Size effects in ductile failure of porous materials containing two populations of voids

Micromechanisms of fracture in nodular cast iron: From experimental findings towards modeling strategies – A review

“…For instance it is found that oblate voids whose long axis are aligned normal to the main loading direction lead to an earlier void coalescence [19], the reason why cast iron with lamellar graphite has considerably lower strains to failure than NCI. For low stress triaxialities there is also a moderate effect of the third invariant of the stress deviator (expressed typically by the Lode parameter) on the strain to failure [133].…”

“…In order to overcome this problem in [133] an implicit gradient-enriched nonlocal GTN model was used for the matrix thus also incorporating the mean distance l 2 of secondary voids. It is found that the ratio of l 2 to the distance of primary voids k influences especially the coalescence stage: the larger k is compared to l 2 , the earlier the primary voids coalesce.…”

“…Deformed configurations of the unit cells at final failure for various internal lengths showing different remaining ligament widths (from[133]). …”

Void coalescence in ductile solids containing two populations of voids

“…They extended the original Thomason's criterion for internal necking by heuristically incorporating the softening of the matrix material induced by the presence of the secondary voids. Recently, Zybell et al [49] used 3D unit cells with either a cubic primitive or a body-centered cubic distribution of primary voids, while taking the effect of secondary voids by modeling the base material of the unit cells with a nonlocal Gurson model in both cases. The main finding of their study is that, for a constant volume fraction of the secondary voids, the load carrying capacity of the material increases with increasing secondary void size.…”

“…When the void size is smaller than the characteristic length, strain gradient plasticity effects should be accounted for (see e.g. Zybell et al [49] and the references therein).…”