  When a granular mixture involving grains of different sizes is shaken,
sheared, mixed, or left to flow, grains tend to separate by sizes in a process
known as size segregation.
  In this study, we explore the size segregation mechanism in granular chute
flows in terms of pressure distribution and granular micro-structure.
Therefore, 2D discrete numerical simulations of bi-disperse granular chute
flows are systematically analysed. Based on the theoretical models by Gray and
Thornton 2005 and Hill and Tan 2014, we explore the stress partition in the
phases of small and large grains, discriminating between contact stresses and
kinetic stresses. Our results support both gravity-induced and
shear-gradient-induced segregation mechanisms. However, we show that the
contact stress partition is extremely sensitive to the definition of the
partial stress tensors, and more specifically, to the way mixed contacts (i.e.
involving a small grain and a large grain) are handled, making conclusions on
gravity-induced segregation uncertain.
  By contrast, the computation of the partial kinetic stress tensors is robust.
Kinetic pressure partition exhibits a deviation from continuum mixture theory
of a significantly larger amplitude than contact pressure, and display a clear
dependence on the flow dynamics. Finally, using a simple approximation for the
contact partial stress tensors, we investigate how contact stress partition
relates with the flow micro-structure, and suggest that the latter may provide
an interesting proxy for studying gravity-induced segregation.
