Introduction, principle and application analysis of shape memory alloy
Introduction
Shape Memory Alloys (SMA) is a new type of functional material that can undergo phase change under temperature and stress. It has unique shape memory effect, phase change pseudo-elasticity, etc. It is widely used in aerospace, Medical equipment, machinery and electrical appliances, and other fields.
Image source: smartlab
Characteristics - memory ability
After the plastic deformation of the shape memory alloy, it is heated above a certain temperature and can return to the shape before deformation, that is, it has a shape memory effect (SME).
It is widely known that on July 20, 1969, American astronauts left the human footprint on the moon for the first time on the moon, and transmitted information between the moon and the earth through a hemispherical antenna with a diameter of several meters. This behemoth-like antenna is made of a shape memory alloy material.
The upper right corner antenna is a shape memory alloy material
Image source: NASA
First, do it according to the predetermined requirements above its transition temperature, then lower the temperature and press it into a ball, and put it into the lunar module to go to heaven. After being placed on the moon, under the sunlight, the transition temperature of the alloy is reached, and the antenna "records" its original appearance and becomes a hemisphere.
Characteristic - superelastic
Another unique property of shape memory alloys is the large "pseudoelastic" or "superelastic" at high temperatures (austenitic state), which means that the bearing capacity of this alloy is several times or even several times larger than that of ordinary metals. Can recover the strain.
Image source: science.jrank
Shape memory principle
The principle of remembering the shape of a memory alloy is different from that of a polymer elastic material. For example, the rubber band we are familiar with, the principle of restoring its shape is the opening and separation of the internal rubber chain of internal cross-linking and entanglement.
The reason why the shape memory alloy has the deformation recovery ability is the thermoelastic martensitic transformation generated inside the material during the deformation process. The low temperature phase (martensite) produced by the thermoelastic martensitic transformation undergoes a reversible transformation to a high temperature phase (austenite) upon heating.
Schematic diagram of shape memory process
Image source: smartlab
category
It has been found that there are many types of alloys having a shape memory effect, and can be classified into three major categories: nickel-titanium, copper, and iron. The shape memory alloys that have been put into practical use are only Ni-Ti alloys and Cu alloys.
Recently, Yukiko et al. of Tohoku University in Japan found that Mg-Sc alloy exhibits 4.4% superelasticity at -151 ° C and can be recovered by heated shape, and the density is only about 2 g/cm 3 , compared with the actual nickel-titanium shape memory alloy. Lower one third. This lightweight magnesium-rhenium shape memory alloy has enormous potential for application in areas where weight control is critical, such as aerospace.
Relationship between specific gravity and maximum superelastic strain of shape memory alloy
Image source: Science
Application of shape memory alloy
Aerospace
In December 2017, NASA released a non-pneumatic tire made of shape memory alloy jointly developed with Goodyear. This tire can be used as a traditional tire in addition to the Mars exploration mission. The alternative is used on Earth.
Image source: NASA
The Hubble Space Telescope (HST) uses an arm made of shape memory alloy. When it reaches space, the temperature of the sun heats the shape memory arm above the critical temperature, returning it to its original shape and automatically releasing the solar panel.
Image source: NASA
The shape memory alloy is used to change the camber angle of the wing, or the relative angle between the top and bottom of the wing.
Image source: wired
mechanical industry
Micromachines of various shapes
Image source: JohnsonMatthey
SmartFlex alloy wire
Image source: SAES Getters
A shape memory alloy tubing joint was prepared using a Ti-Ni-Fe alloy having a phase transition point of about -150 °C. This tubing connector can be used on fighter aircraft.
Image source: JohnsonMatthey
Image source: uzone.univs
Biological Engineering
The memory esophagus can expand into a new esophagus in the throat. If necessary, add ice cubes to the esophagus. The "esophagus" can be easily removed when it is cold contracted, improving the quality of life of patients with esophageal cancer who have lost their feeding function.
Image source: smartlab
Shape memory alloys mimic human muscles and tendons, and can be made into controlled "muscles" using piezoelectric materials or shape memory alloys.
Image source: University of cornell
Nickel-titanium shape memory alloy bone plate.
Image source: Smyr
Orthodontic wire: NiTi shape memory alloys can sustain a more constant corrective force than other materials.
Image source: jmmedical
Shape memory alloy for hip replacement.
Image source: washington.edu
A blood vessel stent is fabricated using a shape memory alloy.
Image source: Lakeview Center
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