Understanding nonlinear viscoelastic parameters to write UMAT ?

More Shreeraman Swamynathan's questions See All

Dependence of Eigen Frequency on load for a non-linear system??

02 March 2017 7,700 17 View

Can I compare the results of a Transient Dynamic Analysis with that of a harmonic analysis?

31 December 2016 7,663 5 View

Mode-Mixity computation in 'Interface crack' ?

07 August 2016 146 1 View

Conformal meshing problem - "Without Multi-body-part" - Ansys R16 ?

06 July 2016 2,371 0 View

Plane_Stress, Plane_Strain and 3D - Simple doubt.. :( ?

05 June 2016 6,112 5 View

Fracture mechanics - Can I model a bimaterial crack in Ansys V16 Workbench?

05 June 2016 8,854 10 View

Extracting element id's from a set of elements - ANSYS Scripting?

05 June 2016 8,732 1 View

UMAT Non linear Viscoelasticity - Algorithm?

02 March 2016 2,306 6 View

How to handle the 4th order tensors in UMAT?

02 March 2016 3,749 2 View

Relaxation test - Abaqus?

01 February 2016 8,495 4 View

How to define and get results (stresses) for certain points of a model in abaqus, using python? When the size of the model changes?

I want to do a parameter study of a aixsymmetric cylinder in Abaqus. I want to create several jobs where I get the stresses for 3 different points in my model. These points are defined. I wrote a...

01 March 2021 10,078 1 View

LOAD DISPLACEMENT CURVES Stiffness increasing in ANSYS non linear analysis. HOW CAN I CORRECT IT?

Hi. I am doing non linear FE analysis using a new material beam under flexural 2 point loading using ANSYS. I have defined a bilinear material model. The solution has converged. In results I am...

01 March 2021 9,911 3 View

Joint behaviour in Abaqus is not captured well?

I am working on roof joint and trying to simulate the behaviour in Abaqus. I am successful in running the model but the final graph does not follow the experimental curve in the negative direction...

01 March 2021 6,661 3 View

Which one is easier and better at modeling slender masonry structures? ANSYS or ABAQUS?

I need to model masonry and reinforced concrete minarets for my MSc thesis. Which one is easier and better at modeling slender masonry structures? ANSYS or ABAQUS? (Or any other program for just...

01 March 2021 736 3 View

How to assign different material properties to each element in Abaqus ?

Hello, I am writing a python script to generate my model and write the input file. The problem is I have 1000 elements in my mesh and I want to assign different material properties to each...

01 March 2021 9,511 3 View

How to define tie constraint between rigid body and another part in dynamic explicit model of Abaqus?

Hi dear researchers I connected a rigid body into the part of my structure by tie constraint and then I added displacement to rigid body, in static general step every thing is fine and these two...

28 February 2021 3,442 2 View

How to modify Johnson cook equation in ABAQUS?

I wanted to add an extra parameter to the existing Johnson cook equation in the ABAQUS simulation. How to add those extra parameters. Ref: A modified Johnson-Cook material model with strain...

28 February 2021 4,841 3 View

How can we simulate an hyperelastic-viscoelastic behavor with Ansys APDL?

I am working on modeling and simulation of biomecanical material behaviour, I have succeded on simulating skin using anisotropic hyperelastic material, on APDL and in our lab's finite element...

28 February 2021 552 3 View

For modelling epoxy-based matrices (in composites), which model in ABAQUS is the most suitable, Concrete damaged plasticity or Drucker-Prager model?

I am working on developing a micromechanical FE model for predicting kink-band formation in UD composites. To model matrix plasticity, which model, out of Concrete Damaged Plasticity and...

28 February 2021 5,415 1 View

How to find the right number of integration points in second order 3d finite elements?

I am familiar with finite element simulations and numerical schemes like the Gauss Legendre quadrature. I also know that the Gauss integration yields exact values for polynomials up to degree 2n-1...

27 February 2021 6,818 3 View

Anshul Faye

I have not gone through and understood complete paper. But when I see it, it think that it is correct that, for a constant applied stress you will get constant nonlinear parameters (i.e g0,g1,g2,a). This is also clear from Fig.1 which plots these parameter with effective stress. Thus for a constant effective stress you will get corresponding constant values of g0,g1,g2, a.

I Hope this helps you.

Shreeraman Swamynathan

@ Anshul Faye

First of all thanks for valuable answer.. I still have some doubts..

Let's assume the parameters are constant for a constant applied stress. Fig.1 as you mentioned holds good if effec.stress (sigma) is the applied stress. Further on, creep and relaxation curves (Fig.5,6,7) are all plotted for applied stress of sigma_0, meaning sigma_0 is the applied stress ? (again confusing)

The constitutive law is given as strain = function (stress,internal variables). Now what I need for UMAT is, I input strain increment and get updated stress increments for every time step. In that case, how to evaluate the non-linear parameters as they are functions of stresses at current time step ?Correct me if I am wrong..

Thanks for your time

Shree

Hi,

1. Yes, in Fig. 1 constants are plotted as a function of effective stress. I did not get the definition of effective stress in the paper, but whatever it is it will be a function of applied stress only. Thus, effective stress being constant being constant will mean that applied stress is also constant.

2. I am also confused about you 2nd point. Because in UMAT, incremental strain is input and incremental stress is output. I need to think about it. I will update the post if I get it.

Look at the attached paper. On Pg. 4, they give a flow chart for a similar kind of constitutive model. Same algorithm in work in present case also.

Article Implementation and Validation of Schapery-Rand Anisotropic V...

Thanks a lot for your response and the referenced paper.. I am still in the lookout for a feasible solution.. I will go through the attached paper.. Do post here if you get any updates.. Btw may I know if you have prior experience writing UMATs for such material models?

Thanks and Regards

I have experience with UMAT for an elastic-viscoplastic material model for polymer, but not with Schapery's model.

Hello..

Thanks for your prompt repsonse. I am newbie in UMAT. I just wanted to know if I could ask somebody willing to help, in case I meet a dead end.

I went through the paper you sent.. In page 3, just before section IV, they have briefed on the process. I still don't understand one part, as to how trial stress (sigma_trial) is calculated from non-linear parameters of the previous time step.. All the other things are fine..

Awaiting your response

Frank Richter

Hallo Shree,

for the implementation of UMAT you may seek assistance from the ABAQUS mailing list

https://groups.yahoo.com/group/ABAQUS

I am the author of the thesis "Upsetting and Viscoelasticity of Vitreous SiO2: Experiments, Interpretation and Simulation"

https://depositonce.tu-berlin.de/handle/11303/1574

when you will find the implementation of a nonlinear Maxwell model

Good luck

Frank

Hey Frank,

Thanks for the reply. I did already look into your Thesis report. Good work. I am currently stuck in a state where I am not able to understand the formulation of the constitutive law. I think only after this, I can work on algorithm and then start with coding UMAT. It would be great if any of you could clarify it in the first place.

Hello Shree,

please find attached the private communication written up by Dr. Alexandru which is referred to in a footnote of my PhD thesis. Have fun.

The theory is probably taken from

Trostel: Mathematische Grundlagen der Technischen Mechanik III, Materialmodelle

Verlag: Vieweg, 1999

My PhD supervisor also gave up.

Thanks again Frank. I could follow it vaguely, would love to have an English version of the pdf if at all you have it.

An english version does not exist

Maziar tour sangsaraki

Hello.

Does anyone have an example of UMAT for nonlinear kinematic hardening?

my problem is how to convert constitutive equations to be suitable for UMAT code.