2017 Vol. 37, No. 5
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2017, 37(5): 785-792.
doi: 10.11883/1001-1455(2017)05-0785-08
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In this work, a hypervelocity impact acoustic emission signal feature extraction method was proposed to detect damages experienced by the honeycomb core sandwich structure impacted by space debris by using hypervelocity impact acoustic emission signals. Varieties of hypervelocity impact acoustic emission signals were obtained through experiments based on the hypervelocity impact acoustic emission on the aluminum honeycomb core sandwich, their time-frequencies and the modes of the waves on the honeycomb plate were analyzed, the modes of the signals were differentiated, and the wavelet energy fraction and entropy were calculated, both by using the Daubechies wavelet decomposition, with the relationship between these parameters and the damage delineated and the contribution of each parameter gauged by the Kruskal-Wallis test. The results show that, to a certain degree, the wavelet energy fraction and the entropy of information are able to identify the damage patterns. Specifically, the energy fraction with a frequency above 250 kHz exhibits a better identifying capability, while signals of a lower frequency out of the ultrasonic range exert disturbance on the damage identification.
In this work, a hypervelocity impact acoustic emission signal feature extraction method was proposed to detect damages experienced by the honeycomb core sandwich structure impacted by space debris by using hypervelocity impact acoustic emission signals. Varieties of hypervelocity impact acoustic emission signals were obtained through experiments based on the hypervelocity impact acoustic emission on the aluminum honeycomb core sandwich, their time-frequencies and the modes of the waves on the honeycomb plate were analyzed, the modes of the signals were differentiated, and the wavelet energy fraction and entropy were calculated, both by using the Daubechies wavelet decomposition, with the relationship between these parameters and the damage delineated and the contribution of each parameter gauged by the Kruskal-Wallis test. The results show that, to a certain degree, the wavelet energy fraction and the entropy of information are able to identify the damage patterns. Specifically, the energy fraction with a frequency above 250 kHz exhibits a better identifying capability, while signals of a lower frequency out of the ultrasonic range exert disturbance on the damage identification.
2017, 37(5): 793-798.
doi: 10.11883/1001-1455(2017)05-0793-06
Abstract:
In the shot PTS-151 experiments the maximum velocity measured on the magnetically driven aluminum flyer plate with a thickness of 370 μm was 18 km/s, while that with a thickness 482 μm was 19 km/s. In this work, the data from the shot PTS-151 experiments on PTS were simulated and analyzed using the two dimensional magneto-hydro dynamics code MDSC2. The numerical simulation shows that the meaning of the maximum velocity measured in the shot PTS-151 should be different from that of the maximum velocity as reported in the related literatures where, as the free surface of the flyer plate was not ablated during the experiment, the maximum velocity measured was the flyer plate's free surface velocity. In the shot PTS-151 experiments the free surface was ablated in the measurement of the two flyer plates, and therefore the maximum velocity measured by VISAR was the velocity of the last solid surface inside them just before they were totally ablated. In our simulation, if the initial free surface is not ablated, the maximum initial free surface velocity calculated is 7 km/s with the 370 μm thick flyer plate and 11.8 km/s with the 482 μm thick flyer plate, far below the velocity actually measured in the shot PTS-151 experiments. A new flyer plate was re-designed on the basis of the current condition of the shot PTS-151, with 680 μm as the optimal thickness, which would both prevent the free surface from ablation and achieve the maximum velocity of 17.5 km/s.
In the shot PTS-151 experiments the maximum velocity measured on the magnetically driven aluminum flyer plate with a thickness of 370 μm was 18 km/s, while that with a thickness 482 μm was 19 km/s. In this work, the data from the shot PTS-151 experiments on PTS were simulated and analyzed using the two dimensional magneto-hydro dynamics code MDSC2. The numerical simulation shows that the meaning of the maximum velocity measured in the shot PTS-151 should be different from that of the maximum velocity as reported in the related literatures where, as the free surface of the flyer plate was not ablated during the experiment, the maximum velocity measured was the flyer plate's free surface velocity. In the shot PTS-151 experiments the free surface was ablated in the measurement of the two flyer plates, and therefore the maximum velocity measured by VISAR was the velocity of the last solid surface inside them just before they were totally ablated. In our simulation, if the initial free surface is not ablated, the maximum initial free surface velocity calculated is 7 km/s with the 370 μm thick flyer plate and 11.8 km/s with the 482 μm thick flyer plate, far below the velocity actually measured in the shot PTS-151 experiments. A new flyer plate was re-designed on the basis of the current condition of the shot PTS-151, with 680 μm as the optimal thickness, which would both prevent the free surface from ablation and achieve the maximum velocity of 17.5 km/s.
2017, 37(5): 799-806.
doi: 10.11883/1001-1455(2017)05-0799-08
Abstract:
Craters are the main response-induced form of underground explosion loadings. A series of field experiments were conducted in low-moisture and saturated sand in a large-scale experiment pit to study crater formation induced by underground explosions. The influence of charge mass, burial depth and moisture content on the crater diameter were analyzed. The results showed that, for a crater in sand with a low-moisture content, the eventual form may fall into one of the three types, formed respectively by enclosed explosion, cast blasting and soil collapse. The critical scaled burial depth for a crater from the enclosed explosion is about 2.3 m/kg1/3, that for crater from cast blasting is 1.5 m/kg1/3 or less, and that for a crater from soil collapse is 1.5~2.3 m/kg1/3. For a crater in saturated sand, the soil particles close to the crater were liquefied due to porewater pressure rise under explosion loadings. Thus, the lateral dimension of a crater was enlarged due to the flow and the collapse of the soil particles. The diameter of the crater in saturated sand can extend up to 1.25~1.35 times that of the crater in low-moisture sand under the same explosion loading. The greatest scaled burial depth of an enclosed explosion in saturated sand may reach 2.5 m/kg1/3 based on the experiments.
Craters are the main response-induced form of underground explosion loadings. A series of field experiments were conducted in low-moisture and saturated sand in a large-scale experiment pit to study crater formation induced by underground explosions. The influence of charge mass, burial depth and moisture content on the crater diameter were analyzed. The results showed that, for a crater in sand with a low-moisture content, the eventual form may fall into one of the three types, formed respectively by enclosed explosion, cast blasting and soil collapse. The critical scaled burial depth for a crater from the enclosed explosion is about 2.3 m/kg1/3, that for crater from cast blasting is 1.5 m/kg1/3 or less, and that for a crater from soil collapse is 1.5~2.3 m/kg1/3. For a crater in saturated sand, the soil particles close to the crater were liquefied due to porewater pressure rise under explosion loadings. Thus, the lateral dimension of a crater was enlarged due to the flow and the collapse of the soil particles. The diameter of the crater in saturated sand can extend up to 1.25~1.35 times that of the crater in low-moisture sand under the same explosion loading. The greatest scaled burial depth of an enclosed explosion in saturated sand may reach 2.5 m/kg1/3 based on the experiments.
2017, 37(5): 807-812.
doi: 10.11883/1001-1455(2017)05-0807-06
Abstract:
In this paper, we figured out a numerical simulation method involving the mechanical, thermal and chemical properties of the Steven test based on the thermo-mechanical coupled material model to simulate the Steven test of the plastic bonded explosive 9501. In this model, the stress-strain relationship is described by the dynamic plasticity model, the impact-induced thermal effect depicted by the isotropic thermal material model, the chemical reaction is described by the Arrhenius reaction rate law, with the effects of heating and melting on mechanical properties and thermal properties of materials also taken into account. Specific to the standard Steven test, the numerical model was validated by comparing the obtained deformation of the target and the ignition threshold of the PBX 9501 with the experimental data in the references. The calculated results are in good agreement with the experimental data, suggesting that this method is capable of simulating the Steven test. Compared to the previous models, this model does not need to incorporate experiential ignition criterion and therefore can be used more widely in the study of thermo-mechanical responses and local ignition of explosives subjected to low velocity impact.
In this paper, we figured out a numerical simulation method involving the mechanical, thermal and chemical properties of the Steven test based on the thermo-mechanical coupled material model to simulate the Steven test of the plastic bonded explosive 9501. In this model, the stress-strain relationship is described by the dynamic plasticity model, the impact-induced thermal effect depicted by the isotropic thermal material model, the chemical reaction is described by the Arrhenius reaction rate law, with the effects of heating and melting on mechanical properties and thermal properties of materials also taken into account. Specific to the standard Steven test, the numerical model was validated by comparing the obtained deformation of the target and the ignition threshold of the PBX 9501 with the experimental data in the references. The calculated results are in good agreement with the experimental data, suggesting that this method is capable of simulating the Steven test. Compared to the previous models, this model does not need to incorporate experiential ignition criterion and therefore can be used more widely in the study of thermo-mechanical responses and local ignition of explosives subjected to low velocity impact.
2017, 37(5): 813-821.
doi: 10.11883/1001-1455(2017)05-0813-09
Abstract:
The normal restitution coefficient (NRC) is a key parameter that determines the trajectory of the stone during a rockfall. In this study, using a test equipment and a sound-sampling technique developed by ourselves, we first measured the NRC of sandstone spheres and analyzed its influencing factors, i.e. the particle size, the impact velocity, the hydrous state and the elastic properties of the plate, and then we examined the size effect, the rate effect and the energy dissipation mechanism of the NRC. The results show that the NRC of sandstone spheres has a complex size effect which, with the increase of the size of sandstone spheres, at first increases and then decreases. The analysis shows that there exists two energy dissipation mechanisms, i.e. the viscoelastic dissipation and the elastoplastic damage dissipation, interacting with each other, which result in the complex size effect; that, due to the heterogeneity of sandstones, the velocity effect of the NRC is obvious when the diameter of the sandstone particle is small, while this effect is unobservable when the diameter is over 5 cm; that, compared with the NRC of air-drying sandstones, the saturation can cause the viscoelastic dissipation and elastoplastic damage dissipation to increase; and that the equivalent elastic modulus has a great impact on the NRC, i.e. the greater the equivalent elastic modulus, the smaller the NRC.
The normal restitution coefficient (NRC) is a key parameter that determines the trajectory of the stone during a rockfall. In this study, using a test equipment and a sound-sampling technique developed by ourselves, we first measured the NRC of sandstone spheres and analyzed its influencing factors, i.e. the particle size, the impact velocity, the hydrous state and the elastic properties of the plate, and then we examined the size effect, the rate effect and the energy dissipation mechanism of the NRC. The results show that the NRC of sandstone spheres has a complex size effect which, with the increase of the size of sandstone spheres, at first increases and then decreases. The analysis shows that there exists two energy dissipation mechanisms, i.e. the viscoelastic dissipation and the elastoplastic damage dissipation, interacting with each other, which result in the complex size effect; that, due to the heterogeneity of sandstones, the velocity effect of the NRC is obvious when the diameter of the sandstone particle is small, while this effect is unobservable when the diameter is over 5 cm; that, compared with the NRC of air-drying sandstones, the saturation can cause the viscoelastic dissipation and elastoplastic damage dissipation to increase; and that the equivalent elastic modulus has a great impact on the NRC, i.e. the greater the equivalent elastic modulus, the smaller the NRC.
2017, 37(5): 822-828.
doi: 10.11883/1001-1455(2017)05-0822-07
Abstract:
In this paper, we analyzed the waveforms of the two explosions that occurred on Dec.11, 2007 and Oct.9, 2006 as recorded using the HIA seismic station and the PS12 borehole seismic array. The results show that a borehole station can raise the signal-to-noise ratio (SNR) of the P waves to 4.6 times that of the common station at the same distance. With the beamforming technique, the SNR of the beamforming waveform from the PS12 is 3 times that from the single borehole station and over 10 times than that of the waveform recorded by the HIA. So the PS12 borehole seismic array can effectively improve the SNR of weak signals.
In this paper, we analyzed the waveforms of the two explosions that occurred on Dec.11, 2007 and Oct.9, 2006 as recorded using the HIA seismic station and the PS12 borehole seismic array. The results show that a borehole station can raise the signal-to-noise ratio (SNR) of the P waves to 4.6 times that of the common station at the same distance. With the beamforming technique, the SNR of the beamforming waveform from the PS12 is 3 times that from the single borehole station and over 10 times than that of the waveform recorded by the HIA. So the PS12 borehole seismic array can effectively improve the SNR of weak signals.
2017, 37(5): 829-836.
doi: 10.11883/1001-1455(2017)05-0829-08
Abstract:
An experimental investigation of Richtmyer-Meshkov (R-M) instability in the elliptic heavy gas cylinder was presented in detail. The shock-induced instability was studied in a horizontal shock tube using the planar laser-induced fluorescence (PLIF). The gas cylinder surrounded by air was composed of SF6 and acetone vapor. By adjusting the ratio of the long axis to the short one in the gas cylinder was achieved the evolution of three types of initial interface accelerated by a Mach 1.25 shock. After the calibration, concentration map were obtained. Furthermore, the congregation, transfer and dissipation in the concentration field was revealed. With a larger aspect ratio, the gas cylinder has a wider deposition of baroclinic vorticity, resulting in a faster evolution. When the evolution is rapid, a jet occurs in the trail structure due to the collision of the vortex pair. It was demonstrated that the initial configuration directly determines the strength and spacing distance of the vortex pair at early times, thereby exerting a significant influence on the instability evolution at later times.
An experimental investigation of Richtmyer-Meshkov (R-M) instability in the elliptic heavy gas cylinder was presented in detail. The shock-induced instability was studied in a horizontal shock tube using the planar laser-induced fluorescence (PLIF). The gas cylinder surrounded by air was composed of SF6 and acetone vapor. By adjusting the ratio of the long axis to the short one in the gas cylinder was achieved the evolution of three types of initial interface accelerated by a Mach 1.25 shock. After the calibration, concentration map were obtained. Furthermore, the congregation, transfer and dissipation in the concentration field was revealed. With a larger aspect ratio, the gas cylinder has a wider deposition of baroclinic vorticity, resulting in a faster evolution. When the evolution is rapid, a jet occurs in the trail structure due to the collision of the vortex pair. It was demonstrated that the initial configuration directly determines the strength and spacing distance of the vortex pair at early times, thereby exerting a significant influence on the instability evolution at later times.
2017, 37(5): 837-843.
doi: 10.11883/1001-1455(2017)05-0837-07
Abstract:
Based on the incompressible-rigid-plastic material assumption and the slip line field theory, the resistance function of a rigid projectile penetrating a semi-infinite target at a low velocity was obtained with a single admissible velocity field. A three-stage resistance curve of a rigid projectile impacting on a thin target was analyzed under multiple velocity fields, where the critical conditions for scabbing or perforation were calculated. The methods and formulae for local effects on reinforced concrete slab under low-velocity impact were further verified using comparative analysis of the results from the experiments, the UMIST formulae, the Kuibyshev formulae, and the present paper's calculations. The relationships between the normalized critical scabbing/perforation thickness, and the nose-shape factor, the impact factor and the reinforcement factor were examined to present potential guide to experimental studies.
Based on the incompressible-rigid-plastic material assumption and the slip line field theory, the resistance function of a rigid projectile penetrating a semi-infinite target at a low velocity was obtained with a single admissible velocity field. A three-stage resistance curve of a rigid projectile impacting on a thin target was analyzed under multiple velocity fields, where the critical conditions for scabbing or perforation were calculated. The methods and formulae for local effects on reinforced concrete slab under low-velocity impact were further verified using comparative analysis of the results from the experiments, the UMIST formulae, the Kuibyshev formulae, and the present paper's calculations. The relationships between the normalized critical scabbing/perforation thickness, and the nose-shape factor, the impact factor and the reinforcement factor were examined to present potential guide to experimental studies.
2017, 37(5): 844-852.
doi: 10.11883/1001-1455(2017)05-0844-09
Abstract:
To characterize the function of water droplets in the restraining and attenuation of the explosive shock wave inside of a cabin, we built several models of a sing layer in z-axis with different sizes of a single droplet and rows of droplets using numerical simulation, analyzed the shock wave interacting with them, observed the interaction process and the change of the droplet forms, summarized the shock wave's attenuation regularities, and obtained some conclusions. The results show that, in the single droplet model, smaller droplets were broken more rapidly and regularly, while bigger droplets tend to break out little droplets more and earlier but less regularly on the whole; that single droplets of different sizes had an effect of attenuation on the shock wave, with an obvious correlation between the increase of the droplet size and that of the attenuation; and that the rows had the most obvious effect of attenuation on the shock wave, with a linear relation between the increase of the droplet number and that of attenuation effect at the same droplet density.
To characterize the function of water droplets in the restraining and attenuation of the explosive shock wave inside of a cabin, we built several models of a sing layer in z-axis with different sizes of a single droplet and rows of droplets using numerical simulation, analyzed the shock wave interacting with them, observed the interaction process and the change of the droplet forms, summarized the shock wave's attenuation regularities, and obtained some conclusions. The results show that, in the single droplet model, smaller droplets were broken more rapidly and regularly, while bigger droplets tend to break out little droplets more and earlier but less regularly on the whole; that single droplets of different sizes had an effect of attenuation on the shock wave, with an obvious correlation between the increase of the droplet size and that of the attenuation; and that the rows had the most obvious effect of attenuation on the shock wave, with a linear relation between the increase of the droplet number and that of attenuation effect at the same droplet density.
2017, 37(5): 853-862.
doi: 10.11883/1001-1455(2017)05-0853-10
Abstract:
In the present study the early-stage deformation of a liquid drop in the high-speed flow induced by a planar shock wave was experimentally investigated using the shock tube facility and high-speed photography technique. It was found that the variation of the flow and drop conditions may cause significant divergences in the morphology of the drop deformation, even though such classical dominant parameters such as the Weber number or the Reynolds number are conserved. The divergences are mainly on the lee side of the drop, involving major characteristics of the circular ridges, the wrinkle band and the concave-plane convex profile of the lee side polar zone. Numerical simulations of the flow around a sphere show evident correspondence between the deformation patterns and the flow structures as well as the aerodynamic forces distributed along the sphere surface. For further evaluation and understanding of the detailed deformation features, a set of equations were deduced from hydrodynamic theories with necessary simplification. Feeding the equations with the aerodynamic data from numerical simulations, the calculation results indicate that, the main mechanism behind the deformation on the lee side of the drop is the squeezing effect of the uneven pressure distribution, rather than the accumulation effect of the surfacial flow induced by friction, with the former about two orders higher than the latter. Moreover, the drop profiles calculated following the pressure acting theory were found to agree quite well with the real drop patterns, not only in the deformation characteristics but also in the order of deformation magnitudes.
In the present study the early-stage deformation of a liquid drop in the high-speed flow induced by a planar shock wave was experimentally investigated using the shock tube facility and high-speed photography technique. It was found that the variation of the flow and drop conditions may cause significant divergences in the morphology of the drop deformation, even though such classical dominant parameters such as the Weber number or the Reynolds number are conserved. The divergences are mainly on the lee side of the drop, involving major characteristics of the circular ridges, the wrinkle band and the concave-plane convex profile of the lee side polar zone. Numerical simulations of the flow around a sphere show evident correspondence between the deformation patterns and the flow structures as well as the aerodynamic forces distributed along the sphere surface. For further evaluation and understanding of the detailed deformation features, a set of equations were deduced from hydrodynamic theories with necessary simplification. Feeding the equations with the aerodynamic data from numerical simulations, the calculation results indicate that, the main mechanism behind the deformation on the lee side of the drop is the squeezing effect of the uneven pressure distribution, rather than the accumulation effect of the surfacial flow induced by friction, with the former about two orders higher than the latter. Moreover, the drop profiles calculated following the pressure acting theory were found to agree quite well with the real drop patterns, not only in the deformation characteristics but also in the order of deformation magnitudes.
2017, 37(5): 863-870.
doi: 10.11883/1001-1455(2017)05-0863-08
Abstract:
In order to characterize the explosion of the gasoline vapor/air mixture, we introduced the unstretched laminar burning velocity of premixed gasoline vapor/air flame to the research of the mixture. The unstretched laminar burning velocity was experimentally studied and compared with those of two mixture gases consisting of such major compositions of gasoline as isooctane and n-heptane, respectively. The results show that the unstretched laminar burning velocity of the prepared gasoline vapor/air mixture is lower than those of the isooctane/air mixture gas and the n-heptane/air misture gas, but it takes on a similar tendency to change with the equivalence ratio, i.e. the unstretched laminar burning velocity firstly increases and then decreases with the increase of the equivalence ratio, and the maximum value can be obtained at the equivalence ratio of 1.
In order to characterize the explosion of the gasoline vapor/air mixture, we introduced the unstretched laminar burning velocity of premixed gasoline vapor/air flame to the research of the mixture. The unstretched laminar burning velocity was experimentally studied and compared with those of two mixture gases consisting of such major compositions of gasoline as isooctane and n-heptane, respectively. The results show that the unstretched laminar burning velocity of the prepared gasoline vapor/air mixture is lower than those of the isooctane/air mixture gas and the n-heptane/air misture gas, but it takes on a similar tendency to change with the equivalence ratio, i.e. the unstretched laminar burning velocity firstly increases and then decreases with the increase of the equivalence ratio, and the maximum value can be obtained at the equivalence ratio of 1.
2017, 37(5): 871-878.
doi: 10.11883/1001-1455(2017)05-0871-08
Abstract:
In order to study the dynamic mechanical properties of 2A16-T4 aluminum alloy, experiments for the alloy at quasi-static, intermediate, and high strain rates were performed using an electronic multi-purpose testing machine, a high velocity hydraulic servo-testing machine and a split Hopkinson press bar (SHPB) at room temperature, and the stress-strain curves at different strain rates were obtained, with a modified Johnson-Cook constitutive model fitted. The dynamic mechanical properties at intermediate strain rates and its influence on the constitutive model's parameters were analyzed. The results show that the strain rate hardening effect on the 2A16-T4 aluminum alloy is not obvious between 10-4~102 s-1, but it is obvious between 102~103 s-1, decreasing with the increase of the plastic strain. In addition, this effect is obvious between 10-4~103 s-1, decreasing with the increase of the strain rate. Moreover, the fitted results of modified Johnson-Cook constitutive model agree well with the experiment results, representing well the alloy's dynamic mechanical properties, which can improve the precision of the model's rate-sensitive parameters over a wide range of strain rates.
In order to study the dynamic mechanical properties of 2A16-T4 aluminum alloy, experiments for the alloy at quasi-static, intermediate, and high strain rates were performed using an electronic multi-purpose testing machine, a high velocity hydraulic servo-testing machine and a split Hopkinson press bar (SHPB) at room temperature, and the stress-strain curves at different strain rates were obtained, with a modified Johnson-Cook constitutive model fitted. The dynamic mechanical properties at intermediate strain rates and its influence on the constitutive model's parameters were analyzed. The results show that the strain rate hardening effect on the 2A16-T4 aluminum alloy is not obvious between 10-4~102 s-1, but it is obvious between 102~103 s-1, decreasing with the increase of the plastic strain. In addition, this effect is obvious between 10-4~103 s-1, decreasing with the increase of the strain rate. Moreover, the fitted results of modified Johnson-Cook constitutive model agree well with the experiment results, representing well the alloy's dynamic mechanical properties, which can improve the precision of the model's rate-sensitive parameters over a wide range of strain rates.
2017, 37(5): 879-886.
doi: 10.11883/1001-1455(2017)05-0879-08
Abstract:
To obtain the failure modes of aeronautical rivets under dynamic loading, dynamic failure experiments were carried out for six aeronautical rivets at different speeds and in different loading conditions on a high-speed servo hydraulic test machine using clamps specially designed, and the experiment data were achieved concerning the failure modes of the rivets working under pure tension, pure-shear, 30° combined tension-shear and 60° combined tension-shear. The results showed that the failure modes and the failure load of the rivets were closely related with the loading speed and the loading conditions. The failure constitutive parameters were obtained by fitting the experiment results, the failure constitutive equations of the rivets in the general case were also derived.
To obtain the failure modes of aeronautical rivets under dynamic loading, dynamic failure experiments were carried out for six aeronautical rivets at different speeds and in different loading conditions on a high-speed servo hydraulic test machine using clamps specially designed, and the experiment data were achieved concerning the failure modes of the rivets working under pure tension, pure-shear, 30° combined tension-shear and 60° combined tension-shear. The results showed that the failure modes and the failure load of the rivets were closely related with the loading speed and the loading conditions. The failure constitutive parameters were obtained by fitting the experiment results, the failure constitutive equations of the rivets in the general case were also derived.
2017, 37(5): 887-892.
doi: 10.11883/1001-1455(2017)05-0887-06
Abstract:
For the "abnormal discharge" phenomenon of the pulse signal electric probe due to the micro-jetting, we proposed a K+Rx equivalent circuit model of the micro-jetting and conducted the explosive loading experiments to explain the discharging mechanism of the electric probe conducted by the micro-jetting. According to the X-ray testing data, the discharging position of the electric probe obtained was in the transition zone from the micro-jetting to the micro-spall, and the abnormal discharge phenomena of the electric probe were classified into three types. Thus we proposed a circuit simulation model where the micro-jetting is equivalent to a K+Rx circuit. By adjusting the parameters of the K+Rx equivalent circuit model, the three types of the "abnormal discharging" phenomena of the electric probe were simulated. The simulation results show that the K+Rx equivalent circuit model provides an excellent explanation for the discharging of the pulse signal electric probe conducted by the micro-jetting.
For the "abnormal discharge" phenomenon of the pulse signal electric probe due to the micro-jetting, we proposed a K+Rx equivalent circuit model of the micro-jetting and conducted the explosive loading experiments to explain the discharging mechanism of the electric probe conducted by the micro-jetting. According to the X-ray testing data, the discharging position of the electric probe obtained was in the transition zone from the micro-jetting to the micro-spall, and the abnormal discharge phenomena of the electric probe were classified into three types. Thus we proposed a circuit simulation model where the micro-jetting is equivalent to a K+Rx circuit. By adjusting the parameters of the K+Rx equivalent circuit model, the three types of the "abnormal discharging" phenomena of the electric probe were simulated. The simulation results show that the K+Rx equivalent circuit model provides an excellent explanation for the discharging of the pulse signal electric probe conducted by the micro-jetting.
2017, 37(5): 893-898.
doi: 10.11883/1001-1455(2017)05-0893-06
Abstract:
Strain growth, whose related research has so far been concerned mostly with its behavior during the plastic response inside a spherical shell, poses a threat to the safety of explosion containment vessels. In the present work, the strain growth of the spherical vessel during the plastic response was observed by the experiment, and the strain growth factor (the ratio of the maximum strain of the strain curve to the first peak strain) reached up to 1.16. It was found through the theoretical analysis on the spherical shell response that it was the blast loading with three periodic pulses on the inner wall of the spherical vessel that brought about the strain growth, and that the first two pulses were mainly responsible for the strain growth.
Strain growth, whose related research has so far been concerned mostly with its behavior during the plastic response inside a spherical shell, poses a threat to the safety of explosion containment vessels. In the present work, the strain growth of the spherical vessel during the plastic response was observed by the experiment, and the strain growth factor (the ratio of the maximum strain of the strain curve to the first peak strain) reached up to 1.16. It was found through the theoretical analysis on the spherical shell response that it was the blast loading with three periodic pulses on the inner wall of the spherical vessel that brought about the strain growth, and that the first two pulses were mainly responsible for the strain growth.
2017, 37(5): 899-905.
doi: 10.11883/1001-1455(2017)05-0899-07
Abstract:
A series of underground explosions whose yield is confined at a limited level ranging from a few kilograms to a hundred were carried out in the Quaternary Period hardpan. The law of seismic wave propagation on small yield chemical explosion was investigated in the experiments. The results show that the duration of the seismic waves were shorter in the near field, the horizontal vibration amplitudes was stronger than the perpendicular ones, and the particle velocity increases exponentially with the increase of the yield. An index in the horizontal direction was approximately 1.09, while that in the perpendicular direction was approximately 0.77. The particle velocity exponentially decreases with the increases of the distance. The attenuating index in the horizontal direction is 2.07 and that in the vertical direction is 1.57. It is shown that the Sadauskas model, the obvious model, and the double extreme model can all quantitatively describe the seismic particle velocity on small yield underground explosions but they differ in the inverse precision of the parameters. Here, the difference in the residual of the double extreme model is the least. In other words, the parameters inversed by using the double extreme model are closest to the data actually observed.
A series of underground explosions whose yield is confined at a limited level ranging from a few kilograms to a hundred were carried out in the Quaternary Period hardpan. The law of seismic wave propagation on small yield chemical explosion was investigated in the experiments. The results show that the duration of the seismic waves were shorter in the near field, the horizontal vibration amplitudes was stronger than the perpendicular ones, and the particle velocity increases exponentially with the increase of the yield. An index in the horizontal direction was approximately 1.09, while that in the perpendicular direction was approximately 0.77. The particle velocity exponentially decreases with the increases of the distance. The attenuating index in the horizontal direction is 2.07 and that in the vertical direction is 1.57. It is shown that the Sadauskas model, the obvious model, and the double extreme model can all quantitatively describe the seismic particle velocity on small yield underground explosions but they differ in the inverse precision of the parameters. Here, the difference in the residual of the double extreme model is the least. In other words, the parameters inversed by using the double extreme model are closest to the data actually observed.
2017, 37(5): 906-912.
doi: 10.11883/1001-1455(2017)05-0906-07
Abstract:
To determine the effect of inert gas (N2 and CO2) on the process of mine gas explosion, we carried out mine gas explosion experiments in a medium-size pipe with the volume fractions of N2 or CO2 filled in three components of mine gas samples which were respectively 0%, 9% and 14%, and successfully obtained the explosion suppression characteristics of N2 and CO2. Then we conducted comparative analysis of the explosion overpressure histories and explosion suppression capacity of inert gas N2 and CO2 in the gas explosion process. The results show that the gas explosion overpressure decreases significantly with the increase of N2 or CO2 volume fraction in the mixed gases, and the explosion suppression capacity of CO2 is better than that of N2. Moreover, the explosion suppression effect of N2 and CO2 is much more obvious when the gas sample has a higher CH4 concentration.
To determine the effect of inert gas (N2 and CO2) on the process of mine gas explosion, we carried out mine gas explosion experiments in a medium-size pipe with the volume fractions of N2 or CO2 filled in three components of mine gas samples which were respectively 0%, 9% and 14%, and successfully obtained the explosion suppression characteristics of N2 and CO2. Then we conducted comparative analysis of the explosion overpressure histories and explosion suppression capacity of inert gas N2 and CO2 in the gas explosion process. The results show that the gas explosion overpressure decreases significantly with the increase of N2 or CO2 volume fraction in the mixed gases, and the explosion suppression capacity of CO2 is better than that of N2. Moreover, the explosion suppression effect of N2 and CO2 is much more obvious when the gas sample has a higher CH4 concentration.
2017, 37(5): 913-922.
doi: 10.11883/1001-1455(2017)05-0913-10
Abstract:
Uniaxial compression experiments of K9 glass spheres with a diameter of 8mm were conducted to obtain the fracture responses of brittle particles at five loading velocities, i.e.2×10-7 and 2×10-6m/s for quasi-static loading and 3.4, 7.1 and 10.6m/s for impact loading using a split Hopkinson pressure bar. Based on the Weibull distribution and recovery specimen products, a novel model combing the tensile failure and the shear failure was proposed to explain the process of the breaking evolution, revealing the relationship of the loading velocity and the three breaking zones. The model was validated using numerical simulation. Our study can serve as valuable reference for the study of the dynamic failure of brittle granular materials.
Uniaxial compression experiments of K9 glass spheres with a diameter of 8mm were conducted to obtain the fracture responses of brittle particles at five loading velocities, i.e.2×10-7 and 2×10-6m/s for quasi-static loading and 3.4, 7.1 and 10.6m/s for impact loading using a split Hopkinson pressure bar. Based on the Weibull distribution and recovery specimen products, a novel model combing the tensile failure and the shear failure was proposed to explain the process of the breaking evolution, revealing the relationship of the loading velocity and the three breaking zones. The model was validated using numerical simulation. Our study can serve as valuable reference for the study of the dynamic failure of brittle granular materials.
2017, 37(5): 923-928.
doi: 10.11883/1001-1455(2017)05-0923-06
Abstract:
In the present study, to analyze how the parameters of the coil's pulsed current affect the pinching characteristics of the shaped charge jet (SCJ), theoretical models considering the induced current density, the magnetic flux intensity and the pinching electromagnetic force distribution of uneven SCJ in the coil's pulsed current were established, a finite element model of the SCJ and the coil was built, and the effect of the pulsed current parameters of the magnetic exciting coil on the SCJ was analyzed. The results show that as the pulsed current amplitude of the coil increases, so do the induced current density, the magnetic flux density and the pinching electromagnetic force of the SCJ, that the effective deformation of the SCJ occurs only when the pulsed current density amplitude through the coil is bigger than 1×1010 A/m2, and that with the increase of the pulsed current frequency of the coil, the induced current density, the magnetic flux density and the pinching electromagnetic force of the SCJ show a certain degree of the skin effect, and the skin layer gradually becomes thinner within a certain frequency range. Analysis shows that it is when the pulsed current frequency of the coil is between 50 kHz and 100 kHz that the effective deformation of the SCJ can be ensured, thereby delaying its breakage process.
In the present study, to analyze how the parameters of the coil's pulsed current affect the pinching characteristics of the shaped charge jet (SCJ), theoretical models considering the induced current density, the magnetic flux intensity and the pinching electromagnetic force distribution of uneven SCJ in the coil's pulsed current were established, a finite element model of the SCJ and the coil was built, and the effect of the pulsed current parameters of the magnetic exciting coil on the SCJ was analyzed. The results show that as the pulsed current amplitude of the coil increases, so do the induced current density, the magnetic flux density and the pinching electromagnetic force of the SCJ, that the effective deformation of the SCJ occurs only when the pulsed current density amplitude through the coil is bigger than 1×1010 A/m2, and that with the increase of the pulsed current frequency of the coil, the induced current density, the magnetic flux density and the pinching electromagnetic force of the SCJ show a certain degree of the skin effect, and the skin layer gradually becomes thinner within a certain frequency range. Analysis shows that it is when the pulsed current frequency of the coil is between 50 kHz and 100 kHz that the effective deformation of the SCJ can be ensured, thereby delaying its breakage process.
2017, 37(5): 929-936.
doi: 10.11883/1001-1455(2017)05-0929-08
Abstract:
To investigate the influence of a non-parallel end-face for a short cylinder rock specimen on dynamic mechanical test results, we carried out numerical simulation of the SHPB test for rock material in 9 non-parallelisms and 5 Young's moduli using the finite element analysis software LS-DYNA, with the HJC constitutive model chosen for the rock material. The numerical simulation results show that when the non-parallelism of the rock specimen end-face is below 0.40%, the influence of the non-parallel end-face on the dynamic stress test results is negligible, while the influence of the non-parallel end-face on the dynamic strain test results is much bigger. When the Young's modulus remains the same, there is an approximately linear relation between the test error of the average strain rate and the non-parallelism or between the test error of the peak strain and the non-parallelism. When the non-parallelism remains the same, there is also an approximately linear relation between the test error of the average strain rate and the Young's modulus or between the test error of the peak strain and the Young's modulus. After conducting the binary linear regression analysis for the test error of the average strain rate and the test error of the peak strain obtained from numerical simulation, a correction formula for the average strain rate and the peak strain is proposed for the SHPB test of non-parallel end-face rock specimens.
To investigate the influence of a non-parallel end-face for a short cylinder rock specimen on dynamic mechanical test results, we carried out numerical simulation of the SHPB test for rock material in 9 non-parallelisms and 5 Young's moduli using the finite element analysis software LS-DYNA, with the HJC constitutive model chosen for the rock material. The numerical simulation results show that when the non-parallelism of the rock specimen end-face is below 0.40%, the influence of the non-parallel end-face on the dynamic stress test results is negligible, while the influence of the non-parallel end-face on the dynamic strain test results is much bigger. When the Young's modulus remains the same, there is an approximately linear relation between the test error of the average strain rate and the non-parallelism or between the test error of the peak strain and the non-parallelism. When the non-parallelism remains the same, there is also an approximately linear relation between the test error of the average strain rate and the Young's modulus or between the test error of the peak strain and the Young's modulus. After conducting the binary linear regression analysis for the test error of the average strain rate and the test error of the peak strain obtained from numerical simulation, a correction formula for the average strain rate and the peak strain is proposed for the SHPB test of non-parallel end-face rock specimens.
2017, 37(5): 937-944.
doi: 10.11883/1001-1455(2017)05-0937-08
Abstract:
There have been numerous bird-strike accidents in which substantial damage to the airframe occurred even though the striking force involved did not reach the energy standard currently required, showing that only taking mass and velocity into account in bird-strike prevention cannot guarantee airframe safety. In order to find out the effect of the bird yaw/pitch orientation on the safety of different aircraft structures, the dynamic responses on the panel, the radome, and the plane wing's leading edge were investigated. The results show that the bird-strike resistance of the structure is significantly affected by the bird's yaw/pitch orientation, and different structural characteristics lead to different dynamic responses. The greater the attitude angle, the more energy absorbed for the energy-absorbing structure, and accordingly the safer the protected structure; for the load-bearing structure, the greater the attitude and the larger the high stress area on the structure, the more vulnerable the structure. Therefore, in the evaluation of aircraft structures' bird-strike resistance capability, apart from doing the bird-strike experiment, it is also necessary to investigate different responses of various bird yaw/pitch orientations to the hazardous parts of aircraft structures through numerical simulation.
There have been numerous bird-strike accidents in which substantial damage to the airframe occurred even though the striking force involved did not reach the energy standard currently required, showing that only taking mass and velocity into account in bird-strike prevention cannot guarantee airframe safety. In order to find out the effect of the bird yaw/pitch orientation on the safety of different aircraft structures, the dynamic responses on the panel, the radome, and the plane wing's leading edge were investigated. The results show that the bird-strike resistance of the structure is significantly affected by the bird's yaw/pitch orientation, and different structural characteristics lead to different dynamic responses. The greater the attitude angle, the more energy absorbed for the energy-absorbing structure, and accordingly the safer the protected structure; for the load-bearing structure, the greater the attitude and the larger the high stress area on the structure, the more vulnerable the structure. Therefore, in the evaluation of aircraft structures' bird-strike resistance capability, apart from doing the bird-strike experiment, it is also necessary to investigate different responses of various bird yaw/pitch orientations to the hazardous parts of aircraft structures through numerical simulation.
2017, 37(5): 945-950.
doi: 10.11883/1001-1455(2017)05-0945-06
Abstract:
Powerful techniques have been developed for calculating the plane wave response of horizontally layered models. This method is quite general and is widely used in synthetic wave algorithms. Using this method, we can describe the displacements in terms of a linear combination of the moment tensor elements, and the moment tensor for an arbitrarily oriented dislocation can be given by this method. The moment tensor can be used to distinguish natural earthquakes and underground nuclear experiments according to its different elements. In this paper we rewrite the formula and estimate the reliability of the non-double-couple solutions on the basis of error analysis that includes the variance of modeling and of the noise in the data. Our analysis of synthetic data shows that this method is robust and can be used in the real data analyses. The result is significant for monitoring nuclear explosions by using data from just a few monitoring stations or even from a single station.
Powerful techniques have been developed for calculating the plane wave response of horizontally layered models. This method is quite general and is widely used in synthetic wave algorithms. Using this method, we can describe the displacements in terms of a linear combination of the moment tensor elements, and the moment tensor for an arbitrarily oriented dislocation can be given by this method. The moment tensor can be used to distinguish natural earthquakes and underground nuclear experiments according to its different elements. In this paper we rewrite the formula and estimate the reliability of the non-double-couple solutions on the basis of error analysis that includes the variance of modeling and of the noise in the data. Our analysis of synthetic data shows that this method is robust and can be used in the real data analyses. The result is significant for monitoring nuclear explosions by using data from just a few monitoring stations or even from a single station.
2017, 37(5): 951-956.
doi: 10.11883/1001-1455(2017)05-0951-06
Abstract:
In order to establish a calculation model for the dynamic blast overpressure field, a correction factor was introduced into the Baker formula, a model for calculating the peak overpressure only in a static blast. The method to obtain the correction factor containing the moving velocity, the azimuth and the scaled distance was established. For getting the function of the correction factor, spherical charge models with the typical moving velocity were established using the shock physical explicit Eulerian dynamic (SPEED) to simulate the dynamic blast process in the air. The peak overpressure in the typical azimuth and scaled distance was obtained. Based on the numerical results, a new calculation model was constructed using the data fitted. The result of the numerical simulation indicates that the corrected formula is a universal calculation model, capable of predicting the peak overpressure in dynamic blast.
In order to establish a calculation model for the dynamic blast overpressure field, a correction factor was introduced into the Baker formula, a model for calculating the peak overpressure only in a static blast. The method to obtain the correction factor containing the moving velocity, the azimuth and the scaled distance was established. For getting the function of the correction factor, spherical charge models with the typical moving velocity were established using the shock physical explicit Eulerian dynamic (SPEED) to simulate the dynamic blast process in the air. The peak overpressure in the typical azimuth and scaled distance was obtained. Based on the numerical results, a new calculation model was constructed using the data fitted. The result of the numerical simulation indicates that the corrected formula is a universal calculation model, capable of predicting the peak overpressure in dynamic blast.
2017, 37(5): 957-963.
doi: 10.11883/1001-1455(2017)05-0957-07
Abstract:
For the evaluation of the applicability of the single degree of freedom (SDOF) model in the structural antiknock design, the dynamic response of the simply supported steel column under explosion load was simulated using both the SDOF model and the ANSYS/LS-DYNA in this paper. By the comparison of the two calculation results, the scope of application of the SDOF model was analyzed according to the finite element simulation. The results show that the displacements calculated using the SDOF model can be divided into three different phases including the finite deformation, in which the SDOF model agrees well with the DYNA simulation, the critical deformation, and the buckling failure deformation, according to the amplitude size in the free vibration. The ratio of the cross section's depth to its width and that of the flange's width to its thickness have significant effect on the dynamic failure forms of the steel column, namely the bigger the ratio of the depth to the width and the smaller the ratio of the width to the thickness, the more prone it is for the buckling to suffer out-of-plane bending and twisting. In the SDOF model, it is feasible to calculate the strain and the strain rate in the plastic deformation phase by assuming the plastic hinge distribution length and the stress-magnified coefficient in the Cowper-Symonds constitutive relation by using the time-dependent strain rate.
For the evaluation of the applicability of the single degree of freedom (SDOF) model in the structural antiknock design, the dynamic response of the simply supported steel column under explosion load was simulated using both the SDOF model and the ANSYS/LS-DYNA in this paper. By the comparison of the two calculation results, the scope of application of the SDOF model was analyzed according to the finite element simulation. The results show that the displacements calculated using the SDOF model can be divided into three different phases including the finite deformation, in which the SDOF model agrees well with the DYNA simulation, the critical deformation, and the buckling failure deformation, according to the amplitude size in the free vibration. The ratio of the cross section's depth to its width and that of the flange's width to its thickness have significant effect on the dynamic failure forms of the steel column, namely the bigger the ratio of the depth to the width and the smaller the ratio of the width to the thickness, the more prone it is for the buckling to suffer out-of-plane bending and twisting. In the SDOF model, it is feasible to calculate the strain and the strain rate in the plastic deformation phase by assuming the plastic hinge distribution length and the stress-magnified coefficient in the Cowper-Symonds constitutive relation by using the time-dependent strain rate.
2017, 37(5): 964-968.
doi: 10.11883/1001-1455(2017)05-0964-05
Abstract:
Damage could occur to a more severe degree in an internal blast than in an air blast with respect to box-shaped structures. In the present study, a blast experiment was performed using 98.4, 194.7 and 355.8 g TNT explosives, respectively on three box-shaped specimens 600 mm in length and 4 mm in plate-thickness, to obtain their deformation features and observe the outward bulges at the center of their plate wall. It was found that the central deflection of the wall increases with the increase of the TNT mass. An empirical equation is proposed by fitting the linear relationship of the deflection thickness ratio and the TNT mass. The dynamic response of the wall was analyzed using the 3D digital image correlation (DIC) technique. The outward bulge was produced in the wall center after the explosion and at the same time the deflection increased with time passing by and the deformation propagated towards the wall edge all around. After the deflection reached the maximum value, the deformation of the wall experienced several oscillations.
Damage could occur to a more severe degree in an internal blast than in an air blast with respect to box-shaped structures. In the present study, a blast experiment was performed using 98.4, 194.7 and 355.8 g TNT explosives, respectively on three box-shaped specimens 600 mm in length and 4 mm in plate-thickness, to obtain their deformation features and observe the outward bulges at the center of their plate wall. It was found that the central deflection of the wall increases with the increase of the TNT mass. An empirical equation is proposed by fitting the linear relationship of the deflection thickness ratio and the TNT mass. The dynamic response of the wall was analyzed using the 3D digital image correlation (DIC) technique. The outward bulge was produced in the wall center after the explosion and at the same time the deflection increased with time passing by and the deformation propagated towards the wall edge all around. After the deflection reached the maximum value, the deformation of the wall experienced several oscillations.
2017, 37(5): 969-975.
doi: 10.11883/1001-1455(2017)05-0969-07
Abstract:
At first, we analyzed the numerical stability of the explicit exact algorithm developed for the viscoplastic material, and then found that the explicit exact algorithm is not absolutely stable, deduced a necessary criterion that the time step should be kept below a certain value to guarantee the constitutive calculation stability. A series of numerical examples were presented to validate the reliability of the present stability analysis on the explicit exact algorithm. The results of the numerical examples show that the effective stress is unstable while the stability criterion for the constitutive calculation is not satisfied, but a complex deformation process including the elastic load, the plastic load, the elastic unload, the reverse elastic load and the reverse plastic load is accurately described while the stability criterion is satisfied. Further numerical results indicate that the stability criterion can accurately predict the relationships between the maximum time step and each parameter.
At first, we analyzed the numerical stability of the explicit exact algorithm developed for the viscoplastic material, and then found that the explicit exact algorithm is not absolutely stable, deduced a necessary criterion that the time step should be kept below a certain value to guarantee the constitutive calculation stability. A series of numerical examples were presented to validate the reliability of the present stability analysis on the explicit exact algorithm. The results of the numerical examples show that the effective stress is unstable while the stability criterion for the constitutive calculation is not satisfied, but a complex deformation process including the elastic load, the plastic load, the elastic unload, the reverse elastic load and the reverse plastic load is accurately described while the stability criterion is satisfied. Further numerical results indicate that the stability criterion can accurately predict the relationships between the maximum time step and each parameter.
2017, 37(5): 976-982.
doi: 10.11883/1001-1455(2017)05-0976-07
Abstract:
The present study addresses the potential damage that might be suffered by the test device of a projectile body as a result of the gun powder gas coming from the clearance opened in the projection base for installing an ejection device for the recovery of the penetration data. A seal structure of the clearance was designed and a model was built for analyzing the dynamical state of the gunpowder gas flowing in the clearance. The chamber pressure and the seal cavity pressure of the seal structure were tested by experiment. The results show that the gas in the gunpowder combustion was a compressible gas, flowing in a subsonic condition in the powder chamber and the contracting clearance channel, but in a supersonic condition in the expansion seal cavity. When the gunpowder gas in the projection base was sealed by the seal structure and kept at a temperature of 2 166.5 K, a density of 360 kg/m3 and a pressure of 242.9 MPa, the pressure for the residual gas in the seal cavity was 0.49 MPa. The maximum pressure of the test curve in the seal cavity pressure was 0.18 MPa, fairly consistent with the theoretical results. These results can serve as reference for fabricating the seal of the high temperature and high pressure gunpowder gas in the projection base.
The present study addresses the potential damage that might be suffered by the test device of a projectile body as a result of the gun powder gas coming from the clearance opened in the projection base for installing an ejection device for the recovery of the penetration data. A seal structure of the clearance was designed and a model was built for analyzing the dynamical state of the gunpowder gas flowing in the clearance. The chamber pressure and the seal cavity pressure of the seal structure were tested by experiment. The results show that the gas in the gunpowder combustion was a compressible gas, flowing in a subsonic condition in the powder chamber and the contracting clearance channel, but in a supersonic condition in the expansion seal cavity. When the gunpowder gas in the projection base was sealed by the seal structure and kept at a temperature of 2 166.5 K, a density of 360 kg/m3 and a pressure of 242.9 MPa, the pressure for the residual gas in the seal cavity was 0.49 MPa. The maximum pressure of the test curve in the seal cavity pressure was 0.18 MPa, fairly consistent with the theoretical results. These results can serve as reference for fabricating the seal of the high temperature and high pressure gunpowder gas in the projection base.
