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J.a. Araújo - One of the best experts on this subject based on the ideXlab platform.
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multiaxial fatigue life estimation based on combined Deviatoric strain amplitudes
International Journal of Fatigue, 2014Co-Authors: E N Mamiya, F C Castro, L Malcher, J.a. AraújoAbstract:Abstract This contribution presents a model for multiaxial fatigue life estimation where a combination of Deviatoric strain amplitudes defines the fatigue parameter. It also takes into account the influences of both hydrostatic stresses and mean Deviatoric stresses. Assessment considers 211 proportional and non-proportional strain-controlled programs reported in the literature, including a number of cases with mean strains/stresses, for three steels and two aluminum alloys. The resulting life estimates correlates well with the experiments, falling in most cases within a factor of two bandwidth.
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multiaxial fatigue life estimation based on a piecewise ruled s n surface
International Journal of Fatigue, 2011Co-Authors: E N Mamiya, F C Castro, R D Algarte, J.a. AraújoAbstract:Abstract A multiaxial model for fatigue life estimation, formulated in terms of a piecewise ruled S–N surface, is proposed. The first ruled surface considers the sum of a Deviatoric stress amplitude and the maximum hydrostatic stress as an exponential function of the number of cycles to failure. For small magnitudes of the hydrostatic stress, another surface is defined by considering only the effect of the Deviatoric stress amplitude upon the expected fatigue life. The Deviatoric stress amplitude was computed by the maximum prismatic hull concept. The model proved successful when compared with other multiaxial criteria for available data.
E N Mamiya - One of the best experts on this subject based on the ideXlab platform.
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multiaxial fatigue life estimation based on combined Deviatoric strain amplitudes
International Journal of Fatigue, 2014Co-Authors: E N Mamiya, F C Castro, L Malcher, J.a. AraújoAbstract:Abstract This contribution presents a model for multiaxial fatigue life estimation where a combination of Deviatoric strain amplitudes defines the fatigue parameter. It also takes into account the influences of both hydrostatic stresses and mean Deviatoric stresses. Assessment considers 211 proportional and non-proportional strain-controlled programs reported in the literature, including a number of cases with mean strains/stresses, for three steels and two aluminum alloys. The resulting life estimates correlates well with the experiments, falling in most cases within a factor of two bandwidth.
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multiaxial fatigue life estimation based on a piecewise ruled s n surface
International Journal of Fatigue, 2011Co-Authors: E N Mamiya, F C Castro, R D Algarte, J.a. AraújoAbstract:Abstract A multiaxial model for fatigue life estimation, formulated in terms of a piecewise ruled S–N surface, is proposed. The first ruled surface considers the sum of a Deviatoric stress amplitude and the maximum hydrostatic stress as an exponential function of the number of cycles to failure. For small magnitudes of the hydrostatic stress, another surface is defined by considering only the effect of the Deviatoric stress amplitude upon the expected fatigue life. The Deviatoric stress amplitude was computed by the maximum prismatic hull concept. The model proved successful when compared with other multiaxial criteria for available data.
F C Castro - One of the best experts on this subject based on the ideXlab platform.
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multiaxial fatigue life estimation based on combined Deviatoric strain amplitudes
International Journal of Fatigue, 2014Co-Authors: E N Mamiya, F C Castro, L Malcher, J.a. AraújoAbstract:Abstract This contribution presents a model for multiaxial fatigue life estimation where a combination of Deviatoric strain amplitudes defines the fatigue parameter. It also takes into account the influences of both hydrostatic stresses and mean Deviatoric stresses. Assessment considers 211 proportional and non-proportional strain-controlled programs reported in the literature, including a number of cases with mean strains/stresses, for three steels and two aluminum alloys. The resulting life estimates correlates well with the experiments, falling in most cases within a factor of two bandwidth.
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multiaxial fatigue life estimation based on a piecewise ruled s n surface
International Journal of Fatigue, 2011Co-Authors: E N Mamiya, F C Castro, R D Algarte, J.a. AraújoAbstract:Abstract A multiaxial model for fatigue life estimation, formulated in terms of a piecewise ruled S–N surface, is proposed. The first ruled surface considers the sum of a Deviatoric stress amplitude and the maximum hydrostatic stress as an exponential function of the number of cycles to failure. For small magnitudes of the hydrostatic stress, another surface is defined by considering only the effect of the Deviatoric stress amplitude upon the expected fatigue life. The Deviatoric stress amplitude was computed by the maximum prismatic hull concept. The model proved successful when compared with other multiaxial criteria for available data.
Shengqi Yang - One of the best experts on this subject based on the ideXlab platform.
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creep and long term permeability of a red sandstone subjected to cyclic loading after thermal treatments
Rock Mechanics and Rock Engineering, 2018Co-Authors: Shengqi YangAbstract:Long-term experiments were performed on red sandstones after different thermal treatments (25, 300, 700 and 1000 °C) under multi-step loading and unloading cycles and a confining pressure of 25 MPa. Furthermore, to quantitatively analyse the temperature influence on the deformation behaviours of the specimens, the concept of the temperature–strain rate was proposed to describe the relationship between strain and temperature, and the experimental results were corrected to identical temperatures (i.e., 20 °C), to overcome the influence of periodic fluctuations in ambient temperature. The results show that the axial mean temperature–strain rate first increased as temperature increased from 25 to 300 °C and then decreased with increasing temperature, whereas the lateral mean temperature–strain rate decreased with increasing temperature. The total strain was divided into the instantaneous elastic strain, the instantaneous plastic strain, the visco-elastic strain and the visco-plastic strain. The total axial strain increased with increasing Deviatoric stress, and the irrecoverable strain increased with increasing loading and unloading history. Furthermore, the total axial strain increased with increasing temperature; specifically, at 1000 °C, it was approximately two times that at 700 °C and three times those at 25 and 300 °C. The instantaneous elastic strain and the instantaneous plastic strain increased approximately linearly with increasing Deviatoric stress, whereas the creep strain varied with Deviatoric stress in complicated ways at different temperatures. However, under identical Deviatoric stress, the instantaneous elastic strain and the instantaneous plastic strain increased slightly as temperature increased from 25 to 700 °C and then increased substantially as temperature reached 1000 °C, whereas the variations in the creep strain, the visco-elastic strain and the visco-plastic strain were dependent on temperature and stress level. Finally, the permeability first decreased slightly as temperature increased from 25 to 300 °C and then increased with increasing temperature.
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evaluation of creep mechanical behavior of deep buried marble under triaxial cyclic loading
Arabian Journal of Geosciences, 2015Co-Authors: Shengqi Yang, Peng Xu, P G Ranjith, Guo Fei Chen, Hongwen JingAbstract:Triaxial compression experiments were carried out on deep-buried marble specimens to investigate their short-term and creep mechanical behavior under cyclic loading. First, based on the results of short-term triaxial experiments, the elastic, plastic, and strength behaviors of marble were analyzed. The results show that for the same confining pressure, the elastic modulus of marble remains basically constant at the lower axial Deviatoric level but decreases slowly after yielding strength; in contrast, the plastic modulus reduces rapidly with the increase of axial Deviatoric stress. However, the elastic and plastic moduli of the tested marble were quite independent of the confining pressure. The relationship between axial Deviatoric stress and plastic deformation of marble can be described well by the interface model. The peak strength of marble under higher stress increases with the confining pressure, which can be better described in accordance with the Mohr–Coulomb criterion. And then, in accordance with the experimental results of marble creep under triaxial cyclic loading, the instant elastic and plastic strains, and the visco-elastic and visco-plastic strains were all separated successfully, which provided a better foundation for constructing a visco-elasto-plastic creep model of rock. The creep strain rate of marble under different Deviatoric stresses is analyzed, which shows that the steady-state creep rate of marble increases nonlinearly with the increase of axial Deviatoric stress. In the end, the creep mechanical behavior of marble under cyclic loading is theoretically analyzed using the creep model. The results show that Burgers creep model can describe the creep behavior of marble under the loading condition satisfactorily but is inadequate to describe the creep behavior of marble under the unloading condition. Therefore, by adopting the fundamental hypothesis of visco-plastic mechanics, a visco-elasto-plastic creep model of rock material is constructed, which can describe the unloading creep behavior of marble better than Burgers creep model. The creep model curve agrees very well with the experimental results, which verifies the proposed visco-elasto-plastic creep model.
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influences of pore pressure on short term and creep mechanical behavior of red sandstone
Engineering Geology, 2014Co-Authors: Shengqi Yang, Hongwen Jing, Long ChengAbstract:Abstract Short-term and creep tests for saturated red sandstone under different pore pressures were carried out by a rock servo-controlled triaxial equipment. Based on the experimental results, the influences of confining pressure and pore pressure on short-term mechanical behavior of red sandstone are firstly analyzed. The results show that the peak strength of dry red sandstone increases with the confining pressure, which can be better expressed by the nonlinear Hoek–Brown criterion than the linear Mohr–Coulomb criterion. But with the increase of pore pressure, the peak strength and elastic modulus of saturated red sandstone all decrease step by step. The short-term failure mode of red sandstone is dependent of the confining pressure, but independent of the pore pressure. And then, the influence of pore pressure and axial Deviatoric stress on the creep mechanical behavior of saturated red sandstone is analyzed quantitatively. Creep contribution to rock deformation increases with the pore pressure, and the specimens show significant time-dependent effect at higher Deviatoric stresses. However, the steady-state creep rate of saturated red sandstone increases nonlinearly but the viscosity coefficient decreases gradually with increasing axial Deviatoric stress and pore pressure. An exponential function is suggested to characterize the relationship between the creep parameters (including creep strain, steady-state creep rate and viscosity coefficient) and the axial Deviatoric stress, and pore pressure. The calculated curves using the proposed function are compared with the experimental results, which is in a good agreement with the experimental data. In the end, the mechanism that the pore pressure and Deviatoric stress affect the creep deformation of saturated red sandstone is discussed in detail. The presented experimental results on short-term and creep mechanical behavior of red sandstone under different pore pressures are very significant for evaluating the long-term stability and safety of deep underground rock mass engineering.
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triaxial mechanical creep behavior of sandstone
Mining Science and Technology (china), 2010Co-Authors: Shengqi Yang, Yuzhou JiangAbstract:Abstract Based on laboratory results of time-dependent mechanical behavior tests, we investigated short-term and mechanical creep behavior of sandstone, observed in conventional triaxial compression experiments at room temperature, using a servo-controlled rheology testing machine. Given our short-term experimental test results, we confirmed Deviatoric creep stress levels of sandstone. Multiple Deviatoric stress levels were applied in steps to each sample. Each Deviatoric stress level before the final failed Deviatoric stress was maintained for 48 h or longer. Time-dependent variations of axial strains of sandstone samples are discussed and evaluated. During the creep tests, complete tertiary creep curves of sandstone were observed under failed Deviatoric stress levels with different confining pressures. Slices of coal in sandstone samples can lead to distinct tertiary creep deformation failure.
Nobumichi Tamura - One of the best experts on this subject based on the ideXlab platform.
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residual lattice strain in quartzites as a potential palaeo piezometer
Geophysical Journal International, 2020Co-Authors: H R Wenk, Brian Chandler, Kai Chen, Nobumichi TamuraAbstract:Author(s): Wenk, HR; Chandler, BC; Chen, K; Li, Y; Tamura, N; Yu, R | Abstract: If a crystal lattice is subjected to a stress, it becomes distorted and no longer represents the ideal crystal symmetry, and if the stress introduces defects such as dislocations, some of this distortion is preserved after the applied stress is removed. In this study, we investigate lattice distortion in quartz at the micron scale with synchrotron X-ray Laue diffraction. From Laue images the local Deviatoric strain tensor is derived and corresponding stresses are calculated based on elastic properties. The method is applied to metasedimentary quartzites from the Bergell Alps that were deformed at conditions of greenschist facies metamorphism. The residual palaeostrain is represented in maps of the Deviatoric strain tensor components and with Deviatoric strain axis pole figures. Data suggest overall shortening perpendicular to the schistosity plane but with considerable asymmetry relative to foliation and lineation, probably attributed to simple shear. Crystallographic pole figures from Laue diffraction agree with neutron diffraction and EBSD measurements and display quartz c-axes girdle distributions with maxima also perpendicular to schistosity. The method shows promise to be used as a palaeo-piezometer to unravel the stress field during tectonic deformation.