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Tiêu đề Mechanics of Aircraft Materials
Người hướng dẫn Dr. Ly Hung Anh
Trường học Department of Aerospace Engineering – Faculty of Transportation Engineering
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Nội dung

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Composite and Non-metallic

Mechanics of Aircraft Materials

Department of Aerospace Engineering – Faculty of Transportation Engineering

Dr Ly Hung Anh

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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

 Composition: 2 phases

 Composition: 2 phases

 Resin: continuous and surrounding other phase.

 Reinforcement: surrounded by the resin, to enhance the

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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

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 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

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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

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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

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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

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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

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 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

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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

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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

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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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