The fracture network of hydraulic crack is significantly influenced by the bedding plane in coalbed methane extraction.Under mode Ⅱ loading,crack deflection holds a key position in hydraulic cracking,especially in hy...The fracture network of hydraulic crack is significantly influenced by the bedding plane in coalbed methane extraction.Under mode Ⅱ loading,crack deflection holds a key position in hydraulic cracking,especially in hydraulic shearing.This study first analyzed the crack deflection theory of layered rock.The semi-circle bending test under asymmetric loading is performed,and the four-dimensional Lattice Spring Model(4D-LSM)is established to examine how the bedding parameters affect coal crack propagation under mode Ⅱ dominant loads.The 4D-LSM results are comparable to the coal loading test results under quasi-mode Ⅱ and the analytical prediction of crack deflection theory.During mode Ⅱ loading,the coal crack propagation is greatly influenced by the angle,strength,and elastic modulus of the bedding plane,while the effects of thickness and spacing of bedding are insignificant.The crack of coal tends to propagate towards the bedding,following a decrease in bedding angle,a decrease in bedding strength,and an increase in elastic modulus.With higher bedding strength,spacing,and thickness,the peak load on the coal sample is higher.The influences of bedding strength,elastic modulus,spacing,and thickness on the peak load of coal samples and its anisotropy gradually decrease.It is proved that compared with the tangential stress ratio and traditional energy release ratio theories,the corrected energy release ratio criterion can more accurately predict the direction of crack deflection of coal,especially under mode Ⅱ loading.The results can provide assistance in the design of initiation pressure and fracturing direction in coal seam hydraulic fracturing.展开更多
A new fracture criterion was proposed. The physical explanation of the criterion is that crack will propagate when the minimum strain energy density in iso hoop stress curve reach a critical strength of the material c...A new fracture criterion was proposed. The physical explanation of the criterion is that crack will propagate when the minimum strain energy density in iso hoop stress curve reach a critical strength of the material considered. The resulting curve of critical fracture of mixed mode cracks shows that the present fracture is efficient and more accurate than the previous criteria.展开更多
Fracture processes in ship-building structures are in many cases of a 3-D character. A finite element （FE） model of an all fracture mode （AFM） specimen was built for the study of 3-D mixed mode crack fracture beha...Fracture processes in ship-building structures are in many cases of a 3-D character. A finite element （FE） model of an all fracture mode （AFM） specimen was built for the study of 3-D mixed mode crack fracture behavior including modes Ⅰ,Ⅱ, and Ⅲ. The stress intensity factors （SIFs） were calculated by the modified virtual crack closure integral （MVCCI） method, and the crack initiation angle assessment was based on a recently developed 3-D fracture criterion--the Richard criterion. It was shown that the FE model of the AFM-specimen is applicable for investigations under general mixed mode loading conditions, and the computational results of crack initiation angles are in agreement with some available experimental findings. Thus, the applicability of the FE model of the AFM-specimen for mixed mode loading conditions and the validity of the Richard criterion can be demonstrated.展开更多
Anti symmetric four point bending specimen with different loading point positions was used to study effect of loading point position on fracture mode of rock in order to explore a feasible method for achieving Mode Ⅱ...Anti symmetric four point bending specimen with different loading point positions was used to study effect of loading point position on fracture mode of rock in order to explore a feasible method for achieving Mode Ⅱ fracture and determining Mode Ⅱ fracture toughness of rock, K ⅡC . Numerical and experimental results show that the distance between the inner and outer loading points, L 1+ L 2, has a great influence on stresses at notch tip and fracture mode. When L 1+ L 2>0.5 L or 0.1 L < L 1+ L 2<0.5 L , maximum principal stress σ 1 exceeds the tensile strength σ t. The ratio of τ max / σ 1 is relatively low or high and thus Mode Ⅰ or mixed mode fracture occurs. When L 1+ L 2< 0.1 L , σ 1 is smaller than σ t and the ratio of τ max / σ 1 is much higher, which facilitates the occurrence of Mode Ⅱ fracture.展开更多
The dynamic stress intensity factor history for a half plane crack in an otherwise unbounded elastic body, with the crack faces subjected to a traction distribution consisting of two pairs of suddenly-applied shear li...The dynamic stress intensity factor history for a half plane crack in an otherwise unbounded elastic body, with the crack faces subjected to a traction distribution consisting of two pairs of suddenly-applied shear line loads is consid- ered. The analytic expression for the combined mode stress intensity factors as a function of time is obtained. The method of solution is based on the application of integral transforms and the Wiener-Hopf technique. Some features of the solutions are discussed and graphical numerical results are presented.展开更多
Finite element method(FEM)has been used to analyze the stress and strain fields and the stress tri-axial levels around the tip of the crack under mode-Ⅱ loading.The results show that: under mode-Ⅱ loading,the direct...Finite element method(FEM)has been used to analyze the stress and strain fields and the stress tri-axial levels around the tip of the crack under mode-Ⅱ loading.The results show that: under mode-Ⅱ loading,the direction of the maximum tensile stress and that of the maximum tri-axial levels(R_ )exist at an angle of-75.3°from the original crack plane:the maximum shear stress and R_ =0 exist along the original crack plane. Mode-Ⅱ loading experiment using BHW-35 steel at different temperatures show that there are two kinds of fracture mode.opening mode(or tensile mode)and sliding mode(or shear mode).A de- crease in temperature causes the fracture mode to change from shear mode to tensile mode.For BHW- 35 steel,this critical temperature is about-90C.Actually.under any kind of loading mode(mode Ⅰ,mode Ⅱ,mode Ⅲ or mixed mode),there always exist several kinds of potenital fracture modes (for example,opening mode.sliding mode.tearing mode or mixed mode).The effect of temperature under mode-Ⅱ loading is actually related to the change of the elastic-plastic properties of the material.展开更多
The capability of several types of flat PDC cutters to withstand combined loads were tested and evaluated by the impact and cutting of single PDC cutter on granite in a linear impact cutting table. The primary failure...The capability of several types of flat PDC cutters to withstand combined loads were tested and evaluated by the impact and cutting of single PDC cutter on granite in a linear impact cutting table. The primary failure modes of PDC cutters withstanding different combined loads were investigated and analyzed. The suggestions of enhancing PDC cutters to be suitable for drilling very hard rock have been made.展开更多
A theoretical approach is presented for analyzing the ply crackingin general symmetric lami- nates subjected to any combination ofin-plane mechanical loading and uniform temperature changes. Theequivalent constraint m...A theoretical approach is presented for analyzing the ply crackingin general symmetric lami- nates subjected to any combination ofin-plane mechanical loading and uniform temperature changes. Theequivalent constraint model proposed by the authors in a previouswork is used to account for the cracking in- teraction betweenlaminae in the laminates. By using a superposition schemce and thestress field solutions the energy release rate for a ply cracking isexplicitly as a function of stiffness reduction parameters of thelaminates. The ratio of mode Ⅰ to mode Ⅱ is introduced formconstruction of the fracture criterion. The effects of the laminateparameters and the crack spacing on the energy release rate and themode mixity are illustrated. Finally, the model is used to predictthe thermomechanical load for the first-ply-cracking.展开更多
岩石受压激发电流(pressure-stimulated rock current,PSRC)变化是岩体破裂观测与地壳灾变感知研究的重要内容,但缺乏岩石含水状态与加载模式对PSRC变化特征的影响探究与机理辨析.本文以粒度相对均匀的闪长岩为实验对象,特别制备了方柱...岩石受压激发电流(pressure-stimulated rock current,PSRC)变化是岩体破裂观测与地壳灾变感知研究的重要内容,但缺乏岩石含水状态与加载模式对PSRC变化特征的影响探究与机理辨析.本文以粒度相对均匀的闪长岩为实验对象,特别制备了方柱-锥体闪长岩试件,采用高精度静电计与声发射探测仪,同步观测单、双轴局部加载破裂过程中充分干燥、自然干燥和充分饱水试件的受压端与非受压端之间PSRC及声发射变化,并分析其特征差异,辨析其内在机理.研究揭示:(1)全部试件受力中后期均呈现PSRC显著增长,包括毛刺型、持续增大型和瞬时台阶型,其增幅受含水状态和加载模式综合影响;(2)岩石临失稳前,PSRC均呈现剧烈脉冲式振荡特征,其中单、双轴模式下充分饱水试件的峰值PSRC分别是充分干燥试件的1.3倍和7.1倍,而自然干燥试件的峰值PSRC受加载模式影响不大;(3)自然干燥试件中的微量孔隙水对正空穴电荷传递有损耗作用,而充分饱水试件的流体电动势效应对PSRC变化影响显著,闪长岩所含石英矿物对PSRC的贡献可以忽略.本文揭示的岩石临失稳前PSRC剧变现象、峰值差异及内在机理,对于发展岩体灾变监测预警新技术和构造地震孕震区遥感识别新方法有重要意义.展开更多
This paper is devoted to investigate the robust H∞sliding mode load frequency control(SMLFC) of multi-area power system with time delay. By taking into account stochastic disturbances induced by the integration of re...This paper is devoted to investigate the robust H∞sliding mode load frequency control(SMLFC) of multi-area power system with time delay. By taking into account stochastic disturbances induced by the integration of renewable energies,a new sliding surface function is constructed to guarantee the fast response and robust performance, then the sliding mode control law is designed to guarantee the reach ability of the sliding surface in a finite-time interval. The sufficient robust frequency stabilization result for multi-area power system with time delay is presented in terms of linear matrix inequalities(LMIs). Finally,a two-area power system is provided to illustrate the usefulness and effectiveness of the obtained results.展开更多
基金financially supported by the National Natural Science Foundation of China(Grant Nos.52225402,U1910206)the National Key Research and Development Project of China(Grant No.2022YFC3004602).
文摘The fracture network of hydraulic crack is significantly influenced by the bedding plane in coalbed methane extraction.Under mode Ⅱ loading,crack deflection holds a key position in hydraulic cracking,especially in hydraulic shearing.This study first analyzed the crack deflection theory of layered rock.The semi-circle bending test under asymmetric loading is performed,and the four-dimensional Lattice Spring Model(4D-LSM)is established to examine how the bedding parameters affect coal crack propagation under mode Ⅱ dominant loads.The 4D-LSM results are comparable to the coal loading test results under quasi-mode Ⅱ and the analytical prediction of crack deflection theory.During mode Ⅱ loading,the coal crack propagation is greatly influenced by the angle,strength,and elastic modulus of the bedding plane,while the effects of thickness and spacing of bedding are insignificant.The crack of coal tends to propagate towards the bedding,following a decrease in bedding angle,a decrease in bedding strength,and an increase in elastic modulus.With higher bedding strength,spacing,and thickness,the peak load on the coal sample is higher.The influences of bedding strength,elastic modulus,spacing,and thickness on the peak load of coal samples and its anisotropy gradually decrease.It is proved that compared with the tangential stress ratio and traditional energy release ratio theories,the corrected energy release ratio criterion can more accurately predict the direction of crack deflection of coal,especially under mode Ⅱ loading.The results can provide assistance in the design of initiation pressure and fracturing direction in coal seam hydraulic fracturing.
文摘A new fracture criterion was proposed. The physical explanation of the criterion is that crack will propagate when the minimum strain energy density in iso hoop stress curve reach a critical strength of the material considered. The resulting curve of critical fracture of mixed mode cracks shows that the present fracture is efficient and more accurate than the previous criteria.
文摘Fracture processes in ship-building structures are in many cases of a 3-D character. A finite element （FE） model of an all fracture mode （AFM） specimen was built for the study of 3-D mixed mode crack fracture behavior including modes Ⅰ,Ⅱ, and Ⅲ. The stress intensity factors （SIFs） were calculated by the modified virtual crack closure integral （MVCCI） method, and the crack initiation angle assessment was based on a recently developed 3-D fracture criterion--the Richard criterion. It was shown that the FE model of the AFM-specimen is applicable for investigations under general mixed mode loading conditions, and the computational results of crack initiation angles are in agreement with some available experimental findings. Thus, the applicability of the FE model of the AFM-specimen for mixed mode loading conditions and the validity of the Richard criterion can be demonstrated.
文摘Anti symmetric four point bending specimen with different loading point positions was used to study effect of loading point position on fracture mode of rock in order to explore a feasible method for achieving Mode Ⅱ fracture and determining Mode Ⅱ fracture toughness of rock, K ⅡC . Numerical and experimental results show that the distance between the inner and outer loading points, L 1+ L 2, has a great influence on stresses at notch tip and fracture mode. When L 1+ L 2>0.5 L or 0.1 L < L 1+ L 2<0.5 L , maximum principal stress σ 1 exceeds the tensile strength σ t. The ratio of τ max / σ 1 is relatively low or high and thus Mode Ⅰ or mixed mode fracture occurs. When L 1+ L 2< 0.1 L , σ 1 is smaller than σ t and the ratio of τ max / σ 1 is much higher, which facilitates the occurrence of Mode Ⅱ fracture.
基金The project supported by the National Natural Science Foundation of China
文摘The dynamic stress intensity factor history for a half plane crack in an otherwise unbounded elastic body, with the crack faces subjected to a traction distribution consisting of two pairs of suddenly-applied shear line loads is consid- ered. The analytic expression for the combined mode stress intensity factors as a function of time is obtained. The method of solution is based on the application of integral transforms and the Wiener-Hopf technique. Some features of the solutions are discussed and graphical numerical results are presented.
文摘Finite element method(FEM)has been used to analyze the stress and strain fields and the stress tri-axial levels around the tip of the crack under mode-Ⅱ loading.The results show that: under mode-Ⅱ loading,the direction of the maximum tensile stress and that of the maximum tri-axial levels(R_ )exist at an angle of-75.3°from the original crack plane:the maximum shear stress and R_ =0 exist along the original crack plane. Mode-Ⅱ loading experiment using BHW-35 steel at different temperatures show that there are two kinds of fracture mode.opening mode(or tensile mode)and sliding mode(or shear mode).A de- crease in temperature causes the fracture mode to change from shear mode to tensile mode.For BHW- 35 steel,this critical temperature is about-90C.Actually.under any kind of loading mode(mode Ⅰ,mode Ⅱ,mode Ⅲ or mixed mode),there always exist several kinds of potenital fracture modes (for example,opening mode.sliding mode.tearing mode or mixed mode).The effect of temperature under mode-Ⅱ loading is actually related to the change of the elastic-plastic properties of the material.
基金Project(5 0 1740 5 6)supportedbytheNationalNaturalScienceFoundationofChina project(De -FG0 3 )supportedbytheNevatakUndertheDepartmentofEnergy USA
文摘The capability of several types of flat PDC cutters to withstand combined loads were tested and evaluated by the impact and cutting of single PDC cutter on granite in a linear impact cutting table. The primary failure modes of PDC cutters withstanding different combined loads were investigated and analyzed. The suggestions of enhancing PDC cutters to be suitable for drilling very hard rock have been made.
基金the National Natural Science Foundation of China (No.19972076)the Germen Research Foundation (DFG)
文摘A theoretical approach is presented for analyzing the ply crackingin general symmetric lami- nates subjected to any combination ofin-plane mechanical loading and uniform temperature changes. Theequivalent constraint model proposed by the authors in a previouswork is used to account for the cracking in- teraction betweenlaminae in the laminates. By using a superposition schemce and thestress field solutions the energy release rate for a ply cracking isexplicitly as a function of stiffness reduction parameters of thelaminates. The ratio of mode Ⅰ to mode Ⅱ is introduced formconstruction of the fracture criterion. The effects of the laminateparameters and the crack spacing on the energy release rate and themode mixity are illustrated. Finally, the model is used to predictthe thermomechanical load for the first-ply-cracking.
文摘岩石受压激发电流(pressure-stimulated rock current,PSRC)变化是岩体破裂观测与地壳灾变感知研究的重要内容,但缺乏岩石含水状态与加载模式对PSRC变化特征的影响探究与机理辨析.本文以粒度相对均匀的闪长岩为实验对象,特别制备了方柱-锥体闪长岩试件,采用高精度静电计与声发射探测仪,同步观测单、双轴局部加载破裂过程中充分干燥、自然干燥和充分饱水试件的受压端与非受压端之间PSRC及声发射变化,并分析其特征差异,辨析其内在机理.研究揭示:(1)全部试件受力中后期均呈现PSRC显著增长,包括毛刺型、持续增大型和瞬时台阶型,其增幅受含水状态和加载模式综合影响;(2)岩石临失稳前,PSRC均呈现剧烈脉冲式振荡特征,其中单、双轴模式下充分饱水试件的峰值PSRC分别是充分干燥试件的1.3倍和7.1倍,而自然干燥试件的峰值PSRC受加载模式影响不大;(3)自然干燥试件中的微量孔隙水对正空穴电荷传递有损耗作用,而充分饱水试件的流体电动势效应对PSRC变化影响显著,闪长岩所含石英矿物对PSRC的贡献可以忽略.本文揭示的岩石临失稳前PSRC剧变现象、峰值差异及内在机理,对于发展岩体灾变监测预警新技术和构造地震孕震区遥感识别新方法有重要意义.
基金supported in part by the National Natural Science Foundation of China(61673161)the Natural Science Foundation of Jiangsu Province of China(BK20161510)+2 种基金the Fundamental Research Funds for the Central Universities of China(2017B13914)the 111 Project(B14022)the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD)
文摘This paper is devoted to investigate the robust H∞sliding mode load frequency control(SMLFC) of multi-area power system with time delay. By taking into account stochastic disturbances induced by the integration of renewable energies,a new sliding surface function is constructed to guarantee the fast response and robust performance, then the sliding mode control law is designed to guarantee the reach ability of the sliding surface in a finite-time interval. The sufficient robust frequency stabilization result for multi-area power system with time delay is presented in terms of linear matrix inequalities(LMIs). Finally,a two-area power system is provided to illustrate the usefulness and effectiveness of the obtained results.
