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Problem about the Jacobian matrix (DDSDDE) in UMAT

Submitted by yth on Fri, 03/03/2017 - 06:00

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ABAQUS UMAT

Hi all friends,

I have a basic question. Why the Jacobian matrix (DDSDDE) in UMAT is defined as:

∂Δσ/∂Δε

rather than:

∂σ/∂ε

And what's the difference between them

Thank you all for your help,

Tianhao Yan

bolt preloading Abaqus

Submitted by CMiculas on Mon, 02/27/2017 - 16:41

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Hellor,

I am trying to make a comparison between methods of applying bolt preloading in Abaqus.

1. bolt load method - which works fine

2. predefined field, initial stress - not really working.

I have created the following steps:

Step

initial - BC + initial state of stress in bolt shank (this step works - see Fig. 3 & 4)

How can I calculate "Transverse Shear Stiffness" for shell and beam elements?

Submitted by Qusay on Sun, 02/26/2017 - 17:02

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I read through ABAQUS manual to calculate "Transverse Shear Stiffness" , but the result doesn't match between(UMAT & GUI modeling).

Please help if you have any information

Thanks in advance

What's the difference between Cohesive Zone Model and Joints Element in discrete element method?

Submitted by xi xun on Sat, 02/25/2017 - 23:55

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education

Hi,

I am a PhD student working on rock mechanics. I have studied Cohesive Method for a few times. But I am confused on What the special functions the Cohesive element have compared with Discrete method?

For one DEM software UDEC， model is consisted of solid elements and joints elements. What's the difference between Cohesive element and Goodman element?

Local mesh refinement using Gmsh

Submitted by rajan_prithivi on Thu, 02/23/2017 - 15:31

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GMSH

meshing

# Finite Element modeling

Hello All,

I am using Gmsh for creating a finite element mesh. After I create the volume mesh, Is there a way to do a local mesh refinement around a particular point (say x,y,z) and within a sphere of given radius.

Kindly help !

-Prithivi

UMAT for Kinematic hardening

Submitted by Qusay on Tue, 02/21/2017 - 18:30

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research

I just followed the code that ABAQUS presented (Copied below), but I'm getting very strange results comparing with ABAQUS GUI, what's wrong with that?

Please help if you have experience

SUBROUTINE UMAT(STRESS, STATEV, DDSDDE, SSE, SPD, SCD, RPL,

1 DDSDDT, DRPLDE, DRPLDT, STRAN, DSTRAN, TIME, DTIME, TEMP, DTEMP,

2 PREDEF, DPRED, CMNAME, NDI, NSHR, NTENS, NSTATV, PROPS, NPROPS,

ABAQUS UMAT CPFEM Subroutine

Submitted by yek567 on Fri, 02/17/2017 - 05:22

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Abaqus VUMAT Plasticity Adiabatic temperature

abaqus johnson-cook plasticity model

Dear All,

We are working on Equal Channel Angular Pressing (ECAP) project and we are trying to implement CPFEM with Abaqus UMAT, there are few examples online but we could not able to run them on abaqus 6.13 with any subroutine. Does anyone have any working subroutines on related subject?

Kind Regards

Yunus Emre Kulhan

Prony series with temperature dependent stiffness

Submitted by augustus on Tue, 02/14/2017 - 21:31

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linear viscoelasticity

thermoviscoelasticity

Hello,

I have implemented a viscoelastic model (Simo/Hughes approach: Prony series for small strain)

in Abaqus using Umat and it works fine for dynamic isothermal simulations (I validated with the Prony series implemented in Abaqus).

Now, I want to consider thermal loads (I have temperature dependent stiffnesses from a DMA experiment).

How should I use these temperature dependent stiffnesses in the model?

Can we obtain the stress value at a particular x,y,z ( inside an element) in Abaqus using Python ?

Submitted by rajan_prithivi on Mon, 02/13/2017 - 23:31

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I understand that we can do this using a path operation in GUI. But how do we do this using Python ?

I have been using Python for quite a while to obtain stress values at the integration points using
myOdb.steps[stepName].frames[-1].fieldOutputs['S']

But is there a direct command to obtain stress or any other field ouput at a particular x,y,z ? To do this manually, i have to find the associated element and interpolate the values which is a tedious job.