Analysis of Sandwich Panels

[TDI]

I'm looking for an analysis method for a sandwich panel subjected to out of plane shear loads which takes into account the shear capacity of the face sheets.
Facings are carbon fibre with nomex core approx 50mm deep. Currently I'm assuming the shear is carried on the core only but this is giving a low margin. If I could include the face sheet I may be able to show the design as being OK.

 

[GBor]

Low margin, but not negative? Sounds like the design is OK, but how thick are the facesheets?

 

[rb1957]

out-of-plane shear of the faces <<< out-of-plane shear of core ...
like GBor above ... +ve margin is all you need, why chase another % or two ?

 

[JJ22mW]

The best way to get transverse load capability of a panel is by obtaining test data. Manufacturers like Gillfab post their panel strength data on their website.

 

[40818]

I think that the reference to it being a low margin is to be taken as being a negative M.S or less than 1.0 R.F

50mm thick nomex core, sounds like A350?

You state that you think you could show it good if you include the face sheets, but are looking for a method to do so. How do you think the separate inclusion of the skins will ai the core shear? How are you calculating the core shear, and if by FE how have you modelled it?

 

[RPstress]

If you're using the distance between facesheet centerlines for the shear thickness (as is usually recommended) then the facings are already included.

You might get a little bit more by by doing a hand analysis including shear stiffness, but this would be fairly non-standard analysis. A detailed FE analysis would account for everything in theory, but might well give higher peaks than by hand.

If you're not using distance between facing centelines then you probably should be. This assumes the shear builds up linearly through the facing to a constant value across the core. See the usual sandwich analysis suspects.

 

[rb1957]

we're all thinking in terms of transverse shear ... what'd you think you be gained with large displacements instead ?

 

[Allanon81]

You may have another issue to consider... if the out-of-plane shear is due to bending, then the shear flow around the panel will cause an in-plane shear stress. Thus, you can't go over the in-plane allowable given by the core anyway.