UMAT

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.

Hi,

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.

Hi,

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 ?

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.

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!!

Hi everyone,

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,
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:

CArray STATEV:

C3*NSLPTL+1 - 6*NSLPTL:current components of normals to slip

Cslip planes

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,

最近,我纵容自己的进步amage 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: