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A spatiotemporally-nonlocal continuum field theory of polymer networks

Science China(Physics,Mechanics & Astronomy) 2023年第5期66卷 155-172页

作者： Yiyuan Jiang Li Li yujin hu State Key Laboratory of Digital Manufacturing Equipment and Technology School of Mechanical Science and EngineeringHuazhong University of Science and TechnologyWuhan 430074China

A physically-based continuum theory that captures the microstructure-dependent and temporal effects of both permanent and transient polymer networks is still lacking,despite the fact that it is greatly needed for the analysis of polymeric *** fill in this gap,this work proposes a physically-based spatiotemporally nonlocal continuum field theory.A general frame-work is established that quantitatively connects microscopic descriptions of polymer networks(chain energetics,chain-length distribution,assembly structure of the interpenetrating network,and rate of bond exchange reactions)to key components in the spatiotemporally nonlocal constitutive relations(explicit form of the nonlocal kernel function,magnitude of nonlocal characteris-tic length,two-phase weighting factors,and explicit form of the relaxation function),based on three hypotheses on the continuum viewpoint of the underlying discrete network structure:the existence of a finite bottom bound of volume to define intensive quan-tities,uniformity of energy density field inside the representative volume of a polymer network,and the condition for initiation of chain *** the general framework to a permanent 8-chain concentric network yields a concrete two-phase nonlocal elasticity constitutive relation,where the explicit form of the kernel function can be derived by simply assuming an implicit *** to a transient network with bond exchange reactions yields a spatiotemporally nonlocal constitutive *** spatiotemporally nonlocal continuum theory can be helpful for exploring transformative and subversive high-performance materials involving the specific spatial stacking and arrangement of functional units through artificial design.

关键词： spatiotemporal nonlocality polymer network transient network bond exchange reactions microstructure-dependent effect

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Damping of aluminum-matrix composite reinforced by carbon nanotube:Multiscale modeling and characteristics

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Science China(Technological Sciences) 2023年第4期66卷 1062-1074页

作者： WANG Fei LI Li TANG HaiShan WANG XueLin hu yujin State Key Laboratory of Digital Manufacturing Equipment and Technology School of Mechanical Science and EngineeringHuazhong University of Science and TechnologyWuhan 430074China

It is a crucial requirement for structure-damping materials to attain both stiffness and damping;unfortunately,the two properties are usually mutually *** study interestingly demonstrates that introducing Ni atoms into the interface of carbon nanotube(CNT)reinforced aluminum-matrix composites can defeat the conflict of stiffness versus *** originates from the gradient variation of the modulus and energy dissipation in the effective interfacial *** rule of mixture is modified by taking the interface contribution into account,and a gradient damping model is proposed to account for the contribution of the interface energy *** dynamics simulations confirm that the proposed multiscale modulus and damping models can describe the elastic modulus and damping behavior of the composites with different volume fractions and different diameters of *** gradient interface slip caused by the lattice mismatches and misfit dislocations between Ni-coated CNT and aluminum is one of the pathways for achieving unprecedented levels of the product of stiffness and damping.

关键词： molecular dynamics interfacial dissipation elastic modulus damping loss modulus

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Abnormal enhancement to the quality factors of carbon nanotube via defects engineering

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Nano Materials Science 2022年第3期4卷 259-265页

作者： Ke Duan Li Li Sihan Liu yujin hu Xuelin Wang State Key Lab of Digital Manufacturing Equipment and Technology School of Mechanical Science and EngineeringHuazhong University of Science and TechnologyWuhan430074China

Low quality(Q) factor is often the limiting factor for high performance carbon nanotube(CNT) resonators. The most commonly used approach to enhance the Q factor of CNTs is to reduce/eliminate the intrinsic ***, we show surprisingly that hole defects of suitable size and position are able to enhance the Q factor of CNT, which strongly contradicts to the common notion that the presence of defects promote intrinsic dissipation via defects dissipation. By analyzing the strain distribution, we find that such abnormal enhancement in Q factor of defected CNT originates from a coupling competition mechanism between the atomic mismatch around defected atoms and the thermoelastic damping. Although the presence of holes will introduce an additional defect dissipation source, suitable holes are capable of reducing the energy dissipation arisen from the thermoelastic damping, through changing the spatial strain field of defected CNT. This coupling competition mechanism provides a new route for designing high performance CNT resonators via defects engineering.

关键词： Defects engineering CNT resonator Q factor

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Rational design of thermoelastic damping in microresonators with phase-lagging heat conduction law

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Applied Mathematics and Mechanics(English Edition) 2022年第11期43卷 1675-1690页

作者： Yu FU Li LI Hongfang CHEN Xuelin WANG Ling LING yujin hu State Key Laboratory of Digital Manufacturing Equipment and Technology School of Mechanical Science and EngineeringHuazhong University of Science and TechnologyWuhan 430074China

The design of thermoelastic damping(TED)affected by the phase-lagging non-Fourier heat conduction effects becomes significant but challenging for enlarging the quality factor of widely-used microresonators operating in extreme situations,including ultra-high excitation frequency and ultra-low working ***,there does not exist a rational method for designing the TED in the framework of non-Fourier heat conduction *** work,therefore,proposes a design framework to achieve low thermoelastic dissipation of microresonators governed by the phase-lagging heat conduction *** equation of motion and the heat conduction equation for phase-lagging TED microresonators are derived first,and then the non-Fourier TED design problem is proposed.A topology optimization-based rational design method is used to resolve the design *** is more,a two-dimensional(2D)plain-strain-based finite element method(FEM)is developed as a solver for the topology optimization *** on the suggested rational design technique,numerical instances with various phase lags are *** results show that the proposed design method can remarkably reduce the dissipation of microresonators by tailoring their substructures.

关键词： microresonator non-Fourier damping factor topology optimization

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Instability of functionally graded micro-beams via micro-structure-dependent beam theory

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Applied Mathematics and Mechanics(English Edition) 2018年第7期39卷 923-952页

作者： Xiaobai LI Li LI yujin hu School of Mechanical Science and Engineering Huazhong University of Science and Technology

This paper focuses on the buckling behaviors of a micro-scaled bi-directional functionally graded （FG） beam with a rectangular cross-section, which is now widely used in fabricating components of micro-nano-electro-mechanical systems （MEMS/NEMS） with a wide range of aspect ratios. Based on the modified couple stress theory and the principle of minimum potential energy, the governing equations and boundary conditions for a micro-structure-dependent beam theory are derived. The present beam theory incorporates different kinds of higher-order shear assumptions as well as the two familiar beam theories, namely, the Euler-Bernoulli and Timoshenko beam theories. A numerical solu- tion procedure, based on a generalized differential quadrature method （GDQM）, is used to calculate the results of the bi-directional FG beams. The effects of the two exponential FG indexes, the higher-order shear deformations, the length scale parameter, the geomet- ric dimensions, and the different boundary conditions on the critical buckling loads are studied in detail, by assuming that Young＇s modulus obeys an exponential distribution function in both length and thickness directions. To reach the desired critical buckling load, the appropriate exponential FG indexes and geometric shape of micro-beams can be designed according to the proposed theory.

关键词： bi-directional functionally graded(FG)material buckling modified couplestress theory micro-beam

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Dynamics of structural systems with various frequency-dependent damping models

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Frontiers of Mechanical Engineering 2015年第1期10卷 48-63页

作者： Li LI yujin hu Weiming DENG Lei LU Zhe DING School of MechaniCs alcience and Technology Science and Engineerinwu ghan 430074 ChinaHuazhang University of

The aim of this paper is to present the dynamic analyses of the system involving various damping models. The assumed frequency-dependent damping forces depend on the past history of motion via convolution integrals over some damping kernel functions. By choosing suitable damping kernel functions of frequency-dependent damp- ing model, it may be derived from the familiar viscoelastic materials. A brief review of literature on the choice of available damping models is presented. Both the mode superposition method and Fourier transform method are developed for calculating the dynamic response of the structural systems with various damping models. It is shown that in the case of non-deficient systems with various damping models, the modal analysis with repeated eigenvalues are very similar to the traditional modal analysis used in undamped or viscously damped systems. Also, based on the pseudo-force approach, we transform the original equations of motion with nonzero initial conditions into an equivalent one with zero initial conditions and therefore present a Fourier transform method for the dynamics of structural systems with various damping models. Finally, some case studies are used to show the application and effectiveness of the derived formulas.

关键词： damping viscoelasticity dynamic analysis,mode superposition method Fourier transform method

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RESEARCH ON PROCESS AND PLAN OF DISASSEMBLY

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Chinese Journal of Mechanical Engineering 2001年第1期14卷 12-17页

作者： hu Junjun Multimedia Research Division, Guangdong Telecommunication Academy of Science and Technology Li Chenggang hu yujin Cai Xueyuan Zhou Ji huazhong University of Science and Technology 广东省电信科学技术研究院广东广州华中科技大学湖北

With the viewpoint of integrating all phases of product life cycle,product disassembly problem is discussed An kind of logical net methodology for product disassembly modeling is presented An channel of converting product assembly model into disassembly model,such as logical net, is proposed,and the minimization cost problem and its linear programming model are given

关键词： Life cycle Disassembly Logical net

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桁架分析方法在机构运动分析中的应用

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华中科技大学学报（自然科学版） 2006年第4期34卷 82-85页

作者：王学林胡于进华中科技大学机械科学与工程学院湖北武汉430074

运用图论理论,建立了静定桁架分析方法与机构运动分析方法的对应关系,将桁架分析中的通路法拓展到平面机构运动分析,提出了连杆机构运动分析的广义回路法.建立了桁架节点位移方程与机构速度方程的对应关系,将桁架有限元分析直接应用于... 详细信息

运用图论理论,建立了静定桁架分析方法与机构运动分析方法的对应关系,将桁架分析中的通路法拓展到平面机构运动分析,提出了连杆机构运动分析的广义回路法.建立了桁架节点位移方程与机构速度方程的对应关系,将桁架有限元分析直接应用于机构速度计算.运用通路法和桁架有限元法建立机构运动方程,方法通用,实现简单,且只与机构中杆件的方位有关,与机构中各杆件的长度无关.

关键词：机构桁架回路图论

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戏曲和电视的缘分——从“非常有戏”节目看上海戏曲和电视媒体的合作轨迹

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上海戏剧 2007年第6期 36-39页

作者：胡宇锦

戏曲和电视很是有缘。戏曲是中国最古老艺术样式之一，从宋元杂剧成熟期起算，距今已有上千年历史。电视发明于上世纪20年代的英国，不过在中国普及还是80年代前后的事情，中国电视事业最多不过40岁芳龄。古老的戏曲艺术、新兴的传播媒... 详细信息

戏曲和电视很是有缘。戏曲是中国最古老艺术样式之一，从宋元杂剧成熟期起算，距今已有上千年历史。电视发明于上世纪20年代的英国，不过在中国普及还是80年代前后的事情，中国电视事业最多不过40岁芳龄。古老的戏曲艺术、新兴的传播媒介，在80年代前后就开始了紧密合作，成就了千年良缘。而戏曲市场和电视事业均十分发达、领全国风气之先的上海，不仅成了双方的“介绍人”、“证婚者”，而且也成了这一良缘的主办方和主办地。

关键词：戏曲艺术电视媒体合作上海中国电视事业节目缘分 80年代

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话剧上海(一)

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上海戏剧 2007年第11期 8-12页

作者：胡宇锦

不中不西文明新戏登场 2007年，中国话剧迎来了它的百岁诞辰。5月，京沪两地话剧演员在人民大会堂合作演出话剧交响剧诗《吁天》，作为向中国话剧百年诞辰的献礼。这场交响剧诗的名称，来自中国话剧的开山之作——《黑奴吁天录》。

关键词：中国话剧《黑奴吁天录》上海人民大会堂合作演出话剧演员百年诞辰剧诗

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