Transcript Engineering materials

Advanced Engineering materials
Types of Materials
High density
 Medium to
high melting
point
 Medium to
high elastic
modulus
 Reactive
 Ductile

Polymers
Ceramics
Metals
•
•
•
•
•
Low density
High melting
point
Very high
elastic
modulus
Unreactive
Brittle
•
•
•
•
•
Very low
density
Low melting
point
Low elastic
modulus
Very
reactive
Ductile and
brittle types
Organics
(wood, paper, textiles)
•
•
•
•
•
•
Sustainable
Recyclable
Biodegradable
Easily worked
Flammable
Share properties
of composites
Metals and Alloys
Metals are the most common of the elements.
Strong, with good conductivity for electricity and
heat. Mostly easily worked.
 Bronze
for spearheads and axes
 Steel
 Aluminium, Magnesium
 Titanium: as strong as steel but 45% lighter
 Shape memory alloys
Polymers
Flexible Thermoplastic (PE, PU)
Rigid Thermoplastic (PVC, PS)
Rigid Thermosets (EP, PF)
Elastomers or rubbers
Ceramics
Examples:
A ceramic is a
composite
consisting of
hard granules
bound together
by a ‘glue’ often
like glass.
Stone
Limestone (CaCO3)
Sandstone (SiO2)
Granite (aluminosilicates)
Cement and Concrete
Mixtures of lime (CaO),
silica (SiO2) and
alumina (Al2O3)
The CaO reacts with water
and carbon dioxide from the air
to form Ca2CO3 (limestone)
Microstructure of ceramics
Pottery ceramic
Engineering ceramic – Al2O3
Properties of ceramics







Extremely hard and resistant to wear
Very high melting point
Resistant to chemical attack
High compressive strength
Low and variable tensile strength
Low density ( as compared to steel)
Ceramic components are not easy to make
because of their high mp and hard/brittle so can’t
be machined.
Organic materials







Have been used since the stone age eg wood or
bone handle for stone axe.
Fibre for ropes
Sinew for bow string
Timber for houses and furniture
Paper and cardboard for packaging
Composites e.g. srbp for electrical components
Glues and varnishes
Wood





Has a grain structure with directionally
oriented fibers
High compressive strength
Good tensile strength along grain axis
Weak across grain
Prone to decay and infestation eg
woodworm – however look at timber used
for staithes at Dunston
Composites
In its most basic form
a composite material is
one which is composed
of at least two
elements working
together to produce
material properties that
are different to the
properties of those
elements on their own.
The properties of a
material depend on the
kind of stress it is
exposed to. For
example concrete has a
good compressive
strength, but a low
tensile strength. This is
overcome by reinforcing
with steel rods - making
a composite.
Types of stress
Tension
Shear
Compression
Flexion
Tensile strength and tensile modulus
Tensile strength
Tensile modulus (stiffness)
Three main groups of
engineering composites

Polymer matrix composites

Metal matrix composites

Ceramic matrix composites
Polymer matrix composites
These are the most common composites in
use today. Also known as FRP - Fibre
Reinforced Polymers (or Plastics) these
materials use a polymer-based resin as the
matrix, and a variety of fibers such as glass,
carbon and Aramid (Kevlar) as the
reinforcement.
PMC Bulk material
Resin systems such as epoxies and polyesters
have limited use for the manufacture of structures
on their own, since their mechanical properties
are not very high when compared to, for example,
most metals. However, they have other desirable
properties for engineering, particularly their ability
to be easily formed into complex shapes.
Reinforcement
Materials such as glass, aramid (kevlar), carbon and boron
have extremely high tensile and compressive strength but
in ‘solid form’ these properties are not readily apparent.
This is due to the fact that when stressed, random surface
flaws will cause each material to crack and fail well below
its theoretical breaking point. To overcome this problem,
the material is produced in fiber form, so that, although the
same number of random flaws will occur, they will be
restricted to a small number of fibers with the remainder
exhibiting the material’s theoretical strength.
Crack propagation in bulk
reinforcement material
Crack propagation in fiber
reinforcement material
When stressed individual fibres may
break at a flaw, but the overall
strength of the material is not
prejudiced as the matrix bonds the
remaining fibres together.
Even quite short fibre whiskers or
particles can enhance the strength of
the matrix, particularly with respect
to tensile and flexural stresses.
Matrix and reinforcement combined



When the resin systems are combined with reinforcing
fibers such as glass, carbon and Aramid (Kevlar),
exceptional properties can be obtained.
The resin matrix spreads the load applied to the
composite between each of the individual fibers and also
protects the fibers from damage caused by abrasion and
impact.
High strengths and stiffness, ease of moulding complex
shapes, high environmental resistance all coupled with
low densities, make the resultant composite superior to
metals for many applications.
Properties of PMC’s
Since PMC’s combine a resin
system and reinforcing
fibers, the properties of the
resulting composite material
will combine some of the
properties of the resin on its
own with those of the fibers
on their own.
Metal matrix composites
Increasingly found in the automotive industry, these
materials use a metal such as aluminium as the matrix,
and reinforce it with particles or fibers such as silicon
carbide SiC.
Particulate SiCp/Al and whisker SiCw/Al were extensively
characterized and evaluated during the 1980s.
MMC’s can also use continuous fibre reinforcement (e.g.
Graphite / Aluminium or Graphite / Magnesium)
Expensive and difficult to produce, MMC’s are mainly used
where their special benefits (e.g. weight saving) outweigh
cost considerations – such as on the space shuttle.
Metal matrix composites



Composites with aluminium and magnesium
matrices have been investigated extensively, and
recently steel matrix composites have gathered
increased interest.
In these composites, stainless steels, tool steels
and precipitation hardened steels have been
used as the matrix material.
The particulate reinforcements can be oxides
(Al2O3, Y2O3), carbides (TiC, Cr3C2, VC, NbC),
nitrides (TiN, Si3N4), and borides (TiB2, CrB2).
Ceramic matrix composites
Ceramics have a high compressive strength
but low tensile strength. Combining with a
high tensile reinforcement gives very strong
hard materials.
Used in high temperature environments,
such as jet engines, CMC’s use a ceramic as
the matrix and reinforce it with short fibres,
or whiskers such as those made from silicon
carbide and boron nitride.
Super hard coatings
About coatings:




Diamond
B-C-N (Boron – Carbon – Nitrogen) coatings
Ti – B – N
and Ti – B – C – N
Biocompatible super hard coatings for medical
devices
Nanostructured materials
Fullerenes:
Molecular structures of carbon




‘Fullerenes’ is a generic term for the third carbon
molecule that follows graphite and diamond.
Fullerenes are composed of a network structure, either in
a spherical or a tubular form, where 60 or more carbon
atoms are strongly bonded together.
The atoms that make up Fullerenes are the same carbon
atoms as those in graphite.
C60 is one of the representative examples, and is a
spherical aggregate of 60 carbon atoms, with a diameter
of approximately 0.7 nanometers
(one nanometer equals 1/1,000,000,000 meter).
Fullerene structures
Applications of fullerenes





Electrochemical properties – use in batteries and
fuel cells
Gas Storage properties – storage of hydrogen
Mechanical properties – lubricants and super
hard materials
Electrical properties – superconductors
Optical properties
Carbon nanotubes


Carbon nanotubes are fibers with a tensile
strength many times that of steel
They are being postulated as a solution to
the construction of a ‘space elevator’
where a geostationary satellite is tethered
to the earth, and elevators run up and
down the cable raising materials into orbit.
Aerogels

Made of inexpensive silica, aerogels can be fabricated in
slabs, pellets, or most any shape desirable and have a
range of potential uses. By mass or by volume, silica
aerogels are the best solid insulator ever discovered.
Aerogels transmit heat only one hundredth as well as
normal density glass. Sandwiched between two layers of
glass, transparent compositions of aerogels make
possible double-pane windows with high thermal
resistance. Aerogels alone, however, could not be used
as windows because the foam-like material easily
crumbles into powder. Even if they were not pulverized
by the impact of a bird, after the first rain they would
turn to sludge and ooze down the side of the house.
Aerogels as insulators


Aerogels are a more efficient, lighter-weight, and less
bulky form of insulation than the polyurethane foam
currently used to insulate refrigerators, refrigerated
vehicles, and containers.
They have another critical advantage over foam. Foams
are blown into refrigerator walls by chlorofluorocarbon
(CFC) propellants, the chemical that is the chief cause of
the depletion of the earth's stratospheric ozone layer.
According to the Environmental Protection Agency, 4.5 to
5 percent of the ozone shield over the United States was
depleted over the last decade.
Facts about aerogels







They are 39 times more insulating than the best fibreglass
insulation.
They are 100 times less dense than glass.
A wafer thin layer is sufficient to protect a hand from a blowtorch
just inches away from it.
A block the size of a person weighs less than a pound, looks like it
would blow away in a slight breeze, yet could support a small car.
They were used as insulation on the rover vehicle of the Mars
Pathfinder.
The Marshall Space Flight Center has already provided specifications
for aerogels to over 50 companies and research institutes for
products as diverse as diving suits, industrial insulation, medical
containers and windows.
The value of the worldwide market for low-cost aerogels is
projected to reach $10 billion by the year 2005.
Applications of aerogels

Solid insulation


Silica aerogels are very light in weight and
have an R-value up to R25 per inch
Electrodes for batteries

Vanadium oxide aerogels have very promising
properties for use in Lithium cells
Today’s news
Organic-inorganic hybrids





Under investigation by Prof J McKenzie at
UCLA
Textile composites
Organic composites
Geopolymers – a better cement / concrete
Conjugated polymers

For semiconductors and light emitting devices
Resources



www.azom.com A to Z of materials
http://www.seas.ucla.edu/ms/
http://www.plasticsusa.com/polylist.html
datasheets for all common plastics


http://www.materials.ac.uk/
http://bell-labs.com/org/physicalsciences/