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Uniaxial Stress (uniaxial + stress)

Distribution by Scientific Domains

Polymers and Materials Science	60%
Physics and Astronomy	30%

Selected Abstracts

Effect of Uniaxial Stress Upon the Electromechanical Properties of Various Piezoelectric Ceramics and Single Crystals

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2006
D. Viehland
A systematic investigation of the stress-dependent (,) electromechanical properties of various ferroelectric ceramics and single crystals has been performed. Studies have been carried out on "hard" and "soft" piezoelectrics, electrostrictive ceramics, and various orientations of (1,x)Pb(Mg1/3Nb2/3)O3,(x) PbTiO3 PMN,x%PT single crystals. The large signal piezoelectric constant, acoustic power density, and coupling coefficient have been determined by calculation. The results are compared, in order to develop an understanding of the relative merits of the different types of active acoustic materials. [source]

Continuum Mechanical Approach to Sintering of Nanocrystalline Zirconia,

ADVANCED ENGINEERING MATERIALS, Issue 10 2005
R. Zuo
Nanocrystalline 3,mol,% yttria-stabilized zirconia was sinter-forged isothermally under varying external uniaxial stresses. The applied uniaxial stresses were relatively low, compared to the intrinsic sintering stress of the material studied. Uniaxial sintering stresses and uniaxial viscosities were experimentally determined as function of density by means of a continuum mechanical approach which involves measuring the sintering rate of a free-sintered specimen, and a specimen sintered under the application of an external uniaxial stress. The uniaxial viscosity increased strongly with density only in the final stage sintering regime. The magnitude of the uniaxial sintering stress exhibited a decrease with density. [source]

Simulation of the Stress-Assisted Densification Behavior of a Powder Compact: Effect of Constitutive Laws

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2008
Héctor Camacho-Montes
The densification of powders with linear and nonlinear viscous behavior (Scherer and Riedel models) and with power-law-deformation (Khun,McMeeking) behavior was studied under hot pressing and sintering forging conditions. Several numerical experiments, designated cases in this work, were performed to study the effect of (i) the uniaxial stress exerted by the piston and (ii) the rate of the uniaxial stress. The stress state was calculated using the finite-element program ANSYS for each case. Considering the mesoscopic behavior of the powders, densification rates were obtained. The similarities and differences between predictions from the three constitutive models are highlighted. The relationship between the constitutive behavior and the most effective stress state is one of the focuses of this study. For example, we show that under constant stress loading, hot pressing more effectively promotes densification than sinter forging for constitutive behaviors that do not follow the power-law creep. In general, as expected, the increase of uniaxial applied stress and piston velocity favored densification. However, the increase in densification depends strongly on the constitutive law. [source]

Synthesis and Magneto-mechanical Properties of Ce-TZP/La M-Type Hexaferrite Composite

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2002
Takashi Kojima
An in situ composite composed of ceria-stabilized tetragonal zirconia polycrystals (Ce-TZP) and La{Co0.5Fe0.5(Fe0.9Al0.1)11}O19 was synthesized from a powder mixture of Ce-TZP, La(Fe0.9Al0.1)O3, Fe2O3, Al2O3, and CoO. The dense Ce-TZP dispersed with platelike La{Co0.5Fe0.5(Fe0.9Al0.1)11}O19 crystals as a second phase were formed after sintering from 1250° to 1350°C. The saturation magnetization of the insitu composite Ce-TZP/La{Co0.5Fe0.5(Fe0.9Al0.1)11}O19 was proportional to the mass fraction of the hexaferrite second phase in Ce-TZP. The coercivity of the composite with a 20 mass% of second phase decreased from 9.14 to 2.52 kOe (from 728 to 201 kA/m) after the pulverization of the composite. The susceptibility (,) increased by 15%,25% under uniaxial stress on the composite. The change of the susceptibility (,,/,) value increased with decreasing the mass fraction of the second phase in the composite. The ,, was found to increase linearly with applied stress and abruptly change on cracking, which is expected for the application in fracture sensing of the composite. [source]

Tension and stress in the rat and rabbit stomach are location- and direction-dependent

NEUROGASTROENTEROLOGY & MOTILITY, Issue 3 2005
J. Zhao
Abstract, Distension studies in the stomach are very common. It is assumed in pressure,volume (barostat) studies of tone and tension in the gastric fundus that the fundus is a sphere, i.e. that the tension in all directions is identical. However, the complex geometry of the stomach indicates a more complex mechanical behaviour. The aim of this study was to determine uniaxial stress,strain properties of gastric strips obtained from rats (n = 12) and rabbits (n = 10). Furthermore, we aimed to study the gastric zero-stress state since the stomach is one of the remaining parts of the gastrointestinal tract where residual strain studies have not been conducted. Longitudinal strips (in parallel with the lesser curvature) and circumferential strips (perpendicular to the lesser curvature) were cut from the gastric fundus (glandular part) and forestomach (non-glandular part). The residual stress was evaluated as bending angles (unit: degree per unit length and negative when bending outwards). The residual strain was computed from the change in length between the zero-stress state and no-load state. The stress,strain test was performed using a tensile test machine. The thickness and width of each strip were measured from digital images. The strips data were compared with data obtained in the intact stomach in vitro. Most residual stresses and strains were bigger in the glandular part than in the forestomach, and in general the rat stomach had higher values than the rabbit stomach. The glandular strips were stiffer than the forestomach strips and the longitudinal glandular strips were stiffer than the circumferential glandular strips (P < 0.05). The gastric strips were stiffer in rats than in rabbits (P < 0.01). The data obtained in the intact rat stomach confirmed the strips data and indicated that those were obtained in the physiological range. In conclusion, the biomechanical properties of the gastric strips from the rat and rabbit are location-dependent, direction-dependent and species-dependent. The assumption in physiological pressure,volume studies that the stomach is a sphere with uniform tension is not valid. Three-dimensional geometric data obtained using imaging technology and mechanical data are needed for evaluation of the stomach function. [source]

Compaction of Powders due to Vibrations and Shocks

PARTICLE & PARTICLE SYSTEMS CHARACTERIZATION, Issue 4 2004
Roman Linemann
Abstract Bulk density and compactibility of bulk materials play an important role in process engineering. Reliable data are required for dimensioning plants and for supplying load data for static design. Furthermore, the data are useful for the production of sintered materials or catalyst beds and the characterization of bulk materials. While compression by normal stress can be reproduced and mathematically described, the influence of shocks and vibrations remains very poorly understood. All known standard methods for bulk material compression under vibrations and shocks are based on individual equipment. The parameters of shocks or vibrations, however, have not yet been defined. Therefore, an investigation was carried out to examine the influence of uniaxial stress and defined shocks and vibrations on bulk material compression. The shocks and vibrations were controlled by an electrodynamic shaker. The first results for highly disperse Kaolin powders are presented. Using the chosen parameters, the random mode and the uniaxial compression cause the highest increase in density. High compression rates can also be obtained by shocks. With sinusoidal vibrations much lower bulk densities can be reached. [source]

Effects of uniaxial stress on the magnetic properties of thin films and GMR sensors prepared on polyimide substrates

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 8 2008
Berkem Özkaya
Abstract The effects of externally applied uniaxial stress on the magnetic properties of Co thin films and pseudo-spin-valve (PSV) structures on flexible polyimide substrates were investigated. The advantage of the polyimide substrate is its flexibility and high elasticity (,1%), which cannot be achieved using conventional crystalline substrates. The Co layers exhibit a macroscopic easy axis induced by the preparation process. When the stress is applied perpendicular to the induced in-plane easy axis, the magnetic domains in the film rotate towards the applied stress direction, which was confirmed using Kerr microscopy and magneto-optical Kerr effect (MOKE) magnetometer measurements. A Co/Cu/Ni PSV system was prepared on polyimide substrate with dc magnetron sputtering. Applying uniaxial stress leads to opposite rotation of the magnetisation directions in both layers to each other due to different signs of the magnetostriction coefficients of Co and Ni. The magnetisation and giant magnetoresistance (GMR) curves under applied stress were recorded using in situ MOKE and current in-plane four-point probe techniques, respectively. When the stress is applied perpendicular to the external magnetic field (Hext), the operating range of the GMR sensor increases, whereas the sensitivity decreases. Anisotropy energies and saturation magnetostriction values of the Co and Ni layer were determined by fitting the GMR and magnetisation curves using a micromagnetic model. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Uniaxial stress study of the Cu,H complex in ZnO

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 12 2006
E. V. Lavrov
The cover picture of the current issue refers to the article by Lavrov and Weber which was selected as Editor's Choice [1]. The picture shows a microscopic model of the Cu,H complex investigated in the paper. The complex consists of a substitutional Cu atom at the Zn site with an H atom located between nearby O and Cu in the basal plane of the ZnO lattice. The atoms are shown in different colors: yellow for copper, red for hydrogen, cyan for oxygen, and grey for zinc. Hydrogen forms a strong bond with the O atom which gives rise to a local vibrational mode at 3192 cm,1 investigated in the paper under uniaxial stress. The c -axis is parallel to the Cu,O bond pointing to the top of the figure. The authors work at the Institute of Applied Physics/Semiconductor Physics, TU Dresden, Germany. [source]