Advanced Search

2007 Vol. 33, No. 07

  Previous Issue | Next Issue 
Display Method:
Orbital maintenance and control of spacecraft fly-around with finite-thrust
Shi Peng, Li Baojun, Zhao Yushan
2007, 33(07): 757-760.
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 1005
Abstract:
Based on the linear dynamics model, the relevant issues of orbital maintenance and control of spacecraft fly-around with finite-thrust was studied. Firstly, aimed at the problem of orbital control of spacecraft fly-around, the exact dynamics model was derived and the linear dynamics equation was presented. Secondly, based on the linear quadratic optimal control theory, the feedback control system for fly-around orbit was designed. To realize finite-thrust, a limited nonlinear function to restrict the control acceleration was presented. The numerical simulation show the control system has asymptotic stability, faster convergence rate and higher control accuracy. Lastly, from calculating the engine-s working time of different relative position errors, estimate the cost of fuel for orbit control and maintenance.
Adaptive fuzzy sliding mode attitude control for large angle slew maneuvering of flexible satellite
Chen Yu, Dong Chaoyang, Wang Qing, Zhang Minglian
2007, 33(07): 761-764.
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 985
Abstract:
An adaptive fuzzy sliding mode control was proposed for the attitude stabilization of flexible satellite during large angle slew maneuvering. The dynamic model of the satellite with flexible appendages was derived by Lagrange equation. The sliding mode control was designed to make the state of system reach sliding mode surface in finite time. The adaptive fuzzy system was used to approximate the strong couple nonlinear function between rigid central body and flexible appendage dynamics during large angle slew maneuvering. The sign function was replaced by the saturation function so as to attenuate the chattering phenomena and avoid exciting higher frequency elastic mode. The fuzzy rules were employed to gain the size of boundary layer. Simulation results show that not only attitude stabilization of satellite with high precision is achieved, but also the elastic vibration of flexible appendage is suppressed effectively, and the system is robustness against system uncertainties and environmental disturbances.
Simulation and analysis of pilots′ manipulation based on SimMechanics
Wang Rui, Zhuang Damin
2007, 33(07): 765-768.
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 1308
Abstract:
According to human dimensions of chinese male pilot and the chinese manhood anthropometric data, the rigid model for the pilot′s upper limbs was established. Referring to the requirement about cabin layout in GJB and flight quality criterion in HB, Two operation movements of the pilot, pulling and pushing stick, were simulated using SimMechannics which is a simulation module of Matlab. Analysis type is inverse dynamics. When work load and athletic rule of end effectors are given, the actual joints′ torques could be ciphered out by simulation, and then the three-dimensional comfortable manipulation area could be acquired according to given comfort criterion. The result suggests that workload isn′t changed, but the calculated area in the case of pushing stick is different from that of pulling stick. Therefore, there is a correlation between manipulation characters and the range of comfortable manipulation area. When dealing with pilots′ ergonomics evaluation or optimizing cockpit layout design, It is necessary to analyze matters with an eye to manipulation characters.
Moving-mass attitude control law based on genetic algorithm
Qin Li, Yang Ming, Guo Qing
2007, 33(07): 769-772.
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 939
Abstract:
The ability of the moving-mass attitude control system was investigated to control a vehicle with three-axial stabilization in intra-atmospheric space. And the general nonlinear motion equations with three internal moving masses were provided. For the fast self-learning and adaptive capacities of radial basis function (RBF) networks, used it as the controller to calculate the moving masses′ position. With the coordination of the control, the masses were positioned independently to generate the modest attitude corrections for the vehicle. At the same time, the weights of the networks were optimized by genetic algorithm (GA).At last, the influence to the system performance caused by the moving masses′ motion was discussed and the system stability was analyzed. Simulation results show that the system stabilization can be satisfied to realize efficiently attitude adjustment for the vehicle, and the dynamic performances of the system are improved.
Mixing enhancement in round jet exhaust using pulsed blowing: 3-D numerical simulations
Li Jiajun, Eriqitai
2007, 33(07): 773-776.
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 892
Abstract:
The 3-D flow fields of the round jets with pulsed jet blowing for mixing enhancement were simulated numerically. This work uses a technique for injecting high frequency and high intensity signals into subsonic shear layers for the purpose of jet mixing enhancement. The finite volume method, RNG k-ε turbulence model were employed to solve N-S equation. Numerical simulations of low Mach 0.23 and high Mach number 0.9 jets exhausting into fluid were conducted. Three cases are considered in detail: a unforced case and two cases that are forced with flapping modes at Strouhal numbers 0.2 and 0.4.These simulations show that pulsed jet blowing at either frequency causes the jet to expand rapidly in the plane parallel with the actuators and to contract in the plane perpendicular to the actuators, the intensity of motion and associated mixing are higher when the excitation Strouhal number is around 0.2, and small injection flow rates can provide tremendous increases in velocity decay rates.
Second generation wavelet packet construction and aircraft engine weak damage identification
Jiang Hongkai, Wang Zhongsheng
2007, 33(07): 777-780.
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 871
Abstract:
To identify weak damage of aircraft engine rolling bearing, a new method to construct second generation wavelet packet was presented. In this method, the decomposition and reconstruction procedures of second generation packet were designed, and the second generation packet operators which lock on to the dominant signal structure were calculated. The vibration signal of rolling bearing was decomposed with second generation wavelet packet, and the signal at each frequency band was reconstructed. The reconstruction signals were demodulated with Hilbert transform, and envelope spectrum at each band was obtained. The dB values of fault feature frequency components corresponding envelope spectrum at each frequency band were calculated, and the maximal dB value of fault feature frequency components was extracted to identify damage of rolling bearing. The proposed damage identification method was used to analyze simulation signal and experimental signal from a rolling bearing with weak outer race damage, and results confirm the advantages of second generation wavelet packet for rolling bearing damage identification.
Aerodynamic characteristic analysis of high-aspect ratio elastic wing
Ma Tielin, Ma Dongli, Zhang Hua
2007, 33(07): 781-784.
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 2084
Abstract:
The aerodynamic performance and flying safety of long-endurance unmanned aerial vehicle (UAV) are largely affected by the aeroelastic distortion of its high-aspect ratio wing. High-aspect ratio wing of UAV is bended and twisted by the air load during flight and couldn-t be treated as a traditional rigid wing. The effect of static aeroelastic distortion to the aerodynamic characteristic for a real high-aspect ratio sweepforward wing of composite material under different load statuses was analyzed. The integrated design method combined aerodynamic with structural was adopted in this analysis using associated computational fluid dynamics (CFD) program FLUENT and computational structual dynamics (CSD) program NASTRAN. The result shows a lift-drag ratio drop and a remarkable increase on rolling and yawing moments which affect the portrait and lateral aerodynamic performance of UAV negatively. The result also shows that the CFD/CSD coupling computational methodology is reliable to be used aerodynamic-structural integrated design of elastic wing.
Discrete ray path tracing on aircraft
Wang Bingqie, Su Donglin, Zhang Xiaolei
2007, 33(07): 785-788.
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 1160
Abstract:
A novel diffraction ray tracing method on convex surfaces of electronic warfare special aircraft was investigated. Quickly-3D-model of aircraft was carried out, and surface grids were meshed on the model to provide surface discrete grids data. Enough points can be achieved by minutely modeling or interpolating splines and nodes. Base on tracing area was selected and grid nodes were managed, according to Fermat principle, the length of geodesic path between the source and incept point can be calculated quickly and veraciously with the method of improved dynamic programming on the platform surface discrete grids served as. Then, discrete geometrical theory of diffraction(GTD) and uniform geometrical theory of diffraction(UTD) ray tracing on aircraft was realized with the method of recursive method. This work provided an approach for quickly analyzing antenna isolation with numerical method.
Numerical simulation of converging-diverging nozzle flow in pulse detonation rocket engine
Li Qiang, Fan Wei, Yan Chuanjun
2007, 33(07): 789-792.
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 974
Abstract:
Exhaust nozzle is one of the key components of pulse detonation rocket engine (PDRE). Exhaust nozzle can be used to improve the propulsion performance of PDRE. Method of characteristic (MOC) was used to calculate one-dimensional CJ(Chapman-Jouguet)detonation wave propagating in the ideal detonation tube. The unsteady blowdown process after the CJ detonation wave reach the exit of detonation tube was two-dimensional axisymmetric numerical simulated. The results of numerical simulation demonstrated the development of the unsteady flow field, and the unsteady waves and vortexes were discussed. Contrary to PDRE without nozzle, the CD nozzle can augment propulsive performance by 18.24%.
Analytical model of aeroelastic stability of hingeless rotor blade with composite flexures
Shi Qinghua, Xiang Jinwu
2007, 33(07): 793-797.
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 891
Abstract:
An analytical model for predicting the aeroelastic behavior of hingeless rotor blade with arbitrary section was presented, and the effect of composite flexures on aeroelastic stability was investigated. The analysis of rotor blade was simplified as a line sectional properties analysis and a nonlinear beam analysis. Sectional properties included the in and out of plane warping deformation and the one-dimensional moderate deformation theory was used for the aeroelastic behavior of composite rotor blade. The quasi-steady strip theory with dynamic inflow effects was used to obtain the aerodynamic loads acting on the blade, based on finite element theory, formulations of hingeless rotor blade system aeroelastic stability calculation was developed. In the present work, the aeroelastic behavior of hingeless rotor blade system with composite flexures was studied. Numerical tests was carried out for the valid of the aeroelastic model. The numerical results show that the structural couplings of the composite flexures has great effects on the aeroelastic stability of the rotor system blade, and based on the relations between aeroelastic stability and ply angle, an advanced composite rotor blade would be obtained.
UT-BLUE filter for target tracking
Wang Wei, Dai Mingqiang, Zhang Zhihua
2007, 33(07): 798-802.
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 899
Abstract:
In tracking maneuvering targets application with radar, target dynamics are usually modeled in the Cartesian coordinates. In the cases target motion model are always very accurate but nonlinear ,while target measurements are directly available in the original sensor coordinates. By means of combinatin of unscented transformation and best linear unbiased filter , a new filter named unscented transformation-best linear unbiased estimator(UT-BLUE) filter was proposed to solve the above nonlinear tracking problem. In this filter, by way of nonlinear target motion model, unscented transformation was first used to predict state of the true target and its covariance, and then they were directly estimated while keeping the measurement error in sensor (polar) coordinate system. Algorithm analysis and simulation were conducted to compare it with extended Kalman filter(EKF) and unscented Kalman filter(UKF) , and results indicate that the new filter is more effective and available.
Fast focused imaging algorithm for circular scanning SAR
Sun Bing, Zhou Yinqing, Li Tianchi, Guo Caihong
2007, 33(07): 803-806.
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 1093
Abstract:
Image formation for circular scanning synthetic aperture radar (CS-SAR) was investigated. The work principle and echo signal model of CS-SAR were described. A focused image algorithm based on spectrum analysis was presented. This focused algorithm was able to correct the range cell migration within each burst echo of CS-SAR, so it was suitable to form high precision image for CS-SAR. The algorithm flow chart and the deducing process of the algorithm for burst data were given, and the whole process flow chart for CS-SAR based on this algorithm was given also. Compared to classic unfocused Doppler beam sharpening (DBS) algorithm, this algorithm has a little more computational loads but much more imaging precision, compared to extended chirp scaling (ECS) algorithm, it has less precision but much less computational loads. It is competent for fast focused imaging for CS-SAR. The computer simulation results validates that this focused algorithm can be used to image accurately for CS-SAR.
Design intelligent carrier tracking loop based on software GPS receiver
Tang Bin, Yu Xiaqiong, Dong Xurong, Zhao Xinshu
2007, 33(07): 807-810.
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 2197
Abstract:
Minimal invasive surgery assisted robot was developed in Robotics Institute in Beijing University of Aeronautics and Astronautics. Based on the requirement of neurological stereotactic surgery, dexterity of the robot was analyzed. Using concept of service sphere and service section, definition of dexterity was proposed at any point inside the workspace of the five degree-of-freedom robot, then, analysis method of workspace dexterity was proposed. Dexterity distribution within the workspace was given using numerical analysis and graphical display, and the result was verified through experiment on the robot physical prototype. With the help of dexterity distribution in workspace, reliable reference can be supplied for surgery operation planning.
Zenith blind zone of two-axis stabilized platform
Dong Xiaomeng, Zhang Ping
2007, 33(07): 811-815.
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 1397
Abstract:
Zenith blind zone is a phenomenon which the line of sight can not track the target when the target maneuvers in the narrow offboresight of the missile. Utilizing the geometrical relation of photoelectric imaging guidance, the rectangular coordinates and polar coordinates stabilized platform were analyzed. Moreover, the models of zenith blind zone for polar coordinates stabilized platform were presented and the reason of this type of zenith blind zone was analyzed. Furthermore, the zenith blind zone for polar coordinates stabilized platform was simulated in three different rate conditions of target maneuver in Simulink environment of Matlab. Finally, a PID control approach based on variable parameters per different areas was proposed. Aiming at a vertical maneuver mode of target, this variable parameters based PID control method was simulated using Matlab in contrast to general PID control. The results show that the zenith blind zone models for polar coordinates stabilized platform conform to the actual situation and the variable parameter based PID control approach can improve the characters of the target tracking.
Robust H∞ control for systems with delayed state and input
Xia Hongwei, Ling Mingxiang, Wen Qiyong, Wang Changhong
2007, 33(07): 816-820.
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 863
Abstract:
The problem of robust H∞ state feedback controller design for the generalized continuous time systems with time-varying delays in states and control inputs and parameter uncertainties residing in a polytope were investigated. A new improved performance criterion for the existence of robust H∞ controller was presented by introducing two slack matrices. Then a H∞ state feedback controller was derived directly from the criterion, which guarantees not only the quadratic stability of the closed-loop systems but also the H∞ norm bound within a predefined level. The newly proposed criterion exhibits a kind of separation between the systems matrices and the positive definite Lyapunov matrices. As a result, the vertex-dependent Lyapunov functions can be adopted to deliver a less conservative result. An iterative algorithm was developed to further refine the sub-optimal controller. Moreover, this contribution addressed an effective method to obtain new criteria with less conservativeness based on existing research results. A numerical example was employed to illustrate the effect of the proposed approach.
Multicast routing algorithms with low tree cost for LEO satellite networks
Cheng Lianzhen, Zhang Jun, Liu Kai
2007, 33(07): 821-825.
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 1672
Abstract:
To resolve the channel resources waste problem of the typical source-based multicast routing algorithm in low earth orbit (LEO) satellite networks, a new core-based shared tree algorithm called the core-cluster combination shared tree (CCST) algorithm and its improved one (i.e. w-CCST algorithm) were proposed. The (w-)CCST algorithm consists of the dynamic approximate center (DAC) core selection method and the (weighted) core-cluster combination multicast routing construction method. The core-cluster combination method takes core node and its nearest group member in hops as initial core-cluster, and extends it to construct entire multicast tree step by step by a shortest path scheme between newly-generated core-cluster and surplus group members, which can greatly improve transport bandwidth utilization. In the w-CCST algorithm, a weighted factor was proposed to decrease end-to-end propagation delay and meanwhile increase tree cost a bit to support some real-time applications with strict delay requirements. Simulation results show that tree cost performance of the CCST algorithm is greatly better than that of other algorithms, while end-to-end propagation delay performance of the w-CCST algorithm is better than that of the CCST algorithm.
Optimization of loading trajectory for skin stretch forming process
Zhang Yanmin, Zhou Xianbin
2007, 33(07): 826-829.
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 1157
Abstract:
Loading trajectory is the key factor in skin stretch forming. First the loading trajectory of double curve skin was designed through the analytic method, then the parameters were changed to the machine-s instructions which were used as design variables. The method of combining finite element analysis and optimization algorithms was proposed to acquire the reasonable loading trajectory. Optimization mathematics model was set up in order to reduce springback and improve the fittability. The reasonable loading trajectory was found through the numerical simulation and sequential quadratic programming optimization algorithm under the restrictive of maximal thickness strain. Experiment was done according to the reasonable loading trajectory. Both numerical simulation and experiment results show that the precision, strain distributing and thickness uniformity of skin are improved greatly.
Multi sheet hydroforming of complicated thin wall part and numerical simulation
Li Tao, Lang Lihui, An Dongyang, Wang Ling
2007, 33(07): 830-833.
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 1472
Abstract:
Sheet hydroforming has proven to be an effective method for manufacturing complicated parts. The multi-sheet hydroforming technology of complicated thin wall aerocraft part was investigated. Effects of key process parameters including the shape of pre-forming punch,corresponding pre-forming depth,and cavity pressure on the forming process of the finally formed parts were explored in multi-hydrodynamic deep drawing by using the finite element numerical simulation methods. Failure types including fracture and wrinkling during sheet hydroforming were discussed. The successful region of the maximal cavity pressure was provided during the forming process of the final formed parts. The measures of controlling forming quality were presented, and process parameters were optimized. According to the results of the numerical simulation, the experimental confirmations were carried on by using the equipment of sheet hydroforming which had been developed independently. It is shown that the results from the simulation are in reasonable agreement with those from experiment.
Analysis of multiple-impact forces between flexible-rods
Tian Ali, Yin Xiaochun
2007, 33(07): 834-837.
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 877
Abstract:
The multiple-impact phenomena usually exist in many engineering structural system and the calculation of impact force is a key problem. The present study is aimed at the calculation method of the impact force of the longitudinal multiple-impact problem. The transient wave response approach was presented to investigate the history of the multiple impact forces based on the theory of transient wave propagation. The wave effect was sufficiently considered. The transient wave response approach could avoid solving the impact force from the strongly nonlinear equation coupled of impact force with impact motions. The flexible system of two flexible rods with longitudinal multiple impacts was investigated accurately in numerical example. The higher the initial impact velocity is, the bigger the impact forces will be. The impact forces in the previous third impact processes increase slowly with the impact number. The phenomena of "sub-impact" can be captured. The present method provides an effective method for reference to further investigate the multiple-impact problem in the more complex flexibility systems and the longtime dynamic behavior.
Design and analysis of a rover mechanism based on the metamorphic principle
Zhang Ketao, Fang Yuefa, Fang Hairong
2007, 33(07): 838-841.
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 1161
Abstract:
A kind of special six-bar spherical metamorphic mechanism was proposed. The configuration transformation was analyzed, and the adjacency matrixes under various metamorphic mechanisms were put forward. According to the mechanism characteristic at its different configuration, the metamorphic mechanism was used in the body design of a rover mechanism. The body can transform the configuration itself, and the robot can take the two manners of locomotion (walking in 4-leg mode, moving in wheeled-vehicle mode.), so the rover mechanism has high capability to adapt planet and other exploration terrain. The design of the novel metamorphic robot was described, and its degree of freedom(DOF) at different configuration was introduced. Some typical configurations were illustrated.
Techniques of machining feature mapping from design-by-feature model
Yu Fangfang, Zheng Guolei, Ren Wenjie, Du Baorui
2007, 33(07): 842-845.
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 1245
Abstract:
To pick up the machined area automatically in numerical control programming, a new methodology for recognizing machining features from a design feature model was presented based on the study about the product modeling method in the design-by-feature systems, product information models (geometric and topological information model, feature relationship model which usually named feature specification tree), the relationships between these two information models, the machining feature class definition in aircraft structure parts, interacting relationships between design features and machining features. By touring the feature specification tree, judging the features- relationships and querying the feature-s surfaces,the feature mapping method from a design-by-feature model constructed the feature attribute adjacency graph (FAAG) and recognized the machining features by matching boundary patterns in the local feature area, then extracted the machined information such as the machined area, the avoided area, the tool approach direction. It can be used to recognize the aircraft wainscots parts.
Processing and microstructure of Al2O3/YAG eutectic ceramic by laser rapid remelting
Su Haijun, Zhang Jun, Liu Lin, Fu Hengzhi
2007, 33(07): 846-850.
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 2102
Abstract:
Laser rapid remelting experiments were conducted on the preparation of Al2O3/YAG eutectic ceramic in-situ composite to investigate the microstructure characteristic and growth behavior under an ultra-high temperature gradient and different laser scanning rates of 0.01~2.0mm/s, and to explore the relationship between the laser processing parameters and the microstructure. The results show that the laser remelted Al2O3/YAG eutectic is composed of irregularly and continuously distributed Al2O3 and YAG phases without grain boundary and any other phase. The volume fraction of Al2O3 is (45.0±2.0)%. The two phases couple each other and complexly interweave, in which the microstructure belongs to the typical lamellar structure of rapidly solidified anomalous eutectic. The eutectic spacing is very small and decreases from about 1~2μm to 0.5μm as the laser scanning rate increases from 0.02~2.0mm/s. The synthetical themal analysis(STA) shows that the eutectic temperature of Al2O3/YAG is 2096K, matching the phase diagram of Al2O3-Y2O3 system.
Impact energy absorption and dynamic viscoelasticity of composites
He Chenghong, Zhang Zuoguang, Li Yubin, Sun Zhijie
2007, 33(07): 851-855.
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 1467
Abstract:
The energy absorptions of composite laminates reinforced respectively by glass fiber, carbon fiber, aramid fiber, and UHMWPE fiber (separately named as GFRP, CFRP, AFRP and DFRP), were investigated under the low velocity impact. The load sensibilities on dynamic viscoelasticity of composite fiber bundles of these four kinds of fibers were analyzed by using the EPLEXOR500 dynamic mechanical thermal analyzer under high loads. The impact tests show that the impact energy absorption is close related to the fiber properties and failure modes. The impact energy absorptions of AFRP and DFRP laminates through ductile failures are much higher than those of GFRP, and CFRP laminates through brittle failures. Dynamic mechanical thermal analysis of composite fiber bundles show the load effects as that storage modulus increase and loss tangents decrease with the increasing static load, while the case is just reverse with the increasing dynamic load. In these effects, the organic fibers exhibit more serious load sensibilities and non-linearity than the inorganic fibers. These four laminates show the same sequence DFRP>AFRP>GFRP>CFRP on energy absorption as the load sensibility of storage modulus or the value of loss tangent of composite fiber bundles. This reflectes the correlation of the macroscopic impact performance and viscoelasticity which is close associated with material microstructure.
PZT nanoparticles synthesized by sol-hydrothermal method and properties
Lin Haibo, Liu Haitao, Wang Fuchi, Cao Maosheng
2007, 33(07): 856-859.
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 1246
Abstract:
PZT nanopowders were fabricated at low temperature by modified sol-hydrothermal method, and the effects of the sintering parameter such as sintering temperature, keeping time on the density, grain size, piezoelectric and dielectric properties of the PZT ceramic were investigated. The results show that the particle size distribution of the PZT nanopowders synthesized 270℃ is homogeneous with pure perovskite structure (20~30nm). The optimal properties of the obtained piezoelectric PZT ceramic sintered at 1150℃ for 2h are planna electromechanical coupling factor: 0.50, mechanical quality factor: 410, piezoelectric constant: 220pC/N, dielectric constant: 1060, respectively. Compared with conventional solid reaction methods for PZT powders, the advantage of the modified sol-hydrothermal method are low synthesis temperature and high sintering activity of the powders.
Method for simulating mechanical behavior of syntactic foam plastics by artificial neural networks
Zou Bo, Lu Zixing
2007, 33(07): 860-864.
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 894
Abstract:
Application of artificial neural networks (ANN) method on the mechanical behavior simulation of syntactic foam plastics was discussed. Firstly, factors influencing on the mechanical behavior and mechanical properties simulated and predicted were separately taken as input and output quantities. Secondly, Four-layer neural networks model was established to simulate and predict the mechanical properties and constitutive relationship of syntactic foam plastics by means of back-propagation algorithm. The numerical results show that the trained ANN model can preferably simulate and predict the mechanical behavior of material, such as Young′s modulus, yield strength and stress-strain curves under different strain rates or temperatures. Additionally, by comparison among three different modified training methods, it is found that Bayesian regularization back-propagation has the best capacity of improving network generalization, Levenberg-Marquardt(LM) back-propagation would converge fastest, and gradient descent momentum & adaptive learning rate back-propagation need long-end iterative process before the same precision in calculation is achieved.
Low oxygen partial pressure self-fusing Al-Si coating formed on surface of Ti alloy and its oxidation resistance
Zhou Wei, Zhao Yuguang
2007, 33(07): 865-868.
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 951
Abstract:
An Al-Si fusing coating was successfully produced by means of the low oxygen partial pressure high-temperature fusing technique for the improvement of the high-temperature oxidation resistance of Ti-6Al-4V alloy. Unlike the Si-modified aluminide coating, this technique is much effective and cheap without the need for long time diffusion for the formation of the Al-Si fusing coating, and the concentrations of the oxidation-resistant elements, Al and Si, in the coating can be controlled by adjusting powder mixing ratio. X-ray diffraction(XRD) shows that the Al-Si fusing coating is mainly composed of Ti5Si3 and TiAl3 phases. Cyclic oxidation tests at 923K for 52h in air reveals that the mass gains of the low oxygen partial pressure self-fusing Al-Si coating (LOPPF) is rapid in the initial 10h oxidation and keeps slow in the following oxidation; However, for the Si-modified aluminide coating, it keeps a rapid oxidation rate throughout the oxidation time.
Effects on residual stresses of Ti6Al4V electron beam welding line by laser shock processing
Lu Jinzhong, Zhang Yongkang, Qian Xiaoming, Ren Xudong
2007, 33(07): 869-872.
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 1046
Abstract:
Laser shock processing radiates metals by high power density (GW/cm2), short pulse (ns level) laser beam to produce the high strength impact wave and become residual stress of several hundreds MPa. Moreover, Laser shock processing has been shown to harden the surface and improve the mechanical properties of some structural metal components. The surface of Ti6Al4V titanium alloy welding line by electron beam welding (EBW) was processed by repetition-rate Nd:glass laser and repetition-rate Nd:glass laser & mechanical peening. Effects on residual stress of the Ti6Al4V alloy welding line by two technicses have been analyzed. The results are shown that residual stress distributions of the Ti6Al4V alloy welding line by two technicses are clearly improved, and residual stress distributions the latter are more clearly. In particular compressive residual on the subsurface increased with the increase of depth, maximum residual stress appears at the depth of 20~30μm apart from surface.

Copyright © Journal of Beijing University of Aeronautics and Astronautics

Address: Editorial Department of Journal of Beijing University of Aeronautics and Astronautics, 37 Xueyuan Road, Haidian District, Beijing Post Code: 100191 Email: jbuaa@buaa.edu.cn

Supported by: Beijing Renhe Information Technology Co., Ltd.