13th International Conference on Fracture June 16–21, 2013, Beijing, China -4- Figure 1. Variation of J-integral at maximum load with the notch root radius for the plain mortar One may observe that the variation of Jm with ρ is in agreement with the effect normally detected for metallic and nonmetallic materials, where the J-integral value at fracture initiation varies linearly with the root radius. As fracture initiation in the plain mortar occurs essentially at the maximum load, Jm can, therefore, be considered a good estimate of the J-integral value corresponding to the event of failure initiation in the mortar. For small root radii (ρ ≤ 1.5 mm), though, Jm becomes independent of ρ, remaining at a constant level discriminated as JIc and considered as a material characteristic. The limiting root radius, which is equivalent approximately to 1.5 mm, is also considered a material constant of microstructural significance, apparently compatible with the fact that the sand, used as a constituent of the mortar mixture, had a maximum particle size of 2 mm. As to the reinforced mortars, the variation of Jm with the notch root radius is presented in Fig. 2, for both the 25 and 45 mm sisal fibers, in comparison with the Jm level of the plain mortar. In addition to the extremely beneficial effect of fibers on the mortar’s fracture resistance, the figure also indicates that a better fracture resistance of the mortar was associated with the use of 45 mm sisal fibers.
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