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Laser fabrication of cooling holes in certain parts of the aero-engine components involves percussion or trepan drilling at acute angles (e.g., 16-30 deg) to the surface. These parts are often covered with plasma sprayed ceramic thermal barrier coatings (TBCs) to protect them from reaching excessive temperatures in hot engine environments. Delamination of the TBC is the main problem of laser drilling acute angled holes in the coated components. The present study investigates the mechanisms involved in the development of the delamination cracks. A significant role of melt ejection in the formation of cracks and the delamination at the coating/coating interface of the leading edge of a laser-drilled inclined hole was identified. It is shown that the delamination mechanisms at the TBC coating/bond coating and the bond coating/substrate interfaces are different. Melt ejection induced stresses were identified as the key mechanisms for the former type, while the thermal effects dominates the latter type. [DOI: 10.1115/1.4000102] Keywords: laser drilling, thermal barrier coating, delamination

This paper presented the stress distribution in a thick walled cylinder under thermal shock. Dirac function was introduced to model thermal shock. An analytical solution of the temperature field was obtained by Laplace transform. Based on the temperature solution, the thermal stress response of the thick walled cylinder was solved. The time dependent variations of the temperature field--thermal stress field--were discussed, and the effect of cylinder radius ratio on the problem was given. The exploration in this paper will lay a theoretical reference to further study on the decrease in fatigue damage of the superhigh pressure tubular reactor under thermal shock. [DOI: 10.1115/1.3066882] Keywords: thermal shock, thick wall cylinder, thermal stress, ultrahigh pressure tubular reactor

The interaction integral method that is equipped with the nonequilibrium formulation is generalized to evaluate the nonsingular T-stress as well as mixed-mode stress intensity factors in orthotropic functionally graded materials under thermomechanical loads. This paper addresses both Mode-I and mixed-mode fracture problems and considers various types of orthotropic material gradation. The orthotropic thermomechanical material properties are graded spatially and integrated into the element stiffness matrix using the direct Gaussian formulation. The types of orthotropic material gradation considered include exponential, power-law, and hyperbolic-tangent functions, and the numerical formulation is generalized for any type of smooth material gradation. The T-stress and mixed-mode stress intensity factors are evaluated by means of the interaction integral method developed in conjunction with the finite element method. The accuracy of numerical results is assessed by means of thermomechanically equivalent problems. [DOI: 10.1115/1.2936234] Keywords: functionally graded material (FGM), thermal fracture, stress intensity factor (SIF), T-stress, interaction integral, finite element method (FEM)

Despite enormous progress in laser aided direct metal/material deposition (LADMD) process many issues concerning the adverse effects of process parameters on the stability of a variety of properties and the integrity of microstructure have been reported. Comprehensive understanding of the transport phenomena and heat transfer analysis is essential to predict the thermally induced stresses in the deposited materials. A complete model that provides a quantitative relationship between process parameters, temperature history, phase transformation kinetics, and the thermal stresses is highly desirable. This paper examines the effect of deposition patterns and phase transformation kinetics on induced thermal stresses. The proposed model is based on the metallo-thermomechanical theory for sequentially coupled temperature, phase transformation, and stress/strain fields. Finite element analysis of various deposition processes illustrates the significant effect of deposition patterns on induced thermal stresses. Raster scan, spiral in-to-out, and spiral out-to-in patterns, in conjunction with their experimental verification, have been discussed in this paper. The existing model can easily accommodate any deposition pattern a user may want to study with slight modifications. The effect of substrate preheating on thermal stress is also studied and some reductions in thermal residual stress were observed. The importance of considering phase transformation effects is also verified through the comparison of the magnitudes of residual stresses with and without the inclusion of phase transformation kinetics. The simulation has been carried out for H13 tool steel deposited on a mild steel substrate. [DOI: 10.1115/1.2401620]

This paper describes the 'thermal opening technique' for enhancing the ultrasonic response of a tightly closed crack. In this approach, thermal stress is generated by cooling the part locally to reduce the crack closure stress in stainless steel plate, which improves sensitivity to detect the scattering wave from the crack surface; this has however not been successful by the usual ultrasonic inspection technique without introducing the thermal stress. It has been observed that the enhancement of the scattering wave continues for several hours after removing the thermal stress. This valuable and unique characteristic of the scattering wave is related to the change in the contact condition between the mating crack surfaces. Finally, a method is proposed for the evaluation of the depth of tightly closed crack from the difference in the time-of-flight between the scattering wave and the corner echo. The quantitative characteristic of the method is also verified experimentally. [DOI: 10.1115/1.2389026] Keywords: ultrasonic inspection, closed crack, scattering wave, signal enhancement, thermal stress

Repeated thermal shock cracking is common in the operation of pressure equipment where water and steam are present. Surprisingly, it is not fully covered in the ASME Boiler and Pressure Vessel code nor in fitness-for-purpose recommended practice such as API 579. An example of thermal shock stresses occurs when hot surfaces are exposed to splashing of cold water. This eventually may lead to crack nucleation and crack growth. However, not all thermal shock cracks lead to failures (such as rupture, leak, or, in more brittle material, fragmentation), indeed the most frequent situation is that the cracking arrests at a depth of a few millimeters. This paper presents a unique experimental study and analysis of the information being gained from this study in terms of design guidelines and crack growth mechanisms. In the experiments, cracks are initiated and then grown in low carbon steel specimens exposed to repeated thermal shock. The test-rigs achieve large thermal shocks through the repeated water quenching of heated flat plate specimens. The effect of steady state loads on the growth and environmental effects due to the aqueous nature of the testing environment are found to be major contributors to the crack growth kinetics. The most important findings are that the conditions leading to both the initiation and the arrest of cracks can be identified and that the depth of a starter notch contributes little to the crack propagation. [DOI: 10.1115/1.2389029] Keywords: thermal shock, cracking, initiation, growth, arrest, design, fitness for purpose

In this work, a gouged section of 1080 railroad rail steel is examined using metallographic techniques to characterize the nature of the damage. The gouging was performed by a rocket sled at Holloman Air Force Base, riding on VascoMax 300 steel shoes at 2.1 km/s. The damaged rail is evaluated in detail to examine material phase changes, shear bands, and heat effects. The results are compared to samples of the virgin material, machined and prepared exactly as they are prior to the Holloman AFB High Speed Test Track (HHSTT) runs. The gouged section was examined using optical microscopy, scanning electron microscope (SEM), and other techniques. The resulting microstructure is presented and compared to the virgin material. Material mixing, shear band formation, and significant thermal damage, consistent with a high energy gouging event, are confirmed. In addition, the material phase change evident in this approach allows us to estimate the thermal conditions present during the formation of the gouge. This thermal history, establishes a profile by which related research in gouge simulation can be validated against. A one-dimensional heat conduction model is presented that validates the cooling rates required to generate the presented microstructure. [DOI: 10.1115/1.2389030]

Approximate solutions were derived for the transient through steady-state thermal-stress fields developed in thick-walled vessels subjected to a potentially arbitrary thermal shock. In order to accomplish this, Duhamel's integral was first used to relate the arbitrary thermal loading to a previously derived unit kernel for tubular geometries. Approximate rules for direct and inverse Laplace transformations were then used to modify the resulting Volterra equation to an algebraically solvable and relatively simple form. The desired thermoelastic stress distributions were then determined using the calculated thermal states and elasticity theory. Good agreement was seen between the derived temperature and stress relationships and earlier analytical and finite-element studies of a cylinder subjected to an asymptotic exponential heating on the internal surface with convection to the outer environment. It was also demonstrated that the derived relationships can be used to approximate the more difficult inverse (deconvolution) thermal problem for both exponential (monotonic) and triangular (non-monotonic) load histories. The use of polynomial of powers [t.sup.n/2] demonstrated the feasibility, of employing the method with empirical data that may not be easily represented by standard functions. For any of the direct and inverse cases explored, the resulting relationships can be used to verify, calibrate, and/or determine a starting point for finite-element or other numerical methods. [DOI: 10.1115/1.2389002]

Fatigue crack propagation properties of welded joints were investigated on steel plate for boilers and other pressure vessels. The fatigue crack propagation properties at 300[degrees]C became similar to those at room temperature when the thermal stress could be reduced down to -1 MPa by using center cracked type specimen with longitudinal slits and a specially designed furnace. The tensile residual stress was +152 MPa in the as-welded joint, and +12 MPa after PWHT. The fatigue threshold was about 2.7, 5.1 and 7.3 MN/[m.sup.3/2] for weld metal in the as-welded condition, after PWHT and the base metal, respectively. [DOI: 10.1115/1.1563628] Keywords: Fatigue Crack Propagation, Thermal Stress, Welded Joint, Residual Stress, Steel

A closed-form, analytical solution is presented for the transient, plane thermal stress analysis of a linearly elastic, homogeneously orthotropic hollow cylinder subjected to an arbitrary temperature distribution. The thermoelastic solution, obtained by a stress function approach, can be used as the basis for the corresponding thermoviscoelastic solution for thermorheologically simple viscoelastic materials by invoking the viscoelastic Correspondence Principle. This solution can also be directly extended to the class of weakly inhomogeneously orthotropic cylinders using perturbation methods. The transient asymmetric temperature field is characterized by Fourier-Bessel eigenfunction expansions. The analytically derived stress function satisfies a linear, fourth-order inhomogeneous partial differential equation and the Cesaro integral conditions, which assure the existence of a single-valued displacement field. The corresponding thermal stresses are then computed by the stress-stress function relations. A key feature of the analytical solution is that the hoop, radial, and shear stresses, due to the transient arbitrary temperature distribution, are expressed explicitly in terms of the scalar temperature field. A polymer composite example is presented to validate the current method and to qualitatively illustrate the distribution of thermal stresses due to an asymmetric temperature distribution. Numerical results are presented for the thermally driven hoop, radial and (interlaminar) shear stresses in a hollow, hoop-wound glass/epoxy cylinder. This analysis demonstrates that potentially debilitating interlaminar shear stresses can develop in laminated composites when subjected to an even modest transient asymmetric temperature distribution. Their magnitudes depend on the severity of the spatial and temporal thermal gradients in the circumferential direction. While still relatively low compared to the hoop stress, the shear stress may cause thermal failure due to the typically low interlaminar shear strengths of laminated composite materials. [DOI: 10.1115/1.1491268]

Considered in this paper is a piezoelectric material strip containing an embedded crack or an edge crack perpendicular to its boundaries. The problem is solved for a strip that is suddenly heated or cooled from the top surface. The bottom surface is assumed to be zero temperature or thermally insulated. First the transient temperature and the stress distributions in an uncracked strip are calculated. Then, these stresses are used as the crack surface traction with opposite sign to formulate the mixed boundary value problem. This leads to a singular integral equation of Cauchy-type, which is then solved numerically. The numerically results for stress intensity factor are computed as a function of the normalized time and the crack size. The temperature and the thermal stress distributions for the uncracked problem are also included. [DOI: 10.1115/1.1429935]

In this study, tensile tests of 63Sn/37Pb solder were carried out at various strain rates from [10.sup.-5] [s.sup.-1] to [10.sup.-1] [s.sup.-1] over a wide temperature range from -40 [degrees] C to 125 [degrees] C to study the effect of strain rate and testing temperature on the mechanical properties in a systematic manner. based on these experimental data, a set of empirical formulae was derived by a statistical method to describe the effect of temperature and strain rate in a quantitative manner and explain the variation in the mechanical properties published in other reports. It is concluded that the empirical formulae can be used to characterize the mechanical properties of 63Sn/37Pb over a wide range of temperatures and strain rates.

In this study, both two-dimensional and three-dimensional finite element analyses were used to study the stress distribution in and deflection of the flip chip assembly under thermal loading. It is found that the three-dimensional results compared favorably with experimental measurements, while the two-dimensional results consistently overestimate both stresses and deflection. Among the two-dimensional models, the plane stress assumption seems to yield results closer to the full three-dimensional predictions. Furthermore, three-dimensional models were used to investigate the effect of printed wiring board size on the overall deflection of the flip-chip assembly. This size effect of the printed wiring board has significant implications on the design of multi-chip modules. The results indicate that a square array placement pattern is preferable to a staggered array for multiple chip modules in order to reduce mechanical interaction between chips. For square arrays, such mechanical interaction between chips can be neglected when the minimum distance between adjacent chips is more than 2 times the chip size.

The article discusses stress distribution in coated fibrous composites subjected to a temperature change. Numerical calculations of the stress distribution are performed, and a decrease of the coating plasticity is found.

The article describes the effect of weather conditions in China on bituminous pavement. Analysis of the thermal stress field and the optimum thickness of the pavement is presented.

Coupled vapor/liquid flow in miniature passages with micro grooves is discussed. A two-dimensional model was developed to better calculate friction factors. Longitudinal pressure gradients in liquid and vapor flows in a miniature heat pipe were calculated and the capillary limit estimated and compared with existing experimental results showing that coupled liquid-vapor is needed to predict performance characteristics of miniature axially grooved heat pipes. Effect of liquid-vapor frictional interaction on the liquid flow goes down with curvature of the interface. Shear stresses at the interface are significantly nonuniform.

In the electronic industry, the dominant failure mode for solder joints is assumed to be thermal cycling. When semiconductor devices are used in vibrating environment, such as automotive and military applications, dynamic stresses contribute to the failure mechanism of the solder joint, and can become the dominant failure mode. In this paper, a damage mechanics based unified constitutive model for Pb40/Sn60 solder joints has been developed to accurately predict the thermomechanical behavior of solder joints under concurrent thermal and dynamic loading. It is shown that simultaneous application of thermal and dynamic loads significantly shorten the fatigue life. Hence, damage induced in the solder joint by the vibrations have to be included, in fatigue life predictions to correctly predict the reliability of solder joints. The common practice of relating only thermal cycling induced inelastic strain to fatigue life can be inadequate to predict solder joint reliability. A series of parametric studies were conducted to show that contrary to popular opinion all dynamic loading induced strains are not elastic. Hence, vibrations can significantly affect the fatigue life and reliability of solder joints in spite of their small mass.

During the passage of a debris particle through an EHD contact, mechanical stresses due to particle compression and thermal stresses due to particle frictional heating produce a thermoelastic/plastic stress field, which governs the way a possible damage is generated. In the present paper, the complete three-dimensional solution of the thermoelastic distortion of surfaces due to the compression of a soft, ductile debris particle in an EHD line contact is presented both theoretically and through a realistic example. It is found that thermal stresses increase the likelihood of yielding and produce a characteristic 'omega' shaped thermoelastic displacement. The important outcome of this work is the construction of a map which shows the critical particle size to cause damage (plastic deformations) in combination with operational parameters as the lubricant film thickness and relative sliding velocity of the contact.

Green's functions of the external force boundary value problem for an infinite plane with an arbitrary shaped hole, that is subjected to heat, under adiabatic and isothermal boundary conditions are obtained for two cases. The first case has the heat source and heat sink located within the plane while the other case has the heat source located within the plane but has the heat sink at infinity. The two cases are studied by using complex stress functions, temperature function, a rational mapping function and the thermal dislocation method.

Thermal stresses were studied in freezing of biomaterials containing significant amounts of water. An apparent specific heat formulation of the energy equation and a viscoelastic model for the mechanics problem were used to analyze the transient axi-symmetric freezing of a long cylinder. Viscoelastic properties were measured in an Instron machine. Results show that, before phase change occurs at any location, both radial and circumferential stresses are tensile and keep increasing until phase change begins. The maximum principal tensile stress during phase change increases with a decrease in boundary temperature (faster cooling). This is consistent with experimentally observed fractures at a lower boundary temperature. Large volumetric expansion during water to ice transformation was shown to be the primary contributor to large stress development. For very rapid freezing, relaxation may not be significant, and an elastic model may be sufficient.

The development of thermal stresses in ingots during the vacuum arc remelting (VAR) as well as specialized permanent mold casting (PMC) process was modeled via numerical solution of the two-dimensional, nonsteady-state heat conduction and stress equilibrium equations. The numerical analysis was carried out in conjunction with experimental studies of the mechanical properties and microstructure of a cracked VAR titanium aluminide ingot. Numerical solutions were obtained for different values of ingot diameter, crucible-ingot interface heat transfer coefficients, and lengths of the melted-and-resolidified ingot. For both VAR and PMC, model predictions revealed that the maximum tensile thermal stresses are developed at the bottom of the ingot; the magnitude of such stresses increases with ingot diameter and the magnitude of the interface heat transfer coefficients. The microstructural analysis of a cracked ingot indicated that the thermal cracking occurred in the temperature range where the alloy has very little ductility. The predicted development of large tensile stresses correlates well with observations of thermal cracking during VAR of near-gamma titanium aluminide alloy ingots. By contrast, the predicted thermal stresses developed during PMC are lower, thus suggesting an attractive alternative to VAR to obtain sound, crack-free ingots.

An analytical and numerical heat conductivity model was developed for predicting the extent of the formation of the heat affected zone (HAZ) in unidirectional fiber-reinforced plastics induced by laser grooving. Results obtained from the model show that the smallest HAZ is generated by a grooving parallel to fiber orientation, while the largest HAZ is produced by a grooving perpendicular to fiber orientation. The simulation results were also found in good correlation with experimental results.

A study was conducted to analyze the benefits of applying the Cosserat Spectrum theory to boundary value problems in thermoelasticity. A solution technique for thermoelasticity was determined using heat flow examples. Results indicated that theory supports the fast convergence of discrete Cosserat eigen functions and optimizes the elastic energy based on a variational thermoelastic principle for such functions.

A study was conducted to examine the influence of relaxation times and thermomechanical coupling on wave spectrum in dynamic theory of generalized thermoelasticity. The basic equations of generalized thermoelastic theory were determined from the motion and energy balance equations. Results indicated that relaxation times and thermomechanical coupling terms had no effects on spectral relations. Findings also showed that coupling terms support a non-negligible influence on the phase velocities of thermoelastic waves.

A study was conducted on thermal stresses in an inwardly solidifying sphere. A solution was presented which accounts for thermal expansion associated with temperature gradients and volume changes linked with phase transition.The frozen medium was modeled as an elastic-perfectly plastic. Parametric studies using appropriate material properties and cryopreservation protocols indicated that strains associated with phase transition led to higher stresses than those associated with thermal expansion.

Design research has established an elastodynamic solution to describe an orthotropic thick cylindrical shell's thermal shock stresses. The use of transform analysis including Hankel and Laplace techniques is described. Stress wave propagation has a significant effect on thermal shock stresses in an environment of thermal loading.

Thermal stress research has established a technique to analyse elliptical anisotropic inclusion embedded in an infinite anisotropic matrix in the presence of a uniform heat flow. Conformal mapping, analytical continuation and superposition techniques are described.

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 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.

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.

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.

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.

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.