2019 Vol. 39, No. 1
Display Method:
2019, 39(1): 012201.
doi: 10.11883/bzycj-2017-0291
Read OL
PDF 
Cited by
Abstract:
In order to study the effect of high rotation on the shell-penetration of 30 mm shaped charge and the mechanism of spin-compensation, we simulated the overwhelm process of the fluted liner for the 30 mm rifle gun using the SPH method of LS-DYNA finite element software, and found that the actual movement of particles can be decomposed into centripetal motion and tangential motion around the center circle. We then put forward the four stages of the overwhelm process, those of the early crush, the buffer, the particle velocity increase in the fluted liner area and the central particle interaction. The jet forming layer rotates in a counterclockwise direction, whereas the material forming the pestle body rotates in the opposite direction. The results show that the special design of the fluted liner can compensate the negative impact of the rotating disturbance on the penetration effect of the 30 mm shaped charge. The compensating rotating speed of the projectile is 379 r/s and larger.
In order to study the effect of high rotation on the shell-penetration of 30 mm shaped charge and the mechanism of spin-compensation, we simulated the overwhelm process of the fluted liner for the 30 mm rifle gun using the SPH method of LS-DYNA finite element software, and found that the actual movement of particles can be decomposed into centripetal motion and tangential motion around the center circle. We then put forward the four stages of the overwhelm process, those of the early crush, the buffer, the particle velocity increase in the fluted liner area and the central particle interaction. The jet forming layer rotates in a counterclockwise direction, whereas the material forming the pestle body rotates in the opposite direction. The results show that the special design of the fluted liner can compensate the negative impact of the rotating disturbance on the penetration effect of the 30 mm shaped charge. The compensating rotating speed of the projectile is 379 r/s and larger.
2019, 39(1): 012202.
doi: 10.11883/bzycj-2017-0406
Abstract:
In this work we investigated the damage effects on the caisson gravity wharf using an on-situ test of the wharf model under 1 kg TNT explosion in air, in water and inside the internal structure, and obtained the corresponding damage modes of the wharf model under the different explosion conditions, with the emergent repair proposals presented addressing to the respective damage modes. The results showed that a blast hole was observed locally on parts on the wharf model's panel for air explosion, that lots of cracks developed on the blast side and nearby area of the wharf model for water explosion, and that under the blast in the wharf model's internal structure, the cabins underwent huge deformations and were destroyed while the middle of the model's panel plate was lifted and thrown away. At the same weight of the explosive charge, the damage degree appears minimum under air explosion while it appears the maximum under explosion inside the model's internal structure.
In this work we investigated the damage effects on the caisson gravity wharf using an on-situ test of the wharf model under 1 kg TNT explosion in air, in water and inside the internal structure, and obtained the corresponding damage modes of the wharf model under the different explosion conditions, with the emergent repair proposals presented addressing to the respective damage modes. The results showed that a blast hole was observed locally on parts on the wharf model's panel for air explosion, that lots of cracks developed on the blast side and nearby area of the wharf model for water explosion, and that under the blast in the wharf model's internal structure, the cabins underwent huge deformations and were destroyed while the middle of the model's panel plate was lifted and thrown away. At the same weight of the explosive charge, the damage degree appears minimum under air explosion while it appears the maximum under explosion inside the model's internal structure.
2019, 39(1): 012301.
doi: 10.11883/bzycj-2018-0264
Abstract:
We studied the effect of the explosive mass and the heating rate on the slow cook-off characteristics of DNAN based casting explosive by designing a new roasting test device, and examined the thermal reaction characteristics of the mixed explosive by performing a multipoint temperature experiment at two heating rates, 1℃/min and 0.055℃/min, respectively. The results showed that the explosive mass and the heating rate jointly affected the response characteristics of the roasting bombs. The same roasting bombs at the heating rate of 0.055℃/min was more intense than that at the heating rate of 1℃/min. The placement posture and the thickness of the end cover also affected the intensity of the response of the roasting bombs.
We studied the effect of the explosive mass and the heating rate on the slow cook-off characteristics of DNAN based casting explosive by designing a new roasting test device, and examined the thermal reaction characteristics of the mixed explosive by performing a multipoint temperature experiment at two heating rates, 1℃/min and 0.055℃/min, respectively. The results showed that the explosive mass and the heating rate jointly affected the response characteristics of the roasting bombs. The same roasting bombs at the heating rate of 0.055℃/min was more intense than that at the heating rate of 1℃/min. The placement posture and the thickness of the end cover also affected the intensity of the response of the roasting bombs.
2019, 39(1): 012302.
doi: 10.11883/bzycj-2017-0271
Abstract:
In this work, to obtain the critical detonation velocity calculation model about the cylindrical covered charge impacted by fragments, we added the correction terms to the velocity calculation based on the Picatinny engineering criterion. We found out about the influence of the fragment impact angle and the charge curvature radius on the critical detonation velocity using the AUTODYN software through simulating the tungsten fragment impact cylindrical steel casing filled with B explosive. Based on the fitting expression, we established the critical velocity calculation model of the explosive initiation considering the impact angle and the charge shape function. The model calculation values are in good agreement with the experimental data and the simulation results, thereby suggesting that the model can provide a better prediction of the impact initiation of the cylindrical covered charge.
In this work, to obtain the critical detonation velocity calculation model about the cylindrical covered charge impacted by fragments, we added the correction terms to the velocity calculation based on the Picatinny engineering criterion. We found out about the influence of the fragment impact angle and the charge curvature radius on the critical detonation velocity using the AUTODYN software through simulating the tungsten fragment impact cylindrical steel casing filled with B explosive. Based on the fitting expression, we established the critical velocity calculation model of the explosive initiation considering the impact angle and the charge shape function. The model calculation values are in good agreement with the experimental data and the simulation results, thereby suggesting that the model can provide a better prediction of the impact initiation of the cylindrical covered charge.
2019, 39(1): 013101.
doi: 10.11883/bzycj-2018-0037
Abstract:
By using plate impact and velocity interferometry, the dynamic tensile fracture (spall) of shocked pure vanadium was studied in the pressure range of 5.2-9.0 GPa, where the average tensile strain rate was in the range of 0.47×105-1.19×105 s-1. All the vanadium samples used here were made by the hot isostatic pressing (HIP) method. Our results show that the HIP vanadium has a higher spall strength than those given in literatures, which lies in the range of 4.0-5.3 GPa, and increases with both the shock pressure and tensile strain rate. The higher spall strength of the HIP vanadium can be ascribed to the higher purity and fewer initial defects in material than those made by the remelting method. Additionally, the analysis on elastic precursor wave in vanadium indicates a power decay of Hugoniot elastic limit (σHEL) with the dimensionless thickness of the sample (hs/h0), where h0 is a unit length. The coefficient and exponent of the power function best fitting the experimental data are 3.246 and -0.386, respectively, when the vanadium sample's thickness hs is no greater than 6 mm.
By using plate impact and velocity interferometry, the dynamic tensile fracture (spall) of shocked pure vanadium was studied in the pressure range of 5.2-9.0 GPa, where the average tensile strain rate was in the range of 0.47×105-1.19×105 s-1. All the vanadium samples used here were made by the hot isostatic pressing (HIP) method. Our results show that the HIP vanadium has a higher spall strength than those given in literatures, which lies in the range of 4.0-5.3 GPa, and increases with both the shock pressure and tensile strain rate. The higher spall strength of the HIP vanadium can be ascribed to the higher purity and fewer initial defects in material than those made by the remelting method. Additionally, the analysis on elastic precursor wave in vanadium indicates a power decay of Hugoniot elastic limit (σHEL) with the dimensionless thickness of the sample (hs/h0), where h0 is a unit length. The coefficient and exponent of the power function best fitting the experimental data are 3.246 and -0.386, respectively, when the vanadium sample's thickness hs is no greater than 6 mm.
2019, 39(1): 013102.
doi: 10.11883/bzycj-2017-0280
Abstract:
Cellular material under high-speed impact is deformed in a mode of layer-wise propagation of crushing bands, which can be characterized by the plastic shock models. In this paper, we obtained the one-dimensional stress distribution of a random honeycomb under constant-velocity compression using the cross-sectional stress calculation method, analyzed the shockwave propagation, and examined the relation between the shockwave velocity and the impact velocity obtained by different methods under high-velocity impact. The results show that the shockwave speed is overestimated by the R-PP-L (rate-independent, rigid-perfect plastic-locking) model, but the shockwave speeds obtained by the R-PH (rate-independent, rigid-plastic hardening) model and the one-dimensional shock theory are close to that of finite element simulation. The relation between the shockwave velocity and the impact velocity tends to be linear at high impact velocities, and the shockwave speed reduces to a constant with the decrease of the impact velocity. In light of these characteristics and based on the plastic shockwave model, we developed a uniformly approximated model is developed to characterize the relation between the shockwave velocity and the impact velocity and the dynamic stress-strain relation of cellular material.
Cellular material under high-speed impact is deformed in a mode of layer-wise propagation of crushing bands, which can be characterized by the plastic shock models. In this paper, we obtained the one-dimensional stress distribution of a random honeycomb under constant-velocity compression using the cross-sectional stress calculation method, analyzed the shockwave propagation, and examined the relation between the shockwave velocity and the impact velocity obtained by different methods under high-velocity impact. The results show that the shockwave speed is overestimated by the R-PP-L (rate-independent, rigid-perfect plastic-locking) model, but the shockwave speeds obtained by the R-PH (rate-independent, rigid-plastic hardening) model and the one-dimensional shock theory are close to that of finite element simulation. The relation between the shockwave velocity and the impact velocity tends to be linear at high impact velocities, and the shockwave speed reduces to a constant with the decrease of the impact velocity. In light of these characteristics and based on the plastic shockwave model, we developed a uniformly approximated model is developed to characterize the relation between the shockwave velocity and the impact velocity and the dynamic stress-strain relation of cellular material.
2019, 39(1): 013103.
doi: 10.11883/bzycj-2017-0281
Abstract:
In this work, for the traditional square honeycombs, we obtained a joint-based hierarchical honeycomb model with the negative Poisson's ratio (NPR) by replacing the structural nodes of the original honeycombs having smaller inner concave structures. We numerically investigated the dynamic responses and energy absorption characteristics of these honeycombs with NPR under in-plane crushing using the explicit dynamic finite element analysis (DFEA), revealing that, apart from the impact velocity and the relative density, the in-plane dynamic properties of the honeycombs also depend upon the cell micro-structure. Compared with those of the square honeycombs, the dynamic strengths and energy absorption abilities of these honeycombs are obviously improved. Under low or moderate velocity crushing, the specimens exhibit the obvious "neck shrinkage" phenomenon of auxetic materials, and show the unique plateau stress enhancement effect. Based on the energy absorption efficiency method and the one-dimensional shockwave theory, the empirical formulae of densification strain and dynamic plateau stress were given to predict the dynamic load-bearing capacity of the honeycombs with NPR. Our study can serve as a guidance for the multi-objective optimal dynamic design of auxetic cellular materials.
In this work, for the traditional square honeycombs, we obtained a joint-based hierarchical honeycomb model with the negative Poisson's ratio (NPR) by replacing the structural nodes of the original honeycombs having smaller inner concave structures. We numerically investigated the dynamic responses and energy absorption characteristics of these honeycombs with NPR under in-plane crushing using the explicit dynamic finite element analysis (DFEA), revealing that, apart from the impact velocity and the relative density, the in-plane dynamic properties of the honeycombs also depend upon the cell micro-structure. Compared with those of the square honeycombs, the dynamic strengths and energy absorption abilities of these honeycombs are obviously improved. Under low or moderate velocity crushing, the specimens exhibit the obvious "neck shrinkage" phenomenon of auxetic materials, and show the unique plateau stress enhancement effect. Based on the energy absorption efficiency method and the one-dimensional shockwave theory, the empirical formulae of densification strain and dynamic plateau stress were given to predict the dynamic load-bearing capacity of the honeycombs with NPR. Our study can serve as a guidance for the multi-objective optimal dynamic design of auxetic cellular materials.
2019, 39(1): 013301.
doi: 10.11883/bzycj-2017-0266
Abstract:
In this work, we studied the compressive mechanical properties of polyethylene at different strain rates and obtained the stress-strain curves of polyethylene at different strain rates using static and dynamic experiments. We analyzed the stress-strain curves of polyethylene and discovered that the elastic modulus and the yield strength of polyethylene increase with the increase of the strain rate, and polyethylene has obvious viscoelasticity. The stress-strain curves have similar trends at different strain rates after polyethylene enters the plastic stage. We established a constitutive model of elastic zone, yield point and plastic zone according to compressive mechanical properties of polyethylene. The yield point and the plastic section of the model are in good agreement with the experimental results. As the elastic section adopts the linear elastic model, a certain deviation from the experimental results was observed, which can approximately describe the elastic behavior of the material.
In this work, we studied the compressive mechanical properties of polyethylene at different strain rates and obtained the stress-strain curves of polyethylene at different strain rates using static and dynamic experiments. We analyzed the stress-strain curves of polyethylene and discovered that the elastic modulus and the yield strength of polyethylene increase with the increase of the strain rate, and polyethylene has obvious viscoelasticity. The stress-strain curves have similar trends at different strain rates after polyethylene enters the plastic stage. We established a constitutive model of elastic zone, yield point and plastic zone according to compressive mechanical properties of polyethylene. The yield point and the plastic section of the model are in good agreement with the experimental results. As the elastic section adopts the linear elastic model, a certain deviation from the experimental results was observed, which can approximately describe the elastic behavior of the material.
2019, 39(1): 013302.
doi: 10.11883/bzycj-2017-0287
Abstract:
In this study, to improve the penetration capability of the homogeneous long rod, a problem whose solution has hit a bottleneck, we designed a new pre-composited rod fabricated with high density tungsten alloy and high hardness tungsten carbide. It was validated through experiment and numerical simulation that our newly-designed rod can form a sharp nose shape in the steady penetration stage by cashing in on the different properties of different materials to improve the penetration capability of the long rod. Based on the experimental and simulated results, we presented a full description of the physical image of the pre-composited rod's normal penetration into a steel target, which can be divided into three sections, those of the cratering, the composited rod, and the homogeneous rod, with their theoretical models established respectively, thus obtaining the calculation model of the total pre-composited rod's penetration depth. The rationality of the model was verified by comparing it with the experiment and simulation results. The conclusions from our study are helpful for the kinetic design of weapons using the new long rod.
In this study, to improve the penetration capability of the homogeneous long rod, a problem whose solution has hit a bottleneck, we designed a new pre-composited rod fabricated with high density tungsten alloy and high hardness tungsten carbide. It was validated through experiment and numerical simulation that our newly-designed rod can form a sharp nose shape in the steady penetration stage by cashing in on the different properties of different materials to improve the penetration capability of the long rod. Based on the experimental and simulated results, we presented a full description of the physical image of the pre-composited rod's normal penetration into a steel target, which can be divided into three sections, those of the cratering, the composited rod, and the homogeneous rod, with their theoretical models established respectively, thus obtaining the calculation model of the total pre-composited rod's penetration depth. The rationality of the model was verified by comparing it with the experiment and simulation results. The conclusions from our study are helpful for the kinetic design of weapons using the new long rod.
2019, 39(1): 013303.
doi: 10.11883/bzycj-2017-0313
Abstract:
Addressing the projectile crush during high-speed penetration, we designed projectiles with two different shell thicknesses and conducted experiment for penetrating high-strength rock target at 1 000 m/s. The experimental results showed that projectiles with different shell thicknesses were completely broken and failed to effectively penetrate the rock target while the rock target was only comminuted on the surface, and that the fragmentation of the projectile tip during high-speed penetration in rock target was different from that in the thin metal target. In addition, based on the experimental results, we established the simulation model of the projectile penetrating the rock target using Autodyn-3D. Combining the SPH method with the Mott distribution failure model, we performed the numerical simulation of the projectile's crush process and revealed the mechanism of the projectile's breaking. Furthermore, we examined the influence of the simulated charge and the small range of different high velocities on the projectile's crush. The experimental results and the proposed numerical method can serve as reference for further study of the projectile's structure during high velocity penetration.
Addressing the projectile crush during high-speed penetration, we designed projectiles with two different shell thicknesses and conducted experiment for penetrating high-strength rock target at 1 000 m/s. The experimental results showed that projectiles with different shell thicknesses were completely broken and failed to effectively penetrate the rock target while the rock target was only comminuted on the surface, and that the fragmentation of the projectile tip during high-speed penetration in rock target was different from that in the thin metal target. In addition, based on the experimental results, we established the simulation model of the projectile penetrating the rock target using Autodyn-3D. Combining the SPH method with the Mott distribution failure model, we performed the numerical simulation of the projectile's crush process and revealed the mechanism of the projectile's breaking. Furthermore, we examined the influence of the simulated charge and the small range of different high velocities on the projectile's crush. The experimental results and the proposed numerical method can serve as reference for further study of the projectile's structure during high velocity penetration.
2019, 39(1): 014101.
doi: 10.11883/bzycj-2017-0253
Abstract:
Accidents resulting from combustible dust explosion occur frequently and pose a serious hazard to the safety of industrial production. Dust concentration is a critical factor involved in the explosion leading to such accidents, and therefore its precise and fast measurement can provide an intrinsically safe and real-time monitoring technology for preventing such accidents. In this paper, we proposed a new measuring technique based on the fiber Bragg grating and the optical fiber collimator. We first explained the measurement theory and constructed the measuring and experimental device, and then performed experiments on wheat dusts with three grain sizes of 200 meshes, 300 meshes and 400 meshes and carried out the related investigation. The results show that the optical power output of the device and the dust concentration are linearly correlated. We also carried out contrastive experiments with the dust concentration obtained using the standard weighing method, and verified the effectiveness of the FBG measuring technique proposed. This study provides a new way to conduct dust concentration monitoring, and holds broad prospects for further research and application.
Accidents resulting from combustible dust explosion occur frequently and pose a serious hazard to the safety of industrial production. Dust concentration is a critical factor involved in the explosion leading to such accidents, and therefore its precise and fast measurement can provide an intrinsically safe and real-time monitoring technology for preventing such accidents. In this paper, we proposed a new measuring technique based on the fiber Bragg grating and the optical fiber collimator. We first explained the measurement theory and constructed the measuring and experimental device, and then performed experiments on wheat dusts with three grain sizes of 200 meshes, 300 meshes and 400 meshes and carried out the related investigation. The results show that the optical power output of the device and the dust concentration are linearly correlated. We also carried out contrastive experiments with the dust concentration obtained using the standard weighing method, and verified the effectiveness of the FBG measuring technique proposed. This study provides a new way to conduct dust concentration monitoring, and holds broad prospects for further research and application.
2019, 39(1): 014201.
doi: 10.11883/bzycj-2017-0199
Abstract:
The method of manufactured solutions (MMS) is a fundamental part of code verification for the coupling codes with complex multi-physics process, the MMS for multi-dimension Lagrangian radiation hydrodynamics with large deformation meshes is very sparse yet. In this paper, a new constructed method of manufactured solutions for 2D Lagrangian radiation hydrodynamic equations was proposed based on the derivative relations of physical variables between the Lagrangian space and the Eulerian space. The manufactured solution models without additional source terms in the mass equation could be used to solve diffusion problems on fluid moving meshes and were applied to the verification of the 2D Lagrangian radiation hydrodynamic codes. The numerical results show that the observed order of accuracy matches the formal order of accuracy.
The method of manufactured solutions (MMS) is a fundamental part of code verification for the coupling codes with complex multi-physics process, the MMS for multi-dimension Lagrangian radiation hydrodynamics with large deformation meshes is very sparse yet. In this paper, a new constructed method of manufactured solutions for 2D Lagrangian radiation hydrodynamic equations was proposed based on the derivative relations of physical variables between the Lagrangian space and the Eulerian space. The manufactured solution models without additional source terms in the mass equation could be used to solve diffusion problems on fluid moving meshes and were applied to the verification of the 2D Lagrangian radiation hydrodynamic codes. The numerical results show that the observed order of accuracy matches the formal order of accuracy.
2019, 39(1): 015101.
doi: 10.11883/bzycj-2018-0224
Abstract:
In view of its differences from the conventional polyurea elastomer, we investigated the penetration resistance and fracture mechanism of coatings made from high-hardness polyurea sprayed on steel plates, using the ballistic experiment to obtain the ballistic limit of uncoated and coated steel plates subjected to 3.3 g cubic fragments, in consideration of polyurea coatings on the front side, the back side and on both sides in coated plates. We also analyzed the penetration resistance, fracture patterns and micro-morphologies of the coatings in different coated structures. The results indicate that the front coatings with severe fractures exhibited a high energy absorption capability, thereby improving the penetration resistance of the coated plates whereas, however, the back coatings that had been destroyed before the steel plates exhibited a lower energy absorption capability, which was bad for raising the penetration resistance. Under the fragment impact, polyurea coatings exhibited obvious velocity effects, thickness effects and micro-morphological characteristics, reflecting the differences of energy absorption in each configuration.
In view of its differences from the conventional polyurea elastomer, we investigated the penetration resistance and fracture mechanism of coatings made from high-hardness polyurea sprayed on steel plates, using the ballistic experiment to obtain the ballistic limit of uncoated and coated steel plates subjected to 3.3 g cubic fragments, in consideration of polyurea coatings on the front side, the back side and on both sides in coated plates. We also analyzed the penetration resistance, fracture patterns and micro-morphologies of the coatings in different coated structures. The results indicate that the front coatings with severe fractures exhibited a high energy absorption capability, thereby improving the penetration resistance of the coated plates whereas, however, the back coatings that had been destroyed before the steel plates exhibited a lower energy absorption capability, which was bad for raising the penetration resistance. Under the fragment impact, polyurea coatings exhibited obvious velocity effects, thickness effects and micro-morphological characteristics, reflecting the differences of energy absorption in each configuration.
2019, 39(1): 015102.
doi: 10.11883/bzycj-2017-0288
Abstract:
In this work, we investigated the impact resistance and damage mechanism of RC beams under impact loading using numerical simulation based on impact tests. We established a damage evaluation method based on the cross-sectional damage factor with the finiteness of the impact area and impact time taken into consideration, and analyzed the influence of impact parameters on the dynamic response and damage level of RC beams by conducting examination of such parameters as the stirrups pacing, boundary condition, impact or nose shape, and impact location. The results indicate that the damage assessment method proposed in this study can visually describe the damage distribution along the length of RC beams, that the end fixed constraints can effectively change the energy dissipation mechanism of RC beams and improve the impact resistance capability, that the impact location directly affects the beams' crack distribution and failure mode, and that the impact area and nose shape have a certain influence on the damage distribution of RC beams.
In this work, we investigated the impact resistance and damage mechanism of RC beams under impact loading using numerical simulation based on impact tests. We established a damage evaluation method based on the cross-sectional damage factor with the finiteness of the impact area and impact time taken into consideration, and analyzed the influence of impact parameters on the dynamic response and damage level of RC beams by conducting examination of such parameters as the stirrups pacing, boundary condition, impact or nose shape, and impact location. The results indicate that the damage assessment method proposed in this study can visually describe the damage distribution along the length of RC beams, that the end fixed constraints can effectively change the energy dissipation mechanism of RC beams and improve the impact resistance capability, that the impact location directly affects the beams' crack distribution and failure mode, and that the impact area and nose shape have a certain influence on the damage distribution of RC beams.
2019, 39(1): 015201.
doi: 10.11883/bzycj-2017-0286
Abstract:
To find about the dynamic response patterns of surrounding rock in which mine earthquake and mined-out area exist side by side, and obtain the mechanism leading to disasters under the coupled action of the two, we conducted a percussion test on circular plates having holes and established a model for it. The model test shows that negative acceleration is monitored in the surrounding rock, that the negative acceleration is unrelated with the gravity effect, and that tangential acceleration is also monitored. With the increase of the diameter of the hole, the tangential acceleration around the circular plate exponentially increased. According to the results of the experiment, we arrived at the mechanisms leading to disasters under the coupled action of mine earthquake and mined-out area, including the intensified subsidence and caving in overburden of the goaf, the formation of the horizontal acceleration in shared rock pillars of mined-out area pointing to the source location, the formation of the horizontal shear acceleration in the upper part of the surrounding rock where mine earthquake and mined-out area exist side by side. Comprehensive analysis of the test data, size effect of mined-out area and zoom effect of mine vibration load, do not affect the test results.
To find about the dynamic response patterns of surrounding rock in which mine earthquake and mined-out area exist side by side, and obtain the mechanism leading to disasters under the coupled action of the two, we conducted a percussion test on circular plates having holes and established a model for it. The model test shows that negative acceleration is monitored in the surrounding rock, that the negative acceleration is unrelated with the gravity effect, and that tangential acceleration is also monitored. With the increase of the diameter of the hole, the tangential acceleration around the circular plate exponentially increased. According to the results of the experiment, we arrived at the mechanisms leading to disasters under the coupled action of mine earthquake and mined-out area, including the intensified subsidence and caving in overburden of the goaf, the formation of the horizontal acceleration in shared rock pillars of mined-out area pointing to the source location, the formation of the horizontal shear acceleration in the upper part of the surrounding rock where mine earthquake and mined-out area exist side by side. Comprehensive analysis of the test data, size effect of mined-out area and zoom effect of mine vibration load, do not affect the test results.
2019, 39(1): 015301.
doi: 10.11883/bzycj-2017-0307
Abstract:
In this study we investigated the explosive compaction-sintering for fabricating a high-density tungsten/copper alloy on a copper surface. First, 50% W-50% Cu tungsten/copper alloy powder and 75% W-25% Cu were prepared by mechanical alloying. Next, the alloy powders were pre-compacted and sintered in hydrogen atmosphere, followed by explosive compaction. Then, a high-density tungsten/copper gradient material was obtained with the coatings and the matrix tightly bonded and the copper enriched at the interfaces between the tungsten/copper particles. The tungsten grains in the 50% W-50% Cu layer did not grow, and in the 75% W-25% Cu layer the tungsten and copper were enriched in local regions. Porosity tests were carried out, the porosity of the 50% W-50% Cu layer was 0.04%, and that of the 75% W-25% Cu layer was 0.11%. The contents of tungsten and copper in the coatings were similar to the added ratio of the tungsten powder and copper powder. The hardness of the tungsten/copper gradient layer exhibited a tendency of gradient change, varying between 125-341, much bigger than 50, that of the copper.
In this study we investigated the explosive compaction-sintering for fabricating a high-density tungsten/copper alloy on a copper surface. First, 50% W-50% Cu tungsten/copper alloy powder and 75% W-25% Cu were prepared by mechanical alloying. Next, the alloy powders were pre-compacted and sintered in hydrogen atmosphere, followed by explosive compaction. Then, a high-density tungsten/copper gradient material was obtained with the coatings and the matrix tightly bonded and the copper enriched at the interfaces between the tungsten/copper particles. The tungsten grains in the 50% W-50% Cu layer did not grow, and in the 75% W-25% Cu layer the tungsten and copper were enriched in local regions. Porosity tests were carried out, the porosity of the 50% W-50% Cu layer was 0.04%, and that of the 75% W-25% Cu layer was 0.11%. The contents of tungsten and copper in the coatings were similar to the added ratio of the tungsten powder and copper powder. The hardness of the tungsten/copper gradient layer exhibited a tendency of gradient change, varying between 125-341, much bigger than 50, that of the copper.
2019, 39(1): 015401.
doi: 10.11883/bzycj-2017-0244
Abstract:
In the present study, to find out about the effects of particle size distributions on the flame temperatures of polymethyl methacrylate (PMMA) dust clouds, we measured the flame temperatures of PMMA dust clouds with different particle size distributions using the thermocouple and high-speed colorimetric method. The results show that, due to the faster pyrolysis/volatilization rate of 100 nm dust particle, the temperature was able to reach 1 551℃ while the maximum temperature of 30 μm dust cloud was only 1 108℃. The maximum flame temperature and high temperature flame area increased and then decreased with the increase of PMMA dust particle size for micron-scale. The pyrolysis/volatilization time scale of 20 μm dust particles was close to the combustion reaction time scale because of their good dispersibility. As a result, the maximum temperature and high temperature flame area were the largest among the particles with different particle size distributions.
In the present study, to find out about the effects of particle size distributions on the flame temperatures of polymethyl methacrylate (PMMA) dust clouds, we measured the flame temperatures of PMMA dust clouds with different particle size distributions using the thermocouple and high-speed colorimetric method. The results show that, due to the faster pyrolysis/volatilization rate of 100 nm dust particle, the temperature was able to reach 1 551℃ while the maximum temperature of 30 μm dust cloud was only 1 108℃. The maximum flame temperature and high temperature flame area increased and then decreased with the increase of PMMA dust particle size for micron-scale. The pyrolysis/volatilization time scale of 20 μm dust particles was close to the combustion reaction time scale because of their good dispersibility. As a result, the maximum temperature and high temperature flame area were the largest among the particles with different particle size distributions.
