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2014 Vol. 35, No. 6
Published: 2014-12-28
509
The Study on the Deformation Mechanisms and Mechanical Properties of TiN Nanorod under the Axial Tensile Process Based on Molecular Dynamic
The software package lammps based on molecular dynamic with Modified Embedded-Atom Method(2NN MEAM) is used to simulate the tensile fracture behavior of single crystal TiN nanorod. The mechanical property of TiN with different cross sections is analyzed under different strain rates and different temperatures along [100]、[111] directions. The tensile process is described in detail. The study has found that the tensile direction, cross section size, tension strain rate and temperature all have different effects on the tensile process, yield stress, elastic modulus of TiN nanorod. The larger the cross section, the lower the yield stress along [100] direction tension, however, the larger the cross section, the larger the yield stress along [111] direction tension. The yield stress and yield strain increase with strain rate, but strain rate has little effect on the yield modulus. When the temperature of simulation system rises, the yield stress, yield strain and yield modulus of TiN material tend to be smaller, but the fracture strain will be larger. Under different tension condition, the tensile process of TiN nanorod all contains elastic deformation, plastic deformation and fracture stage. The elastic modulus along [100] direction is always lager than that along [111] direction.
2014 Vol. 35 (6): 509-516 [
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517
Elastic Deformation Perturbed Magnetostatic Fields of the Generalized Flamant Problem for a Half-Plane Ferromagnetic Structure in Earth Magnetic field
The magnetostatic field perturbed by elastic deformation of the generalized Flamant problem for the half-plane ferromagnetic structure in earth magnetic field is solved analytically by the Fourier transform method. The results of a concentrated force problem degenerated from this problem is derived from the present expressions. The numerical results show that the distribution of the generalized Flamant load can affects the elastic deformation of the structure, and then affects the distributions and the values of the magnetostatic field perturbed by elastic deformation; the distributions of magnetostatic field are directly related to the distributions of the maximum load area, and the values of magnetostatic field are positively associated with the values of the forces; in addition, the magnetostatic field perturbed by elastic deformation increases with the decreasing distance away from the structure surface, and it increases as the size of the load distribution increases.
2014 Vol. 35 (6): 517-526 [
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693
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527
The Relation between Rayleigh Wave Velocity and the Texture Coefficients in Cubic Crystallite Orthorhombic Sheets
An orthogonal plate is an orthorhombic aggregate of tiny crystallines. The orientation distribution of crystals in the polycrystal (described by the texture coefficients in the orientation distribution function ODF) affects the propagation velocity of Rayleigh wave. Introduced the texture coefficient of polycrystalline into material elastic tensor, through the characteristic value method and the linearization processing, get the relation between the texture coefficient of cubic crystallite orthorhombic with Rayleigh wave velocity. On this basis, through the measurement of Rayleigh wave velocity to get the texture coefficient, and compared with the texture coefficient which measured by ultrasonic transverse wave and longitudinal wave velocity. The results measured by two methods are similar.
2014 Vol. 35 (6): 527-533 [
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568
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534
Refined Theory of Transversely Isotropic Thermoelastic Beam for Bending Deformation
The analysis of a beam is a basically two-dimensional problem. At first, we obtain the displacement and stress components of thermoelastic beam using general solution and Lur’e method without ad hoc assumptions. In the case of the beam under nonhomogeneous boundary conditions, we obtain the approximate beam equation. If the temperature item is omitted, the refined theory of transversely isotropic thermoelastic beam can be degenerated into the refined theory of beam for a transversely isotropic body.
2014 Vol. 35 (6): 534-538 [
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523
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539
Structural robust optimization design based on convex model
There exist a great amount of uncertain factors in actual engineering. In order to involve these uncertain factors in analytical model, it has been expressed as convex variables. In addition, the convex model was further classified into hyper-ellipsoidal model and interval model. After pointing out the intrinsic difference between these two kinds of models, the principle for applying which one of the models within the analysis has indicated according to the available testing points. After standardized the convex variables, the difference and relation between the two models for the optimization and solution process have presented. With the analysis mentality available from hyper-ellipsoidal model, the basic method about robust optimization for interval model was emphasized. After classification for the interval variables within the optimization process, the characteristics of robust optimization were highlighted with different constraint condition. Using target-performance-based analytical scheme, the algorithm, solution step and convergence criteria for robust optimization have presented with only one reliability index. Numerical examples and engineering problems are used to demonstrate the effectiveness and correctness of the proposed approach.
2014 Vol. 35 (6): 539-544 [
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551
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545
Analysis of the influence of cure temperature on interfacial behavior of carbon fibre/epoxy matrix
Analytical study was performed to determine the interface behavior affected by interfacial properties and the thermal residual stress. A cohesive zone model governed by the elastic-softening law described the fiber/matrix interface was used to simulate the thermal residual stress developed during the curing process and the fiber axial stress during fragmentation process. The interfacial properties of carbon fiber/epoxy resin cured either at room temperature or at high temperature were obtained. The results indicates that, compared with the room temperature curing, after high temperature curing, the interfacial shear strength increases slightly, and the interfacial fracture toughness increases significantly. The interface softening appears early, but the interface debonding is delayed after high temperature curing. In addition, both the fiber axial and interfacial radial thermal residual stresses delay the interface softening, and the interface debonding is delayed by the interfacial radial thermal residual stress.
2014 Vol. 35 (6): 545-551 [
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263
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论文
559
CHARACTERISTIC STUDY ON ENERGY DISSIPATIONS IN FLAT LAP STRUCTURE
A modified friction model of energy dissipations in flat lap structure has been established, which can be degraded into both Coulomb Friction Model of energy dissipations and Goodman’s hypothesis under certain conditions. Numerical calculations of a certain kind of flat lap structure have been carried out and showed that the dissipation values obtained from Coulomb Friction Model make a good match with that from experimental results under small external loads. However, it becomes unavailable as external loads grow larger. On the other hand, the power-law relationship results obtained from modified friction model coincide better with experimental results than that from Coulomb Friction Model. Dissipation values obtained from modified friction model show smaller errors than that from Coulomb Friction Model under both small and large external loads. Modified friction model shows a better description of the characteristics of energy dissipations in flat lap structure.
2014 Vol. 35 (6): 559-565 [
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239
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566
The free vibration analysis of single layer eccentric cylindrical thin shells
starting with the geometry characteristic of the cross section of eccentric cylindrical shell, the eccentric problem is converted into a circumferentially varying thickness problem. The vibration equations are written in a matrix differential equation by using the transfer matrix of the state vector of the shell. The natural frequencies of eccentric cylindrical shell are calculated and are compared to those of cylindrical shell. The main parameters which influence the natural frequency are analyzed, and the relationships between these parameters and the natural frequency are given. This paper not only proposed an effective new method to obtain the natural frequencies of an eccentric cylindrical shell, but also could be as a new idea and method for detecting the eccentricity of eccentric cylindrical shell.
2014 Vol. 35 (6): 566-573 [
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246
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574
Study of compact wear rule affected by tooth-distributing angle of PDC bit based on torsion vibration
Due to the research status and deficiencies of composite plate wear affected by tooth-distributing angle of PDC bit, this paper presents a research method of compact wear rule affected by tooth-distributing angle of PDC bit based on torsion vibration. Using the typical geometry knowledge of PDC bit, we analyze the relationship of tooth-distributing angles of PDC bit and the effect on the cutting arc length, cutting area, etc. And the torsion vibration model of PDC bit is established, thus obtaining the key parameters under the vibration condition, such as displacement, velocity, rotating speed, etc. Then we use wear theory to analyze the effect of tooth-distributing angle on compact wear law. The results show that: different values of backrake angle will cause the wear rule of PDC bit’s compact to change significantly, while cutting edge angle has a very complicated effect on volume wear rate of PDC bit. As the important parameters of tooth distribution, the values of backrake angle and cutting edge angle have seriously affected PDC bit’s performance. Therefore, to optimize and take reasonable values will help to improve service life of PDC bit’s compact. The method and conclusions of the paper have some reference significance to the study of failure mechanisms of PDC bit’s compact.
2014 Vol. 35 (6): 574-582 [
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205
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568
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583
Non-probabilistic robust optimization design of structures based on interval model
DOI:
The structural robust optimization with uncertain parameters described by interval models is investigated. Comparing with the traditional optimization design, the non-probabilistic reliability index has been involved as an constraint condition in the robust optimization model. The relationship between the target of non-probabilistic reliability index and the fluctuation range of uncertain parameters is described by the geometric meaning of the reliability index. The non-probabilistic robust optimization design model is converted into a two-level optimization model. The minimization for non-linear performance function was carried out according to the fluctuant range of the non-probabilistic reliability index within the inner-lever optimization, so as to avoid the calculation of reliability index directly. For the linear performance function, the uncertain parameters could be describe as the target value of non-probabilistic reliability index with explicit expression, and therefore the two-level robust optimization is easily converted into a single-level deterministic optimization. The advantages of the proposed method lie in clear geometric characterization, computing convenience and high calculation efficiency. Numerical examples show the validity and efficiency of the proposed method.
2014 Vol. 35 (6): 583-589 [
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216
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571
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