Week 3-1

General Properties of Metals

Outline
General Properties of Metals
Cast irons
Cast steels
Wrought steels
Steel numbering system
Steel alloys
Aluminum alloys
Other alloys
Outline
General Properties of Metals
Nonmetals general properties
Materials Selection
Product Analysis
Case Study
Materials Selection Charts
Bigger Picture
Case Study (2)

Learning Outcome
Purpose : Material selection
Resources:
Appendix A: Mechanical property data
Figure 2-17 :Young’s module
Material manufacturers handbook
Learning Outcome
General Properties of Metals

Cast irons
Advantages: relatively low cost and ease of fabrication
Density is slight higher than steel
Week in tension, high compressive strength
Carbon content 2-4.5% Not easily welded
White cast iron
With no graphite.
Gray cast iron
Most commonly used form of cast iron. (Graphite: helps machining and casting)
Cast irons
General Properties of Metals

Cast steels
Has much less carbon than cast iron
Mechanical properties superior to cast iron but inferior to wrought steel
Classes
Low carbon: <0.2%
Medium carbon: 0.2-0.5%
High carbon: >0.5%
Cast Steels
General Properties of Metals

Wrought steels
“Wrought” refers to all processes that manipulate the shape of the material without melting it.
Hot-rolled steel
Change the shape at elevated temperature, rough surface
Good choice for steel members used for building and machine frame construction
Cold-rolled steel
Changing shape at room temperature
Very good polished surface
Sheets, strips, plates, round and rectangular bars, tubes, etc.
Wrought Steels
General Properties of Metals

Steel numbering system
Steel numbering system
General Properties of Metals

Steel alloys
Steel alloys
General Properties of Metals

Aluminum alloys
Aluminum is the most widely used nonferrous metal.
Low density, good strength-to-weight ratio, ductility, high conductivity, corrosion resistance and reasonable price are its main properties.
Alloys have significantly greater strength, and extensively used in aircraft and automotive industries.
Aluminum alloys
General Properties of Metals

Aluminum alloys
Aluminum alloys
General Properties of Metals

Other alloys
Titanium alloys are among the newest of engineering materials.
Magnesium alloys are lightest of the commercial metals but is relatively weak.
Pure copper is soft, weak and malleable and is used primarily for piping, flashing, electrical conductors and motors.
Other alloys
General Properties of Metals

Nonmetals general properties
Polymers
Thermoplastic and thermosets
Ceramics
Compounds of metallic and non-metallic elements.
Composites
Combination of strong, fibrous material such as glass or carbon fibers glued in a matrix of resin such as epoxy or polyester.
Nonmetals
General Properties of Metals

Materials Selection: Decisions, decisions!
So many materials, so much information.
How do we decide?
How do we begin to choose?
First we need to look at the function of the product – product analysis
Decisions
Materials Selection

Product Analysis
Just what it says – analyse the product!
What does it do?
How does it do it?
Where does it do it?
Who uses it?
What should it cost?
Product Analysis
Materials Selection

Case Study – a bike
What is the function of a bike – obvious?
How does the function depend on the type of bike?
Racing
Touring
Mountain bike
Commuter
Childs
Case Study
Materials Selection

Bike Frame
Case Study
Materials Selection

Frame Design Detail
Case Study
Materials Selection

Case Study – a bike
How is it made to be easily maintained?
What should it look like (colours etc.)?
What should it cost?
How has it been made comfortable to ride?
How do the mechanical parts work and interact?
Case Study
Materials Selection

System Analysis – the bike
When we analyse a system we need to break the system down into individual components and then analyse each one.
The bike breaks down into various parts:
Frame
Forks
Wheels
Saddle
Etc.
Case Study
Materials Selection

System Analysis – the bike
We now need to look at the following for each part:
Requirements (mechanical, ergonomic, aesthetic etc.)
Function
How many are going to be made?
What manufacturing methods are we going to use?
Case Study
Materials Selection

Manufacturing
Oh No!
We have to actually make it!
This is a key question which has a massive influence on materials selection.
e.g. The frame, what materials could we use?
Manufacturing
Materials Selection

Frame Materials
Steel –
Strong, stiff, heavy, but cheap
Aluminium –
weaker, lighter, more expensive than steel
Composite–
strong, stiff, very light, but expensive to buy and to fabricate
Case Study
Materials Selection

What Properties?
Mechanical –
Strength, modulus etc.
Physical –
Density, melting point.
Electrical –
Conductivity, resistivity.
Aesthetic –
Appearance, texture, colour
Process ability –
Ductility, mould ability
And last, but not least………important.
Cost, cost, cost!
What Properties?
Materials Selection

Where do I find the data?
Textbooks
Databooks
Manufacturer’s literature
Internet Sites
Where to find?
Materials Selection

Textbooks
Good for general information.
Some have tables of properties.
Not good for detailed specifications and properties.
A useful first point of call.
Textbooks
Where to find?

Databooks
One of the quickest sources of detailed information.
Usually contain grades and specifications as well as properties.
Small and perfectly formed – pocketbooks
Easy to navigate around.
Databooks
Where to find?

Manufacturer’s literature
Variable in quality and usefulness.
Often only cover their products.
Usually do not compare materials.
Can be subjective.
Good for final selection before ordering.
Manufacturer’s literature
Where to find?

Internet Sites
Lots of poorly presented information.
Google searches bring up lots of rubbish.
Hard to find technical information.
Best to use non-commercial sites.
Internet Sites
Where to find?

Materials Selection Charts
Charts
Materials Selection

Materials Selection Charts
Charts
Materials Selection

Materials Selection Charts
Charts
Materials Selection

Modulus - Density Chart
Modulus spans 5 orders of magnitude.
0.01 GPa for foams to 1000 GPa for diamond.
The charts therefore use logarithmic scales, where twice the distance means ten times.
This makes it possible to show the full range on one chart.
Charts
Materials Selection

Materials Selection Charts
Allow easy visualisation of properties.
Show lots of different materials.
Can be ‘drilled down’ to specifics.
Show balances of properties.
Ideal for a first ‘rough cut’ selection.
Charts
Materials Selection

Bigger Picture
Is the product performance driven or cost driven?
This makes a huge difference when choosing materials.
Bigger Picture
Materials Selection

Manufacturing Process
Although we usually choose materials first sometimes it is the shape and process which is the limiting factor.
Manufacturing Process
Materials Selection

Case Study (2) Drink Container
What are the requirements?
Case Study (2)
Materials Selection

Case Study (2) Drink Container
Provide leak free environment for storing liquid.
Comply with food standards & protect liquid from health hazards.
For fizzy drinks, withstand pressure.
Brand image & identity
Easy to open
Easy to store & transport
Cheap for high volumes
Case Study (2)
Materials Selection