Seminar on

Materials for automotive structures

Contents

Introduction Steel Plastics Polymer composites Magnesium Plant fiber Aluminium and its alloys Conclusion References

Introduction In this study we are going to discuss about the

materials selection for automotive structural applications, particularly in cars. There are many materials which are suitable for automotive structural applications like steel, aluminium and its alloys, magnesium, plastics, polymer composites, natural fibers, etc.

Steel Nitrogenized low carbon steel(bake-hardened ) - YS- 415 to480 MPa.

Interstial-free (IF) steels - Press formability, high strength and damage

resistance. - Additives- Phosphorus and manganese.

Rephosphorized (0.07-0.12P) low carbon steels - YS- 275to345 MPa. - Formability not good but spring back is good.

High-strength steel (HSS) - YS - 210 MPa to 550 MPa. - Cost as much as 50% more than traditional mild steels - Laser welding, hydro forming, and tailored blanks.

1. High strength low alloy steels (HSLA) - 0.15C-1.3Mn. - YS-300-600 MPa. - Spring back is good.

2. Dual phase low alloy steels (DPLA) - YS-(300-350 MPa) - Additives-manganese and silicon. - Due to work hardening, YS upto 500 MPa is obtained.

3. Ultra-high-strength steel (UHSS) - YS - 550 MPa. -Sandwich steel which is made from a

thermoplastic(polypropylene) core. -Up to 36% lighter and 50% stiffer.

Steel Monocoque chassisAdvantages: -Cheaper.-Inherently good crash protection.- Space efficient.Disadvantage: - Heavy.-Impossible for mass production.

Ultra light steel auto body (ULSAB) MonocoqueAdvantage: Stronger and lighter compared to conventional Monocoque without increasing mfg. cost.Disadvantage: Still not strong or light enough for the best sports cars.

Surface treatment of steel

Phosphate film (primer) applied after welding.

Electro painting  - Car(cathode) and electrolyte(anode).

Elecrolytically deposited zinc(ex. - zinc-aluminum silicon baths).

 

PlasticsAccount for about 10% of the weight of the typical

family car.Large proportion of the plastics used are polyolefins.polyolefins (i.e. polypropylene and polyethylene) and

plastic foams applications are - chrome-plated interior trim - heating ducts - fuel tanks - bumpers and battery trays Plastic body panels - Resist corrosion. - Have a high quality surface finish. - Better resistance to stone chipping than steel.

Polymer composites Reaction injection moulding (RIM) - Polyurethane and polyurea. - Mould shrinkage is much reduced. - Lower product cost. - Better dent resistance Resin transfer moulding (RTM) - Polyester and vinyl ester Sheet moulding compound (SMC) - 25 to 40 wt% chopped glass fibers in a

polyester matrix. - Greater stiffness. Thermoplastic Olefin( TPO) nanocomposites

Carbon fiber

Carbon fiber Monocoque Chassis Advantage: - Superior stiffness yet lighter weight. Disadvantage: -Engine’s vibration is directly transferred

to body and cockpit. - By far the most expensive. Used in McLaren F1 (1933), Ferrari F50

(1996), Lamborghini Diablo GT (1999) and most of today’s sport cars.

Applications of carbon fiber

Magnesium Why Magnesium? - Magnesium is abundant. Sea

water contains 0.13% Mg. - Mg is 36% lighter per unit

volume than Al and 78% lighter than iron (Fe).

- Highest strength-to-weight ratio .

- Better casting properties. - High part integration. - Recyclable.

Mg is used in car doors, instrument panels, roof rails etc

Alloy AM60 - Used especially for

doors. - 40% weight reduction. - High strain rate

increase YS and ductility, beneficial for impact.

- Properties of AM60 remain almost constant from - 40°C to 80°C.

Body Chassis

a)Unibody and closuresb)Glass hardwareExterior and interior trim bodyc)Electrical seatsd)doorse)Instrument panel

a)Suspension b)steeringc)Systemd)Bumper systeme)Brake systemf)Sub framesg)Fuel storage h)systemi)Chassis j)Electricalsk)Exhaust systeml)Wheels and tires

Plant fibers

Classification of plant fibers

Flax/sisal fiber with epoxy resin matrix is used for door panels .

Trim parts in Brazilian trucks, made of a mixture of jute, coffee bag wastes and polypropylene bags.

Coconut fibers bonded with natural latex used for seat cushions.

Manufacturing processes

Compression Molding of – Resinated plant fiber mats – Plant fiber/PP hybrid mats – NMT (Natural fiber mat reinforced

thermoplastics) comparable to GMT(Glass fiber mat. Reinforced thermoplastics).

– EXPRESS process (extrusion-compression molding)

Structural reaction injection molding (S-RIM). Injection molding with short fiber

reinforcement. 

Properties of plant fiber

Fig. : Bending test

Fig. : Tensile strength versus impact behavior

Plant fibers are processable below 230°C.

Best results were achieved with thermoset binders.

Till now mostly limited to interiors.

15% lesser in wt. then glass fiber.

Aluminium and its alloys  Density- 2700Kg/m3

0.8mm thick steel sheet is replaced by 1.2mm thick Al sheet.

50% wt. saving. Corrosion resistance. Easy to recycle- 1/5th of original energy is

sufficient. Welding(TIG, MIG, Spot) and adhesive

bonding are means for joining. Chassis- Unitary construction and Space

frame construction.

Figure above: The unitary construction of the Ford aluminium intensive vehicle. (Courtesy of the Aluminium Extruders Association).

Figure below : Space frame chassis of Audi A8.

A1- Mg 5xxx wrought alloy series - Work-hardened , non-heat-treatable alloys. - Ex.:- 5251, 5754 6xxx (A1-Mg-Si) alloys series. - Bake hardened, heat treatable alloys. - Strength, formability and corrosion

resistance properties are good. - Dent resistance. - Ex.:- 6009 (A1-1.1 Si-0.6Mg-0.35Mn) 6010 (A1-1.1 Si-0.8Mg-0.50Mn-0.4Cu)

TABLE : Typical mechanical properties of some body sheet alloys: Polmear 8 from Starke 9 and Davies and Goodyed.

Secondary weight savings - Powertrain, brakes, fuel tank, crash management systems etc.

Aluminium used in new European cars has risen from 50kg in 1990 to 132kg in 2005 and is predicted to grow by another 25kg by 2010.

Primary weight savings -

 

Advantages of aluminium Crash design is complex -High mass-specific energy

absorption. - 50% thicker sections. - High quality die casted

structure. Handling - Reducing body wt. lowers the

centre of gravity. Fuel efficiency -100 kg mass reduction

achieved on a car avoids 9 grams of CO2 per km at the exhaust pipe.

Conclusion

So far we discussed how automotive industry is working on reducing the cost of other automotives (cars), in particular in the body structure and for chassis, presently used in sport and luxury cars, so that they can also find their place in smaller cars.

In the future there is no doubt that existing trends to increased reinforced polymer use from bumpers to bonnets will continue, extending to most bolt-on assemblies. Certainly the dominance of steel in the automotive industry is being challenged by plastics and aluminium. In the longer term aluminium alloy or high strength composite spaceframe structures may be the key for selection.

References

Selection and use of engineering by J A Charles, F A A Crane and J A G Furness (1997).

Automotive Application of Natural Fibers Composite by Gayer U. and Schuh. Th. (1996). Automotive Materials: Technology Trends and Challenges in the 21st Century by Alan I.Taub - MRS bulletin. Volume 31.April 2006.

European aluminium association websites i) www.aluminium.org ii) www.alucars.org Wikipedia 

Carbon fiber composite body Structures for the 2003 Dodge Viper by Mark Bruderick, Douglas Denton and Michael Shinedling, DaimlerChrysler Corporation and Michael Kiesel, Quantum Composites Inc.

Steel and Iron Technologies for Automotive Light weighting by John M. DeCicco, Environmental Defense, March 3, 2005.

Potential Automotive Uses of Wrought Magnesium Alloys by L. Gaines, R. Cuenca, F. Stodolsky,(1) and S. Wu(2) - Argonne National Laboratory Transportation Technology R&D Center 9700 S. Cass Avenue Argonne, IL 60439.

Website- http://www.autozine.org/technical_school/chassis/tech_chassis.htm

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