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Deformation, Phase Transformation and Recrystallization in the Shear Bands Induced by High-Strain Rate Loading in Titanium and Its Alloys

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Journal of Materials Science & Technology 2006年第6期22卷 737-746,I0003,I0004页

作者： Yongbo XU yilong bai M.A.Meyers Shenyang National Laboratory for Materials Science Institute of Metal Research Chinese Academy of Sciences Shenyang 110016 China Laboratory for Non-linear Mechanics of Continuous Media Institute of Mechanics Chinese Academy of Sciences Beijing 100080 China Department of Mechanical and Aerospace Engineering University of California San Diego La Jolla CA 920930-0411 USA

α-titanium and its alloys with a dual-phase structure （α＋β） were deformed dynamically under strain rate of about 10^4 s^-1. The formation and microstructural evolution of the localized shear bands were characterized by scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. The results reveal that both the strain and strain rate should be considered simultaneously as the mechanical conditions for shear band formation, and twinning is an important mode of deformation. Both experimental and calculation show that the materials within the bands underwent a superhigh strain rate （9×10^5 S^-1） deformation, which is two magnitudes of that of average strain rate required for shear band formation; the dislocations in the bands can be constricted and developed into cell structures; the phase transformation from α to α2 within the bands was observed, and the transformation products （α2） had a certain crystallographic orientation relationship with their parent; the equiaxed grains with an average size of 10 μm in diameter observed within the bands are proposed to be the results of recrystallization.

关键词： Localized shear bands Microstructure Dislocations Twinning Phase transformation Recrystallization

MECHANISMS UNDERLYING TWO KINDS OF SURFACE EFFECTS ON ELASTIC CONSTANTS

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Acta Mechanica Solida Sinica 2009年第6期22卷 605-622页

作者： Yizhe Tang Zhijun Zheng Mengfen Xia yilong bai State Key Laboratory of Nonlinear Mechanics （LNM） Institute of Mechanics Chinese Academy of Sciences Beijing 100190 China Graduate University of Chinese Academy of Sciences Beijing 100049 China Department of Physics Peking University Beijing 100871 China

Recently, people are confused with two opposite variations of elastic modulus with decreasing size of nano scale sample： elastic modulus either decreases or increases with decreasing sample size. In this paper, based on intermolecular potentials and a one dimensional model, we provide a unified understanding of the two opposite size effects. Firstly, we analyzed the microstructural variation near the surface of an fcc nanofilm based on the Lennard-Jones potential. It is found that the atomic lattice near the surface becomes looser in comparison with the bulk, indicating that atoms in the bulk are located at the balance of repulsive forces, and the elastic moduli decrease with the decreasing thickness of the film accordingly. In addition, the decrease in moduli should be attributed to both the looser surface layer and smaller coordination number of surface atoms. Furthermore, it is found that both looser and tighter lattice near the surface can appear for a general pair potential and the governing mechanism should be attributed to the surplus of the nearest force to all other long range interactions in the pair potential. Surprisingly, the surplus can be simply expressed by a sum of the long range interactions and the sum being positive or negative determines the looser or tighter lattice near surface respectively. To justify this concept, we examined ZnO in terms of Buckingham potential with long range Coulomb interactions. It is found that compared to its bulk lattice, the ZnO lattice near the surface becomes tighter, indicating the atoms in the bulk are located at the balance of attractive forces, owing to the long range Coulomb interaction. Correspondingly, the elastic modulus of one-dimensional ZnO chain increases with decreasing size. Finally, a kind of many-body potential for Cu was examined. In this case, the surface layer becomes tighter than the bulk and the modulus increases with deceasing size, owing to the long range repulsive pair interaction, as well as the cohesive many-body interaction caused by t

关键词： size effect elastic modulus surface effect atomic/molecular potential surface layer

FORMULATION OF STATISTICAL EVOLUTION OF MICROCRACKS IN SOLIDS

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Acta Mechanica Sinica 1991年第1期7卷 59-66页

作者： yilong, bai Fujiu, Ke Mengfen, Xia Laboratory for Non-Linear Mechanics of Continuous Media Institute of Mechanics Chinese Academy of Sciences Beijing China

The paper presents a principal formulation of statistical evolution of microcracks, occurring in solids, subjected to external loading. In particular, the concept of ideal microcracks is elaborated, in order to describe the fundamental features of damage resulting from nucleation and extension of microcracks. Relevant average damage functions are also discussed.

关键词： micro-cracks statistical evolution number density

SELF-ADAPTIVE MOLECULE/CLUSTER STATISTICAL THERMODYNAMICS METHOD FOR QUASI-STATIC DEFORMATION AT FINITE TEMPERATURE

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Acta Mechanica Solida Sinica 2011年第1期24卷 92-100页

作者： Hao Tan Haiying Wang Mengfen Xia Fujiu Ke yilong bai State Key Laboratory of Nonlinear Mechanics (LNM) Institute of Mechanics Chinese Academy of Sciences Beijing 100190 China Graduate University of Chinese Academy of Sciences Beijing 100871 China Physics School of Peking University Beijing 100871 China School of Physics and Nuclear Energy Engineering Beijing University of Aeronautics and Astronautics Beijing 100191 China

Hybrid molecule/cluster statistical thermodynamics （HMCST） method is an efficient tool to simulate nano-scale systems under quasi-static loading at finite temperature. In this paper, a self-adaptive algorithm is developed for this method. Explicit refinement criterion based on the gradient of slip shear deformation and a switching criterion based on generalized Einstein approximation is proposed respectively. Results show that this self-adaptive method can accurately find clusters to be refined or transferred to molecules, and efficiently refine or trans- fer the clusters. Furthermore, compared with fully atomistic simulation, the high computational efficiency of the self-adaptive method appears very attractive.

关键词： self-adaptive slip shear deformation particle method approximation refinement criterion switching criterion

Systolic B-1 Circuit in Galois Fields Based on a Quaternary Logic Technique

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Journal of Beijing Institute of Technology 2020年第2期29卷 177-183页

作者： Haixia Wu yilong bai Tian Wang Xiaoran Li Long He School of Information and Electronics Beijing Institute of TechnologyBeijing 100081China

In order to improve the circuit complexity and reduce the long latency of B-1 operations,a novel B-1 operation in Galois Field GF(24)is presented and the corresponding systolic realization based on multiple-valued logic(MVL)is proposed.The systolic structure employs multiplevalued current mode(MVCM)by using dynamic source-coupled logic(SCL)to reduce the initial delay and the transistor and wire counts.The performance is evaluated by HSPICE simulation in 0.18μm CMOS technology and a comparison is conducted between our proposed implementation and those reported in the literature.The initial delay and the sum of transistors and wires in our MVL design are about 43%and 13%lower,respectively,in comparison with other corresponding binary CMOS implementations.The systolic architecture proposed is simple,regular,and modular,well suited for very large scale integration(VLSI)implementations.The combination of MVCM circuits and relevant algorithms based on MVL seems to be a potential solution for high performance arithmetic operations in GF(2k).

关键词： multiple-valued logic(MVL) systolic B^-1 circuit Galois Fields

Design of AB^2 in Galois Fields Based on Multiple-Valued Logic

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Journal of Beijing Institute of Technology 2019年第4期28卷 764-769页

作者： Haixia Wu Long He Xiaoran Li yilong bai Minghao Zhang School of Information and Electronics Beijing Institute of TechnologyBeijing 100081China

A new AB^2 operation in Galois Field GF(24)is presented and its systolic realization based on multiple-valued logic(MVL)is proposed.The systolic structure of the operation employs multiple-valued current mode(MVCM)by using dynamic source-coupled logic(SCL)to reduce the transistor and wire counts,and the initial delay.The performance is evaluated by HSPICE simulation with 0.18.μm CMOS technology.A comparison is conducted between our proposed implementation and those reported in the literature.The transistor counts,the wire counts and the initial delay in our MVL design show savings of about 23%,45%,and 72%,in comparison with the corresponding binary CMOS implementation.The systolic architecture proposed is simple,regular,and modular,well suited for very large scale integration(VLSI)implementation.The combination of MVCM circuits and relevant algorithms based on MVL seems to be a potential solution for high performance arithmetic operations in GF(2^k).

关键词： multiple-valued logic(MVL) AB^2 operation Galois Fields

Comparison of shear banding in BMGs due to thermal-softening and free volume creation

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Science China(Physics,Mechanics & Astronomy) 2008年第9期51卷 1367-1379页

作者： LIU LongFei DAI LanHong bai yilong KE FuJiu Hunan Provincial Key Laboratory of Health Maintenance for Mechanical Equipment Hunan University of Science and TechnologyXiangtan 411201China State Key Laboratory of Nonlinear Mechanics(LNM) Institute of MechanicsChinese Academy of Sci-encesBeijing 100190China Department of Applied Physics Beijing University of Aeronautics and AstronauticsBeijing 100088China

This paper reports a comparative study of shear banding in BMGs resulting from thermal softening and free volume creation. Firstly,the effects of thermal softening and free volume creation on shear instability are discussed. It is known that ther-mal softening governs thermal shear banding,hence it is essentially energy related. However,compound free volume creation is the key factor to the other instability,though void-induced softening seems to be the counterpart of thermal softening. So,the driving force for shear instability owing to free volume creation is very dif-ferent from the thermally assisted one. In particular,long wave perturbations are always unstable owing to compound free volume creation. Therefore,the shear instability resulting from coupled compound free volume creation and thermal softening may start more like that due to free volume creation. Also,the compound free volume creation implies a specific and intrinsic characteristic growth time of shear instability. Finally,the mature shear band width is governed by the corre-sponding diffusions (thermal or void diffusion) within the band. As a rough guide,the dimensionless numbers: Thermal softening related number B,Deborah number (denoting the relation of instability growth rate owing to compound free volume and loading time) and Lewis number (denoting the competition of different diffusions) show us their relative importance of thermal softening and free volume creation in shear banding. All these results are of particular significance in understanding the mechanism of shear banding in bulk metallic glasses (BMGs).

关键词： metallic glasses shear bands diffusion instability

Dynamic constitutive equation of GFRP obtained by Lagrange experiment

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Chinese Science Bulletin 2000年第13期45卷 1164-1169页

作者： SHANG Jialan bai yilong XU Suzhen CAI Xiaoye Instilule of Mechanics Chinese Academy of SciencesBeijing 100080China Beijing Inslilule of Special Eleclronic and Mechanical Devices Beijing 100076China

The note presents a method of constructing dynamic constitutive equations of material by means of Lagrange experiment and analysis. Tests were carried out by a light gas gun and the stress history profiles were recorded on multiple Lagrange positions. The dynamic constitutive equations were deduced from the regression of a series of data which was obtained by Lagrange analysis based upon recorded multiple stress histories. Here constitutive equations of glass fibre reinforced phenolic resin composite(GFRP) in uniaxil strain state under dynamic loading are given. The proposed equations of the material agree well with experimental results.

关键词： impact loading dynamic constitutive equation Lagrange analysis.

A Physics‑Based Seismic Risk Assessment of the Qujiang Fault:From Dynamic Rupture to Disaster Estimation

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International Journal of Disaster Risk Science 2024年第1期15卷 165-177页

作者： yilong Li Zijia Wang Zhenguo Zhang Yuhao Gu Houyun Yu School of National Safety and Emergency Management Beijing Normal UniversityZhuhai 519087China Department of Earth and Space Sciences Southern University of Science and TechnologyShenzhen 518055China Guangdong Provincial Key Laboratory of Geophysical High-Resolution Imaging Technology Southern University of Science and TechnologyShenzhen 518055China

This study achieved the construction of earthquake disaster scenarios based on physics-based methods-from fault dynamic rupture to seismic wave propagation-and then population and economic loss estimations.The physics-based dynamic rupture and strong ground motion simulations can fully consider the three-dimensional complexity of physical parameters such as fault geometry,stress field,rock properties,and terrain.Quantitative analysis of multiple seismic disaster scenarios along the Qujiang Fault in western Yunnan Province in southwestern China based on different nucleation locations was achieved.The results indicate that the northwestern segment of the Qujiang Fault is expected to experience significantly higher levels of damage compared to the southeastern segment.Additionally,there are significant variations in human losses,even though the economic losses are similar across different scenarios.Dali bai Autonomous Prefecture,Chuxiong Yi Autonomous Prefecture,Yuxi City,Honghe Hani and Yi Autonomous Prefecture,and Wenshan Zhuang and Miao Autonomous Prefecture were identified as at medium to high seismic risks,with Yuxi and Honghe being particularly vulnerable.Implementing targeted earthquake prevention measures in Yuxi and Honghe will significantly mitigate the potential risks posed by the Qujiang Fault.Notably,although the fault is within Yuxi,Honghe is likely to suffer the most severe damage.These findings emphasize the importance of considering rupture directivity and its influence on ground motion distribution when assessing seismic risk.

关键词： Earthquake disaster loss estimation Physics-based earthquake scenario simulation Qujiang Fault Rupture directivity Seismic risk assessment