Porous NiTi shape memory alloys have applications in the biomedical and aerospace fields. Recent developments in metal additive manufacturing have made fabrication of near-net-shape porous products with complicated geometries feasible. There have also been developments in tailoring site-specific microstructures in metals using additive manufacturing. Inspired by these developments, we explore two related mechanistic phenomena in a simplified representation of porous shape memory alloys. First, we computationally elucidate the connection between pore geometry, stress concentration around pores, grain orientation, and strain-band formation during tensile loading of NiTi. Using this, we present a method to engineer local crystal orientations to mitigate the stress concentrations around the pores. Second, we experimentally document the growth of cracks around pores in a cyclically loaded superelastic NiTi specimen. In the areas of stress concentration around holes, cracks are seen to grow in large grains with [1 1 0] oriented along the tensile axis. This combined work shows the potential of local microstructural engineering in reducing stress concentration and increasing resistance to propagation of cracks in porous SMAs, potentially increasing the fatigue life of porous SMA components.

Graphene plasmonic resonators have been broadly studied in the terahertz and mid-infrared ranges because of their electrical tunability and large confinement factors, which can enable the dramatic enhancement of light–matter interactions. In this work, we demonstrate that the characteristic scaling laws of resonant graphene plasmons change for smaller (<40 nm) plasmonic wavelengths and that those changes modify the optical confinement properties of graphene plasmonic resonators, allowing their operational frequency to be expanded into the short-wave infrared (SWIR). These effects are realized in centimeter-scale arrays of graphene resonators as narrow as 12 nm, which are created using a novel, bottom-up block copolymer lithography method. Measurements of these structures reveal that their plasmonic resonances are strongly influenced by nonlocal and quantum effects, which push their resonant frequency well into the SWIR (free-space wavelength ∼2.2 μm), 75% higher frequency than previous experimental works. The confinement factors of these resonators reach 137 ± 25, among the largest reported in literature for any type of 2D optical resonator. The combined SWIR response and large confinement of these structures make them an attractive platform to explore ultrastrongly enhanced spontaneous emission.

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