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Nickel adsorption in two Oxisols and an Alfisol as affected by pH, nature of the electrolyte, and ionic strength of soil solution

MOREIRA, Cindy Silva; CASAGRANDE, Jose Carlos; ALLEONI, Luis Reynaldo Ferracciu; CAMARGO, Otavio Antonio de; BERTON, Ronaldo Severiano
Fonte: SPRINGER HEIDELBERG Publicador: SPRINGER HEIDELBERG
Tipo: Artigo de Revista Científica
ENG
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Background, aim, and scope The retention of potentially toxic metals in highly weathered soils can follow different pathways that variably affect their mobility and availability in the soil-water-plant system. This study aimed to evaluate the effects of pH, nature of electrolyte, and ionic strength of the solution on nickel (Ni) adsorption by two acric Oxisols and a less weathered Alfisol. Materials and methods The effect of pH on Ni adsorption was evaluated in surface and subsurface samples from a clayey textured Anionic `Rhodic` Acrudox ( RA), a sandy-clayey textured Anionic `Xantic` Acrudox (XA), and a heavy clayey textured Rhodic Kandiudalf (RK). All soil samples were equilibrated with the same concentration of Ni solution (5.0 mg L(-1)) and two electrolyte solutions (CaCl(2) or NaCl) with different ionic strengths (IS) (1.0, 0.1 and 0.01 mol L(-1)). The pH of each sample set varied from 3 to 10 in order to obtain sorption envelopes. Results and discussion Ni adsorption increased as the pH increased, reaching its maximum of nearly pH 6. The adsorption was highest in Alfisol, followed by RA and XA. Competition between Ni(2+) and Ca(2+) was higher than that between Ni(2+) and Na(+) in all soil samples, as shown by the higher percentage of Ni adsorption at pH 5. At pH values below the intersection point of the three ionic strength curves (zero point of salt effect)...

Microshear Bond Strength of Self-etching Systems Associated with a Hydrophobic Resin Layer

MORAES, Andre Guaraci De Vito; FRANCCI, Carlos; CARVALHO, Ceci Nunes; SOARES, Silvio Peixoto; BRAGA, Roberto Ruggiero
Fonte: QUINTESSENCE PUBLISHING CO INC Publicador: QUINTESSENCE PUBLISHING CO INC
Tipo: Artigo de Revista Científica
ENG
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57.03242%
Purpose: To evaluate in vitro the microshear bond strength of adhesive systems applied to dentin according to manufacturers` instructions, associated or not with a hydrophobic layer of unfilled resin. Materials and Methods: Six self-etching adhesives (Clearfil SE Bond, Kuraray Medical; AdheSE, lvoclar Vivadent; Xeno III, Dentsply; I Bond, Heraeus-Kulzer; Bond Force, Tokuyama; Futurabond DC, Voco) were tested. The labial dentin of sixty bovine incisors was exposed, and the teeth were divided into two groups according to the application or not of an extra hydrophobic resin layer (Scotchbond Multi Purpose Plus, bottle 3). Six composite cylinders (Filtek Z250, 3M ESPE) were built up on each treated surface. Specimens were stored in distilled water at 37 C for 24 h and then subjected to the microshear bond strength test in a universal testing machine at a crosshead speed of 0.5 mm/min. Microshear bond strength values were analyzed by 2-way ANOVA and Tukey`s post-hoc test. Failure mode was determined using a stereomicroscope under 20X magnification. Results: The application of the hydrophobic resin layer did not affect bond strength, except for AdheSE. However, the bond strengths with the hydrophobic layer were similar among the six tested systems (Clearfil: 17.1 +/- 7.9; AdheSE: 14.5 +/- 7.1; Xeno III: 12.8 +/- 7.7; I Bond: 9.5 +/- 5.8; Bond Force: 17.5 +/- 4.1; Futurabond: 7.7 +/- 2.3). When used as recommended by the manufacturers...

Estudo da distribuição de tensões e da resistência à tração de interfaces adesivas dentina-resina de duas formas de espécimes submetidos a diferentes protocolos de envelhecimento acelerado; Study of stress distribution and tensile bond strength of dentin-resin adhesive interfaces of two types of specimens submitted to different protocols of accelerated aging

Sanches, Luciana Katty Figueiredo
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
Publicado em 08/07/2011 PT
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O acelerado e freqüente desenvolvimento de novos materiais e técnicas restauradoras tornam necessárias avaliações rápidas que estimem seus desempenhos clínicos. Este estudo avaliou protocolos de envelhecimento acelerado, in vitro, capazes de simular o desempenho de restaurações adesivas frente aos desafios inerentes ao ambiente oral. Foram utilizados 36 molares hígidos, cortados ao meio e divididos aleatoriamente em 12 grupos. Em todos os grupos foi realizada a exposição da superfície dentinária, delimitação da área de adesão e condicionamento ácido da superfície, seguida a aplicação do Sistema Adesivo Scotchbond Multiuso, e colocação da resina composta Z100, em incrementos. Foram confeccionados 6 grupos em formato de palito e 6 grupos em formato de haltere: dois grupos não foram submetidos à ciclagem térmica e mecânica (STSM-P e STSM-H); outros dois foram submetidos à ciclagem térmica (1.000 ciclos; 5-55ºC; 1min em cada banho) e não a mecânica (CTSM-P e CTSM-H); dois ainda foram submetidos à ciclagem mecânica com dispositivo Nova Ética e não a térmica (STNE-P e STNE-H); dois foram submetido à ciclagem mecânica com dispositivo Nova Ética (500.000 ciclos), acrescido de ciclagem térmica (CTNE-P e CTNE-H); outros dois por fim...

An investigation of electrolytic surface damages and electroplated crhomium effects on fatigue behavior of high strength steel

De Amorim, Carlos Eduardo Silva; Voorwald, Herman Jacobus Cornelis; Dos Santos Vieira, Luiz Fábio; Pigatin, Walter Luis
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Conferência ou Objeto de Conferência
ENG
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57.01238%
Fatigue crack initiation occurs at the surface, although sub surface nucleation has also been reported. Localized imperfections like inclusions close to surface and surface small pits can result in crack sources. Coatings are not always beneficial by fatigue point of view too. Mechanical properties of the covering material can change considerably the fatigue behavior of base metal due to residual surface stresses, to micro cracks or to hydrogen embrittlement. This paper is concerned with analysis of electrolytic etch on the fatigue resistance of a 35NCD16 high strength steel in a mechanical condition of (1760 - 1960) MPa, and analysis of electroplated hard chromium effects on the fatigue resistance in a strength condition of 989 MPa. Hardness impression was used as a reference parameter in case of electrolytic etch. In both cases, experimental data showed that fatigue strength of 35NCD16 steel was considerably reduced. Copyright © 2001 Society of Automotive Engineers, Inc.

Effect of cyclic compressive loading on the bond strength of an adhesive system to dentin after collagen removal

Santos, Paulo Henrique dos; Sinhoreti, Mário Alexandre Coelho; Consani, Simonides; Sobrinho, Lourenço Correr; Adabo, Gelson Luis; Vaz, Luis Geraldo
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 127-131
ENG
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Purpose: The objective of this study was to verify the effect of cyclic compressive loading on the shear bond strength of an adhesive system following collagen removal. Materials and Methods: Sixty bovine teeth were divided into 4 groups based on the adhesive procedure used: groups 1 and 2 - etching with 35% phosphoric acid and application of the Single Bond adhesive system; groups 3 and 4 - after etching, a 10% sodium hypochlorite solution was applied for 1 min before the application of the adhesive. In all the specimens, a Z100 resin cylinder was built up over the bond area. Groups 2 and 4 were submitted to 500,000 cycles with a load of 100 N. Results: The mean values for the shear bond test (MPa) were: group 1: 7.37 ± 1.15; group 2: 5.72 ± 1.66; group 3: 5.95 ± 1.21; group 4: 3.66 ± 1.12. There was no difference between groups 1 and 2 (p > 0.01). Between groups 1 and 3, 2 and 4, and 3 and 4 there was a significant difference (p < 0.01). The majority of the specimens demonstrated an adhesive failure. Conclusion: The application of sodium hypochlorite on dentin decreased the values of shear bond strength, as did the load cycling in the group treated with sodium hypochlorite.

Factors affecting the strength of denture repairs: Topics of interest

Seó, Rosangela Seiko; Neppelenbroek, Karin Hermana; Filho, João Neudenir Ariolli
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 302-310
ENG
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Fracture of dentures is a common clinical finding in daily prosthodontic practice, resulting in great inconvenience to both patient and dentist. A satisfactory repair should be cost-effective, simple to perform, and quick; it should also match the original color and not cause distortion to the existing denture. Different repair materials, surface designs, and mechanical and chemical surface treatments have been recommended in order to obtain stronger repairs. This article reviews some of the available literature with regard to the most important factors that may influence the strength of denture repairs. © 2007 by The American College of Prosthodontists.

The impact of hydrofluoric acid etching followed by unfilled resin on the biaxial strength of a glass-ceramic

Posritong, Sumana; Borges, Alexandre Luiz Souto; Chu, Tien-Min Gabriel; Eckert, George J.; Bottino, Marco A.; Bottino, Marco C.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica
ENG
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57.03242%
Objectives: To evaluate the null hypotheses that hydrofluoric (HF) acid etching time would neither decrease the biaxial flexural strength of a glass-based veneering ceramic nor enhance it after silane and unfilled resin (UR) applications. Methods: Disc-shaped IPS e.max ZirPress specimens were allocated into 12 groups: G1-control (no-etching), G2-30 s, G3-60 s, G4-90 s, G5-120 s, G6-60 s + 60 s. Groups (G7-G12) were treated in the same fashion as G1-G6, but followed by silane and UR applications. Surface morphology and roughness (Ra and Rq) of the ceramics were assessed by means of scanning electron microscopy (SEM) and profilometry, respectively. Flexural strength was determined by biaxial testing. Data were analyzed by two-way ANOVA and the Sidak test (α = 0.05). Weibull statistics were estimated and finite element analysis (FEA) was carried out to verify the stress concentration end areas of fracture. Results: The interaction (etching time vs. surface treatment) was significant for Ra (p = 0.008) and Rq (0.0075). Resin-treated groups presented significantly lower Ra and Rq than non-treated groups, except for the 60 s group (p < 0.005). SEM revealed that etching affected the ceramic microstructure and that the UR was able to penetrate into the irregularities. A significant effect of etching time (p = 0.029) on flexural strength was seen. G7-G12 presented higher strength than G1-G6 (p < 0.0001). None of experimental groups failed to show 95% confidence intervals of σ 0 and m overlapped. FEA showed lower stress concentration after resin treatment. Significance: HF acid etching time did not show a damaging effect on the ceramic flexural strength. Moreover...

Statistical analysis of compressive strength of concrete specimens

Aguiar, J. L. Barroso de; Veiga, E.; Oliveira, Pedro
Fonte: Elmaarefa Printing House Publicador: Elmaarefa Printing House
Tipo: Conferência ou Objeto de Conferência
Publicado em //2003 ENG
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This paper presents the statistical analysis of compressive strength of concrete specimens delivered in a laboratory of Northern of Portugal. Three types of concretes were analyzed defined as C20, C25 and C30. In the study we used the results of three years, 1995 to 1997. The one-sample Kolmogorov-Smirnov Test was used to verify the normal distribution of the strength results. The results presented in this paper are important for predicting the performance of structural elements and for calculating resistance factors for limit state design codes. As concrete is made in majority on site, conformity is more difficult than for other construction materials produced on factories. For the first analysis the concrete applied on the different sites were separated in groups. A total of 82 groups of concrete produced in 20 sites, were analyzed. We verified that in about 32% of the groups the characteristic compressive strength established for the design was not achieved. For the second analysis the total results were considered, without separation by site or by group. When the exigency was classes C20 or C25, the characteristic compressive strength was below the exigency. On the contrary, for the concrete mentioned as C30, the characteristic compressive strength was above the exigency.

Linear dimensional change, compressive strength and detail reproduction in type IV dental stone dried at room temperature and in a microwave oven

Silva,Marcos Aurélio Bomfim da; Vitti,Rafael Pino; Consani,Simonides; Sinhoreti,Mário Alexandre Coelho; Mesquita,Marcelo Ferraz; Consani,Rafael Leonardo Xediek
Fonte: Faculdade De Odontologia De Bauru - USP Publicador: Faculdade De Odontologia De Bauru - USP
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/10/2012 EN
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The type IV dental stone is widely used for the fabrication of dyes and master casts for fixed and removable partial prostheses. It is typically normal to wait at least 24 hours for the casts to dry prior to beginning the laboratory procedures. The waiting time has been shown to be greatly reduced by using microwave drying. OBJECTIVE: This study evaluated the influence of drying techniques at room temperature and microwave oven on the linear dimensional change, compressive strength and detail reproduction in type IV dental stones. MATERIAL AND METHODS: Three type IV dental stone brands were selected; elite Rock, Shera Premium and Durone IV. Two different drying protocols were tested in 4 groups (n=10); G1 - room temperature (25±4ºC) dried for 2 hours; G2 - room temperature dried for 24 hours; G3 - room temperature dried for 7 days and G4 - microwave oven dried at 800 W for 5 minutes and after 2 hours at room temperature. After drying, the samples were assayed for dimensional charges. The sample surface was submitted to the ImageTool 3.0 software for compressive strength in a universal testing machine with a cell load of 50 KN at a crosshead speed of 0.5 mm/minutes and the detail reproduction was analyzed with a stereomicroscope at 25x magnification. The statistical analysis of the linear dimensional change and compressive strength data were conducted by the ANOVA test followed by the Tukey test (p<0.05). Detailed reproduction values were reported in percentages. RESULTS: For the compressive strength test...

(Finite) statistical size effects on compressive strength

Weiss, Jérôme; Girard, Lucas; Gimbert, Florent; Amitrano, David; Vandembroucq, Damien
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
EN
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Large structures generally fail under stresses significantly lower than those of small ones. This is the size effect on strength, one of the oldest problems of engineering, already discussed by Leonardo da Vinci and Edmé Mariotte centuries ago. One classical explanation is the weakest-link hypothesis: The larger the “chain” is, the larger the probability to find a weak link whose breaking will set the failure of the whole chain. We show, however, that it is irrelevant in the case of compressive loading, a situation particularly crucial for, e.g., geotechnical problems. Interpreting compressive failure as a critical transition between an “intact” and a “failed” state, we quantitatively explain the size effects on compressive strength of materials such as concrete, rocks, coal, ice, or granular materials.

Comparative Evaluation of Impact Strength of Fragment Bonded Teeth and Intact Teeth: An In Vitro Study

Venugopal, L; Lakshmi, M Narasimha; Babu, Devatha Ashok; Kiran, V Ravi
Fonte: International Society of Preventive and Community Dentistry Publicador: International Society of Preventive and Community Dentistry
Tipo: Artigo de Revista Científica
EN
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57.036953%
Background: To test and compare the impact strength of fragment bonded teeth with that of intact teeth by using impact testing machine (pendulum type) as a mode of load. Materials and Methods: Forty extracted, maxillary, central incisors selected for this study (20 control group and 20 experimental group). In experimental group, teeth crowns were fractured with a microtome at 2.5 mm from mesioincisal angle cervically, fractured portion is attached to original crown portion with 3 M single bond dentin bonding agent and 3 M Z ‘100’, composite resin. Impact strength of fragment bonded teeth and intact teeth tested with impact testing machine and compared. Results: Mean impact strength of fragment bonded teeth (30.76 KJ/M2 ) is not statistically significant deferent from mean impact strength of intact teeth (31.11 KJ/M2 ). Conclusion: Mean impact strength of fragment bonded teeth is not statistically different with that of intact teeth. Hence, after fracture of teeth if it is restored with fragment reattachment by using 3 M single bond dentin bonding agent and 3 M Z ‘100’ composite resin is having impact strength like that of intact teeth. How to cite the article: Venugopal L, Lakshmi MN, Babu DA, Kiran VR. Comparative evaluation of impact strength of fragment bonded teeth and intact teeth: An in vitro study. J Int Oral Health 2014;6(3):73-6.

Influ??ncia da composi????o do primer sobre a resist??ncia de uni??o ?? microtra????o em sistema adesivo autocondicionante experimental; Influence of experimental self-etching primers composition on microtensile bond strength

MADRUGA, Francine Cardozo
Fonte: Universidade Federal de Pelotas; Odontologia; Programa de P??s-Gradua????o em Odontologia; UFPel; BR Publicador: Universidade Federal de Pelotas; Odontologia; Programa de P??s-Gradua????o em Odontologia; UFPel; BR
Tipo: Dissertação Formato: application/pdf
POR
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57.03098%
The aim of this study was to investigate the influence of different functional monomer concentrations/HEMA in self-etching primers solvents on microtensile bond strength (μTBS) of an experimental adhesive system. Seventy bonive incisors were allocated in seven groups (n=20). Six experimental self-etching primers were synthesized with different concentratios of acidic monomer (MPF); 0, 15, 30, 50, 70 and 100 (wt %)(Groups EMa0, EMa15, EMa30, EMa50, EMa70, EMa100 respectively). Adhesive system Clearfil SE Bond (CSEB, Kuraray) was used as control. Coating adhesive resin AP-50 was prepared Seventy bovine incisors were randomized and allocate in seven groups. Vestibular enamel was grounded to expose the superficial coronal dentin, witch that was polished wet to create a standardized smear layer with 600 grit silicon paper. After rinsing, water was removed with a piece of absorbent paper, leaving the surface visibly dried. The prepared dentin surfaces were etched with primer and air-dried, after coating adhesive resin was applied and light activated with LED SDI Radii?? (1400mW/cm2). The composite resin was inserted in two increments and were ligth activated for 20 s each. After storage for 24 hours, the specimens were sectioned with a refrigerated diamond saw at low-speed. To investigate immediate microtensile bond strength (μTBS) statistical analysis were performed (one-way ANOVA plus Tukey s post-hoc test...

干湿循环下复合固废填料配比对强度的影响; Effect of mixture proportions on compressive strength of composite geomaterial subjected to drying-wetting cycles

He, Z.; Deng, A.; Zhou, Y.D.; Wang, H.
Fonte: Tongji Daxue * Cailiao Kexue yu Gongcheng Xueyuan Publicador: Tongji Daxue * Cailiao Kexue yu Gongcheng Xueyuan
Tipo: Artigo de Revista Científica
Publicado em //2011 ZH
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Nine series of samples of composite lightweight geomaterials were produced by mixing waste foundry sand, fly ash, expanded polystyrene (EPS) bead, water and Portland cement in proportions, which were exposed to designated drying-wetting (D-W) cycles. Uniaxial compression tests were carried out on the samples to investigate the effect of mix proportions onto the structural integrity of the geomaterial. Results indicate that the geomaterial offers promise as soil-cement mixtures after up to 8 D-W cycles. Along with increase of cement content, the compressive strength of the geomaterial gains in initial 2-3 D-W actions. To add fly ash properly enhances the strength gain and D-W resistance of the geomaterial. Although EPS addition prompts the light weight of the geomaterial, its addition, if above 1% (by mass), will lead to strength loss. Optimal mix proportions for the geomaterial are suggested. = 通过对不同配比的9组复合固废轻质填料(简称轻质填料)试样在不同干湿循环次数下的单轴抗压强度试验,分析了干湿循环下各组分掺入比对轻质填料抗压强度的影响.结果表明:轻质填料经历8次干湿循环后仍有较好的力学性能,达到或超过水泥土的强度要求.随着水泥掺量的增加...

Effects of freeze-thaw action and composition on compression strength of WFS-FA-EPS fills

Deng, A.; He, Z.; Wang, H.
Fonte: American Society of Civil Engineers; Virginia, US Publicador: American Society of Civil Engineers; Virginia, US
Tipo: Conference paper
Publicado em //2010 EN
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A frost-resistant earth fill was proposed by mixing waste foundry sand (WFS), fly ash (FA), expandable polystyrene (EPS) beads, Portland cement and water in proportions, which was known as WFS-FA-EPS fill. This study examined the unconfined compressive strength (UCS) weakening susceptibility of a range of WFS-FA-EPS specimens prepared at designated compositions which were exposed to freeze-thaw (F-T) cycling from 20 ºC to −15 ºC and up to 5 times. It was found that the inclusion of EPS reduced the unit weight of the fill materials by 20-40%. The majority of UCS loss was found suffered in the first F-T impact. Cement component clearly enhanced the anti-frost capability of materials. Components of EPS and FA also improved the F-T resistance of materials. Water was the main factor leading to F-T impairment, and should be prudentially added into the mixture. Inclusion of EPS beads was able to mitigate the frost impact by the means of reducing UCS loss. The optimal contents were 1.08% for EPS bead and 30% for FA.; http://ascelibrary.org/doi/book/10.1061/geoshanghai2010; An Deng, Zhongyi He, and Haibo Wang

Insights into the fracture mechanisms and strength of amorphous and nanocomposite carbon

Fyta, Maria G.; Remediakis, Ioannis N.; Kelires, Pantelis C.; Papaconstantopoulos, Dimitrios A.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 15/05/2006
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Tight-binding molecular dynamics simulations shed light into the fracture mechanisms and the ideal strength of tetrahedral amorphous carbon and of nanocomposite carbon containing diamond crystallites, two of the hardest materials. It is found that fracture in the nanocomposites, under tensile or shear load, occurs inter-grain and so their ideal strength is similar to the pure amorphous phase. The onset of fracture takes place at weakly bonded sp^3 sites in the amorphous matrix. On the other hand, the nanodiamond inclusions significantly enhance the elastic moduli, which approach those of diamond.; Comment: 6 pages, 4 figures

Strength of nanotubes, filaments and nanowires from sonication-induced scission

Huang, Y. Y.; Knowles, T. P. J.; Terentjev, E. M.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 17/07/2009
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We propose a simple model to describe the cavitation-induced breakage of mesoscale filaments during their sonication in solution. The model predicts a limiting length below which scission no longer occurs. This characteristic length is a function of the tensile strength and diameter of the filament, as well as the solvent viscosity and cavitation parameters. We show that the model predicts accurately experimental results for materials ranging from carbon nanotubes to protein fibrils, and discuss the use of sonication-induced breakage as a probe for the strength of nanostructures.

Bond strength of hard chairside reline resins to a rapid polymerizing denture base resin before and after thermal cycling; Resistência de união de resinas rígidas para reembasamento imediato a resina para base de prótese de rápida polimerização antes e após termociclagem

Neppelenbroek, Karin Hermana; Pavarina, Ana Cláudia; Gomes, Mauricio Neves; Machado, Ana Lucia; Vergani, Carlos Eduardo
Fonte: Universidade de São Paulo. Faculdade de Odontologia de Bauru Publicador: Universidade de São Paulo. Faculdade de Odontologia de Bauru
Tipo: info:eu-repo/semantics/article; info:eu-repo/semantics/publishedVersion; ; Formato: application/pdf
Publicado em 01/12/2006 ENG
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OBJETIVO: Esse estudo avaliou a resistência de união ao cisalhamento de 4 resinas rígidas para reembasamento imediato (Kooliner, Tokuso Rebase Fast, Duraliner II, Ufi Gel Hard) a uma resina para base de prótese de rápida polimerização (QC-20) submetida a 2 ciclos de polimerização (A e B), antes e após termociclagem. MATERIAIS E MÉTODOS: Cilindros (3,5 mm x 5,0 mm) das resinas reembasadoras foram unidas aos cilindros de resina QC-20 polimerizados pelo ciclo A (água fervente - 20 minutos) ou B (água fervente; remoção do calor-20 minutos; água fervente-20 minutos). Para cada combinação resina reembasadora/ciclo de polimerização, 10 corpos-de-prova (grupos CAt e CBt) foram termociclados (5 e 55 ºC; intervalo de tempo 30 segundos; 2.000 ciclos); os outros 10 foram testados sem termociclagem (grupos CAwt e CBwt). Os testes de resistência de união ao cisalhamento (0,5 mm/min) foram realizados sobre os corpos-de-prova e o tipo de falha avaliado. Os dados foram analisados por análise de variância (ANOVA) e teste de Newman-Keuls (alfa=0,05). RESULTADOS: A resina QC-20 demonstrou a menor resistência de união entre os materiais reembasadores (p; PURPOSE: This study assessed the shear bond strength of 4 hard chairside reline resins (Kooliner...

Optimization of the Tensile and Flexural Strength of a Wood-PET Composite

Cruz-Salgado,Javier; Alonso-Romero,Sergio; Domínguez-Domínguez,Jorge; Zitzumbo-Guzmán,Roberto
Fonte: Facultad de Ingeniería, UNAM Publicador: Facultad de Ingeniería, UNAM
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/03/2015 EN
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The large amount of disposable bottles presently produced makes the search for alternative products that reuse these materials imperative. Wood-plastic composites are sustainable, organic materials, that show potential for the development of environmentally friendly products. This paper presents the optimization of tensile and flexural strength of a wood-plastic composite made ​​from polyethylene-terephthalate, as thermoplastic resin, and sawdust as fiberfill. The goal of this study was to establish the operating conditions that provide the optimum properties of the wood-plastic composites, with minimal variance. The particle size of the fiber filler was taken as a noise factor. The response surface methodology, by contour lines, in a combined design of experiment was applied.

Estimation of rock strength from quantitative assessment of rock texture

Ozturk,C.A; Nasuf,E; Kahraman,S
Fonte: Journal of the Southern African Institute of Mining and Metallurgy Publicador: Journal of the Southern African Institute of Mining and Metallurgy
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2014 EN
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The compressive strength of rock (σc) has an important effect on design of structures in rock engineering. Compressive strength can be determined in the laboratory using the uniaxial compressive strength (UCS) test. Some other index tests, such as the point load test, are also used, particularly when suitable samples for UCS are not available. The quantification of rock texture has introduced a new method in rock engineering for estimating the mechanical and physical properties of rock materials from microscopic investigations. The aim of this study is to quantify rock texture to estimate rock strength from the texture coefficient (TC), which is determined from a statistical assessment of thin section images. Rock texture is quantified by twelve different images from a single thin section to increase the reliability of texture analysis. A data-set is prepared to investigate correlations between TC and σc. The statistical correlations are computed after classifying of the rock samples based on their lithology as well as grain features. Equations derived based on the results of this study are used to predict the approximate value of compressive strength from the texture coefficient. This method is particularly useful for preliminary studies in rock engineering projects prior to detailed site investigation.

The viability of using the Witwatersrand gold mine tailings for brickmaking

Malatse,M.; Ndlovu,S.
Fonte: Journal of the Southern African Institute of Mining and Metallurgy Publicador: Journal of the Southern African Institute of Mining and Metallurgy
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/04/2015 EN
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The Witwatersrand Basin is the heart of South Africa'a gold mining industry. The cluster of gold mines located in the Witwatersrand Basin generates a significant amount of mine tailings, which have adverse effects on the environment and ecological systems. In addition, disposal costs are very high. The exponential population growth in the Witwatersrand area has resulted in pressure on the reserves of traditional building materials. Quarrying for natural construction material is very expensive and damages the landscape. This work therefore examines the use of gold mine tailings in the production of bricks. Different mixing ratios of gold tailings, cement, and water were used. The resulting bricks were then cured in three different environments - sun dried, oven dried at 360°C, and cured in water for 24 hours. The bricks were then tested for unconfined compressive strength, water absorption, and weight loss. The results showed that the mixture with more cement than tailings had a compressive strength of approximately 530 kN/m². It was also found that the best brick curing system was in a water environment. Bricks made from tailings cost more than conventional bricks because of the higher quantity of cement used, but the manufacturing process consumes less water. Overall...