dehydration, and atrophy. Controlling wrinkle morphologies including orientation, wavelength, and amplitude is very important and necessary for various practical applications.Generally, the orientation of wrinkles is determined by the stress distribution of the film. Unidirectional strain results in stripe-like wrinkles perpendicular to the strain axis [4,5] while multidirectional strain leads to disordered labyrinth-like or ordered herringbone wrinkles. [6,7] Introduction of film impurity can induce local strain anisotropy and guide wrinkle orientation, achieving highly ordered wrinkle arrays. [8,9] The wavelength of wrinkles depends on the film thickness [10] and the modulus ratio of film to substrate. [11] It can range from submicron to macroscale (kilometers in tectonic plates for instance). The amplitude of wrinkles is directly proportional to the wavelength and the square root of strain. [12,13] The aspect ratio of wrinkle (the ratio of amplitude to wavelength) is merely dependent on the strain. The previous studies showed that the wrinkle amplitude or aspect ratio is usually uniform for a homogeneous sample. [4][5][6][7] As the compression is beyond a critical value (20-30%), the homogeneous wrinkles evolve into localized patterns such as folds, ridges, and delaminations. [13][14][15][16][17] Localized wrinkles can be also observed in disordered or heterogeneous films such as single-wall carbon nanotubes, glassy polymers, and diblock copolymers due to spontaneous strain localization. [18,19] Artificial thickness or modulus inhomogeneities of film-substrate systems are frequently used to induce various complex arrays of localized patterns by mechanical loading. [20][21][22] Although localized patterns in disordered or artificially inhomogeneous systems have been extensively investigated, the formation and evolution of heterogeneous wrinkles (with unequal wavelengths or amplitudes compared with the sinusoidal wrinkles) in a homogeneous system remain unknown up to now. In this study, we report a novel way to tailor the heterogeneous wrinkles in metal/polydimethylsiloxane (PDMS) bilayer system by the combination of mechanical loading and heat treatment. The novelty of this work is concluded as following. First, the heterogeneous wrinkles in this study spontaneously form at small strain condition and evolve into homogeneous structures as the compression increases. This process is in contrast to Spontaneous wrinkled surfaces in nature usually possess unique physical and chemical properties. Inspired by nature and stimulated by practical application, artificial wrinkle patterns have received increasing interest recently. Here, the controllable heterogeneous wrinkles in metal films deposited on polydimethylsiloxane substrates by combination of mechanical loading and heat treatment is reported. It is found that the wrinkles are spontaneously localized at small strain condition due to the uneven distribution of wrinkle amplitudes on the film surface. The morphological features and underlying mechanisms of such wrink...
Origami structures are highly demanded for engineering applications. Using origami folding to design and actuate mechanisms and machines offers attractive opportunities. In this paper, we design a crawling robot driven by pneumatic foldable actuators (PFAs) based on Miura-ori, according to the parallel foldable structure and different control patterns, which can perform different movements. The PFA inspired from Miura-ori is composed of a folding part, transition part, and sealing part, made by flexible materials and a paper skeleton. This actuator can obtain a large deformation by folding under negative pressure due to its own characteristics, and the relationship between deformation and pressure is analyzed. According to the different folding and unfolding times of left and right actuators, the crawling robot can perform both linear and turning movements. The speed of the robot is about 5 mm/s and it can turn at a speed of about 15°/s. The crawling robot uses the ability of the foldable structure to cope with the challenges of different environments and tasks.
Dielectric elastomer (DE) is a soft material that can deform to a large degree under the action of an electric field. In this paper, multilayer DE films were stacked in parallel to prepare a 20-layer dielectric elastomer actuator (DEA). This DEA could provide a peak output force of 30 N, which significantly improves the driving performance of the DEA and provides conditions for large load driving of the DEA. As a new driving method, the DEA was applied to a jumping robot, and the heavy-weight robot accomplished jumping motion after several cycles of energy storage.
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