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Stress Analysis (stress + analysis)

Distribution by Scientific Domains

Engineering	50%
Polymers and Materials Science	23%
Medical Sciences	13%
3 Other Domains	14%

Selected Abstracts

Evaluation of Damage Evolution in Ceramic-Matrix Composites Using Thermoelastic Stress Analysis

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2000
Thomas J. Mackin
Thermoelastic stress analysis (TSA) has been used to monitor damage evolution in several composite systems. The method is used to measure full-field hydrostatic stress maps across the entire visible surface of a sample, to quantify the stress redistribution that is caused by damage and to image the existing damage state in composites. Stress maps and damage images are constructed by measuring the thermoelastic and dissipational thermal signatures during cyclic loading. To explore the general utility of the method, test samples of several ceramic-matrix and cement-matrix composites have been fabricated and tested according to a prescribed damage schedule. The model materials have been chosen to illustrate the effect of each of three damage mechanisms: a single crack that is bridged by fibers, multiple matrix cracking, and shear bands. It is shown that the TSA method can be used to quantify the effect of damage and identify the operative damage mechanism. Each mechanism is identified by a characteristic thermal signature, and each is shown to be effective at redistributing stress and diffusing stress concentrations. The proposed experimental method presents a new way to measure the current damage state of a composite material. [source]

Stress analyses of laminates under cylindrical bending

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 1 2008
Tarun Kant
Abstract A semi-analytical approach for evaluation of stresses and displacements in composite and sandwich laminates under cylindrical bending subjected to transverse load has been developed in this paper. Two dimensional (2D) partial differential equations (PDEs) of such a laminate are obtained by imposing plane-strain conditions of elasticity. The fundamental dependent variables are so selected in this formulation that they satisfy the continuity of displacements and transverse interlaminar stresses at the laminate interface through the thickness. The set of governing PDEs are transformed into a set of coupled first-order ordinary differential equations (ODEs) in thickness direction by assuming suitable global orthogonal trigonometric functions for the fundamental variables satisfying the boundary conditions. These ODEs are numerically integrated by a specially formulated ODE integrator algorithm involving transformation of a two-point boundary value problem (BVP) into a set of initial value problems (IVPs). Numerical studies on both composite and sandwich laminates for various aspect ratios are performed and presented. Accuracy of the present approach is demonstrated by comparing the results with the available elasticity solution. It is seen that the present results are in excellent agreement with the elasticity solutions. Some new results for sandwich laminates and for uniform loading condition are presented for future reference. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Stress analysis in a post-restored tooth utilizing the finite element method

JOURNAL OF ORAL REHABILITATION, Issue 5 2003
M. Toparli
summary ,This study utilized the finite element method (FEM) to predict distribution of stresses in dentin of an endodontically treated tooth, restored with cast post and cores. For this investigation an axisymmetric model of a maxillary second pre-molar that included an alveolar bone was analysed. The three tooth models evaluated were Ti,Ti alloy, NiCr,AuPd alloy and Ti,NiCr alloy as post-material and crown material with porcelain. A load of 200 N at an angle of 45° to the longitudinal axis was applied on the occlusal margin of each model. The tooth was assumed isotropic, homogenous and elastic. The author prepared a calculation program using fortran 77. Investigation of the stress distributions was made in five regions; namely bottom of post, top of post, cole, metal,cement interface and metal,porcelain interface. The distributions of radial and axial stresses were plotted with length of radial. [source]

Stress analysis of the anterior tibial post in posterior stabilized knee prostheses

JOURNAL OF ORTHOPAEDIC RESEARCH, Issue 4 2007
Chang-Hung Huang
Abstract Recent retrieval studies have indicated a high incidence of polyethylene wear on the anterior tibial post caused by impingement. This study investigated the influences of post-cam design features and component alignment on the stress distribution in the anterior tibial post when subjected to the impingement loading. Two three-dimensional finite element models of posterior stabilized knee prostheses were constructed, one with flat on flat (FF) and another with curve on curve (CC) contact surfaces between anterior tibial post and femoral cam. The polyethylene insert was modeled with elastoplastic properties. Nine cases, three hyperextension angles (0°, 5°, and 10°) combined with three axial tibial rotations (0°, 2.5°, and 5°) simulating different component alignments were analyzed. A vertical compressive load of 2,000 N and an extension moment of 45 Nm were applied simultaneously. The FF model had larger stress increases than the CC model in both hyperextension and tibial rotation compared with the neutral position. The maximum increase for the FF model was 68% in peak contact stress, 125% in von Mises stress, and 58% in tensile stress in the extreme case of 10° of hyperextension combined with 5° of axial rotation. Stress concentration was found at the anterior corner of the post in the FF model; this was not found in the CC model. The curve on curve design can reduce edge loading on the tibial post, especially during axial tibiofemoral rotation. © 2007 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 25:442,449, 2007 [source]

The effect of plasticity on incipient mixed-mode fatigue crack growth

FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 7 2003
P. DAHLIN
ABSTRACT Several criteria for the prediction of incipient crack path direction of non-proportional mixed-mode fatigue cracks, immediately after a change of load from steady mode I conditions are investigated. The analysis is based on two-dimensional plane strain FE-simulations in which the actual elasto-plastic stress distribution is used for the MTS, MTSR and MEPSR criteria. The purpose of the analysis is to compare the numerical results with experimental results as well as with previous predictions based on solely elastic stress analyses, taken from the literature. It is shown that the influence from elasto-plastic deformation on crack branching direction is of utmost importance. It is found that the incipient crack growth of metals falls into two categories: high strength metals follow the MTSp criterion whereas more ductile metals follow the MTSRp criterion. The subscript p indicates that the elasto-plastic evaluation of the respective criterion should be used. [source]

Effects of splinted prosthesis supported a wide implant or two implants: a three-dimensional finite element analysis

CLINICAL ORAL IMPLANTS RESEARCH, Issue 4 2005
Heng-Li Huang
Abstract Objectives: Three-dimensional finite element (FE) models of splinted prosthetic crowns were studied and stress analyses were evaluated with different types of implant support, including standard, wide or two implant(s) for partial, posterior edentulous restorations. Material and methods: The FE models were constructed based on a cadaver mandible containing the 2nd premolar and the 1st molar. The crowns of these two teeth were modeled as connected and disconnected to mimic the splinted and non-splinted designs, respectively. One standard implant was placed at the premolar region, while three types of implant support, one at a time (the standard implant, wide implant and two implants), were used to support the molar crown. A 100 N oblique load was applied to the buccal cusp on each crown. The FE simulation was validated experimentally via strain gauge measurement. Results: The experimental data were well correlated with the FE predictions (r2=0.97). When compared with the standard implant used in the molar area, the wide implant and two implants reduced the peak stress in crestal bone by 29,37% for both splinted and non-splinted cases. Inserting the standard implant into both the premolar and molar area, the bone stresses were identical for splinted and non-splinted designs. However, splinting the adjacent crowns has shown to decrease the bone stresses at the premolar region by 25%, while the wide implant or two implants were placed at the molar region. Conclusion: The biomechanical advantages of using the wide implant or two implants are almost identical. The benefit of load sharing by the splinted crowns is notable only when the implants on the premolar and molar regions have different supporting ability. Résumé Des modèles d'éléments finis (FE) tridimensionnels de couronnes prothétiques attachés ont étéétudiés et les analyses de stress ont étéévalués avec différents types de support d'implants comprenant le standard, le large ou deux implants pour des restaurations postérieures partielles. Les modèles FE ont été construits sur base de mandibule de cadavre contenant deux prémolaires et une molaire. Les couronnes de ces deux dents ont été modelées comme connectées et non-connectées pour mimer respectivement les modèles avec attache ou sans. Un implant standard a été placé dans la région prémolaire tandis que trois types d'implants supportaient en un temps (l'implant standard, l'implant large et deux implants) ont été utilisés pour porter la couronne molaire. Une charge oblique de 100 N a été appliquée sur la cuspide vestibulaire de chaque couronne. La simulation FE a été validée expérimentalement via une mesure par jauge de force. Les données expérimentales étaient en bonne corrélation avec les prévisions FE (r2=0,97). Comparés à l'implant standard utilisé dans la zone molaire, l'implant large et la combinaison de deux implants réduisait le pic de stress dans l'os crestal de 29 à 37% tant dans les cas attachés que non-attachés. En insérant l'implant standard dans la zone prémolaire et molaire, le stress osseux était identique pour les modèles attachés et non-attachés. Cependant, l'attache reliant les couronnes adjacentes s'accompagnait d'une dimininution des stress osseux dans la région prémolaire de 25%, tandis que l'implant large ou les deux implants étaient placés dans la région molaire. Les avantages biomécaniques de l'utilisation d'un implant large ou de deux implants sont quasi identiques. Le bénéfice d'une charge partagée par les couronnes solidarisées n'est visible que lorsque les implants des régions prémolaires et molaires ont des capacités de support différentes. Zusammenfassung Ziel: Bei der Rekonstruktion von Lücken im hinteren Seitenzahnbereich untersuchte man in einem dreidimensionalen Finiteelement-Modell (FE) zementierte Kronen und wertete in Belastungs-Analysen verschiedene Implantatabstützungen aus, nämlich auf Standardimplantaten, Wide neck-Implantaten oder auf zwei Implantaten. Material und Methoden: Das FE-Modell basierte auf den Werten eines Leichenunterkiefers in der Region des zweiten Prämolaren und ersten Molaren. Die Kronen auf diesen beiden Zähne wurden jeweils zusammenhängend und einzeln modelliert, so dass man die verblockte und unverblockte Situation nachempfinden konnte. In der Prämolarenregion implantierte man ein Standartimplantat. In der Molarenregion wählte man jeweils eine von drei verschiedenen Varianten der Abstützung für die Kronen: ein Standardimplantat, ein Wide neck-Implantat oder zwei Implantate. Auf den buccalen Höcker jeder Krone liess man schräg eine Kraft von 100 N auftreffen. Die FE-Simulation eichte man experimentell mit Hilfe von Dehnmessstreifen. Resultate: Die experimentellen Daten korrelierten sehr gut mit den FE-Voraussagen (r2=0.97). Verglich man die in der Molarenregion verwendeten Standartimplantate mit den Wide neck-Implantaten und zwei Implantaten, so reduzierte sich die Spitzenbelastung im crestalen Knochen um 29,37%, bei den verblockten wie auch bei den unverblockten Versionen. Setzte man sowohl im Prämolaren wie auch im Molarengebiet Standardimplantate, so war die Knochenbelastung für die verblockte wie auch für die unverblockte Version gleich gross. Wenn aber das Wide neck-Implantat oder zwei Implantate in der Molarenregion gesetzt worden waren, so vermochte die Verblockung der Implantat-Kronen die Knochenbelastung in der Prämolarenregion um 25% zu senken. Zusammenfassung: Ob man das Wide neck-Implantat oder zwei Implantate verwendet, die biomechanischen Vorteile sind beinahe identisch. Man erreicht durch das Verblocken von Kronen erst dann einen spürbaren Vorteil bezüglich Lastenverteilung, wenn die Implantate in der Prämolaren- und Molarenregion verschiedene Tragfähigkeiten aufweisen. Resumen Objetivos: Se estudiaron modelos tridimensionales de elementos finitos (FE) de coronas protésicas y se evaluó el análisis de estrés con diferentes tipos de soporte implantario, incluyendo implantes estándar, anchos o dos implantes, para restauraciones parciales en posteriores edéntulos. Material y métodos: Se construyeron dos modelos FE basados en mandíbula de cadáver conteniendo el 2° premolar y el 1er molar. Las coronas de estos dos dientes se modelaron como conectadas y desconectadas para imitar los diseños conectados y desconectados, respectivamente. Se colocó un implante estándar en la región premolar, mientras que para soportar la corona molar se colocaron tres tipos de implantes, uno a la vez, (un implante estándar, un implante ancho y dos implantes). Se aplicó una carga oblicua de 100N en la cúspide bucal de cada corona. La simulación de elementos finitos se validó experimentalmente por medio de medición de tensión. Resultados: Los datos experimentales se correlacionaron bien con las predicciones FE (r2=0.97). Al comparase a los implantes estándar usados en el área molar, el implante ancho y dos implantes redujeron el pico de estrés en el hueso crestal en un 29,37% tanto para los caso ferulizados como para los no ferulizados. Al insertar el implante estándar tanto en la región premolar como en la molar, los estrés óseos fueron idénticos para los diseños ferulizados como para los no ferulizados. De todos modos, la ferulización de las coronas adyacentes mostró un descenso del estrés óseo en un 25%, mientras el implante ancho o los dos implantes se colocaron en la región molar. Conclusión: Las ventajas biomecánicas de usar el implante ancho o dos implantes fueron casi idénticas. El beneficio de compartir la carga al ferulizar las coronas es notable solo cuando los implantes en las regiones premolar y molar tienen diferente capacidad de soporte. [source]

Three-dimensional thermoelastic stresses in off-axis oriented single crystals with hexagonal symmetry

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 3 2007
K. Böttcher
Abstract A three-dimensional (3D) thermoelastic stress analysis is carried out on a single crystal with axisymmetric geometry but with a hexagonal crystallographic symmetry. The crystallographic orientation is off-axis with respect to the cylindrical coordinate system. By applying a Fourier series expansion with respect to the rotational angle , of the cylindrical coordinates, the 3D boundary value problem is reduced to a sequence of 2D ones on the meridian plane, which are solved by the finite-element method. In our example, the off-axis orientation is towards a direction of high symmetry, and therefore only four of the six stress tensor components are non-zero. In the end, the stress tensor is projected onto the slip system of the crystal. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Raman spectroscopic and X-ray investigation of stressed states in diamond-like carbon films

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 1-2 2005
R. Krawietz
Abstract The non-destructive characterization of intrinsic stress is very important to evaluate the reliability of devices based on diamond-like carbon (DLC) films. Whereas the only requirement for the X-ray diffraction method is a crystalline state of specimen, Raman spectroscopic stress analysis is restricted to materials showing intensive and sharp Raman peaks. On the other hand, Raman spectroscopy offers the possibility to measure stress profiles with lateral resolution of about 1 micron. The results of stress measurements in DLC films using both X-ray diffraction and Raman spectroscopy are found in very good correspondence. Mean stress in carbon films consisting of very small crystallites on silicon substrates has been determined by measuring and fitting the stress profiles in the substrate near artificial vertical film edges. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Instability investigation of cantilevered seacliffs

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 11 2008
Adam P. Young
Abstract Wave action is a fundamental mechanism in seacliff erosion, whereby wave undercutting creates an unstable cantilevered seacliff profile and can lead to large catastrophic cliff failures, thus threatening coastal infrastructure. This study investigated the instability of two such failures that occurred in Solana Beach, California, by combining terrestrial LIDAR scanning, cantilever beam theory and finite element analysis. Each landslide was detected by evaluating the surface change between subsequent high resolution digital terrain models derived from terrestrial LIDAR data. The dimensions of failed cantilever masses were determined using the surface change measurements and then incorporated into failure stress analysis. Superimposing stress distributions computed from elastic cantilever beam theory and finite element modeling provided a method to back-calculate the maximum developed tensile and shear stresses along each failure plane. The results of the stress superposition revealed that the bending stresses caused by the cantilevered load contributed the majority of stress leading to collapse. Both shear and tensile failure modes were investigated as potential cliff failure mechanisms by using a comparison of the back-calculated failure stresses to material strengths found in laboratory testing. Based on the results of this research, the tensile strength of the cliff material was exceeded at both locations, thus causing the cliffs to collapse in tension. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Three-dimensional finite-element model of the human temporomandibular joint disc during prolonged clenching

EUROPEAN JOURNAL OF ORAL SCIENCES, Issue 5 2006
Miho Hirose
In the temporomandibular joint (TMJ), overloading induced by prolonged clenching appears to be important in the cascade of events leading to disc displacement. In this study, the effect of disc displacement on joint stresses during prolonged clenching was studied. For this purpose, finite-element models of the TMJ, with and without disc displacement, were used. Muscle forces were used as a loading condition for stress analysis during a time-period of 10 min. The TMJ disc and connective tissue were characterized as a linear viscoelastic material. In the asymptomatic model, large stresses were found in the central and lateral part of the disc through clenching. In the retrodiscal tissue, stress relaxation occurred during the first 2 min of clenching. In the symptomatic model, large stresses were observed in the posterior part of the disc and in the retrodiscal tissue, and the stress level was kept constant through clenching. This indicates that during prolonged clenching the disc functions well in the asymptomatic joint, meanwhile the retrodiscal tissue in the symptomatic joint is subject to excessive stress. As this structure is less suitable for bearing large stresses, tissue damage may occur. In addition, storage of excessive strain energy might lead to breakage of the tissue. [source]

Thermal Shock Damage of a 3D-SiC/SiC Composite,

ADVANCED ENGINEERING MATERIALS, Issue 11 2005
S. Wu
Thermal shock of a three-dimensional (3D) SiC/SiC composite prepared by chemical vapor infiltration (CVI) process was conducted using water quenched method. Thermal shock damage of the composite was assessed by SEM characterization and measurement mechanical properties using three-point flexure after quenching. After quenched from 1200°C to 25°C water for 100 cycles, the composite retained 80% of the original flexural strength in the longitudinal direction while cracked through the width direction. Thermal shock damage of the composite was analyzed by thermal stress analysis based on the braiding structure of the composite as well as the distribution and shape of flaws referred to residual pores in the matrix. The braided structure and the dimension difference resulted in the anisotropy of mechanical properties and the matrix pores configuration of the composite, which led to the thermal shock damage anisotropy of the composite. [source]

Fatigue performance of metallic reverse-bent joints

FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 9 2009
G. FESSEL
ABSTRACT Adhesively bonded lap shear joints have been investigated widely and several ideas have been proposed for improving joint strength by reducing bondline stress concentrations. These include application of adhesive fillets at the overlap ends and use of adhesive with graded properties in the overlap area. Another, less common, approach is to deform the substrates in the overlap area in order to obtain a more desirable bondline stress distribution. Previous work carried out by the authors on a number of different substrate materials indicated that a reverse-bent joint geometry is useful for increasing joint strength. Results from static stress analysis and experimental testing demonstrated that significant improvements could be achieved. This paper presents results of further work carried out to assess the fatigue performance of reverse-bent joints. Substrates with different yield and plastic deformation characteristics were used and the effects of different overlap lengths on strength were examined. The results of this research show that the improvements obtained under static tests conditions translate to even higher benefits in fatigue. The paper also explains the failure mechanism of the joints under fatigue loading. [source]

Study of crack growth in solid propellants

FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 10 2001
E. E. Gdoutos
The stress and displacement fields in an edge-cracked sheet specimen made of a solid propellant and subjected to a uniform displacement along its upper and lower faces was studied. The solid propellant was simulated as a hyperelastic material with constitutive behaviour described by the Ogden strain energy potential. A non-linear finite deformation analysis was performed based on the finite element code ABAQUS. A detailed analysis of the stress field in the vicinity of the crack tip was undertaken. The deformed profiles of the crack faces near the crack tip were determined. The results of stress analysis were coupled with the strain energy density theory to predict the crack growth behaviour including crack initiation, stable crack growth and final termination for two specimens with different dimensions. Crack growth resistance curves representing the variation of crack growth increment versus applied displacement were drawn. [source]

The cycle of instability: stress release and fissure flow as controls on gully head retreat

HYDROLOGICAL PROCESSES, Issue 1 2001
A. J. C. Collison
Abstract Gully head and wall retreat has commonly been attributed to fluvial scour and head collapse as a result of soil saturation, sapping or piping. The empirical evidence to substantiate these conceptual models is sparse, however, and often contradictory. This paper explores the hydrological and mechanical controls on gully head and wall stability by modelling the hydrology, stability and elastic deformation of a marl gully complex in Granada Province, south-east Spain. The hydrological and slope-stability simulations show that saturated conditions can be reached only where preferential fissure flow channels water from tension cracks into the base of the gully head, and that vertical or subvertical heads will be stable unless saturation is achieved. Owing to the high unsaturated strengths of marl measured in this research, failure in unsaturated conditions is possible only where the gully head wall is significantly undercut. Head retreat thus requires the formation of either a tension crack or an undercut hollow. Finite-element stress analysis of eroding slopes reveals a build up of shear stress at the gully head base, and a second stress anomaly just upslope of the head wall. Although tension cracks on gully heads have often been attributed to slope unloading, this research provides strong evidence that the so called ,sapping hollow' commonly found in the gully headwall base is also a function of stress release. Although further research is needed, it seems possible that ,pop out' failures in river channels may be caused by the same process. The hydrological analysis shows that, once a tension crack has developed, throughflow velocity in the gully headwall will increase by an order of magnitude, promoting piping and enlargement of this weakened area. It is, therefore, possible to envisage a cycle of gully expansion in which erosion, channel incision or human action unloads the slope below a gully head, leading to stress patterns that account for the tension crack and a stress-release hollow. The tension crack promotes faster throughflow, encouraging hollow enlargement and piping, which undercut the gully head. The tension crack permits the development of positive pore-water pressures behind the gully head, leading either to failure or contributing to toppling. Finally the debris may be eroded by fluvial action, unloading a new section of slope and completing the cycle of gully head retreat. Copyright © 2001 John Wiley & Sons, Ltd. [source]

A continuum mechanics-based framework for boundary and finite element mesh optimization in two dimensions for application in excavation analysis

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 4 2005
Attila M. Zsáki
Abstract The determination of the optimum excavation sequences in mining and civil engineering using numerical stress analysis procedures requires repeated solution of large models. Often such models contain much more complexity and geometric detail than required to arrive at an accurate stress analysis solution, especially considering our limited knowledge of rock mass properties. This paper develops an automated framework for estimating the effects of excavations at a region of interest, and optimizing the geometry used for stress analysis. It eliminates or simplifies the excavations in a model while maintaining the accuracy of analysis results. The framework can equally be applied to two-dimensional boundary and finite element models. The framework will have the largest impact for non-linear finite element analysis. It can significantly reduce computational times for such analysis by simplifying models. Error estimators are used in the framework to assess accuracy. The advantages of applying the framework are demonstrated on an excavation-sequencing scenario. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Comparison between cohesive zone models

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 11 2004
K. Y. Volokh
Cohesive zone models (CZMs) are widely used for numerical simulation of the fracture process. Cohesive zones are surfaces of discontinuities where displacements jump. A specific constitutive law relating the displacement jumps and proper tractions defines the cohesive zone model. Within the cohesive zone approach crack nucleation, propagation, and arrest are a natural outcome of the theory. The latter is in contrast to the traditional approach of fracture mechanics where stress analysis is separated from a description of the actual process of material failure. The common wisdom says that only cohesive strength,the maximum stress on the traction,separation curve,and the separation work,the area under the traction,separation curve,are important in setting a CZM while the shape of the traction,separation curve is subsidiary. It is shown in our note that this rule may not be correct and a specific shape of the cohesive zone model can significantly affect results of the fracture analysis. For this purpose four different cohesive zone models,bilinear, parabolic, sinusoidal, and exponential,are compared by using a block-peel test, which allows for simple analytical solutions. Numerical performance of the cohesive zone models is considered. It appears that the convergence properties of nonlinear finite element analyses are similar for all four CZMs in the case of the block-peel test. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Numerically exact integration of a family of axisymmetric finite elements

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 4 2003
T. E. Price
Abstract Axisymmetric finite element stress analysis involves repeated integration of a rational polynomial integrand. For elements near the axis of symmetry, such integrals are quasi-singular, are difficult to integrate numerically, and can lead to significant computational errors. This paper describes a Gaussian quadrature procedure to integrate exactly, within computational limits, a class of rational polynomials over undistorted triangular and quadrilateral finite elements. The procedure's accuracy and efficiency are illustrated through a numerical example. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Improved implementation and robustness study of the X-FEM for stress analysis around cracks

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 8 2005
E. Béchet
Abstract Numerical crack propagation schemes were augmented in an elegant manner by the X-FEM method. The use of special tip enrichment functions, as well as a discontinuous function along the sides of the crack allows one to do a complete crack analysis virtually without modifying the underlying mesh, which is of industrial interest, especially when a numerical model for crack propagation is desired. This paper improves the implementation of the X-FEM method for stress analysis around cracks in three ways. First, the enrichment strategy is revisited. The conventional approach uses a ,topological' enrichment (only the elements touching the front are enriched). We suggest a ,geometrical' enrichment in which a given domain size is enriched. The improvements obtained with this enrichment are discussed. Second, the conditioning of the X-FEM both for topological and geometrical enrichments is studied. A preconditioner is introduced so that ,off the shelf' iterative solver packages can be used and perform as well on X-FEM matrices as on standard FEM matrices. The preconditioner uses a local (nodal) Cholesky based decomposition. Third, the numerical integration scheme to build the X-FEM stiffness matrix is dramatically improved for tip enrichment functions by the use of an ad hoc integration scheme. A 2D benchmark problem is designed to show the improvements and the robustness. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Two simple and efficient displacement-based quadrilateral elements for the analysis of composite laminated plates

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 11 2004
Y. X. Zhang
Abstract Two simple 4-node 20-DOF and 4-node 24-DOF displacement-based quadrilateral elements named RDKQ-L20 and RDKQ-L24 are developed in this paper based on the first-order shear deformation theory (FSDT) for linear analysis of thin to moderately thick laminates. The deflection and rotation functions of the element sides are obtained from Timoshenko's laminated composite beam functions. Linear displacement interpolation functions of the standard 4-node quadrilateral isoparametric plane element and displacement functions of a quadrilateral plane element with drilling degrees of freedom are taken as in-plane displacements of the proposed elements RDKQ-L20 and RDKQ-L24, respectively. Due to the application of Timoshenko's laminated composite beam functions, convergence can be ensured theoretically for very thin laminates. The elements are simple in formulation, and shear-locking free for extremely thin laminates even with full integration. A hybrid-enhanced procedure is employed to improve the accuracy of stress analysis, especially for transverse shear stresses. Numerical tests show that the new elements are convergent, not sensitive to mesh distortion, accurate and efficient for analysis of thin to moderately thick laminates. Copyright © 2004 John Wiley & Sons, Ltd. [source]

A new variable-order singular boundary element for two-dimensional stress analysis

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 3 2002
K. M. Lim
Abstract A new variable-order singular boundary element for two-dimensional stress analysis is developed. This element is an extension of the basic three-node quadratic boundary element with the shape functions enriched with variable-order singular displacement and traction fields which are obtained from an asymptotic singularity analysis. Both the variable order of the singularity and the polar profile of the singular fields are incorporated into the singular element to enhance its accuracy. The enriched shape functions are also formulated such that the stress intensity factors appear as nodal unknowns at the singular node thereby enabling direct calculation instead of through indirect extrapolation or contour-integral methods. Numerical examples involving crack, notch and corner problems in homogeneous materials and bimaterial systems show the singular element's great versatility and accuracy in solving a wide range of problems with various orders of singularities. The stress intensity factors which are obtained agree very well with those reported in the literature. Copyright © 2002 John Wiley & Sons, Ltd. [source]

FFS contact searching algorithm for dynamic finite element analysis

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 7 2001
Fujun Wang
Abstract A new contact searching algorithm for general contact systems is proposed in this paper. Due to that the smooth and accurate geometry description is crucial to the contact stress analysis, we have worked out a free-formed-surface (FFS) algorithm specialized to model the contacting surface with the C1 boundary continuity and the exact boundary condition definition. Moreover, the geometrical description using the FFS produces those data required for determining the actual contact direction and calculating the exact contact penetration. Numerical simulation results demonstrate that our contact searching algorithm is robust and capable to simulate three-dimensional contact problems accurately. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Photoelastic stress analysis in perforated (Rochette) resin bonded bridge design

JOURNAL OF ORAL REHABILITATION, Issue 5 2000
H. M. Ziada
Rochette described the perforated cast metal bonded design for splinting periodontally compromised teeth. The design was later used for replacing missing teeth. The main causes of failure of the perforated (Rochette) type design were attributed to inappropriate case selection and erosion of the composite from perforations. The aim of this study was to analyse the effect of stress magnitude and direction on failure of perforated resin bonded bridges (RBBs). The objective was to compare stress magnitudes in this design with those reported on the non-perforated RBBs. Photoelastic modelling materials were selected to represent the relative stiffnesses of a posterior mandibular and an anterior maxillary perforated (Rochette) type design. The sizes of the models were scaled to ×2·5 in order to enhance visual analysis of the stress patterns. Stress magnitudes were quantified from isochromatic fringes and stress directions were evaluated from stress trajectories. These revealed a high-stress concentration around the perforations, particularly for those at the proximo-lingual/palatal (connector) areas. This experimental study revealed that the main reason for failure of Rochette designs is deformation at the perforations. [source]

Evaluation of Damage Evolution in Ceramic-Matrix Composites Using Thermoelastic Stress Analysis

Residual stress analysis of an autofrettaged compound cylinder under machining process

MATERIALWISSENSCHAFT UND WERKSTOFFTECHNIK, Issue 3 2009
E.-Y. Lee
Autofrettage; Schrumpfpassung; Verbundzylinder; Bearbeitungsprozess Abstract The autofrettage process is used to manufacture pressure vessels and cylinders that can withstand high internal pressure. A multi-layered cylinder was assembled by a shrink fit. Autofrettaged compound cylinder can resist higher internal pressure than a thick cylinder having the same dimension and extend its life time. Inner and outer surfaces of the autofrettaged compound cylinder have to be manufactured into exact dimensions. The distribution of residual stress can change after the machining process. The machining procedure of inner and outer surfaces also affects the distribution of residual stress as a function of the machining procedure. In this study, the distribution of residual stresses of an autofrettaged compound cylinder as machining procedure was investigated using analytical and numerical analyses. [source]

Numerical and experimental investigation of the deformational behaviour of plastic containers

PACKAGING TECHNOLOGY AND SCIENCE, Issue 5 2001
D. Karalekas
Abstract A numerical and experimental study was undertaken to investigate the deformational behaviour of a plastic grooved container used to store agrochemical solutions when loaded under columnar crush conditions. Finite element analysis was implemented to calculate stresses and deformations at various critical points of the container. A non-linear elastoplastic analysis was performed, based on the ABAQUS FEM computer program. The results of the stress analysis were coupled with a yield criterion to predict the initiation of plastic deformation. The numerically obtained results are compared to those obtained experimentally. It was found that the numerically calculated strains at predetermined locations of the plastic container were in good agreement with the experimentally measured ones. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Elastic-plastic stress analysis of cracked structures using the boundary element method

PROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2009
Wilhelm Weber
The application of the boundary element method (BEM) for the 3D-stress analysis of cracked structures considering elastic-plastic material behavior is presented. For separating the coincident crack surfaces the DUAL-BEM is utilized. The relevant boundary integral equations (BIE) , the strongly singular displacement BIE and the hypersingular traction BIE , are evaluated in the framework of a collocation procedure. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Efficient simulation of 3D fatigue crack growth based on boundary elements

PROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2005
K. Kolk
The three-dimensional simulation of fatigue crack growth under the consideration of 3D effects is presented to follow complex crack paths as realistic as possible from the macroscopic point of view. This aim is mainly based on two aspects. Firstly, an accurate stress analysis is performed by the boundary element method in terms of the 3D Dual BEM. Secondly, a suitable 3D crack growth criterion based on experimental observations is utilized. Due to the non-linearity of crack growth the whole procedure is embedded in an advanced incremental crack growth algorithm. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]