iMechanica - Comments

Derivative of Metric Tensor

Svyatoslav Derezin — Fri, 03 Feb 2012 20:15:55 -0500

Hi Mohsen,

I see you are a great fan of forth-order tensors :) The computation of the derivative of the square root is a very tough thing, isn't it?

The question is again of course too general. I suppose you have two distinct configurations of the same body and want to compute some 'geometrical' stiffness tensor. Unfortunately, I don't see any possibility how to do it very shortly. Please, consult the following works:

J.E.Marsden, T.J.R.Hughes Mathematical foundations of elasticity. 1983

J.C.Simo, J.E.Marsden On the rotated stress tensor and the material version of the Doyle-Ericksen formula. 1984

M.Itskov The derivative with respect to a tensor: some theoretical aspects and applications. 2002

O.Kintzel Fourth-order tensors - tensor differentiation with application to continuum mechanics. Part II: Tensor analysis on manifolds. 2005

M.Itskov Tensor algebra and tensor analysis for engineers. 2009

Although I didn't find there exactly what you need, I think these works will be of some interest for you, especially those of Jerry Marsden and co-authors. In the works of Itskov you will find statements like "the derivative with respect to the metric tensor seems to be meaningless since in the Euclidean space g represents the identity tensor", but I wouldn't take them too seriously. Yes, it's true in each tangent space the metric tensor should act as the identity map, but a-priori it is not clear how the information about the global structure (the curvature of the manifold) may influence the derivative.

Svyatoslav

wire rope

Amit Acharya — Fri, 03 Feb 2012 12:54:38 -0500

Biswajit,

Would wire ropes be a good idealization of soft helical springs? Both you and I know of one application from our u/g days where that stuff is really useful!

In any case, if you think that is relevant, you may want to look up the work of G. A . Costello.

- Amit

Thanks

Harsha Tirumala — Fri, 03 Feb 2012 10:41:59 -0500

Interesting link sir.

I have implemented the EFG

J.T.B. Overvelde — Fri, 03 Feb 2012 08:27:24 -0500

I have implemented the EFG method for solving the PDE momentum equations. You can find a Matlab implementation here. If you like to know more, feel free to ask!

Hi Martin

Ali43 — Fri, 03 Feb 2012 08:15:30 -0500

I just wonder the way that I can find access to the Crach FEM model that you mentioned.i mean it semas a user defined material but where can I find it s code.

I want to use it for implementation of a material model for the anisotropic hardening material behaviour in Abaqus.

Thanks i advance

Impelemtation of material model for anisotropic hardening

Ali43 — Fri, 03 Feb 2012 07:43:47 -0500

I am a master student and should implement material model for anisotropic hardening in Abaqus.Does any one can help me through the task!!!!!

Thanks

I got that paper

rajeshpnair — Fri, 03 Feb 2012 02:15:14 -0500

sorry to all of you.

i got the paper "NUMERICAL MODELLING OF
DISCONTINUA" from 4shared.com

thank you

Dear Sir, Sorry for being

kajalschopra — Thu, 02 Feb 2012 21:38:36 -0500

Dear Sir,

Sorry for being repetitive..I'm actually from the Structural Engineering stream -not Mechanical and am thus not confortable with questions you asked.

Yes,I shall read the book you mentioned.I have read mostly Elements of Strength of Materials by Timoshnko,Mechanics of Structures by Timoshinko and use the e-book by Alan Bower as a reference.

Sorry again

Re: yield surface

Biswajit Banerjee — Thu, 02 Feb 2012 18:01:56 -0500

I though I had answered that question in my previous comment.

Let me ask you a question.

When you roll a billet of steel into a sheet, does the billet undergo plastic deformation? Has the material yielded? When you cut a sample out of the rolled sheet for tensile testing is the material still elastic?

I think you should read a book on mechanics of materials before you get into all these issues. Boresi et al. "Advanced mechanics of materials" comes to mind.

-- Biswajit

You mentioned an error, and

Marcus Rademacher — Thu, 02 Feb 2012 13:06:05 -0500

You mentioned an error, and you only showed a warning. Is Abaqus/Explicit able to run, or does it exit? If the latter, what error is reported.

The warning you are seeing is because you have boundary conditions applied to nodes on a rigid body. Rigid bodies only have 6 DOF for the whole part, and those are defined on a reference point. So no nodes on a rigid body should have a *Boundary card applied to it, except on the reference point node specified on your *Rigid Body card.

I don't know that this issue would give you poor results, since Abaqus would probably just ignore the BCs applied to nodes other than the reference point, but give it a shot and see if it fixes your issue.

My Company - Red Cedar Technology

Surface based cohesive behavior

SAJIB — Thu, 02 Feb 2012 08:53:35 -0500

Hi Rajnish,

I am interested to learn about friction based simulation between Concrete and FRP. I am modeling a FRP strengthened RC beam. FRP is in tension face.

I have simulated the behavior using surface based simulation and got good results with delamination. As there is considerations (Knn) in surface based model for constraining normal behavior between FRP and concrete there is no need for constraining the FRP and concerte in normal direction. But what should i do in case of Friction based analysis instead of cohesive analysis?

I have used the following keywords:

*CONTACT PAIR,INTERACTION=Friction,adjust=0.5,small sliding,TYPE=node TO SURFACE
FRP_top,bottom_concrete_surface
*surface interaction,name=friction
*friction,TAUMAX=4.11,ELASTIC SLIP=0.005
0.018,
*SURFACE BEHAVIOR,pressure-overclosure=HARD

but I didnt apply any constrain between FRP top and concrete bottom. Do i need to constrain ??

using friction based simulation i dont find any effectiveness of FRP. The load carrying capacity of beam should be greater than control beam. but i dont get it using the friction based simulation. can you help me at this poin?? I am stuck here for a long time.

Thanking You
Sajib

Surface-based cohesive behavior

leo — Thu, 02 Feb 2012 06:44:37 -0500

Hi Rajnish,

I'm using surface-based cohesive behavior to predict delamination in compoistes. In my model, two surfeces with idential meshes contact with each other, but I found the delamination areas given by these two surfaces were different. Do you have any idea on why this occurs? thanks!

Leo

crack modelling

bhupendra — Thu, 02 Feb 2012 04:30:31 -0500

Hello Avinash

I think it is better to go with University of Alberta Ansys tutorial. it givesyou some idea.

crack modelling

avinash07 — Thu, 02 Feb 2012 02:15:40 -0500

any one can help how to do full crack modelling in ansys. in my project in symmetric condition. if possiable then show how to do using GUI command.

Ajit R. Jadhav — Thu, 02 Feb 2012 02:04:14 -0500