HMTM: Hygromorphic-Thermobimetal Composites as a Novel Approach to Enhance Passive Actuation of Adaptive Façades

Typical adaptive facades rely on mechanical actuators that respond to the outdoor climate and regulate its effect on indoor spaces. With the emergence of ubiquitous computing, several studies have independently utilized the latent properties of programmable materials, such as the hygroscopic properties of wood and the difference in expansion coefficient of metals, to passively program material response. Motion stimuli vary for each material however, involving changes in humidity and temperature fluctuation for wood and metals respectively. This paper introduces Hygromorphic-Thermobimetal (HMTM), as a low-tech low-cost passive programmable composite. A series of physical experiments are conducted to deduce design parameters that induce specific actuation mechanisms based on the stimulation of both hygroscopic properties in wood and metal expansion through temperature variation. This allows for an extended implementation of the hygroscopic properties of wood and its actuation configurations in hot arid climates, where variation in temperature, rather than humidity, is more dominant.