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Requirements for Automotive
Body Materials
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Summary of Requirements of Body Materials
1. Performance Factors (strength, stiffness, ductility, toughness,
impact properties, density)
2. Manufacturing Factors (ease of formability, joinability and
surface finishing, volume of production)
3. Cost Factors (raw materials costs, manufacturing costs, cost of
change, in-service costs, end-of-life costs)4. In-service Factors (ease of repair, availability of repair sites,
corrosion resistance, fatigue resistance)
5. Environmental Factors (resource availability, pollution during
primary and secondary processing, recyclability, end-of-life
disposal)
6. Miscellaneous Factors (legislation, fashion, customer
perception, etc.)
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Comparison of Tensile Properties
210 210
70
45
121.5
300
450
300
240
70
40
0
50
100
150
200
250
300
350
400
450
500
MildSteel(DC05)
HighStrengthSteel
(HSLA350)
AlalloyAA6111
MgAlloyAZ91
SMC(polyester-
25%glass)
Polypropylene
(PP)
Youngs Modulus, E (GN/m3)
Tensile Strength, TS (MN/m3)
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4
7.8 7.8
2.7
1.8 1.8
0.9
0
1
2
3
4
5
6
7
8
9
MildSteel
(DC05)
HSLA350
AlalloyAA6111
MgAlloyAZ91
SMC(polyester-
25%
glass)
Polypropylene
(PP)
Den
sity,r
(g/cm3)
Comparison of Density
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5
27 27 26 25
72
40
60
110
130
4045
0
20
40
60
80
100
120
140
M
ildSteel(DC05)
HighStrengthSteel
(HSLA350)
AlalloyAA6111
MgAlloyAZ91
S
MC(polyester-
25%glass)
Polypropylene
(PP)
Specific Modulus (E/ )
Specific Strength (TS/ )
Comparison of Specific Tensile Properties
r
r
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6
690810 800
15
3440
3030
11201010
3830
2140
1840
0
500
1000
1500
2000
2500
3000
3500
4000
4500
MildSteel(DC05)
CoatedDC05
HighStrengthSteel
SteelScrap
6XXXAlalloy
5XXXAlalloy
Alalloysegregated
scrap
Alalloynon-
segregatedscrap
Mgcastingalloy
SMC(glass-
polyester) P
P
Price(/tonne)
Approximate Costs of Automotive Body Alloys
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0
10
20
30
40
50
60
70
80
90
100
Mild Steel
(DC05)
Hot Dip
Galvanised
DC05
5XXX
Al Alloy
6XXX
Al Alloy
AZ91C
Mg Alloy
AZ91E
Mg Alloy
(purer)
Relative Corrosion Performance
Approximate Relative Rates of Corrosion
in Automotive Metals (Mild Steel = 100)
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Materials Trends
0
10
20
30
40
50
60
70
80
1975 1980 1985 1990 2000 2005
C
ontributiontoVeh
icleWeight(%)
Steel
Elastomers
Plastics
Aluminium
Other
Materials
used inGerman
Passenger
Cars
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Why Steel?
Readily available
Relatively cheap Excellent combination of strength, stiffness and ductility
Good sheet formability
Clear fatigue limit
Joining technology is well known Finishing technology is well known
Design with steel is well known
Why not Steel?
High density
Poor corrosion resistance
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Types of Automotive Steels
Mild Steel:
Cold Rolled, Low Carbon Steel Hot Rolled, Low Carbon Steel
High Strength Steels:
High Strength, Low Alloy (HSLA) or Microalloyed Steel Dent Resistant Steels (Bake Hardening steel,
Rephosphorised Steel)
Dual Phase (DP) and Complex Phase (CP) Steel
Martensitic Steel
Transformation-Induced Plasticity (TRIP) Steel
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High Formability
Mild Steel (DC06)
Complex Phase Steel (CP900)
Microalloyed Steel (H 350 LA)
200
400
600
800
1000
1200
TrueStress,s(
MPa)
Hot Rolled Mild
Steel (DD11)
Bake HardenableSteel (H 260 BD)
Dual Phase Steel (H 300 X)
Martensitic Steel (MS 1100)
TRIP Steel (TRIP 700)
Properties of Automotive Steels
(before bake)(after bake)
0.05 0.10 0.15 0.20 0.25
True Strain, e or
0.30
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0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
HRMildSteel
DC05
BakeHardened
Rephosphorised
HSLA
DualPhase
TRIP
Martensitic
RelativeCos
t(DC05=1)
Relative Costs of Automotive Steels
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10
20
30
40
50
200 300 400 500 600 700 800
Elongation(%)
Tensile Strength (MPa)
Relationship between Ductility and
Strength in Automotive Steels
900 1000
Direction
of development
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Typical Modern Useage of High Strength Steels
MS
MS
MS
MS
MS
MS
MS
MS
MS
BH BH
BH
(iso)
MS
IFMS
IF
IF
B256 (New Fiesta) - 45% HSS, 55% MS(MS = Mild Steel, IF = Interstitial-Free Steel, BH = Bake Hardening Steel)
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Why Aluminium Alloys? Readily available
Low density (2700 kg/m3, cf. 7800kg/m3 for steel)
High specific strength (strength:weight ratio)
High specific stiffness (when thickness effect taken into account)
Corrosion resistant (but.)
Recyclable (but.)
Finishing technology is well known
Why not Aluminium Alloys? Expensive (~2000/tonne, cf. ~400/tonne for mild uncoated steel)
Limited formability Design with Aluminium is less well understood
No fatigue limit
Different joining technologies need to be employed
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Principal Aluminium Alloys
Aluminium Association (AA) grades:1XXX >99%Al
2XXX Al-Cu Past use in US, for closures
3XXX Al-Mn4XXX Al-Si Castings (4XX)
5XXX Al-Mg Structural sheet & extrusions
6XXX Al-Mg-Si Skin sheet & extrusions
7XXX Al-Zn Skin sheet & extrusions
8XXX Al-X
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Design ImplicationsBody-in White (BIW) options:
Monocoque
Spaceframe
Hybrid
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COMPOSITES
DEFINITION: A UNIFIED COMBINATION OF TWO
OR MORE PHYSICALLY DISTINCT AND
MECHANICALLY SEPARABLE MATERIALSPROVIDING A COMBINATION OF PROPERTIES
THAT CANNOT BE ACHIEVED IN THE ORIGINAL
CONSTITUENTS.
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NOTE THAT THEY WOULDNORMALLY BE USED IN LOW-
VOLUME CAR PRODUCTION
(
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REINFORCED POLYMERS
FOR AUTOMOTIVE BODY
APPLICATIONS? VERY LOW DENSITY MAKING CARS FASTER AND
FUEL EFFICIENT
HIGH STRENGTH AND HIGH STRENGTH TO
WEIGHT RATIO CAN BE ACHIEVED
LOW-COST MOULDS CAN BE MADE
PROCESS SKILLS LEVELS CAN BE LEARNTQUICKLY
DIIFFERENT TYPES OF FIBRES ARE AVAILABLE
(KEVLAR, CARBON, GLASS) GIVING DIFFERENT
PROPERTIES
Wh t t i l ti i t t i
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What material properties are important in
choosing frame material? First, there are three
types of material properties:
Physical - Density, color, electrical conductivity, magnetic
permeability, and thermal expansion.
Mechanical - Elongation, fatigue limit, hardness, stiffness, shear
strength, tensile strength, and toughness.
Chemical - Reactivity, corrosion resistance, electrochemical
potential, irradiation resistance, resistance to acids, resistance to
alkalis, and solubility.
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Chassis Materials
STEEL ALUMINUM
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Titanium
Titanium has an association with space tech, and isregarded by many people as an "ultimate" material.
It has a density roughly half that of steel, and also a
little over half the stiffness value. It's a similar
situation with regards to ultimate and yieldstrengths.
Only alloynot raw
MAGNESIUM
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MAGNESIUM
Magnesium is the lightest metal that's likely to beused in a vehicle chassis, with a density about
quarter that of steel. This weight advantage helps to
compensate for the fact that it's strength and rigidity
is below even aluminium, and with careful design canbe used to build a light, stiff structure.
Currently, the use of magnesium in vehicles is
generally restricted to cast shapes for mountingbrackets, braces and so on, though several
manufacturers are working on using magnesium
sheet and extruded sections where possible.
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fibreglass
Raw plastics do not have anywhere near enough stiffness to beused for structural components in cars. If strands of glass are
added to the mixture, though, their properties improve
remarkably. This gives you a Glass Fibre Reinforced Plastic
(GFRP or GRP), most commonly referred to as fibreglass.
Traditionally, fibreglass has been used for specialist applications
like sports cars most of all, and is often used in conjunction with a
separate chassis or subframes rather than alone. Even if a
bodyshell is made to be a stand-alone fibreglass structure, metal
inserts are still usually used to spread the load at mounting pointsetc.
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CARBON FIBRE:
Carbon Fibre Reinforced Plastic The key to this is that, unlike fibreglass, where the
strands are pretty much random, carbon fibre uses a
woven matt of fibres - this is what gives it it's
distinctive appearance.
use of carbon fibre tends to be restricted to large,
reasonably flat panels (such as roof panels and
bonnets), where the best "bang for buck" weightsavings can be found.