| 1. |
- Michikami, Tatsuhiro, et al.
(författare)
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The influence of chondrules on sub-mm fragment shape distributions in Allende impact experiments
- 2024
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Ingår i: Icarus. - : Elsevier. - 0019-1035 .- 1090-2643. ; 415
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Tidskriftsartikel (refereegranskat)abstract
- The surfaces of sub-kilometer-sized asteroids directly explored by spacecraft, such as Itokawa, Ryugu and Bennu, are covered with blocks and/or regolith particles, whose shapes are considered clues to understanding their formation and evolution on the asteroid's surface. Ryugu particles returned by the Hayabusa2 mission are likely fragments resulting from impacts because their shapes resemble impact fragments from laboratory experiments. However, there is a lack of laboratory impact experiments examining the shapes of fragments in carbonaceous chondrites, thought to originate from carbonaceous asteroids such as Ryugu and Bennu. The measured sizes of Ryugu particles are in the mm and sub-mm range, similar to the sizes of chondrules. Also, carbonaceous chondrites are generally structurally weaker than the basalts and granites often used in previous laboratory impact experiments. Differences in the strength of the chondrules and matrix might affect the overall strength of the meteorite. In this study, as a first step towards a better understanding of impact fragment shapes in carbonaceous chondrites, we conducted impact experiments on the carbonaceous meteorite Allende (CV3). A spherical alumina projectile with 1.0 mm and a glass projectile with 0.80 mm in diameter were fired into 1–2 cm-sized Allende targets at nominal impact velocities of 2.0 and 4.0 km/s, respectively. To investigate the correlation between the chondrules (typically sub-mm in size) and the shapes of fine fragments, we measured the shape distributions of sub-mm impact fragments using X-ray microtomography. We observed several impact fracture surfaces along the chondrule boundaries. In addition, these fragments tended to be rounder than fragments from previous impact experiments. However, because the total number of these fragments is relatively small, the fragments were found to have the same overall shape distribution as previous laboratory impact fragments, Itokawa particles and Ryugu particles. This may imply that impact fragment shapes are independent of the bulk material strength. These findings will be useful for understanding the formation process of regolith layers on asteroid surfaces, Itokawa particles, Ryugu particles, and Bennu particles.
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| 2. |
- Natsui, Shungo, et al.
(författare)
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Characteristics of solid flow and stress distribution including asymmetric phenomena in blast furnace analyzed by discrete element method
- 2010
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Ingår i: ISIJ International. - : Iron and Steel Institute of Japan. - 0915-1559 .- 1347-5460. ; 50:2, s. 207-214
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Tidskriftsartikel (refereegranskat)abstract
- Since the solid flow in blast furnace is composed of each particle motion, the discontinuous phenomena of burden descending can be occasionally observed. Understanding of the solid flow is important for blast furnace operation. Discrete Element Method (DEM) can offer the behavior for each particle of burden in the furnace. Three dimensional analysis of solid motion containing the ununiform region became possible with using DEM.In the present study, a blast furnace of 2000 m3 inner volume with 16 tuyeres was taken as the object for the simulation. Firstly, the stream line of solid, velocity variation and stress field in blast furnace were simultaneously analyzed by using the characteristic of DEM on each particle movement. Especially, the transient behavior on velocity and stress distribution during charging and slipping were calculated. The fundamental characteristics of burden descending became clear. Secondly, this study has focused on the asymmetric phenomena in the blast furnace on the basis of the above results. In this calculation, number of active tuyere was intentionally varied. The stress network showed the remarkable change in this case. Moreover, it was found that many local slips between particles were distributed in the bosh and they concentrated on the region nearby the active raceway due to the weakened stress. The stress network is closely related the particle velocity distribution. The consumption rate of coke in the tuyere significantly affected on the circumferential uniformity. Totally, the discontinuous burden descending and the characteristic of particle movement were essentially understood.
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