13th International Conference on Fracture June 16–21, 2013, Beijing, China -3- 3. Experimental result analysis 3.1. Moisture content evolution The first results concern the moisture content evolution during drying tests. The graphic in Figure 1 is characterized by a first linear evolution corresponding to the free water migration. At the end of test, we can observe the moisture content equilibrium around 8%. While shrinkage swelling effect start below the fiber point saturation, it is necessary to detect this point. Assuming that the fiber point saturation gives a non linearity in the time moisture content curve, a zoom of the last graph provides an estimation of the specific moisture content value of 30% corresponding to the point saturation fiber limit. This value is further confirmed by studying strain deformations, Figure 2. Moisture content evolution and fiber point saturation localization 3.2. Strain evolution The mark tracking method allows the calculation of displacements of each black mark center. The mechanical exploration requests the definition of strains and, more precisely, radial and tangential components. With this consideration, a specific derivation of displacement fields must be operated. Let us consider a perfect circular slice with a polar referential centered at this center, Figure 3. M' is the image of the displacement of M. Figure 3. Polar referential in a perfect circular slice In order to identify each black mark, Figure 4 proposes a notification by the intersection between 0 10 20 30 40 50 60 70 80 30 40 50 60 70 80 90 100 Moisture content (%) Time (h) x y M r M’ U x y U U x U y r U U r U
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