V. N. Semenov

Evolution of stress-strain state in structured rock specimens under uniaxial loading

The comprehensive experimental studies into the change in the stress-strain state of rock specimens subjected to uniaxial loading until failure, using the automated digital speckle photography analysis shows that when the stress reaches 50% of the limit strength of the specimens, low-frequency micro-deformation processes begin in the specimens under slow (quasi-static) stiff loading. The amplitude of the deformation-wave processes depends on the level of the pre-set macro-loading. Wave packets are plotted for averaged microstrains obtained in sandstone and marble specimens under uniaxial compression. Fourier transforms are used to define the amplitude-frequency characteristics of four micro-deformation stages: elastic, nonlinearly elastic, post-peak and residual strength stages. Elastic oscillations with frequency 0.5–4 Hz appear at the pre-failure stage and continue at the post-peak loading stage.

Genesis and evolution of discontinuities in geomaterials: Theory and a laboratory experiment

The authors designed and manufactured a test stand to study origination and evolution of discontinuities in rocks. Based on the laboratory experimental data obtained for artificial geomaterials and the new-developed geomechanical model, the state equation for shear deformation of a discontinuity is synthesized.

Nonlinear deformation–wave processes in various rank coal specimens loaded to failure under varied temperature

Aiming to build up a phenomenological basis for the theory of interaction between geomechanical, thermal and physicochemical processes in methane-bearing coal in Kuzbass, the authors performed a set of laboratory bench tests on uniaxial stiff loading of various rank coal specimens. The pressure versus temperature dependences are obtained for coal specimens with granite gaskets using high-precision scanning computerized thermal imager. It is shown that temperature changed in coal specimens subjected to loading to failure is connected with volatile content and internal energy relaxation of methane in Kuzbass coal. Using jointly thermal imaging and laser measuring equipment ALMEC-tv for high-precision and detail control of deformation–wave processes in loaded coal specimens by speckle-method, it has for the first time been proved that nonlinear pendulum-type movements of structural elements are possible in coal specimens with varied temperature field, which is of fundamental importance for actualization of previously ignored mass and gas exchange processes in high-stress coal beds of different grade composition under mining,

Measuring equipment and test bench to control evolution of acoustic-deformation and heat fields induced in solids under failure by fluids

The authors have developed a procedure and a test bench for studying evolution of various nature physical fields in modeling geomedium fracture by fluids. The test bench performs synchronous recording of macro- and micro-deformation, heat and acoustic emission induced in physical models of geomedium under loading to discontinuity. The experimental procedure has been trialed. The analysis of the synchronized test data allows a conclusion on the existence of time–space relationship between different nature physical fields induced during failure of solids.

Character of strengthening of an initially orthotropic material when subjected to simple and complex loadings. Communication 1

ConclusionsWe have carried out an experimental study of the inelastic properties of solids with simple and complex loadings, producing pure shear strains and the subsequent imposition of strain states of pure shear.1.The data from experiments with biaxial tension on a specimen of the zirconium alloy E-110 demonstrate the presence of initial anisotropy of the elastic deformation and strength properties.2.The test specimens have three orthogonal planes of elastic symmetry of the material, directed respectively along the axis of the specimen, along the tangential direction to the cylinder generatrix, and along the radial direction. These are the principal axes. The elastic constants were determined in the direction of these axes.3.We have pointed out a trajectory of preliminary simple and complex loading that leads to an increase of strength and deformation properties of the material in one of the principal directions of the stress tensor, in comparison with the analogous properties in the case of simple loading. Such a trajectory consists of loading accompanied by partial unloading in one of the directions of preliminary plastic deformation, interruption of the increase of plastic strains in this direction, and an excess of the magnitude of the second principal stress over the first.4.Regardless of the prehistory of simple and complex loading of the initially orthotropic material, accompanied by partial unloading in the direction of the preliminary plastic deformation, a repeated simple loading σz=2σϕ, equivalent to the action of pure shear with the imposition of hydrostatic pressure, leads to a change in the deformation properties, i.e., to isotropic strengthening of the material. The onset of plasticity in such a repeated simple loading is determined by the stress intensity at the end of the first section of the preliminary loading trajectory, and the point at which this onset occurs is independent of the magnitude of the second principal stress and the intensity of stresses at the end of the second section of complex loading of the preliminary loading trajectory. This indicates that the onset and development of plastic strains along specific slip areasT is determined solely by the magnitude of the maximum tangential stress, and is independent of plastic slips along the other areasT12 orT23.

Experimental investigation of plastic pure-shear deformation under simple and complex loadings

ConclusionsThe inelastic properties of solid bodies under simple and complex loadings that result in pure-shear strain and successive superposition of deformed states of pure shear are investigated experimentally. The strain anisotropy that develops in this case is satisfactorily described by the hypothesis of anisotropic hardening, which must be considered in constructing constitutive relationships of the theory of plasticity of rocks.For these types of loads, there are uniqueσi(ɛi) andσ1(ɛ1) cuves that can be used as rating curves for the material in calculations.These effects may be used as a production procedure for controlling the anisotropy of the metal in tubular structural components in mining-machine building and the creation of prescribed (improved) strength properties in these components.

Investigation of Strength of Anisotropic Rocks under Axial Compression and Lateral Pressure

The article describes the theoretical and experimental research into the strength of cylindrical specimens made of layered and anisotropic geomaterials exposed to axial compression and lateral pressure. The tests used INSTRON 8802 versatile servohydraulic fatigue testing system. The experimental results are the relationships between the ultimate strength and bedding angle in specimens of an artificial material, meta-siltstone and shale. The experimental data agree well with the theoretical calculations.