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AN ADAPTIVE EFG-FE cOuPlING METHOD FOR THE NuMERIcAl SIMulATION OF ExTRuSION PROcESSES

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Acta Metallurgica Sinica(English letters) 2008年第5期21卷 380-388页

作者： l.c. liu x.H. Doug c.x. li National Die ＆ Mold cAD Engineering Research center Shanghai Jiaotong University Shanghai 200030 China

An adaptive EFG-FE coupling method is proposed and developed for the numerical simulation of lateral extrusion and forward-backward extrusion. Initially, the simulation has been implemented by using a conventional FE model. During the deforming process, mesh quality is checked at every incremental step. Distorted elements are automatically converted to EFG nodes, whereas, the less distorted elements are reserved. A new algorithm to generate EFG nodes and interface elements is presented. This method is capable of dealing with large deformation and has higher computational efficiency than using an EFG method wholly. Numerical results demonstrate that the adaptive EFG-FE coupling method has reasonable accuracy and is effective for local bulk metal forming such as extrusion processes.

关键词： Meshless method coupling method Numerical simulation Extrusion process

Mechanical properties of gas hydrate-bearing sediments during hydrate dissociation

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Acta Mechanica Sinica 2018年第2期34卷 266-274页

作者： x.H.Zhang D.S.luo x.B.lu l.l.liu c.l.liu Institute of Mechanics Chinese Academy of SciencesBeijing 100190China college of Engineering University of Chinese Academy of SciencesBeijing 100049China Key laboratory of Gas Hydrate Ministry of Land and ResourcesQingdao 266071China Qingdao Institute of Marine Geology Qingdao 266071China

The changes in the mechanical properties of gas hydrate-bearing sediments(GHBS) induced by gas hydrate(GH) dissociation are essential to the evaluation of GH exploration and stratum instabilities. Previous studies present substantial mechanical data and constitutive models for GHBS at a given GH saturation under the non-dissociated condition. In this paper, GHBS was formed by the gas saturated method, GH was dissociated by depressurization until the GH saturation reached different dissociation degrees. The stress–strain curves were measured using triaxial tests at a same pore gas pressure and different confining pressures. The results show that the shear strength decreases progressively by 30%–90% of the initial value with GH dissociation, and the modulus decreases by 50% –75%. Simplified relationships for the modulus, cohesion, and internal friction angle with GH dissociated saturation were presented.

关键词： Gas hydrate-bearing sediments Dissociation Mechanical properties Shear strength Triaxial test

Homotopy analysis solutions for the asymmetric laminar flow in a porous channel with expanding or contracting walls

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Acta Mechanica Sinica 2011年第2期27卷 208-214页

作者： x.-H. Si l.-c. Zheng x.-x. Zhang Y. chao Applied Science School University of Science and Technology Beijing 100083 Beijing China Department of Mechanical Engineering University of Science and Technology Beijing100083 Beijing China Research Institute of chemical Defense of the El.A 102205 Beijing China

In this paper, the asymmetric laminar flow in a porous channel with expanding or contracting walls is investigated. The governing equations are reduced to ordinary ones by using suitable similar transformations. Homotopy analysis method （HAM） is employed to obtain the expres- sions for velocity fields. Graphs are sketched for values of parameters and associated dynamic characteristics, especially the expansion ratio, are analyzed in detail.

关键词： Homotopy analysis method · Expanding or contracting wall · Asymmetric laminar flow · Porous channel · Expansion ratio

A Novel Melt Processing for Mg Matrix composites Reinforced by Multiwalled carbon Nanotubes

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Journal of Materials Science & Technology 2016年第12期32卷 1303-1308页

作者： H.l.Shi x.J.Wang c.l.Zhang c.D.li c.Ding K.Wu x.S.Hu School of Materials Science and Engineering Harbin Institute of Technology

carbon nanotubes（cNTs） reinforced Mg matrix composites were fabricated by a novel melt *** novel processing consisted of two courses：cNTs pre-dispersion and ultrasonic melt *** ball-milling was employed to pre-disperse cNTs on Zinc（Zn） *** cNT entanglements were well dispersed to single cNT or tiny clusters on Zn *** ultrasonic melt processing further dispersed cNTs in the Mg melt,especially tiny cNT ***,a uniform dispersion of cNTs was achieved in the as-cast *** extrusion further improved the distribution of *** increased both the strength and elongation of the matrix ***,the elongation of the matrix alloy was enhanced by 40%.Grain refinement and the pulling-out of cNTs resulted in the evident improvement of ductility for the composites.

关键词： Pre-dispersion carbon nanotubes Magnesium matrix composites ultrasonic

Machine learning guided automatic recognition of crystal boundaries in bainitic/martensitic alloy and relationship between boundary types and ductile-to-brittle transition behavior

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Journal of Materials Science & Technology 2021年第25期84卷 49-58页

作者： x.c.li J.x.Zhao J.H.cong R.D.K.Misra x.M.Wang x.l.Wang c.J.Shang collaborative Innovation center of Steel Technology University of Science and Technology BeijingBeijing 100083China Department of Metallurgical Materials and Biomedical EngineeringUniversity of Texas at El Paso500 W.University AvenueEl PasoTX 79968USA

Gradient boosting decision tree(GBDT)machine learning(Ml)method was adopted for the first time to automatically recognize and conduct quantitative statistical analysis of boundaries in bainitic microstructure using electron back-scatter diffraction(EBSD)*** spite of lack of large sets of EBSD data,we were successful in achieving the desired accuracy and accomplishing the objective of recognizing the *** with a low model accuracy ofusing Euler angles or axis-angle pair as characteristic features,the accuracy of the model was significantly enhanced to about 88%when the Euler angle was converted to overall misorientation angle(OMA)and specific misorientation angle(SMA)and considered as important *** this model,the recall score of prior austenite grain(PAG)boundary was~93%,high angle packet boundary(OMA>40°)was~97%,and block boundary was~96%.The derived outcomes of Ml were used to obtain insights into the ductile-to-brittle transition(DBTT)***,Ml modeling approach suggested that DBTT was not determined by the density of high angle grain boundaries,but significantly influenced by the density of PAG and packet *** study underscores that Ml has a great potential in detailed recognition of complex multi-hierarchical microstructure such as bainite and martensite and relates to material performance.

关键词： Machine learning Feature engineering Automatic recognition lath structure crystallography

Discovery of new MAx-phase-like layered ternary carbide V_(8)P_(6)c:crystal structure,thermal expansion,and elastic properties

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Journal of Materials Science & Technology 2024年第7期174卷 55-62页

作者： H.x.chen l.Sheng Z.l.Zhang x.c.Wen D.l.Yang x.Y.Ye P.Q.Dai School of Materials Science and Engineering Fujian University of TechnologyFuzhou 350118China Beijing Synchrotron Radiation Facility Institute of High Energy PhysicsChinese Academy of ScienceBeijing 100049China Fujian Provincial Key laboratory of Advanced Materials Processing and Application Fuzhou 350118China State Key laboratory of Structural chemistry Fujian Institute of Research on the Structure of MatterChinese Academy of SciencesFuzhou 350002China

Due to the laminated structure,MAx phases and MAx-phase-like compounds possess outstanding dam-age tolerance capability with good thermal/electrical conductivity and other charming functional prop-erties,showing a bright future for structural-functional ***,a new MAx-phase-like ternary car-bide V_(8)P_(6)c with layered characteristics was *** to the alternate stacking of hexagonal-arranged M/A/x atom layers in MAx phases,V_(8)P_(6)c has a layered structure formed by a repeated stacking of the slabs consisting of V_(6)c-octahedrons and VP 6-distorted-octahedrons in three-atomic layers *** thermal expansion anisotropy was revealed,with the thermal expansion coefficients(TEcs)along a-axis,c-axis,and the average value,equal toα_(a)=8.55(5)μK^(−1),α_(c)=10.23(5)μK^(−1),andα_(l)=9.14(5)μK^(−1),*** dilation along the c-axis was mainly dominated by out-plane V-P bonds be-tween layered *** to the pressure-dependent lattice parameters,the polycrystalline bulk modulus(B_(0)=185(9)GPa)and high compressibility anisotropy factor(B_(a)/B_(c)=1.64)was ***-while,the second-order elastic constants were calculated,and the elastic moduli,E=303 GPa,B=198 GPa,G=122 GPa,andν=0.246,were *** the weak connection between layer slabs by out-plane V1-P bond was revealed by the bond stiffness model,with a bond stiffness close to the M-A bond in MAx ***,good damage tolerance capability was predicted according to Paugh’s ratio(G/B=0.616)and cauchy pressure(P_(a)=0 GPa,P_(c)=-7.5 GPa),even better than those of typical MAx *** discovery of V_(8)P_(6)c provides a new member of MAx-phase-like damage-tolerant ceramic with relatively low density,moderate thermal expansion,and anisotropic compressibility,and the unique lay-ered structure is inspiring for exploring new layered ternary ceramics.

关键词： New ternary carbide MAx phase Thermal expansion Elastic constants Anisotropy

Observations on the Formation of ultrafine Ferrite Grain Size in Steels by Physical Simulation Routes

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Journal of Materials Science & Technology 2003年第Z1期19卷 112-114页

作者： l.x. Pan l.P. Karjalainen M. c. Somani university of Oulu Department of Mechanical Engineering P.O. Box 4200 FIN-90014 Oulu Finland University of Oulu Department of Mechanical Engineering P.O. Box 4200 FIN-90014 Oulu Finland University of Oulu Department of Mechanical Engineering P.O. Box 4200 FIN-90014 Oulu Finland

Some observations are reported on the simulation of two thermomechanical routes to produce ultrafine ferrite grainsize in steels. One c-Mn grade and Nb, Nb-Ti and Nb-high Ti bearing steels were used in the tests performed ona Gleeble simulator and a laboratory rolling mill. The routes included severe hot deformation of prior grain-refinedaustenite at the temperature close to Ar3 (DIF) and static recrystallization of fine-grained cold-rolled martensite(SRM). It was observed that the hot deformation induces the formation of ferrite above the Ar3 temperature of thesteel, but severe reductions are required for the complete transformation. Strain of 1.2 can result in about 70% offerrite with the grain size of about 1.4～2μm in all the studied steels. Similarly, in short annealing of cold-workedmartensite, the static recrystallization can also lead to a grain size of about 1.5 μm. The distribution of carbonvaries in the microstructures, carbon being in the second phase in the DIF route and in carbide particles in the SRMroute, which may have a significant influence on the mechanical properties and the thermal stability of ultrafine grainstructure.

关键词： ultrafine grain size, Steels, Physical simulation, Strain-induced ferrite, cold rolling and annealing

Microstructure and Mechanical Properties of Dissimilar Double-Side Friction Stir Welds Between Medium-Thick 6061-T6 Aluminum and Pure copper Plates

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Acta Metallurgica Sinica(English letters) 2022年第12期35卷 2027-2046页

作者： J.x.Tang l.Shi c.S.Wu M.x.Wu S.Gao MOE Key lab for liquid-Solid Structure Evolution and Materials Processing Institute of Materials JoiningShandong UniversityJinan 250061China State Grid Henan Electric Power Research Institute Zhengzhou 450052China School of Mechanical Engineering Qilu University of Technology(Shandong Academy of Sciences)Jinan250353China

It is difficult to achieve Al/cu dissimilar welds with good mechanical properties for medium-thick plates due to the inherent high heat generation rate at the shoulder-workpiece contact interface in conventional friction stir ***,doubleside friction stir welding is innovatively applied to join 12-mm medium-thick 6061-T6 aluminum alloy and pure copper dissimilar plates,and the effect of welding speeds on the joint microstructure and mechanical properties of Al/cu welds is systematically *** reveals that a sound Al/cu joint without macroscopic defects can be achieved when the welding speed is lower than 180 mm/min,while a nonuniform relatively thick intermetallic compound(IMc)layer is formed at the Al/cu interface,resulting in lots of local microcracks within the first-pass weld under the plunging force of the tool during friction stir welding of the second-pass,and seriously deteriorates the mechanical properties of the *** the increase of welding speed to more than 300 mm/min void defects appear in the joint,but the joint properties are still better than the welds performed at low welding speed conditions since a continuous uniform thin IMcs layer is formed at the Al/cu *** maximum tensile strength and elongation of Al/cu weld are,respectively,135.11 MPa and 6.06%,which is achieved at the welding speed of 400 mm/*** addition,due to the influence of welding distortion of the first-pass weld,the secondpass weld is more prone to form void defects than the first-pass weld when the same plunge depth is applied on both *** double-side friction stir welding is proved to be a good method for dissimilar welding of medium-thick Al/cu plates.

关键词： Double-side friction stir welding Medium-thick plate Dissimilar welding Microstructures Intermetallic compounds Mechanical properties

Morphology control and Optical Absorption Properties of Ag Nanoparticles by Ion Implantation

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Journal of Materials Science & Technology 2009年第5期25卷 669-672页

作者： G.x. cai F. Ren x.H. xiao l.x. Fan x.D. Zhou c.Z. Jiang Key laboratory of Acoustic and Photonie Materials and Devices of Ministry of Education Wuhan University Wuhan 430072 China

Ion implantation is a powerful method for fabricating nanoparticles in dielectric. For the actual application of nanoparticle composites, a careful control of nanoparticles has to be achieved. In this letter, the size, distribution and morphology of Ag nanoparticles are controlled by controlling the ion current density, ion implantation sequence and ion irradiation dose. Single layer Ag nanoparticles are formed by Ag^＋ ion implantation at current density of 2.5 μ^A/cm2. By Ag and cu ions sequential implantation, the size of single layer Ag nanoparticles increases. While, by cu and Ag ions sequential implantation, uniform Ag nanoparticles with wide distribution are formed. The morphology of Ag nanoparticles changes to hollow and sandwiched nanoparticles by cu^＋ ion irradiation to doses of 3×10^16 and 5×10^16 ions/cm^2. The optical absorption properties of Ag nanoparticles are also tailored by these ways.

关键词： Nanoparticles Ion implantation Transmission electron microscopy