assignment 1 , bit dull :-) Purely a presentation - internal links don't work!

1. 6505 Assignment 1
Interactive Resource
Anton Taverne
April 6th 2012

2. Introduction
Engineers must make informed decisions about how items can best be constructed.
A thorough understanding of materials is thus an essential part of an Engineering Studies
course, as indicated by the following Course Outcomes.
Table 1: Syllabus Outcomes
P1.2 explains the relationship between properties, structure, uses and applications
of materials in engineering
H1.2 differentiates between the properties and structure of materials and justifies
the selection of materials in engineering applications
P2.1 describes the types of materials, components and processes and explains their
implications for engineering development
H2.1 determines suitable properties, uses and applications of materials, components
and processes in engineering
(Board of Studies 2011 pp 11,12)
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3. Explicit or implied reference to engineering materials appears in all of the modules in the syllabus.
Table 2 Syllabus Content
Relevant modules (Preliminary) (HSC)
Personal and public
Telecommunicatio
Braking systems
Civil structures
ns engineering
fundamentals
Aeronautical
engineering
engineering
Engineering
Engineered
Biomedical
transport
products
Syllabus topics
 classification of materials •
 properties of materials • • • •
 structure of materials • • • •
 metals • • • • • •
 forming processes • • • •
 polymers • • • • •
 ceramics • • • •
 composites • • • •
 modification of materials • • •
 engineering applications of materials • • •
 recyclability of materials • •
 materials for braking systems •
 historical developments of products • •
 construction & processing materials used over time • • •
(Board Of Studies 2011)
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4. About this resource
It contains information about polymers and plain carbon steel, including:
general structure
properties
applications
methods of modifying the structure, and hence the properties
methods of shaping and forming the material into useful products
It combines explanatory material with tables summarizing significant features, giving
students an overview, and links to other resources.
Activities vary from simple identification exercises to questions requiring synthesis of
concepts, encouraging further research, so that the course outcomes are met, and students
can answer the question …..
“What should I use to make this?”
4

5. Polymers
Polymers are long chain molecules consisting of repeating units called monomers.
They are covalent compounds, typically involving a carbon backbone and other non-metal elements.
Carbon has 6 protons in the nucleus and therefore 6 electrons, 2 locked up in the inner shell and 4 in the outer shell
available for forming bonds. The outer shell of carbon can accommodate 8 electrons. Hydrogen has one electron in its
outer shell, which can accommodate 2 electrons. For both atoms to have a stable arrangement of electrons, with full
outer shells, electrons are shared.
Fig 1 Electron Sharing in Covalent Bonds
Surrounding each central carbon atom are 8 electrons – 4 from its own outer shell, 1 from each neighboring
carbon and 1 from each neighboring hydrogen.
(The end carbons have a single electron available for forming a bond with the next available ethylene molecule,
breaking one of its double bonds)
The covalent structure means polymers do not normally conduct electricity.
5

6. Polymers can be classified in different ways.
Table 3 Polymer Classifications
Addition Condensation
Thermosetting Thermoplastic Elastomer
Homopolymers Copolymers
…On to Crystallinity …
6

7. Addition Polymers (1)
Addition polymers are formed when the double bond of each monomer is broken, allowing the monomers to join.
The process of polymerization is typically initiated with a peroxide molecule to break the first bond. The most
common addition polymers are made from ethylene molecules, in which one or more of the original hydrogen atoms
in ethylene have been replaced.
For example: polypropylene is formed from ethylene with a hydrogen atom substituted by a methyl group.
Fig 2 Addition polymerisation
7

8. Addition Polymers (2)
Two of the factors that influence the properties of polymers are branching and substitution.
If the long carbon chains have extensive branching, it is difficult for the branches to get close together. The dispersion
forces that attract molecules to each other are therefore quite weak. For example low density polyethylene (LDPE)
has extensive branching, has a low density and therefore floats in water, and is quite flexible, making it useful for
wrapping. High density polyethylene (HDPE) is much more rigid and does not float readily in water.
Fig 3 Branching
LDPE HDPE
In Polystyrene, there is a large, flat benzene ring with many electrons on each monomer. This allows for much
stronger dispersion forces between the polymer strands, making polystyrene a very hard and rigid polymer.
The Chlorine atoms in Polyvinylchloride makes PVC, used extensively in downpipes and drainage pipes, fire
resistant, rigid and somewhat brittle.
8

9. Condensation Polymers
Condensation Polymers are usually formed from two different monomers, typically with water as a by-product.
Polyesters can be made from alcohols and carboxylic acids
Fig 4 Polyesters
The properties of condensation polymers are
further influenced by the lengths of the
carbon chains between the functional groups,
the presence of other atoms and the extent
of hydrogen bonding between the strands.
For example, in polyamides, there is a
relatively positive hydrogen atom attached to
the nitrogen and a relatively negative oxygen
atom. The hydrogen from one strand is
attracted to the oxygen of the other by
relatively strong ‘hydrogen bonding’.
Fig 5 Polyamides In polyesters there are no such relatively
positive hydrogen atoms.
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10. Homopolymers and Copolymers
Homopolymers - one type of monomer, e.g. polyethylene.
Copolymers - two or more monomers arranged in different possible ways.
Fig 6 Copolymer structures (Course Notes)
Alternating: Block: Random: Graft:X
X
XOXOXOX OXXXXOXXXX OOXOOXXXOXX OOOOOOOOO
X
X
X
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11. Thermosoftening polymers, Thermosetting polymers and Elastomers
Thermoplastics have weak bonds between the strands. Heating allows the molecules to disentangle
and move around. On cooling, the plastic resolidifies in its new shape.
When thermosetting plastics are heated, chemically active sites on the chains form strong bonds
between the chains, resulting in a three-dimensional amorphous (non-crystalline) structure that cannot
become soft again.
Elastomers (rubbers) can be stretched, (firstly untangling the chains, then stretching the bonds holding
the chains together), and will return to their original shape when released.
Thermosetting rubbers typically have crosslinks formed by sulfur atoms.
Within the structure of thermoplastic elastomers are strong, rigid ‘domains’ which prevent sliding at
room temperature, and flexible chains that give it the rubber qualities. At sufficiently high
temperatures, they deform in the manner characteristic of thermoplastics.
(Course notes)
11

12. Crystallinity
Polymer strands may be tangled in a seemingly random fashion (amorphous regions) or with the
molecules neatly ordered and packed close together (crystalline regions).
The latter restrict movement and are denser, with reduced optical clarity.
Plastics with a lot of crystallinity will shrink more on cooling, and will be more rigid, brittle and less
ductile.
(Course notes)
Fig 7 Crystallinity
Crystalline regions
Amorphous regions
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13. Modifications
The properties of specific polymers can be modified in several ways. (Course notes)
Table 4 Effect of modifications on properties
Modification Comment
Longer chains Increase tensile strength
Branching Increase tensile strength and stiffness, reduce density
Large groups of atoms in chain Increase stiffness
Cross-linking Increase rigidity
More crystalline regions Higher density, tensile strength and rigidity
Orientation of the molecules Different properties in different directions
Copolymerisation Various effects
Blending Various effects
Additives :
Stabilisers Protect from UV
Plasticisers Increase flexibility and mouldability
Flame retardants Reduce flammability
Pigments and dyes Provide colour
Fillers : These can greatly reduce the cost
Glass fibres Increase impact and tensile strength
Mica Reduce electrical conductivity
Graphite Reduce friction
Wood flour Increase tensile strength
Gas Produce foams
Carbon black Strengthen and protect from UV
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14. Activities for Polymers
Activity 1: Match the desired properties with the purpose of the polymer, and suggest suitable
polymers. Research the structural features of the polymer that contribute to the relevant
property.
Activity2: Suggest appropriate objects that could be formed using the forming methods described.
Activity 3: Explore the Macrogalleria website. Find examples of polymers relevant to engineering,
focusing on how their structures relate to their properties and uses.
http://www.pslc.ws/macrog.htm
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15. METALS
In metal atoms there are typically very few electrons in the outer shell.
To achieve the more stable inert gas electron configuration, metals tend to lose
these outer electrons.
Metals can be visualized as positive metal ions in a ‘sea’ of delocalized electrons.
These electrons move freely, making metals good conductors of electricity.
Other typical metal properties (malleability, ductility, thermal conductivity) result
from the relative mobility of metal ions that are surrounded by very small free
electrons compared to the lack of mobility of those surrounded by large anions, as
found in ionic compounds like salt.
When different metals combine, there are no discrete molecules or fixed ratios of
positive and negative ions. A wide range of ‘alloys’ (not ‘compounds’) can thus be
formed.
15

16. STEEL
STEEL is an alloy of Iron with up to 2% Carbon.
The iron exists in one of two allotropic forms –
Austenite (FCC)- which exists at high temperatures
Ferrite (BCC) at low temperatures.
Martensite (BCT) forms if hot steel is cooled quickly. Carbon becomes trapped in the FCC structure as iron
tries to form the BCC structure, causing distortion and internal stresses.
Fig 7
Face Centered Cubic
<http://ecee.colorado.edu/~bart/book/fcc.gif >
Fig 8
Body Centered Cubic
<http://ecee.colorado.edu/~bart/book/bcc.gif>
Fig 9
Body Centered Tetragonal
<://www.tf.uni-kiel.de/matwis/amat/def_en/kap_1/illustr/bravais5.gif >
16

17. Factors influencing the properties of steel
Carbon content
Atoms other than iron and carbon (Not included here)
The way the atoms are arranged in microstructures
The grain size and grain flow
How it has been treated
How it has been shaped and formed
…on to cutting methods ……
17

18. Carbon Content
Table 7 Categories of steel and their uses
(Scanned from Copeland Vol 1 p.95)
18

19. Microstructures
Table 8 Steel microstructures: (Copeland 1 p 95)
Name Alias Structure T Dissolved C Properties Effect on steel
Austenite Gamma iron FCC >723 degrees < 2% Soft, ductile NA at room T
Ferrite Alpha iron BCC As steel cools .. <0.025% Soft, ductile
Cementite Iron Carbide (Fe3C) Hard, brittle Hardness up,
toughness, and
ductility down
Pearlite Layers of 0.83%
cementite and
ferrite
Martensite BCT Rapid quenching >0.03% < 1.3% Hard Greater
hardness,
brittle
Fig 11 Martensite
Fig 10 Plain Steel Microstructures
Microstructure
(Scanned from Copeland (2000) p.93)
(Scanned from Course Notes)
Activity 4: Use the data in table 8 to explain
the trends observed in figure 12
Fig 12 (Scanned from Copeland (2000) p.93)
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20. Grain size and Uniformity
Having a uniform grain size makes the steel easier to machine.
Smaller grains make the steel harder and stronger, but less ductile.
Larger, regular grains allow easier movement of the grains.
Grain flow continuity
Steel that has been forged into shape (left) with continuous grain flow
is stronger than steel that has been cut to shape (right).
Fig 13 Grain flow
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21. Modifications (1)
Work hardening
If a metal is bent or beaten at temperatures below its recrystallisation temperature, atoms slip along
shear planes, distorting the metal.
Discontinuities in the crystal structure allow slip to occur more easily, by moving the discontinuities
through the structure.
With greater deformation, the discontinuities can become jammed, restricting the movement of
atoms, resulting in greater hardness prior to fracture.
( Copeland 2000, p 66)
Recrystallisation
When the steel is heated sufficiently and allowed to cool, any grains that were work hardened or
stressed are replaced by unstressed grains, whose axes are approximately the same length.
Recrystallisation reduces internal stresses, hardness and strength, while it increases ductility and
grain size.
(Course notes)
21

22. Modifications (Heat)
Table 9 : Heat treatment of steels (Course notes)
Annealing Relief stresses
Uniform grain structure
Soften the metal for further working or machining
Process Effect Comments
Full Heat to red heat, Form austenite on heating, pearlite /ferrite Effect depends on C%
(900degrees) then cool very or pearlite or pearlite/cementite
slowly
Process / subcritical ~600 deg Ferrite recrystallised pearlite remains Not as soft as full annealing
Cool in air elongated
Spherodising High C > 0.3 % content Kept Produces spheres of cementite Easy to machine. Hard brittle speroids
at ~680 several hours then pushed away by cutting tool edge.
cool slowly
Normalising To red heat, then cool in air Small, uniform grain Improve machinability
so faster cooling
Hardening Red heat, quick cool Forms martensite Hard, brittle
Not much use.
Tempering Heat hardened steel to Carbon atoms escape from martensite to Lowers tensile strength / hardness but more
below 723 degrees, form fine cementite ductile, impact resistance
“soaking”, slow cooling
Case or surface hardening Keeps the core soft and tough, gives the surface greater wear resistance
carburising Red heat, soak in Carbon- Increase C content of surface
rich atmosphere
flame For large objects. C% > 0.3
induction Passing electric current Smaller objects. C% > 0.3
through
nitriding Change surface composition
by diffusing Nitrogen into
hot steel
22

23. Annealing Activity (part 1)
23

24. Annealing Activity (part 2)
24

25. Forming and Shaping
Sandcasting
Casting Activity 6: Videos
Hot Working
Drawing
Spinning
Image from
Powder Processing http://i1.ytimg.com/vi/XcxDY7vQnPo/default.jpg
Investment casting
Activity 7: Find suitable examples of steel items made with each
method, and indicate why that method is appropriate.
Consider factors such as the intricacy of the component,
Image from
the finish produced and the run size. http://i1.ytimg.com/vi/tyrXq_u1OH0/default.jpg
25

26. Cutting Methods
Activity 8a: Video Water jet
Image from
http://www.youtube.com/watch?v=wPYwrFwQrN4
Activity 8b: Find examples of items cut by the different methods described,
indicating why the method is particularly suitable for that item.
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27. Joining Methods
Materials can be joined by:
introducing another substance that :
reacts chemically to form a strong bond
that melts and resolidifies
melting and solidifying the materials themselves at their boundary
Activity 9b: Recommend and justify joining methods
for the different applications
Activity 9a: videos
Arc Welding Friction Welding
Image from Image from
http://i1.ytimg.com/vi/Te http://i2.ytimg.com/vi/-
BX6cKKHWY/default.jpg aEuAK8bsQg/default.jpg
27

28. APPLICATIONS
Activity 10: Identify the relevant properties of, and the type of steel typically
used for a range of engineering purposes.
Indicate how the steel is best treated for the application.
28

29. Bibliography and References
READING:
Board of Studies, New South Wales (2011) “Engineering Studies Syllabus Stage 6” Retrieved February 10th, 2012 from
http://www.boardofstudies.nsw.edu.au/syllabus_hsc/pdf_doc/engineering-studies-st6-syl-from2013.pdf
Copeland, P. L. (2005) Engineering Studies: The definitive Guide Volume 2 . (2nd ed.). Helensburgh, NSW: Anno Domini 2000 Pty Ltd
Copeland, P. L. (2000) Engineering Studies: The definitive Guide Volume 1. Helensburgh, NSW: Anno Domini 2000 Pty Lt
Course Notes 2011: “1. Engineering Materials and Applications” EDUC6505 Engineering Education Studies 2 University of Newcastle
Metcalfe, P. & Metcalfe, R. (2009) Excel Senior High School Engineering Studies. (2nd ed.). Glebe, NSW: Pascal Press
VIDEOS
http://www.youtube.com/watch?v=_FIsrYzyvlg&feature=player_detailpage Water Jet
http://www.youtube.com/watch?v=XcxDY7vQnPo&feature=player_detailpage Sand casting
http://www.youtube.com/watch?feature=player_detailpage&v=tyrXq_u1OH0 Investment casting
http://www.youtube.com/watch?v=TeBX6cKKHWY&feature=player_detailpage Plasma arc
http://www.youtube.com/watch?feature=player_detailpage&v=-aEuAK8bsQg Friction welding
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