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Interlaminar stresses near the free edge of a multi-layered structure under thermal and mechanical loads are significantly affected by nonlinear and inelastic material properties. Most previous studies of the subject ignored such effects and obtained singular or extremely severe and localized stress fields in boundary regions based strictly on the assumption of linearly elastic stress-strain relation. In the present paper, a variational method, using approximate stress functions and the principle of complementary energy, is developed to study the thermal stress in a three-layer beam including a thin, compliant, non-linearly elastic middle layer. It is found that the elastic softening behavior of the thin layer results in dispersion of the interlaminar stresses and widening of the boundary region. Hence the use of toughened, compliant bonding layers may produce a beneficial effect by alleviating local concentration of interlaminar stresses.

Leadless chip resistors (LCR) made by two different manufacturers and surface mounted on glass/epoxy printed circuit board (PCB) were subjected to thermal cycling between -55 [degrees] C to 125 [degrees] C in order to induce thermal fatigue failure/damage. The test units were subjected to a maximum of 250 thermal cycles. Solder joints in both types of LCRs were examined in scanning electron microscope and a relative comparison of the extent of fatigue damage is presented. The failure mechanism is associated with cracking in the eutectic composition Sn/Pb solder initiated at the stress concentration sites. A nonlinear, time-dependent finite element modeling analysis has been performed to determine critical stress concentration sites in the solder joint. Key parameters leading to the initiation of solder damage are identified, and recommendations are made to improve the design in terms of solder configuration such as the radius of corner of the alumina substrate and the standoff height.

Long-term reliability of electronic packaging has become a greater challenge as a result of ever increasing power requirements and the decreasing size of electronic packages. In this study, the effects of three variables on plated-through hole (PTH) design have been investigated on the thermal cycling fatigue lives in four-layered printed wiring boards (PWB's). These three variables were evaluated at two levels each: (a) hole size (0.030 and 0.040 in.), (b) internal pad (presence or absence), and (c) epoxy-plugged holes (plugged or unplugged). The electrical resistance was measured on 40 test boards with [2.sup.3] design of 8 daisy-chain PTH nets each. Full factorial analysis and analysis of variance indicate that all three factors had significant influence on PTH fatigue life, but no two-factor or three-factor interactions were found. Metallurgical analysis reveals that the failure mechanism is barrel cracking near the internal pad. This mechanism has been illustrated by a finite element analysis in this study and correlated by a SEM stereoimaging analysis in the literature. The increase of electrical resistance with thermal cycles correlates well with an analytical barrel crack model. The crack length in each net at specific cycles is calculated, but fails to match predictions from a fracture mechanics model.

This paper summarizes the results of a study of the tribological behavior of ceramic materials in unlubricated oscillating/fretting contact with particular emphasis on frictionally-generated surface temperatures. The study was carried out using an oscillating contact device coupled to an infrared microscope. The contact geometry consists of a stationary spherical specimen loaded against a thin sapphire optical flat driven by an electromagnetic shaker. With this system, measurements can be made of friction, wear, and surface temperature over a wide range of loads, frequencies, and vibration amplitudes. Four ceramic materials were investigated, namely zirconium oxide (zirconia), tungsten carbide, and two different forms of aluminum oxide (alumina and sapphire). The first important finding was that each material exhibited unique and characteristic tribological behavior. Instantaneous variations in friction and surface temperature occurring within a single cycle of oscillation (e.g., in less than 0.005 seconds) could readily be measured with this technique. By digitizing the surface temperature, friction, and velocity signals, comparisons are made in the time and frequency domains. Frequency content correlations are determined using Fourier transform techniques. In addition, instantaneous frictional heat generation rates are calculated using the digitized friction and velocity data. Based on a series of experiments at constant oscillation frequency and amplitude, a correlation appears to exist between wear and surface temperature for the ceramics studied. Sapphire-on-sapphire and zirconia-on-sapphire produced the highest wear and the highest surface temperature rises (ca. 130-140 K). Tungsten carbide-on-sapphire produced the lowest wear and lowest surface temperature rise, while alumina exhibited intermediate behavior. In all cases, the rate of frictional heat generation was relatively low. It may be that the rapid fluctuations in surface temperature under these conditions--with two major temperature peaks per cycle--could lead to a kind of thermal stress fatigue of the ceramics as a wear mechanism. The use of the IR microscope in the scanning mode, coupled with scanning electron microscopy O' the wear scars and theoretical treatment of sub-divided areas, can shed light on the nature and distribution of real areas of contact.

This paper describes the concept of a three-dimensional histogram used for the statistical interpretation of randomly varying harmonics. The new method is based on the measurement of the time duration of each harmonic value. This idea is consistent with the existing instrumentation technology and can enhance the effectiveness of real-time data acquisition to determine the effect and the limits of voltage and current distortions.

A model to predict the temperature-induced added loss in dual-coated optical fibers is presented. Longitudinal and lateral temperature-induced forces, originating from fiber irregularities and from the mismatch among the expansion coefficients of the glass fiber and of the coatings, are consistently included in the model. Both the bendings of the glass fiber and of the coating are considered. Transmission losses are explicitly computed according to Petermann's theory on the microbending of single-mode fibers.

A new method is presented to compute the mechanical compliance and thermal stress in surface mount leads of arbitrary shape. It involves expressing the profile polynomially by a computer-generated spline curve, and numerically integrating the generalized Castigliano formulas. Comparisons to data in the literature, generated by standard analytical and experimental techniques, show excellent agreement. An example is presented to show typical results obtainable by using the model.

The paper considers the distribution of temperature and thermal stresses in a bilayer slab which consists of a substrate and a thin coating subjected to a local short heat pulse. The heat source is distributed uniformly over a circular spot on a surface of the coating. The temperature and thermal stresses distributions in a slab are found analytically in a closed form using Laplace and Hankel integration transforms. The analytic relation is obtained for the evaluation of components of stress tensor in a coating as a function of a Fourier number and radius of heat source.

The out-of-plane displacement field around two plated holes with different pad diameters in an FR-4 printed wiring board was measured for a single 30 degrees C-210 degrees C-30 degrees C temperature cycle using electro-optic holographic interferometry. At the end of the temperature cycle, the outside edge of the pad was raised above the level of the laminate and the inside edge was depressed below the level of the laminate. This indicates that the barrel is plastically deformed in compression to a total strain of approximately 0.58-0.66 percent which is well above typical yield strains of 0.2 percent. The smaller diameter pad was inclined more than the large diameter pad, but the residual compressive strain in the barrel was roughly the same. Both the residual compressive strain and the inward inclination of the pad are in conflict with the predictions of most finite element models of plated hole deformation. However, there were cracks at the pad-barrel interface which are not included in finite element models. The residual compressive deformation of the barrel is attributed to inelastic deformation of the FR-4 matrix at the high end of the thermal cycle. The stress in the barrel was estimated using an approximate elastic analysis of pad deflections. The estimated stress for different hole diameters for the same pad diameter was roughly proportional to the ratio of their barrel plating cross-sectional areas for a 30-150 degrees C temperature change. The elastic analysis is shown to predict (unrealistic) tensile barrel stresses at the end of the full temperature cycle.

Thin film morphological variations such as formation of hillocks, whiskers, voids and pits, which influence electronic device reliability, are caused by thermal stresses. An analytical theory developed with natural simplifying assumptions aids the physical study of thermal stress in thin films. The assumptions include thermoelastic, thermoelastic-plastic behavior of various substances of thin films.

A time-dependent thermal compressible elastohydrodynamic lubrication of line contact model has been developed to investigate the effects of a single bump or dent in heavily loaded rolling/sliding contacts. The results illustrate the transient behavior of the film thickness, pressure and temperature distributions as a bump or a dent travels through the contact. The multigrid multilevel technique was used to simultaneously solve the discretized time dependent Reynolds, elasticity and energy equations. The effects of various loads and speeds have been investigated. Results are presented for the nondimensional loads of W = 1.3 X 10 to the -4, 2.3 X 10 to the -4 and nondimensional speeds ranging from U = 1 X 10 to the -11 to U = 10 to the -10 under pure rolling and rolling/sliding conditions.

A general solution was applied to the hygrothermoelastic interface problem with discontinuity between dissimilar anisotropic media to show that the hygrothermal stress had an identical trig-log character as those derived for the elastic problem. The heat or moisture flux revealed an inverse square-root singularity. Hygrothermal stress which is due to heat flow and moisture concentration transfer causes material failure when it becomes singular at the discontinuity.

An analysis of tunneling cracks in constrained layers reveal that a thin, brittle layer bonded between tougher substrates is vulnerable to cracking under residual and applied stresses. The crack begins from an 'equi-axed flaw' confined by the tunneling of the substrates in the brittle layer. The energy release rate at the front of a steady-state tunnel is computed using plane strain fields.

Buried pipelines operating at elevated temperatures experience high longitudinal compressive stresses because the surrounding soil prevents thermal expansion. At high operating temperatures, buried pipelines can push through the soil at bends and buckle catastrophically. In soft soils they can lose lateral stability, and they can develop plastic failures. Thermally induced problems can be prevented with varying degrees of success by using thicker wall pipe, higher strength steel, longer radius bends, deeper burial, better backfill compaction, and/or prestressing during construction. Prestressing is most appropriate for pipelines operating at temperatures more than 80 degrees C above ambient. One technique for prestressing a buried pipeline, that has been found to be both easy and economical for a liquid sulphur pipeline in Alberta, is to heat it with hot air and bury it while it is still hot. Pipe diameter and prestressing temperature both have a significant impact on the kind of heating equipment that is required.

Polymer concrete (PC) has been widely used for floor and bridge overlays, but because of the differences in the coefficients of thermal expansion between Portland-cement concrete (PCC) and PC, there is concern about possible delamination at the interface. This paper is a report of the results of two experimental studies. The first was an investigation of crack propagation, stiffness deterioration, and delamination of PC-PCC composite members subjected to load cycles at room temperature. The second was an investigation of the interface shear stresses and longitudinal normal stresses of PC-PCC beams under various uniform thermal loads ranging from approximately 3 degrees F (16 degrees C) to 140 degrees F (60 degrees C). A hypothesis of the thermal phase was that interface shear stresses are localized near the ends of the beams. It was observed that: (1) Test beams survived 2,000,000 load cycles without delamination and without significant loss of stiffness; (2) interface shear stresses are end bound; and (3) the effective length of the end zone in which shear stresses are concentrated is approximately equal to the depth of the composite member.

A fundamentally based chemical-thermodynamic multifactor stress aging functional relation requiring experimentally based constants is developed, based upon various theoretical models. The specific example presented is that for 120 V aromatic polyimide insulated wire. The stresses of water, temperature, and mechanical strain are included and electrical stress is considered. The results of over 2000 specimens are fitted to the theoretical trends. For a single independent variable function, the resulting relation reduces to the classical Arrhenius curve. The three independent variable relations presented here is applied to data from laboratory aging experiments that simulate insulation deterioration occurring in actual aircraft service experience. The results used in age categorization of US Navy aircraft are generated from wire specimens taken from active aircraft. The paradigm does not use ab initio based constants because of uncertainties in the theoretical development, two forms of which are presented. It is the aim of this presentation to provide a plausible, intuitively meaningful syllogism having elements transferable to other insulation materials/devices/systems. That transfer will require proper recognition of specific chemical mechanisms in the life calculation routine, constrained by practical secondary effects and the need of nonstandard statistics.

Testing of thermal resistance of masonry walls is very expensive and can be accomplished only on fabricated blocks. Manufacturers and designers thus need a reliable tool for the prediction of the r-values before producing forms. The paper compares results obtained by the two common simplified computation methods with those derived from a more-accurate three-dimensional (30) finite-difference thermal analysis. The paper shows that the method of combined parallel heat-flow paths yields a better approximation to the accurate analysis than the method of series of layers perpendicular to the main heat flow. Theoretical results are also compared to data from test measurements of 18 hollow-core blocks with side indentations and two other blocks. Computations overestimate the measured values by up to 20%. Since measurements have their own inaccuracies and uncertainties, it is concluded that a reliable conservative value can be obtained by reducing the values estimated with the 3D method by 20%.

Thermal effects have been frequently associated with concrete-bridge damage. The nonlinear temperature distributions that arise in bridges are not easily estimated and are often considered in a simplified way, which may lead to structural behavior problems. In the present paper, a discussion of current design-code provisions is referred to and an approach studied in Southwest Europe is presented. The estimation of the temperature distributions considers a numerical technique for the resolution of the Fourier heat-transfer equation and its associated boundary conditions. This technique is based on the finite-element method and takes into account the geometry of the bridge cross section, the thermal properties of concrete and asphalt, the location of the bridge, and the climatic conditions. The results of a parametric study developed to evaluate design thermal vertical differences for typical concrete bridge sections are presented. The numerical technique is also applied to the analysis of special cases in which an accurate estimation of thermal effects is necessary.

A first-order perturbation study was conducted on three-dimensional transient interlaminar thermal stresses of a symmetric composite laminate. The solution of thick laminate requires the first-order study, as suggested by the numerical findings for a four-layer angle-ply laminate. The zeroth-order perturbation solution is precise solely in the case of thin laminate. The pressure of singular behavior of free-edge stresses is an area of ambivalence.

The thermal stability of InGaAs/InGaAsP quantum wells was investigated by analyzing the influence of interdiffusion on the photoluminescence and Raman spectra. A blue shift which cannot be attributed solely to intermixing of the cationic species was observed. The structures remained lattice matched after annealing in the temperature range of 650 to 750 degres celsius. Thermal stability was observed up to a temperature of 650 degrees celsius.

We have detailed the effects of annealing and temperature on the residual microstress at the matrix interface in rubber-filled and glass bead-filled epoxy resin systems. We found that annealing renders changes in residual microstress. The closer the annealing temperature to the glass transition temperature of the sample, the more pronounced the annealing effect on the stress. Also, we examined the interfacial residual microstress and found a linear relationship with annealing temperature. A description of the mechanism of the interfacial microstress buildup is proposed.

A thermohydrodynamic (THD) analysis is introduced for calculation of the performance characteristics of cryogenic liquid annular seals in the turbulent flow regime. A full-inertial bulk-flow model is advanced for momentum conservation and energy transport. The liquid material properties depend on the local absolute pressure and temperature. Heat flow to the rotor and stator is modeled by bulk-flow heat transfer coefficients. An approximate analytical solution is obtained to the governing equations when the seal operates at a steady-state and concentric condition. The temperature-rise in the fluid film of a cryogenic liquid seal is found to be composed of four sources due to viscous dissipation, pressure extrusion work, surface heat transfer and kinetic energy variation. For incompressible adiabatic flows, the fluid temperature rises linearly along the axial direction. The approximate analytical solution provides a useful tool for preliminary design and a better understanding of seal performance. Full numerical predictions of load, leakage, temperature, and rotordynamic coefficients for a high speed liquid oxygen seal are given in Part II to show the importance of thermal effects on seal performance. The accuracy of the approximate concentric seal analysis is then demonstrated by comparison to the results from the full numerical solution.

In this paper dealing with the tilting pad journal bearing, experimental results are presented which show that, at higher shaft speeds, the leading-edge-groove (LEG) design has significantly lower operating temperatures to those of the conventional design of tilting pad journal bearing. Subsequent theoretical analysis has shown that this reduction in pad operating temperature is the result of feeding cool oil directly to the leading edge of the pad. This has the effect of reducing the amount of hot oil carried over from one pad to the next.

The magnetic and thermal characteristics of Fe-Zr-Co/Fe-Zr-Co-N multilayered thin films prepared by sputtering and electron cyclotron resonance plasma nitridation were investigated. The results showed that the incorporation of Co to the material dramatically increased its magnetic properties. The soft magnetic properties of the material exhibited excellent stability under heat treatment.

Experiments were performed to determine the degradation of acetate, propionate, and butyrate, and the maximum methanogenic activity of granular sludge from the thermophilic anaerobic digestion (55 degrees C) of pure molasses under shock temperature conditions. The compositions of acetate, propionate, and butyrate that were used as substrates were 25:35:40, respectively. On two duplicate batch reactors (I and II) running in parallel and at a pH of 7, the tests were performed at 63 degrees C during the first volatile fatty acid (VFA) addition (first feeding or first experiment) and at 55 degrees C after the second VFA addition. During the first and second VFA additions, there was a lag phase. In the first experiment, by the end of 160 hours, after the initial concentrations of butyrate and acetate had been completely degraded, only 35-55% of the initial concentration of propionate was converted to acetate. The maximum methanogenic activities of the first feeding were not high because the population of propionate degrading bacteria was low and these bacteria were negatively affected from the shock temperature changes. In the second experiment, with the same sludge, the maximum methanogenic activities on second VFA additions were about 1.3 times higher than those of the first VFA additions. This increase may be due to a faster adaptation of the sludge and an increase of the population of the propionate degrading bacteria as a result of returning to the optimum temperature conditions.

An approximate thermal contact conductance correlation which does not depend upon the surface asperity slope was developed. Published surface texture data for 65 specimens were used to establish a relationship between the average roughness and the RMS asperity slope, which was then used to develop a new approximate thermal contact conductance correlation. The investigation was conducted for a range of surface roughness typical of contacting surfaces. Comparison to limited test data and to 2080 simulated contact joints, indicates the new approximate thermal contact conductance correlation has an expected RMS error of approximately 23 percent.

During normal power cycling of the electronic equipment, the differing coefficients of thermal expansion result in differential elongations. Because each level of packaging is subject to mounting constraints, the differential strains result in bending and shear stresses. Repeated duty cycling can cause fatigue at joints, at interfaces between different materials, at interconnection locations, or cause delamination of composite materials. Accelerated Thermal Cycling (ATC) is done to simulate the fatigue failures that may arise because of this power cycling. The current practice is to determine ATC stresses by assuming that the temperatures of various layers are equal and constant. In this study, we have relaxed the isothermal assumption and we provide results for thermal stresses and strains in a first level package. This is accomplished by accurately determining the transient temperature fields in various layers of the package. Temperature variations for different heat transfer coefficients have also been calculated. The results indicate that realistic estimates of thermal stresses and strains are only possible with models that allow for temperature variation in the body of the package. High equivalent stress values are obtained at the chip-heat sink interface and in the bumps connecting the leads to the chip.

Solder is being extensively used in electronic packages for both electrical and mechanical connection. Solder joints are subjected to severe operating conditions and hence their reliability is very critical for the packages. Simulation is very effective for understanding, predicting and design improvement of electronic packages where solder is the prime joiner, however all the material response complexities of solder over the temperature regime it is subjected to should be modelled. Solder in electronic components very often operates at 0.6 to 0.8 times it's melting point. In this regime the time dependent material response (creep and stress relaxation) is very significant and can no longer be ignored. Also the plastic and creep responses of solder alloys have a very strong dependence on temperature. A nonlinear finite element based methodology has been developed for simulation of solder alloy over its full regime of material behavior, also accounting for the strong temperature dependence. This includes elastic, time independent plastic, and time dependent viscoplastic response. The methodology has been used for predicting the response of a flip chip with 95Pb5 percent Sn peripheral bumps subjected to thermal cycling. Correlation is observed between the location of failure in the bump and the maximum inelastic strain. The importance of doing a multicycle simulation is demonstrated and a direction is indicated for the bump size modification for flip chip bump design improvements for greater reliability.

The thermally-induced transformation of retained austenite in carburized steels is studied. Experiments are conducted wherein heat-treated smooth fatigue specimens are subjected to axial and diametral strains using a uniaxial 89-kN ATS Long Term Fatigue Machine connected to a SoMat Model 1100 Test Control and Data Acquisition System. Results indicate that the transformation rate is linear with time and highly dependent on the hydrostaticstress.

The thermal stresses in a ceramic coating bonded to a metal substrate generated by heat flux conditions in an engine were studied. Edge delamination of the coating was related to the displacements of an interface crack between the ceramic and the metal. The effects of varying the thermal expansion coefficients of the ceramic, the bond coat and the metal, thin moduli of elasticity, their thicknesses and the initial stress-free temperature were determined.

The thermal stresses in a metallic thin film bonded to a ceramic coating on a metal substrate, generated by heat flux conditions in an engine, were studied. The film yields as a result of differential contraction and its thermo-plastic behavior is determined. Edge delamination of the film is related to the displacements of an interface edge crack between the film and ceramic. The effects of varying the surface roughness of the interface, the thickness of the film, the film material, the thermal expansion coefficients and the moduli of elasticity of the ceramic and metal on the stresses in the film and the crack are studied.

For investigating the origin of residual stresses in welded joints, the transient thermal stresses in a carbon-manganese-silicon steel (JIS SM41B), a cast martensitic stainless steel (JIS SCS5), an austenitic stainless steel (JIS SUS304), and a titanium alloy (Ti-6Al-4V) were investigated by subjecting round bar specimens, in which both ends were fixed, to thermal of cycles. The specimens were heated in air by high-frequency induction. The cyclic thermal straining tests were conducted for the case of a single thermal cycle and the case of multiple thermal cycles, using a closed-loop, servo-controlled testing machine. The experimental results made clear that the transient thermal stress behavior was dependent on metallurgical effects, such as phase transformations, strain hardening, the Bauschinger effect, etc. The effects on phase transformation on the transient thermal stress behavior of SCS5 and SM41B were especially remarkable. However, the effects of phase transformations on the residual stresses due to the thermal straining cycle were negligible in SM41B and not observed in both SUS304 and Ti-6Al-4V. The residual stresses tended to increase with increase of the peak temperature of thermal cycles in SM41B, SUS304 and Ti-6Al-4V. However, when the peak temperature increased above 600 degrees C in SCS5, the residual stress rapidly decreased and became compressive because of the expansion due to the martensite transformation. This study led to the conclusion that the transient thermal stresses for various peak temperatures could easily be obtained by an incremental step test using a single specimen and that this incremental step test could simply estimate the residual stress character of butt-welded joints.

Sandwich panels made of thin skins and a lightweight core expand and/or bow when subjected to temperature changes. The significance of induced thermal stresses in the panels depends on material properties. The effects of bonding layers on these stresses were not investigated in available works on the structural analysis of sandwich panels. This paper presents elasticity solutions for thermal stresses in sandwich panels with interlayer slip. The effects of finite bonding stiffnesses on the structural behavior of the panels are investigated. The numerical results show that the bonding stiffness, up to a certain level, has a strong effect on panel structural response. The answer to what constitutes perfect bonding is best answered in terms of the ratio of the core stiffness to the bonding stiffness. A heat chamber is designed and used to test sandwich specimens under different temperature changes. The experimental values for normal stresses in the skins are in good agreement with the present theory.

The finite element method is proposed as a method to solve for the thermal stresses in passivated and unpassivated lines. Results show that increases in unpassivated line stresses are in direct proportion to increases in linewidth and substrate rigidity. On the other hand, increases in passivated line stresses are inversely dependent on linewidth decreases as these approach a square cross section.

A proposed method in predicting solder joints' fatigue life is based on fracture mechanics and performs well in simulation tests. Results show that, for the cases studied, an n = 3 stress exponent is appropriate. A time-dependent plastic strain introduced into the constitutive equation contributes to 20-30% of the overall strain and to the increase of fatigue cracks. The suggested failure standards used in the study is shown to be conservative although conform well with theoretical predictions.

X-ray scattering and Raman spectroscopy were used to investigate the atomic structure and thermal stability of W/C multilayers formed by magnetron sputtering. The results showed that a WC interface compound was formed during the multilayer deposition. The multilayers exhibited better stability at high temperatures and less period expansion. Carbon in the multilayer was observed to be more graphitized.

The effect of thermal stresses on optical fibers was studied at low temperatures since optical fiber packaging was found to cause thermal expansion mismatch between the glass and coating materials. Results of the study show that thermal bending loss is avoided when the Young's modulus of primary coating is increased and that of the secondary coating reduced when the thickness of the polymeric coatings is increased.

In the cooldown phase of the deposition process, plasma-sprayed ceramic barrier coatings generate large residual stresses. In this paper, a scheme for the analysis of the thermal stresses is given, which accounts for the nonuniformity of the temperature field, and for the microstructure of the coating. The considered microstructural data include the morphology and orientation pattern of the porosities. The case of a coated sphere is studied, as an application. In this connection, the coating structure is computer-simulated, and the temperature profile is numerically determined.

The isothermal fatigue of the interconnections between a leaded chip carrier (LCC) and a printed wiring board (PWB) is studied. An LCC connected to a PWB by tin-based solder joints was subjected to simulated thermal cycling displacements at varying temperature levels. The electrical resistance of the solder specimens were also measured and recorded. It was found that high cycling frequency improved the fatigue life and reduced the hysteresis load of the specimen.

The characteristics of a high pin count plastic-quad-flat-pack (PQFP) finite element model is discussed. The PQFP three-dimensional model was developed to provide a systematic integrated circuit package analysis technique. It is capable of analyzing different thermomechanical stresses and thermal characterization experienced by the package under various manufacturing and testing conditions, such as thermal cycling and forced air cooling. These features make PQFP a very useful tool in electronic packaging systems.

A method for determining the interlaminar thermal stresses in laminated multi-layered beams under varying temperature levels is discussed. Thermal expansion in every beam layer is calculated using high-order polynomial expansions of the stress functions in conjunction with a computer program. This technique can be very useful in analyzing the thermal expansion behavior of multi-layered beams with the least amount of effort.

The influence of the bonding layer thickness of multi-layered electronic components on thermal stresses is studied. Since solder and adhesive materials are commonly used in the fabrication of electronic components, their effects on the components' performance were investigated. The alternating technique was applied on a three-layer composite strip to determine the material's thermal stress distribution with regard to its dimension. It was found that solder joint dimension has significant effects on the edge stress value.

A technique for measuring the mechanical behavior of high lead lead-tin solder joints under varying temperature levels was evaluated. Solder joint specimen were fabricated using different kinds of alpha metals and their initial characteristics were analyzed by shear and strain equations. The specimen were then subjected to various temperature profiles using a laboratory thermal chamber and their behavioral change was studied. Results indicate that the technique can be useful in investigating the thermomechanical characteristics of different kinds of alloys and related materials.

The isothermal and thermomechanical fatigue characteristics of 63Sn/37Pb solder are studied. Since solder joints undergo thermomechanical stresses during actual operation, it is important to determine the effects of such stresses. Solder specimen were subjected to isothermal and thermomechanical tests under varying temperature levels and their fatigue lives were calculated through numerical approaches. Results reveal that grain boundary is the main cause of 63Sn/37Pb solder failures.

A thermosolid mechanics analysis based on sound thermodynamic and mechanical principles is derived for a thermoelastic solid in which the elastic coefficient is temperature-dependent, and thus the TEC (thermal expansion coefficient) must be stress-dependent. The theory is applied to the case of slender elastic members with full axial restraint and subjected to a uniform increase in temperature. Numerical results are presented for a wide range of materials and slenderness ratios.

Studies were made on the thermal shock resistance of flat packages (FP) to determine the correlations among thermal stress, polymer strength and median life. FP from a composite of different epoxy molding compounds were used to test thermal shock resistance. Results of the study indicated that when glass transition temperature, coefficient of linear expansion and modulus of elasticity values decrease, the median life to crack initiation increases. Median life depends on the cross-sectional areas of the FP and the lead frame, and is directly proportional to polymer strength.

The consumption of hot-fillable poly(ethylene terephthalate) bottles is extremely large and is still increasing in Japan. This type of bottle is generally manufactured by the heat-set method using hot molds after stretch-blow molding. In this study, the method is simulated using a setting application in which sheets can be stretched constraining their sizes on a hot aluminum block. The crystallinities of the sheets are found to depend on the thermal history, i.e., the duration and temperature of the heat-set cycle. Heat-setting mitigates thermal-shrinkage of the sheets which is due to the increase in crystallinity or in the tense segments in the amorphous region. The structure of the heat-set sheet varies depending on the original stretched sheet. For a sample of low draw ratio, the crystallinity does not increase because of the heat-set. For a sample of medium draw ratio, the crystallinity increases greatly and the tense segments in the amorphous region also increase because of heat-set. For a sample of high draw ratio, the crystallinity increases a little but the numbers of the crystallite and tense segments in the amorphous region do not change with the heat-set., The structural changes and reasons behind a decreased thermal shrinkage of polyethylene terephthalate (PET) sheets during heat-setting is investigated. Stretched PET sheets are heated on a heat-setting apparatus. Results show that the decreased thermal shrinkage is attributed to crystallinity. As the heat-set temperature increases, crystallinity increases and thermal shrinkage is decreased. Crystallinity depended on the draw ratio, molecular orientation and the heat-set or non-heat set of the sheets.

The thermal stability characteristics of four kerosine-type fuels are examined using a heated-tube apparatus that allows independent control of fuel pressure, fuel temperature, tube-wall temperature, and fuel flow rate. It is a closed loop system, and fuel flows through the heated tube for periods ranging from 6 to 22 h. The deposition rates of carbon on the tube walls are measured by weighing the tube before and after each test. The results obtained show that tube-wall and fuel temperatures both have a marked influence on deposition rates, the impact of fuel temperature being stronger than that of wall temperature. It is also found that deposition rates increase continuously with increases in tube-wall temperature. This finding contradicts the results of previous studies, which had led to the conclusion that deposition rates increase with increase in wall temperature up to a certain value, beyond which any further increase in wall temperature causes the deposition rate to decline., The effects of temperature on thermal stability was studied on four kerosine-type fuels using a fuel thermal stability rig. The apparatus is a closed loop system that distributes fuel over various temperatures, flow rates and pressures. Results show that tube-wall and fuel temperatures affect deposition rates. Deposition rates are directly proportional to the tube-wall temperature. This reverses earlier findings that deposition rates increase with wall temperatures only up to a certain point after which it begins to decline.