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Residual stresses and thermoviscoelastic deformation of a laminated film utilized for film insert molding was investigated through measurement of thermal expansion coefficient (CTE) and relaxation modulus. Thermoviscoelastic deformation of the film was also analyzed with numerical analysis by applying measured relaxation modulus, CTE, and residual stress to finite element method (FEM). Stress relaxation of the pristine film showed significantly different behavior from that of the unannealed film during annealing. Effects of the CTE and relaxation modulus on the thermoviscoelastic deformation were predicted by considering thermal shrinkage and structural relaxation. Moreover, numerical results on thermoviscoelastic deformation were in good agreement with experiments when initial stress distribution in the solid specimen was applied to the numerical analysis. POLYM. ENG. SCI., 52:1121-1127, 2012. © 2011 Society of Plastics Engineers, INTRODUCTION Film insert molding (FIM), known as in-mold decorating, is one of the various coating technologies to perform surface modification of injection molded parts. In general, a film is inserted [...]

Using cylindrical specimens with short gauge length, bulk cavitation is successfully generated in high-density polyethylene copolymers (HOPE) under tensile loading. The bulk cavitation is generated without the presence of sharp notch, and therefore, crack growth is not involved in the rupture process. The bulk cavitation is investigated in two types of HOPE that have different molecular characteristics. Test results indicate that bulk cavitation can be introduced in both the types of HOPE, for which the loading level is most easily identified using plots of true axial stress versus stroke. The main difference in the rupture process occurs during the postcavitation stretch. Using specimens of sufficiently long gauge length, constitutive equations for the HDPEs are determined and applied to finite element modeling of specimens with short gauge length. The results show that the hydrostatic stress level in specimens of short gauge length is about twice as high as that in specimens of long gauge length, supporting the conclusion on bulk cavitation from rubber testing. For HOPE, this study shows that the rise of hydrostatic stress level leads to the suppression of necking, to allow the bulk cavitation to dominate the deformation process. POLYM. ENG. SCI., 52:1005-1014, 2012. © 2011 Society of Plastics Engineers, INTRODUCTION Cavitation is known to be involved in many materials during the failure process [1-3], For polymers, its occurrence often results in a whitening appearance that is similar to that [...]

The advanced constitutive model KHSM for structured clays, which incorporates the effects of loss of structure within an elastoplastic framework, has been implemented in a finite element procedure and used to investigate the failure height and pore-water pressures of embankment A constructed at Saint Alban, Quebec. For the purpose of model comparison, simulations were also performed using the standard bubble model (KHM) without destructuration. The numerical predictions of pore-water pressures and settlements are also compared with field measurements. The results clearly demonstrate the importance of including the effects of loss of structure in the analysis. Key words: structured clays, constitutive models, numerical analysis, embankments, full-scale tests, failure. Le modele constitutif avance pour les argiles structurees KHSM, qui integre les effets de la perte de structure dans un cadre elasto-plastique, a ete implante dans une procedure par elements finis et utilise pour etudier la hauteur de rupture et les pressions interstitielles du talus A, construite a Saint-Alban, Quebec. Afin de comparer les modeles, des simulations ont aussi ete realisees avec le modele de bulle standard (KHM) sans destructuration. De plus, les predictions numeriques de pression interstitielle et de tassement ont ete comparees avec les mesures prises sur le terrain. Les resultats demontrent clairement l'importance d'inclure les effets de la perte de structure lors de l'analyse. Mots-cles : argiles structurees, modeles constitutifs, analyse numerique, talus, essai a grande echelle, rupture. [Traduit par la Redaction], Introduction Design and construction of engineered structures on soft soils is becoming more commonplace because of the lack of better land available for construction in both developed and developing regions [...]

The vertical uplift resistance of a group of two horizontal coaxial strip anchors, embedded in a general c-Φ soil (where c is the unit cohesion and Φ is the soil friction angle), has been determined by using the lower bound finite element limit analysis. The variation of uplift factors [F.sub.c] and [F.sub.γ], due to the components of soil cohesion and unit weight, respectively, with changes in depth (H)/width (B) has been established for different values of vertical spacing (S)/B. As compared to a single isolated anchor, the group of two anchors provides a significantly greater magnitude of [F.sub.c] for Φ ≤ 20° and with H/B ≥ 3. The magnitude of [F.sub.c] becomes almost maximum when S/B is kept closer to 0.5H/B. On the other hand, with the same H/B, as compared to a single anchor, hardly any increase in [F.sub.γ] occurs for a group of two anchors. Key words: anchors, failure, finite elements, limit analysis, optimization, soils. La resistance au soulevement vertical d'un groupe de deux ancrages coaxiaux horizontaux, enfonces dans un sol de type general c-Φ (ou c est la cohesion unitaire et φ est l'angle de friction du sol), a ete determinee en utilisant l'analyse limite par elements finis a frontiere inferieure. La variation des facteurs de soulevement [F.sub.c] et [F.sub.γ] selon les variations de H/B, associes aux composantes de cohesion du sol et de poids unitaire, respectivement, a ete etablie pour differentes valeurs de S/B. Comparativement a un seul ancrage isole, le groupe de deux ancrages permet d' augmenter significativement la magnitude de [F.sub.c] pour Φ ≤ 20° et avec H/B ≥ 3. La magnitude de [F.sub.c] atteint presque un maximum lorsque S/B est maintenu pres de 0,5 H/B. Par contre, pour un meme H/B,iln'y a pratiquement pas d'augmentation de [F.sub.γ] pour un groupe de deux ancrages comparativement a un ancrage isole. Mots-cles : ancrages, rupture, elements finis, analyse limite, optimisation, sols. [Traduit par la Redaction], Introduction A number of experimental as well as theoretical investigations have been carried out by different researchers to determine the vertical uplift resistance of a single isolated plate anchor (Meyerhof [...]

To ensure public safety, existing bridges are often evaluated for their load-bearing capacity. Realistic evaluation must take into account the actual nonlinear stress-strain characteristics of the bridge materials and the interaction among its structural components at all stages of loading up to failure. The finite element method is particularly suitable for this type of analysis, but nonlinear finite element formulations involve many assumptions that must be verified before any practical application. In this study, the accuracy of a nonlinear finite element program developed by the authors for the analysis of composite steel-concrete bridges is checked by comparing its results with experimental data from simply supported and continuous beams tested by others and from a 1/3 scale multi-girder composite bridge tested by the authors. Good agreement is observed between the measured and the computed load-deflection responses and strains at all stages of loading up to the maximum load, which demonstrates the accuracy of the finite element formulation and the validity of its assumptions. Key words: analysis, bridge, composite, concrete, finite element, load distribution, reinforced, steel. La capacite portante des ponts existants est souvent evaluee pour assurer la securite du public. Une evaluation realiste doit tenir compte des caracteristiques non lineaires de contrainte-deformation des materiaux du pont et de l'interaction entre ses composantes structurales a toutes les etapes de chargement jusqu'a la rupture. La methode par elements finis est particulierement bien appropriee pour ce type d'analyse, mais les formulations des elements finis non lineaires impliquent de poser plusieurs hypotheses qui doivent etre verifiees avant toute utilisation pratique. Cette etude verifie la precision du programme d'elements finis non lineaires developpe par les auteurs pour l'analyse des ponts composites acier-beton en comparant les resultats aux donnees experimentales obtenues d'essais sur des poutres continues et a simple support realises par d'autres auteurs ainsi qu'aux donnees d'essais des auteurs sur un pont composite a plusieurs poutres a l'echelle 1/3. Une bonne correlation est remarquee entre les reponses et les contraintes de charge-deformation mesurees et calculees a toutes les etapes de chargement jusqu'a la charge maximale, ce qui demontre la precision de la formulation des elements finis ainsi que la validite de ses hypotheses. Mots-cles : analyse, pont, composite, beton, elements finis, distribution de charges, arme, acier. [Traduit par la Redaction], 1. Introduction Composite bridges, comprising a concrete slab connected to steel girders by means of shear connectors, are quite common. Cost-effectiveness and ease of construction make these structures popular; consequently, [...]

The finite element method (FEM) has become a standard tool for solving complex problems in geotechnical engineering. Many different advanced constitutive models for fine-grained soils have been developed in recent years, which can consider various phenomena of soil. Generally, the number of constitutive parameters increases with phenomena incorporated in the model, and their determination is one of the key issues in numerical modeling in geotechnics. Normally, experimental data, experience, and back analyses based on engineering judgment are used to arrive at appropriate input parameters for a particular model. However, this procedure is not always satisfactory, especially when the number of required input parameters is large. In this paper, a population-based algorithm has been used to determine the constitutive parameters for a geotechnical boundary value problem, namely a floating stone column foundation under an embankment. Measurements of surface settlements and excess pore-water pressures at different depths are available for calibration. A subsequent statistical assessment of the calibration results is followed to assess the quality of the identified parameters in dependency of the different set of measurements evaluated. As a major result of this research, measures of the utility and reliability of the constitutive models for further predictive computations can be estimated. Key words: numerical modeling, clays, constitutive relations, creep, field instrumentation, ground improvement. La methode par elements finis (MEF) est devenue un outil standard pour solutionner des problemes complexes en genie geotechnique. Plusieurs modeles constitutifs avances differents, pour des sols a granulometrie fine et pouvant considerer des phenomenes varies dans les sols, ont ete developpes dans les dernieres annees. Generalement, le nombre de parametres constitutifs augmente selon les phenomenes incorpores dans le modele, et leur determination est un probleme important relie a la modelisation numerique en geotechnique. Normalement, les donnees experimentales, l'experience et les retro- analyses basees sur un jugement d'ingenierie sont utilisees pour arriver aux parametres d'entree appropries pour un modele donne. Cependant, cette procedure n'est pas toujours satisfaisante, particulierement lorsque le nombre de parametres d' entree requis est grand. Dans cet article, un algorithme base sur la population a ete utilise pour determiner les parametres constitutifs d'un probleme de valeur frontiere en geotechnique, soit une fondation faite d'une colonne en pierre flottante sous un remblai. Des mesures des tassements de surface et de la pression interstitielle excessive a differentes profondeurs sont disponibles pour le calibrage. Une analyse statistique subsequente des resultats du calibrage est realisee pour evaluer la qualite des parametres identifies en dependance aux differents ensembles de donnees evalues. Un resultat majeur de cette recherche est la possibilite d'estimer les mesures de l'utilite et de la fiabilite des modeles constitutifs pour des calculs predictifs supplementaires. Mots-cles : modelisation numerique, argiles, relations constitutives, fluage, instrumentation de terrain, amelioration du sol. [Traduit par la Redaction], Introduction There is an increasing demand for the application of advanced numerical methods in geotechnical engineering. Existing commercial finite element (FE) codes provide many different types of constitutive models to [...]

The methodology proposed in this work uses the local measured strain rate history as the applied 'load* to the finite element (FE) 'material point'. Next, with this strain rate history, two objective functions related to the true stress-strain and volumetric strain response could be minimized to identify some of the material parameters of the constitutive model. The whole identification process, of the nine material parameters required, is described in detail. In addition, a short description of the hyperelastic-viscoplastic constitutive model used is given with an experimental program including mainly uniaxial tensile tests at different strain rates. The thermoplastic material investigated here is a mineral and rubber modified polypropylene (PP) compound. The main experimental data uses 3D digital image correlation (DIC) to determine full-field displacements and deduce true stress-strain, volume dilatation, and local strain rates curves during deformation. POLYM. ENG. SCI., 52:438-448, 2012. ©2011 Society of Plastics Engineers, INTRODUCTION Polymers are widely used in the transport industry, specially, when structural components and passengers/pedestrian safety are in focus. The experience in using polymers in impact protection and structural systems, [...]

Three-dimensional finite difference analyses have been carried out to investigate the behaviour of a single pile used to stabilize a slipping mass of soil by embedment into a stable stratum. Analyses were initially carried out to determine the reduction in the limiting pile-soil lateral force per metre length, [p.sub.u], close to the unconfined ground surface. The analyses then explore the failure mechanisms for landslide stabilizing piles categorized by Viggiani. The effects of varying the strength of the slip plane interface between the sliding and stable strata, and of a sloping ground surface on the behaviour of the pile are then investigated. The results from numerical models with a rigid pile, a distinct plane of sliding, and a horizontal ground surface, as assumed by Viggiani, agree well with his theoretical mechanisms. Lower values of [p.sub.u] close to the ground surface and adjacent to the sliding plane are found to reduce the maximum shear resistance that piles can provide to the slipping mass when compared with Viggiani's theoretical solutions. Further analyses show that the strength of the slip plane interface has a considerable influence on pile behaviour, and that the slope of the ground surface is only significant above a certain angle. Key words: slope stability, slope stabilization, finite element analysis, laterally loaded piles, pile-soil interaction, undrained. Des analyses par difference finie en trois dimensions ont ete realisees pour etudier le comportement d'un pieu simple, utilise pour stabiliser une masse de sol glissante par enfoncement dans une couche inferieure stable. Des analyses ont d'abord ete effectuees pour determiner la reduction de la force laterale limite pieu-sol par metre lineaire, pu, pres de la surface du sol non confine. Les analyses ont ensuite explore les mecanismes de rupture de pieux stabilisateurs de glissements de terrain categorises par Viggiani. Les effets sur le comportement du pieu de la variation de la resistance de l'interface du plan de glissement entre les couches de sol glissantes et stables, ainsi que de l'inclinaison de la surface du sol, ont ete etudies. Les resultats de modeles numeriques etablis avec un pieu rigide, un plan de glissement et une surface de sol horizontale distincte, tel que suppose par Viggiani, concordent bien avec ses mecanismes theoriques. On a observe que des valeurs de pu pres de la surface du sol et adjacentes au plan de glissement reduisent la resistance au cisaillement maximale que les pieux peuvent offrir a la masse glissante, en comparaison avec les solutions theoriques de Viggiani. Des analyses plus approfondies ont demontre que la resistance de l'interface du plan de glissement a une influence considerable sur le comportement du pieu, et que l'inclinaison de la surface du sol est significative seulement lorsqu'elle est au-dessus d'un certain angle. Mots-cles : stabilite de pente, stabilisation de pente, analyse par elements finis, pieux charges lateralement, interaction pieusol, non draine. [Traduit par la Redaction], Introduction Discrete piles have been used to stabilize landslides for many decades (De Beer and Wallays 1970; Ito and Matsui 1975; Fukuoka 1977; Sommer 1979; Allison et al. 1991; Hong [...]

This paper investigates the undrained stability of a plane strain circular tunnel in clay, where the shear strength profile is assumed to increase linearly with depth. Stability solutions for a variety of geometries and soil conditions are found using rigid-block upper bound methods as well as finite element limit analysis (which gives both upper and lower bounds). The latter procedures employ a discrete form of the bound theorems of classical plasticity, use a bespoke conic programming scheme to solve the resulting optimization problems, and bracket the true collapse load to within 5% for all the cases considered. Results from the study are summarized in the form of stability charts as well as an approximate closed-form expression that can be used by practising engineers. Key words: tunnels, stability, limit analysis, finite element method. Cet article etudie la stabilite a l'etat non draine en deformation en plan d'un tunnel circulaire dans l'argile, dans lequel on considere que le profil de resistance au cisaillement augmente de facon lineaire avec la profondeur. Les solutions de stabilite pour une variete de geometries et de conditions de sol sont determinees a l'aide de methodes a frontiere superieure de blocs rigides, ainsi qu'avec les analyses par elements finis (qui donne des frontieres inferieures et superieures). Ces dernieres procedures impliquent une forme discrete des theoremes des frontieres de la plasticite classique, utilisent un code de programmation conique sur mesure afin de solutionner les problemes d'optimisation, et donnent une valeur de la charge d'effondrement reelle a l'interieur de 5% pour tous les cas consideres. Les resultats de l'etude sont resumes sous forme de tables de stabilite ainsi qu'en tant qu'expression fermee approximative qui peut etre utilisee par les ingenieurs praticiens. Mots-cles : tunnels, stabilite, analyse limite, methode par elements finis. [Traduit par la Redaction], Introduction This paper investigates the undrained stability of a circular tunnel in clay where the shear strength increases linearly with depth. The stability of the tunnel is found using numerical [...]

A procedure is developed where stresses from a finite element analysis are incorporated into a limit equilibrium framework to evaluate the stability of three-dimensional slopes. An independent stress-deformation analysis is performed to calculate the internal stress state for the slope. The stress distribution is imported into the three-dimensional slope stability analysis in the form of a regular grid. The slip surfaces considered in the limit equilibrium analysis are ellipsoidal and discretized using a series of triangular planes. The normal and shear force acting at the centroid of individual triangular planes can be computed from the internal stress distribution. Subsequently, the factor of safety of a selected slip surface can be calculated directly without using an iterative procedure. A series of verification examples are presented to confirm that the proposed method provides the required accuracy and flexibility to assess the stability of slopes typically encountered in practice. Sensitivity analyses are presented to show how the procedure used to compute the forces acting on each triangular plane, the number of planes used to discretize the slip surface, and Poisson's ratio influence the computed factors of safety, but do not limit the successful application of the methodology. Key words: three-dimensional slope stability, stress-based slope stability, Poisson's ratio. Cet article presente une procedure dans laquelle les contraintes d'une analyse par elements finis sont incluses dans un systeme d'equilibre limite pour evaluer la stabilite de pentes en trois dimensions. Une analyse independante en contrainte-deformation est realisee afin de calculer l'etat des contraintes internes de la pente. La distribution des contraintes est importee dans l'analyse de stabilite de pente en trois dimensions sous la forme d'une grille rectangulaire. Les surfaces de glissement considerees dans l'analyse d'equilibre limite sont ellipsoidales et discretisees a l'aide d'une serie de plans triangulaires. Les forces normales et de cisaillement exercees au centroide des plans triangulaires individuels peuvent etre calculees a partir de la distribution des contraintes internes. Ensuite, le facteur de securite d'une surface de glissement selectionnee peut etre calcule directement sans avoir recours a une procedure iterative. Une serie d' exemples de verification sont presentes pour confirmer que la methode proposee fournit la precision et la flexibilite necessaire pour evaluer la stabilite de pentes typiquement rencontrees sur le terrain. Des analyses de sensibilite sont presentees pour demontrer comment la procedure utilisee pour calculer les forces qui agissent sur chaque plan triangulaire, le nombre de plans utilises pour discretiser la surface de glissement, et le ratio de Poisson influencent les facteurs de securite calcules, mais sans limiter l'application adequate de la methodologie. Mots-cles : stabilite de pente en trois dimensions, stabilite de pente basee sur les contraintes, ratio de Poisson. [Traduit par la Redaction], Introduction A variety of procedures are available to evaluate the stability of slopes ranging from simple expressions such as the use of a stability number to rigorous numerical methods. The [...]

The consolidation of the soft foundation soil of a geogrid-reinforced embankment, improved with prefabricated vertical drains (PVDs), is modelled in this paper using two-dimensional (2D) plane strain coupled finite element (FE) analysis to predict long-term multiple behaviour characteristics (e.g., settlement, lateral displacement, excess pore-water pressure response, geosynthetic strain) of the embankment. Two sets of analyses were carried out with the foundation soil being modelled using relatively simple elastic-viscoplastic (EVP) models. A nonlinear creep function was used in association with them. The input material parameters were determined from extensive laboratory testing or were taken from reliable sources except for the horizontal permeability, which was systematically back-estimated using oedometer test data and the first year of field settlement data. The results from both analyses were compared with the long-term (up to 6 years) field-monitoring data and were found to be in good agreement with the field measurements. Key words: viscoplasticity, soft clay, embankments, plane strain analysis, creep, time-dependency. La consolidation du sol mou de fondation d'un remblai renforce d'une geogrille, amelioree a l'aide de drains verticaux prefabriques (DVP), est modelisee avec une analyse par elements finis (EF) en deux dimensions (2D) de la deformation en plan couplee afin de predire les caracteristiques multiples de son comportement a long terme (ex : tassement, deplacement lateral, pression interstitielle excessive, deformation du geosynthetique). Deux series d'analyses ont ete realisees dans lesquelles le sol de fondation etait modelise par des modeles elasto-viscoplastiques (EVP) relativement simples. Une fonction non-lineaire de fluage a ete utilisee en association avec ces modeles. Les parametres initiaux des materiaux ont ete determines par de nombreux essais en laboratoire, ou ont ete pris de sources fiables, sauf pour la permeabilite horizontale. Celle-ci a ete estimee par retro-analyse des donnees des essais odometriques et de la premiere annee des donnees de tassement in situ. Les resultats des deux analyses ont ete comparees avec les donnees de suivi in situ a long terme (jusqu'a 6 ans), et la correspondance avec les donnees de terrain est bonne. Mots-cles : visco-plasticite, argile molle, remblais, analyse de deformation en plan, fluage, dependance au temps. [Traduit par la Redaction], Introduction Elastoplastic models like the one named modified Cam clay (MCC) (Roscoe and Burland 1968) have been used to model the behaviour of clay with considerable success (e.g., Rowe et [...]

In this paper, a three-dimensional (3D) finite element (FE) model is developed to simulate the pullout behaviour of a soil nail in a soil-nail pullout box under different overburden and grouting pressures. The FE model simulates all the procedures of a pullout test on a grouted soil nail in a compacted and saturated completely decomposed granite (CDG) soil. The stress-strain behaviour of the CDG soil is described by a modified Drucker-Prager/Cap model, while that of the soil-nail interface is represented by the Coulomb friction model. Triaxial experiment data are used to calibrate the soil parameters in the soil constitutive model. The interface parameters are determined from back-analysis with the laboratory soil-nail pullout data. The soil stress variations surrounding the soil nail during drilling, grouting, saturation, and pullout are all well simulated by the FE modelling and compared with available test data. The comparisons between the modelling and experimental data have shown that the established FE can well simulate the pullout behaviour of a soil nail in a soil mass. Based on this, the verified FE model has the potential to simulate the performance of a soil nail in a field soil slope. Key words: soil nailing, pull-out resistance, finite element, overburden pressure, grouting pressure, slope. Dans cet article, un modele tridimensionnel par elements finis (EF) est developpe dans le but de simuler le comportement en retrait d'un clou de sol dans une boite de retrait de clou de sol sous differentes pressions des terres et pressions de cimentation. Le modele EF simule toutes les procedures d'un essai de retrait sur un clou de sol cimente dans un sol de granite compacte et completement decompose (GCD). Le comportement en contrainte-deformation du sol GCD est decrit a l' aide du modele Drucker-Prager/Cap modifie, tandis que l' interface sol-clou est representee par le modele de friction de Coulomb. Des donnees d' essais triaxiaux sont utilisees pour calibrer les parametres du sol dans le modele constitutif du sol. Les parametres de l' interface sont determines par retro-analyse des donnees des essais de retrait des clous de sol realises en laboratoire. Les variations des contraintes du sol entourant le clou durant le forage, la cimentation, la saturation et le retrait sont toutes bien simulees par la modelisation EF et se comparent bien aux donnees d'essais disponibles. Les comparaisons entre la modelisation et les donnees experimentales ont demontre que le modele EF etabli peut bien simuler le retrait d'un clou de sol d'une masse de sol. Ainsi, le modele EF verifie a le potentiel de simuler la performance d'un clou de sol dans une pente sur le terrain. Mots-cles : clou de sol, resistance au retrait, elements finis, pression des terres, pression de cimentation, pente. [Traduit par la Redaction], Introduction Grouted soil nails have been widely used in Hong Kong as an economical and efficient method to stabilize existing and new-cut slopes. More than 200 slopes and retaining walls [...]

Starting with the principle of stationary potential energy, this paper develops the governing differential equations of equilibrium and boundary conditions for shear deformable thin-walled beams with open cross-section. Unlike conventional solutions, the formulation is based on a non-orthogonal coordinate system, in which the selected origin is generally offset from the section centroid. The exact solution of the resulting coupled differential equations of equilibrium is derived and used to develop exact shape functions. A finite element based on the exact shape functions is then formulated. Through a series of examples, the adoption of non-orthogonal coordinates is shown to enable the seamless modelling of structural members with eccentric boundary conditions and (or) stepwise cross-sectional variations. Key words: shear deformation, thin-walled beams, finite element, exact solution, coped beams, eccentric supports. En se basant sur le principe de l'energie potentielle stationnaire, cet article developpe des equations differentielles gouvernant les conditions d'equilibre et limites de poutres a paroi mince et a profil ouvert, deformables en cisaillement. Contrairement aux solutions conventionnelles, la formulation est basee sur un systeme de coordonnees non orthogonales dans lequel l' origine choisie est generalement decalee par rapport au centre d'aire de la section. La solution exacte des equations differentielles couplees de l' equilibre qui en resultent est obtenue et utilisee pour developper des fonctions de formes exactes. Un element fini base sur les fonctions de formes exactes est ensuite formule. Une serie d'exemples montre que l'adoption de coordonnees non orthogonales permet une modelisation de facon transparente des elements structuraux avec des points d'appui excentriques et (ou) des variations progressives du profil. Mots-cles : deformation en cisaillement, poutres a parois minces, element fini, solution exacte, poutres en contre-profile, supports excentriques. [Traduit par la Redaction], 1. Introduction In structural analysis, the well known Euler-Bernoulli and Vlasov beam theories (1961) are most extensively used in predicting displacements and stresses in members. These theories neglect the shear [...]

A successive initiation finite element modeling approach is presented in which an empirical continuum damage model, energy partitioning damage evolution model, developed by the author is used to update state of damage and constitutive properties of the material under thermomechanical cyclic loading and accumulate damage in the elements. Plastic and viscoplastic damages are evaluated based on the plastic and viscoplastic work densities obtained through finite element. Constitutive properties are updated elementwise at each step of the process based on the state of damage in each element. The elements that have reached the damage threshold are removed from the structure to initiate and propagate fatigue crack. This successive initiation approach is used to model crack initiation and propagation in Pb-free solder material under thermomechanical loading. A case study is presented, damage propagation path and pattern are compared with typical experimental results, and the accuracy of the model was verified. [DOI: 10.1115/1.4002722]

The load carrying capacity of a component or structure with varying material properties (inhomogeneous) is investigated using various lower- and upper-bound limit load multi-pliers in the context of variational principles. In order to evaluate the different limit load multipliers, the elastic modulus adjustment procedure is used to obtain statically admissible stress and kinematically admissible strain fields. The proposed upper and lower bound limit load estimates are compared with the results obtained from inelastic finite element analysis for two- and three-dimensional geometries. [DOI: 10.1115/1.4001219]

A new method employing the fitting of a least squares plane to stress distribution obtained from a finite element analysis for evaluating categorized values is presented. The property of a least squares fit, i.e., the preservation of volume under stress distribution and the plane of consideration, is used in evaluating various numerical integrals. The procedure is demonstrated through application to a typical shell nozzle junction. [DOI: 10.1115/1.4001521] Keywords: stress category, least squares fit, membrane and bending stresses

An important issue in engineering application of the 'design by analysis' approach in pressure vessel design is how to decompose an overall stress field obtained by finite element analysis into different stress categories defined in the ASME B&PV Codes III and VIII-2. In many pressure vessel structures, it is difficult to obtain [P.sub.L] + [P.sub.b] due to the lack of information about primary bending stress. In this paper, a simple approach to derive the primary bending stress from the finite element analysis was proposed with application examples and verifications. According to the relationship of the bending stress and applied loads or the relationship of the bending stress and displacement agreement, it is possible to identify loads causing primary bending stress for typical pressure vessel structures. By applying the load inducing primary bending stress alone and necessary superposition, the primary bending stress and corresponding stress intensity [P.sub.L] + [P.sub.b] can be determined for vessel design, especially for axisymmetric problems. [DOI: 10.1115/1.4001656] Keywords: pressure vessel, design by analysis, primary bending stress, FEM analysis, stress classification

There are still some challenges, such as grid quality, numerical stability, and boundary schemes, in the practical application of high-order finite difference schemes for complex configurations. This study presents some improved strategies that indicate potential engineering applications of high-order schemes. The formally fifth-order weighted compact nonlinear scheme developed by the authors is implemented on point-matched multiblock structured grids, which are generated over complex configurations to ensure the grid quality of each component block. The information transmission between neighboring blocks is carried out by new characteristic-based interface conditions that directly exchange the spatial derivatives on each side of an interface by means of a characteristic-based projection to keep the high-order accuracy and high resolution of a spatial difference scheme. The high-order scheme combined with the interface conditions is shown to be asymptotically stable. The engineering-oriented applications of the high-order strategy are demonstrated by solving several two- and three-dimensional problems with complex grid systems. DOI: 10.2514/1.J050285

The seismic stability analysis of rock slope is implemented using a block element method (BEM) in this paper. Based on the formulations of the matrices of stiffness, mass, and damping, the dynamic governing equation for the rock block system is established. The Wilson method is used to solve the dynamic governing equation, and the viscoelastic artificial boundary condition is introduced to treat the unbound domain problem. The proposed method is applied to the seismic stability analysis of the intake slope in a hydropower project, from which the dynamic safety factors of key block element combinations during earthquake and their dynamic amplification factors of acceleration are evaluated. DOI: 10.1061/(ASCE)GT.1943-5606.0000391 CE Database subject headings: Seismic analysis: Boundaries; Slopes; Rocks; Safety factor. Author keywords: Block element method: Seismic analysis: Viscoelastic artificial boundary condition; Rock slope; Dynamic safety factor.

This paper addresses the development of a hybrid-mixed finite-element formulation for the geometrically exact quasi- static analysis of elastic planar framed structures, modeled using the two-dimensional Reissner beam theory. The proposed formulation relies on a modified principle of complementary energy, which involves, as independent variables, the generalized vectors of stress resultants and displacements and, in addition, a set of Lagrange multipliers used to enforce the stress continuity between elements. The adopted finite-element discretization produces numerical solutions that strongly satisfy the equilibrium differential equations in the elements, as well as the static boundary conditions. It consists, therefore, in a true equilibrium formulation for arbitrarily large displacements and rotations. Furthermore, as it does not suffer from shear locking or any other artificial stiffening phenomena, it may be regarded as an alternative to the standard displacement-based formulation. To validate and assess the accuracy of the proposed formulation, some benchmark problems are analyzed and their solutions are compared with those obtained using the standard two-node displacement-based formulation. Numerical analyses of convergence of the proposed finite-element formulation are also included. DOI: 10.1061/(ASCE)EM.1943-7889.0000190 CE Database subject headings: Beams; Frames; Hybrid methods: Finite element method; Geometry. Author keywords: Planar beams; Geometrically exact analysis; Framed structures; Complementary energy principles; Hybrid-mixed finite elements; Equilibrated solutions.

We show, to the best of our knowledge, the first simulation result of the strong plasmonic field coupling and enhancement at the Ag/Si interface of a silver core/protruded silicon shell nanocylinder by using the finite-element method. The strong plasmon field, with a slow effective phase velocity accumulated at the Ag/Si interface, which results from the large effective index of the surface plasmon due to the nearly identical real parts with opposite signs of the permittivities of silver and silicon at 633 nm, is analyzed. When the silicon shell has shallow protrusions of proper periodicity to meet the phase matching condition between the incident light and the surface plasmon wave at the Ag/Si interface, a higher scattered electric field and a higher sensitivity to the refractive index change of the surrounding medium can be achieved. Furthermore, a feasible implementation of the core-shell nanocylinder design concept is studied and discussed. OCIS codes: 240.6680, 250.5403.

The effect of tether-riser dynamics on the response characteristics of deep water tension leg platforms in water depths 900 m and 1800 m under random waves is investigated using a developed nonlinear finite element analysis program in the time-domain. Updated Lagrangian coordinates and incremental iterative solution based on Newmark's integration scheme are adopted. Linear wave theory is used. Relative velocity form of Morison's equation is used for estimating the wave forces. Current forces are also included in the analysis. Results are reported in the form of statistical values of responses. The statistical values of responses are found to increase with water depth and significant increase is observed when risers are included. [DOI: 10.1115/1.4001432] Keywords: tether-riser dynamics, random waves, tension leg platforms, Morison's equation, nonlinear finite element analysis

In this paper, a novel multiscale hierarchical model based on finite element analysis and neural network computation was developed to link mesoscopic and macroscopic scales to simulate the bone remodeling process. The finite element calculation is performed at the macroscopic level, and trained neural networks are employed as numerical devices for substituting the finite element computation needed for the mesoscale prediction. Based on a set of mesoscale simulations of representative volume elements of bones taken from different bone sites, a neural network is trained to approximate the responses at the meso level and transferred at the macro level. [DOI: 10.1115/1.4002536] Keywords: multiscale, hierarchical, bone remodeling, finite element, neural network

Spine degeneration is a pathology that will affect 80% of the population. Since the intervertebral disks play an important role in transmitting loads through the spine, the aim of this study was to evaluate the biomechanical impact of disk properties on the load carried by healthy (Thompson grade I) and degenerated (Thompson grades III and IV) disks. A three-dimensional parametric poroelastic finite element model of the L4/L5 motion segment was developed. Grade I, grade II, and grade IV disks were modeled by altering the biomechanical properties of both the annulus and nucleus. Models were validated using published creep experiments, in which a constant compressive axial stress of 0.35 MPa was applied for 4 h. Pore pressure (PP) and effective stress ([S.sub.E]) were analyzed as a function of time following loading application (1 min, 5 min, 45 min, 125 min, and 245 min) and discal region along the midsagittal profile for each disk grade. A design of experiments was further implemented to analyze the influence of six disk parameters (disk height (H), fiber proportion (%F), drained Young's modulus ([E.sub.a], [E.sub.n]), and initial permeability ([k.sub.a], [k.sub.n]) of both the annulus and nucleus) on load-sharing for disk grades I and IV. Simulations of grade I, grade III, and grade IV disks agreed well with the available published experimental data. Disk height (H) had a significant influence (p Keywords: lumbar intervertebral disk, finite element model, poroelasticity, disk degeneration, compression

A new flow-structure interaction method is presented, which couples a sharp-interface immersed boundary method flow solver with a finite-element method based solid dynamics solver. The coupled method provides robust and high-fidelity solution for complex flow-structure interaction (FSI) problems such as those involving three-dimensional flow and viscoelastic solids. The FSI solver is used to simulate flow-induced vibrations of the vocal folds during phonation. Both two- and three-dimensional models have been examined and qualitative, as well as quantitative comparisons, have been made with established results in order to validate the solver. The solver is used to study the onset of phonation in a two-dimensional laryngeal model and the dynamics of the glottal jet in a three-dimensional model and results from these studies are also presented. [DO]: 10.1115/1.4002587] Keywords: immersed boundary method, finite-element method flow-structure interaction, phonation, flow-induced vibration

High birefringence induced by rhombic air-hole photonic crystal fibers (PCFs) is numerically analyzed by using the finite-element method. The birefringence of a few kinds of PCFs was investigated with different parameters related to rhombic holes, including the rhombic-hole shape, size, and spacing. It was found that the birefringence of the proposed rhombic-hole PC F in this study is relatively larger than that of an elliptical-hole PCF with the same air-filling fraction (f = 0.0375) when the ratio of the rhombic-hole diagonal length is equal to the elliptical-hole ellipticity. OCIS codes: 060.0060, 060.5295.

A hydrogel consists of a cross-linked polymer network and solvent molecules. Depending on its chemical and mechanical environment, the polymer network may undergo enormous volume change. The present work develops a general formulation based on a variational approach, which leads to a set of governing equations coupling mechanical and chemical equilibrium conditions along with proper boundary conditions. A specific material model is employed in a finite element implementation, for which the nonlinear constitutive behavior is derived from a free energy function, with explicit formula for the true stress and tangent modulus at the current state of deformation and chemical potential. Such implementation enables numerical simulations of hydrogels swelling under various constraints. Several examples are presented, with both homogeneous and inhomogeneous swelling deformation. In particular, the effect of geometric constraint is emphasized for the inhomogeneous swelling of surface-attached hydrogel lines of rectangular cross sections, which depends on the width-to-height aspect ratio of the line. The present numerical simulations show that, beyond a critical aspect ratio, creaselike surface instability occurs upon swelling. [DOI: 10.1115/1.4001715] Keywords: hydrogel, swelling, large deformation, surface instability

Development of a new meshless technique is described that presents certain advantages over conventional meshless schemes due to unique weights that force alignment of the derivative approximation. The method is completely meshless, yet retains the low storage and simple flux distribution technique that are characteristic of finite volume methods. The new method is based on the well-known Taylor series expansion method with least squares. The proposed weighting scheme significantly reduces storage and computational requirements compared to other meshless schemes. The scheme is shown to be analogous to finite volume schemes in many ways, but it still lacks a discrete telescoping property and is not discretely conservative. The method is applied to the Euler equations in two dimensions. Results are presented that agree well with established methods. DOI: 10.2514/1.J050127

Structural reliability problems involving the use of advanced finite-element models of real-world structures are usually defined by limit-states expressed as functions (referred to as limit-state functions) of basic random variables used to characterize the pertinent sources of uncertainty. These limit-state functions define hyper-surfaces (referred to as limit-state surfaces) in the high-dimensional spaces of the basic random variables. The hyper-surface topology is of paramount interest, particularly in the failure domain regions with highest probability density. In fact, classical asymptotic reliability methods, such as the first- and second-order reliability method (FORM and SORM), are based on geometric approximations of the limit-state surfaces near the so-called design point(s) (DP). This paper presents a new efficient tool, the multidimensional visualization in the principal planes (MVPP) method, to study the topology of high-dimensional nonlinear limit-state surfaces (LSSs) near their DPs. The MVPP method allows the visualization, in particularly meaningful two-dimensional subspaces denoted as principal planes, of actual high-dimensional nonlinear limit-state surfaces that arise in both time-invariant and time-variant (mean out-crossing rate computation) structural reliability problems. The MVPP method provides, at a computational cost comparable with SORM, valuable insight into the suitability of FORM/SORM approximations of the failure probability for various reliability problems. Several application examples are presented to illustrate the developed MVPP methodology and the value of the information provided by visualization of the LSS. DOI: 10.1061/(ASCE)EM.1943-7889.0000183 CE Database subject headings: Finite element method; Structural reliability; Limit states; Imaging techniques. Author keywords: Nonlinear finite-element method; Structural reliability analysis; Limit-state surface; Hyper-surface topology; Multidimensional visualization.

A beam finite-element formulation following Euler-Bernoulli beam theory is presented for geometrically and materially nonlinear analysis of rectangular concrete-filled steel tube (RCFT) beam-columns. The formulation is geared for conducting transient dynamic analysis of composite steel/concrete frame structures. The element stiffness and internal forces were derived through adopting a mixed finite-element approach based on the Hellinger-Reissner variational principle. The load transfer between the steel and concrete constitutive materials was provided through steel and concrete interface via friction and interlocking. Six extra translational degrees-of-freedom (DOFs) were added to the conventional 12 DOF beam element to quantify the differential displacement between the two media. The formulation was verified for a range of geometrically nonlinear test problems and geometrically and materially nonlinear RCFT experimental test specimens from the literature. Strong correlation and convergence characteristics were achieved compared to the published results. DOI: 10.1061/(ASCE)EM.1943-7889.0000179 CE Database subject headings: Beams; Finite element method; Slip; Beam columns; Tubes; Dynamic analysis. Author keywords: Beam finite element; Mixed finite-element formulation; Corotational formulation; Slip; Composite beam-column; Concrete-filled steel tube.

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.

A nonlinear, large deformation beam/column formulation is used to model the behavior of the human spine under compressive load. The stabilizing roles of muscles are accounted for using Patwardhan's assumption that muscles act to direct the load along the tangent of the column. Three aspects of the spinal structure are then investigated. First, we look at the effects of two different assumptions for the action of muscles, leading to significant differences in the spine behavior. Second, the difference in mechanical properties between the vertebrae and the spinal disks is explored. Third, a nonlinear mechanical response of the spinal disk that arises from a two-step hierarchical homogenization technique is used. It is found that these factors have an important influence on the overall behavior of the spine structure. The present formulation offers a versatile model to investigate various features of the human spine, while remaining affordable computationally. It also provides an interesting framework for future multiscale studies of the human spine. DOI: 10.1061/(ASCE)EM.1943-7889.0000176 CE Database subject headings: Bioengineering; Stability; Finite element method; Deformation; Beams; Columns. Author keywords: Biomechanics; Stability; Nonlinear beam theory; Finite elements.

Three-dimensional finite element analyses were performed to study the behavior of piles in sloping ground under undrained lateral loading conditions. Piles of different diameter and length in sloping cohesive soils of different undrained shear strength and several ground slopes were considered. Based on the results of the finite element analyses, analytical formulations are derived for the ultimate load per unit length and the initial stiffness of hyperbolic p-y curves. New p-y criteria for static loading of piles in clay are proposed, which take into account the inclination of the slope and the adhesion of the pile-slope interface. These curves are used through a commercial subgrade reaction computer code to parametrically analyze the effect of slope inclination and pile adhesion on lateral displacements and bending moments. To validate the proposed p-y curves, a number of well documented lateral load tests are analyzed. Remarkable agreement is obtained between predicted and measured responses for a wide range of soil undrained shear strength and pile diameter, length, and stiffness. DOI: 10.1061/(ASCE)GT.1943-5606.0000373 CE Database subject headings: Piles; Lateral loads; Clays; Finite element method; Numerical analysis; Lateral pressure; Soil-pile interactions; Slopes. Author keywords: Piles; Lateral loads; Clays; Finite-element method; Numerical analysis; Lateral pressure; Soil-pile interactions; Slopes; p-y curves; Adhesion.

Mine backfilling is a process whereby mine tailings mixed with small amounts of cement are placed hydraulically into mined-out voids ('stopes') to stabilize the rockmass and allow full extraction of adjacent ore. A containment barricade is constructed to block the access point at the base of the stope, the design of which requires calculation of the total stress on the barricade during and following filling. For fine-grained backfill containing cement, the rate of development of stresses is governed by the rates of filling, consolidation, and cement hydration, each with its own timescale. As 'consolidation' in backfill undergoing hydration can be dominated by 'self-desiccation', this mechanism must also be incorporated. Interaction between the backfill and the stope walls ('arching') also has an influence. The paper describes a finite element (FE) model ('Minefill-2D') that can model these interactions, although only in a two-dimensional (planestrain or axisymmetric) fashion. It is shown that arching significantly influences the total stress distribution in a typical stope during filling, but only if and when effective stress develops. For cemented backfill, arching sometimes does not fully mobilize the cement bond strength, so that assessment of arching using traditional limit equilibrium methods is often not appropriate. Key words: stope mining, mine backfill, paste fill, arching, self-desiccation. Resume : Le remblayage minier est un procede dans lequel des rejets miniers ayant des petites quantites de ciment ajoutees sont places de facjon hydraulique dans les chantiers excaves, dans le but de stabiliser le massif rocheux et d'extraire le minerais adjacent. Une barricade est construite pour bloquer le point d'accesa la base du chantier. La conception de cette barricade neecessite un calcul des contraintes totales sur la barricade pendant et apres le remplissage. Dans le cas des remblais cimentesa granulometrie fine, le taux de developpement des contraintes depend des taux de remplissage, de consolidation et d'hydratation du ciment, chacun de ces proceedes ayant son propre rythme. Puisque la consolidation d'un remblai en hydratation peut etre determinee par la dessiccation, ce dernier meecanisme doit aussi etre inclus. L'interaction entre le remblai et les murs du chantier (effet d'arche) a aussi une influence. Cet article decrit un modele par elements finis (Minefill-2D) qui permet de modeliser ces interactions, ceci en deux dimensions (plan et axisymeetrique). Il est demontre que l'effet d'arche influence de facon significative la distribution des contraintes totales dans un chantier typique durant le remplissage, mais seulement si et quand une contrainte effective se developpe. Dans le cas des remblais cimentes, l'effet d'arche ne mobilise parfois pas entierement la resistance des liens cimentaires, alors revaluation del'effet d'arche par les methodes traditionnelles d'eequilibre limites est souvent inapproprieee. Mots-cles: minage par chantier, remblai minier, remblai en pate, effet d'arche, dessiccation. [Traduit par la Redaction], Introduction Mine backfill is a process adopted at many underground hardrock mine sites worldwide (Thomas and Holtham 1989; Potvin et al. 2005). This is the process of depositing mine tailings [...]

We rigorously analyze and compare preferential-order waveguide grating output couplers using the finite-difference time-domain method in the total-field/scattered-field formulation for TE and TM polarizations. Four kinds of preferential-order grating couplers are studied: volume holographic grating couplers, slanted parallelogrammic surface-relief grating couplers, double-corrugated surface-relief grating couplers, and reflecting-stack surface-relief grating couplers. The outcoupling efficiencies and branching ratios of the couplers, revealing their preferentiality, are calculated and compared with the rigorous coupled-wave analysis leaky-mode method. In addition, their performance is examined in terms of the main design parameters and the excitation wavelength. OCIS codes: 050.0050, 050.1950, 050.1960, 050.7330, 260.2110.

Relationship between accuracy and number of velocity particles in velocity slip phenomena was investigated by numerical simulations and theoretical considerations. Two types of 2D models were used: the octagon family and the D2Q9 model. Models have to possess the following four prerequisites to accurately simulate the velocity slip phenomena: (a) equivalency to the Navier--Stokes equations in the N-S flow area, (b) conservation of momentum flow [P.sub.xy] in the whole area, (c) appropriate relaxation process in the Knudsen layer, and (d) capability to properly express the mass and momentum flows on the wall. Both the octagon family and the D2Q9 model satisfy conditions (a) and (b). However, models with fewer velocity particles do not sufficiently satisfy' conditions (c) and (d). The D2Q9 model fails to represent a relaxation process in the Knudsen layer and shows a considerable fluctuation in the velocity slip due to the model's angle to the wall. To perform an accurate velocity slip simulation, models with sufficient velocity particles, such as the triple octagon model with moving particles of 24 directions, are desirable. [DOI: 10.1115/1.4002359]

Abdominal aortic aneurysm (AAA) is the gradual weakening and dilation of the infrarenal aorta. This disease is progressive, asymptomatic, and can eventually lead to rupture--a catastrophic event leading to massive internal bleeding and possibly death. The mechanical environment present in AAA is currently thought to be important in disease initiation, progression, and diagnosis. In this study, we utilize porohyperelastic (PHE) finite element models (FEMs) to investigate how such modeling can be used to better understand the local biomechanical environment in AAA. A 3D hypothetical AAA was constructed with a preferential anterior bulge assuming both the intraluminal thrombus (ILT) and the AAA wall act as porous materials. A parametric study was performed to investigate how physiologically meaningful variations in AAA wall and ILT hydraulic permeabilities affect luminal interstitial fluid velocities and wall stresses within an AAA. A corresponding hyperelastic (HE) simulation was also run in order to be able to compare stress values between PHE and HE simulations. The effect of AAA size on local interstitial fluid velocity was also investigated by simulating maximum diameters (5.5 cm, 4.5 cm, and 3.5 cm) at the baseline values of ILT and AAA wall permeability. Finally, a cyclic PHE simulation was utilized to study the variation in local fluid velocities as a result of a physiologic pulsatile blood pressure. While the ILT hydraulic permeability was found to have minimal affect on interstitial velocities, our simulations demonstrated a 28% increase and a 20% decrease in luminal interstitial fluid velocity as a result of a 1 standard deviation increase and decrease in AAA wall hydraulic permeability, respectively. Peak interstitial velocities in all simulations occurred on the luminal surface adjacent to the region of maximum diameter. These values increased with increasing AAA size. PHE simulations resulted in 19.4%, 40.1%, and 81.0% increases in peak maximum principal wall stresses in comparison to HE simulations for maximum diameters of 35 mm, 45 mm, and 55 mm, respectively. The pulsatile AAA PHE FEM demonstrated a complex interstitial fluid velocity field the direction of which alternated in to and out of the luminal layer of the ILT. The biomechanical environment within both the aneurysmal wall and the ILT is involved in AAA pathogenesis and rupture. Assuming these tissues to be porohyperelastic materials may provide additional insight into the complex solid and fluid forces acting on the cells responsible for aneurysmal remodeling and weakening. [DOI: 10.1115/1.4002370] Keywords: aneurysm, porohyperelastic, permeability, finite element model

The multiple normal loading-unloading process of an elastic-plastic sphere by a rigid flat is analyzed using finite element method for stick contact condition and both kinematic and isotropic hardening models. The behavior of the global contact parameters as well as the stress field within the sphere tip is presented for several loading cycles. It was found that under stick contact condition, secondary plastification occurs even after the second loading cycle and that the hardening model used has little effect on the loading-unloading process. The cyclic loading process gradually converges into elastic shakedown. [DOI: 10.1115/1.4002103] Keywords: spherical contact, elastic-plastic contact, contact condition, multiple loadings, hardening