Abstract
The effect of the notch sharpening on the fracture toughness obtained under linear elastic fracture mechanics has been analyzed in an amorphous polycarbonate. The samples for fracture characterization were sharpened via the traditional contact steel razor blade technique and the noncontact femtosecond laser ablation technique. The values of the fracture toughness of the specimens sharpened through femtosecond laser ablation were lower than those measured on samples sharpened using a steel razor blade. Moreover, the former was in plane strain state, but the latter did not verify the size criterion. The damage produced ahead of the crack tip through plastic deformation in the steel razor blade sharpened samples over the lack of damage in the femtolaser sharpened specimens explains the differences in the fracture toughness. It has been proven that there is a relationship between the plastic deformation at the crack front and the stress state. This has been assessed through the application of a fracture criterion for dissipative systems with small scale yielding.
Highlights
The influence of crack sharpness on the fracture toughness values of polymeric materials has recently caught the attention of the scientific community
Both sharpening techniques resulted in similar initial crack tip radii for these polymers, and the fracture toughness determined from the samples sharpened via the femtolaser showed lower values than those obtained from the specimens sharpened via the traditional razor blade technique independently of the material under study
These differences reached in the copolymer values up to 11%, 75%, and 90% when the crack growth initiation parameters were computed under linear elastic fracture mechanics (LEFM), elastic-plastic fracture mechanics (EPFM) and Post-Yielding Fracture Mechanics (PYFM) conditions, respectively, [3] and radical changes in the J-R curves obtained under EPFM approximation in the polycarbonate [4]
Summary
The influence of crack sharpness on the fracture toughness values of polymeric materials has recently caught the attention of the scientific community. Several works have appeared in the literature highlighting the role of the notch sharpening technique on the fracture parameters of either semicrystalline heterogeneous polymeric materials such as ethylene-propylene block copolymers [1,2,3] or amorphous polymers such as polycarbonate [4] In all these studies, the values of the fracture toughness obtained using different approaches were determined from samples sharpened via two procedures: a noncontact technique based on the femtosecond laser ablation (femtolaser) and the traditional contact technique using a razor blade. The abrupt differences between the fracture toughness values, especially under EPFM [3, 4] and PYFM [3] obtained from samples sharpened via different techniques
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