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Continuously change elastic modulus during runtime using element strain rate

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Posts: 16
Topic starter
(@Poshman)
Active Member
Joined: 8 years ago

Hi all ...

I am using a material which is rate dependant (elastic modulus increases with increase in strain rate), though i dont want to use viscoelastic model that comes with Abaqus as i am not looking into the relaxation and creep aspect. I am monotonously loading the material till failure so no talk of relaxation as i am not loading the material in fatigue.

Assuming that i have a continuous function which takes in the strain-rate and gives out elastic modulus, the strain-rate i should get from each element in each increment based on that the function will give a new young,s modulus which i will update the same element for the next increment. This procedure is done for all the elements in the mesh.

How this procedure can be implemented? I am using Abaqus/Explicit. Thanks all.

Priya

IIT

Delhi

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Posts: 3998
(@jorgen)
Member
Joined: 5 years ago

You can implement that behavior into a VUMAT subroutine. It actually should not be too hard to do.

Note that it is not a good general purpose approach to have a stiffness depend directly on the strain rate. The strain-rate can change
in a discontinuous manner, so then your modulus and stress can then also change discontinuously, which is typically not physical.

-Jorgen

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Posts: 5
(@MackDonny)
Active Member
Joined: 11 years ago

Currently, I also need to implement a similar elastic model in VUMAT, and the modulus is strain rate dependent using a function. Then I want to identify the parameters of strain rate function using a inverse method. Is there any progress for your case? Thanks.

Haibin

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Posts: 2
(@Ecoflex)
New Member
Joined: 9 years ago

Hi Haibin....Did you make your subroutine work? I

Hi Habin,

i am also dealing with the similar issue. Did you manage to run the subroutine for change of elastic modulus with strain rate.

Anil

[QUOTE=cuba20052001,10724]Currently, I also need to implement a similar elastic model in VUMAT, and the modulus is strain rate dependent using a function. Then I want to identify the parameters of strain rate function using a inverse method. Is there any progress for your case? Thanks.

Haibin

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Posts: 2
(@Ecoflex)
New Member
Joined: 9 years ago

Hi Jorgan,
I agreed with the comment you made for elastic modulus dependency with strain rate as strain rate for an element is too noisy. But, is there any way, we can manage to run these type of simulations in lsdyna or Abaqus using some subroutines. Your reply will be appreciated.

Anil
Wayne State University

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Posts: 3998
(@jorgen)
Member
Joined: 5 years ago

Yes. The [URL= http://www.veryst.com/what-we-offer/polymer-modeling ]PolyUMod[/URL] library has material models that support that exact behavior.

-Jorgen

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Posts: 5
(@MackDonny)
Active Member
Joined: 11 years ago

[QUOTE=ey6652,13426]Hi Habin,
i am also dealing with the similar issue. Did you manage to run the subroutine for change of elastic modulus with strain rate.

Anil

Hi Anil,

Its possible to change elastic module with strain rate, but I used some inverse strategies to identify the strain rate dependent model and found the error of identified parameters (in strain rate dependent model) was significant. Im not sure whether its because of the calculation of strain rate in VUMAT.
Haibin

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