| 4D printed of autonomous bioinspired shapechanging composite for space applications |
| Future Space exploration and settlement will require rethinking the design of structures and the use of materials in a more sustainable way. Currently, large temperature variations encountered in space represents a major challenge for structures made of composite materials. Inspiration from nature (i.e., biomimicry) and 4D printing are emerging approaches for developing new paradigmatic materials that may overcome these limitations and contribute to a sustainable development in space. For example, biological structures found in the dispersal mechanism of seeds like pine cone scales and wheat awn are capable of withstanding environmental changes (temperature, humidity…) to offer an autonomous shape change function due to their asymmetric (bilayer) structural architecture. In addition – and unlike most of the current man-made engineering applications - these biological organisms can simultaneously combine morphing with high mechanical performance.
The application of Biomimicry to materials design can therefore lead to a new generation of autonomously reconfigurable materials based on customised architectures and sensitive to environmental changes, such as thermomorphic composites. The manufacturing of these materials is made possible by the recent development of 4D printing, a new disruptive method of designing and manufacturing smart materials, in which the final shape-change function is encoded within the printed multi-scale architecture.
The aim of this work is to take inspiration from the microstructure of a single plant fibres and their tubular architecture made of stiff cellulose microfibrils wound around a compliant polysaccharide matrix. We are proposing here a new concept of programmable shape-change metamaterial 4D printed with a tubular architecture whose actuation (rotation and Torque) is triggered by temperature variation. This new material concept combines the high mechanical strength of continuous fibre reinforced composites with the shape shaping performance of polymers. For the first time, we have developed an original rotative printer for high-performance continuous-fibre composites. The sequential process methodology is applied for multi-material printing, in which the active layer of pure polymer PA6.6 is first printed and serves as the functional mandrel. The active layer here has a high thermal expansion coefficient. A passive layer of continuous carbon fibre/PA6-1 is then wrapped around the polymer layer. The passive layer provides the mechanical stiffness and actuation authority; the wrapping around the polymer layer imitates the distribution of the cellulose microfibrils that are embedded in the polysaccharide matrix in the S2 layer of plant fibre cell walls.
The application of a variation of temperature combined with the anisotropic asymmetric architecture triggers rotational morphing (i.e., displacement and torque). In conjunction with this, we have developed an original experimental procedure for assessing the contribution of the architecture of the material (e.g. composite angle, composite surface fraction, composite and polymer thickness) on the performance of the rotational morphing. In parallel, a thermo-elastic numerical model based on the theory of laminates is proposed to establish a framework for designing these architected materials.
The present work opens avenues to engineer new autonomous and ubiquitous paradigmatic assemblies for autonomous structural morphing in space - from solar trackers, to solar louvers, antennae and dust shields.
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