Molecular chain orientation in polycarbonate during equal channel angular extrusion: Experiments and simulations

The objective of this contribution is to provide some insights of the molecular chain orientation in polycarbonate (PC) during an equal channel angular extrusion (ECAE) process. Experimentally, wide-angle X-ray scattering was carried out to characterize the microstructure of the ECAE-deformed glassy amorphous polymer. The deformation behavior of the PC specimen in the ECAE process was simulated using a physically-based viscohyperelastic-viscoplastic constitutive model that was implemented into a finite element code. The large inelastic deformation response of the glassy amorphous polymer was modeled by assuming that the deformation mechanisms are split into an intermolecular resistance and a molecular network resistance. The intermolecular resistance captures the initial response and the yielding rate-dependence due to the isotropic resistance to deformation resulting from intermolecular barriers to chain-segment rotation. The molecular network resistance reproduces the anisotropic strain hardening response at large strains due to stretching and chain orientation. The progressive molecular chain orientation during the ECAE process and its distribution were analyzed. The predicted results, favorably compared with the experimental observations, show a high degree of anisotropy and heterogeneity in orientation of polymer molecular chains in the ECAE-deformed PC.