Honeycomb Core Shear Stress Hand Calculation

[stressoblivion]

Hello experts, can you shed some light on going about calculating the transverse shear stress in the honeycomb core of a sandwich panel using hand calcs?

Scenario: An attachment fitting on top of it fastened with 8 screws and potted inserts, about 5.0" tall moment arm due to an axial (parallel to the panel) load of about 7000lb. The fitting base is 8.0"x2.0"x0.25".
The panel has 2 plies of phenolic fiberglass skins on both sides (each side 0.02" thick) and it is about 1.0" thick total with a 1/8"-3.0# phenolic aramid core. It has bonded 0.063" Al 6061 doublers on both sides. I am trying to determine if I really need to use a solid foam core in the area, or use potting compound just under the crushing edges of the fitting, or simply use a higher density core... to deal with the core crush due to the heavy load.

Thank you....

 

[SWComposites]

do you have a specific question about the analysis? can you post a detailed figure, your free-body-diagram with all loads, dimensions, etc and your stress analysis? do you have the material properties for all of the core options?

 

[stressoblivion]

Hi SWComposites, thanks for the reply..

The core has a typical short beam allowable of about 80psi for a 3# density.

Using simple statics, force and moment balance, and using end supports at an 8" span, for the 5" overturning moment arm at the top and taking moments about the side that reacts the compressive load, we have 7000*5 - R*8 = 0 => R = 4375lb, a force couple at both ends balancing the overturning moment.

Assuming a 4x2x4 perimeter piece of active core taking this compressive load on one end, we have a running load of 4375/10 = 437.5lb/in. Since the core is about 0.96" thick, we have a transverse shear stress of about 456psi, well over my allowable of 80psi.... so therein lies the problem, assuming I got the hand calc right... any feedback on the hand clac? I have tried to attach a word file, hope you can open it....

Thanks a lot...