Development of auxetic structures for variable stiffness beams

Finished: 2022-06-23

Individual assignment

Birds have the ability to morph and stiffen their wings during flight to adapt their flight behavior. The change in stiffness results in a different interaction with the air around the wings. Research into robotics currently draws inspiration from these distributed variable stiffness and control methods in nature to create bio-inspired, more energy-efficient robots.

In previous work, we studied variable stiffness mechanisms for bending stiffness of beams in a robotic bird wing as part of the PortWings project ( However, most of these mechanisms are either expensive, need a difficult fabrication process, have a bulky set-up, or cannot deal with fast actuation. One option that still needs proper exploration for variable stiffness applications in robotics is the field of auxetic structures. Auxetics are structures or materials with a negative Poisson's ratio. This means that they expand perpendicular to the applied force when stretched, due to their internal structure. The idea of the assignment is to use this expansion upon an axial load to change the torsional and bending stiffness of the beam, either through a variable cross-section or through jamming with another structure.
Furthermore, 3D printing is an ideal tool to create this kind of structure due to the geometric freedom and rapid and lightweight manufacturing. It has already been used to create various auxetic structures for robotics, showing its suitability.

Therefore, the goal of this assignment is to study auxetic structures for variable stiffness beams through theory and experiments with 3D printing as a manufacturing method. The assignment includes:

- Study the basics of auxetic structures in literature
- Explore and model designs for variable stiffness auxetic structures
- Manufacture designs by means of 3D-printing
- Experimentally test the performance of designs