bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermal Cycling Reliability and Delamination of Anisotropic Conductive Adhesives Flip Chip on Organic Substrates With Emphasis on the Thermal Deformation
Authors: Kwon Woon-Seong , Yim Myung-Jin , Paik Kyung-Wook , Ham Suk-Jin , Lee Soon-Bok
Published: June 2005

One of the most important issues whether anisotropic conductive film (ACF) interconnection technology is suitable to be used for flip chip on organic board applications is thermal cycling reliability. In this study, thermally induced deformations and warpages of ACF flip chip assemblies as a function of distance from neutral point (DNP) and ACF materials properties were investigated using in situ high sensitivity moire´ interferometry. For a nondestructive failure analysis, scanning acoustic microscopy investigation was performed for tested assemblies. To elucidate the effects of ACF material properties and DNP on the thermal cycling reliability of ACF assembly, Weibull analysis for the lifetime estimation of ACF joint was performed, and compared with thermal deformations of ACF flip chip assembly investigated by moire´ interferometry. Results indicate that the properties of ACF have a significant role in the thermal deformation and reliability performance during thermal cycling testing. Therefore, optimized ACF properties can enhance ACF package reliability during thermal cycling regime.
Development of Novel Filler Technology for No-Flow and Wafer Level Underfill Materials
Authors: Rubinsztajn Slawomir , Buckley Donald , Campbell John , Esler David , Fiveland Eric , Prabhakumar Ananth , Sherman Donna , Tonapi Sandeep
Published: June 2005

Flip chip technology is one of the fastest growing segments of electronic packaging with growth being driven by the demands such as cost reduction, increase of input/output density, package size reduction and higher operating speed requirements. Unfortunately, flip chip package design has a significant drawback related to the mismatch of coefficient of thermal expansion (CTE) between the silicon die and the organic substrate, which leads to premature failures of the package. Package reliability can be improved by the application of an underfill. In this paper, we report the development of novel underfill materials utilizing nano-filler technology, which provides a previously unobtainable balance of low CTE and good solder joint formation.
Reliability of an 1657CCGA (Ceramic Column Grid Array) Package With 95.5SN3.9AG0.6CU Lead-Free Solder Paste on PCBS (Printed Circuit Boards)
Authors: Lau John , Dauksher Walter
Published: June 2005

In many applications such as computers and telecommunications, the IC chip sizes are very big, the on-chip frequency and power dissipation are very high, and the number of chip I/Os is very large. The CCGA (ceramic column grid array) package developed by IBM is one of the best candidates for housing these kinds of chips. There are two parts in this study. One is to show that the two-parameter Weibull life distribution is adequate for modeling the thermal-fatigue life of lead-free solder joints. This is demonstrated by comparing the two-parameter and three-parameter Weibull distributions with life test data of an 1657-pin CCGA package with the 95.5 wt %Sn3.9 wt %Ag0.6 wt %Cu lead-free solder paste on lead-free printed circuit boards under thermal cycling conditions. The other part of this study is to determine the time-history creep strain energy density of the 1657-pin CCGA solder column with two different solder paste materials, namely, 95.5 wt %Sn3.9 wt %Ag0.6 wt %Cu and 63 wt %Sn37 wt %Pb and under three different thermal cycling profiles, namely, 25↔75°C, 0↔100°C, and −25↔125°C. The effects of these solder pastes and temperature conditions on the thermal-fatigue life of the high-lead (10 wt %Sn90 wt %Pb) solder columns of the CCGA package are provided and discussed.
Jet Impingement Cooling of Chips Equipped With Cylindrical Pedestal Profile Fins
Authors: Chung Y. S. , Lee D. H. , Ligrani P. M.
Published: June 2005

Surface Nusselt numbers, pressure coefficients, and flow visualizations are presented which are measured as a turbulent jet, with a fully developed velocity profile, impinges on the cylindrical pedestal and on the surrounding flat surface. Thermochromic liquid crystals and shroud-transient techniques are used to measure spatially resolved surface temperature distributions, which are used to deduce local Nusselt numbers. Dimensionless pedestal heights H/D are 0, 0.5, 1.0, and 1.5, the jet Reynolds number Re is 23,000, and the surface distance to nozzle diameter L/d ranges from 2 to 10. Local Nusselt numbers drastically increase with a radial distance away from the stagnation point on top of the pedestal for H/D values of 0.5, 1.0, and 1.5. These are partially due to the small flow recirculation zones present on top of the pedestal, and mixing associated with the separation of flow streamlines near the edge of the upper surface on the pedestal. Local Nusselt numbers are also augmented at flat surface locations corresponding to positions where shear layers reattach downstream of the pedestal. In general, augmentation magnitudes become more pronounced as H/D becomes smaller because of greater vortex influences. Corresponding local Nusselt numbers, beneath shear layer reattachment locations for H/D=0.5, are 35 to 80% higher than values measured at the same flat surface locations when no pedestals are employed.
Bottom End-Closure Design Optimization of DOT-39 Non-Refillable Refrigerant Cylinders
Authors: Kisioglu Y. , Brevick J. R. , Kinzel G. L.
Published: June 2005

This study addresses the problem of stability (standing of cylinders upright) of DOT-39 nonrefillable refrigerant cylinders using both experimental and finite element analysis (FEA) approaches. When these cylinders are designed using traditional methods they often suffer permanent volume expansion at the bottom end closure and become unstable when they are pressure tested experimentally. In this study, experimental investigations were carried out using hydrostatic pressure tests with water. In the case of numerical investigations, FEA models were developed for three-dimensional (3D) axisymmetric quasi-static conditions. The FEA models were constructed using nonhomogenous material nonlinearity and geometrical nonuniformity conditions. The results obtained from both FEA models and experimental tests were compared. To eliminate the instability of these cylinders, a design of experiment technique was employed to optimize the bottom end-closure design using the FEA models.
Determination of Conditional Probability of Dynamic Ductile Axial Crack Arrest for Conventionally-Rolled, Lower-Toughness Linepipe Materials
Authors: Rudland David L. , Wilkowski Gery M. , Kawaguchi Shinobu , Hagiwara Naoto
Published: June 2005

This paper presents an analytical procedure to predict the conditional probability of dynamic ductile axial crack arrest within one pipe joint length for pipeline materials operating at temperature above the brittle-to-ductile transition temperature. The analysis assumes there is an event to initiate a rupture with probability of one, so that the probability of a fracture event occurring is the probability of the rupture event (i.e., from mechanical damage) times the conditional probability of arrest within one pipe joint. The underlying deterministic model centers on the Battelle Two-Curve approach with a correction to predict the arrest length given the actual material toughness relative to the minimum arrest toughness. Past full-scale experimental results were used to develop statistical parameters that were used with the deterministic model in a Monte Carlo analysis. This model was calibrated for linepipe materials with a toughness less than 150J and a grade less than X65. Example cases are presented to demonstrate the variation of the probability of arrest with the pipeline operating conditions.
Plastic Loads for Internally Pressurized Toroidal Shells
Authors: Błachut J.
Published: June 2005

Tests on two internally pressurized toroidal shells are described in this paper. These were laboratory scale models manufactured by welding 90°, 316L steel elbows. The outside diameter of the toroids was about 310.0 mm, radius of the tube was about 41.0 mm, and the wall thickness was about 3.0 mm. Comparison of experimental and numerical plastic loads, based on pressure versus volume change plots, is given. The magnitude of experimentally derived plastic loads was about 16.0 MPa which was close to the numerical predictions. Both shells failed by developing cracks in welds, at nozzles, at pressure of about 33.0 MPa.
Design and Thermal Characteristics of a Synthetic Jet Ejector Heat Sink
Authors: Mahalingam Raghav , Glezer Ari
Published: June 2005

The design and thermal performance of a synthetic-air-jet-based heat sink for high-power dissipation electronics is discussed. Each fin of a plate-fin heat sink is straddled by a pair of two-dimensional synthetic jets, thereby creating a jet ejector system that entrains cool ambient air upstream of the heat sink and discharges it into the channels between the fins. The jets are created by periodic pressure variations induced in a plenum by electromagnetic actuators. The performance of the heat sink is assessed using a thermal test die encased in a heat spreader that is instrumented with a thermocouple. The case-to-ambient thermal resistance under natural convection with the heat sink is 3.15°C∕W. Forced convection with the synthetic jets enables a power dissipation of 59.2W at a case temperature of 70°C, resulting in a case-to-ambient thermal resistance of 0.76°C∕W. The synthetic-jet heat sink dissipates ∼40% more heat compared to steady flow from a ducted fan blowing air through the heat sink. The synthetic jets generate a flow rate of 4.48 CFM through the heat sink, resulting in 27.8 W/CFM and thermal effectiveness of 0.62. The effect of fin length on the thermal resistance of the heat sink is discussed. Detailed measurements on an instrumented heat sink estimate that the average heat transfer coefficients in the channel flow between the fins is 2.5 times that of a steady flow in the ducts at the same Reynolds Number.
Finite Element Analysis of Die-Strength Testing Configurations for Thin Wafers
Authors: Sun X. K. , Xin X. J. , Pei Z. J.
Published: June 2005

This paper presents an assessment of four die-strength testing configurations using finite element analysis. The simulation indicates that ring-on-ring configuration is the best because it generates a uniform stress field on a large die surface area. The four-point-bend configuration ranks second and the three-point-bend configuration is third. The pin-on-ring configuration is the worst because the stress gradient is severe in the central region. To minimize uncertainty in the loading positions, it is advised that loading rings or bars with small radii be used.
An Experimental and Numerical Study of a Liquid Mixing Device for Microsystems
Authors: Fushinobu Kazuyoshi , Nakata Masashi
Published: June 2005

A microfluidic mixing device for microsystems with electroosmotic flow (EOF)-driven liquid pumping is proposed and examined experimentally and numerically. Microchannels with SiO2 or Al2O3 wall are fabricated by using surface micromachining technique, and the EOF velocity for each microchannel is measured. A sample device where part of the SiO2 wall is covered with a patterned Al2O3 thin film is fabricated to demonstrate the proposed flow pattern change. Results of numerical calculations suggest mixing enhancement effect.
Submodeling Analysis for Path-Dependent Thermomechanical Problems
Authors: Wang Tong Hong , Lai Yi-Shao
Published: June 2005

In a finite element analysis, when localized behavior of a large model is of particular concern, generally one would refine the mesh until it captures the local solution adequately. Submodeling is an alternative way for solving this kind of problem. It provides a relatively accurate solution at a modest computational cost. For a valid submodeling analysis, the boundaries of the submodel should be sufficiently far away from local features so that St. Venant’s principle holds. Moreover, special treatments are required for solving problems that involve path-dependent characteristics. This paper presents a general procedure to perform submodeling analyses for path-dependent thermomechanical problems without a priori assumptions on the structural response. The procedure was benchmarked using a bimaterial strip and demonstrated through analyses on a bump chip carrier package assembly. The procedure is conducive to the numerical assessment of fatigue lives of electronic packages.
Yield Function for Solder Elastoviscoplastic Modeling
Authors: Dube M. , Kundu T.
Published: June 2005

Field reliability extrapolations from accelerated tests necessitate simulation of a variety of material behaviors under general loading conditions. The Hierarchical Incremental Single Surface (HiSS) yield function (Desai, C. S., 2001, Mechanics of Materials and Interfaces: The Disturbed State Concept, CRC Press, Boca Raton, FL.) has been applied extensively to a wide range of materials, from solders and silicon to ceramics and geotechnical materials, for simulating continuous-yield elastoplastic and elastoviscoplastic behavior. This work presents a continuous-yield function that avoids problems with HiSS for thermal and tensile loading. Validations are presented for eutectic Pb∕Sn data of Wang et al. (Wang, Z., Desai, C.S., and Kundu, T., 2001, “Disturbed State Constitutive Modeling and Testing of Joining Materials in Electronic Packaging,” report to NSF for Materials Processing and Manufacturing Division Grant 9812686, University of Arizona, Tucson, AZ). Limitations on the range of validity of the elastoplastic and the Perzyna elastoviscoplastic formulations are discussed.
Hygrothermal Cracking Analysis of Plastic IC Package
Authors: Yang Ji Hyuck , Lee Kang Yong
Published: June 2005

The purposes of the paper are to consider the failure phenomenon by delamination and crack when the encapsulant of plastic IC package under hygrothermal loading in the IR soldering process shows elastic and viscoelastic behaviors and to suggest the optimum design by the approaches of stress analysis and fracture mechanics. The model for analysis is the plastic Small Outline J-lead package with a dimpled diepad. On the package without a crack, the stress analysis is done and the possibility of delamination is considered. For the model fully delaminated between the chip and the dimpled diepad, J-integrals in low temperature and C(t)-integrals in high temperature are calculated for the various design variables and the fracture integrity is discussed. Finally, the optimal values of design variables to depress the delamination and crack growth in the plastic IC package are obtained.
Experimental Study of Void Formation in High-Lead Solder Joints of Flip-Chip Assemblies
Authors: Wang Daijiao , Panton Ronald L.
Published: June 2005

Understanding the formation of voids in solder joints is important for predicting the long-term reliability of solder interconnects. This paper reports experimental research on the formation of void bubbles within molten solder bumps in flip-chip connections. For flip-chip-soldered electronic components, which have small solder volume, voids can be more detrimental to reliability. A previous theory based on thermocapillary flow reveals that the direction of heating influences void formation. Using different heating profiles, 480 solder joints of flip-chip assemblies were processed. A high-lead 90Pb∕8Sn∕2Ag solder was employed in the experiments. The solder samples were microsectioned to determine the actual size or diameter of the voids. A database on sizes and locations of voids was then constructed. More defective bumps, 80%, and higher void volume were found when the solder was melted from top (flip-chip side) to bottom (test board side). The observation on cases with melting direction from bottom to top had 40% defective bumps. The results show that a single big void is near the solder bump center with a few small voids near the edge. This supports the numerical study based on the thermocapillary theory. When the melting direction was reversed, many small voids appear near the edge. Big and middle-size voids tend to stay in the middle and outer regions from top towards middle layer of the bump. This experimental finding does not completely agree with the interpretation on the formation of voids by thermocapillary theory, however, the results do show that heat flux direction plays significant role in the formation and distribution of void bubbles in molten solder.
High Temperature Corrosion of Boiler Steels Under Chlorine-Containing Surface Deposits
Authors: Klevtsov Ivan , Tallermo Harri , Bojarinova Tatjana , Crane Roger
Published: June 2005

The high-temperature corrosion resistance of several boiler steels was tested experimentally in laboratory and industrial conditions in the presence of chlorine-containing external deposits. The empirical kinetic equations for the calculation of corrosion depth, depending on operational time and temperature, were established and the dependence of corrosion resistance of the austenitic steels on the alloying elements ratio Ni–Cr was analyzed.
Coupled Nonlinear Barge Motions, Part II: Stochastic Models and Stability Analysis
Authors: Yim Solomon C. S. , Nakhata Tongchate , Huang Erick T.
Published: June 2005

A computationally efficient quasi-two-degree-of-freedom (Q2DOF) stochastic model and a stability analysis of barges in random seas are presented in this paper. Based on the deterministic 2DOF coupled roll-heave model with high-degree polynomial approximation of restoring forces and moments developed in Part I, an attempt is made to further reduce the DOF of the model for efficient stochastic stability analysis by decoupling the heave effects on roll motion, resulting in a one-degree-of-freedom (1DOF) roll-only model. Using the Markov assumption, stochastic differential equations governing the evolution of probability densities of roll-heave and roll responses for the two low-DOF models are derived via the Fokker-Planck formulation. Numerical results of roll responses for the 2DOF and 1DOF models, using direct simulation in the time domain and the path integral solution technique in the probability domain, are compared to determine the effects of neglecting the influence of heave on roll motion and assess the relative computational efforts required. It is observed that the 1DOF model is computationally very efficient and the 2DOF model response predictions are quite accurate. However, the nonlinear roll-heave coupling is found to be significant and needs to be directly taken into account, rendering the 1DOF roll-only model inadequate for practical use. The 2DOF model is impractical for long-duration real-time response computation due to the insurmountable computational effort required. By taking advantage of the observed strong correlation between measured heave and wave elevation in the experimental results, an accurate and efficient Q2DOF model is developed by expressing the heave response in the 2DOF model as a function of wave elevation, thus reducing the effective DOF to unity. This Q2DOF model is essential as it reduces the computational effort by a factor of 10−5 compared to that of the 2DOF model, thus making practical stochastic analysis possible. A stochastic stability analysis of the barge under operational and survival sea states specified by the U.S. Navy is presented using the Q2DOF model based on first passage time formulation.
CFD Analysis of Current-Induced Loads on Large Caisson at Supercritical Reynolds Number
Authors: Chakrabarti Subrata K. , Debus Kristian K. , Berkoe Jonathan , Rosendall Brigette
Published: June 2005

The newly constructed Tacoma Narrows Bridge Piers represent large concrete floating caissons during their construction. For designing their mooring system the current force applied on the caissons in the Narrows must be known. The flow field around the caisson is highly complex and the calculation of the current load on the caisson by analytical means is difficult. On the other hand, model tests suffer from the distortion in the Reynolds number. Therefore, a two-prong approach was undertaken. Besides the fixed model test of the caissons for current forces, a CFD analysis of the flow around the caisson is chosen. A three-dimensional CFD approach is considered more appropriate than a two-dimensional one, since the bottom contour at the site is irregular and water depth is rather shallow. This paper discusses the CFD method and the results obtained from such analysis. The numerical analysis was carried out in both ebb and flood flow of the tidal current in the basin. One of the difficulties of the computational method is the very high Reynolds number encountered by the large current and large size of the caisson. The analysis is performed in both model and full scales so that the difference in the results may be investigated. Also, since the model test data are available, comparisons are made between the CFD and model test results on the drag and lift forces on the caisson.
Nonlinear Free-Surface and Viscous-Internal Sloshing
Authors: Valentine Daniel T. , Frandsen Jannette B.
Published: June 2005

This paper examines free-surface and internal-pycnocline sloshing motions in two-dimensional numerical wave tanks subjected to horizontal excitation. In all of the cases studied, the rectangular tank of liquid has a width-to-depth ratio of 2. The first set of results are based on an inviscid, fully nonlinear finite difference free-surface model. The model equations are mapped from the physical domain onto a rectangular domain. Case studies at and off resonance are presented illustrating when linear theory is inadequate. The next set of results are concerned with analyzing internal waves induced by sloshing a density-stratified liquid. Nonlinear, viscous flow equations are solved. Two types of breaking are discussed. One is associated with a shear instability which causes overturning on the lee side of a wave that moves towards the center of the container; this wave is generated as the dominant sloshing mode recedes from the sidewall towards the end of the first sloshing cycle. The other is associated with the growth of a convective instability that initiates the formation of a lip of heavier fluid above lighter fluid behind the crest of the primary wave as it moves up the sidewall. The lip grows into a bore-like structure as it plunges downward. It falls downward behind the primary wave as the primary wave moves up the sidewall and ahead of the primary wave as this wave recedes from the sidewall. This breaking event occurs near the end of the first cycle of sloshing, which is initiated from a state of rest by sinusoidal forcing.
Design of Joint Angle Profiles for a Planar Five-Link Bipedal System
Authors: Wu Q. , Chan C. Y.
Published: June 2005

A set of joint angle profiles for a five-link bipedal model walking on level ground is designed. One feature of the joint angle profiles is that after an impulsive energy injection at an early stage of each step, the mechanical energy of the bipedal system remains constant for the rest of the step. This feature is of special interest in the studies of energetics of bipedal walking and can be beneficial to the design of modern energy-storing prosthetic feet. The joint angle profiles also satisfy four kinematic constraints, i.e., the walking speed, stance knee bias, upright posture of the trunk and motion coordination. To obtain acceptable gait patterns, a set of parameters is carefully tuned to satisfy extra conditions (repeatable gait, no hyperextension, and no scuffing at the swing knee). This work can provide some insight into the mechanics of bipedal walking and has potential to establish a framework for estimating the optimal energy storage of modern prosthetic feet.
Parallel Dynamics Computation and H∞ Acceleration Control of Parallel Manipulators for Acceleration Display
Authors: Yamane Katsu , Nakamura Yoshihiko , Okada Masafumi , Komine Noriaki , Yoshimoto Ken’ichi
Published: June 2005

In this paper, we propose a control scheme of parallel manipulators focusing on the accuracy of acceleration on the end plate, an important factor when parallel manipulators are used as acceleration displays such as a driving simulator. In order to achieve a smooth and accurate acceleration on the end plate, we combine two controllers: A dynamic controller to achieve accuracy of the position and to stabilize the system, and an H∞ controller to feedback the acceleration of the end plate to cope with the unmodeled dynamics such as mechanical flexibility and friction. The main problem of dynamic control is computational complexity. We applied parallel processing to reduce the latency and realized real-time dynamic control. The designed H∞ controller is added outside the closed loop of dynamic control to remove the vibration of the structure and the influence of unmodeled dynamics.
Impact Control in Hydraulic Actuators
Authors: Sekhavat P. , Wu Q. , Sepehri N.
Published: June 2005

Every manipulator contact task that begins with a transition from free motion to constraint motion may exhibit impacts that could drive the system unstable. Stabilization of manipulators during this transition is, therefore, an important issue in contact task control design. This paper presents a discontinuous controller to regulate the transition mode in hydraulic actuators. The controller, upon sensing a nonzero force, positions the actuator at the location where the force was sensed, thus, exerting minimal force on a nonmoving environment. The scheme does not require force or velocity feedback as they are difficult to measure throughout the short transition phase. Also, no knowledge about the environment or hydraulic parameters is required for control action. Due to the discontinuity of the control law, the control system is nonsmooth. First, the existence, continuation and uniqueness of Filippov’s solution to the system are proven. Next, the extension of Lyapunov stability theory to nonsmooth systems is employed to guarantee the global asymptotic convergence of the entire system’s state towards the equilibrium point. Complete dynamic characteristics of hydraulic functions and Hertz-type contact model are included in the stability analysis. Experiments are conducted to verify the practicality and effectiveness of the proposed controller. They include actuator collisions with hard and soft environments and with various approach velocities.
A Neural Network Controller for a Class of Nonlinear Non-Minimum Phase Systems with Application to a Flexible-Link Manipulator
Authors: Talebi H. A. , Patel R. V. , Khorasani K.
Published: June 2005

This paper investigates the problem of controlling a nonlinear nonminimum phase system. An output re-definition strategy is first introduced to guarantee stable zero dynamics. This output re-definition scheme is applicable to a class of open-loop stable nonlinear systems whose input–output maps contain nonlinear terms in the output and linear terms in the input. No explicit knowledge about the nonlinearities of the system is required. The nonlinearities of the system are identified by a neural network. The identified neural network model is then used in modifying the zero dynamics of the system. A stable∕anti-stable factorization is performed on the zero dynamics of the system. The new output is re-defined using the neural identifier and the stable part of the zero dynamics. A controller is then designed based on the new output whose zero dynamics are stable and can be inverted. An experimental setup of a single-link flexible manipulator is considered as a practical case study of a nonlinear nonminimum phase system. Experimental results are presented to illustrate the advantages and improved performance of the proposed tracking controller over both linear and nonlinear conventional controllers in the presence of unmodeled dynamics and parameter variations.
Robust Stability of Sequential Multi-input Multi-output Quantitative Feedback Theory Designs
Authors: Kerr Murray L. , Jayasuriya Suhada , Asokanthan Samuel F.
Published: June 2005

This paper re-examines the stability of multi-input multi-output (MIMO) control systems designed using sequential MIMO quantitative feedback theory (QFT). In order to establish the results, recursive design equations for the SISO equivalent plants employed in a sequential MIMO QFT design are established. The equations apply to sequential MIMO QFT designs in both the direct plant domain, which employs the elements of plant in the design, and the inverse plant domain, which employs the elements of the plant inverse in the design. Stability theorems that employ necessary and sufficient conditions for robust closed-loop internal stability are developed for sequential MIMO QFT designs in both domains. The theorems and design equations facilitate less conservative designs and improved design transparency.
Performance Limitation and Autotuning of Inverse Optimal PID Controller for Lagrangian Systems
Authors: Choi Youngjin , Chung Wan Kyun
Published: June 2005

The PID trajectory tracking controller for Lagrangian systems shows performance limitation imposed by inverse dynamics according to desired trajectory. Since the equilibrium point cannot be defined for the control system involving performance limitation, we define newly the quasiequilibrium region as an alternative for equilibrium point. This analysis result of performance limitation can guide us the autotuning method for PID controller. The quasiequilibrium region is used as the target performance of autotuning PID trajectory tracking controller. The autotuning law is derived from the direct adaptive control scheme, based on the extended disturbance input-to-state stability and the characteristics of performance limitation. Finally, experimental results show that the target performance can be achieved by the proposed automatic tuning method.
Distributed Parameter-Dependent Modeling and Control of Flexible Structures
Authors: Wu Fen , Yildizoglu Suat E.
Published: June 2005

In this paper, distributed parameter-dependent modeling and control approaches are proposed for flexible structures. The distributed model is motivated from distributed control design, which is advantageous in reducing control implementation cost and increasing control system reliability. This modeling approach mainly relies on a central finite difference scheme to capture the distributed nature of the flexible system. Based on the proposed distributed model, a sufficient synthesis condition for the design of a distributed output-feedback controller is presented using induced L2 norm as the performance criterion. The controller synthesis condition is formulated as linear matrix inequalities, which are convex optimization problems and can be solved efficiently using interior-point algorithms. The distributed controller inherits the same structure as the plant, which results in a localized control architecture and a simple implementation scheme. These modeling and control approaches are demonstrated on a non-uniform cantilever beam problem through simulation studies.
Acceleration-Driven-Damper (ADD): An Optimal Control Algorithm For Comfort-Oriented Semiactive Suspensions
Authors: Savaresi Sergio M. , Silani Enrico , Bittanti Sergio
Published: June 2005

The problem considered in this paper is the design and analysis of control strategies for semiactive suspensions in road vehicles. The most commonly used control framework is the well-known Sky–Hook (SH) damping. Two-state or linear approximation of the SH concept are typically implemented. The goal of this paper is to analyze the optimality of SH-based control algorithms, and to propose an innovative control strategy, named Acceleration-Driven-Damper (ADD) control. It is shown that ADD is optimal in the sense that it minimizes the vertical body acceleration (comfort objective) when no road-preview is available. This control strategy is extremely simple; it requires the same sensors of the SH algorithms, and a simple two-state controllable damper. In order to assess and to compare the closed-loop performance of the SH and ADD control strategies, both a theoretical and a numerical analysis of performance are proposed.
Failure Modes of Flip Chip Solder Joints Under High Electric Current Density
Authors: Basaran C. , Ye H. , Hopkins D. C. , Frear D. , Lin J. K.
Published: June 2005

The failure modes of flip chip solder joints under high electrical current density are studied experimentally. Three different failure modes are reported. Only one of the failure modes is caused by the combined effect of electromigration and thermomigration, where void nucleation and growth contribute to the ultimate failure of the module. The Ni under bump metallization–solder joint interface is found to be the favorite site for void nucleation and growth. The effect of pre-existing voids on the failure mechanism of a solder joint is also investigated
Creep Prediction of a Printed Wiring Board For Separable Land Grid Array Connector
Authors: Cepeda-Rizo J. , Yeh Hsien-Yang
Published: June 2005

The paper presents a study of creep behavior of a printed wiring board caused by the mechanical fastening of separable connector, known as a land grid array. Time-temperature superposition method was employed to predict the lifetime creep behavior. A low-cost testing method based on the ASTM D790 three-point bending procedure was developed to predict and characterize creep of polymeric materials under low temperature, low stress, and large elapsed times.
Snap-Curing Electrically Conductive Formulation for Solder
Replacement Applications
Authors: Mościcki Andrzej , Felba Jan , Sobierajski Tadeusz , Kudzia Józef
Published: June 2005

Pb-free soldering and the use of electrically conducive adhesives in the electronics industry are a segment of the global trend towards a lead-free environment. In comparison to lead-free solders, current commercial isotropic conductive adhesives are characterized by lower conductivity and need much more time for curing. Usually, a few minutes at 150°C are enough only for precuring. In this paper we describe the developed family of formulations with a curing time of several seconds at 150°C. There are single-component formulations, solvent-free type, prepared in a special way on the base of the common, accessible resins. They have very convenient handling properties; e.g., no drying on open screen during printing process. Viscosity depends on the resin and may be intentionally changed. Shelf life for all these formulations is about 12months at room temperature in closed containers. Refrigeration is not necessary. Unfortunately, the material needs the highest quality and purity of electronic grade silver fillers. The total permitted level of impurities is estimated as less than 10ppm. However, this is, rather, an advantage of the silver-filled adhesives.
New Dynamic Modeling of Flexible-Link Robots
Authors: Lee Ho-Hoon
Published: June 2005

This paper shows that the conventional Lagrangian modeling of flexible-link robots does not fully incorporate the bending mechanism of flexible links. The conventional link deflection model allows free link elongation in addition to link deflection; the link elongation increases as link deflection increases. The link elongation, however, causes certain degrees of modeling inaccuracy in association with the rotational motion of the links. Therefore, this paper proposes a new link deflection model, compatible with the bending mechanism of flexible links. Then a new nonlinear dynamic model is derived based on the new link deflection model, fixing the modeling inaccuracy of the conventional dynamic model.
Analysis of Surface Crack in Cylinder by Finite Element Alternating Method
Authors: Kamaya Masayuki , Nishioka Toshihisa
Published: June 2005

The finite element alternating method (FEAM), in conjunction with the finite element analysis (FEA) and the analytical solution for an elliptical crack in an infinite solid subject to arbitrary crack-face traction, is used for evaluating the stress intensity factor (SIF) of surface cracks in a cylinder. The major advantage of this method is that the SIF can be calculated by using the FEA results for an uncracked body. A newly developed system allows the FEAM to be performed by a simple method, which consists of the conventional FEA for an uncracked body and a subroutine for the FEAM alternating procedure. It is shown that the system can derive the precise SIF of circumferential, longitudinal, and inclined surface cracks in a cylinder. The crack growth predictions are performed for an inclined crack and projected longitudinal and circumferential crack in a cylinder. The results suggests that the crack characterizing procedure prescribed in Sec. XI may cause an unconservative evaluation in the crack growth prediction, and that the FEAM is valid for complex problems, to which the SIF evaluation by the FEA cannot be adopted easily.
Stress Concentration Effects in Short Cylindrical Vessels With Holes Subjected to Tension: A Complete Account
Authors: Troyani Nando , Jaimes Nelson , Sterlacci Gaetano , Gomes Carlos J.
Published: June 2005

Whenever regular geometric discontinuities are present the so called stress concentration factors concept is widely used in both analysis and design of loaded components especially when subjected to fatigue, frequently the working condition of vessels. However, recent observations suggest that the influence of member length on the magnitude of the stated factors was not considered in previous analyses. In this work, this observation was studied in the context of cylindrical vessels and it was found that in this case, as well, length could be a critical factor when computing stresses developed as a result of externally applied loads. Accordingly, the values of the finite element calculated theoretical stress concentration factors are computed, for the case of short circular cylinders with circular holes subjected to axial tension, in the context of elastic shell theory, and are presented in a fashion similar to existing published results. It is shown that significantly larger stress concentrations appear for shorter members. The transition length concept defining the threshold between long cylinders and short cylinders is discussed in the context of this study and reported as well.
10-Year Experience With T23(2.25Cr-1.6W) and T122(12Cr-0.4Mo-2W) in a Power Boiler
Authors: Komai N. , Masuyama F. , Igarashi M.
Published: June 2005

Tungsten strengthened ferritic steels, 2.25Cr-1.6W-V-Nb and 12Cr-0.4Mo-2W-V-Nb-Cu have been developed and approved by the ASME Boiler and Pressure Vessels Code Committee for use in Section I construction, designated as T23 and T122, respectively. A field exposure test installing both steel tubes in service along with comparative materials in the tertiary superheater and secondary reheater of a 156MW utility power boiler has been conducted since April 1993. The tubes were removed to confirm their material properties and corrosion/steam oxidation behaviors after 1-year, 3-year, 6-year, and 10-year periods of service. The tensile and creep rupture strengths of both steels showed no remarkable change during service. Examination of steam oxidation scale on the inner surface of the tubes indicated that the scale growth rate of T122 was extremely small following 1-year service. The growth rate and morphology of steam oxidation scale is discussed, as compared with conventional materials.
Fabrication, Construction, and Operation Problems for Grade 91 Fossil Power Components
Authors: Cohn Marvin J. , Henry Jeffrey F. , Nass Dan
Published: June 2005

The use of creep strength enhanced ferritic alloys, such as Grade 91, in fossil power plants has become popular for high temperature applications. Since Grade 91 has higher stress allowables than Grade 22, a designer can specify thinner component wall thicknesses, resulting in lower throughwall thermal stresses during transient events and lower material and pipe support costs. During the past two decades, Grade 91 has been used successfully in fossil power plants. However, this alloy has had some incidents of premature failures. Case histories discuss such factors as excessively hard material, extremely soft material, overheating failures, and improper mill processing. This compilation also discusses likely root causes and solutions to avoid these potential Grade 91 problems.
Stress Combination for Fatigue Analysis of Ship Structures
Authors: Shin Yung S. , Kim Booki , Fyfe Alexander J.
Published: June 2005

A methodology for calculating the correlation factors to combine the long-term dynamic stress components of ship structure from various loads in seas is presented. The proposed methodology is valid for a stationary ergodic narrow-banded Gaussian process. The total combined stress in short-term sea states is expressed by linear summation of the component stresses with the corresponding combination factors. This expression is proven to be mathematically exact when applied to a single random sea. The long-term total stress is similarly expressed by linear summation of component stresses with appropriate combination factors. The stress components considered here are due to wave-induced vertical bending moment, wave-induced horizontal bending moment, external wave pressure, and internal tank pressure. For application, the stress combination factors are calculated for longitudinal stiffeners in midship cargo and ballast tanks of a crude oil tanker. It is found that the combination factors strongly depend on wave heading and period in the short-term sea states. It is also found that the combination factors are not sensitive to the selected probability of exceedance level of the stress in the long-term sense.
Enhancing Damping of Aluminium Using SiC and∕or Ge
Authors: Srikanth Narasimalu , Gupta Manoj
Published: June 2005

Metallic material with enhanced stiffness and damping characteristics is actively sought in the design of dynamic mechanical systems for mechanical components. Germanium is known to remain distinct in an aluminium matrix without forming any intermetallic phases. The effect of the presence of germanium particles in the aluminium matrix is of interest and can be studied in terms of variation in overall damping property, which signifies the internal friction arising at the matrix-particle interface. Damping was measured using an impact-based vibration measurement of a suspended beam coupled with circle-fit approach. Results showed the presence of 1.9 vol. % of Ge in the Al matrix increases the damping capacity by 46% compared to pure Al which is equal to the improvement offered by the presence of 10.2 vol. % of SiC particulates. The present work also extends the study of the additional reinforcement rendered by the presence of SiC particulates along with Ge particulates. The experimental observation of this enhancement in damping characteristics has been rationalized in terms of the microstructural changes such as the presence of plastic zones at the matrix-reinforcement interface.
Thermomechanical Fatigue Behavior of a Directionally Solidified Ni-Base Superalloy
Authors: Shenoy M. M. , Gordon A. P. , McDowell D. L. , Neu R. W.
Published: June 2005

A continuum crystal plasticity model is used to simulate the material behavior of a directionally solidified Ni-base superalloy, DS GTD-111, in the longitudinal and transverse orientations. Isothermal uniaxial fatigue tests with hold times and creep tests are conducted at temperatures ranging from room temperature (RT) to 1038°C to characterize the deformation response. The constitutive model is implemented as a User MATerial subroutine (UMAT) in ABAQUS (2003, Hibbitt, Karlsson, and Sorensen, Inc., Providence, RI, v6.3) and a parameter estimation scheme is developed to obtain the material constants. Both in-phase and out-of-phase thermo-mechanical fatigue tests are conducted. A physically based model is developed for correlating crack initiation life based on the experimental life data and predictions are made using the crack initiation model.
A Mechanistic Approach to Matrix Cracking Coupled with Fiber–Matrix Debonding in Short-Fiber Composites
Authors: Nguyen Ba Nghiep , Tucker Brian J. , Khaleel Mohammad A.
Published: June 2005

A micro–macro mechanistic approach to damage in short-fiber composites is developed in this paper. At the microscale, a reference aligned fiber composite is considered for the analysis of the damage mechanisms such as matrix cracking and fiber–matrix debonding using the modified Mori–Tanaka model. The associated damage variables are defined, and the stiffness reduction law dependent on these variables is established. The stiffness of a random fiber composite containing random matrix microcracks and imperfect interfaces is then obtained from that of the reference composite, which is averaged over all possible orientations and weighted by an orientation distribution function. The macroscopic response is determined using a continuum damage mechanics approach and finite element analysis. Final failure resulting from saturation of matrix microcracks, fiber pull-out and breakage is modeled by a vanishing element technique. The model is validated using the experimental results found in literature as well as the results obtained for a random chopped fiber glass–vinyl ester system. Acoustic emission techniques were used to quantify the amount and type of damage during quasi-static testing.
Optimizing the Ogden Strain Energy Expression of Rubber Materials
Authors: Beda T.
Published: June 2005

The Ogden strain energy expression is expanded to an optimal number of terms characterizing materials to predict any response of any mode of deformation well. The effect of each term generating the model is highlighted in the corresponding state of deformation, i.e., influence domain: Moderate stretch, transition, or stiffening region, with the help of the proposed method.
Localized Necking Criterion for Strain-Softening Materials
Authors: Chow C. L. , Jie M. , Wu X.
Published: June 2005

The paper presents the development of a localized necking criterion based on the singularity of acoustic tensor. This criterion is applicable to materials exhibiting strain-softening behavior. The tensor form of the criterion is deployed in simple mathematical expressions, based on which the forming limit diagrams (FLDs) of strain-softening materials can be determined. At the left-hand side of a FLD, or the negative strain ratio region, a closed-form expression of localized band inclination is derived as a function of the strain-ratio value. At the right-hand side of a FLD, or the positive strain ratio regions, the localized band is assumed to be perpendicular to major strain according to the MK [Marciniak and Kuczynski (1967)] model. On both sides of the FLD, the localized necking criteria are analytically expressed by elements of tangent modulus matrix. For the sake of illustration of the proposed criterion, a special case of localized necking employing associative and isotropic plasticity is presented. The material chosen for the illustration is AA-6061 at an elevated temperature. The proposed criterion is also applicable to the formability of other metals at high temperatures and other strain-softening materials such as rocks.
Fatigue Crack Identification in Tensile-Shear Spot Welded Joints by Dynamic Response Characteristics
Authors: Wang G. , Barkey M. E.
Published: June 2005

A theoretical model for the estimation of fatigue crack length of tensile-shear spot welded specimen is developed which incorporates the natural frequency and mode variation. The model is based on the concept that the propagation of cracks causes a release of strain energy, which is related to the structural modal shape. The effect of the structural mode shape and crack location is also explained. The model, experimental, and finite element results indicate that the existence of cracks cause the reduction of natural frequencies and change of natural modes, and that the mode shape of the structure and crack location will affect the magnitude of the change of these dynamic variables. The predictions of the model are compared with the experimental data and finite element analysis results and agreement is found to be consistent.