13th International Conference on Fracture June 16–21, 2013, Beijing, China -5- Figure 5. AE signal energy vs. time. The signal energies of the AE events detected during the test are reported in Fig. 5, distinctly for each sensor. The average value of the total released AE signals energy is estimated as 126·103 msV. 3. Particle simulations The simulations have been carried out with ESyS-Particle, an open source implementation of the Distinct Element Method [17]. ESyS-Particle has been developed in-house within the Earth Systems Science Computational Centre (ESSCC) at the University of Queensland [18] since 1994. The simulation is based on direct integration of the Newton’s motion equations with the Verlet algorithm. The normal interaction between colliding particles is linear and proportional to the particle small overlapping, whereas Coulomb friction, with both static and dynamic friction coefficients, rules the tangential interaction. In addition, bonded links are established between neighbor particles, according to the scheme in Figure 6. The bonded link is elastic perfectly brittle. The rupture of the bond is based on a fracture criterion that accounts for the axial, shear, torsion and bending behavior. The particles are filled together with the random packing algorithm LSMGenGeo [18], on the base of the maximum and minimum particle radius, which in our case correspond respectively to the maximum and minimum concrete aggregate radius (i.e. rmax=7.5 mm, rmin=1.5 mm). Figure 6. Scheme of the bonded interaction between two particles .
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