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# Composite Structure Optimisation Methedology

## Composite Structure Optimisation Methedology

(OP)
Hi All

I am new to composite FEA and currently trying to build a full composite fuselage.
I need to optimize if force weight and am currently struggling with finding any type of methodology to do so.

Do you guys have anything that works wells for you?

I try for example to create a laminate with -90 -60 -45 -30 0 0 30 45 60 90 equal thickness plies and apply it on my whole model. I can then see which plies are failing first and remove them and reinforce the ply that has fibers perpendicular to the one that is failing.

All i can find in literature are papers on code developed to auto generate this optimization but i cant find the logic behind it and really understand how i should be approaching the material optimisation of this fuselage.

Thanks for the help

### RE: Composite Structure Optimisation Methedology

Hello.
I don't have a lot of experience working with numerical optimization point of view. But, I have participated in establishing many other lay-ups using a more basic approach. And based on that, I would say that the optimum lay-up would probably require fewer different fiber directions than what you are considering. Usually one strives to keep a quasi-istropic lay-up (i.e. 0,+/-45,90 or 0, +/-30, +/-60,90) with the 0 aligned in the main load direction. For an airplane fuselage I would imagine the main load to be hoop stresses, but I'm not 100% sure on this.
Also regarding your optimization logic, I would say that it depends on what type of failure you have, if you have transverse failure, your approach makes sense, however if it is fiber failure I would reinforce parallel to the fiber direction of the failed ply.

### RE: Composite Structure Optimisation Methedology

a) dump the FEA for now
b) figure out the basic load cases
c) make free body diagram of each load case; calculate by hand the axial, hoop and shear load/widths in various locations
d) if you are planning stiffeners and frames, you will need to optimize/select the spacing, section properties
e) using simple laminate analysis code, determine appropriate layups for each location
f) check skin bay buckling using classical methods
g) only once you have rough size the acreage areas should you even start to think about building an FEM

### RE: Composite Structure Optimisation Methedology

(OP)
Hi SWComposites

I am not sure tha'ts the correct approach in my current situation.
I have calculated the ultimate load cases of the fuselage and have frozen baseline for it that i just need to be just need to be below failure.
The fuselage has a complicated aerodynamic shape with several frames, floors, wing connectors and wing connectors. It is past the point of analytical methods and in the real of FEM now.
The frame positioning and sizing has also been frozen and is based on previous simulations, expert observations, state of the art airplanes etc...
There are certain areas now that just need reinforcement. I am just wondering what methodology works best to optimize ply location and direction.

Also this fuselage is for a low flying airplane so hoop stresses aren't a major issue. More focused on high empennage loads from pull up maneuvers and load coming from a pinned high wing/strut configuration.

Thanks for the help!

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