homogenized parameters

[moliPHD]

Hi friends,
I am looking for homogenized parameters (E11, E22, E33, G12, G13, G23, PR12, PR13, PR23) of a sandwich material orthotropic,
can someone help me.
best regards.

 

[RPstress]

Is your sandwich core foam or honeycomb? And if honeycomb what sort? Metallic or what? (If foam then it will contribute a little bit to the E11, E22 and G12.)

Also, I'm unfamiliar with 'PR' as a property notation. What is that?

 

[moliPHD]

The core of the sandwich is a Metallic honeycomb (Aluminium), I mean by "PR":"The Poisson's Ratio".
Best Regards.

 

[RPstress]

E11, E22 and G12 for the whole honeycomb sandwich are usually taken to be the Es and G of the facings in the 1-, 2- and 12-directions. Do the facings have different moduli from each other?

To a large extent the G13 and G23 are the core shear moduli (G13 is usually the G for the L direction, i.e. shearing in the ribbon direction which means the in the plane of the L-direction walls). Do the L and T directions for the core line up with the 1- and 2-directions?

G13 and G23 are 'to a large extent' because you can attempt to allow for the contribution of the skins to the shear stiffness, but this is not usual. Finding a through-thickness shear stiffness for the skins may not be easy and depends on what the skins are made of.

E33 is the core through-thickness compression and tension modulus. The compression modulus may be the only one available. It may pay to work out an approximation for what the core modulus is from the area of core walls times the modulus of the metal (10.2 Msi compression or 10.1 Msi tension if it's 5052 or 5056 (usually the extra-hard condition for foil (usually something like T39, one grade up on Tx8 full-hard), though the condition nominally doesn't affect modulus). Choosing the reference area sensibly is quite important and this depends on what the form of the core is. If it's a hexagonal core, either choose a basic hexagon plus half the length of the six walls sticking off it, or use an isosceles triangle of three half-length walls (one of which has to be in the L direction). Remember to use double the thickness for L-direction walls which are actually two walls bonded together in every hex core I've come across. You can ignore the presence of any adhesive used for the node bonds (bonding the L-direction walls together).

For thick skins you may wish to allow for the through-thickness stiffness of the skins. Finding what their through-thickness stiffness is may be a problem as well.

PR12 and PR21 are the PRs for the skins (d'oh! clouts self on forehead for not seeing what PR was for). PR13 and PR23 are usually taken as 0. Usually the G12 for the core is approximated as 0, which renders the PRs irrelevant. (Hexagonal core is basically a mechanism rather than a material, with a PR12 of 1.0 if it has exactly hexagonal cells, but E11, E22 and G12 are all zero if the walls are taken to be hinged at their corners. You may find finite experimental values for in-plane moduli but usually they're very small and are usually ignored.)

Note that the shear moduli and the 3-direction compression modulus go severely non-linear as the walls begin to buckle. There is very little data for curves to failure of honeycomb cores—or of foams come to that. If you need such information a good relationship with a supplier and contacting their tech support helpline may be your only option.

 

[moliPHD]

First, I would like to thank you Sir for the importance that you give to my question. really your answer helped me.

The sandwich faces have the same properties (E, G, and PR).

If you can give me some references on which you based your answer. So give me some guidance on the helpline that I can contact them.

Best Regards.

 

[RPstress]

Since your facings are identical it makes your life a bit easier (if they have the same thickness as well as the same E, G and nu there's no extension-bending coupling to worry about).

Not sure of references to back up what I wrote. Try Hexcel's website (look for "HexWeb Honeycomb Attributes and Properties" and "HexWeb Honeycomb Sandwich Design Technology"; these two largely replace the older TSB 120 and TSB 124 references and have a lot of basic honeycomb and honeycomb panel information). One of them is at

http://www.hexcel.com/Resources/Dat...eets/Honeycomb_Sandwich_Design_Technology.pdf

; there is also another useful ref at

http://www.hexcel.com/Resources/Dat...ets/Sandwich_Panel_Fabrication_Technology.pdf

.

Diab should also get a mention (mainly foam rather than honeycomb):

http://www.diabgroup.com/en-GB/Sandwich-technology/Manual

.

A thesis by Stromsoe is also quite informative: "Modeling of in-plane crushed honeycomb cores with applications to rampdown sandwich structure closures",

http://sdsu-dspace.calstate.edu/bitstream/handle/10211.10/1193/Stromsoe_Jeremy.pdf?sequence=1

.

The classic sandwich references are "An Introduction to Sandwich Construction" by Zenkert, "Analysis and Design of Structural Sandwich Panels" by Allen and "Honeycomb Technology" by Tom Bitzer. These are well worth buying though Bitzer's is not cheap if bought new and Allen's is out of print. MIL-HDBK-23 is another (canceled like all mil handbooks these days) freebie worth downloading (I can't find where I found it (I found it back in Sep-2006), so I'm uploading it to Engineering.com).

Most of what I wrote rests on the assumption that the honeycomb has in-plane stiffness and strength approaching zero. This is demonstrably true if you have any lying around. If you need to make an FE model with core modeled explicitly then it is conventional to put in about 1 to 10 psi for the honeycomb Es and G (an E of zero often upsets FE systems). If the core contributes nothing to in-plane stiffness than in-plane stiffness is all down to the skins.

 

[moliPHD]

Thank you so much Sir
Best regards.