1. Special Technologies
An Introduction to
SMART MATERIALS
Mehrshad Mehrpouya
mehrshad.mehrpouya@uniroma1.it
Sapienza University of Rome
Department of Mechanical and Aerospace Engineering
2. Mehrshad Mehrpouya
PhD. Fellow Industrial Production Engineering
Sapienza University of Rome, Rome, Italy
M.Sc. Manufacturing Systems Engineering
University Putra Malaysia (UPM)
LinkedIn: www.linkedin.com/in/mehrpouya
Email : mehrshad.mehrpouya@uniroma1.it
Office no: 16
Sapienza University of Rome
Department of Mechanical and Aerospace Engineering
3. Department of Mechanical and Aerospace Engineering
Special Technology
Types of Materials
- Metals
- Ceramics
- Polymers
- Composites
- Semiconductors
4. Department of Mechanical and Aerospace Engineering
Special Technology
A metal is a material (an element, compound, or alloy) that is typically hard, opaque,
shiny, and has good electrical and thermal conductivity. Example: several uses of steel
and pressed aluminum as shown in the pictures.
Metals
5. Department of Mechanical and Aerospace Engineering
Special Technology
METALS
FERROUS METALS
NON-FERROUS METALS
8. Department of Mechanical and Aerospace Engineering
Special Technology
Ceramics exhibit very strong ionic and/or covalent bonding (stronger than the metallic
bond) and this confers the properties commonly associated with ceramics: high hardness,
high compressive strength, low thermal and electrical conductivity and chemical inertness.
Examples: glass, porcelain.
Ceramic
9. Department of Mechanical and Aerospace Engineering
Special Technology
Ceramic
Engineering ceramics are used to fabricate components for applications in many
industrial sectors, including ceramic substrates for electronic devices, turbocharger
rotors, and tappet heads for use in automotive engines.
Ceramic substrates
for electronic
devices
Ceramic turbocharger
rotor assembly made
from silicon nitride
Courtesy of NGK/NTK
Spark Plug Co.
10. Department of Mechanical and Aerospace Engineering
Special Technology
A polymer is a large molecule, or
macromolecule, composed of many
repeated subunits. Because of their
broad range of properties, both
synthetic and natural polymers play
an essential and ubiquitous role in
everyday life. Polymers range from
familiar synthetic plastics such as
polystyrene to natural biopolymers
such as DNA and proteins that are
fundamental to biological structure
and function. Polymers also include
“Plastics” and rubber materials.
Polymers
11. Department of Mechanical and Aerospace Engineering
Special Technology
Polymers are bound by covalent forces
and also by weak van der Waals
forces, and usually based on C and H.
They decompose at moderate
temperatures (100 – 400 C), and are
lightweight. Examples: plastics
rubber.
Polymers
12. Department of Mechanical and Aerospace Engineering
Special Technology
Polymer composite materials:
reinforcing glass fibers in a
polymer matrix.
Composites
A composite material is a material made from two or more constituent materials
with significantly different physical or chemical properties that, when combined,
produce a material with characteristics different from the individual components.
13. Department of Mechanical and Aerospace Engineering
Special Technology
Semiconductors
The bonding is covalent
(electrons are shared between
atoms). Their electrical
properties depend strongly on
minute proportions of
contaminants. Examples: Si,
Ge, GaAs.
This behavior and the interactions
between charge carriers and photons
and phonons allows semiconductors
to store binary information, form logic
gates, and convert between voltage,
light, heat, and force as sensors and
emitters.
Silicon crystals are the most common
semiconducting materials used
in microelectronics and photovoltaics.
14. Department of Mechanical and Aerospace Engineering
Special Technology
Semiconductors
Semiconductors are a special case of electronic
material that combines two differently
electrically conductive materials. A
semiconductor is also known as a P-N junction,
where one material allows ‘loose’ electrons to
move through an ordered structure, and the
other allows holes (where an electron could
be, but is not) to move in the same way.
16. Department of Mechanical and Aerospace Engineering
Special Technology
What are smart materials?
Smart materials are materials that
have one or more properties that can
be significantly altered in a controlled
fashion by external stimuli, such as
stress, temperature, moisture, pH,
electric or magnetic fields.
17. Department of Mechanical and Aerospace Engineering
Special Technology
What are the examples?
• Piezoelectric materials
• Shape memory alloys
• Magnetic shape memory alloys
• Magnetorheological
• PH sensitive polymers
• Halochromic materials
• Thermochromic materials
• Chromogenic systems
• Electrochromic
• Smart Grease
18. Department of Mechanical and Aerospace Engineering
Special Technology
What are Piezoelectric materials?
Piezoelectric materials are materials that produce a voltage when stress is
applied. Since this effect also applies in the reverse manner, a voltage across the
sample will produce stress within the sample. Suitably designed structures
made from these materials can therefore be made that bend, expand or
contract when a voltage is applied.
19. Department of Mechanical and Aerospace Engineering
Special Technology
Piezoelectric materials have the ability to generate an electrical charge.
A mechanical stress is applied to the
smart material.
This causes a small electrical charge to
be generated.
In return, the shape of the solid
changes by a small amount.
A car’s cigarette lighter is a good example of how
piezoelectric materials are used in a every day application.
21. Department of Mechanical and Aerospace Engineering
Special Technology
What are shape memory alloys?
Shape memory alloys and shape memory polymers are thermo-
responsive materials where deformation can be induced and
recovered through temperature changes.
23. Department of Mechanical and Aerospace Engineering
Special Technology
Shape memory alloys change shape at set temperatures.
One of the most common alloys is a
combination of nickel and titanium.
This shape memory alloy can be treated
so that when it reaches a set
temperature it contracts.
When it cools it then returns to its original
shape.
They become deformed once heated above the transformation temperature, but
regain their shape as they cool.
24. Department of Mechanical and Aerospace Engineering
Special Technology
Shape memory alloy wire is called smart wire as it remembers its shape.
When a small electrical current
passes through the wire it becomes
smart.
It remembers to change shape.
The wire becomes shorter.
This shortening can be used to
control a robotic hand.
In the future, this may help scientists produce
artificial motion that is more similar to the range
of human movement.
25. Department of Mechanical and Aerospace Engineering
Special Technology
Magnetic shape-memory alloys (MSMAs),
or ferromagnetic shape-memory alloys
(FSMAs), are ferromagnetic materials which
exhibit large strains under the influence of
an applied magnetic field due to martensitic
phase transformation.
Magnetic shape-memory alloys (MSMAs)
27. Department of Mechanical and Aerospace Engineering
Special Technology
Magnetorheological
Magnetorheological fluid (MR fluid) is a type of smart material that has the
ability to change state when placed in a magnetic field.
These fluids are composed of iron-like
particles.
In their normal state they are fluid.
When placed in a magnetic field the
particles are attracted to each other and
join up to form a solid.
Currently, these materials are not widely used. It is thought of as a more
futuristic smart material.
28. Department of Mechanical and Aerospace Engineering
Special Technology
PH sensitive polymers
• pH sensitive or pH responsive polymers are materials which will
respond to the changes in the pH of the surrounding medium by
varying their dimensions. Such materials increase its size (swell) or
collapse depending on the pH of their environment. This behavior is
exhibited due to the presence of certain functional groups in the
polymer chain
29. Department of Mechanical and Aerospace Engineering
Special Technology
PH sensitive polymers
The sensor is prepared by entrapping within a polymer matrix a pH sensitive dye that
responds, through visible colour changes (see the Figure) to spoilage volatile compounds that
contribute to a quantity known as Total Volatile Basic Nitrogen (TVB-N).
30. Department of Mechanical and Aerospace Engineering
Special Technology
Halochromic Materials
• Halochromic materials are commonly
materials that change their colour as a result
of changing acidity. One suggested
application is for paints that can change
colour to indicate corrosion in the metal
underneath them.
31. Department of Mechanical and Aerospace Engineering
Special Technology
Thermochromic materials
Thermochromic materials react to changes in temperature.
Tiny capsules in thermochromic ink
contain liquid crystals.
As the temperature changes these
crystals move.
The reorientation of the crystals causes a
change in colour at a specific temperature.
This sensitivity causes them to temporarily change colour when they are exposed to
heat.
32. Department of Mechanical and Aerospace Engineering
Special Technology
ThermochromicColour-changing thermochromic
pigments are now routinely made
as inks for paper and fabrics – and
incorporated into injection
moulded plastics.
A new type of phosphorescent
pigment, capable of emitting light
for up to 10 hours, has opened up
entirely new design opportunities
for instrumentation, low-level
lighting systems etc.
Warm Cool
35. Department of Mechanical and Aerospace Engineering
Special Technology
Chromogenic systems
• Chromogenic systems change colour in response to electrical, optical or
thermal changes. These include electrochromic materials, which change
their colour or opacity on the application of a voltage (e.g. liquid crystal
displays), thermochromic materials change in colour depending on their
temperature, and photochromic materials, which change colour in
response to light - for example, light sensitive sunglasses that darken
when exposed to bright sunlight.
36. Department of Mechanical and Aerospace Engineering
Special Technology
Photochromic materials
This causes them to undergo a reversible change of colour when exposed to a certain
amount of light.
Photochromic lenses become dark
when they are exposed to UV
radiation.
Once the UV radiation is removed,
the lenses gradually return to their
normal state.
They can be made of either glass or
plastic.
37. Department of Mechanical and Aerospace Engineering
Special Technology
Electrochromic
Electrochromism is the phenomenon
displayed by some materials of
reversibly changing colour by using
bursts of charge to cause
electrochemical redox reactions in
electrochromic materials. Various
types of materials and structures can
be used to construct electrochromic
devices, depending on the specific
applications.
39. Department of Mechanical and Aerospace Engineering
Special Technology
Electrochromic
• Flip a switch and an
electrochromic window can
change from clear to fully
darkened or any level of tint in-
between.
• The action of an electric field
signals the change in the
window's optical and thermal
properties. Once the field is
reversed, the process is also
reversed. The windows operate
on a very low voltage -- one to
three volts -- and only use
energy to change their
condition, not to maintain any
particular state, like Boeing 787
Dreamliner.
40. Department of Mechanical and Aerospace Engineering
Special Technology
Smart Grease
Smart grease is a particularly sticky and viscous gel with
almost magical shear characteristics. It can be used in
prototype applications to improve performance or it
can be used in novel applications such as wound-up
motors to provide uniform speed and torque output.
The example illustrated here is a simple elastic band
motor comprising a pill container, elastic, wheel and
securing/winding rod. If, under normal circumstances,
the wheel is wound up and released, it will spin rapidly
and slow down. If a tiny amount of smart grease is
added between the friction surfaces, the wheel will turn
at a uniform (very slow) speed and the stored energy
will be released uniformly.
Piezoelectric materials are used in airbag systems, in the generation and detection of sonar waves, microphones, smart skis and creating ultrasound images.
Piezoelectric materials are used in airbag systems, in the generation and detection of sonar waves, microphones, smart skis and creating ultrasound images.
Obviously, no one can know for sure what the future applications of magnetorheological fluid will be for definite. However, some very real possibilities include:
body armour which is flexible but becomes rigid upon coming into contact with a metallic object, such as a bullet
dampers for large structures in areas prone to earthquakes
shock absorbers for the automotive industry
suspension systems for military and defence vehicles
human prosthetics.
Thermochromic materials can be used in thermometers, to indicate when a pan is hot enough for cooking to begin (Tefal thermospot), battery testers, clothing ranges, novelty items, e.g. coffee cups coated with thermochromic paint so that an image appears when the drink is poured and thermal printers.
A possible application of photochromic materials could be in the field of energy-efficient windows. They could also be used to create photochromic clothing. This would work in a similar way to Hypercolour T-shirts, but would react to light rather than body heat.
