2016 Vol. 36, No. 1
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2016, 36(1): 1-8.
doi: 10.11883/1001-1455(2016)01-0001-08
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Abstract:
To find effective protection for fluid-filled structures subjected to high-speed projectile penetration, we studied the characteristics of a structure bearing impact loads when undergoing high velocity rod projectile penetration using dynamic nonlinear finite element, and analyzed the process of the impact load, the load strength, the projectile initial velocity, and water scale, and their effects on the front and rear plates that bear the impact. Our results show that the initial penetrating effect (pit-opening) on the liquid-filled structure forms incident shock waves, which will have a high peak pressure but a short duration, and produce multiple reflections in the liquid. Along with the penetration process in the liquid, the cavitation will occur and result in a cavitation pressure load which will reach a small peak value with a long duration. Local high pressure load will be formed due to the rear plate hindering the liquid flow, and incident shock wave and local high pressure increase with the increase of the initial projectile velocity but decrease with the increase of the length of the waters. According to different characteristics of shock load borne by different parts of the structure, the front and rear plates are divided into three different areas, and a simplified model was established for each.
To find effective protection for fluid-filled structures subjected to high-speed projectile penetration, we studied the characteristics of a structure bearing impact loads when undergoing high velocity rod projectile penetration using dynamic nonlinear finite element, and analyzed the process of the impact load, the load strength, the projectile initial velocity, and water scale, and their effects on the front and rear plates that bear the impact. Our results show that the initial penetrating effect (pit-opening) on the liquid-filled structure forms incident shock waves, which will have a high peak pressure but a short duration, and produce multiple reflections in the liquid. Along with the penetration process in the liquid, the cavitation will occur and result in a cavitation pressure load which will reach a small peak value with a long duration. Local high pressure load will be formed due to the rear plate hindering the liquid flow, and incident shock wave and local high pressure increase with the increase of the initial projectile velocity but decrease with the increase of the length of the waters. According to different characteristics of shock load borne by different parts of the structure, the front and rear plates are divided into three different areas, and a simplified model was established for each.
2016, 36(1): 9-16.
doi: 10.11883/1001-1455(2016)01-0009-08
Abstract:
In this work we developed a one-dimensional elastic-plastic reactive magnetic hydrodynamic code SSS/MHD with multi-medium, multi-cavities and coupling with external circuits on experimental configurations, based on the Lagrange code SSS. The key problems in coding were resolved through defining the configuration boundary coupling with circuits and unifying the treatment of the magnetic field boundary conditions of various configurations. The advantages of our coding are mainly shown in that, on the one hand, the various magnetic hydrodynamic experiment configurations-including both planar and cylindrical ones-can be handled in a unified fashion and, on the other, that the magnetic and reactive hydrodynamic calculation can be simultaneously conducted. Thus, following our way of coding, two typical experiments were calculated, i.e. the magnetic driven isentropic compression planar explosive and the explosive detonation driven liner for flux compression, the results of which accord with the experimental results.
In this work we developed a one-dimensional elastic-plastic reactive magnetic hydrodynamic code SSS/MHD with multi-medium, multi-cavities and coupling with external circuits on experimental configurations, based on the Lagrange code SSS. The key problems in coding were resolved through defining the configuration boundary coupling with circuits and unifying the treatment of the magnetic field boundary conditions of various configurations. The advantages of our coding are mainly shown in that, on the one hand, the various magnetic hydrodynamic experiment configurations-including both planar and cylindrical ones-can be handled in a unified fashion and, on the other, that the magnetic and reactive hydrodynamic calculation can be simultaneously conducted. Thus, following our way of coding, two typical experiments were calculated, i.e. the magnetic driven isentropic compression planar explosive and the explosive detonation driven liner for flux compression, the results of which accord with the experimental results.
2016, 36(1): 17-23.
doi: 10.11883/1001-1455(2016)01-0017-07
Abstract:
The plastic-bonded explosives (PBX) simulation model with heterogeneous crystal grain and binder was presented using the discrete element method(DEM). By loading opposite flyers at both ends of the explosive sample, the dynamic compression simulation was performed adopting velocity as the boundary condition instead of stress as the boundary condition in the Hopkinson test, and replicated the compression process in the Hopkinson test. The stress-strain curves and their corresponding damage fracture images under different loading-unloading paths in the explosive sample were captured. Our simulation results indicated that the stress distribution in PBX is not uniform and the stress propagates in the form of stress bridges between crystals due to the heterogeneous structure. The actual stress in PBX can be higher than that shown by the curve's peak stress. The samples on the unloading hysteresis curves reveal local damage, while those on the completely softening curves indicate fractures resulting from integral instability.
The plastic-bonded explosives (PBX) simulation model with heterogeneous crystal grain and binder was presented using the discrete element method(DEM). By loading opposite flyers at both ends of the explosive sample, the dynamic compression simulation was performed adopting velocity as the boundary condition instead of stress as the boundary condition in the Hopkinson test, and replicated the compression process in the Hopkinson test. The stress-strain curves and their corresponding damage fracture images under different loading-unloading paths in the explosive sample were captured. Our simulation results indicated that the stress distribution in PBX is not uniform and the stress propagates in the form of stress bridges between crystals due to the heterogeneous structure. The actual stress in PBX can be higher than that shown by the curve's peak stress. The samples on the unloading hysteresis curves reveal local damage, while those on the completely softening curves indicate fractures resulting from integral instability.
2016, 36(1): 24-30.
doi: 10.11883/1001-1455(2016)01-0024-07
Abstract:
In the cases of the perforation of a single-layered metal plate struck by a blunt rigid projectile, along with the increase of the plate thickness and that of the projectile velocity, the failure mode of the metal plate may transform from shear plugging to adiabatic shear plugging. Therefore, regarding the perforation of double-layered or multi-layered plates, the failure modes of various plates can be quite different. In this work we investigated these different perforation modes by conducting experimental analyses on the perforations of single- and double-layered Weldox E steel plates with air space. Our results indicate that, in the case of a higher initial striking velocity, the failure mode of the first layer plate is adiabatic shear plugging, while that of the second layer plate is adiabatic shear plugging or shear plugging as the striking velocity of the projectile slows down. We conclude that the final failure mode of the double-layered plates is the mixture of both shear plugging and adiabatic shear plugging.
In the cases of the perforation of a single-layered metal plate struck by a blunt rigid projectile, along with the increase of the plate thickness and that of the projectile velocity, the failure mode of the metal plate may transform from shear plugging to adiabatic shear plugging. Therefore, regarding the perforation of double-layered or multi-layered plates, the failure modes of various plates can be quite different. In this work we investigated these different perforation modes by conducting experimental analyses on the perforations of single- and double-layered Weldox E steel plates with air space. Our results indicate that, in the case of a higher initial striking velocity, the failure mode of the first layer plate is adiabatic shear plugging, while that of the second layer plate is adiabatic shear plugging or shear plugging as the striking velocity of the projectile slows down. We conclude that the final failure mode of the double-layered plates is the mixture of both shear plugging and adiabatic shear plugging.
2016, 36(1): 31-37.
doi: 10.11883/1001-1455(2016)01-0031-07
Abstract:
In order to investigate the characteristics of pulse gas flow generator with different nozzle structures and analyze those of the flow field and their tendencies to change, we achieved the shock wave profiles generated by the gas flow generators and obtained experimental photos of flow field by using high-speed photography technology and controlling the light sources. Next, we studied the influence of different nozzles on air flow patterns using the polynomial fitting method to acquire the overpressure of shock wave, the attenuation rules of velocity corresponding with change of distance. Moreover, taking advantage of image processing technology, we collected effective data of the air flow from experimental images and, according to the first order exponential decay equation, we deduced the gas flow displacements and the variation rules of velocity corresponding with changes of time. Our results will help to better understand and use the relevant parameters of shock wave and gas flow and thus provide effective reference to optimized design for the equipment.
In order to investigate the characteristics of pulse gas flow generator with different nozzle structures and analyze those of the flow field and their tendencies to change, we achieved the shock wave profiles generated by the gas flow generators and obtained experimental photos of flow field by using high-speed photography technology and controlling the light sources. Next, we studied the influence of different nozzles on air flow patterns using the polynomial fitting method to acquire the overpressure of shock wave, the attenuation rules of velocity corresponding with change of distance. Moreover, taking advantage of image processing technology, we collected effective data of the air flow from experimental images and, according to the first order exponential decay equation, we deduced the gas flow displacements and the variation rules of velocity corresponding with changes of time. Our results will help to better understand and use the relevant parameters of shock wave and gas flow and thus provide effective reference to optimized design for the equipment.
2016, 36(1): 38-42.
doi: 10.11883/1001-1455(2016)01-0038-05
Abstract:
The energy release process and damage characteristics of thermobaric explosive (TBE), a non-ideal explosive, differ from those of a normal explosive. In the present work, free-field explosion experiments were done to study the shock wave characteristics of TBE. The typical TBE grains and TNT grains with different magnitude order were tested and the shock wave parameters of TBE and TNT were obtained and fitted following the explosion similarity principle. Then a comparative research of TBE and TNT was done to show the characteristics of TBE. The results show that the peak pressure of TBE isn't obviously advantageous compared with that of TNT because it is only slightly higher than TNT at middle and far field. The positive phase time and impulse are related not only with the shock wave intensity and propagation distance but also with the explosive quality, so the specific impulse and specific positive phase time were studied. The correlation of the specific positive phase time between TBE and TNT is not definite. The specific impulse of TBE is higher than that of TNT at the same contrastive distance. When it is less than 2 m/kg1/3, the specific impulse of TBE is 2 times that that of TNT. The curves of the peak pressure and the specific impulse was introduced to describe the characteristics of the shock wave, showing that the specific impulse of TBE is larger than that of TNT under the same peak pressures. When the peak pressure is between 20 kPa to 50 kPa, the damage degree is below middle level but when the specific impulse of TBE is 40%-60% higher than that of TNT serious damage is generated. As an important damage factor in the free field explosion, the impulse should be taken into account when evaluating the power of TBE.
The energy release process and damage characteristics of thermobaric explosive (TBE), a non-ideal explosive, differ from those of a normal explosive. In the present work, free-field explosion experiments were done to study the shock wave characteristics of TBE. The typical TBE grains and TNT grains with different magnitude order were tested and the shock wave parameters of TBE and TNT were obtained and fitted following the explosion similarity principle. Then a comparative research of TBE and TNT was done to show the characteristics of TBE. The results show that the peak pressure of TBE isn't obviously advantageous compared with that of TNT because it is only slightly higher than TNT at middle and far field. The positive phase time and impulse are related not only with the shock wave intensity and propagation distance but also with the explosive quality, so the specific impulse and specific positive phase time were studied. The correlation of the specific positive phase time between TBE and TNT is not definite. The specific impulse of TBE is higher than that of TNT at the same contrastive distance. When it is less than 2 m/kg1/3, the specific impulse of TBE is 2 times that that of TNT. The curves of the peak pressure and the specific impulse was introduced to describe the characteristics of the shock wave, showing that the specific impulse of TBE is larger than that of TNT under the same peak pressures. When the peak pressure is between 20 kPa to 50 kPa, the damage degree is below middle level but when the specific impulse of TBE is 40%-60% higher than that of TNT serious damage is generated. As an important damage factor in the free field explosion, the impulse should be taken into account when evaluating the power of TBE.
2016, 36(1): 43-49.
doi: 10.11883/1001-1455(2016)01-0043-07
Abstract:
In this work, based on the traditional pulse generators, we present an electromagnetic induction generator driven by explosion as a new technology of electromagnetic pulse generator. Having described the working process of the generator, we simulated and calculated the shock process of the explosion. Furthermore, we established the model for the working circuit of the generator with initial voltage and static magnetic, obtaining the calculation method of the induced voltage. An experimental generator with initial static magnetic provided by permanent magnet was designed, and the generators respectively fitted with two different explosives were tested. The experimental results show that the generator driven by higher detonation velocity of explosive can produce higher peak and shorter rise time voltage pulse, which are found to be a little lower than the calculation results due to the simplification in theoretical calculation of the magnetic field of the core and the velocity of shock wave.
In this work, based on the traditional pulse generators, we present an electromagnetic induction generator driven by explosion as a new technology of electromagnetic pulse generator. Having described the working process of the generator, we simulated and calculated the shock process of the explosion. Furthermore, we established the model for the working circuit of the generator with initial voltage and static magnetic, obtaining the calculation method of the induced voltage. An experimental generator with initial static magnetic provided by permanent magnet was designed, and the generators respectively fitted with two different explosives were tested. The experimental results show that the generator driven by higher detonation velocity of explosive can produce higher peak and shorter rise time voltage pulse, which are found to be a little lower than the calculation results due to the simplification in theoretical calculation of the magnetic field of the core and the velocity of shock wave.
2016, 36(1): 50-56.
doi: 10.11883/1001-1455(2016)01-0050-07
Abstract:
Explosive welding interface structure determines the quality of composite materials. However, analyses on the interfaces morphology so far remain limited on the qualitative level and quantitative analysis methods have not been well established. In our work we took explosive welding interface morphology as research subject, extracted the fractal dimensions and multi-fractal spectrums of interface based on the fractal theory to understand its morphological characteristics. First, we obtained the interface structure by three-dimensional ultra-depth microscopy. Then we dealt with it by picture analysis techniques to gain its binary image. Furthermore, we calculated the fractal dimensions and multi-fractal spectrum of the images by fractal geometry. Following the fractal theory, the fractal dimension is the macroscopic characteristics of the welding interfaces and the multi-fractal spectrum reflects their degree of fluctuation and the ratio of distribution. Thus taking fractal dimension and multi-fractal spectrum into account when describing welding interface structure can make up for what is lacking in the qualitative analysis and achieve the quantitative analysis.
Explosive welding interface structure determines the quality of composite materials. However, analyses on the interfaces morphology so far remain limited on the qualitative level and quantitative analysis methods have not been well established. In our work we took explosive welding interface morphology as research subject, extracted the fractal dimensions and multi-fractal spectrums of interface based on the fractal theory to understand its morphological characteristics. First, we obtained the interface structure by three-dimensional ultra-depth microscopy. Then we dealt with it by picture analysis techniques to gain its binary image. Furthermore, we calculated the fractal dimensions and multi-fractal spectrum of the images by fractal geometry. Following the fractal theory, the fractal dimension is the macroscopic characteristics of the welding interfaces and the multi-fractal spectrum reflects their degree of fluctuation and the ratio of distribution. Thus taking fractal dimension and multi-fractal spectrum into account when describing welding interface structure can make up for what is lacking in the qualitative analysis and achieve the quantitative analysis.
2016, 36(1): 57-63.
doi: 10.11883/1001-1455(2016)01-0057-07
Abstract:
This paper aims to obtain the parameters for the failure model based on the Charpy impact test, which has been widely used to study dynamic fracture properties of metallic materials. Based on the explicit dynamic finite element method in ABAQUS, FEM model of Charpy impact test was conducted. We began by discussing the accuracy of the parameters of JC constitutive model and the grid size of the fracture section of V-notch specimen. Then, based on the orthogonal design method, we designed a set of parameters for JC failure model and obtained using finite element calculation the samples of the parameters and impact energy. Next, we obtained the regression equations containing the parameters and impact energy by regression analysis and finally, by solving these regression equations, we achieved the comparatively accurate parameters for JC failure model for Q370d steel. These parameters will be useful for engineering applications and our method will be a valuable way to obtain parameters for other kinds of materials, especially without necessarily meeting the conditions of performing some tests.
This paper aims to obtain the parameters for the failure model based on the Charpy impact test, which has been widely used to study dynamic fracture properties of metallic materials. Based on the explicit dynamic finite element method in ABAQUS, FEM model of Charpy impact test was conducted. We began by discussing the accuracy of the parameters of JC constitutive model and the grid size of the fracture section of V-notch specimen. Then, based on the orthogonal design method, we designed a set of parameters for JC failure model and obtained using finite element calculation the samples of the parameters and impact energy. Next, we obtained the regression equations containing the parameters and impact energy by regression analysis and finally, by solving these regression equations, we achieved the comparatively accurate parameters for JC failure model for Q370d steel. These parameters will be useful for engineering applications and our method will be a valuable way to obtain parameters for other kinds of materials, especially without necessarily meeting the conditions of performing some tests.
2016, 36(1): 64-68.
doi: 10.11883/1001-1455(2016)01-0064-05
Abstract:
Numerical Hopkinson bar experiments of hat-shaped specimens with different geometries were carried out using ANSYS/LS-DYNA to investigate the effects resulting from varying the geometrical dimensions of specimens. Results show that the stress value calculated by the classic formula deviated drastically from the theoretical value, when the width t the of shear zone was larger than 0.2 mm. When the width t was 1.0 mm, the calculated stress value would even rise up to twice as much as close to the theoretical value. Further research with the split model revealed that the deviation of the stress mainly occurred as a result from the expansion deformation of the brim portion of the hat-shaped specimen. An improved method of data processing for the hat-shaped specimen was also presented based on the numerical simulation results. Finally, the method was also validated by SHPB experiments with cylinder specimens and hat-shaped specimens with different dimensions.
Numerical Hopkinson bar experiments of hat-shaped specimens with different geometries were carried out using ANSYS/LS-DYNA to investigate the effects resulting from varying the geometrical dimensions of specimens. Results show that the stress value calculated by the classic formula deviated drastically from the theoretical value, when the width t the of shear zone was larger than 0.2 mm. When the width t was 1.0 mm, the calculated stress value would even rise up to twice as much as close to the theoretical value. Further research with the split model revealed that the deviation of the stress mainly occurred as a result from the expansion deformation of the brim portion of the hat-shaped specimen. An improved method of data processing for the hat-shaped specimen was also presented based on the numerical simulation results. Finally, the method was also validated by SHPB experiments with cylinder specimens and hat-shaped specimens with different dimensions.
2016, 36(1): 69-74.
doi: 10.11883/1001-1455(2016)01-0069-06
Abstract:
Eccentric warhead is a typical directional warhead, and its explosive wave is adjusted to improve the fragments' velocity in a specified area. The kinematic equation of a case was established in the polar coordinate system, and the Whitham method was adopted to realize the interaction of a double symmetric explosive wave, thus obtaining the trace of the triple wave point, the pressure and the height of the Mach stick, which were then calculated. By the combination of the kinematic equation and the Mach reflection, formula were deduced to evaluate the fragments' velocity in the Mach area. Comparison of the results obtained with AUTODYN 2D simulation shows that they are in good agreement. Double symmetric initiations increase the fragment's velocity by more than 30%, and the variation of the angle between initiations has little effect on the fragments' distribution and velocity.
Eccentric warhead is a typical directional warhead, and its explosive wave is adjusted to improve the fragments' velocity in a specified area. The kinematic equation of a case was established in the polar coordinate system, and the Whitham method was adopted to realize the interaction of a double symmetric explosive wave, thus obtaining the trace of the triple wave point, the pressure and the height of the Mach stick, which were then calculated. By the combination of the kinematic equation and the Mach reflection, formula were deduced to evaluate the fragments' velocity in the Mach area. Comparison of the results obtained with AUTODYN 2D simulation shows that they are in good agreement. Double symmetric initiations increase the fragment's velocity by more than 30%, and the variation of the angle between initiations has little effect on the fragments' distribution and velocity.
2016, 36(1): 75-80.
doi: 10.11883/1001-1455(2016)01-0075-06
Abstract:
Based on the theory of dynamic spherical cavity expansion, the model of the petaling penetration at low speed and the round hole penetration at high speed were established to describe the penetration by the grooved-tapered projectile and the penetration depths were calculated using the models. Our results indicate that the error of the penetration depth between the theoretical calculation and the experimental data is less than 11% when the initial velocity is below 1000 m/s, and this error reaches about 20% when the initial velocity is above 1 000 m/s. Comsidering the experimental error caused by the separated targets, we believe that the models can be used to predict the penetration depth for the grooved-tapered projectile penetrating concrete targets.
Based on the theory of dynamic spherical cavity expansion, the model of the petaling penetration at low speed and the round hole penetration at high speed were established to describe the penetration by the grooved-tapered projectile and the penetration depths were calculated using the models. Our results indicate that the error of the penetration depth between the theoretical calculation and the experimental data is less than 11% when the initial velocity is below 1000 m/s, and this error reaches about 20% when the initial velocity is above 1 000 m/s. Comsidering the experimental error caused by the separated targets, we believe that the models can be used to predict the penetration depth for the grooved-tapered projectile penetrating concrete targets.
2016, 36(1): 81-86.
doi: 10.11883/1001-1455(2016)01-0081-06
Abstract:
In this work, to study the overpressure distribution characteristics for multiple cloud explosion, we carried out a numerical simulation using LS-DYNA of the process of blast waves interaction for four non-circular cross-section clouds, with the computational results verified and compared with experimental data. Furthermore, based on our analysis of the peak overpressure located from 0 m to 20 m in the vertical direction and the processes of blast-waves interaction in the central area, we obtained the variation of the overpressure close to the ground versus the horizontal distances in four directions including 0°, 90°, 135° and 180°. Our results show that three blast waves occur in sequence over the central ground area, and there exists an increasingly higher pressure towards the central area. In the 45° vertical section, blast waves consist of incident wave, reflection wave and Mach wave.
In this work, to study the overpressure distribution characteristics for multiple cloud explosion, we carried out a numerical simulation using LS-DYNA of the process of blast waves interaction for four non-circular cross-section clouds, with the computational results verified and compared with experimental data. Furthermore, based on our analysis of the peak overpressure located from 0 m to 20 m in the vertical direction and the processes of blast-waves interaction in the central area, we obtained the variation of the overpressure close to the ground versus the horizontal distances in four directions including 0°, 90°, 135° and 180°. Our results show that three blast waves occur in sequence over the central ground area, and there exists an increasingly higher pressure towards the central area. In the 45° vertical section, blast waves consist of incident wave, reflection wave and Mach wave.
2016, 36(1): 87-92.
doi: 10.11883/1001-1455(2016)01-0087-06
Abstract:
The Richtmyer-Meshkov (RM) instability in a heavy gas (SF6) cylinder surrounded by ambient air is experimentally studied using a high-speed video camera in combination with a laser sheet. The evolving gas cylinder at intermediate to later stages was reshocked by the reflected shock wave at different times along with the changes of the endwall distance, which was achieved by designing a movable endwall for the test section in a horizontal shock tube. It is demonstrated that different endwall distances result in different evolutions of the reshocked interface. For a short endwall distance, the effect of the baroclinic mechanism on the interface evolution is significant and a secondary vortex pair is formed, while for a long endwall distance, the effect of the pressure perturbation mechanism is significant and the streamwise compression of the interface instead of vortex structure is clearly observable. In addition, quantitative analysis is conducted by measuring the position and the integral scale of the interface from sequences of images.
The Richtmyer-Meshkov (RM) instability in a heavy gas (SF6) cylinder surrounded by ambient air is experimentally studied using a high-speed video camera in combination with a laser sheet. The evolving gas cylinder at intermediate to later stages was reshocked by the reflected shock wave at different times along with the changes of the endwall distance, which was achieved by designing a movable endwall for the test section in a horizontal shock tube. It is demonstrated that different endwall distances result in different evolutions of the reshocked interface. For a short endwall distance, the effect of the baroclinic mechanism on the interface evolution is significant and a secondary vortex pair is formed, while for a long endwall distance, the effect of the pressure perturbation mechanism is significant and the streamwise compression of the interface instead of vortex structure is clearly observable. In addition, quantitative analysis is conducted by measuring the position and the integral scale of the interface from sequences of images.
2016, 36(1): 93-100.
doi: 10.11883/1001-1455(2016)01-0093-08
Abstract:
In view of seismic-wave detection, laws of waveform change, and the vibration-reducing effect that different millisecond time intervals have on millisecond blasting in underground engineering, we conducted research on optimal microsecond time interval in the underground blasting for the construction of an urban tunnel passing through complex strata through theoretical and numerical analysis based on the so-called "a soft layer on top of a hard layer" soil condition found with the Guan-Hui inter-city expressway project and the related field test data. Our results show that the effect of millisecond blasting in the complex strata is preferable, the optimal microsecond time interval of the first and second guns is 50-70 ms; under the same surrounding rock conditions, the duration of the vibration waveforms and the main shock phases increase with the distance from the center of the explosion; meanwhile under the unfavorable surrounding rock conditions, the vibration waveforms are more likely to appear superimposed; with the increase of the microsecond time interval, the main shock phases of the first and second guns gradually separate, the vibration-reducing rate fluctuates significantly between 0 and 35 ms and is less than stable; in the complex strata, with the same distances from the center of the explosion at the two measuring points, the points above the hole area have significant influences with relatively greater vibration velocity.
In view of seismic-wave detection, laws of waveform change, and the vibration-reducing effect that different millisecond time intervals have on millisecond blasting in underground engineering, we conducted research on optimal microsecond time interval in the underground blasting for the construction of an urban tunnel passing through complex strata through theoretical and numerical analysis based on the so-called "a soft layer on top of a hard layer" soil condition found with the Guan-Hui inter-city expressway project and the related field test data. Our results show that the effect of millisecond blasting in the complex strata is preferable, the optimal microsecond time interval of the first and second guns is 50-70 ms; under the same surrounding rock conditions, the duration of the vibration waveforms and the main shock phases increase with the distance from the center of the explosion; meanwhile under the unfavorable surrounding rock conditions, the vibration waveforms are more likely to appear superimposed; with the increase of the microsecond time interval, the main shock phases of the first and second guns gradually separate, the vibration-reducing rate fluctuates significantly between 0 and 35 ms and is less than stable; in the complex strata, with the same distances from the center of the explosion at the two measuring points, the points above the hole area have significant influences with relatively greater vibration velocity.
2016, 36(1): 101-106.
doi: 10.11883/1001-1455(2016)01-0101-06
Abstract:
In the present study, the dynamic response and shock-resisting properties of aluminum alloy lattice core sandwich panels under underwater shock loading were investigated using the non-explosive underwater shock loading device. The dynamic response of the sandwich plates was observed using a high-speed camera in collecting more information about the dynamic deformation history of the lattice sandwich plates. Based on the comparison of the experimental results of single-layered panels with the corresponding area mass, the effects of the lattice sandwich panel on the shock-resisting performance were studied. The results show that there is a quantitative relationship between the maximum deformation of the air-back plate of the lattice sandwich panels and the non-dimensional impulse of the underwater shock.
In the present study, the dynamic response and shock-resisting properties of aluminum alloy lattice core sandwich panels under underwater shock loading were investigated using the non-explosive underwater shock loading device. The dynamic response of the sandwich plates was observed using a high-speed camera in collecting more information about the dynamic deformation history of the lattice sandwich plates. Based on the comparison of the experimental results of single-layered panels with the corresponding area mass, the effects of the lattice sandwich panel on the shock-resisting performance were studied. The results show that there is a quantitative relationship between the maximum deformation of the air-back plate of the lattice sandwich panels and the non-dimensional impulse of the underwater shock.
2016, 36(1): 107-112.
doi: 10.11883/1001-1455(2016)01-0107-06
Abstract:
Tool steel and copper were welded together using underwater explosive welding technique, which is preferably adopted for the welding of super-thin and super-hard brittle materials. In this work we carried out experimental research using inclined welding setup for high velocity explosive. Underwater explosive welding process was numerically simulated using ANSYS/LS-DYNA, the simulated results from which show that the colliding velocity decreases in the welding direction. The micro-characterization indicates that wavy is the dominant interface structure and the wavy structure decreases in the welding direction, according with the simulation. In addition, the micro-hardness test of tool steel welded with copper reveals a slight increase of hardness close to the interface.
Tool steel and copper were welded together using underwater explosive welding technique, which is preferably adopted for the welding of super-thin and super-hard brittle materials. In this work we carried out experimental research using inclined welding setup for high velocity explosive. Underwater explosive welding process was numerically simulated using ANSYS/LS-DYNA, the simulated results from which show that the colliding velocity decreases in the welding direction. The micro-characterization indicates that wavy is the dominant interface structure and the wavy structure decreases in the welding direction, according with the simulation. In addition, the micro-hardness test of tool steel welded with copper reveals a slight increase of hardness close to the interface.
2016, 36(1): 113-120.
doi: 10.11883/1001-1455(2016)01-0113-08
Abstract:
Experimental studies of the oblique water-exit of slender bodies are conducted using high-speed camera technology to capture the whole process for exploring the mechanism of the formation, development and collapse of the cavity and examining the factors that affect the cavity evolution. By comparing the process of the vertical and oblique water-exit of slender bodies, this paper analyzes how the initial inclination angle bear on the cavity evolution and the new features that are found during the formation, development and pinch-off of the cavity. The dependence of the slender body's water-exit trajectory and posture on the initial inclination angle and head shape is also discussed, illustrating that the trajectory and posture have a nonlinear relationship with the initial inclination angle, but are closely relevant to the shoulder cavity's closed position. The blunt head shape will increase the stability of the cavity and change the dynamics of the body.
Experimental studies of the oblique water-exit of slender bodies are conducted using high-speed camera technology to capture the whole process for exploring the mechanism of the formation, development and collapse of the cavity and examining the factors that affect the cavity evolution. By comparing the process of the vertical and oblique water-exit of slender bodies, this paper analyzes how the initial inclination angle bear on the cavity evolution and the new features that are found during the formation, development and pinch-off of the cavity. The dependence of the slender body's water-exit trajectory and posture on the initial inclination angle and head shape is also discussed, illustrating that the trajectory and posture have a nonlinear relationship with the initial inclination angle, but are closely relevant to the shoulder cavity's closed position. The blunt head shape will increase the stability of the cavity and change the dynamics of the body.
2016, 36(1): 121-128.
doi: 10.11883/1001-1455(2016)01-0121-08
Abstract:
In order to study the perforation characteristics generated by a spherical 2A12 aluminum projectile impacting cylindrical shell steel free beams at high-speed, the experiments of a spherical projectile loaded by a two-stage light gas gun impacting cylindrical shell free beams were performed. Simulations were carried out to study different factors such as projectile speed, cylindrical shell diameter and thickness that influence the perforation diameter. Our simulation and experimental results are basically consistent. An empirical correlation of perforation diameter and related parameters was deduced combining dimension analysis and simulation. The results show that the radial and axial perforation diameters increase with the increase of the impact velocity when the thickness and diameter of the cylindrical shell remains unchanged; the radial and axial perforation diameter decreases with the increase of the diameter of the cylindrical shell when the projectile velocity and thickness are remain unchanged; the radial and axial perforation diameters decrease with the increase of the cylindrical shell thickness when the projectile velocity and cylindrical shell diameter remain unchanged.
In order to study the perforation characteristics generated by a spherical 2A12 aluminum projectile impacting cylindrical shell steel free beams at high-speed, the experiments of a spherical projectile loaded by a two-stage light gas gun impacting cylindrical shell free beams were performed. Simulations were carried out to study different factors such as projectile speed, cylindrical shell diameter and thickness that influence the perforation diameter. Our simulation and experimental results are basically consistent. An empirical correlation of perforation diameter and related parameters was deduced combining dimension analysis and simulation. The results show that the radial and axial perforation diameters increase with the increase of the impact velocity when the thickness and diameter of the cylindrical shell remains unchanged; the radial and axial perforation diameter decreases with the increase of the diameter of the cylindrical shell when the projectile velocity and thickness are remain unchanged; the radial and axial perforation diameters decrease with the increase of the cylindrical shell thickness when the projectile velocity and cylindrical shell diameter remain unchanged.
2016, 36(1): 129-134.
doi: 10.11883/1001-1455(2016)01-0129-06
Abstract:
In this work we carried out an experimental study along with a numerical simulation of the processes of a droplet deformation and breakup induced by an incident shock wave. The numerical results basically agreed with the experimental results but also identified the conditions under which discrepancies might occur. The results provide a full show of the whole processes of the droplet deformation and breakup: first, the droplet is deformed due to the shock wave compressing and RM instability, then small fogdrops are divorced from the deformed droplet, and in the end the droplet is completely broken up into fogdrops. Due to differences in such flow parameters as droplet diameter, the incident shock wave number, droplet varieties, etc., the development processes of droplets may have markedly different speed although they share similar trends. The results also show that the increase of Weber number accelerates the breakup of the droplet whereas that of Ohnesorge number and viscosity contains it.
In this work we carried out an experimental study along with a numerical simulation of the processes of a droplet deformation and breakup induced by an incident shock wave. The numerical results basically agreed with the experimental results but also identified the conditions under which discrepancies might occur. The results provide a full show of the whole processes of the droplet deformation and breakup: first, the droplet is deformed due to the shock wave compressing and RM instability, then small fogdrops are divorced from the deformed droplet, and in the end the droplet is completely broken up into fogdrops. Due to differences in such flow parameters as droplet diameter, the incident shock wave number, droplet varieties, etc., the development processes of droplets may have markedly different speed although they share similar trends. The results also show that the increase of Weber number accelerates the breakup of the droplet whereas that of Ohnesorge number and viscosity contains it.
2016, 36(1): 135-144.
doi: 10.11883/1001-1455(2016)01-0135-10
Abstract:
With the potential increase of terrorist attacks and blasting accidents, bridge safety has become a major public concern and greater attention is paid to the safety assessment of bridges under blast load. In this paper, the most recent research of bridges under blast load is systematically analyzed. Firstly, the simplified theories and dynamic response of pier, deck, cable and tower under blast load are sequentially analyzed and it has been demonstrated that the continuity, redundancy and robustness affect the progressive collapse of a bridge. Based on the review of the latest study on the progressive collapse of architecture and bridges and, in view of the relevant standards, the features of bridges' progressive collapse and shortages in the design methods are analyzed. Secondly, the recent study on bridge safety assessment, including load capacity evaluation, endurance evaluation and adaptability evaluation, is reviewed. Thirdly, a study of two specific blast problems of bridges, which are blasting demolition and dynamic response and damage of the bridge under near surface blast, is presented. Finally, suggestions are put forward aiming at rectifying the shortage in the recent bridge safety research
With the potential increase of terrorist attacks and blasting accidents, bridge safety has become a major public concern and greater attention is paid to the safety assessment of bridges under blast load. In this paper, the most recent research of bridges under blast load is systematically analyzed. Firstly, the simplified theories and dynamic response of pier, deck, cable and tower under blast load are sequentially analyzed and it has been demonstrated that the continuity, redundancy and robustness affect the progressive collapse of a bridge. Based on the review of the latest study on the progressive collapse of architecture and bridges and, in view of the relevant standards, the features of bridges' progressive collapse and shortages in the design methods are analyzed. Secondly, the recent study on bridge safety assessment, including load capacity evaluation, endurance evaluation and adaptability evaluation, is reviewed. Thirdly, a study of two specific blast problems of bridges, which are blasting demolition and dynamic response and damage of the bridge under near surface blast, is presented. Finally, suggestions are put forward aiming at rectifying the shortage in the recent bridge safety research
