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Cracking Patterns (cracking + pattern)

Distribution by Scientific Domains

Polymers and Materials Science	75%

Selected Abstracts

Modeling of water absorption induced cracks in resin-based composite supported ceramic layer structures

JOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 1 2008
Min Huang
Abstract Cracking patterns in the top ceramic layers of the modeled dental multilayers with polymer foundation are observed when they are immersed in water. This article developed a model to understand this cracking mechanism. When water diffuses into the polymer foundation of dental restorations, the foundation will expand; as a result, the stress will build up in the top ceramic layer because of the bending and stretching. A finite element model based on this mechanism is built to predict the stress build-up and the slow crack growth in the top ceramic layers during the water absorption. Our simulations show that the stress build-up by this mechanism is high enough to cause the cracking in the top ceramic layers and the cracking patterns predicted by our model are well consistent with those observed in experiments on glass/epoxy/polymer multilayers. The model is then used to discuss the life prediction of different dental ceramics. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 2008 [source]

Einfluß der Elementfugen auf die Durchbiegung von Flachdecken

BETON- UND STAHLBETONBAU, Issue 3 2006
Manfred Curbach Prof. Dr.-Ing.
Das Verformungsverhalten von Flachdecken in Elementbauweise unterscheidet sich von einer reinen Ortbetondecke aufgrund der vorhandenen Elementfugen. Die damit verbundenen lokalen Querschnittsschwächungen erfordern schon auf niedrigem Lastniveau eine Umlagerung der Belastung in angrenzende Feld- und Stützbereiche. Die Folge der Lastumlagerung sind anfänglich höher beanspruchte Deckenbereiche und eine frühere Rißbildung im Vergleich zu einer reinen Ortbetondecke. Mit steigender Belastung kommt es jedoch zur Annäherung der Rißzustände von Fertigteil- und Ortbetondecken, wie anhand nichtlinearer Berechnungen nachgewiesen werden konnte. Der relative Unterschied in der Durchbiegung wird deutlich reduziert. Auf Gebrauchslastniveau liegen die Verformungen der Fertigteildecken etwa 5% über denen der reinen Ortbetondecke. Influence of Bond Joints on Deformation of precast Slabs Precast slabs and in-situ concrete slabs vary in their deflection behaviour due to the bond joints between the precast concrete units. The diminished cross section of the bond joints require a redistribution of internal forces to adjoining field and support areas already at a small load. The consequence of this redistribution are higher demands in these slab areas and an earlier crack initiation in comparison to the in-situ concrete slabs. With an increase of the loading the cracking pattern of the precast slabs and the in-situ concrete slabs converge as the nonlinear FE-calculation have shown. The relative difference in deformation is clearly reduced. At the service load the deformation of the precast slabs is only 5% higher than the deformation of the in-situ concrete slabs. [source]

Electric Field-Directed Convective Assembly of Ellipsoidal Colloidal Particles to Create Optically and Mechanically Anisotropic Thin Films

ADVANCED FUNCTIONAL MATERIALS, Issue 20 2009
Manish Mittal
Abstract A method of simultaneous field- and flow-directed assembly of anisotropic titania (TiO2) nanoparticle films from a colloidal suspension is presented. Titania particles are oriented by an alternating (ac) electric field as they simultaneously advect towards a drying front due to evaporation of the solvent. At high field frequencies (,,>,,25,kHz) and field strengths (E,>,300,V cm,1), the particles orient with their major axis along the field direction. As the front recedes, a uniform film with thicknesses of 1,10,µm is deposited on the substrate. The films exhibit a large birefringence (,n,,,0.15) and high packing fraction (,,=,0.75,±,0.08), due to the orientation of the particles. When the frequency is lowered, the particle orientation undergoes a parallel,random,perpendicular transition with respect to the field direction. The orientation dependence on field frequency and strength is explained by the polarizability of ellipsoidal particles using an interfacial polarization model. Particle orientation in the films also leads to anisotropic mechanical properties, which are manifested in their cracking patterns. In all, it is demonstrated that the field-directed assembly of anisotropic particles provides a powerful means for tailoring nanoparticle film properties in situ during the deposition process. [source]