Introduction: A.U.X.E.chair : Design and Fabrication of an Adaptive Auxetic Chair
I have always been fascinated by the magical transformation of geometry or those shape-changing toys as a kid. Then I grew up and went to school, and thanks to Mathematics I realized that the "magic" is actually the intelligence of geometry and material properties. Some years later while doing my Masters degree, I learned that these metamaterials are called "auxetics" and became determined to assist from its intelligence to make something useful for our daily life, just like those toys for a kid.
That's a brief summary of how " A.U.X.E.chair " was born; a new concept for designing adaptive and shape-changing furniture.
I did this project together with Ahmad Razavi and Zhiqi Lin, as a seminar project within ITKE institute and BIOMAT at the University of Stuttgart.
Step 1: Aim
This project aims to design and fabricate a piece of auxetic furniture which its shape adapts to the user's body figure. But let's start first by the definition of auxetics, they are commonly described as " structures or materials that have a negative Poisson's ratio. It means when they are stretched in one direction, they expand in the other direction." Cool huh? Well, we believe that the smartness in the behavior of this metamaterials is very potent in creating shape-change and adaption.
Of course, due to the science-based nature of this project, we are not the inventors of auxetics. Auxetics was first invented in 1978 by the Berlin researcher K. Pietsch. Since then, researchers continued working on this topic, one of my favorites is this one by MIT Media Lab so far:
Kinetix - MIT Media Lab
However, our contribution to this scientific research is to continue exploring their behavior on a larger scale and possibly defining functionality while integrating fabrication techniques and material properties.
Step 2: Design
First of all, download the file ( it basically helps you to know the size of each wood piece and where there should be rigid/flexible joints) . Then all you need to do is to go to the wood workshop and cut the wood pieces. For the rigid joints, we basically did the female joinery download the file joints and use CNC for cutting.
You have to install rhinoceroses ( we used rhino 6). I attached a link for downloading here:
Rhinoceros 6 download
In our study case, there is a higher level of dependency between design, structure, and material. Since the behavior of the chair and the right choice of material and geometry are interdependent, our design process starts digitally. We started by exploring different 2d patterns and their deformations, in order to achieve an auxetic behavior.
As you can see in the third image, we can break down our design into 3 main parts: rigid body, rigid joints, and elastic joints. The amount of elasticity of the flexible joints, size of the rigid body units and stiffness of the rigid joints were all parameters which needed to be taken into consideration in order to achieve the desired deformation.
We also did a rough deformation analysis was also done with KIWI!3d ( grasshopper plugin) in order to have a better estimation of the expected deformation.
However, the result was a fairly good start point to understand the behavior in a more tangible way, but we soon realized that physical prototyping was a better approach to anticipate and test the ideas than digital simulation. So we continued the research with physical prototyping.
Step 3: Prototyping
So the fun part begins!
We started prototyping in microscale and 1:1 scale in order to see the fabrication limitations, design potentials, and structural performance.
We started experimenting with smaller scale components, using wood steaks as a rigid body, epoxy resin asrigid joints and tubes aselastic joints.
Result: What was understood was that the epoxy resin connections are not strong enough and will break, and also in the flexible joints there should be a mechanism which guides the bending direction of the elastic part!
Then with a jump of scale to 1:1, a much better understanding of the deformation radius according to the elasticity and flexibility of the hinges was observed. It was also a given that a huge amount of spatial change was achieved with a minimum force. Although the first prototype with one 2D unit was not the design goal for the chair, it has the most spatial change.
Then we continued the prototyping process by connecting two units together in xy plane. The same amount of deformation freedom was achieved since the units were not constrained in 3D, so as a more pleasant design. This prototype also demonstrated the spatial potential of creating positive and negative spaces. The rotation of the rigid elements in either divergent or convergent direction resulted in this behavior.
Result: Although the bottom rigid elements are not perpendicular to the ground after deformation ( last image), the whole system is yet stiff and stable. Finally, the last prototype was produced as a proof of concept for scalability and various shape deformation. It consists of 4 cubic parts, which each acts perfectly as an individual unit!
Step 4: Fabrication and Assembly
We can break down our design in three parts regarding three different behaviors, so we proposed three different materials to achieve those behaviors. The materials we used can be listed as below:
- wood glue
- metal hinges (27)
- silicon rubber
- shrinking tube + lighter ( for micro scale)
- dried timber wood (3mm*1mm* (n)mm)
For a rigid body of the structure, wood can perform well for the rigid body of the structure as well as the rigid joints where there is a lot of force concentration. For the elastic parts, silicon rubber is applicable since it gives freedom to move and also transfers forces between elements. Regarding materials we are using, our method would include two main steps first is to cut the wood pieces in the desired shapes for both rigid body and rigid joints(making whole rigid parts) then doing final assembly by connecting elastic parts.
Our tools for assembly which are shown in the photo are consist of wood glue, metal hinges, rubber, screws, and screwdriver. Gluing rigid joints is the first step of the assembly where rigid body woods are connecting to rigid joint cubes with a male/female joinery system. After all the rigid joineries were done pieces were put together regarding our design and places where flexible joints are happening were marked. Metal hinges are screwed to the edges of wood sticks. Hinges are keeping the rigid parts together while they have the flexibility of movement in one axis which results in the final movement of the whole system.
Step 5: Final Product
Step 6: Outlook
Maybe it is not the most comfortable chair now, but for us this project was more or less a proof of concept for a conceptual drift in designing shape changing furniture, and considering our limited time and student budget we decided to go for bigger units, which means bigger holes and less chance to be comfortable while sitting on it!
However, considering the unit based nature of this design proposal, it is believed that a human interaction approach is a great match for this research. We would like to create this vision of reconfigurability of the single units in various configurations in order to achieve the desired design for each user. Moreover, since the assembly technique is quite straightforward, the users can easily engage in the reconfiguration process and become designers themselves.
Last but not least, if you had any ideas, insights, questions, comments and etc. don't hesitate to ask me! :)