×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Contact US

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Displacements in Abaqus Subroutine Umat?

Displacements in Abaqus Subroutine Umat?

Displacements in Abaqus Subroutine Umat?

(OP)
Hello

I have one very important question: I want to program the subroutine Umat in Abaqus 6.5. My basic element types are coh2d4 and coh3d8. The problem now, when i want to start programming i use the traction-separation law. This law describe as the words say: traction (stress) vs. separation (displacements). But - this is problem- i can not get the displacements von the Subroutine umat. This just give me the stran;dstran and i have to use displacements.
Does anybody knows how i cam get displacement in abaqus umat or is it impossible? This means - no programming for umat with traction-separation?

Thank you all for help.

Regards K.

RE: Displacements in Abaqus Subroutine Umat?

It should be quite simple.

UMAT is supplied with current coordinates (COORDS) of the integration points.

You can use state variables to store the initial coordintates of the integration points.

Call SDVINI subroutine to store the initial coordinates values. (you have to set Material Property ->Depvar=3 (for 3D problem and use *INITIAL CONDITIONS,TYPE=SOLUTION,USER to order to have SDVINI called).

In SDVINI code something like this:
STATEV(1)=COORDS(1)
STATEV(2)=COORDS(2)
STATEV(3)=COORDS(3)

Then in UMAT compute the displacemets as:
u1=COORDS(1)-STATEV(1)
u2=COORDS(2)-STATEV(2)
u3=COORDS(3)-STATEV(3)

You should set NLGEOM=ON, otherwhise the COORDS will not be updated as the integration is performed over the initial (i.e. undeformed) element domain.

RE: Displacements in Abaqus Subroutine Umat?

(OP)
Thanks a lot for your help!

It is getting a little bit better now. But it is not programming if you don´t have another problem:

I want to update stress - this means i have to use the increment of the displacement: delta u(2). When i do like you suggested, i get the displacement for the end of the step, but not for every increment, which i have to use for calculating and updating stresses.
In umat you have like Kinc but this is only the number of the inc - useless!?

Hopefully my last question about the start in doing my umat.

Greetings and Regards

K.

RE: Displacements in Abaqus Subroutine Umat?

According to my first suggestion you obtain the total displacements for each time increment, not only at the end of the step as you said.

To use the displacement increments then you can update  STATEV(i) in UMAT to store the current coordinates.

delta_u1=COORDS(1)-STATEV(1)
delta_u2=COORDS(2)-STATEV(2)
delta_u3=COORDS(3)-STATEV(3)

STATEV(1)=COORDS(1)
STATEV(2)=COORDS(2)
STATEV(3)=COORDS(3)

If you need both total displacements and displacement increments just dimensions STATEV to 6 (Depvar=6) and use for example the STATEV(1...3) to store the initial coordinates and STATEV (4...6) to store the coordinates from the previous time increment.

Regards.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Resources

Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close