FAILURE OF A POROUS SOLID FROM A DEEP NOTCH

A finite strain finite element method is used to examine the stress st ate near the tip of a deep notch in an elastic-plastic porous solid. T he notch is loaded in mode I plane strain tension and small scale yiel ding is assumed. Two rate independent strain hardening material models are used: a version of the Gurson model (1977) and the more recent FK M model developed by Fleck, Kuhn and McMeeking (1992). Under increasin g K-I, void growth is initially stable and independent of mesh dimensi on. Localization of plastic flow sets in at a finite value K-i, and th e deformation field is mesh-size dependent thereafter. The initiation of crack growth at the notch root is assumed to occur when a critical level of porosity is attained. The results show that the shape of the plastic zone for both the Gurson and the FKM material is highly depend ent on the initial porosity. In the case of low initial porosity, the plastic zone shape is similar to that of a fully dense material; at hi gher initial porosities the plastic zone is concentrated ahead of the notch tip. The effect of the initial void volume fraction on the poros ity field and the critical stress intensity factor is studied, and the mesh-size dependence of the results is discussed. The analysis is use ful for prediction of the notched strength of porous metals.