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Table of Content
10 June 2005, Volume 27 Issue 3
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    Yang Dingning Yang
    2005, 27(3):  0-0.  doi:10.6052/1000-0992-2003-186
    Abstract ( 2551 )   PDF (2311KB) ( 1255 )  
    Among the family of CAD/CAM/CAE, CAD and CAM are more straight-forward in concept, while CAE covers a wider area and is fast developing. Now CAE has developed from numerical computation to simulation, towards a realization of virtual reality with CAE and CAD being closely combined. With the development of FEM and new artificial intelligence algorithms including ANN and GA, not only detailed designs but also global designs are supported by CAE. On the basis of a R {\&} D scheme, CAE is analyzed in terms of its target, physical content and algorithm. The application of finite-element-based and AI-based algorithms in conceptual design phase is illustrated. Advances of the modern design optimization are reviewed. The progress of CAE and some important research directions in a near future are discussed.
    2005, 27(3):  0-0.  doi:10.6052/1000-0992-2004-171
    Abstract ( 1855 )   PDF (542KB) ( 999 )  
    A mathematical model of rubbing and impact for a nonlinear rotor-box is proposed in the paper. By means of numerical simulation, bifurcation diagrams are obtained under different system parameters. Meanwhile, the effect of the different system parameters on the bifurcation is analyzed in the numerical simulation. Poincare mappings are given on relevant system parameters and frequencies. Finally, the effect of the different system parameters on the rub-impact characteristics of the nonlinear rotor-box system is discussed. The variation of the eccentricity may influence chaotic motions and bifurcation phenomena and an increase of damping causes a gradual reduction of the chaotic bands, but an increase of rub-impact stiffness increases the chaotic bands and causes a complex motion.
    2005, 27(3):  0-0.  doi:10.6052/1000-0992-2004-172
    Abstract ( 797 )   PDF (434KB) ( 991 )  
    The light-duty honeycomb sandwich structures with high specific-strength and specific-stiffness are applied widely in the satellite projects. The shear modulus is especially difficult to obtain accurately. This paper focuses on the shear modulus analysis method using the finite element method based on the thin plate theory. The results were found to agree better with experiments than other methods.
    Application study
    2005, 27(3):  0-0.  doi:10.6052/1000-0992-2004-183
    Abstract ( 2391 )   PDF (612KB) ( 1400 )  
    This paper calculates the inertia of a disc by angular acceleration law and time law, respectively with the data of JIJG-I's rigid body inertia experimental apparatus, and it is indicated that the angular acceleration law gives better results than the time law by 1 to 2 orders of magnitude in precision. The main factors of the time law and the angular acceleration law are pointed out.
    2005, 27(3):  0-0.  doi:10.6052/1000-0992-2004-211
    Abstract ( 1846 )   PDF (638KB) ( 902 )  
    By means of coordinate transformation, the part of stresses in the expression of stress field caused by temperature at the moment of application of transient current on the plate with a side-crack was separated and expressed in polar coordinate. The stress field near the penetrate crack tip of type I was obtained. Through adding the stress field caused by temperature to the stress caused by tension loaded in the distance, the stress field in the current-carrying plate with a side-crack under the action of mechanical loading could be obtained in polar coordinate. An example is provided.
    2005, 27(3):  0-0.  doi:10.6052/1000-0992-2004-232
    Abstract ( 1185 )   PDF (576KB) ( 615 )  
    The main task of mechanical analyses on over constraint mechanism is the solution of the compatibility equation of distortion, but it is difficult to obtain the solution directly because its direct kinematics is not completely established. A method to solve the compatibility equation of distortion indirectly is put forward based on the kinematic constraint relation. The principle and the complete procedures about the planar and the space mechanisms are given, respectively. The results show that the method is effective especially for complicated over constraint parallel manipulator. At last, how to use the method to solve the multi-degree over constraint mechanism is discussed.
    Application study
    2005, 27(3):  0-0.  doi:10.6052/1000-0992-2004-272
    Abstract ( 1936 )   PDF (333KB) ( 637 )  
    It is the result of natural evolution that an earthworm with a multi-sectional non-smooth wavy surface can perfectly adapt its living environment. An earthworm moving in soil needs less longitudinal muscle contract force and less energy than those required to move a similar sized cylindrical body. The computational analysis shows that such an earthworm body with the wavy surface can reduce its muscle contract force by 1.12{\%}, and a similar amount of energy as well.
    2005, 27(3):  0-0.  doi:10.6052/1000-0992-2004-324
    Abstract ( 1774 )   PDF (917KB) ( 680 )  
    Based on creep deformation theory, using finite element numerical calculating method with ANSYS commercial software as calculation platform, the creep deformation computational model for composite structure shell is established. For composite structure blast oxygen furnace (BOF) composed of magnesia-graphite refractory, due to the high thermal conductivity of magnesia-graphite refractory, a high temperature will appeared on the shell in the BOF. This results in shell creep deformation to a greater or lesser degree and reduces its service life. The BOF shell creep deformation is studied in this paper, the result provides some hints to control shell creep deformation and prolong shell service life. With the finite element computational model, the simulation results agree quite well with the spot measurements.
    Application study
    2005, 27(3):  0-0.  doi:10.6052/1000-0992-2004-371
    Abstract ( 1209 )   PDF (800KB) ( 633 )  
    Considering the heterogeneous property of rock mass, a statistical constitutive model is developed and is implemented in LS-DYNA by using the user defined material subroutine. In the constitutive model of the rock mass, a two parameter Weibull's distribution is used to simulate the statistical properties of the tangential modulus and the strength of the rock mass. The rationality of the model is demonstrated by a numerical test.
    Interesting mechanics story
    2005, 27(3):  0-0.  doi:10.6052/1000-0992-2004-377
    Abstract ( 1354 )   PDF (553KB) ( 552 )  
    Using Somigiliana's formula, the general solutions and hypersingular integral equations for a three-dimensional impermeable crack problem in an infinite transversely isotropic piezoelectric solid under mechanical and electrical loads are given. The unknown functions are the discontinuities of the elastic displacements and electrical potential of the crack surface. Then, a numerical technique to solve the hypersingular integral equations is proposed based on the boundary element method combined with the finite-part integral method. Finally, a rectangular crack under mechanical tension and electrical fields is analyzed, and the numerical results of the stress and electric displacement intensity factors are presented. It is shown that the numerical solutions are satisfactory, which shows that the present approach is powerful to solve three-dimensional crack problems of piezoelectric materials.
    2005, 27(3):  0-0.  doi:10.6052/1000-0992-2004-386
    Abstract ( 1281 )   PDF (954KB) ( 712 )  
    Using response surface methodology (RSM), the responses of a system can be expressed in the explicit form of the design variables. For fitting response surfaces, the central symmetric design and the quasi-simplex design are developed according to central composite design and simplex design, respectively, in an attempt to cut down the computational cost involved in repetitive structural analyses with the accuracy being guaranteed. For a common optimization problem, the RSM can formulate it into an optimal model linearly or nonlinearly constrained. The optimization toolbox of Matlab can be employed to find the optima. The crashworthiness design shows that the application of the proposed experimental design methods and optimal model can achieve good accuracy and efficiency.
    2005, 27(3):  0-0.  doi:10.6052/1000-0992-2004-438
    Abstract ( 1372 )   PDF (928KB) ( 844 )  
    It is a fundamental problem of the rock mechanical measurements in material testing machine how to measure the rock deformation exactly. Rock uniaxial compression tests were carried out in two different testing machine so as to investigate the effect of machine stiffness on the deformation measurement. The energy transfer and conversion of testing system and sample during the loading and unloading processes are analyzed in this paper. It is found that the elastic accumulation energy of material testing machine affects the mechanical measurement of rocks. Moreover a revised method is proposed which can be adopted to calculate the deformation of rock during the test.
    2005, 27(3):  0-0.  doi:10.6052/1000-0992-2004-455
    Abstract ( 1954 )   PDF (625KB) ( 670 )  
    The concrete plank is an object usually found in the demolition blasting. It is the basic piece of structure or building. Attenuation rule of the peak value of explosion stress wave vs. distances is one of the theoretical bases for designing engineering blasting parameters. Through numerical computation, attenuation rule on the peak value of explosion stress wave vs. distances in the concrete plank is studied in this paper. The study results show that the attenuation of explosion stress wave is more rapid in the concrete plank, compared with that in the infinite concrete medium. The attenuation exponent of the peak value of stress wave vs. distance decreases with increase of explosive charge mass. The change ratio of attenuation exponent decreases rapidly with increase of explosive charge. That can explain that big explosive charge mass cannot improve the breaking quality of concrete plank, which will produce strong air shock wave and flying pieces and that the bigger explosive consumption per cubic concrete should be taken, compared with blasting of concrete body, as can be seen from the results in the paper.
    2005, 27(3):  0-0.  doi:10.6052/1000-0992-2004-467
    Abstract ( 1265 )   PDF (933KB) ( 655 )  
    A new structural damage identification method using static displacement of limited tests based on the grey correlation theory is first proposed in this paper. The grey correlation coefficient of displacement curvature and static displacement curvature assurance coefficient is defined and used to locate damage in the structure firstly, and an iterative estimation scheme for solving nonlinear optimization programming problems based on the quadratic programming technique is used to identify the damage magnitude. A numerical example of a two-fixed beam with single or multiple damages is used to examine the capability of the proposed method to locate and identify damages. The factors of measurement noise and incomplete test data are also discussed. The numerical results show that the damage in the structure can be identified correctly through static displacement curvature assurance coefficient, and the damage magnitude can be identified with a high degree of accuracy, regardless of the number of measured displacement nodes. This proposed method requires only limited static test data, which is easily available in practice, and has wide applications in structural damage detection.
    2005, 27(3):  0-0.  doi:10.6052/1000-0992-2004-500
    Abstract ( 1937 )   PDF (650KB) ( 1113 )  
    The traditional method of determining vehicle's center of gravity is first introduced, then the mechanics model for monitoring vehicle's center of gravity based on the pressure sensor is proposed. This model can be used to monitor the weight and center position in real time of the motor vehicles, offer the safe travel speed and provide important parameters for developing the monitoring system in real time for center of gravity of automobile.
    2005, 27(3):  0-0.  doi:10.6052/1000-0992-2005-003
    Abstract ( 2037 )   PDF (476KB) ( 813 )  
    Based on the Kirchhoff's theory the planar vibrations of a thin elastic rod with circular cross section are studied. The dynamical equations of the rod are established in the Frenet coordinates of the centerline as the reference frame. In the case of planar motion the torsional vibration is decoupled from the flexural vibration. The torsional vibration of a rod with arbitrary planar shape and the flexural vibration of a straight rod without torsion under axial compression are discussed. It is proved that conditions of Lyapunov's and Euler's stability of equilibrium of a straight rod in static analysis are necessary conditions of its dynamic stability. The influence of the axial force and the inertial effect of the cross section on the natural frequency of flexural vibration is considered.
    2005, 27(3):  0-0.  doi:10.6052/1000-0992-2005-108
    Abstract ( 1860 )   PDF (1586KB) ( 808 )  
    Many multi-scale mechanical problems concerning multiple physical levels are crucial in aeronautic and astronautic safety. Multi-scale problems are great challenges with respect to current mechanical concepts and theories. In this paper, taking spallation in Al alloy and brittle fracture in rocks as typical examples, we discuss typical features, difficulties and potential solutions to multi-scale problems. It is shown that a reasonable characterization and treatment of the trans-scale coupling and trans-scale sensitivity are keys to the multi-scale problems.