In-plane Stress (in-plane + stress)

Distribution by Scientific Domains


Selected Abstracts


Effects of initial conditions and growth temperature on the properties of nonpolar a -plane AlN grown by LP-HVPE

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S2 2009
Jie-Jun Wu
Abstract AlN was grown on r - and c -plane sapphire substrates by low-pressure hydride vapor phase epitaxy (LP-HVPE). Nitridation and buffer methods were used and compared. Results show that the buffer method is appropriate for the growth of a-plane AlN. In-plane stresses were measured and found to be different in the two in-plane directions parallel and perpendicular to the AlN c -axis. In-plane stress anisotropy is reduced at high temperature leading to a smoother surface, partly owing to a decreased difference in the growth rates between two in-plane directions. However, too high a temperature decreases the crystal quality of a-plane AlN. Thus, there exists an optimal temperature range for the growth of a-plane AlN, in which improved crystal and surface qualities can both be obtained. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Inelastic constitutive properties and shear localization in Tennessee marble

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 2 2001
D. J. Holcomb
Abstract The inelastic response of Tennessee marble is modelled by an elastic plastic constitutive relation that includes pressure dependence of yield, strain-softening and inelastic volume strain (dilatancy). Data from 12 axisymmetric compression tests at confining pressures from 0 to 100 MPa are used to determine the dependence of the yield function and plastic potential, which are different, on the first and second stress invariants and the accumulated inelastic shear strain. Because the data requires that the strain at peak stress depends on the mean stress, the locus of peak stresses is neither a yield surface nor a failure envelope, as is often assumed. Based on the constitutive model and Rudnicki and Rice criterion, localization is not predicted to occur in axisymmetric compression although faulting is observed in the tests. The discrepancy is likely due to the overly stiff response of a smooth yield surface model to abrupt changes in the pattern of straining. The constitutive model determined from the axisymmetric compression data describes well the variation of the in-plane stress observed in a plane strain experiment. The out-of-plane stress is not modelled well, apparently because the inelastic normal strain in this direction is overpredicted. In plane strain, localization is predicted to occur close to peak stress, in good agreement with the experiment. Observation of localization on the rising portion of the stress,strain curve in plane strain does not, however, indicate prepeak localization. Because of the rapid increase of mean stress in plane strain, the stress,strain curve can be rising while the shear stress versus shear strain curve at constant mean stress is falling (negative hardening modulus). Copyright © 2001 John Wiley & Sons, Ltd. [source]


Structural Characterization of Cobalt Thin Films Grown by Metal-Organic CVD,

CHEMICAL VAPOR DEPOSITION, Issue 5 2005
F. Chioncel
Abstract Cobalt thin films were produced by metal-organic CVD from C5H5Co(CO)2, at various temperatures and for various deposition times. The films have been grown onto glass substrates with no buffer. The crystalline structure, morphology, and composition of the films were analyzed by X-ray diffractometry (XRD), field-emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), and Auger electron spectroscopy (AES). Routine XRD patterns were collected in symmetric geometry for phase identification and the sin2, diffraction technique was employed to calculate the average in-plane stress. Structural studies indicate that the films tend to grow in island mode, as predicted by theory, and have a structure between that of face-centered cubic (fcc) and hexagonal close-packed (hcp) cobalt. There is significant in-plane tensile stress at the interface with the substrate, which relaxes to a compressive stress an order of magnitude lower at the surface. The films have a relatively low impurity content, as determined by AES, except near the surface. [source]


Constrained Sintering of a Glass Ceramic Composite: II.

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2009
Symmetric Laminate
The sintering behavior of symmetric laminates has been experimentally measured and modeled. Two cases are distinguished: (i) sintering of a viscous layer between viscous substrates and (ii) sintering of a viscous layer between elastic substrates. A simple model based on a persisting isotropic microstructure allowed computation of developing in-plane stresses. These in conjunction with a viscous Poisson's coefficient were taken to predict out-of-plane stresses and finally densification rate. This approach, however, proved unsuccessful to predict the large observed differences in densification rate between laminates constrained by either green or dense alumina substrates. The discrepancy was found to be due to widely different microstructures developing with different degrees of elastic constraint. Pore area and pore and particle orientation were determined to quantify these microstructural changes. [source]


Polarized Raman scattering studies of nonpolar a -plane GaN films grown on r -plane sapphire substrates by MOCVD

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 15 2006
Haiyong Gao
Abstract Nonpolar (110) a -plane GaN thin films were grown on r -plane (102) sapphire substrates by low-pressure metal organic chemical vapor deposition (MOCVD). The stress characteristics of the a -plane GaN films were investigated by means of polarized Raman scattering spectra in backscattering configurations. The experimental results show that there are strong anisotropic in-plane stresses within the epitaxial a -plane GaN films by calculating the corresponding stress tensors. The temperature dependence of Raman scattering spectra was studied in the range from 100 K to 550 K. The measurements reveal that the Raman phonon frequencies decrease with increasing temperature. The temperature at which nonpolar a -plane GaN films are strain free is discussed. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]