Deformation mechanisms in nanoporous metals: Effect of ligament shape and disorder

The current work presents a numerical modelling approach for investigating the effect of ligament shape and disorder on the macroscopic mechanical response of nanoporous gold (NPG). The approach starts from a 'single ligament' analysis with respect to three fundamental deformation modes, bending, torsion, and compression, that depend on the ligament shape. It can be shown that the predictive capability of the highly computationally efficient beam model is sufficient for a large variation in ligament shapes. Using a representative volume element (RVE) composed of such ligaments, different degrees of disorder are included. For both the single ligament and RVE models, the cylindrical beam serves as a common reference to compare the results when varying the ligament shape. From the comparison of the RVE elastic response with the single ligament results and the further analysis of statistical information from the elements in the RVE, it is found that bending is the major deformation mode for perfectly ordered RVEs, whereas torsion gains importance for increasing RVE disorder. The effect of compression of the ligaments can be neglected in general. It is concluded that the transition to torsion deformation due to disorder is the cause of the strongly reduced lateral expansion during compression deformation of NPG.