4D Printing of Hygroscopic Wood Based Actuators for Climate Responsive Skin

Date

2023-7-26

Author

Nas, Mehmet Oğuz

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Adaptive building systems are designed to enhance user comfort while decreasing energy consumption. However, sensing the environment and generating relevant motion requires complex systems. The cost of the installation, maintenance, and energy consumption of these traditional systems obstruct their widespread adoption. A more efficient solution can be found in nature by utilizing the inherent properties of materials. Recent research inspired by pinecones revealed that wood bilayers with different swelling and shrinking ratios can passively shape change in response to environmental humidity. The morphing direction is dictated by fiber orientation, which can be controlled by extrusion-based 3D printers. While hygroscopic wood actuators hold significant promise as climate-responsive building skins, challenges persist in motion predictability, response speed, and scalability. Consequently, this research investigates mesostructural and macrostructural design space for controlled, scalable motion. A systematic study on design and fabrication parameters was conducted in a controlled environment to observe actuation dynamics. Using the collected data, a model was developed to control and predict shape changes in macrostructural design explorations. Two implementations are proposed: the first harnesses combined actuators for motion amplification, while the latter employs bistability to regulate actuation speed. Experiments at scales of ½ and 1:1, using wood-based filament and wood veneer actuators, validate that coupled actuators significantly enhance actuation speed. Moreover, it is demonstrated that the triggering humidity level of the shapeshifts can be tuned thanks to the prestressed bistable structures. This is promising in terms of adaptivity to various climatic conditions and providing higher energy efficiency in buildings.

Subject Keywords

4D Printing, Climate-Responsive Skin, Shape-Changing Materials, Hygroscopic Wood Bilayer, Pre-stressed Bistability

URI

https://hdl.handle.net/11511/105209

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Graduate School of Natural and Applied Sciences, Thesis