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Internal Stress (internal + stress)

Distribution by Scientific Domains

Polymers and Materials Science	60%
Chemistry	13%

Distribution within Polymers and Materials Science

Ceramics	33%

Selected Abstracts

Abscheidung von Palladium und Palladiumlegierungen mit hohen Schichtdicken für die Mikrosystemtechnik

MATERIALWISSENSCHAFT UND WERKSTOFFTECHNIK, Issue 2 2007
E. Günther
Palladium and palladium alloys; Heavy deposits are used; Microsystems technology; Internal stress; Graph of current density vs. potential Abstract Die Abscheidung von Metallen und Legierungen in Mikrostrukturen erfordert meist eine Schichtdicke größer als 100 ,m, die der Strukturhöhe entspricht. Für die Nutzung von Edelmetallen in Mikrosystemen ist die Abscheidung von spannungsarmen, rissfreien, porenfreien und duktilen Schichten notwendig. Da die kommerziell abgeschiedenen Edelmetallschichten nur bis etwa 10 ,m qualitätsgerecht abgeschieden werden können, sind geeignete Zusätze und Variation der Abscheidungsbedingungen erforderlich, um mikrosystemtaugliche Elektrolyte zu entwickeln. Charakterisierung der Schichteigenschaften, Parameter der Abscheidungstechnologie und Anwendungsbeispiele werden aufgeführt. Erste Ergebnisse werden vorgestellt und diskutiert. Deposition of Thick Palladium and Palladium Alloy Layers for Microsystems Technology Layers of metals and alloys deposited in microstructures usually require to be thicker than the 100 ,m which is the approximate height of the structure. The deposited form of noble metals used in microsystems must be non-stressed, ductile and free of cracks and pores. As the thickness of layers deposited from commercial noble metal electrolytes will rarely exceed 10 ,m without loss of quality, developing an electrolyte system suitable for microsystems involves finding appropriate additives and deposition parameters. Details are given of deposit characterisation, the parameters of the deposition technology and some practical examples. Initial results are presented and discussed. [source]

Nucleus pulposus glycosaminoglycan content is correlated with axial mechanics in rat lumbar motion segments

JOURNAL OF ORTHOPAEDIC RESEARCH, Issue 9 2006
John I. Boxberger
Abstract The unique biochemical composition and structure of the intervertebral disc allow it to support load, permit motion, and dissipate energy. With degeneration, both the biochemical composition and mechanical behavior of the disc are drastically altered, yet quantitative relationships between the biochemical changes and overall motion segment mechanics are lacking. The objective of this study was to determine the contribution of nucleus pulposus glycosaminoglycan content, which decreases with degeneration, to mechanical function of a rat lumbar spine motion segment in axial loading. Motion segments were treated with varying doses of Chondroitinase-ABC (to degrade glycosaminoglycans) and loaded in axial cyclic compression-tension, followed by compressive creep. Nucleus glycosaminoglycan content was significantly correlated (p,<,0.05) with neutral zone mechanical behavior, which occurs in low load transition between tension and compression (stiffness: r,=,0.59; displacement: r,=,,0.59), and with creep behavior (viscous parameter ,1: r,=,0.34; short time constant ,1: r,=,0.46). These results indicate that moderate decreases in nucleus glycosaminoglycan content consistent with early human degeneration affect overall mechanical function of the disc. These decreases may expose the disc to altered internal stress and strain patterns, thus contributing through mechanical or biological mechanisms to the degenerative cascade. © 2006 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res [source]

STRESS RELAXATION BEHAVIOUR OF FROZEN SUCROSE SOLUTIONS

JOURNAL OF TEXTURE STUDIES, Issue 1 2004
X. XU
ABSTRACT The stress relaxation behaviour of two frozen sucrose solutions (7% and 19%) during indentation in the temperature range of -20C to -40C were investigated. The stress relaxation is similar to that of pure polycrystalline ice, which is controlled by steady-state creep. The steady state creep rate exponent, m, of 7% and 19% sucrose solutions lies between 2.3 and 3.6. The steady state creep rate constant, B, of 19% sucrose solution is greater than that of 7% sucrose solution. It is suggested that the steady-state creep rate exponent m depends on contributions from the proportions of favourably oriented grains, unfavourably oriented grains and grain boundaries to creep and that these components depend on the value of internal stress which is related to the hardness of samples at the different testing temperatures. The steady-state creep rate constant B depends on the mobility of dislocations in sucrose solutions which, in turn, depends on the temperature and the concentration of sucrose. [source]

Roles of Ba/Ti Ratios in the Dielectric Properties of BaTiO3 Ceramics

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2001
Jung-Kun Lee
The effect of the Ba/Ti ratio on microstructure, dielectric/ferroelectric properties, and domain width was studied using optical microscopy, ,(T) curves, D,E hysteresis, and transmission electron microscopy. Although Ti-excess samples showed abnormal grain growth and a decrease of room-temperature permittivity due to a liquid phase at grain boundaries, its ferroelectric properties were similar to those of stoichiometric BaTiO3 ceramics. However, in Ba-excess samples, an increase of permittivity and ferroelectric properties different from those of stoichiometry were found. Changes in domain width and ferroelectric transition behavior indicated that the variation of dielectric properties was related to the internal stress. It is proposed that this internal stress originated from differences in the thermal expansion coefficient between the matrix and the second phase. [source]

Time-cure-temperature superposition for the prediction of instantaneous viscoelastic properties during cure

POLYMER ENGINEERING & SCIENCE, Issue 6 2000
Yongsung Eom
The relative sequence of shrinkage and evolution of modulus of a thermoset resin during cure leads to the build-up of internal stresses, especially if the resin is constrained by the presence of other materials in the form of a substrate or reinforcing fibers. To enable prediction of the levels of internal stress generated during processing and to determine appropriate processing windows, the evolution of the modulus of an epoxy-amine system during cure has been characterized and described with a phenomenological model. A combined reaction kinetics model is used to determine the degree of conversion of the epoxy over any complete range of cure. The chemorheological properties of the resin are measured as a function of curing temperature with a torsional parallel plate rheometer. A new phenomenological approach for time-cure-temperature superposition is proposed for predicting the relaxation modulus at any moment during cure and at any cure temperature. The combination of these two models provides a full description of the instantaneous viscoelastic properties during cure. This approach, which can be adapted to any curing resin, provides suitable tools for the analysis of viscoelastic stress build-up following any industrially relevant cure cycle. [source]

The effects of the potential and polarization time on the performance of ionic polymer metal composite actuators: a control of forward and reverse displacements

POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 5 2007
Eiichi Shoji
Abstract This paper focuses on the dependence of various waveforms of the potential on the displacement of Nafion-platinum based IPMC actuators at 40 and 90% relative humidity (RH). In comparison with simpler square waveforms, a waveform that is being composed by inclusion of a rest potential of 0,V has given a longer displacement. This benefit was effective at lower humidity conditions. By a polarization, the actuators show three major displacement processes of maximum forward displacement, steady forward displacement, and maximum reverse displacement. Here, the dependence of the potential and polarization time on these displacements has been carefully examined. An increase in the forward displacement by the potential does not strongly affect a slower reverse relaxation. To give a suitable relaxation period before a polarity switching of the potential seems effective to release the internal stress of the actuator. An elevated drive potential has decreased in the bending speed apparently. Finally, it has been noted that the ,recovery' of the maximum displacement is possible if a suitable waveform is applied to the actuator. This recovery effect is more remarkable at higher dive potential. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Structure of nanocrystalline anatase solved and refined from electron powder data

ACTA CRYSTALLOGRAPHICA SECTION A, Issue 4 2002
T. E. Weirich
Energy-filtered Debye,Scherrer electron powder data have been successfully employed to determine the structure of nanocrystalline anatase (TiO2). The performed structure analysis includes determining the unit cell, space group, solving the structure via direct methods from extracted intensities and refining the structure using the Rietveld technique. The refined structural parameters for space group I41amd are a = 3.872,(2), c = 9.616,(5),Å with titanium at 0.5,0.75,0.375 and oxygen at 0.5,0.75,0.1618,(6). The obtained structure indicates low internal stress as judged from the almost regular geometry of the TiO6 building blocks. Striking resemblance with the anatase structure determined previously by Burdett, Hughbanks, Miller, Richardson & Smith [J. Am. Chem. Soc. (1987). 109, 3639,3646] from neutron diffraction on coarse-grained material gives strong support for the correctness of the structure determined here. The result of the present study shows that the methods originally developed for determining structures from X-ray powder data work equally well with data from electron powder diffraction. This may open the window for structural investigations on the vast number of nanocrystalline materials and thin films whose structures are difficult to determine by X-ray diffraction since they are frequently only available in small quantities. [source]

Growth and Properties of TiCl4 -Derived CVD Titanium Oxide Films at Different CO2/H2 Inputs,

CHEMICAL VAPOR DEPOSITION, Issue 5 2003
D.-H. Kuo
Abstract Crystalline titanium oxide films with a thickness of 0.09,0.55,,m were prepared at temperatures below 500,°C by CVD using a mixture of titanium tetrachloride (TiCl4), carbon dioxide (CO2), and hydrogen (H2) as reactants. Film thickness decreased with increasing substrate temperature and CO2/H2 input. Nanosized microstructure was obtained at high CO2/H2 input due to the growth retardation of reacted HO-TiCl3* by the unreacted TiCl4 and CO2. That film composition, i.e., the O/Ti ratio, increased with temperature and the CO2/H2 input can be explained by growth kinetics. Unlike film thickness, internal film stress increased with increasing substrate temperature. Adhesion was controlled by compressive internal stress due to the weak bonding between film and substrate. Two growth mechanisms are proposed to explain the tensile and compressive stress states in films produced by CVD. The adsorption-controlled reaction has a film in compressive stress that increases with an increase in temperature. On the other hand, thermally activated CVD produces a film in tensile stress that decreases with an increase in substrate temperature. [source]

Fractal response of physiological signals to stress conditions, environmental changes, and neurodegenerative diseases,

COMPLEXITY, Issue 5 2007
Nicola Scafetta
In the past two decades the biomedical community has witnessed several applications of nonlinear system theory to the analysis of biomedical time series and the development of nonlinear dynamic models. The development of this area of medicine can best be described as nonlinear and fractal physiology. These studies have been intended to develop more reliable methodologies for understanding how biological systems respond to peculiar altered conditions induced by internal stress, environment stress, and/or disease. Herein, we summarize the theory and some of our results showing the fractal dependency on different conditions of physiological signals such as inter-breath intervals, heart inter-beat intervals, and human stride intervals. © 2007 Wiley Periodicals, Inc. Complexity 12: 12,17, 2007 [source]

Modelling the hysteresis in the velocity pattern of slow-moving earth flows: the role of excess pore pressure

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 4 2005
T. W. J. van Asch
Abstract This paper describes the velocity pattern of a slow-moving earth flow containing a viscous shear band and a more or less rigid landslide body on top. In the case of small groundwater fluctuations, Bingham's law may describe the velocity of these slow-moving landslides, with velocity as a linear function of excess shear stress. Many authors have stated that in most cases a non-linear version of Bingham's law best describes the moving pattern of these earth flows. However, such an exponential relationship fails to describe the hysteresis loop of the velocity, which was found by some authors. These authors showed that the velocity of the investigated earth flows proved to be higher during the rising limb of the groundwater than during the falling limb. To explain the hysteris loop in the velocity pattern, this paper considers the role of excess pore pressure in the rheological behaviour of earth flows by means of a mechanistic model. It describes changes in lateral internal stresses due to a change in the velocity of the earth flow, which generates excess pore pressure followed by pore pressure dissipation. Model results are compared with a hysteresis in the velocity pattern, which was measured on the Valette landslide complex (French Alps). Copyright © 2005 John Wiley & Sons, Ltd. [source]

A Polycrystalline Approach to the Cyclic Behaviour of f.c.c. Alloys , Intra-Granular Heterogeneity

ADVANCED ENGINEERING MATERIALS, Issue 9 2009
Xavier Feaugas
For several decades, the plastic deformation mechanisms of f.c.c. metals under cyclic loading have received considerable attention. The extensive work on this subject has gradually lead to the identification of the physical processes to be included in a formal scheme of fatigue behavior. Accordingly, we propose a review of the physical mechanisms of plastic deformation in f.c.c. metals and alloys to define the state-of-the-art and motivate future studies. The aim is to demonstrate the importance of a good knowledge of the heterogeneous nature of deformation at the intra-granular scale in defining a physical model of cyclic behavior. A large characterization of the different stages associated with the evolution of heterogeneous dislocation structures during tensile and cyclic loadings is given for an austenitic stainless steel AISI 316L. A unified view of these various structures is proposed in the form of a modified Pedersen's map [,max,=,f(,pcum), where ,max is the maximum plastic strain and ,pcum the cumulative plastic strain] in the case of tensile loading and different kinds of cyclic loading: uni-axial and multi-axial tests under stress or strain amplitude control. The specificities of each domain defined in the map are discussed in terms of long-range internal stresses in order to formalize, in a simple composite scheme, the intra-granular stress,strain field. The importance of taking into account this scheme and the nature of the different dislocations populations in a polycrystalline model is illustrated. [source]

Effect of A-Site Ionic Radius on the Structure and Microwave Dielectric Characteristics of Sr1+xSm1,xAl1,xTixO4 Ceramics

INTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 2010
Min Min Mao
SrSmAlO4 microwave dielectric ceramics were modified by Sr/Ti cosubstitution for Sm/Al. The effects of radius difference of A-site ions on the microwave dielectric characteristics were investigated together with the structure. Sr1+xSm1,xAl1,xTixO4 (x=0, 0.05, 0.10, and 0.15) ceramics were prepared by a solid-state reaction approach. X-ray diffraction studies revealed a single-phase K2NiF4 -type solid solution with corresponding peaks shifting to lower 2, as x increased. Minor inhomogeneous grain morphology for x=0.05 and a trace amount of second phases for x=0.10, 0.15 were detected by backscattered-electron microscopy and energy-dispersive X-ray analysis. With increasing Sr/Ti cosubstitution, the dielectric constant ,r increased from 18.4 to 20.4, and the temperature coefficient of resonant frequency ,f was adjusted from ,1.8 to 7.4 ppm/°C almost linearly. However, the Q×f value decreased from 74,500 GHz at x=0,53,000 GHz at x=0.15. The internal stresses caused by the decreased tolerance factor and the large ionic radii difference between Sr2+ and Sm3+ should be the predominant reasons for such a decrease in the Q×f value. The high-resolution transmission electron microscopic results revealed an increase in the lattice distortion with increasing Sr/Ti cosubstitution, and subsequently supported the above conclusion upon the increased internal stresses. [source]

Mechanically Stable Monoclinic Zirconia,Nickel Composite

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2002
José S. Moya
A dense (>98% theoretical density), residual-stress-free m-ZrO2/40 vol% nickel composite with K IC, 5.4 MPa·m1/2 and ,f, 225 MPa has been obtained using a simple wet processing route and subsequent sintering at 1430°C in a 90% argon/10% hydrogen atmosphere. The mechanism for release of internal stresses by the composite developed during the t , m transformation on cooling is explained in terms of plastic flow in the infinite nickel cluster formed at the percolation threshold. [source]

Nanostructured antiferromagnetic spin glass in doped Ge near the insulator,metal transition

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3 2008
A. G. Zabrodskii
Abstract It is shown that, on the insulator side of the insulator , metal transition, the single spin density exponentially disappears as T , 0. Such spins are bound into pairs to give an antiferromagnetic (AFM) phase. Upon an increase in temperature the AFM phase is destroyed, the single-spin density, and, as a result, ESR absorption signal becomes stronger. The temperature dependencies of the densities of the pairs and single spins are typical of a chaotic distribution of neutral donors. In this case, there is no Neel temperature. In low degree of compensation, the crystal lattice of Ge with the AFM phase is actually a nanostructured system characterized by anisotropic internal stresses that are the strongest along one of the [110] directions. These stresses give rise to anisotropy of the g-factor which is responsible for experimentally observed splitting of the ESR line. The compensating impurities destroy the AFM phase and reduce this splitting. Local stresses are present in this case, too, but now they appear because of the Coulomb interaction of oppositely charged impurities and have no preferred orientation. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]