Showing papers on "Hydrostatic stress published in 1977"

An Explanation on Fatigue Limit under Combined Stress

Abstract: Fatigue crack initiates in the slip band and exists also in it near fatigue limit; many slip bands are apt to appear in the direction of the maximum shearing stress; crack propagates by the normal tensile stress; the maximum shearing stress on a plane at fatigue limit is reduced by the effect of the normal stress on the same plane. From these results of the experiment, a new criterion is proposed, which coincides with the Gough's empirical formula for the brittle materials under combined stress. As the plane of the maximum shearing stress is varied by the various combination of torsion and bending, the isotropic material should be used in the combined stress experiment. In this paper, the results of experiments on three isotropic and one anisotropic materials are discussed and compared with the criteria proposed up to the present.

Photoelasticity for stress analysis under high hydrostatic pressure

Abstract: Experimental research relative to pressure effects on the mechanical behavior of materials is frequently handicapped by the difficulties associated with making load and deformation measurements in a hostile environment. The application of photoelasticity in high-pressure experiments provides a means for studying the effect of hydrostatic stress on varying stress fields. The purpose of this paper is to examine the feasibility of using the photoelastic method of stress analysis in a high-pressure environment. The unusual feature of this application is the finite elastic deformations suffered by the photoelastic model under high pressure. As a result, the mechanical and stress-optical properties of the model materials are functions of pressure. Another important feature in this study is the selection of a suitable model material. Since the model must come into contact with the liquid pressure media, chemical and absorption resistance are essential considerations. Although it was found that photoelastic investigations can be carried out at high pressure, limitations are imposed by the presence of the optical vessel and pressurized fluid.

Liquefaction potential of dams and foundations; report 3, development of an elastic-plastic constitutive relationship for saturated sand

Abstract: This report describes the initial attempt at developing a three-dimensional constitutive relationship for saturated sand. An isotropic constitutive relationship has been constructed, within the framework of the incremental theory of plasticity, that qualitatively simulates some of the features of the stress-strain-pore pressure response of saturated sand. It accounts for the hysteretic behavior of pressure- volumetric strain response of sand, the effect of superimposed hydrostatic stress on shearing response, and the shear-induced volume change. It does not, however, treat strain-softening behavior and does not predict progressive increase of pore pressure under low-amplitude (subyield) cyclic loading conditions. The behavior of the constitutive relationship under conventional undrained triaxial test condition is examined and correlated with experimental data for saturated Reid Bedford Model sand. A recommendation is made that the present constitutive relationship be extended to quantitatively simulate the basic features of the stress- strain-pore pressure response of saturated sand, including the strain- softening behavior and the progressive increase of pore pressure observed under cyclic loading conditions. /Author/

Primitive stress in the underground mines at Kitwe-Nkana area Zambia, Africa

Abstract: At the Kitwe-Nkana copper-bearing structure there are two underground mines: Mindola Mine and Nkana Mine. The original design for underground mining was on the traditional assumption that the principal load was to the weight of roofing sediments, and that horizontal stresses are equal to one-third of the vertical stresses. But during mining excavation into deeper levels, it was realized that the lateral stress is greater than the vertical (active tectonic lateral stress field), also that stressed and unstressed zones (passive tectonic stress), depend on structure geometry, that in the deeper part an almost hydrostatic stress (frozen stress field) exists and finally a zone with high stress concentration (pressure zone). It appears that after a certain depth vertical stresses and lateral stresses vary considerably in orientation and magnitude. The direction of the major principal stress is perpendicular to the bedding plane, and minor principal stress along the bedding plane. In this paper the quality of the compound of virgin stress in the ore formation is assumed on the basis of the relationship between geometry and physics of geological structures and primitive stress, as well as on the basis of underground stress measurement data.