bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Rainbow Trout (Oncorhynchus mykiss) Plasma Protein on the Gelation of Alaska Pollock (Theragra chalcogramma) Surimi
Authors: Li D.K. , Lin H. , Kim S.M.
Published: April 2008

ABSTRACT:  The effect of rainbow trout plasma protein (RPP) on the gelation of Alaska pollock surimi was determined to evaluate the possibility of its commercialization as a new protein additive. For modori gel, the breaking force, deformation, whiteness, and water holding capacity increased as the addition amount of RPP (0 to 0.75 mg/g) increased, and decreased at higher concentration of RPP (0.75 to 1.50 mg/g) (P < 0.05). Protein solubility of modori gel in the mixture of SDS, urea, and β‐mercaptoethanol decreased as the addition amount of RPP increased up to 0.75 mg/g, and increased at higher concentration of RPP (0.75 to 1.50 mg/g) (P < 0.05). The contents of trichloroacetic acid‐soluble peptide decreased as the addition amount of RPP (0 to 1.50 mg/g) increased (P < 0.05). Based on the result of sodium dodecyl sulfate (SDS)‐polyacrylamide gel electrophoresis (PAGE), most myosin heavy chain of surimi was not degraded when RPP was added. Thus, RPP was supposed to act as a protease inhibitor in the gelation of Alaska pollock surimi. An RPP of 0.75 mg/g was the optimal concentration to prevent the gel weakening of Alaska pollock surimi. Compounds with molecular weights less than 10 kDa in RPP had no significant effect on the gelation of Alaska pollock surimi based on the result of the dialyzed RPP.
Plant Metabolites and Nutritional Quality of Vegetables
Authors: Hounsome N. , Hounsome B. , Tomos D. , Edwards‐Jones G.
Published: April 2008

ABSTRACT:  Vegetables are an important part of the human diet and a major source of biologically active substances such as vitamins, dietary fiber, antioxidants, and cholesterol‐lowering compounds. Despite a large amount of information on this topic, the nutritional quality of vegetables has not been defined. Historically, the value of many plant nutrients and health‐promoting compounds was discovered by trial and error. By the turn of the century, the application of chromatography, mass spectrometry, infrared spectrometry, and nuclear magnetic resonance allowed quantitative and qualitative measurements of a large number of plant metabolites. Approximately 50000 metabolites have been elucidated in plants, and it is predicted that the final number will exceed 200000. Most of them have unknown function. Metabolites such as carbohydrates, organic and amino acids, vitamins, hormones, flavonoids, phenolics, and glucosinolates are essential for plant growth, development, stress adaptation, and defense. Besides the importance for the plant itself, such metabolites determine the nutritional quality of food, color, taste, smell, antioxidative, anticarcinogenic, antihypertension, anti‐inflammatory, antimicrobial, immunostimulating, and cholesterol‐lowering properties. This review is focused on major plant metabolites that characterize the nutritional quality of vegetables, and methods of their analysis.
Pilot‐Scale Production of Conjugated Linoleic Acid‐Rich Soy Oil by Photoirradiation
Authors: Jain V.P. , Proctor A. , Lall R.
Published: April 2008

ABSTRACT:  Conjugated linoleic acid (CLA) is found naturally in dairy and beef products at levels of 0.2% to 2% of the total fat. A more concentrated source of dietary CLA, low in saturated fat, would be highly desirable to obtain optimum CLA levels of about 3 g/d. We recently reported photoisomerization of soy oil with iodine catalysis to be a simple way of producing CLA in laboratory without high‐energy input or expensive enzymes and microorganisms. However, a long irradiation time of 144 h has been a limitation for this technique to be of practical value. The objectives of this study were to build a pilot plant unit to rapidly produce high‐CLA soy oil by photoirradiation and optimize the processing parameters to obtain high‐CLA soy oil. Degassed oil with dissolved‐iodine catalyst was irradiated by UV lamps in an illuminated laminar flow unit (ILFU). The ILFU consists of 2 borosilicate glass plates in a silicone lined stainless steel frame. The static mode of operation yielded 5.7% of total CLA isomers and performed twice as well than the continuous mode with 2.5% of total CLA. Irradiating oil in a static mode with reflective surfaces increased the CLA yields 3‐fold to 16.4%. About 22% of total CLA isomers can be rapidly produced from soy oil linoleic acid with 0.35% iodine catalyst in a 0.5‐cm‐thick oil layer maintained at 48 °C for 12 h. The peroxide value and GC‐MS analysis did not identify any volatile compounds characteristic of lipid oxidation. This study is a definitive step toward the commercialization of large‐scale production of CLA‐rich soy oil.
Molecular and Physical Characteristics of Squid (Todarodes pacificus) Skin Collagens and Biological Properties of Their Enzymatic Hydrolysates
Authors: Nam K.A. , You S.G. , Kim S.M.
Published: April 2008

ABSTRACT:  The physicochemical properties of squid skin collagens and biological activity of their enzymatic hydrolysates were determined to produce more value‐added materials. The amino acid compositions of the inner and outer squid skin collagens were similar, but distinct from that of bovine tendon collagen in respect to the higher levels of aspartic acid, arginine, threonine, and serine, and of the lower levels of alanine, proline, and hydroxyproline. SDS‐PAGE patterns suggested that squid skin collagen consisted of at least 2 different polypeptides (α1 and α2 chains) and their cross‐linked chains. The molecular weights of α1 and α2 chains of bovine tendon collagens were higher than those of the corresponding α1 and α2 chains of squid skin collagens. The denaturation temperatures of inner and outer skin collagens were 27.1 and 27.3 °C, respectively, which were about 9 °C lower than that of bovine tendon collagen. Water holding capacities of inner and outer squid skin collagens were relatively similar, but were significantly greater than that of bovine tendon collagen. The maximum hydrolysis of squid skin collagens was obtained as follows: for outer skin collagen, enzyme concentration, 3.5%; hydrolysis time, 83 min; pH 7.0; hydrolysis temperature, 60 °C, whereas for inner skin collagen, enzyme concentration, 3.2%; hydrolysis time, 83 min; pH 7.0; hydrolysis temperature, 60 °C. The enzymatic hydrolysates of outer and inner skin collagens were separated by Sephacryl S‐100 column, resulting in the production of 3 fractions (F1, F2, and F3). F3 fraction exhibited higher antioxidant, tyrosinase inhibitory, and antielastase activities than the other fractions.
Influence of Health and Environmental Information on Hedonic Evaluation of Organic and Conventional Bread
Authors: Annett L.E. , Muralidharan V. , Boxall P.C. , Cash S.B. , Wismer W.V.
Published: April 2008

ABSTRACT:  Grain from paired samples of the hard red spring wheat cultivar “Park” grown on both conventionally and organically managed land was milled and baked into 60% whole wheat bread. Consumers (n= 384) rated their liking of the bread samples on a 9‐point hedonic scale before (blind) and after (labeled) receiving information about organic production. Consumers liked organic bread more (P < 0.05) than conventional bread under blind and labeled conditions. Environmental information about organic production did not impact consumer preference changes for organic bread, but health information coupled with sensory evaluation increased liking of organic bread. Ordinary least squares (OLS) and binary response (probit) regression models identified that postsecondary education, income level, frequency of bread consumption, and proenvironmental attitudes played a significant role in preference changes for organic bread. The techniques used in this study demonstrate that a combination of sensory and econometric techniques strengthens the evaluation of consumer food choice.
Evaluation of Exopolysaccharide Production by Leuconostoc mesenteroides Strains Isolated from Wine
Authors: Montersino S. , Prieto A. , Muñoz R. , De Las Rivas B.
Published: April 2008

ABSTRACT:  Exopolysaccharide (EPS)‐producing lactic acid bacteria are responsible for the alteration of wine and other fermented beverages. The potential to produce EPS was investigated for Leuconostoc mesenteroides strains isolated from Spanish grape must and wine. Most strains were able to produce EPS from sucrose containing media. Based on their EPS‐producing phenotype and on their EPS monosaccharide composition, the L. mesenteroides strains analyzed could be arranged in 2 groups. One group comprises mucoid strains producing a glucan polymer, and the other group includes strains producing a fructan polymer. The presence of a glucosyltransferase encoding gene in the glucan producing L. mesenteroides strains was assayed by PCR. Two primer sets, PF1‐PF8 and GTFF‐GTFR, were used to amplify internal fragment of known glucosyltransferase genes. None of the glucan‐producing strains gave a positive amplicon by the primer sets used. Therefore, new tools need to be developed to broaden the range of potentially spoiling agents detected by PCR in fermented beverages.
Social Strain, Structural Breakdown, Political Opportunity, and Collective Action
Authors: Buechler Steven M.
Published: April 2008

Sociology traditionally identified social strain and structural breakdown as causes of collective action. Such explanations were widely interpreted as endorsing social order and viewing its breakdown and the resulting collective action in a negative light. In the 1970s, advocates of the resource mobilization perspective criticized strain and breakdown explanations and this negative connotation of collective action. Rather than strain or breakdown, these theorists explained collective action in terms of solidarity, interests, and resources. Despite these criticisms, strain and breakdown explanations persisted at the margins of mainstream social movement theory. Moreover, the resource mobilization approach invoked ‘opportunity’ to explain collective action. There is a strong resemblance between ‘strain and breakdown’ and ‘opportunity’. Both explain collective action in terms of external, facilitating conditions, but opportunity explanations connote a more favorable evaluation of the resulting collective action. Such resemblances suggest the viability of a synthesis between older and newer explanations of collective action.
Mapping space for water: screening for urban flash flooding
Authors: Hankin B. , Waller S. , Astle G. , Kellagher R.
Published: April 2008

This paper builds on the ‘Flooding from Other Sources’ project (HA4a), funded as part of Defra's Making Space for Water strategy. The HA4a study concluded that flood risk mapping is feasible for many of the sources of flooding that were investigated, which are not currently covered by the Environment Agency Flood Map, using existing flow modelling and GIS tools. However, there are some major constraints in terms of the need to undertake extensive data collection to allow the generation of useful flood maps that are not dominated by modelling uncertainties. The project anticipated that different levels of data collection and modelling might be needed for different purposes, given the hierarchical nature of UK flood risk assessment and management in the United Kingdom under PPS25 and the EC Floods Directive. This paper compares and contrasts three different approaches to urban flood modelling using topographic analysis, blanket extreme rainfall and semi‐coupled sewer/overland routing. The UK summer floods 2007 have highlighted the pressing need for mapping the risk from urban flash flooding, and the Pitt Review has recommended that areas at high risk from surface waters should be urgently identified. This can be done now at some level of detail, and we can be guided as to what level, from our increasing knowledge of vulnerable populations, from records of historical flooding and by using some of the screening methods described herein.
Chlamydophila psittaci Infections in Humans during an Outbreak of Psittacosis from Poultry in Germany
Authors: Gaede W. , Reckling K.‐F. , Dresenkamp B. , Kenklies S. , Schubert E. , Noack U. , Irmscher H.‐M. , Ludwig C. , Hotzel H. , Sachse K.
Published: April 2008

In 2005, an outbreak of severe respiratory disease in a mixed poultry flock that was infected with Chlamydophila (C.) psittaci led to dissemination of the infection to at least 100 small poultry farms in 11 districts of Central Germany. At the same time, a total of 24 persons in contact with poultry from one of the flocks reported flu‐like symptoms to their physician, thus suggesting zoonotic transmission. Within 3 weeks, seven individuals had to be hospitalized, with three of them requiring intensive care. Analysis of ompA sequences from chlamydial isolates and directly from clinical samples revealed the presence of both genotype A and E/B of C. psittaci at the source of the outbreak and in contact flocks. Genotype A was also detected in the three severely ill patients. The findings of the present study demonstrate the high zoonotic potential of avian chlamydiae. To ensure speedy eradication of psittacosis in poultry flocks and effective treatment of infected humans, fast, sensitive and species‐specific detection of the causative agent is essential, as well as close collaboration between regional public health services, attending physicians and the diagnostic laboratories involved.
Numerical Modeling of Second-Phase Particle Effects on Localized Deformation
Authors: Inal Kaan , Simha Hari M. , Mishra Raja K.
Published: April 2008

A new finite element analysis based on rate dependent crystal plasticity theory has been developed to investigate the effects of second-phase particles on the initiation and propagation of localized deformation in the form of shear bands. The new model can incorporate electron backscatter diffraction data into finite element analyses. The numerical analysis not only accounts for crystallographic texture (and its evolution) but also accounts for grain morphologies. A unit-cell approach has been adopted where an element or a number of elements of the finite element mesh are considered to represent a single crystal within the polycrystal aggregate. Second-phase particles in the form of finite elements with stiff elastic properties are randomly distributed within the unit cell. Numerical simulations of unixial tension, in-plane plane strain tension, and balanced biaxial tension have been performed by models with and without second-phase particles for a direct chill-cast AA5754 aluminum alloy sheet. The effects of various parameters, such as second-phase particle distribution, texture evolution, and strain paths on particle induced localized deformation patterns, are also investigated.
High-Resolution Methods for Characterizing Mesoscale Dislocation Structures
Authors: Landon C. D. , Adams B. L. , Kacher J.
Published: April 2008

It has become apparent through experimentation at the micro- and nanolevels that the crystalline defects known as dislocations have significant effects on a material’s properties. Accordingly, a complete material state description must include the characterization of the dislocated state. However, this characterization presents a twofold problem: resolution and representation. In general, high-resolution microscopy techniques are only useful for considering a few dislocations at a time, but automated high-speed methods are only capable of resolving dislocation densities well above the average density in a typical annealed metal. The second challenge is developing a method of representation for the dislocated state. Unlike most state quantities, dislocation lengths are not conserved and complete representation would require tracking of position, momentum, and interactions, as well as the creation and annihilation of dislocations. Such a scheme becomes unwieldy when considering the large numbers of dislocations involved in common crystal plasticity. In 1970, Kröner (“Initial Studies of a Plasticity Theory Based Upon Statistical Mechanics,” Inelastic Behaviors of Solids (Materials Sciences and Engineering), M. F. Kanninen et al., eds., McGraw-Hill, New York, pp. 137–147), a pioneer in the continuum representation of dislocations, proposed a statistical method using n-point correlations to classify the dislocated state in a compact form. In addition to providing a convenient form, the correlations naturally identify dipoles, multipoles, and other higher order structures, such as cells, networks, and braids. As formulated, Kröner’s method would require high-resolution microscopy techniques, which limits its utility for experimental measurements. The current work presents a modification to Kröner’s method that would allow it to be used within the currently available resolution limits of bulk microscopy. Furthermore, in this work, newly developed microscopy techniques are employed to refine those resolution limits to more significant levels. The high-resolution bulk dislocation characterization is applied to a well-annealed nickel specimen and the results including visualizations of mesoscale structures are presented.
Modeling Damage Evolution in Friction Stir Welding Process
Authors: He Youliang , Dawson Paul R. , Boyce Donald E.
Published: April 2008

The evolution of voids (damage) in friction stir welding processes was simulated using a void growth model that incorporates viscoplastic flow and strain hardening of incompressible materials during plastic deformation. The void growth rate is expressed as a function of the void volume fraction, the effective deformation rate, and the ratio of the mean stress to the strength of the material. A steady-state Eulerian finite element formulation was employed to calculate the flow and thermal fields in three dimensions, and the evolution of the strength and damage was evaluated by integrating the evolution equations along the streamlines obtained in the Eulerian configuration. The distribution of internal voids within the material was qualitatively compared with experimental results, and a good agreement was observed in terms of the spatial location of voids. The effects of pin geometry and operational parameters such as tool rotational and travel speeds on the evolution of damage were also examined.
Effect of Size-Dependent Cavitation on Micro- to Macroscopic Mechanical Behavior of Rubber-Blended Polymer
Authors: Riku Isamu , Mimura Koji , Tomita Yoshihiro
Published: April 2008

In rubber-blended polymer, the onset of cavitation in the particles relaxes the high triaxiality stress state and suppresses the onset of crazing in the polymer. As a result, large plastic deformation is substantially promoted compared with single-phase polymer. On the other hand, it is also well known that the onset of cavitation depends on the size of particle. To investigate the size dependence of cavitation behavior in the particle, a theoretical analysis is done employing a void model under plane strain condition, which takes into account the surface tension and the limiting stretch of the void. Continuously, to study the effect of the size-dependent cavitation on the micro- to macroscopic mechanical behavior of the blend, a computational model is proposed for the blend consisting of irregularly distributed heterogeneous particles containing the void with surface force. The results indicate that when the size of the particle decreases to a critical value that depends on both the initial shear modulus of particle and the surface tension on the surface of void, the increase of the critical stress for the onset of cavitation becomes remarkable and consequently, the onset of cavitation is eliminated. When the particle is embedded in polymer, the relation between average normal stress, which is acting on the interface of particle and matrix, and volumetric strain of particle shows dependence on the size of particle but no dependence on the triaxiality of macroscopic loading condition. For the blend consisting of particles smaller than the critical value, the onset of cavitation is eliminated in particles and as a result, the conformation of the shape of particle to the localized shear band in matrix becomes difficult and the shear deformation behavior tends to occur all over the matrix. Furthermore, in this case, the area of the maximum mean stress is confined to the area adjacent to the particle and the value of it increases almost linearly throughout the whole deformation process, which would lead to the onset of crazing in matrix. On the other hand, it is clarified that the onset of cavitation is predominant in the localized microscopic region containing heterogeneous particles and therefore, the plastic deformation is promoted in this region.
Probing Microstructure Dynamics With X-Ray Diffraction Microscopy
Authors: Suter R. M. , Hefferan C. M. , Li S. F. , Hennessy D. , Xiao C. , Lienert U. , Tieman B.
Published: April 2008

We describe our recent work on developing X-ray diffraction microscopy as a tool for studying three dimensional microstructure dynamics. This is a measurement technique that is demanding of experimental hardware and presents a challenging computational problem to reconstruct the sample microstructure. A dedicated apparatus exists at beamline 1-ID of the Advanced Photon Source for performing these measurements. Submicron mechanical precision is combined with focusing optics that yield ≈2μmhigh×1.3mm wide line focused beam at 50keV. Our forward modeling analysis approach generates diffraction from a simulated two dimensional triangular mesh. Each mesh element is assigned an independent orientation by optimizing the fit to experimental data. The method is computationally demanding but is adaptable to parallel computation. We illustrate the state of development by measuring and reconstructing a planar section of an aluminum polycrystal microstructure. An orientation map of ∼90 grains is obtained along with a map showing the spatial variation in the quality of the fit to the data. Sensitivity to orientation variations within grains is on the order of 0.1deg. Volumetric studies of the response of microstructures to thermal or mechanical treatment will soon become practical. It should be possible to incorporate explicit treatment of defect distributions and to observe their evolution.
In Situ Imaging of High Cycle Fatigue Crack Growth in Single Crystal Nickel-Base Superalloys by Synchrotron X-Radiation
Authors: Liu Liu , Husseini Naji S. , Torbet Christopher J. , Kumah Divine P. , Clarke Roy , Pollock Tresa M. , Jones J. Wayne
Published: April 2008

A novel X-ray synchrotron radiation approach is described for real-time imaging of the initiation and growth of fatigue cracks during ultrasonic fatigue (f=20kHz). We report here on new insights on single crystal nickel-base superalloys gained with this approach. A portable ultrasonic fatigue instrument has been designed that can be installed at a high-brilliance X-ray beamline. With a load line and fatigue specimen configuration, this instrument produces stable fatigue crack propagation for specimens as thin as 150μm. The in situ cyclic loading/imaging system has been used initially to image real-time crystallographic fatigue and crack growth under positive mean axial stress in the turbine blade alloy CMSX-4.
Hot Tearing in Steels During Solidification: Experimental Characterization and Thermomechanical Modeling
Authors: Olivier Cerri , Yvan Chastel , Michel Bellet
Published: April 2008

Hot tearing is a major defect in castings or semifinished cast products. It corresponds to the opening of cracks in the mushy zone and, more precisely, in the areas with high fraction of solid (typically 0.9 and beyond) when the material is subjected to deformations leading to local tensile stress. Various kinds of criteria have been developed to highlight a risk of formation of hot tears. The aim of this study is to evaluate their capability to predict the occurrence of hot tears correctly. In order to do so, two kinds of tests have been analyzed with the use of a thermomechanical finite element model.
Polycrystal Plasticity Based Predictions of Strain Localization in Metal Forming
Authors: Bernier Joel V. , Barton Nathan R. , Knap Jaroslaw
Published: April 2008

In this study, a multiscale material model is employed to simulate two metal forming processes: 2D plane strain compression and a 3D biaxial bulge test. A generalized Taylor-type polycrystal model is employed to describe the fine scale viscoplastic response of the material, while the coarse scale response is computed using a multiphysics finite element code. The coupling between the local responses of the textured polycrystal and the continuum level is achieved via an adaptive sampling framework, which is shown to greatly reduce the total number of fine scale evaluations required to achieve a specified error tolerance. The anisotropy represented at the fine scale is sufficient to observe strain localization in both forming processes. For the case of idealized plane strain compression, a fairly diffuse yet distinct patterning of plastic strain localization develops in a manner consistent with experimental observations. The application of friction constraints to the compression surfaces—as is present in channel die compression tests—dramatically strengthens and redistributes the localization patterns. The simulated biaxial bulge test also demonstrates strain localization that is in agreement with the locations of diffuse necks in experimental observations. The tests are conducted using a federated multiple-program multiple-data simulation, which allows for load balancing between the coarse and fine scale calculations. Such a simulation framework is capable of efficiently embedding physically robust, but computationally expensive material models in component scale simulations appropriate to design decisions.
Dislocation Density Tensor Characterization of Deformation Using 3D X-Ray Microscopy
Authors: Larson B. C. , Tischler J. Z. , El-Azab Anter , Liu Wenjun
Published: April 2008

Three-dimensional (3D) X-ray microscopy with submicron resolution has been used to make spatially resolved measurements of lattice curvature and elastic strain over two-dimensional slices in thin deformed Si plates. The techniques and capabilities associated with white-beam 3D X-ray microscopy are discussed, and both theoretical and experimental considerations associated with the measurement of Nye dislocation density tensors in deformed materials are presented. The ability to determine the local geometrically necessary dislocation (GND) density in the form of a dislocation density tensor, with micron spatial resolution over mesoscopic length scales, is demonstrated. Results are shown for the special case of an elastically bent (dislocation free) thin Si plate and for a similar thin Si plate that was bent plastically, above the brittle-to-ductile transition temperature, to introduce dislocations. Within the uncertainties of the measurements, the known result that GND density is zero for elastic bending is obtained, and well-defined GND distributions are observed in the plastically deformed Si plate. The direct and absolute connection between experimental measurements of GND density and multiscale modeling and computer simulations of deformation microstructures is discussed to highlight the importance of submicron-resolution 3D X-ray microscopy for mesoscale characterization of material defects and to achieve a fundamental understanding of deformation in ductile materials.
Polycrystal Simulations Investigating the Effect of Additional Slip System Availability in a 6063 Aluminum Alloy at Elevated Temperature
Authors: Maniatty Antoinette M. , Littlewood David J. , Lu Jing
Published: April 2008

In order to better understand and predict the intragrain heterogeneous deformation in a 6063 aluminum alloy deformed at an elevated temperature, when additional slip systems beyond the usual octahedral slip systems are active, a modeling framework for analyzing representative polycrystals under these conditions is presented. A model polycrystal that has a similar microstructure to that observed in the material under consideration is modeled with a finite element analysis. A large number of elements per grain (more than 1000) are used to capture well the intragranular heterogeneous response. The polycrystal model is analyzed with three different sets of initial orientations. A compression test is used to calibrate the material model, and a macroscale simulation of the compression test is used to define the deformation history applied to the model polycrystal. In order to reduce boundary condition effects, periodic boundary conditions are applied to the model polycrystal. To investigate the effect of additional slip systems expected to be active at elevated temperatures, the results considering only the 12 {111}⟨110⟩ slip systems are compared to the results with the additional 12 {110}⟨110⟩ and {001}⟨110⟩ slip systems available (i.e., 24 available slip systems). The resulting predicted grain structure and texture are compared to the experimentally observed grain structure and texture in the 6063 aluminum alloy compression sample as well as to the available data in the literature, and the intragranular misorientations are studied.
Mechanical Properties of Crimped Mineral Wools: Identification From Digital Image Correlation
Authors: Witz Jean-François , Roux Stéphane , Hild François , Rieunier Jean-Baptiste
Published: April 2008

Crimped mineral wools are characterized by a strongly anisotropic microstructure, whose local preferential orientation is highly heterogeneous. It is proposed to identify the local anisotropic elastic behavior through a combination of different tools based on image analysis. First, the local orientation map is determined from a reference image. Second, a series of images captured at different loading stages is analyzed with a digital image correlation code to estimate the displacement field. Last, an inverse analysis is applied to evaluate the four elastic moduli of the local elastic properties. This procedure is tested against a set of experimental data on mineral wool with different crimping structures.
Transfer Function Formulation of Constrained Distributed Parameter Systems, Part II: Applications
Authors: Chung C. H. , Tan C. A.
Published: April 2008

In this paper, the application of the transfer function formulation and the generalized displacement method (GDM) to the analysis of constrained distributed parameter systems is illustrated. Two kinds of classical examples are considered. In the constrained free-free beam example, it is shown how the GDM gives the eigensolutions without requiring knowledge of the normal modes of the unconstrained beam. In the string on a partial elastic foundation example, mode localization and eigenvalue loci veering phenomena are examined. It is shown that mode localizaation can occur in spatially symmetric systems and for modes whose frequency loci do not veer.
Dualities in Free Vibration of Minimum Surface Membranes
Authors: Tabarrok B. , Tong Liyong
Published: April 2008

For the linear free vibration of minimum surface membranes, the governing equations and the associated variational functional are derived. Using the basic geometrical characteristics of any two minimum surface membranes, the analysis brings to light the existence of geometrically different surface membranes with identical surface areas, natural frequencies, and vibrating modes.
Modeling of One-Dimensional Thermomechanical Erosion of High-Temperature Ablatives
Authors: Yang B. C. , Cheung F. B. , Koo J. H.
Published: April 2008

A one-dimensional material erosion model has been developed to describe the simultaneous processes of thermochemical ablation and mechanical erosion of ablatives exposed to high-temperature particle-laden flows. The model accounts for the effect of mechanical erosion due to thermochemical weakening of the material and the influence of particle impact on the thermochemical ablation. Numerical calculations of the erosion depth (i.e., surface recession) have been made for various thermal and particle loading conditions. The predicted results are found to agree reasonably well with available experimental data.
Eshelby Tensor for an Elastic Inclusion With Slightly Weakened Interface
Authors: Qu Jianmin
Published: April 2008

The Eshelby tensor for an ellipsoidal inclusion in an elastic matrix of infinite extent is considered in this paper. Instead of assuming perfect bonding between the inclusion and the matrix, the interface between the inclusion and the matrix is modeled by a spring layer of vanishing thickness. The inclusion- matrix interface is said to be slightly weakened if the compliance of the spring layer is much smaller than that of the matrix material. By virtue of the Betti-Rayleigh reciprocal identity in linear elasticity, an integral representation for the displacement field due to an elastic inclusion with a spring layer interface is derived. Explicit expressions of the Eshelby tensor for an ellipsoidal inclusion with slightly weakened interface are obtained through an iteration procedure developed from the integral representation.
Stresses in Narrow Regions
Authors: Keller J. B.
Published: April 2008

A method for calculating the stress distribution in a narrow region of an elastic plate is presented. It consists in treating the narrow region by beam theory, treating the rest of the plate by any computational or analytical method, and matching the results of these two calculations. It is illustrated by finding the stress distribution in the narrow region of a plate, between a straight edge and a nearby hole, when the plate is under tension. The same method can be applied to three-dimensional bodies with thin plate-like or shell-like regions.
Cyclic Viscoplastic Constitutive Equations, Part I: A Thermodynamically Consistent Formulation
Authors: Chaboche J.-L.
Published: April 2008

Cyclic viscoplastic constitutive equations are increasingly used for the inelastic analysis of structures under severe thermomechanical conditions. The purpose of the paper is to show how the classical models can be modified in order to follow the general principles of thermodynamics with internal variables. Using the restrictive framework of standard generalized materials, the state variables associated to various kinds of kinematic and isotropic hardening are selected. The evolution equations for these internal variables are then formulated in a slightly less restrictive form. For each hardening process, the separation of the total plastic work into energy dissipated as heat and energy stored in the material is discussed in detail.
Elastic-Plastic Finite Element Analysis of Repeated Indentation of a Half-Space by a Rigid Sphere
Authors: Kral E. R. , Komvopoulos K. , Bogy D. B.
Published: April 2008

The elastic-plastic contact problem of a rigid sphere indenting a homogeneous halfspace is analyzed with the finite element method. Emphasis is placed on the load range between elastic and fully plastic deformation, which has not yet been fully investigated. The rigid sphere is modeled by contact elements, thus eliminating the need to assume a particular pressure profile. Different elastic properties, with both elastic-perfectly plastic and isotropic strain hardening behaviors, are considered. Up to four complete frictionless load-unload cycles are applied to a peak load of 300 times the load necessary for the initiation of yielding. Results for the contact pressure, surf ace and subsurface stresses, initiation and growth of the plastic zone, and yielding of the half-space during unloading are presented. The effect of residual displacements on the contact pressure during subsequent load cycles is examined. The influence of strain hardening on the loading and residual stresses is analyzed and the consequences for crack initiation are discussed in light of these results. The accumulation of plastic strain in the yielding regions is tracked through the subsequent load cycles as the material approaches a steady-state elastic cycle, and the significance of the loading and residual stresses on the deformation characteristics is interpreted in the context of finite element results.
Local Delamination Growth in Layered Systems Under Compressive Load
Authors: Madenci E. , Westmann R. A.
Published: April 2008

This paper addresses the problem of delamination growth prior to its buckling using mathematical techniques appropriate for mixed boundary value problems. The formulation presented herein does not require buckling as a necessary condition for delamination growth. By employing the stability equations of elasticity theory, solutions to the problem of an infinite layer with a slightly imperfect circular delamination subjected to axisymmetric and uniaxial in-plane compressive loading are presented. This approach permits the determination of the stress intensity factors under specified initial imperfections for applied compressive stress.
On the Mode Splitting of Degenerate Mechanical Systems Containing Cracks
Authors: Shen I. Y. , Mote C. D.
Published: April 2008

This paper presents sufficient conditions governing mode splitting in a two-dimensional, degenerate, mechanical system whose eigensolutions satisfy the Helmholtz equation. When cracks are introduced into such systems, a pair of repeated vibration modes may remain repeated or become distinct (termed split modes) depending on the location and geometry of the cracks. Two types of split modes can occur. Split modes of the first kind are a pair of split modes in which one mode undergoes a frequency shift but the other does not. In contrast, split modes of the second kind are a pair of split modes in which both modes undergo frequency shifts. A sufficient condition for split modes of the first kind is derived through an orthogonal transformation of repeated eigenmodes of the perfect system. Sufficient conditions for repeated modes and split modes of the second kind are derived through an asymptotic analysis. Numerical examples on square and circular domains illustrate the analytical predictions on mode splitting.
Near-Tip Fields in a Notched Body With Dislocations and Body Forces
Authors: Wu Kuang-Chong , Chang Fong-Tai
Published: April 2008

The dominant stress fields due to a dislocation and/or a body force near the tip of an isotropic or anisotropic notched body are derived. The structures of the neartip stress fields for anisotropic materials are constructed by using Stroh ’s formalism for anisotropic elasticity. The intensity coefficients contained in the near-tip fields are determined by Betti’s reciprocity theorem. Special attention is given to orthotropic and isotropic materials. Some explicit results of intensity coefficients due to concentrated forces on the notch faces and dislocations at the wedge bisector are also provided.
Analytical Solutions for a Spinning Rigid Body Subject to Time-Varying Body-Fixed Torques, Part I: Constant Axial Torque
Authors: Longuski J. M. , Tsiotras P.
Published: April 2008

Analytic solutions are derived for the general attitude motion of a near-symmetric rigid body subject to time-varying torques in terms of certain integrals. A methodology is presented for evaluating these integrals in closed form. We consider the case of constant torque about the spin axis and of transverse torques expressed in terms of polynomial functions of time. For an axisymmetric body with constant axial torque, the resulting solutions of Euler’s equations of motion are exact. The analytic solutions for the Eulerian angles are approximate owing to a small angle assumption, but these apply to a wide variety of practical problems. The case when all three components of the external torque vector vary simultaneously with time is much more difficult and is treated in Part II.
Domains of Attraction of a Forced Beam by Interpolated Mapping
Authors: Lee W. K. , Ghang M. R.
Published: April 2008

A nonlinear dissipative dynamical system can often have multiple attractors. In this case it is important to study the global behavior of the system by determining the global domain of attraction of each attractor. In this paper we study the global behavior of a forced beam with two-mode interaction. The governing equation of motion is reduced to two second-order nonlinear nonautonomous ordinary differential equations. When ω2 ≈ 3ω1 and Ω ≈ ω1, the system can have two asymptotically stable steady-state periodic solutions, where ω1, ω2 and Ω denote natural frequencies of the first and second modes and the excitation frequency, respectively. Both solutions have the same period as the excitation period. Therefore, each of them shows up as a period-1 solution in Poincare map. We show how interpolated mapping method can be used to determine the two four-dimensional domains of attraction of the two solutions in a very effective way. The results are compared with the ones obtained by direct numerical integration.
Steady Motion of a Thread Over a Rotating Roller
Authors: Yang R.-J.
Published: April 2008

Dynamic equations of steady motion governing the behavior of threads over rotating arbitrary-axisymmetric rollers are derived. Various types of boundary conditions resulting in initial value or boundary value problems are discussed. Analytical solutions for the case of a circular cylinder are found. Two of the integrals obtained are exact. The third one, being a perturbation result, is thus approximate. Comparisons of results for a circular cylinder with those for tapered and parabolic rollers are made.
The Mechanics of Ideal Forming
Authors: Chung K. , Richmond O.
Published: April 2008

In this paper, the mechanics of ideal forming theory are summarized for general, three-dimensional, nonsteady processes. This theory has been developed for the initial stages of designing deformation processes. The objectives is to directly determine configurations, both initial and intermediate, that are required to ideally form a specified final shape. In the proposed theory, material elements are prescribed to deform along minimum plastic work paths, assuming that the materials have optimum formabilities in such paths. Then, the ideal forming processes are obtained so as to have the most uniform strain distributions in final products without shear tractions. As solutions, the theory provides the evolution of intermediate shapes of products and external forces as well as optimum strain distributions. Since the requirement of ideal forming to follow minimum work paths involves an over determination of the field equations, the theory places constraints on constitutive and boundary conditions. For example, tool interfaces must be frictionless and yield conditions must have vertices to achieve self-equilibrating three-dimensional deformations in most cases. Despite these constraints, the theory is believed to provide a useful starting point for deformation process design.
The Effect of Wire Rope Mechanics on the Material Properties of Cord Composites: An Elasticity Approach
Authors: Shield C. K. , Costello G. A.
Published: April 2008

An analytical model is presented for the behavior of cord reinforced rubber composite plates taking into account the extension-twisting coupling of the cord based on an equilibrium formulation. The effect of the cord mechanics on the unidirectional lamina properties is investigated for various modulus ratios and geometries. The equations of equilibrium are derived for the unidirectional plate. Solutions are found for the following plate problems, uniaxial tension along the cord direction, uniaxial tension perpendicular to the cord direction, and pure shear. These solutions are used to obtain average material properties and to investigate the influence of cord mechanics on the plate response. For very flexible synthetic rubbers, the behavior of the unidirectional lamina exhibits a good deal of extension twisting coupling, whereas for stiffer vulcanized rubbers, the rubber acts to restrain the cords from unwinding.
Three-Dimensional Unilateral Frictionless Contact Problem for Finite Bodies
Authors: Rabinovich V. L. , Sipcic S. R. , Sarin V. K.
Published: April 2008

The numerical solution of the three-dimensional frictionless contact problem is obtained by means of a boundary element discretization of a variational inequality and its related extremum principle. The discretization leads to a finite dimensional quadratic programming problem, solved by a modification of the gradient projection method. The associated Green’s function is approximated using a standard direct boundary element procedure. The numerical method is applicable to any type of contacting bodies geometry under arbitrary loading. The examples considered were chosen such as to illustrate a distinct ability of the method to capture the influence of a body shape on the contact area and pressure acting in it. It has been demonstrated that the symmetry properties of the Green’s operator hold only asymptotically for the discretized problem.
Distributed Transfer Function Analysis of Complex Distributed Parameter Systems
Authors: Yang B.
Published: April 2008

This paper presents a new analytical and numerical method for modeling and synthesis of complex distributed parameter systems that are multiple continua combined with lumped parameter systems. In the analysis, the complex distributed parameter system is first divided into a number of subsystems; the distributed transfer functions of each subsystem are determined in exact and closed form by a state space technique. The complex distributed parameter system is then assembled by imposing displacement compatibility and force balance at the nodes where the subsystems are interconnected. With the distributed transfer functions and the transfer functions of the constraints and lumped parameter systems, exact, closed-form formulation is obtained for various dynamics and vibration problems. The method does not require a knowledge of system eigensolutions, and is valid for non-self-adjoint systems with inhomogeneous boundary conditions. In addition, the proposed method is convenient in computer coding and suitable for computerized symbolic manipulation.
On Statistics of First-Passage Failure
Authors: Cai G. Q. , Lin Y. K.
Published: April 2008

The event in which the response of a randomly excited dynamical system passes, for the first time, a critical magnitude zc is investigated. When the response variable in question can be modeled as a one-dimensional diffusion process, defined on [zl, zc], the statistical moment of the first passage time of an arbitrary order is governed by the classical Pontryagin equation, subject to suitable boundary conditions. It is shown that, when a boundary is singular, it must be either an entrance, a regular boundary, or a repulsive natural boundary in order that a solution for the Pontryagin equation is physically meaningful. Boundary conditions are obtained for three types of singular boundaries and applied to the second-order oscillators in which the amplitude or energy process can be approximated as a Markov process. Illustrative examples are given of linear and nonlinear oscillators under additive and/or multiplicative random excitations.
Bifurcation Effects in Ductile Metals With Nonlocal Damage
Authors: Leblond J. B. , Perrin G. , Devaux J.
Published: April 2008

The purpose of this paper is to investigate some bifurcation phenomena in a porous ductile material described by the classical Gurson (1977) model, but with a modified, nonlocal evolution equation for the porosity. Two distinct problems are analyzed theoretically: appearance of a discontinuous velocity gradient in a finite, inhomogeneous body, and arbitrary loss of uniqueness of the velocity field in an infinite, homogeneous medium. It is shown that no bifurcation of the first type can occur provided that the hardening slope of the sound (void-free) matrix is positive. In contrast, bifurcations of the second type are possible; nonlocality does not modify the conditions of first occurrence of bifurcation but does change the corresponding bifurcation mode, the wavelength of the latter being no longer arbitrary but necessarily infinite. A FE study of shear banding in a rectangular mesh deformed in plane strain tension is finally presented in order to qualitatively illustrate the effect of finiteness of the body; numerical results do evidence notable differences with respect to the case of an infinite, homogeneous medium envisaged theoretically.