Honeycomb Core Poisson Ratio
Honeycomb Core Poisson Ratio
(OP)
Hi, I would like to ask if I use lamination for calculating sandwich properties, what Poisson ratio should I use for the aluminium core?
I usually assume 10 for nomex... But I'm not sure... Thanks!
I usually assume 10 for nomex... But I'm not sure... Thanks!
RE: Honeycomb Core Poisson Ratio
RE: Honeycomb Core Poisson Ratio
I use my lamination excel tool to calculate the equivalent sandwich E or Bending Stiffness...for Aluminum facesheet and core but it seems not getting same value as the formula below...
For the formula below, is it correct that the E is the facesheet E? Thanks!
RE: Honeycomb Core Poisson Ratio
The bending stiffness formula is wrong. Instead of hc should use (hc + hp). Ie distance between midplanes of facesheets.
RE: Honeycomb Core Poisson Ratio
and, yes, it is the facing properties, not the core, that are relevant to these calcs.
another day in paradise, or is paradise one day closer ?
RE: Honeycomb Core Poisson Ratio
So basically, the properties of honeycomb depends highly on the facesheet for in-plane properties... but bending would depend on the height of the core.
I was trying to see if Al sandwich can replace Al solid in term of light weight and more stiffer... but based on the calculation, although the weight can be saved about 20%, the stiffness is smaller except bending stiffness could be improved... unless otherwise using prepreg facesheet ..
RE: Honeycomb Core Poisson Ratio
yes, a sandwich will have slightly lower bending stiffness than a solid plate, but much lower weight.
To retain the same bending stiffness, the sandwich panel would need to be slightly thicker.
To use "preg" or composite (Carbon, or E-glass) faces in lieu or Al would also restore stiffness, at the expense of material (and handling) costs.
another day in paradise, or is paradise one day closer ?
RE: Honeycomb Core Poisson Ratio
The core is filled partially/discretely, or completely, with thermosetting potting compound. This is typically epoxy resin filled with glass or phenolic microballons or 'other low density/rigid fillers/reinforcement materials'... or are injection-filled with foaming [self expanding] epoxy/etc potting mixtures.
These compounds reinforce the filled honeycomb cell [added crush resistance] and rigidize the foil walls [from buckling/shear loads] and increase adhesion contact area and greatly increase resistance to moisture/fluids intrusion [filling voids and increased cell sealing].
Potting is invariably used at fastener [hole] penetrations with or without an embedded insert... and for areas that are machined 'thin/flimsy'.
Regards, Wil Taylor
o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]
RE: Honeycomb Core Poisson Ratio
RE: Honeycomb Core Poisson Ratio
The only core stiffness properties that typically matter are the thru thickness shear moduli.
RE: Honeycomb Core Poisson Ratio
I notice from some literature directly use foam modulus into FEM...
RE: Honeycomb Core Poisson Ratio
RE: Honeycomb Core Poisson Ratio
When I tried to use orthotropic material model, I could not get a reasonable results as I set all thru thickness properties to 1E-6. I get the result similar to isotropic model when I use same shear modulus in three axes...
RE: Honeycomb Core Poisson Ratio
Aluminum-skin + aluminum HC core + aluminum-skin is generally NOT referred-to as 'composite honeycomb [sandwich Assy]'... it is an aluminum honeycomb sandwich Assy.
To be a composite/hybrid honeycomb sandwich Assembly, at least one layer... one or both face-sheets and/or HC-core... must be non-metallic [fiber + resin].
Regards, Wil Taylor
o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]
RE: Honeycomb Core Poisson Ratio
RE: Honeycomb Core Poisson Ratio
another day in paradise, or is paradise one day closer ?
RE: Honeycomb Core Poisson Ratio
@SWComposites, yes. I am modeling the sandwich with a single shell element as I can quickly update the model for sizing.
But I notice a problem in ANSYS - thru thickness issue.
I make assumption for the core properties (set the modulus, shear modulus and poisson ratio to small value in three directions) and then I model the stack up Al facesheet + Al HC core + Al facesheet in Ansys but I notice that there is buckling mode appear in modal analysis which I do not expect it happens.
Same issue happen if I assume the Alu sandwich as orthotropic material with assuming very small value in thru thickness properties for G13, G23.
Note: I obtain E11, E22, V12 and G12 from lamination calculation and I use it to model sandwich in single shell by assuming it orthotropic.
Appreciate your thoughts!
RE: Honeycomb Core Poisson Ratio
RE: Honeycomb Core Poisson Ratio
RE: Honeycomb Core Poisson Ratio
The plate shear modulus unit was wrong. The result looks reasonable after I fix it. Appreciate everyone for your kindness!
0.5 mm facesheet (Al 2024) + 9 mm HC + 0.5 mm facesheet (Al2024)
Based on the lamination calculation, E11 = 7240 Mpa, G12 = 2758 Mpa and V12 = 0.33
It seems the honeycomb core thru thickness properties might be wrong. I am checking the properties ...
RE: Honeycomb Core Poisson Ratio
I usually see panels/parts designed to withstand ultimate design + a-lot... then typically fail suddenly by localized crushing/crippling/delaminating/core-shearing.
This design practice is simply because of practical material thickness [face-sheets, honeycomb foil/hex-size], cutting/machining, adhesive edging/close-out and a variety of 'penetrations requirements' [thru fasteners, cutouts, etc],etc, etc. The difference between a perfect min-weight design and a practical slightly heavier design is a few percent... while added 'robustness' helps endure 'wild-card' long-term environmental effects [way too many possibilities to discuss here].
Be aware of: (a) damage at/along edges/closeouts, and a other mountings [an amazing variety of reasons]; Or (b) moisture intrusion [or other fluids such as oil, fuel, etc] ... leading to internal corrosion and/or lowered adhesive glass transition temps; or (c) extreme point [puncture] loads or added mass; (d) electrical bonding/grounding requirements; (e) extreme temperature variations/requirements [Example: my jet was designed of -65F to +160F... but has endured actual conditions of -100F to +190F].
Regards, Wil Taylor
o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]
RE: Honeycomb Core Poisson Ratio
another day in paradise, or is paradise one day closer ?