泡沫金属的随机力学模拟以确定介观尺度行为的开始
Stochastic mechanical modeling of metallic foams to determine onset of mesoscale behavior
摘要：
金属泡沫对许多新出现的应用至关重要，其中包括防止微流星体和轨道碎片造成的超高速撞击。泡沫固有的随机微观结构导致的特征尺度和介观尺度长度上的性能变化使得其性能的预测模型具有挑战性。它还阻碍了用这种泡沫制造的部件的优化，这对于航天器设计来说是一个特别严重的问题，因为在航天器设计中，成本和质量之间的平衡还必须与部件故障的灾难性结果相平衡。为了解决这个问题，我们计算的特征尺度之间的临界过渡长度，其中的机械性能是由单个功能，和中尺度，其中的行为是由合奏的功能。在中尺度上，属性的分布-就期望值和标准变率而言-是一致和可预测的。肯塔基州随机结构工具包（KRaSTk）的应用，以确定从特征尺度过渡到介观尺度的计算量代表金属泡沫在一个范围内的密度降低。当立方样品体积的边长比特征长度大约10倍时，发现发生过渡。比较KRaSTk计算收敛刚度分布与商业金属泡沫的实验测量发现，在所有降低密度的期望值和标准变异性非常一致。最后，我们观察到，代表性MMOD撞击的直径比泡沫在任何降低的密度下的特征尺度到中尺度过渡短约30倍。因此，特徴将决定对超高速撞击的反应，而不是整体（或甚至中尺度）结构。
英文摘要：
Metallic foams are crucial to many emerging applications, among them shielding against hypervelocity impacts caused by micrometeoroids and orbital debris. The variability of properties at feature-scale and mesoscale lengths originating from the foam's inherently random microstructure makes predictive models of their properties challenging. It also hinders the optimization of components fabricated with such foams, an especially serious problem for spacecraft design where the balance between cost and mass must also be balanced against the catastrophic results of component failure. To address this problem, we compute the critical transition length between the feature-scale, where mechanical properties are determined by individual features, and the mesoscale, where behavior is determined by ensembles of features. At the mesoscale, distributions of properties -- with respect to both expectation value and standard variability -- are consistent and predictable. The Kentucky Random Structure Toolkit (KRaSTk) is applied to determine the transition from feature-scale to mesoscale for computational volumes representing metallic foams at a range of reduced densities. The transition is found to occur when the side length of a cubic sample volume is ~10x greater than the characteristic length. Comparing KRaSTk-computed converged stiffness distributions with experimental measurements of a commercial metallic foam found excellent agreement for both expectation value and standard variability at all reduced densities. Lastly, we observe that the diameter of a representative MMOD strike is ~30x shorter than the feature-scale to mesoscale transition for the foam at any reduced density. Therefore, features will determine response to hypervelocity impacts, rather than bulk (or even mesoscale) structure.
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