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Research was conducted to study the flux at which thermal stress approaches yield strength for several materials in a configuration similar with heat flux systems. Some of the refractory metals had ductile-to-brittle transition temperatures in the operating temperature range around 200 degrees C. Results showed that hardened copper alloys had the highest flux among the materials tested. They also indicated that temperature was directly proportional to the heat flux during localized heating.

A study was conducted on hot hole stressed SiO2/Si interface behavior at elevated temperatures. The results show significant damages in stressed devices at temperatures higher than 300-degrees celsius. The damages were found to be caused by two hole injection-induced thermally activated processes. The results also indicate that the two defect types are related but not similar.

Cross-sectional transmission electron microscopy and current-voltage and capacitance-voltage measurements were employed to examine the thermal performance of Ti/Pt/u Schottky gates on GaAs metal-semiconductor field-effect transistors. A layered structure of Ti/Ti-Ga/Ti-As/GaAs was observed at >350-degrees C annealing temperature. Results were found to be in agreement with proposed advanced unified GaAs defect model.

A study was conducted on the influence of thermal treatment of low-temperature GaN buffer layers on the surface morphology and crystalline quality of GaN layers grown on sapphire (0001) substrates through metalorganic chemical vapor deposition. The thermal effects during temperature ramping were found to significantly impact the quality of subsequent high-temperature GaN layers. The mechanisms associated with defect formation, high-temperature growth initiation and nucleus formation were also determined.

A study was conducted on the influence of heat stress on Na+-glucose cotransport using porcine-derived renal epithelial cell line monolayers. Release of alkaline phosphatase or lactate dehydrogenase show that mild heat shock is not associated with luminal membrane surface area or cell survival. Results also show that Na+-glucose cotransport is both protected and improved through heat shock protein treatment.

A study was conducted on the impact of mannosylglycerate on the protection against freeze-drying of enzymes taken from thermophilic, mesophilic and hyperthermophilic sources. Results show that 2-0-Besta-mannosylglycerate, which accumulates in certain thermophilic organisms, is effective in stabilizing enzymes. Results also indicate the potential biotechnological applications of the solute.

A thermal post-buckling analysis was developed for solving the problem of imperfect composite laminated plates subjected to nonuniform thermal loading and resting on two-parameter elastic foundations. The analysis employs a mixed Galerkin-perturbation method. Results show that the foundation stiffness, plate aspect ratio, fiber orientation, thermal load ratio and initial geometrical imperfection significantly affect the characteristics of thermal post-buckling.

A study was conducted on the thermal strain and stress distribution on silicon-based Planar-Lightwave-Circuits (PLC) substrates and the stress concentration on silicon terrace structures prepared for mounting active optical equipment. Three-point-bending tests were used to determine the fracture strength of silicon. The findings indicate the reliability of the PLC substrate for a new family of optical components.

A study was conducted on the fatigue life of an underfilled flip-chip package using Coffin-Manson relation and finite element modeling-computed solder shear strain. The results of the numerical simulations were employed in the analysis of the parametric sensitivity of the thermal strain in the solder joints and the axial and shear stress in the underfill material. The findings indicate an agreement between the predicted improvement in the number of cycles-to-failure of the underfilled flip-chip and the empirical observation.

A study was conducted on the plastic-creep behavior and stress relaxation behavior due to temperature cycling or isothermal cyclic loading. The findings indicate that long high-temperature and low-temperature dwell times do not contribute to the increase of the cyclic inelastic equivalent strain range in solder joints in an accelerated temperature cycling test. Proposals on some testing processes of temperature cycling and isothermal fatigue tests are also presented.

A study was conducted on thermally induced viscoplastic deformation and low cycle fatigue behavior of the lead-tin solder joints in a 32 mm ceramic ball grid array (CBGA) surface mount package. The nonlinear finite element model results indicate that the maximum viscoplastic strains happen in and around the edge CBGA solder joint. Moreover, the cyclic creep strain was found to be highly significant. The equivalent plastic strain is directly proportional to cyclic frequency and ramp rate but inversely proportional to hold time.

Some 6,016 employees in 21 Israeli industrial plants were studied to examine the association between indoor temperature control (TC) at the workplace and working heart rates (HR) of industrial workers. The resting HR, working HR, workload, age and health-related habits of the subjects were collected, as well as the outdoor temperatures and the TC status of the plants. Although no significant difference was noted in the mean working HR of subjects working with TC and those without TC in the outdoor temperature range, the study suggests that indoor temperature control in plants moderates the cardiovascular strain in working subjects during cold and hot days.

Recent experimental studies revealed that the thermal pressure in a diamond-anvil cell with laser heating can be large. Accounting for this pressure is therefore important for treatment of experimental results. In earlier studies, we developed an MgO model that was demonstrated to perform very well for calculations of thermoelastic properties. Here, we study the effect of thermal stress on the behavior of MgO under high pressure and temperature conditions using molecular dynamics and the earlier developed interatomic potential. The simulations show that thermal stress can produce such effects as dynamic recrystallization, which may be interpreted as onset of convective-like motion and which may cause a change in the slope of laser power-temperature curve. Because these two criteria are used for the identification of melting, it is possible that what was interpreted as melting in previous experiments with MgO was in reality recrystallization.

An analysis of thermal deformation and stress resultants in rectangular antisymmetric cross-ply and angle-ply laminates using the generalized Levy-type method in connection with the state variable approach is presented. The thermoelastic behavior is revealed when deflections are calculated for laminates being subjected to linearly varying temperature fields through the thickness while having sinusoidal distribution of thermal loading.

An analysis was made on a simple analytical stress model for evaluating thermally induced shearing stresses in a long cylindrical bi-material assembly adhesively bonded at its ends and subjected to the change in temperature. The study emphasized on the interaction of the 'global' thermal mismatch stresses. The result indicates that the developed analytical stress model can help in the analysis and design of fiber optic assemblies.

Nonisothermal flow of a polymer melt in a cold mold cavity introduces stresses that are partly frozen-in during solidification. Flow-induced stresses cause anisotropy of mechanical, thermal, and optical properties, while the residual thermal stresses induce warpage and stress-cracking. In this study, the influence of the holding stage on the residual thermal stress distribution is investigated. Calculations with a linear viscoelastic constitutive law are compared with experimental results obtained with the layer removal method for specimens of polystyrene (PS) and acrylonitrile butadiene-styrene (ABS). In contrast to slabs cooled at ambient pressures, which show the well-known tensile stresses in the core and compressive stresses at the surfaces, during the holding stage in injection molding, when extra molten polymer is added to the mold to compensate for the shrinkage, tensile stresses may develop at the surface, induced by the pressure during solidification., INTRODUCTION Injection molding is a flexible production technique for the manufacturing of polymer products. During processing, the polymer experiences a complex deformation and temperature history that affects the final properties [...]

An analysis of the steady-state thermal bending of a thick rectangular plate is carried out by a tenth-order theory of moderately thick plates. The boundary conditions for a temperature field are considered to be a partially prescribed constant temperature on the top face, zero temperature at the bottom face and two edges, and no flux at the two edges. The temperature field is rigorously analyzed by the theory of three-dimensional heat conduction. The mechanical boundary conditions of the plate are considered traction-free at the top and bottom faces, the two opposite edges are simply supported, and the other two edges are free. The displacement and stress field is analyzed exactly by a particular solution deduced from part of a three-dimensional elasticity solution and a homogeneous solution consisting of three solutions to plane stress, generalized plane stress, and antisymmetric stress. Numerical results for thermal stresses and displacements are presented. One of the normal stresses at the top face becomes discontinuous at the boundary of the prescribed surface temperature.

The presence of water in the free volumes of a carbon-phenolic composite affects the restraining stress during heating. The stress magnitude is proportional to initial moisture content. A graphical representation of the variation of restraining stress with temperature, and the position of glass transition temperature at 0% and 4% moisture content are given. An analytical approach studies the specimen by formulating the equation for diffusion of water and the partial pressure equation.

A study determines the laser heat induced thermal stress field on the surface of an elastic half-space, for mixed-mode structure beams. The two lowest order modes from a cylindrical laser resonator undergo superposition leading to a spatial heat energy distribution on the material surface. The shapes of temporal pulses from the laser depend on the temporal pulse profile. Tensile radial and circumferential stresses near the axis depend on the subsurface shear stresses and a compressive normal stress. A laser pulse with temporal profile, and radial intensity distribution, applies heat on the material.

Increasing the thermal efficiency by higher turbine inlet temperatures is one of the most important aims in the area of gas turbine development. Because of the high temperatures, the turbine vanes and blades have to be cooled, and also knowledge of the mechanically and thermally stressed parts in the hottest zones of the rotor is of great interest. The prediction of the temperature distribution in a gas turbine rotor containing closed, gas-filled cavities, for example, in between two disks, has to account for the heat transfer conditions encountered in these cavities. In an entirely closed annulus, forced convection is not present, but a strong natural convection flow exists, induced by a nonuniform density distribution in the centrifugal force field. In Bohn et al. (1994), experimental and numerical investigations on rotating cavities with pure centripetal heat flux had been carried out. The present paper deals with investigations on a pure axially directed heat flux. An experimental setup was designed to realize a wide range of Ra numbers (2 [multiplied by] [10.sup.8] < Ra < 5 [multiplied by] [10.sup.10]) usually encountered in cavities of gas turbine rotors. Parallel to the experiments, numerical calculations have been conducted. The numerical results are compared with the experimental data. The numerical scheme is also used to account for the influence of Re on heat transfer without changing Ra. This influence could not be pointed out by experiments, because a variation of the Re-Ra characteristic of the employed annuli was not possible. It was found that the numerical and experimental data are in quite good agreement, with exception of high Ra, where the numerical scheme predicts higher heat transfer than the experiments show. One reason may be that in the experiments the inner and outer cylindrical walls were not really adiabatic, an assumption used in the numerical procedure. Moreover, the assumption of a two-dimensional flow pattern may become invalid for high Ra. The influence of three-dimensional effects was studied with the three-dimensional version of the numerical code. In contrast to the radial directed heat transfer, it was found that Nu is much smaller and depends strongly on Re, whereas the radial heat transfer is only weakly influenced by Re.

Temperatures generated in the workpiece during straight surface plunge grinding follow a transient behavior as the grinding wheel engages with and disengages from the workpiece, and throughout the entire grinding pass for workpieces which are shorter than needed to reach a quasi-steady state condition. In the present paper, a thermal model is developed for the transient temperature distribution under regular and creep-feed grinding conditions. Numerical results obtained using a finite difference method indicate that the workpiece temperature rises rapidly during initial wheel-workpiece engagement (cut in), subsequently reaches a quasi-steady state value if the workpiece is sufficiently long, and increases still further during final wheel-workpiece disengagement (cut out) as workpiece material is suddenly unavailable to dissipate heat. Cooling by a nozzle directed at the end face of the workpiece should significantly reduce the temperature rise during cut out.

Environmental Scanning Electron Microscopy (E-SEM) is a technique which provides the capability to investigate surface morphologies over a variety of controllable environmental conditions. This paper discusses the principal of the E-SEM and presents three experimental investigations of failure mechanisms in electronic packages using E-SEM techniques. The first is a study of thermally induced failures of MMIC devices. The second investigation focuses on mechano-sorptive properties of multilayer thin-film polyimides. The third investigation concentrates on relative humidity and thermal cycling effects on interfacial bonding characteristics of resin/fiber interfaces in printed wiring boards, and microcracks surrounding plated-through-holes.

Several workers have demonstrated the presence of singular stress fields near the edge of a bimaterial interface subject to thermal gradients. Many of the analyses in the literature are limited to linear elastic materials and are useful as first estimates of stresses in such assemblies. However, a time-dependent stress analysis is necessary when viscoelastic materials such as polymer films are bonded to elastic substrates. This paper shows the relevance of viscoelastic modeling in demonstrating the effects of combined temperature and moisture loading on bimaterial interfaces and viscoelastic films sandwiched between elastic substrates. A 2-D finite element method for linear hygrothermoviscoelasticity based on an incremental creep strain rate form is developed. The correspondence principle of linear viscoelasticity is invoked and comparisons between FEA and analytical solutions are demonstrated. Moisture is modeled using Fick's law and the thermorheologically simple material (TSM) postulate is extended to incorporate a moisture shift function in analogy with temperature. The analysis of a polyimide film sandwiched between elastic substrates subject to a thermal cycle with diffusion from the free edge shows stress reversals for the peel stresses that may explain failure modes not anticipated by an elastic analysis.

Thermo-mechanical behavior of various levels of electronic packaging products is studied by moire and microscopic moire interferometry. The global deformations of packages with complex geometries and the local deformations of solder interconnections are determined by displacement measurements of high sensitivity and high spatial resolution. Several packaging studies are reviewed. They include analyses of thin small outline package, leadless chip carrier package, surface mount array package, chip/organic carrier package, deformation near a plated through hole, and determination of an effective CTE. In-situ and quantitative nature of the methods leads to more accurate and realistic understanding of the macro and micro mechanical behavior of packaging assemblies and interconnections, which in turn, facilitates design evaluation and optimization at an early stage of product development.

In an earlier work, thermal stresses in soldered pins were calculated under the assumption of an elastically deforming solder barrel. In the present analysis, the nonlinear, temperature dependent stress-strain curve of solder, without creep, is taken into account, yielding an elasto-plastic foundation modulus function. For the thermal mismatch loading, the total temperature range [Delta]T (e.g., 0-100 [degrees] C) is divided into a finite number n of temperature stages, and the final responses are superposed from the n contributions each of which done using an isothermal stress calculation. Three solders (Sn-Pb solders 63/37, 70/30, and 10/90), were investigated; the solder barrel thickness and mismatch temperature range were also variable parameters. Comparisons with elastic solder foundation calculation results show that thermal and inelastic solder stress/strain dependence should be included especially in the higher (over 75 [degrees] C) temperature range.

Failures in electronic packaging under thermal fatigue often result from cracking in solder joints due to creep/fatigue crack growth. A nonlinear, time-dependent finite element analysis was performed to study the effect of critical design parameters on thermal reliability of leadless chip capacitor or resistor solder joints. The shear strain range based on thermal hysteresis response was used to study the sensitivity of various parameters, such as solder stand-off height, fillet geometry, Cu-pad length, and component length and thickness. The results were used as guidelines for designing reliable solder joints. In addition, an analytical model for the solder joint assembly was derived. It can be used as an engineering approach for rapid assessment of large numbers of design parameters. The accuracy and effectiveness of the analytical model were evaluated by comparing with finite element results.

This study correlates previously published fatigue life data with the hysteresis energy, and compares this to the previous correlation's with the applied plastic strain. It was found that, while the hysteresis energy could be used to describe the fatigue life, corrections must be made to account for the temperature and strain rate dependence of the flow stress. Because of these factors, it is believed that the plastic strain, and not the hysteresis energy, is the true governing factor in determining the fatigue life. Part I (described here) covers only the influence of temperature and cycle frequency for symmetric cycling. Part II, to be published, will deal with hold time and asymmetric cycling.

The intense, localized stress field produced by a temperature load in a multilayered structure may be significantly affected by the local geometry of the free edge. We examine here the stepped edge problem associated with bonding an elastic layer (silicon chip) to a single or multilayer substrate with a slightly larger length. Stress functions are introduced in various rectangular regions and the continuity of tractions are enforced across all inter-region boundaries. Furthermore, continuity of displacements is enforced across the junction of the two segments of the base laminate. The analysis results indicate that even a minute protrusion of the edge of the base laminate relative to the attached chip may cause significant changes in the peeling and shearing stresses in the end region of the interface.

The ability of solder joint life-prediction algorithms to predict the failure of solder joints due to temperature-cycling induced creep-fatigue has been investigated using representative leadless chip carriers (LCCs) as the test vehicle. Four different algorithms are assessed: the classic Coffin-Manson algorithm, a modified Coffin-Manson algorithm with dependency on peak stress, and two strain-energy based algorithms. JPL's special purpose nonlinear finite element computer program was used to dynamically simulate the solder joint response to the standard NASA temperature cycling environment, which ranges from -55 [degrees] C to +100 [degrees] C with a 4-hour period. The computed stress-strain history provided the inputs needed by each of the failure algorithms. To test the accuracy of the analytical predictions, three different sizes of LCCs (68 pins, 28 pins, and 20 pins) were subjected to an experimental test program using the same 4-hour temperature cycle as used in the analytical predictions. The three different sized ceramic packages, each with a 50-mil pitch, provided a range of cyclic strain ranges and solder fillet geometries so as to test the algorithms against realistic electronic packaging variables. The study highlights limitations in the historical Coffin-Manson relationship, and points up possible improvements associated with incorporating a stress modifier into the Coffin-Manson equation. This modification is also somewhat simpler and more accurate than the energy-density based algorithms, which also performed quite well.

The plastic deformation kinetics of 95.5Sn4CuO.5Ag solder joints were determined in monotonic loading shear over the temperature range of 25 [degrees]-150 [degrees] C using three types of tests: (a) constant shear rate, (b) constant shear stress (creep), and (c) differential tests (changes in shear rate or temperature during an otherwise isothermal constant shear rate test). The deformation kinetics were evaluated in terms of the Dorn high temperature plastic deformation equation [[first derivative of [Gamma] with respect to time].sub.p] = A [Mu]b/kT D[(b/d).sup.p] [([Tau]/[Mu]).sup.n] where [[first derivative of [Gamma] with respect to time].sub.p] is the shear rate, [Mu] the shear modulus, b the Burgers vector, D the appropriate diffusion coefficient, d the grain size and [Tau] the shear stress. A, p, and n are constants whose values depend on the rate controlling mechanism. It was found that n increased with stress from [approximately]4 at 2 MPa to [approximately]20 at 25 MPa, relatively independent of temperature. The activation [Delta]H was determined to be 21.1 [+ or -] 2 kcal/mole. The constant A, however, decreased with temperature from a value of [approximately][10.sup.18] at 25 [degrees] C to [approximately][10.sup.10] at 150 [degrees] C. The values of n and [Delta]H suggest that dislocation glide and climb is the rate controlling mechanism and hence that p [approximately equal to] 0. It is speculated that the large decrease in A with temperature may be the result of an effect on the microstructure.

Predicting stress levels caused by thermal effects is a main factor in the correct design of structures; both relate to aspects of the maximum stress limitation and the durability of constructions. A numerical procedure based on the finite-element method for the stress-strain analysis of concrete structures exposed to time- and space-variable thermal loads is presented in this paper. Different environmental conditions can be simulated by means of suitable boundary conditions imposed on the differential equations governing the phenomenon. In particular, the seasonal and daily variation of external temperature is considered. The presented procedure can also consider the heat generation phenomenon, due to the hydration reaction of the cement, which can cause considerable temperature gradient and related mechanical stresses, especially for thick concrete casting. The stress-strain-thermal analyses of a concrete dam (Sa Stria dam, Sardegna, Italy) and a typical bridge section (i.e., box-girder cross section) are carried out to prove the effectiveness and reliability of this numerical method in practical structural design.

A previously developed flowing single-pass heat-exchanger test rig (Phoenix rig) has been used to evaluate the effectiveness of various additives and the kinetic mechanism of both deposit formation and oxygen consumption. The Phoenix rig has been modified to include not just a heated single tube, but also a cooling test section and both hot and cold filters. The effects of flow conditions, antioxidants, and metal deactivator additives on the location and amount of the deposit are discussed. In general, antioxidants were effective at reducing the deposits on the hot test section, but almost invariably caused increased plugging of cool downstream filters. Downstream plugging of cool filters also increased with decreased temperatures in the heated section or with increased flow. Tests with both oxygen-saturated and oxygen-depleted fuels have shown that the solubility of oxygen is linearly related to the fraction of oxygen in a sparge gas, and that the amount of deposit is linearly related to the total quantity of dissolved oxygen passed. Finally, in contrast to initial modeling efforts, the consumption of oxygen is shown to be significantly more complex than a simple bimolecular, pseudo-first-order in oxygen, process. It is found to be much closer to pseudo-zero-order in the early stages, decaying to pseudo-first-order when the oxygen nears depletion.

Numerical studies help examine the thermoelastic and diffusion-induced stresses in crystalline solids developed by directional crystallization technique. The generalized relations between the elastic moduli help represent the coupling dependence of the elastic moduli on the composition and temperature of the solids. The relations elucidate the association between the elastic moduli measured at constant composition and temperature and by acoustic methods.

An experimental method is presented to study laser weld induced thermal strain using digital image analysis enhanced moire interferometry. A phenomenon that occurs in the assembly of optical components is that the final optimum coupled power will randomly change upon completion of the laser weld process. The change in power is due to residual thermal stresses being generated in the welded components. For single mode devices, relative motions of the components in the order of 1 [[micro]meter] could result in a 1 dB degradation of coupled power. The behavior of thermal strain is unpredictable since the relative orientation of the optical components at the optimum alignment is random. The goal of this investigation was to perform a baseline study of parameters affecting laser weld thermal strain. The first phase of the work was to study thermal strain induced by a single weld on a flat Kovar plate. The results show that thermal strain is independent of material inhomogeneity. However, this investigation did reveal asymmetry of the power distribution in the weld laser with a principal axes offset +30 deg from horizontal. The second phase of the experiment was to characterize thermal strain resulting from welding on an interface of two Kovar plates. The results indicate that thermal strain at the center of two welds is not affected by welds that are greater than 1 mm apart. Also, thermal strain levels at locations adjacent to the weld are not significantly affected by weld separation distance. This study successfully demonstrated that digital image analysis enhanced moire interferometry can be used in the study of laser weld induced thermal strain. Digital image processing, fractional fringe analysis, and high frequency specimen gratings increase sensitivity levels to enable the technique to be used to characterize submicron thermal distortions.

Birefringence induced by thermal stress in bow-tie optical fibers is studied in detail by the use of the finite-element method. Results of computer modeling show that a higher degree of birefringence can be obtained with the use of a larger cladding and larger stress-applying zones in the fiber.

Stresses produced by a thermal gradient in the wall of a partially filled horizontal cylindrical vessel are presented. Three different thermal gradients are considered: 1) a discontinuous temperature change; 2) a hyperbolic temperature change; and 3) a linear temperature change at the liquid level. Thermal shock effects are also presented.

We have developed a highly sensitive method for measuring thermal expansion, mechanical strain, and creep rates. We use the well-known technique of observing laser speckle with a pair of linear array cameras, but we employ a data-processing approach based on a two-dimensional transform of the speckle histories from each camera. This technique can effect large gauge sizes, which are important in the assessment of the spatial statistics of creep. Further, the algorithm provides simultaneous global estimates of the strain rates at both small- and large-scale sizes. This feature may be of value in the investigation of materials with different short- and long-range orders. General advantages of our technique are compact design, modest resolution requirements, insensitivity to slow surface microstructure changes (as seen with oxidation), and insensitivity to zero-mean-noise processes such as turbulence and vibration. Herein we detail the theory of our technique and the results of a number of experiments. These tests are intended to demonstrate the performance advantages and limitations of the transform method of processing speckle strain-rate data.

Thermoelastic instability in an automotive disk brake system is investigated experimentally under drag braking conditions. The onset of instability is clearly identifiable through the observation of nonuniformities in temperature measured using embedded thermocouples. A stability boundary is established in temperature/speed space, the critical temperature being attributable to temperature-dependence of the brake pad material properties. It is also found that the form of the resulting unstable perturbations or eigenfunctions changes depending upon the sliding speed and temperature.

The local coefficient of thermal expansion (CTE) mismatch between compliant surface mount component leads and the solder that is used to attach the components to a printed wiring board can dramatically influence the thermal fatigue life of the solder joint. To quantify the contribution of the local CTE mismatch to the overall thermal fatigue damage of the solder joint, a finite element thermal fatigue simulation using an energy partitioning technique is used to compare four different lead end shapes. The four lead configurations considered are J-lead, and three gullwings leads; one with the foot parallel to the board surface, one with the foot sloped slightly downward towards the board, and one with the foot sloped slightly upward. The dimensions of the leads are purposely chosen so that the in-plane compliance is equal for the different lead shapes, only the shape of the lead end varied. Comparisons are first made with equal solder join heights and then the solder height of the gull-wing lead is varied between 0.05 to 0.23 mm (2 to 9 mils). The influence of the solder wetting angle is also investigated.

An elastic analysis is developed to provide estimates of the stresses in area array solder joints during thermal excursions. The analysis provides a rapid quantitative evaluation of the important stresses during elastic deformation, and may serve as a basis for the qualitative understanding of the loading of interconnects during thermal and power cycles.