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TRANSCRIPT
University of central Florida
Shape Memory Alloy (SMA)
ETG 6933 - Advanced Topics in Technology
Frederick Kaiser
8/1/2010
ContentsI. Executive Summary.............................................................................................................................3
II. Introduction.........................................................................................................................................4
III. History.............................................................................................................................................5
IV. Accidental Discovery........................................................................................................................6
V. Nitinol Phases and Properties..............................................................................................................7
VI. Introduction into the Market...........................................................................................................8
VII. Current State of the Technology....................................................................................................10
VIII. Future Prediction of Shape Memory Alloy (SMA)..........................................................................13
1. Medicine........................................................................................................................................13
2. Consumer Goods...........................................................................................................................15
3. Robotics.........................................................................................................................................17
IX. Potential Technology.....................................................................................................................19
1. Mechanical Fuzes..........................................................................................................................20
2. Electrical Fuzes..............................................................................................................................20
3. SMA Actuator...............................................................................................................................21
X. References.........................................................................................................................................24
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I. Executive Summary
There are two stories that are in circulating about the discovery of Smart Memory Alloy
(SMA). The commercial name for SMA is Nitinol.
The first story of the discovery of Nitinol is hard to verify, but there is a population of
people who believe. A study was conducted for Wright Patterson in the late 40’s that indicated a
more abstract explanation for the discovery of Nitinol. The study showed that first tine the metal
alloys that demonstrated shape recovery was being examined by the U.S. Military. These studies
were thought to have started shortly after the Roswell Crash where similar material was reported
to have been found. Importantly, even after decades, the Nickel-Titanium metal system (Nitinol)
remains the material that defines "morphing metal." Any earlier observation of "pseudo-
elasticity" was with a metal alloy that did not utilize Nickel and Titanium- and that was not
developed for that property. (Bragalia, 2009)
The Story of the discovery of Nitinol is easier to verify, sense there are witnesses who
were present, at the discovery of shape memory characteristics of Nitinol and they recorded what
they saw. The timeline and activities that led to the discovery was recorded by the metallurgists,
William J. Buehler and Dr. David S. Muzzey. (Kauffman, 1993) Nitinol (Nickel-Titanium Alloy)
was being developed as a durable metal to use for the nosecone for spacecrafts, the material that
was to be used on the nosecone was expected to be exposed to 1000’s of degree and violent
turbulence at the time a spacecraft is reentering the atmosphere from low space orbit. During a
demonstration meeting, fire from a pipe lighter was exposed to the accordion shaped strip of
Nitinol, and then something unexpected and amazing happened. The accordion shaped Nitinol
strip straightened out into its original flat shape. (Kauffman, 1996)
Even though, the shape memory alloy (SMA) may have been invented by
Extraterrestrials and left on Earth after a crash in the 1940’s. A more plausible explanation would
be an accidental discovery made by an engineer, looking to solve totally unrelated problem. We
will be focusing on the discovery made by William Buehler, and the further development of
Nitinol in the market place and the future of this shape memory alloy (SMA).
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II. Introduction
Shape Memory Alloy (SMA) is the generic name for this family of alloys, there are other
alloys that are considered a SMA, but it all started with the Nickel-titanium alloy. The other
SMA alloys include copper-aluminum-nickel, copper-zinc-aluminum, and iron- manganese-
silicon alloys. (Borden, 1991) Nickel-titanium alloy, also, generically called (Nitinol) derived
from (Nickel Titanium Naval Ordnance Laboratory), was discovered in 1961 by William J.
Buehler. Reference Figure 1. William J. Buehler was a researcher at the Naval Ordnance
Laboratory in White Oak, Maryland. (Kauffman, 1993) Like other discoveries the Nickel-
titanium alloy was come about by accident when a strip of Nickel-titanium alloy was bent out
shape and when heated stretch back into its original shape. This event was witnessed many times
by both William J. Buehler and Dr. David S. Muzzey. (Kauffman, 1993)
Figure 1 - William J. Buehler in 1968
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III. History
Between 1952 and 1958, at the Naval Ordnance Laboratory, Buehler a metallurgist, to
cure boredom experienced in between projects, would experiment on iron-aluminum alloy.
William J. Buehler had completed research on a series of iron-aluminum alloys, for the Naval
Ordnance Laboratory (NOL) in 1958. At NOL, Buehler was working on the in-house project
which was to find an appreciate metal that could handle the heat and turbulence experienced by a
spacecraft on reentry into the atmosphere from low space orbit. Buehler’s job on the in-house
project was to provide physical and mechanical property data on existing metals and alloys for
computer-assisted boundary layer calculations. These calculations were to simulate the heating,
etc. of a reentry body through the earth’s atmosphere. The job of working out calculation started
to become boring and Buehler started to think of different alloy conditions that may solve the
reentry problem. (Kauffman, 1996)
Buehler consulted Max Hansen’s recently published Constitution of Binary Alloys which
was the latest text available about binary constitution diagrams, showing the solid-state phase
relationships of two–component metallic alloys as a function of composition and temperature.
Starting with sixty intermetallic compound alloys and then narrowing down to twelve, Buehler,
was able to select an alloy that exhibited considerably more impact resistance and ductility than
the other eleven alloys. That metal combination was an equiatomic nickel–titanium alloy.
(Kauffman, 1996)
In 1959, Buehler, decided to concentrate his research efforts on nickel-titanium alloy
which he gave new name (Nitinol). Nitinol exhibited favorable attributes that were needed for
the nose cone of spacecraft during orbital reentry. (Kauffman, 1996)
Following the startling acoustic damping discovery, other seemingly related unique
changes were observed. More interestingly, these changes also occurred in about the same
temperature range as the acoustic damping change. Examples of some of these correlatable
phenomena were: (Kauffman, 1996)
Polished plane metallographic alloy surface when heated slightly (100 °C to 200 °C; 212
°F to 392 °F) exhibited an obvious eruption or recon touring of the surface. Plate-like surface
shearing occurred and appeared to form along certain crystallographic planes.
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Microhardness indentations made at room temperature remained stable in size at room
temperature. However, when heated slightly (100 °C to 200 °C; 212 °F to 392 °F), they tended to
significantly reduce in size.
Metallography specimens polished using standard Al2O3 abrasive followed by etching
always revealed a typical acicular martensitic structure that one would typically find in quench-
hardened steel. It was only after very careful diamond polishing (with minimal surface strain)
that the true NITINOL base structure was revealed.
Acoustic damping, strain, and microstructure combined with minor temperature variation
were all, in their way, trying to tell me that this was an overtly dimensionally mobile alloy
capable of major atomic movement in a rather low temperature regime—near room temperature.
IV. Accidental Discovery
In 1961, preparing for meeting to demonstrate the fatigue-resistant properties of Nitinol,
Buehler, prepared a (.010 inch thick) strip. At room temperature he bent the strip into an
accordion shape, so it could be pulled out of shape and bounce back. Buehler gave the Nitinol
strip to his assistant to bring to the laboratory management meeting, because he was able to
attend. At the laboratory management meeting, the strip was passed around the members of the
meeting, as a prop. The members of the meeting pulled and twisted the nickel–titanium alloy.
One of the Associate Technical Directors, Dr. David S. Muzzey, who was a pipe smoker, applied
heat from his pipe lighter to the compressed strip. To everyone’s amazement, the Nitinol
stretched out longitudinally. The mechanical memory discovery, while not made in Buehler’s
metallurgical laboratory, was the missing piece of the puzzle of the earlier mentioned acoustic
damping and other unique changes during temperature variation. The unattended actions during a
management meeting made accidental discovery of an amazing alloy, that will be used many
new and innovative inventions. (Kauffman, 1996)
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V. Nitinol Phases and Properties
Nitinol has phase change while still solid; these phase changes are known as martensite
and austenite. Martensite and austenite phase changes "involve the rearrangement of the position
of particles within the crystal structure of the solid" the discovery of the shape-memory effect.
Dr. Frederick E. Wang. (Kauffman, 1993) Nitinol is in the martensite phase under the shift of
temperature. The alteration temperature varies from different compositions from -50 °C to 166
°C. (Jackson, 1997) Nitinol can be bend into varies shapes in the martensite phase, to reshape the
Nitinol back into its original character the Nitinol must held into position and heated to
approximately 500 °C. By heating the Nitinol the atoms are realigned into a compact and regular
pattern resulting into a rigid cubic arrangement known as the austenite phase. (Kauffman, 1993)
The parent shape is achieved in the austenite phase. The Nitinol can phase shifted back and forth
from martensite to austenite for millions of cycles with no breakdown on the composite alloy.
(Jackson, 1997)
The production method of Nitinol varies, current existing techniques of producing nickel-
titanium alloys include vacuum melting techniques such as electron-beam melting, vacuum arc
melting or vacuum induction melting. The Nitinol is made into cast ingot in a press forge or
rotary forge into in to rods or wire. The working temperature for Nitinol is between 700 °C and
900 °C. The cold working method for Nitinol is similar to the fabrication of titanium wire. To
produce wires ranging in size from .075mm to 1.25mm in diameter carbide and diamond dies
must be used to produce the wire. A change to the mechanical and physical properties of Nitinol
will occur when the alloy is cold worked. (Jackson, 1997)
General the properties of Nitinol is comparable to other alloys, its melting point is around
1240 °C to 1310 °C, and its density is around 6.5 g/cm³. Other physical properties due differ
from other alloys such as temperatures with various compositions of elements include electrical
resistivity, thermoelectric power, Hall coefficient, velocity of sound, damping, heat capacity,
magnetic susceptibility, and thermal conductivity. (Jackson, 1997) The large force generated
upon returning to its original shape is a very useful property. Other useful properties of Nitinol
are its "excellent damping characteristics at temperatures below the transition temperature range,
its corrosion resistance, its nonmagnetic nature, its low density and its high fatigue strength"
these properties translate into many uses for Nitinol. Reference Table 1. (Jackson, 1997)
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PHYSICAL PROPERTIESMelting Point 2390°F 1310°CDensity 0.234 lb/in3 6.5 g/cm3
Electrical Resistivity 30 μohm-in 76 μohm-cmModulus of Elasticity 4-6 x 106 psi 28-41 x 103 MPaCoefficient of Thermal Expansion 3.7 x 10-6/°F 6.6 x 10-6/°CMECHANICAL PROPERTIESUltimate Tensile Strength (min. UTS)
160 x 103 psi 1100 MPa
Total Elongation (min) 10% 10%SHAPE MEMORY PROPERTIESLoading Plateau Stress @ 3%/ strain (min)
15 x 103 psi 100 MPa
Shape Memory Strain (max) 8.0% 8.0%Transformation Temperature (Af) 140° F 60° C
Table 1 - Nitinol SM495 Wire Properties (Nitinol, 2010)
VI. Introduction into the Market
The first successful product that used Nitinol was created for the Grumman Aerospace
Corporation by Raychem Corporation. Raychem Corporation Cryofit “shrink-to-fit” coupler was
used as a coupler to tightly fit hoses together. Grumman Aerospace was having a problem with
the hydraulic lines in the F-14 jet fighter, the existing hydraulic line couplers would leak (below
–120 °C; –184 °F). Raychem Corporation found that when a Nitinol tube is placed into liquid
nitrogen between (−196 °C; −321 °F) and (−210 °C; −346 °F), the tube size could be easily be
expanded with a tapered mandrel rod. The ends of the hydraulic pipe were inserted into the
Nitinol coupler tube and the assembly was then allowed to warm, to a temperature lower than –
120 °C; –184 °F. The Nitinol tube would revert back to its original shape coupling the hydraulic
tubes together. The Nitinol tube applied very high associated force, provided a continuously
clamping and totally sealed joint at well below the required –120 °C (–184 °F) temperature. The
Cryofit Nitinol coupler was used on the F-14 jet fighter from that point on. The same coupler or
similar couplers are being used air craft that require that specifications. (Kauffman, 1996)
Nitinol has a variety of applications some are used in military, medical, safety, and
robotics. The military have been using Nitinol coupler since the late 60’s, these coupler are used
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for hydraulic lines. (Kauffman, 1993) In the medical field Nitinol is used for tiny tweezers and
heart stints and catheters through blood vessels. Nitinol is used in Orthodontic to help straighten
teeth. Eyeglass frames are made of Nitinol, so if they bend they spring back in to shape. A safety
application for Nitinol is in fire sprinklers as an anti-scaling device and also water faucets and
shower heads. (Kauffman, 1993) Fire sprinklers using Nitinol achieve more reliable water flow
starts and stops. (Kauffman, 1993) To simulate human muscle motion, Nitinol components are
being used in robotics actuators and micromanipulators. (Rogers, 1995) Other applications for
Nitinol would include household appliances such as thermal sensitivity deep frying baskets,
woman bras making them comfort to the bodies shape for better comfort, Nitinol engine mounts
and suspension parts that control vibration more efficiently, and structure members for bridges
and building. Reference Figures 2, 3, 4, 5. (Falcioni, 1997)(Rogers, 1995)
Figure 2 - Wire for Braces Figure 3 - Stent for Clogged Arteries
Figure 4 – Frames for Eyeglasses Figure 5 - Clot Trapping Filter for blood Vessels
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VII. Current State of the Technology
The use of Shape Memory Alloy in the future is wide open, possible application could be
engines in cars and airplanes, and a motor for generating electricity. Nitinol can be used in
automobile frame and replace body panels, so if in an impact the original shape can be returned
with else. (Kauffman, 1993) Nitinol can be used to form smart louvers for eliminate engine heat
more efficiently. SMA’s is ideal for fasteners, seals, connectors, and clamps. Tighter connections
and easier and more efficient installations result from the use of shape memory alloys. (Borden,
1991)
Nitinol has the mechanical and electrical properties that will allow it to be used to make
more efficient electric motors. Dynalloy Inc. is a 20-year-old company that markets a line of
SMA wire called Flexinol that is used as actuators by a wide variety of manufacturers. Flexinol
is made of nickel-titanium alloy. It comes wrapped on spools like traditional wire, with diameters
ranging from 0.001 to 0.02 inch. Dynalloy claims that one 100- meter spool of Flexinol can
replace approximately 1,000 electric motors. The wire contracts anywhere from 2 percent to 5
percent of its length, like muscles, when it is heated. (Weber, 2010) Nitinol motors are planned
as addition power source for future electric and hybrid cars. Shape memory alloys can be used to
turn exhaust heat energy into energy. For instance, energy harvesting from waste heat will drive
an electric generator to power a battery. Reference Figure 6. (Weber, 2010)
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Figure 6 – SMA Wire Motor Used for Additional Force
The aerospace industry is also searching for new SMA applications. By using the
material, engineers at Boeing, General Electric Co. and Goodrich Corp. developed a variable
geometry chevron that reduces commercial aircraft engine noise. Chevrons are zigzag or saw
tooth shapes at the back end of the nacelle and the engine exhaust nozzle, with tips that are bent
slightly into the airflow. This creates vortices that form at each chevron, enhancing the mixing
rate of the adjacent flow streams. When the chevrons enhance mixing by the right amount, jet
engine noise diminishes. (Weber, 2010)
Traditionally, automakers use hundreds of cable actuators, small electromagnetic motors
and other mechanical devices to adjust mirrors, seats and headrests; operate windows and door
locks; raise antennas; and release latches. Many of these components can be replaced with SMA.
(Weber, 2010) Using Nitinol wire automaker will be able to make louvers the open when, when
the engine heat is high enough to make the alloy react. On demand control of airflow into the
engine compartment uses a shape memory alloy activated louver system. The results are
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improved aerodynamics, drag reduction and repaid warm-up during cold starts. Reference
Figure 7. (Weber, 2010)
Figure 7 – SMA Controlled Louvers
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VIII. Future Prediction of Shape Memory Alloy (SMA)
Shape Memory Alloy (SMA) or Nitinol with it potential use as a muscle metal; it is like
an actuator without all the extra parts. Present day actuators use different methods mechanics to
achieve movement such as pneumatics, electricity, and hydraulics. A Nitinol wire has only a
wire strain and a heat source that heat source can be direct or induced by electric current. Nitinol
simplicity lends itself to diverse applications in different industries such as medicine, industrial,
robotics, and etc. the potential is unlimited.
1. Medicine
The application of Shape Memory Alloy (SMA) or Nitinol in medicine is not new; its use
in medicine has been around for few decades. The present day uses of Nitinol are for such
devices as tension wires on dental orthodontics braces and in cardiovascular medicine Nitinol is
being used for heart stints and blood vessel catheters. Nitinol wire is being used to make nearly
indestructible frame for eye glasses, because SMA eyeglass frames will bounce back to the
original shape after being bent. (Kauffman, 1993)
During surgery suture must sewn up to close up wounds and stop the possible spread of
infection, historical this is done with synthetic, including the absorbables polyglycolic acid,
polylactic acid, and polydioxanone as well as the non-absorbables nylon and polypropylene. The
surgical suture is a medical device used to hold body tissues together after an injury or surgery. It
generally consists of a needle with an attached length of thread. A number of different shapes,
sizes, and thread materials have been developed over its millennia of history. Reference Figure 8.
(Braun, 2010)
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Figure 8 – Surgical Suture
In the near future Shape memory alloys such as super-elastic nickel-titanium can be used
for surgical needles and hinge less needle drivers. Nitinol Devices and Components, Inc. in
collaboration with Endoscopic Surgery and Allied Technologies is currently evaluating the
application of shape memory alloys such as Nickel Titanium for endoscopic surgical needles and
needle drivers. The first prototypes make use of the super elasticity of Nickel Titanium alloys.
The stress/strain characteristics of super elastic materials are distinctly different from
conventional materials like spring steel. A plateau is reached at low stresses and large elastic
strains can be accumulated with little stress increase. This behavior allows promising new
designs and functions of endoscopic suturing devices. (Melzer, 1994)
Surgical needles made from Nitinol resist irreversible kinking and give a "built-in
indication" of the stress applied to tissue, since the needle continuously bends once a certain
stress level is reached. The stress remains nearly constant for further bending of the needle, thus
tissue damage can be avoided. This seems crucial in endoscopic sewing use the tactile feedback
is very much reduced so that optical perception is the only precise means of control. However,
the needles require further experimental test and the delicate processing needs further
development. (Melzer, 1994)
To improve needle driver performance and enhance the design for cleaning and durability
purposes, Endoscopic Surgery and Allied Technologies have developed so called hinge less
instruments , all hinges and bolts at the tip of the instrument have been replaced by a single part
for the jaws and inner rod. The instrument uses an intermediate tube which closes the two jaws
when slipped over the flexible parts of the jaws. The super elasticity allows a precise and
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controlled grip of both needle and thread. In the first locking position, the thread can be grasped
without destroying the inner structure, as this is usually the case when the suture is gripped with
a conventional needle driver. The grasping of any suture with tungsten-reinforced holders may
lead to severe damage to the suture, with subsequent breakage. In the second locking position, a
firm grip is achieved to maintain the needle position. The instrument can easily be disassembled
and cleaned and the jaws element can be replaced if wear and tear occurs. Further tests and
clinical trials are required to confirm the initial findings on hinge less needle drivers. Reference
Figure 9. (Melzer, 1994)
Figure 9 - Endoscopic Surgery
Nitinol alloy properties will more likely used in conjunction with other technologies to
heal the infirmed or repair lifelong impediments. Nitinol alloys suturing development in
endoscopic surgery is just a single future development using smart memory alloy.
2. Consumer Goods
Nitinol has unlimited application potential in technology, it can be used as a strong
actuator and to move objects in a small space by providing heat or electrical current. Currently,
Nitinol is used in women’s bras as a wire support that holds its shape under the most demanding
use. Nitinol will soon be used more in fashion, then just underwear support.
Designers have been experimenting with innovative materials for years. Once-
revolutionary synthetic fabrics such as polyester, Spandex, Gore-Tex and Ultrasuede are now
15
used in a wide range of apparel and footwear. Recently, hip, Los Angeles-based denim designer
Serfontaine Jeans started using DuPont's Lycra T400, which is made from multicomponent
yarns, to create stretch jeans that don't lose their elasticity, thereby virtually eliminating the need
for a belt. (Ejiofor, 2006)
Students at MIT's Media Lab are also experimenting with affordable wearable technology
using fabrics imbued with various metals, such as organza, copper, carbon and stainless steel;
they have produced conductive clothing that is still soft to the touch. Amanda Parkes, an MIT
student, has been studying how Nitinol, changes shape during fluctuations in temperature. With
the application of a small amount of heat, a Nitinol-based long-sleeve shirt can become short
sleeved in seconds, while still being able to revert back to its original shape. Reference Figure 10
& 11. (Ejiofor, 2006)
Figure 10 – Shape Changing Boots Figure 11 – Actuating Shirt
The automobile has been part of American life for more than a century changing little for many
of those years. The engines are still run on either gasoline or diesel, and there are a dozen of
hydraulic pumps and electric motors all through the interior of the vehicle. Smart materials
“remember” their original shape and can return to it, opening new possibilities for many movable
features, such as replacing the electric motors traditionally used to activate car seats, windows
and locks. There are numerous applications for the technology in the automotive, aerospace,
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appliance, medical and electronics industries. (Weber, 2010) The dynamic nature of smart
memory alloy can be used in the outer body panels of future automobiles to allow them to
change to fit their environment to optimize their operating functions. General Motors engineers
have been developing Air dams, which are important to reducing aerodynamics drag at highway
speeds are frequently damaged by low-speed impacts with parking bumpers, ramps, and snow
and ice. An air dam activated by shape memory alloy can monitor vehicle speed, the use of four-
wheel drive and the presences of snow to intuitively lower or raise the dam to optmize3 aero
drag. Reference Figure 12. (Weber, 2010)
Figure 12 – Aerodynamic Air Dam
These are only few of the future consumer product developments of Nitinol. Smart
memory alloy will be used anywhere an engineer will find way to make a product better, quicker,
faster, and more reliable.
3. Robotics
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Today the assembly line robot uses hydraulic, pneumatics, and electric actuators and
solenoids. Tomorrow’s large robots will probable use the same technology, but the small; the
microbots will be using Nitinol muscle. There will not enough space inside a machine the size of
house fly to contain the same mechanical systems as it larger cousins.
For a new class of soft robotic platforms, development of flexible and robust actuators is
quintessential. Remarkable resilience, shape memory effect, high energy density, and scalability
are attributed to nickel titanium (NiTi) making it an excellent actuator candidate for meso-scale
applications. The presented fiber is 400µm in diameter and 0.5m in length exhibiting 50%
contraction and 1226J/kg of energy density with 40g of force. By changing the geometry of the
spring, force-displacement characteristics can be tuned. (Sangbae, 2009)
Harvard Microrobotics Lab research focuses on design, fabrication, control, and analysis
of biologically-inspired microrobots and soft robots. They are gaining expertise in
microfabrication and microsystem design, combined with insights from arthropods; enable
Harvard Microbotics Lab to create high-performance aerial and ambulatory microrobots. Such
robotic platforms can be used for search and rescue operations, assisted agriculture,
environmental monitoring, and exploration of hazardous environments. Reference Figure 13.
(Harvard, 2009)
Figure 13 - Harvard Microrobotic Fly
In 2007, a life-size, robotic fly has taken flight at Harvard University. Weighing only 60
milligrams, with a wingspan of three centimeters, the tiny robot's movements are modeled on
those of a real fly. While much work remains to be done on the mechanical insect, the
researchers say that such small flying machines could one day be used as spies, or for detecting
18
harmful chemicals. The researchers must still design a control system for the robot, so robotic fly
can release from its tethers and still flies straight. (Ross, 2007)
Recreating a fly's efficient movements in a robot roughly the size of the real insect was
difficult, however, because existing manufacturing processes couldn't be used to make the
sturdy, lightweight parts required. The motors, bearings, and joints typically used for large-scale
robots wouldn't work for something the size of a fly. To fabricate the robotic fly some extremely
small parts can be made using the processes for creating microelectromechanical systems.
Ultimately, the Harvard Microrobotics Lab research team developed its own fabrication process.
Using laser micromachining, researchers cut thin sheets of carbon fiber into two-dimensional
patterns that are accurate to a couple of micrometers. Sheets of polymer are cut using the same
process. By carefully arranging the sheets of carbon fiber and polymer, the researchers are able
to create functional parts. Reference Figure 14. (Ross, 2007)
Figure 14 - 60 milligrams Robotic Fly
A use for such a tiny robot could the detection of chemicals in the air. Tiny, lightweight
sensors need to be integrated as well. Chemical sensors could be used, for example, to detect
toxic substances in hazardous areas so that people can go into the area with the appropriate safety
gear. Wood and his colleagues will also need to develop software routines for the fly so that it
will be able to avoid obstacles. (Ross, 2007)
The applications of Smart Memory Alloy (SMA) are as varied as the imagination.
Predicting the future use of SMA is a misnomer, the future use of SMA will be a evolving
process of research and development.
IX. Potential Technology
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Narrowing down the potential of Smart Memory Alloy (SMA) technology is a difficult
endeavor, since I believe that this technology will be applied whenever such material properties
are beneficial. Smart Memory Alloys application can find in many areas of technology, as long
as the designers and their management are willing to look outside the box.
I will discuss a possible new ream that I have not found Smart Memory Alloy (SMA)
being used, and that is the area of munitions fuzing. The area of fuzing I referring to is the fuzes
used in the bomb that are deployed from aircraft. Currently, the within fuzes there are redounded
safety systems the keep the fuze from arming, when it is not appropriate. This system is called
the fuze safing and arming (S&A). The majority of the fuzes used by the United States Air Force
and Navy are the FMU-152A/B, FMU-139C/D, FMU-143E/B, and FMU-156. (Fuze, 2010)
With today's highly destructive weapons, there must be a high degree of assurance that the
weapon will not detonate until it has reached the target that it is intended to destroy. This
assurance is provided by the safing and arming device (S&A). (Fuzing, 2010) Fuzes are
normally divided into two general classes—mechanical and electrical. (Fuzing, 2010) Either
Mechanical or Electrical a fuze must be design to meet the following requirements:
It must remain safe in stowage, while it is handled in normal movement, and during
loading and downloading evolutions.
It must remain safe while being carried aboard the aircraft.
It must remain safe until the bomb is released and is well clear of the delivery aircraft
(arming delay or safe separation period).
Depending upon the type of target, the fuze may be required to delay the detonation of
the bomb after impact for a preset time (functioning delay). Functioning delay may vary
from a few milliseconds to many hours.
It should not detonate the bomb if the bomb is accidentally released or if the bomb is
jettisoned in a safe condition from the aircraft. To provide these qualities, a number of
design features are used. Most features are common to all types of fuzes.
1. Mechanical Fuzes
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In its simplest form, a mechanical fuze is like the hammer and primer used to fire a rifle
or pistol. A mechanical force (in this case, the bomb impacting the target) drives a striker into a
sensitive detonator. The detonator ignites a train of explosives, eventually firing the main or filler
charge. A mechanical bomb fuze is more complicated than the simple hammer and primer.
(Fuzing, 2010)
2. Electrical Fuzes
Electrical fuzes have many characteristics of mechanical fuzes. They differ in fuze
initiation. An electrical impulse is used to initiate the electrical fuze rather than the mechanical
action of arming vane rotation. An electrical pulse from the delivery aircraft charges capacitors
in the fuze as the bomb is released from the aircraft. Arming and functioning delays are produced
by a series of resistor/capacitor networks in the fuze. The functioning delay is
electromechanically initiated, with the necessary circuits closed by means of shock-sensitive
switches. The electric bomb fuze remains safe until it is energized by the electrical charging
system carried in the aircraft. Because of the interlocks provided in the release equipment,
electrical charging can occur only after the bomb is released from the rack or shackle and has
begun its separation from the aircraft; however, it is still connected electrically to the aircraft's
bomb arming unit. At this time, the fuze receives an energizing charge required for selection of
the desired arming and impact times. (Fuzing, 2010)
3. SMA Actuator
In most modern precision bomb fuzes the safing and arming safety devices uses
Pyrotechnic Devices to lock, unlock, and provide the energy to move interior fuze parts. The
suppliers for the specialized pyrotechnic devices are dwindling, there are three or four
manufactures left in the United States. Being such a limited number of manufacturers of these
devices, reliability and on time delivery is a consistent problem. A reliable alternative needs to
be found and developed. SMA actuators show promise as a replacement for pyrotechnic devices,
because of the superior properties that displayed by SMA. A simple SMA actuator can made to
work in conjunction with other devices to achieve the desired effect of a pyrotechnic actuator.
Reference Figure 15.
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Figure 15 – SMA Actuator
A simple SMA Actuator can be designed to use the strength and reliability of alloy
replacing the pyrotechnics. A SMA wire is attached is a piston that is used to lock the safing and
arming device into place. An electric current is conducted through the wire; the resistance that is
caused by the wire generates sufficient heat throughout the wire. The atoms in the wire
reposition, becoming more ordered and compact, the wire shrinks becoming shorter in length.
The action of the shrinking wire pulls the actuator piston in the direction shown in figure 1. The
safing and arming device is than free move. The SMA wire can be designed to spin a rotor.
Reference Figure 16.
Figure 16 – SMA Rotor Actuator
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Another simple device is to use the SMA wire to make rotor spin. A current is applied
across the Wire, making heat from the resistance of the wire. One end of the wire is fixed
connected and the on end is connected to the rotor. The SMA wire contracts, pulling the rotor
connected end of the wire, causing the rotor to spin in a circular path. The rotor can than align an
explosive train, arming the fuze. Reference Figure 16.
The required temperature that fuze must survive and still function is -54º C to 65º C as
stated in MIL-STD-310 and MIL-STD-810. The advantages of using SMA actuator wire to make
actuators, is it does not activate if exposed to heat above 77º C like a polytechnic device.
(Eaglepicher, 2008) SMA wire does not react unless the heat it is exposed to is above 482º C.
(Kauffman , 1996) If a polytechnic device is exposed to extreme cold the function can be
negatively affected. SMA wire must be exposed to -210 °C to it will not function. A
polytechnics device can, also, malfunctions from the internal structures such as voids in the
polytechnic change or a broken bridge wire. Reference Figure 17.
Figure 17 – Polytechnics Device
Replacing the polytechnic devices with SMA actuator devices is possible, but more
research is needed to achieve the same or superior performance. Bomb fuze safing and arming
systems in bomb is just a single possible future development of smart memory alloy.
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