Hi All,

I'm presently working on modelling of guided ultrasonic wave scattering at defect using Abaqus/CAE. Can anyone help me with some tutorial materials on modelling of crack or notch in a through-hole of a plate?

Warm Rgrds.

Jo Ukpai

Hi everyone,

I have a question about the calculation of sress in MD sumulation.
The concept of stress in a continuum body is well known, which is Cauchy stress, defined as the average amount of force exerted per unit area. In MD simulation virial stress is generally used as a equivalent of the continuum Cauchy stress. Of course we can get the stress tensor of per atom according to the Virial theory, but the problem is what is the meaning of the stress in the strain-stress curve of nanowire. How to calculate this stress? Is it still F/A? Have anyone had such good experience?
Any guiding would be greatly appreciated. Thanks.

Best regards,

LIBO

Dear Imechanica friends

  I have just had a paper rejected by International Journal of Fatigue!!  But I feel extremely happy. 

And I will tell you why: It reminds me that Paul Paris declared that his fundamental contribution to Fracture Mechanics was rejected 3 times before becoming the standard of Crack Propagation! 

I attach entirely the paper, the rejection letter, the reviewers reports. They are funny to read!  These reviewers have a hard time to avoid the content of the paper, and avoid the arguments.  Regards, Michele Ciavarella,   www.micheleciavarella.it

Place: University of Texas at Austin, WRW 312

Time: Friday 3:00 - 4:30 pm, May 23 - August 22, 2008

Faculty advisors: Chad Landis and Rui Huang

Speakers: postdocs and graduate students, including guest speakers from other groups

Tentative schedule:

(Date, Seminar title, Speaker name, Group affiliation)
 

In the attached manuscript, we present enriched FE formulations to impose Bloch-periodic boundary conditions. Bloch-periodic BCs arise in the description of wave-like phenomena in periodic media: periodic composites, Schrodinger equation in quantum mechanics, photonic band-gap materials, etc. For a perspective, see the J-Club on elastodynamic bandgaps and metamaterials that was organized by Biswajit Banerjee

The criteria of Cermelli and Gurtin (2001, J. Mech. Phys. Solids) for choosing a geometric dislocation tensor in finite plasticity are reconsidered. It is shown that physically reasonable alternate criteria could just as well be put forward to select other measures; overall, the emphasis should be on the connections between various physically meaningful measures as is customary in continuum mechanics and geometry, rather than on criteria to select one or another specific measure.

A network of polymers can imbibe a large quantity of a solvent and swell, resulting in a gel.  The swelling process can be markedly influenced by a mechanical load and geometric constraint.  When the network, solvent, and mechanical load equilibrate, the gel usually swells by a field of inhomogeneous and anisotropic deformation.  We show that this field in the swollen gel is equivalent to that in a hyperelastic solid.  We implement this theory in the finite-element package, ABAQUS, and analyze examples of swelling-induced deformation, contact, and bifurcation.  Because commercial software like ABAQUS is widely available, this work may provide a powerful tool to study complex phenomena in gels.

I am using Meshless Petrov-Galerkin Method(MLPG) for non-rectangular domains. There is a flexibility of using any shape for weight function and also for local quadrature  domain. Here in my case case weight function domain and local quadrature domains are same.

 I want to know that  , for non-rectangular domains,how the different shapes of weight functions (specially circular or rectangular) will affect accuracy of the result  ?

Just published in this month's Journal of Materials Research--a study on poroelastic nanoindentation characterization for hydrated bone samples.  Poroelastic problems are notoriously difficult to incorporate into routine materials characterization due to the paucity of problems with closed-form solutions.  However, in some cases, a master-curve does exist and parameter identification can be accomplished without requiring inverse finite element analysis and optimization for every condition.  The abstract follows, linked from here .

Poroelastic nanoindentation responses of hydrated bone, J. Mater. Res. 23 (2008) 1307.

Hello,

 Is there any gait/biomechanics data out there that would give me the muscle moment (aka internal torque) about the ankle generated by the tibialis anterior (TA) when it is eccentrically contracting during loading response?  This phase of gait occurs just after heel strike, where the TA allows the foot to drop in a controlled manner.  Of course, the moment is dependent on several factors, mainly body weight, stature, and walking speed.  So, I'm wondering if there is an equation with independent variables of weight and height giving a typical value for the moment when an adult person is walking at some "average" speed.

Laser shock peening (LSP) is an innovative surface treatment technique, which has been successfully applied to improve fatigue performance of metallic components. The key beneficial characteristic after LSP treatment is the presence of compressive residual stresses beneath the treated surface of metallic materials, mechanically produced by high magnitude shock waves induced by a high-energy laser pulse. Finite element analysis method has been applied in order to predict the residual stresses and plastic deformation induced by LSP. 

Abstract of paper recently accepted for publication in Journal of Applied Physics:

I am a new ABACUS user and i would like to model a shoulder bones with applying muscles forces on it.  I hope if any one has an idea of applying finite element as well that will be great.

It is generally believed that similar to soluble ligand-induced signal transduction, mechanotransduction initiates at the local force-membrane interface (e.g., at focal adhesions) by inducing local conformational changes or unfolding of membrane-bound proteins, followed by a cascade of diffusion-based or translocation-based signaling in the cytoplasm. However, all published reports, including past studies with the reporter type of construct extended here, were limited in timescale to address this fundamental issue.

dear Imechanica friends

 I see the discussion on the Engineering Challenges is not really getting anywhere, despite it is put in the front page for ages!  

Zhigang Suo himself said he feels "dizzy" by reading them

"Big challenges usually make people dizzy and disoriented, feelings that then translate to indifference"

He is quite right!  And now I understand why!

He suggests to start with teaching, but Pradeed responds and changes completely subject!

Michelle Oyen says she doesn't like the choice of the themes, and says "they are not readily mechanics topics at all. "!

Nadine Aubry says exactly the opposite!

Xin-Lin Gao and I had the pleasure of guest-editing a special  issue on "scale effects in mechanics" for the journal, Mathematics and Mechanics of Solids (editor: Professor David Steigmann , UC Berkeley).

Professor Jerry Ericksen (Timoshenko awardee, 1979 ) kindly provided an authoritative review of the Cauchy-Born rule. In addition, the special issue contains six other notable papers. Interested folks can get an overview of the special issue and the contained papers by reading the attached preface.

I just wanted to know if i can consider one part of a FE model as a meshless part and form the global stiffness matrix just by assembling the meshfree stiffness matrix corresponding to the meshfree zone and the FE stiffness matrix of the rest. And then apply the boundary conditions to the model and solve. I would use RKPM to generate the meshfree stiffness matrix. 

for example mesh a square plate into 4  elements , suppose ele 1,2,3 are e finite elements and  the rest of the domain is discretized using nodes. such that there are 4 nodes on the four corners of the forth piece. and many other nodes in the interior.

Dear Imechanica friends: in connection to the www.engineeringchallenges.org and Roberto Ballarini post suggesting the presidential Candidates Obama, Clinton and McCain do not seem to respond to the Sciencedebate2008, and see the call for "Science White House" by Nobel prize winners David Baltimore and Ahmed Zewail, the USA seems to be in a big Science Crisis, which is called already in Scientific Literature the American PARADOX (see below). In very short, this is due to the fact that the ONLY real big thing for the American (and European) public is Sport and TV stars. There is "legs-drain" of David and Victoria Beckham ---- the public and politicians do not care of the "brain-drain" of best people like for example people who already running operations in both US and in Asia (see the A* program in Singapore). And not even of Nobel-prize-winner-drain!!!

Carbon nanotubes as strong fibers in CNT-composites are subjected to large deformations in radial direction. They provide strength as well as structural damping in the composite. Despite being strong in the axial direction, CNTs are rather soft in the radial direction.

can i now about the theoritical formul for natural frequency of leaf spring.

any document on manufracture of composite leaf spring

Many researchers have already used micromechanical modeling techniques such as Mori-Tanaka (M-T), Self-consistent methods and dilute inclusion models depending on volume fraction and shape of the inclusions, etc., to predict the overall mechanical properties of CNT/polymer composites.  However, we know that at nano scales the phenomenological behavior of material is different in comparison with micro or macro scales. Although the effects of waviness, interactions, agglomeration, etc.

Hi everybody.  My name is Ada. I am a new user on this forum.

I am working with microcantilevers (MCs). Recently I experienced lack of sensitivity. I use  MCs coated with nanostructured gold and I use SAM to attach different biological molecules e.g. Protein A, IgG, antiIgG. Everything was working fine until recently.

Would enybody have any sugestions what might be wrong?

Thanks,

Ada 

On Friday, April 25th, 2008, the 20th Annual Melosh Competition for the Best Student Paper in Finite Element Analysis was held at Duke University.  The competition resulted in a tie between Ludovic Chamoin (of the University of Texas, Austin) and Irina Kalashnikova (of Stanford University).   Here is a picture of the 2008 Melosh Medalists with the judges, Leo Franca and Nicolas Moes:

 From L to R: Leo Franca, Ludovic Chamoin, Irina Kalashnikova, Nicolas Moes.  

Here is a recent work on the Poisson's ratio of carbon nanotube sheet [1]. From the experimental results, the researchers found that the Poisson's ratio could change from 0.06 to -0.20 as the content of MWNTs increasing from 0~100%. The interesting zero Poisson's ratio and auxetic materials were thus found.  

Ref. [1] Sign Change of Poisson's Ratio for Carbon Nanotube Sheets. Science 25 April 2008: 504-507

Ying Li

Department of Engineering Mechanics, Tsinghua University