Initial Report on Nitinol
Nitinol Information:
Nitinol is an alloy, typicallymade of about 55%-56% nickel and 44%-45% titanium by weight. The amount of each metal in the alloy varies based on the desired properties. Nitinol can either act as a shape memory alloy (SMA) or a super elastic alloy depending on its composition. It is important to note that even very small changes in the composition of the alloy can drastically change its properties (Dynalloy, Inc.).Nitinol exhibiting SM characteristics is of most interests for designing a deployable de-orbit device for a CubeSat.
The NDC Company, located in Fremont, California, offers a Nitinol alloy, known as Nitinol SM495 consisting of 54.5% Ni by weight. The transformation temperature of this alloy (temperature at which the alloy will assume its trained shape) is 60oC(NDC). This alloy is available as a round wire with a diameter ranging from 0.004"-0.250" (0.10mm-6.35mm) in diameter.
SMAs, such as Nitinol, must be "trained" to a certain shape which it will assume after being heated to or above its transformation temperature. Training works by fixing the alloy in the desired shape as it is annealed at 500-550oC. Higher temperatures result in lower tensile strengths. According to NDC, annealing times vary from less than a minute to 10-20 minutes based on how much Nitinol is being trained and the annealing method being used. NDC simply recommends experimenting to find the optimal temperature and time for annealing. After annealing, Nitinol parts should be cooled quickly, preferably by quenching in water, to avoid unwanted aging of the material (NDC).
This project will require the fabrication of a wire frame sphere, which will necessitate joining together the wires. Nitinol can effectively be bonded to itself through welding provided the weld is protected by an inert atmosphere and the amount of material effected by heat from the welding process is kept to a minimum. NDC recommends laser, TIG, or resistance welding be used (NDC).
Nitinol exhibits strong resistance to corrosion thanks to a titanium oxide layer which coats the metal. Unfortunately this coating makes it difficult to join the metal by soldering. Nitinol also has an effectively infinite shelf under normal conditions at room temperature (NDC).
Some Personal Thoughts:
NDC's website has a wealth of information on the properties of Nitinol. They provide material data sheets, information on working with and machining the material, and even have a database of scholarly articles on Nitinol. I highly recommend spending some time on the site if you would like more information.
In addition to providing the metal, NDC provides fabrication and prototyping services. Memry Corporation provides similar services. Dynalloy, Inc. sells Nitinol but does not appear to provide fabrication services and their SMA's are primarily intended to act as actuators (they may still be useful for the purposes of this project though).
If the team decides to continue pursuinga SMA frame in parallel to our work with sublimating compounds then I would like to contact these companies for quotes on how much it may cost to have a wire frame sphere fabricated. Having professionals fabricate the frames for us may be preferable to attempting to do it ourselves given some of the challenges involved in properly training and welding Nitinol. Cost and resources available to us at the university will be a significant factor in determining whether fabrication is performed in house or by a private company.
From what I've read I feel that Nitinol could be made into a very effective deployment mechanism. A Nitinol frame will add bulk and it remains to be seen if a way to efficiently fold the frame small enough for use on a CubeSat remains can be devised. Also, of major concern is the potential for the thin wire frame to tear or puncture the polymer membrane it is meant to support. Hopefully, through experimentation, solutions can be found for these problems, but first we must determine if we can source the material and create a prototype economically.
Further Reading:
Nitinol SM495 Material Data Sheet from NDC:
NDC Company Website:
Memry Corporate Website
Dynalloy, Inc. Company Website
Shape Memory Alloy Shape Training Tutorial from a University of Michigan class
A paper from St. Petersburg State University, Russia on the use of SMAs in space engineering
Works Cited
Dynalloy, Inc. Introduction to Nitinol. 2011. 19 January 2011 <
NDC. Nitinol Facts. 2011. 19 January 2011 <
—. Nitinol SM495 Wire Material Data Sheet. 2011. 19 January 2011 <