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Overvelde, Johannes

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Overvelde

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Johannes

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Overvelde, Johannes
Author's Publications: search.filters.isAuthorOfPublication.6068f19d-293b-460e-9229-72d0c7e200e9

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Now showing 1 - 9 of 9
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    Characterization of a Mechanically Tunable Gyroid Photonic Crystal Inspired by the Butterfly Parides Sesostris
    (Wiley, 2015) Pouya, Caroline; Overvelde, Johannes; Kolle, Mathias; Aizenberg, Joanna; Bertoldi, Katia; Weaver, James; Vukusic, Pete
    Dynamically tunable three-dimensional photonic materials offer potential for the development of novel optical technologies. For spectral ranges of interest, however, the systematic and high-throughput characterization of their optical responses as a function of physical deformation remains elusive. This arises from challenges associated with their nanoscale fabrication, deformation, and structural and optical characterization. By exploiting the scale-invariance of Maxwell’s equations and of the elastic material response, we demonstrate the systematic characterization of a tunable macro-scale replica of the gyroid structure found in Parides sesostris butterflies’ wing scales. This scaled replica of the natural photonic crystal was fabricated from a UV cross-linkable elastomer capable of large-range reversible linear deformation via high-resolution additive manufacturing. The controlled deformation of this periodic elastomer-based photonic crystal allowed for a systematic variation of its optical response. Microwave spectroscopy, electromagnetic and mechanical Finite-Element Analysis, and x-ray computed micro-tomography were used to gain a detailed understanding of the gyroid’s compression-induced deformation and the resulting modification of its electromagnetic properties. This approach enables controlled and rapid prototyping and optimization of any desired photonic architecture at macroscopic dimensions prior to the fabrication of its nano/microscopic analogue relevant for manipulating smaller wavelength radiation for use in a wide range of technological applications.
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    Amplifying the response of soft actuators by harnessing snap-through instabilities
    (Proceedings of the National Academy of Sciences, 2015) Overvelde, Johannes; Kloek, Tamara; D’haen, Jonas J. A.; Bertoldi, Katia
    Although instabilities have traditionally been avoided as they often represent mechanical failure, here we embrace them to amplify the response of fluidic soft actuators. Besides presenting a robust strategy to trigger snap-through instabilities at constant volume in soft fluidic actuators, we also show that the energy released at the onset of the instabilities can be harnessed to trigger instantaneous and significant changes in internal pressure, extension, shape, and exerted force. Therefore, in stark contrast to previously studied soft fluidic actuators, we demonstrate that by harnessing snap-through instabilities it is possible to design and construct systems with highly controllable nonlinear behavior, in which small amounts of fluid suffice to generate large outputs.
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    A 3D-printed, functionally graded soft robot powered by combustion
    (American Association for the Advancement of Science (AAAS), 2015) Bartlett, Nicholas; Tolley, M. T.; Overvelde, Johannes; Weaver, J; Mosadegh, Bobak; Bertoldi, Katia; Whitesides, George; Wood, Robert
    Roboticists have begun to design biologically inspired robots with soft or partially soft bodies, which have the potential to be more robust and adaptable, and safer for human interaction, than traditional rigid robots. However, key challenges in the design and manufacture of soft robots include the complex fabrication processes and the interfacing of soft and rigid components. We used multimaterial three-dimensional (3D) printing to manufacture a combustion-powered robot whose body transitions from a rigid core to a soft exterior. This stiffness gradient, spanning three orders of magnitude in modulus, enables reliable interfacing between rigid driving components (controller, battery, etc.) and the primarily soft body, and also enhances performance. Powered by the combustion of butane and oxygen, this robot is able to perform untethered jumping.
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    Discontinuous Buckling of Wide Beams and Metabeams
    (American Physical Society (APS), 2015) Coulais, Corentin; Overvelde, Johannes; Lubbers, Luuk A.; Bertoldi, Katia; van Hecke, Martin
    We uncover how nonlinearities dramatically alter the buckling of elastic beams. First, we show experimentally that sufficiently wide ordinary elastic beams and specifically designed metabeams ---beams made from a mechanical metamaterial--- exhibit discontinuous buckling, an unstable form of buckling where the post-buckling stiffness is negative. Then we use simulations to uncover the crucial role of nonlinearities, and show that beams made from increasingly nonlinear materials exhibit increasingly negative post-buckling slope. Finally, we demonstrate that for sufficiently strong nonlinearity, we can observe discontinuous buckling for metabeams as slender as 1% numerically and 5% experimentally.
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    Rational design of reconfigurable prismatic architected materials
    (Springer Nature, 2017) Overvelde, Johannes; Weaver, James; Hoberman, Chuck; Bertoldi, Katia
    Advances in fabrication technologies are enabling the production of architected materials with unprecedented properties. Most such materials are characterized by a fixed geometry, but in the design of some materials it is possible to incorporate internal mechanisms capable of reconfiguring their spatial architecture, and in this way to enable tunable functionality. Inspired by the structural diversity and foldability of the prismatic geometries that can be constructed using the snapology origami technique, here we introduce a robust design strategy based on space-filling tessellations of polyhedra to create three-dimensional reconfigurable materials comprising a periodic assembly of rigid plates and elastic hinges. Guided by numerical analysis and physical prototypes, we systematically explore the mobility of the designed structures and identify a wide range of qualitatively different deformations and internal rearrangements. Given that the underlying principles are scale-independent, our strategy can be applied to the design of the next generation of reconfigurable structures and materials, ranging from metre-scale transformable architectures to nanometre-scale tunable photonic systems.
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    Reconfigurable origami-inspired acoustic waveguides
    (American Association for the Advancement of Science (AAAS), 2016) Babaee, Sahab; Overvelde, Johannes; Chen, Elizabeth; Tournat, V.; Bertoldi, Katia
    We combine numerical simulations and experiments to design a new class of reconfigurable waveguides based on three-dimensional origami-inspired metamaterials. Our strategy builds on the fact that the rigid plates and hinges forming these structures define networks of tubes that can be easily reconfigured. As such, they provide an ideal platform to actively control and redirect the propagation of sound. We design reconfigurable systems that, depending on the externally applied deformation, can act as networks of waveguides oriented along one, two, or three preferential directions. Moreover, we demonstrate that the capability of the structure to guide and radiate acoustic energy along predefined directions can be easily switched on and off, as the networks of tubes are reversibly formed and disrupted. The proposed designs expand the ability of existing acoustic metamaterials and exploit complex waveguiding to enhance control over propagation and radiation of acoustic energy, opening avenues for the design of a new class of tunable acoustic functional systems.
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    Embracing Compliance and Instabilities to Achieve Function in Mechanical Metamaterials and Devices
    (2016-04-26) Overvelde, Johannes; Bertoldi, K.; Rycroft, C.; Suo, Z.; Mahadevan, L.
    The use of soft materials has led to the development of soft devices that have the potential to be more robust, adaptable, and safer for human interaction than traditional rigid systems. State-of-the-art developments push these robotic systems towards applications such as soft rehabilitation and diagnostic devices, exoskeletons for gait assistance, grippers that can handle diverse objects, and electronics that can be embedded in the human body. Furthermore, compliance has found its way into the design of materials that derive their properties from their structure, not from their chemical composition (i.e. metamaterials or architected materials). Applications of metamaterials range from tunable auxetic behavior, stiffness, optical properties and phononic and acoustic band-gap behavior to tunable surface properties such as the drag coefficient, and chemistry. These examples illustrate the potential of using compliance to create new and improved functionality in structural and robotic applications. While the geometrical non-linearities and instabilities that arise when using soft or flexible materials directly complicate the design process and fall outside the scope of traditional engineering, exactly these non-linearities make the systems inherently capable of rich behavior. As such, to bring these systems closer to application and to uncover their true potential, we need to gain a better understanding of the principles that govern their behavior. The main focus of this dissertation is on the design of non-linear structures and devices that exhibit a nontrivial relation between input and output (i.e. loading and response). I propose analytical, computational and relatively simple experimental techniques that allow us to effectively explore the design space, and that lead to an understanding of the relation between shape and function in compliant systems. More specifically, I explore the effect of the shape and boundary conditions in periodic porous structures and soft deformation sensors, propose a new type of soft inflatable actuators that harnesses snap-through instabilities to achieve instantaneous changes in length, force and pressure, and develop a design strategy that enables mechanical metamaterials for which the volume and shape can be dramatically reconfigured. Altogether, the proposed techniques and case studies can inform simplified routes for the design of tunable mechanical metamaterials and soft devices over a wide range of length scales.
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    Compaction through Buckling in 2D Periodic, Soft and Porous Structures: Effect of Pore Shape
    (Wiley Blackwell, 2012) Overvelde, Johannes; Shan, Sicong; Bertoldi, Katia
    Soft cellular structures that comprise a solid matrix with a square array of holes open avenues for the design of novel soft and foldable structures. Our results demonstrate that by simply changing the shape of the holes the response of porous structure can be easily tuned and soft structures with optimal compaction can be designed.
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    Switching Periodic Membranes via Pattern Transformation and Shape Memory Effect
    (The Royal Society of Chemistry, 2012) Li, Jie; Shim, Jongmin; Deng, Justin; Overvelde, Johannes; Zhu, Xuelian; Bertoldi, Katia; Yang, Shu
    We exploited mechanical instability in shape memory polymer (SMP) membranes consisting of a hexagonal array of micron-sized circular holes and demonstrated dramatic color switching as a result of pattern transformation. When hot-pressed, the circular holes were deformed to an array of elliptical slits (with width of tens of nanometers), and further to a featureless surface with increasing applied strain, therefore, switching the membrane with diffraction color to a transparent film. The deformed pattern and the resulting color change can be fixed at room temperature, both of which could be recovered upon reheating. Using continuum mechanical analyses, we modeled the pattern transformation and recovery processes, including the deformation, the cooling step, and the complete recovery of the microstructure, which corroborated well with experimental observations. We find that the elastic energy is roughly two-orders of magnitude larger than the surface energy in our system, leading to autonomous recovery of the structural color upon reheating. Furthermore, we demonstrated two potential applications of the color switching in the SMP periodic membranes by (1) temporarily erasing a pre-fabricated "Penn" logo in the film via hot-pressing and (2) temporarily displaying a "Penn" logo by hot-pressing the film against a stamp. In both scenarios, the original color displays can be recovered.