2017 Vol. 37, No. 4
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2017, 37(4): 577-584.
doi: 10.11883/1001-1455(2017)04-0577-08
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To investigate quantitatively the effect of argon dilution on the detonation instability of C2H2-O2 mixture, we carried out a digital comparison of smoked foils from C2H2-O2 mixtures with different Argon dilutions (with an volume fraction of 50%, 70%, and 85%, respectively) in two tubes (with an inner diameter of 50.8 mm and 63.5 mm, respectively) producing transverse waves of regular and irregular spacing and, based on the smoked foils, obtained under different initial pressures the histogram, the standard deviation and the autocorrelation function, which we then used to quantify the spacing irregularity for different cellular detonation structures. Each smoked foil was digitized and separated into left-running and right-running waves for subsequent analysis. The histogram, the standard deviation and the autocorrelation function showed consistent tendency. As the Ar dilution's volume fraction rose, the trajectory of the triple points became more regular. Similarly, mixtures of different Argon dilutions showed different degrees of irregularity in the analysis of the histograms and the autocorrelation function of the transverse waves' spacing. The proportion of the dominant mode of C2H2-O2-85%Ar, C2H2-O2-70%Ar, and C2H2-O2 were 33%, 23%, and 20%, respectively, while their standard deviation was 2.66~6.60 mm, 5.37~10.96 mm, and 27.63~36.67 mm, and their autocorrelation function peak values were higher by 1/3, 1/6, and 1/7 times. A polynomial fitted curve of the dilution and the irregularity was drawn from the standard deviation data to provide a selection basis for the instability degree and the Ar dilution's volume fraction.
To investigate quantitatively the effect of argon dilution on the detonation instability of C2H2-O2 mixture, we carried out a digital comparison of smoked foils from C2H2-O2 mixtures with different Argon dilutions (with an volume fraction of 50%, 70%, and 85%, respectively) in two tubes (with an inner diameter of 50.8 mm and 63.5 mm, respectively) producing transverse waves of regular and irregular spacing and, based on the smoked foils, obtained under different initial pressures the histogram, the standard deviation and the autocorrelation function, which we then used to quantify the spacing irregularity for different cellular detonation structures. Each smoked foil was digitized and separated into left-running and right-running waves for subsequent analysis. The histogram, the standard deviation and the autocorrelation function showed consistent tendency. As the Ar dilution's volume fraction rose, the trajectory of the triple points became more regular. Similarly, mixtures of different Argon dilutions showed different degrees of irregularity in the analysis of the histograms and the autocorrelation function of the transverse waves' spacing. The proportion of the dominant mode of C2H2-O2-85%Ar, C2H2-O2-70%Ar, and C2H2-O2 were 33%, 23%, and 20%, respectively, while their standard deviation was 2.66~6.60 mm, 5.37~10.96 mm, and 27.63~36.67 mm, and their autocorrelation function peak values were higher by 1/3, 1/6, and 1/7 times. A polynomial fitted curve of the dilution and the irregularity was drawn from the standard deviation data to provide a selection basis for the instability degree and the Ar dilution's volume fraction.
2017, 37(4): 585-590.
doi: 10.11883/1001-1455(2017)04-0585-06
Abstract:
Since probability distributions of input parameters are usually assigned subjectively for uncertainty quantification (UQ) in numerical simulations, the selection of distributions may have significant effect on analysis results of UQ. In this paper, to calibrate more precisely the parameters of JWL equation of state in the cylinder test, we proposed to adopt Bayesian methods that provide estimators and posterior distributions of calibration parameters. Further, we investigated the effects of model assumptions on estimators and posterior distributions of calibration parameters. Our study shows that, owing to the information of cylinder tests they contain, the posterior distributions can be used as initial probability distributions of the input parameters in UQ to reduce the epistemic uncertainty.
Since probability distributions of input parameters are usually assigned subjectively for uncertainty quantification (UQ) in numerical simulations, the selection of distributions may have significant effect on analysis results of UQ. In this paper, to calibrate more precisely the parameters of JWL equation of state in the cylinder test, we proposed to adopt Bayesian methods that provide estimators and posterior distributions of calibration parameters. Further, we investigated the effects of model assumptions on estimators and posterior distributions of calibration parameters. Our study shows that, owing to the information of cylinder tests they contain, the posterior distributions can be used as initial probability distributions of the input parameters in UQ to reduce the epistemic uncertainty.
2017, 37(4): 591-599.
doi: 10.11883/1001-1455(2017)04-0591-09
Abstract:
The scattering of the SH-wave by a circular cavity near the vertical boundary in the piezoelectric bi-material half-space was analyzed using the Green function method and the mirror method to obtain the steady state response. The analytical expression of the wave function was obtained on the horizontal boundaries using the mirror method. This function was the stress-free and electric-displacement-free. According to the continuity condition on the vertical boundary, the first kind of Fredholm integral equations were established, thereby obtaining the analytical expression of the dynamic stress concentration factor and the electric field intensity concentration factor around the edge of the circular cavity by the conjunction method. The influence of the frequencies of the incident wave, the incident angle and the media parameter, etc., on the dynamic stress concentration factor and the electric field intensity concentration factor was examined and compared with existing literatures using calculating examples. The numerical results show that serious damage occurs when the high-frequency incident SH wave comes in vertically.
The scattering of the SH-wave by a circular cavity near the vertical boundary in the piezoelectric bi-material half-space was analyzed using the Green function method and the mirror method to obtain the steady state response. The analytical expression of the wave function was obtained on the horizontal boundaries using the mirror method. This function was the stress-free and electric-displacement-free. According to the continuity condition on the vertical boundary, the first kind of Fredholm integral equations were established, thereby obtaining the analytical expression of the dynamic stress concentration factor and the electric field intensity concentration factor around the edge of the circular cavity by the conjunction method. The influence of the frequencies of the incident wave, the incident angle and the media parameter, etc., on the dynamic stress concentration factor and the electric field intensity concentration factor was examined and compared with existing literatures using calculating examples. The numerical results show that serious damage occurs when the high-frequency incident SH wave comes in vertically.
2017, 37(4): 600-610.
doi: 10.11883/1001-1455(2017)04-0600-11
Abstract:
Using a gas gun driven high-speed aluminum metal foam projectile, we investigated experimentally the dynamic responses of the solid steel plate, the aluminum matrix syntactic foam sandwich panel and the aluminum foam sandwich panel, whose front and back plates made both from the Q235 steel, under the impact loading. The experimental results showed that using metal foam projectile impact can simulate the explosion load, that the deformation of the sandwich panel can be divided into two stages, i.e. the core compression and the global deformation, and that the shock resistance of the aluminum matrix syntactic foam sandwich panel is stronger than that of the solid steel plate and the aluminum foam sandwich panel. Based on the experiments, we also performed the corresponding finite element simulations using the LS-DYNA software. The simulation results showed that the velocity and the length of the metal foam projectile have obvious effect on the contact force, revealing a linear relationship. The core foam's strength has an obvious effect on the equal-mass and equal-thickness sandwich panel's shock-resistance behaviors. As the sandwich panel's deflection is sensitive to the thickness of the front and the back plate, the deflection of the panel will decrease if the thickness of the back plate is bigger than that of the front plate. The recommended material for the plate should be of low-stiffness, high-ductility and high tensile fracture strain.
Using a gas gun driven high-speed aluminum metal foam projectile, we investigated experimentally the dynamic responses of the solid steel plate, the aluminum matrix syntactic foam sandwich panel and the aluminum foam sandwich panel, whose front and back plates made both from the Q235 steel, under the impact loading. The experimental results showed that using metal foam projectile impact can simulate the explosion load, that the deformation of the sandwich panel can be divided into two stages, i.e. the core compression and the global deformation, and that the shock resistance of the aluminum matrix syntactic foam sandwich panel is stronger than that of the solid steel plate and the aluminum foam sandwich panel. Based on the experiments, we also performed the corresponding finite element simulations using the LS-DYNA software. The simulation results showed that the velocity and the length of the metal foam projectile have obvious effect on the contact force, revealing a linear relationship. The core foam's strength has an obvious effect on the equal-mass and equal-thickness sandwich panel's shock-resistance behaviors. As the sandwich panel's deflection is sensitive to the thickness of the front and the back plate, the deflection of the panel will decrease if the thickness of the back plate is bigger than that of the front plate. The recommended material for the plate should be of low-stiffness, high-ductility and high tensile fracture strain.
2017, 37(4): 611-620.
doi: 10.11883/1001-1455(2017)04-0611-10
Abstract:
Based on the local interaction theory, we proposed a penetration depth model for projectiles with an arbitrary nose-shape penetrating into a concrete target in consideration of the cratering stage related to nose-shape and normalized nose-shape function. Furthermore, using the method of maximum depth of penetration, we presented an expression about the normalized control parameter of the nose-shape and the classical variational optimization of the nose-shape. The local interaction model prediction and simulation results accord well with the experimental data of different projectile nose shapes. The optimal analysis and simulation show that, when the relative radius of the projectile nose is small, the optimal spherical-tip projectile is similar to corresponding optimal sharp-tip projectile, and the optimized truncated-tip projectiles have better penetration performance than that of the corresponding sharp-tip projectile. Compared with other nose-shaped projectiles, the optimized truncated-conical projectile has a relatively greater penetration depth. As the shape of the projectile nose affects its overload in the penetration process, the optimized shape of the projectile nose can effectively improve the penetration depth of the projectile.
Based on the local interaction theory, we proposed a penetration depth model for projectiles with an arbitrary nose-shape penetrating into a concrete target in consideration of the cratering stage related to nose-shape and normalized nose-shape function. Furthermore, using the method of maximum depth of penetration, we presented an expression about the normalized control parameter of the nose-shape and the classical variational optimization of the nose-shape. The local interaction model prediction and simulation results accord well with the experimental data of different projectile nose shapes. The optimal analysis and simulation show that, when the relative radius of the projectile nose is small, the optimal spherical-tip projectile is similar to corresponding optimal sharp-tip projectile, and the optimized truncated-tip projectiles have better penetration performance than that of the corresponding sharp-tip projectile. Compared with other nose-shaped projectiles, the optimized truncated-conical projectile has a relatively greater penetration depth. As the shape of the projectile nose affects its overload in the penetration process, the optimized shape of the projectile nose can effectively improve the penetration depth of the projectile.
2017, 37(4): 621-628.
doi: 10.11883/1001-1455(2017)04-0621-08
Abstract:
Based on an analysis of the PELE (penetrator with enhanced lateral efficiency) penetrating thin metal targets, the deformation process of the front-end projectile was divided into two distinct phases: one-dimensional decomposition in the axial direction and the free conversion in the radial direction, for experimental study. Based on the shock wave theory, we obtained the shock wave compression energy of the front end of the projectile and, on the basis of the conservation of energy and the assumption of two-stage deformation, presented a method for determining the scattered radial velocity of the PELE jacket fragments behind the target. The calculated results in a variety of conditions are fairly consistent with the experimental results. The theoretical analysis showed that the maximum radial velocity of the PELE jacket fragments depends on the radial expansion of both the jacket and the filling part under the shock compression, the former playing a major role in the overall expansion of the projectile whereas the maximum radial velocity of the PELE jacket fragments increasing with the bulk modulus and the Poisson's ratio of the jacket and the filling part. The results suggest that the lateral expansion of both the jacket and the filling part should be taken into account when calculating the radial velocity of the PELE fragments.
Based on an analysis of the PELE (penetrator with enhanced lateral efficiency) penetrating thin metal targets, the deformation process of the front-end projectile was divided into two distinct phases: one-dimensional decomposition in the axial direction and the free conversion in the radial direction, for experimental study. Based on the shock wave theory, we obtained the shock wave compression energy of the front end of the projectile and, on the basis of the conservation of energy and the assumption of two-stage deformation, presented a method for determining the scattered radial velocity of the PELE jacket fragments behind the target. The calculated results in a variety of conditions are fairly consistent with the experimental results. The theoretical analysis showed that the maximum radial velocity of the PELE jacket fragments depends on the radial expansion of both the jacket and the filling part under the shock compression, the former playing a major role in the overall expansion of the projectile whereas the maximum radial velocity of the PELE jacket fragments increasing with the bulk modulus and the Poisson's ratio of the jacket and the filling part. The results suggest that the lateral expansion of both the jacket and the filling part should be taken into account when calculating the radial velocity of the PELE fragments.
2017, 37(4): 629-636.
doi: 10.11883/1001-1455(2017)04-0629-08
Abstract:
To investigate the ballistic resistance and failure mode of three different low-carbon alloy steel plates subjected to ultra-high strength low alloy steel projectiles, we used the typical bulletproof special steels SS and AS and the commonly used Q235A steel for our study in the present research, obtained their static tensile and compression performance and the dynamic mechanical behavior at the strain rate of 1 000 to 6 000 s-1 by static tension, compression and split Hopkinson pressure bar tests respectively, and analyzed the relationship between material composition and mechanical performance. We also obtained the ballistic limits of these plates (14.5~15.9 mm thick) subjected to two ultra-high strength low alloy steel projectiles by ballistic gun experiments. Furthermore, we compared the specific energy absorption and failure mode of the steel plates under various conditions and analyzed the relationship between the mechanical performance and the failure mode. The results showed a positive correlation between the ballistic resistance and the yield strength, but the differences between the ballistic resistances of the three steel plates are less than that between the yield strength. Finally, the failure mechanism of different steel plates is correlated with different mechanical parameters: for the AS steel plates with a high content of Si and Mn, the main determinant of fracture failure is its shear strength, as is characterized by great hardness and brittleness, while for SS and Q235A steel plate with a low content of Si and Mn the main determinant is its compressive and shear strength, as is characterized by good plasticity.
To investigate the ballistic resistance and failure mode of three different low-carbon alloy steel plates subjected to ultra-high strength low alloy steel projectiles, we used the typical bulletproof special steels SS and AS and the commonly used Q235A steel for our study in the present research, obtained their static tensile and compression performance and the dynamic mechanical behavior at the strain rate of 1 000 to 6 000 s-1 by static tension, compression and split Hopkinson pressure bar tests respectively, and analyzed the relationship between material composition and mechanical performance. We also obtained the ballistic limits of these plates (14.5~15.9 mm thick) subjected to two ultra-high strength low alloy steel projectiles by ballistic gun experiments. Furthermore, we compared the specific energy absorption and failure mode of the steel plates under various conditions and analyzed the relationship between the mechanical performance and the failure mode. The results showed a positive correlation between the ballistic resistance and the yield strength, but the differences between the ballistic resistances of the three steel plates are less than that between the yield strength. Finally, the failure mechanism of different steel plates is correlated with different mechanical parameters: for the AS steel plates with a high content of Si and Mn, the main determinant of fracture failure is its shear strength, as is characterized by great hardness and brittleness, while for SS and Q235A steel plate with a low content of Si and Mn the main determinant is its compressive and shear strength, as is characterized by good plasticity.
2017, 37(4): 637-642.
doi: 10.11883/1001-1455(2017)04-0637-06
Abstract:
The protection performance and mechanism of explosive reactive armors (ERA) with composite rubber armor as its front or back plate were investigated using experiments and numerical simulation, and the results were examined in comparison with ERA using conventional steel plates of the same area density. The experimental results show that the protection performance of ERA with composite rubber armor as the front or back plates are superior to that of the ERA with steel plates, and the optimal performance is achieved when the rubber composite armor is used as the back plate. The numerical simulation results show that the back plate velocity of the composite rubber armor is 16% higher than that of the ERA with steel plates, the space between the two moving plates of the composite rubber armor and the boundary effect contribute significantly to reducing the length of the escaping shaped charge jet.
The protection performance and mechanism of explosive reactive armors (ERA) with composite rubber armor as its front or back plate were investigated using experiments and numerical simulation, and the results were examined in comparison with ERA using conventional steel plates of the same area density. The experimental results show that the protection performance of ERA with composite rubber armor as the front or back plates are superior to that of the ERA with steel plates, and the optimal performance is achieved when the rubber composite armor is used as the back plate. The numerical simulation results show that the back plate velocity of the composite rubber armor is 16% higher than that of the ERA with steel plates, the space between the two moving plates of the composite rubber armor and the boundary effect contribute significantly to reducing the length of the escaping shaped charge jet.
2017, 37(4): 643-648.
doi: 10.11883/1001-1455(2017)04-0643-06
Abstract:
A novel shelly cellular material made of PVC lining and foamed ceramics shell was developed in this paper. Large scaled explosion tests were performed to study the damage condition and energy absorption performances of civil defense engineering using sand or the novel shelly cellular material as the attenuation layer. The test results show that the energy dissipation capacity of the shelly cellular material is better than that of sand, and the maximum stress in the test using novel material as the attenuation layer decreases by about 50% compared to that when using sand as the attenuation layer under the same explosion loading. In addition, the damage degree is much smaller compared with the conventional shelly cellular material. Therefore, it can be concluded that the novel shelly cellular material can significantly improve the capability of civil defense engineering and have broad prospects of military application.
A novel shelly cellular material made of PVC lining and foamed ceramics shell was developed in this paper. Large scaled explosion tests were performed to study the damage condition and energy absorption performances of civil defense engineering using sand or the novel shelly cellular material as the attenuation layer. The test results show that the energy dissipation capacity of the shelly cellular material is better than that of sand, and the maximum stress in the test using novel material as the attenuation layer decreases by about 50% compared to that when using sand as the attenuation layer under the same explosion loading. In addition, the damage degree is much smaller compared with the conventional shelly cellular material. Therefore, it can be concluded that the novel shelly cellular material can significantly improve the capability of civil defense engineering and have broad prospects of military application.
2017, 37(4): 649-660.
doi: 10.11883/1001-1455(2017)04-0649-12
Abstract:
A field blast test including 6 specimens was conducted to investigate the effect of the axial compression ratio, the scaled distance, the hollow ratio and the shape of the facing blasting side on the dynamic response of ultra-high performance steel fiber reinforced concrete-filled double skin steel tube columns (UHPSFRCFDST). Then a three dimensional finite element model (3D FEM) was built using the LS-DYNA software to analyse the dynamic response and damage mechanism of UHPSFRCFDST columns under blast loading, and it was validated by comparison of simulation with blast testing results. Based on this model, the effect of such key parameters as the axial compression ratio, the hollow ratio, the steel ration, the thickness and strength of the inner or outer steel tube, on the blast-resisting performance of UHPSFRCFDST columns was presented. The results indicate that the 3D FEM can accurately describe the dynamic response of UHPSFRCFDST columns under blast loading. The blast-resisting performance of UHPSFRCFDST columns can be improved by increasing the axial compression ratio in a certain range, whereas the damage of the specimens will aggravate when this ratio goes above a critical value. Moreover, the blast-resisting performance of UHPSFRCFDST columns can be enhanced by reducing the hollow ratio or the diameter to thickness ratio of the inner and outer steel tube, and the effect can also be achieved by increasing the steel proportion or the strength of the outer steel tube. However, the strength of the inner steel tube has little effect on the blast-resisting performance of UHPSFRCFDST columns.
A field blast test including 6 specimens was conducted to investigate the effect of the axial compression ratio, the scaled distance, the hollow ratio and the shape of the facing blasting side on the dynamic response of ultra-high performance steel fiber reinforced concrete-filled double skin steel tube columns (UHPSFRCFDST). Then a three dimensional finite element model (3D FEM) was built using the LS-DYNA software to analyse the dynamic response and damage mechanism of UHPSFRCFDST columns under blast loading, and it was validated by comparison of simulation with blast testing results. Based on this model, the effect of such key parameters as the axial compression ratio, the hollow ratio, the steel ration, the thickness and strength of the inner or outer steel tube, on the blast-resisting performance of UHPSFRCFDST columns was presented. The results indicate that the 3D FEM can accurately describe the dynamic response of UHPSFRCFDST columns under blast loading. The blast-resisting performance of UHPSFRCFDST columns can be improved by increasing the axial compression ratio in a certain range, whereas the damage of the specimens will aggravate when this ratio goes above a critical value. Moreover, the blast-resisting performance of UHPSFRCFDST columns can be enhanced by reducing the hollow ratio or the diameter to thickness ratio of the inner and outer steel tube, and the effect can also be achieved by increasing the steel proportion or the strength of the outer steel tube. However, the strength of the inner steel tube has little effect on the blast-resisting performance of UHPSFRCFDST columns.
2017, 37(4): 661-669.
doi: 10.11883/1001-1455(2017)04-0661-09
Abstract:
To improve the energy utilization and fragmentation effect in rock blasting, the explosion energy partitions of end initiation and continuous side initiation were analyzed. In addition, field blasting tests were conducted in Xiangshuigou Quarry, and the results show significant differences in the partition of shock and gas energy between the two initiation methods. The effective energy utilization of these two initiation methods in different rocks varies considerably. On this basis, a selection principle of initiation methods for rocks with different intensities was put forward. The continuous side initiation with a detonating cord is advantageous in soft and fissured rocks and contour blasting, while blasting for graded material in hard rock, the end initiation is recommended instead of the side initiation.
To improve the energy utilization and fragmentation effect in rock blasting, the explosion energy partitions of end initiation and continuous side initiation were analyzed. In addition, field blasting tests were conducted in Xiangshuigou Quarry, and the results show significant differences in the partition of shock and gas energy between the two initiation methods. The effective energy utilization of these two initiation methods in different rocks varies considerably. On this basis, a selection principle of initiation methods for rocks with different intensities was put forward. The continuous side initiation with a detonating cord is advantageous in soft and fissured rocks and contour blasting, while blasting for graded material in hard rock, the end initiation is recommended instead of the side initiation.
2017, 37(4): 670-676.
doi: 10.11883/1001-1455(2017)04-0670-07
Abstract:
The dynamic interaction between the surrounding rock and the initial supporting structure is essential for determining the load of the underground structure and designing the supporting structure. Using the nonlinear dynamic finite element procedure of ANSYS/LS-DYNA and the fluid-solid coupling algorithm, we simulated the underground arch structures with different spans subjected to the shock wave produced by an explosion perpendicular to the vault. Based on the wave theory we also analyzed the dynamic interaction force between the surrounding rock and the supporting structure and the applicability of the dynamic load equation, and obtained the variation of the maximum interaction. The results show that, at a perpendicular explosion that occurs 1~25 m away from the vault, the structures with 14~25 m spans experience partial failure on the vault while the concrete structure of the whole structure forms overall cracks. The maximum dynamic interaction force is observed when the explosion occurs at a distance 4 m. Our study can serve as a basis in determining the maximum load for the design of the surrounding rock and the underground structure.
The dynamic interaction between the surrounding rock and the initial supporting structure is essential for determining the load of the underground structure and designing the supporting structure. Using the nonlinear dynamic finite element procedure of ANSYS/LS-DYNA and the fluid-solid coupling algorithm, we simulated the underground arch structures with different spans subjected to the shock wave produced by an explosion perpendicular to the vault. Based on the wave theory we also analyzed the dynamic interaction force between the surrounding rock and the supporting structure and the applicability of the dynamic load equation, and obtained the variation of the maximum interaction. The results show that, at a perpendicular explosion that occurs 1~25 m away from the vault, the structures with 14~25 m spans experience partial failure on the vault while the concrete structure of the whole structure forms overall cracks. The maximum dynamic interaction force is observed when the explosion occurs at a distance 4 m. Our study can serve as a basis in determining the maximum load for the design of the surrounding rock and the underground structure.
2017, 37(4): 677-684.
doi: 10.11883/1001-1455(2017)04-0677-08
Abstract:
In this paper, against the background of the Huangdeng gravity dam and in consideration of the influence of the concrete's high strain rate, we established a fully-coupled numerical model for the dam-water-air-explosive using the Lagrange-Euler coupling method, and studied the antiknock performance of the overflow dam subjected to contact explosion loading. The dynamic response and damage of the overflow dam under the condition of withholding a full reservoir of water were compared with that under the condition of withholding an empty reservoir. Further, the response of the overflow dam subjected to underwater explosion at different explosion points was also investigated. The results show that, subjected to the same underwater explosion, the dynamic response and damage degree of the overflow dam withholding a full reservoir were significantly higher than those of the dam withholding an empty reservoir, and the weak points of the overflow dam were mainly located at the dam's overflow spillway on the top and the upstream slope. Therefore, it is concluded that research on the antiknock performance of an overflow dam subjected to underwater contact explosion should focus on the damage characteristics of the dam withholding a full reservoir.
In this paper, against the background of the Huangdeng gravity dam and in consideration of the influence of the concrete's high strain rate, we established a fully-coupled numerical model for the dam-water-air-explosive using the Lagrange-Euler coupling method, and studied the antiknock performance of the overflow dam subjected to contact explosion loading. The dynamic response and damage of the overflow dam under the condition of withholding a full reservoir of water were compared with that under the condition of withholding an empty reservoir. Further, the response of the overflow dam subjected to underwater explosion at different explosion points was also investigated. The results show that, subjected to the same underwater explosion, the dynamic response and damage degree of the overflow dam withholding a full reservoir were significantly higher than those of the dam withholding an empty reservoir, and the weak points of the overflow dam were mainly located at the dam's overflow spillway on the top and the upstream slope. Therefore, it is concluded that research on the antiknock performance of an overflow dam subjected to underwater contact explosion should focus on the damage characteristics of the dam withholding a full reservoir.
2017, 37(4): 685-691.
doi: 10.11883/1001-1455(2017)04-0685-07
Abstract:
Being of a complex hierarchical structure with energy closed in it for its intrinsic friction and cohesion, the rock mass can be regarded as a medium with the properties of internal energy source and energy collection. The equivalent impact energy factor corresponding to the rock mass under high in situ stress subjected to the weak disturbance was presented, and the calculation method of the irreversible deformation region radius under the large-scale underground explosion was deduced. Compared with the method by Kocharyan G G, et al, the calculation method presented in this paper has a clearer physical principle and wider application.
Being of a complex hierarchical structure with energy closed in it for its intrinsic friction and cohesion, the rock mass can be regarded as a medium with the properties of internal energy source and energy collection. The equivalent impact energy factor corresponding to the rock mass under high in situ stress subjected to the weak disturbance was presented, and the calculation method of the irreversible deformation region radius under the large-scale underground explosion was deduced. Compared with the method by Kocharyan G G, et al, the calculation method presented in this paper has a clearer physical principle and wider application.
2017, 37(4): 692-698.
doi: 10.11883/1001-1455(2017)04-0692-07
Abstract:
Microspall is an essential problem in both theoretical investigation and engineering application in shock physics. The Asay window, originally developed to diagnose the multi-spall behavior of material, was recently employed to probe the microspall, but its ability for probing the problem calls for further demonstration, and the corresponding signal also needs further explanation. In this paper, wave propagation analysis indicates that the sample bearing microspall can be separated into several different characteristic regions, the experiments performed demonstrate that the Asay window can sensitively distinguish these regions as far as a reasonable experimental configuration is set up, and even the features of the micro jet particles can be detected. So the technique was proved of great value for dynamic fragmentation studies.
Microspall is an essential problem in both theoretical investigation and engineering application in shock physics. The Asay window, originally developed to diagnose the multi-spall behavior of material, was recently employed to probe the microspall, but its ability for probing the problem calls for further demonstration, and the corresponding signal also needs further explanation. In this paper, wave propagation analysis indicates that the sample bearing microspall can be separated into several different characteristic regions, the experiments performed demonstrate that the Asay window can sensitively distinguish these regions as far as a reasonable experimental configuration is set up, and even the features of the micro jet particles can be detected. So the technique was proved of great value for dynamic fragmentation studies.
2017, 37(4): 699-704.
doi: 10.11883/1001-1455(2017)04-0699-06
Abstract:
The creation of helium atoms is one of the main damaging mechanisms in neutron irradiated metals and is therefore a major concern in related scientific research. Recent researches under static loading conditions showed that the creation of helium atoms in metals is of great academic significance, for their precipitation into bubbles can cause substantial deterioration of the mechanical properties of materials. In this paper, based on experimental results so far published, a damage model is adopted combining inertial effect, initial void size and damage, to investigate the influence of helium bubbles in aluminum on its dynamic spall properties. The numerical calculation results show that the damage growth is insensitive to the pressure inside the bubble and the temperature produced by plastic deformation; the inner stress decreases more quickly and the porosity increases more slowly with the increase of the initial damage; the damage increases more slowly with the increase of the initial size of the helium bubble due to the inertial effect. Therefore, the study on the spall response of metals with helium bubbles should focus on the initial size of the helium bubble, the initial damage and the inertial effect at high loading rates.
The creation of helium atoms is one of the main damaging mechanisms in neutron irradiated metals and is therefore a major concern in related scientific research. Recent researches under static loading conditions showed that the creation of helium atoms in metals is of great academic significance, for their precipitation into bubbles can cause substantial deterioration of the mechanical properties of materials. In this paper, based on experimental results so far published, a damage model is adopted combining inertial effect, initial void size and damage, to investigate the influence of helium bubbles in aluminum on its dynamic spall properties. The numerical calculation results show that the damage growth is insensitive to the pressure inside the bubble and the temperature produced by plastic deformation; the inner stress decreases more quickly and the porosity increases more slowly with the increase of the initial damage; the damage increases more slowly with the increase of the initial size of the helium bubble due to the inertial effect. Therefore, the study on the spall response of metals with helium bubbles should focus on the initial size of the helium bubble, the initial damage and the inertial effect at high loading rates.
2017, 37(4): 705-711.
doi: 10.11883/1001-1455(2017)04-0705-07
Abstract:
Using finite element simulation, we investigated the spalling of such brittle materials as concrete and rock, studied the attenuation mechanism governing the stress wave propagation through the specimen of brittle materials, and found two kinds of mechanisms: the small amplitude linear attenuation of the elastic wave due to the geometric dispersion of the large size specimen, and the exponential decay of the viscoplastic wave associated with the strain rate due to the constitutive relation. Based on this, we proposed a peak fitting formula of exponential type stress wave with a constant term. It is suggested that we should choose a slender specimen in the spalling test in which the attenuation of the stress wave can be ignored. In addition, we studied the spalling damage of concrete and rock. The scab thickness obtained from the finite element method agrees well with one-dimensional stress wave theory, verifying that the method for determining the spalling strength by one-dimensional stress wave theory is effective. By comparing the scab shape and the tensile stress wave of the brittle material loading by three kinds of the incident wave, we proved that it is more feasible to obtain a flatter spalling cross-section and more precise strength by using an asymmetric incident wave.
Using finite element simulation, we investigated the spalling of such brittle materials as concrete and rock, studied the attenuation mechanism governing the stress wave propagation through the specimen of brittle materials, and found two kinds of mechanisms: the small amplitude linear attenuation of the elastic wave due to the geometric dispersion of the large size specimen, and the exponential decay of the viscoplastic wave associated with the strain rate due to the constitutive relation. Based on this, we proposed a peak fitting formula of exponential type stress wave with a constant term. It is suggested that we should choose a slender specimen in the spalling test in which the attenuation of the stress wave can be ignored. In addition, we studied the spalling damage of concrete and rock. The scab thickness obtained from the finite element method agrees well with one-dimensional stress wave theory, verifying that the method for determining the spalling strength by one-dimensional stress wave theory is effective. By comparing the scab shape and the tensile stress wave of the brittle material loading by three kinds of the incident wave, we proved that it is more feasible to obtain a flatter spalling cross-section and more precise strength by using an asymmetric incident wave.
2017, 37(4): 712-718.
doi: 10.11883/1001-1455(2017)04-0712-07
Abstract:
To explore the dynamic mechanical behaviors of the concrete corroded by salt solution, we fabricated concrete specimens of ordinary Portland cement with fly ash of 15% mass fraction and, having them immersed for 60 d in NaCl and Na2SO4 solutions with a 15% mass fraction, studied their dynamic mechanical properties using a ∅100 mm split Hopkinson pressure bar apparatus. Then, based on the macro phase-only statistical damage theory and the Weibull distribution theory, we built a dynamic statistical damage constitutive model for the specimen's mechanical behaviors. The results indicate that the dynamic compressive strength of the corroded specimens experiences a significant decrease, and the declines of the specimens corroded by NaCl are bigger than those corroded by Na2SO4. Based on the closely fitted curves of the model and the experiment, this established model can accurately estimate the dynamic mechanical behaviors of concrete under impact loading.
To explore the dynamic mechanical behaviors of the concrete corroded by salt solution, we fabricated concrete specimens of ordinary Portland cement with fly ash of 15% mass fraction and, having them immersed for 60 d in NaCl and Na2SO4 solutions with a 15% mass fraction, studied their dynamic mechanical properties using a ∅100 mm split Hopkinson pressure bar apparatus. Then, based on the macro phase-only statistical damage theory and the Weibull distribution theory, we built a dynamic statistical damage constitutive model for the specimen's mechanical behaviors. The results indicate that the dynamic compressive strength of the corroded specimens experiences a significant decrease, and the declines of the specimens corroded by NaCl are bigger than those corroded by Na2SO4. Based on the closely fitted curves of the model and the experiment, this established model can accurately estimate the dynamic mechanical behaviors of concrete under impact loading.
2017, 37(4): 719-726.
doi: 10.11883/1001-1455(2017)04-0719-08
Abstract:
By carrying out model experiments, we investigated the internal load characteristics of the broadside cabin of the defensive structure subjected to underwater contact explosion near the free surface. According to the damage of the experimental models and the pressure profile measured by sensors, we described the interaction between underwater explosion products and the broadside cabin of the defensive structure, and analyzed the pressure change of gas in the broadside cabin of the structure. The results show that the gas pressure in the broadside cabin of the structure can be divided into the shock wave phase, the quasi-static pressure phase and the negative pressure phase, and the broadside cabin is damaged mostly by the shock wave and quasi-static pressure. In addition the specific-impulse of the quasi-static pressure is several times bigger than that of the shock wave, and the effect of the negative pressure on the damage of the broadside cabin is negligible.
By carrying out model experiments, we investigated the internal load characteristics of the broadside cabin of the defensive structure subjected to underwater contact explosion near the free surface. According to the damage of the experimental models and the pressure profile measured by sensors, we described the interaction between underwater explosion products and the broadside cabin of the defensive structure, and analyzed the pressure change of gas in the broadside cabin of the structure. The results show that the gas pressure in the broadside cabin of the structure can be divided into the shock wave phase, the quasi-static pressure phase and the negative pressure phase, and the broadside cabin is damaged mostly by the shock wave and quasi-static pressure. In addition the specific-impulse of the quasi-static pressure is several times bigger than that of the shock wave, and the effect of the negative pressure on the damage of the broadside cabin is negligible.
2017, 37(4): 727-733.
doi: 10.11883/1001-1455(2017)04-0727-07
Abstract:
In this paper, the horizontal water-entry experiments of truncated-ogive projectiles at the velocity range of 100~150 m/s were conducted using a light-gas gun and a high-speed camera to record the whole water-entry process. The characteristics of the velocity attenuation and the drag coefficients of truncated-ogive projectiles were obtained, and the trajectory stability and the characteristics of velocity attenuation for the flat-nosed, the ogive-nosed and the truncated ogive-nosed projectiles were compared and analyzed. The cavity expanding behaviors induced by the truncated ogive-nosed projectile's water entry were studied and a theoretical model of the cavity expansion was established. The relationships between the radial cavity radius, cavity wall velocity and time, penetration distance at fixed locations and fixed times were obtained, and good agreements were found between the experimental observations and the theoretical analysis.
In this paper, the horizontal water-entry experiments of truncated-ogive projectiles at the velocity range of 100~150 m/s were conducted using a light-gas gun and a high-speed camera to record the whole water-entry process. The characteristics of the velocity attenuation and the drag coefficients of truncated-ogive projectiles were obtained, and the trajectory stability and the characteristics of velocity attenuation for the flat-nosed, the ogive-nosed and the truncated ogive-nosed projectiles were compared and analyzed. The cavity expanding behaviors induced by the truncated ogive-nosed projectile's water entry were studied and a theoretical model of the cavity expansion was established. The relationships between the radial cavity radius, cavity wall velocity and time, penetration distance at fixed locations and fixed times were obtained, and good agreements were found between the experimental observations and the theoretical analysis.
2017, 37(4): 734-740.
doi: 10.11883/1001-1455(2017)04-0734-07
Abstract:
The assessment of the behavior of large yellow croakers (Pseudosciaena crocea) in response to underwater acoustic waves entails clear and exact indices of assessment. In this work we collected data of underwater acoustic waves of coastal mountain blasting and underwater explosion using two types of acoustic instruments (Pulse 3560 and DSG) monitored at the sea stations, recorded large yellow croakers′ behavioral characteristics, and carried out the index study of two signal parameters, peak pressure and sound exposure level, in combination with comparative analysis of the croakers′ in situ behaviors. The results showed that, when the pressure amplitudes of the acoustic waves resulting from underwater explosion and mountain blasting were high, the momentary maximal sound energy would reach a momentary maximum value, affecting the croakers′ behavior and safety. On the other hand, when the pressure amplitudes were lower but the time of exposure to the acoustic waves were long, the continual accumulation of sound energy would also affect the large yellow croakers′ behavior. As a result, the levels of the exposure to the two blasting sound waves in different exposure times were very much consistent, and the croakers′ abnormal behaviors were observed at sound exposure levels higher than 150 dB. So, an important conclusion was derived, combined with large yellow croakers′ behavior and related academic research, that sound exposure level can be taken as an important factor, which was the total energy received over the sound exposure time, and should be used to assess the influence of the underwater acoustic waves on the large yellow croaker in underwater explosion and coastal mountain blasting.
The assessment of the behavior of large yellow croakers (Pseudosciaena crocea) in response to underwater acoustic waves entails clear and exact indices of assessment. In this work we collected data of underwater acoustic waves of coastal mountain blasting and underwater explosion using two types of acoustic instruments (Pulse 3560 and DSG) monitored at the sea stations, recorded large yellow croakers′ behavioral characteristics, and carried out the index study of two signal parameters, peak pressure and sound exposure level, in combination with comparative analysis of the croakers′ in situ behaviors. The results showed that, when the pressure amplitudes of the acoustic waves resulting from underwater explosion and mountain blasting were high, the momentary maximal sound energy would reach a momentary maximum value, affecting the croakers′ behavior and safety. On the other hand, when the pressure amplitudes were lower but the time of exposure to the acoustic waves were long, the continual accumulation of sound energy would also affect the large yellow croakers′ behavior. As a result, the levels of the exposure to the two blasting sound waves in different exposure times were very much consistent, and the croakers′ abnormal behaviors were observed at sound exposure levels higher than 150 dB. So, an important conclusion was derived, combined with large yellow croakers′ behavior and related academic research, that sound exposure level can be taken as an important factor, which was the total energy received over the sound exposure time, and should be used to assess the influence of the underwater acoustic waves on the large yellow croaker in underwater explosion and coastal mountain blasting.
2017, 37(4): 741-747.
doi: 10.11883/1001-1455(2017)04-0741-07
Abstract:
A computational study of the interaction between shock waves and a spherical flame was carried out using the ninth-order WENO and the tenth-order central difference schemes, and the influence of shock intensity and flame size on the interaction process was investigated. It can be found from the results of our study that the increase of the shock intensity and the flame size can both induce detonation in the flow field, but the influence of the shock intensity is relatively stronger. Further, the detonation induced by shock wave can lead to quick flame expansion and increase its heat release rate, thereby affecting the combustion characteristics. Besides, the detonation wave will quickly burn out the combustible gas, merge the previously existing reflected shock waves in the propagation process, and form local high pressure zones, which can significantly alter the flow field structure.
A computational study of the interaction between shock waves and a spherical flame was carried out using the ninth-order WENO and the tenth-order central difference schemes, and the influence of shock intensity and flame size on the interaction process was investigated. It can be found from the results of our study that the increase of the shock intensity and the flame size can both induce detonation in the flow field, but the influence of the shock intensity is relatively stronger. Further, the detonation induced by shock wave can lead to quick flame expansion and increase its heat release rate, thereby affecting the combustion characteristics. Besides, the detonation wave will quickly burn out the combustible gas, merge the previously existing reflected shock waves in the propagation process, and form local high pressure zones, which can significantly alter the flow field structure.
2017, 37(4): 748-758.
doi: 10.11883/1001-1455(2017)04-0748-11
Abstract:
To study the interaction process of the plane incident shock wave with the magnetized R22 heavy gas column, we numerically simulated the deformation process of the shock-wave-induced R22 heavy gas column resulting from Kelvin-Helmholtz (KH) and Richtmyer-Meshkov (RM) instabilities under different initial conditions, and analyzed the jet focusing and inducing process by the transmitted shock wave. When the magnetic field was taken into consideration, the CTU + CT algorithm satisfying the divergence equation of the magnetic field at any time was adopted in the numerical simulation. The results show that the magnetic field is capable of restraining the instability of the shock-wave-induced R22 gas column. Both the normal magnetic field (vertical to the flow direction) and the tangential magnetic field (parallel to the flow direction) can inhibit the RM instability. However, the restraining of the normal magnetic field is more effective than that of the tangential one with regard to the KH instability, as it can not only inhibit the vortex train rolling up on the interface but also prevent the bound vortex from developing. Besides, it is found that the magnetic field has little influence on the jet, and the magnetic energy at the jet point can suppress the jet attenuation to some extent while the normal magnetic field can reduce the peak pressure and velocity when the transmitted shock wave is focused.
To study the interaction process of the plane incident shock wave with the magnetized R22 heavy gas column, we numerically simulated the deformation process of the shock-wave-induced R22 heavy gas column resulting from Kelvin-Helmholtz (KH) and Richtmyer-Meshkov (RM) instabilities under different initial conditions, and analyzed the jet focusing and inducing process by the transmitted shock wave. When the magnetic field was taken into consideration, the CTU + CT algorithm satisfying the divergence equation of the magnetic field at any time was adopted in the numerical simulation. The results show that the magnetic field is capable of restraining the instability of the shock-wave-induced R22 gas column. Both the normal magnetic field (vertical to the flow direction) and the tangential magnetic field (parallel to the flow direction) can inhibit the RM instability. However, the restraining of the normal magnetic field is more effective than that of the tangential one with regard to the KH instability, as it can not only inhibit the vortex train rolling up on the interface but also prevent the bound vortex from developing. Besides, it is found that the magnetic field has little influence on the jet, and the magnetic energy at the jet point can suppress the jet attenuation to some extent while the normal magnetic field can reduce the peak pressure and velocity when the transmitted shock wave is focused.
2017, 37(4): 759-765.
doi: 10.11883/1001-1455(2017)04-0759-07
Abstract:
To explore the influence of the inerting agent with different particle sizes on the flame propagation of the combustible industrial dust, by establishing a vertical dust combustion pipe experiment platform, we investigated the effects of the particle size of sodium bicarbonate on the characteristics of the burning flame propagation of aluminum powder. The results show that, under the condition of 30% mass fraction of sodium bicarbonate, the sodium bicarbonate powder with an average particle size of 30 μm has a good inhibitory effect on the flame propagation speed of aluminum powder with an average particle size of 15 μm, and there exists a correlation between the particle size of the inerting powder and the combustible industrial dust. The inerting inhibiting effect of sodium bicarbonate powder on the flame temperature of aluminum is inversely proportionate to its particle size. It was found that sodium bicarbonate powder can decrease the thickness of the preheating zone of aluminum powder flame, which decreases at first and then increases with the increase of the particle size of the sodium bicarbonate. Finally, we also examined the mechanism underlying the influence of sodium bicarbonate particle size on the flame propagation of aluminum powder.
To explore the influence of the inerting agent with different particle sizes on the flame propagation of the combustible industrial dust, by establishing a vertical dust combustion pipe experiment platform, we investigated the effects of the particle size of sodium bicarbonate on the characteristics of the burning flame propagation of aluminum powder. The results show that, under the condition of 30% mass fraction of sodium bicarbonate, the sodium bicarbonate powder with an average particle size of 30 μm has a good inhibitory effect on the flame propagation speed of aluminum powder with an average particle size of 15 μm, and there exists a correlation between the particle size of the inerting powder and the combustible industrial dust. The inerting inhibiting effect of sodium bicarbonate powder on the flame temperature of aluminum is inversely proportionate to its particle size. It was found that sodium bicarbonate powder can decrease the thickness of the preheating zone of aluminum powder flame, which decreases at first and then increases with the increase of the particle size of the sodium bicarbonate. Finally, we also examined the mechanism underlying the influence of sodium bicarbonate particle size on the flame propagation of aluminum powder.
2017, 37(4): 766-772.
doi: 10.11883/1001-1455(2017)04-0766-07
Abstract:
According to the national standards of oil and gas pipeline fire test in China (GB13347—92), six DN50 crimped ribbon deflagration arrestors belonging to Group ⅡA were tested by experiments, and the flameproof velocity of every single arrestor was obtained. The experimental results show that the expansion ratio, the length of the narrow channel and the cross-section of the narrow passage are the three dominant factors that influence the flameproof velocity. Based on this analysis, the relation between the flameproof velocity and the expansion ratio, the thickness of the crimped ribbon element and the cross-section of the narrow passage were presented. The results indicate that the flameproof velocity is proportional to the length of the narrow channels and the square of expansion ratio, whereas it is inversely proportional to the feature size of the cross-section. This study can provide guidance in the design and manufacture of crimped ribbon deflagration arrestors.
According to the national standards of oil and gas pipeline fire test in China (GB13347—92), six DN50 crimped ribbon deflagration arrestors belonging to Group ⅡA were tested by experiments, and the flameproof velocity of every single arrestor was obtained. The experimental results show that the expansion ratio, the length of the narrow channel and the cross-section of the narrow passage are the three dominant factors that influence the flameproof velocity. Based on this analysis, the relation between the flameproof velocity and the expansion ratio, the thickness of the crimped ribbon element and the cross-section of the narrow passage were presented. The results indicate that the flameproof velocity is proportional to the length of the narrow channels and the square of expansion ratio, whereas it is inversely proportional to the feature size of the cross-section. This study can provide guidance in the design and manufacture of crimped ribbon deflagration arrestors.
2017, 37(4): 773-778.
doi: 10.11883/1001-1455(2017)04-0773-06
Abstract:
To study the characteristics of the methane-air mixture exploding in a closed spherical container, we determined the appropriate combustion products and chemical equilibrium temperature using the chemical equilibrium calculation software, thereby predicting the maximum explosion pressure of the mixture. The MATLAB program based on the flame growth model was adopted to calculate the curve showing the relationship between the explosion pressure and time. The calculation processes were verified by the comparison of the obtained results with the experimental data, and the origin of the error was also identified. Further, it is found that the empirical formula of the deflagration index KG derived from the flame growth model is well fitted with the experimental date near the chemical equivalent line.
To study the characteristics of the methane-air mixture exploding in a closed spherical container, we determined the appropriate combustion products and chemical equilibrium temperature using the chemical equilibrium calculation software, thereby predicting the maximum explosion pressure of the mixture. The MATLAB program based on the flame growth model was adopted to calculate the curve showing the relationship between the explosion pressure and time. The calculation processes were verified by the comparison of the obtained results with the experimental data, and the origin of the error was also identified. Further, it is found that the empirical formula of the deflagration index KG derived from the flame growth model is well fitted with the experimental date near the chemical equivalent line.
2017, 37(4): 779-784.
doi: 10.11883/1001-1455(2017)04-0779-06
Abstract:
Vehicles are apt to catch fire easily in high-temperature weather or in traffic accidents. When their fuel tanks cook off, an explosion may occur, thereby posing a hazard to personal safety. To investigate the cook-off performance of fuel tanks, we conducted 4 tests on 76L fuel tanks under different airtight conditions and infillings, and obtained the surface and internal temperatures and the size of the fireballs using an infrared thermal imager, thermocouples and a camera. The experimental results show that the explosion may occur when the fuel outlets are closed and the fuel tank is not filled with explosion suppression balls. In our experiments, the highest surface temperature of the explosion fireball was above 1800K, and the volume of the fireball was 1600 times more than that of the fuel tank. The explosion suppression balls filled in the tanks decreased the highest surface temperature and sizes of the jet fire. Under the same conditions, the average heating rate and the highest temperature of the diesel fuel vapor were 36.0% and 16.2% lower than that of the gasoline vapor respectively.
Vehicles are apt to catch fire easily in high-temperature weather or in traffic accidents. When their fuel tanks cook off, an explosion may occur, thereby posing a hazard to personal safety. To investigate the cook-off performance of fuel tanks, we conducted 4 tests on 76L fuel tanks under different airtight conditions and infillings, and obtained the surface and internal temperatures and the size of the fireballs using an infrared thermal imager, thermocouples and a camera. The experimental results show that the explosion may occur when the fuel outlets are closed and the fuel tank is not filled with explosion suppression balls. In our experiments, the highest surface temperature of the explosion fireball was above 1800K, and the volume of the fireball was 1600 times more than that of the fuel tank. The explosion suppression balls filled in the tanks decreased the highest surface temperature and sizes of the jet fire. Under the same conditions, the average heating rate and the highest temperature of the diesel fuel vapor were 36.0% and 16.2% lower than that of the gasoline vapor respectively.
