On the effect of the different notching techniques on the fracture toughness of PETG

The fracture toughness of poly (ethylene terephthalate) modified glycol (PETG) has been evaluated using notch sharpening techniques which could be grouped into contact and non-contact procedures. Razor blade tapping, razor blade sliding, razor pressing and broaching are part of the first group, while the femtolaser technique belongs to the second one. Not all the contact procedures generated valid sharp cracks for fracture parameter assessment; indeed none of the samples sharpened via razor sliding generated acceptable sharp cracks. The results revealed that the non-contact femtolaser technique produced the sharpest cracks in this polymer, with crack tip radii of only 0.5 μm, leading to the lowest fracture toughness values. On the contrary, the traditional notch sharpening technique based on razor tapping, recommended in ISO, ESIS and ASTM protocols and standards, generated larger crack tip radii than those introduced via femtolaser and, consequently, resulted in higher fracture toughness values. Both broaching and pressing methods created specimens with smaller crack tip radii compared to those obtained by razor tapping, and hence resulting in intermediate fracture toughness values.