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456 results on '"Peng, Hailong"'

3. Atomic-scale Deformation Process of Glasses Unveiled by Stress-induced Structural Anisotropy

Author

Dong, Jie, Peng, Hailong, Wang, Hui, Tong, Yang, Wang, Yutian, Dmowski, Wojciech, Sun, Baoan, Egami, Takeshi, Wang, Weihua, and Bai, Haiyang

Subjects
Condensed Matter - Materials Science
Abstract

Experimentally resolving atomic-scale structural changes of a deformed glass remains challenging owing to the disordered nature of glass structure. Here, we show that the structural anisotropy emerges as a general hallmark for different types of glasses (metallic glasses, oxide glass, amorphous selenium, and polymer glass) after thermo-mechanical deformation, and it is highly correlates with local nonaffine atomic displacements detected by the high-energy X-ray diffraction technique. By analyzing the anisotropic pair density function, we unveil the atomic-level mechanism responsible for the plastic flow, which notably differs between metallic glasses and covalent glasses. The structural rearrangements in metallic glasses are mediated through cutting and formation of atomic bonds, which occurs in some localized inelastic regions embedded in elastic matrix, whereas that of covalent glasses is mediated through the rotation of atomic bonds or chains without bond length change, which occurs in a less localized manner., Comment: 19 pages, 4 figures

Published
2022

10. Non-monotonic dynamic correlations beneath the surface of glass-forming liquids

Author

Peng, Hailong, Liu, Huashan, and Voigtmann, Thomas

Subjects
Condensed Matter - Statistical Mechanics
Abstract

Collective motion over increasing length scales is a signature of the vitrification process of liquids. We demonstrate the emergence of distinct static and dynamic length scales probed near the free surface in fully equilibrated glass-forming liquid films, and their connection to the bulk properties of the system. In contrast to a monotonically growing static correlation length, the dynamic correlation length that measures the extent of surface-dynamics acceleration into the bulk, displays a striking non-monotonic temperature evolution that is robust also against changes in detailed interatomic interaction. The maximum of dynamic correlations defines a cross-over temperature $T_*$ that we show to agree with a morphological change of cooperative rearrangement regions (CRR) of fast particles in the bulk liquids. The cross-over occurs at a temperature larger than the critical temperature Tc of mode-coupling theory (MCT). We link it to the point where fast-particle motion decouples from structural relaxation that can be defined rigorously within a recent extension of MCT, the stochastic $\beta$-relaxation theory (SBR).

Published
2021
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14. Fast crystal growth in deeply undercooled ZrTi melts.

Author

Yan, Zhihuang, Huang, Feiqi, Wu, Yanxue, Liu, Huashan, and Peng, Hailong

Abstract

We investigate the growth of crystals in Zr50Ti50 melts by classical molecular-dynamics simulations with an embedded atom method and a Stillinger–Weber potential model. Both models display fast solidification rates that can be captured by the transition state theory or the Ginzburg–Landau theory at small undercoolings. Fast crystal-growth rates are found to be affected by the pre-existing ordering in liquids, such as the body-centered cubic-like and icosahedral-like structures. The interface-induced ordering unveiled by the crystal-freezing method can explain the rate difference between these two models. However, these orderings fail to rationalize the temperature evolution of the growth rate at deep undercoolings. We correlate the growth kinetics with the detailed dynamical processes in liquids, finding the decoupling of hierarchic relaxation processes when collective motion emerges in supercooled liquids. We find that the growth kinetics is nondiffusive, but with a lower activation barrier corresponding to the structural relaxation or the cage-relative motion in ZrTi melts. These results explore a new relaxation mechanism for the fast growth rate in deeply undercooled liquids. [ABSTRACT FROM AUTHOR]

Published
2024
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21. Formation and dilatation of shear bands in a Cu-Zr metallic glass: A free volume perspective

Author

Tang, Chunguang, Peng, Hailong, Chen, Yu, and Ferry, Michael

Subjects
Condensed Matter - Materials Science
Abstract

We study the tensile deformation behaviour of metallic glass Cu$_{50}$Zr$_{50}$ as a function of quenching rate using molecular dynamics simulations. The atomic scale shearing is found to be independent on atomic free volume, and the macroscopic correlation between the yield strength and the density (or average free volume) is a coincidence that the samples with large free volume also have a low density of shear-resistant local five-fold symmetry. In the relatively slowly quenched ($\leq 10^{10}$ K/s) samples, shear bands have a dilatation about 0.5\%, which compares well with recent experiment results. In contrast, although more active local shearing occurs in the rapidly quenched samples, shear bands are not observed. This is because the strain energy disperses into local atomic shearing at the macroscopically elastic stage and, hence, is not sufficient for shear band activation, resulting in homogeneous deformation and appreciable plasticity., Comment: preprint before peer-review

Published
2019
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30. Precise Orbit Determination for Maneuvering HY2D Using Onboard GNSS Data.

Author

Xu, Kexin, Zhou, Xuhua, Li, Kai, Wang, Xiaomei, Peng, Hailong, and Gao, Feng

Subjects
ORBIT determination, GLOBAL Positioning System, ORBITS (Astronomy), LASER ranging, ROOT-mean-squares, OCEAN dynamics
Abstract

The Haiyang-2D (HY2D) satellite is the fourth ocean dynamics environment monitoring satellite launched by China. The satellite operates on a re-entry frozen orbit, which necessitates orbital maneuvers to maintain its designated path once the satellite's sub-satellite point deviates beyond a certain threshold. However, the execution of orbit maneuvers presents a significant challenge to the field of Precise Orbit Determination (POD). The thesis selects the on-board GPS data of HY2D satellite in December 2023 and five maneuvering days of that year. Employing a multifaceted approach that includes the assessment of observational data quality, orbit overlap, external orbit validation, and SLR (Satellite Laser Ranging) verification, the research delves into precise orbit determination during both maneuver and non-maneuver periods. The results indicate that: (1) The average number of satellites tracked by the receiver is 6.4; (2) During the non-maneuver periods, the average RMS (Root Mean Square) value of the radial difference in the 6-h overlapping arc segment is 0.66 cm, and the three-dimensional position difference is about 1.16 cm; (3) When compared with the precision science orbits (PSO) provided by CNES (Centre National d'Études Spatiales), the average values of the RMS values of the differences in the radial (R), transverse (T), and normal (N) directions during the non-maneuver and maneuver periods are respectively 1.32 cm, 2.31 cm, 1.92 cm and 3.04 cm, 8.78 cm, 2.72 cm. (4) The SLR verification of the orbit revealed a residual RMS of 2.24 cm. This suggests that by incorporating the modeling of maneuver forces during the maneuver periods, the impact of orbital maneuvers on orbit determination can be mitigated. [ABSTRACT FROM AUTHOR]

Published
2024
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