Development of a Material Design Space for 4D-Printed Bio-Inspired Hygroscopically Actuated Bilayer Structures with Unequal Effective Layer Widths

Abstract

(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.

The Design of 4D‐Printed Hygromorphs: State‐of‐the‐Art and Future Challenges

“…This observation has been experimentally confirmed by Kruger et al. [ 59 ] for wood fibers reinforced PLA. Increasing the active layer stiffness or width leads, on the contrary, to increase the actuation authority.…”

“…Timoshenko Equation (Equation (1)) adapted from Ref. [59]) (δMC = 0.8; β = 1000). a) Influence of the passive and active stiffness on the curvature ( t p = 0.2 mm, t a = 0.1 mm, w p = 1.0 mm and w a = 1.0).…”

“…• Assess the actuation capability of the material system • Compare actuation to thermocompressed actuators • Control actuation and responsiveness with printing parameters Kruger et al ( 2021) [59] • PLA & Short wood fibers • Control actuation with mesostructure printing patterns (layer width, layer thickness)…”

Bridging the Gap: From Biomechanics and Functional Morphology of Plants to Biomimetic Developments

“…Krüger et al [10] have developed a material design space for 4D-printed bioinspired bilayer structures with hygroscopic actuation that takes into account unequal effective layer widths and deflections under self-weight. The curvature of various bilayer strips has been described using an adapted Timoshenko model, and its ability to predict curvatures has been validated in experiments.…”

Design, fabrication and application of self-spiraling pattern-driven 4D-printed actuator

“…Four-dimensional printing using anisotropic methods relies on structural and process design to facilitate manufacturing and offer more precise control. Thanks to years of research on smart materials and structure design [4][5][6] , there are now various methods to stimulate 3D shape changes of printed actuators in the temporal dimension 7 . In order to change the configured operation or function in response to an environmental stimulus 8 , one can activate the active material in a controlled manner, such as by using various materials to respond to different stimulation sources (light sources, heat sources, magnetic fields, electric fields, solution concentrations, etc.)…”