Influence of the notch sharpening technique on the fracture toughness of bulk ethylene-propylene block copolymers

The effect of the notch sharpening procedure on the fracture toughness computed under linear-elastic and elastic-plastic conditions (at low and high loading rates, respectively) of a bulk ethylene-propyle ne block copolymer has been investigated. The specimens utilized for fracture characterization were sharpened using a steel razor blade and the femtosecond laser ablation technique. The crack growth initiation parameter, J(IC), determined with the help of the elastic-plastic fracture approach, and the fracture toughness, K-IC, obtained with specimens verifying linear-elastic fracture mechanics assumptions, of the steel razor blade sharpened samples were higher than that of the femtolaser sharpened specimens. The plastic deformation occurring ahead of the crack tip during the sharpening method seems to be the reason for the dissimilarity of the fracture values. Moreover, the strain hardening suffered by the material close to the notch tip reduces the stable crack growth resistance evaluated under elastic-plastic conditions. (C) 2009 Elsevier Ltd. All rights reserved.