JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - 33

Development of a carbon-thermoplastic hub for the H160 helicopter

(Figure 10). The interest of thermoplastic
resins in dynamic system components is
thus confirmed.

different technological parts. These factors
are quite low regarding the porosity level
(Figure 27).

Concerning the effect of impacts up to 30
joules on the real hub, there is no significant
damage, as observed on the Starflex® hub [1].
Loading frequency:
effect on material strength
Some authors noticed that loading frequency has an effect on strength by generating
internal heating [3]. This effect could be
simulated and checked, particularly with
ILSS specimens. This effect was studied
on technological specimens equipped with
thermal sensors, under dynamic interlaminar shear stress. The applied dynamic
load corresponds to the fatigue limit at 106
cycles. Two frequencies were tested: 5.7
Hz (1 per rev. of the H160 rotor) and 11.4
Hz. Thermal stabilization occurred after
around 10 minutes. The temperature was
extrapolated at the centre of the specimen
and an increase of a few degrees Celsius
was estimated, with no consequence on the
component strength.

Delamination propagation
To tackle any possible delamination in such
thick parts, dedicated studies were conducted on coupons and full-scale components. A
propagation curve (Figure 28) was derived
from a "four bending points" test [4]. The
energy release rate (G) obtained was a combination of mode I and mode II propagation
(GI and GII).
The delamination propagation rate was
evaluated on a full-scale component. The
propagation rate observed was quite low and
there was no propagation under a certain
threshold. These tests demonstrated a "failsafe behaviour".

Effect of porosity
Knock-down factors were established by
fatigue and static tests on coupons from

Creeping effect
This phenomenon was assessed for the bolted connection between the composite hub
and the metal main rotor shaft. Dedicated
studies on coupons exposed to accelerated
ageing and extreme conditions are still running. The first results show that this effect
is not significant. In addition, tightening
torque measurements are going on and will
continue for 2 years on a full-scale component exposed to natural environment effects.
Conclusion
The development of such a part involves
huge efforts in different areas. In particular,
some key issues are now under control
such as sizing in terms of interlaminar shear
stress, fatigue behaviour and the production
process.

Fig. 27: Effect of porosity

Fig. 28: Carbon-PEEK
delamination propagation curve

Fig. 29: The H160 prototype in flight

This type of modelling is now more accessible to a much wider range of markets and
industries and engineers. It is no longer necessary to be a professional in composites or
optimization to be able to advance a design
software as Express.
This technology will bring several benefits to
the H160 helicopter:
- Weight saving contributing to improved
performance;
- Good fatigue and damage tolerance
behaviour, resulting in higher customer
satisfaction and safety;
- "Green" aspect as the material is REACh
compliant, with less stringent storage conditions than thermoset materials, inducing
less environmental effects;
- Lower manufacturing cost compared with
a metal hub.
More information:
www.airbus.com
References
[1] J.M. Besson, Y. Marino, "The Starflex® flying
all over the world and always in evolution", 37th
European Rotorcraft Forum, 2011
[2] H. Bansemir, J.M. Besson, K. Pfeifer,
"Eurocopter development and substantiation
of composite structures with regard to damage
tolerance", 27th European Rotorcraft Forum, Sept.
11-14, 2000, Moscow
[3] Fatigue in composites - Harrish - Chapt.
11, Fatigue of thermoplastic composites, E. K.
Gamstedt, A. Berglund, KTH, Sweden
[4] H. Bansemir, S. Burghagen, M. Gädke "Das
Delaminationsverhalten von unidirektionalverbunden als grundlage fur die charakterisierung
und dimensionierung von FVW Strukturen".
Deutscher Luft -und Raumfahrtkongress, 2005,
Friedrichshafen, 25-29 September
[5] W.I. Lee, M.F. Talbott, G.S. Springer and
L.A. Berglund, "Effects of cooling rate on the
crystallinity and mechanical properties of
thermoplastic composites", Journal of Reinforced
Plastics and Composites, Vol. 6, No. 1 (January
1987), pp. 2-12,
Composites, Volume 18, Issue 5,
November 1987, page 416

N°116 October 2017

/ jec composites magazine

http://www.airbus.com

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