1. Material Selection and Production Methods
Robert Love, Venkat Jayaraman
July 8, 2008
SSTP Seminar – Lecture 5

2. Overview Topics: Basic Material, Properties, Production
Polymers
Metals
Ceramics
Composites
Material Selection
Discussion
Activity
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3. Polymers - Introduction
Examples: PET, ABS, PVC, PETE
Polymer – A large molecule of repeating structural units connected by covalent bonds
Wide variety of applications
Structural and non structural
Mass-manufactured and one off
Polypropylene
Metals
Polymers
The most obvious one is low density for ease of transport and installation, but corrosion resistance is also important for products destined for a long life in a building
electrical insulation since non-conducting
toughness to resist mechanical abuse such as impact
vibration attenuation
low weight
one shot manufacture
Application areas of polymers

4. Polymers – Properties and Classification
Electrical insulation since non-conducting
Toughness to resist mechanical abuse such as impact
Vibration attenuation
Low weight
Ease of manufacture
Ease of transportation and installation
Classification based on properties
Fiber
Elastomer
Plastic

5. Elastomer
Elastomers – Class of polymers which return to their original shape after the applied stress is removed.
Vulcanization – Curing process of rubber involving high heat and formation of cross links with sulfur
Uncured natural rubber is sticky and can easily deform when warm, and is brittle when cold. In this state it cannot be used to make articles with a good level of elasticity. The reason for inelastic deformation of unvulcanized rubber can be found in the chemical nature: rubber is made of long polymer chains. These polymer chains can move independently towards each other, and this will result in an irreversible change of shape. By the process of vulcanization crosslinks are formed between the polymer chains, so the chains cannot move independently anymore. As a result, when stress is applied the vulcanized rubber will deform, but upon release of the stress, the rubber article will go back to its original shape.

6. Plastics Thermoplastics – Soften on heating and harden on cooling
Individual strands
Can be remoulded after heating
Thermosets –
Polymers are crosslinked
Cant melt
Thermosets are generally harder, more rigid and more brittle, and their mechanical properties are not heat sensitive
The reason for this is that thermoplastics have relatively weak forces of attraction between the chains, which are overcome when the material is heated, unlike thermosets, where the cross-linking of the molecules is by strong chemical bonds.
(Recycle codes)

7. Mechanical properties comparison
Stress Strain Comparison
Explain the stress-strain curve on the board

8. Polymer Production Common-Injection Molding, Thin Films
Like the machines in amusement parks that make you a plastic animal…
Yep, Lego’s are made of these!
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9. Metals Examples: Molecular Structure Applications
Steel, Aluminum, Magnesium, Gold, Zinc, Silver, Platinum, Alloys, Superalloys
Molecular Structure
Metallic Bonding: “Sea of electrons”
Crystal Lattice
Applications
Electronics, Structures, Jewelry
One of the things I hope you see is how the atomic structure of a material determines it’s bulk properties, which determine it’s applications
Great site:
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10. Properties of Metals Electrical Heat Structural Corrosion
High conductivity, low resistivity
Heat
Excellent conductors, high melting point
Structural
Heavy, fairly to very strong, ductile/malleable, may be strengthened by cold work or heat treatment or annealed to reduce strength
Corrosion
Some highly reactive, some very non-reactive, some radioactive
Note the connection b/t these properties and their
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11. Metal Production
Don’t forget to at least discuss quenching!
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12. Metal Production
Physical Vapor Deposition, Chemical Vapor Deposition, E-Beam Lithography w/Photoresist
MEMS/NEMS devices
Keep in mind that BULK production is not the only way of making these materials! Use a scanning electron microscope, photoresists etc
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13. Ceramics Examples Structure Applications
Silicon Carbide (SiC), Silica (SiO2), TiC , PZT, Fe3O4, ZnO
Structure
Ionic or Covalent Bonding
Formed by heat addition
Generally metal+nonmetal
Applications
High temperature shields, brake pads, pottery, knives, coatings, electronics
Silica (sand), Titanium Carbide-space shuttle, PZT: lead zirconate titanate-a piezoelectric, Ferrite-in magnetic memory-ie your hard drive, Rust (Iron Oxide), Zinc Oxide-semiconductor
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14. Properties of Ceramics
Electronic
Insulators (some exceptions:piezoelectrics PZT), Semi-conductors, superconductivity
Heat
Low conductivity, high melting point
Structural
Heavy, brittle, very strong, low impact resistance (toughness), stiff, high hardness
Corrosion
Generally very unreactive, highly scratch resistant
Grasp an intuitive feel for how the material behaves by KNOWING it’s atomic structure!
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15. Ceramic Production
Particles->Slurry->Casting, Hand/Kiln (Sintering)
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16. Composites Examples Structure Applications
Concrete, Polymer Matrix + Carbon/Glass/Kevlar fiber
Structure
Matrix + Reinforcement
Combo of 2 of previous 3 material classifications
Applications
Pressure Chambers, Bikes, Aircraft
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17. Properties of Composites
IT DEPENDS!!!
Electrical
Usually insulators, some intentionally made conductive
Heat
Generally heat resistant, depends on matrix
Structural
Tailor made strength properties (weight reduction), high stiffness and strength to weight ratio
Corrosion
May have issues
Often expensive!
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18. Composite Production Basic Sequence:
By hand: Layup (wet or prepreg) on mold/tool, Vacuum Bag, Bake, Release
May have automatic-tape/winding machines
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19. Material Selection
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20. Activity Think of a need and a product What material(s) do you need?
What are important properties to consider in the material selection process?
How will you make this product?
Have them in groups and deciding on a product (?)
Give them a material property comparison chart, give example applications…point to the walls if necessary and ask why they think they made them out of concrete or use paint…etc
Hand’s on demo’s: shape memory alloys? Katana?
Making a sword:
How could you characterize a material you’ve never seen before?
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21. Approximate Temperature
Color
Approximate Temperature °F °C K
Faint Red
930
500
770
Blood Red
1075
580
855
Dark Cherry
1175
635
910
Medium Cherry
1275
690
965
Cherry
1375
745
1020
Bright Cherry
1450
790
1060
Salmon
1550
845
1115
Dark Orange
1630
890
1160
Orange
1725
940
1215
Lemon
1830
1000
1270
Light Yellow
1975
1080
1355
White
2200
1205
1480
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