# viscoelasticity

## apparent paradox: for a sliding flat punch on a viscoelastic halfspace, friction is zero or not?

dear Imechanica friends here is an apparent paradox: for a sliding flat punch on a viscoelastic halfspace, friction is zero or not?  Certainly there seems to be viscoelastic dissipation, but the pressure is also normal to dispacements, so am I missing something obvious here?

## VUMAT viscoelasticity (Maxwell model)

Dear all,

I would like to ask you for advice. I am about to simulate a pull-through test (see attached picture) of a cladding panel made of a material with highly viscoelastic behaviour. I have parameters for Maxwell model (Prony series) obtained from test. I expect large deformation and probably cone failure (or tearing of the cladding panel). Therefore I would like to use Abaqus/Explicit. The problem is that I cannot use *visco step together with Explicit. Is there any way to solve it?

## Question reg ABAQUS-VUMAT and Updated Lagrangian formulation.

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Hello all,

I am working on implementing a viscoelastic constitutive model from a hyperelastic stored energy potential (for finite-elasticity) and a dissipation potential (for the viscouls evolution). The elastic constitutive relation, hence derived from the stored energy potential is rate-independent and it is expressed as T(Cauchy's Stress) = f(B), where B is the Left-cauchy green deformation tensor.

The evolution equation is derived out in an objective rate form, which I am integrating over time using a 2nd order accurate explicit method.

My question:

## UMAT Non linear Viscoelasticity - Algorithm verification?

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Hello everybody,

My task is to write a UMAT for Non-linear Viscoelasicity based on Schapery's model in ABAQUS. I have coded the routine, but I am still not able to predict correct response. I tried to debug it as much as I can. I understand that it would be difficult for anybody to understand my code. So, I have attached a flowchart (pdf) of the whole algorithm that I follow. It would be nice if you could check that and correct me if I am wrong.

Regards

Shree

## ageing viscoelastic

Hello everone

I am recently interested in viscoelastic composite materials with ageing effect. I will be very pleased if someone can advise me how to find a constitutive law with ageing effect.

sincerely

## Online finite element analysis of nanoindentation (indentation)

Dear All,

We (the NanoBIO Node at Illinois ) have a preliminary release of an online finite element analysis of nanoindentation (indentation) tool using FEAP

This preliminary release is limited to linear elastic material, axisymmetric geometry, spherical rigid indenter, and various boundary conditions.

## Residual stresses in elastic medium upon uniform cooling

Hi All,

I am a student working on a project involving the effect of residual stresses in elastic and viscoealstic materials. I have a related question: When an easltic body is heated to a certain temperature (say 400 deg C) and then cooled uniformly to room temperature (20 deg C) with a constant cooling rate "q", does this generate any "un-desirable" (residual) stresses within the elastic body? i.e at a steady state - room temperature, does the final stress state within the body would be non-zero? Else, it would eventually reach a state of zero stresses? How?

## Nanobrücken 2014 Nanomechanical Testing Workshop

The Nanobrücken 2014
Nanomechanical Testing Workshop
will take place March 26-28, 2014 at INM -
Leibniz Institute for New Materials in Saarbrücken, Germany. This will be the
4th edition of the now-annual Nanobrücken workshop series. This year's
Keynote Speaker will be Andrew Minor (University of California, Berkeley).

## UMAT Multi-element Error

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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

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

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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