devices, [26,27] to small-scale nano- [28][29][30] and DNA origamis. [31] A common theme in these studies is to exploit the sophisticated shape transformations from folding. For example, an origami robot is typically fabricated in a 2D flat configuration and then folded into the prescribed 3D shape to perform its tasks. The origamis have been treated essentially as linkage mechanisms in which rigid facets rotate around hingelike creases (aka "rigid-folding origami"). Elastic deformation of the constituent sheet materials or the dynamics of folding are often neglected. Such a limitation in scope indeed resonates the origin of this field, that is, folding was initially considered as a topic in geometry and kinematics.However, the increasingly diverse applications of origami require us to understand the force-deformation relationship and other mechanical properties of folded structures. Over the last decade, studies in this field started to expand beyond design and kinematics and into the domain of mechanics and dynamics. Catalyzed by this development, a family of architected origami materials quickly emerged (Figure 1). These materials are essentially assemblies of origami sheets or modules with carefully designed crease patterns. The kinematics of folding still plays an important role in creating certain properties of these origami materials. For example, rigid folding of the classical Miura-ori sheet induces an in-plane deformation pattern with auxetic properties (aka negative Poisson's ratios). [32,33] However, elastic energy in the deformed facets and creases, combined with their intricate spatial distributions, impart the origami materials with a rich list of desirable and even unorthodox properties that were never examined in origami before. For example, the Ron-Resch fold creates a unique tri-fold structure where pairs of triangular facets are oriented vertically to the overall origami sheet and pressed against each other. Such an arrangement can effectively resist buckling and create very high compressive load bearing capacity. [34] Other achieved properties include shape-reconfiguration, tunable nonlinear stiffness and dynamic characteristics, multistability, and impact absorption.Since the architected origami materials obtain their unique properties from the 3D geometries of the constituent sheets or modules, they can be considered a subset of architected cellular solids or mechanical metamaterials. [35][36][37][38][39] However, the origami materials have many unique characteristics. The rich geometries of origami offer us great freedom to tailor targeted Origami, the ancient Japanese art of paper folding, is not only an inspiring technique to create sophisticated shapes, but also a surprisingly powerful method to induce nonlinear mechanical properties. Over the last decade, advances in crease design, mechanics modeling, and scalable fabrication have fostered the rapid emergence of architected origami materials. These materials typically consist of folded origami sheets or modules with intricate 3D geomet...

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The goal of this research is to develop a generic earthworm-like locomotion robot model consisting of a large number of segments in series and based on which to systematically investigate the generation of planar locomotion gaits and their correlation with a robot’s locomotion performance. The investigation advances the state-of-the-art by addressing some fundamental but largely unaddressed issues in the field. These issues include (a) how to extract the main shape and deformation characteristics of the earthworm’s body and build a generic model, (b) how to coordinate the deformations of different segments such that steady-state planar locomotion can be achieved, and (c) how different locomotion gaits would qualitatively and quantitatively affect the robot’s locomotion performance, and how to evaluate them. Learning from earthworms’ unique morphology characteristics, a generic kinematic model of earthworm-like metameric locomotion robots is developed. Left/right-contracted segments are introduced into the model to achieve planar locomotion. Then, this paper proposes a gait-generation algorithm by mimicking the earthworm’s retrograde peristalsis wave, with which all admissible locomotion gaits can be constructed. We discover that when controlled by different gaits, the robot would exhibit four qualitatively different locomotion modes, namely, rectilinear, sidewinding, circular, and cycloid locomotion. For each mode, kinematic indexes are defined and examined to characterize their locomotion performances. For verification, a proof-of-concept robot hardware is designed and prototyped. Experiments reveal that with the proposed robot model and the employed gait controls, locomotion of different modes can be effectively achieved, and they agree well with the theoretical predictions.

In this research, the capability of utilizing fluidic flexible matrix composites (F2MC) for autonomous structural tailoring is investigated. By taking advantage of the high anisotropy of flexible matrix composite (FMC) tubes and the high bulk modulus of the pressurizing fluid, significant changes in the effective modulus of elasticity can be achieved by controlling the inlet valve to the fluid-filled F2MC structure. The variable modulus F2MC structure has the flexibility to easily deform when desired (open-valve), possesses the high modulus required during loading conditions when deformation is not desired (closed-valve — locked state), and has the adaptability to vary the modulus between the flexible/stiff states through control of the valve. In the current study, a 3D analytical model is developed to characterize the axial stiffness behavior of a single F 2MC tube. Experiments are conducted to validate the proposed model, and the test results show good agreement with the model predictions. A closed/open modulus ratio as high as 56 times is achieved experimentally. With the validated model, an F2MC design space study is performed. It is found that by tailoring the properties of the FMC tube and inner liner, a wide range of moduli and modulus ratios can be attained. By embedding multiple F 2MC tubes side by side in a soft matrix, a multi-cellular F2MC sheet with a variable stiffness in one direction is constructed. The stiffness ratio of the multi-cellular F2MC sheet obtained experimentally shows good agreement with a model developed for this type of structure. A case study has been conducted to investigate the behavior of laminated [+60/0/-60] s multi-cellular F2MC sheets. It is shown that the laminate can achieve tunable, steerable, anisotropy by selective valve control.

AbstraIn this research, we investigate in-depth the nonlinear energy transmission phenomenon in a metastable modular metastructure and develop efficient tools for the design of such systems. Previous studies on a one-dimensional (1D) reconfigurable metastable modular chain uncover that when the driving frequency is within the stopband of the periodic structure, there exists a threshold input amplitude, beyond which sudden increase in the energy transmission can be observed. This onset of transmission is caused by nonlinear instability and is known as supratransmission. Due to spatial asymmetry of strategically configured constituents, such transmission thresholds could shift considerably when the structure is excited from different ends and therefore enabling the non-reciprocal energy transmission. This one-way propagation characteristic can be adaptable via reconfiguring the metastable modular system. In this new study, we build upon these findings and advance the state of the art by (a) exploring the different mechanisms that are able to activate the onset of supratransmission and their implications on wave energy transmission potential, and (b) developing an effective design tool -a localized nonlinear-linear model combined with harmonic balancing and transfer matrix analyses to analytically and efficiently predict the critical threshold amplitude of the metastable modular chain. These investigations provide important new understandings of the rich and intricate dynamics achievable by nonlinearity, asymmetry, and metastability, and create opportunities to accomplish adaptable non-reciprocal wave energy transmission. IntroductionNon-reciprocity of wave propagation refers to the unidirectional wave transmission between two points in space and it necessitates breaking the time-reversal symmetry of the system [1] [2]. Motivated by oneway flow of electrical energy using diodes, in recent years, significant research attention have been devoted to realize non-reciprocal wave propagation in other energy forms such as acoustic [3] [4] [5] [6] [7] [8] [9] [10] [11], elastic [12] [13], thermal [14] [15] and optical energy [16] [17]. These contributions can be loosely categorized into two domains: using linear systems with symmetry breaking mechanism [5] [10] [12] [17] or utilizing nonlinear systems [3] [4] [6] [7] [8] [9] [11] [13] [14] [15] [16]. While