Modeling damage and deformation in impact simulations
Modeling damage and deformation in impact simulations
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DOI：
10.1111/j.1945-5100.2004.tb00337.x
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发表时间：
2004-02-01
影响因子：
2.2
通讯作者：
Ivanov, BA
中科院分区：
文献类型：
--
作者：
Collins, GS;Melosh, HJ;Ivanov, BA
数值模拟是研究大型撞击坑形成的有力工具，但必须用观测证据加以验证。对撞击事件周围目标的损害和变形进行定量分析，为验证陆地撞击坑的数字模型提供了一种很有希望的手段，特别是在最后原始撞击坑形态不明确或未知的情况下。在本文中，我们讨论了脆性材料的行为方面的重要性，准确模拟周围的损伤和变形的影响事件和护理需要解释的结果。我们证明了这一点与一个例子模拟的影响到陆地，花岗岩目标，产生一个10公里直径的瞬态陨石坑。模拟结果以损伤（反映整体破碎的标量）和塑性应变的形式示出，包括总塑性应变（永久剪切变形的累积量，与剪切方向无关）和净塑性应变（考虑剪切方向的永久剪切变形量）。损伤和塑性应变均在靠近撞击点处最大，并随径向距离的增大而减小。然而，从向下和向外的挖掘流到向内和向上的坍塌流的流动模式的逆转意味着净塑性应变可能显着低于总塑性应变。脆性岩石中的塑性应变是非常不均匀的;然而，连续体建模要求在撞击事件期间目标的变形根据应用于大体积岩石的平均应变来描述（与滑动的各个区域之间的间距相比大）。本文表明，平滑的平均应变的模型预测是完全一致的实际应变集中沿着非常狭窄的区域。此外，我们建议，模型预测的总累积应变应与可观察到的体积密度和地震速度的变化。
Numerical modeling is a powerful tool for investigating the formation of large impact craters but is one that must be validated with observational evidence. Quantitative analysis of damage and deformation in the target surrounding an impact event provides a promising means of validation for numerical models of terrestrial impact craters, particularly in cases where the final pristine crater morphology is ambiguous or unknown. In this paper, we discuss the aspects of the behavior of brittle materials important for the accurate simulation of damage and deformation surrounding an impact event and the care required to interpret the results. We demonstrate this with an example simulation of an impact into a terrestrial, granite target that produces a 10 km-diameter transient crater. The results of the simulation are shown in terms of damage (a scalar quantity that reflects the totality of fragmentation) and plastic strain, both total plastic strain (the accumulated amount of permanent shear deformation, regardless of the sense of shear) and net plastic strain (the amount of permanent shear deformation where the sense of shear is accounted for). Damage and plastic strain are both greatest close to the impact site and decline with radial distance. However, the reversal in flow patterns from the downward and outward excavation flow to the inward and upward collapse flow implies that net plastic strains may be significantly lower than total plastic strains. Plastic strain in brittle rocks is very heterogeneous; however, continuum modeling requires that the deformation of the target during an impact event be described in terms of an average strain that applies over a large volume of rock (large compared to the spacing between individual zones of sliding). This paper demonstrates that model predictions of smooth average strain are entirely consistent with an actual strain concentrated along very narrow zones. Furthermore, we suggest that model predictions of total accumulated strain should correlate with observable variations in bulk density and seismic velocity.