Weiqiu Chen

Microstructured elastomeric surfaces with reversible adhesion and examples of their use in deterministic assembly by transfer printing

Reversible control of adhesion is an important feature of many desired, existing, and potential systems, including climbing robots, medical tapes, and stamps for transfer printing. We present experimental and theoretical studies of pressure modulated adhesion between flat, stiff objects and elastomeric surfaces with sharp features of surface relief in optimized geometries. Here, the strength of nonspecific adhesion can be switched by more than three orders of magnitude, from strong to weak, in a reversible fashion. Implementing these concepts in advanced stamps for transfer printing enables versatile modes for deterministic assembly of solid materials in micro/nanostructured forms. Demonstrations in printed two- and three-dimensional collections of silicon platelets and membranes illustrate some capabilities. An unusual type of transistor that incorporates a printed gate electrode, an air gap dielectric, and an aligned array of single walled carbon nanotubes provides a device example.

Elasticity solution for free vibration of laminated beams

Abstract Based on the two-dimensional theory of elasticity, a new approach combining the state space method and the differential quadrature method is presented in this paper for freely vibrating laminated beams. Applying the differential quadrature method to the state space formulations along the axial direction of the beam, new state equations about state variables at discrete points are obtained. Using matrix theory, the solution can be easily derived, which can very conveniently deal with the continuity conditions. Frequency equation governing the free vibration of laminated beams is then derived and the natural frequencies are obtained. No other assumption on deformations and stresses along the thickness direction is introduced, so that the present method is efficient for laminated beams with arbitrary thickness. It also can cope with arbitrary boundary conditions without applying Saint-Venant’s principle. Numerical examples of multi-layered beams and sandwich beams are performed. Results are verified by comparing them with the published results obtained from various finite element methods and shear beam theories.

On free vibration of a functionally graded piezoelectric rectangular plate

SummaryOn the basis of three-dimensional theory equations of transversely isotropic piezoelasticity, two independent state equations with variable coefficients are derived. To this end, separation formulae for displacements and shear stresses are employed. A laminated approximation is used to transform the state equations to the ones with constant coefficients in each layer. The free vibration problem of a piezoelectric rectangular plate with a functionally graded property is then investigated. Discussion on the boundary conditions is presented.

Free vibration analysis of generally laminated beams via state-space-based differential quadrature

A new method of state-space-based differential quadrature is presented for free vibration of generally laminated beams. By discretizing the state space formulations along the axial direction using the technique of differential quadrature, new state equations at discrete points are established. Applying end conditions and using matrix theory, the general solution is derived. Taking account of the boundary conditions at the top and bottom planes, frequency equation governing the free vibration of generally laminated beams is then formulated. The method is validated by comparing numerical results with that available in the literature.

On piezoelastic contact problem for a smooth punch

This paper firstly conducts a systematic three-dimensional investigation of the problem of a rigid smooth punch bonded to a transversely isotropic piezoelectric half-space. The potential theory method is employed and generalized to take into account the effect of the electric field. In contrast to pure elasticity, two potentials are introduced. For an arbitrarily shaped punch, two governing equations are derived, which can be solved using numerical methods. Particularly, a closed-form, exact solution is obtained for a flat centrally loaded circular punch which is maintained at a constant electric potential.

Two-dimensional analysis of magnetoelectric effects in multiferroic laminated plates

Two-dimensional equations for coupled extensional, flexural, and thickness-shear motions of laminated plates of piezoelectromagnetic layers are obtained from 3-dimensional equations. The equations are used to analyze magnetoelectric couplings in the extensional deformation of a laminated plate of piezoelectric and piezomagnetic layers. Magnetoelectric effects in 4 specific configurations of laminates are calculated and examined.

Dynamic behavior of cable-stayed beam with localized damage

An elastic continuous model is presented for the inclined cable with damage which is described as reduction of the axial stiffness. The damage effect on the static configuration of the cable under self-weight is investigated through a numerical solution. Hamilton’s principle is then employed to derive the governing equations for the in-plane dynamic motion of the cable-stayed beam with cable damage. The linear eigenmodes are obtained via the method of reverberation-ray matrix after a standard condensation procedure. A single-degree-of-freedom nonlinear model is obtained by the single-mode discretization. The homotopy analysis method is then successfully applied to get the frequency-amplitude relationship, which enables the influence of cable damage on the nonlinear dynamic behavior of the system to be characterized.

The Magnetoelectric Effects in Multiferroic Composite Nanofibers

In this letter, we analyze the quasistatic and dynamic magnetoelectric responses of multiferroic composite nanofibers consisting of both ferroelectric and ferromagnetic phases and demonstrate that the nanofibers exhibit magnetoelectric responses orders of magnitude higher than multiferroic composite thin films of similar compositions. The analysis suggests that the multiferroic nanofibers are promising for magnetoelectric applications.

Fundamental solutions for plane problem of piezoelectric materials

Based on the basic equations of two-dimensional, transversely isotropic, piezoelectric elasticity, a group of general solutions for body force problem is obtained. And by utilizing this group of general solutions and employing the body potential theory and the integral method, the closed-form solutions of displacements and electric potential for an infinite piezoelectric plane loaded by point forces and point charge are acquired. Therefore, the fundamental solutions, which are very important and useful in the boundary element method (BEM), are presented.

A Mechanochemical Model of Cell Reorientation on Substrates under Cyclic Stretch

We report a theoretical study on the cyclic stretch-induced reorientation of spindle-shaped cells. Specifically, by taking into account the evolution of sub-cellular structures like the contractile stress fibers and adhesive receptor-ligand clusters, we develop a mechanochemical model to describe the dynamics of cell realignment in response to cyclically stretched substrates. Our main hypothesis is that cells tend to orient in the direction where the formation of stress fibers is energetically most favorable. We show that, when subjected to cyclic stretch, the final alignment of cells reflects the competition between the elevated force within stress fibers that accelerates their disassembly and the disruption of cell-substrate adhesion as well, and an effectively increased substrate rigidity that promotes more stable focal adhesions. Our model predictions are consistent with various observations like the substrate rigidity dependent formation of stable adhesions and the stretching frequency, as well as stretching amplitude, dependence of cell realignment. This theory also provides a simple explanation on the regulation of protein Rho in the formation of stretch-induced stress fibers in cells.