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Mechanical metamaterials offer exotic properties based on local control of cell geometry and their global configuration into structures and mechanisms. Historically, these have been made as continuous, monolithic structures with additive manufacturing, which affords high resolution and throughput, but is inherently limited by process and machine constraints. To address this issue, we present a construction system for mechanical metamaterials based on discrete assembly of a finite set of parts, which can be spatially composed for a range of properties such as rigidity, compliance, chirality, and auxetic behavior. This system achieves desired continuum properties through design of the parts such that global behavior is governed by local mechanisms. We describe the design methodology, production process, numerical modeling, and experimental characterization of metamaterial behaviors. This approach benefits from incremental assembly, which eliminates scale limitations, best-practice manufacturing for reliable, low-cost part production, and interchangeability through a consistent assembly process across part types.

A Mach-scale, rigid, counter-rotating coaxial rotor system, 80 inches in diameter and operating at a tip speed of 190 m/s was tested in hover in two configurations: two-bladed single rotor and two bladed counter-rotating coaxial rotor. Individual upper and lower rotor steady and vibratory hub loads were collected at four operating conditions for each rotor configuration. An in-place, uncoupled dynamic calibration was performed on both upper and lower rotor load cells using an electrodynamic shaker to correct unsteady thrust load measurements. The lower coaxial rotor exhibits significant four-per revolution vibrational loads with an average amplitude 11% of the mean thrust Full span three-dimensional blade deformations were measured for a single lower rotor blade at 11 azimuth locations between 66 • and 126 • with 6 • resolution via the digital image correlation (DIC) optical method. From these measurements high resolution elastic axis flap-bending displacements, as well as blade sectional pitch angles were extracted and examined. The lower coaxial rotor was found to operate at higher pitch angles while also exhibiting increased variation in tip bending displacement when compared to the isolated rotor at similar blade loadings.

The aim of this study was to investigate the short- and long-term effects induced by rapid maxillary expansion (RME) on the shape of the maxillary and circummaxillary structures by means of thin-plate spline (TPS) analysis. The sample consisted of 42 patients who were compared with a control sample of 20 subjects. The treated subjects underwent Haas-type RME, followed by fixed appliance therapy. Postero-anterior (PA) cephalograms were analysed for each treated subject at T1 (pre-treatment), T2 (immediate post-expansion), and T3 (long-term observation), and were available at T1 and T3 for the control group (CG). The mean age at T1 was 11 years and 10 months for both groups. The mean chronological ages at T3 were 20 years, 6 months for the treated group (TG) and 17 years, 8 months for the control group. The study focused on shape changes in the maxillary, nasal, zygomatic, and orbital regions. TPS analysis revealed significant shape changes in the TG. They consisted of an upward and lateral displacement of the two halves of the naso-maxillary complex as a result of active expansion in the short-term, and normalization of maxillary shape in the transverse dimension in the long-term (the initial transverse deficiency of the maxilla in the treated group was eliminated by RME therapy both in the short- and long-term). At the end of the observation period, the nasal cavities were larger when compared with both their pre-expansion configuration and the final configuration in the controls. RME with the Haas appliance appears to be an efficient therapeutic means to induce permanent favourable changes in the shape of the naso-maxillary complex.

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