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Mike Ciavarella's picture

Does anyone know a collection of Lennard Jones potential material constants??

I am trying to find out the theoretical adhesive strength limit of a few materials, or more precisely the ratio adhesive strength limit to elastic modulus. I think this is after all part of the Lennard-Jones constants potential - theoretical adhesive strength limit is simply the maximum of the curve.

About me

Non-newtonian fluid is an interesting field.

How do I resize my window for easier reading?

The Drupal software we use for iMechanica makes the blog posts very wide. It may be a little uncomfortable to read from the far left of the window to the far right. With a window so wide, it's easy to lose your place in the reading in moving to the next line of text.

Markus J. Buehler's picture

Large-scale hierarchical molecular modeling of nanostructured biological materials

There have been several posts recently discussing new directions in computational mechanics. Here is a review article that appeared recently that may be of interest.

Large-scale hierarchical molecular modeling of nanostructured biological materials

Make your Excel calculations read like text books!

Download our free XLC software which gives MS Excel the capability of displaying cell formulae as mathematical equations. Your worksheets will read like text books, they'll be easy to understand and easy to check. Download worked solutions and solved problems from our Repository or ask for help in the Forum. It's all free, so join our community and together let’s make it grow!

ExcelCalcs helps users in the following ways:

es 246 project:plane strain extrusion- slip line field solution vs.FEM solution

hi Nanshu Lu,

i'm savita jain. i have project some what related to your topic. can i have results of your final coparision of slip line and FEM solutions.please let me know about any progress in your work.

Will Fong's picture

MATLAB Implementation of AVI

I work with AVI in my research so I have included a MATLAB implementation of AVI for the 1-D harmonic oscillator. The code will solve the equation a + gamma * v + (k1 + k2 + k3) x = 0 with any initial conditions x(0) and v(0). Here the spring constant has been artifically split into three spring constants to simulate multiple potentials. If there is only one potential AVI simplifies to the usual Velocity Verlet integrator. The friction term is absorbed into the k1 term in the implementation. The main idea in the implementation is to construct the propagation matrix for the system (x,v) for the different potentials.

MichelleLOyen's picture

Poroelasticity references

Given the growing interest in poroelasticity within this forum, I thought I would post the link to "Poronet" -- the poromechanics internet resources network.  In particular, there is a nice long pdf chapter on the fundamentals of poroelasticity from Detournay and Cheng, 1993, which has become one of the standard references in the field. 

Stress or strain: which one is more fundamental?

In between stress and strain, which one is the more fundamental physical quantity? Or is it the case that each is defined independent of the other and so nothing can be said about their order? Is this the case?

CAD/CAM/CAE Outsourcing India

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Cycle Sequence of Fatigue Crack Initiation and Growth at the Submicron Scale

I recently used focused ion beam to fabricate some small structures, such as free-standing micro-beams, in LIGA Ni thin films and applied cyclic loads to those small micro-beams. In such a way, dynamics of fatigue crack initiation and growth can be revealed. Part of my results has been attached with this post.

Mike Ciavarella's picture

Contact mechanics of rough surfaces: is Persson's theory better than Greenwood & Willamson?

A recent string of papers originated from Persson's paper in the physics literature contain a number of interesting new ideas, but compare, of the many theories for randomly rough surfaces, only Persson's and Bush et al, BGT. These papers often assume the original Greenwood and Williamson (GW) theory [1] to be inaccurate, but unfortunately do not test it, assuming BGT to be its better version. The original GW however is, I will show below, still the best paper and method today (not surprisingly, as not many papers have the level of 1300 citations), containing generally less assumptions than any other model, including the constitutive equation which does not need to be elastic! I just submitted this Letter to the Editor: On "Contact mechanics of real vs. randomly rough surfaces: A Green's function molecular dynamics study" by C. Campaña and M. H. Müser, EPL, 77 (2007) 38005. C. Campaña and M. H. Müser also make several questionable statements, including a dubious interpretation of their own results, and do not even cite the original GW paper; hence, we find useful to make some comments.

Henry Tan's picture

experimentally, stresses cannot be measured directly

Experimentally, loading to a mechanical system can be applied either through the displacement control or the force control.

However, the responses of the system can only be measured in displacements, and hence strains.

Is Strain Gradient Elasticity Relevant for Nanotechnologies?

Determination of Strain Gradient Elasticity Constants for Various Metals, Semiconductors, Silica, Polymers and the (Ir) relevance for Nanotechnologies

Strain gradient elasticity is often considered to be a suitable alternative to size-independent classical elasticity to, at least partially, capture elastic size-effects at the nanoscale. In the attached pre-print, borrowing methods from statistical mechanics, we present mathematical derivations that relate the strain-gradient material constants to atomic displacement correlations in a molecular dynamics computational ensemble. Using the developed relations and numerical atomistic calculations, the dynamic strain gradient constants have been explicitly determined for some representative semiconductor, metallic, amorphous and polymeric materials. This method has the distinct advantage that amorphous materials can be tackled in a straightforward manner. For crystalline materials we also employ and compare results from both empirical and ab-initio based lattice dynamics. Apart from carrying out a systematic tabulation of the relevant material parameters for various materials, we also discuss certain subtleties of strain gradient elasticity, including: the paradox associated with the sign of the strain-gradient constants, physical reasons for low or high characteristic lengths scales associated with the strain-gradient constants, and finally the relevance (or the lack thereof) of strain-gradient elasticity for nanotechnologies.

Zhigang Suo's picture

Poroelasticity, or migration of matter in elastic solids

A sponge is an elastic solid with connected pores. When immersed in water, the sponge absorbs water. When a saturated sponge is squeezed, water will come out. More generally, the subject is known as diffusion in elastic solids, or elasticity of fluid-infiltrated porous solids, or poroelasticity. The theory has been applied to diverse phenomena. Here are a few examples.

Zhigang Suo's picture

An interview with New World Times (新世界时报)

The following interview appeared in New World Times (新世界时报)on 23 February 2007.

特约编辑:弥递雅

(以下简称):锁志刚教授您好!首先非常感谢您接受我的采访。我是从ISI科学论文引证系统知道您。2002年8月各个领域的统计中,论文引证最多的文章有你和(John Hutchinson)教授的论文。据统计您的论文当年被引用达三百多次,目前已经达到七百多次。您能否给我们一些关于您的背景介绍?

Xiaoyan Li's picture

Simulating Fullerene Ball Bearings of Ultra-low Friction

We report the direct molecular dynamics simulations for molecular ball bearings composed of fullerene molecules (C60 and C20) and multi-walled carbon nanotubes. The comparison of friction levels indicates that fullerene ball bearings have extremely low friction (with minimal frictional forces of  5.283×10-7 nN/atom and  6.768×10-7 nN/atom  for C60 and C20 bearings) and energy dissipation (lowest dissipation per cycle of  0.013 meV/atom  and  0.016 meV/atom  for C60 and C20 bearings). A single fullerene inside the ball bearings exhibits various motion statuses of mixed translation and rotation. The influences of the shaft's distortion on the long-ranged potential energy and normal force are discussed. The phonic dissipation mechanism leads to a non-monotonic function between the friction and the load rate for the molecular bearings.

Michael H. Suo's picture

Del.icio.us

Del.icio.us is a social bookmarking web service. One might say, why do I need del.icio.us if I have bookmarking capabilities built right into my browser? Well, here are some reasons:

  • del.icio.us uses a non-hierarchical categorization system, that is, instead of organizing your bookmarks in folders, you assign tags to them.

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.

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