Composites in Aerospace Applications

7/31/2019 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.

Documents

Composites in Aerospace Applications