Programming Shape-change: Integrative computational design of materials, mesostructures, and mechanisms for 4D printing

Integrative computational design of materials, mesostructures, and motion mechanisms for 4D printing

Introduction

Shape-changing structures can transform in response to external stimuli, and through such shape-change adapt to their surrounding environment. The conventional approach for developing such structures relies heavily on using sensors, actuators, and regulating devices. This constructional subdivision into multiple electromechanical elements results in high construction costs, high energy consumption, high maintenance, and often a lack of longevity and functional robustness. Biological systems, in contrast, have evolved fundamentally different strategies to achieve adaptiveness through passive shape-change. Hygroscopic plant structures, such as the pinecone scales, are prominent examples. Through utilizing inherent hygroscopic material properties, these structures can move in response to environmental stimuli (relative humidity) without consuming metabolic energy. Furthermore, their motion is highly tuned through hierarchical material structuring in plant’s cellular structure, which facilitates their precise motion and environmentally adaptive functionalities.

In recent years, hygroscopic plant structures have inspired the development of self-shaping and shape-changing structures for architectural applications. At the ICD, natural wood veneer composites have been used to develop weather-responsive building facades that provide adaptive shading and ventilation. In large scale, wooden bilayers have been employed for self-shaping manufacturing of architectural elements. Furthermore, previous research has shown the possibility to use additive manufacturing to digitally fabricate shape-changing wood-based structures, a process known as 4D printing. However, replicating the functionality and intricate motion and adaptation mechanisms found in natural organisms is still far beyond reach. Among major limitations are creating structures that respond to target ranges of environmental stimuli, with predictable and programmable temporal-spatial shape-change, that can operate reliably and repeatedly over many cycles of actuation.

Research Aim

This research aims to enable higher functionality and programmability of 4D printed humidity-responsive shape-changing structures. Learning from nature, this can be achieved by co-designing material properties and structuring in hierarchical length scales, from micro to macro scale. In micro scale, materials can be engineered to have inherent stimuli-responsive (hygroscopic) properties while being compatible with 3D printing processes. In meso scale, 3D printing can be utilized to arrange the mesoscale material structuring inside printed elements, thus tuning and physically programming the shape-change. In macro-scale, novel motion mechanisms with added functionalities, such as motion amplification, can be computationally designed, simulated, and digitally fabricated via 3d printing. Through such an integrative approach, 4D printed structures can be engineered with tunable responsiveness, shape-change, and (multi-)functionality.

Core hypotheses

The core hypothesis of this research is that computational design and digital fabrication can be employed in multiple length scales and processes to develop bioinspired shape-changing structures with enhanced functionality and programmability. The core hypothesis is broken into three sub-hypothesis, as follows:

I.    Printing-compatible materials can be co-designed for 4D printing to have varying stiffness and hygro-responsiveness. These materials can then be used to develop humidity-responsive smart structures with fast, reversible, and cyclic motion. 

II.    The temporal-spatial shape-change of 4D printed structures can be physically programmed by tuning their mesostructures. Using the FFF method, such mesostructures are directly constructed by the FFF extrusion paths, which can be computationally designed.

III.    Through developing customized computational fabrication processes that integrate design, simulation, and 3D printing toolpath and GCode generation, novel motion mechanisms with added functionalities (such as motion amplification) can be achieved.

Methodology

The research hypotheses are investigated through a series of case studies, in which computational design is employed alongside empirical data acquisition through physical prototyping and testing. The first study investigates the design of shape-changing structures in macro scale, focusing on the development of computational fabrication workflows for design, simulation (geometric shape prediction), and fabrication of self-shaping bending and curved folding structures. The second case study focuses on the design and fabrication of mesoscale material structuring. A series of experiments are undertaken to gather empirical data and establish the relationship between FFF toolpath design parameters with the timescale and kinematics of shape-change. The third study focuses on the design and customized production of materials, which will be undertaken through collaboration with research partners from IKT (Uni Stuttgart) and CPI (Uni Freiburg). The customized materials are then used to develop 4D printed structures, which are examined and evaluated for their range of responsiveness, reversibility, and repeatability of shape-change. The final case study will investigate the integration of all three aspects in the development of a 1:1 scale architectural demonstrator. 

Expected results

This doctoral research presents an integrative computational fabrication approach for developing highly functional and tunable shape-changing structures realized by 4D printing. Through designing material properties and structuring in hierarchical length scales, the responsiveness, shape change, and functionality of these structures can be physically programmed. This shape-change can be utilized in two types of processes, namely one-time self-shaping and cyclic shape-change. The one-time self-shaping structures showcase how complex mechanisms, such as origami tessellations, can self-fold and self-assemble from flat into folded state without any external intervention, only by utilizing the activity of the material system itself. The cyclic shape-changing structures demonstrate constant adaptiveness of shapes in response to the environment, mimicking nature in achieving adaptive functionalities with consuming minimal energy. In both cases, the structures show how the architecture and built environment can be in tune with the environment, being powered by and at the same time empowering the earth.

ICD Institute for Computational Design and Construction, University of Stuttgart

Yasaman Tahouni, Prof. Achim Menges

German Federal Ministry of Food and Agriculture within the framework program Renewable Resources (FNR) (22018116)

State Ministry of Baden-Wuerttemberg for Sciences, Research and Arts (MWK) (33-7533.-30-121/15/3)

Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany’s Excellence Strategy – EXC 2120/1–390831618 (FIT_Bridge)

University of Stuttgart, Wissens- und Technologietransfer (WTT) (ZeroFassade)

Tahouni, Y., Krüger, F., Poppinga, S., Wood, D., Pfaff, M., Rühe, J., Speck, T. and Menges, A., 2021. Programming sequential motion steps in 4D-printed hygromorphs by architected mesostructure and differential hygro-responsiveness. Bioinspiration & Biomimetics. DOI: 10.1088/1748-3190/ac0c8e

Tahouni, Y., Cheng, T., Wood, D., Sachse, R., Thierer, R., Bischoff, M. and Menges, A., 2020. Self-shaping Curved Folding: A 4D-printing method for fabrication of self-folding curved crease structures. In Symposium on Computational Fabrication (pp. 1-11). DOI: 10.1145/3424630.3425416

Krüger, F., Thierer, R., Tahouni, Y., Sachse, R., Wood, D., Menges, A., ... & Rühe, J.,  2021. Development of a material design space for 4D-printed bio-inspired hygroscopically actuated bilayer structures with unequal effective layer widths. Biomimetics, 6(4), 58. DOI: 10.3390/biomimetics6040058