bluuebunny/crossref_metadata_2025 huggingface dataset:
Retinal arterioles have impaired reactivity to hyperoxia in type 1 diabetes
Authors: Justesen Birgitte L. , Mistry Paresh , Chaturvedi Nish , Thom Simon A. , Witt Nicholas , Köhler Dennis , Hughes Alun D. , Sjølie Anne Katrin
Published: July 2009

Purpose:  Diabetes has adverse effects on the retinal microvasculature. The purpose of this study was to compare the effects of inhalation of hypoxic, hyperoxic and normoxic–hypercapnic gas mixtures on retinal vessel diameter in people with and without diabetes.

Methods:  Sixty‐one participants (aged 24–50 years) 29 with (male : female ratio 2.6 : 1) and 32 without (male : female ratio 0.7 : 1) diabetes, inhaled hypoxic, hyperoxic and normoxic–hypercapnic gas mixtures for 3–5 mins. The diameters of arterioles and venules were measured using digital retinal images taken before and after gas inhalation.

Results:  There was no significant difference in the diameters of arterioles and venules prior to gas inhalation in people with and without diabetes. Inhalation of the hyperoxic gas mixture caused a statistically significant decrease in arteriolar and venular diameters without altering mean arterial pressure significantly. Arteriolar vasoconstriction in response to the hyperoxic gas mixture was significantly reduced in people with diabetes (3.95% versus 7.75%; p = 0.04), but venular vasoconstriction did not differ significantly. A hypoxic gas mixture caused increased arteriolar and venular diameter and a normoxic–hypercapnic gas mixture had no significant effect on vessel diameter. Responses to hypoxic and normoxic–hypercapnic gas did not differ significantly between diabetes and non‐diabetes subjects.

Conclusions:  Type 1 diabetes impairs retinal arteriolar responses to hyperoxia. Abnormalities in retinal arteriolar reactivity in response to oxygen may play a role in the development of diabetic retinopathy and this technique may represent a simple means of identifying early abnormalities in the reactivity of retinal arterioles in diabetes.
Diagnostic accuracy of Heidelberg Retina Tomograph III classifications in a Turkish primary open‐angle glaucoma population
Authors: Bozkurt Banu , Irkec Murat , Arslan Umut
Published: July 2009

Purpose:  This study aimed to evaluate the diagnostic accuracy of Moorfields regression analysis (MRA) and the glaucoma probability score (GPS) in primary open‐angle glaucoma (POAG) and to measure the level of agreement between the two algorithms in classifying eyes as normal or abnormal in a Turkish population.

Methods:  We prospectively selected 184 healthy subjects and 158 subjects with POAG, who underwent an ophthalmological examination, visual field analysis and imaging with the Heidelberg Retina Tomograph II, using HRT III software, Version 3.0. The diagnostic accuracies of the two classifications were measured when the borderline was taken as either normal (highest specificity criteria) or abnormal (highest sensitivity criteria). The agreement between them was calculated using the unweighted kappa (κ) coefficient.

Results:  Optic nerve head topographic parameters showed statistically significant differences between the control and POAG groups (p < 0.001). The parameters with the highest area under the receiver operating characteristic curves were global GPS (0.86), cup : disc area (0.85), rim : disc area (0.85) and vertical cup : disc (0.85). According to the highest specificity criteria, MRA had a sensitivity of 67.7% and a specificity of 95.1%, whereas the GPS had a sensitivity of 70.9% and a specificity of 88.0%. According to the highest sensitivity criteria, MRA had a sensitivity of 81.0% and a specificity of 75.0%, whereas the GPS had a sensitivity of 89.2% and a specificity of 57.6%. A moderate agreement of 68% (233 eyes) with a κ coefficient of 0.51 was found between MRA and the GPS.

Conclusions:  The GPS automated classification showed similar sensitivity to MRA, but considerably lower specificity, when applied in a Turkish population.
Management of congenital nasolacrimal duct obstruction
Authors: Takahashi Yasuhiro , Kakizaki Hirohiko , Chan Weng O. , Selva Dinesh
Published: July 2009

Our review aims to provide an update of management protocols for congenital nasolacrimal duct obstruction (CNDO). Although early probing performed before the age of 1 year was traditionally recommended, many reports have since confirmed high frequencies of spontaneous resolution during the first year of life. Accordingly, a ‘wait‐and‐see’ approach, combined with conservative therapies, is judged to be the best option in infants aged < 1 year. By contrast, persistent obstruction beyond 1 year of age warrants probing as a first‐line interventional therapy. However, the optimal timing for probing remains controversial. Although there remains a high possibility of spontaneous resolution after the first year of age, this must be balanced against the decrease in success rates for probing that accompanies advancing age. If conservative management fails, persistent CNDO beyond 1 year of age should be managed either by further observation or by primary probing according to the severity of symptoms. In patients in whom probing fails, advanced treatment such as balloon catheter dilation, silicone tube intubation or dacryocystorhinostomy may be considered.
Contracting in the shadow of the law
Authors: Chakravarty Surajeet , MacLeod W. Bentley
Published: July 2009

Economic models of contract typically assume that courts enforce obligations based on verifiable events (corresponding to the legal rule of specific performance). As a matter of law, this is not the case. This leaves open the question of optimal contract design given the available remedies used by the courts. This article shows that American standard form construction contracts can be viewed as an efficient mechanism for implementing building projects given existing legal rules. It is shown that a central feature of these contracts is the inclusion of governance covenants that shape the scope of authority and regulate the ex post bargaining power of parties. Our model also implies that the legal remedies of mistake, impossibility and the doctrine limiting damages for unforeseen events developed in the case of Hadley v. Baxendale are efficient solutions to the problem of implementing complex exchange.
Comparative advertising: disclosing horizontal match information
Authors: Anderson Simon P. , Renault Régis
Published: July 2009

Improved consumer information about horizontal aspects of products of similar quality leads to better consumer matching but also to higher prices, so consumer surplus can go up or down, while profits rise. With enough quality asymmetry, though, the higher‐quality (and hence larger) firm's price falls with more information, so both effects benefit consumers. This occurs when comparative advertising is used against a large firm by a small one. Comparative advertising, as it imparts more information, therefore helps consumers. Although it also improves the profitability of the small firm, overall welfare goes down because of the large loss to the attacked firm.
Do retail gasoline prices respond asymmetrically to cost shocks? The influence of Edgeworth Cycles
Authors: Noel Michael
Published: July 2009

Asymmetric price cycles similar to Edgeworth Cycles are appearing in increasingly many retail gasoline markets in the United States and worldwide. The asymmetry in the cycles can give rise to a finding of asymmetric price responses to cost shocks (asymmetric passthrough). This article estimates asymmetric passthrough for the market of Toronto, which exhibits cycles, and decomposes it into two components—that part explainable by the cycles and that part driven by other unknown sources. Significant asymmetric passthrough is found, with increases passed through more quickly than decreases. A significant cause of the finding is the presence of the cycles themselves.
Analysis of clonally related environmental Vibrio cholerae O1 El Tor isolated before 1992 from Varanasi, India reveals origin of SXT‐ICEs belonging to O139 and O1 serogroups
Authors: Mohapatra Saswat S. , Mantri Chinmay K. , Mohapatra Harapriya , Colwell Rita R. , Singh Durg V.
Published: July 2009

In this study, we report the presence of SXT in environmental Vibrio cholerae O1 El Tor strains isolated before 1992 from Varanasi, India. All isolates, except one, were resistant to Tm, and/or Sul, Sm, Fr, Na and Am. None contained plasmids. PCR and DNA sequencing revealed the presence of SXT containing dfrA1 and/or sulII, strAB in six isolates and dfr18, sulII and strAB in five isolates. Three clinical V. cholerae O1 isolated during 1992 contained the antibiotic resistance gene cassette aadA1 in the class 1 integron. Conjugation experiments, followed by PCR analysis of transconjugants, provided evidence of the transferable nature of SXT and associated antibiotic resistance genes, and its integration into the prfC site. Results of phylogenetic analysis of the intSXT gene of clonally similar V. cholerae showed a clear difference between dfr18+ and dfrA1+V. cholerae O1 isolates. This is the first report of the occurrence of SXT harbouring sulII, strAB, dfr18 and/or dfrA1 genes in environmental V. cholerae O1 isolated prior to 1992 from Varanasi, India, and suggests emergence of SXT+ antibiotic‐resistant V. cholerae O139 and O1 from an environmental V. cholerae progenitor by acquisition of SXT and antibiotic‐resistant gene clusters.
Laparoscopic gastric surgery in Asia
Authors: Yang Han‐Kwang
Published: July 2009

Laparoscopic gastric surgery has been popular in Asia since 1991. Laparoscopic gastrectomies are widely performed in Korea and Japan because of high incidence of early gastric cancer. Short‐term and long‐term outcomes after laparoscopic surgery for gastric cancer were actively reported, but waiting for multicenter randomized controlled trial. Education including domestic training workshop and international collaboration promise to progress advanced laparoscopic gastric surgery with robot and augmented reality surgery.
Laparoscopic Colorectal Surgery in Asia
Authors: Li Michael , CHEUNG Hester Yui Shan , CHUNG Cliff Chi Chiu
Published: July 2009

Laparoscopic colorectal surgery in Asia has gone a long way since 1992. In this article, the authors attempted to unfold the history of laparoscopic colorectal surgery in Asia, and report on the latest development. It is concluded that laparoscopic colorectal surgery will continue to flourish in Asia, and we will be entering a new era of endo‐laparoscopic surgery and robotic assisted laparoscopic surgery.
Degradation Effects on Industrial Gas Turbines
Authors: Kurz Rainer , Brun Klaus , Wollie Meron
Published: July 2009

This paper provides a discussion on how degradation develops and affects the performance of the gas turbine. Because the function of a gas turbine is the result of the fine-tuned cooperation of many different components, the emphasis of this paper is on the gas turbine and its components as a system. Therefore, the interaction of components is studied in detail. An engine model is subjected to various types of degradation, and the effect on operating parameters is studied. The focus is on three areas: How does component degradation impact the operating points of the engine compressor, how does component degradation impact full load and part load gas turbine performance characteristics, and how does component degradation impact measurable engine operating parameters. Experimental data are provided that supports the theoretical conclusion. Parameters that indicate levels of degradation are outlined, thus providing guidance for condition monitoring practice.
Evaluation of the Phase Composition, Crystallinity, and Trace Isotope Variation of SiC in Experimental TRISO Coated Particles
Authors: de Villiers Johan P. R. , Roberts James , Ngoepe Noko , Tuling Alison S.
Published: July 2009

The SiC layers in experimental tristructural-isotropic (TRISO) coated particles with zirconia kernels were evaluated for their phase composition, impurity levels, crystal perfection, and twinning of the crystallites in the layers. This evaluation was necessary to compare the different SiC layers and relate these properties to various quality tests and ultimately to manufacturing parameters in the chemical vapor deposition (CVD) coater. Identification of the various polytypes was done using electron diffraction methods. This is the only method for the unequivocal identification of the different polytypes. The 3C and 6H polytypes were positively identified. The SiC in some samples is disordered. This is characterized by planar defects, of different widths and periodicities, giving rise to streaking in the diffraction pattern along the [111] direction of the 3C polytype. Polarized light microscopy in transmission easily distinguishes between the cubic (beta) and noncubic (alpha) SiC in the layers and provides valuable information about the distribution of these phases in the layers. Raman spectroscopy was used to examine the distribution of Si in the SiC layers of the different samples. Two samples contain elevated levels of Si (∼50%), with the highest levels on the inside of the layers. The elevated Si levels also occur in most of the other samples, albeit at lower Si levels. This was also confirmed by the use of scanning electron microscope (SEM) electron backscatter analysis. Rietveld analysis using X-ray diffraction is presently the only reliable method to quantify the polytypes in the SiC layer. It was found that the SiC layer consists predominantly (82–94%) of the 3C polytype, with minor amounts of the 6H and 8H polytypes. Impurities in the SiC and PyC could be measured with sufficient sensitivity using laser ablation inductively coupled mass spectrometry (LA-ICP-MS). The SiC and PyC layers are easily located from the intensity of the C13 and Si29 signals. In most cases the absolute values are less important than the variation of impurities in the samples. Elevated levels of the transition elements Cu, Ni, Co, Cr, and Zn are present erratically in some samples. These elements, together with Ag107 and Ag109, correlate positively, indicating impurities, even metallic particles. Elevated levels of these transition elements are also present at the SiC/outer pyrolytic carbon (OPyC) interface. The reasons for this are unknown at this stage. NIST standards were used to calibrate the impurity levels in the coated particles. These average from 1 ppm to 18 ppm for some isotopes.
Acoustic Microscopy at Low Frequency
Authors: Kundu Tribikram
Published: July 2009

A new design of the acoustic microscopy experimental set up is proposed and analyzed in this paper. The proposed microscope can operate at low frequency (0.1 to 3 MHz) and can be efficiently used in fracture mechanics, structural, and geomechanics applications. In the new design there is no buffer rod and the transducer is proposed to have a shape of a cylindrical shell to produce a line focus beam which is necessary to measure material anisotropy. A line receiver is introduced instead of standard transducer-cum-receiver arrangements. A line receiver can receive only one specularly reflected ray and a few critically reflected rays and thus produces less complicated interference pattern or acoustic material signature (AMS) which is easier to analyze. The shape of the generated AMS depends on the exact location of the receiver strip. Finally, theoretically synthesized AMS of an aluminum plate for different receiver locations are presented.
Initiation, Propagation, and Kinking of an In-Plane Crack
Authors: Ma Chien-Ching
Published: July 2009

Consider an infinite linear elastic body containing a semi-infinite crack loaded by a longitudinal stress pulse parallel to the crack face. After the stress wave strikes the crack at time t = 0, the stress gradually intensifies at the crack tip. At some finite delay time tt, the crack begins to extend straight ahead with constant speed vo. At some later time tb, the crack suddenly stops, then kinks and propagates with constant speed vc, making an angle δ with the original crack. The exact full field solution of the propagating crack is constructed by using a superposition of fundamental solutions for a particular class of problems. When the crack suddenly stops, the stress field for a stationary crack with the new crack length is radiated out from the stopped crack tip. The dynamic stress intensity factor at the kinked crack tip can then be obtained by using a perturbation method.
A Refined Small Strain and Moderate Rotation Theory of Elastic Anisotropic Shells
Authors: Schmidt R. , Reddy J. N.
Published: July 2009

A general refined shell theory that accounts for the transverse deformation, small strains, and moderate rotations is presented. The theory can be reduced to various existing shell theories including: the classical (i.e., linear Kirchhoff-Love) shell theory, the Donnell-Mushtari-Vlasov shell theory, the Leonard-Koiter-Sanders moderate rotations shell theory, the von Ka´rma´n type shear-deformation shell theory and the moderate-rotation shear-deformation plate theory developed by Reddy. The present theory is developed from an assumed displacement field, nonlinear strain-displacement equations that contain small strain and moderate rotation terms, and the principle of virtual displacements. The governing equations exhibit strong coupling between the membrane and bending deformations, which should alter the bending, stability, and post-buckling behavior of certain shell structures predicted using the presently available theories.
Circular Elastic Plates on Elastic Unilateral Edge Supports
Authors: Celep Zekai , Turhan Dog˘an , Al-Zaid Rajeh Zaid
Published: July 2009

The response of an elastic circular plate supported unilaterally by elastic springs along its edge is studied. A load which is uniformly distributed along a circular arc of the plate is considered. The loss of the contact along the edge of the plate, the variations of deflections and those of reactions are presented. The influences of the position of loading, the spring constant, and Poisson’s ratio are shown in various figures.
Large Elastic Deformation of Shear Deformable Shells of Revolution: Numerical and Experimental Results
Authors: Kempski M. H. , Taber L. A. , Su Fong-Chin
Published: July 2009

Through an integrating matrix approach, a numerical solution is obtained to the equations governing large elastic deformation of a clamped circular cylinder due to internal pressure. The shell equations include the effects of large strains, thickness changes, and transverse shear deformation. The numerical solution is compared to results from an asymptotic analysis and from experiments on rubber cylinders. A specialized Rivlin-Saunders strain-energy density function is assumed for the rubber, with material constants determined from tensile tests and deformed cylinder profiles at a high inflation pressure.
An Analytical Model for Unanchored Fluid-Filled Tanks Under Base Excitation
Authors: Natsiavas S.
Published: July 2009

A set of equations is derived describing the dynamic response of cylindrical liquid storage tanks under horizontal ground excitation. The structure consists of a flexible cylindrical tank with a roof and a bottom plate and rests on a flexible ground through a rigid foundation. Portion of the base of the tank may separate from and lift off the foundation during ground motion. The solution of the hydrodynamic problem is first found in closed form. Then, Hamilton’s principle is applied and the equations governing the behavior of the coupled fluid/structure/ground system are derived. During this procedure, the base uplifting is modeled by an appropriate rotational nonlinear spring placed between the base of the tank and the foundation.
A Recursive Formulation for the Dynamic Analysis of Open Loop Deformable Multibody Systems
Authors: Changizi K. , Shabana A. A.
Published: July 2009

In this paper, a recursive formulation for the spatial kinematic and dynamic analysis of open chain mechanical systems containing interconnected deformable bodies, each of which may undergo large translational and rotational displacements, is developed. While approximation techniques such as the finite element method, Rayleigh-Ritz methods, or experimentally identified modal parameters can be used to introduce the elastic coordinates that describe the deformation of the bodies with respect to selected body references, the large rotational and translational displacements of a set of intermediate joint axes are described using a minimum set of relative translational and rotational coordinates. A set of time-invariant quantities that depend on the assumed displacement field and provide a systematic approach to study the spatial dynamics of open loop mechanical systems are obtained. The method developed is applicable to open loop mechanical systems containing revolute, prismatic and cylindrical joints. Furthermore, the formulation developed is independent of the type of finite element or the modal identification technique used.
Experimental Observation of Amplitude- and Phase-Modulated Responses of Two Internally Coupled Oscillators to a Harmonic Excitation
Authors: Nayfeh A. H. , Zavodney L. D.
Published: July 2009

An experiment is performed on a two degree-of-freedom mechanical system having quadratic nonlinearities and linear natural frequencies ω1 and ω2 approximately in the ratio of two-to-one (i.e., ω2 ≈ 2ω1). When the lower mode is excited by a harmonic excitation whose frequency Ω is nearly equal to ω1, amplitude- and phase-modulated responses of the system have been observed for a range of the excitation frequency Ω, in qualitative agreement with the results of a second-order perturbation theory.
A Method for Testing Numerical Integrations of Equations of Motion of Mechanical Systems
Authors: Kane T. R. , Levinson D. A.
Published: July 2009

It is common practice to use conservation principles, such as the principles of conservation of energy or angular momentum, to test results of numerical integrations of differential equations of motion of mechanical systems. This paper deals with a testing method that can be used even when no conservation principle is applicable.
Timoshenko’s Shear Coefficient From a Beam Subjected to Gravity Loading
Authors: Stephen N. G.
Published: July 2009

The Kennard and Leibowitz method of obtaining the shear coefficient, by equating center-line curvature of a Timoshenko beam to the curvature of a beam subjected to uniform gravity loading, is extended to arbitrary monosymmetric sections. The resulting expression for the coefficient is evaluated for several sections and comparison made with experimental and exact theoretical results.
Formulation of Stochastic Linearization for Symmetric or Asymmetric M.D.O.F. Nonlinear Systems
Authors: Spanos P-T. D.
Published: July 2009

A formulation of the method of stochastic linearization so that it is applicable for symmetric or asymmetric nonlinear systems is presented. Formulas for the generation of the equivalent linear system are given. The solution procedure for determining nonstationary or stationary system response statistics is outlined.
A New Cumulative Damage Model—Part 4
Authors: Bogdanoff J. L. , Kozin F.
Published: July 2009

Application of the new cumulative damage model to two sets of fatigue crack growth data is presented. It is shown that the model can describe the statistical features of crack growth including mean and variance of time to reach a specified crack length, cumulative distribution of time to reach a specified crack length, and sample function behavior. Moreover, this is done with very little effort.
Fluid Forces on Rods Vibrating in Finite Length Annular Regions
Authors: Mulcahy T. M.
Published: July 2009

Approximate expressions for the fluid forces acting on a central, rigid rod translating periodically in a finite length annular region of confined fluid are derived from the Navier-Stokes equations for a range of geometric and fluid parameters where viscous damping is significant. Based on the derived forces, lumped added mass, and linear dashpot modeling of an annular gap support typically found in nuclear reactors is employed to predict the fundamental frequency and modal damping of a single beam. Test methods and results for the same beam are presented which indicate the force expressions are applicable for small fluid motions.
A Model of Pressure and Flow Distribution in Branching Networks
Authors: Popel A. S.
Published: July 2009

The objective of this work is to provide a mechanical description of steady-state flow of Newtonian fluid in a branching network that consists of rigid vessels of different diameters. Solution of this problem is of importance for better understanding of the mechanics of blood flow within the microcirculation. The developed branching network model predicts a wide distribution of the hydrodynamic pressure and flow in the vessels of the same caliber (flow heterogeneity). The obtained results are compared with predictions of a simple series-parallel network model. It is shown that this model provides an accurate approximation to the values of the mean pressure and flow given by the branching network model.
Constitutive Equations of Elastoplastic Materials With Elastic-Plastic Transition
Authors: Hashiguchi K.
Published: July 2009

Constitutive equations of elastoplastic materials with an elastic-plastic transition observed in the loading state after a first yield are presented by introducing a new parameter denoting the ratio of the size of a loading surface in the transitional state to that of a yield surface in the classical idealization which ignores the transitional state. These equations involve a reasonably simplified rule for the kinematic hardening. They would describe reasonably not only the hardening behavior but especially the softening behavior which requires our careful consideration about the elastic-plastic transition. From these equations, moreover, we derive plastic constitutive equations specifically of metals and granular media which exhibit very different plastic behaviors. Besides, brief discussions are provided concerning the existing constitutive equations describing the elastic-plastic transition.
Numerical Analysis of Elliptic-Hyperbolic Plastic Flow in Torsion
Authors: Lee Y. K. , Swedlow J. L.
Published: July 2009

A method for solving elastic-perfectly plastic problems is presented, such that the mixed elliptic-hyperbolic field may be modeled properly. The method is applied to torsion of a rectangular bar which, although coarsely meshed, exhibits features observed experimentally. In particular, initiation and growth of behavior akin to shear banding is captured. A torque-twist curve is obtained well beyond the peak torque.
Inelastic Analysis of Transverse Deflection of Plates by the Boundary Element Method
Authors: Morjaria M. , Mukherjee S.
Published: July 2009

A numerical scheme for time-dependent inelastic analysis of transverse deflection of plates of arbitrary shape by the boundary element method is presented in this paper. The governing differential equation is the inhomogeneous biharmonic equation for the rate of small transverse deflection. This complicated boundary-value problem for an arbitrarily shaped plate is solved by using a novel combination of the boundary element method and finite-element methodology. The number of unknowns, however, depends upon the boundary discretization and is therefore less than in a finite-element model. A combined creep-plasticity constitutive theory with state variables is used to model material behavior. The computer code developed can solve problems for an arbitrarily shaped plate with clamped or simply supported boundary conditions and an arbitrary loading history. Some illustrative numerical results for clamped and simply supported rectangular and triangular plates, under various loading histories, are presented and discussed.
Failure Criteria for Unidirectional Fiber Composites
Authors: Hashin Z.
Published: July 2009

Three-dimensional failure criteria of unidirectional fiber composites are established in terms of quadratic stress polynomials which are expressed in terms of the transversely isotropic invariants of the applied average stress state. Four distinct failure modes—tensile and compressive fiber and matrix modes—are modeled separately, resulting in a piecewise smooth failure surface.
A Mixed-Mode Crack Analysis of Isotropic Solids Using Conservation Laws of Elasticity
Authors: Yau J. F. , Wang S. S. , Corten H. T.
Published: July 2009

A simple and convenient method of analysis for studying two-dimensional mixed-mode crack problems is presented. The analysis is formulated on the basis of conservation laws of elasticity and of fundamental relationships in fracture mechanics. The problem is reduced to the determination of mixed-mode stress-intensity factor solutions in terms of conservation integrals involving known auxiliary solutions. One of the salient features of the present analysis is that the stress-intensity solutions can be determined directly by using information extracted in the far field. Several examples with solutions available in the literature are solved to examine the accuracy and other characteristics of the current approach. This method is demonstrated to be superior in its numerical simplicity and computational efficiency to other approaches. Solutions of more complicated and practical engineering fracture problems dealing with the crack emanating from a circular hole are presented also to illustrate the capacity of this method.
Stress-Intensity Factors and Complex Path-Independent Integrals
Authors: Theocaris P. S. , Ioakimidis N. I.
Published: July 2009

Path-independent integrals about crack tips may be used to estimate stress-intensity factors at crack tips in plane and antiplane elasticity problems. In this paper a new class of such integrals is established by using complex stress functions and the trivial application of the Cauchy theorem of complex analysis. Both the simple Westergaard complex potentials of plane and antiplane elasticity and the more general Muskhelishvili complex potentials will be used for the construction of appropriate path-independent integrals. Two applications of these integrals to the theoretical determination of stress-intensity factors at crack tips are presented. An optical method for the experimental determination of stress-intensity factors at crack tips, based on the use of appropriate complex path-independent integrals, is also proposed.
Closed-Form Inversion of the Axisymmetric Integrated Photoelasticity Equations
Authors: Doyle J. F.
Published: July 2009

The purpose of the present Note is to show how the general axisymmetric photoelastic problem can be solved using only the integrated data. Indeed, the axisymmetric problem is reduced to a quasi-plane problem in that only a fringe photograph plus a plot of the family of isoclinics is sufficient to yield a complete solution. The formulation includes the treatment of thermoelastic and residual stress problems.
Pipe Flow of Plastic Materials
Authors: Yang W. H.
Published: July 2009

Plastic materials behave as both solids and fluids. When forced to move in a pipe, they flow as a solid plug with a slipping boundary. Depending on the cross-sectional shape of the pipe, the slipping boundary may not coincide with the inner boundary of the pipe. When such is the situation, there exist dead regions in the flow. This is undesirable when the material is time degradable as those encountered in the food processing and chemical industry. Two formulations of nonlinear programming problems governing the pipe flow are presented. They correspond, respectively, to the lower bound and upper bound theorems of plasticity. An efficient method is developed for the nonlinear programming problem formulated from the upper bound theorem. Application of the method to two examples are demonstrated.
Exact Dynamic Surface Response for Sub and Through-Surface Slip
Authors: Brock L. M.
Published: July 2009

The motion of edge dislocations and slip on fault planes are important mechanisms involving sub and through-surface slip. Here exact solutions for largely arbitrary in-plane slip in a half plane along zones normal to the surface are derived and the general wave-front pattern described. For two examples of finite zones of uniform slip, the displacements on the free surface of the half plane are examined. In the case of the slip zone passing through the half-plane surface, separate and prominent systems of surface waves are seen to be generated at the surface-zone intersection point. Data illustrating this and other behavior is presented.
Fracture Criteria of Fibrous Laminated Composites Under In-Plane Multidirectional Loading
Authors: Tirosh J. , Mast P. , Beaubien L. , Mulville D. , Sutton S. , Wolock I.
Published: July 2009

A study on the validity of various fracture criteria of angle-ply-laminated composites is presented for in-plane loading. Special emphasis is given to the vectorial presentation of the J-integral as a suitable candidate for fracture characterization of composites under general combined loading. The combined loading which is composed of a simultaneous tension, shear and in-plane bending in any desired proportion, has been produced in a highly computerized fashion by a specially devised apparatus at the U.S. Naval Research Laboratory. The fracture data of several angle ply laminates of carbon/epoxy composite (T300/5208) result from prescribing the foregoing three combined radial loading until fracture. Aided by numerical stress analysis (finite-element program) the data points are cast into more well-known descriptions; namely, crack-opening displacement versus crack-sliding displacement. Mode-I stress-intensity factor (KI) versus Mode-II stress-intensity factor (KII) and energy-release rate vector Jx versus Jy. The main outcome is that the data displayed on the J-integral plane have a highly distinctive nature of aligning the data points along straight lines, thus a clear discrimination between the fracture properties of different angle-ply laminates can be characterized by only two parameters. The ability to infer fracture conditions in subcomponents from tests on small coupons is assessed.
Two-Mode Buckling of an Elastically Supported Plate and Its Relation to Catastrophe Theory
Authors: Hui D. , Hansen J. S.
Published: July 2009

Classical buckling and initial postbuckling of a geometrically imperfect infinite plate on a nonlinear elastic foundation under two independent applied compressive loads are analyzed. The plate is assumed to have imperfections of the same form as the buckling modes. It is found that single mode behavior occurs when the two independent loads Nx and Ny are unequal. A two-mode case occurs when the two applied loads are equal and the form of the instability falls into the category of the parabolic umbilic type one or type two, depending on the quadratic and cubic spring constants. The importance of the contribution of the quartic term and imperfection-sensitivity is examined. The analysis is studied within the context of Koiter’s general theory of multimode postbuckling behavior.
On the Localization of Buckling Patterns
Authors: Tvergaard V. , Needleman A.
Published: July 2009

The possibility of localization of a buckling pattern is investigated for a class of structures in which the initial buckling mode is periodic. A simple model indicates that the basic mechanism of localization involves a bifurcation at the maximum load point. This model also illustrates a clear analogy between localization of a buckling pattern in a structure under compressive loading and the phenomenon of necking in a bar under tensile loading. An analysis of the bifurcation that leads to localization, carried out for the more realistic structural model of a column on a softening foundation, demonstrates a delay between the maximum load point and the bifurcation point. A finite-element analysis of an elastic-plastic plate strip under axial compression shows the development of localization for a low hardening material, whereas localization does not occur in a plate made of a high hardening material for which no maximum load is reached.
Natural Frequencies of Mindlin Circular Plates
Authors: Irie T. , Yamada G. , Aomura S.
Published: July 2009

The natural frequencies of vibration based upon the Mindlin plate theory are tabulated for uniform circular plates with free, simply supported, and clamped edges for the first several tens modes.
Shear and Rotatory Inertia Effects on the Large Amplitude Vibration of the Initially Imperfect Plates
Authors: Celep Z.
Published: July 2009

In this paper, the free flexural vibration of an elastic rectangular plate having initial imperfection is investigated including the effects of transverse shear and rotatory inertia. It is assumed that the vibration occurs with large amplitudes which leads to nonlinear differantial equations. On the basis of an assumed vibration mode, the modal equation of the plate is obtained and solved numerically.
Elasto/Viscoplastic Analysis of Thin Circular Plates Under Large Strains and Large Deformations
Authors: Takezono S. , Nakamachi E. , Yamaguchi T.
Published: July 2009

In this paper the elasto/viscoplastic analysis of thin circular plates under large strains and large deformations is studied by the use of the finite-element method based on the membrane shell theory. As the constitutive relation for the materials Perzyna’s equation which in the plastic range takes into account the viscosity of the material is employed. The criterion for yielding used in this analysis is the von Mises yield theory. The geometric nonlinearity is treated with incremental method and the solutions at any stage are obtained by summation of the incremental values. The experiments are carried out for the thin circular aluminum plates, and the variations of the deformations and the stresses with loading rate are analyzed. The elasto/viscoplastic solutions from the prediction method agree fairly well with the values experimentally determined for the circular plates. The method can be used to generate plasticity solutions in a simple manner when stationary conditions are reached.
The Dynamic Three-Parameter Method for Determination of Stress-Intensity Factors From Dynamic Isochromatic Crack-Tip Stress Patterns
Authors: Rossmanith H. P.
Published: July 2009

Correction methods for the determination of dynamic stress-intensity factors from isochromatic crack-tip stress patterns are developed within the framework of a Westergaard-type stress-function analysis where higher-order terms of the series expansions of the stress functions are retained. The addition σox to the extensional stress σx, is regarded as a first correction term, and the far-field correction term which is proportional to r1/2 is referred to as the β-correction. The β-term represents effects that are due to particular loading systems and situations including finite specimen boundaries. The associated method to determine K can be termed a three-parameter method since it contains K, α, and β as parameters. The correction methods, i.e., velocity correction and higher-order term corrections, permit modification of the “static” crack velocity versus stress-intensity factor (c-K) relationship by correcting the static K for the influence of crack speed and higher-order terms. The results show that both corrections assist the interpretation of current photoelastic c-K-data even though the crack speeds do not exceed one third of the shear wave speed.
Fatigue Crack Closure Following a Step-Increase Load
Authors: Lo K. K.
Published: July 2009

A Dugdale-Barenblatt model is used to examine the effects of crack closure following a step increase in the applied cyclic loading. Complex function formulation is employed to calculate opening and contact loads. It is shown that the effect of previous history of loading on crack growth is significant only when the extent of crack growth is within about one plastic zone size.
A No-Slip Edge Crack on a Bimaterial Interface
Authors: Mak A. F. , Keer L. M.
Published: July 2009

A solution for an interface edge crack whose surfaces experience no tangential slip is presented. At the crack tip, KI is found to be identical to that for a surface crack in a homogeneous medium. Moreover, the shear stress is singular both at the surface and at the crack tip, with KII at the crack tip being equal to −βKI, where β is Dundurs’ constant. The crack opening displacements were calculated using a successive approximation scheme, which shows remarkable speed of convergence in this case.
Multiple Scattering of Waves in Irregularly Laminated Composites
Authors: Weaver R. L. , Pao Yih-Hsing
Published: July 2009

The transition matrix formulation of multiple scattering is applied to the problem of wave propagation in a one-dimensional layered medium. The effect of geometrical irregularity in an otherwise periodic layered structure is investigated in detail for the case of elastic waves propagating normally to elastic layers embedded in elastic, or in viscoelastic matrix media. The irregularity is found to widen and diminish the stop bands and soften the sharp band features characteristic of a fully periodic structure, and to generate scattering losses with a consequent increase in the attenuation of the coherent wave field.
Vibrations of Rectangular Plates With Nonuniform Elastic Edge Supports
Authors: Leissa A. W. , Laura P. A. A. , Gutierrez R. H.
Published: July 2009

Two methods are introduced for the solution of free vibration problems of rectangular plates having nonuniform, elastic edge constraints, a class of problems having no previous solutions in the literature. One method uses exact solutions to the governing differential equation of motion, and the other is an extension of the Ritz method. Numerical results are presented for problems having parabolically varying rotational constraints.
Acoustoelastic Effect of Rayleigh Surface Wave in Isotropic Material
Authors: Hirao M. , Fukuoka H. , Hori K.
Published: July 2009

The acoustoelastic effect is investigated for the Rayleigh surface wave propagating in a homogeneous isotropic material. The initial deformations considered are uniform and nonuniform only in the direction of depth. The formulas for the velocity change versus the change in the applied static stress are derived in the first-order approximation. The result for the uniform case, reducing to that of Hayes and Rivlin, exhibits no dispersion and the velocity change proportional to the principal strains. To be noted is the result that the Rayleigh wave becomes dispersive under the nonuniform stress state, depending roughly on the product of the wave number and the characteristic depth over which the stress varies. The dispersion is remarkable for the relatively low frequency and diminishes as the frequency increases. The analytical results are verified by measurements with mild-steel samples on the basis of the sing-around technique.
Vibration of an Elastic Circular Plate on an Elastic Half Space—A Direct Approach
Authors: Krenk S. , Schmidt H.
Published: July 2009

The axisymmetric problem of a vibrating elastic plate on an elastic half space is solved by a direct method, in which the contact stresses and the normal displacements of the plate are taken as the unknown functions. First, the influence functions that give the displacements in terms of the stresses are determined for the half space and the plate. Displacement continuity then takes the form of an integral equation. Due to the half space the kernel is weakly singular, and a special solution technique that accounts for this is employed. The solution implies a direct matrix relation between the expansion coefficients of the contact stresses and plate deformations. The solution technique is valid for all frequencies and avoids asympototic expansion in terms of the frequency. The plate is represented by the theory of Reissner and Mindlin, which imposes physical limitations for high frequencies, but the method is easily extended to more general plate theories as well as nonsymmetric oscillations. The results include displacement and phase curves for rigid disks, power input for elastic plates, and typical stress and deformation distributions at selected phase angles. The results show considerable influence from the elastic properties of the plate.
Linear Spatial Stability of Developing Flow in a Parallel Plate Channel
Authors: Gupta S. C. , Garg V. K.
Published: July 2009

It is found that even a 5 percent change in the velocity profile produces a 100 percent change in the critical Reynolds number for the stability of developing flow very close to the entrance of a two-dimensional channel.
Stress Distribution Around a Circular Hole in Square Plates, Loaded Uniformly in the Plane, on Two Opposite Sides of the Square
Authors: Erickson M. , Durelli A. J.
Published: July 2009

The complete stress distribution around a circular hole, located in the center of a square plate, has been determined photoelastically for the case of the plate loaded uniformly on two opposite sides. The study was conducted parametrically for a range of the ratio D/W of the diameter of the hole to the side of the square from 0.20 to 0.83. The results obtained permit the determination of the stresses for any biaxial condition and verify a previous solution obtained for the case of the pressurized hole. The experimental procedure is briefly described.
A Model to Estimate Forces on Conical Penetrators Into Dry Porous Rock
Authors: Forrestal M. J. , Longcope D. B. , Norwood F. R.
Published: July 2009

A model to predict the forces on conical-nosed penetrators for normal impact into dry rock targets is developed. The target medium is described by a linear hydrostat, a linear shear failure-pressure relation, and the material density. A cylindrical cavity expansion approximation to the target response permits one-dimensional wave propagation calculations in the radial coordinate. The equations of motion are reduced, via a similarity transformation, to a nonlinear ordinary differential equation. This equation is solved numerically by a shooting technique which employs an asymptotic expansion to the solution near the wave front. Results include stress wave profiles in the target and curves for the stress on the penetrator nose as a function of its velocity for a wide range of realistic target parameters. Finally, results from the theory are compared with the deceleration history of a penetrator in a field test and reasonable correlation is observed.
Finite-Element Solution of Elastic-Plastic Boundary-Value Problems
Authors: Prevost J. H. , Hughes T. J. R.
Published: July 2009

It is demonstrated that elastic-plastic failure states may be captured in finite-element models by employing (1) the elastic-plastic material stiffness to form the global stiffness, (2) reduced/selective integration techniques to alleviate mesh “locking” due to incompressibility, and (3), in the case of symmetrical configurations, an imperfection in the form of a weak element.
Asymptotic Distributions for the Failure of Fibrous Materials Under Series-Parallel Structure and Equal Load-Sharing
Authors: Smith R. L. , Phoenix S. L.
Published: July 2009

Asymptotic distributions are obtained for both the strength and the time to failure of a fibrous material for which mild bonding or friction exists between fibers. The analysis is based on the chain-of-bundles probability model, and equal load sharing is assumed for the nonfailed fiber elements in each bundle. Asymptotic results are obtained for the difficult but useful case where k, the number of bundles in the chain, grows very rapidly with respect to n, the number of fibers in each bundle. For both strength and time to failure, a classical extreme value distribution is found to be the asymptotic distribution, and the parameters are given in terms of certain fiber properties. The results apply to long, flexible fibrous structures such as yarns and cables.