Influência da angulação do preparo coronário na resistência à fratura de restaurações cerâmicas à base de Y-TZP

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

The potential of novel primers and universal adhesives to bond to zirconia

Objectives: To investigate the adhesive potential of novel zirconia primers and universal adhesives to surface-treated zirconia substrates.Methods: Zirconia bars were manufactured (3.0 mm x 3.0 mm x 9.0 mm) and treated as follows: no treatment (C); air abrasion with 35 mu m alumina particles (S); air abrasion with 30 mu m silica particles using one of two systems (Rocatec or SilJet) and; glazing (G). Groups C and S were subsequentially treated with one of the following primers or adhesives: ZP (Z-Prime Plus), AZ (AZ Primer); MP (Monobond Plus); SU (ScotchBond Universal) and; EA (an Experimental Adhesive). Groups Rocatec and SilJet were silanized prior to cementation. Samples form group G were further etched and silanized. Bars were cemented (Multilink) onto bars of a silicate-based ceramic (3.0 mm x 3.0 mm x 9.0 mm) at 90 degrees angle, thermocycled (2.500 cycles, 5-55 degrees C, 30 s dwell time), and tested in tensile strength test. Failure analysis was performed on fractured specimens to measure the bonding area and crack origin.Results: Specimens from group C did not survive thermocycling, while CMP, CSU and CEA groups survived thermocycling but rendered low values of bond strength. All primers presented a better bond performance after air abrasion with Al2O3 particles. SilJet was similar to Rocatec, both presenting the best bond strength results, along with SMP, SSU and CEA. G promoted intermediate bond strength values. Failure mode was predominately adhesive on zirconia surface combined to cohesive of the luting agent.Conclusions: Universal adhesives (MP, SU, EA) may be a considerable alternative for bonding to zirconia, but air abrasion is still previously required. Air abrasion with silica particles followed by silane application also presented high bond strength values. (C) 2013 Elsevier Ltd. All rights reserved.

Efeito do tratamento térmico em cerâmica feldspáticas silanizada na adesão do cimento resinoso

Pós-graduação em Odontologia Restauradora - ICT

Desenvolvimento e validação de um novo protocolo para ciclagem térmica de materiais dentários

Pós-graduação em Odontologia Restauradora - ICT

Effect of cleansing methods on saliva-contaminated zirconia: an evaluation of resin bond durability

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Lifetime comparison of Y-TZP/porcelain crowns under different loading conditions

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

HIGH TEMPERATURE RARE EARTH COMPOUNDS: SYNTHESIS, CHARACTERIZATION AND APPLICATIONS IN DEVICE FABRICATION

As the area of nanotechnology continues to grow, the development of new nanomaterials with interesting physical and electronic properties and improved characterization techniques are several areas of research that will be remain vital for continued improvement of devices and the understanding in nanoscale phenomenon. In this dissertation, the chemical vapor deposition synthesis of rare earth (RE) compounds is described in detail. In general, the procedure involves the vaporization of a REClx (RE = Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho) in the presence of hydride phase precursors such as decaborane and ammonia at high temperatures and low pressures. The vapor-liquid-solid mechanism was used in combination with the chemical vapor deposition process to synthesize single crystalline rare earth hexaboride nanostructures. The crystallographic orientation of as-synthesized rare earth hexaboride nanostructures and gadolinium nitride thin films was controlled by judicious choice of specific growth substrates and modeled by analyzing x-ray diffraction powder patterns and crystallographic models. The rare earth hexaboride nanostructures were then implemented into two existing technologies to enhance their characterization capabilities. First, the rare earth hexaboride nanowires were used as a test material for the development of a TEM based local electrode atom probe tomography (LEAP) technique. This technique provided some of the first quantitative compositional information of the rare earth hexaboride systems. Second, due to the rigidity and excellent conductivity of the rare earth hexaborides, nanostructures were grown onto tungsten wires for the development of robust, oxidation resistant nanomanipulator electronic probes for semiconductor device failure analysis.

Micro-mechanical bond strength tests for the assessment of the adhesion of GIC to dentine

Background. The aim of this study is to critically evaluate the bond strength (BS) of Glass-Ionomer Cements (GIC) to dentine with microtensile (mu TBS) and microshear (mu SBS) BS tests by assessing their rankings and failure patterns. Methods. Samples were made on flat dentine surfaces and submitted to mTBS and mSBS. The materials used were: high viscosity GIC (Ketac (TM) Molar Aplicap-KM), resin-modified GIC (Fuji II-FII), nano-filled resin-modified GIC (Ketac (TM) N100-N100) and an etch-and-rinse adhesive system with a composite resin (Adper (TM) Single Bond 2 and Z100 (TM)-Z100). All tests were performed with a Universal Testing Machine (24 h water storage, crosshead speed of 1 mm/min). Debonded surfaces were examined with a stereomicroscope (x40) to identify the failure mode. The data was analyzed with two-way ANOVA (p < 0.05) and LSD test. Results. Means were statistically different regarding the tests and materials, indicating that values for BS obtained for each material depend on the test performed. Failure analysis revealed that failures produced by mTBS were mainly cohesive for KM and FII. mu SBS failures were mainly adhesive or mixed for all materials. For the mTBS, the rank was Z100 > FII > KM = N100, whereas for the mSBS it was Z100 = FII = KM > N100. Conclusion: It may be concluded that distinct micro-mechanical tests present different failure patterns and rankings depending on the material to be considered.

A new damage model for composite laminates

Aircraft composite structures must have high stiffness and strength with low weight, which can guarantee the increase of the pay-load for airplanes without losing airworthiness. However, the mechanical behavior of composite laminates is very complex due the inherent anisotropy and heterogeneity. Many researchers have developed different failure progressive analyses and damage models in order to predict the complex failure mechanisms. This work presents a damage model and progressive failure analysis that requires simple experimental tests and that achieves good accuracy. Firstly, the paper explains damage initiation and propagation criteria and a procedure to identify the material parameters. In the second stage, the model was implemented as a UMAT (User Material Subroutine), which is linked to finite element software, ABAQUS (TM), in order to predict the composite structures behavior. Afterwards, some case studies, mainly off-axis coupons under tensile or compression loads, with different types of stacking sequence were analyzed using the proposed material model. Finally, the computational results were compared to the experimental results, verifying the capability of the damage model in order to predict the composite structure behavior. (C) 2011 Elsevier Ltd. All rights reserved.

Theoretical models to predict the mechanical behavior of thick composite tubes

This paper shows theoretical models (analytical formulations) to predict the mechanical behavior of thick composite tubes and how some parameters can influence this behavior. Thus, firstly, it was developed the analytical formulations for a pressurized tube made of composite material with a single thick ply and only one lamination angle. For this case, the stress distribution and the displacement fields are investigated as function of different lamination angles and reinforcement volume fractions. The results obtained by the theoretical model are physic consistent and coherent with the literature information. After that, the previous formulations are extended in order to predict the mechanical behavior of a thick laminated tube. Both analytical formulations are implemented as a computational tool via Matlab code. The results obtained by the computational tool are compared to the finite element analyses, and the stress distribution is considered coherent. Moreover, the engineering computational tool is used to perform failure analysis, using different types of failure criteria, which identifies the damaged ply and the mode of failure.

Studio microstrutturale e tribologico di componenti per motori idraulici a pistoni radiali a colonna di fluido

Lo studio condotto ha lo scopo di aumentare la vita in esercizio di motori idraulici a pistoni radiali a colonna di fluido, studiandone e migliorandone il comportamento tribologico. Questa tipologia di motori è adatta per generare alte coppie a basse velocità e si impiega in sistemi di movimentazione lenta per carichi pesanti. Il contatto in condizioni di strisciamento fra cilindri telescopici ed albero eccentrico rotante, può portare all’usura dei componenti coinvolti e quindi al trafilamento dell’olio che circola nel motore, causando cali di efficienza. Lo studio ha previsto un’indagine del tipo Failure Analysis su componenti del motore sottoposti a prove a banco. Successivamente, è stato condotto uno studio tribologico, al fine di valutare il comportamento del sistema e definire possibili modifiche ai componenti per il miglioramento del motore. Dalla Failure Analysis, è emerso che il meccanismo di usura prevalente risulta essere l’abrasione a due corpi. Le prove tribologiche di laboratorio, condotte in condizioni che hanno permesso di riprodurre i meccanismi di usura dominanti nelle prove a banco, hanno dato luogo a transizioni sia nell’attrito che nell’usura, il cui verificarsi dipende da: carico applicato, distanza di strisciamento, durezza dei materiali a contatto.

Processing and Composition Effects on the Fracture Behavior of Spray-Formed 7XXX Series Al Alloys

The fracture properties of high-strength spray-formed Al alloys were investigated, with consideration of the effects of elemental additions such as zinc,manganese, and chromium and the influence of the addition of SiC particulate. Fracture resistance values between 13.6 and 25.6 MPa (m)1/2 were obtained for the monolithic alloys in the T6 and T7 conditions, respectively. The alloys with SiC particulate compared well and achieved fracture resistance values between 18.7 and 25.6 MPa (m)1/2. The spray-formed materials exhibited a loss in fracture resistance (KI) compared to ingot metallurgy 7075 alloys but had an improvedperformance compared to high-solute powder metallurgy alloys of similar composition. Characterization of the fracture surfaces indicated a predominantly intergranular decohesion, possibly facilitated by the presence of incoherent particles at the grain boundary regions and by the large strength differentialbetween the matrix and precipitate zone. It is believed that at the slip band-grain boundary intersection, particularly in the presence of large dispersoids and/or inclusions, microvoid nucleation would be significantly enhanced. Differences in fracture surfaces between the alloys in the T6 and T7 condition were observed and are attributed to inhomogeneous slip distribution, which results in strain localization at grain boundaries. The best overall combination of fracture resistance properties were obtained for alloys with minimum amounts of chromium and manganese additions.

Schadensanalyse hochfester Faserseile

Bis heute werden in Unstetigförderern, wie Kränen und Aufzügen, fast ausschließlich Stahldrahtseile und Stahlketten eingesetzt. Gleichwohl weisen diese Zugmittel wesentliche Nachteile, wie z. B. eine hohe Ei-genmasse, geringe Biegeflexibilität und Korrosionsempfindlichkeit, auf. Um den stetig wachsenden Anforderungen insbesondere im Bereich der „laufenden Seile“ gerecht werden zu können, müssen alternative Zugmittel, unter Verwendung neuer Technologien und Werkstoffe, entwickelt und durch systematische Untersuchungen zur Serienreife geführt werden. Hochfeste Faserseile weisen bereits heute vielversprechende mechanische Eigenschaften hinsichtlich Zugfestigkeit, Schwingungsverhalten und Biegewechselfestigkeit auf. Dennoch ist ihr Einsatz aufgrund fehlender systematischer Untersuchungen, unzureichender Dimensionierungsgrundlagen sowie fehlender Verfahren zur Ablegereifeerkennung, zum gegenwärtigen Zeitpunkt nicht möglich. Mit Hilfe neuer Techniken und Verfahren, wie beispielsweise einer Mehrzonenbiegewechselmaschine für die Seilprüfung und der Computertomographie für die Seilanalyse sollen neue Erkenntnisse über das Ver-schleißverhalten von Faserseilen gewonnen und daraus abgeleitet neue Seilkonstruktionen sowie Ablegekriterien entstehen.

Evaluating statistical methods used to estimate the number of postsynaptic receptors.

Calcium levels in spines play a significant role in determining the sign and magnitude of synaptic plasticity. The magnitude of calcium influx into spines is highly dependent on influx through N-methyl D-aspartate (NMDA) receptors, and therefore depends on the number of postsynaptic NMDA receptors in each spine. We have calculated previously how the number of postsynaptic NMDA receptors determines the mean and variance of calcium transients in the postsynaptic density, and how this alters the shape of plasticity curves. However, the number of postsynaptic NMDA receptors in the postsynaptic density is not well known. Anatomical methods for estimating the number of NMDA receptors produce estimates that are very different than those produced by physiological techniques. The physiological techniques are based on the statistics of synaptic transmission and it is difficult to experimentally estimate their precision. In this paper we use stochastic simulations in order to test the validity of a physiological estimation technique based on failure analysis. We find that the method is likely to underestimate the number of postsynaptic NMDA receptors, explain the source of the error, and re-derive a more precise estimation technique. We also show that the original failure analysis as well as our improved formulas are not robust to small estimation errors in key parameters.

Preliminary temperature accelerated life test (ALT) on lattice mismatched triple-junction concentrator solar cells-on-carriers

A temperature accelerated life test on concentrator lattice mismatched Ga0.37In0.63P/Ga0.83In0.17As/Ge triple-junction solar cells-on-carrier is being carried out. The solar cells have been tested at three different temperatures: 125, 145 and 165°C and the nominal photo-current condition (500X) is emulated by injecting current in darkness. The final objective of these tests is to evaluate the reliability, warranty period, and failure mechanism of these solar cells in a moderate period of time. Up to now only the test at 165°C has finished. Therefore, we cannot provide complete reliability information, but we have carried out preliminary data and failure analysis with the current results.