Composites Part B: Engineering, 2008, Vol. 39, No. 6, pp. 933-961.

A phase field method is developed to investigate the morphological evolution of a vesicle in an electric field, taking into account coupled mechanical and electric effects such as bending, osmotic pressure, surface tension, flexoelectricity, and dielectricity of the membrane. The energy of the system is formulated in terms of a continuous phase field variable and the electric potential. The governing equations of the phase field and the electric field are solved using the Galerkin weighted residual approach. The validation and robustness of the algorithm are verified by direct comparisons of the obtained numerical solutions with relevant experimental results. The morphological evolution of an axisymmetric vesicle under an electric field is studied in detail. The results demonstrate that the present method can simulate complex morphological evolutions of vesicles under coupled mechanical–electrical fields.

This study aimed to develop a method to construct tensegrity structures from elementary cells, defined as structures consisting of only one bar connected with a few strings. Comparison of various elementary cells leads to the further selection of the so-called 'Zshaped' cell, which contains one bar and three interconnected strings, as the elementary module to assemble the Z-based spatial tensegrity structures. The graph theory is utilized to analyse the topology of strings required to construct this type of tensegrity structures. It is shown that 'a string net can be used to construct a Z-based tensegrity structure if and only if its topology is a simple and bridgeless cubic graph'. Once the topology of strings has been determined, one can easily design the associated tensegrity structure by adding a deterministic number of bars. Two schemes are suggested for this design strategy. One is to enumerate all possible topologies of Z-based tensegrity for a specified number of bars or cells, and the other is to determine the tensegrity structure from a vertex-truncated polyhedron. The method developed in this paper allows us to construct various types of novel tensegrity structures.

Surface effects often play a significant role in the physical properties of micro- and nanosized materials and structures.In this letter,the authors presented a theoretical model directed towards investigation of the effects of both surface elasticity and residual surface tension on the natural frequency of microbeams.A thin surface layer was introduced on the upper and lower surfaces to rationalize the near-surface material properties that are different from the bulk material.An explicit solution is derived for the natural frequency of microbeams with surface effects.This study might be helpful for the design of microbeam-based sensors and some related measurement techniques.

Journal of the Mechanics and Physics of Solids, 2008, Vol. 56, No. 9, pp. 2844–2862.

This letter reports a simple and versatile approach for extracting bionanofibers from natural materials using the ultrasonic technique.Bionanofibers have been fabricated from various materials,e.g.,spider and silkworm silks,chitin fibers,collagen,cotton,bamboo,and ramee and hemp fibers.The obtained nanofibers have uniform diameters in the range of 25-120 nm and possess the optimized hierarchical structures and superior properties of natural materials which have formed after the evolution of many millions of years.This methodology might be valuable to provide a convenient,versatile,and environmentally benign fabrication method for producing bionanofibers at an industrial scale.

Phase transformational shakedown of a structure refers to a status that plastic strains cease developing after a finite number of loading cycles,and subsequently the structure undergoes only elastic deformation and alternating phase transformations with limited magnitudes.Due to the intrinsic complexity in the constitutive relations of shape memory alloys (SMA),there is as yet a lack of effective methods for modeling the mechanical responses of SMA structures,especially when they develop both phase transformation and plastic deformation.This paper is devoted to present an algorithm for analyzing shakedown of SMA structures subjected to cyclic or varying loads within specified domains.Based on the phase transformation and plastic yield criteria of von Mises-type and their associated flow rules,a simplified three-dimensional phenomenological constitutive model is first formulated accounting for different regimes of elastic-plastic deformation and phase transformation.Different responses possible for SMA bodies exposed to varying loads are discussed.The classical Melan shakedown theorem is extended to determine a lower bound of loads for transformational shakedown of SMA bodies without necessity of a step-bystep analysis along the loading history.Finally,a simple example is given to illustrate the application of the present theory as well as some basic features of shakedown of SMA structures.It is interesting to find that phase transformation may either increase or decrease the load-bearing capacity of a structure,depending upon its constitutive relations,geometries and the loading mode.

Smart-Cut is a recently established,advanced technology for fabricating high-quality silicon-on-insulator (SOI) systems andhas foundmany other successful applications.It meets almost all the high requirements for processing and manufacturing SOI wafers,which provide the basis of ultra-large-scale integration device structures of modern microelectronic industry.In the present paper,we present a fundamental study on the basic mechanisms in the Smart-Cut technology from the viewpoints of mechanics and physics.First,a model for defect nucleation induced by hydrogenion implantation is establishedbasedon the continuum mechanics theory accounting for the crystal structure of silicon.This model is used to provide an upper bound on the implantation dose of hydrogen ions,one of the most important process parameter in the Smart-Cut technology.An analytical formulation is derived to calculate the defect density as a function of the H-implantation dose and the temperature.Then,the splitting of SOI wafers in the Smart-Cut technology is analyzedusing the elastic fracture mechanics theory.Accounting for the embrittlement and diffusion effects of hydrogen,a lower bound of the implantation dose of hydrogen ions is derived,which agrees reasonably with experimental observations.Furthermore,the effects of the handle wafer adopted in the Smart-Cut technique are examined on the splitting process.It is found that the handle wafer leads to uniform crack propagation and higher uniformity in the thickness of the final SOI systems,in comparison with conventional techniques to produce SOI substrates, and prohibits the blistering and flaking failure of an H-implanted wafer.This work provides not only a fundamental understanding to the physical mechanisms associated with the Smart-Cut technology but also a useful reference for determining the process parameters of SOI industrial production.

We here demonstrate that surface charges on a spherical soft particle may induce its morphology instabillity. It is found that various patterns can be obtained by varying the surface charge density. The critical condition for the occurrence of surface instability and the wavelength of the induced surface patterns are derived analytically and, thereby, the morphological phase diagram of soft particles can be provided easily. Besides the electric stress, surface tension also plays a significant role in the surface evolution process. In addition, the morphological evolution behavior of a soft particle is demonstrated to exhibit distinct dependence on its size. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3177189]

Water striders are a type of insect with the remarkable ability to stand effortlessly and walk quickly on water.This article reports the water repellency mechanism of water strider legs.Scanning electron microscope (SEM) observations reveal the uniquely hierarchical structure on the legs,consisting of numerous oriented needle-shaped microsetae with elaborate nanogrooves.The maximal supporting force of a single leg against water surprisingly reaches up to 152 dynes,about 15 times the total body weight of this insect.We theoretically demonstrate that the cooperation of nanogroove structures on the oriented microsetae,in conjunction with the wax on the leg,renders such water repellency.This finding might be helpful in the design of innovative miniature aquatic devices and nonwetting materials.