Design And Analysis Of Programmable Non-rigid Square-twist Origami Metamaterials

Metamaterials have unusual physical properties that are produced by designing topology and deformation of their microstructures based on the basic physical laws.The previous studies have allowed metamaterials at the forefront of an interdisciplinary research field.Origami,a famous design method,has been used in creating metamaterials,where both rigid and non-rigid structures show unique mechanical properties.This dissertation investigates metamaterials created by a mixture of rigid and non-rigid origami units and proposes geometric design rules and property programming approaches.Notice that the rigid units have received kinematic analysis,which contributes to the available theoretical model for mechanical research.Thus,this dissertation focuses on the study of non-rigid units and the programmability of mixture metamaterials.The highlights of this dissertation are listed as follows.First,based on the uniaxial tension experimental results,a theoretical model of the non-rigid square-twist type 2 unit is proposed by building an equivalent rigid pattern with an additional virtual crease.Two deformation paths with a bifurcation are found by the theoretical calculation of the type 2 unit.The comparison between theoretical and experimental results proves that square-twist type 2 unit tends to follow a lowenergy deformation path.The research reveals successfully programmable mechanical properties by tuning geometrical parameters and material stiffness.Next,due to the complex deformation and unavailable equivalent model method,an empirical model is presented to study the non-rigid square-twist type 1 unit by combining biaxial tension experiments and finite element modeling.A three-stage deformation process,including tightening,unlocking,and flattening,is unveiled in the type 1 unit through a detailed analysis.The empirical model correlates geometric/material parameters of the origami structure and its mechanical behaviors and further offers accurately predicting and programmable mechanical properties based on specific engineering requirements.Finally,a design method is proposed to create tessellated and graded metamaterials by rationally arranging units with different types and geometric parameters according to the analysis of units’ mechanical behaviors.The energy,initial peak force,and maximum stiffness of metamaterials are proved to be the summation of the corresponding properties of the component units.The programmability of metamaterials can be achieved by establishing the relationship between the mechanical properties and the types,proportions,geometric and material parameters of the units.This dissertation significantly improves the design principle and property programmability of origami-based metamaterials.The design method of mixing rigid and non-rigid origami units inspires a new class of programmable origami metasheets for complex engineering applications.