Selection of Materials

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