Heat-actuated Auxetic Facades

Highly transformable materials can be used as adaptive exterior shading systems by leveraging the relationship between external stimuli (heat) and reconfigurable facades in order to design new passive kinetic systems. Reversible transformations were explored using materials that exhibit two-way shape memory behavior such as shape memory polymers and shape memory alloys coupled with auxetic patterns. Initial prototypes were made using multi material 3D printing with shape memory polymers. The larger scale prototypes were made with high density foams cut with Robotic water jets.The preferred geometries selected belong to a family of auxetic patterns that are composed of small units which buckle individually under the influence of external forces that cause porosities throughout the entire structure to open and close gradually. Due to the unique negative Poisson ratio in auxetics, a single applied force is able to actuate a whole grid of cells. The resulting movement of the cells on a facade system offers novel functionality as well as intriguing aesthetics. Furthermore, the proposed dynamic system can help reduce the total energy consumption of a building while improving its daylight performance and comfort for its inhabitants. In order to test the daylighting performance of the proposed shading system, a dynamic shading system using auxetic pattern was applied to a facade in Cairo, Egypt which was then simulated and optimized using Honeybee in Grasshopper. Based on the results, this system lead to a marked improvement in both daylighting and energy performance compared to a static non-response shading device.