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Plastic Poisson’s Ratio of Nanoporous Metals: A Macroscopic Signature of Tension–Compression Asymmetry at the Nanoscale
journal contribution
posted on 2017-09-05, 00:00 authored by Lukas Lührs, Birthe Zandersons, Norbert Huber, Jörg WeissmüllerThe
suggestion, based on atomistic simulation, of a surface-induced
tension−compression asymmetry of the strength and flow stress
of small metal bodies so far lacks experimental confirmation. Here,
we present the missing experimental evidence. We study the transverse
plastic flow of nanoporous gold under uniaxial compression. Performing
mechanical tests in electrolyte affords control over the surface state.
Specifically, the surface tension, γ, can be varied in situ
during plastic flow. We find that decreasing γ leads to an increase
of the effective macroscopic plastic Poisson ratio, νP. Finite element simulations of a network with surface tension confirm
the notion that νP of nanoporous gold provides a
signature for a local tension–compression asymmetry of the
nanoscale struts that form the network. We show that γ promotes
compression while impeding tensile elongation. Because the transverse
strain is partly carried by the elongation of ligaments oriented normal
to the load axis, the surface-induced tension–compression asymmetry
acts to reduce νP. Our experiment confirms a decisive
contribution of the surface tension to small-scale plasticity.