JEC COMPOSITES MAGAZINE - Issue #129 - July/August 2019 - 25

Spotlights from the world of lightweighting

Concept for an aircraft wheel
During take-off, landing and taxiing, high
static, dynamic and thermal loads are generated
that aircraft wheels must withstand reliably.
Conventional aircraft wheels are usually forged
aluminium components that can weigh up to
100 kg. With the development of an aircraft
nose wheel made of carbon fibre-reinforced
plastic (CFRP), Fraunhofer LBF wants to
demonstrate a lightweight potential of up to
40%.
Composite materials make up 22% of the large
Airbus A380. This figure rises to more than
50% in the cutting-edge A350 XWB. Here,
large parts of the fuselage and the wing units are
made of ultra-light CFRP. But there have been
no significant lightweight advancements in aircraft wheels since the 1980s. Fraunhofer LBF
already demonstrated promising lightweight
design potential by substituting CFRP wheels
for metal in the automotive sector. Now, the
institute intends to open this field of innovation
by developing the first CFRP nose wheel for an
A320.
To identify an optimum lightweight structure,
basic geometric concepts were developed in
the concept phase and evaluated with regard
to their stiffness in relation to various load
cases. The identified lightweight structure was
confirmed by topology optimization. The aim
of the project is to produce 10 wheel prototypes
using an RTM process and to test them under
the certification tests provided. The project
is funded by the EU under the Clean Sky II
Framework Programme.
Thermoformable thermoplastic
sandwich structures
Organosandwich panels consisting of a folded
thermoplastic honeycomb core and face sheets
made of thermoplastic laminates (e.g. laminated glass fibre-reinforced UD tape layers)
can be manufactured in a very cost-efficient
continuous production process. For large-area
structures mainly subject to bending loads,
sandwich construction offers an enormous
lightweight potential. By using a core material
that keeps the two thin face layers apart, weight
savings of more than 80% are possible compared to a monolithic construction.
As part of an R&D project, the Fraunhofer
Institute for Microstructure of Materials and
Systems IMWS, together with its Pilot Plant
Centre for Polymer Synthesis and Polymer

specializes in resource-efficient technologies
and the development of, among others, fibre
composites based on polyurethane using the
HP-RTM (High-Pressure Resin Transfer
Moulding) process. The components in sandwich construction are based on a polyurethane
foam core and fibre cover layers drenched
with cured polyurethane. The RTM facility
allows the manufacture of three-dimensional
components with a multilayer structure up to 2
m × 1.8 m × 1 m. The component surface can
be functionalised using special forming tools,
e.g. with bionic structures.
The recently expanded RTM plant can accelerate the preparation of large structural elements
and leads to improved, uniform properties. The
flexible dosage enables varying the ratios of
two polyol components with different curing
Fig. 1: Lightweight materials are expanding to aircraft wheels (C) Fraunhofer LBF

Processing and ThermHex Waben GmbH, are
developing a new technology for processing
organosandwich structures in short cycle times
to manufacture high-volume parts, as required
e.g. by the automotive industry. Within
this hybrid one-shot process, semi-finished
organosandwich panels are thermoformed
and functionalized via an injection moulding
process.
Next-generation composites
The Fraunhofer Project Group Materials
Recycling and Resource Strategies IWKS

speeds during a single injection while the isocyanate share remains constant. Therefore, the
ratio of a polyol with a low curing speed is much
higher at the beginning of the injection than the
ratio of the second polyol with a higher curing
speed. During the three-component injection
process, the ratio of the slowly hardening
polyol steadily decreases while the ratio of the
faster hardening one simultaneously increases.
The resin mixture thus offers the advantage of
curing uniformly within the whole component
body.
More information: www.initiativeleichtbau.de

Fig. 2: Thermoformed organosandwich structure with folded ThermHex honeycomb core ©Fraunhofer IMWS/
Sven Döring

N°129 July - August 2019

/ jec composites magazine

http://www.initiativeleichtbau.de

JEC COMPOSITES MAGAZINE - Issue #129 - July/August 2019

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #129 - July/August 2019