Micromechanics of complex three-dimensional microstructures

Material microstructures often contain non-uniformly distributed features of complex geometry. Attributes of three-dimensional microstructural geometry have dominant influence on the mechanical behavior of materials. Therefore, it is of interest to incorporate quantitative description of actual three-dimensional microstructures in micromechanical analysis of materials. In this contribution, a methodology has been developed to perform finite element (FE)-based simulations on complex three-dimensional microstructures, through its application to cast microstructure of A356 Al-alloy containing non-uniformly distributed pores of complex geometry. As expected, the simulations reveal that the distributions of local stresses and strains depend on size, orientation, and spatial arrangement of the pores in a complex manner. FE-simulations on the three-dimensional pore structure have been used to simulate the growth of the voids by the McClintock rule. These simulations clearly demonstrate that unit cell model can be used in the study the void growth behavior of materials at the stress levels close to global yield stress, and it overestimates the void growth at the stress levels significantly higher global yield stress. The FE-simulations reveal a general trend that larger voids have a higher percentage increase in their volume. Therefore, at a given applied stress level, absolute rate of volume change of a pore increases with its initial pore volume in a non-linear manner. These observations are supported by experimental measurements of pore growth. It is shown that micromechanical response does not vary significantly if the pores are replaced by equivalent ellipsoids, and such a model can be used to simulate the growth of non-uniformly distributed voids of complex geometry at all stress levels.