Shape These types of material are known as a

Shape Memory Alloy And Morphing

            As advancement continues in the
materials being used for manufacturing of aircraft with that came a new
practice, morphing. Morphing is where a material in our case undergoes a
uniform transformation into a new shape. Now morphing could be the only
possibility if you have a material that can withstand undergoing transformation
and hold another shape without losing its endurance. These types of material
are known as a shape-memory alloy (SMA). 
Now, to be a shape memory alloy that material should be flexible enough
to change its shape when demanded and withhold its strength and perform at
excess temperatures. Also, to have a phase change of these materials they would
be experiencing the thermal or automated action.

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            Shape memory alloys are bound to
have some sort of resilience in them. Although shape memory alloy has been in
existence for many years, yet they haven’t been used in any mainstream
environment for that reason there aren’t many shape memory alloys. The main
reason being no one has completely explored the elasticity of materials.

Nonetheless, there are some studies where they conducted studies of materials
elasticity. The most common alloys used in these applications are Cu, Al, Ni,
and Ti. A study done by International company Rilem conducted an experiment in
testing the materials where mechanical stress is present to materials and
through a stress and strain curve and along with this they also another factor
of different temperatures and then they study the material characteristics;
below is the result of their experiment

Figure
1 Rilem Experiment Results

In a
similar sense, a study at Texas A&M University was conducted where they
installed shape memory alloy tubes in the wing where the purpose of this was to
“initiate spanwise wing twisting” which is to reduce the drag during
taking off. So, by adding a slight twist to the wing would reduce the angle of
attack through the span of the wing hence, reducing drag. Although the result
of this study was not as much as strong enough for a full-scale wing. Below are
pictures of the SMA torque tube in a wing.

Figure
2 Texas A&M University Study

Another
challenge for this shape memory alloy is the rigidity of the materials after
undergoing transformations. This is where a laser additive manufacturing (LAM)
of shape memory alloy conducted by an Institute in Indore, India. Their study
shows that composite of Ni and Ti significantly improves the phase changing
transformation compared to the other materials like Cu. On the other hand, the
manufacturing cost of this composite is quite expensive so the next step in
this is to find a viable solution for manufacturing.

             Another challenge is the type of material
being used for morphing. When a morphing takes place, the material can go
through an excessive amount of stress which in some cases can rupture the
material. A study at Pennsylvania State University found that a suitable
material for this kind of application is to be made of composite or aluminum.

Which shows that for morphing a material doesn’t have to be flexible. Another
study introduced by Gandhi, Farhan says, “airfoil composed of a cellular
core and stiff face-sheets… the skin’s flexural stiffness must not be too low
in order to keep a good aerodynamic shape” in Figure 3, we can clearly see
that by just having a cellular core can make the structure flexible to some
extent. In this same study, they found out that a honeycomb
cellular structure and specifically honeycomb which has positive angles proved
to be a much stronger structure that can go through heavy loads and withstand
up to ten times greater strains compared to a structure without any cellular
structure. In addition, to having a honeycomb cellular structure rigidity the
same results were found regardless of the thickness of the material being used
and having this kind cellular structure also was viable for the purpose that it
is being used for since it would reduce strain at some stages.     

 

 

Figure
3 Ghandi Cellular Core Structure

In
contrast, there are companies like Lockheed Martin already have aircraft that
have morphing structures, but the difference is that their structure moves in
all, but the idea here is to have a fixed structure to extend or change its
shape by flexing. But, just like shape memory alloys structures that are
flexible are expensive to manufacture and there aren’t also many options in
terms of materials. In addition, controlling these types of materials can be
also a challenge itself. As you can see, the idea of having materials that are
flexible and can change its shape has many advantages to it but for now: first
of all, there aren’t many materials viable enough for this type of application.

Secondly, manufacturing shape memory alloy is no easy task and it also not a
low-cost process.