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### Author Topic: Calculation of the bending stiffness for effective laminates  (Read 1481 times)

#### scotch86

• Client
• Posts: 5
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##### Calculation of the bending stiffness for effective laminates
« on: December 19, 2014, 04:53:58 AM »
Hi,

can anybody explain how HS is calculating the bending stiffness D for effective laminates?

I thought the bending stiffness is calculated by an simply approach based on the A-Matrix. For example A11 * t^3/12.

Thanks in advanced.

#### James

• Administrator
• Posts: 230
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##### Re: Calculation of the bending stiffness for effective laminates
« Reply #1 on: December 19, 2014, 10:27:45 AM »
The Dij of the effective laminates are calculated as Dij = Et^3/(12(1-v^2)).

I hope this is helpful.

-James

#### scotch86

• Client
• Posts: 5
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##### Re: Calculation of the bending stiffness for effective laminates
« Reply #2 on: December 19, 2014, 11:46:53 AM »
Thank you James for the answer.

If I compare the bending stiffness Dij of the effective laminate with the discrete reference laminate  the difference is huge.

E.g. D11= 56365 (reference laminate)
D11= 87644 (With your approache)

I know there is a difference between discrete and effective laminates. The difference is about 50%, I think this difference is too much.

This approache leads to much higher values. For my point of view this is not correct. There is any literature (paper) about that? I have not found any information.

Could you please give me further support?

Thanks!

#### James

• Administrator
• Posts: 230
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##### Re: Calculation of the bending stiffness for effective laminates
« Reply #3 on: December 19, 2014, 11:52:05 AM »
You're correct. When you're using effective laminates HyperSizer doesn't know the true stacking sequence so the Effective laminate Dij is an approximation.
See: http://hypersizer.com/help/#Materials/EffLam/el-limitations.php%3FTocPath%3DFeatures%7CMaterials%7CEffective%2520Laminates%7CUsing%2520Effective%2520Laminates%7C_____2

It seems like you are analyzing a thin laminate that is highly biased toward D11 (0 degree plies at IML/OML). I would suggest to create DLs and use those for sizing. Once you have the EL result you can easily create a range of DLs. When HyperSizer creates the DLs it will attempt to bias them by modifying the sequence of plies. See: http://hypersizer.com/help/#CompositeOpt/Discrete Laminates.php%3FTocPath%3DFeatures%7CMaterials%7CDiscrete%2520Laminates%7C_____2

I hope this is helpful
-James