Ricerc@Sapienza

Cellular materials have a bulk matrix with a larger number of voids named also cells. Metallic foams made by powder technology represent stochastic closed cells. The related inhomogeneity leads to a scattering of results both in terms of stress-strain curves and maximum strength. Scattering is attributed to relative density variations and local cell discontinuities and it is confirmed also in case of dynamic loading. Finite element simulations through geometrical models that are able to capture the void morphology (named "mesoscale models"), confirm these results and some efforts have been already done to quantify the relationship between shape irregularities and mechanical behavior.
Stress-strain curves obtained from mechanical tests, both with and without strain-rate effects, may be discussed in terms of mechanical behavior and statistical descriptors of the porosity. Then, 3D-model of the specimens may be generated assigning as input the above-mentioned statistical distribution of the porosity. Due to the peculiarity of the cell morphology of aluminum foams made by powder compacts technology (e.g. single larger cells), stress-strain localization has been demonstrated as one of the reasons of the scattering found during the experiments.
In this research the implementation of a foam modeling approach, based on a surface tessellation provided by a Voronoi diagram, is applied to obtain a final model that respects specific assigned cell morphologies already studied experimentally. Doing so, a proper validation of this aspects may be done and reported.
Moreover the quantification of the stress-strain scatter and the effects induced by the cell morphology, may help in the definition or calibration of a material model able to reproduce the investigated foam mechanical behavior.