13th International Conference on Fracture June 16–21, 2013, Beijing, China -3- load F divided by the area of the initial net section: T (W –a). Figure 1. Typical features of semi-crystalline fracture surfaces for 50 ≤ %F ≤ 80 Following fracture mechanics theory [2], the energy release rate G can be expressed as: G = f(a/W) U (1) where f(a/W) is a function of the crack depth ratio and the specimen geometry; U the area under the load versus δ plot. Here both a/W and specimen geometry were kept constant so G was assumed to be proportional to the area under σnet versus δ. Note that this area is homogeneous to an energy density and can be directly calculated from experimental data. In the following, it will be integrated and split into two fracture energies: Ei during the loading path up to the maximum σnet and Ep corresponding to the consecutive decrease in σnet. For brittle fracture Ep = 0, Ei is therefore related to the critical energy release rate. It is representative of the toughness of the material. For the general case where Ep ≠ 0, the total fracture energy Et = Ei + Ep can be linked to the Charpy impact fracture strength [3-5] but adapted here to quasi-static loading of the specimen. Both Ei and Et will then be considered here to follow the toughness improvement according to the PVDF content. 200 µm Initial crack front 10 µm 50 µm
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