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Selection of Materials
Selection of Materials
Light
Cheap
Strong enough to withstand expected forces
Rigid
Durable
What qualities are important in your final product?
Selection of Materials
How can we measure and compare these qualities?
- Rupees per kilogram
- Kg per m3 (Density)
- Maximum Force (N) per m2
- Youngs Modulus
- Toughness
Cost
Light/Heavy?
Strength
Rigid
Durable
How light is my material?
Density is a measure of lightness
Density is the mass per unit volume
Density (kg/m3)
Steel 7900
Wood 800
Water 1000
wood steel
water
Density
Density is the mass per unit volume
Do polythene and PVC float or sink?
Density (kg/m3)
Polythene 960
PVC 1600
Water 1000
Polythene PVC
water
Density Density is the mass per unit volume
I have a mild steel sheet
The density is 7900 kg/m3
1m
2m
0.004 m thick
Volume (m3) = x x1 m 2 m 0.004 m
= 0.008
Mass (kg) = x 0.008 m3 7900 kg/m3
= 63
How rigid is my material?
The ‘Youngs Modulus’ is how we measure stiffness
1 N1 N
Small Youngs Modulus
Low Stiffness
Large Youngs Modulus
High Stiffness
How durable is my material?
During manufacture, materials will get small cracks
These cracks may get bigger very fast, or very slowly
Fatigue crack video
The tougher the material, the slower a small crack turns into a big crack
steel glass
How environmentally friendly is my material?
1) Energy used during manufacture
Often extracting a material can use a lot of energy
For example extracting aluminium requires a temperature of 2000 oC.
This uses up fuel resources, and also large processes need constant supplies of electricity, diverting power away from places such as Pabal.
How environmentally friendly is my material?
2) CO2 produced during manufacture
When we burn fuel/use electricity we release CO2
CO2 contributes to global warming
How environmentally friendly is my material?
3) Recyclability
Force on 1 column = /
Self Weight = 1,4000N
10,3000N 6
= 1,7000 N
Wind Load = 8,9000N
How strong must my material be?
Force (N/m2) = x
Load = 1,7000N
1,7000N 400
x0.0025 m2
How strong must my material be?
Strength is measured in N per square metre
Does this post have a cross section of 1 square metre?
5cm
5cm
Estimate Area Cross Section =
=0.05m0.05m
How many 0.0025 m2’s fit into 1 square metre?
= /
=
1 m2 0.0025 m2
400
The force on 0.0025 m2 is 20,000 N
How much force is on 1 m2 ?1m is 400 times bigger than 0.0025 m2
6,800,000=
Str
eng
th -
Co
st
1
4
2
3
6.8
MP
a
Str
eng
th -
Co
stMaterial Strength-Cost
Cast iron 2
Low carbon steel 2
Medium carbon steel
2
High carbon steel 2
Stainless steel
Aluminium 3
Copper
Wood (along grain) 1
Wood (across grain)
Bamboo 1
PVC 1
Polythene 1
Cement
Concrete
Den
sity
- C
ost
1
4
2
3
Den
sity
- C
ost
Material Strength-Cost
Density-Cost
Cast iron 2 2
Low carbon steel
2 2
Medium carbon steel
2 2
High carbon steel
2 2
Aluminium 3 2
Wood (along grain)
1 1
Bamboo 1 2
PVC 1 1
Polythene 1 2
Str
eng
th -
Den
sity
1
4
2
3
Str
eng
th -
Den
sity
Material Strength-Cost
Density-Cost
Strength-Density
Cast iron 2 2 3
Low carbon steel
2 2 2
Medium carbon steel
2 2 2
High carbon steel
2 2 2
Aluminium 3 2 2
Wood (along grain)
1 1 1
Bamboo 1 2 1
PVC 1 1 1
Polythene 1 2 1
Sti
ffn
ess
- D
ensi
ty
1
4
2
3
Sti
ffn
ess
- D
ensi
tyMaterial Strength
-CostDensity-Cost
Strength-Density
Stiffness-Density
Cast iron 2 2 3 3
Low carbon steel
2 2 2 2
Medium carbon steel
2 2 2 2
High carbon steel
2 2 2 2
Aluminium 3 2 2 1
Wood (along grain)
1 1 1 2
Bamboo 1 2 1 3
PVC 1 1 1
Polythene 1 2 1
To
ug
hn
ess
- D
ensi
ty
1
4
2
3
To
ug
hn
ess
- D
ensi
ty Material Strength-Cost
Density-Cost
Strength-Density
Stiffness-Density
Toughness-Density
Cast iron 2 2 3 3 3
Low carbon steel
2 2 2 2 1
Medium carbon steel
2 2 2 2 2
High carbon steel
2 2 2 2 3
Aluminium 3 2 2 1 1
Wood (along grain)
1 1 1 2 2
Bamboo 3 2 1 3
Price (GBP/kg)0.05 0.1 0.2 0.5 1 2 5
Rec
ycle
False
True
Bamboo
Wood, typical across grain
Wood, typical along grain
Cement
Stainless steel
Copper
Aluminum alloys
Polythene
PVC
High carbon steel
Medium carbon steel
Low carbon steel
Cast iron, gray
Concrete
Price (£/kg)
Rec
ycle
Yes
False
Rec
ycle
- C
ost
1
4
2
3
Rec
ycle
- C
ost
Material Strength-Cost
Density-Cost
Strength-Density
Stiffness-Density
Toughness-Density
Recycle-Cost
Cast iron 2 2 3 3 3 1
Low carbon steel
2 2 2 2 1 1
Medium carbon steel
2 2 2 2 2 1
High carbon steel
2 2 2 2 3 1
Aluminium 3 2 2 1 1 1
Wood (along grain)
1 1 1 2 2
Price (GBP/kg)0.05 0.1 0.2 0.5 1 2 5
Embo
died
ene
rgy,
prim
ary
prod
uctio
n (M
J/kg
)
1
10
100
Wood
Stainless steel
Copper
Aluminum alloys
Polythene
PVC
Medium carbon steel
High carbon steel
Low carbon steel
Cast iron, gray
Bamboo
Cement
Concrete
Price (£/kg)
En
erg
y R
equ
ired
fo
r p
rod
uct
ion
(M
J/kg
)
Pri
ce -
En
erg
y 1
4
2
3
Pri
ce -
En
erg
yMaterial Stren
gth-Cost
Density-Cost
Strength-Density
Stiffness-Density
Toughness-Density
Recycle-Cost
Energy-Cost
Total
Cast iron
2 2 3 3 3 1 1 15
Low carbon steel
2 2 2 2 1 1 2 12
Medium carbon steel
2 2 2 2 2 1 2 13
High carbon steel
2 2 2 2 3 1 2 14
Aluminium
3 2 2 1 1 1 3 13