bluuebunny/crossref_metadata_2025 huggingface dataset:
A Multi‐stateSalmonellaTyphimurium Outbreak Associated with Frozen Vacuum‐packed Rodents used to Feed Snakes
Authors: Fuller C. C. , Jawahir S. L. , Leano F. T. , Bidol S. A. , Signs K. , Davis C. , Holmes Y. , Morgan J. , Teltow G. , Jones B. , Sexton R. B. , Davis G. L. , Braden C. R. , Patel N. J. , Deasy M. P. , Smith K. E.
Published: April 2008

From December 2005 through January 2006, the Minnesota Department of Health (MDH) identified four human clinical isolates ofSalmonellaTyphimurium that were indistinguishable by pulsed‐field gel electrophoresis (PFGE). During routine interviews, three of the cases reported attending the same junior high school and two handled snakes in the science classroom. MDH collected environmental samples from the school’s science classroom forSalmonellaculturing; these included environmental samples and frozen vacuum‐packed mice purchased over the internet to feed the classroom snakes.

Through PulseNet, a national molecular subtyping surveillance network for enteric bacteria, 21 humanS. Typhimurium isolates with indistinguishable PFGE patterns were identified in the United States since December 2005. Each state determined whether these human cases had recent exposure to snakes fed vacuum‐packed rodents. Texas state officials conducted tracebacks of the vacuum‐packed mice and collected samples at the breeding facility.

Nineteen of 21 cases were interviewed, and seven reported contact with frozen vacuum‐packed rodents from the same internet‐based supplier in Texas. In Minnesota, the outbreak PFGE subtype ofS.Typhimurium was isolated from the snakes, frozen feed rodents, and the classroom environment. Three human cases were identified in Michigan, Pennsylvania, and Wyoming. The outbreak PFGE subtype ofS.Typhimurium was isolated from the Pennsylvania case’s frozen rodents and the Michigan case’s pet snake. The outbreak PFGE subtype ofS. Typhimurium was also isolated from the supplier’s rodent facility.

This was aS.Typhimurium outbreak associated with frozen rodents. Human transmission likely occurred through direct contact with snakes and contaminated environmental surfaces. This report represents the second recent multi‐state salmonellosis outbreak associated with commercially distributed rodents. Stronger oversight of the commercial rodent industry is warranted.
Defect Occurrence and Modeling for the Thermomechanical Processing of Aerospace Alloys
Authors: Semiatin S. L. , Nicolaou P. D. , Thomas J. P. , Turner T. J.
Published: April 2008

Mechanism-based models for the evolution of defects during the thermomechanical processing of aerospace titanium- and nickel-based alloys are reviewed. These defects include those comprising microstructural/metal-flow irregularities and those that are damage related (i.e., cracks and cavities). The development of undesirable/nonuniform microstructures and cavities during the mill processing of alpha/beta titanium alloys is addressed first. Relatively simple, diffusion-based models of spheroidization and coarsening are applied to quantify the propensity for microstructure nonuniformities. Similarly, first-order micromechanical models have been formulated to estimate the effect of local crystallographic texture on nonuniform flow, the generation of triaxial stresses, and cavity growth/closure in alpha/beta titanium alloys with a colony-alpha microstructure. The occurrence of nonuniform grain structures (and so-called ALA, or “as large as,” grains) in cast, wrought, and powder-metallurgy superalloys is also discussed. A physics-based model to treat the topology of recrystallization and the evolution of ALA grains in such materials is proposed.
Modeling Strain Localization Using a Plane Stress Two-Particle Model and the Influence of Grain Level Matrix Inhomogeneity
Authors: Hu Xiaohua , Wilkinson David S. , Jain Mukesh , Mishra Raja K.
Published: April 2008

The role of dilute small particles on the development of strain localization under uniaxial tension has been studied by finite element analysis using a plane stress model with two small hard particles embedded in Al matrix. The influence of particle alignment and interparticle spacing in a homogeneous and inhomogeneous matrix are investigated. When the matrix material is a homogeneous continuum, there are small localization strains when close packed and aligned along the loading direction. In the case of an inhomogeneous matrix with grains of different strengths represented by their Taylor factors, the location of localization band is insensitive to the interparticle spacing, but mainly determined by grain-level inhomogeneity. This is because the particles are dilute and small compared with the matrix grains. The particles, however, can decrease the localization strains when they straddle the localization band.
Stress Gradient Induced Strain Localization in Metals: High Resolution Strain Cross Sectioning via Synchrotron X-Ray Diffraction
Authors: Croft M. , Jisrawi N. , Zhong Z. , Horvath K. , Holtz R. L. , Shepard M. , Lakshmipathy M. , Sadananda K. , Skaritka J. , Shukla V. , Sadangi R. K. , Tsakalakos T.
Published: April 2008

Strain localization in the presence of a stress gradient is a phenomenon common to many systems described by continuum mechanics. Variations of this complex phenomenon lead to interesting nonlinear effects in materials/engineering science as well as in other fields. Here, the synchrotron based energy dispersive x-ray diffraction (EDXRD) technique is used for high spatial resolution profiling of both compression and tension induced strain localization in important materials/engineering problems. Specifically, compression induced strain localization in shot peened materials and tension induced strain localization in the plastic zones adjoining the faces of a fatigue crack are profiled. The utility of the EDXRD synchrotron technique for nondestructively cross-sectioning strain variations on small length scales (down to 10–20μm) is described. While the strain field profiling relies on the shift of the Bragg lines, the data show that plastic deformation regions can also consistently be seen in the broadening of the Bragg peaks through the full width at half maximum parameter. Quantitative correlations between the synchrotron based x-ray determined deformations and surface deformations, as measured by optical surface height profiling, are also made.
Dynamic Dislocation-Defect Analysis and SAXS Study of Nanovoid Formation in Aluminum Alloys
Authors: Westfall L. , Diak B. J. , Singh M. A. , Saimoto S.
Published: April 2008

Crystalline defects other than the essential dislocations are produced by dislocation intersections resulting in debris, which can transform into loops, point defects, and∕or nanovoids. The stress concentrations ahead of slip clusters promote void formation leading to incipient cracks. To evaluate the progression of these processes during deformation, dynamic dislocation-defect analysis was applied to nominally pure aluminum, Al–Mg, and Al–Cu alloys. In the case of nanovoid formation, small angle X-ray scattering (SAXS) was used to quantitatively assess if the void size and its volume fraction can be determined to directly correlate with the measured thermodynamic response values. The SAXS signal from the nanovoids in nominally pure aluminum is distinctly measurable. On the other hand, thermomechanical processing of even nominally pure aluminum results in the formation of nanoprecipitates, which requires future calibration.
On Predicting Nucleation of Microcracks Due to Slip-Twin Interactions at Grain Boundaries in Duplex Near γ-TiAl
Authors: Kumar D. , Bieler T. R. , Eisenlohr P. , Mason D. E. , Crimp M. A. , Roters F. , Raabe D.
Published: April 2008

Simkin et al. (2003, “A Factor to Predict Microcrack Nucleation at Gamma-Gamma Grain Boundaries in TiAl,” Scr. Mater., 49(2), 149–154) proposed a relationship for predicting crack initiation in γ-TiAl in a scenario where a mechanical twin interacts with a grain boundary. This correlation (quantified using a fracture initiation parameter or fip) was based only on the geometry of the Burgers vectors as they are related to slip transfer across the grain boundary and the Mode I type opening force experienced by the grain boundary. Generally, a fip is a mathematical combination of factors that allow weak boundaries to be probabilistically identified in the context of a state of stress. This paper further develops this approach by considering the inclusion of the mismatch between the slip planes in the grain boundary and a parameter that accounts for the different elastic properties in adjoining grains. Also, the significance of primary twin (slip) systems versus secondary slip systems is assessed. When compared to fips that can be constructed through a variety of other combinations of nine geometrical parameters that could affect grain boundary damage nucleation, the fip obtained by multiplying Simkin’s original parameter by Emin∕Emax, the ratio of Young’s modulus in the stress direction in the two grains, is best able to distinguish between cracked and intact grain boundary populations. Cracked and intact boundaries are also characterized to assess tilt and twist character and whether they are low Σ (or coincident site lattice) boundaries (using a cubic criterion). It is also shown that fips based on Σ values or the tilt and twist character of the boundary lead to an unacceptably high probability of incorrectly distinguishing between cracked and intact grain boundaries, implying that these are not critical parameters affecting crack nucleation at the grain boundary in duplex near-γ TiAl. The paper closes with a discussion on how combined microscopic and crystal plasticity finite element analyses provide insights on local stress-strain relationships that can be used to evaluate a fip in the context of heterogeneous deformation in multigrain ensembles.
Crack Tip Fields in a Single Edge Notched Aluminum Single Crystal Specimen
Authors: Patil Swapnil D. , Narasimhan R. , Biswas P. , Mishra R. K.
Published: April 2008

We report a combined experimental and computational study of a low constraint aluminum single crystal fracture geometry and investigate the near-tip stress and strain fields. To this end, a single edge notched tensile (SENT) specimen is considered. A notch, with a radius of 50μm, is taken to lie in the (010) plane and its front is aligned along the [101] direction. Experiments are conducted by subjecting the specimen to tensile loading using a special fixture inside a scanning electron microscope chamber. Both SEM micrographs and electron back-scattered diffraction (EBSD) maps are obtained from the near-tip region. The experiments are complemented by performing 3D and 2D plane strain finite element simulations within a continuum crystal plasticity framework assuming an isotropic hardening response characterized by the Pierce–Asaro–Needleman model. The simulations show a distinct slip band forming at about 55deg with respect to the notch line corresponding to slip on (11¯1)[011] system, which corroborates well with experimental data. Furthermore, two kink bands occur at about 45deg and 90deg with respect to the notch line within which large rotations in the crystal orientation take place. These predictions are in good agreement with the EBSD observations. Finally, the near-tip angular variations of the 3D stress and plastic strain fields in the low constraint SENT fracture geometry are examined in detail.
Damage Development During Superplasticity of Light Alloys
Authors: Boissière R. , Blandin J. J. , Salvo L.
Published: April 2008

Superplastic forming (SPF) of metallic alloys allows the production of components with particularly complex shapes since in this regime, due to the predominance of grain boundary sliding (GBS), the material exhibits a high plastic stability. However, in many light alloys (i.e., Al or Mg alloys), superplastic deformation induces damage leading to premature fracture. Despite extensive work in the past, the mechanisms of damage induced by superplastic deformation remain under debate. In particular, due to the important contribution of GBS, voids with very irregular shapes frequently develop, resulting in a difficulty to obtain reliable experimental data from conventional quantitative metallography. It is the reason why the use of X-ray microtomography, providing 3D images of material bulk, is a particularly fruitful technique to investigate damage processes in superplastic materials. Thanks to this technique, damage development during superplastic deformation of Al and Mg alloys is investigated and the three main steps of damage development (nucleation, growth, and coalescence) are discussed.
Transfer Function Formulation of Constrained Distributed Parameter Systems, Part I: Theory
Authors: Tan C. A. , Chung C. H.
Published: April 2008

Analysis of constrained distributed parameter systems by the transfer function formulation is presented. The methodology is suitable for symbolic computation coding. The distributed system is an assembly of distributed elements. A generalized displacement method (GDM) is developed to evaluate the free and forced responses of the system. It is shown that, while classical methods require the satisfaction of both the displacement and force boundary conditions at the subsystem interfaces, GDM only needs to impose generalized force constraints. The continuity of generalized displacements at the interfaces is embedded in the present formulation. Thus, computation efforts are greatly reduced, in particular, for systems with a large number of distributed subsystems. Eigenfunctions of constrained systems are obtained by solving a finite-dimensional eigenvalue problem governing the generalized coordinate vector. The formulation can be applied to damped and non-selfadjoint systems.
Localized Elasticae for the Strut on the Linear Foundation
Authors: Hunt G. W. , Wadee M. K. , Shiacolas N.
Published: April 2008

Localized solutions, for the classical problem of the nonlinear strut (elastica) on the linear elastic foundation, are predicted from double-scale analysis, and confirmed from nonlinear volume-preserving Runge-Kutta runs. The dynamical phase-space analogy introduces a spatial Lagrangian function, valid over the initial post-buckling range, with kinetic and potential energy components. The indefinite quadratic form of the spatial kinetic energy admits unbounded solutions, corresponding to escape from a potential well. Numerical experimentation demonstrates that there is a fractal edge to the escape boundary, resulting in spatial chaos.
End Shortening Relation and Stability of Columns on Nonlinear Foundation
Authors: Oyesanya M. O.
Published: April 2008

We derive the end shortening relations for both the primary and secondary bifurcation states of columns on nonlinear foundation and use Budiansky’s pictorial stability theorem to show the instability of these states.
Viscoelastic Microbuckling of Fiber Composites
Authors: Slaughter W. S. , Fleck N. A.
Published: April 2008

A theoretical study is given of viscoelastic microbuckling of fiber composites. The analysis is formulated in terms of general linear viscoelastic behavior within the kink band. Material outside the kink band is assumed to behave elastically. Two specific forms of linear viscoelastic behavior are considered: a standard linear viscoelastic model and a logarithmically creeping model. Results are provided as deformation versus time histories and failure life versus applied stress. Failure is due to either the attainment of a critical failure strain in the kink band or to the intervention of a different failure mechanism such as plastic microbuckling.
Effect of Initial Void Shape on the Occurrence of Cavitation Instabilities in Elastic-Plastic Solids
Authors: Tvergaard V. , Hutchinson J. W.
Published: April 2008

A void in an infinite elastic-plastic material grows without bound when a cavitation stress limit is reached. Such unstable void expansion, driven by the elastic energy stored in the surrounding material, has been studied for the relatively simple case of spherically symmetric conditions and also for a spherical void in an axisymmetric remote stress field. The analyses are here extended to consider the effect of a void with an initially prolate or oblate spheroidal shape. Numerical unit cell analyses are carried out for a power-hardening elastic-plastic material subject to various axisymmetric remote stress states. For the range of void shapes analyzed it is found that the critical cavitation stress state shows very little influence of the initial void shape.
Rudnicki and Rice’s Analysis of Strain Localization Revisited
Authors: Perrin G. , Leblond J. B.
Published: April 2008

In a celebrated paper published in 1975, Rudnicki and Rice (RR) analyzed the conditions for strain localization in pressure-sensitive dilatant materials. This paper corrects certain results in their work that are relevant in exceptional cases. RR found that the normal to the plane of localization was generally orthogonal to the direction of the intermediate principal stress; however, when a certain inequality was satisfied, it was orthogonal to the direction of the minimum principal stress. In contrast, it is shown here that the normal to the plane of localization is always orthogonal to the direction of the intermediate principal stress; but there is a special case where it is parallel to the direction of either the maximum or the minimum principal stress, and in this case the expression of the critical hardening modulus at localization differs from that given by RR.
Fundamental Solutions for a Poroelastic Half-Space With Compressible Constituents
Authors: Rajapakse R. K. N. D. , Senjuntichai T.
Published: April 2008

This paper presents a comprehensive analytical treatment of the three-dimensional response of a poroelastic half-space with compressible constituents. General solutions for equations of equilibrium expressed in terms of displacements and variation of fluid volume are derived by applying Fourier expansion, Hankel transforms, and Laplace transforms with respect to the circumferential, radial, and time coordinates, respectively. The general solutions are used to derive a set of fundamental solutions corresponding to circular ring loads and to a fluid source applied at a finite depth below the free surface of a poroelastic half-space. The circumferential variation of the ring loads and the fluid source is described by appropriate trigonometric terms. Fundamental solutions presented in this paper can be used to model arbitrarily distributed loadings and a fluid source as well as a number of other problems encountered in geomechanics and energy resource explorations. In addition, these fundamental solutions can be used as the kernel functions in the development of boundary integral equation methods for a poroelastic half-space. Solutions for buried circular patch loads/fluid sink and concentrated loads/fluid sink are also deduced. Numerical evaluation of the fundamental solutions is also discussed. Comparisons are presented for time domain solutions obtained by using the Stehfest’s and Schapery’s schemes for Laplace inversion. A selected set of numerical solutions are presented to portray the features of consolidation process in six different poroelastic materials under buried patch loads and a sink.
Dynamic Holographic-Electronic Speckle-Pattern Interferometry
Authors: Ahmadshahi M. A. , Krishnaswamy Sridhar , Nemat-Nasser S.
Published: April 2008

The development of a nondestructive, full-field, quantitative optical technique, and its feasibility to study dynamic deformations of opaque and diffusively reflecting solids under transient loads, are discussed. The technique involves recording a sequence of dynamically changing two-beam speckle interference patterns (also called holographic speckle patterns) of a rapidly deforming body which is doubly illuminated by a laser light source. The time sequence of speckle patterns is recorded by means of a high-speed camera on an ultra-sensitive 35-mm film. The developed negatives are then digitized by a CCD camera into an image processing system. An initial speckle pattern corresponding to the undeformed state of the object is taken as the reference, and subsequent speckle patterns are digitally subtracted (reconstructed) from it to produce time- varying fringe patterns corresponding to the relative deformation of the test object. In order to gain confidence that the technique can be used to record truly transient deformation, it is tested here on a vibrating plate at resonance, thereby obtaining the evolution of the fringe pattern during 1/2 cycle of deformation corresponding to 160 μs.
An Experimental-Numerical Method for Nonlinear Structural Mechanics
Authors: Starmans F. J. M. , Brekelmans W. A. M. , Janssen J. D.
Published: April 2008

A maximum likelihood estimator and the finite element method are used to construct a tool for estimating the state of continuous structures from measured structural data. These structural data can, for example, consist of displacements of material points and stresses or strains at material points. The statistical uncertainty of the measured data is supposed to be known. An approximation for the uncertainty of the estimated state can be given. The analyzing tool, elaborated for the geometrically nonlinear rigid plastic case, is useful for evaluation of feasibility and accuracy of experimental set-ups. An example of application of the tool is presented.
Tunneling Cracks in Constrained Layers
Authors: Ho S. , Suo Z.
Published: April 2008

A thin, brittle layer bonded between tougher substrates is susceptible to cracking under residual and applied stresses. Such a crack initiates from an equi-axed flaw, confined by the substrates, tunneling in the brittle layer. Although tunneling is a three-dimensional process, the energy release rate at the front of a steady-state tunnel can be computed using plane strain fields. Several technically important problems are analyzed, including tunnels in adhesive joints, shear fracture, and kinked tunnels in a reaction product layer. The concept is finally applied to microcracking in brittle matrix composites caused by thermal expansion mismatch.
The Initial Post-buckling and Growth Behavior of Internal Delaminations in Composite Plates
Authors: Kardomateas G. A.
Published: April 2008

The initial post-buckling and growth behavior of delaminations in plates is studied by a perturbation procedure. In this work, no restrictive assumptions regarding the delamination thickness and plate length are made, i.e., the usual thin film assumptions are relaxed. The perturbation procedure is based on an asymptotic expansion of the load and deformation quantities in terms of the distortion parameter of the delaminated layer, the latter being considered a compressive elastica. Closed-form solutions for the load and midpoint delamination deflection versus applied compressive displacement during the initial post-buckling phase are derived. Moreover, closed-form expressions for the energy release rate and the mixity ratio (i.e., Mode II versus Mode I) at the delamination tip are produced. A higher Mode I component is found to be present during the initial post-buckling phase for delaminations of increasing ratio of delamination thickness over plate thickness, h/T (i.e., delaminations further away from the surface). Moreover, the-energy release rate corresponding to the same applied strain is larger for a higher h/T ratio. The reduced growth resistance of these configurations is verified by experimental results on unidirectional composite specimens with internal delaminations.
Active Stiffness Control of Cable Vibration
Authors: Fujino Yozo , Warnitchai Pennung , Pacheco B. M.
Published: April 2008

To suppress cable vibrations, active stiffness control, which changes the tension as a positive use of parametric excitation, is studied. An optimal algorithm is obtained from energy analysis and verified by experiment on a scale model. Numerical investigation is then made on the control of a combined system of cable and single-degree- of-freedom structure; the degree-of-freedom of the latter is along the cable axis. It is found by numerical simulation that instability occurs when the mass ratio of cable to structure is large, or when the frequency ratio of structure to cable is close to 2.0.
A Conservation Theorem for Constrained Multibody Systems
Authors: Wang J. T.
Published: April 2008

This paper presents a general conservation theorem for multibody systems subject to simple nonholonomic constraints. It is applicable to both conservative and nonconservative systems. The derivation of this theorem is based on Kane’s equations with undetermined multipliers. A power equation and a first integral of motion have been derived. They emerge in physically meaningful forms and include expressions for evaluating the power and energy flowing into the system. Like Kane’s equations, the power equation and the first integral of motion are derived in matrix form. This makes them particularly useful for the computer formulation and solution of multibody system dynamics.
The Incremental Variational Principles for Frictional Contact Problems of Linear Elasticity
Authors: Zboinski G.
Published: April 2008

Four types of the most frequently used variational functional are employed in order to form the inequality principles of the kineto-static contact problem of two elastic bodies in the common relative motion. As the general case, the principle based on the Hu- Washizu functional is proposed. The principles formed with the Reissner type, potential energy, and complementary energy functionals are derived as the special cases.
The Effect of Fiber Poisson Expansion in Micro-Indentation Tests
Authors: Meda G. , Hoysan S. F. , Steif P. S.
Published: April 2008

The fiber micro-indentation push-in test is studied in detail for the case of a Coulomb friction interface law. Using an integral equation method, as well as a finite element method, we investigate the “Poisson effect”; that is, the tendency for the loading to raise the normal stresses at the interface which can, in turn, augment the shear stresses. Results of the detailed analyses are compared with those of an approximate analysis which neglects the induced normal stresses and with one that includes them. A favorable comparison with the latter approximation enables us to assess the effect of material parameters on the strength of the “Poisson effect.”
Component Modal Synthesis Methods Based on Hybrid Models, Part I: Theory of Hybrid Models and Modal Truncation Methods
Authors: Jezequel L. , Seito H. D.
Published: April 2008

The assembly of structures along continuous boundaries poses great difficulties for expressing generalized boundary coordinates in modal synthesis, especially in the context of experiments. In order to solve such problems, a hybrid modal synthesis method is proposed in this study. This approach is based on the intermediate problem theory of Weinstein and brings out the duality between the formulation in displacement and the formulation in force. Generalized boundary coordinates are defined by introducing static deformations resulting from force distribution or displacement distribution along the boundaries depending on which formulation is to be used. By introducing integral operators associated with intermediate problems, two new methods of modal truncation can be proposed.
Component Modal Synthesis Methods Based on Hybrid Models, Part II: Numerical Tests and Experimental Identification of Hybrid Models
Authors: Jezequel L. , Setio H. D.
Published: April 2008

A double modal synthesis method in which compatibility conditions at substructure interfaces are ensured by the introduction of loaded modes is presented in this study. These loaded modes, which are obtained by introducing mass loading or stiffness loading along the boundaries, are used to define generalized boundary coordinates. Thus the hybrid models presented in the first part of this study are developed so that they can be derived from test data as results of independent modal identifications. Unlike in classical modal synthesis methods, in this double modal synthesis method, it is not necessary to clamp the interfaces, which is always difficult to carry out during vibration tests. By introducing loaded modes, generalized boundary coordinates which represent boundary deformability in the frequency range under study can be defined.
Angular Momentum of a Torque-Free Deforming Axisymmetric Gyro
Authors: Rimrott F. P. J. , Janabi-Sharifi F.
Published: April 2008

Attitude drift and attitude stability studies of torque-free gyros involve an angular momentum that is constant in magnitude and direction. The problem is to find suitable coordinates to describe the gyro’s behavior, and then to express the (constant) angular momentum in these coordinates. Expressions for small deformation are available. In the present paper the expression, in floating coordinates, for the angular momentum of a torque-free deforming axisymmetric gyro in terms of inertia moments and angular velocity components is extended to beyond small deformations. The angular momentum expression is written first in its general form. Thqn the angular momentum is expressed in matrix form for the calculation of angular momentum components for arbitrarily large deformation. Finally, three models are presented to illustrate the application of the angular momentum expression obtained.
Theoretical Simulation of an Anomalous Response in a Torsional Oscillator
Authors: Negahban M.
Published: April 2008

In a torsional oscillator, constructed by stretching a hollow cylindrical natural rubber member and connecting one end to a fly wheel and the other end to a fixed support, an anomalous behavior has been experimentally observed which is attributed to crystallization in the rubber. The anomalous behavior is observed when the rubber is stretched to more than 3.5 times its initial length and is characterized by a reduction in the period of the oscillator during stress relaxation. This indicates a gradual increase in the torsional rigidity of the rubber which can be explained by crystallization. Analyzing the response of the oscillator based on modeling the rubber as an incompressible isotropic elastic or viscoelastic material predicts a behavior opposite to that observed in the experiments. Using a model developed for characterizing mechanical response during crystallization in polymers, the anomalous behavior of the oscillator is reproduced.
Mode-Locking and Chaos in a Jeffcott Rotor With Bearing Clearances
Authors: Choi Sang-Kyu , Noah Sherif T.
Published: April 2008

A complex mode-locking (or entrainment) structure underlying the nonlinear whirling phenomenon of a horizontal Jeffcott rotor with a discontinuous nonlinearity (bearing clearance) was identified. A winding number is introduced as a measure of the ratio between two frequencies involved in the aperiodic whirling motions of the rotor system considered. Utilizing the winding number map, it was revealed that the alternating periodic and quasi-periodic responses take place according to the Farey number tree. The winding number varies in the form of the so-called “Devil’s staircase” as a certain system parameter varies. From the mode-locking pattern in the parameter space of the forcing amplitude and frequency, it was observed that as the forcing amplitude increases, the size of each locking interval increases so that its growth takes place in the form of “Arnol’d tongues,” where the winding number remains a rational number. Moreover, inside each locking zone, i.e., each “Arnol’d tongue,” there exist many smaller tongues similar to the main tongue, in which a sequence of period-doubling bifurcations leading to chaos occurred. The boundaries of each locking zone was obtained using a fixed-point algorithm along with the Floquet theory for checking the stability of the periodic solutions. The winding numbers were estimated utilizing a fixed-point algorithm modified to obtain quasi-periodic responses. A jump phenomenon was also observed by tracking multiple periodic solutions for several parameters of the rotor system.
A Rotation Rate Sensor Based Upon a Rayleigh Resonator
Authors: Clarke N. S. , Burdess J. S.
Published: April 2008

Rayleigh waves generated by line loads on the surface of an elastic half-space experience a change in both amplitude and wave number if the medium undergoes rotation. Use is to be made of this to form the basis of a rotation sensor. The relative changes are, however, extremely small. It is the purpose of this paper to show how, by use of the properties of Rayleigh waves, the changes induced by rotation may be amplified while the basic wave is not. This is achieved by use of a Rayleigh resonator with carefully chosen characteristics. The basic theory of such a resonator has been worked out in Clarke et al. (1989) and Clarke and Burdess (1991) and is here extended to account for rotational effects. It is shown that it should be possible to construct a practicably sized device, based upon this theory, to act as a robust rotation rate sensor.
Boundary Layer Transient Hygroscopic Stresses in Orthotropic Thick Shells Under External Pressure
Authors: Kardomateas G. A. , Chung C. B.
Published: April 2008

An exact elasticity solution is obtained for the stresses and displacements in an orthotropic cylindrical shell loaded by an external pressure under imposed constant moisture concentrations on the inner and outer surfaces. The material properties are assumed moisture independent and a displacement approach is used. Since the moisture diffusion process is relatively slow, the hygroscopic stresses are confined for practical time values to a boundary layer region near the surfaces. Illustrative results are presented for graphite-epoxy material regarding the boundary layer hygroscopic effect on the stress field with respect to time and the coupling of mechanical loading (external pressure) and moisture diffusion. For this material, it is shown that this effect is more pronounced for the axial component of stress.
Thermo-Elastoviscoplastic Buckling Behavior of Plates
Authors: Simitses G. J. , Song Y.
Published: April 2008

The thermo-elastoviscoplastic buckling behavior of plates is investigated. The analysis is based on nonlinear kinematic relations and nonlinear rate-dependent unified constitutive equations which include both Bodner-Partom’s and Walker’s material models. A finite element approach is employed to predict the inelastic buckling behavior. Numerical examples are given to demonstrate the effects of several parameters, which include temperature, small initial imperfections, and the thickness of the plate. Comparisons of buckling responses for the two models, Bodner-Partom’s and Walker’s, are also presented.
The Internal Stresses in Wound Rolls With the Presence of a Nip Roller
Authors: Good J. K. , Wu Z. , Fikes M. W. R.
Published: April 2008

Models which can be used to calculate the internal stresses within wound rolls of web material have all been confined to the center winding technique to date. In this publication, a new boundary condition is presented which will allow existing models to calculate the internal stresses within a wound roll which has been center wound with an undriven nip roller impinged upon the outside of the roll. Experimental verification of the new boundary condition is presented.
Analysis of High-Speed Rotating Disks With Variable Thickness and Inhomogeneity
Authors: Yeh Kai-Yuan , Han R. P. S.
Published: April 2008

A rotating disk with varying thickness and inhomogeneity, and subjected to a steady, inhomogeneous temperature field is analyzed. To handle the arbitrary profile, the disk is discretized into a series of uniform annular disks possessing constant material properties and then solved by the step-reduction method. Analytic expressions for thermoelastic stresses are given, and based on these results, the formulation is extended to include the calculation of shrink fit, the solving of the inverse problem for equistrength rotating disks, and the computations of plastic stresses and creep at elevated temperatures.
Thermal Stresses in a Bimaterial Joint: An Experimental Analysis
Authors: Post D. , Wood J. D. , Han B. , Parks V. J. , Gerstle F. P.
Published: April 2008

An experimental analysis was conducted on a bimaterial plate subjected to a uniform change of temperature. Whole-field displacement measurements U and V were made on the free surface by means of high-sensitivity moire interferometry, and stresses were calculated from these data. Stresses resembled those of stress singularities, but they reached finite tensile and compressive peaks on opposite sides of the interface. The peaks and a severe stress gradient between them occurred in a narrow zone of about ±25 μm from the interface. The results pertain to an elastic three-dimensional body.
A Note on Oscillatory Couette Flow in a Rotating System
Authors: Ganapathy R.
Published: April 2008

An alternative solution is proposed for the oscillatory Ekman boundary layer flow bounded by two parallel plates in relative motion (Muzumder, 1991). The solution brings out among other things, the phenomenon of resonance which is of importance in rotating systems.
Green Functions for Cylindrical Elastic Waves in Aluminum: Comparison Between Theory and Experiments
Authors: Mourad A. , Castagne`de B. , Mottay E.
Published: April 2008

A comparison between experimental and theoretical displacement fields for the tangential force problem (which is a model of the thermoelastic regime for laser generated ultrasound) at an aluminum interface is reported. The numerical predictions are based on a standard formulation of the transient generation of elastic waves along a line source. In the configuration of a purely elastic thin plate, the cylindrical elastic waves are then detected on the other side by a point-like receiver. The experimental works is carried out with a pulsed Nd:YAG laser for the generation and a laser interferometric probe for the detection of ultrasonic waves.
Antiplane Shear Deformations for Homogeneous and Inhomogeneous Anisotropic Linearly Elastic Solids
Authors: Horgan C. O. , Miller K. L.
Published: April 2008

Antiplane shear deformations of a cylindrical body, with a single displacement field parallel to the generators of the cylinder and independent of the axial coordinate, are one of the simplest classes of deformations that solids can undergo. They may be viewed as complementary to the more familiar plane deformations. Antiplane (or longitudinal) shear deformations have been the subject of the considerable recent interest in nonlinear elasticity theory for homogeneous isotropic solids. In contrast, for the linear theory of isotropic elasticity, such deformations are usually not extensively discussed. The purpose of the present paper is to demonstrate that for inhomogeneous anisotropic linearly elastic solids the antiplane shear problem does provide a particularly tractable and illuminating setting within which effects of anisotropy and inhomogeneity may be examined. We consider infinitesimal antiplane shear deformations of an inhomogeneous anisotropic linearly elastic cylinder subject to prescribed surface tractions on its lateral boundary whose only nonzero component is axial and which does not vary in the axial direction. In the absence of body forces, not all arbitrary anisotropic cylinders will sustain an antiplane shear deformation under such tractions. Necessary and sufficient conditions on the elastic moduli are obtained which do allow an antiplane shear. The resulting boundary value problems governing the axial displacement are formulated. The most general elastic symmetry consistent with an antiplane shear is described. There are at most 15 independent elastic coefficients associated with such a material. In general, there is a normal axial stress present, which can be written as a linear combination of the two dominant shear stresses. For a material with the cylindrical cross-section a plane of elastic symmetry (monoclinic, with 13 moduli), the normal stress is no longer present. For homogeneous materials, it is shown how the governing boundary value problem can be transformed to an equivalent isotropic problem for a transformed cross-sectional domain. Applications to the issue of assessing the influence of anisotropy and inhomogeneity on the decay of Saint-Venant end effects are described.
The Contact Behavior Between Laminated Composite Plates and Rigid Spheres
Authors: Wu Enboa , Yen Ching-Shih
Published: April 2008

The contact behavior between a composite laminate and a rigid sphere is discussed in this paper using a method derived from the three-dimensional anisotropic elasticity theory. Response of the plate and the force-indentation ( F − α ) relationship were obtained by constructing an exact Green’s function of the laminate. Agreement between the prediction and the experimental data reported by others is excellent before laminates are damaged. The F - α relationship is approximately proportional to the out-of-plane Young’s modulus and is influenced by the plate thickness. The effects of changing the in-place Young’s moduli, all the shear moduli, stacking sequences and span of the laminates are insignificant unless identation is large. Further, the modified Hertz law underestimates the contact force for the same indentation.
Circularly Cylindrical and Plane Layered Media in Antiplane Elastostatics
Authors: Honein T. , Honein E. , Herrmann G.
Published: April 2008

In this paper we consider, within the framework of the linear theory of elasticity, the problem of circularly cylindrical and plane layered media under antiplane deformations. The layers are, in the first instance, coaxial cylinders of annular crosssections with arbitrary radii and different shear moduli. The number of layers is arbitrary and the system is subjected to arbitrary loading (singularities). The solution is derived by applying the heterogenization technique recently developed by the authors. Our formulation reduces the problem to solving linear functional equations and leads naturally to a group structure on the set t of real numbers such that −1 < t < 1. This allows us to write down the solution explicitly in terms of the solution of a corresponding homogeneous problem subjected to the same loading. In the course of these developments, it is discovered that certain types of inclusions do not disturb a uniform longitudinal shear. That these inclusions, which may be termed “stealth,” are important in design and hole reinforcements is pointed out. By considering a limiting case of the aforementioned governing equations, the solution of plane layered media can be obtained. Alternatively, our formulation leads, in the case of plane layered media, to linear functional equations of the finite difference type which can be solved by several standard techniques.
Two-Dimensional Contact on an Anisotropic Elastic Half-Space
Authors: Fan Hui , Keer L. M.
Published: April 2008

The two-dimensional contact problem for a semi-infinite anisotropic elastic media is reconsidered here by using the formalism of Es he I by et al. (1953) and Stroh (1958). The approach of analytic function continuation is employed to investigate the half-space contact problem with various mixed boundary conditions applied to the half-space. A key point of the solution procedure suggested in the present paper is its dependence on a general eigenvalue problem involving a Hermitian matrix. This eigenvalue problem is analogous to the one encountered when investigating the behavior of an interface crack (Ting, 1986). As an application, the interaction between a dislocation and a contact strip is solved. The compactness of the results shows their potential for utilization to solve the problem of contact of a damaged anisotropic half-space.
Static Axisymmetric Hertzian Contacts Subject to Shearing Forces
Authors: Munisamy R. L. , Hills D. A. , Nowell D.
Published: April 2008

A numerical method is used to resolve the classic Mindlin-Cattaneo partial slip problem for contact between similar and between dissimilar bodies. It is shown that, for similar bodies, the surface frictional energy dissipation is concentrated off the plane of symmetry although the overall dissipation is similar to that predicted by the classical solution. This effect is enhanced for certain combinations of dissimilar materials, where the process of frictional shakedown leads to a displaced contact and hence additional shear compliances.
Random Vibrational Response and Stability Study of Long-Span Bridges
Authors: Billah K. Y. R. , Shinozuka M.
Published: April 2008

A random vibrational response study of a dynamical system is presented. In particular, suspension bridge stability analysis in the presence of turbulence is addressed. The effects of turbulence on the well-understood deterministic stability of section models using aerodynamic functions are explored emphasizing governing physical mechanisms. For this purpose, the primary emphasis is placed on the nonlinear control parameter (square of the upstream flow velocity) and the resulting nonlinear noise term. To this end, it is pointed out that the introduction of “nonwhite” nonlinear noise for the excitation forces is of paramount importance. Further, it is concluded that this invoking of nonwhite noise is necessary to avoid inconsistencies involved with the usual assumption of Gaussian white noise. Finally, numerical simulation of nonwhite, nonlinear noise and subsequent integration of the single-degree-of-freedom torsional equation of motion involving varying “time scales” are carefully carried out. The numerical tests for sample stability provide some new results that are consistent with existing experimental observations.
Ultrasonic Evaluation of Stiffness Tensor Changes and Associated Anisotropic Damage in a Ceramic Matrix Composite
Authors: Audoin B. , Baste S.
Published: April 2008

After describing the crucial role of microcracking in the behavior of ceramic matrix composites, we introduce a phenomenological model in the framework of continuum damage mechanics, where damage is defined as the change of the tensor of elasticity. For damage identification, we have developed a specific ultrasonic device. This immersion set-up was connected to a suitable data processing system for an optimum recovery of the stiffness matrix coefficients from convenient sets of velocity measurements. Linked to a tensile machine, it enabled us to measure the stiffness changes and the anisotropic damage induced by a uniaxial tensile test.
Optimal Cool Down in Nonlinear Thermoviscoelasticity With Application to Graphite/Peek (APC-2) Laminates
Authors: Lee K. , Weitsman Y.
Published: April 2008

Many thermoplastic resin composite laminates, such as those made of APC-2, undergo a substantial temperature drop during their post-manufacturing cool down. This thermal excursion induces significant residual thermal stresses into the laminate due to the mutual geometric constraints among the multidirectional plies. In view of the considerable time-dependent relaxation which occurs during the cooling process, the residual thermal stresses exhibit strong dependence on the temperature history. However, in view of the high magnitudes of those stresses, the relaxation behavior is viscoelastically nonlinear. This paper demonstrates that it is possible to obtain an optimal cool-down path which minimizes the residual thermal stresses in APC-2 composites upon the termination of the cooling process.
Integrated Damping Mechanics for Thick Composite Laminates and Plates
Authors: Saravanos D. A.
Published: April 2008

A method for predicting the damped dynamic characteristics of thick composite laminates and plates is presented. Unified damping mechanics relate the damping of composite plates to constituent properties, fiber volume ratio, fiber orientation, laminate configuration, plate geometry, temperature, and moisture. Discrete layer damping mechanics for thick laminates, entailing piecewise continuous displacement fields and including the effects of interlaminar shear damping, are described. A semi-analytical method for predicting the modal damping and natural frequencies of thick simply-supported specialty composite plates is included. Applications demonstrate the validity, merit, and ranges of applicability of the new theory. The applications further illustrate the significance of interlaminar shear damping, and investigate the effects of lamination, thickness aspect ratio, fiber content, and temperature.