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size effect on the microstructure, phase transformation behavior, and mechanical properties of NiTi shape memory alloys fabricated by laser powder bed fusion

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Journal of Materials Science & Technology 2023年第26期157卷 200-212页

作者： Hao Jiang Xiebin Wang Rui Xi Guichuan Li Huiliang Wei Jiangwei Liu Bo Zhang Sergey Kustov Kim Vanmeensel Jan Van Humbeeck Guoqun Zhao Key Laboratory for Liquid-Solid Structural Evolution and Processing of Materials(Ministry of Education) Shandong UniversityJinan 250061China Department of Materials Engineering University of Leuven(KU Leuven)Heverlee B3001Belgium School of Mechanical Engineering Nanjing University of Science and TechnologyNanjing 210094China School of Energy and Power Engineering Shandong UniversityJinan 250061China Shandong Institute of Medical Device and Pharmaceutical Packaging Inspection Jinan 250101China Departament de Física Universitat de les Illes BalearsCra Valldemossa km 7.5Palma de Mallorca E07122Spain

In this work,NiTi samples with different thicknesses(0.15-1.00 mm)were fabricated by laser powder bed fusion(LPBF)under variable scanning speeds(500-1200 mm s^(-1)).The densification behavior,phase transformation behavior,and mechanical properties of the sample with different thicknesses are *** results indicate a strong size effect in the LPBF-fabricated NiTi *** decrease of the sample thickness results in(i)the increase of porosity,(ii)the decrease of the number of adhered NiTi powder particles at the surface,(iii)the monotonous decrease of the martensitic transformation temperatures(MTTs),and(iv)the decrease of the shape recovery *** influence of sample thickness on the melt-pool behavior,and thus the microstructure and performance of NiTi alloys are *** is suggested that the melt-pool is deeper and narrower in the thin samples than in the thick *** conclude that,apart from the LPBF process conditions,the sample dimensions have also to be considered to fabricate NiTi structures with predictable properties.

关键词： Shape memory alloy NiTi Additive manufacturing Laser powder bed fusion size effect

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Insights into the size effect of ZnCr_(2)O_(4)spinel oxide in composite catalysts for conversion of syngas to aromatics

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Green Energy & Environment 2023年第2期8卷 530-537页

作者： Yi Fu Youming Ni Wenhao Cui Xudong Fang Zhiyang Chen Zhaopeng Liu Wenliang Zhu Zhongmin Liu National Engineering Laboratory for Methanol to Olefins Dalian National Laboratory for Clean EnergyDalian Institute of Chemical PhysicsChinese Academy of SciencesDalian116023LiaoningChina University of Chinese Academy of Sciences Beijing100049China

Direct conversion of syngas to aromatics(STA)over oxide-zeolite composite catalysts is promising as an alternative method for aromatics ***,the structural effect of the oxide component in composite catalysts is still ***,we investigate the size effect by selecting ZnCr_(2)O_(4)spinel,as a probe oxide,mixing with H-ZSM-5 zeolite as a composite catalyst for STA *** CO conversion,aromatics selectivity and space-time yield(STY)of aromatics are all significantly improved with the crystal size of ZnCr_(2)O_(4)oxide decreases,which can mainly attribute to the higher oxygen vacancy concentration and thus the rapid generation of more C1oxygenated intermediate *** on the understanding of the size-performance relationship,ZnCr_(2)O_(4)-400 with a smaller size mixing with H-ZSM-5 can achieve32.6%CO conversion with 76%aromatics *** STY of aromatics reaches as high as 4.79 mmol g_(cat)^(-1)h^(-1),which outperforms the previously reported some typical *** study elucidates the importance of regulating the size of oxide to design more efficient oxidezeolite composite catalysts for conversion of syngas to value-added chemicals.

关键词： size effect Syngas conversion Aromatics ZnCr_(2)O_(4)oxide H-ZSM-5 zeolite

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Strong size effect on deformation twin-me diate d plasticity in body-centered-cubic iron

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Journal of Materials Science & Technology 2023年第13期144卷 235-242页

作者： Ligong Zhao Guoxujia Chen He Zheng Shuangfeng Jia Kaixuan Li Renhui Jiang Lei Li Ying Zhang Huayu Peng Peili Zhao Ziyang Huang Jianbo Wang School of Physics and Technology Center for Electron MicroscopyMOE Key Laboratory of Artificial Micro-and Nano-structuresand Institute for Advanced StudiesWuhan UniversityWuhan 430072China Suzhou Institute of Wuhan University SuzhouJiangsu 215123China Wuhan University Shenzhen Research Institute ShenzhenGuangdong 518057China

Deformation twinning serves as an important mode of plastic dissipation processes in nanoscale body-centered cubic(BCC)metals,but its origin and spatio-temporal features are ***,applying in situ tensile experiments,we report a strong size effect on mediating the twinning behaviors and twin boundary(TB)-dislocation interaction mechanisms in BCC iron(Fe)nanowires(NWs).There exists a critical diameter(d)of∼2.5 nm,above which the deformation twinning rather than dislocation slip dominates the *** the traditional reflection TBs,the intermediate isosceles TBs are consis-tently observed as mediated by the 1/12partial ***,we uncover two distinct TB-related deformation mechanisms,including twin variant re-orientation and TB cracking for NWs with d17 nm,*** molecular dynamics and statics simulations provide the basic underlying mechanisms for size-dependent plasticity,which have been largely overlooked in previous experimental *** findings highlight the importance of grain size in mediating the deformation behaviors in Fe,serving as possible guidance for exploring single-crystalline and poly-crystalline Fe-based materials(***)with optimized mechanical performance.

关键词： size effect Full dislocation,Isosceles twin boundary Twin variant rotation TB cracking

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Influence of mandrel-cores filling on size effect of cross-section distortion of bimetallic thin-walled composite bending tube

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Chinese Journal of Aeronautics 2023年第3期36卷 421-435页

作者： Yingxia ZHU Miaomiao WAN Wei CHEN Yun WANG Wenbin TU Fan XU School of Mechanical Engineering Jiangsu UniversityZhenjiang 212013China School of Mechanical Engineering Guilin University of Aerospace TechnologyGuilin 541004China

Two new size factors of cross-section hollow coefficient and bending degree are introduced to reveal the size effect of bending forming of bimetallic composite *** coefficient and bending degree can limit the commonly used bent tube to the size description range of(0,2.00).The evolution laws of the cross-section distortion forms in the hollow coefficient-bending degree interval are revealed as well as the action of the mandrel-cores on the size *** show the mandrel-cores filling can expand the forming limit of the bent tube,but also bring two other forming defects of wrinkle and *** identification factor(hollow coefficient multiply bending degree)provides a method for querying the cross-section distortion forms of all composite bending *** the identification factor interval(0,1.00),the distribution area of bending forming defects of the composite tube is *** thin-walled composite bending tube collapses when identification factor in(0,0.39),wrinkles when identification factor in[0.39,0.50),and ruptures when identification factor in[0.50,1.00).The mathematical model of size effect is derived,by which the average cross-section distortion rate is found to distribute like a radial leaf in the hollow coefficient-bending degree qualified forming *** best forming zone is hollow coefficient 0.46-0.68,and bending degree 0.25-0.47.

关键词： Bending Bimetallic composite tube Cross-section distortion size factor size effect Mandrel

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Tailoring mechanical properties of PμSL 3D-printed structures via size effect

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International Journal of Extreme Manufacturing 2022年第4期4卷 261-268页

作者： Wenqiang Zhang Haitao Ye Xiaobin Feng Wenzhao Zhou Ke Cao Maoyuan Li Sufeng Fan Yang Lu Department of Mechanical Engineering City University of Hong KongKowloonHong Kong SAR 999077People's Republic of China Nano-Manufacturing Laboratory(NML) City University of Hong Kong Shenzhen Research InstituteShenzhen 518057People's Republic of China Department of Mechanical and Energy Engineering Southern University of Science and TechnologyShenzhen 518055People's Republic of China Hubei Key Laboratory of Theory and Application of Advanced Materials Mechanics Wuhan University of TechnologyWuhan 430070People's Republic of China School of Mechano-Electronic Engineering Xidian UniversityXi'an 710071People's Republic of China State Key Laboratory of Materials Processing and Die&Mould Technology School of Materials Science and EngineeringHuazhong University of Science and TechnologyWuhan 430074People's Republic of China School of Mechanics and Safety Engineering Zhengzhou UniversityZhengzhou 450001People's Republic of China

Projection micro stereolithography(PμSL)has emerged as a powerful three-dimensional(3D)printing technique for manufacturing polymer structures with micron-scale high resolution at high printing speed,which enables the production of customized 3D microlattices with feature sizes down to several ***,the mechanical properties of as-printed polymers were not systemically studied at the relevant length scales,especially when the feature sizes step into micron/sub-micron level,limiting its reliable performance prediction in micro/nanolattice and other metamaterial *** this work,we demonstrate that PμSL-printed microfibers could become stronger and significantly more ductile with reduced size ranging from 20μm to 60μm,showing an obvious size-dependent mechanical behavior,in which the size decreases to 20μm with a fracture strain up to~100%and fracture strength up to~100 *** size effect enables the tailoring of the material strength and stiffness of PμSL-printed microlattices over a broad range,allowing to fabricate the microlattice metamaterials with desired/tunable mechanical properties for various structural and functional applications.

关键词： 3D printing projection micro-stereolithography(PμSL) size effect microfiber mechanical properties microlattice metamaterial

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Specimen size effect on the fracture energy of architected stretchable materials

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International Journal of Smart and Nano Materials 2023年第4期14卷 420-439页

作者： Xiao Li Libo Men Yilin Yu Zhaoyang Hou Zhengjin Wang State Key Laboratory for Strength and Vibration of Mechanical Structures Department of Engineering MechanicsSchool of Aerospace EngineeringXi'an Jiaotong UniversityXi'anPR China

Architected stretchable materials with well-organized microarchitectures evolve very rapidly due to their potential in customizing mechanical properties and achieving exotic *** many applications,the architected stretchable materials are required to sustain large deformation,and their fracture is ***,the size effect on the fracture of architected stretchable materials is still ***,we study this issue by experiment and finite element *** is found that the fracture energy of architected stretchable materials increases with the specimen size ratio,H/h,within a *** H/h reaches a transition ratio,Rt,the fracture energy approaches a *** transition ratio differentiates the size-dependent and size-independent fracture behavior of architected stretchable *** mechanical properties of constituent material only have a minor effect on the transition *** degree of constraint and stress concentration at the node,which are affected by the geometry of the unit-cell,dominate the specimen size *** result gives a practical guidance in choosing the specimen size to measure the steady state fracture energy of this class of *** work provides insights into the fracture of architected stretchable materials and design for fractureresistant architected stretchable devices.

关键词： Architected stretchable materials fracture energy size effect transition ratio

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size effect and growth options over firm lifecycle

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Journal of Management Science and Engineering 2022年第2期7卷 197-212页

作者： Qiang Li Hao Liu Yong Zeng School of Manggement and Economics Univeriy of Electronic Science aond Tec hnology of ChinaCherngdu611731China School of Finance.Guongdong Univerity of Foreign Studies.Cuangzhou 510006.China Institute of Financial Openess and Asset Management Guangzhou510006China

The size effect can be attributed to the relative importance of growth options versus assets-in-place in total *** incorporating the changing trend of growth options over firm lifecycle into the dynamic investment model developed by Berk et al.(1999)。this paper demonstrates that the gradual exhausting or exercising of growth options would cause a downward pattern of size effect over firm lifecycle,while new growth options created by R&D or innovative investments can intensify size *** a sample of listed firms in USA stock market during the period of 1963-2018,both cross-sectional evidence on individual stocks and time-series evidence on portfolios analysis support theoretical preditions well,and empirical findings are robust for different methodologies,different measures of the exerci sing/creating of growth options,and for China's stock market.

关键词： Growth options size effect Firm lifecycle Stock returns|

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size effect on transverse free vibrations of ultrafine nanothreads

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中国物理B:英文版 2023年第9期32卷 21-27页

作者：郑卓群李晗宿柱丁楠徐旭占海飞王立峰 State Key Laboratory of Mechanics and Control for Aerospace Structures Nanjing University of Aeronautics and AstronauticsNanjing 210016China School of Management Science and Information Engineering Jilin University of Finance and EconomicsChangchun 130117China College of Mathematics Jilin UniversityChangchun 130012China College of Civil Engineering and Architecture Zhejiang UniversityHangzhou 310058China School of Mechanical Medical and Process EngineeringQueensland University of TechnologyBrisbane 4001Australia

Due to their unique properties and appealing applications,low dimensional sp^(3)carbon nanostructures have attracted increasing attention *** on the beam theory and atomistic studies,this work carries out a comprehensive investigation on the vibrational properties of the ultrathin carbon nanothreads(NTH).size effect is observed in transverse free vibrations of *** quantify such effects,the modified couple stress theory(MCST)is utilized to modify the Timoshenko beam *** to the first four order frequencies of NTHs from atomistic simulations,the critical length scale parameter of MCST is calibrated as 0.1 *** is shown that MCST has minor effect on the first four order modal shapes,except for the clamped *** makes the modal shapes at the clamped boundary closer to those observed in atomistic *** study suggests that to some extent the MCST-based Timoshenko beam theory can well describe the transverse vibration characteristics of the ultrafine NTHs,which are helpful for designing and fabricating the NTH-based nanoscale mechanical resonators.

关键词： carbon nanothread size effect natural frequency modal shapes molecular dynamics simulation

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size effect for achieving high mechanical performance body-centered cubic metals and alloys

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Science China Materials 2018年第12期61卷 1495-1516页

作者： Yan Lu Xinyu Shu Xiaozhou Liao Beijing Key Lab and Institute of Microstructure and Properties of Advanced Materials Beijing University of Technology Department of Material Science and Engineering National University of Singapore School of Aerospace Mechanical and Mechatronic Engineering The University of Sydney

Submicron and nanostructured body-centered cubic(BCC) metals exhibit unusual mechanical performance compared to their bulk coarse-grained counterparts, including high yield strength and outstanding ductility. These properties are important for their applications in micro-, nano-and even atomic-scale devices as well as for their usages as components for enhancing the performances of structural materials. One aspect of the unusual mechanical properties of small-sized BCC metals is closely related to their dimensional confinement. Decreasing the dimensions of single crystalline metals or the grain sizes of polycrystalline metals contributes significantly to the strengthening of the small-sized BCC *** the last decade, significant progress has been achieved in understanding the plasticity and deformation behaviors of small-sized BCC metals. This paper aims to provide a comprehensive review on the current understanding of size effects on the plasticity and deformation mechanisms of small-sized BCC metals. The techniques used for in situ characterization of the deformation behavior and mechanical properties of small-sized samples are also presented.

关键词： body-centered cubic metals size effect plastic deformation mechanical properties

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size effect on cubic and prismatic compressive strength of cement paste

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Journal of Central South University 2015年第10期22卷 4090-4096页

作者：苏捷叶缙垚方志赵明华 College of Civil Engineering Hunan University

A series of compression tests were conducted on 150 groups of cement paste specimens with side lengths ranging from 40 mm to 200 mm. The specimens include cube specimens and prism specimens with height to width ratio of 2. The experiment results show that size effect exists in the cubic compressive strength and prismatic compressive strength of the cement paste, and larger specimens resist less in terms of strength than smaller ones. The cubic compressive strength and the prismatic compressive strength of the specimens with side length of 200 mm are respectively about 91% and 89% of the compressive strength of the specimens with the side length of 40 mm. Water to binder ratio has a significant influence on the size effect of the compressive strengths of the cement paste. With a decrease in the water to binder ratio, the size effect is significantly enhanced. When the water to binder ratio is 0.2, the size effects of the cubic compressive strength and the prismatic compressive strength of the cement paste are 1.6 and 1.4 times stronger than those of a water to binder ratio of 0.6. Furthermore, a series of formulas are proposed to calculate the size effect of the cubic compressive strength and the prismatic compressive strength of cement paste, and the results of the size effect predicted by the formulas are in good agreement with the experiment results.

关键词： size effect cement paste water to binder ratio cubic compressive strength prismatic compressive strength

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