By considering the effect of hydraulic pressure filled in wing crack and the connected part of main crack on the stress intensity factor at wing crack tip, a new wing crack model exerted by hydraulic pressure and far ...By considering the effect of hydraulic pressure filled in wing crack and the connected part of main crack on the stress intensity factor at wing crack tip, a new wing crack model exerted by hydraulic pressure and far field stresses was proposed. By introducing the equivalent crack length lcq of wing crack, two terms make up the stress intensity factor K1 at wing crack tip： one is the component K（1） for a single isolated straight wing crack of length 2l subjected to hydraulic pressure in wing crack and far field stresses, and the other is the component K1^（2） due to the effective shear stress induced by the presence of the equivalent main crack. The FEM model of wing crack propagation subjected to hydraulic pressure and far field stresses was also established according to different side pressure coefficients and hydraulic pressures in crack. The result shows that a good agreement is found between theoretical model of wing crack proposed and finite element method （FEM）. In theory, an unstable crack propagation is shown if there is high hydraulic pressure and lateral tension. The wing crack model proposed can provide references for studying on hydraulic fracturing in rock masses.展开更多
Switching expansion reduction(SER)uses a switch valve instead of the throttle valve to realize electronically controlled pressure reduction for high pressure pneumatics.A comprehensive and interactive pneumatic simula...Switching expansion reduction(SER)uses a switch valve instead of the throttle valve to realize electronically controlled pressure reduction for high pressure pneumatics.A comprehensive and interactive pneumatic simulation model according to the experimental setup of SER has been built.The mathematical model considers heat exchanges,source air pressure and temperature,environmental temperatures and heat transfer coefficients variations.In addition,the compensation for real gas effect is used in the model building.The comparison between experiments and simulations of SER indicates that,to compensate the real gas effect in high pressure discharging process,the thermal capacity of air supply container in simulation should be less than the actual value.The higher the pressure range,the greater the deviation.Simulated and experimental results are highly consistent within pressure reduction ratios ranging from 1.4 to 20 and output air mass flow rates ranging from 3.5 to 132 g/s,which verifies the high adaptability of SER and the validity of the mathematic model and the compensation method.展开更多
The high-flowing sand-concrete （HFSC） containing natural sands as aggregate was carried out. The high fluidity and stability of HFSC can be achieved by tailoring the mix design parameters, such as fine to coarse san...The high-flowing sand-concrete （HFSC） containing natural sands as aggregate was carried out. The high fluidity and stability of HFSC can be achieved by tailoring the mix design parameters, such as fine to coarse sand ratio, dosage of additions, water to binder ratio and dosage of admixtures. Mini-cone slump test, v-fl.mnel time test and viscosity model parameters were used to characterize the behaviour of HFSC in fresh state. The mechanical compressive strength in 28 d was also determined. A factorial design approach was used to establish models highlighting the effect of each mix-parameter on measured properties of HFSC. The derived models are valid for mixtures made with 0 to 0.3 of dune sand to total sand ratio, 82 to 418 kg/m3 of marble powder, 0.42 to 0.46 of water/binder ratio and 1.3% to 1.9% of superplasticizer high water-reducer. The results show that the derived models constitute very efficient means for understanding the influence of key mix-parameters on HFSC properties and are useful in selecting the optimum mix proportions, by simulating their impact on fluidity, stability and compressive strength.展开更多
基金Projects(10972238,51074071,50974059)supported by the National Natural Science Foundation of ChinaProject(10JJ3007)supported by the Natural Science Foundation of Hunan Province,China+1 种基金Project(11C0539)supported by Scientific Research Fund of Hunan Provincial Education Department,ChinaProject(200905)supported by Open Research Fund of Hunan Provincial Key of Safe Mining Techniques of Coal Mines,China
文摘By considering the effect of hydraulic pressure filled in wing crack and the connected part of main crack on the stress intensity factor at wing crack tip, a new wing crack model exerted by hydraulic pressure and far field stresses was proposed. By introducing the equivalent crack length lcq of wing crack, two terms make up the stress intensity factor K1 at wing crack tip： one is the component K（1） for a single isolated straight wing crack of length 2l subjected to hydraulic pressure in wing crack and far field stresses, and the other is the component K1^（2） due to the effective shear stress induced by the presence of the equivalent main crack. The FEM model of wing crack propagation subjected to hydraulic pressure and far field stresses was also established according to different side pressure coefficients and hydraulic pressures in crack. The result shows that a good agreement is found between theoretical model of wing crack proposed and finite element method （FEM）. In theory, an unstable crack propagation is shown if there is high hydraulic pressure and lateral tension. The wing crack model proposed can provide references for studying on hydraulic fracturing in rock masses.
基金Project(51205421)supported by the National Natural Science Foundation of ChinaProject(2012M521647)supported by the Postdoctoral Science Foundation of China
文摘Switching expansion reduction(SER)uses a switch valve instead of the throttle valve to realize electronically controlled pressure reduction for high pressure pneumatics.A comprehensive and interactive pneumatic simulation model according to the experimental setup of SER has been built.The mathematical model considers heat exchanges,source air pressure and temperature,environmental temperatures and heat transfer coefficients variations.In addition,the compensation for real gas effect is used in the model building.The comparison between experiments and simulations of SER indicates that,to compensate the real gas effect in high pressure discharging process,the thermal capacity of air supply container in simulation should be less than the actual value.The higher the pressure range,the greater the deviation.Simulated and experimental results are highly consistent within pressure reduction ratios ranging from 1.4 to 20 and output air mass flow rates ranging from 3.5 to 132 g/s,which verifies the high adaptability of SER and the validity of the mathematic model and the compensation method.
文摘The high-flowing sand-concrete （HFSC） containing natural sands as aggregate was carried out. The high fluidity and stability of HFSC can be achieved by tailoring the mix design parameters, such as fine to coarse sand ratio, dosage of additions, water to binder ratio and dosage of admixtures. Mini-cone slump test, v-fl.mnel time test and viscosity model parameters were used to characterize the behaviour of HFSC in fresh state. The mechanical compressive strength in 28 d was also determined. A factorial design approach was used to establish models highlighting the effect of each mix-parameter on measured properties of HFSC. The derived models are valid for mixtures made with 0 to 0.3 of dune sand to total sand ratio, 82 to 418 kg/m3 of marble powder, 0.42 to 0.46 of water/binder ratio and 1.3% to 1.9% of superplasticizer high water-reducer. The results show that the derived models constitute very efficient means for understanding the influence of key mix-parameters on HFSC properties and are useful in selecting the optimum mix proportions, by simulating their impact on fluidity, stability and compressive strength.
