Instrumented Puncture Test of High-Density Polyethylene: Identification of Critical Displacement Points and Effects of Puncture Rate and Sample Thickness

High Resolution Image Download MS PowerPoint Slide Instrumented puncture tests were performed on high-density polyethylene (HDPE) sheets using a flat-ended indenter and a clamped specimen holder. By correlating in situ morphology with puncture force–displacement curves, a consistent set of characteristic displacements was identified for a range of samples with different thicknesses. D C marks the critical displacement where a bending-to-stretching transition, accompanied by stress concentration, drawing of the crown wall, and the onset of microfibrillation, sets in. D D corresponds to the displacement where the maximum force within the fibrillation-dominated regime is reached. A puncture step-cycle test protocol separated recoverable and residual displacements, quantitatively validating the inferred elastoplastic sequence. Based on an energy partition at D C, the critical energy ( U C ), total absorbed energy ( U total ), and plastic dissipation energy ( U P ) were determined, and a puncture-specific ductile ratio ( D.R. p ) was proposed to quantify ductile energy dissipation. Under the present experimental conditions, systematic variations in puncture rate (2–800 mm/min) and specimen thickness (0.47–2.63 mm) reveal two critical thresholds: a transition from quasi-static to rate-dominated response at approximately 80 mm/min and a plate-like to film-like mechanism boundary at approximately 1.2 mm. These results establish a physical framework for mechanistic interpretation and ductility quantification in the puncture behavior of polymers.