Composites in Aerospace Applications
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Transcript of Composites in Aerospace Applications
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Application of composites in Aerospace
SUBMITTED TO MADE BY
KURUVILLA JOSEPH GAURAV VAIBHAV
SC11B147
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CONTENTS
1.INTRODUCTION TO COMPOSITES IN AEROSPACE
2.DETAILS ABOUT MATRIX AND PHASE FORM
3.APPLICATION OF ADVANCED COMPOSITES
AND ITS DIVISION
4.USE OF COMPOSITES IN AIRCRAFT DESIGN
5.COMPOSITES IN COMMERCIAL PLANE
6.DAMAGE DETECTION AND ITS CHARACTERISATION
7.CONCLUSION
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Composites in Aerospace Application :
The unrelenting passion of the aerospace industry to enhance the performance
of commercial and military aircraft is constantly driving the development ofimproved high performance structural materials. Composite materials are one
such class of materials that play a significant role in current and future
aerospace components. Composite materials are particularly attractive to
aviation and aerospace applications because of their exceptional strength and
stiffnessstiffness-to-density ratios and superior physical properties.
A composite material typically consists of relatively strong, stiff fibres in a
tough resin matrix. Wood and bone are natural composite materials: woodconsists of cellulose fibres in a lignin matrix and bone consists of
hydroxyapatite particles in a collagen matrix. Better known man-made
composite materials, used in the aerospace and other industries, are carbon-
and glass-fibre-reinforced plastic (CFRP and GFRP respectively) which consist of
carbon and glass fibres, both of which are stiff and strong (for their density),
but brittle, in a polymer matrix, which is tough but neither particularly stiff nor
strong. Very simplistically, by combining materials with complementary
properties in this way, a composite material with most or all of the benefits
(high strength, stiffness, toughness and low density) is obtained with few or
none of the weaknesses of the individual component materials.
CFRP and GFRP are fibrous composite materials; another category of
composite materials is particulate composites. Metal matrix composites
(MMC) that are currently being developed and used by the aviation and
aerospace industry are examples of particulate composites and consist,
usually, of non-metallic particles in a metallic matrix; for instance silicon
carbide particles combined with aluminium alloy.
Probably the single most important difference between fibrous and particulate
composites, and indeed between fibrous composites and conventional metallic
materials, relates to directionality of properties. Particulate composites and
conventional metallic materials are, nominally at least, isotropic, i.e. their
properties (strength, stiffness, etc.) are the same in all directions, fibrous
composites are anisotropic, i.e. their properties vary depending on the
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direction of the load with respect to the orientation of the fibres. Imagine a
small sheet of balsa wood: it is much easier to bend (and break) it along a line
parallel to the fibres than perpendicular to the fibres. This anisotropy is
overcome by stacking layers, each often only fractions of a millimetre thick, on
top of one another with the fibres oriented at different angles to form a
laminate. Except in very special cases, the laminate will still be anisotropic, but
the variation in properties with respect to direction will be less extreme. In
most aerospace applications, this approach is taken a stage further and the
differently-oriented layers (anything from a very few to several hundred in
number) are stacked in a specific sequence to tailor the properties of the
laminate to withstand best the loads to which it will be subjected. This way,
material, and therefore weight, can be saved, which is a factor of primeimportance in the aviation and aerospace industry.
Another advantage of composite materials is that, generally speaking, they can
be formed into more complex shapes than their metallic counterparts. This not
only reduces the number of parts making up a given component, but also
reduces the need for fasteners and joints, the advantages of which are
twofold: fasteners and joints may be the weak points of a component a rivet
needs a hole which is a stress concentration and therefore a potential crack-initiation site, and fewer fasteners and joints can mean a shorter assembly
time. Shorter assembly times, however, need to be offset against the greater
time likely to be needed to fabricate the component in the first place. To
produce a composite component, the individual layers, which are often pre-
impregnated (pre-preg) with the resin matrix, are cut to their required
shapes, which are all likely to be different to a greater or lesser extent, and
then stacked in the specified sequence over a former (the former is a solid or
framed structure used to keep the uncured layers in the required shape prior
to, and during, the curing process). This assembly is then subjected to a
sequence of temperatures and pressures to cure the material. The product is
then checked thoroughly to ensure both that dimensional tolerances are met
and that the curing process has been successful.
Shorter assembly times, however, need to be offset against the greater time
likely to be needed to fabricate the component in the first place. To produce a
composite component, the individual layers, which are often pre-impregnated
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(pre-preg) with the resin matrix, are cut to their required shapes, which are
all likely to be different to a greater or lesser extent, and then stacked in the
specified sequence over a former (the former is a solid or framed structure
used to keep the uncured layers in the required shape prior to, and during, the
curing process). This assembly is then subjected to a sequence of temperatures
and pressures to cure the material. The product is then checked thoroughly to
ensure both that dimensional tolerances are met and that the curing process
has been successful. Shorter assembly times, however, need to be offset
against the greater time likely to be needed to fabricate the component in the
first place. To produce a composite component, the individual layers, which
are often pre-impregnated (pre-preg) with the resin matrix, are cut to their
required shapes, which are all likely to be different to a greater or lesserextent, and then stacked in the specified sequence over a former (the former is
a solid or framed structure used to keep the uncured layers in the required
shape prior to, and during, the curing process). This assembly is then subjected
to a sequence of temperatures and pressures to cure the material. The
product is then checked thoroughly to ensure both that dimensional
tolerances are met and that the curing process has been successful.
Toughened epoxy
skins constitute about 75 per cent of the exterior area.
In total, about 40 per cent of the structural weight of the
Eurofighter is carbon-fibre reinforced composite material.
Application of advanced composites to aerospace can be divided into four
categories:
(1) aircraft,
(2) rotorcraft,
(3) spacecraft/missiles, and
(4) engines/nacelle.
Within each category a further division is possible. For example, aircraft can
be divided into combat aircraft, large transport, and small aircraft, and furtherdivided into military and commercial applications. The design and
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manufacturing technology is different for each of the above categories; the
difference is largely dependent upon the requirements set forth by each
category. A brief description of the requirements and constraints of each
category is delineated below to help explain the
impact on the design and manufacturing
technology:
Aircraft
Combat.
This application requires high performance (weight, strength, stiffness are
critical) and tolerance of severe environments. It involves moderate
production rates and moderate durability. Many complex structures are
required, resulting in high cost.
An automatic tape layup (ATL) machine is currently used for manufacturing
large, somewhat flat structures, such as skins. An automatic cutting machine
(ACM) is used to cut plies and fabrics for hand layup. Most of the complex and
small parts are made by labor intensive hand layup. Large Military Transport
and Bomber. This application involves moderate to high performance in
moderate to severe environments. Moderate production rates are typical and
moderate to long durability is required. A mixture of large and small structures
with both simple and complex shapes is fabricated for this application. The
result is relatively high cost.
Rotorcraft
This is a high performance application. Weight, strength, stiffness, and
durability are critical. Operating environments are severe. Production rates are
low to moderate. Battle damage tolerance is important. There is a high usage
of composites (e.g., in rotor blades, tail blades, fuselages, and booms).
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Spacecraft and Missiles
This is a high to ultra-high performancearea. Weight, strength and stiffness are
extremely critical. There are numerous
special and unique requirements. These
vehicles operate in severe to extremely
severe environments. Very low production
rates are typical for some spacecraft (e.g., satellites) but high for some others
(e.g., small missiles). There is essentially no durability requirement -- it is a
"one shot" deal.
Engine/Nacelle
There are uniquely high performance requirements for this application. These
parts operate in severe environments. There is a high demand for durability.
For fan blades, there is an acoustic environment issue, and net shape and
complex contour are requirements. Relatively high production rates are a
feature. recision hand layup is required currently for blade manufacturing. Tow
placement is also used for this application. A combination of filament winding
and hand layup is used for nacelles. Honeycomb construction is used for
acoustic sound absorption in nacelles. Precision co-curing techniques are used
for cascades.
A trends analys is highlighted a number of key areas of research that will
be needed to meet the expected trends in materials , processes and
applications. In materials, these were:
Natural fibre composites, including wood fibres
Polymeric fibres such as PET, PP and PE
Nano-reinforced fibres
Self-reinforced polymers
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Reactive thermoplastics
New commodity materials (e.g. PA, ABS, PBT, PET, and
TPU)
High performance materials (e.g. fluoropolymers, LCPs and
PEKK)
Bio-derived matrices
Thermoplastic nanocompos ites.
Modelling techniques and long-term performance characterisation of
these materials is also needed. For processing technologies, the
following were regarded as important research needs:
Thermoplastic RTM
New LFT injection processes
Hybrid moulding processes (e.g. thermohydroforming) and structures
Press and stamping processing routes
Thermoplastic pultrusion and extrusion
Diaphragm forming
Filament winding
Fibre placement and automated tape-laying.
Future needs in nanotechnology were identified below:
Materials Research Infrastructure
Self-reinforced polymers Nano-reinforcement Fibre spinning, continuous
lamination
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lines, twin screw extruder Nano-reinforced fibres Self-reinforced polymers or
other,Twin screw extruders, fibre-spinning matrices, improved stiffness and
temperature
Composites in Aerospace Applications
The unrelenting passion of the aerospace industry to enhance the
performance of commercial and military aircraft is constantly driving the
development of improved high performance structural materials.
Composite materials are one such class of materials that play asignificant role in current and future aerospace components. Composite
materials are particularly attractive to aviation and aerospace
applications because of their exceptional strength and stiffness-to-
density ratios and superior physical properties.
A composite material typically consists of relatively strong, stiff fibres in a
tough resin matrix. Wood and bone are natural composite materials:
wood consists of cellulose fibres in a lignin matrix and bone consists of
hydroxyapatite particles in a collagen matrix. Better known man-made
composite materials, used in the aerospace and other industries, are
carbon- and glass-fibre-reinforced plastic (CFRP and GFRP
respectively) which consist of carbon and glass fibres, both of which are
stiff and strong (for their density), but brittle, in a polymer matrix, which is
tough but neither particularly stiff nor strong. Very simplistically, by
combining materials with complementary properties in this way, a
composite material with most or all of the benefits (high strength,
stiffness, toughness and low density) is obtained with few or none of the
weaknesses of the individual component materials.
CFRP and GFRP are fibrous composite materials; another categoryof composite materials is particulate composites. Metal matrixcomposites (MMC) that are currently being developed and used bythe aviation and aerospace industry are examples of particulatecomposites and consist, usually, of non-metallic particles in a metallicmatrix; for instance silicon carbide particles combined with aluminium
alloy.
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Probably the single most important difference between fibrous andparticulate composites, and indeed between fibrous composites andconventional metallic materials, relates to directionality of properties.Particulate composites and conventional metallic materials are,
nominally at least, isotropic, i.e. their properties (strength, stiffness,etc.) are the same in all directions, fibrous composites areanisotropic, i.e. their properties vary depending on the direction of theload with respect to the orientation of the fibres. Imagine a smallsheet of balsa wood: it is much easier to bend (and break) it along aline parallel to the fibres than perpendicular to the fibres. Thisanisotropy is overcome by stacking layers, each often only fractionsof a millimetre thick, on top of one another with the fibres oriented atdifferent angles to form a laminate. Except in very special cases, the
laminate will still be anisotropic, but the variation in properties withrespect to direction will be less extreme. In most aerospaceapplications, this approach is taken a stage further and the differently-oriented layers (anything from a very few to several hundred innumber) are stacked in a specific sequence to tailor the properties ofthe laminate to withstand best the loads to which it will be subjected.This way, material, and therefore weight, can be saved, which is afactor of prime importance in the aviation and aerospace industry.
Another advantage of composite materials is that, generally speaking,they can be formed into more complex shapes than their metalliccounterparts. This not only reduces the number of parts making up a
givencomponent, butalsoreducesthe needforfasteners
and joints,theadvantages ofwhich are
tw ofold: fasteners and joints may be the weak points of a component a rivet needs a hole which is a stress concentration and thereforea potential crack-initiation site, and fewer fasteners and joints canmean a shorter assembly time.
Shorter assembly times, however, need to be offset against thegreater time likely to be needed to fabricate the component in the first
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place. To produce a composite component, the individual layers,which are often pre-impregnated (pre-preg) with the resin matrix, arecut to their required shapes, which are all likely to be different to agreater or lesser extent, and then stacked in the specified sequence
over a former (the former is a solid or framed structure used to keepthe uncured layers in the required shape prior to, and during, thecuring process). This assembly is then subjected to a sequence oftemperatures and pressures to cure the material. The product is thenchecked thoroughly to ensure both that dimensional tolerances aremet and that the curing process has been successful (bubbles orvoids in the laminate might have been formed as a result ofcontamination of the raw materials, for example).
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Use of Composites in Aircraft Design
Initially, composite materials were used only in secondary structure, but
as knowledge and development of the materials has improved, their use
in primary structure such as wings and fuselages has increased. Thefollowing table lists some aircraft in which significant amounts of
composite materials are used in the airframe. Initially, the percentage by
structural weight of composites used in manufacturing was very small, at
around two percent in the F15, for example. However, the percentage
has grown considerably, through 19 percent in the F18 up to 24 percent
in the F22. The image below, from Reference 1, shows the distribution of
materials in the F18E/F aircraft. The AV-8B Harrier GR7 has composite
wing sections and the GR7A features a composite rear fuselage.
Composite materials are used extensively in the Eurofighter: the wing
skins, forward fuselage, flaperons and rudder all make use of
composites. Toughened epoxy skins constitute about 75 percent of the
exterior area. In total, about 40 percent of the structural weight of the
Eurofighter is carbon-fibre reinforced composite material. Other
European fighters typically feature between about 20 and 25 percent
composites by weight: 26 percent for Dassaults Rafael and 20 to 25percent for the Saab Gripen and the EADS Mako.
The B2 stealth bomber is an interesting case. The requirement for
stealth means that radar-absorbing material must be added to the
exterior of the aircraft with a concomitant weight penalty. Composite
materials are therefore used in the primary structure to offset this
penalty.
The use of composite materials in commercial transport aircraft isattractive because reduced airframe weight enables better fuel economy
and therefore lowers operating costs. The first significant use of
composite material in a commercial aircraft was by Airbus in 1983 in the
rudder of the A300 and A310, and then in 1985 in the vertical tail fin. In
the latter case, the 2,000 parts (excluding fasteners) of the metal fin
were reduced to fewer than 100 for the composite fin, lowering its weight
and production cost. Later, a honeycomb core with CFRP faceplates
was used for the elevator of the A310. Following these successes,composite materials were used for the entire tail structure of the A320,
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which also featured composite fuselage belly skins, fin/fuselage fairings,
fixed leading-and trailing-edge bottom access panels and deflectors,
trailing-edge flaps and flap-track fairings, spoilers, ailerons, wheel doors,
main gear leg fairing doors, and nacelles. In addition, the floor panels
were made of GFRP. In total, composites constitute 28 percent of the
weight of the A320 airframe.
The A340-500 and 600 feature additional composite structures, including
the rear pressure bulkhead, the keel beam, and some of the fixed
leading edge of the wing. The last is particularly significant, as it
constitutes the first large-scale use of a thermoplastic matrix composite
component on a commercial transport aircraft. The use of composites
enabled a 20 percent saving in weight along with a lower production timeand improved damage tolerance.
The A380 is about 20-22 percent composites by weight and also makes
extensive use of GLARE (glass-fibre reinforced aluminium alloy), which
features in the front fairing, upper fuselage shells, crown and side
panels, and the upper sections of the forward and aft upper fuselage.
GLARE laminates are made up of four or more 0.38 mm (0.015 in) thick
sheets of aluminium alloy and glass fibre resin bond film. GLARE offers
weight savings of between 15 and 30 percent over aluminium alloy along
with very good fatigue resistance. The top and bottom skin panels of the
A380 and the front, centre and rear spars contain CFRP, which is also
used for the rear pressure bulkhead, the upper deck floor beams, and for
the ailerons, spoilers and outer flaps. The belly fairing consists of about
100 composite honeycomb panels.
Lightweight magnetic composites for aircraft
applications
Carbon fibers/polymer matrix composites tend to be used more widely
instead of aluminum
structures in the aircraft and
aerospace industry. There
are many reasons that
explain the increasing interest
for this class of composites
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due to the lightweight, high strength, high stiffness, good fatigue life,
excellent corrosion resistance and low cost manufacturing. Moreover, a
considerable effort is paid to improve the thermal/electrical conductivity
and the electromagnetic shielding effectiveness of lightweight
composites. It is well known that in operation, the engines of the aircraft
generate a large amount of electrical current during start up. This
electrical current is undesirable and must be conducted away.
Otherwise, the electronic components need to be protected against
electromagnetic waves produced by other sources placed inside or
outside the aircraftcomposites are increasingly being used in the aircraft
and spacecraft industry.
Nowadays, a significant amount of advanced polymer composites isused for military and commercial aircraft and satellite components.
Because of their low density, superior physical and mechanical
properties and low cost manufacturing, these materials have replaced
metals, such as aluminum alloys, in many applications . Passenger
aircraft Boeing 747 and 767 have composite parts, such as doors,
rudders, elevators, ailerons, spoilers, flaps, fairings, to lower the weight,
increase the payload and the fuel efficiency .
.During the last decade, a considerable effort has been spent with
finding solutions for obtaining lightweight and ultra-lightweight
composites to be used in aerospace applications. The quality of the
resin matrix can be improved with additives such as carbon filler, carbon
whiskers, carbon nanotubes .
Composites in commercial plane
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Damage Detection And Characterization
Composite defects or damage come from manufacturing or service
exposure. Defects and handling damages that occur during
manufacturing are controlled by in-process and postprocess QCs.Despite stringent controls, some defects and damage are likely to occur,
requiring factory disposition.
Most processing anomalies
that are allowed to enter the
field are much smaller than
damage considered from
service. This relates to
advanced NDI proceduresused in the factory. Factory
NDI methods are more
stringent than those that can
be practically applied in the
field. Hence, design criteria
must account for larger field damage to accommodate practical
maintenance practices. One type of manufacturing defect that has posed
field problems relates to weak bonds, where bond surfacecontamination, tooling, or curing problems lead to insufficient bond
strength. This manufacturing defect is best controlled in-process
because factory NDI performed after cure typically will not detect the
problem. Composite design criteria have protected against this problem
by making sure there is redundant design detail and damage tolerance
to ensure the associated debonding can be found in service.
There are many types of composite defects and damage that can arise
in the field. Field damages can result from (1) dropped tools, (2) service
vehicle, jetway, or work-stand collisions, (3) aircraft-handling accidents,
(4) dropped parts, (5) improperly installed fasteners, (6) bird strikes, (7)
foreign object impacts (e.g., runway debris), (8) overheating, (9) fluid
contamination, (10) flight overloads, and (11) sonic fatigue. Note that
many of these damages are due to foreign object impact, which is one of
the primary safety issues for composite structures. Repeated loads, by
themselves, typically do not lead to service damage because of
relatively flat composite fatigue curves and a need to account for
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accidental damage in design criteria, which reduces the working strain
levels. Exceptions where fatigue has been a problem usually relates to
bad design detail, where secondary out-plane loads occur in service,
damaging the weak direction of the composite.
Other field damages are due to environmental conditions, including (1)
hail, (2) lightning, (3) ultraviolet (UV) radiation, (4) high-intensity radiated
fields, (5) rain erosion, (6) moisture ingression, and (7) ground-air-
ground cycles (temperature, pressure, and moisture excursions).
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Conclusion
As we have seen composites play a very important role in development
of aerospace industry in the future. They are verymuch better than
composites and their performance is far more superior than normal used
elements like duranium.they can increase payloads or fuel usage.also
their usage can increase the efficiency, durability,life time and
usability.presentky their use is mainly rstricted to advanced ceramics but
in future probably they will be integrated into yhe lives of man just like
metals.
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ACKNOWLEDGEMENTS
Lectures and notes of kuruvilla sir are the main sources of my project.Books on
aerospace materialsand website sources also contributed to my work.