志联

Space Technology Applications:

　　One of the most encouraging applications of shape memory alloys is in space technology. On July 20, 1969, Apollo 11's lunar module landed on the moon, realizing humanity's dream of first landing on the moon. After the astronauts landed on the moon, they placed a hemispherical antenna several meters in diameter on the moon to send and receive information to Earth. The antenna, several meters long, was placed in a small lunar module. The antenna was made of a newly invented shape memory alloy. This very thin shape memory alloy material was first prepared under normal conditions according to predetermined requirements, then the temperature was lowered, and it was pressed into a ball. The ball was placed in the lunar module and then taken to the sky. After being placed on the moon, the temperature rose in the sunlight. When the temperature reached the transition temperature, the antenna would "remember" its true appearance and become a huge hemisphere.

Mechanical Applications:

　　Shape memory alloys are widely used. For example, mechanical fasteners, pipe couplings, fire alarms, sockets and brazing for integrated circuits in electronic instruments and equipment, artificial heart valves, vertebral correction rods, cranioplasty, oral and dental orthopedics, and mandibular reconstruction surgery. It will also play a magical role in communication satellites, color TVs, temperature controllers, and toys. It will also become a new material in modern navigation, aviation, aerospace, transportation, and textile fields. Shape memory alloys have been used in pipeline connections and automated control. Shells made of shape memory alloys can replace welding. The method is to expand the pipe ends by about 4% at low temperatures. During assembly, the sleeves are fitted together. Once heated, the contraction of the sleeve restores it to its original shape, forming a tight connection. The hydraulic system of US Navy aircraft used 100,000 such connectors, with no leaks or damage for many years. Repairing damaged ships and submarine oil pipelines with shape memory alloy fittings is very convenient. In some places where construction is inconvenient, shape memory alloy pins are made and heated into holes. The tail end of the pin automatically separates and curls, forming a one-sided component.

　　Shape memory alloys are particularly suitable for thermomechanical and isothermal automatic control. Room temperature automatic opening and closing arms have been made. It can open ventilation windows on sunny days and automatically close them when the room temperature drops at night. There are many design schemes for shape memory alloy thermal engines, which can work between two low-temperature difference media, thus opening up new ways to utilize industrial cooling water, nuclear reactor waste heat, ocean temperature difference, and solar energy. The current common problem is low efficiency, only 4%-6%, which needs further improvement.

Medical Uses:

　　Shape memory alloys have also attracted considerable attention in medical applications. For example, bone plates can not only fix two broken bones, but also generate compressive force during the restoration process, forcing the broken bones to connect together. Orthodontic wires, long clips for brain aneurysms and vasectomy, and support plates for spinal correction are all activated by body temperature after implantation. Thrombosis filters are also a new shape memory alloy product. After the corrected filter paper is implanted into the vein, the filter paper gradually recovers into a mesh shape, thereby preventing 95% of blood clots from flowing into the heart and lungs.

　　An artificial heart is a relatively complex organ. Muscle fibers made of shape memory alloys match the elastic membrane ventricle and can simulate ventricular contraction. Now the pumping has been successful.

　　Because shape memory alloys are a "living alloy," using their shape change at a certain temperature, various automatic control devices can be designed, and their application range is constantly expanding.

Earliest Applications:

　　Shape memory alloys were first applied to pipe couplings and fasteners. Shape memory alloys (SMA) are used to make sleeves with an inner diameter 4% smaller than the outer diameter of the connecting pipe. Then, at liquid nitrogen temperature, the sleeve expands by about 8%. During assembly, the sleeve is taken out from liquid nitrogen and inserted into the connecting pipe from both ends. When the temperature rises to normal temperature, the sleeve contracts to form a seal. This connection is tight and well-sealed, much better than welding. It is especially suitable for dangerous occasions such as aviation, aerospace, nuclear industry, and submarine oil pipelines.

More Uses:

　　Currently, shape memory effect and superelasticity have been widely used in various fields of medicine and life sciences.