AMIF2014 – [Automotive] Pankaj Mallick, Materiali attuali e futuri per automobili leggere

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Current and Future Materials for Lightweight Automobiles

Dr. P.K. MallickWilliam E. Stirton Professor of Mechanical EngineeringDirector, Center for Lighweighting Automotive Materials and Processing

University of Michigan-DearbornDearborn, MI 48128

[email protected]

Challenges for the Automotive Industry

Fuel Consumption Greenhouse Gas (GHG) Emission Safety Performance

Power (Acceleration) Comfort (Size, NVH, Ride Quality, etc.) Functionality Entertainment

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CAFE

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• CAFE standards for passenger cars:• Started with 18 mpg in 1978• 33.5 mpg in 2013• 35.5 mpg by 2016• 54.5 mpg by 2025

• Corporate Average Fuel Economy (CAFE) – mandatory minimum fuel economy standards for all cars and light trucks manufactured in USA

• Automobile companies pay penalty if they do not meet the fleet average CAFÉ standard.

CAFE Standard

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CAFE – Fleet Performance

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Global CO2 Emission (1900-2010)

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Sources of CO2 Emission (2010)

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Technological Trends for Future Automobiles Green Automobiles

Increase fuel economy Reduce pollution Reduce greenhouse gas effect Improve life-cycle value

Design Challenges Improved powertrain design Energy alternatives (EV, Hybrids, Fuel Cell, etc.) Vehicle weight reduction Reduce frictional and other losses Improved aerodynamic design Reduced tire rolling resistance

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Role of Advanced Materials

Provide required performance, safety and comfort

Reduce vehicle weight Reduce energy consumption in

production and manufacturing Reduce resource depletion Reduce effect on environmental

emissions

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Materials Scenario Steels

Mild Steels, High Strength Steels, Advanced High Strength Steels

Aluminum Alloys Magnesium Alloys Composites

CFRP, GFRP

Materials in US Automobiles

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Materials

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Materials

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Material % of Vehicle Weight

Major Application Areas

Steel 55 Body structure, body panels, engine and transmission components, suspension components, driveline components

Cast Iron 9 Engine components, brakes, suspension components

Aluminum Alloys 8.5 Engine block, wheels, radiator

Copper Alloys 1.5 Wiring, electrical components, radiator

Polymers (Plastics ) and Polymer Matrix Composites

9 Interior components, electrical and electronic components, fuel line components

Elastomers 4 Tires, trims, gaskets

Glass 3 Windshield, windows

Others 10 Fluids, lubricants, etc.

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Steels Advantages

High modulus (207 GPa) Wide range of strength depending on the type of

steel (up to 1500 MPa) High to excellent formability Good to excellent weldability Highly recyclable Low cost

Disadvantages High density (7.87 g/cm3)

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Steels Mild Steels (MS)

Plain carbon steels Interstitial free steels

High Strength Steels (HSS) Bake-hardenable (BH) steels Solution strengthened steels (SSS) High strength low alloy (HSLA) steels

Advanced High Strength Steels (AHSS) Dual phase (DP) steels Transformation-induced plasticity (TRIP) steels Martensitic steels Boron steels

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Steels

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Steels

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Distribution of MS, HSS and AHSS

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Applications of AHSS

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Applications of AHSS

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2011 Honda CR-Z

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Applications of AHSS

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Challenges for AHSS

Formability Springback

Edge Cracks

Joining – Spot welding is possible with proper adjustments in process parameters

Uniformity in Properties

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Aluminum Alloys

Advantages Low density (2.7 g/cm3 vs. 7.87 g/cm3 for steel) High strength-to-density ratio High thermal conductivity Both casting and wrought alloys are available Highly recyclable, but requires separation by alloy type

Disadvantages Lower modulus than steel’s Lower formability More difficult to weld compared to steel Comparatively higher cost

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Aluminum Alloys

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Aluminum Alloys

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Aluminum Spaceframe

Audi A8 First all aluminum

spaceframe in a production vehicle (1994)

Aluminum extrusions in the spaceframe and aluminum body panels

Self-piercing riveting, spot welding and weld bonding

40% weight saving

Aluminum Spaceframe

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Aluminum Spaceframe

Ford GT (2005) Aluminum Space- frame

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Aluminum Body

2015 Ford F-150 Pickup Truck (in production)

• 6000-series Aluminum Alloy for Body Panels

• Self-Piercing Riveted Joints with and without Adhesives

• Weight Reduction 700 lbs. (1,545 kg)

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Magnesium Alloys

Advantages Low density (1.74 g/cm3 vs. 7.87 g/cm3 for steel) High strength-to-density ratio High damping Casting alloys are highly castable

Disadvantages Comparatively low modulus Corrosion problems Wrought alloys have poor formability at room temperature Difficult to weld High cost

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Magnesium Alloys Front Crossmember

(Z06 Corvette) Engine Block

(Ford Duratec)

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Developments in New Manufacturing and Joining Technologies Tube and Sheet Hydroforming Superplastic Forming Tailor-Welded Blanking High Pressure Die Casting Semi-Solid Casting Laser Welding Friction Stir Welding Friction Stir Spot Welding Self-Piercing Riveting Weld Bonding/Rivet Bonding

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Polymer Matrix Composites

Advantages Very low density (1.2 – 1.6 g/cm3 vs. 7.87 g/cm3 for steel) High strength-to-density ratio High modulus-to-density ratio Design flexibility – can be tailor made per requirement High damping No corrosion

Disadvantages Can be moisture and temperature sensitive Moderate to high cost

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Polymer Matrix Composites

Many options: Fiber

Glass or Carbon Fibers Short or Continuous Fibers Unidirectional, Multi-directional or Random

Matrix Thermoset Polymer (epoxies, polyesters, vinyl

esters) Thermoplastic Polymer (polypropylenes,

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Polymer Matrix Composites (PMC)

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Current PMC used in high volume production automobiles use Glass fibers, not carbon fibers Short or long, not continuous Random, not uni- or multi-directional Thermoset polymers (either polyesters or vinyl

esters) for body panels and components Thermoplastic polymers for semi-structural and

functional components

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Current Use of Polymer Matrix Composites (PMC)

All PMC in current automobiles use E-glass fibers Short Fiber Thermoplastics (SFT)

Interior components, such as instrument panels Functional components, such as gears, switches

Long Fiber Thermoplastics (LFT) Interior components, such as interior door panels

Glass Mat Thermoplastics (GMT) Interior components, such as interior door panels Exterior components, such as bumper beams

Sheet Molding Compounds (SMC) Body panels, both exterior and interior Body components, such as bumper beams

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Potential Applications of PMC in Lightweight Automotive Structure

Body Panels Body Structural Components

Door intrusion beams, Roof rail sections, Cross beams, etc.

Frame and Sub-frame Sections Chassis Components

Control arms, Struts, etc.

Body-in-White Structure

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Carbon Fiber Composites (CFRP)

CFRP has a higher weight saving potential than GFRP.

Status of CFRP in the Auto Industry Has found niche and limited applications in high

performance, low production volume cars Used extensively in motor sports (Formula 1) Currently, there are no applications in high

production volume cars due to High price ($16/kg or higher) Limited availability

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Carbon Fiber Composite Applications:A Few Examples (2004 Model Year)

Vehicle Production Volume

Component

Porsche Carrera GT

1,500 in 3 years

Body panels, structure, engine subframe

BMW M3 CSL 1,000/yr. Roof, front air dam, rear spoiler

Mercedes SLR 500/yr. Body panels and structure

Acura NSX-R <200/yr. Hood, rear spoiler

Corvette Z06 3,000/yr. Hood

Dodge Viper 2,500/yr. Windshield frame, front end structure, door panels

Mazda RX-8 60,000/yr. Driveshaft

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CFRP Applications

BMW M6 Roof Panel

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CFRP Applications Wheel Carrier and Strut

Seat Structure

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CFRP Applications

Front Crush Members (SLR McLaren)

CFRP Applications

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Front Crash Box in Audi

Crushed Crash Box

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Developments Needed for PMC

Develop processing technology for thermoplastic matrix composites

Develop low cost carbon fibers Develop faster curing thermoset resins Develop long-term durability and design

data Develop more accurate design and

processing simulation techniques

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Nanocomposites Reinforcement types

Nanoclay Carbon Nanofibers Carbon Nanotubes

Their modulus and strength are much higher than that of glass and carbon fibers. For example: Modulus of crabon nanotubes is 1,100 GPa compared to 230 GPa for high strength carbon fibers

Only 3-5% (by volume) of nano-reinforcements can produce properties comparable to the ones produced by 30-40% (by volume) of glass or carbon fibers.

Electrical, optical, thermal and diffusion properties are also improved by significant amounts.

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Nanocomposites Examples of Nanoclay composites automotive

applications The first application was the Timing Belt Cover

(Toyota) using 4.2 wt.% nanoclay in nylon6 Engine covers, body side moldings, cargo floors, seat

backs, fuel lines Carbon nanofiber or carbon nanotube

composites are yet to be used in production vehicles Cost Manufacturing issues

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Mass Reduction/Cost Penalty

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SEA and Environmental Factors (Relative Values)

Material Specific Energy Absorption(kJ/kg)

Production Energy (kJ/kg)

CO2

Emission (kg/kg)

DQ 1 1 1

DP 1.25 1.4 1

AA 1.6 8.2 6

CFRP 4 11.5 10

GFRP 2.75 4.8 4

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Concluding Remarks Future lightweight vehicles will contain multiple

structural materials. Steels, especially advanced high strength steels (AHSS),

will continue to be used in safety-related structures Aluminum and CFRP may find greater use in body panels,

body components and chassis components. Cast magnesium and titanium may find increasing use in

engine and powertrain components.

Joining, repair and recycling are the three major issues to overcome in a multi-material vehicle.

Cost and customer acceptance are another major concerns.

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Reference Book Title: “Materials, design and

manufacturing for lightweight vehicles”

Editor: Prof. P. K. Mallick

Publisher: Woodhead Publishing UK

Year: 2010

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Thank you.