Understanding microcracking near coalesced fracture generation is critically important for hydrocarbon and geothermal reservoir characterization as well as damage evaluation in civil engineering structures. Dense and ...Understanding microcracking near coalesced fracture generation is critically important for hydrocarbon and geothermal reservoir characterization as well as damage evaluation in civil engineering structures. Dense and sometimes random microcracking near coalesced fracture formation alters the mechanical properties of the nearby virgin material. Individual microcrack characterization is also significant in quantifying the material changes near the fracture faces （i.e. damage）. Acoustic emission （AE） monitoring and analysis provide unique information regarding the microcracking process temporally, and infor- mation concerning the source characterization of individual microcracks can be extracted. In this context, laboratory hydraulic fracture tests were carried out while monitoring the AEs from several piezoelectric transducers. In-depth post-processing of the AE event data was performed for the purpose of under- standing the individual source mechanisms. Several source characterization techniques including moment tensor inversion, event parametric analysis, and volumetric deformation analysis were adopted. Post-test fracture characterization through coring, slicing and micro-computed tomographic imaging was performed to determine the coalesced fracture location and structure. Distinct differences in fracture characteristics were found spatially in relation to the openhole injection interval. Individual microcrack AE analysis showed substantial energy reduction emanating spatially from the injection interval. It was quantitatively observed that the recorded AE signals provided sufficient information to generalize the damage radiating spatially away from the injection wellbore.展开更多
Among the triggering factors of postearthquake bedrock landslides, rainfall plays an important role. However, with slope variation, the mechanism of its effects on the failure of rock landslides is not dear. Here, fro...Among the triggering factors of postearthquake bedrock landslides, rainfall plays an important role. However, with slope variation, the mechanism of its effects on the failure of rock landslides is not dear. Here, from the viewpoint of fracture mechanics, and based on post-earthquake conditions, the mechanisms of crack propagation, water infiltration and development of the sliding surface were investigated. Then, according to the upper boundary theorem, the effects of water infiltrated into fractures on the stability of rock slopes were analyzed quantitatively. Finally, an example is presented to verify the theory. The results show that the propagation and coalescence of cracks and the lubrication of incipient sliding surfaces are the main causes of the failure of post-earthquake rock landslides in response to rainfall.展开更多
Investigations of the growth,interaction,and coalescence of cracks are important because they help to provide tools for the more realistic modeling of rock masses containing low persistence discontinuities and better ...Investigations of the growth,interaction,and coalescence of cracks are important because they help to provide tools for the more realistic modeling of rock masses containing low persistence discontinuities and better estimations of the strength and stiffness of a rock material.Understanding the coalescence mechanism is useful for justifying the mechanism of continental crustal deformation,evaluating the structural failure of slopes with rock bridges,and analyzing the stability of tunnels when a mode I or mix mode failure mechanism is involved.The evaluation of crack growth can provide valuable information about the mechanism for the formation of new geological structures,and the formation,evolution,and growth of faults.This paper reports the results of diametrical compression tests on rocklike disk-shaped specimens.Each specimen contained two pre-existing open or closed flaws.The growth,interaction,and coalescence of the pre-existing flaws were investigated both physically and numerically.A hybrid bonded particle-finite element system was used in the numerical simulation.The results of the physical and numerical studies were in good agreement.In particular,the induced crack patterns showed close agreement in the physical and numerical tests.Digital microscope image processing was used in the physical tests to study the dislocations along the initial flaws.It was shown that wing crack formation was responsible for the failure of the specimen when flaws were inclined with respect to the loading direction.The crack growth and linkage were shown to be affected by the friction between faces of the flaws.In addition,the slip distributions at the flaws surfaces were illustrated and examined to understand the crack propagation mechanism.The effects of the flaws on the disk failure loads were assessed both numerically and experimentally as well.展开更多
Radiation-induced helium bubbles are detrimental to the mechanical properties of metals, usually causing severe hardening and embrittlement. Hexagonal close-packed(HCP) α-Zr alloys are one of the primary structural m...Radiation-induced helium bubbles are detrimental to the mechanical properties of metals, usually causing severe hardening and embrittlement. Hexagonal close-packed(HCP) α-Zr alloys are one of the primary structural materials for nuclear applications, however, the effect of helium bubbles on their deformation and fracture behaviors still remains unexplored. Here, we found that ordered helium bubbles prefer to align along the basal plane in HCP α-Zr. Micro-scale in situ tensile tests revealed that helium bubbles less than 8 nm in size can increase the critical resolved shear stress of the prismatic slip. However, once the helium bubbles are larger than 8 nm, a bubble-softening effect happens due to a decrease in number density of helium bubbles and an increase in porosity. Once the Schmid factor of basal slip is considerably higher than prismatic slip, bubble coalescence along the basal plane becomes the major failure mode in helium-irradiated α-Zr.展开更多
The influence of hydrogen embrittlement on the fatigue behaviors of AISI 304 stainless steel is investigated. The fatigue endurance limits of the untreated and hydrogen-embrittled materials were almost the same at 400...The influence of hydrogen embrittlement on the fatigue behaviors of AISI 304 stainless steel is investigated. The fatigue endurance limits of the untreated and hydrogen-embrittled materials were almost the same at 400 MPa, and hydrogen embrittlement had little influence even though the sample contained about 8.1 times more hydrogen. Thus, the sensitivity of hydrogen gas in this material is very low. A surface crack initiation, growth, coalescence, and micro ridge model is proposed in this study. Slip line formation?⇒microcrack formation?⇒increases in the crack width, and blunting of the crack tip as it grows?⇒formation of many slip lines because of deformation in the shear direction?⇒growth of the crack in the shear direction, forming micro ridges, coalescence with adjacent cracks ⇒?continuous initiation, growth, coalescence, and ridge formation of surface cracks and specimen breakage.展开更多
The hydraulic fracturing operation is highly complex in fractured reservoirs.The fundamental key to a successful operation is processing and analysis of the propagation of hydraulic fracturing in a natural fracture ne...The hydraulic fracturing operation is highly complex in fractured reservoirs.The fundamental key to a successful operation is processing and analysis of the propagation of hydraulic fracturing in a natural fracture network.In this paper,the hydraulic fracturing process is evaluated in a fractured reservoir in southwest Iran.The developing process of induced fracture in a natural fracture network is analysed by the Distinct Element Method(DEM).After determining the fluid flow regime in the natural fractures of the reservoir,hydraulic fracturing is applied along different lengths of the reservoir and in each range,the production rate is checked.Fluid flow in natural fractures after the hydraulic fracturing operation is shown and evaluated in order to evaluate the induced fracture effectiveness in enhancing fluid flow regimes in the reservoir.The reverse suction phenomenon which causes changes in the fluid flow pattern in fractures and will thus affect the production rate is also studied in this paper.Fracture coalescence will cause the induction of natural fractures to hydraulically fracture without their intersection;this is one of the significant parameters in hydraulic fracturing in naturally fractured reservoirs which is also discussed in detail.This paper can present valuable information on fluid flow analysis before and after applying hydraulic fracturing in a fractured reservoir and solve some essential ambiguities in this area.展开更多
基金financial support for much of the early development of the AE analysis methods was provided by the U.S. Department of Energy (DOE) (Grant No. DE-FE0002760)
文摘Understanding microcracking near coalesced fracture generation is critically important for hydrocarbon and geothermal reservoir characterization as well as damage evaluation in civil engineering structures. Dense and sometimes random microcracking near coalesced fracture formation alters the mechanical properties of the nearby virgin material. Individual microcrack characterization is also significant in quantifying the material changes near the fracture faces （i.e. damage）. Acoustic emission （AE） monitoring and analysis provide unique information regarding the microcracking process temporally, and infor- mation concerning the source characterization of individual microcracks can be extracted. In this context, laboratory hydraulic fracture tests were carried out while monitoring the AEs from several piezoelectric transducers. In-depth post-processing of the AE event data was performed for the purpose of under- standing the individual source mechanisms. Several source characterization techniques including moment tensor inversion, event parametric analysis, and volumetric deformation analysis were adopted. Post-test fracture characterization through coring, slicing and micro-computed tomographic imaging was performed to determine the coalesced fracture location and structure. Distinct differences in fracture characteristics were found spatially in relation to the openhole injection interval. Individual microcrack AE analysis showed substantial energy reduction emanating spatially from the injection interval. It was quantitatively observed that the recorded AE signals provided sufficient information to generalize the damage radiating spatially away from the injection wellbore.
基金supported by The National Basic Research Program of China (also called 973 Program) (Grant No. 2008CB425802)the National Natural Science Foundation of China (Grant No. 40872181)
文摘Among the triggering factors of postearthquake bedrock landslides, rainfall plays an important role. However, with slope variation, the mechanism of its effects on the failure of rock landslides is not dear. Here, from the viewpoint of fracture mechanics, and based on post-earthquake conditions, the mechanisms of crack propagation, water infiltration and development of the sliding surface were investigated. Then, according to the upper boundary theorem, the effects of water infiltrated into fractures on the stability of rock slopes were analyzed quantitatively. Finally, an example is presented to verify the theory. The results show that the propagation and coalescence of cracks and the lubrication of incipient sliding surfaces are the main causes of the failure of post-earthquake rock landslides in response to rainfall.
文摘Investigations of the growth,interaction,and coalescence of cracks are important because they help to provide tools for the more realistic modeling of rock masses containing low persistence discontinuities and better estimations of the strength and stiffness of a rock material.Understanding the coalescence mechanism is useful for justifying the mechanism of continental crustal deformation,evaluating the structural failure of slopes with rock bridges,and analyzing the stability of tunnels when a mode I or mix mode failure mechanism is involved.The evaluation of crack growth can provide valuable information about the mechanism for the formation of new geological structures,and the formation,evolution,and growth of faults.This paper reports the results of diametrical compression tests on rocklike disk-shaped specimens.Each specimen contained two pre-existing open or closed flaws.The growth,interaction,and coalescence of the pre-existing flaws were investigated both physically and numerically.A hybrid bonded particle-finite element system was used in the numerical simulation.The results of the physical and numerical studies were in good agreement.In particular,the induced crack patterns showed close agreement in the physical and numerical tests.Digital microscope image processing was used in the physical tests to study the dislocations along the initial flaws.It was shown that wing crack formation was responsible for the failure of the specimen when flaws were inclined with respect to the loading direction.The crack growth and linkage were shown to be affected by the friction between faces of the flaws.In addition,the slip distributions at the flaws surfaces were illustrated and examined to understand the crack propagation mechanism.The effects of the flaws on the disk failure loads were assessed both numerically and experimentally as well.
基金supported financially by the National Key Research and Development Program of China (No. 2017YFB0702301)the National Natural Science Foundation of China (Nos. 51471128 and 51621063)+1 种基金the Innovation Project of Shannxi Province (No. 2017KTPT-12)111 Project of China (No. BP2018008)
文摘Radiation-induced helium bubbles are detrimental to the mechanical properties of metals, usually causing severe hardening and embrittlement. Hexagonal close-packed(HCP) α-Zr alloys are one of the primary structural materials for nuclear applications, however, the effect of helium bubbles on their deformation and fracture behaviors still remains unexplored. Here, we found that ordered helium bubbles prefer to align along the basal plane in HCP α-Zr. Micro-scale in situ tensile tests revealed that helium bubbles less than 8 nm in size can increase the critical resolved shear stress of the prismatic slip. However, once the helium bubbles are larger than 8 nm, a bubble-softening effect happens due to a decrease in number density of helium bubbles and an increase in porosity. Once the Schmid factor of basal slip is considerably higher than prismatic slip, bubble coalescence along the basal plane becomes the major failure mode in helium-irradiated α-Zr.
文摘The influence of hydrogen embrittlement on the fatigue behaviors of AISI 304 stainless steel is investigated. The fatigue endurance limits of the untreated and hydrogen-embrittled materials were almost the same at 400 MPa, and hydrogen embrittlement had little influence even though the sample contained about 8.1 times more hydrogen. Thus, the sensitivity of hydrogen gas in this material is very low. A surface crack initiation, growth, coalescence, and micro ridge model is proposed in this study. Slip line formation?⇒microcrack formation?⇒increases in the crack width, and blunting of the crack tip as it grows?⇒formation of many slip lines because of deformation in the shear direction?⇒growth of the crack in the shear direction, forming micro ridges, coalescence with adjacent cracks ⇒?continuous initiation, growth, coalescence, and ridge formation of surface cracks and specimen breakage.
文摘The hydraulic fracturing operation is highly complex in fractured reservoirs.The fundamental key to a successful operation is processing and analysis of the propagation of hydraulic fracturing in a natural fracture network.In this paper,the hydraulic fracturing process is evaluated in a fractured reservoir in southwest Iran.The developing process of induced fracture in a natural fracture network is analysed by the Distinct Element Method(DEM).After determining the fluid flow regime in the natural fractures of the reservoir,hydraulic fracturing is applied along different lengths of the reservoir and in each range,the production rate is checked.Fluid flow in natural fractures after the hydraulic fracturing operation is shown and evaluated in order to evaluate the induced fracture effectiveness in enhancing fluid flow regimes in the reservoir.The reverse suction phenomenon which causes changes in the fluid flow pattern in fractures and will thus affect the production rate is also studied in this paper.Fracture coalescence will cause the induction of natural fractures to hydraulically fracture without their intersection;this is one of the significant parameters in hydraulic fracturing in naturally fractured reservoirs which is also discussed in detail.This paper can present valuable information on fluid flow analysis before and after applying hydraulic fracturing in a fractured reservoir and solve some essential ambiguities in this area.
