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SMART MATERIALS & THEIR ENGINEERING APPLICATIONS
Smart materials are materials that have one or more properties which can be significantly
altered in a controlled fashion by external stimuli, such as temperature, pH, stress, moisture,
electric or magnetic field.
Smart materials can also be defined as materials that sense and react to environmental
conditions or stimuli. These materials undergo transformations through physical/chemical
interactions.
We can also call them stimuli responsive materials or intelligent materials.
e.g. Self-healing paints, Thermo chromic ink
Examples of smart materials by response type Type Response to Stimulus Example Stimulus Piezoelectric material s Produce an electrical charge Mechanical stress or pressure Eg.Quartz Shape-memory materials Recover original shape Heat Eg. Nitinol
pH sensitive
materials
Change solubility, shape pH Eg. Hydrogels Magnetostrictive Deformation Magnetic Field Eg. Terfenol-D Thermochromic Change color Temp. Eg. titanium dioxide
materials & PbI Photochromic materials Change color Light, especially UV Eg. Azobenzenes Electrochromic materials Change color Electric voltage Eg. Tungsten Oxide Thermo-responsive materials Change shape or other properties Temperature Eg. PNIPAM
Shape-memory Alloys (SMAs)
Shape memory alloys (SMAs) are a class of metallic alloys that can return to their original,
"memorized" shape after being deformed, when heated to a specific transformation temperature.
This effect is due to a phase change in the alloy's crystalline structure, which can be triggered by
heat or stress. Common applications include aerospace, medical implants, and actuators, with
some examples of SMAs being Nitinol (Nickel-Titanium) and Copper-based alloys.
Eg. NITINOL
Nickel titanium, also known as nitinol , is a metal alloy of nickel and titanium, where the two elements are present in roughly equal atomic percentages. Nitinol has two phases or crystalline structures, a high temperature (austenite) and a low temperature (martensite).
Synthesis
Nitinol is synthesized by melting pure Nickel and Titanium powders in a vacuum or inert atmosphere using methods like vacuum arc remelting (VAR) or vacuum induction melting (VIM). Other methods
3 Fatigue Resistance: It has excellent resistance to fatigue, meaning it can withstand many
cycles of stress and strain without breaking.
4 Corrosion Resistance: Nitinol has good resistance to corrosion, which is crucial for its use in
medical implants.
Common applications
Medical Devices: Nitinol is widely used for medical devices because of its biocompatibility and
flexibility.
Stents: Its superelasticity allows it to be compressed to fit through a catheter, and it then expands
to its pre-programmed shape inside the blood vessel.
Orthodontic Braces: The wires used in braces are often made of nitinol {because they can be
bent out of the way during application and will return to their original shape} to gently guide
teeth into alignment.
Other devices: It is also used in devices like vena cava filters for blood clot retrieval and in
some surgical tools.
Actuators: It is useful in actuators for robotics and other mechanical systems.
Eyewear: Resilient and flexible eyeglass frames that resist bending.
Electronics: Retractable antennas in cell phones, hinges in small gadgets,
and components for optical image stabilization
Vibration damping: Used in applications like concrete and as a damping
material in other industrial settings.
Novelty items: Can be found in novelty products like self-bending spoons.
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Piezoelectric materials A piezoelectric material is a substance that generates an electric charge when subjected to mechanical stress, and conversely, deforms when an electric field is applied. This property is known as the piezoelectric effect, and it allows these materials to convert mechanical energy into electrical energy and vice versa. Examples include quartz crystals, which are used in watches, and piezoelectric ceramics found in sensors and actuators.. Quartz Quartz , widely distributed mineral of many varieties that consists primarily of silica, or silicon dioxide (SiO 2 ). Minor impurities such as Li, Na, K, and Ti may be present. Quartz is found globally in all three types of rock: igneous, metamorphic, and sedimentary. Because it is resistant to weathering, quartz grains are also concentrated in soils, rivers, and beaches worldwide.
Its hardness makes it suitable for use as an abrasive and in applications like foundry
sand.
Industrial uses:
Glassmaking: Used to make glass.
Heaters: Translucent fused-quartz tubes are used to sheathe heating elements in room
heaters and industrial furnaces.
Scientific equipment: Quartz glassware is used in chemistry labs when higher
temperatures or higher UV transmission are needed.
Gemstone: Used as a gemstone in various colors and forms, such as clear rock crystal,
and rose quartz.
Quartz has a wide range of uses, including in electronics and technology for things like
semiconductors, radios,; in construction and industry for glass, ceramics, & kitchen countertops; cosmetics and as gemstones for jewellery.
