Relevance of the femtolaser notch sharpening to the fracture of ethylene-propylene block copolymers

The effect of the notch sharpening on the fracture toughness measured under Linear Elastic Fracture Mechanics (LEFM), Elastic-Plastic Fracture Mechanics (EPFM) and Post-Yielding Fracture Mechanics (PYFM) approaches has been evaluated. Bulk and film specimens of an ethylene-propylene block copolymer have been analyzed. The samples for fracture characterization were sharpened using a steel razor blade and the femtosecond laser ablation technique. Both notching techniques give rise to crack tip radii of the very same size. The fracture toughness of the specimens sharpened via femtolaser were ∼10%, ∼75% and ∼90% lower than that of the specimens sharpened via razor blade when determined with the help of LEFM, the EPFM approach as the multiple specimen method, and by the Essential Work of Fracture, respectively. Both in the bulk samples as in the films, the presence of plastic deformation, either large or small, occurring ahead of the crack tip during the sharpening seems to be the reason for the difference in the fracture values.