Análise do desempenho físico-mecânico de painéis compensados de Pinus sp. produzidos com adesivos aquosos a base de poliacetato de vinila e de homopolímero vinílico

This study aimed to evaluate the physico-mechanical performance of three PVA adhesive formulations according to the Brazilian standards for plywood testing and to evaluate the results with those presented in the technical literature and specified in normative documents. The study presents the production process of the panels, the obtaining of samples and, finally, the implementation of physico-mechanical characterization tests based on plywood Brazilian standards. For the panels production it was used a gramature of 120 g / m² and applied a pressure of 15 bars and two temperature combinations and pressing time for each adhesive. The commercial adhesives used were PVA 1810, PVA 1060 and Vinyltec 239. The physical tests conducted were thickness swelling, density, moisture content and water absorption. The mechanical tests were static flexion, for the determination of elasticity modulus (MOE) and rupture modulus (MOR), and shear in the glue line. Among the three formulations studied none showed good performance in the presence of water. However, other trials in the adhesive showed better results and closer to the commercially equivalent used, in the case the urea-formaldehyde, was the PVA 1810, that can be applied in non-structural uses and in environments without the presence of moisture

Effect of surface treatments on the shear bond strength of luting cements to Y-TZP ceramic

Statement of problem Because zirconia is a glass-free material, alternative surface treatments such as airborne-particle abrasion or silica coating should be used for long-term bonding. However, these surface treatments in combination with different bonding agents and luting cements have not yet been studied. Purpose The purpose of the study was to evaluate the effect of surface treatments on the shear bond strength (SBS) of luting cements to Y-TZP ceramic. Material and methods Zirconia disks (N=240) were airborne-particle abraded with the following particles (n=48): 50 μm Al2O3; 120 μm Al2O3; 30 μm silica-coated Al2O3 (Rocatec Soft); 120 μm Al2O3+110 μm silica-coated Al2O3 (Rocatec Plus); and Rocatec Plus. After silanization of the zirconia surface, composite resin disks were bonded with (n=12) RelyX Luting 2; RelyX ARC; RelyX U100; and Panavia F. The bonded specimens were thermocycled (10 000 cycles) and tested for SBS. Failure mode was determined with a stereomicroscope (×20). The morphology and elemental composition of airborne-particle abraded surfaces were evaluated with scanning electron microscopy (×500) and energy-dispersive x-ray spectroscopy (×50). Results Surface treatments, cements, and their interaction were significant (P<.001). For RelyX ARC, Rocatec Soft and Rocatec Plus provided the highest SBS. In general, surface treatments did not influence the SBS of RelyX U100 and Panavia F. Regardless of the cement, no significant difference was found between 50 μm and 120 μm Al2O3 particles, between Rocatec Soft and Rocatec Plus, or between Rocatec Plus and 120 μm Al2O3 particles+Rocatec Plus. All groups showed adhesive failures. Different particle sizes provided differences in morphological patterns. The elemental composition comprised Al and Al/Si for alumina and silica-abraded zirconia. Conclusions Particle size did not influence the SBS of the groups abraded exclusively with alumina or silica-coated particles. RelyX ARC was more surface-treatment dependent than RelyX U100 or Panavia F.

The effect of thermal cycling on the shear bond strength of porcelain/Ti-6Al-4V interfaces

The aim of the study was to evaluate the effect of thermal cycling on the shear bond strength of the porcelain/Ti-6Al-4V interfaces prepared by two different processing routes and metallic surface conditions. Polished and SiO2 particle abraded Ti-6Al-4V alloy and Triceram bonder porcelain were used to produce the interfaces. Porcelain-to-metal specimens were processed by conventional furnace firing and hot pressing. Thermal cycling was performed in Fusayama's artificial saliva for 5000 cycles between 5 +/- 1 and 60 +/- 2 degrees C. After thermal cycling, shear bond tests were carried out by using a custom-made stainless steel apparatus. The results were analyzed using t-Student test and non-parametric Kruskal-Wallis test (p<0.01). Most of the polished-fired specimens were fractured during thermal cycling; thus, it was not possible to obtain the shear bond strength results for this group. Sandblasted-fired, polished-hot pressed, and sandblasted-hot pressed specimens presented the shear bond strength values of 76.2 +/- 15.9, 52.2 +/- 23.6, and 59.9 +/- 22.0 MPa, respectively. Statistical analysis indicated that thermal cycling affected the polished specimens processed by firing, whereas a significant difference was not observed on the other groups. (C) 2015 Elsevier Ltd. All rights reserved.

Prediction of soil shear strength in agricultural and natural environments of the Brazilian Cerrado

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Fatigue surviving, fracture resistance, shear stress and finite element analysis of glass fiber posts with different diameters

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Hygrotermal effects evaluation using the losipescu shear test for glare laminates

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Evaluation of the shear bond strength of the union between two CoCr-alloys and a dental ceramic

Introduction: Based on the importance of the integrity of the metal/ceramic interface, the purpose of this work was to evaluate the shear bond strength of the metal-ceramic union of two Co-Cr alloys (Wirobond C, Bego; Remanium 2000, Dentaurum) combined with Omega 900 ceramic (Vita Zahnfabrik). Material and Method: Eleven cylindrical matrixes were made for each alloy, and the metallic portion was obtained with the lost wax casting technique with standardized waxing of 4mm of height and of 4mm of diameter. The ceramic was applied according to the manufacturer's recommendations with the aid of a teflon matrix that allowed its dimension to be standardized in the same size as the metallic portion. The specimens were submitted to the shear bond test in an universal testing machine (EMIC), with the aid of a device developed for such intention, and constant speed of 0.5mm/min. Results and Conclusions: The mean resistance was 48.387MPa for Wirobond C alloy, with standard deviation of 17.718, and 55.956MPa for Remanium 2000, with standard deviation of 17.198. No statistically significant difference was observed between the shear strength of the two metal-ceramic alloys.

Shear strength of a natural and compacted tropical soil

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Ultrasound Transient Shear Wave Elasticity Imaging for Tendon Tissue

Degeneration of tendon tissue is a common cause of tendon dysfunction with the symptoms of repeated episodes of pain and palpable increase of tendon thickness. Tendon mechanical properties are directly related to its physiological composition and the structural organization of the interior collagen fibers which could be altered by tendon degeneration due to overuse or injury. Thus, measuring mechanical properties of tendon tissue may represent a quantitative measurement of pain, reduced function, and tissue health. Ultrasound elasticity imaging has been developed in the last two decades and has proved to be a promising tool for tissue elasticity imaging. To date, however, well established protocols of tendinopathy elasticity imaging for diagnosing tendon degeneration in early stages or late stages do not exist. This thesis describes the re-creation of one dynamic ultrasound elasticity imaging method and the development of an ultrasound transient shear wave elasticity imaging platform for tendon and other musculoskeletal tissue imaging. An experimental mechanical stage with proper supporting systems and accurate translating stages was designed and made. A variety of high-quality tissue-mimicking phantoms were made to simulate homogeneous and heterogeneous soft tissues as well as tendon tissues. A series of data acquisition and data processing programs were developed to collect the displacement data from the phantom and calculate the shear modulus and Young’s modulus of the target. The imaging platform was found to be capable of conducting comparative measurements of the elastic parameters of the phantoms and quantitatively mapping elasticity onto ultrasound B-Mode images. This suggests the system has great potential for not only benefiting individuals with tendinopathy with an earlier detection, intervention and better rehabilitation, but also for providing a medical tool for quantification of musculoskeletal tissue dysfunction in other regions of the body such as the shoulder, elbow and knee.

Contrasted crustal sources as defined by whole-rock and Sr-Nd-Pb isotope geochemistry of neoproterozoic early post-collisional granitic magmatism within the Southern Brazilian Shear Belt, Camboriu, Brazil

The early phase of post-collisional granitic magmatism in the Camboriu region, south Brazil, is represented by the porphyritic biotite +/- hornblende Rio Pequeno Granite (RPG; 630-620 Ma) and the younger (similar to 610 Ma), equigranular, biotite +/- muscovite Serra dos Macacos Granite (SMG). The two granite types share some geochemical characteristics, but the more felsic SMG constitutes a distinctive group not related to RPG by simple fractionation processes, as indicated by its lower FeOt, TiO2, K2O/Na2O and higher Zr Al2O3, Na2O, Ba and Sr when compared to RPG of similar SiO2 range. Sr-Nd-Pb isotopes require different sources. The SMG derives from old crustal sources, possibly related to the Paleoproterozoic protoliths of the Camboriu Complex, as indicated by strongly negative epsilon Nd-t (-23 to -24) and unradiogenic Pb (e.g., Pb-206/Pb-204 = 16.0-16.3; Pb-207/Pb-204 = 15.3-15.4) and confirmed by previous LA-MC-ICPMS data showing dominant zircon inheritance of Archean to Paleoproterozoic age. In contrast, the RPG shows less negative epsilon Nd-t (-12 to -15) and a distinctive zircon inheritance pattern with no traces of post-1.6 Ga sources. This is indicative of younger sources whose significance in the regional context is still unclear; some contribution of mantle-derived magmas is indicated by coeval mafic dykes and may account for some of the geochemical and isotopic characteristics of the least differentiated varieties of the RPG. The transcurrent tectonics seems to have played an essential role in the generation of mantle-derived magmas despite their emplacement within a low-strain zone. It may have facilitated their interaction with crustal melts which seem to be to a large extent the products of reworking of Paleoproterozoic orthogneisses from the Camboriu Complex. (C) 2012 Elsevier Ltd. All rights reserved.

Effect of surface area and air-drying distance on shear bond strength of etch-and-rinse adhesive

We evaluated the effects of air-drying distance and bond surface area on the shear bond strength of a 2-step etch-and-rinse adhesive. A total of 120 bovine anterior teeth were equally divided into 6 main groups based on bonding surface area. The main groups were divided into sub-groups (n = 5) according to air-drying distance. The shear strength was determined using a universal testing machine at a crosshead speed of 0.5 mm/min. The averaged results were subjected to two-way ANOVA and Tukey's test (alpha = 0.05). Two-way ANOVA testing identified no significant cross-product interactions (p > 0.05), but the main factors of area (p < 0.0001) and air-drying distance (p < 0.00001) significantly affected the mean bond strength. Shorter air-drying distances improved bond strength, and increased surface area decreased the bond strength.

Experimental analysis of reinforced concrete block masonry spandrels using pre-fabricated planar trussed bars

Masonry spandrels together with shear walls are structural components of a masonry building subjected to lateral loads. Shear walls are the main components of this structural system, even if masonry spandrels are the elements that ensure the connection of shear wall panels and the distribution of stresses through the masonry piers. The use of prefabricated truss type bars in the transversal and longitudinal directions is usually considered a challenge, even if the simplicity of the applications suggested here alleviate some of the possible difficulties. This paper focus on the experimental behavior of masonry spandrels reinforced with prefabricated trusses, considering different possibilities for the arrangement of reinforcement and blocks. Reinforced spandrels with three and two hollow cell concrete blocks and with different reinforcement ratios have been built and tested using a four and three point loading test configuration. Horizontal bed joint reinforcement increased the capacity of deformation as well as the ultimate load, leading to ductile responses. Vertical reinforcement increased the shear strength of the masonry spandrels and its distribution play a central role on the shear behavior. (C) 2011 Elsevier Ltd. All rights reserved.

Shear bond strength between Ni-Cr alloy bonded to a ceramic substrate

Shear bond strength between Ni-Cr alloy bonded to a ceramic substrate Introduction: The aim of this study was to evaluate the shear bond strength between a Ni-Cr alloy and a ceramic system submitted or not to thermocycling. Materials and methods: Forty-eight cylinder blocks of Ni-Cr with 3.0 mm diameter by 4.0 mm hight and 48 disc-shaped specimens (7.0 mm in diameter by 2.0 mm thick) composed of ceramic were prepared. The Ni-Cr cylinder blocks were randomised in two groups of 24 specimens each. One group was submitted to air-particle abrasion (sandblasting) with 50 mu m Al2O3 (0.4-0.7 MPa) during 20 s, and the other group was submitted to mechanical retentions with carbide burrs. Each group was subdivided into other two groups (n = 12), submitted or not to thermocycling (500 cycles, 5-55 degrees C). The cylinder blocks were bonded to the disc-shaped ceramic specimens under 10 N of load. The shear bond strengths (MPa) were measured using a universal testing machine at a cross head speed of 0.5 mm/min and 200 kgf of load. The data were submitted to statistical analysis (ANOVA and Tukey's test). Results: The air-particle abrasion group exhibited significantly higher shear bond strength when compared to drilled group (p < 0.05). Conclusions: Thermocycling decreased significantly the bond strengths for all groups tested.

Unconfined shear strength of compacted unsaturated plastic soils

A central goal in unsaturated soil mechanics research is to create a smooth transition between traditional soil mechanics approaches and an approach that is applicable to unsaturated soils. Undrained shear strength and the liquidity index of reconstituted or remoulded saturated soils are consistently correlated, which has been demonstrated by many studies. In the liquidity index range from 1 (at w(l)) to 0 (at w(p)), the shear strength ranges from approximately 2 kPa to 200 kPa. Similarly, for compacted soil, the shear strength at the plastic limit ranges from 150 kPa to 250 kPa. When compacted at their optimum water content, most soils have a suction that ranges from 20 kPa to 500 kPa; however, in the field, compacted materials are subjected to drying and wetting, which affect their initial suction and as a consequence their shear strength. Unconfined shear tests were performed on five compacted tropical soils and kaolin. Specimens were tested in the as-compacted condition, and also after undergoing drying or wetting. The test results and data from prior literature were examined, taking into account the roles of void ratio, suction, and relative water content. An interpretation of the phenomena that are involved in the development of the undrained shear strength of unsaturated soils in the contexts of soil water retention and Atterberg limits is presented, providing a practical view of the behaviour of compacted soil based on the concept of unsaturated soil. Finally, an empirical correlation is presented that relates the unsaturated state of compacted soils to the unconfined shear strength.

Shear bond strength between different materials bonded with two resin cements

Background: The aim of this study was to compare the shear bond strength between Ni-Cr alloy specimens bonded to air-abraded Ni-Cr, bur-abraded Ni-Cr, etched ceramic and etched enamel substrates using the resin cements RelyX ARC or Enforce. Materials and methods: Ni-Cr specimens were made and sandblasted with Al2O3 airborne-particles. Disc-shaped patterns were made for each of the four experimental substrates: Ni-Cr treated with Al2O3 airborne-particles, Ni-Cr treated with diamond bur abrasion, etched enamel and etched ceramic. Results: Significant differences in shear bond strength were found between the different materials and luting agents evaluated. The Ni-Cr alloy cylinders bonded to Ni-Cr surfaces sandblasted with 50 lm Al2O3 particles and bonded with Enforce achieved the highest bond strength when compared with other substrates (28.9 MPa, p < 0.05). Bur-abraded metal discs had lowest values, regardless the cement used (2.9 and 6.9 MPa for RelyX and Enforce, respectively). Etched enamel and etched ceramic had similar shear bond strengths within cement groups and performed better when RelyX was used. Conclusions: Bonding Ni-Cr to Ni-Cr and ceramic may result in similar and higher bond strength when compared to Ni-Cr/enamel bonding. For metal/metal bonding, higher shear bond strength was achieved with resin cement Enforce, and for metal/ceramic and metal/enamel bonding, RelyX had higher results.