This document provides an introduction to smart materials. It discusses various types of materials including metals, ceramics, polymers, composites and semiconductors. It then focuses on smart materials, defining them as materials that can significantly change one or more properties in a controlled way due to external stimuli like stress, temperature, moisture or electric/magnetic fields. Examples of smart materials discussed include piezoelectric materials, shape memory alloys, magnetorheological fluids and thermochromic materials. The document describes how each of these materials changes structure or property in response to different stimuli.

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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

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Types of Materials
- Metals
- Ceramics
- Polymers
- Composites
- Semiconductors

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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

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METALS
FERROUS METALS
NON-FERROUS METALS

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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

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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.

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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

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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

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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.

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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.

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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.

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Smart Materials

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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.

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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

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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.

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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.

20. What are Piezoelectric materials?

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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.

22. What are shape memory alloys?

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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.

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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.

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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)

26. Magnetic shape-memory alloys (MSMAs)

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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.

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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

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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).

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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.

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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.

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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

33. Thermochromic

34. Thermochromic

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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.

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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.

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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.

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Electrochromic

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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.

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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.

41. Smart Grease

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