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Hygroscopic Assembly
The aim of Hygroscopic Assembly is to combine material science research with current digital design and fabrication technologies to increase the load capacities and speed of passively actuated "4D" structures.
This research project was executed while I was a researcher at the Digital Manufacturing & Design Centre at the Singapore University of Technology & Design.
The enabling material technology in this work is chitosan, a naturally occurring hygroscopic (water-absorbing) material that can be processed into a fiber-reinforced composite film.
Chitosan exhibits shrinking forces due to capillary pressure. Integrating this material into cantilevering trusses enables the creation of kinematic structural systems that can autonomously transform in response to water. Different capacities for shape change of the cantilever can be tuned by programming changes in depth and by prescribing specific rotational range within 3D-printed joints. This allows contingent, material-based shape changes of the cantilever to be mediated through geometric means, leading to a predictable range of movement.
To explore the morphospace of this novel structural class, a design and simulation pipeline within Grasshopper was established. The Kangaroo Physics plugin was utilized to model the shape change based on an input expansion of the chitosan films and the initial geometry of the truss. This shape change design was then linked to a generative tool to populate bespoke geometries of the rotational joints.
The variability in truss member angles and in rotation at each node of the truss to provide the desired curvature change called for a generative parametric design tool to model the geometrically complex joints. This tool was based on the Exoskeleton Grasshopper plugin which provided the raw 3D mesh thickened around the line network representing the truss members meeting at their nodes. This mesh then had to be split into male and female parts with internal cavities for mechanical parts to enable rotation. The parametric tool was created so that joint geometries could be automatically generated whenever there was a change in truss geometry or desired shape change.
The components of the truss are rationalized as a kit-of-parts with assembly logic included in the geometric design of each custom part. These joints were fabricated using state-of-the-art carbon fiber-reinforced 3D printing technologies. Physical testing on small-scale prototypes was conducted to calibrate the Kangaroo shape change simulations.
Research culminated in a 2m-long prototype to demonstrate scale and speed of actuation (4 minutes to total saturation and 20 minutes to full evaporation).
These truss systems were presented as a proof-of-concept application of load-bearing components for walkway canopies in monsoon cities that protect from wind-driven rain and allow better ventilation in their dry state.
