Hi everyone, 

hi, someone know how run abaqus models using user subroutines, I can run one umat with one model, but i need to run two umats in an unique model in a simple step..Thanks for you help!!

Luis. 

Hi, everyone,

Does anyone have some experience on using UMAT to do dynamic analysis? Please give me some help on the problems i encountered.

I just attended USNCCM11, and heard from a presentation that there should be free code for polymer viscoplasticity model from M.C. Boyce.Unfortunately, I googled from half an hour and dowloaded nothing this afternoon. Can anybody give more info ?

Thanks in advance !

Hi all,

Hi all,
I 'd like to ask whether anyone has applied XFEM for a user-material (UMAT). What is the process to do that? Could anyone provide some advice, documentation or guidelines?

All the best,
            
Panos

p.s. I 've heard that a UEL code is needed to couple XFEM with UMAT.

Hi all,

     I want to set up a critical shear strain - normal stress criterion, in UMAT by prof. Huang. For the strains it is easy to get a critical strain along a slip plane; but for the stresses the notation is quite weird. It is not the same! See below:

C       Array STATEV:

Dear all,
      I am using a Abaqus modeller with fortran subroutines. I have written a UMAT subroutine and now want to apply some damage initiation-evolution criteria. But I get the following error: a damage initiation property was used with a user material.
I wanted to apply the criteria externally from the subroutine.. How can I go through with this problem? I tried different criteria (stress and strain based) to check if it is a matter of the output variables... No result..
Is it the case that I should have my damage code within UMAT?
All the best,

        Panos

Recently, I indulged myself into the progressive damage simulation of composite materials. I firstly used the USDFLS to create several fields to define certain kinds of damage, such as fiber crack, matrix crack, shear damage and delamination. One curious thing that I experienced into this is that ABAQUS/Standard informed me that "Stiffness defined by engineering constants is not physically reasonable. Check choice of poisson's ratios". I checked the data and changed some to comply with the rules of the transversely isotropic materials and the program proceeded. 

Hi,

We are using the user subroutine UMAT in ABAQUS for varying the material properties in a thin plate. For any static analysis this subroutine is working perfectly fine. However, while using UMAT during natural frequency extraction, ABAQUS is not completing the analysis and is giving a very vague following error message in the log file:

I have funding for software development to provide a UMAT interface in the parallel versions of the code from Smith I.M. and Griffiths D.V. "Programming the Finite Element Method", 4th Edition, Wiley, 2004.

I would be interested to hear about any open source UMATs available for download. I'd also like to hear from anyone who might like to use their closed source UMATs in a parallel environment.

The funding has been awarded by the UK National HPC Service HECToR to encourage the greater use of HECToR for Structural Engineering.

The project runs from 1 December 2010 to 30 November 2011. Further details can be found at  http://tinyurl.com/23favxu

Dear all,

I have several questions about how to use existing constitutive law of material to code UMAT in Abaqus. I have carried out experiment for several powder materials, including metal, ceramic, polymer powders. The powder aggregate is compacted in a cylindrical die. After the compaction, relationships between axial stress and axial strain, radial stress and axial strain are obtained. The material under such condition is always treated as elastic plastic material.

Hi

***ERROR: THE SOLUTION-DEPENDENT STATE VARIABLE INDEX MUST BE AN INTEGER",

this is a error which pops out when i try to run Huang's single crystal UMAT. Do anybody have experienced the same kind of error

Karthic 

Dear All,

 I think that many students are looking for some tutorials about writing a UMAT in ABAQUS.

You can find a comprehensive tutorial for elastic problems.

This file contains: 

• Motivation

• Steps Required in Writing a UMAT or VUMAT

Here is a UMAT using an  elastic viscoplastic model for soil

Modifed Cam-clay model coupled with viscosity.

Detailed information can be found in the link

http://www.eng.uwo.ca/research/grc/software.htm

ABAQUS - UMAT (Free Download for Research Purposes)

A user-defined subroutine in ABAQUS for viscous soils.

Introduction:

Hi, friends,

Now, I am implementing the non-local continuum theory in ABAQUS through UMAT programming.

Unfortunately, I have been obstacled by the following question:

On one hand, in non-local continuum theory, the non-local strain of every particular integration point is determined by the global strain field all over the specimen.

Hello,

Now I want to simulate the change Young's modulus due to the mechanical stimulus in soft tissue. In our soft tissue(scaffold) we have seeded living cells and these cells produce the collagen fiber type-II which could be interpreted as change of Young's modulus. The Young's modulus of neighbour elements of the cells have to change depending on the Young's modulus of former elements like domino.

I have two constitutitve equations programmed in UMAT i. e. for scaffold and for fibers and they run good.

I want to show the Young modulus change of the neighbor elements depending on the state of the former elements. Has anybody ideas?

I would be very very lucky if any could help me

I am working with shape memory alloys (nitinol), and am in that respect investigating fracture behaviour of NiTi, using, among other things, simulations in ABAQUS. ABAQUS doesn't have a material model that include plasticity unless you pay for it. I am wondering if anyone have implemented either of the following models as a UMAT, and if you are willing to share the code with me.

The models I am interested in are:

Dear all, 

Hi All,

 Thanks for your help so far. I have one last question to the forum. Please do answer whatever you know. How can I compute Material Jacobian for my UMAT subroutine? 

best regards

--dinesh

I want to implement the elasto-plastic model for cyclic loadings (I suppose
something like chaboche) into the UMAT subroutine in my ABAQUS  model ,
but I haven't enough knowldge for do this. I read some book like mechanichs of solid materials but i don't understand how to implement my constitutive law into the subroutine. until the load is static i don't have many problems, but when i work with cyclic load I'm non able to generate a cyclic increments of plastic behaviou.

Can anyone kindly help me or
post me an example of the subroutine?

I hope my english was sufficient.
Thank you very much
Best regards
Bojan Huljev

Hi,

I am in process of implementing the Bergstroem-Boyce Model. In a first
step I am just considering the hyperlastic part of it (Network A:
8-chain). I have implemented this part in a UMAT using a numerical
approach for the elasticity tensor (Forward Difference Approximation
with perturbation of F).

I have two problems:

1.
------------------------
In order to keep my UMAT as easy to read as possible I have tried to keep the FDA in a separate file using

call KFDA_Jaumann(dfgrd1,......)

to call the KFDA_Jaumann.for which includes the numerical approach.

Now when I run the job using the command window I get an error in the log file:

Hi everyone,

    I have a question about the objectivity tensor in ABAQUS software. Below is my question.   

Hi

I’m trying to develop a VUMat routine so I’ve already
started to learn its features. I recently got this problem that what exactly
the variable stepTime means! I created a model with 3 steps including the initial
step and I coded my routine somehow that when the stepTime is equal to 0 it
prints something into a file. Surprisingly only once in whole analysis the
stepTime would be 0 and that’s exactly at the beginning of the analysis when
totalTime is in fact 0. Could anyone please explain why this happens?

Thanks

Hi everyone,

I am trying to build polycrystal plasticity model  by using UMAT subroutine in ABAQUS. As we know, the orientation of grain is always espressed by Euler's angles. What I want to know is  how to assign different initial orientations to different grains using Euler's angles in Umat subroutine. Could anybody tell me how to do? Is there any example ?

Many Thanks,

Yuanpei