materials used in vehicle bodies-2 (2)

8/11/2019 Materials Used in Vehicle Bodies-2 (2)

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M.Tech.Automotive Engg II semPESIT -2009 Body and Chassis Engg

Prepared by RAVISHANKAR.V.KMob:9449600854 Email: [email protected]

Plastics

Thermoplastic Thermo set.

Thermoplastics, if exposed to

heat, will melt in two to seven

minutes.

Thermo sets will keep their shape

until they are a charred, smoking

mess

Examples: grocery bags, piano

keys and some automobile parts

Examples :

kid's Toy, dinner sets.

Soften when heated.No chemical change.When cooled- back to normal

Soften only oncechemical change takes place

Burns only with smoke.

Plastic Classification based on the reaction to Heat

Ex:

Polyethylene. Polypropylene,Polystyrene.

Ex:

Phonolic. Epoxy resins.Unsaturated Plastics, Amino resins.


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Mechanical Properties

Tensile strength

Elongation

Compressive

strength Creep

Shear strength Flexural strength

Torsional strength Modulus

Impact strength

Specific gravity Water absorbtion

Coefficient of Friction(COF)


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TensileStrength

Mechanical Properties

Elongation


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Compressive

Strength

Measured in

pounds persquare inch (PSI)

Higher PSI =harder tocompress

Creep

Associated with compressive strength

Creep at room temperature is called

cold flow


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ShearStrength

FlexuralStrength


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TorsionalStrength


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Modulus

Also referred to as stiffness

Used in conjunction with strengths (flexural modulus, tensile

modulus, etc.)

Higher modulus = stiffer material Measured in PSI

Impact Strength

Izod Impact Tensile Impact Gardner Impact


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Specific Gravity

Related to the density of material Can be used to determine the weight

of material

Specific gravity of less than 1.0 willfloat in water


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Water Absorption

Measured by the percentage of swell

Think of a sponge as having high

percentage absorption


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Coefficient of Friction (COF)

Resistance to sliding (slickness) Low COF = more slippery (think of

wet ice as having lowest COF)


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Thermal Properties

Coefficient of thermal expansion Heat deflection temperature

Continuous service temperature

Melting point

Thermal conductivity


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Coefficient of Thermal Expansion(CTE)

Change in size as temperaturechanges

Lower value = less change withtemperature


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Heat Deflection Temperature(HDT)

Temperature up to which a material can

perform, under load, without distorting

Used most widely to predict

performance


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Continuous Service Temperature(CST)

Highest temperature a material canwithstand and still retain at least 50% of

its properties Measured in degrees Fahrenheit, in air

In high temperatures, both CST andHDT must be considered


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Melting Point

Temperature at which a crystallinethermoplastic

changes from solid to liquid


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Thermal Conductivity

How much heat a material will conduct

Most plastics are good insulators (do

not conduct heat well)

Higher value = more heat conducted

Thermal conductivity of plastics is 300 to

2,500 times less than most metals


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Electrical Properties

Volume resistivity

Surface resistivity

Flammability


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Volume Resistivity

Ability of electricity to flow through a

material

Measured in ohms/cm

Lower value = more easily current flows

Higher value = better resistor or

insulator


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Surface Resistivity Ability of electricity to flow over the

surface of a material

Same measurements as volume

resistivity


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Most favorable ratings are given to

materials that extinguish themselves

rapidly, and do not drip flamingparticles

Flammability


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Types ofThermoplastics

Amorphous plastics (shapeless)

High performance Engineering

Commodity

Amorphous CommodityThermoplasticsKey Characteristics

Low cost, temperature resistance and strength

Good dimensional stability

Bonds well

Excellent transparency (Polycarbonate only)

High stiffness.

Excellent dimensional stability.

Good surface finish.

Flame retardance.

Semi-Crystalline Commodity

ThermoplasticsKey Characteristics

Low cost, temperature resistance

and strength

Excellent chemical resistance

Low COF

Near zero moisture absorption

Very good electrical properties

Good toughness

Semi-crystalline plastics

High performance

Engineering

Commodity


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Semi crystalline Plastics

Polyamide 6 and 66:

Properties: High rigidity.

Hardness.High heat resistance.Impact resistance.Abrasion/chemical/stress crack resistance.

Applications 1. Under bonnet components.2. Mechanical applications

3.Bumper.4.Body embellishment (Wheel rims, Handles)5.Lighting, Head lamp reflectors, Mirrors.


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Blended Plastics:

Blended Plastics are used in large area Body Panels.

Which require following properties.

Temperature resistanceLow temperature impact resistance.Toughness.Petrol resistance.

Stiffness.

Applications : Large Body panels.Injection moulded bumper.


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Other facts and applications of plastics in vehicle bodies.

Plastics with

Vacuum metalising.

Electroplating.

It is used in

Mirror Housing.

Control Knobs.

Winder handler.

Decorative metallic trim.


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Plastic thin parts property requirements for plastics;

1. Tough and resistant to occasional impact.2. Impervious to attack by weather, road salts and extremes of

temperatures.3. Low tensile strength No Heavy stresses.

4. Cheap and capable of being formed into highly individual and complexshapes.

The main plastics types in this category are Thermoplastics andThermosetting resins.

These can be pressed, stamped, blow moulded, vacuum formed, injectionmoulded any decorative shape.


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Acrylic plastics:

Tensile strength. 35-75 N/m2

Modulus of elasticity 1550-3250 N/m2

Inert to most chemicals.Complete stability against petroleum products.

Acetal resins:

Used in cams, sprockets, small leaf springs.

Housing cover plates, knobs and Lever.

Highest fatigue endurance limits.

Reduced friction and noise


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Other things:Plastic can be self colored Painting cost will be reduced

But large scale panels Painting is necessary to obtain the uniformity.

Plastics can be chrome plated.

Chrome plating avoids corroding the base body.

For joining thermoplastics adhesives are used

But now they can be welded also

Hot gas weldingUltrasonic and vibrations methods .

Induction, resistance and microwave process.


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Plastics Obtained with additional polymerization have wide application in

the construction of vehicle bodies.

Ploythene and polystyrene are used in many types of films and battery

cases where metal is not suitable.

Very economical because of their weight volume ratio

Range of density up to 1.00gm/cm3.

Expanded polystyrene can be used as thermo or acoustic insulatingboards with densities as low as 0.05 gm/cm3.

Another product is polyvinyl chloride (PVC).

It is used in covering, upholstery, roofing in case of convertibles.

Specific gravity of PVC is 1.20- 1.60

Ploythene and polystyrene


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GLASSESINTRODUCTION:

More and more glass being used in car.

Pillars are becoming slimmer and glass areas are increasing asmanufactures approach the ideal of almost complete all round vision inthe virtual elimination of blind spots.

Windscreens have becomes wider and deeper.


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CLASSIFICATION

TOUGHENED GLASS:

Uniformly toughened glass is produced by completelyDifferent process, involving heating of the glass followed by rapid cooling.

Usually toughened glass is produced by heating the glass in furnace to just belowIts softening point. At this temperature it is withdrawn from the furnace and chilledBy blasts of cold air. The rapid cooling hardens and shrinks the outside of theglass; the inside cools more slowly

LAMINATED GLASS:

Plastic coated laminated safety glass in an ordinary laminated glass which has

soft elastic polyurethane films bonded on to the inner surface to provide

Improved passenger protection. if fragmentation occurs.

In some cases the adhesive namely gelatine is used to hold the together.


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Definitions of glass types as per ARAI

Uniformly Toughened Safety Glass: A glass plane consisting a single layerof glass, which has been subjected to special treatment to increase its

mechanical strength and to condition its fragmentation after shattering.

Laminated Safety Glass: Laminated Safety Glass means two or more piecesof glass held together by an intervening layer or layers of plastic materials. Thelaminated safety glass will crack and break under sufficient impact, but thepieces of the glass tend to adhere to the plastic material and do not fly, and if a

hole is produced, the edges will be less jagged than they would be in the caseof an ordinary glass.


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GLASSES : Other Facts.

Britaish standards: BS 857, ECER43,

Most Laminated wind screens used are 4.4 mm,5mm,5.8mm, or 6.8 mm in overallThickness, with a 0.76 mm PVB interlayer.

Large coaches and lorry wind screens are 7.8 mm thick( 4.8 mm thick glass + 0.76 mm interlayer + 3mm Glass)


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materials used in vehicle bodies-2 (2)

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