2019 Vol. 39, No. 2

Explosion Physics
Influence of an enhanced injector on DDT process
RAO Feixiong, LEI Zhidi, DING Jue, WENG Peifen
2019, 39(2): 022101. doi: 10.11883/bzycj-2017-0284
In the flow where the shock wave, the flame and the jet exist simultaneously, the successful process of deflagration to detonation transition (DDT) is the key to the pulse detonation engine (PDE). One kind of injector was designed, and the feasibility of enhancing deflagration to detonation transition in detonation chamber was validated by numerical simulation based on C2H2/O2/Ar reaction. The mechanism analysis of the hot spot initiating detonation was made. The device can excite instability in the flow field, generate eddies, and accelerate the exchange of energy and mass. The flow field generates hot spots, which accelerate the flame speed and catch up with the leading shock wave. The position of the ejector affects the velocity of the leading shock wave. Within a certain range, the higher the velocity of the leading shock wave is, the easier the hot spot generated by the collision will trigger the combustion-to-detonation transition process.
A theoretical model for the evaluation of protective capability of a sandwich bulkhead structure in the close range of warhead explosion
LI Dian, HOU Hailiang, ZHU Xi, CHEN Changhai, LI Mao
2019, 39(2): 022201. doi: 10.11883/bzycj-2017-0351
In order to make up for the shortcomings in protective structure design based on simple anti-blast or anti-armor load, a theoretical model was proposed for evaluating the protective capability of sandwich bulkhead in the close range of a warhead explosion, and its protection capability should meet the requirements of both the ballistic performance and the overall deformation and destruction. The first step is to calculate the combined damage load under warhead explosion. Then, based on the ballistic theory model, it can be used to evaluate whether the composite structure meets the requirements of the ballistic resistance. If it is satisfied, the requirements of composite sandwich bulkhead on overall deformation and failure under the combined load of shock wave and fragment group are further checked according to the combined damage theory model, and the criterion is whether the rear panel is broken or being torn. The experimental results are in good agreement with those of the domestic experimental results, which shows that the theoretical evaluation model is reasonable.
Numerical study of near-field underwater explosion of cylindrical aluminized explosive by the method of characteristics
LI Xiaojie, YANG Chenchen, YAN Honghao, WANG Xiaohong, WANG Yuxin, ZHANG Chengjiao
2019, 39(2): 022301. doi: 10.11883/bzycj-2017-0412
Based on the previously proposed method of characteristics containing an entropy variate, the non-ideal effect of aluminum combustion is portrayed by controlling the energy release in non-isentropic flow. Combined with a simple Chapman-Jouguet model and a JWL-Miller equation of state, it is obtained the near-field parameters for the underwater explosion of the cylindrical aluminized explosive. Comparing the simulation results with the experimental data, it is found that this method can give a good prediction for the propagation of shock wave and the bubble expansion of detonation products as well as the reflection of internal compression wave. The results show that this method can be applied to the near-field calculation of underwater explosion of aluminum explosive, and even the evaluation of explosive performance or the estimation of underwater energy output.
Impact Dynamics
Blast-resistant performance of aluminum foam-protected reinforced concrete slabs
GAO Haiying, LIU Zhongxian, YANG Yekai, WU Chengqing, GENG Jiaying
2019, 39(2): 023101. doi: 10.11883/bzycj-2018-0284
n order to study the blast-resistant protective effect of the aluminum foam slab as porous energy absorbing material on the engineering structure, using an outdoor explosion test, the dynamic response and failure modes of reinforced concrete (RC) slabs with different aluminum foam protective layers under blast loading were studied, and the finite element model was established by using the LS-DYNA software. Through comparison with the test, the feasibility of the model was verified. The dynamic responses of RC slabs with or without aluminum foam protective layers were compared and analyzed, and the effects of aluminum foam density gradient distribution and longitudinal reinforcement ratio were analyzed. The results show that the finite element model can accurately describe the dynamic response of RC slabs with aluminum foam protective layers. Aluminum foam protective layers can effectively reduce the deflection of reinforced concrete slabs and reduce the damage of specimens. The aluminum foam density increases from bottom to top, which has the best blast-resistant performance on RC slabs. Moreover, increasing the reinforcement ratio can improve the blast-resistant performance of aluminum foam-protected RC slabs.
On strength of aluminum under high pressure and high strain rate based on crystal plasticity theory
PAN Hao, WANG Shengtao, WU Zihui, HU Xiaomian
2019, 39(2): 023102. doi: 10.11883/bzycj-2018-0084
Dynamic behaviors of metal materials are very complex under extreme loading conditions such as high pressure and high strain rate loading. Actually, many mechanisms and effects are contained in the dynamic response of metal materials. In this paper, a thermoelastic-viscoplastic crystal plasticity model is developed to study the plastic deformation of aluminum (Al) materials under high pressure and high strain rate loading. In the model for single crystal, both the thermally-activated mechanism and the phonon drag mechanism are considered for dislocation glide which make the model applicable for a much wide deformation rate range. In addition, the density of the mobile and immobile dislocation is formulated according to the annihilation and multiplication mechanism. A general harden model is utilized to take strain harden, pressure harden and temperature soften into consideration. Moreover, a high-order Euler elastic equation is adopted to describe the non-linear elastic deformation of the materials in large elastic deformation. Furthermore, based on the model developed for single crystal plastic deformation, a polycrystalline model is developed according to the Taylor model and the crystal plasticity finite element method, respectively. The dislocation glide speed in Al materials is predicted by the model and the results agree quite well with the experimental results in a wide shear stress range because both thermally-activated mechanism and phonon drag mechanism are considered for dislocation glide. With the model, the shear strengths of both single crystal and polycrystalline are predicted, and it is found out that the shear strength of Al materials increases with increasing of the load pressure. Besides, significant anisotropy of the shear strength is revealed for single crystal Al materials although it is a typical FCC crystal with high symmetry. Finally, texture evolution of polycrystalline Al materials is studied with the model and the preferred orientation effect of the crystal is found for different loading pressures. Moreover, the preferred orientation effect is more significant for high loading pressure.
Cavity expansion response of concrete targets under penetration
NIU Zhenkun, CHEN Xiaowei, DENG Yongjun, YAO Yong
2019, 39(2): 023301. doi: 10.11883/bzycj-2017-0368
The LS-DYNA was used to simulate the process of a rigid projectile normally penetrating into a concrete target. Based on the two threshold values of ultimate compressive strain and ultimate tensile strain of the concrete, the cavity expansion response regions of the concrete target were identified and the size of each concrete response region in the penetration process was obtained. The effect of the penetration velocity on the crushed and cracked regions of the concrete was analyzed. The relationships between the boundary expansion velocity of the crushed/cracked regions and the penetration velocity were discussed. The results indicate that with increasing the initial impacting velocity, the interface velocities of the crushed/cracked regions and the radius of the crushed region increase, but the radius of the cracked region decreases. At last, the cracked region may disappear when the penetration velocity achieves a certain critical value.
Study on wall damage of vessel in high-speed fragment impact liquid-filled vessel
MA Liying, LI Xiangdong, ZHOU Lanwei, LAN Xiaoying, GONG Xiaoze, YAO Zhijun
2019, 39(2): 023302. doi: 10.11883/bzycj-2018-0009
We analyzed the influence of the impact energy on the damage degree of the front and rear walls and verified it by experiments. The results show that the hydrodynamic ram formed by a high-speed fragment impacting the liquid-filled vessel affects the vessel's front and rear walls and that the degree of the damage can be divided into three levels:the cracks are not observed on the front and rear walls; cracks are observed on the rear wall surface but on the front wall surface; cracks are observe on both front and rear walls and the rear wall is petal-type cracked. The maximum deformation of the front and rear walls and the total number of cracks in the front and rear walls increase with the increase of the impact energy of the fragments during the fragment impact process of the liquid-filled vessel.
Influnence of side water on anti-collision performance of a ship
HU Jinwen, YOU Xiaojian, WEN Xinyi, PENG Xiaojun, LI Tianyao
2019, 39(2): 023303. doi: 10.11883/bzycj-2017-0319
In order to evaluate the anti-collision characteristics of a side tank impacted by a large object, the anti-collision performances of the outer side shell and the inner side shell under different impact velocity and tank waterlines were analyzed on the basis of the finite element method and the simplified theory method. The results show that the water can significantly enforce the anti-collision performance of the double-side structure, but the increasement is limited, and the water affects weakly the failure of the outer shell, but which has a great influence on the broken reaction force of the inner side shell. When the velocity of the bulbous bow gradually increases, the broken reaction forces of the outer side shell and the inner shell gradually increase, but the increasing rates tend to be gentle gradually, and the increasing rate for the broken reaction force of the outer side shell tends to be gentle faster than that for the inner side shell. And the analysis on different tank waterlines shows that, when the waterline of the side tank is above the impacted stong frame, the anti-collision characteristics are less affected. When the waterline of the side tank is below the impacted strong frame, the anti-collision characteristics of the side outer shell are less affected, but the waterline has a great influence on the anti-collision characteristics of the inner side shell, and the differences increase corresponding to different waterlines with increasing the collision velocity of the bulbous bow.
Research on penetration of small size fragment to single soldier protection equipment
ZHOU Jie, ZHI Xiaoqi, XU Jinbo, YUE Zhonghao
2019, 39(2): 023304. doi: 10.11883/bzycj-2018-0023
In order to find out whether the small size fragment can penetrate the ordinary single-soldier bulletproof clothes and bulletproof helmets effectively, the spherical fragment has been selected as the object, obtained the limit velocities of the 0.2 g spherical tungsten alloy fragment penetrating the level Ⅲ body armor and level Ⅳ bulletproof helmet. The thickness of Q235 equivalent targets of body armor and bulletproof helmet is obtained by the means of numerical simulation, and the influence rule of the fragment's mass on the limit velocity is investigated.The conclusions is important to the development of new anti-infantry weapons and soldier's basic protective equipments.
Experimental Techniques & Numerical Methods
Pretightening load design for bolt of closure flange structure under intensive impulse loading
CHENG Shuai, ZHANG Dezhi, LIU Wenxiang, YIN Wenjun, SHI Yingju, CHEN Bo, LI Yan
2019, 39(2): 024101. doi: 10.11883/bzycj-2018-0007
In this article, to figure out an optimal pretightening load selection for a closure flange structure under intense impulsive loading, we designed an experimental system based on the SHPB platform and the hydraulic principle and investigated the dynamic response process of a closure flange structure. The results showed that a minimum extreme point was observed on the curve of the total tensile strain of the bolt under the pretightening and impulsive loading versus the impulse peak. Further more, we obtained the variation pattern of the total tensile strain of the bolt with the change of the impulse peak and decay, which can be used as basis for the structural design and the selection of the bolt preload for a sealing flange under intense impulsive loading.
Similarity relations of underwater explosion in centrifuge and pressurizing vessels
SONG Ge, LONG Yuan, ZHONG Mingshou, WANG min, WU Jianyu
2019, 39(2): 024102. doi: 10.11883/bzycj-2017-0321
The collective effect of underwater explosion shock wave and bubble pulsation does not meet the traditional geometric similarity relation, and the scaled model test must be carried out in a closed pressurized tank or centrifuge apparatus. Through the dimensional analysis and π theorem, the similarity theory of the model tests was deduced. The prototype condition and model conditions with the scaled ratio of 1/20 and 1/30 were simulated based on LS-DYNA, which shows the similarity relations and application scope of the pressurized model and centrifugal model. The shock wave, bubble radius and bubble period can meet the similarity relations but the bubble motion and jet can not meet the similarity relations in the pressurized model; and the shock wave and bubble pulsation almost meet the similarity relations in the centrifugal model.
Study on measurement of gas temperature and pressure after explosion in closed cavity at small-scaled distance
ZHANG Jijun, ZHANG Dongliang, ZHAO Jianwei, ZHANG Baoguo, CUI Yunxiao
2019, 39(2): 024103. doi: 10.11883/bzycj-2018-0039
For the purpose of accurate measurement of temperature and pressure changes in cavity explosion, a gas temperature and pressure after explosion measurement system was built for closed explosion based on K-type thermocouple and pressure transmitter. By designing a heat-insulation protection device, sensors' sensitive areas and signal modulation modules were installed in two different seal cavities independently. By doing this, sensors' survival under blast wave was raised. Sensors and the protect device were tested at the scaled distance of 0.86 m/kg1/3. Gas temperature and pressure after explosion efficient changing progress was gained and sensors can be restored to the initial state. The test result shows that by installing K-type thermocouple and pressure transmitter to proper protecting device, gas temperature and pressure changing progress after explosion can be measured at small scaled closed explosion.
Numerical simulation on complete process of three-dimensional bench blasting in an open-pit mine based on CDEM
FENG Chun, LI Shihai, ZHENG Bingxu, CUI Xiaorong, JIA Jianjun
2019, 39(2): 024201. doi: 10.11883/bzycj-2017-0393
Blasting mining is the most important part of the total cost control in an open pit mine, and numerical simulation is an effective method to optimize the design of blasting mining and to analyse blasting effect. By using the continuum-discontinuum element method (CDEM), the three-dimensional bench blasting process of the open pit mine is simulated. The Landau explosive model is adopted to precisely calculate the blasting effect, and the elastic-damage-fracture constitutive law is used to describe the damage and fracture process of rock. By adopting the semi-spring target face and semi-edge target edge combined contact algorithm, the collision, flying and accumulation process of large number of fragments is simulated efficiently. The numerical simulation of the small scale blasting process with the single free surface is carried out. The block distributing curve and volume of the crater obtained by numerical simulation are more or less the same as those obtained by experiment, which demonstrates that CDEM and corresponding models described in this paper are good at simulating the rock blasting process. Based on the blasting technology in the south region in Anqian open-pit mine, a generalized three-dimensional bench blasting model with 3 rows and 21 bore holes is set up, and the complete process from explosive detonation to muckpile formation is carried out. Numerical results show that, except the tensile crack behind the blasting area, the muckpile shape and heaving height obtained by numerical simulation are accordant with the ones obtained by field test to some extent, which demonstrates the feasibility to simulate the three-dimensional bench blasting by CDEM.
An improved finite particle method for discontinuous interface problems
WANG Lu, YANG Yang, XU Fei
2019, 39(2): 024202. doi: 10.11883/bzycj-2017-0390
The finite particle method(FPM) is an important improvement for the smoothed particle hydrodynamics(SPH) method, which effectively improves the calculation accuracy of boundary particles. However, when the discontinuous physical field is solved by the FPM, the accuracy in the vicinity of the discontinuous interface is greatly reduced, and the non-singularity of the matrix must be satisfied in the FPM, which requires an elaborate handling of the interface. Based on the discontinuous SPH(DSPH) method, this paper proposed an improved FPM-discontinuous special FPM(DSFPM), which considers the discontinuous interface, aiming to improve the computational accuracy at the interface and further improve the efficiency and stability of the FPM. In this paper, the estimation accuracy of the DSFPM was analyzed firstly, and then the algorithm flow diagram of the DSFPM to deal with the small deformation and large deformation problems was demonstrated. Next, the DSFPM, DSPH and FPM were used to simulate the small deformation problem-elastic aluminum blocks impact. By comparing the velocity and stress of the aluminum blocks and computational time, we verified the accuracy and computational efficiency of the DSFPM. Finally, the simulation of the large deformation problem was realized by a combining method with the DSFPM and DFPM.
Applied Explosion Mechanics
Design and experimental verification of a wing leading edge structure
REN Jibin, WANG Bin, WANG Zhen, LIU Jun, SUO Tao, LI Yulong
2019, 39(2): 025101. doi: 10.11883/bzycj-2017-0407
In order to improve the anti-bird strike performance of a wing leading edge to meet the airworthiness requirements, the simulation-test-simulation methodology was adopted for the optimization of the leading edge. Firstly, the anti-bird strike responses of two kinds of the new leading edges, with the triangular plate structure and the front wall structure, respectively, were investigated via finite element simulation. The simulation results show the anti-bird strike performance of the leading edge with the front wall structure is better than those of the leading edges with the original structure and the triangular plate structure. During the bird strike process, the front wall structure can utilize the damaged skin's deformation to absorb energy, thus leading to the improvement of the anti-bird strike performance of the leading edge. The experiment was then carried out to verify not only the accuracy of the numerical simulation method but also the ability of the front wall structure against bird strike. Then, the validated model was used to analyze the influence of the leading edge structural parameters. With the weight reduction of 30%, the optimized wing leading edge structure with the front wall achieved a good performance of anti-bird strike.
On collapsing disintegration and vibration of a cooling tower subjected to blasting demolition
FEI Honglu, ZHANG Chaoyi, LÜ Jinqi, ZHANG Longfei
2019, 39(2): 025201. doi: 10.11883/bzycj-2017-0414
In order to study the blasting demolition of the cooling tower with compound incisions, the plastic hinge theory is used to analyze the motion state of the cooling tower in the whole collapse process. The mathematical model for the tower body instantly hitting the ground is established. And the maximum linear strain theory is considered to be the mechanical basis for the breakage of the tower wall. Analysis is carried out by the MATLAB numerical software. Analyzed results display that in addition to the wall at the incisions, the upper tower wall will undergo breakup and disintegration. This phenomenon coincides with the actual situation. When the explosive is determined, the coordinate value of the upper broken section decreases with the increase of the rotational extremum of the plastic hinge. In addition, the peak vibration velocity induced by the continuous collapse of the tower body hit the ground with blink section plastic hinge extreme increases. This conclusion is deducted by analyzing the of the tower-body continuous collapse that is the most harmful to the surrounding buildings during the blasting process. In view of that, the excessive total delay time should be avoided for the cooling-tower blasting in the future, so as to control the rotation angle of the tower and reduce the harm induced by cooling-tower blasting to surrounding buildings.
Calculation and application of hole by hole blasting vibration superposition based on measured delay times of detonators
WU Haojun, GONG Min
2019, 39(2): 025202. doi: 10.11883/bzycj-2017-0415
It's important to calculate the superposed vibration velocity of multi-segments' millisecond blasting for low vibration velocity control in urban tunnels, but each segments of non-electric detonators have delay errors which can't be ignore in vibration's millisecond superposition under a low vibration velocity criterion. If each waves initiated one by one in consider of delay ranges between segments, it will forms a huge number of probable superposed vibration velocity curves which will result in no way to find a solution. To solve this, single-hole blast curve is took as wave of blast source, Fourier series is used to fit the curve. According to the measured time delay ranges of each segments' detonators, logical language is used to write MATLAB routine such as multistage nested loops, it is succeeded to get the probable superposed vibration velocity curves of 8 segments' millisecond blasting. The influence of the delay errors on the blast vibration is analyzed from the same segment and the different segments. The second free surface creation time is determined by compare the computed superposed vibration curve with measured blasting vibration curve. All the probable vibration curves are superposed within the delay ranges of each segments before the surface's formation, the maximum charge is selected as the designed one whose maximum peak result is safe. The application in a tunnel project shows that the second free surface created at 60ms and the maximum superposed vibration velocity is 0.62 cm/s by 1.0 kg design charge, which is in good agreement with the measured results in the field.
Flame propagation characteristics of lycopodium dust explosion under explosion pressure accumulation conditions
YU Jianliang, JI Wentao, YAN Xingqing, YU Xiaozhe, HOU Yujie
2019, 39(2): 025401. doi: 10.11883/bzycj-2017-0436
An experimental setup which can withstand high pressure with good visibility was built. Flame propagation characteristics of lycopodium dust explosion were investigated under explosion pressure accumulation conditions. The experimental results showed that a space-dispersed fascicle-like flame structure was formed after the explosion of lycopodium dust under explosion pressure accumulation conditions. The flame front with a serrate structure was observed. However, on further increasing the dust concentration the flame continuity as well as the luminance increased and reached the top at the concentration of 750 g/m3. The velocity fluctuation during the flame propagation process of lycopodium dust explosion at different concentrations was found. But the fluctuation frequency decreased with the increase of dust concentration. The average flame propagation velocity increased and then decreased with the increase of dust concentration and reached the top at the dust concentration of 750 g/m3. The value of flame velocity was higher in the early stage, but lower in the later stage.
Effect of CO2-ultrafine water mist on initial explosion characteristics of CH4/Air
PEI Bei, WEI Shuangming, CHEN Liwei, PAN Rongkun, WANG Yan, YU Minggao, LI Jie
2019, 39(2): 025402. doi: 10.11883/bzycj-2018-0147
In order to study the effect of CO2 and ultrafine water mist on the initial 9.5% methane/air explosion characteristics, a high speed schlieren system and a constant volume combustion bomb were used to study the 9.5% methane/air explosion characteristics. By changing the dilution volume fraction of CO2 and mass concentration of ultrafine water mist respectively, the change rules of flame propagation speed and explosion overpressure were analyzed under two separate and combined actions. The results show that the ultrafine water mist with a mass concentration of 58.3 g/m3 enhanced the instability of the flame and accelerated flame acceleration and explosion overpressure. This indicates that the insufficiency of the ultrafine water mist can produce detonation promotion, and the methane explosion will be suppressed only when the ultrafine water mist is sufficient. When CO2 and ultrafine water mist act together, it can avoid the explosion phenomenon caused by ultrafine water mist, weaken the instability of spherical flame significantly, reduce the propagation velocity of the spherical flame, decrease the explosion overpressure and the mean rate of pressure rise, and delay the arrival time of the overpressure peak. This study can provide a guidance for the prevention of methane explosion.
Explosion overpressure of hydrogen cloud in catalytic reforming process
JIANG Nan, Bi Yixing, LÜ Dong, WANG Lu, MU Yangyang
2019, 39(2): 025403. doi: 10.11883/bzycj-2017-0371
Because the structure and shape of processing equipment in petrochemical industry are complex normally, the explosion overpressure of gas is hard to be predicted by traditional explosion overpressure models. Base on the computational fluid dynamics software (FLACS) and the accident model of the catalytic reforming process, the effects of different factors (obstacle shape, leakage position) on the explosion overpressure of hydrogen at different times and different monitoring points were investigated. The explosion overpressure models for overpressure, combustion heat of hydrogen and distance from the center of gas cloud were established. The results show that, the overpressure approximately follows a linear relationship with scaled distance in a logarithmic coordinate system; the explosion overpressure model should be modified for different kinds of obstacles; when the leakage time achieves 5 minutes, the accident occurring in the middle of the reactor shows increasing overpressure obviously.