2010 Vol. 30, No. 3

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Article
Damage modes of stiffened plates subjected to underwater explosion load
ZHU Xi, MOU Jin-Lei, WANG Heng, ZHANG Zhen-Hua
2010, 30(3): 225-231. doi: 10.11883/1001-1455(2010)03-0225-07
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Abstract:
The commerical finite element software MSC.Dytran was used to numerically investigate the damage modes of stiffened plates under underwater explosion loads in the case of the different charge quantities and stand-off distances. Some experiments were conducted to confirm the numerical results. The factors which affected the damage mode of stiffened plates were analyzed. On the basis of the analyzed results the critical loads were proposed to distinguish the different damage mode. At the same time the criterion between the contact explosion and the noncontact explosion was put forward from the damage modes of stiffened plates.
Characteristics of ultra-high performance cementitious composites under explosion
RONG Zhi-Dan, SUN Wei, ZHANG Yun-Sheng, ZHANG Wen-Hua
2010, 30(3): 232-238. doi: 10.11883/1001-1455(2010)03-0232-07
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Ultra-high performance cementitious composites (UHPCC) were prepared by substitution ofultra-fine industrial waste powder for large quantity of cement by weight and replacement of groundfine quartz sand with natural fine sand with the maximum particle diameter of 2.5 mm. And in theprepared UHPCC,the basalt stones with high elastic module and high strength were added,whosemaximum particle diameters was 15 and 10 mm,respectively. Nine contact-explosion tests were per-formed for concrete targets and the macroscopic damages were described. The explosive compressioncoefficients were computed by the explosion-induced infundibular crater size and a formula was pro-posed to calculate the explosion-induced infundibular crate depth. The results indicate that the pre-pared UHPCC have remarkable anti-explosion and anti-scabbing properties and that the explosioncompression coefficient is inversely proportional to the square root of tensile strength.
Dynamic deformations of 921A steel pure shear hat-shaped specimen in SHPB tests
LI Ji-Cheng, CHEN Xiao-Wei, CHEN Gang
2010, 30(3): 239-246. doi: 10.11883/1001-1455(2010)03-0239-08
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A series of numerical simulations of SHPB test using 921A steel pure shear hat-shaped specimens are conducted with ANSYS/LS-DYNA and validated by the SHPB tests in the present paper. Integrated with the theory of stress wave in a SHPB system,the wave propagation in the bars and the dynamic deformations of the specimen under different loading rate (or stress pulse ) are analyzed,and typical wave shapes are identified for different loading rates. Numerical test of SHPB under ultrahigh strain rate are specially conducted,which is unable to be done realistically. The different deformation and failure of the hat-shaped specimens under different loading rate are distinguished,and the applicability of strain waves in the bars under ultrahigh loading rate is also discussed.
Acoustic emission experiment of rock failure under coupled static-dynamic load
WANG Qi-Sheng, WAN Guo-Xiang, LI Xi-Bing
2010, 30(3): 247-253. doi: 10.11883/1001-1455(2010)03-0247-07
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The acoustic emission(AE) tests of rock failure were made on the SHPB test system and the law of the AE energy was obtained under coupled static-dynamic load. The AE energy presents two different features:mode I,the energy decays rapidly after the peak of the energy,however,the energy rises at the end of the loading and the inflection point appears; mode II,the energy decays slowly after the peak of the energy and the inflection point does not appear. The effect of the axial static load and impact on the AE energy was analyzed. The results show that the peak value of the AE energy decreases with the increase of the axial static load; when the axial static load is located at the elastic stage,the pre-peak of the AE energy increases slowly; when the axial static load exceeds the elastic stage,the pre-peak of the AE energy increases rapidly with the increase of the axial static load. The peak and pre-peak of the AE energy decrease with the increase of the dynamic strain rate. It is useful for both theory and practice to seek the precursory characteristics of the AE of rock mass under coupled static-dynamic load.
A calculation method for supercavity profile about a slender cone-shaped projectile traveling in water at subsonic speed
ZHANG Zhi-Hong, MENG Qing-Chang, GU Jian-Nong, WANG Chong
2010, 30(3): 254-261. doi: 10.11883/1001-1455(2010)03-0254-08
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By adopting the irrotational and steady motion of the ideal compressible fluid and the supercavity with the Riabushinsky scheme of closure,an integro-differential equation was derived for the supercavitating flow around a slender cone-shaped projectile traveling in water at subsonic speed by using the slender-body theory and the matched-asymptotic-expansions method. The first-and second-order approximation solutions for the supercavity shapes considering the compressibility effect were obtained,and the calculation precision was improved. The influences of the flow compressibility on the supercavity profiles were analyzed under the high-speed impact of the gun-launched projectile. With the increase of Mach number,the supercavity shape expands markedly. The calculated characteristic parameters for the supercavity profiles are in agreement with the theoretical and experimental results.
Large eddy simulation for the multi-viscosity-fluid and turbulence
BAI Jin-Song, WANG Tao, ZOU Li-Yong, LI Ping
2010, 30(3): 262-268. doi: 10.11883/1001-1455(2010)03-0262-07
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Abstract:
Based on the multi-viscous-fluid piecewise parabolic method,the Smagorinsky and Vreman subgrid eddy viscosity models were employed to the Navier-Stokes equations. A two-dimensional computational code MVFT(multi-viscosity-fluid and turbulence) was developed for computing the multi-viscosity-fluids and the turbulent induced by the fluid interface instability. By applying the developed MVFT code,numerical computations were conducted by the Smagorinsky and Vreman subgrid eddy viscosity models,respectively to simulate the Richtmyer-Meshkov instability experiment of a shock-accelerated heavy gas cylinder in LANL. The heavy gas column shapes,the flow field velocities and the vortex properties were analyzed and compared with the existent experimental and calculated results. It is indicated that the Vreman subgrid eddy viscosity model is superior to the Smagorinsky's in this simulation. The developed MVFT method and code are suitable for simulating the interface instability and turbulence mixing complex process.
Penetration of cylindrical-nose-tip projectiles into concrete targets
SUN Chuan-Jie, LU Yong-Gang, ZHANG Fang-Ju, LI Hui-Min
2010, 30(3): 269-275. doi: 10.11883/1001-1455(2010)03-0269-07
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Abstract:
Penetration experiments were conducted for several typical cylindrical-nose-tip projectiles (CNTP) into concrete targets with the compressive strengths of 9.0,28.4 MPa. The penetration mechanism was elementarily obtained by observing the recovered projectiles and the post-test targets. Thereby,a dimensionless parameter S2 was proposed to describe the target strength degradation and a parameter bt was brought forward to picture the cylindrical penetration pore radius. And then,the two parameters were introduced into the penetration formula by Forrestal et al to develop a new theoretical model for the penetration of CNTP into concrete. For the 28.4-MPa-strength concrete,the theoretical predictions by the new model agree well with the experimental data. For the 9.0-MPa-strength concrete,the theoretical predictions do not accord well with the experimental data but can still reflect the penetration mechanism of CNTP. Finally,two approaches were put forward for the penetration improvement of CNTP by decreasing S2 and increasing bt.
Effect of different explosion or shock seismic inputs on efficiency of a whole vibration-isolating system
DU Jian-Guo, XIE Qing-Liang, FENG Jin-Ji, LI Li-Sha
2010, 30(3): 276-282. doi: 10.11883/1001-1455(2010)03-0276-07
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Abstract:
A drum-shaped steel wire rope isolator was applied to a two-floor steel construction to achieve a whole vibration-isolating system. Numerical simulation was carried out by the finite element method to explore the vibration-isolating efficiency of the achieved system input by explosion or shock signals with uniform forms. By changing the primary pulse duration and peak value,the vibration-isolating ratio was calculated to investigate the influences of the primary pulse duration and peak value on the vibration-isolating ratio. It is helpful to understand the vibration-isolating mechanism and develop vibration-isolating research.
Performance of a 60 kJ electric gun
CHEN Lin, DAI Ying-Min, SU Jian-Jun, FENG Shu-Ping, XIE Wei-Ping, WANG Hui, REN Jing, WU Shou-Dong, LI Ye
2010, 30(3): 283-287. doi: 10.11883/1001-1455(2010)03-0283-05
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A 100 kV/60 kJ electric gun was developed. The electrical character and geometric scale of the load,as well as the experimental setup,were presented. The experimental results indicate that the flyer has good integrality and high flatness. The electric gun can accelerate the 0.15-mm-thick Mylar flyer with the diameter of 18 mm (53 mg) to 8.1 km/s,and the 0.2-mm-thick Mylar flyer with the diameter of 12 mm (32 mg) to 9.6 km/s,respectively. The 60 kJ electric gun has high driving capability and can be used as an effective driver to carry out dynamic response of materials under high strain rates and some other relative investigations.
Prediction of the lower flammability limits of hydrocarbons based on the quantitative structure-property relationship studies
PAN Yong, JIANG Jun-Cheng, WANG Rui
2010, 30(3): 288-294. doi: 10.11883/1001-1455(2010)03-0288-07
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The quantitative relationships between the lower flammability limits (LFL) and the molecular structures of hydrocarbon compounds were investigated based on the quantitative structure-property relationship (QSPR) studies. Various structure parameters were calculated to describe the structure characteristics of the molecules based on their structures. A set of structure parameters which have significant contribution to the LFL were chosen as the molecular descriptors by employing the variable selection method of genetic algorithm (GA). Both the multiple linear regression (MLR) and support vector machine (SVM) were employed to model the possible quantitative relationship existed between these selected descriptors and LFL,respectively,and the corresponding prediction models for the LFL of hydrocarbons based on the molecular structures were constructed. The models were tested by internal and external validations. The results showed that,for both models,the predicted LFL values agreed well with the experimental ones,and the predicted errors were within the range of the experimental error of LFL measurements. The mean absolute error and the root mean square error for the test set of SVM model were 0.036% and 0.046%,respectively,which were better than those of the MLR model and previous models. This paper provides a new method for predicting LFL of hydrocarbons for engineering.
Application of DCD scheme to computation of two-phase flow interior ballistics for fractured propellant bed
YUAN Lai-Feng, RUI Xiao-Ting, WANG Guo-Ping, CHEN Tao
2010, 30(3): 295-300. doi: 10.11883/1001-1455(2010)03-0295-06
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A new computational method of two-phase flow interior ballistics which can be used to study the launch safety problem of propellant charge is put forward based on the DCD scheme. By rewriting the form of items about pressure in dynamics equation group of gas-solid two-phase flow,the uniform disposal of gas and solids with the same scheme are realized,and it does not need to treat them respectively. It does not need artificial filtering or numerical viscosity while using the DCD scheme,so the computational accuracy is improved. In an instance the two-phase flow interior ballistics of a howitzer is computed,the computational results agree with the test results. The influence of different fracture degree of propellant charge on launch safety is numerically simulated by the DCD scheme,in which fractured propellant charge bed is considered as a mixed charge configuration. The barrel pressure evolvement and dangerous barrel pressure,which are difficult to be reflected by the computational methods,appear in the computational results for interior ballistic of fractured propellant charge bed.
Dynamic response of foam sandwich plates subjected to impact loading
SONG Yan-Ze, WANG Zhi-Hua, ZHAO Long-Mao, ZHAO Yong-Gang
2010, 30(3): 301-307. doi: 10.11883/1001-1455(2010)03-0301-07
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Aluminum foam projectiles were used to dynamically load clamped quadrate sandwich plates with an aluminum foam core and monolithic solid plates. A laser Doppler velocimeter and a laser displacement transducer were applied to measure the impact velocities of the foam projectiles and the deflection-time histories at the midpoints of the back faces of the plates,respectively. Deformation and failure modes of the sandwich and monolithic plates were exhibited to discuss the effects of the projectile impulse,the face sheet thickness and the core density and thickness on the structural responses of the plates. It is found that there is the maximum permanent deflection at the midpoint of the back face,the deflection at the plate brim is the least and the whole deformation profile takes on a dome shape with flower-shaped deformation. The results indicate that the permanent deflection of the back face can be effectively controlled to improve the capacity of energy absorption of sandwich plates by increasing the face sheet or core thickness. The structural response is sensitive to the projectile impulse or the core density and the permanent deflection is proportional to the projectile impulse or the core density. The experimental results can provide help for the optimum design of cellular metallic sandwich structures.
Pressure desensitization of emulsion explosives sensitized by compound sensitizers
WANG Yin-Jun, LI Yu-Jing, GAN De-Huai
2010, 30(3): 308-313. doi: 10.11883/1001-1455(2010)03-0308-06
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Abstract:
To find out the relationship between the sensitizer and the emulsion explosive pressure desensitization,the pressure desensitization of the emulsion explosives was studied which were sensitized respectively with two types of compound sensitizers of chemical foaming agent + hollow glass microballoon particles and hollow glass microballoon particles + expanded perlite. The pressure desensitization degrees were calculated with the explosion wave crest value of the emulsion explosive which was tested under water after it was pressed by the host charge' explosion wave,and the pressure desensitization degrees of the emulsion explosives with the compound sensitizers were compared with that of the emulsion explosives with a single sensitizer. The results indicates that the pressure desensitization degrees of the emulsion explosives sensitized with the first compound method are between that of the emulsion explosives sensitized by single chemical foaming agent and that of the emulsion explosives sensitized with single hollow glass microgalloon,for example,the desensitization degrees at the 10 cm pressed spacing are 1.000,0.983,0.210 respectively,and that the pressure desensitization degrees of the emulsion explosives sensitized with the second compound method are less than that of the emulsion explosive sensitized respectively by the single sensitizer of hollow glass microgalloon and expanded perlite,their desensitization degrees at the 10 cm pressed spacing are 0,0.274,0.618 respectively. Results show that the pressure desensitization of the emulsion explosives was caused mainly by the combining effect of the anti-pressure performance of the sensitizer particles or bubbles and the partial emulsion breakage around the micro-interfaces between the particles and emulsion matrix.
ZHANG Ding-Shan, WANG Hao, FENG Guo-Zeng, LIU Bin, GUO Jin-Yan
2010, 30(3): 314-319. doi: 10.11883/1001-1455(2010)03-0314-06
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Temperature change of earth penetrators during penetration into concrete target
Effects of plane shock loading on structure of Ti6Al4V alloy
WEN Xia, YANG Shi-Yuan, WANG Jun-Xia, ZHANG Lin, LIU Xiao-Nan
2010, 30(3): 320-324. doi: 10.11883/1001-1455(2010)03-0320-05
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Ti6Al4V alloy samples were symmetrically and asymmetrically impacted by using a one-stage light gas gun. The recovered samples were analyzed by the scanning electron microscopy and X-ray diffraction. Results indicate that with the increasing of the impact speeds,the samples are distorted to different degrees. Meanwhile,the microcracks induced by the shock wave cause the material damage and the material damage accelerates the production and extension of the microcracks. Furthermore,the X-ray diffraction analysis shows that the impact can improve the crystallization of the material and there forms a metastable structure during the cooling process that can advances to some extent the impact toughness.
Explosion mechanism of carbon powder
LAI Cheng-Feng, DUAN Zi-Hua, ZHANG Yong-Fa, ZHANG Lao-Lao
2010, 30(3): 325-328. doi: 10.11883/1001-1455(2010)03-0325-04
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Abstract:
Aimed at the explosion of the CH4/CO2 reforming reaction,a series of investigations were carried out to explore the explosion characteristics of the carbon powder. It is indicated that the higher the volatile content in the carbon powder,the greater the explosion intensity. The coal powder samples and the explosion products were analyzed by the industry and SEM. The industry analysis shows that after explosion the volatile content in the coal powder decrease 5%10%,the ash content increases slightly and the moisture content changes weakly. The SEM analysis reveals that the explosion products appear similar to spheres and smoother than the original samples,and that the coal powder cannot combust sufficiently. Investigated results display the explosion mechanism that the volatile matter is firstly released from the heated coal powder samples and joins in reaction,consequently causes explosion. In essence,the carbon powder explosion is a gas explosion.
Design and impact analysis of a high-g accelerometer
SHI Yun-Bo, ZHU Zheng-Qiang, LIU Xiao-Peng, DU Kang, LIU Jun
2010, 30(3): 329-332. doi: 10.11883/1001-1455(2010)03-0329-04
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To meet the test requirements in special situation,a high-g accelerometer structure with four-terminal fixed beam-island was designed. The dynamic characteristics of the accelerometer were test by using the Hopkinson bar impact calibration device. The test results show that the sensitivity of the sensor is 1.2 V/g and the linearity is 5%. The output signal is proper when impact by 2105 g. So the designed accelerometer can effectively meet the special test requirements such as high impact and strong vibration,and it can be applied to the penetration system.
Design and realization of an acceleration measurement system by using Model 1221
ZHU Yi-Chao, GAO Cheng, LI Yan-Xin, CHEN Yong-Guang
2010, 30(3): 333-336. doi: 10.11883/1001-1455(2010)03-0333-04
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A small-size acceleration measurement system based on ARM system was designed by using acceleration chip Model 1221 and expanding the external memory. Combined with the communication port,the application software was developed to display,store and deal with the data measured. By measuring the centripetal acceleration of the rotating body at the uniform velocity,this system was calibrated. The blast acceleration produced by shaking table was surveyed,and then the data were compared. The results show that the size of this system is smaller,the intelligent extent is higher,the dynamic range is greater and the memory capacity is larger.