Phyllosilicate minerals, due to their sheets structure and morphology, are known to cause anisotropy in bulk rock properties and make the bulk rock more compliant. Accurately characterizing the micromechanical behavior of phyllosilicate minerals from laboratory observations, which eventually translates to the bulk rock behavior, is still challenging due to their fine-grained nature. Recent advances in atomistic simulations open the possibility of theoretically investigating such mineral mechanical behavior. We compare the elastic properties of biotites recovered by spherical nanoindentation with those predicted from density functional theory (DFT) simulations to investigate to what extent theoretical predictions reproduce actual phyllosilicate properties. Spherical nanoindentation was conducted using schist rocks from Poorman Formation, South Dakota, USA, to recover continuous indentation stress-strain curves. Loading in the layer-normal orientation shows an average indentation modulus () of about 35 GPa, while loading in the layer-parallel orientation gives a higher average of about 95 GPa. To facilitate comparison, the elastic stiffness constants (c_ij) determined from DFT were converted to indentation modulus () using solutions proposed in this study. The majority of the nanoindentation modulus results are below the values inferred from the simulation results representing ideal defect-free minerals. We suggest that crystal defects present at the nano-scale, potentially ripplocations, are the dominant cause of the lower indentation modulus recovered from nanoindentation compared to those inferred from DFT simulations. Results highlight the importance of acknowledging the defects that exist down to the nano-scale as it modifies the mechanical properties of phyllosilicates compared to its pure defect-free form.

中文翻译：

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通过球形纳米压痕和原子模拟恢复的黑云母弹性特性的比较——层状硅酸盐中纳米级缺陷的影响

众所周知，页硅酸盐矿物由于其片状结构和形态，会导致大块岩石特性的各向异性，并使大块岩石更柔顺。从实验室观察中准确表征层状硅酸盐矿物的微观力学行为，最终转化为大块岩石的行为，由于其细粒性质，仍然具有挑战性。原子模拟的最新进展开启了从理论上研究此类矿物机械行为的可能性。我们将通过球形纳米压痕回收的黑云母的弹性特性与密度泛函理论 (DFT) 模拟预测的特性进行比较，以研究理论预测在多大程度上再现了实际的页硅酸盐特性。使用来自Poorman Formation的片岩进行球形纳米压痕，美国南达科他州，恢复连续压痕应力-应变曲线。层法向加载显示平均压痕模量 () 约 35 GPa，而层平行取向的加载给出了约 95 GPa 的更高平均值。为了便于比较，弹性刚度常数（Ç _IJ）从DFT确定转变为压痕模（) 使用本研究中提出的解决方案。大多数纳米压痕模量结果低​​于从代表理想无缺陷矿物的模拟结果推断出的值。我们认为，与从 DFT 模拟推断的那些相比，纳米级存在的晶体缺陷，潜在的裂变，是从纳米压痕中恢复的压痕模量较低的主要原因。结果强调了承认存在于纳米级的缺陷的重要性，因为与纯无缺陷形式相比，它改变了页硅酸盐的机械性能。