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Comparison of oxidation-growth stresses in NiO film measured by deflection and calculated using creep analysis or finite-element modeling

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OXIDATION OF METALS 2002年第5-6期57卷 499-521页

作者： Huntz, AM Calvarin Amiri, G Evans, HE Cailletaud, G Univ Paris 11 CNRS UMR 8647 LEMHE F-91405 Orsay France Univ Birmingham Sch Met & Mat Birmingham B15 2TT W Midlands England ENSMP CNRS UMR 8647 Ctr Mat F-91003 Evry France

An attempt was made to determine the strain and the stresses generated by the growth of an oxide film using several approaches: an experimental one by means of deflection tests and modeling using either a recently developed creep analysis or a finite-element simulation. A new deflection apparatus was developed and NiO growth studied during the early stages of oxidation of a Ni80Cr20 alloy at 900degreesC, since many microstructural, kinetics and mechanical data are available for this system. The comparison of experiments and modeling indicate that the oxide layers are mostly subjected to compressive stresses when NiO is growing and the stress level and evolution clearly show that viscoplastic strain occurs in both the substrate and the oxide during oxidation. The comparison between the two modeling approaches with experiment leads to good agreement and suggests that the compressive-growth stresses derive from the lateral expansion of the fraction of new oxide that is formed within the oxide layer.

关键词： oxide-growth stresses NiO deflection analytical-creep modeling finite-element modeling

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Investigating membrane breakdown of neuronal cells exposed to nonuniform electric fields by finite-element modeling and experiments

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IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING 2002年第10期49卷 1195-1203页

作者： Heida, T Wagenaar, JBM Rutten, WLC Marani, E Univ Twente Inst Biomed Technol Dept Biomol Engn Fac Elect Engn NL-7500 AE Enschede Netherlands Leiden Univ Neuroregulat Grp Dept Neurosurg Fac Med NL-2300 RC Leiden Netherlands

High electric field strengths may induce high cell membrane potentials. At a certain breakdown level the membrane potential becomes constant due to the transition from an insulating state into a high conductivity and high permeability state. Pores are thought to be created through which molecules may be transported into and out of the cell interior. Membrane rupture may follow due to the expansion of pores or the creation of many small pores across a certain part of the membrane surface. In nonuniform electric fields, it is difficult to predict the electroporated membrane area. Therefore, in this study the induced membrane potential and the membrane area where this potential exceeds the breakdown level is investigated by finite-element modeling. Results from experiments in which the collapse of neuronal cells was detected were combined with the computed field strengths in order to investigate membrane breakdown and membrane rupture. It was found that in nonuniform fields membrane rupture is position dependent, especially at higher breakdown levels. This indicates that the size of the membrane site that is affected by electroporation determines rupture.

关键词： electropermeabilization electroporation finite-element modeling membrane breakdown nonuniform electric fields

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Nonlinear finite-element modeling of Concrete Bridge Girders Prestressed with Carbon Fiber-Reinforced Polymers

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JOURNAL OF BRIDGE ENGINEERING 2024年第8期29卷

作者： Zheng, Bo-Tong Gencturk, Bora Belarbi, Abdeldjelil Poudel, Prakash Univ Southern Calif Dept Civil & Environm Engn Los Angeles CA 90007 USA Univ Houston Dept Civil & Environm Engn Houston TX 77004 USA

Concrete beams (girders) prestressed with steel cables are widely used in highway bridges. The prestressed steel cables are prone to area loss due to corrosion. The high stress level and deteriorated bond due to corrosion further risks the structural integrity of these beams. Therefore, corrosion-resistant fiber-reinforced polymer (FRP) reinforcement has been investigated as a substitute for prestressed steel in pretensioned concrete beams. While generating data on such members, especially at a large scale, is a slow and costly affair, validated finite-element models (FEMs) can be leveraged to accelerate the process. This paper presents an FEM strategy for carbon fiber-reinforced polymer (CFRP) prestressed beams that is convenient yet sufficiently accurate. A series of AASHTO Type-I beams with a composite deck were previously tested by the authors and the data from those tests were used to validate the developed FEM approach. Thereafter, a parametric study was conducted using the developed FEM, and the results were used to investigate the behavior of such pretensioned concrete beams beyond the scope of the experimental work. The investigated parameters included prestress ratio, modulus, and reinforcement ratio of the prestressing CFRP reinforcement, and the properties of the concrete and the composite deck. The influence of these parameters on the cracking load, precracking and postcracking stiffnesses, flexural capacity, and maximum deflection of the beam was examined. The results indicate that the prestress ratio influences the cracking load and deflection in CFRP-prestressed beams, with FRP properties affecting postcracking behavior and failure modes. The tensile strength and rupture strain of FRP, respectively, affect the bending capacity and deflection, while the concrete properties have a minor impact on the beam behavior.

关键词： finite-element modeling Bridges Reinforced concrete Prestressing Carbon fiber-reinforced polymers (CFRP)

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Mixed-Order finite-element modeling of Magnetic Material Degradation Due to Cutting

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IEEE TRANSACTIONS ON MAGNETICS 2018年第6期54卷 1-8页

作者： Sundaria, Ravi Lehikoinen, Antti Hannukainen, Antti Arkkio, Antero Belahcen, Anouar Aalto Univ Dept Elect Engn & Automat Espoo 15500 Finland Aalto Univ Dept Math & Syst Anal Espoo 11100 Finland

As a part of manufacturing of electrical machines, electrical sheets are cut to the desired shape by various cutting techniques, such as punching and laser cutting. This cutting process degrades the magnetic material near the cut edge, which should be included in the finite-element modeling of electrical machines. However, due to the nature of the cutting effects, the existing finite-element modeling of the cutting effect results in computationally heavy simulations. This paper investigates the application of mixed-order elements to model the cutting effect. The second-order nodal triangular elements are used near the cut edge, whereas transition/first-order elements are applied in the remaining solution domain. Furthermore, the accuracy of the presented method is analyzed with the traditional method. According to the simulations, the mixed-order elements returned accurate results significantly faster than the traditional finite-element-based approaches. Furthermore, the effect of the cutting on the machine performance is also studied by comparing its results briefly.

关键词： Core loss cut edge cutting electrical machines finite-element modeling mixed-order elements punching steel laminations

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An adaptive mesh h-refinement algorithm for the finite-element modeling of sheet forming

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JOURNAL OF MATERIALS PROCESSING TECHNOLOGY 1999年第1-3期91卷 183-190页

作者： Xing, HL Wang, S Makinouchi, A RIKEN Inst Phys & Chem Res Mat Fabricat Lab Wako Saitama 35101 Japan

An error-estimation method based on side curvature is presented to estimate the accuracy of the finite-element discretization of a deformed sheet, especially one with sharp or quasi-sharp corners. The combination of the three basic operations to the side of element, i.e. side splitting, diagonal swapping and sharp-angle treating, is proposed and used. At the same time, using the internal angles of the corresponding elements as the basic variables, a spring model is presented to define the position of a new node. Finally, two examples are presented to show the efficiency and the accuracy of this algorithm. (C) 1999 Elsevier Science S.A. All rights reserved.

关键词： adaptive mesh refinement finite-element modeling sheet forming superplastic forming plastics blow molding

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Study of electromigration-induced formation of discrete voids in flip-chip solder joints by in-situ 3D laminography observation and finite-element modeling

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ACTA MATERIALIA 2016年第0期117卷 100-110页

作者： Chang, Yuan-Wei Cheng, Yin Xu, Feng Helfen, Lukas Tian, Tian Di Michiel, Marco Chen, Chih Tu, King-Ning Baumbach, Tilo Karlsruhe Inst Technol ANKA Inst Photon Sci & Synchrotron Radiat IPS D-76344 Eggenstein Leopoldshafen Germany Natl Chiao Tung Univ Dept Mat Sci & Engn Hsinchu 30010 Taiwan Karlsruhe Inst Technol Lab Applicat Synchrotron Radiat LAS D-76049 Karlsruhe Germany ESRF 71 Ave Martyrs F-38000 Grenoble France Univ Calif Los Angeles Dept Mat Sci & Engn Los Angeles CA 90095 USA

In the microelectronics industry the flip-chip (FC) technology is broadly used to enhance the packaging density. However, the small size and the unique geometry of the FC solder joints induce the electro-migration (EM) reliability issue. In this study, a pair of lead-free solder joints (SAC1205) was EM tested by a current of 7.5 x 10(3) A/cm(2). During the tests, X-ray laminography was applied to observe the microstructure evolution in-situ. Laminography enables the non-destructive observation of the bump microstructure and allows for a quantitative three-dimensional (3D) analysis. After EM testing for 650 h, a new EM failure mechanism was found, differing from the two well-known models, the pancake void propagation and the under-bump-metallization dissolution. Here, a few pre-existing small voids grew and simultaneously many new voids formed and grew over the entire EM testing period. Most of the nucleating voids were distributed in the current crowding region, a few also located in the low-current density region. As the testing time increased, voids increasingly coalesced with each other, forming a porous network which occupied a large part of the interface area and caused the EM failure. A finite element (FE) method was then applied to analyze the interplay between the microstructure evolution and current density redistribution. A series of 3D FE models was built based on the laminography images for the different testing stages. The current density distribution from the FE analysis indicates that the formation of discrete voids did not affect the global current density distribution until a major coalescence of the voids occurred. 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 around individual void found in the new mechanism that is held responsible for the EM retardation. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

关键词： Electromigration Flip-chip Laminography Synchrotron radiation finite-element modeling

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Transformation-mismatch plasticity of NiAl/ZrO₂ composites -: finite-element modeling

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MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 2002年第1-2期335卷 128-136页

作者： Zwigl, P Dunand, DC Northwestern Univ Dept Mat Sci & Engn Evanston IL 60208 USA Intel Corp Folsom CA 95630 USA

A coupled thermo-mechanical finite-element model was developed to describe transformation-mismatch plasticity resulting from mismatch stresses produced by allotropic particles within a creeping matrix. A composite consisting of a NiAl matrix with 10 vol.% zirconia allotropic particles was modeled in two dimensions for a range of externally-applied stress values. The instantaneous composite strain developed during the zirconia transformation is found to increase linearly with the applied stress, in agreement with continuum-mechanical, closed-form models for transformation-mismatch plasticity. This instantaneous strain is smaller than the total strain accumulated over a half temperature cycle, indicating that mismatch stresses produced during the transformation relax by matrix creep long after the particles have transformed. Also, the total composite strain calculated after a full temperature cycle is in good agreement with strains determined experimentally on a NiAl-10% ZrO2 composite. Finally, the internal stress distribution within the transforming composite is determined numerically and compared to simple analytical averages. (C) 2002 Elsevier Science B.V. All rights reserved.

关键词： superplasticity phase transformations finite-element modeling NiAl ZrO2

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Evaluation of Fatigue Behavior of Lead-Free Solder Joints in Four-Point Bending Test by finite-element modeling

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IEEE TRANSACTIONS ON COMPONENTS PACKAGING AND MANUFACTURING TECHNOLOGY 2017年第12期7卷 1957-1964页

作者： Sabuncuoglu, Baris Vanhee, Filip Willems, Geert Vandevelde, Bart Vandepitte, Dirk Interuniv Microelect Ctr B-3001 Leuven Belgium Katholieke Univ Leuven Dept Mech Engn B-3001 Leuven Belgium Univ Turkish Aeronaut Assoc Mechatron Engn Dept TR-06790 Ankara Turkey Katholieke Univ Leuven B-3001 Leuven Belgium

Fatigue performance of solder joints in four-point bending test is evaluated by finite-element modeling. A simplified modeling technique is implemented in order to focus on the behavior of the critical solder joint. The fatigue life is estimated by taking into account the creep behavior of the solder joints and the utilization of Morrow's fatigue model. Fatigue life curves are generated for room temperature and two elevated temperatures with the critical orientation of chip scale packages on the test board. The results are compared with the real four-point bending test conducted for two different temperatures. In addition, some parametric studies are conducted including the significance of test temperature, copper wiring structure, and the dwell time in the cyclic loading profile. Besides these, the structural integrity of the test board is also checked.

关键词： Fatigue fatigue finite-element modeling four-point bending solder joint reliability

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element Size and Other Restrictions in finite-element modeling of Reinforced Concrete at Elevated Temperatures

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JOURNAL OF ENGINEERING MECHANICS 2013年第10期139卷 1325-1333页

作者： Carstensen, Josephine Voigt Jomaas, Grunde Pankaj, Pankaj Tech Univ Denmark Dept Civil Engn DK-2800 Lyngby Denmark Univ Edinburgh Sch Engn Edinburgh EH9 3JL Midlothian Scotland

One of the accepted approaches for postpeak finite-element modeling of RC comprises combining plain concrete, reinforcement, and interaction behaviors. In these, the postpeak strain-softening behavior of plain concrete is incorporated by the use of fracture energy concepts. This study attempts to extend this approach for RC at elevated temperatures. Prior to the extension, the approach is investigated for associated modeling issues and a set of limits of application are formulated. The available models of the behavior of plain concrete at elevated temperatures were used to derive inherent fracture energy variation with temperature. It is found that the currently used tensile elevated temperature model assumes that the fracture energy decays with temperature. The existing models in compression also show significant decay of fracture energy at higher temperatures (>400 degrees) and a considerable variation in values. Application of the evaluated fracture energy values shows that these impose severe element size and reinforcement ratio limits. The effect of the limits is illustrated for a RC specimen.

关键词： Reinforced concrete Cracking Fire safety Constitutive relations finite element method Temperature effects RC Cracking Fire safety Constitutive models finite-element modeling Elevated temperature

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Evaluating micromechanical properties at surfaces using nanoindentation with finite-element modeling

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INTERNATIONAL JOURNAL OF DAMAGE MECHANICS 2003年第4期12卷 377-387页

作者： Knapp, JA Follstaedt, DM Myers, SM Sandia Natl Labs Radiat Solid Interact & Proc Dept Albuquerque NM 87185 USA

Detailed finite-element modeling of nanoindentation data is used to obtain accurate mechanical properties of very thin films or surface-modified layers independently of the properties of the underlying substrates. These procedures accurately deduce the yield strength, elastic modulus, and layer hardness, and greatly increase the usefulness of indentation testing with very thin surface layers. Moreover, extraction of the effective Young's modulus in the near surface region should enable mechanical damage studies on a small scale. This paper presents a brief overview of the procedures involved and illustrates them with He-implanted Ni.

关键词： nanoindentation mechanical properties finite-element modeling

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