The role of notch sharpening on the J-fracture toughness of thermoplastic polymers

The effect of the notch sharpening on the fracture toughness obtained under Elastic–Plastic Fracture Mechanics (EPFMs) approach has been analyzed in two different types of thermoplastic polymers, a semicrystalline multi-phase ethylene–propylene block copolymer and an amorphous polycarbonate. The samples for fracture characterization were sharpened using a steel razor blade and the femtosecond laser ablation technique. Both notching techniques gave rise to the very same size of crack tip radii, 1–2 μm. For all the materials under study, the fracture toughness values of the specimens sharpened through femtosecond laser ablation were lower than those measured on samples sharpened using a steel razor blade. The largest differences were achieved for the amorphous polycarbonate. The damage produced ahead of the crack tip through plastic deformation in the steel razor blade sharpened samples over against the lack of damage in the femtolaser sharpened specimens explains the disparity in the fracture values. Besides, the stress state ahead of the crack tip is closely related to the plastic deformation zone to specimen thickness ratio. The fracture toughness values determined from the femtolaser sharpened samples were all in plane strain conditions while the values of the fracture toughness obtained from the steel razor blade sharpened specimens were not.