Showing papers on "Hydrostatic stress published in 1988"
TL;DR: In this article, the presence of shear-wave velocity anisotropy in sedimentary rocks was confirmed by transmitting a polarized shear wave in a rock sample and receiving a signal on an orthogonally polarized receiver.
Abstract: A systematic laboratory study of shear-wave velocity anisotropy in sedimentary rocks has been carried out as a function of both hydrostatic and uniaxial stress. The presence of shear-wave velocity anisotropy in sedimentary rocks was confirmed by transmitting a polarized shear wave in a rock sample and receiving a signal on an orthogonally polarized receiver. The magnitude of the observed velocity anisotropy is dependent upon the magnitude and nature of the applied stress and the lithology of the rock sample. Shales exhibit significant velocity anisotropy independent of both uniaxial and hydrostatic stress, which suggests the presence of preferentially aligned minerals. Sandstones also exhibit significant velocity anisotropy, but the anisotropy is strongly dependent upon the stress. Hydrostatic stress was found to diminish the velocity anisotropy and uniaxial stress was found to enhance it. This implies the presence of preferentially oriented cracks. Limestones exhibit weak velocity anisotropy. These laboratory observations may be helpful in in situ identification of lithology.
51 citations
TL;DR: In this article, the slip-line field solutions for three-point bend specimens are reviewed for both deep and shallow notches and the fracture analysis of low strength metal specimens can be used.
Abstract: The slip-line field solutions for three-point bend specimens are reviewed for both deep and shallow notches. Plastic constraint factors, hydrostatic stress at the notch root and rotation constant to enable the crack upp opening displacement to be determined are given for a wide range of notch geometries. These values can be used in the fracture analysis of low strength metal specimens.
38 citations
TL;DR: In this paper, the authors presented a method for obtaining the individual stress components from this bulk stress data by taking into account the boundary conditions and the expected form of the stress distribution, and the particular case of a strip loaded across part of its boundary is treated in detail.
38 citations
TL;DR: In this article, a yield criterion and basic flow equations for finite elastoplastic deformation of porous materials are derived using a specific micromechanical model of moninteracting spherical pores, with the matrix material being of the von Mises types.
21 citations
TL;DR: In this article, it is shown that the magnitude of the tensile stresses is about equal to the sintering pressure and that densification under a superimposed pressure should lead to full density and eliminate processing flaws.
Abstract: Sintering ceramic/ceramic composites is difficult if the constituents have widely different sintering rates. The differential sets up internal, tensile hydrostatic stress. This stress retards the shrinkage of the composite. In addition, the tensile components of internal stresses can potentially generate flaws. Analysis has shown that the magnitude of the tensile stresses is about equal to the sintering pressure. Therefore, densification under a superimposed pressure, about two to five times the sintering pressure, should lead to full density and eliminate processing flaws. Since the sintering pressure has been measured to be {approx} 1 MPa in several studies, it is likely that low-pressure, hot isostatic pressing can be used to produce dense and reliable ceramic/ceramic composites. Experimental results on a model system, which support the above hypothesis, are presented.
20 citations
TL;DR: In this article, a unified theory is proposed that captures not only such time-dependent phenomena as creep, stress relaxation and rate sensitivity but also demonstrates a sensitivity to hydrostatic stress, which assures the inelastic boundary value problem is well posed with unique solutions.
9 citations
TL;DR: In this paper, a series of tests were designed to allow the independent variation of segregating impurities and locally applied stress levels to determine the effects of applied stress on impurity enrichment and fracture of grain boundaries in as-quenched material.
Abstract: An investigation of brittle intergranular crack nucleation at high temperatures in 2.25Cr-lMo steel is presented. A series of tests was designed to allow the independent variation of segregating impurities (e.g., sulfur and phosphorus) and locally applied stress levels to determine the effects of applied stress on impurity enrichment and fracture of grain boundaries in as-quenched material. The study utilized blunt notched specimens with suitable finite element stress analyses, together with high resolution Auger electron surface analysis techniques. It is shown that the imposition of a tensile hydrostatic stress enhances the segregation of elemental sulfur to grain boundariesprior to the nucleation of high temperature brittle intergranular cracks. The location of enriched grain boundaries relative to the peak stress regions in notched specimens is discussed, and possible mechanisms for the observed sulfur enrichment presented.
7 citations
TL;DR: In this article, a transversely isotropic infinite solid containing an annular crack subjected to heat absorption and heat exchange on the crack surface is analyzed by means of the Transversely Isotropic Potential Functions (TIF).
Abstract: The present paper is concerned with transient thermal stress in a transversely isotropic infinite solid containing an annular crack subjected to heat absorption and heat exchange on the crack surface. Since it is very difficult to obtain an analytical solution for the temperature field, the finite-difference method with respect to a time variable is introduced. Thermal stress is analyzed by means of the transversely isotropic potential functions method. Numerical calculations of the stress intensity factors in transverse isotropy were carried out for a transversely isotropic graphite. Furthermore, the effects of anisotropies of the material constants on the stress intensity factors are investigated.
5 citations
3 citations
01 Jan 1988
TL;DR: In this article, a stress-based finite element methodology that uses the endochronic theory to model elasto-plastic structural behavior is presented, implemented through a "tangent" stiffness formulation using a discretization of four-fields consisting of: 1) stress, 2) displacement, 3) magnitude of plastic strain, and 4) hydrostatic stress.
Abstract: A stress-based finite element methodology that uses the endochronic theory to model elasto-plastic structural behavior is presented. xhe methodology is implemented through a “tangent” stiffness formulation using a discretization of four-fields consisting of: 1) stress, 2) displacement, 3) magnitude of plastic strain, and 4) hydrostatic stress. The four-field approach allows elastically incompressible materials and materials that become incompressible due to plastic flow to be modeled. The stress-based element has been demonstrated to give more accurate solutions for displacements and stresses than conventional displacement models [1]. The more accurate stress solution obtained with stress-based formulations allow fewer elements to be used. In addition, the more accurate stress solution combined with a reduced number of elements usually leads to faster convergence rates. The magnitude of plastic strain is included as an unknown variable to treat the case of perfect or near perfect plasticity. The hydrostatic stress is retained as a global field variable to ensure that the incompressibi1ity constraint associated with fully plastic flows or with elastically incompressible materials does not “lock” the element.