Ligament and joint sizes govern softening in nanoporous aluminum

The present computational study demonstrates that softening of an open cell nanoporous aluminum structure subjected to tensile loading can be significantly reduced when the size of ligaments and the joints that connect them in the structure is designed to be sufficiently small. It is found using molecular dynamics simulations that the softening becomes slightly slower with increasing porosity for the structures with porosity less than or equal to 72%, and stress localization is observed during softening. In contrast, for structures with more than 75% porosity, softening is much slower, and stress delocalization occurs during softening. It is argued that at relatively high porosity, softening is governed by both the ligament size and the joint size because their compliance becomes high enough to allow the overloading stress due to ligament rupture to be redistributed more effectively throughout the structure.