User login


You are here


Inaccurate UMAT result in SMP model

Choose a channel featured in the header of iMechanica: 


I have written a UMAT subroutine similar to the one shown in abaqus 6.11 subroutine manual 1.1.40 with a slight differences indicative of the material's rheological model.
my expanded isotropic model looks like:
sigma_x - sigmav_x/3 + vbar*sigma_dot_x + kappa*sigma_dot_x =
lambda*eplv + 2*mu*epl_x + lamdabar*eplv_dot_x +2*mubar*epl_x

Soud Choudhury's picture

Need help for running UMAT of Dr. Huang's single crystal

Hello Everyone,

I am a new member of imechanica. I have started to learn UMAT of Abaqus to model my material behavior ( Cu6Sn5, HCP) using crystal plasticity finite element model. I found Dr. Huang's single crystal UMAT to start learning UMAT and I thought that it would be a great guide to start though it is written for FCC mat. But unfortunately I was not able to run the UMAT with it's input file.

Abaqus UMAT implementation

Choose a channel featured in the header of iMechanica: 


I have a thermo-mechanical constitutive model for polymer and want to implement it in ABAQUS through two user subroutines namely UMAT and UEXPAN but I dont know how to use them together. Also, in UEXPAN, I need to pass in the strain tensor as information but I dont see 'STRAN' variable in the list of variables passed in to UEXPAN in Abaqus documentation. Does anyone know answer to this?



reading nodal values (EFENRRTR) into a UMAT routine


I am using the VCCT method to model crack propagation and I am finding the value of G/Gc is too large for any sensible time step (1e-25).

I am attempting to incorporate a time incrementation scheme into my UMAT which monitors EFENRRTR and modifies the time step (or PNEWDT) according to it's value.

LSDYNA UMAT- history variable choice


I'm presently working on implementing anisotropic yield criteria in LSDYNA as UMAT.

I understand from the LSDYNA documents that effective plastic strain is a default history variable.  So when we code, can we omit the update of effective plastic strain as a history variable? If so, where is it stored and how is it retrieved during post-processing ?

In Abaqus UMAT, is DDSDDE the same with "effective deviatoric elasticity"?

Free Tags: 

Hi all,


In Abaqus Theory Manual 4.6.1, there is a concept called "effective deviatoric elasticity". I think that term is actually DDSDDE, i.e. the consistent linearized tangent moduli. 


But why is it called "effective  DEVIATORIC elasticity"? It sounds like we missed the volumetric part (but only considering the isochoric part).


I would really appreciate it if someone could help me with this. Thanks!



In Abaqus, how to get SSE in UMAT?

Choose a channel featured in the header of iMechanica: 
Free Tags: 

Hi all,


I have been writing a UMAT function with modified hyper-visco-elastic model. My question is: after I got the Cauchy stress at the end of step, how do I get the SSE (elastic strain energy density)?


If it is only hyper-elastic I would have known (since the strain energy function itself is given). However, if it is viscoelastic, how should I calculate?


PS: I would also appreciate it if anyone could shed some light in getting SPD, SCD as well. Thanks a lot!



ABAQUS - Does Newton's method affect the convergence rate of higher order incremental scheme such as RK4 implemented via UMAT?

Hello everyone,

I'm currently doing an analysis on the convergence rate of an incremental model that I have implemented in ABAQUS using a UMAT. Here's the BIG lines of the problem:

1) In UMAT : Solution of a differential equation using explicit Runge-Kutta 4 (RK4), which has a 4th order convergence rate, yields the stress state "S". (In my problem, stresses are applied)


Hello everyone,

 I am running a UMAT on ABAQUS. However, I need to call another subroutine : URDFIL. I have included the URDFIL subroutine in the same file as the UMAT subroutine.

The problem is that when I run the program, ONLY the UMAT subroutine runs. It looks as if ABAQUS ignores completely the URDFIL subroutine (It doesn't run it at all). Do we have to include anything 

specific in the INPUT file in order for ABAQUS to take the URDFIL into account?

Thanks for the help!

- Jack


Controlling the time incrementation scheme in ABAQUS

Hello everyone,


I am currently writing a UMAT for non-linear viscoelastic materials. In order to do some verifications,

I need to be able to customize the time incrementation scheme. For example, the first increment would 

have a time step of 1E-5s while the other increments would have constant time step of 1E-2s. I know this is not a

very straightforward problem, but I really need to be able to do that. I am currently trying to combine my UMAT with other subroutines

Meshing with UEL/UMAT element

Hello All,

Does anyone have any idea how to automate meshing  using USER DEFINED ELEMENTS (for Example UEL) in Abaqus using python. Actually I need to mesh an arbitrary shaped structure  with 9-Node Quadrilateral Element. Abaqus doesn't support meshing of  9 Node Quad Element (S9R) either. 

bitamendi's picture

Active Research groups in Computational Plasticity

Choose a channel featured in the header of iMechanica: 

Hello everyone,


I'm last year PhD student. I would appreciate if someone could advice me about active research groups in Computational Plasticity (material models, hardening models, yield criteria, UMAT) in California or Australia.


I'm looking for an interesting research group to find a post-doc but I don't know from where start.


Thansks to everyone!!

bitamendi's picture

Active Research groups in Computational Plasticity


Hello everyone,


I'm last year PhD student. I would appreciate if someone could advice me about active research groups in Computational Plasticity (material models, hardening models, yield criteria, UMAT) in California or Australia.


I'm looking for an interesting research group to find a post-doc but I don't know from where start.


Thansks to everyone!!

Two UMATS in one Subroutine

Dear All,

I have the problem. i created very simple example with two elements. To one element i prescribed the behaviour Mat1, to another element Mat2. I tried to use two different UMATS for this two elements.

I created Subroutine Myname.f, in which i use CMNAME if (CNMAME.EQ.'MAT1) THEN





Then i put two UMATS in the same SUBROUTINES ,

But as a result the program gives MISTAKE , it says that The UMAT doesn't exist

What is the mistake?

Umats with Abaqus

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!!



Does anyone know things needs to know before doing dynamic analysis using umat

Hi, everyone,

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

Look for free-code UMAT on polymer viscoplasticity model of M.C. Boyce

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 !

Combining UMAT with XFEM

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,

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

Crystal Plasticity Modelling

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:

C       3*NSLPTL+1 - 6*NSLPTL  :  current components of normals to slip

C                                 slip planes

Damage modeling with UMAT

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,

How can I model the progressive damage of composite materials

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. 

Natural Frequency Extraction in conjunction with UMAT in ABAQUS


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:


Subscribe to RSS - UMAT

Recent comments

More comments


Subscribe to Syndicate