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MD simulations of loading rate dependence of detwinning deformation in nanocrystalline Ni

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Science China(Physics,Mechanics & Astronomy) 2013年第3期Mechanics & Astronomy) .卷 491-497页

作者： SU Hao tang qiheng State Key Laboratory of Nonlinear Mechanics Institute of MechanicsChinese Academy of Sciences

Molecular dynamics simulations are performed to investigate the deformation behavior of nanocrystalline Ni with pre-twin atom *** simulation sample is composed of four grains with average size 12 *** simulation technique of isobaric-isothermal ensemble(NPT) with high pressure is applied to obtain a sample with two circle *** uniaxial tensile and shear loading,as well as different detwinning deformation behaviors are *** uniaxial tension the detwinning deformation is induced by the event of grain growth,and it is supported by local energy *** the shear loading the detwinning deformation is related to the loading *** results show that there may be a critical shear *** the shear rate is sufficiently high the circle twin is found to be failed;as the shear rate is less than that rate,the size of circle twin become smaller and gradually approach a constant *** simulation results are in good agreement with experiment observation.

关键词： molecular dynamics simulation detwinning loading rate

A new thermo-elasto-plasticity constitutive theory for polycrystalline metals

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Acta Mechanica Sinica 2015年第3期31卷 338-348页

作者： Cen Chen qiheng tang Tzuchiang Wang State Key Laboratory of Nonlinear Mechanics Institute of Mechanics Chinese Academy of Sciences

In this study, the behavior of polycrystalline metals at different temperatures is investigated by a new thermo-elasto-plasticity constitutive theory. Based on solid mechanical and interatomic potential, the constitutive equa- tion is established using a new decomposition of the deformation gradient. For polycrystalline copper and magnesium, the stress-strain curves from 77 to 764 K （copper）, and 77 to 870 K （magnesium） under quasi-static uniaxial loading are calculated, and then the calculated results are compared with the experiment results. Also, it is determined that the present model has the capacity to describe the decrease of the elastic modulus and yield stress with the increasing temperature, as well as the change of hardening behaviors of the polycrystalline metals. The calculation process is simple and explicit, which makes it easy to implement into the applications.

关键词： Thermo-elasto-plasticity constitutive theory Yield stress Hardening behaviors Finite temperature

A new thermo-elasto-plasticity constitutive equation for crystals

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Science China(Physics,Mechanics & Astronomy) 2015年第5期58卷 99-108页

作者： CHEN Cen tang qiheng WANG TzuChiang State Key Laboratory of Nonlinear Mechanics Institute of Mechanics Chinese Academy of Sciences

Based on the crystal plasticity theory and interatomic potential, in this paper a new thermo-elasto-plasticity constitutive model is proposed to study the behavior of metal crystals at finite temperature. By applying the present constitutive model, the stress-strain curves under uniaxial tension at different temperatures are calculated for the typical crystal A1, and the calculated results are compared with the experimental results. From the comparisons, it can be seen that the present theory has the capability to describe the thermo-elasto-plastic behavior of metal crystals at finite temperature through a concise and explicit calculation process.

关键词： thermo-elasto.plasticity theory constitutive equation interatomic potential critical resolved shear stress hardening

EFFECT OF TEMPERATURE ON DISLOCATION EMISSION FROM CRACK TIP FOR BCC METAL MO

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Acta Mechanica Solida Sinica 1998年第3期11卷 189-198页

作者： tang qiheng Wang Tzuchiang Chinese Acad Sci Inst Mech LNM Beijing 100080 Peoples R China

The effect of thermally activated energy on the dislocationemission from a crack tip in BCC metal Mo is simulated in this *** on the correlative reference model on which the flexi- bledisplacement boundary scheme is introduced naturally, the simulationshows that as temperature in creases the critical stress intensityfactor for the first dislocation emission will decrease and the totalnumber of emitted dislocations increase for the same external *** dislocation velocity and exten- sive distance among partialdislocations are not sensitive to temperature.

关键词： correlative reference model flexible displacement boundary moleculardynamics

A continuum thermal stress theory for crystals based on interatomic potentials

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Science China(Physics,Mechanics & Astronomy) 2014年第2期57卷 208-217页

作者： LIU XiaoLei tang qiheng WANG TzuChiang State Key Laboratory of Nonlinear Mechanics Institute of MechanicsChinese Academy of Sciences

This paper presents a new continuum thermal stress theory for crystals based on interatomic *** effect of finite temperature is taken into account via a harmonic *** EAM potential for copper is adopted in this paper and verified by computing the effect of the temperature on the specific heat,coefficient of thermal expansion and lattice *** we calculate the elastic constants of copper at finite *** calculation results are in good agreement with experimental *** thermal stress theory is applied to an anisotropic crystal graphite,in which the Brenner potential is *** dependence of the thermodynamic properties,lattice constants and thermal strains for graphite is *** calculation results are also in good agreement with experimental data.

关键词： thermal stress theory interatomic potential thermal strain finite temperature

Thermodynamic properties and constitutive relations of crystals at finite temperature

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Science China(Physics,Mechanics & Astronomy) 2012年第6期55卷 918-926页

作者： tang qiheng WANG TzuChiang SHANG BaoShuang LIU Feng State Key Laboratory of Nonlinear Mechanics Institute of MechanicsChinese Academy of SciencesBeifing 100190China

The dynamics equation for each individual atom is established directly around the equilibrium state of the system of N atoms based on the inter-atomic potential energy of EAM *** the theory of lattice dynamics and periodical boundary condition,the 3N×3N stiffness matrix in eigen equations of vibration frequencies for a parallelepiped crystal is reduced to a 3n×3n matrix of eigen equations of vibration frequencies for a unit *** constitutive relation of the crystal at finite temperature is extracted based on the quantum-mechanical *** thermodynamic properties and the stress-strain relationships of crystal Cu with large plastic deformation at different temperatures are calculated,the calculation results agree well with experimental data.

关键词： lattice wave theory molecular dynamics thermodynamic properties constitutive model interatomic potential

Effects of Bamboo Fiber Length and Loading on Mechanical,Thermal and Pulverization Properties of Phenolic Foam Composites

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Journal of Bioresources and Bioproducts 2019年第1期4卷 51-59页

作者： qiheng tang Lu FANG Wenjing GUO Research Institute of Wood Industry Chinese Academy of ForestryBeijing 100091China College of Furnishings and Industrial Design Nanjing Forestry UniversityNanjing 210037China

In order to improve the mechanical properties and toughness of phenolic foams,a reinforcement method using two kinds of bamboo fibers was optimized with respect to the fiber *** compressive and flexural properties,thermal stability,friability and morphology of the phenolic foam composites were *** mechanical properties of the pristine foam and composites were evaluated by measuring the compressive *** results showed that the greatest mechanical properties were achieved by incorporating 2.5wt%of the reinforcement,and the compressive and flexural strengths of the two composites increased by 26.21%and 24.35%,respectively,compared with that of the pristine *** results of thermogravimetric testing demonstrated that the addition of bamboo fiber imparted better thermal stability to the phenolic foam,which was mainly attributed to the higher initial thermal decomposition temperature of the bamboo ***,the influences of both reinforcements on the thermal stability of the material were *** incorporation of bamboo fiber decreased the friability of the phenolic ***,the reduction in friability of the foam composites with longer lengths were higher than that in foams with shorter bamboo ***,the morphology and cell sizes of the fiber-reinforced phenolic foams were analyzed by scanning electron microscopy,the results indicated strong bonding between the fibers and phenolic matrix,and the incorporation of the bamboo fibers into the foam resulted in increased cell size of the ***,the thermal conductivity and flame resistance of the phenolic foams reinforced by the bamboo fibers were also measured.

关键词： phenolic foam bamboo fiber composite mechanical property microstructure

STRESS FIELD OF A DAMAGED MATERIAL NEAR THE CRACK TIP

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Acta Mechanica Sinica 1987年第3期3卷 231-238页

作者： tang qiheng Wang Tzuchiang (Institute of Mechanics,Academia Sinica) Institute of Mechanics Academia Sinica Taiwan

In this paper,a deformation theory of phsticity for damaged materials is *** expression for H near a crack tip is ***,the stress and strain fields near the cracktip are presented.

关键词： damaged materials deformation theory of plasticity asymptotic expression crack tip stress and strain fields

In-situ controllable synthesis of carbon dots for patterned ﬂuorescent wood ﬁlms rapid fabrication strategy

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Aggregate 2024年第3期5卷 362-373页

作者： Xueqi Chen Jie Zhang Lei Zhang qiheng tang Yongping Chen Wenjing Guo Liang Chang Wood Composites Laboratory Research Institute of Wood IndustryChinese Academy of ForestryBeijingP.R.China

Fluorescent-patterned materials are widely used in information storage and ***,preparing a patternedﬂuorescent display on a matrix currently requires a time-consuming(hours or even days)and complex multi-step ***,a rapid and mild technique developed for the in-situ controllable synthe-sis ofﬂuorescent nitrogen-doped carbon dots(NCDs)on eco-friendly transparent woodﬁlms(TEMPO-oxidized carboxyl woodﬁlm[TOWF])within a few min-utes was developed.A wood skeleton was employed as the carbon precursor for NCD synthesis as well as the matrix for the uniform and controlled distribution of ***,the in-situ synthesis mechanism for preparing NCDs in TOWF was *** resultingﬂuorescent woodﬁlms have excellent tensile strength(310.0015.57 MPa),high transmittance(76.2%),high haze(95.0%),UV-blocking±properties in the full ultraviolet(UV)range,andﬂuorescent performance that can be modiﬁed by changing the heating *** patterning was sim-ply achieved by regulating the in-situ NCD synthesis regions,and theﬂuorescent patterns were formed within 10 ***ﬂuorescent-patterned woodﬁlms can effec-tively store and encrypt information,and they can interact with external information through a transparent *** work provides a green and efﬁcient strategy for fabricatingﬂuorescent information storage and encryption materials.

关键词： carbon dots ﬂuorescent pattern information encryption in-situ synthesis woodﬁlm