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Thermal conductivity of thin insulating films determined by tunnel magneto-Seebeck effect measurements and finite-element modeling

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JOURNAL OF PHYSICS D-APPLIED PHYSICS 2018年第22期51卷 224006-224006页

作者： Huebner, Torsten Martens, Ulrike Walowski, Jakob Muenzenberg, Markus Thomas, Andy Reiss, Guenter Kuschel, Timo Bielefeld Univ Ctr Spinelect Mat & Devices Dept Phys Univ Str 25 D-33615 Bielefeld Germany Greifswald Univ Inst Phys Felix Hausdorff Str 6 D-17489 Greifswald Germany Leibniz Inst Solid State & Mat Res Dresden IFW Dr Inst Metall Mat Helmholtzstr 20 D-01069 Dresden Germany

In general, it is difficult to access the thermal conductivity of thin insulating films experimentally by electrical means. Here, we present a new approach utilizing the tunnel magneto-Seebeck effect (TMS) in combination with finite-element modeling (FEM). We detect the laser-induced TMS and the absolute thermovoltage of laser-heated magnetic tunnel junctions with 2.6 nm thin barriers of MgAl2O4 (MAO) and MgO, respectively. A second measurement of the absolute thermovoltage after a dielectric breakdown of the barrier grants insight into the remaining thermovoltage of the stack. Thus, the pure TMS without any parasitic Nernst contributions from the leads can be identified. In combination with FEM via COMSOL, we are able to extract values for the thermal conductivity of MAO (0.7 W (K . m)(-1)) and MgO (5.8 W (K . m)(-1)), which are in very good agreement with theoretical predictions. Our method provides a new promising way to extract the experimentally challenging parameter of the thermal conductivity of thin insulating films.

关键词： spin caloritronics magnetic tunnel junctions tunnel magneto-Seebeck effect thermal conductivity thin insulating films finite-element modeling

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Dynamic finite element modeling and Simulation of Soft Robots

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Chinese Journal of Mechanical Engineering 2022年第2期35卷 45-55页

作者： Liang Ding Lizhou Niu Yang Su Huaiguang Yang Guangjun Liu Haibo Gao Zongquan Deng State Key Laboratory of Robotics and Systems Harbin Institute of TechnologyHarbin 150001China Department of Aerospace Engineering Ryerson UniversityTorontoON M5B 2K3Canada

Soft robots have become important members of the robot community with many potential applications owing to their unique flexibility and security embedded at the material *** increasing number of researchers are interested in their designing,manufacturing,modeling,and ***,the dynamic simulation of soft robots is difficult owing to their infinite degrees of freedom and nonlinear characteristics that are associated with soft materials and flexible geometric *** this study,a novel multi-flexible body dynamic modeling and simulation technique is introduced for soft *** actuators for soft robots are modeled in a virtual environment,including soft cable-driven,spring actuation,and pneumatic driving.A pneumatic driving simulation was demonstrated by the bending modules with different materials.A cable-driven soft robot arm prototype and a cylindrical soft module actuated by shape memory alley springs inspired by an octopus were manufactured and used to validate the simulation model,and the experimental results demonstrated adequate *** proposed technique can be widely applied for the modeling and dynamic simulation of other soft robots,including hybrid actuated robots and rigid-flexible coupling *** study also provides a fundamental framework for simulating soft mobile robots and soft manipulators in contact with the environment.

关键词： Soft robot finite-element modeling Dynamic simulation

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Influence of thin-film metallic glass coating on fatigue behavior of bulk metallic glass: Experiments and finite element modeling

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MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 2017年 692卷 146-155页

作者： Yu, Chia-Chi Chu, Jinn P. Jia, Haoling Shen, Yu-Lin Gao, Yanfei Liaw, Peter K. Yokoyama, Yoshihiko Natl Taiwan Univ Sci & Technol Dept Mat Sci & Engn Taipei 10607 Taiwan Univ Tennessee Dept Mat Sci & Engn Knoxville TN 37996 USA Univ New Mexico Dept Mech Engn Albuquerque NM 87131 USA Tohoku Univ Inst Mat Res Sendai Miyagi 9808577 Japan

A coating of the Zr-based thin-film metallic glass (TFMG) was deposited on the Zr50Cu30Al10Ni10 bulk metallic glass (BMG) to investigate shear-band evolution under four-point-bend fatigue testing. The fatigue endurance limit of the TFMG-coated samples is 33% higher than that of the BMG. The results of finite-element modeling (FEM) revealed a delay in the shear-band nucleation and propagation in TFMG-coated samples under applied cyclic-loading. The FEM study of spherical indentation showed that the redistribution of stress by the TFMG coating prevents localized shear-banding in the BMG substrate. The enhanced fatigue characteristics of the BMG substrates can be attributed to the TFMG coatings retarding shear-band initiation at defects on the surface of the BMG.

关键词： Metallic glass Four-point-bend fatigue Shear band finite-element modeling

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Nonlinear Coupled Field finite element Procedure for modeling of Shape Memory Alloy Components in Multi-physics Applications

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MECHANICS OF ADVANCED MATERIALS AND STRUCTURES 2010年第2期17卷 145-156页

作者： Serry, M. Y. Raboud, D. W. Moussa, W. A. Univ Alberta Dept Mech Engn Edmonton AB T6G 2G8 Canada Amer Univ Cairo Sch Sci & Engn New Cairo Egypt

In this paper, we introduce a one-dimensional finite element procedure for modeling shape memory alloy components used in multi-physics based applications including MEMS and biomedical applications. The procedure addressed in this paper is based on a sequential solution of two main finite-element procedures which are then combined after each iteration. The procedure was applied to model an SMA wire and the results were compared with corresponding numerical and experimental results from the literature for different loading cases and boundary conditions. The results showed very good agreement with both experimental and numerical results. The procedure was found to be capable of capturing system characteristics such as structural and thermal non-linearity, variable SMA material properties and the ability to model coupled electrical, thermal and structural loading and boundary conditions and was general enough to be extensible to various geometrical shapes and different SMA constitutive models.

关键词： shape memory alloys finite-element modeling MEMS biomedical multi-physics non-linear

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A strategy for the finite element modeling of FRP-confined concrete columns subjected to preload

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ENGINEERING STRUCTURES 2018年 173卷 1054-1067页

作者： Ferrotto, M. F. Fischer, O. Cavaleri, L. Univ Palermo Dept Civil Environm Aerosp Mat Engn Viale Sci I-90128 Palermo Italy Tech Univ Munich Chair Concrete & Masonry Struct Theresienstr 90 D-80333 Munich Germany

Compressive behavior of columns strengthened by means of an outer elastic confinement provided e.g. by fiber-reinforced polymer (FRP) jackets has become a main topic in the field of structural retrofitting. In details, the problem of the response assessment of strengthened columns is still under study. Many analytical formulations have been proposed to describe the compressive behavior of confined concrete under both monotonic and cyclic loads. However, the effect of a stress/strain level in the columns already present prior to apply the confinement has been generally neglected until now, also because of the lack of well defined strategies of modeling. In this frame, here, (1) a FEM assessment strategy is presented and discussed referred to FRP-confined reinforced concrete columns subjected to monotonic compressive loads;(2) to this aim, first, a modified stress-strain law for the concrete is proposed for the FE analysis able to capture the softening/hardening behaviour differently from the laws of unconfined concrete commonly used as input;(3) then a law to fix the parameters defining the hardening/softening characteristics starting from the characteristics of the unconfined concrete and of the FRP wrapping is provided. After calibrating and validating the above strategy in the case of non preloaded elements, the compressive behavior in the presence of preload is analyzed numerically and compared with experimental results to evaluate the reliability of the FE model approach proposed. Through the paper, the procedure for the definition of the law to fix the hardening/softening parameters of the concrete is described.

关键词： Preloading Confinement Confined concrete fiber reinforced polymer (FRP) Confinement lateral pressure finite-element modeling Concrete damaged plasticity model ABAQUS

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Unstructured finite element modeling thermally sprayed cermet coatings post-treatment by pulsed high-energy fluxes

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COMPOSITE STRUCTURES 2016年第0期158卷 387-399页

作者： Solonenko, O. P. Golovin, A. A. RAS Siberian Branch Khristianovich Inst Theoret & Appl Mech 4-1 Inst Str Novosibirsk 630090 Russia

Thermal spraying of cermet coatings made of composite powders which particles consist of ultrafine carbide inclusions in metal or metal alloy matrix gives wide opportunities of creation of coatings for extreme application conditions. However, the high content of carbide inclusions in the cermet particles is the reason of their low level deformation at impact with substrate or coating surface that results in porosity of plasma as-sprayed layer. Decrease in coating porosity at simultaneous increase of its bond strength with substrate is possible by means of subsequent pulsed high-energy treatment. The problem consists in binder melting at minimum impact on carbide inclusions and substrate. Because the experimental development of this technology is rather multivariate procedure, a preliminary computer optimization is very perspective. The computing experiments were carried out, which allowed to optimize power density in a single pulse and its duration depending on thickness and porosity of the deposited TiC-NiCr layers. (C) 2016 Elsevier Ltd. All rights reserved.

关键词： Cermet powder Binder Ultrafine carbide inclusions Splat Thermally sprayed coating Porosity Pulsed high-energy treatment finite-element modeling

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Shearography inspection of monolithic CFRP composites: finite element modeling approach for assessing an adequate strategy of artificial defects representing delamination 11

Shearography inspection of monolithic CFRP composites: finit...

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Conference on Optical Measurement Systems for Industrial Inspection XI held at SPIE Optical Metrology Symposium

作者： Vandenrijt, J-F Xiong, H. Lequesne, C. Blain, P. Georges, M. Univ Liege Ctr Spatial Liege Liege Sci Pk B-4031 Angleur Belgium Samtech Siemens Rue Chasseurs ArdennaisLiege Sci Pk B-4031 Angleur Belgium

ISBN: (数字)9781510627925

ISBN: (纸本)9781510627925

Delamination in carbon fiber reinforced polymer (CFRP) laminated composites is an important problem for industry. Nondestructive inspection (NDI) methods aim at locating such defects. Shearography is a full-field NDI method that could be considered to detect them. Reference plates for assessing performances of NDI methods for detecting delamination use artificial defects of several types introduced in reference CFRP matrices. Although they are standardized for usual ultrasound testing, these artifacts are not necessarily adequate for shearography. We have studied this problem by comparing shearography experiment and simulations by finite element analysis. We show the convergence with experiments on the case of flat bottom hole artifacts. Then we discuss the adequateness of other artifacts through simulations.

关键词： Speckle interferometry Shearography Nondestructive inspection finite-element modeling Composite materials

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Study of Discrete Voids Formation in Flip-Chip Solder Joints due to ElectromigrationUsing In-Situ 3D Laminography and finite-element modeling

Study of Discrete Voids Formation in Flip-Chip Solder Joints...

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IEEE ELectronics Packaging Technology Conference

作者： Yuan-Wei Chang Yin Cheng Feng Xu Lukas Helfen Tian Tian Marco Di Michiel Chih Chen King-Ning Tu Tilo Baumbach ANKA/Institute for Photon Science and Synchrotron Radiation (IPS) Karlsruhe Institute of Technology (KIT) 76344 Eggenstein-Leopoldshafen Germany Department of Materials Science and Engineering UCLA Los Angeles California 90095-595 US ESRF The European Synchrotron 71 avenue des Martyrs 38000 Grenoble France Department of Materials Science and Engineering National Chiao Tung University Hsin-chu 30010 Taiwan R.O.C

ISBN: (纸本)9781509043705

Nowadays, the microelectronics industry broadly uses the flip-chip technology to enhance the packaging density. However, the small size and the unique geometry of the flip-chip solder joints induce the electromigration (EM) reliability issue. In this study, a Pb-free solder joints (SAC1205) was EM tested by a current of 7.5x10~3 A/cm~2. During the tests, a three-dimensional (3D) X-ray laminography method was applied to in-situ observe the microstructure evolution. The laminography method allows for the non-destructive observation and provides the quantitative analysis among three dimensions. After EM testing for 650 hr, a new EM failure mechanism was found rather than the well-known models, the pancake void propagation and the under-bump-metallization dissolution. According to the laminography images at different testing stages, many voids simultaneously formed and grew during the entire procedure of testing. Most of them distributed in the current crowding region, but a few also located in the low-current-density region. As the testing time increased, voids grew bigger, coalesced with each other, and finally became large voids which occupied the interface and caused EM failure. The finite-element (FE) method was also applied to analyze the interplay between the microstructure evolution and current density redistribution. A series of 3D FE models were built based on the laminography images at different testing stages. The current density distribution from the FE analysis indicates that the multiple voids formation does not affect the global current density distribution until the voids merged together and became very large voids in the late stage of EM testing. The relieving of the global current crowding in the pancake void model was not found in this new EM failure mechanism. It was the local current crowding found in the new model that responsible for the EM retardation.

关键词： EM Study finite-element modeling

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A finite element Method for modeling Edge Effects in Composite Laminates with Different Ply Orientations

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JORDAN JOURNAL OF CIVIL ENGINEERING 2022年第4期16卷 549-566页

作者： Numayr, Karim S. Ababneh, Ayman N. Almashaqbeh, Hashem K. Isra Univ Dept Civil Engn Amman Jordan Jordan Univ Sci & Technol Dept Civil Engn Irbid Jordan

A finite element (FE) method is used for modeling edge effects in composite laminates with different ply orientations. Two types of three-dimensional isoperimetric FE methods have been used. One in the interior region has standard linear shape functions, while the other in the exterior region has special shape functions for which an exponential variation is derived using the perturbation technique. The exponential shape functions are introduced to an originally written FE program which uses special mesh generation and numerical integration, as well as other subroutines. The proposed FE solution is found to be in good agreement with the solutions available in the literature.

关键词： finite-element modeling Perturbation technique Laminated composites Edge effect Delamination

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3D Computational modeling of Blast Transmission through the Fluid-Filled Cochlea and Hair Cells

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ANNALS OF BIOMEDICAL ENGINEERING 2025年第3期53卷 718-730页

作者： Bradshaw, John J. Brown, Marcus A. Jiang, Yijie Gan, Rong Z. Univ Oklahoma Sch Biomed Engn Norman OK 73019 USA Univ Oklahoma Sch Aerosp & Mech Engn 865 Asp Ave Room 200 Norman OK 73019 USA

PurposeVeterans commonly suffer from blast-induced hearing disabilities. Injury to the sensitive organ of Corti (OC) or hair cells within the cochlea can directly lead to hearing loss, but is very difficult to measure experimentally. Computational finite element (FE) models of the human ear have been used to predict blast wave transmission through the middle ear and cochlea, but these models lack a representation of the OC. This paper reports a recently developed 3D FE model of the OC to simulate the response of hair cells to blast waves and predict possible injury *** of the OC model consist of the sensory cells, membranes, and supporting cells with endolymphatic fluid surrounding them inside the scala media. Displacement of the basilar membrane induced by a 31-kPa blast overpressure derived from the macroscale model of the human ear was applied as input to the OC model. The fluid-structure interaction coupled analysis in the time domain was conducted in *** results derived from the FE model include the strains and displacements of the outer hair cells, stereociliary hair bundles (HBs), reticular lamina, and the tectorial membrane (TcM). The highest structural strain was concentrated around the connecting region of the HBs and the TcM, potentially indicating detachment due to blast exposure. Including the interstitial fluid in the OC created a realistic environment and improved the accuracy of the results compared to the previously published OC model without *** microscale model of OC was developed in order to simulate blast overpressure transmission through the fluid-filled cochlea and hair cells. This FE model represents a significant advancement in the study of blast wave transmission through the inner ear, and is an important step toward a comprehensive multi-scale model of the human ear that can predict blast-induced injury and hearing loss.

关键词： Ear finite-element modeling Cochlea Organ of Corti Blast overpressure

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