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Porous metals represent a class of materials where the interplay of ligament length, width, node structure, and local geometry/curvature offers a rich parameter space for the study of critical length scales on mechanical behavior. Colloidal crystal templating of three-dimensionally ordered macroporous (3DOM, i.e., inverse opal) tungsten provides a unique structure to investigate the mechanical behavior at small length scales across the brittle-ductile transition. Micropillar compression tests show failure at 50 MPa contact pressure at 30 °C, implying a ligament yield strength of approximately 6.1 GPa for a structure with 5% relative density. In situ SEM frustum indentation tests with in-plane strain maps perpendicular to loading indicate local compressive strains of approximately 2% at failure at 30 °C. Increased sustained contact pressure is observed at 225 °C, although large (20%) nonlocal strains appear at 125 °C. The elevatederature mechanical performance is limited by cracks that initiate on planes of greatest shear under the indenter.
Bibliographical noteFunding Information:
This work was supported primarily by the MRSEC Program of the National Science Foundation under Award Number DMR-1420013. The authors would like to thank Erica Lilleodden for helpful discussions related to the analysis of DIC results. The authors would also like to thank Bill Gerberich for discussions and suggestions for future work. Parts of this work were carried out in the Characterization Facility, University of Minnesota, which receives partial support from NSF through the MRSEC program. Additional thanks to Nick Seaton (UMN Characterization Facility) for assistance with SEM and FIB.
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Reporting period for MRSEC
- Period 7