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Zhou, Zhidong; Jiang, Quan
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The thin stiff films on prestretched compliant substrates can form wrinkles, which can be controlled in micro and nanoscale systems to generate smart structures. Recently, buckled piezoelectric/ferroelectric nanoribbons have been reported to show an enhancement in the piezoelectric effect and stretchability, which can be applied in energy harvesting devices, sensors and memory devices instead of polymeric polyvinylidine fluoride (PVDF). This paper studies the buckling and postbuckling process of ferroelectric thin films bonded to the prestretched soft layer, which in turn lies on a rigid support. Nonlinear electromechanical equations for the buckling of thin piezoelectric plates are deduced and employed to model the ferroelectric film poled in the thickness direction. Two buckling modes are analyzed and discussed: partially deadhered buckling and fully adhered buckling. Transition from one buckling mode to the other is predicted and the effect of piezoelectricity on the critical buckling condition of piezoelectric film is examined.
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Qi, Dexuan; Zhang, Yitong; Ning, Jiaxing; Xu, Jiafu
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1 Citations
Kinkbands in rocks have been widely observed in nature and imitated in the laboratory, and the mechanism of their formation has attracted much attention from various researchers for many years. In this paper, a twophase equilibrium model is presented in which the kinkbands are considered as a highstrain phase and the other regions outside kinkbands as a lowstrain phase and the discontinuity of the deformation gradient and stresses is permitted across the interface between those two phases. Based on the present model, we conduct the analysis for the rocks under plane strain compression by finding the minimum value of the compressive loading at which the governing equations have real, physically acceptable solutions. It is revealed that for the rocks with strainsoftening behaviour, twophase equilibrium solutions exist, and the critical value of the compressive loading, the inclination angle of the kinkband, and the stresses and strains inside and outside kinkbands can all be determined by the solution, which are in good agreement with experimental measurements and observations.
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By
Qu, Shaoxing; Li, Ke; Li, Tiefeng; Jiang, Hanqing; Wang, Miao; Li, Zhenhua
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9 Citations
The performance of dielectric elastomer (DE) transducers is significantly affected by viscoelastic relaxationinduced electromechanical dissipations. This paper presents an experimental study to obtain the rate dependent stressstretch relation of DE membranes (VHB™9473) subjected to pure shear like loading and electric loading simultaneously. Stretching rate dependent behavior is observed. The results also show that the tensile force decreases as the voltage increases. The observations are compared with predictions by a viscoelastic model of DE. This experiment may be used for further studies of dynamic electromechanical coupling properties of DEs.
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By
Wu, Bo; Chen, Zhenpeng; Zhang, Xiong; Liu, Yan; Lian, Yanping
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1 Citations
In a bird strike, the bird undergoes large deformation like flows; while most part of the structure is in small deformation, the region near the impact point may experience large deformations, even fail. This paper develops a coupled shellmaterial point method (CSMPM) for bird strike simulation, in which the bird is modeled by the material point method (MPM) and the aircraft structure is modeled by the Belytschko–Lin–Tsay shell element. The interaction between the bird and the structure is handled by a particletosurface contact algorithm. The distorted and failed shell elements will be eroded if a certain criterion is reached. The proposed CSMPM takes full advantages of both the finite element method and the MPM for bird strike simulation and is validated by several numerical examples.
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By
Yuan, Hong; Lin, Zifeng
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1 Citations
Fiber reinforced polymer (FRP) composites are increasingly being used for the repair and strengthening of deteriorated concrete structural components through adhesive bonding of prefabricated strips/plates and the wet layup of fabric. Interfacial bond failure modes have attracted the attention of researchers because of the importance. The objective of the present study is to analyse the interface failure mechanism of reinforced concrete continuous beam strengthened by FRP. An analytical solution has been firstly presented to predict the entire debonding process of the model. The realistic bilinear bondslip interfacial law was adopted to study this problem. The crack propagation process of the loaded model was divided into four stages (elastic, elasticsoftening, elasticsofteningdebonded and softeningdebonded stage). Among them, elasticsofteningdebonded stage has four substages. The equations are solved by adding suitable stress and displacement boundary conditions. Finally, critical value of bond length is determined to make the failure mechanism in the paper effective by solving the simultaneously linear algebraic equations. The interaction between the upper and lower FRP plates can be neglected if axial stiffness ratio of the concretetoplate prism is large enough.
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By
Zhang, Wenjun; Wang, Shuqi; Lin, Min; Han, Yulong; Zhao, Guiping; Lu, Tian Jian; Xu, Feng
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6 Citations
Cells tend to form hierarchy structures in native tissues. Formation of cell aggregates in vitro such as cancer spheroids and embryonic bodies provides a unique means to study the mechanical properties and biological behaviors/functions of their counterparts in vivo. In this paper, we review stateoftheart experimental approaches to assess the mechanical properties and mechanicallyinduced responses of cell aggregates in vitro. These approaches are classified into five categories according to loading modality, including micropipette aspiration, centrifugation, compression loading, substrate distention, and fluid shear loading. We discussed the advantages and disadvantages of each approach, and the potential biomedical applications. Understanding of the mechanical behavior of cell aggregates provides insights to physical interactions between cells and integrity of biological functions, which may enable mechanical intervention for diseases such as atheromatosis and cancer.
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By
Abbasnejad, Behrokh; Rezazadeh, Ghader; Shabani, Rasool
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39 Citations
Based on the Modified Couple Stress Theory, a functionally graded microbeam under electrostatic forces is studied. The FGM microbeam is made of two materials and material properties vary continuously along the beam thickness according to a powerlaw. Dynamic and static pullin voltages are obtained and it is shown that the static and dynamic pullin voltages for some materials cannot be obtained using classic theories and components of couple stress must be taken into account. In addition, it is shown that the values of pullin voltages depend on the variation through the thickness of the volume fractions of the two constituents.
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By
Li, Cheng; Lim, C. W.; Yu, Jilin
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12 Citations
The torsional static and dynamic behaviors of circular nanosolids such as nanoshafts, nanorods and nanotubes are established based on a new nonlocal elastic stress field theory. Based on a new expression for strain energy with a nonlocal nanoscale parameter, new higherorder governing equations and the corresponding boundary conditions are first derived here via the variational principle because the classical equilibrium conditions and/or equations of motion cannot be directly applied to nonlocal nanostructures even if the stress and moment quantities are replaced by the corresponding nonlocal quantities. The static twist and torsional vibration of circular, nonlocal nanosolids are solved and discussed in detail. A comparison of the conventional and new nonlocal models is also presented for a fully fixed nanosolid, where a lowerorder governing equation and reduced stiffness are found in the conventional model while the new model reports opposite solutions. Analytical solutions and numerical examples based on the new nonlocal stress theory demonstrate that nonlocal stress enhances stiffness of nanosolids, i.e. the angular displacement decreases with the increasing nonlocal nanoscale while the natural frequency increases with the increasing nonlocal nanoscale.
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By
Liu, ZhiYuan; Wang, Lin; Sun, XiPing
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1 Citations
The nonlinear forced vibrations of a cantilevered pipe conveying fluid under base excitations are explored by means of the full nonlinear equation of motion, and the fourthorder Runge–Kutta integration algorithm is used as a numerical tool to solve the discretized equations. The selfexcited vibration is briefly discussed first, focusing on the effect of flow velocity on the stability and postflutter dynamical behavior of the pipe system with parameters close to those in previous experiments. Then, the nonlinear forced vibrations are examined using several concrete examples by means of frequency response diagrams and phaseplane plots. It shows that, at low flow velocity, the resonant amplitude near the firstmode natural frequency is larger than its counterpart near the secondmode natural frequency. The secondmode frequency response curve clearly displays a softeningtype behavior with hysteresis phenomenon, while the firstmode frequency response curve almost maintains its neutrality. At moderate flow velocity, interestingly, the firstmode resonance response diminishes and the hysteresis phenomenon of the secondmode response disappears. At high flow velocity beyond the flutter threshold, the frequency response curve would exhibit a quenchinglike behavior. When the excitation frequency is increased through the quenching point, the response of the pipe may shift from quasiperiodic to periodic. The results obtained in the present work highlight the dramatic influence of internal fluid flow on the nonlinear forced vibrations of slender pipes.
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