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# How to generate bending stiffness from equation of a curve?

## How to generate bending stiffness from equation of a curve?

(OP)
Dear friends,

I am modeling a composite beam with layered airfoil like shells wrapped over one another and need to find the cross sectional properties. I know the equations of the airfoil curves but could not implement the theory to calculate the bending stiffness. I studies a lot but did not find how to relate the equations of the airfoil to the curvature equations that is used to generate the Euler-Bernoulli beam theory. Can anybody help me to give an idea how to implement the equation of the airfoil layers to find cross sectional properties?. All the composite books, I have seen only thin plate like structures.

Thanks
Pratik

### RE: How to generate bending stiffness from equation of a curve?

You need to sum the effective E * I for each of the shells. E is going to be a bit tricky, it is the modulus in bending, which may require a bit of work to establish for a composite.

If the airfoils are non symmetric then you'll also need to find the neutral axis, and modify I by using the parallel axis theorem. This is something you should have covered in the first two years of your engineering degree, check your lecture notes.

Cheers

Greg Locock

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### RE: How to generate bending stiffness from equation of a curve?

I assume you're making a laminate shell for a wing. The best way is to use a laminate property card in your favourite FEA. Alternatively, research "laminate material properties" and you should get something to build the local property. Failing that, build your wing and test it with simple loads.

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