290 Figure 9 shows the top view of the rock-breaking surface after penetration and fragmentation. Figure 9 - Changes in surface crater morphology under double inserted teeth penetration velocity and depth As shown in Figure 9 (Crater Morphology of Dual Spherical and Conical Inserts), it can be observed that the craters formed by dual insert penetration encompass both the "area surrounding the penetration points" and the "region between the two inserts." Their morphology and extent exhibit clear patterns with changes in penetration parameters: Influence of Penetration Velocity: Regardless of the insert geometry or penetration depth, as the penetration velocity increases from 0.6 mm/min to 1.8 mm/min, the crater area shows a linear decreasing trend. This is because under high-velocity penetration, the rock failure mode shifts more towards "local impact fracturing," where energy concentrates near the penetration points and is less likely to diffuse into the inter-tooth region. Concurrently, the elliptical shape of the crater changes with velocity: the semi-minor axis gradually contracts, indicating that the "lateral extent" of the fractured zone decreases as velocity rises, making the crater more elongated and narrow. Influence of Penetration Depth: Under the same insert geometry and velocity, when the penetration depth increases from 2.5 mm to 4.0 mm, the crater area progressively expands. This occurs because greater depth enhances the compressive action of the dual inserts on the rock, making internal fractures more prone to propagate into the inter-tooth region. Furthermore, the position of the "lowest point" within the crater shifts. At d=2.5 mm, the lowest points are concentrated near the penetration points (indicating energy is primarily applied to the insert-rock contact zones). In contrast, at d=4.0 mm, the lowest points extend progressively into the region between the inserts (suggesting fractures have interconnected across the two inserts, forming a depression spanning the inter-tooth area). This demonstrates that increased depth enhances the "synergistic fracturing effect" between the dual inserts. Detailed Features at d=4.0 mm: Taking the 4.0 mm depth as an example, energy transfer during dual insert penetration is more complete at this depth. The elliptical crater morphology becomes fuller (the semi-minor axis length is greater than that at the same velocity for d=2.5 mm), and the degree of fragmentation in the inter-tooth region is
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