Compressive behavior and deformation mechanism of nanoporous open-cell foam with ultrathin ligaments

The compressive response of nanoporous (np) Au with different porosities and ultrathin ligaments of widths 0.5-16 nm is investigated through molecular dynamics (MD) simulations. From the results of the uniaxial compressive loading, it was found that these materials behave in a ductile manner and possess characteristic high yield strength, suggesting that these unique materials may even be stronger than bulk Au and also have the advantage of being highly porous. Their deformation behavior shows three characteristic stages, namely: (1) the linear elastic region, (2) the work hardening region, and (3) the densification region. Surprisingly, even with extremely small ligament widths, where surface stress becomes significant, scaling equations can predict the relative yield strength given the relative density of the nanoporous foam. Through examination of the crystallographic defects at different strain levels, the strain hardening behavior has been attributed to defects in the crystal structure that accumulate at the joints which connect ligaments in the np-Au structures. This is shown to be consistent with experimental results on np-Au under compression and predictions from a published model, thereby proving that the dominant deformation mechanism is ligament bending at the joints of the structure.