A new shear-compression experiment for investigating
the influence of hydrostatic pressure (mean stress)
on the large deformation shear response of elastomers is
presented. In this new design, a nearly uniform torsional
shear strain is superposed on a uniform volumetric
compression strain generated by axially deforming specimens
confined by a stack of thin steel disks. The new
design is effective in applying uniform shear and multiaxial
compressive stress on specimens while preventing buckling
and barreling during large deformation under high loads.
By controlling the applied pressure and shear strain
independently of each other, the proposed setup allows for
measuring the shear and bulk response of elastomers at
arbitrary states within the shear-pressure stress space.
Thorough evaluation of the new design is conducted via
laboratory measurements and finite element simulations.
Practical issues and the need for care in specimen
preparation and data reduction are explained and discussed.
The main motivation behind developing this setup is to aid
in characterizing the influence of pressure or negative
dilatation on the constitutive shear response of elastomeric
coating materials in general and polyurea in particular.
Experimental results obtained with the new design illustrate
the significant increase in the shear stiffness of polyurea
under moderate to high hydrostatic pressures