Compressive strength of hollow microlattices: Experimental characterization, modeling, and optimal design
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Scott W. Godfrey Computer Science Department, University of California at Irvine, Irvine, California 92697
Tobias A. Schaedler, Alan J. Jacobsen, and William B. Carter Sensors and Materials Lab, HRL Laboratories, LLC, Malibu, California 90265 (Received 4 February 2013; accepted 16 May 2013)
Recent advances in multiscale manufacturing enable fabrication of hollow-truss based lattices with dimensional control spanning seven orders of magnitude in length scale (from ;50 nm to ;10 cm), thus enabling the exploitation of nano-scale strengthening mechanisms in a macroscale cellular material. This article develops mechanical models for the compressive strength of hollow microlattices and validates them with a selection of experimental measurements on nickel microlattices over a wide relative density range (0.01–10%). The limitations of beam-theory-based analytical approaches for ultralight designs are emphasized, and suitable numerical (finite elements) models are presented. Subsequently, a novel computational platform is utilized to efficiently scan the entire design space and produce maps for optimally strong designs. The results indicate that a strong compressive response can be obtained by stubby lattice designs at relatively high densities (;10%) or by selectively thickening the nodes at ultra-low densities.
I. INTRODUCTION
Metallic cellular materials have long been shown to possess unique combinations of low weight, high stiffness and strength, and substantial energy absorption at relatively low crushing stress.1,2 Additionally, when designed with interconnected porosity, the open volume in the architecture can be exploited for active cooling or energy storage, providing unique opportunities for multifunctionality.3–7 At a given relative density (defined as the mass density of the cellular medium divided by the mass density of the solid constituent), topologically architected cellular structures (e.g., periodic architectures) are vastly superior to stochastic foams, by virtue of a more efficient stress transfer mechanism between the macroscale and the unit-cell level: when appropriately designed, each unit-cell element (whether a truss or a shell feature) will largely experience tension or compression under the applied external loads, with minimal bending.1,8 This guarantees full exploitation of the mechanical properties of the base material, providing the cellular material exceptional mechanical efficiency (in terms of specific stiffness and strength). Over the past decade, a number of cellular topologies have been investigated and characterized, ranging from truss-like concepts8–10 to prismatic (honeycomb-type) designs.11,12 From a manufacturing perspective, nearly all these materials have been a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2013.160 J. Mater. Res., Vol. 28, No. 17, Sep 14, 2013
http://journals.cambridge.org
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built with ingenious assembly techniques combined with high-temperature brazing.13,14 As a result, the smallest dimensional fea
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