Página 11 dos resultados de 5983 itens digitais encontrados em 0.127 segundos

Punching Strength of Flat Slabs with Unbraced Shear Reinforcement

Trautwein, Leandro Mouta; Bittencourt, Tulio Nogueira; Gomes, Ronaldo Barros; Bella, Joao Carlos Della
Fonte: AMER CONCRETE INST Publicador: AMER CONCRETE INST
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
56.797617%
This paper analyzes the punching strength of concrete flat slabs with shear reinforcement that does not embrace flexural reinforcement. This paper also reports the results of tests of slabs without shear reinforcement. Finally, this paper shows some comparisons of tests of similar slabs without shear reinforcement and slabs with different types of shear reinforcement. The obtained results show that the use of shear reinforcement elements without embracement in the flexural reinforcement improves the punching strength of reinforced concrete flat slabs.; Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP)

Verificação simultânea dos estados limites últimos e de serviço em análises não-lineares de peças de concreto armado submetidas à flexão pura ; Simultaneous verification of the ultimate limit states and of serviceability in nonlinear analysis of reinforced concrete beams subjected to pure bending

Vasconcelos, Geilson Márcio Albuquerque de
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Relevância na Pesquisa
56.667095%

Effect of testing methods on the bond strength of resin to zirconia-alumina ceramic: microtensile versus shear test

Valandro, Luiz F.; Ozcan, Mutlu; Amaral, Regina; Vanderlei, Aleska; Bottino, Marco A.
Fonte: Japanese Soc Dental Materials Devices Publicador: Japanese Soc Dental Materials Devices
Tipo: Artigo de Revista Científica Formato: 849-855
ENG
Relevância na Pesquisa
56.7909%
This study tested the bond strength of a resin cement to a glass-infiltrated zirconia-alumina ceramic after three conditioning methods and using two test methods (shear-SBS versus microtensile-MTBS). Ceramic blocks for MTBS and ceramic disks for SBS were fabricated. Three surface conditioning (SC) methods were evaluated: (1) 110-mu m Al(2)O(3)+Silanization; (2) Chairside silica coating+silanization: (3) Laboratory silica coating+silanization. Following surface conditioning, the resin cement (Panavia F) was bonded to the conditioned ceramics. Although no statistically significant differences (p=0.1076) were seen between the test methods, results yielded with the different surface conditioning methods showed statistically significant differences (p<0.0001) (SC2=SC3>SC1.). As for the interaction between the factors, two-way ANOVA showed that it was not statistically significant (p=0.1443). MTBS test resulted in predominantly mixed failure (85%), but SBS test resulted in exclusively adhesive failure. on the effects of different surface conditioning methods, chairside and laboratory tribochemical silica coating followed by silanization showed higher bond strength results compared to those of aluminum oxide abrasion and silanization, independent of the test method employed.

Estudo da fadiga em liga de alumínio aeronáutico 7475-T761

Serrano, Alexandre Costa
Tipo: Trabalho de Conclusão de Curso Formato: 100 f.
POR
Relevância na Pesquisa
56.67052%
This work will address the study of fatigue conditions with constant load in an alloy of aluminum analysis 7475 - T761, so we can better understand the conditions of the aircrafts which contain this alloy in their structures. A literature review, which was discussed the concepts of fracture mechanics, fatigue, aeronautical components, chemical analysis of aluminum alloys, fatigue problems that appears in the aircrafts, metallographic analysis, and testing of optical microscopy tensile, fatigue and microhardness, surface analysis (MEV) study of the chemical composition of the alloy in question, the main causes of crashes, was performed, completing the work, analysis of data from tensile test, hardness and fatigue together with the interpretation of images of optical microscopy and scanning electron was taken. The data indicated the high mechanical strength of the alloy, along with its microstructure indicating elongated grains and high surface contour, which shows such resistance by hindering the movement of dislocations. The grooves are clearly shown in the MEV images as well as the classic with increased fatigue loading and subsequent reduction of the number of cycles to rupture behavior shown in the graphs. Therefore we observed the optimal behavior is supported by the league when subjected to fatigue loadings; Este trabalho contempla o estudo sobre condições de fadiga com carregamento constante em uma liga de análise de alumínio 7475 - T761...

Molecular dynamics simulations of nonpolarizable inorganic salt solution interfaces: NaCl, NaBr, and NaI in transferable intermolecular potential 4-point with charge dependent polarizability (TIP4P-QDP) water

Fonte: American Institute of Physics Publicador: American Institute of Physics
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
56.673027%
We present molecular dynamics simulations of the liquid-vapor interface of 1M salt solutions of nonpolarizable NaCl, NaBr, and NaI in polarizable transferable intermolecular potential 4-point with charge dependent polarizability water [B. A. Bauer , J. Chem. Theory Comput. 5, 359 (2009)]; this water model accommodates increased solvent polarizability (relative to the condensed phase) in the interfacial and vapor regions. We employ fixed-charge ion models developed in conjunction with the TIP4P-QDP water model to reproduce ab initio ion-water binding energies and ion-water distances for isolated ion-water pairs. The transferability of these ion models to the condensed phase was validated with hydration free energies computed using thermodynamic integration (TI) and appropriate energy corrections. Density profiles of Cl−, Br−, and I− exhibit charge layering in the interfacial region; anions and cation interfacial probabilities show marked localization, with the anions penetrating further toward the vapor than the cations. Importantly, in none of the cases studied do anions favor the outermost regions of the interface; there is always an aqueous region between the anions and vapor phase. Observed interfacial charge layering is independent of the strength of anion-cation interactions as manifest in anion-cation contact ion pair peaks and solvent separated ion pair peaks; by artificially modulating the strength of anion-cation interactions (independent of their interactions with solvent)...

Entropy of single-file water in (6,6) carbon nanotubes

Waghe, Aparna; Rasaiah, Jayendran C.; Hummer, Gerhard
Fonte: American Institute of Physics Publicador: American Institute of Physics
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
56.67052%
We used molecular dynamics simulations to investigate the thermodynamics of filling of a (6,6) open carbon nanotube (diameter D = 0.806 nm) solvated in TIP3P water over a temperature range from 280 K to 320 K at atmospheric pressure. In simulations of tubes with slightly weakened carbon-water attractive interactions, we observed multiple filling and emptying events. From the water occupancy statistics, we directly obtained the free energy of filling, and from its temperature dependence the entropy of filling. We found a negative entropy of about −1.3 kB per molecule for filling the nanotube with a hydrogen-bonded single-file chain of water molecules. The entropy of filling is nearly independent of the strength of the attractive carbon-water interactions over the range studied. In contrast, the energy of transfer depends strongly on the carbon-water attraction strength. These results are in good agreement with entropies of about −0.5 kB per water molecule obtained from grand-canonical Monte Carlo calculations of water in quasi-infinite tubes in vacuum under periodic boundary conditions. Overall, for realistic carbon-water interactions we expect that at ambient conditions filling of a (6,6) carbon nanotube open to a water reservoir is driven by a favorable decrease in energy...

Enhancing the Strength of an Optical Trap by Truncation

Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
56.667095%
Optical traps (tweezers) are beginning to be used with increasing efficacy in diverse studies in the biological and biomedical sciences. We report here results of a systematic study aimed at enhancing the efficiency with which dielectric (transparent) materials can be optically trapped. Specifically, we investigate how truncation of the incident laser beam affects the strength of an optical trap in the presence of a circular aperture. Apertures of various sizes have been used by us to alter the beam radius, thereby changing the effective numerical aperture and intensity profile. We observe significant enhancement of the radial and axial trap stiffness when an aperture is used to truncate the beam compared to when no aperture was used, keeping incident laser power constant. Enhancement in trap stiffness persists even when the beam intensity profile is modulated. The possibility of applying truncation to multiple traps is explored; to this end a wire mesh is utilized to produce multiple trapping that also alters the effective numerical aperture. The use of a mesh leads to reduction in trap stiffness compared to the case when no wire mesh is used. Our findings lead to a simple-to-implement and inexpensive method of significantly enhancing optical trapping efficiency under a wide range of circumstances.

Bond Strength of Composite Resin to Pulp Capping Biomaterials after Application of Three Different Bonding Systems

Jaberi-Ansari, Zahra; Mahdilou, Maryam; Ahmadyar, Maryam; Asgary, Saeed
Fonte: Tabriz University of Medical Sciences Publicador: Tabriz University of Medical Sciences
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
56.6595%
Background and aims. Bonding of composite resin filling materials to pulp protecting agents produces an adhesive joint which is important for the quality of filling as well as success of restoration. We aimed to assess the bond strength of composite resin to three pulp capping biomaterials: Pro Root mineral trioxide aggregate (PMTA), Root MTA (RMTA) and calcium enriched mixture (CEM) cement, using three bonding systems [a total-etch (Single Bond) and two self-etch systems (Protect bond and SE Bond)].

Proposta de método de ensaio para determinação da resistência ao cisalhamento paralelo às fibras de madeiras mediante esforço induzido por puncionamento do corpo de prova

Hara, Massayuki Mario
POR
Relevância na Pesquisa
56.673276%
This research aims to examine the procedures and results of test methods proposed for the identification of the shear strength of wood fibers in parallel direction. Aims to observe the imperfections of existing methods, aiming to propose a new test method in which some of the problems shown can be minimized or reduced. The method proposed by NBR 7190/97 uses a rectangular prismatic body of evidence with a tooth to prevent its rotation caused by asymmetry in the application of force that causes the shear. The method proposed by SANTOS NETO (1999) also uses a prismatic body of evidence with alternating partial interruptions in cross sections, which provide requests shear at pre-selected regions. Alternatively, the paper presents two methods: the first test method suggested is analogous to the standard test, but applying the load symmetrically to shear two sections so as to prevent rotation of the body. This method revealed problems that occurred because of the proportions between the shear stresses and strains of crushing by compression on the surface of application of loads and the anticipation of breaking the shear rupture of traction on the underside of the body of evidence. A second procedure is proposed, leading to shear stress by punching a simple prismatic body of evidence and without cutouts...

Impact strength of P/M Fe-Mo-P sintered steels

Cantón Soria, Juan Manuel
Tipo: info:eu-repo/semantics/bachelorThesis; info:eu-repo/semantics/masterThesis Formato: application/octet-stream; application/octet-stream; application/pdf; application/pdf
Relevância na Pesquisa
56.663433%
Powder metallurgy is a metalworking process used to fabricate parts of simple or complex shape from a wide variety of metals and alloys in the form of powders. The process involves shaping of the powder and subsequent bonding of its individual particles by heating or mechanical working. In current research were carried out different analysis in order to obtain impact strength and other features of sintered Fe-P-Mo steels with sponge iron NC 100.24 as reference material. Addition of phosphorous as alloying element improves the impact properties and dimensional behavior mainly due to two different aspects.

Deposition and characterization of duplex treated coating system applied on hot work steel AISI H13; Deposici??n y caracterizaci??n de un sistema de recubrimiento duplex aplicado sobre acero para trabajo en caliente AISI H13

Bejarano Gait??n, Gilberto; Arroyave Franco, Mauricio; G??mez Botero, Maryori
Tipo: article; Art??culo; publishedVersion
ENG
Relevância na Pesquisa
56.666074%
AISI H13 steel is widely used for extrusion moulds and other hot work tools fabrication, due to its high toughness, strength and hardness around 56 HRC (Rockwell C) -- However, this steel possesses a relatively low wear resistance, which reduces its life time under high loading conditions -- The aim of this work was to enhance the wear resistance of the steel H13 using the following surface treatments:austenitizing + quenching + tempering (further called ???tempering???), tempering and bath nitriding, tempering and coated with chromium nitride (CrN), tempering + bath nitriding + coated with CrN (further called ???Duplex coating???) -- The properties of the treated samples were compared with each other in dependence of the made surface treatment -- The coatings were deposited using the r.f. balanced magnetron sputtering deposition technique -- The total thickness of the coatings was maintained at 5 ??m, while the thickness of the nitrided zone was approximately 140 ??m -- The microstructure and the crystalline phase composition were investigated by Scanning -- Electron Microscopy (SEM) and X-ray diffraction (XRD) technique, respectively -- The hardness and the adhesion of the coatings were determined by micro indentation measurements and the Rockwell indentation test...

The heterogeneous partial oxidation of light alkanes

Su, Yee San, 1977-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 138 leaves; 10902571 bytes; 10920469 bytes; application/pdf; application/pdf
EN_US
Relevância na Pesquisa
56.67392%
(cont.) With this approach, an upper bound on the yield for OCM was computed. Results showed that even with optimal surface chemistry, strict limits existed on the attainable yield. Surface energetics necessary for superior OCM performance were identified and the origins of these requirements elucidated. The resulting upper bound on OCM yield under conventional, packed-bed, continuous-feed operation was found to be 28%. The catalytic properties of LiCl/sulfated ZrO₂-based catalysts were explored for ODHE. LiCl was shown to strongly interact with the acid sites on sulfated ZrO₂ (SZ), influencing its catalytic behavior. Two approaches were taken to modify the nature/strength of the LiCl-support interaction. Firstly, LiCl/Nd₂O₃-impregnated MoO/ZrO₂ and WOx/ZrO₂ were examined. Unlike SZ, these supports allowed for the tailoring of MoO[sub]x and WO[sub]x surface densities, which in turn drastically altered their ODHE performance. The poor stability of these supports, however, rendered them inferior to SZ. Secondly, the effects of dopant incorporation on the catalytic behavior of LiCI/MO,/SZ were studied. Si-doped ZrO₂-based catalysts synthesized via the sol-gel method were found to exhibit superior activity, selectivity and stability for ODHE. Sulfate decomposition experiments related the ODHE activity of these materials to the influence of the Si dopant on the sulfate binding strength. The sol-gel synthesis conditions were optimized with respect to sol pH...

Effects of different surface treatments and accelerated artificial aging on the bond strength of composite resin repairs

Melo,Marco Aurélio Veiga de; Moysés,Marcos Ribeiro; Santos,Saulo Galvão dos; Alcântara,Carlos Eduardo Pinto; Ribeiro,José Carlos Rabelo
Tipo: Artigo de Revista Científica Formato: text/html
Relevância na Pesquisa
56.6595%
The purpose of the present study was to assess the bond strength of composite resin repairs subjected to different surface treatments and accelerated artificial aging. 192 cylindrical samples (CSs) were prepared and divided into 24 groups (n = 8). Half of the CSs were stored in water for 24 h, and the other half were subjected to C-UV accelerated aging for non-metallic specimens. The treatments were phosphoric acid + silane + adhesive (PSA); phosphoric acid + adhesive (PA); diamond bur + phosphoric acid + silane + adhesive (DPSA); diamond bur + phosphoric acid + adhesive (DPA); air abrasion + phosphoric acid + silane + adhesive (APSA); and air abrasion + phosphoric acid + adhesive (APA). The repair was performed and the specimens were again aged as described above. A control group (n = 8) was established and did not receive any type of aging or surface treatment. The specimens were loaded to failure in shear mode with a crosshead speed of 0.5 mm/min until fracture. Data were analyzed by one-way ANOVA/Tukey's test (p < 0.05). No statistically significant differences were found among DPSA, DPA, APSA, APA, and the control group. The aged PSA and PA achieved low bonding values and were statistically different from the control group, whereas the non-aged PSA and PA presented no statistically significant difference from the control group. Repairs with the proposed surface treatments were viable on both recent and aged restorations; however...

Influence of a knot on the strength of a polymer strand

Saitta, A. Marco; Soper, Paul D.; Wasserman, E.; Klein, Michael L.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
56.80026%
Many experiments have been done to determine the relative strength of different knots, and these show that the break in a knotted rope almost invariably occurs at a point just outside the entrance' to the knot. The influence of knots on the properties of polymers has become of great interest, in part because of their effect on mechanical properties. Knot theory applied to the topology of macromolecules indicates that the simple trefoil or overhand' knot is likely to be present with high probability in any long polymer strand. Fragments of DNA have been observed to contain such knots in experiments and computer simulations. Here we use {\it ab initio} computational methods to investigate the effect of a trefoil knot on the breaking strength of a polymer strand. We find that the knot weakens the strand significantly, and that, like a knotted rope, it breaks under tension at the entrance to the knot.; Comment: 3 pages, 4 figures

Ab Initio Calculations of the Walls Shear Strength of Carbon Nanotubes

Bichoutskaia, E.; Ershova, O. V.; Lozovik, Yu. E.; Popov, A. M.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
56.664873%
The dependence of the energy of interwall interaction in double-walled carbon nanotubes (DWNT) on the relative position of walls has been calculated using the density functional method. This dependence is used to evaluate forces that are necessary for the relative telescopic motion of walls and to calculate the shear strength of DWNT for the relative sliding of walls along the nanotube axis and for their relative rotation about this axis. The possibility of experimental verification of the obtained results is discussed.; Comment: 4 pages, 1 figure

An Overview of Multiscale Simulations of Materials

Lu, Gang; Kaxiras, Efthimios
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
56.7534%
Multiscale modeling of material properties has emerged as one of the grand challenges in material science and engineering. We provide a comprehensive, though not exhaustive, overview of the current status of multiscale simulations of materials. We categorize the different approaches in the spatial regime into sequential and concurrent, and we discuss in some detail representative methods in each category. We classify the multiscale modeling approaches that deal with the temporal scale into three different categories, and we discuss representative methods pertaining to the each of these categories. Finally, we offer some views on the strength and weakness of the multiscale approaches that are discussed, and touch upon some of the challenging multiscale modeling problems that need to be addressed in the future.; Comment: 29 pages, 7 figures (send email to the authors for higher quality figures)

Chain Ends and the Ultimate Strength of Polyethylene Fibers

O'Connor, Thomas C.; Robbins, Mark O.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
56.6595%
We use large scale molecular dynamics (MD) simulations to determine the tensile yield mechanism of orthorhombic polyethylene (PE) crystals with finite chains spanning $10^2-10^4$ carbons in length. We find the yield stress $\sigma_y$ saturates for long chains at 6.3 GPa, agreeing well with experiments. We show chains do not break but always yield by slip, after nucleation of 1D dislocations at chain ends. Dislocations are accurately described by a Frenkel-Kontorova model parametrized by the mechanical properties of an ideal crystal. We compute a dislocation core size $\xi\approx25$\AA\ and determine the high and low strain rate limits of $\sigma_y$. Our results suggest characterizing the 1D dislocations of polymer crystals as an efficient method for numerically predicting the ultimate tensile strength of aligned fibers.

Variable Coupling Strength of Silicene on Ag(111)

Feng, Baojie; Li, Wenbin; Qiu, Jinglan; Cheng, Peng; Chen, Lan; Wu, Kehui
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
56.66168%
We performed a scanning tunneling microscopy and spectroscopy (STM/STS) study on the electronic structures of of root(3)Xroot(3)-silicene on Ag(111). We find that the coupling strength of root(3)Xroot(3)-silicene with Ag(111) substrate is variable at different regions, giving rise to notable effects in experiments. These evidences of decoupling or variable interaction of silicene with the substrate are helpful to in-depth understanding of the structure and electronic properties of silicene.; Comment: 10 pages, 4 figures

Anomalous behaviour of molybdenum in steel welds

Choudhary, Habib Ullah
Fonte: University of Cambridge; Department of Materials Science and Metallurgy Publicador: University of Cambridge; Department of Materials Science and Metallurgy
Tipo: Thesis; Doctoral
Relevância na Pesquisa
56.670986%
The addition of molybdenum to steel welds in quite small concentrations leads to a variety of anomalous microstructural and mechanical property effects. In some cases, the effects manifest even when there are no obvious changes in microstructure at the resolution of a transmission electron microscope. There are two particular discrepancies. A quantitative analysis of molybdenum-containing steel welds indicates that there is a degree of strengthening which cannot be explained by the known solid solution or microstructural effects of molybdenum in steels. Secondly, in multirun welds, the addition of molybdenum appears to make the microstructure which evolves during solidification (the primary microstruet1lre) extremely stable. These and other associated phenomena are examined in this thesis. The molybdenum effects mentioned above have been reproduced in detail, using a series of 'high-purity' multirun welds. Having confirmed that molybdenum increases the fraction of primary microstructure in such welds, an attempt was made to see whether the effect is attributable to a change in the austenitisation characteristics with alloying additions. Extensive work using dilatometric techniques backed by microscopy analysis has demonstrated that molybdenum does not lead to any substantial or unexpected changes in the ability to form austenite. The second hypothesis...

Effect of superficial treatment on the tensile bond strength of two reliners and a thermopolymerizable resin;

Leal, Cristiane Maria Brasil; Muzilli, Carlos Alberto; Miranda, Milton Edson; Pinto, José Renato Ribeiro; Mello, José Antônio Nunes