2008 Vol. 28, No. 4
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2008, 28(4): 289-292.
doi: 10.11883/1001-1455(2008)04-0289-04
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Abstract:
Deformation and mechanical property of aluminium foams with lower densities were experimentally studied at different strain rates. Results show as follows: (1) the deformation characteristic of Al foams at a lower strain rate presents an initial crushing down of the cell support along shear direction (localized deformation); (2) the volume strain of Al alloy foams varies linearly with the engineering strain, Poissons ratio increases exponentially with strain at lower strain rates, but at higher strain rates, Poissons ratio first decreases, then keeps about 0.1; (3) at lower strain rates, the deformation of Al alloy foams is more uniform than that at high strain rates, but at higher strain rates, there is greater shearing deformation accompanying the high strain-rate deformations; (4) Al foam shows lower strain-rate dependence at the room temperature when strain is below about 0.4.
Deformation and mechanical property of aluminium foams with lower densities were experimentally studied at different strain rates. Results show as follows: (1) the deformation characteristic of Al foams at a lower strain rate presents an initial crushing down of the cell support along shear direction (localized deformation); (2) the volume strain of Al alloy foams varies linearly with the engineering strain, Poissons ratio increases exponentially with strain at lower strain rates, but at higher strain rates, Poissons ratio first decreases, then keeps about 0.1; (3) at lower strain rates, the deformation of Al alloy foams is more uniform than that at high strain rates, but at higher strain rates, there is greater shearing deformation accompanying the high strain-rate deformations; (4) Al foam shows lower strain-rate dependence at the room temperature when strain is below about 0.4.
2008, 28(4): 293-297.
doi: 10.11883/1001-1455(2008)04-0293-05
Abstract:
The transition processes of supersonic combustion in a dual-mode scramjet were investigated by means of directly-connected tests under the simulated conditions corresponding to the flying altitude of 25 km and the Mach number of 6. Pressure distribution on the wall of the combustor and one-dimensional simulation indicate that the combustion mode transition can be carried out by altering fuel injection position and equivalence ratio. Comparison of switch sequences of different fuel-injection position shows that the combustion mode changes are determined by the fuel distribution in a combustor, but the combustor has a certain ability to resist fuel disturbance.
The transition processes of supersonic combustion in a dual-mode scramjet were investigated by means of directly-connected tests under the simulated conditions corresponding to the flying altitude of 25 km and the Mach number of 6. Pressure distribution on the wall of the combustor and one-dimensional simulation indicate that the combustion mode transition can be carried out by altering fuel injection position and equivalence ratio. Comparison of switch sequences of different fuel-injection position shows that the combustion mode changes are determined by the fuel distribution in a combustor, but the combustor has a certain ability to resist fuel disturbance.
2008, 28(4): 298-303.
doi: 10.11883/1001-1455(2008)04-0298-06
Abstract:
This paper briefly reports our recent progresses in the analytical and numerical studies on the dynamic fragmentation of brittle materials. The research renders a universal function for estimating the fragment size from the material parameters and the external strain rate. The curve of this function is plotted against the popular energy models, which was firstly presented by Grady and later modified by Glenn and Chudnovsky, to show the differences. Comparisons with other numerical results and the experimental data show that the present model is more reasonable. Based on the theoretical analysis, we discuss further on the design and conduction of the experiments which are aimed to study the brittle fragmentation phenomenon.
This paper briefly reports our recent progresses in the analytical and numerical studies on the dynamic fragmentation of brittle materials. The research renders a universal function for estimating the fragment size from the material parameters and the external strain rate. The curve of this function is plotted against the popular energy models, which was firstly presented by Grady and later modified by Glenn and Chudnovsky, to show the differences. Comparisons with other numerical results and the experimental data show that the present model is more reasonable. Based on the theoretical analysis, we discuss further on the design and conduction of the experiments which are aimed to study the brittle fragmentation phenomenon.
2008, 28(4): 304-309.
doi: 10.11883/1001-1455(2008)04-0304-06
Abstract:
Based on the exploding fracturing principle, an experimental device on rock fracturing was developed to study the rock cracking mechanism by pressure pulses. According to the laws of energy and momentum conservation, the calculation models of the peak pressure and the pressurization rate were presented, which were revised by the 16 times steel core experiments and the models precision were proved for the average relative deviations between the experimental results and the calculated results were 2.56% and 4.04% separately. The calculation models can guide the experiment. Thirty nine times experiments on rock cracking show that shock energy and pressurization rates are the main factors influencing the status of rock cracking and the foremost factor affecting the fracture number is the pressurization rate, which there is an apparent critical pressurization rate. The precise correlation of the fracture number was regressively analyzed by using the gray relational theory and the multivariate second-degree polynomial method on the experiment results. The study is important for the design and application of the explosive fracturing technology in the oil and gas field.
Based on the exploding fracturing principle, an experimental device on rock fracturing was developed to study the rock cracking mechanism by pressure pulses. According to the laws of energy and momentum conservation, the calculation models of the peak pressure and the pressurization rate were presented, which were revised by the 16 times steel core experiments and the models precision were proved for the average relative deviations between the experimental results and the calculated results were 2.56% and 4.04% separately. The calculation models can guide the experiment. Thirty nine times experiments on rock cracking show that shock energy and pressurization rates are the main factors influencing the status of rock cracking and the foremost factor affecting the fracture number is the pressurization rate, which there is an apparent critical pressurization rate. The precise correlation of the fracture number was regressively analyzed by using the gray relational theory and the multivariate second-degree polynomial method on the experiment results. The study is important for the design and application of the explosive fracturing technology in the oil and gas field.
2008, 28(4): 310-315.
doi: 10.11883/1001-1455(2008)04-0310-06
Abstract:
In order to explore stress wave propagation and action of control holes for deep-hole blasting in coal seams, based on parameters of blasting, explosive and coal mass got from the Songzao coal and electricity company, a numerical simulation model of linear charge blasting in coal seams was built by means of 3D numerical simulation. The stress propagation feature and effective area of gas drainage by blasting action were analyzed in the soft coal bed with the control holes. The study indicate that the average effective stress in boundary of the control holes which are constructed before blasting is 48%~66% higher than that at the same location without control holes. With the increase of the distance between the blasting hole and control holes, effectives stress decreases in coal seams, but average stress ratio at the same locations with and without control holes increases. Simulated results are in agreement with the gas draining data got from the coal mine before and after blasting. It is necessary that the control hole is pre-arranged before detonation.
In order to explore stress wave propagation and action of control holes for deep-hole blasting in coal seams, based on parameters of blasting, explosive and coal mass got from the Songzao coal and electricity company, a numerical simulation model of linear charge blasting in coal seams was built by means of 3D numerical simulation. The stress propagation feature and effective area of gas drainage by blasting action were analyzed in the soft coal bed with the control holes. The study indicate that the average effective stress in boundary of the control holes which are constructed before blasting is 48%~66% higher than that at the same location without control holes. With the increase of the distance between the blasting hole and control holes, effectives stress decreases in coal seams, but average stress ratio at the same locations with and without control holes increases. Simulated results are in agreement with the gas draining data got from the coal mine before and after blasting. It is necessary that the control hole is pre-arranged before detonation.
2008, 28(4): 316-323.
doi: 10.11883/1001-1455(2008)04-0316-08
Abstract:
By theory and numerical simulation, influences of direction and location of defects on expanding fracture of a metal cylinder were analyzed and a new explanation was preasented by the microdefect methods. A computational model for the cylinder containing microdefects was adopted to explore influences of microdefects on expanding fracture of a metal cylinder. Computational results show that microdefects can quicken the radial extension of the cylinder and mutual impenetration of shear extensions. Analysis indicates that the experimental expanding fracture strain is different from the fracture strain as a material parameter offered to the computational program during rupture of the cylinder along its wall thickness directoion, and the two strains have a certain relation.
By theory and numerical simulation, influences of direction and location of defects on expanding fracture of a metal cylinder were analyzed and a new explanation was preasented by the microdefect methods. A computational model for the cylinder containing microdefects was adopted to explore influences of microdefects on expanding fracture of a metal cylinder. Computational results show that microdefects can quicken the radial extension of the cylinder and mutual impenetration of shear extensions. Analysis indicates that the experimental expanding fracture strain is different from the fracture strain as a material parameter offered to the computational program during rupture of the cylinder along its wall thickness directoion, and the two strains have a certain relation.
2008, 28(4): 324-330.
doi: 10.11883/1001-1455(2008)04-0324-07
Abstract:
The dynamic responses of discrete multilayered wound ribbon vessels(DMWRV) subjected to internal explosion loading were numerically simulated by using LS-DYNA3D. Several kinds of winding angles were considered. The simulated results were compared with the experimental results, theoretical analysis and numerical results of a monobloc thick-walled high-pressure vessel. Compared results indicate the following: (1) the stress distribution in the ribbon layers of DMWRV is homogeneous; (2) the bigger the winding angle is, the bigger the final displacement of the outermost layer is subjected to the same TNT; (3) the DMWRV has excellent property of leak before burst at worst, which is impossible for the monobloc thick-walled high pressure vessel. Simulated results are helpful to establish the engineering design criteria of the explosion containment vessels.
The dynamic responses of discrete multilayered wound ribbon vessels(DMWRV) subjected to internal explosion loading were numerically simulated by using LS-DYNA3D. Several kinds of winding angles were considered. The simulated results were compared with the experimental results, theoretical analysis and numerical results of a monobloc thick-walled high-pressure vessel. Compared results indicate the following: (1) the stress distribution in the ribbon layers of DMWRV is homogeneous; (2) the bigger the winding angle is, the bigger the final displacement of the outermost layer is subjected to the same TNT; (3) the DMWRV has excellent property of leak before burst at worst, which is impossible for the monobloc thick-walled high pressure vessel. Simulated results are helpful to establish the engineering design criteria of the explosion containment vessels.
2008, 28(4): 331-335.
doi: 10.11883/1001-1455(2008)04-0331-05
Abstract:
The response spectrum theory widely applied in earthquake engineering was employed to investigate blasting seismic waves induced by tunnel excavation. After numerical differential calculating for blasting vibration velocity data, an original acceleration wave curve involving with high-frequency noises was obtained. When the high-frequency noise was cleared up by wavelet transform, an accurate and clear blasting vibration acceleration curve was obtained. And then the acceleration data were used to calculate the response spectrum of blasting vibration. Response spectrum analysis of blasting vibration induced by tunnel excavation was performed with a vast amount of monitoring data in diferent projects. The result shows that response spectrum of blasting vibration induced by tunnel excavation has some same charactors. Response spectrum curves generally have a distinct peak point. At the peak point, the period is less than 100 ms. In addition, based on coordinating and suming up a great deal of response spectrum curves induced by tunnel excavation, the design response spectrum curves were presented. This research can provide a guide for studying the blasting seismic effect.
The response spectrum theory widely applied in earthquake engineering was employed to investigate blasting seismic waves induced by tunnel excavation. After numerical differential calculating for blasting vibration velocity data, an original acceleration wave curve involving with high-frequency noises was obtained. When the high-frequency noise was cleared up by wavelet transform, an accurate and clear blasting vibration acceleration curve was obtained. And then the acceleration data were used to calculate the response spectrum of blasting vibration. Response spectrum analysis of blasting vibration induced by tunnel excavation was performed with a vast amount of monitoring data in diferent projects. The result shows that response spectrum of blasting vibration induced by tunnel excavation has some same charactors. Response spectrum curves generally have a distinct peak point. At the peak point, the period is less than 100 ms. In addition, based on coordinating and suming up a great deal of response spectrum curves induced by tunnel excavation, the design response spectrum curves were presented. This research can provide a guide for studying the blasting seismic effect.
2008, 28(4): 336-340.
doi: 10.11883/1001-1455(2008)04-0336-05
Abstract:
In this paper, we analyze the metallographes of the recovered Cu slug and get the results of reduction in the recrystallized grain size and rise in the temperature, which were caused by the two action processes, i.e. the shock wave action in the liner and the following squeeze-shear plastic deformation of the liner. The analysed result shows that the dynamic superplastic deformation conditions for liner materials were satisfied before the jet was formed. Meanwhile the process of a dynamic superplastics deformation is consistent with a mechanically driven subgrain rotation mechanism.
In this paper, we analyze the metallographes of the recovered Cu slug and get the results of reduction in the recrystallized grain size and rise in the temperature, which were caused by the two action processes, i.e. the shock wave action in the liner and the following squeeze-shear plastic deformation of the liner. The analysed result shows that the dynamic superplastic deformation conditions for liner materials were satisfied before the jet was formed. Meanwhile the process of a dynamic superplastics deformation is consistent with a mechanically driven subgrain rotation mechanism.
2008, 28(4): 341-349.
doi: 10.11883/1001-1455(2008)04-0341-09
Abstract:
The present paper discusses the influence of different interaction of steel bars and concrete in LS-DYNA code on the perforation of reinforced concrete. Numerical simulations on the experiments by Hanchak S J, et al, are conducted and redisplay the deformation and failure of projectiles and reinforced concretes. Also this paper analyzes the effect of impact location of reinforced concrete on the terminal ballistic performance. The proposed numerical simulation methods may be further employed to discuss the structure, mesh size and area density of reinforcing bars on the perforation of reinforced concrete.
The present paper discusses the influence of different interaction of steel bars and concrete in LS-DYNA code on the perforation of reinforced concrete. Numerical simulations on the experiments by Hanchak S J, et al, are conducted and redisplay the deformation and failure of projectiles and reinforced concretes. Also this paper analyzes the effect of impact location of reinforced concrete on the terminal ballistic performance. The proposed numerical simulation methods may be further employed to discuss the structure, mesh size and area density of reinforcing bars on the perforation of reinforced concrete.
2008, 28(4): 350-354.
doi: 10.11883/1001-1455(2008)04-0350-05
Abstract:
A new method of coating another metals at the interfaces of amorphous foils before explosive welding was propsoed to explore the influences of coating materials on temperature of amorphous foils during explosive welding. The coated amorphous foils were simplified as homogeneous materials by scaling the heat-conduction coefficient to analyze the temperature field at the explosive welding interfaces of the uncaoted and coated Fe78B13Si9 amorphous foils with the thickness of 30 m. Combined with the square wave model of the temperature field, a one-dimensional heat-conduction equation was developed and the initial and boundary conditions were obtained. Comparisons of the temperature distributing curves show as follows: (1) in the coated system, the energy of plastic collision is concentrated in the coating layer and the heat-affected zone can be remarkably minimized; (2) the average temperature rise in the coated systems is about 280 K lower than that in the uncoated system; (3) the cooling rate after plating copper is up to 107 K/s. Researched results indicate that the Fe-based bulk metallic glasses in the coated amorphous foils can be protected and the explosive welding windows are effectively enlarged.
A new method of coating another metals at the interfaces of amorphous foils before explosive welding was propsoed to explore the influences of coating materials on temperature of amorphous foils during explosive welding. The coated amorphous foils were simplified as homogeneous materials by scaling the heat-conduction coefficient to analyze the temperature field at the explosive welding interfaces of the uncaoted and coated Fe78B13Si9 amorphous foils with the thickness of 30 m. Combined with the square wave model of the temperature field, a one-dimensional heat-conduction equation was developed and the initial and boundary conditions were obtained. Comparisons of the temperature distributing curves show as follows: (1) in the coated system, the energy of plastic collision is concentrated in the coating layer and the heat-affected zone can be remarkably minimized; (2) the average temperature rise in the coated systems is about 280 K lower than that in the uncoated system; (3) the cooling rate after plating copper is up to 107 K/s. Researched results indicate that the Fe-based bulk metallic glasses in the coated amorphous foils can be protected and the explosive welding windows are effectively enlarged.
2008, 28(4): 355-359.
doi: 10.11883/1001-1455(2008)04-0355-05
Abstract:
Pre-splitting blasting is often used in slope engineering construction, pre-splitting parameters have important effects on reducing blasting vibrations. Pre-splitting blasting experiments were carried out to obtain normal pre-splitting blasting parameters such as hole diameter, hole space, gunpowder charge line density, and uncoupling factor. Ideal pre-splitting blasting parameters for four different hole diameters gained by the code ANSYS/LS-DYNA agree with the blasting experiments. By regression analysis, a simple fomula was given to choose the pre-splitting blasting parameters and to guide the succedent construction. Practice shows that combination of blasting experiments and numerical simulations is helpful to optimize pre-splitting blasting parameters.
Pre-splitting blasting is often used in slope engineering construction, pre-splitting parameters have important effects on reducing blasting vibrations. Pre-splitting blasting experiments were carried out to obtain normal pre-splitting blasting parameters such as hole diameter, hole space, gunpowder charge line density, and uncoupling factor. Ideal pre-splitting blasting parameters for four different hole diameters gained by the code ANSYS/LS-DYNA agree with the blasting experiments. By regression analysis, a simple fomula was given to choose the pre-splitting blasting parameters and to guide the succedent construction. Practice shows that combination of blasting experiments and numerical simulations is helpful to optimize pre-splitting blasting parameters.
2008, 28(4): 360-366.
doi: 10.1188/1001-1455(2008)04-0360-07
Abstract:
Dynamical responses of a cabin model under far-field underwater explosion load were experimentally measured and theortically analyzed. The scale model was designed by referring to a representive cabin of naval ships and was used to assess the shock response of common hull steel models. The shock motions of the model were recorded by the accelerometers mounted on the model bulkheads and deck plate. The geometry characteristics of the charge and model and the disposals of the accelerometers were presented. Researched results are helpful to the future model experiments.
Dynamical responses of a cabin model under far-field underwater explosion load were experimentally measured and theortically analyzed. The scale model was designed by referring to a representive cabin of naval ships and was used to assess the shock response of common hull steel models. The shock motions of the model were recorded by the accelerometers mounted on the model bulkheads and deck plate. The geometry characteristics of the charge and model and the disposals of the accelerometers were presented. Researched results are helpful to the future model experiments.
2008, 28(4): 367-371.
doi: 10.11883/1001-1455(2008)04-0367-05
Abstract:
The dynamic mechanical properties of dry and water-saturated fast-growing poplar wood under dynamic compression was investigated by the split Hopkinson bar techanique and compared with the quasi-static compression experiment. The failure mechanism of the poplar wood discussed at high strain rates. Results show the following characters: (1) the compressive stress-strain curves of poplar wood are similar to those of other cellular solids which are characterized by three distinct region: elastic region, collapse region and densification region; (2) the fibers of the dry poplar samples after shock occur local bucking and collapse, but the fiber bundles of the water-saturated poplar samples detach along the grain direction due to the water in the cellular lumens which is incompressible and can not be extruded at high strain rates. (3) the strain rate effect of the poplar wood is evident.
The dynamic mechanical properties of dry and water-saturated fast-growing poplar wood under dynamic compression was investigated by the split Hopkinson bar techanique and compared with the quasi-static compression experiment. The failure mechanism of the poplar wood discussed at high strain rates. Results show the following characters: (1) the compressive stress-strain curves of poplar wood are similar to those of other cellular solids which are characterized by three distinct region: elastic region, collapse region and densification region; (2) the fibers of the dry poplar samples after shock occur local bucking and collapse, but the fiber bundles of the water-saturated poplar samples detach along the grain direction due to the water in the cellular lumens which is incompressible and can not be extruded at high strain rates. (3) the strain rate effect of the poplar wood is evident.
2008, 28(4): 372-377.
doi: 10.11883/1001-1455(2008)04-0372-06
Abstract:
The paper presents a new explosion vessel which is used for the recovery of warhead fragments. The vessel contains some water in its bottom and there is some knock-down bombproof material to resist the bomb fragments. The bombproof material can be used repeatedly, realizes effective recovery of fragments. Recovered fragments can reflect really the blast-fragmentation warhead when the projectle explodes. The explosion tests are carried out in the vessel to explore the characteristic of fragments. It approves that it is feasible to use the vessel in the warhead fragmentized tests.
The paper presents a new explosion vessel which is used for the recovery of warhead fragments. The vessel contains some water in its bottom and there is some knock-down bombproof material to resist the bomb fragments. The bombproof material can be used repeatedly, realizes effective recovery of fragments. Recovered fragments can reflect really the blast-fragmentation warhead when the projectle explodes. The explosion tests are carried out in the vessel to explore the characteristic of fragments. It approves that it is feasible to use the vessel in the warhead fragmentized tests.
2008, 28(4): 378-383.
doi: 10.11883/1001-1455(2008)04-0378-06
Abstract:
Based on ideal detonation and rigid body kinematics, a new model was proposed to explore the movement law of a controllable rotation discrete rod. Movement states of the rods with different dimensions and different leaning angles were analyzed and compared with the experimental results.Comparisons show that the proposed model can discribe the motion states of the controllable rotation discrete rods and provide a refer for the design of the warhead with a controllable rotation discrete rod.
Based on ideal detonation and rigid body kinematics, a new model was proposed to explore the movement law of a controllable rotation discrete rod. Movement states of the rods with different dimensions and different leaning angles were analyzed and compared with the experimental results.Comparisons show that the proposed model can discribe the motion states of the controllable rotation discrete rods and provide a refer for the design of the warhead with a controllable rotation discrete rod.
