Most of the carbonates in the Tarim Basin in northwest China are low-porosity and low-permeability rocks. Owing to the complexity of porosity in carbonates, conventional rock- physics models do not describe the relati...Most of the carbonates in the Tarim Basin in northwest China are low-porosity and low-permeability rocks. Owing to the complexity of porosity in carbonates, conventional rock- physics models do not describe the relation between velocity and porosity for the Tarim Basin carbonates well. We propose the porous-grain-upper-boundary （PGU） model for estimating the relation between velocity and porosity for low-porosity carbonates. In this model, the carbonate sediments are treated as packed media of porous elastic grains, and the carbonate pores are divided into isolated and connected pores The PGU model is modified from the porous-grain-stiff-sand （PGST） model by replacing the critical porosity with the more practical isolated porosity. In the implementation, the effective elastic constants of the porous grains are calculated by using the differential effective medium （DEM） model. Then, the elastic constants of connected porous grains in dry rocks are calculated by using the modified upper Hashin-Shtrikman bound. The application to the Tarim carbonates shows that relative to other conventional effective medium models the PGU model matches the well log data well.展开更多
The effect of porosity on compressive,bending,and tensile properties of the porous tantalum scaffolds fabricated by electron beam powder bed fusion(EB-PBF)was investigated.The porous tantalum scaffolds with porosity f...The effect of porosity on compressive,bending,and tensile properties of the porous tantalum scaffolds fabricated by electron beam powder bed fusion(EB-PBF)was investigated.The porous tantalum scaffolds with porosity from 69%to 77.8%were obtained by varying the designed porosity and adjusting the processing parameters.It is found that the pores and unfused powder decrease with the increase of deposited energy density.The decrease of porosity leads to an improvement in mechanical properties.The relevancy between compressive/bending/tensile yield strength and relative density can be described appropriately by exponential model,while the relationship between elastic modulus and relative density is in good agreement with the Gibson-Ashby model.All the porous tantalum scaffolds exhibit good ductility in compressive,bending and tensile tests.No fragmentation of struts is observed during the compression process,but cracks are formed on the strut surface after 90°bending,mainly due to the high sensibility to defects caused by the oxide.展开更多
The permeability and porosity of coal seams are anisotropic, and the variation of confining stress may induce deformation in coal samples. In order to study these characteristics, experiments and model analyses were c...The permeability and porosity of coal seams are anisotropic, and the variation of confining stress may induce deformation in coal samples. In order to study these characteristics, experiments and model analyses were conducted to understand the behaviors of anisotropic stress sensitivity of lean coal samples. The results showed as the closure of cleats and the generation of micro-cracks, the strong stress sensitivity of coal samples and the discrete changes in porosity were caused by confining pressure changes. In the compression period, the anisotropy trend first increased, and then decreased. In the direction perpendicular to the bedding plane, the permeability decrease rate and the irreversible damage rate were the highest. In the direction parallel to the cleats, permeability recovery rate was higher and the irreversible damage rate was lower along butt cleats. Compared to the cube root of permeability to porosity, a 1/6 power relationship was proved to be closer to the experiment results, the new relationship had the highest fit level in the face cleat direction, and the lowest fit level in the vertical direction展开更多
Based on the process of reinforcing soft soil using cement in laboratory, the porosity of test samples under different pressures conditions were determined through mercury intrusion porosimetry. The experiment was int...Based on the process of reinforcing soft soil using cement in laboratory, the porosity of test samples under different pressures conditions were determined through mercury intrusion porosimetry. The experiment was introduced and the law of porosity variation was summarized. The results show that when stress is between 0 and 0.15--0.2 qu, porosity decreases along with the pressure, then porosity has increased in the wake of the pressure until the sample damaged. It can provide an experimental basis for exploring the failure mechanism of cement stabilized soil from the microscopic view and the study to establish the microcosmic constitutive model of cement stabilized soil.展开更多
基金supported by the National Basic Research Program of China(2013CB228602)the National High Technology Research Program of China(2013AA064202)the National Science and Technology Major Project of China(Grant No.2011ZX05004-003)
文摘Most of the carbonates in the Tarim Basin in northwest China are low-porosity and low-permeability rocks. Owing to the complexity of porosity in carbonates, conventional rock- physics models do not describe the relation between velocity and porosity for the Tarim Basin carbonates well. We propose the porous-grain-upper-boundary （PGU） model for estimating the relation between velocity and porosity for low-porosity carbonates. In this model, the carbonate sediments are treated as packed media of porous elastic grains, and the carbonate pores are divided into isolated and connected pores The PGU model is modified from the porous-grain-stiff-sand （PGST） model by replacing the critical porosity with the more practical isolated porosity. In the implementation, the effective elastic constants of the porous grains are calculated by using the differential effective medium （DEM） model. Then, the elastic constants of connected porous grains in dry rocks are calculated by using the modified upper Hashin-Shtrikman bound. The application to the Tarim carbonates shows that relative to other conventional effective medium models the PGU model matches the well log data well.
基金supported by the Key R&D Program of Guangdong Province,China(Nos.2019B090904001,2018B090906003)。
文摘The effect of porosity on compressive,bending,and tensile properties of the porous tantalum scaffolds fabricated by electron beam powder bed fusion(EB-PBF)was investigated.The porous tantalum scaffolds with porosity from 69%to 77.8%were obtained by varying the designed porosity and adjusting the processing parameters.It is found that the pores and unfused powder decrease with the increase of deposited energy density.The decrease of porosity leads to an improvement in mechanical properties.The relevancy between compressive/bending/tensile yield strength and relative density can be described appropriately by exponential model,while the relationship between elastic modulus and relative density is in good agreement with the Gibson-Ashby model.All the porous tantalum scaffolds exhibit good ductility in compressive,bending and tensile tests.No fragmentation of struts is observed during the compression process,but cracks are formed on the strut surface after 90°bending,mainly due to the high sensibility to defects caused by the oxide.
基金＊ Supported by the National Science ＆ Technology Major Project of China （2011ZX05038-001） the National Natural Science Foundation of China （2009CB219604）
文摘The permeability and porosity of coal seams are anisotropic, and the variation of confining stress may induce deformation in coal samples. In order to study these characteristics, experiments and model analyses were conducted to understand the behaviors of anisotropic stress sensitivity of lean coal samples. The results showed as the closure of cleats and the generation of micro-cracks, the strong stress sensitivity of coal samples and the discrete changes in porosity were caused by confining pressure changes. In the compression period, the anisotropy trend first increased, and then decreased. In the direction perpendicular to the bedding plane, the permeability decrease rate and the irreversible damage rate were the highest. In the direction parallel to the cleats, permeability recovery rate was higher and the irreversible damage rate was lower along butt cleats. Compared to the cube root of permeability to porosity, a 1/6 power relationship was proved to be closer to the experiment results, the new relationship had the highest fit level in the face cleat direction, and the lowest fit level in the vertical direction
基金Supported by projects of the Natural Science Foundation of China (Nos. 40902077,41172236,41111120084)the Basic Research Project of Jilin University (No. 200903198)
文摘Based on the process of reinforcing soft soil using cement in laboratory, the porosity of test samples under different pressures conditions were determined through mercury intrusion porosimetry. The experiment was introduced and the law of porosity variation was summarized. The results show that when stress is between 0 and 0.15--0.2 qu, porosity decreases along with the pressure, then porosity has increased in the wake of the pressure until the sample damaged. It can provide an experimental basis for exploring the failure mechanism of cement stabilized soil from the microscopic view and the study to establish the microcosmic constitutive model of cement stabilized soil.
