Honeycomb Core Properties, Sandwich Composite

[Senophoe]

Hi everyone,

Most guidelines I read mention it's possible to model aluminum honeycombs as 2D Orthotropic. Taking a look at manufacturers datasheets, I feel the properties force us to use 3D Orthotropic. But I'm not sure and I'd like your opinion. For example, the properties below are from Hexcel HexWeb. Look how I put those properties in the Femap 3D Orthotropic Material card. Is it correct? Is it a problem to have E1 = E2 = G12 = v23 = v13 = 0?



And also, if I were to model this honeycomb as a 2D Orthotropic material, would it be ok to use the properties like below? Notice I use E1 = E2 = very low value, because the in-plane stiffness of sandwich comes from the facesheets. Doesn't it result in wrong values not having the compressive modulus value of 75 ksi in the material card properties? Also, is it ok to leave G12 = 0?

 

[SWComposites]

Is it a problem to have E1 = E2 = G12 = v23 = v13 = 0?

Yes, as it can cause numerical issues.
I have successfully used E1 = E2 = 100 psi, G12 = 50 psi, v12 = v13 = v23 = 0

And for 2D modelling, the elements do not need or use E33 properties.

 

[Senophoe]

Yes, as it can cause numerical issues.
I have successfully used E1 = E2 = 100 psi, G12 = 50 psi, v12 = v13 = v23 = 0

And for 2D modelling, the elements do not need or use E33 properties.

But take a look at the datasheet properties in my first post. Notice from the datasheet the only properties (I circulated them in orange) for honeycomb are:

E3 = 75 ksi
G12 = 22 ksi
G23 = 45 ksi
And the compressive strength, and shear strength in the out-of-plane direction.

Every manufacturer give only those properties in their datasheet, no exception.

For this honeycomb, would it be reasonable to use like below?

E1 = E2 = G12 = 1E-6, which is virtually zero, since the honeycomb shouldn't carry the in-plane loads.

Would these be the correct properties to use for both 2D and 3D honeycomb?

 

[dcascap]

Yes, for 2D and 3D honeycomb it would be a good. E3 does not have a meaning in 2D shell elements. And yes, you don't put 0, just a very small value compared to the other values. If you're running a linear analysis it will be fine. For non linear you could start getting convergence issues depending of the solution used.

 

[SWComposites]

Sigh, I know exactly what is on the datasheets.

E3 = 75 ksi
G12 = 22 ksi
G23 = 45 ksi

you meant G13 not G12.

E1 = E2 = G12 = 1E-6, which is virtually zero, since the honeycomb shouldn't carry the in-plane loads.

Would these be the correct properties to use for both 2D and 3D honeycomb?

there is no "correct" value for those properties; you need to enter something that does not cause numerical problems with the FE solution. I gave you values that have worked successfully. If you want to use something else then figure it our for yourself.

 

[rb1957]

1E-6 is too small ... you have nearly 12 orders of magnitude between real values and "zero" ... this is not good.

100 is near enough to "zero" as the real values are many thousands. try 100, 10, 1000 see what the difference is ... not much.
And don't forget the real world ... just because those values are not listed on the spec sheet doesn't mean that they are "zero". It means that the properties are hard to measure and have little impact on the results.

is a poission's ratio of 0.3 correct ? (maybe you can use "0" and the program understands to calculate from E and G