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Effect of static annealing on superplastic behavior of a friction stir welded Ti-6Al-4V alloy joint and microstructural evolution during deformation

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Journal of Materials Science & Technology 2022年第35期130卷 112-123页

作者： c.l.Jia l.H.wu P.Xue D.R.Ni B.l.Xiao Z.Y.Ma Shi-changxu Innovation center for Advanced Materials Institute of Metal ResearchChinese Academy of SciencesShenyang 110016China School of Materials Science and Engineering University of Science and Technology of ChinaShenyang 110016China Key laboratory of Nuclear Materials and Safety Assessment Institute of Metal ResearchChinese Academy of SciencesShenyang 110016China

Structural integration is one of the most critical developing directions in the modern aerospace field,in which large-scale complex components of Ti alloys are proposed to be fabricated via the method of welding + superplastic ***,the undesired strain localization appeared during superplastic deformation of the entire joint has largely hindered the development of this *** our study,a combination process of friction stir welding(FSW) + static annealing+ superplastic deformation was first time proposed to eliminate severe local *** achieve this result,a fully fine lamellar structure was obtained in the nugget zone(NZ) via FSW,which was totally different from the mill-annealed structure in the base material(BM).After annealing at 900℃ for 180 min,the BM and NZ then exhibited the similar elongation of> 500% and similar flow stress at 900 ℃,3 × 10^(-3)s^(-1),which was the precondition for achieving uniform superplastic deformation in the entire ***,the different microstructures in the BM and NZ tended to become the similar equiaxed structure after deformation,which was the result of different microstructural evolution mechanisms in the NZ and *** the NZ,there was a static and dynamic spheroidization of the fully lamellar structure during the process,which could largely reduce the flow softening of the fully lamellar *** the BM,a new view of "langdon-cRSS theory"(cRSS,critical resolved shear stress) was proposed to describe the fragmentation of the coarse equiaxed structure,which established the relationship between grain boundary sliding and intragranular deformation during deformation.

关键词： Friction stir welding Titanium alloys Superplasticity Static annealing Microstructure

Substrate concentration effect on gene expression in genetic circuits with additional positive feedback

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Science china(Technological Sciences) 2018年第8期61卷 1175-1183页

作者： wu lulu WANG Pei lü JinHu Academy of Mathematics and Systems Science Chinese Academy of Sciences School of Mathematical Sciences University of Chinese Academy of Sciences School of Mathematics and Statistics Henan University School of Automation Science and Electrical Engineering State Key Laboratory of Software Development Environment and Beijing Advanced Innovation Center for Big Data and Brain Machine Intelligence Beihang University

In gene regulatory networks, gene regulation loops often occur with multiple positive feedback, multiple negative feedback and coupled positive and negative feedback forms. In above gene regulation loops, auto-activation loops are ubiquitous regulatory motifs. This paper aims to investigate a two-component dual-positive feedback genetic circuit, which consists of a double negative feedback circuit and an additional positive feedback loop(APFl). We study effect of substrate concentration on gene expression in the single and the networked systems with APFls, respectively. We find that substrate concentration can tune stochastic switch behavior in the signal system and then we explore relationship of substrate concentration with positive feedback strength in aspect of stochastic switch behavior. Furthermore, we also discuss gene expression and stochastic switch behavior in the networked systems with APFls. Based on analysis in the networked systems, we discover that genes express in some specific cells and do not express in the other cells when the expression achieves its steady state. These results can be used to well explain the character of regionalization in the expression of genes and the phenomenon of gene differentiation.

关键词： substrate concentration additional positive feedback loop stochastic switch behavior gene expression gene differ-entiation

Measurement and Prediction of Insertion Force for the Mosquito Fascicle Penetrating into Human Skin

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Journal of Bionic Engineering 2009年第2期6卷 143-152页

作者： X Q Kong c W wu State Key laboratory of Structural Analysis for Industrial Equipment Department of Engineering MechanicsDalian University of Technology

Mosquitoes are exceptional in their ability to pierce into human skin with a natural ultimate painless microneedle, named fascicle. Here the structure of the Aedes albopictus mosquito fascicle is obtained using a Scanning Electron Microscope (SEM), and the whole process of the fascicle inserting into human skin is observed using a high-speed video imaging technique. Direct measurements of the insertion force for mosquito fascicle to penetrate into human skin are reported. Results show that the mosquito uses a very low force (average 18 μN) to penetrate into the skin. This force is at least three orders of magnitude smaller than the reported lowest insertion force for an artificial microneedle with an ultra sharp tip to insert into the human skin. In order to understand the piercing mechanism of mosquito fascicle tip into human multilayer skin tissue, a numerical simulation is conducted to analyze the insertion process using a nonlinear finite element method. A good agreement occurs between the numerical results and the experimental measurements.

关键词： biomimetic microneedle mosquito fascicle mechanics penetration

Effect of Silver content on Microstructure and Properties of Brass/steel Induction Brazing Joint Using Ag-cu-Zn-Sn Filler Metal

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Journal of Materials Science & Technology 2011年第4期27卷 377-381页

作者： J. cao l.X. Zhang H.Q. Wang l.Z. wu J.c. Feng State Keylab of Advanced Welding Production Technology Harbin Instituteof Technology Harbin 150001 China center for composite Materials and Structures Harbin Institute of Technology Harbin 150001 China

The induction brazing of brass to steel using Ag-cu-Zn-Sn filler metal was investigated in this study. The influence of A8 content on the microstructure and properties were analyzed by means of optical microscopy, scanning electron microscopy and electron probe microanalysis. Defect free joint was achieved using Ag- cu-Zn-Sn filler metal. The microstructure of the joint was mainly composed of Ag-based solid solution and cu-based solid solution. The increase of A8 content and the cooling rate both led to the increase of the needle like eutectic structure. The tensile strength decreased with the increase of Ag content. The tensile strength at room temperature using Ag25cuZnSn filler metal reached 445 MPa. All fractures using Ag-cu-Zn-Sn filler metal presented ductile characteristic.

关键词： Induction brazing Brass Steel Microstructure Tensile strength

MIcROSTRUcTURAl STUDIES OF FRIcTION STIR WElDED AZ31 MAGNESIUM AllOY

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Acta Metallurgica Sinica(English letters) 2004年第5期17卷 747-753页

作者： H.Zhang S.B.lin l.wu J.c.Feng StateKeylab.ofAdvancedWeldingProductionTechnology HarbinInstituteofTechnologyHarbin150001China

Friction stir welding achieves the weld in solid phase by locally introducing frictional heating and plastic flow arising from rotation of the welding tool, which results in changes in the local microstructure of magnesium alloy. The purpose in the paper is to study the microstructures of friction stir welded AZ31 magnesium alloy. Residual microstructures, including dynamic re-crystallization zone and nugget structures have been systematically investigated utilizing optical microscopy (OM), scanning electric microscopy (SEM), transmission electron microscopy (TEM) with energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and micro-hardness. AZ31 magnesium alloy has been successfully friction stir welded and exhibits the variations of microstructure including dynamically recrystallized, equaxied grains in the weld nugget. Residual hardness in the nugget was found slightly lower than the parent but not too obvious.

关键词： friction stir welding AZ31magnesium alloy weld nugget thermo- mechanically affected zone microstructure

Regulation of thermoelastic properties of concave-packaged DNA adsorption films and its relevant microcantilever detection signals

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Acta Mechanica Sinica 2021年第4期37卷 705-711,I0004页

作者： c.X.wu N.H.Zhang c.Y.Zhang J.Z.wu School of Mechanics and Engineering Science Shanghai UniversityShanghai 200444China Shanghai Key laboratory of Mechanics in Energy Engineering Shanghai Institute of Applied Mathematics and MechanicsShanghai 200072China

The packing patterns have close correlation with the thermoelastic properties of DNA adsorption films and the relevant detection signals of *** this paper,we investigate the influence of packing patterns on the thermoelastic properties of DNA adsorption films,the detection signals of microcantilevers and their temperature ***,the Parsegian's empirical potential based on a mesoscopic liquid crystal theory is employed to describe the interaction energy among coarse-grained DNA cylinders;then,the thought experiment method and the force balance method of nonlinear elastic network nodes are combined to characterize the elastic modulus,prestress and thermal expansion coefficient of DNA adsorption films;finally,based on an effective macroscopic continuum model for DNA microbeam deformation,we study the microcantilever resonance frequency shifts caused by DNA adsorptions and the temperature effect on the microcantilever static deflections,*** show that,compared with the convex-packaged,the re-entrant honeycomb packing pattern endows DNA adsorption films with a larger adjustable range of the elastic modulus and prestress,so as to make DNA-microcantilevers having an enhanced dynamic detection signal whereas a weaker response to temperature *** results are expected to provide a new option for the regulation design of DNA composite materials and microbeam sensors.

关键词： DNA-microbeam Packaging pattern Elastic property Thermal expansion coefficient Detection signal

小世界、结构洞与城市创新的网络机制:来自长三角城市群的证据

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管理工程学报 2025年第2期39卷 14-26页

作者：袁燕吴妍杨大鹏浙江科技大学经济与管理学院浙江杭州310023 浙江金融职业学院电子商务与新消费研究院浙江杭州310018 中共浙江省委党校工商管理教研部浙江杭州311121

近年来,创新网络作为区域和城市创新驱动力的重要性得到了广泛关注。一些研究将网络关系视为知识在城市内和城市间传播的渠道,并通过网络分析视角洞察城市创新的结构和动态。然而,城市创新的网络机制,特别是数字经济发展背景下的数字赋... 详细信息

近年来,创新网络作为区域和城市创新驱动力的重要性得到了广泛关注。一些研究将网络关系视为知识在城市内和城市间传播的渠道,并通过网络分析视角洞察城市创新的结构和动态。然而,城市创新的网络机制,特别是数字经济发展背景下的数字赋能城市创新能力提升机制还有待进一步研究。本文利用长三角城市群26个城市2009年—2018年联合申请专利数据构建了城市创新网络,探讨了网络结构属性——小世界和结构洞对城市创新能力的影响。结果表明,小世界与城市创新能力呈“倒U型”关系,数字经济发展水平正向调节了二者之间的“倒U型”关系,结构洞对城市创新能力具有正向影响。本文厘清了创新网络结构对城市创新能力的影响,回应了以往研究关于小世界和结构洞对创新影响的理论争议,为区域创新的理论研究提供了新颖性观点,深化了对城市群创新发展规律的认识,对推进中国城市群协同创新具有重要意义。

关键词：创新网络城市创新能力专利合作数字经济

Microstructure and Properties of In Situ Si and Fe-rich Particles Reinforced Al Matrix composites Assisted with Ultrasonic Vibration

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Acta Metallurgica Sinica(English letters) 2014年第5期27卷 862-868页

作者： Shulin lü Shusen wu chong lin Ping An State Key laboratory of Materials Processing and Die & Mould Technology Huazhong University of Science and Technology

In this research, the in situ Si and Fe-rich particles reinforced Al matrix composites were fabricated by rheocasting （Rc） process assisted with ultrasonic vibration （USV）. After USV treatment, the polygonal primary Si crystals were refined into particles with average diameter of about 15-23 μm, and the fraction of primary Si declined to about 5.4-6.5 vol%. The coarse plate-like δ-Al4（Fe,Mn）Si2 phase was transformed into fine particles with average diameter of about 17-20 μm, and the fraction of particle-like Fe-bearing particles is about 3.6-5.3 vol%. The ultimate tensile strength of the Rc composites increases with the increase of Fe content at 350 ℃. The increase of the elevated temperature strength of the composites is mainly attributed to the refinement of δ-Al4（（Fe,Mn）Si2 phase and the increase of the volume fraction of the Fe-bearing compounds. compared with the composites without USV, the Rc composites assisted with USV have thinner mechanical mixing layer in wear test, which corresponds to smaller wear rate.

关键词： Fe-bearing phase Metal matrix composites Microstructure Properties Ultrasound

Effects of high-pressure rheo-squeeze casting on the Fe-rich phases and mechanical properties of Al-17Si-(1,1.5)Fe alloys

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International Journal of Minerals,Metallurgy and Materials 2018年第9期25卷 1018-1026页

作者： chong lin Shu-sen wu Shu-lin lü Ping An He-bao wu State Key laboratory of Materials Processing and Die & Mould Technology Huazhong University of Science and Technology Hubei Provincial Key laboratory of chemical Equipment Intensification and Intrinsic Safety Wuhan Institute of Technology

The effects of high pressure rheo-squeeze casting(HPRc) on the Fe-rich phases(FRPs) and mechanical properties of Al-17 Si-(1,1.5)Fe alloys were investigated. The alloy melts were first treated by ultrasonic vibration(UV) and then formed by high-pressure squeeze casting(HPSc). The FRPs in the as-cast HPSc Al-17 Si-1 Fe alloys only contained a long, needle-shaped β-Al5 Fe Si phase at 0 MPa. In addition to the β-Al5 Fe Si phase, the HPSc Al-17 Si-1.5 Fe alloy also contained the plate-shaped δ-Al4 Fe Si2 phase. A fine, block-shaped δ-Al4 Fe Si2 phase was formed in the Al-17 Si-1 Fe alloy treated by UV. The size of FRPs decreased with increasing pressure. After UV treatment, solidification under pressure led to further refinement of the FRPs. considering alloy samples of the same composition, the ultimate tensile strength(UTS) of the HPRc samples was higher than that of the HPSc samples, and the UTS increased with increasing pressure. The UTS of the Al-17 Si-1 Fe alloy formed by HPSc exceeded that of the Al-17 Si-1.5 Fe alloy formed in the same manner under the same pressure. conversely, the UTS of the Al-17 Si-1 Fe alloy formed by HPRc decreased to a value lower than that of the Al-17 Si-1.5 Fe alloy formed in the same manner.

关键词： high pressure rheo-squeeze casting Al-17Si-(1,1.5)Fe alloys Fe-rich phases mechanical properties