Experimental fracture mechanics analysis of tearing in oriented polyethylene films using digital image correlation and full-field solid mechanics post-processing

The tearing resistance of blown polyethylene films is one of their most important performance characteristics, and yet remains one of the least understood. The present work concerns the development of a new approach to rigorously measuring tearing resistance in-situ while also quantifying the material mechanics underlying tearing, and the application of this new technique to tearing of metallocene-catalyzed linear-low density polyethylene blown films with either a high or low extent of locked-in processing-induced microstructural pre-orientation. An experimental/numerical framework, VDIC, was developed to measure tearing resistance and crack tip mechanics in-situ during tearing of tough polyethylene films, employing digital image correlation (DIC) mapping of the deformation process and post-processing of DIC data to calculate the stress tensor field, energy density field, and crack growth resistance curve (JR), utilizing a sophisticated constitutive model engine and expansive material model library previously developed for finite element analysis of polymers. This experimental/numerical framework obviates the need for finite element analysis (FEA) of fracture to calculate tearing resistance and crack tip stress fields—and in fact offers distinct advantages over FEA—including reduced sensitivity to model error, avoidance of simulation convergence challenges, and the elimination of the requirement to a priori impose a material failure model to study stable crack propagation. Graphic abstract