Accepted Manuscripts

Hyeonu Heo, Kwangwon Kim, Addis Tessema, Addis Kidane and Jaehyung Ju
J. Eng. Mater. Technol   doi: 10.1115/1.4038029
Adding programmable function to elastic metamaterials makes them versatile and intelligent. The objective of this study is to design and demonstrate thermo-mechanically tunable metamaterials with a compliant porous structure (CPS) and to analyze their thermo-mechanical behaviors. CPS, the unit cell of the metamaterial, is composed of rectangular holes, slits, and bi-material hinges. By decomposing kinematic rotation of a linked arm and elastic deformation of a bi-material hinge, a thermo-mechanical constitutive model of CPS is constructed, and the constitutive model is extended to a three-dimensional (3D) polyhedron structure for securing isotropic thermal properties. Temperature-dependent properties of base materials are implemented to the analytical model. The analytical model is verified with finite element (FE) based numerical simulations. A controllable range of temperature and strain is identified that is associated with a thermal deformation of the bi-material hinge and contact on the slit surfaces of CPS. We also investigate the effect of geometry of CPS on the thermal expansion and effective stiffness of the metamaterial. The metamaterial with CPS has multiple transformation modes in response to temperature while keeping the same mechanical properties at room temperature, such as effective moduli and Poisson's ratios. This work will pave the road toward the design of programmable metamaterials with both mechanically- and thermally- tunable capability, providing unique thermo-mechanical properties with a programmable function.
TOPICS: Metamaterials, Temperature, Hinges, Thermomechanics, Constitutive equations, Design, Finite element analysis, Geometry, Thermal deformation, Roads, Stiffness, Mechanical properties, Thermal properties, Computer simulation, Kinematics, Rotation, Thermal expansion, Deformation
Ahmad A Mousa, Gert Heinrich, Udo Wagenknecht and Omar Arrabeyat
J. Eng. Mater. Technol   doi: 10.1115/1.4037169
Exfoliated graphite (EXG) was prepared from commercially available natural graphite flakes (NGF), through strong acid treatment followed by thermal shock at 950 oC. The EXG sheets were characterized with respect to their thermal stability via thermo-gravimetric analysis (TGA) and Raman spectra. Their morphology and particle size were evaluated using scanning electron microscope (SEM) and particle size analyzer. The potential of EXG as reinforcement on the mechanical and thermal properties of the dynamically vulcanized polystyrene/styrene butadiene rubber (PS/SBR) composites were evaluated. The influence of EXG on the electrical properties of the composites was measured as well.
TOPICS: Composite materials, Thermal properties, Graphite, Particle size, Raman spectra, Thermal shock, Thermal stability, Electrical properties, Scanning electron microscopes, Styrene-butadiene rubber

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