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STATISTICAL MODEL FOR FRACTURE TOUGHNESS OF A MODIFIED Al-7Si-0.45Mg CAST ALLOY

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Acta Metallurgica Sinica(English Letters) 1990年第4期3卷 262-267页

作者： zhang Guobin chen Changqi beijing university of aeronautics and astronautics,beijing,China Dept.of Materials Science and Engineering,beijing university of aeronautics and astronautics,beijing 100083,China

The statistical model for the fracture toughness of a modified Al-7Si-0.45Mg cast alloy has been proposed on the basis of analysis of the correlation between the size distribution of crack nuclei and Si particles and of the micromechanism of *** suitable criterion of frac- ture toughness according to the model has been *** model has found a good explana- tion for the fracture feature,fracture toughness and microstructure,and agreed with the ex- periments very well.

关键词： cast Al alloy fracture toughness statistical model

A THREE-DIMENSIONAL TURBULENCE MODEL WITH ROTATIONAL VECTOR

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Chinese Journal of aeronautics 1993年第1期 53-58页

作者： Zu Guo-jun,chen Mao-zhang (beijing university of aeronautics and astronautics,beijing,China,100083)

The rotating terms in Reynolds stress equations (RSEs) are analyzed, and the appropriatemodellings to these terms are proposed in this paper. By means of the local equilibriumof turbulence production, dissipation and rotating terms, a nonisotropicthree-dimensional turbulence model which contains the rotational vector is proposed. Thismodel is appropriate to wild three-dimensional shear flows. It has been applied to the calculationsof two kinds of three dimensional turbulent boundary layers on rotating helicalblade and compressor rotor blade; the results are compared with experiments and the computationresults with C-S model, showing that the present model can improve the predictioncapability of near wall parameters to a certain extent. Moreover, this model is simpleand can be regarded as the extension of Bradshaw’s model in three dimensional flows.

关键词： A THREE-DIMENSIONAL TURBULENCE MODEL WITH ROTATIONAL VECTOR

Formal Development of Feedback Control System with Fault Accommodation

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Journal of Systems Engineering and Electronics 1998年第4期9卷 22-30页

作者： Gao Jianping & chen zongji(Department of Automatic Control,beijing university of aeronautics and astronautics, 100083, P. R. China) Department of Automatic Control Beijing University of Aeronautics and Astronautics. 100083. P. R. China

Control systems are vulnerable to faults in control loops where faults may cause abruptand damaging responses. These systems with fault accommodation are becoming more and moreimportant while appearing in flight control, robots control and nuclear reactor control etc, andcalling for more rigorous development approach. A formal approach is explored in this parer, basedon Extended Duration Calculus, for the development of such kind of systems. A typical exampleof control system with fault accommodation, two-level control system, is used for illstrating ourapproach. Its high level consists of an event-driven supervisor which reeds to the change of plant dueto faults occurrence, and its low level consists of normal controller, reconfigured controller and othercomponents with FDI (Fault Detection and Isolation) mechanism. Firstly performance and systemspecifications of the case are formulated in EDC; Then they are refined step wisely into specificationsof the supervisor and the low level components. Finally the whole system performance is verified inEDC framework.

关键词： Control system Fault accommodation EDC Refinement FDI Formal verification

CREEP BEHAVIOR OF γ-TiAl POLYSYNTHETICALLY TWINNED CRYSTALS

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Acta Metallurgica Sinica(English Letters) 1996年第6期9卷 577-583页

作者： Y.G. zhang J.G. Lin Y.J. Zhou and C.Q. chen(Department of Materials Science and Engineering, beijing university of aeronautics and astronautics,beijing 100083, China beijing Univ of aeronautics and Astronautics Beijing China

Creep behavior of γ-TiAl polysynthetically twinned (PST) crystals has been investigated at temperature between 700 and 800℃. The results show that the creep behavior of the crystals is strongly dependent on the angle between the lamellar boundaries and loading axis. The samples with the angle φ=45 deg. have the lowest creep resistance, while the samples with φ=0 deg., rather than φ=90 deg.,show the strongest creep resistance. The stress exponent and creep activation energy for the power law creep vary with the orientations of samples, which indicates that the creep mechanisms of the samples with different angle φ are quite *** deformation substructure has been examined by transmission electron microscopy (TEM),which shows that both gliding, perhaps also climbing, of dislocations and twinning contribute to the creep deformation with some particular observation in the samples with φ=90 deg. in which rotation of the γ plates across a true twin boundary was observed, which indicates the deformation mechanism of the samples is different from the samples in other orientations.

关键词： TiAl alloy PST crystal creep behavior lamellar microstructure

DEFORMATION　AND　FRACTURE　MECHANISMS　OF　TWO－PHASE　TiAl－BASED　ALLOYS　WITH　FULLY　LAMELLAR　MICROSTRUCTURE

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Acta Metallurgica Sinica(English Letters) 1995年第Z1期8卷 359-368页

作者： Y. G .zhang, C. Q. chen (beijing university of aeronautics and astronautics, beijing 100083, China)Q. Xu (beijing Laboratory of Electron Microscopy, Chinese Academy of Sciences. beijing,China)M. C. Chaturvedi (The university of Manitoba, Winnipeg, Manito beijing Univ of aeronautics and Astronautics Beijing China

A two-phase TiAl-based alloy with fully lamellar structure has been deformed al room temperature and the deformed microstructures have been examined in dtails by optical microscopy(OM), scanning electron microscopy(SEM) and transmission electron microscopy(TEM) . Deformation mechanisms in the γ-TiAl phase has been defined and the role of grain boundaries in the deformation and fracture has been assessed Some of the mechanisms of interactions between twinning or gliding dislocations and three types of γ γ domain boundaries or γ α_2 interface in a lamellar grain have been identified and resistance of the various domain boundaries or the interface to the propagation of twinning has been evaluated

关键词： TiAl Deformation mechanism Lamellae Twinning

MODIFIED　WEIGHTED　GRADIENT　PROJECTION　METHOD　AND　RESEARCH　TO　THE　KINEMATIC　CONTROL　OF　REDUNDANT　MANIPULATORS

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Chinese Journal of aeronautics 1996年第3期9卷 217-224页

作者： chen Weihai Yang Zongxu zhang Qixian(Institute for Robottes, beijing university of aeronautics and astronautics, beijing, China, 100083)Zhao Zhanfang(Institute for Robotics Research, beijing Institute of Technology, beijing, China, 100081) Institute for Robotics Beijing Univ. Aero. and Astronaut. Beijing 100083 China Institute for Robotics Research Beijing Institute of Technology Beijing 100081 China

To raise the optimizing ability of the redundant manipulators, a modified weighted gradient projection method(MWGPM) to optimize kinematics is *** new concepts, the matrix weightability measure(MWM) and the self-motion declinability measure(SMDM) are proposed. Thus the weighting ability of the weighting matrix and the self-motion amplitude decided by the homogeneous solution could be continuously regulated. MWGPM has the merits which belong to both the least-norm solution (WLN), and gradient projection method(GPM), and it can obtain ideal optimizing effects at low joint velocities, which has been verified by simulation.

关键词： robots kinematics optimization control

PREDICTION-BASED ADAPTIVE CONTROL OF NONLINEAR DISCRETE-TIME SYSTEMS

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PREDICTION-BASED ADAPTIVE CONTROL OF NONLINEAR DISCRETE-TIME...