iMechanica - VUMAT - Comments

You can convert between different rate forms

Wei Hong — Thu, 27 Nov 2008 15:14:03 -0500

Hi Shunlai,

I think the way abaqus treat stress/strain rate is more or less determined by its corotational local coordinate system. So direct implementation of orther rate forms are not so easy. But if you have a constitutive relation in the form of one type of stress/strain rate, you can easily convert it into the rate form used by Abaqus.

If not so straightforward to convert analytically, you can treat it as following. Expand everything around the current configuration, and neglect all higher order terms in the increment of strain/displacement. By doing that, the constitutive relation is a small-deformation relation, and the rate forms do not really matter, since the rigid-body rotation is already taken care of by abaqus, before passing into UMAT/VUMAT

Hope this helps.

Wei

decomposition of F

Xiaoteng Wang — Mon, 06 Oct 2008 06:20:33 -0400

Hi Zhangli,

Sorry I missed the V when I read your VUMAT thread.:)

Anyway I think you can achieve the decomposition of F. VUMAT provides the stretch tensors at both current step and previous step.

Another thing is the deformation gradient is objective (rotation free), so you dont need to rotate it.

Wang

Thanks. Rotation tensor

zhpeng — Fri, 03 Oct 2008 14:57:04 -0400

Thanks.

Rotation tensor is not provided in VUMAT, and I think polar decomposition of F is still required.

Also ROTSIG is for ABAQUS Stand. I am using VUMAT (Explicit).

Zhangli

Hi Zhangli, The

Xiaoteng Wang — Thu, 02 Oct 2008 23:59:27 -0400

Hi Zhangli,

The deformation gradient F is already provided by ABAQUS and you can directly use it in UMAT programming. I think the rotation and stretch tensor is also provided. Since you are using Hyperelastic hypothesis, you should define your own configuration using UMAT. ABAQUS provides a utility routine ROTSIG to rotate the stress or stress like tensor such as back stress, etc.., but maybe that utility routine is based on Hypoelastic decomposition. Please refer to ABAQUS manual and I hope you can get some ideas. Good luck.

Xiaoteng Wang

Abaqus Process Automation Portal

Sprunger — Mon, 29 Sep 2008 13:11:49 -0400

Hello, Re: Sharing Abaqus UMAT and VUMAT subroutines.SIMULIA has an “Abaqus Process Automation Portal” http://www.simulia.com/PAPortal/This portal provides a mechanism to the SIMULIA (Abaqus) community for collaboration through discussion forums for GUI customization and scripting techniques. Users can upload, download, and share solutions and process automation components.

The Abaqus Process Automation Portal is approaching its 5 year anniversary and many engineers found it to be a useful resource. Almost 3000 registered members currently exist and this number continues to increase steadily.

Regards, Rene

It's an old topic.

Shunlai.Zang — Sun, 24 Aug 2008 09:05:30 -0400

Just as open source vs. closed source

But I think sharing knowledges is a good thing.

Shunlai

UMAT for Shape Memory Alloys

msimsek — Wed, 20 Aug 2008 12:40:21 -0400

Hi,

I am an M.Sc. mechanical engineering student and I am trying to model super elastic property of shape memory alloys in ABAQUS. I am new to ABAQUS and trying to learn it by reading the tutorials. It seems I have to use UMAT but I dont know how to use it or how to create a subroutine for my case. If anybody helps, makes contribution it would be appreciated.

Look forward to getting some responses.

Thanks

Miray

searching Umat Vumat

Tosche96 — Sun, 20 Jul 2008 15:59:56 -0400

Hello,

I'am looking for a vumat or umat file for thixotropic material! Has somebody already written such kind of file for abaqus! I want to simulate thixoforming / semi-solid process!

thx

I can't agree more!

Liu Jinxing — Thu, 10 Jul 2008 04:14:51 -0400

I can't agree more! Furthermore, this problem doesnot exist on ABAQUS uniquely. This same idea can be also helpful to ANSYS, Nastran and so on!

Dispersity!!!

RoozbehSanaei — Mon, 30 Jun 2008 08:24:31 -0400

http://imechanica.org/node/3433

User element help

Y. Kajee — Mon, 30 Jun 2008 08:18:05 -0400

I realise this is an old post.

I am in the process of developing my first user element in Abaqus, and finding it rather difficult.

The application requires modelling muscle behaviour. Hence a spring model (linear at this stage) with 3 elements: 2 in series with each other, and these 2, parallel to the third was implemented.

My problem involves static condensation of the stiffness matrix. (similar to mixed-methods)

Any advice/assistance would be great.

Regards

Request for UEL or UMAT in ABAQUS or LS-DYNA or a source code

Babak — Wed, 25 Jun 2008 14:04:21 -0400

Dear friend

I am Babak, a Ph.D. candidate in geotechnical engineering, school of civil engineering in university of Tehran (UT), Iran. (www.ut.ac.ir). My research topic is about “Capturing shear band in slope and excavation in static and seismic conditions”. I look for a model which can handle shear banding and strain localization in geological materials specially soils. I really appreciate your favor whether help me in this regard. Any helpful comments about source code, open source software or even a hint which can help me to follow it are appreciated. I am completely ready to do joint research with someone else.

Truly yours,

Babak Ebrahimian

Ph.D. Candidate in Geotechnical Engineering

University College of Engineering

School of Civil Engineering

University of Tehran

Tehran, Iran

Postal Code: 11155-4563, Enghelab St., Tehran, Iran.Mobile Phone: (0098-912)5506553Phone Number: (0098-311)4416302Fax: (0098-311)4343275

Email: bebrahimian@ut.ac.ir

Dear Mr.

ho1mo — Fri, 20 Jun 2008 17:34:14 -0400

Dear Mr. Azadpoor,

Hi,

I am Hojat Mohamadi from Iran.

I and my team work for generation a book that completely explain modeling and analyzing the mechanical events by ABAQUS, step by step, and consists of fundamental of /CAE, creating input files and ABAQUS programming .

I have no problem in fundamental of /CAE and input files because of my experience, but I have no reference in ABAQUS proggraming and will be happy if you guide me about it.

Therewith, may be explaine me about ABAQUS programming(specially UMAT) and is the ABAQUS Documentation enough?

My e-mail: Ho1mo@yahoo.com

Thanks a lot for your kindly response.

Hojat Mohamadi

Graduation Project

alper_tastan — Sat, 07 Jun 2008 19:34:00 -0400

Hello;

In my graduation project, the instructor wanted from me to work the UMAT Subroutines in ABAQUS. I am looking for someone who can help to me about this issue. I really got an urge for completin this project and really need of somebody's help.

From now am thanking to the ones who will help to me.

I am lettin my msn adress for the ones who want to contact with me...:

alper_tastan@hotmail.com

looking for cohesive zone element user subroutine

Wang Y.L — Sun, 01 Jun 2008 00:17:29 -0400

Mr. Gao

I am a new comer of imechanic, I got your webpage though the search engine Google, but I could not enter it, I dont know why.

I knew you have a user subrotine about the cohesive zone and you are willing to share it with others, resently I am studing the CZM and what to simulate the surface problems with the FEM, but I am stumpt by the subrotine. I hope you can help me and send the subrotine to my email(baishalang2002@163.com). Thank you very much.

Excuse for my poor english, I am a university student from HEU,China. Expect your reply.