Investigation of local heterogeneity effects on additive manufacturing cellular structures

Abstract Cellular structures applied in additive manufacturing (AM) designs typically exhibit finite pattern sizes and significant local property/quality variability. Due to the non-homogeneous unit cell boundary conditions, much of existing understanding with the stress distribution and failure characteristics of cellular structures based on homogenization treatment becomes unreliable. In this work, an analytical modeling-based investigation was carried out to understand the significance of local property heterogeneity to the typical AM finite-size cellular structures. A full-scale cellular model was utilized in order to account for both the effects of boundary conditions and local stress heterogeneity. A perfectly elastic material model was adopted, and an iterative elemental thickening was employed as a means of introducing local heterogeneity. The analytical modeling was first verified via finite element simulation and validated with experimentation using AM and subsequently utilized for the study. Multiple two dimensional (2D) and three-dimensional (3D) cellular unit cell topologies were included in the investigation. The results showed the compound relationship between the cellular unit cell topology design, pattern size, the local heterogeneity and the fracture characteristics of the cellular structures. For 2D diamond and 3D body centered cubic designs, the fracture characteristics of the structures are highly dominated by the local criticality of elements at the center region. On the other hand, for re-entrant auxetic and octahedral structures, the local stress criticality is more scattered and less sensitive to local heterogeneity, which potentially corresponds to more stringent quality control requirement ultimately in their applications.