Ansys 12 Plasticity
Ansys 12 Plasticity
(OP)
Distinguished members:
I have found myself troubled by ANSYS. I'm trying to perform a nonlinear analysis in order to observe its plastic behavior (the structure i'm developing, it's a steel stack, or pipe)
The problem is that so far, ANSYS 12 only allows me to perform this analysis by aplying a displacement. But what really interests me, it is to be able to perform a load-based analysis to acchieve plasticity, with different types of loads (wind, earthqueake, whatever)
If anyone can help me with this, you would make me the happiest man alive.
Best regards!
I have found myself troubled by ANSYS. I'm trying to perform a nonlinear analysis in order to observe its plastic behavior (the structure i'm developing, it's a steel stack, or pipe)
The problem is that so far, ANSYS 12 only allows me to perform this analysis by aplying a displacement. But what really interests me, it is to be able to perform a load-based analysis to acchieve plasticity, with different types of loads (wind, earthqueake, whatever)
If anyone can help me with this, you would make me the happiest man alive.
Best regards!





RE: Ansys 12 Plasticity
Steve
Stephen Seymour, PE
Seymour Engineering & Consulting Group
www.seymourecg.com
RE: Ansys 12 Plasticity
I have encountered convergence problems. I can not check its behavior post yielding point, perfect plasticity.
A simple analysis of a steel pipe, with a load of 1(whatever unit) on its top.
My main problem is to succesfully acchieve perfect plasticity. Which i have been able to do performing a displacement-based analysis.
RE: Ansys 12 Plasticity
This may be one place you might be having issues at. Another is you may want to introduce more load steps to ensure stability.
Steve
Stephen Seymour, PE
Seymour Engineering & Consulting Group
www.seymourecg.com
RE: Ansys 12 Plasticity
yield strenght: 3.55E+08 Pa
Tangent Modulus: 5E+08 Pa (I'm still figuring out the tangent modulus)
And I am using 50 load steps. That part is the one I can not acchieve, that the stress remains constant and the strain continues.
I will keep trying though, thank you again mr Steve.
RE: Ansys 12 Plasticity
What Young's modulus do you have?
The issue I spoke of in my previous post regarding the stress remaining constant after the last data point on your stress vs. plastic strain curve pertained to the multi-linear isotropic hardening model. Using the bilinear is much easier.
Are there any singularities in the model? Such as point loads or point constraints?
Steve
Stephen Seymour, PE
Seymour Engineering & Consulting Group
www.seymourecg.com
RE: Ansys 12 Plasticity
I'm so sorry I took so long to reply (I was away, no internet, almost in the middle-age)...
My model does not have any singularities that could cause a problem related to that. In fact, I am keeping it simple in order to go slowly testing it so it can work.
Actually (after several tests this last week) I was able to acchieve plasticity, but only using a displacement based method.
Now I am facing another kind of trouble in which I hope someone can help me out.
New Challenge:
My chimney has a Tuned mass damper(TMD) on its top. I'm trying to model this TMD in order to get lesser vibrations.
If you Mr Steve have come across such problem in the past, I would appreciate your help on this new challenge.
Best regards!
RE: Ansys 12 Plasticity
Can you send (put on eng-tips) the input file for plasticity problem?
I will try to help you but I can do this only after I see the input file.
Kind regards,
juzz
RE: Ansys 12 Plasticity
Here I attached the .x_t file that is the basic geometry i am using. My main problem was that i have only acchieved in a different model on a displacement-based method, but never with a load-based method.
And the other problem I am working on, it is to design a Tuned mass damper on its top (or something that can reproduce its function).
Best regards, thank you for interesting.
RE: Ansys 12 Plasticity
First, the input you put there is only for geometry (I presume, seems a transfer from Parasolid). Anyway, I need to have the mesh and the boundary and loading conditions because the solver use these information and not the geometry.
When I asked for an input file I meant a file that can be loaded in ansys via command "read input file from....".
Anyway, open your model in Ansys, be sure that everything is selected, that all loads are applied and all boundary conditions set. After that type in the command line window from Ansys the following command:
cdwrite, db, model,
It will generate a file in your folder called "model.cdb". Provide this file, please.
Regarding the tuned mass damper, basically this is a mass connected to the chimney by a spring and a damper. Probably you try using this for damping vibrations excited by vortex shedding (wind dynamic effect). My advice is to represent the chimney as a 2-D bar (BEAM3 element) and connect the mass (MASS21 element) by intermediate of some combination of spring and dashpot (COMBIN14 for example).
With this model setup you will have to perform a harmonic response analysis (see Structural Analysis Guide from ANSYS help for procedure).
Kind regards,
Juzz
RE: Ansys 12 Plasticity
I'm sorry about that. I thought of that, because i use ANSYS 12.1 and it works with this system of modules. I know there must be a way to export to a .cdb file, but I'm not really sure how to. The .wbpj is too large to attach it here.
Anyhow, i performed on that same model a simple mesh with a max. size of 380mm. I tried by using multiple forces just on the top of it: 5tonnef, 15 tonnef...and the problem is that at some point it does not converge into a solution.
My question are these:
- can i perform a load-based non-linear analysis? will I acchieve plasticity?
-I have to run a couple of earthquakes on my chimney, do you know any tutorial about this? I have used different softwares (SAP, etabs, etc) to perform this task, but I am kind of new on ANSYS, and actually i started off using ansys 12, never used the ones before this.
Thank you again for your time and fine will.
RE: Ansys 12 Plasticity
RE: Ansys 12 Plasticity
RE: Ansys 12 Plasticity
You can do a sensitivity study where you start with a tangent modulus only slightly less than the elastic modulus. Then see how the solution changes as you do runs with progressively smaller tangent moduli.
As for dynamic analysis (such as harmonic response), most of the those solutions can only be done with a linear model. If nonlinear effects are important, then you would have to do something like a direct (full) transient solution.
RE: Ansys 12 Plasticity
RE: Ansys 12 Plasticity
I tried different methods to model the moving load, i think that part work pretty well; but the problem is TMD doesnt work.
In fact, it works when I do the Harmonic analysis on the system, but when it comes to transient analysis (moving load), tmd doesnt work.
Ive been fooling around for 2months. im stuck!
so, if you can help me through this, it would be REALLY appreciated.
Cheers,
Fahim
RE: Ansys 12 Plasticity
RE: Ansys 12 Plasticity
How do you check wheter is working the TMD or is not?
Please tell us more about your problem.
RE: Ansys 12 Plasticity
RE: Ansys 12 Plasticity
Marcus