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INTEGRATED RESEARCH INTO FEATURES OF PHYSICAL FIELDS IN MODEL GEOMEDIUM WITH DISCONTINUITY GENERATED UNDER EXTERNAL STRESSES
Abstract
The authors have carried out uniaxial compression tests of 200 mm side cube specimens made of artificial layered geomaterial with the bedding angles of 0, 30, 45, 60 and 90 deg and with the different strength of the layers to study the process of deformation to failure using the multiparametric equipment designed for synchronous recording of physical fields of stresses, macrostrains, microseismic emission (MSE) and microstrains by speckle method. The integrated analyses of MSE signals, microstrains, stresses and strains has shown that each of the selected methods offers satisfactory characterization of evolution of crack formation. Moreover, there is a clear interconnection between the regular patterns of change in MSE parameters, microstrains and their velocities and the stressпїЅdeformation diagram. In the first loading stage, under stresses not to exceed 0.25пїЅ0.5 of the peak load, a few MSE signals are recorded at a wideband frequency. The field of the microstrains is chaotically non пїЅ uniform, and there is nearly no variation in the microstrain field components. In the second stage of deformation, at the stresses from 0.4пїЅ05 to 0.7пїЅ0.8 of the ultimate strength, the number of MSE signals grows, their amplitudes increase, the frequency spectrum narrows and shifts toward the lower frequencies. The field of the microstrains becomes more nonuniform, zones of maximum microstrains appear, where microstrains exceed average values over the surface of the specimen. In the third stage of loading under stresses from 0.8 of the ultimate strength and up to the peak load, the number of MSE signals grows several times as compared with the previous deformation stage, the amplitude of the signals grows, too, while the frequency spectrum considerably narrows and even more shifts toward the lower frequencies. The maps of the space пїЅ and пїЅ time distribution of MSE signals demonstrate their essentially nonuniform distribution within the volume of the specimen. The localization of the zones of maximum microstrains in a specimen is reflective of the initiation of a main crack; the place where the main crack reaches the specimen surface can be determined under stresses lower than the peak load. When the main crack reaches the surface of a specimen, a strong low пїЅ frequency signal is generated. Under the uniaxial compression of the cubic specimens of geomaterial, the macroscopic fracture modes are in the good agreement with the spatial location of MSE signals and with the fields of the microstrains.
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References7
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