PSI - Issue 6

A.D. Lovtsov et al. / Procedia Structural Integrity 6 (2017) 122–127 Author name / Structural Integrity Procedia 00 (2017) 000–000

126

5

Table 1. Numerical results for stated increase in number of incremental steps Number of increments per second Maximum vertical displacement of mass in row, m

Maximum axial force, kN

500

3.908 3.899 3.895 3.892 3.892 3.892

12.82 14.03 14.68 15.05 15.09 15.12

1000 2000 5000 6000 7000

The displacements of the masses and axial forces in the elastic elements are computed. The tire in the first row starts to move, the next tire in the second row starts its movement in 0.02 s after the first one. Second tire approaches to the first one, during upward movement, while the first tire’s speed slows down. Thus, the heights of the tires at 0.2 t  s are almost leveled. Vertical displacement of the tire in row 1 reached its maximum value of 3.89 m for 0.872 t  s. Positions of masses at 0.2 t  s, 0.5 t  s, and 0.872 t  s are shown in Fig. 3, a. Incompressible elements “switch on” and “switch off” due to deformation of the system. “Switched on” elements are shown using bold lines.

Fig. 3. Positions of blasting mat at various t , s with different impulse intervals (a) 0.02 sec; (b) 0.2 sec. Site video of explosion process was used to analyze experimental results. According to video data, the flight height of the tire in row 1 reached its maximum value of 3.8 m for 0.88 seconds. The model of geometrically nonlinear system with unilateral constraints for simulation of gas permeable blasting mat corresponds with experimental results. Simulation results for the same blasting mat but with impulse intervals equal 0.2 seconds are shown on Fig. 3, b. In this case vertical displacement of the mass in row 1 reached the maximum value of 3.22 m for 0.988 seconds and maximum axial force is 16.22 kN. The masses approach each other at the top point. If blast initiation is made in the following sequence: row 3, row 2 and then row 4 with 0.02 seconds intervals the effectiveness of blasting mat decreases. The blasting mat rises on the height of 4.98 m and maximum axial force is 18.18 kN. 4. Conclusion Dynamic model of gas permeable blasting mat is proposed in this research. It is represented by concentrated masses interacting with unilateral foundation and by elastic weightless incompressible elements. Large displacements and unilateral constraints are specific features of this model. Explosive loading is simulated by instantaneous impulses applied at different times to different masses. Numerical experiments showed that axial forces in elastic elements and maximum flight height of the masses depend on detonation sequence of the blast holes. Employed mathematical model was verified by full-scale experiment.