2018 Vol. 38, No. 2
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2018, 38(2): 241-249.
doi: 10.11883/bzycj-2016-0238
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In this study we conducted an experiment on the jetting flow induced by underwater wire explosion at an interface with a quasi-static hemispherical pit, in which the interfacial pit was created by the dripping of a liquid drop. Further, using high-speed video photography and Fluent numerical simulation, we revealed the development and features of the jetting flow, tested and verified the applicability of the pit creation method. The experimental results show that the explosion induces a slim and smooth central jet that arises from the bottom of a pit, and a circular side jet arises from the boundary region of the tube, which differs from the known jetting phenomenon without a pit at the surface. Further study reveals the central jet is a result of the energy concentration effect of the pit under impact and the circular side jet is caused by a combined effect of the disturbed initial interface and the friction of the tube wall. Both jets rise with an early constant velocity after a short acceleration process. Examination of the explosion energy indicates that the velocities of the two jets increase linearly with the charging voltage (or equivalently the square root of the explosion energy).The explosion energy barely affects the general feature of the central jet but has a significant influence on the appearance of the side jet.
In this study we conducted an experiment on the jetting flow induced by underwater wire explosion at an interface with a quasi-static hemispherical pit, in which the interfacial pit was created by the dripping of a liquid drop. Further, using high-speed video photography and Fluent numerical simulation, we revealed the development and features of the jetting flow, tested and verified the applicability of the pit creation method. The experimental results show that the explosion induces a slim and smooth central jet that arises from the bottom of a pit, and a circular side jet arises from the boundary region of the tube, which differs from the known jetting phenomenon without a pit at the surface. Further study reveals the central jet is a result of the energy concentration effect of the pit under impact and the circular side jet is caused by a combined effect of the disturbed initial interface and the friction of the tube wall. Both jets rise with an early constant velocity after a short acceleration process. Examination of the explosion energy indicates that the velocities of the two jets increase linearly with the charging voltage (or equivalently the square root of the explosion energy).The explosion energy barely affects the general feature of the central jet but has a significant influence on the appearance of the side jet.
2018, 38(2): 250-257.
doi: 10.11883/bzycj-2017-0198
Abstract:
As the impact velocity increases, the penetration mechanism varies from rigid penetration to semi-liquid penetration and fluid penetration, each of which follows a wholly different analytical model. In the semi-liquid penetration stage, the mass loss of the projectile body begins to increase obviously, leading to serious decrease of the penetration efficiency and the penetration depth at the increase of the impact velocity. The intrinsic analytical model of rigid penetration was deducted by analysis of the real deformation and stress states of different damage zones. Based on the proposed relationship between penetration and velocity, we established the equation of penetration depth in account of the projectile mass loss, proposed the hypothesis of fluid and rigid region of fluid penetration under hypervelocity impact and, by adopting the laws of conservation of momentum and Bernoulli equation, presented the formulas for penetration resistance, and deduced the corresponding equations of penetration depth using the relational expression of the projectile mass loss. By comparison of the result of calculation with experimental data of penetration into granite, we proved the reliability of the formulas for the three stages, showing them in good compatibility in penetration depth and mass loss of the projectile with each other, and verifying a full agreement between their variation and experimental results.
As the impact velocity increases, the penetration mechanism varies from rigid penetration to semi-liquid penetration and fluid penetration, each of which follows a wholly different analytical model. In the semi-liquid penetration stage, the mass loss of the projectile body begins to increase obviously, leading to serious decrease of the penetration efficiency and the penetration depth at the increase of the impact velocity. The intrinsic analytical model of rigid penetration was deducted by analysis of the real deformation and stress states of different damage zones. Based on the proposed relationship between penetration and velocity, we established the equation of penetration depth in account of the projectile mass loss, proposed the hypothesis of fluid and rigid region of fluid penetration under hypervelocity impact and, by adopting the laws of conservation of momentum and Bernoulli equation, presented the formulas for penetration resistance, and deduced the corresponding equations of penetration depth using the relational expression of the projectile mass loss. By comparison of the result of calculation with experimental data of penetration into granite, we proved the reliability of the formulas for the three stages, showing them in good compatibility in penetration depth and mass loss of the projectile with each other, and verifying a full agreement between their variation and experimental results.
2018, 38(2): 258-265.
doi: 10.11883/bzycj-2017-0019
Abstract:
This paper presents a novel method for directly measuring material strength under dynamic loading, namely the technique of magnetically applied pressure shear (MAPS). The relationship between the stress deviation and the yield strength under MAPS was analyzed theoretically and numerically. The time-space evolutions of the stress deviation and yield strength under MAPS were characterized and calculated. Experiments were conducted based on the CQ-4 and 10 T quasi-static magnetic field generator, both developed by ourselves, using a dual laser heterodyne velocimetry (DLHV), to study the technology of MAPS under ramp wave loadings. The compression strengths of cold rolled pure aluminum and polished pure aluminum under ramp loading were measured and the reliable experimental data were obtained. The results show that the technique of MAPS provides a novel and reliable technique for directly measuring high-pressure strength and can be reliably applied
This paper presents a novel method for directly measuring material strength under dynamic loading, namely the technique of magnetically applied pressure shear (MAPS). The relationship between the stress deviation and the yield strength under MAPS was analyzed theoretically and numerically. The time-space evolutions of the stress deviation and yield strength under MAPS were characterized and calculated. Experiments were conducted based on the CQ-4 and 10 T quasi-static magnetic field generator, both developed by ourselves, using a dual laser heterodyne velocimetry (DLHV), to study the technology of MAPS under ramp wave loadings. The compression strengths of cold rolled pure aluminum and polished pure aluminum under ramp loading were measured and the reliable experimental data were obtained. The results show that the technique of MAPS provides a novel and reliable technique for directly measuring high-pressure strength and can be reliably applied
2018, 38(2): 266-270.
doi: 10.11883/bzycj-2016-0252
Abstract:
In the present study we carried out the dynamic compression experiments of steel fiber reinforced concrete with the fiber volume ratios of 0%, 0.75% and 1.5% using the ∅75 mm large-diameter split Hopkinson pressure bar experimental system to obtain the stress-strain curves at different strain rates. The experimental results show that with the increase of the fiber content and the strain rate, both the peak strain and the peak stress of the steel reinforced concrete rise higher, and the strain softening is observed after the peak stress. Based on the assumption that there are two independent factors controlling the dynamic behavior of the steel fiber reinforced concrete, one related to the strain to indicate the nonlinear stress-strain behavior and the other related to the strain rate to express the strain rate effect, a new type of the dynamic nonlinear visco-plastic constitutive equation was proposed. The details concerning how to get the equation and the material parameters were discussed thoroughly. The experiment curves were fitted using the least squares optimization numerical simulations. Good agreement between the numerical simulations and the experiment curves was achieved, thereby concluding that the new constitutive relation proposed is perfect for steel fiber reinforced concrete.
In the present study we carried out the dynamic compression experiments of steel fiber reinforced concrete with the fiber volume ratios of 0%, 0.75% and 1.5% using the ∅75 mm large-diameter split Hopkinson pressure bar experimental system to obtain the stress-strain curves at different strain rates. The experimental results show that with the increase of the fiber content and the strain rate, both the peak strain and the peak stress of the steel reinforced concrete rise higher, and the strain softening is observed after the peak stress. Based on the assumption that there are two independent factors controlling the dynamic behavior of the steel fiber reinforced concrete, one related to the strain to indicate the nonlinear stress-strain behavior and the other related to the strain rate to express the strain rate effect, a new type of the dynamic nonlinear visco-plastic constitutive equation was proposed. The details concerning how to get the equation and the material parameters were discussed thoroughly. The experiment curves were fitted using the least squares optimization numerical simulations. Good agreement between the numerical simulations and the experiment curves was achieved, thereby concluding that the new constitutive relation proposed is perfect for steel fiber reinforced concrete.
2018, 38(2): 271-278.
doi: 10.11883/bzycj-2016-0216
Abstract:
In this paper we studied a pseudo arc-length method for high-precision and high-resolution calculation, a problem that has been a great challenge for numerical simulation of strong discontinuity for explosion shock wave. By the introduction of the arc-length parameters, the mesh will move adaptively and gather automatically in the strong discontinuity singular areas, which will help to improve the grid resolution. We wrote 2D programs based on theoretical work, and conducted the program verification using the man maufactured solution. Through error analysis and numerical results, it was demonstrated that this method was more efficient in improving the calculation accuracy than the finite volume method. Finally we applied the pseudo arc-length method to 2D gas detonation wave propagation problems and studied the capture effect in the wave front and the formation of detonation cellular structure.
In this paper we studied a pseudo arc-length method for high-precision and high-resolution calculation, a problem that has been a great challenge for numerical simulation of strong discontinuity for explosion shock wave. By the introduction of the arc-length parameters, the mesh will move adaptively and gather automatically in the strong discontinuity singular areas, which will help to improve the grid resolution. We wrote 2D programs based on theoretical work, and conducted the program verification using the man maufactured solution. Through error analysis and numerical results, it was demonstrated that this method was more efficient in improving the calculation accuracy than the finite volume method. Finally we applied the pseudo arc-length method to 2D gas detonation wave propagation problems and studied the capture effect in the wave front and the formation of detonation cellular structure.
2018, 38(2): 279-288.
doi: 10.11883/bzycj-2016-0224
Abstract:
The dynamic response of hybrid corrugated sandwich plates subjected to combined effects of blast and fragment loading was analyzed using finite element analysis code LS-DYNA. The effects of charge mass, loading type and filling strategy on deformation/failure pattern of hybrid corrugated sandwich plates were investigated. The comparison of anti combined loadings performance to three equivalent structures (solid plate, double-layered plate and corrugated sandwich plate) was made. Finally, the energy absorption characteristics of hybrid corrugated sandwich panels were discussed. Numerical results show that the damage extent of hybrid corrugated sandwich plates under bare fragment cluster loading or combined blast and fragment loading is more severe than that caused by bare blast loading. When the charge mass is small, the performances of corrugated sandwich plate and hybrid corrugated sandwich plate are superior to equivalent solid plate and double-layered plate. The corrugated sandwich panels with fully filling configuration possess the best damage resistance, followed by that with upper space filling configuration, and that with lower space filling configuration has the worst. All the structures fractured catastrophically when the charge mass is large. For energy absorption, the corrugated core is the main energy absorption part under bare blast loading, while the front face becomes the main energy absorption part under the other two loading conditions.
The dynamic response of hybrid corrugated sandwich plates subjected to combined effects of blast and fragment loading was analyzed using finite element analysis code LS-DYNA. The effects of charge mass, loading type and filling strategy on deformation/failure pattern of hybrid corrugated sandwich plates were investigated. The comparison of anti combined loadings performance to three equivalent structures (solid plate, double-layered plate and corrugated sandwich plate) was made. Finally, the energy absorption characteristics of hybrid corrugated sandwich panels were discussed. Numerical results show that the damage extent of hybrid corrugated sandwich plates under bare fragment cluster loading or combined blast and fragment loading is more severe than that caused by bare blast loading. When the charge mass is small, the performances of corrugated sandwich plate and hybrid corrugated sandwich plate are superior to equivalent solid plate and double-layered plate. The corrugated sandwich panels with fully filling configuration possess the best damage resistance, followed by that with upper space filling configuration, and that with lower space filling configuration has the worst. All the structures fractured catastrophically when the charge mass is large. For energy absorption, the corrugated core is the main energy absorption part under bare blast loading, while the front face becomes the main energy absorption part under the other two loading conditions.
2018, 38(2): 289-294.
doi: 10.11883/byzcj-2016-0251
Abstract:
In this work we at first designed and performed some small-scale explosion compaction (EC) outdoor experiments to study the application of EC technology in loess and to verify the feasibility and reliability of numerical simulation by computer software so that the risk of field experiments of EC on existing highways can be avoided. Then, we established the finite element models using the material parameters and the geometric dimensions of the outdoor experiments. Numerical simulations were carried out using ANSYS/LS-DYNA in combination with the above finite element models. By comparing the numerical simulation results with the measured ones in three aspects: the volume of the explosion cavities, the soil density after EC and the peak compressive stress acting on the soil, the feasibility and reliability of using ANSYS/LS-DYNA to simulate the EC of loess were verified. Moreover, the variation laws in the above three aspects were obtained. Our work can provide reference for numerical simulation of EC according to the conditions and the geometrical dimensions of actual loess subgrade.
In this work we at first designed and performed some small-scale explosion compaction (EC) outdoor experiments to study the application of EC technology in loess and to verify the feasibility and reliability of numerical simulation by computer software so that the risk of field experiments of EC on existing highways can be avoided. Then, we established the finite element models using the material parameters and the geometric dimensions of the outdoor experiments. Numerical simulations were carried out using ANSYS/LS-DYNA in combination with the above finite element models. By comparing the numerical simulation results with the measured ones in three aspects: the volume of the explosion cavities, the soil density after EC and the peak compressive stress acting on the soil, the feasibility and reliability of using ANSYS/LS-DYNA to simulate the EC of loess were verified. Moreover, the variation laws in the above three aspects were obtained. Our work can provide reference for numerical simulation of EC according to the conditions and the geometrical dimensions of actual loess subgrade.
2018, 38(2): 295-301.
doi: 10.11883/bzycj-2016-0186
Abstract:
By using an electronic universal testing machine and a modified split Hopkinson pressure bar device, the uniaxial compressive mechanical behaviours of glass used as the windshield of aircraft was tested. The experiments were finished at two quasi-static strain rates(4×10-4, 4×10-3s-1) and two high strain rates(200, 400 s-1). The glass fracture progress was also recorded by a high-speed camera. The experimental results show as follows. Catastrophic brittle failure was observed for the specimens tested at different strain rates. With the increase of strain rate, the compressive strength of the glass increases remarkably. By the fracture images and fragmentation forms, it is known that under compressive loads, the cracks initiate and propagate in the length direction under lateral tensile stress. Then the cracks connect and contact with each other, resulting in fragmentation of the specimen. The strain rate effect is explained properly in the point of microcrack initiation and development as well as energy dissipation.
By using an electronic universal testing machine and a modified split Hopkinson pressure bar device, the uniaxial compressive mechanical behaviours of glass used as the windshield of aircraft was tested. The experiments were finished at two quasi-static strain rates(4×10-4, 4×10-3s-1) and two high strain rates(200, 400 s-1). The glass fracture progress was also recorded by a high-speed camera. The experimental results show as follows. Catastrophic brittle failure was observed for the specimens tested at different strain rates. With the increase of strain rate, the compressive strength of the glass increases remarkably. By the fracture images and fragmentation forms, it is known that under compressive loads, the cracks initiate and propagate in the length direction under lateral tensile stress. Then the cracks connect and contact with each other, resulting in fragmentation of the specimen. The strain rate effect is explained properly in the point of microcrack initiation and development as well as energy dissipation.
2018, 38(2): 302-308.
doi: 10.11883/bzycj-2016-0230
Abstract:
In this study we carried out a series of experiments on large specimens (1 m×1 m×0.5 m) of coal and concrete using an explosive device and similar material test bench with multi-channel electro hydraulic servo to improve the application of the supercritical CO2 gas explosion in the low permeability coal seam and study the fracture mechanism of gas explosion. The internal deformation and failure information were recorded using a dynamic strain gauge, and fractures distribution in the blasting hole were observed using an industrial speculum. The gas explosion stress waves and the damage morphology after blasting show that damage areas from near to far are divided into a crushing zone, a cracking zone and a seismic zone. It is the corresponding formation mechanism that the supercritical CO2 impacts on the medium surrounding explosion hole, thereby forming the spherical wave, whose compressive strength is higher than that of the medium. Under the action of the radial compressive stress, the medium undergoes crushing destruction, and the crushing zone is thus formed. With the stress wave propagating, progressive attenuation of energy is not strong enough to cause the medium's compression failure. Brittle material is only good at resisting compression, but fails under tension. Circumferential stress generated by the stress waves still cause radial cracks. The high pressure CO2 gas with quasi-static loading action enters into fracture and forms a gas wedge that leads to the fracture's further development, called the forming of the cracking zone. Outside the cracking zone, the medium only vibrates under the low energy stress wave and no obvious damage occurs, and thus it is called the vibration area. The curve of the crack expansion velocity and distance from the gas explosion hole are in accordance with the "S" curve. High speed crack expansion occurs in the crushing zone, while the low velocity expansion occurs in the cracking zone. The farther away from the explosion hole, the smaller the peak strain of the measuring points, and the more complex the jointed fissure in the structure within the same distance; the greater the magnitude of the peak strain that decreases, the more different the strain waves.
In this study we carried out a series of experiments on large specimens (1 m×1 m×0.5 m) of coal and concrete using an explosive device and similar material test bench with multi-channel electro hydraulic servo to improve the application of the supercritical CO2 gas explosion in the low permeability coal seam and study the fracture mechanism of gas explosion. The internal deformation and failure information were recorded using a dynamic strain gauge, and fractures distribution in the blasting hole were observed using an industrial speculum. The gas explosion stress waves and the damage morphology after blasting show that damage areas from near to far are divided into a crushing zone, a cracking zone and a seismic zone. It is the corresponding formation mechanism that the supercritical CO2 impacts on the medium surrounding explosion hole, thereby forming the spherical wave, whose compressive strength is higher than that of the medium. Under the action of the radial compressive stress, the medium undergoes crushing destruction, and the crushing zone is thus formed. With the stress wave propagating, progressive attenuation of energy is not strong enough to cause the medium's compression failure. Brittle material is only good at resisting compression, but fails under tension. Circumferential stress generated by the stress waves still cause radial cracks. The high pressure CO2 gas with quasi-static loading action enters into fracture and forms a gas wedge that leads to the fracture's further development, called the forming of the cracking zone. Outside the cracking zone, the medium only vibrates under the low energy stress wave and no obvious damage occurs, and thus it is called the vibration area. The curve of the crack expansion velocity and distance from the gas explosion hole are in accordance with the "S" curve. High speed crack expansion occurs in the crushing zone, while the low velocity expansion occurs in the cracking zone. The farther away from the explosion hole, the smaller the peak strain of the measuring points, and the more complex the jointed fissure in the structure within the same distance; the greater the magnitude of the peak strain that decreases, the more different the strain waves.
2018, 38(2): 309-315.
doi: 10.11883/bzycj-2016-0271
Abstract:
Effected by micro-jetting, the usual measuring technologies are hard to recognise the front surface of micro-spall of a metal sample that is of complex structure. In this paper, a step-signal electric-probe measuring technology is proposed to solve this problem. The abnormal discharging phenomenon of the conventional electric probe is analyzed under the effect of micro-jetting and the step-signal producing circuit is designed. Explosive load experiments on Sn metal samples are carried out. The discharging signals of the conventional electric probe and step signal electric probe are compared and the useful information of the step signal is analyzed. Compared to X-ray photograph, we get that the position where the high voltage of step signal responses is the front surface of micro-spall. The results of the experiment show that the step-signal electric probe is able to distinguish the effect of micro-jetting and recognise the front surface of micro-spall of the metal samples under explosive load.
Effected by micro-jetting, the usual measuring technologies are hard to recognise the front surface of micro-spall of a metal sample that is of complex structure. In this paper, a step-signal electric-probe measuring technology is proposed to solve this problem. The abnormal discharging phenomenon of the conventional electric probe is analyzed under the effect of micro-jetting and the step-signal producing circuit is designed. Explosive load experiments on Sn metal samples are carried out. The discharging signals of the conventional electric probe and step signal electric probe are compared and the useful information of the step signal is analyzed. Compared to X-ray photograph, we get that the position where the high voltage of step signal responses is the front surface of micro-spall. The results of the experiment show that the step-signal electric probe is able to distinguish the effect of micro-jetting and recognise the front surface of micro-spall of the metal samples under explosive load.
A dynamic damage constitutive model for rockmass with intermittent joints under uniaxial compression
2018, 38(2): 316-323.
doi: 10.11883/bzycj-2016-0261
Abstract:
The intermittent joints have obvious effect on the strength and deformability of engineering rockmass. The joint is assumed to be a kind of macroscopic damage to the rockmass in the damage mechanics, therefore the damage tensor is adopted to describe its effect on the rockmass. Now three kinds of joint parameters such as the geometrical ones, strength ones and deformational ones are proposed in the academic circles to describe the joint physical and mechanical properties. However, the existing calculation methods of the rockmass damage tensor consider only the joint geometrical or strength parameters, not its deformational parameters such as normal stiffness and shear stiffness. Therefore, on the basis of the existing studies, the fracture and damage theory is adopted to propose the damage tensor calculation formula of the rockmass caused by an intermittent joint under uniaxial compression, and then that caused by one row or multi-row of joints in one set is given by considering the interaction of the joints. Secondly, based on the rock mesoscopic dynamic damage constitutive model and the viewpoint of macroscopic and mesoscopic damage coupling, a dynamic damage constitutive model for the rockmass with intermittent joints is proposed which can consider the joint geometrical, strength or deformational parameters at the same time. Finally, the effects of joint parameters and load strain rate on the rockmass dynamic mechanical behaviors are discussed with the proposed model. It is found the decrease in the joint length and the increase in the joint friction angle will increase the dynamic climax strength and elastic modulus of the rockmass. While with increasing the joint normal stiffness and shear stiffness, the dynamic climax strength and elastic modulus of the rockmass decrease and increase, respectively. While when the joint normal stiffness and shear stiffness increase in the same proportion, the dynamic climax strength and elastic modulus of the rockmass increase. The dynamic climax strength of the rockmass has a positive correlation with the load strain rate.
The intermittent joints have obvious effect on the strength and deformability of engineering rockmass. The joint is assumed to be a kind of macroscopic damage to the rockmass in the damage mechanics, therefore the damage tensor is adopted to describe its effect on the rockmass. Now three kinds of joint parameters such as the geometrical ones, strength ones and deformational ones are proposed in the academic circles to describe the joint physical and mechanical properties. However, the existing calculation methods of the rockmass damage tensor consider only the joint geometrical or strength parameters, not its deformational parameters such as normal stiffness and shear stiffness. Therefore, on the basis of the existing studies, the fracture and damage theory is adopted to propose the damage tensor calculation formula of the rockmass caused by an intermittent joint under uniaxial compression, and then that caused by one row or multi-row of joints in one set is given by considering the interaction of the joints. Secondly, based on the rock mesoscopic dynamic damage constitutive model and the viewpoint of macroscopic and mesoscopic damage coupling, a dynamic damage constitutive model for the rockmass with intermittent joints is proposed which can consider the joint geometrical, strength or deformational parameters at the same time. Finally, the effects of joint parameters and load strain rate on the rockmass dynamic mechanical behaviors are discussed with the proposed model. It is found the decrease in the joint length and the increase in the joint friction angle will increase the dynamic climax strength and elastic modulus of the rockmass. While with increasing the joint normal stiffness and shear stiffness, the dynamic climax strength and elastic modulus of the rockmass decrease and increase, respectively. While when the joint normal stiffness and shear stiffness increase in the same proportion, the dynamic climax strength and elastic modulus of the rockmass increase. The dynamic climax strength of the rockmass has a positive correlation with the load strain rate.
2018, 38(2): 324-330.
doi: 10.11883/bzycj-2016-0235
Abstract:
It is well known that the ultrafine silicon dioxide powder has a certain suppressing effect on the wheat starch flame. In this work, we explore the difference in this effect on the silicon dioxide powder due to different particle sizes, the changes of flame propagation, temperature, velocity and other parameters of the wheat starch combustion by adding 10 μm and 30 nm silicon dioxide powders. The experimental results show that the ultrafine silicon dioxide powder can reduce the wheat starch's burning reaction strength. The 30 nm powder produces a more effective suppression than the 10 μm powder. When the wheat starch powder's particle size is below 25 μm, The ultra fine powders with a mass concentration of 0.43 kg/m3 and a grain size of 30 nm can significantly decrease the wheat starch's flame brightness, reducing its maximum temperature by 38.07%, its maximum and average velocities by 42.25% and 65.59%, respectively. The ultrafine silicon dioxide exerts mainly an effect of physical suppression, which is inversely proportional to the particle size of wheat starch grains. The smaller the wheat starch grain size, the better the effect of silicon dioxide suppression.
It is well known that the ultrafine silicon dioxide powder has a certain suppressing effect on the wheat starch flame. In this work, we explore the difference in this effect on the silicon dioxide powder due to different particle sizes, the changes of flame propagation, temperature, velocity and other parameters of the wheat starch combustion by adding 10 μm and 30 nm silicon dioxide powders. The experimental results show that the ultrafine silicon dioxide powder can reduce the wheat starch's burning reaction strength. The 30 nm powder produces a more effective suppression than the 10 μm powder. When the wheat starch powder's particle size is below 25 μm, The ultra fine powders with a mass concentration of 0.43 kg/m3 and a grain size of 30 nm can significantly decrease the wheat starch's flame brightness, reducing its maximum temperature by 38.07%, its maximum and average velocities by 42.25% and 65.59%, respectively. The ultrafine silicon dioxide exerts mainly an effect of physical suppression, which is inversely proportional to the particle size of wheat starch grains. The smaller the wheat starch grain size, the better the effect of silicon dioxide suppression.
2018, 38(2): 331-338.
doi: 10.11883/bzycj-2016-0240
Abstract:
In this paper, based on two-dimensional conservation element and solution element(CE/SE), we simulated the detonation process of CRDE with gasoline and oxygen-enriched air to study the influence of liquid fuel on the detonation characteristics of the continuous rotating detonation engine. The effects of different droplet radiuses and equivalence ratios on the detonation parameters were analyzed. Our calculation results show that the velocity of the detonation wave and the peak values of the detonation pressure and temperature decreased with the increase of the droplet radius, and the peak values of the pressure and temperature became unstable during the propagation of the detonation wave. However, the detonation wave were not initiated successfully when the radius rose to 70 μm. The velocity of the detonation wave and the average thrust of CRDE increased with the rising of the equivalence ratio, while the peak values of the detonation pressure, temperature and gas phase's circumferential velocity increased first and then decreased. The peak values of the detonation pressure and temperature reached the maximum when the equivalence ratio was about 1.1, while the maximum of the gas phase's circumferential velocity occurred when the equivalence ratio was about 0.9.The fuel-based specific impulse decreased at the increase of the equivalence ratio.
In this paper, based on two-dimensional conservation element and solution element(CE/SE), we simulated the detonation process of CRDE with gasoline and oxygen-enriched air to study the influence of liquid fuel on the detonation characteristics of the continuous rotating detonation engine. The effects of different droplet radiuses and equivalence ratios on the detonation parameters were analyzed. Our calculation results show that the velocity of the detonation wave and the peak values of the detonation pressure and temperature decreased with the increase of the droplet radius, and the peak values of the pressure and temperature became unstable during the propagation of the detonation wave. However, the detonation wave were not initiated successfully when the radius rose to 70 μm. The velocity of the detonation wave and the average thrust of CRDE increased with the rising of the equivalence ratio, while the peak values of the detonation pressure, temperature and gas phase's circumferential velocity increased first and then decreased. The peak values of the detonation pressure and temperature reached the maximum when the equivalence ratio was about 1.1, while the maximum of the gas phase's circumferential velocity occurred when the equivalence ratio was about 0.9.The fuel-based specific impulse decreased at the increase of the equivalence ratio.
2018, 38(2): 339-344.
doi: 10.11883/bzycj-2016-0231
Abstract:
It is necessary to determine the greatest possible load that a civil building can bear in a gas explosion in a quick safety assessment of the building. In this paper, according to the principle of virtual displacements, we derived the function relationships between the slab's surface load and its bending stiffness, maximum deflection, flexural stiffness and geometric boundary conditions, at the time of gas explosion, using the Galerkin variational method, and reversely we derived the slab's pseudo static load and maximum deflection by combining them with the slab's maximum deflection collected in the actual in-situ explosion test. The result shows that the pressure curve range of the sidewall falls within the numerical simulation results of the gas explosion, with an error of only 2% between the method and the finite element method. The static analysis of the structure in combination with the pseudo static load can provide a reference for the rapid assessment of structural safety. Also, following the site check of the building after the explosion, we proposed constructing measures for preventing continuous collapse that might result from gas explosion in a civil building.
It is necessary to determine the greatest possible load that a civil building can bear in a gas explosion in a quick safety assessment of the building. In this paper, according to the principle of virtual displacements, we derived the function relationships between the slab's surface load and its bending stiffness, maximum deflection, flexural stiffness and geometric boundary conditions, at the time of gas explosion, using the Galerkin variational method, and reversely we derived the slab's pseudo static load and maximum deflection by combining them with the slab's maximum deflection collected in the actual in-situ explosion test. The result shows that the pressure curve range of the sidewall falls within the numerical simulation results of the gas explosion, with an error of only 2% between the method and the finite element method. The static analysis of the structure in combination with the pseudo static load can provide a reference for the rapid assessment of structural safety. Also, following the site check of the building after the explosion, we proposed constructing measures for preventing continuous collapse that might result from gas explosion in a civil building.
2018, 38(2): 345-352.
doi: 10.11883/bzycj-2016-0214
Abstract:
The propagation and spatial distribution of the divergent shock wave in PMMA under the restriction of a metal cylindrical shell were studied using experiment and numerical simulation. The flyer was driven by the cylinder high explosive initiated by a detonator at the center of the free surface and the inner pressure of PMMA was measured by PVDF. The experiment shows that the closer to the axis at a unique spot, the smaller the first pressure amplitude, which is the result of the increased impacted area of PMMA by the forward convex-shaped flyer due to the divergent shock wave and the increased integrative and accumulative effect of the pressure beyond the axis. But during the subsequent propagation of the shock wave, the closer to the axis, the smaller the pressure amplitude, which is the result of the interaction between the shock wave front and the reflection of the divergent shock wave from the cylindrical shell. The numerical simulation was performed well by adjusting the severe distortion of the mesh which may cause the termination of the calculation. The trend of the numerical result is in qualitative agreement with that of the experiment. Finally, we discussed the effect of different shell materials on the law of the distribution of the shock wave, and it is shown that the subsequent pressure increases as the heavy density of the cylindrical shell increases.
The propagation and spatial distribution of the divergent shock wave in PMMA under the restriction of a metal cylindrical shell were studied using experiment and numerical simulation. The flyer was driven by the cylinder high explosive initiated by a detonator at the center of the free surface and the inner pressure of PMMA was measured by PVDF. The experiment shows that the closer to the axis at a unique spot, the smaller the first pressure amplitude, which is the result of the increased impacted area of PMMA by the forward convex-shaped flyer due to the divergent shock wave and the increased integrative and accumulative effect of the pressure beyond the axis. But during the subsequent propagation of the shock wave, the closer to the axis, the smaller the pressure amplitude, which is the result of the interaction between the shock wave front and the reflection of the divergent shock wave from the cylindrical shell. The numerical simulation was performed well by adjusting the severe distortion of the mesh which may cause the termination of the calculation. The trend of the numerical result is in qualitative agreement with that of the experiment. Finally, we discussed the effect of different shell materials on the law of the distribution of the shock wave, and it is shown that the subsequent pressure increases as the heavy density of the cylindrical shell increases.
2018, 38(2): 353-358.
doi: 10.11883/bzycj-2016-0218
Abstract:
In this paper, we tested the minimum ingition energy (MIE) of methane at low temperature using an experimental apparatus fabricated by ourselves to characterize the explosion of methane at a low temperature ranging from -90 to 0 ℃ and under a pressure ranging from 0.1 to 0.5 MPa. It was found that, within the scope of the study, as the pressure increases, the MIE of methane decreases and does so faster with the increase of the initial pressure under low pressure but more slowly under high pressure; as the temperature increases, the MIE of methane also decreases and does so faster with the increase of the initial temperature at low pressure but more slowly under high pressure; the MIE of methane is approximately linear with the reciprocal of the square of the pressure and the that of the temperature.
In this paper, we tested the minimum ingition energy (MIE) of methane at low temperature using an experimental apparatus fabricated by ourselves to characterize the explosion of methane at a low temperature ranging from -90 to 0 ℃ and under a pressure ranging from 0.1 to 0.5 MPa. It was found that, within the scope of the study, as the pressure increases, the MIE of methane decreases and does so faster with the increase of the initial pressure under low pressure but more slowly under high pressure; as the temperature increases, the MIE of methane also decreases and does so faster with the increase of the initial temperature at low pressure but more slowly under high pressure; the MIE of methane is approximately linear with the reciprocal of the square of the pressure and the that of the temperature.
2018, 38(2): 359-366.
doi: 10.11883/bzycj-2016-0211
Abstract:
The effect of the large-scale explosion venting component on the interior deflagration pressure at different volume fractions of ethylene was studied by installing a vent panel on the end of the cavity whose size is 2 m×1.2 m×0.6 m. Two vent panels with different vent static-pressures were selected to be tested under the ethylene volume fraction ranging from 4% to 11% and three typical pressure-time curves were obtained. The result shows that the actual breakdown-pressure of the vent component was larger than that under a static load and there existed a maximum breakdown-pressure under the optimum concentration. The opening duration of the vent component had an important impact on the cavity interior pressure and it was as much as up to several tens of milliseconds at low-concentration. However, the opening duration was only a few milliseconds at stoichiometric concentration and the Lee JHS model still has good applicability for a rectangular cavity with a large-scale venting component. When the ethylene volume fraction is high, the large-scale venting component would cause the outside air to pour into the cavity and react with unburned gas as a result of having an overly large relief area, thereby leading to a secondary explosion, so increasing the relief area would bring damage to the structure under a high volume fraction.
The effect of the large-scale explosion venting component on the interior deflagration pressure at different volume fractions of ethylene was studied by installing a vent panel on the end of the cavity whose size is 2 m×1.2 m×0.6 m. Two vent panels with different vent static-pressures were selected to be tested under the ethylene volume fraction ranging from 4% to 11% and three typical pressure-time curves were obtained. The result shows that the actual breakdown-pressure of the vent component was larger than that under a static load and there existed a maximum breakdown-pressure under the optimum concentration. The opening duration of the vent component had an important impact on the cavity interior pressure and it was as much as up to several tens of milliseconds at low-concentration. However, the opening duration was only a few milliseconds at stoichiometric concentration and the Lee JHS model still has good applicability for a rectangular cavity with a large-scale venting component. When the ethylene volume fraction is high, the large-scale venting component would cause the outside air to pour into the cavity and react with unburned gas as a result of having an overly large relief area, thereby leading to a secondary explosion, so increasing the relief area would bring damage to the structure under a high volume fraction.
2018, 38(2): 367-372.
doi: 10.11883/bzycj-2016-0209
Abstract:
This paper studies the radial energy output of double-layer charge overpressure detonation based on the tests of single charge and double-layer charge explosion carried out on shock wave overpressure using ideal and non-ideal explosive of TNT, JO-8 and Hesar. The shock wave overpressure at 2, 3, 4 m was measured using the free filed piezoelectric sensor. The pattern of the shock wave overpressure and impulse varying with the distance was obtained by eliminating the zero-drift and integrating the software Origin. The effect of the charge structure and material was also examined. The results show that the overpressure of TNT/JO-8 double-layer charge in the radial direction was not improved as compared with the single charge with the same volume while the shock wave impulse exhibited a positive gain and increased with the distance. The material selection for the double-layer charge has great influence on the shock wave impulse. The overpressure gain at 4 m was about 15% for the non-ideal/ideal charge, which is much more beneficial in the radial output than for the ideal/ideal charge.
This paper studies the radial energy output of double-layer charge overpressure detonation based on the tests of single charge and double-layer charge explosion carried out on shock wave overpressure using ideal and non-ideal explosive of TNT, JO-8 and Hesar. The shock wave overpressure at 2, 3, 4 m was measured using the free filed piezoelectric sensor. The pattern of the shock wave overpressure and impulse varying with the distance was obtained by eliminating the zero-drift and integrating the software Origin. The effect of the charge structure and material was also examined. The results show that the overpressure of TNT/JO-8 double-layer charge in the radial direction was not improved as compared with the single charge with the same volume while the shock wave impulse exhibited a positive gain and increased with the distance. The material selection for the double-layer charge has great influence on the shock wave impulse. The overpressure gain at 4 m was about 15% for the non-ideal/ideal charge, which is much more beneficial in the radial output than for the ideal/ideal charge.
2018, 38(2): 373-380.
doi: 10.11883/bzycj-2016-0232
Abstract:
In this work, by inserting an additional sheet, called the middle sheet, between the upper and lower sheets of a traditional single-layer foam core sandwich panel consisting of a core with bonded with two sheets on either side, we fabricated sandwich panels with five structures that have the same dimensions and weights by changing the position of the middle sheet. The ratios of the upper core thickness to the total core thickness are 0:30, 10:30, 15:30, 20:30 and 30:30, respectively. On the basis of dimensional analysis, we conducted numerical analysis of the sandwich panels subjected to hailstone impact using the nonlinear finite element program LS-DYNA, and investigated the influence of the middle sheet's position on the energy absorption, energy dissipation and dynamic response of the sandwich panel. The numerical results show that the middle sheet provides an effective protection for the lower core, and the anti-impact performance of the sandwich panel exhibited a tendency to change from strong to weak and then from weak to strong as the middle sheet moved along the direction of the hailstone impact. The results of the numerical simulation offer a reference for the optimization design of the sandwich structures under hailstone impact.
In this work, by inserting an additional sheet, called the middle sheet, between the upper and lower sheets of a traditional single-layer foam core sandwich panel consisting of a core with bonded with two sheets on either side, we fabricated sandwich panels with five structures that have the same dimensions and weights by changing the position of the middle sheet. The ratios of the upper core thickness to the total core thickness are 0:30, 10:30, 15:30, 20:30 and 30:30, respectively. On the basis of dimensional analysis, we conducted numerical analysis of the sandwich panels subjected to hailstone impact using the nonlinear finite element program LS-DYNA, and investigated the influence of the middle sheet's position on the energy absorption, energy dissipation and dynamic response of the sandwich panel. The numerical results show that the middle sheet provides an effective protection for the lower core, and the anti-impact performance of the sandwich panel exhibited a tendency to change from strong to weak and then from weak to strong as the middle sheet moved along the direction of the hailstone impact. The results of the numerical simulation offer a reference for the optimization design of the sandwich structures under hailstone impact.
2018, 38(2): 381-389.
doi: 10.11883/bzycj-2016-0198
Abstract:
An experimental study on the characteristics of propane/air and propane/hydrogen/air flame propagation, at ambient temperature and pressure, was carried out in a narrow-gapped micro-chamber shaped like a disk and 150 mm in diameter, which was ignited by a spark igniter; photographs of the flame propagation were obtained with a high-speed camera at a gap distance of 2.0, 2.5, 3.0 and 5.0 mm, respectively; and the flame was observed to be smooth, wrinkled, and broken. As the flame equivalence ratio increases or the height of the gap decreases, the flame wrinkles occur earlier. The flame speed in the micro-chamber was slightly lower than that in the conventional-scale chamber, and it gradually decreased as the flame radius increased. As the gap height decreased, the flame propagation speed increased at first and then decreased, reaching the maximum at the gap height of 3 mm in the micro-chamber. As the heat loss increased, the micro scale effects played an important role in reducing the flame speed and enhancing the flame instability. Addition of hydrogen raised the flame propagation speed, and led to the detonation observed in the micro-chamber at a gap width of 2.5 mm.
An experimental study on the characteristics of propane/air and propane/hydrogen/air flame propagation, at ambient temperature and pressure, was carried out in a narrow-gapped micro-chamber shaped like a disk and 150 mm in diameter, which was ignited by a spark igniter; photographs of the flame propagation were obtained with a high-speed camera at a gap distance of 2.0, 2.5, 3.0 and 5.0 mm, respectively; and the flame was observed to be smooth, wrinkled, and broken. As the flame equivalence ratio increases or the height of the gap decreases, the flame wrinkles occur earlier. The flame speed in the micro-chamber was slightly lower than that in the conventional-scale chamber, and it gradually decreased as the flame radius increased. As the gap height decreased, the flame propagation speed increased at first and then decreased, reaching the maximum at the gap height of 3 mm in the micro-chamber. As the heat loss increased, the micro scale effects played an important role in reducing the flame speed and enhancing the flame instability. Addition of hydrogen raised the flame propagation speed, and led to the detonation observed in the micro-chamber at a gap width of 2.5 mm.
2018, 38(2): 390-396.
doi: 10.11883/bzycj-2016-0180
Abstract:
To investigate the stress relieving mechanism and the effect of the non-coupling blasting on the high-stress area in a coal tunnel, we carried out theoretical analysis and laboratory experiment, followed by in-situ verification and numerical simulation. The results show that, in the laboratory experiment, although blasting can obviously relieve its stress in specimen, the existence of the hulking stress results in increasing the stress recovery rate after the blasting. Therefore a stress relieving method was proposed which combines blasting and pre-splitting drilling with discharging pulverized coal; the verification of the stress-relieving effect on the roadway sides in the high-stress area shows that the method can effectively reduce the high-stress concentration near the roadway.
To investigate the stress relieving mechanism and the effect of the non-coupling blasting on the high-stress area in a coal tunnel, we carried out theoretical analysis and laboratory experiment, followed by in-situ verification and numerical simulation. The results show that, in the laboratory experiment, although blasting can obviously relieve its stress in specimen, the existence of the hulking stress results in increasing the stress recovery rate after the blasting. Therefore a stress relieving method was proposed which combines blasting and pre-splitting drilling with discharging pulverized coal; the verification of the stress-relieving effect on the roadway sides in the high-stress area shows that the method can effectively reduce the high-stress concentration near the roadway.
2018, 38(2): 397-403.
doi: 10.11883/bzycj-2016-0177
Abstract:
Dynamic behaviors of metal materials subjected to intense shock loading is presently a focus in basic research and engineering application in the field of shock wave study. This work investigated dynamic behaviors within the metal Pb loaded by two oblique shock waves via Smooth Particle Hydro dynamic (SPH) method, with an emphasis on the influence of different initiation points on the dynamic behaviors in the collision zone. Utilizing the shock polar theory, we obtained the critical angle for an incident oblique shock wave varying with the Mach number, which indicated a transition from regular to Mach reflection. The comparison of the numerical data with the theoretical plot confirmed the interaction of two oblique shock waves, thus essentially revealing the Mach reflection and the formation of the Mach stem. As the distance of the initiation point from the Pb surface increases, so do both the incident pressure and the angle for an oblique shock wave, including also the generated Mach stem. Based on the free surface velocity profiles, we calculated the width of the Mach stem and the Mach angle, the results being in good agreement with the theoretical prediction.
Dynamic behaviors of metal materials subjected to intense shock loading is presently a focus in basic research and engineering application in the field of shock wave study. This work investigated dynamic behaviors within the metal Pb loaded by two oblique shock waves via Smooth Particle Hydro dynamic (SPH) method, with an emphasis on the influence of different initiation points on the dynamic behaviors in the collision zone. Utilizing the shock polar theory, we obtained the critical angle for an incident oblique shock wave varying with the Mach number, which indicated a transition from regular to Mach reflection. The comparison of the numerical data with the theoretical plot confirmed the interaction of two oblique shock waves, thus essentially revealing the Mach reflection and the formation of the Mach stem. As the distance of the initiation point from the Pb surface increases, so do both the incident pressure and the angle for an oblique shock wave, including also the generated Mach stem. Based on the free surface velocity profiles, we calculated the width of the Mach stem and the Mach angle, the results being in good agreement with the theoretical prediction.
2018, 38(2): 404-408.
doi: 10.11883/bzycj-2016-0191
Abstract:
Focusing on the state of explosion overpressure field, a number of pressure transducers were installed in the axial and radial directions in the large-scale space. The explosion overpressure fields at different volume fractions of natural gas were recorded. When the volume fraction of natural gas was close to the lower limit of expolsion, three types of pressure curves existed. Former shock wave generated at the beginning of the explosion process was found as well with the further combustion wave. The developments in the axial and radial directions were found different obviously. Different from the instability of pressure in the radial direction, the overpressure development in the axial direction was more suitable to describe the whole developing process of overpressure.
Focusing on the state of explosion overpressure field, a number of pressure transducers were installed in the axial and radial directions in the large-scale space. The explosion overpressure fields at different volume fractions of natural gas were recorded. When the volume fraction of natural gas was close to the lower limit of expolsion, three types of pressure curves existed. Former shock wave generated at the beginning of the explosion process was found as well with the further combustion wave. The developments in the axial and radial directions were found different obviously. Different from the instability of pressure in the radial direction, the overpressure development in the axial direction was more suitable to describe the whole developing process of overpressure.
2018, 38(2): 409-418.
doi: 10.11883/bzycj-2016-0256
Abstract:
In this paper, the process of the plane incident shock wave shocking a magnetized R22 heavy circular gas column with different initial magnetic field was numerically studied based on the magneto-hydrodynamic (MHD) equation and CTU+CT method. The numerical results clearly describe the development of the instabilities induced by the shock waves on the interface of the R22 gas column with different initial magnetic field, and reveal the mechanism of the magnetic field governing the instabilities. In addition, the influence of different magnetic field strengths on the instabilities was analyzed, and it was found that when the magnetic field strength is small, the vortex layer attaches to the interface; that, with the increase of the magnetic field strength, the vortex layer gradually separates from the interface and the mean vorticity increases; and, finally, that the instabilities on the interface are brought under control. Meanwhile, with the increase of the magnetic field, the average enstrophy decreases, and the vertical magnetic field exerts a better inhibition effect on the average enstrophy than the parallel magnetic field. Thus the average enstrophy can fairly well reflect the effect of the magnetic field on the instabilities.
In this paper, the process of the plane incident shock wave shocking a magnetized R22 heavy circular gas column with different initial magnetic field was numerically studied based on the magneto-hydrodynamic (MHD) equation and CTU+CT method. The numerical results clearly describe the development of the instabilities induced by the shock waves on the interface of the R22 gas column with different initial magnetic field, and reveal the mechanism of the magnetic field governing the instabilities. In addition, the influence of different magnetic field strengths on the instabilities was analyzed, and it was found that when the magnetic field strength is small, the vortex layer attaches to the interface; that, with the increase of the magnetic field strength, the vortex layer gradually separates from the interface and the mean vorticity increases; and, finally, that the instabilities on the interface are brought under control. Meanwhile, with the increase of the magnetic field, the average enstrophy decreases, and the vertical magnetic field exerts a better inhibition effect on the average enstrophy than the parallel magnetic field. Thus the average enstrophy can fairly well reflect the effect of the magnetic field on the instabilities.
2018, 38(2): 419-425.
doi: 10.11883/bzycj-2016-0222
Abstract:
A series of experiments were carried out to explore the effects of high-g shock load on the electrical parameters (capacitance and leakage current) of the solid tantalum capacitor. The results show that the capacitance increases with the increase of the shock load and the leakage current increases exponentially with the rising shock load. After the shock load, the electrical parameters return to their initial values as demonstrated. The variations of the tantalum capacitors' electrical parameters were explained by a combination of three mechanisms: the shock-induced elastic deformation of the tantalum capacitor that leads to the capacitance's increase, the shock-induced micro-defects and shock-induced rise of the electron traps concentration that leads to the leakage currents' increase.
A series of experiments were carried out to explore the effects of high-g shock load on the electrical parameters (capacitance and leakage current) of the solid tantalum capacitor. The results show that the capacitance increases with the increase of the shock load and the leakage current increases exponentially with the rising shock load. After the shock load, the electrical parameters return to their initial values as demonstrated. The variations of the tantalum capacitors' electrical parameters were explained by a combination of three mechanisms: the shock-induced elastic deformation of the tantalum capacitor that leads to the capacitance's increase, the shock-induced micro-defects and shock-induced rise of the electron traps concentration that leads to the leakage currents' increase.
Validity analysis of materials' dynamic tensile SHTB experimental technique at ultrahigh temperature
2018, 38(2): 426-436.
doi: 10.11883/bzycj-2016-0259
Abstract:
In this work we investigated several key issues in view of the dynamic tensile experimental technique used in the split Hopkinson tension bar at ultra high temperature by performing numerical simulation, experimental verification and tests of several typical materials' dynamic tensile property at high temperature. The results show that the stress distribution was uniform for the flat tensile specimen with a hook joint after its gauge section size was optimized. The flow stress curve of the hook joint flat tensile specimen coincided well with that of the thread specimen, and no evident shake was observed in the strain rising stage. Through accurate pneumatic control, effective rapid synchronous assembly and loading of the specimen could be achieved at the same time when the loading wave arrived. When the temperature of the specimen reached 1 200 ℃, the average temperature of the specimen only dropped about 1.3% and the temperature rise of the loading bars kept below 180 ℃ during the whole cold contact between the high temperature specimen with the cold loading bars as well as in the process of the stress wave loading the specimen. To validate this experimental technique, tests were conducted at the temperature as high as about 1 200 ℃ for the dynamic tensile mechanical properties of a few materials such as 3D printed TC4 and single crystal nickel-base superalloy DD6.
In this work we investigated several key issues in view of the dynamic tensile experimental technique used in the split Hopkinson tension bar at ultra high temperature by performing numerical simulation, experimental verification and tests of several typical materials' dynamic tensile property at high temperature. The results show that the stress distribution was uniform for the flat tensile specimen with a hook joint after its gauge section size was optimized. The flow stress curve of the hook joint flat tensile specimen coincided well with that of the thread specimen, and no evident shake was observed in the strain rising stage. Through accurate pneumatic control, effective rapid synchronous assembly and loading of the specimen could be achieved at the same time when the loading wave arrived. When the temperature of the specimen reached 1 200 ℃, the average temperature of the specimen only dropped about 1.3% and the temperature rise of the loading bars kept below 180 ℃ during the whole cold contact between the high temperature specimen with the cold loading bars as well as in the process of the stress wave loading the specimen. To validate this experimental technique, tests were conducted at the temperature as high as about 1 200 ℃ for the dynamic tensile mechanical properties of a few materials such as 3D printed TC4 and single crystal nickel-base superalloy DD6.
2018, 38(2): 437-442.
doi: 10.11883/bzycj-2016-0241
Abstract:
In this paper we investigated underwater-explosion shock wave propagation using the ultrahigh-speed simultaneous framing and streak photography, a system newly developed by ourselves. The results show that this system is able to record simultaneously the same spatiotemporal 1D and 2D high-resolution images of underwater explosion shock wave propagation and observe the underwater explosion shock wave propagation process of TNT with a diameter of 66mm and a length of 60 mm, and that the average propagation speed and pressure of the shock wave interface can be obtained based on the experiment, thereby providing reference for efficiency evaluation in the design of underwater weapons.
In this paper we investigated underwater-explosion shock wave propagation using the ultrahigh-speed simultaneous framing and streak photography, a system newly developed by ourselves. The results show that this system is able to record simultaneously the same spatiotemporal 1D and 2D high-resolution images of underwater explosion shock wave propagation and observe the underwater explosion shock wave propagation process of TNT with a diameter of 66mm and a length of 60 mm, and that the average propagation speed and pressure of the shock wave interface can be obtained based on the experiment, thereby providing reference for efficiency evaluation in the design of underwater weapons.
2018, 38(2): 443-454.
doi: 10.11883/bzycj-2016-0201
Abstract:
In this paper the simplified calculation methods of internal pressure, structure load and dynamic response in gas deflagration in buildings were reviewed based on the current research achievements of gas explosion in confined space, including mainly the characteristics of deflagration pressure and structural load, the computation models of deflagration pressure and structural response. The empirical correlations of venting deflagration pressure based on experiment data and simplified calculation methods of venting deflagration pressure reflecting the fundamental physical process were examined in detail. The applicability of various models and the influences of deflagration load characteristics on the structural response were analyzed. The simplified calculation models for engineering that considering the influence of building functions were discussed with some advices given. In terms of the deflagration pressure calculation model, the ignition position, geometric characteristics of the blast chamber, turbulence effect of flame propagation and open process of venting structures should be considered. It was concluded that in terms of the calculation method of the structural dynamic response, some influencing factors such as deflagration load time-history, static-dynamic coupling loading and structure supporting load change should be taken into account.
In this paper the simplified calculation methods of internal pressure, structure load and dynamic response in gas deflagration in buildings were reviewed based on the current research achievements of gas explosion in confined space, including mainly the characteristics of deflagration pressure and structural load, the computation models of deflagration pressure and structural response. The empirical correlations of venting deflagration pressure based on experiment data and simplified calculation methods of venting deflagration pressure reflecting the fundamental physical process were examined in detail. The applicability of various models and the influences of deflagration load characteristics on the structural response were analyzed. The simplified calculation models for engineering that considering the influence of building functions were discussed with some advices given. In terms of the deflagration pressure calculation model, the ignition position, geometric characteristics of the blast chamber, turbulence effect of flame propagation and open process of venting structures should be considered. It was concluded that in terms of the calculation method of the structural dynamic response, some influencing factors such as deflagration load time-history, static-dynamic coupling loading and structure supporting load change should be taken into account.
2018, 38(2): 455-464.
doi: 10.11883/bzycj-2017-0117
Abstract:
A semi-confined vessel was built to study the explosion of the gasoline/air mixture ignited by a pilot flame. The flame propagation at different gasoline/air volume fractions were characterized through the flame images from a high-speed camera. The pressures development at different gasoline/air volume fractions were characterized according to the pressure data acquired by a high-frequency pressure sensor. The results showed that the gasoline/air volume fraction had a significant influence on the flame's species, propagation velocity, pressure and pressure rise rate. The flame exhibited an obvious zoning phenomenon, was observed to divide into a flame kernel and a flame front. The speed of the vertical flame front was faster than that of the horizontal flame front. The pressure development process went through four stages, and produced a phenomenon of two pressure peaks. A strong coupling effect was formed between the flame and the pressure wave in the process of the gasoline/air explosion
A semi-confined vessel was built to study the explosion of the gasoline/air mixture ignited by a pilot flame. The flame propagation at different gasoline/air volume fractions were characterized through the flame images from a high-speed camera. The pressures development at different gasoline/air volume fractions were characterized according to the pressure data acquired by a high-frequency pressure sensor. The results showed that the gasoline/air volume fraction had a significant influence on the flame's species, propagation velocity, pressure and pressure rise rate. The flame exhibited an obvious zoning phenomenon, was observed to divide into a flame kernel and a flame front. The speed of the vertical flame front was faster than that of the horizontal flame front. The pressure development process went through four stages, and produced a phenomenon of two pressure peaks. A strong coupling effect was formed between the flame and the pressure wave in the process of the gasoline/air explosion
2018, 38(2): 465-472.
doi: 10.11883/bzycj-2015-0242
Abstract:
In this paper, we studied the characteristics of the fuel-air mixture explosion using an experiment system built in a short pipe containing a weakly confined face at the end, with the following results achieved. (1) Multiple pressure peaks were observed due to the rupture, discharge, external explosion, accompanied with the Helmholtz oscillation. (2) The constraint surface produced a strengthening effect on the explosion overpressure, the maximum internal overpressure being 24.23 kPa and the maximum external overpressure being 5.45 kPa, respectively 4.9 and 2.7 times that of the pressure as compared in an unconstrained structure. (3) The morphological changes of the flame can be divided into four stages, those of the laminar combustion, the mutation and acceleration, the external explosion, and the extinction. Due to the influence of such factors as turbulence, interface instability and baroclinic effects, the flame shape was folded and crimped, forming a tulip during the mutation and acceleration stage and a sphere during the external explosion stage. (4) During the laminar combustion stage, the weakly confined face had a lessening effect on the flame speed, with 3.5 m/s as its maximum, which is reduced by 41.3%. In the states of mutation-acceleration and external explosion, the destruction of the confined surface had a strengthening effect on the flame speed, with 80.2 m/s as its maximum, which is enhanced by 106.2%. (5) The flame development made a significant difference at different concentrations. The flame can break through the weak confinement and form an external explosion at low and medium concentration, while at high concentration, the flame was unable to do so.
In this paper, we studied the characteristics of the fuel-air mixture explosion using an experiment system built in a short pipe containing a weakly confined face at the end, with the following results achieved. (1) Multiple pressure peaks were observed due to the rupture, discharge, external explosion, accompanied with the Helmholtz oscillation. (2) The constraint surface produced a strengthening effect on the explosion overpressure, the maximum internal overpressure being 24.23 kPa and the maximum external overpressure being 5.45 kPa, respectively 4.9 and 2.7 times that of the pressure as compared in an unconstrained structure. (3) The morphological changes of the flame can be divided into four stages, those of the laminar combustion, the mutation and acceleration, the external explosion, and the extinction. Due to the influence of such factors as turbulence, interface instability and baroclinic effects, the flame shape was folded and crimped, forming a tulip during the mutation and acceleration stage and a sphere during the external explosion stage. (4) During the laminar combustion stage, the weakly confined face had a lessening effect on the flame speed, with 3.5 m/s as its maximum, which is reduced by 41.3%. In the states of mutation-acceleration and external explosion, the destruction of the confined surface had a strengthening effect on the flame speed, with 80.2 m/s as its maximum, which is enhanced by 106.2%. (5) The flame development made a significant difference at different concentrations. The flame can break through the weak confinement and form an external explosion at low and medium concentration, while at high concentration, the flame was unable to do so.
