Effect of Grain Shape and Relative Humidity on the Nonlinear Elastic
Properties of Granular Media
This study focuses on unraveling the microphysical origins of the
nonlinear elastic effects, which are pervasive in the Earth’s crust.
Here, we examine the influence of grain shape on the elastic
nonlinearity of granular assemblies. We find that the elastic
nonlinearity of angular sand particles is of the same order of magnitude
as that previously measured in spherical glass beads. However, while the
elastic nonlinearity of glass beads increases by an order of magnitude
with RH, that of sand particles is rather RH independent. We attribute
this difference to the angularity of sand particles: absorbed water on
the spherical grains weakens the junctions making them more nonlinear,
while no such effect occurs in sand due to grain interlocking.
Additionally, for one of the nonlinear parameters that likely arises
from shearing/partial slip of the grain junctions, we observe a sharp
amplitude threshold in sand which is not observed in glass beads.