bluuebunny/crossref_metadata_2025 huggingface dataset:
A Method for Exact Series Solutions in Structural Mechanics
Authors: Wang J. T.-S. , Lin C.-C.
Published: February 2008

A systematic analysis method for solving boundary value problems in structural mechanics is presented. Euler-Lagrange differential equations are transformed into integral form with respect to sinusoidal weighting functions. General solutions are represented by complete sets of functions without being concerned with boundary conditions in advance while all boundary conditions are satisfied in the process. The convergence of results is assured, and the procedure leads to pointwise exact solutions. A number of simple structural mechanics problems of stress, buckling, and vibration analyses are presented for illustrative purposes. All results have verified the exactness of solutions, and indicate that this unified method is simple to use and effective.
Vibration Considerations in Foil-Bearing Design
Authors: Renshaw A. A.
Published: February 2008

The semianalytic foil-bearing solution algorithm of Eshel and Elrod (1965) is extended to the solution of the linearized, free vibration problem for one-dimensional self-pressurized foil bearings. The results demonstrate that unwanted variations in the spacing between the moving foil and the stationary bearing surface can be eliminated through proper design. The penetration depth through which vibration of the free span penetrates into the foil bearing is determined by two exponential exponents, one describing inlet penetration, the other describing outlet penetration. When the inlet exponent is large and negative and the outlet exponent is large and positive, there is negligible coupling between the vibration of the free spans and the vibration of the spacing between the foil and the stationary bearing surface. This decoupling is desirable in magnetic recording and web handling applications and can be achieved by properly selecting two dimensionless parameters, one describing the ratio of the viscous forces to the tape tension, the other describing the ratio of the tape transport speed to the wave speed in the tape. The values of these two parameters in current designs of both magnetic tape recording and web-handling devices are consistent with the design goal of minimizing foil vibration over the bearing. The inlet and outlet exponents are the roots of a fourth-order polynomial, and, in most cases, good estimates for these roots can be found without explicitly solving the foil-bearing problem. The effects of the air compressibility, tape bending stiffness, and slip flow are also investigated. Tape bending stiffness is found to play a significant role in vibration coupling. These results provide new insight into the influence of vibration on foil-bearing design.
Wavelet Analysis of Laser-Generated Surface Waves in a Layered Structure With Unbond Regions
Authors: Wu T.-T. , Chen Y.-Y.
Published: February 2008

This paper presents the results on the utilization of a wavelet transform to study the dispersion of laser-generated surface waves in an epoxy-bonded copper-aluminum layered specimen with and without unbond areas. Laser ultrasonic experiments based on the point-source/point-receiver (PS/PR) technique were undertaken to measure surface wave signals in a layered specimen. The wavelet transform with a Morlet wavelet function was adopted to analyze the group velocity dispersion of the surface wave signals. A novel hybrid formula for group velocity dispersion is proposed for measurements across unbond regions. Results and data obtained are in good agreement with calculated and experimental dispersion curves. The general behavior of the group velocity dispersion for different measurement, configurations can be utilized to differentiate the unbond regions in a layered structure.
Macrocrack-Microcrack Interaction in Piezoelectric Materials, Part II: Numerical Results and Discussions
Authors: Chen Y.-H. , Han J.-J.
Published: February 2008

Numerical results are shown in figures and tables. The major features for the traditional stress intensity factors and the electric displacement intensity factor against the microcrack location angle and the distance of the microcrack center from the macrocrack tip are discussed. It is shown that, unlike single-crack problems, the mechanical loading and the electric loading are coupled together since the microcrack not only releases the near-tip stresses, but also disturbs the near-tip electric field. Furthermore, the influence of the electric loading on the mechanical strain energy release rate (MSERR) at the macrocrack tip is discussed in detail. It is found that the variable nature of the MSERR against the normalized electric loading is monotonic and proportional wherever the parallel microcrack is located near the macrocrack tip. However, the slope of the MSERR's curve considering microcracking diverges far from those without considering microcracking. This finding reveals that, besides the two sources of microcrack shielding discussed by Hutchinson (1987) for brittle solids, the disturbance of the near-tip electric field due to microcracking really provides another source of shielding for piezoelectric solids.
Exact Solutions for Two-Dimensional Time-Dependent Flow and Deformation Within a Poroelastic Medium
Authors: Barry S. I. , Mercer G. N.
Published: February 2008

Exact analytic solutions are derived for the time-dependent deformation of a poroelastic medium within a two-dimensional finite domain. Solutions are given with a specific set of boundary conditions for the case of a source of fluid at an arbitrary point and for an applied pressure on the boundary. These solutions are ideal for testing numerical schemes for poroelastic flow and deformations due to their relative simplicity.
Some Problems of a Rigid Elliptical Disk-Inclusion Bonded Inside a Transversely Isotropic Space: Part I
Authors: Rahman M.
Published: February 2008

The paper addresses the problem of contact of an elliptical inclusion in the form of a thin disk, bonded in the interior of a transversely isotropic space. The inclusion is assumed to be absolutely rigid and in perfect contact with the medium. Three different cases of loading are considered, namely, (a) the inclusion is loaded in its plane by a shearing force, whose line of action passes through the center of the disk; (b) the inclusion is rotated by a torque whose axis is perpendicular to the plane of the inclusion; (c) the medium is under uniform stress field at infinity in a plane parallel to the plane of the inclusion. In the first part of the article, the problems corresponding to all three cases are reduced, in a unified manner, to a system of coupled two-dimensional integral equations by using the theory of two-dimensional Fourier transforms. In the second part, closed-form solutions for these equations are obtained by using Dyson’s theorem and Willis’ generalization of Galin’s theorem. Explicit expressions for the stress intensity factors near the edge of the inclusion are extracted from these solutions. Numerical results are plotted illustrating how these coefficients vary with transverse isotropy and the parametric angle of the ellipse. The results can be used to determine the critical failure load and angle of crack initiation for solids containing elliptical inclusions.
Some Problems of a Rigid Elliptical Disk-Inclusion Bonded Inside a Transversely Isotropic Space, Part II: Solutions of the Integral Equations
Authors: Rahman M.
Published: February 2008

This is a sequel to the first part of the two-part paper, which addresses the problem of contact of a rigid elliptical disk-inclusion bonded in the interior of a transversely isotropic space under three different types of loading, namely (a) the inclusion is loaded in its plane by a shearing force, whose line of action passes through the center of the inclusion; (b) the inclusion is rotated by a torque whose axis is perpendicular to the plane of the inclusion; (c) the medium is under uniform stress field at infinity in a plane parallel to the plane of the inclusion. In Part I, the problems corresponding to all three cases of loading have been reduced, in a unified manner, to a system of coupled two-dimensional integral equations. Next, based on Dyson’s theorem and Willis’ generalization of Galin’s theorem, the general structure of solution of the coupled integral equations has been established. In this part, closed-form solutions to these equations are derived by using Dyson’s theorem. Full elastic field in the plane of the inclusion is evaluated and it is shown that the stress field near the edge of the inclusion exhibits the familiar square root singularity in linear fracture mechanics. Explicit expressions for the stress intensity factors near the edge of the inclusion are extracted from these solutions. Numerical results are plotted illustrating how these coefficients vary with transverse isotropy and the parametric angle of the ellipse. The results can be used to determine the critical failure load and angle of initial crack propagation for solids containing elliptical inclusions.
A “Second Law” for Structures: An Insightful Approach to the Design of Plane Frames
Authors: French M. J.
Published: February 2008

This paper introduces a new aid to the design of economical plane structures, based on the twin concepts of structural task, which is an invariant for a given load system and given constraints on where material may be placed, and (absolute) pertinacity, which is the product of force and member length. An optimum (Michell) structure has task equal to pertinacity for every element of every member. The ratio u of task to pertinacity is unity everywhere in an optimum structure, and constitutes a utility factor: u may be negative for a member, that is, it is possible for a member to increase the task to be borne by the rest of the structure. A parallel is drawn with First and Second Law analysis in thermodynamics.
Transverse Normal Stress Effects in Multilayered Plates
Authors: Carrera E.
Published: February 2008

An evaluation of transverse normal stress σzz effects in multilayered plate modeling is given in this paper. Mixed theories with continuous interlaminar transverse shear and normal stresses have been formulated on the basis of Reissner's theorem (Reissner, 1984). The case in which the number of the displacement variables preserves independence by the number of constitutive layers, N1, has been investigated. Classical models based on standard displacement formulations have been discussed for comparison purposes. The analysis of transverse stress effects has been conducted by allowing a constant, linear, and higher-order distribution of the transverse displacement components in the plate thickness directions. Related two-dimensional models are compared for the static response of symmetrically and unsymmetrically layered, simply supported plates made of isotropic as well as orthotropic layers. The conducted numerical investigation and comparison with available results have above all led to the following conclusions. The possibility of including σzz makes the used mixed theories more attractive that other available modelings. σzz plays a fundamental role in thick laminate plates analysis. Such a role increases in transversely anisotropic multilayered plate analysis. With an increase of the plate thickness, a very accurate description of σzz requires modelings whose number of independent variables depends on N1.
Steady-State Deflection of a Circular Plate Rotating Near Its Critical Speed
Authors: Chen Jen-San
Published: February 2008

The steady-state response of a disk spinning near its critical speed and under space-fixed time-invariant load is analyzed by using von Karman’s nonlinear plate model. It is found that as the disk rotates beyond a modified critical speed there exist three steady-state deflections, among which only one is in the same direction as the applied load and is stable in the presence of space-fixed damping.
Maximizing the Natural Frequencies and Transverse Stiffness of Centrally damped, Circular Disks by Thickening the Clamped Part of the Disk
Authors: Renshaw A. A.
Published: February 2008

The natural frequencies and transverse stiffness of centrally damped, circular disks are computed taking into account the flexibility of the central clamp and the thickness of the damped part of the disk. When compared to experimental vibration data, these predictions are more accurate than the traditional, perfect clamping predictions, particularly, for zero and one-nodal-diameter vibration modes. The reduction in natural frequency or transverse stiffness caused by clamping flexibility can be mitigated either by increasing the clamping stiffness or by increasing the hub thickness, defined here as the thickness of the disk sandwiched by the central clamp. A design study of these two alternatives for both stationary and rotating disks shows that increasing the hub thickness is often a more attractive design alternative.
The Nonlinear Sloshing of Liquid in Tank With Pitching
Authors: Yin L. , Wang B. , Ma X. , Zou J.
Published: February 2008

In this paper, a method used to analyze the sloshing of liquid in a tank subjected to forced pitching and (or) yawing oscillation is presented. First, a variational principle for a liquid in a container under pitching and (or) yawing oscillation is proposed. Based on the preceding variational principle and new Lagrangian, the nonlinear sloshing of liquid in a circle cylindrical tank under pitching excitation is studied analytically for the first time.
An Approach to Characterize Nonlinear Viscoelastic Material Behavior Using Dynamic Mechanical Tests and Analyses
Authors: Golden H. J. , Strganac T. W. , Schapery R. A.
Published: February 2008

Linear viscoelastic properties may be rapidly identified using dynamic mechanical analysis methods, yet these traditional methods do not properly identify nonlinear viscoelastic response. Herein, dynamic mechanical methodologies are extended to provide an approach for nonlinear characterization. The proposed method is based on Schapery's nonlinear viscoelastic model extended to dynamic mechanical theory. The oscillatory loading during a dynamic test is addressed within the nonlinear viscoelastic model. An experimental protocol is established. Analyses and experiments are performed for the characterization of thin-film polyethylene to validate the approach.
Analysis of Thin-Walled Closed Beams With General Quadrilateral Cross Sections
Authors: Kim J. H. , Kim Y. Y.
Published: February 2008

This paper deals with the one-dimensional static and dynamic analysis of thin-walled closed beams with general quadrilateral cross sections. The coupled deformations of distortion as well as torsion and warping are investigated in this work. A new approach to determine the functions describing section deformations is proposed. In particular, the present distortion function satisfies all the necessary continuity conditions unlike Vlasov's distortion function. Based on these section deformation functions, a one-dimensional theory dealing with the coupled deformations is presented. The actual numerical work is carried out using two-node C0 finite element formulation. The present one-dimensional results for some static and free-vibration problems are compared with the existing and the plate finite element results.
On the Equilibrium Conditions of Nonstationary Mechanical Systems
Authors: Kazic M. , Bulatovic R.
Published: February 2008

The equilibrium problem of nonstationary systems is studied. The starting point is the principle of virtual work (PVW). Contrary to stationary problems, some additional conditions (along with PVW) should be satisfied. Proof of Gantmacher’s postulate is derived. A new approach is given, and some results of other authors are discussed.
Representation of Stokes Flow Through a Planar Contraction by Papkovich-Fadle Eigenfunctions
Authors: Rogerson M. A. , Yeow Y. L.
Published: February 2008

Stokes flow through a planar contraction is represented by matching together two series of Papkovich-Fadle eigenfunctions. Each series represents the solution in one of the unbounded rectangular regions upstream and downstream of the contraction plane. The coefficients of the series are obtained by weakly enforcing C3 matching conditions at the contraction plane using the Galerkin method. A post-processing technique is used to improve the appearance of the streamline plots near the singularity in the solution at the re-entrant corner of the channel. The pressure variation along the channel, as well as the excess pressure drop due to the contraction and the size of the upstream recirculating zone versus the contraction ratio, are presented. Channel contraction ratios of between two and six are considered.
Almost Classically Damped Continuous Linear Systems
Authors: Natsiavas S. , Beck J. L.
Published: February 2008

The dynamic response of a general class of continuous linear vibrating systems is analyzed which possess damping properties close to those resulting in classical (uncoupled) normal modes. First, conditions are given for the existence of classical modes of vibration in a continuous linear system, with special attention being paid to the boundary conditions. Regular perturbation expansions in terms of undamped modeshapes are then utilized for analyzing the eigenproblem as well as the vibration response of almost classically damped systems. The analysis is based on a proper splitting of the damping operators in both the field equations and the boundary conditions. The main advantage of this approach is that it allows application of standard modal analysis methodologies so that the problem is reduced to that of finding the frequencies and mode shapes of the corresponding undamped system. The approach is illustrated by two simple examples involving rod and beam vibrations.
Frequency Clusters in the Spectrum of Annular Cylinders
Authors: Tzou K. I. , Wickert J. A. , Akay A.
Published: February 2008

As the length of a traction-free annular cylinder is increased, distinct members within any family of radial or longitudinal shear modes have natural frequencies that asymptotically approach a common nonzero value. Such modes, potentially having significantly different numbers of nodes along the cylinder’s generator, can have natural frequencies that are indistinguishable from one another within the resolution of test equipment or numerical simulation. The three-dimensional vibration model discussed here predicts the formation of narrow “frequency clusters” with the cylinder’s increasing length, the converged value of which bounds from below the frequencies of all modes within a particular family. In addition to these spectral characteristics, frequency clusters have implications for the forced response of annular cylinders. For the particular families of modes that are of interest here, the steady-state harmonic response at frequencies near a cluster can be spatially confined with displacements that decay rapidly away from the point of maximum response. At other driving frequencies, the response is distributed more uniformly along the length of the cylinder. The derived analytical model is compared with results from laboratory measurements, and from the predictions of wave propagation theory in the limit of infinite cylinder length.
An Iterative Approach to Dynamic Elastic-Plastic Analysis
Authors: Giambanco F. , Palizzolo L. , Cirone L.
Published: February 2008

The step-by-step analysis of structures constituted by elastic-plastic finite elements, subjected to an assigned loading history, is here considered. The structure may possess dynamic and/or not dynamic degrees-of-freedom. As it is well-known, at each step of analysis the solution of a linear complementarity problem is required. An iterative method devoted to solving the relevant linear complementarity problem is presented. It is based on the recursive solution of a linear complementarity, problem in which the constraint matrix is block-diagonal and deduced from the matrix of the original linear complementarity problem. The convergence of the procedure is also proved. Some particular cases are examined. Several numerical applications conclude the paper.
Stress Singularity Analysis of a Crack Terminating at the Interface of an Anisotropic Layered Composite
Authors: Poonsawat P. , Wijeyewickrema A. C. , Karasudhi P.
Published: February 2008

The order of stress singularities at the tip of an inclined crack terminating at the interface of an anisotropic layered composite is investigated. Both fully bonded and frictional interfaces are considered. The expressions for stresses and displacements are obtained by using the Stroh formalism. The stresses at the crack tip are expressed in the form σij=r−kFij(θ), where k is the crack-tip singularity. The singularity k is obtained by solving a characteristic equation which incorporates the effects of the interface and the crack faces. The problem can be visualized as two wedges created by a crack, pressing on a half-plane. For the frictional interface, depending on the relative slip directions of the two wedges, both the case of the two wedges slipping in opposite directions and the case of the two wedges slipping in the same direction are treated. In the numerical calculation of the singularities, a high modulus graphite/ epoxy layered composite is used and the effect of the crack inclination on the stress singularity k is graphically presented. In general, there are three roots of k for the fully bonded interface, while there are only two roots of k for the slipping interface.
Transient Bending Wave Propagation in Anisotropic Plates
Authors: Fa¨llstro¨m K.-E. , Lindblom O.
Published: February 2008

In this paper we study transient propagating bending waves. We use the equations of orthotropic plate dynamics, derived by Chow about 25 years ago, where both transverse shear and rotary inertia are included. These equations are extended to include anisotropic plates and an integral representation formula for the bending waves is derived. Chow’s model is compared with the classical Kirchoff’s model. We also investigate the influence of the rotary inertia. Comparisons with experimental data are made as well.
How Compliant Should a Die-Attachment be to Protect the Chip From Substrate Bowing?
Authors: Suhir E.
Published: February 2008

The purpose of the analysis is to find out whether die attachment can be made compliant enough to protect the chip from excessive bowing of the substrate. We showed that in a typical situation, when the substrate (card) has a significantly larger flexural rigidity than the chip, the mechanical behavior of the chip-substrate assembly is governed by a parameter u=lK/4D14, where l is half the chip’s length, D1 is its flexural rigidity, and K is the through thickness spring constant of the attachment. We found that in order for a die attachment to have an appreciable effect on chip bowing, this parameter should be considerably smaller than 2.5. In the performed numerical example, for a 2 rail thick die attachment, this value corresponds to Young’s modulus of only 2300 psi. Therefore we conclude that conventional epoxy adhesives cannot provide sufficient buffering effect in this case, and, if such adhesives are used, the curvature of the die will be practically the same as the curvature of the substrate. In this situation, thinner dies will result in lower bending stresses. However, if low modulus die attachment materials, such as silicone gels, are considered, then employment of thicker dies might be advisable.
Jet-Flow Scavenging of a Curing Oven—Part II: Numerical Simulation
Authors: Zwick K. J. , Ayyaswamy P. S. , Cohen I. M.
Published: February 2008

In this part the heat, mass, and momentum transfer within a curing over that is commonly used in microelectronic manufacturing have been numerically analyzed. The local partial pressure of the vapor is a determining factor in the promotion of contamination. Based on the results of this study a new design is recommended. The significant features of the new design are: (i) ability to maintain the partial pressure of the vapor below the saturation pressure corresponding to the temperature at every location within the oven, and (ii) improved facility for scavenging of the vapor. Qualitative comparisons of results obtained here with flow visualizations (Part I) are excellent.
A Thermal Fatigue Failure Mechanism of 58Bi-42Sn Solder Joints
Authors: Mei Zequn , Holder Helen
Published: February 2008

Surface mount components soldered with 58Bi–42Sn on printed circuit boards fell off after about 500 cycles of−45°C ↔ 100°C in a thermal chamber. Failure analysis revealed that the failure was caused by dissolving of Pb from either HAL (hot air leveled) board surfaces or component lead coatings into the Bi-Sn solder joints, forming 52Bi–32Pb–16Sn eutectic phase that melts at 95°C. The dissolving of Pb occurred primarily at reflow, when the Bi-Sn was molten. During the thermal cycling, the small amount (<7 volume % of a Bi-Sn solder joint) of the low melting eutectic phase provided liquid channels for fast atom transportation, causing exceptionally significant grain growth and phase agglomeration in the whole volume of the solder joint, which in turn caused dramatic reduction in mechanical strength of the solder joints. Solutions to the failure may be either using Pb-free coating on both board surfaces and component leads, or limiting the product service temperature to below 95°C.
Ball Grid Array Thermomechanical Response During Reflow Assembly
Authors: Voth T. E. , Bergman T. L.
Published: February 2008

The thermomechanical response of ball-grid array assemblies during reflow soldering is considered here. Experiments are performed to investigate the thermomechanical response of a representative system and the results are used to validate a numerical model of system behavior. The conclusions drawn from the experimental studies are used to guide development of a process model capable of describing more realistic BGA soldering scenarios. Process model predictions illustrate the system’s thermomechanical response to thermal and mechanical processing conditions, as well as component properties. High thermal conductivity assemblies show the greatest sensitivity to mechanical loading conditions.
Application of Phase Change Materials to Thermal Control of
Electronic Modules: A Computational Study
Authors: Pal D. , Joshi Y. K.
Published: February 2008

A computational model is developed to predict the performance of phase change materials(PCMs) for passive thermal control of electronic modules during transient power variations or following an active cooling system failure. Two different ways of incorporating PCM in the module are considered. One is to place a laminate of PCM outside the multichip module, and the other is to place the PCM laminate between the substrate and the cold plate. Two different types of PCMs are considered. One is n-Eicosene, which is an organic paraffin, and the other one is a eutectic alloy of Bi/Pb/Sn/In. Computations are performed in three dimensions using a finite volume method. A single domain fixed grid enthalpy porosity method is used to model the effects of phase change. Effects of natural convection on the performance of PCM are also examined. Results are presented in the form of time-wise variations of maximum module temperature, isotherm contours, velocity vectors, and melt front locations. Effects of PCM laminate thickness and power levels are studied to assess the amount of PCM required for a particular power level. The results show that the PCMs are an effective option for passive cooling of high density electronic modules for transient periods.
Numerical Simulation of Impingement Air Cooling From LSI Packages
With Large Plate Fins by the Penalty Finite Element Method
Authors: Tanaka T. , Matsushima H. , Ueki A. , Atarashi T.
Published: February 2008

Steady state three-dimensional incompressible flow analysis based on the two-equation model of turbulence is performed. The finite element method employing the penalty function formulation by Hughes et al. (1979) is used. To reduce the computational time and computer storage, the conjugate gradient method is applied to solve algebraic equations. In applying the conjugate gradient method, the equations are preconditioned so as to arrive at converged solutions effectively. The problem cited in this study is the impingement air cooling of the large scale integrated circuit package with large plate fins. The calculated velocity vectors show good agreement with the result of flow visualization. The calculated temperature distributions also agree well with the experimental temperatures. This suggests the usefulness of this kind of numerical simulation in the research and development of new cooling technologies.
Correlation Between LDA and Ultrasound Heart Catheter Measurements in a Stenosed Arterial Model
Authors: Liepsch D. , Poll A. , Blasini R.
Published: February 2008

Ultrasound heart catheters are used to measure the velocity in coronary arteries. However, the act of introducing a catheter into the vessel disturbs the very flow being measured. We used laser Doppler anemometry to measure the velocity distribution in an axially symmetric model, both with and without a catheter inserted. The catheter reduced the center-line velocity by as much as 60 percent at a distance of 2 mm downstream from the catheter, and by as much as 25 percent at a distance of 10 mm. This means the velocity measured with an ultrasound catheter does not show the maximum velocity of the undisturbed flow in the tube center. In the constriction, however, the measured velocities with the LDA and ultrasound catheter are almost the same. Thus, catheter measurements in the stenosis achieve accurate results. The velocity profile in the stenosed areas is flattened over nearly the whole cross section. The velocity is extremely reduced only close to the wall. The measurements outside of the stenosis lead to large differences which need to be studied carefully in the future. The disturbed flow finally disappeared 15 mm downstream of the catheter. The measurements were done at steady flow using a glycerine water solution with a dynamic viscosity of 4.35m Pas. In future studies, these experiments will be repeated for pulsatile flow conditions using non-Newtonian blood-like fluids.
Mathematical Modeling of Noninvasive Blood Pressure Estimation Techniques—Part I: Pressure Transmission Across the Arm Tissue
Authors: Ursino Mauro , Cristalli Cristina
Published: February 2008

A mathematical model of the arm tissue mechanical behavior under the effect of external pressure loads is presented. The model has been used to study stress and strain distribution across the tissue, and pressure transmission to the brachial artery, when the arm is compressed by two adjacent cuffs independently inflated. Using this configuration, the tissue elastic parameters (Young modulus and Poisson ratio) can be individually identified using a simple and noninvasive experimental procedure. Model validation has been achieved by comparing its results with data obtained experimentally on 10 subjects. These comparisons demonstrate that the proposed model may constitute a simple but valid new tool able to describe tissue behavior, subjected to external pressures, with sufficient accuracy. Joined with a model of brachial hemodynamics, it might contribute to improve our understanding of noninvasive blood pressure estimation techniques.
Bending of Blood Vessel Wall: Stress-Strain Laws of the Intima-Media and Adventitial Layers
Authors: Xie Jiaping , Zhou Jianbo , Fung Y. C.
Published: February 2008

In order to determine the stress-strain relationship of the inner (intima and media) and outer (adventitia) layers of blood vessels in the neighborhood of the zero-stress state, bending experiments were performed on aortic strips of rats. In the experiments, one end of a strip was clamped, and a force was applied on the other end. The deflection curves of the strips were measured. By regarding the aortic strip as a curved beam, the classical beam theory was employed to analyze the strain distribution from the experimental data. A computer program dealing with nonlinear equations and nonlinear least squares optimization was developed. Strains were referred to the zero-stress state. The load-deflection relationship was then used to determine the stress-strain relationship. Certain forms of the stress-strain laws were assumed. The linear laws fit the experimental data accurately, probably because the strains during bending are quite small, although the rotations are large. The Young’s modulus of the inner layer, which consists of endothelial and smooth muscle cells and elastic lamina, was found to be three to four times larger than that of the outer layer which consists of collagen with a small amount of fibroblasts and elastin. The residual stresses and strains at the no-load state were calculated from the deduced stress-strain relationship. It is shown that large errors (up to 50 percent) in the values of the residual strains will occur if the wall material was treated as homogeneous, i.e., if the layered constitution was ignored.
Measurement of Wall Deformation and Flow Limitation In a Mechanical Trachea
Authors: Walsh C. , Sullivan P. A. , Hansen J. S. , Chen L.-W.
Published: February 2008

A mechanical model of the human trachea is investigated experimentally. A modified version of an earlier model, it consists of a square sectioned rigid tube in which part of one wall is removed, and replaced by a prestretched flat latex membrane. Air is drawn from atmosphere through an inlet into the rigid upstream tube; it then flows through the flexible section and finally through a rigid section Into a plenum chamber where suction is applied. As the membrane collapses in response to flow, the transmural pressure and deflection are measured at the mid-point. These values are used in conjunction with a finite deformation membrane wall theory to determine the elastic constant in a nonlinear material constitutive equation. This equation is used to predict the tube law. Results show that the flow limits at the long wave speed predicted by this law. Thus it behaves as a conventional collapsible tube while having the advantage of a rational wall model.
A New Device and Method for Controlling the Load in Rabbit Medial Collateral Ligament Reconstructions
Authors: King G. J. W. , Damson E. L. , Frank C. B. , Shrive N. G.
Published: February 2008

In order to study the effect of intra-operative tensioning on the laxity and strength of healing ligament grafts in an animal model, a method of quantifying graft tension was needed. In this study a sensitive ligament tensioning device was developed to measure accurately the prefixation loads in the rabbit medial collateral ligament (MCL) graft. To verify that reproducible changes in ligament tension could be created with the tensioning device, a group of animals had their MCL grafts replaced at one of three different graft loads (tight, anatomic, or loose). The tensioning device consists of two posts which move relative to one another by means of an axial screw. The movable post, which is inserted into the tibial bone island of the MCL graft has a series of strain gauges which can measure the tension applied to the graft. The stationary post attaches to the tibial shaft, permitting the ligament graft to be tensioned relative to this fixed point. After graft tensioning and fixation, the animals were euthanized immediately postoperatively and their ligament load-deformation behavior was measured using an Instron materials testing machine. Specific measures of low load behavior was taken to quantify ligament laxity. Our results demonstrate that the tensioning device was capable of reproducibly altering prefixation graft load intra-operatively as well as MCL laxity immediately postoperatively. A baseline of laxity values was thus developed to follow changes in this laxity measure for future studies of MCL graft healing in this model.
Instrumented Forceps for Measurement of Nerve Compression Forces
Authors: Nawwar A. M. , Sherif M. F. , Barakat N. G.
Published: February 2008

Compression (or crushing) is used to induce nerve injury in test rats to study nerve degeneration and regeneration. The compression forces could be applied using a variety of techniques developed by several investigators. The lack of precise control of the applied compression may be the source of significant variations among observations. In this study, a Mosquito and dressing forceps were used. The Mosquito forceps was calibrated to determine the tip load corresponding to the clamping position. The dressing forceps was modified, instrumented with strain gauges and calibrated to directly measure the force applied at its tip. These two forceps were used to induce known and controlled nerve compression in 75 male Wistar rats (280–300g). The applied forces were of the order of 40N and 20N, for the Mosquito and dressing forceps, respectively.
Estimation of Cerebral Blood Flow From Thermal Measurement
Authors: Wei Datong , Saidel G. M. , Jones S. C.
Published: February 2008

A thermal method has been developed to quantify continuous perfusion changes with self-calibration. A dynamic, one-dimensional bio-heat transfer model of the thermal probe and tissue describes the system response to either continuous or transient heating. A nonlinear least-squares fit of the model to experimental data yields estimates of the baseline perfusion and other model parameters. With a partial analytical solution of the model, the optimal estimation procedure is two orders of magnitude more efficient than with a total numerical solution of the model system. Experimental data is used to estimate the operating relations between perfusion and the temperature measurement. A new procedure has also been presented to obtain the dynamic response of the system for continuous measurement of perfusion.
Direct Measurement of the Adhesive Fracture Resistance of CVD Diamond Particles
Authors: Kamiya S. , Takahashi H. , Saka M. , Abe´ H.
Published: February 2008

Diamond film produced by chemical vapor deposition (CVD) is being used in the electronics industry because of their excellent properties. In order to measure the adhesive strength of CVD diamond, external load is directly applied in a scanning electron microscope to the CVD diamond particles that sparsely appear on silicon substrate in the early stage of deposition. These particles are called nuclei when they are small and grow into contact with each other to form polycrystalline CVD diamond film. Diamond film was supposed to adhere to the substrate at only these discrete nucleation points, which might result in weak adhesive strength. We measure the maximum load, as the adhesive fracture resistance, required to scratch off the particles with 2–13 μm diameter. Adhesive fracture resistance is found to increase with the diameter of the particle. Hence we conclude that CVD diamond does not adhere only at the nucleation points but that the whole contact area to the substrate is responsible for its adhesive strength.
Nonlinear Dynamic Analysis of Surface Mount Interconnects: Part II—Applications
Authors: Basaran C. , Chandaroy R.
Published: February 2008

Using the unified constitutive model and the finite element procedure presented in Part I (the preceding paper), a material nonlinear time domain dynamic analysis of a solder joint was studied for low cycle and high cycle fatigue. Thermal effects were not included in order to understand the dynamic behavior of a Pb40/Sn60 solder joint without noise-effects from thermal behavior. The latter decision was a result of observations reported in Steinberg (1988), that having in-phase or out-of-phase thermal loading in conjunction with vibrations makes a significant difference in the fatigue life. The study of fatigue under concurrent loading will be the subject of another paper.
Minimization of Heat Sink Mass Using CFD and Mathematical Optimization
Authors: Craig K. J. , de Kock D. J. , Gauche´ P.
Published: February 2008

This paper describes the use of CFD and mathematical optimization to minimise heat sink mass given a maximum allowable heat sink temperature, a constant cooling fan power and heat source. Heat sink designers have to consider a number of conflicting parameters. Heat transfer is influenced by, amongst others, heat sink properties (such as surface area), airflow bypass and the location of heat sources, whilst size and/or mass of the heat sink needs to be minimized. This multiparameter problem lends itself naturally to optimization techniques. In this study a commercial CFD code, STAR-CD, is linked to the DYNAMIC-Q method of Snyman. Five design variables are considered for three heat source cases. Optimal designs are obtained within six design iterations. The paper illustrates how mathematical optimization can be used to design compact heat sinks for different types of electronic enclosures.
Application of Noncircular Primary-Air Inlet Geometries in the Inshot Burners of Residential Gas Furnaces
Authors: Kolluri P. , Kamal A. , Gollahalli S. R.
Published: February 2008

Experiments with an inshot burner used in residential natural gas furnaces are presented. The concentrations of NOx, NO, and CO in the combustion products of partially aerated natural gas flames were measured in a laboratory combustion chamber. When the conventional circular venturi inlet of the inshot burner was replaced by elliptic venturi inlets, an increase of up to 30 percent in the primary-air entrainment and a decrease of up to 20 percent in the NOx emission index were observed. Temperature field measurements in the flames were in conformity with the emission index measurements.
Comprehensive Modeling of Turbulent Flames With the Coherent Flame-Sheet Model—Part I: Buoyant Diffusion Flames
Authors: Blunsdon C. A. , Beeri Z. , Malalasekera W. M. G. , Dent J. C.
Published: February 2008

A modified version of the computational fluid dynamics code KIVA-II was used to model the transient behavior of buoyant turbulent diffusion flames burning in still air. Besides extensions to the range of permitted boundary conditions and the addition of buoyancy terms to the turbulence model, KIVA-II was augmented by a version of the coherent flame-sheet model, Tesner’s soot generation model, Magnussen’s soot oxidation model, and an implementation of the discrete transfer radiation model that included both banded and continuum radiation. The model captured many of the features of buoyant turbulent flames. Its predictions supported experimental observations regarding the presence and frequency of large-scale pulsations, and regarding axial distributions of temperature, velocity, and chemical species concentrations. The radial structure of the flame was less well represented. The axial radiative heat flux distribution from the flame highlighted deficiencies in the soot generation model, suggesting that a model of soot particle growth was required.
Surface Graft Copolymerization Enhanced Lamination of Poly(tetrafluoroethylene) Film to Copper and Epoxy-Based Print Circuit Board (PCB)
Authors: Zhang J. , Cui C. Q. , Lim T. B. , Kang E. T.
Published: February 2008

Lamination of poly(tetrafluoroethylene) (PTFE) film to a copper foil or to an epoxy-based print circuit board (PCB) Substrate (FR4®) was carried out. Lamination was achieved during surface graft copolymerization of glycidyl methacrylate (GMA) on an Ar plasma pretreated PTFE film at elevated temperature and in the presence of an epoxy resin adhesive. The plasma pretreatment introduces peroxides which are thermally degraded into free radicals to initiate the graft polymerization of GMA on the PTFE surface. The graft copolymerization with concurrent lamination is carried out in the complete absence of a polymerization initiator or system degassing. The modified surfaces and interfaces are characterized by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The adhesion strength between the PTFE film and copper or the FR4® substrate was assessed by the T-peel strength test method. The adhesion strength was affected by plasma pretreatment time, as well as the grafting and curing temperature. The PTFE/GMA-epoxy resin/Cu and PTFE/GMA-epoxy resin/FR4 assemblies exhibit significant higher interfacial adhesion strengths compared to those assemblies in which only epoxy resin or GMA was used. They also exhibit better interfacial adhesion reliability. The PTFE/GMA-epoxy resin/Cu and PTFE/GMA-epoxy resin/FR4® joints delaminated by cohesive failure inside the bulk of PTFE film. The results suggest that the enhanced adhesion between the graft-modified PTFE film and copper or FR4® surfaces is attributable to the formation of covalent bonds between the tethered GMA graft chains on PTFE and the network of epoxy resin.
Combustion Technology for Low-Emissions Gas-Turbines: Some Recent Modeling Results
Authors: Correa S. M. , Hu I. Z. , Tolpadi A. K.
Published: February 2008

Computer modeling of low-emissions gas-turbine combustors requires inclusion of finite-rate chemistry and its intractions with turbulence. The purpose of this review is to outline some recent developments in and applications of the physical models of combusting flows. The models reviewed included the sophisticated and computationally intensive velocity-composition pdf transport method, with applications shown for both a laboratory flame and for a practical gas-turbine combustor, as well as a new and computationally fast PSR-microstructure-based method, with applications shown for both premixed and nonpremixed flames. Calculations are compared with laserbased spectroscopic data where available. The review concentrates on natural-gas-fueled machines, and liquid-fueled machines operating at high power, such that spray vaporization effects can be neglected. Radiation and heat transfer is also outside the scope of this review.
Thermohydraulic Analysis of Ground as a Heat Source for Heat Pumps Using Vertical Pipes
Authors: Kangas M. T.
Published: February 2008

In this study, the use of the ground as the heat source for a heat pump was studied by computer simulation. The heat extraction system consisted of vertical pipes drilled into the ground where groundwater was present. Along with available thermal energy, potential environmental effects, such as freezing and thermal pollution, were examined. It was found that the presence of groundwater enhances system performance by decreasing the possibility of freezing but, on the other hand, increases the range of thermal effects in the ground. The temperature of the ground as well as extraction arrangements also have a significant effect on system performance.
The Application of Scanning Acoustic Microscopy in a Bone Remodeling Study
Authors: Shieh Sheu-Jane , Zimmerman M. C. , Langrana N. A.
Published: February 2008

Scanning acoustic microscopy (SAM) was used in the evaluation of bone remodeling around a cylindrical unicortical defect. SAM is a technique for the nondestructive evaluation of materials, and has only recently been employed as an orthopaedic research tool. The utility of SAM was demonstrated by using it to measure an elastic property known as acoustic impedance. Specifically, the acoustic impedance of bone formed by remodeling around a cylindrical defect was measured. The defects were filled with either a low modulus “void” or rigid inclusion to create various states of stress in the bone in the vicinity of the defect. After six months of implantation of the inclusions in the sheep metatarsal, new bone formation on periosteal and endosteal surfaces about the defect region was observed. These regions of new bone were less stiff and had 18.0 ± 6.5% lower acoustic impedance than the pre-existing bone in the intracortical region of the metatarsal. There was no difference in the degree of new bone formation about void and rigid inclusions. Both underwent significant adaptational changes in response to the elevated stress about the defect. These changes affected the basic structure of the bone cross-section at the level of the defect and effectively reduced the stress levels about the defect. By using SAM to measure acoustic impedance, it was seen that little internal remodeling occurred in the intracortical region. Hence, the primary mechanism of strain-induced bone remodeling observed in this experimental model was surface remodeling.