JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - 31

Development of a carbon-thermoplastic hub for the H160 helicopter

plies sliding in this area, some porosities and
waviness were created. The final optimization was only reached during Step 3.
Step 3 "2/5"(Figure 16): Validating the
feasibility of a part with a variable thickness
and centering pieces that are part of the
mould.

- Main rotor torque;
- Lift load;
- Rotating bending moment;
- Rotating shear load.
These loads generate various stresses in the
hub's carbon fabrics:
- Tensile (warp/weft);
- Compressive (warp/weft);
- Bending (warp/weft);
- In-plane shear stress;
- Interlaminar shear stress (ILSS).

Fig. 16: Variable-thickness part and centering pieces

In a first step, static and fatigue tests were
conducted on standard coupons under tension, compression, bending, in-plane shear,
ILSS, impact, etc. Different environmental
conditions were studied. The goal was to
have a complete material database (n plies
of 0°/90° fabrics).

The third step froze major process parameters such as:
- Positioning of the centering pieces;
- Tolerances/gaps required by the centering
piece;
- Stacking sequence, particularly in the
variable-thickness area.
The process reproducibility was also established through these "2/5" manufactured
parts. The downstream industrial phases
including machining, drilling and finishing
operations were developed during that
step. Finally, the manufacturing process was
validated for thick parts under compression
using a complex metal mould.

Fig. 17: Stacking sequence

Step 4: Manufacturing the complete hub
(Figure 18). Only a few adjustments were
necessary thanks to the previous steps, and
this was achieved in a short time.

Fig. 18: The H160 main rotor hub

Sizing phase
The hub's in-flight loads are the following:
- Centrifugal load;

In a second step, complementary tests were
performed on thick technological specimens (about 20 mm) with the same stacking sequence as standard specimens and
a quasi-isotropic lay-up. These specimens
were taken from parts with a geometry close
to the hub or cut out from the hub during
the development phase. The design values
for the hub were derived from these studies.
The compression mode is not critical for
such a thick part and two main failure
modes were investigated:
- Static mode: two types of failure can
occur: resin and fibre failure, respectively.
The fibre accounts for the critical failure
mode, and the bending coupon is the
most representative one (long bending
tests, see Figure 21). The resin behaviour
was established through a short bending
test (Figure 20);
- Fatigue mode: the resin was studied as the
fibre is not significantly sensitive to fatigue
(in tensile mode). The bending coupon
was the most representative one (short
bending tests, see Figure 20).
- In the case of the hub, the resin failure did
not result in complete failure but in local
damage.
After optimizing the manufacturing process,
the static failure values from standard
coupons (0°/90°) were quite in accordance

Fig. 19: Main rotor hub loads

Fig. 20: Technological specimens, "3 short bending
points" test

Fig. 21: Technological specimens, "3 long bending
points" test

with the technological ones (thicker and
quasi-isotropic lay-up). Standard computation tools were used for this comparison.
The ILSS values in static and fatigue mode
were quite close for the standard and technological coupons.
Regarding the ILSS fatigue behaviour, two
different areas were underlined (Figure 22):

N°116 October 2017

/ jec composites magazine

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #116 - October 2017