“…Relevant works include Acharya and Bassani (1995), Wang (2000, 2002a), Gao and Huang (2001), Abu Al-Rub and Voyiadjis (2006) and Askari et al (2015). With the strain gradient plasticity theories, size effect found in various micro-tests can be effectively predicted, such as the thin wire torsion and ultrathin beam bending (Fleck et al, 1994;Wang, 2000, 2002a;Huang et al, 2000;Gao and Huang, 2001;Mao et al, 2013;Bardella and Panteghini, 2015), the micro-and nano-indentation (Nix and Gao, 1998;Abu AlRub and Voyiadjis, 2006;Chen et al, 2007;Ouyang et al, 2010;Ma et al, 2012), compression of micropillars (Kiener et al, 2011;Zhang et al, 2014;Lin et al, 2016) as well as uniaxial compression and tension of particle-reinforced metal matrix composites (PMMC) (Fleck and Hutchinson, 1997;Chen and Wang, 2002b;Aghababaei and Joshi, 2011;Azizi et al, 2013;Legarth, 2015). The strain gradient theories have also been successfully applied to study some other interesting issues at micro-scales.…”