2022 Vol. 42, No. 8
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2022, 42(8): 082201.
doi: 10.11883/bzycj-2021-0326
Abstract:
In order to investigate the temporal and spatial distribution of the stress wave in the soil produced by buried explosion, the ANSYS/AUTODYN software was employed for modelling and simulation, and the ground shock effect of explosion in soil was analyzed. Based on the relationship between the pressure and volumetric strain of Luoyang loess obtained by predecessors, the relationship between the pressure and density of the impact compaction in the SAND model was modified. The numerical model was validated by the test data, which were measured from the contact explosion and semi-buried explosion test in loess. Then, a total of 22 numerical simulation conditions were examined to study the influence of the scaled buried depth of the charge and the type of the explosive on the ground shock subzones. The results show that as the depth of the soil medium increases, the peak of induced ground shock decreases, while the peak of direct ground shock increases, until the peak of the pressure-time curve and the peak in the vertical stress-time curve finally merge into a single peak. According to the characteristics of the pressure and vertical stress at various depths, the stress wave field in soil can be divided into three subzones consisting of surface subzone, near-surface subzone and central subzone. With the increase of the scaled buried depth of the charge, the central subzone rapidly increases, the surface subzone rapidly decreases, and the near-surface subzone gradually increases from zero, when the scaled buried depth of the charge ranges from −0.05 m/kg1/3 to 0.075 m/kg1/3. The distribution of the ground shock subzones tends to be stable, when the scaled buried depth of the charge ranges from 0.1 m/kg1/3 to 0.4 m/kg1/3. The energy of the explosive coupling into the air and soil mediums is affected by the type of the explosive. In certain extent, the angle of the ground shock subzones is linearly related to the ratio of the air-blast overpressure impulse to the impulse of the direct ground shock stress.
In order to investigate the temporal and spatial distribution of the stress wave in the soil produced by buried explosion, the ANSYS/AUTODYN software was employed for modelling and simulation, and the ground shock effect of explosion in soil was analyzed. Based on the relationship between the pressure and volumetric strain of Luoyang loess obtained by predecessors, the relationship between the pressure and density of the impact compaction in the SAND model was modified. The numerical model was validated by the test data, which were measured from the contact explosion and semi-buried explosion test in loess. Then, a total of 22 numerical simulation conditions were examined to study the influence of the scaled buried depth of the charge and the type of the explosive on the ground shock subzones. The results show that as the depth of the soil medium increases, the peak of induced ground shock decreases, while the peak of direct ground shock increases, until the peak of the pressure-time curve and the peak in the vertical stress-time curve finally merge into a single peak. According to the characteristics of the pressure and vertical stress at various depths, the stress wave field in soil can be divided into three subzones consisting of surface subzone, near-surface subzone and central subzone. With the increase of the scaled buried depth of the charge, the central subzone rapidly increases, the surface subzone rapidly decreases, and the near-surface subzone gradually increases from zero, when the scaled buried depth of the charge ranges from −0.05 m/kg1/3 to 0.075 m/kg1/3. The distribution of the ground shock subzones tends to be stable, when the scaled buried depth of the charge ranges from 0.1 m/kg1/3 to 0.4 m/kg1/3. The energy of the explosive coupling into the air and soil mediums is affected by the type of the explosive. In certain extent, the angle of the ground shock subzones is linearly related to the ratio of the air-blast overpressure impulse to the impulse of the direct ground shock stress.
2022, 42(8): 082202.
doi: 10.11883/bzycj-2021-0281
Abstract:
In the current design of the dynamic damage field of the fragment warheads, the central blind area effect is regarded as an essential factor affecting the warhead damage efficiency improvement. The axially-enhanced warhead has become an important design means to eliminate the dynamic central blind area of the warhead, which attracts more and more attention from relevant researchers. In the present paper, based on the smoothed particle hydrodynamics (SPH) computation method, a series of numerical models for the shell breaking and fragment dispersion processes of axially-reinforced warheads with non-filler, polyurethane filler nylon filler and explosive filler, respectively, at the end under the explosive loadings are established, and used to study the influence of the characteristics of the fillers in the front of the warhead on the dynamic response of the shell. It is found from the numerical simulations that the filler has a significant influence on the velocity of the fragments in the front of the warhead but a minor influence on the dispersion angle of the fragments. The mechanism of the influence of the non-reactive filler on the fragment velocity is analyzed by comparing the velocity history curves of the specific fragments. The results show that the polyurethane foam filling can significantly delay the acceleration process of the explosive shock wave to the forward fragment and reduce the explosive load to a certain extent. The nylon filler can reduce the acceleration of the forward fragment and the acceleration of the lateral fragment to a certain extent. Thus, the explosion loading is guided to be evenly distributed around the circumference of the end position. Considering the synthesis of the involved velocity of the warhead, using low-density and low-mass filler instead of head charge has the same dynamic damage effect of improving the energy utilization efficiency of the axially-enhanced warhead. The numerical models established in this paper and the research finding can provide some reference for the dynamic damage field design of conventional fragment warheads.
In the current design of the dynamic damage field of the fragment warheads, the central blind area effect is regarded as an essential factor affecting the warhead damage efficiency improvement. The axially-enhanced warhead has become an important design means to eliminate the dynamic central blind area of the warhead, which attracts more and more attention from relevant researchers. In the present paper, based on the smoothed particle hydrodynamics (SPH) computation method, a series of numerical models for the shell breaking and fragment dispersion processes of axially-reinforced warheads with non-filler, polyurethane filler nylon filler and explosive filler, respectively, at the end under the explosive loadings are established, and used to study the influence of the characteristics of the fillers in the front of the warhead on the dynamic response of the shell. It is found from the numerical simulations that the filler has a significant influence on the velocity of the fragments in the front of the warhead but a minor influence on the dispersion angle of the fragments. The mechanism of the influence of the non-reactive filler on the fragment velocity is analyzed by comparing the velocity history curves of the specific fragments. The results show that the polyurethane foam filling can significantly delay the acceleration process of the explosive shock wave to the forward fragment and reduce the explosive load to a certain extent. The nylon filler can reduce the acceleration of the forward fragment and the acceleration of the lateral fragment to a certain extent. Thus, the explosion loading is guided to be evenly distributed around the circumference of the end position. Considering the synthesis of the involved velocity of the warhead, using low-density and low-mass filler instead of head charge has the same dynamic damage effect of improving the energy utilization efficiency of the axially-enhanced warhead. The numerical models established in this paper and the research finding can provide some reference for the dynamic damage field design of conventional fragment warheads.
2022, 42(8): 083101.
doi: 10.11883/bzycj-2022-0145
Abstract:
Shell nacre is a nature material with high strength and toughness, and the excellent performance is mainly derived from multi-scale, multi-hierarchy with “brick and mortar” structure. Inspired by the special structure of shell, a finite element model of nacre-like brick and mortar structures was created and the explosion experiment was carried out. In the experiment, the sample was destroyed catastrophically at the explosion impulse of 0.047 N·s, with the fall of the center. Additionally, shear failure existed around the clamping end of the specimen, which is in good agreement with the numerical simulation results. On this basis, the dynamic response of nacre-like brick and mortar models under explosive load was explored. Five different failure modes were analyzed, including: mode Ⅰ, inelastic deformation without damage; mode Ⅱ, partial damage with damage in the back surface; mode Ⅲ, through-wall failure in the center of specimen; mode Ⅳ, through-wall failure in the center of specimen and shear failure at the clamping end; mode Ⅴ, devastating damage with large drop through in the center and shear failure. The thresholds critical of different failure modes were obtained based on the simulation results. The threshold value for the one-layer brick and mortar structure was 0.019 N·s, and this value increased to 0.047 N·s for the five-layer brick and mortar structure. When the impulse exceeds the threshold value, catastrophic damage occurrs. The effects of the number of stacked layers on the response of the brick and mortar models were analyzed. With the increase of the number of stacked layers, the failure mode of the structure changes from devastating damage to inelastic deformation. Additionally, the threshold value for brick and mortar structure under explosion load increased with the increase of the number of stacked layers. Finally, the toughening mechanism of nacre-like brick and mortar structure was given, including crack deflection and microcrack.
Shell nacre is a nature material with high strength and toughness, and the excellent performance is mainly derived from multi-scale, multi-hierarchy with “brick and mortar” structure. Inspired by the special structure of shell, a finite element model of nacre-like brick and mortar structures was created and the explosion experiment was carried out. In the experiment, the sample was destroyed catastrophically at the explosion impulse of 0.047 N·s, with the fall of the center. Additionally, shear failure existed around the clamping end of the specimen, which is in good agreement with the numerical simulation results. On this basis, the dynamic response of nacre-like brick and mortar models under explosive load was explored. Five different failure modes were analyzed, including: mode Ⅰ, inelastic deformation without damage; mode Ⅱ, partial damage with damage in the back surface; mode Ⅲ, through-wall failure in the center of specimen; mode Ⅳ, through-wall failure in the center of specimen and shear failure at the clamping end; mode Ⅴ, devastating damage with large drop through in the center and shear failure. The thresholds critical of different failure modes were obtained based on the simulation results. The threshold value for the one-layer brick and mortar structure was 0.019 N·s, and this value increased to 0.047 N·s for the five-layer brick and mortar structure. When the impulse exceeds the threshold value, catastrophic damage occurrs. The effects of the number of stacked layers on the response of the brick and mortar models were analyzed. With the increase of the number of stacked layers, the failure mode of the structure changes from devastating damage to inelastic deformation. Additionally, the threshold value for brick and mortar structure under explosion load increased with the increase of the number of stacked layers. Finally, the toughening mechanism of nacre-like brick and mortar structure was given, including crack deflection and microcrack.
2022, 42(8): 083102.
doi: 10.11883/bzycj-2021-0456
Abstract:
The influence of assembly cushions on the fracture of an expanding metal cylindrical shell was studied. The velocity of the outer surface of the shell with or without a cushion in it was measured by a Doppler pins system (DPS) array, and images with the obvious influence of an inner cushion on the fracture of the shell were recorded by the high-speed photography. Compared with the area without the cushion, the outer surface of the cylindrical shell in the cushion area experienced a process of first convex and then concave movement, which made the radial displacement of the surface repeatedly misplace, leading to a final displacement of 0.34 mm lower. This displacement difference may lead to the radial shear fracture of the cylindrical shell. Besides, in the experiment, a crack appeared on both sides of the cushion/gap interface (7.5° deviation on the cushion side and 9° deviation on the gap side). These cracks were resulted from the disturbance of two sparse stress waves, which were generated from the cushion/gap interface and then transmitted to the outer surface of the cylindrical shell. The fracture mode is different from both circumferential tensile fracture and shear fracture along 45° direction. This new fracture mode is closely related to the dynamic mechanical properties of the cylindrical shell’s material. Further numerical simulation analysis shows that the influence of the assembly cushion on the fracture mechanism of the cylindrical shell includes three aspects: firstly, the additional mass effect; secondly, the amplitude change of the explosive impact loading after it passing through the cushion, and the asynchronous difference of the impact loading sequence with other parts; and thirdly, the influence of the propagation of surface waves, which originate from the interface between the cushion and the gap, on the subsequent development behavior of the cylindrical fracture mode .
The influence of assembly cushions on the fracture of an expanding metal cylindrical shell was studied. The velocity of the outer surface of the shell with or without a cushion in it was measured by a Doppler pins system (DPS) array, and images with the obvious influence of an inner cushion on the fracture of the shell were recorded by the high-speed photography. Compared with the area without the cushion, the outer surface of the cylindrical shell in the cushion area experienced a process of first convex and then concave movement, which made the radial displacement of the surface repeatedly misplace, leading to a final displacement of 0.34 mm lower. This displacement difference may lead to the radial shear fracture of the cylindrical shell. Besides, in the experiment, a crack appeared on both sides of the cushion/gap interface (7.5° deviation on the cushion side and 9° deviation on the gap side). These cracks were resulted from the disturbance of two sparse stress waves, which were generated from the cushion/gap interface and then transmitted to the outer surface of the cylindrical shell. The fracture mode is different from both circumferential tensile fracture and shear fracture along 45° direction. This new fracture mode is closely related to the dynamic mechanical properties of the cylindrical shell’s material. Further numerical simulation analysis shows that the influence of the assembly cushion on the fracture mechanism of the cylindrical shell includes three aspects: firstly, the additional mass effect; secondly, the amplitude change of the explosive impact loading after it passing through the cushion, and the asynchronous difference of the impact loading sequence with other parts; and thirdly, the influence of the propagation of surface waves, which originate from the interface between the cushion and the gap, on the subsequent development behavior of the cylindrical fracture mode .
2022, 42(8): 083201.
doi: 10.11883/bzycj-2021-0450
Abstract:
The detonation position and the shape of the explosive have a significant influence on the pressure of the underwater explosion shock wave, which makes it possible to use a small charge to form a shock wave that is equivalent to a large charge in a local direction. A charge design method to adjust the amplitude and duration of shock wave pressure was established based on the slender charge structure and parameter optimization design to carry out an underwater explosion shock resistance test of ship structure or equipment using a small charge. Firstly, based on the simple wave theory, the principle of shock wave pressure control and the objective function and constraint conditions of optimal design of charge parameters are given. Then, an independently developed software is used to study the energy of underwater explosion of slender charge, and the confidence degree of numerical simulation is verified through experiments. It is found that the influence of initiation position and charge shape on the pressure peak and duration of the underwater explosion shock wave is significant. The duration of shock wave pressure of slender charge column underwater explosion can be determined by geometric approximation. Finally, to further investigate the effectiveness of the proposed method, two charge schemes equivalent to the shock wave pressure of the prototype were designed and verified by numerical simulation. The prototype is taken from the pressure-time curve of the underwater explosion shock wave with TNT equivalent to 1000 kg and a stand-off of 100 m. The comparison results show that the designed charge can form a shock wave pressure-time curve equivalent to that of the prototype on the side of the initiation end within a predetermined duration. Since the bubble pulse is not considered, the established method applies only to the middle and far-field explosion shock problem.
The detonation position and the shape of the explosive have a significant influence on the pressure of the underwater explosion shock wave, which makes it possible to use a small charge to form a shock wave that is equivalent to a large charge in a local direction. A charge design method to adjust the amplitude and duration of shock wave pressure was established based on the slender charge structure and parameter optimization design to carry out an underwater explosion shock resistance test of ship structure or equipment using a small charge. Firstly, based on the simple wave theory, the principle of shock wave pressure control and the objective function and constraint conditions of optimal design of charge parameters are given. Then, an independently developed software is used to study the energy of underwater explosion of slender charge, and the confidence degree of numerical simulation is verified through experiments. It is found that the influence of initiation position and charge shape on the pressure peak and duration of the underwater explosion shock wave is significant. The duration of shock wave pressure of slender charge column underwater explosion can be determined by geometric approximation. Finally, to further investigate the effectiveness of the proposed method, two charge schemes equivalent to the shock wave pressure of the prototype were designed and verified by numerical simulation. The prototype is taken from the pressure-time curve of the underwater explosion shock wave with TNT equivalent to 1000 kg and a stand-off of 100 m. The comparison results show that the designed charge can form a shock wave pressure-time curve equivalent to that of the prototype on the side of the initiation end within a predetermined duration. Since the bubble pulse is not considered, the established method applies only to the middle and far-field explosion shock problem.
2022, 42(8): 083202.
doi: 10.11883/bzycj-2021-0444
Abstract:
To investigate the mechanics, deformation, and energy evolution characteristics of concrete under dynamic loading, impact compression tests at impact velocities of 5, 6, and 7 m/s, and splitting tensile tests at 4 m/s were carried out on concrete specimens with aggregate volume rates of 0, 32%, 37%, and 42% using a 100 mm diameter split Hopkinson pressure bar (SHPB) device. The failure process of concrete specimens was acquired by a high-speed camera, and the damaged concrete fragments were collected and sorted. Furthermore, the fractal dimension of fragments was calculated by dividing the fragments into different grades. The stress and strain of the concrete specimen were obtained through the corresponding calculation formulas. The relationships between specimen deformation, dynamic strength, and fractal dimension with impact velocity and aggregate rate were studied, and the expression for dynamic strength with respect to impact velocity and aggregate rate was developed. In addition, the fractal dimension was used to characterize the surface roughness of the concrete fragments, and the function expression between crack surface energy and fractal dimension was established. The relationship between sample absorption energy and crack surface energy was analyzed and compared. The results show that deformation hysteresis occurs when concrete specimens are destroyed and the failure is mainly in the form of splitting tensile damage. The dynamic strength increases with the increase of impact velocity and aggregate ratio, the dynamic strength of concrete can be better predicted by using the proposed dynamic strength formula. The fractal dimension of concrete breaking fragments, absorbed energy and crack surface energy all increase with the increase of impact velocity and decrease with the increase of aggregate rate, and the absorbed energy is always higher than the crack surface energy. The highest conversion rate of absorbed energy is achieved when the aggregate rate is 37%, with approximately 91% converts to crack surface energy.
To investigate the mechanics, deformation, and energy evolution characteristics of concrete under dynamic loading, impact compression tests at impact velocities of 5, 6, and 7 m/s, and splitting tensile tests at 4 m/s were carried out on concrete specimens with aggregate volume rates of 0, 32%, 37%, and 42% using a 100 mm diameter split Hopkinson pressure bar (SHPB) device. The failure process of concrete specimens was acquired by a high-speed camera, and the damaged concrete fragments were collected and sorted. Furthermore, the fractal dimension of fragments was calculated by dividing the fragments into different grades. The stress and strain of the concrete specimen were obtained through the corresponding calculation formulas. The relationships between specimen deformation, dynamic strength, and fractal dimension with impact velocity and aggregate rate were studied, and the expression for dynamic strength with respect to impact velocity and aggregate rate was developed. In addition, the fractal dimension was used to characterize the surface roughness of the concrete fragments, and the function expression between crack surface energy and fractal dimension was established. The relationship between sample absorption energy and crack surface energy was analyzed and compared. The results show that deformation hysteresis occurs when concrete specimens are destroyed and the failure is mainly in the form of splitting tensile damage. The dynamic strength increases with the increase of impact velocity and aggregate ratio, the dynamic strength of concrete can be better predicted by using the proposed dynamic strength formula. The fractal dimension of concrete breaking fragments, absorbed energy and crack surface energy all increase with the increase of impact velocity and decrease with the increase of aggregate rate, and the absorbed energy is always higher than the crack surface energy. The highest conversion rate of absorbed energy is achieved when the aggregate rate is 37%, with approximately 91% converts to crack surface energy.
2022, 42(8): 083301.
doi: 10.11883/bzycj-2021-0251
Abstract:
To study the crater’s characteristics of carbon fiber/epoxy composite targets at the impact velocity of 3.0－6.5 km/s, experiments of some composite targets impacted by spherical aluminum projectiles were carried out by applying a two-stage light gas gun in China Aerodynamics Research and Development Center. The targets were one kind of unidirectional braiding laminates made of carbon fiber and epoxy. The density of the targets was 1.5 g/cm3 and the size was 100 mm×100 mm×20 mm. The targets were clamped by two aluminum plates in experiments. One aluminum plate with the thickness of 2.5 mm was set 40 mm behind the targets to test fragments after the targets. The projectile diameter ranged from 1.00 mm to 3.05 mm. The damage feature of each target was obtained. A central crater surrounded with a shallow spalling region was observed in all recovered targets. Different from a semi-spherical crater, the central crater had a proximately quadrate edge, a semi-spherical bottom and a tough and rugged wall. The shallow spalling region was extremely irregular. The parameters of the crater and the shallow spalling region, such as the crater depth, the superficial area of the crater, the superficial area of the spalling region, were measured and analyzed. Moreover, the variations of the dimensionless crater depth p/dp, the dimensionless equivalent crater diameter Dh/dp and the equivalent diameter De of the spalling region with the impact velocity and energy were analyzed. Results show that the p/dp depends on the density ratio ρp/ρt with a power of 1/2, and on the impact velocity vi with a power of 2/3. The results are in good agreement with NASA’s hypervelocity experiments on reinforced carbon-carbon targets. The relationship of Dh/dp with ρp/ρt and vi is similar to that of p/dp with ρp/ρt and vi. De is a power function of impact kinetic energy. The crater-shape coefficient p/Dh is slightly greater than 0.5, which means the crater depth is larger than the crater radius.
To study the crater’s characteristics of carbon fiber/epoxy composite targets at the impact velocity of 3.0－6.5 km/s, experiments of some composite targets impacted by spherical aluminum projectiles were carried out by applying a two-stage light gas gun in China Aerodynamics Research and Development Center. The targets were one kind of unidirectional braiding laminates made of carbon fiber and epoxy. The density of the targets was 1.5 g/cm3 and the size was 100 mm×100 mm×20 mm. The targets were clamped by two aluminum plates in experiments. One aluminum plate with the thickness of 2.5 mm was set 40 mm behind the targets to test fragments after the targets. The projectile diameter ranged from 1.00 mm to 3.05 mm. The damage feature of each target was obtained. A central crater surrounded with a shallow spalling region was observed in all recovered targets. Different from a semi-spherical crater, the central crater had a proximately quadrate edge, a semi-spherical bottom and a tough and rugged wall. The shallow spalling region was extremely irregular. The parameters of the crater and the shallow spalling region, such as the crater depth, the superficial area of the crater, the superficial area of the spalling region, were measured and analyzed. Moreover, the variations of the dimensionless crater depth p/dp, the dimensionless equivalent crater diameter Dh/dp and the equivalent diameter De of the spalling region with the impact velocity and energy were analyzed. Results show that the p/dp depends on the density ratio ρp/ρt with a power of 1/2, and on the impact velocity vi with a power of 2/3. The results are in good agreement with NASA’s hypervelocity experiments on reinforced carbon-carbon targets. The relationship of Dh/dp with ρp/ρt and vi is similar to that of p/dp with ρp/ρt and vi. De is a power function of impact kinetic energy. The crater-shape coefficient p/Dh is slightly greater than 0.5, which means the crater depth is larger than the crater radius.
2022, 42(8): 083302.
doi: 10.11883/bzycj-2021-0294
Abstract:
To study the crater effect of the projectile penetrating a thick concrete target, the crater phenomenon in the penetration test was summarized, the predictive effect of the empirical formula on the crater depth, crater diameter, and crater angle was analyzed. Using the dimensional analysis method, new calculation formulas for the crater formation effect and energy consumption at the crater formation stage were established. The formulas for the crater formation effect take into account the influence of factors such as impact velocity, target strength, reinforcement ratio, projectile diameter, and projectile mass. Based on the new calculation formulas, parameterized analysis of the influencing factors of pit formation effect and the energy consumption of pit formation was performed. The results show that the dimensionless crater depth is greatly affected by the strength of the concrete target, the reinforcement ratio, and the projectile mass. For reinforced concrete, with the increase of the impact velocity, the crater depth increases first, then decreases, and then increases. Within the common range of penetration velocity and mass, the crater angle is in the range from 15° to 24°, and the mass has little effect on the crater angle. The energy consumption of the crater formation on the front surface accounts for 10% to 25% of the total kinetic energy of the projectile, and the reinforcement ratio and the strength of the target plate have a weak effect on the proportion of the energy consumption of the crater. The proportion of the energy consumed in the crater stage increases as the mass of the projectile decreases. The calculation results by the new crater effect calculation formulas for the crater depth, crater diameter, and crater angle are in good agreement with the experimental data, which can provide a reference for the design of penetrating projectiles and engineering protection.
To study the crater effect of the projectile penetrating a thick concrete target, the crater phenomenon in the penetration test was summarized, the predictive effect of the empirical formula on the crater depth, crater diameter, and crater angle was analyzed. Using the dimensional analysis method, new calculation formulas for the crater formation effect and energy consumption at the crater formation stage were established. The formulas for the crater formation effect take into account the influence of factors such as impact velocity, target strength, reinforcement ratio, projectile diameter, and projectile mass. Based on the new calculation formulas, parameterized analysis of the influencing factors of pit formation effect and the energy consumption of pit formation was performed. The results show that the dimensionless crater depth is greatly affected by the strength of the concrete target, the reinforcement ratio, and the projectile mass. For reinforced concrete, with the increase of the impact velocity, the crater depth increases first, then decreases, and then increases. Within the common range of penetration velocity and mass, the crater angle is in the range from 15° to 24°, and the mass has little effect on the crater angle. The energy consumption of the crater formation on the front surface accounts for 10% to 25% of the total kinetic energy of the projectile, and the reinforcement ratio and the strength of the target plate have a weak effect on the proportion of the energy consumption of the crater. The proportion of the energy consumed in the crater stage increases as the mass of the projectile decreases. The calculation results by the new crater effect calculation formulas for the crater depth, crater diameter, and crater angle are in good agreement with the experimental data, which can provide a reference for the design of penetrating projectiles and engineering protection.
2022, 42(8): 083303.
doi: 10.11883/bzycj-2021-0389
Abstract:
In order to study the damage mechanism of the shaped charge warhead with a combined charge liner to the water containing composite structure, the formation and penetration process of the penetrator formed by the combined charge liner were studied based on the arbitrary Lagrangian-Euler (ALE) fluid structure coupling algorithm in the LS-DYNA. The damage of the shaped charge warhead with composite liner to the target was verified by experiments. A hemispherical liner eccentric to the axis was designed at the top of the original eccentric sub-hemispherical liner. The forming process of the penetrator, the response state of the water medium, the dynamic energy loss in the process of penetrating the target and the damage mechanism to the target were analyzed for the warhead with the combined liner. The results show that the design of the sub-hemispherical liner on the top of the eccentric sub-hemispherical liner can form a slender rod-like jet at the front of the penetrator, which can increase the whole length of the penetrator and the velocity of the head penetrator. In the process of the target, the head rod-like penetrators form a cavity to help the subsequent penetrators follow with low resistance. Through the analysis of the damage process to the target, it is found that the first layer of target directly connected with the warhead will be affected by both the high-speed impact of the penetrator and the strong shock wave transmitted by the explosion wave along the water medium. With the increase of the thickness of the water layer, the intensity of the explosion shock wave propagating along the water will be rapidly attenuated, and the effect of the explosion shock wave becomes less obvious to the subsequent target. The experimental verification was carried out by the warhead with composite liner structure. The perforation size of each target was compared and analyzed. The experimental results are in good agreement with the numerical simulation results, and the maximum error is within 15%.
In order to study the damage mechanism of the shaped charge warhead with a combined charge liner to the water containing composite structure, the formation and penetration process of the penetrator formed by the combined charge liner were studied based on the arbitrary Lagrangian-Euler (ALE) fluid structure coupling algorithm in the LS-DYNA. The damage of the shaped charge warhead with composite liner to the target was verified by experiments. A hemispherical liner eccentric to the axis was designed at the top of the original eccentric sub-hemispherical liner. The forming process of the penetrator, the response state of the water medium, the dynamic energy loss in the process of penetrating the target and the damage mechanism to the target were analyzed for the warhead with the combined liner. The results show that the design of the sub-hemispherical liner on the top of the eccentric sub-hemispherical liner can form a slender rod-like jet at the front of the penetrator, which can increase the whole length of the penetrator and the velocity of the head penetrator. In the process of the target, the head rod-like penetrators form a cavity to help the subsequent penetrators follow with low resistance. Through the analysis of the damage process to the target, it is found that the first layer of target directly connected with the warhead will be affected by both the high-speed impact of the penetrator and the strong shock wave transmitted by the explosion wave along the water medium. With the increase of the thickness of the water layer, the intensity of the explosion shock wave propagating along the water will be rapidly attenuated, and the effect of the explosion shock wave becomes less obvious to the subsequent target. The experimental verification was carried out by the warhead with composite liner structure. The perforation size of each target was compared and analyzed. The experimental results are in good agreement with the numerical simulation results, and the maximum error is within 15%.
2022, 42(8): 083304.
doi: 10.11883/bzycj-2021-0336
Abstract:
A 12.7-mm projectile may remain intact or be broken during penetrating into steel targets with different strengths. However, previous simulations were limited to simulating a single situation. To break this limitation, the numerical simulation methods of the 12.7-mm projectile penetration into steel targets were studied, leading to a projectile-target model which was capable of simulating both the intact and broken cases. In the intact projectile case, the ballistic tests were implemented to study the dynamic behavior of the 12.7-mm projectile penetrating into the 603 steel targets. Two different modeling algorithms based on the finite element method (FEM) and the smooth particle hydrodynamics particles (SPH) method, respectively, were compared with the experimental results. Then the influences of finite element and particle sizes on the numerical results were studied to establish the numerical model to simulate the intact projectile case. Furthermore, the established model was applied to simulate the broken projectile case by changing the target material and the element sizes. The numerical results were then compared with the experimental results. The numerical study shows that the projectile and target should be discretized using the FEM and SPH, respectively, for simulating the intact case. Meanwhile, a large ratio between the finite element mesh size and the SPH particle spacing should be used, such as 5.3. Otherwise, an abnormal numerical deformation may occur around the projectile head, which is inconsistent with the experimental result. This model can also be used to simulate the broken projectile case, as verified with the experimental results. However, the large ratio between the finite element mesh size and the SPH particle spacing leads to numerical problems and abort of simulations. To overcome this difficulty, an FEM/SPH coupled projectile-target model is proposed, in which the projectile was discretized using coarse meshes close to the surface and fine meshes in the core region. Numerical results show that the proposed projectile-target model can be used to simulate the penetration process no matter the projectile remains intact or broken.
A 12.7-mm projectile may remain intact or be broken during penetrating into steel targets with different strengths. However, previous simulations were limited to simulating a single situation. To break this limitation, the numerical simulation methods of the 12.7-mm projectile penetration into steel targets were studied, leading to a projectile-target model which was capable of simulating both the intact and broken cases. In the intact projectile case, the ballistic tests were implemented to study the dynamic behavior of the 12.7-mm projectile penetrating into the 603 steel targets. Two different modeling algorithms based on the finite element method (FEM) and the smooth particle hydrodynamics particles (SPH) method, respectively, were compared with the experimental results. Then the influences of finite element and particle sizes on the numerical results were studied to establish the numerical model to simulate the intact projectile case. Furthermore, the established model was applied to simulate the broken projectile case by changing the target material and the element sizes. The numerical results were then compared with the experimental results. The numerical study shows that the projectile and target should be discretized using the FEM and SPH, respectively, for simulating the intact case. Meanwhile, a large ratio between the finite element mesh size and the SPH particle spacing should be used, such as 5.3. Otherwise, an abnormal numerical deformation may occur around the projectile head, which is inconsistent with the experimental result. This model can also be used to simulate the broken projectile case, as verified with the experimental results. However, the large ratio between the finite element mesh size and the SPH particle spacing leads to numerical problems and abort of simulations. To overcome this difficulty, an FEM/SPH coupled projectile-target model is proposed, in which the projectile was discretized using coarse meshes close to the surface and fine meshes in the core region. Numerical results show that the proposed projectile-target model can be used to simulate the penetration process no matter the projectile remains intact or broken.
2022, 42(8): 084101.
doi: 10.11883/bzycj-2021-0343
Abstract:
Aiming at the problem that the initiation mode of the explosion device is highly dependent on the gunpowder products in the simulation experiments of large-scale underground explosions in a vacuum chamber, and based on the similarity theory of underground explosions and the principle of the two-stage gas gun, a micro explosion device initiated by a synchronous launcher of marbles driven by two-stage high-pressure gas was developed independently. A glass enclosure with compressed gas (filled by air compressor) was used to simulate the high-pressure cavity generated at the beginning of a real underground explosion. Two-stage high-pressure gas was used to drive marbles to break the glass shell synchronously, thus releasing the high-pressure gas in the spherical shell to simulate the ejection of gas products in a real underground explosion. The pressure in the launcher chamber is 4 MPa, and the residual steady-state gas pressure in the glass enclosure is about 3 kPa. The above set of the launch parameters can be used for simulation experiments of real underground explosions with an equivalent of 0−20 kt TNT. Through high-speed imaging of the air and water blasting sphericity tests, the reliability of the explosion device and the sphericity of the blasting effect were verified. When there is a difference in the internal and external pressure of the glass spherical shell, the cracks of the shell are fully developed and the fragments are evenly distributed. The applicability test shows that the blasting mechanism and blasting effect of the explosion device can meet the requirements of the simulation experiment of large-scale underground explosions in the vacuum chamber, and the device has the characteristics of high efficiency, low pollution, convenient operation, good repeatability, good controllability and low requirements for site conditions, which can provide a novel technology for the simulation experiments of large-scale underground explosions in the vacuum chamber.
Aiming at the problem that the initiation mode of the explosion device is highly dependent on the gunpowder products in the simulation experiments of large-scale underground explosions in a vacuum chamber, and based on the similarity theory of underground explosions and the principle of the two-stage gas gun, a micro explosion device initiated by a synchronous launcher of marbles driven by two-stage high-pressure gas was developed independently. A glass enclosure with compressed gas (filled by air compressor) was used to simulate the high-pressure cavity generated at the beginning of a real underground explosion. Two-stage high-pressure gas was used to drive marbles to break the glass shell synchronously, thus releasing the high-pressure gas in the spherical shell to simulate the ejection of gas products in a real underground explosion. The pressure in the launcher chamber is 4 MPa, and the residual steady-state gas pressure in the glass enclosure is about 3 kPa. The above set of the launch parameters can be used for simulation experiments of real underground explosions with an equivalent of 0−20 kt TNT. Through high-speed imaging of the air and water blasting sphericity tests, the reliability of the explosion device and the sphericity of the blasting effect were verified. When there is a difference in the internal and external pressure of the glass spherical shell, the cracks of the shell are fully developed and the fragments are evenly distributed. The applicability test shows that the blasting mechanism and blasting effect of the explosion device can meet the requirements of the simulation experiment of large-scale underground explosions in the vacuum chamber, and the device has the characteristics of high efficiency, low pollution, convenient operation, good repeatability, good controllability and low requirements for site conditions, which can provide a novel technology for the simulation experiments of large-scale underground explosions in the vacuum chamber.
2022, 42(8): 084201.
doi: 10.11883/bzycj-2022-0342
Abstract:
When the structural wall moves over a fixed grid, the structure coverage will change, resulting in many dead and emerging elements. To avoid the influence of malformation and reconstruction of body-fitted grids on the calculation efficiency and accuracy of the fluid-structure interaction problems with coupled boundary movement on the fixed grid, an improved numerical method for describing the interaction between an immersed rigid body and fluid based on a sharp-interface is proposed. In this method, both the fluid and solid are regarded as pure fluid domains in the whole computational domain, and the solid boundary is divided into several Lagrangian grid points. The flow parameter or velocity is reconstructed by interpolation at the interface element, which is then directly used as the boundary condition of the flow field, thus reflecting the influence of the wall boundary conditions. The method constructs the calculation structure of “virtual point, force point and vertical foot point”, and the velocity of the virtual point is obtained by bilinear interpolation. Then, the velocity of the force point is calculated by forcing the solid boundary to meet the no-slip condition, and the equations of the coupling system based on the immersion boundary method are finally solved to realize the numerical simulation of the flow with a complex moving boundary. The numerical program for this immersed boundary method is established using C++, then the accuracy and reliability of the proposed method are validated by comparison with the literature and experimental results of the basic numerical example of flow around a cylinder. Furthermore, the effects of the structural shape and the angle of attack on the trailing vortex structure, the vortex shedding frequency, and the lift/ coefficient characteristics of the flow around the elliptical cylinder have been analyzed. The anti-symmetric S-type, “P+S” Ⅰ-type and “P+S” Ⅱ-type trailing vortex shedding modes, as well as the variation laws of the vortex structure size, vortex shedding frequency and lift-drag coefficients ratio with axis ratio and angle of attack, are captured. The critical angle of attack (25°) corresponding to the maximum lift-drag ratio is determined as 25°.
When the structural wall moves over a fixed grid, the structure coverage will change, resulting in many dead and emerging elements. To avoid the influence of malformation and reconstruction of body-fitted grids on the calculation efficiency and accuracy of the fluid-structure interaction problems with coupled boundary movement on the fixed grid, an improved numerical method for describing the interaction between an immersed rigid body and fluid based on a sharp-interface is proposed. In this method, both the fluid and solid are regarded as pure fluid domains in the whole computational domain, and the solid boundary is divided into several Lagrangian grid points. The flow parameter or velocity is reconstructed by interpolation at the interface element, which is then directly used as the boundary condition of the flow field, thus reflecting the influence of the wall boundary conditions. The method constructs the calculation structure of “virtual point, force point and vertical foot point”, and the velocity of the virtual point is obtained by bilinear interpolation. Then, the velocity of the force point is calculated by forcing the solid boundary to meet the no-slip condition, and the equations of the coupling system based on the immersion boundary method are finally solved to realize the numerical simulation of the flow with a complex moving boundary. The numerical program for this immersed boundary method is established using C++, then the accuracy and reliability of the proposed method are validated by comparison with the literature and experimental results of the basic numerical example of flow around a cylinder. Furthermore, the effects of the structural shape and the angle of attack on the trailing vortex structure, the vortex shedding frequency, and the lift/ coefficient characteristics of the flow around the elliptical cylinder have been analyzed. The anti-symmetric S-type, “P+S” Ⅰ-type and “P+S” Ⅱ-type trailing vortex shedding modes, as well as the variation laws of the vortex structure size, vortex shedding frequency and lift-drag coefficients ratio with axis ratio and angle of attack, are captured. The critical angle of attack (25°) corresponding to the maximum lift-drag ratio is determined as 25°.
2022, 42(8): 085201.
doi: 10.11883/bzycj-2021-0324
Abstract:
In order to deeply explore the propagation and attenuation law of column charge blasting stress waves or seismic waves, and to improve the prediction model of the blasting peak vibration velocity, a theoretical study on the blasting peak vibration velocity was carried out. First of all, based on the Heelan short-column charge theory, the concept of the equivalent radius of action was introduced, and the attenuation equation for the blasting peak vibration velocity under the action of the internal instantaneous excitation load was obtained. Then, the concepts of the equivalent action radius and equivalent blasting load were applied to the theoretical derivation of the blasting peak vibration velocity. The attenuation laws of the blast-induced vibration in cutting hole sections and non-cutting hole sections were studied, respectively. Finally, based on the dimensional harmony theorem, the reliability and universality of the attenuation model were verified. Combined with an example of tunnel blasting project, the attenuation laws of the blasting peak vibration velocities corresponding to different segments of detonators and different types of blast holes were studied. The results show that the improved formula can well fit the peak velocities of the above two types of blasting vibrations, which can accurately reflect the transmission law of the tunnel blasting vibration. In addition, the expressions of the charge form of the improved formula under the conditions of spherical charge and columnar charge were discussed, and the prediction effects of various fitting models were compared. The comparison results show that using the equivalent radius of action as a fitting reference variable can comprehensively consider the influence of different detonator positions and different blast hole types on the blasting vibration attenuation law. The reference variables of the statistical data show that the fitting effect obtained by the improved formula is the best, which can provide a reference for similar research of tunnel blasting vibration.
In order to deeply explore the propagation and attenuation law of column charge blasting stress waves or seismic waves, and to improve the prediction model of the blasting peak vibration velocity, a theoretical study on the blasting peak vibration velocity was carried out. First of all, based on the Heelan short-column charge theory, the concept of the equivalent radius of action was introduced, and the attenuation equation for the blasting peak vibration velocity under the action of the internal instantaneous excitation load was obtained. Then, the concepts of the equivalent action radius and equivalent blasting load were applied to the theoretical derivation of the blasting peak vibration velocity. The attenuation laws of the blast-induced vibration in cutting hole sections and non-cutting hole sections were studied, respectively. Finally, based on the dimensional harmony theorem, the reliability and universality of the attenuation model were verified. Combined with an example of tunnel blasting project, the attenuation laws of the blasting peak vibration velocities corresponding to different segments of detonators and different types of blast holes were studied. The results show that the improved formula can well fit the peak velocities of the above two types of blasting vibrations, which can accurately reflect the transmission law of the tunnel blasting vibration. In addition, the expressions of the charge form of the improved formula under the conditions of spherical charge and columnar charge were discussed, and the prediction effects of various fitting models were compared. The comparison results show that using the equivalent radius of action as a fitting reference variable can comprehensively consider the influence of different detonator positions and different blast hole types on the blasting vibration attenuation law. The reference variables of the statistical data show that the fitting effect obtained by the improved formula is the best, which can provide a reference for similar research of tunnel blasting vibration.
2022, 42(8): 085202.
doi: 10.11883/bzycj-2021-0316
Abstract:
The collapse of the support part and break in the air of the reinforced concrete chimney during blasting demolition seriously affect engineering safety. Monitoring and analysis of a 180m chimney demolition were carried out to analyze the mechanism of these phenomena and distinguish them. Based on the characteristics of the stress-strain curve of concrete, the progressive failure process of the support part is analyzed. The static equilibrium equation of the cross-section is constructed, and the discrimination model for the instability and support part collapse of the chimney is proposed. By establishing the dynamic response model of the chimney above the blasting notch under the bottom impact, the propagation characteristics of the stress wave in the chimney are analyzed. The results show that the ratio of gravity moment to resisting moment can be used as a criterion of instability determination, considering the distribution characteristics of stress and strain in the cross-section of the support part. The compression failure of the concrete in the support part is almost inevitable under large eccentric compression. The necessary condition to prevent support part collapse of the chimney is that the minimum residual bearing capacity of the support part is not less than the weight of the chimney. When the chimney with a certain initial velocity impacts the foundation at the end of the support part collapse, an impact load will be generated and cause the strain in the middle of the chimney greater than the strain at the bottom. The elevation amplification effect of dynamic strain is an important reason for the chimney breaking in the air. The higher the chimney is, the shorter the impact duration is, and the more significant the dynamic strain elevation amplification effect is. As the height increases, the position of the most dangerous section of the chimney will move from the middle and lower to the middle and upper.
The collapse of the support part and break in the air of the reinforced concrete chimney during blasting demolition seriously affect engineering safety. Monitoring and analysis of a 180m chimney demolition were carried out to analyze the mechanism of these phenomena and distinguish them. Based on the characteristics of the stress-strain curve of concrete, the progressive failure process of the support part is analyzed. The static equilibrium equation of the cross-section is constructed, and the discrimination model for the instability and support part collapse of the chimney is proposed. By establishing the dynamic response model of the chimney above the blasting notch under the bottom impact, the propagation characteristics of the stress wave in the chimney are analyzed. The results show that the ratio of gravity moment to resisting moment can be used as a criterion of instability determination, considering the distribution characteristics of stress and strain in the cross-section of the support part. The compression failure of the concrete in the support part is almost inevitable under large eccentric compression. The necessary condition to prevent support part collapse of the chimney is that the minimum residual bearing capacity of the support part is not less than the weight of the chimney. When the chimney with a certain initial velocity impacts the foundation at the end of the support part collapse, an impact load will be generated and cause the strain in the middle of the chimney greater than the strain at the bottom. The elevation amplification effect of dynamic strain is an important reason for the chimney breaking in the air. The higher the chimney is, the shorter the impact duration is, and the more significant the dynamic strain elevation amplification effect is. As the height increases, the position of the most dangerous section of the chimney will move from the middle and lower to the middle and upper.
