Discussion:
UMAT-Strain Softening
sivom manchiraju
2004-01-30 05:00:31 UTC
Permalink
Hi,
I am trying to model strain softening in brittle material.
(composites). When I was working with ABAQUS explicit, my VUMAT gave
me good results. Now Beacause of some reasson I have to work in
implicit and the problem is not converging.Even a simple case of a
plate subjected to point load is not converging.
I have tried quite a few softening models. The material is
orthotropic and even a simple straight line kind of softening model
is not converging.But If I drop stresses to zero if the material
fails all of a sudden, then I get solution. Its when I try to
incorporate strain softening, Abaqus stops the analysis in the
middle. The same model works in explicit, so I have carefully
checked my stress strain relations and its derivatives,jacobian
matrix and I think its correct.

I wanted to know if some one has worked on continuum damage models
in abaqus standard. Does it work in standrad or this convergence is
a common problem. Even a straight line softening model, and a simple
point load case is not converging.That makes me write this email
asking for help.

Thanks,
Sivom.
Michigan State University.
Shiladitya Basu
2004-01-30 14:41:34 UTC
Permalink
Post by sivom manchiraju
I wanted to know if some one has worked on continuum damage models
in abaqus standard. Does it work in standrad or this convergence is
a common problem. Even a straight line softening model, and a simple
point load case is not converging.That makes me write this email
asking for help.
... a point load case is not as simple as you might think. if you are using
a strain softening model, your system will be inherently unstable in
load-control (ie, when you specify CLOAD at a node). you can try specifying
displacement instead and see what happens.


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sivom manchiraju
2004-01-30 19:35:23 UTC
Permalink
Hi,
I had tried both load control and displacement control before writing
the mail.
Is there anything else I can do to improve convergence? If some one
has time to look at the code, I can send the code to him too.
Thanks,
Sivom.
Michigan State University.
Post by Shiladitya Basu
Post by sivom manchiraju
I wanted to know if some one has worked on continuum damage models
in abaqus standard. Does it work in standrad or this convergence is
a common problem. Even a straight line softening model, and a simple
point load case is not converging.That makes me write this email
asking for help.
... a point load case is not as simple as you might think. if you are using
a strain softening model, your system will be inherently unstable in
load-control (ie, when you specify CLOAD at a node). you can try specifying
displacement instead and see what happens.
**************************************************************************
Post by Shiladitya Basu
* DON'T CHANGE YOUR MIND TO ACHIEVE HARMONY
*
Post by Shiladitya Basu
*
*
Post by Shiladitya Basu
* SHILADITYA BASU 1320 BEAL AVENUE
*
Post by Shiladitya Basu
* DOCTORAL CANDIDATE (STRUCTURES) ANN ARBOR, MI-48109
*
Post by Shiladitya Basu
* DEPT. OF AEROSPACE ENGINEERING (734)-764-4319
*
Post by Shiladitya Basu
*
*
**************************************************************************
JUAN GOMEZ
2004-01-30 23:59:04 UTC
Permalink
Dear Sivon,

What type of constitutive model are you using?. A rate
independent elastoplastic constitutive model should render the
problem mesh-dependent (loss of ellipticity) when you have
softening. Are you using your own UMAT? If that is the case what
model is it?.

Thanks

Juan
Post by sivom manchiraju
Hi,
I had tried both load control and displacement control before
writing
the mail.
Is there anything else I can do to improve convergence? If
some one
has time to look at the code, I can send the code to him too.
Thanks,
Sivom.
Michigan State University.
Post by Shiladitya Basu
Post by sivom manchiraju
I wanted to know if some one has worked on continuum
damage models
Post by Shiladitya Basu
Post by sivom manchiraju
in abaqus standard. Does it work in standrad or this
convergence is
Post by Shiladitya Basu
Post by sivom manchiraju
a common problem. Even a straight line softening model,
and a simple
Post by Shiladitya Basu
Post by sivom manchiraju
point load case is not converging.That makes me write this
email
Post by Shiladitya Basu
Post by sivom manchiraju
asking for help.
... a point load case is not as simple as you might think.
if you
are using
Post by Shiladitya Basu
a strain softening model, your system will be inherently
unstable in
Post by Shiladitya Basu
load-control (ie, when you specify CLOAD at a node). you can
try
specifying
Post by Shiladitya Basu
displacement instead and see what happens.
**************************************************************************
Post by sivom manchiraju
Post by Shiladitya Basu
* DON'T CHANGE YOUR MIND TO ACHIEVE HARMONY
*
Post by Shiladitya Basu
*
*
Post by Shiladitya Basu
* SHILADITYA BASU 1320 BEAL AVENUE
*
Post by Shiladitya Basu
* DOCTORAL CANDIDATE (STRUCTURES) ANN ARBOR,
MI-48109
*
Post by Shiladitya Basu
* DEPT. OF AEROSPACE ENGINEERING (734)-764-4319
*
*
*
Post by Shiladitya Basu
*
*
**************************************************************************
=====
JUAN GOMEZ
188 KENVILLE RD
APARTMENT D
BUFFALO, NY 14215
(716)836-0107

__________________________________
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Sivom Manchiraju
2004-01-31 13:33:01 UTC
Permalink
Hi,
Yes, I am using my own UMAT. The model is for
composite material. I started of with modelling
softening based on weibuls distribution but as it
didnt work, I tried a straight line softening curve.
Even that is not working.
Has some one used this kind of model in implicit? and
did the resuls converse?
Thanks for the suggestion on loss of elipticity. I
will go through Bazants book again.
Thanks,
Sivom.


--- JUAN GOMEZ <***@yahoo.com> wrote:
---------------------------------
Dear Sivon,

What type of constitutive model are you using?. A rate
independent elastoplastic constitutive model should
render the
problem mesh-dependent (loss of ellipticity) when you
have
softening. Are you using your own UMAT? If that is the
case what
model is it?.

Thanks

Juan
Post by sivom manchiraju
Hi,
I had tried both load control and displacement
control before
Post by sivom manchiraju
writing
the mail.
Is there anything else I can do to improve
convergence? If
Post by sivom manchiraju
some one
has time to look at the code, I can send the code to
him too.
Post by sivom manchiraju
Thanks,
Sivom.
Michigan State University.
Post by Shiladitya Basu
Post by sivom manchiraju
I wanted to know if some one has worked on
continuum
Post by sivom manchiraju
damage models
Post by Shiladitya Basu
Post by sivom manchiraju
in abaqus standard. Does it work in standrad or
this
Post by sivom manchiraju
convergence is
Post by Shiladitya Basu
Post by sivom manchiraju
a common problem. Even a straight line softening
model,
Post by sivom manchiraju
and a simple
Post by Shiladitya Basu
Post by sivom manchiraju
point load case is not converging.That makes me
write this
Post by sivom manchiraju
email
Post by Shiladitya Basu
Post by sivom manchiraju
asking for help.
... a point load case is not as simple as you
might think.
Post by sivom manchiraju
if you
are using
Post by Shiladitya Basu
a strain softening model, your system will be
inherently
Post by sivom manchiraju
unstable in
Post by Shiladitya Basu
load-control (ie, when you specify CLOAD at a
node). you can
Post by sivom manchiraju
try
specifying
Post by Shiladitya Basu
displacement instead and see what happens.
**************************************************************************
Post by sivom manchiraju
Post by Shiladitya Basu
* DON'T CHANGE YOUR MIND TO ACHIEVE
HARMONY
Post by sivom manchiraju
*
Post by Shiladitya Basu
*
*
Post by Shiladitya Basu
* SHILADITYA BASU 1320
BEAL AVENUE
Post by sivom manchiraju
*
Post by Shiladitya Basu
* DOCTORAL CANDIDATE (STRUCTURES) ANN
ARBOR,
Post by sivom manchiraju
MI-48109
*
Post by Shiladitya Basu
* DEPT. OF AEROSPACE ENGINEERING
(734)-764-4319
Post by sivom manchiraju
*
Post by Shiladitya Basu
* UNIVERSITY OF MICHIGAN
*
Post by Shiladitya Basu
* FRANCOIS-XAVIER BAGNOUD BLDG
*
Post by Shiladitya Basu
*
*
**************************************************************************
=====
JUAN GOMEZ
188 KENVILLE RD
APARTMENT D
BUFFALO, NY 14215
(716)836-0107

__________________________________
Do you Yahoo!?
Yahoo! SiteBuilder - Free web site building tool. Try
it!
http://webhosting.yahoo.com/ps/sb/
JUAN GOMEZ
2004-01-31 15:03:30 UTC
Permalink
I don't think is just as simple as using a straight line
softening curve. The question is, what will happen to the
material jacobian(DDSDDE) matrix within your UMAT s your model
starts softening. A good way of treating this problem is in:

de Borst, R., "A generalization of J2-flow theory for polar
continua." Computer Methods in Applied Mechanics and
Engineering. 103, p347-362. (1993).

On the other hand. If it is possible I would like to take a
quick look at your subroutine.
Post by Sivom Manchiraju
Hi,
Yes, I am using my own UMAT. The model is for
composite material. I started of with modelling
softening based on weibuls distribution but as it
didnt work, I tried a straight line softening curve.
Even that is not working.
Has some one used this kind of model in implicit? and
did the resuls converse?
Thanks for the suggestion on loss of elipticity. I
will go through Bazants book again.
Thanks,
Sivom.
---------------------------------
Dear Sivon,
What type of constitutive model are you using?. A rate
independent elastoplastic constitutive model should
render the
problem mesh-dependent (loss of ellipticity) when you
have
softening. Are you using your own UMAT? If that is the
case what
model is it?.
Thanks
Juan
Post by sivom manchiraju
Hi,
I had tried both load control and displacement
control before
Post by sivom manchiraju
writing
the mail.
Is there anything else I can do to improve
convergence? If
Post by sivom manchiraju
some one
has time to look at the code, I can send the code to
him too.
Post by sivom manchiraju
Thanks,
Sivom.
Michigan State University.
Post by Shiladitya Basu
Post by sivom manchiraju
I wanted to know if some one has worked on
continuum
Post by sivom manchiraju
damage models
Post by Shiladitya Basu
Post by sivom manchiraju
in abaqus standard. Does it work in standrad or
this
Post by sivom manchiraju
convergence is
Post by Shiladitya Basu
Post by sivom manchiraju
a common problem. Even a straight line softening
model,
Post by sivom manchiraju
and a simple
Post by Shiladitya Basu
Post by sivom manchiraju
point load case is not converging.That makes me
write this
Post by sivom manchiraju
email
Post by Shiladitya Basu
Post by sivom manchiraju
asking for help.
... a point load case is not as simple as you
might think.
Post by sivom manchiraju
if you
are using
Post by Shiladitya Basu
a strain softening model, your system will be
inherently
Post by sivom manchiraju
unstable in
Post by Shiladitya Basu
load-control (ie, when you specify CLOAD at a
node). you can
Post by sivom manchiraju
try
specifying
Post by Shiladitya Basu
displacement instead and see what happens.
**************************************************************************
Post by Sivom Manchiraju
Post by sivom manchiraju
Post by Shiladitya Basu
* DON'T CHANGE YOUR MIND TO ACHIEVE
HARMONY
Post by sivom manchiraju
*
Post by Shiladitya Basu
*
*
Post by Shiladitya Basu
* SHILADITYA BASU 1320
BEAL AVENUE
Post by sivom manchiraju
*
Post by Shiladitya Basu
* DOCTORAL CANDIDATE (STRUCTURES) ANN
ARBOR,
Post by sivom manchiraju
MI-48109
*
Post by Shiladitya Basu
* DEPT. OF AEROSPACE ENGINEERING
(734)-764-4319
Post by sivom manchiraju
*
Post by Shiladitya Basu
* UNIVERSITY OF MICHIGAN
*
Post by Shiladitya Basu
* FRANCOIS-XAVIER BAGNOUD BLDG
*
Post by Shiladitya Basu
*
*
**************************************************************************
Post by Sivom Manchiraju
=====
JUAN GOMEZ
188 KENVILLE RD
APARTMENT D
BUFFALO, NY 14215
(716)836-0107
__________________________________
Do you Yahoo!?
Yahoo! SiteBuilder - Free web site building tool. Try
it!
http://webhosting.yahoo.com/ps/sb/
http://groups.yahoo.com/group/abaqus
---------------------------------
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Your use of Yahoo! Groups is subject to the Yahoo!
Terms of Service.
________________________________________________________________________
Post by Sivom Manchiraju
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Go to http://in.mobile.yahoo.com
=====
JUAN GOMEZ
188 KENVILLE RD
APARTMENT D
BUFFALO, NY 14215
(716)836-0107

__________________________________
Do you Yahoo!?
Yahoo! SiteBuilder - Free web site building tool. Try it!
http://webhosting.yahoo.com/ps/sb/
sivom manchiraju
2004-01-31 16:44:25 UTC
Permalink
Thanks. I will send you my UMAT shortly. I am updating the jacobian
based on the new stress - strain relation during softening process.

Thanks,
Sivom.
Post by JUAN GOMEZ
I don't think is just as simple as using a straight line
softening curve. The question is, what will happen to the
material jacobian(DDSDDE) matrix within your UMAT s your model
de Borst, R., "A generalization of J2-flow theory for polar
continua." Computer Methods in Applied Mechanics and
Engineering. 103, p347-362. (1993).
On the other hand. If it is possible I would like to take a
quick look at your subroutine.
Post by Sivom Manchiraju
Hi,
Yes, I am using my own UMAT. The model is for
composite material. I started of with modelling
softening based on weibuls distribution but as it
didnt work, I tried a straight line softening curve.
Even that is not working.
Has some one used this kind of model in implicit? and
did the resuls converse?
Thanks for the suggestion on loss of elipticity. I
will go through Bazants book again.
Thanks,
Sivom.
---------------------------------
Dear Sivon,
What type of constitutive model are you using?. A rate
independent elastoplastic constitutive model should
render the
problem mesh-dependent (loss of ellipticity) when you
have
softening. Are you using your own UMAT? If that is the
case what
model is it?.
Thanks
Juan
Post by sivom manchiraju
Hi,
I had tried both load control and displacement
control before
Post by sivom manchiraju
writing
the mail.
Is there anything else I can do to improve
convergence? If
Post by sivom manchiraju
some one
has time to look at the code, I can send the code to
him too.
Post by sivom manchiraju
Thanks,
Sivom.
Michigan State University.
Post by Shiladitya Basu
Post by sivom manchiraju
I wanted to know if some one has worked on
continuum
Post by sivom manchiraju
damage models
Post by Shiladitya Basu
Post by sivom manchiraju
in abaqus standard. Does it work in standrad or
this
Post by sivom manchiraju
convergence is
Post by Shiladitya Basu
Post by sivom manchiraju
a common problem. Even a straight line softening
model,
Post by sivom manchiraju
and a simple
Post by Shiladitya Basu
Post by sivom manchiraju
point load case is not converging.That makes me
write this
Post by sivom manchiraju
email
Post by Shiladitya Basu
Post by sivom manchiraju
asking for help.
... a point load case is not as simple as you
might think.
Post by sivom manchiraju
if you
are using
Post by Shiladitya Basu
a strain softening model, your system will be
inherently
Post by sivom manchiraju
unstable in
Post by Shiladitya Basu
load-control (ie, when you specify CLOAD at a
node). you can
Post by sivom manchiraju
try
specifying
Post by Shiladitya Basu
displacement instead and see what happens.
**************************************************************************
Post by JUAN GOMEZ
Post by Sivom Manchiraju
Post by sivom manchiraju
Post by Shiladitya Basu
* DON'T CHANGE YOUR MIND TO ACHIEVE
HARMONY
Post by sivom manchiraju
*
Post by Shiladitya Basu
*
*
Post by Shiladitya Basu
* SHILADITYA BASU 1320
BEAL AVENUE
Post by sivom manchiraju
*
Post by Shiladitya Basu
* DOCTORAL CANDIDATE (STRUCTURES) ANN
ARBOR,
Post by sivom manchiraju
MI-48109
*
Post by Shiladitya Basu
* DEPT. OF AEROSPACE ENGINEERING
(734)-764-4319
Post by sivom manchiraju
*
Post by Shiladitya Basu
* UNIVERSITY OF MICHIGAN
*
Post by Shiladitya Basu
* FRANCOIS-XAVIER BAGNOUD BLDG
*
Post by Shiladitya Basu
*
*
**************************************************************************
Post by JUAN GOMEZ
Post by Sivom Manchiraju
=====
JUAN GOMEZ
188 KENVILLE RD
APARTMENT D
BUFFALO, NY 14215
(716)836-0107
__________________________________
Do you Yahoo!?
Yahoo! SiteBuilder - Free web site building tool. Try
it!
http://webhosting.yahoo.com/ps/sb/
http://groups.yahoo.com/group/abaqus
---------------------------------
Yahoo! Groups Links
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Your use of Yahoo! Groups is subject to the Yahoo!
Terms of Service.
________________________________________________________________________
Post by Sivom Manchiraju
Yahoo! India Mobile: Download the latest polyphonic ringtones.
Go to http://in.mobile.yahoo.com
=====
JUAN GOMEZ
188 KENVILLE RD
APARTMENT D
BUFFALO, NY 14215
(716)836-0107
__________________________________
Do you Yahoo!?
Yahoo! SiteBuilder - Free web site building tool. Try it!
http://webhosting.yahoo.com/ps/sb/
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