bluuebunny/crossref_metadata_2025 huggingface dataset:
Local Buckling and Failure of Pultruded Fiber-Reinforced Plastic Beams
Authors: Bank L. C. , Nadipelli M. , Gentry T. R.
Published: April 2008

An experimental investigation of the local compression flange buckling and failure of commercially produced pultruded fiber-reinforced plastic (FRP) I-shaped beams is described in this paper. Results of tests on pultruded E-glass/polyester and E-glass/vinylester composite material beams are described. The test configuration was designed to cause local buckling and ultimate failure of the compression flange of the beams and to prevent global lateral-torsional buckling. The beams were stiffened to prevent crippling and warping at the supports, and local tensile failure at the load points. All beams were monitored with strain gages and LVDT’s. Buckling loads, failure loads, buckling stresses, deflections, and failure modes are reported. Effective mechanical properties of the beams, obtained from overall flexural and shear strain data, are presented. A discussion of the different failure characteristics of the polyester and the vinylester beams is provided.
Approximate Models for Ductile Metals Containing Nonspherical Voids—Case of Axisymmetric Oblate Ellipsoidal Cavities
Authors: Gologanu Mihai , Leblond Jean-Baptiste , Devaux Josette
Published: April 2008

The aim of this paper is to extend the classical Gurson (1977) analysis of a hollow rigid ideal-plastic sphere loaded axisymmetrically to an ellipsoidal volume containing a confocal oblate ellipsoidal cavity. An “expansion” velocity field satisfying conditions of homogeneous boundary strain rate is used to derive a two-field estimate of the overall yield criterion. The latter is shown to be reducible, with a few approximations, to a Gurson-like criterion depending on the “shape parameter” of the cavity. The accuracy of this estimate is assessed through comparison with some results derived from a numerical minimization procedure. An approximate evolution equation for the shape parameter is also presented; comparison with some finite element simulations suggests a slight modification of the theoretical formula leading to considerably enhanced agreement.
Double-Inclusion Model and Overall Moduli of Multi-Phase Composites
Authors: Hori Muneo , Nemat-Nasser Sia
Published: April 2008

The double-inclusion model consists of an ellipsoidal inclusion of arbitrary elasticity, containing another ellipsoidal heterogeneity of arbitrary elasticity, size, and orientation, which are embedded in an infinitely extended homogeneous domain of yet another arbitrary elasticity. Average field quantities for the double inclusion are obtained analytically, and used to estimate the overall moduli of two-phase composites. The technique includes the self-consistent and other related methods as special cases. Furthermore, exact bounds for the overall moduli are obtained on the basis of the double-inclusion model. The double-inclusion model has been generalized (Nemat-Nasser and Hori, 1993) to a multi-inclusion model, where, again, all the average field quantities are estimated analytically. The application of the multiinclusion model includes a composite containing inclusions with multi-layer coatings.
Damage Mechanisms in Ti3Al Matrix Composites
Authors: Kouris Demitris , Marshall David
Published: April 2008

The paper discusses experimental observations and some related theoretical results associated with the mechanical response of two Ti3Al matrix composites, subjected to transverse loading. Both composites contain continuous unidirectional fibers; however, there are considerable differences in the composition of the two interfaces. The Ti3Al/SCS-6 system contains brittle reaction products around the fibers that degrade the strength of the composite. The second composite consists of a Ti3Al matrix reinforced by sapphire fibers that are strongly bonded to the matrix. Experimental observations indicate that the damage mechanisms in the two composites are substantially different. Utilizing elastic analyses of the local stress field, an attempt was made to explain the dependence of the observed damage mechanisms on the residual field and the properties of the interface.
Damage Mechanisms Modeling for Ceramic Composites
Authors: Ladeve`ze P. , Gasser A. , Allix O.
Published: April 2008

For ceramic composites, continuum damage mechanics models are built, which include information coming from both the “micro” and “macro” scales. These models are constitutive relations which, when included in a structural analysis code, are able to predict the damage state of the studied structure at any time and at any point until final fracture.
Constitutive Equations of Power-Law Composites and Failure of Materials Having Multiple Cracks
Authors: Lin S. C. , Hirose Y. , Mura T.
Published: April 2008

Based upon the Mori-Tanaka method, the constitutive equations of power-law materials and the failure criteria of multiple cracks materials are investigated. The piecewise linear incremental approach is also employed to analyze the effective stress and strain of the power-law materials. Results are presented for the case of pure shear where the matrix is a power-law material with rigid or void inhomogeneities. For the multiple cracked materials, the Griffith fracture criterion is applied to determine the critical volume fraction which causes the catastrophic failure of a material. The failure criteria of penny shaped, flat ellipsoidal, and slit-like cracked materials are examined and it is found that the volume fraction of cracks and critical applied stress are in linear relation.
A Micromechanics-Based Constitutive Model for Polycrystalline Ice
Authors: Premachandran R. , Horii Hideyuki
Published: April 2008

In this paper a constitutive-model based on micromechanics is given to predict the time dependent ductile behavior of ice under compressive load. It is presumed creep and microcracking are the two dominant mechanisms in the ductile range. The proposed model is formulated on the idea that shear slip along the basal plane is the cause of the permanent deformation of ice, and that microcracking is caused by the local stress due to the mismatch strain. A single crystal is modeled as an inclusion constrained in a polycrystalline matrix with random orientation of the basal plane. Eshelby’s solution is used to estimate the local stress due to the mismatch strain. Maximum tensile stress criterion is adopted to predict microcracking and then crack density is predicted as a function of time. The stress-strain relation of the polycrystalline ice is calculated on the basis of single crystal property in which effect of internal structural changes is incorporated as the reduction of constraint of the surrounding matrix with increasing microcracking. The model predictions for constant load and constant strain rate tests are shown to demonstrate the validity of the model. The constitutive model is implemented in finite element analysis code and a small-scale indentation test is simulated as an example.
A Progressive Damage Mechanics in Particle-Reinforced Metal-Matrix Composites Under High Triaxial Tension
Authors: Tohgo Keiichiro , Weng G. J.
Published: April 2008

The energy approach recently proposed by Qiu and Weng (1992) is introduced to estimate the equivalent stress of the ductile matrix in Tohgo and Chou’s (1991) incremental damage theory for particulate-reinforced composites containing hard particles. In such a composite debonding of the particle-matrix interface is a significant damage process, as the damaged particles have a weakening effect while the intact particles have a reinforcing effect. In Tohgo-Chou’s theory, which describes the elastic-plastic behavior and the damage behavior of particulate-reinforced composites, it was assumed that the debonding damage is controlled by the stress of the particle and the statistical behavior of the particle-matrix interfacial strength, and that the debonded (damaged) particles are regarded as voids, resulting in an increased void concentration with deformation. On the other hand, Qiu-Weng’s energy approach provides a reasonable equivalent stress of the matrix in the porous material and particulate-reinforced composite even under a high triaxiality. The incremental damage theory developed here enables one to calculate the overall stress-strain response and damage evolution of the composite under high triaxial tension. The stress-strain relations for porous material obtained by the present incremental theory are completely consistent with that obtained by Qiu and Weng. The influence of the debonding damage on the stress-strain response is demonstrated for particulate-reinforced composites.
Modeling the Effect of Oxidation on Damage in SiC/Ti-15-3 Metal Matrix Composites
Authors: Wittig L. A. , Allen D. H.
Published: April 2008

In this paper, a micromechanical analysis is performed on a single ply continuous fiber SiC/Ti-15V-3Al-3Sn-3Cr (Ti-15-3) metal matrix composite to study the complex interactions between the composite microstructural components and the surrounding environment at high temperatures. Finite elements are incorporated to model oxygen diffusing into the free suface of a representative volume element (RVE) during cool down from the processing temperature. The resulting residual stress distribution is investigated assuming thermoelastic material models for the matrix, oxide layer, and fiber. Results indicate that the oxidized surface layer is prone to cracking upon subsequent mechanical loading, and this effect is strongly temperature dependent.
The Transition to Quasi-Periodicity for Molten Plastics in Large Amplitude Oscillatory Shear
Authors: Adrian D. W. , Giacomin A. J.
Published: April 2008

Large amplitude oscillatory shear (LAOS) experiments on three grades of LLDPE including one commercial film blowing resin showed an interesting transition in the shear stress response to LAOS. The shear stress response is initially a nonsinusoidal standing wave which then undergoes a transition to quasi-periodicity. Many line-broadened odd and even harmonics were found in the shear stress amplitude spectra of the quasi-periodic responses. The transition time depends on shear strain amplitude and frequency, but it did not correlate with the weight average molecular weight of the LLDPE’s.
Small Punch Testing for Determining the Material Toughness of Low Alloy Steel Components in Service
Authors: Foulds J. , Viswanathan R.
Published: April 2008

The toughness of the low alloy ferritic steel material of structural components operating at elevated temperatures can degrade during service due to embrittling phenomena such as carbide coarsening and temper embrittlement. The extent of degradation and the current level of toughness are critical inputs to component structural integrity assessments and to operation and maintenance planning. Conventional test methods for measuring toughness require the removal of large material samples from the in-service component, which is generally impractical. However, the recent development of relatively nondestructive, miniature sample removal systems and the small punch test technique (which utilizes nonstandard, miniature specimens) now provides a convenient, practical means of evaluating the material of an in-service component for toughness and related mechanical properties. This paper describes the small punch test technique with selected examples of its application to various grades of low alloy ferritic steel.
Dynamic Crack Growth in a Power Hardening Viscoplastic Material
Authors: Shenoy Vijay B. , Kumar R. Krishna
Published: April 2008

In this paper a finite element analysis of steady-state dynamic crack growth under mode I plane strain small scale yielding conditions has been performed in a power law hardening rate dependent plastic material, characterized by the Perzyna over stress model. A modified version of the rate tangent modulus method has been used to update the stress. The main objective of the work is to obtain a quantitative relationship between dynamic fracture toughness ratio (K/Kss) and crack speed. A plastic strain criteria proposed by McClintock (1968) has been applied to obtain this relationship. It is found that dynamic stress intensity factor increases with velocity for all values of βˆ (a normalized viscosity parameter). At a low value of βˆ, which corresponds to high rate sensitivity, the fracture toughness ratio (K/Kss) increases with hardening. On the other hand, at a higher βˆ, the ratio increases initially and falls subsequently, with increasing hardening.
A Spring Foundation Model for Mode I Failure of Laminated Composites Based on an Energy Criterion
Authors: Song Seung J. , Waas Anthony M.
Published: April 2008

A mechanical model which can predict mode I delamination failure of laminated composites has been developed. A beam on a nonlinear spring foundation was used to model experimental results obtained from DCB type fracture specimens. The entire thickness of the beam specimen was used as a spring length, and a nonuniform strain distribution throughout the spring length was utilized, based on the 2-D asymptotic solution of the stress field near a crack tip. The failure condition of the spring foundation is based on an energy criterion. Mode I fracture tests were performed to verify the current model using two types of laminated composite DCB specimens. The current model reproduced the experimental results of pulling force versus crack opening displacement curves very closely for a wide range of resin layer thickness of the specimens. The current model has a potential capability of being extended to solve 2-D crack problems, where the evolution of an arbitrary shape of 2-D crack geometry will be predicted as a part of the solution of the current model.
A Micromechanics Model for Thermoelastic Properties of Plain Weave Fabric Composites
Authors: Hahn H. T. , Pandey R.
Published: April 2008

A micromechanics model is presented to predict thermoelastic properties of composites reinforced with plain weave fabrics. A representative volume element is chosen for analysis and the fiber architecture is described by a few simple functions. Equations are developed to calculate various phase fractions from geometric parameters that can be measured on a cross section. Effective elastic moduli and effective thermal expansion coefficients are determined under the assumption of uniform strain inside the representative volume element. The resulting model is similar to the classical laminated theory, and hence is easier to use than other models available in the literature. An experimental correlation is provided for a number of Nicalon SiC/CVI SiC and Graphite/CVI SiC composite laminates.
Finite Element Mesh Refinement for Discontinuous Fiber Reinforced Composites
Authors: Kim H. G. , Grosse I. R. , Nair S. V.
Published: April 2008

This paper is concerned with the development of a generalized approach for mesh refinement in a short fiber reinforced composite. Mesh refinement procedures are based on the calculation of the error in energy norm for global convergence and the traction differential approach at the fiber/matrix interface for local convergence. The mesh refinement strategy is based on the use of elongated elements at the fiber/matrix interface, yielding significantly different mesh patterns than obtained by conventional mesh refinement approaches. This difference may have a critical bearing on the subsequent thermo-mechanical properties predicted by finite element analysis (FEA). It is found that the use of elongated (i.e., high aspect ratio) elements for mesh refinement results in a much more rapid computational convergence rate than obtained by conventional meshes. Converged local solutions are obtained with significantly less degrees-of-freedom (DOF) than by conventional mesh refinement methods.
Comparison of the Effects of Debonds and Voids in Adhesive Joints
Authors: Rossettos J. N. , Lin P. , Nayeb-Hashemi H.
Published: April 2008

An analytical model is developed to compare the effects of voids and debonds on the interfacial shear stresses between the adherends and the adhesive in simple lap joints. Since the adhesive material above the debond may undergo some extension (either due to applied load or thermal expansion or both), a modified shear lag model, where the adhesive can take on extensional as well as shear deformation, is used in the analysis. The adherends take on only axial loads and act as membranes. Two coupled nondimensional differential equations are derived, and in general, five parameters govern the stress distribution in the overlap region. As expected, the major differences between the debond and the void occur for the stresses near the edge of the defect itself. Whether the defect is a debond or a void, is hardly discernible by the stresses at the overlap ends for central defect sizes up to the order of 70 percent of the overlap region. If the defect occurs precisely at or very close to either end of the overlap, however, differences of the order of 20 percent in the peak stresses can be obtained.
The Use of Holographic Phase Shifting in Assessing Unbonds in GRP Plates
Authors: Soh C. C. , Shang H. M. , Chau F. S. , Hung Y. Y.
Published: April 2008

During holographic inspection of glass fiber reinforcesd plastic (GRP) laminated plates, perturbation in the fringe patterns not only reveals the presence of an unbond but also enables estimation of its depth. The accuracy of estimation depends, among other factors, on the accuracy in determining the fringe orders within the boundary of perturbation. This study shows that phase shifting using a single reference beam enables determination of fractional fringe orders at any point on the test surface. When applied to the assessment of the detected unbond, this simple technique gives a more accurate estimation of the unbond depth than conventional holography.
Data Management for the Evaluation of Residual Stresses by the Incremental Hole-Drilling Method
Authors: Vangi Dario
Published: April 2008

The semidestructive incremental hole-drilling method commonly used to evaluate residual stresses is exceedingly sensitive to experimental errors, with sensitivity increasing as hole depth increases. To determine stress variations through the engine thickness, it is necessary to use accurate drilling methods, as well as suitable mathematical models and procedures to minimize the errors associated with residual stress measurement. This work examines the effects of measurement errors on the evaluation of residual stresses with the integral method. An enhanced procedure for managing the experimental data is proposed that allows evaluation of the residual stresses with thickness variations.
A Comparison of Redundant Deformation Factors in the Drawing of Round Section Bars
Authors: Cetlin P. R. , Silva A. P.
Published: April 2008

The experimental drawing of SAE 1008 steel bars was performed for different reductions in area (r) and die semi-angles (α). The redundant deformation factor (φ) was evaluated for each case using two techniques: microhardness profiles and stress-strain curves superposition. The experimental values of φ obtained by the two techniques were not in agreement.
Thermal Effects During Infrared Solder Reflow—Part I: Heat Transfer Mechanisms
Authors: Fernandes N. J. , Bergman T. L. , Masada G. Y.
Published: April 2008

An experimental study has been conducted to reveal the relevant heat transfer mechanisms which exist within an infrared reflow oven. Simulated card assemblies are used and their transient thermal responses, induced by combined radiative and convective heating, are measured. A simple numerical model is developed with which relevant heat transfer mechanisms are identified and quantified. The study shows that radiative and mixed convective heat transfer processes induce a variety of system thermal responses. Model predictions, which incorporate measured forced convection heat transfer coefficients and accurate descriptions of surface-to-surface radiative exchange, are in excellent agreement with experimental data for cases where the thermally induced buoyancy forces within the oven air are relatively small. The results of the experimental and analytical study provide guidelines for the development of more sophisticated models of the infrared reflow process.
Liquid Immersion Cooling of a Longitudinal Array of Discrete Heat Sources in Protruding Substrates: I—Single-Phase Convection
Authors: Heindel T. J. , Incropera F. P. , Ramadhyani S.
Published: April 2008

Experiments have been performed using water and FC-77 to investigate heat transfer from an in-line 1 x 10 array of discrete heat sources, flush mounted to protruding substrates located on the bottom wall of a horizontal flow channel. The data encompass flow regimes ranging from mixed convection to laminar and turbulent forced convection. Buoyancy-induced secondary flows enhanced heat transfer at downstream heater locations and provided heat transfer coefficients comparable to upstream values. Upstream heating extended enhancement on the downstream heaters to larger Reynolds numbers. Higher Prandtl number fluids also extended heat transfer enhancement to larger Reynolds numbers, while a reduction in channel height suppressed buoyancy driven flows, thereby reducing enhancement. The protrusions enhanced the transition to turbulent forced convection, causing the critical Reynolds number to decrease with increasing row number. The transition region was characterized by large heater-to-heater variations in the average Nusselt number.
Liquid Immersion Cooling of a Longitudinal Array of Discrete Heat Sources in Protruding Substrates: II—Forced Convection Boiling
Authors: Heindel T. J. , Ramadhyani S. , Incropera F. P.
Published: April 2008

Forced convection boiling experiments have been performed for an in-line 1 x 10 array of discrete heat sources, flush mounted to protruding substrates located on the bottom wall of a horizontal flow channel. FC-72, a dielectric fluorocarbon liquid, was used as the heat transfer fluid, and the experiments covered a range of flow velocities, degrees of fluid subcooling, and channel heights. The maximum heater-to-heater surface temperature variation was less than 2.5°C and was insensitive to channel height under conditions of fully developed nucleate boiling. Although the fluid velocity influenced the heat flux for partially developed nucleate boiling, its influence was muted for fully developed nucleate boiling. The heat flux associated with a departure from nucleate boiling increased with increasing velocity, subcooling, and channel height; however, the effect of channel height was only significant when all of the upstream heaters were energized.
Heat Transfer and Flow Characteristics of Two-Dimensional Jets Impinging on Heated Protrusions With Crossflow of the Spent Air
Authors: Whidden G. L. , Stevens J. , Webb B. W.
Published: April 2008

The flow structure and local heat transfer characteristics of two-dimensional slot jets impinging on heated protrusions has been investigated. The spent air was constrained to exit at one end of the channel, forming a crossflow. The effects of three parameters on the heat transfer were examined for an array of five protruding heat sources. They include the jet slot width, distance between the jet exit and the protrusion, and the average jet Reynolds number. Laser-Doppler velocimeter measurements were made to detail the mean and turbulent flow structure in the channel. Experimental results reveal that the flow and heat transfer are dominated by turbulent transport even for Reynolds numbers as low as 300. Two transport mechanisms were identified affecting the heat transfer. The first was jet impingement, the second being crossflow of the spent air. A complex interaction between the two mechanisms was observed. At low nozzle-protrusion spacing with large slot jets the heat transfer was dominated by the crossflow, whereas for high nozzle-protrusion spacing and small jets, transport was dominated by jet impingement. It is postulated that the highest average Nusselt number occurs when the jets and the crossflow influence act with near-equal intensity.
Automated Measurement of Flank Wear of Circuit Board Drills
Authors: Ramirez Ciro N. , Thornhill R. Joe
Published: April 2008

The results of automated measurements of flank wear of drills used in circuit board drilling are presented. The measurement technique uses a machine vision system to increase measurement speed and reduce measurement variability. A flank area wear parameter is compared to the commonly used flank width wear measurement, and is shown to be more consistent, in agreement with similar work by T. I. Liu using multifaceted crankshaft drills.
State-of-the-Art and Trends in the Thermal Packaging of Electronic Equipment
Authors: Bar-Cohen Avram
Published: April 2008

The incessant improvements in IC technology have made it possible to conceptualize “information appliances” providing nearly unimaginable scalar, vector, and massively parallel information processing capability in small and relatively cheap computing platforms. The successful commercialization of such systems requires substantially shortened “time-to-market”, as well as dramatically reduced cost-of-ownership, and places extraordinary demands on packaging and physical design. A science-based physical design methodology, which can guide the development, selection, and evaluation of advanced packaging technology, will be needed to generate these sophisticated products. Mechanical engineers must play a major role in replacing the conventional “trial and error” development process with a science-based design methodology.
Effects of Orientation on Critical Heat Flux From Chip Arrays During Flow Boiling
Authors: Gersey C. O. , Mudawar I.
Published: April 2008

Boiling experiments were performed with FC-72 on a series of nine in-line simulated microelectronic chips in a flow channel to ascertain the effects of channel orientation on critical heat flux (CHF). The simulated chips, measuring 10 mm × 10 mm, were flush-mounted to one wall of a 20 mm × 5 mm flow channel. The channel was rotated in increments of 45 degrees through 360 degrees such that the chips were subjected to coolant in upflow, downflow, or horizontal flow with the chips on the top or bottom walls of the channel with respect to gravity. Flow velocity was varied between 13 and 400 cm/s for subcoolings of 3, 14, 25, and 36°C and an inlet pressure of 1.36 bar. While changes in angle of orientation produced insignificant variations in the single-phase heat transfer coefficient, these changes had considerable effects on the boiling pattern in the flow channel and on CHF for velocities below 200 cm/s,’ with some chips reaching CHF at fluxes as low as 18 percent of those corresponding to vertical upflow. Increased subcooling was found to slightly dampen this adverse effect of orientation. The highest CHF values were measured with near vertical upflow and/or upward-facing chips, while the lowest values were measured with near vertical downflow and/or downward-facing chips. These variations in CHF were attributed to differences in flow boiling regime and vapor layer development on the surfaces of the chips between the different orientations. The results of the present study reveal that, while some flexibility is available in the packaging of multi-chip modules in a two-phase cooling system, some orientations should always be avoided.
Parametric Studies for Thermal Design of Surface Mounted Components of Standard Electronic Modules
Authors: Hadim A. , Nagurny N. J.
Published: April 2008

Parametric studies are performed on heat transfer in surface-mounted components of conduction cooled Standard Electronic Modules (SEMs). Thermal network models are developed for the various components that are used in the SEMs. The models are validated by comparing the results with available experimental results from various test modules. An interfacing software package for thermal analysis (IN-STAN) is used to generate the thermal network representations of the models and a thermal network analyzer is used to perform the analysis. Several studies are performed to analyze the effects of important thermal design parameters including: chip and carrier size, cavity floor thickness, air gap thickness, die and carrier materials, and solder material.
A Physics of Failure Approach to Component Placement
Authors: Osterman M. D.
Published: April 2008

Traditionally, placement techniques have focused on improving rotability based on minimizing the total wire length between interconnected components. However, electronic card assembly (ECA) reliability, which is measured in terms of time to failure, cycles to failure, or the hazard rates of the individual components, the interconnections, and the PWB, is also affected by component placement. This paper discusses component placement for reliability based on a failure model which incorporates component temperature, a base operating temperature, a threshold temperature, and change in temperature. Placement procedures are developed so as to minimize the time to failure or the total hazard rate of the components on a PWB utilizing a forced convection cooling.
Shape and Force Relationships for Molten Axisymmetric Solder Connections
Authors: Katyl R. H. , Pimbley W. T.
Published: April 2008

The analysis for equilibrium shapes of axial symmetric solder connections is presented, which includes the consideration of surface tension, external, and gravitation forces. Four methods of calculating the shapes are explained. The analysis and calculation methods are applied to molten solder drops in contact with wettable circular pads, and to controlled collapse interconnections. A discussion of planar arrays of nonidentical solder connections, and the control of connector shape and height by the use of such nonuniformity is included.
Nonlinear Dynamic Response of a Printed Circuit Board to Shock Loads Applied to Its Support Contour
Authors: Suhir E.
Published: April 2008

We evaluate the nonlinear dynamic response of a flexible printed circuit board (PCB) to the following two types of shock loads acting on its support contour: 1) suddenly applied constant acceleration and 2) periodic instantaneous impacts. The purpose of the analysis is to determine the maximum accelerations experienced by the electronic components and devices surface mounted on the board. We show that when the support contour is immovable (nondeformable) and the deflections are large, it is important to account for the nonlinear effects. These are due to the in-plane (“membrane”) forces in the PCB and can possibly result in substantially higher accelerations than those predicted by a linear theory. The obtained formulas are easy-to-use and enable one to evaluate the maximum displacements (amplitudes), velocities, and accelerations of the surface-mounted devices, as well as the maximum dynamic stresses in the board. These formulas can be helpful when choosing the appropriate PCB type and dimensions, and the most rational lay-out of the components on the board.
Comparison of Modeling Techniques for the Vibration Analysis of Printed Circuit Cards
Authors: Pitarresi J. M. , Primavera A. A.
Published: April 2008

The estimation of the mechanical reliability of components on a vibrating circuit card continues to be an important part of the overall reliability assessment for electronic packages. To achieve a good vibration reliability estimate it is necessary to have an accurate representation of the dynamic response of the card. This can be realized by having the modal characteristics of the circuit card, i.e., its natural frequencies and mode shapes, accurately modeled. It is the primary objective of this paper to review some of the current modeling techniques for the dynamic characterization of circuit cards populated with components. Performance assessments include tangible factors such as accuracy of predicted frequencies and mode shapes, as well as less tangible factors such as ease of use. The circuit cards considered in this study are intended to be representative of small to medium sized logic, memory, and processor cards used in commercial electronics; the card is composed of laminated copper and FR-4 glass epoxy, typically without a bonded heat sink or intermediate stiffeners, and it may be populated with both SMT and PIH components.
Microelectronics and the Built-Up-Bar Theory
Authors: Mirman B.
Published: April 2008

The Built-up-Bar (BUB) theory is presently gaining recognition in microelectronics. This theory offers a useful method for computing stresses and strains in multilayered structures. However, it cannot be safely applied outside of the inherent assumptions that facilitated the convenient simplification of the general equations. This paper discusses methods for solution of basic equations of the BUB theory and cautions analysts about certain pitfalls.
The Distribution of the Stress Intensity Factor Along the Front of the Growing Crack in an Optical Glass Fiber
Authors: Muraoka M. , Abe´ H. , Aizawa N.
Published: April 2008

The stress intensity factor K1 along the front edge of a growing small crack in a silica optical fiber was evaluated by 3-D boundary element analysis based on the crack geometry observed during the delayed fracture test. The variation of K1 was shown to be little along the front of the growing crack. The crack velocity in the direction normal to the crack front was able to be expressed as a power function of K1 at each position on the crack front. The crack velocity was also shown to be larger at a position closer to the fiber surface for each value of K1.
A New Method for Measuring Adhesion Strength of IC Molding Compounds
Authors: Nishimura Asao , Hirose Isao , Tanaka Naotaka
Published: April 2008

Adhesion strength evaluation of molding compounds is a critical issue in structural design and material selection for IC plastic packages. However, since conventional adhesion tests can only give apparent adhesion strengths, which include the effect of residual stress, their results cannot be used for design purposes. This paper proposes a new strength evaluation method which can experimentally separate residual stress from adhesion strength. In this method, three-point bending tests of ENF specimens are performed in both directions. Residual stress is then cancelled by simply averaging the apparent strengths for both directions. The method’s validity is verified by experiments and stress analyses of specimens composed of an IC molding compound and Alloy 42 lead frame material. Adhesion strength is expressed in terms of the stress intensity factor of the interface crack. It is confirmed that constant strengths can be obtained independently of specimen dimensions.
PCB Trace Thermal Analysis and Effective Conductivity
Authors: Lemczyk T. F. , Mack B. L. , Culham J. R. , Yovanovich M. M.
Published: April 2008

The electrical current carrying capability of a surface or buried trace located within a fiberglass printed circuit board (PCB), is of important interest in the microelectronics industry. The maximum allowable trace power, hence local integrity and maximum allowable operating temperature, will depend on several parameters including the circuit board thermal conductivity, thickness, trace size and location. A two-dimensional, steady-state thermal conduction analysis is made on a finite, plane homogeneous medium (PCB), to examine the trace behavior. The trace is modeled as a zero-thickness, strip heat source with specified uniform temperature, and it’s position in the medium is varied. A two-dimensional thermal analysis is also performed on a multilayered cell model with finite heat source, to establish an accurate, effective thermal conductivity for a typical PCB. Results are tabulated and presented graphically for both the two-dimensional trace and effective conductivity models.
Effects of Channel Height and Planar Spacing on Air Cooling of Electronic Components
Authors: Copeland David
Published: April 2008

A series of experiments was performed to study forced convection from rectangular arrays of electronic components. Effects of channel height, planar spacing, component row number, and approach velocity are assessed. Correlations for the temperature rise of a component due to its own power and due to heating by upstream modules are presented. The components used were aluminum-capped ceramic pin grid array modules, of the same shape as “flatpacks”, measuring 37 mm square and 5.8 mm tall. The space between the rows and columns of modules was varied from near zero to about one module length. Channel height ranged from about two to five times module height. The air approach velocity ranged from 0.5 to 5.5 meters per second, corresponding to module length Reynolds numbers from 1000 to 11000. The heat transfer coefficient varied from 25 to 75 W/m2K. The temperature rise of a component due to its own power was found to be a strong function of velocity and less dependent on channel height and row number. The effect of velocity was weaker on the densest configuration than on the two sparser spacings. The two densest spacings had little dependence on channel height; the sparsest configuration had only a weak dependence on row number. The temperature rise of components downstream of a heated component exhibited similar but stronger dependence on velocity and channel height and the same dependence on row number.
On the Use of Micro Heat Pipes as an Integral Part of Semiconductor Devices
Authors: Mallik A. K. , Peterson G. P. , Weichold M. H.
Published: April 2008

A transient three-dimensional numerical model was developed to determine the potential advantages of constructing an array of very small (100 μm diameter) heat pipes as an integral part of semiconductor chips. Because of the high effective thermal conductivity, this array of heat pipes functions as a highly efficient heat spreader. The numerical model presented here, when given the physical parameters of the chip and the locations and magnitude of the internal heat generation, is capable of predicting the time dependent temperature distribution, localized heat flux, and temperature gradients occurring within the chip. The results of this modeling effort indicate that significant reductions in the maximum chip temperature, thermal gradients and localized heat fluxes can be obtained through the incorporation of arrays of micro heat pipes. Utilizing heat sinks located on the edges of the chip perpendicular to the axis of the heat pipes and an optimized array density of 1.35 percent, reductions in the maximum chip temperature of up to 40 percent were achieved.
Low Temperature Transient Liquid Phase (LTTLP) Bonding for Au/Cu and Cu/Cu Interconnections
Authors: Hou M. M. , Eagar Thomas W.
Published: April 2008

The Low Temperature Transient Liquid Phase Diffusion Bonding (LTTLP) process has been used to reduce the residual stresses and hence, improve the thermal fatigue performance of bonds between dissimilar electronic packaging materials. Aluminum oxide plated with either gold or copper has been bonded to copper heatsinks at temperatures less than 160°C, using In-Sn eutectic solders. After two hours at the bonding temperature, Cu/In-Sn/Cu joints exhibit a remit temperature in excess of 470°C and provide static strengths up to four times greater than the original solder bonds. Au/In-Sn/Cu joints do not exhibit a high remit temperature due to the formation of a stable Au-In-Sn phase which melts below 130°C. Both types of joints exhibited acceptable thermal fatigue performance for the conditions which were studied.
Predicted Residual Bow of Thin Plastic Packages of Integrated Circuit Devices
Authors: Suhir E.
Published: April 2008

Thin plastic packages are prone to residual bows caused by the thermal contraction mismatch of the constituent materials: silicon (chip), metal (leadframe), and epoxy (encapsulant). Since excessive bow can make normal mounting of a plastic package on a printed wiring board difficult, it is important that such a bow can be predicted, minimized, and, if possible, avoided. Accordingly, in this analysis we develop a simple and easy-to-apply calculation method for the prediction of the residual thermally-induced bow in a thin elongated plastic package. We use the obtained formula for the curvature to determine whether the chip/leadframe assembly can be positioned within the epoxy encapsulant in such a way that no residual bow occurs. We show that employment of epoxy encapsulants with elevated coefficients of thermal expansion can be an effective means to reduce the bow, and that application of thin and/or low expansion leadframes is also desirable. The calculated bow, obtained for a 1mm thick, 14mm long package, agrees satisfactorily with the finite-element solution. The results of our analysis can be utilized as a guidance in the evaluation of the expected bow, as well as for a rational physical design of thin plastic packages.
Predicting Thermal Fatigue Lifetimes for SMT Solder Joints
Authors: Sauber J. , Seyyedi J.
Published: April 2008

A power-law type creep equation has been added to finite element models to calculate solder joint response to time, temperature, and stress level. The ability of the models to predict solder joint behavior was verified by running a series of creep tests. The models were then solved to determine the solder joint creep strains which occur during thermal cycling. These creep strains were used to predict the degradation of pull strength resulting from thermal cycling. More than 8,600 solder joints were thermally cycled and then individually pull tested to verify the accuracy of the method.
Quantitative Solder Wetting Measurement for DCA Assembly
Authors: Melton Cynthia M. , Raleigh Carl J. , Yarling Susan M.
Published: April 2008

A quantitative dynamic solder wettability measurement technique was utilized to evaluate the effects of reflow processing on the wettability parameters associated with solder ball alloys. This technique enables the examination of the final degree of solder wetting and the continuous monitoring of wetting as a function of time during the reflow process under nitrogen atmosphere. An experimental design approach employing a 24 full factorial experiment was formulated to illustrate the use of this measurement technique investigating the final result of wetting. Solder wettability was determined with respect to the contact angle, base diameter and height of the reflowed solder ball alloy. The most significant effect estimates with respect to contact angle were solder flux and pad metallization. Solder ball alloy was found to significantly impact the base diameter and height of the reflowed solder. The effect of solder flux activators and pad metallizations on the subsequent continuous solder wettability wetting rates and amount of molten solder spread of solder ball alloys during reflow were measured. Reflow with a relatively more activated solder flux material was found to enhance the rate of solder wetting of the pad metallization.
Active Air Control System Development Using Charge Air Integrated Manifold Engine Numerical Simulation (CAIMENS)
Authors: Grauer Diana K. , Chapman Kirby S. , Keshavarz Ali
Published: April 2008

This paper reports on an investigation into the transient, compressible flow physics that impact the trapped equivalence ratio. A comprehensive, variable geometry, multicylinder turbocharger-reciprocating engine computer simulation (T-RECS) has been developed to illustrate the effect of airflow imbalance on an engine. A new model, the charge air integrated manifold engine numerical simulation (CAIMENS), is a manifold flow model coupled with the T-RECS engine processor that uses an integrated set of fundamental principles to determine the crank angle-resolved pressure, temperature, burned and unburned mass fractions, and gas exchange rates for the cylinder. CAIMENS has the ability to show the transient impact of one cylinder firing on each successive cylinder. The pulsation model also describes the impact of manifold pressure drop on in-cylinder peak pressure and the pressure wave introduced to the intake manifold by uncovering the intake ports. CAIMENS provides the information necessary to quantify the impact of airflow imbalance, and allows for the visualization of the engine system before and after airflow correction. The model shows that not only does the manifold pressure drop have a significant impact on the in-cylinder peak pressure but it also has an impact on the pressure wave introduced to the intake manifold as the ports are opened. Also, each cylinder has a considerable impact on the airflow into each successive cylinder.
Confirmation of Creep and Fatigue Damage in Pb/Sn Solder Joints
Authors: Attarwala A. I. , Tien J. K. , Masada G. Y. , Dody G.
Published: April 2008

Solder joints of leadless surface mounted components, which were thermally cycled, were studied to determine their failure mode and to compare the results with work done on bulk solder specimens. Previous studies done on the characterization of the mechanical properties of cyclically tested bulk Pb/Sn solder of different compositions show that their deformation behavior is a result of an interaction between creep and fatigue damage processes. Fractographic forensics of the failed solder joints also showed damage due to both creep and fatigue processes. Fatigue striations were observed side by side with creep voids and extensive intergranular cracking. The crack growth rate (da/dn) was calculated to be around 0.25 μm/cycle. It is also established that the failure is crack propagation controlled. It was found that the crack initiation site on at least one of the joints was a tin rich area. The size of the voids varied from 0.1 μm to 0.5 μm.
Thermomechanical Fatigue Life Prediction of 63Sn/37Pb Solder
Authors: Guo Q. , Cutiongco E. C. , Keer L. M. , Fine M. E.
Published: April 2008

Isothermal and thermomechanical fatigue of 63Sn/37Pb solder is studied under total strain-controlled tests. A standard definition of failure is proposed to allow inter-laboratory comparison. Based on the suggested failure criterion, load drop per cycle, the Young’s modulus and the ratio of the maximum tensile to maximum compressive stresses remain constant, and the fatigue response of the solder is stable before failure, although cyclic softening was observed from the beginning. Experimental results of isothermal fatigue tests for a total strain range from 0.3 to 3 percent show that the log-log plot of the number of cycles to failure versus the plastic strain range has a kink at the point where the elastic strain is approximately equal to the plastic strain. In this paper, it is shown how the isothermal fatigue life of near-eutectic solder at lower strain ranges can be predicted by using the experimental data of fatigue tests at high strain ranges and early stage information of a fatigue test at the strain range in question. A thermomechanical fatigue life prediction is also given based on a dislocation pile-up model. Comparison with experimental results shows a good agreement.