Micro and nano damage observations of martensitic and austenitic open cell cast foams

Abstract

In current study a detailed investigation of the 304 austenitic and 420 martensitic foams damage has been carried out at all hierarchical levels. In-situ compression testing of foams and microtensile testing of single struts have been conducted in scanning electron microscope (SEM). Strain field analysis has been carried out by Digital image correlation (DIC) method. Nano damage has been applied by Nanoindentation on the unloaded and compressed foams. 304 foams depicted a ductile failure at each scale, while 420 foams failed with a tremendous brittleness, such that no real plateau regime has been observed. At microscale 420 struts ruptured with an intergranular cracking, while 304 struts underwent transformation induced plasticity (TRIP) effect with significant ductility. Although 304 steel struts have higher strength, 420 steel foams exhibited a higher strength due to their high hardness. Since there is not a plastic bending of the 420 struts, load is distributed homogenously to all struts. For this reason, it was concluded that the hardness and ductility of struts are the dominating factors in the foam deformation.