Measurement of plane stress essential work of fracture (EWF) for polymer films: effects of gripping and notching methodology

Abstract

The double-edge-notched-tension (DENT) geometry is widely used in the essential work of fracture (EWF) method to measure the plane-stress fracture toughness (we) values for ductile polymer film. In the measurement, the ligament l has to satisfy the requirement that 3−5t≤l≤min(W/3,2rp). Due to this “valid ligament range” requirement, different gripping methods may have to be employed for films of different thickness. In this study, the so-called “direct gripping” and “drilled hole gripping” methods were investigated. It was concluded that the we values were independent of the sample width and the gripping methods. Two different notching techniques were used to pre-notch the specimens, and it was concluded that the same we values were obtained irrespective of the notching method used. Finally, the experimentally measured we for polyethylene terephthalate glycol (PETG) films of different thickness are in good agreement with the theoretical predicted values.