Presentation Information
[PPS05-P01]Low-Velocity Impact Cratering experiments at small projectile-grain size ratio
*Yuta Goto1, Ikuro Sumita1 (1.Earth and Planetary Science course, Division of Geosciences and Civil Engineering, Graduate School of Natural Science and Technology, Kanazawa University)
Keywords:
Crater profile,Gravity-dominated regime,Strength-dominated regime,Armoring,Deepening
Asteroid Itokawa has a rubble-pile structure, implying that impactor sizes can be comparable to the grain size consisting the asteroid (Miyamoto et al, 2007). Guttler et al. (2012) showed that when the ratio of projectile diameter to target grain size (ψ) is small, crater sizes are suppressed by armoring. Tatsumi and Sugita (2018) further investigated the effects of ψ, and the ratio of impact energy to particle fragmentation energy (ξ) at impact velocities in the range of 70 m/s to 6 km/s. For rubble-pile asteroids, impact velocities can be as small as escape velocities (~10-1 m/s), such that there will be no fragmentation. Although low-velocity cratering has long been studied (Walsh et al, 2003), experiments at ψ<10 are still limited (Maiti and Roy, 2024). Here we investigate the morphology, size, and formation processes of craters formed under low impact velocity at 0.5<ψ<10.
1. Methods
We fill a cylindrical container (180 mm diameter, 90 mm depth) with spherical glass beads, and stainless-steel sphere was dropped to form craters. Drop heights h is varied in the range of 30-2166 mm. Five projectile diameters (Dp=2-19.05mm), and three target grain diameters (Dt=0.2mm, (ψ=10-95.25), 0.8mm (ψ=2.5-23.8), 4.0mm (ψ=0.5-4.76)) were used. Impact energy ranged from 10-4 to 10-1 J, with ξ=10-4-103. Crater shape was measured, and formation processes were recorded using a high-speed camera.
2. Results
At low energy (E<=10-3-10-2 J), craters with partially exposed projectiles formed similar to those observed in cohesive sand targets (Takita and Sumita, 2013). With increasing impact energy (E>=10-3-10-2 J), the crater transitioned to conical shapes. At even higher impact energy (E>10-2 J), for Dt=0.2mm, craters with central peaks formed. The main results of our experiments can be summarized as follows:
(1) For Dt=0.2mm, 0.8mm the crater diameter scales as ∝E0.25 and ∝E0.23(gravity-regime). For Dt=4mm, the crater diameter scales as ∝E0.36(strength-regime).
(2) When E<=10-2 J, and for Dt=4mm, crater diameters are smaller, indicating armoring. When E>=10-2 J, the crater depth for Dt=4mm case becomes larger than those of other two smaller grain sizes (deepening).
(3) Under the same impact energy, the crater floor slope (depth/diameter), the mass of ejecta expelled outside the container, and the ejecta ejection angle are all largest for Dt=4mm, whereas the penetration depth is smallest for Dt=4mm.
3. Discussion
At Dt of the order of 0.1 mm, experiments indicate gravity regime scaling, which is consistent with previous works (Walsh et al, 2003, Hayashi and Sumita, 2017). Here we discuss the results for Dt=4mm. For the same impact energy, the penetration depth is shallowest for Dt=4mm. At E<10-2 J the crater diameter is smaller, which likely originated from this effect. At E>10-2 J, the craters are deeper. Pouliquen (1999) reported that as the ratio (layer thickness(h)/grain diameter(d)) decreases, the critical slope angle for the onset of granular flow increases, indicating that the granular flow is suppressed. At E>10-2 J, when scaled by the grain size, crater diameters are 100-250 (Dt=0.2mm), 25-50 (Dt=0.8mm), and 5-25 (Dt=4mm). A steeper slope angle and deeper crater likely originated from this flow suppression effect.
4. Summary
Low-velocity impact cratering was investigated using glass beads targets whose particle size range from fine (0.2 mm) to coarse (4 mm). Experiments show that when fine to medium sized particles (Dt=0.2, 0.8mm) are used, gravity regime scaling applies, whereas when coarse-particles (Dt =4.0mm) are used, it transition to strength regime. In the low-energy range (E<10-2 J), crater diameter is suppressed in coarse targets. On the other hand, in the high-energy (E>10-2 J) range, deeper craters forms in coarse targets.
1. Methods
We fill a cylindrical container (180 mm diameter, 90 mm depth) with spherical glass beads, and stainless-steel sphere was dropped to form craters. Drop heights h is varied in the range of 30-2166 mm. Five projectile diameters (Dp=2-19.05mm), and three target grain diameters (Dt=0.2mm, (ψ=10-95.25), 0.8mm (ψ=2.5-23.8), 4.0mm (ψ=0.5-4.76)) were used. Impact energy ranged from 10-4 to 10-1 J, with ξ=10-4-103. Crater shape was measured, and formation processes were recorded using a high-speed camera.
2. Results
At low energy (E<=10-3-10-2 J), craters with partially exposed projectiles formed similar to those observed in cohesive sand targets (Takita and Sumita, 2013). With increasing impact energy (E>=10-3-10-2 J), the crater transitioned to conical shapes. At even higher impact energy (E>10-2 J), for Dt=0.2mm, craters with central peaks formed. The main results of our experiments can be summarized as follows:
(1) For Dt=0.2mm, 0.8mm the crater diameter scales as ∝E0.25 and ∝E0.23(gravity-regime). For Dt=4mm, the crater diameter scales as ∝E0.36(strength-regime).
(2) When E<=10-2 J, and for Dt=4mm, crater diameters are smaller, indicating armoring. When E>=10-2 J, the crater depth for Dt=4mm case becomes larger than those of other two smaller grain sizes (deepening).
(3) Under the same impact energy, the crater floor slope (depth/diameter), the mass of ejecta expelled outside the container, and the ejecta ejection angle are all largest for Dt=4mm, whereas the penetration depth is smallest for Dt=4mm.
3. Discussion
At Dt of the order of 0.1 mm, experiments indicate gravity regime scaling, which is consistent with previous works (Walsh et al, 2003, Hayashi and Sumita, 2017). Here we discuss the results for Dt=4mm. For the same impact energy, the penetration depth is shallowest for Dt=4mm. At E<10-2 J the crater diameter is smaller, which likely originated from this effect. At E>10-2 J, the craters are deeper. Pouliquen (1999) reported that as the ratio (layer thickness(h)/grain diameter(d)) decreases, the critical slope angle for the onset of granular flow increases, indicating that the granular flow is suppressed. At E>10-2 J, when scaled by the grain size, crater diameters are 100-250 (Dt=0.2mm), 25-50 (Dt=0.8mm), and 5-25 (Dt=4mm). A steeper slope angle and deeper crater likely originated from this flow suppression effect.
4. Summary
Low-velocity impact cratering was investigated using glass beads targets whose particle size range from fine (0.2 mm) to coarse (4 mm). Experiments show that when fine to medium sized particles (Dt=0.2, 0.8mm) are used, gravity regime scaling applies, whereas when coarse-particles (Dt =4.0mm) are used, it transition to strength regime. In the low-energy range (E<10-2 J), crater diameter is suppressed in coarse targets. On the other hand, in the high-energy (E>10-2 J) range, deeper craters forms in coarse targets.