hongli; Yang, Hyun-Ik

2016-01-01

Biaxial (BX) and triaxial (TX) composite laminates with ±45° angled plies have been widely used in wind turbine blades. As the scale of blades increases, BX and TX laminates with shallow-angled plies (i.e. off-axis ply angle shallow-angled BX and TX laminates are critical considering their locations in a wind turbine blade, and therefore in this study, the uniaxial static compression tests were conducted using BX and TX laminates with angled-plies of ±45°, ±35°, and ±25°, for the purpose of evaluation. On the other hand, Mori-Tanaka mean field homogenization method was employed to predict elastic constants of plies in BX and TX laminates involved in tests; linear regression analyses of experimentally measured ply strengths collected from various sources were then performed to estimate strengths of plies in BX and TX laminates; finally, Tsai-Wu, Hashin, and Puck failure criteria were chosen to predict compressive strengths of BX and TX laminates. Comparison between theoretical predictions and test results were carried out to illustrate the effectiveness of each criterion. The compressive strength of BX laminate decreases as ply angle increases, and the trend was successfully predicted by all three failure criteria. For TX laminates, ±35° angled plies rather than ±45° angled plies led to the lowest laminate compressive strength. Hashin and Puck criteria gave good predictions at certain ply angles for TX laminates, but Tsai-Wu criterion was able to capture the unexpected strength variation of TX laminates with ply angle. It was concluded that the transverse tensile stress in 0° plies of TX laminates, which attains its maximum when the off-axis ply angle is 35°, is the dominant factor in failure determination if using Tsai-Wu criterion. This explains the unexpected strength variation of TX laminates with ply angle, and also indicates that proper selection of ply angle is the key to fully utilizing the advantages of shallow-angled laminates.

A constitutive framework for modelling thin incompressible viscoelastic materials under plane stress in the finite strain regime

Science.gov (United States)

Kroon, M.

2011-11-01

Rubbers and soft biological tissues may undergo large deformations and are also viscoelastic. The formulation of constitutive models for these materials poses special challenges. In several applications, especially in biomechanics, these materials are also relatively thin, implying that in-plane stresses dominate and that plane stress may therefore be assumed. In the present paper, a constitutive model for viscoelastic materials in the finite strain regime and under the assumption of plane stress is proposed. It is assumed that the relaxation behaviour in the direction of plane stress can be treated separately, which makes it possible to formulate evolution laws for the plastic strains on explicit form at the same time as incompressibility is fulfilled. Experimental results from biomechanics (dynamic inflation of dog aorta) and rubber mechanics (biaxial stretching of rubber sheets) were used to assess the proposed model. The assessment clearly indicates that the model is fully able to predict the experimental outcome for these types of material.

Research on self-calibration biaxial autocollimator based on ZYNQ

Science.gov (United States)

Guo, Pan; Liu, Bingguo; Liu, Guodong; Zhong, Yao; Lu, Binghui

2018-01-01

Autocollimators are mainly based on computers or the electronic devices that can be connected to the internet, and its precision, measurement range and resolution are all defective, and external displays are needed to display images in real time. What's more, there is no real-time calibration for autocollimator in the market. In this paper, we propose a biaxial autocollimator based on the ZYNQ embedded platform to solve the above problems. Firstly, the traditional optical system is improved and a light path is added for real-time calibration. Then, in order to improve measurement speed, the embedded platform based on ZYNQ that combines Linux operating system with autocollimator is designed. In this part, image acquisition, image processing, image display and the man-machine interaction interface based on Qt are achieved. Finally, the system realizes two-dimensional small angle measurement. Experimental results showed that the proposed method can improve the angle measurement accuracy. The standard deviation of the close distance (1.5m) is 0.15" in horizontal direction of image and 0.24"in vertical direction, the repeatability of measurement of the long distance (10m) is improved by 0.12 in horizontal direction of image and 0.3 in vertical direction.

Modeling of biaxial gimbal-less MEMS scanning mirrors

Science.gov (United States)

von Wantoch, Thomas; Gu-Stoppel, Shanshan; Senger, Frank; Mallas, Christian; Hofmann, Ulrich; Meurer, Thomas; Benecke, Wolfgang

2016-03-01

One- and two-dimensional MEMS scanning mirrors for resonant or quasi-stationary beam deflection are primarily known as tiny micromirror devices with aperture sizes up to a few Millimeters and usually address low power applications in high volume markets, e.g. laser beam scanning pico-projectors or gesture recognition systems. In contrast, recently reported vacuum packaged MEMS scanners feature mirror diameters up to 20 mm and integrated high-reflectivity dielectric coatings. These mirrors enable MEMS based scanning for applications that require large apertures due to optical constraints like 3D sensing or microscopy as well as for high power laser applications like laser phosphor displays, automotive lighting and displays, 3D printing and general laser material processing. This work presents modelling, control design and experimental characterization of gimbal-less MEMS mirrors with large aperture size. As an example a resonant biaxial Quadpod scanner with 7 mm mirror diameter and four integrated PZT (lead zirconate titanate) actuators is analyzed. The finite element method (FEM) model developed and computed in COMSOL Multiphysics is used for calculating the eigenmodes of the mirror as well as for extracting a high order (n system inputs and scanner displacement as system output. By applying model order reduction techniques using MATLABR a compact state space system approximation of order n = 6 is computed. Based on this reduced order model feedforward control inputs for different, properly chosen scanner displacement trajectories are derived and tested using the original FEM model as well as the micromirror.

Residual stress measurement in a metal microdevice by micro Raman spectroscopy

International Nuclear Information System (INIS)

Song, Chang; Du, Liqun; Qi, Leijie; Li, Yu; Li, Xiaojun; Li, Yuanqi

2017-01-01

Large residual stress induced during the electroforming process cannot be ignored to fabricate reliable metal microdevices. Accurate measurement is the basis for studying the residual stress. Influenced by the topological feature size of micron scale in the metal microdevice, residual stress in it can hardly be measured by common methods. In this manuscript, a methodology is proposed to measure the residual stress in the metal microdevice using micro Raman spectroscopy (MRS). To estimate the residual stress in metal materials, micron sized β -SiC particles were mixed in the electroforming solution for codeposition. First, the calculated expression relating the Raman shifts to the induced biaxial stress for β -SiC was derived based on the theory of phonon deformation potentials and Hooke’s law. Corresponding micro electroforming experiments were performed and the residual stress in Ni–SiC composite layer was both measured by x-ray diffraction (XRD) and MRS methods. Then, the validity of the MRS measurements was verified by comparing with the residual stress measured by XRD method. The reliability of the MRS method was further validated by the statistical student’s t -test. The MRS measurements were found to have no systematic error in comparison with the XRD measurements, which confirm that the residual stresses measured by the MRS method are reliable. Besides that, the MRS method, by which the residual stress in a micro inertial switch was measured, has been confirmed to be a convincing experiment tool for estimating the residual stress in metal microdevice with micron order topological feature size. (paper)

Residual stress measurement in a metal microdevice by micro Raman spectroscopy

Science.gov (United States)

Song, Chang; Du, Liqun; Qi, Leijie; Li, Yu; Li, Xiaojun; Li, Yuanqi

2017-10-01

Large residual stress induced during the electroforming process cannot be ignored to fabricate reliable metal microdevices. Accurate measurement is the basis for studying the residual stress. Influenced by the topological feature size of micron scale in the metal microdevice, residual stress in it can hardly be measured by common methods. In this manuscript, a methodology is proposed to measure the residual stress in the metal microdevice using micro Raman spectroscopy (MRS). To estimate the residual stress in metal materials, micron sized β-SiC particles were mixed in the electroforming solution for codeposition. First, the calculated expression relating the Raman shifts to the induced biaxial stress for β-SiC was derived based on the theory of phonon deformation potentials and Hooke’s law. Corresponding micro electroforming experiments were performed and the residual stress in Ni-SiC composite layer was both measured by x-ray diffraction (XRD) and MRS methods. Then, the validity of the MRS measurements was verified by comparing with the residual stress measured by XRD method. The reliability of the MRS method was further validated by the statistical student’s t-test. The MRS measurements were found to have no systematic error in comparison with the XRD measurements, which confirm that the residual stresses measured by the MRS method are reliable. Besides that, the MRS method, by which the residual stress in a micro inertial switch was measured, has been confirmed to be a convincing experiment tool for estimating the residual stress in metal microdevice with micron order topological feature size.

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

KAUST Repository

Majumdar, Apala

2011-12-01

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

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

Science.gov (United States)

Scheidegger, Noemy; Ferris, Mark; Phillips, Nigel

2014-01-01

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

Stress analyses of flat plates with attached nozzles. Vol. 2: Experimental stress analyses of a flat plate with one nozzle attached

International Nuclear Information System (INIS)

Battiste, R.L.; Peters, W.H.; Ranson, W.F.; Swinson, W.F.

1975-07-01

Vol. 1 of this report compares experimental results with theoretical stress distributions for a flat plate with one nozzle configuration and for a flat plate with two closely spaced nozzles attached. This volume contains the complete test results for a flat plate with one nozzle attached that was subjected to 1:1 and 1:2 biaxial planar loadings on the plate, to a thrust loading on the nozzle, and to a moment loading on the nozzle. The plate tested was 36 x 36 x 0.375 in., and the attached nozzle had an outer dia of 2.625 in. and a 0.250-in.-thick wall. The nozzle was located in the center of the plate and was considered to be free of weld distortions and irregularities in the junction area. (U.S.)

The correlation between mechanical stress and magnetic anisotropy in ultrathin films

International Nuclear Information System (INIS)

Sander, D.

1999-01-01

The impact of stress-driven structural transitions and of film strain on the magnetic properties of nm ferromagnetic films is discussed. The stress-induced bending of film-substrate composites is analysed to derive information on film stress due to lattice mismatch or due to surface-stress effects. The magneto-elastic coupling in epitaxial films is determined directly from the magnetostrictive bending of the substrate. The combination of stress measurements with magnetic investigations by the magneto-optical Kerr effect (MOKE) reveals the modification of the magnetic anisotropy by film stress. Stress-strain relations are derived for various epitaxial orientations to facilitate the analysis of the substrate curvature. Biaxial film stress and magneto-elastic coupling coefficients are measured in epitaxial Fe films in situ on W single-crystal substrates. Tremendous film stress of more than 10 GPa is measured in pseudomorphic Fe layers, and the important role of film stress as a driving force for the formation of misfit distortions and for inducing changes of the growth mode in monolayer thin films is presented. The direct measurement of the magneto-elastic coupling in epitaxial films proves that the magnitude and sign of the magneto-elastic coupling deviate from the respective bulk value. Even a small film strain of order 0.1% is found to induce a significant change of the effective magneto-elastic coupling coefficient. This peculiar behaviour is ascribed to a second-order strain dependence of the magneto-elastic energy density, in contrast to the linear strain dependence that is valid for bulk samples. (author)

Combined loading effects on the fracture mechanics behavior of line pipes

Energy Technology Data Exchange (ETDEWEB)

Bravo, R.E.; Cravero, S.; Ernst, H.A. [Tenaris Group, Campana (Argentina). SIDERCA R and D Center

2009-12-19

For certain applications, pipelines may be submitted to biaxial loading situations. In these cases, it is not clear the influence of the biaxial loading on the fracture mechanics behavior of cracked pipelines. For further understanding of biaxial loading effects, this work presents a numerical simulation of ductile tearing in a circumferentially surface cracked pipe under biaxial loading using the computational cell methodology. The model was adjusted with experimental results obtained in laboratory using single edge cracked under tension (SENT) specimens. These specimens appear as the better alternative to conventional fracture specimens to characterize fracture toughness of cracked pipes. The negligible effect of biaxial loadings on resistance curves was demonstrated. To guarantee the similarities of stress and strains fields between SENT specimens and cracked pipes subjected to biaxial loading, a constraint study using the J-Q methodology and the h parameter was used. The constraint study gives information about the characteristics of the crack-tip conditions. (author)

The effect of stress state on zirconium hydride reorientation

Science.gov (United States)

Cinbiz, Mahmut Nedim

correlating the finite element stress-state results with the spatial distribution of hydride microstructures observed within the optical micrographs for each sample. Experiments showed that the hydride reorientation was enhanced as the stress biaxiality increased. The threshold stress decreased from 150 MPa to 80 MPa when stress biaxiality ratio increased from uniaxial tension to near-equibiaxial tension. This behavior was also predicted by classical nucleation theory based on the Gibbs free energy of transformation being assisted by the far-field stress. An analysis of in situ X-ray diffraction data obtained during a thermo-mechanical cycle typical of vacuum drying showed a complex lattice-spacing behavior of the hydride phase during the dissolution and precipitation. The in-plane hydrides showed bilinear lattice expansion during heating with the intrinsic thermal expansion rate of the hydrides being observed only at elevated temperatures as they dissolve. For radial hydrides that precipitate during cooling under stress, the spacing of the close-packed {111} planes oriented normal to the maximum applied stress was permanently higher than the corresponding {111} plane spacing in the other directions. This behavior is believed to be a result of a complex stress state within the precipitating plate-like hydrides that induces a strain component within the hydrides normal to its "plate" face (i.e., the applied stress direction) that exceeds the lattice spacing strains in the other directions. During heat-up, the lattice spacing of these same "plate" planes actually contract due to the reversion of the stress state within the plate-like hydrides as they dissolve. The presence of radial hydrides and their connectivity with in-plane hydrides was shown to increase the ductile-to-brittle transition temperature during tensile testing. This behavior can be understood in terms of the role of radial hydrides in promoting the initiation of a long crack that subsequently propagates under

Stress hysteresis and mechanical properties of plasma-enhanced chemical vapor deposited dielectric films

Science.gov (United States)

Thurn, Jeremy; Cook, Robert F.; Kamarajugadda, Mallika; Bozeman, Steven P.; Stearns, Laura C.

2004-02-01

A comprehensive survey is described of the responses of three plasma-enhanced chemical vapor deposited dielectric film systems to thermal cycling and indentation contact. All three films—silicon oxide, silicon nitride, and silicon oxy-nitride—exhibited significant nonequilibrium permanent changes in film stress on thermal cycling or annealing. The linear relationship between stress and temperature changed after the films were annealed at 300 °C, representing a structural alteration in the film reflecting a change in coefficient of thermal expansion or biaxial modulus. A double-substrate method was used to deduce both thermoelastic properties before and after the anneal of selected films and the results were compared with the modulus deconvoluted from small-scale depth-sensing indentation experiments (nanoindentation). Rutherford backscattering spectrometry and hydrogen forward scattering were used to deduce the composition of the films and it was found that all the films contained significant amounts of hydrogen.

A methodology for interpretation of overcoring stress measurements in anisotropic rock

International Nuclear Information System (INIS)

Hakala, M.; Sjoeberg, J.

2006-11-01

The in situ state of stress is an important parameter for the design of a repository for final disposal of spent nuclear fuel. This report presents work conducted to improve the quality of overcoring stress measurements, focused on the interpretation of overcoring rock stress measurements when accounting for possible anisotropic behavior of the rock. The work comprised: (i) development/upgrading of a computer code for calculating stresses from overcoring strains for anisotropic materials and for a general overcoring probe configuration (up to six strain rosettes with six gauges each), (ii) development of a computer code for determining elastic constants for transversely isotropic rocks from biaxial testing, and (iii) analysis of case studies of selected overcoring measurements in both isotropic and anisotropic rocks from the Posiva and SKB sites in Finland and Sweden, respectively. The work was principally limited to transversely isotropic materials, although the stress calculation code is applicable also to orthotropic materials. The developed computer codes have been geared to work primarily with the Borre and CSIRO HI three-dimensional overcoring measurement probes. Application of the codes to selected case studies, showed that the developed tools were practical and useful for interpreting overcoring stress measurements conducted in anisotropic rock. A quantitative assessment of the effects of anisotropy may thus be obtained, which provides increased reliability in the stress data. Potential gaps in existing data and/or understanding can also be identified. (orig.)

Free vibration and biaxial buckling analysis of magneto-electro-elastic microplate resting on visco-Pasternak substrate via modified strain gradient theory

Science.gov (United States)

Jamalpoor, A.; Ahmadi-Savadkoohi, A.; Hosseini-Hashemi, Sh

2016-10-01

This paper deals with the theoretical analysis of free vibration and biaxial buckling of magneto-electro-elastic (MEE) microplate resting on Kelvin-Voigt visco-Pasternak foundation and subjected to initial external electric and magnetic potentials, using modified strain gradient theory (MSGT). Kirchhoff plate model and Hamilton’s principle are employed to extract the governing equations of motion. Governing equations were analytically solved to obtain clear closed-form expression for complex natural frequencies and buckling loads using Navier’s approach. Numerical results are presented to reveal variations of natural frequency and buckling load ratio of MEE microplate against different amounts of the length scale parameter, initial external electric and magnetic potentials, aspect ratio, damping and transverse and shear stiffness parameters of the visco-Pasternak foundation, length to thickness ratio, microplate thickness and higher modes. Numerical results of this study illustrate that by increasing thickness-to-material length scale parameter ratio, both natural frequency and buckling load ratio predicted by MSGT and modified couple stress theory are reduced because the non-dimensional length scale parameter tends to decrease the stiffness of structures and make them more flexible. In addition, results show that initial external electric and initial external magnetic potentials have no considerable influence on the buckling load ratio and frequency of MEE microplate as the microplate thickness increases.

Stress analysis of two-dimensional cellular materials with thick cell struts

International Nuclear Information System (INIS)

Lim, Do Hyung; Kim, Han Sung; Kim, Young Ho; Kim, Yoon Hyuk; Al-Hassani, S.T.S.

2008-01-01

Finite element analyses (FEA) were performed to thoroughly validate the collapse criteria of cellular materials presented in our previous companion paper. The maximum stress (von-Mises stress) on the cell strut surface and the plastic collapse stress were computed for two-dimensional (2D) cellular materials with thick cell struts. The results from the FEA were compared with those from theoretical criteria of authors. The FEA results were in good agreement with the theoretical results. The results indicate that when bending moment, axial and shear forces are considered, the maximum stress on the strut surface gives significantly different values in the tensile and compressive parts of the cell wall as well as in the two loading directions. Therefore, for the initial yielding of ductile cellular materials and the fracture of brittle cellular materials, in which the maximum stress on the strut surface is evaluated, it is necessary to consider not only the bending moment but also axial and shear forces. In addition, this study shows that for regular cellular materials with the identical strut geometry for all struts, the initial yielding and the plastic collapse under a biaxial state of stress occur not only in the inclined cell struts but also in the vertical struts. These FEA results support the theoretical conclusion of our previous companion paper that the anisotropic 2D cellular material has a truncated yield surface not only on the compressive quadrant but also on the tensile quadrant

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

International Nuclear Information System (INIS)

Hermsmeyer, S.; Reimann, J.

2002-01-01

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

Multi-mode technique for the determination of the biaxial Y{sub 2}SiO{sub 5} permittivity tensor from 300 to 6 K

Energy Technology Data Exchange (ETDEWEB)

Carvalho, N. C., E-mail: natalia.docarmocarvalho@research.uwa.edu.au; Le Floch, J-M.; Tobar, M. E. [School of Physics, The University of Western Australia, Crawley 6009 (Australia); ARC Centre of Excellence for Engineered Quantum Systems (EQuS), 35 Stirling Hwy, Crawley 6009 (Australia); Krupka, J. [Instytut Mikroelektroniki i Optoelektroniki PW, Koszykowa 75, 00-662 Warsaw (Poland)

2015-05-11

The Y{sub 2}SiO{sub 5} (YSO) crystal is a dielectric material with biaxial anisotropy with known values of refractive index at optical frequencies. It is a well-known rare-earth (RE) host material for optical research and more recently has shown promising performance for quantum-engineered devices. In this paper, we report the first microwave characterization of the real permittivity tensor of a bulk YSO sample, as well as an investigation of the temperature dependence of the tensor components from 296 K down to 6 K. Estimated uncertainties were below 0.26%, limited by the precision of machining the cylindrical dielectric. Also, the electrical Q-factors of a few electromagnetic modes were recorded as a way to provide some information about the crystal losses over the temperature range. To solve the tensor components necessary for a biaxial crystal, we developed the multi-mode technique, which uses simultaneous measurement of low order whispering gallery modes. Knowledge of the permittivity tensor offers important data, essential for the design of technologies involving YSO, such as microwave coupling to electron and hyperfine transitions in RE doped samples at low temperatures.

Recent Advances in High Cycle Fatigue

National Research Council Canada - National Science Library

Nicholas, Ted

2003-01-01

.... In this paper, in addition to developing approaches for predicting fatigue limits under various mean stresses and biaxial stress states, methods are presented for accounting for service-induced damage...

The Evaluation of the Effect of Strain Limits on the Physical Properties of Magnetorheological Elastomers Subjected to Uniaxial and Biaxial Cyclic Testing.

OpenAIRE

Gorman, Dave; Murphy, Niall; Ekins, Ray; Jerrams, Stephen

2017-01-01

Magnetorheological Elastomers (MREs) are “smart” materials whose physical properties are altered by the application of magnetic fields. In a previous study by the authors [1], variations in the physical properties of MREs have been evaluated when subjected to a range of magnetic field strengths for both uniaxial and biaxial cyclic tests. By applying the same magnetic field to similar samples, this paper investigates the effect of both the upper strain limit and the strain amplitude on the pro...

Investigations on the influence of the stress state on fracture-mechanical values

International Nuclear Information System (INIS)

Schmidt, P.

1979-01-01

Fracture toughness obtained from specimen can be applied to construction elements only when the same stress state exists. In standardised fracture-mechanical tests plain strain is realised. Using the stress intensity factor, a critical crack length or a critical load can be obtained. Above these values a crack propagates in an unstable way. The specimen are tested under uni-axial load. In this paper investigations have been made whether a biaxial load increases the stress state over the plain strain and whether consequently a decrease of the critical fracture toughness and a shift of the temperatures Tsub(g)sub(y) and Tsub(s) results which characterise the fracture behaviour of steel. In order to answer these questions the tests were made which induced due to their geometry an additional nominal stress parallel to the crack front in spite of uni-axial loading. The results were compared with those from specimen without an additional nominal stress and having in their cross section under same test conditions nearly the same plain strain. The fracture toughness of both specimen types were compared at temperatures between 142 K and 252 K and correlated to other material-characterising values. The tests were completed by stress analysis and by comparing the crack opening displacement. Due to the additional stress, Tsub(g)sub(y) was found to be 20 K higher than for the reference specimen. The fracture toughness decreases significantly in certain temperature ranges. The plastic stress concentration factor was comperatively higher and the remaining plastic crack opening decreases up to 25%. (orig.) [de

Reactor pressure vessel structural integrity research

International Nuclear Information System (INIS)

Pennell, W.E.; Corwin, W.R.

1994-01-01

Development continues on the technology used to assess the safety of irradiation-embrittled nuclear reactor pressure vessels (RPVs) containing flaws. Fracture mechanics tests on RPV steel, coupled with detailed elastic-plastic finite-element analyses of the crack-tip stress fields, have shown that (1) constraint relaxation at the crack tip of shallow surface flaws results in increased data scatter but no increase in the lower-bound fracture toughness, (2) the nil ductility temperature (NDT) performs better than the reference temperature for nil ductility transition (RT NDT ) as a normalizing parameter for shallow-flaw fracture toughness data, (3) biaxial loading can reduce the shallow-flaw fracture toughness, (4) stress-based dual-parameter fracture toughness correlations cannot predict the effect of biaxial loading on shallow-flaw fracture toughness because in-plane stresses at the crack tip are not influenced by biaxial loading, and (5) an implicit strain-based dual-parameter fracture toughness correlation can predict the effect of biaxial loading on shallow-flaw fracture toughness. Experimental irradiation investigations have shown that (1) the irradiation-induced shift in Charpy V-notch vs temperature behavior may not be adequate to conservatively assess fracture toughness shifts due to embrittlement, and (2) the wide global variations of initial chemistry and fracture properties of a nominally uniform material within a pressure vessel may confound accurate integrity assessments that require baseline properties

Biaxial Properties of the Left and Right Pulmonary Arteries in a Monocrotaline Rat Animal Model of Pulmonary Arterial Hypertension.

Science.gov (United States)

Pursell, Erica R; Vélez-Rendón, Daniela; Valdez-Jasso, Daniela

2016-11-01

In a monocrotaline (MCT) induced-pulmonary arterial hypertension (PAH) rat animal model, the dynamic stress-strain relation was investigated in the circumferential and axial directions using a linear elastic response model within the quasi-linear viscoelasticity theory framework. Right and left pulmonary arterial segments (RPA and LPA) were mechanically tested in a tubular biaxial device at the early stage (1 week post-MCT treatment) and at the advanced stage of the disease (4 weeks post-MCT treatment). The vessels were tested circumferentially at the in vivo axial length with matching in vivo measured pressure ranges. Subsequently, the vessels were tested axially at the mean pulmonary arterial pressure by stretching them from in vivo plus 5% of their length. Parameter estimation showed that the LPA and RPA remodel at different rates: axially, both vessels decreased in Young's modulus at the early stage of the disease, and increased at the advanced disease stage. Circumferentially, the Young's modulus increased in advanced PAH, but it was only significant in the RPA. The damping properties also changed in PAH; in the LPA relaxation times decreased continuously as the disease progressed, while in the RPA they initially increased and then decreased. Our modeling efforts were corroborated by the restructuring organization of the fibers imaged under multiphoton microscopy, where the collagen fibers become strongly aligned to the 45 deg angle in the RPA from an uncrimped and randomly organized state. Additionally, collagen content increased almost 10% in the RPA from the placebo to advanced PAH.

An evaluation of the processing conditions, structure, and properties (biaxial flexural strength and antibacterial efficacy) of sintered strontium-zinc-silicate glass ceramics.

Science.gov (United States)

Looney, Mark; Shea, Helen O'; Gunn, Lynda; Crowley, Dolores; Boyd, Daniel

2013-05-01

The use of artificial bone grafts has increased in order to satisfy a growing demand for bone replacement materials. Initial mechanical stability of synthetic bone grafts is very advantageous for certain clinical applications. Coupled with the advantage of mechanical strength, a material with inherent antibacterial properties would be very beneficial. A series of strontium-doped zinc silicate (Ca-Sr-Na-Zn-Si) glass ceramics have been characterized in terms of their crystalline structure, biaxial flexural strength and antibacterial efficacy based on the identification of optimum sintering conditions. All three glass ceramics, namely, BT110, BT111, and BT112 were found to be fully crystalline, with BT111 and BT112 comprising of biocompatible crystalline phases. The biaxial flexural strengths of the three glass ceramics ranged from 70 to 149 MPa and were shown to be superior to those of clinically established ceramics in dry conditions and following incubation in simulated physiological conditions. The bacteriostatic effect for each glass ceramic was also established, where BT112 showed an inhibitory effect against three of the most common bacteria found at implantation sites, namely, Enterococcus faecalis, methicillin-resistant Staphylococcus aureus (MRSA), and Pseudomonas aeruginosa. The results of the evaluation suggest that the materials studied offer advantages over current clinical materials and indicate the potential suitability of the glass ceramics as therapeutic bone grafts.

Non-linear analysis and the design of Pumpkin Balloons: stress, stability and viscoelasticity

Science.gov (United States)

Rand, J. L.; Wakefield, D. S.

Tensys have a long-established background in the shape generation and load analysis of architectural stressed membrane structures Founded upon their inTENS finite element analysis suite these activities have broadened to encompass lighter than air structures such as aerostats hybrid air-vehicles and stratospheric balloons Winzen Engineering couple many years of practical balloon design and fabrication experience with both academic and practical knowledge of the characterisation of the non-linear viscoelastic response of the polymeric films typically used for high-altitude scientific balloons Both companies have provided consulting services to the NASA Ultra Long Duration Balloon ULDB Program Early implementations of pumpkin balloons have shown problems of geometric instability characterised by improper deployment and these difficulties have been reproduced numerically using inTENS The solution lies in both the shapes of the membrane lobes and also the need to generate a biaxial stress field in order to mobilise in-plane shear stiffness Balloons undergo significant temperature and pressure variations in flight The different thermal characteristics between tendons and film can lead to significant meridional stress Fabrication tolerances can lead to significant local hoop stress concentrations particularly adjacent to the base and apex end fittings The non-linear viscoelastic response of the envelope film acts positively to help dissipate stress concentrations However creep over time may produce lobe geometry variations that may

Tuning magnetism by biaxial strain in native ZnO.

Science.gov (United States)

Peng, Chengxiao; Wang, Yuanxu; Cheng, Zhenxiang; Zhang, Guangbiao; Wang, Chao; Yang, Gui

2015-07-07

Magnetic ZnO, one of the most important diluted magnetic semiconductors (DMS), has attracted great scientific interest because of its possible technological applications in optomagnetic devices. Magnetism in this material is usually delicately tuned by the doping level, dislocations, and local structures. The rational control of magnetism in ZnO is a highly attractive approach for practical applications. Here, the tuning effect of biaxial strain on the d(0) magnetism of native imperfect ZnO is demonstrated through first-principles calculations. Our calculation results show that strain conditions have little effect on the defect formation energy of Zn and O vacancies in ZnO, but they do affect the magnetism significantly. For a cation vacancy, increasing the compressive strain will obviously decrease its magnetic moment, while tensile strain cannot change the moment, which remains constant at 2 μB. For a singly charged anion vacancy, however, the dependence of the magnetic moment on strain is opposite to that of the Zn vacancy. Furthermore, the ferromagnetic state is always present, irrespective of the strain type, for ZnO with two zinc vacancies, 2VZns. A large tensile strain is favorable for improving the Curie temperature and realizing room temperature ferromagnetism for ZnO-based native semiconductors. For ZnO with two singly charged oxygen vacancies, 2Vs, no ferromagnetic ordering can be observed. Our work points the way to the rational design of materials beyond ZnO with novel non-intrinsic functionality by simply tuning the strain in a thin film form.

Tensile creep of beta phase zircaloy-2

International Nuclear Information System (INIS)

Burton, B.; Reynolds, G.L.; Barnes, J.P.

1977-08-01

The tensile creep and creep rupture properties of beta-phase zircaloy-2 are studied under vacuum in the temperature and stress range 1300-1550 K and 0.5-2 MN/m 2 . The new results are compared with previously reported uniaxial and biaxial data. A small but systematic difference is noted between the uniaxial and biaxial creep data and reasons for this discrepancy are discussed. (author)

Modeling of the cold work stress relieved Zircaloy-4 cladding tubes mechanical behavior under PWR operating conditions

International Nuclear Information System (INIS)

Richard, F.; Delobelle, P.; Leclercq, S.; Bouffioux, P.; Rousselier, G.

2003-01-01

This paper proposes a damaged viscoplastic model to simulate, for different isotherms (320, 350, 380, 400 and 420 degC), the out-of-flux anisotropic mechanical behavior of cold work stress relieved Zircaloy-4 cladding tubes over the fluence range 0-85.1024 nm -2 (E > 1 MeV). The model, identified from uni and biaxial tests conducted at 350 and 400 degC, is validated from tests performed at 320, 380 and 420 degC. This model is able to simulate strain hardening under internal pressure followed by a stress relaxation period (thermal creep), which is representative of a pellet cladding mechanical interaction occurring during a power transient (class 2 incidental condition). Both the integration of a scalar state variable, characterizing the damage caused by a bombardment with neutrons, and the modification of the static recovery law allowed us to simulate the fast neutron flux effect (irradiation creep). (author)

Development of a Weibull model of cleavage fracture toughness for shallow flaws in reactor pressure vessel material

Energy Technology Data Exchange (ETDEWEB)

Bass, B.R.; Williams, P.T.; McAfee, W.J.; Pugh, C.E. [Oak Ridge National Lab., Heavy-Section Steel Technology Program, Oak Ridge, TN (United States)

2001-07-01

A primary objective of the United States Nuclear Regulatory Commission (USNRC) -sponsored Heavy-Section Steel Technology (HSST) Program is to develop and validate technology applicable to quantitative assessments of fracture prevention margins in nuclear reactor pressure vessels (RPVs) containing flaws and subjected to service-induced material toughness degradation. This paper describes an experimental/analytical program for the development of a Weibull statistical model of cleavage fracture toughness for applications to shallow surface-breaking and embedded flaws in RPV materials subjected to multi-axial loading conditions. The experimental part includes both material characterization testing and larger fracture toughness experiments conducted using a special-purpose cruciform beam specimen developed by Oak Ridge National Laboratory for applying biaxial loads to shallow cracks. Test materials (pressure vessel steels) included plate product forms (conforming to ASTM A533 Grade B Class 1 specifications) and shell segments procured from a pressurized-water reactor vessel intended for a nuclear power plant. Results from tests performed on cruciform specimens demonstrated that biaxial loading can have a pronounced effect on shallow-flaw fracture toughness in the lower-transition temperature region. A local approach methodology based on a three-parameter Weibull model was developed to correlate these experimentally-observed biaxial effects on fracture toughness. The Weibull model, combined with a new hydrostatic stress criterion in place of the more commonly used maximum principal stress in the kernel of the Weibull stress integral definition, is shown to provide a scaling mechanism between uniaxial and biaxial loading states for 2-dimensional flaws located in the A533-B plate material. The Weibull stress density was introduced as a matrice for identifying regions along a semi-elliptical flaw front that have a higher probability of cleavage initiation. Cumulative

Development of a Weibull model of cleavage fracture toughness for shallow flaws in reactor pressure vessel material

International Nuclear Information System (INIS)

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

2001-01-01

A primary objective of the United States Nuclear Regulatory Commission (USNRC) -sponsored Heavy-Section Steel Technology (HSST) Program is to develop and validate technology applicable to quantitative assessments of fracture prevention margins in nuclear reactor pressure vessels (RPVs) containing flaws and subjected to service-induced material toughness degradation. This paper describes an experimental/analytical program for the development of a Weibull statistical model of cleavage fracture toughness for applications to shallow surface-breaking and embedded flaws in RPV materials subjected to multi-axial loading conditions. The experimental part includes both material characterization testing and larger fracture toughness experiments conducted using a special-purpose cruciform beam specimen developed by Oak Ridge National Laboratory for applying biaxial loads to shallow cracks. Test materials (pressure vessel steels) included plate product forms (conforming to ASTM A533 Grade B Class 1 specifications) and shell segments procured from a pressurized-water reactor vessel intended for a nuclear power plant. Results from tests performed on cruciform specimens demonstrated that biaxial loading can have a pronounced effect on shallow-flaw fracture toughness in the lower-transition temperature region. A local approach methodology based on a three-parameter Weibull model was developed to correlate these experimentally-observed biaxial effects on fracture toughness. The Weibull model, combined with a new hydrostatic stress criterion in place of the more commonly used maximum principal stress in the kernel of the Weibull stress integral definition, is shown to provide a scaling mechanism between uniaxial and biaxial loading states for 2-dimensional flaws located in the A533-B plate material. The Weibull stress density was introduced as a matrice for identifying regions along a semi-elliptical flaw front that have a higher probability of cleavage initiation. Cumulative

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

International Nuclear Information System (INIS)

Iijima, Y.; Hosaka, M.; Sadakata, N.; Saitoh, T.; Kohno, O.; Takeda, K.

1997-01-01

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 J c sample, and agreed well with Norris close-quote equation for thin strip conductors. However, the low J c 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

Core structure and dynamics of non-Abelian vortices in a biaxial nematic spinor Bose-Einstein condensate

Science.gov (United States)

Borgh, Magnus O.; Ruostekoski, Janne

2016-05-01

We demonstrate that multiple interaction-dependent defect core structures as well as dynamics of non-Abelian vortices can be realized in the biaxial nematic (BN) phase of a spin-2 atomic Bose-Einstein condensate (BEC). An experimentally simple protocol may be used to break degeneracy with the uniaxial nematic phase. We show that a discrete spin-space symmetry in the core may be reflected in a breaking of its spatial symmetry. The discrete symmetry of the BN order parameter leads to non-commuting vortex charges. We numerically simulate reconnection of non-Abelian vortices, demonstrating formation of the obligatory rung vortex. In addition to atomic BECs, non-Abelian vortices are theorized in, e.g., liquid crystals and cosmic strings. Our results suggest the BN spin-2 BEC as a prime candidate for their realization. We acknowledge financial support from the EPSRC.

Elastic strain engineering of quantum dot excitonic emission in nanomembranes and optical resonators

Energy Technology Data Exchange (ETDEWEB)

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

2010-07-01

We study the effect of an external biaxial stress on the light emission of single InGaAs/GaAs(001) quantum dots (QD) embedded in a 200 nm-thick-membrane. Reversible and bi-directional spectral tuning of QD excitonic emission is demonstrated via a simple electro-mechanical device. The most intriguing finding is that biaxial strain is a reliable tool to engineer the QD electronic structure and reach color coincidence between exciton and biexciton emission, providing a vital prerequisite for the generation of polarization entangled photon pairs through a time reordering strategy. The physical origin of this new phenomenon is discussed based on the empirical pseudopotential calculations. With similar technique we study the effect of biaxial stress on single QDs embedded in microring resonators. The microrings can be reversibly stretched or squeezed, resulting in a controllable engineering of both QD emissions and optical modes. Our results open up a new tuning strategy to study cQED with semiconductor quantum dots.

Stress and Reliability Analysis of a Metal-Ceramic Dental Crown

Science.gov (United States)

Anusavice, Kenneth J; Sokolowski, Todd M.; Hojjatie, Barry; Nemeth, Noel N.

1996-01-01

Interaction of mechanical and thermal stresses with the flaws and microcracks within the ceramic region of metal-ceramic dental crowns can result in catastrophic or delayed failure of these restorations. The objective of this study was to determine the combined influence of induced functional stresses and pre-existing flaws and microcracks on the time-dependent probability of failure of a metal-ceramic molar crown. A three-dimensional finite element model of a porcelain fused-to-metal (PFM) molar crown was developed using the ANSYS finite element program. The crown consisted of a body porcelain, opaque porcelain, and a metal substrate. The model had a 300 Newton load applied perpendicular to one cusp, a load of 30ON applied at 30 degrees from the perpendicular load case, directed toward the center, and a 600 Newton vertical load. Ceramic specimens were subjected to a biaxial flexure test and the load-to-failure of each specimen was measured. The results of the finite element stress analysis and the flexure tests were incorporated in the NASA developed CARES/LIFE program to determine the Weibull and fatigue parameters and time-dependent fracture reliability of the PFM crown. CARES/LIFE calculates the time-dependent reliability of monolithic ceramic components subjected to thermomechanical and/Or proof test loading. This program is an extension of the CARES (Ceramics Analysis and Reliability Evaluation of Structures) computer program.

Effect of cyclic block loading on character of deformation and strength of structural materials in plane stressed state

International Nuclear Information System (INIS)

Kul'chitskij, N.M.; Troshchenko, A.V.; Koval'chuk, B.I.; Khamaza, L.A.; Nikolaev, I.A.

1982-01-01

The paper is concerned with choice of conditions for preliminary cyclic block loading, determination of fatigue failure resistance characteristics for various structural materials under regular and selected block loading, investigation of the preliminary cyclic loading effect on regularities of elastoplastic deformation of materials concerned in the biaxial stressed state. Under selected conditions of cyclic block loading the character of damage accumulation is close to the linear law for the materials of high-srength doped steel, and VT6 alloys of concern. These materials in the initial state and after preliminary cyclic loading are anisotropic. Axial direction is characterized by a higher plastic strain resistance for steel and tangential direction - for VT6 alloy. The generalized strain curves for the materials in question are not invariant as to the stressed state type. It is stated that the effect of preliminary unsteady cyclic loading on resistance and general regularities of material deformation in the complex stressed state is insignificant. It is observed that stress-strain properties of the materials tend to vary in the following way: plastic strain resistance of the steel lowers and that of VT6 rises, anisotropy of the materials somehow decreases. The variation in the material anisotropy may be attributed to a decrease in residual stresses resulting from preliminary cyclic loading

Foreshocks and Aftershocks Detected from Stick-slip Events on a 3 m Biaxial Apparatus and their Relationship to Quasistatic Nucleation and Wear Processes

Science.gov (United States)

Wu, S.; Mclaskey, G.

2017-12-01

We investigate foreshocks and aftershocks of dynamic stick-slip events generated on a newly constructed 3 m biaxial friction apparatus at Cornell University (attached figure). In a typical experiment, two rectangular granite blocks are squeezed together under 4 or 7 MPa of normal pressure ( 4 or 7 million N on a 1 m2 fault surface), and then shear stress is increased until the fault slips 10 - 400 microns in a dynamic rupture event similar to a M -2 to M -3 earthquake. Some ruptures nucleate near the north end of the fault, where the shear force is applied, other ruptures nucleate 2 m from the north end of the fault. The samples are instrumented with 16 piezoelectric sensors, 16 eddy current sensors, and 8 strain gage rosettes, evenly placed along the fault to measure vertical ground motion, local slip, and local stress, respectively. We studied sequences of tens of slip events and identified a total of 194 foreshocks and 66 aftershocks located within 6 s time windows around the stick-slip events and analyzed their timing and locations relative to the quasistatic nucleation process. We found that the locations of the foreshocks and aftershocks were distributed all along the length of the fault, with the majority located at the ends of the fault where local normal and shear stress is highest (caused by both edge effects and the finite stiffness of the steel frame surrounding the granite blocks). We also opened the laboratory fault and inspected the fault surface and found increased wear at the sample ends. To explore the foreshocks' and aftershocks' relationship to the nucleation and afterslip, we compared the occurrence of foreshocks to the local slip rate on the laboratory fault closest to each foreshock in space and time. We found that that majority of foreshocks were generated from local slip rates between 1 and 100 microns/s, though we were not able to resolve slip rate lower than about 1 micron/s. Our experiments provide insight into how foreshocks and

Intrinsic stress in ZrN thin films: Evaluation of grain boundary contribution from in situ wafer curvature and ex situ x-ray diffraction techniques

International Nuclear Information System (INIS)

Koutsokeras, L. E.; Abadias, G.

2012-01-01

Low-mobility materials, like transition metal nitrides, usually undergo large residual stress when sputter-deposited as thin films. While the origin of stress development has been an active area of research for high-mobility materials, atomistic processes are less understood for low-mobility systems. In the present work, the contribution of grain boundary to intrinsic stress in reactively magnetron-sputtered ZrN films is evaluated by combining in situ wafer curvature measurements, providing information on the overall biaxial stress, and ex situ x-ray diffraction, giving information on elastic strain (and related stress) inside crystallites. The thermal stress contribution was also determined from the in situ stress evolution during cooling down, after deposition was stopped. The stress data are correlated with variations in film microstructure and growth energetics, in the 0.13-0.42 Pa working pressure range investigated, and discussed based on existing stress models. At low pressure (high energetic bombardment conditions), a large compressive stress is observed due to atomic peening, which induces defects inside crystallites but also promotes incorporation of excess atoms in the grain boundary. Above 0.3-0.4 Pa, the adatom surface mobility is reduced, leading to the build-up of tensile stress resulting from attractive forces between under-dense neighbouring column boundary and possible void formation, while crystallites can still remain under compressive stress.

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

Science.gov (United States)

Karakolis, Thomas; Callaghan, Jack P

2015-01-01

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

Biodegradable multilayer barrier films based on alginate/polyethyleneimine and biaxially oriented poly(lactic acid).

Science.gov (United States)

Gu, Chun-Hong; Wang, Jia-Jun; Yu, Yang; Sun, Hui; Shuai, Ning; Wei, Bing

2013-02-15

A layer-by-layer (LBL) approach was used to assemble alternating layers of sodium alginate (ALG)/polyethyleneimine (PEI) on biaxially oriented poly(lactic acid) (BOPLA) films in order to produce bio-based all-polymer thin films with low gas permeability. Increasing the depositing of ALG and PEI from 0 to 30 layers results in large thickness variations (from 0 to 3.92 μm). After 30 ALG/PEI layers are deposited, the resulting assembly has an OTR of 1.22 cm(3)/(m(2) day atm). When multiplied by thickness, the resulting oxygen permeability (OP) is found to be less than 3.8×10(-17) cm(3) cm/cm(2) s Pa, which is almost 3 orders of magnitude lower than that of uncoated BOPLA film (1.8×10(-14) cm(3)cm/cm(2) s Pa). At the same time, the resulting multilayer-coated BOPLA films maintain high optical clarity and tensile properties. This unique barrier thin film has become a promising alternative to non-biodegradable synthetic food packaging materials. Copyright © 2012 Elsevier Ltd. All rights reserved.

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

International Nuclear Information System (INIS)

Dimakis, E.; Domagala, J.; Iliopoulos, E.; Adikimenakis, A.; Georgakilas, A.

2007-01-01

The in-plane lattice parameters of InN, GaN and Al 2 O 3 in a InN/GaN/Al 2 O 3 (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 Al 2 O 3 substrate's lattice and there is no rearrangement of misfit dislocations at the InN/GaN and GaN/Al 2 O 3 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.)

Stress assessment in piping under synthetic thermal loads emulating turbulent fluid mixing

Energy Technology Data Exchange (ETDEWEB)

Costa Garrido, Oriol, E-mail: oriol.costa@ijs.si; El Shawish, Samir, E-mail: samir.elshawish@ijs.si; Cizelj, Leon, E-mail: leon.cizelj@ijs.si

2015-03-15

Highlights: • Generation of complex space-continuous and time-dependent temperature fields. • 1D and 3D thermo-mechanical analyses of pipes under complex surface thermal loads. • Surface temperatures and stress fluctuations are highly linearly correlated. • 1D and 3D results agree for a wide range of Fourier and Biot numbers. • Global thermo-mechanical loading promotes non-equibiaxial stress state. - Abstract: Thermal fatigue assessment of pipes due to turbulent fluid mixing in T-junctions is a rather difficult task because of the existing uncertainties and variability of induced thermal stresses. In these cases, thermal stresses arise on three-dimensional pipe structures due to complex thermal loads, known as thermal striping, acting at the fluid-wall interface. A recently developed approach for the generation of space-continuous and time-dependent temperature fields has been employed in this paper to reproduce fluid temperature fields of a case study from the literature. The paper aims to deliver a detailed study of the three-dimensional structural response of piping under the complex thermal loads arising in fluid mixing in T-junctions. Results of three-dimensional thermo-mechanical analyses show that fluctuations of surface temperatures and stresses are highly linearly correlated. Also, surface stress fluctuations, in axial and hoop directions, are almost equi-biaxial. These findings, representative on cross sections away from system boundaries, are moreover supported by the sensitivity analysis of Fourier and Biot numbers and by the comparison with standard one-dimensional analyses. Agreement between one- and three-dimensional results is found for a wide range of studied parameters. The study also comprises the effects of global thermo-mechanical loading on the surface stress state. Implemented mechanical boundary conditions develop more realistic overall system deformation and promote non-equibiaxial stresses.

A multi-axis confocal rheoscope for studying shear flow of structured fluids

KAUST Repository

Lin, Neil Y. C.

2014-03-01

We present a new design for a confocal rheoscope that enables uniform uniaxial or biaxial shear. The design consists of two precisely positioned parallel plates with a gap that can be adjusted down to 2 ±0.1 μm, allowing for the exploration of confinement effects. By using our shear cell in conjunction with a biaxial force measurement device and a high-speed confocal microscope, we are able to measure the real-time biaxial stress while simultaneously imaging the material three-dimensional structure. We illustrate the importance of the instrument capabilities by discussing the applications of this instrument in current and future research topics in colloidal suspensions. © 2014 AIP Publishing LLC.

Distribution and viability of fetal and adult human bone marrow stromal cells in a biaxial rotating vessel bioreactor after seeding on polymeric 3D additive manufactured scaffolds

Directory of Open Access Journals (Sweden)

Anne eLeferink

2015-10-01

Full Text Available One of the conventional approaches in tissue engineering is the use of scaffolds in combination with cells to obtain mechanically stable tissue constructs in vitro prior to implantation. Additive manufacturing by fused deposition modeling is a widely used technique to produce porous scaffolds with defined pore network, geometry, and therewith defined mechanical properties. Bone marrow derived mesenchymal stromal cells (MSCs are promising candidates for tissue engineering based cell therapies due to their multipotent character. One of the hurdles to overcome when combining additive manufactured scaffolds with MSCs is the resulting heterogeneous cell distribution and limited cell proliferation capacity. In this study, we show that the use of a biaxial rotating bioreactor, after static culture of human fetal MSCs (hfMSCs seeded on synthetic polymeric scaffolds, improved the homogeneity of cell and extracellular matrix (ECM distribution and increased the total cell number. Furthermore, we show that the relative mRNA expression levels of indicators for stemness and differentiation are not significantly changed upon this bioreactor culture, whereas static culture shows variations of several indicators for stemness and differentiation. The biaxial rotating bioreactor presented here offers a homogeneous distribution of hfMSCs, enabling studies on MSCs fate in additive manufactured scaffolds without inducing undesired differentiation.

Frictional response of simulated faults to normal stresses perturbations probed with ultrasonic waves

Science.gov (United States)

Shreedharan, S.; Riviere, J.; Marone, C.

2017-12-01

We report on a suite of laboratory friction experiments conducted on saw-cut Westerly Granite surfaces to probe frictional response to step changes in normal stress and loading rate. The experiments are conducted to illuminate the fundamental processes that yield friction rate and state dependence. We quantify the microphysical frictional response of the simulated fault surfaces to normal stress steps, in the range of 1% - 600% step increases and decreases from a nominal baseline normal stress. We measure directly the fault slip rate and account for changes in slip rate with changes in normal stress and complement mechanical data acquisition by continuously probing the faults with ultrasonic pulses. We conduct the experiments at room temperature and humidity conditions in a servo controlled biaxial testing apparatus in the double direct shear configuration. The samples are sheared over a range of velocities, from 0.02 - 100 μm/s. We report observations of a transient shear stress and friction evolution with step increases and decreases in normal stress. Specifically, we show that, at low shear velocities and small increases in normal stress ( 5% increases), the shear stress evolves immediately with normal stress. We show that the excursions in slip rate resulting from the changes in normal stress must be accounted for in order to predict fault strength evolution. Ultrasonic wave amplitudes which first increase immediately in response to normal stress steps, then decrease approximately linearly to a new steady state value, in part due to changes in fault slip rate. Previous descriptions of frictional state evolution during normal stress perturbations have not adequately accounted for the effect of large slip velocity excursions. Here, we attempt to do so by using the measured ultrasonic amplitudes as a proxy for frictional state during transient shear stress evolution. Our work aims to improve understanding of induced and triggered seismicity with focus on

Effect of plastic deformation and strain history on X-ray elastic constants

International Nuclear Information System (INIS)

Iadicola, Mark A.; Foecke, Tim

2005-01-01

The use of X-ray diffraction to measure residual stress in a crystalline material is well known. This method is currently being reapplied to the surface measurement of in situ stresses during biaxial straining of sheet metal specimens. This leads to questions of precision and calibration of the method through plastic deformation. Little is known of the change, with plastic work, in the X-ray elastic constants (XECs) that are required by the technique for stress measurement. Experiments to determine the formability of various materials using this stress measurement technique in conjunction with a typical Marciniak test (with the Raghavan variation of specimen shapes) have been performed assuming a constant value for XECs. New results of calibration experiments are presented which admit the possibility of variation of the XECs with plastic strain history and initial texture of the material. Adjustment of the data from the previously performed formability experiments is shown. Additionally, various phenomena are captured including initial yielding, change of XECs with plastic strain level (both with uniaxial and biaxial strain histories), and some of the effects of texture on the technique. This technique has potential application in verification of the assumptions made during other standard testing methods (in-plane biaxial specimen geometries and bulge testing), verifying stress predictions from finite element analyses (i.e. benchmarking experiments such as BM3), analysis of stress states in localized deformation (yield point effects), and tracking of the effect of prestraining on material formability through the process of multistage forming

On the Novel Biaxial Strain Relaxation Mechanism in Epitaxial Composition Graded La1−xSrxMnO3 Thin Film Synthesized by RF Magnetron Sputtering

Directory of Open Access Journals (Sweden)

Yishu Wang

2015-11-01

Full Text Available We report on a novel method to fabricate composition gradient, epitaxial La1−xSrxMnO3 thin films with the objective to alleviate biaxial film strain. In this work, epitaxial, composition gradient La1−xSrxMnO3, and pure LaMnO3 and La0.67Sr0.33MnO3 thin films were deposited by radio frequency (RF magnetron sputtering. The crystalline and epitaxy of all films were first studied by symmetric θ–2θ X-ray diffraction (XRD and low angle XRD experiments. Detailed microstructural characterization across the film thickness was conducted by high-resolution transmission electron microscopy and electron diffraction. Four compositional gradient domains were observed in the La1−xSrxMnO3 film ranging from LaMnO3 rich to La0.67Sr0.33MnO3 at the surface. A continuous reduction in the lattice parameter was observed accompanied by a significant reduction in the out-of-plane strain in the film. Fabrication of the composition gradient La1−xSrxMnO3 thin film was found to be a powerful method to relieve biaxial strain under critical thickness. Besides, the coexistence of domains with a composition variance is opening up various new possibilities of designing new nanoscale structures with unusual cross coupled properties.

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

Energy Technology Data Exchange (ETDEWEB)

Richard D’Costa, Vijay, E-mail: elevrd@nus.edu.sg; Wang, Wei; Zhou, Qian; Yeo, Yee-Chia, E-mail: eleyeoyc@nus.edu.sg [Department of Electrical and Computer Engineering, National University of Singapore, Singapore 117583 (Singapore); Soon Tok, Eng [Department of Physics, National University of Singapore, Singapore 117551 (Singapore)

2014-01-13

The complex dielectric function of biaxially strained Ge{sub 1−x}Sn{sub x} (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 E{sub 1}, E{sub 1} + Δ{sub 1}, E{sub 0}′, and E{sub 2} 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 E{sub 1} and E{sub 1} + Δ{sub 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.

Effect of laser shock peening on residual stress and fatigue life of clad 2024 aluminium sheet containing scribe defects

International Nuclear Information System (INIS)

Dorman, M.; Toparli, M.B.; Smyth, N.; Cini, A.; Fitzpatrick, M.E.; Irving, P.E.

2012-01-01

Highlights: ► Effect of laser peen intensity on local residual stress fields in 2024 aluminium. ► Peening induces significant changes in surface topography and local hardness. ► Residual stress at peen spot centre in tension, spot overlap in compression. ► Notched fatigue lives increased; crack morphology correlated to residual stress field. ► Large peening power densities can cause fatigue life reduction in notched samples. - Abstract: Laser peening at a range of power densities has been applied to 2 mm-thick sheets of 2024 T351 aluminium. The induced residual stress field was measured using incremental hole drilling and synchrotron X-ray diffraction techniques. Fatigue samples were subjected to identical laser peening treatments followed by scribing at the peen location to introduce stress concentrations, after which they were fatigue tested. The residual stresses were found to be non-biaxial: orthogonal to the peen line they were tensile at the surface, moving into the desired compression with increased depth. Regions of peen spot overlap were associated with large compression strains; the centre of the peen spot remaining tensile. Fatigue lives showed moderate improvement over the life of unpeened samples for 50 μm deep scribes, and slight improvement for samples with 150 μm scribes. Use of the residual stress intensity K resid approach to calculate fatigue life improvement arising from peening was unsuccessful at predicting the relative effects of the different peening treatments. Possible reasons for this are explored.

Evaluation of Biaxial Mechanical Properties of Aortic Media Based on the Lamellar Microstructure

Directory of Open Access Journals (Sweden)

Hadi Taghizadeh

2015-01-01

Full Text Available Evaluation of the mechanical properties of arterial wall components is necessary for establishing a precise mechanical model applicable in various physiological and pathological conditions, such as remodeling. In this contribution, a new approach for the evaluation of the mechanical properties of aortic media accounting for the lamellar structure is proposed. We assumed aortic media to be composed of two sets of concentric layers, namely sheets of elastin (Layer I and interstitial layers composed of mostly collagen bundles, fine elastic fibers and smooth muscle cells (Layer II. Biaxial mechanical tests were carried out on human thoracic aortic samples, and histological staining was performed to distinguish wall lamellae for determining the dimensions of the layers. A neo-Hookean strain energy function (SEF for Layer I and a four-parameter exponential SEF for Layer II were allocated. Nonlinear regression was used to find the material parameters of the proposed microstructural model based on experimental data. The non-linear behavior of media layers confirmed the higher contribution of elastic tissue in lower strains and the gradual engagement of collagen fibers. The resulting model determines the nonlinear anisotropic behavior of aortic media through the lamellar microstructure and can be assistive in the study of wall remodeling due to alterations in lamellar structure during pathological conditions and aging.

Epitaxial YBa2Cu3O7 on biaxially textured (001) Ni: An approach to high critical current density superconducting tapes

International Nuclear Information System (INIS)

Norton, D.P.; Goyal, A.; Budai, J.D.

1997-01-01

In-plane aligned, c-axis oriented YBa 2 Cu 3 O 7 (YBCO) films with superconducting critical current densities, J c , as high as 700,000 amperes per square centimeter at 77 kelvin have been grown on thermo-mechanically, rolled-textured (001) Ni tapes using pulsed-laser deposition. Epitaxial growth of oxide buffer layers directly on biaxially textured Ni, formed by recrystallization of cold-rolled pure Ni, enables the growth of 1.5 micrometer-thick YBCO films with superconducting properties that are comparable to those observed for epitaxial films on single crystal oxide substrates. This result represents a viable approach for producing long-length superconducting tapes for high current, high field applications at 77 kelvin

Green-Kubo relations for the viscosity of biaxial nematic liquid crystals

Science.gov (United States)

Sarman, Sten

1996-09-01

We derive Green-Kubo relations for the viscosities of a biaxial nematic liquid crystal. In this system there are seven shear viscosities, three twist viscosities, and three cross coupling coefficients between the antisymmetric strain rate and the symmetric traceless pressure tensor. According to the Onsager reciprocity relations these couplings are equal to the cross couplings between the symmetric traceless strain rate and the antisymmetric pressure. Our method is based on a comparison of the microscopic linear response generated by the SLLOD equations of motion for planar Couette flow (so named because of their close connection to the Doll's tensor Hamiltonian) and the macroscopic linear phenomenological relations between the pressure tensor and the strain rate. In order to obtain simple Green-Kubo relations we employ an equilibrium ensemble where the angular velocities of the directors are identically zero. This is achieved by adding constraint torques to the equations for the molecular angular accelerations. One finds that all the viscosity coefficients can be expressed as linear combinations of time correlation function integrals (TCFIs). This is much simpler compared to the expressions in the conventional canonical ensemble, where the viscosities are complicated rational functions of the TCFIs. The reason for this is, that in the constrained angular velocity ensemble, the thermodynamic forces are given external parameters whereas the thermodynamic fluxes are ensemble averages of phase functions. This is not the case in the canonical ensemble. The simplest way of obtaining numerical estimates of viscosity coefficients of a particular molecular model system is to evaluate these fluctuation relations by equilibrium molecular dynamics simulations.

Development and application of a material law for steel-fibre-reinforced concrete with regard to its use for pre-stressed concrete reactor vessels

International Nuclear Information System (INIS)

Schimmelpfennig, K.; Borgerhoff, M.

1995-01-01

On the basis of the evaluation of many publications on the mechanical behaviour of steel fibre reinforced concrete (SFRC) and on the results of experiments using an SFRC especially developed for pre-stressed concrete reactor vessels (PCRVs), a material law for SFRC including general multiaxial stress conditions has been developed. From fibre pull-out tests described in the literature and by use of the experimental results, relations describing the capable tensile stress in SFRC after cracking, as a function of crack width, have been derived. There is a significant increase in the biaxial compressive strength of SFRC compared with plain concrete. The improved behaviour under multiaxial stress conditions, with one of the principal stresses being tensile, is outlined in comparison with different formulations of failure envelopes of plain concrete. For the purpose of verifying the material law implemented in the computer program used, analyses have been carried out for experiments with SFRC beams. After some modification concerning the shear behaviour, load-displacement curves and realistic crack propagations which correspond well have been obtained. In the stand-tube area in the centre of a PCRV top cap the use of SFRC is advantageous because of the difficulties concerning the arrangement of reinforcement in the concrete between the tubes. (orig.)

Residual stress investigation of copper plate and canister EB-Welds Complementary Results

International Nuclear Information System (INIS)

Gripenberg, H.

2009-03-01

The residual stresses in copper as induced by EB-welding were studied by specimens where the weld had two configurations: either a linear or a circumferential weld. This report contains the residual stress measurements of two plates, containing linear welds, and the full-scale copper lid specimen to which a hollow cylinder section had been joined by a circumferential EB-weld. The residual stress state of the EB-welded copper specimens was investigated by X-ray diffraction (XRD), hole drilling (HD) ring core (RC) and contour method (CM). Three specimens, canister XK010 and plates X251 and X252, were subjected to a thorough study aiming at quantitative determination of the residual stress state in and around the EB-welds using XRD for surface and HD and RC for spatial stress analysis. The CM maps one stress component over a whole cross section. The surface residual stresses measured by XRD represent the machined condition of the copper material. The XRD study showed that the stress changes towards compression close to the weld in the hollow cylinder, which indicates shrinkage in the hoop direction. According to the same analogy, the shrinkage in the axial direction is much smaller. The HD measurements showed that the stress state in the base material is bi-axial and, in terms of von Mises stress, 50 MPa for the plates and 20 MPa for the cylinder part of the canister. The stress state in the EB-welds of all specimens differs clearly from the stress state in the base material being more tensile, with higher magnitudes of von Mises stress in the plate than in the canister welds. The HD and RC results were obtained using linear elastic theory. The RC measurements showed that the maximum principal stress in the BM is close to zero near the surface and it becomes slightly tensile, 10 MPa, deeper under the surface. Welding pushed the general stress state towards tension with the maximum principal stress reaching 50 MPa, deeper than 5 mm below the surface in the weld. The

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

International Nuclear Information System (INIS)

Behera, Harihar; Mukhopadhyay, Gautam

2014-01-01

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 (δ). ML-ZnS gets buckled for compressive strain greater than 0.92% ; the buckling parameter Δ(= 0.00 Å for planar ML-ZnS) linearly increases with increasing compressive strain (Δ = 0.435 Å at δ = −5.25%). A tensile strain of 2.91% turns the direct ML-ZnS band gap into indirect. Within our considered strain values of |δ| < 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. (paper)

Determination of global and local residual stresses in SOFC by X-ray diffraction

International Nuclear Information System (INIS)

Villanova, Julie; Sicardy, Olivier; Fortunier, Roland; Micha, Jean-Sebastien; Bleuet, Pierre

2010-01-01

Solid Oxide Fuel Cell (SOFC) is a high-performance electrochemical device for energy conversion. A single cell is composed of five layers made of different ceramic materials: anode support, anode functional layer, electrolyte, cathode functional layer and cathode. The mechanical integrity of the cell is a major issue during its lifetime, especially for the electrolyte layer. Damage of the cells is mainly due to the high operating temperature, the 'redox' behaviour of the anode and the brittleness of the involved materials. Since residual stresses are known to play a significant role in the damage evolution, it is important to determine them. For this purpose, residual stresses in an anode-supported planar SOFC were measured by X-ray diffraction. Firstly, macroscopic stresses in each phase of each layer were studied using the sin 2 ψ method on a laboratory X-ray goniometer at room temperature. This technique enables the calculation of residual stress of the material from the measurement of the crystal lattice deformation. The electrolyte has been found under bi-axial compressive stress of -920 MPa. Secondly, X-ray measurements controlling depth penetration were made in the electrolyte using grazing incidence method. The results show that the stress is not homogenous in the layer. The first five micrometers of the electrolyte have been found less constrained (-750 MPa) than the complete layer, suggesting a gradient of deformation in the electrolyte from the interface with the Anode Functional Layer to the free surface. Finally, local stress measurements were made on the electrolyte layer by X-ray synchrotron radiation that allows high accuracy measurement on the (sub-) micrometer scale. Polychromatic and monochromatic beams are used to determine the complete strain tensor from grain to grain in the electrolyte. First results confirm the macroscopic stress trend of the electrolyte. These X-ray techniques at different scales will contribute to a better understanding

Strain distribution and failure mode of polymer separators for Li-ion batteries under biaxial loading

Science.gov (United States)

Kalnaus, Sergiy; Kumar, Abhishek; Wang, Yanli; Li, Jianlin; Simunovic, Srdjan; Turner, John A.; Gorney, Phillip

2018-02-01

Deformation of polymer separators for Li-ion batteries has been studied under biaxial tension by using a dome test setup. This deformation mode provides characterization of separator strength under more complex loading conditions, closer representing deformation of an electric vehicle battery during crash event, compared to uniaxial tension or compression. Two polymer separators, Celgard 2325 and Celgard 2075 were investigated by deformation with spheres of three different diameters. Strains in separators were measured in situ by using Digital Image Correlation (DIC) technique. The results show consistent rupture of separators along the machine direction coinciding with areas of high strain accumulation. The critical first principal strain for failure was independent of the sphere diameter and was determined to be approximately 34% and 43% for Celgard 2325 and Celgard 2075 respectively. These values can be taken as a criterion for internal short circuit in a battery following an out-of-plane impact. A Finite Element (FE) model was built with the anisotropic description of separator behavior, derived from tensile tests in orthogonal directions. The results of simulations predicted the response of separator rather well when compared to experimental results for various sizes of rigid sphere.

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

Directory of Open Access Journals (Sweden)

Raúl Gregor

2015-01-01

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

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

International Nuclear Information System (INIS)

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

2013-01-01

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. (paper)

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

Energy Technology Data Exchange (ETDEWEB)

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

2015-06-01

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

In-pile creep behaviour of Zry-4 and ZrNb3Sn1 cladding under uniaxial and biaxial stress

International Nuclear Information System (INIS)

Boehner, G.; Wildhagen, B.; Wilhelm, H.

1987-01-01

An irradiation programme - started in 1977 - was performed at the research reactor FRG-2 at Geesthacht, Germany, as a joint project of GKSS and KWU in order to study the in-pile creep behaviour of zirconium alloy cladding tubes of PWR fuel rods. The test objective was to establish a data base which allows refined modelling of the in-pile creep phenomenon. A wide test matrix was realized in which each of the precisely monitored test conditions (hoop stress, temperature, fast neutron flux) was varied separately. Different cladding materials (Zircaloy-4 and Zirconium-Niob-Tin alloy ZrNb3Sn1) were subjected to those varying test conditions. Cladding tube specimens of 10.75 mm outer diameter were irradiated in test capsules under various stress conditions and levels up to approx. 6000 h, at temperatures ranging from 300 0 C to 400 0 C and fast neutron flux (E > 1 MeV) of approx. 3x10 13 cm -2 .s -1 . Diametrical and/or axial creep deformation of all tubes were measured in the Hot Cells several times in the course of the tests. In order to extract the irradiation induced creep strain some out-pile experiments were carried out under the very same test conditions as the in-pile tests concerned. (orig./GL)

Synthesis and physical properties of zinc-oxide textured films by using a filtered preheated hydrothermal

International Nuclear Information System (INIS)

Qiu, Jijun; Shin, Dongmyeong; He, Weizhen; Kim, Hyungkook; Hwang, Yoonhwae; Li, Xiaomin; Gao, Xiangdong

2014-01-01

Axially (c-axis)-oriented ZnO thick films with a ∼8.1 μm thickness were fabricated on ZnO seed layer coated substrates by using a filtered preheated hydrothermal solution. The thick films composed of single-crystal ZnO microrods with various diameters were formed by coalescing each nanorod together along their side surfaces. From the X-ray diffraction result a biaxial stress exists was found to exist in the as-grown thick films, and the stress gradually increased with increasing annealing temperatures from 200 to 550 .deg. C due to a degradation in the crystalline quality. The biaxial stress is responsible for the red-shift of the optical band gap of the ZnO thick films. Photoluminescence and Hall results revealed that the optical and the electrical properties of the thick films were degenerated after high-temperature annealing (> 200 .deg. C), which was due to the introduction of point defects, such as oxygen interstitials and zinc vacancies.

Continuum and micro-mechanics treatment of constraint in fracture

International Nuclear Information System (INIS)

Dodds, R.H. Jr.; Shih, C.F.

1993-01-01

This paper explores the fundamental concepts of the J-Q description of crack-tip fields, the fracture toughness locus and micromechanics approaches to predict the variability of macroscopic fracture toughness with constraint under elastic-plastic conditions. While these concepts derived from plane-strain considerations, initial applications in fully 3-D geometries are very promising. Computational results are presented for a surface cracked plate containing a 6:1 semi-elliptical, a=t/4 flaw subjected to remote uniaxial and biaxial tension. Crack-tip stress fields consistent with the J-Q theory are demonstrated to exist at each location along the crack front. The micromechanics model employs the J-Q description of crack-front stresses to interpret fracture toughness values measured on laboratory specimens for fracture assessment of the surface cracked plate. The computational results suggest only a minor effect of the biaxial loading on the crack tip stress fields and, consequently, on the propensity for fracture relative to the uniaxial loading. 45 refs., 19 figs., 3 tabs

Synthesis and physical properties of zinc-oxide textured films by using a filtered preheated hydrothermal

Energy Technology Data Exchange (ETDEWEB)

Qiu, Jijun [Pusan National University, Busan (Korea, Republic of); Shin, Dongmyeong; He, Weizhen; Kim, Hyungkook; Hwang, Yoonhwae [Pusan National University, Miryang (Korea, Republic of); Li, Xiaomin; Gao, Xiangdong [Chinese Academy of Sciences, Shanghai (China)

2014-11-15

Axially (c-axis)-oriented ZnO thick films with a ∼8.1 μm thickness were fabricated on ZnO seed layer coated substrates by using a filtered preheated hydrothermal solution. The thick films composed of single-crystal ZnO microrods with various diameters were formed by coalescing each nanorod together along their side surfaces. From the X-ray diffraction result a biaxial stress exists was found to exist in the as-grown thick films, and the stress gradually increased with increasing annealing temperatures from 200 to 550 .deg. C due to a degradation in the crystalline quality. The biaxial stress is responsible for the red-shift of the optical band gap of the ZnO thick films. Photoluminescence and Hall results revealed that the optical and the electrical properties of the thick films were degenerated after high-temperature annealing (> 200 .deg. C), which was due to the introduction of point defects, such as oxygen interstitials and zinc vacancies.

Use of variational principles for solution of infinitely redundant continuum problem with special reference to containment vessels

International Nuclear Information System (INIS)

Stefanou, G.D.

1982-01-01

The calculation of time-deepndent stresses in concrete structures operating at elevated temperatures is discussed. The method described is of a direct formulation technique and it is based on the principles of the calculus of variation. The paper mainly deals with the application of the method to a large and infinitely redundant continuum problem. The analytical procedure of the variational principle is also described and the mathematical expressions are developed for uniaxial and biaxial stress problems. The solution for the biaxial state of stress is carried out by a two-dimensional finite element stiffness analysis. A step-by-step method developed by the author using two-dimensional finite element stiffness analysis is also described in APPENDIX 3. Both methods are then applied to a real problem for which experimental data exist from Ref. (1) Predicted analytical values obtained by both methods are compared with experimental results. The method is suitable for predicting the distribution of stress in the end slabs of containment vessels. These slabs are perforated to permit fuel loading by the charging machine. (author)

Stress relaxation of La1/2Sr1/2MnO3 and La2/3Ca1/3MnO3 at solid oxide fuel cell interfaces

International Nuclear Information System (INIS)

Lussier, A.; Dvorak, J.; Stadler, S.; Holroyd, J.; Liberati, M.; Arenholz, E.; Ogale, S.B.; Wu, T.; Venkatesan, T.; Idzerda, Y.U.

2008-01-01

Interfacial stress is thought to have significant effects on electrical and oxygen transport properties in thin films of importance in solid oxide fuel cell applications. We investigate how in-plane biaxial stress modifies the electronic structure of La 2/3 Ca 1/3 MnO 3 and La 1/2 Sr 1/2 MnO 3 thin films prepared by pulsed laser deposition on three different substrates to vary the in-plane stress from tensile to compressive. The electronic structure was probed by X-ray absorption spectroscopy of the Mn L 2,3 -edge to characterize the interfacial disruption in this region in an element-specific, site-specific manner. The compressive or tensile interfacial strain modifies the relative concentrations of La and Sr in the interfacial region in order to achieve a better lattice match to the contact material. This atomic migration generates an interfacial region dominated by a compound with a single valency for the transition metal ion, resulting in a severe barrier to oxygen and electron transport through this region

Apparent Dependence of Rate- and State-Dependent Friction Parameters on Loading Velocity and Cumulative Displacement Inferred from Large-Scale Biaxial Friction Experiments

Science.gov (United States)

Urata, Yumi; Yamashita, Futoshi; Fukuyama, Eiichi; Noda, Hiroyuki; Mizoguchi, Kazuo

2017-06-01

We investigated the constitutive parameters in the rate- and state-dependent friction (RSF) law by conducting numerical simulations, using the friction data from large-scale biaxial rock friction experiments for Indian metagabbro. The sliding surface area was 1.5 m long and 0.5 m wide, slid for 400 s under a normal stress of 1.33 MPa at a loading velocity of either 0.1 or 1.0 mm/s. During the experiments, many stick-slips were observed and those features were as follows. (1) The friction drop and recurrence time of the stick-slip events increased with cumulative slip displacement in an experiment before which the gouges on the surface were removed, but they became almost constant throughout an experiment conducted after several experiments without gouge removal. (2) The friction drop was larger and the recurrence time was shorter in the experiments with faster loading velocity. We applied a one-degree-of-freedom spring-slider model with mass to estimate the RSF parameters by fitting the stick-slip intervals and slip-weakening curves measured based on spring force and acceleration of the specimens. We developed an efficient algorithm for the numerical time integration, and we conducted forward modeling for evolution parameters ( b) and the state-evolution distances (L_{{c}}), keeping the direct effect parameter ( a) constant. We then identified the confident range of b and L_{{c}} values. Comparison between the results of the experiments and our simulations suggests that both b and L_{{c}} increase as the cumulative slip displacement increases, and b increases and L_{{c}} decreases as the loading velocity increases. Conventional RSF laws could not explain the large-scale friction data, and more complex state evolution laws are needed.

Electron beam induced modifications in flexible biaxially oriented polyethylene terephthalate sheets: Improved mechanical and electrical properties

Energy Technology Data Exchange (ETDEWEB)

Chaudhary, N. [Accelerator & Pulse Power Division, Bhabha Atomic Research Centre, Mumbai, 400 085 (India); Koiry, S.P. [Technical Physics Division, Bhabha Atomic Research Centre, Mumbai, 400 085 (India); Singh, A., E-mail: asb_barc@yahoo.com [Technical Physics Division, Bhabha Atomic Research Centre, Mumbai, 400 085 (India); Tillu, A.R. [Accelerator & Pulse Power Division, Bhabha Atomic Research Centre, Mumbai, 400 085 (India); Jha, P.; Samanta, S.; Debnath, A.K. [Technical Physics Division, Bhabha Atomic Research Centre, Mumbai, 400 085 (India); Aswal, D.K., E-mail: dkaswal@yahoo.com [Technical Physics Division, Bhabha Atomic Research Centre, Mumbai, 400 085 (India); Mondal, R.K. [Radiation Technology Development Division, Bhabha Atomic Research Centre, Mumbai, 400 085 (India); Acharya, S.; Mittal, K.C. [Accelerator & Pulse Power Division, Bhabha Atomic Research Centre, Mumbai, 400 085 (India)

2017-03-01

In the present work, we have studied the effects of electron beam irradiation (with dose ranging from 2 to 32 kGy) on mechanical and electrical properties of biaxially oriented polyethylene terephthalate (BOPET) sheets. The sol-gel analysis, Fourier transformation infra-red (FTIR), X-ray photoelectron spectroscopy (XPS) characterizations of the irradiated BOPET sheets suggest partial cross-linking of PET chains through the diethylene glycol (DEG). The mechanical properties of BOPET, such as, tensile strength, Young's modulus and electrical resistivity shows improvement with increasing dose and saturate for doses >10 kGy. The improved mechanical properties and high electrical resistivity of electron beam modified BOPET sheets may have additional advantages in applications, such as, packaging materials for food irradiation, medical product sterilization and electronic industries. - Graphical abstract: Irradiation of BOPET by electron beam leads to the formation of diethylene glycol that crosslink's the PET chains, resulting in improved mechanical properties and enhanced electrical resistivity. - Highlights: • BOPET exhibit improved tensile strength/Young's modulus after e-beam exposure. • Electrical resistivity of BOPET increases after e-beam exposure. • Cross-linking of PET chains through diethylene glycol was observed after e-beam exposure.

Development of partial safety factors for the design of partially prestressed rectangular sections in biaxial flexure

International Nuclear Information System (INIS)

Chatterjee, Aritra; Bhattacharya, Baidurya; Agrawal, Gunjan; Mondal, Apurba

2011-01-01

Partial safety factors (PSFs) used in reliability-based design are intended to account for uncertainties in load, material and mathematical modeling while ensuring that the target reliability is satisfied for the relevant class of structural components in the given load combination and limit state. This paper describes the methodology in detail for developing a set of optimal reliability-based PSFs for the design of rectangular partially prestressed concrete sections subjected to biaxial flexure. The mechanical formulation of the flexural limit state is based on the principle behind prestressed concrete design recommended by IS 1343 and SP16 and failure is defined as tensile cracking of concrete extending beyond the depth of cover. The applied moments are combined according to Wood's criteria. The optimization of the PSFs is based on reliability indices obtained from first order reliability analysis of the structural components; Monte Carlo simulations are performed in each run to determine the capacity statistics and dependence between capacity and applied loads (effected through the axial loads influencing moment capacity corresponding to cracking). Numerical examples involving flexural design of partially prestressed concrete shell elements in nuclear power plant containments under accidental pressure load combination are provided. (author)

Monitoring Poisson’s Ratio Degradation of FRP Composites under Fatigue Loading Using Biaxially Embedded FBG Sensors

Science.gov (United States)

Akay, Erdem; Yilmaz, Cagatay; Kocaman, Esat S.; Turkmen, Halit S.; Yildiz, Mehmet

2016-01-01

The significance of strain measurement is obvious for the analysis of Fiber-Reinforced Polymer (FRP) composites. Conventional strain measurement methods are sufficient for static testing in general. Nevertheless, if the requirements exceed the capabilities of these conventional methods, more sophisticated techniques are necessary to obtain strain data. Fiber Bragg Grating (FBG) sensors have many advantages for strain measurement over conventional ones. Thus, the present paper suggests a novel method for biaxial strain measurement using embedded FBG sensors during the fatigue testing of FRP composites. Poisson’s ratio and its reduction were monitored for each cyclic loading by using embedded FBG sensors for a given specimen and correlated with the fatigue stages determined based on the variations of the applied fatigue loading and temperature due to the autogenous heating to predict an oncoming failure of the continuous fiber-reinforced epoxy matrix composite specimens under fatigue loading. The results show that FBG sensor technology has a remarkable potential for monitoring the evolution of Poisson’s ratio on a cycle-by-cycle basis, which can reliably be used towards tracking the fatigue stages of composite for structural health monitoring purposes. PMID:28773901

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

International Nuclear Information System (INIS)

Zidane, I; Guines, D; Léotoing, L; Ragneau, E

2010-01-01

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)

Endochronic theory for inelasticity and failure analysis of concrete structures

Energy Technology Data Exchange (ETDEWEB)

Bazant, Z.P.; Bhat, P.D.; Shieh, C.L.

1976-12-01

A gradual accumulation of inelastic strain can be most conveniently described in terms of the so-called intrinsic time, whose increment depends on the time increment as well as the strain increments. This approach, which gives a particularly simple description of irreversibility of strain at unloading and cyclic loading, was previously developed for metals and is extended herein to concrete by introducing the hydrostatic pressure sensitivity of inelastic strain, the inelastic dilatancy produced by deviator strains, and the strain-softening tendency at high stress. Failure envelopes are obtained as a collection of the peaks of stress-strain diagrams. By comparison with experimental data from the literature, it is demonstrated that the proposed model predicts quite closely: stress-strain diagrams for concretes of different strength; uniaxial, biaxial and triaxial stress-strain diagrams and failure envelopes; failure envelopes for combined torsion and compression, lateral strains and volume expansion in uniaxial and biaxial tests; the behavior of spirally confined concrete; hysteresis loops or repeated high compression; cyclic creep up to 10/sup 6/ cycles; the strain rate effect; the decrease of long time strength; and the increase of short-time strength due to low stress creep.

Endochronic theory for inelasticity and failure analysis of concrete structures

International Nuclear Information System (INIS)

Bazant, Z.P.; Bhat, P.D.; Shieh, C.L.

1976-12-01

A gradual accumulation of inelastic strain can be most conveniently described in terms of the so-called intrinsic time, whose increment depends on the time increment as well as the strain increments. This approach, which gives a particularly simple description of irreversibility of strain at unloading and cyclic loading, was previously developed for metals and is extended herein to concrete by introducing the hydrostatic pressure sensitivity of inelastic strain, the inelastic dilatancy produced by deviator strains, and the strain-softening tendency at high stress. Failure envelopes are obtained as a collection of the peaks of stress-strain diagrams. By comparison with experimental data from the literature, it is demonstrated that the proposed model predicts quite closely: stress-strain diagrams for concretes of different strength; uniaxial, biaxial and triaxial stress-strain diagrams and failure envelopes; failure envelopes for combined torsion and compression, lateral strains and volume expansion in uniaxial and biaxial tests; the behavior of spirally confined concrete; hysteresis loops or repeated high compression; cyclic creep up to 10 6 cycles; the strain rate effect; the decrease of long time strength; and the increase of short-time strength due to low stress creep

A nonlocal continuum model for the biaxial buckling analysis of composite nanoplates with shape memory alloy nanowires

Science.gov (United States)

Farajpour, M. R.; Shahidi, A. R.; Farajpour, A.

2018-03-01

In this study, the buckling behavior of a three-layered composite nanoplate reinforced with shape memory alloy (SMA) nanowires is examined. Whereas the upper and lower layers are reinforced with typical nanowires, SMA nanoscale wires are used to strengthen the middle layer of the system. The composite nanoplate is assumed to be under the action of biaxial compressive loading. A scale-dependent mathematical model is presented with the consideration of size effects within the context of the Eringen’s nonlocal continuum mechanics. Using the one-dimensional Brinson’s theory and the Kirchhoff theory of plates, the governing partial differential equations of SMA nanowire-reinforced hybrid nanoplates are derived. Both lateral and longitudinal deflections are taken into consideration in the theoretical formulation and method of solution. In order to reduce the governing differential equations to their corresponding algebraic equations, a discretization approach based on the differential quadrature method is employed. The critical buckling loads of the hybrid nanosystem with various boundary conditions are obtained with the use of a standard eigenvalue solver. It is found that the stability response of SMA composite nanoplates is strongly sensitive to the small scale effect.

General planar transverse domain walls realized by optimized transverse magnetic field pulses in magnetic biaxial nanowires

Science.gov (United States)

Li, Mei; Wang, Jianbo; Lu, Jie

2017-02-01

The statics and field-driven dynamics of transverse domain walls (TDWs) in magnetic nanowires (NWs) have attracted continuous interests because of their theoretical significance and application potential in future magnetic logic and memory devices. Recent results demonstrate that uniform transverse magnetic fields (TMFs) can greatly enhance the wall velocity, meantime leave a twisting in the TDW azimuthal distribution. For application in high-density NW devices, it is preferable to erase the twisting so as to minimize magnetization frustrations. Here we report the realization of a completely planar TDW with arbitrary tilting attitude in a magnetic biaxial NW under a TMF pulse with fixed strength and well-designed orientation profile. We smooth any twisting in the TDW azimuthal plane thus completely decouple the polar and azimuthal degrees of freedom. The analytical differential equation describing the polar angle distribution is derived and the resulting solution is not the Walker-ansatz form. With this TMF pulse comoving, the field-driven dynamics of the planar TDW is investigated with the help of the asymptotic expansion method. It turns out the comoving TMF pulse increases the wall velocity under the same axial driving field. These results will help to design a series of modern magnetic devices based on planar TDWs.

Crack mode and life of Ti-6Al-4V under multiaxial low cycle fatigue

Directory of Open Access Journals (Sweden)

Takamoto Itoh

2015-10-01

Full Text Available This paper studies multiaxial low cycle fatigue crack mode and failure life of Ti-6Al-4V. Stress controlled fatigue tests were carried out using a hollow cylinder specimen under multiaxial loadings of λ=0, 0.4, 0.5 and 1 of which stress ratio R=0 at room temperature. λ is a principal stress ratio and is defined as λ=II/I, where I and II are principal stresses of which absolute values take the largest and middle ones, respectively. Here, the test at λ=0 is a uniaxial loading test and that at λ=1 an equi-biaxial loading test. A testing machine employed is a newly developed multiaxial fatigue testing machine which can apply push-pull and reversed torsion loadings with inner pressure onto the hollow cylinder specimen. Based on the obtained results, this study discusses evaluation of the biaxial low cycle fatigue life and crack mode. Failure life is reduced with increasing λ induced by cyclic ratcheting. The crack mode is affected by the surface condition of cut-machining and the failure life depends on the crack mode in the multiaxial loading largely.

Evaluation of biaxial flexural strength and modulus of filled and unfilled adhesive systems = Avaliação da resistência flexural biaxial e módulo de flexão de sistemas adesivos

Directory of Open Access Journals (Sweden)

Liberti, Michele Santana

2009-01-01

Full Text Available Objetivo: O objetivo deste estudo foi avaliar a resistência flexural e o módulo de flexão de dois sistemas adesivos, através de ensaio de resistência flexural biaxial. Metodologia: Os adesivos (Pentron Clinical Technologies estudados foram: Bond 1 (B1 e NanoBond (NB. Treze discos de cada adesivo foram preparados com dimensões aproximadas de 6,1 mm de diâmetro e 0,6 mm de espessura. Os discos de adesivos foram confeccionados utilizando-se moldes de teflon e fotopolimerizados com aparelho XL 3000 (3M ESPE. Após armazenamento por 10 dias, os discos foram testados em máquina universal de ensaio (Instron 5844, com velocidade de 1,27 mm/min. Os dados foram submetidos à análise de variância (1 fator ao nível de significância de 0,05. Resultados: Os valores médios (±DP de resistência flexural para os adesivos foram (em MPa: B1- 89,7±7,6 e NB- 131,1±9,5. Os valores médios de módulo flexural (±DP foram (em MPa: B1- 1999,9±258,4 e NB- 2314,5±271,0. Conclusão: O adesivo contendo partículas de carga (NB mostrou maiores valores de resistência flexural e módulo de flexão que o adesivo B1

Biomimetic fetal rotation bioreactor for engineering bone tissues-Effect of cyclic strains on upregulation of osteogenic gene expression.

Science.gov (United States)

Ravichandran, Akhilandeshwari; Wen, Feng; Lim, Jing; Chong, Mark Seow Khoon; Chan, Jerry K Y; Teoh, Swee-Hin

2018-04-01

Cells respond to physiological mechanical stresses especially during early fetal development. Adopting a biomimetic approach, it is necessary to develop bioreactor systems to explore the effects of physiologically relevant mechanical strains and shear stresses for functional tissue growth and development. This study introduces a multimodal bioreactor system that allows application of cyclic compressive strains on premature bone grafts that are cultured under biaxial rotation (chamber rotation about 2 axes) conditions for bone tissue engineering. The bioreactor is integrated with sensors for dissolved oxygen levels and pH that allow real-time, non-invasive monitoring of the culture parameters. Mesenchymal stem cells-seeded polycaprolactone-β-tricalcium phosphate scaffolds were cultured in this bioreactor over 2 weeks in 4 different modes-static, cyclic compression, biaxial rotation, and multimodal (combination of cyclic compression and biaxial rotation). The multimodal culture resulted in 1.8-fold higher cellular proliferation in comparison with the static controls within the first week. Two weeks of culture in the multimodal bioreactor utilizing the combined effects of optimal fluid flow conditions and cyclic compression led to the upregulation of osteogenic genes alkaline phosphatase (3.2-fold), osteonectin (2.4-fold), osteocalcin (10-fold), and collagen type 1 α1 (2-fold) in comparison with static cultures. We report for the first time, the independent and combined effects of mechanical stimulation and biaxial rotation for bone tissue engineering using a bioreactor platform with non-invasive sensing modalities. The demonstrated results show leaning towards the futuristic vision of using a physiologically relevant bioreactor system for generation of autologous bone grafts for clinical implantation. Copyright © 2018 John Wiley & Sons, Ltd.

Prediction of stress- and strain-based forming limits of automotive thin sheets by numerical, theoretical and experimental methods

Science.gov (United States)

Béres, Gábor; Weltsch, Zoltán; Lukács, Zsolt; Tisza, Miklós

2018-05-01

Forming limit is a complex concept of limit values related to the onset of local necking in the sheet metal. In cold sheet metal forming, major and minor limit strains are influenced by the sheet thickness, strain path (deformation history) as well as material parameters and microstructure. Forming Limit Curves are plotted in ɛ1 - ɛ2 coordinate system providing the classic strain-based Forming Limit Diagram (FLD). Using the appropriate constitutive model, the limit strains can be changed into the stress-based Forming Limit Diagram (SFLD), irrespective of the strain path. This study is about the effect of the hardening model parameters on defining of limit stress values during Nakazima tests for automotive dual phase (DP) steels. Five limit strain pairs were specified experimentally with the loading of five different sheet geometries, which performed different strain-paths from pure shear (-2ɛ2=ɛ1) up to biaxial stretching (ɛ2=ɛ1). The former works of Hill, Levy-Tyne and Keeler-Brazier made possible some kind of theoretical strain determination, too. This was followed by the stress calculation based on the experimental and theoretical strain data. Since the n exponent in the Nádai expression is varying with the strain at some DP steels, we applied the least-squares method to fit other hardening model parameters (Ludwik, Voce, Hockett-Sherby) to calculate the stress fields belonging to each limit strains. The results showed that each model parameters could produce some discrepancies between the limit stress states in the range of higher equivalent strains than uniaxial stretching. The calculated hardening models were imported to FE code to extend and validate the results by numerical simulations.

Role of contact couples and couple stress in the behaviour of granular media

International Nuclear Information System (INIS)

Dedecker, F.; Dubujet, P.; Cambou, B.

1998-01-01

This paper analyses the interest of taking into account contact couples in the granular material description as well as considering the inadequacy of the micropolar description. The study is made on two types of samples: one which takes into account contact couples, and the other which does not. The response of these two media, which are submitted to a biaxial test, is analysed from both the micromechanic and macroscopic viewpoints. A numerical study which is performed on these two samples shows the influence of the presence of couples on the local static variables as well as on the macroscopic behaviour. A statistical homogenization approach is analysed to simulate the effects of couples. Due to the presence of an internal variable, a numerical study proves that this approach is relevant. This internal variable allows the taking into consideration of the influence of contact couples. A first step in the description of couples versus contact orientation is made by the introduction of the standard deviation. Finally, the inadequacy of the micropolar description which takes into account micropolar stresses is pointed out. (orig.)

Crystal defects and related stress in Y2O3 thin films: Origin, modeling, and consequence on the stability of the C-type structure

International Nuclear Information System (INIS)

Lacroix, Bertrand; Paumier, Fabien; Gaboriaud, Rolly J.

2011-01-01

We study the impact that the crystal defects have on the C-type structure of rare earth sesquioxide thin films grown by ion-beam sputtering, through the example of Y 2 O 3 . By monitoring the energy of the argon beam used in the sputter deposition process (between 600 and 1200 eV), we show that it is possible to control the microstructure (defects concentration, stress state and phase) in the oxide layer. Two main types of defects, ascribed to the 'atomic peening effect', are evidenced by high-resolution transmission electron microscopy, Rutherford backscattering spectroscopy, and nuclear reaction analysis experiments: anti-Frenkel pairs, leading to a disorder on the oxygen-vacancy network, and oxygen-vacancy dislocations loops, to accommodate the strong nonstoichiometry. From a macroscopic measurement of the residual stresses in the as-deposited and the annealed layers, through x-ray diffraction and the sin 2 Ψ method, we have modeled the related stress state using an enhanced triaxial stress model. In the as-grown films, we evidence the coexistence of a biaxial and a hydrostatic stress, due to inclusions of atomic size defects. Quantitative information of the concentration and the nature of each type of defect (size effect) have also been determined, in good agreement with experiments. Interestingly, in the most energetic growth conditions corresponding to the highest degree of disorder on the oxygen-vacancy network and to the highest stress field in the film, we demonstrate that it is possible to stabilize an unexpected and metastable non equilibrium fluorite-like phase (X-type).

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

Energy Technology Data Exchange (ETDEWEB)

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

2013-10-15

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

Modelization of ratcheting in biaxial experiments

International Nuclear Information System (INIS)

Guionnet, C.

1989-08-01

A new unified viscoplastic constitutive equation has been developed in order to interpret ratcheting experiments on mechanical structures of fast reactors. The model is based essentially on a generalized Armstrong Frederick equation for the kinematic variable; the coefficients of the dynamic recovery term in this equation is a function of both instantaneous and accumulated inelastic strain which is allowed to vary in an appropriate manner in order to reproduce the experimental ratcheting rate. The validity of the model is verified by comparing predictions with experimental results for austenitic stainless steel (17-12 SPH) tubular specimens subjected to cyclic torsional loading under constant tensile stress at 600 0 C [fr

Caracterización del inicio y crecimiento de grietas de interfaz entre fibra y matriz bajo cargas transversales biaxiales usando el modelo de interfaz elástica lineal-frágil

OpenAIRE

Távara Mendoza, Luis Arístides; Mantic, Vladislav; Graciani Díaz, Enrique; Blázquez Gámez, Antonio; París Carballo, Federico

2011-01-01

En el presente trabajo se estudia el inicio y crecimiento de una grieta de interfaz entre fibra y matriz bajo cargas transversales biaxiales de tracción - tracción y tracción - compresión. Se considera un problema simplificado en relación a una lámina unidireccional real, con una fibra inmersa en una matriz cuyas dimensiones externas son mucho más grandes que el radio de la fibra. El objetivo es predecir por un lado las cargas de fallo (cargas criticas) que originan el despegue en ...

Anisotropically biaxial strain in non-polar (112-0) plane In x Ga1-x N/GaN layers investigated by X-ray reciprocal space mapping.

Science.gov (United States)

Zhao, Guijuan; Li, Huijie; Wang, Lianshan; Meng, Yulin; Ji, Zesheng; Li, Fangzheng; Wei, Hongyuan; Yang, Shaoyan; Wang, Zhanguo

2017-07-03

In this study, the indium composition x as well as the anisotropically biaxial strain in non-polar a-plane In x Ga 1-x N on GaN is studied by X-ray diffraction (XRD) analysis. In accordance with XRD reciprocal lattice space mapping, with increasing indium composition, the maximum of the In x Ga 1-x N reciprocal lattice points progressively shifts from a fully compressive strained to a fully relaxed position, then to reversed tensile strained. To fully understand the strain in the ternary alloy layers, it is helpful to grow high-quality device structures using a-plane nitrides. As the layer thickness increases, the strain of In x Ga 1-x N layer releases through surface roughening and the 3D growth-mode.

A phenomenological SMA model for combined axial–torsional proportional/non-proportional loading conditions

International Nuclear Information System (INIS)

Bodaghi, M.; Damanpack, A.R.; Aghdam, M.M.; Shakeri, M.

2013-01-01

In this paper, a simple and robust phenomenological model for shape memory alloys (SMAs) is proposed to simulate main features of SMAs under uniaxial as well as biaxial combined axial–torsional proportional/non-proportional loadings. The constitutive model for polycrystalline SMAs is developed within the framework of continuum thermodynamics of irreversible processes. The model nominates the volume fractions of self-accommodated and oriented martensite as scalar internal variables and the preferred direction of oriented martensitic variants as directional internal variable. An algorithm is introduced to develop explicit relationships for the thermo-mechanical behavior of SMAs under uniaxial and biaxial combined axial–torsional proportional/non-proportional loading conditions and also thermal loading. It is shown that the model is able to simulate main aspects of SMAs including self-accommodation, martensitic transformation, orientation and reorientation of martensite, shape memory effect, ferro-elasticity and pseudo-elasticity. A description of the time-discrete counterpart of the proposed SMA model is presented. Experimental results of uniaxial tension and biaxial combined tension–torsion non-proportional tests are simulated and a good qualitative correlation between numerical and experimental responses is achieved. Due to simplicity and accuracy, the model is expected to be used in the future studies dealing with the analysis of SMA devices in which two stress components including one normal and one shear stress are dominant

Ab initio elastic properties and tensile strength of crystalline hydroxyapatite.

Science.gov (United States)

Ching, W Y; Rulis, Paul; Misra, A

2009-10-01

We report elastic constant calculation and a "theoretical" tensile experiment on stoichiometric hydroxyapatite (HAP) crystal using an ab initio technique. These results compare favorably with a variety of measured data. Theoretical tensile experiments are performed on the orthorhombic cell of HAP for both uniaxial and biaxial loading. The results show considerable anisotropy in the stress-strain behavior. It is shown that the failure behavior of the perfect HAP crystal is brittle for tension along the z-axis with a maximum stress of 9.6 GPa at 10% strain. Biaxial failure envelopes from six "theoretical" loading tests show a highly anisotropic pattern. Structural analysis of the crystal under various stages of tensile strain reveals that the deformation behavior manifests itself mainly in the rotation of the PO(4) tetrahedron with concomitant movements of both the columnar and axial Ca ions. These results are discussed in the context of mechanical properties of bioceramic composites relevant to mineralized tissues.

The small displacement elastic solution to the ball-on-ring testing method

DEFF Research Database (Denmark)

Frandsen, Henrik Lund

2012-01-01

The ball-on-ring experiment is used for testing of the biaxial strength of ceramics. In this work the solution for the stress distribution and displacements of the disc specimen in the ball-on-ring experiment are determined on closed form. The solution comprises the displacement field and its...

On the testing equipment and experimental techniques for the investigation of the photoviscoelastic behaviour of soft polymers

International Nuclear Information System (INIS)

Weber, H.

1983-01-01

Creep tests with uniaxial stress and pure shear have been carried out in order to determine the behaviour of soft plastics, which is governed by a non-linear material law, and to apply it to the photoelastic analysis of biaxial stress in plastic components under quasistatic and isothermal loads. The test facility is described as well as the technique applied to correct stress/creep curves for sigma=const. Results are presented for plane and tubular samples of soft PVC and an unsaturated polyester. (orig.) [de

Fabrication of high temperature superconductors

Science.gov (United States)

Balachandran, Uthamalingam; Dorris, Stephen E.; Ma, Beihai; Li, Meiya

2003-06-17

A method of forming a biaxially aligned superconductor on a non-biaxially aligned substrate substantially chemically inert to the biaxially aligned superconductor comprising is disclosed. A non-biaxially aligned substrate chemically inert to the superconductor is provided and a biaxially aligned superconductor material is deposited directly on the non-biaxially aligned substrate. A method forming a plume of superconductor material and contacting the plume and the non-biaxially aligned substrate at an angle greater than 0.degree. and less than 90.degree. to deposit a biaxially aligned superconductor on the non-biaxially aligned substrate is also disclosed. Various superconductors and substrates are illustrated.

Comparison of first quadrant yield loci for Ti--6Al--4V with those predicted by Knoop hardness measurements

International Nuclear Information System (INIS)

Amateau, M.F.; Hanna, W.D.

1975-01-01

Knoop hardness impressions were used to construct biaxial yield loci in Ti--6A l--4V for a variety of textures. These results were compared with partial yield loci in the first quadrant, determined from flow stress measurements at three stress ratios. In each case, the Knoop hardness technique was not sufficiently sensitive to predict the shape of the yield locus, the largest discrepancy occurring for the most anisotropic sample. (U.S.)

Dual characteristics of yield and ultimate strength as applied to two grades of beryllium

International Nuclear Information System (INIS)

Priddy, T.G.; Benzley, S.E.; Johnson, R.L.

1977-02-01

Published yield and ultimate biaxial strength data for two grades of beryllium are correlated with the use of a macroscopic failure model. Cross sections of the resulting surfaces in three-dimensional stress space are drawn to illustrate the expected transition from ductile to brittle fracture for triaxial tension states of stress. The usefulness of these models to the prediction of fracture in ductile materials is discussed. 5 tables, 8 figures, 11 references

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

International Nuclear Information System (INIS)

Lee, Jin Seung; Lee, Seung S

2008-01-01

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

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

Energy Technology Data Exchange (ETDEWEB)

Clair, A. [Laboratoire Interdisciplinaire Carnot de Bourgogne, UMR 5209 CNRS, Universite de Bourgogne, 9 Avenue Alain Savary, BP 47870, 21078 Dijon Cedex (France); Foucault, M.; Calonne, O. [Areva ANP, Centre Technique Departement Corrosion-Chimie, 30 Bd de l' industrie, BP 181, 71205 Le Creusot (France); Lacroute, Y.; Markey, L.; Salazar, M.; Vignal, V. [Laboratoire Interdisciplinaire Carnot de Bourgogne, UMR 5209 CNRS, Universite de Bourgogne, 9 Avenue Alain Savary, BP 47870, 21078 Dijon Cedex (France); Finot, E., E-mail: Eric.Finot@u-bourgogne.fr [Laboratoire Interdisciplinaire Carnot de Bourgogne, UMR 5209 CNRS, Universite de Bourgogne, 9 Avenue Alain Savary, BP 47870, 21078 Dijon Cedex (France)

2011-05-15

Research highlights: > Surface strains measured using nanogauge were compared to the texture obtained by EBSD. > Statistics of the principal strain discern the grains according to the Schmid factor. > Strain hotspots were localized near a triple junction of alloy 600 under tensile loading. > Asymetrical profile of the GB strains is a criterion for surface cracking initiation. - Abstract: A key element for analyzing the crack initiation in strained polycrystalline alloys is the local quantification of the surface strain distribution according to the grain texture. Using electron backscattered diffraction, the local microstructure was determined to both localize a triple junction and deduce the local Schmid factors. Kernel average misorientation (KAM) was also used to map the areas of defect concentration. The maximum principal strain and the in-plane shear strain were quantified using the biaxial nanogauge. Distortions of the array of nanodots used as spot markers were analyzed near the triple junction. The crystallographic orientation and the surface strain were then investigated both statistically for each grain and locally at the grain boundaries. The superimposition of microstructure and strain maps allows the high strain gradient (reaching 3-fold the applied strain) to be localized at preferential grain boundaries near the triple junction. The Schmid factors and the KAM were compared to the maximum principal strain and the in-plane shear strain respectively. The polycrystalline deformation was attributable first to the rotation of some grains, followed by the elongation of all grains along their preferential activated slip systems.

Effect of Alumina Addition to Zirconia Nano-composite on Low Temperature Degradation Process and Biaxial Strength

Directory of Open Access Journals (Sweden)

Moluk Aivazi

2016-12-01

Full Text Available Ceramic dental materials have been considered as alternatives to metals for dental implants application. In this respect, zirconia tetragonal stabilized with %3 yttrium, is of great importance among the ceramic materials for endosseous dental implant application. Because of its good mechanical properties and color similar to tooth. The aim and novelty of this study was to design and prepare Y-TZP nano-composite to reduce the degradation process at low temperature by alumina addition and maintaining submicron grain sized. Also, flexural strength of nano-composite samples was evaluated. Toward this purpose, alumina-Y-TZP nano-composites containing 0–30 vol% alumina (denoted as A-Y-TZP 0-30 were fabricated using α-alumina and Y-TZP nano-sized by sintering pressure less method. The synthesized samples were characterized using x-ray diffraction, field emission scanning electron microscopy equipped with energy dispersive x-ray spectroscopy techniques. Nano-composite samples with high density (≥96% and grain sized of ≤ 400 nm was obtained by sintering at 1270 °C for 170 min. After low temperature degradation test (LTD, A-Y-TZP20 and A-Y-TZP30 not showed monoclinic phase and the flexural strength in all of samples were higher than A-Y-TZP0. It was concluded that the grains were remained in submicron sized and A-Y-TZP20 and A-Y-TZP30 did not present biaxial strength reduction after LTD test.

Biaxial (Tension-Torsion) Testing of an Oxide/Oxide Ceramic Matrix Composite

Science.gov (United States)

2013-03-01

11 3.1 NextelTM 720/AS Dogbone and Straightsided Specimen Layups . . . . . . . . 15 3.2 Prepreg processing steps of NextelTM 720/AS composite...the laminate in the test section, used for producing circum- ferential or axial stresses, should be minimized to avoid adding a high radial stress...provided fabrication process in Figure 3.2. The process followed the fabric, prepreg , and layup process versus the fiber tow and filament winding

Elasto-plastic impact of hemispherical shell impacting on hard rigid sphere

Science.gov (United States)

Raftopoulos, D. D.; Spicer, A. L.

1976-01-01

An analysis of plastic stress waves for cylindrical metallic projectile in impact is extended to an analysis of a hemispherical shell suffereing plastic deformation during the process of impact. It is assumed that the hemispherical shell with a prescribed launch velocity impinges a fixed rigid sphere of diameter equal to the internal diameter of the shell. The dynamic biaxial state of stress present in the shell during deformation is investigated. The analysis is valuable for studying the state of stress during large plastic deformation of a hemispherical shell.

Modeling of damage in ductile cast iron – The effect of including plasticity in the graphite noduless

DEFF Research Database (Denmark)

Andriollo, Tito; Thorborg, Jesper; Tiedje, Niels Skat

2015-01-01

In the present paper a micro-mechanical model for investigating the stress-strain relation of ductile cast iron subjected to simple loading conditions is presented. The model is based on a unit cell containing a single spherical graphite nodule embedded in a uniform ferritic matrix, under...... the assumption of infinitesimal strains and plane-stress conditions. Despite the latter being a limitation with respect to full 3D models, it allows a direct comparison with experimental investigations of damage evolution on the surface of ductile cast iron components, where the stress state is biaxial in nature...

Stress corrosion cracks initiation of recrystallized Zircaloy-4 in iodine-methanol solutions

International Nuclear Information System (INIS)

Mozzani, N.

2013-01-01

During the pellet-cladding interaction, Zirconium-alloy fuel claddings might fail when subjected to incidental power transient in nuclear Pressurized Water Reactors, by Iodine-induced Stress Corrosion Cracking (I-SCC). This study deals with the intergranular initiation of I-SCC cracks in fully recrystallized Zircaloy-4, in methyl alcohol solution of iodine at room temperature, with the focus on critical mechanical parameters and iodine concentration. It was carried out with an approach mixing experiments and numerical simulations. An anisotropic and viscoplastic mechanical behavior model was established and validated over a wide range of loadings. With numerous constant elongation rate tensile tests and four points bending creep tests, the existence of a threshold iodine concentration I0 close to 10 -6 g.g -1 was highlighted, necessary to the occurrence of I-SCC damage, along with a transition concentration I1 close to 2.10 -4 g.g -1 . Above I1 the mechanism changes, leading to a sped up crack initiation and a loss of sensitivity towards mechanical parameters. The importance of concentration on parameters such as crack density, crack average length and intergranular and transgranular crack velocities was evidenced. Experimental results show that plastic strain is not required for I-SCC crack initiation, if the test time is long enough in the presence of stress. Its main influence is to rush the occurrence of cracking by creating initiation sites, by way of breaking the oxide layer and building up intergranular stress. Below I1, the critical strains at initiation show a substantial strain rate sensitivity. In this domain, a threshold stress of 100 MPa was found, well below the yield stress. Thanks to the combined use of notched specimens and numerical simulations, a strong protective effect of an increasing stress bi-axiality ratio was found, both in the elastic and plastic domains. Proton-irradiated samples, up to a dose of 2 dpa, were tested in the same conditions

Fractal patterns of fracture in sandwich composite materials under biaxial tension

Science.gov (United States)

Fang, Jing; Yao, Xuefeng; Qi, Jia

1996-04-01

The paper presents a successful experiment to generate a fractal pattern of branching cracks in a brittle material sandwiched in ductile plates. A glass sheet bonded between two polycarbonate plates was heated at different levels of temperatures and the stress field due to the difference of thermal coefficients of the materials was solved by combining the results from isochromatic fringes and thermal stress analysis. At a critical degree of temperature, a crack was initiated at a point and soon produced crack branches to release the stored energy. A tree—like fractal patterns of the branch cracks was then developed with the growth of the branches that subsequently produced more branches on their ways of propagation. The fractal dimension of the fracture pattern was evaluated and the mechanism of the fragmentation was analyzed with the help of the residual stress field of isochromatic and isoclinic patterns.

Stress effects in ferroelectric perovskite thin-films

Science.gov (United States)

Zednik, Ricardo Johann

The exciting class of ferroelectric materials presents the engineer with an array of unique properties that offer promise in a variety of applications; these applications include infra-red detectors ("night-vision imaging", pyroelectricity), micro-electro-mechanical-systems (MEMS, piezoelectricity), and non-volatile memory (NVM, ferroelectricity). Realizing these modern devices often requires perovskite-based ferroelectric films thinner than 100 nm. Two such technologically important material systems are (Ba,Sr)TiO3 (BST), for tunable dielectric devices employed in wireless communications, and Pb(Zr,Ti)O3 (PZT), for ferroelectric non-volatile memory (FeRAM). In general, the material behavior is strongly influenced by the mechanical boundary conditions imposed by the substrate and surrounding layers and may vary considerably from the known bulk behavior. A better mechanistic understanding of these effects is essential for harnessing the full potential of ferroelectric thin-films and further optimizing existing devices. Both materials share a common crystal structure and similar properties, but face unique challenges due to the design parameters of these different applications. Tunable devices often require very low dielectric loss as well as large dielectric tunability. Present results show that the dielectric response of BST thin-films can either resemble a dipole-relaxor or follow the accepted empirical Universal Relaxation Law (Curie-von Schweidler), depending on temperature. These behaviors in a single ferroelectric thin-film system are often thought to be mutually exclusive. In state-of-the-art high density FeRAM, the ferroelectric polarization is at least as important as the dielectric response. It was found that these properties are significantly affected by moderate biaxial tensile and compressive stresses which reversibly alter the ferroelastic domain populations of PZT at room temperature. The 90-degree domain wall motion observed by high resolution

Development of biaxially textured buffer layers on rolled-Ni substrates for high current YBa2Cu3O7-y coated conductors

International Nuclear Information System (INIS)

Paranthaman, M.; Goyal, A.; Norton, D.P.

1996-01-01

This paper describes the development of 3 buffer layer architectures with good biaxial textures on rolled-Ni substrates using vacuum processing techniques. The techniques include pulsed laser ablation, e-beam evaporation, dc and rf magnetron sputtering. The first buffer layer architecture consists of an epitaxial laminate of Ag/Pd(Pt)/Ni. The second buffer layer consists of an epitaxial laminate of CeO 2 /Pd/Ni. The third alternative buffer layer architecture consists of an epitaxial laminate of YSZ/CeO 2 /Ni. The cube (100) texture in the Ni was produced by cold rolling followed by recrystallization. Crystallographic orientations of the Pd, Ag, CeO 2 , and YSZ films grown were all (100). We recently demonstrated a critical- current density of 0.73x10 6 A/cm 2 at 77 K and zero field on 1.4 μm thick YBa 2 Cu 3 O 7-y (YBCO) film. This film was deposited by pulsed laser ablation on a YBCO/YSZ/CeO 2 /Ni substrate

Interpreting strain measurements when drilling anisotropic rocks: return of experience from using CSIRO cells in Tournemire argillite

International Nuclear Information System (INIS)

Ben Ouanas, Abdelmonem

2010-01-01

In Geomechanics, determining the state of stress and the rheology of rock massif can be obtained by measuring the strain response of the ground under the effect of a known stress. A method among others is to use a cell integrated (with strain gauges oriented in different directions) installed in a borehole and secured to the mass through an epoxy glue. This measurement is used, notably, to determine the stress state in situ by the 'overcoring' method and the elastic parameters of the rock from the 'biaxial' test. Between November 2005 and January 2006, a geomechanical testing campaign was conducted in the argillaceous formation of the Tournemire experimental site (Aveyron, France) using CSIRO Hi cells. The strain measurements obtained during overcoring and biaxial tests have shown unusual phenomena, which have made difficult the determination of anisotropic elastic parameters of the rock and the access to the site stress. Therefore, through researches for explanations of the origin of these phenomena, this thesis aimed to improve and contribute to the understanding of the Tournemire argillite behaviour and to upgrade the measurement protocol as well as the interpretation of cells CSIRO's strain. The approach was, firstly, to issue a number of hypotheses to explain certain phenomena observed in literature. In a second step, these hypotheses were tested through analytical and numerical modelling of the biaxial and overcoring tests then through the realization of new experiments in situ within laboratory on argillite, and also on materials tests (cement, sample of glue). It is concluded that the unusual phenomena observed are essentially the result of the conditions for implementing in situ CSIRO's cell. The study particularly focused on the artefacts induced by the visco-plastic behaviour of the epoxy glue when it is incompletely polymerised. The role of damage on the rock generated by drilling operations is also discussed. Some practical recommendations for

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

Directory of Open Access Journals (Sweden)

Gustavo Fabián Molina

2013-01-01

Full Text Available 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 (Group 2, and heated with LED lamp of 1400 mW/cm2 for 60 s while setting (Group 3. Samples were stored for 48 hours in distilled water at 37°C until tested. BFS was tested, using a universal testing machine at a crosshead speed of 1 mm/min. Data were analyzed, using ANOVA test with the Bonferroni correction (α=0.05. Heating the glass-ionomer cements with an LED curing light of 1400 mW/cm2 during setting for 30 s increased the BFS value of all GICs. No statistically significant difference in mean BFS scores was found between the EQUIA system and ChemFil Rock at 30 s and 60 s. The mean BFS value was statistically significantly higher for the EQUIA system and ChemFil Rock than for Fuji 9 Gold Label and Ketac Molar Easymix at all exposure times.

Fatigue life assessment under multiaxial variable amplitude loading

International Nuclear Information System (INIS)

Morilhat, P.; Kenmeugne, B.; Vidal-Salle, E.; Robert, J.L.

1996-06-01

A variable amplitude multiaxial fatigue life prediction method is presented in this paper. It is based on a stress as input data are the stress tensor histories which may be calculated by FEM analysis or measured directly on the structure during the service loading. The different steps of he method are first presented then its experimental validation is realized for log and finite fatigue lives through biaxial variable amplitude loading tests using cruciform steel samples. (authors). 9 refs., 7 figs

STRESS - STRAIN CURVE ANALYSIS OF WOVEN FABRICS MAD E FROM COMBED YARNS TYPE WOOL

Directory of Open Access Journals (Sweden)

VÎLCU Adrian

2014-05-01

Full Text Available The paper analyses the tensile behavior of woven fabrics made from 45%Wool + 55% PES used for garments. Analysis of fabric behavior during wearing has shown that these are submitted to simple and repeated uni-axial or bi-axial tensile strains. The level of these strains is often within the elastic limit, rarely going over yielding. Therefore the designer must be able to evaluate the mechanical behavior of such fabrics in order to control the fabric behavior in the garment. This evaluation is carried out based on the tensile testing, using certain indexes specific to the stress-strain curve. The paper considers an experimental matrix based on woven fabrics of different yarn counts, different or equal yarn count for warp and weft systems and different structures. The fabrics were tested using a testing machine and the results were then compared in order to determine the fabrics’ tensile behavior and the factors of influence that affect it.From the point of view of tensile testing, the woven materials having twill weave are preferable because this type of structure is characterized by higher durability and better yarn stability in the fabric. In practice, the woven material must exhibit an optimum behavior to repeated strains, flexions and abrasions during wearing process. The analysis of fabrics tensile properties studied by investigation of stress-strain diagrams reveals that the main factors influencing the tensile strength are: yarns fineness, technological density of those two systems of yarns and the weaving type.

Rock mechanics research in the Coeur d'Alene mining district

Energy Technology Data Exchange (ETDEWEB)

Corp, E. L.

1980-05-15

Over the past 20 years, the Bureau of Mines and mining companies of the Coeur d'Alene district have conducted cooperative research on problems of ground control. For the past six years emphasis has been placed on research to improve deep shaft design and to control rock bursts during cut-and-fill stoping. Finite-element modeling and construction of small-scale circular and rectangular test shafts have shown that circular openings are stable only when stresses are hydrostatic or weakly biaxial. Under a strongly-biaxial horizontal stress field, a rectangular shaft has a greater depth capability if its long axis can be oriented parallel to the major stress and normal to the bedding and joint system. Steel sets appear preferable to wood sets or concrete lining. Based on underground tests at Hecla's Star mine, destressing or preconditioning of the vein rock prior to mining was shown to be an effective means of controlling rock bursts. Drilling and shooting a radial pattern of longholes before stope mining starts has preconditioned or softened the vein material to the extent that seismic energy release during mining is reduced and no bursting occurred. Increased burst and seismic activity while mining about the preconditioned zone points out the need to precondition an entire stope block before mining.

Material properties characterization - concrete

International Nuclear Information System (INIS)

England, G.L.; MacLeod, J.S.

1978-01-01

A review is presented of the six contributions in the SMiRT 4 conference to Session H5 on structural analysis of prestressed concrete reactor pressure vessels. These relate to short term stress-strain aspects of concrete loaded beyond the linear range in uniaxial and biaxial stress fields, to some time and temperature dependent properties of concrete at working stress levels, and to a programme of strain-gauge testing for the assessment of concrete properties. From the information discussed, it is clear that there are difficulties in determining material properties for concrete, and these are summarised. (UK)

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

KAUST Repository

Pancheri, Francesco Q.; Dorfmann, Luis

2014-01-01

model to derive stress-stretch relations to validate the experimental data. The material model parameters are determined using the primary loading path in uniaxial and equibiaxial tension. Excellent agreement is found when the model is used to predict

Are bi-axial proximal sesamoid bone fractures in the British Thoroughbred racehorse a bone fatigue related fracture? A histological study.

Science.gov (United States)

Kristoffersen, M; Hetzel, U; Parkin, T D H; Singer, E R

2010-01-01

To investigate whether microfractures and alterations in the trabecular bone area are associated with catastrophic bi-axial proximal sesamoid bone fractures (PSBF). Proximal sesamoid bones (PSB) from 10 racehorses with PSBF and from 10 control racehorses without musculoskeletal injury were examined using the bulk basic fuchsin method. Bone histomorphometric and microfracture analysis was performed, and cases and controls compared using two-sample t-test, paired t-test, and Mann-Whitney U test. There was no significant difference in the microfracture density and the trabecular bone area between bones from case and control horses, and between fractured and non-fractured bones in case horses. Microfracture density was low in the areas of the PSB examined. Microfracture density was not significantly different between groups, indicating that propagation of micro-cracks is an unlikely predisposing pathologic alteration in PSBF in British racehorses. There was no significant difference in the bone surface area between groups, which one would expect if modelling, adaptation and an increase in bone density were associated with PSBF fracture in the case horses. Therefore, PSBF in the British racehorse does not appear to be associated with microfractures of the trabecular bone of the PSB. The PSB fractures might represent an acute monotonic fracture; however, the aetiology of the fractures remains unknown with additional research required.

Numerical Study of Mechanical Response of Pure Titanium during Shot Peening

Science.gov (United States)

Wang, Y. M.; Cheng, J. P.; Yang, H. P.; Zhang, C. H.

2018-05-01

Mechanical response of pure titanium impacted by a steel ball was simulated using finite element method to investigate stress and strain evolution during shot peening. It is indicated that biaxial residual stress was obtained in the surface layer while in the interior triaxial residual stress existed because the S33 was comparable to S11 and S22. With decreasing the depth from the top surface, the stress was higher during impacting, but the stress relief extent became more significant when the ball rebounded. Therefore the maximum residual stress was formed in the subsurface layer with depth of 130 μm. As for the residual strain, it is shown that the maximum residual strain LE33 was obtained at the depth of 60 μm corresponding to the maximum shear stress during impacting.

The choice of a constitutive formulation for modeling limb flexion-induced deformations and stresses in the human femoropopliteal arteries of different ages.

Science.gov (United States)

Desyatova, Anastasia; MacTaggart, Jason; Poulson, William; Deegan, Paul; Lomneth, Carol; Sandip, Anjali; Kamenskiy, Alexey

2017-06-01

Open and endovascular treatments for peripheral arterial disease are notorious for high failure rates. Severe mechanical deformations experienced by the femoropopliteal artery (FPA) during limb flexion and interactions between the artery and repair materials play important roles and may contribute to poor clinical outcomes. Computational modeling can help optimize FPA repair, but these simulations heavily depend on the choice of constitutive model describing the arterial behavior. In this study finite element model of the FPA in the standing (straight) and gardening (acutely bent) postures was built using computed tomography data, longitudinal pre-stretch and biaxially determined mechanical properties. Springs and dashpots were used to represent surrounding tissue forces associated with limb flexion-induced deformations. These forces were then used with age-specific longitudinal pre-stretch and mechanical properties to obtain deformed FPA configurations for seven age groups. Four commonly used invariant-based constitutive models were compared to determine the accuracy of capturing deformations and stresses in each age group. The four-fiber FPA model most accurately portrayed arterial behavior in all ages, but in subjects younger than 40 years, the performance of all constitutive formulations was similar. In older subjects, Demiray (Delfino) and classic two-fiber Holzapfel-Gasser-Ogden formulations were better than the Neo-Hookean model for predicting deformations due to limb flexion, but both significantly overestimated principal stresses compared to the FPA or Neo-Hookean models.

Rock mechanics research in the Coeur d'Alene mining district

Energy Technology Data Exchange (ETDEWEB)

Corp, E. L.

1980-05-15

Over the past 20 years, the Bureau of Mines and mining companies of the Coeur d'Alene district have conducted cooperative research on problems of ground control. For the past six years emphasis has been placed on research to improve deep shaft design and to control rock bursts during cut-and-fill stoping. Factors contributing to ground control problems include: depth of mining ranging to 8000 feet; local tectonic activity that in many instances has produced horizontal stresses exceeding the vertical; unequal horizontal stresses at ratios ranging between 1.25 and 2.73; major faults, joints, and bedding planes; and hard, brittle quartzite rock capable of concentrating high levels of stress. Finite-element modeling and construction of small-scale circular and rectangular test shafts have shown that circular openings are stable only when stresses are hydrostatic or weakly biaxial. Under a strongly-biaxial horizontal stress field, a rectangular shaft has a greater depth capabiity if its long axis can be oriented parallel to the major stress and normal to the bedding and joint system. Steel sets appear preferable to wood sets or concrete lining. Based on underground tests at Hecla's Star mine, destressing or preconditioning of the vein rock prior to mining was shown to be an effective means of controlling rock bursts. Drilling and shooting a radial pattern of longholes before stope mining starts has preconditioned or softened the vein material to the extent that seismic energy release during mining is reduced and no bursting occurred. Increased burst and seismic activity while mining above the preconditioned zone points out the need to precondition an entire stope block before mining.

Prediction of failure of highly irradiated Zircaloy clad tubes under reactivity initiated accidents

International Nuclear Information System (INIS)

Jernkvist, L.O.

2003-01-01

This paper deals with failure of irradiated Zircaloy tubes under the heat-up stage of a reactivity initiated accident (RIA). More precisely, by use of a model for plastic strain localization and necking failure, we theoretically analyse the effects of local surface defects on clad ductility and survivability under RIA. The results show that even very shallow surface defects, e.g. arising from a non-uniform or partially spilled oxide layer, have a strong limiting effect on clad ductility. Moreover, in presence of surface defects, the ability of the clad tube to expand radially without necking failure is found to be extremely sensitive to the stress biaxiality ratio σ zz /σ θθ , which is here assumed to be in the range from 0 to 1. The results of our analysis are compared with clad ductility data available in literature, and their consequences for clad failure prediction under RIA are discussed. In particular, the results raise serious concerns regarding the applicability of failure criteria, which are based on clad strain energy density. These criteria do not capture the observed sensitivity to stress biaxiality on clad failure propensity. (author)

Hyper-elastic modeling and mechanical behavior investigation of porous poly-D-L-lactide/nano-hydroxyapatite scaffold material.

Science.gov (United States)

Han, Quan Feng; Wang, Ze Wu; Tang, Chak Yin; Chen, Ling; Tsui, Chi Pong; Law, Wing Cheung

2017-07-01

Poly-D-L-lactide/nano-hydroxyapatite (PDLLA/nano-HA) can be used as the biological scaffold material in bone tissue engineering as it can be readily made into a porous composite material with excellent performance. However, constitutive modeling for the mechanical response of porous PDLLA/nano-HA under various stress conditions has been very limited so far. In this work, four types of fundamental compressible hyper-elastic constitutive models were introduced for constitutive modeling and investigation of mechanical behaviors of porous PDLLA/nano-HA. Moreover, the unitary expressions of Cauchy stress tensor have been derived for the PDLLA/nano-HA under uniaxial compression (or stretch), biaxial compression (or stretch), pure shear and simple shear load by using the theory of continuum mechanics. The theoretical results determined from the approach based on the Ogden compressible hyper-elastic constitutive model were in good agreement with the experimental data from the uniaxial compression tests. Furthermore, this approach can also be used to predict the mechanical behaviors of the porous PDLLA/nano-HA material under the biaxial compression (or stretch), pure shear and simple shear. Copyright © 2017 Elsevier Ltd. All rights reserved.

Biaxial Failure Analysis of Graphite Reinforced Polyimide and Epoxy Fabric Composites

National Research Council Canada - National Science Library

Kumosa, Maciej

2001-01-01

.... In the experimental part of this research, numerous XRD measurements were made to determine residual strains and stresses in embedded Al and Ag inclusions placed in four ply 8 harness satin (8HS...

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

International Nuclear Information System (INIS)

Okubo, P.G.; Dieterich, J.H.

1981-01-01

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/m 2 at a normal stress of 1.1 MPa to 0.8 J/m 2 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

Effect of Low-Pressure Nitrogen DC Plasma Treatment on the Surface Properties of Biaxially Oriented Polypropylene, Poly (Methyl Methacrylate) and Polyvinyl Chloride Films

International Nuclear Information System (INIS)

Mortazavi, S. Hamideh; Ghoranneviss, Mahmood; Pilehvar, Soheil; Esmaeili, Sina; Zargham, Shamim; Hashemi, S. Ebrahim; Jodat, Hamzeh

2013-01-01

In this study, commercial biaxially oriented polypropylene (BOPP), polyvinyl chloride (PVC) and poly (methyl methacrylate) (PMMA) films were treated with nitrogen plasma over different exposure times in a Pyrex tube surrounded by a DC variable magnetic field. The chemical changes that appeared on the surface of the samples were investigated using Fourier transform infrared (FT-IR) spectroscopy and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy after treatment for 2 min, 4 min and 6 min in a nitrogen plasma chamber. Effects of the plasma treatment on the surface topographies and contact angles of the untreated and plasma treated films were also analyzed by atomic force microscopy (AFM) and a contact angle measuring system. The results show that the plasma treated films become more hydrophilic with an enhanced wettability due to the formation of some new polar groups on the surface of the treated films. Moreover, at higher exposure times, the total surface energy in all treated films increased while a reduction in contact angle occurred. The behavior of surface roughness in each sample was completely different at higher exposure times. (plasma technology)

Nonlocal vibration and biaxial buckling of double-viscoelastic-FGM-nanoplate system with viscoelastic Pasternak medium in between

Energy Technology Data Exchange (ETDEWEB)

Liu, J.C. [College of Civil Engineering and Architecture, Zhejiang University, Hangzhou 310058 (China); Zhang, Y.Q., E-mail: cyqzhang@zju.edu.cn [College of Civil Engineering and Architecture, Zhejiang University, Hangzhou 310058 (China); State Key Laboratory of Mechanical Structural Strength and Vibration, Xi' an Jiaotong University, Xi' an 710049 (China); Fan, L.F. [College of Architecture and Civil Engineering, Beijing University of Technology, Beijing 100084 (China)

2017-04-11

The general equation for transverse vibration of double-viscoelastic-FGM-nanoplate system with viscoelastic Pasternak medium in between and each nanoplate subjected to in-plane edge loads is formulated on the basis of the Eringen's nonlocal elastic theory and the Kelvin model. The factors of the structural damping, medium damping, small size effect, loading ratio, and Winkler modulus and shear modulus of the medium are incorporated in the formulation. Based on the Navier's method, the analytical solutions for vibrational frequency and buckling load of the system with simply supported boundary conditions are obtained. The influences of these factors on vibrational frequency and buckling load of the system are discussed. It is demonstrated that the vibrational frequency of the system for the out-of-phase vibration is dependent upon the structural damping, small size effect and viscoelastic Pasternak medium, whereas the vibrational frequency for the in-phase vibration is independent of the viscoelastic Pasternak medium. While the buckling load of the system for the in-phase buckling case has nothing to do with the viscoelastic Pasternak medium, the buckling load for the out-of-phase case is related to the small size effect, loading ratio and Pasternak medium. - Highlights: • Vibration of double-viscoelastic-FGM-nanoplate system under in-plane edge loads is investigated. • Biaxial buckling of the system with simply supported boundary conditions is analyzed. • Explicit expression for the vibrational frequency and buckling load is obtained. • Impacts of viscoelastic Pasternak medium on vibrational frequency and buckling load are discussed. • Influences of structural damping, small size effect and loading ratio are also considered.

Doped LZO buffer layers for laminated conductors

Science.gov (United States)

Paranthaman, Mariappan Parans [Knoxville, TN; Schoop, Urs [Westborough, MA; Goyal, Amit [Knoxville, TN; Thieme, Cornelis Leo Hans [Westborough, MA; Verebelyi, Darren T [Oxford, MA; Rupich, Martin W [Framingham, MA

2010-03-23

A laminated conductor includes a metallic substrate having a surface, a biaxially textured buffer layer supported by the surface of the substrate, the biaxially textured buffer layer comprising LZO and a dopant for mitigating metal diffusion through the LZO, and a biaxially textured conductor layer supported by the biaxially textured buffer layer.

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

International Nuclear Information System (INIS)

Christen, D.K.; Feenstra, R.; Kroeger, D.M.; Lee, D.F.; List, F.A.; Martin, P.M.; Norton, D.P.; Paranthaman, M.; Park, C.; Royal, A.; Specht, E.D.; Verebelyi, D.T.

1999-01-01

High critical current YBa 2 Cu 3 O 7-y (referred to as YBCO) coated conductors were fabricated with a layer sequence of YBCO/YSZ/CeO 2 /Ni. The cube (100) texture in the starting Ni substrates was obtained by cold rolling followed by recrystallization. A thin CeO 2 (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 l0 6 A/cm 2 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 CeO 2 layers; YBCO films were also grown on CeO 2 -buffered YSZ (100) single crystal substrates using e-beam co-evaporated Y-BaF 2 -Cu precursors followed by a post-annealing process. A transport critical current density of over 1 x lO 6 A/cm 2 at 77 K was obtained on a 0.3 m thick YBCO film in zero field

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

Science.gov (United States)

Bagheri, Hossein; Hooshmand, Tabassom; Aghajani, Farzaneh

2015-09-01

This study aimed to evaluate the effect of different ceramic surface treatments after machining grinding on the biaxial flexural strength (BFS) of machinable dental ceramics with different crystalline phases. Disk-shape specimens (10mm in diameter and 1.3mm in thickness) of machinable ceramic cores (two silica-based and one zirconia-based ceramics) were prepared. Each type of the ceramic surfaces was then randomly treated (n=15) with different treatments as follows: 1) machined finish as control, 2) machined finish and sandblasting with alumina, and 3) machined finish and hydrofluoric acid etching for the leucite and lithium disilicate-based ceramics, and for the zirconia; 1) machined finish and post-sintered as control, 2) machined finish, post-sintered, and sandblasting, and 3) machined finish, post-sintered, and Nd;YAG laser irradiation. The BFS were measured in a universal testing machine. Data based were analyzed by ANOVA and Tukey's multiple comparisons post-hoc test (α=0.05). The mean BFS of machined finish only surfaces for leucite ceramic was significantly higher than that of sandblasted (P=0.001) and acid etched surfaces (P=0.005). A significantly lower BFS was found after sandblasting for lithium disilicate compared with that of other groups (Pceramics was affected by the type of ceramic material and surface treatment method. Sandblasting with alumina was detrimental to the strength of only silica-based ceramics. Nd:YAG laser irradiation may lead to substantial strength degradation of zirconia.

In-situ neutron diffraction during biaxial deformation

International Nuclear Information System (INIS)

Van Petegem, S.; Wagner, J.; Panzner, T.; Upadhyay, M.V.; Trang, T.T.T.; Van Swygenhoven, H.

2016-01-01

A change in strain path may have a significant effect on the mechanical response of metals. In order to understand or even predict the macroscopic behaviour under such conditions a detailed knowledge on the microstructural evolution is crucial. Yet relatively little work has been done to quantify and understand how the inter- and intragranular strains are affected during a change in strain path. In this work we present a new multiaxial deformation rig that allows performing in situ proportional and non-proportional loading under neutron diffraction. We demonstrate the capabilities of this new setup for the case of a 316 L stainless steel. We show that the nature and magnitude of intergranular strain strongly depends on the applied stress state and demonstrate that micro yielding and internal strain recovery are responsible for the observed transient softening during a 90° strain path change. We anticipate that this new characterization method will provide previously inaccessible microstructural data that can serve as input for benchmarking current state-of-the-art crystal plasticity models.

Determination of type, magnitude and direction of residual stresses generated in the welding of AISI H-13 steel with the hole drilling method

International Nuclear Information System (INIS)

Mejia; I; Maldonado, C; Bedolla, A; Velez, M; Medina, A; Bejar, L

2006-01-01

AISI H-13 steel is considered to be a highly ultra resistant steel because its resistance to stress surpasses 1380 MPa. This steel is widely used in tools that heavily used, especially under high temperatures, such as: awls, molds for pressing, extrusion dies, extrusion tools from heat impact, tools for producing screws, bolts, rivets and taps, molds for centrifugal smelting, tools for presses with shaped pieces, knives for hot cutting, among others. The weldability of AISI H-13 steel is generally poor, but it is possible if the proper precautions are taken. Cracking is perhaps the factor that most limits the weldability of AISI H-13 steel. The tendency to crack during welding for this type of steel occurs in the base metal and the zone close to the supporting material (cold cracking). The interlayer covering technique is used in the repair, welding and recovery of pieces of high alloy steels in order to avoid cracking and to lower the residual stresses generated by obstructed contraction and martensitic transformation. This work defined the type, magnitude and direction of residual stresses at different distances starting from the center of the welded union on the 25.4 mm thick AISI H-13 steel sheet. The welding was carried out in a test piece with Y-Groove geometry following JIS Z 3158 standard, using the SMAW process and an AISI 312 stainless steel interlayer between the base metal and the supporting metal. The hole-drilling method was used to measure the type, magnitude and direction of residual stresses using extensometric gauge rosette CEA-06-062UM-120 and CEA-06-062RE-120 following the guidelines established by ASTM E 837 standard. Based on the relaxed deformations that were measured, the type, magnitude and direction of residual stresses were determined with the H-DRILL residual stress program for biaxial condition. The results indicate that under these welding conditions the residual strains at different distances from the welded union are from stress and

A three dimensional elastoplastic cyclic constitutive law with a semi discrete variable and a ratchetting stress

International Nuclear Information System (INIS)

Geyer, P.; Proix, J.M.; Jayet-Gendrot, S.; Schoenberger, P.; Taheri, S.

1995-01-01

The study of cyclic elastoplastic constitutive law is, at the moment, focused on non proportional loadings, but for uniaxial loadings some problems remain, as for example the ability for a law to describe simultaneously ratcheting (constant increment of strain) in non symmetrical ones. We propose a law with a discrete memory variable, the plastic strain at the last unloading, and a ratchetting stress which, in addition to previous phenomena, describes the other hand the choice of all macroscopic variables is justified by a microscopic analysis. The extension to 3D situations of this law is proposed. The discrete nature of the memory leads to discontinuity problems for some loading paths, a modification is then proposed which uses a differential evolution law. For large enough uniaxial cycles, the uniaxial law is nevertheless recovered. An incremental form of he implicit evolution problem is given, and we describe the implementation of this model in the Code Aster a thermomechanical structural software using the f.e.m. developed at Electricite de France. For a 316 stainless steel we present comparisons between experiments and numerical results in uniaxial and biaxial ratchetting and non proportional strain controlled test (circular, square, stair loading). (authors). 13 refs., 10 figs

Thermoforming of HDPE

Science.gov (United States)

McKelvey, David; Menary, Gary; Martin, Peter; Yan, Shiyong

2017-10-01

The thermoforming process involves a previously extruded sheet of material being reheated to a softened state below the melting temperature and then forced into a mould either by a plug, air pressure or a combination of both. Thermoplastics such as polystyrene (PS) and polypropylene (PP) are commonly processed via thermoforming for products in the packaging industry. However, high density polyethylene (HDPE) is generally not processed via thermoforming and yet HDPE is extensively processed throughout the packaging industry. The aim of this study was to investigate the potential of thermoforming HDPE. The objectives were to firstly investigate the mechanical response under comparable loading conditions and secondly, to investigate the final mechanical properties post-forming. Obtaining in-process stress-strain behavior during thermoforming is extremely challenging if not impossible. To overcome this limitation the processing conditions were replicated offline using the QUB biaxial stretcher. Typical processing conditions that the material will experience during the process are high strain levels, high strain rates between 0.1-10s-1 and high temperatures in the solid phase (1). Dynamic Mechanical Analysis (DMA) was used to investigate the processing range of the HDPE grade used in this study, a peak in the tan delta curve was observed just below the peak melting temperature and hence, a forming temperature was selected in this range. HPDE was biaxially stretched at 128°C at a strain rate of 4s-1, under equal biaxial deformation (EB). The results showed a level of biaxial orientation was induced which was accompanied by an increase in the modulus from 606 MPa in the non-stretched sample to 1212MPa in the stretched sample.

Facility for in-reactor creep testing of fuel cladding

International Nuclear Information System (INIS)

Kohn, E.; Wright, M.G.

1976-11-01

A biaxial stress creep test facility has been designed and developed for operation in the WR-1 reactor. This report outlines the rationale for its design and describes its construction and the operating experience with it. The equipment is optimized for the determination of creep data on CANDU fuel cladding. Typical results from Zr-2.5 wt% Nb fuel cladding are used to illustrate the accuracy and reliability obtained. (author)

Catastrophic biaxial proximal sesamoid bone fractures in UK Thoroughbred races (1999-2004): horse characteristics and racing history.

Science.gov (United States)

Kristoffersen, M; Parkin, T D H; Singer, E R

2010-07-01

Catastrophic biaxial proximal sesamoid bone fractures (PSBF) have not yet been described in detail in the UK racing population. To determine the incidence and relative risk (RR) of PSBF in different types of racing in the UK; and to describe horse-level characteristics and racing histories of horses sustaining these injuries. Distal limbs were collected from all racehorses suffering catastrophic fractures during racing at all 59 racecourses in the UK, in a prospective study from February 1999 to December 2004. Post mortem investigation identified the anatomical location and type of fracture. Horse, racing history, race and racecourse details were obtained. Characteristics of the horses that sustained PSBF were described. The incidence and RR of PSBF in the different types of racing in the UK were calculated. Thirty-one horses suffered PSBF during the study period. The incidence of PSBF in all types of race was 0.63 per 10,000 starts (31/494,744). The incidence was highest in flat races on all weather surfaces (1.63 per 10,000 starts: 12/73,467; RR = 4.4 when compared to turf flat racing). Affected horses had an average age of 5.6 years and had started a mean of 28 races at the time of fracture. There is a strong association between type of racing surface and PSBF. Horses competing in flat races on all weather surfaces have an increased risk of PSBF. These fractures appear to happen in experienced horses with several starts, with few fractures occurring within the first season of racing. Further research should focus on identification of underlying pathology of these fractures. Epidemiological studies aimed at the identification of risk factors for PSBF in the UK racing population would require a large number of cases acquired over many years given the relatively low incidence of PSBF.

Test Method Variability in Slow Crack Growth Properties of Sealing Glasses

Science.gov (United States)

Salem, J. A.; Tandon, R.

2010-01-01

The crack growth properties of several sealing glasses were measured by using constant stress rate testing in 2 and 95 percent RH (relative humidity). Crack growth parameters measured in high humidity are systematically smaller (n and B) than those measured in low humidity, and crack velocities for dry environments are 100x lower than for wet environments. The crack velocity is very sensitive to small changes in RH at low RH. Biaxial and uniaxial stress states produced similar parameters. Confidence intervals on crack growth parameters that were estimated from propagation of errors solutions were comparable to those from Monte Carlo simulation. Use of scratch-like and indentation flaws produced similar crack growth parameters when residual stresses were considered.

Weibull statistics effective area and volume in the ball-on-ring testing method

DEFF Research Database (Denmark)

Frandsen, Henrik Lund

2014-01-01

The ball-on-ring method is together with other biaxial bending methods often used for measuring the strength of plates of brittle materials, because machining defects are remote from the high stresses causing the failure of the specimens. In order to scale the measured Weibull strength...... to geometries relevant for the application of the material, the effective area or volume for the test specimen must be evaluated. In this work analytical expressions for the effective area and volume of the ball-on-ring test specimen is derived. In the derivation the multiaxial stress field has been accounted...

Spatiotemporal complexity of 2-D rupture nucleation process observed by direct monitoring during large-scale biaxial rock friction experiments

Science.gov (United States)

Fukuyama, Eiichi; Tsuchida, Kotoyo; Kawakata, Hironori; Yamashita, Futoshi; Mizoguchi, Kazuo; Xu, Shiqing

2018-05-01

We were able to successfully capture rupture nucleation processes on a 2-D fault surface during large-scale biaxial friction experiments using metagabbro rock specimens. Several rupture nucleation patterns have been detected by a strain gauge array embedded inside the rock specimens as well as by that installed along the edge walls of the fault. In most cases, the unstable rupture started just after the rupture front touched both ends of the rock specimen (i.e., when rupture front extended to the entire width of the fault). In some cases, rupture initiated at multiple locations and the rupture fronts coalesced to generate unstable ruptures, which could only be detected from the observation inside the rock specimen. Therefore, we need to carefully examine the 2-D nucleation process of the rupture especially when analyzing the data measured only outside the rock specimen. At least the measurements should be done at both sides of the fault to identify the asymmetric rupture propagation on the fault surface, although this is not perfect yet. In the present experiment, we observed three typical types of the 2-D rupture propagation patterns, two of which were initiated at a single location either close to the fault edge or inside the fault. This initiation could be accelerated by the free surface effect at the fault edge. The third one was initiated at multiple locations and had a rupture coalescence at the middle of the fault. These geometrically complicated rupture initiation patterns are important for understanding the earthquake nucleation process in nature.

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

Directory of Open Access Journals (Sweden)

Jose A. Rodríguez-Gutiérrez

2014-05-01

Full Text Available An analytical method that calculates both the short- and long-term response of slender columns made of high-strength concrete (HSC and tubes filled with concrete with generalized end conditions and subjected to transverse loads along the span and axial load at the ends (causing a single or double curvature under uniaxial or biaxial bending is presented. The proposed method, which is an extension of a method previously developed by the authors, is capable of predicting not only the complete load-rotation and load-deflection curves (both the ascending and descending parts but also the maximum load capacity. The columns that can be analyzed include solid and hollow (rectangular, circular, oval, C-, T-, L-, or any arbitrary shape cross sections and columns made of circular and rectangular steel tubes filled with HSC. The fiber method is used to calculate the moment-curvature diagrams at different levels of the applied axial load (i.e., the M-P-φ curves, and the Gauss method of integration (for the sum of the contributions of the fibers parallel to the neutral axis is used to calculate the lateral rotations and deflections along the column span. Long-term effects, such as creep and shrinkage of the concrete, are also included. However, the effects of the shear deformations and torsion along the member are not included. The validity of the proposed method is presented in a companion paper and compared against the experimental results for over seventy column specimens reported in the technical literature by different researchers.

A Discrete Element Method Approach to Progressive Localization of Damage in Granular Rocks and Associated Seismicity

Science.gov (United States)

Vora, H.; Morgan, J.

2017-12-01

Brittle failure in rock under confined biaxial conditions is accompanied by release of seismic energy, known as acoustic emissions (AE). The objective our study is to understand the influence of elastic properties of rock and its stress state on deformation patterns, and associated seismicity in granular rocks. Discrete Element Modeling is used to simulate biaxial tests on granular rocks of defined grain size distribution. Acoustic Energy and seismic moments are calculated from microfracture events as rock is taken to conditions of failure under different confining pressure states. Dimensionless parameters such as seismic b-value and fractal parameter for deformation, D-value, are used to quantify seismic character and distribution of damage in rock. Initial results suggest that confining pressure has the largest control on distribution of induced microfracturing, while fracture energy and seismic magnitudes are highly sensitive to elastic properties of rock. At low confining pressures, localized deformation (low D-values) and high seismic b-values are observed. Deformation at high confining pressures is distributed in nature (high D-values) and exhibit low seismic b-values as shearing becomes the dominant mode of microfracturing. Seismic b-values and fractal D-values obtained from microfracturing exhibit a linear inverse relationship, similar to trends observed in earthquakes. Mode of microfracturing in our simulations of biaxial compression tests show mechanistic similarities to propagation of fractures and faults in nature.

Borehole stability in densely welded tuffs

International Nuclear Information System (INIS)

Fuenkajorn, K.; Daemen, J.J.K.

1992-07-01

The stability of boreholes, or more generally of underground openings (i.e. including shafts, ramps, drifts, tunnels, etc.) at locations where seals or plugs are to be placed is an important consideration in seal design for a repository (Juhlin and Sandstedt, 1989). Borehole instability or borehole breakouts induced by stress redistribution could negate the effectiveness of seals or plugs. Breakout fractures along the wall of repository excavations or exploratory holes could provide a preferential flowpath for groundwater or gaseous radionuclides to bypass the plugs. After plug installation, swelling pressures exerted by a plug could induce radial cracks or could open or widen preexisting cracks in the rock at the bottom of the breakouts where the tangential compressive stresses have been released by the breakout process. The purpose of the work reported here is to determine experimentally the stability of a circular hole in a welded tuff sample subjected to various external boundary loads. Triaxial and biaxial borehole stability tests have been performed on densely welded Apache Leap tuff samples and Topopah Spring tuff samples. The nominal diameter of the test hole is 13.3 or 14.4 mm for triaxial testing, and 25.4 mm for biaxial testing. The borehole axis is parallel to one of the principal stress axes. The boreholes are drilled through the samples prior to applying external boundary loads. The boundary loads are progressively increased until breakouts occur or until the maximum load capacity of the loading system has been reached. 74 refs

Insulation structure of thermonuclear device

International Nuclear Information System (INIS)

Suzuki, Takayuki; Usami, Saburo; Tsukamoto, Hideo; Kikuchi, Mitsuru

1998-01-01

The present invention provides an insulating structure of a thermonuclear device, in which insulation materials between toroidal coils are not broken even if superconductive toroidal coils are used. Namely, a tokamak type thermonuclear device of an insulating structure type comprises superconductive toroidal coils for confining plasmas arranged in a circular shape directing the center each at a predetermined angle, and the toroidal coils are insulated from each other. The insulation materials are formed by using a biaxially oriented fiber reinforced plastics. The contact surface of the toroidal coils and the insulating materials are arranged so that they are contact at a woven surface of the fiber reinforced plastics. Either or both of the contact surfaces of the fiber reinforced plastics and the toroidal coils are coated with a high molecular compound having a low friction coefficient. With such a constitution, since the interlayer shearing strength of the biaxially oriented fiber reinforced plastics is about 1/10 of the compression strength, the shearing stress exerted on the insulation material is reduced. Since a static friction coefficient on the contact surface is reduced to provide a structure causing slipping, shearing stress does not exceeds a predetermined limit. As a result, breakage of the insulation materials between the toroidal coils can be prevented. (I.S.)

MOD approach for the growth of epitaxial CeO2 buffer layers on biaxially textured Ni-W substrates for YBCO coated conductors

International Nuclear Information System (INIS)

Bhuiyan, M S; Paranthaman, M; Sathyamurthy, S; Aytug, T; Kang, S; Lee, D F; Goyal, A; Payzant, E A; Salama, K

2003-01-01

We have grown epitaxial CeO 2 buffer layers on biaxially textured Ni-W substrates for YBCO coated conductors using a newly developed metal organic decomposition (MOD) approach. Precursor solution of 0.25 M concentration was spin coated on short samples of Ni-3 at%W (Ni-W) substrates and heat-treated at 1100 C in a gas mixture of Ar-4%H 2 for 15 min. Detailed x-ray studies indicate that CeO 2 films have good out-of-plane and in-plane textures with full-width-half-maximum values of 5.8 deg. and 7.5 deg., respectively. High temperature in situ XRD studies show that the nucleation of CeO 2 films starts at 600 C and the growth completes within 5 min when heated at 1100 C. SEM and AFM investigations of CeO 2 films reveal a fairly dense microstructure without cracks and porosity. Highly textured YSZ barrier layers and CeO 2 cap layers were deposited on MOD CeO 2 -buffered Ni-W substrates using rf-magnetron sputtering. Pulsed laser deposition (PLD) was used to grow YBCO films on these substrates. A critical current, J c , of about 1.5 MA cm -2 at 77 K and self-field was obtained on YBCO (PLD)/CeO 2 (sputtered)/YSZ (sputtered)/CeO 2 (spin-coated)/Ni-W

STRESS - STRAIN CURVE ANALYSIS OF WOVEN FABRICS MAD E FROM COMBED YARNS TYPE WOOL

OpenAIRE

VÎLCU Adrian; HRISTIAN Liliana; BORDEIANU Demetra L.; VÎLCU Catalin

2014-01-01

The paper analyses the tensile behavior of woven fabrics made from 45%Wool + 55% PES used for garments. Analysis of fabric behavior during wearing has shown that these are submitted to simple and repeated uni-axial or bi-axial tensile strains. The level of these strains is often within the elastic limit, rarely going over yielding. Therefore the designer must be able to evaluate the mechanical behavior of such fabrics in order to control the fabric behavior in the garment. This evaluation is ...

Chairside CAD/CAM materials. Part 2: Flexural strength testing.

Science.gov (United States)

Wendler, Michael; Belli, Renan; Petschelt, Anselm; Mevec, Daniel; Harrer, Walter; Lube, Tanja; Danzer, Robert; Lohbauer, Ulrich

2017-01-01

Strength is one of the preferred parameters used in dentistry for determining clinical indication of dental restoratives. However, small dimensions of CAD/CAM blocks limit reliable measurements with standardized uniaxial bending tests. The objective of this study was to introduce the ball-on-three-ball (B3B) biaxial strength test for dental for small CAD/CAM block in the context of the size effect on strength predicted by the Weibull theory. Eight representative chairside CAD/CAM materials ranging from polycrystalline zirconia (e.max ZirCAD, Ivoclar-Vivadent), reinforced glasses (Vitablocs Mark II, VITA; Empress CAD, Ivoclar-Vivadent) and glass-ceramics (e.max CAD, Ivoclar-Vivadent; Suprinity, VITA; Celtra Duo, Dentsply) to hybrid materials (Enamic, VITA; Lava Ultimate, 3M ESPE) have been selected. Specimens were prepared with highly polished surfaces in rectangular plate (12×12×1.2mm 3 ) or round disc (Ø=12mm, thickness=1.2mm) geometries. Specimens were tested using the B3B assembly and the biaxial strength was determined using calculations derived from finite element analyses of the respective stress fields. Size effects on strength were determined based on results from 4-point-bending specimens. A good agreement was found between the biaxial strength results for the different geometries (plates vs. discs) using the B3B test. Strength values ranged from 110.9MPa (Vitablocs Mark II) to 1303.21MPa (e.max ZirCAD). The strength dependency on specimen size was demonstrated through the calculated effective volume/surface. The B3B test has shown to be a reliable and simple method for determining the biaxial strength restorative materials supplied as small CAD/CAM blocks. A flexible solution was made available for the B3B test in the rectangular plate geometry. Copyright © 2016 The Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Thermal-mechanical fatigue of high temperature structural materials

Science.gov (United States)

Renauld, Mark Leo

Experimental and analytical methods were developed to address the effect of thermal-mechanical strain cycling on high temperature structural materials under uniaxial and biaxial stress states. Two materials were used in the investigation, a nickel-base superalloy of low ductility, IN-738LC and a high ductility material, 316 stainless steel. A uniaxial life prediction model for the IN-738LC material was based on tensile hysteresis energy measured in stabilized, mid-life hysteresis loops. Hold-time effects and temperature cycling were incorporated in the hysteresis energy approach. Crack growth analysis was also included in the model to predict the number of TMF cycles to initiate and grow a fatigue crack through the coating. The nickel-base superalloy, IN-738LC, was primarily tested in out-of-phase (OP) TMF with a temperature range from 482-871sp°C (900-1600sp°F) under continuous and compressive hold-time cycling. IN-738LC fatigue specimens were coated either with an aluminide, NiCoCrAlHfSi overlay or CoNiCrAlY overlay coating on the outer surface of the specimen. Metallurgical failure analysis via optical and scanning electron microscopy, was used to characterize failure behavior of both substrate and coating materials. Type 316 SS was subjected to continuous biaxial strain cycling with an in-phase (IP) TMF loading and a temperature range from 399-621sp°C (750-1150sp°F). As a result, a biaxial TMF life prediction model was proposed on the basis of an extended isothermal fatigue model. The model incorporates a frequency effect and phase factors to assess the different damage mechanisms observed during TMF loading. The model was also applied to biaxial TMF data generated on uncoated IN-738LC.

Analysis of Precursors Prior to Rock Burst in Granite Tunnel Using Acoustic Emission and Far Infrared Monitoring

OpenAIRE

Liang, Zhengzhao; Liu, Xiangxin; Zhang, Yanbo; Tang, Chunan

2013-01-01

To understand the physical mechanism of the anomalous behaviors observed prior to rock burst, the acoustic emission (AE) and far infrared (FIR) techniques were applied to monitor the progressive failure of a rock tunnel model subjected to biaxial stresses. Images of fracturing process, temperature changes of the tunnel, and spatiotemporal serials of acoustic emission were simultaneously recorded during deformation of the model. The b-value derived from the amplitude distribution data of AE wa...

Analytic study of plastic instabilities during tension or compression tests on a metallic plate bi-axially loaded in its plane: symmetric and antisymmetric modes with respect to the median plane

International Nuclear Information System (INIS)

Jouve, Dominique

2012-01-01

This report is a continuation of the thesis [23], devoted to the onset of necking plastic instabilities during tension tests on metallic plates bi-axially loaded in their plane. We are also interested here in compression tests, and in the development of antisymmetric defects with respect to the median plane of the plate. As in the thesis, we search for the dominant mode, i.e. the most unstable pair of wavelengths (λ1, λ2) in the loading plane. An approximate analytical formulation for the growth rate is proposed, especially for plane-strain tests in the absence of viscous effects, and for static tests in tension in the x1 and x2 loading directions. In that latter case, we retrieve published results [14][15]. For plane-strain tests, we show that infinitely dense networks of shear bands inclined at 45 deg. with respect to the loading direction instantaneously occur when heat softening prevails over work-hardening. (author)

Three-Dimensional Packing Structure and Electronic Properties of Biaxially Oriented Poly(2,5-bis(3-alkylthiophene-2-yl)thieno[3,2- b ]thiophene) Films

KAUST Repository

Cho, Eunkyung

2012-04-11

We use a systematic approach that combines experimental X-ray diffraction (XRD) and computational modeling based on molecular mechanics and two-dimensional XRD simulations to develop a detailed model of the molecular-scale packing structure of poly(2,5-bis (3-tetradecylthiophene-2-yl) thieno[3,2-b]thiophene) (PBTTT-C 14) films. Both uniaxially and biaxially aligned films are used in this comparison and lead to an improved understanding of the molecular-scale orientation and crystal structure. We then examine how individual polymer components (i.e., conjugated backbone and alkyl side chains) contribute to the complete diffraction pattern, and how modest changes to a particular component orientation (e.g., backbone or side-chain tilt) influence the diffraction pattern. The effects on the polymer crystal structure of varying the alkyl side-chain length from C 12 to C 14 and C 16 are also studied. The accurate determination of the three-dimensional polymer structure allows us to examine the PBTTT electronic band structure and intermolecular electronic couplings (transfer integrals) as a function of alkyl side-chain length. This combination of theoretical and experimental techniques proves to be an important tool to help establish the relationship between the structural and electronic properties of polymer thin films. © 2012 American Chemical Society.

The Mechanical and Fracturing of Rockburst in Tunnel and Its Acoustic Emission Characteristics

Directory of Open Access Journals (Sweden)

Xiangxin Liu

2018-01-01

Full Text Available The phenomenon of acoustic emission (AE is associated with rock failure and rock fracturing. In order to investigate the influence of tectonic stress on rockburst in tunnel, a biaxial loading experiment system was used in this study. The excavation operation is undertaken at the center of samples to monitor the tunnel forming process in situ, and the different horizontal stresses can be studied by using the AE monitoring technique. The dynamical fracturing process of the tunnel model was summarized, and the timing parameters of AE signals in rockburst stages were obtained. The curves of AE energy and cumulative AE energy with time show a “step-like” rising trend before the occurrence of rockburst. The evolution of macro- and mesocracks is captured, and the mechanical conditions for a “V-shaped” rockburst pit are derived. As the horizontal stress increases, the effect of excavation unloading becomes more pronounced, and the damage caused by the rockburst intensifies. In the early stage of rockburst evolution, the fracturing type follows a model of tensile-shear mix model. A positive relationship between the ratio of shear fracturing type and the horizontal stress can be noted when the rock is about to burst, and the high intensity and the high energy released of from the rock-fracturing event have become evident. Thus, the results indicate that one should focus on monitoring both sides of the surrounding rock of the tunnel so as to extract the characteristics of the process of tunnel in tunnel. The applications of biaxial loading system and during an excavation operation provide a useful tool to simulate the rock burst in tunnel at an engineering site.

The effect of academic stress and attachment stress on stress-eaters and stress-undereaters.

Science.gov (United States)

Emond, Michael; Ten Eycke, Kayla; Kosmerly, Stacey; Robinson, Adele Lafrance; Stillar, Amanda; Van Blyderveen, Sherry

2016-05-01

It is well established that stress is related to changes in eating patterns. Some individuals are more likely to increase their overall food intake under conditions of stress, whereas others are more likely to consume less food when stressed. Attachment style has been linked to disordered eating and eating disorders; however, comparisons of eating behaviors under attachment versus other types of stress have yet to be explored. The present laboratory study examined the eating patterns in self-identified stress-undereaters and stress-eaters under various types of stress. More specifically, the study examined the effects of academic and attachment stress on calorie, carbohydrate and sugar consumption within these two groups. Under the guise of critiquing student films, university students viewed either one of two stress-inducing videos (academic stress or attachment stress, both designed to be emotionally arousing) or a control video (designed to be emotionally neutral), and their food intake was recorded. Results demonstrated that the video manipulations were effective in inducing stress. Differential patterns of eating were noted based on group and stress condition. Specifically, stress-undereaters ate fewer calories, carbohydrates and sugars than stress-eaters in the academic stress condition, but not in the attachment stress or control condition. Findings suggest that specific types of stressors may influence eating behaviors differently. Copyright © 2016 Elsevier Ltd. All rights reserved.

A study on the plasticity of soda-lime silica glass via molecular dynamics simulations

Science.gov (United States)

Urata, Shingo; Sato, Yosuke

2017-11-01

Molecular dynamics (MD) simulations were applied to construct a plasticity model, which enables one to simulate deformations of soda-lime silica glass (SLSG) by using continuum methods. To model the plasticity, stress induced by uniaxial and a variety of biaxial deformations was measured by MD simulations. We found that the surfaces of yield and maximum stresses, which are evaluated from the equivalent stress-strain curves, are reasonably represented by the Mohr-Coulomb ellipsoid. Comparing a finite element model using the constructed plasticity model to a large scale atomistic model on a nanoindentation simulation of SLSG reveals that the empirical method is accurate enough to evaluate the SLSG mechanical responses. Furthermore, the effect of ion-exchange on the SLSG plasticity was examined by using MD simulations. As a result, it was demonstrated that the effects of the initial compressive stress on the yield and maximum stresses are anisotropic contrary to our expectations.

Prediction of equibiaxial loading stress in collagen-based extracellular matrix using a three-dimensional unit cell model.

Science.gov (United States)

Susilo, Monica E; Bell, Brett J; Roeder, Blayne A; Voytik-Harbin, Sherry L; Kokini, Klod; Nauman, Eric A

2013-03-01

Mechanical signals are important factors in determining cell fate. Therefore, insights as to how mechanical signals are transferred between the cell and its surrounding three-dimensional collagen fibril network will provide a basis for designing the optimum extracellular matrix (ECM) microenvironment for tissue regeneration. Previously we described a cellular solid model to predict fibril microstructure-mechanical relationships of reconstituted collagen matrices due to unidirectional loads (Acta Biomater 2010;6:1471-86). The model consisted of representative volume elements made up of an interconnected network of flexible struts. The present study extends this work by adapting the model to account for microstructural anisotropy of the collagen fibrils and a biaxial loading environment. The model was calibrated based on uniaxial tensile data and used to predict the equibiaxial tensile stress-stretch relationship. Modifications to the model significantly improved its predictive capacity for equibiaxial loading data. With a comparable fibril length (model 5.9-8μm, measured 7.5μm) and appropriate fibril anisotropy the anisotropic model provides a better representation of the collagen fibril microstructure. Such models are important tools for tissue engineering because they facilitate prediction of microstructure-mechanical relationships for collagen matrices over a wide range of microstructures and provide a framework for predicting cell-ECM interactions. Copyright © 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Strain engineering of magnetic state in vacancy-doped phosphorene

Energy Technology Data Exchange (ETDEWEB)

Ren, Jie [Hunan Provincial Key Laboratory of Micro–Nano Energy Materials and Devices, Xiangtan University, Xiangtan 411105, Hunan (China); Zhang, Chunxiao, E-mail: zhangchunxiao@xtu.edu.cn [Hunan Provincial Key Laboratory of Micro–Nano Energy Materials and Devices, Xiangtan University, Xiangtan 411105, Hunan (China); Li, Jin [Hunan Provincial Key Laboratory of Micro–Nano Energy Materials and Devices, Xiangtan University, Xiangtan 411105, Hunan (China); Guo, Zhixin [Department of Physics, Xiangtan University, Xiangtan 411105, Hunan (China); Xiao, Huaping, E-mail: hpxiao@xtu.edu.cn [Hunan Provincial Key Laboratory of Micro–Nano Energy Materials and Devices, Xiangtan University, Xiangtan 411105, Hunan (China); Zhong, Jianxin [Hunan Provincial Key Laboratory of Micro–Nano Energy Materials and Devices, Xiangtan University, Xiangtan 411105, Hunan (China)

2016-09-23

Inducing and manipulating the magnetism in two-dimensional materials play an important role for the development of the next-generation spintronics. In this letter, the effects of the biaxial strain on magnetic properties of vacancy-doped phosphorene are investigated using first-principles calculation. We find although only SV956 doping induces magnetism for unstrained phosphorene, the biaxial strain induces nonzero magnetic moment for SV5566 and DVa doped phosphorene. The biaxial strain also modulates the magnetic state for SV956, SV5566 and DVa doped phosphorene. The local magnetic moment derives from the spin polarization of the dangling bonds near the vacancy. The biaxial strain influences the local bonding configuration near the vacancy which determines the presence of dangling bonds, and then modulates the magnetic state. Our findings promise the synergistic effect of strain engineering and vacancy decoration is an effective method for the operation of phosphorene-based spintronic devices. - Highlights: • Investigation of the magnetic moment of vacancy-doped phosphorene by DFT calculation. • The modulation of the magnetic moment by the biaxial strain. • The analysis of the bonding configuration with the biaxial strain. • The analysis of the electronic structures to explain the evolution of the magnetic moment. • The effects of the biaxial strain on the band gap and doping levels.

Assessment of an improved multiaxial strength theory based on creep-rupture data for Inconel 600

International Nuclear Information System (INIS)

Huddleston, R.L.

1993-01-01

A new multiaxial strength theory incorporating three independent stress parameters was developed and reported by the author in 1984. It was formally incorporated into ASME Code Case N47-29 in 1990. The new theory provided significantly more accurate stress-rupture life predictions than obtained using the classical theories of von Mises, Tresca, and Rankins (maximum principal stress), for Types 304 and 316 stainless steel tested at 593 and 600 degrees C respectively under different biaxial stress states. Additional results for Inconel 600 specimens tested at 816 degrees C under tension-tension and tension-compression stress states are presented in this paper and show a factor of approximately 2.4 reduction in the scatter of predicted versus observed lives as compared to the classical theories of von Mises and Tresca and a factor of about 5 as compared to the Rankins theory. A key feature of the theory, which incorporates the maximum deviatoric stress, the first invariant of the stress tensor, and the second invariant of the deviatoric stress tensor, is its ability to distinguish between life under tensile versus compressive stress states

Hydrides blister formation and induced embrittlement on zircaloy-4 cladding tubes in reactivity initiated conditions

International Nuclear Information System (INIS)

Hellouin-De-Menibus, A.

2012-01-01

Our aim is to study the cladding fracture with mechanical tests more representative of RIA conditions, taking into account the hydrides blisters, representative strain rates and stress states. To obtain hydride blisters, we developed a thermodiffusion setup that reproduces blister growth in reactor conditions. By metallography, nano-hardness, XRD and ERDA, we showed that they are constituted by 80% to 100% of δ hydrides in a Zircaloy-4 matrix, and that the zirconium beneath has some radially oriented hydrides. We modeled the blister growth kinetics taking into account the hysteresis of the hydrogen solubility limit and defined the thermal gradient threshold for blister growth. The modeling of the dilatometric behavior of hydrided zirconium indicates the important role of the material crystallographic texture, which could explain differences in the blister shape. Mechanical tests monitored with an infrared camera showed that significant local heating occurred at strain rates higher than 0.1/s. In parallel, the Expansion Due to Compression test was optimized to increase the bi-axiality level from uniaxial stress to plane strain (HB-EDC and VHB-EDC tests). This increase in loading bi-axiality lowers greatly the fracture strain at 25 C and 350 C only in homogeneous material without blister. Eventually, the ductility decrease of unirradiated Zircaloy-4 cladding tube in function of the blister depth was quantified. (author) [fr

Biaxial stress-strain behavior of chemical and physical gels of poly(vinyl alcohol)

Czech Academy of Sciences Publication Activity Database

Meissner, Bohumil; Matějka, Libor

2008-01-01

Roč. 49, č. 10 (2008), s. 2560-2567 ISSN 0032-3861 R&D Projects: GA AV ČR IAA400500701 Institutional research plan: CEZ:AV0Z40500505 Keywords : poly(vinyl alcohol) gels * pure shear behavior * constitutive equation Subject RIV: CD - Macromolecular Chemistry Impact factor: 3.331, year: 2008

Focused ion beam induced deflections of freestanding thin films

International Nuclear Information System (INIS)

Kim, Y.-R.; Chen, P.; Aziz, M. J.; Branton, D.; Vlassak, J. J.

2006-01-01

Prominent deflections are shown to occur in freestanding silicon nitride thin membranes when exposed to a 50 keV gallium focused ion beam for ion doses between 10 14 and 10 17 ions/cm 2 . Atomic force microscope topographs were used to quantify elevations on the irradiated side and corresponding depressions of comparable magnitude on the back side, thus indicating that what at first appeared to be protrusions are actually the result of membrane deflections. The shape in high-stress silicon nitride is remarkably flat-topped and differs from that in low-stress silicon nitride. Ion beam induced biaxial compressive stress generation, which is a known deformation mechanism for other amorphous materials at higher ion energies, is hypothesized to be the origin of the deflection. A continuum mechanical model based on this assumption convincingly reproduces the profiles for both low-stress and high-stress membranes and provides a family of unusual shapes that can be created by deflection of freestanding thin films under beam irradiation

Increased component safety through improved methods for residual stress analysis. Subprojects. Consideration of real component geometries (phase 1). Final report

International Nuclear Information System (INIS)

Nau, Andreas; Scholtes, B.

2014-01-01

Residual stresses can be result in both detrimental as well as beneficial consequences on the component's strength and lifetime. A most detailed knowledge of the residual stress state is a pre-requisite for the assessment of the component's performance. The mechanical methods for residual stress measurements are classified in non-destructive, destructive and semi-destructive methods. The two commonly used (semi-destructive) mechanical methods are the hole drilling and the ring core method. In the context of reactor safety research of the Federal Ministry of Economic Affairs and Energy (BMWi), two fundamental and interacting weak points of the hole drilling as well as of the ring core method are investigated. On the one hand, there are effects concerning geometrical boundary conditions of the components and on the other hand, there are influences of plasticity due to notch effects. Both aspects affect the released strain field, when the material is removed and finally, the calculated residual stresses. The first issue mentioned above is under the responsibility of Institute of Materials Engineering - Metallic Materials (Kassel University) and the last one will be investigated by University of Stuttgart-Otto-Graf-Institut - materials testing institute. Within the framework of this project it could be demonstrated that updated calibration coefficients lead to more reliable residual stress calculation in contrast to existing ones. These findings are valid for points of measurements on components without geometrical boundary effects like edges or shoulders. Reasons are high developed Finite-Element software packages and the opportunity of modelling the point of measurement (hole geometry, layout of the strain gauges) and its vicinity more in detail. Special challenges are multi-axial residual stress depth distributions and the geometry of components composing edges and claddings. Unlike existing analyses considering uni-axial and homogeneous stress states, bi-axial

Fracture behavior of shallow cracks in full-thickness clad beams from an RPV wall section

International Nuclear Information System (INIS)

Keeney, J.A.; Bass, B.R.; McAfee, W.J.

1995-01-01

A testing program is described that utilizes full-thickness clad beam specimens to quantify fracture toughness for shallow cracks in weld material for which metallurgical conditions are prototypic of those found in reactor pressure vessels (RPVs). The beam specimens are fabricated from an RPV shell segment that includes weld, plate and clad material. Metallurgical factors potentially influencing fracture toughness for shallow cracks in the beam specimens include material gradients and material inhomogeneities in welded regions. The shallow-crack clad beam specimens showed a significant loss of constraint similar to that of other shallow-crack single-edge notch bend (SENB) specimens. The stress-based Dodds-Anderson scaling model appears to be effective in adjusting the test data to account for in-plane loss of constraint for uniaxially tested beams, but cannot predict the observed effects of out-of-plane biaxial loading on shallow-crack fracture toughness. A strain-based dual-parameter fracture toughness correlation (based on plastic zone width) performed acceptably when applied to the uniaxial and biaxial shallow-crack fracture toughness data

Internal-strain effect on the valence band of strained silicon and its correlation with the bond angles

Energy Technology Data Exchange (ETDEWEB)

Inaoka, Takeshi, E-mail: inaoka@phys.u-ryukyu.ac.jp; Yanagisawa, Susumu; Kadekawa, Yukihiro [Department of Physics and Earth Sciences, Faculty of Science, University of the Ryukyus, 1 Senbaru, Nishihara, Okinawa 903-0213 (Japan)

2014-02-14

By means of the first-principles density-functional theory, we investigate the effect of relative atom displacement in the crystal unit cell, namely, internal strain on the valence-band dispersion of strained silicon, and find close correlation of this effect with variation in the specific bond angles due to internal strain. We consider the [111] ([110]) band dispersion for (111) ((110)) biaxial tensility and [111] ([110]) uniaxial compression, because remarkably small values of hole effective mass m* can be obtained in this dispersion. Under the practical condition of no normal stress, biaxial tensility (uniaxial compression) involves additional normal compression (tensility) and internal strain. With an increase in the internal-strain parameter, the energy separation between the highest and second-highest valence bands becomes strikingly larger, and the highest band with conspicuously small m* extends remarkably down to a lower energy region, until it intersects or becomes admixed with the second band. This is closely correlated with the change in the specific bond angles, and this change can reasonably explain the above enlargement of the band separation.

EFAM ETM 97 - the ETM method for assessing the significance of crack-like defects in engineering structures, comprising the versions ETM 97/1 and ETM 97/2

Energy Technology Data Exchange (ETDEWEB)

Schwalbe, K.H.; Zerbst, U.; Kim, Y.J.; Brocks, W.; Cornec, A.; Heerens, J. [GKSS-Forschungszentrum Geesthacht GmbH (Germany). Inst. fuer Werkstofforschung; Amstutz, H. [Technische Univ. Darmstadt (Germany). Fachgebiet Werkstoffmechanik

1998-09-01

EFAM ETM 97 is a document of the GKSS Procedure `Engineering Flaw Assessment Method (EFAM)`. It describes methods for estimating the crack driving force for cracks in structural components in terms of the crack tip opening displacement, {delta}{sub 5}, and the J-integral. It consists of several modules covering particular application problems. Appendices to this document provide solutions for the stress intenstiy factor and the yield load, as well as informtion on transferability of fracture parameters and on the treatment of bi-axial and mixed mode loadings. A second assessment route is also given in an appendix. (orig.) [Deutsch] EFM ETM 97 ist ein Dokument der GKSS-Prozedur `Engineering Flaw Assessment Method (EFAM)`. Es beschreibt Methoden zur Abschaetzung der bruchmechanischen Beanspruchung fuer Risse in Bauteilen in Form der Rissspitzenverschiebung {delta}{sub 5} oder des J-Integrals. Es besteht aus mehreren Moduln fuer bestimmte Anwendungsprobleme. In Anhaengen werden Loesungen fuer den Spannungsintensitaetsfaktor und die Fliesslast, Informationen zur Uebertragbarkeit von Kennwerten und zur Behandlung von biaxialer und Mixed-Mode-Beanspruchung angeboten. Eine zweite Bewertungsroute ist in einem weiteren Anhang beschrieben. (orig.)

Modeling sintering of multilayers under influence of gravity

DEFF Research Database (Denmark)

Frandsen, Henrik Lund; Olevsky, Eugene; Tadesse Molla, Tesfaye

2013-01-01

, which describes the combined effect of sintering and gravity of thin multilayers, is derived and later compared with experimental results. It allows for consideration of both uniaxial and biaxial stress states. The model is based on the Skorohod-Olevsky viscous sintering framework, the classical...... laminate theory and the elastic-viscoelastic correspondence principle. The modeling approach is then applied to illustrate the effect of gravity during sintering of thin layers of cerium gadolinium oxide (CGO), and it is found to be significant. © 2012 The American Ceramic Society....

Constitutive equations for the Doi-Edwards model without independent alignment

DEFF Research Database (Denmark)

Hassager, Ole; Hansen, Rasmus

2010-01-01

We present two representations of the Doi-Edwards model without Independent Alignment explicitly expressed in terms of the Finger strain tensor, its inverse and its invariants. The two representations provide explicit expressions for the stress prior to and after Rouse relaxation of chain stretch......, respectively. The maximum deviations from the exact representations in simple shear, biaxial extension and uniaxial extension are of order 2%. Based on these two representations, we propose a framework for Doi-Edwards models including chain stretch in the memory integral form....

Stress Management: Job Stress

Science.gov (United States)

Healthy Lifestyle Stress management Job stress can be all-consuming — but it doesn't have to be. Address your triggers, keep perspective and ... stress triggers, it's often helpful to improve time management skills — especially if you tend to feel overwhelmed ...

Ceramic strengthening by tuning the elastic moduli of resin-based luting agents.

Science.gov (United States)

Spazzin, Aloísio O; Bacchi, Ataís; Alessandretti, Rodrigo; Santos, Mateus B; Basso, Gabriela R; Griggs, Jason; Moraes, Rafael R

2017-03-01

Resin-based luting agents (RBLAs) with tuned elastic moduli (E) were prepared and their influence on the strengthening, reliability, and mode of failure of luted feldspar ceramic was investigated. RBLAs with low E (2.6GPa), intermediate E (6.6GPa), and high E (13.3GPa) were prepared and used to coat acid-etched ceramic disks. Positive (untreated ceramic) and negative (acid-etched ceramic) control groups were tested. The response variables (n=30) were biaxial flexural strength (σ bf , MPa), characteristic strength (σ 0 , MPa), and Weibull modulus at the ceramic surface (z=0) and luting agent surface (z=-t 2 ). A 3D finite element analysis simulated the biaxial flexural test. Fractographic analysis and morphology of the bonded interfaces were analyzed using scanning electron microscopy. The RBLAs improved σ bf and σ 0 at z=0, particularly those with intermediate and high E, whereas the mechanical reliability was only affected in the negative control. At z=-t 2 , differences between all RBLAs were observed but the structural reliability was independent of the RBLA tested. Increasing E of the RBLA was associated with increased stress concentration at the RBLA and reduced stresses reaching the ceramic. Failures originated on the ceramic surface at the ceramic-cement interface. In the high E group, failure sometimes originated from the RBLA free surface. All RBLAs completely filled the ceramic irregularities. Increased E of the RBLA reduced the variability of strength, the stress reaching the ceramic structure, and sometimes altered the origin of failure. The use of high E RBLAs seems beneficial for luting feldspar ceramics. Copyright © 2017 The Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Cyclic softening based on dislocation annihilation at sub-cell boundary for SA333 Grade-6 C-Mn steel

Science.gov (United States)

Bhattacharjee, S.; Dhar, S.; Acharyya, S. K.; Gupta, S. K.

2018-01-01

In this work, the response of SA333 Grade-6 C-Mn steel subjected to uniaxial and in-phase biaxial tension-torsion cyclic loading is experimented and an attempt is made to model the material behaviour. Experimentally observed cyclic softening is modelled based on ‘dislocation annihilation at low angle grain boundary’, while Ohno-Wang kinematic hardening rule is used to simulate the stress-strain hysteresis loops. The relevant material parameters are extracted from the appropriate experimental results and metallurgical investigations. The material model is plugged as user material subroutine into ABAQUS FE platform to simulate pre-saturation low cycle fatigue loops with cyclic softening and other cyclic plastic behaviour under prescribed loading. The stress-strain hysteresis loops and peak stress with cycles were compared with the experimental results and good agreements between experimental and simulated results validated the material model.

Ambient temperature testing of the G-tunnel heated block

International Nuclear Information System (INIS)

Zimmerman, R.M.; Board, M.P.; Hardin, E.L.; Voegele, M.D.

1984-01-01

The G-Tunnel heated block experiment is being conducted on the Nevada Test Site (NTS) as part of the Nevada Nuclear Waste Storage Investigations project (NNWSI). The purpose of the ambient temperature testing phase is to evaluate rock-mass mechanical properties of a block (≅8 m/sup 3/) under biaxial stress changes up to 7.5 MPa above an initialization in situ value of 3.1 MPa. Results indicate that the modulus of deformation ranges from 9.7 to 17.0 GPa and Poisson's ratio ranges from 0.21 to 0.33. In general, the higher values of the modulus and Poisson's ratio were influenced by fracture propagations parallel to the compressive stress field. Other measurements indicated that cross-hole compression (p) wave velocities and single fracture permeability values were relatively insensitive to stress changes above the in situ value

Measurement of components of load parallel to cracks in a proof of safety against fracture

International Nuclear Information System (INIS)

Amstutz, H.; Seeger, T.

1992-01-01

Largely standardized processes are now available in the R6 concept, the engineering approach and the engineering treatment model (ETM) according to Schwalbe, which make judgment and quantitative assessment of the fracture and failure behaviour of components with cracks and faults similar to cracks possible. When using the process on components with a multi-axial basic stress state, the question arises for pure mode I stresses, to what extent and in what form the effect of the load parallel to the cracks can be included in the concepts. Based on a numerical study with finite elements, the connections between global bi-axial load and local stress conditions are shown in the article, using the example of the J integral, and are discussed regarding taken them into account in the proof of safety against fracture. (orig.) [de

Effect of furnace type and ceramming heat treatment conditions on the biaxial flexural strength of a canasite glass-ceramic.

Science.gov (United States)

Johnson, A; Shareef, M Y; van Noort, R; Walsh, J M

2000-07-01

To assess the effect of different heat treatment conditions when using two different furnace types on the biaxial flexural strength (BFS) of a fluorcanasite castable glass-ceramic. Two furnace types, one a programmable furnace (PF), the other a dental laboratory burnout furnace (DLF), were used with various ceramming times to determine their effect on the BFS of a fluorcanasite castable glass-ceramic. The glass-ceramic material was cast to produce discs of 12 mm diameter and 2 mm thickness using the lost wax casting process (n = 80). After casting, both furnace types were used to ceram the discs. Half the discs were not de-vested from the casting ring before ceramming but cerammed in situ (DLF) and half were de-vested before ceramming (PF). All the discs were given a nucleation heat treatment at 520 degrees C for 1 h and then cerammed at 860 degrees C using four heat soak times (0.5, 1, 2 and 3 h). The DLF furnace had a rate of climb of 13 degrees C/min and the PF furnace had a rate of climb of 5 degrees C/min to 520 degrees C and 3 degrees C/min to 860 degrees C. After ceramming the discs were de-vested and the BFS determined using a Lloyd 2000R tester. The maximum BFS values seen for both furnace types were almost identical (280 MPa), but were achieved at different heat soak times (1 h DLF, and 2 h PF). The only significant differences in BFS values for the two furnaces were between the 0.5 and 2 h heat soak times (p < or = 0.05). Individual differences were seen between results obtained from each furnace type/heat soak times evaluated (p < or = 0.05). Already available dental laboratory burnout furnaces can be used to ceram fluorcanasite glass-ceramic castings to the same BFS values as more expensive and slower specialist programmable furnaces.

Reduction of the Mg acceptor activation energy in GaN, AlN, Al0.83Ga0.17N and MgGa δ-doping (AlN)5/(GaN)1: the strain effect

Science.gov (United States)

Jiang, Xin-He; Shi, Jun-Jie; Zhang, Min; Zhong, Hong-Xia; Huang, Pu; Ding, Yi-Min; He, Ying-Ping; Cao, Xiong

2015-12-01

To resolve the p-type doping problem of Al-rich AlGaN alloys, we investigate the influence of biaxial and hydrostatic strains on the activation energy, formation energy and band gap of Mg-doped GaN, AlN, Al0.83Ga0.17N disorder alloy and (AlN)5/(GaN)1 superlattice based on first-principles calculations by combining the standard DFT and hybrid functional. We find that the Mg acceptor activation energy {{E}\\text{A}} , the formation energy {{E}\\text{f}} and the band gap {{E}\\text{g}} decrease with increasing the strain ɛ. The hydrostatic strain has a more remarkable impact on {{E}\\text{g}} and {{E}\\text{A}} than the biaxial strain. Both {{E}\\text{A}} and {{E}\\text{g}} have a linear dependence on the hydrostatic strain. For the biaxial strain, {{E}\\text{g}} shows a parabolic dependence on ɛ if \\varepsilon ≤slant 0 while it becomes linear if \\varepsilon ≥slant 0 . In GaN and (AlN)5/(GaN)1, {{E}\\text{A}} parabolically depends on the biaxial compressive strain and linearly depends on the biaxial tensible strain. However, the dependence is approximately linear over the whole biaxial strain range in AlN and Al0.83Ga0.17N. The Mg acceptor activation energy in (AlN)5/(GaN)1 can be reduced from 0.26 eV without strain to 0.16 (0.22) eV with the hydrostatic (biaxial) tensible strain 3%.

Good stress, bad stress and oxidative stress: insights from anticipatory cortisol reactivity.

Science.gov (United States)

Aschbacher, Kirstin; O'Donovan, Aoife; Wolkowitz, Owen M; Dhabhar, Firdaus S; Su, Yali; Epel, Elissa

2013-09-01

Chronic psychological stress appears to accelerate biological aging, and oxidative damage is an important potential mediator of this process. However, the mechanisms by which psychological stress promotes oxidative damage are poorly understood. This study investigates the theory that cortisol increases in response to an acutely stressful event have the potential to either enhance or undermine psychobiological resilience to oxidative damage, depending on the body's prior exposure to chronic psychological stress. In order to achieve a range of chronic stress exposure, forty-eight post-menopausal women were recruited in a case-control design that matched women caring for spouses with dementia (a chronic stress model) with similarly aged control women whose spouses were healthy. Participants completed a questionnaire assessing perceived stress over the previous month and provided fasting blood. Three markers of oxidative damage were assessed: 8-iso-prostaglandin F(2α) (IsoP), lipid peroxidation, 8-hydroxyguanosine (8-oxoG) and 8-hydroxy-2'-deoxyguanosine (8-OHdG), reflecting oxidative damage to RNA/DNA respectively. Within approximately one week, participants completed a standardized acute laboratory stress task while salivary cortisol responses were measured. The increase from 0 to 30 min was defined as "peak" cortisol reactivity, while the increase from 0 to 15 min was defined as "anticipatory" cortisol reactivity, representing a cortisol response that began while preparing for the stress task. Women under chronic stress had higher 8-oxoG, oxidative damage to RNA (pstress and elevated oxidative stress damage, but only among women under chronic stress. Consistent with this model, bootstrapped path analysis found significant indirect paths from perceived stress to 8-oxoG and IsoP (but not 8-OHdG) via anticipatory cortisol reactivity, showing the expected relations among chronically stressed participants (p≤.01) Intriguingly, among those with low chronic stress

Multiscale mechanics of TRIP-assisted multiphase steels: II. Micromechanical modelling

International Nuclear Information System (INIS)

Lani, F.; Furnemont, Q.; Van Rompaey, T.; Delannay, F.; Jacques, P.J.; Pardoen, T.

2007-01-01

The stress and strain partitioning between the different phases of transformation-induced plasticity (TRIP)-aided multiphase steels is evaluated using a mean field homogenization approach. The change of the austenite volume fraction under straining is predicted using a micromechanics-based criterion for the martensitic transformation adapted to the case of small, isolated, transforming austenite grains. The parameters of the model are identified from the mechanical response and transformation kinetics measured under uniaxial tension for two steels differing essentially by the austenite stability. The model is validated by comparing the predictions with tests performed under different loading conditions: pure shear, intermediate biaxial and equibiaxial. An analysis of the effect of the austenite stability on strength and ductility provides guidelines for optimizing properties according to the stress state

Effect of pressurization on helical guided wave energy velocity in fluid-filled pipes.

Science.gov (United States)

Dubuc, Brennan; Ebrahimkhanlou, Arvin; Salamone, Salvatore

2017-03-01

The effect of pressurization stresses on helical guided waves in a thin-walled fluid-filled pipe is studied by modeling leaky Lamb waves in a stressed plate bordered by fluid. Fluid pressurization produces hoop and longitudinal stresses in a thin-walled pipe, which corresponds to biaxial in-plane stress in a plate waveguide model. The effect of stress on guided wave propagation is accounted for through nonlinear elasticity and finite deformation theory. Emphasis is placed on the stress dependence of the energy velocity of the guided wave modes. For this purpose, an expression for the energy velocity of leaky Lamb waves in a stressed plate is derived. Theoretical results are presented for the mode, frequency, and directional dependent variations in energy velocity with respect to stress. An experimental setup is designed for measuring variations in helical wave energy velocity in a thin-walled water-filled steel pipe at different levels of pressure. Good agreement is achieved between the experimental variations in energy velocity for the helical guided waves and the theoretical leaky Lamb wave solutions. Copyright © 2016 Elsevier B.V. All rights reserved.

Damage study of an austenitic stainless steel in high cycle multiaxial fatigue regime;Etude de l'endommagement d'un acier inoxydable austenitique par fatigue multiaxiale a grand nombre de cycles

Energy Technology Data Exchange (ETDEWEB)

Poncelet, M. [CEA Saclay, DEN, SRMA, 91 - Gif-sur-Yvette (France); Barbier, G.; Raka, B.; Vincent, L.; Desmorat, R. [LMT Cachan, ENS Cachan/CNRS/UPMC/PRES Univ. Sud Paris, 94 - Cachan (France); Barbier, G. [EDF R and D / LaMSID, 92 - Clamart (France)

2010-02-15

Biaxial fatigue tests are performed up to 1 000 000 cycles at room temperature. Cross specimens of 304L steel thinned in their centre to initiate crack, are loaded by a biaxial testing machine. The strain at the centre of the sample is measured during loading using a stroboscopic Digital Image Correlation (DIC) technique, and crack initiation on the whole gauge zone is early detected by a second DIC-based measurement. A special optical assembly is designed to allow for simultaneous measurements. Three types of loadings are performed: equi-biaxial with a loading ratio R = 0.1, equi-biaxial with loading ratio R = -1, pseudo uniaxial (cyclic loading at R 0.1 in one direction and constant loading in the other). First results are commented. (authors)

Creating periodic local strain in monolayer graphene with nanopillars patterned by self-assembled block copolymer

Energy Technology Data Exchange (ETDEWEB)

Mi, Hongyi; Mikael, Solomon; Seo, Jung-Hun; Gui, Gui; Ma, Alice L.; Ma, Zhenqiang, E-mail: nealey@uchicago.edu, E-mail: mazq@engr.wisc.edu [Department of Electrical and Computer Engineering, University of Wisconsin–Madison, Madison, Wisconsin 53706 (United States); Liu, Chi-Chun; Nealey, Paul F., E-mail: nealey@uchicago.edu, E-mail: mazq@engr.wisc.edu [Department of Chemical and Biological Engineering, University of Wisconsin–Madison, Madison, Wisconsin 53706 (United States)

2015-10-05

A simple and viable method was developed to produce biaxial strain in monolayer graphene on an array of SiO{sub 2} nanopillars. The array of SiO{sub 2} nanopillars (1 cm{sup 2} in area, 80 nm in height, and 40 nm in pitch) was fabricated by employing self-assembled block copolymer through simple dry etching and deposition processes. According to high resolution micro-Raman spectroscopy and atomic force microscopy analyses, 0.9% of maximum biaxial tensile strain and 0.17% of averaged biaxial tensile strain in graphene were created. This technique provides a simple and viable method to form biaxial tensile strain in graphene and offers a practical platform for future studies in graphene strain engineering.

Room Temperature Shear Band Development in Highly Twinned Wrought Magnesium AZ31B Sheet

Science.gov (United States)

Scott, Jon; Miles, Michael; Fullwood, David; Adams, Brent; Khosravani, Ali; Mishra, Raja K.

2013-01-01

Failure mechanisms were studied in wrought AZ31B magnesium alloy after forming under different strain paths. Optical micrographs were used to observe the shear band formation and regions of high twin density in samples strained under uniaxial, biaxial, and plane strain conditions. Interrupted testing at 4 pct effective strain increments, until failure, was used to observe the evolution of the microstructure. The results showed that shear bands, with a high percentage of twinned grains, appeared early in the samples strained under biaxial or plane strain tension. These bands are similar to those seen in uniaxial tension specimens just prior to failure where the uniaxial tensile ductility was much greater than that observed for plane strain or biaxial tension conditions. A forming limit diagram for AZ31B, which was developed from the strain data, showed that plane strain and biaxial tension had very similar limit strains; this contrasts with materials like steel or aluminum alloys, which typically have greater ductility in biaxial tension compared to plane strain tension.

Evaluating the fracture toughness and flexural strength of pressable dental ceramics: an in vitro study.

Science.gov (United States)

Gurram, Ravi; Krishna, C H Vamsi; Reddy, K Mahendranadh; Reddy, G V K Mohan; Shastry, Y Mahadev

2014-12-01

The study was undertaken to evaluate the biaxial flexural strength, biaxial flexural strength after etching with 9 % HF acid and fracture toughness of three commonly used pressable all ceramic core materials. Ninety glass ceramic specimens were fabricated from three commercially available leucite based core ceramic material (1) Esthetic Empress, (2) Cergo, and (3) Performance Plus. Thirty discs of each material were divided into three groups of 10 discs each. Biaxial flexural strength (30 discs,) Biaxial flexural strength for samples treated with 9 % HF acid (30 discs) and fracture toughness (30 discs) were evaluated. Core material Performance Plus had the lowest biaxial strength of 124.89 MPa, Cergo had strength of 152.22 MPa and the highest value of 163.95 was reported for Esthetic Empress. For samples treated 9 % HF, Performance Plus had the lowest biaxial strength of 98.37 MPa, Cergo had strength of 117.42 MPa and the highest value of 143.74 was reported for Esthetic Empress. Core material Performance Plus had the lowest fracture toughness of 1.063 MPa, Cergo had strength of 1.112 MPa and the highest value of 1.225 was reported for Esthetic Empress. The results shows that Esthetic Empress had better mechanical properties compared to Cergo had Performance Plus in relation to the parameters tested.

Stress

Science.gov (United States)

... can be life-saving. But chronic stress can cause both physical and mental harm. There are at least three different types of stress: Routine stress related to the pressures of work, family, and other daily responsibilities Stress brought about ...

Fatigue and creep to leak tests of proton exchange membranes using pressure-loaded blisters

Energy Technology Data Exchange (ETDEWEB)

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

2009-12-01

In this study, three commercially available proton exchange membranes (PEMs) are biaxially tested using pressure-loaded blisters to characterize their resistance to gas leakage under either static (creep) or cyclic fatigue loading. The pressurizing medium, air, is directly used for leak detection. These tests are believed to be more relevant to fuel cell applications than quasi-static uniaxial tensile-to-rupture tests because of the use of biaxial cyclic and sustained loading and the use of gas leakage as the failure criterion. They also have advantages over relative humidity cycling test, in which a bare PEM or catalyst coated membrane is clamped with gas diffusion media and flow field plates and subjected to cyclic changes in relative humidity, because of the flexibility in allowing controlled mechanical loading and accelerated testing. Nafion {sup registered} NRE-211 membranes are tested at three different temperatures and the time-temperature superposition principle is used to construct stress-lifetime master curve. Tested at 90 C, 2%RH extruded Ion Power {sup registered} N111-IP membranes have a longer lifetime than Gore trademark -Select {sup registered} 57 and Nafion {sup registered} NRE-211 membranes. (author)

Prediction of Ductile Failure in the Stretch-Forming of AA2024 Sheets

International Nuclear Information System (INIS)

Vallellano, C.; Guzman, C.; Garcia-Lomas, F. J.

2007-01-01

A number of ductile failure criteria are nowadays being used to predict the formability of aluminium alloy sheets. Generally speaking, integral criteria (e.g. those proposed by Cockcroft and Latham, Brozzo et al., Oyane et al Chaouadi et al., etc.) have been probed to work well when the principal strains are of opposite sign, i.e. in the left side of the Forming Limit Diagram (FLD). However, when tensile biaxial strains are present, as occurs in stretch-forming practice, their predictions are usually very poor and even non-conservatives. As an alternative, local criteria, such as the classical Tresca's and Bressan and Williams' criteria, have demonstrated a good capability to predict the failure in some automotive aluminum alloys under stretching. The present work analyses experimentally and numerically the failure in AA2024-T3 sheets subjected to biaxial stretching. A series of out-of-plane stretching tests have been simulated using ABAQUS. The experimental and the numerical FLD for different failure criteria are compared. The influence on the failure of the hydrostatic pressure and the normal stress to the fracture plane is also discussed

Chemical solution deposition method of fabricating highly aligned MgO templates

Science.gov (United States)

Paranthaman, Mariappan Parans [Knoxville, TN; Sathyamurthy, Srivatsan [Knoxville, TN; Aytug, Tolga [Knoxville, TN; Arendt, Paul N [Los Alamos, NM; Stan, Liliana [Los Alamos, NM; Foltyn, Stephen R [Los Alamos, NM

2012-01-03

A superconducting article includes a substrate having an untextured metal surface; an untextured barrier layer of La.sub.2Zr.sub.2O.sub.7 or Gd.sub.2Zr.sub.2O.sub.7 supported by and in contact with the surface of the substrate; a biaxially textured buffer layer supported by the untextured barrier layer; and a biaxially textured superconducting layer supported by the biaxially textured buffer layer. Moreover, a method of forming a buffer layer on a metal substrate includes the steps of: providing a substrate having an untextured metal surface; coating the surface of the substrate with a barrier layer precursor; converting the precursor to an untextured barrier layer; and depositing a biaxially textured buffer layer above and supported by the untextured barrier layer.

A Membrane Model from Implicit Elasticity Theory

Science.gov (United States)

Freed, A. D.; Liao, J.; Einstein, D. R.

2014-01-01

A Fungean solid is derived for membranous materials as a body defined by isotropic response functions whose mathematical structure is that of a Hookean solid where the elastic constants are replaced by functions of state derived from an implicit, thermodynamic, internal-energy function. The theory utilizes Biot’s (1939) definitions for stress and strain that, in 1-dimension, are the stress/strain measures adopted by Fung (1967) when he postulated what is now known as Fung’s law. Our Fungean membrane model is parameterized against a biaxial data set acquired from a porcine pleural membrane subjected to three, sequential, proportional, planar extensions. These data support an isotropic/deviatoric split in the stress and strain-rate hypothesized by our theory. These data also demonstrate that the material response is highly non-linear but, otherwise, mechanically isotropic. These data are described reasonably well by our otherwise simple, four-parameter, material model. PMID:24282079

A macroscopic model to simulate the mechanically induced martensitic transformation in metastable austenitic stainless steels

International Nuclear Information System (INIS)

Perdahcıoğlu, E.S.; Geijselaers, H.J.M.

2012-01-01

Mechanically induced martensitic transformation and the associated transformation plasticity phenomena in austenitic stainless steels are studied. The mechanisms responsible for the transformation are investigated and put into perspective based on experimental evidence. The stress and strain partitioning into the austenite and martensite phases are formulated using a mean-field homogenization approach. At this intermediate length-scale the average stress in the austenite phase is computed and utilized to compute the mechanical driving force resolved in the material. The amount of transformation and the transformation plasticity is derived as a function of the driving force. The mechanical response of the material is obtained by combining the homogenization and the transformation models. The model is verified by mechanical tests under biaxial loading conditions during which different transformation rates are observed. As a final verification of the model, a bending test is used which manifests the stress-state dependency of the transformation.

Load-dependent extracellular matrix organization in atrioventricular heart valves: differences and similarities.

Science.gov (United States)

Alavi, S Hamed; Sinha, Aditi; Steward, Earl; Milliken, Jeffrey C; Kheradvar, Arash

2015-07-15

The extracellular matrix of the atrioventricular (AV) valves' leaflets has a key role in the ability of these valves to properly remodel in response to constantly varying physiological loads. While the loading on mitral and tricuspid valves is significantly different, no information is available on how collagen fibers change their orientation in response to these loads. This study delineates the effect of physiological loading on AV valves' leaflets microstructures using Second Harmonic Generation (SHG) microscopy. Fresh natural porcine tricuspid and mitral valves' leaflets (n = 12/valve type) were cut and prepared for the experiments. Histology and immunohistochemistry were performed to compare the microstructural differences between the valves. The specimens were imaged live during the relaxed, loading, and unloading phases using SHG microscopy. The images were analyzed with Fourier decomposition to mathematically seek changes in collagen fiber orientation. Despite the similarities in both AV valves as seen in the histology and immunohistochemistry data, the microstructural arrangement, especially the collagen fiber distribution and orientation in the stress-free condition, were found to be different. Uniaxial loading was dependent on the arrangement of the fibers in their relaxed mode, which led the fibers to reorient in-line with the load throughout the depth of the mitral leaflet but only to reorient in-line with the load in deeper layers of the tricuspid leaflet. Biaxial loading arranged the fibers in between the two principal axes of the stresses independently from their relaxed states. Unlike previous findings, this study concludes that the AV valves' three-dimensional extracellular fiber arrangement is significantly different in their stress-free and uniaxially loaded states; however, fiber rearrangement in response to the biaxial loading remains similar. Copyright © 2015 the American Physiological Society.

Assessment of Workplace Stress: Occupational Stress, Its Consequences, and Common Causes of Teacher Stress.

Science.gov (United States)

Hansen, Jo-Ida; Sullivan, Brandon A.

This chapter introduces teachers and other education professionals to the assessment of occupational stress. It begins with a brief discussion of what occupational stress is, and overview of the consequences of prolonged stress, and a review of the common causes of teacher stress. Next, it presents methods for reducing occupational stress through…

Method of depositing an electrically conductive oxide film on a textured metallic substrate and articles formed therefrom

Science.gov (United States)

Christen, David K.; He, Qing

2001-01-01

The present invention provides a biaxially textured laminate article having a polycrystalline biaxially textured metallic substrate with an electrically conductive oxide layer epitaxially deposited thereon and methods for producing same. In one embodiment a biaxially texture Ni substrate has a layer of LaNiO.sub.3 deposited thereon. An initial layer of electrically conductive oxide buffer is epitaxially deposited using a sputtering technique using a sputtering gas which is an inert or forming gas. A subsequent layer of an electrically conductive oxide layer is then epitaxially deposited onto the initial layer using a sputtering gas comprising oxygen. The present invention will enable the formation of biaxially textured devices which include HTS wires and interconnects, large area or long length ferromagnetic and/or ferroelectric memory devices, large area or long length, flexible light emitting semiconductors, ferroelectric tapes, and electrodes.

Countermeasures to stress corrosion cracking by stress improvement

International Nuclear Information System (INIS)

Umemoto, Tadahiro

1983-01-01

One of the main factors of the grain boundary stress corrosion cracking occurred in the austenitic stainless steel pipes for reactor cooling system was the tensile residual stress due to welding, and a number of methods have been proposed to reduce the residual stress or to change it to compressive stress. In this paper, on the method of improving residual stress by high frequency heating, which has been applied most frequently, the principle, important parameters and the range of application are explained. Also the other methods of stress improvement are outlined, and the merit and demerit of respective methods are discussed. Austenitic stainless steel and high nickel alloys have good corrosion resistance, high toughness and good weldability, accordingly they have been used for reactor cooling system, but stress corrosion cracking was discovered in both BWRs and PWRs. It occurs when the sensitization of materials, tensile stress and the dissolved oxygen in high temperature water exceed certain levels simultaneously. The importance of the residual stress due to welding, induction heating stress improvement, and other methods such as heat sink welding, last pass heat sink welding, back lay welding and TIG torch heating stress improvement are described. (Kako, I.)

Buffer layers for REBCO films for use in superconducting devices

Science.gov (United States)

Goyal, Amit; Wee, Sung-Hun

2014-06-10

A superconducting article includes a substrate having a biaxially textured surface. A biaxially textured buffer layer, which can be a cap layer, is supported by the substrate. The buffer layer includes a double perovskite of the formula A.sub.2B'B''O.sub.6, where A is rare earth or alkaline earth metal and B' and B'' are different transition metal cations. A biaxially textured superconductor layer is deposited so as to be supported by the buffer layer. A method of making a superconducting article is also disclosed.

Childhood Stress

Science.gov (United States)

... Safe Videos for Educators Search English Español Childhood Stress KidsHealth / For Parents / Childhood Stress What's in this ... and feel stress to some degree. Sources of Stress Stress is a function of the demands placed ...

Bone stress in runners with tibial stress fracture.

Science.gov (United States)

Meardon, Stacey A; Willson, John D; Gries, Samantha R; Kernozek, Thomas W; Derrick, Timothy R

2015-11-01

Combinations of smaller bone geometry and greater applied loads may contribute to tibial stress fracture. We examined tibial bone stress, accounting for geometry and applied loads, in runners with stress fracture. 23 runners with a history of tibial stress fracture & 23 matched controls ran over a force platform while 3-D kinematic and kinetic data were collected. An elliptical model of the distal 1/3 tibia cross section was used to estimate stress at 4 locations (anterior, posterior, medial and lateral). Inner and outer radii for the model were obtained from 2 planar x-ray images. Bone stress differences were assessed using two-factor ANOVA (α=0.05). Key contributors to observed stress differences between groups were examined using stepwise regression. Runners with tibial stress fracture experienced greater anterior tension and posterior compression at the distal tibia. Location, but not group, differences in shear stress were observed. Stepwise regression revealed that anterior-posterior outer diameter of the tibia and the sagittal plane bending moment explained >80% of the variance in anterior and posterior bone stress. Runners with tibial stress fracture displayed greater stress anteriorly and posteriorly at the distal tibia. Elevated tibial stress was associated with smaller bone geometry and greater bending moments about the medial-lateral axis of the tibia. Future research needs to identify key running mechanics associated with the sagittal plane bending moment at the distal tibia as well as to identify ways to improve bone geometry in runners in order to better guide preventative and rehabilitative efforts. Copyright © 2015 Elsevier Ltd. All rights reserved.

Modeling of delayed strains of concrete under biaxial loadings. Application to the reactor containment of nuclear power plants; Modelisation des deformations differees du beton sous sollicitations biaxiales. application aux enceintes de confinement de batiments reacteurs des centrales nucleaires

Energy Technology Data Exchange (ETDEWEB)

Benboudjema, F

2002-12-15

The prediction of delayed strains is of crucial importance for durability and long-term serviceability of concrete structures (bridges, containment vessels of nuclear power plants, etc.). Indeed, creep and shrinkage cause cracking, losses of pre-stress and redistribution of stresses, and also, rarely, the ruin of the structure. The objective of this work is to develop numerical tools, able to predict the long-term behavior of concrete structures. Thus, a new hydro mechanical model is developed, including the description of drying, shrinkage, creep and cracking phenomena for concrete as a non-saturated porous medium. The modeling of drying shrinkage is based on an unified approach of creep and shrinkage. Basic and drying creep models are based on relevant chemo-physical mechanisms, which occur at different scales of the cement paste. The basic creep is explicitly related to the micro-diffusion of the adsorbed water between inter-hydrates and intra-hydrates and the capillary pores, and the sliding of the C-S-H gel at the nano-porosity level. The drying creep is induced by the micro-diffusion of the adsorbed water at different scales of the porosity, under the simultaneous effects of drying and mechanical loadings. Drying shrinkage is, therefore, assumed to result from the elastic and delayed response of the solid skeleton, submitted to both capillary and disjoining pressures. Furthermore, the cracking behavior of concrete is described by an orthotropic elastoplastic damage model. The coupling between all these phenomena is performed by using effective stresses which account for both external applied stresses and pore pressures. This model has been incorporated into a finite element code. The analysis of the long-term behavior is also performed on concrete specimens and prestressed concrete structures submitted to simultaneous drying and mechanical loadings. (author)

Flexible nanomembrane photonic-crystal cavities for tensilely strained-germanium light emission

Energy Technology Data Exchange (ETDEWEB)

Yin, Jian; Wang, Xiaowei; Paiella, Roberto [Department of Electrical and Computer Engineering and Photonics Center, Boston University, 8 Saint Mary' s Street, Boston, Massachusetts 02215 (United States); Cui, Xiaorui; Sookchoo, Pornsatit; Lagally, Max G. [Department of Materials Science and Engineering, University of Wisconsin – Madison, 1509 University Avenue, Madison, Wisconsin 53706 (United States)

2016-06-13

Flexible photonic-crystal cavities in the form of Si-column arrays embedded in polymeric films are developed on Ge nanomembranes using direct membrane assembly. The resulting devices can sustain large biaxial tensile strain under mechanical stress, as a way to enhance the Ge radiative efficiency. Pronounced emission peaks associated with photonic-crystal cavity resonances are observed in photoluminescence measurements. These results show that ultrathin nanomembrane active layers can be effectively coupled to an optical cavity, while still preserving their mechanical flexibility. Thus, they are promising for the development of strain-enabled Ge lasers, and more generally uniquely flexible optoelectronic devices.

Mechanical Characterization of Rigid Polyurethane Foams

Energy Technology Data Exchange (ETDEWEB)

Lu, Wei-Yang [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States). Mechanics of Materials

2014-12-01

Foam materials are used to protect sensitive components from impact loading. In order to predict and simulate the foam performance under various loading conditions, a validated foam model is needed and the mechanical properties of foams need to be characterized. Uniaxial compression and tension tests were conducted for different densities of foams under various temperatures and loading rates. Crush stress, tensile strength, and elastic modulus were obtained. A newly developed confined compression experiment provided data for investigating the foam flow direction. A biaxial tension experiment was also developed to explore the damage surface of a rigid polyurethane foam.

EFAM ETM 97 - the ETM method for assessing the significance of crack-like defects in engineering structures, comprising the versions ETM 97/1 and ETM 97/2

International Nuclear Information System (INIS)

Schwalbe, K.H.; Zerbst, U.; Kim, Y.J.; Brocks, W.; Cornec, A.; Heerens, J.; Amstutz, H.

1998-01-01

EFAM ETM 97 is a document of the GKSS Procedure 'Engineering Flaw Assessment Method (EFAM)'. It describes methods for estimating the crack driving force for cracks in structural components in terms of the crack tip opening displacement, δ 5 , and the J-integral. It consists of several modules covering particular application problems. Appendices to this document provide solutions for the stress intensity factor and the yield load, as well as information on transferability of fracture parameters and on the treatment of bi-axial and mixed mode loadings. A second assessment route is also given in an appendix. (orig.) [de

Work-related stress and posttraumatic stress in emergency medical services.

Science.gov (United States)

Donnelly, Elizabeth

2012-01-01

Recent research efforts in emergency medical services (EMS) has identified variability in the ability of EMS personnel to recognize their level of stress-related impairment. Developing a better understanding of how workplace stress may affect EMS personnel is a key step in the process of increasing awareness of the impact of work-related stress and stress-related impairment. This paper demonstrates that for those in EMS, exposure to several types of workplace stressors is linked to stress reactions. Stress reactions such as posttraumatic stress symptomatology (PTSS) have the potential to negatively influence the health of EMS providers. This research demonstrates that two different types of work-related stress and alcohol use influence the development of PTSS. A probability sample of nationally registered emergency medical technician (EMT)-Basics and EMT-Paramedics (n = 1,633) completed an Internet-based survey. Respondents reported their levels of operational and organizational types of chronic stress, critical incident stress, alcohol use, and PTSS. Ordinary least squares regression illustrated that when demographic factors were controlled, organizational and operational forms of chronic stress, critical incident stress, and alcohol use were all significant predictors of PTSS (p stress and critical incident stress (p stress and alcohol use (p stress reaction. Higher levels of chronic stress, critical incident stress, and alcohol use significantly related to an increased level of PTSS. Further, for those reporting high levels of alcohol use or critical incident stress, interactions with high levels of chronic operational stress were associated with higher rates of PTSS. For those interested in the impact of work-related stress in EMS, these findings indicate that attention must be paid to levels of stress associated with both critical incident exposure as well as the chronic stress providers experience on a day-to-day basis.

Solution of the ratchet-shakedown Bree problem with an extra orthogonal primary load

International Nuclear Information System (INIS)

Bradford, R.A.W.

2015-01-01

The complete shakedown and ratcheting solution is derived analytically for a flat plate subject to unequal biaxial primary membrane stresses and a cyclic secondary bending stress in one in-plane direction (x). The Tresca yield condition and elastic-perfectly plastic behaviour are assumed. It is shown that the results can be expressed in the form of a “universal” ratchet diagram applicable for all magnitudes of orthogonal load. For sufficiently large cyclic bending stresses, tensile ratcheting can occur in the x direction if the x direction primary membrane stress exceeds half that in the orthogonal direction. Conversely, for sufficiently large cyclic bending stresses ratcheting in the x direction will be compressive if the x direction primary membrane stress is less than half that in the orthogonal direction. When the x direction primary membrane stress is exactly half that in the orthogonal direction ratcheting cannot occur however large the cyclic secondary bending stress. - Highlights: • A complete shakedown and ratcheting solution is derived analytically. • The problem is Bree-like but with an extra orthogonal primary load. • The ratchet diagram can be expressed in a form applicable to any orthogonal load. • Tensile ratcheting can occur if the primary load exceeds half the orthogonal load. • Compressive ratcheting can occur for smaller primary loads

Bruxism affects stress responses in stressed rats.

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Sato, Chikatoshi; Sato, Sadao; Takashina, Hirofumi; Ishii, Hidenori; Onozuka, Minoru; Sasaguri, Kenichi

2010-04-01

It has been proposed that suppression of stress-related emotional responses leads to the simultaneous activation of both sympathetic and parasympathetic divisions of the autonomic nervous system (ANS) and that the expression of these emotional states has a protective effect against ulcerogenesis. In the present study, we investigated whether stress-induced bruxism activity (SBA) has a physiological effect of on the stress-induced changes of the stomach, thymus, and spleen as well as blood leukocytes, cortisol, and adrenaline. This study demonstrated that SBA attenuated the stress-induced ulcer genesis as well as degenerative changes of thymus and spleen. SBA also attenuated increases of adrenaline, cortisol, and neutrophils in the blood. In conclusion, expression of aggression through SBA during stress exposure attenuates both stress-induced ANS response, including gastric ulcer formation.

Nuclear stress test

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... Persantine stress test; Thallium stress test; Stress test - nuclear; Adenosine stress test; Regadenoson stress test; CAD - nuclear stress; Coronary artery disease - nuclear stress; Angina - nuclear ...

The shape of change in perceived stress, negative affect, and stress sensitivity during mindfulness based stress reduction

NARCIS (Netherlands)

Snippe, E.; Dziak, J.J.; Lanza, S.T.; Nyklicek, I.; Wichers, M.

2017-01-01

Both daily stress and the tendency to react to stress with heightened levels of negative affect (i.e., stress sensitivity) are important vulnerability factors for adverse mental health outcomes. Mindfulness-based stress reduction (MBSR) may help to reduce perceived daily stress and stress

The Shape of Change in Perceived Stress, Negative Affect, and Stress Sensitivity During Mindfulness-Based Stress Reduction

NARCIS (Netherlands)

Snippe, Evelien; Dziak, John J.; Lanza, Stephanie T.; Nykliek, Ivan; Wichers, Marieke

Both daily stress and the tendency to react to stress with heightened levels of negative affect (i.e., stress sensitivity) are important vulnerability factors for adverse mental health outcomes. Mindfulness-based stress reduction (MBSR) may help to reduce perceived daily stress and stress

Stress and Protists: No life without stress.

Science.gov (United States)

Slaveykova, Vera; Sonntag, Bettina; Gutiérrez, Juan Carlos

2016-08-01

We report a summary of the symposium "Stress and Protists: No life without stress", which was held in September 2015 on the VII European Congress of Protistology in partnership with the International Society of Protistologists (Seville, Spain). We present an overview on general comments and concepts on cellular stress which can be also applied to any protist. Generally, various environmental stressors may induce similar cell responses in very different protists. Two main topics are reported in this manuscript: (i) metallic nanoparticles as environmental pollutants and stressors for aquatic protists, and (ii) ultraviolet radiation - induced stress and photoprotective strategies in ciliates. Model protists such as Chlamydomonas reinhardtii and Tetrahymena thermophila were used to assess stress caused by nanoparticles while stress caused by ultraviolet radiation was tested with free living planktonic ciliates as well as with the symbiont-bearing model ciliate Paramecium bursaria. For future studies, we suggest more intensive analyses on protist stress responses to specific environmental abiotic and/or biotic stressors at molecular and genetic levels up to ecological consequences and food web dynamics. Copyright © 2016 Elsevier GmbH. All rights reserved.

Implication of changing loading conditions on structural health monitoring utilising guided waves

Science.gov (United States)

Mohabuth, Munawwar; Kotousov, Andrei; Ng, Ching-Tai; Rose, L. R. Francis

2018-02-01

Structural health monitoring systems based on guided waves typically utilise a network of embedded or permanently attached sensors, allowing for the continuous detection of damage remote from a sensor location. The presence of damage is often diagnosed by analysing the residual signals from the structure after subtracting damage-free reference data. However, variations in environmental and operational conditions such as temperature, humidity, applied or thermally-induced stresses affect the measured residuals. A previously developed acoustoelastic formulation is here extended and employed as the basis for a simplified analytical model to estimate the effect of applied or thermally-induced stresses on the propagation characteristics of the fundamental Lamb wave modes. It is noted that there are special combinations of frequency, biaxial stress ratio and direction of wave propagation for which there is no change in the phase velocity of the fundamental anti-symmetric mode. The implication of these results in devising effective strategies to mitigate the effect of stress induced variations in guided-wave damage diagnostics is briefly discussed.

Oxidative stress adaptation with acute, chronic, and repeated stress.

Science.gov (United States)

Pickering, Andrew M; Vojtovich, Lesya; Tower, John; A Davies, Kelvin J

2013-02-01

Oxidative stress adaptation, or hormesis, is an important mechanism by which cells and organisms respond to, and cope with, environmental and physiological shifts in the level of oxidative stress. Most studies of oxidative stress adaption have been limited to adaptation induced by acute stress. In contrast, many if not most environmental and physiological stresses are either repeated or chronic. In this study we find that both cultured mammalian cells and the fruit fly Drosophila melanogaster are capable of adapting to chronic or repeated stress by upregulating protective systems, such as their proteasomal proteolytic capacity to remove oxidized proteins. Repeated stress adaptation resulted in significant extension of adaptive responses. Repeated stresses must occur at sufficiently long intervals, however (12-h or more for MEF cells and 7 days or more for flies), for adaptation to be successful, and the levels of both repeated and chronic stress must be lower than is optimal for adaptation to acute stress. Regrettably, regimens of adaptation to both repeated and chronic stress that were successful for short-term survival in Drosophila nevertheless also caused significant reductions in life span for the flies. Thus, although both repeated and chronic stress can be tolerated, they may result in a shorter life. Copyright © 2012 Elsevier Inc. All rights reserved.

The impact of static stress change, dynamic stress change, and the background stress on aftershock focal mechanisms

Science.gov (United States)

Hardebeck, Jeanne L.

2014-01-01

The focal mechanisms of earthquakes in Southern California before and after four M ≥ 6.7 main shocks provide insight into how fault systems respond to stress and changes in stress. The main shock static stress changes have two observed impacts on the seismicity: changing the focal mechanisms in a given location to favor those aligned with the static stress change and changing the spatial distribution of seismicity to favor locations where the static stress change aligns with the background stress. The aftershock focal mechanisms are significantly aligned with the static stress changes for absolute stress changes of ≥ 0.02 MPa, for up to ~20 years following the main shock. The dynamic stress changes have similar, although smaller, effects on the local focal mechanisms and the spatial seismicity distribution. Dynamic stress effects are best observed at long periods (30–60 s) and for metrics based on repeated stress cycling in the same direction. This implies that dynamic triggering operates, at least in part, through cyclic shear stress loading in the direction of fault slip. The background stress also strongly controls both the preshock and aftershock mechanisms. While most aftershock mechanisms are well oriented in the background stress field, 10% of aftershocks are identified as poorly oriented outliers, which may indicate limited heterogeneity in the postmain shock stress field. The fault plane orientations of the outliers are well oriented in the background stress, while their slip directions are not, implying that the background stress restricts the distribution of available fault planes.

Strain-dependent diffusion behavior of H within tungsten

International Nuclear Information System (INIS)

Ding, Wenyi; He, Haiyan; Liu, Changsong; Ding, Rui; Chen, Junling; Pan, Bicai

2014-01-01

The diffusion behaviors of H in tungsten, a promising material serving as the first wall facing the plasma in nuclear reactors, under either biaxial strain or isotropic strain are theoretically studied. We find that under the isotropic strain, an individual H atom may diffuse along all pathways, and under the biaxial strain, it preferably migrates along the direction perpendicular to the loaded strain. Moreover, in the case of either the isotropic or the biaxial strain, the loaded compressive strain weakens the diffusion of H, while the loaded tensile strain enhances the diffusion of H in bulk W.

Strain-dependent diffusion behavior of H within tungsten

Energy Technology Data Exchange (ETDEWEB)

Ding, Wenyi; He, Haiyan [Department of Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China); Liu, Changsong [Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, P.O. Box 1129, Hefei 230031 (China); Ding, Rui; Chen, Junling [Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031 (China); Pan, Bicai, E-mail: bcpan@ustc.edu.cn [Department of Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China); Hefei National Laboratory for Physical Science at Microscale, University of Science and Technology of China, Hefei, Anhui 230026 (China)

2014-06-15

The diffusion behaviors of H in tungsten, a promising material serving as the first wall facing the plasma in nuclear reactors, under either biaxial strain or isotropic strain are theoretically studied. We find that under the isotropic strain, an individual H atom may diffuse along all pathways, and under the biaxial strain, it preferably migrates along the direction perpendicular to the loaded strain. Moreover, in the case of either the isotropic or the biaxial strain, the loaded compressive strain weakens the diffusion of H, while the loaded tensile strain enhances the diffusion of H in bulk W.

Stress field models from Maxwell stress functions: southern California

Science.gov (United States)

Bird, Peter

2017-08-01

The lithospheric stress field is formally divided into three components: a standard pressure which is a function of elevation (only), a topographic stress anomaly (3-D tensor field) and a tectonic stress anomaly (3-D tensor field). The boundary between topographic and tectonic stress anomalies is somewhat arbitrary, and here is based on the modeling tools available. The topographic stress anomaly is computed by numerical convolution of density anomalies with three tensor Green's functions provided by Boussinesq, Cerruti and Mindlin. By assuming either a seismically estimated or isostatic Moho depth, and by using Poisson ratio of either 0.25 or 0.5, I obtain four alternative topographic stress models. The tectonic stress field, which satisfies the homogeneous quasi-static momentum equation, is obtained from particular second derivatives of Maxwell vector potential fields which are weighted sums of basis functions representing constant tectonic stress components, linearly varying tectonic stress components and tectonic stress components that vary harmonically in one, two and three dimensions. Boundary conditions include zero traction due to tectonic stress anomaly at sea level, and zero traction due to the total stress anomaly on model boundaries at depths within the asthenosphere. The total stress anomaly is fit by least squares to both World Stress Map data and to a previous faulted-lithosphere, realistic-rheology dynamic model of the region computed with finite-element program Shells. No conflict is seen between the two target data sets, and the best-fitting model (using an isostatic Moho and Poisson ratio 0.5) gives minimum directional misfits relative to both targets. Constraints of computer memory, execution time and ill-conditioning of the linear system (which requires damping) limit harmonically varying tectonic stress to no more than six cycles along each axis of the model. The primary limitation on close fitting is that the Shells model predicts very sharp

Manage Stress

Science.gov (United States)

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