Encyclopedia of Smart Materials (Vols 1 and 2) - M. Schwartz (2002) Episode 11 pptx

P1: FCH/FYX P2: FCH/FYX QC: FCH/UKS T1: FCH PB091-S-DRV-I January 24, 2002 15:42 922 SHAPE MEMORY ALLOYS, APPLICATIONS Loading Loading Unloading Unloading Deformation Strain Deformation Strain Stress Stress Removal of Load Removal of Load Applied Loading Applied Loading Applied Heating Initial Position Initial Position Superelastic EffectShape Memory Effect AC B D Figure 1. Typical SMA behavior in tensile tests and bending applications: (a) stress-strain curve of shape memory (martensite) material, (b) schematic of a shape memory application, (c) stress– strain curve ofsuperelastic (austenite) in tension, (d) superelastic behavior ina bending application. Shape-memory alloys may also be trained to exhibit a two-way shape memory effect. Similar to the thermal shape-memory effect, two-way shape memory (TWSM) requires special thermomechanical processing to impart shape memory in both martensitic and austenitic phases. A trained shape in the austenitic phase reverts to a sec- ond trained shape upon cooling, allowing the material to cycle between two different shapes. This TWSM is theoret- ically ideal for many shape-memory applications; however, practical uses are limited due to behavior instability and complex processing requirements. Superelastic Effect. This effect, known also as pseudoe- lastic, describes material strains that are recovered isothermally to yield mechanical shape-memory behavior. The phenomenon is essentially the same as the thermal shape-memory effect, although the phase transformation to austenite (A f ) occurs at temperatures below the expected operating temperature. If the austenitic phase is strained by an applied load, a martensitic phase is induced by stress, and the twinning process occurs as if the material had been cooled to its martensitic temperature. When the applied load is removed, the material inherently prefers the austenitic phase at the operating temperature, and its strain is instantly recovered. A typical stress–strain curve is depicted in Fig. 1c, and a schematic example of a superelastic application is shown in Fig. 1d. The stress– strain curve indicates a difference in stress levels dur- ing loading and unloading, that is known as superelastic stress–strain hysteresis. Alloys Several alloys have been developed that display vary- ing degrees and types of shape-memory behavior. The most commercially successful have been Ni–Ti, Ni–Ti-X and Cu-based alloys, although Ni–Ti and ternary Ni–Ti–X alloys are used in more than 90% of new SMA applications (6). Ni–Ti alloys are more expensive to melt and produce than copper alloys, but they are preferred for their duc- tility, stability in cyclic applications, corrosion resistance, biocompatibility, and higher electrical resistivity for resis- tive heating in actuator applications (6). The most common Cu-based alloys, Cu–Al–Ni and Cu– Zn–Al, are used for their narrow thermal hysteresis and adaptability to two-way memory training. Ni–Ti ternary alloys are used to enhance other parameters. Examples include Ni–Ti–Nb for wide thermal hysteresis, Ni–Ti–Fe for extremely low TTR, Ni–Ti–Cr for TTR stability during thermomechanical processing, and Ni–Ti–Cu for narrow thermal hysteresis and cyclic stability (7). P1: FCH/FYX P2: FCH/FYX QC: FCH/UKS T1: FCH PB091-S-DRV-I January 24, 2002 15:42 SHAPE MEMORY ALLOYS, APPLICATIONS 923 Material Forms SMAs are manufactured in many of the conventional forms expected of metal alloys: drawn round wire, flat wire, tubing, rolled sheet, and sputtered thin films. Additional forms include shaped components, centerless ground ta- pered wires and tubing, alternate core wire (Ni–Ti filled with a conductive or radiopaque material), PTFE coated wire, stranded wire, and embedded composites. At present, Ni–Ti–X alloys are the most readily available in all of these forms. The processing of SMA material is critical for optimiz- ing shape-memory behavior. Many adjustments can be made to optimize the properties of a material form for a particular application; however, most efforts are made to optimize a balance of strain recovery, ductility, and ten- sile strength. SMAs such as Ni–Ti are melted using ex- treme purity and composition control, hot worked to bars or plates, cold worked to their final form, and subjected to specialized thermomechanical treatments to enhance their shape-memory properties. DESIGNING WITH SHAPE MEMORY ALLOYS Shape-memory alloys have intrigued engineers and inven- tors for more than 30 years. One might conclude from the large number of SMA patents that have been issued and the knowledge that relatively few of the ideas have been commercially successful that the majority of these designs have not fully accounted for the unique behaviors, limita- tions, and constraints of SMAs. The focus of this section is to highlight the properties best used in SMA applications and to discuss SMA design considerations. Functional Properties SMA applications are often categorized in terms of the spe- cific material property used. The majority of these pro- perties are either thermal shape memory or mechanical shape memory (superelastic), but some unique properties are only indirectly related to these shape-memory effects. General categories of applications are classified according to these properties. Shape Memory. The thermally activated ability of a shape memory material to change shape yields several types of applications that can be summarized in three dis- tinct categories: applications that use the shape change to display motion, those that actuate, and those that harness stresses produced from constraining the recovery of the shape-memory material. Displayed motion, also referred to as free recovery, de- scribes applications that exploit the pure motion of thermal shape memory (8). An example ofthisapplication,a moving butterfly, is displayed in Fig. 2. These butterflies, produced by Dynalloy, Inc., use a specially processed form of Ni–Ti wire to move wings back and forth for thousands of cycles without significant signs of fatigue. This processed wire, known as Flexinol TM , changes shape via cyclic heating by electric current. The small mass of the butterfly body is sufficient to extend the Ni–Ti wire when cooled, but the Ni–Ti wire can contract and close the wings when heated to its stronger austenitic shape. Actuation applications are designed to perform work. A simplified example is a mass suspended from a shape- memory tension spring. When cooled, the weaker marten- sitic phase deforms,andthe spring is extended by the mass. When heated to austenite, the spring recovers its shape with forces sufficient to lift the weight, resulting in actua- tion that performs work. Constrained recovery applications use the change in material strength from martensite to austenite to pro- duce a stress that can be harnessed as a clamping force. A popular example of a constrained recovery application is a shape-memory coupling which is expanded at low temperatures, then heated to shrink and clamp to join two pipes. Superelasticity. Unlike thermal shape-memory applica- tions, which can be categorized into several types, appli- cations that exploit this mechanical shape memory are defined as those that require high strain recovery at Figure 2. Photograph of a Flexinol TM actuated butterfly (cour- tesy of Dynalloy, Inc.). P1: FCH/FYX P2: FCH/FYX QC: FCH/UKS T1: FCH PB091-S-DRV-I January 24, 2002 15:42 924 SHAPE MEMORY ALLOYS, APPLICATIONS Figure 3. Suture retrieval loops designed to recover their shape once deployed from a 6 fr. cannula (courtesy of Shape Memory Applications, Inc.). operating temperatures. Many examples of applications that use superelasticity are found in the medical indus- try (Fig. 3), but one of the most well known is found in consumer eyeglass frames marketed as Flexon ® by Mar- chon Eyewear, Inc. (Fig. 4). Energy Absorption for Vibrational Damping. An energy absorbing ability found in both the martensitic and austenitic phases of SMAs is indirectly related to their shape-memory behavior. The energy absorption of SMA materials has demonstrated excellent vibrational damp- ing characteristics, which can be harnessed for use in various damping applications. The types of devices that exploit this property are classified in three categories of damping : martensitic, martensitic transformation, and superelastic. Martensitic damping devices operate by using only the martensitic phase of SMAs. Energy is absorbed by the martensite during its twin reorientation process, and acco- mmodates large strains for high-amplitude, low-frequency loading. They offer the best damping characteristics of the three categories, and although they cannot recover large strains without subsequent heating, they provide excellent damping properties across a broad temperature range. Martensitic transformation damping elements are de- signed to operate near martensitic transition temperatures for peak performance in vibrational attenuation. This peak is due to a sharp increase in internal friction dur- ing the martensitic phase transformation. These damping elements offer ideal properties for low-amplitude, high- frequency vibrations within a small operating temperature range (9). This type of device could be used in ski materi- als to damp vibrations when the ski is in contact with snow (6). Superelastic damping devices use the plateau hystere- sis portion of the stress–strain curve for properties similar to those of a rubber band. Superelastic SMA materials are pretensioned to reach this stress–strain plateau, and any additional strains are accommodated easily by changes in P1: FCH/FYX P2: FCH/FYX QC: FCH/UKS T1: FCH PB091-S-DRV-I January 24, 2002 15:42 SHAPE MEMORY ALLOYS, APPLICATIONS 925 Figure 4. Deformation resistant eyeglass frames (courtesy of Marchon Eyewear, Inc.). the applied load. This property optimizes a combination of damping capacity, shape recovery, and temperature range of operation (9). Unlike martensitic damping elements, superelastic devices recover their original shape when vi- brational loading is removed. Suggested superelastic ten- sioning devices are presented in a U.S. patent regarding hysteretic damping (10); one example is shown in Fig. 5 (9). These SMA tension elements cycle through a superelas- tic stress–strain hysteresis to dissipate energy and serve as a damping mechanism. Vibrations due to environmen- tal impacts such as violent winds and earthquakes deform the tensioned elements, and when the vibrational impact is lessened, the elements recover their shapes. Cavitation-Erosion Resistance. Cavitation erosion is a phenomenon that affects equipment and machinery in many industries. Small bubbles explode with large Figure 5. Schematic of a superelastic damping device, using loops of SMA wire in tension. Reprinted with permission from D.E. Hodgson and R.C. Krumme, Damping in Structural Applications, SMST Proceedings, 1994. impacts, causing pitting and erosion in metallic surfaces and reducing the service life of expensive equipment. Both the martensitic and austenitic phases of SMAs have dis- played cavitation-erosion resistance; they recover from im- pact and minimize material loss when exposed to vibratory cavitation. Studies that explored the performance of Ni–Ti on stainless steels have indicated that both martensitic and austenitic Ni-Ti have significant potential for covering and protecting equipment that suffers wear from cavita- tion erosion. Ni–Ti cladding could be used in applications such as machinery, hydraulics, large hydroelectric genera- tor turbines, and ship propellers (11). Low Elastic Modulus. The martensitic phase of SMA ma- terials is soft and pliable, in contrast to the stiff, springy characteristics of the austenitic phase. This softness, or low effective (nonlinear) elastic modulus, is often used in applications that require deformability and excellent fatigue characteristics. This property is exploited alone or in conjunction with a shape-memory effect in fatigue- resistant applications. An example of a low elastic modulus application is shown in Fig. 6: a martensitic tool developed by St. Jude Medical, Inc., is used by surgeons during open heart surgery to orient a tissue-restraining device. During this procedure, surgeons must make adjustments to optimize the tool geometry for each patient, and the use of SMAs allow surgeons to bend the martensitic handle to an ap- propriate angle. Upon completing the operation, the tool is sterilized in an autoclave where it is exposed to elevated temperatures and reverts to its trained, austenitic shape. Due to its ability to recover large strains repeatedly, these tools are marketed for both fatigue resistance and shape- memory properties. Design Constraints and Considerations When assessing a potential design challenge, designers are often anxious to develop a solution that uses the unique and exciting properties of SMAs. It is critical, however, for designers to understand the complexity of SMA behavior. As a general rule, if conventional materials and designs can be applied to yield an acceptable and desirable result, the use of SMAs to provide an alternative solution will increase complexity and cost. SMAs are best used when their unique properties are necessary for design success— when conventional materials cannot meet the demands of the application. The design of SMA applications requires more than tra- ditional design techniques and textbook methods. Due to the many unique properties of SMA materials, several con- siderations specific to SMA design must be addressed and accounted for. This section discusses the majority of issues that should be addressed before designing an application using SMAs. General Guidelines Recoverable Strain. The expected recoverable strain of SMA material must be within the limitations of the alloy P1: FCH/FYX P2: FCH/FYX QC: FCH/UKS T1: FCH PB091-S-DRV-I January 24, 2002 15:42 926 SHAPE MEMORY ALLOYS, APPLICATIONS Figure 6. Medical tools and devices. Left to right: Flexible martensitic, Ni–Ti handle developed by St. Jude Medical for open heart surgery procedures; superelastic, tapered guidewire core; shaped Ni–Ti tubing component; retractable, superelastic component within a small diameter cannula (courtesy of Shape Memory Applications, Inc.). chosen. For example, Ni–Ti may recover 8% strain for a single cycle application, but less than 4% for higher cycle applications. Recommended strain limits are 6% for Ni–Ti and 2% for Cu–Zn–Al for lower cycle applications and 2% and 0.5% for higher cycle applications, respectively (3). A maximum strain recovery of about 2% is expected for ap- plications that require two-way shape memory (12). High Temperature Stability. Alloy stability must be con- sidered when an application requires or will be subject to high operating temperatures. Ni–Ti alloys tend to be the most stable of all SMAs at elevated temperatures and can withstand exposure to temperatures up to approximately 250 ◦ C before previously memorized shaping is deleted. For Cu–Zn–Al, this maximum temperature is around 90 ◦ C. Fatigue. SMA fatigue can be defined as degradation of any or all of its functional properties. SMAs affected by application cycle quantity, frequency, temperature range, stress, and strain may fatigue by fracture, decreasing recoverable strain, shifting transformation temperatures, or decreasing recovery stress. Manufacturability. SMA materials are infamously dif- ficult to machine. Tool wear is rapid for conventional machining methods such as turning, milling, drilling, and tapping (2). Currently, the most successful machining tech- niques include surface grinding, abrasive cutting, EDM, and laser cutting. Component shaping must be considered as well; the memories of SMA shapes are trained at high temperatures,typicallyaround 500 ◦ C (932 ◦ F). Unlike most conventional materials that may be cold formed, SMAs must be rigidly clamped in a desired shape and exposed to these elevated temperatures. Designing for assembly is also an important manufac- turing consideration. Fastening SMAs to other materials by bonding and joining presents additional challenges. Be- cause SMAs are designed to exhibit strains up to 8% and other materials have a strain limit of less than 1%, when the two are rigidly joined, the conventional material may break during operation. This often causes problems in us- ing plated or painted SMA materials because the coating on the SMA will often crack and flake during the strains of operation. Cost. Most SMAs are inherently more expensive than conventional materials due to the higher cost of both raw material components and processing methods. The com- positional control necessary for the raw forms of SMA P1: FCH/FYX P2: FCH/FYX QC: FCH/UKS T1: FCH PB091-S-DRV-I January 24, 2002 15:42 SHAPE MEMORY ALLOYS, APPLICATIONS 927 Figure 7. Finite element analysis model of a self-expandable Ni–Ti stent: displays a quantified mapping of stress and strain amplitudes in both expanded and compressed positions (courtesy of Pacific Consultants, LLC). material requires special furnaces and processes, the se- quence of cold working and annealing to ensure opti- mal SMA properties is extensive, and the special tooling and fixturing required for producing the many forms and shapes of the materials increase the cost of using SMAs. Computer Modeling Capability. Finite element analysis (FEA), often used in conventional material design, has also been used to model the behavior of SMAs. The analysis is difficult, however, and should not depend on standard ma- terial templates and subroutines because the functional properties of SMAs rely on nonstandard factors, such as composition and processing history. Highly specific and complex modeling techniques must account for the state of the SMA material once formed in its trained shape, and then must incorporate the nonlinearity of the stress–strain curve, the property dependence on temperature, and the difference between loading and unloading stress behavior. Figure 7 is an illustration of a FEA model of a superelastic coronary stent that was achieved by using custom model- ing subroutines to predict mechanical properties. Shape Memory Applications Temperature Cycling. Thermally activated SMA applica- tions require temperature control to optimize the effect of shape memory. To harness the unique properties ob- tained from martensitic transformations, temperatures usually cycle between the extremes of the SMA temper- ature hysteresis. Depending on the alloy selected, this hysteresis might be smaller than 1 ◦ C (1.8 ◦ F) or larger than 100 ◦ C (180 ◦ F). Applications must incorporate a method of heating and cooling SMA components through their hystereses; the rate of cycling for a shape-memory de- vice is limited by the rate of temperature cycling. The butterfly example of Fig. 2 has a hysteresis of about 30 to 50 ◦ C. The Flexinol TM actuator wire is heated to a temperature above 90 ◦ C to contract, but must be cooled to approximately 40 ◦ C to transform to martensite. This application uses ambient air for cooling—only a few seconds are required for the wire to cool and stretch with the mass of the butterfly body. A few alloys have been developed to reduce or to increase this temperature hys- teresis, as mentioned earlier. In addition, a secondary martensitic phase transformation found in many SMAs, called an R-phase transformation, can be exploited for its hysteresis of less than 2 ◦ C. Although recoverable strains are limited to about 0.5% by this transformation, it may be ideal for certain applications (13). Power. SMAs require thermal energy for memory acti- vation that is most often delivered as direct heat or applied current for resistive heating. Applications that use ther- mal shape memory must account for the power require- ments of the material, the connection of the power source to the SMA, space requirements to house the source, and any safety mechanisms necessary to prevent overheating. Force Requirements. SMA applications typically exploit the strength differential between the martensitic and austenitic phases of the material. In many actuating de- vices, an SMA element is paired with a conventional material element to serve as a biasing mechanism. The conventional element, such as a steel coil spring, displaces the SMA element when martensitic, but yields to the SMA P1: FCH/FYX P2: FCH/FYX QC: FCH/UKS T1: FCH PB091-S-DRV-I January 24, 2002 15:42 928 SHAPE MEMORY ALLOYS, APPLICATIONS when heated to its stronger austenitic phase. This enables a one-way shape memory element to behave as a two- way shape-memory device. The forces delivered at each of the temperature extremes must be considered in SMA design. Superelastic Applications Operating Temperature Range. The temperature range of operation for a superelastic application must be above the A f temperature for optimal superelasticity, but must also be below its M d temperature (the temperature at which martensite can no longer be stress induced). This range is typically 50 to 80 ◦ C above the A f (14). Force Requirements. As operating temperatures in- crease above the SMA A f temperature, loading and un- loading stresses increase as a function of the Clausius– Clapeyron equation (14). Due to variations in the latent heat of transformation among alloy types, the increase in stress, as temperature changes, ranges from 2.5 MPa/ ◦ Cto more than 15 MPa/ ◦ C (15). SMA APPLICATIONS Applications that use each of the unique properties of SMAs have been designed, prototyped, and marketed throughout the world. This section provides examples of these applications and includes some discussion of design choices, material limitations, and SMA behavior. These examples are categorized by industry to demonstrate the varied and widespread use of SMA applications. Aeronautics/Aerospace Many of the initial product ideas and applications that incorporate SMAs were pioneered in the fields of aero- nautics and aerospace. SMA materials are used in these industries to take advantage of properties such as high power-to-mass ratios and ideal actuating behavior in zero-gravity conditions. Designs that use these prop- erties replace heavier, more complex conventional de- vices because of reduced weight, design simplicity, and reliability. Cryofit ® Hydraulic Pipe Couplings. SMA couplings were the first successful commercial application of shape-memory alloys (Fig. 8). In 1969, Raychem Corpora- tion introduced shrink-to-fit hydraulic pipe couplings for F-14 jet fighters that were built by Grumman Aerospace Corporation. This coupling is fabricated from a Ni–Ti–Fe alloy whose martensitic transformation temperature is be- low −120 ◦ C. It is machined at room temperature to an inner diameter approximately 4% smaller than the outer diameter of the piping it is designed to join. When cooled below −120 ◦ C by liquid nitrogen, the coupling is forced to a diameter 4% greater than the pipe diameter for an overall internal strain of about 8%. When warmed above its TTR, the coupling diameter decreases to form a tight seal be- tween the pipes (16). This shape-memory application of constrained recovery continues to be a commercial and financial success. Despite the difficulties of cooling the couplings to liquid nitrogen temperatures for expansion and storage, the aerospace in- dustry has welcomed their many advantages over tradi- tional pipe-joining techniques such as welding or brazing. Installation is simple, less costly, and does not rely on high levels of operator skill. The replacement of couplings and hydraulic lines is straightforward, and the possibility of annealing and damaging the hydraulic lines as in welding or brazing is eliminated (2). Frangibolt ® Release Bolts. Shape-memory bolts were developed by the TiNi Alloy Company to replace conven- tional exploding bolt devices in aerospace release mech- anisms. The bolts are used to attach spacecraft acces- sories during launch and to release them after launch by using an activated heating element (17). A martensitic, shape-memory cylinder is compressed and assembled to a notched bolt. When activated by an electrical heater, the cylinder increases in length and delivers a force greater than 22 kN (5000 lbs) to fracture the bolt at its notch (18). These release bolts were used successfully aboard the spacecraft Clementine in 1994, and have improved upon designs for conventional explosive mechanisms by eliminating the risks of off-gassing, accidental activation during shipment, and potential spacecraft damage during explosions. Mars Sojourner Rover Actuator. An SMA wire was used to actuate a glass plate above a small solar cell on the Rover unit during the recent Pathfinder/Sojourner mission to Mars. A material adhesion experiment performed dur- ing the mission used the actuator to replace large, heavy motors and solenoids. A small, simple length of Ni–Ti wire heated and contracted when the Rover applied power and pulled a glass plate away from the solar cell to allow com- parison of sunlight intensity with and without the plate. The rate of dust collection was then determined, and the resulting data will be used to design cleaning methods for future missions to Mars (19). Self-Erectable Antenna. A prototype space antenna was constructed by Goodyear Aerospace Corporation. Designed to fold compactly at room temperature, the device would unfold into a large, extended antenna shape when heated by solar energy (2). Although this did not become a com- mercial success, the concept is feasible, and the prototype has served as a model for similar designs pursued within the aerospace industry. Smart Airplane Wings. Composite structures that have SMA wires embedded can be used to change the shape of an airplane wing. The embedded wires may be activated P1: FCH/FYX P2: FCH/FYX QC: FCH/UKS T1: FCH PB091-S-DRV-I January 24, 2002 15:42 SHAPE MEMORY ALLOYS, APPLICATIONS 929 Figure 8. Shape memory devices. Clockwise from top left: memory card ejector mechanism for laptop computers; Cryofit ® hydraulic pipe couplings; Cryocon ® electrical connector; fire safety lid release for public garbage receptacles (courtesy of Shape Memory Applications, Inc.). to constrict and improve the vibrational characteristics of the wing, heated to change their effective modulus to re- duce vibration, or activated to alter the shape of the wing for optimal aerodynamics. All of these properties can be used to produce an adaptive airplane wing that alters as environmental conditions change to improve efficiency and reduce noise. Space System Vibrational Damper. Vibrational dampers comprised of composite materials using pre-strained, embedded SMA wire or ribbons can reduce unwanted mo- tion in various space systems. A sensor detects vibration in the system and sends a signal to activate the embedded composite, which then alters the structural dynamics to damp or cancel the existing vibration (1). Consumer Products SMA devices and components have been used in high- volume consumer products for more than 20 years. Al- though many consumers who use these products are un- aware of their SMA components, there is a growing public awareness of SMAs due to recently marketed items that advertise their merits. Flexon ® Optical Frames. Superelastic eyeglass frames marketed by Marchon Eyewear, Inc., are one of the most widely known uses for SMAs. They are frequently advertised in television commercials and can be found at most optical frame retailers. The components of eyeglass frames that are most susceptible to bending, the bridge and temples, are wire forms of Ni-Ti, the remainder of the frame is comprised of conventional materials for adjusting purposes and cost savings. Due to the high strain recovery capability of Ni-Ti, these frames are highly deformation- and kink-resistant (Fig. 4). Marchon is aware of the high strain and high cycle fatigue limitations of Ni-Ti materi- als, as demonstrated by the marketing brochures that ap- propriately suggest bending and twisting limits that are within the design guidelines for the material. Portable Phone Antennae. The growing demand for portable phones has resulted in a high-volume applica- tion for superelastic Ni-Ti material because most cell P1: FCH/FYX P2: FCH/FYX QC: FCH/UKS T1: FCH PB091-S-DRV-I January 24, 2002 15:42 930 SHAPE MEMORY ALLOYS, APPLICATIONS phone antennae produced today are Ni–Ti wires coated with polyurethane. The superelasticity resists permanent kinking and withstands the abuses of user handling during the lifetime of portable phones. Greenhouse Window Opener. An SMA that has a small temperature hysteresis is used as an actuator to open and close greenhouse windows at predetermined temperatures for automatic temperature control. The opener is a spring- loaded hinge that has a Cu–Zn–Al shape-memory spring and a conventional metal biasing spring. The SMA spring is compressed by the biasing spring at temperatures be- low 18 ◦ C, and the window is closed. The SMA spring acti- vates around 25 ◦ C, overcomes the force of the bias spring, and opens the window (21). This actuator design relies on reduced thermal hysteresis using a biasing force. As the SMA spring cools to 18 ◦ C, although not sufficiently cool to completely transform to its softer martensitic phase, it is transformed enough to accommodate deformation via stress-induced martensite. Recorder Pen Mechanism. A shape-memory pen driver was designed by The Foxboro Company in the early 1970s to replace conventional pen-drive mechanisms, which used a galvanometer to actuate a pen arm. The replacement used Ni–Ti wires pretensioned in a driver unit and actu- ated by heat from an induction coil in response to input signals. The new design reduced the number of moving parts, improved reliability, and decreased costs. The new recorder pen units were first introduced in 1972; by 1980 more than 500,000 units were produced (16,21). Nicklaus Golf Clubs. Superelastic SMA golf club inserts were developed by Memry Corporation for a line of Jack Nicklaus golf clubs. The damping properties of the inserts hold the golf ball on the club face longer and provide more spin and greater control for golfers (22). Brassiere Underwires. Superelastic Ni–Ti shapes that conform to the user’s body are ideal for underwire applica- tions, because they are unaffected by the temperatures and external forces from repeated washings. Wires are shaped in predetermined configurations, using either round wire or flat ribbon. The product is a commercial success in Asia, but the increased cost compared to that of conventional underwires has prevented the product from entering mar- kets in North America and Europe. Residential Thermostatic Radiator Valve. SMA actuators have been used to regulate the temperature of residen- tial radiators. An actuator expands when the room tem- perature increases, overcomes a biasing spring force, and closes a radiator hot water valve. Assisted by the biasing spring, the SMA temperature hysteresis can be as low as 1.2 ◦ C (21). The thermostatic valve can be adjusted via a knob that alters the compression of the biasing spring— the more compression it exerts, the higher the tempera- ture required for the SMA actuator coil to activate and close the hot water valve (16). Rice Cooker Valve. SMA valve mechanisms have been successfully employed to improve the performance of rice cookers. The mechanism, comprised of an SMA spring and a bias spring, is inserted into the top lid of a rice cooker. The valve is open while rice cooks and steam is generated, but when the rice is finished cooking, the SMA spring cools and the bias spring closes the valve to keep the rice warm. A Ni–Ti–Cu alloy is used for the SMA spring because of its low strain, high cycle fatigue properties. Although its re- covery force decreases due to repeated cycling, this applica- tion has demonstrated repeatability for more than 30,000 cycles, which corresponds to several daily operations for 10 years (23). Robotic Doll. SMA actuator wires were designed to move the arms and legs of a doll to display human characteristics. The application is technically feasible, and prototypes were successful; however, the power required to activate the wires was too great. The battery changes required were sufficiently frequent to limit market accep- tance of the product. Miscellaneous Products. Furukawa Electric Co. Ltd. of Japan produced SMA-actuating air-conditioning louvers to deflect air up or down, depending on temperature. They also manufactured coffee makers that use temperature- control valves to initiate the brewing process when water starts to boil (24). Other products include superelastic fish- ing lures, superelastic SONY Eggo TM headphones for the minidisk Walkman ® , and novelty items, such as a magic teaspoon that has a memory. The teaspoon is given to some- one to stir a hot drink, and when the spoon is exposed to the hot liquid, it is immediately transformed to a bent position. Commercial/Industrial Safety Many safety devices for temperature sensing and actua- tion have been successfully used in actual operation. The following examples have all been sold in consumer or industrial markets. Antiscald MemrySafe ® Valve. An SMA valve was de- signed to shut off a faucet’s hot water source when wa- ter temperatures become too high (above 50 ◦ C). The valve reopens when the water cools to safer temperatures and protects the user from scalding water. ShowerGard ® , BathGard ® , and Flow-Gard ® are similar products, and all have been marketed in retail hardware stores. Firechek ® Valve. A safety device that employs an SMA actuator is often used in industrial process lines to shut off a gas supply in the event of fire. Exposure to high temperatures activates a valve and cuts off the pneumatic pressure that controls flammable gas cylinders and process line valves (25). Circuit Breakers. SMAs have been used in circuit break- ers to replace conventional bimetals. Due to the high forces required in large circuit breakers, a series of levers must be employed to amplify the forces available from bi- metals. Cu–Al–Ni alloys have been used in this application [...]... their use in engineering and BIBLIOGRAPHY 1 L McD Schetky, Proc: Shape Memory Alloys Power Alto, CA, 19 94, pp 4 .1 4 .11 Tokyo, Japan, 19 88, Vol 9, p 583 9 D.E Hodgson and R.C Krumme, Proc 1st Int Conf Shape Memory Superelastic Technol Pacific Grove, CA, 19 94, pp 3 71 376 10 Hysteretic Damping Apparatus and Methods, US Pat 5, 842, 312 , Dec 1, 19 98, R.C Krumme and D.E Hodgson 11 R.H Richman, C.A Zimmerly,... D.E Hodgson and R.C Krumme, Proc 1st Int Conf Shape Memory Superelastic Technol Pacific Grove, CA, 19 94, pp 3 71 376 10 Hysteretic Damping Apparatus and Methods, US Pat 5, 842, 312 , Dec 1, 19 98, R.C Krumme and D.E Hodgson 11 R.H Richman, C.A Zimmerly, O.T Inal, D.E Hodgson, and A.S Rao, Proc 1st Int Conf Shape Memory Superelastic Technol., Pacific Grove, CA, 19 94, pp 17 5 18 0 12 J Perkins and D Hodgson,... strains easily (dε/dH approaches infinity), and even for large Ku , it magnetizes easily (dM/dH 10 7 1. 0 m εy m εy Ku (J/m3) 0.0 0.5 0.5 1. 0 0.0 µoH (T) m εy 0.5 1. 0 0.0 µoH (T) 0.5 1. 0 µoH (T) 10 6 1. 0 m εy m m εy 0.0 0.5 µoH (T) 10 5 10 5 0.5 1. 0 0.0 0.5 εy 1. 0 0.0 µoH (T) 10 6 (1/ 2)Ceffεo 2 (J/m3) 0.5 1. 0 µoH (T) 10 7 Figure 10 Graphs of reduced magnetization, m and reduced strain, ε y = ε/εo from Eq (3)... field of about 2 kOe and an ac field of ± 1kOe about that bias, would result in actuation at the drive frequency with an output strain of about 2% peak-to-peak The value of d 31 under such actuation is about 1% per kOe or 12 .5 × 10 −8 m/A This value compares Strain (%) 1. 1 0.9 10 0 15 0 200 250 Actuation frequency (Hz) 3 Figure 15 Frequency dependence of peak field gener system shown in Fig 13 (upper curve) and. .. V.V Kokorin, and R.C O’Handley Appl Phys Lett 69: 19 66 (19 96) K Ullakko, J.K Huang, V.V Kokorin, and R.C O’Handley Scripta Mater 36: 11 33 (19 97) 5 G.H Haertling J Am Ceram Soc 82: 797 (19 99) Phys Rev B57: 2659 (19 98) 13 T Kanomata, K Shirahawa and T Kaneko, J Ma Mtls 76–82, 65 (19 87) 14 A.A Gonzalez-Comas, E Obrad´ , L Manosa, A P o Chernenko, B.J Hattink, and A Labarta Phys Rev (19 99) 15 M Taya Unpublished... Corporation, and Mid´ Technologies The crystals used in our e study were grown by Dr V.V Kokorin, Institute of Metallurgy, Kiev (Fig 1) and by Dr Tom Lograsso of Ames Laboratory, Department of Energy (Figs 6, 11 , and 14 ) BIBLIOGRAPHY 1 V.A Chernenko, E Cesari, V.V Kokorin, and N Vitenko Scrip Metall Mater 33: 12 39 (19 95) 2 R.D James and M Wuttig SPIE 2 715 : 420 (19 96) 3 K Ullakko J Mat Eng Perform 5: 405 (19 96)... field cyc of comparison, piezoelectrics show strains of o (5) and the leading magnetostrictive material, T (Tb0.33 Dy0.67 Fe2 ), shows a field-induced strain 0.24% (6,7) The strain-versus-temperature (ε-T) curves o elastic martensite, Fig 1( a), bear little resem the ε-H curves of Fig 1( b) The former typical Strain Af Ms 260 270 280 Temperature (K) 290 (b) 5 5 H [11 0] 0 −5 −5 [11 0] Strain (10 −4) [0 01] Strain... Butterworth-Heinemann, London, 19 90, pp 3–20 15 K.N Melton, in Engineering Aspects of Shape Memory Alloys, Butterworth-Heinemann, London, 19 90, pp 21 35 16 L.McD Schetky, Sci Am 2 41( 5): 79, 81 (19 79) 17 http://www.sma-mems.com /aero.htm 18 J.D Busch, Proc 1st Int Conf Shape Memory Superelastic Technol pp 259–264, Pacific Grove, CA, 19 94 19 http://www.robotstore.com /mwmars.html 20 Marchon Company Brochure, 19 98... successful applications of these Fe-based alloys are couplings This type of application is based on the one-way effect The recovery stresses are moderate but sufficient (12 ) Cu-Based Alloys [ (1, 3 ,13 16 )] Copper-based shape-memory alloys are derived from Cu–Zn, Cu–Al, and Cu–Sn systems The composition range of these alloys corresponds to that of the well-known β-Hume–Rothery phase In most shape-memory alloys,... includes contributions twin-boundary motion and magnetization rotati the twin variants ( 32) In the strong anisotropy limit, the sample is m only by twin-boundary motion rather than mag Figure 9 Two-dimensional representation of field-induced twin-boundary motion The parameters fi (i = 1, 2) are the volume fractions of variants 1 and 2 and δ f = f1 − 1 describes the dis2 placement of the twin boundary from . Aspects of Shape Memory Alloys, Butterworth-Heinemann, London, 19 90, pp. 21 35. 16 . L.McD. Schetky, Sci. Am. 2 41( 5): 79, 81 (19 79). 17 . http://www.sma-mems.com/aero.htm. 18 . J.D. Busch, Proc. 1st K.N. Melton, in Engineering Aspects of Shape Memory Alloys, Butterworth-Heinemann, London, 19 90, pp. 21 35. 16 . L.McD. Schetky, Sci. Am. 2 41( 5): 79, 81 (19 79). 17 . http://www.sma-mems.com/aero.htm. 18 Aspects of Shape Memory Alloys, Butterworth-Heinemann, London, 19 90, pp. 14 9 15 7. 38. J.F. Krumme, Connection Technol. Lake, 19 87. 39. http://www.sma-mems.com/t film.htm 40. A.D. Johnson and J.D.