Browsing by Author "Tahouni, Yasaman"

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Open Access
Cross-sectional 4D-printing : upscaling self-shaping structures with differentiated material properties inspired by the large-flowered butterwort (Pinguicula grandiflora)
(2023) Sahin, Ekin Sila; Cheng, Tiffany; Wood, Dylan; Tahouni, Yasaman; Poppinga, Simon; Thielen, Marc; Speck, Thomas; Menges, Achim
Extrusion-based 4D-printing, which is an emerging field within additive manufacturing, has enabled the technical transfer of bioinspired self-shaping mechanisms by emulating the functional morphology of motile plant structures (e.g., leaves, petals, capsules). However, restricted by the layer-by-layer extrusion process, much of the resulting works are simplified abstractions of the pinecone scale’s bilayer structure. This paper presents a new method of 4D-printing by rotating the printed axis of the bilayers, which enables the design and fabrication of self-shaping monomaterial systems in cross sections. This research introduces a computational workflow for programming, simulating, and 4D-printing differentiated cross sections with multilayered mechanical properties. Taking inspiration from the large-flowered butterwort (Pinguicula grandiflora), which shows the formation of depressions on its trap leaves upon contact with prey, we investigate the depression formation of bioinspired 4D-printed test structures by varying each depth layer. Cross-sectional 4D-printing expands the design space of bioinspired bilayer mechanisms beyond the XY plane, allows more control in tuning their self-shaping properties, and paves the way toward large-scale 4D-printed structures with high-resolution programmability.
Open Access
Development of a material design space for 4D-printed bio-inspired hygroscopically actuated bilayer structures with unequal effective layer widths
(2021) Krüger, Friederike; Thierer, Rebecca; Tahouni, Yasaman; Sachse, Renate; Wood, Dylan; Menges, Achim; Bischoff, Manfred; Rühe, Jürgen
(1) Significance of geometry for bio-inspired hygroscopically actuated bilayer structures is well studied and can be used to fine-tune curvatures in many existent material systems. We developed a material design space to find new material combinations that takes into account unequal effective widths of the layers, as commonly used in fused filament fabrication, and deflections under self-weight. (2) For this purpose, we adapted Timoshenko’s model for the curvature of bilayer strips and used an established hygromorphic 4D-printed bilayer system to validate its ability to predict curvatures in various experiments. (3) The combination of curvature evaluation with simple, linear beam deflection calculations leads to an analytical solution space to study influences of Young’s moduli, swelling strains and densities on deflection under self-weight and curvature under hygroscopic swelling. It shows that the choice of the ratio of Young’s moduli can be crucial for achieving a solution that is stable against production errors. (4) Under the assumption of linear material behavior, the presented development of a material design space allows selection or design of a suited material combination for application-specific, bio-inspired bilayer systems with unequal layer widths.
Open Access
Integrating ionic electroactive polymer actuators and sensors into adaptive building skins: potentials and limitations
(2020) Neuhaus, Raphael; Zahiri, Nima; Petrs, Jan; Tahouni, Yasaman; Siegert, Jörg; Kolaric, Ivica; Dahy, Hanaa; Bauernhansl, Thomas
Building envelopes separate the confined interior world engineered for human comfort and indoor activity from the exterior world with its uncontainable climatic forces and man-made immission. In the future, active, sustainable and lightweight building skins are needed to serve as an adaptive interface to govern the building-physical interactions between these two worlds. This article provides conceptual and experimental results regarding the integration of ionic electroactive polymer sensors and actuators into fabric membranes. The ultimate goal is to use this technology for adaptive membrane building skins. These devices have attracted high interest from industry and academia due to their small actuation voltages, relatively large actuation and sensing responses and their flexible and soft mechanical characteristics. However, their complex manufacturing process, sophisticated material compositions and their environmental sensitivity have limited the application range until now. The article describes the potentials and limitations of employing such devices for two different adaptive building functionalities: first, as a means of ventilation control and humidity regulation by embedding small actuated apertures into a fabric membrane, and second, as flexible, energy- and cost-efficient distributed sensors for external load monitoring of such structures. The article focusses on designing, building and testing of two experimental membrane demonstrators with integrated polymer actuators and sensors. It addresses the challenges encountered and draws conclusions for potential future optimization at the device and system level.
Open Access
Plants as inspiration for material-based sensing and actuation in soft robots and machines
(2023) Speck, Thomas; Cheng, Tiffany; Klimm, Frederike; Menges, Achim; Poppinga, Simon; Speck, Olga; Tahouni, Yasaman; Tauber, Falk; Thielen, Marc
Because plants are considered immobile, they remain underrepresented as concept generators for soft robots and soft machines. However, plants show a great variety of movements exclusively based on elastic deformation of regions within their moving organs. The absence of gliding parts, as found in the joints of vertebrates and insects, prevents stress concentration and attrition. Since plants have no central control unit (brain), stimulus-sensing, decision-making and reaction usually take place noncentrally in the hierarchically structured materials systems of the moving organs, in what can be regarded as an example of physical intelligence. These characteristics make plants interesting models for a new group of soft robots and soft machines that differ fundamentally from those inspired by animals. The potential of such plant-inspired soft robots and machines is shown in six examples and is illustrated by examples applied in architecture and medicine.
Open Access
Programming shape-change : integrative computational design of materials, mesostructures, and motion mechanisms for 4D-printing
(Stuttgart : Institute for Computational Design and Construction, University of Stuttgart, 2024) Tahouni, Yasaman; Menges, Achim (Prof.)
Shape-changing material systems are advantageous as passively actuated mechanisms for generating movement, with architectural applications ranging from adaptive building skins to the self-shaping manufacturing of building components. 4D printing, a technique that combines stimuli-responsive materials with additive manufacturing, is a promising method for the fabrication and programming of shape-changing structures. However, limitations in material responsiveness, programmability of shape-change, and the robustness of structures have constrained their functionality and real-world applicability. This dissertation introduces an integrative computational fabrication approach for the development of 4D printed hygroscopic material systems based on co-designing materials, mesostructures, and motion mechanisms. By tuning the material properties and structuring at hierarchical length scales, highly functional and precisely programmable 4D printed material systems have been developed. This material programming approach has been demonstrated through three studies, each focusing on one of the aforementioned aspects: by co-designing biobased cellulose-filled materials for 4D printing, the responsiveness of structures to target ranges of ambient relative humidity levels has been tuned; by precisely designing the mesoscale material structuring inside the 4D printed elements, their spatial and temporal shape change has been programmed; and through the development and utilization of computational fabrication workflows for 4D printing, novel motion mechanisms with enhanced functionality, such as motion amplification, have been created. The proposed material programming methodology and the developed material system have been implemented in the design and fabrication of SolarGate, a 4D printed, weather-responsive façade system installed on the LivMatS Biomimetic Shell. Consisting of 424 4D printed shading elements, the SolarGate regulates the solar heat gain of the building by providing adaptive shading in response to daily and seasonal weather cycles without consuming any operational energy. These results showcase the potential for creating an architecture that is highly functional, ecological, and in tune with the environment, being powered by and at the same time empowering the earth.