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# Classical Laminate Theory (CLT) Composites Question

## Classical Laminate Theory (CLT) Composites Question

(OP)
Hey guys,

can anyone shed some light on classical laminate theory (CLT)? Let's say I have a laminate made from 3 plies: 2 outter carbon fiber plies and 1 inner fiber glass ply...

I go through the Q, Q bar, and ABD matrices steps... Now, lets say i have my inverse ABD matrices. this can be multiplied by the force and moments (N & M) vector to get me the strain and curvature (epsilon & k) vector... Ok, so I calculate it out and now I have my strain... I can find stress too (only per ply)...

Can any of this data get me the displacement or the young's modulus of the entire laminate?! It seems like CLT is solely for stress and strain and doesn't take into account any other important factors... Just not sure how useful it really is other than stress or strain. One might argue that you can use Hooke's law after (sigma = E*epsilon), but this is only for isotropic materials. Not orthotropic.

Let me know.
Thanks

### RE: Classical Laminate Theory (CLT) Composites Question

Modulus of the entire laminate is calculated from the inverseA matrix. See any CLT text.

Displacement is a structural response. The CLT stiffness or compliance matrices are plugged into beam or plate theory equations, or a FEM, or such and displacements can be determined.

### RE: Classical Laminate Theory (CLT) Composites Question

(OP)
Hey @SWcomposites,

Thank you so much! That actually helps a lot. I have done a lot of reading on CLT but haven't seen anything about how the modulus is calculated from the inverse A... Just curious if you could point me to a book or a formula?

and that makes sense about the displacement. Thank you.

### RE: Classical Laminate Theory (CLT) Composites Question

This is for a symmetric laminate. For an unsymmetric laminate, it is not as straightforward (and not shown).

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