Deriving the production rules of shape-shifting grammars for adaptive façades: The case of hygromorphic thermo-bimetal composites (HMTM)

Shape shifting mechanisms have long been introduced for adaptive façades. More recently, these mechanisms have relied on latent properties of materials rather than complex mechanical actuators. There has been a gap however in identifying rules for the underlying input variables and motion responses of such passive actuating mechanisms. In this paper, we introduce a shape shifting grammar for HMTM, a novel hygromorphic thermo-bimetal composite that responds to variation in temperature and humidity, through laminating layers of Beech as a hardwood and Aluminum; a metal with a high expansion coefficient. Based on a series of physical experiments in a sealed temperature chamber and image analysis using Kinovea tracking software, we identify production rules that map embedded and controlled parameters of the composite material configuration to a desired deflection and motion response. We derive grammars for both simple and complex motion responses based on different variations of variables, terminals, and production rules.