Abstract
Toughness assessment of ductile polymers is still an open issue, especially at high loading rates, the main challenge being to measure intrinsic values. An original approach derived from linear elastic fracture mechanics (LEFM) is presented. It consists of determining experimentally the size of the plastic zone developed at the vicinity of the crack tip using specimens of different ligament lengths. The effective and intrinsic fracture mechanics parameters, K eff and G eff, can be obtained, respectively, from the slopes of the plots of F max vs. BW 1/2/f(a effl/W) and U ini vs. BWΦ(a eff2/W), with a eff1=a+r p and a eff2=a+d p, in such a way that the plastic zone radii, r p, and diameters, d p, are determined numerically using an iteration procedure so that all data fall on a line through the origin. This plastic zone corrected LEFM method is exemplified with isotactic polypropylene (iPP), ethylene-propylene modified iPP (iPP/EPR) and rubber toughened PMMA (r-PMMA). Its applicability between 0.0001 and 6 m/s and its limits near the ductile-brittle transitions are discussed. The necessity of a combined approach, conventional LEFM–corrected LEFM, to evaluate the impact performance of polymers is highlighted.
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