  We present measurements of the stress response of packings formed from a wide
range of particle shapes. Besides spheres these include convex shapes such as
the Platonic solids, truncated tetrahedra, and triangular bipyramids, as well
as more complex, non-convex geometries such as hexapods with various arm
lengths, dolos, and tetrahedral frames. All particles were 3D-printed in hard
resin. Well-defined initial packing states were established through
preconditioning by cyclic loading under given confinement pressure. Starting
from such initial states, stress-strain relationships for axial compression
were obtained at four different confining pressures for each particle type.
While confining pressure has the largest overall effect on the mechanical
response, we find that particle shape controls the details of the stress-strain
curves and can be used to tune packing stiffness and yielding. By correlating
the experimentally measured values for the effective Young's modulus under
compression, yield stress and energy loss during cyclic loading, we identify
trends among the various shapes that allow for designing a packing's aggregate
behavior.
