[Objective]The work is devoted to the study of irreversible deformation of artificial samples subjected to a set of standard experiments,with an aim to study their mechanical properties.The principal idea of the study...[Objective]The work is devoted to the study of irreversible deformation of artificial samples subjected to a set of standard experiments,with an aim to study their mechanical properties.The principal idea of the study is related to the preparation of an artificial material with an established constitutive behavior model.The existence of such a well-described material provides future opportunities to conduct controllable experiments on various mechanical processes in rock-like material for further development and validation of theoretical models used in rock mechanics.[Methods]A set of artificial samples was prepared for careful assessment through a number of loading tests.Experimental work was carried out to determine the rheological properties under conditions of triaxial compression tests and uniaxial tension.Triaxial loading tests are completed for 9 samples with varying radial stress levels(0-5 MPa).The samples are loaded up to the yield point with control of radial and volumetric strain.The experimental results,which contain the obtained interrelationships between axial and radial stresses and strains,are analyzed using the Drucker-Prager yield surface.Material hardening is taken into account through the non-associated plastic flow law with the cap model.Numerical modeling of sample loading is performed through the finite difference method.Mathematical model parameters are adjusted to minimize the discrepancy between numerical modeling results and experimental data.The design of a series of experimental studies necessary to determine all the parameters of the model has been studied.[Results]It is shown that the formulated mathematical model allows to reliably reproduce the inelastic behavior of the studied material,and it can be used to solve a set of applied problems in continuum mechanics,the problem of numerical simulation of hydraulic fracture growth in an elastoplastic medium in particular.It was found that for the entire range of applied lateral loads(0-5 MPa),the elastic limit varied from 2 to 4 MPa,after which the material began to behave plastically.It was also determined that at lateral loads≥3 MPa,compaction began to appear in the material beyond the yield point.Judging by the dependence of volumetric strains under a lateral load equal to 1.4 MPa,compaction should begin to appear even at lateral loads lower than 3 MPa.[Conclusion]Taking the plastic behavior of the material into account is necessary when moving on to modeling the hydraulic fracturing process in such a material,and the resultant plasticity parameters for the model material can be used for numerical modeling of elastoplastic deformation of the rock under consideration,including processes such as hydraulic fracture growth in a poroelastoplastic medium.[Significance]The suggested procedure to interpret results of experimental studies can be used for further numerical modeling of mechanical processes in rock masses with inelastic strain accumulation.This opportunity can increase the reliability of geomechanical models used for the optimization of hydrocarbon fields development.展开更多
The fracture initiation behavior for hydraulic fracturing treatments highlighted the necessity of proposing fracture criteria that precisely predict the fracture initiation type and location during the hydraulic fract...The fracture initiation behavior for hydraulic fracturing treatments highlighted the necessity of proposing fracture criteria that precisely predict the fracture initiation type and location during the hydraulic fracturing process.In the present study,a Mohr-Coulomb criterion with a tensile cut-off is incorporated into the finite element code to determine the fracture initiation type and location during the hydraulic fracturing process.This fracture criterion considers the effect of fracture inclination angle,the internal friction angle and the loading conditions on the distribution of stress field around the fracture tip.The results indicate that the internal friction angle resists the shear fracture initiation.Moreover,as the internal friction angle increases,greater external loads are required to maintain the hydraulic fracture extension.Due to the increased pressure of the injected water,the tensile fracture ultimately determines the fracture initiation type.However,the shear fracture preferentially occurs as the stress anisotropy coefficient increases.Both the maximum tensile stress and equivalent maximum shear stress decrease as the stress anisotropy coefficient increases,which indicates that the greater the stress anisotropy coefficient,the higher the external loading required to propagate a new fracture.The numerical results obtained in this paper provide theoretical supports for establishing basis on investigating of the hydraulic fracturing characteristics under different conditions.展开更多
In order to obtain the earth pressure coefficient at rest (K0) at higher consolidation pressures during secondary compression, a series of K0 tests for saturated reconstituted clay were conducted. The results indicate...In order to obtain the earth pressure coefficient at rest (K0) at higher consolidation pressures during secondary compression, a series of K0 tests for saturated reconstituted clay were conducted. The results indicate that the measured K0 in secondary compression can be described by equations related to internal friction angle, secondary compression coefficient, compression index, recompression index, and sediment time. Effects of consolidation pressures and sediment time on K0 during secondary compression can be attributed to cementation (part of cohesion) increase and internal friction angle decrease. Cementation increase leads to nonlinear variation for K0 and internal friction angle decrease results in increase of K0. K0 computed by equations associated with internal friction angle is overestimated at apparent lower consolidation pressures with different sediment time, which agrees with the measured values well at apparent higher consolidation pressures.展开更多
The debris from exploded buildings can ricochet after colliding with the ground,thus increasing the debris travel distance and danger from any associated impacts or collisions.To reduce this danger,the travel distance...The debris from exploded buildings can ricochet after colliding with the ground,thus increasing the debris travel distance and danger from any associated impacts or collisions.To reduce this danger,the travel distance of ricocheted debris must be accurately predicted.This study analyzed the change in the travel distance of ricocheted concrete debris relative to changes in the properties of a sand medium.Direct shear tests were conducted to measure the change in internal friction angle as a function of temperature and water content of the sand.Finite element analysis(FEA)was then applied to these variables to predict the speed and angle of the debris after ricochet.The FEA results were compared with results of low-speed ricochet experiments,which employed variable temperature and water content.The travel distance of the debris was calculated using MATLAB,via trajectory equations considering the drag coefficient.As the internal friction angle decreased,the shear stress decreased,leading to deeper penetration of the debris into the sand.As the loss of kinetic energy increased,the velocity and travel distance of the ricocheted debris decreased.Changes in the ricochet velocity and travel distance of the debris,according to changes in the internal friction angle,indicated that the debris was affected by the environment.展开更多
To explore the penetration resistance of calcareous sand media,penetration tests have been conducted in the velocity range of 200-1000 m/s using conical-nosed projectiles with a diameter of 14.5 mm.Further,a pseudo fl...To explore the penetration resistance of calcareous sand media,penetration tests have been conducted in the velocity range of 200-1000 m/s using conical-nosed projectiles with a diameter of 14.5 mm.Further,a pseudo fluid penetration model applicable to the penetration of rigid projectiles in sand media is established according to the approximate flow of compacted sand in the adjacent zone of penetration.The correlation between the impedance function of projectile-target interaction and the internal friction features of pseudo fluid is clarified,and the effects of sand density,cone angle of nose-shaped projectile,and dynamic hardness on the penetration depth are investigated.The results verify the feasibility,wide applicability,and much lower error(with respect to the experimental data)of the proposed model as compared to the Slepyan hydrodynamic model.展开更多
文摘[Objective]The work is devoted to the study of irreversible deformation of artificial samples subjected to a set of standard experiments,with an aim to study their mechanical properties.The principal idea of the study is related to the preparation of an artificial material with an established constitutive behavior model.The existence of such a well-described material provides future opportunities to conduct controllable experiments on various mechanical processes in rock-like material for further development and validation of theoretical models used in rock mechanics.[Methods]A set of artificial samples was prepared for careful assessment through a number of loading tests.Experimental work was carried out to determine the rheological properties under conditions of triaxial compression tests and uniaxial tension.Triaxial loading tests are completed for 9 samples with varying radial stress levels(0-5 MPa).The samples are loaded up to the yield point with control of radial and volumetric strain.The experimental results,which contain the obtained interrelationships between axial and radial stresses and strains,are analyzed using the Drucker-Prager yield surface.Material hardening is taken into account through the non-associated plastic flow law with the cap model.Numerical modeling of sample loading is performed through the finite difference method.Mathematical model parameters are adjusted to minimize the discrepancy between numerical modeling results and experimental data.The design of a series of experimental studies necessary to determine all the parameters of the model has been studied.[Results]It is shown that the formulated mathematical model allows to reliably reproduce the inelastic behavior of the studied material,and it can be used to solve a set of applied problems in continuum mechanics,the problem of numerical simulation of hydraulic fracture growth in an elastoplastic medium in particular.It was found that for the entire range of applied lateral loads(0-5 MPa),the elastic limit varied from 2 to 4 MPa,after which the material began to behave plastically.It was also determined that at lateral loads≥3 MPa,compaction began to appear in the material beyond the yield point.Judging by the dependence of volumetric strains under a lateral load equal to 1.4 MPa,compaction should begin to appear even at lateral loads lower than 3 MPa.[Conclusion]Taking the plastic behavior of the material into account is necessary when moving on to modeling the hydraulic fracturing process in such a material,and the resultant plasticity parameters for the model material can be used for numerical modeling of elastoplastic deformation of the rock under consideration,including processes such as hydraulic fracture growth in a poroelastoplastic medium.[Significance]The suggested procedure to interpret results of experimental studies can be used for further numerical modeling of mechanical processes in rock masses with inelastic strain accumulation.This opportunity can increase the reliability of geomechanical models used for the optimization of hydrocarbon fields development.
基金Project(2017YFC1503102)supported by the National Key Research and Development ProgramProjects(51874065,U1903112)supported by the National Natural Science Foundation of China。
文摘The fracture initiation behavior for hydraulic fracturing treatments highlighted the necessity of proposing fracture criteria that precisely predict the fracture initiation type and location during the hydraulic fracturing process.In the present study,a Mohr-Coulomb criterion with a tensile cut-off is incorporated into the finite element code to determine the fracture initiation type and location during the hydraulic fracturing process.This fracture criterion considers the effect of fracture inclination angle,the internal friction angle and the loading conditions on the distribution of stress field around the fracture tip.The results indicate that the internal friction angle resists the shear fracture initiation.Moreover,as the internal friction angle increases,greater external loads are required to maintain the hydraulic fracture extension.Due to the increased pressure of the injected water,the tensile fracture ultimately determines the fracture initiation type.However,the shear fracture preferentially occurs as the stress anisotropy coefficient increases.Both the maximum tensile stress and equivalent maximum shear stress decrease as the stress anisotropy coefficient increases,which indicates that the greater the stress anisotropy coefficient,the higher the external loading required to propagate a new fracture.The numerical results obtained in this paper provide theoretical supports for establishing basis on investigating of the hydraulic fracturing characteristics under different conditions.
基金Projects(50534040, 50974117) supported by the National Natural Science Foundation of ChinaProject(20110491489) supported by China Postdoctoral Science FoundationProject(2011QNA03) supported by Fundamental Research Funds for Central Universities, China
文摘In order to obtain the earth pressure coefficient at rest (K0) at higher consolidation pressures during secondary compression, a series of K0 tests for saturated reconstituted clay were conducted. The results indicate that the measured K0 in secondary compression can be described by equations related to internal friction angle, secondary compression coefficient, compression index, recompression index, and sediment time. Effects of consolidation pressures and sediment time on K0 during secondary compression can be attributed to cementation (part of cohesion) increase and internal friction angle decrease. Cementation increase leads to nonlinear variation for K0 and internal friction angle decrease results in increase of K0. K0 computed by equations associated with internal friction angle is overestimated at apparent lower consolidation pressures with different sediment time, which agrees with the measured values well at apparent higher consolidation pressures.
基金This study was financially supported by the Foundation Research Program[grant number UD170027GD]of the Agency for Defense Development and the Defense Acquisition Program Administration of the Republic of Korea.
文摘The debris from exploded buildings can ricochet after colliding with the ground,thus increasing the debris travel distance and danger from any associated impacts or collisions.To reduce this danger,the travel distance of ricocheted debris must be accurately predicted.This study analyzed the change in the travel distance of ricocheted concrete debris relative to changes in the properties of a sand medium.Direct shear tests were conducted to measure the change in internal friction angle as a function of temperature and water content of the sand.Finite element analysis(FEA)was then applied to these variables to predict the speed and angle of the debris after ricochet.The FEA results were compared with results of low-speed ricochet experiments,which employed variable temperature and water content.The travel distance of the debris was calculated using MATLAB,via trajectory equations considering the drag coefficient.As the internal friction angle decreased,the shear stress decreased,leading to deeper penetration of the debris into the sand.As the loss of kinetic energy increased,the velocity and travel distance of the ricocheted debris decreased.Changes in the ricochet velocity and travel distance of the debris,according to changes in the internal friction angle,indicated that the debris was affected by the environment.
基金funded by the National Natural Science Foundation of China(Grant No.12072371)Jiangsu Natural Science Foundation(Grant No.BK20221528)。
文摘To explore the penetration resistance of calcareous sand media,penetration tests have been conducted in the velocity range of 200-1000 m/s using conical-nosed projectiles with a diameter of 14.5 mm.Further,a pseudo fluid penetration model applicable to the penetration of rigid projectiles in sand media is established according to the approximate flow of compacted sand in the adjacent zone of penetration.The correlation between the impedance function of projectile-target interaction and the internal friction features of pseudo fluid is clarified,and the effects of sand density,cone angle of nose-shaped projectile,and dynamic hardness on the penetration depth are investigated.The results verify the feasibility,wide applicability,and much lower error(with respect to the experimental data)of the proposed model as compared to the Slepyan hydrodynamic model.
