A shape-memory admixture (SMA, acute metal, anamnesis metal, anamnesis alloy, beef wire, acute alloy) is an admixture that "remembers" its original, cold-forged shape: abiding the pre-deformed appearance by heating. This actual is a lightweight, solid-state another to accepted actuators such as hydraulic, pneumatic, and motor-based systems. Shape-memory alloys accept applications in industries including medical and aerospace.
Sunday, 18 December 2011
Overview
The three capital types of shape-memory alloys are the copper-zinc-aluminium-nickel, copper-aluminium-nickel, and nickel-titanium (NiTi) alloys but SMAs can additionally be created by alloying zinc, copper, gold and iron. NiTi alloys are about added big-ticket and change from austenite to martensite aloft cooling; Mf is the temperature at which the alteration to martensite completes aloft cooling. Accordingly, during heating As and Af are the temperatures at which the transformation from martensite to austenite starts and finishes. Repeated use of the shape-memory aftereffect may advance to a about-face of the appropriate transformation temperatures (this aftereffect is accepted as anatomic fatigue, as it is carefully accompanying with a change of microstructural and anatomic backdrop of the material).1
The alteration from the martensite appearance to the austenite appearance is alone abased on temperature and stress, not time, as best appearance changes are, as there is no circulation involved. Similarly, the austenite anatomy receives its name from animate alloys of a agnate structure. It is the capricious diffusionless alteration amid these two phases that after-effects in appropriate properties. While martensite can be formed from austenite by rapidly cooling carbon-steel, this action is not reversible, so animate does not accept shape-memory properties.
Sma wire.jpg
In this figure, ξ(T) represents the martensite fraction. The aberration amid the heating alteration and the cooling alteration gives acceleration to hysteresis area some of the automated activity is absent in the process. The appearance of the ambit depends on the actual backdrop of the shape-memory alloy, such as the alloying.2 and assignment hardening.3
edit One-way vs. two-way appearance memory
Shape-memory alloys accept altered shape-memory effects. Two accepted furnishings are one-way and two-way appearance memory. A schematic of the furnishings is apparent below.
one-way appearance memoryTwo-way built-in appearance memory
The procedures are actual similar: starting from martensite (a), abacus a capricious anamorphosis for the one-way aftereffect or astringent anamorphosis with an irreversible bulk for the two-way (b), heating the sample (c) and cooling it afresh (d).
edit One-way anamnesis effect
When a shape-memory admixture is in its algid accompaniment (below As), the metal can be angled or continued and will authority those shapes until acrimonious aloft the alteration temperature. Aloft heating, the appearance changes to its original. When the metal cools afresh it will abide in the hot shape, until askew again.
With the one-way effect, cooling from aerial temperatures does not account a arresting appearance change. A anamorphosis is all-important to actualize the low-temperature shape. On heating, transformation starts at As and is completed at Af (typically 2 to 20 °C or hotter, depending on the admixture or the loading conditions). As is bent by the admixture blazon and agreement and can alter amid −150 °C and 200 °C.
edit Two-way anamnesis effect
The two-way shape-memory aftereffect is the aftereffect that the actual remembers two altered shapes: one at low temperatures, and one at the high-temperature shape. A actual that shows a shape-memory aftereffect during both heating and cooling is alleged two-way appearance memory. This can additionally be acquired after the appliance of an alien force (intrinsic two-way effect). The acumen the actual behaves so abnormally in these situations lies in training. Training implies that a appearance anamnesis can "learn" to behave in a assertive way. Under accustomed circumstances, a shape-memory admixture "remembers" its high-temperature shape, but aloft heating to balance the high-temperature shape, anon "forgets" the low-temperature shape. However, it can be "trained" to "remember" to leave some reminders of the askew low-temperature action in the high-temperature phases. There are several means of accomplishing this.4 A shaped, accomplished article acrimonious above a assertive point will lose the two-way anamnesis effect, this is accepted as "amnesia".
The alteration from the martensite appearance to the austenite appearance is alone abased on temperature and stress, not time, as best appearance changes are, as there is no circulation involved. Similarly, the austenite anatomy receives its name from animate alloys of a agnate structure. It is the capricious diffusionless alteration amid these two phases that after-effects in appropriate properties. While martensite can be formed from austenite by rapidly cooling carbon-steel, this action is not reversible, so animate does not accept shape-memory properties.
Sma wire.jpg
In this figure, ξ(T) represents the martensite fraction. The aberration amid the heating alteration and the cooling alteration gives acceleration to hysteresis area some of the automated activity is absent in the process. The appearance of the ambit depends on the actual backdrop of the shape-memory alloy, such as the alloying.2 and assignment hardening.3
edit One-way vs. two-way appearance memory
Shape-memory alloys accept altered shape-memory effects. Two accepted furnishings are one-way and two-way appearance memory. A schematic of the furnishings is apparent below.
one-way appearance memoryTwo-way built-in appearance memory
The procedures are actual similar: starting from martensite (a), abacus a capricious anamorphosis for the one-way aftereffect or astringent anamorphosis with an irreversible bulk for the two-way (b), heating the sample (c) and cooling it afresh (d).
edit One-way anamnesis effect
When a shape-memory admixture is in its algid accompaniment (below As), the metal can be angled or continued and will authority those shapes until acrimonious aloft the alteration temperature. Aloft heating, the appearance changes to its original. When the metal cools afresh it will abide in the hot shape, until askew again.
With the one-way effect, cooling from aerial temperatures does not account a arresting appearance change. A anamorphosis is all-important to actualize the low-temperature shape. On heating, transformation starts at As and is completed at Af (typically 2 to 20 °C or hotter, depending on the admixture or the loading conditions). As is bent by the admixture blazon and agreement and can alter amid −150 °C and 200 °C.
edit Two-way anamnesis effect
The two-way shape-memory aftereffect is the aftereffect that the actual remembers two altered shapes: one at low temperatures, and one at the high-temperature shape. A actual that shows a shape-memory aftereffect during both heating and cooling is alleged two-way appearance memory. This can additionally be acquired after the appliance of an alien force (intrinsic two-way effect). The acumen the actual behaves so abnormally in these situations lies in training. Training implies that a appearance anamnesis can "learn" to behave in a assertive way. Under accustomed circumstances, a shape-memory admixture "remembers" its high-temperature shape, but aloft heating to balance the high-temperature shape, anon "forgets" the low-temperature shape. However, it can be "trained" to "remember" to leave some reminders of the askew low-temperature action in the high-temperature phases. There are several means of accomplishing this.4 A shaped, accomplished article acrimonious above a assertive point will lose the two-way anamnesis effect, this is accepted as "amnesia".
Pseudo-elasticity
One of the bartering uses of shape-memory admixture exploits the pseudo-elastic backdrop of the metal during the high-temperature (austenitic) phase. The frames of account glasses accept been fabricated of shape-memory admixture as they can abide ample deformations in their high-temperature accompaniment and again instantly backslide aback to their aboriginal appearance aback the accent is removed. This is the aftereffect of pseudoelasticity; the martensitic appearance is generated by affirmation the metal in the austenitic accompaniment and this martensite appearance is able of ample strains. With the abatement of the load, the martensite transforms aback into the austenite appearance and resumes its aboriginal shape.
This allows the metal to be bent, askance and pulled, afore reforming its appearance aback released. This agency the frames of shape-memory admixture glasses are claimed to be "nearly indestructible" because it appears no bulk of angle after-effects in abiding artificial deformation.
The martensite temperature of shape-memory alloys is abased on a cardinal of factors including admixture chemistry. Shape-memory alloys with transformation temperatures in the ambit of 60–1450 K accept been made.
This allows the metal to be bent, askance and pulled, afore reforming its appearance aback released. This agency the frames of shape-memory admixture glasses are claimed to be "nearly indestructible" because it appears no bulk of angle after-effects in abiding artificial deformation.
The martensite temperature of shape-memory alloys is abased on a cardinal of factors including admixture chemistry. Shape-memory alloys with transformation temperatures in the ambit of 60–1450 K accept been made.
History
The aboriginal appear accomplish appear the analysis of the shape-memory aftereffect were taken in the 1930s. According to Otsuka and Wayman, A. Ölander apparent the pseudoelastic behavior of the Au-Cd admixture in 1932. Greninger and Mooradian (1938) empiric the accumulation and dematerialization of a martensitic appearance by abbreviating and accretion the temperature of a Cu-Zn alloy. The basal abnormality of the anamnesis aftereffect absolute by the thermoelastic behavior of the martensite appearance was broadly appear a decade after by Kurdjumov and Khandros (1949) and additionally by Chang and Read (1951).1
The nickel-titanium alloys were aboriginal developed in 1962–1963 by the United States Naval Ordnance Class and commercialized beneath the barter name Nitinol (an acronym for Nickel Titanium Naval Ordnance Laboratories). Their arresting backdrop were apparent by accident. A sample that was angled out of appearance abounding times was presented at a class administration meeting. One of the accessory abstruse directors, Dr. David S. Muzzey, absitively to see what would appear if the sample was subjected to calefaction and captivated his aqueduct lighter beneath it. To everyone's admiration the sample continued aback to its aboriginal shape.56
There is addition blazon of SMA, alleged a ferromagnetic shape-memory admixture (FSMA), that changes appearance beneath able alluring fields. These abstracts are of accurate absorption as the alluring acknowledgment tends to be faster and added able than temperature-induced responses.
Metal alloys are not the alone thermally-responsive materials; shape-memory polymers accept additionally been developed, and became commercially accessible in the backward 1990s.
The nickel-titanium alloys were aboriginal developed in 1962–1963 by the United States Naval Ordnance Class and commercialized beneath the barter name Nitinol (an acronym for Nickel Titanium Naval Ordnance Laboratories). Their arresting backdrop were apparent by accident. A sample that was angled out of appearance abounding times was presented at a class administration meeting. One of the accessory abstruse directors, Dr. David S. Muzzey, absitively to see what would appear if the sample was subjected to calefaction and captivated his aqueduct lighter beneath it. To everyone's admiration the sample continued aback to its aboriginal shape.56
There is addition blazon of SMA, alleged a ferromagnetic shape-memory admixture (FSMA), that changes appearance beneath able alluring fields. These abstracts are of accurate absorption as the alluring acknowledgment tends to be faster and added able than temperature-induced responses.
Metal alloys are not the alone thermally-responsive materials; shape-memory polymers accept additionally been developed, and became commercially accessible in the backward 1990s.
Crystal structures
Many metals accept several altered clear structures at the aforementioned composition, but best metals do not appearance this shape-memory effect. The appropriate acreage that allows shape-memory alloys to backslide to their aboriginal appearance afterwards heating is that their clear transformation is absolutely reversible. In best clear transformations, the atoms in the anatomy will biking through the metal by diffusion, alteration the agreement locally, alike admitting the metal as a accomplished is fabricated of the aforementioned atoms. A capricious transformation does not absorb this circulation of atoms, instead all the atoms about-face at the aforementioned time to anatomy a fresh structure, abundant in the way a parallelogram can be fabricated out of a aboveboard by blame on two opposing sides. At altered temperatures, altered structures are adopted and back the anatomy is cooled through the alteration temperature, the martensitic anatomy forms from the austenitic phase.
edit Manufacture
Shape-memory alloys are about fabricated by casting, appliance exhaustion arc melting or consecration melting. These are specialist techniques acclimated to accumulate algae in the admixture to a minimum and ensure the metals are able-bodied mixed. The batten is again hot formed into best sections and again fatigued to about-face it into wire.
The way in which the alloys are "trained" depends on the backdrop wanted. The "training" dictates the appearance that the admixture will bethink back it is heated. This occurs by heating the admixture so that the dislocations re-order into abiding positions, but not so hot that the actual recrystallizes. They are acrimonious to amid 400 °C and 500 °C for 30 minutes. Typical variables for some alloys are 500 °C and for added than 5 minutes.
They are again shaped while hot and are cooled rapidly by abatement in baptize or by cooling with air.
edit Properties
The copper-based and NiTi-based shape-memory alloys are advised to be engineering materials. These compositions can be bogus to about any appearance and size.
The crop backbone of shape-memory alloys is lower than that of accepted steel, but some compositions accept a college crop backbone than artificial or aluminum. The crop accent for Ni Ti can ability 500 MPa. The aerial amount of the metal itself and the processing requirements accomplish it difficult and big-ticket to apparatus SMAs into a design. As a result, these abstracts are acclimated in applications area the cool adaptable backdrop or the shape-memory aftereffect can be exploited. The best accepted appliance is in actuation.
One of the advantages to appliance shape-memory alloys is the aerial akin of recoverable artificial ache that can be induced. The best recoverable ache these abstracts can authority after abiding accident is up to 8% for some alloys. This compares with a best ache 0.5% for accepted steels.
edit Manufacture
Shape-memory alloys are about fabricated by casting, appliance exhaustion arc melting or consecration melting. These are specialist techniques acclimated to accumulate algae in the admixture to a minimum and ensure the metals are able-bodied mixed. The batten is again hot formed into best sections and again fatigued to about-face it into wire.
The way in which the alloys are "trained" depends on the backdrop wanted. The "training" dictates the appearance that the admixture will bethink back it is heated. This occurs by heating the admixture so that the dislocations re-order into abiding positions, but not so hot that the actual recrystallizes. They are acrimonious to amid 400 °C and 500 °C for 30 minutes. Typical variables for some alloys are 500 °C and for added than 5 minutes.
They are again shaped while hot and are cooled rapidly by abatement in baptize or by cooling with air.
edit Properties
The copper-based and NiTi-based shape-memory alloys are advised to be engineering materials. These compositions can be bogus to about any appearance and size.
The crop backbone of shape-memory alloys is lower than that of accepted steel, but some compositions accept a college crop backbone than artificial or aluminum. The crop accent for Ni Ti can ability 500 MPa. The aerial amount of the metal itself and the processing requirements accomplish it difficult and big-ticket to apparatus SMAs into a design. As a result, these abstracts are acclimated in applications area the cool adaptable backdrop or the shape-memory aftereffect can be exploited. The best accepted appliance is in actuation.
One of the advantages to appliance shape-memory alloys is the aerial akin of recoverable artificial ache that can be induced. The best recoverable ache these abstracts can authority after abiding accident is up to 8% for some alloys. This compares with a best ache 0.5% for accepted steels.
Applications
Industrial
edit Aircraft
See also: Aircraft
Boeing, General Electric Aircraft Engines, Goodrich Corporation, NASA, and All Nippon Airways developed the Variable Geometry Chevron appliance shape-memory admixture that reduces aircraft's agent noise.
edit Piping
See also: Piping
The aboriginal customer bartering appliance for the actual was as a shape-memory coupling for piping, e.g. oil band pipes for automated applications, baptize pipes and agnate types of brim for consumer/commercial applications.
edit Automotive
See also: Automotive
The aboriginal aerial aggregate artefact (> 5Mio actuators / annual) is an automotive valve appliance anatomy to run low burden pneumatics /bladders in a car bench to acclimatize the curve (lumbar abutment / bolsters). The accounting of basical all allowances of SMA over solenoids (noise/EMC/weight/package (form factor)/power consumption) was the acute agency to alter the accepted technology by SMA. Breadth in added applications usually aloof 2 or 3 SMA allowances are advised and arrest from replacing the 'old' technologies.
edit Telecommunication
See also: Telecommunication
The additional aerial aggregate appliance was an AF Autofocus actuator for a acute phone. In this moment there are altered companies alive on an OIS (optical angel stabilisation) bore apprenticed by SMA wires.
edit Robotics
See also: Robotics
There accept additionally been bound studies on appliance these abstracts in robotics, for archetype the hobbyist apprentice Stiquito (and "Roboterfrau Lara"7), as they accomplish it accessible to actualize actual ablaze robots. Weak credibility of the technology are activity inefficiency, apathetic acknowledgment times, and ample hysteresis.
edit Medicine
Shape-memory alloys are activated in medicine, for example, as fixation accessories for osteotomies in orthopaedic surgery, in dental braces to apply connected tooth-moving armament on the teeth.
The backward 1980s saw the bartering addition of Nitinol as an enabling technology in a cardinal of minimally invasive endovascular medical applications. While added cher than stainless steel, the cocky accretion backdrop of Nitinol alloys bogus to BTR (Body Temperature Response), accept provided an adorable another to airship abundant accessories in stent grafts breadth it gives the adeptness to acclimate to the appearance of assertive claret argosy back apparent to anatomy temperature. On average, 50% of all borderline vascular stents currently accessible on the common bazaar are bogus with Nitinol.
edit Optometry
Eyeglass frames fabricated from titanium-containing SMAs are marketed beneath the trademarks Flexon and TITANflex. These frames are usually fabricated out of shape-memory alloys that accept their alteration temperature set beneath the accepted allowance temperature. This allows the frames to abide ample anamorphosis beneath stress, yet achieve their advised appearance already the metal is unloaded again. The actual ample allegedly adaptable strains are due to the stress-induced martensitic effect, breadth the clear anatomy can transform beneath loading, acceptance the appearance to change briefly beneath load. This agency that eyeglasses fabricated of shape-memory alloys are added able-bodied adjoin actuality accidentally damaged.
edit Orthopedic surgery
This breadth needs absorption from an able on the subject. See the allocution folio for details. WikiProject Anesthetic or the Anesthetic Portal may be able to advice recruit an expert. (February 2009)
Memory metal has been activated in orthopedic anaplasty as a fixation-compression accessory for osteotomies, about for lower acme procedures. The device, usually in the anatomy of a ample staple, is stored in a refrigerator in its adaptable anatomy and is built-in into pre-drilled holes in the cartilage beyond an osteotomy. As the basic warms it allotment to its non-malleable accompaniment and compresses the awkward surfaces calm to advance cartilage union.8
edit Dentistry
The ambit of applications for SMAs has developed over the years, a above breadth of development actuality dentistry. One archetype is the prevalence of dental braces appliance SMA technology to apply connected tooth-moving armament on the teeth; the nitinol archwire was developed in 1972 by orthodontist George Andreasen.9 This revolutionized analytic orthodontics and has additionally had an aftereffect on cilia optic development. Andreasen's admixture has a blooming appearance memory, accretion and application aural accustomed temperature ranges because of its geometric programming.
Harmeet D. Walia after activated the admixture in the accomplish of basis aqueduct files for endodontics.
edit Materials
edit Aircraft
See also: Aircraft
Boeing, General Electric Aircraft Engines, Goodrich Corporation, NASA, and All Nippon Airways developed the Variable Geometry Chevron appliance shape-memory admixture that reduces aircraft's agent noise.
edit Piping
See also: Piping
The aboriginal customer bartering appliance for the actual was as a shape-memory coupling for piping, e.g. oil band pipes for automated applications, baptize pipes and agnate types of brim for consumer/commercial applications.
edit Automotive
See also: Automotive
The aboriginal aerial aggregate artefact (> 5Mio actuators / annual) is an automotive valve appliance anatomy to run low burden pneumatics /bladders in a car bench to acclimatize the curve (lumbar abutment / bolsters). The accounting of basical all allowances of SMA over solenoids (noise/EMC/weight/package (form factor)/power consumption) was the acute agency to alter the accepted technology by SMA. Breadth in added applications usually aloof 2 or 3 SMA allowances are advised and arrest from replacing the 'old' technologies.
edit Telecommunication
See also: Telecommunication
The additional aerial aggregate appliance was an AF Autofocus actuator for a acute phone. In this moment there are altered companies alive on an OIS (optical angel stabilisation) bore apprenticed by SMA wires.
edit Robotics
See also: Robotics
There accept additionally been bound studies on appliance these abstracts in robotics, for archetype the hobbyist apprentice Stiquito (and "Roboterfrau Lara"7), as they accomplish it accessible to actualize actual ablaze robots. Weak credibility of the technology are activity inefficiency, apathetic acknowledgment times, and ample hysteresis.
edit Medicine
Shape-memory alloys are activated in medicine, for example, as fixation accessories for osteotomies in orthopaedic surgery, in dental braces to apply connected tooth-moving armament on the teeth.
The backward 1980s saw the bartering addition of Nitinol as an enabling technology in a cardinal of minimally invasive endovascular medical applications. While added cher than stainless steel, the cocky accretion backdrop of Nitinol alloys bogus to BTR (Body Temperature Response), accept provided an adorable another to airship abundant accessories in stent grafts breadth it gives the adeptness to acclimate to the appearance of assertive claret argosy back apparent to anatomy temperature. On average, 50% of all borderline vascular stents currently accessible on the common bazaar are bogus with Nitinol.
edit Optometry
Eyeglass frames fabricated from titanium-containing SMAs are marketed beneath the trademarks Flexon and TITANflex. These frames are usually fabricated out of shape-memory alloys that accept their alteration temperature set beneath the accepted allowance temperature. This allows the frames to abide ample anamorphosis beneath stress, yet achieve their advised appearance already the metal is unloaded again. The actual ample allegedly adaptable strains are due to the stress-induced martensitic effect, breadth the clear anatomy can transform beneath loading, acceptance the appearance to change briefly beneath load. This agency that eyeglasses fabricated of shape-memory alloys are added able-bodied adjoin actuality accidentally damaged.
edit Orthopedic surgery
This breadth needs absorption from an able on the subject. See the allocution folio for details. WikiProject Anesthetic or the Anesthetic Portal may be able to advice recruit an expert. (February 2009)
Memory metal has been activated in orthopedic anaplasty as a fixation-compression accessory for osteotomies, about for lower acme procedures. The device, usually in the anatomy of a ample staple, is stored in a refrigerator in its adaptable anatomy and is built-in into pre-drilled holes in the cartilage beyond an osteotomy. As the basic warms it allotment to its non-malleable accompaniment and compresses the awkward surfaces calm to advance cartilage union.8
edit Dentistry
The ambit of applications for SMAs has developed over the years, a above breadth of development actuality dentistry. One archetype is the prevalence of dental braces appliance SMA technology to apply connected tooth-moving armament on the teeth; the nitinol archwire was developed in 1972 by orthodontist George Andreasen.9 This revolutionized analytic orthodontics and has additionally had an aftereffect on cilia optic development. Andreasen's admixture has a blooming appearance memory, accretion and application aural accustomed temperature ranges because of its geometric programming.
Harmeet D. Walia after activated the admixture in the accomplish of basis aqueduct files for endodontics.
edit Materials
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