For the problem of hydraulic fracture propagation when weakening the hard roof in fully mechanized top-coal caving stope of ultra-thick coal seam, based on the stress arch theory and the fracture mechanics, a two-dime...For the problem of hydraulic fracture propagation when weakening the hard roof in fully mechanized top-coal caving stope of ultra-thick coal seam, based on the stress arch theory and the fracture mechanics, a two-dimensional model for hydraulic fracture of the roof in the stope was established to investigate the propagation laws of hydraulic fracture. The result shows that, after mining, the principal stress direction of overlaying rock deflects to form the stress arch, whose arrow height and arch thickness increase with the increase of the mining width and the side pressure coefficient. Within the influence range of stress arch, the hydraulic fracture in hard roof deflects towards the stope direction in the course of propagation and forms the ‘‘arch" fracture, which cuts off the roof below the fracture in a laminated way. The deflection angle of hydraulic fracture increases with the increase of the mining width, but decreases with the increase of the side pressure coefficient and the fractured horizon. This research can provide theoretical basis for the application of hydraulic fracturing method in the stope roof weakening.展开更多
Drop weight impact tester was used to accurately measure the bending impact resistance of various parts of Phyllostachys edulis,commonly known as moso bamboo,with a growth cycle of 3–8 years.Cellulose crystallinity i...Drop weight impact tester was used to accurately measure the bending impact resistance of various parts of Phyllostachys edulis,commonly known as moso bamboo,with a growth cycle of 3–8 years.Cellulose crystallinity in the bottom(B),middle(M)and top(T)of bamboo at different ages was calculated using peak height analysis in X-ray diffraction.Heatmap of Spearman correlation analysis was used to represent the correlation between chemical composition and impact mechanics.The breaking load(BL),fracture energy(FE)and impact deflection(ID)of 3–8-year-old bamboo were found to be in the range of~670–2120 N,~5.17–15.55 J,and~3.60–~17.76 mm,respectively.As the growth period of bamboo rises,the cellulose crystallinity at the B and T decreases first and then increases,while that for the M increases first and then remains stable.Similarly,the bending impact performance of bamboo was found to become stable with its growth and age.The flexural impact and toughness of the 4-year-old bamboo base material were better than other specimens.The enhancement in the bending impact properties of bamboo at different growth periods was influenced by the lignin content,while the value of FE was mainly positively correlated with ash,cold and hot water extracts and benzyl alcohol content.However the content of holocellulose and pentosan,air-dry density and,base density negatively influenced the FE.With the change in the height of the bamboo,the correlation between its impact mechanical properties and chemical composition gradually decreased.This study provides data support and theoretical basis for the age-appropriate thinning and application of moso bamboo.展开更多
In this study, an orthogonal array experiment is conducted by using a transparent fracture network replica. Image processing and theoretical analysis are performed to investigate the model sealing efficiency(SE), fact...In this study, an orthogonal array experiment is conducted by using a transparent fracture network replica. Image processing and theoretical analysis are performed to investigate the model sealing efficiency(SE), factors influencing SE, and the effect of flowing water on propagation. The results show that grout propagation can be classified into three patterns in the fracture network: sealing off, partial sealing,and major erosion. The factors controlling the SE in a descending order of the amount of influence are the initial water flow speed, fracture aperture, grout take, and gel time. An optimal value for the combination of the gel time and grout take(artificial factors) can result in a good SE. The grouting and seepage pressures are measured, and the results reveal that their variations can indicate the SE to some extent. The SE is good when the seepage pressure at each point increases overall;the frequent fluctuations in the seepage pressure indicate a moderately poor SE, and an overall decline in the seepage pressure indicates a major erosion type. The deflection effect of grouting shows an approximately elliptical propagation with the long axis expanding along the wider fracture opening, demonstrating further application in grouting design.展开更多
In the Changqing Oilfield in northwest China, when traditional petroleum exploitation encounters forestry reserves or water source protection areas, sectorial well-factory design is proposed. The most distinct feature...In the Changqing Oilfield in northwest China, when traditional petroleum exploitation encounters forestry reserves or water source protection areas, sectorial well-factory design is proposed. The most distinct feature of a sectorial well-factory is the deviation of the well from the minimum horizontal principal stress, resulting in hydraulic fracture deflection after the initiation, along with possible well interference (i.e., fracture hit) and fracture coalescence in the oblique wells. Four indexes describing well deflection are then proposed according to fracture morphology. Several fracturing designs, including stage arrangement, fracturing sequences, and fracturing techniques are applied to study the feasibility of the sectorial well-factory design. The results show that the “gradual” or “sparse” stage arrangement, large injection rate, and simultaneous multifracture treatment can help to optimize the fracture morphology and stimulation design. However, the subsequent stress shadowing effect usually adversely affects the fracturing of adjacent wells. With a small initial horizontal stress difference, large injection rate and staggered stage arrangement can achieve ideal stimulation performance. Our results can provide a guidance for optimizing stimulation design in unconventional well-factory while taking into account environmental protection.展开更多
The hybrid SiC foam-SiC particles/Al double interpenetrating composites to be used as the brake materials of high speed train were fabricated by squeeze casting technique. The influence of the type of matrix on the me...The hybrid SiC foam-SiC particles/Al double interpenetrating composites to be used as the brake materials of high speed train were fabricated by squeeze casting technique. The influence of the type of matrix on the mechanical properties and the fracture mechanism of the hybrid composites was investigated. The interface bond in the hybrid composites is good for the composites have the unique double interpenetrating structure. The ductile matrix resists the propagation of the microcracks in the struts. During the microcrack propagation process, the energy absorption and the fracture surface area are increased, which increases the ductility of the hybrid composites. The compressive strength of the hybrid composite reinforced by the SiC with the total volume fraction of 53% is 660 MPa, which is higher than that of traditional composite reinforced by single SiC particles.展开更多
基金Financial supports for this work,provided by the National Natural Science Foundation of China (No.51104191)the China Postdoctoral Science Foundation (2016M602655)the Program for Changjiang Scholars and Innovative Research Team in University of China (No.IRT13043)
文摘For the problem of hydraulic fracture propagation when weakening the hard roof in fully mechanized top-coal caving stope of ultra-thick coal seam, based on the stress arch theory and the fracture mechanics, a two-dimensional model for hydraulic fracture of the roof in the stope was established to investigate the propagation laws of hydraulic fracture. The result shows that, after mining, the principal stress direction of overlaying rock deflects to form the stress arch, whose arrow height and arch thickness increase with the increase of the mining width and the side pressure coefficient. Within the influence range of stress arch, the hydraulic fracture in hard roof deflects towards the stope direction in the course of propagation and forms the ‘‘arch" fracture, which cuts off the roof below the fracture in a laminated way. The deflection angle of hydraulic fracture increases with the increase of the mining width, but decreases with the increase of the side pressure coefficient and the fractured horizon. This research can provide theoretical basis for the application of hydraulic fracturing method in the stope roof weakening.
基金Fundamental Research on Impact Toughness and Response Mechanism of Bamboo-woven Structural Materials Funded of International Center for Bamboo and Rattan(1632020016).
文摘Drop weight impact tester was used to accurately measure the bending impact resistance of various parts of Phyllostachys edulis,commonly known as moso bamboo,with a growth cycle of 3–8 years.Cellulose crystallinity in the bottom(B),middle(M)and top(T)of bamboo at different ages was calculated using peak height analysis in X-ray diffraction.Heatmap of Spearman correlation analysis was used to represent the correlation between chemical composition and impact mechanics.The breaking load(BL),fracture energy(FE)and impact deflection(ID)of 3–8-year-old bamboo were found to be in the range of~670–2120 N,~5.17–15.55 J,and~3.60–~17.76 mm,respectively.As the growth period of bamboo rises,the cellulose crystallinity at the B and T decreases first and then increases,while that for the M increases first and then remains stable.Similarly,the bending impact performance of bamboo was found to become stable with its growth and age.The flexural impact and toughness of the 4-year-old bamboo base material were better than other specimens.The enhancement in the bending impact properties of bamboo at different growth periods was influenced by the lignin content,while the value of FE was mainly positively correlated with ash,cold and hot water extracts and benzyl alcohol content.However the content of holocellulose and pentosan,air-dry density and,base density negatively influenced the FE.With the change in the height of the bamboo,the correlation between its impact mechanical properties and chemical composition gradually decreased.This study provides data support and theoretical basis for the age-appropriate thinning and application of moso bamboo.
基金supported by the Natural Science Foundation of China under (Nos. 42172293, 4190020747, and 41472268)。
文摘In this study, an orthogonal array experiment is conducted by using a transparent fracture network replica. Image processing and theoretical analysis are performed to investigate the model sealing efficiency(SE), factors influencing SE, and the effect of flowing water on propagation. The results show that grout propagation can be classified into three patterns in the fracture network: sealing off, partial sealing,and major erosion. The factors controlling the SE in a descending order of the amount of influence are the initial water flow speed, fracture aperture, grout take, and gel time. An optimal value for the combination of the gel time and grout take(artificial factors) can result in a good SE. The grouting and seepage pressures are measured, and the results reveal that their variations can indicate the SE to some extent. The SE is good when the seepage pressure at each point increases overall;the frequent fluctuations in the seepage pressure indicate a moderately poor SE, and an overall decline in the seepage pressure indicates a major erosion type. The deflection effect of grouting shows an approximately elliptical propagation with the long axis expanding along the wider fracture opening, demonstrating further application in grouting design.
基金funded by the National Natural Science Foundation of China(42077247,52104029)the Fundamental Research Funds for the Central Universities.
文摘In the Changqing Oilfield in northwest China, when traditional petroleum exploitation encounters forestry reserves or water source protection areas, sectorial well-factory design is proposed. The most distinct feature of a sectorial well-factory is the deviation of the well from the minimum horizontal principal stress, resulting in hydraulic fracture deflection after the initiation, along with possible well interference (i.e., fracture hit) and fracture coalescence in the oblique wells. Four indexes describing well deflection are then proposed according to fracture morphology. Several fracturing designs, including stage arrangement, fracturing sequences, and fracturing techniques are applied to study the feasibility of the sectorial well-factory design. The results show that the “gradual” or “sparse” stage arrangement, large injection rate, and simultaneous multifracture treatment can help to optimize the fracture morphology and stimulation design. However, the subsequent stress shadowing effect usually adversely affects the fracturing of adjacent wells. With a small initial horizontal stress difference, large injection rate and staggered stage arrangement can achieve ideal stimulation performance. Our results can provide a guidance for optimizing stimulation design in unconventional well-factory while taking into account environmental protection.
基金Projects(01306016, 01307148) supported by Key Laboratory of Ministry of Education for Conveyance and Equipment (East China Jiaotong University), ChinaProject(09497) supported by the Young Science Foundation of Jiangxi Provincial Education Office, ChinaProject(50765005) supported by the National Natural Science Foundation of China
文摘The hybrid SiC foam-SiC particles/Al double interpenetrating composites to be used as the brake materials of high speed train were fabricated by squeeze casting technique. The influence of the type of matrix on the mechanical properties and the fracture mechanism of the hybrid composites was investigated. The interface bond in the hybrid composites is good for the composites have the unique double interpenetrating structure. The ductile matrix resists the propagation of the microcracks in the struts. During the microcrack propagation process, the energy absorption and the fracture surface area are increased, which increases the ductility of the hybrid composites. The compressive strength of the hybrid composite reinforced by the SiC with the total volume fraction of 53% is 660 MPa, which is higher than that of traditional composite reinforced by single SiC particles.
