Shear Stress on Composite Beam (Divinycell + CFRP) 1

[gui1993ac]

Hello to all!

This is my first post here.
Im designing a main wing spar where a Divinycell rectangular core will be laminated with 90 degrees carbon fiber on the four sides, to make a home building easier and possible.
In order to do so, I started with a analytical beam model that supports the aerodynamic diatribution. Im facing problems on the calculation of the shear stress, since the max shear stress (on the neutral beam axis) happens on a section that has 3mm carbon fiber on the sides and a 150mm width Divinycell core. I suppose the core will resist most of shear stress, but im not sure on how to calculate the shear stress on this composite section. My first assumption was that the core should resist alone to all of the shear stress, since in the carbon fiber on this orientation, will have very poor shear properties. But im not quite sure if this is a good assumption, or if thr carbon fiber will be sure to resist the stresses if i consider only the core. Since this is a preliminary model that will be later calculated in CAE software, any good enough aproximations for a simple design can be used by now.

Any insights on that would be greatly appreciatted!

Best Regards,

Guilherme

 

[tbuelna]

I did not see any mention of whether the spar fabric is pre-preg, laid up dry and infused, or laid up wet. It is much easier to achieve precise fiber alignment with pre-preg materials than with wet lay up. Precise fiber alignment is important for buckling performance of the UD plies in the spar cap.

Would there be any benefit to interweaving the web bias plies between the UD spar cap plies, rather than simply stacking the UD plies on top of the bias plies?