Stick-slip Dynamics in Penetration Experiments on Simulated Regolith
Stick-slip Dynamics in Penetration Experiments on Simulated Regolith
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DOI：
10.3847/psj/ac3de2
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发表时间：
2020-11
影响因子：
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通讯作者：
Jack Featherstone;R. Bullard;Tristan Emm;A. Jackson;R. Reid;Sean Shefferman;A. Dove;J. Colwell;J. Kollmer;K. Daniels
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文献类型：
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作者：
Jack Featherstone;R. Bullard;Tristan Emm;A. Jackson;R. Reid;Sean Shefferman;A. Dove;J. Colwell;J. Kollmer;K. Daniels
许多行星体的表面，包括小行星和小卫星，都覆盖着尘埃到鹅卵石大小的风化层，在重力和接触力的作用下，这些风化层被微弱地附着在表面。了解风化层对外部扰动的反应将允许仪器，包括用于此类表面的传感器和锚定机构，实施优化的设计原则。我们分析了插入松散表土模拟物的柔性探针的行为，作为探针速度和环境重力加速度的函数，以探索相关的动力学。EMPANADA实验（需要在小行星上锚定或挖掘的应用程序的弹射最小化协议）进行了几次抛物线飞行。它采用经典的颗粒物理技术，光弹性，来量化柔性探针插入双分散系统时的动力学，厘米大小的模型颗粒。我们确定了在不同速度和四种不同重力水平（陆地、火星、月球和微重力）下探测器插入过程中整个系统的力链结构。我们确定了离散的，粘滑失效事件，其频率随着重力加速度的增加而增加。在微重力环境中，粘滑行为可以忽略不计，我们发现更快的探针插入可以抑制存在的粘滑行为。我们得出的结论是，碎石堆小行星上的风化层的机械反应可能与在较大的行星物体上发现的力学反应截然不同，并且将地面实验扩展到微重力条件下可能无法捕获完整的物理动力学。
The surfaces of many planetary bodies, including asteroids and small moons, are covered with dust to pebble-sized regolith held weakly to the surface by gravity and contact forces. Understanding the reaction of regolith to an external perturbation will allow for instruments, including sensors and anchoring mechanisms for use on such surfaces, to implement optimized design principles. We analyze the behavior of a flexible probe inserted into loose regolith simulant as a function of probe speed and ambient gravitational acceleration to explore the relevant dynamics. The EMPANADA experiment (Ejecta-Minimizing Protocols for Applications Needing Anchoring or Digging on Asteroids) flew on several parabolic flights. It employs a classic granular physics technique, photoelasticity, to quantify the dynamics of a flexible probe during its insertion into a system of bi-disperse, centimeter-sized model grains. We identify the force chain structure throughout the system during probe insertion at a variety of speeds and for four different levels of gravity: terrestrial, Martian, lunar, and microgravity. We identify discrete, stick-slip failure events that increase in frequency as a function of the gravitational acceleration. In microgravity environments, stick-slip behaviors are negligible, and we find that faster probe insertion can suppress stick-slip behaviors where they are present. We conclude that the mechanical response of regolith on rubble-pile asteroids is likely quite distinct from that found on larger planetary objects, and scaling terrestrial experiments to microgravity conditions may not capture the full physical dynamics.