The answer of Hassan it's good one, as start of learn about visco analysis in Abaqus, as principle level.

Rosy,

In Abaqus 6.x-Documentation-Abaqus Example Problems Manual see Section 1.1.12 Transient loading of a viscoelastic bushing, and Section 1.3.2 Superplastic forming of a rectangular box, which is quite similar to Visco simulation and analysis.

These are typical requirements in hot-metal forming (e.g. at constant temperature).

There are different ways of doing it in Abaqus. One would be to define rate dependency in Addition to plastic behavior (as some Researcher suggest), load tabulated stress-strain data sets for different strain rates, and writing a UMAT or even VUMAT by yourself.

In the ResearchGate community there are some people who published on this topic. You may contact them directly for further advise.

Haidong Yu, Yongjin Guo, Xinmin Lai

Rate-dependent behavior and constitutive model of DP600 steel at strain rate from 10−4 to 103s−1

Rosy,

To run a Visco analysis in ABAQUS you'll need to set a few material properties:

1. An instantaneous modulus and Poisson ratio in the "Elastic" section.

2. The Prony series parameters (gi, Ti, ki in a time domain, different paramters if frequency domain) under the Viscoelastic section (under "Elastic").

Both 1 and 2 parameters are experimentally determined and can be derived by fitting a Prony series to set of creep data or frequency sweep data. The form of the Prony series can be found in the ABAQUS documentation. Often it may be easier to find the Poisson ratio from literature, as the experimental derivation may be rather involved.

I have generalized the procedure here. If you have a more specific question on any details please ask!

The answer of Hassan it's good one, as start of learn about visco analysis in Abaqus, as principle level.

Rosy,

In Abaqus 6.x-Documentation-Abaqus Example Problems Manual see Section 1.1.12 Transient loading of a viscoelastic bushing, and Section 1.3.2 Superplastic forming of a rectangular box, which is quite similar to Visco simulation and analysis.

Rosy,

Looking at your question again I'm wondering whether the problem you want to model is truly visco-plastic, or is it a viscoelastic model with a permanent deformation remaining after sufficient relaxation time?

There aren't any direct viscoplastic analysis methods in ABAQUS, although it is possible to perform viscoelastic analysis with a Burger type behavior, meaning they have a residual strain even after very long recovery times.

The exact conversion method used to convert a Burger's model to an ABAQUS input Prony series is available in the paper linked in this post. There also seems to be a downloadable copy of it in another forum post if you do a Google search on "Burger Model convert to Prony series ABAQUS".

http://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=5541456&url=http%3A%2F%2Fieeexplore.ieee.org%2Fxpls%2Fabs_all.jsp%3Farnumber%3D5541456

Rosy, your question is very laconic.

Is you problem connected with elevated temperature or rather with strain-rate dependent material behavior?

If it is stain-rate dependency, the simplest way is the use of Johnson-Cook model.

In Abaqus, define

Plastic behavior -> hardening: Johnson -Cook

when Suboptions -> Rate Dependent-> Johnson-Cook

Parameters for common Johnson-Cook model are probably easiest to find for many materials.

I agree with Artur IIuk comment. If its Strain-rate dependent model.

I would create dynamic- Explicit step and make use of the Johnson-cook material model.

When I used to do superplastic forming I used a power law creep type model; you may need to use a creep subroutine if you have both hot creep and superplastic forminng in different parts of your sheet(s), as they have different power indices (say 4.3 and 1.43 for Ti6Al4V). [strain rate as a function of deviatoric stress raised to a power]

Though quite often I would only use the superplastic element of the material model.

There is a danger with using an "explicit" type solver as superplastic flow is, itself, more elliptic than the cold plasticity of metals or even the hot creep properties. This was particularly obvious when modelling the quilting effect of a multilayer bonded structure - as it is very much dominated by the stress transmission.

The book by Pilling and Ridley on superplasticity could be a useful source for appropriate material models