Notes on Core Materials (Handbook Vol 6)
The purpose of core
The main purpose of core is to separate, support and stabilize face sheets, mainly by increasing thickness and increasing bending rigidity.
Can also provide thermal and or acoustic insulation
Aramid and foam based cores (such as Gurit, the foam used in Daybreak’s topshell, or Nomex, the honeycomb planned to be used in 24/26 cycle topshell) are very good insulators, and that is something that should be taken into consideration since as of now, our array cells can only operate at a max temp of between 70-75 F.
Metal based cores are better when it comes to heat since even though they are conductive, they also lead to fast heat dissipation.
If you want more info on core and info on array cooling, look at Array Cooling Testing
Core is usually relatively low density when compared to face sheets and adhesives
There are many different types of core, some of which we have used and others which we haven't, however for the scope of these notes I am going to stick to just honeycomb as this is the only core material we plan of using for next gen as of now.
Honeycomb cores can be densified in local area by under-expanding or crushing cells together
Densified core has properties increased approx. in proportion to density increase
Thermal conductivity of core depends on conductivity of core material, radiation between face sheets and convection between core cells
There is a formula at the bottom of page 3-4 of the handbook which allows for calculation of effective conductivity of core sheet
Again, as stated earlier, nonmetallic cores are better thermal insulators.
*Note, info on Kevlar Honeycomb is also given however I haven’t included it as to keep this doc relevant to what we will be using
*Note: For testing aluminum honeycomb panels we are using McMaster’s 3000 series aluminum which just seems to be 3003 aluminum, but given how testing goes, we may look to get a stronger type of aluminum if we think it is necessary.
Estimation of core properties
If core properties haven’t been established yet, it is possible to get a reasonable estimation by considering material, density, and configuration
Conversely, if certain core properties are required then they can be reasonable determined
We need to try this instead of estimating the density of our core loll
For cellular (honeycomb) metallic cores, density and elastic moduli can be estimated from foil or ribbon material, thickness of ribbons, and core cell size and shape
For hexagonal cores (which is what we generally use) core density can be calculated using the formula
Where
Wc = Core density
Wo = density of foil or ribbon materials
t = thickness of ribbon or foil
s = cell size (diameter of an inscribed circle)
Core modulus of elasticity in through-thickness direction (z axis i think so height of panel pretty much?) can be estimated using the formula
Where
Ec = modulus of elasticity for core
Eo = modulus of elasticity of foil or ribbon material