Vehicle Body MaterialsVehicle Body Materials - Plastics & Composites

Department of Automobile Engineering

T.Veeramahantesh Swamy

Professor & HOD

Plastics

� Polymerization

� Thermoplastics and Thermosetting Plastics

� Amorphous and Crystalline Plastics

� Future of Plastics in the automotive industry

� GRP (Composite materials)

Plastics - polymerization

� Term plastics in the broadest sense encompasses

� Organic materials, which are based on� Polymers, which are produced by� The conversion of natural products or by synthesis from

primary chemicals coming from oil, natural gas and coal.

� Basic building blocks of plastics are monomers/polymers.

� To get advantage two different plastics, two different monomers can be combined in a copolymer. Different property plastics can be achieved.

Plastics….

� The properties of plastics can also be enhanced by mixing in other materials, such as graphite or molybdenum disulphide (for lubrication), glass fiber or carbon fiber (for stiffness), plasticizers (to increase flexibility) and a range of other additives (to make them resistant to heat and light).

Few Plastics Properties

7-12

17-85

55-56

35

Comp. Strength MN/sq.m

10-25

17-58

52-54

32-35

Tensile strength MN/sq.m

200-4503500-4800

56-851.16-1.35

PVC

10-1401380-3400

850.99-1.10

ABS

180-4001250-1300

1851.04Nylon 11

20-300900-1400

100-120

0.9Polypropelene

.Elongation %

Mod. of Elasticity MN/sq.m

Melting Point

Density kg/ cu.m.

Thermoplastics and Thermosetting Plastics

� The simplest way of classifying plastics is by their reaction to heat.

� Thermoplastics: materials soften to become plastic when heated, no chemical change taking place during the process. When cooled they again become hard and will assume any shape into which they were moulded when soft.

� Thermosetting: materials, as the name implies, will soften only once. During heating a chemical change takes place and the material cures; thereafter the only effect of heating is to char or burn the material.

Classification based on performance

Amino resinsPolyurethane foamPolyvinyl chloride

Diallyl phthalatePolycarbonatesABS (acrylonitrile butadiene styrene)

Alkyd resinsPolyphenylene sulphide

SAN (styrene/ acrylonitrile copolymer)

Unsaturated polyesters

PolyacetalsPolystyrene

Epoxy resinsPolyamidesPolypropylene

PhenolicPolyesters (thermoplastics)

Polyethylene

Thermosetting plastics

Engineering thermoplastics

General Purpose thermoplastics

Amorphous Plastics

Amorphous plastics basically are of three major types;� ABS: acrylonitrile butadiene styrene� PC: polycarbonate� ABS/PC blend

Following are the mechanical properties.� High stiffness� Good impact strength� Temperature resistance� Excellent dimensional stability� Good surface finish� Electrical properties� Flame retardance (when required)� Excellent transparency (polycarbonates only)

Amorphous Plastics

� In the automotive industry use is made of the good mechanical properties, the thermal resistance and the surface finish. The applications are:

1. Body embellishment

2. Interior cladding

3. Lighting where, apart from existing applications of back lamp clusters, polycarbonate is expected to replace glass for head lamp lenses.

Semi-crystalline Plastics

There are two types:� Polyamide 6 to 66 types� Polybutylene terephthalate (PBT)Semi-crystalline plastics have the following

properties:� High rigidity� Hardness� High heat resistance� Impact resistance� Abrasion, chemical and stress crack

resistance.

Semi-crystalline Plastics

� Major applications in automotive sector are:

1. Under bonnet components

2. Mechanical applications

3. Bumpers, using elastomeric PBT for paint online

4. Body embellishment (wheel trims, handles, mirrors)

5. Lighting, headlamp reflectors.

Blended Plastics

� Blended plastics have been developed to overcome inherent specific disadvantages of individual plastics. For large area body panels the automotive industry demands the following properties:

� Temperature resistance

� Low-temperature impact resistance

� Toughness (no splintering)

� Petrol resistance

� Stiffness

Polycarbonate plus Polybutylene terephthalate to form Macroblend PC/PBT which is used for injection moulded bumpers

Plastic applications

Following properties of thermo plastics and thermo setting resins make them find useful applications in automobiles:

� Tough and resistant to occupational impact� Withstand attack by weather and hazards

that reduce older forms of body embellishments to pitted, rusted, dull, crumbling metal.

� Have low tensile strength or flexural strength� They can be pressed, stamped, blow

moulded, vacuum formed and injection moulded.

Plastic applications

Following are applications:� Plastic products can be decorated by vacuum

metallizing and electroplating. They have replaced metals in a lot of automotive applications such as, control knobs and winder handles as well as decorative metallic trim.

� Mechanical properties of acrylic resins are highest among the thermo plastics. Typical values are a tensile strength of 35 – 75 MN/ sq.m. and a modulus of elasticity of 1550 – 3250 MN/ sq.m. These properties apply to relatively short loadings and when long term service is expected tensile strength of acrylics must be limited to 10MN/sq.m. to avoid surface cracking.

� Particular advantage of plastics is they are completely stable with petroleum products and salts.

Plastic applications

� Acetal resins are mostly used for mechanical parts like cams, sprockets and small leaf springs but also find application for housings, cover plates, knobs and levers.

� Have highest fatigue endurance, coupled with reduced friction and noise admirably qualify (acetal resins) for small gearing applications within the vehicle.

� Plastics can be self-coloured so that painting costs are eliminated and accidental scrataching remains inconspicuous and they can be given a simulated metal finish.

� Plastics can be chrome plated either over a special under coating which helps to protect and fix the finish or by metal spraying or by vacuum deposition. Coating can be thin and saves cost.

� Polymer materials are joined by adhesives. But now thermo plastics can now be welded by hot gas welding.

� COMPOSITE MATERIALS

Glass Reinforced Plastics (GRP)

� Glass-reinforced plastic (GRP), also known as glass fiber-reinforced plastic (GFRP),is a composite materialmade of a plastic (resin) matrix reinforced by fine fibersmade of glass.

� Reinforcement can range between almost particle shaped chopped-stands to woven mats akin to those used in laminates.

� The plastic matrix may be epoxy, a thermosetting plastic(most often polyester or vinylester) or thermoplastic

� The glass reinforcement can be extremely strong , depending on conditions; for example a single filament drawn to about 12 microns has an ultimate tensile stress of 3.5GN/sq.m.

� GRP is a lightweight, strong material with very many uses, including boats, automobiles, water tanks, roofing, pipes and cladding.

Typical GRP mix

A typical GRP mix for heavy duty automotive use is:

� Glass fibre 40.0

� Resin 40.0

� Monomer 0.41

� Filler 16.5

� Lubricant 0.08 and

� Preform binder 2.0 in %.

Mechanical properties for such a mix are

� Tensile strength 165kN/sq.m.

� Elastic modulus 9.6 MN/sq.m.

� Shear strength 110kN/sq.m.

Production

� The manufacturing process for GRP fiber glass uses large furnaces to gradually melt the sand/chemical mix to liquid form, then extrude it through bundles of very small orifices (typically 17-25 micrometres in diameter for E-Glass, 9 micrometres for S-Glass). These filaments are then sizedwith a chemical solution. The individual filaments are now bundled together in large numbers to provide a roving. The diameter of the filaments, as well as the number of filaments in the roving determine its weight.

� This is typically expressed in yield-yards per pound (how many yards of fiber in one pound of material, thus a smaller number means a heavier roving, example of standard yields are 225yield, 450yield, 675yield) or in tex-grams per km (how many grams 1 km of roving weighs, this is inverted from yield, thus a smaller number means a lighter roving, examples of standard tex are 750tex, 1100tex, 2200tex).

Manufacturing techniques

� Pultrusion Process (Continuous manufacturing)

� 1 – Continuous roll of reinforced fibers/woven fiber mat2 - Tension roller3 - Resin bath4 - Resin soaked fiber5 - Die and heat source6 - Pull mechanism7 - Finished hardened fiber reinforced polymer

�Hand / Spray lay up

Design considerations

� Thin walls are desirable in press moulding for reducing cure time. Thickness should be in the range of 7.6<t<6.35mm for sheet.

� Design approach is to integrate parts into as small a number of individual moldings as possible so as to save fabrication cost and avoid stress concentration.

� Double curvature should be used wherever possible to increase stiffness.

� Local strength and stiffness to be increased by molding in ribs.

� Recommended safety factors in design are:� Short term static 2, Long term static 2, Variable

unidirectional 4, Repeated 5, Reversed & alternating 5, Impact loads 10.

GRP Properties

821.02.0E-glass/epoxy

2101.07.8Steel

551.797.0S-glass/epoxy

1131.591.5A-S/epoxy

760.472.8Aluminium

Tensile Modulus GPa

Tensile Strength GPa

Sp.GrMaterial

1747 VW Lupo Rear bumper X-Type

� VOLKSWAGEN LUPO Rear Bumper Version RS1.

� Designed exclusively for Volkswagen Lupo model. Made to the Highest UK standards of GRP Glass fibre Reinforced Plastic known for its flexibility, strength and light weight. Easy to fit.

Modulus of Elasticity (E).

� An important property of many structural materials is their ability to regain their original shape after a load is removed. These materials are called elastic. Steel, glass and rubber are elastic; putty or modeling clay are not elastic. Each of these materials is elastic to varying degrees; steel and glass are both more elastic than rubber.

� The degree of elasticity, or "stiffness" of a material is called its Modulus of Elasticity (E). Given the modulus of elasticity, possible deformations can be calculated for any material and loading.

� The Modulus of Elasticity is represented by E = Stress / Strain. � This relationship is found as the slope of the curve of the stress-

strain curve from initial loading to the proportional limit. � A higher value of the modulus indicates a more brittle material

(i.e. glass, ceramics). A very low value represents a ductile material (i.e. rubber).