JEC COMPOSITES MAGAZINE - Issue #112 - April/May 2017 - 51

AERONAUTICS
structures

Optimisation of sandwich composite
structures for space applications
CédriC julien, Ph.D., Research Scientist,
FrançoiS-Xavier iriSarri, Ph.D.,
Research Scientist, dimitri bettebghor,
Ph.D., Research Scientist,
Onera
Florian lavelle, Materials and
Structures Engineer, kevin mathiS,
Materials and Structures Engineer,
CNES

With the increasing use of advanced composite materials in launcher structures comes the issue of the optimum design of composite structures. Over
the past years, the space industry has been experiencing an important change.
What was a steady-state dominated by a handful of major companies and
institutions now has to face a new impulsion coming from disruptive companies
all over the world. The space economy is growing; private players, applications
and projects are multiplying.

T

Still looking for
the best design practice
However, this replacement dynamics
slowed down in the past decades as composite solutions were not always competitive in terms of costs or even performance
compared to metallic ones. Many reasons
can explain this: higher performance of
aluminium alloy technology (material
characteristics and effective assembly
processes); high experimental support for

A novel tool covering
the whole design process
The past decades have seen the development
of automation, and growth in materials and

manufacturing process solutions, which
have opened the door to higher production
rates, robustness and quality, but also the
ability to manufacture more diversified,
complex and functionalized designs. At the
same time, new methodologies are emerging that make behaviour predictions more
precise, resulting in lower experimental
efforts and more complex designs, and
enable design optimisation.
But a research effort is now needed to devise
new design tools for launcher structures.
To face the increasingly complex design
of composite structures, and owing to the
relative absence of integrated composite
design tools, CNES and Onera decided to
join their efforts in developing a novel tool
for the optimum design of composite structures, which aims to cover the whole design
process of a structure, from the search for
the structural concept to the prediction of
damage and failure in the most critical areas.
This joint work is performed within the
framework of the R&T Launchers CNES/
ONERA. This tool would take into account
many specificities of these materials - especially their anisotropic non-linear behaviour
and manufacturing constraints - and be
applicable to a wide range of structures,
from shells to lattice and wound structures,
and of processes (hand lay-up, fibre placement, thermo-moulding, etc.). This article
presents the outcome of the first step of this

Feature Aeronautics

he key to success in this competition
seems to be cost reduction together
with quick adaptability to market
evolutions (fast developments, performance improvement and solutions for new
applications). Composite materials are
clearly a key technology in this struggle.
Due to their better density/performance
ratio, composite materials have replaced
metal step by step in launchers as a key
driver to maximize payload. With compression-dominated structures prone to buckling, CFRP and aluminium honeycomb
sandwich materials have become a natural
solution for fairings, payload adaptors,
inter-stage skirts, etc. Moreover, wound
composites offer an interesting alternative
to steel and aluminium for high-pressure
tanks.

the development of composite structures,
thus increasing costs and limiting material
and concept choices; limitations in manufacturing processes (difficulties to control
quality and reproducibility, difficulties to
manufacture complex shapes such as double curvatures, etc.); but also limitations in
design methods.
Indeed, the aerospace and aeronautics
industries are still looking for the best
practice to design composite structures.
The most advanced methods currently used
are either very expensive computationally,
or require massive and costly experimental
validations, thus limiting their use to the
most critical parts only. For more common
parts, design is conducted with a traditional
approach relying on conservative guidelines
that hamper the development of design
tools that would really take advantage of the
design freedom offered by composite structures. This results in oversized structures as a
means to compensate for their lack of sound
physical basis, so that the specific features
and advantages of composite materials are
not fully exploited, and composite solutions
are often undervalued compared to metallic
solutions, which are much more readily
available and easy to model.

/ jec composites magazine

51

No112 April - May 2017
Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #112 - April/May 2017
