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Micromechanical Exfoliation and Graphene: 1999 papers and brief discussion of them

The discovery of a new material type, graphene and extremely thin platelets of graphite, was discussed in several articles from my research group published in 1999:

Lu XK, Huang H, Nemchuk N, and Ruoff RS, Patterning of highly oriented pyrolytic graphite by oxygen plasma etching, APPLIED PHYSICS LETTERS, 75, 193-195 (1999).

Jinglei Yang's picture

A good beginning of 2007

In the very beginning of 2007 I have four papers published or accepted (one is independent research and others are collaborated). All of them are the work done in my doctoral period. The topic is focusing on the enhancement of creep resistance of polymers by incorporating of nanofillers including particles and CNTs.

Teng Li's picture

Journal Club Theme of March 2007: Mechanics of Flexible Electronics

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Flexible electronics is an emerging technology with an exciting array of applications, ranging from paper-like displays, skin-like smart prosthesis, organic light emitting diodes (OLEDs), to printable solar cells. These potential applications will profoundly impact various facets of our daily life, and excite our curiosity on: what's the future of newspapers and books? Will OLEDs replace light bulbs and fluorescent lamps, and emerge as future lighting source? Can we power electronic devices everywhere cordlessly? Significant progress has been made in the past several years, especially as sizable investments flux in. For example, Polymer Vision just released the first commercial product of rollable display (as shown in the figure) after secured $26M investment in January 2007. The future success of this emerging technology largely relies on:

Three-dimensional anisotropic elasticity - an extended Stroh formalism

Tom Ting and I have recently developed a method of extending Stroh's anisotropic formalism to problems in three dimensions. The unproofed paper can be accessed at http://www-personal.umich.edu/~jbarber/Stroh.pdf .

Vikram Gavini's picture

Quasi-continuum orbital-free density-functional theory : A route to multi-million atom electronic structure (DFT) calculation

I would like to share the research work I have been pursuing over the past four years. I believe, through this forum, I will be able to reach researchers with various backgrounds and expertise. Suggestions and comments from members will be very useful. I am also attaching links to preprints of manuscripts describing this work. Please follow these links:

http://www-personal.umich.edu/~vikramg/academic/Preprints/QC-OFDFT.pdf

Ashkan Vaziri's picture

Multi-Axial Failure Models for Fiber-Reinforced Composites

The increasing use of fiber-reinforced composites accentuates the need for developing multi-axial fatigue failure models for these materials. In this article (attached), we proposed several multiaxial fatigue failure models for fiber-reinforced composites considering the contribution of mean and cyclic normal stress/strain and shear stress/strain at the plane of failure and examined their capability for predicting the fatigue life of the E-glass/epoxy composite materials.

Accuracy and error estimation in extended finite element methods

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Stephane Bordas, Marc Duflot and Pierre-Olivier Bouchard announce the WCCM8 mini-symposium Link to detailed pdf description 3d error estimation by extended moving least squares

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Which phenomenological flow stress model is the best?

A couple of years ago a colleague who wanted to simulate high-speed machining asked me: " Which is the best phenomenological flow stress model for metals?" I wasn't able to give an answer right away and decided to look in the literature.

What I found was, every ten years or so, a new model appears in the literature that tries to solve some of the problems of older models. However, a clear ranking of models has not been established yet.

Roozbeh Sanaei's picture

what's most advanced open source program to multi-scale simulation?

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I recently interested in multi-sclae modelling problems. and i want to know what's most advanced open source program to multi-scale simulation?

L. Roy Xu's picture

TEM image showing uniformly distributed nano-fibers inside epoxy matrix

We observed that all nanofibers are curved not straight. So the Young’s modulus of the nanocomposite material is always lower than the model prediction using traditional micro-mechanics theory assuming straight nanofibers/nanotubes, as reported by Prof. Y. Huang’s group at UIUC.

Markus J. Buehler's picture

Mesoscale modeling of mechanics of carbon nanotubes: Self-assembly, self-folding and fracture

Using concepts of hierarchical multi-scale modeling, we report development of a mesoscopic model for single wall carbon nanotubes with parameters completely derived from full atomistic simulations. The parameters in the mesoscopic model are fit to reproduce elastic, fracture and adhesion properties of carbon nanotubes, in this article demonstrated for (5,5) carbon nanotubes. The mesoscale model enables one to model the dynamics of systems with hundreds of ultra-long carbon nanotubes over time scales approaching microseconds.

2007 Melosh Competition Finalists Announced

The six finalists for the 19th Annual Robert J. Melosh Medal Competition for the Best Student Paper in Finite Element Analysis were announced last Friday. They are

Baskar Ganapathysubramanian, Cornell University

Damodara Reddy's picture

What are the appropriate values of Young's modulus and wall thickness of single-walled carbon nanotubes (SWCNTs)?

Hi All, Simulations and experimental results show the wide range of values for Young’s modulus (0.5 to 5.5 TPa) and wall thickness (0.066 to 0.34 nm) of carbon nanotubes (CNTs) in literature. Most of the published results say that the set of values (Young’s modulus and wall thickness of CNT) are 1 TPa  and 0.34 nm, and the product is around 0.34 TPa-nm. In my point of view this set of values may be appropriate for multi-walled carbon nanotubes. Can we use the same set of values for analysis of single-walled carbon nanotubes (SWCNTs)?  The interlayer distance between the graphene layers is 0.34 nm. Can we use this value as wall thickness of SWCNT or do we need to use atomic thickness instead of 0.34 nm?

 

Perturbation analysis of a wavy film in a multi-layered structure

A free surface in a multi-layer can experience an undulation due to surface diffusion during fabrication or etching process. In order to analyze the undulation, the elasticity solution for the undulating film is needed. Considering the undulation as a perturbation of a flat surface, a boundary value problem for 2D elasticity is formulated. The solution procedure is straightforward, but very lengthy especially for a multi-layer.

Arun K. Subramaniyan's picture

Equivalence of Virial stress to Continuum Cauchy Stress

Calculating stresses in MD simulations is a controversial topic. There are two different schools of thought about the equivalence of the virial stress to the continuum Cauchy stress; for and against. Some argue based on momentum balance, that only the potential contribution to the virial stress should be considered as the continuum Cauchy stress. However, others assert that the total virial stress that contains both the kinetic and potential parts is indeed the quantity that corresponds to the Cauchy stress in continuum mechanics. We used a simple thermo-elastic analysis to verify the validity of using the total virial stress as the continuum Cauchy stress and found that the total virial stress is indeed the continuum Cauchy stress.

Guide vanes flutter/vibration

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Greetings co-researchers,

I am currently designing a full-scale Impulse turbine (2 to 3 m diameter, 0.5 hub to tip ratio) for extracting of energy from waves.The turbine will be connected to a shore based device oscillating water column (OWC), so the airflow through the turbine is bidirectional (i.e. reverses as the wave enters and recedes in the OWC). This means we have to use symmetrical entry and exit guide vanes. These vanes are fixed, not movable.·        The guide vanes are slender, approximately; height 700mm, chord length 600mm and thickness 2 to 5mm. Their role is to redirect the air flow from the axial direction to an angle of 60o ·        The rotor rotation speed is low (100 RPM to 1000 RPM). ·        The airflow is incompressible (Mach number < 0.3) and unsteady as it is related to the wave energy, which means the mass flow inlet to the turbine changes randomly (from zero to a maximum value say 10kg/s). One of the good approximations to this airflow is a sinusoid, but even this is extremely difficult to simulate in Fluent 6.2 CFD.I have done some preliminary forced vibration response analysis of the guide vanes. As far as I can see, the main cause of any vibration of the guide vanes would be the changes on pressure caused by the chopping of the flow by the rotor (i.e. the passing frequency of the rotor/guide vanes assembly). I plan to measure these pressure variations using pressure tapings on an experimental turbine test rig. 

Please could you comment whether in your experience the main source of guide vane vibration would be the chopping of the fluid flow by the rotor. Also I would appreciate it if you have done any experimental or analytical data on this problem.

atmaca's picture

Crack Propagation

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Hi

I have an investigation on Crack Propagation.

How can i predict the path of a crack.

Please help me!

Giuseppe Carbone's picture

Stick slip instabilities of hot cracks in rubber: The influence of flash temperature

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Here you find a preprint version of a paper published in PRL 95, 114301 (2005) [also see Eur. Phys. J. E. 17, 261-281 (2005)] where the authors present a theory to explain why instabilities, e.g. stick-slip motion, is observed when cracks propagate in rubber materials.

Mike Ciavarella's picture

friction and plasticity: new avenues of research?

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Based on some recent results by Anders Klabring, myself and Jim Barber, showing rigorously that Melan’s theorem only works for a very restricted class of frictional problems, we suggest possible ave

Mike Ciavarella's picture

Some notes on Luan and Robbin's papers on contact and adhesion at atomic scale

As I promised, I start with some brief notes on themes loved by Ken Johnson to hopefully raise some interest for discussion on iMechanica. Regards, Mike

L. Roy Xu's picture

Tensile strength and fracture toughness of nanocomposite materials

Are not as high as we expected although very stiff and strong nanotubes or nanofibers (Young’s modulus E~1000GPa) are added into soft polymer matrices like epoxy (E~4GPa).  In our early investigation on the  systematic mechanical property characterizations of nanocomposites (Xu et al., Journal of Composite Materials, 2004--among top 5 in 2005;and top 10 in 2006 of the Most-Frequently-Read Articles in Journal of Composite Materials.) have shown that there was a very small increase (sometimes even decrease) of critical ultimate tensile/bending strengths, and mode-I fracture toughnesses in spite of complete chemical treatments of the interfacial bonding area, and uniform dispersions of nanofibers (click to view a TEM image). Similar experimental results were often reported in recent years. Therefore, mechanics analysis is extremely valuable before we make these “expensive” nanocomposite materials. Our goal is to provide in-depth mechanics insight, and future directions for nanocomposite development. Till now, nanocomposite materials are promising as multi-functional materials, rather than structural materials. Here we mainly focus on two critical parameters for structural materials: tensile strength and fracture toughness. We notice that other mechanical parameters such as compressive strengths and Young’s moduli of nanocomposite materials have slight increase over their matrices.

Ashkan Vaziri's picture

"Persistence of a pinch in a pipe" by L. Mahadevan, Ashkan Vaziri and Moumita Das

The response of low-dimensional solid objects combines geometry and physics in unusual ways, exemplified in structures of great utility such as a thin-walled tube that is ubiquitous in nature and technology.

MichelleLOyen's picture

Viscoelastic Contacts

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I was a little bit surprised in the introduction of this new forum to see mention of elastic and plastic contacts but no specific mention of viscoelastic contacts.

In the era of commercially-available instruments for indentation testing, the examination of viscoelastic contact mechanics, both in the context of polymers and biological tissues, seems to have taken on new life. To a first approximation, for indentation testing in the time domain, the fundamental mechanics has not much advanced beyond a few classic papers of the 1960s: Lee and Radok, J. Appl. Mech. 27 (1960) 438 and Ting TCT, J. Appl. Mech. 88 (1966) 845. However, the implementation of techniques for analysis of experimental data has progressed substantially. With spherical indenters the use of linearly viscoelastic models for characterization of a material creep or relaxation function is straightforward. Recent experimental studies have confirmed this, while more lingering questions remain for sharp contacts including Berkovich pyramidal indenters (most commonly shipped with commercial indenters). Sharp contacts seem to give rise to nonlinearly viscoelastic responses. Other topics of recent interest include frequency-domain measurements and examination of oscillating contacts and adhesion. (Although not mentioned in the listing of KLJ's most-loved topics in contact mechanics, viscoelastic contact has been the subject of several recent KLJ publications!)  Although research in viscoelastic contact mechanics has been strong in recent years, perhaps a challenge remains in the dissemination of information and the establishment of approachable experimental techniques for use by non-experts.

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