8
2 State of the art
[DuP03]. This leads to orthotropic mechanical properties of the paper, with the machine
direction (MD) being superior in terms of modulus and strength if compared to the cross
direction (XD) (E1 > E2 in Figure 4). Nomex is generally fabricated into honeycomb using
the adhesive bonding method and the expansion process [Bit97]. Here, adhesive lines
are placed on the paper material, before it is cut into sheets and stacked to form a solid
block. Expanding this block leads to the desired honeycomb lattice, which is subsequently dipped in phenolic resin and oven cured so that it retains its shape. This process
leads to uneven cell wall thicknesses with the bonded cell walls being twice as thick as
the free single walls. Due to the orthotropic nature of the Nomex paper, the orientation
of the material in the final honeycomb core is of interest. This depends on the orientation
of the adhesive lines before stacking the paper sheets. In applications where honeycomb
cores with large extend in L-direction are required, the adhesive is applied in cross line
[Bit97]. This way the L-direction length of the honeycomb is not restricted by the width
of the Nomex paper roll. It is assumed that this is the standard case for cabin interior
applications, which require large planar segments. The manufacturing process along
with the assumed material orientations is illustrated in Figure 4.
Figure 4 Manufacturing of Nomex honeycomb and material orientations [See17]
2.1.3 Bonded sandwich panel
There are two main methods of bonding sandwich panels, vacuum bag processing and
press moulding. In the vacuum bag process panels can be cured in an oven or in an autoclave for increased pressure (Figure 5). The vacuum bag is commonly used for curved
shapes and press moulding for flat panels [Bit97], [Hex00]. In cabin interior applications
both processes are common due the fact that both, curved and flat panels, can be found
in cabin interior monuments. However, the load carrying sandwich components in partitions, galleys and hatracks are typically manufactured from flat panels. Regardless the
Calendered
paper roll
mac hine direc tion
(roll direc tion )
E 2
E 1
Cell wall
material sheets
cross direction
(web direction)
E 2
E 1
L
W
T
t
2 t
Cured
honeycomb
core
Adhesive lines in crossline (web direciton)
2 State of the art
[DuP03]. This leads to orthotropic mechanical properties of the paper, with the machine
direction (MD) being superior in terms of modulus and strength if compared to the cross
direction (XD) (E1 > E2 in Figure 4). Nomex is generally fabricated into honeycomb using
the adhesive bonding method and the expansion process [Bit97]. Here, adhesive lines
are placed on the paper material, before it is cut into sheets and stacked to form a solid
block. Expanding this block leads to the desired honeycomb lattice, which is subsequently dipped in phenolic resin and oven cured so that it retains its shape. This process
leads to uneven cell wall thicknesses with the bonded cell walls being twice as thick as
the free single walls. Due to the orthotropic nature of the Nomex paper, the orientation
of the material in the final honeycomb core is of interest. This depends on the orientation
of the adhesive lines before stacking the paper sheets. In applications where honeycomb
cores with large extend in L-direction are required, the adhesive is applied in cross line
[Bit97]. This way the L-direction length of the honeycomb is not restricted by the width
of the Nomex paper roll. It is assumed that this is the standard case for cabin interior
applications, which require large planar segments. The manufacturing process along
with the assumed material orientations is illustrated in Figure 4.
Figure 4 Manufacturing of Nomex honeycomb and material orientations [See17]
2.1.3 Bonded sandwich panel
There are two main methods of bonding sandwich panels, vacuum bag processing and
press moulding. In the vacuum bag process panels can be cured in an oven or in an autoclave for increased pressure (Figure 5). The vacuum bag is commonly used for curved
shapes and press moulding for flat panels [Bit97], [Hex00]. In cabin interior applications
both processes are common due the fact that both, curved and flat panels, can be found
in cabin interior monuments. However, the load carrying sandwich components in partitions, galleys and hatracks are typically manufactured from flat panels. Regardless the
Calendered
paper roll
mac hine direc tion
(roll direc tion )
E 2
E 1
Cell wall
material sheets
cross direction
(web direction)
E 2
E 1
L
W
T
t
2 t
Cured
honeycomb
core
Adhesive lines in crossline (web direciton)