Fractal damage and crack propagation of PMMA in multiple slit charge blasting

Abstract

To study the formation mechanism and propagation characteristics of explosive cracks of slit charges with different slit numbers, the propagation law was analyzed using PMMA as the test material and a digital laser dynamic caustics explosion loading test system. The ABAQUS explicit dynamic analysis module is used to simulate the generation process of the initial crack in slotted charge blasting, and the propagation law of stress waves under the action of slotted charges with different numbers of slots is revealed. Based on fractal theory, the damage values in the slit and non-slit directions are calculated quantitatively. The results show that when the number of slits of the slit charge is two, three, and four, the directional crack along the slit direction of the charge can be controlled. The Von Mises stress along the slit direction near the blast hole wall is 9.5–15.6 times that in the non-slit direction, and it gradually tends to equalize with the increase in the distance from the center of the blast hole. In the process of crack propagation, the propagation speed and dynamic stress intensity factor of the exploded main crack of the specimen exhibit an oscillatory downward trend. The propagation law is the same for all the main cracks in the same specimen. Increasing the number of slits can increase the overall energy utilization of the specimen. When the number of slits is two, three, and four, the damage value (0.6130–0.638) of the burst crack in the cutting direction of the specimen is significantly greater than that in the non-cutting direction (0.4540–0.4885).