286 ∑ ∑= i i i m r rd d ) ( (4) In the equation: di is the average particle size of rock fragments in different standard sieve sizes; ri is the corresponding mass percentage of rock fragments for the given di. 3. EXPERIMENTAL RESULTS AND ANALYSIS According to Table 2, dual insert indentation rock-breaking tests were conducted under pressure, with the results shown in Figure 5. (a) Spherical-spherical dual inserts (d=2.5mm) (b) Spherical-spherical dual inserts (d=4.0mm) (c) Conical-conical dual inserts (d=2.5mm) (d) Conical-conical dual inserts (d=4.0mm) Figure 5 - The penetration depth-to-load curves of spherical and conical double inserted tooth under different penetration depth and velocity As shown in Figure 5, the load-penetration depth curves during dual insert penetration into rock exhibit varying degrees of jump-like growth. As the penetration depth increases, the number of fluctuations in the curves gradually rises. This test was set up with two penetration depths. When the penetration depth was 2.5 mm, the first load fluctuation for the sphericalspherical geometry occurred between 1.16 mm and 2.14 mm, whereas for the conical-conical geometry, it occurred between 1.55 mm and 2.50 mm. This indicates that as the number of conical inserts increases, the penetration depth at which rock breakage first occurs also increases. The addition of conical inserts is more favorable for penetrating the rock but less conducive to initiating rock breakage. When the penetration depth was 4.0 mm, the penetration depth of the first load fluctuation followed the same pattern as at 2.5 mm. Furthermore, as the proportion of conical inserts increases within the combined geometry, the peak load gradually decreases, as detailed in Figure 5. -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 0 5 10 15 20 25 30 35 Peak load/kN Penetration depth /mm v=0.6mm/min v=0.9mm/min v=1.2mm/min v=1.5mm/min v=1.8mm/min (a) 0 1 2 3 4 5 0 5 10 15 20 25 30 35 Peak load/kN Penetration depth /mm v=0.6mm/min v=0.9mm/min v=1.2mm/min v=1.5mm/min v=1.8mm/min (b) -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 0 5 10 15 20 25 30 Peak load/kN Penetration depth /mm v=0.6mm/min v=0.9mm/min v=1.2mm/min v=1.5mm/min v=1.8mm/min (c) 0 1 2 3 4 0 5 10 15 20 25 30 35 Peak load/kN Penetration depth /mm v=0.6mm/min v=0.9mm/min v=1.2mm/min v=1.5mm/min v=1.8mm/min (d)
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