The maximum Mode Ⅰ and Mode Ⅱ stress intensity factors(SIFs), KI,kmax(θ) and KII,kmax(θ)(0°<θ<360°), of inclined parallel multi-crack varying with relative positions(including horizontal and verti...The maximum Mode Ⅰ and Mode Ⅱ stress intensity factors(SIFs), KI,kmax(θ) and KII,kmax(θ)(0°<θ<360°), of inclined parallel multi-crack varying with relative positions(including horizontal and vertical spacings) are calculated by the complex function and integration method to analyze their interacting mechanism and determine the strengthening and weakening zone of SIFs. The multi-crack initiation criterion is established based on the ratio of maximum tension-shear SIF to predict crack initiation angle, load, and mechanism. The results show that multi-crack always initiates in Mode Ⅰ and the vertical spacing is better not to be times of half crack-length for crack-arrest, which is in good agreement with test results of the red-sandstone cube specimens with three parallel cracks under uniaxial compression. This can prove the validity of the multi-crack initiation criterion.展开更多
When hydraulic fractures intersect with natural fractures,the geometry and complexity of a fracture network are determined by the initiation and propagation pattern which is affected by a number of factors.Based on th...When hydraulic fractures intersect with natural fractures,the geometry and complexity of a fracture network are determined by the initiation and propagation pattern which is affected by a number of factors.Based on the fracture mechanics,the criterion for initiation and propagation of a fracture was introduced to analyze the tendency of a propagating angle and factors affecting propagating pressure.On this basis,a mathematic model with a complex fracture network was established to investigate how the fracture network form changes with different parameters,including rock mechanics,in-situ stress distribution,fracture properties,and frac treatment parameters.The solving process of this model was accelerated by classifying the calculation nodes on the extending direction of the fracture by equal pressure gradients,and solving the geometrical parameters prior to the iteration fitting flow distribution.With the initiation and propagation criterion as the bases for the propagation of branch fractures,this method decreased the iteration times through eliminating the fitting of the fracture length in conventional 3D fracture simulation.The simulation results indicated that the formation with abundant natural fractures and smaller in-situ stress difference is sufficient conditions for fracture network development.If the pressure in the hydraulic fractures can be kept at a high level by temporary sealing or diversion,the branch fractures will propagate further with minor curvature radius,thus enlarging the reservoir stimulation area.The simulated shape of fracture network can be well matched with the field microseismic mapping in data point range and distribution density,validating the accuracy of this model.展开更多
The fracture of materials under the action of compressive forces, directed along cracks which are parallel in plane can,lot be described within the framework of the linear fracture mechanics. The criteria of fracture ...The fracture of materials under the action of compressive forces, directed along cracks which are parallel in plane can,lot be described within the framework of the linear fracture mechanics. The criteria of fracture of the Griffith-Irvin or COC type, used in classical linear fracture mechanics, are not applicable in this problem, since these forces have no influence on stress intensity coefficients and on values of cracks opening([1, 2]). The problems of such a class may be described only by using new approaches. One of possible approaches is presented by the first author, which involves using linearized relations, derived from exact non-linear equations of deformable solid body mechanics([3, 4, 5]). It should be remarked here that this approach has been widely used in problems of deformable bodies stability. As a criterion of the initiation of fracture the criterion of local instability near defects of the crack type is used. In these cases the process of loss of stability initiates the fracture process.展开更多
A general initial water penetration(seepage) fracture criterion for concrete is proposed to predict whether or not harmful water penetration(hydraulic fracturing),other than microcracking,will occur in concrete struct...A general initial water penetration(seepage) fracture criterion for concrete is proposed to predict whether or not harmful water penetration(hydraulic fracturing),other than microcracking,will occur in concrete structures in a severe high water pressure environment.The final regression,of the different macroscopic failure types in concrete to microscopic ModeⅠ c racking,allows the use of only one universal criterion to indicate the damage.Thus,a general initial water penetration fracture criterion is approximately defined as a strain magnitude of 1000×10-6,based on the concept of tensile strain derived from experimental results in the relevant literature.Then,the locations of harmful water penetration fracture(hydraulic fracture) in the high arch dam mass of the Jinping first class hydropower project are analyzed using the nonlinear finite element method(FEM) according to the proposed criterion.The proposed criterion also holds promise for other concrete structures in high water pressure environments.展开更多
基金The authors are grateful for the financial supports from the National Natural Science Foundation of China(51874351,51474251)Hunan Provincial Innovation Foundation For Postgraduate,China(CX2018B047)the Open Sharing Fund for the Large-scale Instruments and Equipments of Central South University,China(CSUZC201923).
文摘The maximum Mode Ⅰ and Mode Ⅱ stress intensity factors(SIFs), KI,kmax(θ) and KII,kmax(θ)(0°<θ<360°), of inclined parallel multi-crack varying with relative positions(including horizontal and vertical spacings) are calculated by the complex function and integration method to analyze their interacting mechanism and determine the strengthening and weakening zone of SIFs. The multi-crack initiation criterion is established based on the ratio of maximum tension-shear SIF to predict crack initiation angle, load, and mechanism. The results show that multi-crack always initiates in Mode Ⅰ and the vertical spacing is better not to be times of half crack-length for crack-arrest, which is in good agreement with test results of the red-sandstone cube specimens with three parallel cracks under uniaxial compression. This can prove the validity of the multi-crack initiation criterion.
文摘When hydraulic fractures intersect with natural fractures,the geometry and complexity of a fracture network are determined by the initiation and propagation pattern which is affected by a number of factors.Based on the fracture mechanics,the criterion for initiation and propagation of a fracture was introduced to analyze the tendency of a propagating angle and factors affecting propagating pressure.On this basis,a mathematic model with a complex fracture network was established to investigate how the fracture network form changes with different parameters,including rock mechanics,in-situ stress distribution,fracture properties,and frac treatment parameters.The solving process of this model was accelerated by classifying the calculation nodes on the extending direction of the fracture by equal pressure gradients,and solving the geometrical parameters prior to the iteration fitting flow distribution.With the initiation and propagation criterion as the bases for the propagation of branch fractures,this method decreased the iteration times through eliminating the fitting of the fracture length in conventional 3D fracture simulation.The simulation results indicated that the formation with abundant natural fractures and smaller in-situ stress difference is sufficient conditions for fracture network development.If the pressure in the hydraulic fractures can be kept at a high level by temporary sealing or diversion,the branch fractures will propagate further with minor curvature radius,thus enlarging the reservoir stimulation area.The simulated shape of fracture network can be well matched with the field microseismic mapping in data point range and distribution density,validating the accuracy of this model.
文摘The fracture of materials under the action of compressive forces, directed along cracks which are parallel in plane can,lot be described within the framework of the linear fracture mechanics. The criteria of fracture of the Griffith-Irvin or COC type, used in classical linear fracture mechanics, are not applicable in this problem, since these forces have no influence on stress intensity coefficients and on values of cracks opening([1, 2]). The problems of such a class may be described only by using new approaches. One of possible approaches is presented by the first author, which involves using linearized relations, derived from exact non-linear equations of deformable solid body mechanics([3, 4, 5]). It should be remarked here that this approach has been widely used in problems of deformable bodies stability. As a criterion of the initiation of fracture the criterion of local instability near defects of the crack type is used. In these cases the process of loss of stability initiates the fracture process.
基金supported by the National Basic Research Program of China ("973" Program) (Grant No 2007CB714104)the National Natural Science Foundation of China (Grant Nos 51079045, 50779009 and 51008114)
文摘A general initial water penetration(seepage) fracture criterion for concrete is proposed to predict whether or not harmful water penetration(hydraulic fracturing),other than microcracking,will occur in concrete structures in a severe high water pressure environment.The final regression,of the different macroscopic failure types in concrete to microscopic ModeⅠ c racking,allows the use of only one universal criterion to indicate the damage.Thus,a general initial water penetration fracture criterion is approximately defined as a strain magnitude of 1000×10-6,based on the concept of tensile strain derived from experimental results in the relevant literature.Then,the locations of harmful water penetration fracture(hydraulic fracture) in the high arch dam mass of the Jinping first class hydropower project are analyzed using the nonlinear finite element method(FEM) according to the proposed criterion.The proposed criterion also holds promise for other concrete structures in high water pressure environments.
