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Xuanhe Zhao's picture

Electromechanical hysteresis and coexistent states in dielectric elastomers

Active polymers are being developed to mimic a salient feature of life: movement in response to stimuli. Large deformation can lead to intriguing phenomena; for example, recent experiments have shown that a voltage can deform a layer of a dielectric elastomer into two coexistent states, one being flat and the other wrinkled. This observation, as well as the needs to analyze large deformation under diverse stimuli, has led us to reexamine the theory of electromechanics.

Simulating explosions

Recently Henry talked about software that could be used to simulate explosions and introduced CartaBlanca. Luming asked whether anyone had used the software, how good it was, and whether one needed Java to implement models into CartaBlanca.

MichelleLOyen's picture

New Micromechanics Book

This message about a new book came over the PoroNet (poroelasticity network) mailing list:

Dear Colleagues:

      I would like to inform you that my book "Micromechanics of Heterogeneous Materials” (containing around 700 pages, 140 figures, 3000 formulae, and 1200 references) should be published by Springer on 07.06.07. [Details are on the web http://www.springer.com/west/home/engineering?SGWID=4-175-22-173670290-d...|toc ] .

      In the framework of a unique scheme of the proposed multiparticle effective field method, we have undertaken in this book an attempt to analyze the wide class of statical and dynamical, local and nonlocal, linear and nonlinear multiscale problems of composite materials with deterministic (periodic and nonperiodic), random (statistically homogeneous and inhomogeneous, so-called graded) and mixed (periodic structures with random imperfections) structures in bounded and unbounded domains, containing coated or uncoated inclusions of any shape and orientation and subjected to coupled or uncoupled, homogeneous or inhomogeneous external fields of different physical natures.

        Any the remarks and comments regarding the book will be fully appreciated.

Fang Wang's picture

BRAIN TEMPERATURE AND INTRACRANIAL PRESSURE – A QUANTITATIVE BIOLOGICAL-THERMAL-MECHANICAL PERSPECTIVE

The present paper studies the effect of intracranial temperature (ICT) change on intracranial pressure (ICP). Thermal and mechanical effects were analyzed using a 3D finite element model of the human head.

Ashfaq Adnan's picture

Why larger time step is not allowed in Molecular Dynamics Simulation?

Hi, 

I am trying to understand why MD simulation crashes if larger time step (~100 fs) is applied to integrate the equation of motion. I know that there are two major things play role in solving F = ma and obtaining equilibrium solution. One is the accuracy, and the other is numerical stability of the integration algorithm.

Fang Wang's picture

Effects of Head Size and Morphology on Dynamic Responses to Impact Loading

Head responses subjected to impact loading are studied using the finite element method. The dynamic responses of the stress, strain, strain energy density and the intracranial pressure govern the intracranial tissues and skull material failures, and therefore, the traumatic injuries.

Henry Tan's picture

Sandwich structures

This blog is on the sandwich structures.

JDI's picture

Science, 6, April, 2007 Direct-Current Nanogenerator Driven by Ultrasonic Waves

Choose a channel featured in the header of iMechanica: 

What can we do in this discovery and creation?

By Xudong Wang, Jinhui Song, Jin Liu, Zhong Lin Wang*

Seungtae Choi's picture

Scale bridging mechanics: Nanoscale planar field projection of atomic decohesion and slip in crystalline solids

I would like to introduce my recent paper on field projection method with Prof. K.-S. Kim at Brown University. When atomistic simulations or atomic resolution experiments are carried out to analyze deformation energetics of atomic lattices near a crack tip, the results of the atomic positions and the total energy of the system have not been systematically converted to field quantities such as stresses or tractions near the crack tip. In this study, we introduce a mathematically consistent way of defining and measuring the cohesive tractions, separations and surface stresses in an atomic decohesion process zone using the atomic displacement data at some distance away from the crack tip. The method is called “nano-scale planar field projection method.” This is a generalization of the method developed for isotropic homogeneous solids by Hong and Kim (2003). The formulation introduced here is applicable to interface cracks between anisotropic solids as well as to cracks in homogeneous solids whether they are anisotropic or isotropic. The field projection method is then applied to a crack tip field in gold, simulated atomistically. The atomistic simulation is made with an embedded atom method (EAM) potential for a crystal decohesion along [112] direction in a (111) plane. Then, the details of energy partition in various modes of nano-scale separation processes are analyzed with the field projection method.

How to include the surface effect aournd a nano-sized crack

Choose a channel featured in the header of iMechanica: 

Dear Mechanicians,

I am reading some papers on the surface effects of nano-sized elements(bars,beams, plates, films) or defects(inhomogeneities, inclusions, cavities) these days. Some researchers have studied the surface effects on the stress state around a circular hole or an elliptic hole. I wonder if there is any research work on the surface effect around a nano-sized crack. Thank you!

Fang Wang's picture

BIOMECHANICAL STUDY OF GOLF BALL IMPACT ON CHILD’S HEAD USING THE FINITE ELEMENT METHOD

Head traumatic injury due to the impact of a flying golf ball is one of the severest injuries sustained on a golf course. This paper presents numerical simulation results based on the finite element (FE) method to investigate head injuries in children due to impacts by flying golf balls.

Ying Li's picture

How to characterize the interface?

Recently, I am interested in the interface between two different masses. But, I don’t know how to characterize the interface between them, especially the adhesive strength and the mechanics model.

huang peng's picture

Impact and explosion mechanics in China

Choose a channel featured in the header of iMechanica: 

Impact and explosion mechanics in China

Impact and explosion mechanics is a muti-discipline subject , which concern mechanics, physics, and chemistry. As you know, explosive wave propagation and penetration problems are researched in impact and explosion mechanics.

How to simulate corrosion layer using ABAQUS

Dear Forum Members:

Does anyone have a chance to simulate a corrosion layer using ABAQUS? If yes, could you please explain to me what type of constitutive model you use; i.e. UMAT?

Thank you and best regards,

information needed

Would anyone have spec sheets for the load cell of the LIDO multijoint systemII?

I want to convert the torque readings from volts to newton-meter. I know LIDO dynamometer gives output as torque. But, our lab does not have any spec sheets or manuals, as this system is an old donated system.

Xiaodong Li's picture

On the uniqueness of measuring elastoplasticproperties from indentation

Indentation is widely used to measure material mechanical properties such as hardness, elastic modulus, and fracture toughness (for brittle materials). Can one use indentation to extract material elastoplastic properties directly from the measured force-displacement curves? Or simply, is it possible to obtain material stress-strain curves from the corresponding indentation load-displacement curves? In an upcoming paper in JMPS titled "On the uniqueness of measuring elastoplastic properties from indentation: The indistinguishable mystical materials," Xi Chen and colleagues at Columbia University and National Defense Academy, Japan show the existence of "mystical materials", which have distinct elastoplastic properties yet they yield almost identical indentation behaviors, even when the indenter angle is varied in a large range. These mystical materials are, therefore, indistinguishable by many existing indentation analyses unless extreme (and often impractical) indenter angles are used. The authors have established explicit procedures of deriving these mystical materials. In many cases, for a given indenter angle range, a material would have infinite numbers of mystical siblings, and the existence maps of the mystical materials are also obtained. Furthermore, they propose two alternative techniques to effectively distinguish these mystical materials. The study in this paper addresses the important question of the uniqueness of indentation test, as well as providing useful guidelines to properly use the indentation technique to measure material elastoplastic properties.

Ashkan Vaziri's picture

Flexible Probes for Characterizing Surface Topology: From Biology to Technology

In nature, several species use flexible probes to actively explore their environment, and acquire important sensory information, such as surface topology and texture, water/air flow velocity, etc. For example, rats and other rodents have an array of facial vibrissae (or whiskers) with which they gather tactile information about the external world.  The complex mechanisms, by which mechanical deformations of the probe lead to neuronal activity in the animal’s nervous system are still far from being understood. This is due to the intricacy of the deformation mechanics of the flexible sensors, the processes responsible for transforming the deformation to electrical activity, and the subsequent representation of the sensory information by the nervous system. Understanding how these mechanosensory signals are transduced and extracted by the nervous system promises great insight into biological function, and has novel technological applications. To understand the mechanical aspect of sensory transduction, here we monitored the deformation of a rat’s vibrissa as it strikes rigid objects with different topologies (surface features) during locomotion, using high-speed videography. Motivated by our observations, we developed detailed numerical models to study the mechanics of such flexible probes. Our findings elucidate how active sensation with vibrissae might provide sensory information and in addition have direct implications in several technological areas. To put this in perspective, we propose strategies in which flexible probes can be used to characterize surface topology at high speeds, which is a desirable feature in several technological applications such as memory storage and retrieval. (The full article is attached)

Amit Acharya's picture

Toward averaging nonlinear dynamics

Attached is a paper outlining ideas for averaging autonomous dynamics, based on a dynamical systems point of view.

People interested in computational multiscale modeling, especially of the sequential kind, as well as nonequilibrium statistical mechanics may find these ideas useful.

fengliu's picture

From self-bending of nanofilms to fabrication of nanotubes

We demonstrate, by theoretical analysis and molecular dynamics simulation, a mechanism for fabricating nanotubes by self-bending of nanofilms under intrinsic surface stress imbalance due to surface reconstruction. A freestanding Si nanofilm may spontaneously bend itself into a nanotube without external stress load, and a bilayer SiGe nanofilm may bend into a nanotube with Ge as the inner layer, opposite of the normal bending configuration defined by misfit strain.

Lakshmana B K's picture

Fluid-Structure Interaction study on artery help needed

I am now doing my project on "Fluid-Structure Interaction study on artery", using ANSYS-9.0, I am doing 3-D FSI analysis using fluid142 & solid185 using FSI solver. I have written a macro as per the help file specified in FSI, ANSYS under coupled field approach.

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