Use of Digital Image Correlation to study the effect of temperature on the development of plastic instabilities in a semi-crystalline polymer

Abstract: The plastic deformation processes that occur in a tensily deformed High Density Polyethylene specimen were studied from full-field strain and strain rate measurements obtained by 3D DIC (Digital Image Correlation).The tensile tests were performed every 10{\textdegree}C from room temperature to 120{\textdegree}C . For temperatures below 60{\textdegree}C , it is shown that the strain localization effect becomes less pronounced when the temperature increases. For temperatures higher than 60{\textdegree}C , the material is found to exhibit double yielding behavior. By analyzing the DIC data in Lagrangian representation, it was possible to quantitatively highlight the strain localization effect that is specifically associated with the second yield. The second yield strain (E_{Y_2}) was measured and appeared to be independent of temperature. For temperatures smaller than 60{\textdegree}C , it was found that the threshold strain corresponding to (E_{Y_2}) also marks the onset of the deformation process phase during which the volume strain strongly increases. Based on previous studies of our research team and on literature we concluded that the critical strain (E_{Y_2}) corresponds to the onset of the lamellar morphology destruction. At high strain levels, the neck stabilization phase was shown to proceed according to a strain driven scheme characterized by threshold strains that are temperature independent. The experimental values of the threshold strain marking the onset of the stabilization phase are found to be in good agreement with those found using the Haward-Thackray model.