Aircraft

"Shape-Memory" Metal Alloys or Other Novel "Smart" Materials

Buck Rogers, Watch Out!

Source: NASA
http://science.nasa.gov/headlines/y2001/ast01mar_1.htm?list109259 

March 1, 2001

NASA researchers are studying insects and birds, and using "smart" materials with uncanny properties to develop new and mindboggling aircraft designs.

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"Birds are so much more maneuverable than our airplanes are today. Birds can hover, they can fly backwards and sideways. And insects -- oh forget it! -- upside down, loop-de-loop, all sorts of things."

Anna McGowan, program manager for the Morphing Project at NASAís Langley Research Center

-- The "personal aircraft" that replaces the beloved automobile in peopleís garages may still lie in the realm of science fiction or Saturday-morning cartoons, but researchers at NASAís Langley Research Center (LaRC) are developing exotic technologies that could bring a personal "air-car" closer to reality.

And air-cars are just the beginning.

Self-healing wings that flex and react like living organisms, versatile bombers that double as agile jet fighters, and swarms of tiny unmanned aircraft are just a few of the science-fiction-like possibilities that these next-generation technologies could make feasible in the decades ahead.

Above right: Tomorrowís airplanes could have self-bending wings, which might operate without flaps --thus reducing drag and saving on fuel costs. Click above right image for movie about some of the next-generation technologies being developed at LaRC. Image courtesy of Robert C. Byrd National Technology Transfer Center.

At the core of this impending quantum leap in aerospace technology are "smart" materials -- substances with uncanny properties, such as the ability to bend on command, "feel" pressure, and transform from liquid to solid when placed in a magnetic field.

"This is technology that most people arenít aware even exists," said Anna McGowan, program manager for the Morphing Project at LaRC, which develops these new technologies.

Left: Anna McGowan, program manager for the Morphing Project at NASAís Langley Research Center.

The task of the Morphing Project is to envision what cutting-edge aerospace design will be like 20 years from now and begin developing the technologies to make it happen.

For example, a personal air-car needs to be compact, yet able to fly at both very low and very high speeds.

"We know that to get a íJetsonsí vehicle, youíre probably going to need a wing that can undergo a radical configuration change," McGowan said. "The kind of wing you need at very low speed and the kind of wing you need at high speeds are completely different."

Some airplanes today can already reorient their wings, such as the Navyís F-14 Tomcat and the B-1 supersonic bomber. These planes use rigid wings mounted to large, heavy pivots in the planeís body.

In contrast, Morphing Project scientists envision a wing that will unfurl on command using "shape-memory" metal alloys or other novel "smart" materials. The material of the wing itself would bend to create the new shape.

Shape-memory alloys have the unusual property of snapping back to their original shape with great force when a certain amount of heat is applied. Any shape can be "trained" into the alloy as its original shape.

An artistís conception illustrating some of the features that may define cutting-edge aircraft 20 years from now. In addition to self-bending wings, this rendition shows piezoelectric sensors that provide real-time strain data, enabling the plane to "feel" the motion of its wings as birds do. Synthetic jets allow the plane to minutely alter the flow of air over the wings, providing subtle aerodynamic control as feathers do.

Among the exotic "smart" materials being developed by the Morphing Project, shape-memory alloys are relatively ordinary.

Imagine seeing a bullet shot through a sheet of material, only to have the material instantly "heal" behind the bullet! Remember, this is not science fiction. Self-healing materials actually exist, and LaRC scientists are working to unravel their secrets.

"What we did at NASA-Langley was basically dissect that material to answer the question, íhow does it do that?í" McGowan said. "By doing so, we can actually get down to computational modeling of these materials at the molecular level."

"Once we understand the materialís behavior at that level, then we can create designer ísmartí materials," she added.

LaRC is also developing customized variations of piezoelectric materials. These substances link electric voltage to motion. If you contort a piezoelectric material a voltage is generated. Conversely, if you apply a voltage, the material will contort.

Scientists can use such properties to design piezoelectric materials that function as strain sensors or as "actuators" -- devices that create small motions in machines, like the moving of wing flaps.

Left: This thin, flexible film contains a piezoelectric material that responds to the bend by producing a voltage thatís detected by the electrodes seen at the bottom left of the image.

Combined with micro-electronics, these materials could lead to a radical advance in airplane design.

"When we look 20 years into the future, we see airplanes that have distributed self-assessment and repair in real time," McGowan said.

"To make this technology possible, you would need to distribute these actuators and sensors throughout the wings. Thatís similar to how the human body operates. We have muscles and nerves all over our bodies -- so we are aware of whatís happening to our bodies and we can respond to it in a number of ways."

The resemblance to biology doesnít end there. One avenue of Morphing Project research is to examine how nature does the things that it does well. Scientists hope they can learn lessons from this tutelage to improve their own designs.

"Nature does some things that we canít even get close to doing. Birds are so much more maneuverable than our airplanes are today. Birds can hover, they can fly backwards and sideways. And insects -- oh forget it! -- upside down, loop-de-loop, all sorts of things. We canít even get close to that [yet]," McGowan said.

Called "biomimetics," this practice of learning from nature has led to the development of -- among other things -- a facsimile of bone.

Bone is very light because of its porous interior, but itís also very strong. LaRC scientists can make structures similar to bone by injecting polymer microspheres into composite shells of the desired shape, then heating the spheres to make them fuse together like tiny soap bubbles.

Right: LaRC scientists are studying nature to understand how birds and insects achieve their high degree of efficiency and maneuverability.

"If you can have the strength and lightweightness of these bone-like structures that Iím talking about, then add in nerve-like sensors and these flexible actuators, what youíre going to end up with is an extremely light-weight, very strong, self-sensing, self-actuating structure."

Compare that vision to the rigid, numb, heavy structures airplanes are made of today, and youíll get a sense of the dramatic difference "smart" materials could make in aerospace design.

As with all basic science, the applications of these "smart" materials will extend to technologies outside of the aerospace industry.

"We are working very closely with two different commercialization groups funded by NASA," McGowan said, "and the outlook for this technology is on the order of millions of applications."

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