Today we bring you to our blog a type of material with increasing importance, and it is none other than shape memory materials.
These materials have the particularity of being able to be deformed, and later recover their original shape when applying an external stimulus (usually temperature). As we mentioned a while ago in another post, it is a smart material.
Como ejemplo, ¿a quién no se le ha doblado un cubierto o un alfiler? ¿Os imagináis que con dejarlos en el radiador recuperaran su forma original? Con este tipo de materiales es posible, y sus ventajas no se quedan ahí.
As we have mentioned, shape memory materials, after undergoing a deformation, can regain their original shape. If we describe it like this, its behaviour seems similar to that of elastic materials, but in reality, they are very different. Its uniqueness lies in the fact that when the force that causes the deformation disappears, its deformed shape is maintained, and it is necessary to raise the temperature of the material so that it returns to its original state.
This recovery of the original shape with temperature is due to the change of the internal structure of the material. These materials tend to have a laminar and fibrillar arrangement at low temperature, which easily allows deformations, as some sheets can move with respect to others; this is called the martensitic state. When heated, the material itself begins to have a much more rigid cubic arrangement, which no longer allows the movement of the material and therefore neither the deformations; This is called the austenitic state. This transition from the laminar structure to the cubic structure has such force as to return the material to its original shape and undo all the deformations suffered. Once the temperature is lowered again, the material is arranged in a laminar shape again and can be deformed again. This process is typical of the atomic arrangement of the material, which means that it can be repeated countless times without affecting its behavior, and thus avoiding, for example, mechanical breakages due to wear or fatigue in sensors or valves.
To get these materials to go from the martensitic phase to the austenitic phase, as we have said, it is necessary to increase their temperature. This can be achieved by providing heat, or very conveniently, by applying electricity. The fact that the temperature of these materials can be increased or decreased using electricity, as we have said, makes them ideal candidates for acting as actuators or sensors. The recovery of the deformations is always the same at the same temperature, which means that they can serve as very precise actuators and sensors. In addition, the deformations that usually occur in these materials are carried out faster than in other types of materials used regularly in these types of applications.
We have discussed that shapeshifting materials can regain their original shape when subjected to heat, and then can be deformed again. This is very convenient for some applications, but in others such as actuators, what is needed is to change from one position to another, both being fixed. Is this possible? The answer is yes, it is possible, since there are shape-change materials that present two shape memories at different temperatures. This makes it possible to set the geometry of the material at two different and known temperatures, which is very convenient.
The most widely used shape memory materials so far are those of a metallic nature. Among them, the so-called Nitinol (Nickel and Titanium alloy), is one of the most used due to its good properties. Even so, there are other metal alloys that also have shape memory, such as Copper, Zinc and Aluminum (Cu-Zn-Al) alloys; Copper, Aluminum and Nickel (Cu-Al-Ni); o Iron, Manganese and Silicon (Fe-Mn-Si).
Until recently, these types of materials were only obtained of a metallic nature, but research in this field that has taken place in recent years has led to the appearance of plastic shape memory materials. These, due to their plastic nature, are very promising, for example, in applications where lighter parts are desired. Also shape-changing or self-healing plastic materials have properties similar to shape memory materials.
Other types of shape materials that are still under study and their use has not expanded as widely are shape memory ceramics and shape memory ferromagnetic materials. Even so, we are sure that in the future all these types of materials will have a great impact.
Here we show you some examples of its application:
One of the applications that is beginning to expand right now is to use these materials to join pipes, without the need for welding. The principle used is simple, you take a shape memory material, you place it inside the tubes, and then you apply heat to it so that it recovers its original shape, with a larger diameter, in order to solidly fix the tubes. The very pressure exerted by the material from inside the tubes makes them stick together and it is very difficult to separate them, in some cases they resist better than welds.
The same principle is used for example in the healthcare sector to open obstructions in the body. Small stents are built that can be inserted into blocked veins or arteries, and when in contact with body heat, they expand, allowing blood to pass through again.
These are some applications of these materials in tubular geometries, but their field of application and possible geometries is very wide. For example, it can be applied to the bodies of cars or airplanes, to modify their geometry while they circulate and therefore improve their aerodynamics, thus reducing the amount of fuel they use. If we think of actuators, whose function is to move from one position to another, the vast majority in the future could be made of shape-shifting materials!
Currently, we can find shape memory materials in medical equipment and healthcare supplies, from dental implants to surgical tools (they are easy to sterilize). Also in everyday objects, such as underwired bras, which use one’s own body heat to regain their shape, or in mattresses, which regain their shape after suffering deformations due to sitting on them. As these materials are light, resistant and capable of operating at high temperatures, they are also widely used in aerospace components such as rockets and space probes.
Due to all the possible applications and advantages that these materials present, we believe that in the coming years they will give a lot to talk about and we will find them more and more in more products without realizing it, since they are in full swing and are being studied more and more.
Did you find the blog interesting? Do you want to know more about shape memory materials? Don’t hesitate and contact us!
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