2014 Vol. 34, No. 4
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2014, 34(4): 385-391.
doi: 10.11883/1001-1455(2014)04-0385-07
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Abstract:
Dynamic buckling of thin rectangular plates under elastic compression waves caused by unaxial impact was investigated. Governing equations and a supplementary restraint-equation at compression wave front were obtained on the basis of energy transformation and conservation during buckling of plates; the real buckling displacement must fulfill the governing equations and the supplementary restraint-equation. Based on the requirements of above relations, a numerical method was established to solve the problem, and the relations of the amplitude of impulsive loads, buckling modes and critical buckling length were studied. Research results indicate that: critical buckling length decreases with the increase of impact load when the ratio of width to thickness of plate is fixed; the first order parameter of dynamic critical force is about 1.5 times of the same order parameter of static compression critical force; with weakening of boundary constraints, a smaller buckling load is required to cause the plate to buckle and transverse inertia increase gradually.
Dynamic buckling of thin rectangular plates under elastic compression waves caused by unaxial impact was investigated. Governing equations and a supplementary restraint-equation at compression wave front were obtained on the basis of energy transformation and conservation during buckling of plates; the real buckling displacement must fulfill the governing equations and the supplementary restraint-equation. Based on the requirements of above relations, a numerical method was established to solve the problem, and the relations of the amplitude of impulsive loads, buckling modes and critical buckling length were studied. Research results indicate that: critical buckling length decreases with the increase of impact load when the ratio of width to thickness of plate is fixed; the first order parameter of dynamic critical force is about 1.5 times of the same order parameter of static compression critical force; with weakening of boundary constraints, a smaller buckling load is required to cause the plate to buckle and transverse inertia increase gradually.
2014, 34(4): 392-396.
doi: 10.11883/1001-1455(2014)04-0392-05
Abstract:
Ejecta mixing takes place at the meta-gas interface under strong shock, where the breakup of ejected particles is a very important affecting factor. By adopting Taylor analogy breakup (TAB) model, the breakup effect of the melted lead on its transportation in helium gas was analyzed. The calculation adopted the two-phase flow (including gas and particle) numerical program. From the simulation results, some significant mechanical quantities were obtained, including the breakup time and sizes of the ejected particles. Meantime, the lead ejecta mixing process was simulated considering that the particle breakup was consistent with the experiments. These results give some important references in understanding the process of ejecta mixing.
Ejecta mixing takes place at the meta-gas interface under strong shock, where the breakup of ejected particles is a very important affecting factor. By adopting Taylor analogy breakup (TAB) model, the breakup effect of the melted lead on its transportation in helium gas was analyzed. The calculation adopted the two-phase flow (including gas and particle) numerical program. From the simulation results, some significant mechanical quantities were obtained, including the breakup time and sizes of the ejected particles. Meantime, the lead ejecta mixing process was simulated considering that the particle breakup was consistent with the experiments. These results give some important references in understanding the process of ejecta mixing.
2014, 34(4): 397-403.
doi: 10.11883/1001-1455(2014)04-0397-07
Abstract:
Impact limit equations of honeycomb sandwich panel are the key of risk assessment of the spacecraft's impact from space debris. At present, the indicators of prediction ability mainly are the rate of correctly prediction (including the total rate and the safe rate) based on the prediction probability, and prediction error (including the absolute error and the relative error) based on the deviation of diameter predicted. In order to improve the prediction ability of equations, the variation of each predictive indicator in coefficient space of the equations was described based on 131 experimental data of honeycomb sandwich panel from the literature. And hierarchical analysis was used to investigate the promotion of prediction indicators of the equations. The results show that, equation optimization lead to accurately optimization of indicators of prediction probability, quickly optimization of prediction error. The total rate of correctly prediction can be used in the study of spacecraft's in-orbit protective properties as the primary indicator, and the safe rate of correctly prediction can be used in the security evaluation of design as the primary indicator. The prediction ability of the optimized equation has been greatly enhanced compared with the original equation.
Impact limit equations of honeycomb sandwich panel are the key of risk assessment of the spacecraft's impact from space debris. At present, the indicators of prediction ability mainly are the rate of correctly prediction (including the total rate and the safe rate) based on the prediction probability, and prediction error (including the absolute error and the relative error) based on the deviation of diameter predicted. In order to improve the prediction ability of equations, the variation of each predictive indicator in coefficient space of the equations was described based on 131 experimental data of honeycomb sandwich panel from the literature. And hierarchical analysis was used to investigate the promotion of prediction indicators of the equations. The results show that, equation optimization lead to accurately optimization of indicators of prediction probability, quickly optimization of prediction error. The total rate of correctly prediction can be used in the study of spacecraft's in-orbit protective properties as the primary indicator, and the safe rate of correctly prediction can be used in the security evaluation of design as the primary indicator. The prediction ability of the optimized equation has been greatly enhanced compared with the original equation.
2014, 34(4): 404-408.
doi: 10.11883/1001-1455(2014)04-0404-05
Abstract:
There are various models of the debris cloud produced by normal impact of spherical projectile, but a common ground of the models is that the head shape of the debris cloud is ellipsoidal. In order to identify the head shape of the debris cloud, a new method was presented, which extracts the edge of the debris cloud image, searches for the optimal quadratic function fitting of the edge, and then adjudge the head shape according to fitting results. The optimal fitting algorithm of quadratic function was given as well. Based on four of debris cloud images of references, the recognition was carried out after extraction of their head shape and the optimal quadratic function fitting, and the results show that there are three images with parabolic head shape, one image with elliptic head shape. Thus, the head shape of debris clouds includes not only the rotation ellipsoid, but also the rotation paraboloid.
There are various models of the debris cloud produced by normal impact of spherical projectile, but a common ground of the models is that the head shape of the debris cloud is ellipsoidal. In order to identify the head shape of the debris cloud, a new method was presented, which extracts the edge of the debris cloud image, searches for the optimal quadratic function fitting of the edge, and then adjudge the head shape according to fitting results. The optimal fitting algorithm of quadratic function was given as well. Based on four of debris cloud images of references, the recognition was carried out after extraction of their head shape and the optimal quadratic function fitting, and the results show that there are three images with parabolic head shape, one image with elliptic head shape. Thus, the head shape of debris clouds includes not only the rotation ellipsoid, but also the rotation paraboloid.
2014, 34(4): 409-414.
doi: 10.11883/1001-1455(2014)04-0409-06
Abstract:
Nose shape of projectiles is an important factor influencing the penetration ability. For high speed/ultra high speed kinetic energy penetration of ideal rigid projectiles, this factor is becoming more serious. Based on the classical cavity expansion theory and designing scheme of double-ogival nose, this paper analyses the relationship between nose shape factor and the characteristic parameters of double ogive, and obtains the influence of modified nose projectiles on the penetration performance. It puts forward the design scheme of modified nose penetration body with smaller penetration resistance. The comparison among the results of nose penetration test, proves that this analysis and method are reasonable and feasible, and can be used in judgement for the design of high speed penetrator nose shape.
Nose shape of projectiles is an important factor influencing the penetration ability. For high speed/ultra high speed kinetic energy penetration of ideal rigid projectiles, this factor is becoming more serious. Based on the classical cavity expansion theory and designing scheme of double-ogival nose, this paper analyses the relationship between nose shape factor and the characteristic parameters of double ogive, and obtains the influence of modified nose projectiles on the penetration performance. It puts forward the design scheme of modified nose penetration body with smaller penetration resistance. The comparison among the results of nose penetration test, proves that this analysis and method are reasonable and feasible, and can be used in judgement for the design of high speed penetrator nose shape.
2014, 34(4): 415-420.
doi: 10.11883/1001-1455(2014)04-0415-06
Abstract:
The explosion induced fracture of metallic cylinder under different detonating modes was simulated. The results show that different detonating modes lead to significant differences on the pressure and apply work history of the cylindrical shell. A semi-decoupling numerical method was proposed to thin the mesh size of the metallic cylinder and to simulate the process of destruction of cylindrical shell under different detonating modes with higher degree of accuracy. Theoretical analysis shows that this method is reasonable. The shear bands appearing during the fracture of metallic cylindrical shell was reproduced using this semi-decoupling method.
The explosion induced fracture of metallic cylinder under different detonating modes was simulated. The results show that different detonating modes lead to significant differences on the pressure and apply work history of the cylindrical shell. A semi-decoupling numerical method was proposed to thin the mesh size of the metallic cylinder and to simulate the process of destruction of cylindrical shell under different detonating modes with higher degree of accuracy. Theoretical analysis shows that this method is reasonable. The shear bands appearing during the fracture of metallic cylindrical shell was reproduced using this semi-decoupling method.
2014, 34(4): 421-426.
doi: 10.11883/1001-1455(2014)04-0421-06
Abstract:
In order to predict detonation velocity of composite explosive accurately (esp. aluminium-containing explosive), a new equation of predicting detonation velocity of composite explosive was derived in the weighted-volume method. With the new equation, prediction of detonation velocity was carried out for more than 50 kinds of composite explosive. The predictions show a good agreement with the experiment data. The maximum error of prediction was less than 3%. The average error of prediction was less than 1%. Compared with that of commonly used methods such as BKW and Urizar, the prediction accuracy of the new equation was significantly improved.
In order to predict detonation velocity of composite explosive accurately (esp. aluminium-containing explosive), a new equation of predicting detonation velocity of composite explosive was derived in the weighted-volume method. With the new equation, prediction of detonation velocity was carried out for more than 50 kinds of composite explosive. The predictions show a good agreement with the experiment data. The maximum error of prediction was less than 3%. The average error of prediction was less than 1%. Compared with that of commonly used methods such as BKW and Urizar, the prediction accuracy of the new equation was significantly improved.
2014, 34(4): 427-432.
doi: 10.11883/1001-1455(2014)04-0427-06
Abstract:
For the first time, MgH2powders both as sensitizers and energetic materials in the emulsion explosive was studied on the effects of shock－wave resistance with shock－wave generator and experiments of underwater explosion.Compared with emulsion explosive sensitized by glass microspheres, emulsion explosive sensitized by MgH2presents much smaller ratio of pressure desensitization and stronger explosive effect; the microstructure of emulsion explosive was studied with the scanning electron microscope.And the result show that demulsification of emulsion explosive and decrease of effective"hot spot"are key reasons of decrease in detonation pressure of emulsion explosive.
For the first time, MgH2powders both as sensitizers and energetic materials in the emulsion explosive was studied on the effects of shock－wave resistance with shock－wave generator and experiments of underwater explosion.Compared with emulsion explosive sensitized by glass microspheres, emulsion explosive sensitized by MgH2presents much smaller ratio of pressure desensitization and stronger explosive effect; the microstructure of emulsion explosive was studied with the scanning electron microscope.And the result show that demulsification of emulsion explosive and decrease of effective"hot spot"are key reasons of decrease in detonation pressure of emulsion explosive.
2014, 34(4): 433-438.
doi: 10.11883/1001-1455(2014)04-0433-06
Abstract:
An improved split Hopkinson pressure bar device was applied and a direct impact Hopkinson experimental program with long bullets was designed to measure the dynamic properties of closed-cell aluminum foam under high temperatures. Stress-time curves of both ends of aluminum foam specimens were obtained. It is found that the temperature markedly influence the stress uniformity of the specimens. As the temperature increases, the stress non-uniformity in the specimen becomes serious under the same impact velocity. Thus, both the increment in the test temperature and the impact velocity will cause stress non-uniformity of aluminum foam specimens. For aluminum foams, homogeneous deformation mode is dominant when the impact velocity is low, and the meso-scopic deformation pattern may vary but the stress field of the foam specimen is macroscopically homogeneous. Finally, the SHPB experiment is used to obtain the stress-strain curve under high temperature and high strain rate, after ensuring homogeneous deformation of the specimen.
An improved split Hopkinson pressure bar device was applied and a direct impact Hopkinson experimental program with long bullets was designed to measure the dynamic properties of closed-cell aluminum foam under high temperatures. Stress-time curves of both ends of aluminum foam specimens were obtained. It is found that the temperature markedly influence the stress uniformity of the specimens. As the temperature increases, the stress non-uniformity in the specimen becomes serious under the same impact velocity. Thus, both the increment in the test temperature and the impact velocity will cause stress non-uniformity of aluminum foam specimens. For aluminum foams, homogeneous deformation mode is dominant when the impact velocity is low, and the meso-scopic deformation pattern may vary but the stress field of the foam specimen is macroscopically homogeneous. Finally, the SHPB experiment is used to obtain the stress-strain curve under high temperature and high strain rate, after ensuring homogeneous deformation of the specimen.
2014, 34(4): 439-443.
doi: 10.11883/1001-1455(2014)04-0439-05
Abstract:
This paper presents a 3D numerical simulation of expanding process of high pressure cylindrical bubbles in underwater explosion. Level set method was used to track gas-water interface. The detail on precise definition of initial level set values of cylindrical bubble was also provided. The flow field was solved by Euler equation with fifth-order WENO spatial discretization and fourth-order R-K (Runge-Kutta) time discretization. HJ-WENO was employed to discretized level set equation. The flow states at grid nodes just next to gas-water interface were updated by RGFM algorithm. Pressure cloud pictures at different times, the shape changes of high pressure bubbles and pressure peak at given points were offered. Some interesting conclusions are concluded, as that high pressure cylindrical bubble becomes ellipsoidal gradually during expanding process, the expansion of bubbles nearby the wall is restricted in the normal by reflected wave, and expansion of double cylindrical bubbles is restricted by shock wave from each other. The numerical results also show excellent performance of RGFM and high accuracy scheme when applied to simulation of high pressure cylindrical bubbles expanding.
This paper presents a 3D numerical simulation of expanding process of high pressure cylindrical bubbles in underwater explosion. Level set method was used to track gas-water interface. The detail on precise definition of initial level set values of cylindrical bubble was also provided. The flow field was solved by Euler equation with fifth-order WENO spatial discretization and fourth-order R-K (Runge-Kutta) time discretization. HJ-WENO was employed to discretized level set equation. The flow states at grid nodes just next to gas-water interface were updated by RGFM algorithm. Pressure cloud pictures at different times, the shape changes of high pressure bubbles and pressure peak at given points were offered. Some interesting conclusions are concluded, as that high pressure cylindrical bubble becomes ellipsoidal gradually during expanding process, the expansion of bubbles nearby the wall is restricted in the normal by reflected wave, and expansion of double cylindrical bubbles is restricted by shock wave from each other. The numerical results also show excellent performance of RGFM and high accuracy scheme when applied to simulation of high pressure cylindrical bubbles expanding.
2014, 34(4): 444-450.
doi: 10.11883/1001-1455(2014)04-0444-07
Abstract:
The experimental investigation of thin circular plate of pseudo-elastic TiNi alloy under fixed supports and transversal impact loading was conducted using a revised apparatus of Hopkinson bar. The experimental result of pseudo-elastic TiNi alloy was compared with that of A3 steel. The nature of dynamic mechanical response of the structure in spatio-temporal scale, including the propagation of flexural wave in the plate, evolution of transformation zones and full-field out-of-plane displacement were derived. The results show that transformation zones and transformation hinge may generate near the center of the plate (about 5 mm) because of two-dimensional diffusion effect of the circular plate under impact loading. After unloading, the transformation hinge disappeared, and obvious residual deformation was observed in the A3 steel plate. The impact response of thin circular plate of TiNi alloy is controlled by the thermo-elastic martensite phase transformation and inverse transformation, which differs from the conventional elastic-plastic mechanism.
The experimental investigation of thin circular plate of pseudo-elastic TiNi alloy under fixed supports and transversal impact loading was conducted using a revised apparatus of Hopkinson bar. The experimental result of pseudo-elastic TiNi alloy was compared with that of A3 steel. The nature of dynamic mechanical response of the structure in spatio-temporal scale, including the propagation of flexural wave in the plate, evolution of transformation zones and full-field out-of-plane displacement were derived. The results show that transformation zones and transformation hinge may generate near the center of the plate (about 5 mm) because of two-dimensional diffusion effect of the circular plate under impact loading. After unloading, the transformation hinge disappeared, and obvious residual deformation was observed in the A3 steel plate. The impact response of thin circular plate of TiNi alloy is controlled by the thermo-elastic martensite phase transformation and inverse transformation, which differs from the conventional elastic-plastic mechanism.
2014, 34(4): 451-456.
doi: 10.11883/1001-1455(2014)04-0451-06
Abstract:
This paper was dedicated to developing a numerical model which could predict the delamination of composite T-joint structures caused by high velocity impact of hailstone. Experiments of hailstone impact and subsequent numerical analyses were performed to study the performance of composite T-joints under hailstone impact. The smooth particle hydrodynamic (SPH) approach and the cohesive zone model (CZM) were both employed in numerical simulations to predict the delamination of composite T-joints, and the numerical results show good agreement with that of experiments such as delamination size and displacement of the composite T-joints. In addition, based on the numerical simulation, the influence of calculation parameters on the damages of the T-joints were investigated, and the results show that the velocity, the dimension and the impact angle of hailstone had great influence on the damage of the composite T-joint structures. The numerical simulation show an approximately linear relationship between the impact energy and the delamination size. The peak force of impact and the delamination size increase with the increase of the impact angle.
This paper was dedicated to developing a numerical model which could predict the delamination of composite T-joint structures caused by high velocity impact of hailstone. Experiments of hailstone impact and subsequent numerical analyses were performed to study the performance of composite T-joints under hailstone impact. The smooth particle hydrodynamic (SPH) approach and the cohesive zone model (CZM) were both employed in numerical simulations to predict the delamination of composite T-joints, and the numerical results show good agreement with that of experiments such as delamination size and displacement of the composite T-joints. In addition, based on the numerical simulation, the influence of calculation parameters on the damages of the T-joints were investigated, and the results show that the velocity, the dimension and the impact angle of hailstone had great influence on the damage of the composite T-joint structures. The numerical simulation show an approximately linear relationship between the impact energy and the delamination size. The peak force of impact and the delamination size increase with the increase of the impact angle.
2014, 34(4): 457-463.
doi: 10.11883/1001-1455(2014)04-0457-07
Abstract:
In order to increase cavity diameter and meet the penetration depth requirement of jet penetration into concrete, a double-layered liner that could form a jacketed jet was designed. Moreover, three types of penetration modes during the process of jacketed jet penetration into concrete, including homogeneous jet penetration, "bi-erosion" and "co-erosion", were discussed. Thus, an analytical model for predicting the crater size generated by jacketed jet penetration into concrete is presented. The X-ray measurement show that the state of jacketed jet is fine, and the jet diameter increases with thickness increase of aluminum liner. Penetration experiments show that cavity diameter increases with thickness increase of aluminum liner, and penetration depth agrees with the requirement. The hole profile calculated with the analytical model is in good agreement with the experimental data.
In order to increase cavity diameter and meet the penetration depth requirement of jet penetration into concrete, a double-layered liner that could form a jacketed jet was designed. Moreover, three types of penetration modes during the process of jacketed jet penetration into concrete, including homogeneous jet penetration, "bi-erosion" and "co-erosion", were discussed. Thus, an analytical model for predicting the crater size generated by jacketed jet penetration into concrete is presented. The X-ray measurement show that the state of jacketed jet is fine, and the jet diameter increases with thickness increase of aluminum liner. Penetration experiments show that cavity diameter increases with thickness increase of aluminum liner, and penetration depth agrees with the requirement. The hole profile calculated with the analytical model is in good agreement with the experimental data.
2014, 34(4): 464-470.
doi: 10.11883/1001-1455(2014)04-0464-07
Abstract:
Deformation behavior of closed-cell metallic foam under uniaxial dynamic compression was investigated using the finite element method of ABAQUS/Explicit code. The random 3D Voronoi technique was employed to construct foam specimens. Three deformation modes, namely the quasi-static homogeneous mode, the transitional mode and the shock mode, had been observed in the foam specimens with increasing of impact velocity. A deformation mode map with coordinates of relative density and impact velocity was presented for the foam considered. Two parameters, namely the stress uniformity index and the deformation localization index, were introduced to identify two critical impact velocities of mode transitions. The numerical results of critical impact velocities were compared with the predictions using the theoretical formulas from the literature. Based on the numerical and theoretical results of critical impact velocities, a scheme is suggested to determine the locking strain. It is found that the locking strain obtained from this scheme is between the densification strain and the complete densification strain.
Deformation behavior of closed-cell metallic foam under uniaxial dynamic compression was investigated using the finite element method of ABAQUS/Explicit code. The random 3D Voronoi technique was employed to construct foam specimens. Three deformation modes, namely the quasi-static homogeneous mode, the transitional mode and the shock mode, had been observed in the foam specimens with increasing of impact velocity. A deformation mode map with coordinates of relative density and impact velocity was presented for the foam considered. Two parameters, namely the stress uniformity index and the deformation localization index, were introduced to identify two critical impact velocities of mode transitions. The numerical results of critical impact velocities were compared with the predictions using the theoretical formulas from the literature. Based on the numerical and theoretical results of critical impact velocities, a scheme is suggested to determine the locking strain. It is found that the locking strain obtained from this scheme is between the densification strain and the complete densification strain.
2014, 34(4): 471-475.
doi: 10.11883/1001-1455(2014)04-0471-05
Abstract:
An infrared detector system was introduced into the apparatus of the split Hopkinson pressure bar. Real-time temperature of the dynamic deformed specimens of pseudo-elastic TiNi alloy and aluminium alloy was measured with calibrated curves of temperature and voltage. The temperature results varied significantly. During loading, the temperature of two kinds of materials kept to rise. The main difference of temperature evolution of two kinds of specimen appeared during unloading. For specimen of aluminium alloy, temperature during unloading kept constant as the maximum temperature during loading. In contrast, temperature of specimen of TiNi alloy decreased significantly. The difference of temperature evolution of specimens reflects that there are different mechanisms of deformation and temperature variation for two kinds of materials. The measured temperature in the infrared method was in good agreement with the temperature calculated by the principle of energy conservation. It means that the infrared method is adaptable for real-time measurement of transient temperature.
An infrared detector system was introduced into the apparatus of the split Hopkinson pressure bar. Real-time temperature of the dynamic deformed specimens of pseudo-elastic TiNi alloy and aluminium alloy was measured with calibrated curves of temperature and voltage. The temperature results varied significantly. During loading, the temperature of two kinds of materials kept to rise. The main difference of temperature evolution of two kinds of specimen appeared during unloading. For specimen of aluminium alloy, temperature during unloading kept constant as the maximum temperature during loading. In contrast, temperature of specimen of TiNi alloy decreased significantly. The difference of temperature evolution of specimens reflects that there are different mechanisms of deformation and temperature variation for two kinds of materials. The measured temperature in the infrared method was in good agreement with the temperature calculated by the principle of energy conservation. It means that the infrared method is adaptable for real-time measurement of transient temperature.
2014, 34(4): 476-482.
doi: 10.11883/1001-1455(2014)04-0476-07
Abstract:
An improved split Hopkinson bar was used for testing the dynamic tensile behaviour of low strength materials. This device included an aluminum transmitted bar and the semiconductor gages to capture the weak strain signal. For material of aramid fiber silk, the stress equilibrium on both sides of specimen as well as the test speed was verified; a comparison between the measurements from semiconductor strain gauge and from resistance strain gauge was made; the stress-strain curves of tested material under various impact velocities were obtained; the failure process of specimen was captured by a high-speed camera. The experimental results show that the design of the experiment method is feasible.
An improved split Hopkinson bar was used for testing the dynamic tensile behaviour of low strength materials. This device included an aluminum transmitted bar and the semiconductor gages to capture the weak strain signal. For material of aramid fiber silk, the stress equilibrium on both sides of specimen as well as the test speed was verified; a comparison between the measurements from semiconductor strain gauge and from resistance strain gauge was made; the stress-strain curves of tested material under various impact velocities were obtained; the failure process of specimen was captured by a high-speed camera. The experimental results show that the design of the experiment method is feasible.
2014, 34(4): 483-488.
doi: 10.11883/1001-1455(2014)04-0483-06
Abstract:
Based on the split Hopkinson pressure bar (SHPB), a new loading experimental technology was developed for conducting expanding ring test which is used to study the dynamic tensile deformation and the fracture (fragmentation) properties of materials. The loading fixture includes a hydraulic cylinder filled with incompressible fluid, which is pushed by a piston connected to the input bar. As the liquid is driven, it expands the metallic ring specimen in the radial direction. The approximately incompressible property of the liquid makes it possible to drive the specimen in very high radial velocity by low velocity movement of piston, according to the large sectional area ratio of the cylinder to specimen. The ring specimens of LY12 aluminum alloy were tested by this experimental technology. The results show apparent increase of the fragment number and the fracture strain of the specimen with the increase of the impact velocity.
Based on the split Hopkinson pressure bar (SHPB), a new loading experimental technology was developed for conducting expanding ring test which is used to study the dynamic tensile deformation and the fracture (fragmentation) properties of materials. The loading fixture includes a hydraulic cylinder filled with incompressible fluid, which is pushed by a piston connected to the input bar. As the liquid is driven, it expands the metallic ring specimen in the radial direction. The approximately incompressible property of the liquid makes it possible to drive the specimen in very high radial velocity by low velocity movement of piston, according to the large sectional area ratio of the cylinder to specimen. The ring specimens of LY12 aluminum alloy were tested by this experimental technology. The results show apparent increase of the fragment number and the fracture strain of the specimen with the increase of the impact velocity.
2014, 34(4): 489-494.
doi: 10.11883/1001-1455(2014)04-0489-06
Abstract:
The main factors which influence ignition performance of igniter tube with large ratio of length to diameter and consolidated charge were compared by simulation with the calculation program, and the ignition performance was analyzed in different construction parameters and charge conditions. The influence law is summarized on construction parameters and charge conditions of igniter tube by analysis of the results. The diameter of fire hole, the height of the first hole, the hole area in unit length and charge density evidently effect on the ignition pressure and ignition characteristics. The diameter of fire hole, the height of the first hole, the hole area in unit length are the primary influencing factors of decompressing velocity after the diaphragm breaking, and the charge density effects on the permeability of charge bed and free movement of flame propagation. All of four factors evidently effect on the safety, the transient characteristics and the conformance of ignition.
The main factors which influence ignition performance of igniter tube with large ratio of length to diameter and consolidated charge were compared by simulation with the calculation program, and the ignition performance was analyzed in different construction parameters and charge conditions. The influence law is summarized on construction parameters and charge conditions of igniter tube by analysis of the results. The diameter of fire hole, the height of the first hole, the hole area in unit length and charge density evidently effect on the ignition pressure and ignition characteristics. The diameter of fire hole, the height of the first hole, the hole area in unit length are the primary influencing factors of decompressing velocity after the diaphragm breaking, and the charge density effects on the permeability of charge bed and free movement of flame propagation. All of four factors evidently effect on the safety, the transient characteristics and the conformance of ignition.
2014, 34(4): 495-500.
doi: 10.11883/1001-1455(2014)04-0495-06
Abstract:
In order to obtain the casting speed of rock in pin-point blasting of sloping surface, a research was carried out by the field test, theoretical analysis, the high-speed photography and numerical simulation. The results of research show that maximum casting speed of rock was in the range of 18-28 m/s which was reached in 93-105 ms after detonation; along the direction of detonation propagating, maximum casting speed of rock increased to a platform firstly, then declined with the same motion resistance; in the end of pin-point blasting, the rock fall as free-faller, and the casting speed of rock vibrated due to the collision of rock; the process of pin-point blasting of sloping surface was simulated with the RHT constitutive model and parameters assorted. The result of numerical simulation was proved by the measurement of high-speed photography
In order to obtain the casting speed of rock in pin-point blasting of sloping surface, a research was carried out by the field test, theoretical analysis, the high-speed photography and numerical simulation. The results of research show that maximum casting speed of rock was in the range of 18-28 m/s which was reached in 93-105 ms after detonation; along the direction of detonation propagating, maximum casting speed of rock increased to a platform firstly, then declined with the same motion resistance; in the end of pin-point blasting, the rock fall as free-faller, and the casting speed of rock vibrated due to the collision of rock; the process of pin-point blasting of sloping surface was simulated with the RHT constitutive model and parameters assorted. The result of numerical simulation was proved by the measurement of high-speed photography
2014, 34(4): 501-507.
doi: 10.11883/1001-1455(2014)04-0501-07
Abstract:
Compared with entropy stable schemes, entropy consistent schemes control entropy production more exactly and effectively eliminate phenomena such as expansion shocks and spurious oscillations. By using WENO (weighted essentially non-oscillatory) reconstruction of higher order at cell interfaces, a WENO type entropy consistent scheme for hyperbolic conservation laws is presented. The one-dimentional Burgers equation and Euler equations are used to test the proposed scheme. The numerical experiments demonstrate that the scheme is accurate and essentially non-oscillatory.
Compared with entropy stable schemes, entropy consistent schemes control entropy production more exactly and effectively eliminate phenomena such as expansion shocks and spurious oscillations. By using WENO (weighted essentially non-oscillatory) reconstruction of higher order at cell interfaces, a WENO type entropy consistent scheme for hyperbolic conservation laws is presented. The one-dimentional Burgers equation and Euler equations are used to test the proposed scheme. The numerical experiments demonstrate that the scheme is accurate and essentially non-oscillatory.
2014, 34(4): 508-512.
doi: 10.11883/1001-1455(2014)04-0508-05
Abstract:
In order to investigate the characteristics of muzzle noise, a numerical study on jet noise induced by complex flows discharging from 7.62 mm gun is achieved. Because of the complex flows structure, it is not easy to study muzzle noise by direct simulation of CAA in current level of computational condition. CFD-CAA hybrid method is applied. At first, the muzzle flow is calculated by using LES. Using the obtained data, the jet noise is carried out by using FW-H equation. The feasibility of the numerical method is verified by comparing with the experiment. Then, the jet noise of 7.62 mm gun is numerically studied by using the hybrid method. Based on the numerical results, the jet noise directivity is analyzed and the contour of sound pressure level is also drawn. Results indicate that jet noise is mainly concentrated in the near muzzle region and the maximum jet noise mainly occurs in the range of 30°-60°.
In order to investigate the characteristics of muzzle noise, a numerical study on jet noise induced by complex flows discharging from 7.62 mm gun is achieved. Because of the complex flows structure, it is not easy to study muzzle noise by direct simulation of CAA in current level of computational condition. CFD-CAA hybrid method is applied. At first, the muzzle flow is calculated by using LES. Using the obtained data, the jet noise is carried out by using FW-H equation. The feasibility of the numerical method is verified by comparing with the experiment. Then, the jet noise of 7.62 mm gun is numerically studied by using the hybrid method. Based on the numerical results, the jet noise directivity is analyzed and the contour of sound pressure level is also drawn. Results indicate that jet noise is mainly concentrated in the near muzzle region and the maximum jet noise mainly occurs in the range of 30°-60°.
