2006 Vol. 26, No. 1
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2006, 26(1): 1-6.
doi: 10.11883/1001-1455(2006)01-0001-06
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Abstract:
Three-dimensional (3D) numerical simulations of impact and perforation of concrete targets by projectiles have been performed by incorporating FEM with SPH algorithm. The projectile is divided into quadrilateral elements, and the concrete target is divided into smooth particles. In order to form the elements conveniently, the projectile element consists of three characteristic parts with assembly functions. The sliding surface algorithm for interfaces of SP-FE (smooth particles-finite elements) has been formulated, and to raise the computational efficiency, the slave particles and their connected particles are defined in the pre-processing subroutine. The calculated examples have shown that the combination algorithm of FEM with SPH and the related code could be used to simulate the impact and perforation of concrete targets by projectiles. The differences between 3D and 2D computations for vertical impact as well as the comparison with experimental data are presented here.
Three-dimensional (3D) numerical simulations of impact and perforation of concrete targets by projectiles have been performed by incorporating FEM with SPH algorithm. The projectile is divided into quadrilateral elements, and the concrete target is divided into smooth particles. In order to form the elements conveniently, the projectile element consists of three characteristic parts with assembly functions. The sliding surface algorithm for interfaces of SP-FE (smooth particles-finite elements) has been formulated, and to raise the computational efficiency, the slave particles and their connected particles are defined in the pre-processing subroutine. The calculated examples have shown that the combination algorithm of FEM with SPH and the related code could be used to simulate the impact and perforation of concrete targets by projectiles. The differences between 3D and 2D computations for vertical impact as well as the comparison with experimental data are presented here.
2006, 26(1): 7-11.
doi: 10.11883/1001-1455(2006)01-0007-05
Abstract:
The ability to accelerate metal plates of aluminized explosives containing micrometer and nanometer aluminum powder has been investigated experimentally with a VISAR interferometer. In the case of nanometer aluminum powder, the free surface velocity of metal plates was larger and the reaction time was decreased by 35.1% compared with that in the case of normal aluminized explosives. The influence of morphology of oxidizer AP on aluminized explosive performances was explored. The ability of the aluminized explosive made from RDX/Al composite with physical-chemical method was larger and its detonation reaction time was shorter than that made with mechanical mixing. When RDX in the aluminized explosive was replaced by an oxygen-enriched explosive, a 10% higher metal plate velocity resulted.
The ability to accelerate metal plates of aluminized explosives containing micrometer and nanometer aluminum powder has been investigated experimentally with a VISAR interferometer. In the case of nanometer aluminum powder, the free surface velocity of metal plates was larger and the reaction time was decreased by 35.1% compared with that in the case of normal aluminized explosives. The influence of morphology of oxidizer AP on aluminized explosive performances was explored. The ability of the aluminized explosive made from RDX/Al composite with physical-chemical method was larger and its detonation reaction time was shorter than that made with mechanical mixing. When RDX in the aluminized explosive was replaced by an oxygen-enriched explosive, a 10% higher metal plate velocity resulted.
2006, 26(1): 12-20.
doi: 10.11883/1001-1455(2006)01-0012-09
Abstract:
In order to investigate the dynamic tension strength of rocks, the flattened Brazilian disc specimens were subjected to diametral impact with different projectile speeds by using the split Hopkinson pressure bar (SHPB) of 100 mm in diameter where a thin aluminum circular plate was used as a pulse shaper. The strain rate, failure time, failure pattern and the relationship between load and strain during the failure process have been analyzed to get some conclusions about the tensile strength and the elastic modulus of marble at high strain rates. The influence of stress nonuniformities near two flattened ends of specimens on test results was taken into account. Meanwhile, the validity of dynamic split tension tests has been confirmed by the numerical simulation of the dynamic stress distribution in flattened Brazilian disc specimens using the finite element technique.
In order to investigate the dynamic tension strength of rocks, the flattened Brazilian disc specimens were subjected to diametral impact with different projectile speeds by using the split Hopkinson pressure bar (SHPB) of 100 mm in diameter where a thin aluminum circular plate was used as a pulse shaper. The strain rate, failure time, failure pattern and the relationship between load and strain during the failure process have been analyzed to get some conclusions about the tensile strength and the elastic modulus of marble at high strain rates. The influence of stress nonuniformities near two flattened ends of specimens on test results was taken into account. Meanwhile, the validity of dynamic split tension tests has been confirmed by the numerical simulation of the dynamic stress distribution in flattened Brazilian disc specimens using the finite element technique.
2006, 26(1): 21-26.
doi: 10.11883/1001-1455(2006)01-0021-06
Abstract:
Integrated armors, including reactive armors, and composite ceramic armors, have better protection performances. According to the theory of the long rod impacting on composite armors and the momentum theorem for impact on reactive armors, a calculation model of long rod penetration into the integrated armors has been proposed in this paper. The model indicates that integrated armors with the same area density as the composite ceramic armors have better protection abilities, then lighter and better armors could be designed with this model.
Integrated armors, including reactive armors, and composite ceramic armors, have better protection performances. According to the theory of the long rod impacting on composite armors and the momentum theorem for impact on reactive armors, a calculation model of long rod penetration into the integrated armors has been proposed in this paper. The model indicates that integrated armors with the same area density as the composite ceramic armors have better protection abilities, then lighter and better armors could be designed with this model.
2006, 26(1): 27-32.
doi: 10.11883/1001-1455(2006)01-0027-06
Abstract:
Based on a Ruby-laser schlieren system, the flow-field of detonation diffraction in a bifurcated tube has been experimentally studied. By employing the ruby laser and a bandpass filter of 15 nm FWHM, the combustion luminescence was successfully removed in experiments. By setting proper predetermined time delay of the synchronization unit, schlieren image series at the different time were obtained. The results show that the transverse waves, leading shock and reaction zone can be clearly observed in the consecutive images. Influenced by the rarefaction waves from the left sharp corner, the leading shock was disturbed and separated from the reaction zone. Therefore, the detonation wave was degenerated into a deflagration wave. The decoupled leading shock and the winkled reaction front can also be identified in the schlieren images. Re-initiation was induced by the leading shock reflection on the right wall in the vertical branch. Mach reflections of the disturbed detonation waves occur in both the vertical and the horizontal branches. With increasing the initial pressure of the premixed mixture, it was earlier for the disturbed detonation waves to be recovered to self-sustaining detonation waves in the vertical and horizontal branches.
Based on a Ruby-laser schlieren system, the flow-field of detonation diffraction in a bifurcated tube has been experimentally studied. By employing the ruby laser and a bandpass filter of 15 nm FWHM, the combustion luminescence was successfully removed in experiments. By setting proper predetermined time delay of the synchronization unit, schlieren image series at the different time were obtained. The results show that the transverse waves, leading shock and reaction zone can be clearly observed in the consecutive images. Influenced by the rarefaction waves from the left sharp corner, the leading shock was disturbed and separated from the reaction zone. Therefore, the detonation wave was degenerated into a deflagration wave. The decoupled leading shock and the winkled reaction front can also be identified in the schlieren images. Re-initiation was induced by the leading shock reflection on the right wall in the vertical branch. Mach reflections of the disturbed detonation waves occur in both the vertical and the horizontal branches. With increasing the initial pressure of the premixed mixture, it was earlier for the disturbed detonation waves to be recovered to self-sustaining detonation waves in the vertical and horizontal branches.
2006, 26(1): 33-38.
doi: 10.11883/1001-1455(2006)01-0033-06
Abstract:
A two-dimensional nonlinear mass-spring-bar model is presented in this paper to simulate the deformation of metallic foams with heterogeneous density in layers or in local regions. The metallic foam is modeled as an array of discrete lump masses linked with elastic-plastic springs in the loading direction and constrained by hinged extensible rods transversely to the loading direction. The effects of the heterogeneity in metallic foams on their deformation under impact have been analysed.
A two-dimensional nonlinear mass-spring-bar model is presented in this paper to simulate the deformation of metallic foams with heterogeneous density in layers or in local regions. The metallic foam is modeled as an array of discrete lump masses linked with elastic-plastic springs in the loading direction and constrained by hinged extensible rods transversely to the loading direction. The effects of the heterogeneity in metallic foams on their deformation under impact have been analysed.
2006, 26(1): 39-45.
doi: 10.11883/1001-1455(2006)01-0039-07
Abstract:
This paper presents an experimental investigation on the dynamic buckling of a Kiewitt8 single-layer reticulated shell model under drop hammer impact. The history curves of impact actions and axial forces were measured. The impact buckling modes and failure patterns were observed with a high-speed camera. The results show that the impact actions of drop hammer on the model have triangular impulse shapes, whose max-values have a close relation to hammer momentum and the model stiffness. Acting periods of impact varied from 3.00 to 22.36 ms and their sudden increase correspond to impact buckling occurrence. The response time of axial force was 0.2～0.4 ms later than the impact. The results also show that the reticulated shell model has the higher resistance to impact after its buckling and has not collapsed progressively under the stronger impact.
This paper presents an experimental investigation on the dynamic buckling of a Kiewitt8 single-layer reticulated shell model under drop hammer impact. The history curves of impact actions and axial forces were measured. The impact buckling modes and failure patterns were observed with a high-speed camera. The results show that the impact actions of drop hammer on the model have triangular impulse shapes, whose max-values have a close relation to hammer momentum and the model stiffness. Acting periods of impact varied from 3.00 to 22.36 ms and their sudden increase correspond to impact buckling occurrence. The response time of axial force was 0.2～0.4 ms later than the impact. The results also show that the reticulated shell model has the higher resistance to impact after its buckling and has not collapsed progressively under the stronger impact.
2006, 26(1): 46-52.
doi: 10.11883/1001-1455(2006)01-0046-07
Abstract:
The compressive deformation behavior of open-celled aluminum foams with different densities and morphologies was tested under quasi-static and dynamic loading conditions. High strain rate experiments were conducted using a split Hopkinson pressure bar technique at strain rates ranging from 500 s-1 to 2 000 s-1. The experimental results show that the compressive stress-strain curves of aluminum alloy foams are characterized by three stages appeared in general foam materials, namely elastic, collapse and densification ones. Compared with that of relative density, the effect of cell size on the dynamic properties can be negligible. The yield stress is insensitive to strain rates, and the deformation is spatially uniform for the open-celled aluminum alloy foams in a wide range of strain rates.
The compressive deformation behavior of open-celled aluminum foams with different densities and morphologies was tested under quasi-static and dynamic loading conditions. High strain rate experiments were conducted using a split Hopkinson pressure bar technique at strain rates ranging from 500 s-1 to 2 000 s-1. The experimental results show that the compressive stress-strain curves of aluminum alloy foams are characterized by three stages appeared in general foam materials, namely elastic, collapse and densification ones. Compared with that of relative density, the effect of cell size on the dynamic properties can be negligible. The yield stress is insensitive to strain rates, and the deformation is spatially uniform for the open-celled aluminum alloy foams in a wide range of strain rates.
2006, 26(1): 53-58.
doi: 10.11883/1001-1455(2006)01-0053-06
Abstract:
A smoothed particle hydrodynamics (SPH) algorithm based on the Riemann solution has been presented in this paper. The improved SPH algorithm is applied to simulate the 2D axisymmetrical impact of projectiles on thin target plates. The effects of plate thickness, projectile shape and impact velocity on the debris clouds have been studied. The characteristics of the simulated debris clouds are in agreement with the experimental results, which show that SPH method is effective in modeling the hypervelocity impact problems.
A smoothed particle hydrodynamics (SPH) algorithm based on the Riemann solution has been presented in this paper. The improved SPH algorithm is applied to simulate the 2D axisymmetrical impact of projectiles on thin target plates. The effects of plate thickness, projectile shape and impact velocity on the debris clouds have been studied. The characteristics of the simulated debris clouds are in agreement with the experimental results, which show that SPH method is effective in modeling the hypervelocity impact problems.
2006, 26(1): 59-64.
doi: 10.11883/1001-1455(2006)01-0059-06
Abstract:
The dynamic response of two-walled long pressure vessels with flat-wound ribbons subjected to an internal pressure with rectangular shape has been analyzed with the rigid-plastic model. The models of plastic deformation are given under middle and high loadings, respectively. The formulas of the limit pressure, response time and residual displacement of the vessels are proposed. Numerical results show that the static limit pressure of the vessel is less than that of monolithic vessel, the residual displacement of the vessel is more than that of the inner shell and monolithic ones, and the shock-resistantance of the vessel is greater than that of monolithic vessel under loading pressure less than 24.5 MPa.
The dynamic response of two-walled long pressure vessels with flat-wound ribbons subjected to an internal pressure with rectangular shape has been analyzed with the rigid-plastic model. The models of plastic deformation are given under middle and high loadings, respectively. The formulas of the limit pressure, response time and residual displacement of the vessels are proposed. Numerical results show that the static limit pressure of the vessel is less than that of monolithic vessel, the residual displacement of the vessel is more than that of the inner shell and monolithic ones, and the shock-resistantance of the vessel is greater than that of monolithic vessel under loading pressure less than 24.5 MPa.
2006, 26(1): 65-70.
doi: 10.11883/1001-1455(2006)01-0065-06
Abstract:
Under the conservative scheme, flux components are reconstructed with the component by component versions. Then the quasi-linear systems are solved by the multiple WENO reconstruction based on the 1st order up wind scheme. The level set equation is used to capture the interface movement. Finally the two algorithms are applied to simulate the muti-component fluid flow. Satisfied numerical results have been obtained.
Under the conservative scheme, flux components are reconstructed with the component by component versions. Then the quasi-linear systems are solved by the multiple WENO reconstruction based on the 1st order up wind scheme. The level set equation is used to capture the interface movement. Finally the two algorithms are applied to simulate the muti-component fluid flow. Satisfied numerical results have been obtained.
2006, 26(1): 71-78.
doi: 10.11883/1001-1455(2006)01-0071-08
Abstract:
The mechanics problem in structural design of earth penetrating weapons (EPW) has been presented in this paper. There exists a maximum penetration depth for a pure KE projectile when its geometric configuration and impact conditions are specified. However, the structural optimization of EPW, especially the mechanical design of projectile body, is quite beneficial to improve the penetration capability. Analyses are conducted on designs of projectile nose, warhead rear cover, backfill ratio, projectile shape, materials, and the scaling law as well as the design of concrete target. Some examples are given to demonstrate the theoretical results.
The mechanics problem in structural design of earth penetrating weapons (EPW) has been presented in this paper. There exists a maximum penetration depth for a pure KE projectile when its geometric configuration and impact conditions are specified. However, the structural optimization of EPW, especially the mechanical design of projectile body, is quite beneficial to improve the penetration capability. Analyses are conducted on designs of projectile nose, warhead rear cover, backfill ratio, projectile shape, materials, and the scaling law as well as the design of concrete target. Some examples are given to demonstrate the theoretical results.
2006, 26(1): 79-83.
doi: 10.11883/1001-1455(2006)01-0079-05
Abstract:
The dynamic buckling in single-wall carbon nanotubes subjected to impact torque loading has been investigated with a continum model. A single-wall carbon nanotube can be modeled as an elastic cylindrical shell of semi-infinite length. The dynamic buckling under impact torque is reduced to a bifurcation problem caused by the torsion stress wave propagation. The bifurcation problem can be converted to the solutions for a set of nonlinear equations. The numerical computation has been carried out, and the effects of various parameters on the dynamic buckling are discussed. It is found that a single-wall carbon nanotube has powerful resistance to impact torque, the critical shearing stress for dynamic buckling may reach up to a few hundred GPa.
The dynamic buckling in single-wall carbon nanotubes subjected to impact torque loading has been investigated with a continum model. A single-wall carbon nanotube can be modeled as an elastic cylindrical shell of semi-infinite length. The dynamic buckling under impact torque is reduced to a bifurcation problem caused by the torsion stress wave propagation. The bifurcation problem can be converted to the solutions for a set of nonlinear equations. The numerical computation has been carried out, and the effects of various parameters on the dynamic buckling are discussed. It is found that a single-wall carbon nanotube has powerful resistance to impact torque, the critical shearing stress for dynamic buckling may reach up to a few hundred GPa.
2006, 26(1): 84-90.
doi: 10.11883/1001-1455(2006)01-0084-07
Abstract:
Based on the uncoupled fluid-structure interaction theory, a numerical model has been proposed to study the fracture mechanism of rocks under water jet impact. The jet flow characteristics and the stress distributions in the system are calculated with and without taking account of the pore-fluid coupling. The numerical results show if no pore-fluid coupling is considered, the maximum principal stress will be located at the impact surface and the radial distance from the impact center is directly proportional to the corresponding standoff distance, meanwhile the maximum shear stress occurs about half of the nozzle diameter downward the impact center. On the other hand, when water jets impinge on the saturated rocks in which fluid flows according to the Darcys law, the maximum principal stress occurs about 0.4 time of the nozzle diameter downward the impact center. The results can provided some ideas in considering the rock damage criterion for rock failure mechanism study under water jet impact.
Based on the uncoupled fluid-structure interaction theory, a numerical model has been proposed to study the fracture mechanism of rocks under water jet impact. The jet flow characteristics and the stress distributions in the system are calculated with and without taking account of the pore-fluid coupling. The numerical results show if no pore-fluid coupling is considered, the maximum principal stress will be located at the impact surface and the radial distance from the impact center is directly proportional to the corresponding standoff distance, meanwhile the maximum shear stress occurs about half of the nozzle diameter downward the impact center. On the other hand, when water jets impinge on the saturated rocks in which fluid flows according to the Darcys law, the maximum principal stress occurs about 0.4 time of the nozzle diameter downward the impact center. The results can provided some ideas in considering the rock damage criterion for rock failure mechanism study under water jet impact.
2006, 26(1): 91-96.
doi: 10.11883/1001-1455(2006)01-0091-06
Abstract:
The factors to affect the momentum partition and transition of stress waves passing an interface of two media have been analysed in this paper. In order to adjust the amplitude and width of the stress impulse in targets, the dependence of velocity and impactor thickness, as well as the flatness area of the wave front in targets are discussed. The examples of the planar GPa pressure explosive loading devices and its applications are given.
The factors to affect the momentum partition and transition of stress waves passing an interface of two media have been analysed in this paper. In order to adjust the amplitude and width of the stress impulse in targets, the dependence of velocity and impactor thickness, as well as the flatness area of the wave front in targets are discussed. The examples of the planar GPa pressure explosive loading devices and its applications are given.
