bluuebunny/crossref_metadata_2025 huggingface dataset:
Performance Characterization of Multifunctional Structure-Battery Composites for Marine Applications
Authors: Rohatgi Aashish , Thomas James P. , Qidwai M. A. Siddiq , Pogue William R.
Published: August 2009

The aim of our work is to design, fabricate and characterize multifunctional structure-power composites for marine applications such as in unmanned underwater vehicles. Three types of structure-power (or structure-battery (SB)) specimens were fabricated using fiber-reinforced polymers and closed-cell foam as the structural components, and commercial-off-the-shelf lithium-polymer cells as the power-plus-structure component. This paper details the mechanical and electrical characterization of the S-B composites while a companion paper deals with the design and fabrication issues. The three multifunctional designs are: integrated SB laminate with lithium-polymer pouch cells embedded on one side, SB sandwich with cells embedded within a closed-cell polymeric foam along the neutral axis, and a SB modular stiffener that can be attached and removed from a host-structure. Unifunctional composites (i.e. without embedded cells) were also fabricated for comparison with the multifunctional composites. The embedded cells show identical charge-discharge electrical performance as their un-embedded counterparts, thus, indicating that the composite fabrication procedures did not adversely affect their electrical performance. Ragone curves (energy density vs. power density) of the S-B composites show that the targeted energy density of 50 Wh/L was achieved in the SB modular stiffener design. The bending stiffnesses of the integrated SB and SB modular stiffener designs were ∼7x greater than the unifunctional design while the multifunctional sandwich specimens were ∼17% stiffer than their unifunctional counterparts. Tests are currently being conducted to determine the affect of mechanical flexure (constant displacement) on embedded cell discharge and charge characteristics, and conversely, cell discharge and charge on the load and deflection during flexure.
Seismic Wave Reflection From a Permeable Layer: Low-Frequency Asymptotic Analysis
Authors: Silin Dmitriy , Goloshubin Gennady
Published: August 2009

We study elastic wave propagation in a fluid-saturated porous medium. Low-frequency asymptotic analysis of Biot’s model of poroelasticity yields the wave velocity, attenuation, and wave number as power series with respect to a small dimensionless parameter. This parameter is the product of kinematic reservoir fluid mobility, imaginary unity, and the frequency of the signal. The simplified asymptotic relationships lead to explicit formulae for reflection and transmission coefficients for a planar wave crossing an interface between two permeable media. Theoretical calculations predict a peak of reflection from a thin highly-permeable lens in a low-frequency range. An explicit formula relates the resonance frequency to reservoir fluid mobility and reservoir thickness. The results have immediate practical implications for seismic modeling and attribute analysis.
An Atomic Model of Cellulose Network in Wood Cell Wall
Authors: Wang Ying , Chen Youping
Published: August 2009

Wood is composed of parallel columns of long hollow cells which are made up of layered composite of semi-crystalline cellulose fibrils embedded in an amorphous matrix of hemicellulose and lignin. The extraordinary mechanical performance of wood is believed to result from a molecular mechanism operated through hydrogen bond connection. However, the molecular interactions, the assembly method of cell-wall components, as well as the molecular mechanisms responsible for the deformation of wood, are not well understood yet. Progress in studying the superior mechanical properties of wood cell is severely hindered because of this fact. To overcome this barrier, the foremost step is to build up an atomic model of the native cellulose fibril network, which is the dominant polysaccharide in wood cell walls. Then, in this work, we proposed the atomic models to study the cellulose network which includes a single cellulose microfibril (MF), and a thin film which is built up by first secondary layers (S1) and second secondary layers (S2) composed of cellulose MF with periodic boundary conditions. Additionally, we investigated the length effect of the microfibril and compared the effect of explicit water solvent environment with the vacuum environment. Moreover, the spatial arrangements of these atomic models have been determined by molecular mechanics simulation (energy minimization). The hydrogen bond length of the crystalline part of the inner cellulose was evaluated using first principle calculation.
The Effects of Curvature, Relaxation and Mechanical Deformation on the Electronic Properties of Single-Walled Carbon Nanotubes
Authors: Qian Dong , Zheng Qingjin
Published: August 2009

We present a framework based on coupling FEM/continuum method with quantum mechanical model for studying the effects of curvature, relaxation and mechanical deformation on the electronic properties of single-walled carbon nanotubes. The rehybridization and curvature effects, which are important for carbon nanotubes with both rotational and helical symmetries, is incorporated in the developed coarse grained model as an extension to the Bloch’s theorem. Based on extensive studies, we report the significant contribution of curvature-induced rehybridization, relaxation effect to the finite band gaps in small radius zigzag and chiral tubes that were predicted to be metallic (mod (n-m, 3) = 0) from the graphite-based models. Our calculation indicates the significant changes in the band gaps as linear functions of the applied tensile strain with the exception of armchair tubes. Transitions from metal to semi-conductor and vice versa are observed. Similar switch in conducting behavior is also present in the twisting case, while the band structures are observed to be insensitive to the applied bending. The deformation-band gap relation obtained in this work differs significantly with prior studies that use either phenomenological relations or empirical potentials for resolving the bond geometry. These differences highlight the importance of concurrent coupling.
The Structural Design of Front Motorbike Suspensions
Authors: Croccolo D. , Cuppini R. , Vincenzi N.
Published: August 2009

The fundamental goal of this paper is to provide a methodology useful for the structural design and optimization of front motorbike suspensions. Two different types of shaft-hub couplings are normally used to assembly the whole suspension: (i) an interference-fit coupling (between the fork and the steering pin) and (ii) a clamped joint (between the fork and the leg and between the leg and the wheel pin). Firstly the Design of Experiment method has been applied in order to evaluate the static friction coefficient μll. Secondly a mathematical model, based on the thick-wall cylinder theory, has been developed in order to calculate the tensile state in the fork-pin couplings. Finally other mathematical models have been defined with the aim to calculate the maximum bending stress and the mean coupling pressure generated in the fork-leg and in the wheel-clamp couplings. The research results have been used to realize an innovative software (Leg Design©) that is useful to design and to verify the whole front motorbike suspensions with correct and effective results obtained for different geometries and material combinations.
Application of a Crystal Orientation Method for Matching Surfaces Along a Fracture Line
Authors: Lograsso Barbara K. , Lograsso Thomas A. , Glamm Ryan J.
Published: August 2009

The overall objective of this study was to evaluate whether surface crystal orientation can be used to associate metal fracture fragments. This study examined the orientations of the fractured crystals across the fracture plane for two surfaces determined to be a matching fracture by conventional methods. This study used Electron Back-Scattered Diffraction (EBSD), sometimes known as Orientation Imaging Microscopy (OIM), to determine the crystallographic orientation of individual metal crystals along the length of the fracture on a surface perpendicular to the actual fracture surface. This investigation examined the uniqueness of crystal orientations within a metal and examined the requirements necessary for determination of crystallography using EBSD. This study also examined the crystallographic information as to whether it is sufficiently reliable characteristic from which a quantitative determination could be made that two separate pieces of metal are, in fact, from a single piece.
Design and Fabrication of Multifunctional Structure-Power Composites for Marine Applications
Authors: Qidwai M. A. Siddiq , Pogue William R. , Thomas James P. , Rohatgi Aashish
Published: August 2009

Various subsystems in marine applications, especially unmanned underwater vehicles, compete for space. Multifunctional structure-battery (SB) composites combine structure and power functions through the use of high-performance fiber reinforced polymer layers and lithium ion cell batteries, to create volumetric opportunities for increase in overall power generation capacity and/or payload. This paper focuses on the design and fabrication aspects of the SB composites. The design objectives are to achieve or exceed structural performance of traditional marine composites while attaining a volumetric energy density of 50 Wh/L with similar buoyancy levels and dimensional sizes. The design process reveals that all four objectives can be achieved only if the components related to energy storage have the same mechanical and physical properties as the material being replaced. With commercially available batteries, at least three out of four objectives are met for the proposed SB designs. Selection of materials and fabrication methods are heavily influenced by the temperature limit of the battery cells, cell surface preparation for adhesion and load transfer, and power bussing layout. A companion paper addresses multifunctional performance characterization of these composites.
Flow of Nano and Micron Size Particles in a Cylindrical Cavity
Authors: Ahuja Suresh
Published: August 2009

Flow of particles is analyzed by considering driving force from applied shear energy (rotating augers). against constraints of extrinsic constraints (consolidation, boundary) and intrinsic constraints (cohesion, compressibility and inter-particle forces). Both Discrete Element Method (DEM) and Continuum Models are used to analyze powder flow with DEM uses models at particle level and is therefore requires costly computation where as Continuum Models are less accurate for complicated geometries and free surfaces. The cohesive (tensile) stress for an assembly of cohesive particles is an increasing function of volume fraction but depends only weakly on shear rate. As the particle volume fraction is decreased, the dependence of the tensile stress on shear rate grows, but for all volume fractions, this dependence is much weaker than that of the total stress. Empirical correlations are costly to obtain for predicting developer flow from frequent bench experiments (Freeman tester, Jenike shear cell and Seville tester) and tests in fixtures and housings. A rheological equation can be used to analyze shear stress, normal stress, cohesive stress and dynamic coefficient of friction in a shear cell. Experimental results are compared with the existing models.
Spatially-Varying Compact Multi-Point Flux Approximations for 3-D Adapted Grids With Guaranteed Monotonicity
Authors: Lambers James V. , Gerritsen Margot G.
Published: August 2009

We propose a new single-phase local transmissibility upscaling method for adapted grids in 3-D domains that uses spatially varying and compact multi-point flux approximations (MPFA). The multi-point stencils used to calculate the fluxes across coarse grid cell faces are required to honor three generic flow problems as closely as possible while maximizing compactness. We also present a corrector method that adapts the stencils locally to guarantee that the resulting pressure matrix is an M-matrix. Finally, we show how the computed MPFA can be used to guide adaptivity of the grid.
Dispersive Wave Propagation in the Nonlocal Peridynamic Theory
Authors: Weckner Olaf , Silling Stewart , Askari Abe
Published: August 2009

Peridynamics is a nonlocal formulation of continuum mechanics that is oriented toward deformations including discontinuities, especially fractures. However already the linear elastic problem is considerably more complex than the corresponding local problem governed by the NAVIER equations. For example, the presence of long-range forces leads to the dispersion of elastic waves. The amount of dispersion is governed by the peridynamic horizon, a length-scale that naturally appears in in the equation of motion. Another example is the emergence and propagation of discontinuities that can be observed by studying the RIEMANN problem. In this presentation we show how FOURIER transformations can be used to find a representation of the solution of the general inhomogeneous initial value problem for the 3D linear bond-based peridynamic formulation. Several examples illustrate this approach and show the importance of the peridynamic horizon. Finally we demonstrate how the nonlinear dispersion relation can be used to capture experimentally measure dispersion relations.
Development of Conductive Polymer Micro Cantilever for Conductivity Measurement
Authors: Du Ping , Lin Xi , Zhang Xin
Published: August 2009

Conductive polymers are an unusual class of organic materials that exhibit high electrical conductivity at room temperature. Some reduction or oxidation (redox) state dependent properties (conductivity, color, volume, permeability) can be easily controlled by electrical stimuli, which makes it possible to construct transistors, OLEDs, actuators and membranes. In this work, we focus on the actuator aspect, where the volume change relies on the ions and solvent flux. We synthesize the polypyrrole by electrochemical deposition and derive the relationship between the film thickness and the growth rate. We further develop a novel process to fabricate single layer micro cantilever structures for conductivity measurements. The conductivity of the final structure could achieve around 5.40 S/cm.
Tie Simplex Based Parameterization for Compositional Reservoir Simulation
Authors: Voskov Denis , Tchelepi Hamdi A.
Published: August 2009

In this work, we generalize the Compositional Space Parameterization (CSP) approach, which was originally developed for compositional two-phase reservoir flow simulation. Tie-line based parameterization methods [1]–[3] were motivated by insights obtained from MOC (Method of Characteristics) theory. The MOC based analytical theory [4] has provided deep understanding of the interactions between thermodynamics and flow. In our adaptive framework, tie-lines are used to represent the solution route of multi-component multiphase displacements. The tie-line information is used as a preconditioner for EOS computations in general-purpose compositional flow simulation.
Energy Absorbing Characteristics of a Graded Honeycomb Structure Under Impact
Authors: Ali Muhammad
Published: August 2009

Energy absorption is becoming a challenging issue in various applications where safety is a primary concern. Increasing demands on crash protection systems in the arena of public safety confirms the need for superior energy absorbing materials and structures to meet stringent requirements for alleviating the impact damage. In this paper, a compact energy absorbing honeycomb structure is presented; the structure is reproduced from the graded cellular geometry observed in a banana peel. The energy absorbing characteristics of the structure at high impact velocities are studied by means of non-linear dynamic finite element simulations using ABAQUS. The structure mitigates impact in a confined space through a uniform layer wise collapsing mechanism. As compared to static and low dynamic cases, an increase in the crushing strength of the structure is observed for high impact loads. An analytical model is presented, which predicts the behavior of the structure adequately for high impact velocities.
Synthesis and Characterization of Low Density Polyethylene (LDPE) Reinforced With Functionalized CNTs
Authors: Khan Mujibur R. , Mahfuz Hassan , Kyriacou Andreas
Published: August 2009

A systematic approach was undertaken to increase strength, modulus, and toughness of low density polyethylene (LDPE) filaments through infusion of functionalized CNT and ultra high molecular weight polyethylene (UHMWPE). CNTs were functionalized with OH functional groups using chemical treatment. Functionalized CNTs and UHMWPE were first dry mixed with LDPE, and filaments were then drawn using a melt extrusion process. Loading of UHMWPE varied from 8–10 wt% while that of CNT was at 2–4 wt%. LDPE has been infused first with UHMWPE, and then with both UHMWPE and CNT, and filaments were extruded. Neat LDPE filaments were also extruded as control samples. Individual filaments from each category were tested under tension according to ASTM D3379-75. In addition, differential scanning calorimetry (DSC) and X-ray diffraction (XRD) studies were also conducted to measure changes in thermal and crystalline behavior. Filament tests have revealed that the tensile elongation of LDPE can be increased by about 200% with the addition of 10 wt% UHMWPE. This is however, is accompanied by a loss of about 50% ultimate tensile strength. In the next step, when 2 wt% CNTs and 8 wt% UHMWPE are added, tensile strength of the composite filament is restored to the level of neat LDPE (∼ 25 MPa) with an increase in modulus by 44% and in ultimate fracture strain by about 60% compared to that of neat LDPE. The source of improvement has been traced as formation of copolymer between LDPE and UHMWPE and strong interfacial interaction between the CNT and the polymers.
Approximate Macroscale Constitutive Relations Using a Finite Element Based Constitutive Equations for Microscale Contact
Authors: Sepehri Ali , Farhang Kambiz
Published: August 2009

Three dimensional elastic-plastic contact of two nominally flat rough surfaces is considered. Equations governing the shoulder-shoulder contact of asperities are derived based on the asperity-asperity constitutive relations from a finite element model of their elastic-plastic interaction. Shoulder-shoulder asperity contact yields a slanted contact force consisting of both tangential (parallel to mean plane) and normal components. Multiscale modeling of the elastic-plastic rough surface contact is presented in which asperity-level FE-based constitutive relations are statistically summed to obtain total force in the normal and tangential direction. The equations derived are in the form of integral functions and provide expectation of contact force components between two rough surfaces. An analytical fusion technique is developed to combine the piecewise asperity level constitutive relations. This is shown to yield upon statistical summation the cumulative effect resulting in the contact force between two rough surfaces with two components, one in the normal direction and a half-plane tangential component.
A New Mixed Finite Element and its Related Finite Volume Discretization on General Hexahedral Grids
Authors: Matringe Se´bastien F. , Juanes Ruben , Tchelepi Hamdi A.
Published: August 2009

Modern reservoir simulation grids are generally composed of distorted hexahedral elements populated with heterogeneous and possibly full-tensor coefficients. The numerical discretization of the reservoir flow equations on such grids is a challenging problem. Finite volume methods based on a two-point flux approximation (TPFA) do not properly account for grid distortion or permeability anisotropy that is misaligned with the grid. Multipoint flux approximation (MPFA) methods have been developed to overcome these shortcomings. Although implemented and used in virtually every commercial reservoir simulator, a proof of convergence for MPFA methods on three-dimensional hexahedral grids has remained elusive. Here, we present a link between MPFA and a new mixed finite element methods (MFEM) on hexahedral grids, which provides a powerful mathematical framework for the analysis of MPFA. First, we introduce a new mixed finite element on 3D hexahedra. The new element defines a velocity field with bilinear normal components through element faces. Thus, the new velocity field is defined by four degrees of freedom per face, which are the normal components of the velocity field at the vertices of each face. The new space is compatible with a piecewise constant pressure discretization and yields a convergent discretization. The application of a vertex-based quadrature rule reduces the new mixed finite element method to a multipoint flux control volume method. For Cartesian grids, this is in fact the classical MPFA O-method. This provides for the first time a direct link between MFEM and MPFA on hexahedral grids, which we use to establish convergence of MPFA for 3D rectangular grids.
Coarse-Grained Modeling and Simulation of Nanoscale Systems Based on Discrete Hyper-Elastic Model
Authors: Qian Dong , Zheng Qingjin
Published: August 2009

The subject of developing equivalent continuum models from the atomistic models has attracted significant attention in recent years. An outstanding issue in extending the continuum model to smaller scales is the size effect. Such a size effect is intimately related to the discrete nature of the atomic structure and nonlocal interaction among the atoms. In many of the existing continuum approaches, discrete variables are introduced in the constitutive model to account for these non-continuum effects. In this paper, we present a discrete hyperelasticity model as an alternative. Our approach, however, is fundamentally different from the conventional approach in that it treats the concept of deformation mapping in the discrete sense. The resulting deformation measure is referred to as spatial secant and the corresponding material model is called the spatial secant model. We then formulate the potential energy density functional and derive stress-like measure based on the spatial secant. After a brief description on the formulation and its comparison with the classical hyper-elastic model, we show the application of this model to both low-dimensional carbon nanostructures and general three-dimensional nanostructures. The concept of geometric-exact mapping is discussed through the examples. Comparisons with full-scale molecular mechanics simulations are made to illustrate the robustness of this approach.
Stress Analysis of Hygrothermal Delamination of Quad Flat No-Lead (QFN) Packages
Authors: Zhang Minshu , Lee S. W. Ricky , Fan Xuejun
Published: August 2009

Interfacial delamination is a major reliability issue of Quad Flat No-lead (QFN) packages under the JEDEC-MSL preconditioning and reflow process. Failures will occur when the hygrothermal stress exceeds the interfacial strength. Simulation based on finite element model is a popular method for studying the failure mechanism. However, the non-accurate material properties and the lack of experiment validations always constrain the Finite Element Analysis (FEA) at the artificial parametric study stage. To further investigate the interfacial delamination, a complex system including both simulation and experiment validation is established in this study. A dummy QFN is fabricated first as the test vehicle for the subsequent study. Then the related finite element model is built to reveal the interfacial stress distribution when the packages are subjected to the pure thermal loading and hygrothermal loading, respectively. Once the interfacial stress is derived, the strength approach is applied here to indicate the high risk area where delamination will occur. Finally, the analyses from simulation are verified by Moisture Sensitivity Level (MSL) tests using dummy samples. In this paper, a superposition method is used to integrate the thermo-mechanical and hygro-mechanical stress, with considering the non-uniform moisture distribution during reflow. Such a method is different from the previously method in literature. Results show that the shear stress is dominant along all the interfaces. From the comparison between simulation and experiments, the strength approach is applied to evaluate the package reliability successfully. Both simulation and experiment results show that the molding compound/lead-frame interface around the junction of die attach fillet would be the initiation of delamination.
Numerical and Experimental Investigation of Dynamic Characteristics of the Bottom Outlet of Vaniar Dam
Authors: Daneshmand Farhang , Zare Amin , Bazargan-Lari Yousef , Assadsangabi Babak , Liaghat Tahere
Published: August 2009

Dynamic characteristics of the service gate of Vaniar Dam are studied in this paper. Feature of pressure fluctuations induced by turbulence on the skin plate at different local openings is investigated, which is the basic dynamic load acting on the gate. The Fast Fourier Transform (FFT) algorithm is used to convert a digital signal in the time-domain into a set of points in the frequency-domain. Finite Element Method (FEM) is also used to analyze the free vibration characteristics of the gate at different openings. The paper presents a numerical procedure based on the finite element discretization that treats vibration analysis of the service gate. The natural frequencies obtained by FEM are compared with the frequencies of pressure fluctuations measured in the hydraulic model test of the outlet to investigate the avoidance of resonance phenomena at the gates. The mode shapes of the gate are also presented.
A Finite Element Approach for Nonhomogeneous Nonlocal Elastic Problems
Authors: Pisano Aurora , Sofi Alba , Fuschi Paolo
Published: August 2009

The paper deals with the implementation of a method, known in the relevant literature as Nonlocal Finite Element Method, for solving 2D boundary value problems in the context of nonhomogeneous nonlocal elasticity. The method, founded on a consistent thermodynamic formulation, is here improved making use of a phenomenological strain-difference-based nonhomogeneous nonlocal elasticity model. The latter assumes a two components local/nonlocal constitutive relation in which the stress is conceived as the sum of two contributions governed by the standard elastic moduli tensor and by a nonlocal stiffness tensor, respectively. Two numerical examples are presented and the obtained results are discussed both to verify the reliability of the method and to show its potential and limits for the analysis of nonhomogeneous nonlocal elastic problems.
Magnetostrictive Particles Modeled in a Fluid
Authors: Bouza Antonio M. , Anjanappa M.
Published: August 2009

This paper describes a computational scheme for the modeling of magnetostrictive material in a fluid utilizing the immersed finite element method (IFEM). The IFEM is used for the modeling of magnetostrictive particles (MPs) in a fluid with the goal of capturing changes to viscosity. The IFEM approach entails having an Eulerian fluid mesh for an entire computational domain, a single continuum, with MPs being immersed deformable solid structures in the fluid as unique Lagrangian meshes moving on top of a fluid mesh. The interaction between these deformable structures and the surrounding fluid is accomplished by distributing forces and interpolating velocities between these two domains, fluid and solid, utilizing the Reproducing Kernel Particle Method (RKPM) delta function. MPs are modeled to enable a future physical system exploiting the Joule and Villari effects to measure the relative changes to viscosity. This sensing action is directly proportional to a fluid’s viscosity, e.g. different fluid viscosities result in different signal signatures.
Quasi-Variational Principles of Large Elastic Deformation in Non-Conservative Systems Based on Base Forces Theory and its Application
Authors: Liu Zongmin , Liang Lifu , Fan Tao
Published: August 2009

Based on base forces theory framework, the basic equations of time boundary value problem of large elastic deformation in non-conservative systems are defined. According to the corresponding relations between generalized forces and generalized displacements, the basic equations of elasto-dynamics are multiplied by corresponding virtual quantities, integrated and then added algebraically. Considering that both body forces and surface forces are fellow forces, the generalized Hamilton-type quasi-variational principles with three kinds of variables of large elastic deformation based on base forces theory in non-conservative systems are established. Then they are degenerated. Applying the Hamilton-type quasi-potential energy principle, analytic solutions of large deformation cantilever beam problem in non-conservative systems is obtained. Finally, some correlative problems are discussed.
A Mesoscale Model for Molecular Interaction in Functionalized Nanopores
Authors: Liu Yaling , Iqbal Samir M.
Published: August 2009

Nanopores have been used to detect DNA translocation and gene detection. However, the interaction between DNA and nanopore is still not well understood due to the small size of DNA/nanopore and dynamic translocation process. Very recently, various chemical modifications have been applied on nanopore surface for improved signal yield and selective detection. Thus, it is important to characterize the interaction between DNA and chemically modified nanopores. This paper intends to develop an understanding of the interaction between DNA and chemically modified nanopore surface and the translocation process of DNA by probing the DNA-nanopore interaction mechanisms through computational modeling. The DNA-nanopore interaction will be explored through a model that links atomistic DNA-nanopore interaction to meso-scale particle dynamics. Critical interrelationships between physical properties of the nanopore (surface properties, sizes, roughness etc.), electric field strength, and translocation kinetics will be established. This research not only advances the molecular-level understanding of the DNA-nanopore interface, but would also help design lab-on-chip devices for molecule based diagnosis.
Interfacial Debonding and Stress Field Analysis on a Single Fiber Composite Using FEM
Authors: Pan Yi , Pelegri Assimina A.
Published: August 2009

Fiber debonding in a bundled fiber reinforced polymer composite is investigated by using finite element method and cohesive zone model. Fiber and matrix are modeled as isotropic and linear elastic materials. Fiber/matrix interface is represented by a cohesive zone model governed by the traction-separation law. Effects of interfacial strength on interfacial debonding and stress field in the bundled fiber composite are examined. The stress field of the debonding composite is compared to that of perfectly bonded composite.
Estimation of Cyclic Strain Hardening Exponent and Cyclic Strength Coefficient of Steels by Artificial Neural Networks
Authors: Ghajar R. , Alizadeh K. J. , Naserifar N.
Published: August 2009

The objective of this paper is to demonstrate the applicability of artificial neural networks on estimation of the cyclic strain hardening exponent and cyclic strength coefficient of steels on the basis of monotonic tensile tests properties. In order to demonstrate this applicability, steels tensile data was extracted from the literatures and two separate neural networks was conducted. One set of data was used for training networks and remaining of data for testing them. The regression analysis was used to check the system accuracy for training and test data at the end of learning. Comparing results of neural networks with values obtained from direct fitting of experimental data was indicated that cyclic strain hardening exponent and cyclic strength coefficient, which characterize the stable curves of true stress amplitude versus true plastic strain amplitude, were predicted reasonable. It was concluded that predicted stable cyclic true stress-strain curve properties by trained neural network are more accurate compared to approximate relations based on low-cycle fatigue properties.
Computational Plaque Vulnerability Index for Atherosclerotic Carotid Plaque Assessment Based on In Vivo MR-Image
Authors: Teng Zhongzhao , Huang Xueying , Yuan Chun , Canton Gador , Liu Fei , Ferguson Marina , Hatsukami Thomas S. , Tang Dalin
Published: August 2009

Carotid atherosclerotic plaque (CAP) may rupture without warning and cause acute cardiovascular syndromes such as stroke, which is the No.3 killer in USA and a leading cause of serious disabilities. Available screening and diagnosis techniques are insufficient to identify those victims before the event occurs. Noninvasive methods to identify new and emerging biomarkers to assess plaque vulnerability and predict possible rupture before the fatal event are urgently called for.
Experimental Characterization of Microstructure Evolution in Austenitic Stainless Steel With Phase Transformation
Authors: Beese Allison , Mohr Dirk
Published: August 2009

The phase transformation in cold-rolled stainless steel 301LN sheets is investigated experimentally. A series of uniaxial experiments is performed to investigate the effect of initial anisotropy on the martensitic transformation kinetics. Three methods are employed to measure the martensite content: (1) X-ray diffraction, (2) micrography and (3) magnetic induction. The first two methods require interrupted tests while the third method allows for the in-situ detection of changes of the martensite volume ratio. All three methods show that the rate of austenite-to-martensite transformation is loading direction dependent. In particular, the magnetic induction technique appears to be sufficiently sensitive to detect these relative differences. However, the results also show that the determination of the absolute martensite volume content can only be quantified with poor accuracy due to the limited accuracy of X-ray diffraction and micrography.
Drop-Weight Impact Responses of Woven Hybrid Glass-Graphite/Toughened Epoxy Composites
Authors: Sevkat E. , Liaw B. M. , Delale F. , Raju B. B.
Published: August 2009

A hybrid experimental and 3-D dynamic nonlinear finite element approach was used to study damage in 101.6mm × 101.6mm composite panels subject to drop-weight impact up to 50 J. The specimens tested were made of hybrid woven S2-glass-IM7 graphite fibers/toughened epoxy (cured at 177°C). The composite panels were damaged by impacts using a pressure-assisted Instron-Dynatup 8520 instrumented drop-weight impact tester. During the low velocity impact tests, the time-histories of impact-induced dynamic strains and impact forces were recorded. Two types of drop-weight impact tests were conducted. The first focused on the effect of different shapes of the impactor and the second involved progression of the damage in the composite when impacted repeatedly. The commercially available 3-D dynamic nonlinear finite element software, DYNA, was then used to simulate the experimental results of drop-weight tests using different shapes of the impactor. Good agreement between experimental and FEM results has been achieved when comparing dynamic force, strain histories and damage patterns from experimental measurements and finite element simulations.
Model-Based Computation of Functional Gains for Feedback Control of Vortex Shedding
Authors: Ahktar Imran , Borggaard Jeff , Burns John A. , Zietsman Lizette
Published: August 2009

Proper orthogonal decomposition (POD) is used to develop a reduced-order model of the flow past a circular cylinder. We introduce a control mechanism into the reduced-order model as a means to favorably perturb the flow to reduce vortex shedding. The feedback control for the fluid actuators is represented in terms of functional gains. These functional gains are integral kernels of the standard feedback operator and are useful in control of partial differential equations. These functional gains give us physical insight into how the control mechanism is operating. In some cases, these functional gains can provide information about the optimal placement of actuators and sensors.
Numerical Simulation of Scale Effects in Contacting Rough Surfaces
Authors: Streator Jeffrey L.
Published: August 2009

It is well known that surface topography is composed of multiple length scales. Yet it remains a challenge to ascertain how the various length scales affect the contact area and contact stresses. Several micro-contact models exist in the literature that seek to account for the multi-scale nature of surface topography through fractal or spectral descriptions. A limitation of most such micro-contact models is that they neglect the interaction between asperity contacts. In the current work, a deterministic numerical simulation of contact is performed on the contact between a rigid flat and a rough, elastic surface whose heights vary in a single dimension (i.e., y(x)). A simulated surface profile is created and then “sampled” at several resolutions to create a set of related profiles of various levels of refinement. Contact is investigated with each of the simulated surfaces to gain insight as to the role of various length scales.
Mechanical Properties of α-Helices Estimated Using Molecular Dynamics and Finite Element Simulations
Authors: Honarmandi Peyman , Bransford Philip , Kamm Roger D.
Published: August 2009

Mechanical properties of biomolecules and their response to mechanical forces may be studied using Molecular Dynamics (MD) simulations. However, high computational cost is a primary drawback of MD simulations. This paper presents a computational framework based on the integration of the Finite Element Method (FEM) with MD simulations to calculate the mechanical properties of polyalanine α-helix proteins. In this method, proteins are treated as continuum elastic solids with molecular volume defined exclusively by their atomic surface. Therefore, all solid mechanics theories would be applicable for the presumed elastic media. All-atom normal mode analysis is used to calculate protein’s elastic stiffness as input to the FEM. In addition, constant force molecular dynamics (CFMD) simulations can be used to predict other effective mechanical properties, such as the Poisson’s Ratio. Force versus strain data help elucidate the mechanical behavior of α-helices upon application of constant load. The proposed method may be useful in identifying the mechanical properties of any protein or protein assembly with known atomic structure.
Measurement Techniques Using Both Shock Tube and Explosive Tests to Assess Material Performance in Reducing Primary Blast Lung Injury
Authors: Carboni Marina G. , Piscitelle Louis , DeCristofano Barry , Maffeo Michael , Segars Ronald , Chan Philemon , Ho Kevin
Published: August 2009

The goal of this work is to investigate methods to utilize small scale shock tube testing as a screening procedure for the development of primary blast lung injury protective concepts. For this analysis it is critical to understand and appropriately relate the performance of the material system when challenged in a shock tube test to the material performance under full scale explosive testing. Measurement techniques with shock tubes and explosive tests were used to evaluate shock loading of materials and subsequent stress wave transmission in relation to injury criteria identified in the literature. The materials tested included soft and rigid ballistic materials and foam. Shock tube experimentation was performed with a single, flush pressure sensor mounted behind materials. A full scale test device was created that could be used to obtain pressure measurements under a protective material concept during full scale explosive testing. The device was a Modified Blast Test Device (MBTD) of cylindrical shape with pressure sensors mounted flush to the surface on a circle around the device’s circumference. Pressure measurements without materials and behind materials were gathered in all test scenarios for comparison. The pressure data were used to analyze peak pressure, specific impulse, dP/dtmax, normalized work and acoustic wave transmission. Results of the full scale experimental effort are compared with shock tube results.
Photosensitization of Ruthenium(II) Complex on Titania for Photocatalytic H2 Evolution Under Visible-Light Irradiation
Authors: Peng Tianyou , Dai Ke , Yi Huabing , Ke Dingning , Cai Ping
Published: August 2009

Hydrogen production over dye-sensitized Pt/P25 under visible-light irradiation was investigated by using methanol or TEOA as an electron donor. The binuclear Ru(II) dye (Ru2(bpy)4L1-PF6) shows the best photosensitization in both sacrificial reagent solutions due to its larger conjugation system and “antenna effect”, which is loosely linked with TiO2 and exhibits more steady and higher increases in H2 evolution upon prolonging the irradiation time in comparison with the tightly linked N719. The dynamic equilibrium between the linkage of ground dye and divorce of oxidized dye from TiO2 can enhance the electron injection and hinder the backward transfer, and then improve the H2 evolution efficiency.
Size Effect on Strength of Bi-Material Joints of Steel With Fiber-Polymer Composite
Authors: Bazˇant Zdeneˇk P. , Le Jia-Liang , Caner Ferhun C. , Yu Qiang
Published: August 2009

Metal-composite joints between steel ribs and advanced fiber-polymer composites are an effective structural system for hybrid ship hulls. Similar joints are of interest for fuel-efficient aircraft. The current designs of such joints are generally based on the strength criterion, which ignores fracture mechanics. Aimed at an efficient and reliable design, this study investigates the size effect on the strength of these joints theoretically, numerically and experimentally. The analytical formulation of the size effect is asymptotically anchored at the large-size limit in linear elastic fracture mechanics (LEFM). The bi-material corner of the joint is shown to have a singular stress field with complex singularity. The strength of the joint is determined by the energy criterion for the macrocrack initiation at the corner, from which the large-size asymptote of the size effect law has been derived. A general approximate size effect law, spanning all sizes and various joint angles, is further derived via asymptotic matching. Numerical analysis with cohesive fracture model is used to design the experiments. Experimental studies involve the testing of geometrically similar hybrid joint specimens with the size ratio of 1 : 4 : 12. The analytical, numerical and experimental studies all indicate that the strength of bimaterial metal-composite joints is subjected to a strong size effect.
Effect of Bending Dynamics of Piezoelectric Patch Actuator on Lamb Wave Displacement Field
Authors: Huang H. , Pamphile T.
Published: August 2009

Lamb wave is a special type of elastic wave that is widely employed in structural health monitoring systems for damage detection. Recently, piezoelectric (piezo) patches are becoming popular for Lamb wave excitation and sensing because it can be utilized as an actuator and a sensor. All published work assumed that the Lamb wave displacement field generated by a piezo patch actuator is axi-symmetric. However, we experimentally observed that the displacement fields excited by the piezo patch actuator are directional and this directionality is frequency dependent. In this paper, we present a simulation model that explains this phenomenon by incorporating the bending deformation of the piezo actuator into the calculations of the Lamb wave generation. The driving forces acting on the host plate are calculated from the out-of-plane deformation of the piezo patch through the deformation of the bonding layer. Treating these forces as tone-burst point loads, the displacement field excited by the piezo patch is constructed from the displacement solutions of time-harmonic point loads. Simulation results confirmed that a piezo patch vibrating at certain vibration mode can result in the directional and frequency dependant displacement fields observed by the experiment.
Rhodobacter capsulatus
Catalyzes Light-Dependent Fe(II) Oxidation under Anaerobic Conditions as a Potential Detoxification Mechanism
Authors: Poulain Alexandre J. , Newman Dianne K.
Published: August 2009

Diverse bacteria are known to oxidize millimolar concentrations of ferrous iron [Fe(II)] under anaerobic conditions, both phototrophically and chemotrophically. Yet whether they can do this under conditions that are relevant to natural systems is understood less well. In this study, we tested how light, Fe(II) speciation, pH, and salinity affected the rate of Fe(II) oxidation by
Rhodobacter capsulatus
SB1003. Although
R. capsulatus
cannot grow photoautotrophically on Fe(II), it oxidizes Fe(II) at rates comparable to those of bacteria that do grow photoautotrophically on Fe(II) as soon as it is exposed to light, provided it has a functional photosystem. Chelation of Fe(II) by diverse organic ligands promotes Fe(II) oxidation, and as the pH increases, so does the oxidation rate, except in the presence of nitrilotriacetate; nonchelated forms of Fe(II) are also more rapidly oxidized at higher pH. Salt concentrations typical of marine environments inhibit Fe(II) oxidation. When growing photoheterotrophically on humic substances,
R. capsulatus
is highly sensitive to low concentrations of Fe(II); it is inhibited in the presence of concentrations as low as 5 μM. The product of Fe(II) oxidation, ferric iron, does not hamper growth under these conditions. When other parameters, such as pH or the presence of chelators, are adjusted to promote Fe(II) oxidation, the growth inhibition effect of Fe(II) is alleviated. Together, these results suggest that Fe(II) is toxic to
R. capsulatus
growing under strictly anaerobic conditions and that Fe(II) oxidation alleviates this toxicity.
Multiplexed Bead-Based Mesofluidic System for Detection of Food-Borne Pathogenic Bacteria
Authors: Jin Sheng-Quan , Yin Bin-Cheng , Ye Bang-Ce
Published: August 2009

In the present study, a simple and rapid multiplexed bead-based mesofluidic system (BMS) was developed for simultaneous detection of food-borne pathogenic bacteria, including
Staphylococcus aureus
,
Vibrio parahaemolyticus
,
Listeria monocytogenes
,
Salmonella
,
Enterobacter sakazakii
,
Shigella
,
Escherichia coli
O157:H7, and
Campylobacter jejuni
. This system is based on utilization of isothiocyanate-modified microbeads that are 250 μm in diameter, which were immobilized with specific amino-modified oligonucleotide probes and placed in polydimethylsiloxane microchannels. PCR products from the pathogens studied were pumped into microchannels to hybridize with the oligonucleotide-modified beads, and hybridization signals were detected using a conventional microarray scanner. The short sequences of nucleic acids (21 bases) and PCR products characteristic of bacterial pathogens could be detected at concentrations of 1 pM and 10 nM, respectively. The detection procedure could be performed in less than 30 min with high sensitivity and specificity. The assay was simple and fast, and the limits of quantification were in the range from 500 to 6,000 CFU/ml for the bacterial species studied. The feasibility of identification of food-borne bacteria was investigated with samples contaminated with bacteria, including milk, egg, and meat samples. The results demonstrated that the BMS method can be used for effective detection of multiple pathogens in different foodstuffs.
Inhibition of
Listeria monocytogenes
in Cooked Ham by Virulent Bacteriophages and Protective Cultures
Authors: Holck A. , Berg J.
Published: August 2009

Protective cultures can be used successfully as an additional hurdle together with phages to reduce growth of
Listeria monocytogenes
on sliced cooked ham. Addition of phages resulted in a rapid 10-fold reduction of
L. monocytogenes
. After 14 to 28 days of storage, a 100-fold reduction was observed in samples with phages and protective culture compared to results for samples with phages alone.