The high temperature split Hopkinson pressure bar （SHPB） compression experiment is conducted to obtain the data relationship among strain, strain rate and flow stress from room temperature to 550 C for aeronautical ...The high temperature split Hopkinson pressure bar （SHPB） compression experiment is conducted to obtain the data relationship among strain, strain rate and flow stress from room temperature to 550 C for aeronautical aluminum alloy 7050-T7451. Combined high-speed orthogonal cutting experiments with the cutting process simulations, the data relationship of high temperature, high strain rate and large strain in high-speed cutting is modified. The Johnson-Cook empirical model considering the effects of strain hardening, strain rate hardening and thermal softening is selected to describe the data relationship in high-speed cutting, and the material constants of flow stress constitutive model for aluminum alloy 7050-T7451 are determined. Finally, the constitutive model of aluminum alloy 7050-T7451 is established through experiment and simulation verification in high-speed cutting. The model is proved to be reasonable by matching the measured values of the cutting force with the estimated results from FEM simulations.展开更多
Pressure oscillation in solid rocket motor is believed to be the results of the interaction between the flow instability and the acoustics of combustion chamber.Several reasonable and necessary hypothesizes are given ...Pressure oscillation in solid rocket motor is believed to be the results of the interaction between the flow instability and the acoustics of combustion chamber.Several reasonable and necessary hypothesizes are given to establish an equation to describe this coupling.A cold flow motor called CVS60D(corner vortex shedding 60°)was designed to study the flow-acoustic coupling based on theoretical analysis.Experimental investigations were carried out to determine the acoustics of CVS60D.Corner vortex shedding is generated at the backward facing step which is designed similar to the geometry of the motor with finocyl propellant after the burnout of its fins.A pintle was used to modify the velocity in the duct to change the frequency of vortex shedding.It is found that large amplitude pressure oscillation occurs when the pintle moves to a range of specific position,which indicates that the frequency of vortex shedding is close to one order of acoustic modes of combustion chamber.The amplitude of pressure oscillation changes as the pintle moves.展开更多
Low-speed flow experiments in which ultra-fine copper tubes are used to simulate micro-fractures in carbonate strata are conducted to analyze the variations of gas flow state in fractures of different fracture heights...Low-speed flow experiments in which ultra-fine copper tubes are used to simulate micro-fractures in carbonate strata are conducted to analyze the variations of gas flow state in fractures of different fracture heights,determine flow state transition limit and transition interval,and establish the calculation method of flow state transition limit.The results show that the ideal Hagen-Poiseuille flow is the main form of gas flow in large fractures.Due to the decrease of fracture height,the gas flow in the fracture changes from Hagen-Poiseuille flow with ideal smooth seam surface to non-Hagen-Poiseuille flow,and the critical point of the transition is the boundary of flow state transition.After the fracture height continues to decrease to a certain extent below the boundary of the flow state transition fracture height,the form of gas flow gradually changes to the ideal Darcy flow,thus the transition interval of the gas flow state in the closing process of fracture can be determined.Based on the three-dimensional microconvex body scanning of the fracture surface,the material properties of fracture and properties of fluid in the fracture,a method for calculating the boundary of flow state transition is established.The experimental test and theoretical calculation show that the limit of the fracture height for the transition from pipe flow to Darcy flow is about twice the sum of the maximum height of the microconvex bodies on the upper and lower sides of the fracture.展开更多
文摘The high temperature split Hopkinson pressure bar （SHPB） compression experiment is conducted to obtain the data relationship among strain, strain rate and flow stress from room temperature to 550 C for aeronautical aluminum alloy 7050-T7451. Combined high-speed orthogonal cutting experiments with the cutting process simulations, the data relationship of high temperature, high strain rate and large strain in high-speed cutting is modified. The Johnson-Cook empirical model considering the effects of strain hardening, strain rate hardening and thermal softening is selected to describe the data relationship in high-speed cutting, and the material constants of flow stress constitutive model for aluminum alloy 7050-T7451 are determined. Finally, the constitutive model of aluminum alloy 7050-T7451 is established through experiment and simulation verification in high-speed cutting. The model is proved to be reasonable by matching the measured values of the cutting force with the estimated results from FEM simulations.
基金Sponsored by the National Nature Science Foundation of China(10602047)
文摘Pressure oscillation in solid rocket motor is believed to be the results of the interaction between the flow instability and the acoustics of combustion chamber.Several reasonable and necessary hypothesizes are given to establish an equation to describe this coupling.A cold flow motor called CVS60D(corner vortex shedding 60°)was designed to study the flow-acoustic coupling based on theoretical analysis.Experimental investigations were carried out to determine the acoustics of CVS60D.Corner vortex shedding is generated at the backward facing step which is designed similar to the geometry of the motor with finocyl propellant after the burnout of its fins.A pintle was used to modify the velocity in the duct to change the frequency of vortex shedding.It is found that large amplitude pressure oscillation occurs when the pintle moves to a range of specific position,which indicates that the frequency of vortex shedding is close to one order of acoustic modes of combustion chamber.The amplitude of pressure oscillation changes as the pintle moves.
基金Supported by the Science and Technology Cooperation Project of the CNPC-SWPU Innovation Alliance(2020CX010401)。
文摘Low-speed flow experiments in which ultra-fine copper tubes are used to simulate micro-fractures in carbonate strata are conducted to analyze the variations of gas flow state in fractures of different fracture heights,determine flow state transition limit and transition interval,and establish the calculation method of flow state transition limit.The results show that the ideal Hagen-Poiseuille flow is the main form of gas flow in large fractures.Due to the decrease of fracture height,the gas flow in the fracture changes from Hagen-Poiseuille flow with ideal smooth seam surface to non-Hagen-Poiseuille flow,and the critical point of the transition is the boundary of flow state transition.After the fracture height continues to decrease to a certain extent below the boundary of the flow state transition fracture height,the form of gas flow gradually changes to the ideal Darcy flow,thus the transition interval of the gas flow state in the closing process of fracture can be determined.Based on the three-dimensional microconvex body scanning of the fracture surface,the material properties of fracture and properties of fluid in the fracture,a method for calculating the boundary of flow state transition is established.The experimental test and theoretical calculation show that the limit of the fracture height for the transition from pipe flow to Darcy flow is about twice the sum of the maximum height of the microconvex bodies on the upper and lower sides of the fracture.
