Additive manufacturing is rapidly evolving and opening new possibilities for many industries. This article gives an overview of the current status of additive manufacturing with polymers and polymer composites. Various types of reinforcements in polymers and architectured cellular material printing including the auxetic metamaterials and the triply periodic minimal surface structures are discussed. Finally, applications, current challenges, and future directions are highlighted here.

Syntactic foams containing 60 vol% of hollow glass microballoons in epoxy matrix are modified with untreated nanoclays using combined mechanical and ultrasonication methods. Effects of nanoclays on flexure and thermal behavior of syntactic foams are investigated by adding different amount of nanoclays in the range of 1-3% by weight. Microscopic examinations and physical property characterization are performed to determine the interactions among constituent materials and the void formation during fabrication. It is found that the syntactic foams with 2 wt% nanoclays show the highest improvement in flexural properties ($42% strength and $18% modulus) and dynamic mechanical properties ($30% storage modulus and $28% loss modulus) properties. Thermal decomposition temperature is found to be unaffected by the addition of nanoclays, whereas a continuous reduction in the coefficient of thermal expansion (CTE) is observed. An examination of failure surface indicates that the failure is initiated on the tension side of the flexure sample due to fracturing of microballoons.

Electrocharging assisted process has been used to incorporate carbon in Aluminum 6061 and 7075 alloys ensuing significant improvements of the ultimate tensile strength, hardness, and electrical conductivity. This work investigates the presence of carbon, its structure, carbon-metal bonding, surface characterization and dispersion of carbon incorporated in Al alloys by electrocharging assisted process. Networks of Graphene nanoribbons with 3D epitaxy and preferred orientation along the <110> and <112> directions of Al are evident by transmission electron microscopy and spectrum imaging of the C-K edge electron energy loss spectra. X-ray photoelectron spectroscopy and Raman scattering corroborate sp 2 carbon in Al-6061, and hybrid sp 2-sp 3 in Al-7075 with added carbon. Kelvin probe force microscopy substantiates the presence of carbon in the Al matrix. Phonon density of states derived from first-principles calculations predicts C-Al Raman active modes whilst density functional theory indicates covalent bonding between carbon and Al. This method of incorporation of graphene nanostructures in metals with strong carbon-metal bonding can open up new avenues for incorporation of sp 2 carbon structures in other materials.

Microspheres filled epoxy composites are fabricated, using two types of hollow glass microspheres, namely, Fillite‐500 and K‐15. Fillite‐500 microspheres are relatively stronger and denser (avg. crushed strength ∼17 MPa and density ∼0.45 kg/m3) than K‐15 microspheres (avg. crushed strength ∼2 MPa and density ∼0.15 kg/m3). Each type of microspheres in the range of 10–70 vol% are added into a low viscosity two‐part epoxy resin (SC‐15) system in several steps and are mixed together meticulously to avoid breakage of the microspheres during mixing. The epoxy/microspheres mixture is then cured at room temperature (about 70°F) inside an oven for 24 h followed by post curing at 200°F for 4 h. One of the objectives of this research is to determine the maximum amount of microspheres that can be mixed uniformly without aid of diluents. Microstructural examinations reveal that the microspheres are fairly distributed uniformly through out the epoxy matrix up to 70 vol% for Fillite‐500 and 60 vol% for K‐15. It is found that addition of microspheres results in the reduction of density of the neat epoxy up to 28% with Fillite‐500 and up to 54% with K‐15. Thermo mechanical analysis results show that the coefficient of thermal expansion of epoxy matrix is reduced up to 66% with Fillite‐500 and up to 51% with K‐15.Compressive behavior for the epoxy/Fillite‐500 system is found to be different than the epoxy/K‐15 system. Failure analysis results indicate that the failure processes are also different for both the systems. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers

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