Table of Content

30 September 2017, Volume 38 Issue 9

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Contents

2017, 38(9):  0. 

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Paper

Research on Critical Open and Close Pressures of an Oil Discharge Valve for High Speed Wet Shifting Clutch

LOU Wei-peng, ZHENG Chang-song, LI He-yan, CHEN Jian-wen, ZHANG Zhou-li, MA Yuan

2017, 38(9):  1665-1672.  doi:10.3969/j.issn.1000-1093.2017.09.001

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For the imperfect discharge of oil in the piston chamber during the rotation of wet clutch at a high speed, a centrifugal oil discharge valve structure is researched. A mathematical model of oil discharge valve is established based on the force analysis, and the movement process of steel ball in oil discharge valve is analyzed. A test system for wet clutch system with oil discharge valve is developed. The critical open and close pressures of the oil discharge valve are studied through experiment. The simulated and experimental results show that the oil discharge valve can effectively discharge the remaining oil in the piston chamber when the wet clutch separates at a high speed, and the critical open and close pressure features of the oil discharge valve are obtained. The critical open and close pressures increase with the increase in the tilting angle of valve body, α, and the radius of steel ball, r_b . According to the changing feature, a computing method for calculating α and r_b from the minimum value of critical open pressure and the maximum value of critical close pressure is proposed. Key

Research on Wear Model for Cylinder Liners in Vehicle Diesel Engines under Dynamic Load

WANG Xian-cheng, YANG Shao-qing, MA Ning, ZHAO Wen-zhu

2017, 38(9):  1673-1680.  doi:10.3969/j.issn.1000-1093.2017.09.002

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In order to realize the numerical simulation on wear of diesel engine cylinder liner under dynamic load, the model and simplified mechanism of dynamic wear of cylinder liner are determined and presented based on the analysis of surface morphology of cylinder liner in overhaul diesel engine. A common expression of wearing depth is derived based on Archard adhesive wear model and two-body abrasive wear model. The response surface model is used to establish the numerical relationship between wear coefficient and dynamic load by analyzing the wear experimental data. The wear calculation model is verified by two groups of wear experiments under alternate loads. The test calculated results show that the maximum calculation error of wear mass is 6.15%, and the proposed model has reliable accuracy. Key

Image Detection Method for Tank and Armored Targets Based on Hierarchical Multi-scale Convolution Feature Extraction

SUN Hao-ze, CHANG Tian-qing, WANG Quan-dong, KONG De-peng, DAI Wen-jun

2017, 38(9):  1681-1691.  doi:10.3969/j.issn.1000-1093.2017.09.003

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A target detection method based on hierarchical multi-scale convolution feature extraction is proposed for the image detection of tank and armored targets. The idea of transfer learning is used to mo-dify and fine-tune the structure and parameters of VGG-16 network according to the target detection task, and the region proposal network and the detection sub-network are combined to realize the accurate detection of targets. For the region proposal network, the multi-scale proposals are extracted from the convolution feature maps of different resolutions to enhance the detection capability of small targets. For the object detection sub-network, the feature maps with high-resolution convolution are used to extract the targets, and an upsampling layer is added to enhance the resolution of the feature maps. With the help of multi-scale training and hard negative sample mining, the proposed method achieves the excellent results in the tank and armored target data set, and its detection accuracy and speed are better than the those of current mainstream detection methods. Key

Simulation and Measurement of Surface Transient Temperature Field of High-speed Current-carrying Armature

ZHANG Yu-yan, SUN Sha-sha, WANG Zhen-chun, CAO Hai-yao, ZHAN Zai-ji

2017, 38(9):  1692-1698.  doi:10.3969/j.issn.1000-1093.2017.09.004

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The high-speed sliding electrical contact leads to the friction and wear problems under special conditions. The transient temperature rise between the armature and the rail is a main factor to cause the material failure in the condition of big current. In order to study the factors to cause the temperature rise of armature, a two-dimensional finite element model of friction pair is established based on the theory of heat transfer, and the method for controlling the single variable is used to study the influence rule of simulation parameters on the armature temperature rise. The results show that the maximum temperature of armature increases with the increase in current, sliding distance and friction coefficient of contact surface. The maximum temperature varies in a “U” trend with the increase in the contact pressure. On this basis, the surface temperature measurement experiment of electrical contact element was conducted. The experimental results are consistent basically with the theoretical analysis results, which shows the effectiveness of the simulation model. This research achievement is expected to provide a technique basis for how to select the appropriate material of the contact pair, reduce the temperature rise, and improve the electrical contact property. Key

Optimal Fire Distribution of a Rocket Launcher against Area Target

LI Chen-ming， HUAN Chao， SHI Huai-long

2017, 38(9):  1699-1704.  doi:10.3969/j.issn.1000-1093.2017.09.005

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An optimal fire distribution method based on distributed firing efficiency evaluation is proposed to improve the firing efficiency of a rocket launcher. The models of firing efficiency evaluation and fire distribution are established. The mean relative damage area is considered as the index of firing efficiency evaluation, and the maximal firing efficiency is considered as the object function. The firing point and coordinate could be calculated by integrating the microgrid of area target. Two firing methods, i.e., single point firing and distributed multi-point firing, are designed for the calculation of firing efficiency. The calculated results show that the firing efficiencies of both methods increase with the increase in ammunition consumption, and the firing efficiency of optimal fire distribution method is 17.28% higher than that of single point firing method. Key

Influence of Boattail on the Magnus Effect of Spinning Non-finned Projectile at Small Angles of Attack

LEI Juan-mian, ZHANG Jia-wei, TAN Zhao-ming

2017, 38(9):  1705-1715.  doi:10.3969/j.issn.1000-1093.2017.09.006

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In order to study the influence of boattail on the Magnus effect of spinning projectile at small angles of attack, the configurations with various boattail angles (θt ) and lengths (L_t/D) are numerically simulated. The variations of the aerodynamic force and moment with Ma, θ_t and L_t/D are obtained. According to the aerodynamic characteristics and flow field structure, the effects of boattail on Magnus effect are studied in details，and the mechanism of the Magnus effect for spinning projectile is analyzed. The results show that component of Magnus force along -z direction increases with θ_t and L_t/D due to the asymmetric distortion of the boundary layer. Meanwhile, the force along z-direction due to the asymmetric circumferential shear stress distortion decreases gradually with θ_t and L_t/D, while increasing with Ma. The force along -z direction due to the asymmetric distortion of axial and circumferential pressures increases with θ_t , L_t/D, and Ma for Ma≥1, while decreasing with Ma for Ma<1. Key

Jamming Mechanism of Frequency Sweep Jamming to FM Doppler Fuze

LI Ze, YAN Xiao-peng, LI Ping, HAO Xin-hong, WANG Jian-tao

2017, 38(9):  1716-1722.  doi:10.3969/j.issn.1000-1093.2017.09.007

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In order to reveal the jamming mechanism of frequency sweep jamming to FM Doppler fuze, the response of FM Doppler fuze under the condition of frequency sweep jamming is deduced based on the analysis of the operational principle of FM Doppler fuze and the frequency sweep jamming signal feature. The jamming mechanism of frequency sweep jamming to FM Doppler fuze is elucidated, and the simulation analysis and experimental verification are carried out. Theoretical derivation, simulation analysis and experiment indicate that, compared with single-frequency jamming, frequency sweep jamming is fault-tolerant, and can successfully jam the FM Doppler fuze by reasonably setting the sweeping parameters; but its jamming effect will get worse when the FM Doppler fuze employs the strict logic timing judgment between different harmonics. Key

Experimental Research on Dynamic Mechanical Behavior of TC18 Titanium Alloy under Medium and High Strain Rates

RAN Chun， CHEN Peng-wan, LI Ling, ZHANG Wang-feng

2017, 38(9):  1723-1728.  doi:10.3969/j.issn.1000-1093.2017.09.008

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Strain and strain rate are two important factors that affect the mechanical behavior of materials, and the split Hopkinson pressure bar (SHPB) technique is one of the effective ways to realize different strain and strain rate loading conditions. To study the plastic deformation and fracture behavior of TC18 titanium alloy under dynamic loading (ranging from 300 to 3 000 s^-1), a series of dynamic compression tests on TC18 titanium alloy have been performed by means of SHPB technique at room temperature. The different strain and strain rate loading conditions are realized by changing the length and velocity of the striker. Macro true stress-true strain curves are obtained under different strain rate loading, so are the true stress-true strain curves under the same strain rate with different strain loading conditions. The effects of strain hardening and strain rate hardening on the dynamic mechanical properties of TC18 titanium alloy are discussed. Results indicate that the collapse of specimen occurs along a plane inclined at an angle of about 45° to the compression axis, namely, shear failure is the main failure mechanism for TC18 titanium alloy under compression loading at room temperature, and it is dependent on strain and strain rate; the higher the strain rate is, the larger the flow stress (or yield stress) of TC18 titanium alloy is, therefore, the material shows clearly evident strain rate hardening effect; and the analyses of microstructure and fracture morphology show that adiabatic shear bands are the precursor to the crack formation and fracture.Key

Mini Momentum Probe Technique for Diagnosis of Micro-spall Fracture of Material

CHEN Hao-yu, HONG Ren-kai, CHEN Yong-tao, ZHANG Shi-wen, REN Guo-wu, MO Jun-jie

2017, 38(9):  1729-1735.  doi:10.3969/j.issn.1000-1093.2017.09.009

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A mini momentum probe is designed to diagnose the micro-spall fractures of material. On the basis of traditional momentum sensor, the structure of the sensing interface and protective film is improved, and the numerical simulation and joint diagnosis experiment technology are used to research the speed measurement results of mini momentum probe. Research result shows that the improved momentum probe can be used to obtain steady high quality signals, and the test duration can be extended; and the probe miniaturization leads to a deviation of measured speeds at some time intervals, but the measured speeds before the first speed peak time are credible, and can be used for the quantitative diagnosis of spatial density distribution of micro-spall fracture of material.Key

Study of Anti-blasting Ability of Damaged Underground Arch Structure after Earthquake

TANG Ting, ZHOU Jian-nan

2017, 38(9):  1736-1744.  doi:10.3969/j.issn.1000-1093.2017.09.010

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The evaluation of anti-blasting ability of underground structures has become a new research subject since earthquake can seriously damage the underground structures. A semicircular arch structure with radius of arch of 3.0 m and height of side wall of 3.0 m is simulated, and seven kinds of cracks at different locations are presumed. TrueGrid is used to construct a mesh model, and then the anti-blasting ability of underground arch structure is numerically simulated by LS-DYNA. The results show that the anti-blasting ability of underground arch structure with a crack is dropped by more than 50%. The anti-blasting ability of underground arch structure is affected by the location of cracks. The cracks between floor and side wall have the greatest effects on its anti-blasting ability and the cracks in arch crown have the least effects on its anti-blasting ability. The anti-blasting ability of arch structure with multi-cracks is not obviously different to that of arch structure with a single crack, and the anti-blasting ability is equal to the least value of anti-blasting ability when the cracks exist singly. Key

Identification of Damage Modes of Concrete under Compressive Loading Based on Wavelet Transform

WANG Zong-lian, REN Hui-lan, NING Jian-guo

2017, 38(9):  1745-1753.  doi:10.3969/j.issn.1000-1093.2017.09.011

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In order to acquire the physical information about the evolution of microcraks in concrete in real time, three typical types of acoustic emission (AE) signals are identified by the wavelet transform of experimentally collected AE signals.The whole compressive fracture process of concrete is divided into four stages,i.e., microvoid compressive closure, crack initiation, crack growth and crack coalescence, on the basis of the event density fluctuation of AE signals andthe fracture theory of brittle materials. Based on the inverse proportional relationship between the frequency of AE signal and crack size, and the distribution characteristics of the three types of AE signals at four fracture stages, the AE signals are associated with crack initiation, crack growth (or microvoid compressive closure) and crack coalescence, respectively. The experimental results show that the rise times and frequencies of AE signals caused by crack initiation, crack growth (or microvoid compressive closure) and crack coalescence increase in turns and decrease gradually, respectively, which conform to the strain energy release theory. Key

Time-domain Correlation Algorithm of Cognitive Frequency Hopping Based on Power Spectrum Cancellation

LI Tong, MIAO Cheng-lin, LYU Jun

2017, 38(9):  1754-1760.  doi:10.3969/j.issn.1000-1093.2017.09.012

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Cognitive frequency hopping technology is to apply cognitive radio to frequency hopping communication. The spectrum hole in cognitive frequency hopping spectrum can be detected effectively to avoid the collision of frequency points and improve the spectral efficiency to update the frequency hopping points. The time-domain correlation algorithm in spectrum detection technology for cognitive radio has some defects in anti-interference, universality and real-time performance due to the existence of noise and primary signals. A time-domain correlation algorithm based on power spectrum cancellation is proposed to detect the cognitive frequency hopping spectrum. The proposed algorithm can be used to improve the detection probability of signals. Moreover, it can overcome the noise uncertainty and restrain the primary signals. Theoretical analysis and computer simulation demonstrate that the time-domain correlation algorithm based on power spectrum cancellation is superior to traditional time-domain correlation algorithm. Key

Task Scheduling of Phased Array Radar Based on Hybrid Adaptive Genetic Algorithm

ZHANG Hao-wei, XIE Jun-wei, ZHANG Zhao-jian, ZONG Bin-feng, CHEN Tang-jun

2017, 38(9):  1761-1770.  doi:10.3969/j.issn.1000-1093.2017.09.013

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A hybrid adaptive genetic algorithm is proposed for the task scheduling of phased array radar. An optimal scheduling model for phased array radar is established. The performance and efficiency of the algorithm are improved by optimizing the initial population by the chaos theory, adopting the selection strategy of elite reservation and mixed ranking, and designing the adaptive crossover and mutation operators. A heuristic pulse interleaving algorithm is presented based on the adaptive genetic algorithm. It could utilize the waiting period in a task to execute the transmitting period or receiving period of other task. The simulated results demonstrate that the proposed algorithm provides better results and search solutions more quickly than the genetic algorithm. Moreover, compared with the heuristic scheduling algorithm, the proposed algorithm improves the scheduling success ratio, time utilization ratio and high value ratio, and decreases the average time shift ratio efficiently. Key

Research on Infrared Dim-small Target Tracking Algorithm with Template Sliding Confidence Constraint

ZENG Yi-liang, LAN Jin-hui, ZOU Jin-lin

2017, 38(9):  1771-1778.  doi:10.3969/j.issn.1000-1093.2017.09.014

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The infrared dim-small target has a small portion of image pixel and low SNR, which makes it difficult to detect and track the target especially in noise and clutter. A dim-small target tracking method with fixed template sliding confidence constraint, on the basis of the fast adaptive median filter to suppress the infrared background, is presented. A prediction of trajectory with orthogonal transformation and confidence region is proposed. Weighted parameters are used to enhance the convergence of target function and the prediction accuracy of the next position. The size of sliding search window is calculated from the position difference of the adjacent points on trajectory to search the matched feature point with the predicted position in the next frame and make further parallel processing. The trajectory sliding confidence is used to verify the authenticity of trajectory and update the target trajectory for accurate tracking. The proposed algorithm is tested with infrared dim-small target video. The results show that the proposed method shows better performance in target tracking with lower mean square error deviation and mean square error. Furthermore, the good performance of noise elimination and image information protection also verifies the effectiveness of the algorithm. Key

Novel Target Direction-of-arrival Estimation Method for Underwater Small-scale Moving Array

GUO Tuo, WANG Ying-min, ZHANG Li-chen

2017, 38(9):  1779-1785.  doi:10.3969/j.issn.1000-1093.2017.09.015

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The underwater small-scale moving array is limited by its small aperture and sample size for direction of arrival (DOA) estimation of coherent target. The passive synthetic aperture technique is used to solve the problem of insufficient aperture. The spectral separation of sample covariance matrix is stu-died in the case of coherent target. A DOA estimation method for coherent target based on main feature space is proposed, which uses small snapshots. In the simulation, the proposed method can still distinguish the four targets correctly when the ratio of the number of sensors to the number of samples is 5; in the water tank experiment, the above ratio is 4.8, and it can identify three adjacent targets clearly. The proposed method can achieve better resolution for coherent targets in small samples, which meets the application needs of small-scale motions array of targeting, and requires no priori information of signal source number.Key

Spatial Curvilinear Path Following Control of Underactuated AUV

MIAO Jian-ming, WANG Shao-ping, FAN Lei, LI Yuan

2017, 38(9):  1786-1796.  doi:10.3969/j.issn.1000-1093.2017.09.016

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Based on the modified back-stepping technique, a simple and robust spatial curvilinear path following controller for the underactuated autonomous underwater vehicles (AUVs) with model uncertainties and input saturation is presented. A path following error dynamics model is constructed in a moving Serret-Frenet frame, and the kinematic controller and dynamic controller are developed based on line-of-sight (LOS) guidance algorithm and virtual moving target method. Differing from the traditional integrator backstepping technique, the proposed method is to introduce the integral tracking errors into the controller design to improve the robustness against the uncertainties. The dynamic model is used to solve the non-causal form caused by the coupled underactuated degrees. The nonlinear tracking differentiators (NTDs) are employed to construct the numerical solution of differential virtual control commands to tackle the problem of “explosion of terms” in the traditional back-stepping process, and the dynamic controller expressions are simplified. Simulations demonstrate that the designed controller realizes the spatial curvilinear path following control of underactuated AUV with model parameter uncertainties and input saturation, and its accuracy and robustness are more excellent than those of the traditional back-stepping control. Key

Influence of Structural Interspace on Anti-penetration Performance of Para-aramid Fiber-reinforced Composite Armor System

LI Mao， HOU Hai-liang， ZHU Xi， HUANG Xiao-ming， LI Dian， CHEN Chang-hai， HU Nian-ming

2017, 38(9):  1797-1805.  doi:10.3969/j.issn.1000-1093.2017.09.017

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Three different composite armor systems with 50 mm width or no interspace between different parts were designed to simulate sandwich bulkhead, in which 5 mm-thick steel plate and 10 mm-thick steel plate are used as front and back plates, respectively, and the para-aramid fiber-reinforced plate (AFRP) with areal density of about 60 kg/m² is used as sandwich core. Ballistic experiments are carried out to study the anti-penetration performance of the three para-aramid fiber-reinforced composite armor systems subjected to normal impact by 40 g cylindrical fragments at about 1 630 m/s. The failure modes of surface plate and sandwich core of the composite armor system are presented, the anti-penetration mechanisms of the composite armor systems are analyzed, and the anti-penetration performances of the three composite armor systems are compared. The experimental results show that interspace between different parts has significant effect on the failure modes of AFRP and anti-penetration performance of composite armor system. Key

Estimation Method for Instantaneous Frequency of Echo Signal of Projectile in Bore

WANG Jian, HAN Yan, WANG Li-ming, ZHANG Pi-zhuang, CHEN Ping

2017, 38(9):  1806-1814.  doi:10.3969/j.issn.1000-1093.2017.09.018

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The microwave interferometer can obtain the Doppler echo signal containing interior ballistic motion information. In order to estimate the instantaneous frequency of echo signal effectively, a mathematical model of motion curve of projectile in bore is established based on polynomial fitting. The methods of short-time Fourier transform, Wigner-Ville distribution, polynomial chirplet transform (PCT) are used to analyze the simulation echo signals of projectiles with different noise and experimental echo signals of projectiles, respectively. The results show that the PCT method which uses transform kernel based on polynomial frequency modulated wavelet has the best time-frequency concentration and accuracy of instantaneous frequency estimation (IFE) and good anti-interference ability compared with the other methods. The research results show that the PCT method is suitable for IFE of projectile's signals. Key

Weapon System Reliability Qualification Test Scheme Based on Reliability Growth

LI Da-wei， RUAN Min-zhi， YOU Kun

2017, 38(9):  1815-1821.  doi:10.3969/j.issn.1000-1093.2017.09.019

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The test samples are limited for reliability qualification test of weapon system in most cases, therefore more engineering tests are difficult to be implemented. In order to evaluate fully the reliability index of weapon system, the reliability growth progress is described by using discrete AMSAA model, and the point estimation of reliability is obtained. The determination method of prior distribution, which is relatively objective and conservative, is presented by comparing the evaluated result of reliability growth test and the specified value of development general requirements. The determination thought and method of reliability qualification test scheme are proposed based on Bayes theory. The operating steps of determination method are illustrated by taking a weapon for example. It also demonstrates that the proposed method is available for engineering. The numerical simulations show that the determination method can be used to reduce the number of tests effetely on the precondition of test evaluation requirements. Key

Analysis of Travel Performance of Pneumatic Tire on Unpaved Road by Discrete-finite Element Method

ZHENG Zu-mei， ZANG Meng-yan， ZENG Hai-yang

2017, 38(9):  1822-1829.  doi:10.3969/j.issn.1000-1093.2017.09.020

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A combined discrete-finite element method is proposed to simulate the interaction between the pneumatic tire and the granular sand, where the continuum based finite element method is used for the pneumatic tire and the discrete element method is used for the free-flowing particles. Interactions between the pneumatic tire and the sand are described by using a contact detection algorithm. A PID-controller model based on automatic control theory is applied on the base of forced-slip principle to ascertain the loading conditions of tire. A corresponding numerical analysis code is implemented into the in-house developed code, named ORV-SAND, to simulate the tire travel performance. Travel parameters of pneumatic tires with different tread patterns (i.e. smooth and block), such as gross tractive force, drawbar pull, running resistance and sinkage, are investigated under different slip conditions. The simulated results are basically corresponded with the experimental results. It is demonstrated that the proposed discrete-finite element method and the numerical method have enormous potential in studying the interaction between the pneumatic tire and the granular sand. Key

Research Notes

Load Spectrum Compiling for Transmission Shaft of Tracked Vehicle Based on Kernel Density Estimation

LIU Hai-ou, ZHANG Wen-sheng, XU Yi, ZHAO Zi-ye

2017, 38(9):  1830-1838.  doi:10.3969/j.issn.1000-1093.2017.09.021

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For establishing the high reliability load spectrum for transmission shaft of military tracked vehicle on the typical road, the torque and relevant vehicle data similar to that in real service conditions was collected through vehicle experiments, and the confidence level of load data samples was calculated based on the criteria of least testing times. A load spectrum compiling procedure is designed based on 2-D kernel density estimation on account of the irregular 2-D distribution of amplitude and mean values in test load data. In the load spectrum compiling procedure, two times of rain-flow counting are adopted: the first rain-flow counting result is used to deduce the extrema of amplitude and mean values, and the second rain-flow counting result is used to extrapolate the kernel density. This compiling procedure can not only obtain better fitting of amplitude and mean distribution, but also achieve the reasonable extrapolation of the experimental rain-flow matrix. Goodman equation and the equivalent damage conversion method are used to derive 8-level program block load spectrum from 2-D load spectrum, and a loading method for the combination of torque and rotational speed is presented. 0.8 times of eighth amplitude are chosen as the value of small load from the perspective of fatigue damage, and total cycles are decreased by 99.33% while total damage is decreased only by 0.29%, which can accelerate the fatigue loading test. Key

Optimization of Radiator Core Shape of Vehicle Engine Based on CFD

SUO Wen-chao， XU Xiang， GENG Fei

2017, 38(9):  1839-1844.  doi:10.3969/j.issn.1000-1093.2017.09.022

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A radiator air side CFD model and an optimization model of radiator core shape based on CFD are established for reducing the airflow pressure drop and the volume of vehicle engine radiator core to save the cooling fan power and the vehicle engine compartment space. Under the precondition of satisfying the requirement of heat dissipating capacity, the shape of a plate-fin radiator core is optimized based on genetic algorithm by taking the air side pressure drop and the volume of its core as the target functions. The heat dissipation performance of the optimized radiator was verified. The optimized results show that the proposed optimization model is feasible. The primary and secondary sequences of the variables affecting the optimization targets are found by using an orthogonal experimental design method. And the height of radiator core has the most significant influence on the air side pressure drop and the volume of radiator core when the air flow rate is constant. Key

3D Printing of Military Helmet Liner Structure Based on Topology Optimization

JIANG Miao-wen , YAN Jian-zhuo, CHEN Ji-min

2017, 38(9):  1845-1853.  doi:10.3969/j.issn.1000-1093.2017.09.023

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A lightweight design method of military helmet liner structure based on the topology optimization technology is presented for the lightweight design of military helmet. The advantages of 3D printing in the shape of complex structures are taken to set up a lightweight design process for the helmet liner structure, in which includes the computer modeling, numerical simulation, 3D printing, and engineering verification. A topological optimization algorithm based on the minimum potential energy is summarized according to the finite element analysis method. In the design process, the computer-aided design software UG is used to perform 3D modeling for design objects, and the computer-aided analysis software HyperMesh in HyperWorks is used to build a finite element model, and view the displacement results of the topology optimization model whether the design structure meets the constraints through OptiStruct in HyperWorks for the topology optimization. In order to meet the functions of the energy absorption and anticollision, a honeycomb-type energy absorbing structure is added on the side of topologically optimized helmet liner. In experiment, solidThinking Inspire software is used to verify the helmet liner with the honeycomb structure. The simulation shows that the maximum equivalent stresses of Von-Mises before and after topology optimization are similar. The experimental model is tested, and the load capacities of helmets before and after optimization are compared. The experimental results show that, in the case of certain constraints and functional requirements, the purpose of the lightweight design can be achieved, the weight reduction can reach to 17.14%, and the maximum bearing capacity of the topologically optimized structure reaches to 93.72% of the original structure. At the same time, 3D printing technology with numerical simulation can shorten the research and development cycle, and improve manufacturing efficiency. Key

Experimental Research and Optimization of Process Parameters in the Electrical Discharge Machining of Monocrystalline Silicon

XIN Bin， LI Shu-juan， LI Yu-xi

2017, 38(9):  1854-1861.  doi:10.3969/j.issn.1000-1093.2017.09.024

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In order to solve the problem that the material removal rate, the surface roughness and the electrode loss cannot be simultaneously taken into account in electrical discharge machining, the influences of peak current, pulse width and pulse interval on the material removal rate, surface roughness and electrode loss in the electrical discharge machining of P-type monocrystalline silicon are analyzed through central composite design experiments. The response surface method is used to establish a second-order relational model of material removal rate, surface roughness and electrode loss. The results of variance analysis indicate that the proposed model has good fitting degree and adaptability. A process parameter optimization model is established by analyzing the constraints of the actual processing conditions on the process parameters to improve the material removal rate in the electrical discharge machining of monocrystalline silicon, and reduce both the surface roughness and the electrode loss, and the NSGA- II–based algorithm is designed to solve the optimization problems. The average relative errors of validation results of material removal rate, surface roughness and electrode loss under the condition of the optimal solution are 4.9%, 5.2% and 5.7%, respectively, compared with the theoretical optimal values. The verification tests show that the proposed algorithm can achieve the process parameters optimization of silicon materials in the electrical discharge machining. Key

Study of Equipment Material Demand Prediction Method Based on Time-continuous Grey Markov Model

ZHANG Lei, LI Shi-min, ZHU Gang

2017, 38(9):  1862-1866.  doi:10.3969/j.issn.1000-1093.2017.09.025

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The time continuous and state discrete grey Markov model is used to predict the demand of equipment maintenance materials. The state intervals are set according to the changing amplitude and distribution of consumed maintenance materials. The one-step Markov transition matrix is calculated by states transition. Kolmogorov differential equations are used to solve the time functions of state probabilities and establish the prediction equations of state probabilities. The grey positioning coefficient is determined from the probability values of predicted states. The case analysis shows that the prediction accuracy of the improved grey Markov model is higher than those of GM(1, 1) model, traditional grey Markov residual error correction model and grey Markov chain model. Its validity and practicability were proven during the prediction of equipment material demand.Key

Effect of Weave Process of Fabric Liner on Tribological Properties of Self-lubricating Spherical Plain Bearing

QIU Ming， ZHOU Da-wei， PANG Xiao-xu

2017, 38(9):  1867-1872.  doi:10.3969/j.issn.1000-1093.2017.09.026

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Two kinds of self-lubricating fabric liner made of polytetrafluoroethylene (PTFE)/Kevlar fiber were prepared by using different weave processes. The tribological properties of self-lubricating spherical plain bearing with two kinds of liners are studied under certain conditions， and the worn surface morpho-logies of the liners and the counterfaces are investigated under a scanning electron microscope (SEM) and an energy dispersive spectrometer (EDS). The results show that spherical plain bearings with the liner A (two kinds of fibers were mixed into the yarn firstly， and they were woven into fabric together with Kevlar fibers) present poor tribological properties under the condition of high frequency and heavy load. The serious fatigue wear and adhesive wear occurred on the worn surfaces of the liner A. However，the spherical plain bearings with the liner B（PTFE and Kevlar fibers were woven into fabric， and the friction surface was rich in PTFE fibers and the bonding surface was rich in Kevlar fibers）present better tribological properties compared with the liner A. And the wear resistance of the self-lubricating spherical plain bearings is significantly improved. Slight adhesive wear and abrasive wear occurred on the worn surfaces of the liner B. So the weave process for the liner has a great influence on the tribological properties of spherical plain bearings. Key