Effect of Defect on Elastic-Plastic and Creep Behavior of Cellular Materials

Abstract

Cellular solids, such as foams, are widely used in engineering applications. In these applications, it is important to know their mechanical properties and the variation of these properties with the presence of defects. Several models have been proposed to obtain the mechanical properties of cellular materials. However, some of these models are based on idealized unit cell structures, and are not suitable for finding the mechanical properties of cellular materials with defects. Furthermore, the creep response changes in cellular solids when the exposed temperature is higher than 1/3 of the material’s melting temperature. The objective of this work is to understand the effect of missing walls and filled cells on mechanical and creep behavior of both the regular hexagonal and non-periodic Voronoi structures using finite element analysis. The finite element analysis showed that on average the non periodic structures have inferior mechanical properties compared to that of the regular hexagonal structures with the same relative density. The yield stress of Voronoi structures had a mean of 27% lower compared to that of the hexagonal structure with the same relative densities. Defects, introduced by removing cell walls at random locations, caused a sharp decrease in the effective mechanical properties of both Voronoi and periodic hexagonal honeycombs. However, our results indicated that elastic properties of Voronoi Structures are more sensitive to missing walls when compared to those of regular honeycomb structures. The yield strength of Voronoi and regular honeycombs exhibited the similar sensitivity to cell wall removal. For creep analysis, the results suggest that removal of struts dramatically increases the creep rate. In the case of filled cells, regular honeycomb structures showed less sensitivity to the defect compared to Voronoi structures. The overall elastic modulus of the structure increased by 11% when 5% of cells were filled in regular hexagonal honeycombs while for Voronoi structure it had more significant effect (22% increase). The results also show that filled cell did not have a significant effect on yield strength of the regular and Voronoi structures.