The objective of this program is to investigate the inelastic response of polymeric materials under multiaxial compression, with pressures in the range of 1 GPa. Polycarbonate, polymethylmethacrylate and polyethylene are take to be examples to be examined. These polymers exhibit significant pressure sensitivity in their elastic, inelastic and viscoelastic response. These are also technically very important polymers, very much in commercial use. The main innovation presented in this proposal is a new experimental scheme of confined compression, where all the strain and stress components are carefully measured. The resulting deformation is macroscopically homogeneous and geometrically stable. Preliminary experiments have shown that the configuration works as expected. With this configuration, it is proposed to examine the pressure dependence of the initial modulus, yielding and inelastic behavior under multiaxial loading, and linear viscoelastic behavior of the three polymers listed above. It should be noted that the proposed experiments are "clean" experiments in the sense that no assumptions regarding the material behavior are embedded in interpreting the experimental results. Thus, the results can be used to provide checks on the many mechanistic as well as phenomenological theories of polymer behavior.
