Effect of Uncoupling Coefficient on the Expansion and Fractal Characteristics of Bursting Cracks of Slit Packs
In order to study the perforation crack extension and damage evolution law under the radial air-uncoupled charge blasting of slit packs,the rock material is simulated with Plexiglas plate(PMMA)medium,and the transmission dynamic focal dispersion line test system is used to study the perforation explosion mechanical behaviour of the slit packs with radial uncoupling coefficients of 1.14,1.28,1.42,1.71,and 1.86.The results show that:The main crack expansion is divided into two stages,the first stage(0-150 μs),under the action of the bursting gas and the explosive stress wave,the crack expansion rate peaks at the moment of crack opening,and then immediately decreases;the second stage(150-330 μs),due to the action of the reflective stress wave,the crack continues to expand until it stops.When K=1.71,the explosive main crack extends the longest distance along the direction of the slit,produces the least number of secondary cracks,and the angle of the left and right main cracks is nearly horizontal;when K=1.28 and 1.42,the length of the main crack extension and the number of secondary cracks produced are the second longest;and when K=1.86 and 1.14,the length of the crack extension is shorter,and the number of secondary cracks produced is the highest.Radial uncoupling coefficient is greater than or less than 1.71,the energy generated by the explosion is not fully utilised,the peak expansion velocity of the blast-generated main crack,the peak dynamic strength factor is small.The fractal dimension of the Region Ⅱ,Ⅳ decreases as the radial uncoupling coefficient increases,the rate of change is relatively large.In the region Ⅰ,due to the proximity of the source of the explosion,the overall fractal dimension is large,the rate of change is small.When K=1.71,the formation of the crushed zone around the gun hole damage variable is the smallest.
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