Laboratoire de Physique Théorique de la Matière Condensée, Paris Sorbonne Universités UPMC, BP 121, 4 Place Jussieu, 75252 Paris Cedex 05, France.
Materials Sciences and Structures Division, Ecole des Mines de Saint-Etienne, LGF UMR No. 5307, CNRS, 158 Cours Fauriel, 42023 Saint-Etienne Cedex 2, France.
Phys Rev E. 2016 Mar;93(3):033001. doi: 10.1103/PhysRevE.93.033001. Epub 2016 Mar 2.
Plasticity in amorphous silica is unusual: The yield stress decreases with hydrostatic pressure, in contrast to the Mohr-Coulomb response commonly found in more compact materials such as bulk metallic glasses. To better understand this response, we have carried out molecular dynamics simulations of plastic response in a model glass with open structure. The simulations reproduce the anomalous dependence of yield stress with pressure and also correctly predict that the plastic response turns to normal once the material has been fully compacted. We also show that the overall shape of the yield surface is consistent with a quadratic behavior predicted assuming local buckling of the structure, a point of view that fits well into the present understanding of the deformation mechanisms of amorphous silica. The results also confirm that free volume is an adequate internal variable for a continuum scale description of the plastic response of amorphous silica. Finally, we also investigate the long-range correlations between rearrangement events. We find that strong intermittency is observed when the structure remains open, while compaction results in more homogeneous rearrangements. These findings are in agreement with recent results on the effect of compression on the middle range order in silicate glasses and also suggest that the well-known volume recovery of densified silica at relatively low temperatures is in fact a form of aging.
屈服应力随静水压力降低，与更致密的材料（如块状金属玻璃）中常见的 Mohr-Coulomb 响应相反。为了更好地理解这种响应，我们对具有开放结构的模型玻璃的塑性响应进行了分子动力学模拟。模拟再现了屈服应力随压力的异常依赖性，并且还正确地预测了一旦材料完全压实，塑性响应就会变为正常。我们还表明，屈服面的整体形状与假设结构局部屈曲的二次行为预测一致，这种观点与目前对非晶态二氧化硅变形机制的理解非常吻合。结果还证实，自由体积是描述非晶态二氧化硅塑性响应的连续体尺度描述的合适内部变量。最后，我们还研究了重排事件之间的长程相关性。我们发现，当结构保持开放时，会观察到强烈的间歇性，而压实则导致更均匀的重排。这些发现与最近关于压缩对硅酸盐玻璃中中程有序的影响的结果一致，并且还表明，在相对较低的温度下致密二氧化硅的众所周知的体积恢复实际上是一种老化形式。
