2023 Author: Bryan Walter | [email protected]. Last modified: 2023-05-21 22:24
American engineers have learned to create fabrics with built-in functional fibers. One type of fiber consists of a shape memory alloy and allows the fabric to bend, the second contains an alloy with a low temperature and changes the stiffness of the fabric, and the third works as a touch sensor. An article about the development was published in the journal Proceedings of the National Academy of Sciences.
A number of engineers and researchers in the field of materials science are developing technologies for smart clothes - one that could independently act as separate wearable devices. The simplest approach to smart clothes is to integrate a sensor into a regular jacket or sweatshirt that syncs with a smartphone. For example, such a jacket was developed by Google and Levi's. There are also more complex examples, in which a significant part of the clothing is equipped with unusual components. For example, there are developments in which the fabric of clothing was equipped with dozens of temperature and motion sensors or a luminous layer. But in most cases, all these "additives" do not change the basic properties of the fabric.
Engineers from Yale University, led by Rebecca Kramer-Bottiglio (Rebecca Kramer-Bottiglio), have come up with new ways to embed additional elements into the fabric that make it active. They proposed three types of fibers with different properties that can either be used alone or together to create a multifunctional device or garment.
The first is an active fiber made from nitinol, a shape memory alloy. Engineers heated the filaments to 390 degrees Celsius and gave it a basic shape. It was then cooled and deformed into the shape required for a particular application. After that, the alloy can be heated by several tens of degrees by passing an electric current through it, and it will return to its basic form, given at a high temperature. The authors proposed to make nitinol actuators not circular in cross-section, but rectangular with an aspect ratio of 1: 2, 5. This prevents the actuator from turning outside a given bending plane. They also decided to integrate the actuators into the fabric not one at a time, but in pairs on opposite sides. This allows, after bending the tissue in one direction, to bend it in the opposite direction, activating the antagonist actuator.
The second type is a fiber with variable stiffness. It is 46 percent Field alloy and 54 percent epoxy and is structured as an epoxy matrix with metallic inclusions. There is also a steel wire inside for electric heating. In the range from 45 to 60 degrees Celsius, epoxy resin undergoes a transition between glassy and viscous states, at which its hardness changes significantly. In Field's alloy, the phase transition occurs at a temperature of 62 degrees Celsius. Heating by current occurs very quickly, and it takes about 20 seconds to cool down below the glass transition temperature of the epoxy resin.
The third type is a sensor consisting of polydimethylsiloxane and carbon nanoparticles. It acts as a conductor, which greatly changes the conductive properties with slight stretching. It can be printed or applied by hand to fabric and used as a shape change or breakage sensor.
Work stages of the three prototypes
As an example, the authors showed three prototypes. One of them is an active tourniquet worn on the arm. It is able to detect surface damage by changing the readings of the sensor strip and in this case shrinks around the arm using shape memory fibers and increases its own rigidity using epoxy metal fibers. The second prototype is an expandable cushion, which then fixes the new shape with fibers with variable stiffness and supports the weight of the load. The third prototype is an aircraft that can twist a wing around the fuselage.
There are other notable developments in the smart fabric area. For example, we previously talked about flexible microbial fuel cell fabric and 3D printed fabric with buttons.
