FACTORS CONTROLLING THE FRACTURE-RESISTANCE OF BRITTLE CELLULAR MATERIALS

Previous work on brittle cellular solids has indicated that the fracture toughness may be independent of cell size. The results showed agreement with two theoretical approaches proposed by Maiti et al. to predict the toughness of porous cellular solids. One approach indicates a strut strength and cell size dependence of the bulk material toughness, whereas the other depends only on the toughness of the solid portion. The present work attempted to experimentally discern between the two approaches and identify the controlling parameters governing the mechanical behavior. Reticulated vitreous carbon samples were oxidized to introduce surface flaws into the struts. The toughness and compressive strength of the bulk material were measured before and after oxidation. Fractographic analysis of the fracture surface of individual struts was essential in being able to estimate the strut strength. It was concluded that it is the strut strength which controls the strength and toughness of the bulk cellular solid.