Materials II
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Transcript of Materials II
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Materials II:Engineering Materials
ENSC 489
September 28, 2015
Mike Henrey
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Classes of materials
Metals
Ferrous
Non-ferrous (not Fe or C)
Alloys
Polymers
Thermoplastics
Thermosets
Ceramics
Composites
Natural
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How to choose a material
1. Materials first approach
Which materials will satisfy the functional
requirements of the part?
2. Manufacturing process first approach
Which manufacturing processes will satisfy the
functional requirements
Which materials are compatible with these processes?
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How to choose a material
3. Ratings/Rankings:
If Youngs Modulus is important, rank all the materials
in terms of Youngs modulus per unit cost In this case, you might choose a stone or concrete
(similar E to a composite, at 1/100 the cost per unit
volume)
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Metals
Metals used in applications requiring:
High strength
Cyclical loading High temperature performance
High electrical or thermal conductivity
Magnetic properties
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Cast Iron
>2% carbon
Easy and inexpensive to manufacture
Low tensile strength and low ductility vs. other
materials
Used where tensile strength is non-critical
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Steel
Carbon steel
Alloy of iron and carbon (
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Copper
One of the oldest materials (used since 9000 BC)
Abundant and easy formability
Excellent conductor of heat and electricity
Addition of impurities generally reduce conductivity
Easily soldered or welded
Does not withstand fatigue well (bad for cyclic
loads)
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Aluminum
Non-sparking and non-magnetic
Many grades, presence of alloy metals changes
properties significantly
About 1/3 the stiffness of steel
Electrically and thermally conductive
Excellent machinability (many diverse methods)
Low fatigue strength
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Titanium
High temperature performance (operates to 500 C)
About half the density of ferrous metals (~4400
kg/m3 vs. 8000 kg/m3), similar strength
Biocompatible material
Applications in aerospace, military, medical
prostheses and implants, sports
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Engineering plastics
Plastics are used when certain properties are
required:
High strength to weight ratio
Electrically insulative
Chemical resistance
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Thermoplastics
Reversible temperature/pressure behavior
Melts to a liquid when heated
Becomes brittle when cooled
Typically cost effective manufacturing process (vs.
thermoset)
Shorter process times
Lower tooling costs
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Thermoplastics
ABS and PLA: both can be used in Makerbot 3D
printers as a filament
Polypropylene
Textiles
Ropes Reusable containers
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Identification symbols
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PVC
Excellent chemical resistance
High strength to weight ratio
Low cost
Poor temperature performance
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Acrylics
High clarity (good optical components), about half
the density of glass
Relatively high cost
Trademarks: Lucite and Plexiglass, generally called
PMMA
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Polycarbonate
Transparent
Lower density vs. acrylic
Higher impact strength vs. acrylic
Commercial name: Lexan
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Nylon
Low coefficient of friction
1/10 density of steel
Resistant to fatigue, heat and impact
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Acetal
Universal engineering plastic
High stiffness
Resistant to fatigue, temperature
Not suitable in radiation environments
Commercial names: Delrin, Celcon or Aceton Many grades suitable for food processing
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PTFE
Commercial name Teflon
Non-stick coating
Low friction - even a gecko cannot stick to PTFE!
Non-reactive
Good electrical insulator, especially at highfrequencies
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Stratasys ABSPlus
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Thermoset
Cures through addition of energy
Crosslinking process
Initiated by UV, heat
Example: vulcanization (rubber tires)
Suitable for moulding
With reinforcement materials (glass/carbon fibers),
these compete with metals
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Polymide
Commercial names: Vespel, Kapton
Cryogenic and high temperature performance
Good electrical insulator
Available as a thermoplastic and thermoset
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PDMS (Sylgard 184)
Polydimethylsiloxane
Viscoelastic: over long times or high
temperatures, it flows
2 part mixture, once mixed it cures in
short time (3 hours at 60 C or 24 hours at
RT)
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Synthetic gecko adhesives
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Ceramics
Body with crystalline, partly crystalline or glass
structure
In-organic and non-mettalic
Generally brittle and hard
Electrically and thermally insulative
High temperature performance
Can be piezoelectric
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Composites
Combination of 2 or more materials to obtain a final
material with enhanced properties
May make the final product:
Stronger
Lighter
Less expensive
777-Dreamliner is 50% composite
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Carbon fiber
Composite of carbon and polymer
High strength to mass ratio
Applications:
Aircraft
High performance vehicles (F1 cars)
Bicycles Spacecraft
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Fiber glass
Common name of glass-reinforced plastic
Applications
Boats Small aircraft
Weave direction important
Properties depend on resin used
Vs. carbon fiber, heavier and less stiff, but isinsulative
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Kevlar
Trademark name (DuPont) for a high tensile-
strength synthetic fiber
5 times stronger than steel (per mass)
Applications
Cryogenics (slightly stronger at low temps)
Personal armor and protection
Bicycle tires
Rope
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Metal Matrix Composite
(MMC)
Two parts
One is always a metal
The other may be metal, ceramic, organic etc.
Landing gear of an F16
Silicon carbide
Titanium matrix
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Cermet
Material comprised of ceramic and metallic
components
Used in:
Resistors and capacitors
Space applications
Machine tools
Has high temperature properties (like ceramics) and
metallic properties (ductility, conductivity)
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Natural Materials
Rubber
Wood
Glass
Silicon
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The future of materials
Shape memory alloys (robotics, biomedical)
Composites (nuclear reactors, military, space)
High temperature superconducting magnets (MRI,
magnetic levitation trains)
High performance plastics (automobile)
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Smart materials
One or more properties can be altered
SMA
Substantial shape change with temperature
Can be used to mimic human tendons in a robot
Piezoelectric
Deformation gives an electrical current Current causes a deformation
Many uses as a sensor (airbag sensor)