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

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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

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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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