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Stacking sequence & moment of inertia

Stacking sequence & moment of inertia

Stacking sequence & moment of inertia

(OP)
Hello,

Quick question fairly simple for most of you but I am confused.

In the following sentences, please assume that E is the Young Modulus (MPa), I the second moment of inertia (mm4), t the thickness in mm and h the distance of the ply from the neutral axis.

To determine the EI value of a laminate, that allows one to improve the stacking sequence, one obvioulsy needs to know the E value( which I am happy to determine) but also the I value.

I know that it can be assumed as the sum of the ((Ei^3/12)+(tihi)2.

Which makes it very easy to find. But I am actually making a spreadsheet, that I will post if some of you need once finished and checked, and I can't find the relative height of a ply from the neutral axis. At least I can't make the process automatic as

Do you see my problem? Basically the NA is at half the laminate thickness but the height depends on the n° of ply and the thickness of the ply.

Is there a mean to find the I from a baseline (say the inner ply) and then convert it as a usual I from a neutral axis?

I hope I have been clear enough for you to help me.

Thanks a lot by advance. Vincent
 

RE: Stacking sequence & moment of inertia

You need to find the position of neutral axis and then using the Huygens theorem you could find the Inertia relative to Neutral axis.
To find the neutral axis of a set of layers:
Assuming a strip of one units width:
Sum(E*thk*1*thk)/Sum(E*thk*1)

In the attached spreadsheet you can find an example.

Onda

RE: Stacking sequence & moment of inertia

(OP)
Thank you so much. My spreasheet for the skins is ready. i will include the cores as soon as possible and post it as I am sure this could serve other persons. I double check it with the Bureau veritas free software and so far so good.

Onda, thanks a lot. Vincent

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