On tearing of ductile polymer films using the essential work of fracture (EWF) method

The essential work of fracture (EWF) technique has been well established and accepted for the fracture characterization of ductile polymer films under in-plane (mode I) loading. In the present study, the technique has been further developed for the characterization of out-of-plane (mode III) tearing fracture of some ductile polymer films including PETG (polyethylene-terephthalate-glycol), PP homopolymer (H0) and a PP copolymer (C1). A two-zone model was proposed to describe the deformation and fracture behaviour of the tearing ligament. In the first zone, which is called zone A and is adjoining the initial crack-tip, the outer plastic zone height increases with the torn ligament length. At the end of zone A, the height of the plastic zone has saturated, and the deformation has entered zone B. The height of the outer plastic zone remains constant with further increase of torn ligament length. The zone B model is applicable to films with a large stabilized plastic zone (such as H0 and C1). It is observed that the tearing specific essential fracture work as measured from the zone A and zone B models are similar confirming the EWF concept can be applied to the mode III out-of-plane tearing of polymer films.