117638104 Composites for Automobiles

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DEPARTMENTOFPOLYMERENGINEERINGANDTECHNOLOGY

2012

Compositesfor

Automobiles

[Typethedocumentsubtitle]FahadJamshed

U N I V E R S I T Y O F P U N J A B , L A H O R E


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What are automobile composites?

The automotive composite materials are premium engineered materials, which by definition must

have the ability to possess high strength to weight ratio, stiffness, and fatigue resistance, quality

to dissipate or absorb the energy of impact. The ease of fabrication is another important factor.

By precise explanation of the automotive composite we meant a material containing reinforcing

filler embedded within the polymeric material to provide appreciable mechanical properties

described above. [1, 21]

What are the problems with the existing technology/materials?

The existing technology based on metals is being replaced by light weight composites due to the

following facts.

Metals are prone to wear; composites like epoxy/carbon fiber are less prone to wear. Metals are not well protected from sratches and wear, composites provide self healing

coatings. [12]

Metals are heavy weight, e.g. in case of aluminum driving shaft, it is being rapidlyreplaced by carbon/epoxy, whose specific elastic modulus is four times the aluminum.

[13]

Composites are less prone to stress concentration effects as compared to metals. [13] Metals have poor energy absorbing, front deign and bumper material of a car is prepared

by E glass/ epoxy composites, which absorbs energy of collision [29]

Steel and aluminum cannot produce unibody design, by using various techniques likeSRIM and Stamp forming produces unique unibody design which provide most efficient

mass reduction approach in automobiles. [23]

How polymer matrix composites (PMC) can benefit automobile applications.

PMCs containing both the micro size fillers and nano size particulate reinforcing fillers are being

used intensively in automobile industry. There are some potential advantages in using PMCs:

Due to their high specific strength and modulus. Composite manufacturing techniques provide excellent part consolidation Reduced weight causes batter fuel saving and performance, Light-weight subsystems

such as hoods and deck lids are extensively used. [16]

Over 75% of fuel consumption relates directly to vehicle weight. Reducing weight canimprove the price-to performance ratio of transportation systems.[16]


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Lower cost of tooling, plants and investment. improved ride performance (reduced noise, vibration, and harshness); Corrosion resistance: in contrast to chrome VI that is used in automobiles as coating,

doesnt have long term corrosion resistance. Using SiO2 nano particles enriched coating,

corrosion resistance is long term. [2, 3, 23, 21 ]

Polymer matrix containing nano particles as reinforcing agents

Nano composites are ultra fine phase dimensions, typically of the order of a few nanometers.

They possess unique properties not shared by their micro composite counterparts. [17]

They are dispersed properly in matrix either by heat or solvent, their proper dispersion markedly

improves the mechanical properties which include increased modulus and strength. Excellent

barrier properties, improved solvent and heat resistance, lower flammability, anti glare and

scratch resistant properties. [18]

For automobiles the nanoparticles, -fibers, -dots, - layers, - pores, -whiskers, -tubes can be

dispersed in a matrix, or arranged on a surface, referred as nanocomposites. [30]

Reinforcing fillers used in automotive industry

The following fillers are extensively used in automobile industry.

Glass fiber E grade [8]

Carbon fiber [10]SiO2 nano particles [6,3]

Carbon black

Layered silicate [5]

Alumina nano particles [6]

Zinc oxide ZnO, and silicon carbide SiC [12]

TiO2 [28]

The most common reinforcing fillers for automobile application

The following fillers are used for reinforcement in automobile industry.

SiO2 nano particles are used for scratch resistant, and anti glare coatings on mirrors. [3,11]

Carbon fiber is used to attain premium mechanical properties and to fabricate car outer shell.

[13]

Glass fiber is used for car body, bumpers and hoods and drive shaft. [8,14]


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Zinc oxide ZnO, and silicon carbide SiC wear resistant coatings, suppress crack growth [30]

Materials, Fabrication and characterization

Some important polymer composites for automobiles

Most important PMCs are as follows:

E glass/epoxy light weight drive shaft fabrication [7-9]

Layered silicate protection coatings [5-6]

Alumina nano particles in silane improving mechanical properties [18]

Silica nano particles coatings for scratch resistance. [6]

Polypropylene / E glass fiber automotive dashboard

Nafion PEM with nano silica improve fuel cell electrode [30]

Production of few polymeric composites

E glass/ epoxy driving shaft

The E glass acts as a reinforcing agent and gives tensile strength and thermal stability. The epoxy

is a matrix which has good elongation to failure and high strength. It also provides good wetting

of fiber, has batter dimensional stability and low curing shrinkage [8]

PMCs has batter fatigue characteristics and cracks dont grow further like in metals and the

fibers terminate their growth [7]

The angle of winding has to be controlled. 90o

is best for buckling strength and 45 makes the

maximum shear strength [7]

Filament winding is used to manufacture driving shaft. The process consist of wrapping the resin

impregnated roving onto a rotating mandrel specimen under precise tension. Geometric patterns

such as coil and helix are used. For winding operation, a carriage which lay the fiber band onto

the mandrel at required angle and speed is used. Fiber tension is controlled by roller guides. Theangle of fibers is kept at 40

oto 90

o[9].

Polymer layered slicate coatings


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PLS nano coatings are sheets of nano meters thick with high aspect ratio, high strength and high

surface area. Their (1-5%) loading in matrix introduces premium properties such thermal

stability, barrier performance and anti corrosion [11]

A few weight percent loading of layered silicate into the elastomeric epoxy or polyurethane

appreciably enhance the tensile strength and toughness [5]

The resin used is epoxy and desired amount of layered silicate is added. The mixture is heated at

elevated temperatures and curing agents are added. The mixture is cast and mold. Heat the cast

in an oven to 121oC over 30 min. Hold at 121

oC for 2h, then reheat to 177

oC for 30 min. finally

cool it to ambient temperature.

To apply it on a metallic surface, toluene (10% wt) and xylene (10% wt) with a curing agent is

employed. Then its left to dry for 30 minutes. The present coating provide resistance from

corrosion, wear and scratches [11]

Silica nano particles coatings:

Silica nano particles SiO2 and Zn and Fe2O3 in conjunction with the epoxy resin and corrosion

inhibitors to provides excellent corrosion and scratch resistance properties. Epoxy provides the

vital properties like chemical resistance, insulation, adhesion to heterogeneous materials. While

silica nano particles can fill cavities and cause crack bridging [17]

To prepare the coating, all nano particles have to disperse so they dont aggregate. Various

solvents like water, polar solvents, and even acrylate monomers are used to prepare stable

dispersions of nano particles.

Epoxy composites are prepared by dispersing nanoparticles by heating process may cause

agglomeration but solvent gives excellent dispersal of particles in resin, but the curing agents are

added to improve the dispersion in coating.

Particles about 1 wt % of the total weight of resin and curing agent, were added to the acetone-

resin solution, stirred up to 1550 rpm (Model 14-503, Fisher Scientific Inc) and sonication for

10 min. curing agent- acetone solution was added to the mixture followed by stirring and

sonication for 10 min. The substrate which has to coat is dipped in the final mixture and kept in a

dry place at room temperature to allow full cure [17].

Common methods to produce composites


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For thermoplastic matrix

1- Injection molding 2- thermoforming 3- GMT sheet Molding 4- Rotational Molding[19]

For thermosetting matrix

1- Hand lay up 2- spray up 3- compression molding with prepeg 4- injection compressionmolding 5- Reaction injection molding (RIM) 6- Structural reaction injection molding

(S-RIM) 7- Resin transfer molding (RTM) 8- Pultrusion 9- Filament winding [19]

We shall discuss the few techniques in detail, which are widely used in automotive industry.

Compression Molding

Glass mate thermoplastic composites GMTs either chopped or continuous are processed by this

technique.

The GMTs are heated by three zone infrared heaters to achieve uniform heating. After heating,

the GMTs are transferred to the matched steel tool, maintained typically 100oC below the

melting temperature. Pressure is applied by a

hydraulic press and glass fibers are forced into

the flowing matrix, the tool is cooled and the

matrix is consolidated. The flash is removed and

article is ejected from tool. [22]

Stamp forming process

Stamp forming process is used for continuous long fibers, a pre-consolidated flat laminate is

heated above its melting point of thermoplastic matrix, is quickly transferred to a mold, where it

is stamped to conform to the mould geometry [20]

In fact, a stamp forming process, as schematically illustrated in Fig. is used to produce the

automotive sporting car seats. Thermoforming process brings the sandwich into the sheet shape,

with welding the edges of open sheet together. [21]


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An optimized joining between the sheet faces at end tails is necessary

Resin transfer molding

RTM inovolves the interaction between the polymeric resin in liquid phase and fiber porous

medium at a number of different length scale. [24]

Used for large and complex shape composites. Its low pressure < 5 atm and low temperature

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117638104 Composites for Automobiles