Nov 21, 2015 | By Tess

If you’ve been wracking your brain to figure out how artist Behnaz Farahi designed her recent 3D printed wearables project “Caress the Gaze,” you’ll be excited to hear that she has released an Instructables detailing how she created the piece using SMA actuators.

Farahi’s Caress the Gaze is a 3D printed neckpiece that combines aspects of fashion and art, with interactivity and corporeal experience. Aesthetically the piece looks like it is made of a feather-like material, and it is this 3D printed texture that is so crucial to the garment’s design. That is, the feather-like quills that make up the surface texture are capable of detecting the gaze of passersby and move and contract as the person’s gaze looks at the body.

The Instructables guide aims to show how Farahi herself used Shape Memory Alloys (SMAs) to create such a tactile and dynamic 3D printed piece, though it does not restrict the user to making a garment such as hers, as she points out that the technology and method can be used in architecture, and industrial objects in addition to wearables.

In her work, Farahi used an Objet Connex500 3D printer which is capable of multimaterial printing, though she points out that while this feature is necessary to achieve what she made, interesting results could also be achieved using any desktop 3D printer and PLA materials.

In short, Shape Memory Alloys were developed as actuators able to mimic biological muscle functions. SMAs work often work through heat activation to change the shape of a material back to its initial stage. That is, the material possesses a memory of its initial form, so to speak.

In order to create a dynamic 3D printed object such as Farahi’s she stresses that is it also important to understand auxetic structures as she uses both SMAs and 3D printing in order to make them. Auxetic structures are responsible for the expanding and contracting of the Caress the Gaze garment. In short, an auxetic structure displays an unusual mechanical behavior when it is stretched as the structure’s materials become thicker in a perpendicular direction to which it is stretched. This behavior is due to the internal structure of the material, as can be seen in the video below:

To make the materials “come alive,” however, Farahi had to combine both the auxetic structures with embedded SMAs, which were all assembled after 3D printing.

Farahi used multimaterial 3D printing as it allowed her to make composite materials with different flexibilities and densities in a single print run. In designing her object she opted to use softer materials such as Tango black+ for the joints, and a more rigid material, Vero White, for the other sections, which allowed for the final product to contract and expand.

Once the 3D prototypes had been printed, Farahi explains that she began to experiment with and observe the mechanical behaviors they exhibited when they were activated with SMA actuators. During this process, she used various sizes, temperatures, and spring pitches in her SMAs.

She does note that working with SMAs can pose some difficulties, as she says on her Instructables page, “One of the challenges in designing a dynamic system with SMAs or flexinol is that unlike servo motors which you can control their motions and location, you have less control of their motion. Precise SMA position control is actually possible but not so easy.” This imprecision is due to the fact that SMA wires do not have equal cooling and heating curvatures.

Next, Farahi lays out three methods for designing an SMA actuator which include using weight and gravity, using a biased spring which would push the SMA into its extended state, and finally by using material properties. She explains, “The material behavior plays an important role in this method by storing and releasing bending energy during the heating and cooling phases of the SMA wire…The mechanical properties of the material which is inherently springy applies an initial tension to the SMA wire. Therefore, by heating the wire, it contracts and produces additional curvature in the structure.”

For her project, Farahi opted to use the material properties method. In her application of it for Caress the Gaze, she placed SMA actuators between the nodes of the stiff material in the 3D printed structures which meant that when activated the combination of the material properties of the PLA and the auxetic structure of the object made for an organic seeming and silent movement of the object.

Farahi also notes that it is important not to solder anything to SMA actuators and suggests using crimp tubes for the various connections between electrical wires and joints.

In terms of design, the possibilities are many, though Farahi herself says she was inspired by animal and fish scale systems. She developed her design using Grasshopper in Rhinoceros.

If you are feeling ambitious and want to explore the possibilities of dynamic design in 3D printing using SMA actuators, Farahi’s own exploration can be a guide for you!



Posted in 3D Printing Application



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