ABSTRACT

Pop-in is a widely observed phenomenon in nanoindentation. In this paper, dislocation evolution in pop-in processes is analysed in detail through molecular dynamics (MD) simulations. We found that a large number of dislocations nucleate homogeneously at the initiation of pop-in, followed by extensive dislocation propagation, which is the dominant mode of plastic deformation during pop-in. Moreover, we noted that establishing the correct dislocation evolution mechanisms of pop-in can serve to explain the overshoot phenomenon observed in nanoindentation experiments. Through our MD analysis on the obtained dislocation structures, therefore, we were able to propose a model that can predict the total length of dislocations associated with the plastic processes underneath a spherical indenter. In addition, the Taylor model was used to verify that our proposed dislocation length model sits well with the MD simulated force-displacement curves of nanoindentation. In fact, the MD simulated linear relation between critical force and indentation depth during pop-in is consistent with the Hertzian and Taylor models. Our MD simulations, therefore, can provide significant insight into the experimentally observed pop-in phenomena.

摘要

弹入是在纳米压痕中被广泛观察到的现象。在本文中，通过分子动力学（MD）模拟详细分析了弹出过程中的位错演化。我们发现，大量的位错在爆裂开始时会均匀地成核，然后发生大量的位错扩散，这是爆裂过程中塑性变形的主要方式。此外，我们注意到建立正确的弹出式位错演化机制可以用来解释纳米压痕实验中观察到的过冲现象。因此，通过对获得的位错结构进行MD分析，我们能够提出一个模型，该模型可以预测与球形压头下方塑性过程相关的位错总长度。此外，采用泰勒（Taylor）模型验证了我们提出的位错长度模型与纳米压痕的MD模拟力-位移曲线吻合良好。实际上，在弹出过程中，MD模拟的临界力和压入深度之间的线性关系与Hertzian和Taylor模型一致。因此，我们的MD模拟可以提供对实验观察到的弹出现象的重要见解。