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Lecture

Smart wooden actuators

Wednesday (07.06.2017)
14:30 - 14:50 Förde II
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Since the advent of shape memory alloys and bimetals, a multitude of smart actuators have been created from different classes of responsive materials. Whereas down-scaling to micrometer-sized systems has been demonstrated, the multi-step synthesis of such actuators, especially of those with anisotropic properties, in combination with limitations in mechanical properties, presents a major obstacle in the development of large-scale actuators. Wood offers a unique combination of anisotropic responsiveness, mechanical properties, and good workability, which makes it an ab initio smart material for the development of a new class of large-scale, humidity-responsive actuators. Benefit is hereby taken from the circumventing of the complex synthesis steps, as this is done by nature. Implementing the bilayer principle, specific reversible actuation patterns can be programmed into such wooden bilayer systems. Using the theory of bimetals and more complex, material adapted models, we are able to predict and tune the pattern and magnitude of actuation of such wooden bi-layered systems as a function of fiber orientation and geometric parameters. The pronounced anisotropy of wood and its naturally present size limitations require material adapted design principles for upscaling. As sensor and motor are embedded in the material, simple and autonomous actuators can be created. In outdoor applications, the actuation of these elements is solar driven and controlled. Thus, such smart wooden bilayers can function as motor elements of a new generation of autonomous, intelligent, and sustainable climate adaptive building shells. We compare simulation studies with bilayer experiments in lab condition and perform long-term field studies for elucidating the long-term behavior in full weathering condition [3]. By hierarchical structuring, the range, pattern, and speed of actuation can be enlarged. Based on this fundamental research aspects, we have built demonstrators for an autonomous, solar-driven tracking system for photovoltaic modules and for shading systems for building facades.

Speaker:
Additional Authors:
  • Chiara Vailati
    ETH Zürich
  • Dr. Falk Wittel
    ETH Zürich
  • Philippe Grönquist
    Empa