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Accurate Stiffness Measurement of Ultralight Hollow Metallic Microlattices by Laser Vibrometry

Abstract

Recent progress in advanced manufacturing enables fabrication of macro-scale hollow metallic lattices with unit cells in the millimeter range and sub-unit cell features at the submicron scale. If designed to minimize mass, these metallic microlattices can be manufactured with densities lower than 1 mg/cm3, making them the lightest metallic materials ever demonstrated. Measuring the compressive stiffness of these ultralight lattices with conventional contact techniques presents a major challenge, as the lattices buckle or locally fracture immediately after contact with the loading platens is established, with associated reduction in stiffness. Non-contact resonant approaches have been successfully used in the past for modulus measurements in solid materials, at both small and large scales. In this work we demonstrate that Laser Doppler Vibrometry coupled with Finite Elements Analysis is a suitable technique for the reliable extraction of the Young’s modulus in ultralight microlattices.

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Notes

  1. A stubby geometry, with a very low L/D ratio, is heavily affected by the boundary conditions, as a significant fraction of the bar nodes are on the boundary. Fully constraining all the boundary nodes against rotations, and imposing a symmetric deformation, results in excessive stiffening, as in practice minor rotations between cells can occur. Furthermore, stubby geometries are more affected by the details of the nodal fillets, which are difficult to capture exactly.

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Acknowledgments

This work was financially supported by the Office of Naval Research under Grant No.N00014-11-1-0884 (program manager: D. Shifler). This support is gratefully acknowledged. The authors are also thankful to Tobias Schaedler, Alan J. Jacobsen, William B. Carter of HRL Laboratories for providing samples and for useful discussions.

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Correspondence to L. Valdevit.

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Salari-Sharif, L., Valdevit, L. Accurate Stiffness Measurement of Ultralight Hollow Metallic Microlattices by Laser Vibrometry. Exp Mech 54, 1491–1495 (2014). https://doi.org/10.1007/s11340-014-9917-8

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  • DOI: https://doi.org/10.1007/s11340-014-9917-8

Keywords

  • Metallic microlattices
  • Young’s modulus
  • Laser doppler vibrometry
  • Natural frequency
  • Finite element simulation