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Vertical Loading (vertical + loading)

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Medical Sciences	50%

Selected Abstracts

Lateral stress caused by horizontal and vertical surcharge strip loads on a cross-anisotropic backfill

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 14 2005
Cheng-Der Wang
Abstract This study derives analytical solutions for estimating the lateral stress caused by horizontal and vertical surcharge strip loads resting on a cross-anisotropic backfill. The following loading types are employed in this work: point load, line load, uniform strip load, upward linear-varying strip load, upward nonlinear-varying strip load, downward linear-varying strip load and downward nonlinear-varying strip load. The cross-anisotropic planes are assumed to be parallel to the horizontal surface of the backfill. The solutions proposed herein have never been mentioned in previous literature, but can be derived by integrating the point load solution in a Cartesian co-ordinate system for a cross-anisotropic medium. The calculations by the presented solutions are quick and accurate since they are concise and systematized. Additionally, the proposed calculations demonstrate that the type and degree of material anisotropy and the horizontal/vertical loading types decisively influence the lateral stress. This investigation presents examples of the proposed horizontal and vertical strip loads acting on the surface of the isotropic and cross-anisotropic backfills to elucidate their effects on the stress. The analytical results reveal that the stress distributions accounting for soil anisotropy and loading types are quite different from those computed from the available isotropic solutions. Restated, the derived solutions, as well as realistically simulating the actual surcharge loading circumstances, provide a good reference for the design of retaining structures for the backfill materials are cross-anisotropic. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Vertical dynamic response of a rigid foundation embedded in a poroelastic soil layer

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 11 2009
Y. Q. Cai
Abstract A simplified analytical method is presented for the vertical dynamic analysis of a rigid, massive, cylindrical foundation embedded in a poroelastic soil layer. The foundation is subjected to a time-harmonic vertical loading and is perfectly bonded to the surrounding soil in the vertical direction. The soil underlying the foundation base is represented by a single-layered poroelastic soil based on rigid bedrock while the soil at the side of the foundation is modeled as an independent poroelastic layer composed of a series of infinitesimally thin layers. The behavior of the soil is governed by Biot's poroelastodynamic theory and its governing equations are solved by the use of Hankel integral transform. The contact surface between the foundation base and the soil is smooth and fully permeable. The dynamic interaction problem is solved following standard numerical procedures. The accuracy of the present solution is verified by comparisons with the well-known solutions obtained from other approaches for both the elastodynamic interaction problem and poroelastodynamic interaction problem. Numerical results for the vertical dynamic impedance and response factor of the foundation are presented to demonstrate the influence of nondimensional frequency of excitation, soil layer thickness, poroelastic material parameters, depth ratio and mass ratio on the dynamic response of a rigid foundation embedded in a poroelastic soil layer. Copyright © 2008 John Wiley & Sons, Ltd. [source]

The effect of retainer thickness on posterior resin-banded prostheses: a finite element study

JOURNAL OF ORAL REHABILITATION, Issue 11 2004
T.-S. Lin
summary, According to its design concept, a resin-bonded prosthesis, compared with the conventional fixed partial denture, is a weak and unstable structure. Therefore, a resin-bonded prosthesis induces a higher failure rate, especially in the posterior region. Recently, adhesion agents have been profoundly improved. However, the design guidelines of posterior resin-bonded prostheses (RBP) have seldom been evaluated from a biomechanical perspective. The objective of this study was to investigate the biomechanical effects of the retainer thickness on posterior RBP using the finite element method. A solid model of a posterior mandibular resin-bonded prosthesis, which employed the second molar and second premolar as the abutment teeth, was constructed and meshed with various retainer thickness (ranging from 0·2 to 1·0 mm). Horizontal and vertical loadings of 200 N were applied respectively at the central fossa of the pontic to examine the stress level at the interface between the retainer and abutment teeth. All exterior nodes in the root, below the cementoenamel junction were fixed as the boundary condition. The results showed that horizontal loading would induce higher interfacial stresses than the vertical loading which indicated that the horizontal component of the occlusal force plays a more important role in evaluating the debonding phenomenon. Further, the peak interfacial stresses increased as the retainer thickness decreased and, based on the fitted relation between retainer thickness and interfacial stresses, a 0·4 mm retainer thickness was suggested as the minimum required to prevent severe interfacial stresses increasing. [source]

Biomechanics of the rostrum in crocodilians: A comparative analysis using finite-element modeling

THE ANATOMICAL RECORD : ADVANCES IN INTEGRATIVE ANATOMY AND EVOLUTIONARY BIOLOGY, Issue 8 2006
Colin R. McHenry
Abstract This article reports the use of simple beam and finite-element models to investigate the relationship between rostral shape and biomechanical performance in living crocodilians under a range of loading conditions. Load cases corresponded to simple biting, lateral head shaking, and twist feeding behaviors. The six specimens were chosen to reflect, as far as possible, the full range of rostral shape in living crocodilians: a juvenile Caiman crocodilus, subadult Alligator mississippiensis and Crocodylus johnstoni, and adult Caiman crocodilus, Melanosuchus niger, and Paleosuchus palpebrosus. The simple beam models were generated using morphometric landmarks from each specimen. Three of the finite-element models, the A. mississippiensis, juvenile Caiman crocodilus, and the Crocodylus johnstoni, were based on CT scan data from respective specimens, but these data were not available for the other models and so these,the adult Caiman crocodilus, M. niger, and P. palpebrosus,were generated by morphing the juvenile Caiman crocodilus mesh with reference to three-dimensional linear distance measured from specimens. Comparison of the mechanical performance of the six finite-element models essentially matched results of the simple beam models: relatively tall skulls performed best under vertical loading and tall and wide skulls performed best under torsional loading. The widely held assumption that the platyrostral (dorsoventrally flattened) crocodilian skull is optimized for torsional loading was not supported by either simple beam theory models or finite-element modeling. Rather than being purely optimized against loads encountered while subduing and processing food, the shape of the crocodilian rostrum may be significantly affected by the hydrodynamic constraints of catching agile aquatic prey. This observation has important implications for our understanding of biomechanics in crocodilians and other aquatic reptiles. Anat Rec Part A, 288A:827,849, 2006. © 2006 Wiley-Liss, Inc. [source]

Force transmission of one- and two-piece morse-taper oral implants: a nonlinear finite element analysis

CLINICAL ORAL IMPLANTS RESEARCH, Issue 4 2004
Murat Cavit Çehreli
Abstract Purpose: To compare force transmission behaviors of one-piece (1-P) and two-piece (2-P) morse-taper oral implants. Material and methods: A three-dimensional finite element model of a morse-taper oral implant and a solid abutment was constructed separately. The implant,abutment complex was embedded in a Ø 1.5 cm × 1.5 cm acrylic resin cylinder. Vertical and oblique forces of 50 N and 100 N were applied on the abutment and solved by two different analyses. First, contact analysis was performed in the implant,abutment complex to evaluate a 2-P implant. Then, the components were bonded with a separation force of 1020 N to analyze a 1-P implant. Results: Von Mises stresses in the implant, principal stresses, and displacements in the resin were the same for both designs under vertical loading. Under oblique loading, principal stresses and displacement values in the resin were the same, but the magnitudes of Von Mises stresses were higher in the 2-P implant. The principal stress distributions around both implants in the acrylic bone were similar under both loading conditions. Conclusion: 2-P implants experience higher mechanical stress under oblique loading. Nevertheless, the 1-P- or 2-P morse-taper nature of an implant is not a decisive factor for the magnitude and distribution of stresses, and displacements in supporting tissues. Résumé Le but de cette étude a été de comparer les comportements de la transmission de la force desimplants buccaux en deux pièces. Un modèle d'éléments finis tridimensionnels d'un implant buccal et d'un pilier solide ont été construits séparément. Le complexe implant/pilier a été enfoui dans un cylindre de résine acrylique d'un diamètre 1,5 × 1,5 cm. Des forces obliques et verticales de 50 et 100 N ont été appliquées sur les piliers et analysées par deux méthodes. D'abord, l'analyse de contraste a été effectuée dans le complexe implant/pilier pour évaluer un implant en deux pièces. Ensuite, les composants ont été reliés avec une force de séparation de 1020N pour analyser un implant en une pièce. Les stress de Von Mises dans l'implant, les principaux stress et les déplacements dans la résine étaient les mêmes pour les deux modèles sous charge verticale. Lorsqu'une charge oblique était appliquée, les stress principaux et les valeurs de déplacements dans la résine étaient semblables mais l'amplitude des stress de Von Mises était plus importante dans l'implant à deux pièces. Les distributions des stress principaux autour des deux implants dans l'os acrylique était semblable sous les deux conditions de charge. Les implants en deux pièces subissent un stress mécanique plus important sous une charge oblique. Cependant, l'implant en une ou deux pièces avec un cône morse n'est pas un facteur décisif sur l'amplitude et la distribution des stress, et les déplacements des tissus de support. Zusammenfassung Ziel: Die Kraftübertragungsverhältnisse von ein- und zweiteiligen oralen Implantaten mit konischem Sitz der Sekundärteile zu untersuchen. Material und Methode: Es wurde je ein separates dreidimensionales Finite Element Modell eines oralen Implantats mit konischem Sitz der Sekundärteile und ein Massivsekundärteil konstruiert. Der Implantat-Sekundärteilkomplex wurde in einem Zylinder aus Acryl mit Durchmesser 1.5cm und Länge 1.5cm eingebettet. Vertikale und schräge Kräfte von 50 N und 100 N wurden auf das Sekundärteil appliziert und durch zwei verschiedene Analysen ausgewertet. Zuerst wurde eine Kontaktanalyse im Implantat-Sekundärteilkomplex zur Auswertung eines zweiteiligen Implantats durchgeführt. Dann wurden die Komponenten mit einer Separationskraft von 1020 N verbunden, um ein einteiliges Implantat zu analysieren. Resultate: Unter vertikaler Belastung waren der Van Mises Stress im Implantat, der generelle Stress und die Displatzierung im Kunststoff für beide Konstruktionen gleich. Unter schräger Belastung waren der generelle Stress und die Displatzierungswerte im Kunststoff die gleichen, jedoch war das Ausmass des von Mises Stress im zweiteiligen Implantat grösser. Die generelle Stressverteilung im Akrylknochen um die Implantate war unter beiden Belastungsbedingungen ähnlich. Schlussfolgerung: Zweiteilige Implantate erleiden grösseren mechanischen Stress unter schräger Belastung. Jedoch ist die ein- oder zweiteilige Konstruktion mit konischem Sitz der Sekundärteile bei Implantaten kein entscheidender Faktor für das Ausmass und die Verteilung des Stresses und für die Displatzierung in den Verankerungsgeweben. Resumen Intención: Comparar los comportamientos de transmisión de fuerzas de implantes orales en cono morse de una o dos piezas. Material y métodos: Se construyeron separadamente un modelo tridimensional de elemento finito de un implante oral de cono morse y un pilar sólido. El complejo implante-pilar se embebió en un cilindro de resina acrílica de , 1.5 cm × 1.5 cm. Se aplicaron fuerzas oblicuas de 50 N y 100 N sobre el pilar y se resolvieron por medio de dos análisis diferentes. Primero, se llevó a cabo un análisis de contacto en el complejo implante-pilar para evaluar un implante de dos piezas. Después, se unieron los componentes con una fuerza de separación de 1020 N para analizar un implante de una sola pieza. Resultados: El estrés de Von Mises, el estrés principal, y el desplazamiento en la resina fueron los mismos para ambos diseños bajo carga vertical. Bajo carga oblicua, los valores de estrés principal y desplazamiento en resina fueron los mismos, pero la magnitud de los estreses de Von Mises fueron mayores en los implantes de dos piezas. Las distribuciones del estrés principal alrededor de ambos implantes in el hueso acrílico fueron similares bajo ambas condiciones de carga. Conclusión: Los implantes de dos piezas experimentan un estrés mecánico mas alto bajo carga oblicua. Sin embargo, la naturaleza de un implante de cono morse de una o dos piezas no es un factor decisivo en la magnitud y distribución de los estreses, y desplazamientos en los tejidos de soporte. [source]