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AA Emtech Emergent Technologies & Design at the Architectural Association
Fibre Composite Adaptive Systems
Konstantinos Karatzas and Maria Mingallon
Introduction
‘Thigmo-morphogenesis’ refers to the changes in shape, structure and material properties of biological organisms that are produced in response to transient changes in environmental conditions. Existing architectural smart systems are aggregated actuating components externally controlled, whose process of change is essentially different from that of thigmo-morphogenesis, where sensing, actuation and control are an integrated within the element itself. Emulating such morpho-mechanical system with sensors, actuators, computational and control firmware embedded in a fibre composite skin was the aim of our thesis. A thorough investigation of the composite materials available provided us a firm starting point from which the system’s geometry and structure could be developed. The technology includes the use of shape memory alloys as actuators, fibre optics as sensors and glass fibres as structural elements, all being integrated into a polymer matrix. Modelling the processes and material properties and their complex geometries was accomplished through advanced computational techniques.
Biomimicry
Form, structure, geometry, material, and behaviour are factors which cannot be separated from one another. For example, the veins in a leaf contribute to the overall form of the leaf, its structure and geometry. At the micro scale the fibre organisation compliments to the responsive behaviour of the leaf. The veins display an integral coherence within the multiple functions they perform due to the multiple levels of hierarchy in the material organisation. Such level of integrated functionality is the premise of our research which aims to integrate sensing and actuation into a fibre composite material system. Fibre composites which are anisotropic and heterogeneous offer the possibility for local variations in their properties. Embedded fibre optics are used to sense multiple parameters while shape memory alloys (SMA) are integrated in the composite material for actuation. The definition of the geometry, both local and global complements the adaptive functions providing the system with ‘Integrated Functionality.
Geometry
The geometry was approached from two different scales: local and global. The local geometry emerges from the topological definition of a single cell as the smallest unit within the material system. The proliferation of these single cell topologies responds to very specific rules which govern the fusion of the local and global geometries -overall form- with the fibre composite material. This part of the project involved the manipulation of complex geometries where digital simulation was vital. Modelling the range of different geometries that the system could adopt after having sensed a change in the environmental conditions, required the development of codes in both visual basic and vb.net, as well as the use of associative modelling software such as Grasshopper for Rhinoceros. The aim was to generate ‘structural depth’ in the out-of plane dimension; this arrangement can easily be achieved through the use of corrugations where the stiffness of the structure mostly depends on the height of the ‘waves’. Varying the local height of the corrugations would therefore lead to a structure with stiffer differentiated areas which ultimately contribute to the structure as a whole. Once the geometrical arrangement was decided it was necessary to establish the strategy of ‘adaptation’ at the local level.
Experiments
Physical experiments constituted a great part of this research, providing as well a firm base onto which the computation model was constructed. A series of physical experiments were undertaken aiming to the understanding of the materials, testing of the sensing technologies and control units, and finally to the development of the final model which performed the desired sensing and actuation functions. The base material for our final model is a glass fibre reinforced epoxy resin. It is a sandwich structure with four SMA ribbons embedded and strain gauges attached on the surface. When there is curvature change on the gauge -due to an external load-, a signal is sent to the processing unit and after translating the signal the actuation circuit that follows is turned on/off. The actuation controller has two inputs; the set and process value of the temperature on the SMAs. When it is switched on, it starts heating the alloys by turning on the heating patches. The heating process stops, when the process temperature becomes equal to the set temperature of the system. This means that the actuation temperature of the SMAs has been reached and as a result, we have full shape change.
Conclusions
The fibre composite adaptive system developed displays ‘Integrated Functionality’. Factors such as form, structure, geometry and performance form a cohesive synergetic whole which complement one another. Biological organisms display emergent properties as they are organised in complex assemblies over several hierarchical scales. The proposed fibre composite adaptive system possesses multiple organisational scales that have different assembly logics at each scale which augment to their performative abilities. Hence the system displays emergent behaviour which is not a mere sum of it’s parts. The synergy between assembly logics in all scales results in a system which has the potential to adapt and self-organise efficiently to the transient changes in the environmental conditions.