  In their papers, Lu et al. analysed experimental data from in-situ
transmission electron microscopy (TEM) and concluded that local stress
concentration at grain boundary-twin boundary (GB-TB) intersections in
nanotwinned (nt-) metals increases as the TB thicknesses is reduced (below
${\lambda}$ $\leq$ 18 nm). However, here, by analysing the raw experimental
data in Lu et al. together with finite element simulations and dimensional
analysis, we show that the measurement of local stress concentration in a
nt-material is highly sensitive to the adopted averaging box size due to the
high stress gradient near GB-TB intersections as well as to the TB location in
the nt-grain. By careful analysis of the raw data, a completely reverse trend,
which is consistent with well-established laws of continuum mechanics, can be
captured.
