### Author Topic: Stiffness Requirements File in General FEA Constraints  (Read 11686 times)

#### oyama

• Client
• Posts: 1
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##### Stiffness Requirements File in General FEA Constraints
« on: June 14, 2021, 02:17:02 AM »
Hi,
How can I define "Stiffness Requirements File"?

I use Express for sizing composite structure, and I try to optimize with respect to the stiffness(Nodal deformation), but I don't want to use iteration. Then, I try to define "Stiffness Requirements File".

Any help would be welcome.

Sincerely,

#### BStier

• Posts: 3
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##### Re: Stiffness Requirements File in General FEA Constraints
« Reply #1 on: July 08, 2021, 07:35:51 AM »
Hello oyama,

you can use the "Stiffness Requirements File" in Express by defining the file path in the: Analysis Criteria -> Stiffness Criteria dialog.

This way, you can define a minimum required stiffness (ABD matrix diagonal) for every individual element in your model.

The file format is as follows:
___________________________________
-1
#of Entries (i.e. number of elements you want to define a stiffness target for)
ElId, [dummy], A11, A22, A33, D11, D22, D33

-1
____________________________________

A simple example file defining the minimum (required) stiffness for elements with ID 1 through 10 is attached to this post.

Now, during element sizing optimization, these minimum stiffness requirements will be fulfilled (if your design restrictions allows for it; e.g. if max gauge is high enough for your chosen material).

I hope this helps!
-- Bertram