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This paper examines the effect of tire footprint and contact stress distribution under various combinations of tire pressures and tire loads on the pavement response through 3-D finite element static analysis with linear elastic material model. Analyzed footprints include a field-measured footprint and two cases of simplified ones. Our results indicate that factors including tire load, the distribution of contact stress, and the shape of footprint will affect the tensile strains at the bottom of the asphalt concrete layer as well as the compressive strains on the top of the subgrade. However, the compressive strains on the top of the subgrade are more sensitive to tire load than the shape of footprint. The research demonstrated that pavement response analysis could be carried out using field-measured footprints instead of the simplified approximations. Reduced tire pressure was effective in reducing the tensile strains at the bottom of asphalt concrete layer, but did not decrease significantly the compressive strains at the top of the subgrade. Key words: tire-pavement contact stress, tire footprint, tire pressure, pavement response, asphalt concrete pavement, strain, finite element analysis. Le present article etudie l'effet de l'empreinte des pneus et de la distribution de la contrainte de contact selon diverses combinaisons de pressions et de charges de pneus sur la reponse de la chaussee au moyen d'une analyse statique tridimensionnelle par elements finis selon une modelisation elastique lineaire du materiau. Les empreintes analysees comprennent une empreinte mesuree sur le terrain et deux cas d'empreintes simplifiees. Nos resultats indiquent que les facteurs telles la charge du pneu, la distribution de la contrainte de contact et la forme de l'empreinte auront un effet sur la contrainte de tension au bas de la couche de beton bitumineux et sur les contraintes de deformation sur le dessus de la couche de fondation. Toutefois, les contraintes de deformation sur le dessus de la couche de fondation sont plus sensibles a la charge du pneu qu'a la forme de l'empreinte. La recherche a demontre que l'analyse de la reponse de la chaussee pourrait etre realisee en utilisant des empreintes mesurees sur le terrain plutot que des approximations simplifiees. Une pression de pneu reduite a permis de reduire les contraintes de tension au bas de la couche de beton bitumineux, mais n'a pas reduit de maniere significative les contraintes de deformation sur le dessus de la couche de fondation. [Traduit par la Redaction] Mots-cles : contrainte de contact pneu-chaussee, empreinte de pneus, pression de pneu, reponse de la chaussee, chaussee en beton bitumineux, contrainte, analyse par elements finis., 1. Introduction The critical pavement damage mechanisms in flexible pavements are fatigue cracking in the asphalt concrete (AC) layer and rutting in the subgrade (Huang 1993). Fatigue cracking develops in [...]

Foundation conditions are studied for a series of apartment buildings in a shore area reclaimed from the Nakdong River estuary delta west of Busan, South Korea, in full-scale field tests on two 600 mm, post-driving grouted, concrete cylinder piles instrumented with strain gages, driven through compressible layers and a short distance into underlying dense sand at depths of 56 m (Shinho) and 35 m (Myeongji). One test pile was provided with an O-cell so that after an initial Ocell test, a subsequent head-down test only affected pile shaft resistance. The purpose was to evaluate drivability of the piles, magnitude of the drag load due to consolidating soils, and potential settlement (downdrag) of the piled foundations. Early in the study, it became apparent that the internal process of heating and cooling of the grout during the hydration process and swelling from absorption of water affected the strain records and the assessment of residual load in the test piles during the wait time before the static loading test. The paper reports the measurements, analyses, and method for determining residual load, strain-dependent modulus of test piles, and actual load distribution in the test piles. The results are correlated to cone penetration test (CPTU) sounding data and effective stress analysis. Key words: concrete piles, concrete modulus, swelling, strain measurement, drag load, settlement. Les conditions des fondations d'une serie de blocs a appartements situes dans une region cotiere rehabilitee du delta de l'estuaire de la riviere Nakdong a l'ouest de Busan, Coree du Sud, ont ete etudiees a l'aide d'essais sur le terrain a l' echelle reelle sur deux pieux cylindriques en beton, instrumentes de jauges de deformation de 600 mm et cimentes apres la mise en place, enfonces a travers des couches compressibles et a travers une faible distance de sable dense sous-jacent, a des profondeurs de 56 m (Shinho) et de 35 m (Myeongji). Une cellule O a ete installee sur un des pieux, de sorte qu'apres l'essai en cellule O initial, un essai subsequent affecte seulement la resistance de l'arbre du pieu. L'objectif etait d'evaluer la facilite d' enfoncement des pieux, la magnitude de la charge de trainee causee par la consolidation des sols, et le tassement potentiel (trainee vers le bas) des fondations des pieux. Au debut de l'etude, il a ete observe que le processus interne de rechauffement et refroidissement du ciment durant l'hydratation et le gonflement cause par l'absorption d'eau affectent le register des deformations et l'evaluation de la charge residuelle dans les pieux d'essai durant la periode d'attente avant les essais en chargement statique. L'article presente les mesures, les analyses et une methode pour determiner la charge residuelle, le module de dependance des deformations des pieux, et la distribution des charges actuelles dans les pieux d' essai. Les resultats sont correles avec des resultats d'essai de penetration au cone (≪ CPTU ≫) et d'analyse des contraintes effectives. Mots-cles: pieux en beton, module du beton, gonflement, mesure des deformations, charge de trainee, tassement. [Traduit par la Redaction], Introduction The Nakdong River estuary delta area covers a large area west of the city of Busan, South Korea, and is composed of very thick deposits of compressible and, originally, [...]

Finite-element analysis of strain localization based on classical theory of continuum mechanics suffers from pathological mesh dependence when strain softening models are used. For quasistatic problems, the mesh dependence is demonstrated through an analysis of the tangent stiffness matrix of a one-dimensional problem. To regularize the mesh dependence, a nonlocal strain softening model is proposed, which is based on the nonlocal plasticity theory and the representative line element. Both analytical and numerical solutions of strain localization with the proposed model are developed and compared with each other. The model is also applied in the numerical simulation of a direct tensile test of a concrete specimen in the existing literature, and reasonable agreement is achieved between numerical solutions and the experimental response. DOI: 10.1061/(ASCE)EM.1943-7889.0000184 CE Database subject headings: Strain softening; Localization; Plasticity; Finite element method. Author keywords: Strain softening; Localization; Plasticity; Finite-element method.

An improved method based on pseudostatic and limit-equilibrium analysis is proposed for evaluating seismic (static plus dynamic) active earth pressures induced by backfill behind movable rigid retaining walls. The proposed method can take into account the effects of strain localization and postpeak shear resistance reduction in the dense backfill soil during a strong earthquake, and the main improvement over the existing method is that a simple analytical solution is provided. DOI: 10.1061/(ASCE)GT.1943-5606.0000291 CE Database subject headings: Seismic effects; Earth pressure; Strain; Localization; Limit equilibrium. Author keywords: Seismic active earth pressure; Strain localization; Pseudostatic; Limit equilibrium; Postpeak reduction.

Internal surfaces of pressure vessels used in many industrial sectors are subjected to corrosive effects leading to cavities. In this study, corrosive cavities on investigated pressure vessels are classified according to their shapes and dimensions. Distribution of stress was experimentally investigated around regions of different types of cavities using three-dimensional photoelastic models. An empirical expression is proposed to determine where maximum stress occurs in type of ellipsoidal cavil, in the case of uniaxial loading. The obtained results show quite high stress levels around the cavity regions in pressure vessels, which increase the risk of crack formation. [DOI: 10.1115/1.4000508] Keywords: pressure vessel, corrosive deject, photoelasticity, three-dimensional stress distribution

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

Like microelectronic circuits, microelectromechanical systems (MEMS) devices are susceptible to damage by electrostatic discharge (ESD). At Sandia National Laboratories, polysilicon electrothermal MEMS actuators have been subjected to ESD pulses to examine that susceptibility. Failures, in the form of cracks at points of high stress concentration, occurred that could not be explained by thermal degradation of the polysilicon caused by excessive heating, or by excessive displacement of the legs of the actuator of the same nature that occur in normal operation. One hypothesis presented in this paper is that the internal magnetic forces between the legs of the actuator, resulting from the ESD-associated high current pulses, might produce vibrations of amplitude sufficient to produce these cracks. However, a dynamic analysis based on simple beam theory, indicated that such cracks are unlikely to occur, except under rather extreme conditions. On the other hand, these same current pulses also cause resistive heating of the legs and, therefore, thermally induced compression that can lead to buckling. Buckling stresses, particularly when augmented by magnetic forces, can readily explain failure. Both the magnetic and thermal analyses were performed using the human body model and the machine model of ESD. A justification for ignoring shuttle motion and eddy currents induced in the substrate during the ESD pulse is presented, as well. [DOI: 10.1115/1.2723813] Keywords: electrothermal actuator, micromechanics, failure analysis, magnetic forces, thermal expansion, buckling of beams

The structural mechanics of interlock that causes the surface to adopt a mode of behavior similar to the conventional flexible pavements is one of the unique characteristics of the behavior of concrete block pavements. A way in which pavers dissipate stresses applied by rolling loads has been investigated at the University of Newcastle (U.K.) from 1996 to 2000 and an understanding of the interlock process thereby developed. This paper explains the theoretical details of the interlock mechanism for vertical and rotational interlock excluding horizontal interlock and it demonstrates how it can be used to establish the nature and value of interlock. It shows how surface loading produces patterns of stress within the bedding sand as patch loading rolls across pavers. Their resolution of the structural mechanics clarifies many hitherto unexplained bedding material failures by examining the way in which the local vertical stress transients develop and travel through bedding materials. The performances of pavers having different geometries are also compared in terms of the bedding material stress distribution underpinning the interlock mechanism. DOI: 10.1061/(ASCE)0733-947X(2007)133:5(318) CE Database subject headings: Blocks; Concrete blocks; Stress distribution; Contact pressure; Road surface; Interfaces; Mechanics; Pavements.

Honeycomb fiber-reinforced polymer (HFRP) sandwich panels with sinusoidal core geometry have been used extensively for new construction and replacement of bridge decks. The core geometry used consists of large cavities and represents a new type of core configuration. This study is concerned with the behavior of HFRP panels under transverse shear considering skin effect, and addresses the two contributing factors due to shear warping and bending warping. Shear warping corresponds to the assumption of having a hinge connection between facesheet and core, and bending warping is induced for the assumption of a rigid connection. All previous studies have been focused mainly on shear warping, neglecting for the most part bending warping. A closed-form solution based on proper description of displacement field at the interface is derived considering shear warping. The accuracy of this solution is verified by finite-element (FE) results. The FE model is then applied to study bending warping effect, and also the core-facesheet constraint or interface bonding effect. The equivalent shear stiffness and the stress distributions subject to skin effect are defined, and suggestions for future design considerations are given. DOI: 10.1061/(ASCE)0733-9399(2007)133:3(247) CE Database subject headings: Fiber reinforced polymers; Sandwich structures; Honeycomb structure; Skin friction; Stress distribution; Finite element method; Parameters.

The interference fit provided by solid rivets introduces a residual stress field beneficial to the fatigue life of riveted joints. Evolution in riveting technology has led to force-controlled riveters which provide greater consistency over the rivet installation process and the resulting residual stress field. By reexamining the rivet installation process and its effects on the formation of residual stresses, the fatigue benefits of rivets could be further exploited. Using a 3-D finite element model, installation of universal and countersunk rivets in monolithic aluminum sheet has been studied. Aspects of accepted riveting practice, including the degree of rivet flushness and the rivet squeeze force were found to play significant roles in the formation of residual stresses. Residual stresses beneath the rivet head were also found to be influenced primarily by through-thickness compression of the joined sheets during riveting, challenging the traditional analogy of riveting to radial expansion processes.

In memory of my friends Isaac Feldman (1954-73), Amir Moses (1954-96), and Ilan Ramon (1954-2003). Abstract: The classical stress concentration factor is regarded as the ratio between the maximal value [...]

One of the inherent problems of multi-limbed mobile robotic systems is the problem of multi-contact force distribution; the contact forces and moments at the feet required to support it and those required by its tasks are indeterminate. A new strategy for choosing an optimal solution .[or the contact fierce distribution of multi-limbed robots with three feet in contact with the environment in three-dimensional space is presented. The incremental strategy of opening up the friction cones is aided by using the 'force space graph' which indicates where the solution is positioned in the solution space to give insight into the quality of the chosen solution and to provide robustness against disturbances. The 'margin against slip with contact point priority' approach is also presented which finds an optimal solution with different priorities given to each foot contact point. Examples are presented to illustrate certain aspects of the method and ideas for other optimization criteria are discussed. Keywords: multi-contact force distribution, contact force solution, optimization, margin against slip, contact point priority, force space graph, solution volume representation, multi-limbed robots

We report measurements of the effective tensile strength [F.sub.c] of commercial 'multigrade' oils (in the SAE viscosity grades 5W-30 and 10W-40) over a range of temperatures T, which are representative of those encountered under their normal operating conditions (in the range 20[degrees]C [less than or equal to] T [less than or equal to] 140[degrees]C). Also reported are the values of [F.sub.c] that are obtained for Newtonian silicone oils over a range of shear viscosities. In the experiments reported herein, samples of liquid are subjected to dynamic stressing by a pressure-tension cycle, this being a feature of the conditions experienced by a lubricant within a dynamically loaded journal bearing and the method used to estimate [F.sub.c] avoids reliance on direct measurements of substantial dynamic tensions using conventional pressure transducers. [DOI: 10.1115/1.1881692] Keywords: Effective Tensile Strength, Cavitation, Cavitation Threshold, Dynamic Stressing

Layered structures are used in industry due to their better cost-to-strength and weight-to-strength performance compared with conventional structures. This paper presents a simple and systematic procedure to estimate the limit load for those layered structures that can undergo plastic collapse. The extended Mura's variational principle is used in conjunction with repeated elastic finite element analyses (FEA). The elastic parameters are modified in order to ensure that the repeated analyses lead to a stress distribution close to the limit state. The secant modulus of a given element within the finite element discretization scheme is employed to simulate the plastic flow parameter [[mu].sup.0], and rapid convergence of estimated multipliers to the exact value is achieved. By using the notion of 'leap-frogging' to limit state, improved lower-bound values of limit loads have been obtained. The method has been applied to layered cylinders and beams. [DOI: 10.1115/1.1498845]

Byline: V. A. Maksimyuk (1), I. S. Chernyshenko (1) Abstract: The feasibility of overcoming 'cutoff' effects in four versions of the theory employing classical and mixed functionals is analyzed for sample problems involving the stress concentration near a hole in composite spherical shells with different thicknesses and transverse shear rigidities. Recommendations on the choice of theory are given depending on the shell parameters. A class of 'not very thick' shells with a low shear rigidity is found for which all the versions of the theory yield an acceptable computational accuracy. Author Affiliation: (1) Institute of Mechanics, National Academy of Sciences of Ukraine, Kiev Article History: Registration Date: 06/10/2004

A new study seeks to develop a hypothesis that will describe the primary features of the failure wave phenomenon in shocked glasses.

A polynomial expression is developed for the stress distribution near a circular hole in a composite laminate under biaxial loading. The model is successful in predicting notched strength of multidirectional laminates.

Research was conducted to prove that the scalability of the Ti-silicidation process will be hampered by the local mechanical stress induced during the silicidation reaction even after the introduction of a preamorphization method to enhance the C54 TiSi2 nucleation. Results provide evidence that a higher stress is produced in the silicon substrate during the Ti salicidation than during the low stress Co/Ti-salicidation process.

A study was conducted to analyze a stress distribution in elliptical inclusions supporting a sliding interface and uniform shear eigenstrain. An inherent nonlinear dependence of the stress on applied eigenstrain was also examined. Results indicated the existence of a nonvanishing stress in nearly circular inclusions. Findings also showed that the stress in nearly spherical inclusions decreases when the inclusion is less spherical.

This paper addresses problems of interpreting the results of loading tests in a residual homogeneous, cohesive-frictional soil. Data are presented comparing load-settlement behavior measured from tests carried out using circular steel plates ranging from 0.30 to 0.60 m diameter and square concrete footings ranging in size from 0.40 to 1.00 m. This paper stresses the need to express test results in terms of dimensionless variables in a plot of normalized applied pressure versus settlement-to-diameter ratio. In this space, the effect of the size of the loaded area on measured settlement and on bearing capacity is shown to be negligible for this residual soil site. This approach implies that a unique relationship between normalized pressure and settlement-to-diameter ratio is observed for both small and large vertical displacements. Interpretation of load tests is made within the context of elastic- and elastoplastic theories. For ultimate bearing capacity, reduced strength parameters are used to provide a realistic estimation of ultimate loads. Finally, a numerical approach is proposed for predicting the complete load-settlement behavior of shallow foundations on cemented soil deposits.

Shear stress distribution around vertical wall abutments is studied experimentally, and maximum shear stresses that occur at the upstream corner of vertical wall abutments are determined. Shear stress distributions are presented for Froude numbers ranging from 0.30 to 0.90 and for protrusion ratios (ratio of protrusion length perpendicular to direction of flow to total channel width) of 0.1, 0.2, and 0.3. Shear stress at the nose region of an abutment can be expressed as the sum of stresses due to contraction and the abutment structure alone. An expression for the nose shear amplification factor, [[Lambda].sub.nose], defined as the ratio of the bottom shear stress at the nose region to the approach flow shear stress, is derived. This amplification is due to the contraction and to the presence of a protrusion. In the computation of total shear stresses due to vertical wall abutments, expressions for the shear stress amplification at short contracted reaches, [[Lambda].sub.nose], and amplification due to abutment structure alone, [[Lambda][prime].sub.nose], are presented. Shear stresses around vertical wall abutments are amplified up to a factor of 10 and velocities are increased by up to 50% depending upon flow conditions and abutment protrusion ratios. Results are compared with previous experimental and numerical studies for shear stress distribution around groins and spur dikes. Local scour is mainly caused by increased flow velocity and shear intensity. By quantifying the shear amplification and by identifying regions of shear concentration, the method developed in this paper can be used to determine sediment sizes needed to protect structures against local scour.

Cold formed structural members are fabricated from sheet steels that must meet various material requirements prescribed in applicable national design standards. These requirements ensure that 1) stress concentrations can be redistributed and 2) members and connections can undergo a minimum amount of displacement without a loss in structural performance. The 1996 Australian/New Zealand AS/NZS 4600 and both North American cold formed steel design standards, CSA-S136 and AISI, allow for the use of thin (t < 0.9 mm in AS/NZS 4600), high strength ([f.sub.y] = 550 MPa) sheet steels if the yield stress and ultimate strength are reduced to 75% of their minimum specified values. This paper provides a summary of results detailing the behavior of bolted connections tested in shear, which were composed of 0.42 mm G550, 0.60 mm G550, and 0.60 mm G300 sheet steels (to the 1993 Australian standard AS 1397). Recommendations concerning the adequacy of current design standards with respect to the design of thin sheet steel bolted connections are made, along with the calibration of applicable limit states resistance equations for the three observed modes of failure: end pullout, bearing, and net section fracture.

In this paper, a new method of fast fatigue life prediction under broad band (BB) random loading is proposed, which is based on statistical theory of the peak distribution of a stationary Gaussian random process and the concept of equivalent stress range. The equivalent stress range in the model can be calculated directly by frequency domain parameters, obviating the need for cycle-by-cycle counting and damage summation. The new method offers a great advantage when compared with any other existing approximate methods that are based on the peak stress distribution.

A method for quasi-static analysis of a layered viscoelastic system with different loading and temperature histories is presented. First, the response of the system to the unit step load with a constant temperature is obtained from the corresponding elastic solution. The response to a transient load is then obtained through a linear superposition integral using the unit response as the kernel function. The effects of spatially homogeneous, transient temperature on the mechanical response of the system are taken into account through the time-temperature superposition principle. The method is not based on the Laplace transform-based correspondence principle and no transform-inversion process is required. An illustration of the method is presented through an analysis of the stresses and the displacements in a three-layer, elastic-viscoelastic, composite half-space subjected to a distributed surface load and different temperature conditions.

In this paper, a general solution of an n-layer inclusion problem in a limited region is obtained for the first time. The solutions of three-layer inclusion problems in a limited region under uniform strain field and under uniform stress field are given also. These solutions with undetermined constants are all expressed in closed form. The validity of these solutions is verified by numerical examples of several special cases. These solutions will enable us to study various stress distributions and elastic behavior of concrete materials in microscale.

This paper investigates the free vibration of thick plates with rounded corners subject to different boundary conditions. The periphery of this class of plates is defined by a superelliptical function, and the degree of roundedness can be adjusted by a superelliptical power to acquire the level of stress distribution desired. The Ritz method is employed to derive the governing eigenvalue equation, where the Ritz function consists of polynomials that include a basic function to impose the various boundary constraints. A higher-order shear deformation plate theory is used to account for the effects of transverse shear deformation. The numerical accuracy is ascertained by studying the convergence characteristics of the plate vibration frequencies and, where possible, by comparing the solutions with existing literature. In this paper, the results presented include sensitivities of free vibration frequencies to variations in geometry, boundary constraints and thickness, and also their interactions.

A study was conducted on the confining pressure-caused crushing of granular particles. Results show that particle crushing is reduced by enhancing mineral hardness and that smaller amounts of breakage for a given stress is achieved with stronger or harder particles. Results are consistent with those obtained from the crushing of sedimentary rock-derived oversized particles.

A study was conducted on the influence of mechanical and electromagnetic stresses on the critical current properties of Nb3Sn cables used as superconducting generator field winding conductors. The cables were subjected to a transverse compressive mechanical force of up to 29.4MPa and a magnetic field of up to 7T. The critical current remained constant and was not affected by mechanical stresses of up to 10,000 loading cycles. The critical current, however, decreased after being subjected to compressive and tensile electromagnetic stresses.

Variational and constructive definitions of weight functions were found equivalent for an angularly inhomogeneous wedge. It was found that weight functions for notches or cracks showing the intensity of the stress singularity at the tip as functionals of the loadings present can be defined. A combination of eigenfunctions or variational deviations of energies can result from the definition.

A study developed a model that can be used to predict transient stress distributions in wound rolls made of orthotropic viscoelastic materials with nonlinear moduli. The viscoelastic behavior is characterized by a generalized Maxwell model with allowance for pressure dependent radial behavior. The numerical results agree with the analytical solution for a simplified isotropic case and with other published works regarding this subject.

A study presented an analytical method, based on a heuristic decomposition technique, for solving an infinitely long borehole in an isotropic, poroleastic medium, inclined to the far-field principal stresses. The solution produced three basic predicaments such as the poroelastic plane-strain, an elastic uni-axial and an elastic antiplane shear problems. The solutions to these problems are presented.

Published elastic stress concentration factors are shown to underestimate stresses in the root of a shoulder filleted shaft in bending by as much as 21 percent, and in tension by as much as forty percent. For this geometry, published charts represent only approximated stress concentration factor values, based on known solutions for similar geometries. In this study, detailed finite element analyses were performed over a wide range of filleted shaft geometries to define three useful relations for bending and tension loading: (1) revised elastic stress concentration factors, (2) revised elastic von Mises equivalent stress concentration factors and (3) the maximum stress location in the fillet. Updated results are presented in the familiar graphical form and empirical relations are fit through the curves which are suitable for use in numerical design algorithms. It is demonstrated that the first two relations reveal the full multiaxial elastic state of stress and strain at the maximum stress location. Understanding the influence of geometry on the maximum stress location can be helpful for experimental strain determination or monitoring fatigue crack nucleation. The finite element results are validated against values published in the literature for several geometries and with limited experimental data.

The perturbed Lagrangian approach and Coulomb's law of friction are integrated as a finite element analysis of frictional constraint in fiber-reinforced composite materials. The method focuses on fiber pull-out resistance as a factor in energy absorption during material failure. A matrix collapse due to the pulled fiber generates a 'pinching' effect, while broken fibers produce a 'plug' effect.

The base current degradation of poly-emitter bipolar junction transistors occurs during the reverse-bias condition due to the induction of hot-carrier effects. The application of forward bias voltage improves the degraded current. A model analyzes the effects under alternating current stresses. The model provides accurate predictions of the relationship between the excess base current and the stress time for different stress conditions.

The failure probability of notched tensile bars is calculated using the multi-axial Weibull theory. The influence exerted by the stress concentration factor, the stress gradient in the notch root, and the Weibull exponent is analyzed.

A finite-element analysis of the creep and plastic deformation that occurred in soldered joints of a multichip module during power cycling is reported. The analysis, which considered the stress distribution among components in the package as a function of time, found that nonuniform stress distribution determines the inelastic deformation and service life of solder joints. It also underscored the important role played by component material and geometry in improving the fatigue life of solder joints.

Fatigue life as a function of number of stress cycles has been determined for three-layer titanium-aluminum-titanium thin-film specimens. For nominal stresses ranging from 50 to 90 percent of the upper-bound ultimate strength, the fatigue lives ranged up to 76 cycles. In all specimens, active cracks were observed after only a few stress cycles. These cracks grew with repeated cycling. The fatigue life was reached when the specimen could no longer sustain the maximum cyclic stress.

Stress in dense polymer systems is classically viewed as being molecular in character and is based on the entropic spring concept. A description on the atomic level has been developed on the basis of extensive computer simulations. An important new concept is the intrinsic monomer stress (IMS), the individual monomer contribution to the macroscopic stress referred to a local moving coordinate system in which the backbone bonds attached to that monomer are fixed. The IMS is time-independent and, for a given polymer system at fixed density, has the same value in the equilibrium melt, with the melt undergoing stress relaxation, and in the deformed cross-linked system., Dense polymer systems above their glass transition temperatures, whether cross-linked as in rubber and other elastomers or uncross-linked as in polymer melts, play important roles in technology and biology. As [...]

The screw stress concentration for six nut-bolt connections embodying three different thread profiles and two nut shapes is measured photoelastically. Buttress (nearly zero flank angle), trapezoidal (15-deg flank angle), and triangular (30-deg flank angle) thread forms are examined in combination with standard and lip-type nuts. The effect of the thread profile on the screw stress concentration appears to be dependent upon the kind of nut considered. If the fastening incorporates a standard nut, the buttress thread is stronger than the triangular one, which, in turn, behaves better than the trapezoidal contour. The improvement is roughly a 20-percent reduction in the stress concentration factor from the trapezoidal to the buttress thread. In the case of lip nut, conversely, this tendency is somewhat reversed, with the trapezoidal thread performing slightly (but not decidedly) better than the other two shapes. Finally, averaged over all three thread forms, the lip nut exhibits a stress concentration factor which is about 50 percent lower than that of the standard nut.

Application of ray theory to the problem of stress-focusing effect in a uniformly heated solid cylinder facilitates the representation of stress waves in terms of ray series. Mathematical analysis of stress waves expressed in an infinite series indicates that the stress waves attain peak values periodically at a constant time and the order of singularity of the stresses in a cylinder subjected to instantaneous heating is O(P-2). Stress-focusing effects are achieved when the surface of the cylinder reflects stress waves, which gather radially inward to the center.

The electric field (E) and velocity (v) which were calculated from falling ball experiments show two kinds of retarding forces E(2) and vE(2). E(2) is related to sheer stress, varies with volume fraction and is independent of particle size, while vE(2) is proportional to particle size and volume. The forces in E(2) deal with chain stretching and breaking at constant temperatures, while the impact action on chains influences vE(2).

A smooth depression on the surface of a stretched half-plane amplifies the stress at the tip of a smooth protrusion and the surface stress at the trough of depression. A routine perturbation methodology is used to establish the related stress concentration factors, in relation to a small aspect ratio that estimates the marginal unevenness of the surface. Matched asymptotic expansion was used to achieve the required analytic solution in cases where corners exist for the depression protrusion profile.

How do boundary conditions influence strain localization in concrete loaded in compression? To answer this question, compressive tests were performed on prismatic specimens of mortar. The blocking or nonblocking of rotation of the top platen of the press and the use or absence of an antifriction system have led us to consider four different boundary conditions. The onset of strain localization and its development in the course of loading are determined by the stereophotogrammetric method. The results obtained show that rotation (when it is free) always starts after the peak load. The postpeak portion of the load-displacement curve depends to a very large extent on the boundary conditions: the use of an antifriction system increases the mean slope of this part. But, on the other hand, the onset of strain localization occurs at the peak, whatever the boundary conditions.

In the thin shell analysis of welded pad reinforced nozzles in pressure vessels, no contact between pad and vessel is often assumed. The significance of this contact force to the stress distribution in the structure is little known. In this paper, stress results from the finite element analysis, which includes the contact force between the pad and the vessel, are reported. A comparison of the finite element results with those from thin shell analysis and experiments shows that the finite element method with contact assumption yields improved theoretical prediction for the stress distribution. The effect of both the gap and friction between the pad and the vessel are also investigated.

Factors influencing the spread of voids in interconnecting lines were determined and characterized by using simple theoretical models. Earlier studies in this field were also analyzed by explaining the redistribution of stress induced by the existence of a void in the line and by the progressive reduction of stress by the increase in the void. The variation in stress and strain around the void were computed as a function of time. The rate of void growth was also measured.

A numerical study of polarization switching in 1.3-micrometer InGaAsP ridge-wageguide lasers under stress conditions is presented. It describes the polarization switching between the transverse electric and transverse magnetic modes in terms of the injection current using several biaxial tensile and compressive stress profiles. A general laser model adapted to consider the effects of stress on the laser's gain and effective index is employed. Results indicate the cause of mode switching to be the variance in the modal pumping efficiency when the current is changing.

The intergranular stress corrosion cracking (IGSCC) of sensitized Type 304 stainless steel (SS) has been investigated by slow strain rate tests (SSRTs) in 289 [degrees] C water containing sulfate impurity. Both smooth and circumferentially notched specimens were used to assess the effects of strain concentrations on stress corrosion cracking (SCC). Experiments were conducted over a range of nominal strain rates of [10.sup.-5] to [10.sup.-7] [s.sup.-1]. A comparison of the results observed for the smooth and notched specimens suggest that the estimated growth rates of small cracks in SSRT specimen geometry is influenced by the presence of strain concentrations. In particular, the average crack growth rates estimated from tests performed at the same nominal strain rate are observed to increase with the notch depth, and power-law relationships exist between strain rate and SCC parameters such as failure time crack growth rate. The strain concentration factors at the notch roots of Type 304 specimens subjected to axial load have been estimated by finite-element elastic-plastic stress analyses, as well as by Neuber's rule. The nominal and crack-tip strain the effects on SCC in both smooth and notched specimens are interpreted in terms of a model based on elastic-plastic fracture mechanics and film-rupture mechanisms that invoke diffusion-controlled SCC growth kinetics.

The effects of strain-softening nonlinearly viscoelastic solids on crack-tip stress and deformations fields is studied using finite element analysis. A nonlinearly viscoelastic constitutive model was used in the study. Results show that strain softening decreases stress concentration at the crack tip. A strain softened material zone exists from the crack tip and along the crack line which can result to crazes that promote microvoid nucleation and growth.