arXiv subjects

Jeongin Paeng

Publications and source records attributed to Jeongin Paeng.

3 recordsLinked to original sources

arXiv2025

Filling a gap in materials mechanics: Nanoindentation at high constant strain rates upto $10^5 s^{-1}$

A central focus in high strain rate research is understanding the dynamic behavior of materials at strain rates where a strength upturn is observed. While strength upturns at strain rates of $10^3$ to $10^4~\mathrm{s}^{-1}$ have been widely reported in the literature, their occurrence in certain materials remains controversial, and the underlying physics driving this phenomenon is not yet fully understood. Current mechanical testing methods are limited, as no single technique spans the full strain rate range of $10^1$ to $10^5~\mathrm{s}^{-1}$ where this phenomenon is expected, and a unified technique would enable consistent post-deformation characterization with minimal error. To address this, we developed a customized piezoelectric in situ nanomechanical test setup, enabling constant indentation strain rates up to $10^5~\mathrm{s}^{-1}$ for the first time. Using this system, we examined rate-dependent hardness in single-crystalline molybdenum, nanocrystalline nickel, and amorphous fused silica over strain rates from $10^1$ to $10^5~\mathrm{s}^{-1}$, remarkably revealing a hardness upturn in all three materials. Further, post-deformation analysis of single-crystalline molybdenum revealed that the hardness upturn was primarily driven by increased dislocation density, with phonon drag -- traditionally considered a dominant contributor -- playing a minimal role.

cond-mat.mtrl-sci↗

arXiv2022

E-beam-enhanced solid-state mechanical amorphization of alpha-quartz: Reducing deformation barrier via localized excess electrons as mobile anions

Under hydrostatic pressure, alpha-quartz undergoes solid-state mechanical amorphization wherein the interpenetration of SiO4 tetrahedra occurs and the material loses crystallinity. This phase transformation requires a high hydrostatic pressure of 14 GPa because the repulsive forces resulting from the ionic nature of the Si-O bonds prevent the severe distortion of the atomic configuration. Herein, we experimentally and computationally demonstrate that e-beam irradiation changes the nature of the interatomic bonds in alpha-quartz and enhances the solid-state mechanical amorphization at nanoscale. Specifically, during in situ uniaxial compression, a larger permanent deformation occurs in alpha-quartz micropillars compressed during e-beam irradiation than in those without e-beam irradiation. Microstructural analysis reveals that the large permanent deformation under e-beam irradiation originates from the enhanced mechanical amorphization of alpha-quartz and the subsequent viscoplastic deformation of the amorphized region. Further, atomic-scale simulations suggest that the delocalized excess electrons introduced by e-beam irradiation move to highly distorted atomic configurations and alleviate the repulsive force, thus reducing the barrier to the solid-state mechanical amorphization. These findings deepen our understanding of electron-matter interactions and can be extended to new glass forming and processing technologies at nano- and microscale.

cond-mat.mtrl-sci↗

arXiv2020

Glass shaping at nanoscale: Mechanical forming of brittle amorphous silica by engineered inelastic interaction of scanning electrons with matter

Amorphous silica deforms viscoplastically at elevated temperatures, as is common for brittle glasses. The key mechanism of viscoplastic deformation involves interatomic bond switching, which is known to be a thermally activated process. In this study, through systematic in-situ compression tests by scanning electron microscopy, the viscoplastic deformation of amorphous silica is observed without thermal activation. Furthermore, ductility does not increase monotonically with acceleration voltage and current density of the SEM e-beam but is maximized by a factor of three at a specific acceleration voltage and current density conditions (compared to beam-off conditions). A Monte Carlo simulation of the electron-matter interaction shows that the unique trends of viscoplastic deformation correlate with the interaction volume, i.e., the region within the material where inelastic electron scattering occurs. Changing the size of the migrating atomic clusters can lead to facility in rearrangements of the intramolecular bonds, hence leading to more sustained bond switching. Based on the interaction volume the mechanical shaping of small-scale amorphous silica structures under e-beam irradiation can be modeled with high-precision supporting the idea that this relatively low-voltage e-beam-irradiation induced viscoplastic-deformation technique holds great potential for advancing amorphous silica structure manufacturing and developing e-beam assisted manufacturing for covalently bonded non-metallic materials.

cond-mat.mtrl-sci↗