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THE RATE-INDEPENDENT CONSTITUTIVE MODELING FOR POROUS AND MULTI-PHASE nanocrystalline materials

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Acta Mechanica Solida Sinica 2007年第1期20卷 13-20页

作者： Zhou Jianqiu Li Yunnling Zhang Zhenzhong Department of Mechanical Engineering Nanjing University of Technology Nanjing 210009 China Department of Material Science and Engineering Nanjing University of Technology Nanjing 210009 China

To determine the time-independent constitutive modeling for porous and multi- phase nanocrystalline materials and understand the effects of grain size and porosity on their mechanical behavior, each phase was treated as a mixture of grain interior and grain bound- ary, and pores were taken as a single phase, then Budiansky＇s self-consistent method was used to calculate the Young＇s modulus of porous, possible multi-phase, nanocrystalline materials, the prediction being in good agreement with the results in the literature. Further, the established method is extended to simulate the constitutive relations of porous and possible multi-phase nanocrystalline materials with small plastic deformation in conjunction with the secant-moduli approach and iso-strain assumption. Comparisons between the experimental grain size and porosity dependent mechanical data and the corresponding predictions using the established model show that it appears to be capable of describing the time-independent mechanical behaviors for porous and multi-phase nanocrystalline materials in a small plastic strain range. Further discussion on the modification factor, the advantages and limitations of the model developed were present.

关键词： nanocrystalline materials constitutive modeling multi-phase porosity plastic deformation

Is the Crystalline Lattice Structure in nanocrystalline materials Different from the Perfect Crystal Lattice?

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Journal of materials Science & Technology 1993年第6期9卷 419-422页

作者： Ke LU National Key Laboratory for RSA,Institute of Metal Research,Academia Sinica,Shenyang,110015,ChinaManling SUI Department of materials Science and Engineering,Northeastern University,Shenyang 110006,China

A thermodynamic analysis of the ultrafine crystallites in nanocrystalline materials was presented in this *** was deduced that the structure of the nm-sized crystalline grains is different from the perfect crystal lattice,characterized by two possible structure changes;supersaturation of alloy ele- ments and crystal lattice distortion resulted from supersaturation of *** experimental ev- idences in the literature,which are in agreement of the thermodynamic consideration,indicate that the structure changes in the nm-sized crystallite seems to be a consequential feature of the nanocrystalline materials.

关键词： nanocrystalline materials crystal lattice thermodynamics

Mechanical model for yield strength of nanocrystalline materials under high strain rate loading

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Mechanical model for yield strength of nanocrystalline mater...

Rate dependent rheological stress-strain behavior of porous nanocrystalline materials

The 9th National Conference on Rheology

作者：朱荣涛周剑秋马璐张振忠 School of Mechanical Engineering Nanj ing University of Technology School of Mechanical Engineering Nanjing University of Technology School of materials Science and Engineering Nanjing University of Technology

＜正＞To understand the high strain rate deformation mechanism and determine the grain size,strain rate and porosity dependent yield strength of nanocrystalline materials,a new mechanical model based on the deformation mechanism of nanocrystalline materials under high strain rate loading was *** a first step of the research,the yield behavior of the nanocrystalline materials under high strain rate loading was mainly concerned in the model and uniform deformation was assumed for simplification. nanocrystalline materials were treated as composites consisting of grain interior phase and grain boundary phase,and grain interior and grain boundary deformation mechanisms under high strain rate loading were analyzed,then Voigt model was applied to coupling grain boundary constitutive relation with mechanical model for grain interior phase to describe the overall yield mechanical behavior of nanocrystalline *** predictions by the developed model on the yield strength of nanocrysatlline materials at high strain rates show good agreements with various experimental *** discussion was presented for calculation results and relative experimental observations.

关键词： nanocrystalline materials deformation mechanism modeling yield strength high strain rate

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Rate dependent rheological stress-strain behavior of porous ...

Enhanced Hydrogen Embrittlement Resistance via Cr Segregation in nanocrystalline Fe-Cr Alloys

The 9th National Conference on Rheology

作者：李慧周剑秋 School of Mechanical and Power Engineering Nanjing University of Technology

＜正＞To completely understand the rate-dependent stress-strain behavior of the porous nanocrystalline materials,it is necessary to formulate a constitutive model that can reflect the complicated experimentally observed stress-strain relations of nanocrystaUine *** nanocrystalline materials consisting grain interior and grain boundary are considered as viscoplastic and porous materials for the reasons that their mechanical deformation is commonly governed by both dislocation glide and diffusion,and pores commonly exist in the nanocrystalline materials.A constitutive law of the unified theory reflecting the stress-strain relations was established and verified by experimental data of bulk nanocrystalline Ni prepared by hydrogen direct current arc plasma evaporation method and hot *** effect of the evolution of porosity on stress-strain relations was taken into account to make that the predicted results can keep good agreements with the corresponding experimental results.

关键词： stress-strain porous nanocrystalline materials rate dependent porosity

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Acta Metallurgica Sinica(English Letters) 2023年第12期36卷 1925-1935页

作者： Linshuo Dong Feiyang Wang Hong-Hui Wu Mengjie Gao Penghui Bai Shuize Wang Guilin Wu Junheng Gao Xiaoye Zhou Xinping Mao Beijing Advanced Innovation Center for materials Genome Engineering Innovation Research Institute for Carbon NeutralityUniversity of Science and Technology BeijingBeijing 100083China Institute of Steel Sustainable Technology Liaoning Academy of MaterialsShenyang 110004China Department of materials Science and Engineering Shenzhen MSU-BIT UniversityShenzhen 518172China

Hydrogen is a clean fuel with numerous sources,yet the hydrogen industry is plagued by hydrogen embrittlement(HE)issues during the storage,transportation,and usage of hydrogen *** can compromise material performance during service,leading to significant safety hazards and economic *** the current work,the influence of element Cr on the HE resistance of nanocrystalline Fe-Cr alloys under different hydrogen concentrations and strain rates was *** hybrid Monte Carlo(MC)and molecular dynamics(MD)simulations,it was found that Cr atoms were segregated at grain boundaries(GB)and inhibited the GB ***,Cr segregation improved the strength and plasticity of the nanocrystalline Fe-Cr alloys,especially the HE ***,the Cr segregation reduced the diffusion coefficient of hydrogen and inhibited hydrogen-induced *** work provided new insight into the development of iron-based alloys with high HE resistance in the future.

关键词： Hydrogen embrittlement Molecular dynamics simulations Cr segregation Grain boundary nanocrystalline materials

Improving the incorporation of indium component for InGaN-based green LED through inserting photonic crystalline in the GaN layer

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Journal of Semiconductors 2022年第7期43卷 84-88页

作者： Yunqi Li Xinwei Wang Ning Zhang Xuecheng Wei Junxi Wang Institute of First Medical Center Chinese PLA General HospitalBeijing 100853China State Key Laboratory of Solid-State Lighting Institute of SemiconductorsChinese Academy of SciencesBeijing 100083China

We report on the effect of inserted photonic crystalline(Ph-C) in the GaN epitaxial layer on the incorporation of the indium component for the InGaN-based green LED. The adoption of Ph-C in the GaN layer shifted the Raman peak value of E2mode of GaN to lower frequency and resulted in a tensive stress relief. The stress relief can be attributed to strained lattices restoring in the matrix of Ph-C and the GaN pseudo-epitaxy over the air-void of the Ph-C. Moreover, the HRXRD rocking curves and AFM results show that the insertion of Ph-C also improves the crystal quality. With the inserted Ph-C, the indium component in the multiple quantum wells of the green LED(Ph-C LED) was enhanced. This resulted in a 6-nm red-shift of the peak wavelength. Furthermore, the LOP of the Ph-C LED was enhanced by 10.65% under an injection current of 20 mA.

关键词： epitaxial growth nanocrystalline materials semiconductors Raman stress relief X-ray techniques

Fabrication of a Gradient Nano-/Micro-structured Surface Layer on an Al–Si Casting Alloy by Means of Ultrasonic–Electropulsing Coupling Rolling Process

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Acta Metallurgica Sinica(English Letters) 2018年第12期31卷 1258-1264页

作者： Xiao-Pei Li Song-Zhu Kure-Chu Toru Ogasawara Hitoshi Yashiro Hai-Bo Wang Zi-Zhen Xu Xiao-Hui Li Guo-Lin Song Guo-Yi Tang Advanced materials Institute Graduate School at ShenzhenTsinghua University School of materials Science and Engineering Tsinghua University Department of Chemistry and Bioengineering Iwate University

By using a novel surface modification technique named ultrasonic-electropulsing coupling rolling （UECR） process on an Al-Si casting alloy rod, the surface of material was smoothened significantly. Meanwhile, a strengthened layer with agradient change in hardness was obtained in the outer surface, corresponding to a homogeneous gradient nano-/micro-structure. The thickness of nanometer-thick laminated structures was at least 40 μm, which was much thicker thanconventional ultrasonic rolling process. During UECR, the formation of the well-defined nanocrystalline structure wasattributed to the high strain rate and simultaneous annealing process realized by ultrasonic impact and electropulsingtreatment.

关键词： nanocrystalline materials Indentation and hardness Al-Si alloy Microstructure

Brittle-ductile behavior of a nanocrack in nanocrystalline Ni:A quasicontinuum study

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Chinese Physics B 2012年第9期21卷 196-203页

作者：邵宇飞杨鑫赵星王绍青 Institute of Applied Physics and Technology Department of General StudiesLiaoning Technical University Department of Mathematics and Physics Liaoning University of Technology Shenyang National Laboratory for materials Science Institute of Metal ResearchChinese Academy of Sciences

The effects of stacking fault energy, unstable stacking fault energy, and unstable twinning fault energy on the fracture behavior of nanocrystalline Ni are studied via quasicontinuum simulations. Two semi-empirical potentials for Ni are used to vary the values of these generalized planar fault energies. When the above three energies are reduced, a brittle-to-ductile transition of the fracture behavior is observed. In the model with higher generalized planar fault energies, a nanocrack proceeds along a grain boundary, while in the model with lower energies, the tip of the nanocrack becomes blunt. A greater twinning tendency is also observed in the more ductile model. These results indicate that the fracture toughness of nanocrystalline face-centered-cubic metals and alloys might be efficiently improved by controlling the generalized planar fault energies.

关键词： atomistic simulations nanocrystalline materials fracture grain boundaries

Structural and dielectric properties of doped ferrite nanomaterials suitable for microwave and biomedical applications

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Progress in Natural Science:materials International 2015年第3期25卷 419-424页

作者： Imran Sadiq Shahzad Naseem Muhammad Naeem Ashiq M.A.Khan Shanawer Niaz M.U.Rana Centre of Excellence in Solid State Physics University of the Punjab Institute of Chemical Sciences Bahauddin Zakariya University Department of Physics BUITEMS 4. Department of Physics University of Sargodha

The sol-gel auto-combustion method was adopted to synthesize nanomaterials of single-phase X-type hexagonal ferrites with the composition of Sr;Gd;Ni;Fe;Cd;O;（x=0.00,0.02,0.04,0.06,0.08,0.10 and y = 0,0.1,0.2,0.3,0.4,0.5）.The structural properties were carried out by XRD analysis and the lattice parameters show variation with the doping of *** average particle size measured by TEM was in the range of 8-10 nm which is beneficial in obtaining suitable signal-to-noise ratio in recording media and biomedical *** room temperature resistivity enhanced with the increase of the dopant *** increase in resistivity indicates that the synthesized materials can be considered good for the formation of the multilayer chip inductors（MLCIs） as well as for the reduction of eddy current *** dielectric constant decreased with the increase in the frequency which is the general reported trend of the hexagonal ferrites and can be explained on the basis of Koop’s theory and Maxwell-Wagner *** abnormal dielectric behavior indicates the formation of small polarons in the *** maximum value of tangent loss at low frequencies reflects the application of these materials in medium frequency devices（MF）.

关键词： Sol–gel nanocrystalline materials Thermal properties Electrical properties Dielectric properties