Creating constitutive matrices for honeycomb from manufact. data

[jvh1234]

Hi all,
I am seeking to model an aluminum honeycomb core structure in Comsol as part of a high-frequency (>10kHz) vibrating structure. The honeycomb separates and supports two thin sheets of silica, and the entire structure vibrates in the x-y (1-2) plane.

The honeycomb's material definition in Consol requires that I supply the stiffness (E), poisson's (nu), and shear (G) vectors based on the limited available manufacturer data. What's given in the manufacturer's datasheets are the E33 stiffness (compressive modulus) and the G13 and G23 shear moduli. However, I also need to supply Comsol with the other six independent material properties (E22 E11 G12, and poisson ratios: nu12 nu13 nu23). I have read in places that the in-plane property values of honeycomb (E22 E11 G12)are so small that any trivial, non-zero number can be used as an approximation. I have also read references to a paper that claims both these in-plane properties and the ratios (nu12 nu23 nu13) can be better approximated using percentages of the out-of-plane properties given by the manufacturer. Unfortunately, I cannot find this paper anywhere and do not have the actual percentages.

I would really appreciate it if you, the FE gurus, could confirm/correct the of percentages/approximations in modelling honeycomb, and perhaps guide me with some specific numbers.

Thank you!

 

[ESPcomposites]

Not really a FEM question, but what is the facesheet thickness? You mentioned some papers say the values are trivial and just use a very low value. This is true of typical honeycomb structures. Think about it, you can stretch the honeycomb with your hands. The facesheets will dominate the overall stiffness properties and the honeycomb won't add significant stiffness.

Brian

http://www.espcomposites.com

 

[jvh1234]

Thanks, for the reply, Brian. The facesheets are going to be 1 to 3 mm thick in various configurations. I am hoping to use the honeycomb to support the silica plates and minimize the z-amplitude of surface waves caused by the vibration. in the worst case scenario (resonance), the standing waves on the two plates are antisense in that they've got equal amplitude and opposite sign. By sandwiching the honeycomb between the plates, I'm looking to cancel out the waves through compression and tension in the honeycomb.

John