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Load Direction (load + direction)

Distribution by Scientific Domains

Medical Sciences	50%

Selected Abstracts

Bemessung von Dübeln am Bauteilrand unter Querlast: Ingenieurmäßiger Ansatz zur Berücksichtigung der Lastrichtung

BETON- UND STAHLBETONBAU, Issue 6 2005
Rainer Mallée Dr.-Ing.
Es wird ein allgemeingültiger Bemessungsansatz für Dübel unter Querlast am Bauteilrand bei der Versagensart Betonkantenbruch abgeleitet. Die Richtung der Querlast wird bei der Lastverteilung auf die einzelnen Dübel einer Gruppe berücksichtigt. Damit kann das Modell für Anwendungen ohne und mit Lochspiel sowie für Querlasten und für Torsionsmomente angewendet werden. Design of Anchors close to an Edge under Shear Loads Engineering Approach for Consideration of the Load Direction A universally valid proposal is made for the design of anchors close to an edge under shear loads for concrete edge failure. The angle of the shear load is taken into account during determination of the load distribution on each anchor of a group. Thus the model may be used for applications without and with hole clearance and for shear loads as well as for torsion moments. [source]

,Arching' effect in elastic polycrystals: implications for the variability of fatigue lives

FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 4 2002
S. Pommier
ABSTRACT The paper deals with a study of heterogeneous stress and strain distribution in polycrystals in relation with elastic anisotropy of grains. A similitude with the arching effect widely studied in granular materials is proposed and this concept is extended to heterogeneous polycrystals in which the load transfer is not binary in the way it is in granular media but may vary significantly and suddenly from one grain to another according to the crystal orientation to the load direction. Experiments and 3D finite element analyses show that though the individual orientation of grains is random, the strain and stress distribution is not. A network is formed inside the polycrystal whose scale is larger than the grain size. The load percolation network consists in heavily loaded links whose direction is coincident with the direction of the principal stresses. So, the typical scale for the variability of the local stresses is not the grain size but the size of the load percolation network. Since this scale is found to be rather large in particular for iron, zinc and copper, this effect should contribute significantly to the variability of the fatigue lives of notched vs. smooth components. [source]

Ultrasonic welding of advanced thermoplastic composites: An investigation on energy-directing surfaces

ADVANCES IN POLYMER TECHNOLOGY, Issue 2 2010
Irene Fernandez Villegas
Abstract Ultrasonic welding is considered as one of the most promising welding techniques for continuous fiber-reinforced thermoplastic composites. Intermolecular friction within the bulk, resulting from the application of ultrasonic waves applied on the surfaces, generates the heat required for welding to take place at the interface of the joining members via the so-called "energy directors" (EDs). Energy directors consist of resin protrusions or artificially produced asperities on the composite surfaces and play an important role both in the welding process and in the quality of the resulting welds. This paper presents the results of a study on the effects of configuration of different EDs on the ultrasonic welding of carbon fiber/polyetherimide advanced thermoplastic composites in a near-field setup. Triangular EDs were molded on the surface of consolidated composite laminates with a hot platen press. Single lap-shear-welded samples were produced to investigate the influence of the orientation of the EDs with respect to the load direction, as well as the configuration of multiple EDs. The results indicate that the configuration of multiple transverse EDs was more effective in covering the overlap area, once the resin has melted, causing only a minimum fiber disruption at the welding interface. © 2010 Wiley Periodicals, Inc. Adv Polym Techn 29:112,121, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20178 [source]

Does orthodontic loading influence bone mineral density around titanium miniplates?

ORTHODONTICS & CRANIOFACIAL RESEARCH, Issue 1 2010
An experimental study in dogs
To cite this article: Cornelis MA, Mahy P, Devogelaer JP, De Clerck HJ, Nyssen-Behets C: Does orthodontic loading influence bone mineral density around titanium miniplates? An experimental study in dogs Orthod Craniofac Res 2010;13:21,27 Structured Abstract Authors,,, Cornelis MA, Mahy P, Devogelaer JP, De Clerck HJ, Nyssen-Behets C Objectives,,, To evaluate whether orthodontic loading has an effect on miniplate stability and bone mineral density (BMD) around the screws supporting those miniplates. Setting and Sample Population,,, Two miniplates were inserted in each jaw quadrant of 10 dogs. Material and Methods,,, Two weeks later, coil springs were placed between the miniplates of one upper quadrant and between those of the contralateral lower quadrant. The other miniplates remained non-loaded. The dogs were sacrificed 7 or 29 weeks after surgery, and the jaws were scanned with peripheral Quantitative Computed Tomography (pQCT) to assess BMD. Results,,, The success rate was not significantly different for the loaded and the non-loaded miniplates, but was significantly higher for the maxillary compared to the mandibular ones. Mobility, associated with local inflammation, most often occurred during the transition between primary and secondary stability. pQCT showed higher BMD around mandibular vs. maxillary screws, without significant difference between loaded and non-loaded ones. Furthermore, load direction did not lead to any significant difference in BMD. Conclusion,,, Miniplate stability and BMD of the adjacent bone did not appear to depend significantly on orthodontic loading, but rather on the receptor site anatomy. [source]

Biomechanical aspects of marginal bone resorption around osseointegrated implants: considerations based on a three-dimensional finite element analysis

CLINICAL ORAL IMPLANTS RESEARCH, Issue 4 2004
Eriko Kitamura
Abstract Objectives: Although bone loss around implants is reported as a complication when it progresses uncontrolled, resorption does not always lead to implant loss, but may be the result of biomechanical adaptation to stress. To verify this hypothesis, a three-dimensional finite element analysis was performed and the influence of marginal bone resorption amount and shape on stress in the bone and implant was investigated. Material and methods: A total of nine bone models with an implant were created: a non-resorption (Base) model and eight variations, in which three different resorption depths were combined with pure vertical or conical (vertical,horizontal) resorption. Axial and buccolingual forces were applied independently to the occlusal node at the center of the superstructure. Results: Regardless of load direction, bone stresses were higher in the pure vertical resorption (A) models than in the Base model, and increased with resorption depth. However, cortical bone stress was much lower in the conical resorption models than in both the Base and A models of the same resorption depth. An opposite tendency was observed in the cancellous bone under buccolingual load. Under buccolingual load, highest stress in the implant increased linearly with the resorption depth for all the models and its location approached the void existing below the abutment screw. Conclusions: The results of this analysis suggest that a certain amount of conical resorption may be the result of biomechanical adaptation of bone to stress. However, as bone resorption progresses, the increasing stresses in the cancellous bone and implant under lateral load may result in implant failure. Résumé Bien que la perte osseuse autour des implants soit considérée comme une complication quand elle progresse de manière incontrôlée, la résoption ne se termine pas toujours par la perte de l'implant, mais peut être le résultat de l'adaptation biomécanique au stress. Pour vérifier cette hypothèse, une analyse d'éléments finis en trois dimensions a été effectuée et l'influence de l'aspect et de la quantité de résorption osseuse marginale au stress dans l'os et l'implant a été analysée. Neuf modèles osseux avec un implant ont été créés : un modèle (Base) sans résorption et huit variations dans lesquelles trois profondeurs de résorption différentes ont été combinées avec des résorptions verticales ou coniques (verticale-horizontale). Des forces axiales et vestibulo-linguales ont été appliquées de manière indépendante en occlusal au centre de la superstructure. Quelle que soit la direction de la charge, les stress osseux étaient plus importants dans la résorption verticale pure (A) que dans le modèle de base et augmentaient avec la profondeur de résorption. Cependant, le stress osseux cortical était beaucoup plus faible dans les modèles à résorption conique que dans les modèles Base et A de même profondeur de résorption. Une tendance opposée était observée dans l'os spongieux sous charge vestibulo-linguale. Sous charge vestibulo-linguale, le stress le plus important dans l'implant augmentait linéairement avec la profondeur de résorption pour tous les modèles et sa localisation approchait l'espace existant en-dessous du pilier. Les résultats de cette analyse suggèrent qu'une certaine quantité de résorption conique pourrait être le résultat d'une adaptation biomécanique au stress osseux. Cependant, quand la résorption osseuse progresse les stress s'amplifiant dans l'os spongieux et au niveau de l'implant sous une force latérale peuvent résulter en un échec implantaire. Zusammenfassung Ziel: Auch wenn ein Knochenverlust um Implantate, der unkontrolliert fortschreitet, als Komplikation beschrieben wird, führen solche Resorptionen nicht gezwungenermassen zu einem Implantatverlust. Sie könnten aber Ausdruck einer biomechanischen Adaptation auf die Belastungen sein. Um diese Hypothese zu überprüfen, führte man eine dreidimensionale "Finite-Element"-Analyse durch. Man untersuchte die Zusammenhänge von Ausmass und Form der marginalen Knochenresorption und den entstehenden Kräften im Knochen und Implantat. Material und Methode: Die Arbeitsgrundlage waren 9 Modelle mit je einem Implantat: eines diente als Kontrolle (ohne Resorptionserscheinungen), die anderen acht zeigten drei verschiedene Resortionstiefen in Kombination mit rein vertikalen oder konischen (vertiko-horizontal) Defektformen. Dann liess man, unabhängig von der Okklusionsgestaltung, axiale und buccolinguale Kräfte auf die Mitte der Suprastruktur auftreffen. Resultate: Unabhängig von der Belastungsrichtung war die Knochenbelastung bei den rein vertikalen Resorptionsmodellen (A) grösser als beim Kontrollmodell und sie nahmen mit der Tiefe der Resorption zu. Die Belastung im kortikalen Knochen war aber in den Modellen mit konischen Resorptionen viel geringer als beim Kontrollmodell und den A-Modellen mit denselben Resorptionstiefen. Eine genau umgekehrte Tendenz konnte man im spongiösen Knochen unter buccolingualer Belastung feststellen.Bei einer buccolingualen Belastung nahm die Belastungsspitze beim Implantat bei allen Modellen linear mit der Resorptionstiefe zu und der Ort dieser Belastungsspitze lag im Bereich des Leerraumes genau unterhalb der Schraube des Sekundärteils. Zusammenfassung: Die Resultate dieser Analyse lassen vermuten, dass die konische Resorption bis zu einem gewissen Ausmass das Resultat einer biomechanischen Adaptation auf die Belastung des Knochens ist. Wenn aber die Knochenresorption fortschreitet, können die zunehmenden Belastungen im spongiösen Knochen und im Implantat bei einer lateralen Belastung zum Implantatmisserfolg führen. Resumen Objetivos: Aunque la pérdida de hueso alrededor de los implantes se informa como una complicación cuando progresa incontroladamente, la reabsorción no siempre lleva a la pérdida del implante, pero puede ser el resultado de la adaptación biomecánica al estrés. Para verificar esta hipótesis, se llevó a cabo un análisis tridimensional de elementos finitos y se investigó la influencia de la cantidad de reabsorción de hueso marginal y la forma en el estrés en el hueso y el implante. Material y métodos: Se crearon un total de 9 modelos de hueso con un implante: Un modelo sin reabsorción (Base) y 8 variaciones, el las que se combinaron tres diferentes profundidades de reabsorción con reabsorciones verticales o cónicas puras (vertical,horizontal). Se aplicaron fuerzas axiales y bucolinguales independientemente al nodo oclusal en el centro de la superestructura. Resultados: A pesar de la dirección de la carga, los estreses óseos fueron más altos en los modelos de reabsorción vertical pura (A) que en los modelos Base y se incrementaron con la profundidad de reabsorción. De todos modos, el estrés cortical fue mucho menor en los modelos de reabsorción cónica que en los modelos Base y A con la misma profundidad de reabsorción. Se observó una tendencia opuesta en el hueso esponjoso bajo carga bucolingual. Bajo carga bucolingual, el estrés mas alto en el implante se incrementó linealmente con la profundidad de reabsorción para todos los modelos y su localización se aproximó al espacio existente bajo el tornillo del pilar. Conclusión: Los resultados de este análisis sugieren que cierta cantidad de reabsorción cónica puede resultar de la adaptación biomecánica del hueso al estrés. De todos modos, al progresar la reabsorción ósea, los estrés crecientes en el hueso esponjoso y en el implante bajo carga lateral puede resultar en un fracaso del implante. [source]

Effect of Compromised Cortical Bone on Implant Load Distribution

JOURNAL OF PROSTHODONTICS, Issue 8 2008
vanç Akça DDS
Abstract Purpose: To investigate photoelastically the difference in load distribution of dental implants with different implant neck designs in intact and compromised bone. Materials and Methods: Composite photoelastic models were fabricated using two different resins to simulate trabecular bone and a 1-mm thick layer of cortical bone. The following parallel-sided, threaded implants were centrally located in individual models representing intact and compromised cortical bone: Straumann (4.1-mm diameter × 12-mm length), AstraTech (4.0-mm diameter × 13-mm length), and 3i (3.75-mm diameter × 13-mm length). The compromised cortical bone condition was simulated by contaminating a 1-mm neck portion with Vaseline to impair the implant,resin interface. Vertical and oblique static loads were applied on the abutments, and the resulting stresses were monitored photoelastically and recorded photograhphically. Results: For the fully intact condition, the highest stresses were observed around the crest and apical region for all implant designs under vertical and inclined loads. There were no appreciable differences in magnitude or distribution between implant types. With compromised cortical bone, for all designs and load directions, higher stresses in the supporting structures were observed. Increased stresses were noted especially at the cortical bone,trabecular bone interface. Somewhat lower stress levels were observed with the 3i implant. Conclusions: The condition of implant,cortical bone contact has considerable influence on stress distribution. A compromised cortical bone condition caused higher level stresses for all implant designs tested. [source]