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Question on strain rate.

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

Hi all .. For strain rate dependent yielding materials , we normally input

constant strain rate data as a tabular input to FE packages. However in simulations i have noticed the strain

rate data is very Noisy i.e the values fluctuates very much. How Ls-Dyna or any explicit code

computes strain rate during run time to assign appropriate yield stress, which is ofcourse a function of strain rate.

Thank you.

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

That is a good question. Does the FE theory manuals provide any info.
Perhaps it is simply using the plastic strain rate from the previous increment?

In my modeling I typically avoid using a model in which the flow stress is strain-rate dependent for this specific reason.

-Jorgen

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

Hello Jorgen ... Thanks for the reply. As per the manual they use effective plastic strain rate, the eqn is similar to Von misses stress formula, however plastic strain rate components are used. Now the question is, does using effective plastic strain rate reduce the noise? The value could be a positive but , the noise?. Thanks.

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

Yes, noise can be an issue with that type of material models. As I mentioned, I prefer to use a viscoplastic material model that does not have that issue.

-Jorgen

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