“…In order to obtain a criterion for porous grain boundaries with ellipsoidal voids, a variational approach is adopted in the following. Indeed, variational methods provide a homogenization alternative to limit analysis that has proven fruitful for the study of voided viscoplastic single crystals (Han et al, 2013;Mbiakop et al, 2015a;Song and Ponte-Castañeda, 2017a) and polycrystals (Lebensohn et al, 2011;Nervi and Idiart, 2015;Song and Ponte Castañeda, 2018). In particular, they are expected to yield viscoplastic potentials and to be more convenient to introduce void shape effects.…”