  Powders are a special class of granular matter due to the important role of
cohesive forces. The flow behavior of powders depends on the flow states and
stress and is therefore difficult to measure/quantify with only one experiment.
In this study, the most commonly used characterization tests that cover a wide
range of states are compared: (static, free surface) angle of repose, the
(quasi-static, confined) ring shear steady state angle of internal friction,
and the (dynamic, free surface) rotating drum flow angle are considered for
free flowing, moderately and strongly cohesive limestone powders. The free
flowing powder gives good agreement among all different situations (devices),
while the moderately and strongly cohesive powders behave more interestingly.
Starting from the flow angle in the rotating drum and going slower, one can
extrapolate to the limit of zero rotation rate, but then observes that the
angle of repose measured from the heap is considerably larger, possibly due to
its special history. When we stretch the ring shear test to its lowest
confining stress limit, the steady state angle of internal friction of the
cohesive powder coincides with the flow angle (at free surface) in the zero
rotation rate limit.
