CONTENT

Page no: Introduction 1

Chapter No:1. Composite Material 2-5

2. Fiber Material 6-9

3. Matrix and Filler Materials 10-11

4. The reasons why composites are selected for Aerospace

Applications 12-17

5. Advantage& Disadvantages of Composite 18-19

Conclusion 20

Introduction

Composite material is a material composed of two or more distinct phases(matrix phase and

dispersed phase) which are chemically & physically different.

Composites are used because overall properties of the composites are superior to those of the

individual components.

The primary phase, having a continuous character , is called matrix. Matrix is usually more

ductile and less hard phase. It holds the dispersed phase and shares a load with it.

The second phase (or phases) which is embedded in the matrix is called dispersed phase.

Dispersed phase.

CHAPTER: 1

Composite Material:

Composites, which consist of two or more separate materials combined in a macroscopic

structural unit, are made from various combinations of the other three materials.

The relative importance of the four basic materials in a historical context has been presented by

Ashby (Technology of the 1990s: Advanced Materials and Predictive Design, M.F. Ashby,

Philosophical Transactions of the Royal Society of London, A322, 393-407, 1987) and is shown

schematically below (figure taken from Gibson).

Mankind has used composites since early time; for example, straw-reinforced clay bricks used by

Israelites (the book of Exodus in the Old Testament), plant fiber-reinforced pottery, etc. They

knew from daily use that fiber reinforcement of a material is very effective because many

materials (but not all) are much stronger and stiffer in fiber form than they are in bulk form.

For example, Griffith found that as glass rods and fibers got thinner, they got stronger. He found

that that for very small diameters the fiber strength approached the theoretical cohesive strength

between adjacent layers of atoms, whereas for large diameters the fiber strength dropped to near

the strength of bulk glass.

Fibers allow one to obtain the maximum tensile strength and stiffness of a material, but there are

disadvantages. Fibers alone cannot support longitudinal compressive loads and their transverse

mechanical properties are generally not as good as the corresponding longitudinal (fiber

direction) properties. Thus, there is often the need to place fibers in different directions

depending upon the particular loading application.

Types of Fiber-Reinforced Composites

One generally finds four types of fiber-reinforced composites as shown below (from Gibson).

They differ in how the fibers are utilized to make the composite (orientation and length of

fibers).

Continuous fiber composites are generally "laid-up" in plies (or laminae) with each ply having

fibers oriented in the same direction. A layer of fibers all oriented in the same direction is

imbedded in a homogeneous material (called the matrix) to make a single ply or laminae. For

example, glass-epoxy has a layer of glass fibers running more-or-less parallel within an epoxy

resin matrix material.

Individual plies can be stacked or layered and bonded together with individual ply fiber

directions being selected so as to tailor the lay-up (or laminate) to have desired overall structural

characteristics of the laminate. Under loading, the potential for delamination (or separation of

the laminae) is a major problem because the interlaminar strength is matrix dominated (i.e., if the

matrix is weak, ply delamination can occur).

Woven fiber composites are similar to ordinary cloth used in the textile industry. The woven

fiber may be 2-D (fibers interwoven in 2 directions) or 3-D (fibers interwoven in 3 directions).

Woven fiber composites do not generally have distinct laminae and are not nearly as susceptible

to delamination; however, strength and stiffness are sacrificed due to the fact that the fibers are

not as straight (because of the weaving) as in the continuous fiber laminate.

Chopped fiber composites have fibers that are relatively short and have a random orientation

and distribution of the fibers. Chopped fiber composites generally have mechanical properties

that are considerable poorer than those of continuous fiber composites. However they are

cheaper to manufacture and are used in high-volume applications.

Hybrid composites generally consist of mixed chopped and continuous fibers; or mixed fiber

types such as glass/graphite.

Sandwich composites are also common. They consist of high strength composite facing sheets

(which may be any of the four fiber composites discussed above) bonded to a lightweight foam

or honeycomb core (from Gibson).

Sandwich structures have extremely high flexural stiffness-to-weight ratios and are widely used

in aerospace structures. The design flexibility offered by these and other composite

configurations is obviously quite attractive to designers, and the potential now exist to design not

only the structure, but also the structural material itself.

Almost all of the fiber-reinforced composite types discussed above can be utilized in complex

curved geometries although the manufacturing process may be much more costly and difficult.

For example, wound fiber-reinforced pressure vessels are common and are manufactured by

winding either individual fiber filaments on a mandrel (having the shape of the vessel) or

individual plies are wound on the mandrel. Curved composite material panels on aircraft wings,

fuselage and nacelles are common.All of the composite types have various manufacturing

processes required to bond individual plies.

CHAPTER:2

Fiber Material :

Glass fibers consist primarily of silica (silicon dioxide) and metallic-oxide-modifying elements

are generally produced by mechanical drawing of molten glass through a small orifice. E-glass

accounts for most of the glass fiber production and is the most widely used reinforcement for

composites. The second most popular glass fiber, S-glass, has roughly 30 percent greater tensile

strength and 20 percent greater modulus of elasticity than E-glass but is not as widely used

because of its higher cost.

Graphite or carbon fibers are the most widely used advanced fiber, and graphite/epoxy or

carbon/epoxy composites are now used routinely in aerospace structures. The actual fibers are

usually produced by subjecting organic precursor fibers such as polyacrylonitrile (PAN) or rayon

to a sequence of heat treatments, so that the precursor is converted to carbon by pyrolysis.

Graphite fibers are typically subjected to higher heat treatments than are carbon fibers. Carbon

fibers are typically 90-95% carbon, whereas graphite fibers are at least 99% carbon.

Aramid polymer fibers, produced primarily by E.I. duPont deNemours & Company under the

tradename "Kevlar," were originally developed for use in radial tires. The density of Kevlar is

about half that of glass and its specific strength is among the highest of currently available fibers.

Kevlar also has excellent toughness, ductility, and impact resistance; unlike brittle glass or

graphite fibers.

Boron fibers are actually composites consisting of a boron coating on a substrate of tungsten or

carbon. The diameter of boron fibers is among the largest of all the advanced fibers, typically

0.002-0.008 in. Boron fibers have much higher strength and stiffness than graphite, but they also

have higher density. Boron/epoxy and boron/aluminum composites are widely used in aerospace

structures, but high cost prevents more widespread use.

Silicon carbide (SiC) fibers are used primarily in high-temperature metal and ceramic matrix

composites because of their excellent oxidation resistance and high-temperature strength

retention. SiC whisker-reinforced metals are increasingly being used as alternative to un-

reinforced metals and continuous fiber-reinforced metals. SiC whiskers are quite small, typically

8-20 in. diameter and about 0.0012 in. long so that standard metal-forming processes such as

extrusion, rolling and forging can be easily used.

The list of fibers goes on … On the following pages are a) Selected properties of fibers and

bulk metals, b) Specific strength vs. specific modulus for various fibers and c) Specific strength

vs. specific modulus (stiffness) for various composites (from Gibson). Specific value is the

value of the property divided by its density.

CHAPTER:3

Matrix and Filler Materials:

Polymers, metals and ceramics are all used as matrix materials in composites. The matrix

holds the fibers together in a structural unit,

protects them from external damage,

transfers and distributes the applied loads to the fibers, and

in many cases, contributes some needed property such as ductility, toughness, or

electrical insulation.

Because the matrix must transfer load to the fibers, a strong interface bond between the fiber and

matrix is extremely important; either through a mechanical or chemical bond between fibers and

matrix. Fibers and matrix must obviously be chemically compatible to prevent undesirable

reactions at the interface; this is especially important at high temperature where chemical

reactions can be accelerated.

Service temperature is quite often a controlling factor in consideration of a matrix material.

Listed in order of increasing temperature capability, we have:

Polymers are the most widely used matrix materials. They may be either thermosets (e.g.,

epoxy, polyester, phenolics) or thermoplastics (e.g., polyimide (PI), polyetheretherketone

(PEEK), polyphenylene sulfide (PPS)). Upon curing, thermosets form a highly cross-linked,

three-dimensional molecular network which does not melt at high temperature. Thermoplastics,

however, are based on polymer chains that do not cross-link. As a result, thermoplastics will

soften and melt at high temperature, then harden again upon cooling.

Epoxies and polyesters are also widely used. High grade epoxies are typically cured at about

350F and are generally not used at temperatures about 300F. The advanced thermoplastics

(PEEK, PI and PPS) have melting temperatures in the range of 600-700F. For higher

temperatures, metal, ceramic or carbon matrix materials are required.

Lightweight metals such as aluminum, titanium and magnesium and their alloys such titanium

aluminide and nickel aluminide may be used as matrix materials. For some of these, operating

temperature can be extended to about 2,250F. Advantages of metal matrices include higher

strength, stiffness and ductility (compared to polymers) but at the expense of higher density.

Ceramic matrix materials such as silicon carbide and silicon nitride can be use at temperatures

up to 3,000F. Hoever, ceramics have poor tensile strength are are quite brittle.

Carbon fiber/carbon matrix composites can be used at temperatures approaching 5,000F, but

the cost is such that they are only used in a few critical aerospace applications.

Filler materials are often used as a third component of a composite, and are typically mixed

with the matrix material during fabrication. Fillers do not typically enhance mechanical

properties but are used to alter or improve some other characteristic of the composite. Examples

include: hollow glass microspheres are used to reduce weight, clay or mica particles are used to

reduce cost, carbon black particles are used for protection against ultraviolet radiation, and

alumina trihydrate is used for flame and smoke suppression.

CHAPTER:4

The reasons why composites are selected for Aerospace Applications:

High strength to weight ratio (low density high tensile strength)

High creep resistance

High tensile strength at elevated temperatures

High toughness

Weight is everything when it comes to heavier-than-air machines, and designers have striven

continuously to improve lift to weight ratios since man first took to the air.Composite

materials have played a major part in weight reduction, and today there are three main types in

use: carbon fiber-, glass- and aramid- reinforced epoxy.; there are others, such as boron-

reinforced (itself a composite formed on a tungsten core).

Since 1987, the use of composites in aerospace has doubled every five years, and new

composites regularly appear.

Where Composite Are Used:

Composites are versatile, used for both structural applications and components, in all aircraft and

spacecraft, from hot air balloon gondolas and gliders, to passenger airliners, fighter planes and

the Space Shuttle. Applications range from complete airplanes such as the Beech Starship, to

wing assemblies, helicopter rotor blades, propellers, seats and instrument enclosures.

The types have different mechanical properties and are used in different areas of aircraft

construction. Carbon fiber for example, has unique fatigue behavior and is brittle, as Rolls Royce

discovered in the 1960's when the innovative RB211 jet engine with carbon fiber compressor

blades failed catastrophically due to birdstrikes.

Whereas an aluminium wing has a known metal fatigue lifetime, carbon fiber is much less

predictable (but dramatically improving everyday), but boron works well (such as in the wing of

the Advanced Tactical Fighter). Aramid fibers ('Kevlar' is a well-known proprietary brand owned

by DuPont) are widely used in honeycomb sheet form to construct very stiff, very light bulkhead,

fuel tanks and floors. They are also used in leading- and trailing-edge wing components.

In an experimental program, Boeing successfully used 1,500 composite parts to replace 11,000

metal components in a helicopter. The use of composite-based components in place of metal as

part of maintenance cycles is growing rapidly in commercial and leisure aviation.

Overall, carbon fiber is the most widely used composite fiber in aerospace applications.

The Future of Composites in Aerospace:

With ever increasing fuel costs and environmental lobbying, commercial flying is under

sustained pressure to improve performance, and weight reduction is a key factor in the equation.

Beyond the day-to-day operating costs, the aircraft maintenance programs can be simplified by

component count reduction and corrosion reduction. The competitive nature of the aircraft

construction business ensures that any opportunity to reduce operating costs is explored and

exploited wherever possible.

Competition exists in the military too, with continuous pressure to increase payload and range,

flight performance characteristics and 'survivability', not only of airplanes, but of missiles,

too.Composite technology continues to advance, and the advent of new types such as basalt and

carbon nanotube forms is certain to accelerate and extend composite usage.

Table:4.1- Reinforced materials used in aerospace areas.

Fig:4.2-Above Picture showing the composite polymer used in various areas of an

aeroplane.

Polymeric matrices in aerospace:

Thermoset resins

polyester , Epoxy,Phenol,Polyimide

Thermoplastics

PolyPhenyleneSulifide(PPS),

PolyEtherEtherKetone(PEEK),

PolyEtherimide (PEI)

Some composites in aerospace:

Metals (aluminium, titanium etc.)

Glass

Ceramics

Hybrid(composites)

Carbon aramid reinforced epoxy

Glass Carbon reinforced epoxy

Polymer-matrix composites are valued in the aerospace industry for their stiffness,

lightness, and heat resistance ( see materials science: Polymer-matrix composites).

They are fabricated materials in which carbon or hydrocarbon fibres (and sometimes

metallic strands, filaments, or particles) are bonded together by polymer resins in

either sheet or fibre-wound form.

The Boeing 777 is a long-range wide- body twin-engine jet airliner manufactured by Boeing

commercial airplanes. It is the world's largest twinjet and has a capacity of over 300

passengers, with a range of 5,235 to 9,380 nautical miles (9,695 to 17,370 km) .12%

composites are used.

Fig:4.3 &4.4

Showing

composite

material&ot-

her material

in various

parts on an

aeroplane.

CHAPTER:5

Advantage& Disadvantages of Composite :

We have already touched on a few, such as weight saving, but here is a full list:

Weight reduction - savings in the range 20%-50% are often quoted.

It is easy to assemble complex components using automated layup machinery and rotational

molding processes.

Monocoque ('single-shell') molded structures deliver higher strength at much lower weight.

Mechanical properties can be tailored by 'lay-up' design, with tapering thicknesses of

reinforcing cloth and cloth orientation.

Thermal stability of composites means they don't expand/contract excessively with change in

temperature (for example a 90°F runway to -67°F at 35,000 feet in a matter of minutes).

High impact resistance - Kevlar (aramid) armor shields planes, too - for example, reducing

accidental damage to the engine pylons which carry engine controls and fuel lines.

High damage tolerance improves accident survivability.

'Galvanic' - electrical - corrosion problems which would occur when two dissimilar metals are

in contact (particularly in humid marine environments) are avoided. (Here non-conductive

fiberglass plays a roll.)

Combination fatigue/corrosion problems are virtually eliminated.

CONCLUSION

Composite materials will play an increasingly significant role in aerospace application

B787,A350-XWB used more than 50% composite materials

With their unique combination of properties such as low weight, high strength, low

flammability, smoke density and heat release, non-toxicity and durability, composites are

ideal for many aerospace applications, both for interior and exterior components.