Towards a neutrally stable meta-material consisting of coiled spatially curved shells
Design, evaluation, and optimization of a coiled spatially curved shell structure exhibiting zero-stiffness behaviour during compression to facilitate neutrally stable behaviour in a meta-material
S.L.J. van Hien (TU Delft - Mechanical Engineering)
G. Radaelli – Mentor (TU Delft - Mechatronic Systems Design)
Davood Machekposhti – Graduation committee member (TU Delft - Mechatronic Systems Design)
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Abstract
Meta-materials provide many possibilities with their specially tailored properties on the macro level caused by their micro level structure in the form of unit cells. These unit cells often take the form of Compliant Mechanisms (CM), which have been widely researched. CM are often made neutrally stable to improve their energy efficiency, making it plausible that meta-materials can be made neutrally stable as well. This research aims to create such a neutrally stable meta-material using constant force (zero-stiffness) unit cells. This was achieved by optimizing the geometry of coiled spatially curved shell structures such that their buckling mode under compression facilitated a constant force region under compression. Simulations of the optimized structures within a meta-material lattice are compared to experimental tests performed on 2 different prototypes of such a meta-material. The experimental results show that the force-displacement curves indeed have a constant force trend line under compression. However, the magnitude of the trend line for one experiment is significantly lower than expected in the simulations. Despite this magnitude difference, the shapes of the experimental force-displacement curves are similar to the curves of the simulations. Small regions of neutral stability are observed for the deformed unit cells of the meta-material, but sawtooth-like behaviour of the force-displacement curves around the trend line caused these regions to be small and unstable.