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Using UMAT for time dependent material behavior


thegiving21
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Hi All,
I have isotropic damage model under UMAT subroutine. The model is static. Simple 2d element loaded (displacement) in one edge monotonically. I want to change the history of loading ( e.g. loading-unloading) as function of time. I found out that with tabulat amplitude one can define such loading. However, My question is as follows : After I change the history of loading as function of time, I want to put some conditions of time in UMAT subroutine. For example if I define the history of loading of 1mm from 0 to 200second (0mm to 1mm), and unloading from 200s to 400s (1mm to 0mm), I want to define a loop in UMAT in which we can define an equation (e.g X(t)) which is also function of time, for example if we want to define the equation X(t) in only the interval of time [200s , 400s].

Can anyone explain me how can we apply this in UMAT ?
Thank you.

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Jorgen
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Im not sure I understand why you want that, but since the UMAT is provided the time you can code the stress response any way you like (e.g. to be dependent on the time).

-Jorgen

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thegiving21
Posts: 17
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(@thegiving21)
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Joined: 5 years ago

Thank you for the reply.
I know, in UMAT time is provided, but I want to know how can make a condition in UMAT. for example :
if 200s < t < 400s
X(t)= equation function of time
end if

Can you please explain me how can I define this condition in UMAT ?

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Jorgen
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You can directly code that in your Fortran code. Just use if statements to separate different time periods.
Note, however, that if you are not careful then you may get convergence problems when you switch from one time period to another if the response is not continuous.

-Jorgen

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