Results of uniaxial compression tests of rock samples in electromagnetic fields are presented. The experiments were performed in the Laboratory of Basic Physics of Strength, Institute of Continuous Media Mechanics, Ural Branch of RAS (ICMM). Deformation of samples was studied, and acoustic emission (AE) signals were recorded. During the tests, loads varied by stages. Specimens of granite from the Kainda deposit in Kyrgyzstan (similar to samples tested at the Research Station of RAS, hereafter RS RAS) were subject to electric pulses at specified levels of compression load. The electric pulses supply was galvanic; two graphite electrodes were fixed at opposite sides of each specimen. The multichannel Amsy-5 Vallen System was used to record AE signals in the six-channel mode, which provided for determination of spatial locations of AE sources. Strain of the specimens was studied with application of original methods of strain computation based on analyses of optical images of deformed specimen surfaces in LaVISION Strain Master System. Acoustic emission experiment data were interpreted on the basis of analyses of the AE activity in time, i.e. the number of AE events per second, and analyses of signals' energy and AE sources' locations, i.e. defects.The experiment was conducted at ICMM with the use of the set of equipment with advanced diagnostic capabilities (as compared to earlier experiments described in [Zakupin et al., 2006a[Zakupin et al., , 2006b Bogomolov et al., 2004]). It can provide new information on properties of acoustic emission and deformation responses of loaded rock specimens to external electric pulses.The research task also included verification of reproducibility of the effect (AE activity) when fracturing rates responded to electrical pulses, which was revealed earlier in studies conducted at RS RAS. In terms of the principle of randomization, such verification is methodologically significant as new effects, i.e. physical laws, can be considered fully indubitable if they prove stable when some parameters of the experiment are changed. Parameters may be arbitrarily modified within a small range, and randomization is thus another common statistical significance criterion for sample sets obtained at the same conditions. At ICMM, the experiments were conducted in compliance with the principle of randomization [Bogomolov et al., 2011]. In this respect, the material of specimens, loading conditions and characteristics of the electrical pulses source were similar to those in the experiments at RS RAS.As evidenced by the experiments, during electromagnetic field stimulation, the AE activity is manyfold higher than the background activity before the impact. This supports the research results reviewed in [Bogomolov et al., 2011] concerning the AE activity increment of 20 % due to electric pulses in the field twice less strong than that in our experiments at ICMM.The AE energy distribution analysis shows that cumulative distributions of the number of AE signals vs energy (i.e. the number of AE si...
In this article we consider the viscoelastic deformation of a thick-walled tube, with headers rigidly attached to the ends, under the simultaneous action of internal pressure and longitudinal tension. This type of problem arises in considering the stress-deformation state of the rock near a circular working (e.g., a tunnel) where the external forces can be reduced to axial tension along the working and internal and external pressure. In [1] I attacked this problem by starting with the theory of ideal plasticity ['2]; but in this paper I shall make allowance for strain hardening of the material during plastic deformation.I shall use the model of a viscoelastic body [2] in which the condition of ideal plasticity is replaced by a condition allowing for strain hardening of the material If we know the directions of the principal axes and ol, o8, o 3 (o 1 > o 8 > o3) are the principal stresses and 8 t, e 8, s 3 the principal deformations, then as the condition of plasticity we can take the Trask-Saint-Venant condition, Ol-O 3 = 2rs, where r s is the yield point under tension or compression, and distinguish between states of complete and incomplete plasticity. Plastic deformation is a pure shear in the planes of principal axes 1 and 3.The magnitude of this shear is ?'max = sl'e3; the greatest tangential stress is rma x = (o,-o3)/2. Plastic deformation arises as soon as rma x reaches some limiting value rs; under elastic deformation, rmax = /~ ?'max; rma x = r s = const for plastic deformation and any values of ?'max.Real materials do not obey the law of ideal plasticity; as the plastic deformation increases, the plastic resistance of the material rises. As the law of strain hardening we take a relation between the tangential stress and the shear in the form [3] rma x = f(Ymax). It is considered that this law satisfactorily represents the behavior of viscoelastic bodies under loads such that the principal axes of the stress and deformation tensors coincide and do not vary in spatial orientation.The form of the strain-hardening law follows naturally from the Trask-Saint-Venant theory of flow for an ideal plastic body, provided that we take account of strain hardening. When we do so, the condition of plasticity becomes where )'e is the limiting elastic shear (the shear at the onset of plastic flow), /~p is the plastic shear modulus, and we shall assume that ~p = const during plastic deformation.In the direction of the middle principal stress o 8 no plastic deformations will occur; o 8 is related by the elastic law to the deformation [2].Let us take the internal radius of the tube as unity, and its external radius as R, and let us take the generators of the tube as the direction of the z-axis. The tube will expand under the action of the internal pressure P; at its ends we apply equal and opposite forces of magnitude F. We shall assume that the tube is long so that the distributions of stresses and deformations in normal cross sections sufficiently far from the ends can be assumed identical. From the condition of constancy...
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