ANALYSES OF STRAIN LOCALISATION IN HDPE BUTTERFLY SPECIMEN DURING BIAXIAL TESTS USING DIGITAL IMAGE CORRELATION

This work presents a study of high density polyethylene (hdpe) strain under biaxial loading. An Arcan apparatus is achieved in order to load a newly-designed flat specimen called "butterfly specimen" to various combinations of tensile and shear loading. These specimens have a central region with a minimal thickness (1mm); witch constitutes a small area where the strain and the stress should be uniform before necking. All tests are conducted on an Instrone tensile machine at constant speed of the upper cross-head (v = 0,5 mm/min) at the ambient temperature. Displacement fields are measured in the central area of the specimens, during the tests, by coupling digital image correlation (DIC) with imaging using high-speed CCD cameras placed in front of the specimen. The experimental results show a strain localisation in the specimen gauge section.