Introduction
The engineers working for the aerospace industry are always searching for new materials that can help them solve the problems faced by astronauts. Extreme temperatures outside the Earth’s atmosphere make it difficult for astronauts to live in outer space. Aside from difficulties created by extreme temperatures, aerospace engineers are also looking for ways to cram equipment and other important materials into a small spacecraft. Thus, there is a need for versatile materials. Shape Memory Alloys (“SMA”) satisfies the requirements of the aerospace industry because of its shape memory effect.
How It Works
In order to understand the shape memory effect, it is important to review the principles of elasticity and plasticity. Consider for instance a solid object, such as a matchstick. A matchstick has a tendency to stay in shape unless an outside force is introduced that will cause it to break. One can expect this type of behavior, because a matchstick is an example of a solid material. On the other hand, a rubberized object, such as a dog’s chewy toy is also an example of a solid material. However, it is possible to stretch or squeeze the said rubbery material because of the principle of elasticity.
Solid materials that are made of plastic exhibit a property called plasticity. In other words, if one introduces an outside force strong enough to bend the plastic into a different shape, the object stays in that new shape even after the bending force was no longer applied to the said object. The matchstick and the rubber toy have no memory of their shape (Lin 1). Shape memory alloys are different because the object reverts back to its original shape in response to heat or electromagnetic fields (Lin 1).
Design and Examples
The primary requirement is a special type of alloy, such as: nickel-titanium and iron-manganese-silicon alloys (Popovic 67). Nevertheless, it is important to point out that the three main types of shape memory alloys are: 1) copper-zinc-aluminum-nickel; 2) copper-aluminum-nickel; and 3) nickel-titanium alloys (Popovic 67). It is possible to demonstrate the shape memory effect of an SMA because it can change its structure while remaining solid (Popovic 67). In contrast to most objects found in nature, it is impossible to change shape without changing its phase. For example, the transformation of ice cubes into potable water requires the change of phase. In the case of an SMA, it is possible to go through a radical change in shape while remaining in a solid state.
The ability to transition from one structure to the next while remaining solid is made possible by the ability to change phase in response to heat or electromagnetic fields, because shape memory alloys have a high temperature phase called the austenite and a low-temperature phase called the martensite (Woodford 1).
Experts in crystal physics made clarifying remarks that the structural changes occur at the atomic level (Woodford 1). These changes are imperceptible to the naked eye. In order to develop materials and designs that are beneficial to the aerospace industry, engineers must determine the “parent shape” of the material. Once the “parent shape” had been identified, it is imperative to hold this position and heat the SMA-based material to about 500 degrees Celsius (Lin 1). The application of high temperature forces the atoms in the material to arrange themselves “into the most compact and regular pattern possible” (Lin 1). Once the heated material reaches a certain point and the atoms are arranged in a rigid and stable manner, engineers call this the austenite phase (Woodford 1).
The removal of heat forces the material to revert to the martensite phase. In this particular phase, it is easy to manipulate the SMA-based material into various shapes. In other words, it is possible to flatten or twist the material. Engineers are able to manipulate the shape of the material, because they know that once the material is exposed to high temperatures it will revert to its “parent shape” (Motamedi 151).
The United States of America’s National Aeronautics and Space Administration discovered a practical application of SMA-based materials when designing the Hubble Space Telescope. Engineers needed to secure the fragile solar panels within the body of the telescope while being launched into outer space. Using shape memory metals, the said space telescope was packed inside the Space Shuttle (Lin 1). However, when the said telescope was released from the transporter, the rays of the sun heated the special alloy, and as a result it was compelled to return to its predetermined shape. Once the heat from the sun activated the alloy, it extended outward and caused the solar panels to spring out from the body of the telescope (Lin 1).
Other applications include the creation of “morphing wings of aircraft, self-deployable sun sails inside a spacecraft, and cold hibernated memory foam products” (Meng and Li 5). As a result, aerospace engineers are now able to develop better aircrafts because they are no longer limited by conventional materials. For example, engineers can use SMA-based technologies to eliminate the use of socket welds and compression fittings in order to create lighter but stronger aircrafts (Rao, Srinivasa and Reddy 22). It must be made clear that the elimination of certain materials made it easier to reinforce the aircraft without integrating additional elements to the design.
Conclusion
The shape memory effect capability of SMA-based materials enabled engineers to develop cutting-edge design for the aerospace industry. Shape memory materials are made possible by the ability of engineers to change the shape of the material while in a solid state. The unique properties of the alloy enabled the manufacturers to determine the “parent shape” of the material after applying heat. Interestingly, the absence of heat makes it easy to deform or shape the material based on the requirements of aerospace engineers. The best example was the manipulation of the shape of the Hubble Telescope when it was stored inside the Space Shuttle. The ability to deform the shape of the arms of the telescope allowed the engineers to secure the sensitive solar panels within the body of the telescope. However, when the telescope was ejected out of the Space Shuttle and floating in outer space, the sun’s rays significantly increased the temperature of the alloy. After reverting back to its “parent shape” the telescope was able to extend its arms and release the solar panels without the need of additional gadgets. SMA-based materials are not only useful when it comes to creating compact designs. It is also useful in creating strong but lightweight aircraft. This is made possible by the elimination of conventional materials, because engineers have found a way to secure joints and edges without using weld and other fittings.
Works Cited
Lin, Richard. Shape Memory Alloys and Their Applications. 2014. Web.
Meng, Harper and Guoqiang Li. “Controlled Activation Schemes of SMPs for Aerospace Applications.” Shape Memory Polymers for Aerospace Applications. Ed. Gyaneshwar Tandon. Lancaster, PA: DESTech Publications, 2016. 1-31. Print.
Motamedi, Edward. MOEM: Micro-Opto-Electro-Mechanical Systems. Bellingham, Washington: The International Society for Optical Engineering, 2005. Print.
Popovic, Marko. Biomechanics and Robotics. New York: CRC Press, 2013. Print.
Rao, Ashwin, A.R. Srinivasa and J.N. Reddy. Design of Shape Memory Alloy. New York: Springer, 2015. Print.
Woodford, Chris. Shape Memory Materials. 2014. Web.