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2014 Vol. 35, No. 5
Published:
417
Recent progress in atomic-scale friction
Atomic-scale friction is one of the most hot topics in nanotribology. A great number of studies have shown that the behavior of atomic-scale friction is obviously different from that of macroscopic friction, which creates a big attraction for the mechanics community. In this article, we review the recent progress in atomic-scale friction. We first introduce the main approaches that are commonly used in studying atomic-scale friction. Then, we pay special attention to some key factors that have significant influences on the atomic-scale friction, such as load, temperature, speed, surface configuration, etc; and some novel phenomena that can only be observed at the nano-scale, such as superlubricity, negative friction coefficient, edge effect, etc. Finally, we give a brief perspective to the future study on the atomic-scale friction.
2014 Vol. 35 (5): 417-440 [
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314
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441
Finite Element Analysis of Strain Gradient on the Vibration of Single-layered Graphene Sheets
The vibration of single-layered graphene sheets (SLGS) is investigated using a new finite element method based on nonlocal continuum plate model with second order strain gradient taken into consideration. The paper starts with dynamic equation of Kirchhoff plate of strain gradient elasticity. Then a 4-node 24-degree of freedom (DOF) plate element is developed to discretize the higher order partial differential equations with the small scale effect taken into consideration. The finite element results are in good agreement with theoretical results in analyzing simply-supported SLGS, which validated the reliability of the finite element method. Finally, the finite element method is used to study the vibration of graphene sheets with different size,wave length，boundary conditions and the nonlocal parameter which show the small scale effects.
2014 Vol. 35 (5): 441-450 [
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401
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451
NONLINEAR 3-D DYNAMICS MODELING AND ANALYSIS OF CURVED BOUNDARY CYLINDRICAL SHELL WITH LARGE ROTATION
Considering geometric nonlinearity, the 3-D dynamic behavior of curved boundary cylindrical shell with large rotation under non-uniform internal pressure along its axial direction is studied. Based on Nayfeh and Pai’s[1] theoretical system of shell, the mixed nonlinear 3-D dynamics model with internal force and displacement variables is first derived. Then with the basic assumption about its static and dynamic deformation modes, the 3-D Multi-degree of Freedom governing equations based on the obtained static solution are established using Lagrange’s equation, and an efficient numerical method combined with difference method is developed after linearization and order reduction to the equations, which avoids the difficulty of solving the mixed model due to its strong nonlinearity. The present method is verified to be valid by comparing with results obtained from LS-DYNA. The influences of element number on the FEM and time step on our method are also investigated and find that precision is improved with the decrease of the computing time step and tends to be stable finally. Meanwhile, the 3-D dynamic deformation modes under a linear distribution load were obtained, which are closely related with the load distribution. So one can change or design the load distribution to realize different dynamic deformation modes, which is useful for structural design and optimization of the curved boundary cylindrical shell structure in engineering application.
2014 Vol. 35 (5): 451-457 [
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238
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论文
458
PHOTOTHERMAL RESPONSE IN SEMICONDUCTING MICROSTRUCTURE PRODUCED BY LASER EXCITATION
Recently, the photothermal methods are widely used as a detection way in micro-electromechanical system (MEMS) and nano-electromechanical system (NEMS), especially in situations where other techniques are not useful. The plasma wave and thermal wave, generated by the absorbed intensity-modulated optical excitation, play the dominant role in the PT experiments for most semiconducting and microelectronics structures. So, the study of photothermal response of a sample under different excitation was very important. In this paper green function method was used to solve 3-dimensional coupled plasma wave and heat conduction equations. The expressions of carrier density and temperature were derived analytically and the space distribution were given graphically for different heat sources.
2014 Vol. 35 (5): 458-463 [
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229
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464
STUDY ON ELASTIC SUB-IMPACTS OF SIMPLY SUPPORTED STEEL BEAM STRUCK BY ROUND-NOSED MASS
The sub-impact behavior of a simply supported beam struck by a round-nosed mass, including the sub-impact phenomenon, sub-impact durations and sub-impact conditions, were tested by a set of sub-impact experimental device self-designed, simulated numerically by the three-dimensional dynamic finite element method and analyzed by the Hertz impact theory. The sub-impact phenomenon was observed by the tests and simulations. By comparing the results of test, simulation and theoretical analysis, it is found that the first sub-impact process is dominated by local impact-contact deformation and can be described by the Hertz impact theory. The subsequence sub-impacts have much different characteristics from the first sub-impact, and their impact durations vary random in large ranges. The further investigation has found that the processes of the subsequence sub-impacts are dominated together by the local impact-contact deformation and the beam vibrations, and the impact force responses become complicated because of the beam vibrations. The numerical simulations show that the first vibration mode of the beam decreases its amplitude suddenly and changes its phase angle obviously when sub-impacts taken place. The numerical simulations also show that the sub-impact conditions relate to the ratio of the round-nosed mass to the beam equivalent mass, initial impact velocity, impact position, initial impact momentum, length and thickness of test beam. It is found that the sub-impact conditions can be represented by a mass ratio threshold. The present investigation illustrates that the couple mechanical effect of local impact deformation and structural vibration make a plenty of sub-impact behavior. It is necessary to further investigate the phenomenon of sub-impact by test, numerical simulation and theoretical analysis, so as to have a comprehensive understand of impact behavior of flexible systems.
2014 Vol. 35 (5): 464-475 [
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215
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476
Theoretical analysis about non-probabilistic reliability base on interval model
Considering the great amount of uncertainty factors existing in actually engineering, the uncertain parameters in the structure were described as one special case of convex variables, that is, the interval variables. According to the definition of reliability-index based on interval model, the non-probabilistic reliability analysis was carried out with analytical approach. In order to avoid the loss of the probable failure point, analytical model starts from 2-D plane and 3-D space. After division of domain within 2-D and 3-D, the probable failure points can only exist on the extreme points and the root points of the limit state function. after simple comparison directly, it is easy to find the most probable failure point and to acquire the reliability-index. Furthermore, the low-dimensional analytical scheme has been extended to high- dimensional case. The equation numbers used for calculating the extreme point and the root point has obtain, which can be useful to avoid the loss of the probable failure point and meaningful for optimizing searching in this researching field. Finally, two kinds of examples were presented and compared with existing computation. The agreement shows that the analytical approach in the paper is correct.
2014 Vol. 35 (5): 476-484 [
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222
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487
Interface Stress of the coating of steel surface and substrate under the sand shock
DOI:
Interfacial stress between coating of steel surface and substrate based on the kinetic of the analysis in the application of contact mechanics and the mirror point of interface mechanics was analyzed, and calculating the interfacial stress of the coating of steel surface and substrate under the sand shock. The experimental results indicate that, the interface normal stress of steel and coating increases with impact velocity, a larger interfacial stress in the vicinity of the impact point and smaller away from the point, the interface normal stress increases with the impact angle and reaches a maximum at 90°, and it reaches the a maximum at 45° when a certain distance between the point and the stress. Interfacial shear stress also increases with impact velocity, and it reaches a maximum at 30°. Interfacial shear stress reaches a maximum by the distance x = 1mm from the impact point to the interface.
2014 Vol. 35 (5): 487-492 [
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216
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简报
493
STRONGLY NONLINEAR SUPERHARMONIC RESONANCE AND CHAOTIC MOTION OF AXIALLY MOVING STRIP THIN PLATE IN MAGNETIC FIELD
In this paper, the nonlinear vibration and chaotic motion of the axially moving current-conducting strip thin plate with an external harmonic force in magnetic field is studied. Improved multiple-scale method is employed to derive the strongly nonlinear superharmonic resonance bifurcation-response equation of the strip thin plate in transverse magnetic field. By using the singularity theory, the corresponding transition variety and bifurcation which contain two parameters of the universal unfolding for this nonlinear system are obtained. Numerical simulations are carried out to plot the bifurcation diagrams, corresponding maximum Lyapunov exponent diagrams and dynamical response diagrams with respect to the bifurcation parameters such as magnetic induction intensity, axial tension, external force amplitude and external excited frequency. The influences of different bifurcation parameters on period doubling motion and chaotic motion behaviors of superharmonic resonance system are analyzed. The results show that the complex dynamic behaviors of resonance system can be controlled by changing the corresponding parameters.
2014 Vol. 35 (5): 493-504 [
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222
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507
A receding contact plan problem between two elastic layer
DOI:
This paper considers the smooth receding contact between two elastic layer when the two bodies are pressed together. Using Fourier integral transform, the plan elasticity equations are converted analytically into a singular integral equation. Then the problem is solved numerically using Chebychev polynomials and an iterative scheme. At last, the numerical examples are conducted to investigate the effect of the shear modulus and the top contact half-length on the contact pressure and on the half-length of the receding contact is analyzed.
2014 Vol. 35 (5): 507-508 [
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333
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