bluuebunny/crossref_metadata_2025 huggingface dataset:
Measurement of Void Fraction in Magnetic Fluid Using Electromagnetic Induction
Authors: Shuchi S. , Yamaguchi H. , Takemura M.
Published: June 2003

A new technique of measuring void fraction in magnetic fluid using electromagnetic induction was proposed. In order to establish the measuring method, a feasibility study was conducted experimentally with an aid of numerical analysis. From the results of static experiment and numerical analysis, it was obtained that there exists a linear relationship between the void fraction and the measured electromotive force, when induction coils were connected in series for Helmholtz excitation coils, regardless of distribution of air bubbles in magnetic fluid. By applying the calibrated linear relationship to actual two-phase situations, it was revealed that the proposed method yielded quite reasonable account for measuring the void fraction, showing excellent agreement with the mechanical measured data in the two-phase flow apparatus, and with the published correlation of the drift flux model. From the results of the present investigation, it was proved that the proposed technique is feasible for the actual measurement of void fraction in two-phase flow of magnetic fluid.
Numerical Study of the Flow Around a Bus-Shaped Body
Authors: Krajnovic´ Sinisˇa , Davidson Lars
Published: June 2003

Flow around a simplified bus is analyzed using large-eddy simulation. At the Reynolds number of 0.21×106, based on the model height and the incoming velocity, the flow produces features and aerodynamic forces relevant for the higher (interesting in engineering) Reynolds number. A detailed survey of both instantaneous and time-averaged flows is made and a comparison with previous knowledge on similar flows is presented. Besides the coherent structures observed in experimental and previous numerical studies, new smaller-scale structures were registered here. The mechanisms of formation of flow structures are explained and the difference between instantaneous and time-averaged flow features found in the experimental observations is confirmed. Aerodynamic forces are computed and their time history is used to reveal the characteristic frequencies of the flow motion around the body. A comparison is made of pressure and velocity results with experimental data and shows fairly good agreement.
Dense Gas Thermodynamic Properties of Single and Multicomponent Fluids for Fluid Dynamics Simulations
Authors: Colonna Piero , Silva Paolo
Published: June 2003

The use of dense gases in many technological fields requires modern fluid dynamic solvers capable of treating the thermodynamic regions where the ideal gas approximation does not apply. Moreover, in some high molecular fluids, nonclassical fluid dynamic effects appearing in those regions could be exploited to obtain more efficient processes. This work presents the procedures for obtaining nonconventional thermodynamic properties needed by up to date computer flow solvers. Complex equations of state for pure fluids and mixtures are treated. Validation of sound speed estimates and calculations of the fundamental derivative of gas dynamics Γ are shown for several fluids and particularly for Siloxanes, a class of fluids that can be used as working media in high-temperature organic Rankine cycles. Some of these fluids have negative Γ regions if thermodynamic properties are calculated with the implemented modified Peng-Robinson thermodynamic model. Results of flow simulations of one-dimensional channel and two-dimensional turbine cascades will be presented in upcoming publications.
Slip Flow in a Curved Tube
Authors: Wang C. Y.
Published: June 2003

The viscous flow in a curved tube with partial slip on the boundary occurs in many practical situations. The problem is formulated in curved tube coordinates and solved by perturbation for small curvature. The mutual interaction of slip, curvature, and inertia causes changes in the axial flow, surface shear, and secondary flow. It is found that the net flow increases with increased slip and decreased Reynolds numbers.
Separated Flow in Bends of Arbitrary Turning Angles, Using the Hodograph Method and Kirchhoff’s Free Streamline Theory
Authors: Chu S. S.
Published: June 2003

The problem of separated flow in bends of arbitrary turning angles has been examined. The method of analysis is based on the inviscid flow theory coupled with Kirchhoff’s separation model. The physical flow problem is first transformed to the hodograph domain, and then into a rectangular computational region using properly selected flow parameters. The solution is first established in the hodograph plane. The final flow pattern including the inner and outer walls of the bend, the separation streamline, and other flow properties in the physical plane are subsequently obtained through direct integration. The results of the present analysis are compared with those of Lichtarowicz and Markland as well as Mankbadi and Zaki.
A Graphical Method to Find the Secondary Instantaneous Centers of Zero Velocity for the Double Butterfly Linkage
Authors: Foster David E. , Pennock Gordon R.
Published: June 2003

The Aronhold-Kennedy theorem cannot locate all of the instantaneous centers of zero velocity for a planar, single-degree-of-freedom, indeterminate linkage. This paper presents a graphical technique that will locate the secondary instantaneous centers of zero velocity for a well-known indeterminate linkage; namely, the double butterfly linkage. Only one of the secondary instant centers of this eight-bar linkage needs to be located with the proposed technique; the remaining instant centers can then be located using the Aronhold-Kennedy theorem. The first step in the graphical method is to regard the double butterfly linkage as two six-bar linkages. This is accomplished by replacing the ternary link pinned to the ground by two binary links, removing the pin which connects the two coupler links, and attaching a slider to each coupler link at the coupler pin. The second step is to reduce two of the five-bar loops of the double butterfly linkage to four-bar loops by instantaneously freezing the aforementioned binary links. The paper shows how these two important steps are used to locate the absolute instant centers for the two coupler links of this indeterminate eight-bar linkage.
Altered Mechanical Behavior of Epicardium Due to Isothermal Heating Under Biaxial Isotonic Loads
Authors: Harris J. L. , Wells P. B. , Humphrey J. D.
Published: June 2003

Recent isothermal biaxial isotonic tests suggest that increasing the temperature hastens the rate of denaturation of epicardium whereas increasing the mechanical load during heating delays this process, findings that are consistent with prior uniaxial tests on tendons. Yet, contrary to uniaxial reports, a clear time-temperature-load equivalency was not found in this multiaxial setting. There is, therefore, a need to delineate multiaxial thermomechanical behavior in greater detail, and ultimately, to correlate changes therein with the underlying microstructure. Toward this end, we describe a new experimental approach for quantifying heating-induced changes in the multiaxial mechanical response of thin sheet-like specimens. Illustrative results are presented for bovine epicardium subjected to nine different thermomechanical loading protocols. Among other results, it is shown that thermal damage tends to increase the stiffness at low strains and that overall changes in extensibility correlate well with the degree of thermal damage independent of the specific thermomechanical protocol. Multiaxial changes in behavior are nevertheless complex, and there is a need for significantly more testing before constitutive relations can be formulated.
Thermal Resistances of Circular Source on Finite Circular Cylinder With Side and End Cooling
Authors: Yovanovich M. M.
Published: June 2003

General solution for thermal spreading and system resistances of a circular source on a finite circular cylinder with uniform side and end cooling is presented. The solution is applicable for a general axisymmetric heat flux distribution which reduces to three important distributions including isoflux and equivalent isothermal flux distributions. The dimensionless system resistance depends on four dimensionless system parameters. It is shown that several special cases presented by many researchers arise directly from the general solution. Tabulated values and correlation equations are presented for several cases where the system resistance depends on one system parameter only. When the cylinder sides are adiabatic, the system resistance is equal to the one-dimensional resistance plus the spreading resistance. When the cylinder is very long and side cooling is small, the general relationship reduces to the case of an extended surface (pin fin) with end cooling and spreading resistance at the base. The special case of an equivalent isothermal circular source on a very thin infinite circular disk is presented.
Thermal and Mechanical Model for Rigid Cylinder Indenting an Elastic Layer Resting on Rigid Base: Application to Turned Surfaces
Authors: Zhang Zhe , Marotta E. E. , Ochterbeck J. M.
Published: June 2003

Models are presented for the solution of the thermal and mechanical problem of a rigid metallic cylinder indenting an elastic layer with finite thickness which rests on a rigid substrate without friction. The models were extended to turned surfaces applications. With introduction of an equivalent isothermal flux distribution for the mixed boundary problem—constant temperature over the contact area while adiabatic elsewhere along the top surface—an approximate analytical thermal model was developed. The solution was compared to a numerical solution under certain cases. Both solutions in turn compare very well with the generalized three-dimensional expression proposed by prior investigators. The mechanical model predicts the contact half-width under varying mechanical properties, layer dimensions, and applied load. The mechanical contact problem was solved numerically by substituting the displacement variable with a truncated polynomial to get a system of linear equations from which the dimensionless contact half-width was derived. The model is valid throughout a wide range of parameters, including mechanical properties and geometric dimensions. To explicitly predict the dimensionless contact half-width as a function of dimensionless load, a curve was fitted to the numerically obtained solution.
Thermal Interfacing Techniques for Electronic Equipment—A Perspective
Authors: Nakayama Wataru , Bergles Arthur E.
Published: June 2003

This paper reviews the existing knowledge base about thermal contact resistance in cooling electronic equipment, and also highlights some novel issues that are emerging with the advent of compact electronic equipment. Where a high contact pressure is tolerable, such as in cooling power electronic devices, the experimental data and the theoretical models that have been developed to this day provide useful guides for the management of contact resistance. In such applications the compression load and a technique to enhance interface heat transfer need be examined, weighing their relative importance in the entire heat transfer system. Using the Yovanovich correlation for contact resistance and assuming water-cooled or air-cooled heat sinks, the contact pressure ranges of practical importance are identified. The case studies revealed that contact pressures around and less than 1–4 MPa are often sufficient to make the contact conductance comparable to the convective conductance in the water-cooled channel. The threshold pressure is much lower for the air-cooled case, around 0.2–0.6 MPa. However, heat transfer data in such intermediate pressure ranges are relatively few. For compact electronic equipment, such as laptop computers, the contact conductance to a thin heat spreader plate is becoming an issue of prime importance. In a constrained space the heat flow across the interface is affected by the heat conduction paths beyond the interface. This is illustrated using an example where warped heat sources are in contact with a heat spreader. It is shown that, with decreasing heat spreader thickness, the warping of the heat source has an increasing influence on the contact resistance.
A Model for Mechanics of Primary Lymphatic Valves
Authors: Mendoza Ernesto , Schmid-Scho¨nbein Geert W.
Published: June 2003

Recent experimental evidence indicates that lymphatics have two valve systems, a set of primary valves in the wall of the endothelial cells of initial lymphatics and a secondary valve system in the lumen of the lymphatics. While the intralymphatic secondary valves are well described, no analysis of the primary valves is available. We propose a model for primary lymphatics valves at the junctions between lymphatic endothelial cells. The model consists of two overlapping endothelial extensions at a cell junction in the initial lymphatics. One cell extension is firmly attached to the adjacent connective tissue while the other cell extension is not attached to the interstitial collagen. It is free to bend into the lumen of the lymphatic when the lymphatic pressure falls below the adjacent interstitial fluid pressure. Thereby the cell junction opens a gap permitting entry of interstitial fluid into the lymphatic lumen. When the lymphatic fluid pressure rises above the adjacent interstitial fluid pressure, the endothelial extensions contact each other and the junction is closed preventing fluid reflow into the interstitial space. The model illustrates the mechanics of valve action and provides the first time a rational analysis of the mechanisms underlying fluid collection in the initial lymphatics and lymph transport in the microcirculation.
On the Anisotropy of Axisymmetric Strained Turbulence in the Dissipation Range
Authors: Jovanovic´ J. , Otic´ I. , Bradshaw P.
Published: June 2003

Partition of the stress dissipation has been studied in an axisymmetric strained flow field to assess the possible existence of local isotropy for turbulence at small scales. This is a simple flow to study because the axes of anisotropy of the Reynolds stresses and of the dissipation tensor are aligned. Using invariant theory, the relationship between the stress and dissipation tensors was derived, satisfying restrictions for the limiting states of turbulence and the assumed behavior for large Reynolds number and small anisotropy. The role of the anisotropy in constraining models for the turbulent dissipation rate and the pressure-strain correlations is discussed. Comparisons of the resulting closure with experimental data for several axisymmetric flows are good within the limitations of the data.
Discrete Noise Prediction of Variable Pitch Cross-Flow Fans by Unsteady Navier-Stokes Computations
Authors: Cho Yong , Moon Young J.
Published: June 2003

The unsteady viscous flow fields of a cross-flow fan are computed by time-accurately solving the two-dimensional incompressible Navier-Stokes equations with the unstructured triangular mesh solver algorithms. Based on pressure fluctuation data acquired at the surfaces of 35 rotating blades and stabilizer, acoustic pressures are predicted by the Ffowcs Williams-Hawkings equation. The aerodynamic noise sources of the cross-flow fan are also identified by correlating the acoustic pressure fluctuations with the unsteady flow characteristics during one revolution of the impeller. The present method is applied to the uniform and random pitch fans to investigate their performance and aeroacoustic noise characteristics, especially the frequency modulation of the tonal noise at the blade passing frequency (BPF).
Measurements Within Vortex Cores in a Turbulent Jet
Authors: Agrawal Amit , Prasad Ajay K.
Published: June 2003

High-pass filtering of instantaneous two-dimensional PIV data is employed to educe vortices occurring in the axial plane of a self-similar turbulent axisymmetric jet. An automated method is used to identify the vortices and to measure circulation, tangential velocity, vorticity, and centrifugal force within their cores (defined here as the region within the largest closed streamline). Results include radial variation of these quantities within vortex cores, and the energy of vortices. We find that the vorticity is maximum at the vortex center and decreases monotonically with the radial coordinate. Results indicate that the center of a larger vortex spins faster than a smaller vortex (in an ensemble averaged sense); however, the trend reverses to give the expected result at the core edge. Vorticity results for different vortex radii collapse upon normalization. The average energy of vortices is seen to increase as the square of the vortex radius. In addition, three possible regimes of vortex number versus vortex size are suggested by our data.
Momentum Thickness Measurements for Thick Axisymmetric Turbulent Boundary Layers
Authors: Cipolla Kimberly M. , Keith William L.
Published: June 2003

Experimental measurements of the mean wall shear stress and boundary layer momentum thickness on long, thin cylindrical bodies are presented. To date, the spatial growth of the boundary layer and the related boundary layer parameters have not been measured for cases where δ/a (a=cylinder radius) is much greater than one. Moderate Reynolds numbers 104<Reθ<105 encountered in hydrodynamic applications are considered. Tow tests of cylinders with diameters of 0.61, 0.89, and 2.5 mm and lengths ranging from approximately 30 meters to 150 meters were performed. The total drag (axial force) was measured at tow speeds up to 17.4 m/sec. These data were used to determine the tangential drag coefficients on each test specimen, which were found to be two to three times greater than the values for the corresponding hypothetical flat-plate cases. Using the drag measurements, the turbulent boundary layer momentum thickness at the downstream end of the cylindrical bodies is determined, using a control volume analysis. The results show that for the smallest diameter cylinders, there is no indication of relaminarization, and a fully developed turbulent boundary layer exists. A scaling law for the momentum thickness versus length Reynolds number is determined from the data. The results indicate that the spatial growth of the boundary layers over the entire length is less than for a comparable flat-plate case.
Vortex-Induced Vibration Characteristics of Two Fixed-Supported Elastic Cylinders
Authors: Wang Z. J. , Zhou Y. , So R. M. C.
Published: June 2003

Interference effects on vortex-induced vibrations of two side-by-side elastic cylinders, fixed at both ends (with no deflection and displacement) in a cross-flow, were experimentally investigated. The dynamic responses of the cylinders were measured using two fiber-optic Bragg grating (FBG) sensors. Simultaneously, a single hot wire was used to measure the velocity in the wake. It has been previously observed that violent resonance occurs when transverse cylinder spacing ratio, T/d, is either large (>2.0) or small (<1.2), but not for intermediate cylinder spacing, i.e., T/d=1.2∼2.0. This work aims to improve the understanding of the physics behind this observation, and mostly focuses on the fluid-structure interaction in the flow regime of intermediate cylinder spacing. It is well known that in this flow regime the fluid dynamics around one cylinder is totally different from that around the other; the vortical structures are characterized by different dominant frequencies, i.e., about 0.1 and 0.3 (normalized), respectively. The present data indicates that the vortical structures at these frequencies are either weak or different in the formation process from the case of T/d>2.0 or T/d<1.2, thus resulting in a weak excitation and subsequently an absence of violent resonance. The interrelationship between the vortical structures generated by the two cylinders is also investigated and interpreted in terms of different vortex generation mechanisms. The different fluid dynamics around each cylinder is further found to be responsible for a deviation between the natural frequencies of the combined fluid-cylinder system associated with each cylinder.
Design of Optimum Plate-Fin Natural Convective Heat Sinks
Authors: Bar-Cohen Avram , Iyengar Madhusudan , Kraus Allan D.
Published: June 2003

The effort described herein extends the use of least-material single rectangular plate-fin analysis to multiple fin arrays, using a composite Nusselt number correlation. The optimally spaced least-material array was also found to be the globally best thermal design. Comparisons of the thermal capability of these optimum arrays, on the basis of total heat dissipation, heat dissipation per unit mass, and space claim specific heat dissipation, are provided for several potential heat sink materials. The impact of manufacturability constraints on the design and performance of these heat sinks is briefly discussed.
The Case for the Elliptical Spine
Authors: McIntyre Gerald L. , Kraus Allan D.
Published: June 2003

The spine (fin) efficiency is abandoned and the input admittance, defined as the ratio of the heat dissipated by the spine to the temperature excess at the spine base, is established as the parameter for comparison of the performance of the spines of circular, square and elliptical cross section. It is shown that the square cross section outperforms the circular cross section and by adjusting the aspect ratio of the elliptical spine, the spine can meet and eventually surpass the performance of the square spine.
Fundamental Performance Limits of Heatsinks
Authors: Copeland David Watabe
Published: June 2003

Dedicated fan-duct-heatsink combinations have become a standard means of cooling computer processors. Most previous studies have considered optimization of fin geometry (pitch and thickness) with overall heatsink dimensions (width, height, length) fixed. The present study considers size requirements for the constraints of fixed air volume flow rate and pressure drop, fixed fan/blower power, and fixed thermal conductance. First, an ideal heatsink with infinite fin thermal conductivity is considered, providing simple power-law prediction of performance. Next, fins of finite thermal conductivity and thickness, as well as effects of developing flow are included in the analysis, permitting prediction and minimization of weight. Models of both levels of complexity can be used, previous to more detailed numerical and/or experimental studies, to design optimized heatsinks.
On the Use of Point Source Solutions for Forced Air Cooling of Electronic Components—Part I: Thermal Wake Models for Rectangular Heat Sources
Authors: Ortega Alfonso , Ramanathan Shankar
Published: June 2003

Analytical solutions are presented for the temperature field that arises from the application of a source of heat on an adiabatic plate or board when the fluid is represented as a uniform flow with an effective turbulent diffusivity, i.e., the so-called UFED flow model. Solutions are summarized for a point source, a one-dimensional strip source, and a rectangular source of heat. The ability to superpose the individual kernel solutions to obtain the temperature field due to multiple sources is demonstrated. The point source solution reveals that the N−1 law commonly observed for the centerline thermal wake decay for three-dimensional arrays is predicted by the point source solution for the UFED model. Examination of the solution for rectangular sources shows that the thermal wake approaches the point source behavior downstream from the source, suggesting a new scaling for the far thermal wake based on the total component power and a length scale given by ε/U. The new scaling successfully collapses the thermal wake for several sizes of components and provides a fundamental basis for experimental observations previously made for arrays of three-dimensional components.
Thermobuoyancy Treatment for Electronic Packaging Using an Improved Advection Scheme
Authors: Darbandi Masoud , Schneider Gerry E.
Published: June 2003

The complex nature of the convective terms in the fluid flow governing equations has caused many researchers to work on estimating more accurate advection term magnitudes by employing better approximate expressions. The trend of progress has been to include more physics of flow in the approximations. However, there is no archival evidence that reports the direct implementation of buoyancy as a physical influence in the advection term modeling. In this work, the influence of buoyancy in an efficient advection term expression is investigated in a control volume context with a collocated grid arrangement. The accuracy of the results obtained by both excluding and including the buoyancy term is evaluated through application to the natural convection heat transfer problem in a cavity at different Rayleigh numbers.
Numerical Investigation of the Steady-State Operation of a Cylindrical Capillary Pumped Loop Evaporator
Authors: Yan Y. H. , Ochterbeck J. M.
Published: June 2003

A cylindrical capillary pumped loop evaporator operating under steady-state conditions was studied using a two-dimensional numerical model. Parameters affecting the phase conditions in the wick structure and thermal-fluid behavior in the evaporator liquid core were studied. The influences of heat load, liquid subcooling, and effective thermal conductivity of the wick structure were specifically selected to evaluate evaporator performance. Either increasing the applied heat flux and/or degree of inlet liquid subcooling resulted in decreased liquid core temperature, which is favorable for proper evaporator operation. This helps prevent conditions that may allow vapor formation in the liquid core as well as result in decreased length of the two-phase region in the wick structure. Decreasing the effective thermal conductivity of the wick also decreases the temperature in the liquid core. For a given liquid subcooling, a minimum heat flux exists below which vapor will generate in the liquid core and render the evaporator nonoperational. Additionally, for a given heat flux, a minimum required liquid subcooling exists as conditions are such that vapor potentially may form in the liquid core when the liquid subcooling is less than a minimum value.
Modeling of Thermal Stress in Microelectronic and Photonic Structures: Role, Attributes, Challenges, and Brief Review
Authors: Suhir E.
Published: June 2003

The role and the attributes of, and challenges in, the predictive modeling of the thermomechanical behavior of microelectronic and photonic structures (packages) are addressed. Merits, shortcomings and interaction of theoretical and experimental approaches are discussed, as well as the role and the interaction of the analytical (“mathematical”) and numerical (computer-aided) modeling. We briefly review the published work in the field, with an emphasis on the analytical modeling of the thermally induced stresses and displacements. The review is based, to a great extent, on the author’s research conducted during his eighteen years tenure with Bell Laboratories, Physical Sciences and Engineering Research Division, Murray Hill, New Jersey. The major message of the article is that a viable and reliable optoelectronic product can be successfully created and delivered to the market in a timely fashion only provided that predictive modeling, whether analytical or numerical, is widely and effectively used, in addition and, preferably, prior to experimental investigations and testing.
Computer-Aided Design of a TSOP II LOC Package Using Taguchi’s Parameter Design Method to Optimize Mold-Flow Balance
Authors: Lee Hung-Lung , Chang Shyang-Jye , Hwang Sheng-Jye , Su Francis , Chen S. K.
Published: June 2003

This paper presents a methodology for TSOP II LOC packaging design. The design objectives are: 1) to optimize mold-flow balance, which in turn minimizes air traps, and 2) to minimize manufacturing variability, which implies optimal quality. A mold-flow simulation tool called C-MOLD is used to evaluate various design configurations. Taguchi’s robust design method is used for manufacturing variability considerations. The simulated results are verified with experimental flow patterns produced by means of “short shots.” In the nomenclature of the Taguchi method, mold-flow balance was chosen as quality characteristics and select a set of design parameters called control factors. The objectives are to find the levels of the control factors, which optimize the flow balance, and, at the same time, minimize the sensitivity of the variations of the control factors.
Analysis of a Turbulent Propeller Inflow
Authors: Huyer Stephen A. , Snarski Stephen R.
Published: June 2003

The unsteady turbulent inflow into a swirl-inducing stator upstream of propeller (SISUP) propeller is presented. The upstream stators and hull boundary layer generate a complex, three-dimensional inflow that was measured using x-wire anemometry. High resolution measurements consisting of 12 locations in the radial direction and 600 in the circumferential direction yielded mean velocity and rms turbulent quantities for a total of 7200 points. The axial, radial, and circumferential velocity fields were thus measured. This enabled the induced velocity due to the stator wakes, the induced velocity due to the propeller, and the turbulent hull boundary layer to be characterized. To assist in decoupling the effects on the velocity field due to the stator and propeller, a potential flow computation of the swirl component was used. Spectra and autocorrelation analysis of the inflow velocity field were used to estimate the integral length scale and lend further insight into the turbulent flow structure. These data can be used to validate computational fluid dynamics codes and assist in developing of turbulent inflow models.
Variable Frequency Microwave Processing of Underfill Encapsulants for Flip-Chip Applications
Authors: Mead Patricia F. , Ramamoorthy Aravind , Pal Shapna , Fathi Z. , Ahmad I.
Published: June 2003

This paper discusses an innovative technique for rapid cure of polymeric encapsulants such as underfills used in direct chip attach devices using variable frequency microwaves (VFM). VFM processing reduces the cure time for underfill encapsulants to 10 min or less, as compared to 30 or more minutes when using convection oven methods. We report here the results of our investigations measuring key material attributes of VFM and conventionally cured underfill encapsulant samples, and we also have characterized voiding and delamination characteristics of flip-chip with underfill test structures. Finally, particle settling in the flip-chip with underfill test structures has been characterized. Our results show that the VFM technique produces underfill attributes that are comparable to conventionally cured samples.
Measurement of Creep and Relaxation Behaviors of Wafer-Level CSP Assembly Using Moire´ Interferometry
Authors: Ham Suk-Jin , Lee Soon-Bok
Published: June 2003

In this paper, the creep and relaxation behaviors of a wafer-level CSP assembly under two types of thermal loading conditions were investigated using high sensitivity moire´ interferometry. One is a thermal load from 100°C to room temperature and the other is from room temperature to 100°C. In the second case, the real-time technique was used to monitor and measure the shear deformations of solder joints and the warpage of the assembly during the test. For the real-time measurements of thermal deformations, a small-sized thermal chamber having an optical window was developed. In addition, the test results obtained from the moire´ interferometry measurements were compared with the predicted values obtained from finite element analysis. It is shown that the deformation values predicted from finite element analysis have a good agreement with those obtained from the tests.
Dynamic Fracture in Brittle Solids at High Rates of Loading
Authors: Zhang Y.-Q. , Hao H.
Published: June 2003

This paper presents a dynamic damage model for predicting fracture and fragmentation of brittle materials subjected to loads with high loading rates. This model is based on the mechanics of microcrack nucleation, growth, and coalescence to formulate the evolution of damage. The damage in the model is assumed to be isotropic and is a function of time and applied stress. The model provides a direct, explicit, and quantitative method to determine the rate-dependent fracture stress and fragment size generated by crack coalescence in the dynamic fragmentation process. It considers the experimental facts that a brittle material does not fail if the applied stress is lower than its static strength and certain time duration is needed for fracture to take place when it is subjected to a stress higher than its static strength. Comparisons between theoretical predictions and test data are made and shown to be in good agreement.
A Symmetric Boundary Element Method/Finite Element Method Coupling Procedure for Two-Dimensional Elastodynamic Problems
Authors: Yu G. Y.
Published: June 2003

In this paper, a symmetric collocation boundary element method (SCBEM)/finite element method (FEM) coupling procedure is given and applied to a two-dimensional elastodynamic problem. The use of symmetry for the boundary element method not only saves memory storage but also enables the employment of efficient symmetric equation solvers. This is especially important for BEM/FEM coupling procedure. Compared with the symmetric Galerkin boundary element method (SGBEM) where double-space integration should be carried out, SCBEM is easier and faster.
A Note on the Estimation of Nonlinear System Damping
Authors: Torvik P. J.
Published: June 2003

System damping for a single mode in resonance is often estimated from a measurement of the bandwidth of the frequency response function. While the bandwidth is customarily measured between the half-power frequencies, it is also possible to choose any other fraction of the maximum amplitude. If the damping is linear, i.e., if the loss factor is independent of amplitude, the same damping will be found with any such choice. While intuition might suggest that the damping of a nonlinear system would be better estimated from a bandwidth taken closer to the maximum amplitude, this is shown to be false.
Creep Indentation of Single Cells
Authors: Koay Eugene J. , Shieh Adrian C. , Athanasiou Kyriacos A.
Published: June 2003

An apparatus for creep indentation of individual adherent cells was designed, developed, and experimentally validated. The creep cytoindentation apparatus (CCA) can perform stress-controlled experiments and measure the corresponding deformation of single anchorage-dependent cells. The apparatus can resolve forces on the order of 1 nN and cellular deformations on the order of 0.1 μm. Experiments were conducted on bovine articular chondrocytes using loads on the order of 10 nN. The experimentally observed viscoelastic behavior of these cells was modeled using the punch problem and standard linear solid. The punch problem yielded a Young’s modulus of 1.11±0.48 kPa. The standard linear solid model yielded an instantaneous elastic modulus of 8.00±4.41 kPa, a relaxed modulus of 1.09±0.54 kPa, an apparent viscosity of 1.50±0.92 kPa-s, and a time constant of 1.32±0.65 s. To our knowledge, this is the first time that stress-controlled indentation testing has been applied at the single cell level. This methodology represents a new tool in understanding the mechanical nature of anchorage-dependent cells and mechanotransductional pathways.
Biaxial Mechanical Response of Bioprosthetic Heart Valve Biomaterials to High In-plane Shear
Authors: Sun Wei , Sacks Michael S. , Sellaro Tiffany L. , Slaughter William S. , Scott Michael J.
Published: June 2003

Utilization of novel biologically-derived biomaterials in bioprosthetic heart valves (BHV) requires robust constitutive models to predict the mechanical behavior under generalized loading states. Thus, it is necessary to perform rigorous experimentation involving all functional deformations to obtain both the form and material constants of a strain-energy density function. In this study, we generated a comprehensive experimental biaxial mechanical dataset that included high in-plane shear stresses using glutaraldehyde treated bovine pericardium (GLBP) as the representative BHV biomaterial. Compared to our previous study (Sacks, JBME, v.121, pp. 551–555, 1999), GLBP demonstrated a substantially different response under high shear strains. This finding was underscored by the inability of the standard Fung model, applied successfully in our previous GLBP study, to fit the high-shear data. To develop an appropriate constitutive model, we utilized an interpolation technique for the pseudo-elastic response to guide modification of the final model form. An eight parameter modified Fung model utilizing additional quartic terms was developed, which fitted the complete dataset well. Model parameters were also constrained to satisfy physical plausibility of the strain energy function. The results of this study underscore the limited predictive ability of current soft tissue models, and the need to collect experimental data for soft tissue simulations over the complete functional range.
Analysis of a Plate Containing a Polygon-Shaped Inclusion With a Uniform Eigencurvature
Authors: Duong C. N. , Yu J.
Published: June 2003

An infinite isotropic plate containing a polygon-shaped inclusion with a uniform eigencurvature is analyzed. An algorithmic closed-form solution of the curvature is derived for both interior and exterior points of the polygon.
The Stress Response of Radially Polarized Rotating Piezoelectric Cylinders
Authors: Galic D. , Horgan C. O.
Published: June 2003

Recent advances in smart structures technology have lead to a resurgence of interest in piezoelectricity, and in particular, in the solution of fundamental boundary value problems. In this paper, we develop an analytic solution to the axisymmetric problem of an infinitely long, radially polarized, radially orthotropic piezoelectric hollow circular cylinder rotating about its axis at constant angular velocity. The cylinder is subjected to uniform internal pressure, or a constant potential difference between its inner and outer surfaces, or both. An analytic solution to the governing equilibrium equations (a coupled system of second-order ordinary differential equations) is obtained. On application of the boundary conditions, the problem is reduced to solving a system of linear algebraic equations. The stress distribution in the tube is obtained numerically for a specific piezoceramic of technological interest, namely PZT-4. For the special problem of a uniformly rotating solid cylinder with traction-free surface and zero applied electric charge, explicit closed-form solutions are obtained. It is shown that for certain piezoelectric solids, stress singularities at the origin can occur analogous to those occurring in the purely mechanical problem for radially orthotropic elastic materials.
Refined First-Order Shear Deformation Theory Models for Composite Laminates
Authors: Auricchio F. , Sacco E.
Published: June 2003

In the present work, new mixed variational formulations for a first-order shear deformation laminate theory are proposed. The out-of-plane stresses are considered as primary variables of the problem. In particular, the shear stress profile is represented either by independent piecewise quadratic functions in the thickness or by satisfying the three-dimensional equilibrium equations written in terms of midplane strains and curvatures. The developed formulations are characterized by several advantages: They do not require the use of shear correction factors as well as the out-of-plane shear stresses can be derived without post-processing procedures. Some numerical applications are presented in order to verify the effectiveness of the proposed formulations. In particular, analytical solutions obtained using the developed models are compared with the exact three-dimensional solution, with other classical laminate analytical solutions and with finite element results. Finally, we note that the proposed formulations may represent a rational base for the development of effective finite elements for composite laminates.
Calibrate Piezoresistive Stress Sensors Through the Assembled Structure
Authors: Lwo Ben-Je , Wu Shen-Yu
Published: June 2003

In this work, a simple assembled structure was designed and fabricated so that the calibration procedures on piezoresistive stress sensors for microelectronic packaging can be simpler, more accurate, and more efficient. After comparing with the previous work results, validity of the aforementioned new structure has been demonstrated through experimental data. Since many accessory experimental facilities employed in traditional calibrations become unnecessary, the new methodology takes great advantage on piezoresistive coefficient extractions, especially for calibration at temperature other than room temperature.
Particle Deposition in Arteries Ex Vivo: Effects of Pressure, Flow, and Waveform
Authors: Chesler Naomi C. , Enyinna Omyekachi C.
Published: June 2003

The goal of this study was to quantify the effect of hemodynamic pressure, flow and waveform perturbations on the deposition of protein-sized particles in porcine carotid arteries ex vivo. An ex vivo perfusion system was used to control the pressure and flow environment for excised arterial tissue. Confocal laser microscopy images revealed that 200 nm particles were deposited intimally and that more spheres were evident along vessels perfused under oscillatory waveform conditions than all others. Under all pressure, flow and waveform conditions, particles were excluded from the media and adventitia of the vessel wall. The steady flow data support the use of Darcy’s Law with pressure-dependent hydraulic permeability to model arterial tissue.
Coefficients of Restitution Based on a Fractal Surface Model
Authors: Lu Chung-Jen , Kuo Ming-Chang
Published: June 2003

Equations of rigid-body mechanics provide a means to predict the post-collision behavior without recourse to highly complex, detailed analysis of deformations during contact. Before the prediction can be completed, the coefficient of restitution, which relates the rebound velocity to the incident velocity, must be estimated properly. The coefficient of restitution depends on the surface topography in addition to the material properties and incident velocity. Recent investigations showed that surface topography can be characterized properly by fractal models. This paper proposes a normal contact model for a fractal surface in contact with a rigid smooth half-space. The fractal surface is constructed based on the Cantor set and composed of elastic-perfectly plastic material. Asymptotic continuous expressions for the load-displacement relations during loading and unloading are derived. Based on these results, we study the effects of surface roughness, material properties and incident velocity on the coefficient of restitution.
Passive Biaxial Mechanical Response of Aged Human Iliac Arteries
Authors: Schulze-Bauer Christian A. J. , Mo¨rth Christian , Holzapfel Gerhard A.
Published: June 2003

Inflation and extension tests of arteries are essential for the understanding of arterial wall mechanics. Data for such tests of human arteries are rare. At autopsy we harvested 10 non-diseased external iliac arteries of aged subjects (52–87 yrs). Structural homogeneity was ensured by means of ultrasound imaging, and anamneses of patients were recorded. We measured the axial in situ stretches, load-free geometries and opening angles. Passive biaxial mechanical responses of preconditioned cylindrical specimens were studied in 37°C calcium-free Tyrode solution under quasistatic loading conditions. Specimens were subjected to pressure cycles varying from 0 to 33.3kPa (250mmHg) at nine fixed axial loads, varying from 0 to 9.90N. For the description of the load-deformation behavior we employed five “two-dimensional” orthotropic strain-energy functions frequently used in arterial wall mechanics. The associated constitutive models were compared in regard to their ability of representing the experimental data. Histology showed that the arteries were of the muscular type. In contrast to animal arteries they exhibited intimal layers of considerable thickness. The average ratio of wall thickness to outer diameter was 7.7, which is much less than observed for common animal arteries. We found a clear correlation between age and the axial in situ stretch λis(r=−0.72,P=0.03), and between age and distensibility of specimens, i.e. aged specimens are less distensible. Axial in situ stretches were clearly smaller (1.07±0.09,mean±SD) than in animal arteries. For one specimen λis was even smaller than 1.0, i.e. the vessel elongated axially upon excision. The nonlinear and anisotropic load-deformation behavior showed small hystereses. For the majority of specimens we observed axial stretches smaller than 1.3 and circumferential stretches smaller than 1.1 for the investigated loading range. Data from in situ inflation tests showed a significant increase of the axial stretch with intraluminal pressure. Thus, for this type of artery the axial in situ stretch of a non-pressurized vessel is not representative of the axial in vivo stretch. None of the constitutive models were able to represent the deformation behavior of the entire loading range. For the physiological loading range, however, some of the models achieved good agreement with the experimental data.
Inertial Shear Forces and the Use of Centrifuges in Gravity Research. What is the Proper Control?
Authors: van Loon Jack J. W. A. , Folgering Erik H. T. E. , Bouten Carlijn V. C. , Veldhuijzen J. Paul , Smit Theo H.
Published: June 2003

Centrifuges are used for 1×g controls in space flight microgravity experiments and in ground based research. Using centrifugation as a tool to generate an Earth like acceleration introduces unwanted inertial shear forces to the sample. Depending on the centrifuge and the geometry of the experiment hardware used these shear forces contribute significantly to the total force acting on the cells or tissues. The inertial shear force artifact should be dealt with for future experiment hardware development for Shuttle and the International Space Station (ISS) as well as for the interpretation of previous spaceflight and on-ground research data.
Application of a Probabilistic Microstructural Model to Determine Reference Length and Toe-to-Linear Region Transition in Fibrous Connective Tissue
Authors: Hurschler Christof , Provenzano Paolo P. , Vanderby, Ray
Published: June 2003

This study shows how a probabilistic microstructural model for fibrous connective tissue behavior can be used to objectively describe soft tissue low-load behavior. More specifically, methods to determine tissue reference length and the transition from the strain-stiffening “toe-region” to the more linear region of the stress-strain curve of fibrous connective tissues are presented. According to a microstructural model for uniaxially loaded collagenous tissues, increasingly more fibers are recruited and bear load with increased tissue elongation. Fiber recruitment is represented statistically according to a Weibull probability density function (PDF). The Weibull PDF location parameter in this formulation corresponds to the stretch at which the first fibers begin to bear load and provides a convenient method of determining reference length. The toe-to-linear region transition is defined by utilizing the Weibull cumulative distribution function (CDF) which relates the fraction of loaded fibers to the tissue elongation. These techniques are illustrated using representative tendon and ligament data from the literature, and are shown to be applicable retrospectively to data from specimens that are not heavily preloaded. The reference length resulting from this technique provides an objective datum from which to calculate stretch, strain, and tangent modulus, while the Weibull CDF provides an objective parameter with which to characterize the limits of low-load behavior.