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#26 2022-08-15 13:34:32

miib
Member
From: 500 km by Rome
Registered: 2021-03-23
Posts: 207

Re: plastic strain larger than total strain?

the last with different BC (file attached)

video :

youtube.com/watch?v=tLzX5_or0IM

we need a guru's opinion. :-)


Attachments:
example_3.zip, Size: 289.38 KiB, Downloads: 27

I ever used code_aster for study.
Code_Aster ??? is the Novacula Occami of the FEM world.
“Non è bene cercare di fermare il progresso della conoscenza. L'ignoranza non è mai meglio della conoscenza.” Enrico Fermi.

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#27 2022-08-17 11:08:22

jacob
Member
From: Dolní Benešov
Registered: 2022-03-07
Posts: 64

Re: plastic strain larger than total strain?

I think I know what the problem was.
Plastic strain EPSP is calculated from engineering strain, but total strain EPSG is from green strain.
Now if I look on the total engineering strain EPSI, it is higher than plastic strain.


Attachments:
Obrázek2.png, Size: 153.48 KiB, Downloads: 26

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#28 2022-08-17 11:43:22

miib
Member
From: 500 km by Rome
Registered: 2021-03-23
Posts: 207

Re: plastic strain larger than total strain?

jacob wrote:

Hello,
are the results correct?
.

yes.
.
.
.
i'm not sponsored by EDF or fascists or communism :-)


I ever used code_aster for study.
Code_Aster ??? is the Novacula Occami of the FEM world.
“Non è bene cercare di fermare il progresso della conoscenza. L'ignoranza non è mai meglio della conoscenza.” Enrico Fermi.

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#29 2022-08-17 12:03:52

mecour
Member
From: Ostrava (Czech)
Registered: 2011-04-04
Posts: 182

Re: plastic strain larger than total strain?

Hello,

first of all I don't understant miib's posts. The question is not related in any way to boundary conditions. There is only simple alarm that it is not possible to compute some fields on discrete elements. 

Jacob wrote:

I think I know what the problem was.
Plastic strain EPSP is calculated from engineering strain, but total strain EPSG is from green strain.
Now if I look on the total engineering strain EPSI, it is higher than plastic strain.

I also think that the small difference is somewhere in this area, but from documentation it looks like that the cumulative plastic strain in VARI_ELGA is computed only from plastic strains and it still does not make sense to me according to your results.

Is the difference significant ?

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#30 2022-08-17 13:42:25

jacob
Member
From: Dolní Benešov
Registered: 2022-03-07
Posts: 64

Re: plastic strain larger than total strain?

In my latest picture I am looking only on the whole strain tensor, not equivalent strain.

When I tried simple uniaxial test with ideally plastic material I should expect constant elastic strain, right?
Sy/E = 200/200e3 = 0.001, which I obtain if I compute resnonl_EPSI_NOEU_EPZZ-resnonl_EPSP_NOEU_EPZZ

Last edited by jacob (2022-08-17 13:43:06)

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#31 2022-08-17 16:35:05

miib
Member
From: 500 km by Rome
Registered: 2021-03-23
Posts: 207

Re: plastic strain larger than total strain?

mecour wrote:

Hello,

first of all I don't understant miib's posts.

sorry,
my internet connection is switched, maybe by Carabinieri, i used the thread to show them same old question opened by others italian user in the past.

:-)

Last edited by miib (2022-08-17 16:36:50)


I ever used code_aster for study.
Code_Aster ??? is the Novacula Occami of the FEM world.
“Non è bene cercare di fermare il progresso della conoscenza. L'ignoranza non è mai meglio della conoscenza.” Enrico Fermi.

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#32 2022-08-17 17:34:50

miib
Member
From: 500 km by Rome
Registered: 2021-03-23
Posts: 207

Re: plastic strain larger than total strain?

mecour wrote:

Hello,

The question is not related in any way to boundary conditions.

true true true !!! i only showed how the elastic return is influenced by BC

mecour wrote:

Hello,

There is only simple alarm that it is not possible to compute some fields on discrete elements.

doubt : how ???
epsilon depend by U vector and its nodal mutual component Ui.j and Uj.i (which goes into the DEPL matrix), although  in your opinion can EPSI (elastic for little deformation) go in accord with EPSP (plastic for great deformation) ???

:-)


I ever used code_aster for study.
Code_Aster ??? is the Novacula Occami of the FEM world.
“Non è bene cercare di fermare il progresso della conoscenza. L'ignoranza non è mai meglio della conoscenza.” Enrico Fermi.

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#33 2022-08-17 17:53:26

jacob
Member
From: Dolní Benešov
Registered: 2022-03-07
Posts: 64

Re: plastic strain larger than total strain?

I think it is calculated from Cauchy strain because of this notation.
E is for green, but in the formula for plastic strain is epsilon.


Attachments:
Screenshot 2022-08-17 185142.png, Size: 150.35 KiB, Downloads: 27

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#34 2022-08-18 07:10:08

mecour
Member
From: Ostrava (Czech)
Registered: 2011-04-04
Posts: 182

Re: plastic strain larger than total strain?

miib wrote:

epsilon depend by U vector and its nodal mutual component Ui.j and Uj.i (which goes into the DEPL matrix), although  in your opinion can EPSI (elastic for little deformation) go in accord with EPSP (plastic for great deformation) ???

I did not compare values. Did you read the firts post of this thread? The question was that is strange that plastic strain computed in VARI_ELGA (VON_MISES) is larger than total strain computed in the fiels EPSG_ELGA.

Jacob wrote:

I think it is calculated from Cauchy strain because of this notation.
E is for green, but in the formula for plastic strain is epsilon.

Of cource you are right. But in the doc. R5.03.02 is written that cumultive plastic strain is computed from plastic strain velocity (attachment). It is just strange that without elastic part it can be larger than total strain even only for small deformation.

Maybe is this part of elasto-plasticity mathematics just too complicated for me.


Attachments:
epsilon_p.png, Size: 204.66 KiB, Downloads: 27

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#35 2022-08-18 07:33:01

jacob
Member
From: Dolní Benešov
Registered: 2022-03-07
Posts: 64

Re: plastic strain larger than total strain?

Velocity? In static problem?
But it is not larger than total strain, you just have to compare EPEQ with VARI_V1, not EPQG, because in compression EPSI > EPSG (quadratic terms are positive so the final value in asb will be lower)

Last edited by jacob (2022-08-18 07:33:23)

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#36 2022-08-18 11:50:18

mecour
Member
From: Ostrava (Czech)
Registered: 2011-04-04
Posts: 182

Re: plastic strain larger than total strain?

Sorry

But now I am lost. In your first post you compare EPGQ_ELGA with VARI_ELGA_V1 (EPSPEQ) and now you said something another.

Maybe we can do the meeting in czech language or in some pub in Ostrava ;-)

By the way velocity of plastic deformation is not something special. In plasticity deformation it is computed from step size.

Last edited by mecour (2022-08-18 12:00:15)

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#37 2022-08-18 12:47:54

miib
Member
From: 500 km by Rome
Registered: 2021-03-23
Posts: 207

Re: plastic strain larger than total strain?

mecour wrote:
miib wrote:

epsilon depend by U vector and its nodal mutual component Ui.j and Uj.i (which goes into the DEPL matrix), although  in your opinion can EPSI (elastic for little deformation) go in accord with EPSP (plastic for great deformation) ???

I did not compare values. Did you read the firts post of this thread? The question was that is strange that plastic strain computed in VARI_ELGA (VON_MISES) is larger than total strain computed in the fiels EPSG_ELGA.

Jacob wrote:

In my latest picture I am looking only on the whole strain tensor, not equivalent strain.

When I tried simple uniaxial test with ideally plastic material I should expect constant elastic strain, right?
Sy/E = 200/200e3 = 0.001, which I obtain if I compute resnonl_EPSI_NOEU_EPZZ-resnonl_EPSP_NOEU_EPZZ

WLF :-)


I ever used code_aster for study.
Code_Aster ??? is the Novacula Occami of the FEM world.
“Non è bene cercare di fermare il progresso della conoscenza. L'ignoranza non è mai meglio della conoscenza.” Enrico Fermi.

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#38 2022-08-18 14:27:09

jacob
Member
From: Dolní Benešov
Registered: 2022-03-07
Posts: 64

Re: plastic strain larger than total strain?

mecour wrote:

Sorry

But now I am lost. In your first post you compare EPGQ_ELGA with VARI_ELGA_V1 (EPSPEQ) and now you said something another.

Maybe we can do the meeting in czech language or in some pub in Ostrava ;-)

By the way velocity of plastic deformation is not something special. In plasticity deformation it is computed from step size.

Why VARI_ELGA_V1 is higher than EPGQ_ELGA I also don't understand because I don't know how V1 is computed, but at least when comparing each component from EPSI and EPSP, EPSP is lower.

Sure, maybe we can.


Attachments:
image_2022-08-18_152706811.png, Size: 90.89 KiB, Downloads: 26

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#39 2022-08-19 08:43:25

jacob
Member
From: Dolní Benešov
Registered: 2022-03-07
Posts: 64

Re: plastic strain larger than total strain?

The reason why I noticed this, is just because I wanted to calculate elastic strain, but I guess you can not just subtract plastic strain from total if you have equivalent strain.
Why code aster does not compute elastic strain?

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#40 2022-08-20 13:57:12

miib
Member
From: 500 km by Rome
Registered: 2021-03-23
Posts: 207

Re: plastic strain larger than total strain?

jacob wrote:

Why code aster does not compute elastic strain?

jacob wrote:

I think it does not exist on the springs, thats all.

miib wrote:

doubt : how ???
epsilon depend by U vector and its nodal mutual component Ui.j and Uj.i (which goes into the DEPL matrix), although  in your opinion can EPSI (elastic for little deformation) go in accord with EPSP (plastic for great deformation) ???

:-)

:-)

Last edited by miib (2022-08-20 14:01:31)


Attachments:
because U vector is the problem's kernel.png, Size: 118.14 KiB, Downloads: 31

I ever used code_aster for study.
Code_Aster ??? is the Novacula Occami of the FEM world.
“Non è bene cercare di fermare il progresso della conoscenza. L'ignoranza non è mai meglio della conoscenza.” Enrico Fermi.

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