Inflatable robots are becoming increasingly popular, especially in applications where safe interactions are a priority. However, designing multifunctional robots that can operate with a single ...pressure input is challenging. A potential solution is to couple inflatables with passive valves that can harness the flow characteristics to create functionality. In this study, simple, easy to fabricate, lightweight, and inexpensive mechanical valves are presented that harness viscous flow and snapping arch principles. The mechanical valves can be fully integrated on‐board, enabling the control of the incoming airflow to realize multifunctional robots that operate with a single pressure input, with no need for electronic components, cables, or wires. By means of three robotic demos and guided by a numerical model, the capabilities of the valves are demonstrated and optimal input profiles are identified to achieve prescribed functionalities. The study enriches the array of available mechanical valves for inflatable robots and enables new strategies to realize multifunctional robots with on‐board flow control.
This work presents several mechanical valves that aim at unloading the complexity of the robotic controls by embedding functionality into the design. Guided by a numerical model, the capabilities of the novel valves have been demonstrated by means of three robotic demos. This study enables new strategies to realize multifunctional robots with on‐board flow control.
The surge in advanced manufacturing techniques has led to a paradigm shift in the realm of material design from developing completely new chemistry to tailoring geometry within existing materials. ...Kirigami, evolved from a traditional cultural and artistic craft of cutting and folding, has emerged as a powerful framework that endows simple 2D sheets with unique mechanical, thermal, optical, and acoustic properties, as well as shape‐shifting capabilities. Given its flexibility, versatility, and ease of fabrication, there are significant efforts in developing kirigami algorithms to create various architectured materials for a wide range of applications. This review summarizes the fundamental mechanisms that govern the transformation of kirigami structures and elucidates how these mechanisms contribute to their distinctive properties, including high stretchability and adaptability, tunable surface topography, programmable shape morphing, and characteristics of bistability and multistability. It then highlights several promising applications enabled by the unique kirigami designs and concludes with an outlook on the future challenges and perspectives of kirigami‐inspired metamaterials toward real‐world applications.
This review outlines the basic deformation mechanisms inherent to kirigami design, summarizes the most distinguished properties of kirigami induced by cutting and folding, and overviews how each property can be leveraged to tackle challenges across various domains. It envisions that this work will inspire further innovation in metamaterials and encourage the community to address the challenges posed by real‐world applications.
Maxwell lattices possess distinct topological states that feature mechanically polarized edge behaviors and asymmetric dynamic responses protected by the topology of their phonon bands. Until now, ...demonstrations of non‐trivial topological behaviors from Maxwell lattices have been limited to fixed configurations or have achieved reconfigurability using mechanical linkages. Here, a monolithic transformable topological mechanical metamaterial is introduced in the form of a generalized kagome lattice made from a shape memory polymer (SMP). It is capable of reversibly exploring topologically distinct phases of the non‐trivial phase space via a kinematic strategy that converts sparse mechanical inputs at free edge pairs into a biaxial, global transformation that switches its topological state. All configurations are stable in the absence of confinement or a continuous mechanical input. Its topologically‐protected, polarized mechanical edge stiffness is robust against broken hinges or conformational defects. More importantly, it shows that the phase transition of SMPs that modulate chain mobility, can effectively shield a dynamic metamaterial's topological response from its own kinematic stress history, referred to as “stress caching”. This work provides a blueprint for monolithic transformable mechanical metamaterials with topological mechanical behavior that is robust against defects and disorder while circumventing their vulnerability to stored elastic energy, which will find applications in switchable acoustic diodes and tunable vibration dampers or isolators.
This study shows how a monolithic topological mechanical metamaterial made from a functional shape memory polymer (SMP) can reversibly explore its topological phase space with only sparse mechanical inputs at its free edges. Phase transitions of SMPs that modulate chain mobility then effectively shield the reconfigurable metamaterial's topological response from its own kinematic stress history, referred to as “stress caching”.
Soft robots offer a myriad of potential because of their intrinsically compliant bodies, enabling safe interactions with humans and adaptability to unpredictable environments. However, most of them ...have limited actuation speeds, require complex control systems, and lack sensing capabilities. To address these challenges, herein, a class of metacaps is geometrically designed by introducing an array of ribs to a spherical cap with programmable bistabilities and snapping behaviors, enabling several unprecedented soft robotic functionalities. Specifically, a centimeter‐sized, sensor‐less metacap gripper is demonstrated that can grasp objects in 3.75 ms upon physical contact or pneumatic actuation with tunable behaviors that have little dependence on the rate of input. The grippers can be readily integrated into a robotic platform for practical applications. The metacap can further enable propelling of a swimming robot, exhibiting amplified swimming speed as well as untethered, electronics‐free swimming with tunable speeds using an oscillating valve. The metacap designs provide new strategies to enable the next‐generation soft robots to achieve high transient output energy and autonomous and electronics‐free maneuvering.
This work presents a new class of metacaps whose extraordinary nonlinear properties have been harnessed to enable several robotic systems with ultrafast yet tunable actuation speed without the need for external sensors or complex control systems. The metacap design strategies pave the way for next‐generation soft robots that are ultrafast, programmable, autonomous, and electronics‐free.
Due to surface tension, a beading instability takes place in a long enough fluid column that results in the breakup of the column and the formation of smaller packets with the same overall volume but ...a smaller surface area. Similarly, a soft elastic cylinder under axial stretching can develop an instability if the surface tension is large enough. This instability occurs when the axial force reaches a maximum with fixed surface tension or the surface tension reaches a maximum with fixed axial force. However, unlike the situation in fluids where the instability develops with a finite wavelength, for a hyperelastic solid cylinder that is subjected to the combined action of surface tension and axial stretching, a linear bifurcation analysis predicts that the critical wavelength is infinite. We show, both theoretically and numerically, that a localized solution can bifurcate sub-critically from the uniform solution, but the character of the resulting bifurcation depends on the loading path. For fixed axial stretch and variable surface tension, the localized solution corresponds to a bulge or a depression, beading or necking, depending on whether the axial stretch is greater than a certain threshold value that is dependent on the material model and is equal to 23 when the material is neo-Hookean. At this single threshold value, localized solutions cease to exist and the bifurcation becomes exceptionally supercritical. For either fixed surface tension and variable axial force, or fixed axial force and variable surface tension, the localized solution corresponds to a depression or a bulge, respectively. We explain why the bifurcation diagrams in previous numerical and experimental studies look as if the bifurcation were supercritical although it was not meant to. Our analysis shows that beading in fluids and solids are fundamentally different. Fluid beading resulting from the Plateau–Rayleigh instability follows a supercritical linear instability whereas solid beading in general is a subcritical localized instability akin to phase transition.
•It is shown that beading in fluids and solids are fundamentally different phenomena.•It is demonstrated that localized necking and bulging are both possible depending on the loading path.•It is shown that there exists an exceptional case in which the bifurcation is super-critical.•Theoretical predictions are verified by numerical simulations.
Propagation of pop ups in kirigami shells Rafsanjani, Ahmad; Jin, Lishuai; Deng, Bolei ...
Proceedings of the National Academy of Sciences - PNAS,
04/2019, Letnik:
116, Številka:
17
Journal Article
Recenzirano
Odprti dostop
Kirigami-inspired metamaterials are attracting increasing interest because of their ability to achieve extremely large strains and shape changes via out-of-plane buckling. While in flat kirigami ...sheets, the ligaments buckle simultaneously as Euler columns, leading to a continuous phase transition; here, we demonstrate that kirigami shells can also support discontinuous phase transitions. Specifically, we show via a combination of experiments, numerical simulations, and theoretical analysis that, in cylindrical kirigami shells, the snapping-induced curvature inversion of the initially bent ligaments results in a pop-up process that first localizes near an imperfection and then, as the deformation is increased, progressively spreads through the structure. Notably, we find that the width of the transition zone as well as the stress at which propagation of the instability is triggered can be controlled by carefully selecting the geometry of the cuts and the curvature of the shell. Our study significantly expands the ability of existing kirigami metamaterials and opens avenues for the design of the next generation of responsive surfaces as demonstrated by the design of a smart skin that significantly enhances the crawling efficiency of a simple linear actuator.
Direct ink writing of liquid crystal elastomers (LCEs) offers a new opportunity to program geometries for a wide variety of shape transformation modes toward applications such as soft robotics. So ...far, most 3D‐printed LCEs are thermally actuated. Herein, a 3D‐printable photoresponsive gold nanorod (AuNR)/LCE composite ink is developed, allowing for photothermal actuation of the 3D‐printed structures with AuNR as low as 0.1 wt.%. It is shown that the printed filament has a superior photothermal response with 27% actuation strain upon irradiation to near‐infrared (NIR) light (808 nm) at 1.4 W cm−2 (corresponding to 160 °C) under optimal printing conditions. The 3D‐printed composite structures can be globally or locally actuated into different shapes by controlling the area exposed to the NIR laser. Taking advantage of the customized structures enabled by 3D printing and the ability to control locally exposed light, a light‐responsive soft robot is demonstrated that can climb on a ratchet surface with a maximum speed of 0.284 mm s−1 (on a flat surface) and 0.216 mm s−1 (on a 30° titled surface), respectively, corresponding to 0.428 and 0.324 body length per min, respectively, with a large body mass (0.23 g) and thickness (1 mm).
3D‐printable photoresponsive gold nanorod/liquid crystal elastomer composite ink is formulated. Taking advantage of both the customizable printed structures from the 3D printing and the remoted, localized actuation from the NIR light, multiple shapes can be achieved, which allows more possible applications for artificial muscles, soft robotics, and other dynamic functional structures.
Transition fronts, moving through solids and fluids in the form of propagating domain or phase boundaries, have recently been mimicked at the structural level in bistable architectures. What has been ...limited to simple one-dimensional (1D) examples is here cast into a blueprint for higher dimensions, demonstrated through 2D experiments and described by a continuum mechanical model that draws inspiration from phase transition theory in crystalline solids. Unlike materials, the presented structural analogs admit precise control of the transition wave’s direction, shape, and velocity through spatially tailoring the underlying periodic network architecture (locally varying the shape or stiffness of the fundamental building blocks, and exploiting interactions of transition fronts with lattice defects such as point defects and free surfaces). The outcome is a predictable and programmable strongly nonlinear metamaterial motion with potential for, for example, propulsion in soft robotics, morphing surfaces, reconfigurable devices, mechanical logic, and controlled energy absorption.
Kirigami, the Japanese art of paper cutting, has recently enabled the design of stretchable mechanical metamaterials that can be easily realized by embedding arrays of periodic cuts into an elastic ...sheet. Here, kirigami principles are exploited to design inflatables that can mimic target shapes upon pressurization. The system comprises a kirigami sheet embedded into an unstructured elastomeric membrane. First, it is shown that the inflated shape can be controlled by tuning the geometric parameters of the kirigami pattern. Then, by applying a simple optimization algorithm, the best parameters that enable the kirigami inflatables to transform into a family of target shapes at a given pressure are identified. Furthermore, thanks to the tessellated nature of the kirigami, it is shown that we can selectively manipulate the parameters of the single units to allow the reproduction of features at different scales and ultimately enable a more accurate mimicking of the target.
Kirigami principles are employed to design inflatables that mimic target shapes upon pressurization. A simple optimization routine enables the inflatables to transform into a family of target shapes at a given pressure. Single units can be selectively manipulated to reproduce features at different scales and ultimately enable a more accurate mimicking of the target.
Deriving the amplitude equation for a buckling mode is an important issue in non-linear elasticity. Focusing on pattern formations in growing tubular tissues, many existing literature often adopted ...the numerical methods. In this paper, we propose a semi-analytical approach for the bilayer tubular structures under growth to derive the amplitude equation of a single wrinkling mode, from which a transition between supercritical and subcritical bifurcations can be determined. In the framework of finite elasticity, a weakly non-linear analysis is carried out and the amplitude equation is deduced by the virtual work method. A semi-analytical solution is obtained, with an analytical expression whose exact coefficients are determined numerically. Then a parametric study is carried out by use of the semi-analytical solution. When the total growth factor is prescribed, the critical mode number governs the amplitude, and a lower mode corresponds to a higher amplitude. When the incremental growth factor after bifurcation is fixed, it turns out that the dependence of the amplitude on the modulus ratio is non-monotonic if the thicknesses of the two layers are specified. For a given geometry, when the modulus ratio ξ>5, the wrinkled amplitude is mainly dominated by the critical mode number, and a smaller critical mode number deepens the wrinkle. However, the amplitude is a decreasing function of ξ when ξ < 5. The obtained analytical solutions are also validated by the corresponding numerical solutions based on the finite element method. The proposed semi-analytical approach is applicable for most variable coefficient problems arising from cylindrical and spherical structures.
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