  Plasticity in soft amorphous materials typically involves collective
deformation patterns that emerge upon intense shearing. The microscopic basis
of amorphous plasticity has been commonly established through the notion of
"Eshelby"-type events, localized abrupt rearrangements that induce flow in the
surrounding material via non-local elastic-type interactions. This universal
mechanism in flowing disordered solids has been proposed despite their
diversity in terms of scales, microscopic constituents, or interactions.
However, we argue that the presence of frictional interactions in granular
solids alters the dynamics of flow by nucleating micro shear cracks that
continually coalesce to build up system-spanning fracture-like formations on
approach to failure. The plastic-to-brittle failure transition is uniquely
controlled by the degree of frictional resistance which is in essence similar
to the role of heterogeneities that separate the abrupt and smooth yielding
regimes in glassy structures.
