Essential work of fracture, crack tip opening displacement, and J-integral relationship for a ductile polymer film

A unique set of double-edge notched tension specimens of a Polyethylene Terephthalate Glycol-modified film was tested in mode I, plane stress. The load was registered on a universal testing machine. The displacements, ligament lengths, and video frames were recorded by a Digital Image Correlation system. With these registered data, the essential work of fracture, J-integral, and crack tip opening displacement (CTOD) fracture concepts have been applied. The onset of crack initiation was through a complete yielded ligament. The analysis showed that the intrinsic specific work of fracture, we, is the specific energy just up to crack initiation, which is an initiation value. we has both a coincident value and the same conceptual meaning as Jo, the J-integral at the onset of crack initiation. The relationship between Jo and CTOD is also determined. The influence on the notch quality when the specimens were sharpened by two different procedures, femtosecond laser ablation and razor blade sliding, was analysed in detail.