User login

You are here

Comments

Subscribe to Comments feed
Comments
Updated: 17 hours 39 min ago

Hello

Sat, 2015-05-02 12:46

In reply to Abaqus system error code 1073741511

Hello

I recommend you become a member of the ABAQUS mailing list
http://groups.yahoo.com/neo/groups/Abaqus/info

This is a moderated list, any posting will be forwarded to subscribers with a delay.

I know what Simulia HQ is watching closely. Someone from HQ replied to one of my postings a couple of years ago in the context of a misprint in the manual

Good luck

Frank

Congratulations!

Fri, 2015-05-01 17:21

In reply to Multiple openings at Active Materials and Structures Lab of USC

Hi Qiming, 

Congratulations for the new position! 

shengqiang

We all know

Fri, 2015-05-01 15:17

In reply to Why Abaqus give incorrect result in plane strain plasticity?!!

It seems that I had better consider it. However, considering J in this simple calculation does not make things OK (such as fictitious stresses).

We all know that the Abaqus give cauchy stresses as a result in current space. It should be pointed that output stresses must be according to the input strain-hardening, but it is not True for near rigid plastic material. You can check it out.

Glad it was fixed. The use of

Fri, 2015-05-01 14:24

In reply to Thank for your advice

Glad it was fixed. The use of the NLGEOM option has an important theoretical background, so you might want to ask your professor about that. One key part of that is the different strain measures used in linear vs. nonlinear analysis. What you saw is where if you rotate an element without stressing or straining it you will actually get nonzero strain output if you use the linear strain measure. If you use a nonlinear strain measure it will correctly output 0.

Thank for your advice

Fri, 2015-05-01 01:54

In reply to First, can you confirm that

Dear Marcus Rademacher,

Thanks to your advice, I found my mistake and corrected it. The problem is I set NLGEOM=off in abaqus Standard. When I run with NLGEOM=on, It work perfectly.

Again, thank you for your useful help.

Sincerely yours,

regarding to my last post,

Thu, 2015-04-30 18:20

In reply to Why Abaqus give incorrect result in plane strain plasticity?!!

regarding to my last post, You can check the abaqus stresses kind in plot result by simple tension example of a rod, if you check it correctly you will realize that abaqus shows cauchy stresses. 

 

Thu, 2015-04-30 15:29

In reply to Why Abaqus give incorrect result in plane strain plasticity?!!

 

First apologize me for typing mistakes, all above stresses should be written in deviatoric parts. It was my first time to write equations in latex and html and it confused and distracted me a lot.
Thanks for your guide about trial stress and FEM application in large deformation plasticity, but I have written J2 large deformation plasticity code before, so please trust me ;-). The point is not the simplicity of yield condition, the point is that whether you have approximated the equivalent plastic strain correctly or not.

In your video you have written below equation to evaluate equivalent plastic strain:

3.16e8=2.5e8+(1e6)*eps

then you have concluded that eps=66 . Actually you mean:

S_von=sig_y_0+K*eps

where K is the isotropic hardening parameter. Your formulation is not reasonable since it is for small deformation theory. You have ignored Jacobian of deformation gradient which is wrong, You should approximate the equivalent plastic strain from this formulation which is better approximation for large deformation theory:

J*S_von=sig_y_0+K*eps

In small deformation theory J or Jacobian is nearly equal to one so the effect of nonlinear geometry is not clear.

 

For checking the correctness of Yield condition that I wrote, please check Simo and Hughes 9.2.14 and 8.2.1.

First, can you confirm that

Thu, 2015-04-30 15:00

In reply to [Help]: Element length increase in bending process without strain increase

First, can you confirm that you're running with NLGEOM=on? Are you using Standard or Explicit? Do the elements look like they're twice as long as they were?

In your field outputs, include "LE" which is the strain components. If those elements have 0 (or nearly 0) strain as measured with LE, then you're fine.

We're not guess,

Thu, 2015-04-30 07:33

In reply to Why Abaqus give incorrect result in plane strain plasticity?!!

First of all, I want to thank you for your comment, but it's not reasonable. You just mentioned the simple relation of Mises plasticity theory. In computational plasticity, for computing the trial stresses and implementation, You can find clearer relation in detail (e.g. Simo and Hughes- Computational inelasticity).

Next, you must use it in FEM code to understand what is occurred in computation procedure.

 

It is worth to mention that the compatibility between stress and strain at This particular situation (Plane strain plasticity) in Abaqus is not True.

my abaqus simulation of time

Wed, 2015-04-29 10:14

In reply to the problem was in a option

my abaqus simulation of time of flight diffraction technique not differentiating diaffracted wave and lateral wave.both gives same amplitude.what to do to gett a better result?.I am doing my work based on "shear wave TOFD by baskaran".any suggestion?

May be the answer is

Tue, 2015-04-28 17:14

In reply to Dear  aslan

Dear amin, I think I found why abaqus gives you strange results. Since you have turned on nlgeom in your solution then your plastic formulation is not the same as small deformation theory.

If we neglet the plastic spin then the yield stress condition can be stated as folllows for large deformation theory:

where is deviatoric part of symmetric mandel stress tensors and  G_y_0 is initial yield stress and R is isotropic hardening parameter. for isotropic materials the above equation can be reduced to:

where is spatial kirchhof stress tensor and the bar on it shows rotated kirchhof stress. since rotation has no effect on above formulation we can rewrite:

 and since the relation between Cauchy stress and Kirchhof stress is:

So it can be said:

where is Cauchy stress and J is jacobi of deformation gradient. The equivalent von Misses stress in abaqus is based on this formulation:

So the yield condition can be stated as follows:

The reason why you estimated unphysical large plastic strain is that you ignored J in your formulation.

 

Dear  aslan

Tue, 2015-04-28 11:33

In reply to Dear amin

Dear  aslan

As it is obviously shown in that simplest example, the reason is completely mathematical. We derived and developed continuum equations for plane strain plasticity and implemented in a Fortran code to resolve this fault.

 

For the Abaqus simulation, the implicit method was used. However, you can also decrease the time step, but you will never get the right results.

Dear amin

Mon, 2015-04-27 18:54

In reply to Why Abaqus give incorrect result in plane strain plasticity?!!

Dear amin

I'm not an expert in abaqus, but your example is interesting, as you mentioned in your video the the strain is not physical....

Is there any contour of equivalaent platic strain?

Was your solution implicit or explicit?

because large substep explicit  gives wrong answeres.

you need to do it in a script

Mon, 2015-04-27 18:19

In reply to initial void ratio for soil

you need to do it in a script file, CAE doesn't support this option very well

You would need to couple the

Mon, 2015-04-27 09:26

In reply to How to make 3 parallel beam elements to work together in abaqus?

You would need to couple the nodes of two beams to the nodes of a master beam (likely the center one). That said, I'm not entirely sure this is a completely valid way to use beam elements. I think you'd be better off using solid elements or shells for this. That'll ensure you capture the transverse effects correctly.

wonderful idea!

Mon, 2015-04-27 00:52

In reply to JAM now publishes a new type of paper: A Perspective

Dear Prof Huang,

Thanks so much for sharing!  I believe this type of papers are very helpful for young researchers in mechanics to understand and learn more about the most important resarch areas in the field.  I look forward to reading more of these papers in JAM.  Thanks!

Looking forward to reading

Sun, 2015-04-26 21:50

In reply to Good news

Looking forward to reading more "Perspective paper"

Good news

Sun, 2015-04-26 21:43

In reply to JAM now publishes a new type of paper: A Perspective

Great to know JAM will include this type of paper. Looking forward to reading more "respective paper". 

This idea leads the times

Sun, 2015-04-26 20:31

In reply to JAM now publishes a new type of paper: A Perspective

Such a type of paper will be very beneficial to readers and we are happy to see that JAM is becoming more and more influential.

Very important

Sun, 2015-04-26 19:57

In reply to JAM now publishes a new type of paper: A Perspective

Dear Yonggang, this is a great idea! Perspective paper is very important to both the academic society and the journal.

Pages

Recent comments

More comments

Syndicate

Subscribe to Syndicate