Mechanical metamaterials are periodic lattices that, by virtue of the unit-cell geometry, exhibit properties beyond conventional materials. Origami allows us to explore interesting 3D geometry by folding flat sheets along predefined creases. The recent popularity of origami in engineering research stems from the advantage it offers in designing reconfigurable structures with tunable and programmable properties. Small-deformation behaviour of origami metamaterials is typically governed by low-energy folding at the creases and panel bending, making these excellent candidates for low-frequency elastic wave propagation. A bandgap is a frequency range in which waves cannot propagate through a medium. Design of origami-based metamaterials with bandgaps requires a thorough understanding of the lattice deformation mechanics, and a study of the modal dynamics of origami lattice structures, which form the two main objectives of this work.
Spatially homogeneous deformations can be useful to the material characterization of origami lattices, whereas inhomogeneous modes allow for the propagation of waves in the system. As a part of the first objective, we have proposed a novel Miura-ori lattice with voids and strips exhibiting a rich space of homogeneous modes, as well as inhomogeneous deformation modes, which are absent in its parent lattice. Additionally, we also developed an intuitive classification scheme to study the space of homogeneous deformation modes.
Towards the fulfilment of the second objective, related to the modal dynamics of origami structures, we have developed mass lumping schemes that improve the accuracy of reduced-order models for origami simulation. We perform experimental modal analysis on metastructures based on the Miura-origami pattern. The specimens are fabricated using a novel manufacturing process where they are 3D-printed with compliant creases in the flat state using polylactic acid, and then manually shaped into the desired folded configuration while immersed in water at elevated temperatures. We perform modal testing using impact hammer and modal shakers to extract frequency response functions. Our results reveal the presence of sizable bandgaps in the low-frequency range (below 1024 Hz) as well as in the higher frequency range (up to 4096 Hz). We find reasonable agreement in the estimation of bandgaps across various choices of manufacturing parameters, instrumentation, and testing methods. Tests performed at multiple folded configurations demonstrate the tunability of the bandgaps. Preliminary finite element simulations with compliant creases have been successful in estimating the extent and size of bandgaps recorded experimentally. The tunable low-frequency bandgaps present in this Miura-origami meta-structures make these promising candidates for vibration isolation and wave-guides.