  We investigate the location of the maximal gradient of the torsion function
on some non-symmetric planar domains. First, for triangles, by reflection
method, we show that the maximal gradient of the torsion function always occurs
on the longest sides, lying between the foot of the altitude and the middle
point. Moreover, via nodal line analysis and continuity method, we demonstrate
that restricted on each side, the critical point of gradient of the torsion
function is unique and nondegenerate. Second, by establishing uniform estimates
for narrow domains, we prove that as a planar domain bounded by two graphs of
function becomes increasingly narrow, the location of maximal gradient of its
torsion tends toward the endpoint of the longest vertical line segment, with
smaller curvature among them. This shows that Saint-Venant's conjecture on
location of fail points is valid for asymptotically narrow domains. Third,
using the reflection method, we prove that for a non-concentric annulus,
maximal gradient of torsion always occurs at the point on the inner ring
closest to the center of the outer ring.
