Effects of Meso Shape Irregularity of Metal Foam on Yield Features under Triaxial Loading

Metallic foam is a typical porous material with heterogeneous meso structures that affect the metallic foam's mechanical properties, in which shape irregularity of meso structures (porous cells) is the key. Shape irregularity of a porous cell reflects the deviation the cell shape from a sphere having the same volume. This paper examines the effects of meso shape irregularity of metallic foam on yield features based on three-dimensional (3D) Voronoi model and the finite element (FE) method. Three cubic foams designed by 3D Voronoi technique were constructed to furnish different statistics of shape irregularity but with the same initial density. Three normal stresses were applied on cubic metallic foam proportionally to implement the triaxial proportional loading in triaxial compression and tension. The yield surface of each 3D Voronoi foam under triaxial loading was calculated, and the influence of shape irregularity on the yield surface was investigated. The results show that the yield surface in (σ_e, σ_m) space may be depicted by an ellipse for metallic foams with different shape irregularities. The meso shape irregularity does clearly affect the yield surface with larger shape irregularity producing a smaller yield surface. This means that the metallic foam with larger shape irregularity yields more easily, and this feature is also reflected in the normalized yield surface for metallic foams with different irregularities.