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2018, 38(12): .

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2018, 38(12): .

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Non-Circular Penetrator Normal Impact Semi-Infinite Target

WANG Xiao-dong, GAO Guang-fa, DU Zhong-hua, PIAO Chun-hua

2018, 38(12): 1211-1216. doi:10.15918/j.tbit1001-0645.2018.12.001

Abstract(814) PDF(405)

Abstract:
To study the penetration characteristics of non-circular penetrators, simulations and analyses of penetration into semi-infinite targets were done on penetrators whose cross-sections were circular, equilateral triangular, and square. Simulation results were verified with the previous experimental data. Simulations were done to study the penetration power of three kinds of penetrators with different cross section shapes and length-diameter ratios of 5, 10 and 15 and two kinds of penetrators with Regular pentagon and Hexagon cross-sections. Results show that non-circular penetrators with bigger length-diameter ratios and higher impacting velocity had good penetration power; the penetrator with an equilateral triangular cross section had the greatest power. A parameter to name the cross section shape factor was put forward. Based on the Alekseevskii-Tate model, an empirical formulae for the impact of non-circular penetrator on semi-infinite targets was built.

Molecular Dynamics Simulation on Characteristics of Crater Formation Induced by Hypervelocity Impact

JU Yuan-yuan, ZHANG Qing-ming, LONG Ren-rong, WU Qiang, GONG Zi-zheng

2018, 38(12): 1217-1221. doi:10.15918/j.tbit1001-0645.2018.12.002

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Based on the open source molecular dynamics program LAMMPS, hypervelocity impact of a spherical aluminum projectile with a diameter of 4.86 nm on the semi-infinite thick aluminum target at the speed of 10 km/s was simulated. The physical process of crater formation was similar to that from a macroscopic impact. The crater depth was consistent with the data from the macro empirical formula and its variation with time was obtained. The propagation characteristics of the shock wave in the target were analyzed. The propagation speed of the shock wave front reached up to 12 km/s during the initial impact, and then the speed gradually decreased and was close to the elastic wave velocity. The observation region around the crater experienced melting state which lasted about 0.07 ps and had a layer thickness of 29 nm. The cooling rate of the observation region around the crater reached the order of 10¹⁵K/s which prevented atom recrystallization. The observation region finally turned into a solid phase amorphous structure.

Dynamic Response of Fully Clamped Circular Aluminum Alloy Plate Subjected to Near Field Explosion

XIE Jiang, JIANG Chao, ZHOU Shu-ting, LI Han, FENG Zhen-yu

2018, 38(12): 1222-1230. doi:10.15918/j.tbit1001-0645.2018.12.003

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A explosive shock experiment on 2024-T3 circular aluminum alloy plate subjected to near field explosion was conducted. Calculations and numerical simulations were implemented with Henrych empirical formula and finite element method, respectively. Shock wave overpressure under near field explosion was compared. Dynamic response characteristics and deformation failure modes of circular aluminum alloy plate were studied, and influences of charge weights and stand-off distances were analyzed. The results showed that under the influence of the impact load, with the increasing of loads, that is, with the increase of charge weight and the decrease of stand-off distance and scaled distance, three kinds of deformation and failure modes of fully clamped circular aluminum alloy plate were exhibited in the following ways:plastic deformation, rupture (tensile failure) with broken hole in the center and rupture with broken hole and fracture of the plate; the plastic deformation first occurred at the fixed boundary of the plate, and then rapidly extended to the central area of the plate; with the increase of stand-off distances, the amplitude of the midpoint displacement of the plate without failure increased in the balance position under the same charge weight. With the decrease of scaled distances, the broken hole size of the plate with rupture in the center gradually increased, and the bulge degree of the plate with tearing in the boundary gradually declined.

Acoustic Emission Test and Damage Fractal Characteristics Analysis of Concrete with Different Initial Porosity

LIU Jing-hong, YANG Yue-fei, XIE Jian, LIU Yong-jian

2018, 38(12): 1231-1236. doi:10.15918/j.tbit1001-0645.2018.12.004

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In order to explore the relationship between the acoustic emission (AE) signal's characteristic parameters and the damage evolution of concrete, the acoustic emission test on concrete specimens with different initial porosities under uniaxial cyclic loading conditions. The activity coefficient was introduced to express the activity level of acoustic emission. A method of evaluating concrete working state based on acoustic emission energy was put forward. Fractal dimension theory was used to analyze the acoustic emission energy sequence evolution characteristics of concrete with different initial porosities. The results showed that the correlation dimension of acoustic emission energy and acoustic emission energy of concrete blocks with different initial porosities was basically the same as that in the loading process, and the critical position of instability failure was equivalent. The concrete damage could be predicted when the peak of acoustic emission energy dropped again, the average energy was more than 100 m V·ms and the activity coefficient slowed down continuously within the 20~70 range. The acoustic emission energy correlation dimension decreased continuously and showed a horizontal trend signaling the ultimate bearing capacity of concrete structure.

Experimental and Numerical Simulation Study on Blasting Seismic Effect of Subway Shallow Buried Tunnel

SHI Lian-song, GAO Wen-xue, WANG Lin-tai

2018, 38(12): 1237-1243. doi:10.15918/j.tbit1001-0645.2018.12.005

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This paper took the Zhongyinggong-Xiaoxigou segment of Xinjiang Urumqi Line 1 subway tunnel as the engineering background. By conducting several vibration monitoring tests on the subway tunnel surface it was found that hollow effect phenomenon existed in the monitoring range of 16 m before and behind the tunnel face of the shallow subway tunnel. As the measure points got further from the tunnel face, hollow effect phenomenon showed the tendency of going up first, declining later, and disappeared finally. In this paper, lagrange algorithm and complete restart were adopted to simulate the blasting of subway shallow tunnel using LS-DYNA program. It showed that hollow effect phenomenon existed in the range of 10 m before and behind the tunnel face of the shallow subway tunnel; this phenomenon was most significant at the point of 6 m before and behind the tunnel face. By changing the blasting of the cut hole charge into multi section blasting, the single-stage detonation dose and the surface vibration effect were reduced. It not only ensured the safety of subway construction but also effectively controlled the impact of tunnel blasting construction on surrounding buildings.

Ballistic Modelling and Experimental Studies of Rifle Bullets Penetrating Ballistic Gelatin

MO Gen-lin, JIN Yong-xi, WANG Xue-jiao, LI Zhong-xin, WU Zhi-lin

2018, 38(12): 1244-1251,1295. doi:10.15918/j.tbit1001-0645.2018.12.006

Abstract(897) PDF(368)

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To study the wounding mechanism of rigid rifle bullets penetrating living tissues, ballistic gelatin was used as the tissue simulant and a simplified spatial ballistic model was established. The drag force, the lift force and the overturning moment were all considered to be functions of the attack angle and the velocity in the velocity coordinate system. Experimental studies of a 7.62 mm rifle bullet and a 5.8 mm rifle bullet were carried out through the reflective mirror system. Translational displacements, vertical displacements, lateral displacements, pitch angles and yaw angles of the two bullets were obtained using the linear transformation method. Analysis shows:the translational motions and the rotational motions of penetrating bullets are both spatial motions; the ballistic model can simulate motions of the tested bullet well; the energy dissipation of the bullet increases with the mass and the equatorial inertia; the polar inertia has little effect on the energy dissipation process.

Experimental Study on Minimum Ignition Energy ofn-Alkane Mists

LIU Xue-ling, ZHANG Qi

2018, 38(12): 1252-1255,1320. doi:10.15918/j.tbit1001-0645.2018.12.007

Abstract(695) PDF(366)

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Withn-alkane of vapor-liquid two-phase mists (n-hexane/n-heptane/n-octane/n-decane) as the research object, the minimum ignition energy ofn-alkane mists was studied. By our self-developed measurement system, the concentrations and SMD ofn-alkane mists were measured, and the results of the minimum ignition energy in 20 L explosion parameter measuring system were obtained. The results show that the minimum ignition energy ofn-alkanes was greater than that of the corresponding pure gas phasen-alkanes; with the increase of particle size, the minimum ignition energy ofn-alkanes increased exponentially, and the minimum ignition energy ofn-alkanes increased by two orders of magnitude in the range of 0~40μm.

Particle Filter for Object Tracking Based on CNN Feature

LI Wei-xing, MA Wei-liang, TIAN Hui, PAN Feng, JI Yu-feng

2018, 38(12): 1256-1262. doi:10.15918/j.tbit1001-0645.2018.12.008

Abstract(755) PDF(464)

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In object tracking algorithms, the target drift and missing are easy to happen in complex environments. A robust tracking algorithm was proposed based on convolutional neural network(CNN) under the particle filter framework. In this algorithm, CNN was utilized to get high-level semantic features of targets and a offline pre-train method was used to learn the general feature representation and improve the training efficiency. Using particle filter framework, the algorithm was arranged to get the reliable target motion state. In addition, two kinds of online updating procedure, long-time and short time, were introduced to deal with the target postures change and some other situations. An online hard example mining strategy was also used to improve the online learning efficiency. The simulation results show that the proposed algorithm can be effectively adapt to complex background, such as occluded, illumination changes, pose variations. Furthermore, we evaluate the proposed algorithm on some challenging videos compared with the state-of-the-art algorithms.

A Low-Cost Eye-Gaze Tracking System Based on Artificial Neural Network Dynamic Calibration Algorithm

WANG Xiang-zhou, ZHANG Xin, ZHENG Shu-hua

2018, 38(12): 1263-1268. doi:10.15918/j.tbit1001-0645.2018.12.009

Abstract(797) PDF(385)

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In order to reduce the cost of eye-gaze tracking system and simplify the complexity of the calibration algorithm,a low-cost eye-gaze tracking system was developed.The Haar-like feature and skin color combination algorithm were used to detect the human face.The active appearance model (AAM) algorithm and the optical flow method were used to locate and track the face feature points.And the pupil center was detected by the gradient vector method.An artificial neural network dynamic calibration algorithm was proposed to improve the tracking accuracy and robustness.Experiments show that the eye-gaze tracking system not only has better robustness,but also has higher precision.The average error of the system is 1.34° at head rest,and 3.26° at head movement.

Research on Motion Optimization for Quadruped Robot Based on Swing-Leg Retraction

SHEN Wei, CHAI Chang-kun

2018, 38(12): 1269-1275. doi:10.15918/j.tbit1001-0645.2018.12.010

Abstract(789) PDF(325)

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In order to improve motion performance of quadruped robot,the phenomenon of swing-leg retraction(SLR)in the motion process was discussed.First,a robot model based on spring-loaded inverted pendulum (SLIP) was built and the impacts of SLR rate on energy loss,friction and impulse were analyzed respectively.Then the comprehensive optimal SLR rate to multi-objective was calculated unified objective method. And an appropriate Bezier trajectory for the study object was planned according to this optimal SLR rate.Simulation experiments show that the optimization of SLR rate is significantly beneficial to robot performance in the aspect of energy loss,friction and impulse.

Characteristics on Temperature of Fiber Acoustic Sensor Based on Fiber Fabry-Perot Cavity

CHENG Jin, WANG Na

2018, 38(12): 1276-1281,1288. doi:10.15918/j.tbit1001-0645.2018.12.011

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A temperature model of fiber acoustic sensors based on fiber Fabry-Perot cavity was proposed, according to the principle of Fabry-Perot interference with low fineness. The temperature model was mainly arranged with the relationships between the interference spectroscopy and temperature, and between the output of the sensor and temperature. According to the model, simulation and experiments results show that, the key factor affecting the temperature characteristics of the sensor is attributed to the difference of the expansion coefficient of materials. To overcome the effects of temperature, a composite fiber ferrule was proposed. A composite ferrule with large expansion coefficient was designed to compensate the length change of fiber Fabry-Perot. This can improve the temperature adaptability of the sensors. The fiber Fabry-Perot cavity acoustic sensor with composite fiber ferrule was tested. The experimental results show that, it can work well in the temperature range of-20~+40℃.

Dynamic Model Parameter Identification of Accelerometer Using Discrete Spectrum Correction and Least Square

WEI Qing-xuan, WANG Jian-lin, HAN Rui, YU Tao, ZHAO Li-qiang

2018, 38(12): 1282-1288. doi:10.15918/j.tbit1001-0645.2018.12.012

Abstract(778) PDF(311)

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Dynamic model parameter identification of accelerometer plays an important role in improving the accuracy of dynamic testing and analysis for vibration and shock. To overcome the influence of the fence effect (FE) on the accuracy of the parameters obtained with dynamic model parameter identification method for accelerometer frequency domain, a dynamic model parameter identification method of accelerometer based on discrete spectrum correction and least square (DSC-LS) was presented. Firstly, the point coordinates at zero frequency of accelerometer were estimated by usingH₁estimator, and the resonant point coordinates were estimated with higher accuracy by combining FFT+FT discrete spectrum correction and LS. Then, according to the feature points coordinates, the dynamic model parameters of accelerometer were calculated. The experimental results show that, the presented method can eliminate the influence of FE efficiently on the accuracy of accelerometer's dynamic model parameters identification and improve the anti-interference capacity for low frequency noise with narrow-band, and improve the identification accuracy of the dynamic model parameters of accelerometer.

Curing Behaviors of HTPB/TDI System via Dynamic Torsional Vibration Method

LI Guo-ping, WU Shu-bao, MA Song, YAO Wei-shang, LUO Yun-jun

2018, 38(12): 1289-1295. doi:10.15918/j.tbit1001-0645.2018.12.013

Abstract(619) PDF(357)

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A dynamic torsional vibration method was applied to on-line monitor the curing behaviour of hydroxyl-terminated polybutadiene/toluene diisocyanate (HTPB/TDI) system at different temperature. According to the diagram of torque change with time, the curing process was divided into three phases:the first phase was the period from liquid stage to the gel point; the second phase was the period from the gel point to the hardening point; the third phase was the period from the hardening point to the curing end-point. During the third stage the internal chemical cross-linking basically completed while the physical cross-linking point still forming. Therefore, the value of torque was growing slowly till the curing end-point. According to the Flory gelation theory, the calculated △E_aof HTPB/TDI system is 41.58 kJ/mol, almost the same result calculated with the FT-IR method. FT-TR method can only reflect the first and the second period of the curing process. And the dynamic torsional vibration method can monitor full-range of the curing process. The infrared diffuse reflectance spectroscopy of HTPB/TDI system validates the dynamic torsional vibration method.

Research on Microstructure and Properties of TiAlN/AlON Nanomultilayers

YAN Hong-juan, LIU Feng-bin, LI Xi-peng, YANG Fei-fei

2018, 38(12): 1296-1301. doi:10.15918/j.tbit1001-0645.2018.12.014

Abstract(711) PDF(366)

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The effects of thicknesses of AlON layer on microstructures and properties of TiAlN/AlON nanomultilayers were studied. TiAlN/AlON nanomultilayers had been deposited on HSS (W6Mo5Gr4V2) by magnetron sputtering system. The microstructure and properties of these nanomultilayers were characterized by X-ray diffraction, vickers hardness tester and universal surface tester. The results show that under "template effect" of TiAlN, amorphous AlON has been crystallized and grow epitaxially with TiAlN. The superhardness effect could be generated in the region with sharp interface. When the thickness of AlON layer is 0.81 nm, the nanomultilayer has highest hardness. The hardness of nanomultilayer is 3 769.6 HV and increases 60.37% than TiAlN coating. When the thickness of AlON layer is bigger than 0.81 nm, the hardness decreases with thickness of AlON layer. The scratch resistance and abrasion resistance are best when the thickness of AlON layer is 0.81 nm.

Stress-Strain Behaviors of End-Crosslinked Elastomer of Quasi-Ideal Random 3,3-Diazidomethyloxetane-Tetrahydrofuran Copolyether

ZHAI Jin-xian, ZHAO Han-peng, GAN Xiao-dong, GUO Xiao-yan

2018, 38(12): 1302-1307. doi:10.15918/j.tbit1001-0645.2018.12.015

Abstract(920) PDF(422)

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The stress stain behaviors of polymers are closely related to the aggregation evolution in the course of strain process, while the study on strain-induced crystallization is mainly focused on the field of homopolymers, polyesters and so on. In this paper, taking hydroxyl terminated 3,3-diazidomethyloxetane(BAMO), tetrahydrofuran(THF) equal molar ratio quasi-ideal random copolyether of poly (3,3-diazidomethyloxetane-co-tetrahydrofuran) (PBT) as a prepolymer, the end-crosslinked PBT elastomer was prepared by a carbmate reaction. The test results of mechanical properties show that, both the stress and strain of the elastomer can monotonously increase with the decreasing of temperature, which rise up to 16.2 MPa, 740% at -40℃ from 0.72 MPa, 72% at 60℃. Therein, the stresses and strains can sharply increase with the decreasing of temperature below -20℃. The analysis of the aggregation evolution of PBT elastomer demonstrated that, the crystallization of BAMO micro-blocks existing in PBT strands is inducted at strain of 320% at -40℃ because of the strand orientation in strain direction and decreasing configuration entropy, which can enforce the interaction among strands and improve the mechanical properties of PBT elastomers. Cyclic tensile tests with a constant strain show that, the stresses gradually decrease with increasing round times, and it strongly depends on the effective strand density of PBT elastomer before test.

Influence of Heating Oxidation on Activity of Micron-Sized Mg-Al Alloy Powders

LIU Yang, REN Hui, SUN Ya-lun, JIAO Qing-jie

2018, 38(12): 1308-1313. doi:10.15918/j.tbit1001-0645.2018.12.016

Abstract(761) PDF(334)

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In order to find out the influence of heating oxidation on the activation change of the micron-sized Mg-Al alloy powder, the effect of particle size and Al/Mg ratio on the activity of the alloy at 71℃ was investigated. And the variation of oxide shell thickness was calculated at the same time. The particle size, morphology and composition of the atomized micron aluminum-magnesium alloy powder were tested by the laser particle size analyzer, the scanning electron microscope, the energy dispersive spectrometer and the X-ray transmission scanning. The gas volumetric method was used to measure the activity of the alloy powder after the thermal oxidation test. The results show that the activities of the atomized micron Al-Mg alloy powder decreased with the increase of particle size and decreased with the increase of Al-Mg-Al alloy ratio at 71℃. The activities of the Al-Mg alloy powder remained almost stable after 24 hours of oxidation.

Design and Operation of Biotreatment System for Space Wastewater and Analysis of Microbial Community Composition

GAO Hai-jun, YANG Yi-fei, GUO Hao

2018, 38(12): 1314-1320. doi:10.15918/j.tbit1001-0645.2018.12.017

Abstract(651) PDF(358)

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Wastewater recycling is one of key technologies for the environmental control and life support system (ECLSS). In this paper,a biological treatment system (BTS) was designed,consisting of two sequencing batch reactor (SBR),an oxygen supplier,a detecting module,and a controlling module. The hygiene wastewater and urine could be treated simultaneously by the system designed,and the effluent water could be used as nutrition solution. When treatment system was under stable operation,the removal rate of chemical oxygen demand (COD) and urea nitrogen reached 99.34%,87.2%,respectively,and the nitrate concentration in effluent water was 1 626.7 mg/L. The composition of microbial community in SBR was analyzed,finding that more than 73.3% of the microorganisms belong to Pseudomonas spp. and Arenimonas spp. in the hygiene wastewater bioreactor,and more than 48.8% of the microorganisms belong to Thauera spp.,Nitrosomonas spp.,and Comamonas spp. in the urine wastewater bioreactor. These microorganisms can play an important role in stabilizing of the BTS. This study provides a theoretical basis for application of BTS for treatment of space wastewater.

2018, 38(12): 1321-1338.

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