bluuebunny/crossref_metadata_2025 huggingface dataset:
Load Distribution in Hypoid Gears
Authors: Simon Vilmos
Published: July 2002

A new approach for the computerized simulation of load distribution in mismatched hypoid gears with point contact is presented. The load distribution calculation is based on the bending and shearing deflections of gear teeth, on the local contact deformations of the mating surfaces, on gear body bending and torsion, on the deflections of the supporting shafts, and on the manufacturing and alignment errors of the mating members. The tooth deflections of the pinion and gear teeth are calculated by FEM, and the tooth contact is treated in a special way: it is assumed that the point contact under load spreads over a surface along the “potential” contact line, which line is made up of the points of the mating tooth surfaces in which the separations of these surfaces are minimal, instead of assuming an elliptical contact pattern. The system of governing equations is solved by approximations and by using the successive-over-relaxation method. The corresponding computer program is developed. The calculations, performed by this program, show that in the case of hypoid gears, the new approach gives a more realistic contact pattern and contact pressure than the usually assumed and applied elliptical contact approach, especially for the tooth pairs contacting on the toe and on the heel of teeth, and in the case of load distribution calculations made in misaligned gear pairs. By using this program the influence of design data on load distribution parameters is investigated and discussed. [S1050-0472(00)00504-3]
Investigations on Internally Ring-Stiffened Joints of Offshore Platforms
Authors: Thandavamoorthy T. S.
Published: July 2002

The paper presents in detail the experimental and numerical investigations on tubular joints that are stiffened internally with three annular rings in order to study their behaviors and evaluate their strengths under axial brace compression loading. The nominal chord and brace diameters of the tested T and Y-joints were 324 and 219 mm and their thicknesses were 12 and 8 mm, respectively. The tested joints are approximately quarter-size when compared to the largest joints in the platforms built in a shallow water depth of 80 m in the Bombay High field. Some of the joints were actually fabricated by a leading offshore agency that is directly involved in the fabrication of prototype structures. Bending of the chord as a whole was observed to be the predominant mode of deformation of the internally ring-stiffened joints in contrast to ovaling and punching shear of the unstiffened joints. Strengths of the internally ring-stiffened joints were found to be almost twice that of unstiffened joints of the same dimensions. A tri-linear stress-strain model that takes into account the strain-hardening characteristics of the material was developed to assess the strength of the internally ring-stiffened joints. Finite element analysis (FEA) was performed to predict the bending deflection of the internally ring-stiffened joints under axial brace compression loading. This FEA used NISA II software package and was based on the tri-linear model proposed in this study. [S0892-7219(00)00104-7]
Optimum Design of Hydrostatic Spherical Bearings in Fluid Film Lubrication
Authors: Kazama Toshiharu
Published: July 2002

The optimum design of hydrostatic spherical bearings in fluid film lubrication is examined theoretically. The analytical solutions are derived for both fitted and clearance types of bearings with capillary and orifice restrictors. The optimal size based on the minimum power loss and the maximum stiffness is presented, and the difference between two types of bearings is discussed. [S0742-4787(00)02204-9]
Thermal Analysis of Flow in the Deformation Phase of Liquid Lubricated Plane Strain Forging
Authors: Bhatt V. K.
Published: July 2002

The generalized energy equation is reduced into a simple form for conduction and convection modes of heat transfer across a hydrodynamic incompressible fluid film in the deformation phase of plane-strain forging. Expressions for the temperature, velocity, and flow distributions are obtained by solving the energy equation with appropriate boundary conditions. Application of this analysis is illustrated for the film formation process in the deformation phase of liquid lubricated plane strain forging. The analysis indicates that the Peclet number plays an important role in deciding the variation of lubricant film thickness with position and time in the deformation phase. [S0742-4787(00)02504-2]
Structural Abstraction in Snap-fit Analysis
Authors: Suri Gaurav , Luscher Anthony F.
Published: July 2002

Snap-fit design has always been more of an art instead of an engineering activity. Research in this area focuses on generating finite element models for predicting the performance of snap-fit features. Such research typically uses fixed-end conditions at the base of the snap-fit feature. Often this is an unrealistic assumption, because snap-fits are usually molded on plastic parts with significant flexibility. The performance of snap-fits can be significantly influenced by this additional flexibility. To predict this performance of snap-fits it often becomes necessary to analyze the entire part, which can be a costly and time consuming process. There is no general methodology in the open literature to incorporate base-part flexibility into the design of snap-fit features. Existing work in this area is inaccurate and limited to certain base-part and snap-fit topologies. This paper proposes a new methodology called structural abstraction for incorporating base-part flexibility into snap-fit feature models. This methodology abstracts base-parts as spring elements with various stiffnesses. The underlying theory and the relevant relationships are developed and the approach is validated using several test cases. Independence of the approach to both base-part and snap-fit topologies is established and shown to be a major advantage of this technique. Use of this methodology will improve snap-fit analysis and give a more accurate estimation of retention strength. It is shown that in certain cases the improvement in accuracy over conventional finite element models of snap-fits can be as high as 70 percent. [S1050-0472(00)02504-6]
Vibrations of a Taut Cable With an External Damper
Authors: Krenk S.
Published: July 2002

A solution is presented of the problem of vibrations of a taut cable equipped with a concentrated viscous damper. The solution is expressed in terms of damped complex-valued modes, leading to a transcendental equation for the complex eigenfrequencies. A simple iterative solution of the frequency equation for all complex eigenfrequencies is proposed. The damping ratio of the vibration modes, determined from the argument of the complex eigenfrequency, are typically determined to within one percent in two iterations. An accurate asymptotic approximation of the damping ratio of the lower modes is obtained. This formula permits explicit determination of the optimal location of the viscous damper, depending on its damping parameter. [S0021-8936(00)00404-9]
Transport Phenomena During Solidification Processing of Functionally Graded Composites by Sedimentation
Authors: Gao J. W. , Wang C. Y.
Published: July 2002

A combined experimental and numerical investigation of the solidification process during gravity casting of functionally graded materials (FGMs) is conducted. Focus is placed on understanding the interplay between the freezing front dynamics and particle transport during solidification. Transparent model experiments were performed in a rectangular ingot using pure water and succinonitrile (SCN) as the matrix and glass beads as the particle phase. The time evolutions of local particle volume fractions were measured in situ by bifurcated fiber optical probes working in the reflection mode. The effects of important processing parameters were explored. It is found that there exists a particle-free zone in the top portion of the solidified ingot, followed by a graded particle distribution region towards the bottom. Higher superheat results in slower solidification and hence a thicker particle-free zone and a higher particle concentration near the bottom. The higher initial particle volume fraction leads to a thinner particle-free region. Lower cooling temperatures suppress particle settling. A one-dimensional multiphase solidification model was also developed, and the model equations were solved numerically using a fixed-grid, finite-volume method. The model was then validated against the experimental results and subsequently used as a tool for efficient computational prototyping of an Al/SiC FGM.
A Novel Control Approach for the Droplet Detachment in Rapid Prototyping by 3D Welding
Authors: Zheng Bing , Kovacevic Radovan
Published: July 2002

Gas metal arc welding (GMAW) of steel in argon-rich shielding usually features free-metal transfer and short-circuiting metal transfer. Projected spray transfer in one droplet per pulse (ODPP) mode in combination with the droplet detachment feedback control is one of the most effective approaches to guarantee high weld quality. This paper explores new methods for controlling mass and heat transfer based on droplet detachment behavior in rapid prototyping by 3D welding. Three groups of experiments are performed based on the different welding current wave forms: pure square wave, square wave combined with sine wave (combined wave), and pure sine wave. Compared with the pure square wave form, the combined wave form can generate a weld bead with a more narrow and shallow penetration profile (the width and depth are 3.04 mm and 0.22 mm, respectively). When a pure sine wave form is used, the droplet is forced to oscillate once at the wire tip (the oscillation cycle equals the pulse cycle) and then detaches smoothly; the droplet is accompanied by a characteristically harmonious sound. Recorded images show that the droplet in a square or combined wave form can be forced to oscillate twice (the oscillation cycle equals half of the pulsed cycle) before it detaches. Careful selection of parameters is required to generate multiple oscillations for the droplet before it detaches. Photos of a weld cross section reveal that the penetration profile can be greatly improved using a combined wave form. The results achieved are not only effective for mass and heat control in rapid prototyping by 3D welding, but also are beneficial for further investigation of the droplet detachment behavior in GMAW.
Fundamental Study on a Novel Gas Turbine Cycle
Authors: Ishida Masaru , Jin Hongguang
Published: July 2002

It is important and necessary to develop a new technology for CO2 capture with less or even no energy penalty to make a breakthrough in greenhouse gas abatement. Towards this objective, we have proposed a novel gas turbine power plant, which is not only to capture CO2 in the stage of combustion, but also to increase thermal efficiency of the power plant. The chemical-looping combustor in the proposed system consists of a fuel reactor (fuel reacts with metal oxide) and an air reactor (the resulting metal reacts with oxygen in air). This new system requires no additional energy consumption for CO2 separation (i.e., no energy penalty) and no CO2 separation equipment. Here, we have identified several breakthrough points in the proposed system and summarized promising results from experimental investigation on the chemical-looping combustion.
Modeling the Fracture of a Sandwich Structure due to Cavitation in a Ductile Adhesive Layer
Authors: Zhang S. , Hsia K. J.
Published: July 2002

The strength and durability of adhesively bonded sandwich structures often depend on the mechanisms of fracture, which in turn depend on the properties of the adhesive and the microstructures of the interface. When the thin adhesive layer is ductile, cavitation either within the layer or along the interface is often the dominant failure mechanism. In the present paper, fracture due to cavity growth in a thin ductile layer is analyzed. A new method utilizing fluid mechanics solutions is developed. Solutions of fluid flow field are used to approximate the plastic deformation field in the corresponding solid body with a cavity. The equilibrium condition is satisfied by using the principle of virtual work rate. Stress-separation curves due to cavitation in the thin layer can thus be obtained. The method is validated by reevaluating the one-dimensional problem of cavity growth in a sphere—a problem for which an exact, analytical solution exists. A two-dimensional plane strain cavitation problem is analyzed using the new method. The stress-separation curves and the fracture resistance due to this mechanism are obtained. The results show that both the stress-separation curves and the fracture resistance are sensitive to the strain-hardening exponent and the initial void size, but not the yield strength of the material. The new method has clear advantages over numerical methods, such as the finite element method, when parametric studies are performed.
Analysis and DSP Implementation of a Broadband Duct ANC System Using Spatially Feedforward Structure
Authors: Bai Mingsian R. , Lin Yujeng , Wu Jian-Da
Published: July 2002

The active control technique for broadband attenuation of noise in ducts, using spatially feedforward structure, is investigated from the viewpoints of both acoustic analysis and control engineering. According to the previous work by Munjal and Eriksson [1], there exists an ideal controller for this problem. The ideal controller is a function of the finite source impedance and is thus independent of the boundary conditions. Despite the simplicity, the ideal controller cannot be practically implemented due to the difficulty of calibration of electro-mechanical parameters. To overcome the problem, the controller is implemented via an equivalent formulation modified from the controller originally proposed by Roure [2]. The modified controller is implemented on a DSP platform, using a FIR filter, an IIR filter and a hybrid filter. The experimental results showed that the system achieved 17.2 dB maximal attenuation in the frequency band 300∼600 Hz. Physical insights and design considerations in implementation phase are also discussed in the paper.
Spatially Resolved Temperature Measurements in a Liquid Using Laser Induced Phosphorescence
Authors: Thomson S. L. , Maynes D.
Published: July 2002

This paper describes recent advances in the development of a temperature measurement methodology based on phosphorescence of a tracer molecule in a liquid. The methodology represents an extension of molecular tagging velocimetry (MTV). MTV is a laser-based technique of obtaining spatially resolved fluid velocity profiles. The methodology has the potential of providing spatially resolved simultaneous measurements of velocity and temperature data over a planar domain. Presently, a method of obtaining temperatures over a range of 30°C with a typical uncertainty of ±1.0–1.5°C has been developed. Recent progress has resulted in a method of generating robust calibration curves for use in subsequent temperature measurements. A discussion of the experimental methodology, calibration curve development, and error analysis is presented. Finally, simultaneous temperature and velocity profile measurements using the method are demonstrated under dynamic conditions.
A Process Map for Consistent Build Conditions in the Solid Freeform Fabrication of Thin-Walled Structures
Authors: Vasinonta Aditad , Beuth Jack L. , Griffith Michelle L.
Published: July 2002

In solid freeform fabrication (SFF) processes involving thermal deposition, thermal control of the process is critical for obtaining consistent build conditions and in limiting residual stress-induced warping of parts. In this research, a nondimensionalized plot (termed a process map) is developed from numerical models of laser-based material deposition of thin-walled structures. This process map quantifies the effects of changes in wall height, laser power, deposition speed and part preheating on melt pool length, which is an essential process parameter to control in order to obtain consistent build conditions. The principal application of this work is to the Laser Engineered Net Shaping (LENS) process under development at Sandia Laboratories; however, the general approach and a subset of the presented results are applicable to any SFF process involving a moving heat source. Procedures are detailed for using the process map to predict melt pool length and predictions are compared against experimentally measured melt pool lengths for stainless steel deposition in the LENS process.
A Pseudo-Rigid-Body Model for Initially-Curved Pinned-Pinned Segments Used in Compliant Mechanisms
Authors: Edwards, Brian T. , Jensen, Brian D. , Howell Larry L.
Published: July 2002

The pseudo-rigid-body model concept allows compliant mechanisms to be analyzed using well-known rigid-body kinematics. This paper presents a pseudo-rigid-body model for initially curved pinned-pinned segments that undergo large, nonlinear deflections. The model approximates the segment as three rigid members joined by pin joints. Torsional springs placed at the joints model the segment’s stiffness. This model has been validated by fabricating several such segments from a variety of different materials. Testing of the force-deflection behavior of these segments verified the accuracy of the model.
Compression Load Dynamics in a Special Helical Blower: A Modeling Improvement
Authors: Mimmi Giovanni , Pennacchi Paolo
Published: July 2002

The instantaneous variation of pressure loads acting on the rotors of positive displacement rotary blowers may produce vibrations and noise that in some case produce the failure of the machine and of the piping. In a previous paper the authors determined the pressure loads acting on the rotors, starting from the geometry of the chambers that are formed during the rotor meshing and the thermodynamic transformation of the working fluid. The calculation of the loads has been made in a quasi-static manner. In this paper the model has been improved by taking into account the effects due to a closed volume chamber at the discharge. This assumption better reproduces the real cases and allows the researchers to perform more efficient calculations and more reliable predictions.
A Theory for Strain-Based Structural System Identification
Authors: Reich G. W. , Park K. C.
Published: July 2002

A theory for structural system identification which utilizes strains and translational displacements as measured outputs is presented. The state variables of the fundamental first-order form consist of the strains and the elemental or substructural rigid-body motion amplitudes. The theory is applicable to, and to some respects, motivated by the advances and expanded use of embedded piezoelectric sensors and fiber optics. A distinct feature of the present theory is its ability to provide rotational flexibility without having to measure rotational quantities. The theory is illustrated by simple ideal examples.
Effects of Bulk Flow Pulsations on Phase-Averaged and Time-Averaged Film-Cooled Boundary Layer Flow Structure
Authors: Jung I.-S. , Ligrani P. M. , Lee J. S.
Published: July 2002

Flow structure in boundary layers film cooled from a single row of round, simple angle holes, and subject to bulk flow pulsations, is investigated, including phase-averaged streamwise velocity variations, and alterations of time-averaged flow structure. The bulk flow pulsations are in the form of sinusoidal variations of velocity and static pressure, and are similar to flow variations produced by potential flow interactions and passing shock waves near turbine surfaces in gas turbine engines. Injection hole length to diameter ratio is 1.6, time-averaged blowing ratio is 0.50, and bulk flow pulsation frequencies range from 0–32 Hz, which gives modified Strouhal numbers from 0–1.02. Profiles of time-averaged flow characteristics and phase-averaged flow characteristics, measured in the spanwise/normal plane at x/d=5 and z/d=0, show that effects of pulsations are larger as imposed pulsation frequency goes up, with the most significant and dramatic changes at a frequency of 32 Hz. Phase shifts of static pressure (and streamwise velocity) waveforms at different boundary layer locations from the wall are especially important. As imposed pulsation frequency varies, this includes changes to the portion of each pulsation phase when the largest influences of static pressure waveform phase-shifting occur. At a frequency of 32 Hz, these phase shifts result in higher instantaneous injectant trajectories, and relatively higher injectant momentum levels throughout a majority of each pulsation period.
Closed-Form Solutions for the Stress Fields Induced by Blunt Wedge-Shaped Indenters in Elastic Half-Planes
Authors: Truman C. E. , Sackfield A.
Published: July 2002

Closed-form expressions are given for the Muskhelishvili potentials created by wedge-shaped indenters contacting elastic half-planes. The potentials are given for normal and sliding contact of both similar and dissimilar materials. Surface values of the tension σxx0 are also presented.
A New Method for Nonlinear Two-Point Boundary Value Problems in Solid Mechanics
Authors: Ramachandra L. S. , Roy D.
Published: July 2002

A local and conditional linearization of vector fields, referred to as locally transversal linearization (LTL), is developed for accurately solving nonlinear and/or nonintegrable boundary value problems governed by ordinary differential equations. The locally linearized vector field is such that solution manifolds of the linearized equation transversally intersect those of the nonlinear BVP at a set of chosen points along the axis of the only independent variable. Within the framework of the LTL method, a BVP is treated as a constrained dynamical system, which in turn is posed as an initial value problem. (IVP) In the process, the LTL method replaces the discretized solution of a given system of nonlinear ODEs by that of a system of coupled nonlinear algebraic equations in terms of certain unknown solution parameters at these chosen points. A higher order version of the LTL method, with improved path sensitivity, is also considered wherein the dimension of the linearized equation needs to be increased. Finally, the procedure is used to determine post-buckling equilibrium paths of a geometrically nonlinear column with and without imperfections. Moreover, deflections of a tip-loaded nonlinear cantilever beam are also obtained. Comparisons with exact solutions, whenever available, and other approximate solutions demonstrate the remarkable accuracy of the proposed LTL method.
A Study on Fundamental Mechanisms of Warp and Recoil in Hemming
Authors: Zhang Guohua , Wu Xin , Hu S. Jack
Published: July 2002

In this paper, the occurrence of recoil and surface warp during the flat surface-straight edge hemming process is investigated. A general-purpose finite element code ABAQUS/Standard is used to simulate the hemming operations. Reverse bending and springback are the fundamental mechanisms that cause surface warp and recoil. Recoil and warp are not independent. One parameter, final equivalent warp, is used to represent both. Pre-hemming target ending position is proposed based on the minimization of the final equivalent warp. The influence of the geometrical and process parameters on recoil and warp are also discussed.
Effects of Bulk Flow Pulsations on Film Cooling With Compound Angle Holes: Heat Transfer Coefficient Ratio and Heat Flux Ratio
Authors: Jung In Sung , Lee Joon Sik , Ligrani P. M.
Published: July 2002

Experiments are conducted to investigate the effects of bulk flow pulsations on film cooling from compound angle holes. A row of five film cooling holes is employed with orientation angles of 0, 30, 60, and 90 deg at a fixed inclination angle of 35 deg. Static pressure pulsations are generated using an array of six rotating shutter blades, which extend across the span of the exit of the wind tunnel test section. Pulsation frequencies of 0 Hz, 8 Hz, and 36 Hz, and time-averaged blowing ratios of 0.5, 1.0, and 2.0 are employed. Corresponding coolant Strouhal numbers based on these values then range from 0.20 to 3.6. Spatially resolved surface heat transfer coefficient distributions are measured (with the film and freestream at the same temperature) using thermochromic liquid crystals. Presented are ratios of surface heat transfer coefficients with and without film cooling, as well as ratios of surface heat flux with and without film cooling. These results, for compound angle injection, indicate that the pulsations cause the film to be spread more uniformly over the test surface than when no pulsations are employed. This is because the pulsations cause the film from compound angle holes to oscillate in both the normal and spanwise directions after it leaves the holes. As a result, the pulsations produce important changes to spatially resolved distributions of surface heat flux ratios, and surface heat transfer coefficient ratios. In spite of these alterations, only small changes to spatially averaged heat transfer coefficient ratios are produced by the pulsations. Spatially averaged surface heat flux ratios, on the other hand, increase considerably at coolant Strouhal numbers larger than unity, with higher rates of increase at larger orientation angles.
Regimes of Contact in Spline Couplings
Authors: Medina S. , Olver A. V.
Published: July 2002

The contact between the male and female teeth of involute spline couplings connecting misaligned transmission shafts has been studied using an elastostatic contact model with stick-slip friction based on the boundary integral element method. The effect on the distribution of pressure and on the slip path during shaft rotation, of a wide range of design parameters and of applied torque and misalignment has been explored. The predicted behavior is classified according to the regime of friction (cyclic stick-slip or gross slip) and to that of the pressure history (uniform, cyclic, discontinuous, or toppled). The magnitude of the maximum tooth load, the axial skewness of the distribution of pressure and a maximum wear depth parameter are presented in terms of dimensionless design and operating parameters. The effect of tooth crowning is briefly examined. The results show a number of previously unreported features including a cyclic tooth load—which declines to zero for certain conditions—and an effective slip amplitude of around half the rigid-body value. This may affect the interpretation of laboratory fretting tests.
Performance of Horizontal Smooth Tube Absorber With and Without 2-Ethyl-Hexanol
Authors: Kyung Ick-Soo , Herold Keith E.
Published: July 2002

Absorption of water vapor into aqueous lithium bromide is a fundamental step in absorption refrigeration. When the liquid film is laminar, the coupled heat and mass transfer process is controlled by mass transfer, resulting in low transfer coefficients. Significant augmentation of mass transfer, and hence of the coupled process, is achieved by introducing a trace amount (on the order of 100 ppm) of 2-ethyl-hexanol. The alcohol acts as a surfactant and drives Marangoni convection that effectively mixes the liquid providing a much higher effective mass diffusivity. The film flow in the presence of the alcohol is noticeably different with a complex, apparently unstructured appearance. The flow activity, which can be easily observed, has never been satisfactorily explained until the recent introduction of the Vapor Surfactant theory. This paper presents a series of experimental results of absorption in an actual chiller facility. The novel features of the work include measurement of the effect of inlet subcooling, discussion of the effect of droplets ejected from the tube bundle and an explanation of the importance of flux in the alcohol augmentation physics.
Spectral Analysis of Nonlinear Water Waves Based on the Hilbert-Huang Transformation
Authors: Schlurmann T.
Published: July 2002

The Hilbert-Huang transformation (HHT) is a new method for analyzing nonlinear and non-stationary data series. The central idea behind the HHT is the so-called empirical mode decomposition (EMD) that numerically decomposes a time-dependent signal into its own underlying characteristic modes. Applying the Hilbert transformation (HT) to each of these disintegrated intrinsic mode function (IMF) subsequently provides the Hilbert amplitude or energy spectrum—producing more accurate spectra and proposing in all probability entirely new physical insights of nonlinear and nonstationary processes. The present paper describes the application of the HHT concerning the spectral frequency analysis of nonlinear transient water waves.
Scale up of a Solar Reactor for Fullerene and Nanotube Synthesis
Authors: Guillard Tony , Flamant Gilles , Robert Jean-Franc¸ois , Rivoire Bruno , Giral Joseph , Laplaze Daniel
Published: July 2002

Conventional methods for the synthesis of fullerenes and carbon nanotubes such as laser or electric arc ablation have failed when the process is scaled up. Our ultimate goal is to scale a solar process up from 2 to 250 kW; this paper shows that our method for achieving this scale-up is valid because we were able to predict process performance variables at the 50 kW level from preliminary experimental results from 2 kW experiments. The key parameters that characterize this process are the carbon soot mass flow rate and the desired product yield. The carbon soot production rate is a function of the target temperature and this can be predicted in a straightforward way from a heat transfer model of the larger system. The yield is a more complicated function of specific reactor variables such as patterns of fluid flow, residence times at various temperatures, and the reaction chemistry, but we have found that for fullerenes it depends primarily on the concentration of carbon vapor in the carrier gas, the target temperature and the temperature distribution in the cooling zone. Using these parameters, we scaled our process up to 50 kW and compared the predicted results to the measured performance. A graphite target 6 cm in diameter was vaporized in an argon atmosphere and a reduced pressure of 120–240 hPa with a solar flux density in the range 600-920W/cm2. Vaporization rates as high as 50 g/h were measured with a fullerene production rate equal to about 2 g/h, i.e., the expected results.
Tensile Mechanical Properties of Three-Dimensional Type I Collagen Extracellular Matrices With Varied Microstructure
Authors: Roeder Blayne A. , Kokini Klod , Sturgis Jennifer E. , Robinson J. Paul , Voytik-Harbin Sherry L.
Published: July 2002

The importance and priority of specific micro-structural and mechanical design parameters must be established to effectively engineer scaffolds (biomaterials) that mimic the extracellular matrix (ECM) environment of cells and have clinical applications as tissue substitutes. In this study, three-dimensional (3-D) matrices were prepared from type I collagen, the predominant compositional and structural component of connective tissue ECMs, and structural-mechanical relationships were studied. Polymerization conditions, including collagen concentration (0.3–3 mg/mL) and pH (6–9), were varied to obtain matrices of collagen fibrils with different microstructures. Confocal reflection microscopy was used to assess specific micro-structural features (e.g., diameter and length) and organization of component fibrils in 3-D. Microstructural analyses revealed that changes in collagen concentration affected fibril density while maintaining a relatively constant fibril diameter. On the other hand, both fibril length and diameter were affected by the pH of the polymerization reaction. Mechanically, all matrices exhibited a similar stress-strain curve with identifiable “toe,” “linear,” and “failure” regions. However, the linear modulus and failure stress increased with collagen concentration and were correlated with an increase in fibril density. Additionally, both the linear modulus and failure stress showed an increase with pH, which was related to an increased fibril length and a decreased fibril diameter. The tensile mechanical properties of the collagen matrices also showed strain rate dependence. Such fundamental information regarding the 3-D microstructural-mechanical properties of the ECM and its component molecules are important to our overall understanding of cell-ECM interactions (e.g., mechanotransduction) and the development of novel strategies for tissue repair and replacement.
Rotating Cavitation in a Centrifugal Pump Impeller of Low Specific Speed
Authors: Friedrichs Jens , Kosyna Gu¨nter
Published: July 2002

The paper describes an experimental investigation of two similar centrifugal pump impellers of low specific speed. Both impellers show rotating cavitation over a wide range of part load operating points. The occurrence of this phenomenon produces a characteristic shape of creeping head-drop compared to the more usual sudden head-drop at “normal” operation points. The onset of rotating cavitation can be assigned to a certain value of the parameter σ/2α meaning the cavity volume in relation to the incidence angle. Optical analysis by video and high-speed camera techniques illustrates the development of this instability mechanism which is mainly driven by an interaction of the cavity closure region and the following blade. Combining these observations and the results of a fourier-transformation the characteristic propagation frequencies of rotating cavitation can be presented for one impeller.
Elastic Wave Propagation in Circumferential Direction in Anisotropic Cylindrical Curved Plates
Authors: Towfighi S. , Kundu T. , Ehsani M.
Published: July 2002

Ultrasonic nondestructive inspection of large-diameter pipes is important for health monitoring of ailing infrastructure. Longitudinal stress-corrosion cracks are detected more efficiently by inducing circumferential waves; hence, the study of elastic wave propagation in the circumferential direction in a pipe wall is essential. The current state of knowledge lacks a complete solution of this problem. Only when the pipe material is isotropic a solution of the wave propagation problem in the circumferential direction exists. Ultrasonic inspections of reinforced concrete pipes and pipes retrofitted by fiber composites necessitate the development of a new theoretical solution for elastic wave propagation in anisotropic curved plates in the circumferential direction. Mathematical modeling of the problem to obtain dispersion curves for curved anisotropic plates leads to coupled differential equations. Unlike isotropic materials for which the Stokes-Helmholtz decomposition technique simplifies the problem, in anisotropic case no such general decomposition technique works. These coupled differential equations are solved in this paper. Dispersion curves for anisotropic curved plates of different curvatures have been computed and presented. Some numerical results computed by the new technique have been compared with those available in the literature.
Damaged-Bone Adaptation Under Steady Homogeneous Stress
Authors: Ramtani S. , Zidi M.
Published: July 2002

In this work an extension of the adaptive-elasticity theory is proposed in order to include the contribution of bone microdamage as a stimulus. Some aspects of damaged-bone tissue adaptation, brought about by a change of the daily loading history, are investigated. In particular, under the assumption of a small strain approximation and isothermal conditions, the solution of the remodeling rate equation for steady homogeneous stress is discussed and the damage effect upon the remodeling time constant is shown. The result is both theoretical and numerical, based on a recent theory of internal damaged-bone remodeling (Ramtani, S., and Zidi, M., 1999, “Damaged-Bone Remodeling Theory: Thermodynamical Approach,” Mechanics Research Communications, Vol. 26, pp. 701–708. Ramtani, S., and Zidi, M., 2001, “A Theoretical Model of the Effect of Continum Damage on a Bone Adaption Model,” Journal of Biomechanics, Vol. 34, pp. 471–479) and motivated by the works of Cowin, S. C., and Hegedus, D. M., 1976, “Bone Remodeling I: Theory and Adaptive Elasticity,” Journal of Elasticity, Vol. 6, pp. 471–479 and Hegedus, D. H., and Cowin, S. C., 1976, “Bone Remodeling II: Small Strain Adaptive Elasticity,” Journal of Elasticity, Vol. 6, pp. 337–352.
Distributions of Stretch and Rotation in Polycrystalline OFHC Cu
Authors: Clayton J. D. , Schroeter B. M. , McDowell D. L. , Graham S.
Published: July 2002

High resolution experimental characterization of material stretch and rotation fields in relatively fine-grained polycrystals has been limited, inhibiting direct comparison with predictions of crystal plasticity theory. In this study, micron scale grids used more commonly in etching of substrates for microelectronic circuits were deposited on specimens of Oxygen Free High Conductivity Copper (OFHC Cu) subsequently subjected to uniaxial compressive deformations to effective strain levels up to unity. Material stretch and rotation fields were assessed for fields of view encompassing on the order of 20 grains. Some rather striking features emerge, including the apparent relative lack of deformation in regions sized on the order of large grains, and the apparent concentration of stretch and rotation in bands surrounding these relatively undeformed areas. Comparisons are drawn with results of 3D crystal plasticity calculations performed on digitized grain structures that conform to representative microstructures in terms of initial grain size and shape distributions. The crystal plasticity simulations predict regions of relatively large rotation and relatively localized stretch traversing multiple grains. The numerical solutions also exhibit slightly higher local stresses in the vicinity of grain boundaries and triple points than in grain interiors, a phenomenon attributed to local lattice misorientation among neighboring grains. However, the crystal plasticity calculations do not, in an average sense, predict larger-than-average maximum stretch or rotation in the grain boundary regions. The numerical solutions are also quite sensitive to initial lattice orientations assigned to the grains. Comments are made regarding the segmentation of slip within the grains and its implications for modeling, based upon direct comparison of results from experiments and simulations.
An Iterative Method for Solving Elasticity Problems for Composite Laminates
Authors: Makeev A. , Armanios E. A.
Published: July 2002

An iterative method for approximate analytical solution of elasticity problems in composite laminates is presented. The stress analysis is performed for laminates in the three-dimensional strain state independent of the longitudinal direction. Predictions of the method are compared with results from existing analytical and numerical models. Simple and accurate approximations for stresses are obtained. [S0021-8936(00)02001-8]
The Response of the System Incorporating an Observer in the Control Loop1
Authors: Polotski Vladimir
Published: July 2002

Transition processes in the SISO system incorporating an observer in the control loop are discussed. The symmetry of the transition matrix with respect to the eigenvalues assigned for the controller and the observer is proved using state space methods. The interrelation with the peaking phenomenon is discussed, asymptotic behavior of the system with a fast observer is analyzed, and illustrative examples are presented. [S0022-0434(00)02102-X]
Exposure of Ceramics and Ceramic Matrix Composites in Simulated and Actual Combustor Environments
Authors: More Karren L. , Tortorelli Peter F. , Ferber Mattison K. , Walker Larry R. , Keiser James R. , Miriyala Narendernath , Brentnall William D. , Price Jeffrey R.
Published: July 2002

A high-temperature, high-pressure, tube furnace has been used to evaluate the long term stability of different monolithic ceramic and ceramic matrix composite materials in a simulated combustor environment. All of the tests have been run at 150 psia, 1204°C, and 15 percent steam in incremental 500 h runs. The major advantage of this system is the high sample throughput; >20 samples can be exposed in each tube at the same time under similar exposure conditions. Microstructural evaluations of the samples were conducted after each 500 h exposure to characterize the extent of surface damage, to calculate surface recession rates, and to determine degradation mechanisms for the different materials. The validity of this exposure rig for simulating real combustor environments was established by comparing materials exposed in the test rig and combustor liner materials exposed for similar times in an actual gas turbine combustor under commercial operating conditions. [S0742-4795(00)02402-9]
Measurements and Correlations of Slider Vibrations and Wear
Authors: Bryant M. D. , York David
Published: July 2002

Studies have shown that micro-vibrations (10–100 μm amplitude, 10 to 100 Hz) of a slider can reduce sliding wear 50 percent, especially rigid body rocking motions that continuously realign the slider face with respect to the counter surface. In this article, clearances between a carbon sample and its holder were varied while sliding over a slightly wavy (8 to 20 μm) steel surface. Undulations on the counter surface induced rigid body vibrations of the slider. Clearances between sample and holder kinematically restricted rigid body rocking motions of the slider: larger clearances permitted more rocking. Measured were motions of the slider, including translations normal to the counter surface, and rotations about axes parallel to the counter surface. Time traces of these displacements were plotted at different sliding speeds. Frequency content and kinetic energies for each measured degree of freedom and the total were extracted. We sought correlations between measured wear and vibration data. Fractional changes in wear rate versus fractional changes in total kinetic energy clustered about a straight line. From these measurements, we found a quantitative relationship between amount of wear and total kinetic energy of vibration. [S0742-4787(00)05001-3]
Experimental Study of Showerhead Cooling on a Cylinder Comparing Several Configurations Using Cylindrical and Shaped Holes
Authors: Reiss H. , Bo¨lcs A.
Published: July 2002

Film cooling and heat transfer measurements on a cylinder model have been conducted using the transient thermochromic liquid crystal technique. Three showerhead cooling configurations adapted to leading edge film cooling of gas turbine blades were directly compared: “classical” cylindrical holes versus two types of shaped hole exits. The experiments were carried out in a free jet test facility at two different flow conditions, Mach numbers M=0.14 and M=0.26, yielding Reynolds numbers based on the cylinder diameter of 8.6e4 and 1.55e5, respectively. All experiments were done at a mainstream turbulence level of Tu=7 percent with an integral length scale of Lx=9.1 mmM=0.14, or Lx=10.5 mmM=0.26, respectively. Foreign gas injection CO2 was used, yielding an engine-near density ratio of 1.6, with blowing ratios ranging from 0.6 to 1.5. Detailed experimental results are shown, including surface distributions of film cooling effectiveness and local heat transfer coefficients. Additionally, heat transfer and heat load augmentation due to injection with respect to the uncooled cylinder are reported. For a given cooling gas consumption, the laid-back shaped hole exits lead to a clear enhancement of the cooling performance compared to cylindrical exits, whereas laterally expanded holes give only slight performance enhancement. [S0889-504X(00)01801-8]
Comparison Between Crack Growth in Fracture Mechanics Specimens and Feature Component Tests Carried Out in a Low-Alloy Steel
Authors: Nikbin Kamran
Published: July 2002

In both power generation plants and the chemical industries, there is a need to assess the significance of defects which may exist in high-temperature equipment operating in the creep range. This paper examines the methods of analysis used in laboratory creep crack growth data and their relevance to crack growth data derived from feature component tests which best simulate actual components under controlled testing condition. The material examined was a 214 Cr 1 Mo steel in the new condition at 550 and 600°C. The creep crack growth properties were determined on compact tension specimens. The data were compared with representative crack growth data from feature test components. These consisted of cracked rings, thick-walled cylinders, and thin-walled tubes containing axial or circumferential defects under combinations of axial and internal pressure loading. Little influence of size or temperature on the measured crack propagation rates was observed when the results were plotted against the creep fracture mechanics parameter C*. This is shown to be because the relevant condition had little effect on the appropriate crack tip creep ductilities of the material. Good correspondence was observed between the compact tension and the feature component tests, suggesting the feasibility of the C* method for predicting short-term laboratory tests using different geometries. [S0094-9930(00)01001-5]
SnO2 by XPS
Authors: Stranick Michael A. , Moskwa Anthony
Published: July 2002

Tin and various tin compounds have wide utility in coatings, electronics, and catalysts, as well as having numerous biological applications. Distinguishing between different tin compounds on surfaces is an important aspect of research in many of these disciplines. In this work, x-ray photoelectron spectroscopy has been used to obtain comparison spectra of a high purity SnO2 powder. Due to rather small core level chemical shifts, it has been shown that differences in the valence band spectra provide the most direct method of distinguishing between SnO2 and SnO using XPS [see J-M. Themlin, M. Chtaib, L. Henrard, P. Lambin, J. Darville, and J-M. Gilles, Phys. Rev. B 46, 2460 (1992); P. M. A. Sherwood, ibid. 41, 10151 (1990); and C. L. Lau and G. K. Wertheim, J. Vac. Sci. Technol. 15, 622 (1978)]. The separation between the Sn 4d core level line and the most intense Sn valence band peak is also characteristic of Sn oxides [see J-M. Themlin, M. Chtaib, L. Henrard, P. Lambin, J. Darville, and J-M. Gilles, Phys. Rev. B 46, 2460 (1992) and P. M. A. Sherwood, ibid. 41, 10151 (1990)]. The valence band spectrum and the valence band–Sn 4d separation reported in this work are consistent with literature data [see J-M. Themlin, M. Chtaib, L. Henrard, P. Lambin, J. Darville, and J-M. Gilles, Phys., Rev. B 46, 2460 (1992); P. M. Sherwood, ibid. 41, 10151 (1990); and C. L. Lau and G. K. Wertheim, J. Vac. Sci. Technol. 15, 622 (1978)]. Auger parameter data may also prove useful for distinguishing between various tin compounds on surfaces. Thus, in addition to core level spectra, valence band and x-ray excited Auger spectra for SnO2 are presented. Data were obtained with a Perkin-Elmer Physical Electronics model 5600 photoelectron spectrometer using monochromatic radiation.
CuCl2 by XPS
Authors: Vasquez Richard P.
Published: July 2002

X-ray photoemission measurements of high purity CuCl2 are presented. XPS studies of Cu compounds in this laboratory have been motivated by the need to identify species on chemically etched high temperature superconductor surfaces [see R. P. Vasquez, M. C. Foote, and B. D. Hunt, J. Appl. Phys. 66, 4866 (1989)].
Ultrathin Al Overlayers on Clean and K-Covered TiO2(110) Surfaces
Authors: Dake L. S. , Lad R. J.
Published: July 2002

The interactions between a variety of ultrathin metal overlayers and the TiO2(110) surface have been the focus of many studies in recent years as part of an effort to understand the chemistry of metal/ceramic interfaces. Aluminum reacts strongly with the stoichiometric, nearly defect-free TiO2 surface, and we were interested in determining if we could alter this interaction by chemically modifying the TiO2 surface with potassium prior to Al deposition. Potassium is of interest because of its use as a promoter in oxide-supported catalysis systems. In this article, we present XPS data for the interaction of Al and K (separately) with clean stoichiometric TiO2, as well as data for the interaction of Al with a TiO2(110) surface covered with a monolayer of K.