2005 Vol. 25, No. 6
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2005, 25(6): 481-486.
doi: 10.11883/1001-1455(2005)06-0481-06
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Abstract:
This paper discusses the propagation of one-dimensional stress waves in a viscoplastic bar with variable section. Based on the constitutive relation theory which includes internal variables, combining with the characteristic relations and the jump conditions across a shock wave, the evolution rules, indudins their differential equations and the analytical expressions, are obtained. For examples, the shock wave evolution rules in bars with Bodner and Johnson-Cook materials and different section-varying forms are discussed. The propagation rules and characteristics of stress waves behind the shock front are also calculated and discussed.
This paper discusses the propagation of one-dimensional stress waves in a viscoplastic bar with variable section. Based on the constitutive relation theory which includes internal variables, combining with the characteristic relations and the jump conditions across a shock wave, the evolution rules, indudins their differential equations and the analytical expressions, are obtained. For examples, the shock wave evolution rules in bars with Bodner and Johnson-Cook materials and different section-varying forms are discussed. The propagation rules and characteristics of stress waves behind the shock front are also calculated and discussed.
2005, 25(6): 487-492.
doi: 10.11883/1001-1455(2005)06-0487-06
Abstract:
The Hopkinson bar technique with a furnace and a driving mechanism is utilized to determine the dynamic property of materials at elevated temperature and high strain rates. The specimen is heated by a furnace independently. While the temperature in specimen reaches the desired temperature, a driving mechanism shifts the transmission bar and the specimen to contact the incident bar, so that the transmission bar, the specimen and incident bar fully contact each other just before the stress wave reaches the interface between incident bar and specimen. The dynamic properties of single crystal copper and polycrystal copper at the temperature range from room temperature to 1 085 K are tested. The results show that the flow stress of both materials decreases with increase of temperature, and strain hardening rates at a temperature below 585 K are greater than that at the temperature above 585 K.
The Hopkinson bar technique with a furnace and a driving mechanism is utilized to determine the dynamic property of materials at elevated temperature and high strain rates. The specimen is heated by a furnace independently. While the temperature in specimen reaches the desired temperature, a driving mechanism shifts the transmission bar and the specimen to contact the incident bar, so that the transmission bar, the specimen and incident bar fully contact each other just before the stress wave reaches the interface between incident bar and specimen. The dynamic properties of single crystal copper and polycrystal copper at the temperature range from room temperature to 1 085 K are tested. The results show that the flow stress of both materials decreases with increase of temperature, and strain hardening rates at a temperature below 585 K are greater than that at the temperature above 585 K.
2005, 25(6): 493-498.
doi: 10.11883/1001-1455(2005)06-0493-06
Abstract:
The numerical simulation of penetration of a functionally graded armour made from Aluminum alloy reinforced by SiC particle was performed. The SiC particle volume fraction varies continuously along the armour thickness followed a power law. The four different armours with the same SiC particle volume fraction, but differen distribution were investigated and compared with steel armour. The results show: The change of the distribution of SiC particle volume fraction along the armour thickness can increase the ability to resist a penetrator. While the SiC particle volume fraction is constant, the higher the SiC particle volume fraction in the surface is, the better the ability of the functionally graded armour against penetration is.The armour with f0=0.8, b=4 show the best anti-penatrator ability among all the cases and it is even better than steel armour.
The numerical simulation of penetration of a functionally graded armour made from Aluminum alloy reinforced by SiC particle was performed. The SiC particle volume fraction varies continuously along the armour thickness followed a power law. The four different armours with the same SiC particle volume fraction, but differen distribution were investigated and compared with steel armour. The results show: The change of the distribution of SiC particle volume fraction along the armour thickness can increase the ability to resist a penetrator. While the SiC particle volume fraction is constant, the higher the SiC particle volume fraction in the surface is, the better the ability of the functionally graded armour against penetration is.The armour with f0=0.8, b=4 show the best anti-penatrator ability among all the cases and it is even better than steel armour.
2005, 25(6): 499-505.
doi: 10.11883/1001-1455(2005)06-0499-07
Abstract:
The assumption of rigid projectile is usually employed to study the penetration/perforation of EPW. It is well known that only two dimensionless numbers, i.e., the impact function I and the geometry function of projectile N, dominate the whole penetration process. The present paper further declares the available range of I and N of EPW, which are likely to be applicable to design the projectile body. The analyses on the compress/stretch and bending of projectiles are conducted to obtain the limit thickness of the cartridges. The minimum thickness of the cartridges and the maximum obliquity angle of projectile, without any bending failure and damage, are formulated in the case of hollow and slender missiles penetrating into concrete targets at different initial velocities. The weakest location of projectile under oblique impact is also predicted. Some suggestions are carried out to define the thickness of cartridge, the local strengthening and the weld locations.
The assumption of rigid projectile is usually employed to study the penetration/perforation of EPW. It is well known that only two dimensionless numbers, i.e., the impact function I and the geometry function of projectile N, dominate the whole penetration process. The present paper further declares the available range of I and N of EPW, which are likely to be applicable to design the projectile body. The analyses on the compress/stretch and bending of projectiles are conducted to obtain the limit thickness of the cartridges. The minimum thickness of the cartridges and the maximum obliquity angle of projectile, without any bending failure and damage, are formulated in the case of hollow and slender missiles penetrating into concrete targets at different initial velocities. The weakest location of projectile under oblique impact is also predicted. Some suggestions are carried out to define the thickness of cartridge, the local strengthening and the weld locations.
2005, 25(6): 506-511.
doi: 10.11883/1001-1455(2005)06-0506-06
Abstract:
A discrete multilayered explosion containment vessel (DMECV) mainly consists of covers, inner shell and steel ribbon layers crossly helically wound on the inner shell. Three DMECV with the same materials and dimensions except helical winding angle were fabricated and used to investigate dynamic response and fracture characteristics of DMECV subjected to internal blast loads at the center. All tested DMECV are damaged in the cylindrical portion near the explosion center. The DMECV with smaller ribbon winding angle has better capacity for withstanding internal explosion. Results also show that DMECV have excellent explosion resistance.
A discrete multilayered explosion containment vessel (DMECV) mainly consists of covers, inner shell and steel ribbon layers crossly helically wound on the inner shell. Three DMECV with the same materials and dimensions except helical winding angle were fabricated and used to investigate dynamic response and fracture characteristics of DMECV subjected to internal blast loads at the center. All tested DMECV are damaged in the cylindrical portion near the explosion center. The DMECV with smaller ribbon winding angle has better capacity for withstanding internal explosion. Results also show that DMECV have excellent explosion resistance.
2005, 25(6): 512-518.
doi: 10.11883/1001-1455(2005)06-0512-07
Abstract:
Detailed chemical reaction model and finite volume method are used to numerically investigate detonation direct initiation induced by the toroidal shock wave focusing in combustible gas mixture. Numerical results show that detonation direct initiation will be initiated by toroidal shock wave focusing in the standard hydrogen-air gas mixture if the incident Mach number is above 3.1. Then the detonation wave interacts with shock waves and contact surfaces, which results in complex wave system. The initiation point is not fixed on the focusing point but varies with the incident shock Mach number. The critical Mach number is influenced by the initial pressure and temperature, but the temperature is the main factor.
Detailed chemical reaction model and finite volume method are used to numerically investigate detonation direct initiation induced by the toroidal shock wave focusing in combustible gas mixture. Numerical results show that detonation direct initiation will be initiated by toroidal shock wave focusing in the standard hydrogen-air gas mixture if the incident Mach number is above 3.1. Then the detonation wave interacts with shock waves and contact surfaces, which results in complex wave system. The initiation point is not fixed on the focusing point but varies with the incident shock Mach number. The critical Mach number is influenced by the initial pressure and temperature, but the temperature is the main factor.
2005, 25(6): 519-527.
doi: 10.11883/1001-1455(2005)06-0519-09
Abstract:
The recent results of dynamical experiments of uni-axile compression, tension and planar impact on concrete are concluded. Several representative constitutive models such as J-H, Forrestal, RHT and Malvar which recently used in numerical simulation on impact and penetration problems are introduced and studied by the way of analysis on limit surfaces, equation of state, definition and evolvement of damage. And some comments are made on the development trends of dynamic mechanical behavior of concrete at last.
The recent results of dynamical experiments of uni-axile compression, tension and planar impact on concrete are concluded. Several representative constitutive models such as J-H, Forrestal, RHT and Malvar which recently used in numerical simulation on impact and penetration problems are introduced and studied by the way of analysis on limit surfaces, equation of state, definition and evolvement of damage. And some comments are made on the development trends of dynamic mechanical behavior of concrete at last.
2005, 25(6): 528-535.
doi: 10.11883/1001-1455(2005)06-0528-08
Abstract:
By means of wavelet transform (WT) and Hilbert-Huang Transform (HHT), a practical blasting vibration signal was analyzed and the presented results show that both WT and HHT are efficient ways for analyzing and processing non-stationary signals, and can draw main characteristic information from signals as well as carry out wave filtration and noise elimination. In HHT the intrinsic mode function (IMF) obtained with empirical mode decomposition (EMD) can reflect the intrinsic physical characteristics of original data and it has no need of using base functions, while in WT selecting mother wavelet is a difficulty problem. Hilbert energy spectrum can clearly express the energy distribution with time and frequency in detail, and most energy are concentrated in a definitive range of time and frequency, but that of wavelet spectrum lines are distributed in a wider frequency range. Besides, the resolving power of time and frequency is restricted from Heisenberg principle in wavelet analysis, while in HHT time resolving power is precise and steady, and frequency resolving is adaptive according to signal intrinsic characteristics. Conclusion can be made that the HHT method is more adaptive than WT analysis in analyzing non-stationary signals and has a wide application on wave in rock transmitting, attenuation law, restructure dynamic response characteristics and blasting vibration damage.
By means of wavelet transform (WT) and Hilbert-Huang Transform (HHT), a practical blasting vibration signal was analyzed and the presented results show that both WT and HHT are efficient ways for analyzing and processing non-stationary signals, and can draw main characteristic information from signals as well as carry out wave filtration and noise elimination. In HHT the intrinsic mode function (IMF) obtained with empirical mode decomposition (EMD) can reflect the intrinsic physical characteristics of original data and it has no need of using base functions, while in WT selecting mother wavelet is a difficulty problem. Hilbert energy spectrum can clearly express the energy distribution with time and frequency in detail, and most energy are concentrated in a definitive range of time and frequency, but that of wavelet spectrum lines are distributed in a wider frequency range. Besides, the resolving power of time and frequency is restricted from Heisenberg principle in wavelet analysis, while in HHT time resolving power is precise and steady, and frequency resolving is adaptive according to signal intrinsic characteristics. Conclusion can be made that the HHT method is more adaptive than WT analysis in analyzing non-stationary signals and has a wide application on wave in rock transmitting, attenuation law, restructure dynamic response characteristics and blasting vibration damage.
2005, 25(6): 536-540.
doi: 10.11883/1001-1455(2005)06-0536-05
Abstract:
The design of focused fragmentation warhead is generally based on the detonation test in the static situation. In actual combat, because of the warhead velocity relative to the target and the fragments initial velocity gradient in existence along the warhead axial, the fragment dynamic ejection angle will be recomposed, the fragment clustering may disperse, and the fragment density on the target will decrease greatly. The simulation of the fragment ejection process and the fragment hitting density on the target under the situation of static detonation and actual combat shows that, the dynamic lethality for focused fragmentation warhead can be achieved at typical interception condition. As a result, a concept of the dynamic lethality for focused fragmentation warhead is developed. The method fulfilling the design of the fragment dynamic focusing for a parallel-focusing fragmentation warhead is given.
The design of focused fragmentation warhead is generally based on the detonation test in the static situation. In actual combat, because of the warhead velocity relative to the target and the fragments initial velocity gradient in existence along the warhead axial, the fragment dynamic ejection angle will be recomposed, the fragment clustering may disperse, and the fragment density on the target will decrease greatly. The simulation of the fragment ejection process and the fragment hitting density on the target under the situation of static detonation and actual combat shows that, the dynamic lethality for focused fragmentation warhead can be achieved at typical interception condition. As a result, a concept of the dynamic lethality for focused fragmentation warhead is developed. The method fulfilling the design of the fragment dynamic focusing for a parallel-focusing fragmentation warhead is given.
2005, 25(6): 541-546.
doi: 10.11883/1001-1455(2005)06-0541-06
Abstract:
Accident of two phase release frequently happens in the chemical, petrochemical and petroleum industry. So accidental release of toxic or flammable chemicals were concerned. In this paper, an Eulerian-Lagrangian approach with two-way coupling was adopted to deal with the dispersion of propane when the breach was occurred in the liquid part. The stochastic model and particle cloud model were utilized to model turbulent dispersion of droplets, which was compared with the results obtained by deterministic model. The mathematic models and calculated results were given, and compared with the experimental data. It is shown that stochastic model can describe the droplet turbulent dispersion and is suitable for two phase jet dispersion with droplet vaporization.
Accident of two phase release frequently happens in the chemical, petrochemical and petroleum industry. So accidental release of toxic or flammable chemicals were concerned. In this paper, an Eulerian-Lagrangian approach with two-way coupling was adopted to deal with the dispersion of propane when the breach was occurred in the liquid part. The stochastic model and particle cloud model were utilized to model turbulent dispersion of droplets, which was compared with the results obtained by deterministic model. The mathematic models and calculated results were given, and compared with the experimental data. It is shown that stochastic model can describe the droplet turbulent dispersion and is suitable for two phase jet dispersion with droplet vaporization.
2005, 25(6): 547-552.
doi: 10.11883/1001-1455(2005)06-0547-06
Abstract:
According to the structure of aircraft carrier and existing anti-ship missile warhead, the structural target with ribbings and experimental semi-armor-piercing warhead were designed with geometer similar principle. The processes of warhead penetrating the ribbings structural and homogeneous targets were investigated experimentally in the shooting range, and the end-point trajectory parameters in hitting conditions and the breakage mode of target were gained. On the basis of the theory of warhead penetrating homogeneous target and with the some hypothesis, the theoretical calculation model for end-point trajectory of warhead penetrating ribbings structural target was found. The results by theoretical calculation to residual velocity of warhead were consistent with that by experimental test.
According to the structure of aircraft carrier and existing anti-ship missile warhead, the structural target with ribbings and experimental semi-armor-piercing warhead were designed with geometer similar principle. The processes of warhead penetrating the ribbings structural and homogeneous targets were investigated experimentally in the shooting range, and the end-point trajectory parameters in hitting conditions and the breakage mode of target were gained. On the basis of the theory of warhead penetrating homogeneous target and with the some hypothesis, the theoretical calculation model for end-point trajectory of warhead penetrating ribbings structural target was found. The results by theoretical calculation to residual velocity of warhead were consistent with that by experimental test.
2005, 25(6): 553-558.
doi: 10.11883/1001-1455(2005)06-0553-06
Abstract:
The method to calculate the start point of transmitted wave and reflected wave relative to incident wave is acquired, based on the assumption of one-dimensional stress used in SHPB experiment. This method not only makes the result of SHPB experiment more accurate, but also standardizes the data processing of SHPB experiment; In addition, to calculating the level of classical incident stress wave, another method based on the principle of conservation of momentum is obtained, which can eliminate the influence of dispersion oscillation on determination of level of classical incident stress wave, and then improve the accuracy of calibrating sensitivity of strain gauge during SHPB experiment. So, this method also standardizes the data processing of SHPB experiment. By both of theoretical calculation and numerical simulation, the accuracy of two methods of data processing is validated.
The method to calculate the start point of transmitted wave and reflected wave relative to incident wave is acquired, based on the assumption of one-dimensional stress used in SHPB experiment. This method not only makes the result of SHPB experiment more accurate, but also standardizes the data processing of SHPB experiment; In addition, to calculating the level of classical incident stress wave, another method based on the principle of conservation of momentum is obtained, which can eliminate the influence of dispersion oscillation on determination of level of classical incident stress wave, and then improve the accuracy of calibrating sensitivity of strain gauge during SHPB experiment. So, this method also standardizes the data processing of SHPB experiment. By both of theoretical calculation and numerical simulation, the accuracy of two methods of data processing is validated.
2005, 25(6): 559-563.
doi: 10.11883/1001-1455(2005)06-0559-05
Abstract:
The dynamic response and failure behavior of AOW rock subjected to tensile loads has been studied experimentally. With the help of an one-stage light gas gun, the AOW rock samples, which were subjected to the plane plate impact by PMMA flyer with different speeds, have been recovered. The impact generated a tensile stress pulse of about 1.5 s duration in AOW rock by superposing rarefaction waves to induce spall. Based on the analyses of macro-and micro-examination for the recovered samples, the dynamic tensile strength of AOW rock was determined as 265.2-314.7 MPa.
The dynamic response and failure behavior of AOW rock subjected to tensile loads has been studied experimentally. With the help of an one-stage light gas gun, the AOW rock samples, which were subjected to the plane plate impact by PMMA flyer with different speeds, have been recovered. The impact generated a tensile stress pulse of about 1.5 s duration in AOW rock by superposing rarefaction waves to induce spall. Based on the analyses of macro-and micro-examination for the recovered samples, the dynamic tensile strength of AOW rock was determined as 265.2-314.7 MPa.
2005, 25(6): 564-568.
doi: 10.11883/1001-1455(2005)06-0564-05
Abstract:
Influence of the optical fiber dispersion and loss on the transmission of fiber-optic pin signals has been estimated in theory. The influence has been measured by experiment. Four optic fibers of different lengths have been used in this experiment. The results indicate that when a step index quartz optical fiber with NA=0.37 is used ，the influence of the optic fiber dispersion on rise time of signals of fiber-optic pin is 5414 ns/km，the loss of optic signals is 4.40.2 dB/km. So when a long fiber is used，a method that can reduce the optic fiber dispersion is necessary.
Influence of the optical fiber dispersion and loss on the transmission of fiber-optic pin signals has been estimated in theory. The influence has been measured by experiment. Four optic fibers of different lengths have been used in this experiment. The results indicate that when a step index quartz optical fiber with NA=0.37 is used ，the influence of the optic fiber dispersion on rise time of signals of fiber-optic pin is 5414 ns/km，the loss of optic signals is 4.40.2 dB/km. So when a long fiber is used，a method that can reduce the optic fiber dispersion is necessary.
2005, 25(6): 569-573.
doi: 10.11883/1001-1455(2005)06-0569-05
Abstract:
The numerical simulation of explosion in concrete with the hydro-code AUTODYN-2D has been presented. The effects on different method and different mesh size in numerical simulation are studied. With the detail example, the maximum shock pressure of concrete target in radial and axial, overload acceleration of back of target and size of damage section, size of blast pit are computed with Lagrange method and SPH method, which have different mesh size. The simulation results are compared with each other and with experiment results, and the proper simulation method and mesh size are demonstrated to the problem of explosion in concrete medium. Lagrange method is adaptable to simulation the maximum shock pressure of concrete target, especially to the area near the explosive point. SPH method has merit to simulate the shape of blast pit and the throw speed of the break. And 10 mm mesh size to Lagrange method and 3 mm particle size to SPH method are suitable to the example problem.
The numerical simulation of explosion in concrete with the hydro-code AUTODYN-2D has been presented. The effects on different method and different mesh size in numerical simulation are studied. With the detail example, the maximum shock pressure of concrete target in radial and axial, overload acceleration of back of target and size of damage section, size of blast pit are computed with Lagrange method and SPH method, which have different mesh size. The simulation results are compared with each other and with experiment results, and the proper simulation method and mesh size are demonstrated to the problem of explosion in concrete medium. Lagrange method is adaptable to simulation the maximum shock pressure of concrete target, especially to the area near the explosive point. SPH method has merit to simulate the shape of blast pit and the throw speed of the break. And 10 mm mesh size to Lagrange method and 3 mm particle size to SPH method are suitable to the example problem.
2005, 25(6): 574-576.
doi: 10.11883/1001-1455(2005)06-0574-03
Abstract:
Model 1000 Ultra-high speed Rotating Mirror Camera is a synchronised camera. It has framing rate from 2106 to 1107 fps, number of frames 160, frame size 7.5 mm10 mm, photographic dynamic resolution 15 mm-1. By use of a field lens located at the image plane of the main objective, the camera images whole, and achieve all the technical targets. The camera runs conveniently under new control system, and two sets of air turbine high speed camera have been simultaneously used. A set of Model 1000 Camera and the pulsed X-ray Cameras have also been synchronistically used in the explosive test field.
Model 1000 Ultra-high speed Rotating Mirror Camera is a synchronised camera. It has framing rate from 2106 to 1107 fps, number of frames 160, frame size 7.5 mm10 mm, photographic dynamic resolution 15 mm-1. By use of a field lens located at the image plane of the main objective, the camera images whole, and achieve all the technical targets. The camera runs conveniently under new control system, and two sets of air turbine high speed camera have been simultaneously used. A set of Model 1000 Camera and the pulsed X-ray Cameras have also been synchronistically used in the explosive test field.
