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.
Innovation and application of the proposed reasearch are:
1. experimental data archiving of the mechanical behaviour of different aluminum foams in the respect of static and dynamic loads. This may be useful also in order to improve industrial applications in crashworthiness design or increase the information in research database. Comparing static and dynamic loads a more detailed evaluation of strain rate sensitivity may be possible.
2. 3D mesoscale FEA modeling of different cell distributions suitable to assess accuracy of FEA in accordance of different kind of materials and loads. This may be abel to improve the understanding of how FEA may evaluate scatter due to cell morphologies. In accordance to this accuracy, FEA of mesoscale models may be used to virtual prototyping new design solution and assess probabilistic indicators for the mechanical behaviour.
3. Cell morphologies are related to manufacturing process set-up. Understanding structural behaviour scattering due to cell morphologies may help the tolerance design/optimal set-up of the manufacturing process, so that integrated product-process design may be carried out. This could be of the utmost importance for foam adoption in structural design.
4. Evaluating the amount of scatter in mechanical behavior due to cell morphologies may help to set-up a material model able to quantify this effect without adopting mesoscale modeling, reducing time and efforts during design.