2.1 Sandwich structures
9
applied bonding method, cabin interior honeycomb sandwich panels are generally fabricated by co-curing the prepregs onto the honeycomb core in a single shot process
[Bit97], [Hex00], [Bla06]. This method not only simplifies the lay-up but also reduces the
weight of the bonded panel, since there is no adhesive added. The bond between face
and core is achieved by adhesive fillets that form at the core-skin bond lines during the
co-curing process. Therefore, the adhesive fillets consist of the thermoset used in the
face sheet prepregs. The fillet condition defines the bond strength and depends on the
used prepreg thermoset, the honeycomb quality as well as process parameters such as
pressure and curing cycle [Yua08]. Therefore, the process parameters have to be tuned
for application in sandwich components. Figure 6 illustrates desirable and undesirable
fillet conditions for honeycomb sandwich panels.
Figure 5 Main honeycomb sandwich panel fabrication methods a) vacuum bag processing; b) flat
press moulding according to Hexcel [Hex01]
Uneven
filleting
Lack of
adhesive
flow
Excessive
adhesive
flow
Short core
no fillet
High core
uplift of skin
One-sided
Equally large fillets that thoroughly wet cell walls
Well formed and desired adhesive fillets