UMAT: role of DDSDDE

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UMAT: role of DDSDDE

Kong-Ping Wong
Hi there,

Out of curiosity, I wonder why DDSDDE is needed by Abaqus as an output
to UMAT.

My question arises in the context of elasto-plasticity.  It seems to
me that the consistent tangent modulus (DDSDDE) would only need to
stay inside the subroutine, as long as I return the stress and the
state variables given the strain and the strain increment.

Why does Abaqus need DDSDDE outside of UMAT?

Thanks,
Kong-Ping Wong
Los Alamos National Lab







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Re: UMAT: role of DDSDDE

Benz-2
DDSDDE is needed to compute the "behavior term" of the tangent
stiffness matrix. It depends on your user behavior and Abaqus cannot
guess how to differentiate your constitutive matrix.

BenZ.

--- In [hidden email], "Kong-Ping Wong" <pingsmail@y...>
wrote:
>
> Hi there,
>
> Out of curiosity, I wonder why DDSDDE is needed by Abaqus as an
output
> to UMAT.
>
> My question arises in the context of elasto-plasticity.  It seems
to

> me that the consistent tangent modulus (DDSDDE) would only need to
> stay inside the subroutine, as long as I return the stress and the
> state variables given the strain and the strain increment.
>
> Why does Abaqus need DDSDDE outside of UMAT?
>
> Thanks,
> Kong-Ping Wong
> Los Alamos National Lab
>






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Re: UMAT: role of DDSDDE

Dave Lindeman
In reply to this post by Kong-Ping Wong
It is required to form the stiffness matrix for the element.  The product of
the stress-strain relationship and strain-displacement relationship (derived
from the element shape functions) are integrated over the element volume to
form a force-displacement relationship (stiffness matrix).  If DDSDDE is not
defined properly, then the tangent matrix will be incorrect, and this may
lead to divergence or, at least, slow convergence.

Regards,

Dave

=============================================
Dave Lindeman              [hidden email]
Sr. CAE Specialist         (TEL) 651-733-6383
3M Company                 (FAX) 651-736-7615
=============================================

----- Original Message -----
From: "Kong-Ping Wong" <[hidden email]>
To: <[hidden email]>
Sent: Tuesday, January 24, 2006 8:16 AM
Subject: [ABAQUS] UMAT: role of DDSDDE


> Hi there,
>
> Out of curiosity, I wonder why DDSDDE is needed by Abaqus as an output
> to UMAT.
>
> My question arises in the context of elasto-plasticity.  It seems to
> me that the consistent tangent modulus (DDSDDE) would only need to
> stay inside the subroutine, as long as I return the stress and the
> state variables given the strain and the strain increment.
>
> Why does Abaqus need DDSDDE outside of UMAT?
>
> Thanks,
> Kong-Ping Wong
> Los Alamos National Lab
>
>
>
>
>
>
>
> Community email addresses:
>   Post message: [hidden email]
>   Subscribe:    [hidden email]
>   Unsubscribe:  [hidden email]
>   List owner:   [hidden email]
>
> Shortcut URL to this page:
>   http://groups.yahoo.com/group/abaqus
> Yahoo! Groups Links
>
>
>
>
>
>



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Re: UMAT: role of DDSDDE

Kong-Ping Wong
In reply to this post by Benz-2
Hi BenZ,

Thanks for your explanation.  I did some extra searching, and found
(from Simo and Hughes' Computational Inelasticity, 1998, chapter 1)
that the consistent stiffness matrix is also used to calculate the
next iteration of the nodal displacement outside of the materials
subroutine.  I am thinking that this may be what ABAQUS/Standard is
doing to converge to a residual that is within tolerance.  That
would also seem to explain why the consistent stiffness matrix is
not needed in VUMAT within ABAQUS/Explicit.

Thanks again,
K. P. Wong

--- In [hidden email], "BenZ" <benjamin_hagege@y...> wrote:
>
> DDSDDE is needed to compute the "behavior term" of the tangent
> stiffness matrix. It depends on your user behavior and Abaqus
cannot

> guess how to differentiate your constitutive matrix.
>
> BenZ.
>
> --- In [hidden email], "Kong-Ping Wong" <pingsmail@y...>
> wrote:
> >
> > Hi there,
> >
> > Out of curiosity, I wonder why DDSDDE is needed by Abaqus as an
> output
> > to UMAT.
> >
> > My question arises in the context of elasto-plasticity.  It
seems
> to
> > me that the consistent tangent modulus (DDSDDE) would only need
to
> > stay inside the subroutine, as long as I return the stress and
the
> > state variables given the strain and the strain increment.
> >
> > Why does Abaqus need DDSDDE outside of UMAT?
> >
> > Thanks,
> > Kong-Ping Wong
> > Los Alamos National Lab







Community email addresses:
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Re: UMAT: role of DDSDDE

Kong-Ping Wong
In reply to this post by Dave Lindeman
Hi Dave,

Thanks for taking time to respond.  Your explanation has been very
helpful, and it is consistent with what I have later found in Simo
and Hughes' Computational Inelasticity book.

K. P. Wong

--- In [hidden email], "Dave Lindeman" <ddlindeman@m...>
wrote:
>
> It is required to form the stiffness matrix for the element.  The
product of
> the stress-strain relationship and strain-displacement
relationship (derived
> from the element shape functions) are integrated over the element
volume to
> form a force-displacement relationship (stiffness matrix).  If
DDSDDE is not
> defined properly, then the tangent matrix will be incorrect, and
this may

> lead to divergence or, at least, slow convergence.
>
> Regards,
>
> Dave
>
> =============================================
> Dave Lindeman              ddlindeman@m...
> Sr. CAE Specialist         (TEL) 651-733-6383
> 3M Company                 (FAX) 651-736-7615
> =============================================
>
> ----- Original Message -----
> From: "Kong-Ping Wong" <pingsmail@y...>
> To: <[hidden email]>
> Sent: Tuesday, January 24, 2006 8:16 AM
> Subject: [ABAQUS] UMAT: role of DDSDDE
>
>
> > Hi there,
> >
> > Out of curiosity, I wonder why DDSDDE is needed by Abaqus as an
output
> > to UMAT.
> >
> > My question arises in the context of elasto-plasticity.  It
seems to
> > me that the consistent tangent modulus (DDSDDE) would only need
to
> > stay inside the subroutine, as long as I return the stress and
the
> > state variables given the strain and the strain increment.
> >
> > Why does Abaqus need DDSDDE outside of UMAT?
> >
> > Thanks,
> > Kong-Ping Wong
> > Los Alamos National Lab








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