arXiv subjects

Chunyu Li

Publications and source records attributed to Chunyu Li.

43 records · Page 3Linked to original sources

arXiv2022

Systematic Builder for All-Atom Simulations of Plastically Bonded Explosives

The shock to detonation transition in heterogeneous plastically bonded explosives is dominated by energy localization into hotspots that arise from the interaction of the shockwave with microstructural features and defects. The complex polycrystalline structure of these materials leads to a network of hotspot that can coalesce into deflagration and detonation waves. Significant progress has been made on the formation and potency of hotspots using atomistic simulations, but most of the work has focused on ideal and isolated defects. Hence, developed a method, denoted PBXGen, to build realistic PBX microstructures for all-atom simulations. PBXGen is generally applicable, and we demonstrate it with two systems: an RDX-polystyrene PBX with a 3D microstructure and a TATB-polystyrene with columnar grains. The resulting structure exhibit key features of PBXs, albeit at smaller scales, and are validated against experimental mechanical and shock properties.

cond-mat.mtrl-sci↗

arXiv2021

Spectral MVIR: Joint Reconstruction of 3D Shape and Spectral Reflectance

Reconstructing an object's high-quality 3D shape with inherent spectral reflectance property, beyond typical device-dependent RGB albedos, opens the door to applications requiring a high-fidelity 3D model in terms of both geometry and photometry. In this paper, we propose a novel Multi-View Inverse Rendering (MVIR) method called Spectral MVIR for jointly reconstructing the 3D shape and the spectral reflectance for each point of object surfaces from multi-view images captured using a standard RGB camera and low-cost lighting equipment such as an LED bulb or an LED projector. Our main contributions are twofold: (i) We present a rendering model that considers both geometric and photometric principles in the image formation by explicitly considering camera spectral sensitivity, light's spectral power distribution, and light source positions. (ii) Based on the derived model, we build a cost-optimization MVIR framework for the joint reconstruction of the 3D shape and the per-vertex spectral reflectance while estimating the light source positions and the shadows. Different from most existing spectral-3D acquisition methods, our method does not require expensive special equipment and cumbersome geometric calibration. Experimental results using both synthetic and real-world data demonstrate that our Spectral MVIR can acquire a high-quality 3D model with accurate spectral reflectance property.

cs.CV↗

arXiv2020

A Hotspots Better Half: Non-Equilibrium Intra-Molecular Strain in Shock Physics

Shockwave interactions with material microstructure localizes energy into hotspots, which act as nucleation sites for complex processes such as phase transformations and chemical reactions. To date, hotspots have been described via their temperature fields. Nonreactive, all-atom molecular dynamics simulations of shock-induced pore collapse in a molecular crystal show that more energy is localized as potential energy (PE) than can be inferred from the temperature field and that PE localization persists through thermal diffusion. The origin of the PE hotspot is traced to large intra-molecular strains, storing energy in modes readily available for chemical decomposition.

cond-mat.mtrl-sci↗

arXiv2019

Pro-Cam SSfM: Projector-Camera System for Structure and Spectral Reflectance from Motion

In this paper, we propose a novel projector-camera system for practical and low-cost acquisition of a dense object 3D model with the spectral reflectance property. In our system, we use a standard RGB camera and leverage an off-the-shelf projector as active illumination for both the 3D reconstruction and the spectral reflectance estimation. We first reconstruct the 3D points while estimating the poses of the camera and the projector, which are alternately moved around the object, by combining multi-view structured light and structure-from-motion (SfM) techniques. We then exploit the projector for multispectral imaging and estimate the spectral reflectance of each 3D point based on a novel spectral reflectance estimation model considering the geometric relationship between the reconstructed 3D points and the estimated projector positions. Experimental results on several real objects demonstrate that our system can precisely acquire a dense 3D model with the full spectral reflectance property using off-the-shelf devices.

cs.CV↗

arXiv2017

Molecular Modeling of the Microstructure Evolution during the Carbonization of PAN-Based Carbon Fibers

Development of high strength carbon fibers (CFs) requires an understanding of the relationship between the processing conditions, microstructure and resulting properties. We developed a molecular model that combines kinetic Monte Carlo (KMC) and molecular dynamics (MD) techniques to predict the microstructure evolution during the carbonization process of carbon fiber manufacturing. The model accurately predicts the cross-sectional microstructure of carbon fibers, predicting features such as graphitic sheets and hairpin structures that have been observed experimentally. We predict the transverse modulus of the resulting fibers and find that the modulus is slightly lower than experimental values, but is up to an order of magnitude lower than ideal graphite. We attribute this to the perfect longitudinal texture of our simulated structures, as well as the chain sliding mechanism that governs the deformation of the fibers, rather than the van der Waals interaction that governs the modulus for graphite. We also observe that high reaction rates result in porous structures that have lower moduli.

cond-mat.mtrl-sci↗

arXiv2015

Atomistic simulations of amorphous polymers in the cloud with PolymerModeler

Molecular dynamics (MD) simulations enable the description of ma- terial properties and processes with atomistic detail by numerically solv- ing the time evolution of every atom in the system. We introduce Poly- merModeler, a general-purpose, online simulation tool to build atomistic structures of amorphous polymers and perform MD simulations on the re- sulting configurations to predict their thermo-mechanical properties. Poly- merModeler is available, free of charge, at nanoHUB.org via an interactive web interface, and the actual simulations are performed in the cloud us- ing nanoHUB.org resources. Starting from the specification of one or more monomers PolymerModeler builds the polymer chains into a simulation cell with periodic boundary conditions at the desired density. Monomers are added sequentially using the continuous configuration bias direct Monte Carlo method, and copolymers can be created describing the desired se- quence of monomers. PolymerModeler also enables users to perform MD simulations on the structures created by the builder using the Dreiding force field and Gasteiger partial atomic charges. We describe the force field im- plementation and the various options for the MD simulations that use the LAMMPS simulator. PolymerModeler MD simulations for a PMMA sam- ple show good structural agreement with experiments and are in good agree- ment with simulations obtained with commercial software.

cond-mat.mtrl-sci↗

arXiv2014

Anomalous compressibility behavior of chromium monoaresenide under high pressure

CrAs was firstly observed possessing the bulk superconductivity (Tc~2 K) under high pressure (0.8 GPa) in the very recent work (Wei Wu, et al. Nature Communications 5, 5508 (2014)). To explore the correlation between the structure and the superconductivity, the high-pressure structure evolution of CrAs was investigated using angle dispersive X-ray diffraction (XRD) method with small steps of ~0.1 GPa in a diamond anvil cell (DAC) up to 1.8 GPa. In the pressure range covered by our current experiment, the structure of CrAs keeps stable. However, the lattice parameters exhibit anomalous compression behaviors. With the pressure increasing, the lattice parameters a and c both show a process of first increasing and then decreasing, and the lattice parameter b goes through a quick contract at 0.35 GPa, which suggests a pressure-induced isostructural phase transition occurs in CrAs around this pressure point. Above the phase transition pressure, the axial compressibilities of CrAs present remarkable anisotropy. The compressibilities along the a- and c-axis are about an order of magnitude smaller than that along the b-axis, which is closely related to the different stacking modes in CrAs6 octahedron along different crystallographic axes. A schematic band model was used for addressing above anomalous compression behavior in CrAs.

cond-mat.str-el↗