Anisotropy development during HDPE necking studied at the microscale with in situ continuous 1D SAXS scans

Abstract

International audienceQuantitative information about microstructural reorganizations which occur during mechanical solicitation is important to increase our knowledge on the rheology of semi-crystalline polymers. This point is investigated here on High Density Polyethylene through the measurement of an anisotropy index calculated from small-angle X-ray scattering (SAXS) patterns. These were obtained in situ on a coherent synchrotron beamline with a very fast scanning of the specimen under tensile test. This allows the anisotropy development of many material points which undergo different deformation paths to be followed, thanks to necking development and propagation. With this field information, the microstructural anisotropy observable is shown to have a given value at a given true strain, meaning that strain pilots the bulk topology. Results apparently departing from that premise are shown indeed to be an experimental artifact: true strains are measured on the specimen surface, necking introduces strain heterogeneities in thickness, and the SAXS technique probes the full volume producing averaging