materials ii

7/25/2019 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)

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