  The mechanical properties of a disordered heterogeneous medium depend, in
general, on a complex interplay between multiple length scales. Connecting
local interactions to macroscopic observables, such as stiffness or fracture,
is thus challenging in this type of material. Here, we study the properties of
a cohesive granular material composed of glass beads held together by soft
polymer bridges. We characterise the mechanical response of single bridges
under traction and shear, using a setup based on the deflection of flexible
micropipettes. These measurements, along with information from X-ray
microtomograms of the granular packings, then inform large-scale discrete
element model (DEM) simulations. Although simple, these simulations are
constrained in every way by empirical measurement and accurately predict
mechanical responses of the aggregates, including details on their compressive
failure, and how the material's stiffness depends on the stiffness and geometry
of its parts. By demonstrating how to accurately relate microscopic information
to macroscopic properties, these results provide new perspectives for
predicting the behaviour of complex disordered materials, such as porous rock,
snow, or foam.
