Inelastic deformation in polymers under multiaxial compression

inelastic deformation in polymers under large deformation is typically accompanied by instabilities. These instabilities can be associated with shear banding, barreling, buckling, etc., and can prevent complete characterization of the constitutive behavior. In this paper, we present an experimental configuration where polymers can be subjected to large homogeneous deformations. The design and operation of the confined compression apparatus is described. Using the apparatus, it is shown that the nonlinear pressure-volume response can be extracted for pressures as high as 1 GPa. The shear response is also extracted from the same experimental data; it is shown that for two polymers, polycarbonate and polymethylmethacrylate, the stress drop observed in uniaxial tests may not represent an intrinsic material property and, further, that by applying high confining pressures plastic deformation may be suppressed completely.