Tearing of Thin Polymer Sheets with Wrinkling

Abstract

In this paper, the tearing behavior of thin polymer sheets was studied experimentally and numerically. First, the specific essential work of fracture for thin biaxially oriented polyethylene terephthalate (Mylar) was measured experimentally. Double-edged notched tensile specimens of Mylar with three different thicknesses and varying ligament lengths were tested. Load-displacement graphs were formed, and the total internal energy was evaluated, from which the specific fracture energy was determined. Next, a finite element analysis was performed to predict the tearing response of polymer sheets. The finite element model incorporated a user-defined cohesive element to properly represent the structural behavior of a thin polymer sheet in the presence of damage, including the propensity of the sheet to wrinkle. The results indicated that the measured specific essential work-of-fracture values were nearly identical for the three separate thicknesses, which confirmed that it is indeed a material property of the Mylar itself. The developed user cohesive element accurately simulated the tearing of thin polymer sheets, producing well-matched nominal stress–strain curves to those by experiments. Analyses were also performed for the double-edged notched tensile configuration with different lengths and a corner-loaded square sheet configuration with a center cut, which showed that the wrinkle deformation significantly affected the tearing behavior of thin polymer sheets.