UMAT

I am learning the polycrystalline crystal plasticity and testing material in ABAQUS and UMAT. Now I am trying to build a RVE by using the truncated octahedrons as the grain shape or Voronoi tessellations.

For truncated octahedrons, I built a truncated octahedrons and assembled them into the grain aggregate in the .inp file, and assign orientations in the UMAT based on the part's name. However, I found it hard to define their interaction between grains. What is their interaction properties and how to define the contact pair in an automatic way?

UMAT Multi-element Error

Submitted by nibalog on Thu, 05/23/2013 - 16:18

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Hello All:

I have written a UMAT code to predict the viscoelastic behaviour within a
shape adaptive structure. I have followed similar steps used in Abaqus
subroutine manual, I have applied this UMAT to a single quad element and
it works as predicted. But when I apply it multiple elements model it
breaks down.

Is there any special command i need to put in UMAT subroutine to account
multi element analysis? I will appreciate all related comments,

UMAT Multi-element Issues

Submitted by nibalog on Thu, 05/23/2013 - 16:14

Hello All:

I have written a UMAT code to predict the viscoelastic behaviour within a shape adaptive structure. I have followed similar steps used in Abaqus subroutine manual, I have applied this UMAT to a single quad element and it works as predicted. But when I apply it multiple elements model it breaks down.

Is there any special command i need to put in UMAT subroutine to account multi element analysis? I will appreciate all related comments,

Thanks

Inaccurate UMAT result in SMP model

Submitted by nibalog on Wed, 04/03/2013 - 22:16

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Hello:

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

where:

sigma = stress

epl = strain

_dot_ are my rate change with time

sigmav = sigmaxx + sigma_yy + sigma_zz ( hydrostatic stress)

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

Submitted by Soud Choudhury on Mon, 02/25/2013 - 19:03

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

Submitted by Mandar Kulkarni on Mon, 02/18/2013 - 04:20

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Hi,

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?

Thanks,

Mandar

reading nodal values (EFENRRTR) into a UMAT routine

Submitted by jodavies03 on Wed, 01/16/2013 - 11:04

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.

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