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Multimillion-to-billion atom molecular dynamics simulations of deformation, damage, nanoindentation, and fracture in silica glass and energetic materials.

机译：二氧化硅玻璃和高能材料中数百万至十亿个原子的分子动力学模拟，包括变形，损伤，纳米压痕和断裂。

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摘要

Multimillion-to-billion molecular dynamics (MD) simulations are carried out to study atomistic mechanisms of deformation, damage and failure in silica glass and energetic materials. The simulations are based on experimentally validated interatomic potentials and employ highly efficiently algorithms for parallel architectures.;The onset of void-void interaction is investigated by performing MD simulations of amorphous silica under hydrostatic tension. The simulations reveal that nanocavities in amorphous silica (a-SiO2), which are linked to Si-O rings, play an important role in void-void coalescence and inter-void ligament failure.;Nanocracks nucleated by the migration of three-fold coordinated Si and nonbridging O on ---Si-O-Si-O--- rings are observed in the multimillion MD simulations of a single void in amorphous silica subjected to a high shear rate. With the increase in shear strain, nanocracks appear on void surfaces and the voids deform into a threadlike structure. At a strain of 40%, the voids break into fragments. The results are similar to experimental and theoretical studies of bubble deformation and breakup under shear.;Defects such as voids are known to be important in the detonation of energetic materials. To investigate deformation of a void in an RDX crystal under high shear rate, we have performed million-atom reactive force field (ReaxFF) MD simulations. Simulations reveal that without breaking a bond, the excess strain energy leads to translational and rotational motion of RDX molecules. At a strain of 13%, molecules with high kinetic energy collapse inward without affecting the rest of the system.;MD simulations of nanoindentation in amorphous silica reveal migration of defects and their recombination in the densified plastic region under and the material pileup region around the indenter. The plastic flow of silica glass is related to the defect transport mechanism where a defect migrates a considerable distance via a chain of bond-switching events[44]. We obtained a hardness value of 7.2 GPa using a sharp indenter and 8.0 GPa for a slightly blunt indenter.;We have also performed nanoindentation simulation on a (100) alpha-RDX crystal surface using ReaxFF. Simulation reveals localized melting and decomposition of RDX molecular fragments. We have found a distinct (210) plane boundary, where molecules above the (210) plane have displaced dramatically and molecules below the plane remain intact. Simulation also shows the fragmented RDX molecules diffuse from the substrate and walk on the indenter surface.
机译：进行了数以百万计的分子动力学（MD）模拟，以研究硅玻璃和高能材料的变形，破坏和破坏的原子机理。该模拟基于经过实验验证的原子间电势，并为并行构架采用高效算法。通过在静水压力下进行无定形二氧化硅的MD模拟，研究了空隙相互作用的发生。模拟结果表明，与Si-O环相连的无定形二氧化硅（a-SiO2）中的纳米腔在空洞聚结和空洞间韧带破坏中起着重要作用;纳米裂纹由三重配位的迁移成核在数百万次对高剪切速率的无定形二氧化硅中的单个空隙进行的MD模拟中，观察到了在--- Si-O-Si-O ---环上的Si和非桥接O。随着剪切应变的增加，纳米裂纹出现在空隙表面，空隙变形为线状结构。在40％的应变下，空隙会破碎成碎片。结果类似于在剪切作用下气泡变形和破裂的实验和理论研究。已知诸如空洞之类的缺陷在高能材料爆轰中很重要。为了研究高剪切速率下RDX晶体中空隙的变形，我们进行了百万原子反作用力场（ReaxFF）MD模拟。仿真表明，在不破坏键的情况下，过量的应变能会导致RDX分子的平移和旋转运动。在13％的应变下，具有高动能的分子会向内塌陷，而不会影响系统的其余部分。无定形二氧化硅中纳米压痕的MD模拟显示缺陷的迁移及其在致密塑料区域下方和材料堆积区域周围的复合。压头。石英玻璃的塑性流动与缺陷传输机制有关，在缺陷传输机制中，缺陷通过键转换事件链迁移了相当长的距离[44]。我们使用锋利的压头获得了7.2 GPa的硬度值，而稍钝的压头获得了8.0 GPa的硬度值。我们还使用ReaxFF在（100）alpha-RDX晶体表面上进行了纳米压痕模拟。仿真揭示了RDX分子片段的局部熔化和分解。我们发现了一个独特的（210）平面边界，其中（210）平面上方的分子已发生剧烈位移，而该平面下方的分子则保持完整。模拟还显示了碎片化的RDX分子从基材扩散并在压头表面上行走。

著录项

  • 作者

    Chen, Yi-Chun.;

  • 作者单位

    University of Southern California.;

  • 授予单位 University of Southern California.;
  • 学科 Condensed matter physics.
  • 学位 Ph.D.
  • 年度 2008
  • 页码 119 p.
  • 总页数 119
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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