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Seminar Report-2011 Shape Memory Alloys

1.Introduction

Shape memory alloys (SMAs) are metals that "remember" their original shapes. SMAs are useful for such things as actuators which are materials that "change shape, stiffness, position, natural frequency, and other mechanical characteristics in response to temperature or electromagnetic fields". The potential uses for SMAs especially as actuators have broadened the spectrum of many scientific fields. The study of the history and development of SMAs can provide an insight into a material involved in cutting-edge technology. The diverse applications for these metals have made them increasingly important and visible to the world.

Nickel-titanium alloys have been found to be the most useful of all SMAs. Other shape memory alloys include copper-aluminum-nickel, copper-zinc-aluminum, and iron- manganese-silicon alloys.(Borden, 67) The generic name for the family of nickel-titanium alloys is Nitinol. In 1961, Nitinol, which stands for Nickel Titanium Naval Ordnance Laboratory, was discovered to possess the unique property of having shape memory. William J. Buehler, a researcher at the Naval Ordnance Laboratory in White Oak, Maryland, was the one to discover this shape memory alloy. The actual discovery of the shape memory property of Nitinol came about by accident. At a laboratory management meeting, a strip of Nitinol was presented that was bent out of shape many times. One of the people present, Dr. David S. Muzzey, heated it with his pipe lighter, and surprisingly, the strip stretched back to its original form.

E & I Dept. CEK P a g e | 1

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http://web.archive.org/web/19990430001744/http:/www.mtm.kuleuven.ac.be/Reports/ScientificReport92-94/Chap1Sec3.html


2.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)



3. 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)



4. General principlesShape memory metal alloy can exist in two different temperature

dependent crystal structures (phases) called martensite (lower temperature ) and austenite ( higher temperature or parent phase ). Several properties of austenite and martensite are notably different

Martensite, is the relatively soft and easily deformed phase of shape memory alloys, which exists at lower temperatures. The molecular structure in this phase is twinned which is the configuration shown in the middle of Figure 2. Upon deformation this phase takes on the second form shown in Figure 2, on the right. Austenite, the stronger phase of shape memory alloys, occurs at higher temperatures. The shape of the Austenite structure is cubic, the structure shown on the left side of Figure 2. The un-deformed Martensite phase is the same size and shape as the cubic Austenite phase on a macroscopic scale, so that no



change in size or shape is visible in shape memory alloys until the Martensite is deformed.

5. Shape Memory EffectThe shape memory effect is observed when the temperature

of a piece of shape memory alloy is cooled to below the temperature Mf. At this stage the alloy is completely composed of Martensite which can be easily deformed. After distorting the SMA the original shape can be recovered simply by heating the wire above the temperature Af. The heat transferred to the wire is the power driving the molecular rearrangement of the alloy, similar to heat melting ice into water, but the alloy remains solid. The deformed Martensite is now transformed to the cubic Austenite phase, which is configured in the original shape of the wire.

The Shape memory effect is currently being implemented in: The space shuttle



Thermostats Vascular Stents Hydraulic Fittings (for Airplanes)

6. Pseudo-elasticity

Pseudo-elasticity occurs in shape memory alloys when the alloy is completely composed of Austenite (temperature is greater than Af). Unlike the shape memory effect, pseudo-elasticity occurs without a change in temperature. The load on the shape memory alloy is increased until the Austenite becomes transformed into Martensite simply due to the loading; this process is shown in Figure 5. The loading is absorbed by the softer Martensite, but as soon as the loading is decreased the Martensite begins to transform back to Austenite since the temperature of the wire is still above Af, and the wire springs back to its original shape.

Some examples of applications in which pseudo-elasticity is used are:



Eyeglass Frames Medical Tools Cellular Phone Antennae

7.Alloy Types

Since the discovery of Ni-Ti, at least fifteen different binary, ternary and quaternary alloy types have been discovered that exhibit shape changes and unusual elastic properties consequent to deformation. Some of these alloy types and variants are shown in table 1.

Table 1. Shape memory alloy types.

· Titanium-palladium-nickel

· Nickel-titanium-copper

· Gold-cadmium

· Iron-zinc-copper-aluminium

· Titanium-niobium-luminium

· Uranium-niobium

· Hafnium-titanium-nickel

· Iron-manganese-silicon

· Nickel-titanium

· Nickel-iron-zinc-aluminium

· Copper-aluminium-iron

· Titanium-niobium

· Zirconium-copper-zinc

· Nickel-zirconium-titanium

The original nickel-titanium alloy has some of the most useful characteristics in terms of its active temperature range, cyclic performance, recoverable strain energy and relatively simple thermal processing. Ni-Ti and other alloys have two generic properties thermally induced shape recovery and super- or pseudo-elasticity. The latter



means that an SMA in its elastic form can undergo a deformation approximately ten times greater than that of a spring-steel equivalent, and full elastic recovery to the original geometry may be expected. This may be possible through several million cycles. The energy density of the alloy can be used to good effect to make high-force actuators - a modern DC brushless electric motor has a mass of 5-10 times that of a thermally activated Ni-Ti alloy, to do the same work.

The super elastic Ni-Ti alloys are “stressed” by simply working the alloy. These stresses can be removed, just as with many other alloys, by an annealing process. The stressed condition is termed stress-induced martensite, which is the equivalent of being cold/hot worked.

SMAs, particularly nickel-titanium, are commercially available from several sources. However, world production is small compared to other metal commodities (about 200 tonnes were produced 1998) owing to difficulties in the melt/forging production process, and so the cost of the material high US$0.30-US$1.50 (UK£0.20-£1.00) per gram for wire forms 1999 prices). Fortunately, most current applications require only small amount of the material. As world production increases (as it has done quite dramatically in the 1990s) so prices should decrease. Wires, strip, rod, bar and sheet are all readily available and alloy foams, sintering powders and sputtering targets of high purity are also produced.



8.Nitinol Phases and PropertiesNitinol 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)

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 MPaTotal 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)



9.PROGRAMMINGThe use of the one way shape memory or super elastic property of

NiTi for a specific application requires a piece of SMA to be molded into the desired shape . the characteristic heat treatment is then done to set the specimen to its final shape . The heat treatment methods used to set shapes in both the shape memory and the super elastic forms of NiTi are similar. Adequate heat treatment parameters are needed to set the shape and properties of the item.

The two way memory training procedure can be made by SME training or SIM training . In SME training the specimen is cooled below Mf and bent the desired shape . It is then heated to a temperature above Af and allowed freely to take its austenite shape . The procedure is repeated 20 – 30 times which completes the training . The sample now assumes its programmed shape upon cooling under Mf and to another shape when heated above Af.

In SIM (stress induced martensite ) training the specimen

is bent just above Ms to produce the preferred variants of SIM and then cooled below Mf temperature. Upon subsequent heating above the Af temperature the specimen takes its original austenitic shape . This procedure is repeated 20-30 times.



10. 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.

10.1.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)

10.1.1 Stents

The property of thermally induced elastic recovery can be used to change a small volume to a larger one. An example of a device using



this is a stent. A stent, either in conjunction with a dilation balloon or simply by self-expansion, can dilate or support a blocked conduit in the human body. Coronary artery disease, which is a major cause of death around the world, is caused by a plaque in-growth developing on and within an artery’s inner wall. This reduces the cross-section of the artery and consequently reduces blood flow to the heart muscle. A stent can be introduced in a “deformed” shape, in other words with a smaller diameter. This is achieved by travelling through the arteries with the stent contained in a catheter. When deployed, the stent expands to the appropriate diameter with sufficient force to open the vessel lumen and reinstate blood flow.

10.1.2. Vena-cava Filters

Vena-cava filters have a relatively long record of successful in-vivo application. The filters are constructed from Ni-Ti wires and are used in one of the outer heart chambers to trap blood clots, which might be the cause of a fatality if allowed to travel freely around the blood circulation system. The specially designed filters trap these small clots, preventing them from entering the pulmonary system and causing a pulmonary embolism. The vena-cava filter is introduced in a compact cylindrical form about 2.0-2.5mm in diameter. When released it forms an umbrella shape. The construction is designed with a wire mesh spacing sufficiently small to trap clots. This is an example of the use of superelastic properties, although there are also some thermally actuated vena cava filters on the market.

10.1.3. Dental and Orthodontic Applications

Another commercially important application is the use of superelastic and thermal shape recovery alloys for orthodontic applications. Archwires made of stainless steel have been employed as a corrective



measure for misaligned teeth for many years. Owing to the limited “stretch” and tensile properties of these wires, considerable forces are applied to teeth, which can cause a great deal of discomfort. When the teeth succumb to the corrective forces applied, the stainless steel wire has to be re-tensioned. Visits may be needed to the orthodontist for re-tensioning every three to four weeks in the initial stages of treatment.

Superelastic wires are now used for these corrective measures. Owing to their elastic properties and extendibility, the level of discomfort can be reduced significantly as the SMA applies a continuous, gentle pressure over a longer period. Visits to the orthodontist are reduced to perhaps three or four per year.

Example of how even a badly fractured face can be reconstructed using bone plates

10.1.4. Robotic Muscles

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There have been many attempts made to re-create human anatomy through mechanical means. The human body however, is so complex that it is very difficult to duplicate even simple functions. Robotics and electronics are making great strides in this field, of particular interest are limbs such hands, arms, and legs.

Shape memory alloys mimic human muscles and tendons very well. SMA's are strong and compact so that large groups of them can be used for robotic applications, and the motion with which they contract and expand are very smooth creating a life-like movement unavailable in other systems.

Creating human motion using SMA wires is a complex task but a simple explanation is detailed here. For example to create a single direction of movement (like the middle knuckle of your fingers) the setup shown in Figure 1 could be used. The bias spring shown in the upper portion of the finger would hold the finger straight, stretching the SMA wire, then the SMA wire on the bottom portion of the finger can be heated which will cause it to shorten bending the joint downwards (as in Figure 1). The heating takes place by running an electric current through the wire; the timing and magnitude of this current can be controlled through a computer interface used to manipulate the joint. There are still some challenges that must be overcome before robotic hands can become more commonplace. The first is generating the computer software used to control the artificial muscle systems within the robotic limbs. The second is creating large enough movements to emulate human flexibility (i.e. being able to bend the joints as far as humans can). The third problem is reproducing the speed and accuracy of human reflexes.



10.2.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 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.

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, 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.

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.



10.3.Robotics

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.

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 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.

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.

11. Potential TechnologyNarrowing 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.

11.1.Mechanical Fuzes

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)

11.2.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)

11.3.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 1.



Figure 1 – 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



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.

11.4.Aircraft Maneuverability

Aircraft maneuverability depends heavily on the movement of flaps found at the rear or trailing edge of the wings. The efficiency and reliability of operating these flaps is of critical importance.

Most aircraft in the air today operate these flaps using extensive hydraulic systems. These hydraulic systems utilize large centralized pumps to maintain pressure, and hydraulic lines to distribute the pressure to the flap actuators. In order to maintain reliability of operation, multiple hydraulic lines must be run to each set of flaps. This complex system of pumps and lines is often relatively difficult and costly to maintain.

Many alternatives to the hydraulic systems are being explored by the aerospace industry. Among the most promising alternatives are piezoelectric fibers, electrostrictive ceramics, and shape memory alloys.

The flaps on a wing generally have the same layout shown on the left, with a large hydraulic system attached to it at the point of the actuator connection. "Smart" wings, which incorporate shape memory alloys, are typically like the wing this system is much more compact and efficient, in that the shape memory wires only require an electric current for movement.



Hinge less shape memory alloy Flap

The shape memory wire is used to manipulate a flexible wing surface. The wire on the bottom of the wing is shortened through the shape memory effect, while the top wire is stretched bending the edge downwards, the opposite occurs when the wing must be bent upwards. The shape memory effect is induced in the wires simply by heating them with an electric current, which is easily supplied through electrical wiring, eliminating the need for large hydraulic lines. By removing the hydraulic system, aircraft weight, maintenance costs, and repair time are all reduced.



12. Advantages and Disadvantages Some of the main advantages of shape memory alloys include: Bio-compatibility Diverse Fields of Application Good Mechanical Properties (strong, corrosion resistant)



The use of NiTi as a biomaterial has severable possible advantages.Its shape memory property and super elasticity are unique characteristics and totally new in the medical field. The possibility to make self-locking, self expanding and self- compressing thermally activated implants is fascinating. As far as special properties and good bio compatibility are concerned, it is evident that NiTi has a potential to be a clinical success in several applications in future.

There are still some difficulties with shape memory alloys that must be overcome before they can live up to their full potential. These alloys are still relatively expensive to manufacture and machine compared to other materials such as steel and aluminum. Most SMA's have poor fatigue properties; this means that while under the same loading conditions (i.e. twisting, bending, compressing) a steel component may survive for more than one hundred times more cycles than an SMA element.



13. Conclusion

The many uses and applications of shape memory alloys ensure a bright future for these metals. Research is currently carried out at many robotics departments and materials science departments. With the innovative ideas for applications of SMAs and the number of products on the market using SMAs continually growing, advances in the field of shape memory alloys for use in many different fields of study seem very promising.


http://www.stanford.edu/~richlin1/sma/sma.html#ROBOT


14. ReferenceBorden, Tom. "Shape-Memory Alloys: Forming a Tight Fit." Mechanical

Engineering. Oct. 1991, p67-72.

Braun Melsungen AG. “History of the Surgical Suture.” www.sutures-bbraun.com . 2010. http://www.sutures-bbraun.com/index.cfm?917A74A92A5AE6266700AD9ACBE9432C . Retrieved on July 24, 2010.

“Eaglepicher Defense.” Eaglepitcher Companies. 2008. http://www.eaglepicher.com/content/view/62/144/. Retrieved on August.

Ejiofor, Mmoma. “Fashions of the Future.” Forbes.com. March 16, 2006. http://www.forbes.com/2006/03/16/future-fashion-trends-cx_me_0316feat_ls.html. Retrieve on July 17, 2010.

Falcioni, John G. "Shape Memory Alloys." Mechanical Engineering. April 1992, p114.

Alloy with a Memory: Its Physical Metallurgy, Properties, and Applications: A Report.” Washington: NASA. 1972.

Kauffman, George and Isaac Mayo. "Memory Metal." Chem Matters. Oct. 1993, p4-7.

Kauffman, George and Isaac Mayo. “The Story of Nitinol: The Serendipitous Discovery of the Memory Metal and Its Applications.” The Chemical Educator. 1996. VOL. 2, NO. 2, S 1430-4171 (97) 021 11–0.

Melzer, Schurr, Lirici, Klemm, Stoeckel, Buess. “Future Trends in Endoscopic Suturing.” Endoscopic Surgery and Allied Technologies. February 1994, Vol. 2, Nr. 1



“Nitinol Devices & Components.” Nitinol SM495 Wire Material Data Sheet. www.nitinol.com, SDS-SM495, Rev. B., http://www.nitinol.com/media/files/material-properties-pdfs/sm495_wire_data%20%5BConverted%5D_v2.pdf. Retrieved on 4 July 2010.

Rogers, Craig. "Intelligent Materials." Scientific American. Sept. 1995, p154-157.

Ross, Rachel. “Robotic Insect Takes Off.” Technology Review. July 19, 2007. http://www.technologyreview.com/printer_friendly_article.aspx?id=19068&channel=computing&section=. Retrieved on July 25, 2010.

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