Dr. Santo Padula has developed testing techniques to support the development of advanced materials like metallic foams and shape memory alloys (SMAs). SMAs are metals that “remember” their original shape. With the application of heat, a deformed SMA returns to its initial form.

NASA Tech Briefs: How do shape memory alloys remember their shape?

Dr. Santo Padula: These materials have an energetic landscape that gives them a unique deformation mode — what we call a “twinning” process. The solid-state phase transformation allows us to manipulate the atomic structure of a metal just by manipulating the way that we either mechanically load or thermally load the system. Merely by heating and cooling the system, we can actually recover all of that shape change.

NTB: What’s possible with this kind of capability?

Dr. Padula: The automotive sector is already using these materials. In fact, almost every lumbar support system in vehicles now is actually SMA-driven, usually using SMA wires as the actuation component. We at NASA are trying to develop new adaptive technologies for large-scale aircraft in the aeronautics world in order to replace flap elements and control surfaces on wings with much more lightweight, compact, and efficient systems. The materials work for pretty much anything that would be actuation-based.

NTB: What is most exciting about this technology? Dr. Padula: We have the ability to very quickly produce stable actuation systems. To be able to now use a simple piece of material — let’s say a tube — to completely replace an entire hydraulic system on an aircraft is a revolution. We’ve actually done demonstrations with Boeing on its 737 aircraft. We’ve flown that plane under aero loads just by heating and cooling a tube, instead of having massive hydraulic actuators, lines, fluids, and pumps, which are very heavy and cost more fuel burn. We’re able to use technologies like the ones being developed to create quality and stable materials that now can begin to replace systems on aircraft that make it cheaper and more efficient to fly.

NTB: What are other commercial markets for SMAs?

Dr. Padula: Shape memory alloys have been heavily used for decades in the biomedical field — everything from catheter tubes to arterial stents. These materials, because of the uniqueness of the solid-state phase transformation, allow us to do similar kinds of applications. We can send a femoral catheter from just inside your groin and snake it all the way to your heart without kinking or the risk of not being able to get it back out.

We’re trying to continue to advance the science of this area so that people can begin to see that there’s another alternative to the conventional metal systems. Once we get to that point, we’ll be at a place, I think, where the design will truly be a paradigm shift.

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