There has recently been a great deal of discussion on imechanica regarding the effects of surface stress on the resonant properties of nanostructures such as nanowires.  The controversy has revolved around the strain-independent part of the surface stress, which can be shown, i.e. by Gurtin et al. APL 1976, 529-530, or by Lu et al, PRB 2005, 085405, to have no effect on the resonant frequency of the nanobeam.  The reason is because in taking the moment, and differentiating the moment to get the beam equation of motion, the strain-independent part of the surface stress drops out as it is constant, while the strain-dependent (surface elastic) part survives the differentiation.

 A linear constitutive thermodynamic relation between thermodynamic force f and flux v.

v = Mf, where M is the phenomological coefficient. 

How to constitute a nonlinear thermodynamic constitutive relation for an unknown system which we expect to exibit nonlinear behaviour?

I am using exponent Drucker-Prager model at the moment, is there anyone can tell me where the follow exponent D-P eqation comes from originally?

(σ e)(σ e)=λ(σt)(σt)-3(λ-1)σmσt

Where λ= is hydrostatic stress sensitivity parameter and equal to σc/σt, σe is effective stress, σm is hydrostatic stress, σc, σt are stresses under compression and tension, respectively.

In a recent rapid communication (see attached paper), using principles of pattern formation, we expose some simple stategies to reliably produce perfect long range order in self-assembling systems. Most self-assembling systems exhibit short ranged order. This imperfection is detrimental to several practical applications. It is almost always possible to produce perfect patterns in small domain sizes but self-assembly over a larger areal span results in defects.

I'm trying to model a composite structure with shell 99 element in Ansys.

I set the thickness and material no. in real constant and prepare an orthotropic material property for that. While ploting the result, as I expect to get the stresses among layers different from other points, but the result is a kind of uniform isotropic graph.

I don't know if any setting other than real constant and material property should be done to get a true result or not. and if I'm true then how can I read the true result.

I will appreciate any help.

Thanks in advance.

N.Dolatabadi

Dear Mechanicians,

Dear iMechanicians,

It seems that nobody here is active in fatigue life prediction focused on the initiation period. I believe it should be here and do not understand why the fracture mechanics has its place here but the initiation of cracks has been forgotten. Although cracks are very interesting there is a lot industrial sectors, where they are not wanted. Is not the reason of the current situation that the available computational tools that are free are mostly related to crack growth?

Regards,

Jan Papuga

For more than 15 years, carbon nanotubes (CNTs) have been the flagship material of nanotechnology. Researchers have conceived applications for nanotubes ranging from microelectronic devices to cancer therapy. Their atomic structure should, in theory, give them mechanical and electrical properties far superior to most common materials.  

Nature 454, 748-753
A Hemispherical Electronic Eye Camera Based on Compressible Silicon Optoelectronics
Ko et al., 2008
http://www.nature.com/nature/journal/v454/n7205/full/nature07113.html

Hi,

Iam a new user of abaqus. I have a subroutine written in *.for format. I also have an input file *.inp . Both these programs are in the same folder. When I try to execute the *.inp file using the command

abaqus job=jobname datacheck interactive

I get a  message saying  "Abaqus/Standard Analysis exited with an error. please see the message file for possible error messages". I looked in the message file and it says ***ERROR: USER SUBROUTINE UMAT IS MISSING.

Then I used the command

abaqus job=jobname user=umat.for

nothing happens and I am out of the command loop.

Can somebody please help me to understand how things work in abaqus?

Lots of thanks in advance.

We measured the elastic properties and intrinsic breaking strength of free-standing monolayer graphene membranes by nanoindentation in an atomic force microscope. The force-displacement behavior is interpreted within a framework of nonlinear elastic stress-strain response, and yields second- and third-order elastic stiffnesses of 340 newtons per meter (N m–1) and –690 Nm–1, respectively. The breaking strength is 42 N m–1 and represents the intrinsic strength of a defect-free sheet. These quantities correspond to a Young's modulus of E = 1.0 terapascals, third-order elastic stiffness of D = –2.0 terapascals, and intrinsic strength of int = 130 gigapascals for bulk graphite. These experiments establish graphene as the strongest material ever measured, and show that atomically perfect nanoscale materials can be mechanically tested to deformations well beyond the linear regime.

Lee, C.; Wei, X.; Kysar, J. W.; and Hone, J. (2008) “Measurement of the Elastic
Properties and Intrinsic Strength of Monolayer Graphene” Science, 321, 385-388.

http://www.sciencemag.org/cgi/content/full/321/5887/385

This is suneel donthamsetty working on metal matrix nanocomposites.i want to analyse aluminium matrix (Sic reinforced)nanocomposites using Ansys software.which type of element is suitable for nanoparticles.can any body answer please.

I need help to determine or contruct the crack reistance (R-curve) of a material that show crack bridging. I have the experimental data of applied load and crack lengths due to these applied loads. the SENB specimen was used and loading was 4-pt-bending. The plot of Kapp versus crack size did not give the usual rising curve which plateaus, but rather increases exponentially. How do I get the Kb (i,e K due to bridging) or the normal R-curve. I am not a mechanical engineer but into applied mechanics.

We have read some papers of stroh formalism and the textbook of Tom Ting, and found that the stroh formalism and the hamilton system proposed by prof.zhong wanxie had some relation. We want to know whether the stroh formalism is enough for the analysis of the anisotropic elastic? Thus's to say, for some problems could not  give the satisfied answer which we may try the hamilton framework. I briefly compare the two methods as follows:

This paper revisits continua with microstructure from a geometric point of view. We model a structured continuum as a triplet of Riemannian manifolds: a material manifold, the ambient space manifold of material particles and a director field manifold. Green-Naghdi-Rivlin theorem and its extensions for structured continua are critically reviewed.

I am trying to model the air inside a 195/65 R16 radial car tire using ABAQUS(6.6.1). I am interested in knowing the air cavity volume and pressure change due to vertical loading. I think fluid elements are the way to go. 

I would appreciate pointers with regard to creating fluid elements (examples, input files etc..) as ABAQUS/CAE does not support this feature.

My ANSYS model is a plate. i need to apply two different loads on the model, one an out-of-plane load and the other an in-plane load. Out of the two loads one load should be kept constant during the analysis and the other load needs to be varied in incremental steps. Is there any way to keep one load constant and increment only the other load in the ANSYS analysis?

I intend to do some tensile testing on some composite materials with very small thickness (about 0.5-1mm) and size 3 cm x 1 cm in a temperature ramp mode. I would like to know the name of such a testing machine or contact if any one has the same?

Dear all

Hello

I am going to silulate machining process, specially grinding.

Should you have any cooment please let me know.

I have one solid Y-strucutre model which i have modelled as assuming beam model in NASTRAN. From NASTRAN i am extracting internal loads (Nodal forces and Nodal Moments) successfully and then i am doing the strength analysis of perticule section by using internal loads. Now i have model the same structure using 3D solid finite element model by assuming Tet Mesh under ABAQUS. Analysis was running perfectly in ABAQUS. Now my problem is how to extract the internal loads from the 3D solid Tet mesh model for the same section. I need help to extract the internal loads from the solid Tet mesh. Please help me i am right now stuck at this point.

I'm working on the numerical solution of the mixed problem in lubricated contacts. Does anyone know if the lubricant equation (Reynolds one) was never solved for film thickness instead of pressure (like actually is done with MGMI techniques) in some pubblication?

The surface stability of thin film/substrate system is an important problem both in the film synthesis and reliability of micro electrical and mechanical system (MEMS). In this work, the elastic anisotropy effect on surface stability of thin film/substrate system was considered. The theoretical analysis indicates that elastic anisotropic influence could play an important role in the surface stability of thin film/substrate system.

I am interested in slope analysis by Meshfree Method, and trying to make out something in the coming years. wish to have friends here in imachanica

We present a top-down hierarchical computational framework for mechanobiology problems, the molecular dynamics decorated finite element method (MDeFEM). The MscL in Escherichia coli was given as an example with its continuum model built under the instruction of MDeFEM framework.  Its gating pathways under various external perturbations were investigated, which are in good agreement with current experimental data and all-atom simulation results. The MDeFEM method showed its advantages and great potential in solving the mechanical responses of large biomolecules with complex geometries, which often involves multiple temporal and spatial scales.