Investigating the Impact of Different Loading Modes on the Mechanical Behavior of a Semi-crystalline Polymer

The study delved into the mechanical behavior of high-density polyethylene HDPE when subjected to various loading conditions. To cover a wider range of stress conditions, we performed experiments using notched round bar samples of varying curvature radii, employing a video-controlled tensile testing apparatus. In addition, we explored traditional mechanical loading scenarios such as uniaxial tension/compression, cyclic loading, and simple shear tests to gain deeper insights into their effects on HDPE’s stress response. The mechanical properties were significantly influenced by stress triaxiality, with higher levels leading to more pronounced damage and reduced hardening. Stress triaxiality also played a role in the early necking observed in uniaxial tests, with a more noticeable reduction in diametral deformation at rupture as stress triaxiality increased. An examination of volumetric strain changes showed deformation and damage mechanisms, highlighting the prominence of plastic volumetric strain under high-stress triaxiality. In the case of simple shear, HDPE exhibited limited work hardening but demonstrated increased plastic hardening at higher strain rates in the compression test. Lastly, cyclic tensile tests unveiled a temporary decrease in the elastic modulus linked to cavitation damage, followed by stabilization and eventual augmentation attributed to apparent plastic flow driven by molecular orientation. These findings contribute significantly to our comprehensive understanding of HDPE’s mechanical response, offering valuable insights for a wide range of industrial applications.