Dispersion and shattering strength of rocky and frozen planetesimals studied by laboratory experiments and numerical simulations
Dispersion and shattering strength of rocky and frozen planetesimals studied by laboratory experiments and numerical simulations
复制标题
通过实验室实验和数值模拟研究岩石和冰冻星子的分散和破碎强度
DOI：
10.1016/j.icarus.2021.114777
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发表时间：
2022
期刊：
影响因子：
3.2
通讯作者：
Hasegawa Sunao
中科院分区：
文献类型：
--
作者：
Arakawa Masahiko;Okazaki Masashi;Nakamura Masato;Jutzi Martin;Yasui Minami;Hasegawa Sunao
我们已经开发了一种方法来调查的整体质量-速度分布的碰撞碎片所产生的灾难性破裂的模拟星子。利用12个铁粒子作为示踪剂的闪光X射线照相技术对靶体内部进行了可视化，并利用X射线图像测量的示踪剂速度估算了整个靶体的速度分布。对四种不同比能量的岩石和冻结星子靶进行了实验室高速撞击实验和数值模拟。这些目标由三种不同的水含量范围从25至45重量%和多孔石膏的孔隙率为51%的冻结粘土。研究了这些目标的破碎强度、Q-S * 和质量速度分布（MVD）。冻结粘土的Q S * 根据含水量的不同而变化3 - 4倍，多孔石膏的Q S * 与含水量较低的冻结粘土几乎相同。数值冲击模拟导致略有不同的Q S * 和MVD值的冻结粘土目标，可能是因为这些样品的部分延性行为。在模拟中很好地再现了由多孔石膏靶产生的MVD。对抛射速度低于某一特定速度的碎片的累积质量进行了研究，以引入一个中值速度v ′，表征质量-速度分布。v定义为累积质量对应于分布中原始目标质量的一半时的速度。冻结粘土的v_（max）值可用经验公式v_（max）= ε Q γ来描述，ε和γ几乎相同，而多孔石膏的v_（max）值约为冻结粘土的1/3。这些实验结果很好地再现了冻结粘土和多孔石膏目标的数值模拟。弥散强度Q D * 可以通过比较v θ和逃逸速度v esc得出，逃逸速度v esc是一个具有有效质量M和半径R的靶体。由此导出了一个表示弥散强度的半理论方程：QD_1 = 1 ε_2 GMR_1/2 1/γ。为了在大尺度上直接确定Q-D *，对包括自引力在内的灾变破裂进行了数值模拟。这些计算表明，用于计算v esc = v的靶体的有效质量应该是原始靶质量的一半，M = M target/2。我们的研究结果表明，这种方法计算的半理论色散强度是适用于大于10公里的机构。
We have developed a method to investigate the whole mass–velocity distribution of impact fragments generated by catastrophic disruption of simulated planetesimals. Flash X-ray radiography including 12 iron particles for tracers was used to visualize the interior of the target, and the velocity distribution of the whole target was estimated by using the velocities of the tracers measured by X-ray images. High-velocity impact experiments in the laboratory and numerical simulations were conducted for four types of targets simulating rocky and frozen planetesimals at various specific energies, Q. These targets consisted of frozen clays with three different water contents ranging from 25 to 45 wt% and porous gypsum with a porosity of 51%. The shattering strength, Q S*, and the mass–velocity distribution (MVD) were studied for these targets. The Q S* of the frozen clays varied by a factor of 3–4 times, depending on the water content, and the Q S* for porous gypsum was almost the same as that for the frozen clays with lower water contents. The numerical impact simulations led to slightly different Q S* and MVD values for the frozen clay targets, possibly because of the partly ductile behavior of these samples. The MVDs resulting from the porous gypsum targets were well reproduced in the simulations. The cumulative mass of fragments with an ejection velocity slower than a specific velocity was examined to introduce a median velocity, v⁎, charactering the mass–velocity distribution. The v⁎ is defined as the velocity at which the cumulative mass corresponds to a half of the original target mass in the distribution. The v⁎ values of the frozen clays were described by the empirical equation v∗= ε Q γ with almost the same ε and γ, irrespective of the water content, but the v⁎ of porous gypsum was about 1/3 that of the frozen clays. These experimental results were well reproduced by the numerical simulations for both frozen clays and porous gypsum targets. The dispersion strength, Q D*, could be derived by comparing v⁎ with the escape velocity, v esc, of a target body with an effective mass, M, and radius, R. From this, a semi-theoretical equation showing the dispersion strength was derived: Q D∗= 1 ε 2 GM R 1/2 1/γ. Numerical simulations of catastrophic disruptions including self-gravity were conducted to directly determine Q D* at large scale. These calculations showed that the effective mass of the target body, which is used in the computation of v esc= v⁎, should be a half of the original target mass, M= M target/2. Our results suggest that this approach for computing the semi-theoretical dispersion strength is suitable for bodies larger than~ 10 km.