Fracture Toughness Evaluation of Medium-Density Polyethylene (MDPE) Under Different SENB Notch Shapes, Crack Sharpness, and Temperature Conditions

This study investigates the influence of various Single Edge Notched Bend (SENB) specimen geometries (45° vs. 30° notch angles) with specimen widths (13.6 mm vs. 15 mm) respectively, crack sharpness, displacement rate (10 mm/min to 100 mm/min at room temperature), and testing temperature on the fracture behavior of Medium-Density Polyethylene (MDPE). Larger specimen sizes showed higher load-displacement values and greater work of fracture with improved standard deviation (STD). Crack sharpness was controlled using blades of two thicknesses (0.09 mm and 0.23 mm), with sharper cracks (0.09 mm blades) mildly improving resistance to crack growth, especially when post-notch conditioning (freezer storage) maintained crack tip sharpness by reducing polymer chain reptation at low temperatures. The effect of displacement rate was more significant, with increasing displacement rate consistently raising the peak load across all samples; however, its influence on fracture behavior was minimal. Temperature-dependent tests revealed MDPE’s fracture behavior at −100°C (brittle) and 20°C (ductile, with large plastic deformation and high fracture energy absorption). This research highlights the importance of specimen size, crack sharpness, displacement rate, and temperature in evaluating MDPE’s fracture behavior, providing insights for accurate material property assessments in pipeline applications.