Mechanics of aircraft materials 3 cdio

A DVANTAGES OF C OMPOSITES High strength to weight ratio Fiber-to-fiber transfer of stress allowed by chemical bonding Modulus stiffness to density ratio 3.5 to 5 times that of steel

Composite and Non-metallic

Mechanics of Aircraft Materials

Department of Aerospace Engineering – Faculty of Transportation Engineering

Dr Ly Hung Anh

I NTRODUCTION

Since the mid-1950s, the use of magnesium, plastic,

fabric, and wood in aircraft construction has nearly

disappeared.

Using of aluminum and aluminum alloys for airframe

construction:

80 percent of airframes in 1950

About 15 percent today for airframe construction

Nowadays, the aircraft construction uses more and more

the nonmetallic materials such as

reinforced plastics

advanced composites

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C OMPOSITE M ATERIALS

A “composite” material is defined as a mixture of

different materials or things to enhance the strength,

ductility, conductivity or whatever desired

characteristics.

Composition: 2 phases

Composition: 2 phases

Resin: continuous and surrounding other phase

Reinforcement: surrounded by the resin, to enhance the

A DVANTAGES OF C OMPOSITES

High strength to weight ratio

Fiber-to-fiber transfer of stress allowed by chemical

bonding

Modulus (stiffness to density ratio) 3.5 to 5 times that of

steel or aluminum

Longer life than metals

Higher corrosion resistance

Tensile strength 4 to 6 times that of steel or aluminum

Greater design flexibility

Bonded construction eliminates joints and fasteners

Very expensive processing equipment

Lack of standardized system of methodology

Great variety of materials, processes, and techniques

General lack of repair knowledge and expertise

Products often toxic and hazardous

Lack of standardized methodology for construction and

C OMPOSITE S AFETY

Composite products can be very harmful to the skin,

eyes, and lungs.

Respirator particle protection is very important to

protecting the lungs from permanent damage from tiny

glass bubbles and fiber pieces.

Methods of protection:

Methods of protection:

Dust masks

Respirator with dust filters (Charcoal filters)

Supplied air mask and hood

Avoid skin contact with the fibers: by wearing long pants

and long sleeves along with gloves or barrier creams.

The eyes protection: using leak-proof goggles (no vent

F IBER R EINFORCED M ATERIALS

Purpose of reinforcement: to provide most of the

Particle: square piece of material with their dimensions

are equal on all axes.

Whisker:

piece of material with the length greater than the width

usually single crystals

very strong and used to reinforce ceramics and metals

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F IBER R EINFORCED M ATERIALS

Fiber:

single filaments that are much longer than they are wide

be made of almost any material, and are not crystalline like

whiskers

base for most composites

base for most composites

smaller than the finest human hair

normally woven into cloth-like materials

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D ISTRIBUTION OF F IBERS ON A L AMINA

Lamina: very thin layer of the resin and the fibers.

Distribution of fibers: 3 ways

Long aligned fibers

Short aligned fibers

Short non-aligned fibers

Short non-aligned fibers

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L AMINATED S TRUCTURE

Manufacture: composing many layers or panels with

different directions of reinforced fibers.

Purpose: increase the strength

in different directions.

Laminate construction is strong and stiff, but heavy. 11

S ANDWICH S TRUCTURE

Laminated structure with a core center is called a

sandwich structure.

The sandwich laminate is equal in strength, and its

weight is much less.

Composition:

Composition:

2 face sheets (lamina sheets)

Core center (honeycomb)

Applications:

Rotor blades of helicopters

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F ABRICATION A S ANDWICH P ANEL

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H ELICOPTER ’ S R OTOR B LADES

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TRANSPARENT PLASTICS

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T RANSPARENT P LASTICS

Classification: according to their reaction to heat

thermoplastic : soften when heated and harden when cooled.

thermosetting: harden upon heating, and reheating has no softening

Laminate transparent plastic: made from transparent plastic

face sheets bonded by an inner layer material, usually

L AMINATED T RANSPARENT P LASTICS

Stretched acrylic is a type of plastic which before being

shaped, is pulled in both directions to rearrange its

molecular structure

Properties:

great resistance to impact

great resistance to impact

Less subject to shatter

Great chemical resistance

Simple edging

Less crazing and scratches detriment

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L AMINATED P LASTIC U SING

Individual sheets of plastic are covered with a heavy

masking paper with pressure sensitive adhesion.

Be careful to avoid scratches and gouges

By sliding sheets against one another

By sliding sheets across rough or dirty tables

store in a cool, dry place away from solvent fumes, heating

coils, radiators, and steam pipes

temperature in the storage room should not exceed 120 °F 18

Resin: polymers which the viscosity varies from a waterlike

consistency to a thick syrup

Reinforcement: glass cloths

Cure or polymerization: use a catalyst, usually benzoyl

peroxide

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R EINFORCED P LASTIC

Solid laminates

constructed of three or more layers of resin impregnated cloths “wet

laminated” together to form a solid sheet facing or molded shape.

Sandwich-type laminates

constructed of two or more solid sheet facings or a molded shape

fiberglass honeycomb or foam-type core

Honeycomb cores:

Reinforcement: glass cloths

Resin: polyester or a combination of nylon and phenol

The specific density and cell size varies over a considerable latitude

Foam-type cores:

combinations of alkyd resins and metatoluene di-isocyanate

esin forms a bond between the facing and the core. 20

R EINFORCED P LASTIC

Properties:

excellent dielectric characteristics

high strength-to-weight ratio

resistance to mildew, rust, and rot

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prevent the entrance of dirt, water, or air.

prevent the loss of fluids, gases, or air

absorb vibration, reduce noise, and cushion impact loads

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N ATURAL R UBBER

Natural rubber has better processing and physical

properties than synthetic or silicone rubber

Properties:

flexibility, elasticity, tensile strength, tear strength

low heat buildup due to flexing (hysteresis)

low heat buildup due to flexing (hysteresis)

swells and often softens in all aircraft fuels and in many

S YNTHETIC R UBBER

Several types: compounded of different materials to give

the desired properties

Butyl: a hydrocarbon rubber with:

superior resistance to gas permeation

resistant to deterioration

physical properties are less than those of natural rubber

resistance with oxygen, vegetable oils, animal fats,

alkalies, ozone, and weathering

swell in petroleum or coal tar solvents

low water absorption rate and good resistance to heat and low

temperature

using temperatures ranging from −65 °F to 300 °F

used with phosphate ester hydraulic fluids (Skydrol), silicone

fluids, gases, ketones, and acetones

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S YNTHETIC R UBBER

Buna: Buna-S and Buna-N

Buna-S rubber :

As water resistant as natural rubber

better aging characteristics

good resistance to heat, but only in the absence of severe flexing

poor resistance to gasoline, oil, concentrated acids, and solvents

used for tires and tubes as a substitute for natural rubber.

Buna-N:

outstanding in its resistance to hydrocarbons and other solvents

poor resilience in solvents at low temperature

good resistance to temperatures up to 300 °F

may be procured for low temperature applications down to −75 °F

fair tear, sunlight, and ozone resistance

good abrasion resistance and good breakaway properties

used for oil and gasoline hose, tank linings, gaskets, and seals. 26

S YNTHETIC R UBBER

Neoprene:

take more punishment than natural rubber

better low temperature characteristics

exceptional resistance to ozone, sunlight, heat, and aging

less like rubber in some of its characteristics than butyl or

less like rubber in some of its characteristics than butyl or

Buna

tear resistance and abrasion resistance is slightly less than

natural rubber

superior resistance to oil

poor resistance to aromatic gasolines

used for weather seals, window channels, bumper pads, oil

resistant hose, and carburetor diaphragms

recommended for use with Freons™

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S ILICONE R UBBER

Silicone rubbers: group of plastic rubber materials made

from silicon, oxygen, hydrogen, and carbon.

Properties:

excellent heat stability

very low temperature flexibility (up to 600 °F)

very low temperature flexibility (up to 600 °F)

resistant to temperatures down to −150 °F

good resistance to oils

reacts to both aromatic and nonaromatic gasolines

Applications: Silastic - one of the best known silicones

used to insulate electrical and electronic equipment

used for gaskets and seals in certain oil systems

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