13th International Conference on Fracture June 16–21, 2013, Beijing, China -3- The experimental device is completed by the crack tip advance monitoring using a CCD camera. The synchronization between images and mechanical data (force and displacement of the machine crossbar) is permitted by using a tracking marker technique of the point of force application, Figure 3. Figure 3. Synchronization with marker tracking method During tests, the environment chamber is regulated in order to impose the equivalent moisture content conditioning. In order to limit creep effects, we impose a high constant displacement speed of 0,5mm/min until the total specimen collapse. In these conditions, the total test time does not exceed 4 minutes. Viscoelastic effects can be neglected in the following of this study. 2.2. Experimental results Experimental results are composed of the force evolutions and the crack tip advance versus displacements. The force displacement curves are posted in Figure 4. First results highlight a decrease of the initial sample stiffness and the strength with eth moisture content increasing. In the other hand, wet samples seem to be characterized by a higher ductility. Figure 4. Force displacement curves under dry and wet conditions 0 100 200 300 400 500 600 700 0 1 2 3 4 5 6 7 8 9 Force (N) Displacement (mm) dry samples wet samples
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