2008 Vol. 28, No. 2
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2008, 28(2): 97-104.
doi: 10.11883/1001-1455(2008)02-0097-08
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Abstract:
An experimental investigation on the high-speed deflagration in the acetylene-oxygen mixture was carried out in a smooth straight tube. The deflagration was generated by putting a perforated plate in the way of a self-sustained detonation wave and interrupting it. Streak schlieren photos were taken to illustrate the averaged structure of the initially transmitted deflagrations near the plate, and pressure transducers were used to trace the further development of the wave front. The high-speed deflagration wave was found to be a complex of precursor shock and flame. With the increase of the initial pressure, it varies from a laminar structure to a turbulent one, and the onset of the latter seems corresponding to the smaller or comparable cellular width of incident detonation to the disturbance scale of perforated plate. This study reveals that deflagrations with laminar structure can not stand the attenuation of background rarefaction and keeps on slowing down, whereas the turbulent one is capable of running up and transiting to a detonation wave. There is an unstable critical case between the mentioned two situations, where the deflagration can propagate for a relatively long distance at a 0.5~0.6 times CJ detonation speed. This critical case matches the constant-volume combustion solution of the Rankine-Hugoniont relations across dual discontinuities.
An experimental investigation on the high-speed deflagration in the acetylene-oxygen mixture was carried out in a smooth straight tube. The deflagration was generated by putting a perforated plate in the way of a self-sustained detonation wave and interrupting it. Streak schlieren photos were taken to illustrate the averaged structure of the initially transmitted deflagrations near the plate, and pressure transducers were used to trace the further development of the wave front. The high-speed deflagration wave was found to be a complex of precursor shock and flame. With the increase of the initial pressure, it varies from a laminar structure to a turbulent one, and the onset of the latter seems corresponding to the smaller or comparable cellular width of incident detonation to the disturbance scale of perforated plate. This study reveals that deflagrations with laminar structure can not stand the attenuation of background rarefaction and keeps on slowing down, whereas the turbulent one is capable of running up and transiting to a detonation wave. There is an unstable critical case between the mentioned two situations, where the deflagration can propagate for a relatively long distance at a 0.5~0.6 times CJ detonation speed. This critical case matches the constant-volume combustion solution of the Rankine-Hugoniont relations across dual discontinuities.
2008, 28(2): 105-109.
doi: 10.11883/1001-1455(2008)02-0105-05
Abstract:
VG(void growth) damage model is generalized to the 2D situations, which counts in the effect of the principal stress direction on the evolution of damage, and is used in the 2D numerical simulations of spallation of steel tube driven by sliding detonation of high explosive GI-920, as well as the explicit fracture algorithm. The different pressure profiles on the outer surface of steel tube between the 1D implosion case and the 2D sliding detonation case are analyzed. Especially the influence of the thickness of high explosive on the pressure profiles is investigated in detail. The numerical results present the distribution and evolution of damage in the steel tube, as well as the initialization and extending of the spalled crack. The initial thicknesses of spalled layer obtained numerically conform to the experiments.
VG(void growth) damage model is generalized to the 2D situations, which counts in the effect of the principal stress direction on the evolution of damage, and is used in the 2D numerical simulations of spallation of steel tube driven by sliding detonation of high explosive GI-920, as well as the explicit fracture algorithm. The different pressure profiles on the outer surface of steel tube between the 1D implosion case and the 2D sliding detonation case are analyzed. Especially the influence of the thickness of high explosive on the pressure profiles is investigated in detail. The numerical results present the distribution and evolution of damage in the steel tube, as well as the initialization and extending of the spalled crack. The initial thicknesses of spalled layer obtained numerically conform to the experiments.
2008, 28(2): 110-115.
doi: 10.11883/1001-1455(2008)02-0110-06
Abstract:
Planar shock wave experiments for OFHC copper were carried out, and the yield stresses of OFHC copper were obtained from the longitudinal and transverse stresses recorded by the manganin gauges. Numerical simulations of the planar shock tests for OFHC copper were performed by using the constructed seven constitutive models and compared with the experimental results. Constitutive models at high pressures and high strain rates were discussed. Results indicate that the Johnson-Cook or Zerilli-Armstrong constitutive models determined by the SHPB tests can not be applied to planar shock experiments.
Planar shock wave experiments for OFHC copper were carried out, and the yield stresses of OFHC copper were obtained from the longitudinal and transverse stresses recorded by the manganin gauges. Numerical simulations of the planar shock tests for OFHC copper were performed by using the constructed seven constitutive models and compared with the experimental results. Constitutive models at high pressures and high strain rates were discussed. Results indicate that the Johnson-Cook or Zerilli-Armstrong constitutive models determined by the SHPB tests can not be applied to planar shock experiments.
2008, 28(2): 116-223.
doi: 10.11883/1001-1455(2008)02-0116-08
Abstract:
The present paper conducts a numerical study on the dynamic plastic buckling of deep penetrating projectiles. Numerical simulations display the different processes of failure and destruction of projectiles with LS-DYNA3D. It confirms that, two failure modes, i.e., crapy buckling and dynamic expansion buckling exist for different length-diameter-ratio projectiles, which have observed in the experimental study. Characteristic acceleration curves correspond to different modes of buckling failure. Two kinetic fields of rigid-plastic three-hinges are constructed to describe the two modes of buckling failure.
The present paper conducts a numerical study on the dynamic plastic buckling of deep penetrating projectiles. Numerical simulations display the different processes of failure and destruction of projectiles with LS-DYNA3D. It confirms that, two failure modes, i.e., crapy buckling and dynamic expansion buckling exist for different length-diameter-ratio projectiles, which have observed in the experimental study. Characteristic acceleration curves correspond to different modes of buckling failure. Two kinetic fields of rigid-plastic three-hinges are constructed to describe the two modes of buckling failure.
2008, 28(2): 124-130.
doi: 10.11883/1001-1455(2008)02-0124-07
Abstract:
The nonlinear dynamics of a gas bubble near the free surface and the cylinder is three-dimensionally computed. The flow field is supposed to be irrotational and incompressible at the underwater explosion impulsive phase. The high-order curved triangular elements are used to disperse the three-dimensional bubble surface. The evolution of the bubble is solved by the boundary integral method, and the singularity of the double layer potential is eliminated by recasting the principal-value integral of the double-layer potential. So the computational result will be more accurate. The real velocity at every node on the boundary surface is solved precisely via the reasonable weighing method, and the elastic mesh technique (EMT) is applied to get the optimum velocity. The mesh-smoothing algorithm is no need during the whole simulating process. Comparisons show that the results by the three-dimensional model are in agreement with those by the axisymmetric model. The present three-dimensional model is used to simulate the interaction between the bubble and the free surface near the cylinder. The behavior of the bubble is strong nonlinear under the combined influence of the free surface and the cylinder.
The nonlinear dynamics of a gas bubble near the free surface and the cylinder is three-dimensionally computed. The flow field is supposed to be irrotational and incompressible at the underwater explosion impulsive phase. The high-order curved triangular elements are used to disperse the three-dimensional bubble surface. The evolution of the bubble is solved by the boundary integral method, and the singularity of the double layer potential is eliminated by recasting the principal-value integral of the double-layer potential. So the computational result will be more accurate. The real velocity at every node on the boundary surface is solved precisely via the reasonable weighing method, and the elastic mesh technique (EMT) is applied to get the optimum velocity. The mesh-smoothing algorithm is no need during the whole simulating process. Comparisons show that the results by the three-dimensional model are in agreement with those by the axisymmetric model. The present three-dimensional model is used to simulate the interaction between the bubble and the free surface near the cylinder. The behavior of the bubble is strong nonlinear under the combined influence of the free surface and the cylinder.
2008, 28(2): 131-137.
doi: 10.11883/1001-1455(2008)02-0131-07
Abstract:
There is a non-equilibrium ionization zone in the detonation plasma resulted from the non-equilibrium heat release of chemical reaction. Because of the low mass ratio between electron and heavy particle in the non-equilibrium ionization zone, the transfer efficiency between electron and heavy particle is low. And this enhances the non-equilibrium character. The double fluid model of electron and heavy particle is established to explore the non-equilibrium phenomenon in the detonation plasma. The parameters of electron and heavy particles in the non-equilibrium ionization zone of the oxy-hydrogen detonation are calculated by this developed model with the different oxy-hydrogen ratio and initial pressure.
There is a non-equilibrium ionization zone in the detonation plasma resulted from the non-equilibrium heat release of chemical reaction. Because of the low mass ratio between electron and heavy particle in the non-equilibrium ionization zone, the transfer efficiency between electron and heavy particle is low. And this enhances the non-equilibrium character. The double fluid model of electron and heavy particle is established to explore the non-equilibrium phenomenon in the detonation plasma. The parameters of electron and heavy particles in the non-equilibrium ionization zone of the oxy-hydrogen detonation are calculated by this developed model with the different oxy-hydrogen ratio and initial pressure.
2008, 28(2): 138-143.
doi: 10.11883/1001-1455(2008)02-0138-06
Abstract:
By MEPH2Y, a two-dimensional finite difference Eulerian hydrocode, this paper simulated the action process of a shaped charge. The process includes the following: (1) the formation and propagation of the detonation wave, and its interaction with other materials; (2) the formation, stretching, decompression and rupture of the jet under high-temperature and high-pressure conditions; (3) the collision of jet (or projectile) with target; (4) the notch formation and dynamic response of the target. The mathematical model and numerical method used in the program were introduced and some simulated results were compared with the experimental results. Comparisons show that the simulated results are in agreement with the experiment results and the MEPH2Y code is appropriate to be used to simulate the shaped charge problems.
By MEPH2Y, a two-dimensional finite difference Eulerian hydrocode, this paper simulated the action process of a shaped charge. The process includes the following: (1) the formation and propagation of the detonation wave, and its interaction with other materials; (2) the formation, stretching, decompression and rupture of the jet under high-temperature and high-pressure conditions; (3) the collision of jet (or projectile) with target; (4) the notch formation and dynamic response of the target. The mathematical model and numerical method used in the program were introduced and some simulated results were compared with the experimental results. Comparisons show that the simulated results are in agreement with the experiment results and the MEPH2Y code is appropriate to be used to simulate the shaped charge problems.
2008, 28(2): 144-148.
doi: 10.11883/1001-1455(2008)02-0144-05
Abstract:
A modified ghost fluid method is developed to avoid the oscillations of pressure and velocity at the interface when the original ghost fluid method (GFM) is applied to a strong shock wave impacting on a material interface. The pressure and velocity of the ghost fluid are replaced respectively by the pressure and velocity of the interface which are obtained by solving a Riemann problem, the density of the ghost fluid is gained by extrapolating the entropy constant. The modified GFM keeps to the simplicity of the original GFM. Numerical tests are carried out by using the modified GFM for a one-dimensional strong shock wave impacting on the gas-gas, gas-liquid interfaces and a jet impacting on the gas-liquid interface. The satisfactory results are achieved.
A modified ghost fluid method is developed to avoid the oscillations of pressure and velocity at the interface when the original ghost fluid method (GFM) is applied to a strong shock wave impacting on a material interface. The pressure and velocity of the ghost fluid are replaced respectively by the pressure and velocity of the interface which are obtained by solving a Riemann problem, the density of the ghost fluid is gained by extrapolating the entropy constant. The modified GFM keeps to the simplicity of the original GFM. Numerical tests are carried out by using the modified GFM for a one-dimensional strong shock wave impacting on the gas-gas, gas-liquid interfaces and a jet impacting on the gas-liquid interface. The satisfactory results are achieved.
2008, 28(2): 149-153.
doi: 10.11883/1001-1455(2008)02-0149-05
Abstract:
Effects of the length-to-diameter (L/D) ratios of specimens on the experimental results were studied by using a split Hopkinson tensile bar, rotating disk indirect bar-bar tensile impact apparatus. The length-to-diameter ratios of the LY12 specimens used in the test range from 1 to 5. Results show that the specimens of L/D2.67 can be used to obtain exact parameters of materials under the proposed conditions, but the specimens of L/D2 can not be used in impact tensile test.
Effects of the length-to-diameter (L/D) ratios of specimens on the experimental results were studied by using a split Hopkinson tensile bar, rotating disk indirect bar-bar tensile impact apparatus. The length-to-diameter ratios of the LY12 specimens used in the test range from 1 to 5. Results show that the specimens of L/D2.67 can be used to obtain exact parameters of materials under the proposed conditions, but the specimens of L/D2 can not be used in impact tensile test.
2008, 28(2): 154-160.
doi: 10.11883/1001-1455(2008)02-0154-07
Abstract:
The meshless material point method (MPM) is introduced to solve the problems that when a bomb is exploded near the building, an analysis on the combining effects of blast wave and fragments on the concrete wall involves the multi-physics field calculations and multi-material coupling. The explosion field, bomb fragments and deformation and fracture of the concrete wall resulted from explosion of bombs with and without a metal case are numerically simulated by using the characteristics of the MPM that a moving boundary or material interface can be easily traced, and the coupling conditions of multiple materials are automatically satisfied. Calculated results show that the meshless MPM is useful for computation of multi-material explosion effect.
The meshless material point method (MPM) is introduced to solve the problems that when a bomb is exploded near the building, an analysis on the combining effects of blast wave and fragments on the concrete wall involves the multi-physics field calculations and multi-material coupling. The explosion field, bomb fragments and deformation and fracture of the concrete wall resulted from explosion of bombs with and without a metal case are numerically simulated by using the characteristics of the MPM that a moving boundary or material interface can be easily traced, and the coupling conditions of multiple materials are automatically satisfied. Calculated results show that the meshless MPM is useful for computation of multi-material explosion effect.
2008, 28(2): 161-165.
doi: 10.11883/1001-1455(2008)02-0161-05
Abstract:
The theory of interior ballistic course of solid traveling charge was studied to increase the initial velocity of a big caliber gun. Based on the good results in tests and numerical simulations in the 30 mm gun of traveling charge, a zero-dimensional interior ballistic model of solid traveling charge was developed by keeping the fire data and charge conditions of the 100 mm gun same and considering the projectile mass variable. The developed model was used to numerically analyze the interior ballistic performances and to explore the effects of traveling charge mass, ignition lag time and charge power shape on the interior pressure and initial velocity of the gun. Computed results can provide an instruction for the design and experiment of the 100 mm gun of traveling charge.
The theory of interior ballistic course of solid traveling charge was studied to increase the initial velocity of a big caliber gun. Based on the good results in tests and numerical simulations in the 30 mm gun of traveling charge, a zero-dimensional interior ballistic model of solid traveling charge was developed by keeping the fire data and charge conditions of the 100 mm gun same and considering the projectile mass variable. The developed model was used to numerically analyze the interior ballistic performances and to explore the effects of traveling charge mass, ignition lag time and charge power shape on the interior pressure and initial velocity of the gun. Computed results can provide an instruction for the design and experiment of the 100 mm gun of traveling charge.
2008, 28(2): 166-171.
doi: 10.11883/1001-1455(2008)02-0166-06
Abstract:
Considering the compressibility of an aluminum-alloy foam and the unavailability of the classic Taylor model to it, a theoretical model used to analyze the Taylor impact experiment of the aluminum-alloy foam was proposed based on some assumptions. The Taylor impact experiment was performed to validate the proposed model and to explore the dynamic mechanical properties of the aluminum-alloy foam. The experimental results show that the strain-rate sensitivity of the studied aluminum-alloy foam is not strong.
Considering the compressibility of an aluminum-alloy foam and the unavailability of the classic Taylor model to it, a theoretical model used to analyze the Taylor impact experiment of the aluminum-alloy foam was proposed based on some assumptions. The Taylor impact experiment was performed to validate the proposed model and to explore the dynamic mechanical properties of the aluminum-alloy foam. The experimental results show that the strain-rate sensitivity of the studied aluminum-alloy foam is not strong.
CDM model and its application to numerical simulation on fiber-reinforced laminate under penetration
2008, 28(2): 172-177.
doi: 10.11883/1001-1455(2008)02-0172-06
Abstract:
A continuum damage constitutive model for the fiber-reinforced laminate was introduced. Penetration of the fiber-reinforced laminate by a flat-ended projectile was numerically simulated by using the 3D finite element software LS-DYNA. Residual velocity of the projectile, deformation and failure modes of the laminate under impact loading were predicted. Evolvement and distribution of the different damage modes were obtained. Simulated results are in agreement with those of the ballistic tests.
A continuum damage constitutive model for the fiber-reinforced laminate was introduced. Penetration of the fiber-reinforced laminate by a flat-ended projectile was numerically simulated by using the 3D finite element software LS-DYNA. Residual velocity of the projectile, deformation and failure modes of the laminate under impact loading were predicted. Evolvement and distribution of the different damage modes were obtained. Simulated results are in agreement with those of the ballistic tests.
2008, 28(2): 178-185.
doi: 10.11883/1001-1455(2008)02-0178-08
Abstract:
Ballistic experiments with projectile velocities of 297~848 m/s were performed by using a 12.7 mm ballistic gun to investigate the anti-penetration and anti-perforation performances of the plain concrete and steel fiber-reinforced concrete (SFRC) with different steel fiber volume fractions and types. The steel fibers include the flat-straight and hooked-end ones, and their range of volume fraction is from 0.01 to 0.05. The impact velocity, maximal penetration depth, crater diameter, target failure model were obtained. The dynamic failure processes of all targets were observed by means of a high-speed camera. Experimental results show that the penetration depth of the projectile in SFRC in which the hooked-end steel fiber volume fraction is 0.05 decreases by 52% compared with that in the plain concrete with the same strength grade, and the quantity and scattering angle of the target debris decrease largely. Therefore SFRC with high volume fraction of deformed steel fibers is effective on anti-penetration and anti-perforation.
Ballistic experiments with projectile velocities of 297~848 m/s were performed by using a 12.7 mm ballistic gun to investigate the anti-penetration and anti-perforation performances of the plain concrete and steel fiber-reinforced concrete (SFRC) with different steel fiber volume fractions and types. The steel fibers include the flat-straight and hooked-end ones, and their range of volume fraction is from 0.01 to 0.05. The impact velocity, maximal penetration depth, crater diameter, target failure model were obtained. The dynamic failure processes of all targets were observed by means of a high-speed camera. Experimental results show that the penetration depth of the projectile in SFRC in which the hooked-end steel fiber volume fraction is 0.05 decreases by 52% compared with that in the plain concrete with the same strength grade, and the quantity and scattering angle of the target debris decrease largely. Therefore SFRC with high volume fraction of deformed steel fibers is effective on anti-penetration and anti-perforation.
2008, 28(2): 186-192.
doi: 10.11883/1001-1455(2008)02-0186-07
Abstract:
The phenomenon of the rock damage and fracture by shock wave of exploding in fractures was simulated via the experiment of exploding on the surface of the cement sample in deep water. The peak pressure decline of shock wave, which was suitable for this experiment, was obtained pm8.2(W1/3/R)1.46. Results indicate that the crushed zone and tensile damage zone dimensions are about 2～5, 20～30 times of the powder characteristic dimension respectively. Approximate energy consumed by shock wave to generate crushed and fracture zone in cement sample is 2%～7% of the total energy.
The phenomenon of the rock damage and fracture by shock wave of exploding in fractures was simulated via the experiment of exploding on the surface of the cement sample in deep water. The peak pressure decline of shock wave, which was suitable for this experiment, was obtained pm8.2(W1/3/R)1.46. Results indicate that the crushed zone and tensile damage zone dimensions are about 2～5, 20～30 times of the powder characteristic dimension respectively. Approximate energy consumed by shock wave to generate crushed and fracture zone in cement sample is 2%～7% of the total energy.
