13th International Conference on Fracture June 16–21, 2013, Beijing, China -6- An exclusion method provides that once the bonded link is broken, the frictional interaction takes place between the neighbor particles. When the maximum and minimum radius of particles are quite different, experience shows that a power-law size distribution is obtained, providing a good approximation of the actual concrete aggregate size distribution. The bending moment is applied to the specimen by means of moving planes, provided that the particles closer to the platens were bonded to the moving planes. (a) (b) Figure 7: Three point bending test: initial configuration (a); final configuration (b). The simulations are carried out at a fixed maximum strain velocity equal to 104s1. A viscous type damping, proportional to the particle velocity is introduced in the simulation. The choice of the damping coefficient (in our case equal to 0.02) is based on the minimum value that regularizes the simulation without affecting the stress-strain behavior. The position and velocity of each particle during the simulation can be recorded at a certain integration time. In order to limit the model complexity and the computational needs, a two-dimensional simulation of three-point bending test and AE acquisition [12] has been performed. The particle discretization was limited to the central region of the beam, where almost uniform bending was simulated imposing the rotation of the extreme sections (shown in red in Fig. 7a). The initial notch is obtained removing the corresponding bonds. As soon as the bonds between particles reach the failure limit, they are removed, and the crack proceeds to the extrados of the beam (Fig. 7b). In the present study, special attention was paid to the simulation of the temporal scaling of the acoustic emission, rather than to provide a detailed interpretation of the experimental test. Nevertheless, the mechanical parameters adopted in the analysis were chosen to better interpolate the experimental strength in the whole dimensional range.
RkJQdWJsaXNoZXIy MjM0NDE=