The ability to engineer micro-granular crystals so that their constituent microspheres can be positioned within lattices as desired would enable the control of extreme stress-wave propagation behavior due to the nonlinear stiffness interactions between their microspheres. Whereas engineered granular media that consists of macro-sized spheres (&gt;1mm) support Hz-kHz stress waves for audible applications, engineered micro-granular crystals support MHz-GHz stress-waves for more extreme high-energy applications. Such applications include armor that controls or redirections the propagation of shock waves caused by explosions or high-speed impacts or acoustic lenses that focus high-frequency phonons for underwater imaging, noninvasive surgery, and material damage detection technologies.&nbsp;Here we propose an approach that utilizes automated optical tweezers to simultaneously assemble many 1-10μm-sized spheres at their intended locations within 3D micro-granular crystals. Unlike existing self-assembly, directed self-assembly, or electrophoretic deposition approaches that can fabricate only a limited selection of ordered micro-granular crystal lattices, the proposed optical tweezers approach possesses the flexibility to arrange microspheres of different materials and sizes anywhere within a lattice to achieve high control over extreme stress-wave propagation behavior. Moreover, the approach is automated to increase the placement accuracy and precision of the microspheres and to dramatically increase the speed of assembly so that large test samples can be fabricated within reasonable build-times. Once fabricated these samples, which can’t be made any other way, are tested to collected data that is used to learn about the extreme mechanics that govern the behavior of these crystals.&nbsp;In addition to being able to manufacture micro-granular crystals, the proposed optical-tweezers-based approach can also manufacture microstructures that store and leverage embedded strain energy within their architecture to achieve unprecedented capabilities. To this end, optical tweezers are used to deform what the system prints as it is being printed with two-photon stereolithography. In this way, strain energy is trapped within desired portions of the architecture’s geometry for later transfer or release upon application of loads to enable a variety of impactful applications.

Manufacturing Micro-Granular Crystals and Other Advanced Microstructures Using Optical Tweezers

Paper Proceedings: https://asmedigitalcollection.asme.org/MSEC/MSEC2021/volume/85062

2021 International Manufacturing Science and Engineering Conference (MSEC2021)

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