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On the Martensitic Transformation Temperatures and Mechanical Properties of NiTi Alloy Manufactured by Selective Laser Melting: Effect of Remelting

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Acta Metallurgica Sinica(English Letters) 2021年第9期34卷 1223-1233页

作者： Jian-Bin Zhan yan-jin Lu jin-Xin Lin College of Chemistry and Materials Science Fujian Normal UniversityFuzhou 350007China Key Laboratory of Optoelectronic Materials Chemistry and Physics Fujian Institute of Research on the Structure of MatterChinese Academy of SciencesFuzhou 350002China

In this study, the infl uence of laser remelting on the relative density, martensitic transformation temperatures(MTTs), and mechanical properties of a NiTi alloy fabricated by selective laser melting(SLM) at a laser power between 15 and 75 W were investigated. A relative alloy density of approximately 99% was achieved in the power range of 45–60 W corresponding to the forming energy density range of 65.45–87.27 J/mm3. The MTTs increased with the increase in the energy density;thus, the initial contents of the B2 and B19′ phases of the SLM-produced NiTi alloy can be tailored by the utilized technique. However, the number of defects such as metallurgical pores and microcracks considerably increased at higher energy densities(> 87.27 J/mm3). Interestingly, the concentration of these defects was reduced by remelting in the energy density range of 21.82–65.45 J/mm3, while the alloy relative density increased to 99.7% ± 0.1% at a remelting energy density of 65.45 J/mm3. The results of tensile testing revealed that when the remelting energy was 75% or 100% of the forming energy input, the ultimate tensile strength and elongation of the alloy significantly increased. Therefore, the remelting strategy represents a promising route for manufacturing NiTi alloys with desired MTT ranges and mechanical properties.

关键词： Selective laser melting NiTi alloy Laser remelting Martensitic transformation temperature

Lower Bounds of Distance Laplacian Spectral Radii of n-Vertex Graphs in Terms of Fractional Matching Number

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Journal of the Operations Research Society of China 2023年第1期11卷 189-196页

作者： jin yan yan Liu Xue-Li Su School of Mathematical Sciences South China Normal UniversityGuangzhou510631GuangdongChina

A fractional matching of a graph G is a function f: E(G)→[0,1] such that for each vertex v, ∑eϵΓG(v)f(e)≤1.. The fractional matching number of G is the maximum value of ∑e∈E(G)f(e) over all fractional matchings f. Tian et al. (Linear Algebra Appl 506:579–587, 2016) determined the extremal graphs with minimum distance Laplacian spectral radius among n-vertex graphs with given matching number. However, a natural problem is left open: among all n-vertex graphs with given fractional matching number, how about the lower bound of their distance Laplacian spectral radii and which graphs minimize the distance Laplacian spectral radii? In this paper, we solve these problems completely.

关键词： Distance Laplacian Spectral radius Fractional matching number

High-order Soliton Matrix for the Third-order Flow Equation of the Gerdjikov-Ivanov Hierarchy Through the Riemann-Hilbert Method

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Acta Mathematicae Applicatae Sinica 2024年第2期40卷 358-378页

作者： jin-yan ZHU Yong CHEN School of Mathematical Sciences Shanghai Key Laboratory of Pure Mathematics and Mathematical PracticeEast China Normal UniversityShanghai 200062China College of Mathematics and Systems Science Shandong University of Science and TechnologyQingdao 266590China

The Gerdjikov-Ivanov(GI)hierarchy is derived via recursion operator,in this article,we mainly investigate the third-order flow GI *** the framework of the Riemann-Hilbert method,the soliton matrices of the third-order flow GI equation with simple zeros and elementary high-order zeros of Riemann-Hilbert problem are constructed through the standard dressing *** advantage of this result,some properties and asymptotic analysis of single soliton solution and two soliton solution are discussed,and the simple elastic interaction of two soliton are *** with soliton solution of the classical second-order flow,we find that the higher-order dispersion term affects the propagation velocity,propagation direction and amplitude of the ***,by means of a certain limit technique,the high-order soliton solution matrix for the third-order flow GI equation is derived.

关键词： Gerdjikov-Ivanov hierarchy third-order flow GI equation Riemann-Hilbert method high-order soliton

Kinetostatic Modeling and Analysis of an Exechon Parallel Kinematic Machine(PKM) Module

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Chinese Journal of Mechanical Engineering 2016年第1期29卷 33-44页

作者： ZHAO yanqin jin yan ZHANG Jun School of Mechanical Engineering Anhui University of Technology School of Mechanical and Aerospace Engineering Queen's UniversityBelfastUK State Key Laboratory for Manufacturing Systems Engineering Xi'an Jiaotong University

As a newly invented parallel kinematic machine（PKM）, Exechon has found its potential application in machining and assembling industries due to high rigidity and high dynamics. To guarantee the overall performance, the loading conditions and deflections of the key components must be revealed to provide basic mechanic data for component design. For this purpose, a kinetostatic model is proposed with substructure synthesis technique. The Exechon is divided into a platform subsystem, a fixed base subsystem and three limb subsystems according to its structure. By modeling the limb assemblage as a spatial beam constrained by two sets of lumped virtual springs representing the compliances of revolute joint, universal joint and spherical joint, the equilibrium equations of limb subsystems are derived with finite element method（FEM）. The equilibrium equations of the platform are derived with Newton＇s 2nd law. By introducing deformation compatibility conditions between the platform and limb, the governing equilibrium equations of the system are derived to formulate an analytical expression for system＇s deflections. The platform＇s elastic displacements and joint reactions caused by the gravity are investigated to show a strong position-dependency and axis-symmetry due to its kinematic and structure features. The proposed kinetostatic model is a trade-off between the accuracy of FEM and concision of analytical method, thus can predict the kinetostatics throughout the workspace in a quick and succinct manner. The proposed modeling methodology and kinetostatic analysis can be further expanded to other PKMs with necessary modifications, providing useful information for kinematic calibration as well as component strength calculations.

关键词： parallel kinematic machine substructure synthesis kinetostatic stiffness Exechon

Microstructure evaluation of shear bands of microcutting chips in AA6061 alloy under the mechanochemical effect

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Journal of Materials Science & Technology 2021年第32期91卷 178-186页

作者： Jiayi Zhang yan jin Lee Hao Wang Department of Mechanical Engineering Faculty of EngineeringNational University of Singapore9 Engineering Drive 1Singapore 117575Singapore

The mechanochemical effect on the microcutting of AA6061 alloy is studied through characterization on the chip. A pronounced reduction of machining forces and chip thickness was observed with mechanochemical effect during microcutting. Furthermore, electron backscattered diffraction(EBSD) and transmission electron microscopy(TEM) observations were performed on the chips and shear bands. The result reveals much coarser grains(24.6 μm in size) in the surfactant-affected chip than that in the surfactant-free chip(13.5 μm). Different grain orientations are induced by microcutting. {100} and{110} grain orientations are majority for surfactant-free chip, and {110} and {100}dominate most for all grain orientations for surfactant-affected chip. Additionally, since less localized shear strain and lower temperature are generated inside the shear band with mechanochemical effect,almost no recrystallization phenomena can be observed in this region. TEM analysis shows that fewer subgrains and dislocations could be observed inside the shear band of the surfactant-affected chip in comparison with the surfactant-free chip. Based on the high-resolution transmission electron microscopic(HRTEM) observations, dislocations were observed at the atomic scale. The results show that the main dislocation motion mode in shear bands of surfactant-free and surfactant-affected chips are dislocation climb and dislocation glide, respectively.

关键词： Mechanochemical effect Microcutting Shear band Chip formation Dislocation

Disjoint Cliques in Claw-free Graphs

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Acta Mathematicae Applicatae Sinica 2018年第1期34卷 19-34页

作者： Su-yun JIANG jin yan School of Mathematics Shandong University

A graph is said to be claw-free if it does not contain an induced subgraph isomorphic to K_（1,3）. Let s and k be two integers with 0≤s≤k and let G be a claw-free graph of order n. In this paper, we investigate clique partition problems in claw-free graphs. It is proved that if n≥3 s ＋4（k-s） and d（x）＋ d（y）≥n-2 s ＋2 k ＋1 for any pair of non-adjacent vertices x, y of G, then G contains s disjoint K3 s and k-s disjoint K4 s such that all of them are disjoint. Moreover, the degree condition is sharp in some cases.

关键词： claw-free graphs disjoint clique degree condition

On 2-Factors with Prescribed Properties in a Bipartite Graph

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Acta Mathematica Sinica,English Series 2006年第4期22卷 1115-1120页

作者： jin yan Gui Zhen LIU School of Mathematics and Systems Science Shandong University Jinan 250100 P. R. China

Liu and yan gave the degree condition for a balanced bipartite graph G = （V1, V2; E） to have k vertex-disjoint quadrilaterals containing any given k independent edges e1,……, ek of G, respectively. They also conjectured that for any k independent edges e1,……, ek of G, G has a 2-factor with k cycles C1, C2, ……, Ck with respect to {e1, e2,……, ek} such that k - 1 of them are quadrilaterals. In this paper, we prove this conjecture.

关键词： Bipartite graph Vertex-disjoint Quadrilateral 2-Factor

On Disjoint Cycles of the Same Length in Tournaments

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Acta Mathematicae Applicatae Sinica 2022年第2期38卷 271-281页

作者： YUN WANG jin yan SHUO ZHU School of Mathematics Shandong UniversityJinan 250100China

A tournament is an orientation of the complete *** form perhaps the most interesting class of digraphs and it has a great potential for *** provide a model of the statistical technique called the method of paired comparisons and they have also been studied in connection with sociometric relations in small *** this paper,we investigate disjoint cycles of the same length in *** 2010,Lichiardopol conjectured that for given integers l≥3 and k≥1,any tournament with minimum out-degree at least(l-1)k-1 contains k disjoint l-cycles,where an l-cycle is a cycle of order ***-Jensen et *** the conjecture for l=3 and Ma et *** that it also holds for l≥*** paper provides a proof of the conjecture for the case of 9≥l≥4.

关键词： tournaments minimum out-degree disjoint cycles

Experimental investigation of the effect of Reynolds number on flow structures in the wake of a circular parachute canopy

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Acta Mechanica Sinica 2014年第3期30卷 361-369页

作者： Zhe-yan jin Sylvio Pasqualini Bo Qin School of Aerospace Engineering and Applied Mechanics Tongji University Institute of Unmanned Aircraft System Beihang University

In the present study, an experimental study was conducted to characterize the effect of Reynolds number on flow structures in the turbulent wake of a circular parachute canopy by utilizing stereoscopic particle image velocime- try （Stereo-PIV） technique. The parachute model tested in the present study was attached by 28 nylon suspension lines and placed horizontally at the test section center of the wind tunnel. The obtained results showed that with the in- crease of Reynolds number, the intensities of the vortices near the downstream region of the canopy skirt were found to increase accordingly. However, the increase of Reynolds number did not result in a significant change in ensemble- averaged normalized x-component of the velocity, ensembleaveraged normalized vorticity, normalized Reynolds stress, and normalized turbulent kinetic energy distributions in the turbulent wake of the circular parachute canopy. The obtained results are very useful to further our understanding about the unsteady aerodynamics in the wake of flexible circular parachute canopies and to constitute a reference for CFD computation.

关键词： Stereo-PIV Circular parachute - Canopy Flexible Turbulent wake