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Energy principle of ferroelectric ceramics and single domain mechanical model

Acta Mechanica Sinica 2007年第5期23卷 531-543页

作者： t.c.Wang LNM Institute of MechanicsChinese Academy of SciencesBeijing 100080China

Many physical experiments have shown that the domain switching in a ferroelectric material is a complicated evolution process of the domain wall with the variation of stress and electric field. According to this mechanism, the volume fraction of the domain switching is introduced in the constitutive law of ferroelectric ceramic and used to study the nonlinear constitutive behavior of ferroelectric body in this paper. the principle of stationary total energy is put forward in which the basic unknown quantities are the displacement ui, electric displacement Di and volume fraction pI of the domain switching for the variant I. Mechanical field equation and a new domain switching criterion are obtained from the principle of stationary total energy. the domain switching criterion proposed in this paper is an expansion and development of the energy criterion. On the basis of the domain switching criterion, a set of linear algebraic equations for the volume fraction PI of domain switching is obtained, in which the coefficients of the linear algebraic equations only contain the unknown strain and electric fields. then a single domain mechanical model is proposed in this paper. the poled ferroelectric specimen is considered as a transversely isotropic single domain. By using the partial experimental results, the hardening relation between the driving force of domain switching and the volume fraction of domain switching can be calibrated. then the electromechanical response can be calculated on the basis of the calibrated hardening relation. the results involve the electric butterfly shaped curves of axial strain versus axial electric field, the hysteresis loops of electric displacement versus electric filed and the evo- lution process of the domain switching in the ferroelectric specimens under uniaxial coupled stress and electric field loading. the present theoretic prediction agrees reasonably with the experimental results given by Lynch.

关键词： Ferroelectric ceramic Domain switching the volume fraction of domain switching Single domain mechanical model

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Equivalent series system to model a multiple friction pendulum system with numerous sliding interfaces for seismic analyses

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Earthquake Engineering and Engineering Vibration 2014年第1期13卷 85-99页

作者： c.S.tsai H.c.Su t.c.chiang Department of civil Engineering Feng Chia University Department of Water Resources Engineering and conservation Feng Chia University Earthquake Proof Systems Inc.

current structural analysis software programs offer few if any applicable device-specifi c hysteresis rules or nonlinear elements to simulate the precise mechanical behavior of a multiple friction pendulum system(MFPS) with numerous sliding *** on the concept of subsystems,an equivalent series system that adopts existing nonlinear elements with parameters systematically calculated and mathematically proven through rigorous derivations is *** aim is to simulate the characteristics of sliding motions for an MFPS isolation system with numerous concave sliding interfaces without prior knowledge of detailed information on the mobilized forces at various sliding *** MFPS with numerous concave sliding interfaces and one articulated or rigid slider located between these interfaces is divided into two subsystems: the fi rst represents the concave sliding interfaces above the slider,and the second represents those below the *** equivalent series system for the entire system is then obtained by connecting those for each subsystem in *** equivalent series system is validated by comparing numerical results for an MFPS with four sliding interfaces obtained from the proposed method with those from a previous study by Fenz and ***,these numerical results demonstrate that an MFPS isolator with numerous concave sliding interfaces,which may have any number of sliding interfaces,is a good isolation device to protect structures from earthquake damage through appropriate designs with controllable mechanisms.

关键词： seismic isolation base isolation earthquake engineering multiple friction pendulum system structural control mathematical modeling equivalent series system

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MULtI-FAcILItY ORDERED MEDIAN PROBLEMS IN DIREctED NEtWORKS

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Journal of Systems Science & complexity 2011年第1期24卷 61-67页

作者： Huajun tANG t. c. Edwin cHENG c. t. NG Faculty of Management and Administration Macao University of Science and Technology Macao China Department of Logistics and Maritime Studies The Hong Kong Polytechnic University Hong Kong China

this paper uses a finite dominating set （FDS） to investigate the multi-facility ordered median problem （OMP） in a strongly connected directed network. the authors first prove that the multi-facility OMP has an FDS in the node set, which not only generalizes the FDS result provided by Kalcsics, et al. （2002）, but also extends the FDS result from the single-facility case to the multiple case, filling an important gap. then, based on this FDS result, the authors develop an exact algorithm to solve the problem. However, if the number of facilities is large, it is not practical to find the optimal solution, because the multi-facility OMP in directed networks is NP-hard. Hence, we present a constant-approximation algorithm for the p-median problem in directed networks. Finally, we pose an open problem for future research.

关键词： Algorithms finite dominating sets multi-facility ordered median problem pseudoequilibria.

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Pushover analysis of reinforced concrete frames considering shear failure at beam-column joints

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Earthquake Engineering and Engineering Vibration 2013年第3期12卷 373-383页

作者： Y.c.Sung t.K.Lin c.c.Hsiao M.c.Lai Bridge Division Center for Research on Earthquake EngineeringTaipei University of Technology (NTUT) chiao tung University taipei University of technology (NtUt)

Since most current seismic capacity evaluations of reinforced concrete （Rc） frame structures are implemented by either static pushover analysis （PA） or dynamic time history analysis, with diverse settings of the plastic hinges （PHs） on such main structural components as columns, beams and walls, the complex behavior of shear failure at beam-column joints （BcJs） during major earthquakes is commonly neglected. this study proposes new nonlinear PA procedures that consider shear failure at BcJs and seek to assess the actual damage to Rc structures. Based on the specifications of FEMA-356, a simplified joint model composed of two nonlinear cross struts placed diagonally over the location of the plastic hinge is established, allowing a sophisticated PA to be performed. to verify the validity of this method, the analytical results for the capacity curves and the failure mechanism derived from three different full-size Rc frames are compared with the experimental measurements. By considering shear failure at BcJs, the proposed nonlinear analytical procedures can be used to estimate the structural behavior of Rc frames, including seismic capacity and the progressive failure sequence of joints, in a precise and effective manner.

关键词： Rc frame beam-column joint pushover analysis capacity curve plastic hinge performance-based seismic evaluation

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Of mice and men： what rodent models don＇t tell us

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cellular & Molecular Immunology 2013年第4期10卷 284-285页

作者： Adam c Drake Koch Institute for Integrative cancer Research atMIt Cambridge MA USA

Work recently published in PNAS by the Inflammation and Host Response to Injury, Large Scale collaborative Research Program1 compared the transcriptional responses in peripheral blood to inflammatory injuries （burns,... 详细信息

关键词： Inflammation Injury human

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PREDIctION FOR FORMING LIMIt OF AL2024t3 SHEEt BASED ON DAMAGE tHEORY USING FINItE ELEMENt MEtHOD

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Acta Mechanica Solida Sinica 2006年第2期19卷 174-180页

作者： tang c.Y. Fan Jianping tsui c.P. Department of Industrial and Systems Engineering The Hong Kong Polytechnic University Hong Kong China School of civil Engineering and Mechanics Huazhong University of Science and Technology Wuhan 430074 China

this paper presents the application of anisotropic damage theory to the study of forming limit diagram of A12024t3 aluminum alloy sheet. In the prediction of limiting strains of the aluminum sheet structure, a finite element cell model has been constructed. the cell model consists of two phases, the aluminum alloy matrix and the intermetallic cluster. the material behavior of the aluminum alloy matrix is described with a fully coupled elasto-plastic damage constitutive equation. the intermetallic cluster is assumed to be elastic and brittle. By varying the stretching ratio, the limiting strains of the sheet under biaxial stretching have been predicted by using the necking criterion proposed. the prediction is in good agreement with the experimental findings. Moreover, the finite element cell model can provide information for understanding the microscopic damage mechanism of the aluminum alloy. Over-estimation of the limit strains may result if the effect of material damage is ignored in the sheet metal forming study.

关键词： forming limit diagram (FLD) anisotropic damage finite element method (FEM) limit strain localized necking elasto-plastic deformation

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Multiscale approach to micro/macro fatigue crack growth in 2024-t3 aluminum panel

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Science china(Physics,Mechanics & Astronomy) 2014年第1期57卷 51-58页

作者： SIH G.c. International center for Sustainability Accountability and Eco-Affordability of the Large and Small (ICSAELS) Lehigh UniversityBethlehem PA 18015 USA Key Laboratory of Pressure Systems and Safety Ministry of Education School of Mechanical Engineering East China University of Science and Technology

When two contacting solid surfaces are tightly closed and invisible to the naked eye, the discontinuity is said to be microscopic regardless of whether its length is short or long. By this definition, it is not sufficient to distinguish the difference between a micro- and macro-crack by using the length parameter. Microcracks in high strength metal alloys have been known to be sev- eral centimeters or longer. considered in this work is a dual scale fatigue crack growth model where the main crack can be mi- cro or macro but there prevails an inherent microscopic tip region that is damaged depending on the irregularities of the micro- structure. this region is referred to as the ＂micro-tip＂ and can be simulated by a sharp wedge with different angles in addition to mixed boundary conditions. the combination is sufficient to model microscopic entities in the form of voids, inclusions, precipitations, interfaces, in addition to subgrain imperfections, or cluster of dislocations. this is accomplished by using the method of ＂singularity representation＂ such that closed form asymptotic solutions can be obtained for the development of fa- tigue crack growth rate relations with three parameters. they include：（1） the crack surface tightness o-＊ represented by cro/cr~ = 0.3-0.5 for short cracks in region I, and 0.1-0.2 for long cracks in region II, （2） the micro/macro material properties reflected by the shear modulus ratio/1＂（=,L/micro/]-/macro varying between 2 and 5） and （3） the most sensitive parameter d＊ being the micro-tip characteristic length d＊（=d/do） whose magnitude decreases in the direction of region I ---~II. the existing fatigue crack growth data for 2024-t3 and 7075-t6 aluminum sheets are used to reinterpret the two-parameter da/dN=c（AK）n relation where AK has now been re-derived for a microcrack with surfaces tightly in contact. the contact force will depend on the mean stress ~m or mean stress ratio R as the primary parameter and on the stress amplitude era

关键词： microcrack macrocrack microstructure singularity multiscaling scale shift micro/macro crack growth 7075-t6 and 2024-t3

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A correlation between pulse diagnosis of human body and health monitoring of structures

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Earthquake Engineering and Engineering Vibration 2004年第1期3卷 117-125页

作者： c.c.chang Henry t.Y.Yang Department of civil Engineering Hong Kong University of Science and TechnologyHong Kong Department of Mechanical and Environmental EngineeringUniversity of California Department of Mechanical and Environmental Engineering University of California

the concept of health monitoring is a key aspect of the field of medicine that has been practiced for a long time. A commonly used diagnostic and health monitoring practice is pulse diagnosis, which can be traced back approximately five thousand years in the recorded history of china. With advances in the development of modern technology, the concept of health monitoring of a variety of engineering structures in several applications has begun to attract widespread attention. Of particular interest in this study is the health monitoring of civil structures. It seem natural, and even beneficial, that these two health-monitoring methods, one as applies to the human body and the other to civil structures, should be analyzed and compared. In this paper, the basic concepts and theories of the two monitoring methods are first discussed. Similarities are then summarized and commented upon. It is hoped that this correlation analysis may help provide structural engineers with some insights into the intrinsic concept of using pulse diagnosis in human health monitoring, which may of be some benefit in the development of modern structural health monitoring methods.

关键词： human health monitoring pulse diagnosis structural health monitoring vibration-based techniques local detection techniques

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Microstructural Evolution of Infrared Brazed cP-ti Using ti-cu-Ni Brazes

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Journal of Materials Science & technology 2011年第2期27卷 131-138页

作者： c.t.chang t.Y.Yeh R.K.Shiue c.S.chang Department of Mechanical Engineering National Hualien Industrial Vocational Senior High SchoolHualien 970TaiwanChina Department of Materials Science and Engineering National Taiwan UniversityTaipei 106TaiwanChina Engineered Materials Solutions 39 Perry AvenueMS 4-1AttleboroMA 02703-2410USA

Microstructural evolution of infrared vacuum brazed cP-ti using two ti-based braze alloys,ti-15cu-15Ni and ti-15cu-25Ni,has been *** infrared brazed joint consisted of eutectic ti 2 cu/ti 2 Ni intermetallic compounds and ti-rich *** eutectic ti 2 cu/ti 2 Ni intermetallic compounds disappeared from the joint after being annealed at 900 c for 1 *** contrast,the depletion rate of both cu and Ni from the braze alloy into cP-ti substrate at 750 c annealing was greatly decreased as compared with that annealed at 900 *** ti 2 cu/ti 2 Ni phases were observed even if the specimen was annealed at 750 c for 15 *** the Ni content of the ti-15cu-25Ni braze alloy is much higher than that of the ti-15cu-15Ni alloy,the amount of eutectic ti 2 cu/ti 2 Ni phases in ti-15cu-25Ni brazed joint is more than that in ti-15ci-15Ni brazed ***,similar microstructural evolution can be obtained from the infrared brazed joint annealed at various temperatures and/or time for both filler metals.

关键词： Infrared Brazing cP-ti ti-cu-Ni fillers Microstructure

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Inflammatory bowel disease: Dcs sense LtB_(4) to drive t_(H)1 and t_(H)17 differentiation

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cellular & Molecular Immunology 2020年第4期17卷 307-309页

作者： Bhagawat c.Subramanian Laboratory of cellular and Molecular Biology National Cancer InstituteNIHBethesdaMD 20892USA

RESEARcH HIGHLIGHt Ulcerative colitis and crohn’s disease are the two major forms of inflammatory bowel disease(IBD)in humans.1 chronic human IBD,such as crohn’s disease,is characterized by features such as intestinal infiltration of immune cells,inflammatory cytokine milieu,intestinal fibrosis and weight loss among others,that lead to chronic and spontaneously recurring intestinal inflammation.2 Several mouse models of IBD have been used by researchers to understand the diverse aspects related to human IBD.1,2 For example,the mouse model of intra-rectal administration of the haptenating agent,2,4,6-trinitrobenzene sulfonic acid(tNBS),which induces mucosal immunity to colonic immunogenic proteins in the host,recapitulates key immunological responses observed in crohn’s disease,such as cytokine secretion patterns,intestinal fibrosis,and immune intolerance.2 the innate immune response is critical to initiate the cytokines production that prime t-cell differentiation in the tNBS *** polarized t-cell responses are hallmarks of IBD and in the tNBS model t_(H)1 and t_(H)17-cell responses predominate as is observed with the signature cytokine secretion profile of IL12/IFNγand IL23/IL17,respectively.

关键词： cytokine immunity tNBS

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