“…explicit [Borst and Pamin, 1996, Fleck and Hutchinson, 1997, Aifantis, 1999, Voyiadjis and Abu Al-Rub, 2005, Polizzotto, 2011] (e.g. via classical strain gradients) or implicit [Perzyna, 1998, Łodygowski and Perzyna, 1997, Dornowski and Perzyna, 2002, Sumelka and Łodygowski, 2011, Sumelka and Łodygowski, 2013, Voyiadjis and Faghihi, 2013, Sumelka, 2013c (i.e. via relaxation time in Perzyna's type viscoplasticity).…”